Post-annealing Process Research Articles

Synthesis of β-Ga2O3:Mg Thin Films by Electron Beam Evaporation and Postannealing

Doping divalent metal cations into Ga2O3 films plays a key role in adjusting the conductive behavior of the film. N-type high-resistivity β-Ga2O3:Mg films were prepared using electron beam evaporation and subsequent postannealing processing. Various characterization methods (X-ray diffraction, X-ray photoelectron spectroscopy, photoluminescence, etc.) revealed that the Mg content plays an important role in affecting the film quality. Specifically, when the Mg content in the film is 3.6%, the S2 film’s resistivity, carrier content, and carrier mobility are 59655.5 Ω·cm, 1.95 × 1014 cm3/C, and 0.53682 cm2/Vs. Also, the film exhibits a smoother surface, more refined grains, and higher self-trapped exciton emission efficiency. The Mg cation mainly substitutes the Ga+ cation at a tetrahedral site, acting as a trap for self-trapped holes.

Promoting the circularity of ceramic materials through cold sintering of aggregates from construction and demolition waste

A ceramic composition containing 95 wt% of construction and demolition waste-like material was consolidated by cold sintering process at 200 °C using KOH water solutions as the liquid medium. The relative density of the samples reaches ∼90 % of the theoretical one for process conditions of 600 MPa and 60 min. A post-annealing process at 1100 °C of the as-cold sintered samples causes a slight increase in the relative density and of their mechanical strength compared with conventionally sintered samples at 1100 °C and increases the shape factor of the Weibull distribution, thus increasing the reliability of the component. It is shown that cold sintering of the material avoids its high pyroplasticity, providing low shrinkage and reducing internal defects in the ceramic. This work represents the first exploration of the viability of manufacturing ceramic tiles with high recycled content contributing to the transition to a greener world.

The role of post-annealing process on the physical, electrical and magnetic properties of nano-sized tin substituted Bi-2212 superconducting ceramics

The role of post-annealing process on the physical, electrical and magnetic properties of nano-sized tin substituted Bi-2212 superconducting ceramics

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.

Hexagonal ZnTiO3 single-crystalline films on α-Al2O3 substrates: Structural and photoelectric properties

Hexagonal ZnTiO3 (h-ZnTiO3) films with stoichiometric were deposited on α-Al2O3 substrates using pulsed laser deposition (PLD) method and post annealing process. The effect of oxygen partial pressure on Zn/Ti atomic ratio, as well as the influence of annealing treatment on the structural and optical properties of the films were investigated in detail. The optimum h-ZnTiO3 film was deposited under 5 Pa oxygen partial pressure and annealed at 800°C, and it exhibited excellent crystalline quality and an optical band gap of 3.72 eV. A photodetector based on the film was fabricated, and its photoresponsivity was approximately 0.18 mA/W under 308 nm ultraviolet light irradiation. This demonstrates that as a wide bandgap semiconductor material, h-ZnTiO3 has potential applications in the field of devices.

Investigation of thermally induced surface composition and morphology variation of magnetron sputtered Sb2Se3 absorber layer for thin film solar cells

One of the most promising semiconductor materials for the development of sustainable thin-film solar cell technology is antimony selenide (Sb2Se3). Its excellent optical and electrical properties have drawn attention lately for potential application in thin-film solar cells. In this study, Sb2Se3 films deposited using the direct current (DC) magnetron sputtering technique have been subjected to a post-annealing process without an extra selenium supply at temperatures between 150 and 450 °C. Without an extra selenium supply, the impact of post-annealing temperature on the surface composition as well as the physical properties of the fabricated films was investigated. The overall evaluations revealed that the post-annealing temperature is highly efficient in altering the physical properties of the Sb2Se3 absorber thin films. We further observed that the post-annealing process improved the crystallization and the heat treatment temperature quite affected preferential orientation. The surface morphology of films exhibited structural deformation at high post-annealing temperatures (> 350 °C). According to optical and electrical characterizations, respectively, the optical energy gap and the resistivity of Sb2Se3 films reduced with an increment in the post-annealing temperature. Based on the XPS result, the variation in temperature of post-annealing led to a change in the surface composition of the films. The findings on the growth of Sb2Se3 thin films indicate the existence of an intermediate growth temperature that permits the growth of Sb2Se3 films to be optimized. The study’s conclusions can serve as a guide to the growth of Sb2Se3 thin films with the desired crystallinity, surface morphology, and composition for thin film solar cell applications.

