Increase Of Annealing Time Research Articles

Grain‐Boundary Grooving of Plasma‐Sprayed Yttria‐Stabilized Zirconia Thermal Barrier Coatings

The focus of this study was to determine the mechanisms responsible for the microstructural changes of plasma‐sprayed 7 wt% Y2O3–ZrO2 thermal barrier coatings with annealing from 800° to 1400°C. Mullins's thermal grooving theories have been applied to plasma‐sprayed TBCs to determine the dominant mass transport mechanism at various temperatures. Grain‐boundary groove widths were measured as a function of annealing time and temperature using atomic force microscopy (AFM). The same collection of grains was analyzed after progressive heat treatments. Surface diffusion was found to be the dominant diffusion mechanism at 1000°C, corresponding to the disappearance of intralamellar cracks at that temperature. At 1100°C, both surface and volume diffusion were active. Volume diffusion, found to be the dominant diffusion mechanism at 1200°C and above, was responsible for the sintering of interlamellar pores observed from AFM analysis of a single, progressively heat‐treated interlamellar boundary. Surface roughening was observed to coarsen with increased annealing time and disappear with increased annealing temperature.

Magnetic and high resolution TEM studies of nanographite derived from nanodiamond

The time evolution of graphitization was analyzed based on the structural and magnetic properties of nanodiamond samples annealed at 1600 °C for various time intervals. High resolution TEM and XRD show that the nanodiamond particles are converted to spherical onions for short annealing time intervals, and then they are completely transformed to polyhedral nanographite through the annealing for 120 min. The in-plane orbital susceptibility χ orb (300 K) analyzed on the basis of Kotosonov’s equation remains fairly constant in the range −5.5 × 10 −6 to −5.9 × 10 −6 emu/g, suggesting that the coherent scattering region (CSR) and the Fermi energy are independent of the annealing times. It also indicates the presence of serious defects affecting the electronic structure of nanographite. As the annealing time increases from 2 to 120 min, the Pauli paramagnetic susceptibility decreases. The broad ESR signal is associated with the spins localized on the edge states of the π-electron graphite network. The ESR linewidth becomes nine times less as the heat-treatment time rises from 2 to 120 min. The relatively large linewidth is associated with the scattering of π-electrons by the edge phonon modes and magnetic interaction between the edge-localized spins. During continuous annealing the nanoparticle structure changes from more defective to less defective and the number of edge-localized spins in a particle drops from ca. 2 to ca. 1 despite the CSR size and the Fermi energy remain practically the same.

Interfacial structure of oxidized AlN(0002)∕Si(111) thin film

We present an interfacial structure formed during the thermal oxidation of epitaxial AlN(0002)∕Si(111) thin film investigated by synchrotron x-ray scattering and transmission electron microscopy. We found that a crystalline interlayer with a thickness of ∼30Å is formed as the AlN film transforms to epitaxial cubic spinel γ-Al2O3 during the initial stage of oxidation. The lattice spacing of such crystalline interlayer is about 5.441 Å, and we believe it to be an aluminum-silicate (AlxSiO2−δ) phase having a diamond structure. As the annealing proceeds further, an amorphous-SiO2 (α-SiO2) layer is formed between the crystalline AlxSiO2−δ interlayer and the resultant γ-Al2O3 film. The α-SiO2 layer grows as the annealing time increases, which indicates that Si atoms diffuse continuously through the crystalline AlxSiO2−δ interlayer.

