Theirexposure to a flux of small size-selected silver nanoparticles hasrevealed remarkably selective adhesion: the graphene channel can bemade fully metallized, while the insulating substrate remains coverage-free.This conspicuous contrast derives from the low binding energy betweenthe metal nanoparticles and a contaminant-free passivated silica surface.In addition to providing physical insight into nanoparticle adhesion,this effect may be of value in applications involving deposition ofmetallic layers on device working surfaces: it eliminates the needfor masking the insulating region and the associated extensive andpotentially deleterious pre- and postprocessing.Nanostructured electronic devices, such as those basedon graphene,are typically grown on top of the insulator SiO Graphene has been extensivelyexplored as a material in microelectronic devices, particularly infield effect transistor (FET) architecture. Its gapless semimetalnature enables fabrication of devices exhibiting ambipolar conductionwith high carrier mobilities tunable via electrostatic gating. Additionally,the electronic structure of the devices’ exposed conductinggraphene channel has been shown, for better or worse, to be easilyaffected by surface adsorbates. This fact has led to many studiesaiming to use adsorbates to modify the carrier populations or bandgapof graphene FETs in order to adapt these devices to various applicationsin a controlled way .8 Nanoparticles possess strong optical resonances, enabling photoinducedcharge transfer into the device10 and a range of otherplasmonics-based graphene device applications13 such as photocatalysis,solar energy conversion, photodetection, and surface-enhanced Ramanscattering. Furthermore, they can serve as anchors for external adsorbates,enhancing the devices’ functionality as sensors.17 Another interesting application is the capability of the grapheneFET channel to detect the superconducting transition at the nanoscale.20For the purpose of device modification, metallic nanoparticlesand nanoclusters display many properties that make them suitable asgraphene surface dopants. Their electron affinities and ionizationenergies are material- and size-dependent, making it possible to varythe amount of charge accepted from or donated to the graphene device.23 The nanoparticles in the beam are typically electrically charged,making it possible to filter them by size using mass spectrometry,measure their flux for accurate dosing, and adjust their kinetic energyfor surface soft landing (or for energetic implantation if desired).Bare metal nanoparticles deposited from the gas phase representa particularly promising category of dopants. In contrast to theircolloidally derived counterparts, gas phase particles do not requiresurface ligands used to prevent coalescence in solution. As such,there is no influence or contamination from ligands or their remnantsand no need for harsh postprocessing required for their removal. Furthermore,there exist methods (such as the magnetron sputtering/condensationsource utilized in the work described below) of producing directedbeams of nanoparticles of a variety of materials, comprising eithersingle elements or alloys with controllable species ratios.24 and high-temperature baking,25 risk damaging the dopant nanoparticles, substantially anduncontrollably altering their properties and their effect on the device.However, there is a drawback to decorating graphene channels byusing a flux of nanoparticles, especially if multiple devices arefabricated on a single oxide wafer: upon exposure to the beam, theentire exposed surface, including the insulating region, may becomemetallized by a nanoparticle film. The conventional solution wouldemploy lithographic techniques in which the devices are covered witha resist, a mask is developed in it so as to expose only the devices’graphene channels, and the resist is removed after nanoparticle deposition.Unfortunately, lithographic resists used to pattern devices have beenshown to alter the electronic properties of graphene and have provento be very difficult, if not impossible, to fully remove once introduced.Furthermore, the available methods, such as acid treatments2. As a consequence, graphene devices can be decorated anddoped by metal nanoparticles and nanoclusters of variable sizes withoutthe need of any postfabrication lithographic patterning.In this work, we describe beam deposition of silver nanoparticlesonto graphene on a silicon dioxide substrate. We discovered that whenthe devices are carefully cleaned prior to deposition, the particlesalmost exclusively coat the graphene and not the surrounding SiO2 substratewith a 285 nm oxide layer (Grolltex). A rectangular channel was etchedout of the graphene layer, uncovering the surrounding silica surface.Details of the procedure and an image of the device can be found inthe Supporting Information. Prior to nanoparticledeposition, the devices were baked at 500 °C for 24–36h in a 10–10–10–9 mbarvacuum chamber to remove residues of EBL resist (poly(methyl methacrylate)resin, PMMA) and other possible contaminants from the surface.25Devices were fabricated from a commercially produced wafer of graphenegrown by chemical vapor deposition (CVD) on a Si/SiO2 wafers (MTI Corp.) were diced and cleanedvia successive30 min ultrasonications in acetone (twice), methanol (twice), isopropylalcohol (twice), and deionized water. During sonication, these blocks(“dies”) were held in covered test tubes to preventany particulates from collecting on the liquid meniscus and potentiallytransferring to the dies upon removal. As will be demonstrated, althoughacetone treatment is considered standard for PMMA removal,28 even this thorough procedure leaves some “sticky islands”on the surface which affect its adsorption properties.For trials that involved only blank silicasurfaces, Si/SiO29 This system consists of three segments:a gas-aggregation source chamber, a mass filter, and a depositionchamber. The base pressure in all chambers prior to deposition wasapproximately 10–9 mbar. In the source (Mantis Nanogen),a silver target  is sputtered by an argon plasmaat a power of 15–25 W. The resulting metal vapor condensesinto nanoparticles while being transported inside a liquid nitrogen-cooledaggregation region by a flow of inert argon and helium gas. The datapresented below were compared for various ratios of the flow ratesof Ar/He through the source , and the conclusions were independent of thisratio. During operation, because of this gas flow the source and depositionpressures rose to ∼10–4 and ∼10–5 mbar, respectively. Because of the configurationof the magnetron block, the majority of nanoparticles are negativelycharged.31A nanoparticlebeam is produced using a DC magnetron gas aggregationsource.Upon exiting the condensation source,the resulting beam passesthrough a quadrupole mass filter (Mantis MesoQ) and enters the depositionchamber, where samples, mounted on a linear translation stage, canbe exposed to it one at a time. The beam is collimated by an aperture,and the nanoparticle ion flux is determined with the help of a picoammeter(Keithley 6487). This establishes the exposure time required for thedesired coverage.32 Scanning electron microscopy verified the results as described below.After deposition, surface imaging was conductedvia atomic forcemicroscopy . In order to avoid disturbingthe weakly bound nanoparticles, the cantilever drive amplitude andset point were tuned to the regime of imaging using long-range attractiveforces.2 that were mounted on the same sample puck and exposed to the beamsimultaneously. The mass spectrometer was set to select Ag nanoparticlesof 6–8 nm diameter ((∼7–15) × 103 atoms) for deposition, at nominal coverages ranging from 0.05 to0.2 of a monolayer. The estimated 140 m/s velocity of the beam33 implies a deposition energy of ∼10 meVper atom. To rule out any possible role of beam profile inhomogeneity,some of the samples also were prepared with the wafers interchanged.To gain insight into the expected coverage of nanoparticles onthe graphene FETs, initial depositions were performed on separatesmall wafers of baked CVD graphene and of cleaned Si/SiO2, even thoughthey were exposed to the same beam flux. 2 (a) and graphene (b) surfaces.In every single trial, the observed density of nanoparticles ongraphene significantly exceeded that on SiO2 substrate where some surface contaminationexists, plainly visible as a filmlike constrast around the dark nanoparticledots. As mentioned above, these patches represent post-lithographyor post-solvent residue which outlasted the cleaning process. On theother hand, clean SiO2 regions contain no adsorbed nanoparticles.To confirm the AFM scan settings and rule out anypotential biasdue to the tip–particle interaction, these observations wereverified by SEM imaging. 2. These patches,which are residue-free, again show no sign of nanoparticle attachment.The adjoining graphene samples were also examined2b, confi2 and grapheneareas of the sample, with the former population significantly lowerthan might have been anticipated and restricted to areas with residuecontamination.Figure S2. The image clearly displays a stark contrast in surface coverageas a consequence of pretreatment. In the “as fabricated”device, the Ag deposition is continuous throughout, nearly to thepoint of obscuring the graphene step edge. In contrast, the precleaneddevice shows a heavy coverage of Ag on the graphene channel but fewnanoparticles on the surrounding oxide. This figure underscores themain results of this work.Finally, we explored whether the effect remainsrobust for heaviercoatings, which would otherwise lead to complete metallization ofthe surface. We deposited 6–8 nm Ag nanoparticles onto graphenedevices at nominal coverages of 3 and 6 monolayers. For comparison,in each deposition cycle one device was subjected to high vacuum bake-outprior to deposition, while another was left “as fabricated”. 2 surfaces.The images in 2 surrounded by grapheneremain free of nanoparticles despite being too small to set up a strongelectric field by themselves. Second, we imaged an “inverse”configuration which had small and electrically isolated patches ofgraphene surrounded by SiO2 and found that the former becamefully covered by nanoparticles, whereas the latter did not (see S3). If the oxide had been exerting a strongelectrostatic repulsion, it would have prevented the nanoparticlesfrom reaching the graphene. These images represent another strikingillustration of the contrast in the nanoparticle adsorptivity betweenSiO2 and graphene. Third, we performed an analogous depositionexperiment using mica, which also is an insulating surface, and foundthat, in contrast with silica, it becomes fully coated with nanoparticles.Because most of the nanoparticlesarrive as ions, one may inquirewhether the effect may be due to electrostatic charging of the oxidesurface. The following observations verify that this is not the case.First, as was shown in 2 surface also can be ruled out. Withoutany graphene to diffuse toward, one would expect to see some formof deposition on the oxide wafers. With graphene present, diffusionwould lead a pile-up of nanoparticles along the edge boundaries,35 which is not observed in anyimages .A purely diffusion-basedmechanism for the lack of surface adsorptionon a clean SiO2 surfaces derives from the very weak attractionbetween the two.We can therefore infer that the behavior of silvernanoparticleson clean SiOSupporting Information, in this mode we observed nanoparticlesdesorbing from pretreated silica surfaces in favor of adhering toan iridium-coated tip, something not seen upon deposition onto unbakeddevices.This conclusion was further supported by theobservation that suchnanoparticles were easily lifted off when the AFM was switched tocontact-mode nanomanipulation. As described in the 2 surface prior to deposition as the dominantfactor in adsorption. They suggest that clean SiO2 is inherentlyuninterested in attaching silver nanoparticles.Taken as a whole, the results presented above pointto the treatmentof the SiO38 It is common practical knowledge in the device fabrication industrythat when depositing Ag or Au electrical contact pads onto siliconoxide wafers, it is necessary first to deposit a thin intermediary“adhesion layer” such as Cr or Ti.36 Without it, noble atom films degrade in ambient conditionsover time and eventually delaminate from the surface.37 It has been proposed to make use of this phenomenon forfabricating multilevel interconnects in semiconductor devices.39Poor adhesion,though not in this extreme, has been observed inatomic deposition of silver thin films onto oxide surfaces.2 surface.37 Thus,the phenomenon reported in our work involves an interplay betweenan inherently weak attractive force and finite-size effects. Thesefactors have been explored by the model calculations described below.While they are impermanent, atomic layersdo coat silica surfacesat least temporarily. This is in contrast to the present nanoparticledeposition data; therefore, size effects also must play a role. Thisis consistent with the behavior of atomic noble-metal films: withtime these films coarsen and form metal domains which then separatefrom the SiO2 surfaces of different roughness.The binding energyEAg/slab) fromthe sum of the energies of the bare slab (Eslab), i.e., graphene or SiO2, and the nanoparticle. A positivebinding energy reflects stronger chemisorption following the usualconvention.41In order to elucidate the atomistic origin of the observed effectwithin a practicable calculation, we compute the energy of interfacialbinding between a silver nanoparticle and graphene and between thenanoparticle and SiO20 nanocluster, which represents a typicalmodel system,45 interfaced with either a 6 × 6 (001) graphene sheet or a 3× 4 (001) SiO2 surface. Details of the simulationare presented in the Supporting Information. The systems used in the simulations are smaller than the experimentalsystems due to computational limitations. Long-range forces may becomemore relevant for the larger nanoparticles, but the general conclusionsare expected to be applicable.To estimate the strengthof the interfacial interaction, we selecta pyramidal Ag2 crystalline structure is hydrophilic47 and is exposed to water vapor during substrate mounting.  