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The increasing demand for high‐performance devices on heat dissipation makes it approach the bottleneck even for metals with high thermal conductivities. The coating of only one layer of graphene, the heat dissipation performances of Cu, Ag, and Al can be further enhanced, e.g., with a maximum temperature reduction by ≈9% for a Cu foil is demonstrated. Molecular dynamics (MD) analysis of spectral phonon transmission reveals that low‐frequency phonons play a significant role in the thermal transport within the Cu/single‐layer graphene (SLG) system, and the high‐frequency phonons exhibit substantial mismatch. It suggests that the thermal anisotropy of graphene enables a rapid heat dispersion in the in‐plane direction and provides an effective thermal insulation in the out‐of‐plane direction. The thermal conductivity calculations demonstrate an enhanced participation of phonons in heat conduction by the graphene layer, indicating a novel heat conduction mechanism in the Cu/single‐layer graphene system. These findings highlight the positive impact of graphene on the heat conduction of metals, and they will hold crucial implications for the design and application of graphene‐based thermal devices is believed. [ABSTRACT FROM AUTHOR]

Bilayer graphene (BLG) grown via chemical vapor deposition (CVD) tends to exhibit twisted stacking. The twist angle θt in twisted BLG (tBLG) provides a new degree of freedom for engineering its electronic and optical properties. In this paper, we investigate the θt-dependent optical absorption in tBLG and deeply understand the electronic structure-optical properties correlations. New absorption peaks, whose wavelengths are modified by θt, are observed on the feature of optical contrast (OC) in tBLG. Under the corresponding energy excitation, the Raman G mode in tBLG exhibits a significant enhancement. Furthermore, the results of θt obtained by OC absorption peak are verified to be consistent with those by the Raman R mode. All these properties are proved to be related to the energy difference between low-energy Van Hove singularities (EVHS) in the density of states of tBLGs. This work builds a relation between optical absorption and twist angle, providing a viable method to identifying twist angles in tBLGs. [ABSTRACT FROM AUTHOR]

Thermal annealing is a necessary step in the standard fabrication process of graphene for removal of polymethyl methacrylate (PMMA). The influence of thermal annealing on monolayer graphene (MLG) has been intensively studied, but that on bilayer graphene (BLG) remains unclear. A key challenge for such investigation is that the Raman spectroscopic method that is usually used on MLG encounters the overlap of featured peaks from the two graphene layers. Herein, the independent featured Raman peaks of the two layers can be detected using isotope‐labeled BLG samples, so that the shift in each spectrum affected by the annealing process can be monitored. Results show that there are compression and doping in MLG and twisted‐stacked BLG (t‐BLG) after annealing. Compared with that in MLG, the annealing‐induced doping level in the adlayer of t‐BLG is lower, and in the top layer of t‐BLG, only a low level of doping and compression remains after thermal annealing. Moreover, the annealing‐induced doping level in AB‐stacked BLG (AB‐BLG) is almost the same with that in t‐BLG, and the originally induced compression during a transfer process is unloaded. These results can provide more understanding for the post‐treatment of graphene on substrates and the characterization of each layer. [ABSTRACT FROM AUTHOR]

Large polymer residues introduced by the graphene transfer process is still a major obstacle limiting the integration of chemical vapor deposition (CVD)-grown graphene into next-generation electronic and photoelectronic devices. Here we use cera alba, a natural and environmental-friendly material that derives from honeycomb, as the supporting layer for ultraclean graphene transfer. The transferred graphene has a low surface roughness with a surface height fluctuation within 5 nm and an only 80.08% average sheet resistance of the polymethyl methacrylate (PMMA)-transferred graphene. Further, the ultraclean graphene is used as electrodes for the PbI2-based UV photodetector and enables a 135% improvement on responsivity. The cera alba assisted transfer method reported here could achieve clean and damage-free graphene transfer, promoting the application of CVD-grown two-dimensional (2D) materials in large-area thin-film electronic and optoelectronic devices. [ABSTRACT FROM AUTHOR]

