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In the present study, we have investigated the effect of magnetic Cr doping on the transport properties of a sputtered Bi2Se3 thin film on the SrTiO3 (110) substrate. The high-resolution x-ray diffraction and Raman spectroscopy measurements revealed the growth of rhombohedral Bi2Se3 thin films. Further electronic and compositional analysis was done by x-ray photoemission spectroscopy and Rutherford backscattering spectroscopy, and the x-value was estimated to be 0.18 in the Bi2−xCrxSe3 thin film. The variation in the resistivity with temperature (2–300 K) revealed the metallic nature in undoped Bi2Se3 up to 30 K and upturn resistivity below 30 K. The Cr-doped Bi2Se3 resistivity data show a traditional semiconducting nature up to 25 K and take an abrupt upturn resistivity below 25 K. The resistivity behavior of both samples was explained by adopting a model that consists of the total resistance, a combination of bulk and surface resistance in parallel. The bulk bandgap value determined by this method is obtained to be 256 meV in an undoped Bi2Se3 thin film. Magnetoconductance data of the undoped thin film revealed a weak anti-localization (WAL) effect, while the Cr-doped thin film showed a weak localization (WL) effect at low temperatures (<50 K). At low magnetic field and low temperature, a competing nature of WAL and WL effects was prominent in the Cr-doped film. A drastic increase in the electrical resistance suggests that Cr doping can significantly modify the electrical properties of Bi2Se3 thin films, which could have potential applications in futuristic devices. [ABSTRACT FROM AUTHOR]

LaNiO3 (LNO) and NdNiO3 (NNO) thin films have been prepared by nebulized spray pyrolysis on (001)-oriented LaAlO3 (LAO) and SrTiO3 (STO) substrates. The stoichiometric nitrate precursor in deionized water was spray pyrolyzed at ~ 300 °C. All films were given annealing treatment at different temperatures to tune the electrical transport behavior. The surface morphology of these films, in general, consists of granular and locally epitaxial regions. Films with electrical transport properties resembling those of similar films prepared by more sophisticated methods like pulsed laser deposition and sputtering are obtained at the annealing temperature range ~ 900–950 °C. High-resolution X-ray diffraction (HRXRD) and glancing incidence XRD bring out the single-phase nature. The films on STO show a small amount of in-plane tensile strain, while those on LAO are under small compressive strain. Annealing at a higher temperature (~ 1000 °C) enhances the tensile strain slightly while the compressive strain is lowered. Such behavior has been attributed to oxygen deficiency. The LNO films on STO and LAO show fairly good metallic behavior, and the electrical transport in the former is described in terms of a model represented by ρ T = ρ 0 - a T 0.5 + b T . In contrast, the electrical resistivity of the LNO/LAO film is described by ρ T = ρ 0 - a T 0.5 + b T + c T 2 . Annealing at high temperatures promotes the insulating state in all the LNO films. The NNO films on LAO substrates show a paramagnetic metallic state which is followed by a metal insulator transition (MIT) on lowering the temperature. The MIT shifts to higher temperatures in 1000 °C annealed films. In contrast, the NNO/STO films show insulating behavior throughout, and annealing at higher temperatures further strengthens the insulating state. The insulator state shows a small polaron hopping kind of transport represented by ρ T = A T e E A / k B T with temperature-dependent activation energies in the range of 100–55 meV. [ABSTRACT FROM AUTHOR]

Magnetic and magnetotransport properties of a ~ 12 nm PrNiO3 (PNO) thin film deposited on (001)-oriented LaAlO3 (LAO) substrate by RF magnetron sputtering are reported. An enlargement in the out-of-plane lattice constant of the film ( a FOP = 0.389 nm) as compared to that of the target ( a c = 0.383 nm) reflects the larger in-plane compressive strain in the film. The appearance of a hump-like feature in the high-resolution ω - 2 θ scan indicates that the film may have defects like grain or twin boundaries. The film undergoes a transition from paramagnetic (PM) to antiferromagnetic (AFM) at T N ≈ 150 K . The pronounced divergence between the zero-field and field-cooled magnetization-temperature curves suggests a magnetically clustered state. At T ≪ T N , the magnetic moment is appreciably larger and resembles an AFM state. At T > T N , the film shows a very weak semiconducting behavior, which is followed by a transition to an insulating state at T < T N . A magnetic field-induced metallic state is seen just below T N and is associated with large thermal hysand teresis. The film also exhibits a negative magnetoresistance which is much larger than reported earlier in nickelates. The observed anomalous behavior could be due to the magnetic field-induced destabilization of the AFM state and spin fluctuations. [ABSTRACT FROM AUTHOR]