This aspect is important because passivation reduces the particle–substratebonding energy by a factor of 5–10.The undercoordinated Si and Oatoms are passivated with −OHand −H, respectively, given that the (001) surface of the α-quartzSiO20/graphene  and of wafers containing manydevices in close proximity. Graphene structures covered by noble metalthin films have attracted interest,57 as have hybrid graphene–nanoparticledevices.In conclusion, extremely high substrate selectivity was foundforthe coating of graphene devices by metal nanoparticles. Size-selectivesilver nanoparticle beam deposition onto properly precleaned devicesdecouples the coverage of the SiO2 surfaces is significantlyweaker than that to graphene. The calculations also call attentionto the role played by charge transfer from the nanoparticle to thesubstrate and by the roughness of the latter. In future work, it willbe valuablud e to further explore the role of size effects in theinterplay between particle charging energies, surface roughness, contactareas, and electron transfer phenomena. It also will be of interestto extend the work to additional substrate materials and nanoparticlesizes, shapes, and compositions, as well as velocities, where nonmonotonicbehavior of adhesion probabilities have been predicted.50The data also highlight the high sensitivity of nanoparticleadsorptionto surface contaminant removal. Model calculations of the interactionbetween silver nanoclusters and graphene or silica substrates confirmthat particle binding to passivated SiO


These findings highlight the potential for friction tuning in lamellar materials and emphasize the significance of understanding nanoscale friction on graphene surfaces.Despite the numerous unique properties revealed through tribology research on graphene, the development of applications that utilize its rich tribological properties remains a long‐sought goal. In this article, a novel approach for reversible patterning of graphene's frictional properties using out‐of‐plane mechanical tapping is presented. The friction force between the atomic force microscopy (AFM) tip and the graphene film is increased by up to a factor of two, which can be attributed to variations in the interfacial binding strength between the graphene and substrate through the tapping process. The reversible and repeatable frictional properties of graphene make it a promising material for information storage applications with a high storage capacity of ≈1600 GB inch −2, allowing for direct writing and erasing of information, akin to a blackboard.The reversible and repeatable frictional properties of graphene induced by out‐of‐plane mechanical tapping make it a promising material for information storage applications with a high storage capacity of ≈1600 GB inch Moreover, graphene and its derivatives are widely used as solid lubricants and protective films to improve the reliability and lifespan of sliding components.Atomically thin 2D lamellar materials, including graphene, hexagonal boron nitride (h‐BN), transition metal dichalcogenides (TMD), and MAXene, possess unique physical and mechanical properties that have the potential to advance a wide range of nanotechnology applications.3, 4 Especially, the intrinsic weak interlayer van der Waals interaction and low out‐of‐plane bending rigidity of 2D materials result in a lifting of the top layer in front of the scanning tip, that is, the puckering effect, leading to friction increasing with decreasing sample thickness. Moreover, the contact quality between the top layer and the scanning tip evolves with scanning time, with friction force gradually increasing for a few initial atomic periods before reaching a constant value. The contact quality and puckering effects become more pronounced as the deformation compliance of 2D materials increases and/or the binding between the 2D membranes and the substrate decreases.Previous studies in the field of tribology in the past years have primarily focused on the graphene's frictional properties on the basal plane and across step edges, which have revealed numerous interesting phenomena such as the dependence of friction on factors like thickness, crystalline orientation, sliding direction, and binding strength to the substrate, etc.22 Esp In this study, we propose a straightforward and efficient method to manipulate friction on graphene by applying out‐of‐plane mechanical tapping using an atomic force microscopy (AFM) tip. This tapping process effectively modifies the binding strength between the graphene and the substrate, as evidenced by discernible changes in the friction force signal. Impressively, our experimental results demonstrate that friction on graphene can be modulated by a factor of up to two. A crucial aspect of our approach is the complete reversibility of the changes in binding strength, enabling precise control over stored contact information, reminiscent of a blackboard. Significantly, this method holds substantial potential for information storage applications, offering a remarkable capacity of ≈1600 GB inch−2 for digital data storage by using a commercial available tip with the typical radius of 10 nm.Despite the mechanisms of friction on graphene based on interfacial contact quality has been well documented from a fundamental perspective, the modulation and utilization of contact quality to intentionally alter the frictional properties remain largely unexplored.27 In 2Figure 2  direction using a Si3N4 tip (MSCT from Bruker), as shown in Figure 2 Figure . To impr The zero applied normal load was defined as the force acting on the cantilever at its equilibrium deflection. Unless stated otherwise, the out‐of‐plane tapping and FFM scanning were performed at fixed rates of 8 and 1 Hz, respectively. Throughout the experiments, the observed topography and adhesion force signals remained remarkably stable, indicating the absence of significant wear.The AFM/FFM system  was employed for all experiments, conducted in an ambient environment with a controlled relative humidity (RH) of 45% to 50% and a temperature of 23 ± 3 °C, unless otherwise specified. The lateral force values reported in this study were calibrated using the wedge calibration method.28 Thez‐direction, systematically acquiring point by point with a step size of typically 10 nm within a specific area. In this process, the AFM tip was repeatedly brought into contact with the graphene surface using a predefined tapping force (FP), and then retracted, generating a series of force–distance curves. The mechanical tapping process closely resembles the adhesion force measurement process, with the main distinction being that in adhesion force measurement, the process was repeated at the same position, whereas in mechanical tapping, the measurement was repeated at subsequent positions.It is important to note that the mechanical tapping process employed in the study shares similarities with the typical tapping mode in atomic force microscopy. In conventional tapping mode AFM, the cantilever oscillated at its resonant frequency, and the interaction force between the tip and the sample surface was deliberately kept very weak to prevent damage to the sample surface. However, in the mechanical out‐of‐plane tapping method, a slightly larger tapping force was applied in the range of several tenths of nanonewtons. This mechanical out‐of‐plane tapping process was achieved by continuously acquiring force–distance curves along the FP=43.6 nN (top panel) and FP=87.3 nN (bottom panel), along the z direction. In principle, the vertical force curve during tapping can be divided into four stages: I) Initially, the vertical force is zero until the AFM tip comes into contact with the sample surface. II) A nearly linear dependence of the vertical force on z‐displacement is observed until the predefined tapping force FP is reached, characterized by the predominant effects of cantilever bending. III) The vertical force shows a nearly linear dependence on displacement during retracting, before reaching the adhesion force Fa. IV) Finally, the vertical force returns to zero when the AFM tip is detached from the sample surface. In Figure Fa force maps of 1μm×1μm are presented, indicating a uniform sample surface and a stable tapping process.Figure  the exposure of graphene to ambient conditions for several days led to the adsorption of contaminants and the formation of quasi‐periodic ripples on the graphene surface. These adsorbates can influence the friction behavior of graphene and weaken the interaction between the AFM tip and graphene. To mitigate the potential influence of adsorbates, all measurements in this study were conducted on newly exfoliated graphene samples and completed within 12 h of exfoliation. Although the specific influence of adsorbates on friction patterning was not investigated in this study, it was observeed that frictional patterns on graphene sheets exposed to ambient conditions for several days were not as distinct as those on newly exfoliated samples. This observation suggests that the presence of adsorbates may reduce the tip‐sample interaction, resulting in less pronounced frictional patterns.As observed in previous studies,30 the3μm s−1. The images were taken over an area of 4 μm × 3 μm. Prior to tapping, the topography .We further demonstrate the capabilities of our tapping method by successfully patterning the graphene film into various shapes, including rectangles with a size of 300 nm × 300 nm Figure , circlesμm s−1, as depicted in Figure FT) and intact area (FB) and the change in friction (FT−FB) as a function of the number of scans. It is observed that the friction force without tapping remains constant throughout the scans, while the friction force with tapping exhibits a linear decrease with increasing scan number. This demonstrates the effectiveness of the tapping method in facilitating efficient data erasure. Furthermore, to enhance the efficiency of data erasure, increasing the normal load during the in‐plane scan can be implemented  also decreases with sample thickness, indicating that graphene patterning occurs only in thin flakes. We also performed a similar patterning process on a thick HOPG sample and observed no friction differences after tapping . While we currently lack a clear understanding of the underlying mechanism, we speculate that the decrease in friction with increasing RH may be related to the presence of water molecules in the environment, which can influence the interaction between the tip and the graphene surface. Interestingly, we observed that the friction enhancement, which represents the difference between the friction forces before and after tapping, remained nearly unchanged across different relative humidity levels. This suggests that the modulation of friction achieved through our tapping method is robust and independent of environmental humidity conditions. Based on these observations, it is noteworthy to mention that enhancing the tip‐graphene interaction force through oxygen plasma pre‐treatment, increasing the number of tapping times, and using alternating tapping points can all contribute to improving the quality of the frictional patterns. These strategies provide means to optimize the friction modulation process and achieve desired patterning results. On the other hand, the tapping speed does not have a significant influence on the patterning process.The present of water molecules can modulate the interaction between the tip and the graphene, we have conducted additional measurements under various conditions by altering the relative humidity of the environment from 8% to 80%. These measurements were performed using a Sie (HOPG).32 WhiFigure −1). The top panels of Figure  For the measurements before tapping, only regular atomic‐scale stick‐slip has been observed. In contrast, for the measurements after tapping, the apparent lateral force strengthening  can be observed, providing strong evidence of contact quality evolution.In the following parts, we will discuss the possible mechanisms. To further investigate the underlying mechanisms, we have conducted atomic resolution stick‐slip measurements before and after tapping, as shown in f Figure 15 For3N4, as the binding energy between Si3N4/graphene is significantly greater than that between SiO2/graphene. During FFM scanning, the graphene that has undergone tapping exhibits increased deformability compared to the untapped graphene. As a consequence, the contact area between the AFM tip and the tapped graphene is larger than that of the untapped graphene, leading to an increase in the friction force. To confirm this hypothesis, we performed tapping experiments on graphene using a SiO2 tip . Y.Z. and W.W. conducted the experiment(s). Y.Z. and W.W. analyzed the results. All authors discussed the results and contributed to writing the manuscript.Supporting InformationClick here for additional data file.