A double-layer YBa 2 Cu 3 O 7-δ /CeO 2 film was prepared on a Hastelloy C276 metal substrate with multi-buffer layers of LaMnO 3 /MgO/Gd 2 Zr 2 O 7 by laser chemical vapor deposition. The CeO 2 film showed a highly (100) preferred orientation with a full width at half maximum of 3.4° of the ω -scan on the (200) reflection and that of 5.0° of the ϕ -scan on the (220) reflection. The YBCO film showed a (110) preferred orientation with coexistence of c -axis-oriented grains. The (110)-oriented YBCO grains showed wedge-shaped morphology while the c -axis-oriented grains had dense surface and cross section. [ABSTRACT FROM AUTHOR]

Many aspects in the chemical vapor deposition (CVD) growth of graphene remain unclear such as its behavior near the catalyst grain boundaries. Here we investigate the CVD growth mechanism of graphene across the Cu grain boundaries using unidirectional aligned graphene domains, which simplifies the analysis of both graphene and Cu to a large extent. We found that for a graphene domain grown across the Cu grain boundary, the domain orientation is determined by the Cu grain where the domain nucleation center is located, and the Cu grain boundary will not change the growth behavior for this graphene domain. This growth mechanism is consistent with the Cu-step-attached nucleation and edge-attachment-limited growth mechanism for H-terminated graphene domains and will provide more guidance for the synthesis of high-quality graphene with less domain boundaries. Chemical vapor deposition growth mechanism of graphene across the Cu grain boundaries was investigated using aligned graphene domains. It is found that for a graphene domain grown across the Cu grain boundary, the domain orientation is determined by the Cu grain where the domain nucleation center is located, and the Cu grain boundary will not change the growth behavior of this graphene domain. This growth mechanism is consistent with the Cu-step-attached nucleation and edge-attachment-limited growth mechanism for H-terminated graphene domains. [ABSTRACT FROM AUTHOR]

Large‐area monolayer (1LG) and multilayer graphene (MLG) grown by chemical vapor deposition (CVD) have been of great technological importance for the graphene electronics and photonics. Such CVD‐grown MLG (CVD‐MLG) flakes consist of multiple single crystal domains, whose stacking orders can be diverse due to the various choices of layer number, stacking sequence, and twist angle. Here, we demonstrated a way to identify the stacking order of CVD‐MLG via Raman spectroscopy. The CVD‐grown 1LG can be identified by comparing its optical contrast or G mode intensity with those of the corresponding mechanically exfoliated 1LG on the same substrate. Once the CVD‐grown 1LG is distinguished, all the layer numbers of CVD‐MLG flakes can be ascertained by the peak positions of their layer‐breathing modes. The stacking sequence of a CVD‐MLG flake can be determined by the shear modes, and the twist angles of twisted interfaces in the CVD‐MLG flake are accessible by the so‐called R modes. In this way, one can determine whether an MLG sample exhibit a fully nonstacked arrangement or if 2 or 3 of these layers are stacked in the AB stacking, including the order where the stacked layers would appear with respect to the nonstacked layers. This reliable way to identify the stacking orders advances an important step for the characterization of CVD‐MLGs, shedding light on tailoring the properties of CVD‐MLGs with specific stacking order on demand. Copyright © 2017 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

CeO2 films were prepared at deposition temperature ranged from 947 to 1096 K (corresponding laser power was from 52 to 185 W) on (100) LaAlO3 single crystal substrate by laser chemical vapor deposition. At deposition temperature of 1027-1096 K (laser power was from 115 to 185 W), highly (100)-oriented CeO2 films with wedge-caped columnar grains were prepared, whose epitaxial growth relationship was CeO2 [100]// LAO [100] (CeO2 [010]// LAO [011]). Their full width at half maximum of the ω-scan on the (200) reflection and that of the ϕ-scan on the (220) reflection were 0.8°-1.8° and 0.7°-1.2°, respectively. The highest deposition rate at which CeO2 film with pure (100) preferred orientation could be obtained was 30 μm h−1. [ABSTRACT FROM AUTHOR]

