We use low-energy electron microscopy to investigate how graphene grows on Cu(111). Graphene islands first nucleate at substrate defects such as step bunches and impurities. A considerable fraction of these islands can be rotationally misaligned with the substrate, generating grain boundaries upon interisland impingement. New rotational boundaries are also generated as graphene grows across substrate step bunches. Thus, rougher substrates lead to higher degrees of mosaicity than do flatter substrates. Increasing the growth temperature improves crystallographic alignment. We demonstrate that graphene growth on Cu(111) is surface diffusion limited by comparing simulations of the time evolution of island shapes with experiments. Islands are dendritic with distinct lobes, but unlike the polycrystalline, four-lobed islands observed on (100)-textured Cu foils, each island can be a single crystal. Thus, epitaxial graphene on smooth, clean Cu(111) has fewer structural defects than it does on Cu(100).
Low-temperature epitaxial growth of refractory transition-metal nitride thin films by means of physical vapor deposition has been a recurring theme in advanced thin-film technology for several years. In the present study, 150-nm-thick epitaxial HfN layers are grown on MgO(001) by reactive high-impulse magnetron sputtering (HiPIMS) with no external substrate heating. Maximum film growth temperatures Ts due to plasma heating range from 70-150 °C, corresponding to Ts/Tm = 0.10-0.12 (in which Tm is the HfN melting point in K). During HiPIMS, gas and sputtered-metal ion fluxes incident at the growi…
High Quality, Transferable Graphene Grown on Single Crystal Cu(111) Thin Films on Basal-Plane Sapphire
目前在Cu表面(多晶箔和薄膜)上生长大面积石墨烯并将其转移到任意衬底的方法在技术上是有吸引力的。然而,石墨烯的质量可以通过在单晶Cu表面上生长而显著提高。在这里,我们表明,高质量,大面积的石墨烯可以生长在外延单晶Cu(111)薄膜上的可重复使用的基面蓝宝石(α-Al 2 O 3(0001))衬底,然后转移到另一个基板。在使石墨烯能够在Cu单晶表面上生长的同时,该方法具有避免与在石墨烯转移期间牺牲体单晶Cu相关联的高成本和对石墨烯的广泛损害的潜力。
Graphene layers grown by chemical vapour deposition (CVD) method and transferred from Cu-foils to the oxidized Si-substrates were investigated by spectroscopic ellipsometry (SE), Raman and X-Ray Photoelectron Spectroscopy (XPS) methods. The optical properties of transferred CVD graphene layers do not always correspond to the ones of the exfoliated graphene due to the contamination from the chemicals used in the transfer process. However, the real thickness and the mean properties of the transferred CVD graphene layers can be found using ellipsometry if a real thickness of the SiO2 layer is tak…
We quantify the mechanisms for manganese (Mn) diffusion through graphene in Mn/graphene/Ge (001) and Mn/graphene/GaAs (001) heterostructures for samples prepared by graphene layer transfer versus graphene growth directly on the semiconductor substrate. These heterostructures are important for applications in spintronics; however, challenges in synthesizing graphene directly on technologically important substrates such as GaAs necessitate layer transfer and anneal steps, which introduce defects into the graphene. \textit{In-situ} photoemission spectroscopy measurements reveal that Mn diffusion …
Crystal orientation relation and macroscopic surface roughness in hetero-epitaxially grown graphene on Cu/mica
石墨烯电子产品对衬底上的清洁、平坦和取向识别的石墨烯有很高的需求。在这项研究中,异质外延石墨烯生长Cu(111)/云母(001)的化学气相沉积进行了研究,以检查的适用性,顶栅绝缘体的石墨烯的研究,以及石墨烯沟道的研究,通过转移到SiO2/Si衬底。在调整石墨烯生长条件后,石墨烯/Cu/云母衬底的表面粗糙度和平均光滑面积分别为~0.34 nm和~100 um 2。石墨烯/Cu/云母衬底中石墨烯的取向可以通过Cu的六方空隙形态来识别。此外,我们证明了相对较高的迁移率~4500 cm ~ 2 V-1 s-1的石墨烯转移到SiO2/Si衬底上。这些结果表明,本发明的石墨烯/Cu/云母衬底可用于石墨烯上的顶栅绝缘体研究。
Epitaxial graphene grown on metallic substrates presents, in several cases, a long-range periodic structure due to a lattice mismatch between the graphene and the substrate. For instance, graphene grown on Ir(111), displays a corrugated supercell with distinct adsorption sites due to a variation of its local electronic structure. This type of surface reconstruction represents a challenging problem for a detailed atomic surface structure determination for experimental and theoretical techniques. In this work, we revisited the surface structure determination of graphene on Ir(111) by using the u…
