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Showing papers on "Van der Pauw method published in 2018"


Journal ArticleDOI
TL;DR: In this article, the authors studied the properties of Si, Ge shallow donors and Fe, Mg deep acceptors in β-Ga2O3 through temperature dependent van der Pauw and Hall effect measurements of samples grown by a variety of methods.
Abstract: We have studied the properties of Si, Ge shallow donors and Fe, Mg deep acceptors in β-Ga2O3 through temperature dependent van der Pauw and Hall effect measurements of samples grown by a variety of methods, including edge-defined film-fed, Czochralski, molecular beam epitaxy, and low pressure chemical vapor deposition. Through simultaneous, self-consistent fitting of the temperature dependent carrier density and mobility, we are able to accurately estimate the donor energy of Si and Ge to be 30 meV in β-Ga2O3. Additionally, we show that our measured Hall effect data are consistent with Si and Ge acting as typical shallow donors, rather than shallow DX centers. The high temperature Hall effect measurement of Fe doped β-Ga2O3 indicates that the material remains weakly n-type even with the Fe doping, with an acceptor energy of 860 meV relative to the conduction band for the Fe deep acceptor. Van der Pauw measurements of Mg doped Ga2O3 indicate an activation energy of 1.1 eV, as determined from the temperature dependent conductivity.

184 citations


Journal ArticleDOI
TL;DR: In this article, the authors studied the properties of Si, Ge shallow donors and Fe, Mg deep acceptors in $\beta$-Ga2O3 through temperature dependent van der Pauw and Hall effect measurements of samples grown by a variety of methods.
Abstract: We have studied the properties of Si, Ge shallow donors and Fe, Mg deep acceptors in $\beta$-Ga2O3 through temperature dependent van der Pauw and Hall effect measurements of samples grown by a variety of methods, including edge-defined film-fed (EFG), Czochralski (CZ), molecular beam epitaxy (MBE), and low pressure chemical vapor deposition (LPCVD). Through simultaneous, self-consistent fitting of the temperature dependent carrier density and mobility, we are able to accurately estimate the donor energy of Si and Ge to be 30 meV in $\beta$-Ga2O3. Additionally, we show that our measured Hall effect data are consistent with Si and Ge acting as typical shallow donors, rather than shallow DX centers. High temperature Hall effect measurement of Fe doped $\beta$-Ga2O3 indicates that the material remains weakly n-type even with the Fe doping, with an acceptor energy of 860 meV relative to the conduction band for the Fe deep acceptor. Van der Pauw measurements of Mg doped Ga2O3 indicate an activation energy of 1.1 eV, as determined from the temperature dependent conductivity.

172 citations


Journal ArticleDOI
TL;DR: In this paper, the homoepitaxy of Si-doped β-Ga2O3 thin films on semi-insulating (010) and (001) Ga 2O3 substrates via low pressure chemical vapor deposition with a growth rate of ≥ 1μm/h was investigated.
Abstract: This paper presents the homoepitaxy of Si-doped β-Ga2O3 thin films on semi-insulating (010) and (001) Ga2O3 substrates via low pressure chemical vapor deposition with a growth rate of ≥1 μm/h. Both high resolution scanning transmission electron microscopy and X-ray diffraction measurements demonstrated high crystalline quality homoepitaxial growth of these thin films. Atomic resolution STEM images of the as-grown β-Ga2O3 thin films on (010) and (001) substrates show high quality material without extended defects or dislocations. The charge carrier transport properties of the as-grown Si-doped β-Ga2O3 thin films were characterized by the temperature dependent Hall measurement using van der Pauw patterns. The room temperature carrier concentrations achieved for the (010) and (001) homoepitaxial thin films were ∼1.2 × 1018 cm−3 and ∼9.5 × 1017 cm−3 with mobilities of ∼72 cm2/V s and ∼42 cm2/V s, respectively.

81 citations


Journal ArticleDOI
TL;DR: In this paper, the morphological and electrical properties of SnSe thin films were studied as a function of the precursor's composition and the substrate temperature, and the results showed that the SnSe films have an orthorhombic crystalline structure.