YBa 2 Cu 3 O 7 − δ (YBCO) films were prepared at deposition rates ranging from 10 to 55μm h −1 on CeO 2 /LaMnO 3 /MgO/Gd 2 Zr 2 O 7 /Hastelloy C276 substrate by spray atomizing and coprecipitating laser chemical vapor deposition. At a deposition rate of 10 μm h −1 , a c -axis-oriented YBCO film with a high critical temperature ( T C ) of 91 K and critical current density ( J C ) of 2.4 MA cm −2 was prepared, which showed an epitaxial growth mode of YBCO [001]//CeO 2 [100] (YBCO [100]//CeO 2 [011]). The full width at half maximum (FWHM) of the ω -scan and that of the φ -scan of the YBCO film were 1.9° and 3.2°, respectively. At a deposition rate of 45 μm h −1 , an a -axis-oriented YBCO film with a T C of 78 K and a J C of 0.4 MAcm −2 was obtained. The YBCO film showed an epitaxial growth mode of YBCO [100]//CeO 2 [100] (YBCO [001]//CeO 2 [011]) and had the FWHM of 4.9° for the ω -scan and that of 9.5° for the φ -scan, respectively. [ABSTRACT FROM AUTHOR]

a -axis-, c -axis-, (103)/(110)- and (113)-oriented YBa 2 Cu 3 O 7− δ (YBCO) films were pareared by spray atomizing and coprecipitating laser chemical vapor deposition. The surface of the a -axis-oriented YBCO film consisted of rectangular needle-like grains whose in-plane epitaxial growth relationship was YBCO [100] // STO [001] (YBCO [001] // STO [100]), and that of the c -axis-oriented YBCO film consisted of dense flat surface with epitaxial growth relationship of YBCO [001] // STO [001] (YBCO [100] //STO [100]). For the (103)/(110)-oriented and (113)-oriented YBCO film, they showed wedge-shaped and triangle-shaped grains, with corresponding in-plane epitaxial growth relationship of YBCO [110] // STO [110] (YBCO [010] // STO [010]) and YBCO [100] // STO [100] (YBCO [113] // STO [111], respectively. [ABSTRACT FROM AUTHOR]

YBa 2 Cu 3 O 7− x film was prepared on (001) SrTiO 3 single crystal substrate by spray atomizing and coprecipitating laser chemical vapor deposition. At laser power of 101–116 W (corresponding deposition temperature was 893–942 K), a -axis-oriented YBa 2 Cu 3 O 7− x film was prepared, which showed an epitaxial growth mode of YBa 2 Cu 3 O 7− x [100]‖SrTiO 3 [001] (YBa 2 Cu 3 O 7− x [001]‖SrTiO 3 [100]). The a -axis-oriented YBa 2 Cu 3 O 7− x film had critical temperature of 75–82 K, with critical current density from 0 to 0.4 MA cm −2 . At laser power of 167–181 W (corresponding deposition temperature was 1093–1154 K), c -axis-oriented YBa 2 Cu 3 O 7− x film was obtained, whose epitaxial growth mode was YBa 2 Cu 3 O 7− x [001]‖SrTiO 3 [001] (YBa 2 Cu 3 O 7− x [100]‖SrTiO 3 [100]). A c -axis-oriented YBa 2 Cu 3 O 7− x film prepared at a deposition rate of 14 μm h −1 showed a high critical temperature of 91 K and critical current density of 2.8 MA cm −2 . [ABSTRACT FROM AUTHOR]

