Physics

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We report on room temperature diode characteristics of ZnO:Al (AZO)/Si heterostructures by current-voltage measurements. In this study, with increasing AZO film thickness, systematic reduction in the turn-on potential (from 3.16 to 1.80 V) and the film stress are observed. Complementary capacitance-voltage studies reveal a decreasing trend in barrier height at the junction with increasing AZO film thickness. A gradual decrease in resistivity takes place with increasing AZO film thickness. Above observations are explained in the framework of AZO thickness dependent variation in grain size and in turn trap density at the grain boundaries influencing carrier transport across the adjacent grains. © 2013 © 2013 Author(s).

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(SoNS) School of Natural Sciences

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AIP Advances

Effect of grain-boundaries on electrical properties of n-ZnO:Al/p-Si heterojunction diodes

This paper examines the features of a generalized position-dependent mass Hamiltonian Hm in a supersymmetric framework in which the constraints of pseudo-Hermiticity and [formula omitted] are naturally embedded. Different representations of the charge operator are considered that lead to new mass-deformed superpotentials [formula omitted] which are inherently [formula omitted]-symmetric. The qualitative spectral behavior of Hm is studied and several interesting consequences are noted. © 2013, American Institute of Physics. All rights reserved.

Journal of Mathematical Physics

[formula omitted]-conserved effective mass Hamiltonians through first and higher order charge operator [formula omitted] in a supersymmetric framework

In this paper a modified design of a solar Parabolic Trough Thermoelectric Receiver (PTTR) tube is presented and its technical feasibility is evaluated theoretically. The innovative driving concept is its cylindrical tri-segmented receiver tube coupled with a thermoelectric generator (TEG). The system is analyzed numerically for a set of operation and design parameters and the results are discussed. This work opens up a promising option which has the potential to improve the conversion of solar thermal energy into electricity through parabolic trough system. We also explored the possibility of multi-component energy conversion using the modified structure. © 2013 IEEE.

Proceedings of the 2013 International Conference on Green Computing, Communication and Conservation of Energy, ICGCE 2013

An innovative design of a tri-segmented parabolic trough solar thermoelectric receiver tube for multi-component energy conversion

We show bounds on five- and six-dimensional universal extra dimension (UED) models from the latest results of the Higgs searches at the LHC and from the electroweak precision data for the S and T parameters. We consider the minimal UED model in five dimensions and the ones in six dimensions, compactified on T2/Z2, T2/(Z2×Z2′), T2/Z4, S2, S2/Z2, the real projective plane, and the projective sphere. The highest possible ultraviolet cutoff scale for each UED model is evaluated from the electroweak vacuum stability by solving the renormalization group equation of the Higgs self-coupling. This scale turns out to be lower than the conventional one obtained from the perturbativity of the gauge coupling. The resultant 95% C.L. lower bounds on the first Kaluza-Klein scale from the LHC results and from the S, T analysis are 600 and 700 GeV in the minimal UED model, while those in the six-dimensional UED models are 800-1300 GeV and 900-1500 GeV, respectively. © 2013 American Physical Society.

Physical Review D - Particles, Fields, Gravitation and Cosmology

Universal extra dimensions after Higgs discovery

This chapter contains sections titled: Introduction Ta Substitution in TiO2: Doping or Alloying? Diluted Magnetic Semiconductors (DMS) Defect-Mediated Ferromagnetism Magnetic Impurity Analysis in Ti1-xTaxO2 System Defect-Induced Ferromagnetism in Ti1-xTaxO2 Film First-Principles Spin-Polarized GGA + U Calculations Mechanism of Defect-Mediated FM Optimization of Ferromagnetism Outlook for Defect-Mediated Properties of Ti1-xTaxO2 References © 2013 Wiley-VCH Verlag GmbH & Co. KGaA.

Functional Metal Oxides: New Science and Novel Applications

Effect of ta alloying on the optical, electronic, and magnetic properties of tio2 thin films

The study of interfacial properties, especially of their change upon lithiation, is a fundamentally significant and challenging topic in designing heterogeneous nanostructured electrodes for lithium ion batteries. This issue becomes more intriguing for Si electrodes, whose ultrahigh capacity is accompanied by large volume expansion and mechanical stress, threatening with delamination of silicon from the metal current collector and failure of the electrode. Instead of inferring interfacial properties from experiments, in this work, we have combined density functional theory (DFT) and ab initio molecular dynamics (AIMD) calculations with time-of-flight secondary ion mass spectrometry (TOF-SIMS) measurements of the lithium depth profile, to study the effect of lithiation on the a-Si/Cu interface. Our results clearly demonstrate Li segregation at the lithiated a-Si/Cu interface (more than 20\% compared to the bulk concentration). The segregation of Li is responsible for a small decrease (up to 16\%) of the adhesion strength and a dramatic reduction (by one order of magnitude) of the sliding resistance of the fully lithiated a-Si/Cu interface. Our results suggest that this almost frictionless sliding stems from the change of the bonding nature at the interface with increasing lithium content, from directional covalent bonding to uniform metallic. These findings are an essential first step toward an in-depth understanding of the role of lithiation on the a-Si/Cu interface, which may contribute in the development of quantitative electrochemical mechanical models and the design of nonfracture-and-always-connected heterogeneous nanostructured Si electrodes. © 2013 American Chemical Society.