In this study, fluorographene nanosheets (FG nanosheets) were prepared via the solvent-ultrasonic exfoliation method. The fluorographene sheets were observed using field-emission scanning electron microscopy (FE-SEM). The microstructure of the as-prepared FG nanosheets was characterized by X-ray diffraction (XRD) and a thermal analyzer (TG). The tribological properties of FG nanosheets as an additive in ionic liquids in high vacuum were compared to that of ionic liquid (IL) with graphene (IL-G). The wear surfaces and transfer films were analyzed via an optical microscope, Raman spectroscopy, scanning electron microscopy (SEM), and X-ray photoelectron spectroscopy (XPS). The results show that FG nanosheets can be obtained from the simple solvent-ultrasonic exfoliation method. The prepared G nanosheets are a sheet, and the longer the ultrasonic time is, the thinner the sheet is. Ionic liquids with FG nanosheets had low friction and a low wear rate under high vacuum conditions. The improved frictional properties were attributed to the transfer film of FG nanosheets and more formation film of Fe-F. The development of space science puts forward high requirements for the long life and high reliability of space moving parts mechanisms. Good lubrication technology is one of the key technologies to improve the long life of space moving parts. Liquid lubrication has a high bearing capacity, good heat transfer performance, and good high-speed lubrication performance, but in high temperatures it will not form a good lubricating oil film due to reduced viscosity, and at low temperatures it will lose fluidity due to excessive viscosity, reducing the lubrication’s performance. Low speeds impact the boundary lubrication condition, making it difficult to form a continuous lubrication film, leading to direct contact between two local metal surfaces, causing serious wear, friction heat, and grinding. This will affect the chemical stability of the lubricating oil, leading to early lubrication failure. The design of the structure of liquid lubrication is relatively complex as it is a heavyweight liquid. In order to meet the needs of high reliability and long life of space moving parts, exploring and developing new lubrication materials and technologies is necessary.It has been found that adding nanosolid particles to liquid lubricant can not only improve the film-forming performance ,2 but al2 hybrid orbit, with a thickness of only one carbon atom. Graphene has excellent physical properties, including mechanical strength, tensile stress, thermal conductivity, etc., and these properties make graphene an appropriate additive, namely one that is durable, has heat resistance, and has a low friction coefficient. In the field of lubrication additives, it is found that graphene can form an early transfer film in the friction process, avoiding the direct contact of the friction pair, thus playing the role of reducing friction and grinding [3O4 nanoparticles and graphene were recombined to obtain Mn3O4@G [3O4 nanoparticles were anchored in the graphene surface and sheet layer. The result has excellent tribological properties and high stability due to the synergistic lubrication between the graphene nanosheets and Mn3O4 nanoparticles. Even at ultralow concentrations (0.075 wt%) and 125 °C, the friction coefficient and wear depth were reduced by 75% and 97%, respectively, compared to the base oil. The synthetic methods and Mn3O4 @G nanocomposites have significant potential for energy saving in various tribological applications.Graphene in carbon-based nano additives is a two-dimensional thin film composed of a hexagonal honeycomb lattice with an sp and spgrinding ,10. He Ygrinding . For the Mn3O4@G , and Mn3Jiang et al. studied the tribological behavior of graphene and graphene oxide (GO) as water-based lubricant additives . The resThe derivatives of graphene mainly include graphene oxide, graphane, and fluorinated graphene (FG) ,20,21,224 additive, which showed good tribological performance under vacuum conditions. In order to further improve its performance, fluorinated graphene was selected as an additive to study the tribology of fluorinated graphene nanosheets in ionic liquids.At present, the preparation of fluorinated graphene mainly includes the following methods ,32,33,34http://carfluor.company.lookchem.cn, accessed on 7 April 2023), N-methyl pyrrolidone (NMP), acetone, and ethanol of analytical grade were all purchased from Tianjin Chemical Reagent Co., Ltd.  and used directly. Further description of the main chemicals is included in Fluorinated graphite . Then, ultrasonic dispersion was carried out with a sonicator for 2 h. Then, 90 μL of the suspension was taken from 2.5 mg/mL IL-FG and diluted to 3 mL with IL, and ultrasonic dispersion was continued for 2 h. A homogeneous suspension of 0.075 mg/mL IL-FG was obtained. An appropriate amount of the liquid lubricant, as mentioned above, was taken and uniformly coated on the surface of the stainless steel substrate, and the thickness of the coating film was not more than 2 μm to obtain a solid–liquid composite lubricating film.First, a suspension of 2.5 mg/mL IL-FG  was prepared by adding 10 mg of FG nanosheets to 4 mL of IL  was used to observe the cross-sectional morphology of the wear scar and measure the wear volume. Each test was repeated 3 times, and the average value was obtained. The wear rate was calculated by the formula [IL-G and IL-FG friction behaviors were investigated on the vacuum friction tester developed by the Lanzhou Institute of Chemical Physics, Chinese Academy of Sciences. The test was carried out at room temperature, the vacuum degree was 10 formula . The weaWhen X-rays are irradiated on an object, coherent scattering occurs, and the coherent scattered waves of each atom may interfere with each other in a specific direction in space and cause diffraction. The diffraction lines’ direction, intensity, and line shape contain much information on the structure of matter. XRD analysis is a material structure analysis method based on X-ray diffraction. Here we used XRD to accurately measure the 2θ angle data of the diffraction peak position. 2 atmosphere, heating rate 20 °C/min. From the thermograms, it is found that both fluorinated graphite and FG nanosheets are very stable before 350 °C with almost no mass loss. The thermal stability of fluorinated graphite is higher than that of fluorinated graphene above 350 °C due to the different surface energy. Graphite fluoride is a multilayer structure; most of the C–C and C–F bonds are wrapped inside the sheet, and only a small part of the C–C and C–F bonds are exposed to the outside. While FG nanosheets are thinner, more C–F bonds are exposed, which is unstable and prone to decomposition after heating. Thus, the thermal stability of FG nanosheets is poor [ is poor .The temperature range of the space field is about minus 120 to 150 °C, and the space lubricant needs good thermal stability. As shown in The thermal analysis test results show that adding additives has little effect on the thermal stability of the ionic liquid, and the quality below 300 °C does not decrease and remains stable. It shows that the nanofluid has good thermal stability. It can meet the conditions of use in space. −1 and G-band at ~1591 cm−1 are ascribed to carbon additives [To further investigate the improvement of FG nanosheets on the antiwear performance, the surface of the wear spots was observed by Raman and SEM, and the results are shown in dditives . In FiguFrom 2 group in the alkyl chain of ILs, whereas the peak at 286.4 eV can be assigned to the C atoms bonded to the N atoms (C*-N in the imidazolium ring) [2 or FeF3, respectively [2 or FeF3, and the FG nanosheet contains more F, so more FeF2 or FeF3 is formed.X-ray photoelectron spectroscopy is a powerful technique providing information about elemental composition and binding conditions. As shown in um ring) . Two addectively ,10. When- in IL and FG nanosheets and the metal substrate surface chemically react, forming FeF2 or FeF3 film. Film containing the F-Fe chemical reaction has excellent lubricating properties and can effectively prevent direct contact between metal surfaces. FG nanosheets that contain more F in the friction process form more FeF2 or FeF3, so compared with GO additives, FG nanosheet additives can further reduce the wear.According to XPS data, it can be inferred that the process of GO and FG nanosheets producing lubrication can be regarded as a process of mechanical and chemical interaction. In the early stage of the tribological test, the thin GO and FG nanosheets easily adsorb onto the metal surface, forming a deposition film on the metal surface to fill and isolate, thereby reducing the direct contact of the surface and reducing the friction of the sliding surface . In the − from ILs reacts with Fe in the steel sheet to create more F compound, which can also protect the steel sheet. Moreover, FG nanosheets contain more F−, so more Fe-F compound is formed on the steel surface, which can protect the steel surface and reduce friction and wear.Using fluorinated graphite as the raw material, fluorinated graphene was successfully prepared by liquid-phase ultrasonic exfoliation. This preparation method is simple, and fluorinated graphene of different sheet sizes can be obtained under different centrifugal separation speeds.The tribological properties of FG nanosheets were studied. Compared with IL-G, IL-FG nanosheets have better tribological properties for steel/steel friction pairs; during the friction process, FG nanosheets are adsorbed on the interface of steel/steel friction pairs to form a protective layer to avoid friction. During the friction process, the FG-2 nanosheets with smaller lamellae can be deposited on the microscopic defect area of the worn surface under the action of compressive stress, thus playing a good role in repairing the worn surface.


