The 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.

Within the framework of quantum mechanics, a unique particle wave packet exists in the form of the Airy function. Its counterintuitive properties are revealed as it propagates in time or space: the quantum probability wave packet preserves its shape despite dispersion or diffraction and propagates along a parabolic caustic trajectory, even though no force is applied. This does not contradict Newton's laws of motion, because the wave packet centroid propagates along a straight line. Nearly 30 years later, this wave packet, known as an accelerating Airy beam, was realized in the optical domain; later it was generalized to an orthogonal and complete family of beams that propagate along parabolic trajectories, as well as to beams that propagate along arbitrary convex trajectories. Here we report the experimental generation and observation of the Airy beams of free electrons. These electron Airy beams were generated by diffraction of electrons through a nanoscale hologram, which imprinted on the electrons' wavefunction a cubic phase modulation in the transverse plane. The highest-intensity lobes of the generated beams indeed followed parabolic trajectories. We directly observed a non-spreading electron wavefunction that self-heals, restoring its original shape after passing an obstacle. This holographic generation of electron Airy beams opens up new avenues for steering electronic wave packets like their photonic counterparts, because the wave packets can be imprinted with arbitrary shapes or trajectories.

Using temperature driven sharp metal-insulator phase transition in single crystal VO(2) nanowires, the realization of a novel gas sensing concept has been tested. Varying the temperature of the nanowire close to the transition edge, the conductance of the nanowire becomes extremely responsive to the tiny changes in molecular composition, pressure, and temperature of the ambient gas environment. This gas sensing analog of the transition edge sensor radiometry used in astrophysics opens new opportunities in gas sensorics.

Tin oxide single nanowires configured as field effect transistors were shown to be operable and tunable alternately as gas sensors or as catalysts under a gaseous atmosphere that simulated realistic ambient conditions. The unusually large surface-to-volume ratio available with nanowires causes adsorption or desorption of donor or acceptor molecules on the nanowire's surface to greatly alter its bulk electron density at relatively small values of the gate voltage. This process can be sensitively monitored as changes in the nanowire's conductivity. The potentially radical change in carrier density can lead to significant changes in the nanowire's sensitivity as a sensor or reciprocally as a catalyst in reactions that involve charge exchange across the nanowire's surface. This leads to the prospect of tuning catalysis or other surface reactions entirely through electronic means.