Surface acoustic waves (SAWs) propagating on piezoelectric substrates offer a convenient, contactless approach to probing the electronic properties of low-dimensional charge carrier systems such as graphene nanoribbons (GNRs). SAWs can also be used to transport and manipulate charge for applications such as metrology and quantum information. In this work, we investigate the acoustoelectric effect in GNRs, and show that an acoustoelectric current can be generated in GNRs with physical widths as small as 200 nm at room temperature. The positive current in the direction of the SAWs, which corresponds to the transportation of holes, exhibits a linear dependence on SAW intensity and frequency. This is consistent with the description of the interaction between the charge carriers in the GNRs and the piezoelectric fields associated with the SAWs being described by a relatively simple classical relaxation model. Somewhat counter-intuitively, as the GNR width is decreased, the measured acoustoelectric current increases. This is thought to be caused by an increase of the carrier mobility due to increased doping arising from damage to the GNR edges. Recent efforts, however, have concentrated on the interactions of SAWs with graphene27, a two-dimensional (2D) carbon allotrope with outstanding physical properties and numerous potential applications30.The transportation of charge in low-dimensional electron systems has attracted significant attention in recent years as a potential route towards nanoscale electronic devices. Surface acoustic waves (SAWs) propagating on piezoelectric materials provide a unique tool for studying and realising such systems. The strong interaction between the piezoelectric fields associated with a SAW, propagating on a piezoelectric substrate, and a charge carrier system is known as the acoustoelectric effect8, and we have previously studied the acoustoelectric response of large-area graphene sheets produced by chemical vapour deposition (CVD) transferred to LiNbO3 SAW devices at room temperature9, low temperature10, and under illumination11. Theoretical and experimental reports have examined DC-biased mono- and multi-layer graphene sheets for SAW amplification13, while others have studied the use of electrolytic solutions14, and gases15 to control the carrier concentration in graphene films, opening up possibilities for low-power chemical sensors. In contrast, by using an ion gel gate to modulate the conductivity of graphene, Bandhu and Nash16 demonstrated that graphene can be used to control the SAW amplitude and velocity shift. Optimization of this approach could lead to a practical, cost-effective voltage-controlled velocity shifter suitable for use in wireless sensor applications16.The ability of piezoelectric potentials to trap and transport charge at the speed of sound enables the generation of acoustoelectric currents. These have been measured in micron-scale graphene monolayers19, and several groups have demonstrated carbon monoxide, hydrogen20, and moisture24 detectors based on SAW-graphene systems.Theoretical studies predict a further variety of physical phenomena arising from SAW-graphene interactions31, there is an absence of research on SAW interactions with graphene nanoribbons (GNRs). It is a well-known disadvantage of graphene that its gapless band structure is not suited to integration with digital electronics, which typically require high on-off ratios32. Patterning graphene into GNRs can open a bandgap that varies as a function of ribbon width, with appropriate fabrication methods32. Additionally, the electric potential associated with SAWs propagating on piezoelectric materials enables the confinement of charge carriers in nearby electronic systems, that could have applications in metrology and quantum computing35.Despite several studies highlighting the potential advantages of incorporating graphene and other 2D materials with SAW devices3 delay lines. The acoustoelectric current was first studied in GNR arrays consisting of 500 nm-wide ribbons, and the measured linear dependence of acoustoelectric current on SAW intensity and frequency is consistent with the interaction between the SAWs and the graphene charge carriers being described by a relatively simple classical relaxation model. We have also investigated the width dependence of the acoustoelectric current in GNRs, with widths ranging from 200–600 nm, with GNRs of different widths all fabricated on the same SAW delay line. The measured increase in acoustoelectric current as the nanoribbon width decreases is attributed to additional p-doping of the GNR edges, raising the Fermi level in the samples and enabling conduction across grain boundaries and charge puddles arising from the polycrystalline nature of CVD graphene.In this manuscript, measurements of an acoustoelectric current generated in GNRs fabricated from monolayer CVD graphene transferred to LiNbO3-GNR SAW devices where the nanoribbons are all of 500 nm width. These are arranged in a 2 mm × 3 mm array, shown schematically in Fig. et al. in investigations of GNR arrays on SiO2/Si36. The use of double-digit interdigital transducers (IDTs) enables the efficient excitation of SAWs at a number of resonant frequencies. The IDTs were pre-defined on the surface by the manufacturer  of the LiNbO3 crystal with an acoustic aperture of 3.25 mm and separation distance 5.4 mm, allowing large-area CVD graphene monolayers to be easily positioned between the transducers without shorting them out. The fundamental frequency of 11 MHz (SAW wavelength of 361.7 μm) corresponds to a digit width of 45.2 μm.We first consider LiNbOae) in the GNRs between contacts A and B  as a function of SAW frequency and RF power, at room temperature under vacuum. Two devices of this design were studied (Devices 1 and 2), with these results obtained from Device 1. Continuous wave SAWs were excited in increments of 1 MHz in the range 1–500 MHz, and each data point represents the mean of five measurements of Iae. The measured current maxima in Fig. 9, confirming its acoustoelectric nature. Iae of up to ~5.5 μA was measured for a SAW frequency fSAW = 442 MHz and an applied RF power of +20.0 dBm. Acoustoelectric currents of the same order of magnitude were measured between contacts B and C, and C and D, similar to that reported by Okuda et al.14. This is significantly larger than values we have previously measured on unpatterned graphene samples, but this is due to improvements in the transfer method we use, leading to improved quality graphene film (which we believe results in a higher carrier mobility). This is reflected in room temperature current-voltage measurements of the GNR arrays on Device 1, under vacuum, which yielded values of sheet resistance of: 10.5 kΩ/□ (A to B); 23.7 kΩ/□; (B to C); and 56.8 kΩ/□ (C to D). These values compare to typical values of approximately 100 kΩ/□ we have measured previously11, including in GNR samples fabricated using our old transfer method The positive sign of Iae in the direction of SAW propagation is indicative of hole transportation, and is consistent with the CVD graphene being p-doped by PMMA residues left during the transfer process37. Raman analysis of Device 1 (Supplementary Information) showed the position of G peak at 1588 cm−1, a blue-shift also consistent with p-doped graphene38. Upon reversal of the SAW direction, the sign of the current also reverses, confirming that the current is induced by the SAWs. Measurements of Iae were found to be stable and reproducible over the course of several weeks. Qualitatively similar results were seen in Device 2, although, due to the significantly higher resistance, 323.6 kΩ/□ between contacts B and C , the acoustoelectric current was approximately 100 nA for the same SAW frequency and intensity. To rule out possible interference effects, measurements of the acoustoelectric current in Device 2 were repeated with RF frequency increments of 0.5 MHz, but the change in the measured current was negligible.Figure 11. A linear dependence of Iae on SAW intensity is confirmed via fitting (solid lines). The inset to Fig. ae on fSAW for a fixed intensity of 3 mW/m (dashed line), where the acoustoelectric current at each frequency has been extracted from the linear fits to the measured Iae in Fig. j is given by:μ is the charge carrier mobility, Q is the phonon pressure given by Q = IΓ/v, I is the SAW intensity, and v is the velocity of the SAW (3979 m/s in 128° YX LiNbO339). The attenuation per unit length Γ is given by a non-monotonic function of the diagonal component of the conductivity tensor σ2D 2:K2 is the piezoelectric coupling coefficient (0.056 in 128° YX LiNbO3), λ is the SAW wavelength, and the attenuation is maximised at a characteristic conductivity σM. Bandhu and Nash have reported σM = 10−7 Ω−1 in graphene-lithium niobate hybrid systems16.In Fig. 40, and it is likely that the lithium niobate also impacts the charge carrier mobility. In previous work in similar samples the mobility μ was estimated as ~5–10 cm2/V.s11. In Device 1 the relatively high conductivity compared to σM (σ2D/σM~1000) is expected to yield relatively low acoustoelectric attenuation of SAWs, via Equation  with the periodicity (10 μm) of the perpendicular graphene bridges in the array. This is similar to the recent study by Mayorov et al.25, in which IDTs were formed from graphene on LiNbO3 for the purpose of SAW generation and detection. This coupling could explain the extremely low SAW intensity and relatively large acoustoelectric currents measured for fSAW = 356 MHz in Devices 1 and 2. Iae measured between contacts B and C of a third device fabricated without the perpendicular bridge structures did not exhibit such behaviour  in the device without bridge structures , as shown schematically in Fig. 28. Subtle differences in fabrication processes can lead to different concentrations of etchant salts and PMMA residues between devices37, which can further affect performance. The fabrication of multiple nanoribbon arrays on the same LiNbO3 SAW delay line both reduces the variability in quality between different width ribbons, but also ensures that the different GNR arrays experience the same SAW intensity at any frequency. Arrays were defined in the acoustic beam path, with a width of 400 μm and a lateral spacing of 20 μm from any neighbouring arrays. All arrays shared a common electrical contact, A, in Fig. To investigate the effect of the GNR width on the acoustoelectric interaction, multiple nanoribbon arrays were fabricated on the same LiNbOae from these arrays are therefore not presented. Arrays of 200, 350, 400, 500, and 600 nm-wide GNRs had sheet resistance of 15.1, 3.7, 3.8, 5.4, and 7.0 kΩ/□ respectively.Current-voltage measurements at room temperature, under vacuum, revealed that contacts A and H were open circuit, and that the array between contacts A and G had a relatively high sheet resistance of 38.8 kΩ/□. Measurements of IfSAW = 356 MHz, consistent with the measurements in Figs λSAW coincides with the periodicity of the perpendicular bridge structures in the arrays. This is the case even without accounting for the frequency response of the IDTs. For SAW frequencies of 11, 33, 97, and 119 MHz the acoustoelectric current generally decreases as the ribbon width increases, so that the largest acoustoelectric current is measured in the smallest ribbons. At SAW frequencies above 205 MHz Iae, decreases significantly when the ribbon width is decreased from 350 nm to 200 nm. A Raman map of the graphene 2D and G peaks taken at a random location in the array of 200 nm-wide GNRs revealed spatial discontinuities of ~15 μm across (see Supplementary Information). As the attenuation of the SAWs by the charge carriers is determined by the conductivity of the graphene on the scale of half the SAW wavelength40, and for fSAW = 205 MHz the SAW wavelength is ~20 μm, the inhomogeneous conduction path in the 200 nm array leads to lower conductivity, lower SAW attenuation, and correspondingly lower acoustoelectric currents at high SAW frequencies, where the dimensions of the inhomogeneities are similar to the SAW wavelength. At frequencies below 205 MHz, where the SAW wavelength is much larger than the scale of the discontinuities, the acoustoelectric current increases when the ribbon width decreases from 350 nm to 200 nm, consistent with the overall trend of increasing current with decreasing ribbon width .In Fig. fSAW = 33 MHz, is plotted as a function of σ2D/σM (solid orange line), where we have taken a value of σM = 10−7 Ω−1, determined for graphene-LiNbO3 hybrids16. The symbols in this plot correspond to the attenuation calculated for each GNR, again using Equation In Fig. 43. In this study, significant p-type doping was observed as the width of the nanoconstriction was decreased, which was attributed to the oxidation of the edges of the constrictions caused by the fabrication process. The increase in the p-type doping was reflected in a shift in the Dirac voltage, with a shift of approximately 3 volts seen between 600 nm and 300 nm wide constrictions. Using the standard capacitor model for graphene on Si/SiO2, this shift in the Dirac point corresponds to a significant increase in the Fermi energy of approximately 15 meV. The conductivity of transferred CVD graphene is known to be limited by grain boundaries, tears, wrinkles and non-homogenous impurities42, and in previous temperature dependent measurements of the acoustoelectric current10, we showed that the mobility was thermally activated, with an activation energy of approximately 60 meV. Although we are unable to directly measure the carrier concentration or Fermi energy in our measurements, an increase in the Fermi energy of 15 meV would cause the mobility to more than double (taking the activation energy to be 60 meV), when the ribbon width is reduced from 600 nm to 300 nm. This is broadly consistent with our measurements, where an increase in the mobility of this order is required to explain the observed increase in the acoustoelectric current. Lee et al.44 also showed how a non-uniform carrier concentration in the graphene can be used to explain the origin the dependence of the mobility on channel width.The increase in conductivity with decreasing GNR width Fig.  is consiμ ~ 5–10 cm2/V.s11. Finally, we believe that the relatively large acoustoelectric currents measured in the array of 200 nm-wide GNRs arise from the dominant effect of poor conductivity leading to increased momentum transfer from the SAW to the graphene charge carriers, rather than the increased mobility arising from increased p-doping seen in the other arrays.Although we cannot directly measure the mobility in these devices, the magnitude of the currents observed in Device 3 Fig.  are simi16, and better understand the role of GNR edges on the mobility and conductivity of these systems. The charge carrier conduction mechanism in graphene arises from several competing mechanisms, and the role of the LiNbO3 substrate in this process is not yet fully understood. We also intend to investigate the effects of changing the bridge periodicity on the acoustoelectric current, tailoring it to coincide with other SAW wavelengths, for example.Further work is now underway to examine the width dependence of the acoustoelectric effect in graphene nanoribbons that are electrostatically gated3 SAW delay lines, with widths up to 600 nm, is consistent with the description of this interaction by a relatively simple classical relaxation model. In 300 μm × 3 mm arrays composed of 500 nm-wide GNRs, an acoustoelectric current of up to ~5.5 μA was measured at a SAW frequency of 442 MHz. Enhanced acoustoelectric currents were observed when perpendicular bridge structures were inserted into the nanoribbon array with a period similar to the SAW wavelength. The increasing acoustoelectric current with decreasing nanoribbon width is thought to be caused by increased doping along the damaged, rough edges introduced by the fabrication process. We believe these measurements provide a stepping stone towards the eventual use of the acoustoelectric effect in graphene nanoribbons for such applications as sensing and metrology.In conclusion, we have demonstrated that the acoustoelectric effect in monolayer CVD graphene nanoribbons on LiNbO45, monolayer graphene produced by chemical vapour deposition on ~5 mm × ~5 mm copper foils (Graphene Supermarket) was transferred in-between the interdigital transducers (IDTs) of commercially available 128° YX LiNbO3 SAW delay lines. These had identical input and output aluminium IDTs defining an acoustic beam width of 3.25 mm and a path length of 5.4 mm. Patterning of the graphene was undertaken using electron beam lithography and an argon (10 W) reactive ion etch. GNRs were aligned such that their long axes lay parallel to the SAW wave vector. For all devices, 20 μm-wide Cr/Au (5 nm and 50 nm respectively) electrical contacts were deposited by thermal evaporation.The devices measured here were fabricated as follows: Via the poly(methyl methacrylate) (PMMA) transfer techniqueDevices supporting 500 nm-wide GNRs only  are shown in the Supplementary Information).The presence of monolayer graphene on the substrate was confirmed using a confocal Raman microscope (WITec Alpha300) equipped with a thermoelectrically cooled CCD detector. A 532 nm wavelength laser was used for the excitation, and a 50x objective lens was used for backscattered light collection with a lateral resolution of 388 nm. The laser power incident on the sample was approximately 2.3 mW, and the 2D and G peaks were located at 2696 cm−6 mbar) with continuous pumping to reduce the accumulation of dopants, at room temperature. Continuous wave SAWs were excited at the input transducer using a Hewlett-Packard 8648C RF signal generator, while Iae was measured using a Keithley K2400 source-measurement unit. Two-terminal current-voltage measurements were used to determine the GNR array conductivities. GNR arrays that were not being characterised were electrically grounded to reduce interference. The SAW amplitude at the output IDT was measured using a LeCroy WaveRunner 204Xi-A digital oscilloscope, and used to estimate SAW intensity.All measurements were made under vacuum (chamber pressure approximately 6 × 10Supplementary materials


We aimed to analyze the frequency and distribution of PD-L1 expression in specimens from prostate cancer (PC) patients using two different anti-PD-L1 antibodies .PD-L1 immunohistochemistry was performed in a tissue microarray consisting of 82 castration-resistant prostate cancer (CRPC) specimens, 70 benign prostate hyperplasia (BPH) specimens, 96 localized PC cases, and 3 PC cell lines, using two different antibodies . Staining images for CD4, CD8, PD-L1, and PanCK of a single PD-L1 positive case were compared, using a newly developed dot-wise correlation method for digital images to objectively test for co-expression.Depending on the antibody used, in tumor cells (TC) only five (E1L3N: 6%) and three (SP263: 3.7%) samples were positive. In infiltrating immune cells (IC) 12 (SP263: 14.6%) and 8 (E1L3N: 9.9%) specimens showed PD-L1 expression. Two PC cell lines  also displayed membranous immunoreactivity. All localized PCs or BPH samples tested were negative. Dot-wise digital correlation of expression patterns revealed a moderate positive correlation between PD-L1 and PanCK expression, whereas both PanCK and PD-L1 showed a weak negative Pearson correlation coefficient between CD4 and CD8.PD-L1 was not expressed in localized PC or BPH, and was only found in a minority of CRPC tumors and infiltrating immune cells. Protein expression maps and systematic dot-wise comparison could be a useful objective way to describe the relationship between immuno- and tumor-related proteins in the future, without the need to develop multiplex staining methods. The therapeutic options for castration-resistant prostate cancer (CRPC) have increased dramatically in the past years. Recent clinical trials have led to the FDA approval of cabazitaxel , abiratein vitro, and mediates clinical anti-tumor activity [Programmed Death Receptor 1 , a member of the extended family of T cell regulators, is expressed on the surface of activated T cells, B cells, and macrophages . Its ligactivity –20. A coactivity –21. PD-Lactivity . In the activity . Recentlactivity . Tumor tactivity .The first aim of this study was to systematically describe the expression of PD-L1 in benign prostatic hyperplasia (BPH), localized prostate cancer (PC), and CRPC using two anti-PD-L1 antibodies. The second aim was to observe if PD-L1 status was dependent on previous treatment modalities. The third aim was to develop a new method to describe the relationship between immune cells and tumor-related proteins using pseudo-colored protein expression maps, and to use dot-wise correlation coefficients of superimposed images as an objective co-location measurement.versus SP263. The comparison of PD-L1 expression (%) with clone SP263 versus E1L3N showed significant correlation coefficients  and 3 PC cell lines. There was no expression of PD-L1 observed in either BPH or localized PC samples (0%). Examples of PD-L1 tumor cell (TC) and immune cell (IC) staining in CRCP specimens and cell lines (clone SP263 and E1L3N) are given in Figure s Figure . No signs Figure , phosphos Figure , phosphos Figure , and Ki-s Figure .n = 10), brain (n = 1), lung (n = 1), or lymph node (n = 1) metastases  was present in 5 of 81 (6%) cases. All five positive specimens were retrieved by palliative transurethral resection of the prostate (TURP), and no PD-L1 expression was found in bone . All patients were treated in different hospitals with the available options: surgical ADT (orchiectomy), chemical ADT ), chemotherapy (docetaxel) or radiotherapy. Inclusion criteria for this retrospective analysis required tissue collection during