Pyrrole oxidized derivatives display more favorable supramolecular interactions with graphene surface. Intermolecular interactions affect the first step of the adsorption process and are important to better understand possible surface modifications for carbon allotropes and to design novel nanofillers in polymer composites.The adsorption of organic molecules on graphene surfaces is a crucial process in many different research areas. Nano-sized carbon allotropes, such as graphene and carbon nanotubes, have shown promise as fillers due to their exceptional properties, including their large surface area, thermal and electrical conductivity, and potential for weight reduction. Surface modification methods, such as the “pyrrole methodology”, have been explored to tailor the properties of carbon allotropes. In this theoretical work, an ab initio study based on Density Functional Theory is performed to investigate the adsorption process of small volatile organic molecules (such as pyrrole derivatives) on graphene surface. The effects of substituents, and different molecular species are examined to determine the influence of the aromatic ring or the substituent of pyrrole’s aromatic ring on the adsorption energy. The number of atoms and presence of π electrons significantly influence the corresponding adsorption energy. Interestingly, pyrroles and cyclopentadienes are 10 kJ mol The adsorption process on solid surfaces plays a critical role in numerous scientific disciplines, ranging from chemistry and physics to materials science and nanotechnology ,5,6,7,8.Density Functional Theory (DFT) calculations together with molecular mechanics (MM) and molecular dynamics (MD) methods can provide information that strongly complements experimental studies ,36,37,38Considering the adsorption of a single molecule on a solid surface, Density Functional Theory has emerged as an interesting tool for studying the ground-state properties of condensed matter systems, particularly with regard to how surface interactions influence the electronic distribution in the molecular orbitals of the volatile organic molecules near a solid surface ,51,52,53In recent years, there has been a growing interest in surface modification techniques aiming to improve the properties of fillers used in advanced technological applications . One proN-substituted pyrrole molecules [N-substituted pyrrole molecules onto the sp2 carbon surface, which then undergoes oxidation and subsequent Diels–Alder cycloaddition, forming covalent bonds with the edges of the carbon allotrope plane. The adsorption and grafting mechanisms of the pyrrole methodology are governed by a complex interplay of supramolecular interactions, which dictate the stability, structure, and properties of the modified surface [Among the diverse approaches investigated, one particularly efficient and reliable procedure is known as the “pyrrole methodology”, which involves the covalent modification of carbon allotrope surfaces using olecules ,76, a me surface . This ap surface ,79.Motivated by the potential of the pyrrole methodology and the need for a detailed understanding of the adsorption process, our study employed ab initio simulations based on DFT to gain deeper insights into the initial steps of the pyrrole methodology and investigate the adsorption behaviors of various compounds on carbon allotropes. Our objectives encompassed not only determining the optimal computational parameters for the simulations but also exploring the interactions between pyrrole molecules and graphene surfaces. Furthermore, we sought to examine the effects of substituents and oxidation on the adsorption process, allowing us to understand how different modifications influence the stability and reactivity of this system.2 carbon allotropes, mainly carbon black, functionalized by means of the “pyrrole methodology” with pyrrole compounds as the ones studied in the research here reported, improved the properties of elastomeric composites for a large-scale application such as the one in tyre compounds [To broaden the scope of our investigation, we expanded our calculations to include other compounds, including alkanes, cyclopentanes, pyrrolidines, and cyclopentadiene derivatives. By exploring a broad range of molecular species, we aimed to uncover the underlying factors governing adsorption and shed light on the role of dispersion and π-π interactions in stabilizing these systems on graphene surfaces, an approach that has already been verified in the recent literature ,81,82,83ompounds ,88. The ompounds . This stIn this section, the results about the adsorption of the different aliphatic and aromatic compounds reported in As described in the Materials and Methods section, linear alkane compounds such as methane, ethane, propane, and butane were considered close to the pristine surface of graphene. The optimized structures are shown to the left of all four panels in The charge density difference iso-surfaces  shown to the right of all four panels in Regarding the ground-state geometries studied, upon considering the plane defined by all carbon atoms in the propane and butane chains, it can be gleaned that this plane is parallel to the graphene plane. As regards the interaction energy, we can observe that as the number of carbon atoms in the chain increases, the interactions with the solid surface increase proportionally, indicating a stabilizing effect due, as mentioned previously, to the favorable dispersion interactions between the C–H bonds and the graphene surface.The results relating to the saturated cyclic systems reported in As described in the Materials and Methods section, cyclopentane compounds were considered adsorbed on the pristine graphene surface. The ground-state structures are shown on the left in Compared to the previous results, considering the structures in the ground-state ranging from 1,2,3-trimethylcyclopentane to 2-butyl-1,3-dimethylcyclopentane, we observed a different arrangement of the structure of the alkyl residue -R with respect to the graphene plane: in fact, if we also consider for these structures the plane defined only by the carbon atoms linked to carbon 2 of the cyclopentane, this plane is now arranged perpendicular to the graphene surface, as reported in the panels on the left of Concerning the strength of the interactions, the adsorption energies were higher when increasing the carbon atoms in linear chain, indicating, as with the alkane compounds, increased supramolecular interactions due to dispersion forces between these cyclopentane derivatives and the graphene surface.Regarding the charge difference density plots  shown on the right in all panels in 3sp-hybridized, there are no planar geometry constraints; thus, the molecules, after adsorption, adjust themselves to maximize the interaction forces due to C–H bonds and the graphene surface.As mentioned previously, regarding the geometry of the interactions in the calculated ground state, the alkyl chains that start from the cyclopentane are perpendicular to the graphene surface, and the adsorbate atoms that are close to the latter seem to contribute more to the overall supramolecular interactions. Moreover, because cyclopentanes are As described in the Materials and Methods section, pyrrolidine derivatives adsorbed on the pristine graphene surface were studied. The lowest total energy structures are reported in the panels on the left in Considering the graphs of the charge density differences for the pyrrolidines  increases as the number of atoms in the molecule increases, specifically in the substituent of the linear alkyl chain, with values ranging from −55.4 kJ mol−1 to −66.3 kJ mol−1 for 1,2,5-trimethylpyrrole and 1-butyl-2,5-dimethylpyrrole, respectively.Even for these systems, the adsorption energy  was adjusted to 20 Å, ensuring a sufficient separation between the graphene layers.Regarding the different types of small organic molecules adsorbed on the surface of graphene, the analyzed compounds and their chemical structures are listed in adsE) was calculated as follows:With regard to adsorption energy, it is important to highlight that to quantify the interaction force between the adsorbate and the investigated surface, adsorption energy (ES+A) maps were calculated using the pp.x software contained in the Quantum ESPRESSO Suite. Δρ was calculated using the following formula:(S+A) is the charge density of the adsorbate/surface system, ρA is the charge density of the molecule , and ρS is the charge density of the investigated surface. Following this methodology, Δρ  shows the variations in the charge density of the graphene–adsorbate system. In the figures, a difference in charge density is shown in red on an iso-surface on which the accumulation of charge is represented, while blue indicates depletion [Above, ρepletion ,98.−1 more stable than the corresponding unsaturated ones. Furthermore, the presence of aldehydic groups in pyrrole derivatives improves the adsorption energy which is therefore more negative. This study provides valuable insights into supramolecular interactions and their influence on the first step of the adsorption process, contributing to the fundamental understanding of surface modifications for carbon allotropes and their applications in polymer composites.The DFT study of pyrroles and pyrrole derivatives adsorbed on graphene surface revealed that adsorption process is predominantly governed by dispersion forces and π–π bonding interactions. The number of atoms in the molecules considered and the presence of π electrons significantly influence the corresponding adsorption energy. A linear dependence of the adsorption energy is found as a function of the number of atoms in the adsorbed molecules. The pyrrole compounds display more favorable supramolecular interactions with graphene surface. In particular, at the same number of atoms in contact with the graphene surface pyrroles and cyclopentadienes are 10 kJ molOverall, the findings of this study offer valuable insights into the complex mechanisms governing adsorption on carbon allotrope surfaces. By elucidating the significant roles of dispersion forces and π–π bonding interactions, this research study contributes to a comprehensive understanding of surface modifications for carbon allotropes and their potential applications in the field of polymer composites. Further study on the adsorption process of these molecules on the graphene surface as single molecules and at higher concentrations will be performed using molecular mechanics and molecular dynamics methods to better understand the contribution of van der Waals interactions in the adsorption process in a more complex supramolecular structure as in previous work .


