Electrical Transport Properties Research Articles

First-principles study on thermal and electrical transport properties of NbGe2 and NbSi2: the role of electron-phonon coupling

Abstract We study coupled electron and phonon transport in NbX2 with X=Ge, Si, in which experimental evidence of strong electron-phonon coupling and hydrodynamic transport has been reported. Based on first-principles calculations at the density functional theory level, we report their thermal and electrical transport properties. We find that phonon-electron scattering strongly affects their phonon thermal conductivity (κ ph) and leads to weak temperature dependence of κ ph, instead of normal inverse temperature dependence when anharmonic three phonon scattering dominates. Moreover, κ ph contributes to quarter of the total thermal conductivity, which differs from typical metals where total thermal conductivity is predominantly from electron part. Different from previous numerical study, our results of electrical resistivity agree well with experimental measurement. The anisotropic property of the transport coeffcients is attributed to the electron and phonon dispersion relation. Moreover, we find negligible effect of electron-phonon drag on the transport property, contrary to expectation from a strongly coupled electron-phonon fluid.

Azaindole: A Candidate Anchor for Regulating Charge Polarity and Inducing Resonance Transmission at the Fermi Level via Dehydrogenation.

Tuning the polarity of charge carriers is essential for designing molecular logic devices in molecular electronics. In this study, the electrical transport properties of a family of azaindole-anchored single-molecule junctions have been investigated using density functional theory combined with the nonequilibrium Green's function method. The obtained results reveal that dehydrogenation is an effective method for reversing the polarity of charge carriers. The molecular junctions based on the entire azaindole unit are n-type and contain electrons as the principal charge carriers, whereas the dehydrogenated junctions are p-type and contain holes as the main carriers. Furthermore, the azaindole anchors undergo a transition from an electron-rich to an electron-deficient state due to dehydrogenation, which is the original cause of the charge carrier polarity conversion. Dehydrogenated molecular junctions also exhibit the Fermi pinning effect and a sharp highest occupied molecular orbital (HOMO) resonance peak at the Fermi level. In addition, using Pt electrodes instead of Au electrodes is a means of producing a HOMO resonance peak a for azaindole-based molecular junctions. This work demonstrates the enormous potential of utilizing azaindole-anchored molecular junctions for the implementation of molecular logic and multifunctional molecular devices.

Large photoresistance and photoinduced magnetoresistance in La0.67Ca0.33MnO3 thin film on silicon substrate

Abstract The effects of light illumination and magnetic field on the electrical transport properties of La0.67Ca0.33MnO3 thin film on a silicon substrate have been studied in detail. Large value of colossal magnetoresistance has been observed under an applied magnetic field in the whole temperature range below 150 K which is related to the presence of both antiferromagnetic and ferromagnetic phase in the sample. A significant amount of resistance drop is caused by light illumination even at extremely low light intensities, ∼−22% with light of 0.3 μW cm−2 intensity and ∼−42% with 6.2 μW cm−2 intensity at 600 nm wavelength. There has been a notable rise in the photoinduced magnetoresistance value, specifically, a significant decrease in resistance occurs in simultaneous presence of magnetic field and light. For 1 T applied magnetic field, MR% rises from −33% in dark to −58% under light illumination at 150 K i.e. ΔMR% is 25%. As the strength of the magnetic field increases, ΔMR% decreases, suggesting that the magnetoresistive photoinduced phenomenon is more pronounced in the presence of mix phases in the sample. This combined enhanced magnetoresistive photoinduced phenomenon is explained by the interaction of photogenerated charge carriers in the sample and applied magnetic field.

