Pre-annealed Samples Research Articles

Defect-induced ordering and disordering in metallic glasses

On the basis of shear modulus measurements on a Pt-based glass, we calculated temperature dependence of the defect concentration c using the Interstitialcy theory. This temperature dependence is compared with temperature dependence of the normalized full width at half maximum (FWHM) γ of the first peak of the structure factor S(q) for the same glass available in the literature. It is found that γ above the glass transition temperature Tg linearly increases with c in the same way for both initial and relaxed (preannealed) samples providing the evidence of defect-induced disordering in the supercooled liquid region independent of glass thermal prehistory. For both states of the samples, the derivative dγ/dc is close to unity. Below Tg, the interrelation between γ and c is entirely different for initial and relaxed samples. In the former case, strong defect-induced ordering upon approaching Tg is observed while relaxed samples do not reveal any clear ordering/disordering. Possible reasons for these observations are discussed.To further investigate the relationship between the normalized FWHM and defect concentration, we performed molecular dynamic simulation of γ(c)-dependence in a high-entropy FeNiCrCoCu model glass. It is found that γ also linearly increases with c while the derivative dγ/dc is again close to unity just as in the case of Pt-based glass.

In-situ irradiation creep behavior of dilute Al-Sc alloys: Using a thin film bulge test method

• In situ thin film bulge test on nc-AlSc is effective method for irradiation induced creep. • Preexisting Al 3 Sc precipitates suppress irradiation induced creep deformation. • Transition regime of AlSc binary system is located between room temperature and 75 °C. In-situ irradiation induced creep(IIC) measurements on a nanocrystalline AlSc 1.1 binary alloy were performed using a thin-film bulge test technique. A thin film bulge technique was employed since any substrate effect can be excluded, and hence is beneficial to analyze the intrinsic properties of specimen. Here, an as-deposited film and a pre-annealed film, both underwent heavy ion irradition with 1.8 MeV Kr ions. Al 3 Sc precipitates in the pre-annealed samples appear to reduce the irradiation creep compliance. Dissolution of these precipitates during irradiation led to increased irradiation creep rates. Microstructural evolution during irradiation was investigated by transmission electron microscopy and high resolution transmission electron microscopy.

Characterization of mechanical and corrosion properties of cryorolled Al 1100 alloy: Effect of annealing and solution treatment

Effect of annealing and solution treatment prior to cryorolling on the formation of initial structure influencing microstructure formation from nano to micron scale and resultant mechanical and corrosion properties in Al 1100 alloy has been studied in detail. Before subjecting to 50% cryorolling, samples were pre-annealed at 250 °C for 2 h and pre-solution treated at 540 °C for 1 h. X-ray diffraction and HRTEM techniques were used to understand the crystallite size, lattice strain and dislocation configuration in the processed alloy. The results indicate that the pre-annealed sample has the highest grain aspect ratio (4.43), the smallest crystallite size (37.53 nm), the highest lattice strain (9.12×10−3) and the highest dislocation density (45.16×1013 m−2) among the tested sample. The pre-annealed sample shows a significant improvement of 43.44%, 24.64% and 20.33% in hardness, ultimate tensile strength and yield strength. Both pre-annealed and pre-solution treated samples show improved corrosion resistance when compared to cryorolled samples without any pre-treatment, with the pre-annealed sample showing the best corrosion resistance.

Optical and structural studies on bio-synthesized ZnO using Citrullus lanatus peel extract

Bio-fabrication of ZnO films using plants, enzymes, and microorganisms has been recognized as an environmentally friendly procedure as an alternative to physical and chemical methods. In this research, the optical and structural properties of ZnO thin film have been investigated using UV-Vis spectrophotometer, X-ray diffraction (XRD), and Scanning Electron Microscopy (SEM), respectively. The ZnO films was prepared by spin-coating the mixed solution of Zn(NO3)2 and watermelon (Citrullus lanatus) peel extract on glass substrate. The ZnO films were then annealed at 400°C for 3h. The UV-Vis absorbance spectra show the strong absorption peaks occurs over a range of wavelengths of 220-380nm, and 190-235 nm for pre-annealed and annealed samples, respectively. The optical band gap of the samples was influenced by the heat treatment. The as-prepared samples synthesized at pH 8 is 3.73 eV and increased up to 5.4 eV after annealed at 400 °C for 3 h. This result suggested that pre-annealed sample has better photocatalytic activity compared to the annealed samples. The XRD pattern of the ZnO films exhibits the ZnO diffraction peaks that correspond to the hkl of hexagonal wurtzite structure. SEM image shows that the morphology of ZnO samples are spherical and rod-like microstructure.