49 citations


Journal ArticleDOI
TL;DR: Vibrational and electrical properties of sputtered films of the copper telluride system are presented and it was possible to obtain single-phase vulcanite (CuTe) from the Cu1.25Te target.
Abstract: Vibrational and electrical properties of sputtered films of the copper telluride system are presented. Despite of its technological importance in photovoltaics, the fundamental properties of copper tellurides are poorly understood. Films were deposited at 200 °C by rf sputtering from targets containing mixtures of copper and tellurium powders at nominal concentrations of Cu1.25Te, Cu1.5Te, Cu1.75Te and Cu2Te. Remarkably for the copper telluride system, it was possible to obtain single-phase vulcanite (CuTe) from the Cu1.25Te target. Two-phase mixtures of rickardite (Cu7Te5) and weissite (Cu2−xTe) were achieved for other cases. Raman spectra were obtained using two laser lines: 633 and 488 nm. Density functional theory was employed to calculate the phonon dispersion curves and density of states for vulcanite. The Raman bands were in good correspondence with the calculated frequencies. In general, the Raman spectra consisted of high-intensity totally symmetric modes superimposed on monotonically decaying signals. These were explained in terms of three contributing phenomena: convolution of vibrational normal modes, phonon-coupled charge density fluctuations and time-varying local-field contributions to the electric susceptibility. Studies on the conductivity, mobility and carrier concentration were carried out by the Van der Pauw method. Micro/nano scale surface potential studies were performed through Kelvin probe force microscopy mapping.

47 citations


Journal ArticleDOI
TL;DR: In this article, a transparent and conductive thin films of indium tin oxide were fabricated on glass substrates by the thermal evaporation technique and the structure and phase purity, surface morphology, optical and electrical properties of thin films were studied by x-ray diffractometry and Raman spectroscopy, scanning electron microcopy and atomic force microscopy.
Abstract: Transparent and conductive thin films of indium tin oxide were fabricated on glass substrates by the thermal evaporation technique. Tin doped indium ingots with low tin content were evaporated in vacuum (1.33 × 10−7 kpa) followed by an oxidation for 15 min in the atmosphere in the temperature range of 600–700°C. The structure and phase purity, surface morphology, optical and electrical properties of thin films were studied by x-ray diffractometry and Raman spectroscopy, scanning electron microcopy and atomic force microscopy, UV–visible spectrometry and Hall measurements in the van der Pauw configuration. The x-ray diffraction study showed the formation of the cubical phase of polycrystalline thin films. The morphological analysis showed the formation of ginger like structures and the energy dispersive x-ray spectrum confirmed the presence of indium (In), tin (Sn) and oxygen (O) elements. Hall measurements confirmed n-type conductivity of films with low electrical resistivity (ρ) ∼ 10−3 Ω cm and high carrier concentration (n) ∼ 1020 cm−3. For prevalent scattering mechanisms in the films, experimental data was analyzed by calculating a mean free path (L) using a highly degenerate electron gas model. Furthermore, to investigate the performance of the deposited films as a transparent conductive material, the optical figure of merit was obtained for all the samples.

46 citations


Journal ArticleDOI
TL;DR: The molecular Sn(iv) complexes have been prepared in good yield from reaction of SnCl4 with the appropriate chalcogenoether ligand in anhydrous hexane and employed as single source precursors for the low pressure chemical vapour deposition of the corresponding tin dichalcogenside thin films.
Abstract: The molecular Sn(iv) complexes, [SnCl4{nBuS(CH2)3SnBu}] (2), [SnCl4(nBu2S)2] (3) and [SnCl4(nBu2Se)2] (4) have been prepared in good yield from reaction of SnCl4 with the appropriate chalcogenoether ligand in anhydrous hexane and, together with the known [SnCl4{nBuSe(CH2)3SenBu}] (1), employed as single source precursors for the low pressure chemical vapour deposition of the corresponding tin dichalcogenide thin films. At elevated temperatures the bidentate ligand precursors, (1) and (2), also form the tin monochalcogenides, SnSe and SnS, respectively. In contrast, (3) gave a mixture of phases, SnS2, Sn2S3 and SnS and (4) gave SnSe2 only. The morphologies, elemental compositions and crystal structures of the resulting films have been determined by scanning electron microscopy, energy dispersive X-ray spectroscopy, grazing incidence X-ray diffraction and Raman spectroscopy. Van der Pauw measurements on the SnS2, SnS and SnSe2 films confirm their resistivities to be 2.9(9), 266(3) and 4.4(3) Ω cm, respectively.

