Solid State Phenomena Vols. 124-126

Abstract: Non-evaporable getters (NEGs) are characterized by two major properties i.e. the activation and gas sorption rate for specific gases. Most of the commercial getters are alloys composed of micron-size powders. There have been speculations on the advantage of using nanosize powders as getter material for the obvious increase in volume to surface area ratio and for effective reaction with gases on size reduced particles. In this study, titanium powders of about 80 nm were prepared by electrical wire explosion method and their gettering properties were measured in accordance to ASTM standard. The activation of nano-size titanium powders was completed at about 450oC and the sorption rate was over 4 times higher than those of the micron-size titanium powders.

Abstract: The synthesis of high-quality monodispersed nanocrystal is very important. Typical synthetic method is rapid nucleation by injection of an organometallic precursor into a solvent maintaining the reaction temperature. Since these methods are discontinuous processes, they are not efficient for large-scale production of monodisperse nanocrystals. In this study, continuous microchannel reaction technique is presented for synthesis of monodisperse lead selenide nanocrystals in a diphenyl ether as high-temperature organic media. The microchannel reactor was used due to its possibility of continuous process and reproducibility of narrow size distribution in nanocrystal synthesis. The synthesis was carried out in microchannel reactor (800 μm diameter) made from PTFE. Lead oleate and TOP-Se were used as organic precursor and diphenyl ether as high-temperature organic solvents. Lead selenide particles with a size of less than 10nm could be continuously prepared by this method. The nanocrystals have been characterized by X-ray diffraction, TEM and optical absorption spectrometer.

Abstract: This study reported the fabrication of tin oxide (SnO2) nanostructures on Co-coated Si substrates by the thermal heating of Sn powders. The microstructures and morphologies of the resultant nanostructures were studied by means of X-ray diffraction (XRD), transmission electron microscopy (TEM), selected area electron diffraction (SAED), and scanning electron microscopy (SEM). The product mainly comprised the tangled nanowires with average diameters in the range of 50-180 nm. The nanostructures were single-crystalline rutile structure of SnO2. The PL measurement with the Gaussian fitting exhibited visible light emission bands centered at 576 nm and 638 nm, respectively. We have discussed the possible growth mechanism of the nanostructures.

Abstract: A hydrothermal method has been used to produce nanoparticles of 3 mol% yttria-stabilized tetragonal zirconia (3Y-TZP) with high fracture toughness. The effects of reaction temperature and pH on crystallite size and sintered density, and the influence of Nb2O5 addition into 3Y-TZP on toughness have been investigated. The particle size increased with increasing the processing parameters and the influence of temperature was more significant than pH. The density of nanosized 3Y-TZP increased with increasing pH up to 9 and then decreased abruptly with further increase. The density increased slightly with the reaction temperature up to 140°C and then changed little with increasing temperature. The toughness increased in proportional to the Nb2O5 content. After sintering for 1 h at 1270°C, the highest relative density of 98% was obtained from nanoparticles of about 17 nm, prepared at 200°C and pH 9, and the toughness of 3Y-TZP was increased from 2.5 to 8.3 MPam1/2 by addition of 1.2 mol% Nb2O5.

Abstract: Formation of size controlled nanohole arrays on semiconductor substrate can be used variously in applications of photonic and electronic device. The unique structure of nanoporous alumina was directly used as an etching mask for pattern transfer into the GaAs substrate. Using the alumina masks prepared at the anodic voltage of 24 V in 0.3 M sulfuric acid solution and 40 V in 0.3 M oxalic acid solution, fabricated were the arrays of nanohole on GaAs substrate by inductively coupled plasma reactive ion etching (ICP-RIE). The etching was conducted in a SiCl4/Ar mixed gas system. The uniform nanohole arrays were formed as replica of ordered lattice pattern of the mask. Depending on property of the alumina mask used, the size of nanohole was controlled to have hole diameter of 60 nm (with the hole density of 1.0 x 1010 cm-2) and of 30 nm (with the hole density of 2.7 x 1010 cm-2), respectively. So, the alumina mask attached on the GaAs substrate mainly determines the distribution and the size of the nanohole arrays. ICP-RIE using nanoporous alumina masks can control the size and the density of nanohole on compound semiconductor substrate.

Abstract: Al-Cr-N coatings were deposited on Si substrate by unbalanced magnetron (UBM) sputtering with Al and Cr targets and Ar and N2 reactive gases at substrate bias of -50V. At a fixed chamber pressure of 0.8 Pa, the microstructure of the coatings was changed from AlN/CrN nanoscale multilayered structure to (Al,Cr)N mixed single layered one with the increase of rotation speed of substrate holder. The residual compressive stress of AlN/CrN nanoscale multilayered coating was higher than that of (Al,Cr)N single layered coating. For the AlN/CrN nanoscale multilayered coating, the residual compressive stress was reduced with increase in total pressure of reactive gases. The AlN/CrN nanoscale multilayered coatings with higher residual compressive stress showed higher hardness and wear resistance.

Abstract: A new type of gas sensor was realized by directly depositing carbon nanotube on nano channels of the anodic alumina oxide (AAO) fabricated on p-type silicon substrate. The carbon nanotubes were synthesized by thermal chemical vapor deposition at a very high temperature of 1200 oC to improve the crystallinity. The device fabrication process was also developed. The contact of carbon nanotubes and p-type Si substrate showed a Schottky behavior, and the Schottky barrier height increased with exposure to gases while the overall conductivity decreased. The sensors showed fast response and recovery to ammonia gas upon the filling (400 mTorr) and evacuation.

Abstract: Combined thermal and mechanical analyses were used to investigate the effect of joint design parameters such as the adhesive thickness and bonding length on stress distributions and torque capacities of tubular adhesive joints with composite adherends. The finite element analysis was employed to calculate the residual thermal stresses due to fabrication, and the mechanical stresses were analyzed using the nonlinear analysis of tubular adhesive joints. The analyses reveal that the stacking angle, adhesive thickness and bonding length have a significant influence on residual thermal stresses, and consequently failure modes and joint strengths.

Abstract: The static and dynamic compressive behaviors of open-cell aluminum alloy foams with virtually the same relative density of 0.4 were investigated. The foams have different cell sizes (0.5mm, 1.5mm, 2.5mm) but similar cell morphology and microstructure. The yield strength of these foams was characterized as a function of strain rate and cell morphology. The experimental results indicated that the mechanical responses of foams are sensitive to strain rate, and dependent of the cell size. The present results are compared in details with recent findings obtained from the aluminum foams.