Temperature-dependent Resistivity Curves Research Articles

Strain and orientation modulated optoelectronic properties of La-doped SrSnO3 epitaxial films

We have studied the structural, electrical, and optical properties of La0.05Sr0.95SnO3 thin films, which exhibited a strong dependence upon the substrate’s orientation and strain. X-ray diffraction results show that the LSSO films grow epitaxially on (001) and (011)-oriented LaAlO3 substrates, and the in-plane compressive strain decreases gradually upon increasing film thickness. Room-temperature resistivity varies from 4.23 (13.0) to 1.37 (4.76) mΩ cm as the film thickness increases for (001) orientation ((011) orientation). Temperature dependent resistivity curves of all the samples show a metal–semiconductor transition (MST), which can be explained by the electron–electron interactions below MST rather than weak localization. Both reducing the in-plane compressive strain and transferring the orientation from (011) to (001) can drive the MST point shifts toward lower temperature, indicative of the enhancement of the metallic transport in the films. The band gap increases upon increasing film thickness due to Burstein-Moss effect. The charge distributions of Sn and O from density functional theory (DFT) calculations illustrate that (001)-plane has a better conductivity. Furthermore, our DFT results also demonstrate that decreasing the in-plane strain will lead to a smaller electron effective mass, thus the increased carrier mobility can be obtained. These comprehensive investigations advance our knowledge of the optoelectronic characteristics and provide valuable insights for future research in related transparent materials.

Enhancement of localized superconductivity in BaFe2As2 films via Co-ion implantation

In this study, we present a novel approach to localized superconductivity induction in BaFe2As2 films via targeted implantation of cobalt (Co) ions. Primarily, our study focuses on the systematic distribution of Co ions and the subsequent evolution of superconducting properties in Co-ion-implanted BaFe2As2 films. Our observations show that Co-ion distribution in the films is congruent with the results of analytical methodologies employed in the semiconductor industry, as confirmed via transmission electron microscopy imaging. The temperature-dependent resistivity curves reveal the concurrent presence of superconducting and non-superconducting regions. Moreover, the superconducting domain demonstrates the typical diamagnetic behavior intrinsic in superconductors. Importantly, Co-ion concentrations of ∼1020 cm−3 can be achieved by finely tuning the beam energy and ion dose. This concentration is instrumental in establishing an effective superconducting percolation pathway within the films.

Growth and characterization of the sputtered type-II topological semimetal PdTe2 thin films and PdTe2/Co60Fe20B20 heterostructures

The topological phases such as Dirac/Weyl semimetals are recently observed in Layered transition metal dichalcogenides (TMDs). The family of materials XTe2 (with X = Pd, Pt and Ni) possesses a type-II topological semimetal (TSM) phase. Here, we report the synthesis of the layered XTe2 thin films using the industry-friendly sputtering technique. The structural and morphological qualities of the sputtered-grown XTe2 thin films are analysed using X-ray diffraction and Raman measurements. The crystallites are highly oriented along the c-axis of the sapphire substrate, which suggests that growth is driven by van der Waals epitaxy. The magneto-transport measurements namely temperature-dependent resistivity and magnetoresistance measurement in out-of-plane field configuration are performed on PdTe2 thin films. The semi-metallic trend and superconducting transition are observed in the temperature-dependent resistivity curve. The weak antilocalization behavior observed in the magnetoconductance curves at a low magnetic field signifies the possibility of a non-zero Berry phase, possibly arising from the Dirac fermionic nature of electronic states. The spin dynamics measurements are performed on the PdTe2/Co60Fe20B20 bilayers. The effective spin mixing conductance and spin current density are found to be ∼2×1020m-2and 2.5MAm-2, respectively in PdTe2/Co60Fe20B20 bilayer which are quite larger than those observed in heavy metal-ferromagnets bilayers, and comparable to MBE-grown topological insulator-ferromagnets heterostructures. This work paves the way to synthesize Te-based layered TMDs using the industrially viable sputtering technique, and demonstrates the prospects for exploring the topological superconductive phase in PdTe2 films and large spin-charge conversion efficiency in PdTe2/Co60Fe20B20 heterostructures.