Thickness-dependent nanoscale friction across the first-order charge density wave phase transition in 1T-TaS2

The layered charge density wave (CDW) phase transition material 1T-TaS2 has garnered significant attention due to its modulable bandgap and electrical transport properties. These unique properties make 1T-TaS2 highly promising for applications in fields such as optoelectronic devices and microstructure physics devices. In various micro-/nanodevices made from quasi-two-dimensional 1T-TaS2, it is often utilized in thin layers, making the understanding of its frictional properties crucial for practical applications. However, the layer-dependent frictional properties of 1T-TaS2 have not been thoroughly investigated. In this article, we examine the CDW phase transition between the nearly commensurate (NCCDW) and commensurate (CCDW) phases in 1T-TaS2 around 183 K using atomic force microscopy, focusing on the number of layers in the samples. Our results indicate that for thicker samples with more than approximately 17 layers, a friction peak is observed during the NCCDW–CCDW phase transition. In contrast, thinner samples do not exhibit this friction peak, and their friction continuously increases as the temperature decreases. This behavior is attributed to the suppressed NCCDW–CCDW phase transition in thinner samples. These results enhance our understanding of the frictional behavior of 1T-TaS2 in the context of micro-/nano-electromechanical systems. Furthermore, our observations offer a straightforward method to identify the NCCDW–CCDW phase transition, providing an alternative to traditional, more complex techniques such as electrical resistance measurements and Raman spectroscopy.

Carrier localization induced by electron-electron interaction and its impact on the electrical transport and magnetic properties of nonstoichiometric IrMnSn

Carrier localization induced by electron-electron interaction and its impact on the electrical transport and magnetic properties of nonstoichiometric IrMnSn

Realizing synergistic optimization of electrical and thermal transport properties in BiCuSeO ceramics via multi-element doping

In this study, the design of high-entropy alloys (multi-element substitution, Al3+/La3+/Sb3+/Y3+) was used to increase material entropy and improve heat scattering to further reduce thermal conductivity. Concurrently, Ca2+ ion hole doping was used to improve its electrical conductivity. Therefore, a series of Bi0.92−xAl0.02La0.02Sb0.02Y0.02CaxCuSeO (x = 0, 0.02, 0.06, 0.10, and 0.14) ceramics was prepared using a combination of high-energy ball milling and cold isostatic pressing. The multi-element substitution of Al0.02La0.02Sb0.02Y0.02Ca0.02 in the Bi site resulted in a minimum thermal conductivity of 0.35 Wm−1K−1, which is one-third of that of intrinsic BiCuSeO. Simultaneously, the conductivity increased up to 10–20 times that of intrinsic BiCuSeO, proportional to the amount of Ca2+ doping. Furthermore, the optimum component Bi0.82Al0.02La0.02Sb0.02Y0.02Ca0.10CuSeO exhibited an extremely high power factor of 568.55 μWm−1K−2 at 773 K, significantly higher than that of pure BiCuSeO (148.7 μWm−1K−2). Consequently, a peak ZT value of approximately 1.12 was achieved at 773 K, which was 4.48 times higher than that of the pristine BiCuSeO specimen (approximately 0.25). Our findings provide a novel strategy to optimize the thermoelectric properties of BiCuSeO and other materials.

Ultrahigh Concentration Hydrogen Doping into TiO2.

We investigate ultrahigh concentration doping of hydrogen (H) into rutile-TiO2 (100) single crystals by low-energy (2.5 keV) hydrogen ion beam irradiation at low temperature (LT). While the hydrogen concentration was limited to H0.3TiO2 at 300 K, in situ nuclear reaction analysis (NRA) revealed ultrahigh concentration doping of hydrogen up to H1.2TiO2 by the LT irradiation at 50 K. The large (∼8.2%) expansion of the out-of-plane lattice constant suggests that hydrogen occupies interstitial sites in rutile TiO2. Hydrogens of early stage irradiation act as electron donors and induce a large increase in conductivity, which is consistent with theoretical studies in the dilute limit. The nature of excess H was investigated in situ by transport and photoemission measurements. After LT excess H doping and postannealing to room temperature, unusual electrical transport properties were observed while maintaining the ultrahigh H concentration. In situ photoemission measurements show that the excessively doped hydrogens by LT irradiation generate a deeper in-gap state (IGS) of metastable nature. Density functional theory predicts the formation of double neighboring interstitial hydrogens as a possible mechanism for the deeper IGS.

