The intensity ratio between two major Raman bands in graphene is one of the most important information for physics of graphene and has been believed to represent various intrinsic properties of graphene without critical assessment of extrinsic effects. We report a micro Raman spectroscopy study on the Raman intensity ratio of the 2D band to the G Raman band of graphene varying the thickness of dielectric layers (SiO_2) underneath it. The ratio is shown to change by almost 370% when the thickness is varied by 60%. The large variation in the ratio is well explained by theoretical calculations considering multiple Raman scattering events at the interfaces. Our analysis shows that the interference effect is critical in extracting the intrinsic 2D to G intensity ratio and therefore must be taken into account in extracting various physical properties of graphene from Raman measurements.
Electrical transport properties of graphene on SiO2 with specific surface structures
在SiO2/Si衬底上转移的石墨烯的迁移率被限制为~ 10，000 cm 2/Vs。如果不了解石墨烯/SiO2相互作用，就难以改善电输运性质。虽然SiO2上的表面结构，如硅烷醇和硅氧烷基团被认可，但SiO2的表面处理和石墨烯特性之间的关系尚未阐明。本文讨论了石墨烯在氧等离子体处理和再氧化法制备的SiO2的特定表面结构上的电输运性质。
Spin-orbit coupling (SOC) in graphene can be greatly enhanced by proximity coupling it to transition metal dichalcogenides (TMDs) such as WSe2. We find that the strength of the acquired SOC in graphene depends on the stacking order of the heterostructures when using hexagonal boron nitride (h-BN) as the capping layer, i.e., SiO2/graphene/WSe2/h-BN exhibiting stronger SOC than SiO2/WSe2/graphene/h-BN. We utilize photoluminescence (PL) as an indicator to characterize the interaction between graphene and monolayer WSe2 grown by chemical vapor deposition. We observe much stronger PL quenching in t…
The unique properties of graphene offer immense opportunities for applications to many scientific fields, as well as societal needs, beyond our present imagination. One of the important features of graphene is the relatively simple tunability of its electronic structure, an asset which extends the usability of graphene even further beyond present experience. A direct injection of charge carriers into the conduction or valence bands, i.e., doping, represents a viable way of shifting the Fermi level. In particular, the electrochemical doping should be the method of choice, when higher doping lev…
We present the full magnetic g tensors of the $^{6}$H$_{5/2}$Z$_{1}$ and $^{4}$G$_{5/2}$A$_{1}$ electronic states for both crystallographic sites in Sm$^{3+}$:Y$_{2}$SiO$_{5}$, deduced through the use of Raman heterodyne spectroscopy performed along 9 different crystallographic directions. The maximum principle g values were determined to be 0.447 (site 1) and 0.523 (site 2) for the ground state and 2.490 (site 1) and 3.319 (site 2) for the excited state. The determination of these g tensors provide essential spin Hamiltonian parameters that can be utilized in future magnetic and hyperfine stu…
We present an \textit{ab initio} study based on density-functional theory of first- and second-order Raman spectra of graphene-based materials with different stacking arrangements and numbers of layers. Going from monolayer and bilayer graphene to periodic graphitic structures, we investigate the behavior of the first-order G-band and of the second-order 2D-band excited by the same set of photon energies. The former turns out to be very similar in all considered graphene-based materials, while in the latter we find the signatures of individual structures. With a systematic analysis of the seco…
Comment on "Raman spectra of misoriented bilayer graphene"
在最近的论文[Phys.Rev.B78，113407（2008）]中，Poncharal等人研究了取向错误的双层石墨烯的拉曼光谱。他们发现，相对于单层石墨烯，错位石墨烯的2D带的蓝移显示出对激发激光能量的强烈依赖性。蓝移随激发能的降低而增加。这一发现与我们对折叠/错误取向的石墨烯的费米速度降低的解释相矛盾[Ni et al.Phys.Rev.B77，235403（2008）]。在这篇评论中，我们提出了更多的实验结果，从我们的小组以及从其他人表明，蓝移确实只是弱依赖于激发能。因此，我们认为，我们的解释的二维蓝移的折叠石墨烯由于费米速度的降低仍然是有效的。
We report the growth, structural and magnetic properties of the less studied Eu-oxide phase, Eu$_3$O$_4$, thin films grown on a Si/SiO$_2$ substrate and Si/SiO$_2$/graphene using molecular beam epitaxy. The X-ray diffraction scans show that highly-textured crystalline Eu$_3$O$_4$(001) films are grown on both substrates, whereas the film deposited on graphene has a better crystallinity than that grown on the Si/SiO$_2$ substrate. The SQUID measurements show that both films have a Curie temperature of about 5.5 K, with a magnetic moment of 0.0032 emu/g at 2 K. The mixed-valency of the Eu cations…
Spin lifetime anisotropy in graphene induced by the SiO2 interface
Catalan Institute of Nanoscience and Nanotechnology (ICN2), CSIC and BIST（加泰罗尼亚纳米科学和纳米技术研究所（ICN2））；University of Wisconsin-Madison（威斯康星大学麦迪逊分校）；Hefei University of Technology（合肥工业大学）；University of California, Santa Cruz（加州大学圣克鲁兹分校）；Montana State University（蒙大拿州立大学）
Intrinsic and Extrinsic Performance Limits of Graphene Devices on SiO2
石墨烯中的线性色散关系[1，2]产生了令人惊讶的预测：由于各向同性散射体（例如白噪声无序[3]或声子[4-8]）引起的电阻率与载流子密度n无关。在这里，我们表明声学声子散射[4-6]确实与n无关，并且在室温（RT）下石墨烯的电阻率仅为30欧姆。在技术相关的载流子密度为10^12 cm^-2时，电声声子散射的平均自由程大于2微米，本征迁移率极限为2x10^5 cm ^2/Vs，超过了已知最高的无机半导体（InSb，~7.7x10^4 cm ^2/Vs[9]）和半导体碳纳米管（~1x10^5 cm ^2/Vs[10]）。我们还表明，SiO2衬底[11，12]的表面声子的非本征散射增加了高于~200 K的强温度依赖性电阻率[8]，将RT迁移率限制为~4x10^4 cm^2/Vs，指出了石墨烯器件衬底选择的重要性[13]。