transurethral resection of the prostate (TURP), or tumor metastasis resection, and rising PSA or clinical progress under androgen deprivation therapy. The first TMA included 78 formalin-fixed paraffin embedded tissue specimens of patients, which were sampled after the diagnosis of CPRC. Suitable areas for prostate tissue retrieval were marked on routine H&E-stained sections. A section of the paraffin block, 0.6 mm in diameter, was punched out of the suitable area and inserted into the recipient block using a tissue arrayer . The whole tissue microarray preparation was accomplished on the paraffin blocks using cores from two different areas of each tumor or control tissue to account for tissue heterogeneity.n = 70), localized PC (n = 96), the androgen-resistant human PC cell lines (PC3 and DU145) and the androgen-sensitive PC cell line (LnCaP). The detailed characteristics of this TMA have been reported previously [The second TMA consisted of BPH samples , deparaffinized, rehydrated and stained with hematoxylin–eosin using standard histological techniques. For immunohistochemical staining of both TMA and large sections, the Ventana Benchmark automated staining system and Ventana reagents  were used. After deparaffinization in xylene, slides were rehydrated in decreasing concentrations of ethanol. Endogenous peroxidase was blocked using the Ventana endogenous peroxidase blocking kit after a rinse with distilled water. For antigen retrieval, slides were heated with cell conditioning solution  according to the manufacturer's instructions.For the detection of the PD-L1 protein in BPH, PC, and cell line specimens, one anti-human PD-L1 rabbit monoclonal antibody was used: E1L3N . For the detection of the PD-L1 protein in CRPC, two anti-human PD-L1 rabbit monoclonal antibodies were used: E1L3N , SP263 . A multi-tumor TMA and a tonsillectomy specimen were used as positive and negative controls to establish the staining protocol for the PD-L1 antibodies. A dilution of 1:1000 resulted in a strong membranous signal without non-specific background staining in positive controls (squamous epithelium of tonsillectomy specimen). PD-L1 negative lung cancer cases were used as negative controls. For the expression maps, primary antibodies against CD4 , CD8 , and PanCK  were applied and adjusted to the Ventana Benchmark system after performing titrations. Immunohistochemistry with antibodies against Phospho-ERK1/2, Phospho-mTOR, Phospho-4E-BP1, and Ki-67 (MIB1) was performed, as previously described .An experienced pathologist (PJW) evaluated all scanned and digitized tissue microarray spots . A second independent observer (CDF) re-evaluated the TMAs. In discrepant cases, the two observers achieved consensus after detailed case discussion. Percentages of PD-L1 positive tumor cells and the staining pattern were evaluated for each punch. PD-L1 expression was recorded if a distinct membranous staining signal on the tumor cell surface was observed. In analogy to the scoring guidelines for non-small cell lung cancer , we usedThe staining images for CD4, CD8, PanCK, and PD-L1 were aligned, superimposed, and normalized for the generation of a pseudo-colored expression map. Whole slide images of one case, and of all performed stainings were digitized  at 40x magnification (approximately 2k-3k x 2k-3k pixels per image). The images of consecutive tissue slices were pre-processed and aligned for dot-wise correspondence in four steps. First, the original images were white-balanced to remove grayish background. Second, the tissue regions were cropped and rotated, translated and rescaled for rigid alignment of the consecutive slices to the middle slice. The background was then removed to exclude background artifacts that could disturb the following finer alignment process. Third, to refine the alignment and to address for morphological changes of the tissues in consecutive slices, we incorporated a non-linear SIFT flow algorithm . For SIFIn summary, the scarce PD-L1 expression in CRPC and absence in localized PC indicates that advanced PC patients may have to be selected carefully when offered checkpoint inhibition. However, prospective clinical trial data is needed. Our results do not confirm that PD-L1 expression can be induced by orchiectomy, LHRH-agonists, anti-androgens, radiation therapy or chemotherapy. Neither did we find an association with PD-L1 expression and ERK- or mTOR signaling activity. Protein expression maps and dot-wise comparison could be a useful objective method to describe the topographical relationship between immunological and tumor-related proteins, in general.


Patterning graphene into various mesoscopic devices such as nanoribbons, quantum dots, etc. by lithographic techniques has enabled the guiding and manipulation of graphene’s Dirac-type charge carriers. Graphene, with well-defined strain patterns, holds promise of similarly rich physics while avoiding the problems created by the hard to control edge configuration of lithographically prepared devices. To engineer the properties of graphene via mechanical deformation, versatile new techniques are needed to pattern strain profiles in a controlled manner. Here we present a process by which strain can be created in substrate supported graphene layers. Our atomic force microscope-based technique opens up new possibilities in tailoring the properties of graphene using mechanical strain. Until recently, focus has been on patterning graphene into nanostructures, mostly with the aim of tailoring its charge transport properties5. However, in such nanostructures electronic states of the rough edges obscure quantum confinement effects6. One promising alternative to lithographically cutting graphene, is applying mechanical strain to it. Changing the charge transport properties of a material by straining its crystal lattice is not a new idea, it has been realized in the silicon industry with success7. Examining the case of graphene, one finds that in order to achieve significant changes in the band structure, large homogeneous strains in the range of 15–20% need to be applied8, making this approach impractical because the maximum failure strain is also of this order9. Furthermore, such a large strain is hard to implement into a working electronic device10. However, periodic strain patterns show promise of creating new functionality in graphene devices, through electron wave guiding, pseudo-magnetic fields, valley polarization etc.19. Since the graphene lattice remains intact in these cases, new physics can be explored without the plague of edge disorder observed in lithographically processed nanostructures. Strain engineering of this kind has been attempted by harnessing moiré patterns22, using the different thermal expansion of graphene and its support23, substrate induced rippling25 and by placing graphene on a pre-patterned substrate32. The drawback of these approaches is that the amount of strain induced, as well as its crystallographic orientation is not easily controlled. Additionally, there is a need for a transfer step to the pre-patterned substrate which may induce defects in the graphene layer. Moiré patterns that form between the graphene and substrate are limited in their applicability, because the pattern is inherently determined by the alignment and lattice parameters of the two materials. Furthermore, with the exception of hexagonal boron nitride21, such moiré patterns are constrained to metallic substrates, making charge transport measurements problematic. Until now, no truly versatile method of introducing strain into graphene has been demonstrated. Here we show that strain patterns can be prepared in a graphene flake on SiO2, through an AFM indentation approach that combines the ability to write tailor made strain profiles, with the possibility to control the crystallographic orientation of the strain.Graphene, being a two-dimensional crystal, has an exposed surface which makes it easy to manipulate its atomic and electronic structure2 capping layer. Being one of the strongest materials known9, it is natural to assume that in an AFM indentation experiment graphene does not get damaged in the initial phase of the indentation, while the SiO2 substrate can undergo plastic deformation. Stopping the indentation before rupture of the graphene occurs, can leave the graphene membrane pinned to the deformed substrate. During indentation, the tip is lowered towards the sample surface until a pre-set cantilever deflection (see Methods). In the next step, the tip is either retracted or moved along a line on the sample surface  and a hexagonal dot pattern (40 nm nearest neighbor dot distance), we have measured the dependence of the 2D peak shift with rotating the polarizer of the incident laser beam. In Fig. 2. On the other hand, the measurement on the line pattern shows a 2D peak position that is up to 1 cm−1 smaller if the polarization vector of the laser is perpendicular to the indent lines (at θ = 15°). Thus, the strain has a uniaxial character, being larger in the direction perpendicular to the indent lines36. In the case of the dot patterns, the 2D peak shift has a slight hexagonal character, which is aligned with the dot pattern  is larger than the elastic energy (Eel) induced in the graphene. To be able to compare the two quantities in the present experiment it is necessary to know the exact geometry of the graphene in the pinned configuration. AFM probes with a nominal tip radius of curvature of 2 nm have been used to image indentation patterns  from 0.7 to 1 nm, fit the AFM height data very well  are much bigger than displacements in-plane, we can safely neglect the in-plane component43, resulting in a strain tensor: h is the out of plane displacement of the graphene layer. We can measure h by AFM topography maps, as long as the AFM tips used for imaging the indentation patterns are much sharper than the ones used to prepare the patterns (see Methods). As an example, the AFM topography of an indentation hole pattern  are used, with a nominal force constant of 40 N/m and a tip radius of 15 nm. Imaging of the indentation patterns was carried out, using AFM tip having a 2 nm nominal tip radius .z velocity of 400 nm/s, until deflection of the cantilever has taken place. In the case of the dot patterns the tip was retracted with the same z velocity and moved to a new position for the next indentation step. In the case of the line patterns after moving towards the sample the tip was dragged across the surface in contact mode without feedback with a velocity of 200 nm/s. Finally the tip was retracted and moved in tapping mode to the new line location. The z displacement of the tip was controlled either by setting a cantilever deflection threshold or by moving the tip towards the sample by 40–100 nm. The final indent depth was used as a control parameter during indentation experiments because of the variability in cantilever spring constant and tip sharpness. The typical cantilever spring constant was 40 N/m, with a tip radius of ~15 nm . However, due to large variability in these parameters, the z movement was incrementally adjusted. An indentation experiment was always followed by imaging the patterned location for the onset of plastic deformation of the SiO2.For the indentation experiments the NanoMan lithography software of Bruker has been used. Between indentation steps the tip was moved in tapping mode. At the begin of indentation the tip was lowered towards the sample surface with a Raman measurements were carried out using a Witec 300rsa+ confocal Raman spectrometer, using a 532 nm or 633 nm excitation laser.Supplementary information


