In this paper, we present a study of the sub-monolayer gold intercalation of graphene on Ir(111) using scanning tunnelling microscopy (STM). We found that Au islands grow following different kinetics than growth on Ir(111) without graphene. Graphene appears to increase the mobility of Au atoms by shifting the growth kinetics of Au islands from dendritic to a more compact shape. Graphene on top of intercalated gold exhibits a moiré superstructure, with parameters significantly different from graphene on Au(111) but almost identical to graphene on Ir(111). The intercalated Au monolayer shows a quasi-herringbone reconstruction with similar structural parameters as on Au(111). Whig metals . In ordeg metals  is used g metals , Cu [13,g metals , and alkg metals ,16, at td Ni bands is entirely recovered upon gold intercalation [11 holes cm−2), which is lower only for graphene on Ir(111). Such a charge transfer leads to a shift of the Dirac point of 0.24 eV above the Fermi level [Gold surfaces are known for their weak interaction with graphene , but alscalation . Gold hacalation ,23. The mi level ,18,23. IGraphene intercalated by gold on Ir(111) has been studied only for thick gold films which exhibit moiré super-structures with a periodicity of 17.0 Å due to the 14.7% lattice mismatch between graphene and Au(111) .In this paper, we present an STM study of graphene on Ir(111) intercalated by a sub-monolayer coverage of gold. We studied the structure of the intercalated gold in terms of the possible influence of graphene on its interaction with the underlying iridium surface.−10 mbar. The setup was used for the characterization of a clean, graphene-covered Ir(111) surface and Au intercalated graphene on Ir(111). The STM measurements were performed on Aarhus STM (SPECS) at room temperature (R.T.). The STM images were recorded while scanning the surface by an electrochemically etched tungsten tip, in constant current mode, with a bias voltage applied to the sample. The STM was calibrated by measurements on the HOPG sample and the STM images were processed with WSxM software 5.0. The Ir(111) sample was a crystal 6 mm in diameter, of 99.99% purity, polished with roughness <0.03 μm and with an orientation accuracy <0.1°. The sample was heated by e-beam heating using a hot filament at a negative potential near the grounded sample. The sample temperature was calibrated by the C-type thermocouple attached to the sample with respect to the heating time and power used and, additionally, values were measured by a K type thermocouple attached to the sample plate. The C-type thermocouple was then removed from the sample to enable multiple graphene preparations and transfer from the sample preparation manipulator to STM.The STM and low energy electron diffraction (LEED) experiments were performed in an ultra-high vacuum (UHV) setup operating at a base pressure of 5 × 10−7 mbar at 1100 K, and a final 5–15 min annealing in UHV at 1150 K. After five such cycles, typically a sharp LEED pattern and large-scale STM images confirmed a clean surface.The Ir(111) sample was cleaned by using cycles consisting of 50 min of 1 keV argon-ion sputtering followed by 10–25 min of annealing in oxygen partial pressure of 1 × 10−8 mbar for 60 s and flash to 1400 K) followed by chemical vapour deposition . This TPG + CVD procedure growth led to a uniform orientation of graphene (referred to as Gr/Ir(111)) with the lattice aligned to the substrate lattice (R0) and at full monolayer coverage. Gold was deposited by resistive heating of a tungsten basket filled with pure gold (purity: 99.999%) heated by the direct current through the W wires, while the sample was kept at the R.T. The intercalation was carried on immediately after Au deposition by sample post-annealing at 800–900 K.The graphene monolayer on Ir(111) was prepared by a temperature programmed growth cycle  before and after Au intercalation by means of LEED. As can be evidenced from the inset in The intercalation of graphene by Au produced a visible impact on the STM images of the Gr/Ir(111) system . They exThe bright areas with enhanced contrast and clear hexagonal structure correspond to the moiré superstructure of non-intercalated graphene. The area characterised by weak moiré modulation is associated with the intercalated graphene regions. From A comparison of the images in We measured the moiré periodicity across the area with intercalated and non-intercalated graphene see . The linSTM images, given in The fact that the gold monolayer between gr and Ir(111) exhibits the same reconstruction with similar structural parameters as the Au(111) surface layer indicates that the structure of the gold overlayer is dominated by the inter-atomic interaction over the adsorbate–substrate one. However, the herringbone pattern is not registered in the Au monolayer on Ir(111), suggesting a noticeable influence of graphene on the observed reconstruction. On the other hand, graphene on Au(111) had no impact on the reconstruction of the surface layer . Having Regarding the metals weakly interacting with graphene, intercalation can change the growth mode, e.g., from cluster to smooth films (ref. ). HoweveTo correctly interpret the emergence of the quasi-herringbone pattern in sub-monolayer Au intercalated between graphene and Ir(111), a theoretical investigation of electron transfer and the potential energy landscape of the system is required.Finally, The graphene grows on Ir(111) in a continuous layer over macroscopic distances and wrinkles, together with multi-atom vacancies are regarded as preferential penetration channels for graphene intercalants which interact weakly with graphene ,38,39,40In conclusion, we have studied the sub-monolayer gold intercalation of graphene on Ir(111). We found that Au islands grow following different kinetics to the growth on Ir(111) without graphene. It appears as if graphene increases the mobility of Au atoms, shifting the growth kinetics of Au islands from dendritic towards a more compact shape. Graphene on top of intercalated gold shows a moiré superstructure with parameters significantly different to graphene on Au(111), but almost identical to graphene on Ir(111). The intercalated Au monolayer exhibits well-known herringbone reconstruction, with similar structural parameters as on Au(111). The explanation of the emergence of this reconstruction requires a theoretical investigation of electron transfer and the potential energy landscape of the system, and is beyond the scope of the present work. Nevertheless, the observed effects can provoke interest in further theoretical calculations, e.g., the DFT of the intercalated gr/Au/Ir(111).


Despite the potential of graphene for building a variety of quantum photonic devices, its centrosymmetric nature forbids the observation of second harmonic generation (SHG) for developing second-order nonlinear devices. To activate SHG in graphene, extensive research efforts have been directed towards disrupting graphene’s inversion symmetry using external stimuli like electric fields. However, these methods fail to engineer graphene’s lattice symmetry, which is the root cause of the forbidden SHG. Here, we harness strain engineering to directly manipulate graphene’s lattice arrangement and induce sublattice polarization to activate SHG. Surprisingly, the SHG signal is boosted 50-fold at low temperatures, which can be explained by resonant transitions between strain-induced pseudo-Landau levels. The second-order susceptibility of strained graphene is found to be larger than that of hexagonal boron nitride with intrinsic broken inversion symmetry. Our demonstration of strong SHG in strained graphene offers promising possibilities for developing high-efficiency nonlinear devices for integrated quantum circuits. Nanostructured platforms for efficient nonlinear optics are the building block of next generation integrated photonic devices. Here the authors provide a straightforward method to engineer the lattice symmetry of monolayer graphene, boosting the SHG signal at low temperature. Among many nonlinear processes, second-order χ(2) nonlinear processes such as second-harmonic generation (SHG)4 and spontaneous parametric down-conversion (SPDC)7 are most frequently used in many applications owing the high χ(2) susceptibility. The χ(2) processes are only possible in materials with broken inversion symmetry. Some of these materials, such as beta barium borate (BBO)8, are extensively used in various applications as they are commercially available. However, these traditional materials have crucial limitations, including low nonlinear susceptibility and phase-matching issues9. Most importantly, those materials only exist in the form of bulk crystals, thus prohibiting them from being scaled down10. Towards the realization of miniaturized, integrated nonlinear photonic devices, the search for materials that can exist in nanometer dimensions with uncompromised nonlinear properties has become an important research topic.Nonlinear optics is a branch of modern optics with many essential applications ranging from material analysis to quantum computing2)11 and hexagonal boron nitride (hBN)12 intrinsically possess broken inversion symmetry. In addition to their strong χ(2) responses, the atomically thin nature of these 2D materials allows overcoming the phase-matching restriction, which has otherwise been a major challenge in developing nonlinear optical devices. Among all the 2D materials, graphene is the most researched material and has thus far attained the greatest amount of attention owing to its superior mechanical13, electrical14, and optical properties15. For example, graphene’s excellent carrier mobility and universal absorption make it an unparalleled material for many optoelectronic applications19. Over the past decade, there has been a vast amount of research works on nonlinear optical responses in graphene23, including saturable absorption20, four-wave mixing22, and third harmonic generation (THG)23. Unfortunately, however, graphene does not allow any intrinsic χ(2) processes because of its preserved inversion symmetry. To break the inversion symmetry in graphene, researchers have recently devised various methods such as applying external electrical bias27, inducing in-plane optical fields28, and exploiting interlayer interaction in multilayer graphene30. However, all these methods do not provide any insight into breaking the lattice inversion symmetry within one layer of graphene, which is crucial in understanding how graphene’s lattice can be further engineered at the most fundamental level. Furthermore, the second-order response created by the in-plane photon momentum is considered weak since the SHG intensity is only proportional to the photon momentum31. Lastly, the requirements of supplying continuous electrical energy and using oblique incidence of optical pumping27 makes these methods unsuitable for making integrated graphene devices.Recently, atomically thin two-dimensional (2D) materials have shown great promise since many of them such as tungsten diselenide (WSeχ(2) response when the temperature of the graphene is reduced to 4 K, which can be explained by resonantly enhanced optical transitions between pseudo-Landau levels (pLLs). Moreover, the experimental benchmarking of our strained graphene against a well-investigated monolayer hBN with an intrinsically broken inversion symmetry allows us to conclude that our strained graphene possesses a 30% larger second-order nonlinearity than hBN. As a result, our approach