YBCO samples as a possible thermoelectric material

We have performed a study of thermoelectric properties of polycrystalline Y Ba2Cu3O7–δ (YBCO) samples syntherized from oxides by solid state reaction. The Seebeck coefficient, (S), electrical resistivity (ϱ) and thermal conductivity (κ) of these Y-based high temperature superconductors were measured in the temperature range between 77 K and 300 K. The samples were submitted to different thermal processes at 600 °C in vacuum in order to change both the oxygen content (7–δ) and its ordering. The Seebeck coefficient was measured by differential method in which the sample is heated periodically with a frequency of 50 mHz. It is positive in whole measurement range and show a weak linear behavior with the temperature and its magnitude change from 3 × 10–5 V/K for the samples annealed during one hour to 1 × 10–3V/K for the samples annealed through 50 hours. The electrical resistivity was measured by standard four-probe method and its behavior changes from metallic to semiconductor as the annealing time is increasing. The magnitude of ϱ(T) increases when the annealing time increases from 6.9 × 10–3 Ω cm to 9.2 × 10–1 Ω cm for the samples annealed 50 hours. The thermal conductivity data was obtained by means of longitudinal heat-flow method in which the sample is heated with a frequency of 30 mHz and κ(T) was calculated from Fourier law. The accuracy of the κ(T) data was 0.1 W/mK. In all samples κ(T) is less than 4 W/mK and exhibit a weak linear behavior with the temperature, its magnitude decreases with the annealing time. The performance of thermoelectric material is determined by the dimensionless merit figure ZT, which is defined in terms of Seebeck coefficient, electrical resistivity and thermal conductivity as: ZT = S2 T/ϱκ. ZT(T) exhibit an enhancement up to reach values close to 0.6 which are comparable to those of conventional thermoelectric semiconductors. This behavior suggests that the charge carrier density and scattering mechanisms can be modify by decreasing the oxygen level present in YBCO samples, which opens the possibility to use these kind of materials as active thermo-elements below room temperature. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

X-ray and cathodoluminescence study on the effect of intentional long time annealing of the InGaN/GaN multiple quantum wells grown by MOCVD

GaN-based InGaN/GaN multiple quantum wells (MQWs) structure having a high-quality epilayer and coherent periodicity was grown by metalorganic chemical vapor deposition. After thermal annealing of InGaN/GaN MQWs, the increase in temperature and annealing time caused the intermixing between the barrier and the wells, which in turn caused a decrease in periodicity on the high-resolution X-ray diffraction patterns. Thereby, we confirmed that the structural performance of InGaN MQWs is successively degrading with increasing thermal annealing temperature. Especially, InGaN MQWs of the sample annealed at 950 °C were profoundly damaged. The cathodoluminescence (CL) measurement indicated that MQWs emission intensity decreases with increasing thermal annealing temperature. Thus, the integrated CL intensity ratio of InGaN MQWs to GaN dramatically decreased while thermal annealing temperatures increased. This result caused the intermixing in MQWs to deteriorate the active layer performance. Furthermore, the peak position of MQWs showed a tendency of the red shift after high thermal annealing. It is suggested that the annealing-induced red shift in MQWs is attributed to the reduction of the inhomogeneity of the In content in the MQWs leading to the reduction of the quantized energies. Consequently, it indicates that the high temperature and the long-time thermal annealing would be inevitably followed by the structural destruction of InGaN MQWs.

Effect of excess oxygen on the electrical properties of transparent p-type conducting CuAlO thin films

Abstract Defect chemistry plays an important role in the p-type conductivity of transparent CuAlO2 thin films. Presence of excess oxygen atoms within the crystallites sites or interstitial sites is responsible for the enhanced hole-conductivity of p-CuAlO2+x thin films. These excess oxygen atoms within the films were induced by post-deposition annealing of the films in oxygen atmosphere. Composition analyses of the films confirmed the presence of nonstoichiometric (excess) oxygen within the films. With increase in the post-deposition annealing time, more and more oxygen atoms were intercalated within the p-CuAlO2+x thin films. Electrical conductivity measurements of the films indicated that with increase in the excess oxygen contents within the films, the p-type conductivity also increased. This observation supports the origin of p-type conduction in CuAlO2+x thin films due to excess oxygen atoms.

Precipitation of [formula omitted] at (1 0 0) [formula omitted] by high-temperature annealing

Formation of HTaO 3 precipitates on the surface of LiTaO 3 subjected to high-temperature annealing, T ∼ 1000 ∘ C , in air has been studied by reflection high-energy electron diffraction (RHEED). Coherence relation has been defined between HTaO 3 and (1 0 0) LiTaO 3 substrate. The development of superstructure ordering of HTaO 3 has been detected with annealing temperature and time increase.

