High-temperature Annealing Research Articles

Effects of high-temperature annealing on vacancy complexes and luminescence properties in multilayer periodic structures with elastically strained GeSiSn layers

Effects of postgrowth high-temperature annealing on vacancy complexes and photoluminescence (PL) from GeSiSn/Si multiple quantum wells (MQWs) are studied. The series of PL peaks related to the vacancy-tin complexes was observed for as-grown samples including different structures, such as GeSiSn/Si MQWs, multilayer periodic structure with GeSiSn quantum dots (QDs), GeSn cross-structures upon GeSiSn/Si MQWs, and thick GeSiSn layers. The PL band intensity is significantly reduced after annealing at 700 °C corresponding to the reduction in vacancy density, as demonstrated by the positron annihilation spectroscopy (PAS) data. Such annealing also results in the appearance of the PL signal related to the interband optical transitions in GeSiSn/Si MQWs. However, the high temperature could negatively impact the sharpness of heterointerfaces due to Sn diffusion, thus limiting the PL efficiency. To improve the luminescence properties of GeSiSn/Si structures, we proposed a two-stage technique combining both the annealing and subsequent treatment of samples in a hydrogen plasma at 200 °C. The plasma treatment significantly reduces the PL band of vacancy-related defects, whereas annealing at a moderate temperature of ∼600 °C prevents the blurring of heterointerfaces. As a result, we demonstrate an increase in the relative efficiency of interband PL of type II GeSiSn/Si MQW structures emitting in the range of 1.5–2 μm.

Thermal annealing effect on phase evolution, physical properties of DC sputtered copper oxide thin films and transport behavior of ITO/CuO/Al Schottky diodes

Herein, we report on the post-annealing temperature effect on the transport behavior of p-CuO/Al Schottky barrier diodes. In addition, the transformation of phase from Cu4O3 to CuO phase was studied. Copper oxide thin films were grown on soda lime glass substrates, and post-annealing temperature's influence on the films’ structural, chemical, morphological, and electrical characteristics was comprehensively examined. X-ray diffraction study revealed the development of polycrystalline tenorite phase (CuO) on annealing. Raman analysis also confirmed the formation of the tenorite phase (CuO) at higher annealing temperatures (400 °C and 500 °C). XPS study revealed the occurrence of the Cu4O3 phase for room temperature deposited sample and CuO phase at the higher annealing temperature. Using current–voltage analysis, the Chueng model, and the thermoelectric emission model, the Schottky behavior between the metal and semiconductor were investigated. The fabricated diode showed a rectification ratio of 103 at ± 2 V, with the barrier height ranging from 0.84 to 1.12 eV due to different annealing treatments. The attributes of the power law were employed to elucidate space charge-limited conduction and the process of tunneling across the density of interface traps in p-CuO/Al Schottky diodes. This study provides valuable insights into the behavior of the p-CuO/Al Schottky junction, enhancing our understanding of its characteristics.

Microstructural evolution of super duplex stainless steel during final annealing: The importance of the grain structure

Flat duplex stainless steel acquires its characteristic banded microstructure during its processing sequence, which ends with a final annealing step aimed at fine tuning the phase ratio to equal parts ferrite and austenite. Besides phase fraction, the grain structures, shapes and morphologies of both phases evolve too during this final step. In the present, it was shown that recrystallization is mostly complete at the end of heating and phase equilibration shortly after. As a consequence, chemical and elastic driving forces are rapidly depleted while the sizes and shapes of phases keep evolving, driven solely by capillarity. Using quantitative measurements that enable decorrelation of coarsening and globularization, it is shown therein that the grain structure of the material as well as the annealing temperature play a crucial role in the intensity of those two phenomena. A high grain boundary density enhances the kinetics of both. A higher annealing temperature, which leads to faster mass transport, favors the increase of the characteristic sizes of the microstructure over its morphological evolution.

