Defect and Diffusion Forum Vol. 272

Abstract: With the development of MEMS, the mechanical properties of micro crystals must to be determined to know the defect, reliability and characterization of MEMS. Young’s modulus is one of the most important properties, which indicates the ability of resisting the elastic deformation. Many methods, such as natural frequency measurement, beam bending tests, membrane bulge test and uniaxial tension test, have been used to measure Young’s modulus of Si, SiN and metals. But there are some limitations when they are used to measure micro crystals in MEMS. This paper puts forward a high accuracy and convenient method----using Raman spectrum to measure Young’s modulus of micro crystals in MEMS, and sets up the measurement system. Measured Young’s modulus of Si and GaAs in [100] crystallographic orientation are 161.113GPa and 84.128GPa respectively, which correspond with the Yong’s modulus in common use now. Based on the values, it can be analyzed if there are some defects in the micro crystals.

Abstract: The 9 and 16 MeV proton irradiations of CMOS Image Sensor in the fluence range from 5x108 to 4x1010 cm-2 and 5x109 to 1x1013 cm-2 have been carried out respectively. The color pictures and dark output images are captured, and the average brightness of dark output images is calculated. The anti-irradiation fluence thresholds for 9 and 16 MeV protons are about 4x1010 and 5x1012cm-2, respectively. These can be explained by the change of the concentrations of irradiation-induced electron-hole pairs and vacancies in the various layers of CMOS image sensor calculated by the TRIM simulation program.

Abstract: Mechanical alloying (MA) is a solid-state powder processing method which has the ability to synthesize a variety of new alloy phases including supersaturated solid solutions, nanocrystalline structures, amorphous phases and intermetallic compounds. In this investigation, the interaction between aluminum and iron caused by MA of Fe-xAl (where X ranged from 30 to 90%) was studied as a function of milling time and post heat-treating temperatures. The sequences of structural and/or phase transformation and the behavior of mechanically alloyed powders have been assessed using XRD, hardness and magnetometer. It was found that during mechanical milling of elemental powder Al and Fe, five milling stages were categorized, namely, particle flattening, welding predominance, equiaxed formation, random welding orientation and steady state composite particles. All milled powders showed nano-sized powder mixtures after milling for 20hrs. When Fe-30%Al powder was milled for 150hrs, a partially ordered AlFe phase was obtained. However, when these saturated solid solutions were heat treated at 500 °C, the AlFe intermetallic was precipitated fully ordered. When the Al content was increased up to 40% and milled for 50hr, the XRD pattern showed a broad halo spectrum which showed the formation of an amorphous phase. When a Fe-60%Al powder mixture was mechanically milled for 50hr, the Al5Fe2 intermetallic formed that was associated with an amorphous phase, which transformed into the Al3Fe intermetallic by heat treating at 500°C. In the case of Fe-75% and Fe-90%Al milled for 150hrs only Al peaks appeared and were shifted to higher angles, suggesting that Fe atoms diffused into Al, leading to the formation of a solid solution.

Abstract: Helium cooled Gas Fast Reactors (GFR) are designed for producing energy more efficiently and improving safety features such as a total retention of fission products (Xe, I, Cs). This study deals with the diffusion of xenon in refractory liners dedicated to the retention of fission products produced in GFR fuels. The material (W, Mo, W-Re, Mo-Re) will be located in the heart of the nuclear fuel element, where the operating temperature is in the 1000°C- 1600°C range. For the investigation of thermally activated rare gas behaviour, a γ-spectrometry analysis experiment has been performed on the 133Xenon implanted refractory liner. Preliminary results on the 133Xenon release at 1600°C from a tungsten single crystal is presented. In spite of the low concentration of implanted gas (~ppm) and simple microstructure, the prevailing mechanism appears to be complex. One and two dimensional diffusion models are used to characterize or discriminate the highlighted phenomena: burst release, diffusion and trapping of rare gas atoms.

