Low refraction properties of F-doped SiOC:H thin films prepared by PECVD

Low refractive index materials which F-doped SiOC:H films were deposited on Si wafer and glass substrate by low temperature plasma enhanced chemical vapor deposition (PECVD) method as a function of rf powers, substrate temperatures, gas flow ratios (SiH₄, CF₄ and N₂O). The refractive index of the F-doped SiOC:H film continuously decreased with increasing deposition temperature and rf power. As the N₂O gas flow rate decreases, the refractive index of the deposited films decreased down to 1.378, reaching a minimum value at an rf power of 180 W and 100 °C without flowing N₂O gas. The fluorine content of F-doped SiOC:H film increased from 1.9 at.% to 2.4 at.% as the rf power was increased from 60 W to 180 W, which is consistent with the decreasing trend of refractive index. The rms (root-mean-square) surface roughness significantly decreased to 0.6 nm with the optimized process condition without flowing N₂O gas.     

Effect of substrate temperature on structural, optical and electrical properties of ZnO thin films deposited by pulsed laser deposition

ZnO thin films were grown by the pulse laser deposition (PLD) method using Si (100) substrates at various substrate temperatures. The influence of the substrate temperature on the structural, optical, and electrical properties of the ZnO thin films was investigated. All of the thin films showed c-axis growth perpendicular to the substrate surface. At a substrate temperature of 500 °C, the ZnO thin film showed the highest (002) peak with a full width at half maximum (FWHM) of 0.39°. The X-ray Photoelectron Spectroscopy (XPS) study showed that Zn was in excess irrespective of the substrate temperature and that the thin film had a nearly stoichiometrical composition at a substrate temperature of 500 °C. The photoluminescence (PL) investigation showed that the narrowest UV FWHM of 15.8 nm and the largest ratio of the UV peak to the deep-level peak of 32.9 were observed at 500 °C. Hall effect measurement systems provided information about the carrier concentration, mobility and resistivity. At a substrate temperature of 500 °C, the Hall mobility was the value of 37.4 cm²/Vs with carrier concentration of 1.36 × 10¹⁸ cm⁻³ and resistivity of 2.08 × 10⁻¹ Ω cm.     

Effects of microstructure on flexural strength of biomorphic C/SiC composites

Biomorphic C/SiC composites were fabricated from different kinds of wood by liquid silicon infiltration (LSI) following a two-step process. In the first-step, the wood is converted into carbon preforms by pyrolysis in a nitrogen atmosphere. The carbon preforms are then infiltrated by silicon melt at 1,560°C under vacuum to fabricate C/SiC composites. The mechanical properties of the C/SiC composites were characterized by flexural tests at ambient temperature, 1,000, and 1,300°C, and the relationship between mechanical properties and microstructure was analyzed. The flexural strength of the biomorphic composites was strongly dependent on the properties of the carbon preforms and the degree of silicon infiltration. The flexural strength increased with increasing SiC content and bulk density of composite, and with decreasing porosity in the C/SiC composite. An analysis of fractographs of fractured C/SiC composites showed a cleavage type fracture, indicating brittle fracture behavior.     

A nickel silicide nanowire microscopy tip obtains nanoscale information

An electric conductive Ni silicide nanowire (NiSi NW) embedding electric force microscopy (EFM) tip was fabricated by the dielectrophoretic method and was used to obtain electric information. Due to the geometric and electric excellence, the NiSi NW provides advantages in imaging and fabrication of the microscopy tip. A lead zirconate titanate (PZT) ferroelectric thin film was positively and negatively polarized, and the polarities were obtained by probing of the NiSi NW EFM tip to give distinctive charging information of the PZT film. Moreover, the NiSi NW EFM probing was adopted to achieve the electrical signal from the NW interconnect. The NiSi NW EFM probe confirmed the uniform electric-potential distribution through the NiSi NW interconnect with a small standard deviation. This demonstrates the feasibility of functional utilizations of the NiSi NW.     

Hierarchical nanostructure generated by decorating SiO(x) nanowires with CoPt nanoparticles

Silicon oxide nanowires were decorated with magnetically hard 3-5?nm-sized CoPt nanoparticles using a simple physical deposition system without any pretreatment of the nanowire surface. High curvature of the nanowire surface together with the weak metal-substrate interaction helped to maintain discrete particle morphology with spherical shapes during deposition. The weak interaction also allowed the preferential nucleation of the deposited film on the pre-existing particles so that the film deposition can be repeated in order to increase the particle size without significantly altering the particle morphology. We expect that this method can be easily extended to create other metal nanoparticle-decorated nanowires.     

ZnO nanowire-based nano-floating gate memory with Pt nanocrystals embedded in Al(2)O(3) gate oxides

The memory characteristics of ZnO nanowire-based nano-floating gate memory (NFGM) with Pt nanocrystals acting as the floating gate nodes were investigated in this work. Pt nanocrystals were embedded between Al(2)O(3) tunneling and control oxide layers deposited on ZnO nanowire channels. For a representative ZnO nanowire-based NFGM with embedded Pt nanocrystals, a threshold voltage shift of 3.8?V was observed in its drain current versus gate voltage (I(DS)-V(GS)) measurements for a double sweep of the gate voltage, revealing that the deep effective potential wells built into the nanocrystals provide our NFGM with a large charge storage capacity. Details of the charge storage effect observed in this memory device are discussed in this paper.     

Temperature and excitation density dependent photoluminescence of sputtering-induced GaAs/AlGaAs quantum dots

GaAs/AlGaAs quantum dots (QDs) are fabricated by low-energy ion beam sputtering and molecular beam epitaxy (MBE) re-growth. Temperature (6.5-78?K) and excitation power density (0.49-3.06?W?cm(-2)) dependent photoluminescence (PL) are presented and discussed in detail. The low-temperature PL emission at 720?nm is attributed to GaAs QDs with height of ～6.1?nm and base width of ～23?nm, calculated based on the quantum box model with infinite potential barrier. The calculated QD dimensions are in good agreement with those obtained from atomic force microscopy (AFM) analysis. Nonradiative recombination and Auger-assisted recombination are found to be the main PL quenching mechanisms at high temperature.