Physics

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The application of a NiO y /NiO x bilayer in resistive switching (RS) devices with x &gt; y was studied for its ability to achieve reliable multilevel cell (MLC) characteristics. A sharp change in resistance brought about by sweeping the voltage, along with an improved on/off ratio (&gt;103) and endurance (104) were achieved in the bilayer structure as compared to the single NiO x layer devices. Moreover, it was found that nonvolatile and stable resistance levels, especially the multiple low-resistance states of Cu/NiO y /NiO x /Pt memory devices, could be controlled by varying the compliance current. All the multilevel resistance states of the Cu/NiO y /NiO x /Pt bilayer devices were stable for up to 500 consecutive dc switching cycles, as compared to the Cu/NiO x /Pt single layer devices. The temperature-dependent variation of the high and low resistance states of both the bilayer and single layer devices was further investigated to elucidate the charge conduction mechanism. Finally, based on a detailed analysis of the experimental results, comparisons of the possible models for RS in bilayer and single layer memory devices have also been discussed. © 2016 IOP Publishing Ltd.

World University root node

(SoNS) School of Natural Sciences

Nanotechnology

Multilevel programming in Cu/NiO y /NiO x /Pt unipolar resistive switching devices

In this study, a non-faradaic electrochemical impedance spectroscopy has been employed for estimation of caffeine concentration in beverages. Impedance spectra were recorded by using a two electrode system without adding any redox reagents in the measured solutions. Electrochemical impedance data of caffeine solutions in pure water and beverages were measured and an appropriate equivalent electrical circuit model is developed to help in this investigative analysis. The interaction of caffeine molecules with the electrodes was primarily correlated to the formation of electrical double-layer at modified interface. Overall system impedance (|Z|), inverse of solution resistance (1/RS) and constant phase element of the system were further investigated from the equivalent electrical circuit and plotted as a function of pure caffeine concentration. Finally, the results obtained from spiked diluted cola beverages were compared with the pure caffeine sample. © 2016 The Authors.

Fulltext

International Journal of Electrochemical Science

Equivalent circuit models and analysis of electrochemical impedance spectra of caffeine solutions and beverages

Titanium dioxide (TiO2) has rich physical properties with potential implications for both fundamental physics and new applications. To date, the main focus of applied research is to tune its optical properties, which is usually done via doping and/or nanoengineering. However, understanding the role of d electrons in materials and possible functionalization of d-electron properties are still major challenges. Herewith, within a combination of an innovative experimental technique, high-energy optical conductivity, and state-of-the-art ab initio electronic structure calculations, we report an emerging, novel resonant exciton in the deep ultraviolet region of the optical response. The resonant exciton evolves upon low-concentration Ta substitution in anatase TiO2 films. It is surprisingly robust and related to strong electron-electron and electron-hole interactions. The d- and f-orbital localization, due to Ta substitution, plays an unexpected role, activating strong electronic correlations and dominating the optical response under photoexcitation. Our results shed light on a new optical phenomenon in anatase TiO2 films and on the possibility of tuning electronic properties by Ta substitution. © 2016 American Physical Society.

Physical Review B

Emerging giant resonant exciton induced by Ta substitution in anatase TiO2: A tunable correlation effect

Post-deposition annealing mediated evolution of self-decorated Au nanoparticles (NPs) on chemically etched Si pyramids is presented. A distinct transformation of Si surfaces from hydrophilic to hydrophobic is initially found after chemical texturing, showing an increase in contact angle (CA) from 58°to 98°(±1°). Further improvement of hydrophobicity with CA up to ∼118°has been established after annealing a 10 nm thick Au-coated Si pyramids at 400°C that led to the formation of Au NPs on Si facets along with self-ordering at the pyramid edges. Detailed x-ray diffraction studies suggest the evolution of crystalline Au NPs on strained Si facets. Microstructural studies, however, indicate no mixing of Au and Si atoms at the Au/Si interfaces, instead of forming Au nanocrystals at 400°C. The improved hydrophobicity of Si pyramids, even with Au NPs can be explained in the light of a decrease in solid fractional surface area according to Wenzel's model. Moreover, a sharp drop in specular reflectance from Si pyramids in the range of 300-800 nm, especially in the ultraviolet region up to ∼0.4\% is recorded in the presence of Au NPs by ultraviolet-visible spectroscopy, reflecting the possible use in photovoltaic devices with improved antireflection property. © 2016 AIP Publishing LLC.

Journal of Applied Physics

Self-decorated Au nanoparticles on antireflective Si pyramids with improved hydrophobicity

Magnetization, resistivity and 11B, 59Co NMR measurements have been performed on the Pauli paramagnet and the superconductors La0.9Y0.1Co2B2 (Tc≈4.2 K) and La(Co0.7Fe0.3)2B2 (Tc≈5.8 K). The site selective NMR experiment reveals the multiband nature of the Fermi surface in these systems. The temperature independent Knight shift and 1/T 1 T clearly indicate the absence of correlated low energy magnetic spin-fluctuations in the normal state, which is in contrast to other Fe-based pnictides. The density of states (DOS) of Co 3d electrons has been enhanced in superconducting La0.9Y0.1Co2B2 and La(Co0.7Fe0.3)2B2 with respect to the non superconducting reference compound LaCo2B2. The occurrence of superconductivity is related to the DOS enhancement.

