Toyanath Joshi

Preparation, characterization, and electrical properties of epitaxial NbO2 thin film lateral devices

Epitaxial NbO2 (110) films, 20 nm thick, were grown by pulsed laser deposition on Al2O3 (0001) substrates. The Ar/O2 total pressure during growth was varied to demonstrate the gradual transformation between NbO2 and Nb2O5 phases, which was verified using x-ray diffraction, x-ray photoelectron spectroscopy, and optical absorption measurements. Electric resistance threshold switching characteristics were studied in a lateral geometry using interdigitated Pt top electrodes in order to preserve the epitaxial crystalline quality of the films. Volatile and reversible transitions between high and low resistance states were observed in epitaxial NbO2 films, while irreversible transitions were found in case of Nb2O5 phase. Electric field pulsed current measurements confirmed thermally-induced threshold switching.

Electrically induced insulator to metal transition in epitaxial SmNiO3 thin films

We report on the electrically induced insulator to metal transition (IMT) in SmNiO3 thin films grown on (001) LaAlO3 by pulsed laser deposition. The behavior of the resistivity as a function of temperature suggests that the primary transport mechanism in the SmNiO3 insulating state is dominated by Efros-Shklovskii variable range hopping (ES-VRH). Additionally, the magnetic transition in the insulating state of SmNiO3 modifies the characteristics of the ES-VRH transport. Systematic DC and pulsed current-voltage measurements indicate that current-induced joule heating is the fundamental mechanism driving the electrically induced IMT in SmNiO3. These transport properties are explained in context of the IMT in SmNiO3 being related to the strong electron-lattice coupling.

STEM Video of Electronically-Driven Metal-Insulator Transitions in Nanoscale NbO 2 Devices

This paper is closed access. This article has been published in a revised form in Microscopy and Microanalysis https://doi.org/10.1017/S143192761600711X. This version is free to view and download for private research and study only. Not for re-distribution, re-sale or use in derivative works.

The role of defects in the electrical properties of NbO2 thin film vertical devices

Epitaxial NbO2 thin films were grown on Si:GaN layers deposited on Al2O3 substrates using pulsed laser deposition. Pulsed current-voltage (IV) curves and self-sustained current oscillations were measured across a 31 nm NbO2 film and compared with a similar device made from polycrystalline NbO2 film grown on TiN-coated SiO2/Si substrate. Crystal quality of the as grown films was determined from x-ray diffractometry, x-ray photoelectron spectroscopy and atomic force microscopy data. The epitaxial film device was found to be more stable than the defect-rich polycrystalline sample in terms of current switching and oscillation behaviors.

STEM EBIC mapping of the metal-insulator transition in thin-film NbO2

This article has been published in a revised form in Microscopy and Microanalysis https://doi.org/10.1017/S1431927617007802. This version is free to view and download for private research and study only. Not for re-distribution, re-sale or use in derivative works.

Erratum: "The role of defects in the electrical properties of NbO2 thin film vertical devices" [AIP Advances 6, 125006 (2016)]

We noticed that Figures 1, 2, and 4(a) in the original publication were of poor quality due to formatting issues. This erratum provides corrected versions of those figures. The original results and discussions were not affected. RHEED images in the inset to the Fig. 1 are now fully visible. Figure 2 shows now properly fitted frames for the AFM image with the correctly placed height scales. Figure 4(a) shows now a correctly presented block diagram for the effective measurement circuit.