Enabling high solubility of ZnO in TiO2 by nanolamination of atomic layer deposition.

Zn-doped TiO2 nanotubes were fabricated by nanolaminated packing of alternating layers of TiO2 and ZnO by atomic layer deposition (ALD) using a polycarbonate (PC) membrane as a template. With 400 cycles of ALD, the nanotubes with a thickness of 28 nm and an outer diameter of 220 nm were obtained after removing the PC membrane by annealing at 450 °C. The doping concentration of ZnO in TiO2 depends on the precursor cycle ratio of ZnO to TiO2. With the precursor cycle ratio of ZnO : TiO2 at 0.04, a uniform bulk solubility of ∼8 at% is obtained, and the surface concentration of Zn is even higher, ∼16 at%. From the depth profiles measured by secondary ion mass spectrometry, Zn is uniformly distributed across the thickness, which is further confirmed by analyses of X-ray photoelectron spectroscopy, X-ray diffraction, and Raman spectroscopy. Additionally, from the transmission electron microscopic observation, the highly doped anatase TiO2 exhibits some regions of severe deformation that results in localized solid-state amorphization.

Photoluminescence of Si nanocrystallites and amorphous oxygen-containing si nanoparticles: the reversible effect of ambient atmosphere on luminescence.

Si nanocrystallites of various sizes and oxygen-containing Si nanoparticles with different oxygen contents were prepared by vapor condensation. The Si nanocrystallites showed a visible light emission from 500 nm to 900 nm with the peak at 800 nm, and the intensity of photoluminescence increased with decreasing the particle size. This photoluminescence observed in vacuum could be quenched by air and hydrogen, and reappeared after the sample chamber was evacuated. The oxygen-containing Si nanoparticles consisting mainly of Si oxide were amorphous and had an average particle size of approximately 20 nm. Increasing the oxygen content of nanoparticles caused a blueshift of the absorption edge in the transmission spectra. A blue-green photoluminescence with two peaks at 500 nm and 800 nm was observed from these oxygen-containing Si nanoparticles. The luminescence intensity increased with the oxygen content of nanoparticles, and was very sensitive to the ambient atmosphere. Much lower intensity was observed in air, but higher intensity could be recovered in vacuum. Surface states and oxygen-induced luminescent centers were proposed to be responsible for the photoluminescence from the Si nanocrystallites and oxygen-containing Si nanoparticles, respectively. The reversible ambient effect in both cases could be explained by surface charge redistribution during the gas adsorption and desorption processes.

On the formation and photoluminescence of Si(1-x)Ge(x) nanoparticles.

Si(1-x)Ge(x) nanoparticles were prepared from two annealed alloy ingots at the compositions of Si:Ge = 9.5:0.5 and 9:1 using a vapor condensation technique under Ar atmosphere. These nanoparticles are all spherical, and increasing the working pressure leads to an increased particle size and size dispersion. Comparing to the alloy ingots, the nanoparticles have a higher average content of Ge. In addition, increasing the working pressure also causes the Si(1-x)Ge(x) nanoparticles to become more Ge-rich. This can be ascribed to the lower melting point and higher kinetic energy of Ge than Si during the evaporation process. The photoluminescence of Si(1-x)Ge(x) nanoparticles ranges from visible light to infrared region, and the luminescence peak exhibits a red shift as the Ge content in the nanoparticles increases. This indicates that the incorporation of Ge into Si has a dominant effect in the radiative recombination process, in comparison with the constant luminescence peak position in the case of pure Si nanoparticles with similar size distribution.