Temperature-dependent Behavior Research Articles

Optimizing TCAD Model and Temperature-Dependent Analysis of Pt/AlN Schottky Barrier Diodes for High-Power and High-Temperature Applications

This research presents a comprehensive investigation and optimization of the Pt/AlN Schottky Barrier diode (SBD) using technology computer-aided design (TCAD) modeling. The study explores the electrical characteristics of AlN SBDs with various metal contacts, including Aluminum (Al), Silver (Ag), Tungsten (W), Gold (Au), Nickel (Ni), and Platinum (Pt). Through the comparative analyses of different metal/AlN Schottky contacts, the Pt/AlN structure emerges as the most promising due to its superior barrier height and lower leakage current. At [Formula: see text]K, the diode demonstrates a barrier height of 2.72[Formula: see text]V, a nearly ideal leakage current of 0.046[Formula: see text]pA, and a breakdown voltage of 363[Formula: see text]V. The research extends to examining the temperature-dependent electrical behavior of Pt/AlN Schottky diodes, particularly for high-power and high-temperature applications. Analysis carried out across temperatures ranging from [Formula: see text]K to [Formula: see text]K reveals a trend of increasing ON resistance and consistently lower leakage current with rising temperature. Importantly, the study indicates that the impact of temperature on the barrier height and breakdown voltage of the diode is negligible, thus rendering it suitable for high-temperature operation. Leveraging the unique properties of AlN as an ultra-wide bandgap material within the III-V compound semiconductor family, this research provides valuable insights into the potential applications of Pt/AlN Schottky contact. The study highlights that the Pt/AlN Schottky contact is effective not only for high-power, high-temperature SBDs but also as superior metal/semiconductor gate contacts for field-effect transistors (FETs). Their suitability is attributed to their ability to handle high voltages, minimize reverse leakage current, and demonstrate improved thermal stability.

Thermal Properties of Athermal Granular Materials.

Dry granular materials consist of a vast ensemble of discrete solid particles interacting through complex frictional forces at the contact points. The particles are so large that these systems are believed to be completely athermal. Here, we arrest the dynamics of a flowing granular material in a steady-state-flow configuration, enabling an isolated examination of aging at the particle contacts without granular rearrangements. Our findings reveal that the evolution of interparticle forces within the arrested athermal granular network results in the spontaneous increase of the system's yield stress. This strengthening process is logarithmic in time with a rate that depends on the temperature. We demonstrate that the material's stress relaxation exhibits similar time- and temperature-dependent behavior, suggesting a shared origin for aging and stress relaxation in these systems governed by thermal molecular processes at the scale of the grain contacts.

Luminescence Nanothermometry: Investigating Thermal Memory in UiO-66-NH2 Nanocrystals.

Metal-organic frameworks (MOFs), a diverse and rapidly expanding class of crystalline materials, present many opportunities for various applications. Within this class, the amino-functionalized Zr-MOF, namely, UiO-66-NH2, stands out due to its distinctive chemical and physical properties. In this study, we report on the new unique property where UiO-66-NH2 nanocrystals exhibited enhanced fluorescence upon heating, which was persistently maintained postcooling. To unravel the mechanism, the changes in the fluorescence signal were monitored by steady-state fluorescence spectroscopy, lifetime measurements, and a fluorescence microscope, which revealed that upon heating, multiple mechanisms could be contributing to the observed enhancement; the MOFs can undergo disaggregation, resulting in a fluorescent enhancement of the colloidally stable MOF nanocrystals and/or surface-induced phenomena that result in further fluorescence enhancement. This observed temperature-dependent photophysical behavior has substantial applications. It not only provides pathways for innovations in thermally modulated photonic applications but also underscores the need for a better understanding of the interactions between MOF crystals and their environments.

Dynamic Behavior of Poly(N-isopropylmethacrylamide) in Neat Water and in Water/Methanol Mixtures.