utilizing unique non-uniform strain and sublattice polarization presents new possibilities for fashioning the χ(2) responses in graphene by fundamentally engineering the material’s symmetry properties. Additionally, our work provides a very convenient, stable, and scalable way to generate the second-order nonlinearity for integrated graphene devices, which holds the promise of practical optoelectronic applications. We believe that this work opens new opportunities for graphene as a promising material for the on-chip nonlinear optoelectronic devices.Herein, we report an experimental observation of a new type of SHG from monolayer graphene deposited on our unique strain-engineering platform. The non-uniform strain in graphene induces a strong polarization between graphene’s two sublattices that are originally balanced. This polarization breaks the sublattice symmetry in graphene, thus enabling a strong second-order response in graphene. The experimentally observed SHG in strained graphene exhibits unconventional features including a significant temperature dependence that is not previously reported graphene. In particular, we observe a nearly 50-time enhancement in graphene’s 33. The two sublattices possess an equal local density of states (LDOS)33. Therefore, the sublattice polarization becomes zero and the sublattice symmetry is preserved. In the strained region, contrastingly, a strong non-uniform strain at the edge of the nanopillar can significantly deform the carbon-carbon bonds and enables one sublattice (dark green dots) to obtain a significantly higher LDOS than the other (light yellow dots), as illustrated in the right ellipse35. This imbalance of the LDOS between the two sublattices results in a non-zero sublattice polarization that breaks the sublattice symmetry. While the existence of this sublattice polarization in graphene has previously been confirmed by scanning tunneling microscopy (STM)35, the influence of which on the optical properties of graphene has not been experimentally studied yet. Here, we exploit this sublattice polarization to observe a strong and unconventional SHG (green beam) upon the excitation of femtosecond laser pulses (red beam) .Figure Figure − and 2D+. We observe a Raman peak shift of 82.6 cm−1 between the 2D peak of unstrained graphene and the 2D− peak of the deformed graphene, yielding a strain of ~1.26%36 . By considering the theoretical lattice deformation38, we calculate the maximum local atomic strain of ~2.4%, which is larger than the measured value of ~1.26%. The discrepancy is ascribed to the limited spatial resolution of the Raman spectroscopy due to a large laser spot size compared to the sharp edges of our graphene nanopillars39.To quantitatively obtain the amount of the induced strain in graphene, we performed Raman spectroscopy in strained graphene on the nanopillar  measurements, we confirmed that the graphene layer used in our study is close to intrinsic  that can generate discrete pLLs44. Here, we develop a new theoretical framework that provides a relationship between non-uniform strain, sublattice polarization, and PMF (See Supplementary Note P to be:a0 (~0.14 nm) is the bond length of pristine graphene, dn is the bond length along the direction δn after strain. δn refers to the three nearest neighbor vectors of a carbon atom  is a constant and ∇ · P is the divergence of P. Figure P and Bps, respectively. P 48 and graphene-based heterostructures31 was theoretically predicted to activate a strong and resonant SHG when the SHG energy matches with inter-Landau level separation. Here, we theoretically extend this phenomenon of the resonant SHG to the case of strained graphene possessing a strong PMF. We show that the resonant SHG via inter pLLs in our strained graphene sample has a strong temperature dependence. First, by using rigorous tight-binding simulations, we calculate the distribution of density of states (DOS) in pristine and strained graphene  because of the sublattice polarization-induced χ(2) nonlinearity. Also, the magnitude of SHG can be strong owing to the resonant optical transitions between pLLs. It should be noted that in pseudo-Landau-quantized graphene, the resonant SHG can be considered as two successive one-photon transitions. Each of these transitions must obey the optical selection rule of li and lf are the pLL index of the initial and final states respectively. As shown in Fig. The PMF generated at the edges of the nanopillar creates discrete pLLs in graphene, which can strongly modify the electrical and optical properties of grapheneDOS Fig. 37. In thχ(2) strength in strained graphene based on a well-reported method of nonlinear bubble diagrams31 (see Supplementary Note χ(2) at 300 K and 4 K, respectively, assuming that the excitation laser wavelength is 1035 nm. At 300 K, local χ(2) at the edges of the nanopillar attains a considerably high value compared to areas away from the nanopillar, owing to the strong sublattice polarization and the resonant SHG enabled by pLLs at these locations. The distribution of χ(2) becomes more interesting at 4 K, where χ(2) becomes extremely large at only certain locations along the edges of the nanopillar  value significantly only at low temperatures (see Supplementary Note χ(2)). Meanwhile, we also consider the temperature-dependent phonon-assisted scattering events which mediate the efficiency of the SHG emission. When the temperature decreases, the scattering rate between the carriers and phonons decreases, leading to a more dominant SHG process, therefore favoring a stronger SHG emission  value over an entire area shown in Fig. Lastly, by adding up the In summary, we have demonstrated the experimental observation of SHG from strained graphene on nanopillar structure. The SHG arises from the sublattice symmetry breaking in graphene due to the non-uniform strain induced by the nanopillars. At a low temperature of 4 K, the SHG intensity is almost 50 times higher than that at room temperature. The drastic enhancement of SHG intensity is explained by the inter-pLL resonance when the strain-induced PMF is present. At a low temperature, the DOS at each pLL is significantly increased owing to a reduced thermal broadening, which strongly enhances the resonant inter-pLL optical transitions and SHG when the energy separation between pLLs matches the SHG energy.49 . This shows that the strain-induced sublattice polarization can be used to modify the point symmetry of graphene and allows us to design new anisotropic SHG patterns. Additionally, we also observe that the intensity of SHG increases when the average height of the nanopillar array increases (see Note 11 of Supplementary Information). This can be explained with the fact that a large PMF forces the LDOS of pseudo-Landau levels to be sharper, and therefore enables a stronger resonance between the pseudo-Landau levels and produces a large SHG intensity. Lastly, we also observe that the SHG intensity in our strained graphene can be tuned by the back gate voltage (see Note 12 of Supplementary Information). Due to the effect of Pauli blocking53. The study of strain-induced nonlinear characteristics in graphene can also be further extended to third harmonic generation or other nonlinear processes, which can be of great use in other nonlinear optoelectronic devices. In addition, circular polarization-dependent or valley-dependent nonlinear processes could be possible in pseudo-Landau-quantized graphene system55, which adds another dimension to the study of nonlinear processes. Interestingly, our simulation result reveals that the sublattice polarization can significantly suppress the LDOS at the zeroth pseudo-Landau level of one sublattice while that of another sublattice remains very large   for 3 min 30 s, forming an array of nanopillars. The square pillars have 500-nm side length and 85-nm height. The whole chip was coated with a 20-nm Al2O3 layer by atomic layer deposition before graphene dry transfer.The nanostructured substrate was patterned using e-beam lithography (EBL) and a wet chemical approach. Patterns for the square arrays were firstly defined in a 380 nm spin-coated polymethyl methacrylate (PMMA) layer. Subsequently, using the patterned PMMA as an etch mask, the SiOGraphene flakes were obtained with Scotch tape by mechanical exfoliation of a small piece of Kish graphite (Graphene Supermarket). The tape with thinned graphene flakes was pushed down onto a polydimethylsiloxane (PDMS) film and then detached. The monolayer flake on PDMS was found under an optical microscope, and then the number of layers was confirmed using Raman spectroscopy. The graphene flake was then aligned and stamped on a nanostructured substrate with an all-dry transfer method using our home-built dry transfer setup.The structural characteristics and morphology of the fabricated sample devices were characterized by field-emission scanning electron microscopy (SEM) (Apreo S FESEM). The electron acceleration voltage in SEM was 5 kV.58. The maximum measured strain is estimated to be 1.26% by assuming a strain-shift coefficient of 65.4% cm–1/%36 between the 2D peak of unstrained graphene and the 2D– peak of the strained graphene.The thickness of graphene flakes and strain distribution in graphene on nanopillars were characterized using a WITec Raman setup with 100× objective lens (NA = 0.9) and 600 lines/mm grating. We used a 532-nm laser at a low laser power of <1 mW to avoid any heating effect. We confirm the graphene sample to be monolayer based on the observation that the 2D peak intensity is ~2 times the G peak intensity2 on the sample. Supplementary Fig. The measurement on graphene’s SHG was performed in the reflection geometry. The sample was placed in an open-cycle cryostat (Janis ST-500) cooled by liquid helium. The temperature for our measurements varies between 4 K and 300 K. The excitation pump pulses were generated from a 1035-nm femtosecond laser with a 120-fs pulse duration and a repetition rate of 76 MHz . The laser was defocused using a focal lens to cover a spot-size area of approximately 15 × 15 μmSupplementary Information


