Showing papers on "Annealing (metallurgy) published in 2005"

Investigation of annealing effects and film thickness dependence of polymer solar cells based on poly(3-hexylthiophene)

Abstract: Regioregular poly(3-hexylthiophene) (RR-P3HT) is a promising candidate for polymer photovoltaic research due to its stability and absorption in the red region. In this manuscript, we report polymer photovoltaic devices based on RR-P3HT:methanofullerene [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) 1:1 weight-ratio blend. We studied the effects of annealing temperature and time on the device performance for devices annealed before and after cathode deposition. Thermal annealing shows significant improvement in the performance for both types of annealing conditions, with postproduction annealing being slightly better. For devices with a 43-nm-thick active layer, maximum power conversion efficiency (PCE) of 3.2% and fill factor up to 67% is achieved under Air Mass 1.5, 100‐mW∕cm2 illumination. We performed atomic force microscopy and ultraviolet-visible absorption spectroscopy on the P3HT:PCBM films to explain the effect of thermal annealing. By keeping the optimized thermal annealing condition and by va...

Silica Spheres Coated with YVO4:Eu3+ Layers via Sol−Gel Process: A Simple Method To Obtain Spherical Core−Shell Phosphors

Abstract: Spherical SiO2 particles have been successfully coated with YVO4:Eu3+ phosphor layers through a Pechini sol−gel process. The resulted YVO4:Eu3+@SiO2 core−shell phosphors were characterized by X-ray diffraction (XRD), Fourier-transform IR spectroscopy, scanning electron microscopy, X-ray photoelectron spectra, transmission electron microscopy, UV/vis absorption spectra, general and time-resolved photoluminescence spectra, as well as kinetic decays. The XRD results demonstrate that the YVO4:Eu3+ layers begin to crystallize on the SiO2 particles after annealing at 400 °C, and the crystallinity increases with raising the annealing temperature. The obtained core−shell phosphors have perfect spherical shape with narrow size distribution (average size ca. 500 nm), nonagglomeration, and smooth surface. The thickness of the YVO4:Eu3+ shells on SiO2 cores could be easily tailored by varying the number of deposition cycles (60 nm for two deposition cycles). The Eu3+ shows a strong photoluminescence (PL) (dominated b...

Mechanical properties and machining performance of Ti1−xAlxN-coated cutting tools

Abstract: The mechanical properties and machining performance of Ti 1− x Al x N-coated cutting tools have been investigated. Processing by arc evaporation using cathodes with a range of compositions was performed to obtain coatings with compositions x =0, x =0.25, x =0.33, x =0.50, x =0.66 and x =0.74. As-deposited coatings with x ≤0.66 had metastable cubic structures, whereas x =0.74 yielded two-phase coatings consisting of cubic and hexagonal structures. The as-deposited and isothermally annealed coatings were characterised by nanoindentation, scanning electron microscopy (SEM) and X-ray diffraction (XRD). Cutting tests revealing tool wear mechanisms were also performed. Results show that the Al content, x , promotes a (200) preferred crystallographic orientation and has a large influence on the hardness of as-deposited coatings. The high hardness (∼37 GPa) and texture of the as-deposited Ti 1− x Al x N coatings are retained for annealing temperatures up to 950 °C, which indicates a superior stability of this system compared to TiN and Ti(C,N) coatings. We propose that competing mechanisms are responsible for the effectively constant hardness: softening by residual stress relaxation through lattice defect annihilation is balanced by hardening from formation of a coherent nanocomposite structure of c-TiN and c-AlN domains by spinodal decomposition. This example of secondary-phase transformation (age-) hardening is proposed as a new route for advanced surface engineering, and for the development of future generation hard coatings.