Heterogeneous monolithic 3D integration for hybrid vertical CMOS inverter using n-type IGTO TFT on p-type Si FET

In this work, a complementary metal oxide semiconductor (CMOS) vertical inverter using heterogeneous monolithic 3D (M3D) integration with p-type Si field-effect transistor (FET) and n-type indium-gallium-tin-oxide (IGTO) thin film transistor (TFT) was implemented and characterized. This CMOS inverter was attained by vertical stacking n-type IGTO TFT on p-type Si FET. Oxide semiconductor materials such as indium-gallium-zinc-oxide (IGZO), indium-tungsten-oxide (IWO), indium oxide (In2O3) and IGTO are being considered as potential options for channel materials in M3D integration technology due to high electrical characteristics and low temperature process. Among them, IGTO was employed as a channel material to achieve high mobility. We fabricated a n-type IGTO TFT using HfO2 and tungsten as a gate dielectric and electrode, respectively. The post-annealing process was conducted at 200–500 °C with 50 °C intervals. The IGTO TFT exhibits a high field-effect mobility (32.9 cm2/Vs), low sub-threshold swing (0.070 V/dec) and stable reliability behaviour (ΔVth < 0.4 V) against various external gate bias temperature stress tests in a low temperature (<500 °C). The stable heterogeneous vertical inverter performance such as voltage-transfer curve (VM = 1.66 V), voltage gain (30.1 V at VDD = 3 V), and noise margin (NMH = 1.22 V, NML = 1.34 V) were well behaved. This M3D integration-based hybrid CMOS inverter can be an alternative knob toward various device applications.

Optical switch with an ultralow DC drift based on thin-film lithium tantalate.

We present an electro-optic (EO) switch with ultralow DC drift on a thin-film lithium tantalate (TFLT) platform, even with SiO2 cladding and without post-annealing processes. The flat Vπ and EO responses have been measured across various driving frequencies, input optical powers, and temperatures. Stable optical switching is achievable in the low-frequency range. The experiment also demonstrated superior long-term stability (up to 2 h) compared to thin-film lithium niobate optical switches under similar on-chip optical power conditions (around -8 dBm).

Surface-Enhanced Raman Scattering on Size-Classified Silver Nanoparticles Generated by Laser Ablation.

This study delved into the complex interplay between the nanostructural characteristics of nanoparticles and their efficacy in surface-enhanced Raman scattering (SERS) for sensitive detection of trace chemical substances. Silver nanoparticles were prepared for the SERS substrate by combining laser ablation, postannealing processes (up to 500 °C), and electrostatic mobility classification, allowing high-purity silver nanoparticles with controlling their sizes (40-100 nm) and aggregate structures. These nanoparticles were then inertially deposited on the substrates to create SERS-active surfaces, employing Rhodamine B as a probe to assess the impact of particle size, shape, and deposition density on SERS effectiveness. Our findings revealed that spherical nanoparticles, especially those approximately 50 nm in diameter, controlled to a spherical structure through gas-phase annealing at 500 °C and subsequent classification, yielded the most significant SERS enhancement. This optimal can be explained by the particle size response of the surface plasmon resonance, where the enhancement of the Raman signal for particles up to 50 nm (1/10 of the laser wavelength used in this study, 532 nm) arises from a balance between the enhancement of dipole moment and the number of "hot spot" regions (respectively proportional to the cube and inverse square of the diameters in theory, leading to a linear relationship between signal intensity and particle diameter); meanwhile, in larger size region than 50 nm, the Raman signal was decreased owing to the attribution of the phase difference between the electric field and dipole moment. Furthermore, we found that a deposition density of 2 μg resulted in nearly a single layer of particles, which is crucial for maximizing SERS hotspots and, consequently, the enhancement effect.