Self-assembly monolayer impact on Schottky diode electrical properties

This study examines the electrical and charge transport properties of p-Si/TiO2/self-assembly monolayer (SAM)/Al type Schottky diodes. The diodes were fabricated by applying the SAM molecule 4′-[(3-methylphenyl)(phenyl)amino]biphenyl-4-carboxylic acid (CT21) onto titanium dioxide (TiO2) synthesized via the sol-gel method. The key parameters, including the ideality factor (n), series resistance (Rs), and barrier height (∅b), were used to assess the impact of CT21 on diode performance. Experimental results revealed that using CT21 at the TiO2/Al interface significantly enhances diode performance. The n decreased from 3.8 in the control diode to 1.9 with CT21. Rs was substantially reduced, and the ∅b increased. The rectification ratio improved from 1x104 in the control diode to 1.1x105 in the CT21-modified diode. These enhancements, due to the CT21 molecule's ability to reduce interface states (Nss) and improve surface properties, underscore the potential of SAM coatings to open a new window in nanoelectronics with better performance and reliability.

Optimization of Thermoelectric Performance of Ag2Te Films via a Co-Sputtering Method.

Providing self-powered energy for wearable electronic devices is currently an important research direction in the field of thermoelectric (TE) thin films. In this study, a simple dual-source magnetron sputtering method was used to prepare Ag2Te thin films, which exhibit good TE properties at room temperature, and the growth temperature and subsequent annealing process were optimized to obtain high-quality films. The experimental results show that films grown at a substrate temperature of 280 °C exhibit a high power factor (PF) of ~3.95 μW/cm·K2 at room temperature, which is further improved to 4.79 μW/cm·K2 after optimal annealing treatment, and a highest PF of ~7.85 μW/cm·K2 was observed at 200 °C. Appropriate annealing temperature effectively increases the carrier mobility of the Ag2Te films and adjusts the Ag/Te ratio to make the composition closer to the stoichiometric ratio, thus promoting the enhancement of electrical transport properties. A TE device with five legs was assembled using as-fabricated Ag2Te thin films. With a temperature difference of 40 K, the device was able to generate an output voltage of approximately 14.43 mV and a corresponding power of about 50.52 nW. This work not only prepared a high-performance Ag2Te film but also demonstrated its application prospects in the field of self-powered electronic devices.

Exploration of electrical conduction mechanisms via modulating sintering period of La0.67Ca0.33MnO3 films in various phase regions

Perovskite manganese oxide films have garnered significant attention due to their unique and diverse physical properties. In this work, La0.67Ca0.33MnO3 (LCMO) films are prepared on LaAlO3 (00l) substrates using the sol−gel spin coating method with varying sintering period (Ps). By optimizing Ps, improvements were observed in the films’ structure, morphology, ionic valence, and temperature−dependent resistivity. The reduction in Mn−O bond length and the increase in Mn−O−Mn bond angle change the degree of MnO6 distortion, resulting in an increased eg bandwidth. As Ps increased, the LCMO films exhibited better crystalline quality. The improved Mn4+/Mn3+ ratio strengthened the double exchange effect, facilitating the carrier hopping of the eg electrons. Analyses of various electrical conduction mechanisms showed that optimized electron scattering behavior, reduced hopping distance, energy and theoretical Curie temperature collectively enhance the temperature coefficient of resistivity (TCR) of LCMO films under optimal Ps. The TCR of the LCMO films reached a maximum value (31.64 % K−1) at Ps = 18 min. These findings offer valuable insights into the main electrical conduction mechanisms in both metallic and semiconducting phases, providing a deeper understanding of the underlying physical processes and offering experimental guidance for optimizing the electrical transport properties of perovskite films.

Enhancing the Thermoelectric Performance of n-Type Mg3.2Sb1.5Bi0.5 by Reducing Lattice Thermal Conductivity through the Incorporation of Chlorine-Containing Compounds.

