Valency

About: Valency is a research topic. Over the lifetime, 1632 publications have been published within this topic receiving 26141 citations.

Comment on “Characterization of As-doped, p-type ZnO by x-ray absorption near-edge structure spectroscopy: Theory”

Abstract: In a recent letter, S. Limpijumnong et al. have simulated the partial density of states for As atoms and compared their simulated results with the x-ray absorption near-edge structure XANES spectrum at As K edge of the ZnO:As film and concluded that our experimental results support their model. The conclusion drawn in Ref. 1 contradicts the use of XANES as a chemical speciation and valency identification technique and hence our experimental interpretation shown in Ref. 2. This spectroscopy is based on the fact that the binding energy of an element varies with its valency and has been routinely used in semiconductors to identify the valency of dopants or reactants. The XANES at As K edge of the As-doped, n-type ZnO Fig. 1 in Ref. 2 reveals As in the oxidation state of 5+ As5+ , signifying the formation of As–O bonding As occupying Zn site and also the presence of 3− oxidation state of As As3− , thereby confirming As–Zn bonding As occupying O site in the as-grown film. However, after rapid thermal annealing RTA , As is only in 3− state indicating that As occupies O sites. This apparently suggests that there is a change in the chemical environment implying that both these films possess different electronic structures. In the as-grown state we have arsenic oxide which is absent after RTA. Therefore, we argued the presence of As3− could be responsible for p-type behavior and compensation of electrons takes place only after RTA. Both the oxidation states of As identified from As K edge and spectral changes at O K edge support such argument. Above approach was followed previously by Fons et al. who used XANES at Cu and N K edges to investigate respectively the valency of Cu in Cu doped epitaxial ZnO films and N doping in ZnO. In a similar way, Cheong et al. used XANES at As K edge to identify the valency of the residual site of As in oxidized AlxGa1−xAs and Rodriguez et al. used XANES at N and O K edges to understand the reaction of NO2 with Zn and ZnO. Limpijumnong et al. projected that our results are in good agreement to support their model just based on the simulation of one particular spectrum and ignored many open questions concerning charge state and all possible defect models. A careful observation of Figs. 2 b –2 d in Ref. 1 shows that As on oxygen defect has unfilled states closer to the valency band maximum than the defect complex AsZn-2VZn and also the As on O defect is relatively shallower. Apart from this, it is not clear why a neutral AsZn-2VZn defect should be responsible for As K edge XANES spectrum of p-type ZnO and also if the defect cluster is neutral, it would result in deep level defect which may not be responsible for making p-type ZnO. In our opinion, there are still many unknowns in their models to resolve, such as the question whether electrically active As acceptors are due to AsO or AsZn-2VZn complex. In other words, it is difficult to account for the type of defects in n-type and p-type ZnO and also to suggest a universal model for these two different chemical compounds and the changes that occur in going from n-type to p-type behavior due to RTA. We believe that confirmation by an experimental tool is more advantageous to understand the underlying physics and the local electronic structure around the acceptor in ZnO.

Atomic excitation and ionization by beta-decay

Abstract: Excitation and ionization probabilities consequent on Β-decay are shown to be predicted satisfactorily for the elements from Li to Kr by the use of one-electron hydrogen-like functions and Slater screening contants. Numerical calculations are presented for the Β-decay of all the valency states of the elements from Li to Kr.

Electronic structures and properties of carbonitride and binary carbide solutions based on titanium and zirconium

Abstract: Experimental results are presented on the metal emission band derived from the valency band of crystals of ZrC-ZrN solid solutions, in particular the MIV, V band of Zr, in a series of intermediate zirconium carbonitrides, where the valency-electron concentration increases monotonically from 8 to 9 electrons per cell with unaltered lattice geometry and a slightly varying lattice parameter. The ZrC-TiC system represents another type of solid solution (MeIV-MeIV-X), in which the number of valency electrons remains unchanged throughout the region of continuous solid-state solubility.

Aromatic co-polyamide for use in fibres and films

Abstract: An aromatic copolyamide contains repeating units of formulae (I), (II) -(OC-Ar -CO-NH-Ar -NH)- (II) and -(OC-Ar -CO-NH-Ar -NH)- (III). Ar , Ar , Ar , Ar = divalent aromatic gps. with their valency bonds in p-position or in a coaxial or parallel position comparable to this; Ar = divalent aromatic gp., different from Ar , with valency bonds in p-position or in a comparable coaxial or parallel position to each other, or is a divalent aromatic gp. with valency bonds in m-position to each other or in a comparably angled position; Y = -O-, -S- or -NR -; R = monovalent organic gp., or esp. H; the Ar gps. may be substituted with 1 or 2 gps. inert to carboxylic acid chlorides.