Showing papers on "Annealing (metallurgy) published in 2004"

Effect of Molecular Weight and Annealing of Poly(3-hexylthiophene)s on the Performance of Organic Field-Effect Transistors

Abstract: The optical, structural, and electrical properties of thin layers made from poly(3-hexylthiophene) (P3HT) samples of different molecular weights are presented. As reported in a previous paper by Kline et al., Adv. Mater 2003, 15, 1519, the mobilities of these layers are a strong function of the molecular weight, with the largest mobility found for the largest molecular weight. Atomic force microscopy studies reveal a complex polycrystalline morphology which changes considerably upon annealing. X-ray studies show the occurrence of a layered phase for all P3HT fractions, especially after annealing at 1.50 degreesC . However, there is no clear correlation between the differences in the transport properties and the data from structural investigations. In order to reveal the processes limiting the mobility in these layers, the transistor properties were investigated as a function of temperature. The mobility decreases continuously with increasing temperatures; with the same trend pronounced thermochromic effects of the P3HT films occur. Apparently, the polymer chains adopt a more twisted, disordered conformation at higher temperatures, leading to interchain transport barriers. We conclude that the backbone conformation of the majority of the bulk material rather than the crystallinity of the layer is the most crucial parameter controlling the charge transport in these P3HT layers. This interpretation is supported by the significant blue-shift of the solid-state absorption spectra with decreasing molecular weight, which is indicative of a larger distortion of the P3HT backbone in the low-molecular weight P3HT layers

Annealing effect on the property of ultraviolet and green emissions of ZnO thin films

Abstract: The mechanism of ultraviolet (UV) and green emission of ZnOthin filmsdeposited on (001) sapphire substrates by pulsed laser deposition was investigated by using postannealing treatment at various annealing temperatures after deposition.Structural, electrical, and optical properties of ZnOfilms have been also observed. As the postannealing temperature increased, the intensity of UV (380 nm) peak and the carrier concentration were decreased while the intensity of the visible (about 490–530 nm) peak and the resistivity were increased. The role of oxygen in ZnOthin film during the annealing process was important to the change of optical properties. The mechanism of the luminescence suggested that UVluminescence of ZnOthin film was related to the transition from near band edge to valence band, and green luminescence of ZnOthin film was caused by the transition from deep donor level to valence band due to oxygen vacancies. The activation energy derived by using the variation of green emission intensity was 1.19 eV.

Chapter 12 – Recrystallization Textures

Abstract: Publisher Summary The recrystallization textures that develop when deformed metals are annealed have been the subject of extensive study. These textures are largely responsible for the directionality of properties observed in many finished products. Recrystallization textures are related to the nature of the nucleation event, the orientation dependence of the rate of nucleation in inhomogeneities of various type and orientation environment, and to the nature, energy and mobility of the boundaries among grains of various orientations. The determination of microtextures by Electron Backscatter Diffraction (EBSD), which enables a correlation to be made between local orientation and microstructure, is now enabling some advances in this field. The development of an annealing texture does not cease when recrystallization is complete. It continues during grain growth and the final texture is not necessarily representative of the texture present when primary recrystallization is complete. There is increasing evidence that the orientation of the material before deformation plays a significant role in determining the recrystallization texture. The purity of a particular metal may strongly influence the recrystallization texture. In many cases very small amounts of second elements may, by affecting the boundary mobility, change the annealing texture completely.

Mn interstitial diffusion in (ga,mn)as.

Abstract: We present a combined theoretical and experimental study of the ferromagnetic semiconductor (Ga,Mn)As which explains the remarkably large changes observed on low-temperature annealing. Careful control of the annealing conditions allows us to obtain samples with ferromagnetic transition temperatures up to 159 K. Ab initio calculations, in situ Auger spectroscopy, and resistivity measurements during annealing show that the observed changes are due to out diffusion of Mn interstitials towards the surface, governed by an energy barrier of 0.7-0.8 eV. Electric fields induced by Mn acceptors have a significant effect on the diffusion.

Transformation-induced plasticity for high strength formable steels

Abstract: Recent advances in the development of high performance steels presenting improved properties of strength and ductility rely on the TRIP effect, i.e. on the mechanically-induced martensitic transformation of the retained austenite dispersed in a soft ferrite-based matrix. As a consequence, the stabilisation and retention of austenite at room temperature have become of primary importance, leading to specifically designed steel grades and thermal or thermomechanical treatments. Particularly, carbon enrichment of the austenite during intercritical annealing and bainite transformation was found to be very effective in retaining austenite. This metastable austenite then progressively transforms during straining, bringing about a large increase of the work hardening rate. This increase results from the stress and strain partitioning continuously evolving with the appearance of the hard martensite. (c) 2004 Elsevier Ltd. All rights reserved.

