Single crystals of SnSe have gained considerable attention in thermoelectrics due to their unprecedented thermoelectric performance. However, polycrystalline SnSe is more favorable for practical applications due to its facile chemical synthesis procedure, processability, and scalability. Though the thermoelectric figure of merit (zT) of p‐type bulk SnSe polycrystals has reached >2.5, zT of n‐type counterpart is still lower and lies around ≈1.5. Herein, record high zT of 2.0 in n‐type polycrystalline SnSe0.92 + x mol% MoCl5 (x = 0–3) samples is reported, when measured parallel to the spark plasma sintering pressing direction due to the simultaneous optimization of n‐type carrier concentration and enhanced phonon scattering by incorporating modular nano‐heterostructures in SnSe matrix. Modular nanostructures of layered intergrowth [(SnSe)1.05]m(MoSe2)n like compounds embedded in SnSe matrix scatters the phonons significantly leading to an ultra‐low lattice thermal conductivity (κlat) of ≈0.26 W m−1 K−1 at 798 K in SnSe0.92 + 3 mol% MoCl5. The 2D layered modular intergrowth compound resembles the nano‐heterostructure and their periodicity of 1.2–2.6 nm in the SnSe matrix matches the phonon mean free path of SnSe, thereby blocking the heat carrying phonons, which result in low κlat and ultra‐high thermoelectric performance in n‐type SnSe.

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.

We present here the study of diffusion and intercalation mechanisms of Li-ion and Na-ion in titanium disulfide (TiS 2 ) films grown by atomic layer deposition (ALD). The layered TiS 2 has been explored here due to the interesting differences between the intercalation mechanisms of Li + and Na + . The ALD grown TiS 2 films further facilitate the study as this method provides compact and dense films with no polymer binder and carbon additives. The diffusion and intercalation processes are observed to depend on the ionic size and character of the solid electrolyte interphase. The increased capacity obtained for the present ALD synthesized samples is attributed to the enhanced anchoring ability of the TiS 2 films, which comprises of an extended nanowall network. The charge transfer resistance (R ct ) obtained from impedance data correlate well with the lithiation steps observed in the galvanostatic discharge-charge studies. At potentials where lithiation takes place, R ct value is observed to drop. This direct correlation is however, not observed between the R ct and sodiation potential. The diffusion coefficients, calculated using GITT and impedance methods, are observed to be independent of the type of Li-salts. However, the variation of diffusion coefficients with the lithiation/sodiation voltages are different. This is attributed to the combined differences in the ionic radii and phase formation. Intercalation-de-intercalation in to TiS 2 coated with alumina is also studied here. Coating with alumina results in a stable SEI. However, coating leads to higher R ct , lower D Li+ and poor capacity retention as a function of cycle number.

High resolution electron energy loss spectroscopy (HR-EELS) is utilized to probe the surface spin canting in nanoparticles of two technologically important magnetic materials, i.e. ). In addition, the role of Dzyaloshinskii-Moriya interaction in stabilizing the spin canting at the nanoparticle surface is discussed. The results demonstrate that HREELS can be a powerful technique to probe the magnetic structure in nano-dimensional systems and has advantages over neutron based techniques in terms of superior spatial resolution, site specific information and ease of sample preparation.3

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

An alternative approach to image simulation in high resolution transmission electron microscopy (HRTEM) is introduced after a comparative analysis of the existing image simulation methods. The alternative method is based on considering the atom center as an electrostatic interferometer akin to the conventional off-axis electron biprism within few nanometers of focus variation. Simulation results are compared with the experimental images of 2D materials of MoS2, BN recorded under the optimum combination of third order spherical aberration C s = − 35 μm and defocus Δ f = 1, 4, and 8 nm and are found to be in good agreement.

Quantitative atom counting of Zn and O atoms in zinc oxide(ZnO)epitaxial thin film by three different routes; reconstruction of phase from side and central band of atomic resolution off-axis and in-line electron holography are presented. It is found that the reconstructed phase from both side and central band and corresponding atom number for both Zn (Z = 30) and O (Z = 8) atom columns are in close agreementalong with the systematic increase in thickness for thinner sample area.However, complete disagreement is observed for thethicker sample area. On the other hand,the reconstructed phase obtained via in-line holography showsno systematic change with thickness.Phase detection limits and atomic model used to count the atoms are discussed.Corresponding author e-mail address: 2 I.