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We have formed SixGe1−x−ySny compounds on Si substrates by ion implantation and annealing and investigated their concentration profiles, crystallization, and optical properties. Ge and Sn ions were implanted in the range (2.5–10) × 1016 Ge/cm2 at 65 keV, and (1.0–4.0) × 1016 Sn/cm2 at 100 keV, resulting in a peak implant dose at a depth of 50 nm for both species. Epitaxially regrown SixGe1−x−ySny layers (110 nm thick) were produced with Ge and Sn contents that allowed bandgap tuning in the (0.88–1.1) eV range. Shifts in photoelectron binding energies (Si 2p, Ge 3d, and Sn 3d) were consistent with ternary compound formation. Sn segregation was observed for annealing temperatures ≥600 °C. A significant increase in the optical absorption coefficient (×104 cm−1 for λ = (800–1700) nm) was observed for SiGe, SiSn, and SiGeSn alloys, with SiGeSn having coefficients several orders of magnitude higher than for Si. Contributions of segregated Sn to these properties were observed. Metastable SixGe1−x−ySny layers were achieved, which may point to a promising route to mitigate Sn incorporation challenges for near-infrared detectors. [ABSTRACT FROM AUTHOR]

The elevation of cytokine levels in body fluids has been associated with numerous health conditions. The detection of these cytokine biomarkers at low concentrations may help clinicians diagnose diseases at an early stage. Here, we report an asymmetric geometry MoS2 diode-based biosensor for rapid, label-free, highly sensitive, and specific detection of tumor necrosis factor-α (TNF-α), a proinflammatory cytokine. This sensor is functionalized with TNF-α binding aptamers to detect TNF-α at concentrations as low as 10 fM, well below the typical concentrations found in healthy blood. Interactions between aptamers and TNF-α at the sensor surface induce a change in surface energy that alters the current-voltage rectification behavior of the MoS2 diode, which can be read out using a two-electrode configuration. The key advantages of this diode sensor are the simple fabrication process and electrical readout, and therefore, the potential to be applied in a rapid and easy-to-use, point-of-care, diagnostic tool. Detection of cytokine biomarkers has the potential to aid in diagnosis and treatment of different diseases. Here, the authors report on the creation of an asymmetric geometry MoS2 diode-based biosensor for the detection of TNF-α as a model biomarker in a proof of concept study. [ABSTRACT FROM AUTHOR]

The coupling of semiconductor quantum dots (QDs) to the surface plasmon (SP) modes of nanohole arrays in a metal film is described. The maximum enhancement occurred when the resonance from the nanohole array matched the QD photoluminescence spectrum.

We report spin transport in electrodeposited Fe/n-GaAs tunnel diodes via three-terminal Hanle measurements. For temperatures between 20K and 150 K, the spin resistance was up to 20 times higher than expected from theoretical calculations and 1000 times larger compared to a vacuum-deposited counterpart. This higher spin resistance was correlated with a higher contact resistance, and a higher concentration of oxygen impurities in the electrodeposited Fe film and interface, as detected via x-ray photoelectron and Auger spectroscopies, and inferred from Fe film nucleation rates. These results can be explained via a small effective tunnel-contact area of 5%, but extra spin filtering via interfacial states or magnetic oxide layers cannot be ruled out. The spin diffusion times (8.5 ± 0.4 ns to 1.8 ± 0.4 ns, for 20K to 150 K) extracted from Lorentzian fits were in good agreement with values obtained from earlier 4-terminal Hanle measurements (7.8 ± 0.4 ns to 3.2 ± 0.4 ns, for 25K to 77 K), both 10 times slower than reported vacuum-deposited contacts. [ABSTRACT FROM AUTHOR]

The ballistic transport and junction stability of epitaxial Au, grown on Si (111) and (001) substrates via electrodeposition, have been investigated as a function of Au thickness (6.7-14.1 nm). Scanning tunneling microscopy (STM) with ballistic emission electron microscopy (BEEM) showed hot electron transmission for diodes with Au thicknesses greater than 7 nm, whereas for thinner samples surface or interfacial oxidation meant that macroscopic current-voltage characteristics gave high barrier heights (0.8 eV) but no detectable BEEM transport at room temperature. Diodes that remained electrically stable for several months after exposure to air also show an atomically abrupt and epitaxial Au/Si interface via cross-sectional transmission electron microscopy. Degradation in rectifying diode properties through surface or interfacial reactions is indicated by poorer STM images and decreasing or no BEEM transmission, correlated with the formation of a continuous interfacial layer. [ABSTRACT FROM AUTHOR]

