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Investigation of CVD graphene as-grown on Cu foil using simultaneous scanning tunneling/atomic force microscopy
摘要： Scanning tunneling microscopy (STM) and atomic force microscopy (AFM) images of graphene reveal either a triangular or honeycomb pattern at the atomic scale depending on the imaging parameters. The triangular patterns at the atomic scale are particularly difficult to interpret, as the maxima in the images could be every other carbon atom in the six-fold hexagonal array or even a hollow site. Carbon sites exhibit an inequivalent electronic structure in HOPG or multilayer graphene due to the presence of a carbon atom or a hollow site underneath. In this work, we report small-amplitude, simultaneous STM/AFM imaging using a metallic (tungsten) tip, of the graphene surface as-grown by chemical vapor deposition (CVD) on Cu foils. Truly simultaneous operation is possible only with the use of small oscillation amplitudes. Under a typical STM imaging regime the force interaction is found to be repulsive. Force–distance spectroscopy revealed a maximum attractive force of about 7 nN between the tip and carbon/hollow sites. We obtained different contrast between force and STM topography images for atomic features. A honeycomb pattern showing all six carbon atoms is revealed in AFM images. In one contrast type, simultaneously acquired STM topography revealed hollow sites to be brighter. In another, a triangular array with maxima located in between the two carbon atoms was acquired in STM topography.
关键词： scanning tunneling microscopy,CVD graphene,simultaneous operation,atomic force microscopy,small amplitude
更新于2025-09-23 15:22:29
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Wafer Scale Graphene Field Effect Transistors on Thin Thermal Oxide
摘要： In this study, we present the feasibility to fabricate back-gated graphene field-effect transistors (GFETs) on 10 nm thermal SiO2 substrate. Here, we compare the mobility of graphene devices at different locations of the transferred CVD graphene. We observed that there is a n-type doping of the graphene devices with Dirac points within ± 0.5 V from an ideal value of 0 V. The downscaling of the back-gate dielectric thickness reduces the operating voltage range, commonly required for low power electronics, and the devices are stable during operation in air under ambient conditions. The extracted contact resistance is comparable to the earlier reports found in literature and this provides a feasibility to fabricate low power futuristic graphene based nanoelectronics.
关键词： CVD graphene,n-type doping,thermal SiO2,mobility,Dirac points,low power electronics,field-effect transistors,graphene,contact resistance
更新于2025-09-23 15:21:01
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Epitaxial growth and electrical performance of graphene/3Ca??SiC films by laser CVD
摘要： High electrical conductivity graphene/epitaxial-3CeSiC (G/epi-3CeSiC) composite films have the potential to the applications such as micro-electro-mechanical systems, distributed Bragg reflectors, solar cells, and photocatalysis in harsh environments. In this study, G/epi-3CeSiC composite films were prepared through laser chemical vapor deposition (LCVD) using hexametyldisilane (HMDS) as a safe single precursor. The electrical conductivity (s) of the composite films reached 2.23 (cid:1) 104 S/m, which is 2.2 times of the highest s reported for G/epi-3CeSiC composite. The deposition rate (Rdep) of the composite film with the highest s is 8.2 times of that of the G/epi-3CeSiC with the highest s ever reported. s of the pure epitaxial 3CeSiC film is only 81.2 S/m, which is the lowest value reported to date of 3CeSiC prepared through CVD using HMDS as a single precursor. Elimination of carbon is beneficial for increasing the breakdown field intensity and decreasing the leakage current of heterojunction when epitaxial 3CeSiC is used as semiconductor material.
关键词： Electrical conductivity,Deposition rate,Laser CVD,Graphene/SiC film,Epitaxial
更新于2025-09-23 15:19:57
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Photocurrent Direction Control and Increased Photovoltaic Effects in All-2D Ultrathin Vertical Heterostructures Using Asymmetric h-BN Tunneling Barriers
摘要： Two-dimensional (2D) materials are atomically thick and without out-of-plane dangling bonds. As a result, they could break the con?nement of lattice matching, and thus can be freely mixed and matched together to construct vertical van der Waals heterostructures. Here, we demonstrated an asymmetrical vertical structure of graphene/hexagonal boron nitride (h-BN)/tungsten disul?de (WS2)/graphene using all chemical vapor deposition grown 2D materials. Three building blocks are utilized in this construction: conductive graphene as a good alternative for the metal electrode due to its tunable Fermi level and ultrathin nature, semiconducting transition-metal dichalcogenides (TMDs) as an ultrathin photoactive material, and insulating h-BNas a tunneling barrier. Such an asymmetrical vertical structure exhibits a much stronger photovoltaic e?ect than the symmetrical vertical one without h-BN. By changing the sequence of h-BN in the vertical stack, we could even control the electron ?ow direction. Also, improvement has been further made by increasing the thickness of h-BN. The photovoltaic e?ect is attributed to di?erent possibilities of excited electrons on TMDs to migrate to top and bottom graphene electrodes, which is caused by potential di?erences introduced by an insulating h-BN layer. This study shows that h-BN could be e?ectively used as a tunneling barrier in the asymmetrical vertical heterostructure to improve photovoltaic e?ect and control the electron ?ow direction, which is crucial for the design of other 2D vertical heterostructures to meet various needs of electronic and optoelectronic devices.
关键词： WS2,asymmetrical vertical heterostructure,photovoltaic,CVD,graphene,2D materials,h-BN
更新于2025-09-11 14:15:04
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Graphene for Si-based solar cells
摘要： In this paper, we report on the single layer graphene synthesis to establish the growth conditions and improve the opto-electronic properties that can be employed in silicon based heterojunction solar cells. To do this, the effect of hydrogen and methane flow on the graphene growth on copper foil in a CVD system was investigated. The analyses were conducted by changing either the hydrogen or the methane flow by keeping all the other growth parameters constant. Single layer graphene growth recipe was established in order to have the optimum optical transmission and sheet resistance values via amending the graphene growth conditions. It was found that the sheet resistance values of the single layer graphene should be lowered further to be used as transparent conductive electrode. However, the combination of graphene with indium tin oxide film functioned well as transparent conductive electrode in the silicon based the solar cells. Additionally, the cell efficiency increased by about 10% as a result of incorporating it with the single layer graphene.
关键词： Raman,Growth,CVD,Graphene,Copper,Solar Cell
更新于2025-09-11 14:15:04