Post-annealed Samples Research Articles

Optical and electric properties of tin oxide (SnO2) with reduced graphene oxide nanocomposite thin films

Due to their superior properties, two-dimensional (2D) nanomaterial materials have become increasingly popular for enhancing SnO2 thin films. In the paper, a thermionic vacuum arc (TVA) deposition system was used to produce a thin film of SnO2 with a reduced graphene oxide (rGO) nanocomposite. SnO2 thin films have become widely used in sensor applications, and these sensors have been shown to work at relatively high temperatures compared to room-temperature semiconductors. As a result, working temperatures affect the material properties. The surface properties of the deposited and post-annealed samples were investigated using field emission scanning electron microscopy integrated with energy dispersive x-ray spectroscopy and atomic force microscopy. The weight ratios of carbon and tin were calculated as 35 % and 65 %, respectively. The mean Z-height of the nanoparticles was determined to be 9 nm, and the distribution of the surface grains is nearly homogeneous. Following the post-annealing process, the thin film's band gap energy decreased from 3.78 eV to 3.25 eV. According to the photoluminescence spectra, emission peaks at 393 nm, 406 nm, and 443 nm were measured. The transmittance spectra of the various post-annealed samples at 150 °C were recorded, and they remained nearly the same. This consistency is a beneficial property of the thin film because SnO2:rGO nanocomposite thin films are designed to operate at relatively high temperatures. The present study investigates the advantages and properties of the post-annealed (repeating annealing) SnO2: rGO thin film.

Improving the Two-Color Temperature Sensing Using Machine Learning Approach: GdVO4:Sm3+ Prepared by Solution Combustion Synthesis (SCS)

The gadolinium vanadate doped with samarium (GdVO4:Sm3+) nanopowder was prepared by the solution combustion synthesis (SCS) method. After synthesis, in order to achieve full crystallinity, the material was annealed in air atmosphere at 900 °C. Phase identification in the post-annealed powder samples was performed by X-ray diffraction, and morphology was investigated by high-resolution scanning electron microscope (SEM) and transmission electron microscope (TEM). Photoluminescence characterization of emission spectrum and time resolved analysis was performed using tunable laser optical parametric oscillator excitation and streak camera. In addition to samarium emission bands, a weak broad luminescence emission band of host VO43− was also observed by the detection system. In our earlier work, we analyzed the possibility of using the host luminescence for two-color temperature sensing, improving the method by introducing the temporal dependence in line intensity ratio measurements. Here, we showed that further improvements are possible by using the machine learning approach. To facilitate the initial data assessment, we incorporated Principal Component Analysis (PCA), t-Distributed Stochastic Neighbor Embedding (t-SNE) and Uniform Manifold Approximation and Projection (UMAP) clustering of GdVO4:Sm3+ spectra at various temperatures. Good predictions of temperature were obtained using deep neural networks. Performance of the deep learning network was enhanced by data augmentation technique.

Optimizing thermoelectric performance of BiSbPbTe thin films through controlled post-annealing: A comprehensive structural and electronic study

This study investigates the structural and electronic properties of BiSbPbTe thin films, focusing on the impact of post-annealing time and temperature. The X-ray diffraction (XRD) analysis reveals a stable rhombohedral phase formation in all samples, with no secondary phases detected within the detection limit. The high crystallinity of the films is confirmed, and post-annealing leads to an increase in peak intensity, indicating enhanced crystalline structure. Surface morphology analysis using scanning electron microscopy (SEM) demonstrates a transition from inhomogeneous features in as-grown films to homogeneous and dense formations in post-annealed films. The grain size increases with post-annealing time, attributed to diffusion, energy minimization, nucleation, growth, and thermal activation processes. The electronic transport properties, including carrier concentration and conductivity, are influenced by post-annealing temperature and duration. A stable carrier concentration is observed for films post-annealed for up to 2 h, while longer durations decrease due to reduced defect vacancies and grain boundaries. The increase in charge carrier mobility, confirmed by SEM results, contributes to enhanced electrical conductivity. The Seebeck coefficient shows an initial enhancement up to 2 h post-annealing, attributed to defect creation and increased grain boundaries. However, further increases in post-annealing duration result in a decrease in the Seebeck coefficient due to enhanced charge carrier mobility and reduced grain boundaries. The thermoelectric power factor (4.4 μW/cm1K2), determined by the square of the Seebeck coefficient and electrical conductivity, reaches its maximum value in the 2-h post-annealed sample, emphasizing the importance of optimizing post-annealing conditions for improved thermoelectric performance.

