Low-temperature Technique Research Articles

Interband electronic transitions and optical phonon modes in size-dependent multiferroic BiFeO3 nanoparticles.

Bismuth ferrite (BiFeO3) multiferroic nanoparticles are synthesized using a low-temperature sol-gel auto-combustion technique. The phase purity is confirmed from X-ray diffraction (XRD) measurements and microstructural, electronic, and optical studies are correlated with the particle size of the bismuth ferrite nanostructured material. We demonstrated bandgap tunability from 2.22 to 1.93 eV with an average crystallite size from 42 to 24.42 nm following the inverse quantum confinement effect dominated by the lattice strain. The degenerate d-d electronic transitions 6A1g → 4T1g and 6A1g → 4T2g from iron dominate in these nanoparticles. The decrease in the energy band gap and the corresponding red shift in the d-d charge transfer transition energies with reduced average crystallite size are attributed to the increased lattice strain and reduced unit cell volume.

Low-temperature open-atmosphere growth of WO3 thin films with tunable and high-performance photoresponse

In-situ orientation tuning of WO3 thin films with high crystallinity is achieved with a low-temperature and open-atmosphere deposition technique. The fabricated devices showed a significant change in photo-response for film orientation.

Low temperature recovery of OFF-state stress induced degradation of AlGaN/GaN high electron mobility transistors

Thermal annealing is a widely used strategy to enhance semiconductor device performance. However, the process is complex for multi-material multi-layered semiconductor devices, where thermoelastic stresses from lattice constant and thermal expansion coefficient mismatch may create more defects than those annealed. We propose an alternate low temperature annealing technique, which utilizes the electron wind force (EWF) induced by small duty cycle high density pulsed current. To demonstrate its effectiveness, we intentionally degrade AlGaN/GaN high electron mobility transistors (HEMTs) with accelerated OFF-state stressing to increase ON-resistance ∼182.08% and reduce drain saturation current ∼85.82% of pristine condition at a gate voltage of 0 V. We then performed the EWF annealing to recover the corresponding values back to ∼122.21% and ∼93.10%, respectively. The peak transconductance, degraded to ∼76.58% of pristine at the drain voltage of 3 V, was also recovered back to ∼92.38%. This recovery of previously degraded transport properties is attributed to approximately 80% recovery of carrier mobility, which occurs during EWF annealing. We performed synchrotron differential aperture x-ray microscopy measurements to correlate these annealing effects with the lattice structural changes. We found a reduction of lattice plane spacing of (001) planes and stress within the GaN layer under the gate region after EWF annealing, suggesting a corresponding decrease in defect density. Application of this low-temperature annealing technique for in-operando recovery of degraded electronic devices is discussed.

High-pressure low-temperature densification of NASICON-based LATP electrolytes for solid-state lithium batteries

Ceramic oxides are promising solid electrolytes for Lithium metal solid-state batteries (SSBs) because of their high ionic conductivity and stability under ambient conditions. Nonetheless, the need for high-temperature densification approaches challenges their processability towards upscaling and their implementation into practical SSB devices. Here, we investigate a High-Pressure Low-Temperature (HPLT) processing technique for the densification of NASICON-based Li1+xAlxTi2-x(PO4)3 (LATP) solid electrolyte, providing an understanding of several key parameters such as temperature, pressure and time. Our results show that nanometric LATP can be densified using the HPLT technique at 200°C within 2 min delivering an ionic conductivity of 6.15×10−5 Scm−1, which is the highest reported value at this temperature without the addition of solvents. On the other hand, by combining HPLT with a short post-heat treatment at 700 or 800 °C for 1 hour, highly dense pellets with an ionic conductivity of 10−4 Scm−1 can be obtained. This represents a reduction of the densification temperature of 400°C compared to conventional high-temperature sintering and shows the potential of HPLT to overcome current densification constraints derived from the use of very high temperatures.