Thermally induced diffusion in GaInNAs∕GaAs and GaInAs∕GaAs quantum wells grown by solid source molecular beam epitaxy

The effects of the thermal annealing induced diffusion on the photoluminescence (PL) of a GaAs∕GaInAs∕GaAs∕GaInNAs∕GaAs quantum well (QW) structure grown by solid source molecular beam epitaxy are studied. The PL experimental results in conjunction with the numerical quantum-mechanical modeling that predicts the changes in the QW confining potential with group-III atomic diffusion, have been used to obtain the values for diffusion coefficient. The activation energies of GaInAs∕GaAs QW (ED,GIA) were found to be between 0.49to0.51eV, while that of GaInNAs∕GaAs QW (ED,GINA) showed comparable values of between 0.6 to a 0.67eV, as annealing time increases from 10to30s. The ED,GIA and ED,GINA values are attributed to the same interstitial diffusion mechanism.

A study on the thermostability of LaNiO 3 films

Thin LaNiO 3- x films with pseudocubic (100) preferred orientation were prepared by rf magnetron sputtering and in situ annealed at 265 °C. X-ray diffraction (XRD) results indicate that the annealing did not cause the lattice distortion of the films. The electric conductivity, the refractive index and the extinction coefficient decrease exponentially as annealing time increases. X-ray photoelectron spectroscopy (XPS) analysis manifested that the oxygen concentration in the LaNiO 3- x film decreased 2.7% after 2 h annealing and the loss of the lattice oxygen in films led to the changes of the properties of the LaNiO 3- x films.

Dynamic mechanical properties of annealed sulfonated poly(styrene- b-[ethylene/butylene]- b-styrene) block copolymers

Solution cast films of lightly sulfonated styrene- b-[ethylene- co-butylene]- b-styrene, (sSEBS) block copolymers were annealed for various times at 120 °C and thermal transitions are evaluated using dynamic mechanical analysis. Increased annealing time and increase in degree of sulfonation increases T g for the PS phase while T g for the EB phase is practically unchanged, and in some cases, there is suggestion of a relaxation due to EB–PS inter-phases. Annealing has a minor effect on the rubbery plateau storage modulus. Thus, annealing primarily alters the PS block phase. EB–PS phase separation appears to be refined with increasing SO 3H content. The region of rubber elasticity extends to higher temperatures with increased degree of sulfonation. A high temperature dynamic mechanical transition that is tentatively attributed to disruption of SO 3H—rich sub-domains within the PS block domains shifts to higher temperature with annealing.

The formation of Ge nanocrystals in a metal–insulator–semiconductor structure and its memory effect

After rapid thermal annealing of an ultra-thin germanium (Ge) layer in a tri-layer insulator structure at 1000°C in argon, the formation of Ge nanocrystals in the structure has been investigated by using high-resolution transmission electron microscopy, X-ray photoelectron spectroscopy and atomic force microscopy. It was found that the Ge layer in the as prepared sample is a mixture of amorphous Ge, GeO 2 and Ge suboxide. After 10 s annealing, Ge is distributed over a much wider amorphous layer than the as prepared case and a few Ge nanocrystals were observed. The density of Ge nanocrystals increases with increasing annealing time from 10 to 200 s, and then decreases as the time increases further to 400 s. A possible mechanism for the formation of Ge nanocrystals was discussed. Current–voltage and capacitance–voltage measurements show that the device with Ge nanocrystals has a pronounced charge storage capability. The electrical charge stored in the device reaches a maximum value when the annealing time increases from 10 to 200 s, and then decreases as the annealing time increases further to 400 s.

Influence of H2- and N2-ambient annealing of indium-tin oxide film on plastic substrate for organic light-emitting diode

Indium tin oxide (ITO) film was deposited on an ARTON plastic substrate using 80 W, direct current (DC) magnetron sputtering on an unheated substrate, then annealed at 150°C under either hydrogen or nitrogen gas for periods ranging from 2 h to 8 h. Film surface morphology, crystal size, crystal orientation, and visible region optical transparency were studied. The grain size was found to increase with increased annealing time. Grain size was larger under nitrogen ambience than under hydrogen ambience. Sheet resistance of as-deposited ITO films was 87Ω/sq, but with nitrogen ambient annealing at 150°C for 8 h, it declined to 65Ω/sq. Average ITO-film transmittance was 88% after an 8-h nitrogen-ambient annealing.