Mg3Sb2-based thermoelectric materials are characterized by their economic efficiency, nontoxicity, and environmental friendliness and represent a highly promising and eco-friendly functional material for midtemperature applications. To achieve a higher thermoelectric performance, we introduced two compounds, LaCl3 and CeCl3, into Mg3.2Sb1.5Bi0.5 under the guidance of first-principles calculations. The Mg3.2Sb1.5Bi0.5 + 0.03CeCl3 sample reached a maximum ZT value of approximately 1.6 at 723 K. The calculations indicate that two n-type dopants, LaCl3 and CeCl3, can adequately improve the band structure of Mg3Sb2, and the introduction of Cl atoms will also lead to lattice distortion and reduce the lattice thermal conductivity (κL). Experimental results demonstrate that the introduction of Cl atoms efficiently reduces the thermal conductivity while improving the electrical transport properties. Specifically, the Mg3.2Sb1.5Bi0.5 + 0.03CeCl3 sample achieved an exceptionally low κL of 0.3 W m-1 K-1 at 723 K, thereby validating the effectiveness of LaCl3 and CeCl3 doping. This work provides valuable insights into achieving thermoelectric decoupling in Mg3Sb2-based thermoelectric materials.

Enhanced Thermoelectric Performance of SnTe via Introducing Resonant Levels

SnTe has emerged as a non-toxic and environmentally friendly alternative to the high-performance thermoelectric material PbTe, attracting significant interest in sustainable energy applications. In our previous work, we successfully synthesized high-quality SnTe with reduced thermal conductivity under high-pressure conditions. Building on this, in this work, we introduced indium (In) doping to further decrease thermal conductivity under high pressure. By incorporating resonance doping into the SnTe matrix, we aimed to enhance the electrical transport properties while maintaining low thermal conductivity. This approach enhances the Seebeck coefficient to an impressive 153 μVK−1 at 735 K, marking a notable enhancement compared to undoped SnTe. Furthermore, we noted a substantial decrease in total thermal conductivity, dropping from 6.91 to 3.88 Wm−1K−1 at 325 K, primarily due to the reduction in electrical conductivity. The synergistic impact of decreased thermal conductivity and heightened Seebeck coefficient resulted in a notable improvement in the thermoelectric figure of merit (ZT) and average ZT, achieving approximately 0.5 and 0.22 in the doped samples, respectively. These advancements establish Sn1−xInxTe as a promising candidate to replace PbTe in thermoelectric applications, providing a safer and more environmentally sustainable option.

Forecast of electric transport property via two models

Temperature and synthesis condition-dependent resistivity are critical parameters for determining the electrical properties of materials. Modeling serves as a powerful tool for predicting the electrical transport characteristics of materials. The first objective of this work was to conduct a quantitative analysis of the reported metallic and insulating resistivity behaviors in double-phase materials. Using non-linear regression, both a phenomenological model and an Asym2sig asymmetric peak model were employed to quantitatively analyze the temperature-dependent resistivity. The fitting results align closely with the observed resistivity-temperature curves. The second objective of this work was to establish a method linking chemical composition (synthesis conditions) to the parameters derived from the two models, calculation on the principle of non-linear curve fitting, two numerical equations are highlighted for quantitatively analyzing chemical composition-dependent parameters. The observed effects of chemical composition on the shift in the temperature-resistive curve, which are fundamental to understanding resistivity behavior, are discussed quantitatively for the first time to our knowledge for resistive-temperature behavior. Hence, the resistivity of both crystalline and non-crystalline materials can be forecasted across various compositions and temperatures using the methods presented, even without experimental data.