Then, the plasmonic tuning methods of 2D nanomaterials are presented from theoretical models to experimental investigations. Furthermore, we reveal the potential applications in photocatalysis, photovoltaics and photodetections, based on the development of 2D nanomaterials, we make a prospect for the future theoretical physics and practical applications.Plasmonics has developed for decades in the field of condensed matter physics and optics. Based on the classical Maxwell theory, collective excitations exhibit profound light‐matter interaction properties beyond classical physics in lots of material systems. With the development of nanofabrication and characterization technology, ultra‐thin two‐dimensional (2D) nanomaterials attract tremendous interest and show exceptional plasmonic properties. Here, we elaborate the advanced optical properties of 2D materials especially graphene and monolayer molybdenum disulfide (MoS Compared with graphene, the carrier mobility of few layered semiconductors is relatively low, but it is much higher than that of the bulk semiconductors as gallium arsenide (GaAs) or silicon of the same thickness.Materials present distinct properties as their size reduce into low‐dimensional regime, where atoms and electrons are restricted to limited free degree, involving strong light‐mater interaction, ultrahigh electric conductivity and excellent mechanical flexibility. In the recent years, many kinds of 2D materials are analyzed ranging from graphene,To solve this problem, the strategy of integrating 2D materials with plasmonic nanomaterials attracts much interest. Owing to the increased light‐harvesting efficiency and enhanced near‐field intensity, hybrid 2D materials show exceptional potential for photocatalysis and photodetections.In this review article, we start from basic optical properties of 2D materials, focus on the properties and tuning methods of plasmons in both 2D materials and hybrid nanomaterials. By discussing properties of individual 2D materials and the coupling effects especially strong coupling effects with the plasmonic integration, we overview the strategies of making use of plasmonic properties and excitonic irradiations to achieve different photoelectric reactions and applications.2The atomic thin 2D nanomaterial sheet presents significant light‐matter interaction phenomena, owing to quantum confinement effect, their electronic structures and optical properties are distinctive from their bulk morphology.2.1FigureBTe/ħ is mainly blocked from absorption. After that, hot electrons and holes are cooled down by the scattering of interband photons, and mainly recombine to each other until the electron‐hole distribution reach equilibrium. From this process, we can notice that the absorption of graphene is a constant related with its inner property and the absorption of multilayer graphene is πα (≈2.3%) for each atom layer because of the weak interlayer coupling of different 2D electron gas layers . Remarkably, this linear‐dispersion property and high‐efficient light trapping characters make graphene useful for transparent electronic devices, ultra‐sensitive photodetectors and other high‐performance optoelectronic devices, notably, the special optical property changes under high excitation intensity. Further research shows that when the concentration of hot carriers increase and become higher than the intrinsic carrier density in graphene. The states near the edge of the conduction and valence bands are filled because Fermions cannot occupy an exactly same state, making light absorption be saturated. Compared with traditional semiconductors like silicon and GaAs this unique saturable character of graphene under strong light excitation makes it promising in the high speed communication field as ultrathin saturable optical fiber absorber, and leads to a new generation of highly integrated low‐noise optical communication system with very low cost.In which α = 2Different from metallic graphene monolayer, semiconducting LTMDCs are chemical compounds comprised of group IV, V and VI elements, which are transition metal element and chalcogen. They follow the compound form as X–M–X, which is two chalcogen layers bond with a transition metal monolayer in the middle, the corresponding atom number ratio is 2: 1 while the conformation can be various.2 is a kind of semiconducting LTMDCs and researches show that the absorption properties are directly influenced by the electronic structure, which follows the rule of quantum confinement. Different from its bulk form, the band gap of monolayer MoS2 transforms from original indirect type to direct type as the atom layers decrease to one, which attributes to quantum confinement and the orbital hybridization of MoS2 atoms, especially pz orbitals of S atoms and d orbitals of Mo atoms, while the direct excitonic transitions rarely change. Notably, d orbitals of Mo atoms play a dominant role in the Brillouin zone K‐point conduction band state. The middle Mo atoms layer restricted between the two layers of S atoms makes the interlayer coupling weak, thus direct excitonic transitions do not change with number of MoS2 layers. However, the states around Γ‐point are also influenced by pz orbitals of S atoms which construct as two layers on both sides of MoS2 monolayer. It enables the hybridized state to interact with adjacent MoS2 layers easily, thus the band gap at Γ‐point shows significant layer dependent properties.Monolayer MoS2 can be further analyzed as many body systems controlled by the Coulomb interaction of electrons and holes.2 to split, and the maximum of split locates at the K point of the Brillouin zone, while the minimum of conduction band also locates at K point.2 is approximately 1.92eV and 2.08eV, and induces two separated absorption peaks in red to near infrared region. The optical transition bandgap energy should take exciton binding energy in consideration, which increases under the influence of the dielectric constants, so less energy is needed to generate an exciton than the transport bandgap energy. Theoretical calculation from the Bethe‐Salpeter equation (BSE) also proves that absorption spectral reflects the movement of A, B exciton peaks when the comprising elements of LTMDCs are changed .For heavier chalcogen species, the effective exciton mass along with the dielectric screening increases, thus the exciton binding energy decreases because the transition energy equals to μex/ε2 approximately, which corresponds to the redshifts of the A and B exciton peaks. The changes of metal atom do not have significant influence on the transition gap of A exciton. But for B exciton, the peak position is very sensitive to the choice of metal atoms owing to the spin‐orbit coupling effects.The electronic structures and optical properties of semiconducting MoS2, which is a kind of direct bandgap semiconductor, strong EL can be observed under electric excitation. By applying voltage on the source and drain electrodes, electrons are injected into conduction band and become strongly bended at the contact area between MoS2 and metal on a high bias condition. This injection process is able to generate excitons effectively, further induces hot carriers which are electrons in majority to be backscattered as well as accumulated on the drain electrode. As a result, the minority carriers of holes in the monolayer MoS2 sheet will be raised from the drain electrode which result in the recombination of electrons and holes and emit photons. Figure 2 device, as shown in the picture, EL is not homogeneously emitted from the monolayer MoS2 but shows a strong accumulation on the metal electrodes. Notably, the area with the most intensive EL signal is the source of carrier injection, where the efficiency of exciton generation reaches its maximum, because the strong band deformation plays dominant role in the hot carrier excitation.As mentioned above, the behaviors of excitons and trions play an important role in LTMDCs luminescence properties. Based on the methods of excitation, there are mainly two categories of 2D material luminescence, which are electroluminescence (EL) and photoluminescence (PL). For monolayer MoS2 sample are well connected  and lasers. While in PL phenomenon, LTMDCs absorb light and generate electrons as well as holes, then emit light when they recombine, which also shows unique potential as a component in new generation of optoelectronic devices.For LTMDCs as monolayer MoSAs for metallic graphene, which is believed to be a zero band gap 2D material, light emission phenomena are also been found and studied by introducing a band gap, or by strong excitation of ultra‐fast laser to the material. The gapless and linear dispersed properties of graphene show unique negative dynamic conductivity in terahertz (THz) spectral region making it possible to be a terahertz laser emitter.2.2Plasmons are a kind of quasiparticle, which describe the collective oscillations of the electron gas in many metals and semiconductors. Metallic plasmons have been profoundly studied in the past decades, since the marvelous electromagnetic and optic properties they show.q. Transverse collective mode, which is also called as transverse electric mode is of higher energy than the Pauli‐blocking level for interband absorption. The plasmonic frequency of transverse electric mode in monolayer graphene is between 1.667FE/ħ and 2FE/ħ, according to this, the plasmonic mode frequency can be freely modified over a broad range, by applying gate voltage and changing the charge carrier density. While the energy of the longitudinal plasmon mode is nearly zero at a very long wavelength, which makes it a gapless mode.Graphene plasmons, however, are quite different from those in metal structures.Since electrons in graphene sheet can be regarded as two dimensional Dirac Fermions, to describe this collective oscillating system of Dirac Fermions, the Hamiltonian at a low energy can be shown as follows:Fv stands for the Fermi velocity, which is approximately 106 m/s, σ is the Pauli matrix, while p follows the definition as pi = −ih2π∇ri, which is the canonical momentum of the specific electron numbered as i. The second item of this equation indicates the interaction between every other electron in this system and