Modification of the CuInSe2 Crystal Surface during Polishing and Annealing

The RBS/channelling technique was used to study the near-surface damage characteristics of CuInSe₂ crystals after polishing with 0.05 μm grade alumina and subsequent annealing up to temperatures of 600 °C. A comparative RUMP and damage density depth profile analysis of the channelling spectra revealed a polish-induced near-surface disordered layer with a thickness close to 40 nm. Up to annealing temperatures of about 400 °C a gradual overall decrease of the defect density in the damaged layer is observed without detectable changes in its thickness. An indium-rich surface layer is formed after vacuum annealing at 600 °C.     

Characterization of nickel–alumina aerogels with high thermal stability

The characterization of NiO–Al₂O₃ aerogels prepared from nickel nitrate and aluminum iso-propoxide through a sol–gel processing and subsequent supercritical drying was performed. The UV–visible, XPS and FT–IR investigations revealed that nickel ions were incorporated into alumina spinel structure as nickel aluminate form, not as nickel oxide, after calcination. TEM observations after the subsequent reduction exhibited uniform and fine nickel particles less than 6 nm diameter throughout the alumina aerogel support with high dispersion, by which not only high thermal stability of the metal at elevated temperatures but also high reforming activity and stability should be brought about. The large surface area and pore volume also provided the catalyst stability through the improvement of the thermal stability of alumina support.     

A Study of Porous and Surface Properties of Nickel-Molybdenum Catalyst Incorporated on Alumina Modified with Sodium and Magnesium Ions

A series of nickel-molybdenum samples supported on alumina modified with sodium or magnesium ions was studied by the BET method, differential thermal analysis (DTA) and IR spectroscopy to determine their surface properties, pore volume and distribution. Modification with sodium and magnesium ions causes a decrease of the surface area of the nickel-molybdenum catalysts. The decrease proceeds with increasing concentration of the modifying ions. Incorporation of these ions does not change the type of catalyst pores (the ink-bottle or bottle types), yet it affects the size and distribution of pores. It was found that sodium ions prevent from the formation of aluminum molybdate, while magnesium ions increase the thermal stability of the catalyst.     

Complex boron redistribution kinetics in strongly doped polycrystalline‐silicon/nitrogen‐doped‐silicon thin bi‐layers

We have investigated the complex behaviour of boron (B) redistribution process via silicon thin bi‐layers interface. It concerns the instantaneous kinetics of B transfer, trapping, clustering and segregation during the thermal B activation annealing. The used silicon bi‐layers have been obtained by low pressure chemical vapor deposition (LPCVD) method at 480 °C, by using in‐situ nitrogen‐doped‐silicon (NiDoS) layer and strongly B doped polycrystalline‐silicon (P⁺) layer. To avoid long‐range B redistributions, thermal annealing was carried out at relatively low‐temperatures (600 °C and 700 °C) for various times ranging between 30 min and 2 h. To investigate the experimental secondary ion mass spectroscopy (SIMS) doping profiles, a redistribution model well adapted to the particular structure of two thin layers and to the effects of strong‐concentrations has been established. The good adjustment of the simulated profiles with the experimental SIMS profiles allowed a fundamental understanding about the instantaneous physical phenomena giving and disturbing the complex B redistribution profiles‐shoulders. The increasing kinetics of the B peak concentration near the bi‐layers interface is well reproduced by the established model.     

Structural control and magnetic properties of electrodeposited Co nanowires

Co nanowires with a preferred orientation were fabricated by direct current electrodeposition into the pores of porous anodic alumina membrane, and the structure of Co nanowires was studied by X-ray diffraction and high-resolution transmission electron microscopy with selected-area electron diffraction. It is found that the crystal structure of Co nanowires lies on the deposition potential. When electrodeposition is performed far from equilibrium conditions, i.e., at a high potential, face-centered cubic Co nanowires are deposited, while hexagonal close packing Co nanowires are formed at the low potential. The experimental results indicate that the orientation of the nanowires has effects on the coercivity for both hexagonal close packing (hcp) and face-centered cubic (fcc) Co.     

Interdiffusion phenomena in InGaAs/GaAs superlattice structures

We have studied structural properties of InGaAs/GaAs superlattice sample prepared by Molecular Beam Epitaxy (MBE) using high resolution X‐ray diffractometer (HRXRD). Increasing strain relaxation and defect generations are observed with the increasing Rapid Thermal Annealing (RTA) temperature up to 775 °C. The higher temperatures bring out relaxation mechanisms; interdiffusion and favored migration. The defect structure and the defects which are observed with the increasing annealing temperature were analyzed. Firstly, the in‐plane and out‐of‐plane strains after the annealing of sample were found. Secondly, the structural defect properties such as the parallel X‐ray strain, perpendicular X‐ray strain, misfit, degree of relaxation, x composition, tilt angles and dislocation that are obtained from X‐ray diffraction (XRD) analysis were carried out at every temperature. As a result, we observed that the asymmetric peaks especially in asymmetric (224) plane was affected more than symmetric and asymmetric planes with lower polar or inclination angles due to c‐direction at low temperature. These structural properties exhibit different unfavorable behaviors for every reflection direction at the increasing temperatures. The reason is the relaxation which is caused by spatially inhomogeneous strain distribution with the increasing annealing temperature. In the InGaAs superlattice samples, this process enhances preferential migration of In atoms along the growth direction. Further increase in the annealing temperature leads to the deterioration of the abrupt interfaces in the superlattice and degradation in its structural properties. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