Structure and properties of mixed valent CeFe2Al8

Temperature dependent magnetic, electrical transport and thermal properties of polycrystalline orthorhombic CeFe2Al8intermetallic compound have been studied along with its isostructural La counterpart, LaFe2Al8. For the cerium compound, low fielddcmagnetization exhibits an antiferromagnetic like ordering (TN) ∼ 4 K. The main feature of the magnetic susceptibility plot is a broad hump spanning a large temperature range, indicating mixed valence of Ce in the compound, in good agreement with reported literature. However, contrary to the reported observations we find that the mixed valence state is very robust and was evident even up to very high magnetic fields (> 2 T). Further, in this work we report 3d core level photoemission spectra of cerium in CeFe2Al8, to understand the valence state of cerium ions in this system. Additionally, from resistivity measurements it is found that, CeFe2Al8is metallic with no indication of any anomaly, till the lowest temperature of measurement. Specific heat measurements show very low value of heat capacity and electronic contribution. The isostructural La analogue, LaFe2Al8compound shows broadness in susceptibility with maxima around 44 K which may be attributed to ordering of Fe moments. The comparison of Ce and La compounds brings out the role of Fe magnetic moments which may be responsible for competing with cerium moments and resulting in the dilution of long-range magnetic order, also contributing to magnetic frustration in CeFe2Al8.

Synthesis and electrical transport properties of superconducting platinum silicide thin films and devices

We evaluate the material characteristics of superconducting platinum silicide (PtSi) thin films as candidate materials for superconducting quantum information devices compatible with silicon technology. These films were synthesized using magnetron sputtering under ultrahigh vacuum conditions, followed by rapid thermal annealing. Polycrystalline PtSi films synthesized by this method have the favorable properties of superconducting critical temperature of 0.95 K and relatively long zero-temperature Ginzburg-Landau coherence length of 76 nm. We further studied coplanar microbridge devices fabricated by electron beam lithography and chlorine-free reactive ion etching, finding that the temperature-dependent critical current density follows the Ginzburg Landau depairing mechanism.

Ultralow lattice thermal conductivity in K2AuBi and its thermoelectric properties

Thermoelectric materials are best known for their prowess to transform the environment’s waste heat into electricity. In an endeavor to explore new thermoelectric prospects, in the present study, we investigate K2AuBi using density functional theory-based first-principles simulations. From our simulations, we find an intrinsically low lattice thermal conductivity of 0.43 W m−1 K−1 at 300 K in K2AuBi. Based on our detailed analysis, we find the reasons for such a low value of lattice thermal conductivity as, low phonon group velocities, short phonon lifetimes, anharmonicity in the lattice vibrations, and significant mean square displacements of K and Au atoms. The large mean square displacements hint at weak bonding and anharmonicity in the lattice vibrations, favoring more phonons scattering. We also find that the vibrations of K-atoms can be related to rattlers, conducive to low lattice thermal conductivity. Our simulations predict a high value, ∼784 μV K−1, of Seebeck coefficient at 700 K on account of the large density of states in the vicinity of Fermi level. Combining our computed lattice thermal conductivity with electrical transport properties, we obtain a high figure of merit, ZT∼ 1.04, at 700 K in K2AuBi.

Electrical Transport Properties of PbS Quantum Dot/Graphene Heterostructures.

The integration of PbS quantum dots (QDs) with graphene represents a notable advancement in enhancing the optoelectronic properties of quantum-dot-based devices. This study investigated the electrical transport properties of PbS quantum dot (QD)/graphene heterostructures, leveraging the high carrier mobility of graphene. We fabricated QD/graphene/SiO2/Si heterostructures by synthesizing p-type monolayer graphene via chemical vapor deposition and spin-coating PbS QDs on the surface. Then, we used a low-temperature electrical transport measurement system to study the electrical transport properties of the heterostructure under different temperature, gate voltage, and light conditions and compared them with bare graphene samples. The results indicated that the QD/graphene samples exhibited higher resistance than graphene alone, with both resistances slightly increasing with temperature. The QD/graphene samples exhibited significant hole doping, with conductivity increasing from 0.0002 Ω-1 to 0.0007 Ω-1 under gate voltage modulation. As the temperature increased from 5 K to 300 K, hole mobility decreased from 1200 cm2V-1s-1 to 400 cm2V-1s-1 and electron mobility decreased from 800 cm2V-1s-1 to 200 cm2V-1s-1. Infrared illumination reduced resistance, thereby enhancing conductivity, with a resistance change of about 0.4%/mW at a gate voltage of 125 V, demonstrating the potential of these heterostructures for infrared photodetector applications. These findings offer significant insights into the charge transport mechanisms in low-dimensional materials, paving the way for high-performance optoelectronic devices.