We report a low-temperature magneto transport study of Bi2Se3 thin films of different thicknesses (40, 80 and 160 nm), deposited on sapphire (0001) substrates, using radio frequency magnetron sputtering technique. The high-resolution x-ray diffraction measurements revealed the growth of rhombohedral c-axis {0003n} oriented Bi2Se3 films on sapphire (0001). Vibrational modes of Bi2Se3 thin films were obtained in the low wavenumber region using Raman spectroscopy. The surface roughness of sputtered Bi2Se3 thin films on sapphire (0001) substrates were obtained to be ~ 2.26–6.45 nm. The chemical and electronic state of the deposited Bi2Se3 was confirmed by X-ray photoelectron spectroscopy and it showed the formation of Bi2Se3 compound. Resistivity versus temperature measurements show the metallic nature of Bi2Se3 films and a slight up-turn transition in resistivity at lower temperatures < 25 K. The positive magneto-resistance value of Bi2Se3 films measured at low temperatures (2–100 K) confirmed the gapless topological surface states in Bi2Se3 thin films. The quantum correction to the magnetoconductivity of thin films in low magnetic field is done by employing Hikami–Larkin–Nagaoka theory and the calculated value of coefficient 'α' (defining number of conduction channels) was found to be 0.65, 0.83 and 1.56 for film thickness of 40, 80 and 160 nm, respectively. These observations indicate that the top and bottom surface states are coupled with the bulk states and the conduction mechanism in Bi2Se3 thin films varied with the film thicknesses. [ABSTRACT FROM AUTHOR]

Thin films of Bi2Se3 were deposited on Si (100) substrates using RF magnetron sputtering at a deposition temperature of 633 K. The surface morphology of Bi2Se3 films revealed the variation of grain sizes with thickness, while elemental analysis showed the stoichiometric Bi2Se3 films. The high-intensity x-ray diffraction peaks along (0003), (0006) and (00015) planes showed the dominant orientation of Bi2Se3 along the c-axis on Si (100). Three prominent Raman characteristic peaks, E2g, A11g, and A21g modes, were observed which revealed a pure hexagonal phase. X-ray photoelectron spectroscopy analysis showed the growth of high-purity Bi2Se3 films. The temperature-dependent electrical conductivity measurements showed the increase in conductivity with temperature due to the semiconducting nature. Seebeck coefficient of these films falls in the range of −153 to −236 µV/K near room temperature. These findings pave the way for economically preparing large-area and high-performance Bi2Se3 thin films for future thermoelectric devices. [ABSTRACT FROM AUTHOR]

We use conducting atomic force microscopy (AFM) in ultra high vacuum to measure the thermoelectric power of Au, Pt, and 3,4,9,10-perylene tetracarboxylic dianhydride (PTCDA) films. Tips coated with thick (1200 nm) Pt films or highly doped diamond film give reproducible data. The thermoelectric power of metal junctions formed with diamond tips is high but dominated by the diamond material thus making diamond tips of limited applicability in thermovoltage AFM. Pt coated tips on Au or Pt films gives small thermovoltage signal, making quantitative analysis of the thermopower on metal sample problematic. The thermovoltage AFM technique appears best suited to study organic thin films and the thermoelectric power of 1.5 nm and 2 nm thick PTCDA deposited on Au measured with Pt tips is -342 and -372 μV/K, respectively. The negative sign indicates that the lowest unoccupied molecular orbital level dominates electrical transport. [ABSTRACT FROM AUTHOR]

We report on magnetic imaging study of regular hexagonal shaped NiFe elements arranged in different configurations. By making use of stray field with moderate strength and well-defined symmetry, which is lacking in vortices formed in circular elements, it is possible to control the relative chirality of vortex in a ring network of hexagons unlike in an array network. However, the alternating chirality of the hexagons disappears when the interelemental spacing becomes large, an element is missing from the ring network, or they are arranged in linear chains. The results can be understood by the symmetry and direction of the stray field generated by the individual elements. [ABSTRACT FROM AUTHOR]