The structure,perfection and annealing behaviour of SiC needles grown by a VLS mechanism

Over 50 different single crystals of SiC, grown by a vapour-liquid-solid mechanism, have been examined by optical and X-ray diffraction methods to determine their structure, perfection and annealing behaviour. All the crystals studied had either the hexagonal close-packed 2H (ABAB…) structure or the cubic close-packed 3C (ABCABC…) structure or a combination of both, and invariably contained a random distribution of stacking faults on their basal planes. The thermal stability of the structures was studied by annealing them between 1300–2200 °C in an inert argon atmosphere, and reexamining the structure of the crystals after each annealing run. Structural transformations were found to commence in different crystals at different temperatures between 1400 and 1800 °C. The transformations were found to be irreversible, not martensitic and appear to involve the nucleation of the new phase by the insertion of stacking faults followed by its growth during the annealing. The mechanism of the solid-state transformations, the influence of faults and impurities, and the thermal stability of different SiC structures are discussed.     

Controllable synthesis of well‐aligned CuO nanotube arrays using porous alumina templates

In order to further enhance the performance of CuO in currently existing applications, well‐aligned CuO nanotube arrays with different diameters were fabricated. During the synthesis process, porous anodic alumina films were fabricated, and then the synthesis of CuO nanotube arrays was realized by using the obtained porous anodic alumina films as templates. The morphology and structure of the obtained products has been confirmed by field‐emission scanning electron microscopy, transmission electron microscopy and X‐ray diffraction measurements. Due to the large surface area of the synthesized products, the prepared CuO nanotube arrays may have potential applications in catalyzing and gas sensing area.     

Texture and structure of nickel-molybdenum catalysts supported on alumina modified with sulfate and phosphate ions

A series of nickel-molibdenum catalysts supported on alumina modified with sulfate and phosphate ions was studied. The studies involved texture evaluation measurements through N₂ adsorption isotherms. Besides, IR spectroscopic and derivatographic studies were carried out. Results of the studies enable us to conclude that modification of the alumina support with the above ions leads to a significant decrease in its surface area and pore volume. Modification does not result in a change of the type of pores of the support, but in the change of their size dimention. The pores present on the surface of the catalyst have the shape of “ink-bottles”. Modification with phosphate ions improves the thermal stability of the catalyst, whereas sulfate ions present on the surface of the catalyst undergo decomposition upon heating of the sample. Phosphate ions inhibit formation of aluminum molybdate, and instead form polymeric layer structures of phosphate on the surface of catalysts. Sulfate ions occur in the form of surface aluminum sulfate.     

Structural,electrical and optical properties of Ge implanted GaSe single crystals grown by Bridgman technique

Structural, optical and electrical properties of Ge implanted GaSe single crystal have been studied by means of X‐Ray Diffraction (XRD), temperature dependent conductivity and photoconductivity (PC) measurements for different annealing temperatures. It was observed that upon implanting GaSe with Ge and applying annealing process, the resistivity is reduced from 2.1 × 10⁹ to 6.5 × 10⁵ Ω‐cm. From the temperature dependent conductivities, the activation energies have been found to be 4, 34, and 314 meV for as‐grown, 36 and 472 meV for as‐implanted and 39 and 647 meV for implanted and annealed GaSe single crystals at 500°C. Calculated activation energies from the conductivity measurements indicated that the transport mechanisms are dominated by thermal excitation at different temperature intervals in the implanted and unimplanted samples. By measuring photoconductivity (PC) measurement as a function of temperature and illumination intensity, the relation between photocurrent (I_PC) and illumination intensity (Φ) was studied and it was observed that the relation obeys the power law, I_PC αΦⁿ with n between 1 and 2, which is indication of behaving as a supralinear character and existing continuous distribution of localized states in the band gap. As a result of transmission measurements, it was observed that there is almost no considerable change in optical band gap of samples with increasing annealing temperatures for as‐grown GaSe; however, a slight shift of optical band gap toward higher energies for Ge‐implanted sample was observed with increasing annealing temperatures. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