the single electron numbered as i. More specifically, this electron‐electron interaction in the two dimensional system can be quantified as potential u(|ri − rj|), which is decided by the length of the distance between each two electrons numbered as i and j. Since the interaction condition is very sensitive to the environmental dielectric constant, suppose a graphene monolayer which is exposed to two kinds of dielectric media, the interaction potential becomes u(rij) = 2e2(ε1 + ε2)rij. For doped graphene, the distance between two electrons is represented as ri – rj ≈1/Fk, where Fk stands for the Fermi wave number. Thus, the second term of the function follows the form as e2kF/ε, considering the first term of the function which describes the kinetic energy in the form of hvFkF/2π, the ratio connecting this two items in the function should follow the definition as cα/Fεv, which links with the fine structure constant. Notably, α is the conventional fine structure constant as discussed above, which indicates the link between absorb properties and intrinsic plasmons of graphene. Furthermore, by changing the dielectric constant of environmental media ε, electromagnetic properties of graphene can be well modulated, which makes graphene promising for more optoelectronic devices. To further discuss the plasmonic properties of graphene under illumination, we consider perpendicular incident light with the energy flux of c4π|Θ|2, the initial and final states are defined as |i> and |j>, the absorbed energy of unit area graphene follows as 2πω|M|2D, where M is the element of matrix reflecting the reaction between light and electrons, D is the density of states and it is linear with ε. The Hamiltonian which describes the interaction between incident light and electrons is in the term of vF σ⋅eiω Θ. By analyzing initial and final states, the interacting matrix can be calculated as 18e2vF2|Θ|2ω2, from which we can further conclude the absorbed energy Wa = πe22h|Θ|2. As a result, the optical conductivity G  ≡  Wa|Θ|2 is theoretically calculated and equals to πe22h, which is independent with the properties of graphene sheet, and the absorption can also be derived as πα, meeting well with the experimental results as shown in FigureIn this simplified function, ntial u|ri − rj|,q in monolayer graphene can be theoretically calculated by the method of Random Phase Approximation (RPA) as:Furthermore, in the long wavelength region, collective oscillations of electrons are restricted by the particle number conservation and current conservation laws, thus the corresponding dispersion relation of plasmon frequency ω and wave vector vg presents the valley degeneracy factor and is equal to 2. The appearance of Dirac constant ħ in the function shows the non‐classical plasmon dispersion property of monolayer graphene in the long wavelength region. Thus, compared with the classical plasmonic oscillation model, plasmons in monolayer graphene layer show unique dispersion characters, which can be well explained by a massless Dirac plasma model differs from any classical analogy. Apart from un‐patterned graphene monolayer, plasmonic properties of graphene nanoribbons are also researched profoundly in the recent years, for the zigzag type of graphene nanoribbon, frequency spectrum of plasmons can be calculated numerically. While for the type of armchair nanoribbon, the method of one‐band approximation within the RPA at γ = 0 can be utilized under the condition of Re[ε] = 0, and the corresponding plasmon frequency ω follows the function as:In this function, n stands for the concentration of electrons in the conduction band of graphene, while qx3/2−ln(qxW), in which the index is related with the doping condition. Furthermore, the single particle spectrum around FE is shown by the curve of excitations between particle and hole, beyond the curve, the dispersion of plasmon mode comes as qx−ln(qxW), thus the plasmons in doped graphene nanoribbons are similar to that of nanowires.For the pristine graphene sample, propagating plasmon mode only exists in the armchair ribbon, which shows characteristic metallic properties. Because of the chirality of the wave functions, plasmon mode in armchair ribbon is unable to decay into particle–hole pairs. While for pristine graphene ribbon of zigzag type, plasmon mode decays into particle–hole pairs easily in a wide spectral range, thus no plasmon mode can be supported. For doped graphene ribbons, plasmon dispersion properties are similar to that of semiconductor nanowires, the dispersion law is defined by the proportion of Plasmons in two dimensional materials have been experimentally observed in many ways, which can be either direct or indirect. For example, the traditional optical measurements, light scattering methods as scattering‐type scanning near‐field optical microscopy (scattering‐type SNOM), angle‐resolved photoemission spectroscopy (ARPES), electron energy loss spectroscopy (EELS), and scanning tunneling spectroscopy (STS).q with the direction parallel to the surface of graphene. All curves show two nondispersing low loss peaks which are marked as P1 with the energy of 67 meV and P2 of 159 meV, P1 comes from the low‐energy π plasmon, which is reported in the previous research on graphitic surface, while the physics origin of P2 peak is Fuchs‐Kliewer (FK) optical phonons supported by both graphitic structures on SiC substrate and the substrate surface itself. This two peaks are combined by the original background and sheet plasmon peaks which make them hard to be observed, while they emerges as the steep intensity drops induced by the increasing of off‐specular angle. Notably, the plasmons with low energy have almost identical dispersion at small q, however the dispersion relation is different from that of q1/2 dispersion with increasing q. In two dimensional graphene sheet, the data falls below the q1/2 curve for the wave number (q/Fk) between 0.1 and 0.5, as shown in Figure FE for the 2D surface state.The Dissipation effect of SPPs can be derived from the propagation length in the unit of SPPs wavelength. The curves in Figure F). In fact, those collective charge density oscillations of the electron gas propagating through the medium with specific dispersion relation can also interact with other quasiparticles. For example surface plasmon polaritons which are the bound states of electrons or holes with collective excitations of a many‐particle system, and induce strong self‐energy effects. It has been theoretically predicted that those composite quasiparticles named plasmarons, which consist of the carrier charges and plasmons in the material. The energy band of plasmarons can be observed by high‐resolution ARPES, which exist in the graphene sheet on SiC substrate.xk and yk, while ED presents the energy of the Dirac point. The right panel shows the Dirac spectrum considering interactions of electrons, and it illustrates the characteristic reconstructed Dirac crossing. Measured by ARPES, the energy band structure of n‐doped graphene on a SiC substrate is presented in the middle, there are four bands crossing at the Dirac energy (ED) instead of two, which indicates states around ED from a single point recombine and change to the shape like a diamond. The strong reconstruction of the massless Dirac Fermions (MDFs) chiral spectrum near the Dirac point of doped graphene supports that the self‐energy comes from the interactions between one charge carrier and the two dimensional collective electron gas in monolayer graphene.Under the driving force of incident electromagnetic field, electrons are collectively pulled from their balance position and screen outer electric field, however, they tend to be moved too strong and then they are forced back by the Coulomb force. This movement is able to continue and form an oscillating system, in which the restoring force comes from the summation of electric field created by all the electrons in the material. The dispersion relation of two dimensional plasmon can be well calculated at the long wavelength . The coupling of five kinds of oscillators is shown by angle‐resolved reflectance spectrum of MoS2/Ag nanodisks hybrid structure  cavity hybrid structure which achieved strong coupling between excitons and plasmons at room temperature.2, a significant Rabi splitting of 101 meV is observed  and exE stand for the energy of empty photonic mode and exciton, V is the interaction potential between photonic mode and exciton, and is equal to ℏΩR/2. polE (kǁ) denotes the eigenvalues of splitting branches and the value depends on the in‐plane component of the incident light momentum kǁ. |α|2 and |β|2 are derived from the Hopfield coefficients, which correspond to the photonic and excitonic contents of the polaritonic states. In a certain system, the dispersion relation of plasmonic modes can be derived, for example, the dispersion function in plasmonic hole array follows the form as:In the function, P is the lattice period, while  corresponds to the scattering orders of SP modes. Considering |k∥| ≤ 2π/P, the dispersion of TM  mode can be written as:In which, By applying this multi‐oscillators model into the strong coupling hybrid structures, dispersion curves can be well fitted in transmission, reflection, and emission spectral. In conclusion, strong light−matter coupling of hybrid structure inspires the designs of ultrathin and high efficient plasmonic polariton devices, enables more methods on chemical reaction rate control and chemical bond vibration studies. But, the interaction properties of excitons, photons, plasmons and phonons in hybrid structures with growing complexity stay unclear, and need to be analyzed in more detail.3The properties of plasmons in 2D nanomaterials show strong dependence on the material band structure, which can be influenced by chemical and electric doping effects. Also, constructing 2D nanomaterials into specific patterns and inducing defects can also modulate the plasmonic properties, which come from the boundary condition. More importantly, 2D nanomaterials hybridized with metal nanostructures give us new ideas for the plasmonic modulation methods since the plasmonic tuning techniques of different metal nanostructures have been profoundly researched and show great possibilities, along with advantage of the strong field enhancement effect.3.1At specific wavelength, the incident electromagnetic wave becomes resonant with the surface plasmon and can be trapped in a subwavelength volume, leading to a strong field enhancement. For doped graphene, the properties of surface plasmon are strongly linked with the in‐plane conductivity, which include the intraband and interband transitions of hot electron hole pairs, and are mainly dependent on the parallel wave vector and wave frequency. Within the RPA method in the local limit, the light matter conditions can be expressed as:FigureT is the temperature, and Bk presents the Boltzmann constant. Since the