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The present work reports preparation of polycrystalline G d F e 1 − x M n x O 3 (x = 0.0 to 0.5) samples with solid-state reaction method and characterization using x-ray diffraction, 57 Fe Mössbauer spectroscopy, magnetization measurements, leakage current density and soft x-ray absorption spectroscopy measurements. Although F e 3 + and M n 3 + have similar ionic radii, noticeable variations in lattice parameters are seen which are attributed to local distortions introduced by Jahn-Teller active M n 3 + doping. Antiferromagnetic transition temperature corresponding to F e 3 + ordering ( T N , F e ) and G d 3 + ordering ( T N , G d ) is found to decrease with Mn doping, which could be due to weakening of Fe-Fe interaction and Gd-Gd interactions respectively. The Mn substitution at Fe site in G d F e O 3 is found to induce F e 3 + spin reorientation transition ( T S R T ) at a critical concentration and T S R T is found to increase with the Mn doping. Temperature dependent 57 Fe Mössbauer measurements have been carried out to study the local distortions by estimating quadrupole shift, the evolution of magnetism and also the spin reorientation transition in G d F e O 3 with Mn doping. Leakage current density is found to increase with Mn doping in G d F e O 3 , initially very fast and almost saturating for higher concentrations of Mn doping due to the formation of multiple oxidation states of dopant Mn at lower concentrations as evidenced from soft x-ray absorption spectroscopy measurements. [ABSTRACT FROM AUTHOR]

Abstract: The effect of poly (3,4-ethylene dioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) interlayer on the Schottky barrier parameters of Pt/n-type Ge Schottky contacts was investigated. The PEDOT:PSS interlayer in between Pt and n-type Ge influences the space charge region of the Pt/n-type Ge Schottky junction, leading to increase in the barrier height. Due to interface dipoles and lateral barrier inhomogeneities caused by the presence of PEDOT:PSS interlayer, Pt/PEDOT:PSS/n-type Ge Schottky contact showed a deviation from the ideal thermionic emission model of the carrier transport at the metal/semiconductor junction. From the reverse current–voltage (I–V) characteristics, the Poole–Frenkel emission and Schottky emission were found to be the dominating carrier conduction mechanisms of Pt/PEDOT:PSS/n-type Ge Schottky contact at lower and higher reverse biases, respectively. [Copyright &y& Elsevier]

Abstract: The particle size effect in the range 10–150nm on the magnetic properties and phase transitions in BiFeO3 samples prepared by spray pyrolysis method has been studied. The phase purity and structure have been investigated by XRD and FTIR spectroscopy analysis. The FTIR peaks of the nanoparticles shift to lower wave number due to increase surface area and grain boundaries. The Fe-SEM and TEM images show that the particles are uniform, dense and of nearly spherical shape nanoparticles. The significant enhancement in magnetization with finite coercive field has been observed in 12nm particle size samples. The increase in magnetization is about four times larger than that of the bulk samples. It has been attributed to the suppression of the cycloidal spin structure due to large uncompensated spins of Fe+3 ions at the surface of the particle and the adsorbate induced spin polarization screening in BFO nanoparticles. The phase transitions above room temperature have been investigated by DTA measurements and show that Néel temperature (T N) and Curie temperature (T c) increase with particle size. The shift in T N and T c values with particle size are fitted well to the finite scaling models. The microscopic parameters like correction length, characteristic microscopic dimension of the system and critical particle size have been evaluated which provide more physical insight in the finite scaling effect in the nanoparticle samples. [Copyright &y& Elsevier]

Abstract: In the present work, we have investigated the current–voltage (I–V) and capacitance–voltage (C–V) characteristics of Au/SiO2/n-GaN metal–insulator–semiconductor (MIS) Schottky diode and compared with Au/n-GaN metal–semiconductor (MS) Schottky diode. Calculations showed that the Schottky barrier height and ideality factor of the MS Schottky diode is 0.79eV (I–V), 0.87eV (C–V) and 1.45, respectively. It is observed that the Schottky barrier height increases to 0.86eV (I–V), 0.99eV (C–V) and ideality factor deceases to 1.3 for MIS diode. For the MS diode, the calculated doping concentration is 4.17×1017 cm−3. However, in the case of the MIS Schottky diode, the decrease in doping concentration is observed and the respective value is 2.08×1017 cm−3. The obtained carrier concentration of the MIS diode is reduced about 50% when compared to the MS diode. The interface state density as determined by Terman''s method is found to be 3.79×1012 and 3.41×1010 cm−2 eV−1 for the MS and MIS Schottky diodes, respectively. The calculated interface densities are 2.47×1011 cm−2 eV−1, 3.35×1011 cm−2 eV−1 and 3.5×1011 cm−2 eV−1 for the sweep rates of 300, 450 and 600mV/s from MOS C–V measurements for the MIS Schottky diode. The interface state density calculated from Terman''s method is found to be increased with sweep rate. From the C–V measurement, it is noted that the decrease in the carrier concentration in MIS diodes as compared to MS diode may be due to the presence of oxide interfacial layer. DLTS measurements have also been performed on MIS Schottky diode and discussed. [Copyright &y& Elsevier]