A study of the effect of annealing on Fe‐doped LiNbO3 by HRXRD, XRT and FT–IR

Abstract: The annealing effect on the structural perfection of Fe-doped LiNbO3 single crystals has been studied by high-resolution X-ray diffractometry (HRXRD), X-ray topography (XRT) and Fourier transform infrared (FT–IR) spectroscopy. The single crystals, prepared by mixing Li2CO3 and Nb2O5 powders in the molar ratio 48.6:51.4 with 0.05 mol% of iron at 1415 (1) K, were grown by the Czochralski (CZ) method along the [001] direction in air and poled during crystal growth by the application of a DC field. Two low-angle (tilt angle ∼1 arc minute) structural grain boundaries were observed in as-grown specimens. FT–IR spectra revealed that these crystals contain OH− and CO32− ionic defects. Grain boundaries and CO32− ionic defects were successfully removed, while the concentration of OH− ions was considerably reduced by post-growth thermal annealing at elevated temperatures.

Formation of Type I-IR and Type II-IR gratings with an ultrafast IR laser and a phase mask.

Abstract: The formation of two grating types in SMF-28 fiber by focusing 125 fs, 0.5-2 mJ pulses through a phase mask onto a fiber sample is studied. The first type, specified as type I-IR, occurs below the damage threshold of the medium. The scaling behavior of the type I-IR gratings with field intensity and annealing properties suggests that their formation is related to nonlinear absorption processes, possibly resulting in color center formation. The second type, denoted as type II-IR, occurs coincidentally with white light generation within the fiber. These type II-IR gratings are stable at temperatures in excess of 1000 masculineC and are most likely a consequence of damage to the medium following ionization.

Self-forming diffusion barrier layer in Cu–Mn alloy metallization

Abstract: Advancement of semiconductor devices requires the realization of an ultrathin diffusion barrier layer between Cu interconnect and insulating layers. The present work investigated the possibility of the self-forming barrier layer in Cu–Mn alloy thin films deposited directly on SiO2. After annealing at 450 °C for 30 min, a Mn containing amorphous oxide layer of 3–4 nm in thickness was formed uniformly at the interface. Residual Mn atoms were removed to form a surface oxide layer, leading to a drastic resistivity decrease of the film. No interdiffusion was detected between Cu and SiO2 within the detection limit of x-ray energy dispersive spectroscopy.

The Effect of Thermal Treatment on the Morphology and Charge Carrier Dynamics in a Polythiophene–Fullerene Bulk Heterojunction

Abstract: The influence of various thermal treatment steps on the morphology and the photoconductive properties of a non-contacted, 50 nm thick blend (50:50 wt.-%) of [6,6]-phenyl C61-butyric acid methyl ester (PCBM) and poly(3-hexyl thiophene) (P3HT) spin-coated from chloroform has been studied using transmission electron microscopy (TEM) and the electrodeless time-resolved microwave conductivity technique. After annealing the film for 5 min at 80 °C, TEM images show the formation of crystalline fibrils of P3HT due to a more ordered packing of the polymer chains. The thermal treatment results in a large increase of the photoconductivity, due to an enhancement of the hole mobility in these crystalline P3HT domains from 0.0056 cm2 V–1 s –1 for the non-annealed sample to 0.044 cm2 V–1 s –1 for the sample annealed at 80 °C. In contrast, the temporal shape of the photoconductivity, with typical decay half-times, τ1/2, of 1 μs for the lowest excitation intensities, is unaffected by the temperature treatment. Further annealing of the sample at 130 °C results in the formation of three different substructures within the heterojunction: a PCBM:P3HT blend with PCBM-rich clusters, a region depleted of PCBM, and large PCBM single crystals. Only a minor increase in the amplitude, but a tenfold rise of the decay time of the photoconductivity, is observed. This is explained by the formation of PCBM-rich clusters and large PCBM single crystals, resulting in an increased diffusional escape probability for mobile charge carriers and hence reduced recombination.

Annealing effects on the properties of copper oxide thin films prepared by chemical deposition

Abstract: We have investigated the annealing effect on the structural, optical and electrical properties of copper oxide films prepared on glass substrates by chemical deposition. The films were annealed in air for different temperatures ranging from 200 to 350 °C. X-ray diffraction patterns showed that the films as-deposited and annealed at 200 and 250 °C are of cuprite structure with composition Cu2O. Annealing at 300 °C converts these films to CuO. This conversion is accompanied by a shift in the optical band gap from 2.20 eV to 1.35 eV. Also this conversion was obtained by the dc electrical conductivity and FTIR spectroscopy measurements.