42 citations


Journal ArticleDOI
TL;DR: In this paper, the performance of cadmium oxide thin films with different cobalt (Co) dopant concentrations in the final spray solution has been investigated, showing that preferential growth is shifted between (111) and (200) depending on the Co- doping concentrations.
Abstract: Present work is focused on the improvement of gas sensing and opto-electronic properties of cadmium oxide (CdO) thin films deposited by chemical spray pyrolysis technique, with different cobalt (Co) dopant concentrations in the final spray solution. The XRD patterns reveal that the preferential growth is shifted between (111) and (200) depending on the Co- doping concentrations. The Cd-O bond vibrations were confirmed by micro-Raman analysis. The oxidization state of metal elements was determined by XPS analysis. The FE-SEM analysis revealed the variation in surface microstructure due to the variation in Co- doping concentration in CdO thin films. The elemental composition of deposited films was estimated using EDS. The formaldehyde gas response of 0.50 wt% Co- doped CdO thin film was 23%. The electrical properties were estimated by Hall measurements in van der Pauw configuration. The 0.50 wt% Co- doped CdO thin film showed a maximum carrier mobility of about 87 cm 2 /Vs and a photocurrent of 2.50 nA at 42 V. The Co- doped CdO thin films showed a high optical transmittance of about 84% in the range of 600–1100 nm. The band gap varies between 2.38 eV and 2.50 eV. The estimated high figure of merit is 4.79 × 10 −3 Ω −1 for 0.50 wt% of Co- doped CdO film.

32 citations


Journal ArticleDOI
TL;DR: In this article, the electrical properties of 19 nm thick Yttrium Iron Garnet (YIG) films grown by liquid phase epitaxy were measured in the high temperature range [300,400]~K using a Van der Pauw four-point probe technique.
Abstract: We report a study on the electrical properties of 19 nm thick Yttrium Iron Garnet (YIG) films grown by liquid phase epitaxy The electrical conductivity and Hall coefficient are measured in the high temperature range [300,400]~K using a Van der Pauw four-point probe technique We find that the electrical resistivity decreases exponentially with increasing temperature following an activated behavior corresponding to a band-gap of $E_g\approx 2$ eV, indicating that epitaxial YIG ultra-thin films behave as large gap semiconductor, and not as electrical insulator The resistivity drops to about $5\times 10^3$~$\Omega \cdot \text{cm}$ at $T=400$ K We also infer the Hall mobility, which is found to be positive ($p$-type) at 5 cm$^2$/(V$\cdot$sec) and about independent of temperature We discuss the consequence for non-local transport experiments performed on YIG at room temperature These electrical properties are responsible for an offset voltage (independent of the in-plane field direction) whose amplitude, odd in current, grows exponentially with current due to Joule heating These electrical properties also induce a sensitivity to the perpendicular component of the magnetic field through the Hall effect In our lateral device, a thermoelectric offset voltage is produced by a temperature gradient along the wire direction proportional to the perpendicular component of the magnetic field (Righi-Leduc effects)

31 citations


Journal ArticleDOI
TL;DR: Terahertz time-domain spectroscopy performed in either reflection mode or transmission modes are indeed very accurate methods for mapping electrical conductivity of graphene, and that both methods are interchangeable within measurement uncertainties.
Abstract: We present a comparative study of electrical measurements of graphene using terahertz time-domain spectroscopy in transmission and reflection mode, and compare the measured sheet conductivity values to electrical van der Pauw measurements made independently in three different laboratories. Overall median conductivity variations of up to 15% were observed between laboratories, which are attributed mainly to the well-known temperature and humidity dependence of non-encapsulated graphene devices. We conclude that terahertz time-domain spectroscopy performed in either reflection mode or transmission modes are indeed very accurate methods for mapping electrical conductivity of graphene, and that both methods are interchangeable within measurement uncertainties. The conductivity obtained via terahertz time-domain spectroscopy were consistently in agreement with electrical van der Pauw measurements, while offering the additional advantages associated with contactless mapping, such as high throughput, no lithography requirement, and with the spatial mapping directly revealing the presence of any inhomogeneities or isolating defects. The confirmation of the accuracy of reflection-mode removes the requirement of a specialized THz-transparent substrate to accurately measure the conductivity.