Abstract: The effect of annealing temperature on the electrical and structural properties of Ni/Ru Schottky rectifiers have been investigated by current–voltage (I–V), capacitance–voltage (C–V), X-ray diffraction (XRD) and secondary ion mass spectrometer (SIMS) measurements. The measured Schottky barrier height for as-deposited Ni/Ru/n-GaN Schottky diode is 0.66eV (I–V) and 0.79eV (C–V). It is observed that the barrier height of the Ni/Ru Schottky contacts increases with an increase in annealing temperature. When the contact is annealed at 600°C for 1min in N2 ambient, a maximum barrier height is achieved and the corresponding values are 0.79eV (I–V) and 0.98eV (C–V). It is observed that significant improvement in the electrical properties of Ni/Ru Schottky rectifier after annealing temperatures as compared to the as-deposited contact. Based on the results of SIMS and XRD, the formation of gallide phases at the Ni/Ru/n-GaN interface could be the reason for the increase of Schottky barrier height at elevated temperatures. Atomic force microscopy results showed that the surface morphology of the Ni/Ru Schottky contact is fairly smooth with a root-mean-square (RMS) roughness of 2.12nm even after annealing at 600°C. These results indicate that the Ni/Ru contacts could be attractive for high-temperature device applications. [Copyright &y& Elsevier]

Vanadium and copper doped sodium phosphate glasses are prepared. EPR and optical absorption investigations are carried out. The results and analysis of the copper doped glass indicate that the copper ions enter the glass matrix as Cu2+ ions. The Cu2+ ion spectra are characteristic of tetragonally elongated octahedral site. The spectra of vanadium doped glass are characteristic of VO2+ and because of the short V&z.dbnd6;O band the distortion appears to be a tetragonally compressed one. Crystal field and spin-Hamiltonian parameters are evaluated. The bonding parameters indicate that bonding between the metal ions and ligands is partially covalent. [Copyright &y& Elsevier]

This paper reviews the microstructural and electrical properties of Au/n-GaN metal/semiconductor (MS) diode with an e-beam evaporated SrTiO 3 (STO) as an insulating layer between the Au and n-GaN substrate. The microstructural properties of STO thin films are assessed by employing XRD and TEM approaches and the results reveal that the STO thin films are formed on n-GaN surface. Then, the Au/STO/n-GaN heterojunction (HJ) type Schottky diode is fabricated and measured its electrical characteristics by current-voltage (I–V) and capacitance-voltage (C–V) techniques. The HJ exhibits lower reverse leakage current compared to the MS diode. Higher barrier height is achieved for the HJ (0.86 eV) than the MS diode (0.67 eV) with ideality factors of 1.86 and 1.21. This implies that the barrier height is modified by the STO insulating layer. Using Z(V,T) i - V d and Ψ S -V plots, the barrier heights of MS diode and HJ are also evaluated and compared with one another. The derived interface state density (N SS) of HJ is lower than the MS diode, demonstrating that the STO layer plays a substantial role in the reduced N SS. Results suggest that the STO thin film is a promising high-k material for the development of new electronic device applications. Image 1 • Microstructural properties of SrTiO 3 films are characterized by XRD and TEM. • Electrical properties of Au/n-GaN MS diode and Au/SrTiO 3 /n-GaN HJ have been studied. • Higher BH is obtained for the HJ than the MS diode. • Interface state density of HJ is lower as compared to the MS diode. [ABSTRACT FROM AUTHOR]