We investigate the collective dynamics of thermoresponsive polymer poly(N-isopropylmethacrylamide) (PNIPMAM) in aqueous solution and in water/methanol mixtures in the one-phase region. In neat water, the polymer concentration c is varied in a wide range around the overlap concentration c*, that is estimated at 23 g L-1. Using dynamic light scattering (DLS), two decays ("modes") are consistently observed in the intensity autocorrelation functions for c = 2-150 g L-1 with relaxation rates which are proportional to the square of the momentum transfer. Below c*, these are attributed to the diffusion of single chains and to clusters from PNIPMAM that are formed due to hydrophobic interactions. Above c*, they are assigned to the diffusion of the chain segments between overlap points and to long-range concentration fluctuations. From the temperature-dependent behavior of the overall scattering intensities and the dynamic correlation lengths of the fast mode, the critical temperatures and the scaling exponents are determined. The latter are significantly lower than the static values predicted by mean-field theory, which may be related to the presence of the large-scale inhomogeneities. The effect of the cosolvent methanol on the dynamics is investigated for polymer solutions having c = 30 g L-1 and methanol volume fractions in the solvent mixtures of up to 60 vol %. The phase diagram was established by differential scanning calorimetry. The slow mode detected by DLS becomes significantly weaker as methanol is added, i.e., the solutions become more homogeneous. Beyond the minimum of the coexistence line, which is located at 40-50 vol % of methanol, the dynamics is qualitatively different from the one at lower methanol contents. Thus, going from the water-rich to the methanol-rich side of the miscibility gap, the change of interaction of the PNIPMAM chains with the two solvents has a severe effect on the collective dynamics.

Analysis of the temperature-dependent plastic deformation of single crystals of quinary, quaternary and ternary equiatomic high- and medium-entropy alloys of the Cr-Mn-Fe-Co-Ni system

ABSTRACT Temperature-dependent plastic deformation behaviors of single crystals of quaternary and ternary equiatomic medium-entropy alloys (MEAs) belonging to the Cr-Mn-Fe-Co-Ni system were investigated in compression at temperatures in the range 9 K to 1373 K. Their critical resolved shear stresses (CRSSs) increase with decreasing temperature below room temperature. There is also a dulling of the temperature dependence of CRSS below 77 K due to dislocation inertial effects that we attribute to a decrease in the phonon drag coefficient. These behaviors were compared with those of previously investigated single crystals of the equiatomic Cr-Co-Ni and Cr-Fe-Co-Ni MEAs, and the equiatomic Cr-Mn-Fe-Co-Ni high-entropy alloy (HEA). The temperature dependence of CRSS and the apparent activation volumes below room temperature can be well described by conventional thermal activation theories of face-centered cubic (FCC) alloys. Above 673 K, there is a small increase in CRSS, which we believe is due to elastic interactions between solutes and mobile dislocations, the so-called Portevin-Le Chatelier (PL) effect. The CRSS at 0 K was obtained by extrapolation of fitted CRSS vs. temperature curves and compared with predictions from solid solution strengthening models of HEA and MEAs.

Synthesis and characterization of structural properties—RT and temperature-dependent dielectric behavior of Gd-substituted nickel nanoferrites

Synthesis and characterization of structural properties—RT and temperature-dependent dielectric behavior of Gd-substituted nickel nanoferrites

Role of Bi/Te co-dopants on the thermoelectric properties of SnSe polycrystals: an experimental and theoretical investigation

A sustainable solution to the energy crisis may be found in thermoelectric materials and generators, capable of transforming thermal energy into electrical energy or vice versa. SnSe is one of the emerging thermoelectric materials with distinctive properties. The main advantages of this compound are earth-abundant, inexpensive, non-toxic and it is also known for its high thermoelectric performance. Here we prepared Bi/Te co-doped SnSe polycrystals; whereas, Bi and Te are added with different compositions such as (x = 0.0,0.02,0.04,0.06 and y = 0.03) in (Sn1-xBixSe1-YTeY) matrix by using the solid-state reaction method. XRD data confirms the samples belong to the orthorhombic crystal system with the Pnma space group. DFT calculations were used to see structural stability and electronic properties for pure and doped SnSe samples. Temperature-dependent semiconducting behavior of the samples has been demonstrated by electrical resistivity. The Seebeck coefficient, correlated with carrier concentration and mobility, validates the p-type behavior for the pristine samples and the n-type behavior for co-doped samples. The dominant behavior of phonon scattering has been demonstrated by thermal conductivity analysis. After co-doping there is decrement in total thermal conductivity was observed which 1.3 times lower than SnSe. A theoretical calculation was used to validate experimental results to estimate electrical properties, Seebeck coefficient, specific heat capacity, thermal conductivity, and power factor using Quantum espresso code with Boltzmann transport Equation. 4% Bi-doped sample displayed a significant increment in electrical conductivity and an enhanced Seebeck coefficient, which led to the power factor enhancement of approximately 2.0 times in contrast to the pristine sample and enhanced ZT of about 0.055 which is 3.43 times higher than the pristine SnSe.Graphical abstract