(100)-oriented CeO 2 films were prepared on (100) MgO single crystal substrate by laser chemical vapor deposition. A (100)-oriented CeO 2 film showed a full width at half maximum value of 1.0° of the ω -scan on the (200) reflection and that of 2.1° of the ϕ -scan on the (220) reflection, respectively. The (100)-oriented CeO 2 films showed cube-on-cube epitaxial growth and had rectangular grains in surface and columnar grains in cross section. The deposition rate of the (100)-oriented CeO 2 films were 16–24 μm h −1 . [ABSTRACT FROM AUTHOR]

Abstract: YBa2Cu3O7−δ (YBCO) films were prepared on a multilayer-coated Hastelloy C276 tape by laser chemical vapour deposition using liquid-source evaporation. The orientation of the YBCO films changed from a-axis to c-axis when the deposition temperature was increased from 1010K to 1090K. The c-axis-oriented YBCO film prepared at 1046K exhibited critical temperature of 92K and critical current density of 1.7MAcm−2 at a deposition rate of 13μmh−1. [Copyright &y& Elsevier]

Abstract: CeO2 and YBa2Cu3O7−δ (YBCO) films were prepared by laser chemical vapor deposition. The (100)-oriented CeO2 films prepared at 975–1088K consisted of columnar grains with pyramidal caps of the CeO2 {111} planes. The deposition rate was 3.0–5.4μmh−1. The (110)-oriented YBCO films were prepared on the (100)-oriented CeO2 films at a deposition temperature of 1004K. The (110)-oriented YBCO films showed wedge-shaped grains. [Copyright &y& Elsevier]

Abstract: Single-crystalline transparent CeO2 films were prepared on (100) SrTiO3 single-crystal substrates by laser chemical vapor deposition. At deposition temperatures ranging from 952 to 1080K, epitaxial (100) CeO2 films grew as columnar grains, which resulted in opaque films. The epitaxial CeO2 film prepared at 1120K exhibited a flat surface and dense cross section. The epitaxial CeO2 films grown on SrTiO3 substrates showed coherent lattice matching at the interface, even at high deposition rates of 15–25μmh−1. The epitaxial relationship was CeO2 [100]//SrTiO3 [100] and CeO2 [011]//SrTiO3 [001]. The epitaxial CeO2 film prepared at 1120K was a highly transparent single-crystalline film, and the transmittance at a wavelength of 600nm reached 97% of the SrTiO3 substrate. [Copyright &y& Elsevier]

Abstract: a-Axis- and c-axis-oriented YBa2Cu3O7–δ (YBCO) films were grown on (100) SrTiO3 substrate by laser chemical vapour deposition (laser CVD). The effect of lattice mismatch between films and substrates on in-plane and out-of-plane crystallinity and critical temperature (T C) was investigated. The preferred orientation changed from a-axis to c-axis as the deposition temperature increased from 928 to 1049K. The c-axis-oriented YBCO showed a minimum of full width at half maximum of 0.5° for the ω-scan and 1.0° for the φ-scan. A smaller mismatch between YBCO films and substrates led a higher crystallinity for in-plane and out-of-plane epitaxial growths. A high T C of 90K was obtained for the c-axis-oriented YBCO films. The deposition rate of the YBCO films was 58–101μmh−1, approximately 60–1000 times higher than that of conventional CVD. [Copyright &y& Elsevier]

Abstract: (100)-oriented CeO2 film was prepared on r-cut sapphire (Al2O3) by laser chemical vapor deposition at laser powers from 123 to 182W with deposition temperatures ranging from 1042 to 1122K. The (100) CeO2 films grew epitaxially on Al2O3 substrate with the in-plane orientation relationship of CeO2 [010] // Al2O3 and CeO2 [001] // Al2O3 . The surface morphology of the CeO2 films was characterized by elongated grains with truncated pyramidal cap. The deposition rate of the CeO2 film was 10–15μmh−1, about 10–15 times higher than those of conventional metalorganic CVD. [Copyright &y& Elsevier]