Chemical modification of lead zirconate titanate piezoceramics through cold-sintering process

This study presents a facile strategy to chemically modify the PZT through the cold-sintering process. The presence of lead oxide phases in the XRD patterns of samples cold-sintered at 290 °C confirms the dissolution of Pb ions from the surface of PZT particles. Post-annealing the samples at 900 °C resulted in a phase pure material with a perovskite structure, wherein the Ba ions had diffused into the lattice of PZT. The post-annealed samples had a multi-faceted grain with equilibrated triple points and a relative density of ∼93%. The electromechanical characterization showed that the d33 of the samples increased with increasing content of Ba in the PZT, reaching a value of 201 ± 80 pm/V. The post-annealed samples displayed ferroelectric switching current behaviors with saturated polarisation loops. The experimental findings reported in this study highlight the potential of the cold-sintering process for chemical modification of lead zirconate titanate electroceramics.

Manufacturing-Enabled Tunability of Linear and Nonlinear Epsilon-Near-Zero Properties in Indium Tin Oxide Nanofilms.

Epsilon-near-zero (ENZ) materials have attracted great interest due to their exotic linear and nonlinear responses, which makes it significant to tune ENZ wavelengths for wavelength-dependent applications. However, studies to achieve tunability in a wide spectral range and link the fabrication parameters with linear and nonlinear ENZ properties have been uncovered. ENZ indium tin oxide (ITO) nanofilms are fabricated by magnetron sputtering, through which the control of ENZ properties is demonstrated. Factors in the sputtering process, such as the gas ratio and annealing, have a great impact on the ITO samples. Tunable ENZ parameters are listed to provide a beneficial database for ENZ ITO, mainly attributed to the change of carrier concentration. The influence of ENZ parameters on optical characteristics via annealing treatment is further explored. The ENZ wavelength is blue-shifted by 609 nm, and the intrinsic loss is reduced by 63.2%, while the ITO samples exhibit better linear scattering properties and stronger field intensity enhancement. Additionally, the laser testing system illustrates the change from reverse saturable absorption to saturable absorption with an absolute modulation depth of 21.9%, improved by 222.1%, and the nonlinear refractive index n2 and nonlinear absorption coefficient β are 2.07 × 10-16 m2 W-1 and -3.16 × 10-10 m W-1 for post-annealed ITO samples, respectively. The proposed sputtering protocol offers a feasible technique to control the linear and nonlinear ENZ performance, which has great potential in laser technology and nanophotonics.

Post-annealing of hematite films: The changes in surface chemistry, lattice dynamics, and photoelectrochemical properties

