Annealing In Order Research Articles

Cooling-Induced Deformation of Polystyrene Spherical Shells

We carried out experiments on cooling-induced deformation (CID) of inertial-fusion fuel capsules. Polystyrene spherical shells were used as test samples. In the experiments, approximately 90 shells were cooled using liquid nitrogen and observed with an optical microscope. Pictures of each shell were recorded at 0°C and −190°C, and they were compared with each other. About a half of the tested shells showed CID, where the maximum deformation was in the order of 1% of the shell radius. Although the polystyrene shells were fabricated by a density-matched emulsion method using both hand-shaken microencapsulation and triple-orifice droplet-generator techniques, we recognized no significant difference in deformation characteristics between these two techniques. The observed CID showed poor reproducibility. We tried annealing in order to prevent CID, but no apparent improvement was recognized.

Poly-Si Thin Film Transistors Fabricated By Employing Selective Si Ion-Implantation And Excimer Laser Annealing

ABSTRACTA new excimer laser annealing method is proposed in order to produce the poly-Si film with low defect density and large grain, by combining the selective Si ionimplantation and excimer laser annealing. Selective Si ion-implantation is employed to form artificial nucleation seeds in a-Si film prior to excimer laser annealing in order to increase the nucleation probability. The grain boundary location in poly-Si film has been controlled through implantation mask, and the grain size around micrometer order is obtained without any other process. TEM result shows that grain boundary is controlled according to mask pattern and the crystallinity of the poly-Si film is improved.

Current-mode chaotic neuron circuit for the traveling salesman problem

In order to install a chaotic neural network to solve the traveling salesman problem (TSP) on an integrated circuit, a chaotic neuron circuit is designed by using a current mode circuit. First, the characteristics of the output function of the neuron circuit are determined by numerical simulation so that they have excellent capability to solve the TSP. Next, the network is designed such that the chaotic neural network consisting of the designed neuron circuits can seek the optimum solution efficiently. Further, a circuit is proposed which realizes chaotic annealing in order to improve the convergence of the chaotic neural network. The ability of the proposed network using the annealing circuit to derive an optimum solution of the TSP is studied. From the simulation results, it is confirmed that the proposed chaotic neuron circuit is suitable for integration of the chaotic neural network to solve the TSP. © 1999 Scripta Technica, Electron Comm Jpn Pt 3, 82(9): 52–62, 1999

Physical aging of an amorphous polyimide: Enthalpy relaxation and mechanical property changes

The physical aging behavior of an isotropic amorphous polyimide possessing a glass transition temperature of approximately 239°C was investigated for aging temperatures ranging from 174 to 224°C. Enthalpy recovery was evaluated as a function of aging time following sub-Tg annealing in order to assess enthalpy relaxation rates, and time-aging time superposition was employed in order to quantify mechanical aging rates from creep compliance measurements. With the exception of aging rates obtained for aging temperatures close to Tg, the enthalpy relaxation rates exhibited a significant decline with decreasing aging temperature while the creep compliance aging rates remained relatively unchanged with respect to aging temperature. Evidence suggests distinctly different relaxation time responses for enthalpy relaxation and mechanical creep changes during aging. The frequency dependence of dynamic mechanical response was probed as a function of time during isothermal aging, and failure of time-aging time superposition was evident from the resulting data. Compared to the creep compliance testing, the dynamic mechanical analysis probed the shorter time portion of the relaxation response which involved the additional contribution of a secondary relaxation, thus leading to failure of superposition. Room temperature stress-strain behavior was also monitored after aging at 204°C, with the result that no discernible embrittlement due to physical aging was detected despite aging-induced increases in yield stress and modulus. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 1931–1946, 1999

Fuzzy rule base learning through simulated annealing

We study the use of simulated annealing to optimize the membership functions of Takagi-Sugeno rules. The necessary adaptation of simulated annealing in order to be efficient for this problem is discussed in detail. The convergence is carefully studied for the test application of the approximation of an analytical function specially built to test the efficiency of the algorithm. The obtained results are compared with gradient descent optimization results. We point out that simulated annealing is particularly interesting in the case (usual in practical implementations) when there are few rules compared to the complexity of the problem.