Abstract: a-axis- and c-axis-oriented YBa2Cu3O7−δ (YBCO) films were epitaxially grown on (100) LaAlO3 substrates by laser chemical vapor deposition. The preferred orientation in the YBCO film changed from the a-axis to the c-axis with increasing laser powers from 77 to 158W (the deposition temperatures from 951 to 1087K). The a-axis-oriented YBCO film showed in-plane epitaxial growth of YBCO [001]//LAO [001], and the c-axis-oriented YBCO film showed that of YBCO [010]//LAO [001]. A c-axis-oriented YBCO film with a high critical temperature of 90K was prepared at a deposition rate of 90μmh−1, about 2–1000 times higher than that of metalorganic chemical vapor deposition. [ABSTRACT FROM AUTHOR]

Abstract: CeO2 films were prepared on LaMnO3/MgO/Gd2Zr2O7 multi-coated Hastelloy C276 tapes by laser chemical vapor deposition at different laser power (P L) from 46 to 101W. Epitaxial (100) CeO2 films were prepared at P L =46–93W (deposition temperature, T dep =705–792K). Epitaxial CeO2 films had rectangular-shaped grains at P L =46–77W (T dep =705–754K), while square-shaped grains were obtained at P L =85–93W (T dep =769–792K). CeO2 films showed a columnar microstructure. Epitaxial (100) CeO2 films with rectangular grains exhibited full width at half maximum of ω-scan on (200) reflection and ϕ-scan on (220) reflection of 3.4–3.2° and 6.0–7.2°, respectively. The deposition rate of the epitaxial (100) CeO2 films had a maximum of 4.6μmh−1 at P L =77W (T dep =754K). [Copyright &y& Elsevier]

Abstract: CeO2 films were prepared on Al2O3 substrates by laser chemical vapor deposition at different laser power (P L) up to 182W. The (100)-oriented CeO2 films were prepared at P L =101–167W (T dep =792–945K). The texture coefficient (TC) of (200) reflection had a maximum of 6.7 at P L =113W (T dep =836K). The (100)-oriented CeO2 films consisted of granular grains and showed a columnar cross section. The deposition rates (R dep) of (100)-oriented CeO2 films showed a maximum of 43μmh− 1 at P L =152W (T dep =912K). [Copyright &y& Elsevier]

Using ethanol as a precursor, single-crystal bilayer graphene domains with dimensions up to hundreds of micrometer, one of the largest reported so far, were synthesized on Cu foils by chemical vapor deposition (CVD). Raman spectroscopy analysis revealed that the bilayers are homogeneously AB-stacked, with very low D-band intensity. Selected area electron diffraction analysis also confirmed the bernal stacking order and the large area crystallinity. Surprisingly, decreasing ethanol pressure in CVD shows an unambiguous tread from self-limited single layer to a multi-layer graphene, and there exists a narrow window of ethanol pressure which is preferred for the formation of large domain bilayer graphene. This suggests the dual effect of ethanol in graphene growth and demonstrates that the formation of different layers of graphene can be controlled by carefully tuning single parameter: ethanol pressure. [ABSTRACT FROM AUTHOR]

We report the realization of field-effect transistors (FETs) made with chemically synthesized multilayer crystal semiconductor WS2. The Schottky-barrier FETs demonstrate ambipolar behavior and a high (∼105×) on/off current ratio at room temperature with current saturation. The behavior is attributed to the presence of an energy bandgap in the ultrathin layered semiconductor crystal material. The FETs also show clear photo response to visible light. The promising electronic and optical characteristics of the devices combined with the chemical synthesis, and flexibility of layered semiconductor crystals such as WS2 make them attractive for future electronic and optical devices. [ABSTRACT FROM AUTHOR]