Interstitial lung diseases (ILDs) are a large group of pulmonary disorders characterized histologically by the cardinal involvement of the pulmonary interstitium. The prototype of ILDs is idiopathic pulmonary fibrosis (IPF), an incurable disease characterized by progressive distortion and loss of normal lung architecture through unchecked collagen deposition. Acute exacerbations are dramatic events during the clinical course of ILDs, associated with high morbidity and mortality. Infections, microaspiration, and advanced lung disease might be involved in the pathogenesis of acute exacerbations. Despite clinical scores, the prediction of the onset and outcome of acute exacerbations is still inaccurate. Biomarkers are necessary to characterize acute exacerbations better. We review the evidence for alveolar epithelial cell, fibropoliferation, and immunity molecules as potential biomarkers for acute exacerbations of interstitial lung disease. Interstitial lung diseases (ILDs) are pulmonary disorders characterized histologically by the involvement of the pulmonary interstitium. Clinical manifestations of these include dyspnea, coughing, hypoxia, and impaired lung function. Several of these conditions are associated with underlying systemic conditions, such as connective tissue diseases (CTDs), asbestos exposure, drug exposure, or allergen exposure, as in hypersensitivity pneumonitis. It is nevertheless unclear in many cases what causes ILDs . IdiopatPatients with ILDs have unpredictable clinical outcomes. There is often a slow but steady progression of the disease in many patients. In some patients, the ILD remains stable, while other patients experience a rapid clinical deterioration. Acute worsening of the ILD (known as acute exacerbation) can also occur. Acute exacerbations may be fatal or may lead to significant worsening of symptoms ,2.Acute exacerbations of interstitial lung diseases (AE-ILDs) refer to a sudden aggravation of symptoms in patients with ILDs. The exacerbations of chronically present ILD were initially recognized in IPF, but they can occur in almost all ILDs. These exacerbations are characterized by increased dyspnea and cough and decreased oxygen saturation. Acute exacerbation of interstitial lung diseases (AE-ILD) is an acute and often morbid deterioration of the patient’s respiratory function leading to hospitalization.-A previous or concurrent diagnosis of IPF.-Deterioration within 30 days.-New bilateral ground glass opacities and/or consolidation on a background of reticular or honeycomb pattern consistent with usual interstitial pneumonia (UIP).-No evidence of pulmonary infection by endotracheal aspiration or bronchoalveolar lavage.-Exclusion of alternative causes, including left heart failure, pulmonary embolism, or an identifiable cause of acute lung injury.The Idiopathic Pulmonary Fibrosis Network (IPFnet) had proposed in 2007 the following definition of an acute exacerbation of IPF :-A previThe above-mentioned criteria were revised in 2016 .-Previous or concurrent diagnosis of IPF.-Acute worsening or development of dyspnea, typically less than one-month duration.-Computed tomography with new bilateral ground-glass opacity and/or consolidation superimposed on a background pattern consistent with the usual interstitial pneumonia pattern.-Deterioration not fully explained by cardiac failure or fluid overload.AE-IPF is defined as an acute, clinically significant respiratory deterioration characterized by evidence of new widespread alveolar abnormality. The revised diagnostic criteria are :-PreviouThe exact causes of AE-ILDs are thought to be related to a variety of factors, including viral infections, environmental exposures such as air pollution, drug toxicity, procedures such as bronchoscopy or VATS, and microaspiration. Regarding the effect of smoking as a risk factor for acute exacerbation of IPF, Song et al. reported that never-smoking status and low FVC were risk factors for AE-IPF . In the Among patients with all forms of ILD with acute exacerbations, 52% of admissions for decline of respiratory function were idiopathic, 20% due to infection, 15% due to subacute progression or end-stage disease, 6% due to heart failure or severe pulmonary hypertension, 4% due to venous thromboembolism, and 2% due to diffuse alveolar hemorrhage or perioperative exacerbation .Further research is necessary to understand the causes of AE-ILDs better and to develop more effective treatments for these exacerbations. Treatment options for AE-ILDs include oxygen therapy, corticosteroids, and antibiotics, but there are no targeted treatments that have been proven to be effective in treating these patients .Diagnosis of AE-ILD can be challenging. The clinical condition of these patients is so severely impaired due to the disease exacerbation that even minimally invasive diagnostic procedures, such as bronchoscopy with bronchoalveolar lavage, can have detrimental effects on the clinical course of the patients. Moreover, invasive lung biopsies are associated with increased procedure-associated mortality, which often makes them an unacceptable diagnostic tool in the clinical setting of an AE-ILD ,9. HenceA biomarker is a biological molecule or genetic feature that can be used to identify the presence of a disease or condition. Biomarkers can be used to diagnose, monitor, and evaluate treatment outcomes for a variety of diseases, including interstitial lung diseases ,11. IdeaThe focus of the present review will be placed on the use of biomarkers for the diagnosis and prognosis of patients with AE-ILDs.Currently, there are no established biomarkers in clinical practice that can predict the onset or outcome of AE-IPF. However, several biomarkers have been proposed as potential predictors of AE-IPF.p = 0.002). In the multivariate analysis, baseline serum KL-6 (both continuous and at a cut-off level of >/= 1300 U/mL) was an independent predictive factor for AE-IPF [The Krebs von den Lungen 6 (KL-6) glycoprotein is a mucin-like, high-molecular-weight protein expressed on the surface membrane of alveolar epithelial cells. Proliferating, stimulated, or injured alveolar epithelial cells release KL-6 into blood vessels. Increased levels of KL-6 in the serum have been found in patients with ILDs . It has r AE-IPF .p = 0.0001). Patients with both initial serum KL-6 >/= 1000 U/mL and serial increase in serum KL-6 had the steepest decline, suggesting a role for KL-6 predicting a worse lung functional status [In another study, IPF patients with increased serum KL-6 levels during follow-up had a significantly steeper decline in FVC than those without increased KL-6  reduce alveolar surface tension and prevent lung collapse. They are synthesized and secreted by alveolar epithelial cells (AEC) II. Patients with IPF, as well as those with other ILDs, have significantly elevated levels of SP-D and SP-A in their serum and BALF ,21.Increased levels of SP-D were observed in patients with AE-IPF compared to those with stable disease . In a meIn the normal process of cell replication, telomeres protect chromosome ends from progressive shortening . AbnormaGrowth differentiation factor 15 (GDF-15), also named macrophage inhibitory cytokine-1 (MIC-1), belongs to the transforming growth factor-β (TGF-β) superfamily. There is an increase in the expression and upregulation of GDF-15 in epithelial cells in IPF. GDF-15 is a useful biomarker for epithelial stress associated with poor IPF outcomes. In a study of 47 patients with AE-IPF and 61 patients with stable IPF, serum GDF-15 levels, as well as the protein and mRNA expressions of GDF-15 in the lung, were significantly elevated in AE-IPF patients compared with stable IPF cases. A serum GDF-15 level above 989.3 pg/mL was a risk factor for AE occurrence, and the level above 1075.76 pg/mL was an independent predictor for survival in IPF cases .mucin 5B (MUC5B) genotype, revealed an independent association between MMP-7 and survival in IPF patients [Matrix metalloproteinases (MMPs) are endopeptidases with zinc in their structure that degrade proteins of the extracellular matrix. Development, morphogenesis, tissue repair, and remodeling rely heavily on the timely degradation of extracellular matrix. By regulating extracellular matrix turnover, MMPs contribute to the pathogenesis of fibrosis ,31,32. Mpatients . It has Biomarkers released by matrix metalloproteinase-mediated degradation of collagen have also been examined in AE-IPF; such a degradation product, versican, was found to be associated with mortality in a study of 68 patients with AE of idiopathic interstitial pneumonias, including 28 patients with AE-IPF .A disintegrin and metalloproteinases (ADAMs) are believed to be involved in the pathogenesis of many fibrosis-related diseases. ADAM-17 was increased in IPF and other ILDs, such as CTD-ILD . ADAM-17Human epididymis protein 4 (HE4) is widely used as a biomarker in ovarian and endometrial cancer. HE4 inhibits the function of various proteases, such as MMPs and serine proteases, suppresses the degradation of type I collagen, and plays a crucial role in the pathogenesis of fibrosis. In a retrospective study of 59 patients with stable IPF and AE-IPF, the expression of serum HE4 was elevated, especially in AE-IPF patients, as was KL-6. In the multivariate analysis, HE4 levels, as well as GAP index, were associated with survival. Histologically, HE4 could be found in the mucosal epithelium of dilated bronchi .The levels of Lysyl oxidase-like proteins (LOXL) have also been associated with increased mortality and progression of IPF; however, a direct association with AE-IPF has not been shown .Circulating fibrocytes are progenitors of fibroblasts and myofibroblasts. IPF patients with stable disease have been shown to have increased circulating fibrocytes , and patNon-structural extra-cellular matrix protein, periostin, promotes mesenchymal cell proliferation and fibrosis through its expression at sites of injury or inflammation. In a recent study, serum monomeric periostin levels were prospectively measured from onset of AE in 37 patients with AE of chronic interstitial pneumonia to day 14, and its association with outcome was evaluated. Serum monomeric periostin levels were significantly higher in patients with AE compared to the ones with stable IPF and decreased significantly in AE survivors compared to AE non-survivors. Furthermore, a decrease of serum monomeric periostin levels in patients with AE was associated with better survival in 3 months after AE (OR 12.4) . ImmunohAn important cytokine involved in tissue repair is osteopontin (OPN). It has been shown that OPN can activate MMP-7 and stimulate fibroblast migration and proliferation . IPF patTLR3 L412F in viral- and bacterial-mediated AE death [The innate immune response to infection and tissue injury is mediated by toll-like receptors (TLRs) . IPF patAE death .TOLLIP have also been reported to be associated with the development and/or prognosis of IPF [TOLLIP rs5743890 was associated with worse survival and a more rapid progression of IPF, which could be useful for stratifying IPF patients at baseline [The toll-interacting protein (TOLLIP) is an inhibitor of the toll-like receptors (TLRs) 2 and 4, which are active in the lung, thereby suppressing tumor necrosis factor-a (TNF-a) and interleukin 6 (IL-6) production. Genetic variants of s of IPF . In IPF baseline . Moreovebaseline .Defensins are proteins secreted by neutrophils which exert antimicrobial activity . Acute eC-X-C motif chemokine ligand 13 (CXCL13) facilitates B-cell trafficking in lymphoid aggregates and inflammatory foci. The presence of elevated CXCL13 protein levels in patients with IPF has been linked to increased mortality, and CXCL13 levels were highest in IPF patients with AE-IPF .S 100 calcium binding proteins 8 and 9 (S100A8 and S100A9) are released mainly by activated neutrophils, which promote inflammation and decrease vascular endothelial cell integrity, consequently inducing further neutrophil extravasation. In ILDs, S100A8 and S100A9 are more often produced in patients with IPF with chronic-phase disease than in patients with other diseases, such as sarcoidosis or CTD-ILD. In a retrospective study of 37 patients with AE, patients with higher levels of S100A8 or S100A9 showed significantly worse 3-month survival than those with lower levels. In the multivariate analysis, the serum levels of both S100A8 and S100A9 were significant prognostic factors of AE-IPF . In anot14 CD36hi CD84hi CCR2− monocyte population. The same phenotype was found in patients with progressive IPF [Immune cells, particularly macrophages and lymphocytes, have been implicated in the pathogenesis of ILDs. CD4+ cells in IPF are in a highly activated status . Decreassive IPF .Increased levels of circulating pro-inflammatory cytokines have been reported during AE-IPF. Interleukin 1b (IL-1b) upregulates interleukin 8 (IL-8), which is critical for neutrophil recruitment. IL-8 is produced