This research deals with tracking changes in the surface chemistry and lattice dynamics of α-Fe2O3 (hematite) thin films upon post-annealing and its correlation with the photoelectrochemical (PEC) properties. The hematite thin films were prepared by the electric field-assisted liquid phase deposition (EA-LPD) method. The as-prepared thin films were heated at three different heating rates: 10, 22, and 80 ℃/min to 350 ℃; and kept for 15 min and then quenched in the air. The structural characterizations showed that the post-annealing process induces oxygen vacancies and the formation of hydroxyl groups on the surface. The extent of the changes in the surface chemistry strongly depends on the heating rate. Such changes in the surface chemistry possess a synergic effect on the PEC properties. Here the post-annealed photoanodes with an 80 ℃/min heating rate showed significantly improved PEC activity and exhibited a maximum photocurrent density ⁓ 0.73 mA.cm−2 at 1.23 V vs. RHE, 2.5 times higher than that for pristine sample. The lattice dynamics investigations suggested that the as-prepared photoanodes are composed of α-FeOOH. Upon post-annealing, α-FeOOH was partially converted into a proto-hematite intermediate phase. The longitudinal optical (LO) modes for the post-annealed samples enhanced as an indicator for the development of lattice disorder, as the results of induced oxygen vacancy defects and hydroxyl groups on the surface.

Effect of partial pressure of oxygen, target current, and annealing on DC sputtered tungsten oxide (WO3) thin films for electrochromic applications

Tungsten oxide (WO3) thin films were prepared on Corning (CG) and Fluorine doped tin oxide (FTO) glass substrates at partial pressure of oxygen (pO2) 4 × 10−2 Pa and 8 × 10−2 Pa using DC magnetron sputtering (DCMs). In this work, we have varied the deposition parameters like pO2, target currents, and temperature. At pO2 4 × 10−2 Pa and 8 × 10−2 Pa samples were deposited at target currents of 50 mA and 100 mA, the maintained growth conditions are RT (substrate temperature 28 °C), Pre annealed (substrate temperature 400 °C), and Post annealed (annealing temperature 400 °C). The samples were systematically characterized for vibrational, structural, optical, and Electrochromic (EC) properties by using Raman, XRD, Uv-Vis spectrometer, and Electrochemical analyzer respectively. XRD analysis reveals that RT-deposited samples show amorphous nature and pre & post-annealed samples show a crystalline nature for both pO2. Optical transmittance was higher at RT-deposited samples at 50 mA (94% & 92%) and lower at 100 mA (87% & 85%) at the wavelength of 600 nm for both pO2. From CV analysis higher cathodic peak current density was observed in RT-deposited samples at 50 mA (−6.49 mAcm−2 & -13.80 mAcm−2) and lower at 100 mA (−5.25 mAcm−2 & -12.88 mAcm−2) for both pO2. The diffusion coefficient was observed at a higher target current at 100 mA (1.06 × 10−7 cm2/s & 9.20 × 10−8 cm2/s). For annealed samples optical and EC properties were decreased for both pO2.

Dopant profiling of ion-implanted GaAs by terahertz time-domain spectroscopy

We investigate terahertz time-domain spectroscopy (THz-TDS) as a non-destructive and non-contact technique for depth profiling of dopants in semiconductors. THz temporal waveforms transmitted through silicon-ion-implanted semi-insulating gallium arsenide substrates, as-implanted or post-annealed by rapid thermal annealing, were analyzed by assuming a multi-layered Gaussian refractive index profile in the ∼sub-micrometer-thick implantation region. The implantation energy and dosages in this work were 200 KeV, 1014, 5 × 1014, and 1015 ions/cm2, respectively. The average values of real (n) and imaginary (κ) parts of refractive indices of an as-implanted sample in the depth range of 0–800 nm are 5.8 and 0.7, respectively, at 0.5 THz and are 6.2 and 0.2, respectively, at 1 THz. On the other hand, the refractive index profile of the post-annealed samples displays a prominent Gaussian-like form, and peak refractive indices (n ∼ 25 and κ ∼ 32.7 at 0.5 THz and n, κ ∼17 at 1 THz) were found to be at the depth of 210 nm. Reconstructed dopant profiles in as-implanted, implanted, and post-annealed substrates were found to be in good agreement with measurements by secondary ion mass spectroscopy as well as simulation by the Monte Carlo method. We were also able to determine accurately the projected range (Rp), straggle (Rs), and concentration of dopants by the analysis of THz-TDS data. The spatial resolution, along the depth direction, of the THz-TDS technique for depth profiling of dopants was estimated to be as small as 8-nm. This work suggests the feasibility of using THz-TDS for nondestructive and non-contact diagnostics for profiling dopants in semiconductors.