The electrical properties of bilayer graphene (BLG) are strongly affected by external forces. Here we use Raman spectroscopy to study the inherent strain states of BLG synthesized by chemical vapor deposition method on Cu, by manipulating 13C isotope atoms to substitute part of one layer in AB-stacked and twisted BLG to differentiate the Raman signals from the two layers. Results show that, both layers of twisted BLG are under compression but the compressive strain in the bottom layer is larger, which is caused by the mismatch of coefficients of thermal expansion between graphene and the substrate, whereas for AB-stacked BLG its top layer is under compression and the bottom layer is under tension due to the interlayer dislocations. These experimental data are further confirmed by molecular dynamics simulations. We believe that a clear understanding of the strain states of chemical-vapor-deposited BLG will provide the necessary route to optimize its future technologies especially in electronics. [Display omitted] • Strain state in each layer of chemical-vapor-deposited bilayer graphene are probed via isotope- labeled Raman spectroscopy. • Both layers of twisted bilayer graphene are under compression and the bottom layer has a larger compressive strain. • The top layer of AB-stacked bilayer graphene is under tension but the bottom layer is under compression. • Molecular dynamics reveals the origin of the strain distributions in twisted and AB-stacked bilayer graphene. [ABSTRACT FROM AUTHOR]

The preparation of scalable graphene films has attracted an enormous attention due to its industrial importance for graphene applications. Here we present a synthesis method of high-quality continuous monolayer graphene films with millimeter-sized domains on ordinary Cu substrates using oxygen-assisted chemical vapor deposition. This method demonstrates a significantly improvement to the resultant graphene such as a largely decreased nucleation density from ∼10 6 to ∼10 1  nuclei/cm 2 , an increased average domain size from ∼0.004 to ∼1.5 mm and a film coverage from 64% to 100%. We attributed the success of this growth to the surface layer formed by bonded oxygen in Cu, which provides a higher priority for catalyzing the nucleation and growth of graphene domains. [ABSTRACT FROM AUTHOR]

A direct liquid injection chemical vapor deposition was utilized to prepare Co 3 O 4 films with a high deposition rate. All the Co 3 O 4 films showed spinel crystalline structures of Co II Co 2 III O 4 . A (111)-orientation preferred Co 3 O 4 film with scattered triangular grains and elongated nano-wall surface morphology was prepared at the deposition temperature ( T dep ) of 773 K, while randomly grown Co 3 O 4 films with porous structures were found with lower or higher T dep . The maximum deposition rate ( R dep ) of Co 3 O 4 films reached 3.6 μm h − 1 , which was around 10 times higher than those previously reported by metal organic CVD method. With increasing T dep , the color of Co 3 O 4 films changed from light to black brown owing to the thickness difference. [ABSTRACT FROM AUTHOR]

Scalable large graphene single crystals have been synthesized by using a backward faced quartz cuvette in a conventional tube furnace. The effect of the restricted chamber in controlling the graphene single crystal growth has been systematically studied by considering the influence of the flow rate and ratio of H 2 and CH 4 experimentally. Numerical simulations were performed to uncover the underlying mechanism. The convection of CH 4 was substantially suppressed inside the cuvette due to the blocking effect by the close-end geometry. The diffusivity of CH 4 is much lower than that of H 2 , resulting in a slow transportation of CH 4 as well. By using the specific experimental parameters, the mass ratio of H 2 and CH 4 increased about 3 times inside the cuvette, leading to preferential growth of graphene single crystals, as observed in our experiments. Meanwhile, the growth of a second layer can be suppressed by the slower feeding of CH 4 than H 2 . Based on these results, we believe that setup of our restricted chamber can provide another growth approach for scalable graphene single crystals and its analysis can help understand more growth dynamics of graphene single crystal inside other irregular CVD conditions such as rolled-up and enclosed Cu foils. [ABSTRACT FROM AUTHOR]