Pressure modified upconversion luminescence of Yb3+ and Er3+-doped Bi3TeBO9 ceramics

Yb3+ and Er3+-doped Bi3TeBO9 ceramics exhibit efficient upconversion luminescence in the visible spectral range upon laser diode excitation at 975 nm. Bi3TeBO9:Yb3+/Er3+ powder was prepared by means of the modified Pechini method. A series of Bi3TeBO9:Yb3+/Er3+ ceramic samples was fabricated using the high-pressure low-temperature technique, by sintering Bi3TeBO9:Yb3+/Er3+ powder under different pressures (2, 4, 6 or 8 GPa). The structure and morphology of the above-mentioned samples were analyzed using XRD, SEM and EDX measurements. The phonon energy of Bi3TeBO9 matrix associated with the vibrations of TeO6 and BO3 molecular groups was revealed using μ-Raman spectroscopy. The low phonon energy of Bi3TeBO9 matrix allows the effective energy transfer between Yb3+ and Er3+ ions as well as the 2H11/2 → 4I15/2, 4S3/2 → 4I15/2 and 4F9/2 → 4I15/2 transitions from the excited to ground states of Er3+ ions, resulting in efficient upconversion emission at 523, 540 and 653 nm, respectively. The decay times determined for all analyzed emissions were longer for Bi3TeBO9:Yb3+/Er3+ ceramics than for the powder sample. The highest values of decay times were detected for the ceramics obtained under a pressure of 8 GPa and were equal to 174, 172 and 175 μs for the emissions at 523, 540 and 653 nm, respectively. The obtained results suggest that Bi3TeBO9:Yb3+/Er3+ ceramics can be proposed as efficient spectral converters in the new type solar cells enhancing the efficiency of the photovoltaic effect.

Microwave dielectric ceramics with low dielectric loss and high temperature stability for LTCC applications

Preliminary tri-layer architecture ZnNb1.8V0.1O5.75-TiO2+CuO–ZnNb1.8V0.1O5.75 ceramics with high-temperature stability and low dielectric loss have been prepared. In the past, the stacked co-firing process could only be used at normal sintering temperatures. In this paper, the effect of the transition layer in ZnNb1.8V0.1O5.75-TiO2+CuO–ZnNb1.8V0.1O5.75 ceramics with tri-layer architecture sintered at low temperatures (950 °C) on the crystalline structure, microscopic structure, and integrated microwave dielectric performance of specimens has been investigated in depth for the first time. This low-temperature stacked-layer co-firing technique can effectively enable the chemical reaction between ZnNb1.8V0.1O5.75 and TiO2+CuO to take place in a rather narrow region (about 20 μm), i.e., the interface of the heterogeneous layers. In this interface, diffusion of Zn, Nb, V, Ti, and Cu can be observed. This heterogeneous interface can act as an in-situ “glue” that holds the layers together well. The effect of TiO2+CuO content on the microwave dielectric performances of laminated architectural specimens under low-temperature sintering was systematically investigated. Among the existing layer architectures, the stack of ZnNb1.8V0.1O5.75-TiO2+CuO–ZnNb1.8V0.1O5.75 with 0.03 wt% TiO2+CuO exhibits the most excellent microwave dielectric performances. τf can be efficiently tuned close to zero (−7.14 ppm/°C), and remarkably, a low dielectric loss (14,587 GHz) and a high value of εr (24.00) are also achieved. This low-temperature sintered tri-layered architecture is designed to help open new avenues for the development of high-performance microwave dielectrics based on existing material systems, providing effective strategies and methods for 5G applications and multilayer packaging technologies.

Low-Temperature Vapor-Phase Growth of 2D Metal Chalcogenides.

2D metal chalcogenides (MCs) have garnered significant attention from both scientific and industrial communities due to their potential in developing next-generation functional devices. Vapor-phase deposition methods have proven highly effective in fabricating high-quality 2D MCs. Nevertheless, the conventionally high thermal budgets required for synthesizing 2D MCs pose limitations, particularly in the integration of multiple components and in specialized applications (such as flexible electronics). To overcome these challenges, it is desirable to reduce the thermal energy requirements, thus facilitating the growth of various 2D MCs at lower temperatures. Numerous endeavors have been undertaken to develop low-temperature vapor-phase growth techniques for 2D MCs, and this review aims to provide an overview of the latest advances in low-temperature vapor-phase growth of 2D MCs. Initially, the review highlights the latest progress in achieving high-quality 2D MCs through various low-temperature vapor-phase techniques, including chemical vapor deposition (CVD), metal-organic CVD, plasma-enhanced CVD, atomic layer deposition (ALD), etc. The strengths and current limitations of these methods are also evaluated. Subsequently, the review consolidates the diverse applications of 2D MCs grown at low temperatures, covering fields such as electronics, optoelectronics, flexible devices, and catalysis. Finally, current challenges and future research directions are briefly discussed, considering the most recent progress in the field.