THE INFLUENCE OF POST-ANNEALING CdS THIN FILMS GROWN ON ZnO SEED LAYER FOR CdTe SOLAR CELLS

In this study, the effect of post-annealing temperature in CdS thin films grown on ZnO seed layer was investigated. CdS thin film and ZnO seed layer were coated by chemical bath deposition method and solution dropping technique, respectively. The structure of the post-annealed samples at 350°C and 400°C consisted of cubic CdS and CdSO3 oxide phases. As a result of recrystallization at 450°C, both hexagonal CdS and cubic CdO phases were formed. While the absorption edge was observed at around 500 nm in all samples, the best transmittance was observed in the sample annealed at 400°C. PL spectra proved the existence of defect types such as deep emission, sulfur vacancy for all samples. Ellipsometer measurements showed that the highest refractive index was in the sample annealed at 400°C. Among the samples, it was concluded that the most suitable window structure for CdTe solar cell applications is CdS thin film post-annealed at 400°C.

High Quality Ge Growth on Si (111) and Si (110) by Using Reduced Pressure Chemical Vapor Deposition

Heteroepitaxial growth of Ge on Si has great interest for various optoelectronic applications such as Ge photodiodes(1). However 4.2% of lattice mismatch causes dislocation formation and island growth. High quality Ge(001) growth techniques are reported in ref.(2-4). Moreover, Ge(111) surface is also interesting because of higher carrier mobility(5). Furthermore, Ge(110) is preferred orientation of virtual substrates for epitaxial graphene growth(6). In the case of the Ge deposition on Si(111) and Si(110) substrates, it seems that the process conditions used for Ge growth on Si(001) are not suitable to realize high crystallinity and smooth surface (7). In this paper, we present a method of high quality and smooth Ge layer growth on Si(111) and Si(110), which is the same level as the Ge growth on Si(001).Epitaxial growth of Ge on Si(111) and Si(110) is carried out using a reduced pressure chemical vapor deposition system. After HF last clean, a wafer is baked at 1000°C and cooled down to 600°C in H2 and further to 300-550°C in N2 to form a hydrogen-free Si surface. Then a 100 nm thick Ge layer is deposited as a seed layer using GeH4 with N2 carrier gas. Afterward the wafer is heated up to 450-650°C in H2 and the main part of Ge is deposited using a H2-GeH4 gas mixture. For threading dislocation density (TDD) reduction, annealing at 800°C in H2 is performed for several times (cyclic annealing) by interrupting the Ge growth. Atomic-force microscopy (AFM) is used for surface roughness analysis. Scanning transmission electron microscopy (STEM) and X-ray diffraction (XRD) are used for structural characterization of the Ge layer. Secco defect etching combined with angle view scanning electron microscopy (SEM) or optical microscope is used for TDD evaluation.Figure 1(a,b) summarize the root mean square (RMS) roughness of Ge(111) and Ge(110) seed layers grown at 300-550°C before and after postannealing at 600-800°C. If the growth temperature is lower than 350°C for Ge(111) and 400°C for Ge(110), a significant increase of the surface roughness is observed after postannealing at 700°C and 800°C, respectively. For both crystal orientations, the lowest RMS roughness is observed by depositing at 450°C for as deposited and postannealed samples. The maintained RMS roughness even after postannealing at 800oC may be indicating good crystal quality even at as deposited condition.To confirm the influence of the growth temperature on the crystallinity, cross section TEM images of the Ge(111) and the Ge(110) seed layers deposited at 300°C and 450°C are shown in Fig. 2(a-d). In the case of Ge growth at 300°C (Fig. 2(a,b)), a very high density of stacking faults (SF) and high surface roughness are observed for both crystal orientations. In contrast, by depositing at 450°C (Fig. 2(c,d)), lower SF density in the Ge layer is observed compared to that at 300°C. By postannealing, an improvement of crystallinity is observed for the Ge seed layers deposited at 450°C. However, in the case of 300°C, the crystallinity cannot be improved by the postannealing, because a too high density of dislocations and SF may cause irregular Ge atom migration. As the result, surface roughening occurs.Figure 3(a,b) show AFM surface roughness images after 5 μm-thick Ge(111) and Ge(110) deposited with cyclic annealing at 800°C, respectively. Clear terraces of ~0.3 and ~0.2 nm, whose heights are close to those of Ge(111) bilayer and Ge(110) monolayer, are observed, respectively. RMS roughness of the Ge(111) and the Ge(110) are 0.51 and 0.35 nm, respectively. These RMS roughnesses are comparable to a level reported for Ge (001) in ref.(1).Figure 4 shows TDD of Ge(111) and Ge(110) surfaces as a function of the Ge thickness deposited with cyclic annealing on Si(111) and Si(110) substrates. For both orientations, TDD of ~4×108 cm-2 is obtained for 500 nm-thick samples. With increasing the Ge thickness, the TDD is reduced and levels below TDD of ~5×106 cm-2 are achieved for both Ge (111) and Ge(110) for 5 μm-thick Ge.These methods enable high quality virtual substrate fabrication not only for (001) surfaces but also for (111) and (110) orientation without a chemical mechanical polishing process. References Lischke et al. Nature Photonics15 (2021) 925Yamamoto et al. Solid-State Electron. 60 (2010) 2Yamamoto et al. Semicond. Sci. Technol. 33 (2018) 124007 M. Hartmann et al. J. Appl. Phys. 95 (2004) 5905 H. Lee et al. IEDM Tech. Digest (2009) 09-457J-H. Lee et al. Science 344 6181(2014) 286M. Hartmann et al. J. Cryst. Growth 310 (2008) 5287 Figure 1