Fermi energy follows the function as EF = hvF2ng, 2Dπ, which indicates the strong dependency of carrier concentration in graphene. Additionally, the higher carrier density ng,2D in graphene will induce plasmonic response to the near infrared region, which broadens the resonant wavelength of graphene efficiently. The second term arises from interband transitions, and plays dominant role in the visible and near infrared region, since the loss is dramatic above 2FE energy. As mentioned above, the optical conductance is a constant in the spectral region. The normalized infrared reflection spectra of monolayer graphene with different carrier density are shown in Figure FE > ω which is on the condition of high enough doping intensity, surface plasmons will be able to propagate within the highly doped graphene sheet with the wave vector as:The first term of equation shows the intraband transitions induced Drude mode response of graphene, as shown in spλ ≈ [4α/(ε + 1) (2FπE/(hω)]0λ. Additionally, the wave vector with the direction out of the plane shows the mode concentration within the subwavelength thickness, which is approximately spλ/2π in z direction. While the propagation distance within the doped graphene plane is much longer, decided by the imaginary part of spk, the SPP distance as the function of transition energy can be well modulated by different doping effects  and becomes negligible at –10 V. While the absorption spectra of the MoS2 sample shows that the doping efficiency of Li+ ions is not high for MoS2, since no distinctive peaks exist for –4 V intercalation. Under continuously decreased voltage, more free electrons generate in the nanoflakes with both 2H and 1T phases further form several absorption peaks at −6 V, and the resonance position meets well with the theoretical prediction as shown in Figure 2 reminds only 1T phase. This significant phase conversion from 2H to 1T enables efficient plasmonic modulation over a wide spectral range. There are more methods of carrier density control such as compacting MoS2 sheet into a FET device with different gate bias voltages, gas physisorption, and chemical doping, which provide more choices for plasmonic tuning of unstructured 2D nanomaterials.Apart from the unshaped graphene, doping effect can also be utilized to tune the plasmons of monolayer semiconductors such as MoS3.2Figurep ≈ 40αEFλ/PE(1 + rε), in which FE and PE represent the Fermi energy and the plasmon energy respectively, λ0 represents the excitation wavelength, and rε is the substrate permittivity. In this way it is speculated that the carrier density in narrow ribbons is greater than that in larger one. When the width reaches values smaller than the plasmon wavelength pλ, the near‐field image , making it possible for a single electron observation form scattering intensity spectrum of this hybrid graphene gold nanorod device. The strong interaction between graphene and metallic plasmon also offers an efficient method to control the plasmon resonances at optical frequency, which can be useful for more practical applications.Plasmonic resonance can be actively tuned by electronic doping as mentioned above, however the modulation range is mainly settled in terahertz and MIR region, the plasmonic tuning of optical frequency remains a challenge. Plasmonics of metallic nanostructures and nanoparticles are deeply researched and it is proved that plasmonic resonances in metallic nanostructures and 2D materials interact with each other strongly, if metallic structures are configured near 2D materials and form a hybridized heterostructure.Bowtie structures can also support strong electrical hot spot, since the sharp corner will concentrate electrons in high intensity.Λ, h, and b are the period, height, and trench width of the grating as well as the graphene ribbon array, and r is the width of the ribbon. The image below illustrates the contour plot of the absorption when the incidence angle is fixed at 50° with varying trench widths while the ribbon width remains the same as the trench width (r = b). It exhibits additional bright bands corresponding to the even‐order plasmons. These findings may facilitate the design of optoelectronic devices and metamaterials structures based on hybrid nanostructures and graphene. Several types of modulators are analyzed and show excellent modulating functions in the telecom wave range at low gating voltages for a very small active device area. Those properties are nearly as the same as traditional waveguide modulators which are silicon‐based, but the ultra‐thin characteristic makes them promising for compact device, and further makes them possible for realization of graphene‐based plasmonic modulators for fast optical communications.Because of the atomic thickness of monolayer graphene, it is difficult for single layer graphene ribbons to achieve efficient absorption. A hybrid system of graphene ribbon arrays are further investigated and find that the localized resonances in metal gratings can couple with the plasmonic resonances in graphene ribbons and increase the absorption to a large degree.2 excitons, localized surface plasmon resonances (LSPRs) of individual silver nanodisks and plasmonic lattice resonances of the nanodisk array these three types of resonances, novel 2D plasmonic polaritonic devices can be realized. Figure The exciton‐plasmon coupling effects give more insight about the tuning of plasmons in hybrid 2D nanomaterials, which have been discussed before and enable us to actively modulate plasmonic properties of 2D nanomaterials via temperature control.2‐Ag hybrid nanostructure and coupled oscillators model for intuitive explanation. The MoS2‐Ag hybrid nanostructures are fabricated by designed Ag‐disk structures onto the surface of MoS2 monolayers, which have strong response to the incident light. The image below shows the absorption spectra of MoS2‐Ag hybrids with disk radius of 60 nm, where the LSP resonance red‐shifts with the increasing of the laser power. Total shifting of 25 nm can be obtained as the laser power increased. This work demonstrates that the plasmonic response of MoS2 monolayers can be effectively modified by the photoexcited excitons, which play a significant role in controlling surface plasmon resonances in MoS2‐Ag hybrid nanostructures. The capability of active control of exciton–plasmon coupling is able to provide new opportunities for high‐performance and ultra‐thin optoelectronics devices.Active tuning methods of plasmons are of more practical interest, for now the working spectral region is mainly in infrared light in graphene. As is known to all that the optical response of graphene is rather weak, the method to increase its absorption in the infrared part of the spectrum has become the key point for its optoelectronic applications.4Some 2D nanomaterials with atomic thin thickness show unique optical properties, such as direct band gap light emission, valley polarized PL and distinctive Raman signals. However, the monolayer regime of 2D nanomaterials provides a significant challenge for weak light‐matter interaction, which limits their applications in light‐emitting and optoelectronic devices. 2D nanomaterials interacting with metal nanomaterials constitute abundant heterostructures, which can modulate and enhance the light‐matter interaction of materials via active plasmonic effects. These modulation results in heterostructures can be concluded into two parts depending on optical signals. On the one hand, metallic nanomaterials can enhance or quench the PL intensity of 2D semiconductors. Spectra splitting of shift can also be observed in strong coupling process of exciton and surface plasmon. On the other hand, the heterostructures employed as sensors can significantly enhance the fingerprint Raman spectra of molecules and other biological samples. Due to extraordinary properties of 2D nanomaterials and the flexibility of parameters control as reviewed above, the potential applications are of growing interest in many fields as highly compacted light emitting devices, sensitive optical sensors, and efficient chemical catalyst driven by light power.4.12 heterostructure observing from the spectral evolution of MoS2 PL with increasing GQDs concentration  can be estimated from the optical intensity, which changes with the doping concentration. This tuning effect is further used to control the degree of MoS2 valley polarization at different GQDs deposition densities. The total PL intensity can be decomposed into exciton and trion recombination. Exciton emission efficiency is sensitive with doping charges, but trion is insensitive with doping charges, because the spectral evolution arises from the competition of exciton and trion recombination. Compared with electric gate doping and chemical doping, it is proved to be an efficient n‐type doping by fabricating 0D/2D heterostructures. These results pave the way for the exploration of light–matter interactions in 2D nanomaterials.The optical properties of metal/2D materials heterostructures benefit greatly from the localized strong electric field induced by surface plasmon. The electric field contributes to the strength of light‐matter interaction resulting in absorption enhancement.on Figure7a.113 2 layer and nanoantennas.Charge transfer is directly affected by the spacer thickness between the metallic nanomaterials and 2D semiconductors. Generally, the decay process may even happen in negligible spacing with few nanometer thickness. When an appropriate spacer layer is precisely designed to separate the direct contact of metal and materials, charge transfer may be blocked, and the non‐radiative transition will be restrained. A manipulation method of the PL intensity from nearly 4‐fold quenching to approximately 3‐fold enhancement is achieved by adding a spacer layer between MoSe2/HfO2/Au film was reported by G. M. Akselrod, which shows remarkable PL enhancement of WSe2 up to 2000‐fold.Another example of restraining the non‐radiative decay is reported by A. Sobhani and his colleagues.2 flakes with high‐quality are fabricated. Large‐area fabrication of nanoparticles allowed us to investigate the interaction between the exciton PL and the plasmonic resonance of the particles. Large–size PL enhancement of CVD MoS2 is reported when it couples with plasmonic nanodisk arrays of which the diameters range from 106 to 227 nm  between MoS2 and Au NPs. 2H‐MoS2 shows semiconductor properties with high stability at room temperature, which is due to the field‐induced splitting of Mo 4d‐orbitals of a D3h‐MoS6 unit into three groups. Hot electrons can jump through the barrier, dope the MoS2 monolayer, lead to a lattice destabilization, through the population of Mo 4d‐orbitals, and then into 1T phase. 