Bao Xi-Mao

Preparation of Si Nanocrystals Using Anodic Porous Alumina Template Formed on Silicon Substrate

A novel technique to extend template application of anodic porous alumina to Si has been reported. First, porous alumina template about 400 nm thick was prepared on silicon substrate by anodizing thin aluminum film with high purity of 99.99% in 15 wt.% sulfuric acid under a constant voltage of 20 V and at an electrolyte temperature of 5°C. Then, amorphous Si layer approximately 50 nm in thickness was deposited onto the surface of template by using electron beam evaporation technique followed by an Xe ion beam bombardment, upon which as-coated Si layer at the pore mouth could be removed into pores smoothly. Three runs were performed by repeating above process of deposition and post bombardment. Finally, samples were annealed at 800°C for 30 min in nitrogen. Transmission electron microscopy and x-ray diffraction analysis reveal Si nanocrystals with a size of 15-20 nm being formed in the pores of template.

Microstructural models of alumina nanotubes and anodic porous alumina film formed in sulphuric acid

Electrochemical stepwise anodization of aluminium in dilute sulphuric acid results in the formation of alumina nanotubes (ANTs) due to the hexagonal split of the anodic porous alumina (APA) film along the cell boundaries containing many voids; that is, the ANTs are the completely detached cell of the APA film. The inner diameters of the ANTs are in the range of 10-20 nm, and the aspect ratio (inner diameter/length) of the ANTs can be about 80. The relations found for pore diameter, cell diameter and barrier layer thickness are around 1, 2.7 and 0.85 nm/V, respectively. Transmission electron microscopy (TEM) reveals that the ANT wall has a three-shell structure: an outer shell (metal/oxide interface) consisting of pure alumina oxide, a middle shell of the hydrated oxide or/and hydroxide and an inner shell (oxide/electrolyte interface) of anion incorporated oxide with the thickness ratio of 1:1:2. The structural change of ANTs induced by e-beam irradiation in TEM indicates that the thermal instability of the hydrated oxide or/and hydroxide within the cell wall might be an alternative origin contributing to the self-organization of the cells, leading to a densely packed triangular cell lattice of the APA film.

Violet light-emission from Ge+-implanted SiO2 films on Si substrate

Germanium ions were implanted into SiO2 films which were thermally grown on crystalline Si at an energy of 60 keV and with doses of 1 ? 1015 and 1 ? 1016 cm-2. Under an ultraviolet excitation of ~ 5.0 eV, the implanted films annealed at various temperatures exhibit intense violet luminescence with a peak at 396 nm. It is ascribed to the T1???S0 transition in GeO, which was formed during implantation and annealing process.

Thermal Annealing of Si+ Implanted Chemical Vapor Deposition SiO2

Ion implantation was used to bring silicon atoms into chemical vapor deposition SiO2. Two bands of photoluminescence spectra at about 540 and 640 nm were observed from the as-prepared samples. Thermal annealing behavior of the photoluminescence was studied. The possible origin of the photoluminescence is discussed.

Influence of C+-implantation dose on blue emission and microstructures of Si-based porous β-SiC

Crystal Si were implanted with different doses of C+ from 1011 to 1017 cm-2 at an energy of 50 keV. β-SiC precipitates were formed by thermal annealing at 1050 °C for 1 h and porous structures were prepared by electrochemical anodization. Under the excitation of ultraviolet, the samples, with C+ dose ≥ 1015 cm-2 have intense blue emission which is stronger than the photoluminescence (PL) intensity of reference porous silicon (PS), and increases as C+ dose increases; the samples with C+ dose ≤ 1014 cm-2 show similar PL spectra to those of PS. The blue peak intensity in PL spectra is correlated with the TO phonon absorption strength of β-SiC in infrared absorption spectra. The transmission electron microscopy study shows that the blue peak is also correlated with the microstructures. Because porous β-SiC is nanometer in size, it is suggested that the quantum confinement effect be responsible for the blue light emission.

Behavior of hydrogen during laser crystallization and RTA of a-Si: H SOI☆☆☆

Abstract The behavior of hydrogen in a-Si: H during laser crystallization and rapid thermal annealing (RTA) has been investigated. High quality crystallized films have been obtained on fused quartz plates by cw Ar + laser scanning. However, poor quality films are obtained on SiO 2 /Si substrates because of the generation of bubbles and holes. A hydrogen content of 11 at.% (5.5 × 10 21 cm −3 ) has been measured in as-deposited a-Si: H films. For the case of fused quartz substrates the hydrogen content decreased to 2 × 10 20 cm −3 during the crystallization process and decreased further to 6 × 10 19 cm −3 after 35 s RTA at 1150°C. The remaining hydrogen is favorable for passivation of defects and grain boundaries.