Magnetic and magnetotransport properties of layered TaCoTe2 single crystals

We present the synthesis of TaCoTe2 single crystals and a systematic investigation of the physical properties of bulk crystals and thin flakes. The crystal shows a semiconducting behavior with temperature decreasing from room temperature and turns to a metallic behavior below 38 K. When the magnetic field is applied, the temperature-dependent resistivity curves show an upturn below 10 K. Furthermore, we find that the TaCoTe2 single crystal can be easily exfoliated from the bulk crystal by the micromechanical exfoliation method. Our measurements suggest that the nanoflakes have properties similar to those of the bulk crystal when the thickness is lowered to 18 nm.

Preparation of PSFO and LPSFO nanofibers by electrospinning and their electronic transport and magnetic properties

Pr0.5Sr0.5FeO3 (PSFO) and La0.25Pr0.25Sr0.5FeO3 (LPSFO) nanofibers are prepared by electrospinning followed by calcination, and their morphologies, microstructures, electronic transports, and magnetic properties are studied systematically. The temperature-dependent resistance curves of PSFO and LPSFO nanofibers are measured in a temperature range from 300 K to 10 K. With the temperature lowering, the resistance increases gradually and then decreases sharply due to the occurrence of ferromagnetic metal phase. The metal–insulator transition temperatures are about 110 K and 180 K for PSFO and LPSFO nanofibers, respectively. The electronic conduction behavior above the transition temperature can be described by one-dimensional Mott’s variable-range hopping (VRH) model. The hysteresis loops and the field-cooled (FC) and zero-field-cooled (ZFC) curves show that both PSFO nanofiber and LPSFO nanofiber exhibit ferromagnetism. Although the doping of La reduces the overall magnetization intensity of the material, it increases the ferromagnetic ratio of the system, which may improve the performance of LPSFO in solid oxide fuel cell.

Significantly enhanced room-temperature TCR and MR of La0.67K0.33-xSrxMnO3 ceramics by adjusting Sr content

Strontium (Sr)-doped La0.67K0.33-xSrxMnO3 (LKSMO) ceramics were obtained by traditional sol-gel method. With increasing Sr content, full width at half maximum (FWHM) for temperature-dependent resistivity curves increased, resistivity decreased, and peak resistivity temperature (TP) shifted toward high temperature. Microstructure of LKSMO ceramics was characterized by X-ray diffraction, scanning electron microscopy, X-ray photoemission spectroscopy, energy dispersive spectrometry, and Fourier transform infrared spectroscopy, etc. Connection between microstructure and properties of ceramics was studied by combining double exchange mechanism, Jahn-Teller effect, and phenomenological percolation model. Electrical transport mechanism of ferromagnetic metal (FMM) and paramagnetic insulator (PMI) regions was employed to explain temperature coefficient of resistivity (TCR) and magnetoresistance (MR) behaviors of as-obtained samples. Various scattering factors, effective mass of itinerant electron, and energy difference between FMM and PMI phases affected FWHM of ρ-T curves in Sr-doped LKSMO ceramics. In sum, these findings provide physical mechanism and experimental guidance for synthesis of high-TCR and MR polycrystalline ceramics at room temperature.