Ductilization of a diffusion-bonded heterostructured AZ31/GW103K/AZ31 alloy by interfacial reinforcement

Heterostructured materials are an emerging class of materials with superior performances that are unattainable by their conventional homogeneous counterparts, and have recently attracted extensive attentions from the materials community. However, due to the hcp crystal structure, the conventional processing methods of heterostructured materials are difficult to be applied in Mg alloys. To overcome the negative effects, namely poor formability and easy oxidation, in Mg alloys, diffusion bonding under an ultra-vacuum condition was employed to prepare multi-layer heterostructured materials with different alloys, i.e. AZ31 (Mg–3Al–1Zn wt. %) and GW103 K (Mg-10Gd-3Y-0.4Zr wt. %) alloys. Moreover, the reinforcement of interface was further improved by interaction of alloying elements during post-annealing. The new formed interfacial phase was found to be the main reason for the reinforcement of interface. Without a decrease of strength, the ductility of post-annealed samples was increased to more than twice of the diffusion bonded ones. Based on high resolution TEM observation, the crystal lattice of the interfacial phase was determined as a fcc structure with a lattice parameter of a = 7.9 Å.

Structure characterization and steam oxidation performance of U3Si2 with Zr alloying additions

Research and development of high uranium density fuels supports the on-going effort to enhance reactor technology, safety, performance, and economics. Among high uranium density fuels, U3Si2 is a favored fuel candidate due to its higher uranium density and improved thermal conductivity when compared to traditional UO2. While U3Si2 demonstrates an improved fuel economy, it suffers from rapid degradation when exposed to water at T > 300°C. In order for U3Si2 to be implemented in water cooled reactors, the water reaction must be understood and mitigated. Reported here is the performance of Zr alloying additions to U3Si2 exposed to high temperature steam oxidation environments. The investigation shows that homogenization heat treatment contributes to a delayed onset of oxidation and an improved homogeneity throughout the arc-melt fabricated alloyed compositions. Of the pre- and post-annealed samples, the post-annealed 7 vol% Zr addition exhibited the highest onset temperature of oxidation. A preliminary computational investigation to complement the experimental analysis assesses the solubility of Zr in U3Si2 and its incorporation in the crystal lattice.