Formulation and characterization of ionically crosslinked gellan gum hydrogels using trilysine at low temperatures for antibody delivery

Research of the nontraditional polysaccharide gellan gum (GG) is a growing space for the development of novel drug delivery systems due to its tunable physic-mechanical properties, biocompatibility, and stability in a wide range of environments. Unfortunately, high temperature crosslinking is often required, representing a limiting factor for the incorporation of thermosensitive therapeutic agents. Here, we demonstrated that GG can be crosslinked at a low temperature (38 °C) using a simple fabrication process that utilizes trilysine as an alternative to traditional mono- or divalent ion crosslinkers. While elevated temperature mixing is still required to form a clear GG solution, crosslinking of 0.5 – 1 % GG (w/v) in the presence of trilysine (0.03 % - 0.05 % w/v) was achieved at 38 °C resulting in hydrogels with suitable working formulations to facilitate syringe loading. Low injection forces (< 20 N), and biocompatibility was evaluated with normal human dermal fibroblast (cell viability > 90 %). Frequency sweep showed a transition from purely liquid-like behavior to gel-like behavior with increased trilysine concentration. A temperature dependent behavior was lost with higher trilysine concentrations, indicating stable hydrogel formation. NMR results suggest that trilysine participates in gelation via both ionic interactions between the primary amines of trilysine and the carboxylate residues of glucuronic acid and hydrogen bonding. Released studies showed that GG hydrogels can entrap and provide sustained release of IgG in relation to the crosslinker, and antibody concentration used, with a burst release within the first 24 h (∼80 % cumulative released) followed by a sustained released for up to 5 days. Overall, findings demonstrate a promising nontoxic injectable hydrogel that requires lower crosslinking temperatures, is simple to manufacture and serves as a carrier of thermosensitive therapeutic agents.

Self-driven intelligent curved hinge based on shape-morphing composites

The space deployable structures based on shape memory polymer composites (SMPCs) possessed excellent self-deployable performance, which effectively avoided the impact and electromagnetic pulse (EMP) caused by the explosion of pyrotechnic devices. In this work, two types of self-driven curved hinges with different angles of 80° and 115° (Type 80 and Type 115) were designed based on SMPCs. The thermomechanical properties and time–temperature-dependent viscoelastic behaviors of SMPCs were systematically investigated. The three-point bending performance and cyclic shape memory performance of the developed hinges were also characterized. In addition, the deployment performances of Type 80 driven 350 g object under different heating powers were investigated in the environment of ± 70 °C and 103 Pa atmospheric pressure. A staircase-like heating strategy was proposed to achieve precise and controllable deployment under this environment. The developed self-driven curved hinges were expected to have tremendous application potential on the flap actuators and optical payload rotating platforms of the satellites.

Temperature-Dependent Mechanical Behaviors and Deformation Mechanisms in a Si-Added Medium-Entropy Superalloy with L12 Precipitation

Temperature-Dependent Mechanical Behaviors and Deformation Mechanisms in a Si-Added Medium-Entropy Superalloy with L12 Precipitation

Temperature-Modulated Evolution of Surface Structures Induces Significant Enhancement of Two-Photon Fluorescent Emission from a Dye Molecule.

