L. Meier

The adsorption of cyclic (alkyl) (amino) carbenes on the monohydride Si(001) surface is explored within density-functional theory. Two different adsorption mechanisms are investigated: the carbene insertion in Si–H bonds and the binding to a surface defect with missing hydrogen. The relative stability of these configurations depends on the hydrogen chemical potential, i.e., the surface preparation conditions as well as on the molecular side groups. The latter are also found to decisively influence the molecular diffusion. Some adsorption configurations are found to give rise to electronic states within the silicon bulk band gap. A sizable reduction of the work function is found upon molecular adsorption.

The band alignment and the electronic states at the GaInP/AInP(001) interface are explored with (hybrid) density functional theory. Thereby, CuPt-type ordered crystals are focused. For the most stable interface, valence and conduction band offsets of 0.04 and −0.58 eV, respectively, are predicted. No interface states occur within the fundamental gap. Generally, the results support the validity of natural band offsets and demonstrate a minor influence of strain and local bonding scenarios on the band alignment.

Hydrogen embrittlement poses a significant challenge in various engineering applications. In this context, the iron/hydrogen system serves as a crucial prototype for examining the interaction between hydrogen and steel. Despite the critical importance of this topic, there is a notable lack of knowledge regarding the influence of surface characteristics on the penetration of hydrogen into materials. To address this gap, we have conducted an extensive review of the existing literature, particularly focusing on how different surface orientations of body-centered cubic (bcc) iron affect the adsorption, diffusion, and subsequent penetration of hydrogen into an iron crystal. The review primarily focuses on computational methods, incorporating experimental data for comparative analysis wherever feasible. This comprehensive synthesis of scattered information leads to several key conclusions. First, there is a systematic relationship between surface geometry and adsorption energy that has previously been overlooked. Second, bulk diffusion characteristics are recovered just a few atomic layers beneath the surface, emphasizing the importance of the initial surface layers in determining initial penetration. Third, penetrating through the surface layers is generally more challenging than further diffusion through bulk iron, with the specifics heavily dependent on the surface orientation. Studies on high-index surfaces are limited. We identify this as an area needing further research, and this review provides a solid foundation for such studies.

This work has been performed as part of the NOHENTRY project, funded by the Energy Transition Fund (Energietransitiefonds) of the Directorate-General Energy (Algemene Directie Energie) of the Federal Public Service for the Economy (FOD Economie) of Belgium. S.C. acknowledges financial support from OCAS NV by an OCAS-endowed chair at Ghent University. The computational resources and services used in this work were provided by the VSC (Flemish Supercomputer Center), funded by the Research Foundation - Flanders (FWO) and the Flemish Government - department EWI.