The near surface damage and recovery of low nitrogen diamond implanted with MeV phosphorus ions

The purpose of this work is to provide a novel perspective for investigating the damage of diamond surfaces implanted by MeV phosphorus (P) ions and recovery of the surfaces after high-temperature annealing. SRIM simulation and low-temperature luminescence spectroscopy were performed to analyze the properties of the samples comprehensively. The results revealed that a certain degree of diamond lattice damage was caused without graphitization by the irradiation of 1 MeV P ions with a fluence value of 1015 ions/cm2. The SRIM simulation revealed that the ions that were implanted into the lattice collided with carbon atoms. These ions stopped at a depth of approximately 0.55 μm and generated intrinsic diamond defects on the diamond near the surface. The simulated defects were confirmed by the appearance of neutral single vacancy (GR1) centers in the photoluminescence (PL) spectrum after annealing at 400 °C. In addition, the annealing behavior of optical centers at 900 °C indicated significant damage recovery, including the disappearance of GR1 centers, combined with the increased intensity, slightly blue-shifted peak position, and narrowed FWHM of the nitrogen-vacancy (NV) center.

An end-capping strategy for shape memory phthalonitrile resins via annealing enables conductivity and wave-absorption

Shape memory polymers (SMPs) with elevated switching temperatures and enduring thermal properties are highly desirable yet challenging in certain aerospace applications. In this study, high-temperature shape memory phthalonitrile resins (SMPNs) were developed using an end-capping strategy with the uniphthalonitrile (UPN) as the end-capping reagent to modulate the density of the cross-linked network. The resultant SMPNs exhibit a glass transition temperature (Tg) at approximately 300 °C, with a shape fixation rate of about 98 % and a shape recovery rate around 97 %. Importantly, these SMPNs also demonstrated exceptional thermal stability, with a thermal decomposition temperature exceeding 445 °C. Additionally, an oxyacetylene ablative test revealed the SMPNs' robust ablative resistance, as the linear ablation rate remained below 0.1 mm/s and the mass ablation rate was less than 0.1 g/s. The commendable shape memory performance and superior high-temperature resistance allowed the SMPNs to successfully undergo the shape recovery process when subjected to a butane flame. Furthermore, after a high-temperature annealing process, the SMPNs exhibited electrical conductivity due to graphitization, even possessing wave-absorbing properties within a specific frequency range. It is foreseeable that these multifunctional SMPNs will have extensive applications in the aerospace sector, given the advancement of smart structures.

Origin of near-failure in Au contacts to polycrystalline β-Ga2O3 at high temperatures using interfacial studies

Suitable contacts to gallium oxide are a controversial topic with contact behavior depending heavily on the pre- and post-processing conditions. Especially for the extreme environment applications such as those involving high temperatures, contact chemistry is varied and severely lacks understanding. Herein, we report on conventional pure Au contacts to polycrystalline β-Ga2O3, used as Schottky contacts, and explore the origin of their near-failure at high temperature up to 850 °C. For this purpose, β-Ga2O3 with Au interdigitated electrodes is subjected to high temperature annealing and their interface chemistry is studied and correlated with device performance for solar-blind photodetection. Around the optimized temperature of 450 °C, the performance of the PDs is found to be maximum, whereas it reduces drastically at 850 °C. Physical damage to the electrodes along with the formation of intermetallic gold-gallium alloy is observed via XPS depth profile studies and found to be the reason for the near-failure of device at extreme conditions. Although the alloy formation begins to slightly appear at 650 °C and reduces the performance, still it does not lead to device breakdown. This study proves that unlike its counterparts GaN and GaAs, which have reported alloy formation at lower temperatures, β-Ga2O3 shows a higher resilience to the formation of Au–Ga alloy and can withstand higher temperatures before the actual device failure is reached. The proposed study shows the stability of standard metal contacts to Ga2O3 based devices, which have far-reaching implications for the future commercialization of wideband gap semiconductor based (opto)electronics.

