Temperature-dependent Characterization Research Articles

Temperature-Dependent Characterization of Long-Range Conduction in Conductive Protein Fibers of Cable Bacteria.

Multicellular cable bacteria display an exceptional form of biological conduction, channeling electric currents across centimeter distances through a regular network of protein fibers embedded in the cell envelope. The fiber conductivity is among the highest recorded for biomaterials, but the underlying mechanism of electron transport remains elusive. Here, we performed detailed characterization of the conductance from room temperature down to liquid helium temperature to attain insight into the mechanism of long-range conduction. A consistent behavior is seen within and across individual filaments. The conductance near room temperature reveals thermally activated behavior, yet with a low activation energy. At cryogenic temperatures, the conductance at moderate electric fields becomes virtually independent of temperature, suggesting that quantum vibrations couple to the charge transport through nuclear tunneling. Our data support an incoherent multistep hopping model within parallel conduction channels with a low activation energy and high transfer efficiency between hopping sites. This model explains the capacity of cable bacteria to transport electrons across centimeter-scale distances, thus illustrating how electric currents can be guided through extremely long supramolecular protein structures.

Pressure-induced band gap enhancement and temperature-dependent thermoelectric characterization of semiconducting Transition Metal Chalcogenides LiMS (M = Cu, Ag)

The first principles study of Transition Metal Chalcogenides LiMS (M = Cu, Ag) has been conducted utilizing the concepts of Density Functional Theory (DFT). Both the compounds possess a cubic structure with space group F-43m. The mechanical stability of LiCuS and LiAgS has been predicted based on the values of elastic tensor. These Chalcogenides possess an interesting electronic band structure which reveals their semiconducting nature with a direct band gap. The electronic structure is further subjected to high pressure and the changes in band gap are deeply observed. For these materials, the changes in band gap in response to applied pressure suggest the possibility of their use in band gap engineering. The phonon curves are investigated over the Brillouin zone's high symmetry directions which reveal the lattice dynamical stability of the presently studied compounds. Moreover, the atoms present at different positions inside a crystal lattice exhibit vibrations of different intensities and in different directions which have been studied through the Eigenvector representations. The thermoelectric properties of LiCuS and LiAgS have been characterized using Boltzmann's theory over the range of temperature between 100 K and 1600 K. The calculated thermoelectric parameters reveal the high thermoelectric efficiency of these materials with excellent values of the figure of merit. The interesting properties of ternary Chalcogenides LiMS (M = Cu, Ag) make them promising candidates for thermoelectric applications.

Temperature-driven spin reorientation transition in van der Waals Cr1.7Te2 ferromagnet

The phenomenon of spin reorientation transition in magnetic materials is truly captivating, as it involves a fascinating change in the direction of magnetic moments. However, the research on spin reorientation transition in two-dimensional (2D) magnetic materials has received limited attention, thus hindering its immense potential for significant advancements in various device applications. In this study, we present a discovery of a spin reorientation transition from an in-plane to an out-of-plane direction in the van der Waals ferromagnet Cr1.7Te2 (Tc = 300 K). This transition occurs at 70 K when the temperature ranges from 3 to 300 K, which is evidenced by the temperature-dependent Hall effect and magnetic anisotropy energy measurements. Notably, the anisotropic evolution observed reveals that the shape anisotropy effect surpasses the magnetocrystalline anisotropy in van der Waals ferromagnet at low temperatures, which is distinct from reported ferromagnetic materials. Furthermore, temperature-dependent x-ray diffraction characterizations confirm that no structural phase transition occurs during this intriguing spin reorientation transition process. These findings establish a strong and solid foundation, offering a promising platform for the design and development of cutting-edge 2D spintronic devices.