Synthesis of manganese oxide electrodes with interconnected nanowire structure as an anode material for rechargeable lithium ion batteries.

Abstract: Manganese oxide electrodes composed of interconnected nanowires are electrochemically synthesized in manganous acetate solution at room temperature without any template and catalyst. Annealing temperature affects the electrode morphology, crystallization, and electrochemical performance. Scanning electron microscope (SEM) results show that nanowires are uniformly distributed and sizes are about 12−18 nm in diameter; the diameter decreases to about 8−12 nm after annealing at 300 °C. X-ray diffraction (XRD) and transmission electron microscope (TEM) images indicate that nanowires have poor crystalline characteristics. The higher the annealing temperature, the higher the crystalline degree is in manganese oxide. The synthesized anode material shows a much larger capacity than the traditional graphite materials for lithium storage. After annealing at 300 °C, the electrode's reversible capacity reaches 800 mAhg-1, and the specific capacity retention remains nearly constant after 100 cycles.

The Role of Retained Austenite on Tensile Properties of Steels with Bainitic Microstructures

Abstract: In high-carbon, silicon-rich steels it is possible to obtain a very fine bainitic microstructure by transformation at low temperatures (200– 300 � C). This microstructure consists of slender ferrite plates, with thicknesses of several tens of nm, in a matrix of retained austenite. Whereas strength is mainly provided by to the fine scale of the ferrite plates (stronger phase), ductility is mostly controlled by the retained austenite (softer phase). Further improvement in ductility is achieved by strain induced transformation of austenite to martensite, the so called TRIP effect. In order to take full advantage of this effect, the mechanical stability of the austenite, i.e., its capability to transform to martensite under strain, must not be too low nor excessively high. Two main aspects of the mechanical stability of the retained austenite, morphology and chemical composition, have been studied to determine the role that these play on the ductility behaviour of the bainitic steels studied. It is suggested that the chemical composition has the strongest effect on the ductility of these new high strength alloys.

A low temperature combination method for the production of ZnO nanowires.

Abstract: The growth of large-area, patterned and oriented ZnO nanowires on silicon using a low temperature silicon?CMOS compatible process is demonstrated. Nanowire synthesis takes place using a thin nucleation layer of ZnO deposited by radiofrequency magnetron sputtering, followed by a hydrothermal growth step. No metal catalysts are used in the growth process. The ZnO nanowires have a wurtzite structure, grow along the c-axis direction and are distributed on the silicon substrate according to the pre-patterned nucleation layer. Room temperature PL measurements of the as-grown nanowires exhibit strong yellow?red emission under 325?nm excitation that is replaced by ultraviolet emission after annealing. This method can be used to integrate patterned 1D nanostructures in optoelectronic and sensing applications on standard silicon CMOS wafers.

Effect of cryo-rolling and annealing on microstructure and properties of commercially pure aluminium

Abstract: Influence of cryo-rolling reduction and annealing of commercially pure (CP) Al is evaluated in four aspects: microstructure, mechanical properties, electrical conductivity and general corrosion. It is shown that by selecting optimal cryo-rolling reduction and subsequent annealing condition result in ultrafine grains in CP Al with good combination of high strength and ductility. Electrical conductivity of the cryo-rolled samples decreased due to increased number of the electron scattering centers (lattice defects and grain boundary area). However, optimization of cryo-rolling and annealing treatment could restore the conductivity coupled with high strength in CP Al. Corrosion behaviour of cryo-rolled CP Al improved after annealing treatment. High dissolution rate and low thermal stability of the ultrafine grain structure could override the anticipated advantage of uniform corrosion in ultrafine grain CP Al.