1T‐MoS2 possesses incomplete occupation of degenerate orbitals, which shows metallic properties. In addition, plasmonic effects also result in spectral broadening and red‐shifting as shown in the figure. The main reason of this tuning is that if hot electrons transfer into MoS2 semiconductor within a non‐radiative decay, the band gap of MoS2 is narrowed. The method of off‐ and in‐resonance control offers selective enhancement of MoS2 PL emission.2 monolayer as shown in Figure 2 above the nanoantenna array is measured by a temperature calibration procedure reaching up to 120 °C ±20 °C. It is nearly two times larger than the temperature of MoS2 without antenna contact. In theoretical prediction, the thermal effects can be interpreted in terms of plasmonic induced light absorption and its conversion into electron‐hole pair in MoS2, which is verified by using green dyadic method (GDM) and Discrete Dipole Approximation (DDA) simulations combined with heat dissipation calculations.Besides the PL intensity changing, peak broadening and energy shifting are also observed due to the plasmonic effect using different contact interfaces. Some researchers reported that plasmonic hot electrons can induce phase transition of MoS2  are collective oscillations of free electrons in metal, which can propagate along the interface of metal and dielectric. Plasmonic waveguides propagating SPPs can realize integrated photonic circuits showing high‐frequency operation rate. Excitons in quantum dots coupling with SPPs are widely reported in the last ten years, such as single‐photon SPPs and quantum coherent. Recent research averts their sights on 2D semiconductor exciton coupling with SPPs. J. Kim's group reported a series of work on exciton‐plasmon conversion in Ag nanowire/MoS2 Figure e. MoS2 P2 gain medium. The atomically flat and thin properties provide fewer scattering losses of SPPs propagation in Ag nanowire.The mechanism is that exciton couples directly with the input laser, and the enhanced primary exciton emission recouples SPPs times and times. This work opens up a shortcut to realize potential TMD optoelectronics coupling with SPPs, and provides a new model of selective PL amplification in recycle principle. Besides the PL enhancement, the SPPs propagation can also be real‐space visualized benefits from the MoS2 film.2 can be continuously tuned from huge enhancement to slight attenuation by changing the morphologies of Ag nanoantenna as shown in Figure 2, the localized resonance of nanoantenna overlaps the excitation energy and MoS2 band gap, which results in dramatic PL enhancement up to 950‐fold. The quantum yield calculated by electrodynamic theory is estimated to 13.9‐fold at the strongest enhancement situation, and the photon collection efficiency slightly decreases from 15% to 13% due to the cover of Ag particles. However, PL weakening is observed in Ag OCT‐MoS2 structure, where the non‐radiative high‐order plasmon plays the dominant role. The field enhancement is still large and calculated as 280‐fold, but the quantum yield and collection efficiency is reduced to 0.2‐fold and 0.26%, respectively. Considering all the effects together, the final PL enhancement is decreased to 0.89‐fold.The PL enhancement is strongly decided on field enhancement, collection efficiency and quantum efficiency.4.22. Graphene is a gapless material, which enables a large‐range light absorption over ultraviolet, visible, infrared and terahertz spectral regimes. The linear dispersion property of graphene provides tunable optical absorption according to n‐type and p‐type doping conditions. The ultrafast carrier mobility and low dissipation rates enable ultrafast conversion and ultrasensitive detection of photons. Besides graphene, LTMDs are a big family with unique electronic and optoelectronic properties. LTMDs are direct band gap semiconductors, which are suitable for light harvesting without momentum dissipation. Because of their distinctive properties as transparency, mechanical flexibility and tunable band gap, LTMDs can offer particular advantages in strong light absorption in visible range. A promising development trend is the combination of plasmonic nanomaterials and 2D crystal heterogeneous stacks, which benefits plasmonic effects and ultrathin thickness resulting in strong light‐matter interaction and sensitive photon detection.2D materials are appealing candidates for a variety of optoelectronic devices because of its ultrathin thickness and distinctive characteristics, which are suitable for transparent electrodes, photovoltaic and photodetection. Among those potential applications, great efforts have been devoted to photodetectors based on monolayer graphene and MoSThe physical mechanism of photodetection based on 2D semiconductors is mainly among the photovoltaic effect, photo‐thermoelectric effect and bolometric effect. The generation of photovoltaic current is arising from the separation of light‐induced electron‐hole pairs by built‐in electric field or source‐drain The built‐in electric field is associated with localized doping and heterojunction with different work‐function. The direction of built‐in electric field determines the photocurrent direction, and it is independent with the overall doping level. The photo‐thermoelectric effect can be generated by hot carriers, which plays a dominant role in graphene p‐n junction or suspended graphene. Because photoexcited e‐h pairs will be transformed into hot electrons due to ultrafast process and strong e‐e scattering. The bolometric effect is based on light‐induced inhomogeneous thermal distribution, which is arising from the change of carrier mobility with variant temperature. In addition, other physical mechanisms can also create photocurrent, including the photogating effect and the plasma‐wave‐assisted mechanism.Figure2 substrate acting as the channel of field effect transistor. In this classic photodetective device, the difference of photocurrent polarities due to photovoltaic and thermoelectric effects are investigated, which are opposite and allow us to directly judge the dominant role with gate bias changing. First, they investigated the thermoelectric effect in a p‐n junction at zero bias. Next, the bolometric response can be determined by measuring the temperature‐dependent current in a gate‐biased device. Finally, a photovoltaic and photo‐induced bolometric effect dominates the photoresponse, which is as large as ten‐times in magnitude compared with the thermoelectric effect. The characteristic photocurrent can be modulated by electrostatic doping of graphene, which offers a proper way to probe the hot‐carriers induced photoresponse and heat dissipation of phonons. Another way to break the mirror symmetry of built‐in potential in graphene device is inducing an asymmetric metallization. The first graphene photodetector is demonstrated in a 10 Gbit s−1 optical data link.−1 at the wavelength of 1.55 um.The mechanism of intrinsic photoresponse of homogeneous graphene with gate bias tuning was reported Figure8a.127 4 A W−1), GaSe (2.8 A W−1), GaS (19 A W−1), In2Se3 (3.95 A W−1), WS2 (22 uA W−1). Besides, the first monolayer MoS2 photodetector exhibits a low photoresponsivity of 7.5 mA W−1, which is at the same level of graphene devices (6.1 mA W−1). The multilayer MoS2 photodetector shows a higher photoresponse up to 100 mA W−1, which can compete with Silicon‐based devices. In 2003, an ultrasensitive monolayer MoS2 photodetector with a photoresponsivity as high as 880 A W−1 at 561 nm was demonstrated, which shows 100,000‐fold enhancement than previous reported.2 monolayer, as well as the contact quality and positioning technique.TMDs with direct band gap can offer additional advantages in photodetection at visible spectral range due to quantum‐mechanical confinement. Benefiting from their layer and mechanical properties, flexible optoelectronic devices of TMDs show great potential in photodetection. With the development of TMDs grown technology, a variety of 2D semiconductor photodetectors have been widely reported performing distinctive superiority as shown in Figure 2 photodetector shows unique interest which is comprised of plasmonic metallic nanostructures.2 at 750 nm (1.65 eV), the incident laser energy is chosen at a much lower energy. Therefore, the photocurrent comes from the hot electrons generated by resonant wire coupling. The mechanism of hot electron induced photocurrent amplification was verified by changing the bias polarity. The relative contribution of hot electrons injection and photothermoelectric effect can be distinguished by the Schottky barrier. The large photogain, as large as 105‐fold enhancement, results in a photoresponsivity of 5.2 A W−1 at 1070 nm, which is comparable with similar silicon‐based hot electron optoelectronic device.The intrinsic absorption of 2D materials is determined by their electronic band gap, which results in photoresponse in a limited spectral range. The heterostructures of metal/2D semiconductor can expand the optical absorption in a large spectral range due to plasmonic effects. The mechanism of surface plasmon enhanced photodetection can be understood in two ways. On the one hand, plasmonic resonances of metal particles are able to generate a large amount of hot electrons, jump and tunnel the potential barrier, and inject into 2D semiconductors resulting in photocurrent. On the other hand, the near‐field enhancement induced by plasmonic effect will enhance the photon absorption contributing to enhanced light‐matter interaction Figure c. A near2/Si substrate, then the thermal annealed nanoparticles was transferred by PMMA film. With the random plasmonic nanoparticles, the photocurrent amplitude is increased up to 2.2 mA W−1 with an average enhancement of the photoresponsivity by more than 400%. This is because of the subwavelength light scattering and plasmonic resonant absorption effect. It shows that plasmonic enhanced graphene photodetectors can greatly enhance the photocurrent and external quantum efficiency by up to 1,500%. And the selective photodetection, among 500 to 650 nm can be realized by varying gold nanoparticles size, enabling highly specific detection of multicolor.Plasmonic Fano resonance has been investigated for a few decades, which is the spectral interference between a broad and narrow resonance. Because the resonant field enhancement is extraordinary high, and the narrow Fano line‐shape is sensitive with the environment, it is quite attractive for 2D photodetection with plasmonic Fano resonant effect. An efficient graphene photodetector was designed by sandwiching plasmonic heptamer antennas between two single layer graphene films Figure d.131 Theh‐BN/Graphene/WS2/Graphene stacked 2D photodetectors shows an enhanced external quantum efficiency as high as 30% due to the strong light‐matter interaction in these atomically thin layers.