Bi2O3 doped indium tin oxide thin films fabricated via liquid metal printing

Indium tin oxide (ITO) is a classical transparent conducting oxide (TCO), which is widely used in semiconductor industry. Reducing the cost of preparing ITO films and further improving its optoelectronic properties are urgent technological challenges to be solved. Here, we proposed to tackle this issue through doping elements in ITO films via liquid metals printing process. Conceptual experiments demonstrate the synthesis of Bi2O3 doped ITO at the centimeter scale using low-temperature fabrication techniques, which display the advantages of high uniformity, strong visible light transmission and low resistivity. The band gap decreases from 3.88 eV to 3.07 eV with increasing doping of Bi2O3 and demonstrates n-type semiconductor nature. The Schottky diodes based on doped ITO films show typical Ohmic contact. The best output current of doped ITO Schottky diodes can reach 1261.7 μA at 10 V, which is about 41 times the output current of the undoped ITO Schottky diodes. Additionally, the nanofilm resistance decreased linearly with increasing Bi mass fraction in ITO film. Moreover, Schottky diodes have good stability in the atmosphere within half a year and multilayer printing can enhance output current. The process as established here offers significant opportunities for future synthesis and fabrication processes in the electronics industries.

Plasma modification of graphene nanoplatelets surfaces

Atmospheric plasma processing, which combines the efficacy of chemical processes and the safety of physical processes, has been used to modify the surface characteristics of graphite-based materials. In this work, two distinct plasma source gases, C4F8 and O2, with the addition of a rotary reactor were used. The effectiveness of modifying the basal plane of intercalated graphite nanoplatelets (GnP) was investigated with various analytical techniques and the visual observation of the dispersion of these plasma-treated GnP in solvents was also reported. It is shown that this low-temperature plasma processing technique can be used to successfully modify the GnP surface without significantly changing the intrinsic structure of the GnP, which is desirable in many applications. With the C4F8 plasma treatment, the immersion characteristics in solvents can be tuned and the functional groups present on the surface can be tailored to produce desired bonding environments. This surface chemistry tunability will provide the needed functionalities in creating graphene-containing composite materials.

An Investigation into the Relative Efficacy of High-Velocity Air-Fuel-Sprayed Hydroxyapatite Implants Based on the Crystallinity Index, Residual Stress, Wear, and In-Flight Powder Particle Behavior.

Due to its resemblance to the bone, hydroxyapatite (HA) has been widely used for bioactive surface modification of orthopedic implants. However, it undergoes significant thermal decomposition and phase transformations at a high operating temperature, leading to premature implant failure. This investigation uses high-velocity air-fuel (HVAF) spray, an emerging low-temperature thermal spray technique, to deposit HA over the Ti-6Al-4V substrate. Coating characteristics, such as the crystallinity index and phase analysis, were measured using X-ray diffraction, Raman analysis, and Fourier transform infrared spectroscopy, residual stress using the sin2ψ method, and tribological performance by a fretting wear test. The coating retained an over 90% crystallinity index, a crystallite size of 41.04 nm, a compressive residual stress of -229 ± 34.5 MPa, and a wear rate of 1.532 × 10-3 mm3 N-1 m-1. Computational in-flight particle traits of HA particles (5 to 60 μm) were analyzed using computational fluid dynamics; it showed that 90% of particles were deposited at a 700 to 1000 m/s velocity and a 900 to 1450 K temperature with a 2.1 ms mean residence time. In-flight particle oxidation was minimized, and particle impact deformation was maximized, which caused severe plastic deformation, forming crystalline, compressive residual stressed coatings. The thermal decomposition model of low-temperature HVAF-sprayed HA particles helped to understand the implants' crystallinity index, residual stress, and tribological characteristics. Hence, this experimental and computational analysis shows that the HVAF process can be a promising candidate for biomedical applications for having strong and durable implants.

