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(a) dielectric constant, (b) dielectric loss and (c) AC conductivity vs. frequency for un-doped and 5 at% Co-doped TiO2 NPs.

In this study, the frequency and temperature dependent dielectric relaxation and electrical conduction mechanisms in NiAl2O4 spinel oxide ceramic have been explored in a frequency range of 50 − 10 × 10 6 Hz over a measured temperature from 163–283 K. The polycrystalline NiAl2O4 was synthesized via solid state reaction route and sintered at 1000 °C. The room temperature x-ray powder diffraction pattern confirmed the formation of NiAl2O4 spinel phase with Fd3m space group. The surface morphology of the sample was investigated by scanning electron microscopy and chemical properties by Fourier transform infrared spectroscopic analysis. Complex impedance studies revealed the presence of relaxation time distribution and charge carriers were found to be thermally activated. The Nyquist plots exhibited depressed semicircles and their fitting by an equivalent circuit model with configuration (RGCG)(RGBCGB) resolved the contributions of grains and grain-boundaries to the electrical transport properties of the material. Electrical conductivity analysis followed the Jonscher’s power law behavior and the frequency exponent suggested small polaron hopping as the governing transport mechanism in NiAl2O4 spinel oxide. Non-Debye type nature of dielectric relaxation was confirmed by the complex modulus analysis whereas dielectric constant and tangent loss analysis verified that the hopping mechanism was thermally activated.

In the present study, pure, Co, Gd, and Co/Gd di-doped ZnO nanoparticles were synthesized via the co-precipitation synthesis route. The prepared samples were characterized through different techniques such as the X-ray diffraction method (XRD), scanning electron microscopy (SEM), UV-Vis spectroscopy, photoluminescence (PL)spectroscopy, and an impedance analyzer and vibrating sample magnetometer (VSM). The XRD pattern shows ZnO’s wurtzite hexagonal crystal structure; moreover, the shifting of characteristic peaks toward the lower angle indicates the inclusion of Co and Co/Gd in the ZnO host lattice. SEM micrographs show various morphologies such as rods, the agglomeration of particles, and spherical nanoparticles. The UV-Vis spectroscopy reveals that the absorption increased in the visible region and there was a substantial redshift for the doped samples. The bandgap decreased from 3.34 to 3.18 eV for the doped samples. The PL spectra show near-edge and inter-band transitions; the origin of inter-band transitions is attributed to the defect states present within the bands. The dielectric constant is strongly frequency dependent and decreases with Co and Co/Gd doping, while the electrical conductivity increases. A VSM study indicates that pure ZnO is diamagnetic, while the Co and Co/Gd doped ZnO nanoparticles showed ferromagnetic behavior. Under UV-visible light irradiation, the Co/Gd-ZnO nanoparticles showed higher photocatalytic activity than the ZnO nanoparticles. The enhanced photocatalytic activity may be attributed to a decreased bandgap with doping.

We investigated the influence of oxygen vacancies (varying) on the structure and properties (dielectric and magnetic) of Co (fixed) and Mn (varied) co-doped ZnO nanoparticles (NPs) fabricated using the chemical precipitation technique. The oxygen vacancies in the lattice increased with an increase in dopants (Co, Mn) concentration. Annealing of the doped nanoparticles decreased their dielectric properties due to reduced grain boundaries caused by enhanced grain growth. Replacement of Zn ions with dopants in the lattice enhanced the samples' electrical conductivities due to the reduction in grain boundaries and increase of charge carriers. The co-doped nanoparticles annealed at 600 °C exhibited some hysteresis loop changes and became ferromagnetic (FM). The magnetization increased with an increase in dopants content in the ZnO matrix, while coercivity decreased. This shows that the properties of the doped samples are strongly related to the number of oxygen vacancies. These results demonstrated that the enhanced dielectric and magnetization responses of Co (fixed) and Mn (varied) co-doped ZnO nanoparticles are strongly correlated with the oxygen vacancies. The enhancement in optical, dielectric, and magnetic properties make transition metals (TM)-doped ZnO nanoparticles suitable for spintronics, and optoelectronic-based applications.

Samples having the composition BaFe12−2xCoxSmxO19 (x = 0.0, 0.2, 0.4, 0.6) are prepared by a WOWS (without water and surfactants) sol–gel technique, and the structural, morphological, and AC and DC electrical and magnetic properties of the samples are investigated. The phase formation of M-type hexaferrite is studied by using indexed x-ray diffraction patterns. Scanning electron microscopy images show that the particle size of the synthesized nanopowder varies from 295 nm to 440 nm. The dielectric constant (e′) exhibits a decreasing trend while the dielectric loss (tan δ) increases with increased doping. DC electrical resistivity (ρDC) is investigated in a temperature range of 373–673 K and indicates an increasing trend with doping. The magnetic hysteresis loops reveal an increase in saturation magnetization (Ms) and remanence (Mr), and a decrease in coercivity (Hc), with the increase in doping content.