30 citations


Journal ArticleDOI
TL;DR: In this article, the conductivity type of ZnO has been determined based on the Fermi-Dirac distribution for doped semiconductors and the Burstein-Moss effect.
Abstract: Fermi-Dirac distribution for doped semiconductors and Burstein-Moss effect have been correlated first time to figure out the conductivity type of ZnO. Hall Effect in the Van der Pauw configuration has been applied to reconcile our theoretical estimations which evince our assumption. Band-gap narrowing has been found in all p-type samples, whereas blue Burstein-Moss shift has been recorded in the n-type films. Atomic Force Microscopic (AFM) analysis shows that both p-type and n-type films have almost same granular-like structure with minor change in average grain size (∼ 6 nm to 10 nm) and surface roughness rms value 3 nm for thickness ∼315 nm which points that grain size and surface roughness did not play any significant role in order to modulate the conductivity type of ZnO. X-ray diffraction (XRD), Energy Dispersive X-ray Spectroscopy (EDS) and X-ray Photoelectron Spectroscopy (XPS) have been employed to perform the structural, chemical and elemental analysis. Hexagonal wurtzite structure has been observed in all samples. The introduction of nitrogen reduces the crystallinity of host lattice. 97% transmittance in the visible range with 1.4 × 107 Ω-1cm-1 optical conductivity have been detected. High absorption value in the ultra-violet (UV) region reveals that NZOs thin films can be used to fabricate next-generation high-performance UV detectors.

Journal ArticleDOI
TL;DR: In this paper, X-ray diffraction (XRD), scanning electron microscopy (SEM), Hebb-Wagner, DC van der Pauw and voltammetry method, respectively.
Abstract: (M = Fe, Cr and Co) doped CaZrO3, CaZr0.7M0.3O3 (M = Fe, Cr and Co), was synthesized by solid state reaction method. Crystalline structure, microstructures, electronic conductivity, total conductivity and sensing performance were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), Hebb-Wagner, DC van der Pauw and voltammetry method, respectively. XRD measurements show that the CaZr0.7M0.3O3 (M = Fe, Cr and Co) samples belong to an orthorhombic perovskite structure. SEM measurements show that the CaZr0.7M0.3O3 (M = Fe, Cr and Co) samples have fine grains with average grain size of 0.5–2 μm. Electrical property measurements show that the CaZr0.7Fe0.3O3 and CaZr0.7Cr0.3O3 samples have the highest electronic conductivity and total conductivity in air, respectively. Sensing performance measurements show that limiting current-type oxygen sensors with 9YSZ solid electrolyte and CaZr0.7M0.3O3 dense diffusion barrier exhibit good limiting current (IL) plateau. Log IL depends linearly on 1000/T. IL depends linearly on oxygen partial pressure.

Journal ArticleDOI
TL;DR: In this article, a p-type, substitutional doping at S-site, MoS2 thin film using Phosphorous (P) as the dopant was synthesized.
Abstract: We report on the successful synthesis of a p-type, substitutional doping at S-site, MoS2 thin film using Phosphorous (P) as the dopant. MoS2 thin films were directly sulfurized for molybdenum films by chemical vapor deposition technique. Undoped MoS2 film showed n-type behavior and P doped samples showed p-type behavior by Hall-effect measurements in a van der Pauw (vdP) configuration of 10×10 mm2 area samples and showed ohmic behavior between the silver paste contacts. The donor and the acceptor concentration were detected to be ∼2.6×1015 cm-3 and ∼1.0×1019 cm-3, respectively. Hall-effect mobility was 61.7 cm2V-1s-1 for undoped and varied in the range of 15.5 ∼ 0.5 cm2V-1s-1 with P supply rate. However, the performance of field-effect transistors (FETs) declined by double Schottky barrier contacts where the region between Ni electrodes on the source/drain contact and the MoS2 back-gate cannot be depleted and behaves as a 3D material when used in transistor geometry, resulting in poor on/off ratio. Nevert...

