Investigation of vacuum evaporated SnTe thin films for their structural, electrical and thermoelectric properties

Remarkable enhancement in figure-of-merit (ZT) value of p-type Tin Telluride (SnTe) thin films is reported in the present investigations. Under high vacuum conditions, all thin films deposited on the glass substrate by using thermal evaporation technique. Thickness of the thin films were kept 55 and 33 nm. Morphological features and the elemental composition of the thin film were investigated using scanning electron microscopy (SEM) and energy-dispersive spectroscopy (EDS) technique respectively. High-resolution transmission electron microscopy (HRTEM) with selected area electron diffraction (SAED) pattern was used to investigate the microstructure of these thin films. For the identification of crystalline features, phase, and nano-crystallites size in all the thin films, the X-ray diffraction (XRD) technique had played a dominant role. The analysis of the XRD data results in a single-phase cubic structure. Atomic force microscopy (AFM) analysis revealed the 2D and 3D view of variable size grains formed on the glass substrate. Four probes method was used to determine the electrical conductivity of these thin films. Electrical measurements revealed the semi-metallic nature of the SnTe thin films. The thermoelectric measurement analysis revealed that the ZT of the thin films was found to be increased as the thickness of the film enhanced. The maximum value of ZT∼1.0 was obtained at room temperature for the film of thickness 55 nm

Microstructural and optical properties investigation of variable thickness of Tin Telluride thin films

A series of Tin Telluride (SnTe) thin films of varied thicknesses are deposited on glass substrates at room temperature using thermal evaporation technique. The optical and microstructural properties of SnTe thin films of thicknesses 33 nm to 275 nm are reported. High-resolution x-ray diffraction patterns of SnTe thin films revealed the polycrystalline nature with [200] orientation having cubic structure. The microstructural and morphological structures of these films were examined using high-resolution transmission electron microscopy and scanning electron microscopy, respectively. The distribution of isotopes of various elements in the thin film along with lateral and longitudinal directions was determined by depth profile measurement using the time of flight - secondary ion mass spectroscopy technique. Fourier transform infrared spectroscopy spectra reveal the molecular vibrations, narrow bandgap property of material and suitability of materials in infrared applications. Longitudinal - optical phonon scattering due to the [222] orientation was observed in the micro-Raman spectra at room temperature which corresponds to a peak in the range 120-130 Raman shift/cm(-1). Hence, the change in optical and microstructural properties at the nano-regime resulted in a shift towards the near-infrared region with an increase in the thickness of the thin films

Physico-chemical characterization of a polycarbonate (PC) surface modified by exposure to dc glow discharge in air

The present investigation describes the changes in the wetting characteristics of a polycarbonate ( PC) surface modified by exposure to dc glow discharge at 2.04 W, as observed by contact angle measurement. The contact angle of droplets of test liquids of deionized water and formamide on PC surface decreases rapidly with increasing time of exposure to dc glow discharge and attains a minimum. Thereafter, the contact angle increases slightly to show a small hump before saturating finally at longer times of exposure. The lowering of contact angle is primarily due to the increasing polar component of surface energy. Fourier transform infrared spectroscopy and electron spectroscopy for chemical analysis indicate that increasing polar surface energy is accompanied by increased oxidized functional groups such as C-O and C=O, thus showing increasing O/C ratio with increasing exposure time. Atomic force microscopy shows increasing adhesion force with increasing exposure time, consistent with the observed adhesion energy estimated from 2.04 W contact angle measurement

Facile Synthesis of Semiconducting Ultrathin Layer of Molybdenum Disulfide

In this paper, we have reported a simple and efficient method for the synthesis of uniform, highly conducting single or few layer molybdenum disulfide (MoS2) on large scale. Scanning Electron Microscopy (SEM) and High Resolution Transmission Electron Microscopy (HRTEM) have been used for the confirmation of mono or few layered nature of the as-synthesized MoS2 sheets. X-ray Photoelectron Spectroscopy (XPS), X-Ray Diffraction (XRD) and Raman Spectroscopy have also been used to study the elemental, phase, and molecular composition of the sample. Optical properties of as-synthesized sample have been probed by measuring absorption and photoluminescence spectra which also compliment the formation of mono and few layers MoS2 Current-voltage (I-V) characteristics of as-synthesized sample in the pellet form reveal that MoS2 sheets have an ohmic character and found to be highly conducting. Besides characterizing the as-synthesized sample, we have also proposed the mechanism and factors which play a decisive role in formation of high quality MoS2 sheets