温度对TiO2-B纳米纤维的结晶度和稳定性的影响

本文以锐钛矿相二氧化钛纳米颗粒和NaOH溶液为前驱物,通过水热反应和退火处理制备了TiO2-B纳米纤维.用XRD、HRTEM和EDS对样品的结构、形貌及其演化进行了表征.讨论了水热反应温度和退火温度对TiO2 -B纳米纤维的结晶度、形貌和热稳定性的影响.结果表明:在160℃、180℃和200℃温度下水热反应,分别得到H2Ti4O9、H2Ti3O7和H2Ti4O9与H2Ti3O7混合的纳米纤维,400℃退火后,无论是H2Ti4O9还是H2Ti3O7纳米纤维都转化为TiO2-B纳米纤维,但从180℃水热反应得到的H2Ti3O7纳米纤维转化的TiO2-B纳米纤维具有较高结晶度和热稳定性.     

Structural changes of mullite precursors in presence of polyethyleneimine

Thermal properties of two powders derived from the same calcined gel with a stoichiometric mullite composition (atomic ratio Al/Si =3/1) wet milled in different solutions were studied by simultaneous differential thermal analysis, thermogravimetry and evolved gas analysis (DTA,TG,EGA, respectively), by density measurements and by ²⁹Si MAS NMR spectroscopy and X-ray diffraction (XRD). Calcined gel was milled either in ethanol or in ethanol with the addition of 0.03 g of polyethyleneimine (PEI) per gram of mullite. DTA, TG and mass spectrometry revealed esterification of unhydrated surface of particles formed by milling in ethanol. The difference in the structural evolution of powders and their dependence on annealing temperature seen in ²⁹Si MAS NMR spectra and XRD patterns is attributed to different degrees of segregation of alumina and silica components, and to differing compositions of transitory spinel phase. In both samples the segregation of silica and alumina was observed at temperatures less than that for mullite crystallization. The degree of segregation was much smaller in the sample milled in ethanol. Therefore, in the latter sample spinel with larger silica content incorporated in γ-Al₂O₃ will crystallize by annealing at 900°C, and Al-rich mullite at 1100°C. Due to greater segregation of silica and alumina component in the presence of PEI, the crystallization of spinel with smaller amounts of silica incorporated into γ-Al₂O₃ is shifted to 1100°C, and orthorhombic mullite to about 1200°C. The influence of PEI is indicated by a larger sintering density at lower temperatures.     

Deposition of thick silica-titania sol-gel films on Si substrates

A process for production of thick (>10 μm) titania-doped silica films on Si substrates by repetitive spin-coating of sol-gel material and rapid thermal annealing for 10 s in the range 800–1200°C is described. The dependence of overall thickness and etch rate in buffered HF on annealing temperature is described, and it is shown that films annealed at low (< 1175°C) temperatures have a relatively large thickness and etch rate. However, films having the properties of fully densified material (minimum thickness and etch rate) can be produced by subsequent consolidation. The film stress characteristics are similar to those phosphosilicate glass formed by the same process: films annealed below a critical temperature (< 1075°C) are under tensile stress at the annealing temperature, and crack before a thick film can be built up. Refractive index data are given; these show that only fully consolidated films have the refractive index expected from their SiO₂ and TiO₂ compositions. Finally, discrepancies in results for thickness of unconsolidated single-layer and multilayer films are explained using a simple model that accounts for the effect of cumulative densification.     

Structure and optical properties of amorphous silicon oxide thin films with different porosities

Amorphous silicon oxide thin films were prepared by evaporation of a silicon oxide powder. Samples were prepared under ultrahigh vacuum, under a flow of hydrogen ions or under a molecular hydrogen atmosphere. Two others sets of samples were prepared using deuterium instead of hydrogen. These five groups of samples were then annealed to different temperatures up to 950 °C and were exposed to the ambient air. The samples present different densities and microstructures. The sample prepared under ultrahigh vacuum is dense, hydrogen free and OH-bond free. Samples prepared under atomic hydrogen and deuterium flows contain Si–H and Si–D bonds, respectively, and are OH-bond free. The sample prepared under a molecular hydrogen atmosphere is very similar to that prepared under a molecular deuterium atmosphere. Both samples are porous and contain Si–H bonds and OH-groups coming from the exposure to the air. All the samples show visible photoluminescence attributed to isolated silicon clusters. The photoluminescence intensity increases with thermal annealing post-treatments up to an optimal annealing temperature. This maximum value is equal to 650 °C for the unhydrogenated sample and the sample prepared under an atomic hydrogen flow and to 800 °C for the sample prepared under a molecular hydrogen atmosphere. This difference is correlated to the different microstructures of the samples. Moreover the strongest photoluminescence intensity is obtained for the porous sample.     