Fluorescence is an essential property of molecules and materials that plays a pivotal role across various areas such as lighting, sensing, imaging, and other applications. For instance, temperature-sensitive fluorescence emission is widely utilized for chemo-/biosensing but usually decreases the intensity upon the increase in temperature. In this study, we observed a temperature-induced enhancement of up to ∼150 times in two-photon fluorescence (TPF) emission from a dye molecule, 4-(4-diethylaminostyry)-1-methylpyridinium iodide (D289), as it interacted with binary complex vesicles composed of two commonly applied surfactants: sodium dodecyl sulfate (SDS) and cetyltrimethylammonium bromide (CTAB). By employing second harmonic generation (SHG) and TPF techniques, we clearly revealed the temperature-dependent kinetic behavior of D289 on the surface of the vesicles and utilized it to interpret the origin of the significant TPF enhancement. Additionally, we also demonstrated a similar heating-induced enhancement of the TPF emission from D289 on the membrane of phospholipid vesicles, indicating the potential application of TPF in temperature sensing in the biology systems. The embedding of D289 in the tightly packed alkane chains was identified as the key factor in enhancing the TPF emission from D289. This finding may provide valuable information for synthesizing fluorescence materials with a high optical yield.

Exploring interfacial properties and thermodynamic parameters of synthesized biodegradable surfactants from Brassica Juncea and their emulsification characteristics

This study investigates the synthesis and characterization of four non-ionic surfactants of different spacer lengths derived from Brassica Juncea (mustard oil) and explore their potential applications. The chemical structures of the surfactants were confirmed by FTIR, 1HNMR spectroscopy and GC. Surface tension values of the surfactants were measured at various temperatures, unveiling temperature-dependent behaviour and associated thermodynamics. The critical micelle concentrations (CMC) of different surfactants were found to be very low (0.064–0.096 mmol/l at 303 K) compared to conventional surfactants. The CMC and the surface tension further decrease significantly with an increase in temperature. Surface-active thermodynamic parameters of the surfactants demonstrate their lower interfacial characteristics and enhanced self-aggregation capability. At CMC, the synthesized surfactants effectively decrease the interfacial tension (IFT) between water and dodecane to a notably low range of 9.5 to 12.1 mN/m, which is further reduced to a range of 3.2 to 6.1 mN/m at optimal salinity. The surfactants also show good emulsification properties, the emulsions formed in the water-dodecane system using the gemini surfactants as emulsifiers were extensively characterized, encompassing phase behaviour and droplet size distribution analysis. These emulsions exhibit favourable viscous properties, with viscosities ranging from 5 to 20 mPa.s at a 5 s-1 shear rate. This study establishes that the synthesized Gemini surfactants are viable candidates for Enhanced Oil Recovery (EOR), showcasing robust stability, interfacial activity, and favourable rheological properties, alongside biodegradability.

An asymmetric polymerized small molecular acceptor with temperature-dependent aggregation and superior batch-to-batch reproducibility for efficient all-polymer solar cells

Polymerized small molecular acceptors (PSMAs) have been instrumental in driving the advancements in power conversion efficiencies (PCEs) of all-polymer solar cells (all-PSCs). However, PSMAs commonly face challenges such as low molecular weights and notable batch-to-batch variation, posing significant obstacles to the transition of all-PSCs from lab to fab. Herein, a novel PSMA, which we refer to PAY-IT with an asymmetric conjugated skeleton is reported. The A–D1A'D2–A-type asymmetric monomer endows PAY-IT a random conjugated backbone, thus offering a desired temperature dependent aggregation behavior, which is hardly observed in conventional PSMAs. This characteristic facilitates chain growth during polymerization, thus yielding high molecular weights and low batch-to-batch sensitivity for the polymer. Moreover, the “S-shape” configuration of the asymmetric monomer endows PAY-IT good planarity and excellent charge transport property. As a result, the all-PSC consisted of PAY-IT and PM6 showcased a remarkable PCE of 14.9 %. More importantly, three batches of PAY-IT with number-average molecular weights ranging from 18.3 to 26.2 kDa exhibited nearly identical PCE (14.4–14.9 %), demonstrating superior batch-to-batch reproducibility of this polymer acceptor. This work explored PSMAs with asymmetric skeleton for the first time, and the results demonstrated a new design concept for the development of state-of-the-art PSMAs with minimal batch-to-batch variation.

