Intense particle beams generated from the interaction of ultrahigh intensity lasers with sample foils provide options in radiography, high-yield neutron sources, high-energy-density-matter generation, and ion fast ignition. An accurate understanding of beam transportation behavior in dense matter is crucial for all these applications. Here we report the experimental evidence on one order of magnitude enhancement of intense laser-accelerated proton beam stopping in dense ionized matter, in comparison with the current-widely used models describing individual ion stopping in matter. Supported by particle-in-cell (PIC) simulations, we attribute the enhancement to the strong decelerating electric field approaching 1 GV/m that can be created by the beam-driven return current. This collective effect plays the dominant role in the stopping of laser-accelerated intense proton beams in dense ionized matter. This finding is essential for the optimum design of ion driven fast ignition and inertial confinement fusion. A detailed understanding of particle stopping in matter is essential for nuclear fusion and high energy density science. Here, the authors report one order of magnitude enhancement of intense laser-accelerated proton beam stopping in dense ionized matter in comparison with currently used models describing ion stopping in matter. Fast ignition (FI) relies even more on a detailed understanding of ultrahigh-current ion stopping in matter, which is therefore considered as a fundamental process of utmost importance to nuclear fusion. In the fast ignition scheme9, a short and intense pulse of energetic charged particles—electrons, protons, or heavy ions—generated by an ultra-high-intensity laser, is directed toward the pre-compressed fusion pellet. The charged-particle beam requirements to achieve ignition have been discussed and studied in detail previously14 based on single-particle stopping theory. However, the collective effects induced by high-current charged-particle beams could alter significantly the projected range, the magnitude of energy deposition, and therefore change the requirements for ignition correspondingly. Besides, in the cases of ion beam-driven inertial confinement fusion and high-energy density science, which require ultrahigh beam intensity from accelerators19, no collective effects on ion stopping processes due to high beam intensity are considered nor—to the best of our knowledge—were they reported in any previous experiments.Alpha-particle stopping in dense ionized matter is essential to achieve ignition in inertial confinement fusion25. In past decades, numerous theoretical models32, some of which can be considered to be further developments of the early work of Bethe28 and Bloch29, are built to describe individual charged particle stopping in dense ionized matter. Only recently experiments with sufficient precision were carried out with dense ionzied matter to distinguish between different models35. In these experiments, incident particles are generated from laser-induced nuclear reactions34, or from traditional accelerators35. Hence the beam intensity was low, and the individual ion stopping theories can be discriminated36.Since the discovery of alpha decay and the availability of energetic fission fragments, it became interesting to study fast particle stopping processes in matter18–1022 W/cm2) have opened up perspectives in many fields of research and application44. By irradiating a thin foil with ultra-high-intensity lasers, an ultrahigh accelerating field (1 TV/m) can be formed and multi-MeV ions with high intensity (1010 A/cm2) in short timescale (~ps) are produced53. Such beams provide experimental opportunities to investigate the beam-driven complex collective phenomena59. In particular, the stopping power for these intense beam could be orders of magnitude higher than that for individual particles if the beam intensity is high enough63. In our previous experiment, we sent the laser-accelerated ion beams directly into the plasma target, and observed that the energy spectra of the ions were significantly downshifted after passing though the dense plasma64. This energy downshift was far beyond the Bethe–Bloch predictions 26, standard stopping model (SSM)32. Through PIC simulation, we attribute the high degree of enhancement to a strong decelerating electric field induced by the intense proton beam. This collective effect is the primary cause for the enhanced stopping, and it is likely to have a major impact on nuclear fusion scenarios like fast ignition, alpha-particle self-heating, as well as ion driven inertial confinement fusion.In this article, we improve the precision of the measurement by using a magnetic dipole to trim out a quasi-monoenergetic proton beam. The dense ionized target is produced by irradiating a tri-cellulose acetate (TCA) foam sample with soft X-rays from a laser-heated hohlraum. Thus the temperature and density are homogeneous across the ionized target. This state can be maintained for a period of more than 10 ns. This period is two to three orders of magnitude longer than the beam duration and the beam-plasma interaction timescale. Therefore, the target can be considered to be quasi-static. This kind of experimental scenario allows for precise measurement of intense proton beam stopping in dense ionized matter. We observed that the energy loss is enhanced by one order of magnitude in comparison  to the predictions from individual-proton stopping theories, Bethe–Bloch1+) and carbon ions with different charge states . They originate at the backside of the target by means of the target normal sheath acceleration (TNSA). The predominant particle species is H1+, because the charge- to-mass ratio is maximum for this species, and is, therefore, more effectively accelerated than the lower charge-to-mass ratio species of carbon ions. The TNSA mechanism results in a broad range of particle energies, which is not favorable for quantitative analysis of the particle energy loss. A magnetic dipole, with entrance and exit slits, was used to generate a monoenergetic beam. The ions, spatially collimated by the 500 μm entrance slit, are dispersed laterally by the magnetic dipole according to their specific p/q value, where p and q are the particle momentum and charge, respectively. A second 500 μm exit slit, selects the quasi-monoenergetic ion pulses. The selected ions consist of different particle species, with similar p/q value, they have, however, different velocities and therefore arrive at the target pulse by pulse with different time delay. In the current case, the C4+ ion pulse lags behind proton pulse by about 30 ns at the plasma target, and C3+, C2+, and C1+ pulses are delayed more, therefore the laser-accelerated carbon ions have no influence on the proton beam stopping measurement.The experiment was carried out at the XG-III laser facility of Laser Fusion Research Center in Mianyang. The experimental layout is displayed in Fig. 9H16O8, density of 2 mg/cm3 and thickness of 1 mm) to produce ionized matter. The hydrodynamic response of the heated foam target under this kind of scheme has been very well-investigated and the state has been well characterized67. Once heated by soft X-rays from hohlraum radiation, the material expansion occurs inside the target between the sponge-like structures. This micro expansion leads to target homogenization, while the volume and density of the entire target stay constant for more than 10 ns. Therefore, homogeneous, ns-long-living, and quasi-static ionized matter is generated. Unlike producing ionized matter through direct heating by high-power lasers—in which case strong electromagnetic fields are generated in the target and will greatly influence the proton transportation behavior70—here the electromagnetic fields resulted from the heating process can be neglected.A gold hohlraum converter was used to generate soft X-rays by interaction of a ns laser pulse (150 J), with the hohlraum walls. The X-rays subsequently irradiated and heated the foam target E/dx = (dE/dx)collision + (dE/dx)collective. The first term (dE/dx)collision describes the collisional stopping induced by binary interaction of the individual projectiles with the individual particles in the plasma. The second term (dE/dx)collective describes the collective stopping induced by the beam-driven electric fields. (dE/dx)collision consists of contributions from free electrons and plasma ions. The ionic contributions for partially ionized plasma include two parts, bound electrons and nuclei. In the current regime, where the protons are much faster than the thermal electrons, the contribution of the nuclei to (dE/dx)collision can be neglected77. Here in this article the nuclear stopping is excluded.The energy loss of intense ion beam in ionized matter is composed of two terms as dIn Fig. 79.In order to understand this enhanced stopping, both collective electromagnetic effects and close particle–particle interactions need to be taken into account. The most appropriate tool to simulate the conditions of the experiment is the particle-in-cell method (PIC), which in recent years has established itself as a state-of-the-art method for solving problems of kinetic plasma physics80, which is able to simulate intense beam-plasma interaction in a self-consistent way, which contains both close collisions and collective electromagnetic fields (see details in “Methods”). The simulation assumes, the incident proton beam to have Gaussian distribution in space and time, with a beam duration of 1 ps and a transverse extension of 1 mm. The energy spectrum is also assumed to be Gaussian, with the peak of the energy distribution at 3.36 MeV and FWHM of 0.10 MeV. The measured ionized target parameters were used as simulation input. The simulation was carried out in Z–Y Cartesian geometry with beam propagating along the Z direction. The size of the simulation box was 1.2 mm × 2.5 mm, with a grid size of 0.75 μm × 25 μm.We used the recently developed PIC code LAPINS16 cm−3, which corresponds to high-current case of 3 × 107 A/cm2, Fig. Ez induced by the beam-driven return current after a propagation distance of about 0.3 mm. A strong decelerating field approaching 109 V/m is generated, and contributes to the proton stopping. The proton energy spectrum after passing through 1 mm of plasma is shown in Fig. 82, where the spatial structure of the electric field is determined by the plasma density. Here the plasma wakefield wavelength is much smaller than the beam length, therefore the wakefield-induced collective acceleration and deceleration cancel out. The central energy of proton spectrum is downshifted by 0.36 MeV after passing through the plasma. As shown in Fig. 11 cm−3 and 8 × 1015 cm−3, which are defined as low- and intermediate-current cases, respectively. For the low-current case, the beam-induced longitudinal electric field Ez after propagating for 0.3 mm in the plasma is shown in Fig. Given the incident proton beam with density of 8 × 10E/dx)collision and (dE/dx)collective. Bethe–Bloch, LP, SSM models, and PIC simulation for low-current case give similar predictions for (dE/dx)collision, which is one order of magnitude lower than the experimental data. PIC simulation for high-current cases shows that when sending a