We studied the effect of high temperature rapid thermal annealing on the electrical and structural properties of Pd/Au Schottky contact to Ga-polarity GaN grown by MBE on p-Si substrate. Current-voltage (I-V), capacitance-voltage (C-V), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD) and atomic force microscopy (AFM) measurements are performed for the electrical and structural characterization of the Schottky diode. It has been observed that there is a significant improvement in barrier height and ideality factor with reduction in leakage current upon annealing. The estimated Schottky barrier height (φ B0 ) for the as-deposited contact is 0.61eV (I-V) and 0.94 eV (C-V). While, the extracted barrier height for 700 °C annealed contact is improved to 0.74 eV (I-V) and 1.09 eV (C-V). In addition, the surface state density is calculated using C-V and it is found that there is ten time reduction in surface state density for 700 °C annealed Pd/Au Schottky contact compared to the as-deposited Schottky contact to semiconductor. X-ray photoelectron spectroscopy (XPS) depth profile results showed that there is out diffusion of Ga into metal film which may have formed metal-gallide phases for the annealed Schottky contacts that was confirmed by X-ray diffraction (XRD) results. It implies a reduction in nitrogen related vacancies and dangling bonds associated with GaN, which could be the reason for increase in the Schottky barrier height. Moreover, the surface morphology of the contacts is analysed by atomic force microscopy (AFM) and it is found that the surface roughness of Schottky contact does not degraded upon annealing. This indicates that the contacts were thermally stable during annealing. [ABSTRACT FROM AUTHOR]

A thin polyethylene oxide (PEO) is formed on p-type InP substrate as an interlayer for electronic alteration of the Ti/p-InP metal/semiconductor (MS) junction. The electrical and frequency dependence characteristics of the Ti/PEO/p-InP metal/interlayer/semiconductor (MIS) junction are explored by I-V , C-V-f and G-f measurements. The mean ideality factor and barrier height (BH) are assessed to be 1.93 and 0.74 eV ( I-V ), and 2.05 and 0.84 eV ( I-V ) for the MS and MIS junctions, respectively. It is found to the BH is increased by 100 meV for the MIS junction contrasted to the MS junction, indicating the BH is modified by the polymer interlayer. An average tunnelling BH is also estimated to be χ = 0.11 eV for the MIS junction. Moreover, the interface state density ( N ss ) is estimated for both MS and MIS junctions by forward I-V characteristics. The N ss and relaxation time ( τ ) are also determined from the C-f and G-f data. The N ss assessed by I-V and C-V methods are comparable with the values extracted by C-f and G-f data. The dielectric constant ( ε '), dielectric loss ( ε ''), tangent loss (tan δ ) and ac electrical conductivity ( σ ac ) parameters are extracted and discussed in the frequency range of 1 kHz-1 MHz at various bias voltage for the MIS junction. The ε ' and ε '' values are found to be reduced with increasing frequency. [ABSTRACT FROM AUTHOR]

Abstract: The variation in electrical characteristics of Mo/n-InP (100) Schottky contacts have been systematically investigated as a function of temperature using current–voltage (I–V) and capacitance–voltage (C–V) measurements in the temperature range 200–400K. The diode parameters like ideality factor n and zero-bias barrier height Φ b0 have been found to be strongly temperature dependent and while the zero-bias barrier height Φ b0(I–V) increases, the ideality factor n decreases with increasing temperature. The I–V characteristics are analyzed on the basis of thermionic emission (TE) theory and the assumption of Gaussian distribution of barrier heights due to barrier inhomogeneities that prevail at the metal–semiconductor interface. The zero-bias barrier height Φ b0 versus 1/2kT plot has been drawn to obtain evidence of a Gaussian distribution of the barrier heights and values of and σ 0 =144meV for the mean barrier height and zero-bias standard deviation have been obtained from this plot, respectively. The modified Richardson plot has given mean barrier height and Richardson constant (A**) as 0.85eV and 2.54Acm−2 K−2, respectively. The temperature dependence of the I–V characteristics of the Mo/n-InP Schottky diode have been successfully explained on the basis of thermionic emission (TE) mechanism with Gaussian distribution of the Schottky barrier heights (SBHs). [Copyright &y& Elsevier]