Study of magnetic and magnetotransport properties in polycrystalline Pr0.6A′0.2Sr0.2MnO3(A′ [formula omitted]Y, La) compounds: Observation of enhanced electron–electron interaction

A comparative study of magnetic, electrical, and magnetotransport properties for the polycrystalline bulk Pr0.6A′0.2Sr0.2MnO3 (A′ ≡ Y, La) compounds has been presented in this article. The aforementioned ABO3 type perovskite compounds have been prepared with considering the average A-site ionic radius (〈rA〉) located around the phase boundary of the ferromagnetic insulator to ferromagnetic metal ground states of the prepared phase diagram for R0.8AE0.2MnO3 (R ≡ trivalent rare earth cations, AE ≡ divalent cations) compounds as a function of 〈rA〉. The decrease in chemical disorder along with an increase in electronic bandwidth from Y to La doping increases the ferromagnetic transition temperature from 90 K to 175 K, respectively, and also suppresses the resistivity as well as magnetoresistance substantially. The temperature-dependent resistivity curves exhibit the metal–insulator like transitions around 100 K and 200 K for the doping with Y and La, respectively. Moreover, a resistivity minimum at low temperature is also observed for both systems. This behavior is best explained using a model, developed considering the presence of electron–electron elastic scattering or interaction at low temperatures. However, the Y doping system exhibits stronger electron–electron interaction compared to the La doping system, since the previous one accommodates a higher chemical disorder and lower electronic bandwidth.

Switching of majority charge carriers by Zn doping in NdNiO3 thin films

We have studied the effects of Zn doping on the structural and electronic properties of epitaxial NdNiO3 thin films grown on single-crystal LaAlO3 (001) (LAO) substrates by pulsed laser deposition. The films are deposited in two sets, one with variation in Zn doping, and another with variation in thickness for undoped and 2% Zn doping. The experimental investigations show that Zn occupies Ni-site and that the films are grown with an in-plane compressive strain on LAO. All the films show metal-to-insulator transitions with a thermal hysteresis in the temperature-dependent resistivity curves except 5% Zn-doped film, which remains metallic. The theoretical fits show non-Fermi liquid behaviour, which gets influenced by Zn doping. The Hall resistance measurements clearly show that Zn doping causes injection of holes in the system which affects the electronic properties as follows: i) the metallic conduction increases by two factors just by 0.5% Zn doping whereas, 5% doping completely suppresses the insulating state, ii) a reversal of the sign of Hall coefficient of resistance is observed at low temperature.

Influence of the metastable state (V++) on the electronic properties of SnO2 nanowires under the influence of light

In general, the properties of oxide materials are directly related to the formation of defects in their structure. In this work, a correlation between the intrinsic defects of SnO2 nanowires with their optoelectronic and transport properties and the influence of illumination was traced. Photoluminescence experiments revealed that SnO2 nanowires are characterized by three emission centers related to oxygen vacancies, V0+ (red), (V0+)iso (yellow/orange), and V0++ (green), the latter being active only below 100 K. This metastable defect was associated with the anomalous behavior observed in the temperature-dependent resistivity curves of ohmic single-nanowire devices under the influence of light. Two activation energies for a single nanowire in different temperature regions (T < 100 K and T > 100 K) were identified by photocurrent measurements. The activation energy for T < 100 K (7 meV) is consistent with the small value obtained in the photoluminescence experiments for the green-emitting center (3 meV). For the high-temperature region (T > 100 K), a higher activation energy value (220 meV) was observed.

Transparent and conductive Sm-doped SrSnO3 epitaxial films

Abstract Perovskite-structured (SmxSr1-x)SnO3 (SSSO) films with x = 0–0.15 were epitaxially grown on LaAlO3(001) substrates by pulsed laser deposition, and the microstructure, transport and optical properties were investigated in detail. X-ray diffraction results show that the lattice constants gradually decrease with the Sm content increasing. Atomic force microscopy images confirm that all the films possess a smooth surface with low surface roughness. X-ray photoelectron spectroscopy measurements prove the existence of Sm3+ state in the doped SSSO films. Hall-effect measurements show that the film at x = 0.06 has the lowest room-temperature resistivity of 5.91 mΩcm and the highest electron mobility of 14.8 cm2/Vs. Temperature-dependent resistivity curves were fitted and explained by weak localization effect and e--e- interactions at low temperatures for films at x = 0.04 to 0.10. Optical transparency of all the films is more than 70% in the wavelength range from 600 to 1800 nm, and the band gaps increase gradually from 4.27 to 4.60 eV with increasing Sm content to 0.06, which can be ascribed to Burstein-Moss effect. Furthermore, the insertion of pure SrSnO3 buffer layer between the substrate and the SSSO film considerably reduces the density of dislocations, thereby leading to the improved electrical transport property. All these results bring rare-earth element Sm a step closer to optoelectronic applications of all-perovskite transparent and conductive oxides.