Notwithstanding numerous density functional studies on the chemically induced transformation of multilayer graphene into a diamond-like film, a comprehensive convincing experimental proof of such a conversion is still lacking. We show that the fluorination of graphene sheets in Bernal (AB)-stacked bilayer graphene (AB-BLG) grown by chemical vapor deposition on a single crystal CuNi(111) surface triggers the formation of interlayer carbon-carbon bonds, resulting in a fluorinated diamond monolayer (F-diamane). Induced by fluorine chemisorption, the phase transition from AB-BLG to single layer di…
We report on a comparative structural characterization of two types of high quality epitaxial graphene layers grown by CVD on 4H-SiC(0001). The layers under study are a single layer graphene on top of a buffer layer and a quasi-free-standing graphene obtained by intercalation of hydrogen underneath the buffer layer. We determine the morphology and structure of both layers by different complementary in-situ and ex-situ surface techniques. We found the existence of large islands in both samples but with different size distribution. Photoemission electron microscopy (PEEM) measurements were perfo…
Improved topological conformity enhances heat conduction across metal contacts on transferred graphene
转移的石墨烯(trG)上的金属接触的热导率可以显着降低从原生石墨烯(grG)上的类似接触的固有值,由于增加的粗糙度,残留物,氧化物和空隙的额外电阻。在本文中,我们比较了Al/trG/Cu界面的热导率(G)与Al/grG/Cu界面的热导率,以了解转移石墨烯上金属接触的热传递。我们的样品是通过化学气相沉积(CVD)在Cu箔上生长的多晶石墨烯和CVD生长的石墨烯转移到蒸发的Cu薄膜上。我们发现,对于生长的CVD石墨烯的Al/grG/Cu界面,在室温下G = 31 MW m ^{-2} K ^{-1},比Al/Cu界面低两个数量级。对于大多数在Cu膜上转移的石墨烯,G = 20 MW m ^{-2} K ^{-1},比生长的CVD石墨烯低35%。我们仔细排除了残留物,原生氧化物和界面粗糙度的贡献,并将生长和转移的CVD石墨烯的热导率的差异归因于石墨烯对Cu衬底的不同程度的一致性。我们发现,50%的接触面积仅使热导率降低了35%,这表明在石墨烯界面处的空隙中发生了少量的热传递。我们通过在300 ° C下退火样品成功地改善了转移石墨烯与衬底的一致性,从而将转移石墨烯的热导率提高到本征值。从Al/trG/Cu和Al/grG/Cu界面的G的温度依赖性测量,我们还证实了声子是金属/石墨烯/金属界面上的主要热载体,尽管石墨烯中诱导的载流子浓度为3 × 10 ^{12} cm ^{-2}。
SnTe topological crystalline insulator nanowires have been grown by molecular beam epitaxy on graphene/SiC substrates. The nanowires have cubic rock-salt structure, they grow along [001] crystallographic direction and have four sidewalls consisting of {100} crystal planes known to host metallic surface states with Dirac dispersion. Thorough high resolution transmission electron microscopy investigations show that the nanowires grow on graphene in the van der Walls epitaxy mode induced when the catalyzing Au nanoparticle mixes with Sn delivered from SnTe flux, providing liquid Au-Sn alloy. The …
In this work, the effect of the ion fluence-dependent defect formation on the modification of surface electronic and optical properties of graphene has been investigated. The chemical vapor deposited (CVD) graphene was irradiated with swift heavy ion (SHI) (70 MeV Si+5) beam at different fluence to study the defect formation mechanism and the role of it in modulating its surface electronic property such as work function. At low ion dose, acceptor doping via vacancy creation was observed; whereas dense electronic excitation dominated extended defects was realized at higher dose, which subsequen…
Tailoring the interlayer twist angle of bilayer graphene (BLG) has a significant influence on its electronic properties, including superconductivity, topological transitions, ferromagnetic states and correlated insulating states. These exotic electronic properties are sensitively dependent on the work functions of bilayer graphene samples. Here, the twisted angle-dependent work functions of CVD-grown twisted bilayer graphene (tBLG) are detailed investigated by Kelvin Probe Force Microscopy (KPFM) in combination with Raman spectra. The thickness-dependent surface potentials of Bernal-stacked mu…