Journal ArticleDOI
TL;DR: In this paper, the authors explored a novel approach to electrode preparation employing amorphous cathode materials and found that the local electronic conductivity in the amorphou cathode surface is enough to preserve its catalytic properties.
Abstract: Lowering the operating temperature of solid oxide fuel cell (SOFC) devices is one of the major challenges limiting the industrial breakthrough of this technology. In this study we explore a novel approach to electrode preparation employing amorphous cathode materials. La0.8Sr0.2CoO3−δ dense films have been deposited at different temperatures using pulsed laser deposition on silicon substrates. Depending on the deposition temperature, textured polycrystalline or amorphous films have been obtained. Isotope exchange depth profiling experiments reveal that the oxygen diffusion coefficient of the amorphous film increased more than four times with respect to the crystalline materials and was accompanied by an increase of the surface exchange coefficient. No differences in the surface chemical composition between amorphous and crystalline samples were observed. Remarkably, even if the electronic conductivities measured by the Van Der Pauw method indicate that the conductivity of the amorphous material was reduced, the overall catalytic properties of the cathode itself were not affected. This finding suggests that the rate limiting step is the oxygen mobility and that the local electronic conductivity in the amorphous cathode surface is enough to preserve its catalytic properties. Different cathode materials have also been tested to prove the more general applicability of the amorphous-cathode route.

Journal ArticleDOI
TL;DR: In this paper, the morphological structure (particle size, pore size, etc.), optical, magnetic and electrical properties of Ni:Fe2O3, Mg:Fe 2O3 and Fe2O 3 thin films which grown by Spray pyrolysis (SP) have been investigated.
Abstract: Iron oxide is a widely used sensitive material for gas sensor applications. They have fascinated much attention in the field of gas sensing and detecting under atmospheric conditions and at 200 °C temperature due to their low cost in production; simplicity and fast of their use; large number of detectable gases. Iron oxide gas sensors constitute investigated for hazardous gases used in various fields. The morphological structure (particle size, pore size, etc.), optical, magnetic and electrical properties of Ni:Fe2O3, Mg:Fe2O3 and Fe2O3 thin films which grown by Spray pyrolysis (SP) have been investigated. XRD, Raman and AFM techniques have been used for structural analysis. AFM measurements have been provided very useful information about surface topography. I-V (Van der Pauw) technique has been used for response of gas sensor. These devices offer a wide variety of advantages over traditional analytical instruments such as low cost, short response time, easy manufacturing, and small size.

Journal ArticleDOI
TL;DR: In this paper, Cadmium sulfide (CdS) thin films were deposited onto glass substrates at different temperatures by the spray pyrolysis technique, and a home-made experimental setup with an automatized perfume atomizer was implemented for the spraying process.

Journal ArticleDOI
20 Sep 2018-Sensors
TL;DR: The results establish the aptness of the as-grown CNT film to be used as an active sensing material in thin film temperature sensors.
Abstract: In this paper, we present the fabrication of an efficient thin film temperature sensor utilizing chemical vapor deposited carbon nanotube (CNT) film as the sensing element on Si substrates, with diamond-like carbon (DLC):Ni as a catalyst in assisting CNT growth. The fabricated sensor showed good electrical response with change in temperature. Relative linear change in resistance of 18.4% for an increase in temperature from 22 °C to 200 °C was achieved. Various characterizing techniques, such as scanning electron microscopy (SEM) and Raman spectroscopy, were used to characterize the films. In an effort to study device performance, van der Pauw and Hall measurements were carried out to study the dependence of resistance on temperature and magnetic fields. Temperature coefficient of resistance of the sensor was calculated as 1.03 × 10-3/°C. All implications arising from the study are presented. The results establish the aptness of the as-grown CNT film to be used as an active sensing material in thin film temperature sensors.