very dense ion bunch into the plasma, strong electric fields can be induced, and the ion bunch is imbedded in the deceleration field. This leads to a significant enhancement of the energy loss, which fairly well explains our observation.In all, the energy loss of laser-accelerated intense proton beam in dense ionized matter consists of  and then the velocity of each particle is replaced by the newly calculated one.In the calculations, three steps are made iteratively: (i) pair of particles are selected randomly in the cell, i.e., either electron–electron, electron–ion, or ion–ion pairs; (ii) for these pair of particles, the binary collisions are associated with changes in the velocity of the particles within the time interval In order to contain both bound and free electrons’ contribution into the binary collision model, we here take the collision frequency between ions and electrons, in the above (ii) step, as,A is the atomic number of stopping medium, Z is the ionization degree of background plasmas, ni is the nucleus density of stopping medium, me is the electron mass, γ is the relativistic factor of the projected ions, β is the velocity of projected ions, Zb is the effective charge state of injected ion beams, which equals ‘1’ for the case of protons in our present studies. In Eq. /Z defines the ratio of bound electrons’ contributions. For fully ionized plasmas, Z → A, the collision frequency between ions and electrons converges tomentclass2pt{minimZ → 0, in contrast, the frequency isFor neutral atoms, At the low-temperature limit, when all electrons are bound at the nucleus, the calculated stopping powers converge to the NIST ones with the average ionization degree approaching zero as the stopping powers of cold materials can be well calculated by Bethe–Bloch formula. With the increase of temperature, more and more bound electrons are ionized, giving rise to an increased stopping power to cold matter. When the temperature is further increased, with ionizations reaching the maximum, lowered stopping power is observed, which is due to the suppression of collision frequency between projected proton beam and hot plasmas in the target.79. To take into account collective electromagnetic effects, the background electron inertia is neglected, and instead the background return current is evaluated by the Ampere’s law Je = (1/2π) ∇ × B − (1/2π)∂E/∂t − Jb − Ji, where B is the magnetic field, E is the electric field, Jb is the injected beam current, and Ji is the background ion current. Applying the continuity equation  ∇ ⋅ J + ∂ρ/∂t = 0 with the total current J = Jb + Ji + Je, where ρ is the charge density, the Poisson equation  ∇ ⋅ E = 2πρ is rigorously satisfied. The electric fields are then obtained from Ohm’s law, E = ηJe − ve × B, where ve is the background electron velocity, and η is the resistivity. Taking advantage of the Monte Carlo collision model, resistivity η is obtained by averaging over all binary collisions at each time step for each simulation cell. Finally, Faraday’s law is used to obtain the magnetic fields ∂B/∂t = − ∇ × E. This field solver, which couples Ampere’s law, Faraday’s law, and Ohm’s law, can completely remove the numerical heating and reduces significantly the numerical expense. With these advantageous features a unique tool is at hand, which can self-consistently model transport and energy deposition of intense charged particles in dense ionized matter.Simulation of large scale plasmas often results in an intractable burden on computer power. Therefore, instead of solving the full Maxwell’s equations, we combine the PIC method with a reduced modelSupplementary InformationPeer Review File


Viral infections alone are a significant cause of morbidity and mortality worldwide and have a detrimental impact on global healthcare and socio‐economic development. The discovery of novel antiviral treatments has gained tremendous attention and support with the rising number of viral outbreaks. In this work, carbonaceous materials, including graphene nanoplatelets and graphene oxide nanosheets, were investigated for antiviral properties. The materials were characterized using scanning electron microscopy and transmission electron microscopy. Analysis showed the materials to be two‐dimensional with lateral dimensions ranging between 1 and 4 µm for graphene oxide and 110 ± 0.11 nm for graphene nanoplatelets. Antiviral properties were assessed against a DNA virus model microorganism at concentrations of 0.5, 1.0 and 2.0 wt/v%. Both carbonaceous nanomaterials exhibited potent antiviral properties and gave rise to a viral reduction of 100% across all concentrations tested. Graphene oxide nanosheets were then incorporated into polymeric fibres, and their antiviral behaviour was examined after 3 and 24 hr. A viral reduction of 39% was observed after 24 hr of exposure. The research presented here showcases, for the first time, the antiviral potential of several carbonaceous nanomaterials, also included in a carrier polymer. These outcomes can be translated and implemented in many fields and devices to prevent viral spread and infection. They cause infection by penetrating and reproducing inside living host cells, consequently causing cellular damage and illness. Viruses enter the body through all possible routes and spread from one person to another through direct or indirect contact with the pathogen Baron, . VirusesEfforts on the next generation of antivirals have been focused on nanomaterials, particularly metallic nanoparticles  were investigated. The carbonaceous nanomaterials were then incorporated into polymeric fibres, and the antiviral activity of the resulting fibres (carriers) was studied to determine whether or not the materials remain effective.In this research, the inhibitory effects of graphene nanoplatelets and graphene oxide nanosheets on 22.12.1.1Graphene oxide nanosheets were prepared from graphite powder following a modified Hummers' method  (PMMA)  and chloroform were acquired from Sigma‐Aldrich and used during fibre manufacture. All solvents and chemicals were of analytical grade and used as received.2.1.2Escherichia coli T4 bacteriophage (ATCC 11303‐TB4) was used as the model organism throughout these experiments. Freeze‐dried cultures were sourced from LGC Standards and cultured following manufacturers’ instructions. Stock cultures of E. coli ATCC 11303 were stored in a MicrobankTM at −20°C, while the bacteriophage was kept at 2°C. Antiviral activity was assessed against this microorganism as it is commonly available and safe to work with in Biosafety Level 2 laboratories.ATCC Medium 129 was prepared using sodium chloride, nutrient agar and nutrient broth sourced from Sigma‐Aldrich. Phosphate buffer saline was used in the antiviral studies and purchased from Sigma‐Aldrich.2.22.2.1Graphene oxide nanosheets were analysed using scanning electron microscopy , while graphene nanoplatelets were analysed using transmission electron microscopy . Graphene oxide nanosheets were sputter‐coated with gold  for 180 s prior to imaging, while graphene nanoplatelet suspensions were prepared and drop‐casted onto carbon grids before imaging. Average diameters were estimated by measuring the width of approximately 100 specimens using ImageJ software .2.2.2E. coli was prepared by incubating a single colony in sterile medium, and a plaque assay was performed to determine the virus concentration at 0, 3 and 24 hr.T4 bacteriophage suspensions containing 0.5, 1.0 and 2.0 w/v% of graphene nanoplatelets or graphene oxide nanosheets in PBS were incubated for up to 24 hr. An actively growing broth culture of 2.2.3PMMA fibres containing 2 wt% of either graphene nanoplatelets or graphene oxide nanosheets were manufactured using pressurized gyration as previously reported  exhibited viral reductions of 20.8 ± 1.6% and 22.4 ± 1.3% for graphene nanoplatelets and graphene oxide, respectively. Further increasing the loading to 4 wt % of graphene nanoplatelets or graphene oxide nanosheets resulted in viral reductions of 26.0 ± 1.7% and 28.9 ± 1.2%, respectively. Fibres containing 8 wt % graphene nanoplatelets or graphene oxide nanosheets displayed the strongest potencies with average viral reductions of 33.6 ± 0.9% and 38.7 ± 1.1%, respectively. These results indicate that the antiviral activity of the nanocomposite fibres is in fact concentration‐dependent. Increasing the loading increases the concentration of graphene‐based nanomaterials on the surface of the fibres. Therefore, more of the active agent is exposed for the virions to interact with. A study by Mori et al  showed aThough the antiviral properties of the graphene loaded fibres were less effective when compared to pure nanoparticles, incorporating them into a polymer broadens their applications and demonstrates how they can be translated into different applications. As the graphene nanomaterials are entrapped in the fibres and not free floating, viral deactivation through direct interaction is not plausible. Therefore, only the secondary mechanism of action, production of reactive oxygen species, is functioning (Matharu et al., 4In the present study, graphene nanoplatelets and graphene oxide nanosheets exhibited antiviral activity towards DNA viruses after 3 hr of exposure. The antiviral mechanism of both materials is attributed to physical and chemical interactions, with direct nanoparticle interaction being the predominant mode of action. Both graphene nanoplatelets and graphene oxide nanosheets showed comparable antiviral activity, suggesting the oxygen functional group is expendable in the antiviral mode of action.The graphene nanoplatelet and graphene oxide polymer fibres also showed antiviral activity. The fibres show much weaker antiviral activity than the pure nanomaterials, suggesting that direct physical interaction is important for antiviral activity.This study reports, for the first time, the antiviral activity of graphene nanoplatelets, graphene oxide and nanosheets and their resulting nanocomposite fibres with a proposal for a potential mechanism of action. As a result, nanocomposites with potent antiviral properties at low concentrations can be produced by exploiting multiple driving forces at nano‐biointerfaces due to functionalization. The data presented here shed light on antiviral development, thus helping push the industry further and alleviating the burden on global health.The authors declare no conflicts of interest. The funders had no role in the design of the study; collection, analyses or interpretation of data; manuscript writing; or decision to publish the results.R.K.M. conceptualized the study, contributed to methodology, involved in validation, performed formal analysis, involved in investigation, wrote the original draft, reviewed and edited the manuscript, visualized the data and involved in project administration. H.P. involved in investigation, provided resources, wrote the original draft, and reviewed and edited the manuscript. B.C. provided resources, wrote the original draft, and reviewed and edited the manuscript. L.C. provided resources, wrote the original draft, reviewed and edited the manuscript, and acquired funding. M.E. provided resources, wrote the original draft, reviewed and edited the manuscript, supervised the study, and acquired funding.