Temperature-dependent characterization of full tensor properties of [111]c poled Mn-doped 28PIN-43PMN-29PT single crystals

The temperature-dependent characterization of full tensor properties of single-domain relaxor-based single crystals (SCs) is important for understanding the influence of temperature on the properties of their multidomain SCs. However, no relevant results have been published because characterization is difficult to achieve using the traditional electric resonance method. In this Letter, the temperature-dependent elastic and piezoelectric properties of single-domain [111]c poled Mn-doped 28Pb(In1/2Nb1/2)O3-43Pb(Mg1/3Nb2/3)O3-29PbTiO3 SCs were investigated in the range of 20–80 °C by resonant ultrasound spectroscopy (RUS) using a rectangular parallelepiped sample. The temperature-dependent dielectric constants were calculated from the measured capacitances of the sample. The results are self-consistent because they were obtained from the same sample. The elastic constants obtained using the ultrasonic pulse-echo method agree closely with those obtained using RUS. Moreover, the experimental results of electric impedance spectrum agree closely with those simulated using the material constants characterized herein, indicating that the characterization is reliable.

LiGdxY1−xF4 and LiGdF4:Eu3+ Microparticles as Potential Materials for Optical Temperature Sensing

In this work, the physical characterization of LiGdxY1−xF4 (x = 0.05, 0.3, 0.7, and 1.0) and LiGdF4:Eu3+ microparticles was performed. The distribution coefficient of LiGdxY1−xF4 (x = 0.05) was determined for the first time (0.84). Based on kinetic characterization data, the LiGdF4 sample was chosen for further Eu3+ doping (0.1 and 1.0 at.%). For the LiGdF4:Eu3+ sample, Eu3+ emission was clearly observed under the excitation of Gd3+. This fact indicates an effective energy transfer from Gd3+ to Eu3+. The temperature-dependent spectral characterization of the LiGdF4:Eu3+ (1.0%) sample revealed that in the 30–250 K temperature range, a broad emission peak is evidenced. Its intensity sharply increases with the temperature decrease. We made a suggestion that this phenomenon is related to the irradiation-induced defects. The integrated luminescence intensity ratio of this broad peak and the Eu3+ emission were taken as temperature-dependent parameters. The sensitivity values are very competitive, and the first maximum occurs at 174 K (3.18%/K). The kinetic characteristics of both Gd3+ and Eu3+ did not demonstrate a notable temperature dependence. The LiGdF4:Eu3+ sample showed the possibility of being used as an optical temperature sensor, operating in the cryogenic temperature range.

Sputtering-grown undoped GeSn/Ge multiple quantum wells on n-Ge for low-cost visible/shortwave infrared dual-band photodetection

Multispectral photodetectors (PDs) operating in visible (VIS) to shortwave infrared (SWIR) wavelength ranges are highly desired for various civil and military applications. Traditional vertical p-i-n SWIR PDs lack the detection ability for VIS light due to photon dissipation in the neutral regions. Herein, an i-n type PD was proposed and demonstrated with sputtering-grown undoped Ge0.92Sn0.08/Ge multiple quantum wells (MQWs) on n-Ge substrate to realize VIS/SWIR dual-band detection from 400 to 2000 nm. Three response peaks resulted from the resonate cavity effect at 430, 660 and 1530 nm, respectively, were observed. Benefiting from the defect-free coherent GeSn/Ge MQWs and low-temperature surface plasma treatment, a remarkably low bulk leakage current density of 5.9 mA/cm2 and a low surface leakage current of 37.5 μA/cm were achieved at room temperature under −1 V, resulting in an ultralow dark current density of 13.36 mA/cm2 for a 200-μm-diameter PD. Temperature-dependent electrical characterizations revealed that the dark current was ideally dominated by carrier diffusion mechanism. Eminent detectivities of 5.2 × 108, 7.1 × 108 and 5.6 × 109 Jones at 410, 660 and 1530 nm, respectively, under −1 V were achieved simultaneously at room temperature. This work provides a path way for fabricating low-cost, VIS/SWIR dual-band PDs with complementary metal–oxide–semiconductor (CMOS) compatible technology.

