Low-Frequency Raman Modes and Electronic Excitations In Atomically Thin MoS2 Crystals

Atomically thin MoS$_{2}$ crystals have been recognized as a quasi-2D semiconductor with remarkable physics properties. This letter reports our Raman scattering measurements on multilayer and monolayer MoS$_{2}$, especially in the low-frequency range ($<$50 cm$^{-1}$). We find two low-frequency Raman modes with contrasting thickness dependence. With increasing the number of MoS$_{2}$ layers, one shows a significant increase in frequency while the other decreases following a 1/N (N denotes layer-number) trend. With the aid of first-principle calculations we assign the former as the shear mode $E_{2g}^{2}$ and the latter as the compression vibrational mode. The opposite evolution of the two modes with thickness demonstrates novel vibrational modes in atomically thin crystal as well as a new and more precise way to characterize thickness of atomically thin MoS$_{2}$ films. In addition, we observe a broad feature around 38 cm$^{-1}$ (~5 meV) which is visible only under near-resonance excitation and pinned at the fixed energy independent of thickness. We interpret the feature as an electronic Raman scattering associated with the spin-orbit coupling induced splitting in conduction band at K points in their Brillouin zone.Comment: 5 pages, 4 figure

Effect of grain alignment on interface trap density of thermally oxidized aligned-crystalline silicon films

The authors report studies of the effect of grain alignment on interface trap density of thermally oxidized aligned-crystalline silicon (ACSi) films by means of capacitance-voltage (C-V) measurements. C-V curves were measured on metal-oxide-semiconductor (MOS) capacitors fabricated on 〈001〉- oriented ACSi films on polycrystalline substrates. From high-frequency C-V curves, the authors calculated a decrease of interface trap density from 2× 1012 to 1× 1011 cm-2 eV-1 as the grain mosaic spread in ACSi films improved from 13.7° to 6.5°. These results demonstrate the effectiveness of grain alignment as a process technique to achieve significantly enhanced performance in small-grained (≤1 μm) polycrystalline Si MOS-type devices. © 2006 American Institute of Physics

Spectroscopic and Structural Properties of Yb3+-Doped and Undoped 2D-Mos2 Thin Films for Optoelectronic and Photonic Device Applications

Molybdenum disulphide (MoS 2 ) has layered structure and is classed as a transition metal-disulphide (TMD) material. Recently it has drawn significant attention for exploring optoelectronic and photonic properties on sub-nanometre scale, with a potential for accessing quantum interactions [1]. The electronic structure and stoichiometry of TMDs make them distinguishable from the metallic graphene, as the TMDs depict a clear bandgap, as in compound semiconductors [2], which is quite attractive for device engineering and applications in photovoltaic, energy storage, and bandgap engineered light-sources [3]. In this research, the fabrication of undoped and Yb 3+ -ion doped MoS 2 nanometre (nm)-scale thin films are discussed using femto-second pulsed laser deposition (fs-PLD) and the structural and spectroscopic properties of fs-PLD are compared with liquid-phase epitaxy grown undoped MoS 2 films. Such a comparative analysis may offer materials fabrication platform in future for engineering optoelectronic and photonic devices on silica glass and silicon platforms

Nano granular metallic Fe - oxygen deficient TiO2−δ_{2-\delta} composite films: A room temperature, highly carrier polarized magnetic semiconductor

Nano granular metallic iron (Fe) and titanium dioxide (TiO$_{2-\delta}$) were co-deposited on (100) lanthanum aluminate (LaAlO$_3$) substrates in a low oxygen chamber pressure using a pulsed laser ablation deposition (PLD) technique. The co-deposition of Fe and TiO$_2$ resulted in $\approx$ 10 nm metallic Fe spherical grains suspended within a TiO$_{2-\delta}$ matrix. The films show ferromagnetic behavior with a saturation magnetization of 3100 Gauss at room temperature. Our estimate of the saturation magnetization based on the size and distribution of the Fe spheres agreed well with the measured value. The film composite structure was characterized as p-type magnetic semiconductor at 300 K with a carrier density of the order of $10^{22} /{\rm cm^3}$. The hole carriers were excited at the interface between the nano granular Fe and TiO$_{2-\delta}$ matrix similar to holes excited in the metal/n-type semiconductor interface commonly observed in Metal-Oxide-Semiconductor (MOS) devices. From the large anomalous Hall effect directly observed in these films it follows that the holes at the interface were strongly spin polarized. Structure and magneto transport properties suggested that these PLD films have potential nano spintronics applications.Comment: 6 pages in Latex including 8 figure

