Showing papers on "Annealing (metallurgy) published in 2007"

Luminescence mechanism of ZnO thin film investigated by XPS measurement

Abstract: The effects of annealing environment on the luminescence characteristics of ZnO thin films that were deposited on SiO2/Si substrates by reactive RF magnetron sputtering were investigated by X-ray photoelectron spectroscopy (XPS) and photoluminescence (PL). An analysis of the O 1s peak of ZnO film revealed that the concentration of oxygen vacancies increased with the annealing temperature from 600 °C to 900 °C under an ambient atmosphere. The PL results demonstrated that the intensity of green light emission at 523 nm also increased with temperature. Under various annealing atmospheres, the analyses of PL indicated that only one emission peak (523 nm) was obtained, indicating that only one class of defect was responsible for the green luminescence. The green light emission was strongest and the concentration of oxygen vacancies was highest when the ZnO film was annealed in ambient atmosphere at 900 °C. The results in this investigation show that the luminescence mechanism of the emission of green light from a ZnO thin film is associated primarily with oxygen vacancies.

Blue luminescent centers and microstructural evaluation by XPS and Raman in ZnO thin films annealed in vacuum, N2 and O2

Abstract: Zinc oxide (ZnO) thin films prepared on sapphire substrates by employing a pulsed laser deposition (PLD) have been annealed in vacuum, N 2 , and O 2 ambient at annealing temperature 600 ° C. X-ray diffraction (XRD) and atomic force microscopy (AFM) observation show that the annealed thin films possess (0 0 0 2) textured feature and form better crystal grains with a large size. X-ray photoelectron spectroscopy (XPS) and Raman analysis show the defects of ZnO thin films annealed in different ambient is distinctly different. The film annealed in vacuum possesses large oxygen vacancies (V o ) and Zn interstitials (Zn i ); while large surface defects exist in film annealed in N 2 ambient. The concentrations of the intrinsic and extrinsic defects are the lowest in ZnO thin film annealed in oxygen gas. Photoluminescence (PL) spectra also reveal that the ultraviolet (UV) emission is the best for thin film annealed in O 2 . The blue emission (2.66 eV) is ascribed to the electronic transition from the donor energy level of Zn interstitials to acceptor energy level of Zn vacancies rather than the O vacancy.

Abruptness of a-Si :H/c-Si interface revealed by carrier lifetime measurements

Abstract: Intrinsic hydrogenated amorphous silicon films can yield outstanding electronic surface passivation of crystalline silicon wafers. In this letter the authors confirm that this is strongly determined by the abruptness of the interface. For completely amorphous films the passivation quality improves by annealing at temperatures up to 260°C, most likely by film relaxation. This is different when an epitaxial layer has been grown at the interface during film deposition. Annealing is in such a case detrimental for the passivation. Consequently, the authors argue that annealing followed by carrier lifetime measurements allows determining whether the interface is abrupt.

Nanostructured mesoporous nickel oxide thin films

Abstract: Nanostructured nickel oxide thin films were prepared by the pulsed laser ablation technique. The effects of annealing on the structural, morphological, electrical and optical properties are discussed. Phase imaging was used to examine the surface contaminants, adhesion and hardness and height imaging to evaluate the height profile of the films. Morphological investigations using atomic force microscopy and scanning electron microscopy indicate a strong influence of the annealing process on the surface roughness and particle size. A self-assembly of nanocrystals agglomerating together to form an island-like structure is observed in films annealed at 773 K. X-ray diffraction and x-ray photoelectron spectroscopy investigations indicate the presence of Ni2O3 in the as-deposited films. A transformation to cubic NiO with growth along (111) and (200) planes with increase of annealing temperature is also observed.

Enhanced mechanical behavior of a nanocrystallised stainless steel and its thermal stability

Abstract: This paper discusses the mechanical properties of a nanocrystallised stainless steel obtained using surface mechanical attrition treatment (SMAT) and the underlying grain refinement mechanism using transmission electron microscopy (TEM). It was shown that grain refinement down to the nanometer range has the potential to significantly improve the mechanical properties of a 316L stainless steel which becomes comparable in strength to titanium alloys. Hence, promising structural applications could be considered for such a material. At the same time, the thermal stability of this nanocrystallised material was studied in the temperature range from 100 to 800 °C. The results show that the nanometer scaled microstructure is retained up to 600 °C and that a controlled annealing treatment could even lead to enhancement of both strength and ductility of this material. All these results are explained in terms of microstructural investigations, X-ray diffraction measurements, tensile and bending tests as well as microhardness measurements.

Orientational order in block copolymer films zone annealed below the order--disorder transition temperature.

