Dmitry S. Muratov

Chemical vapour deposition and characterization of uniform bilayer and trilayer MoS2 crystals

Molybdenum disulfide (MoS2) is a promising two-dimensional semiconductor for applications in electronics, optoelectronics and catalysis. Chemical vapor deposition (CVD) is a popular approach for the large-scale growth of thin MoS2 crystals. As the properties of MoS2 strongly depend on the number of layers, it is important to reliably grow MoS2 crystals with different thicknesses. In this paper, we present a CVD procedure for MoS2 growth from MoO3 and S, which yields predominantly bilayer and trilayer MoS2 triangular islands as opposed to monolayer MoS2 triangles typically observed in similar CVD experiments. The growth of bilayer and trilayer MoS2 crystals is achieved by increasing the flow rate of sulfur after the original nucleation of MoS2 triangles. Most bilayer MoS2 crystals are uniform in height, such that in a typical crystal the top layer fully extends to the edges of the bottom layer. While trilayer MoS2 crystals grown by this procedure are in general less uniform than bilayers and often form terraced structures, it is still common to observe uniform trilayer MoS2 triangles as well. In addition to standard characterization methods for MoS2, such as Raman spectroscopy, atomic force microscopy and photoluminescence microscopy we demonstrate that scanning electron microscopy can be used to distinguish between monolayer and few-layered MoS2 flakes at low accelerating voltages. The field-effect transistors based on CVD-grown MoS2 triangles have electron mobilities reaching ∼10 cm2 V−1 s−1 and ON/OFF ratios reaching ∼105. The reported CVD procedure can be used for growing large quantities of uniform bilayer and trilayer MoS2 crystals for materials studies.

Low-temperature thermal reduction of graphene oxide: In situ correlative structural, thermal desorption, and electrical transport measurements

Elucidation of the structural transformations in graphene oxide (GO) upon reduction remains an active and important area of research. We report the results of in situ heating experiments, during which electrical, mass spectrometry, X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, and transmission electron microscopy (TEM) measurements were carried out correlatively. The simultaneous electrical and temperature programmed desorption measurements allowed us to correlate the onset of the increase in the electrical conductivity of GO by five orders of magnitude at about 150 °C with the maxima of the rates of desorption of H2O, CO, and CO2. Interestingly, this large conductivity change happens at an intermediate level of the reduction of GO, which likely corresponds to the point when the graphitic domains become large enough to enable percolative electronic transport. We demonstrate that the gas desorption is intimately related to (i) the changes in the chemical structure of GO detected by XPS and Ra...

Evaluating Hydrogen Uptake for Two Types of Multi-Wall Carbon Nanotubes from Nitrogen Adsorption/Desorption Data

Two types of multi-wall carbon nanotubes (MWCNT) were studied by low temperature nitrogen adsorption method. Pore size distribution was calculated using non local density functional theory (NLDFT) and Barrett-Joyner-Halenda (BJH) models. The peaks on pore size distribution were attributed to MWCNT with different diameters. Maximum hydrogen uptake by weight was evaluated for both samples and do not exceed 5 % even for the sample with higher specific surface area.

Tris(ethylene diamine) nickel acetate as a promising precursor for hole transport layer in planar structured perovskite solar cells

Owing hysteresis free characteristics and good reproducibility, inverted p-i-n perovskite solar cells (PSC) are gaining large interest in the photovoltaic field. In this context, the need for stable materials calls for the development of robust transporting layers compatible with the fabrication processes of the solar cell. In this study, we introduce a new precursor, tris(ethylene diamine) nickel acetate, for low temperature (280–300 °C) deposition of NiO hole transporting layer. Full characterization of the deposited NiO film layer was performed through XRD, Raman and Auger spectroscopy. We found a direct correlation between device performance and NiO thickness with maximum efficiency exceeding 15% for the thin NiO (10 nm) layer.

Polymer Stabilized Undoped and Copper Doped Cadmium Sulphide Nanoparticles: Polymer Crosslinked, Optical, and Thermal Stability

Cadmium sulfide (CdS) nanoparticles synthesized by utilization of wet chemical technique are grown in polyvinyl alcohol (PVA) matrix. X-ray diffraction (XRD) pattern shows the typical inter-planar spacing corresponding to the cubic phase of CdS. High-resolution transmission electron microscopy (HRTEM) studies show the nanoparticles formation with diameter around 11 nm. Particle size is further determined by dynamic light scattering (DLS) measurement. The polymerization of PVA is confirmed by fourier transform infrared (FTIR) spectroscopy of CdS nanoparticles. UV-visible optical spectroscopy study shows that sharp excitonic bands are largely blue shifted from the absorption onset of bulk CdS and inter band transition of copper doped samples. Thermal stability of the samples is measured by thermogravimetric (TG) analysis which is also studied in details.

Morphology and structure study of dispersed nickel-molybdenum powders produced by different methods

Ni-Mo powders produced by ultrasonic spray pyrolysis and chemical deposition are comparing in this study. Specimens were investigated by low-temperature nitrogen adsorption, x-ray diffraction, x-ray fluorescence, scanning and transmission electron microscopy methods. It was shown that the composition of the two-phase material, produced by ultrasonic spray pyrolysis method, is easy to control. Powders have spherical shape and high specific surface area.