Direct transformation of crystalline MoO3_3 into few-layers MoS2_2

We fabricate large-area atomically thin MoS$_2$ layers through the direct transformation of crystalline molybdenum MoS$_2$ (MoO$_3$) by sulfurization at relatively low temperatures. The obtained MoS2 sheets are polycrystalline (~10-20 nm single-crystal domain size) with areas of up to 300x300 um$^2$ with 2-4 layers in thickness and show a marked p-type behaviour. The synthesized films are characterized by a combination of complementary techniques: Raman spectroscopy, X-ray diffraction, transmission electron microscopy and electronic transport measurements.Comment: 6 figures in main text, 2 figures in supp. inf

Surface Passivation of Germanium Using NH3 Ambient in RTP for High Mobility MOS Structure

Ge CMOS is very striking for the post Si-CMOS technology. However, we have to attempt a number of challenges with regard to materials and their interface control. In this paper we have investigated the control of the interfacial properties of SiO2 / Ge gate stack structures by the thermal nitridation technique. Structural and electrical properties of SiO2 gate-dielectric metal-oxide-semiconductor (MOS) capacitors deposited by sputtering on germanium are studied. The structural characterization confirmed that the thin film was free of physical defects and smooth surface of the films after PDA at 500 °C in N2 ambient. The smooth surface SiO2 thin films were used for Pt / SiO2 / GeON / Ge MOS structures fabrication. The MOS structure yields a low leakage current density of 9.16 × 10 – 6Acm – 2 at 1 V. When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/3100

A Study on MoS 2 Thin Films Electrochemically Deposited in Ethylene Glycol at 165°C

The electrosynthesis of nanoparticle thin films of MoS 2 from solutions of (NH 4 ) 2 MoS 4 in ethylene glycol at 165°C, is described. The as-deposited MoS 2 thin films (~150 nm thick) were X-ray amorphous and exhibited featureless optical absorption spectra over the 1-3.5 eV spectral range. High resolution transmission electron microscopy (HRTEM) revealed the presence of single or double (0002) plane-sized 2H-MoS 2 thin nanoplatelets (~2-3 nm) embedded in an amorphous matrix. Annealing the as-deposited samples under Ar for 1 h at 550°C, resolved a broad and weak-intensity peak in the respective X-ray spectra, identified as th

Textured MoS 2 Thin Films Obtained on Tungsten: Electrical Properties of the W/MoS 2 Contact

Textured films of molybdenum disulfide have been obtained by solid state reaction between the constituents in thin films form when a (200) oriented tungsten sheet is used as substrate. The crystallites have their c axis perpendicular to the plane of the substrate. The annealing conditions are T=1073K and t=30 min. The films are stoichoimetric and p type. Such highly textured films are achieved without foreign atom addition (Ni, Co...). It appears, as shown by x-ray photoelectron spectroscopy, that a thin WS2 layer is present at the interface W/MoS2. The crystallization process is discussed by a van der Waals texturation (pseudoepitaxy) onto dangling bond sulfur terminated surfaces, these surfaces being ordered. After characterization of the W/MoS2 structure by x-ray diffraction and x-ray photoelectron spectroscopy, an upper electrode of tungsten was deposited by sputtering. The electrical properties of these W/MoS2/W structures have been investigated by analyzing the behavior of the current–voltage characteristics as a function of the measuring temperature. It is shown that an ohmic contact is obtained with a contact resistance smaller than the resistance of the MoS2 film