Cobalt Sulfide as Photoelectrode of Photoelectrochemical Hydrogen Generation from Water

This study aimed to synthesize and characterize cobalt sulfide deposited on FTO by hydrothermal method and investigate its photoelectrochemical (PEC) water splitting performance. Cobalt sulfide thin films were produced by annealing at two different temperatures, namely, 400 and 500 °C. X-ray diffraction (XRD) and Fourier transform Raman spectroscopy were used to characterize the phase structure. Scanning electron microscopy was used to observe the morphology. Ultraviolet-visible spectroscopy and linear sweep voltammetry analyses were used to determine the thin-film band gap and evaluate the PEC water splitting performance, respectively. From the XRD and Raman analyses, all the samples produced consisted of mixed phases of Co3S4 and Co9S8. However, each sample contained different percentage phases. The sample annealed at 400 °C contained more Co9S8, whereas that annealed at 500 °C contained comparable amounts of Co3S4 and Co9S8. The morphologies of pre-annealed samples showed vertical flakes with diameters around 200-250 nm and flake thickness around 25-50 nm. When the temperature was increased from pre-annealing temperature to 400 and 500 °C, several flakes were destructed and formed spherical-like clusters. The Tauc plot from absorption analysis showed that the samples annealed at 400 and 500 °C produced similar band gaps at ~2.0 eV. The PEC performance analysis results show that annealing at 400 °C produced the highest photocurrent density of 10 μA/cm2 at a potential of -0.7 V.

The Effect of Pre-Annealing on the Evolution of the Microstructure and Mechanical Behavior of Aluminum Processed by a Novel SPD Method.

A novel continuous process of severe plastic deformation (SPD) named continuous close die forging (CCDF) is presented. The CCDF process combines all favorite advances of multidirectional forging and other SPD methods, and it can be easily scaled up for industrial use. Keeping constant both the cross section and the length of the sample, the new method promotes a refinement of the microstructure. The grain refinement and mechanical properties of commercially pure aluminum (AA1050) were studied as a function of the number of CCDF repetitive passes and the previous conditioning heat treatment. In particular, two different pre-annealing treatments were applied. The first one consisted of a reheating to 623 K (350 °C) for 1 h aimed at eliminating the effect of the deformation applied during the bar extrusion. The second pre-annealing consisted on a reheating to 903 K (630 °C) for 48 h plus cooling down to 573 K (300 °C) at 66 K/h. At this latter temperature, the material remained for 3 h prior to a final cooling to room temperature within the furnace, i.e., slow cooling rate. This treatment aimed at increasing the elongation and formability of the material. No visible cracking was detected in the workpiece of AA1050 processed up to 16 passes at room temperature after the first conditioning heat treatment, and 24 passes were able to be applied when the material was subjected to the second heat treatment. After processing through 16 passes for the low temperature pre-annealed samples, the microstructure was refined down to a mean grain size of 0.82 µm and the grain size was further reduced to 0.72 µm after 24 passes, applied after the high temperature heat treatment. Tensile tests showed the best mechanical properties after the high temperature pre-annealing and 24 passes of the novel CCDF method. A yield strength and ultimate tensile strength of 180 and 226 MPa, respectively, were obtained. Elongation to fracture was 18%. The microstructure and grain boundary nature are discussed in relation to the mechanical properties attained by the current ultrafine-grained (UFG) AA1050 processed by this new method.

Characteristics of oxygen diffusion induced by Al and Li interaction in Al-implanted zinc oxide ceramics

We studied on the oxygen diffusion in two kinds of Al implanted ZnO samples (100 keV, 4 × 1014 ions/cm2). Parts of samples were annealed to diffuse simultaneously Al and Li impurity, and then same concentration distribution of Al and Li were observed. Through the oxygen diffusion experiments, the feature of bulk diffusion in the pre-annealed samples was separated at 950°C so that the large activation energy for bulk diffusion was observed below the pre-annealing temperature. Oxygen diffusion feature was explained as result from interaction between Al and Li for the pre-annealing.

