Room-temperature Applications Research Articles

Comprehensive investigation into the influence of oxygen vacancies on the ferroelectric properties of spin coated bismuth ferrite thin films

Abstract Bismuth ferrite (BFO) is a prime candidate for room-temperature magnetoelectric coupling and multiferroic applications. The rhombohedral R3c phase of BFO is the source of many properties, but the phase purity and oxygen vacancies are still the biggest obstacles to its real-world application. Considering these facts, the present work investigates the effects of oxygen vacancies on the functional properties through manipulation of drying temperatures of spin-cast films, especially at temperatures around 280 °C, where both the secondary phase and oxygen vacancies are prevalent. One of the biggest sources of oxygen vacancy is bismuth volatilisation and our work deals with the situation head-on uncovering the effect of bismuth volatilisation on functional properties. The structural properties were studied using X-ray diffraction (XRD), and deeper insights into the surface topography of the samples were obtained using AFM imaging. The electrical and dielectric characteristics help distinguish and analyse the samples in terms of the presence of resistive switching. PUND studies were performed to determine the ferroelectric properties of the samples. A fifty percent reduction in the oxygen vacancies in the presence of secondary phases was observed when compared with the phase-pure sample, as shown by the XPS analysis. Deeper insights were provided into the valence band spectra by first-principles studies. This work shows that phase purity may not be the singular condition for enhancing functional properties, and fine-tuning the presence of secondary phases and oxygen vacancies may be the way forward. The ferroelectric polarisation in one of the samples exhibits a notably higher value when using chemical solution deposition methods, making it a promising candidate for memory devices.

Improving interfacial strength at room and elevated temperatures in ultrasonic welding of pure titanium: Interlayer-induced phase transformation and concentrated plastic deformation

Ultrasonic welding (USW) of Titanium (Ti) sheets presents several challenges, notably crack formation due to sliding friction. To overcome this problem, the present study applied USW to pure α-Ti sheets both with and without different interlayer metals (Al, Ni, and Fe). Al interlayer improved the strength at room temperature significantly to cause base metal fracture (1700 N) by inducing concentrated plastic deformation, facilitating bonding with Ti while minimizing damage. However, its strength decreased significantly at 150–300 °C, suggesting the limitation of using Al interlayer at elevated temperatures. Conversely, the Ni and Fe interlayers led to a two-phase strength development. This enhancement was due to β-phase transformation, which reduces the interfacial defects and generates a more pronounced β-stabilization effect. The Ni interlayer, which has a higher β-transus point (765 °C) and lower molybdenum equivalency, required a higher welding energy (1800 J) and longer diffusion time into Ti, resulting in a gradual increase in strength due to a slower β-Ti transformation. On the other hand, the Fe interlayer with a lower β-transus point relative to Ti (595 °C) achieved peak strength at a lower welding energy of 1200 J. Both Fe and Ni interlayers displayed only a slight decrease in strength (1500–1600 N) at 300 °C with base metal fracture, revealing better joint performance at higher temperatures. These insights suggest a strategical interlayer selection based on the operation temperature, where Al interlayers were advantageous for low-energy welding at room temperature application, Fe and Ni interlayers offer sufficient strength at elevated temperatures by facilitating the β-Ti formation.

Ultra-long room temperature phosphorescence, intrinsic mechanisms and application based on host-guest doping systems