by phagocytes. Higher concentrations of IL-8 have been found in the BALF of patients with IPF and fibrosis associated with collagen vascular diseases . PatientIL-1b levels have been reported to be higher in patients with AE-IPF than in stable IPF . IncreasInterleukin 6 (IL-6) is a pro-inflammatory, pro-fibrotic cytokine. Increased serum levels of IL-6 above 25.20 pg/mL have been reported to be diagnostic of AE-IPF and to be an independent risk factor for mortality . An incrInterleukin 35 (IL-35) is a cytokine which is considered to have anti-fibrotic and anti-inflammatory effects by affecting interleukin 17 (IL-17) production. IL-35 also prevents the phosphorylation of Smad3, a downstream cascade of transforming growth factor (TGF-b) signaling, thus blocking TGF-b binding to its receptor and preventing the differentiation of T helper 17 (Th17) cells . In a reProteobacteria, Campylobacter spp., and Stenotrophomona spp., while a significant decrease was found in Veillonella spp. and Campylobacter spp [Klebsiella pneumonia accounted for 26%, Mycobacteria tuberculosis for 21%, and Acinetobacter baumannii for 10% of the total strains [Lungs have been traditionally considered sterile of bacteria. In part, this notion was due to the inability of traditional culture techniques to isolate bacteria from lung specimens. The introduction of sequencing of the 16S rRNA gene technique allowed recognition of the fact that bacteria not only exist within the human lung, but they are also altered in lung disease. A higher microbial burden is associated with a worse prognosis in stable IPF. It has been shown that patients with AE-IPF have a higher microbial burden in their lungs, which has been associated with higher morbidity and mortality rates. A significant increase was noticed for cter spp . In sput strains . Althoug strains ,72.miR-25-3p and let-7d-5p in plasma were differentially expressed between AE-IPF and stable IPF, suggesting that a combination of these two mi-RNAs may be a potential biomarker for AE-IPF from IPF [Non-coding RNAs represent a type of epigenetic change, i.e., a gene expression change that does not involve a change in the DNA . Long nofrom IPF .miR-302c, miR-423, miR-210, miR-376C, and miR-185 mi-RNAs were found to be related to the severity of IPF, differentiating fast and slow progressors [In a study, the gressors .In aging-related lung diseases, such as IPF, mitochondrial dysfunction is critical in regulating programmed cell death in alveolar epithelial cells . MitochoHistologically, AE-IPF is characterized by diffuse alveolar damage (DAD) overlying IPF fibrosis. AE-IPF was associated with alveolar hemorrhage in ca. 25% of the patients and with pulmonary thromboembolism in ca. 20%, suggesting that capillary injury and thrombosis play a significant role in AE-IPF . A studyp = 0.036). The NLR before death was also significantly higher than that at admission in patients with AE-IPF who did not survive (p = 0.014) [NLR is a ratio calculated from the absolute number of neutrophils and lymphocytes in the blood. Elevated NLR has been found in IPF patients with acute exacerbation, and it has been proposed that measuring NLR could be used to predict AE-IPF. In a multicenter study using discovery and validation cohorts, high values of NLR (>/=2.9 vs. <2.9) were associated with an increased risk of mortality in IPF (HR 2.04). This was confirmed in the validation cohort. NLR correlated with GAP stage and GAP index, which are widely used scores combining gender, age, and pulmonary function to predict survival in IPF . These r= 0.014) . It is n= 0.014) . Another= 0.014) . NLR is Apart from NLR, other blood cell ratios have been shown to be associated with prognosis in IPF. Such a marker is the PLR . In a poSystemic inflammation response index (SIRI) and aggregate index of systemic inflammation (AISI) as indexes of inflammation have also been reported to correlate with IPF and worse functional status .LCK), IL-2 inducible T-cell kinase (ITK) as part of a 52-gene RNA signature [Multiple biomarker signatures can be used more effectively than a single protein in the diagnosis and prognosis of IPF. The combination of serum MMP-1 and MMP-7 levels, for example, provided higher positive and negative predictive values for the diagnosis of IPF than either protein on its own . Serum bignature , a compoignature , and theignature  have beeignature .2/FiO2 ratio, diffuse HRCT pattern, and serum C-reactive protein (CRP) were significantly associated with 3-month mortality in patients with AE-IPF [PaOh AE-IPF . In anoth AE-IPF .Proteomic comparative analysis of BALF in stable IPF patients vs. AE-IPF revealed that proteins involved in the propagation of β-catenin WNT transduction signal, proteins upregulated in lung carcinogenesis , as well as acute phase proteins involved in protease–antiprotease imbalance (such as a1 antithrypsin fragments) correlated to AE-IPF .One type of idiopathic interstitial pneumonia (IIP) is nonspecific interstitial pneumonia (NSIP). Besides being idiopathic, NSIP can be associated with HIV infection, connective tissue disease, various drugs, and hypersensitivity pneumonitis. In addition, it can occur in combination with other IIPs. The nonspecific nature of NSIP is due to the absence of the histopathologic characteristics of usual interstitial pneumonia (UIP), desquamative interstitial pneumonia (DIP), respiratory bronchiolitis-associated interstitial lung disease (RB-ILD), or acute interstitial pneumonia (AIP) . NSIP isThe development of acute ILD may occur with any CTD, as a de novo acute interstitial pneumonia (AIP) or as an acute exacerbation of an ILD that already exists. Acute exacerbations have been described in rheumatoid arthritis (RA), polymyositis/dermatomyositis (PM/DM), systemic sclerosis (SSc), systemic lupus erythematosus (SLE), and mixed connective tissue disease (MCTD). Common underlying pathology patterns are that of NSIP and UIP . Common Autoimmune biomarkers are particularly useful for the diagnosis of the underlying CTD in the case of a novo presentation of ILD . HoweverAs a major extraarticular feature of RA, lung involvement affects 10–60% of patients. The prevalence of ILD ranges from 5 to 58%, with clinically significant RA-ILD occurring in less than 15% of cases. Antibodies to citrullinated protein antibodies (anti-CCPs) and rheumatoid factors (RFs) are frequently found in the serum of patients with RA. RF levels greater than 90 international units/mL may identify patients at higher risk of ILD . It has Most of the biomarkers tested in IPF have also been tested in RA-ILD . HoweverAge, sex, smoking history, positive RF, and anti-CCP, along with a combinatorial signature of serum biomarkers, including MMP-7, pulmonary and activation-regulated chemokine (PARC), and SP-D, could predict RA-ILD .KL-6 and SP-D have been examined in RA patients with ILD or AE-ILD; no significant difference in their levels in stable RA-ILD and AE-ILD or de novo acute ILD has been reported . A reasoIt has been suggested that the metabolites mannosamine, alliin, kynurenine, and 2-hydroxybutyric acid could successfully discriminate acute ILD in the setting of RA from the stable condition .Radiomic analyses have also been reported to predict mortality in RA-ILD, and its use has been proposed as a digital biomarker .The reported prevalence of ILD in SSc is 50–60% . ILD is In a recent meta-analysis, KL-6, SP-D, and IL-8 in blood and BALF were the best biomarkers of SSc-ILD . PatientThe above-described biomarkers are predictive of progressive ILD and mortality. Progressive disease is a risk factor for AE. It is unclear whether these biomarkers can also depict the development of AE-ILD in SSc-ILD.Hypersensitivity pneumonitis (HP) is an ILD that results from inhalation of organic antigens in susceptible individuals. HP is classified into fibrotic or nonfibrotic , and acuPeriostin is an established biomarker of Th2 immune response and fibrogenesis. Serum periostin has been associated with AE of HP. In a study of 63 patients with HP, 13 with IPF, and 113 controls, a significant positive correlation was found between periostin levels and serum KL-6 levels, CD4/CD8 ratio in bronchoalveolar lavage fluid, and fibrosis score on HRCT, and a significant negative correlation was found between periostin levels and carbon monoxide diffusing capacity. Periostin concentrations exceeding 92.5 ng/mL or 89.5 ng/mL were significantly associated with a worse prognosis and a higher frequency of acute exacerbations in chronic HP patients. An independent prognostic factor in the multivariate analysis was a high serum periostin level (92.5 ng/mL or higher) .Small studies have reported several biomarkers that are associated with AE-ILD in mixed ILD populations. Most of the publications included patients with AE-IPF. The examined biomarkers are the following:A meta-analysis of KL-6 in ILDs reported that ILD patients with severe and progressive disease had higher KL-6 levels. The KL-6 level of patients with severe ILD was 703.41 U/mL higher than in mild ILD. The KL-6 level in the progressive ILD group was 325.98 U/mL higher than that in the non-progressive ILD group. In addition, the KL-6 level of patients in AE of ILD was 545.44 U/mL higher than stable ILD. The higher KL-6 levels in ILD patients predicted poor outcomes. The KL-6 level in patients who died due to ILD was 383.53 U/mL higher than in survivors of ILD. The pooled HR (95%CI) of elevated KL-6 level predicting the mortality of ILD was 2.05 .Most data are derived from patients with IPF but reduced survival has also been reported in patients with SSc-ILD  and dermIn a retrospective study of a mixed population of patients with ILD, elevated D-dimer levels were associated with a ten-fold increase in risk of developing an AE three months after the D-dimer measurement .The soluble mediator IL-6 plays a pleiotropic role in inflammation, immune responses, and fibrosis. In a retrospective study of 83 patients with ILD, high levels of IL-6, along with lower baseline saturations of peripheral oxygen, were independent risk factors for AE. Similar results have been reported in patients with AE-IPF ,67.HBP was significantly higher in patients with AE-ILD at the early stage compared to patients with ILD at the stable phase, and this increase was found in the serum and BALF. With the remission of the disease, there was a linear trend of progressive decline. HBP identified ILD patients who had co-infections .BALF lymphocytosis has been associated with a better prognosis, and BALF neutrophilia with worse prognosis, in a study of 71 patients with AE-ILD. BALF lymphocyte and neutrophil count ≥25% and <20%, respectively, predicted favorable survival after AE .In a recently published study, proteomic analysis was performed in a discovery cohort of 385 patients with various ILDs, including CTD-ILDs, HP, and unclassifiable ILDs. The validation cohort comprised 204 patients. A total of 31 biomarkers were associated with progressive fibrosing ILD in the discovery cohort, with 17 maintaining an association in the validation cohort. Validated biomarkers showed a consistent association with progressive fibrosing ILD irrespective of ILD clinical diagnosis. A proteomic signature comprising 12 biomarkers was derived by machine learning, predicting a progressive fibrosing ILD. Use of this biomarker signature showed not only that progressive fibrotic ILDs, irrespective of aetiology, share common pathogenetic mechanisms but also overcame the modest use performance of other single biomarkers