Multiple-step annealing for 50% enhanced p-conductivity of GaN

In this article, multiple-step rapid thermal annealing (RTA) processes for the activation of Mg doped GaN are compared with conventional single-step RTA processes. The investigated multiple-step processes consist of a low temperature annealing step at temperatures between 350°C and 700°C with dwell times up to 5 min and a short time high temperature step. With optimized process parameters, and multiple-step processes, we achieved p-type free carrier concentrations up to 1–2×10¹⁸ cm⁻³. The best achieved conductivity, so far, lies at 1.2 Ω⁻¹ cm⁻¹. This is a 50% improvement compared to conventional single-step process at 800°C, 10 min.     

The formation of tin oxides in thin-film Sn/C/KCl(100) structures

The formation of oxides upon the thermal annealing (both in air and vacuum) of island tin films grown on a KCl(100) substrate, which was coated by a thin layer of amorphous carbon, has been investigated by transmission electron microscopy. It is established that thermal annealing at temperatures below the tin melting point (T _m) does not lead to phase transitions with the formation of new crystalline oxide phases. At the same time, the films undergo structural changes: the average size of blocks in the substrate plane decreases compared to those in an as-deposited film. Thermal annealing in air at temperatures above the tin melting point leads to the formation of multiphase oxide structures and increases the average size of blocks and islands in the substrate plane. It is shown that preliminary thermal annealing in air at temperatures below T _m hinders oxidation upon subsequent heat treatment.     

Effect of annealing on the structural,electrical and optical properties of nanostructured TiO2 thin films

Nanostructured titanium dioxide thin films were prepared using reactive pulsed laser ablation technique. Effects of annealing on the structural, morphological, electrical and optical properties are discussed. The structural, electrical and optical properties of TiO₂ films are found to be sensitive to annealing temperature and are described with GIXRD, SEM, AFM, UV‐Visible spectroscopy and electrical studies. X‐ray diffraction studies showed that the as‐deposited films were amorphous and at first changed to anatase and then to rutile phase with increase of annealing temperature. Optical constants of these films were derived from the transmission spectra and the refractive index dispersion of the films, subjected to annealing at different temperatures, is discussed in terms of the single oscillator‐Wemple and Didomenico model. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Transient analysis of the cooling process and influence of bottom insulation on the stress in the multicrystalline silicon ingot

Directional solidification is one of the most popular techniques for massive production of multicrystalline silicon. After growth and annealing, the ingot is cooled down by a designed cooling process, which is initialized by descending bottom insulation, and then is controlled both by power ramp‐down rate and by motion of the bottom insulation. Thermal stress is piled up during cooling, and associated crystal defects, such as dislocation and micro‐cracks, may generate and propagate in the ingot. In the paper, transient modeling is applied to study the effect of bottom insulation on the cooling process. Temperature, velocity and thermal stress fields are obtained with linear, parabolic and sinusoidal motions of the insulation. The measured and predicted temperatures at two points of the ingot are found consistent. Distributions of von Mises stress in the ingot at different cooling time are obtained, and the maximum von Mises stresses are presented as a function of the cooling time. Specifically, dislocation‐free regions, evaluated by the critical resolved shear stress model, at certain cooling time, and area fractions of the regions as a function of the cooling time are proposed. The linear motion is further discussed with different moving rates, considering its wide applications in the current industry and convenient realization in control.     

Photoelectrical properties of crystalline titanium dioxide thin films after thermo‐annealing

This paper reports the photoelectrical properties of sol gel derived titanium dioxide (TiO₂) thin films annealed at different temperatures (425‐900°C). The structure of the as‐grown film was found to be amorphous and it transforms to crystalline upon annealing. The trap levels are studied by thermally stimulated current (TSC) measurements. A single trap level with activation energy of 1.5 eV was identified. The steady state and transient photocurrent was measured and the results are discussed on the basis of structural transformation. The photocurrent was found to be maximum for the films annealed at 425°C and further it decreases with annealing at higher temperatures. The photoconduction parameters such as carrier lifetime, lifetime decay constant and photosensitivity were calculated and the results are discussed as a function of annealing temperature. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Effects of annealing on the lattice parameter of polycrystalline CdS thin films

Cubic CdS (β‐CdS) polycrystalline thin films were prepared on glass substrates by chemical synthesis at 80 °C. Samples were subjected to thermal treatments (TT) in the range of temperatures (T) 180 – 500 °C during 30 hours in different ambients. Annealing in air and in H₂ produces in CdS larger lattice parameter enlargements (≤2.5 %) when T of TT increases up to T ≤ 500 °C. Whereas, annealing in Ar + S₂ and vacuum provokes intermediate (≤1.2 %) and smaller (≤0.9 %) maxima values of the lattice parameter increments, respectively. Energy band gap (E_g) as a function of T of TT and as a function of the lattice parameter has been also studied where it was observed that E_g behaves in very different manners depending on the ambient chosen for annealing. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)