Enhancing sodium-ion battery performance through crystalline water-assisted Zn2V2O7 anode material

To make sodium-ion batteries (SIBs) commercially viable, progress in advanced electrode materials has been witnessed to overcome unsatisfactory performance, including low charging/discharging efficiency and short lifespan. Recently, Zn2V2O7 (ZVO) has emerged as a bright anode arising from the distinctive crystal structure and electrochemical properties. Here, the novel approach is utilized to produce ZVO nanoparticles via a combination of wet chemistry and low-temperature solid-phase techniques. More explicitly, the specific discharge capacities of the ZVO-350 anode remain 141.6 mAh g−1 over 100 cycles at 50 mA g−1, demonstrating outstanding cycle stability. Significantly, in-situ X-ray diffraction (XRD) analysis is performed to reveal the operational mechanism and phase transitions of ZVO. Furthermore, the kinetic analysis of ZVO anode is unveiled through pseudo-capacitance calculation and GITT tests. Finally, variable temperature Raman spectroscopy is employed in-situ to test the changes of ZVO with increasing temperature aiming to assess the effect of cooling rate on the ZVO. This work establishes a suitable ZVO anode for SIBs and highlights the formidable energy storage potential in a competitive landscape.

Valence Band Dispersion in Bi-Doped (Ga,Mn)As Epitaxial Layers

The impact of incorporating Bi into (Ga,Mn)As layers on their electronic, band structure, magnetic, and structural properties has been studied. The low-temperature molecular beam epitaxy technique was employed to grow homogeneous (Ga,Mn)(Bi,As) layers with high structural perfection. Post-growth annealing treatment resulted in improved structural and magnetic properties, as well as an increase in the hole concentration in the layers. Modulation photoreflectance spectroscopy confirmed modifications to the valence and split-off band in the (Ga,Mn)(Bi,As) layers. The experimental results are consistent with the valence band model of hole-mediated ferromagnetism in the layers. The (Ga,Mn)(Bi,As) compound combines the properties of (Ga,Mn)As and Ga(Bi,As) ternary compounds, offering the possibility of tailoring the bandgap structure to the requirements of novel device functionalities for future spintronic and photonic applications.

Optimisation of the drying temperature of star anise by low-temperature drying technique combined with microwave

The purpose of this study is to optimise the drying temperature of star anise fruit using the low-temperature drying technique combined with microwaves on a heat pump combined with microwave drying system so that the drying time is shortest and the essential oil is highest. The raw materials used for the research are fresh anise harvested in Van Quan district, Lang Son province in August 2021. Experimentally, the effects of drying temperatures at the levels: 30, 35, 40, 45, 50 and 55oC have been determined on drying time and essential oil content in dried anise fruit (moisture content of anise fruit after drying ≤10%). Research results have determined that the optimal temperature for drying anise fruits using the low-temperature drying technique combined with microwaves is 48.7±1oC, drying time is 530±5 minutes, and the essential oil content in dried star anise fruits reaches 9.9 ml/100 g. These experimental research results have provided a scientific basis for the essential oil content of Lang Son star anise fruit, and technical parameters for drying star anise fruit using low-temperature drying techniques combined with microwaves, helping the production and processing of anise on an industrial scale, increasing the value of goods and serving export purposes.

Room-Temperature Molding of Complex-Shaped Transparent Fused Silica Lenses.

The high hardness, brittleness, and thermal resistance impose significant challenges in the scalable manufacturing of fused silica lenses, which are widely used in numerous applications. Taking advantage of the nanocomposites by stirring silica nanopowders with photocurable resins, the newly emerged low-temperature pre-shaping technique provides a paradigm shift in fabricating transparent fused silica components. However, preparing the silica slurry and carefully evaporating the organics may significantly increase the process complexity and decrease the manufacturing efficiency for the nanocomposite-based technique. By directly pressing pure silica nanopowders against the complex-shaped metal molds in minutes, this work reports an entirely different room-temperature molding method capable of mass replication of complex-shaped silica lenses without organic additives. After sintering the replicated lenses, fully transparent fused silica lenses with spherical, arrayed, and freeform patterns are generated with nanometric surface roughness and well-reserved mold shapes, demonstrating a scalable and cost-effective route surpassing the current techniques for the manufacturing of high-quality fused silica lenses.