This paper addresses the effect of Mn (2%, fixed) and Co (2, 4, and 6%, varied) substitution on the structural, optical, dielectric and magnetic responses of ZnO nanoparticles synthesized by the co-precipitation chemical route. The X-ray diffraction analysis confirms the hexagonal wurtzite structure of ZnO. The incorporation of co-doping in the ZnO host, indicated by peak shifting in the XRD patterns, enhanced the crystallite size of the Mn/Co dual-doped ZnO nanoparticles. The FTIR spectra show a characteristic peak around 875 cm

We report the variations in structural, dielectric and magnetic properties with elevation of calcination temperature of (ZnO, Ni), synthesized by hydrothermal route. Incorporation of Ni in ZnO lattice is accompanied by numerous oxygen vacancies. With increasing calcinations temperature, enhancement in particle size with improvement in crystallization are observed, which is most probably due to grain growth having less number of grain boundaries and enhancement in grain volume. The dielectric behavior gives deep insight of (ZnO, Ni) nanoparticles microstructure. The abrupt increase in A.C. conductivity (σa.c) at high frequencies arises due to the addition of detached charge carrier from trap states to the conduction charge carriers. The (ZnO, Ni) nanoparticles, calcined at different temperatures, show significant changes in the hysteresis loop of ZnO nanoparticles: the loop shows strong ferromagnetic (FM) behavior. The magnetization enhances with increasing the calcination temperature of the particle (Ni, ZnO). Defects (oxygen vacancies) are found to be the main reason for room-temperature ferromagnetism (RTFM) in the (ZnO, Ni) nanoparticles. The enhanced dielectric and magnetic properties of (ZnO, Ni) nanoparticles are strongly correlated with the increase of oxygen vacancies.

In this work, the irreversible effects of an applied electric field on the magnetotransport properties of LaAlO3/SrTiO3 conducting interfaces are investigated, with focus on their multiband character. Samples of different types, namely with either crystalline or amorphous LaAlO3 overlayer, are studied. The two-band analysis highlights the similarity of the electronic properties of crystalline and amorphous interfaces, regardless much different carrier densities and mobilities. Furthermore, filling and depletion of the two bands follow very similar patterns, at least in qualitative terms, in the two types of samples. In agreement with previous works on crystalline interfaces, it is observed that an irreversible charge depletion takes place after application of a first positive back gate voltage step. Such charge depletion affects much more, in relative terms, the higher and three-dimensional dyz, dzx bands than the lower and bidimensional dxy, driving the system through the Lifshitz transition from two-band to single band behavior. The quantitative analysis of experimental data evidences the roles of disorder, apparent in the depletion regime, and temperature. Noteworthy, filling and depletion of the two bands follow very similar patterns in crystalline and amorphous samples, at least in qualitative terms, regardless much different carrier densities and mobilities.

Oxide-based films and nanostructures have emerged as important materials for a wide range of applications such as photovoltaics, optoelectronics, gas sensing and electronics. To develop an appropriate understanding of the properties of these oxides, it is necessary to address the material preparation methods and defect probing issues. This work reports on the synthesis processes of TiO 2 based transparent conductive films, their stoichiometry control and defect identifying, in relation with their electrical and optical properties. Un-doped and TiO 2 :Nb films were deposited by RF co-sputtering from TiO 2 and Nb 2 O 5 targets in Ar plasma. The chemical species present in the plasmas used in deposition process were investigated by optical emission spectroscopy, which was later on correlated with the defects structure of the films. Analysis by X-ray photoelectron spectroscopy shed more light on the nature of the vacancies and on the effect of the latter on the optical and electrical properties of the films. In terms of results, we measured electrical resistivity in the range 10 − 2 –10 − 3 Ω cm for the intrinsically and extrinsically doped films (films doped with oxygen vacancies and Nb + 5 respectively) while the lowest resistivity was obtained for intrinsically-extrinsically co-doped TiO 2 films (7.4 × 10 − 4 Ω cm). The films transparency was also actively determined by the defects in the lattice and highly transparent films (65–85% in the visible range) were obtained by controlling the density of defects. The approach adopted in this work for the generation of oxygen vacancies could be useful for other oxide-based films, where the oxygen vacancies-dependent properties are crucial, for room temperature ferromagnetism and photocatalytic applications.

The authors report a comparative study of the electrical and optical properties of Nb:TiO2 thin films (TNO) in relation with their chemical properties. Two types of niobium containing targets, Nb metal and Nb2O5 oxide were employed simultaneously with ceramic TiO2 target for the films growth, in Ar and Ar-O2 discharge. Niobium is found to incorporate easily and substitutionally into titanium lattice site when deposited from oxide targets in oxygen-deficient discharge (Ar plasma). Consequently, the TNO film exhibits lowest resistivity of 1.4×10−3 Ω cm with optical transparency of more than 80% in the visible region. On the contrary, doping was not effective in case the TNO films were grown from Nb metal and TiO2 targets in Ar and Ar-O2 plasma, probably due to the growth of niobium sub-oxide phases and lack of oxygen vacancies. The possible reasons of diverse electrical properties are discussed and are link with the growth conditions. Our result indicates that highly conductive and transparent doped-TiO2 film can be obtained by choosing appropriate target material and sputtering gas. The obtained results can significantly contribute to the development of transparent electrodes by RF sputtering, a suitable technique for coating on large area substrates.