Profiles of oxygen and titanium point defects in ferromagnetic TiO2 films

Experimentally it is shown that without any oxygen manipulation for TiO2, a strong room temperature ferromagnetism could be expected only in ultra-thin films, with the ideal thickness below 100 nm. Both bulks and nano-powders of TiO2 are diamagnetic, indicating that the surface and its nano-sublayers play very important roles in tailoring the magnetic properties in this type of compound. To shed a new light on the defect-related magnetism in the typical case of anatase TiO2 surfaces, we have performed a series of quantum-mechanical calculations for TiO2 slabs containing Ti or O vacancies in different distances from the (001) surface. The lowest formation energies were obtained for the Ti vacancies in the first sub-surface layer and the O vacancies within the surface. The computed magnetic states reflect complicated structural relaxations of atoms influenced by both the surface and vacant atomic positions. O atoms cannot contribute much to magnetic moment when Ti vacancies are isolated and far from the surface. Ti vacancies in TiO2 are only metastable. The formation energy of Ti interstitials is lower than for Ti vacancies since high-temperature annealing, especially with a lot of O2 available that would fill up O-related defects, and as a result, eliminate most of Ti vacancies. Lower temperatures, less O2, and shorter exposure times may enable not only partial elimination of Ti vacancies but also can facilitate their diffusion into different states of aggregations. In the ferromagnetic films (i.e. thin films below 100 nm), it looks like that the O atoms are located closer to the Ti vacancies.

Effect of Copper Surface Roughness on the High-Temperature Structural Stability of Single-Layer-Graphene.

Graphene (Gr) has shown great potential in the field of oxidation protection for metals. However, numerous studies have shown that Gr will suffer structural degradation on metal surface during high-temperature oxidation, which significantly limited the effectiveness of their oxidation protection. Therefore, understanding the degradation mechanism of Gr is of great interest to enhance their structural stability. Here, the effect of copper (Cu) surface roughness on the high-temperature structural stability of single-layer graphene (SLG) was examined using Cu covered with SLG as a model material. SLG/Cu with different roughness values was obtained via high-temperature annealing of the model material. After high-temperature oxidation at 500 °C, Raman spectra analysis showed that the defect density of the oxidized SLG increased from 41% to 81% when the surface roughness varied from 37 nm to 81 nm. Combined with density functional theory calculations, it was found that the lower formation energy of the C-O bond on rough Cu surfaces (0.19 eV) promoted the formation of defects in SLG. This study may provide guidance for improving the effectiveness of SLG for the oxidation protection of metallic materials.

Reduced graphene oxide assembled on the Si nanowire anode enabling low passivation and hydrogen evolution for long-life aqueous Si-air batteries

Silicon-air batteries (SABs), a new type of semiconductor air battery, have a high energy density. However, some side reactions in SABs cause Si anodes to be covered by a passivation layer to prevent continuous discharge, and the anode utilization rate is low. In this work, reduced graphene oxide (RGO) fabricated via high-temperature annealing or L-ascorbic acid (L.AA) reduction was first used to obtain Si nanowires/RGO-1000 (Si NWs/RGO-1000) and Si nanowires/RGO-L.AA (Si NWs/RGO-L.AA) composite anodes for SABs. It was found that RGO suppressed the passivation and self-corrosion reactions and that SABs using Si NWs/RGO-L.AA as the anode can discharge for more than 700 hours, breaking the previous performance of SABs, and that the specific capacity was increased by 90.8% compared to bare Si. This work provides a new solution for the design of high specific capacity SABs with nanostructures and anode protective layers.

Ferroelectric memory devices using hafnium aluminum oxides and remote plasma-treated electrodes for sustainable energy-efficient electronics

In this work, we adopt a low-temperature sustainable plasma treatment approach for the fabrication of ferroelectric memory devices. From our experimental results, we found that the ferroelectric polarization characteristics of HfAlOx ferroelectric device could be further improved by using low-temperature nitrogen plasma treatment on bottom TiN electrode for surface modification. The low-temperature nitrogen plasma treatment on TiN bottom electrode not only prevent electrode oxidation, but also lowers the generation of defect traps at the interface between ferroelectric HfAlOx and TiN bottom electrode during high-temperature ferroelectric annealing process. Besides, the nitrogen-treated bottom electrode also can improve bias-stress induced instability and cycling endurance of HfAlOx ferroelectric devices due to the effective suppression of randomly distributed defect traps or oxygen vacancies near the surface of bottom electrode.