Journal ArticleDOI
TL;DR: The results point to a new field of applications for QFS 1LG, i.e., as humidity sensors, and the corresponding need for metrology in calibration of graphene-based sensors and devices.
Abstract: The effects of humidity on the electronic properties of quasi-free standing one layer graphene (QFS 1LG) are investigated via simultaneous magneto-transport in the van der Pauw geometry and local work function measurements in a controlled environment. QFS 1LG on 4H-SiC(0001) is obtained by hydrogen intercalation of the interfacial layer. In this system, the carrier concentration experiences a two-fold increase in sensitivity to changes in relative humidity as compared to the as-grown epitaxial graphene. This enhanced sensitivity to water is attributed to the lowering of the hydrophobicity of QFS 1LG, which results from spontaneous polarization of 4H-SiC(0001) strongly influencing the graphene. Moreover, the superior carrier mobility of the QFS 1LG system is retained even at the highest humidity. The work function maps constructed from Kelvin probe force microscopy also revealed higher sensitivity to water for 1LG compared to 2LG in both QFS 1LG and as-grown systems. These results point to a new field of applications for QFS 1LG, i.e., as humidity sensors, and the corresponding need for metrology in calibration of graphene-based sensors and devices.

Journal ArticleDOI
TL;DR: In this paper, a thin film of SnO2:F was prepared by spray pyrolysis technique on glass substrate and the results showed a room temperature sheet resistance of 24 Ω/sq.
Abstract: Thin film of SnO2:F was prepared by spray pyrolysis technique on glass substrate. Surface Morphology, using scanning electron microscope, shows micrograph image with grains size distribution between 16 and 380 nm. Structural characterization by XRD indicates a similar rutile polycrystalline material as SnO2. A four point probe I–V measurement (Van der Pauw method) was used to study electrical properties and the result shows a room temperature sheet resistance of 24 Ω/sq. In addition, a temperature dependence of the electrical response indicates that defect scattering is the main contribution to the DC resistivity. Optical properties were studied by UV–Visible spectroscopy and the spectrum was fitted using Drude-Lorentz model with DC conductivity value (frequency equal to zero) as a fitting condition. Optical result shows average transmittance around 81.2% for the visible frequency range. It indicates a TCO figure of merit value of 5.2 × 10−3 Ω−1. In addition, a first principle calculation using DFT with PBE0 hybrid exchange-correlation was realized to SnO2 and SnO2:F systems in order to understand, from a theoretical point of view, the experimental results. Finally, the FTO film was utilized and evaluated as a transparent electrode in the preparation of a dye-sensitized solar cell.

Journal ArticleDOI
TL;DR: In this article, the authors synthesized thin films of CuAlO2 and CuAl2O4 using the physical vapor deposition technique and subsequent annealing, and the preferred orientations of the thin films were found to be along the (1'1'2) and (3'1 '1' 2' planes, respectively.
Abstract: CuAlO2 and CuAl2O4 thin films were synthesized by the deposition of the precursor metals using the physical vapor deposition technique and subsequent annealing. Annealing was carried out for 4–6 h in open and nitrogen atmospheres respectively at temperatures of 900–1000 °C with control of heating and cooling ramps. The band gap measurements ranged from 3.3 to 4.5 eV. Electrical properties were measured using the van der Pauw technique. The preferred orientations of CuAlO2 and CuAl2O4 were found to be along the (1 1 2) and (3 1 1) planes, respectively. The phase percentages were quantified using a Rietveld refinement simulation and the energy dispersive X-ray spectroscopy indicated that the composition is very close to the stoichiometry of CuAlO2 samples and with excess of aluminum and deficiency of copper for CuAl2O4 respectively. High resolution transmission electron microscopy identified the principal planes in CuAlO2 and in CuAl2O4. Higher purities were achieved in nitrogen atmosphere with the control of the cooling ramps.