Biasing materials for spin-valve read heads

In this paper, the performance of CoNiO, NiO, NiMn and IrMn as exchange biasing materials for use in spin-valve read heads is described. The significant material properties investigated were biasing fields, thermal stability, thickness effects and corrosion resistance. The oxide materials had excellent corrosion resistance, but NiO had poor exchange fields and CoNiO had a poor blocking temperature. NiMn had the best exchange field with an interfacial exchange coupling of 0.25 erg/cm/sup 2/, but it required high temperature annealing in order to realize this. It also had good thermal and corrosion resistance properties. The blocking temperature of the oxides and IrMn were found to diminish with decreasing thicknesses of the antiferromagnets. This effect was determined to be consistent with a finite-size-scaling phenomenon. IrMn was found to have a good combination of the properties investigated, the weakest being its corrosion resistance, which was nevertheless better than FeMn. Spin-valves fabricated with IrMn as the pinning material showed excellent magnetic and thermal properties with MR ratios as high as 10% and good spin-valve responses up to 209/spl deg/C IrMn pinned spin-valves had very good performance for narrow trackwidth elements, with MR ratios as high as 5% and pinning fields of >600 Oe for 0.5 /spl mu/m trackwidth devices.

Dynamics of SrTiO3 surface during wet etching and high-temperature annealing

We have studied the dynamics of SrTiO3(001) surface etching and annealing in order to prepare the best possible surface for thin film deposition. Wet etching in pH-controlled NH4F-HF was used to obtain an atomically flat surface which was terminated by the TiO2 layer, as shown by ion scattering measurements. Annealing of the surface at up to 800°C was needed to stabilize the etched surface and to obtain straight step edges. The preferential TiO2 termination was preserved even after annealing. High-temperature scanning tunneling microscopy was used to determine the optimal annealing conditions and to gain an understanding of the surface migration process, which is essential for the understanding of the film growth process on SrTiO3 substrates at various temperatures.

Light emitting diode structure based on Si nanocrystals formed by implantation into thermal oxide

Light emitting diodes (LED), continuously operable at room temperature, have been fabricated by Si + ion implantation into SiO 2 and subsequent annealing in order to form Si nanocrystals. A highly doped poly-Si layer was used to enhance injection into nanocrystals. Visible electroluminescence (EL) was observed from the LEDs with oxide thickness ⩽180 Å for bias voltages above 8 V. The EL decay transient was similar to stretched-exponential decays observed for photoluminescence (PL) from Si nanocrystals.

Counterdoped very shallow p+/n junctions obtained by B and Sb implantation and codiffusion in Si

In this article we investigate the B and Sb codiffusion upon postimplantation annealing in order to fabricate very shallow p+/n junctions (⩽70 nm), suitable for a complementary metal–oxide–semiconductor technology with a channel length of 0.18 μm. The junctions are prepared by implanting Sb and subsequently BF2, at a higher dose, in an n-type Si substrate. The preamorphization with Sb avoids the B channeling and increases the n-type doping in the junction region, thus confining the depth of the p layer. Furthermore, both the transient enhanced diffusion, being the B implanted in a preamorphized layer, and the standard diffusion, due to the pairing between donors and acceptors, are strongly reduced. This procedure allows us to obtain very shallow junctions even after annealings with relatively high thermal budget, like 800 °C/8 h or 900 °C/1 h, or 950 °C/10 min or 1000 °C/60 s. We verified that dopant diffusion is strongly affected by a direct donor–acceptor interaction, and that good prediction of the experimental results can only be obtained using a simulation code which takes into account the formation of neutral, near immobile, Sb–B pairs.

Titanium oxide thin films for NH3 monitoring: Structural and physical characterizations

Titanium oxide thin films have been deposited by thermal evaporation in vacuum and then have been analyzed before and after a suitable thermal annealing in order to test their application in NH3 gas-sensing technology. In particular, spectrophotometric and conductivity measurements have been performed in order to determine the optical and electrical properties of titanium oxide thin films. The structure and the morphology of such material have been investigated by high resolution electron microscopy and small area electron diffraction.

Correlation of radiation damage effects in high resistivity silicon detectors with results from deep level spectroscopy

Neutron irradiated high resistivity silicon detectors have been subjected to isochronous annealing in order to study the changes in the full depletion voltage and the leakage current. The corresponding evolution of bulk damage induced defect levels was monitored using the TSC method. A single TSC peak is found to be correlated with the transient decay of the depletion voltage which is observed after elevated temperature annealing of inverted detectors. In conjunction with deep level parameters obtained from an I-DLTS study and changes observed in the effective doping concentration and in the leakage current after exposure to high doses of /sup 60/Co-gammas, new insight is gained into the radiation induced device deterioration and the corresponding annealing behavior.