Microstructure and EMW absorption properties of PDCs-SiCN(Ti) ceramics with adjustable SiC nanowires and TiC nanocrystallines

Herein, a novel type of ceramic material exhibiting tunable electromagnetic properties was synthesized using the polymer-derived ceramics (PDCs) method. The precursor employed in this process was a tetrabutyl titanate-modified polysilazane, which ultimately led to the formation of PDCs-SiCN(Ti) ceramics. High-temperature annealing (1400 °C-1500 °C) was used to prepare PDCs-SiCN(Ti) ceramics, which exhibited a unique dual nanostructure comprising SiC nanowires and TiC nanocrystals and served as effective nanoabsorbents. The SiC and TiC contents are closely related to the annealing temperature and induced Ti content. After annealing at 1500 °C, the PDCs-SiCN(Ti) ceramics with the typical A + B + C electromagnetic absorbing structure exhibited excellent electromagnetic wave (EMW) absorption properties. The PDCs-SiCN(Ti) ceramics, with a Ti content of 5 wt%, demonstrated an effective absorption bandwidth (EAB) of 3.8 GHz, which encompassed 90.5 % of the X band, despite having a relatively thin impedance matching thickness of only 2.1 mm. The outstanding EMW attenuation capability of the PDC-SiCN(Ti) ceramics can be ascribed to their large specific surface area and defects combined with the high permittivity of dispersed TiC nanocrystals, which facilitates multiple reflections of EMW within the SiCN matrix. Therefore, this work provides a controllable preparation method for PDCs-SiCN(Ti) ceramics with various microwave absorbing phases.

Optical thermosensor using Cr3+ doped NaGdF4: Yb, Er microcrystals

ABSTRACT In this work, NaGdF4: 20%Yb, 2%Er microcrystals with varying contents of Cr3+ doping were obtained by conventional hydrothermal process. The microcrystal phase structure, morphology, upconversion luminescence mechanism, as well as temperature sensing behaviour under different treatment methods were researched. Based on the thermally coupled 2H11/2 and 4S3/2 levels of Er3+ and the dependence of fluorescence intensity ratio (FIR) on temperature, the optical temperature sensing behaviour of micrometer crystals were experimentally demonstrated. The NaGdF4: 20%Yb, 2%Er, 7%Cr microcrystals treated with high-temperature annealing show the best temperature sensing behaviour within the temperature span of 298–498 K. NaGdF4: 20%Yb, 2%Er, 7%Cr microcrystals with high temperature annealing presented the feasibility and promising properties for optical temperature sensing. The endeavour of emerging materials could lay the groundwork for future sustainable photonics engineering industrial growth.

Ge-doped Sn-Pb assisted by MACl triple metal cation perovskite solar cells with high open-circuit voltage

The potential to achieve the best photovoltaic properties by incorporating Ge into Sn-Pb-based perovskites (PVKs) is theoretically plausible. However, practical implementation is hindered by critical obstacles associated with Ge-containing precursors, such as poor solubility and extremely low stability. Furthermore, the application of Ge in PVKs is limited, particularly when combined with Sn-Pb-based PVK, owing to the instability of Sn and Ge within the same precursor. Herein, we report a groundbreaking method for inserting Ge into Sn-Pb PVK using volatile additives, resulting in high-performance Sn-Pb-Ge triple metal cation PVK solar cells (PSCs). Adding methylammonium chloride facilitates the dissolution of germanium iodide (GeI2) through anion exchange in the precursor, which evaporates during high-temperature annealing after the formation of the PVK films. The resulting low-bandgap PVK (1.228 eV), containing 3 % Ge, exhibits increased grain sizes and a significantly improved open-circuit voltage of 0.834 V, which can be attributed to a reduced energetic offset. The Sn-Pb-Ge triple metal cation PSC exhibits a power conversion efficiency of 20.7 % and enhanced stability.

The phases formed in Sn/Co thin bilayer upon heating

The structure and phases formed in Sn/Co thin films are interesting both from the solid-state chemistry point of view and due to applications of such a metallic bilayer. The phases forming in thin films Sn/Co obtained by thermal vacuum evaporation on two different substrates SiO2 and MgO(100) at different annealing temperatures have been studied. Annealing above 110°С results in intermetallics formation in the films. The hcp-cobalt is grown in the films on SiO2 substrate, and the fcc-Co is observed on MgO(100) substrate. It is found that the stable α-Co3Sn2 intermetallic is formed at higher annealing temperature in film on MgO(100) substrate. We show that transformations related to mass transfer in the Sn/Co bilayers were up to 500°С and were finished upon reaching the thermodynamically equilibrium phase composition at this temperature.