To construct efficient RTP doping systems by simple doping methods, isomers 2-(2-(9H-carbazol-9-yl)benzyl)malononitrile (o-CzCN), 2-(3-(9H-carbazol-9-yl)benzyl)malononitrile (m-CzCN) and 2-(4-(9H-carbazol-9-yl)benzyl)malononitrile (p-CzCN) were designed and synthesized by choosing commercial carbazole. Based on the structure-function relationships of three isomers and excellent compatibility between carbazole and benzocarbazole, 2-(3-(9H-carbazol-9-yl)benzyl)malononitrile (Lm-CzCN) and 2-(3-(5H-benzo[b]carbazol-5-yl)benzyl)malononitrile (m-BCzCN) were prepared by self-made carbazole and 2-naphthylamine. Then, Lm-CzCN/m-BCzCN were constructed and optimized by dissolution and rapid evaporation, as well as tuning the mass ratios between Lm-CzCN and m-BCzCN. Lm-CzCN shows excitation dependent RTP and afterglow lifetimes, as well as concentration dependent RTP emission in poly(vinyl alcohol) films (PVA), while 1% m-BCzCN@PVA film emits bright green afterglow, with RTP and afterglow lifetimes of 2.303 s and 17 s in turn, as well as RTP quantum yield of 0.22. More importantly, Lm-CzCN/m-BCzCN presents ultra-long room temperature phosphorescence, with RTP and afterglow lifetimes of 597.58 ms and 8 s in turn. Moreover, crystals m-CzCN and p-CzCN, as well as Lm-CzCN/m-BCzCN can be excited by visible light of 440 nm, showing yellow afterglow of 1-4 s. Noteworthy, polymorphism o-CzCNY and o-CzCNB were found, whose different emission were investigated by molecular conformation, intermolecular arrangement and stacking patterns. Finally, multiple encryptions were successfully constructed based on the different luminescent properties.

The Spinel-based Pliable Thermoelectric Device for Room Temperature Application

The Spinel-based Pliable Thermoelectric Device for Room Temperature Application

Interface engineering of 2D/2D MoS2/In2S3 heterostructure for highly sensitive NO2 detection at room temperature gas sensor

Rapid industrial growth and technological advancements in recent decades have led to an urbanized society at the expense of the environment due to toxic gas emissions. Therefore, it is imperative to detect trace concentrations of harmful gas with reliable techniques. NO2 is essentially being targeted for detection among all other gases due to its enormous abundance and serious health risks. Recently, 2D-MoS2 with enormous adsorption sites and high chemical reactivity have been employed selectively to detect NO2 at room temperature (RT). Herein, uniform and high surface area MoS2/In2S3 nanosheets (NSs) heterostructures were synthesized by hydrothermal method. HR-TEM analysis confirmed the 2D/2D heterostructures of MoS2/In2S3 nanosheets (NSs), and the increase in surface area of MoS2 from 10 m2/g to 27.2 m2/g upon addition of In2S3, measured through BET analysis. The MoS2/In2S3 sensor demonstrated excellent sensing capability with a response of 185% towards 50 ppm of NO2 at RT (30 ℃). Additionally, the sensor exhibited stable detection for about 36 days, repeatability over 5 cycles, and a detection limit of 450 ppb towards NO2. The synergistic influence of 2D/2D heterostructure with significant active sites and surface area is responsible for the considerable improvement in sensing performance. Therefore, the MoS2/In2S3 nanocomposites demonstrate a facile approach for developing high-performance potentially hazardous gas detectors for RT applications.

Indium-Doped SnO2 Based Surface Acoustic Wave Gas Sensor with Ba0.6Sr0.4TiO3 Film

SnO2-based gas sensors have been widely synthesized and used for the detection of various hazardous gases. However, the use of doped SnO2 in sensing applications has recently attracted increased interest due to the formation of a synergistic effect between the dopant and the host. Moreover, in the case of a surface acoustic wave (SAW) sensor, the piezoelectric material used in the fabrication of the sensor plays a crucial role in defining the response of the SAW sensor. As a ferroelectric material, barium strontium titanate (Ba0.6Sr0.4TiO3) has recently been studied due to its intriguing dielectric and electromechanical properties. Its high acoustic velocity and coupling coefficient make it a promising candidate for the development of acoustic devices; however, its use as a piezoelectric material in SAW sensors is still in its infancy. In this paper, we present the design, fabrication and validation of an indium doped SnO2-based SAW gas sensor on Ba0.6Sr0.4TiO3 thin film for room temperature (RT) applications. Pulsed laser deposition was used to deposit thin films of Ba0.6Sr0.4TiO3 and indium-doped SnO2. Different characterization techniques were employed to analyze the morphology and crystallization of the films. The performance of the fabricated sensor was validated by exposing it to different concentrations of ethanol and then analyzing the recorded frequency shift. The sensor exhibited fast response (39 s) and recovery (50 s) times with a sensitivity of 9.9 MHz/Δ. Moreover, the sensor had good linear response and reproducibility. The fabricated indium-doped SnO2-based SAW gas sensor could be suitable for practical room temperature applications.

