The properties of native oxides on different chemically etched GaAs (100) surfaces were investigated by Auger electron spectroscopy (AES) and x-ray photoelectron spectroscopy (XPS) analyses. The thickness and composition of native oxides depended not only on the kind but also on the sequence of chemical solutions used, and continuous etching was the most effective method for reducing surface oxide. It was also found that the unetched (just polished) wafer had a Ga-rich surface, the H2SO4 mixture-etched wafer had an As rich surface, and the NaOH mixture-etched and the continuously etched wafer had a nearly stoichiometric surface. All the surfaces of measured wafers were As-oxide rich. To understand the mechanism of chemical etching and the surface state of differently treated wafers, AES data were combined with XPS data. Thus the surface state was estimated and a model for native oxidation process was proposed. These results were explained by the pH-dependent solubility of Ga, As, and their oxides, and the reactivity of As in atmosphere after etching.

The growth of facets and the generation of twins on (100) VGF (vertical gradient freeze technique) grown GaAs were investigated using DSL (diluted Sirtl-like etchant with light) photoetching and transmission X-ray topography. Due to the polarity of the (1 11) plane in GaAs, As facets are larger and more irregular than Ga facets and twins always occur on As facets. Twins are initiated at the change of boundary condition which IS affected by temperature gradient and crucible shape. The mechanism of twin generation is explained by considering the edge concavity at the solid-liquid interface and the supercooling required for initial nucleation of a facet. Twins are more often produced in Si-doped crystals than undoped ones due to the constitutional supercooling.

© 2020 Elsevier B.V. A three-dimensional (3D) framework of covalently-bonded layers of bimetallic inorganic oxide, CuMoO4, interlinked by electron-rich organic ligands, which is semiconducting and also ferromagnetic, has been prepared. The structure [Cu(3,8-phenanthroline)0.5MoO4] consists of molybdate tetrahedra corner-shared with clusters of edge-sharing {CuO5N} octahedra. The injection of charge carriers into the inorganic layers by phenanthroline induces different magnetic orderings at different temperatures, orderings which are not found in the structurally-similar [Cu(4,4ʹ-bipyridine)0.5MoO4]. The temperature dependence of the susceptibility shows two low temperature magnetic transitions: weakly ferromagnetic-coupled spins below 15 K coexisting with an antiferromagnetic structure below 10 K. Specific heat capacity shows a finite ground-state electronic specific heat coefficient, γ = 0.094 J/mol·K2, that is higher than that of the bipyridine counterpart (0.068 J/mol·K2), confirming an increase in the electronic density-of-states in the phenanthroline system.