Graphene/hBN heterostructures are promising active materials for devices in the THz domain, such as emitters and photodetectors based on interband transitions. Their performance requires long carrier lifetimes. However, carrier recombination processes in graphene possess sub-picosecond characteristic times for large non-equilibrium carrier densities at high energy. An additional channel has been recently demonstrated in graphene/hBN heterostructures by emission of hBN hyperbolic phonon polaritons (HPhP) with picosecond decay time. Here, we report on carrier lifetimes in graphene/hBN Zener-Klein transistors of ~30 ps for photoexcited carriers at low density and energy, using mid-infrared photoconductivity measurements. We further demonstrate the switching of carrier lifetime from ~30 ps (attributed to interband Auger) down to a few picoseconds upon ignition of HPhP relaxation at finite bias and/or with infrared excitation power. Our study opens interesting perspectives to exploit graphene/hBN heterostructures for THz lasing and highly sensitive THz photodetection as well as for phonon polariton optics. Long carrier lifetimes are beneficial for graphene-based optoelectronics, but carrier recombination processes in graphene possess sub-picosecond characteristic times. Here, the authors report carrier lifetimes ~30 ps at low energy in graphene/hBN Zener-Klein transistors, attributed to interband Auger processes. Importantly, for applications they keep their valuable performance up to room temperature. Graphene/hBN heterostructures are very attractive for the development of interband semiconductor laser schemes at THz frequencies owing to the gap-less electronic band structure of graphene3 and the fine low-doping control. For the realization of a THz laser, carrier lifetimes of a few tens of picoseconds are needed to reach long-lived optical gain. In addition, sensitive THz photodetectors are achievable in graphene/hBN heterostructures owing to the high carrier mobility in encapsulated graphene and its broad absorption spectrum5. For a compromise between sensitivity and speed in such THz photoconductors, carrier lifetimes of a few tens of picoseconds are also required. More generally, the recombination dynamics of non-equilibrium carriers close to the Dirac point in the encapsulated graphene layer plays a crucial role in the performance of interband optoelectronic THz devices and recombination times of at least a few tens of picoseconds are often highly desirable8.Graphene/hBN heterostructures uniquely combine high-quality graphene owing to the use of encapsulating layers12. Mostly, femtosecond visible or near infrared pulses are used to generate hot non-equilibrium carriers of large density at high energies. After photoexcitation, the electron/hole populations are both redistributed (by energy-conserving intraband carrier–carrier scattering) and relaxed  within ∼50 fs. It results in two independent lower-energy broad electron and hole distributions, for which efficient interband Auger recombination processes leads to a single Fermi–Dirac distribution for conduction and valence populations within 100–200 fs. A subsequent cooling process occurs mediated by interband optical phonon emissions within 1–2 ps and by less efficient intraband acoustical phonon scattering13. Very recently, an additional recombination channel with picosecond decay time has been demonstrated in hBN encapsulated graphene relying on the coupling of hot carriers in graphene with hyperbolic phonon polaritons (HPhPs) in the hBN layers15. Few studies have used optical pump with energies lower than optical phonon energy and reported significant slowing of the carrier relaxation16. However, owing to the excitation of a large density of hot carriers, optical phonon emission remained the predominant relaxation channel17. In spite of intensive work, the investigation of recombination dynamic for carriers at low photon energy and fluence remains elusive in graphene, notably under dc bias control.The recombination dynamics of non-equilibrium carriers in graphene has been widely investigatedω = 117 meV) and set graphene at charge neutrality point (CNP) where transport is dominated by interband Zener tunneling19. This provides weak incident photon density and corresponds to a photon energy between the Fermi-level fluctuations  and the optical phonons of graphene and hBN (ℏΩ ≈ 170–200 meV). Focusing on this low-energy domain, we unveil on a strong photoconductive regime involving a remarkably long Auger recombination time (~30 ps) and a switching to a short HPhP emission time at a finite dc bias or mid-infrared optical power. It also allows to investigate the interplay between optical and electrical pumping.Here we use continuous mid-infrared laser excitation . The bottom hBN layer, of thickness 67 nm, limits electrostatic doping to the range ±0.15 × 1012 cm−2. The thickness of the Ni layer is set to 12 nm to be semi-transparent to mid-infrared light with a measured transmission of T = 10.9%. From low-bias resistance measurements at 4 K reported in Fig. 2/Vs, a residual carrier density of n0 = 4 × 1010 cm−2 ascribed to residual charge puddles due to disordered potential likely created by air gaps at the Ni–hBN interface, and a contact resistance Rc = 650 Ω. As discussed in Supplementary Note 20.We investigate a transistor Fig.  fabricatVDS (which follows VCNP = Const. + 0.56 VDS)19. The dark current, Idark, at the CNP and at 4 K follows a superlinear bias dependence  doping; to this end, we compensate for drain doping by a careful calibration of the gate voltage at the CNP as function of 2 laser of wavelength λ = 10.6 µm, i.e. photon energy of 117 meV), we investigated the photoresponse of the graphene/hBN transistor at energies below the in-plane optical phonon energy branch (170–200 meV) of both graphene and hBN. The laser spot diameter is focused on the device with a waist of 21.2 µm quasi-matching the sample length. Figure 22. By contrast, the photocurrent at finite source-drain bias is symmetric with a maximum at the sample center. It has the same polarity as the dark current and its maximum value is seven times larger than the maxima in the unbiased condition. The spatial profile of the photocurrent is well described by the convolution of a constant photoresponse along the channel with the Gaussian profile of the laser beam . As a result, the photoconductive effect, where photoexcited electrons and holes are accelerated in opposite directions by an electric field, dominates over alternative photocurrent mechanisms at the CNP and at finite source-drain bias. As mentioned above, the photocurrent that relies on photoconductive effect is strongly sensitive to electrostatic doping. This is illustrated in Fig. 25, these were in a regime of high-photon energy (>0.7 eV).Let us discuss the competing mechanisms responsible for this photocurrent at finite source-drain bias in grapheneIn the following, we investigate successively three relevant photoconductive regimes: (i) the linear regime where both bias and optical power are low, (ii) the non-linear regimes where either power or bias exceed the linear photoconductive limit, and finally (iii) the full photoconductive response including all regimes.23. The photocurrent reaches the µA range. From these measurements and electrical characterization, we extract the photoexcited carrier density JPC = µ = 3.2 m2/V/s and 9 to ~0.7 × 109 cm−2. Note that the photoinduced electron and hole densities given by 7 cm−2) in ideal intrinsic graphene at T = 4 K. However, it remains relatively weak compared to the residual carrier density. To attain insight into the efficiency of the recombination processes, we can estimate the photoexcited carrier recombination time from the photocarrier densities and light excitation conditions23. The carrier diffusion is disregarded since the illumination and electric field are nearly uniform and the diffusion time is in the nanosecond range, i.e. much longer than recombination times. From a rate-equation approach, it follows that the total number of photoexcited carriers, with average density α0 is the light absorption, Slaser the area of the laser spot, ℏω is the photon energy, τ is a phenomenological carrier lifetime, M is a carrier multiplication factor  and Po the laser power incident on the sample. Po is lower than the incident optical power Pinc by a factor 0.63 due the larger size of the optical Gaussian beam with respect to the sample dimension. The light absorption α0 by the graphene layer is calculated using the transfer matrix method considering the layered geometry of our device (the hBN dielectric film of ~67 nm thickness and the Ni back gate of 12 nm thickness). We calculate the ratio of the electric fields at the graphene plane Et and of the incident light E0 (see Supplementary Note α0 = A(Et/E0)2 = 0.11% where A = 2.3% is the interband absorption in free space of monolayer graphene (in the absence of Pauli blocking at the CNP). We verify that the transmitted light through the device and the semi-transparent Ni electrode is proportional to the incident optical power, indicating no absorption saturation effect. In our experimental conditions, M is predicted to be close to unity. Indeed Jago et al. have calculated that M is typically <1.2 when photocarriers, with initial energy of 0.65 eV, evolve in a dc electric field27. Moreover, Tomadin et al. have predicted that M tends to unity when pump photon energy is lowered below 0.5 eV in undoped graphene sample28. Figure M = 1). We report on an unprecedented carrier lifetime of >30 ps  is expected to be the remaining scattering mechanism involved in the recombination of non-equilibrium carriers (i.e. photoinduced carriers in excess to the dark ones) in hBN/graphene/hBN transistors  with eV0 ~ (ℏΩII – ℏω) ≈ 54–84 meV. We therefore attribute the additional recombination channel to the emission of HPhPs in hBN layer41, consistent with previous works on similar hBN-encapsulated graphene where picosecond HPhP cooling times were reported42. In particular, a similar threshold was observed in noise thermometric experiments using samples of similar mobility19. Indeed, h-BN supports large number of propagating HPhP modes  that can be very efficiently coupled to the carriers in graphene via near-field coupling (i.e. super-Planckian coupling)41. These previous works have also demonstrated that recombination of electron–hole pairs in graphene through the direct coupling with intrinsic optical phonon in graphene (of comparable energy ħΩOP = 170–200 meV) plays a minor role in hBN/graphene heterostructures. This is because non-polar optical phonons are coupled to electrons via the deformation potential, giving rise to a smaller relaxation rate.We now turn to non-linear regimes to further explore the hBN/graphene heterostructure-based devices. At low-incident optical power, we observe in Fig. Γ, dominating over impurity scattering rate (τ < 0.3 ps deduced from the mobility). In graphene, carrier–carrier scattering is prominently collinear (due to momentum/energy conservation), meaning that it preserves momentum direction with respect to electric field orientation. Considering that Fermi velocity is energy independent in single layer graphene, the effect of electric field in carrier acceleration is independent of energy relaxation and therefore reminiscent of a ballistic case. In this picture, the electric field (bias) dependence maps the photocarrier energy distribution with respect to the HPhP energy. Figure eV0 = ℏΩ − ℏω < 0.1 eV. The bias dependence thus provides an energy spectroscopy of the local carrier energy distribution.Figure Δnphoto coupled to the HPhP, which falls in the range of 109 cm−2 for Popt = 1 mW, and the corresponding power drained away by HPhP emission given by PHPhP = ΔnphotoℏωHPhP/τ, which scales with the µW level.As discussed in Supplementary Note Psat ≈ 15 mW, independent of the graphene bias, corresponding to an absorbed optical power of 10 μW. To explain this non-linearity, let us consider that under large illumination, intraband carrier–carrier interactions (with ultrashort relaxation times of ∼20 fs) become more efficient, leading to a broadening of the hot carrier distribution within the electron and valence bands. Some fraction of hot carriers gain energy, potentially exceeding ℏΩII, enabling some photoexcited electron–hole pairs to efficiently recombine in the hyperbolic optical phonon modes of the hBN layer. Consequently, we attribute the photocurrent saturation observed at high incident