Ferromagnetic hysteresis and structural recrystallization in turbostratic graphite

The recent observation of controllable ferromagnetic and superconductive features in highly oriented pyrolytic graphite (HOPG) has attracted significant attention towards application of ferromagnetic carbon materials in data recording and computing technology. In this work we report the observation of ferromagnetic ordering in two turbostratic graphite samples by employing in situ T-XRD, VSM, EDX, T-EPR and Raman Spectroscopy. Existence of room temperature ferromagnetic hysteresis in both the analyzed samples is shown. As indicated by complementary (1) SEM/EDX (2) T-EPR and (3) Raman Spectroscopy analyses, these signals appear to be induced by the defect sites in the samples. However a possible role of the turbostratic arrangement of the carbon layers in this effect can not be excluded. By employing Rietveld refinements and T-XRD we have also investigated the changes in the structure of the turbostratic graphite phase with the increase of the temperature from 298 K to 673 K. Magnetometry was further employed to investigate the magnetic ordering in the graphitic structure of pre-annealed and post-annealed samples.

Fabrication of ZnO nanostructures with tunable luminescence, electrical properties: effect of annealing reaction temperature, ligand and seed layer

In present manuscript, the optical and electrical properties of ZnO thin films under the effect of ligand, synthesis & annealing temperature, seed layer have been studied in detail. ZnO thin film grown at 80 °C reaction temperature tuned transmittance (at 550 nm) to ∼37% (post-annealed sample) as compared to pre-annealed samples’ ∼5%. Observed Refractive index (n) found inversely proportional to their transmittance & refractive index (n) for corresponding sample has been tuned from 1.75 to 1.26. The intensity ratio of near band emission (INBE) to deep band emission (IDBE) is drastically enhanced after annealing of ZnO thin films which is confirmed in photoluminesecnce study. The uniform & dense ZnO nanorods’ growth, optimum transparency & prominent UV range dominated emission bring resistivity down to 1012 ohm-cm. The synthesized ZnO thin films having best suited structural, optical and electrical properties which can be utilized in fabrications of low cost luminesent devices.

Electrical conductivity of OH-bearing omphacite and garnet in eclogite: the quantitative dependence on water content

Eclogite is potentially an important constituent in local regions in the deep crust and upper mantle. The electrical conductivity of omphacite and garnet in eclogite has been measured at 1 GPa and 350–800 °C with pre-annealed OH-bearing samples. The conductivities were determined using a piston–cylinder apparatus and a Solartron-1260 Impedance/Gain Phase Analyser in the frequency range of 106–1 Hz. The sample water contents show almost no change before and after the experimental runs. The conductivity of both omphacite and garnet increases with temperature, and the activation enthalpy is ~ 82 kJ/mol for omphacite and 90 kJ/mol for garnet, which is nearly independent of water content in each mineral. The conduction is probably dominated by protons, and for both minerals, the conductivity increases linearly with water content, with a water content exponent of ~ 1. These data are used to model the bulk conductivity of an eclogite with different water contents and modal compositions. In combination with reported data, the conductivity of the eclogite is similar to that of typical granulites above 600 °C, but is much larger than that of olivine, assuming small to moderate water contents. This would mean that the contribution of eclogites, if present, to the electrical structure of the deep continental crust cannot be easily separated from that of granulites, and that the regional enrichments of eclogites in the upper mantle may cause high electrical anomalies. The results also provide information for the electrical property of orogen-related thickened deep crust where eclogites may be locally abundant, e.g., in the Dabieshan region and the Tibet plateau. At mantle depths, eclogitized portions of subducted slabs are usually of very low conductivities as suggested by geophysical observations, implying small water contents in the constitutive omphacite and garnet and the limited ability of these minerals in recycling water into the deep mantle.

