Silicon nanotubes (SiNTs) have been grown on a porous alumina surface, without the assistance of catalysts, by molecular beam epitaxy (MBE). The flow rate of Si atoms and the corrugated porous alumina surface seem to play an important role in the continuous growth of Si tubular structures. The Figure shows a field‐emission scanning electron microscopy image of the SiNTs grown on a regular array of hexagonal porous alumina.

We investigated the optical properties of ultrathin MoS2 films (number of layers: N = 1, 2, 4, and 12) using Raman spectroscopy, photoluminescence (PL) spectroscopy, and spectroscopic ellipsometry. We estimated the layer thicknesses based on Raman spectra. We characterized the microstructural properties of a single-layer MoS2 film using atomic force microscopy. We measured the lowest-energy A and B excitons using PL spectroscopy. We measured the ellipsometric angles (Ψ and Δ) of MoS2 thin films using spectroscopic ellipsometry, and obtained the dielectric functions as the films' thickness changed from a single layer to multi-layers. We determined the films' optical gap energies from the absorption coefficients. Applying the standard critical point model to the second derivative of the dielectric function (d2ε(E)/dE2), we determined several critical point energies. The d2ε(E)/dE2 spectra showed doublet peaks around 3 eV corresponding to the C and D transitions, as well as doublet peaks around 2 eV corresponding to the A and B transitions. These doublet structures at 3 eV are attributed to the transitions in the Brillouin zone between the Γ and K points.

Amorphous GaInZnO and polycrystalline ZnO thin films are grown by rf magnetron sputtering. Their optical properties are investigated by spectroscopic ellipsometry. The optical gap of the GaInZnO film increases with the increase of Ga content and by annealing. These are attributed to the large band-gap energy of Ga2O3 and the structural relaxation after annealing, respectively. The changes in optical properties show a strong correlation to the device characteristics of GaInZnO thin film transistors: The turn-on voltage increases as the optical gap increases with increasing Ga∕In ratio. This study shows that the GaInZnO thin films are as excellent as transparent oxide semiconductors.

A thickness modulation effect of Hf O 2 interfacial layer between double-stacked Ag nanocrystals for nonvolatile memory device applications

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