Journal ArticleDOI
TL;DR: In this paper, thin films of covellite copper sulphide (CuS) were deposited on FTO substrates using chemical spray pyrolysis technique, and the influence of Cu-to-S molar ratio on structural, surface morphological, optical and electrical properties were systematically investigated using variety of characterization techniques.
Abstract: Thin films of covellite copper sulphide (CuS) were deposited on FTO substrates using chemical spray pyrolysis technique. Influence of Cu-to-S molar ratio on structural, surface morphological, optical and electrical properties were systematically investigated using variety of characterization techniques. Formation of covellite CuS films was confirmed by low angle-XRD and Raman spectroscopy. The field emission scanning electron microscopy analysis revealed the formation of faceted CuS particles without secondary growth. Optical studies exhibited decrease in optical band gap (from 2.21 to 1.69 eV) with increase in Cu-to-S molar ratio. Electrical properties were investigated using Van der Pauw four point probe method and Hall measurements revealed that as-synthesized CuS films have low sheet resistance (1.47–2.45 Ω/□), high carrier mobility (8.90–54.89 cm2/Vs) and high sheet concentration (1016–1018/cm2). The CuS films deposited at optimized Cu-to-S molar ratio (1:2.5) were then further studied for electrochemical impedance spectroscopy and photovoltaic characteristics. A quantum-dot sensitized solar cell incorporating optimized CuS film as counter electrode showed power conversion efficiency of ~ 1.05% with Voc ~ 0.46 V, Isc ~ 1.01 mA/cm2 and fill factor ~ 0.34%. Although the cell is not fully optimized and better results can be anticipated.

Journal ArticleDOI
TL;DR: In this paper, the effect of planar defect on thermal and electron transport as compared to point defect in the rutile TiO2-x has been investigated, and the theoretical calculation based on Klemens-Callaway model have been performed to analyze the thermal conductivity.
Abstract: In this study, we have investigated the effect of planar defect on thermal and electron transport as compared to point defect in the rutile TiO2-x. Two series of bulk TiO2-x (2-x = 2.000, 1.992, 1.985, 1.972, and 1.934) samples were prepared using different heat treatment procedures to clearly identify the presence of point and planar defects via powder X-ray diffraction. The charge carrier density and mobility were determined from Hall effect measurements using van der Pauw method. The elastic properties of the studied materials such as bulk modulus, shear modulus, Young's modulus, compressibility, and Debye temperature were evaluated from the measured sound velocities, while their thermal conductivities were determined from the thermal diffusivities, heat capacities, and densities measured in the temperature range between 300 and 1073 K. The theoretical calculation based on Klemens-Callaway model have been performed to analyze the thermal conductivity. As a result, the effect of planar defects on the carrier mobility was almost equivalent to the effect produced by point defects. On the other hand, the presence of planar defects significantly reduced the thermal conductivity of TiO2-x as compared to point defect due to strong phonon scattering induced by planar defects. This article is protected by copyright. All rights reserved.

Journal ArticleDOI
TL;DR: In this article, a p-type 4H silicon carbide (4H-SiC) van der Pauw strain sensor was presented for the first time, utilizing the strain induced effect in four-terminal devices.
Abstract: This paper presents for the first time a p-type 4H silicon carbide (4H-SiC) van der Pauw strain sensor by utilizing the strain induced effect in four-terminal devices. The sensor was fabricated from a 4H-SiC (0001) wafer, using a 1 μm thick p-type epilayer with a concentration of 1018 cm−3. Taking advantage of the four-terminal configuration, the sensor can eliminate the need for resistance-to-voltage conversion which is typically required for two-terminal devices. The van der Pauw sensor also exhibits an excellent repeatability and linearity with a significantly large output voltage in induced strain ranging from 0 to 334 ppm. Various sensors aligned in different orientations were measured and a high sensitivity of 26.3 ppm−1 was obtained. Combining these performances with the excellent mechanical strength, electrical conductivity, thermal stability, and chemical inertness of 4H-SiC, the proposed sensor is promising for strain monitoring in harsh environments.

Journal ArticleDOI
TL;DR: In this paper, a mixed protonic-electronic conducting nanocomposites comprised of Mo or La doped Nd5.5WO11.5O were prepared by mechanical mixing in a high energy mill and sintering at 1100˚C using either conventional thermal Sintering in the furnace or hot pressing in argon atmosphere.

Journal ArticleDOI
TL;DR: In this article, the relation of structure, oxygen and protonic mobility of oxide and nanocomposite materials with high mixed proton-electronic conductivity is elucidated.