Effect of Initial Microstructure on Properties of Cryorolled Al 5052 Alloy Subjected to Different Annealing Treatment Temperatures

Al 5052 alloy sheets were subjected to different pre-annealing temperatures (150, 200, 250, 300, and 350 °C) prior to cryorolling. The process resulted in Al 5052 alloys with different initial microstructures. The pre-annealed alloy sheets were compared with a cryorolled sample not subjected to pre-annealing. The thicknesses of the alloy samples after cryorolling was reduced by 30%. The pre-annealed cryorolled samples exhibited low crystallite size, and high lattice strain. Among them, the cryorolled sample pre-annealed at 300 °C had the lowest crystallite size, and the highest lattice strain. Changes in initial microstructure of this sample resulted in a significant improvement in its hardness (88 Hv), tensile strength (333 MPa), and corrosion resistance. The sample had the highest corrosion resistance among the cryorolled samples.

Influence of pre-annealing Cu-Sn on the structural properties of CZTSe thin films grown by a two-stage process

In this study CZTSe thin film were synthesized by a two-stage process that included sequential sputter deposition of Cu and Sn layers forming a Cu/Sn structure, pre-annealing the Cu/Sn structure at 200–380 °C for some of the samples, sputtering of additional Zn and Cu over the Cu/Sn structure, evaporation of a Se cap forming a Cu/Sn/Zn/Cu/Se precursor film, and exposing the precursor film to high temperature annealing treatment at 550 °C for 15 min to form the compound. The results of the characterization carried out on the compound layers revealed that the phase content, composition and microstructure of these layers changed noticeably depending on whether or not a pre-annealing step was utilized. Although XRD studies suggested presence of secondary phases, especially in the non-pre-annealed samples, the data was dominated by kesterite CZTSe phase reflections. Raman spectra of the films verified the formation of kesterite CZTSe structure and some other phases, which were determined to be SnSe2 and possibly ZnSe. SEM micrographs showed denser structure in the pre-annealed samples.

Different metastable equilibrium states in metallic glasses occurring far below and near the glass transition

Precise measurements of the high-frequency shear modulus of two bulk Zr- and Pd-based glasses in the initial and strongly preannealed states in a wide temperature range are performed. Isothermal structural relaxation of preannealed samples leads to either decrease or increase of the shear modulus. At temperatures below particular temperature Tpc, one observes cross-over relaxation (decrease→increase) of the shear modulus. The minimal shear modulus attained upon relaxation corresponds to the quasi-metastable equilibrium, which depends both on temperature and thermal prehistory. At higher temperatures T >Tpc, the relaxation always leads to shear modulus decrease towards the “true” metastable equilibrium, which depends only on temperature. The temperature Tpc for both glasses is by ≈ 25 K smaller than the calorimetric glass transition temperature. It is shown that this temperature constitutes the low temperature limit of the linear extrapolation of the shear modulus from the supercooled liquid state. By definition, the temperature Tpc corresponds to the pseudocritical temperature introduced by Kauzmann in 1948 (W. Kauzmann, Chem. Rev. 43 (1948) 219).A detailed discussion of the microscopic relaxation mechanism below and above Tpc based on the Interstitialcy theory is presented.

Effect of annealing temperature on optical properties of silver-PVA nanocomposite

The present article reports the effect of annealing temperature on the morphology and optical properties of silver nanoparticles embedded in polyvinyl alcohol (PVA) matrix. The nanocomposite films prior to annealing shows spherical grains. These films are annealed at five different temperatures (373K, 423K, 473K, 523K and 573K) in vacuum and the effects on surface morphology and optical properties are investigated. The unannealed and annealed films are characterized by FESEM, XRD, FTIR spectra, TGA, UV–vis absorption spectra and photoluminescence (PL) spectra. Scanning electron microscopy images show the change in shape and size with increase of annealing temperature. Spherical shapes of the grains in pre annealed samples get changed to nanocubes and nanorods at higher annealing temperatures of 523K and 573K respectively. UV–vis spectra show a remarkable change of surface plasmon resonance peak with the increase in annealing temperature. XRD shows a characteristic intense peak of silver nano at 2Ө=380 for (111) crystalline plane with no significant change with annealing temperature. Photoluminescence spectra show a tendency of red shift of emission peak.