Monte Carlo simulation of Boron diffusion during low energy implantation and high temperature annealing

ABSTRACTWe use a kinetic Monte Carlo model to simulate the implantation of low energy Boron in Silicon, from 0.5 to 1 keV, at high doses, 1015 ions/cm2. The damage produced by each ion is calculated using UT-Marlowe, based on a binary collision approximation. During implantation at room temperature,, silicon self-interstitials, vacancies and boron interstitials are allowed to migrate and interact. The diffusion kinetics of these defects and dopants has been obtained by ab initio calculations as well as Stillinger Weber molecular dynamics. Clustering of both self-interstitials, vacancies and boron atoms is included. We also model the diffusion of the implanted dopants after a high temperature annealing in order to understand the transient enhanced diffusion (TED) phenomenon. We observe two different stages of TED During the first stage vacancies are present in the lattice together with interstitials and the diffusion enhancement is small. The second stage starts after all the vacancies disappear and gives rise to most of the final TED.

Accurate method for determining the refractive-index profiles of planar waveguides in uniaxial media with the optical axis normal to the surface

A new method for characterization of uniaxial planar waveguides from their measured effective mode indices is presented. The theory is outlined and expressions for efficient computer analysis are given. Uniaxial waveguide samples have been made in c-cut LiNbO(3) by proton exchange with and without post annealing in order to test the method on both steplike and graded-index profiles. The resulting characterization of the samples is discussed in relation to the inverse WKB method. Finally, the importance of incorporating the effects of material birefringence in the characterization of these kinds of waveguides is investigated.

Improvement of Identification Methods using Feed-Forward Neural Networks and Fuzzy Models

This work presents different approaches to improve connectionist and fuzzy models for nonlinear dynamical systems by the introduction of global numeric optimization into the identification process. The developed hybrid techniques make use of genetic algorithms and simulated annealing in order to determine the best parameters for a neural network’s topologie and learning schedule, as well as for the linguistic variables of a fuzzy model. As results an enlarged generalization capability of the models and more robust models for dynamical systems are obtained.

Electrical Characteristics of CoSi2 Layers Formed by Mevva Implantation of Co into Si

AbstractHigh dose Co implantation into Si has been performed with a metal vapor vacuum arc (MEVVA) ion source at an extraction voltage of 70 kV to doses from 8×1016 to 6×1017 ions cm−2 at substrate temperatures (Ts) in the range of 210°C to 700°C. Annealing was performed in nitrogen at various temperatures for various time intervals by either furnace annealing (FA) or rapid thermal annealing (RTA). The electrical properties of the CoSi2 layers formed were studied using resistivity and Hall effect measurements from 10 to 300K. We found that for all the samples prepared by MEVVA implantation, as long as a continuous CoSi2 layer was formed after annealing, a strong temperature dependence of the Hall coefficient was observed with a large peak at around 90 to 110K. The magnitude of the peak also varies depending on the substrate parameters and processing conditions. However, the temperature dependence of the resistivity for these CoSi2 layers follows the atthiessen's rule. We also found that it does not require high substrate temperature nor very high temperature annealing in order to form a CoSi2 layers with low resistivity by MEVVA implantation. Such low resistivity CoSi2 layers can be formed with a substrate temperature as low as 210°C after either RTA at high temperature for a few seconds or FA at a relatively low temperature of 750°C for one hour. The dependence of the electrical properties on Ts is also presented and discussed.

The effect of phosphorus segregation on the intermediate-temperature embrittlement of ferritic, spheroidal graphite cast iron

The objective of this article is to study the effect of phosphorus segregation on the fracture modes of the intermediate-temperature intergranular embrittlement which occur in ferritic, spheroidal graphite cast iron. The specimens were quenched from 820 °C and 500 °C during the furnace-cooling period of ferritization annealing in order to vary the degree of phosphorus segregation, then deformed in tension at various temperatures between 20 °C and 520 °C with a constant crosshead speed of 0.01 mm/s. These two kinds of specimens were also fractured by impact at about -50 °C in the vacuum chamber of a scanning Auger microscope in order to analyze the phosphorus segregation and compare the fracture modes. The results show that the fracture mode of the intermediate-temperature embrittlement is influenced by the history of heat treatment prior to tension. When the specimens were held at 500 °C and quenched from this temperature, the fracture was intergranular. However, the specimens quenched from 820 °C revealed cleavage fracture with cracks propagating radially from a central region with magnesium-rich particles. Identified by transmission electron microscopy (TEM), the particles were MgO. Grain-boundary segregation of phosphorus in the specimen held at 500 °C was confirmed by Auger analysis of the impact fracture surface. Segregation of phosphorus must play an important role in the fracture mode of the intermediate-temperature intergranular embrittlement.

