The spontaneous formation of nanodomains of the Sb-rich layered intergrowth SnmSb2nTe3n+m compounds in a SnTe matrix resulted in ultralow lattice thermal conductivity.

No abstract

We report on the various types of Peierls like two dimensional structural modulations and relative phase stability of 2H and 1T poly-types in MoS 2 -ReS 2 and WS 2 -ReS 2 alloy system. Theoretical calculation predicts a polytype phase transition cross over at ~50 at.% of Mo and W in ReS 2 in both monolayer and bulk form, respectively. Experimentally, two different types of structural modulations at 50% and a modulation corresponding to trimerization at 75% alloy composition is observed for MoS 2 -ReS 2 and only one type of modulation is observed at 50% WS 2 -ReS 2 alloy system. The 50% alloy system is found to be a suitable monolithic candidate for metal semiconductor transition with minute external perturbation.ReS 2 is known to be in 2D Peierls distorted 1T d structure and forms a chain like superstructure. Incorporation of Mo and W atoms in the ReS 2 lattice modifies the metal-metal hybridization between the cations and influences the structural modulation and electronic property of the system. The results offer yet another effective way to tune the electronic 2 structure and poly-type phases of this class of materials other than intercalation, strain, and vertical stacking arrangement. I.

Nanowall network of MoS2 grown by atomic layer deposition shows single crystalline nature and epitaxial relationship with c-sapphire. The nanowall network grown directly on current collector exhibits high capacity, remarkable stability, cyclability and high rate capability over a wide range of operating currents.

Large area MoS 2 and WS 2 van der Waals epitaxial thin films with complete control over number of layers including monolayer is grown by pulsed laser deposition utilizing slower growth kinetics. The films grown on c-plane sapphire show stiffening of A 1g and E 1 2g phonon modes with decreasing number of layers for both MoS 2 and WS 2 . The observed stiffening translate into the compressive strain of 0.52 % & 0.53 % with accompanying increase in fundamental direct band gap to 1.74 and 1.68 eV for monolayer MoS 2 and WS 2 , respectively. The strain decays with the number of layers. HRTEM imaging directly reveals the nature of atomic registry of van der Waals layers with the substrate and the associated compressive strain. The results demonstrate a practical route to stabilize and engineer strain for this class of material over large area device fabrication.

No abstract

We report on the observation of rich variety of crystallographic phase formation in RexMo1-xS2 alloy for x < 0.5. For x < 0.23, no low dimensional super-structural modulation is observed and inter-cation hybridization remains discrete forming dimers to tetramers with increasing Re concentration. For x > 0.23, super-strutural modulaton is observed. Depending on the Re concentrations (x = 0.23, 0.32, 0.38 and 0.45) and its distributions, various types of cation hybridization results in rich variety of low dimensional super-structural modulation as directly revealed by high resolution transmission electron microscopy. These layered alloy system may be useful for various energy and novel device applications.

We report on the chemically stabilized epitaxial w-BN thin film grown on c-plane sapphire by pulsed laser deposition under slow kinetic condition. Traces of no other allotropes such as cubic (c) or hexagonal (h) BN phases are present. Sapphire substrate plays a significant role in stabilizing the metastable w-BN from h-BN target under unusual PLD growth condition involving low temperature and pressure and is explained based on density functional theory calculation. The hardness and the elastic modulus of the w-BN film are 37 & 339 GPa, respectively measured by indentation along <0001> direction. The results are extremely promising in advancing the microelectronic and mechanical tooling industry. 2 Boron Nitride (BN) exhibits numerous allotropes e.g., hexagonal (h-BN, P63/mmc), rhombohedral (r-BN, R3m), cubic (c-BN, Fd3m) and wurtzite (w-BN, P63mc) which are analogous to Carbon (C) allotropes. Among these, h-BN is the most stable form found at room temperature and pressure. c-BN and metastable w-BN can be stabilized, but require extreme temperature (1730-3230 °C) and pressure (5-18 GPa) condition. 1 The equilibrium phase diagram of BN depicts that the stabilization of w-BN requires either c-BN or h-BN as the starting phase and may be difficult to synthesize in pure form. 2 Observation of synthetic w-BN, converted from h-BN at pressure of 11.5 GPa and temperature of 2000K, was first reported in 1963 by Bundy and Wentorf Jr. 3 Subsequently, Various methods e.g., static high-pressure, shock-wave compression method, direct conversion from h-BN have been reported. 4-8 Experimental investigation into the properties of w-BN are scarce because of the difficulty in synthesizing sufficiently large and pure crystals of it. Recently, synthesis of 2 mm diameter and 350 µm thick w-BN crystals with 98% purity (h-BN is the residue phase) under direct conversion method involving high temperature (1500 °C) and pressure (4 GPa) was reported. 7 There are reports on the formation of w-BN and c-BN by thin film growth procedure. 9-13 Polycrystalline (2-20 µm grain size) w-BN film is deposited on amorphous C film by pulsed laser deposition. 11 Only c-BN thin film is deposited on Si (100) substrate by ion assisted pulse laser deposition at 400 °C and 10 -5 Torr. 12 Mixture of c-BN and w-BN has also been reported by PLD on WS2 and ReS2 template. 14 Two-dimensional (2D) layered h-BN (also called white graphene) has recently attracted considerable attention to improve the performance of graphene, other 2D materials such as MoS2and also being explored as an active material for the optoelectronic and energy applications. [15][16] On the other hand, c-BN and w-BN are attractive due to high hardness and the potential in electronic applications remains unexplored. 14,17 In the w-BN structure each atom is tetrahedrally