Semiconductor to metal phase transition in the nucleation and growth of VO2 nanoparticles and thin films

Abstract: The optical and morphological characteristics of vanadium dioxide nanoparticles and thin films during their nucleation and growth phases have been studied by correlating the temperature and sharpness of the transition with the processing parameters. Thermal annealing results in grain growth and improved crystallinity. Normally, larger crystallites show smaller hysteresis, as there is a greater probability of finding a nucleating defect in the larger volume. But at the same time, this improved crystal perfection, which accompanies the thermal annealing and grain growth, tends to a larger hysteresis, as there are fewer nucleating defects within the volume. We show that the width and shape of the hysteresis cycle are thus determined by the competing effects of crystallinity and grain size.

Formation and evolution of luminescent Si nanoclusters produced by thermal annealing of SiOx films

Abstract: Si nanoclusters embedded in SiO2 have been produced by thermal annealing of SiOx films prepared by plasma enhanced chemical vapor deposition. The structural properties of the system have been investigated by energy filtered transmission electron microscopy (EFTEM). EFTEM has evidenced the presence of a relevant contribution of amorphous nanostructures, not detectable by using the more conventional dark field transmission electron microscopy technique. By also taking into account this contribution, an accurate quantitative description of the evolution of the samples upon thermal annealing has been accomplished. In particular, the temperatures at which the nucleation of amorphous and crystalline Si nanoclusters starts have been determined. Furthermore, the nanocluster mean radius and density have been determined as a function of the annealing temperature. Finally, the optical and the structural properties of the system have been compared, to demonstrate that the photoluminescence properties of the system depend on both the amorphous and crystalline clusters.

XPS depth profile analysis of non‐stoichiometric NiO films

Abstract: Antiferromagnetic NiO films used for pinning layers in spin valve systems were prepared by reactive sputtering from an NiO target with variation of the oxygen/argon mixture in the sputter gas. Using XPS depth profiling we investigated the NiOx overstoichiometry (x > 1) in the films that was found by other methods and the chemical changes in the films during annealing. A direct detection of Ni3+ failed because of strong preferential sputtering with the formation of metallic Ni during sputtering. By means of factor analysis a qualitative description of the overstoichiometry is possible. Indirectly it could be shown that metallic Ni is already formed in the oxide layers during annealing. It can be concluded that the stability of the NiOx films decreases with increasing deviation from stoichiometry (x > 1). Copyright © 2004 John Wiley & Sons, Ltd.

Al-doped ZnO thin films by sol–gel method

Abstract: Transparent and conductive high preferential c-axis oriented ZnO thin films doped with Al have been prepared by sol–gel method using zinc acetate and aluminium chloride as cations source, 2-methoxiethanol as solvent and monoethanolamine as sol stabilizer. Film deposition was performed by dip-coating technique at a withdrawal rate of 1.5 cm min−1 on Corning 1737 glass substrate. The effect of dopant concentration, heating treatment and annealing in reducing atmosphere on the microstructure as well as on the electrical and optical properties of the thin films is discussed. The optical transmittance spectra of the films showed a very good transmittance, between 85 and 95%, within the visible wavelength region. The minimum resistivity of 1.3×10−3 Ω cm was obtained for the film doped with 2 wt.% Al, preheated at 400 °C and post-heated at 600 °C, after annealing under a reduced atmosphere of forming gas.

Austenite formation during intercritical annealing

Abstract: A systematic experimental study has been conducted on ferrite recrystallization and intercritical austenite formation for two low-carbon steels with chemical compositions typically used for dual-phase and transformation-induced plasticity (TRIP) steels. Different initial heating rates, holding temperatures, and times were applied to the materials to examine the ferrite recrystallization and austenite formation kinetics. An Avrami model was developed to describe the isothermal ferrite recrystallization behavior and was applied successfully to the nonisothermal conditions. It was found that the initial heating rate affects the isothermal austenite formation kinetics for both the hot-rolled and cold-rolled materials albeit the effect is more pronounced for the cold-rolled material. This can be attributed to the interaction between the ferrite recrystallization and austenite formation processes. Furthermore, it was found that the distribution of austenite phase is also affected by the ferrite recrystallization process. When ferrite recrystallization is completed before the austenite formation (i.e., under sufficiently slow heating rate conditions), austenite is to a large extent randomly distributed in the ferrite matrix. On the other hand, incomplete recrystallization of ferrite due to higher heating rates leads to the formation of banded austenite grains. It is proposed that this observation is characteristic of simultaneous recrystallization and austenite formation where moving ferrite grain boundaries do not provide suitable sites for austenite nucleation.