The quantum spin Hall insulator with large bandgap in functionalized AlBi monolayer

The quantum spin Hall (QSH) insulator exhibits various interesting physical properties. Therefore, researchers have been seeking QSH insulators with large bandgaps suitable for room temperature applications. Here, based on first-principles calculations, we predict that the chlorine atom functionalized AlBi monolayer forms a topological insulator with a large bandgap (Eg = 0.215 eV). Chlorination and SOC effect induce AlBi(Cl)2 band inversion, and phonon spectra calculations demonstrate excellent dynamic stability for AlBi(Cl)2. The Z2 topological invariants, as well as the topological nontrivial edge states further confirm these findings. In addition, we applied the biaxial strains ranging from −5% to 5% to the monolayer, revealing a topological phase transition at −3%, resulting in the emergence of a normal insulator. These interesting features suggest that chlorinated AlBi is a promising material for room temperature spintronic devices.

Mo3S13 Chalcogel: A High-Capacity Electrode for Conversion-Based Li-Ion Batteries.

Despite large theoretical energy densities, metal-sulfide electrodes for energy storage systems face several limitations that impact the practical realization. Here, we present the solution-processable, room temperature (RT) synthesis, local structures, and application of a sulfur-rich Mo3S13 chalcogel as a conversion-based electrode for lithium-sulfide batteries (LiSBs). The structure of the amorphous Mo3S13 chalcogel is derived through operando Raman spectroscopy, synchrotron X-ray pair distribution function (PDF), X-ray absorption near edge structure (XANES), and extended X-ray absorption fine structure (EXAFS) analysis, along with ab initio molecular dynamics (AIMD) simulations. A key feature of the three-dimensional (3D) network is the connection of Mo3S13 units through S-S bonds. Li/Mo3S13 half-cells deliver initial capacity of 1013 mAh g-1 during the first discharge. After the activation cycles, the capacity stabilizes and maintains 312 mAh g-1 at a C/3 rate after 140 cycles, demonstrating sustained performance over subsequent cycling. Such high-capacity and stability are attributed to the high density of (poly)sulfide bonds and the stable Mo-S coordination in Mo3S13 chalcogel. These findings showcase the potential of Mo3S13 chalcogels as metal-sulfide electrode materials for LiSBs.

Precisely Controlled Polymerization of Two-Dimensional Conducting Polymers in Quasi-Liquid Layer Enables Ultrahigh Sensing Performance.

Gas sensors based on conducting polymers offer great potential for high-performance room temperature applications due to their cost-effectiveness, high-sensitivity, and operational advantage. However, their current performance is limited by the deficiency of control in conventional polymerization methods, leading to poor crystallinity and inconsistent material properties. Here, the quasi-liquid layer (QLL) on the ice surface acts as a self-regulating nano-reactor for precise control of thermodynamics and kinetics in the polymerization, resulting in a 7.62nm thick two-dimensional (2D) polyaniline (PANI) film matching the QLL thickness. The ultra-thin film optimizes the exposure of active sites, enhancing the detection of analyte gases at low concentrations. It is validated by fabricating a chemiresistive gas sensor with the 2D PANI film, demonstrating stable room-temperature detection of ammonia down to 10 ppt in ambient air with an impressive 10% response. This achievement represents the highest sensitivity among sensors of this kind while maintaining excellent selectivity and repeatability. Moreover, the QLL-controlled polymerization strategy offers an alternative route for precise control of the polymerization process for conducting polymers, enabling the creation of advanced materials with enhanced properties.

