Discovering electron transfer driven changes in chemical bonding in lead chalcogenides (PbX, where X = Te, Se, S, O)

Understanding the nature of chemical bonding in solids is crucial to comprehend the physical and chemical properties of a given compound. To explore changes in chemical bonding in lead chalcogenides (PbX, where X = Te, Se, S, O), a combination of property-, bond breaking- and quantum-mechanical bonding descriptors have been applied. The outcome of our explorations reveals an electron transfer driven transition from metavalent bonding in PbX (X = Te, Se, S) to iono-covalent bonding in beta-PbO. Metavalent bonding is characterized by adjacent atoms being held together by sharing about a single electron and small electron transfer (ET). The transition from metavalent to iono-covalent bonding manifests itself in clear changes in these quantum-mechanical descriptors (ES and ET), as well as in property-based descriptors (i.e. Born effective charge, dielectric function, effective coordination number (ECON) and mode-specific Grueneisen parameter, and in bond breaking descriptors (PME). Metavalent bonding collapses, if significant charge localization occurs at the ion cores (ET) and/or in the interatomic region (ES). Predominantly changing the degree of electron transfer opens possibilities to tailor materials properties such as the chemical bond and electronic polarizability, optical band gap and optical interband transitions characterized by the imaginary part of the dielectric function. Hence, the insights gained from this study highlight the technological relevance of the concept of metavalent bonding and its potential for materials design

Interface engineering and nanoscale characterization of Zn(S,O) alternative buffer layer for CIGS thin film solar cells

The buffer layers in Cu(In,Ga)Se2 solar cells play a crucial role in device performance, although their thickness is only a few tens of nanometers. Moreover, often Zn(S,O) alternative buffer layers have been studied in view of their structure, band alignment, and optical properties, but not much work exists on their nanoscale chemical properties. This work focuses on the chemical characterization of Zn(S,O) using x-ray photoelectron spectroscopy for determination of the Zn(S,O) and Cu(In,Ga)Se2 depth composition, and atom probe tomography for probing the nano-scale chemical fluctuations at the Zn(S,O)/Cu(In,Ga)Se2 interface. The Zn(O,S) buffer layer was deposited by RF magnetron sputtering. The aim is to study the nanoscale concentration changes and atomic interdiffusion between CIGS and Zn(S,O) after sputter deposition at room temperature and after post-deposition heat treatment at 200°C. © 2015 IEEE

The investigation of boron-doped silicon using atom probe tomography

International audienc

Clustering and nearest neighbour distances in atom probe tomography: The influence of the interfaces

International audienceThe statistical 1NN method is an elegant way to derive the composition of small B-enriched clusters in a random AB solid solution from 3D atomic fields. An extension of this method is proposed that includes the contribution of interface region and provides an estimate of the core composition of clusters. This model is applied to boron-implanted silicon containing boron-enriched clusters. A comparison with the previous model is performed. This new approach gives relevant information, i.e. the core composition of clusters and the cluster-matrix interface width