Critical review on the controllable growth and post-annealing on the heterojunction of the kesterite solar cells

Abstract Kesterite-structured solar cells have drawn significant attention due to their low-cost and environmental friendly composition. Recently, a remarkable certified power conversion efficiency (PCE) of 14.9% has been achieved, indicating a broader prospect for kesterite solar cells. However, this PCE is still far below the theoretical efficiency and the PCE of predecessor Cu(In,Ga)Se2 solar cells, which have been commercialized successfully. The relatively low device efficiency primarily originates from the unfavourable bulk and heterojunction of kesterite solar cell. Therefore, the achievement of high PCE in kesterite solar cells heavily relies on high-quality absorber layers and appropriate heterojunction contact. In this review, we first summarize the recent studies on the controllable growth of kesterite thin film. Based on different fabrication methods, various endeavors in revealing the reaction mechanism and manipulating the growth pathway of kesterite thin films have been introduced. Subsequently, studies related to the optimization of heterojunction by post-annealing process are also summarized. This simple and convenient approach can effectively enhance the heterojunction contact and promote the carrier transportation. Finally, this article discusses the future development strategy and perspectives towards achieving enhanced PCE in kesterite thin film solar cells

3D-Printed Interfacially Jammed Emulsion Aerogels.

3D printing ultralightweight porous structures using direct ink writing (DIW) while maintaining their mechanical robustness is highly challenging. This difficulty is amplified when low ink concentrations are used to create complex geometries. Herein, this shortfall was addressed by interfacially jammed emulsion gels. The gel emerged from the electrostatic interaction among synergized nanomaterials (graphene oxide (GO) and cellulose nanocrystals (CNCs)) in the aqueous phase and a ligand in the oil phase. This interaction led to the jamming of the nanoparticles and the creation of stable emulsion gels. The formed interfacial assemblies were further treated by post-jamming ionic cross-linking with NaHCO3, which dictated the emulsion gels' rheological characteristics, enhancing the ink's viscoelastic properties for high-resolution 3D printing. The customizable emulsion system allows control over porosity from the macro- to the micro-scale and generates complex geometries with desired compositions. By manipulating post-annealing processes and varying concentrations, it is possible to achieve aerogels that feature a remarkably low density (∼2.63 mg/cm3) and adjustable mechanical robustness (elastic modulus of 0.45 MPa). Additionally, this method allows for producing aerogels with flexible or stiff characteristics as required, alongside the capability to tailor specific electromagnetic shielding effectiveness (ranging from 6791 to 19615 dB cm2/g), showcasing the technique's versatility and engineerability.

Enhancement of crystallinity and the optical properties in gamma irradiated and thermally annealed cobalt doped MgTiO3 thin films

We report the crystal structure, surface morphology and optical properties of gamma (γ) irradiated, and thermally annealed cobalt (5 %) doped magnesium titanate thin films. Mg0.95Co0.05TiO3 (MCT) thin films were fabricated on quartz substrates by Radio Frequency magnetron sputtering while substrate temperature was maintained at 300 °C. Firstly, the as-prepared MCT thin films were irradiated by 1.33 MeV 60Co γ – rays with varying doses in the range of 0 – 125 kGy with the intervals of 25 kGy and post-annealing process at 700 °C. The X-ray diffraction pattern of irradiated thin films is amorphous, whereas annealed films are crystalline, which are refined with the Rietveld refinement method by considering the R3¯space group. Dominated crystallite size (39 nm) with low strain is identified for the samples exposed at 75 kGy. In addition to the γ-irradiation of 75 kGy, the optical characteristics revealed that an enhanced bandgap (∼ 4.27 eV) and refractive index (2.26) had been observed for an annealed sample as compared with the bandgap (∼ 3.68 eV) and refractive index (2.10) of as-deposited sample. The influence of γ-irradiation dose and annealing on MCT thin films' structural and optical properties has been discussed. This study demonstrates that the γ–ray irradiated MCT films are potential candidates for anti-reflection coating applications.

Demonstration of a lateral p-NiO/n-GaN JFET fabricated by selective-area regrowth

In this paper, we demonstrated experimentally a lateral GaN-based junction field effect transistor (JFET). A selective area regrowth of p-NiO on the as-grown n-GaN channel layer was developed by magnetron sputtering at room temperature to form the p–n junction. A self-aligned gate process and a post metal annealing process were employed to improve the device performances. The measured results show that the annealed JFET exhibits an ON/OFF ratio exceeding 106 and a higher breakdown voltage up to 814 V without any terminal structure. The breakdown voltage is determined by the reverse breakdown of parasitic PN junction between gate and drain. Further, the threshold voltage of the p-NiO/n-GaN JFET exhibits excellent temperature stability in the range of 300–500 K.