optical power to the enhancement of photoexcited carrier rates that efficiently recombine into HPhPs. As shown in Supplementary Note Δnphoto coupled to the HPhP  and Popt , respectively. We deduce V0 = 0.07 V, P0 = 0.5 mW, 1/Γ1 ≈ 35 ps, and a unique −1/Γ2 ≈ 0.7 ps for both fits. Remarkably, the two different determinations of the threshold, from the onset in Fig. Finally, we enlarge scope to the full photoconductive response including bi-non-linear effects. Figure Pabs. The linear regime appears as a red plateau; the non-linear regimes of Fig. Figure In conclusion, using mid-infrared photoconductivity measurements we have investigated recombination processes of carriers photoexcited at low density and energy in graphene/hBN Zener–Klein transistors. We have shown remarkable long carrier lifetime, ~30 ps, in quasi-intrinsic graphene, ultimately limited by interband Auger processes. Long carrier lifetime in graphene/hBN heterostructures could have important implications for THz lasing and highly sensitive THz photodetection. We have also unveiled the possibility to switch on at finite dc bias or mid-infrared optical power the very efficient electron–hyperbolic phonon recombination channel. This allows the carrier lifetime control, which falls below a few picoseconds upon ignition of HPhP relaxation. Investigating recombination processes for non-equilibrium carriers at low density and energy in alternative materials such as bilayer graphene and topological insulators could provide unique basic physic knowledge. Furthermore, we have investigated the interplay between optical and electrical pumping and demonstrated the opto-electrical pumping of HPhPs in the hBN layer at high Joule power and high optical power. These works could promote graphene/hBN heterostructures as a platform for phonon polariton optics and nanoscale thermal management.2/Si substrates. We identified monolayer graphene sample by optical contrast and Raman spectroscopy, and clean hBN flakes were chosen after bright- and dark-field optical microscopy. Afterwards, we composed the hBN/graphene/hBN van der Waals heterostructures using a hot pick-up technique and we transferred the sandwich on the top of a 12-nm-thick Ni electrode. We localized the encapsulated graphene using Raman spectroscopy and we measured the hBN thickness and roughness using atomic force microscopy. After the sample characterization, we performed e-beam lithography on the heterostructure in order to define the design of the device (W × L = 10.4 µm × 20 µm) on the cleanest region of the sandwich and to obtain an HSQ resist mask. This mask was used to etch (Reactive Ion Etching) the top hBN layer in order to connect the graphene with one-dimensional edge contacts43. The last step of the device fabrication was the e-beam lithography to design the source, drain, and gate electrodes and metal evaporation (Cr-Au).The monolayer graphene and hexagonal BN flakes were produced by micro-mechanical exfoliation of bulk crystals on SiO2 laser delivering 10.6 µm wavelength light modulated at 5 kHz. The laser light is focused on the sample using an aspheric Ge lens. The sample is placed within a liquid He cryostat with ZnSe optical window. The photocurrent signal is measured with a lock-in amplifier. A photovoltaic multiple junction detector is used to measure the mid-infrared light transmitted through the hBN/graphene heterostructure-based device.The experiment is based on a COSupplementary Information


Urogenital sarcoidosis is very rare. PubMed search for “testicular sarcoidosis” returned only 26 articles. It usually affects the epididymis, followed by testis and vas deferens. It typically occurs in young adults. Symptoms are usually asymptomatic unilateral or bilateral scrotal swelling, testicular pain. Testicular sarcoidosis could be diagnosed in patients whose chief complaint is infertility. In the article by Kimura The differential diagnosis of urogenital sarcoidosis includes testicular tuberculosis, malignant lymphoma and testicular tumor.Diagnosis routine usually involves ultrasound examination of scrotum. Gallium‐67 scintigraphy also can be done. Sonographic examination of the scrotum usually reveals multifocal well‐defined, round, hypoechoic intratesticular lesions.The association between infertility and sarcoidosis is unknown. There are several reports on azoospermia and oligozoospermia in patients with sarcoidosis. Several causative explanations are possible. First is replacement of testicular tissue with granulomas. Another is sarcoidosis of epididymis resulting in obstructive azoospermia. Local effect of granuloma on spermatogenesis or systemic manifestation of sarcoidosis as secondary hypogonadism might also happen. Steroid treatment alleviating symptoms of sarcoidosis usually result in improvements in sperm count.Chronic sarcoidosis tends to relapse. Thus, exacerbation of symptoms in patients with testicular sarcoidosis could happen after remission period.The author declares no conflict of interest.


The sudden turn had only a modest effect on capture and error location, and the analyses suggested that the birds had adjusted their tracking to the novel motion. In Experiment o angle. The occluder produced a disruption in capture success but did not delay capture. Error analyses indicated that the birds did not adjust their tracking to the new motion on turn trials following occlusion. The combined results indicate that pigeons can anticipate the future position of a stimulus, and can adapt to sudden, unpredictable changes in motion but do so better after a disappearance than after an occlusion.Despite being observed throughout the animal kingdom, catching a moving object is a complex task and little is known about the mechanisms that underlie this behavior in non-human animals. Three experiments examined the role of prediction in capture of a moving object by pigeons. In Experiment  Successful capture of a moving object is a complex task. It requires the organism to perceive the object, determine its path of movement, plan the object-directed action and move the capturing device  to the correct location for interception  served as the experimental subjects: Black 50 (B50), Violet 42 (V42), and Green 83 (G83). They had recently participated in experiments where they captured simple linear motions . One wall of the chamber was fitted with an 18 × 25 cm resistive touch screen  that was situated in front of a 15-in TFT monitor that was turned on its side. The monitor was set at a resolution of 640 × 480 pixels for the duration of the experiment. On the opposite wall of the chamber was a magazine pellet dispenser  and clicker . Individual 45-mg pigeon pellets were delivered through a rubber tube into a food cup  that was located 2 cm above the grid floor. A houselight was located on the top-right corner of the wall above the food cup; this delivered diffuse illumination to the pigeon chamber at an intensity of approximately 200 lux . A speaker, which was positioned outside the pigeon chambers, emitted a diffuse 60-dB white noise to mask sounds outside of the room.Responses were recorded from the touch screen via a USB touch screen controller . Control of the feeder and houselight was accomplished by a digital I/O card . A video splitter  allowed simultaneous presentation of images to the control room and operant chamber. Two Viglen Genie P4 computers located in an adjacent room delivered the experimental procedures and recorded data in E-prime v1.1. At the time of each peck, the location of the peck and the position of the stimulus were recorded in the form of XY coordinates with a time tag.Because the pigeons had recent experience capturing linear motions  the stimulus travelled in a linear path for a minimum of 7.5 cm and a maximum of 15.0 cm before making a sudden 90° turn; (2) during the pre-turn motion, any pecks that fell on the stimulus had no consequence; (3) following the turn, the normal training contingencies were in place. Pecks on the stimulus were counted as captures and resulted in termination of the trial and food delivery. Misses resulted in the stimulus continuing towards the screen boundary in a linear path. If the pigeon failed to capture the stimulus, it would move smoothly off screen when it reached the opposite side.There were eight types of turn trials, labeled according to pre- and post-turn motion direction: Right-Down, Left-Down, Right-Up, Left-Up, Down-Right, Up-Right, Down-Left, and Up-Left. There were three presentations of each of the turn trials, which were randomly intermixed among the 60 original training trials, yielding a total of 84 trials. In all other respects, testing was administered in the same manner as original training.Capture responses were assessed with two measures. The proportion of trials ending in a capture was the number of trials ending in a capture divided by the total number of trials in a session. The distance travelled before capture was computed from the point where the stimulus first became eligible for capture to the point of capture. Analyses on turn trials were conducted on pecks that occurred after the turn, once the stimulus was eligible for capture. Because the capture area on turn trials was less than on training trials, the data from training trials were truncated to equate capture opportunity on the two trial types. This was accomplished by only including captures that occurred within the initial portion of the straight trial that was equal in distance to the comparable turn trials ; captures occurring beyond this initial area were excluded from the analysis.For the error analysis, anticipatory and lagging errors were examined by determining the error position relative to the center of the stimulus. Errors in the same dimension as the motion (motion-relevant errors) were expressed as lagging behind the stimulus or leading in front of the stimulus.In addition, to examine within-trial history effects on errors, a regression analysis was conducted. It assessed the extent to which the previous and current motion directions predicted the error positions after the turn or following trial onset on straight trials. The previous motion was coded as the initial motion on both turn and straight trials, and the current motion was coded as the post-turn motion on turn trials and as the initial motion on straight trials. For example, on a rightward motion straight trial, the previous motion was rightward and the current motion was rightward, whereas on a rightward-upward turn trial the initial motion was rightward and the current motion was upward. The errors here were entered as error positions which coded the distance of the peck from the center of the stimulus in both the X and Y planes.For all analyses of turn trials, except the regressions, the data was collapsed across motion direction; this was for two reasons. First, although different motions resulted in somewhat different pecking patterns in the straight portion of the trials, the effect of the turn was highly consistent across motion types. Second, due to the small number of turn tests per session the data on turn trials were more variable than on straight trials. By collapsing across motion types, this resulted in an increase in stability of the test data.F = 1.2. There also was no significant effect of session, F < 1, nor was there any interaction between Turn × Session, F < 1. In examining the individual birds, two of the birds performed slightly worse on turn trials and one bird performed similarly on both trial types.The two measures of capture responses are displayed in Fig. F < 1, but there was an effect of session, F = 3.1, p = .047, but no significant effect of Turn × Session, F = 2.4, p = .091. In examining the individual birds, one bird captured the turn stimulus after a comparable distance to the straight trials, one bird was slightly later in capturing the stimulus on turn trials, and one bird was slightly earlier on turn trials. Overall, there was no consistent pattern to the performance across individuals. Panel c displays the distribution of capture locations. The greatest likelihood of capture occurred at the first point of eligibility and the distribution of capture locations did not appear to differ on straight and turn trials. The capture distributions of the individual birds were highly similar in shape to one another.Panel b displays the mean distance travelled from the start of the motion on straight trials or the turning point on turn trials until the point of capture. There was no indication of any effect of the