used for prediction of the clinical course of ILDs .Acute exacerbations are detrimental in the clinical course of ILDs. Early diagnosis before the onset of severe respiratory failure and early recognition of the patients who are more susceptible to AE are of paramount importance for therapeutic decisions in those patients. Despite the fact that treatment of AE in most ILDs is supportive and the use of immunosuppressive treatment—at least in AE-IPF—lacks significant therapeutic effect, early recognition of AE could lead to earlier hospitalization, lower clinical threshold for antibiotic therapy, and faster and probably more extensive diagnostic work-up and decisions for palliative treatment in the right clinical setting. Biomarkers can help in this direction, probably in combination with clinical parameters, lung function indices, and HRCT. Equally important is decision-making, when the diagnosis of an ILD must be first made in the setting of an AE and when the patients are in the intermediate care or intensive care station. Decisions regarding mechanical ventilation, ECMO, and transplantation are often based on the underlying pathology pattern of the ILD.While the understanding of ILD pathogenesis has grown substantially and biomarker research has progressed, the use of biomarkers for AE-ILD in clinical practice remains limited.In case of a de novo diagnosed ILD presenting as an AE, diagnostic tests that are currently used are autoantibodies, which can help to differentiate between idiopathic ILDs and ILDs associated with collagen vascular diseases, and the precipitating antibodies supporting the diagnosis of hypersensitivity pneumonitis. In certain cases, BALF lymphocytosis might support an intensive immunosuppressive treatment for AE-ILD, contrary to a neutrophilic BALF.Despite many biomarkers being studied in AE-ILD , most ofKL-6 and MMP-7 are promising and well-studied biomarkers in IPF that might find their way into routine clinical practice in the future. The same applies for simple markers, such as the NLR. However, it seems that multiple biomarker signatures, combined with clinical data, may provide more accurate information regarding AE-ILDs. Simple biomarkers are, however, of particular interest, since they can be used in medium- and low-resource health systems as well.In prospective clinical trials with large numbers of patients, biomarker analyses in combination with genotyping of these patients may allow the identification of predictors of disease progression and subgroups of patients with varying disease courses ,152,156.


In addition, electrical conductivity and joule heat were significantly improved after microwave post-processing, especially its electromagnetic shielding performance with a shielding coefficient of 53 dB able to be achieved. At the same time, the thermal conductivity is as low as 0.05 W m−1 K−1. The mechanism for the improvement of electromagnetic shielding performance is that (1) microwave reduction effectively enhances the conductivity of the graphene sheet overlapping network; (2) the gas generated by the instantaneous high temperature causes a large number of void structures between the graphene layers, and the irregular interlayer stacking structure makes the reflective surface more disordered, thereby prolonging the reflection path of electromagnetic waves among layers. In summary, this simple and environmentally friendly preparation strategy has good practical application prospects for graphene film products in flexible wearables, intelligent electronic devices, and electromagnetic wave protection.The preparation of freestanding graphene films by convenient and environmentally friendly preparation methods is still the focus of attention in various industrial fields. Here, we first select electrical conductivity, yield and defectivity as evaluation indicators and systematically explore the factors affecting the preparation of high-performance graphene by electrochemical exfoliation, then further post-process it under volume-limited conditions by microwave reduction. Finally, we obtained a self-supporting graphene film with an irregular interlayer structure but excellent performance. It is found that the electrolyte is ammonium sulfate, the concentration is 0.2 M, the voltage is 8 V, and the pH is 11, which were the optimal conditions for preparing low-oxidation graphene. The square resistance of the EG was 1.6 Ω sq The preparation of freestanding graphene films by convenient and environmentally friendly preparation methods is still the focus of attention in various industrial fields. At present, most electromagnetic radiation pollution from systems such as microwave communication, communication base stations, and high-voltage transmission lines is caused by human factors. Electromagnetic radiation not only causes a disturbance or even damage to the normal working of electronic equipment, but its harmful effects on human health are becoming increasingly prominent.2With the rise and commercialization of modern information technology, especially 5G technology, electromagnetic waves, as a medium for disseminating information, have brought convenience to people's production and life in sophisticated electronics, cell phones, and computers.3 The multi-layer reflective interface and electron transfer properties make the research on the construction, assembly and modification of graphene-based films a current research hotspot. The physicochemical properties of individual graphene nanosheets often directly affect the stability of their dispersion, the homogeneity of the assemblies, the integrity of the conductive network and the orderliness of the stacked structure.4–6 Graphene nanosheets are irregularly shaped, which is not conducive to the ordered stacking of film formation. Introducing block polymers, cross-linkers, and nanomaterials into the interlayer of graphene has achieved remarkable results in macroscopic graphene films. Although the dispersion of graphene can be significantly improved, the introduced impurity ions tend to degrade the electrical, thermal, and magnetic properties of graphene films.7–9 In addition, the traditional preparation methods, such as the redox method, mechanical exfoliation method, and liquid deposition method,10–12 have insurmountable problems such as being time-consuming, easy environmental pollution and performance defects caused by hazardous chemicals. The chemical vapour deposition method13 is a complex preparation process. Expensive equipment requires harsh environments such as high temperatures and high vacuum, which need to transfer 2D materials from the metal surface to the target. The manufacturing process is difficult to control and even introduces impurities or defects into 2D materials, resulting in decreased product performance and difficulty removing graphene from the substrate. Therefore, convenient graphene preparation conditions and tunable graphene products are essential for constructing graphene thin films.Graphene-based film materials have good prospects for practical applications in electronics, especially in the field of electromagnetic shielding, occupying an irreplaceable position due to their unique interlayer stacking structure, as well as their good electrical conductivity and ultra-lightness.14 That can be quickly industrially produced using known electrochemical cell design and engineering principles. Various graphite materials, such as graphite flakes, graphite rods, and high-oriented pyrolytic graphite (HOPG), can be used as the carbon source for the electrochemical preparation of graphene.15–17 There are still a tiny amount of oxygen-containing groups on the graphene prepared by electrochemical exfoliation, which usually weakens graphene's electrical conductivity, thermal conductivity, and electromagnetic shielding properties. Many factors affect graphene's electrochemical exfoliation . Zhang et al.18 improved the electrochemical exfoliation efficiency by deploying a method containing organic solvents and cations. Tetrabutylammonium cations in propylene carbonate can intercalate into graphite efficiently under reducing conditions. The product showed an ultra-low defect degree of 0.05 (ID/IG). Justin Raj et al.19 introduced ultrasonic equipment simultaneously as electrochemical exfoliation. The pulse (2/4) of 2 s sonication and 4 s rest time can be used in acidic, neutral and alkaline conditions. Both of them promote the electrochemical exfoliation process; Lei et al.20 explored the effect of high and low voltage on the oxidation degree of graphene, and they evidenced two different regimes during the synthesis by Raman and XPS analysis: slow kinetics of exfoliation at low voltage vs. high concentration of OH˙ radicals at high voltage. Recently, Vaiva Nagyte21 conducted a systematic study of the Raman spectrum of electrochemically exfoliated graphene, produced using different electrolytes and types of solvents in varying amounts. All in all, it is urgent and significant to explore the preparation scheme of graphene with the advantages of easy industrial production, economy, simplicity and environmental friendliness.Electrochemical exfoliation is a top-down graphene preparation method, which has the advantages of simple operation and environmental friendliness  and does not require volatile solvents or reducing agents that can form highly controllable flakes.Here, graphene was prepared by the electrochemical exfoliation method. The effects of electrolyte type, concentration, voltage and pH value on the properties of graphene prepared by electrochemical exfoliation were discussed in detail, with conductivity, yield and defect degree as evaluation indicators. The optimum conditions for the electrochemical exfoliation of graphene with double electrodes were obtained. At the same time, the self-supported graphene films were treated by microwave reduction under volume-limited conditions. The conductivity, thermal conductivity and electromagnetic shielding performance of graphene films before and after microwave reduction were compared and discussed.2.2.1.Graphite (99% C content), chemically pure, Tianjin SKF Co., Ltd.; ammonium sulfate, sulfuric acid, analytical grade, Tianjin Tianli Chemical Reagent Co., Ltd.; ammonium chloride, sodium sulfate, diammonium hydrogen phosphate, tripolyphosphoric acid sodium, analytically pure, Xi'an Chemical Reagent Factory; potassium sulfate, analytically pure, Tianjin Fuyu Fine Chemical Co., Ltd.; sodium hydroxide, analytically pure, Tianjin Hedong District Hongyan Reagent Factory; ultrapure water, self-made in the laboratory.2.2.The EG dispersion liquid was freeze-dried into powder and ultrasonically dispersed in 50 mL of deionised water. The EG dispersion liquid was filtered on a polytetrafluoroethylene membrane with a Buchner funnel, dried in an oven for 4 hours after manually peeling off the substrate, and taken out to obtain a self-supporting graphene film (EGF).2.3.The prepared EGF was laid flat on a 5 mm thick quartz plate, covered with another 5 mm thick plate and fixed. Then put them in the microwave oven, adjust the power to medium, and set the timer to one minute. Then it was taken out to obtain microwave-reduced graphene films (MWEGF). The schematic diagram of MWEGF preparation is shown in 2.4.2.4.1.