Enhanced Gas Sensing by Individual SnO<sub>2</sub> Nanowires and Nanobelts Functionalized with Pd Catalyst ParticlesThe sensing ability of individual SnO(2) nanowires and nanobelts configured as gas sensors was measured before and after functionalization with Pd catalyst particles. In situ deposition of Pd in the same reaction chamber in which the sensing measurements were carried out ensured that the observed modification in behavior was due to the Pd functionalization rather than the variation in properties from one nanowire to another. Changes in the conductance in the early stages of metal deposition (i.e., before metal percolation) indicated that the Pd nanoparticles on the nanowire surface created Schottky barrier-type junctions resulting in the formation of electron depletion regions within the nanowire, constricting the effective conduction channel and reducing the conductance. Pd-functionalized nanostructures exhibited a dramatic improvement in sensitivity toward oxygen and hydrogen due to the enhanced catalytic dissociation of the molecular adsorbate on the Pd nanoparticle surfaces and the subsequent diffusion of the resultant atomic species to the oxide surface.
Thermal Conductivity Reduction and Thermoelectric Figure of Merit Increase by Embedding Nanoparticles in Crystalline SemiconductorsAtomic substitution in alloys can efficiently scatter phonons, thereby reducing the thermal conductivity in crystalline solids to the "alloy limit." Using In0.53Ga0.47As containing ErAs nanoparticles, we demonstrate thermal conductivity reduction by almost a factor of 2 below the alloy limit and a corresponding increase in the thermoelectric figure of merit by a factor of 2. A theoretical model suggests that while point defects in alloys efficiently scatter short-wavelength phonons, the ErAs nanoparticles provide an additional scattering mechanism for the mid-to-long-wavelength phonons.
Comparison of methods to quantify interface trap densities at dielectric/III-V semiconductor interfacesMethods to extract trap densities at high-permittivity (k) dielectric/III-V semiconductor interfaces and their distribution in the semiconductor band gap are compared. The conductance method, the Berglund intergral, the Castagné–Vapaille (high-low frequency), and Terman methods are applied to admittance measurements from metal oxide semiconductor capacitors (MOSCAPs) with high-k/In0.53Ga0.47As interfaces with different interface trap densities. The results are discussed in the context of the specifics of the In0.53Ga0.47As band structure. The influence of different conduction band approximations for determining the ideal capacitance-voltage (CV) characteristics and those of the MOSCAP parameters on the extracted interface trap density are investigated. The origins of discrepancies in the interface trap densities determined from the different methods are discussed. Commonly observed features in the CV characteristics of high-k/In0.53Ga0.47As interfaces are interpreted and guidelines are developed to obtain reliable estimates for interface trap densities and the degree of Fermi level (un)pinning for high-k/In0.53Ga0.47As interfaces.
Epitaxial SrTiO3 films with electron mobilities exceeding 30,000 cm2 V−1 s−1Quantitative Atomic Resolution Scanning Transmission Electron MicroscopyComplete understanding of atomic resolution high-angle annular dark-field ($Z$-contrast) images requires quantitative agreement between simulations and experiments. We show that intensity variations can be placed on an absolute scale by normalizing the measured image intensities to the incident beam. We construct fractional intensity images of a ${\mathrm{SrTiO}}_{3}$ single crystal for regions of different thickness up to 120 nm. Experimental images are compared directly with image simulations. Provided that spatial incoherence is taken into account in the simulations, almost perfect agreement is found between simulation and experiment.