Abstract: We report measurements of rapid ordering and preferential alignment in block copolymer films zone annealed below the order-disorder transition temperature. The orientational correlation lengths measured after approximately 5 h above the glass-transition temperature ( approximately 2 microm) were an order of magnitude greater than that obtained under equivalent static annealing. The ability to rapidly process polymers with inaccessible order-disorder transition temperatures suggests zone annealing as a route toward more robust nanomanufacturing methods based on block copolymer self-assembly.

Thermal stability of ECAP processed pure copper

Abstract: Microstructure and texture evolution of pure copper (99.95%) after equal-channel angular pressing (ECAP) with route Bc up to 12 passes and subsequent heat treatment were investigated. After deformation the samples were annealed at different temperatures. The deformed and annealed states were characterized by X-ray pole figures, electron back scatter diffraction (EBSD), TEM and microhardness tests. It was shown that the observed texture and microstructure changes during subsequent annealing have to be associated with discontinuous recrystallization. The study revealed a very low thermal stability of this ECAP processed pure copper. The observed decrease of the apparent activation energy for recrystallization is most likely due to improved nucleation conditions of ECAP deformed material.

Investigation of Oxygen Vacancy and Interstitial Oxygen Defects in ZnO Films by Photoluminescence and X-Ray Photoelectron Spectroscopy

Abstract: ZnO films prepared at different temperatures and annealed at 900 degrees C in oxygen are studied by photoluminescence (PL) and x-ray photoelection spectroscopy (XPS). It is observed that in the PL of the as-grown films the green luminescence (GL) and the yellow luminescence (YL) are related, and after annealing the GL is restrained and the YL is enhanced. The O 1s XPS results also show the coexistence of oxygen vacancy (Vo) and interstitial oxygen (O-i) before annealing and the quenching of the V-o after annealing. By combining the two results it is deduced that the GL and YL are related to the V-o and O-i defects, respectively.

Annealing of Al2O3 thin films prepared by atomic layer deposition

Abstract: Amorphous Al2O3 thin films were deposited on a Si (1 1 1) substrate at 150 °C in oxygen-rich conditions by atomic layer deposition. Rapid thermal annealing was performed at high temperatures, ranging from 1000 to 1200 °C, to study the crystallization characteristics of the Al2O3 films. X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM), scanning electron microscopy, atomic force microscopy and frequency-dependent capacitance measurements were used to characterize the structural and electrical properties before and after the annealing. It was found that the best crystallization of the Al2O3 film was achieved after annealing at 1150 °C, corresponding to a minimum of full width at half maximum (FWHM) of the Al2O3 (012) XRD peak and the maximum of surface roughness and the capacitances. This suggests that 1150 °C is the optimal transition temperature from amorphous to crystalline and to get the best insulating property for Al2O3 thin film. The formation of the SiO2 interfacial layer after annealing has been observed by HRTEM for the annealed sample, accompanied by a decrease in the thickness of Al2O3 films.

Microstructure, hardness, resistivity and thermal stability of sputtered oxide films of AlCoCrCu0.5NiFe high-entropy alloy

Abstract: The sputtered oxide films of AlCoCrCu0.5NiFe high-entropy alloy were deposited on the silicon wafer using radio frequency sputter system, and subsequently were annealed at 500, 700 or 900 °C. Surprisingly, the sputtered films are of simple structure. With no oxygen addition to the working gas, the AlCoCrCu0.5NiFe high-entropy alloy film is amorphous. When the oxygen content in the working gas is between 10 and 50%, the sputtered oxide films are HCP with lattice constants of a = 0.3583 nm and c = 0.4950 nm. Before annealing, both the resistivity and thickness of the oxide film decrease with increasing oxygen content and the hardness value reaches maximum at 30% O2. No new phases in the oxide films form during annealing, indicating the oxide films are very stable at high temperature. However, the crystal grains tend to grow up and the micro-hole size among grains increases with the annealing temperature. The resistivity of the oxide film steps up with annealing temperature, whereas the hardness value decreases. The oxide-film thickness changes very little during annealing.

p-type conduction in unintentional carbon-doped ZnO thin films

Abstract: p-type conduction has been observed in unintentional carbon-doped ZnO thin films grown by metal organic chemical vapor deposition through postgrowth annealing treatment. The existence of carbon, which has been verified by secondary ion mass spectrometry and x-ray photoelectron spectroscopy, was predicted to immobilize the oxygen in the interstitial site in ZnO thin films after annealing. Using first principles calculations, the formation of carbon-oxygen cluster defect in ZnO was found to be favorable and acts as a shallow acceptor. The cryogenic photoluminescence of the p-type carbon-doped ZnO thin films shows an additional peak located at 3.3564eV, which was attributed to the acceptor (carbon-oxygen cluster defect) bound exciton emission.