Journal ArticleDOI
TL;DR: In this article, simple ink synthesis and printing methods to deposit ZnO photodetectors on a variety of flexible and transparent substrates, including polyimide (Kapton), polyethylene terephthalate, cyclic olefin copolymer (TOPAS), and quartz, were reported.
Abstract: Zinc oxide (ZnO) thin films have remarkable versatility in sensor applications. Here, we report simple ink synthesis and printing methods to deposit ZnO photodetectors on a variety of flexible and transparent substrates, including polyimide (Kapton), polyethylene terephthalate, cyclic olefin copolymer (TOPAS), and quartz. X-ray diffraction analysis revealed the dependence of the film orientation on the substrate type and sintering method, and ultraviolet–visible (UV–Vis) absorption measurements revealed a band edge near 380 nm. van der Pauw technique was used to measure the resistivity of undoped ZnO and indium/gallium-codoped ZnO (IGZO) films. IGZO films showed lower resistivity and larger average grain size compared with undoped ZnO films due to addition of In3+ and Ga3+, which act as donors. A 365-nm light-emitting diode was used to photoirradiate the films to study their photoconductive response as a function of light intensity at 300 K. The results revealed that ZnO films printed by aerosol jet and inkjet techniques exhibited five orders of magnitude photoconductivity, indicating that such films are viable options for use in flexible photodetectors.

Journal ArticleDOI
TL;DR: In this paper, the influence of negative potential on the formation of ceria films was studied with scanning electron microscopy, X-ray diffraction, Raman spectroscopy, van der Pauw measurements, UV-visible spectrographs, and Xray photoelectron spectrograms.

Journal ArticleDOI
TL;DR: In this paper, the solid-state synthesis of high-temperature superconducting YBa2Cu3O7−x was described, and the critical temperatures (Tc0) were determined from magnetoresistance measurements, which are about 91.5 K for all samples and do not depend on sample-forming pressure.
Abstract: This article details the solid-state synthesis of high-temperature superconducting YBa2Cu3O7−x. Tests were carried out on samples formed at different pressures (200, 400, 600 and 800 MPa) before being annealed under pure oxygen. The X-ray diffraction method showed that, regardless of the forming pressure, the samples contain about 97 wt.% of Y-123 phase. SEM images showed a polycrystalline structure of samples of similar grain size and number of pores (intergranular spaces). The values of critical temperatures (Tc0), determined from magnetoresistance measurements, are about 91.5 K for all samples, and the Tc0 temperatures do not depend on sample-forming pressure. Magnetoresistance measurements have shown that samples formed with higher pressures exhibit smaller changes in Tc0 and superconducting transition width ΔT due to the influence of the HDC magnetic field, than the samples formed with lower pressures. Values of specific resistance determined by the use of van der Pauw method at 300 K is about 2 mΩcm for all samples. The critical temperatures (T cintra) of grains and critical current densities at 77 K were determined from AC magnetic susceptibility measurements, and they are about 91.6 K and 400 A cm−2, respectively.

Journal ArticleDOI
TL;DR: In this paper, the effect of Fe content on the performance of a limiting current oxygen sensor with CaZr0.7Fe0.3O3 dense diffusion barrier and YSZ solid electrolyte was investigated.

Journal ArticleDOI
TL;DR: In this paper, the van der Pauw-Hall measurement was used to evaluate the electrical transport performance of graphene by annealing graphene in vacuum to remove the adsorbed dopants and then exposing it in ambient surroundings.
Abstract: Expected for many promising applications in the field of electronics and optoelectronics, a reliable method for the characterization of graphene electrical transport properties is desired to predict its device performance or provide feedback for its synthesis. However, the commonly used methods of extracting carrier mobility from graphene field effect transistor or Hall-bar is time consuming, expensive, and significantly affected by the device fabrication process other than graphene itself. Here we reported a general and simple method to evaluate the electrical transport performance of graphene by the van der Pauw–Hall measurement. By annealing graphene in vacuum to remove the adsorbed dopants and then exposing it in ambient surroundings, carrier mobility as a function of density can be measured with the increase of carrier density due to the dopant re-adsorption from the surroundings. Further, the relationship between the carrier mobility and density can be simply fitted with a power equation to the first level approximation, with which any pair of measured carrier mobility and density can be normalized to an arbitrary carrier density for comparison. We experimentally demonstrated the reliability of the method, which is much simpler than making devices and may promote the standard making for graphene characterization.