Detection of NO2 at ppm-level using Al-doped CeO2 based gas sensor with high sensitivity and selectivity at room temperature

Nanostructured metal oxides have gained significant attraction in the field of gas sensors because of their size-dependent, superior catalytic capabilities with better gas adsorption and desorption behaviour. However, their high operating temperature limits their scalability in real-time applications. In this work, we fabricated the pristine and Al-doped CeO2 nanoparticles for Room-Temperature (RT) NO2 detection. Compared to other interfering gases, the fabricated sensor shows a strong preference for detecting NO2, indicating a high level of selectivity. Interestingly 5% Al-doped CeO2 exhibited a remarkable 247% response to 25 ppm of NO2, which is three times greater than the pristine. Furthermore, the sensor exhibits improved response and recovery times of 64 s and 52 s, respectively. It also demonstrates excellent repeatability and stability of 91% over the period of 56 days. Thus, the significant improvement in the sensing performance is attributed to the increase in oxygen vacancies, charge imbalance and enhancement in specific surface area due to the effect of Al doping. Furthermore, these findings will provide a new approach to develop real-time gas sensors for room temperature applications.

Metal–organic framework thin films: review of their room-temperature synthesis and applications

This review presents diverse growth methods employed in the fabrication of room temperature-synthesized MOF films, emphasizing their significant applications across various fields.

Sustainable heat-driven sound cooler with super-high efficiency

<p>Sustainable cooling technologies with high efficiency are increasingly vital in modern life. Characterized by eco-friendly working substances and no mechanical moving components, the heat-driven thermoacoustic refrigerator (HDTR) makes it a really sustainable choice. However, its practical application has been hindered by its relatively low efficiency. This work reports a breakthrough in thermally-powered sound cooling technology: a super-efficient HDTR. The system incorporates an innovative configuration, ensuring efficient acoustic power matching between the engine and cooler units at high heating temperatures, thereby significantly boosting efficiency. Our experimental findings are exhilarating: the HDTR achieves an unprecedented coefficient of performance (COP) of 1.34 at heating, ambient, and cooling temperatures of 550 ��C, 35 ��C, and 7 ��C, respectively, along with a cooling power of 2.37 kW. To the best of our knowledge, under approximate temperature spans, this COP surprisingly increases by 240% compared to the best result previously reported for HDTRs without using the novel configuration. These results represent a significant advancement in HDTR technology, showing a tremendous potential of the HDTR as an emerging, sustainable cooling technology, particularly for heat-driven room-temperature refrigeration applications.</p>

Ferromagnetic topological states in monolayer vanadium halides toward heterostructure applications

Topological states in two-dimensional materials have garnered significant research attention in recent years, particularly those with intrinsic magnetic orderings, which hold great potential for spintronic applications. Through theoretical calculations, we unveil the superior band topology of monolayer vanadium trihalides, with a specific focus on V2Cl6. These two-dimensional compounds exhibit a half-metallic ferromagnetic ground state, showcasing excellent thermodynamic and mechanical stabilities. Remarkably, clean band crossings with complete spin polarization manifest as phase transitions between Weyl semimetal states and quantum anomalous Hall states under different magnetization directions, and both topological phases yield prominent edge states. Furthermore, Monte Carlo simulations estimate a high Curie temperature of up to 381.3 K, suggesting the potential for spintronic development above room temperature. Taking a step forward, we construct two heterojunctions utilizing selected substrates, MoS2 and h-BN. These substrates not only facilitate a suitable lattice integration but also have a negligible impact on the half-metallicity and band topology. These findings lay the groundwork for exploring practical applications of two-dimensional ferromagnetic topological states. Importantly, the presented material candidates have the potential to accelerate the development of room temperature applications and integrate spintronic devices.

A new thermoelectric Ag8SiSe6 argyrodite for room temperature application: sensitivity of thermoelectric performance to cooling conditions

Ag8SiSe6 is a promising n-type thermoelectric material for near-room temperature applications. We reveal the pronounced relationship between the cooling conditions (including quenching parameters) and thermoelectric properties of Ag8SiSe6 compounds.