Fe-substituted SrCoO3 perovskites as electrode materials for wide temperature-tolerant supercapacitors

Sr-based perovskites represent enormous potential as supercapacitor electrode materials. However, the wide-temperature supercapacitor application for perovskite-based electrodes has not been studied yet. Thus, there is a pressing need for comprehensive research and investigation in the wide-temperature range to unlock the full capabilities of Sr-based perovskite and pave the way for its successful integration into versatile supercapacitor systems. In this study, SrCo1-xFexO3-δ (x = 0.05, 0.10, 0.15 and 0.20) were synthesized by solid-state sintering method, as oxygen-intercalated electrode materials for wide temperature-tolerant supercapacitors. SrCo1-xFexO3-δ contains orthogonal and monoclinic phases for x = 0.05 and x = 0.10, and a stable monoclinic phase can be obtained when the substitution amount is at least 15 %. The best electrochemical performance was obtained in x = 0.10, with a specific capacitance of 526.6 F g−1 at 1 A g−1. This can be attributed to the lowest resistance and richest oxygen vacancies of SrCo0.9Fe0.1O3-δ, which are conducive to oxygen-intercalated energy storage. The SrCo0.9Fe0.1O3-δ@CC//AC@CC supercapacitor device displays a working voltage of 1.6 V and a stable long-term cycle life with 85.71 % capacity retention after 5000 cycles. Furthermore, the temperature-dependent electrochemical characterization indicates an improvement of electrochemical performance for both electrode and device as temperature increases, which may be ascribed to the enhanced ion migration in the electrolyte. From 0 to 85 °C, the specific capacitance of SrCo0.9Fe0.1O3-δ@CC electrode increases from 91.8 to 1035.9 F g−1 at 1A g−1, and the energy density of the device also increases from 7.6 to 26.2 Wh kg−1 when the power density is 800 W kg−1.

Probing the photocurrent in two-dimensional titanium disulfide

Generating photocurrent in a condensed matter system involves the excitation, relaxation, and transportation of charge carriers. As such, it is viewed a potent method for probing the dynamics of non-equilibrium carriers and the electronic band structure of solid state materials. In this research, we analyze the photoresponse of the mechanically exfoliated titanium disulfide (TiS2), a transition metal dichalcogenide whose classification as either a semimetal or a semiconductor has been the subject of debate for years. The scanning photocurrent microscopy and the temperature-dependent photoresponse characterization expose the appearance of a photovoltaic current primarily from the metal/TiS2 junction in an unbiased sample, while negative photoconductivity due to the bolometric effect is observed in the conductive TiS2 channel. The optoelectronic experimental results, combined with electrical transport characterization and angle-resolved photoemission spectroscopy measurements, indicate that the TiS2 employed in this study is likely a heavily-doped semiconductor. Our findings unveil the photocurrent generation mechanism of two dimensional TiS2, highlighting its prospective optoelectronic applications in the future.

Strain, Young’s modulus, and structural transition of EuTiO3 thin films probed by micro-mechanical methods

EuTiO3 (ETO) is a well-known complex oxide mainly investigated for its magnetic properties and its incipient ferro-electricity. In this work, we demonstrate the realization of suspended micro-mechanical structures, such as cantilevers and micro-bridges, from 100 nm-thick single-crystal epitaxial ETO films deposited on top of SrTiO3(100) substrates. By combining profile analysis and resonance frequency measurements of these devices, we obtain the Young’s modulus, strain, and strain gradients of the ETO thin films. Moreover, we investigate the ETO anti-ferro-distortive transition by temperature-dependent characterizations, which show a non-monotonic and hysteretic mechanical response. The comparison between experimental and literature data allows us to weight the contribution from thermal expansion and softening to the tuning slope, while a full understanding of the origin of such a wide hysteresis is still missing. We also discuss the influence of oxygen vacancies on the reported mechanical properties by comparing stoichiometric and oxygen-deficient samples.