Semi-insulating GaAs made by As implantation and thermal annealing

We have demonstrated that it is possible to regrow amorphous layers created by high dose As implantation in GaAs by thermal annealing in order to obtain arsenic precipitates distributed in a GaAs matrix similarly to that observed in low temperature GaAs. The characteristics of the As precipitates can be monitored through appropriate selection of the implantation and annealing conditions. Electrical measurements show that dielectric-like resistivity of surface or buried GaAs layers can be obtained by this method. Results on the growth of epilayers on these semi-insulating regions are also reported.

High effective Schottky barriers on n-type InP using Zn-based metallizations and rapid thermal annealing

Surface barrier diodes using different Zn-based metallizations, which were alloyed using rapid thermal annealing in order to make low-leakage, high barrier metal-semiconductor diodes on n-type InP, have been studied. The electrical properties of diodes using Cr in between the Zn layer and the InP are poor, because Cr and P forms a diffusion barrier-like layer adjacent to the semiconductor surface, which is hard to overcome and, more important, shunts the diode because it forms low effective barriers to n-type InP. For Au/Cr/Zn/Au/lnP diodes, high effective Schottky barriers of 0.76 eV from J-V characteristics and 1.23 eV from C-V characteristics have been measured for the same barrier diodes, indicating that the surface is not fully covered with the high effective barrier height interfacial phase, but that lower effective barrier height interfacial phases are also present. The dominant transport mechanism of carriers across these metal-semiconductor diodes is found to be thermionic emission from J-V-T measurements. and the leakage current density measured at -1 V is 8*10-6-10-5 A cm-2. From depth profiling using Rutherford backscattering spectrometry and near-surface imaging using scanning electron microscopy it is seen that In is depleted from the InP surface due to Zn-P/Cr-P stable phase formation and that it either agglomerates at the surface of the metallization or is incorporated into the Au layer forming stable Au-In and In-O compounds.

Structure and composition requirements for deoxygenation, dehydration, and ketonization reactions of carboxylic acids on TiO 2(001) single-crystal surfaces

The reactivities of TiO 2(001) single-crystal surfaces for acetic acid decomposition were studied by TPD and XPS. Surface structure and composition were varied by a combination of argon ion bombardment and annealing in order to investigate reaction selectivity and to identify the active sites responsible for adsorption and decomposition. Acetic acid adsorbed both molecularly and dissociatively at 200 K, but only dissociatively at 300 K. The molecular species desorbed readily below 300 K. Approximately 15% of the dissociatively adsorbed species (acetates) desorbed as acetic acid at 390 K via recombination with surface hydroxyls. The remaining acetates decomposed at higher temperatures via three different reaction pathways with selectivities dependent on surface composition and structure. Reduced surfaces containing Ti cations of lower valences favored direct deoxygenation of the acetates to fill the oxygen vacancies of the surface. This reaction occurred even at room temperature and deposited atomic carbon on the surface. Oxidized surfaces containing only Ti 4+ cations favored reactions to form volatile molecular products. On the {011}-faceted surface, surface acetates decomposed via net unimolecular dehydration to ketene. On the {114}-faceted surface, the bimolecular reaction of surface acetates to form acetone also took place. The reactions of propionates formed by dissociation of propionic acid were directly analogous to those of acetates: methyl ketene was produced by net unimolecular dehydration on the {011}-faceted surface and 3-pentanone was the bimolecular ketonization product on the {114}-faceted surface. Since the {011}-faceted surface exposes only Ti 4+ cations of fivefold oxygen coordination, these sites were determined to be responsible for the net unimolecular dehydration. Bimolecular ketonization required the coordination of two acetates to a common Ti 4+ cation on a stoichiometric surface. Of the single-crystal surfaces examined, only the {114}-faceted surface presented the necessary fourfold oxygen-coordinated Ti 4+ sites for this reaction.

Formation of Ohmic Contacts to n-GaAs by Solid Phase Epitaxy of Evaporated and Ion Implanted Ge Films

Ge films evaporated on GaAs(100) substrates have been amorphized by ion implantation and recrystallized epitaxially in the solid phase. Ohmic characteristics have been obtained in Ge/n-GaAs heterostructures by implantation of As+ or P+ in Ge and Si+ at the interface. A two-step annealing method was found to be effective to obtain ohmic characteristics. In two-step annealing, the first annealing step at low temperature is for solid phase recrystallization of Ge films; the second step involves rapid high-temperature annealing in order to activate the implanted species. It has also been found that interdiffusion should be minimized in order to obtain good ohmic characteristics.