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Register a new userAdsorption of metal impurities on H-terminated Si surfaces and their influence on the wet chemical etching of Si
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We use first-principles methods to investigate the adsorption of Cu, Pb, Ag, and Mg onto a H-terminated Si surface. We show that Cu and Pb can adsorb strongly while Ag and Mg are fairly inert. In addition, two types of adsorption states are seen to exist for Pb. We also study the clustering energetics of Cu and Pb on the surface and find that while Cu clusters eagerly, Pb may prefer to form only small clusters of a few atoms. This kind of behavior of impurities is incorporated in kinetic Monte Carlo simulations of wet etching of Si. The simulation results agree with experiments supporting the idea that micromasking by Cu clusters and Pb atoms is the mechanism through which these impurities affect the etching process.
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We study strain relaxation and surface damage of GaN nanopillar arrays fabricated using inductively coupled plasma (ICP) etching and post etch wet chemical treatment. We controlled the shape and surface damage of such nanopillar structures through selection of etching parameters. We compared different substrate temperatures and different chlorine-based etch chemistries to fabricate high quality GaN nanopillars. Room temperature photoluminescence and Raman scattering measurements were carried to study the presence of surface defect and strain relaxation on these nanostructures, respectively. We found that wet KOH etching can remove the side wall damages caused by dry plasma etching, leading to better quality of GaN nanopillars arrays. The Si material underneath the GaN pillars was removed by KOH wet etching, leaving behind a fine Si pillar to support the GaN structure. Substantial strain relaxations were observed in these structures from room temperature Raman spectroscopy measurements. Room temperature Photoluminescence spectroscopy shows the presence of whispering gallery modes from these the nano disks structures.
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Adsorption geometry and stability of organic molecules on surfaces are key parameters that determine the observable properties and functions of hybrid inorganic/organic systems (HIOSs). Despite many recent advances in precise experimental characterization and improvements in first-principles electronic structure methods, reliable databases of structures and energetics for large adsorbed molecules are largely amiss. In this review, we present such a database for a range of molecules adsorbed on metal single-crystal surfaces. The systems we analyze include noble-gas atoms, conjugated aromatic molecules, carbon nanostructures, and heteroaromatic compounds adsorbed on five different metal surfaces. The overall objective is to establish a diverse benchmark dataset that enables an assessment of current and future electronic structure methods, and motivates further experimental studies that provide ever more reliable data. Specifically, the benchmark structures and energetics from experiment are here compared with the recently developed van der Waals (vdW) inclusive density-functional theory (DFT) method, DFT+vdW$^{mathrm{surf}}$. In comparison to 23 adsorption heights and 17 adsorption energies from experiment we find a mean average deviation of 0.06 AA{} and 0.16 eV, respectively. This confirms the DFT+vdW$^{mathrm{surf}}$ method as an accurate and efficient approach to treat HIOSs. A detailed discussion identifies remaining challenges to be addressed in future development of electronic structure methods, for which the here presented benchmark database may serve as an important reference.
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