Electrical Transport Characteristics of Vertical GaN Schottky-Barrier Diode in Reverse Bias and Its Numerical Simulation

We investigated the temperature-dependent reverse characteristics (JR-VR-T) of vertical GaN Schottky-barrier diodes with and without a fluorine-implanted edge termination (ET). To understand the device leakage mechanism, temperature-dependent characterizations were performed, and the observed reverse current was modeled through technology computer-aided design. Different levels of current were observed in both forward and reverse biases for the ET and non-ET devices, which suggested a change in the conduction mechanism for the observed leakages. The measured JR-VR-T characteristics of the non-edge-terminated device were successfully fitted in the entire temperature range with the phonon-assisted tunneling model, whereas for the edge-terminated device, the reverse characteristics were modeled by taking into account the emission of trapped electrons at a high temperature and field caused by Poole–Frenkel emission.

Temperature-Dependent Optical Behaviors and Demonstration of Carrier Localization in Polar and Semipolar AlGaN Multiple Quantum Wells

Semipolar AlGaN multiple quantum wells (MQWs) have unique advantages in deep ultraviolet light emitters due to the weak Quantum-Confined Stark Effect. However, their applications are hampered by the poor crystalline quality of semipolar AlGaN thin films. Different treatments were developed to improve the crystal quality of semipolar AlGaN, including a multistep in situ thermal annealing technique proposed by our group. In this work, temperature-dependent and time-resolved photoluminescence characterizations were performed to reveal the carrier localization in the MQW region. The degree of carrier localization in semipolar AlGaN MQWs grown on top of the in situ-annealed AlN is similar to that of conventional ex situ face-to-face annealing, both of which are significantly stronger than that of the c-plane counterpart. Moreover, MQWs on in situ-annealed AlN show drastically reduced dislocation densities, demonstrating its great potential for the future development of high-efficiency optoelectronic devices.

Temperature-Dependent Sheet Resistance and Surface Characterization of Thin Copper Films Bonded to FR4 Composite under Mechanical Vibrations

Electrical boards, also called printed circuit boards, constitute the basis of most electronic devices. These boards are mainly fabricated of thin copper films bonded to fiber epoxy laminates, such as FR4. Being the most important functional component of these devices, they sometimes undergo mechanical stresses such as shock and vibration during transport and operation that can induce electrical failure and malfunction; hence, studies addressing the effects of vibrations on their electrical properties have important applications. In this paper, small cantilever samples made of bare copper bonded to FR4 with three isolated rectangular zones were studied to analyze, for the first time, variations in electrical properties such as sheet resistance and resistivity before and after 200 k, 500 k, and 800 k vibration cycles at three different temperatures (25, 35, and 45 °C). A significant rise in resistance equivalent to 1657% of the initial value was observed from 0 to 800 k vibration cycles. These changes were accompanied by a 95% decrease in conductivity, from 4.1 × 107 to 2.3 × 106 S/m, whereas very little change in the electrical properties was observed due to temperature rise. Surface analysis by ESEM showed cracks ~1 µm in width and several millimeters in length with a crack density of ~8 cracks per mm after 800 k cycles. The surface composition (100% copper) was not altered even upon a high number of vibration cycles, and static drop contact angle measurements of 117–119 degrees indicated an increase in the hydrophobicity of the surface attributed to increased surface roughness and the accumulation of very small air bubbles on the cracks.

Harvesting strong photoluminescence of physical vapor deposited GeSn with record high deposition temperature

In this work, strong photoluminescence (PL) from physical vapor deposited GeSn on Ge-buffered Si is harvested by pursuing high deposition temperature. High-quality Ge0.938Sn0.062 films are obtained through sputtering epitaxy at a record high temperature of 405 °C. The PL peak intensity of the sputtering-grown GeSn is enhanced by 21 times compared to that of GeSn with similar Sn content grown by molecular beam epitaxy at 150 °C. The PL intensity ratio between the sputtering-grown GeSn and Ge virtual substrate reaches a value of 18. Power-dependent and temperature-dependent PL characterizations demonstrate that band-to-band recombination dominates in the sputtering-grown GeSn film. The results indicate that high-temperature sputtering epitaxy, which has the merit of low cost and high-productivity potential, is promising for preparing high-quality GeSn films for optoelectronic applications.

