ZnSe nanotrenches: formation mechanism and its role as a 1D template

High-resolution transmission electron microscopy was used to characterize the microstructures of ZnSe nanotrenches induced by mobile Au-alloy droplets. The contact side interfaces between the AuZnδ alloy droplets and the ZnSe as well as the four side walls of the resulting <011>-oriented nanotrenches were found all belong to the {111} plane family, with the front and back walls being the {111}A planes while the other two side walls being the {111}B planes. These findings offer a deeper understanding on the formation mechanism of the nanotrenches. Pure Au nanodashes were formed upon further deposition of Au on the nanotrenches

Robust estimation of bacterial cell count from optical density

Optical density (OD) is widely used to estimate the density of cells in liquid culture, but cannot be compared between instruments without a standardized calibration protocol and is challenging to relate to actual cell count. We address this with an interlaboratory study comparing three simple, low-cost, and highly accessible OD calibration protocols across 244 laboratories, applied to eight strains of constitutive GFP-expressing E. coli. Based on our results, we recommend calibrating OD to estimated cell count using serial dilution of silica microspheres, which produces highly precise calibration (95.5% of residuals &lt;1.2-fold), is easily assessed for quality control, also assesses instrument effective linear range, and can be combined with fluorescence calibration to obtain units of Molecules of Equivalent Fluorescein (MEFL) per cell, allowing direct comparison and data fusion with flow cytometry measurements: in our study, fluorescence per cell measurements showed only a 1.07-fold mean difference between plate reader and flow cytometry data

Tight-binding approach to electronic structure of carbon nanotubes

The electronic structure and optical properties of single-wall carbon nanotubes (SWCN's) have been studied using a nearest-neighbor empirical tight-binding model. Hybridization of the σ, π, π* and σ* states of the graphene network is shown to be as important as zone-folding effects in determining the metallicity of small radius carbon nanotubes. The energy dispersion relations are further used to calculate the imaginary part of the dielectric function, which can be directly related to the experimental absorption spectrum

MBE grown Fe-based nanostructures

Interest in magnetic nanostructures has increased rapidly because of their potential applications in a number of magnetic nanotechnologies such as high-density magnetic recording media, magnetic field sensors, magnetic nanoprobes for spin-polarized microscopy and cell manipulation in biomedical technology. Successful incorporation of ferromagnetic nanostructures in semiconductors may open a new area in spintronic applications. In this study, two kinds of Fe-based nanostructures were grown by the molecular beam epitaxy (MBE) technique, namely, Fe quantum dots (QDs) and Fe nanowires (NWs). For Fe QDs, a multilayer magnetic QD sample containing 5 layers of Fe QDs embedded in 6 layers of ZnS spacer was grown on a GaP(100) substrate. High resolution transmission electron microscopy (HRTEM) observations reveal that the Fe QDs are single crystalline with spherical shape of diameters around 3 to 4 nm and area density of 1.5 × 1012 cm-2. Its zero-field cooled (ZFC) and field cooled (FC) curves measured at low field (100 Oe) show the magnetic relaxation effect with a blocking temperature around 26 K. The hysteresis loop measured at 5 K shows a coercivity of 83 Oe, confirming the slow relaxation process and coercivity enhancement attributed to the nanoparticle nature of the sample. To study the transport property of Fe QDs, a Au/ZnS/Fe-QDs/ZnS/n+-GaAs Schottky-barrier structure containing 5 layers of Fe QDs was fabricated on a n+-GaAs(100) substrate. Its current-voltage (I-V) characteristics measured from 5 to 295 K display negative differential resistance (NDR) for temperature ≤ 50 K, which is caused by the presence of Fe QDs. The highest peak-to-valley current ratio obtained at 5 K is as high as 15:1. Staircase-like I-V characteristic was also observed at low temperature in some devices fabricated from this structure. Possible mechanisms that can account for the observed unusual I-V characteristics in this structure were discussed. Two types of self-assembled Fe NWs were grown on ZnS/GaP(100) surface under high growth/annealing temperature. The Type-A Fe NWs orient along the ZnS[110] direction with irregular shape, while the type-B Fe NWs orient along either the ZnS[180] or [810] direction with seemingly straight shape. Detailed HRTEM and selected area diffraction (SAD) studies reveal that both types were single-crystalline with their elongated axis along the Fe<100> direction family possibly due to the fact that the easy axis of Fe is along this direction. We have proposed a mean-field model to explain the slight misalignment of the type-B Fe NWs. The I-V characteristic of a single type-B Fe NW measured at room temperature displays a straight line nature corresponding to a resistivity about 2.3 × 10-7Ωm

Ni3Se4/ZnSe Heterostructured Nanowires Grown by Molecular Beam Epitaxy

Ni3Se4/ZnSe heterostructured nanowires with a sharp interface are fabricated using nanocatalysts generated on an annealed Au/Ni/ZnSe trilayer. The top Ni3Se4 section acts as an efficient catalyst to assist ultrafast growth of the bottom ZnSe section. A greater understanding of how the effective area and size of the catalyst affect the growth rate and preferred axial orientation of ultrathin nanowires is obtained. © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

Rocksalt MgS solar blind ultra-violet detectors

Studies using in-situ Auger electron spectroscopy and reflection high energy electron diffraction, and ex-situ high resolution X-ray diffraction and electron backscatter diffraction reveal that a MgS thin film grown directly on a GaAs (100) substrate by molecular beam epitaxy adopts its most stable phase, the rocksalt structure, with a lattice constant of 5.20 angstrom. A Au/MgS/n(+)-GaAs (100) Schottky-barrier photodiode was fabricated and its room temperature photoresponse was measured to have a sharp fall-off edge at 235 nm with rejection of more than three orders at 400 nm and higher than five orders at 500 nm, promising for various solar-blind UV detection applications. Copyright 2012 Author(s). This article is distributed under a Creative Commons Attribution 3.0 Unported License. [http://dx.doi.org/10.1063/1.3690124