Spliceosomal introns are gene segments removed from RNA transcripts by ribonucleoprotein machineries called spliceosomes. In some eukaryotes a second ‘minor’ spliceosome is responsible for processing a tiny minority of introns. Despite its seemingly modest role, minor splicing has persisted for roughly 1.5 billion years of eukaryotic evolution. Identifying minor introns in over 3000 eukaryotic genomes, we report diverse evolutionary histories including surprisingly high numbers in some fungi and green algae, repeated loss, as well as general biases in their positional and genic distributions. We estimate that ancestral minor intron densities were comparable to those of vertebrates, suggesting a trend of long-term stasis. Finally, three findings suggest a major role for neutral processes in minor intron evolution. First, highly similar patterns of minor and major intron evolution contrast with both functionalist and deleterious model predictions. Second, observed functional biases among minor intron-containing genes are largely explained by these genes’ greater ages. Third, no association of intron splicing with cell proliferation in a minor intron-rich fungus suggests that regulatory roles are lineage-specific and thus cannot offer a general explanation for minor splicing’s persistence. These data constitute the most comprehensive view of minor introns and their evolutionary history to date, and provide a foundation for future studies of these remarkable genetic elements.  Spliceosomal introns are sequences in eukaryotic genes that are removed (spliced) from the pre-mRNA transcripts of genes by machinery known as the spliceosome prior to maturation and nuclear export of the final mRNA . For theWhile minor introns were almost certainly present in early eukaryotes  and are Two observations are particularly relevant to the question of minor spliceosomal intron function. First, over the past ten or so years, some studies have proposed roles for minor introns in cellular differentiation, with decreased minor splicing activity driving downregulation of minor intron-containing genes (MIGs) associated with cessation of cell cycling . Most coSecond, minor introns have been reported to show functional biases, being disproportionately found in genes encoding various core cellular functions including DNA repair, RNA processing, transcription and cell cycle functions that largely appear to hold between plants and animals ,31 thou). ParticBecause minor introns possess sequence motifs distinct from major introns ,33, it iintronIC . We used NCBI as our primary resource, since it contains the largest number of species and in many cases serves as the upstream source for a number of other genome resources. Additional species available only from JGI and Ensembl were included for completeness, as were GenBank genomes with available standard annotation files . GenBank annotations in particular are of highly variable quality and may be preliminary, draft or otherwise incomplete, which is one of the reasons we chose to also include annotation BUSCO scores for all species. Accession numbers (where available) and retrieval dates of the data for each species are available on FigShare under the following DOI: https://doi.org/10.6084/m9.figshare.20483655.Genomes and annotations for 3107 eukaryotic species were downloaded from the online databases hosted by NCBI (RefSeq and GenBank), JGI and Ensembl using custom Python scripts, and taxonomic information for each species was retrieved from the NCBI Taxonomy Database  using thINFERNAL v1.3.3 . Then, the program reciprologs (https://github.com/glarue/reciprologs) was used in conjunction with DIAMOND v2.0.13  to identify reciprocal best hits (RBHs) between all pairs of species, and to construct an undirected graph using the RBHs as edges. The maximal cliques of such a graph represent orthologous clusters where all members are RBHs of one another. In certain cases where only orthologous MIGs  were required, reciprologs was run as part of a pipeline using the –subset argument in combination with separately generated lists of MIGs for each species, which dramatically decreases runtime by constraining the query lists to only include MIGs . Full ortholog searches were required for all ancestral density reconstructions as well as all comparisons of minor and major intron conservation/loss . Local roach in .intronIC  as well as intron phase (for introns defined by CDS features) is included in the output of intronIC . These dElaeis guineensis filled the same role. For the analysis of non-canonical intron boundaries in each type of intron (major and minor), homologous clusters were filtered to include only the subset of clusters where at least two introns of the associated type were found; this was done to reduce the likelihood of inclusion of potential false-positive minor introns . In addition, a more stringent score threshold of < 60% minor-type probability (rather than ≤ 90%) was used for the identification of major introns in orthologous intron clusters.The genomes of all species were first analyzed to assess the number of putative non-canonical minor introns they contained, and those with the highest numbers of non-canonical minor introns were used to perform multiple protein-level alignments of orthologous gene sets between different pairs of species. From these alignments, all orthologous intron pairs with a minor intron (minor:minor or minor:major) were collected, and used to build orthologous intron clusters . For animals, human was included in a majority of the alignments to facilitate the generation of larger clusters ; for plants, BUSCO v5.3.2 (eukaryota_odb10). Complete BUSCO scores were then integrated into the overall dataset , where BQ1 is the first quartile of the BUSCO scores of the broad RefSeq category to which the species belongs  and BIQR is the inner quartile range of such scores. The idea behind this metric is to only assign confident minor intron loss to species whose BUSCO scores aren’t extremely low; very low BUSCO scores could indicate real gene loss or incomplete annotations, and neither of those scenarios forecloses on the possibility that the species may have minor introns (whereas a species with a high BUSCO score and a very low number of minor introns/minor snRNAs is more likely to be genuinely lacking either/both). Finally, species with very low numbers of minor introns and minor snRNAs but very high minor intron densities (≥ 1%) were categorized as uncertain to account for a small number of edge cases with massive intron loss and spurious false positives that, due to the low number of total introns, misleadingly appear to be cases of outstandingly high minor intron density (e.g. Leishmania martiniquensis). Importantly, Figure The criteria for absence of minor introns . Each annotated transcript’s length was calculated as the sum of its constituent CDS (coding sequence) features, and the longest isoform was selected for each gene. The number of introns per transcript was computed based on the same CDS data, and combined with the transcript length data to calculate introns/kbp coding sequence (genic intron density) for each gene. Intron lengths were extracted directly from intronIC output, as was intron phase and intron position as a fraction of transcript length. The relative intron position, taken as the point position in the coding sequence where the intron occurs, was calculated as the cumulative sum of the preceding coding sequence divided by the total length of coding sequence in the transcript. For comparisons of intron densities and gene lengths of MIGs and non-MIGs, species with fewer than ten putative minor introns were excluded to avoid inclusion of spurious minor intron calls (inclusion of such introns does not meaningfully change the findings as presented).Transcriptomes for all species were generated using a custom Python script , and differences were evaluated with Mann–Whitney U tests followed by Benjamini–Hochberg correction.To explore the hypothesis that gene age biases might explain differences in average genic intron density and gene length between major and minor introns Figure , GenEra a v1.1.1  was useda priori part of the set of introns in the ancestor of α and β. For all introns shared between a given species pair, for example α and γ (but not necessarily β) Nαγ, the probability of an intron from that set being found in β  isReconstructions of ancestral intron complements in different nodes was performed as described in . BrieflyNαβγ is the number of introns shared between all three species. Deriving these fractions of ancestral introns for each of the aligned species, where the product of the ancestral intron number and the fraction of ancestral introns present in each species. Finally, solving for the number of ancestral introns produces the estimatePerforming the above procedure for both major and minor introns in a given alignment allows for the estimation of the ancestral minor intron density in the corresponding node asRhizophagus irregularis, and those for plants are relative to Lupinus angustifolius. Because multiple species combinations were used to estimate the minor intron density at each ancestral node, we report the average value over all n estimates for each node asWithout a point of reference, however, and the value relative to a reference species as the average ± the standard error of the mean Figure .Homo sapiens (α), the acorn worm Saccoglossus kowalevskii (β) and the sea slug Aplysia californica (γ) as an outgroup. Within these alignments, we found 127 minor introns shared between H. sapiens and S. kowalevskii (Nαβ), 116 between H. sapiens and A. californica (Nαγ), 136 between S. kowalevskii and A. californica (Nβγ) and 102 between all three species (Nαβγ). Given these values, the number of ancestral minor introns in the aligned genes To concretize this process with a specific example, in reconstructing minor intron density for the Chordata-Echinodermata ancestor we used (among others) alignments of orthologs from For major introns, the same procedure yieldsresulting in a final estimate—based on these alignments—of minor intron density in the Chordata-Echinodermata ancestorDividing this estimate by the minor intron density found in the aligned human genes  dependent upon the accuracy of the phylogenetic relationships shown in Supplementary Figure S1. Ideally, we would have perfect confidence in all of the relationships underlying each node’s reconstruction, but such an undertaking is beyond both the scope of this paper and the expertise of its authors. While we have done our best to be assiduous in choosing nodes with well-resolved local phylogenies—which is one reason similar reconstructions have not been provided for a much larger number of nodes from less-confident phylogenetic contexts—it remains the case that our reconstructions are only fully informative with respect to the tree upon which they are based. That being said, unless the phylogeny for a given node is so incorrect as to have mistaken one of the ingroups for the outgroup , the reconstruction should still represent the ancestor of the two ingroup species.intronIC (as determined by the number of minor introns found in species with compelling evidence for a lack of minor splicing) and the high degree of correspondence of its classifications with previously-published data suggests that our analyses are capturing the majority of the minor introns in each alignment.Second, we are relying on the correct identification of minor introns within each species to allow us to identify conserved/non-conserved minor introns in multi-species alignments. Although the field in general lacks a gold-standard set of verified minor introns upon which to evaluate classifier performance, the low empirical false-positive rate of BUSCO completeness, for example), and by using multiple combinations of species to reconstruct each node. In reconstructions based upon large numbers of different alignments, the low standard errors of the estimates give us some confidence that missing data of this kind is unlikely to qualitatively affect our results.There is also the possibility that many minor introns are unannotated in many genomes . This concern is mediated somewhat by the fact that, because we are only considering gene models that produce well-aligning protein sequences across multiple species, our alignments are unlikely to contain unannotated introns of either type. Unannotated minor introns, necessarily residing in unannotated genes would of course not be considered in our analyses, which would reduce the total number of orthologous genes compared and might raise concerns that the chosen samples may not reliably represent the complete data with sufficient confidence. We have done what we can to combat this by choosing species with annotations of high quality . The Salmon output was then formatted with tximport v1.14.2  were retained for further analysis.Single-end RNA-seq reads from previously-published cell-type-specific sequencing of egularis  , and then summarized for each cell type by the mean value of the corresponding replicate z-scores (departing from the reference method in this aspect). Prior to conversion to z-scores, the raw gene expression data was normalized by running the output from tximport through the fpkm function in DESeq2. For group z-score comparisons , the median of the top 50% of z-scores from each group was used. As the z-score calculation requires there to be variation across samples, certain genes/introns were necessarily omitted under this metric.Following the methodology used by Sandberg et al. to assign a proliferation index to cell types , z-scoreIRFinder-S v2.0 . Introns with fewer than five reads supporting either the corresponding exon-exon junction or one of the intron-exon junctions (or both) were excluded. For each intron, the proportion of reads mapped to the intron-exon junction(s) versus the exon-exon junction was used to assign a splicing efficiency value for each sample (see reference for details). Within each cell type, the weighted mean of replicate splicing efficiency values for each intron was calculated in the same manner as for intron retention.Intron splicing efficiency was calculated as previously described . Brieflye v1.2.3   using BLAST v2.9.0+ (−10. Four genes from each splicing system (major and minor) were identified in Rhizophagus by this approach, consisting of orthologs to human minor spliceosome genes ZMAT5 (U11/U12-20K), RNPC3 (U11/U12-65K), SNRNP35 (U11/U12-35K) and SNRNP25 (U11/U12-25K) and major spliceosome genes SF3A1 (SF3a120), SF3A3 (SF3a60), SNRNP70 (U1-70K) and SNRPA1 (U2 A′). Gene expression values generated by Salmon for each set of genes in each cell type were averaged across replicates, and pairwise comparisons between cell types were made for the same set of genes . The significance of differences in expression between paired gene sets from different cell types was assessed using a Wilcoxon signed-rank test, with P-values corrected for multiple testing by the Benjamini–Hochberg method.Orthologs of human spliceosome components were found in  v2.9.0+  with an sqlite-utils v3.32.1 (https://github.com/simonw/sqlite-utils). A virtual private server was established to host the SQLite database, and datasette v0.64.3 (https://github.com/simonw/datasette) was used to enable public access the database via an interactive web interface at https://www.introns.info.Intron metadata for all species identified as containing minor introns in our analyses was collected, including summary statistics for all annotated genes (such as genic intron density and gene length), taxonomic classification information for each species based on the NCBI Taxonomy Database  and linkhttps://doi.org/10.6071/M36Q39.A particular advantage of the approach we have implemented is the ability for users of the database to download selected subsets of the data in accessible formats. The results of a given query, for example, can be downloaded in a variety of plain text formats, and the entire SQLite database file (≈40 GB) can be downloaded directly from the web interface. A compressed version of the same database has been deposited in Dryad at intronIC , while the remaining 672 appear to lack minor introns in all available constituent species . Consistent with previous studies  have well-supported evidence of minor introns in at least one species  and the variosean amoeba Protostelium aurantium . Although the numbers of minor introns in these species conserved as minor introns in other lineages (e.g. human) are very low, in all cases we find at least some degree of conservation. For example, in alignments between human and P. aurantium orthologs, 11% of human minor introns are conserved as minor introns in P. aurantium, comparable to proportions shared between human and many plant species  than previously described. Interestingly, the Blastocystis minor introns we do identify are highly enriched for the AT-AC subtype .As first reported by Gentekaki et al. , the parRhizophagus irregularis has a minor intron density comparable to that of humans , and Basidiobolus meristosporus, in the Zoopagomycota, has one of the highest minor intron densities outside of the Amoebozoa   Figure . Consist) Figure ,34, we dPhytopthora as described previously by other groups , with substantial minor intron conservation to other metazoan lineages  and molluscs (Mollusca) .On the other side of the bilaterian tree, minor intron densities in deuterostomes are far more homogeneous. Vertebrates have consistently high minor intron densities  and Klebsormidium nitens (n = 110), representatives of a group which until now was thought to lack minor splicing entirely (Cyanophora paradoxa (n = 77)  . Notablentirely ,23,34, aAcanthamoeba castellanii has been found to contain both minor splicing apparatus as well as a limited number of introns with minor-like sequences : tardigrades (e.g. Hypsibius exemplaris), Discoba   include the bdelloid rotifers, the springtail (Collembola) subclass of hexapods as well as the Acari (ticks and mites). The latter, in addition to its extreme reduction of minor introns generally also appears to contain a number of cases of complete  loss in the parasitic mite shmania) , Orchropshmania) ,34. We aArabidopsis thaliana)  , althoughaliana) . The clae et al. . For majArabidopsis sequences are present in multiple pairs of orthologs, which suggests that a standard reciprocal-best-hit criteria for ortholog identification was not employed and that certain introns will be counted multiple times within the overall set of alignments. As many minor introns occur in larger paralogous gene families, this methodology could lead to artificial inflation of the calculated minor intron conservation, especially given the small absolute number of minor introns present. To attempt to more thoroughly address the question of minor versus major intron conservation, we identified orthologs in many different pairs of species across a range of evolutionary distances , and calculated intron conservation using the same metric as the previous work. Across more than 100 such comparisons between animals and plants , we find no cases where minor intron conservation exceeds major intron conservation  and estimate fractions of each intron type retained from the ancestral complement. Considering loss to include both sequence deletion as well as type conversion , we found minor intron loss to be more pronounced than major intron loss in the species we examined Figure .We can also decompose the phenomena contributing to the higher degree of loss in minor introns and ask whether the rate of sequence deletion specifically, for example, differs between the two intron types. Somewhat surprisingly, we find that this form of loss is very similar between the two types of introns in species which have lost significant fractions of their minor introns Figure . BecauseHelobdella robusta (HelRob), for example, which seems to have retained a large fraction of its ancestral major introns (Dimorphilus gyrociliatus (DimGyr), found in a clade (Polychaeta) sister to Helobdella, has undergone a seemingly independent loss of minor introns of similar proportion to Helobdella under a very different modality, with loss (deletion) outweighing conversion , someti introns , has lose Figure . By contn Figure . It is uIt has been known for many years that introns often exhibit a 5′ bias in their positions within transcripts . This caArabidopsis thaliana. We were curious to see whether the same patterns were present in our own data and whether they generalized beyond the two species so far examined.Less attention has been paid to the positional biases of minor introns specifically, although at least one study  found thArabidopsis thaliana , the pattern is not broadly significant and is occasionally reversed, albeit only significantly so in animal species with less-dramatic minor intron loss  median minor intron positions more 5′ biased than median major intron positions (as the first two tests do not provide information about which intron type is biased in which direction). Among species meeting these criteria, plants were significantly over-represented (Table P = 8.9 × 10−68 by a Fisher’s exact test). The P-values for the Mann–Whitney U tests supporting the data in Table P = 6.81 × 10−09).Overall, our results point to a less-clear picture than previous work might suggest. While we do find a number of cases in animals where minor introns are more 5′-biased than major introns , after the first nucleotide of a codon (phase 1) or after the second (phase 2). In most species, major introns display a bias toward phase 0 ,88 Figu, while met al.  all have very low absolute numbers of minor introns . Interestingly, its minor intron phase distribution is almost identical to the phase distribution of its major introns (not shown). While this raises the possibility that the minor introns in Blastocystis sp. subtype 1 are false-positives, the fact that we find (a) all four minor snRNAs in the genome, (b) a  number of its minor introns conserved in Lingula anatina (not shown) and (c) putative minor introns in a closely-related species (Blastocystis hominis) provides evidence for their identity as real minor introns. Assuming they are bona fide minor introns, another possible explanation for their relative phase 0 enrichment could be that they have been more recently gained, and (under the conversion hypothesis) have not yet had time to develop the phase bias present in older minor intron sets. More thorough comparative genomics work within the clade after additional species become available would help to clarify the evolutionary picture.The species The vast majority (> 98.5%) of major introns in most eukaryotic genomes begin with the dinucleotide pair GT, and end with the pair AG ,19,35,89Because non-canonical introns do not (by definition) look like normal introns, it can be difficult to differentiate between biological insights and annotation errors when examining eukaryotic splice site diversity at scale. For example, a recent report on non-canonical introns in diverse species described significant enrichment of CT-AC introns in fungi . HoweverOur results in animals Figure  and planAs can be seen in Figure Saccharomyces cerevisiae lack introns entirely. Given the fact that minor introns appear to be arranged non-randomly within genomes .Strikingly, within species containing minor introns, when we compare the genic intron density of MIGs to all other genes, we find that MIGs are universally more intron-dense on average than non-MIGs Figure . FurtherArabidopsis and the fungus Basidiobolus meristosporus  and found that the pattern described above holds in all three genomes even when comparisons are limited to sets of genes within the same age categories . Thus, it appears unlikely that biases in gene age alone could be responsible for the observed patterns. Although an in-depth analysis of this qualitative finding is beyond the scope of the current paper, it represents an underexplored distinction between the two intron types.The fact that minor introns are over-represented in older genes paired with the observation that older genes may skew longer and more intron-dense than younger genes ,92 raisep ≪ 0.0001). One interesting aspect of the data in Figure Drosophila , but includes many additional insect species as well.While a number of studies have compared the length distributions of different intron types in a limited assortment of genomes ,36,93, wDrosophila such that in some species the difference between minor and major is relatively modest  and in others, it’s much more stark ? It should be noted as well that for Drosophila specifically, almost all of the minor introns are conserved within the genus, so the previous example is made more compelling because 100% of the D. busckii minor introns are shared with D. biarmipes, yet are far longer in the latter than the former. It did occur to us to check whether minor introns in these outlier species happen to be (for whatever reason) in genes with longer-than-average intron size, and although we have not done so systematically an examination of a number of more extreme cases found the same pattern recapitulated between minor and major introns of the same genes. For example, in the black soldier fly Hermetia illucens, the median minor intron length is 4019 bp while the median major intron length is only 105 bp. Comparing minor to major within only the minor intron-containing genes changes things, but not qualitatively—the median major intron length increases to 399.5 bp, but the difference between minor and major is still significant .Although it is not clear what immediate conclusions can be drawn from this data, some additional questions are raised: Were shorter minor introns especially selected against in these lineages, such that the remaining minor introns are disproportionately long? What is driving variation within, for example, Homo sapiens (minor intron density 0.276%), Rhizophagus irregularis (minor intron density 0.272%) and Lupinus angustifolius (minor intron density 0.273%), respectively. Figure In an attempt to quantify some of the evolutionary dynamics leading to the variegated pattern of minor intron densities found in extant lineages, we sought to estimate minor intron densities for certain ancestral nodes throughout the eukaryotic tree . For each selected node, we identified pairs of species for which the node is the most recent common ancestor and, in combination with an outgroup species, performed three-way protein-level alignments to allow us to define intron states for each species within the aligned sequences. Then, using the procedure described in , we