θ = 5–40°, and a scan rate of 10° min−1. The sample's infrared (FT-IR) spectrum was obtained by a Fourier transform infrared spectrometer , and the test wavelength range was 4000–400 cm−1. X-ray photoelectron spectroscopy  was used to test the sample's composition. A single-frequency Al Kα (1486.6 eV) ray source was used with a power of 250 W. The pollution carbon peak at 284.8 eV is the calibration standard, and the background vacuum is greater than 10–7 Pa. The structural defects of EG were tested with a Renishaw inVia microscopic confocal laser Raman spectrometer . The incident light wavelength was 325 nm, and the test range was 500–3500 cm−1.The EG, EGF and MWEGF microstructures were observed by scanning electron microscopy  with an accelerating voltage of 20 kV. The layer structure of EG was observed by transmission electron microscope . The accelerating voltage is 200 kV, and the maximum magnification is 200 000 times. An atomic force microscope  was used to test its surface morphology and size in tapping mode. The X-ray diffraction (XRD) test of the sample was carried out using an X-ray diffractometer , using D/max 2200 PC Cu target Kα radiation, 22.4.2.m1 is the mass of the upper layer liquid; m2 is the mass of the lower layer precipitated.The stripped product was ultrasonic, dialysed, and centrifuged at 3000 rpm for 10 min to disperse and purify the unexfoliated particles. The upper-layer solution and the lower-layer precipitate were freeze-dried and weighed, respectively. Then the graphene yield is:2.4.3.Measured with a four-probe tester . The surface temperature was measured with a thermal imaging thermometer . A vector network analyser (Rohde & Schwarz) was used to test the electromagnetic shielding effectiveness of EGF and MWEGF in the frequency range of 8.2–12.4 GHz.3.3.1.4Cl, Na2SO4, (NH4)2SO4, K2SO4, (NH4)2HPO4, and Na5P3O10 were selected as electrolytes, and the electrolytes were screened under the conditions of electrolyte concentration 0.1 M, working voltage 10 V, pH 7, and exfoliate for 2 h.In general, there is a close relationship between its exfoliation quality and electrochemical exfoliation conditions. To this end, we explored the electrochemical preparation conditions in detail, taking the product's yield, conductivity, and defect results as the object of investigation. Firstly, NH−1) and G (1590 cm−1) peaks confirm that graphene has a varying thickness. The characteristic peak at the D (1350 cm−1) band implies defect and disordered carbon. As shown in 4)2SO4 as the electrolyte had an ID/IG value of 0.669, indicating that the degree of graphitisation of the product was relatively low and showed fewer defects. At this time, its conductivity was excellent, the square resistance was only 3.55 Ω sq,−1 and the yield was 47.9%. When (NH4)2SO4 was used as the electrolyte, the graphene yield was higher than other electrolytes, and its conductivity was also the best. It was because the interlayer spacing of graphite was 0.335 nm, while the sulfate ion size was about 0.46 nm, which was similar to the interlayer spacing of graphite. So that it was easier to intercalate into the graphite interlayer than other ions. According to the previous reports,22 the electrolysis and co-intercalation of sulfate ions lead to producing gases such as SO2, O2, and H2. Efficient intercalation and gas eruption facilitate the separation of graphene sheets from adjacent graphene layers. The radius of ammonium ions is more significant than that of sodium ions and potassium ions. Partial intercalation can also be performed at the cathode to promote the expansion of the graphite electrode. After the electrolysis of water, the H+ generated by the electrolysis of water is reduced at the cathode to generate hydrogen to further promote the graphite electrode's exfoliation. Therefore, choosing ammonium sulfate as the electrolyte for electrochemical exfoliation is more appropriate.Raman spectroscopy has been widely used to evaluate graphene defects. The ratio of the signal intensities at 2D (2700 cm4)2SO4 concentrations  on graphene's yield and conductivity were investigated under operating voltage conditions 10 V, pH 7, and stripping for 2 h. The results are shown in −1, as shown in 4)2SO4 was 0.2 M, the ID/IG of graphene was 0.548, and the degree of graphitization was low. Thus, the concentration of (NH4)2SO4 was chosen to be 0.2 M.Then, the effects of (NH4)2SO4 electrolyte solutions with different voltages  on the exfoliated graphene products under the conditions of electrolyte concentration of 0.2 M, pH 7, and stripping time of 2 h were further explored. The results are shown in ID/IG = 0.338 was observed in the prepared graphene. Therefore, 8 V was selected as the appropriate voltage with better yield and conductive. The yield was 60% at this timed was 60%, and the square resistance was 1.3 Ω sq−1.Secondly, the effects of (NH4)2SO4 electrolyte solutions with different pH values  on the exfoliated graphene products  scale" fill="currentColor" stroke="none"><path d="M0 440 l0 -40 320 0 320 0 0 40 0 40 -320 0 -320 0 0 -40z M0 280 l0 -40 320 0 320 0 0 40 0 40 -320 0 -320 0 0 -40z"/></g></svg>C bond in the EG structure and the out-of-plane bending vibration absorption peak of –OH; the absorption peak at 1200 cm−1 corresponds to the stretching vibration of the epoxy group –C–O–C–. The characteristic peak at 1083 cm−1 is the stretching vibration of –C–OH. Theoretically, EG contains some –OH and –C–O–C– because EG may only be partially oxidized.22,23Above all, we explored in detail the microstructure and properties of the product samples of the conditions under optimal experimental conditions. 24 Generally speaking, a low degree of oxidation means that the damage to graphene conjugation was soft, so the integrity of the graphene structure can be guaranteed. C (284. V), C–OH (285.5 eV), CO (287.6 eV), and C(O)–O (290.1 eV). It further showed that the EG surface contained a small amount of hydroxyl and carboxyl groups. In addition, we compared the XRD patterns of multilayer graphene and initial graphite. It can be seen that when the 2θ is about 26.42°, the characteristic peak of the graphite (002) crystal plane was sharp, the degree of crystallinity was high, and the interlayer spacing was about 0.335 nm. Compared with the initial characteristic peak of graphite, the intensity of the characteristic peak of the (002) crystal plane of the multilayer graphene exfoliated by the electrochemical method was weakened, indicating that the graphite expanded and exfoliated, and the degree of crystallization was reduced. The peak width of the characteristic peak increased, indicating that the disorder of the graphite sheet increased. At the same time, compared with pristine graphite rods, the (002) peak position of the EG peak did not shift to a small angle, which means that the interlayer spacing remains unchanged, and the exfoliated graphene product may only contain a small number of functional groups.25Secondly, −1 caused by defects, a strong G peak at 1580 cm−1, and a 2D peak at 2708 cm−1 elevation. The value of ID/IG was only 0.057. This indicates a lower defect level in pristine graphite, as shown in 3 hybridisation of carbon during intercalation and ultrasonication, resulting in the attachment of oxygen-containing functional groups to the graphene edge, introducing a small amount of oxygen-containing functional groups.26–28 The ID/IG value was 0.261, which indicated that the graphene prepared from electrochemical exfoliation had a higher quality, which was much lower than that of thermally reduced or chemically reduced graphene oxide (ID/IG ≈ 1.1–1.5), which further illustrated that graphene process introduced only a small number of structural defects. The G peak was caused by the stretching vibration between carbon atoms of the sp2 structure, which reflects the crystallinity of the graphite. The intensity of the G peak in the figure was more significant, indicating that EG had a complete crystal structure. Compared with graphite rods, the 2D peak of electrochemically exfoliated graphene had a higher degree of symmetry, increased intensity, and a significant left shift in the peak position, confirming that the number of layers decreases when graphite rods are exfoliated into graphene, as shown in Furthermore, the Raman spectrum of pristine graphite presented three characteristic peaks: a very weak D peak at 1350 cm2 hybridised carbon atoms at graphite edges and grain boundaries and, at the same time made two adjacent carbon atoms be hydroxylated. Subsequently, the two hydroxyl groups can interact with each other to form an epoxy ring. Likewise, they can also dissociate to form two carbonyl groups. At this stage, water molecules and sulfate anions co-intercalate to promote the expansion of anode graphite; the partial reduction of sulfate ions and the autooxidation of water generate gas that strips the graphite disperses it into solution. During this reaction process, the electrolysis of water and the intercalation of ions are interactive and synergistically promote graphite exfoliation. In addition to the oxidation reaction of graphite, other reactions take place, including releasing CO2 and O2 through the response. The generation of these gases can exert additional forces on the graphitic layers, separating the weakly bonded graphitic layers from each other. At the same time, under the action of the electric field force, the ammonium ion and the hydroxyl group in the sodium hydroxide generate ammonia gas at the cathode, further promoting the graphite rod's expansion and peeling.17The mechanism for the electrochemical preparation of graphene was generally assumed to be the result of the synergistic effect of ion intercalation and gas exfoliation. The graphite rod in the electrolyte is applied with a voltage, causing the water molecules at the cathode to be consumed. The electrolysis of water usually produces hydrogen ions and hydroxyl radicals. It is worth noting that hydroxyl radicals act as strong nucleophiles in the electrolyte. During constant voltage electrolysis, cations and anions in the electrolyte will move to the cathode and anode, respectively. The edge positions and grain boundaries of graphite were eroded first so that the graphite edges became loose; hydroxyl radicals generated by electrolysis of water acted as strong nucleophiles and continued to attack the spTo further explore the specific process and microscopic mechanism of electrochemical oxidation exfoliation of graphene, the above mechanism hypothesis was verified by observing the morphology of graphite rods during the exfoliation process. A constant bias voltage was applied to the graphite electrode, and the morphology changes of the graphite rod after peeling off for 0–60 min were detected by SEM, as shown in The surface of the graphite rod was flat and had a specific lustre. In the longitudinal direction, it can be seen that the layers were closely combined, showing a sheet or plate structure, and the edges were not warped. When a voltage is applied, graphite's surface and edge morphology change drastically; the graphite rod begins to expand longitudinally. At the same time, the cracks in the graphite layer increase, increasing the interlayer distance. There are many pores inside, forming a loose and porous structure, which is conducive to the further exfoliation of graphene, and many wrinkles are formed on the surface, as shown in 29 In this experiment, we designed a set of quartz-based fixtures to ensure the integrity of the graphene film during reduction. Because we found that the resulting self-supporting graphene films were often broken or incomplete if there was no quartz cover to hold them in place, this was because the graphene film may impact the graphene stack due to uneven heating or the generation of a large amount of gas under microwave radiation. As shown in 30 Thereby changing the flat morphology of the EGF membrane to a raised foam shape with increased thickness. Moreover, the interlayer spacing inside the film will increase compared to before microwave reduction.Microwave reduction has attracted extensive attention in removing graphene due to its efficient and rapid heating method.3.3.