Slow energy relaxation in anharmonic chains with and without on-site potentials: Roles of distinct types of discrete breathers

Slow energy relaxation has been observed in one-dimensional lattices with and without a nonlinear on-site potential; however, a comprehensive understanding of the detailed relaxation process remains elusive. Here we revisit this issue by introducing damping conditions at the free-end boundary of a thermalized lattice. We reveal that, in the long-cooling-time regime considered, for systems with a nonlinear on-site potential, energy relaxation exhibits a strong temperature-dependent behavior and with the increase of temperature, there is a crossover between decaying and non-decaying behaviors, around a crossover temperature point of Tc≃4.2. This non-decaying behavior at higher temperature is attributed to the presence of standing multi Sievers–Takeno discrete breather (DB) states. Conversely, for systems without on-site potentials, relaxation is nearly independent of temperature but dependent on interparticle potential. Notably, we observe that the cubic anharmonicity can generate moving single Page DB states that contribute to the unusual slow energy relaxation within a specific time regime. Our results provide enhanced insights into the mechanisms governing slow energy relaxation during lattice cooling.

Estimating the elastic modulus of concrete under moderately elevated temperatures via impulse excitation technique

PurposeTo evaluate the temperature-dependency of the Young’s and shear moduli of concrete after exposure to moderately elevated temperatures using the non-destructive impulse excitation technique (IET).Design/methodology/approachThe study involved heating the concrete up to 225 °C and measuring the dynamic Young’s and shear moduli using the non-destructive technique of impulse excitation, which measures the natural vibration frequency from a mechanical impulse received by an acoustic sensor. The effects of temperature on the dynamic Young’s and shear moduli were analysed and the importance of the spatial variability of the measured values was also verified.FindingsThe study found that even moderately elevated temperatures (below 225 °C) resulted in a significant permanent reduction in the Young’s modulus of concrete (reduction in the range of 23%–36% for the maximum temperature considered in this research) as well as a modest and permanent reduction in the shear modulus of around 6%. It was also observed that spatial variability of the mechanical properties of concrete plays an important role in the measured values; higher dispersion of the results was found for the values of the Young’s and shear moduli of concrete measured along the height of the beam. The non-destructive test method used in this study was found to be extremely useful in the investigation of heat-related damage in concrete structures for its ease of use, low time consumption and accuracy. The results were consistent with the published literature.Originality/valueThis study provides important insights into the temperature-dependent behaviour of the dynamic Young’s and shear moduli of concrete and highlights the significance of proper consideration of the spatial variability of the measured values. The use of a non-destructive test method for continuous acoustic testing during heating and cooling proved to be effective, and the findings contribute to the fields of materials science and civil engineering in understanding the effects of elevated temperatures on concrete properties. The findings confirm that IET can be easily used to gather important information in the condition assessment and rehabilitation of concrete structures after a fire event. Further studies to foster the application of this technique to real structures are suggested.

Atomistic simulation of temperature dependence of tensile properties and estimation of DBTT of Cu–Ag core–shell nanowires

An atomistic model of Cu-Ag core–shell nanowire using molecular dynamics is proposed. The simulation model was utilized for the evolution of temperature dependent (in the range of 10–500 K) tensile behavior and the identification of ductile-to-brittle transition temperature (DBTT) of single-crystal Cu-Ag core–shell nanowire. The evolution of defects such as point defects, dislocations, and stacking faults, arising from tensile deformation in the mentioned temperature rage were analyzed. The Wigner-Seitz Defect analysis, Dislocation analysis, and Common Neighbor analysis methods were implemented in this study to estimate the various defects concentration in the nanowire. The study identified that Cu-Ag core–shell (core diameter = 4 nm and shell thickness = 1 nm nanowire) exhibits DBTT somewhere in the temperature between 25 K to 30 K. The modulus of elasticity found to be increasing from 19.7 TPa at 10 K to 23.7 TPa at 30 K (within brittle regime), followed by a steep fall to 14.9 TPa at 500 K where fracture seems to be in ductile mode. The observed mechanical properties of the nanowire are discussed in the article in view of the dislocation and stacking faults generation in the core–shell nanostructures.

Interfacial Behavior of Biodegradable Poly(lactic-co-glycolic acid)-Pluronic F127 Nanoparticles and Its Impact on Pickering Emulsion Stability.