Enhancement of the structural, optical and thermoelectric properties of thermally evaporated AgMoO3 thin film by post-annealing

In this manuscript, we have grown the AgMoO3 thin film by a simple thermal evaporated method. To attain the best quality film, post-annealing the grown thin films for different temperatures (450 K, 500 K, and 550 K) was performed. The XRD data shows the formation of AgMoO3 thin film and different secondary phases. The SEM data have shown the small spherical grains on the thin film surface, which confirm the creation of extra secondary phases and the cracks on the film with post-annealing due to intrinsic stress. The absorption coefficient and energy bandgap have also increased with the post-annealing temperature. The Seebeck data indicated an enhancement in Seebeck coefficient value from 237 to 410 μV/K as the as-grown to post-annealed samples. The electrical conductivity measurements also showed an increasing trend. The Seebeck coefficient and electrical conductivity enhancement were increased by creating a different secondary phase that caused the carrier localization. Improved mobility of carriers due to the change in crystal structure has resulted in an increased power factor of 1.19 × 10−3 Wm−1K−2.

Optical, structural, and electrical properties of sputter-deposited SnOx thin films

This study investigated the effect of deposition parameters on the properties of tin oxide (SnOx) thin films deposited by direct current magnetron sputtering using a Sn metal target. As confirmed by optical bandgap, X-ray photoelectron spectroscopy, high-resolution X-ray diffraction and Hall effect measurements, as-grown samples deposited at 7.5 and 10% oxygen partial pressure (OPP) and post-annealed samples deposited at 5% OPP had a p-type SnO phase, whereas samples fabricated with 7.5 and 10% OPP and annealed at 400°C had a n-type SnO2 phase. Post-annealing at 400°C increases the bandgap and injects more oxygen into the SnOx thin film, further oxidizing the sample. In addition, post-annealing greatly increased the carrier concentration of the SnOx thin film, which increased carrier scattering and, in turn, greatly reduced the mobility of the sample. The SnOx thin film deposited at 7.5% OPP and not heat treated showed the best p-type properties, with a Hall mobility of 5.11 cm2/Vs, a hole carrier concentration of 1.13 × 1015 cm−3, and a resistivity of 1082 Ωcm.

Impact of Deep Ultraviolet-Ozone Photoactivation on Dielectric Properties of Amorphous SrTiO<sub>3</sub> Thin Films

Strontium titanate SrTiO3 thin films have been fabricated by radio frequency magnetron sputtering on P-type Si at substrate temperature of 200°C. Two different postdeposition annealing methods were applied on the sputtered films. Specifically, conventional thermal annealing at 300°C for 60 min and photoactivation treatment under deep ultraviolet-ozone for 30 min. The dielectric properties of the SrTiO3 thin films were investigated by fabricating Au/STO/p-Si MOS capacitors. A dielectric constant (κ) with a value of 13 was obtained for as-deposited film, which has a thickness of 107 nm. While post-annealed samples showed elevated values of κ, precisely, 15.33 and 19.32 for films exposed to deep ultraviolet-ozone photoactivation and films annealed at 300°C, respectively. All devices showed a leakage current in the order of 10-8 A/cm2 at 1V. Based on XPS analysis, photo-activated films revealed the lowest percentage of oxygen vacancies, which designates the capability of this technique to enhancing films quality at a lower temperature.