θ was about 26.42°, the crystallisation degree of EGF and MWEGF decreased. Compared with EGF, the half-width of MWEGF was more comprehensive, and the disorder of graphite sheets was further enhanced. Since the full width at half maximum was inversely proportional to the grain size, the smaller the grain diameter, the larger the full width at half maximum. It is indicated that the grain size of MWEGF is smaller than EGF's. It can be seen from the figure that the overall structure of the graphene film had little change before and after microwave reduction. When 23.4.3.4.1.−1, and the conductivity was 9.09 S cm−1, which showed good electrical conductivity. Compared with EGF of the same quality, the conductivity and square resistance of MWEGF obtained after microwave reduction have been improved. When the mass of graphene reaches 70 mg, the square resistance is 0.92 Ω sq−1, and the highest conductivity can reach 22.12 S cm−1. EG was subjected to high temperatures reduction during the microwave reduction process, so a small amount of oxygen-containing functional groups carried by EG were sintered.31 The degree of oxidation of EG prepared was reduced by electrochemical exfoliation, and the electrical conductivity was improved.3.4.2.32 MWEGF is more suitable for thermal insulation because of its relatively low thermal conductivity and high joule electric heating performance.31,333.4.3.34,35 It affects the average regular of nearby electronic equipment and increases the risk of headaches, depression, immune deficiency and other diseases for relevant staff.36–38 Therefore, there is an urgent need for efficient EMI shielding materials to attenuate electromagnetic waves to protect the regular operation of electronic equipment and human health. Developing graphene-based high-performance EMI shielding materials has become a research hotspot in this context. M is negligible. The calculation formulas of SET, SEA and SER are as follows:In the formula: SET, SEA, SER, and SEM, respectively, represent the total electromagnetic shielding effectiveness, electromagnetic wave absorption loss, electromagnetic wave reflection loss and multiple reflection loss of electromagnetic waves; T and R represent the power coefficients of transmission and reflection, respectively.37,39Electronic equipment's operation will generate adverse electromagnetic interference (EMI) to the outside world.A) of EGF and MWEGF far exceeded the electromagnetic reflection ability (SER). The analysis showed MWEGF had better conductivity and larger internal layer spacing than EGF. When the electromagnetic wave passes through the MWEGF film, it is first consumed by the reflection part of the surface conductive network. Then when the electromagnetic wave enters the inside of the MWEGF, it will continuously undergo reflection loss and absorption consumption between the graphene sheets. It is better than EGF, with a relatively compact internal structure and relatively poor conductivity. In addition, the irregular interlayer structure of MWEGF increased the diversity of reflection direction, causing the reflection path to grow. The specific electromagnetic shielding mechanism of MWEGF is shown in It is the electromagnetic shielding effectiveness diagram of EGF and MWEGF with different masses in the 8.2–12.4 GHz frequency range. The attenuation performance of the shielding material is evaluated by SE, as shown in the 4.−1, and the yield was 65%, ID/IG = 0.261 meanwhile, the structural defects were minor. The results show that the C/O value of EG was 5.19, the oxidation degree of the sample was low, the defect degree was small, and the position where the intensity of the characteristic peak of (002) crystal plane weakens remains unchanged. In addition, the C/O value of EG by microwave reduction could be achieved at 6.2, indicating that the graphene prepared by this method had a relatively complete structure and had a good crystal and graphitised form. The analysis results of EGF and MWEGF electrical, thermal and electromagnetic shielding properties show that MWEGF has more electrical conductivity than EGF. Still, EGF has more vital controllable thermal conductivity, possibly due to EGF's tighter internal sheet structure and interlayer. The conductive network is more complete. In addition, due to the high conductivity and irregular and complex interlayer structure of EMWEGF, it shows excellent performance in electromagnetic shielding, with a shielding coefficient of 53 dB, and has good application prospects in electromagnetic pollution protection and stealth.This paper uses conductivity, yield and structure as evaluation factors for the first time to systematically discuss the effects of electrolyte type, concentration, voltage, and pH on the yield and conductivity of graphene prepared by electrochemical exfoliation. Without introducing any organic solvent and other auxiliary equipment, the best conditions for the preparation of graphene by double-electrode electrochemical exfoliation are as follows: the electrolyte is ammonium sulfate, the concentration is 0.2 M, the voltage is 8 V, and the pH is 11. The square resistance of the product sample was 1.6 Ω sqThe authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.


Recent experiments demonstrated that proton transport through graphene electrodes can be accelerated by over an order of magnitude with low intensity illumination. Here we show that this photo-effect can be suppressed for a tuneable fraction of the infra-red spectrum by applying a voltage bias. Using photocurrent measurements and Raman spectroscopy, we show that such fraction can be selected by tuning the Fermi energy of electrons in graphene with a bias, a phenomenon controlled by Pauli blocking of photo-excited electrons. These findings demonstrate a dependence between graphene’s electronic and proton transport properties and provide fundamental insights into molecularly thin electrode-electrolyte interfaces and their interaction with light. Recent experiments have shown that proton transport through graphene electrodes can be promoted by light, but the understanding of this phenomenon remains unclear. Here, the authors report the electrical tunability of this photo-effect, showing a connection between graphene electronic and proton transport properties. Recent experiments demonstrated that the transport takes place mostly around wrinkles and nanoscale ripples in the crystal lattice, in which strain and curvature reduce the energy barrier for proton permeation6. Besides graphene, which is a zero-gap semiconductor, monolayers of hexagonal boron nitride (hBN), a wide-gap insulator, were shown to be even more permeable than graphene; whereas molybdenum disulphide (MoS2), a heavily doped semiconductor, was found to be impermeable to protons4. These results suggested that there was no correlation between the crystal’s proton permeability and its electronic properties and cemented the notion that the Fermi energy of electrons in the material played no role in the proton transport. This notion became contested with experiments in which graphene’s in-plane electron conductivity7 was exploited to fabricate two-dimensional proton-permeable electrodes. In the devices, protons transfer through graphene and combine with electrons to form H2 molecules;10 a process that is accelerated using catalytic nanoparticles10 and takes place with 100% efficiency 10. Unexpectedly, these experiments revealed that solar-simulated illumination can enhance proton permeation through graphene electrodes by an order of magnitude8, a phenomenon that we called the photo-proton effect. However, despite these observations, there is still no understanding of the fundamental mechanism behind this photo-effect, nor on the dependence of proton transport through graphene on the Fermi energy of electrons. In this work, we report the unexpected suppression of the photo-proton effect with a small <1 V bias when the devices are measured under infra-red illumination. We show that this arises due to a shift in the Fermi energy of electrons in graphene under the applied bias, which prevents the absorption of low energy infra-red photons and suppresses light-driven proton transport through graphene. The results provide fundamental understanding of the interaction of photo-excited electrons and protons in molecularly thin electrode-electrolyte interfaces, which we rationalise using the Gerischer model12 of electrochemical interfaces.The defect-free basal plane of monolayer graphene is impermeable to all atoms8  and electrically connected with a proton-injecting electrode . The whole device was placed in a gas-tight optical chamber (IR grade sapphire widow) filled with 100% H2 gas at 100% relative humidity to ensure the high proton conductivity of Nafion. The chamber faced the light source and an optical chopper. The infra-red light source used was either a broadband Bentham IL1 halogen light with an electrically controlled monochromator or individual single frequency lasers. The suspended graphene film was electrically connected into the circuit shown in Fig. −1. We also measured devices under low intensity white light illumination using a Keithley 2636 sourcemeter as reported previously8. For reference, we measured similar devices in which the freestanding film was trilayer graphene, which absorbs light similarly to graphene15 but is impermeable to protons4.The devices studied in this work consisted of a graphene monolayer suspended over a micrometre-sized hole etched into silicon nitride substrates , as reported previously8 Fig. . One sid9. In brief, under an applied bias, protons from Nafion transfer through the basal plane of graphene5. The protons then combine with electrons flowing into graphene from the electrical circuit8 and form adsorbed hydrogen atoms on the Pd nanoparticles on the opposite side of the suspended graphene film  at least twice larger than the Fermi energy, EEF, can be absorbed16. Photons with lower energy are not absorbed because the states accessible to the photo-excited electron are occupied, a phenomenon known as Pauli blocking  voltage dopes graphene with electrons (holes) and shifts the Fermi energy, EF, with respect to the charge neutrality point (NP) according to the relation:7EF = ħvFn the charge carrier density, vF ≈ 1 6 m s−1 the Fermi velocity in graphene and ħ the reduced Planck constant7. Hence, applying a voltage bias raises EF and this will block the absorption.To rationalise these observations, we note that a necessary condition for the photoresponse is the absorption of photons by graphene, which requires exciting electrons from the valence to the conduction band Fig.  inset. Ting Fig.  inset16,EF in our graphene electrodes as a function of applied bias using Raman spectroscopy (Raman spectroscopy characterisation in Methods). Figure V-bias shifts the Fermi energy of the electrodes with respect to the NP. The shifts we observe, of a couple hundred meV (corresponding to high doping of 1012−1013 cm−2), are sufficient to block the absorption of photons in the near infra-red. For example, the suppression of the photoresponse with 1800 nm (≈0.69 