Biodegradable nanoparticle-based emulsions exhibit immense potential in various applications, particularly in the pharmaceutical, cosmetic, and food industries. This study delves into the intricate interfacial behavior of Pluronic F127 modified poly(lactic-co-glycolic acid) (PLGA-F127) nanoparticles, a crucial determinant of their ability to stabilize Pickering emulsions. Employing a combination of Langmuir balance, surface tension, and diffusion coefficient measurements, we investigate the interfacial dynamics of PLGA-F127 nanoparticles under varying temperature and ionic strength conditions. Theoretical calculations are employed to elucidate the underlying mechanisms governing these phenomena. Our findings reveal a profound influence of temperature-dependent Pluronic layer behavior and electrostatic and steric interactions on the interfacial dynamics. Nonlinear changes in surface tension are observed, reflecting the interplay of these factors. Particle aggregation is found to be prevalent at elevated temperatures and ionic strengths, compromising the stability and emulsification efficiency of the formed emulsions. This work provides insights into the rational design of stable and efficient biodegradable nanoparticle-based Pickering emulsions, broadening their potential applications in various fields.

Cobalt(II) Single-Ion Magnet Coordinated by Double Deprotonation of 2,2'-Bipyridine-6,6'-diol Ligands.

In this study, we synthesized a new Co(II) complex, [NMe4]2[Co(bpyO2)2] (1), using deprotonated 2,2'-bipyridine-6,6'-diol ligands (bpyO2 2-). This compound exhibits a significant zero-field splitting (D) value. The far-infrared magneto spectroscopy and high-frequency and field electron paramagnetic resonance (HFEPR) measurements indicated that compound 1 possesses D = -54.8 cm-1 and E ∼ 0 cm-1. These findings were subsequently confirmed by other experimental data, including DC magnetic susceptibilities and variable temperature and variable magnetic field reduced magnetizations. Additionally, we conducted a series of AC magnetic susceptibility measurements to investigate the kinetics of magnetization relaxation. Below 6.6 K and under zero external magnetic field, fast quantum tunneling of magnetization (QTM) dominates (∼570 Hz), and temperature-independent out-of-phase signals are observed. Above 8.1 K, temperature-dependent behavior is observed. Furthermore, we examined the AC magnetic susceptibility behavior under external magnetic fields ranging from 300 to 4000 G. The effect of QTM is significantly reduced in the presence of an external magnetic field. Temperature-dependent behavior is primarily governed by Raman relaxation. Through structural analysis of compound 1 and a series of pure nitrogen-coordinated single-ion magnets (SIMs), we propose that the oxo substituents from the double-deprotonated form of the 2,2'-bipyridine-6,6'-diol ligands donate their negative charge to the pyridine ring, forming amido anion sites. This triggers a more pronounced out-of-phase signal than that observed in pure pyridine-coordinated compounds. Moreover, we observed intermolecular interactions, including intermolecular hydrogen bonding, which, to some extent, influenced the slow relaxation of molecules. Therefore, we speculate that the slow relaxation phenomenon of compound 1 may be attributed to the combination of oxo back-donating effects and intermolecular interactions.

Liquid Phase Exfoliation of Few-Layer Non-Van der Waals Chromium Sulfide.

Exfoliation of 2D non-Van der Waals (non-vdW) semiconductor nanoplates (NPs) from inorganic analogs presents many challenges ahead for further exploring of their advanced applications on account of the strong bonding energies. In this study, the exfoliation of ultrathin 2D non-vdW chromium sulfide (2D Cr2S3) by means of a combined facile liquid-phase exfoliation (LPE) method is successfully demonstrated. The morphology and structure of the 2D Cr2S3 material are systematically examined. Magnetic studies show an obvious temperature-dependent uncompensated antiferromagnetic behavior of 2D Cr2S3. The material is further loaded on TiO2 nanorod arrays to form an S-scheme heterojunction. Experimental measurements and density functional theory (DFT) calculations confirm that the formed TiO2@Cr2S3 S-scheme heterojunction facilitates the separation and transmission of photo-induced electron/hole pairs, resulting in a significantly enhanced photocatalytic activity in the visible region.

Characterization of Temperature-Dependent Behavior in Hot Rolled EN8 Steel

Characterization of Temperature-Dependent Behavior in Hot Rolled EN8 Steel