Amorphous-to-crystal transition of nitrogen- and oxygen-doped Ge2Sb2Te5 films studied by in situ resistance measurements

Abstract: The amorphous-to-crystal transition has been studied through in situ resistance measurements in Ge2Sb2Te5 thin films doped by ion implantation with nitrogen or oxygen The dependence of the electrical resistivity and structure on the annealing temperature and time has been investigated in samples with different dopant concentrations Enhancement of the thermal stability and increase of the mobility gap for conduction have been observed in O- and N-doped amorphous Ge2Sb2Te5 Larger effects have been found in the case of nitrogen doping

Method for forming a thin film and method for fabricating a semiconductor device

Abstract: By conducting a high temperature annealing in a nitrogen atmosphere at a temperature at which a hafnium silicate film undergoes no phase separation, hydrogen contained in the film is removed and prevention of boron penetration is made possible. The present invention provides a method for forming a thin film including a step of forming a hafnium silicate film on a substrate by an atomic layer deposition method and a step of carrying out thermal treatment on the hafnium silicate film at a thermal treatment temperature equal to or higher than a temperature at which hydrogen contained in the hafnium silicate film is removed and lower than a temperature at which the hafnium silicate film undergoes no phase separation, and a method for fabricating a semiconductor device for forming a gate dielectric film using the method for forming a thin film.

Effects of high-dose Mn implantation into ZnO grown on sapphire

Abstract: ZnO films grown by pulsed-laser deposition on c-plane Al2O3 substrates were annealed at temperatures up to 600 °C to produce n-type carrier concentrations in the range 7.5×1015–1.5×1020 cm−3. After high-dose (3×1016 cm−2) Mn implantation and subsequent annealing at 600 °C, all the films show n-type carrier concentrations in the range 2–5×1020 cm−3 and room temperature hysteresis in magnetization loops. The saturation magnetization and coercivity of the implanted single-phase films were both strong functions of the initial anneal temperature, suggesting that carrier concentration alone cannot account for the magnetic properties of ZnO:Mn, and that factors such as crystalline quality and residual defects play a role.

Ab initio study of the annealing of vacancies and interstitials in cubic SiC: Vacancy-interstitial recombination and aggregation of carbon interstitials

Abstract: The annealing kinetics of mobile intrinsic defects in cubic SiC is investigated by an ab initio method based on density-functional theory. The interstitial-vacancy recombination, the diffusion of vacancies, and interstitials to defect sinks (e.g., surfaces or dislocations) as well as the formation of interstitial clusters are considered. The calculated migration and reaction barriers suggest a hierarchical ordering of competing annealing mechanisms. The higher mobility of carbon and silicon interstitials as compared to the vacancies drives the annealing mechanisms at lower temperatures including the vacancy-interstitial recombination and the formation of interstitial carbon clusters. These clusters act as a source of carbon interstials at elevated temperatures. In p-type material the transformation of the silicon vacancy into the more stable vacancy-antisite complex constitutes an annealing mechanism which is activated before the vacancy migration. Recent annealing studies of vacancy-related centers in irradiated 3C-SiC and 4H-SiC and semi-insulating 4H-SiC are interpreted in terms of the proposed hierarchy of annealing mechanisms.

Temperature dependent magnetic anisotropy in (Ga, Mn)As layers

Abstract: It is demonstrated by SQUID measurements that (Ga,Mn)As films can exhibit perpendicular easy axis at low temperatures, even under compressive strain, provided that the hole concentration is sufficiently low. In such films, the easy axis assumes a standard in-plane orientation when the temperature is raised towards the Curie temperature or the hole concentration is increased by low temperature annealing. These findings are shown to corroborate quantitatively the predictions of the mean-field Zener model for ferromagnetic semiconductors. The in-plane anisotropy is also examined, and possible mechanisms accounting for its character and magnitude are discussed.

Characteristics of Al-doped ZnO thin films obtained by ultrasonic spray pyrolysis: effects of Al doping and an annealing treatment

Abstract: Transparent conducting Al-doped ZnO thin films were prepared on silica glass substrates by an ultrasonic spray pyrolysis method. The effects of Al doping and an annealing treatment on electrical and optical properties of ZnO thin films were investigated. Zinc acetate dihydrate, 2-methoxyethanol and aluminum chloride were used as a starting material, a solvent and a dopant source, respectively. The electrical conductivity of ZnO films was improved by Al doping and by annealing in a reducing atmosphere. The minimum electrical resistivity was obtained in the 3 at.% Al-doped film annealed at 500 °C in nitrogen with 5% hydrogen and its value was 1.71×10−2 Ω cm. The average optical transmittance of all films, regardless of a doping concentration and an annealing condition, was higher than 80% in the visible range. The optical direct band gap of films was dependent on the amount of a dopant and the annealing treatment in a reducing atmosphere. The optical direct band gap value of 3 at.% Al-doped films annealed at 500 °C in nitrogen were 3.33 eV.