eV) light in Fig. EF ≈ 0.34 eV. The Raman data show that this EF is indeed achieved in our devices for ≈0.55 V within our experimental scatter of about ±50 mV, in agreement with our photocurrent experiments in Fig. 19 and result in a finite doping of ~5 × 1011 cm−2 at the NP (which is around −0.18 V) evident in the Raman data19.To verify if Pauli blocking could be behind our observations, we determined EF in graphene for a fixed photon energy. However, in principle, the suppression should also be achieved for a fixed EF by decreasing the photon energy until the condition E = 2EF is satisfied  and, from the linear power dependence of the devices’ photoresponse, we extracted their photoresponsivity for each wavelength .The unexpected voltage-gated suppression of the photo-proton effect merits additional characterisation. In the experiments described above, photo-induced proton-electron transport was suppressed by raising V-bias. This leads to shorter cut-off wavelengths for larger V-bias, as per the criterion defined above (99% suppression). Figure y-axis), its corresponding photon energy E (right y-axis) and applied V-bias extracted from all our measurements, at both constant bias  = E(V)/2, which can be compared with the EF(V) relation found in the Raman data  Raman data from Fig. EF, which demonstrates that proton-electron transport in the devices depends on the Fermi energy in graphene.Figure ata Fig. . Figure 12, which considers the role of the band structure of the electrode in the reactivity of an electrochemical interface11 . The rate of transfer is then proportional to the integral of all the possible transfer events across all energy states. For the case of proton transport through graphene accompanied by an electron transfer (reduction process), the rate is:11kWo the Fermi distribution; Te the temperature of the electronic system; Wo22. According to the Fermi distribution, electronic states with energy of up to ~4kBTe above EF are filled (kB the Boltzmann constant), so raising Te increases the number of filled electronic states in graphene for a given EF. Since the hot electron distribution is effectively constant (>1 ps lifetime) for the duration of a proton transfer event , the electronic levels filled with hot electrons can interact with the solution states. This leads to a larger overlap between electronic and solution states, and hence to a faster reaction rate, k . The model predicts that for such Te the reaction rate at a given EF should increase by an order of magnitude with respect to the reaction in the dark (Te = 300 K), in agreement with our observations in Fig. 8. (Gerischer model in Methods). The model also predicts that such photoresponse should increase exponentially with bias, in agreement with our measurements in Fig. 8. Finally, the model naturally incorporates Pauli blocking of the photo-proton effect. If photon absorption is blocked, Te does not rise and the reaction rate does not increase under illumination either. Hence, this model is consistent with all our observations.The key insight from this model is the elucidation of the role of the Fermi distribution and the electronic temperature in our devices’ photoresponse. Illuminating graphene is known to create a long lived (>1 ps) hot electron distribution with high , k Fig. . To vali27. We propose that absorbed photons generate a hot electron distribution in graphene that increases the overlap in energy between electronic and solutions states, leading to a larger number of possible proton-electron transfer events and thus to larger interfacial reactivity, as predicted by the Gerischer model. In the wider context of ion transport phenomena, these results show that protons interact with the electronic system in graphene under a large range of Fermi energies, unlike, for example, metal electrodes in which the Fermi energy is effectively constant for the entire operational voltage window28. Our results also provide insights into molecularly thin electrode-electrolyte interfaces and their interaction with light30, revealing the prominent role of the electron Fermi distribution and electronic temperature. In terms of applications, graphene electrodes are a rare example of a system in which an external stimulus, in this case a voltage, can suppress light driven proton transport for a controllable fraction of the light spectrum. These results could enable the design of light-powered devices in emerging technologies, such as proton-based neuromorphic hardware35, by providing an additional gating mechanism that could enable switching individual elements of these systems or more complex logic operations.Our experiments reveal insights into proton-electron transport across one-atom-thick interfaces, which are increasingly explored due to their unique catalytic properties4. The substrate fabrication follows the recipe in previous reports4. In brief, silicon nitride wafers  were first patterned by photolithography and reactive ion etching (RIE) is then used to remove a 0.8 × 0.8 mm2 section from one of the SiNx layers. The wafer is placed in the 30 wt.% KOH solution to etch out Si, leaving a free-standing SiNx window (100 ×100 μm2). A circular hole  was patterned in the centre of the SiNx window by photolithography and etched by RIE. The suspended graphene membrane was electrically connected with an Au electrode fabricated using photolithography and electron-beam evaporation 8 to 109 Ω for the V-bias we used in this work), which allows measuring the photocurrent from the sample by measuring the voltage drop across this resistor. The sample was biased with a Keithley source metre (2614B) and the photocurrent was measured with a lock-in amplifier (Stanford Research Systems SR865A) using the frequency of the chopper as reference signal37.The chamber containing the sample was mounted on a stage with micro-manipulators. The window in the chamber faced a black tube with a small aperture to block stray light and the opposite end of this tube faced a light chopper (Thorlabs MC2000B). The light sources used were either a Bentham IL1 halogen broadband source or individual frequency lasers (Thorlabs NIR laser series). For measurements with the Bentham system, the light was directed through an electrically controlled single monochromator (Bentham TMc300), which allowed selecting a particular wavelength from 1800 nm to 2500 nm with a resolution of 0.2 nm. To remove higher-order wavelengths from the diffracted light, we used a 1550 nm long pass filter. For measurements with both individual lasers and the Bentham system, the sample was connected into the circuit shown in Supplementary Fig. 8. This instrument uses the light chopper’s frequency as input and filters out all signals that do not have this frequency, including the dark current. This allows us to measure the photocurrent directly. If we were to measure without the lock-in amplifier, we would observe that the dark current rises with bias, as in refs. 10. However, the low intensity light of <1 mW cm−2 used here would yield only a small rise in the total current, that would be difficult to characterise accurately. The lock in amplifier allows us to clearly characterise even this small photo-response.The use of the lock-in amplifier is an important difference of the measurement setup in this work compared to refs. 8.We performed two photocurrent measurement experiments with infra-red light. In the first one, we measured the photocurrent of the samples with variable voltage bias (constant illumination wavelength). In the second experiment, we measured the photocurrent at constant voltage bias (variable illumination wavelength). For this experiment, the wavelength is fixed (within 0.2 nm) for various values between 1800–2300 nm in the Bentham system. To account for variations in the intensity of the light filtered at different wavelengths, we characterised the power density for each wavelength  and for different light intensities (the intensity is controlled by the diaphragm in the system). Supplementary Fig.G-band of graphene is traced as a function of applied bias  reveals the Fermi energy of electrons in graphene and the charge carrier concentration (n) via the following relations38. For electrons, EF [meV] = 21 ΔωG + 75[cm−1], for holes, EF [meV] = −18 ΔωG − 83[cm−1]. Both fittings are consistent with our data within the experimental scatter. For both type of carriers, their density is given by n[cm−2] = (EF/11.65)2 x 1010. We fit the data with the formula EF = ħvF18 is given by C ≈ 3.6 μF cm−2, the gate capacitance and NP = -0.18 V, the neutrality point.For Raman measurements, the samples were placed in the gas-tight optical cell. The Raman spectra was measured using a WITec alpha300 R—Raman microscope with a 514 nm laser. In the experiments, the position of the 39, D(ε). On the other hand, states in solution are modelled by two density functions, Wo(ε) and WR(ε), corresponding to the two different chemical species on the surface of the electrode: the proton (Wo) and the adsorbed hydrogen atom (WR) in our case. Each of these functions is a Gaussian with mean energy equal to ε0 + λ for the reduction states, ε0−λ for the oxidation states, and standard deviation (2λkBT)1/2. In here, ε0 is the standard potential for the reaction, kBT the thermal energy in the solution and λ is the so-called reorganizational energy, which is the energy required for the reactants to undergo the physical transformation involved in the reaction (e.g. change of coordinates). To evaluate the model, we estimate ε0 and λ. For ε0 we take ε0 = 0 V vs SHE (standard hydrogen electrode) for the hydrogen evolution reaction. This potential corresponds to ε0abs ≈ 4.44 V in the so-called absolute scale11, in which the energy of electrons is referred against their energy in vacuum.The Gerischer model is evaluated as follows. On the electrode, the number of electronic states is given by the density of states function for grapheneε0 vs the NP (ε0NP), rather than vs vacuum . Hence, to illustrate the model, we use λ = 0.5 eV, as a representative value for this parameter. We also evaluated the model for several parameters and found that the qualitative insights are insensitive to this number, as long as λ is larger than the activation energy for the process.Since in our experiments we determine the position of the neutrality point (NP) experimentally, we refer kWo dE using the parameters described above. The rate is normalised against the reaction rate calculated for EF = 0 in dark conditions. We find that the rate increases exponentially with EF, both in dark conditions and under illumination, in agreement with our experimental observations. The model also predicts that for an electronic temperature of Te = 1000 K, the reaction rate should increase by over an order of magnitude, in agreement with our observations in Fig. 8. We note that the value of Te arises from a chain of complex processes involving photoexcitation, thermalisation and cooling20, which can be expected to be different in our devices due to the interaction of protons with the electron cloud and the presence of noble metal nanoparticles (e.g. Pd)42. Given these two uncertainties, we ran the model using Te = 1000 K, a value typically reported in the literature for graphene devices20. However, we also ran the model using lower Te = 500 K. This lower temperature does not change the qualitative findings of the model, requiring relatively minor adjustments to the parameters to yield similar results .Supplementary Fig. Supplementary InformationPeer Review File