Materials Science Forum Vols. 539-543

Abstract: Effects of electric field annealing on recrystallization texture and average plastic strain ratio (r value) of IF steel sheet were studied by mean of X ray diffraction ODF analysis and the tensile test. Specimens of 75% cold-rolled IF steel sheet were annealed at 850flC for 25min,with and without electric field annealing respectively. Results show that the electric field annealing does not change the type of recrystallization texture and its formation mechanism in IF deep-drawing steel sheet, but improves the formation and development of recrystallization i-fiber texture, enhances the intensity of i-fiber texture, and retards the formation and development of c-fiber texture. Comparing with the conventional annealing, electric field annealing improves the average plastic strain ratio (r value). Possible reasons for the intensification of recrystallization i-fiber texture with the electric field applied may attribute to the reduction of stored energy, thus hindering the formation of other orientated nuclei and enhancing the nucleating ratio of i-oriented nuclei. And the intensification of recrystallization i-fiber texture was considered as the main reason for the enhancement of the plastic strain ratio (r value) in IF steel sheet.

Abstract: Two processes, the floating catalyst chemical vapor deposition (CVD) process and the rapid heating and cooling (RHC) process, were adopted for synthesizing single walled carbon nanotubes (SWNTs) and multi-walled carbon nanotubes (MWNTs). Batch production of SWNTs and MWNTs with the diameters of 0.8~1.5 nm and 15~40 nm, respectively, were prepared using the floating catalytic chemical vapor deposition (CCVD) process. The production rate is 70±20 mg every 10 minutes. The as-synthesized carbon nanotubes (CNTs) were used for fabricating carbon nanotubes reinforced composites and field emitter for lighting. On the study of nano-composites, around 70% enhancement of tensile strength was detected when 1.5 wt% MWNTs in the form of network structure were introduced to the phenolic matrix. Comparisons on the mechanical properties of the composites reinforced with the network MWNTs and SWNTs were made. Microstructures of the MWNTs and SWNTs were studied by Field Emission Scanning Electron Microscope (FESEM) and High Resolution Transmission Electron Microscope (HRTEM). In the RHC process for fabricating the device for lighting, the carbon nanotube array was grown on a silicon substrate which was pre-coated with a catalyst thin film. The synthesis process was performed in a thermal CVD chamber equipped with a rapid heating apparatus. The as-synthesized CNT array was then transferred onto the substrate which was coated with silver paste. After heat treatment, field emission properties of the CNT-based cathode were tested, high current density of 35 mA/cm2 and low turn-on voltage of 0.65 V/μm were achieved in this work.

Abstract: Sputtered Cu films containing various insoluble substances, such as Cu(W2.3), Cu(Mo2.0), Cu(Nb0.4), Cu(C2.1) and Cu(W0.4C0.7), are examined in this study. These films are prepared by magnetron sputtering, followed by thermal annealing. The crystal structure, microstructure, SIMS depth-profiles, leakage current, and resistivity of the films are investigated. Good thermal stability of these Cu films is confirmed with focused ion beam, X-ray diffractometry, SIMS, and electrical property measurements. After annealing at 400°C, obvious drops in resistivity, to ~3.8 μ-cm, are seen for Cu(W) film, which is lower than the other films. An evaluation of the leakage current characteristic from the SiO2/Si metal-oxide-semiconductor (MOS) structure also demonstrates that Cu with dilute tungsten is more stable than the other films studied. These results further indicate that the Cu(W) film has more thermal stability than the Cu(Mo), Cu(Nb), Cu(C), Cu(WC) and pure Cu films. Therefore, the film is suitable for the future barrierless metallization.

Abstract: The bond interface of a TLP (Transient Liquid Phase) bonded tin has been observed with a TEM to investigate the effect of the liquid phase on the behavior of the superficial oxide film at the interface during the bonding process. In the solid-state-diffusion bonded joint without filler, abundant oxide inclusions were observed to be distributed within a region of a few 100 nm widths along the bond interface. In comparison with this, the liquid phase introduced by the eutectic reaction of the bismuth filler with the tin substrate decreased the width of the interfacial region involving abundant oxide inclusions to form a rather layer structure a few 100 nm thick consisting mainly of SnO2. It also enhanced the annihilation of the uncontacted areas at the interface. The layer of the oxide became discontinuous and coalesced with an increase in bonding temperature and pressure, and areas where no oxide inclusion could be observed at the interface were increased, when the liquid phase was formed. Owing to these effects, the bond strength rose at lower bonding temperatures and pressures when the bismuth filler was applied.

Abstract: It is often said that the sensitivity of a gas sensor made of an oxide semiconductor film is enhanced by making the film porous. However, the porosity of sensor films has not been sufficiently examined. In this study, SnO2 films were deposited using DC magnetron sputtering under various substrate temperatures and discharge gas pressures. In addition to the structural analysis by means of X-ray diffraction and scanning electron microscopy, the density and the BET surface area were measured to clarify the film porosity. The sensitivity to H2 gas of undoped and Pd-doped SnO2 films upon exposure to 1000 ppm H2 was measured at 300
. SnO2 films generally showed a columnar structure. The film deposited at a low temperature and a high pressure showed a low density and a large effective surface area. The H2 sensitivity increased as the density decreased, that is, as the effective surface area increased.

Abstract: La3Ga5SiO14 (LGS) thin films were grown on (200)-textured MgO buffer layer, which was deposited on the silicon wafer, by sputtering at 600°C. These thin films were annealed and transformed form amorphous to the LGS crystalline phase with the heat treatment temperature higher than 1150°C. It was found that the films with LGS crystalline phase showed luminescent characterization whereas the LGS sintered solids did not. The emission peak of the films was found to be 438 nm under the excited light of λex=300nm. Effects of annealed temperature on the luminescent properties of the thin films are investigated. The relationship between the mechanism of luminescence and the crystalline structure of the LGS films are discussed.

Abstract: Hillocks were observed in various thick Al films after annealing for a long time and their density and diameter were measured using an image analysis program. The hillock density decreased while the diameter increased with increasing film thickness. The total hillock volume per unit area of the film is linearly proportional to the film thickness and annealing temperature. Based on the results of our investigation, the effect of the film thickness, grain size and annealing temperature on hillock formation is discussed, and an equation that can be used to predict the hillock density and average hillock diameter is suggested.