calcLimulus polyphemus for one of the two ingroup species, as well as the fact that in any given reconstruction, the calculated intron density is limited to the genes involved in the reconstruction. With similar caveats, the low ancestral minor intron density we report in Zoopagomycota is notable as that group contains Basidiobolus meristosporus, which has the highest minor intron density so far discovered in fungi (0.554%). Overall, these results paint a picture of ancestral minor intron complements as generally analogous to those of minor-intron-rich extant species, and highlight the volatile nature of minor intron loss dynamics throughout eukaryotic diversity. It would be exciting to have these results expanded upon once phylogenetic uncertainty has been reduced throughout the tree and an even greater number of diverse genomes are available for analysis.As shown in Figure Rhizophagus irregularis, a member of the Glomeromycota group of fungi. There is clear correspondence between minor-versus-major spliceosomal sequence characteristics in the two primary differentiating parts of the introns, namely the 5′ splice site and the 3′ branchpoint structure , orders of magnitude higher than in other fungal species previously reported to contain minor introns (≈4 in Rhizopus oryzae and ≈20 in Phycomyces blakesleeanus)   .Rhizophagus, like animals and plants, upregulates splicing of minor introns in proliferating cells. We used published transcriptomic data from five cell types (four replicates each), and assessed likely proliferation profiles of the six cell types using the previously published proliferation index (PI) approach , we found that MIGs were in fact more highly expressed in cell types with higher proliferation scores Figure . On the We next compared the efficiency of minor intron splicing between cell types. Contrary to our hypothesis that minor splicing would be more active in proliferating cells, we found that minor intron retention was in fact significantly (though only modestly) higher in proliferating cells Figure . This reRhizophagus does not appear to be associated with cell proliferation, we probed these patterns more deeply.The observed association between minor intron splicing and cell proliferation in animals resonates with the long-standing finding that minor introns are overrepresented in genes involved in core cellular processes. Given that minor intron splicing in Rhizophagus MIGs revealed a curious pattern in which GO results were highly dependent on the control dataset used. Because of the dearth of Rhizophagus functional annotations, GO analyses were necessarily run by identifying human orthologs of Rhizophagus MIGs. When GO analysis was run on these orthologs as a subset of all human genes, a number of overrepresented functional categories were found, in large part mirroring results for humans. However, we realized that there is a potential bias in this analysis: all human genes present in the Rhizophagus MIG ortholog set have Rhizophagus orthologs, thus excluding most human genes , and in particular animal-specific genes. Remarkably, when we limited our GO analysis control group to human genes with Rhizophagus orthologs, we found much less functional overrepresentation . It is not entirely clear why all MIGs, but not MIGs with Rhizophagus orthologs, show substantial functional differences relative to all genes with Rhizophagus orthologs. Insofar as MIGs are ancient genes, MIGs without Rhizophagus orthologs likely represent losses in fungi; gene losses are likely to be functionally biased, perhaps explaining the observed pattern.Notably, a similar concern applies to human MIGs in general: because nearly all human minor introns are quite old, human MIGs are commensurately old, which could drive functional correlations given known differences in functional categories between genes of different ages. Indeed, when we performed a GO analysis of human MIGs with al genes ), we foual genes . These rOver the past decade , there has been a marked increase in the number of annotated genomes publicly available for bioinformatic analysis. Ten years ago, for example, NCBI had annotated fewer than 60 genomes—it now lists over 1000, and that is counting only annotations performed by NCBI itself. The breadth of data now available has enabled us to undertake a much more sweeping assessment of minor intron diversity than has ever been possible before, uncovering a wide variety of both novel and confirmatory information about minor intron dynamics across the eukaryotic tree.Rhizophagus irregularis to evaluate the origins and potential confounding factors of previously-described functional biases in minor introns through the lens of neutral evolution (Unprecedented minor intron density in the fungus Rhizophagus irregularis). Finally, we have developed an updated, publicly-available database containing minor intron information from more than 1500 species (https://www.introns.info), which we hope will serve as a useful resource for future investigations into the many remaining questions related to minor introns and their evolution.We have shown for the first time the presence of substantial numbers of minor introns as well as minor spliceosomal snRNAs in a variety of lineages previously thought to be lacking them, including green algae, fungi and stramenopiles (see Minor intron enrichment section), as well as a number of cases of potentially complete minor intron loss in both Diptera and Crustacea (Minor intron depletion). In addition, we have described findings contradicting a number of longstanding results in the minor intron literature: compared to major introns, minor introns are almost universally less-well conserved (Minor introns have lower average conservation than major introns), and do not seem—outside of plants—to be especially 5′ biased . Furthermore, we have highlighted underappreciated differences between MIGs and other genes, namely that MIGs are on average longer and more intron-dense than non-MIGs (Minor intron-containing genes are longer and more intron-rich than other genes), differences which are not simply explained by differences in gene age . We have also compiled the largest-scale data on non-canonical minor intron boundaries and minor intron lengths to date , examined variation in the process of intron loss across minor and major introns (Minor intron loss versus conversion), and derived for the first time estimates of ancestral minor intron densities for various eukaryotic clades . We have also made use of our discovery of large numbers of minor introns in the fungus Although we have been as careful as possible in curating the data for this study, as with most computational endeavors of this scale there is bound to be some amount of noise, especially given our reliance on existing gene annotations derived from heterogeneous pipelines. One persistent issue in bioinformatic analyses of minor introns is the lack of a gold standard, empirically-verified set of minor intron sequences. While comparative genomics can do a great deal of heavy lifting in this regard, it is often a time-consuming process at scale and the field in general would benefit greatly from a ground-truth set of minor introns. We look forward to this type of data—based upon minor spliceosome profiling or another similarly-empirical method—being used to improve the accuracy of minor intron identification and as a result, furthering our understanding of minor introns and their evolutionary dynamics.Blastocystis, 92% (11/12) of minor introns in alignments between Blastocystis sp. subtype 1 and Blastocystis hominis lost in B. hominis). We also document the remarkable diversity of the mechanisms by which minor introns are lost from genomes, ranging from almost exclusively deletion in certain lineages to primarily conversion in others.These results underscore a complex history of minor intron evolution. We greatly expand the number of major eukaryotic groups known to contain minor introns including multiple unicellular lineages, highlighting the punctate distribution of minor introns. We show that multiple distantly-related lineages of fungi contain minor intron densities comparable to animals and plants. However, these three groups show dramatically different patterns of minor intron distribution. At one extreme, land plants show a high degree of minor intron stasis, with similar minor intron densities across nearly all studied species. At the other extreme, fungi exhibit a wide diversity, with high minor intron densities in multiple lineages, greatly reduced numbers in multiple others, and complete absence from the globally dominant group Dikarya. Animals are somewhat intermediate, with minor intron presence in nearly all groups, but a range from very high to very low densities, and even multiple independent complete losses of minor introns. Of particular interest is the case of Dipterans, which exhibit massive reduction across the group, and yet almost no cases of complete loss. If is of great interest why these few minor introns have been so strongly retained across this clade. The diversity of minor intron conservation is also observed in terms of rates, with remarkable stasis in some groups (particularly vertebrates) contrasting with rapid turnover within single genera  have all been found to be generally fast-evolving at the genome level, including in terms of ancestral loss of spliceosomal introns overall  likely had modern densities comparable to the most minor intron-rich modern organisms . Coupleoverall  trend for lesser, not greater, conservation of minor introns compared to major introns. Interestingly, we find very similar rates of intron loss by genomic deletion for minor and major introns, suggesting that minor introns’ somewhat lower overall evolutionary conservation reflects minor introns’ ‘extra’ mechanism of loss through conversion to major introns. Our finding of similar rates of minor and major intron deletion is also not as predicted if minor introns are deleterious relative to major introns. Notably, this lack of an excess of minor intron loss is also observed in the lineages experiencing high degrees of minor-to-major conversion, which represent the best candidates for lineages in which minor introns might be deleterious. In total, then, our results suggest that neutral processes can explain much of the observed minor intron pattern across eukaryotes. This is not to say that all minor intron evolution is neutral, particularly in light of important cases of regulated and alternative splicing of minor introns; however, it may be the case that neutral processes govern most minor introns under most circumstances, and thus underlie observed patterns across both genomes and lineages.Our results are not supportive of either of these perspectives as a general explanation for minor introns across eukaryotes. First, we show that apparent functional biases among minor intron-containing genes may be largely explained by minor introns’ bias towards ancient genes: because most minor introns are old, most MIGs are also old, and core cellular processes are over-represented among old genes. This suggests that minor intron distributions across genes could simply reflect largely unbiased minor intron gain in ancestral genomes, followed by a lack of minor gain in more recent evolutionary time. Second, from our preliminary data in the minor intron-rich fungus Prior to the current work, we perceived a chicken and egg problem of functional biases among MIGs ,31 and cWhile this scenario makes sense schematically, is remains a remarkable contention that decreased minor splicing could evolve a function in cell regulation; insofar as MIGs represent a quasi-random subset of ancient genes, it seems likely that a global reduction in minor splicing would have a wide variety of impacts, many of them likely costly. Thus how failure to process a quasi-randomly chosen set of ancestral genes could evolve as a regulatory mechanism remains puzzling, and will require additional work across diverse minor intron-containing lineages.Our results do not support the emerging dominant hypothesis for the existence of minor introns, namely that minor introns provide a means for regulation of cell cycle progression. The reported lack of cell cycle-regulated minor intron splicing in fungi suggests that this association is not a general phenomenon, correspondingly weakening the hypothesis that such a function could explain the persistence of minor introns across eukaryotes generally. However, given the possibility that it may be fungi that are atypical, having secondarily lost this function, discovery and study of additional minor intron-rich lineages is a priority, as is development and testing of alternative hypotheses for the origins and functional biases of minor intron-containing genes.Possible caveats of this analysis arise from two surrogates that we have employed. First, to assess cell cycle activity/proliferation of cell types, we have used orthologs of human genes associated with proliferation. The possibility of turnover of gene expression patterns raises the concern that these genes are not an appropriate gene set to assess proliferation. Indeed, while clear statistical differences in proliferation are seen when PI genes are viewed collectively, only a small fraction (gkad797_Supplemental_FileClick here for additional data file.