turn, t(2) = 2.1.Figure Data Analysis) for each motion type following the turn  with the predictors of previous motion direction, current motion direction, and straight versus turn motion type. The dependent variable was the mean error relative to the center of the stimulus  revealed highly similar pecking patterns on the initial component of the trial in comparison to normal straight trials. And, there was no significant interaction of turn and session, indicating that the birds adapted fairly quickly to the turn stimulus. It therefore seems that the constraint did not impinge on the pigeons’ usual tracking performance.The ability to adjust readily to the turn may have been promoted by the constant visual input available on the trial. Experiment Maccaca mulatta) found that they were able to anticipate the reappearance of a moving stimulus when it disappeared behind an occluder, but if it just disappeared (without apparent reason) they were unable to maintain pursuit over the disappearance  at the point of the turn. Thus, the stimulus reappeared on a different trajectory from the initial motion that was displaced by 90°, but at the correct time given a speed of 3.40 cm/s. There was one turn-disappearance trial for each of the eight possible motion combinations in each session.There were a total of 32 test trials that were randomly intermixed with 40 normal training trials for a total of 72 trials. The contingencies of reinforcement were the same during the latter portion of the test trials (after the turn/disappearance) as for the normal training trials. The birds were tested until they met a criterion of at least 70% correct to each of the test types for two consecutive days; this required 40 sessions for Birds B50 and G83 and 50 sessions for Bird V42.Phase 2 was conducted immediately after Phase 1 and was identical in all respects except that the period of disappearance was increased to 1.32 s (or a movement of 4.5 cm). The birds were trained to the same criterion as Phase 1, requiring 40, 22, and 30 sessions for Birds B50, V42, and G83, respectively.Data Analysis). As seen in the figure (panel a), it appears that the disappearance trials, particularly the straight-disappearance trials, resulted in poorer performance than the normal trials, a result that was verified by the statistical analysis, F = 73.3, p < .05. This effect was driven heavily by Bird V42, which displayed a large disruption in performance following stimulus disappearance, particularly on the Straight-Dis trials. The other birds performed more similarly to all four trial types. There was no effect of the turn on capture success, F = 1.1, no effect of session, F < 1, Turn × Disappearance, F < 1, Disappearance × Session, F < 1, Turn × Session, F < 1, or Disappearance × Turn × Session, F = 1.2.Figure F = 12.4, p = .072. There was also an effect of session on performance, F = 6.1, p < .001, due to improvements in performance over the course of testing. Although performance appeared to improve more for the disappearance and turn trials than for the straight trials, there was no interaction of session with the other variables [all Fs < 1.4]. Given that there were changes over sessions, further comparisons were conducted to assess the effect of disappearance on the mean capture location. Disappearance did result in significantly later capture in block 2, 4, 6, and 11 . The effect of the disappearance on capture location can also be seen in the distribution of capture locations, shown in panel c. Stimulus disappearance resulted in a shift in the distribution so that peak in capture did not occur until around 1.5-2.0 cm after the stimulus reappeared; thereafter the capture distribution declined in a manner similar to the normal straight and turn trials. All three birds displayed a deficit in capture location following disappearance, but the magnitude of the effect varied somewhat across birds .The mean distance travelled before capture is shown in panel b. Here, it was disappearance appeared to result in later capture, but this did not achieve statistical significance, F = 14.1, p = .064. The birds also appeared to lag more on the trials in which the stimulus disappeared briefly, however, again there was no significant effect of disappearance, F < 1, nor was there any interaction of turn and disappearance, F < 1.Figure t = 4.79, p < .001. There were no significant effects of the previous motion, β = .04, t = 1.2, straight versus turn, β = .01, t = .16, or disappearance, β= -.06, t = -.72, on the error locations.A regression on the mean error locations with the predictors of previous motion, current motion, straight versus turn, and disappearance versus constant revealed a similar effect to Experiment F = 6.3, p = .127. There was no effect of turn, F = 2.1, nor was there any Disappearance × Turn interaction, F = 1.8. There also was no effect of session, nor any interaction of session with the other variables, all Fs < 1. In examining the individual birds, all three birds displayed a modest deficit in capturing the Straight-Dis and Turn-Dis stimuli, and one bird exhibited an additional deficit in capturing Turn stimuli. The magnitude of the deficits varied across birds from 10%-30%.Panel a of Fig. F = 26.6, p = .036, where the stimulus was caught later on disappearance trials. There was no effect of the turn, F < 1, or Turn × Disappearance interaction, F = 5.1. There also was no change over sessions, F < 1, nor was there any interaction of session with any of the other variables (largest F = 1.2). The distribution of capture locations (panel c) shows that the peak in capture responses occurred approximately 2.5-3 cm later and then declined gradually. All three birds displayed later capture on disappearance trials (both Straight-Dis and Turn-Dis), but the magnitude varied slightly across birds .Panel b reveals an effect of disappearance on mean capture location, F = 43.5, p < .05. There was also a main effect of disappearance, F = 83.7, p < .01, and a significant Turn × Disappearance interaction, F = 82.3, p < .01. Post-hoc analyses revealed that the interaction was due to the birds pecking significantly ahead of the stimulus on the straight normal trials compared to the other trial types.Figure t = -4.70, p < .001. There was no effect of the previous motion, β = .037, t = 1.0, straight versus turn, β = 0.01, t = .02, or disappearance, β = -.05, t = -.62.A regression examining the role of the current and previous motion on errors on normal and disappearance straight and turn trials revealed the same pattern of results as in the previous phase, with a strong effect of the current motion direction on error locations, β = -.17, The disappearance of the stimulus for either 1.5 cm (0.44 s) or 4.5 cm (1.32 s) had only a modest, non-significant effect on capture success, indicating that the disappearance did not disrupt capture. However, both durations of disappearance caused a decrease in capture efficiency and thus the stimulus was caught later on the disappearance trials. In fact, it appeared that the probability of capture at a given point shifted approximately 1.5 cm later for the trials with a 1.5-cm disappearance and 3 cm later for trials with a 4.5-cm disappearance. This suggests that some disruption to the anticipatory mechanism occurred and that longer periods of disappearance were more disruptive.This idea is supported by the error analyses. The short disappearance had a moderate  effect on the mean error position in that the birds lagged behind the stimulus more. When the stimulus disappeared for a greater period (4.5 cm), there was a greater effect on the mean error position with an increase in lagging errors. Regression analyses revealed that the current motion was the only significant predictor of error locations, indicating that the birds were correctly tracking the post-turn motion, even if they were lagging to a greater extent. If there had been a residual effect of the pre-turn motion on performance, then this would have indicated some persistent effect of the early visual information on pecking locations, but this was not the case.Overall, the pattern of results in the present study is consistent with the notion that the disappearance resulted in a period where the pigeons disengaged from tracking the stimulus. When the stimulus reappeared, there was a lag before tracking was re-engaged and this was greater than the normal lag to begin tracking at the start of a trial. This was seen both in the later capture and greater lagging errors, and the effect was larger when the stimulus disappeared for a longer period. But, once tracking was re-engaged, the birds appeared to track the motion appropriately. = 21.9, p = .043. There was no effect of the turn on capture success, F = 4.6, but there was an Occlusion × Turn interaction, F = 230.1, p = .004. Follow-up analyses indicated that indicated that the Straight-Occ trials resulted in poorer performance than the Straight and Turn-Occ trials. There was no effect of session, F = 1.3, nor any interaction of session with the other variables (largest F = 1.4).Capture responses are displayed in Fig. F = 19.2, p = .048. However, there was no effect of turn, session, or any interactions of turn or session with the other variables (largest F = 1.9). In examining the distributions of capture locations (panel c), it appears that occlusion resulted in a modest shift in the peak capture location of around 0.5-1.0 cm. The individual birds all displayed later capture on the occlusion trials, but the magnitude of the effect varied across birds .There also was a significant main effect of occlusion on the mean capture location, shown in panel b, F = 5.7, but did reveal a main effect of occlusion, F = 48.3, p < .05, with birds lagging more on the occluder trials. There was a also a significant Turn × Occlusion interaction, F = 29.7, p <. 05. Post-hoc analyses revealed that the significant interaction was due to the birds pecking significantly further ahead of the stimulus on the straight normal trials compared to the other motions.Figure t = 2.0, p < .05. The current motion direction did not predict errors β = 0.02, t = .5, and there was once again no overall impact of straight versus turn, β = .03, t = .3, but there was a significant effect of occlusion versus non-occlusion on errors, β = -.19, t = -2.0, p < .05.A regression examining the role of the previous and current motion on post-occlusion errors on normal and occluded straight and turn trials revealed that previous motion direction was the primary predictor of error locations, β = 0.09, A 1.5-cm occlusion of the moving stimulus disrupted capture success on straight-occluder trials. This stands in contrast to the general lack of effect that turns and disappearances had on capture success in the previous experiments. A disruption of capture success indicates a loss of stimulus control over tracking behavior, and that there was a general disruption in the tracking process. It is possible that the presence of a novel stimulus on the screen may have caused this disruption by competing with the moving stimulus for attention, as has been observed in infants  increase in lagging errors. The regression analysis conducted on the errors indicated that the birds successfully adjusted their tracking and used the correct motion following unpredictable turns when visual input was available during the turn  over an occlusion is highly adaptive for both predator and prey animals. Despite this clear adaptive value, pigeons are notoriously poor at recognizing partially occluded objects (e.g., Cerella, The use of touchscreen technology allowed us to monitor both capture and error behavior with great accuracy. However, resistive touchscreens do not count every single peck because some lighter intensity pecks fall below the resistance threshold. As such, some information is likely to be missed and this could affect the results, for example, by reducing capture rates. However, given that this issue is present on all trials we do not believe it impacts our overall interpretation of the results. Another issue relates to how pigeons peck when confronted with smaller objects as used here. When smaller grain-like stimuli are presented, pigeons peck in a manner consistent with how they peck at food (Jenkins & Moore, Wilkinson and Kirkpatrick  found thDespite the apparent differences in the mechanisms underlying their tracking behavior, the pigeons’ responses to disappearances and occlusions appear to be similar to those observed in primates (e.g. von Hofsten et al.