Sub-Tg annealing effect on the kinetics of glass transition and crystallization for a Ti-Zr-Be-Fe bulk metallic glass

The influence of sub-Tg pre-annealing on the kinetics of glass transition and crystallization of a lightweight Ti41Zr25Be28Fe6 bulk metallic glass (BMG) has been investigated by isochronal and isothermal differential scanning calorimetry tests. It was found that sub-Tg annealing obviously enlarges the supercooled liquid region of Ti41Zr25Be28Fe6 BMG, indicating an enhanced thermal stability. The activation energies for glass transition and crystallization of the as-cast and pre-annealed samples have been calculated and compared. The pre-annealed samples possess smaller values of fragility parameter and longer incubation times upon isothermal heating compared with the as-cast sample, indicating a retarded crystallization process. The isothermal crystallization kinetics of the samples with different annealed states has been investigated in terms of the Johnson-Mehl-Avrami equation and local Avrami exponent. The current study reveals a clear sub-Tg annealing effect on the kinetics of glass transition and crystallization of Ti41Zr25Be28Fe6 glassy alloy and the possible mechanisms have also been proposed.

Effect of pre-annealing prior to cold rolling on the precipitation, microstructure and magnetic properties of strip-cast non-oriented electrical steels

A novel processing route involving strip casting, pre-annealing treatment, cold rolling and recrystallization annealing was applied to a Fe-2.6%Si steel to improve the magnetic properties. The impact of as-cast strip pre-annealing on the microstructure, texture, precipitation and magnetic properties were investigated by electron probe micro-analysis, transmission electron microscopy, and X-ray diffraction analysis, etc. It was found that the precipitation of second-phase particles during strip casting was restrained by rapid solidification. The absence of pre-annealing led to the occurrence of a large amount of 20–50nm MnS precipitates in the final annealed sheets, which is responsible for fine grains and high core loss (4.01W/kg) due to grain boundary pinning effect. Although the microstructure and texture of 900–1000°C pre-annealed samples were similar to those of as-cast strip, significant grain coarsening together with the strengthening of λ-fiber texture was observed in the 1100°C pre-annealed strips. In comparison with the case of as-cast strip, a higher amount of large-sized precipitates consisting of manganese sulfide and/or aluminum nitride occurred in matrix after pre-annealing. Correspondingly, in the final annealed sheets, the number density of precipitates with sizes smaller than 100nm was substantially reduced, and 100–200nm and 200–500nm sized particles became more dominant in samples subjected to 30-min and 120-min pre-annealing treatments respectively. In addition, the average grain size of final annealed sheets increased with the pre-annealing temperature and time because of the weakened pining effect of coarsen precipitates. Ultimately, the magnetic induction of samples subjected to pre-annealing was slightly increased and ranged from 1.73T to 1.75T owing to the enhancement of {100} recrystallization texture, and simultaneously the core loss significantly decreased until a minimum of 3.26W/kg was reached. Nevertheless, large number of 200–500nm particles presented during pre-annealing for 120 min could weaken the improvement in core loss which is likely associated with the pinning effect on magnetic domain wall.

Inscription of type I and depressed cladding waveguides in lithium niobate using a femtosecond laser

We describe two types of waveguides (type I and depressed cladding) inscribed in lithium niobate using a variable repetition rate (200kHz-25MHz), 270fs duration fiber laser. The type I modification-based waveguides have propagation losses in the range from 1.2 to 10dB/cm at 1550nm, depending on experimental parameters. These waveguides are not permanent; they deteriorate over time. Such deterioration of waveguides can be slowed down from 30 days to 100 days by pre-annealing the samples and by writing at a 720kHz laser repetition rate. The propagation losses measured at 1550nm show significant improvement for pre-annealed samples. The depressed cladding-inscribed waveguides are permanent, but the propagation loss depends on the number of damage tracks. A track separation of ∼1 μm between adjacent damage tracks yields the lowest propagation loss of 0.5dB/cm at 1550nm for a 40μm diameter waveguide. We observe multimode guidance for sizes in the range of 20-80μm in these waveguide structures at 1550nm. Their crystalline nature is found to remain intact, as inferred from second-harmonic generation within the waveguide region.