• The Al 2 O 3 is applied on the surface of single-crystal LiNi 0.5 Co 0.2 Mn 0.3 O 2 (NCM) by Chemical Vapor Deposition (CVD). • The optimum CVD operation time for Al 2 O 3 is 30 min. • The electrochemical performance of NCM can be significantly improved by the Al 2 O 3 coating prepared by CVD. • The Al 2 O 3 is chemically bonded with the NCM substrate and a trace of Al exists as the dopant on the top surface of NCM. Due to the poor cycle stability at high operating voltage, layered transition-metal oxides (NCM) have limited industrial applications and cover up the appealing properties like high energy density and low price. In this work, Al 2 O 3 is deposited on the surface of single-crystal LiNi 0.5 Co 0.2 Mn 0.3 O 2 (NCM) materials by Chemical Vapor Deposition (CVD) as the inorganic coating layer for the first time. By carefully controlling the deposition intervals, the varied thicknesses of Al 2 O 3 coating could be obtained. Furthermore, according to the CVD, the Al 2 O 3 coating is chemically bonded to the NCM substrates, and a trace of Al exists as a dopant on the top surface. The surface modification layer is detected by X-ray diffraction, field-emission scanning electron microscopy, transmission electron microscopy and X-ray photoelectron spectrometer. The results infer that the combination of Al doping and Al 2 O 3 coating on the top surface of substrate can significantly improve the capacity retention under high voltage up to 4.5 V. The optimum CVD deposition time is 30 min. The modified cathode renders a capacity of 191.9 mA h/g with a retention of 61.3% at 4.5 V after cycling for 100 cycles. The value is superior to its counterpart-the single-crystal NCM without CVD treatment. Surface treatment by controllable CVD paves a new and practical pathway for the broadly application of single-crystal cathode materials of Li ion battery. [ABSTRACT FROM AUTHOR]

How to determine layer number (N) of graphene materials is of primary importance for practical applications. In this work, with 532 nm and 633 nm excitation wavelengths, we used the methods of Raman intensity ratio to identify the layers (N ≤ 4) of ultrathin graphenes prepared by micro-mechanical exfoliation and chemical vapor deposition (CVD). We also analyzed the effects of excitation wavelength and sample preparation method on identification of N. The following results were obtained. The intensity ratio of G mode from graphenes and Si mode from substrate underneath graphenes (I(G)/I G (Si)) increases monotonically with the increase of N, which is affected not only by excitation wavelength but also by sample preparation method. However, the intensity ratio of Si mode from substrate underneath graphenes and Si mode from bare substrate (I G (Si)/I 0 (Si)) decreases monotonically with the increase of N, which is only affected by excitation wavelength but almost not affected by sample preparation method. By contrast, the I G (Si)/I 0 (Si) method using 532 nm laser is a good option for N identification of 1LG-4LG whether the sample preparation method is micro-mechanical exfoliation or CVD. [ABSTRACT FROM AUTHOR]

With ultra-high mechanical strength and inherent lubrication property, graphene exhibits great potential as an atomically thin solid lubricant to address wear problems that affect mechanical function and longevity. Despite the excellent wear resistance of graphene at the nanoscale, wear of graphene is difficult to avoid at micro- to macroscale friction tests in ambient conditions and sensitive to the environmental atmosphere and humidity. As an atomically thin material, contaminants from the environment have a non-ignorable effect on graphene surface properties. To study the influence of airborne contaminants on graphene macroscale wear behavior, we performed sliding tests on new (as-prepared) and aged monolayer chemical vapor deposition grown graphene using a 5 mm-radius lens under load down to 0.1mN. The atomic force microscope characterization demonstrated the existence of airborne contaminants on aged graphene. The tribological experiments showed the aged graphene exhibited better wear resistance than the new one due to that the airborne contaminants separated the counterpart from the graphene wrinkles, from where graphene wear was initiated. Unlabelled Image • The aged graphene exhibits better wear resistance than the new one at macroscale. • The contaminants change the friction interface and affect the wear behavior. • The airborne contaminants on aged graphene surface can be mechanically cleaned. • Graphene wrinkles are too dense to avoid in macroscopic sliding tests. [ABSTRACT FROM AUTHOR]