Defect induced crystal lattice disorder and its effect on the electron-phonon coupling in Fe doped ZnO thin films

We established a strong correlation between the crystal lattice disorder in Fe doped ZnO (FexZn1-xO) thin films and its effect on the electron phonon (e-p) coupling strength (I2LO/I1LO) which decreased with Fe doping concentration, improved with annealing temperature and showed a mixed increasing/decreasing trend by the variation of the argon (Ar) to oxygen (O2) gas ratio (Ar + O2, Ar) in the deposition chamber. Fe doping raised the number of phonon modes, intensity and full width at half maximum (FWHM) of the 1LO phonon modes suggesting the confinement of phonons due to the increased crystal lattice disorder in the FexZn1-xO films. High temperature annealing enhanced the e-p coupling strength reaching a maximum at 500 °C indicating better crystal quality at high temperature. Furthermore, the e-p coupling strength dropped with the doping concentration for the films prepared in Ar + O2 atmosphere and that showed a mixed increasing/decreasing trend for films prepared in Ar atmosphere. This unique physical phenomena confirmed that the coupling strength not only depend on the dopant concentration but also the dopant induced micro/nano defects that modulate the crystal lattice disorder and the coupling strength in doped ZnO. The as prepared FexZn1-xO thin films were highly oriented along the c-axis displaying columnar nanorod (film) like morphology at low (high) Fe doping concentration with the co-existence of both Fe2+ and Fe3+ ions. Fe doping increased the band gap from 3.28 eV for un-doped ZnO to 3.35 eV (1.40 at.% of Fe) and 3.42 eV (3.5 at.% of Fe). Nearly forty (40) thin films were used for a detailed investigation.

Development of a molecular maker for sex identification in Thai commercial date palm (Phoenix dactylifera L.).

Date palm (Phoenix dactylifera L.) is a dioecious plant, with male and female plants having distinct characteristics. Female plants are responsible for fruit production, and only approximately 10% of male plants are necessary for effective pollination. The determination of plant sex occurs during the first flowering, a process that typically spans 3-7 years. However, this extended timeframe results in significant time and valuable plantation resources being expended in the maintenance of trees. To address this issue, the study focused on sex identification of date palms using DNA markers. The research aimed to develop sex-specific markers for certain date palm cultivars, employing the high annealing temperature random amplified polymorphic DNA (HAT-RAPD) technique for accurate and reliable sex identification. In this investigation, 45 RAPD primers underwent screening in both male and female date palm plants to pinpoint sex-specific markers. Out of the total primers tested, only one, OPW-18, exhibited a correlation with sex. OPW-18 produced a distinct band of approximately 400 bp, consistently present in all male plants but absent in all female plants. The male-specific fragment from OPW-18 was cloned and sequenced to facilitate the development of sex-specific sequence-characterized amplified region (SCAR) primers. The outcomes revealed that the newly crafted SCAR primer pair, mspW18-2F and mspW18-2R, successfully amplified a unique fragment of 283 bp exclusively in male plants. This capability allowed the identification of 100% of male plants in the KL1 and Barhi cultivars. These markers prove to be efficient, reliable, and reproducible for early-stage sex identification in plants.

Thermally stable radiative recombination centers within trench structures of red multi-quantum wells

High-Indium (In)-content multi-quantum wells (MQWs) are generally thermally unstable due to poor crystal quality resulting from low-temperature growth. In this study, red emission was achieved by modulating trench structures using dual-colour MQW structures. Impressively, the red MQWs inside deep trenches showed excellent thermal stability despite being grown at low temperatures. After high-temperature annealing at 950 °C for 30 min, the photoluminescence (PL) intensity of red MQWs exhibited a significant reduction of 91.9% outside trenches, while it dropped by only 9.3% inside trenches, as confirmed by confocal PL mapping. Transmission electron microscopy results show that massive In-rich phases and stacking faults appeared in the MQWs outside trenches after annealing. By contrast, the red MQWs inside deep trenches remained intact in lattice arrangement without being significantly damaged. The superior thermal stability of red MQWs inside deep trenches was mainly attributed to the low-defect-density epitaxy of InGaN layers in strain-relaxed states.

