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排序方式: 共有51条查询结果,搜索用时 15 毫秒
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Andrs Kovcs Martial Duchamp Rafal E. Dunin‐Borkowski Rositza Yakimova Pter L. Neumann Hannes Behmenburg Bartosz Foltynski Cristoph Giesen Michael Heuken Bla Pcz 《Advanced Materials Interfaces》2015,2(2)
The implementation of graphene layers in gallium nitride (GaN) heterostructure growth can solve self‐heating problems in nitride‐based high‐power electronic and light‐emitting optoelectronic devices. In the present study, high‐quality GaN layers are grown on patterned graphene layers and 6H–SiC by metalorganic chemical vapor deposition. A periodic pattern of graphene layers is fabricated on 6H–SiC by using polymethyl methacrylate deposition and electron beam lithography, followed by etching using an Ar/O2 gas atmosphere. Prior to GaN growth, an AlN buffer layer and an Al0.2Ga0.8N transition layer are deposited. The atomic structures of the interfaces between the 6H–SiC and graphene, as well as between the graphene and AlN, are studied using scanning transmission electron microscopy. Phase separation of the Al0.2Ga0.8N transition layer into an AlN and GaN superlattice is observed. Above the continuous graphene layers, polycrystalline defective GaN is rapidly overgrown by better quality single‐crystalline GaN from the etched regions. The lateral overgrowth of GaN results in the presence of a low density of dislocations (≈109 cm−2) and inversion domains and the formation of a smooth GaN surface. 相似文献
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Vladimir V. Gorbachuk Luidmila S. Yakimova Alena A. Vavilova Ramilya V. Ziatdinova Ildar Kh. Rizvanov Alexander A. Trifonov Alena I. Samohina Vladimir G. Evtugyn Ivan I. Stoikov 《SILICON》2014,6(4):215-226
For the first time condensed silsesquioxane derivatives of tetratrialkoxysilyl compounds have been characterized by MALDI-TOF mass spectrometry. Tetrasubstituted p-tert-butyl thiacalix[4]arene derivatives containing organosilicon fragments with variable stereochemistry were chosen as organosilicon compounds for polycondensation. Information obtained from mass spectra was used to deduce both the structures of oligomeric derivatives, as well as the structure of silsesquioxane framework. The morphology of formed polysilsesquioxanes was investigated by scanning and transmission electron microscopy. 相似文献
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High spatial density ZnO nanopillars (NPs) have been fabricated on catalyst- and pattern-free Si wafers using atmospheric pressure metal organic chemical vapor deposition (APMOCVD) at a moderate temperature (500?°C). The nanopillar diameter is ~ 35 nm and the length is ~ 150 nm, with a density of ~ 2 × 10(9) cm( - 2). The growth evolution of the nanopillars, providing the (0001)(NP) ? (0001)(ZNO grain) ? (100)(Si surface) epitaxial relationship, is extensively studied by scanning and high resolution transmission microscopy. The approach to obtaining the ZnO 1D structures is explained in terms of selective homoepitaxial growth via the crystallographic anisotropy of the seeding layer. The advanced PL properties of ZnO NPs, e.g. indications of free excitonic and absence of defect emission, are related to their single crystalline nature within one pillar and most probably better stoichiometry and less contamination. The observed efficient monochromatic UV emission from the ZnO NPs at room temperature points toward their potential application as building blocks for nanoscale optoelectronic devices. 相似文献
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Maassen T van den Berg JJ Ijbema N Fromm F Seyller T Yakimova R van Wees BJ 《Nano letters》2012,12(3):1498-1502
We developed an easy, upscalable process to prepare lateral spin-valve devices on epitaxially grown monolayer graphene on SiC(0001) and perform nonlocal spin transport measurements. We observe the longest spin relaxation times τ(S) in monolayer graphene, while the spin diffusion coefficient D(S) is strongly reduced compared to typical results on exfoliated graphene. The increase of τ(S) is probably related to the changed substrate, while the cause for the small value of D(S) remains an open question. 相似文献
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Local electrical characterization of epitaxial graphene grown on 4H-SiC(0001) using electrostatic force microscopy (EFM) in ambient conditions and at elevated temperatures is presented. EFM provides a straightforward identification of graphene with different numbers of layers on the substrate where topographical determination is hindered by adsorbates. Novel EFM spectroscopy has been developed measuring the EFM phase as a function of the electrical DC bias, establishing a rigorous way to distinguish graphene domains and facilitating optimization of EFM imaging. 相似文献
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Vecchio C Sonde S Bongiorno C Rambach M Yakimova R Raineri V Giannazzo F 《Nanoscale research letters》2011,6(1):269
In this work, we present a nanometer resolution structural characterization of epitaxial graphene (EG) layers grown on 4H-SiC
(0001) 8° off-axis, by annealing in inert gas ambient (Ar) in a wide temperature range (T
gr from 1600 to 2000°C). For all the considered growth temperatures, few layers of graphene (FLG) conformally covering the 100
to 200-nm wide terraces of the SiC surface have been observed by high-resolution cross-sectional transmission electron microscopy
(HR-XTEM). Tapping mode atomic force microscopy (t-AFM) showed the formation of wrinkles with approx. 1 to 2 nm height and
10 to 20 nm width in the FLG film, as a result of the release of the compressive strain, which builds up in FLG during the
sample cooling due to the thermal expansion coefficients mismatch between graphene and SiC. While for EG grown on on-axis
4H-SiC an isotropic mesh-like network of wrinkles interconnected into nodes is commonly reported, in the present case of a
vicinal SiC surface, wrinkles are preferentially oriented in the direction perpendicular to the step edges of the SiC terraces.
For each T
gr, the number of graphene layers was determined on very small sample areas by HR-XTEM and, with high statistics and on several
sample positions, by measuring the depth of selectively etched trenches in FLG by t-AFM. Both the density of wrinkles and
the number of graphene layers are found to increase almost linearly as a function of the growth temperature in the considered
temperature range. 相似文献
10.
MOS capacitors have been fabricated on 4H–SiC epilayers grown by physical vapor transport (PVT) epitaxy. The properties were compared with those on similar structures based on chemical vapor deposition (CVD) layers. Capacitance–voltage (C–V) and conductance measurements (G–V) were performed in the frequency range of 1 kHz to 1 MHz and also at temperatures up to 475 K. Detailed investigations of the PVT structures indicate a stable behaviour of the interface traps from room temperature up to 475 K. The amount of positive oxide charge QO is 6.83 × 109 cm−2 at room temperature and decreases with temperature increase. This suggests that the processed devices are temperature stable. The density of interface states Dit obtained by Nicollian–Brews conductance method is lower in the structure based on the PVT grown sample. 相似文献