All devices were prepared on silicon-on-insulator (SOI; Soitec Inc.) wafers. The SOI wafers were pre-doped by thermally diffusing spin-on-dopant (Boron A; Filmtronics, Inc.) with rapid thermal annealing (RTA) at 820C for 3 minutes. The resulting sheet resistance indicates a doping concentration of 2x10 19 cm -3 , with the thickness of the silicon epilayer determined by atomic force microscopy to be 25 nm, 22 nm and 20 nm (depending on the device) with a variance of 1 nm. The nanomesh films (NM) and nanowires (NWA) are fabricated by the SNAP technique [30], while the e-beam nanomesh (EBM) and thin films (TF) are defined by e-beam lithography (EBL).For the NM devices, two perpendicularly aligned Pt nanowire arrays are made using two consecutive superlattice nanowire pattern array (SNAP) procedures on top of an SOI wafer (Soitec, Inc.). SNAP protocols are described in Refs. 17 and 30. For the NWA devices only one SNAP procedure is carried out, resulting in a single, aligned Pt nanowire array. For the EBM and TF devices, e-beam lithography and metallization are used to make the transfer-ready Pt nanostructures. Next, we define the membranes
A lack of inversion symmetry coupled with the presence of time-reversal symmetry endows 2D transition metal dichalcogenides with individually addressable valleys in momentum space at the K and K' points in the first Brillouin zone. This valley addressability opens up the possibility of using the momentum state of electrons, holes, or excitons as a completely new paradigm in information processing. The opportunities and challenges associated with manipulation of the valley degree of freedom for practical quantum and classical information processing applications were analyzed during the 2017 Workshop on Valleytronic Materials, Architectures, and Devices; this Review presents the major findings of the workshop.
Methods and Supplementary Figures Fig. S1. Contrast enhancement/optimization for different substrates.
Materials. Anhydrous inhibitor-free tetrahydrofuran (THF, ≥99.9%, water content <0.002%) and anhydrous cyclohexane (99.5%, water content <0.001%) were purchased from Sigma-Aldrich. These reagents were used as supplied and stored in a glove-box purged with nitrogen. Muscovite mica (Grade V1; round disks of diameter 10 mm) was obtained from Ted Pella. Kish graphite was obtained from Covalent Materials US Inc.Sample preparation. Samples were prepared in a glove-bag (Sigma-Aldrich AtmosBag) that was purged and protected under a continuous flow of ultra-high purity argon, in which the relative humidity (RH) was controlled to be <2%. Humidity was monitored using a Fluke 971 temperature humidity meter. All experiments were performed at room temperature (22±2 °C). Mica disks were first heated in air at 200 °C for 10 min to remove absorbed moisture, and then transferred into the glove-bag. The mica surface was cleaved in the glove-bag and exposed to organic vapors for ~10 s to ~1 min. The partial pressure of organic molecules at the mica surface, which determines the surface coverage at equilibrium, was adjusted by varying the distance between the vapor source and the mica surface. Graphene sheets were deposited onto the mica surface through the standard method of mechanical exfoliation (Novoselov et al. 2005; Lui et al. 2009) of Kish graphite, thus sealing and preserving the adlayers of organic molecules.Identification of graphene layers. Monolayer graphene sheets were identified through optical microscopy and confirmed by spatially resolved Raman spectroscopy (Xu et al. 2010). Raman spectra were recorded with a Renishaw M1000 Micro Raman spectrometer system using a 514.5 nm laser beam and a 2400 lines per mm grating. A confocal optical microscope with a ×100 objective lens was used to record spectra with a spatial resolution of 2 μm. No noticeable D peak was observed in the Raman spectra (Fig. S1), indicating high-crystalline order of our samples.Atomic Force Microscopy. All AFM images were acquired under tapping mode on a Digital Instrument Nanoscope IIIA at ambient conditions. A sharp TESP tip (Veeco) with a radius of end of 8 nm was used. Typical values for the force constant and resonance frequency were 42 N/m and 320 kHz respectively. Height calibrations were performed using the step heights of freshly cleaved graphite samples. Due to the super-flatness of the samples, sometimes the laser interference pattern along the slow-scan axis was hard to avoid, which is more noticeable in large-area scanning and have a period of twice the wavelength of the laser. This is caused by the constructive interference of laser reflected from the sample surface and
Supporting Information MethodsAu(111)/mica substrates (1.4 cm × 1.1 cm; gold thickness: 150 nm) were purchased from SPI. A sealed container containing the Au(111)/mica substrate was opened in a N 2 /water vapor purged glovebag with controlled RH of 40%. The substrate was allowed to equilibrate with the environment for ~5 min, and then graphene sheets were deposited onto the Au(111) surface by mechanical exfoliation of Kish graphite.Thin graphene flakes were first searched for under an optical microscope. Few-layer (<3) graphene was hard to identify on the Au surface, but often appeared around the edges of thicker graphite flakes that can be more readily observed on the surface ( Figure S1). To locate and confirm the few-layer graphene areas, AFM was subsequently performed under tapping mode on a Digital Instrument Nanoscope IIIA. STM studies were carried out using an Omicron LT-STM operating under ultrahigh vacuum (<10 -10 torr) at both room temperature and 77 K. Figure S1
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.