Graphene is one of the most favorite materials for materials science research owing to its distinctive chemical and physical properties, such as superior conductivity, extremely larger specific surface area, and good mechanical/chemical stability with the flexible monolayer structure. Graphene is considered as a supreme matrix and electron arbitrator of semiconductor nanoparticles for environmental pollution remediation. The present review looks at the recent progress on the graphene-based metal oxide and ternary composites for photocatalysis application, especially for the application of the environmental remediation. The challenges and perspectives of emerging graphene-based metal oxide nanocomposites for photocatalysis are also discussed. Graphene is a 2-D material composed of layers of carbon atoms crammed into a honeycomb network and has become an escalating star on the prospect of materials science in the past many years ,2,3. GraThe growth of graphene-based composites provides a significant milestone to multiply the application enactment of metal oxide nanomaterials in photocatalysis, as the hybrids have adaptable and suitable properties with superior performances over the individual oxide nanomaterials. With keeping this in mind, considerable efforts have been made on decorating graphene with metal oxides . GraphenIn this context, focusing on the recent developments, an attempt is made in the present review to discuss the advantages and disadvantages of the composite in comparison with pristine graphene.Different metal oxides-GO/rGO composites, their photocatalytic activities and synthesis process are discussed in the following sections as well as in Table 1. However, the photocatalytic performances of metal oxide-GO/rGO composite photocatalysts for the degradation of different pollutants are tabulated in Table 2.3 catalyst dosage has a substantial impression on the photocatalytic activity. The finest Sulfamethoxazole (SMX) removal efficacy was achieved when rGO-WO3-200 loading was 1.0 g L−1, and this study demonstrated that the dosage of the catalyst is crucial for the photocatalytic activity. SMX degradation over rGO-WO3-200 was significantly influenced by neutral pH and displayed the pre-eminent process [3–nanocomposite and WO3 was achieved by 84% and 40% respectively, attributed to the larger specific surface area and lower band gap energy [3 and rGO sheets and suppressing the electron-hole pair recombination in the WO3-rGO nanocomposite [3/GO composites revealed an enhanced photocatalysis under the visible light, which was two-folds of pure WO3 that reduced the recombination of the photogenerated electron-hole pairs and increased the visible light absorption efficiency [rGO-WO process . Photodep energy . Outcomep energy . The enhomposite . WO3/GO 3O4/rGO composite exhibits better photocatalytic activity in a low concentration of Methyl Orange (MO). The higher stocking dose of Co3O4 on Co3O4/rGO contributes more on the activity [α-MoO3 from 2.82 to 2.51 eV [3O4-rGO hybrids were reported to completely oxidize 20 mg/L phenol in 20 min at 25 °C. Origination of sulfate radicals via Co3O4-mediated activation of peroxymonosulfate (PMS) is responsible for this catalytic effect [3O4/N-doped graphene hybrid exhibits similar catalytic activity but superior stability to Pt, in alkaline solutions. This unusual catalytic activity arises from synergetic chemical coupling effects between Co3O4 and graphene [Coactivity . Degrada 2.51 eV . This syc effect . The Co3graphene .2–GO nanocomposites was examined with different ratios of graphene additions and it was found that higher amount of graphene addition decreased the photocatalytic activity [2-GO photocatalyst showed the similar occurrence. This study demonstrated that TiO2-GO cannot offer truly new visions into the assembly of TiO2 carbon composite as high-performance photocatalysts. The TiO2 particles were found to be in anatase phase and a narrow size distribution was dispersed on the surface of graphene sheets uniformly [2 and G-TiO2 was reported with different reaction times, as shown in 2 [2 (P25)-rGO composite was found to be the most proficient photocatalyst for the degradation of Methylene Blue (MB) and the optimum mass ratio was found to be 1/0.2 [A systematic investigation on the photocatalytic properties of TiOactivity . Liquid-niformly . A compaown in 2 . TiO2 , both under UV and visible light. In this report, photoluminescence studies revealed discrete appeasing of the GO photoluminiscence under visible light and near infrared laser excitation. Hence, it was conferred that GO acts as either an electron acceptor or donor of TiOle light .2 (N-P90), nitrogen-doped reduced graphene oxide (N-rGO), as well as their composites were studied for the photocatalytic activity. N-P90/N-rGO showed enhanced photocatalytic activity, and in the presence of this composite, around 80% MB was degraded by visible light irradiation in 160 min. Enhanced photocatalytic performance is observed in N-P90/N-rGO composites for degradation of MB due to photo-induced and electronic interaction between TiO2 and graphene. Comparison of degradation efficiency of MB under visible light irradiation by P90 TiO2, N-P90, and N-P90/rGO is presented in 2 nanofibers (~10 nm diameters) were synthesized from electrospun rice-shaped TiO2 and potassium titanate was achieved from rice-shaped TiO2. The surface area was increased by 2.5 times after the nanofiber formation of TiO2. The results showed that the photodegradation of MO was found to be higher than bare TiO2 (P-25) nanoparticles [2 of different composition ratios were tested and the formulation of catalyst with 1.2 times higher photocatalytic activity than commercial photocatalyst was reported. This catalyst was able to degrade 3 mg/L MB over 10 consecutive cycles with nominal loss in photocatalytic efficacy. Graphene plays a generous part in obstructing the accretion of TiO2 grains upon calcination at high temperature [2 (rGO-TiO2) nanocomposites was synthesized and examined for the photocatalytic activity by decolorization of Rhodamine B dye (RhB) under UV light. In this study, various parameters, such as dye concentration, rGO content, catalytic dose, and pH, were optimized for the decolorization. The catalysts were found to be more active at natural pH of the dye under the UV-illumination for the degradation of RhB dye. The presence of H2O2 and K2S2O8 increased the decolorization. Further, addition of CO32− and Cl− ions decreased the dye degradation rate [Nitrogen-doped P90 TiOarticles . GO/TiO2perature . A set oion rate .2 nanoparticle-attached graphene/carbon composite nanofibers (TiO2-CCNFs) were synthesized and reported as highly active photocatalysts for photocatalytic degradation of MB under the irradiation of visible light. Graphene was suggested to play the role of an electron acceptor and a photosensitizer, resulting in a higher photodegradation rate and reduced electron-hole pair recombination. CNFs having high surface also improved the photocatalytic activity of TiO2 [TiO of TiO2 .An effective scalable method was developed to make nanocomposites of functional graphene sheets (FGS)/ZnO. In this study, poly (vinyl pyrrolidone) (PVP) component was reported to play a crucial role for loading of ZnO nanoparticles onto FGS by connecting Zn ions on the carbon materials and promoting ZnO nucleation and crystal growth in the precursor-prepared route. Further, FGS/ZnO composite was evaluated for photocatalytic activity and was found to be applicable for a number of environmental issues . ZnO/rGO2/graphene sheet (GS) (5%) composites for H2 evolution from water splitting. This study demonstrated that beyond the critical content of GS (5%), photocatalytic activity was decreased by initiating electron-hole recombination centers. Calcination atmosphere was found to be important and better performance was observed for the samples calcined in nitrogen atmosphere [The calcination atmosphere was found to affect the photocatalytic activity of the TiOmosphere .The use of ZnO-graphene composites (Z-GC) was reported to remove dye from water due to the interaction between the graphene sheets and the ZnO nanoparticles . rGO-ZnO2 atmosphere. The superior photocatalytic performance was due to the synergistic effect of the proficient electron inoculation and low charge carriers in the composite, where GO acted as an electron collector and transporter, leading to unceasing generation of reactive oxygen species for the degradation of MB [2S3 bi-component shell anchored on the rGO sheets were synthesized and reported to show a broad and strong photo-absorption in the visible region. These nanorods also manifested better photocatalytic activity for H2 evolution from the glycerol-water mixtures. The superiority in performance is owing to the elevated light absorption and effective charge separation [The ZnO/GO nanocomposite consisting of flower-like ZnO nanoparticles anchored on graphene-oxide. Further, photocatalytic efficiency of ZnO/GO composite progressed by annealing the product in Non of MB . Core-shparation .2O4 in which the graphene acts as a charge carrier to detain the delocalized electrons. Photocatalytic activity was explored with the variation of the dosage and dye concentration [2O4-graphene hybrid materials (CFGHs) showed ferromagnetic behavior and enhanced photodegradation rate and amended adsorbing capacity due to the assimilation of graphene [2O4 and CdS. Escalation in the concentration of MB was observed as the irradiation time increased for CoFe2O4 due to the desorption of MB during irradiation. G-CoFe2O4/CdS easily separated from aqueous solution in an external magnetic field, as seen from the digital photos of Gr-CoFe2O4/CdS after irradiation [2O4-rGO composite unveiled required photocatalytic performance with excellent recycling stability for the degradation of MB, RhB, and MO under visible-light irradiation [Connexion of the graphene suggestively progressed the photocatalytic performance of the CoFentration . CoFe2O4graphene . The phoadiation . The CoFadiation .2O4-rGO (CF–rGO) nanocomposites hold exceptional microwave absorbing properties and high photocatalytic activity for the degradation of various dyes under visible light irradiation [CoFeadiation . 