Template-assisted growth of Ga-based nanoparticle clusters on Si: effect of post-annealing process on the Ga ion beam exposed 2D arrays fabricated by focused ion beam nanolithography

We demonstrate template-assisted growth of gallium-based nanoparticle clusters on silicon substrate using a focused ion beam (FIB) nanolithography technique. The nanolithography counterpart of the technique steers a focussed 30 kV accelerated gallium ion beam on the surface of Si to create template patterns of two-dimensional dot arrays. Growth of the nanoparticles is governed by two vital steps namely implantation of gallium into the substrate via gallium beam exposure and formation of the stable nanoparticles on the surface of the substrate by subsequent annealing at elevated temperature in ammonia atmosphere. The growth primarily depends on the dose of implanted gallium which is in the order of 107 atoms per spot and it is also critically influenced by the temperature and duration of the post-annealing treatment. By controlling the growth parameters, it is possible to obtain one particle per spot and particle densities as high as 109 particles per square centimetre could be achieved in this case. The demonstrated growth process, utilizing the advantages of FIB nanolithography, is categorized under the guided organization approach as it combines both the classical top-down and bottom-up approaches. Patterned growth of the particles could be utilized as templates or nucleation sites for the growth of an organized array of nanostructures or quantum dot structures.

Study on the effect of size and density of micropores on transparent ceramic damage induced under intense laser irradiation

The increasing utilization of transparent ceramics in laser systems, particularly the magnesium aluminate spinel (MgAl2O4) transparent ceramic, has positioned it as the primary candidate for high energy laser system exit windows. Nevertheless, the increased energy and power of laser output necessitate higher standards for the laser-induced damage threshold in transparent ceramics. Residual micropores within transparent ceramics pose a potential source of damage. In this study, we employed the post-annealing process to effectively modulate the density and size of micropores. We first established the relationship between the density and size of micropores and laser damage threshold, which described the damage morphology of transparent ceramic in detail. Subsequently, we developed a multi-physical field coupled kinetic model of laser damage in micropores, providing a quantitative analysis of how factors such as micropore size and density influence the damage morphology of transparent ceramic surfaces when subjected to laser irradiation. Using time-resolved pumping and probing technology, we conducted in situ detection of laser damage caused by micropores, enabling detailed examination of damage kinetic behavior. Ultimately, this study elucidated the physical mechanism behind micropore-induced transparent ceramic damage. This has significant implications for enhancing the anti-laser damage performance of transparent ceramics in high-intensity laser systems.

Nb2O5 film optical properties and laser-induced damage by phase-change-driven tuning

Niobium oxide (Nb2O5) is widely used in optical and electrical fields because of its high refractive index, wide band gap, high laser-induced damage threshold (LIDT) and high transparency in the ultraviolet to middle-infrared-wavelength range (0.35–7 μm). In this study, Nb2O5 films with different crystalline phases were successfully prepared on BK7 and Si substrates through electron beam evaporation (EB) and post-annealing. Based on the results of X-ray diffraction (XRD) and Raman spectroscopy analysis, the impact of the post-annealing technique on the structure, and optical and physical properties of Nb2O5 films was thoroughly discussed at the molecular level. The crystal phase of an Nb2O5 film and its molecular bonds considerably affect its properties. The Nb2O5(-12 1 2) film prepared in this study exhibited a higher LIDT (17.72 J/cm2) and a higher RMS (0.447 nm) than the corresponding films prepared in previous studies. Following the post-annealing process, the band gap and refractive index of the prepared films were significantly higher than those of the as-deposited film. Thus, this study has significant guiding implications for Nb2O5 film applications and the development costs of the films.

Mechanisms of rapid magnetocaloric enhancement of La–Fe–Co–Si alloy by high-temperature hot compression with large deformation

In this study, the microstructure, phase composition, magnetic transition, and magnetocaloric effect of the LaFe10.6Co0.9Si1.5 alloy hot compressed at high temperatures over 1173 K with a strain rate 0.005 s−1 and reduction ratio 50%–70 % are studied. No La(Fe, Si, Co)13 phase is formed until the hot-compression temperature is elevated to 1273 K and the reduction ratio is increased to 70 %. As a result, 86.8 ± 2 wt% 1:13 phases are rapidly obtained in the LaFe10.6Co0.9Si1.5 ingot. The whole process can be completed within only 10 min and no post-annealing process is needed. This fast formation of the La(Fe, Si, Co)13 phases is possibly induced by the directional atomic diffusion, accelerated atomic diffusion, and the stability of the La(Fe, Si, Co)13 phase and structural relaxation caused by the sufficiently restored elastic energy during the hot compression. The LaFe10.6Co0.9Si1.5 ingot hot compressed at 1273 K with a reduction ratio 70 % at a strain rate 0.005/s exhibits a second-order phase transition and negligible magnetic hysteresis. A large magnetic entropy change of 4.4 J/kg.K and a wide working temperature range of 57 K under 2 T are acquired near room temperature. This study proposes a new efficient hot compression route for processing the La–Fe–Co–Si alloy and enhancing the magnetocaloric effect.