Pressure-induced anomaly of transport properties and structural transition in layered ferromagnetic metal TlCo2S2

In this work, the structural and transport properties of ferromagnetic metal TlCo2S2 with ThCr2Si2-type crystal structure are systematically studied using high-pressure synchrotron x-ray powder diffraction, electrical transport measurements and first-principles calculations. All the resistances of TlCo2S2 between 1.4 GPa and 5.2 GPa exhibit an upturn at TS and an obvious hysteresis is observed below TS when measured in the cooling and heating processes. As the pressure increases, TS gradually increases and the resistances display a metallic behavior without any anomaly in the whole temperature region above 5.2 GPa, indicating that a possible structural phase transition occurs at TS and is beyond the room temperature above 5.2 GPa. High-pressure x-ray diffraction measurements combined with crystal structure prediction indicate that at room temperature TlCo2S2 undergoes a structural phase transition from a tetragonal phase (I4/mmm) to an orthorhombic structure (Bmab) at Pc ≈6.8 GPa, which is consistent with the results of the resistances under high pressure. Our results indicate that a first-order structural phase transition of TlCo2S2 is induced by high pressure and then results in the anomaly of the electrical transport properties.

Manipulating Charge-to-Spin conversion via insertion layer control at the interface of topological insulator and ferromagnet

Strong spin–orbit coupling and highly spin-polarized surface states in topological insulators (TIs) are key parameters that explain their extremely high charge-to-spin conversion (CSC) efficiency at interfaces with ferromagnetic materials (FMs). This study focused on the influence of the insertion layer on the proximity effect occurring in a Co4Fe4B2/Bi2Se3 interface. Various insertion layers, including Au, MgO, and Se, were introduced to modulate the proximity effect from TI to FM and vice versa. X-ray photoelectron spectroscopy and transmission electron microscopy revealed that the Se insertion layer effectively suppresses the formation of an additional Bi layer, reducing intermixing against Co4Fe4B2. Electrical transport properties such as RXX and RXY under a vertical magnetic field show that the Se-inserted structure features the lowest anomalous Hall angle and exhibits a pristine topological surface state, indicating its potential for improving CSC efficiency. The Se-inserted structure exhibits the highest spin Hall angle among various heterostructures, according to results obtained from spin-torque ferromagnetic resonance. These findings highlight the importance of selecting an insertion layer and controlling the interface to optimize the spin-transport properties of TI-based spintronic devices and provide insights into the design of future spin devices.

Structural and Electronic Phase Transitions in Three Stable Tin-Sulfur Metallic Chalcogenides under High Pressure.

As a representative homologous series, tin-bearing metallic chalcogenides (SnxSy) have sparked considerable attention because of their stoichiometric compositions and structural diversities. In this work, three stable compounds, SnS, Sn2S3, and SnS2, were screened from SnxSy and a comprehensive investigation on their structural and electrical transport properties was performed up to 60.1 GPa using a diamond anvil cell (DAC) under different hydrostatic environments. Upon nonhydrostatic compression, SnS underwent the Pnma-to-Cmcm transition accompanied by metallization at 7.6 GPa, followed by the Cmcm-to-Pm3̅m transformation at 17.8 GPa. For SnS2, the pressure-induced metallization and isostructural phase transition (IPT) occurred successively at 31.2 and 46.6 GPa, respectively. As an intermediate composition, Sn2S3 first experienced an IPT at 10.8 GPa, and then, the Pnma-to-Cmcm transition concomitantly with metallization occurred at 16.9 GPa, analogous to the high-pressure structural transformation routes of SnS and SnS2. The 0.6-5.4 GPa pressure hysteresis was detectable for the phase transitions of SnxSy under quasi-hydrostatic and hydrostatic conditions owing to the influence of deviatoric stress. In comprehensive consideration of our high-pressure Raman scattering and electrical conductivity results, the systematic construction of a pressure-phase state diagram on SnxSy not only unveils its composition-structure-property relation but also advances the in-depth exploration for other IVA-VIA metallic chalcogenides.