The structure of wurtzite and zinc blende InAs-GaAs (001) core-shell nanowires grown by molecular beam epitaxy on GaAs (001) substrates has been investigated by transmission electron microscopy. Heterowires with InAs core radii exceeding 11 nm, strain relax through the generation of misfit dislocations, given a GaAs shell thickness greater than 2.5 nm. Strain relaxation is larger in radial directions than axial, particularly for shell thicknesses greater than 5.0 nm, consistent with molecular statics calculations that predict a large shear stress concentration at each interface corner. [ABSTRACT FROM AUTHOR]

The development of ferroelectric properties in barium titanate (BaTiO[sub 3]) polycrystalline films has been investigated as a function of substrate type. The films were deposited by physical vapor deposition (PVD) onto different, Pt-coated substrates (magnesium oxide, thermally oxidized silicon, and sapphire) and annealed at temperatures from 725 to 1050 °C. Grain sizes from 50 to 200 nm were produced, with structural and dielectric properties that showed a marked transition from nonferroelectric to ferroelectric behavior across this range. Anneal temperatures below 950 °C result in films with grain sizes less than 150 nm, and ferroelectric properties that are strongly suppressed, regardless of the substrate. Observations for this temperature range include low dielectric constant (ε), no polarization hysteresis, and no peaks in the temperature dependence of the dielectric constant. The onset of ferroelectric behavior occurs for anneal temperatures above 950 °C, coinciding with the appearance of strong substrate effects on the dielectric properties. Such BaTiO[sub 3] films on Pt/MgO show the largest dielectric constant, remnant polarization, and temperature dependence of ε, while films on Pt/sapphire exhibit the weakest of each of these properties. Films on Pt/barrier/Si exhibit dielectric properties with values in between that of films on Pt/MgO and Pt/sapphire. The dependence of BaTiO[sub 3] ferroelectric properties on the substrate is related to a combination of the BaTiO[sub 3] grain and size orientation, determined partly by the underlying Pt surface, and to the thermal expansion properties of the substrate. However, these factors only influence the BaTiO[sub 3] dielectric properties for those films that exhibit ferroelectric properties. In this way, the anneal temperature and substrate dependence of the films are linked. © 2003 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Electrodeposited thin films of Fe on GaAs with (100), (110) and (111) orientation are studied by using x-rays, transmission electron microscopy and magnetization measurements. The studies have shown that the uniaxial anisotropy arises from the regions of coalescence of the islands of nucleation or from a density of bulk twins.

The article explains the synthesis and optical and spectroscopic properties of a new generation of sensors, which are made from the gold films and are based on the phenomenon of optical transmission. These sensors are shown to be widely used in chemical sensing and several other applications.

A demonstration showing that arrays of nanoholes could be used to fabricate analytical devices for enhanced fluorescence measurements, with fluorescence enhancement through surface plasmons (SP) resonance being tunable through the periodicity of the array is presented. Results suggest that arrays of nanoholes in Au films at resonance could improve both the sensitivity and the limit of detection of fluorescence-based analysis.

Single-crystalline. body-centered-cubic Fe films are electrodeposited on n-GaAs (001)-(111), and (110)-oriented substrates from ferrous ammonium sulphate [Fe(NH4)2SO4] electrolytes. The purity of the epitaxial Fe films and the quality of the epitaxy as indicated by x-ray diffraction and transmission electron microscopy is comparable to vacuum-deposited films.

Ferroelectric properties in barium titanate polycrystalline films were studied. Grain sizes from 50 to 200 nm with properties shifting from nonferroelectric to ferroelectric behavior were observed, when the films were deposited onto Pt-coated substrates and annealed at temperatures from 725 to 1050 degrees C.