Journal of Physics Condensed Matter

Absence of low energy magnetic spin-fluctuations in isovalently and aliovalently doped LaCo2B2 superconducting compounds

Transformation of self-assembled crystalline TiO2 nanorods to amorphous layer, and the corresponding impact on optical-bandgap (Eg) on Si pyramids are investigated by irradiating with 50 keV Ar+-ions. Initially, Eg is found to be reduced from 3.23 to 2.94 eV up to a fluence of 1 × 1016 ions/cm2, and discussed in terms of the rise in oxygen vacancies (VO). However, a sudden increase in Eg to 3.38 eV is detected at a fluence of 1 × 1017 ions/cm2 through evolution of voids by over-saturating VO, manifesting the appearance of degenerate states by shifting the Fermi level above the conduction band minimum via Burstein-Moss effect. © 2016 AIP Publishing LLC.

Applied Physics Letters

Defect-engineered optical bandgap in self-assembled TiO2 nanorods on Si pyramids

Saturation magnetization (Ms) of pristine bi-/tri-layered graphene (denoted as-FLG) is enhanced by over four (4) and thirty-four (34) times to 13.94 × 10-4 and 118.62 × 10-4 emu g-1, respectively, as compared to pristine FLGs (Ms of 3.47 × 10-4 emu g-1), via plasma-based-hydrogenation (known as graphone) and nitrogenation (known as N-graphene) reactions, respectively. However, upon organo-silane treatment on FLG (known as siliphene), the saturation magnetization is reduced by over thirty (30) times to 0.11 × 10-4 emu g-1, as compared to pristine FLG. Synchrotron based X-ray absorption near edge structure spectroscopy measurements have been carried out to investigate the electronic structure and the underlying mechanism responsible for the variation of magnetic properties. For graphone, the free spin available via the conversion of the sp2 → sp3 hybridized structure and the possibility of unpaired electrons from induced defects are the likely mechanism for ferromagnetic ordering. During nitrogenation, the Fermi level of FLGs is shifted upwards due to the formation of a graphitic like extra π-electron that makes the structure electron-rich, thereby, enhancing the magnetic coupling between magnetic moments. On the other hand, during the formation of siliphene, substitution of the C-atom in FLG by a Si-atom occurs and relaxes out the graphene plane to form Si-C tetrahedral sp3-bonding with a non-magnetic atomic arrangement showing no spin polarization phenomena and thereby reducing the magnetization. Thus, plasma functionalization offers a simple yet facile route to control the magnetic properties of the graphene systems and has potential implications for spintronic applications. © 2016 The Royal Society of Chemistry.

RSC Advances

Plasma modification of the electronic and magnetic properties of vertically aligned bi-/tri-layered graphene nanoflakes

In this paper, we discuss the parametric symmetries in different exactly solvable systems characterized by real or complex PT symmetric potentials. We focus our attention on the conventional potentials such as the generalized Pöschl Teller (GPT), Scarf-I, and PT symmetric Scarf-II which are invariant under certain parametric transformations. The resulting set of potentials is shown to yield a completely different behavior of the bound state solutions. Further, the supersymmetric partner potentials acquire different forms under such parametric transformations leading to new sets of exactly solvable real and PT symmetric complex potentials. These potentials are also observed to be shape invariant (SI) in nature.We subsequently take up a study of the newly discovered rationally extended SI potentials, corresponding to the above mentioned conventional potentials, whose bound state solutions are associated with the exceptional orthogonal polynomials (EOPs).We discuss the transformations of the corresponding Casimir operator employing the properties of the so(2,1) algebra.

Journal of Mathematical Physics

Parametric symmetries in exactly solvable real and PT symmetric complex potentials

In this paper, we consider the rational extensions of two different classes of PT symmetric complex potentials namely the asymptotically vanishing Scarf II and asymptotically non-vanishing Rosen–Morse II [ RM-II] and obtain the accompanying bound state eigenfunctions in terms of the exceptional Xm Jacobi polynomials and a certain class of orthogonal polynomials. By considering the asymptotic behavior of the exceptional polynomials, we also derive the reflection and transmission amplitudes for them and discuss the various novel properties of the corresponding amplitudes. © 2016 Elsevier Inc.

Annals of Physics

Scattering amplitudes for the rationally extended PT symmetric complex potentials

Contrary to common expectation, a left-sneutrino can occasionally be the lightest supersymmetric particle. This has important implications in both collider and dark matter studies. We show that same-sign tri-lepton (SS3L) events at the Large Hadron Collider, with any lepton having opposite sign vetoed, distinguish such scenarios, up to gluino masses exceeding 2 TeV. The jets+. MET signal rate is somewhat suppressed in this case, thus enhancing the scope of leptonic signals.