−1 at the resonant wavelength of LSPR.Other types of photodetection devices based on 2D materials and plasmonics have been reported Figure e,f. A pl4.32 as an example, it has many advantages such as earth‐abundant and nontoxicity, while it suffers from a severe weakness—too wide bandgap (3.2 eV). This means the onset wavelength that TiO2 can absorb is about 390 nm. TiO2 can only make use of ultraviolet light which represents 5% of solar spectrum energy. Therefore, the efficiency of TiO2 is undoubtedly low in photocatalysis. In contrast, one of the reasons why single layer MoS2 have aroused great attention is that it is a direct bandgap semiconductor and its bandgap is suitable (1–2 eV).Semiconductors are the most studied photocatalytic materials which are promising to achieve mass applications of photocatalysis. However, no single semiconductor material can realize this goal due to the intrinsic shortcomings.There are mainly three mechanisms involved in the field of plasmon‐enhanced photocatalysis. The first one relies on plasmonic induced hot electrons.As the demand for energy is increasing, it is necessary to substitute renewable and sustainable resources for fossil fuels. Photocatalysis which converts solar energy into chemical energy has attracted great interest. Semiconductor metal oxides are the most often used photocatalytic materials, although the efficiency is far from the level for practical application. Recently, researchers pay great attention to 2D materials for their utilization in photocatalysis due to novel properties, such as high charge mobility rate. Surface plasmons, which can enhance the absorption of visible light, are integrated to improve the performance of 2D materials.2) monolayer in hydrogen evolution reaction (HER). Some researchers deposited Ag nanorattles coated with Au on MoS2 monolayer  to ≈125 uA*cm−2 (excited by on‐resonance 690 nm laser). Furthermore, the authors plotted Tafel curve and obtained that the slope declined from ≈175 mV per decade to ≈155 mV per decade, which illustrated that the reaction rate was accelerated by exciting surface plasmon resonances. Based on this result, they believed that plasmonic hot electron played an important role in the improved performance. They supposed that the doping of plasmonic hot electrons and the stress induced by nanorattles caused the structure phase change of MoS2, resulting in better photocatalytic activity. According to their former work, 2H phase MoS2 would transform into 1T phase with the doping of plasmonic hot electrons. In this work, the new raised Raman peaks of MoS2 deposited with nanorettles confirmed that the 1T phase was produced. Furthermore, they studied the influence of laser power in HER performance. With the increasing of laser power, they found the onset potential gradually decreased and current density went up. This result was accounted that more plasmonic hot electrons were generated when illuminated by higher power incident light. In addition, they derived the phase transition irreversible from the fact that the improved activity was sustained when the laser power is decreased.The introduction of plasmonic nanorattles effectively enhances the performance of molybdenum disulfide , the generated holes moved to the electrode and produced cathode current. While there exit hole scavenger (Na2S and Na2SO3) in solution, the holes would be depleted and the electrons transferred to the anodic electrode, resulting in adverse photocurrent response. By comparing the absorption spectra of the heteronanocrystals with control groups comprised of discrete QDs and Au NPs, they found that the spectra were not simply the sum of these parts and deduced that there was interaction between surface plasmons and excitons.The degradation of organic dyes is of critical significance in environmental protection. Some researchers reported a photocatalyst that could not only enhance the activity of H2 production from water splitting, QD/Au‐G composite also demonstrated best activity among all tested photocatalyst. Besides, the H2 evolution rate was dramatically improved with the help of graphene, which illustrated the positive role of graphene in accelerating H2 generation. In this work, graphene promoted the efficiency because of three causes. The first is graphene has good water‐solubility. Secondly, graphene has excellent conductivity. Therefore, the electrons in QDs could be efficiently transferred, leading to decreased recombination rate. Thirdly, graphene provided more active absorption and reaction sites. However, increasing the content of graphene could not continuously enhance photocatalytic activity as too much graphene could hinder the absorption of incident light and lessened the active reaction sites. The most suitable graphene content was about 1%. The maximum H2 generation rate was 3113 µmol h‐1 g‐1 and the quantum yield was estimated to be 25.4% at 450 nm. This work mainly took advantage of the enhanced near field produced by LSPR, which improved the absorption of QDs and thus facilitated the generation of electron‐hole pairs.Next, they studied the photodegradation performance of QD/Au‐G for methylene blue (MB) and Rhodamine B (RDB). For both kinds of dyes, QD/Au‐G showed better ability in photodegradation than the reference groups. From this result, it was not difficult to infer the active effect of plasmon. As for H2, which realizes the depletion of greenhouse gas CO2 and generation of useful products like methane (CH4) and formic acid (HCOOH). A high‐efficiency CO2 conversion photocatalyst that consisted of graphene coated Au nanoparticles (r‐GO‐AuNPs) was synthetized as shown in Figure 2 molecules were then generated by water splitting. Secondly, the produced H2 reacted with CO2, forming HCOOH and methanol (CH3OH). The UV‐visible spectra showed that Pt‐Au NPs and r‐GO‐AuNPs had almost same plasmon peak, locating at 540 nm. In addition, the extinction spectra did not change after illuminated by Xe lamp for three hours, and r‐GO‐AuNPs showed a litter better performance than Pt‐AuNPs in catalytic efficiency, indicating that r‐GO was possible to substitute for Pt. Meanwhile, this catalyst illustrated excellent production selectivity with HCOOH content higher than 90%. From the experiments measuring the quantum and chemical yield of different photocatalyst, r‐GO‐AuNPs demonstrated best activity with its efficiency far exceeding r‐GO (7.6 times) under the irradiation of Xe lamp. However, the quantum and chemical field of r‐GO‐AuNPs were not dramatically increased when excited by NIR (808 nm) laser, because surface plasmons were not resonantly excited. These experimental results disclosed that both plasmonic material and graphene played positive roles in raising quantum efficiency. The reaction time was estimated to be about 3 hours and the optimum pH was 9.0 for the photoconversion. Interestingly, increasing r‐GO‐AuNPs concentration adequately resulted in better yield, while too much content led to declined efficiency. To mimic natural solar illumination, they measured the quantum and chemical yields under AM 1.5 filter. The result showed much lower yields due to the power density passed solar filter (0.15 W/cm2) was less than that of Xe lamp (5.68 W/cm2).Another important photocatalytic reaction is the reduction of CO2 composite. The pump pulse wavelength was 575 nm and the wavenumber of probe light was 2978 cm−1. They discovered that the plasmonic hot electron transfer process was completed within 220 fs as the transient absorption signal reached maximum at that time after excitation. Similar to the results of quantum and chemical yield, the peak signals of r‐GO‐AuNPs and GO‐AuNPs were 8.7 and 2.8 times higher than the value of pure AuNPs, respectively. In this work, graphene acted as electron acceptor and transporter because the plasmon‐induced hot electrons were firstly moved to the coated graphene layer before transferring to water molecules.To fully explore the contribution of Au NPs, they carried out femtosecond transient absorption experiments on r‐GO‐AuNPs/TiO5In this review, we summarized the plasmonics of 2D nanomaterials, which include 2D materials as graphene, LTMDCs and hybridization with nanoparticles as well as nanostructures. Based on their unique properties and coupling effects, we proposed several research directions for the light‐matter interaction studies, plasmonic tuning methods and potential applications in the future.2 membrane, which may come from inherent defects of 2D materials induced by the configuration or transfer procedure.First, we elaborated the advanced electronic structures and optical properties of 2D materials. The plasmonic properties of 2D materials were further introduced by analyzing the oscillating system of Dirac Fermions. Based on latest studies, we discussed the coupling effect achieved by the LTMDCs/metal nanostructure hybrid system, and the multi‐oscillators model which is promising for analyzing complicated system of more resonant modes. Moreover, controlling configuration properties such as size, contour, position, and crystalline structures is the key point to the practical applications. Thus, a new generation of efficient and accurate fabrication technique is very in need, and new methods for active material manipulating are also required to realize more functional modulations.Then, we reviewed recent researches for the plasmonic tuning of 2D nanomaterials. The types of doping are summarized including electron injection, gas physisorption, and chemical methods, which can tune plasmonic properties by changing the carrier density. According to the boundary condition of SPP, the plasmonic mode of 2D materials can be modulated by constructing it into specific pattern. Furthermore, the hybridization of 2D materials and metal nanomaterials attracts growing interest, since the metallic plasmons interact strongly with excitons and 2D material plasmons. 2D materials hybrid structures such as ZnO/graphene or LTMDCs/photonic crystal compound stacks show potential to be photodiode for photocurrent generation or photodetection,Finally, we elaborated plasmon‐induced applications of 2D nanomaterials. Owing to the ultra‐thin nature and strong light‐emitting properties, 2D nanomaterials have great potential for polarized LEDs and optical labels. 2D materials hybridized with metal nanostructures are also promising for optoelectronic devices such as transparent electrodes, photovoltaic devices and photodetectors. The photocatalytic reactions driven by light are based on the excitation of hot carriers between the interface of metal and semiconductor, which are believed to be promising for environmental friendly energy generation in the future. With the continuing researches on printed electronics based on 2D nanomaterials, inspiring applications are found including wearable sensors and flexible transistors, recently, a method of UV‐pulsed laser technique is carried out to selectively irradiate reduced graphene oxide (RGO) while keeping the high electrical conductivity in the paper‐based circuit. By combining the 3D printing technology, it is even possible to develop graphene/3D nanostructures beyond this planar circuit to enable more favorable possibilities.