Effect of TiO2 on Pd/La2O3-CeO2-Al2O3 Systems during Catalytic Oxidation of Methane in the Presence of H2O and SO2.

New results on the effect of TiO2 on Pd/La2O3-CeO2-Al2O3 systems for catalytic oxidation of methane in the presence of H2O and SO2 have been received. Low-temperature N2-adsorption, XRD, SEM, HRTEM, XPS, EPR and FTIR techniques were used to characterize the catalyst. The presence of Ce3+ on the catalytic surface and in the volume near the lantana was revealed by EPR and XPS. After aging, the following changes are observed: (i) agglomeration of the Pd-clusters (from 8 nm to 12 nm); (ii) transformation of part of the TiO2 from anatase to larger particles of rutile; and (iii)-the increase in PdO/Pd-ratio above its optimum. The modification by Ti of the La2O3-CeO2-Al2O3 system leads to higher resistance towards the presence of SO2 most likely due to the prevailing formation of unstable surface sulfites instead of thermally stable sulfates. Based on kinetic model calculations, the reaction pathway over the Pd/La2O3-CeO2-TiO2-Al2O3 catalyst follows the Mars-van Krevelen mechanism. For evaluation of the possible practical application of the obtained material, a sample of Pd/La2O3-CeO2-TiO2-Al2O3, supported on rolled aluminum-containing stainless steel (Aluchrom VDM®), was prepared and tested. Methane oxidation in an industrial-scale monolithic reactor was simulated using a two-dimensional heterogeneous reactor model.

Effects of coating growth mode on the oxidation behavior of a hybrid Pt/Ru-modified aluminide coating at 1200 ℃

The outward-grown hybrid Pt/Ru-modified aluminide coating (OG coating) and inward-grown hybrid Pt/Ru-modified aluminide coating (IG coating) are obtained by high-temperature low-activity aluminizing and low-temperature high-activity aluminizing techniques respectively. The OG coating and IG coating are oxidized cyclically at 1200 ℃ for 100 h. The OG coating displays better oxidation resistance than the IG coating. This superior performance can be attributed to the higher Ru content at the coating/superalloy interface and lower refractory elemental contents in the OG coating, which effectively decreases the rumpling degree and prevent severe failure on the alumina scale during cyclic oxidation.

Nanopore Structure and Multifractal Characteristics of Continental Shale Oil Reservoir: A Case Study from Ziliujing Shales in the Sichuan Basin

Thermal maturity of the shales from the Ziliujing Formation of the Jurassic age in the Sichuan Basin is in the hydrocarbon generation window, which makes it a candidate for shale oil and gas development. The meso- and macropore characteristics and heterogeneity of shales are important factors affecting the occurrence and development of oil and gas. However, the meso- and macropores of the Ziliujing shales have not been systematically studied. Thus, the mineral compositions and total organic carbon (TOC) of samples from this formation, as well as its pore structure, are analyzed by low-temperature N2 adsorption technique. Moreover, the heterogeneity of the pores was determined by multifractal analysis. The results show that the Ziliujing shales can be classified into three types according to the distributions of mineral compositions of carbonate and mixed and argillaceous shales. Results revealed that the smallest meso- and macropore volume (PV), the smallest specific surface area (SSA), and the largest average pore diameter (APD) occur in the carbonate shales. However, the largest PV and SSA and the smallest APD are observed in the argillaceous shales. The porosity of carbonate shales is mainly concentrated between 5 nm and 30 nm. Compared with carbonate shales, the porosity with pore sizes less than 30 nm of mixed and argillaceous shales shows a rapid increase. Furthermore, inorganic minerals are the main factors affecting the pore distributions, while TOC shows a weak effect. Herein, clay minerals significantly increase the mesopore volume and the pore number with a size of less than 30 nm. The Dq-q curves reveal that the meso- and macropore distributions of Ziliujing shales show multifractal behavior, but the multifractal characteristics of pores of various shales are distinctly different. The information dimension D1, the Hurst exponent H, and the width of the right side D0–D10 are key indicators to distinguish the local variations within the pore structure of different types of shales. The carbonate shales have the largest multifractal spectra width and the smallest D1 and H, while the opposite trend is found for the argillaceous shales. Clay minerals reduce the heterogeneity of the meso- and macropore distributions and increase the pore connectivity. Nevertheless, the carbonate minerals exhibit a reverse trend. Finally, it was found that TOC does not impact pore complexity as much. Collectively, this study supports our understanding of the occurrence of shale oil within various reservoir facies, thereby providing a guideline for future explorations in the Ziliujing Formation of the Jurassic age in the Sichuan Basin.