Synthesis and resistivity of topological metal MoP nanostructures

Due to the increased surface to volume ratios, topological nanomaterials can enhance contributions from the topological surface states in transport measurements, which is critical for device applications that exploit the topological properties. It is particularly important for topological semimetals in which bulk carriers are unavoidable to make them into nanostructures to reveal the nature of the topological surface states, such as the Fermi arcs or nodal lines. Here, we report the nanostructure synthesis of the recently discovered triple-point topological metal MoP by direct conversion of MoO3 nanostructures and study their transport properties. We observe that the initial size of the MoO3 templates critically determines the crystalline quality of the resulting MoP nanostructures: large MoO3 flakes lead to porous MoP flakes, while narrow MoO3 nanowires lead to MoP nanowires without pores. The size-dependent porosity observed in MoP nanostructures is attributed to the volume change during the conversion reaction and nanoscale confinement effects. For MoO3 nanowires with diameters less than 10 nm, the resulting MoP nanowires are single crystalline. The resistivity values of MoP nanostructures are higher than the reported values of MoP bulk crystals owing to the porous nature. However, despite the high porosity present in MoP flakes, the residual resistance ratio is ∼2 and the temperature-dependent resistivity curves do not show any strong surface or grain-boundary scattering. Demonstration of the facile synthesis of MoP nanostructures provides opportunities for careful investigations of the surface states in transport measurements and exploration of future electronic devices, including nanoscale interconnects.

Transport properties for Bi2Se3/La0.7Sr0.3MnO3 composites

Topological insulator/perovskite manganese oxide composites (Bi2Se3/La0.7Sr0.3MnO3) were prepared using the bonded-exfoliated method and the transport properties were studied. The resistivity of the bonded manganese oxide substrate was 6 orders of magnitude larger than that of a Bi2Se3 single crystal, implying that the bonded manganese oxide acted as an insulator substrate. The intrinsic resistance peak of the manganese oxide was present in the temperature-dependent resistivity curve. Metal-insulator transition induced by the magnetic field at a low temperature was observed. The simple parallel model cannot account for the electrical properties, as the conducting manganese oxide grains were bonded by polymeric silicone rubber and resistivity peaks were present only when the thickness of the Bi2Se3 layer was less than 1.043 μm. The spin injection may be present in the composite structure.

Electronic Transport Evidence for Topological Nodal-Line Semimetals of ZrGeSe Single Crystals

Although the band topology of ZrGeSe has been studied via magnetic torque technique, the electronic transport behaviors related to the relativistic Fermions in ZrGeSe are still unknown. Here, we first report systematic electronic transport properties of high-quality ZrGeSe single crystals under magnetic fields up to 14 T. Resistivity plateaus of temperature dependent resistivity curves both in the presence and absence of magnetic fields as well as large, non-saturating magnetoresistance in low-temperature region were observed. By analyzing the temperature- and angular-dependent Shubnikov-de Haas oscillations and fitting it via the Lifshitz-Kosevich (LK) formula with the Berry phase being taken into account, we proved that Dirac fermions dominate the electronic transport behaviors of ZrGeSe and the presence of non-trivial Berry phase. First principles calculations demonstrate that ZrGeSe possesses Dirac bands and normal bands near Fermi surface, resulting in the observed magnetotransport phenomena. These results demonstrate that ZrGeSe is a topological nodal-line semimetal, which provides a fundamentally important platform to study the quantum physics of topological semimetals.