Raman spectroscopic characterization of stacking configuration and interlayer coupling of twisted multilayer graphene grown by chemical vapor deposition
Transport Properties of Graphene Nanoribbon Transistors on Transport Properties of Graphene Nanoribbon Transistors on Chemical-Vapor-Deposition Grown Wafer-Scale Graphene
Graded composition CdxZn1-xTe films were prepared by growing several alternate layers of CdTe and ZnTe by the Isothermal Close Space Sublimation technique. The thickness of both kinds of layers was modified along the structure to produce an increase of the average concentration of CdTe towards the surface of the films. Due to Zn/Cd inter-diffusion during the growth process the sequence of layers was converted into a relatively smooth graded composition film. According to X- ray diffraction characterization the layers grew coherently with the (100) oriented GaAs substrates although they showed …
Method for Transferring High-Mobility CVD-Grown Graphene with Perfluoropolymers
使用无定形聚合物通过化学气相沉积(CVD)生长的石墨烯的转移代表了用于石墨烯基电子器件制造的广泛实施的方法。然而,最常用的聚合物聚甲基丙烯酸甲酯(PMMA)会在石墨烯上留下残留物,从而限制了移动性。在这里,我们报告了一种石墨烯转移和图案化的方法,该方法采用全氟聚合物-Hyronium-作为转移手柄,并保护石墨烯免受光刻胶或其他聚合物的污染。以这种方式转移到LaAlO $_3$ /SrTiO $_3$异质结构上的CVD生长的石墨烯在原子上是干净的,在2 K下在狄拉克点附近具有高迁移率(~ 30,000 cm $^2$ V $^{-1}$ s $^{-1}$)和清晰的量化霍尔和磁阻。局部控制的LaAlO $_3$ /SrTiO $_3$界面金属-绝缘体过渡-通过石墨烯-保留与此转移方法。全氟聚合物(诸如Hyplane)与CVD生长的石墨烯和其他2D材料的使用可以容易地与其他聚合物或光致抗蚀剂一起实施。
Cathodoluminescence Analysis of Defects and Grain Boundaries in Zn3P2 Thin Films Grown on Graphene by MOVPE and MBE
École Polytechnique Fédérale de Lausanne (EPFL)(洛桑联邦理工学院);Lund University(隆德大学);Université Côte d’Azur, CNRS, CRHEA(蔚蓝海岸大学,法国国家科学研究中心,高能物理研究所);Interdisciplinary Center for Electron Microscopy (CIME), EPFL(洛桑联邦理工学院跨学科电子显微镜中心);Ruhr University Bochum(波鸿鲁尔大学);Friedrich-Schiller-Universität Jena(耶拿弗里德里希·席勒大学)
We show the emergence of fractional quantum Hall states in dry-transferred chemical vapor deposition (CVD) derived graphene assembled into heterostructures for magnetic fields from below 3 T to 35 T. Effective composite-fermion filling factors up to $ν^* = 4$ are visible and higher order composite-fermion states (with four flux quanta attached) start to emerge at the highest fields. Our results show that the quantum mobility of CVD-grown graphene is comparable to that of exfoliated graphene and, more specifically, that the $p/3$ fractional quantum Hall states have energy gaps of up to 30 K, we…
Transition metal surfaces catalyse a broad range of thermally-activated reactions involving carbon-containing-species -- from atomic carbon to small hydrocarbons or organic molecules, and polymers. These reactions yield well-separated phases, for instance graphene and the metal surface, or, on the contrary, alloyed phases, such as metal carbides. Here, we investigate carbon phases on a rhenium (0001) surface, where the former kind of phase can transform into the latter. We find that this transformation occurs with increasing annealing time, which is hence not suitable to increase the quality o…
Effects of annealing on chemical vapor deposited graphene are investigated via a weak localization magnetoresistance measurement. Annealing at \SI{300}{\celsius} in inert gases, a common cleaning procedure for graphene devices, is found to raise the dephasing rate significantly above the rate from electron-electron interactions, which would otherwise be expected to dominate dephasing at 4 K and below. This extra dephasing is apparently induced by local magnetic moments activated by the annealing process, and depends strongly on the backgate voltage applied.
Transport in Nanoribbon Interconnects Obtained from Graphene Grown by Chemical Vapor Deposition
我们研究了石墨烯纳米管(GNR)的互连从石墨烯化学气相沉积(CVD)生长。我们报告低场和高场的电气测量在很宽的温度范围内,从1.7到900 K。室温迁移率在100至500 cm 2/V/s的范围内,与来自剥离的石墨烯的GNR相当,这表明体缺陷或晶界在小于CVD石墨烯微晶尺寸的器件中几乎不起作用。在高电场下,峰值电流密度受到焦耳加热的限制,但少量的热工程使我们能够达到约2 x 10^9 A/cm 2,这是纳米级CVD石墨烯互连的最高报告。在低于~5 K的温度下,短GNR充当量子点,其尺寸与其长度相当,突出了金属接触在限制传输中的作用。我们的研究说明了CVD生长GNRs的机会,同时揭示了可变性和接触作为未来的挑战。