Chemical state

About: Chemical state is a research topic. Over the lifetime, 2378 publications have been published within this topic receiving 78183 citations.

Charge Transfer and Molecular Orientation of Tetrafluoro-tetracyanoquinodimethane on a Hydrogen-Terminated Si(111) Surface Prepared by a Wet Chemical Method

Abstract: We investigated the chemical state and molecular orientation of 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F4-TCNQ) adsorbed on a hydrogen-terminated Si(111) (1 × 1) surface using transmission infrared (IR) spectroscopy. We deposited F4-TCNQ molecules on H−Si(111) by a wet chemical method. Similar to evaporated F4-TCNQ molecules on various substrates in vacuum, we observed anionized F4-TCNQ on the H−Si(111) substrate. The incident angle dependence of the IR spectra reveals that this F4-TCNQ anion lies flatly on the surface. On the other hand, minority neutral F4-TCNQ species assume random orientation, judging from the comparison between s- and p-polarized IR spectra. We conclude that the first layer on the H−Si surface is a flat-lying anion species and the upper layers consist of randomly oriented neutral molecules.

Substitution mechanisms in In-, Au-, and Cu-bearing sphalerites studied by X-ray absorption spectroscopy of synthetic compounds and natural minerals

Abstract: Sphalerite is the main source of In – a ‘critical’ metal widely used in high-tech electronics. In this mineral the concentration of In is commonly correlated directly with Cu content. Here we use X-ray absorption spectroscopy of synthetic compounds and natural crystals in order to investigate the substitution mechanisms in sphalerites where In is present, together with the group 11 metals. All the admixtures (Au, Cu, In) are distributed homogeneously within the sphalerite matrix, but their structural and chemical states are different. In all the samples investigated In3+ replaces Zn in the structure of sphalerite. The In ligand distance increases by 0.12 A and 0.09–0.10 A for the 1st and 2nd coordination shells, respectively, in comparison with pure sphalerite. The In–S distance in the 3rd coordination shell is close to the one of pure sphalerite. Gold in synthetic sphalerites is coordinated with sulfur (NS = 2.4–2.5, RAu–S = 2.35 ± 0.01 A). Our data suggest that at high Au concentrations (0.03–0.5 wt.%) the Au2S clusters predominate, with a small admixture of the Au+ solid solution with an Au–S distance of 2.5 A. Therefore, the homogeneous character of a trace-element distribution, which is commonly observed in natural sulfides, does not confirm formation of a solid solution. In contrast to Au, the presence of Cu+ with In exists only in the solid-solution state, where it is tetrahedrally coordinated with S atoms at a distance of 2.30 ± 0.03 A. The distant coordination shells of Cu are disordered. These results demonstrate that the group 11 metals (Cu, Ag and Au) can exist in sphalerite in the metastable solid-solution state. The solid solution forms at high temperature via the charge compensation scheme 2Zn2+↔Me++Me3+. The final state of the trace elements at ambient temperature is governed by the difference in ionic radii with the main component (Zn), and concentration of admixtures.

Diffusion of ion‐implanted In and Tl in SiO2

Abstract: The diffusion of In and Tl implanted into SiO2 has been investigated by means of Rutherford backscattering spectrometry. The diffusion of these elements is shown to be strongly dependent on their chemical state in SiO2. By combining these results with previous results for Ga, a general model has been formulated which describes the incorporation and diffusion of Group III elements in SiO2. The most important parameter of this model is the valence state of these elements in SiO2. In their trivalent state these elements are incorporated on Si sites of the SiO2 network, where they are virtually immobile. On the other hand, interstitial monovalent Group III ions are observed to show rapid diffusion. In addition to this, there is a second independent diffusion process, which is attributed to interstitial migration of InOH or TlOH molecules. After high‐temperature annealing of SiO2 covered with Si3N4, the In and Tl diffusion profiles exhibit a peak at the SiO2‐Si interface. This segregation is tentatively explained by stress relief at the SiO2‐Si interface.