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We report on the observation of the rich variety of crystallographic phase formation in a RexMo1 – xS2 alloy for x < 0.5. For x < 0.23, no low dimensional superstructural modulation is observed and inter cation hybridization remains discrete, forming dimers to tetramers with increasing Re concentration. For x > 0.23, superstructural modulation 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 result in the rich variety of low dimensional superstructural modulation as directly revealed by high resolution transmission electron microscopy. These layered alloy systems may be useful for various energy and novel device applications. [ABSTRACT FROM AUTHOR]

We present quantitative counting of Zn and O atoms in zinc oxide epitaxial thin film by different routes; reconstruction of phase from the side and central bands of atomic resolution off-axis and in-line electron holography. Results show that the reconstructed phase from both the side and the central bands and the corresponding number of Zn (Z = 30) and O (Z = 8) atoms are in close agreement with the systematic increase in the number of atoms for a sample area less than the extinction distance. However, complete disagreement is observed for the sample area more than the extinction distance. On the other hand, the reconstructed phase obtained via in-line holography shows no systematic change with thickness for the same sample. Phase detection limits and the atomic model used to count the atoms are discussed. [ABSTRACT FROM AUTHOR]

The origin of alternating wavy dark-bright stripe-like contrast in strain contrast transmission electron microscopy images of NiCo2O4 (NCO) epitaxial thin films grown by pulsed laser deposition has been investigated. The nanoscale stripe-like pattern is determined to be associated with coexisting rock salt (RS) and inverse spinel crystal phases. The presence of two different phases, not addressed in previous reports, is experimentally confirmed by both electron diffraction and high resolution transmission electron microscopy imaging. First principles based calculations, together with compressive strain present in the films, support the formation of such coexisting crystallographic phases in NCO. Similar microstructural patterns and RS structure are not observed in epitaxial films of two other oxides of the spinel family, namely, NiFe2O4 and CoFe2O4. A correlation between the coexisting structures and the macroscopic physical properties of NCO is discussed. [ABSTRACT FROM AUTHOR]

We report on the detailed microstructural features in a low thermal conductivity Sn1-xSbxTe (x = 0.04, 0.08, 0.15) alloy investigated by transmission electron microscopy and density functional theory calculation. A near theoretical minimum thermal conductivity is obtained for Sn0.85Sb0.15Te alloy composition containing distinct microstructures. The crisscross lines along {111} planes forming nano-scale structures have been identified as areas with Sb replacing both regular Sn sites and Te anti-sites. This leads to the modulation in the {111} inter-planar spacing (d111) and results in superstructure spots in the electron diffraction pattern. The formation of such structures is supported by theoretical calculation. In general, two different phases are observed in the system, one with Sb replacing the regular Sn sites and another with crisscross lines where Sb replaces both the Sn and Te sites. Theoretical calculation further reveals that while the areas with Sb at the regular site give rise to large thermo-power, the areas with Sb substituting regular and anti-sites combination forming a superstructure contribute towards low lattice thermal conductivity and the combined effect increases the zT to ~1. [ABSTRACT FROM AUTHOR]

We report on the various types of Peierls like two dimensional structural modulations and relative phase stability of 2H and 1T poly-types in the RexMo1-xS2 and RexW1-xS2 alloy system. Theoretical calculation predicts a polytype phase transition cross over at ~50 at. % of Mo and W in ReS2 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 are observed for RexMo1-xS2 and only one type of modulation is observed at the 50% RexW1-xS2 alloy system. The 50% alloy system is found to be a suitable monolithic candidate for metal semiconductor transition with minute external perturbation. ReS2 is known to be in the 2D Peierls distorted 1Td structure and forms a chain like superstructure. Incorporation of Mo and W atoms into the ReS2 lattice modifies the metal-metal hybridization between the cations and influences the structural modulation and electronic properties of the system. The results offer yet another effective way to tune the electronic structure and poly-type phases of this class of materials other than intercalation, strain, and vertical stacking arrangement. [ABSTRACT FROM AUTHOR]