85 CF-1adiation . The phoadiation .2O4-3D TiO2 nanocomposite showed an enhancement in the photodegradation of MB as compared to the commercial rutile-phase TiO2 and the pure urchin-like TiO2 (3D TiO2) microparticles. Results specified that the composite showed relatively consistent photocatalytic activity with slight degradation [2O4 composites [CoFeradation . The phomposites . The pho2O4/Ag under visible light (λ > 400 nm) was investigated by in-situ Fourier transform infrared spectroscopy and the correlated mechanisms were suggested. Superficial degradation ratio of 91.9% over rGO/CoFe2O4/Ag was obtained under visible light illumination of 12 h, while only about 21.7% was obtained with commercial P-25 TiO2 [−1, and then, no noteworthy decrease of time was observed when more catalyst was added. Likewise, use of 2 mL of H2O2 was found to be an optimum amount for the photocatalysis reaction (2O4 nanocomposites was queried for the degradation of 4-Chlorophenol (4-CP) under visible light illumination. Activity of rGO-CoFe2O4 composite was seen in the occurrence of PMS  plane confined in the graphene network exhibited an excellent visible-light-driven photocatalytic activity with an ultrafast degradation rate of 1.924 × 10−7 mol g −1 s −1 for MB [Photocatalytic activity of ZnFeadiation . Graphen1 for MB .2O4-rGO nanocomposite was shown due to the active restraint of the recombination of the photo-excited electron-hole pairs by rGO sheets and the generation of ·OH-free radical [2) [2O4-Ag/rGO nanocomposite was higher by the factor of 14.6 and 5.6 times over its counterparts. Photosensitization effect was prevailed by good interaction ensuing in only 80% removal of EE2 though humic acid [2O4 composite exhibited the remarkable catalytic activity toward MB degradation; in the presence of H2O2, the activity enhanced, and the reaction followed a pseudo-first-order kinetics. The complete MB degradation observed at rGO/ZnFe2O4 composites was attributed to the π–π interaction, hydrogen bonding, and electrostatic interaction exerted between the rGO and ZnFe2O4 [The boosted photocatalytic activity of ZnFe radical . The phoical [2) . The psemic acid . rGO/ZnF ZnFe2O4 .2O4-GO (0.25) hetero-architecture demonstrated a considerable lesser emission intensity. Due to their competent electron-transport property, graphene sheets can deliberately reduce the fluorescence of NiFe2O4 fixed on them. Kinetic results indicated that the rate-determining step is the adsorption course of MB [2O4-GO (0.25) shows the best activity compared to other NiFe2O4-G composites  under visible light due to its combined effects of modulated band gap and covalent bonding between BiFeO3 and graphene [RGO-Bile light . BiFeO3-graphene .3O7 (OH)-RGO composite supported the suggested mechanism of charge separation and transport mechanism. A higher degradation rate was obtained using the nanocomposite prepared with a graphene loading of 3 mgmL−1, and when the rGO loading exceeded 3 mgmL−1, degradation efficacy diminished. This arose as extra rGO sheets gathered and stuck the absorption of incident light [Photoluminescence studies of Nbnt light .2 and ZnO exhibited good photocatalytic activity in UV light due to their wide band gap. These two metal oxides are stable in aqueous conditions during photocatalysis. Further, coupling of graphene with TiO2 and ZnO increases the photocatalytic activity due to increases in the photogenerated charge carriers. Metal oxides with magnetic properties of metal ferrites (MFe2O4) offer an added advantage as photocatalysts since they can be recovered by applying an external magnetic field after catalysis. Metal ferrites  materials are proven to be excellent candidates for visible light photocatalytic H2 generation through water splitting. Recycling ability for metal ferrites are far better compared to nano semiconductors like TiO2 and ZnO. MFe2O4 is a class of semiconductor with narrow band gap, which exhibits characteristic visible light response, possess good photochemical stability, and exhibits excellent optical properties.Pristine TiO2O4 absorbs 42–45% of sunlight, whereas TiO2 and ZnO absorbs 4% of sunlight. MFe2O4 are efficient for the degradation of dye degradation and organic pollutant degradation compared to the other metal oxides , with respect to the catalyst and the light source. In MFe2O4 context, recombination of photogenerated charge carriers is the major limitation in semiconductor photocatalysis as it reduces the overall quantum efficiency. In order to enhance the photocatalytic activity, graphene material is coupled with MFe2O4, where the graphene channels the electrons. Comparison of degradation rate for various photocatalytic reaction systems is incongruous since the nature of catalyst and substrate pollutant molecules are different in each reaction. Ferrite nanoparticles have a strong magnetic property, which can be easily used for magnetic separation after photo-mineralization.MFe2+ ion easily bonds with oxygen by giving an electron and super oxide radical. This super oxide radical can oxidize the organic substrate molecule. The Fe3+ ion and Fe2+ ions can show photo-Fenton reactions in presence of in-situ-generated H2O2. This H2O2 generates hydroxyl-free radicals, which are involved in the degradation of pollutants. Predicted mechanism for the rGO-CoFe2O4 composite is shown in Equations (1)–(4).The photocatalytic efficiency depends on the ratio of the photogenerated charge-carrier transfer rate to the rate of electron-hole recombination. For composite structure, M6 composite shows better photocatalyst compared to other catalysts prepared from hydrothermal method  display that h+, O2−, SO4−, and OH are accountable for decomposition of antibiotics. Overall, irrespective of other parameters, the solvothermal method is best and helps in crystal growing and super saturation is achieved by reducing the temperature in the crystal growth zone.Furthermore, the self-redox properties of iron and manganese atoms in MnFeFurther, noble metal  exhibits surface plasmon resonance (SPR), which is a characteristic feature. The SPR frequency of the metal particles can be tuned into visible light absorption by shifting the size of the deposited metal particles on the catalyst. Deposited metal is involved in multiple crucial roles, such as serving as a passive electron sink with high capacity to store electrons to suppress photogenerated charge carrier recombination, facilitates rapid dioxygen reduction to generate free radicals and direct excitation of metals, especially under visible light, and vectorial electron transfer to the conduction band (CB) of metal oxide. Thereby, showing improvement in the photocatalysis for the removal of various organic pollutants/dyes.Graphene nanosheets act as a substrate to support the metal oxides for photocatalytic activity and graphene-based semiconductor photocatalysts are used for environmental remediation. The morphologies of semiconductors, theoretical electronic-structure calculations, and experimental discovery determinations are necessary on GO to persuade the photocatalytic activity, and composition design is an operative method to enhance the photocatalytic properties. Photocatalytic properties depend on the preparative method, and various parameters like initial concentration, oxidant concentration, pH, particle size, number of GO sheets, and source of light should be explored.The interface regulates the efficacy of the electron-hole separation. Currently, only few methods succeed in unswervingly depicting the interaction of GR and nanoparticles. Atomic force microscopy (AFM), Surface-enhanced Raman scattering (SERS), and scanning transmission electron microscope (STEM) may be the best techniques for determining the interaction of graphene and nanoparticles. Finally, studies on the preparation of a ternary composite as a photocatalyst for both UV and visible-light-driven pollutant photodegradation have been studied and reported. Especially, for the design of ternary composite, magnetic materials such as Fe, Co, Mn, etc., as a dopant, and possessing unique advantages, show a remarkable photocatalytic activity and photostability.Further tasks exist in the application of graphene-based composite for the industrial scale. Some innovative applications of the metal oxide-graphene entail specific understanding between the metal oxides and surface of the graphene, which will have a direct impact on the properties of the composite. Designing a structure for the overall photocatalysis process may require further exploiting of GO by chemically modifying methods. A synthetic approach method of GO-based composite structure by using novel materials has not been achieved to date for photocatalysis, but the solutions to the key challenges appear within reach.In view of this, graphene-based composites possess diverse potential applications, individually having dissimilar desires concerning material properties, and it can be projected that the research on graphene-composite materials will have an optimistic future.