Electrospun Perovskite Nanofiber/Poly(vinylidene fluoride-cohexafluoropropylene) Quasi-Solid-State for Lithium-Metal Batteries

Solid-state lithium-metal batteries (SSLMBs) with a composite solid electrolyte (CSE) have great potential for achieving both high energy density and high safety and are thus promising next-generation energy storage devices. Nevertheless, the key bottleneck issues are a high electrode/electrolyte interface resistance and the limited Li+ conductivity of the solid electrolyte. A free-standing CSE consisting of Li0.33La0.557TiO3 (LLTO) nanofibers, poly(vinylidene fluoride-co-hexafluoropropylene (PVDF-HFP), and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) is developed for room-temperature SSLMB applications. First, the calcination temperature for the electrospun LLTO precursor is optimized. The effects of the LLTO filler fraction and the morphology (spherical vs. fibrous) on CSE conductivity are examined. Furthermore, a succinonitrile interlayer (SNI), which is composed of succinonitrile, fluoroethylene carbonate, and LiTFSI, is developed to lower the high interfacial impedance. Compared to a conventional ester-based interlayer (EBI), SNI effectively decreases the Li//CSE interfacial resistance and suppresses unfavorable interfacial side reactions. The derived LiF- and CF x -rich protective layer on the Li electrode surface prevents the accumulation of dead Li and the excessive formation of SEI. Importantly, the dehydrofluorination reactions of PVDF-HFP are adequately mitigated, and a highly conductive and stable Li//CSE interface is achieved owing to SNI. Accordingly, both Li//CSE@SNI//Li and Li//CSE@SNI//LiFePO4 cells exhibit superior charge-discharge properties and cyclability to those of an EBI counterpart. A simple and low-cost interface modification strategy to enhance the performance of SSLMBs is proposed in this paper.

Phase Transition Engineering of Vanadium Dioxide Induced by Oxygen Vacancies

A reconfigurable optical functional system is a pioneering and comprehensive approach for portable future flexible electronics, irrespective of traditional silicon-based technology. VO2 shows tremendous temperature-dependent structural and electrical phase transitions as a complex correlated metal oxide, presenting it as a potential candidate for bolometers, thermal camouflage, and optoelectronics applications. However, the structural stability and high transition temperature restrict room-temperature applications. The present study reports the oxygen vacancies-assisted phase transition engineering in the VO2/muscovite heterostructure. The ion bombardment alters the oxygen stoichiometry of VO2/muscovite thin film at room temperature. A significant decrease in lattice constant has been observed during the transition of the insulating M1 (monoclinic) phase into the metallic R (tetragonal) phase, which was confirmed through high-resolution XRD. The change in oxygen vacancy concentration determined using X-ray photoelectron spectroscopy (XPS) actively suppressed and stabilized the epitaxial thin film of VO2 near room temperature. We investigated whether applying increasing power-mediated ion bombardment for a few minutes affects the oxygen vacancy formation on the VO2/muscovite film’s surface. Consequently, a change in KPFM and 4 orders of magnitude change in resistance of VO2 thin film have been observed. This report reveals the fundamental understanding of controlling the MIT in epitaxial VO2 thin film via facile and clean phase transition engineering techniques for advanced flexible electronic devices.

Tuning Anisotropic Thermoelectric Properties of TiS2–δ Compounds via Intercalating Iron

Layered TiS2 is of great potential in thermoelectrics for room temperature and medium temperature applications due to its tunable transport properties, low environmental impact, low cost, and lightweight. Herein, we prepared FexTiS2–δ with x varying from 0 to 0.05 through a two-step process, involving initial synthesis in sealed tubes followed by spark plasma sintering. Mössbauer spectroscopy indicated that Fe atoms occupy the octahedral sites in the van der Waals gaps and exist in the form of Fe2+ with a high spin state. FexTiS2–δ with x ≤ 0.02 exhibit high in-plane power factors, reaching an average of ~ 1.2 mWm–1K–2. The structural disorder caused by Fe intercalation leads to a significant decrease in out-of-plane lattice thermal conductivity. The anisotropy in the figure of merit, ZT, of FexTiS2–δ is suppressed due to Fe intercalation. Fe0.01TiS2–δ possesses the highest ZT of 0.39 at 625K along the in-plane direction.