Dimensional stability of oriented, rigid poly(vinyl chloride)

AbstractOriented PVC has enhanced properties, but on heating it begins to shrink and eventually reverts to its original dimensions. Thermomechanical analysis was used to study the effects of orientation variables and subsequent annealing or aging on the shrinkage of rigid PVC. The thermal history of the oriented PVC affected its crystallinity and the free volume in the oriented structure. These changes modified the temperature at which the oriented samples began to shrink (i.e., their dimensional stability.) Higher draw and annealing temperatures can be used to improve dimensional stability; however, their effective use is limited because PVC has a peak elongation at 90°C. Increased annealing time also increases dimensional stability. Aging greatly improves the dimensional stability of the material; this process can be accelerated at temperatures up to 60°C. The shrinkage onset temperature can be increased without compromising the enhancement of mechanical properties achieved by orientation. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 3859–3867, 2003

Thermal and morphological properties of main chain liquid crystalline polymers

Temperature modulated differential scanning calorimetry (TMDSC), variable heating rate DSC, and tapping atomic force microscopy (AFM) were used to study semi-crystalline liquid crystalline polymers (LCPs). Main chain LCPs included a random copolyester (Vectra® A950) and an azomethine alternating copolymer. For the azomethine LCP the TMDSC non-reversing signal detected broad exothermic transitions associated with melting and recrystallization as the slow DSC heating scan induced surprisingly large morphological changes. Non-isothermally crystallized Vectra® and some isothermally crystallized samples at lower temperatures exhibited different levels of DSC scan induced crystal reorganization. Such crystal metastability was also studied by variable heating rate DSC and an independent technique for estimating the melting point at very rapid heating rates. The TMDSC characterization of the scan induced crystal perfection in Vectra® was substantially different than for the other polymers studied. In most cases even though crystal perfection was occurring, no clear exotherm was detected in the non-reversing signal. High temperature annealing for long times resulted in degrees of crystal perfection which could be studied by DSC with minimal scan induced reorganization. High resolution tapping AFM was used to elucidate details of crystal morphology for mechanically oriented and non-oriented Vectra® before and after annealing. Structures resembling lamellae were found to be oriented perpendicular to the chain direction in the oriented Vectra®. In the non-oriented film broad and sometimes curved ‘lamellae’ were detected. They were about 1000 nm long and between 20 and 35 nm wide, with the width increasing slightly as a function of increased annealing time at 260 °C melt crystallization conditions. Substructure of the lamellae in both oriented and non-oriented Vectra® consisted of smaller stacked crystallites which are detected by AFM studies of these surfaces.

Morphological healing evolution of intragranular penny-shaped microcracks by surface diffusion: Part II. Experiments

Micron-sized internal microcracks were introduced into rounded bars of pure iron via symmetric tension-compression low-cycle fatigue. The microcracks were found to have irregular penny-shaped morphology with critical diameter of about 30 µm and thickness of 0.5 to 1.5 µm. The location, geometry, initiation, and propagation of these microcracks were quantitatively investigated. After vacuum annealing of the fatigued samples, two-dimensional (2-D) longitudinal sectioning of the intragranular microcracks showed that the crack morphology had evolved from initially elliptical shape into arrays of spherical voids by surface diffusion. A typical configuration involving a microcrack broken into a center spherical void surrounded by a ring of doughnutlike arranged outer cavities was observed along the transverse section of the specimen. Subsequently, the spherical voids were found to shrink and diminish gradually via bulk diffusion as the annealing time increases. The morphological evolution time is found to be in broad agreement with the corresponding results predicted by our finite-element simulation of an intragranular penny-shaped microcrack evolving under surface diffusion.

Morphology and crystallization kinetics in HfO2 thin films grown by atomic layer deposition

We report the effects of annealing on the morphology and crystallization kinetics for the high-κ gate dielectric replacement candidate hafnium oxide (HfO2). HfO2 films were grown by atomic layer deposition (ALD) on thermal and chemical SiO2 underlayers. High-sensitivity x-ray diffractometry shows that the as-deposited ALD HfO2 films on thermal oxide are polycrystalline, containing both monoclinic and either tetragonal or orthorhombic phases with an average grain size of ∼8.0 nm. Transmission electron microscopy shows a columnar grain structure. The monoclinic phase predominates as the annealing temperature and time increase, with the grain size reaching ∼11.0 nm after annealing at 900 °C for 24 h. The crystallized fraction of the film has a strong dependence on annealing temperature but not annealing time, indicating thermally activated grain growth. As-deposited ALD HfO2 films on chemical oxide underlayers are amorphous, but show strong signatures of ordering at a subnanometer level in Z-contrast scanning transmission electron microscopy and fluctuation electron microscopy. These films show the same crystallization kinetics as the films on thermal oxide upon annealing.

