Using a pump-probe method with a 150 fs laser at the wavelength of 1.55 m, we have experimentally demonstrated that single-walled carbon nanotubes ͑SWNT͒ have an exciton decay time of less than 1 ps and a high third-order polarizability, which is reasonably interpreted as due to their azimuthal symmetry. These experimental results reveal that a SWNT polymer composite may be a candidate material for high-quality subpicosecond all-optical switches.

One-dimensional nanoscale epitaxial arrays serve as a great model in studying fundamental physics and for emerging applications. With an increasing focus laid on the Cs-based inorganic halide perovskite out of its outstanding material stability, we have applied vapor phase epitaxy to grow well aligned horizontal CsPbX (X: Cl, Br, or I or their mixed) nanowire arrays in large scale on mica substrate. The as-grown nanowire features a triangular prism morphology with typical length ranging from a few tens of micrometers to a few millimeters. Structural analysis reveals that the wire arrays follow the symmetry of mica substrate through incommensurate epitaxy, paving a way for a universally applicable method to grow a broad family of halide perovskite materials. The unique photon transport in the one-dimensional structure has been studied in the all-inorganic Cs-based perovskite wires via temperature dependent and spatially resolved photoluminescence. Epitaxy of well oriented wire arrays in halide perovskite would be a promising direction for enabling the circuit-level applications of halide perovskite in high-performance electro-optics and optoelectronics.

Through extensive (2ϩ1)-dimensional numerical integration and Monte Carlo simulations, we compute the scaling exponents of a flux redistribution model that is proposed to describe plasma etching and reactive ion etching of surfaces. It is found that, while the surface morphology depends on the etching conditions, the roughness exponent ␣, the growth exponent ␤, and the dynamic exponent z are universal with regard to the details of the re-emission mechanism and are given by ␣Ϸ␤ϷzϷ1. These exponents are in agreement with recent experiments on plasma etch-front roughening.

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We observed a scaling behavior during the shadowing growth of isolated Si, Co, Cu, and W nanocolumnar structures on Si substrates using the oblique angle deposition with substrate rotation ͑also known as glancing angle deposition or simply GLAD͒. The width of the isolated columns, W, grew as a function of column length, d, in a power law form, Wϳd p , where p is the growth exponent and was measured to be ϳ0.28-0.34. It is argued that shadowing without diffusion should lead to pϭ0.50 and would cross over to 0.31 if one considers surface diffusion. It is of great interest to determine the mechanisms that would affect the value of p since it is an important factor that would control the shape, final size, and spacing of the isolated nanocolumns eventually produced.