Tungsten ditelluride (WTe2) has attracted extensive interest because of promising magnetic, electrical, and thermal properties, such as non-saturable large magnetoresistance, pressure-induced superconductivity, and low thermal conductivity, owing to the heavy atomic mass and low Debye temperature. Here, we report the thickness dependence of anisotropic in-plane Raman modes under different temperatures in supported few-layer WTe2. With angle-resolved Raman spectroscopy, supported few-layer WTe2 reveals a temperature-related anisotropy in Raman modes, and the highest degree of anisotropy is obtained between zigzag and armchair directions, which could be resulted from the different phonon group velocities along these directions. In addition, as the thickness of the WTe2 nanosheet decreases from bulk to 10 nm, the anisotropic ratio (χzigzag/χarmchair) increases from 1.09 to 1.45. Such enhancement in the anisotropic ratio could result from the thickness-dependent surface scattering in supported few-layer WTe2. Our study provides guidance to regulate the anisotropy ratio in thermoelectrical and optoelectronic devices, which might inspire the innovation of functional two-dimensional devices in the future.

Vertically oriented graphene (VG) is deposited on a wide range of substrates by plasma-enhanced chemical vapor deposition. Moreover, the growth mode of VG is proven to be bottom-up deposition using isotope labeling. The Raman characteristic features of rhodamine 6G (R6G), an aromatic dye, are acquired using VG as a universal fluorescence quencher. The fluorescence quenching mechanism is likely related to the transfer of energy and photon-excited electrons between dye molecules and VG because not only the fluorescence emission spectrum of R6G greatly overlaps with the UV–vis absorption spectrum of VG, but also the resistance of dye-coated VG decreases under light irradiation. In addition, the Raman features of other aromatic dyes, such as eosin Y, rhodamine B, methylene blue, and gallocyanine, are obtained by the same method.

Although the structure of vertical graphene (VG) is important for various applications, the growth mechanism of VG is not yet fully clear. Here, the impacts of electrical conductivity of substrate on the morphology and structure of VG prepared by plasma-enhanced chemical vapor deposition are studied by scanning electron microscopy and Raman spectroscopy. The results show that VG with greater thickness can be grown on substrate with better electrical conductivity in the same growth time. Even though longer deposition time leads to more VG, more defects might develop in VG, especially at the position furthest away from the substrates. The change of morphology and structure of VG is closely correlated with strength of electric field near the substrate surface, which offers a new approach for orderly growing of VG. The discoveries not only shed light on the growth mechanism of VG, but also are beneficial for promoting the applications of VG.

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In this study, TiN films were deposited on SiO 2 substrates by Atomic Layer Deposition (ALD) using TiCl 4 and NH 3 as precursors. Properties and morphology of the TiN films were characterized by different methods.Using Grazing Incidence X-Ray Diffraction (GIXRD), TiN films demonstrated polycrystalline structure with (111) preferred orientation. Film thickness was measured by Spectroscopic Ellipsometry (SE) and a stable growth rate of 0.0178 nm/cycle was reached after 500 deposition cycles, which was consistent with the essence of ALD as a surface-saturated self-limiting reaction. Film resistivity measured by a four-point probe continuously decreased with increasing deposition cycles until it reached the minimum value of 300 cm at 5000 deposition cycles with a thickness of 87.04 nm. The surface roughness and morphology of the TiN films at different deposition cycles ranging from 50 to 400 were analyzed by Atomic Force Microscopy (AFM). The AFM results indicated that the initial film growth follows the Stranski-Krastanov mode.