Characterization of 4H-SiC Lattice Damage After Novel High Energy Ion Implantation

A multi-energy implantation system has been developed for deep implantation of dopant atoms (Al, B, N, P) in 4H-SiC wafers to fabricate deep junctions for medium and high voltage devices. Energies used range from 13MeV to 66MeV, far higher than those used in conventional implantations. Therefore, lattice damage induced by the implantation process and the recovery by annealing must be characterized in detail for understanding the nature of damage, extent of recovery and its possible effect on device properties. To this end, 4H-SiC wafers with 12 um epilayer were implanted by 13.8 MeV to 65.7 MeV Al and N ions using the multi-energy implantation system. Samples were implanted in the form of alternative Al and N pillars or blanket co-implanted with Al and N. The nature of strains induced by the implantation process in as-implanted and post-annealed samples were investigated using Synchrotron X-ray Rocking Curve Topography (SXRCT) and Reciprocal Space Map (RSM). As-implanted samples are characterized by tensile strains. By comparing samples implanted with different fluences, we have confirmed that implantation with higher total fluence introduces higher levels of strains in the 4H-SiC epilayer.

Microstructure evolution of gadolinium doped cerium oxide under large thermal gradients

The effects of large thermal gradient annealing on the microstructure of 10 mol% gadolinium doped ceria (GDC) were investigated. GDC powder was prepared by solvent deficient method and sintered at 1650 °C for 10 h to achieve dense ceramics with ~8 μm grain size. The densified GDC samples were subsequently annealed using a 60 W infrared laser at over 2100 °C for 1 h under a thermal gradient equivalent to ~0.3–0.5 °C/μm. The post-annealed samples at 2150 °C for 1 h exhibit grains with average length and width of 37 and 28 μm, respectively. Electron backscattered diffraction (EBSD) analysis revealed that the post-annealed sample at 2150 °C consists of grains oriented close to five principal directions (<4 3 10>, <0 0 1> and <13 1 14> on [0 0 1], and <7 6 20> and <7 2 7> on [0 1 0]) within a tolerance angle of ±10°, whereas the grains of the pre-annealed sample are randomly oriented. Gadolinium diffuses 20–30 μm away from the irradiated surface, with the measured composition of regions deeper than 30 μm, Ce0.86Gd0.14O1.93, is close to that of the pre-annealed sample, Ce0.87Gd0.13O1.94. Enhancement of total conductivity of the post-annealed GDC (1.1 × 10-3 S cm-1 at 500 °C, and 2.1 × 10-2 S cm-1 at 700 °C) is observed when compared to the pre-annealed GDC (3.1 × 10-5 S cm-1 at 500 °C, and 1.7 × 10-3 S cm-1 at 700 °C), and points to the decrease in the grain boundary (GB) resistivity. This could be attributed to both the change in GB area and grain alignment.

Improvement of Mechanical Strength of a Hot-Worked Twinning-Induced Plasticity Steel through an Optimum Secondary Annealing Treatment

The microstructure of the twinning-induced plasticity (TWIP) steel microalloyed by Ti (TWIP-Ti) exhibited a wide grain size distribution after applying a thermomechanical treatment. The presence of fine and coarsest grains affected mechanical twinning and properties. This research was directed toward elucidating the effect of an optimum secondary annealing treatment to produce a homogenous microstructure through the release of remnant energy stored during the hot deformation processing of a TWIP-Ti steel. A comprehensive analysis of the effect of annealing parameters on the microstructure and its enhanced mechanical properties in terms of grain size distribution, precipitation strengthening and annealing twin fraction was performed. The microstructural characterization included light optical microscopy and scanning electron microscopy (SEM). SEM line scans were performed to characterize precipitate particles found in the TWIP-Ti steel. Microhardness and tensile tests were performed on the base material (as-solution condition) and post-annealing samples. The Taguchi method was applied to optimize the annealing parameters. Furthermore, image processing was employed to quantify the grain size distribution and annealing twin fraction. The analysis results revealed that upon completion of the second stage of annealing treatment with the optimal parameters, the grain size heterogeneity decreased due to the effect of coarsest grain subdivision. The low SFE of the TWIP-Ti steel, homogenous grain size microstructure and precipitation strengthening produced yield strength and ultimate tensile strength increases of 27% and 8.5%, respectively. The homogenous grain size distribution had a more substantial effect on improving the mechanical properties than the annealing twin fraction.