Current-voltage characteristics and vortex dynamics of superconducting Ba0.54K0.46Fe2As2 single crystal

We have investigated the current (I) - voltage (V) characteristics and vortex dynamics of Ba0.54K0.46Fe2As2 single crystal (BaK122) in H‖ab-plane and H‖c-axis orientations. The single crystal has been prepared by conventional growth method using self flux and characterized by onset Tc = 38.5 K, ΔTc = 1.0 K (offset-onset criterion) and residual resistivity ratio (RRR) ≈ 8. Usually for high-Tc superconductors, I - V curve shows exponential behavior due to flux creep at low magnetic field and it changes to near-linear nature with increase of magnetic field due to flux flow. We have shown that I –V characteristics differ significantly in H‖ab orientations compared to H‖c orientation which might be due to the presence of second magnetization peak (SMP). We have also estimated the activation energy using the Arrhenius plot in the thermally activated flux flow (TAFF) regime from the temperature dependent resistivity curves in both field orientation and have shown the variation of activation energy with magnetic field.

Degenerate and non-degenerate In2O3 thin films by pulsed electron beam deposition

Pulsed electron beam deposition (PED) was used to grow indium oxide thin films on c-cut sapphire single crystalline substrates between room temperature and 500 °C under oxygen gas. A slight difference in oxygen pressure during the PED growth (from 2 × 10−2 to 1.3 × 10−2 mbar) has strong effects on the electrical and optical film properties. The indium oxide thin films grown in these conditions changed from a non-degenerate semiconducting behaviour (at 2 × 10−2 mbar) to a degenerate semiconductor one (at 1.3 × 10−2 mbar), with a metal-insulator transition at 149 K. This crossover from strong to weak localization, evidenced in the temperature dependent resistivity curves, may be due to the effects of a structural disorder in such films. The direct optical band gap was estimated from transmission spectra taking into account non-degenerate/degenerate behaviour.

Preparation, Characterization, Electrical and Magnetic Properties of Mn-Doped Dilute Magnetic Semiconductors

Nanoparticle dilute magnetic semiconductors (DMS) are becoming increasingly important due to their possible applications in spintronics, an emerging field where the conduction process in the materials is a spin-based process. Nanoparticles of Mn-doped ZnO (DMS) material with general formula Zn[Formula: see text]MnxO ([Formula: see text]) were prepared by opting single stage combustion synthesis process. The samples characterized, exhibited formation of monophasic nanoparticles of the sample with average particle size ranging between 17 nm to 23 nm. The calculations of energy bandgap made from UV absorption spectra showed variation of the bandgap from 2.18 eV to 2.32 eV. The magnetic measurements (VSM) made on the samples confirmed formation of a single diamagnetic (Zn[Formula: see text]Mn[Formula: see text]) and two namely (Zn[Formula: see text]Mn[Formula: see text]) (Zn[Formula: see text]Mn[Formula: see text]) paramagnetic samples. It is interesting to see that all the three magnetic profiles exhibit hysteresis type behavior both in diamagnetic form and paramagnetic form. The resistivity of the samples was of the order of 10[Formula: see text] Ohm-cm ([Formula: see text]-cm) at lower temperatures. Temperature-dependent resistivity curves exhibited peaking behavior for all the three samples which is very interesting. Temperature-dependent thermo-power profiles give an indication of [Formula: see text]-type semiconductor behavior with significantly deep and broad minima around 100[Formula: see text] which becomes sharper for sample with higher Mn concentration.

Microstructural, Magnetic and Electrical Properties of Ni2FeGa Heusler Alloys

Ni2FeGa polycrystalline alloys are synthesized by arc melting into single phase β structure and two phase mixture of γ-phase (fcc) and austenite (L21). Annealing improves atomic ordering and β transforms to L21 ordered structure. Effect of alloy composition and processing condition on different phase formation, microstructural, magnetic and electrical properties are discussed. The alloy undergoes first order austenite to martensitic phase transformation at 225 K with low hysteresis of 10 K. The resistivity exhibits a jump upon martensite transformation. This increase in resistivity is being attributed to the change in effective mass of electron upon martensite transformation. The temperature dependent resistivity curve for both austenite and martensite varies linearly with αT suggesting strong electron–phonon scattering. The slope of temperature dependent resistivity curve is higher in case of austenite than that of martensite and is attributed to the increasing role of electron–phonon scattering at high temperature.