Diffusion of zinc in gallium arsenide with the participation isovalent impurities

The diffusion of Zn into GaAs in the presence of indium and phosphorus was studied. Zn diffusion was performed from the gas phase in a hydrogen flow under isothermal conditions (670°C). A GaAs substrate was annealed in In and P vapors in a separate chamber. The annealing conditions simulated the memory effect of a MOVPE reactor and/or the cross-doping during the growth of multilayer structures based on III–V alloys. The aim of the current research was to study the effects of In and P on the Zn diffusion processes in GaAs. The results obtained by secondary-ion mass spectrometry show that, upon a pre-treatment with In and P, both the incorporation efficiency and the diffusion rate of Zn increase. Measurements by Raman spectroscopy confirm the increase in the free-hole concentration in the sub-surface layers in pre-annealed samples. The influence of In and P on the diffusion process was observed at concentrations higher than 1017cm−3.Optical characterization reveals changes in the defect distribution in the GaAs samples. The changes of the recombination processes, caused by In and P, depend on the indium vs. phosphorus ratio. The effective Zn diffusion rate is controlled by this ratio.

Effects of annealing temperature on shape transformation and optical properties of germanium quantum dots**Project supported by Ibnu Sina Institute for Fundamental Science Study, Universiti Teknologi Malaysia through Vote Q.J130000.2526.02H94, O5 and Postdoctoral Research Grant.

The influences of thermal annealing on the structural and optical features of radio frequency (rf) magnetron sputtered self-assembled Ge quantum dots (QDs) on Si (100) are investigated. Preferentially oriented structures of Ge along the (220) and (111) directions together with peak shift and reduced strain (4.9% to 2.7%) due to post-annealing at 650 °C are discerned from x-ray differaction (XRD) measurement. Atomic force microscopy (AFM) images for both pre-annealed and post-annealed (650 °C) samples reveal pyramidal-shaped QDs (density ∼ 0.26× 1011 cm−2) and dome-shape morphologies with relatively high density ∼ 0.92 × 1011 cm−2, respectively. This shape transformation is attributed to the mechanism of inter-diffusion of Si in Ge interfacial intermixing and strain non-uniformity. The annealing temperature assisted QDs structural evolution is explained using the theory of nucleation and growth kinetics where free energy minimization plays a pivotal role. The observed red-shift ∼ 0.05 eV in addition to the narrowing of the photoluminescence peaks results from thermal annealing, and is related to the effect of quantum confinement. Furthermore, the appearance of a blue-violet emission peak is ascribed to the recombination of the localized electrons in the Ge-QDs/SiO2 or GeOx and holes in the ground state of Ge dots. Raman spectra of both samples exhibit an intense Ge–Ge optical phonon mode which shifts towards higher frequency compared with those of the bulk counterpart. An experimental Raman profile is fitted to the models of phonon confinement and size distribution combined with phonon confinement to estimate the mean dot sizes. A correlation between thermal annealing and modifications of the structural and optical behavior of Ge QDs is established. Tunable growth of Ge QDs with superior properties suitable for optoelectronic applications is demonstrated.

Rapid synthesis of CuInSe2 from sputter-deposited bilayer In2Se3/Cu2Se precursors

Binary bilayer glass/Mo/In2Se3/Cu2Se precursors have been used to rapidly form CuInSe2. Considering their possible application to large-area deposition processes, bilayer precursors were deposited by sequential radiofrequency sputtering of In2Se3 and direct current sputtering of Cu2Se onto unheated, Mo-coated glass substrates. High-temperature X-ray diffraction analysis of the glass/Mo/Cu2Se sample confirmed that the as-deposited polycrystalline Cu2−xSe phase is likely transformed to CuSe at approximately 210°C, and then to CuSe2 at 260°C. Further increase in temperature resulted in the peritectic decomposition of CuSe2 to CuSe (+liquid) at approximately 330°C, and then to Cu2−xSe (+liquid) at around 380°C with the release of Se. Pre-annealing of In2Se3/Cu2Se precursors in Se environment resulted in the formation of a liquid phase, which is in equilibrium with CuSe. Rapid, thermal annealing of pre-annealed samples between 500 and 550°C apparently enhanced grain growth and reduced the reaction time to about 3min; this can be explained by a liquid phase-assisted grain growth mechanism.