The ability to define an off state in logic electronics is the key ingredient that is impossible to fulfill using a conventional pristine graphene layer, due to the absence of an electronic bandgap. For years, this property has been the missing element for incorporating graphene into next-generation field effect transistors. In this work, we grow high-quality armchair graphene nanoribbons on the sidewalls of 6H-SiC mesa structures. Angle-resolved photoelectron spectroscopy (ARPES) and scanning tunneling spectroscopy measurements reveal the development of a width-dependent semiconducting gap driven by quantum confinement effects. Furthermore, ARPES demonstrates an ideal one-dimensional electronic behavior that is realized in a graphene-based environment, consisting of well-resolved subbands, dispersing and non-dispersing along and across the ribbons respectively. Our experimental findings, coupled with theoretical tight-binding calculations, set the grounds for a deeper exploration of quantum confinement phenomena and may open intriguing avenues for new low-power electronics. Here, the authors investigate armchair graphene nanoribbons by angle-resolved photoelectron spectroscopy, and show the development of a width-dependent semiconducting gap driven by quantum confinement effects, and an ideal one-dimensional electronic behaviour. Namely, GNRs terminated by zigzag edges demonstrate one-dimensional (1D) single-channel ballistic transport at room temperature5, while those with armchair edges promise a width-dependent semiconducting behavior11. In the view of digital applications, the potential of graphene is limited by the lack of a sizeable bandgap in its electronic structure. Hence, the scalable growth of high-quality armchair GNRs (AGNRs) is essential for the development of future graphene-based technologies. Earlier attempts to produce GNRs involved the patterning of pristine graphene layers using standard lithographic means. However, such top-down approaches severely suffer from the lack of atomic-scale precision, resulting in the formation of disordered and rough edges14. In contrast, the surface-assisted bottom-up approach, for instance the self-assembly of molecular precursors on gold surfaces, was demonstrated to create high-quality GNRs17. The drawback of this method lies in its use of a metallic substrate, and thus its impracticality to be incorporated in a technologically relevant application. In this respect, the production of GNRs on a semiconducting substrate such as SiC is an attractive avenue21. Particularly, the selective growth of AGNRs on the sidewalls of SiC mesa structures, is shown to produce well-defined edge morphologies21 and to provide a better control on the overall ribbon widths as compared to the growth of AGNRs on the 19. Therefore, epitaxial sidewall AGNRs stand as promising candidates for the realization of new tunneling-based field effect concepts22, since going beyond conventional metal-oxide-semiconductor field-effect transistor (MOSFET) architectures, almost defect-free semiconductors are mandatory.Graphene nanoribbons (GNRs) are considered to be the fundamental building blocks for future carbon-based nanoelectronics. The functionality of GNRs is governed by the detailed atomic structure of their edges25. A combination of well-resolved dispersing and non-dispersing subbands, parallel and perpendicular to the ribbon direction respectively, is observed. In fact, a characteristic band structure topology, resembling a triangular prism as expected for 1D confined Dirac electrons, was never realized thus far in a graphene-based environment. Tight-binding (TB) simulations reveal that the detailed subbands measured in ARPES originate from a mixture of metallic and semiconducting AGNRs, indicating the development of a width-dependent bandgap. This is further corroborated by scanning tunneling spectroscopy (STS) measurements, which confirm that individual ribbons can display either metallic or semiconducting behavior.In this work, high-quality AGNRs are formed through the periodic modulation of a graphene sheet grown epitaxially on the sidewalls of 6H-SiC mesa structures. Angle-resolved photoelectron spectroscopy (ARPES) reveals peculiar features that differ from previous GNR band structure measurements26. The armchair edge of graphene is naturally oriented parallel to the [1121 with an average inclination of (26 ± 2)°. This periodic array of mini-facets, which is somewhat reminiscent of a “ladder structure”, can be observed in the scanning tunneling microscopy (STM) image of Fig. N-AGNR to denote a ribbon with N dimers across its width, we find ribbons composed of N ~ 18 dimers, corresponding to a width of about 2 nm as shown in the inset of Fig. 5 AGNRs/mm, a density high enough to allow the use of integrating experimental techniques such as low-energy electron diffraction (LEED) and ARPES.Graphene on 6H-SiC develops in a well-defined epitaxial relationship with respect to the substrate26. The periodic array of mini-facets constituting the SiC sidewall  is described in units of the SiC phase S, which is defined as the phase difference between two electron waves scattered from adjacent terraces separated by a step height of a single SiC bilayer. Assuming that the facets consist of mini-steps equivalent to a single SiC bilayer, we would expect the facet rods to intersect the basal rods only at in-phase conditions, i.e., at integer values of S. However, in Fig. Figure see Fig.  while thpz orbitals and preventing the development of a Dirac cone. However, on the vicinal planes, the strong graphene-SiC interaction is lifted due to the different surface registry of the substrate as compared to the basal plane. Consequently, free-standing AGNRs are developed, generating 1D confined Dirac electrons. The mini-facets themselves are unit-cell high (H = 1.5 nm) and have a periodicity of D = (3.1 ± 0.3) nm. The free-standing ribbons covering the mini-facets are approximately 2 nm wide with an average inclination of (29 ± 1)° relative to the basal plane, as estimated from the ARPES measurements discussed below.Based on the properties revealed by AFM, STM, LEED, and SPA-LEED, a structural model is proposed for AGNRs in Fig. 1. Fig. 29, is also made visible near the Fermi level (EF). The Dirac point is situated at EF, which corresponds to electronically neutral AGNRs. The subband energies are determined by locating the positions of the peak maxima in the second derivative of the energy distribution curve (EDC) taken at 6. In particular, ribbons with N = 3p + 2  are predicted to be metallic , whereas all other widths result in semiconducting ribbons whose bandgaps are inversely proportional to their widths6. Accordingly, we consider in Fig. N-AGNRs with N = 16, 18, and 20, whose widths are in the 2 nm range suggested by our STM data , consistent with the band structures from ARPES and TB. A wide-bandgap nanobuffer layer is also identified in Fig. An overview of the electronic band structure of AGNRs is depicted in Fig. Å−1 Fig. . It is ientclass1pt{minimak-space is a result of 1D confinement as discussed above. Such characteristic 1D behaviors have been examined before in other systems, e.g., using self-organized metallic nanowires on semiconductor surfaces31. The intensity modulation observed in the Fermi surface is mainly due to an undesired parasitic graphene layer that, in small patches, has overgrown the SiC sidewalls and has an estimated surface area coverage on the order of a few percent. A 2D graphene sheet that is grown on an inclined facet would correspond to a 2D hexagonal BZ shifted away from normal emission relative to the basal plane as sketched in Fig. 32). At a photon energy of 40 eV and a spectrometer work function of 4.3 eV as used in the experiment, the −1 from their associated Figure mentclass2pt{minimmentclass2pt{minimk-space, we display the 2D reciprocal space map (RSM), which is constructed by drawing the BZs of the parasitic sidewall graphene layers on top of the LEED pattern  eV is introduced in the electronic structure, which is desirable for defining an n-doped 6H-SiC(0001) wafer pieces  were used as substrates for the AGNR growth. They were atomically flattened via hydrogen etching, which was carried out in an inductively heated reactor equipped with a graphite susceptor39. Mesa structures with a lateral dimension of about 150 nm and a height of 20 nm were defined using a combination of e-beam lithography and reactive ion etching . The selective growth of AGNRs was achieved by annealing the samples in an inductively heated furnace at 1800 °C under 850 mbar of argon atmosphere for 1 min21.Nominally on-axis, single crystalline, 2, simultaneously probing around 2000 AGNRs. All ARPES data were acquired in ultra-high vacuum (UHV) at a sample temperature of 80 K. Additional, preliminary ARPES measurements (not shown in the manuscript) were conducted at the 12 endstation of the UE112 beamline at BESSY II, Helmholtz-Zentrum Berlin.ARPES measurements were carried out at the Bloch beamline of the MAX IV synchrotron facility in Lund, Sweden. High-resolution energy-momentum cuts were measured using a high performance deflector-based DA30 hemispherical analyzer from ScientaOmicron. The energy and angular resolutions were set to 15 meV and 0.1° respectively. The spot-size of the beam measured 10 × 24 µmp < 2 × 10−11 mbar) at 80 K using a commercial Omicron LT-STM. The sample was degassed at an elevated temperature of 800 K for several hours before being transferred to the low-temperature chamber. Several electrochemically etched tungsten tips were utilized during the experiments. A lock-in detection technique was used to accumulate and average over 50 STS spectra taken on each individual ribbon.The STM/STS measurements were performed in UHV  tight-binding (TB) Hamiltonianentclass1pt{minimaSupplementary Information