Microstructural and electrical properties of CuAlO2 ceramic prepared by a novel solvent-free ester elimination process

A novel solvent–free ester elimination technique was designed for the preparation of CuAlO2 ceramic. It involved a direct reaction between aluminum sec-butoxide and copper (II) acetate in the absence of a solvent. Elimination of ester was confirmed from the sharp and intense peak at 1738 cm−1 on the FT-IR spectrum and the characteristic sweet smell obtained from the volatile by-product. The formation of Cu–O–Al mixed metal oxide bridge was demonstrated by a comparative XPS study of the as-prepared material and two separately prepared materials, one having pure Al–O bonds and the other having pure Cu–O bonds. The observed chemical shifts in of O 1s, Al 2p, Cu 2p3/2 and Cu 2p1/2 core levels and the disappearance of the Cu–O satellite peak support this formation. TG-DTA-EGA and XRD analysis revealed the mechanism that lead to the formation of a pure phase of CuAlO2 delafossite under ambient annealing at temperature of 900 °C. The BEI-EDXS and XRD information obtained for ceramic pellets made at different pressures (i.e. 10 MPa, 15 MPa and 20 MPa) also support this pure delafossite phase formation. The semiconductor behavior of the ceramics was confirmed from the temperature dependent resistivity curve and their p-type conductivity from Hall effect measurement.

Improved electrical transport in lightly Er-doped sol–gel spin-coating SnO2 thin films, processed by photolithography

Sol–gel spin-coating SnO2 thin films were deposited and processed through positive photolithography (liftoff), avoiding surface interaction with gaseous oxygen species and leading to samples with higher stability and data reproducibility, when submitted to electrical characterization. Processing includes: (1) a narrow conduction channel, (2) the assembly of electric contacts by ultrasound soldering, (3) deposition of an insulating layer, preventing the surface contact with atmospheric oxygen, which contributes for reliable measurements and the possibility of measuring SnO2 matrix properties without influence of adsorbed oxygen. Lightly Er-doped SnO2 sample (0.05 at.%), processed by this manner, has allowed the observation of a maximum about 50 K, in the temperature-dependent resistivity curve, which has not been found previously. This result is probably related to the combination of free electron concentration, which grows with temperature, and the grain boundary scattering, which decreases with temperature, and is the dominant mechanism for sol–gel SnO2. The processing also assures a remarkable reproducibility in the decay of photo-induced conductivity, yielding reliability to apply a modeling for the determination of important decay parameters, such as capture energy and grain boundary potential barrier.

Multi-step phase-change behavior in Ga30Sb70/SnSe2 nanocomposite multilayer thin films

Multi-step phase-change behavior in Ga30Sb70/SnSe2 nanocomposite multilayer films was investigated for multi-level storage in phase change random access memory in order to increase its storage density. It can be found in the temperature-dependent resistance curves that multi-step phase change happened at the temperature of 210 °C and 270 °C, respectively, which can provide the possibility of high temperature storage. At the constitute of [Ga30Sb70(10 nm)/SnSe2(15 nm)]2 and [Ga30Sb70(25 nm)/SnSe2(25 nm)]1, the nanocomposite multilayer films show well resistance gap between amorphous and crystalline state, which represent the on/off ratios in practical devices and better multi-step prosperities in archival life stability compared to Ge2Sb2Te5 films. The analysis of both XRD patterns and TEM images confirmed the two step phase change in Ga30Sb70/SnSe2 nanocomposite multilayer films. The Ga30Sb70/SnSe2 nanocomposite multilayer film is a promising phase change materials in high density storage device.