The compositional profile and local atomic structure in a Co 40 Fe 40 B 20 thin film sandwiched between two W layers, have been probed combining time-of-flight secondary ion mass spectrometry (ToF-SIMS) and x-ray absorption fine structure spectroscopy techniques in standing wave geometry (SW-XAFS). The data analysis demonstrated inhomogeneities in the composition profile as well as in the local atomic structure around transition metals, along the film thickness. Boron concentration shows a gradual increase from the bottom to the surface of the film The quantitative analysis of the Fe and Co K edges SW-XAFS spectra reveals distinct differences in the local coordination geometry along the film thickness and between the two metals. Specifically, the local structure around Fe appeared to be more disordered on average compared to Co and the bond lengths exhibited significant variation as a function of depth, • SW-XAFS, XRR and TOF-SIMS were used to investigate the local atomic structure in W/Co 40 Fe 40 B 20 /W thin films. • SW-XAFS data show significant differences around Fe and Co, particularly for the Fe-B distribution. • The data analysis describes significant differences in the local coordination of Fe and Co in the film center with respect to the borders. [ABSTRACT FROM AUTHOR]

High resolution x-ray diffraction, strain gauge and Raman spectroscopy measurements of Ca 2 FeAlO 5 as a function of temperature is reported, which provides the evidence of negative thermal expansion (NTE) and strong spin-lattice coupling in this compound. The unit cell showed a decrease in volume with increase in temperature with a distinct jump around 70 °C which corroborates with the magnetic ordering temperature and showed a contraction under magnetic field. The Raman spectra showed variation under magnetic field supporting spin-lattice coupling at room temperature. Most importantly, the NTE ( β ≅ − 6.41 × 10 −5 °C −1 ) is observed from room temperature up to ∼70 °C making it very attractive for applications. [ABSTRACT FROM AUTHOR]

The present work reports the preparation of polycrystalline NdFeO 3 using sol-gel method and characterization using X-ray diffraction (XRD), Raman spectroscopy, bulk magnetization, 57 Fe Mössbauer spectroscopy and ferroelectric measurements. XRD and Raman spectroscopy measurements confirm the phase purity of the prepared sample. The temperature dependent magnetization measurement shows the signatures of spin re-orientation transition ( T SRT ) between 66 and 158 K and magnetic field induced transition at about 2.5 T and 5 K. It is observed from the low temperature (25–300 K) 57 Fe Mössbauer measurements that the temperature variation of hyperfine parameters shows the signatures of T SRT . The observed area ratio of second and third line intensity (A 23 ) in Mössbauer sextet, across T SRT , show deviations from the value characteristic of random spin orientation in polycrystalline sample. In addition, the quadrupole shift changes sign across T SRT indicating the spin-reorientation of Fe 3+ ions. The room temperature leakage current density ( J - E ) measurements indicate that Ohmic contribution and space charge limited conduction are the dominating mechanisms at low and high applied electric fields, respectively, similar to that of other RFeO 3 (R – rare earth) based compounds. Lossy ferroelectric loops were observed at room temperature. [ABSTRACT FROM AUTHOR]

The current–voltage ( I – V ) characteristics of Al/p-type Si Schottky diodes with pristine and 5 wt.% sorbitol-doped organic PEDOT:PSS interlayers have been investigated. It was found that the barrier heights of the diodes with pristine and sorbitol-doped PEDOT:PSS are higher than those of a conventional Al/p-type Si Schottky diode because of the modification of the effective barrier height by the organic interlayer. It is noted that the Al/p-type Si Schottky diode with sorbitol-doped PEDOT:PSS interlayer exhibits higher barrier height and lower series resistance, as compared to Al/p-type Si Schottky diodes with pristine PEDOT:PSS interlayer. In addition, UPS measurements indicate that the position of the HOMO level is closer to the Fermi level for pristine PEDOT:PSS than for sorbitol-doped PEDOT:PSS. As a result, the hole injection barrier height is 0.15 eV lower in the pristine PEDOT:PSS structure than in the sorbitol-doped PEDOT:PSS. This value closely matches the difference in barrier heights (0.12 eV) seen in the I – V measurements. An energy-level alignment diagram is also presented and discussed for the structures studied. The Poole–Frenkel mechanism is found to dominate the reverse leakage current in both structures, indicating the presence of structural defects and trap levels in the organic film. [ABSTRACT FROM AUTHOR]