Band gap shift, structural characterization and phase transformation of CdSe thin films from nanocrystalline cubic to nanorod hexagonal on air annealing

Abstract: Cadmium selenide (CdSe) thin films were deposited on a glass substrate using the chemical bath deposition method at room temperature. The films were deposited using cadmium acetate as a Cd2+ ion source and sodium selenosulfate as a Se2? ion source. The 'as-deposited' CdSe thin films are red in colour and specularly reflective. The 'as-deposited' CdSe layers grew with nanocrystalline cubic phase along with some amorphous phase present, with an optical band gap 'Eg' of 2.3 eV and electrical resistivity of the order of 105?106 ? cm. The 'as-deposited' film is annealed in air at 673 K for 4 h and the effect of annealing on structural, morphological, optical and electrical properties is studied. It is worth noting that after annealing, metastable nanocrystallite cubic phase transforms into stable well crystalline hexagonal phase and films show a 'redshift' of '0.6 eV' in their optical band gap 'Eg'. After annealing, the crystallites' size increases from 45 ? to 180 ?, which results in a decrease in electrical resistivity. These changes have been attributed to the crystallite size dependent properties of CdSe semiconductor thin films.

In-plane uniaxial anisotropy rotations in (Ga,Mn)As thin films

Abstract: We show, by superconducting quantum interference device magnetometry, that in (Ga,Mn)As films the in-plane uniaxial magnetic easy axis is consistently associated with particular crystallographic directions and that it can be rotated from the $[\overline{1}10]$ direction to the [110] direction by low-temperature annealing. We show that this behavior is hole-density dependent and does not originate from surface anisotropy. The presence of uniaxial anisotropy as well its dependence on the hole concentration and temperature can be explained in terms of the $p\text{\penalty1000-\hskip0pt}d$ Zener model of the ferromagnetism assuming a small trigonal distortion.

Effect of Reducing Atmosphere on the Magnetism of Zn1-xCoxO Nanoparticles

Abstract: We report the crystal structure and magnetic properties of Zn1-xCoxO nanoparticles synthesized by heating metal acetates in organic solvent. The nanoparticles were crystallized in wurtzite ZnO structure after annealing in air and in a forming gas (Ar95%+H5%). The X-ray diffraction and X-ray photoemission spectroscopy (XPS) data for different Co content show clear evidence for the Co+2 ions in tetrahedral symmetry, indicating the substitution of Co+2 in ZnO lattice. However samples with x=0.08 and higher cobalt content also indicate the presence of Co metal clusters. Only those samples annealed in the reducing atmosphere of the forming gas, and that showed the presence of oxygen vacancies, exhibited ferromagnetism at room temperature. The air annealed samples remained non-magnetic down to 77K. The essential ingredient in achieving room temperature ferromagnetism in these Zn1-xCoxO nanoparticles was found to be the presence of additional carriers generated by the presence of the oxygen vacancies.

A semiconductor junction formation process including low temperature plasma deposition of an optical absorption layer and high speed optical annealing

Abstract: A method of forming semiconductor junctions in a semiconductor material of a workpiece includes ion implanting dopant impurities in selected regions of the semiconductor material, introducing an optical absorber material precursor gas into a chamber containing the workpiece, generating an RF oscillating toroidal plasma current in a reentrant path that includes a process zone overlying the workpiece by applying RF source power, so as to deposit a layer of an optical absorber material on the workpiece, and optically annealing the workpiece so as to activate dopant impurities in the semiconductor material.

5 nm Ruthenium Thin Film as a Directly Plateable Copper Diffusion Barrier

Abstract: Interfacial stability of electroplated copper on a 5nm ruthenium film supported by silicon, Cu∕(5nmRu)∕Si, was investigated using Rutherford backscattering and high-resolution analytical electron microscopy. Transmission electron microscopy (TEM) imaging shows that a 5nm Ru film is amorphous in contrast to the columnar microstructures of thicker films (20nm). Direct Cu plating on a 5nm Ru film yielded a homogeneous Cu film with over 90% plating efficiency. It is demonstrated that 5nm Ru can function as a directly plateable Cu diffusion barrier up to at least 300°C vacuum anneal. TEM reveals an interlayer between Ru∕Si, which expands at the expense of Ru upon annealing. Electron energy loss spectroscopy analyses show no oxygen (O) across the Cu∕(5nmRu)∕Si interfaces, thereby indicating that the interlayer is ruthenium silicide (RuxSiy). This silicidation is mainly attributed to the failure of the ultrathin Ru barrier at the higher annealing temperature.