Control of the magnetic anisotropy and Curie temperature of monolayer 1T-CrTe2 for room temperature application

Magnetic units with large magnetic anisotropy energy (MAE) and high Curie temperature (Tc) are crucial for spintronic and quantum computing devices, which are a persisting demand for miniaturization of magnetic units. Using first-principles calculations and Monte Carlo simulation, it is found that monolayer 1T-CrTe2 exhibits strong perpendicular magnetic anisotropy with a MAE of approximately 5.29 meV and high Tc of ∼136 K. Interestingly, we find that the MAE and Tc of monolayer 1T-CrTe2 are tunable through electron/hole doping, strain, and heterostructure engineering. The magnetic easy-axis can be adjusted from out of plane to in plane, which is mainly attributed to the coupling between Te atomic orbitals (px, py). Second-order perturbation theory reveals that the spin–orbit coupling interaction between the occupied px and unoccupied py orbitals in opposite spin channel near Fermi level gives rise to negative contribution of MAE. Moreover, Tc can be enhanced to ∼230 K through super–superexchange mechanism of heterostructure due to the electron hopping between t2g/eg orbitals of Cr4+ ions and e1/a1 orbitals of Fe2+ ions. Importantly, we find that Tc can be boosted above room temperature by applying moderate strain (6%), ascribing to significant enhancement of MAE and exchange coupling constant. The present work indicates that monolayer 1T-CrTe2-based two-dimensional materials are very promising for room temperature application in magnetic storage and information processing.

Giant magnetocaloric effect for (Mn, Fe, V)2(P, Si) alloys with low hysteresis

The Fe2P type Mn–Fe–P–Si alloys exhibit a giant magneto-elastic first-order transition, but the large hysteresis limits their performance. Crystal structure evolution and magnetocaloric performance were investigated by varying the Mn and Fe contents at a constant V substitution of 0.02 in Fe2P-type (Mn1.17-xFe0.73-yV0.02) (P0.5Si0.5) (where x + y = 0.02). The V substitution of Fe content shows a larger reduction of hysteresis compared with the same substitution amount of Mn content. During magnetoelastic phase transition, V-substitution reduces the volume change and the volumetric stresses, providing a superior mechanical stability. Compound with the V substitution of Fe (y = 0.02) shows the best magnetocaloric effect with a low thermal hysteresis of 0.6 K. Our developed Mn1.17-xFe0.73-yV0.02P0.5Si0.5 alloys are excellent materials for room-temperature magnetic heat-pumping applications by using a permanent magnet.

Quantifying alignment and quality of graphene nanoribbons: A polarized Raman spectroscopy approach

Graphene nanoribbons (GNRs) are atomically precise stripes of graphene with tunable electronic properties, making them promising for room-temperature switching applications like field-effect transistors (FETs). However, challenges persist in GNR processing and characterization, particularly regarding GNR alignment during device integration. In this study, we quantitatively assess the alignment and quality of 9-atom-wide armchair graphene nanoribbons (9-AGNRs) on different substrates using polarized Raman spectroscopy. Our approach incorporates an extended model that describes GNR alignment through a Gaussian distribution of angles. We not only extract the angular distribution of GNRs but also analyze polarization-independent intensity contributions to the Raman signal, providing insights into surface disorder on the growth substrate and after substrate transfer. Our findings reveal that low-coverage samples grown on Au(788) exhibit superior uniaxial alignment compared to high-coverage samples, attributed to preferential growth along step edges, as confirmed by scanning tunneling microscopy (STM). Upon substrate transfer, the alignment of low-coverage samples deteriorates, accompanied by increased surface disorder. For high-coverage samples, the alignment is preserved, and the disorder on the target substrate is reduced compared to the low-coverage samples. Our extended model enables a quantitative description of GNR alignment and quality, facilitating the development of GNR-based nanoelectronic devices.