High performance, self-powered and thermally stable 200–750 nm spectral responsive gallium nitride (GaN) based broadband photodetectors

We have developed and first reported Au/Ni/Pr2O3/GaN broadband photodetector device with photoresponsivity from 205 nm to 750 nm under self-powered mode. Using the Tauc's plot, the direct optical bandgap was found to be 4.8, 2.45 and 2.35 eV for the as-deposited, 550 °C and 650 °C post annealed samples, respectively. XRD study revealed that the phase of the as-deposited and post-annealed Pr2O3 films on GaN was monoclinic in nature. Atomic force microscopy method was engaged in non-contact mode to investigate the surface morphology of Pr2O3 films on GaN and the rms surface roughness was improved for the 650 °C post-annealed sample as 1.1 nm compared to other samples. In XPS study, two main Pr3d well separated XPS peaks were noticed at 933.5 eV (m) and 953.9 eV (m′) which corresponds to spin-orbit doublets of 3d5/2 and 3d3/2, respectively. In addition, the transient response measurements of the fabricated 650 °C post annealed device confirmed good stability even for the applied bias voltage of 20 V in the entire UV region. Further, the 650 °C post annealed device at 20 V provided best rise and fall times of 0.57 s and 0.41 s at 360 nm, respectively. The responsivity of the fabricated BB PD device at 650 °C revealed the evidence of bias dependency because of photoconductive gain. The attained progress in the fabricated PD device performance was due to the improved light absorption as evidenced from the optical absorption study. This results the transport of photogenerated electron-hole pairs across the bandgap by limiting recombination/trap states and intentionally deposited LT GaN buffer layer at the interface of sapphire/GaN. These results suggest that the developed BB PD device could also have the potential usage in optoelectronic device applications.

Effect of post-annealing on the microstructure and mechanical properties of nanostructured copper

Abstract In the current research, the effect of post-annealing treatment at 200 °C with four different holding times of 5, 10, 30, and 60 min on the asymmetrically cold-rolled pure copper was investigated. The microstructural evolution (via optical microscopy and scanning electron microscopy), mechanical properties (by tensile and hardness tests), and electrical conductivity of the post heat-treated copper sheets were evaluated. The static recrystallization (SRX) took place at a short annealing time due to the large strain stored energy caused by the asymmetric cold rolling as well as the presence of particles. The average grain size of the post-annealed sample for 5 min was about 96 nm. The copper after 60 min post-annealing consisted of many coarse polygonal grains, a few small grains, and multiple twinning (twin chains). The formation of multiple twinning and twin chains was due to the low-temperature annealing (200 °C) of rolled copper. The tensile properties indicated that the strength had a relatively low sensitivity to the increment of annealing time and the produced pure copper exhibited superior thermal stability. The formation of twin chains and the existence of copper oxide particles were responsible for this unusual behavior. The copper annealed for 60 min had a low YS-to-UTS ratio (0.378) and a high work hardening rate, which were equivalent to high formability. For the low annealing times of 5 and 10 min, there were both shear and equiaxed dimples on the fracture surface indicating a combination of ductile shear and ductile fractures. When the time of post-annealing was higher than 30 min, only the ductile dimples could be observed on the fracture surface. The post-annealing treatment for 60 min increased the electrical conductivity to from 84.10 to 87.52 %IACS due to the occurrence of recovery, recrystallization, and grain growth. Finally, it was found that adopting a high enough pre-deformation (96% strain) and a suitable annealing time (60 min) at a low annealing temperature (200 °C) in the pure copper could make a good balance between tensile and electrical properties.