Toughening mechanisms in annealed high density polyethylene under impact

AbstractImpact fracture behavior of annealed high density polyethylene (HDPE) has been studied. Charpy impact test results show that annealing increases the total fracture energy of HDPE and also that the increase in fracture energy is mainly due to the increase in the propagation energy with annealing time. Microscopic studies have been carried out to elucidate the origin of the rise in the propagation energy of the annealed HDPE. It is found that as annealing time increases, microscopically, the failure is more ductile with the formation of fibrillar structure. Based on the morphological study, it is proposed that the increased toughness observed in annealed HDPE is due to the occurrence of micro‐voids (or cavities) as the material yields under mode I dynamic tension. The void generation promotes the formation of fibrous structure, which absorbs greater energy than as‐received HDPE.

Metastable phase accompanying crystallisation of amorphous Al85Ni10Ce5 alloy

Isochronal annealing and isothermal annealing of melt spun amorphous Al85Ni10Ce5 alloy were carried out to investigate the crystallisation behaviour. It has been found that a metastable phase occurring in the crystallisation process, may exist for a certain time but in due course disappears either acting as a nucleus of another phase or transforming into another stable phase with an increase in either annealing temperature or annealing time. Transmission electron microscopy results reveal that Al3Ce may be one of the metastable phases during the isochronal annealing process. Furthermore, microhardness measurements reveal that the specimens containing metastable phases exhibit higher microhardness than the as quenched and as crystallised alloy.

Evaluation of the annealing effect of proton-exchanged LiTaO3 optical waveguides by the line-focus-beam ultrasonic material characterization system

We established an experimental procedure and collected basic data to evaluate the annealing process and effects for proton-exchanged LiTaO3 optical waveguides using the line-focus-beam ultrasonic material characterization (LFB-UMC) system in a frequency range of 100 to 300 MHz. Twelve Z-cut LiTaO3 substrates were proton-exchanged at 260 °C for 14 min in a pyrophosphoric acid solution and annealed at 420 °C for various periods from 10 sec to 24 h. The leaky surface acoustic wave (LSAW) velocities were decreased by the proton exchange, and were then increased and recovered by annealing in all propagation directions as the annealing time increased. The Y-axis propagation is most useful for an evaluation. The LSAW velocities decrease with an increase of the product fH, obtained from the frequency dependences and proton-diffused layer depths analyzed by secondary-ion mass spectrometry. Gradients of the fH dependences of the LSAW velocities become gentler with increases in the annealing time, corresponding to the concentrations and distributions of hydrogen and lithium ions in the proton-diffused layers. The relationships among the LSAW velocities, proton-diffused layer depths, relative concentrations of hydrogen ions at the specimen surfaces, and the annealing times were experimentally obtained. The measurement resolutions of the LFB-UMC system at 225 MHz to the proton-diffused layer depth, the relative concentration of hydrogen ions, and the typical annealing time for 1 min were estimated to be 4 nm, 0.2%, and 0.6 sec.

Ferromagnetic resonance of Fe–Sm–O thin films

In order to investigate the temperature and the annealing conditions dependence of magnetic properties in Fe72.1Sm5.2O22.7(at. %) thin films, such as the effective magnetization Meff, the spectroscopic splitting factor g, and the exchange stiffness constant A, we carried out ferromagnetic resonance (FMR) experiments. Fe–Sm–O thin films were deposited in an argon and oxygen mixed atmosphere using a rf magnetron sputtering apparatus at room temperature. The g is almost constant in the temperature range from 298 to 238 K, but increases with decreasing temperature in the range below 238 K. The A increases slightly with decreasing temperature to 238 K, and then increases linearly below 238 K. When the annealing time increases up to 6 h the Meff is almost constant, but the A decreases slightly with increasing annealing time.