In this work, an attempt has been made to compare the physical properties of conductive films of Nb-doped TiO2 deposited on Kapton polyimide, glass and silicon substrates. Thin films were deposited by radio frequency sputtering at room temperature and subsequently characterized using X-ray diffraction, X-ray photoelectron spectroscopy, UV-VIS-NIR spectroscopy and Hall Effect measurement. Structurally, the films grown on the flexible substrate exhibit more strain and had inferior crystallinity (crystallite size [Formula: see text]13.8 nm) compared to the films deposited on glass and silicon substrates (crystallite size [Formula: see text]27 nm). The film on glass had a resistivity value around [Formula: see text] while the resistivity of the films grown on polyimide was found about five-fold higher. Furthermore, the films deposited on glass substrate showed optical transparency of [Formula: see text]80% in the visible range (400–750 nm). The inferior electrical transport properties of the films grown on polyimide were correlated with the poor crystallinity and cracks induced during the annealing process. Furthermore, various possible routes have been discussed to improve crystallinity and control cracks in the films.

We demonstrate a novel nanoheating scheme that yields very large and uniform temperature gradients up to about 1K every 100nm, in an architecture which is compatible with the field-effect control of the nanostructure under test. The temperature gradients demonstrated largely exceed those typically obtainable with standard resistive heaters fabricated on top of the oxide layer. The nanoheating platform is demonstrated in the specific case of a short-nanowire device., 6 pages, 6 figures

The indirect effect of oxygen background gas on the La/Al ratio during the growth of LaAlO3 (LAO) films by pulsed laser deposition (PLD) is analyzed, in a pressure range between 10^-3 and 10^-1 mbar. We resort to two complementary investigation methods: Rutherford backscattering spectroscopy and spectrally resolved, time-gated imaging of the laser plume. The first technique allows us to analyze the stoichiometry of the deposited films, and the latter allows us to analyze the plume expansion phase of the PLD process by collecting chemically resolved two-dimensional images of the relevant atomic/molecular species. The comparison between the results obtained by the two techniques allows us to highlight the role of the plume-gas interaction in affecting cations stoichiometry. Our results indicate that, in the considered pressure range, the background oxygen pressure affects the cations stoichiometry of the LAO films, besides determining their oxygen content.

The effects of frequency on the alternating-current (AC) conductivity of polycrystalline La0.65Ca0.35MnO3 compounds prepared by solid-state reaction with various heat treatments have been studied. The AC conductivity and magnetoresistance (MR) are affected by the heat treatment temperature. The MR is enhanced at and below the transition temperature (TC). The AC transport behavior of this system shows pronounced negative MR even at small applied magnetic fields for temperatures well below TC. It is observed that such effects originate from spin-dependent scattering at grain boundaries as a consequence of spin disorder at the interfaces of the boundaries and spin scattering within the grains. The real part of the AC conductivity σ′ exhibits a pronounced frequency dependence, measured in the frequency range f < 100 kHz. The minimum occurs at a frequency that is temperature dependent. The MR below TC and the frequency dependence of the AC electrical conductivity σ′(f) are interpreted as being consequences of cluster and grain boundary effects.

The quest for solid-state thermoelectric (TE) conversion has been one of the prime driving forces behind semiconductor research before the discovery of the transistor effect. The achievement of efficient TE devices indeed requires a non-trivial trade-off between interdependent material characteristics and can be expressed in terms of the maximization of the figure of merit ZT = S2T/, where S is the Seebeck coefficient,  and  are the electrical and thermal conductivity, T the average operation temperature. Large ZT values, though, have proven elusive over the past decades despite the great design flexibility offered by semiconductor materials1. Here, we present results on thermovoltages in single InAs nanowire (NW) field effect transistors. Thanks to a buried heating scheme (see Fig. 1), we achieved both a large thermal bias, T > 10K and a strong field-effect modulation of electric conduction through nanostructures randomly positioned on oxidized silicon. This experimental arrangement allows a detailed mapping of S(; T) and the comparison with classic models for thermoelectric transport in degenerate semiconductors. The adopted approximations lead to a novel estimate of the electron mobility e~ 11000 cm2/Vs in the NW. Such value is significantly larger than the one obtain by field-effect, e, FE, on the same wire. The discrepancy can be understood in terms of history effects in the NW free charge filling by electric field, as a consequence of the slow surface and trap charge dynamics. On the other hand, the S vs  dependence is largely independent of spurious charge screening and hysteresis. Our results also indicate that special care should be taken in the interpretation of transport results based on field-effects in these nanostructures.