Fabrication of highly conductive Ti1- xNbxO2 polycrystalline films on glass substrates via crystallization of amorphous phase grown by pulsed laser deposition

Abstract: Nb-doped anatase TiO2 [Ti0.94Nb0.06O2 (TNO)] films with high electrical conductivity and transparency were fabricated on nonalkali glass using pulsed laser deposition and subsequent annealing in a H2 atmosphere. The amorphous films as deposited on unheated substrates were found to crystallize, forming polycrystalline films at around 350°C. The films annealed at 500°C showed resistivity down to 4.6×10−4Ωcm at room temperature and optical transmittance of 60%–80% in the visible region, which are comparable to those of epitaxial films. These results indicate that TNO films have the potential to be practical transparent conducting oxides that could replace indium tin oxide.

Optically Transparent Polycrystalline Al2O3 Produced by Spark Plasma Sintering

Abstract: The spark plasma sintering (SPS) technique was used to produce mid-infrared (IR) transparent alumina with the desired transmittance. An excellent transmittance of 85% has been obtained in a sample sintered at 1300°C for 5 min. The heating rate, sintering time, and annealing have a significant influence on IR transmittance. The improvement in transmission may be attributed to the progressive elimination of residual porosity when applying a slower heating rate, longer sintering time during SPS, and postsinter annealing. It is suggested that localized residual strain/stress at grain boundaries and oxygen vacancy concentration are other factors influencing the optical properties of the SPS-sintered alumina.

Synthesis of large-area and aligned copper oxide nanowires from copper thin film on silicon substrate

Abstract: Large-area and aligned copper oxide nanowires have been synthesized by thermal annealing of copper thin films deposited onto silicon substrate. The effects of the film deposition method, annealing temperature, film thickness, annealing gas, and patterning by photolithography are systematically investigated. Long and aligned nanowires can only be formed within a narrow temperature range from 400 to 500°C. Electroplated copper film is favourable for the nanowire growth, compared to that deposited by thermal evaporation. Annealing copper thin film in static air produces large-area, uniform, but not well vertically aligned nanowires along the thin film surface. Annealing copper thin film under a N2/O2 gas flow generates vertically aligned, but not very uniform nanowires on large areas. Patterning copper thin film by photolithography helps to synthesize large-area, uniform, and vertically aligned nanowires along the film surface. The copper thin film is converted into bicrystal CuO nanowires, Cu2O film, and also perhaps some CuO film after the thermal treatment in static air. Only CuO in the form of bicrystal nanowires and thin film is observed after the copper thin film is annealed under a N2/O2 gas flow.

Effect of Annealing on the Interfacial Structure of Aluminum-Copper Joints

Abstract: The aim of this study is to investigate the structure development and growth kinetics of the interfacial structure of cold roll bonded Al/Cu bimetal sheet. An interfacial structure is developed during the annealing process. The characteristics of the constituent phases at the interface of Al/Cu bimetal are studied by means of scanning electron microscope (SEM), X-ray diffraction (XRD) and transmission electron microscope (TEM). The results indicate that an obvious multi-layers interdiffusion structure is developed at the Al/Cu interface. The diffusion layer is consisted of four intermetallic compounds; Al 2 Cu, AlCu, Al 3 Cu 4 and Al 4 Cu 9 . The growth of these intermetallics during annealing can be achieved by the diffusion process. The activation energies of Al 2 Cu, AlCu + Al 3 Cu 4 , Al 4 Cu 9 and the total intermetallic layer are found to be 97.504, 107.46, 117.52 and 107.85kJ/mol, respectively. These intermetallics generally possess higher hardness values than those of the corresponding base metals. AlCu and Al 3 Cu 4 exhibit much higher hardness than that of Al 2 Cu and Al 4 Cu 9 , which implies lower fracture toughness. The observation of crack propagation paths shows that fracture mainly occurs in the intermetallic compound layers of AlCu and Al 3 Cu 4 , which are located between Al 2 Cu and Al 4 Cu 9 .

Structural Evolution of Tensile-Deformed High-Density Polyethylene during Annealing: Scanning Synchrotron Small-Angle X-ray Scattering Study

Abstract: The structural evolution of high-density polyethylene subjected to uniaxial tensile deformation was investigated as a function of strain and after annealing at different temperatures using a scanning synchrotron small-angle X-ray scattering (SAXS) technique. The results confirm that in the course of tensile deformation intralamellar block slips were activated at small deformations followed by a stress-induced fragmentation and recrystallization process yielding thinner lamellae with their normal parallel to the stretching direction. The original sheared lamellae underwent severe internal deformation so that they were even less stable than the newly developed thinner lamellae. Accordingly, annealing results in a melting of the original crystallites even at moderate strains where the stress-induced fragmentation and recrystallization just sets in and generates a distinctly different form of lamellar stacks aligned along the drawing direction. It was found that the lamellae newly formed during stretching at moderate strains remain stable at lower temperature. Only at a very high annealing temperature of 120 °C can they be melted, leading to an isotropic distribution of the lamellar structure.