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Influence of Oxygen to Argon Ratio on the Structural and Morphological Properties of Nb-Doped SrTiO3 Epitaxial Films Grown by Reactive Ion Beam Sputter Deposition  [PDF]
Gasidit Panomsuwan, Nagahiro Saito
Crystal Structure Theory and Applications (CSTA) , 2013, DOI: 10.4236/csta.2013.21005
Abstract: Nb-doped SrTiO3 (STNO) films were grown on (001)-oriented LaAlO3 substrates by a reactive ion beam sputter deposition at various mixing ratios (OMRs) with a substrate temperature of 800oC. The STNO films exhibited good crystallinity with an epitaxial orientation as characterized by high-resolution X-ray diffraction, grazing-incidence X-ray diffraction, and in-plane pole figure analysis. A decrease of out-of-plane and in-plane lattice constants was observed with an increase of OMR. The surface morphology of the STNO films showed a very dense fine-grain structure. The root-mean-square roughness was found to be increased as the OMR increased. Moreover, the elemental compositions of the STNO films were examined by X-ray photoelectron spectroscopy.
Probing hot electron transport across an epitaxial Schottky interface of SrRuO3/Nb:SrTiO3  [PDF]
S. Roy,A. M. Kamerbeek,K. G. Rana,S. Parui,T. Banerjee
Physics , 2013, DOI: 10.1063/1.4807017
Abstract: SrRuO3 (SRO), a conducting transition metal oxide, is commonly used for engineering domains in BiFeO3. New oxide devices can be envisioned by integrating SRO with an oxide semiconductor as Nb doped SrTiO3 (Nb:STO). Using a three-terminal device configuration, we study vertical transport in a SRO/Nb:STO device at the nanoscale and find local differences in transport, that originate due to the high selectivity of SRO growth on the underlying surface terminations in Nb:STO. This causes a change in the interface energy band characteristics and is explained by the differences in the spatial distribution of the interface-dipoles at the local Schottky interface.
Bipolar Resistive Switching Characteristic of Epitaxial NiO Thin Film on Nb-Doped Substrate
Yongdan Zhu,Meiya Li
Advances in Condensed Matter Physics , 2012, DOI: 10.1155/2012/364376
Abstract: Epitaxial NiO film was grown on 0.7% Nb-doped SrTiO3 substrates by pulsed laser deposition. The I-V characteristics of Ag/NiO/Nb-SrTiO3/In device show reproducible and pronounced bipolar resistive switching without forming process which was induced by the NiO/Nb-SrTiO3 junctions, and the resistive switching ratio HRS/LRS can reach 103 at the read voltage of −0.5 V. Furthermore, the resistance states can be controlled by changing the max forward voltage, reverse voltage, or compliance current, indicating multilevel memories. These results were discussed by considering the role of carrier injection trapped/detrapped at the interfacial depletion region of the heterojunction.
Argon Assisted Growth of Epitaxial Graphene on Cu(111)  [PDF]
Zachary R. Robinson,Parul Tyagi,Tyler R. Mowll,James B. Hannon,Carl A. Ventrice Jr
Physics , 2013, DOI: 10.1103/PhysRevB.86.235413
Abstract: The growth of graphene by catalytic decomposition of ethylene on Cu(111) in an ultra-high vacuum system was investigated with low energy electron diffraction, low energy electron microscopy, and atomic force microscopy. Attempts to form a graphene overlayer using ethylene at pressures as high as 10 mTorr and substrate temperatures as high as 900 $^\circ$C resulted in almost no graphene growth. By using an argon overpressure, the growth of epitaxial graphene on Cu(111) was achieved. The suppression of graphene growth without the use of an argon overpressure is attributed to Cu sublimation at elevated temperatures. During the initial stages of growth, a random distribution of rounded graphene islands is observed. The predominant rotational orientation of the islands is within $\pm1^\circ$ of the Cu(111) substrate lattice.
First-principles study of FeSe epitaxial films on SrTiO3  [PDF]
Kai Liu,Miao Gao,Zhong-Yi Lu,Tao Xiang
Physics , 2015, DOI: 10.1088/1674-1056/24/11/117402
Abstract: The discovery of high temperature superconductivity in FeSe films on SrTiO3 substrate has inspired great experimental and theoretical interests. First-principles density functional theory calculations, which have played an important role in the study of bulk iron-based superconductors, also participate in the investigation of interfacial superconductivity. In this article, we review the calculation results on the electronic and magnetic structures of FeSe epitaxial films, emphasizing on the interplay between different degrees of freedom, such as charge, spin, and lattice vibrations. Furthermore, the comparison between FeSe monolayer and bilayer films on SrTiO3 is discussed.