Nano Letters

Li segregation induces structure and strength changes at the amorphous Si/Cu interface

Primary electron energy (Ep) dependent change in target current was studied on a grounded Au film in the range of 40 to 3500 eV. The current jumped suddenly from a negative to a positive value at ∼650 eV with increasing Ep, while it disappeared in reverse sweep and with increasing substrate temperature. Detailed analysis suggests that Ep dependent surface charging plays a pivotal role in flashover. Prior to critical Ep in the forward sweep, a gradual shift of a double peak-like structure towards high kinetic energy region in the secondary electron spectra also confirms surface charging effect. © 2013 AIP Publishing LLC.

Journal of Applied Physics

Primary electron energy dependent flashover in surface polarity on Au films

The search for oxide-based room-temperature ferromagnetism has been one of the holy grails in condensed matter physics. Room-temperature ferromagnetism observed in Nb-doped SrTiO3 single crystals is reported in this Rapid Communication. The ferromagnetism can be eliminated by air annealing (making the samples predominantly diamagnetic) and can be recovered by subsequent vacuum annealing. The temperature dependence of magnetic moment resembles the temperature dependence of carrier density, indicating that the magnetism is closely related to the free carriers. Our results suggest that the ferromagnetism is induced by oxygen vacancies. In addition, hysteretic magnetoresistance was observed for magnetic field parallel to the current, indicating that the magnetic moments are in the plane of the samples. The x-ray photoemission spectroscopy, the static time-of-flight and the dynamic secondary ion mass spectroscopy and proton induced x-ray emission measurements were performed to examine the magnetic impurities, showing that the observed ferromagnetism is unlikely due to any magnetic contaminant. © 2013 American Physical Society.

Physical Review B - Condensed Matter and Materials Physics

Reversible room-temperature ferromagnetism in Nb-doped SrTiO3 single crystals

The observation of a high-mobility two-dimensional electron gas between two insulating complex oxides, especially LaAlO3 /SrTiO3, has enhanced the potential of oxides for electronics. The occurrence of this conductivity is believed to be driven by polarization discontinuity, leading to an electronic reconstruction. In this scenario, the crystal orientation has an important role and no conductivity would be expected, for example, for the interface between LaAlO3 and (110)-oriented SrTiO3, which should not have a polarization discontinuity. Here we report the observation of unexpected conductivity at the LaAlO3 /SrTiO3 interface prepared on (110)-oriented SrTiO3, with a LaAlO3 -layer thickness-dependent metal-insulator transition. Density functional theory calculation reveals that electronic reconstruction, and thus conductivity, is still possible at this (110) interface by considering the energetically favourable (110) interface structure, that is, buckled TiO 2 /LaO, in which the polarization discontinuity is still present. The conductivity was further found to be strongly anisotropic along the different crystallographic directions with potential for anisotropic superconductivity and magnetism, leading to possible new physics and applications. © 2013 Macmillan Publishers Limited. All rights reserved.

Nature Communications

Anisotropic two-dimensional electron gas at the LaAlO3 /SrTiO3 (110) interface

The interface between the polar LaAlO 3 and nonpolar SrTiO 3 layers has been shown to exhibit various electronic and magnetic phases such as two-dimensional electron gas (2DEG), superconductivity, magnetism, and electronic phase separation. These rich phases are expected due to the strong interplay between charge, spin, and orbital degree of freedom at the interface between these complex oxides, leading to the electronic reconstruction in this system. However, until now all of these new properties have been studied extensively based on the interfaces which involve a polar LaAlO 3 layer. To investigate the role of the ABO 3 polar layer, here we study various combinations of polar/nonpolar oxide (NdAlO 3/SrTiO 3, PrAlO 3/SrTiO 3, and NdGaO 3/SrTiO 3) interfaces which are similar in nature to the LaAlO 3/SrTiO 3 interface. Our results show that all of these new interfaces can also produce 2DEG at their interfaces, supporting the idea that the electronic reconstruction could be the driving mechanism for the creation of the 2DEG at these oxide interfaces. Furthermore, the electrical properties of these interfaces are shown to be governed by the interface strain and the type of cations in the polar overlayers. Our observations may provide an approach to further tune the properties of the 2DEG at the selected polar/nonpolar oxide interfaces. © 2012 American Physical Society.