The in-situ growth ensures good contact between graphene and substrate; therefore, the device performance can remain stable after multiple bending. Our results provide a highly reliable and mass-producible path for graphene-based flexible devices.Graphene is an ideal material for flexible optoelectronic devices due to its excellent electrical and optical properties. However, the extremely high growth temperature of graphene has greatly limited the direct fabrication of graphene-based devices on flexible substrates. Here, we have realized in situ growth of graphene on a flexible polyimide substrate. Based on the multi-temperature-zone chemical vapor deposition cooperated with bonding a Cu-foil catalyst onto the substrate, the growth temperature of graphene was controlled at only 300 °C, enabling the structural stability of polyimide during growth. Thus, large-area high-quality monolayer graphene film was successfully in situ grown on polyimide. Furthermore, a PbS–graphene flexible photodetector was fabricated using the graphene. The responsivity of the device reached 10 With the development of modern communication technology and the internet of things, devices with high foldability and flexural resistance are increasingly developed. Flexible devices can be bent, folded and even stretched, and their applications in electronic skin, smart textiles, electronic eyes and flexible cameras are gaining wide attention ,2,3. Gra2-x catalyst layer used in growth cannot be removed, which limits the use in flexible devices. At present, direct growth of graphene on flexible substrates for device application has not been reported.Growing graphene directly on a flexible substrate is a perfect solution to the above problems, but the growth temperature needs to be lowered than the maximum withstand temperature of the flexible substrate. Now, researchers have developed various methods to synthesize graphene films at low temperatures, including using new liquid–gas carbon sources with low pyrolysis energy ,10,11 an5 A/W. The in situ grown graphene has a good contact with the substrate, thus ensuring the long-term stability of the device in bending. In the experiment, the photocurrent of the device remained unchanged after being bent 100 times. Our results provide a highly reliable and mass-producible path for graphene-based flexible devices.In this paper, we realized the in situ growth of graphene on a flexible polyimide (PI) substrate. Based on the multi-temperature-zone CVD system cooperated with Cu sacrificial layer, the large-area and high-quality monolayer graphene film was successfully obtained at 300 °C. On this basis, a PbS–graphene flexible photodetector was fabricated. The PbS quantum dots (QDs) were spin-coated on the graphene to form a heterojunction. The PbS QDs as light absorption layer greatly enhance the device responsivity. Experiment results show that, under 792 nm laser irradiation, the responsivity of the device reaches 10As shown in 2/Si substrate. −1, 1586 cm−1, and 2661 cm−1, respectively. The D peak represents the defects and disorder of the lattice in graphene [−1 and represents the in-plane vibration pattern of sp2 hybrid carbon atoms. The position of the G peak is very sensitive to the number of graphene layers. In general, it can be calculated by the following equation [Gω is the peak position and n is the number of graphene layers. Bringing the measured G peak into the above equation, we can deduce that the obtained graphene is a monolayer. The 2D peak represents the vibration mode of the two photonic lattices and is secondary to the D peak. For monolayer graphene, the 2D peak is a single symmetrical peak with a half-height width of about 30 cm−1. As the number of layers increases, the symmetry decreases and the 2D peak splits into multiple overlapping peaks. Because the doping and stress of graphene can change the position of the G peak and the 2D peak, we also use the intensity ratio of the 2D peak and the G peak to characterize the number of graphene layers. From ID2/GI is close to 2, which indicates that the graphene is a monolayer and the defect density is very small. With the temperature decrease in Zone III, the intensity of D peak increases, indicating the graphene quality decreased significantly. The reason should be that the diffusion rate of carbon atoms on the metal surface reduced at lower temperatures and more graphene crystal nuclei are formed, resulting in more grain boundaries and stacking [ID2/GI and DI/GI growth at Zone III = 300 °C. The mean intensities of ID2/GI and DI/GI are 1.7 and 0.1, respectively, which means that the obtained graphene is mostly monolayer and of high quality. The FWHM (2D) also is a good argument in a discussion about the number of layers. We randomly selected 10 points in the graphene mapping results and the calculated average FWHM (2D) is 35 cm−1. This indicates that the whole graphene film is mostly monolayer. In order to further verify the effect of gradient temperature on the pyrolysis of methane and growth of graphene, we kept the temperature of the three zones consistent to conduct a comparative experiment of graphene growth. The graphene quality was optimized based on Raman characterization (λ = 532 nm). Due to the weak graphene signal  on PI sugraphene . In highequation :ωG = 158stacking . When th2, therefore the device has a responsivity of about 131 A/W. 2, the responsivity can even be larger than 1 × 105 A/W  of the device, the actual light energy received by the device is not very large. At the same time, the substrate is a transparent material, so the heat generated on the device during the measurement is not large and will not cause damage to the device. Based on this low-temperature growth technique, we grew graphene film in situ on PI substrate and fabricated a graphene-based flexible photodetector. In order to make up the defect of weak light absorption of graphene, a layer of PbS QDs film was spin-coated on the graphene as light absorption layer. We obtained devices with quantum dots films of different thicknesses by changing the quantum dot concentration and the number of spinnings for several times. When PbS thickness is less than 80 nm, the device photocurrent increases with the increase of PbS film thickness, but when the thickness exceeds 80 nm, the device photocurrent begins to decrease. When the thickness of PbS is small (<80 nm), the increase of PbS thickness is beneficial to increase the light absorption of the PbS film, thereby improving the responsivity. However, when the thickness continues to increase (>80 nm), the incident light will be mainly absorbed by the PbS QDs close to the surface, and this part of the QDs is far away from the graphene, and the photogenerated holes cannot be effectively transferred to the graphene channel to generate effective photocurrent.  105 A/W . However2/Si substrate shows that the Dirac point of graphene moves from +25 V to 0 V .We measured the performance of the device under bending condition. In order to effectively and stably control the bending of the device, we adhered the PI substrate to a cylinder. 5 A/W at room temperature. The device has a broad spectral response from 405 nm–1860 nm with a responsivity greater than 60 A/W. In situ growth and device process optimization improve the reliability of the device, and the photoresponse of the device did not change after multiple bending.In summary, a method for in situ growth of graphene on a flexible substrate and its application in flexible photodetectors are reported in this work. A single-crystal Cu foil was bonded onto the PI substrate as a sacrificial layer and high-quality graphene film was grown on the Cu surface at 300 °C by a gradient descent temperature-controlled CVD system. After removing the sacrificial layer, graphene can be obtained directly on the substrate. For photodetector application, a PbS QDs layer was spin-coated on the graphene surface to form a graphene–PbS heterojunction photodetector. Under the irradiation of 792 nm laser, the responsivity of the device can be larger than 102, while the stage was heated to 50 °C and maintained for 1 h. Firstly, we made a Ti–Au electrode array on the PI substrate by lithography, sputtering, and lift-off. There are two main reasons for preparing electrodes before graphene growth. When the Cu sacrificial layer was prepared, the Cu foil needed to be bonded onto the PI surface. It is difficult to achieve a strong bond between metal and organic materials, therefore, the metal electrodes can act as an adhesion layer to assist the bonding of the substrate and the Cu foil. On the other hand, there is no need to fabricate electrodes after graphene growth, avoiding the damage to graphene by electrode process. The Cu foil was attached onto the PI substrate at a pressure of 100 kg/cm4/H2 (1.5 sccm/9 sccm) gas mixture was introduced to grow graphene. The growth time was set to 60 min. Subsequently, the Cu sacrificial layer was removed by penetrating etching. The etchant used was a CuSO4/HCl solution (CuSO4:HCl:H2O = 10 g:50 mL:50 mL). Before etching, the graphene surface was spun on a PMMA (polymethyl methacrylate) layer as protective layer. During etching, the etchant will penetrate through the PMMA and graphene. After the Cu was etched, graphene and PMMA can fall on the PI surface to realize in situ growth. Finally, we removed the PMMA by acetone/ethanol rinse.Then, a PI substrate with a single-crystal Cu sacrificial layer was placed into CVD system. The graphene growth equipment we used is a three-temperature-zone quartz tube furnace with a diameter of 54 mm. The length of each temperature zone is 320 mm. The interval between the zones is 4 cm. The temperature of each zone can be heated and monitored independently. Before heating up, the quartz tube is first rinsed with argon gas for 5 min. Then, the three zones were set to 1000 °C, 750 °C, and 300 °C, respectively. The heating was carried out under a hydrogen atmosphere, the rate was controlled at 20 °C/min, and the air pressure was controlled at 2000 Pa. When the temperature of the first temperature zone reached 1000 °C, the vacuum was reduced to 110 Pa and the CHAfter the growth, the graphene film was patterned by photolithography followed by oxygen plasma etching. The size of graphene channel is 7 μm × 63 μm. Then, PbS QDs dissolved in n-hexane with a density of 20 mg/mL were spin-coated on the surface of graphene, followed by dropwise addition of 0.3 mL TBAI methanol solution (10 mg/mL) and held for 30 s to realize ligand exchange. The electrical properties were measured by an Agilent B1500A source meter. The lasers with different wavelengths were used as light sources to measure the response of the photodetector.