High-resolution dynamic thermal programming platform based on micro thermoelectric device assisted by laser integrated manufacturing

Thermoelectric devices (TEDs) exhibit much application potential in thermal camouflage and encrypted display recently, requiring that TEDs possess large responsivity, high resolution and rapid response with flexible configuration design, which are hardly realized by the traditional complex fabrication process. In this work, an innovative laser integrated manufacturing technology including double-side-printing selective laser melting (D-SLM) and selective laser ablation (SLA) is developed for the construction of the dynamic thermal platform based on micro TEDs. Through experimentally determining the laser process window assisted by external temperature field regulation, a flat p-type film can be directly transformed from n-type Bi2Te3 film by D-SLM. Thus, high-precision p-n patterns without metal joints are obtained from a single locally modified film, whose thermoelectric properties are further boosted by increasing energy density and introducing a post-annealing process. Then, a dynamic thermal platform with designable shapes and small dimensions can be fabricated rapidly whose working principle is also demonstrated. The thermal platform with 4*4 arrays exhibits imaging function with a pixel size of 2 mm×2 mm, a temperature difference of ∼3 K, and a fast response time of 0.143 s. This work offers an exciting yet effective approach to fabricating TEDs for dynamic thermal programmable information displays.

Effective Charge Collection of Electron Transport Layers for High-Performance Quantum Dot Infrared Solar Cells.

Infrared (IR) solar cells, capable of converting low-energy IR photons to electron-hole pairs, are promising optoelectronic devices by broadening the utilization range of the solar spectrum to the short-wavelength IR region. The emerging PbS colloidal quantum dot (QD) IR solar cells attract much attention due to their tunable band gaps in the IR region, potential multiple exciton generation, and facile solution processing. In PbS QD solar cells, ZnO is commonly utilized as an electron transport layer (ETL) to establish a depleted heterostructure with a QD photoactive layer. However, band gap shrinkage of large PbS QDs makes it necessary to tailor the behaviors of the ZnO ETL for efficient carrier extraction in the devices. Herein, the characteristics of ZnO ETL are efficiently and flexibly tailored to match the QD layer by handily adjusting the postannealing process of ZnO ETL. With a suitable temperature, the well-matched energy level alignment and suppressed trap states are simultaneously achieved in the ZnO ETL, effectively reducing the nonradiative recombination and accelerating the electron injection from the QD layer to ETL. As a consequence, a high-performance PbS QD photovoltaic device with power conversion efficiencies (PCEs) of 10.09% and 1.37% is obtained under AM 1.5 and 1100 nm filtered solar illumination, demonstrating a simple and effective approach for achieving high-performance IR photoelectric devices.

The fabrication of ultra-wide bandgap GeO2 thin films by DC magnetron sputtering: The impacts of growth temperature and post-annealing process

Ultra-wide bandgap semiconductors (UWBSs), possessing the bandgap greater than 4 eV, have emerged as an advanced platform for optoelectronic device applications. The exploration of novel UWBSs becomes compelling research focus on the solar blind photodetectors (SBPDs). Here, we have deposited ultra-wide bandgap GeO2 films on c-plane sapphire substrates using direct-current (DC) magnetron sputtering method and investigated the effects of the growth and annealing temperatures on surface morphologies, crystal structure, oxygen vacancies, and bandgap energies of GeO2 films. The high quality GeO2 film with the hexagonal phase can be obtained at the growth temperature of 500 °C, which transforms to the mixture of hexagonal and tetragonal phases after annealing at 900 °C. By analyzing the energy loss spectra of O 1s peaks, GeO2 films exhibit the ultra-wide bandgap ranging from 5.78 to 5.90 eV, which is verified by optical transmittance measurements. Moreover, 200 nm SBPDs based on GeO2 films have been fabricated and an obvious improvement in the photoresponse current of the annealed device has been found due to the induced additional electrons by the hole capture of oxygen vacancies. Our findings on the development of ultra-wide bandgap GeO2 films pave a way towards the realization of robust and high-performance SBPDs.