Nanoarchitectonics on residual carbon from gasification fine slag upon two step low temperature activation for application in supercapacitors

In this paper, the carbon electrode materials were prepared by the KOH-HNO3 low-temperature activation technique using cheap residual carbon from gasification fine slag (CK) as raw materials. The results showed that the prepared material (CKN-2) which obtained by dry-wet sequential activation at 500°C for 1.5h at carbon to KOH ratio of 1:2 and further at 80°C for 1h in 2 mol/L HNO3 solution. The specific capacitance of CKN-2 reached 142 F/g at a current density of 0.5 A/g. CKN-2 was used to assemble a symmetrical (CKN-2//CKN-2) supercapacitor, which exhibited an energy density of 6.80 Wh/kg at a power density of 244.8 W/kg. The CKN-2//CKN-2 capacitor was tested for stability after 10,000 cycles, with a capacitance retention rate of 97%. These results demonstrate that residual carbon from gasification fine slag can be effectively used to produce high-performance carbon electrode materials for supercapacitors using the KOH-HNO3 low-temperature sequential co-activation technique.

Performance improvement of poly(lactic acid) films for bioelectronics with eco-friendly supercritical fluids combined with activated-carbon technique

The rise of bioelectronics has sparked significant interest in exploring biocompatible and environmentally friendly materials including Poly(lactic acid) (PLA), which is the only biologically derived material capable of large-scale production. However, its suitability as an electronic material is limited due to inadequate electrical, optical, and mechanical properties arising from inherent impurities. In this study, lower molecular weight PLA was dissolved in chloroform and spin-coated into ultra-thin (1.689 μm) films as dielectric layer in capacitor devices. We explored the low-temperature supercritical fluid-activated carbon adsorption technique (LTSCF-AC) to remove residual solvent molecules from PLA film and thus improve its comprehensive properties. The leakage current decreased by about 70 times, and the capacitance values decreased and become more stable at different frequencies. The extremely thin PLA film exhibits excellent optical and mechanical properties. In particular, following LTSCF-AC treatment, optical transmittance and refractive index of PLA films improved significantly. Additionally, the Young's modulus increased by 61.5% while tensile strength and elongation at break doubled compared to their initial values. These simultaneous enhancements of insulation, transparency, deformation resistance, and tensile strength highlight the huge potential of low-temperature and eco-friendly LTSCF-AC in improving the performance of PLA. These advancements not only broaden the application of PLA in bioelectronics but also providing new avenues for improving bioelectronic devices.

Thermo-economic evaluations of novel dual-heater regenerative organic flash cycle (DROFC)

Organic Flash Cycle (OFC) is a promising waste heat utilization technique for low and medium temperature. However, throttling exergy loss in the flash and throttling processes substantially reduces the efficiency of basic organic flash cycle (BOFC). The regenerative organic flash cycle (ROFC) can avoid the exergy loss in the throttling process and enhance the thermodynamic performance of OFC. This paper proposes a novel dual-heater regenerative organic flash cycle (DROFC), which can obtain more power output by reducing the flash process exergy loss and eliminating the mixer exergy loss in ROFC. The thermo-economic performance of DROFC was compared with BOFC and ROFC to evaluate its application potential. Eight low-GWP pure organic fluids were selected and the heat sources were 100–200 °C. Results indicate that DROFC could produce more net power output than BOFC and ROFC with a lower specific investment cost. Specifically, with R600 as an example, the maximum net power output percentage gain of DROFC is 41.19% and 29.09%, respectively. DROFC is more suitable for application scenarios where the heat source temperature exceeds the critical temperature of organic fluid. To balance the net power output and levelized cost of electricity, Hydrocarbons with a high critical temperature are appropriate for DROFC.