Disclosing the dependencies of ferroelectric and piezoelectric performances on crystalline states of P(VDF‐TrFE) films by molecular dynamics simulations

AbstractWe present a molecular dynamics simulation method including x‐ray diffractometer pattern calculation, mean square displacement (MSD), and nonbonding energy distribution (NED) to disclose the dependencies of condensed structure on its crystalline process of the poly(vinylidene fluoride‐trifluoroethylene) (P(VDF‐TrFE)) films. For comparison, the P(VDF‐TrFE) solution is casted into the films, and followed that different thermal processes are performed to fabricate the crystalline states of the films. Simulation and experimental results have good consistency, indicating that high temperature annealing can effectively promote all‐trans β phase in the crystal region of P(VDF‐TrFE). As such, P(VDF‐TrFE) 80/20 mol% annealing at 140°C shows a higher MSD (~27.5 Å2) and a faster reducing rate of NED than that of other films, contributing to a large maximum polarization (Ps) of ~15.5 μC cm−2, high a remnant polarization (Pr) of ~11.8 μC cm−2, and an attractive piezoelectric strain coefficient (d33) of −27.1 pC N−1 under 200 MV m−1, respectively, and providing a reference for the applications of P(VDF‐TrFE) in flexible sensors, actuators, transducers, and so forth.

Ultrafast laser-annealing of hydrogenated amorphous silicon in tunnel oxide passivated contacts for high-efficiency n-type silicon solar cells

The tunnel oxide passivated contact (TOPCon) concept has been the brightest star in the field of emerging passivating contact techniques for the last few years. It has shown great potential in industrial applications due to the overwhelming advantages of high device efficiency and low cost. Here, we introduce a novel crystallization method using ultrafast laser-annealing by scanning a laser spot onto the surface of hydrogenated amorphous silicon film in TOPCon solar cells. By circumventing the high-temperature environment of the conventional annealing process, it can prevent a large number of dopant atoms from penetrating inside the crystalline silicon (c-Si) substrate, reducing the Auger recombination. Moreover, we can conduct extensive experiments to clarify the optimal conditions, including laser-annealing modes and process parameters. The hydrogenation experiments reveal that direct appropriation of the traditional hydrogenation method is not applicable. An additional ‘dehydrogenation’ step proves necessary, indicating that the differences in hydrogen content within the films due to the divergence between the principles of laser-annealing and high-temperature annealing are probably responsible for this. Consequently, the proof-of-concept devices using laser-annealing technology realize a champion efficiency of 19.91%,highlighting an alternative technical route with substantial potential to achieve high-efficiency crystalline silicon solar cells.

In Situ Growth of Wafer-Scale Patterned Graphene and Fabrication of Optoelectronic Artificial Synaptic Device Array Based on Graphene/n-AlGaN Heterojunction for Visual Learning.

The unique optical and electrical properties of graphene-based heterojunctions make them significant for artificial synaptic devices, promoting the advancement of biomimetic vision systems. However, mass production and integration of device arrays are necessary for visual imaging, which is still challenging due to the difficulty in direct growth of wafer-scale graphene patterns. Here, a novel strategy is proposed using photosensitive polymer as a solid carbon source for in situ growth of patterned graphene on diverse substrates. The growth mechanism during high-temperature annealing is elucidated, leading to wafer-scale graphene patterns with exceptional uniformity, ideal crystalline quality, and precise control over layer number by eliminating the release of volatile from oxygen-containing resin. The growth strategy enables the fabrication of two-inch optoelectronic artificial synaptic device array based on graphene/n-AlGaN heterojunction, which emulates key functionalities of biological synapses, including short-term plasticity, long-term plasticity, and spike-rate-dependent plasticity. Moreover, the mimicry of visual learning in the human brain is attributed to the regulation of excitatory and inhibitory post-synapse currents, following a learning rule that prioritizes initial recognition before memory formation. The duration of long-term memory reaches 10min. The in situ growth strategy for patterned graphene represents the novelty for fabricating fundamental hardware of an artificial neuromorphic system.