Low-temperature reliability enhancement of system-in-package with silicon-based resistors and its electrothermal analysis

System-in-Package (SiP) is one of the mainstream developments of the integrated circuit industry, whose instability in low-temperature environments restricts its evolution and application. In this study, we propose a reinforcement scheme using silicon-based resistors to overcome the electric reliability issue of SiP under temperatures ranging from −70 °C to −50 °C. By arranging resistors around the SiP substrate to act as thermal engines and controlling their time-varying excitation voltages, the SiP's temperature can be stabilized under different backgrounds, resulting in stable performance that is insensitive to temperature variations. To assess the proposed design precisely, we improve the electrothermal simulation by incorporating the temperature-dependent material characterizations and iteratively calculating the heat transfer coefficient, thereby elevating the accuracy of this multi-physics method. Our three-dimensional simulation and experiment results validate the reliability enhancement of the design and the efficacy of the simulation improvement.

Unraveling the Site-Selective Doping Mechanism in Single-Crystalline BiVO4 Thin Films for Photoelectrochemical Water Splitting

Doping with extrinsic elements in bismuth vanadate (BiVO4, BVO) has been widely exploited for boosting photoelectrochemical (PEC) water splitting. However, changes in the carrier transport behavior of doping, in particular for the Bi-site doping in BVO, are still not well understood. Here, we explore the im pact of site-selective doping on structural variation and electron transport in BVO as well as its implication for designing photoanodes with improved photoelectrochemical (PEC) performance. Two types of single-crystalline doped BVO films, with the V site substituted with Mo (MoV) ions or the Bi site substituted with Gd ions (GdBi), are prepared by pulsed-laser deposition. Compared to pristine BVO, both types of doped photoanodes are found to require thinner films for delivering larger photocurrents, but the underlying doping mechanism appears to be different. Combined with temperature-dependent Raman characterization, X-ray photoelectron microscopy, and solid-state electron transport measurements, it is suggested that GdBi doping facilitates carrier transport by introducing structural distortion and a gentle increase in the oxygen vacancy concentration. This is in contrast to MoV doping, which substantially enhances the donor density and facilitates carrier hopping. This work provides a perspective on understanding the impact of site-selective doping on BVO photoanodes for efficient PEC water splitting.

Predicting the Temperature-Dependent Tensile properties of Polyphenylsulfone using a Machine learning approach

After 200 years of their birth, synthetic polymers are present in over 60 primary forms. Many are largely known and spread, others less common and investigated, such as Polyphenylsulfone (PPSU) which, on the contrary, offers multiple applications. Among them, in particular, many concerns the use of the PPSU at (cold or hot) temperature. But experiments with its temperature-dependent characterization are very few and limited to specific formulations. Machine learning algorithms can fill the gap providing accurate predictions. Specifically, an unsupervised classification was here used for clustering material data with the scope to recognize patterns between PPSU up to the selection of similarities respect to a polymer as reference. Then, a supervised regression was used to predict temperature-dependent tensile properties. A high level of accuracy was achieved, up to 99% in terms of coefficient of determination. This is probably the first time that data regarding the mechanical behavior of PPSU were derived from an approach based on artificial intelligence and machine learning.

Probing electron-phonon and phonon-phonon coupling in type-II Dirac semi-metal NiTe2 via temperature-dependent Raman spectroscopy

We report the temperature-dependent structural characterization of type-II Dirac semimetal NiTe2 in the form of a bulk single crystal and a nanoflake (200 nm thick). Detailed x-ray diffraction study along with Rietveld refinement analysis reveals superior crystallinity and linear thermal expansion coefficient (α T ) of 5.56 × 10−6 and 22.5 × 10−6 K−1 along a or b and c lattice directions, respectively. Temperature evolution of Raman spectra shows non-linear variations in the phonon frequency and full-width half maxima of the out-of-plane A and in-plane E g modes. Raman mode E, corresponding to an in-plane vibration, disappears on decreasing the thickness from bulk to nanoflake. Quantitative analysis with anharmonic model yields dominating electron-phonon interaction over phonon-phonon interaction mediated by three- and four-phonon processes.