In the present work, the thermoelectric properties of potential thermoelectric materials (Bi 1− x In x) 2 Se 2.7 Te 0.3 grown as high-quality single crystals by the melt growth technique were investigated between 10 and 350 K. Powder X-ray diffraction confirms the hexagonal crystal structure of all studied crystals. The high-resolution X-ray diffraction study reveals the direction of growth, single-crystal quality, dislocation density, and the influence of dopants on the inner plane structure of the crystals. A clean surface with very low angle grain boundaries is observed by the field emission scanning electron microscopy. Energy-dispersive X-ray analysis confirms the elemental composition of the crystals. Electrical resistivity has shown degenerate semiconducting behavior with low activation energy. The Seebeck coefficient confirms p -type for the pristine and n -type conducting behavior for the doped samples, with the correlation to the carrier concentration and carrier mobility in the order of 1025/m3 and 10−4 m2/V s, respectively. Thermal conductivity has shown the dominant behavior of phonon scattering. A significant reduction in the electrical resistivity was found for the co-doped (Bi 0.96 In 0.04) 2 Se 2.7 Te 0.3 sample, leading to an enhancement of the power factor (PF) and thermoelectric figure of merit (ZT) by a factor of about 8.0 and 4.1, respectively, as compared to the pristine Bi 2 Se 3 sample at 350 K. The highest ZT value of about 0.285 is achieved for (Bi 0.96 In 0.04) 2 Se 2.7 Te 0.3 at 350 K. [Display omitted] • Indium doped Bi 2 Se 2.7 Te 0.3 belongs to the hexagonal crystal system with the space group R 3 ̅ m. • The high-resolution X-ray diffraction study reveals the direction of growth, single-crystal quality, dislocation density, and the influence of dopants on the inner plane structure of the co-doped crystals. • Electrical resistivity has shown degenerate semiconducting behavior with low activation energy. • The Seebeck coefficient and Hall measurements confirm the unique transition from p-type to n-type nature in the doped samples with carrier concentration of the order 1025 m−3. • A significant reduction in the electrical resistivity was found for the co-doped (Bi 0.96 In 0.04) 2 Se 2.7 Te 0.3 sample, leading to an enhancement of the power factor (PF) and thermoelectric figure of merit (ZT). [ABSTRACT FROM AUTHOR]

The present work reports the appearance of the exchange bias (EB) effect at low temperatures in epitaxial Fe thin film deposited on single crystalline LaAlO 3 (001) substrate. The observed EB effect vanishes around 30 K indicating that it could be due to the formation of antiferromagnetic FeO layer at the interface between Fe and LaAlO 3 substrate. The EB in Fe/LaAlO 3 (001) is further substantiated by comparing the observations with polycrystalline Fe film deposited on silicon substrate, kept adjacent to LaAlO 3 substrate during the deposition. Magnetic microstructure measured by Kerr microscopy corroborates the structural data of Fe film i.e., cubic four-fold anisotropy and isotropic nature for Fe film deposited on LaAlO 3 and silicon substrates, respectively. Further, low temperature Kerr microscopy results reveal that the magnetization reversal process significantly gets modified due to the induced unidirectional anisotropy as a consequence of FeO layer formation at Fe/LaAlO 3 interface. • Magnetic microstructural evidence for the cubic anisotropy in Fe/LaAlO 3. • Appearance of exchange bias in epitaxial Fe/LaAlO 3 thin film. • Change in magnetization reversal due to induced unidirectional anisotropy. [ABSTRACT FROM AUTHOR]

Structural and magnetic properties of Ga substituted cobalt ferrite (CoFe 2-x Ga x O 4) samples are reported in the present work. Phase purity of the prepared samples is studied with x-ray diffraction measurements. The room temperature M-H loops are measured using vibrating sample magnetometer. From the room temperature M-H data, it is observed that Ga substitution results in the soft-magnetic property in CoFe 2 O 4. Saturation magnetization is found to change for higher substitution of Ga (x > 0.2). The cation distribution with Ga substitution is estimated from the analysis of Raman spectroscopy data and in-field 57Fe Mössbauer spectroscopy measurements. Using the obtained complimentary information, it is concluded that the Fe3+ is forced to occupy more octahedral co-ordination with Ga substitution in CoFe 2 O 4. • Substitution effects of Ga in CoFe 2 O 4 (CoFe 2-x Ga x O 4) are studied. • Ga substitution in CoFe 2 O 4 results in soft-magnetic property. • Ferrimagnetic ordering is confirmed by in-field Mössbauer measurements. • Inversion parameter is observed to decrease with Ga substitution. • Fe3+ is forced to occupy more octahedral co-ordination with Ga substitution. [ABSTRACT FROM AUTHOR]