Structural, Optical, and Photoelectrochemical Properties of Mn+−TiO2 Model Thin Film Photocatalysts

Abstract: Mn+−TiO2 thin films (M: Cr, V, Fe, Co) with different M/Ti ratios have been prepared by ion beam induced CVD (IBICVD) with the aim of investigating their structural, optical, and photocatalytic properties. These samples can be considered as model systems to describe the photocatalytic behavior of other Mn+−TiO2 materials reported in the literature. In their “as prepared” state the samples were amorphous and the cations were homogeneously distributed within the TiO2 layer. Crystallization of the thin films upon annealing has been investigated with X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FT-IR). This latter technique has proved to be a suitable and rapid method of crystal phase assessment of TiO2. After annealing at T > 573 K, TiO2 crystallizes into the anatase or rutile structures depending on the type and amount of cations present in the film. The local environment around the different cations has been ascertained by X-ray absorption spectroscopy (XAS). It has been shown that...

Effects of hydrogen annealing on heteroepitaxial-Ge layers on Si: Surface roughness and electrical quality

Abstract: We have studied the effect of hydrogen annealing on the surface roughness of germanium (Ge) layers grown by chemical vapor deposition on silicon using atomic force microscopy and cross-sectional high resolution scanning electron microscopy (HR-SEM). Our results indicate a strong reduction of roughness that approaches 90% at 825°C. The smoother Ge surface allowed for the fabrication of metal-oxide-semiconductor capacitors using germanium oxynitride (GeOxNy) as the gate dielectric. Electrical quality was studied using high frequency capacitance–voltage characteristic of epi-Ge showing negligible hysteresis. We discuss the results in terms of Ge–H cluster formation, which lowers the diffusion barrier, allowing for higher diffusivity and surface mobility. The temperature dependence shows tapering off for temperatures exceeding 800°C, indicating a barrier reduction of ∼92meV.

Diffusion Studies of Copper on Ruthenium Thin Film A Plateable Copper Diffusion Barrier

Abstract: Diffusion studies were carried out on physical vapor deposited Cu/Ru(∼20 nm)/Si samples using secondary ion mass spectroscopy (SIMS) and transmission electron microscopy (TEM). Back side SIMS depth profiling revealed well-defined interfaces and showed that Cu interdiffusion was impeded by Ru thin film up to 450°C vacuum annealing. TEM showed a 20-22 nm Ru barrier layer with a columnar microstructure oriented vertically with respect to Si substrate. TEM results corroborate with SIMS data to indicate stability of the Ru film barrier for annealing temperatures up to 450°C. Direct Cu electroplating on ultrathin Ru barrier layers (<20 nm) was investigated in sulfuric acid. The electroplated Cu film is shiny, smooth, and without agglomeration under scanning electron microscopy. Excellent adhesion between interfacial layers was confirmed by the scribe-peel test. The interfacial characterization results indicate that Ru thin film is a promising candidate as a directly plateable Cu diffusion barrier.

Electronic behaviors of high-dose phosphorus-ion implanted 4H-SiC(0001)

Abstract: High-dose phosphorus-ion (P+) implantation into 4H–SiC (0001) followed by high-temperature annealing has been investigated. Annealing with a graphite cap largely suppressed the surface roughening of implanted SiC. The surface stoichiometry of implanted SiC was examined by x-ray photoelectron spectroscopy. Electronic behaviors of P+-implanted SiC are discussed based on Hall effect measurements. There is no significant difference in the sheet resistance between SiC annealed with a graphite cap and without a graphite cap. The sheet resistance (resistivity) takes a minimum value of 45 Ω/□ (0.9 mΩcm) at an implant dose of 6.0×1016 cm−2. The sheet resistance shows a weak temperature dependence.

Effect of surface NH3 anneal on the physical and electrical properties of HfO2 films on Ge substrate

Abstract: Metal-oxide-semiconductor capacitors were fabricated on germanium substrates by using metalorganic-chemical-vapor-deposited HfO2 as the dielectric and TaN as the metal gate electrode. It is demonstrated that a surface annealing step in NH3 ambient before the HfO2 deposition could result in significant improvement in both gate leakage current and the equivalent oxide thickness (EOT). It was possible to achieve a capacitor with an EOT of 10.5 A and a leakage current of 5.02×10−5 A/cm2 at 1 V gate bias. X-ray photoelectron spectroscopy analysis indicates the formation of GeON during surface NH3 anneal. The presence of Ge was also detected within the HfO2 films. This may be due to Ge diffusion at the high temperature (∼400 °C) used in the chemical-vapor deposition process.