Abstract: The laser-induced mass transfer in thin-film substrate /Cr/Cu/Ni system is studied by means of Auger Electron Spectroscopy (AES). For the laser-pulse energy values, E = 100-170mJ, the diffusion of Cu atoms into Ni layer and their accumulation within this layer are observed, whereas at E > 170mJ the same is true for Cr atoms. The observed phenomena are explained on the basis of calculated temperature distribution in the system at issue during lased action. Enhanced transfer of Cr atoms towards external surface is observed under the irradiation regimes leading to the melting of intermediate copper layer. Diffusion coefficients of copper and chromium calculated from their surface accumulation show an exponential dependence on the laser-pulse energy. Under laser heating, the diffusion processes are more manifested as compared with those under conventional thermal annealing. This is bound up with higher concentration of nonequilibrium defects generated within the irradiation zone.

Abstract: Crack propagation in bcc iron at different strains under low temperature (30K) has been studied using the atomistic simulation. We show that cracks display a brittle character of extension at low strains, and at relative higher strains cracks extend with a periodic series of twins(or SF) bursts. These bursts decrease the crack speed and produce velocity oscillations with an increase in energy dissipation that increases the toughness. Here we also develop a new form of dynamic fracture energy. Using our form of dynamic fracture energy, the results therefore are in quantitative agreement with the theoretical single-crack equation of motion.

Abstract: An EAM interatomic potential for the ordered AlMo3 intermetallic is developed and applied to the study of point defects in the AlMo3. The equilibrium concentrations of vacancies and antisites are calculated using statistical thermodynamics. Results show that antisites are the most abundant type of defect in a range of temperatures and compositions close to stoichiometry. Finally, the diffusion by vacancy mechanism in the same structure is studied through the kinetic Monte Carlo technique. Possible atomic mechanisms of diffusion are suggested and analyzed in some detail.

Abstract: Using the first-principles self-consistent discrete variational method based on density functional theory, we investigated the energetics and the electronic structure of 3d impurity Mn and Cr in the kink on the [100](010) edge dislocation in bcc iron. The calculations of binding energies show that both Mn and Cr can stabilize the system containing kink. We also calculate the structural energy, the interatomic energy, the local density of states and the charge density difference. The results indicate that both Mn and Cr in the kink can enhance the interatomic interaction between the impurity atom and the neighboring Fe atoms due to the hybridization of impurity d-Fe d orbitals. The introduction of the Mn and Cr impurity leads to a strong pinning effect on the dislocation motion in bcc iron, which may explain the solid solute hardening of Mn and Cr.

Abstract: The concentration profile of Cu is modelled using semi-infinite geometry for diffusion couples of α and β phases in Cu-Al system. The dimensionless interface movement parameter γ is calculated, for various combinations of time and temperature, by root bracketing, bisection and inverse quadratic interpolation. A computational procedure is presented to calculate the concentration profile where the interface velocity (dε/dt) is high and/or with steep concentration gradient of the specie in the shrinking phase. In all cases the interface compositions are set at the equilibrium values given in the phase diagram with fixed composition of end members. The calculated profile match well with the experimental concentration profile as reported by Romig [3].

Abstract: This study evaluates the boron diffusion in the Fe2B phase formed at the surface of AISI 1018 steels during the paste boriding process. The treatment was carried out at temperatures of 1123, 1173, 1223 and 1273 K with 2, 4, 5, 6 and 8 h exposure times for each temperature using a 4 mm layer thickness of boron carbide paste over the material surface. The boron diffusion coefficient Fe2B D was determined by the mass balance equation and the boride incubation time assuming that the boride layers obey the parabolic growth law, while the boron concentration profile along the interphase Fe2B/substrate was unknown. The boron diffusion coefficient was interpreted as a function of the treatment temperature, obtaining the activation energy value for diffusion controlled growth of Fe2B boride phase.