Conductivity of LaAlO/SrTiO3 Interfaces made by Sputter Deposition  [PDF]
I. M. Dildar,D. B. Boltje,M. H. S. Hesselberth,Q. Xu,H. W. Zandbergen,S. Harkema
Physics , 2011,
Abstract: We have investigated the properties of interfaces between LaAlO3 films grown on SrTiO3 substrates singly terminated by TiO2. We used RF sputtering in a high-pressure oxygen atmosphere. The films are smooth, with flat surfaces. Transmission Electron Microscopy shows atomically sharp and continuous interfaces while EELS measurements show some slight intermixing. The elemental ratio of La to Al measured by EDX is found to be 1.07. Importantly, we find these interfaces to be non-conducting, indicating that the sputtered interface is not electronically reconstructed in the way reported for films grown by Pulsed Laser Deposition because of the different interplay between stoichiometry, mixing and oxygen vacancies.
Structure and electrical characteristics of Nb-doped SrTiO3 substrates
Yanhong Huang,Huibin Lü,Haizhong Guo,Lifeng Liu,Meng HE,Zhenghao Chen,Yueliang Zhou,Kun Zhao,Kuijuan Jin,Guozen Yang
Chinese Science Bulletin , 2006, DOI: 10.1007/s11434-006-2075-3
Abstract: The studies on structure and electrical characteristic of Nb-doped SrTiO3 (SNTO) substrates by XRD, Hall measurements, R-T and SEM, show that the SNTO substrates with the same Nb-doping concentration have different electrical properties because of the nonuniformity of Nb-doping. The uniformly doped high-quality substrates are extremely important for fabricating multilayer structure and devices. In addition, the experimental results also provide us with SEM method to judge the uniformity of conducting material.
A Single-Crystalline, Epitaxial SrTiO3 Thin-Film Transistor  [PDF]
Kosuke Uchida,Akira Yoshikawa,Kunihito Koumoto,Takeharu Kato,Yuichi Ikuhara,Hiromichi Ohta
Physics , 2009, DOI: 10.1063/1.3407568
Abstract: We report herein fabrication and characterization of a thin-film transistor (TFT) using single-crystalline, epitaxial SrTiO3 film, which was grown by a pulsed laser deposition technique followed by the thermal annealing treatment in an oxygen atmosphere. Although TFTs on the polycrystalline epitaxial SrTiO3 films (as-deposited) exhibited poor transistor characteristics, the annealed single-crystalline SrTiO3 TFT exhibits transistor characteristics comparable with those of bulk single-crystal SrTiO3 FET: an on/off current ratio >10^5, sub-threshold swing ~2.1 V/decade, and field-effect mobility ~0.8 cm^2/Vs. This demonstrates the effectiveness of the appropriate thermal annealing treatment of epitaxial SrTiO3 films.
Unconventional dynamical covalency driven superconductivity in Nb doped SrTiO3  [PDF]
A. Bussmann-Holder,A. R. Bishop,A. Simon
Physics , 2009,
Abstract: Nb doped SrTiO3, the first discovered two-gap superconductor, is shown to be the most unconventional one of the known multiband superconductors, since the smaller of the two superconducting gaps follows a non BCS temperature dependence. Such a behavior stems from two cooperating effects: an extreme anisotropy in the frequency dependent interactions, involving one very soft mode and an almost vanishing interband interaction. In contrast to all other multiband superconductors, the temperature dependence of the superfluid density of Nb doped SrTiO3 is predicted to exhibit an inflection point close to Tc and not close to T=0.
Dimensional crossover of polaron dynamics in Nb:SrTiO3/SrTiO3 superlattices: Possible mechanism of thermopower enhancement  [PDF]
Woo Seok Choi,Hiromichi Ohta,Soon Jae Moon,Yun Sang Lee,Tae Won Noh
Physics , 2009, DOI: 10.1103/PhysRevB.82.024301
Abstract: Using optical spectroscopy, we investigated the electrodynamic properties of Nb:SrTiO3/SrTiO3 superlattices. In these superlattices, a large enhancement of the Seebeck coefficient (S) has been reported with decreasing Nb:SrTiO3 layer thickness [refer to H. Ohta et al., Nature Mater. 6, 129 (2007)]. By analyzing the optical spectra, we found that the polaron plays an important role in determining the electrodynamic properties of the superlattices. With decreasing Nb:SrTiO3 layer thickness from eleven to one unit cell, we observed a threefold enhancement of the polaron effective mass and relaxation time. Such increases were attributed to a dimensional crossover of polaron from 3D to quasi-2D. Moreover, the modified nature of the polaron at low dimensions enhanced the thermoelectric properties of the oxide superlattice, by simultaneously increasing S and preventing the decrease of carrier mobility. Our results indicate that strong electron-phonon coupling can provide an alternative pathway in searching efficient thermoelectric materials.
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