Noise Spectroscopy: A Tool to Understand the Physics of Solar Cells

Noise spectroscopy is essentially focused on the investigation of electric fluctuations produced by physical mechanisms intrinsic to conductor materials. Very complex electrical transport phenomena can be interpreted through the study of the fluctuation properties, which provide interesting information both from the point of view of basic research and of applications. In this respect, low-frequency electric noise analysis was proposed more than twenty years ago to determine the quality of solar cells and photovoltaic modules, and, more recently, for the reliability estimation of heterojunction solar cells. This spectroscopic tool is able to unravel specific aspects related to radiation damage. Moreover, it can be used for a detailed temperature-dependent electrical characterization of the charge carrier capture/emission and recombination kinetics. This gives the possibility to directly evaluate the system health state. Real-time monitoring of the intrinsic noise response is also very important for the identification of the microscopic sources of fluctuations and their dynamic processes. This allows for identifying possible strategies to improve efficiency and performance, especially for emerging photovoltaic devices. In this work are the reported results of detailed electrical transport and noise characterizations referring to three different types of solar cells (silicon-based, organic, and perovskite-based) and they are interpreted in terms of specific physical models.

In-situ synchrotron x-ray diffraction and thermal expansion of TiB2 up to ∼3050 °C

There is an increasing interest in understanding the performance and properties of ultra-high temperature ceramics due to their high melting points (<3000 °C) that make them promising for extreme environment applications. In-situ high temperature X-ray diffraction experiments were performed on TiB2 beads up to ∼3050 °C. For these experiments, TiB2 powders were fabricated into spherical beads via gel casting methods and densified in a high temperature graphite furnace. These sample beads were then levitated in a conical nozzle levitator with reducing atmosphere (3% H2 -Ar) while being heated using a 400 W CO2 laser. During levitation a collimated synchrotron X-ray source was used to perform in-situ, temperature-dependent structural characterizations. The anisotropic coefficients of thermal expansion of TiB2 were characterized as a function of temperature up to ∼3050 °C. Elucidation of these properties are critical for the advancement of TiB2 ceramics and other transition metal di-borides for use in high temperature applications such as hypersonic platforms, nuclear reactors, and atmospheric re-entry.

Exploiting the lower disorder-to-order temperature in polystyrene-b-poly(n-butyl acrylate)-b-polystyrene triblock copolymers to increase their flow resistance at high temperature

This work focuses on the temperature-dependent structural and rheological characterization of polystyrene-b-poly(n-butyl acrylate)-b-polystyrene triblock copolymers (PS-b-PnBA-b-PS) in the melt and, in particular, on their ability to show a lower disorder-to-order temperature (LDOT). To this aim, copolymers of varying block lengths, but keeping the PnBA block as a major component, were synthesized. Small-angle x-ray scattering revealed that the copolymers with short PS blocks (∼10 kg/mol) approach an LDOT but do not cross it. At room temperature, these copolymers exhibit higher moduli compared to a PnBA homopolymer due to the reinforcing effect of the PS but are flowing at temperatures above the glass transition of the PS. Increasing the PS and PnBA block length, to keep the same PS fraction, induces more profound changes in the structural and viscoelastic behaviors. Such a copolymer crosses the LDOT, leading to a microphase-separated and ordered state at high temperature. Contrary to the copolymers with short PS blocks, the flow regime was not reached, even at temperatures well above the glass transition of the PS. Instead, a low-frequency plateau was observed in rheology, showing the increased lifetime of the microphase-separated PS domains. ABA triblock copolymers exhibiting an LDOT behavior could, thus, be of interest for the design of thermoplastic elastomers or pressure-sensitive adhesives that can resist the flow at high temperatures.