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Abstract: Silicon nanowires (SiNWs) were grown on Si(100) and Si(111) substrates by chemical vapour deposition (CVD) via the vapour–liquid–solid (VLS) mechanism with small gold particles used as seeds. In order to control the diameter of nanowires, their density on the substrate and their orientation we controlled the size and the distribution of Au seed particles. This was accomplished using nanosphere lithography (NSL) by which regular arrays of Au nanoparticles can be generated. This allowed us to grow single-crystalline SiNWs perpendicular to the surface of Si(111) substrates. The SiNWs and their Au caps were studied with respect to their morphology and composition using TEM, HREM and EFTEM methods. Clusters of Au are observed along the surface of SiNWs and the existence of a thin Si film on gold particles capping the SiNWs is demonstrated. [Copyright &y& Elsevier]

The suitability of empirical potential molecular statics (MS) simulations to provide an approximate structural description of 90° glide set partial dislocation cores in GaAs is analyzed. This is of interest for investigation of the properties of dislocated nanostructures, which are too large for density functional theory simulations. In the MS method the atomic positions are iteratively relaxed by energy minimization, by using a Tersoff potential parametrization appropriate for nanostructures. We show that for the Ga terminated partial the resulting bond lengths of the atoms in the dislocation core agree within 5–10% with those of previous density functional theory studies, whereas a significant discrepancy appears in the case of the As terminated partial. • Accuracy of Tersoff potential based simulations of dislocations depends on their type. • Reasonable description of Ga terminated 90° partial dislocation core in GaAs. • Inaccurate description of As terminated 90° partial dislocation core in GaAs. [ABSTRACT FROM AUTHOR]

A novel printable die steel was computationally designed and experiemtnally validated for selective laser melting (SLM), utilizing the advantages of the rapid solidification processes. During gas atomization, nanoscale TiN particles are intended to be in situ precipitated at 1790 °C, nucleating δ-ferritic grains. Additionally, the chemical composition is adjusted to stabilize a complete δ-ferritic solidification via Scheil modeling to enhance the printability of the die steel. This work further introduces the concept of the matrix die steels aiming to dissolve solidification and primary carbides during solutionizing at a targeted temperature of 1100 °C. Thus, the C-content is reduced to 1.4 mol.-% (0.3 wt.-%) compared to the benchmark H13 die steel which contains 1.85 mol.-% (0.4 wt.-%). Even though a lower C-content is used, optimizing M 2 C driving force during tempering enables the die steel to achieve a peak hardness of 536 HV. Lastly, a superior thermal conductivity of 40 W m-1 K-1 is predicted at 450 °C for the BCC matrix of the printable matrix die steel. The material design is based on thermo-chemical models interfaced with thermodynamic calculations as implemented in the Calculated Phase Diagram (CALPHAD) method. [Display omitted] [ABSTRACT FROM AUTHOR]

Ordered Si nanopillar arrays have a great potential for e.g. photonic, sensing and electronic devices. In the present article, we investigate the tailoring of Si nanostructure geometries obtained on large areas by nanosphere lithography combined with metal-assisted wet-chemical etching. In particular, the formation of Si nanopencils and, as a new feature of metal-assisted chemical etching, of nanopillars with single and multiple constrictions is demonstrated, which is accomplished by varying the HF/H 2 O 2 ratio of the etching solution without modifying the noble metal film. As a result, it is possible to obtain defined constrictions in high aspect ratio Si nanopillars (length-to-diameter up to 27) with relative diameter reductions of up to around 0.6. Moreover, by controlled oxidation in water vapor nanoscale Si inclusions surrounded by an amorphous SiO 2 shell are obtained. The morphology and structure of these pillar arrays are analyzed by scanning and transmission electron microscopy, complemented by optical reflection measurements. For the pencil-shaped Si nanostructures a reflectivity lower than 3% is found in the visible and infrared wavelength ranges. Nanopillars with multiple constrictions exhibit a significantly reduced thermal conductivity due to phonon backscattering. Therefore, the presented method could be implemented in the large-scale fabrication of advanced thermoelectric devices. • MACE using a high H 2 O 2 concentration leads to a significant lateral etching rate. • Formation of Si nanopencils by two-stage MACE. • Formation of Si nanopillar constrictions by alternating MACE solutions. • Elongated Si nano-islands in SiO 2 by partial oxidation of constricted Si nanopillars. • Highest light absorption of nanocone or nanopencil patterned Si surfaces. [ABSTRACT FROM AUTHOR]