Integration, gap formation, and sharpening of III-V heterostructure nanowires by selective etching

Epitaxial growth of heterostructure nanowires allows for the definition of narrow sections with specific semiconductor composition. The authors demonstrate how postgrowth engineering of III-V heterostructure nanowires using selective etching can form gaps, sharpening of tips, and thin sections simultaneously on multiple nanowires. They investigate the potential of combining nanostencil deposition of catalyst, epitaxial III-V heterostructure nanowire growth, and selective etching, as a road toward wafer scale integration and engineering of nanowires with existing silicon technology. Nanostencil lithography is used for deposition of catalyst particles on trench sidewalls and the lateral growth of III-V nanowires is achieved from such catalysts. The selectivity of a bromine-based etch on gallium arsenide segments in gallium phosphide nanowires is examined, using a hydrochloride etch to remove the III-V native oxides. Depending on the etching conditions, a variety of gap topologies and tiplike structures are observed, offering postgrowth engineering of material composition and morphology

A uniform measurement expression for cross method comparison of nanoparticle aggregate size distributions

The European Commission’s recent recommendation for a definition nanomaterials (2011/696/EU) will require characterisation of materials used in regulated consumer products in terms of number based particle concentration and size distribution. When adopted under food regulations, the definition will be applicable to those food additives that contain a fraction of the particles that are smaller than 100 nm at or above the threshold of 50% in terms of particle number based size distribution. In the view of this we have performed a comparative evaluation of the different analytical methods for the measurement of number based particle size distributions. This study has used synthetic amorphous silica as a an example nano-structured material already widely applied in food processing, and provides a comparison of the six methods deemed suitable for the purpose: scanning electron microscopy in both high vacuum and liquid cell setup; gas-phase electrophoretic mobility molecular analyser; centrifugal liquid sedimentation; nanoparticle tracking analysis; and asymmetric flow field flow fractionation on-line combined with plasma mass spectrometry. The results have highlighted an important question in relation to the effects that the particle shape, chemical composition and agglomeration/aggregation state may have on the size measurement accuracy of the different methods. We propose mass equivalent diameter (MED) as a uniform expression of particle size distribution measurements for aggregated particulate materials allowing comparison of the measurements from different analytical methods. We have detailed how the MED for aggregated materials, such as synthetic amorphous silica, can be derived from measurements by the six methods. This approach enables unambiguous interpretation and comparison of the results between different research studies on nanoparticles and reference materials, and is our best suggestion for a common measure of particle size distributions.JRC.D.2-Standards for Innovation and sustainable Developmen

In Situ TEM Creation and Electrical Characterization of Nanowire Devices

We demonstrate the observation and measurement of simple nanoscale devices over their complete lifecycle from creation to failure within a transmission electron microscope. Devices were formed by growing Si nanowires, using the vapor-liquid-solid method, to form bridges between Si cantilevers. We characterize the formation of the the nature of the connection depends on the flow of heat and V contact between the nanowire and the cantilever, showing that electrical current during and after the moment of contact. We measure the electrical properties and high current failure characteristics of the resulting bridge devices in situ and relate these to the structure. We also describe processes to modify the contact and the nanowire surface after device formation. The technique we describe allows the direct analysis of the processes taking place during device formation and use, correlating specific nanoscale structural and electrical parameters on an individual device basis