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The melting and solidification of as-deposited and recrystallized Bi crystallites, which are deposited on highly oriented 002-graphite, are evaluated by using reflection high-energy electron diffraction (RHEED). During solidification, the Bi films have shown high amount of supercooling relative to [T.sub.0] of Bi and the amount of liquid supercooling is found to decrease linearly with the reciprocal of the average crystallite size.

Vanadium oxide (VO x ) thin films were deposited at various substrate temperatures ( T s ) by spray pyrolysis technique using 0.05 M vanadyl acetylacetonate precursor. V 4 O 9 films are formed at T s = 300 °C, while mixed V 2 O 5 phases are formed at higher T s (400 and 500 °C). Annealing in forming gas of V 4 O 9 films shows the formation of higher content of thermochromic VO 2 phase than V 2 O 5 films. V 4 O 9 films show little higher electric resistivity ( ρ ), higher temperature coefficient of resistance ( TCR ), and higher thermal carrier activation energy ( E a ) than V 2 O 5 films. Annealed VO x films show a 2–3 order of magnitude change in ρ , optical transmission switch of 19–39%, and higher E a than the as deposited films. Annealed films deposited at T s = 500 °C presents a high TCR of −4.6%K −1 . Optical absorption, electronic transitions, and energy gaps of the formed VO x phases have been discussed in relation to its electronic band structure. [ABSTRACT FROM AUTHOR]

Abstract: Melting behavior of as-deposited and recrystallized indium nanocrystals is studied using reflection high-energy electron diffraction in its transmission mode. Indium films with mean thickness ranging from 1.5 to 10 monolayers (ML) deposited on highly oriented graphite at different substrate temperatures are studied. Atomic force microscopy is used to study the crystal size and morphology of the as-deposited and recrystallized nanocrystals. As-deposited films are found to form shallow nanocrystals with a flat top surface of different shapes, while the recrystallized nanocrystals are formed in the more rounded polyhedral shape. The change in the diffraction pattern intensity with temperature is used to probe the melting of the nanocrystals. The melting point is found to be lower than that of the bulk for both types of films and extends over a temperature range due to nanocrystal size distribution. The as-deposited films show an end melting point nearly equal to that of the recrystallized films except for the 1.5-ML film which shows an end melting point ∼10 K lower than the recrystallized film. The deposition temperature is found to have a significant effect on the end melting point of as-deposited nanocrystals, while having a negligible effect on the end melting point of recrystallized nanocrystals. [Copyright &y& Elsevier]

Melting and solidification of indium nanocrystals grown on (002) highly oriented graphite is studied by reflection high-energy electron diffraction operating in a transmission mode through the outer shell of the nanocrystals. When recrystallized from the melt, evaporated indium grows as an ensemble of nanocrystals with particle size distribution that depends on the mean film thickness. Films with mean thickness from 0.5 to 34 ML are investigated. The intensity change of the diffraction pattern with temperature is used to probe the melting and solidification of the nanocrystals. The melting of indium nanocrystals starts at temperatures below the bulk melting temperature, depending on the size distribution of the nanocrystals. Melting continues over a temperature range extending up to that of bulk melting. The liquid skin model of melting and the homogenous melting model are shown to agree with the melting point size dependence. However, line profile analysis of the diffraction pattern shows a reduction in the crystalline volume within the probed shell at high temperatures. This indicates the formation of a liquid layer surrounding the nanocrystals and supports the liquid skin model. All films show supercooling by an amount that increases with the mean film thickness up to 6 ML and remains constant for films with larger mean thickness. [Copyright &y& Elsevier]

First principles calculations based on density functional theory (DFT) using TB-mBJ and SCAN + U methods were used to study the electronic and optical properties of the monoclinic VO 2 (M1) phase. TB-mBJ gives values of the energy gap (E g) and Δd || band splitting in agreement with experiments. Systematic investigation of SCAN + U, U varies from 0 to 10 eV, shows that agreement with experimental values of both E g and Δd || was achieved at U * = 5.75 eV. Moreover, TB-mBJ and SCAN + U * were able to reproduce frequency and polarization dependence of the optical constants that agree with the reported experimental results of the monoclinic VO2 (M1) phase. The high value of U needed to reproduce the experimental values of electronic and optical parameters of the monoclinic VO 2 (M1) phase is a strong indication that VO 2 is a Mott insulator and the Mott-Hubbard scheme plays an important role in the metal-insulator transition. • The electronic and optical properties of the insulating monoclinic VO 2 (M1) phase were studied using TB-mBJ and SCAN+ U. • The size of the energy gap (E g) and d || band splitting and some optical constants of the VO 2 (M1) phase were calculated. • TB-mBJ and SCAN+U gave E g and Δd|| band splitting values in agreement with experiments. • TB-mBJ and SCAN+U were able to predict the frequency and polarization dependence of n , a , ε 1 , ε 2 of the VO 2 (M1) phase. • The current calculations reveal that Mott-Hubbard electron correlation is dominant in the metal-insulator transition in VO 2. [ABSTRACT FROM AUTHOR]