Proliferation of the Light and Gas Interaction with GaN Nanorods Grown on a V-Grooved Si(111) Substrate for UV Photodetector and NO2 Gas Sensor Applications.

Although excellent milestones of III-nitrides in optoelectronic devices have been achieved, the focus on the optimization of their geometrical structure for multiple applications is very rare. To address this issue, we exclusively designed a prototype device to enhance the photoconversion efficiency and gas interaction capabilities of GaN nanorods (NRs) grown on a V-grooved Si(100) substrate with Si(111) facets for photodetector and gas sensor applications. Photoluminescence studies have demonstrated an increased surface-to-volume ratio and light trapping for GaN NRs grown on V-grooved Si(111). GaN NRs on V-grooved Si(100) with Si(111) facets exhibited high photodetection performance in terms of photoresponsivity (217 mA/cm2), detectivity (3 × 1013 Jones), and external quantum efficiency (2.73 × 105%) compared to GaN NRs grown on plain Si(111). Owing to the robust interconnection between NRs and a high surface-to-volume ratio, the GaN NRs grown on V-grooved Si(100) with Si(111) facets probed for NO2 detection with the assistance of photonic energy. The photo-assisted sensing makes it possible to detect NO2 gas at the ppb level at room temperature, resulting in significant power reduction. The device showed high selectivity to NO2 against other target gases, such as NO, H2S, H2, NH3, and CO. The device showed excellent long-term stability at room temperature; the humidity effect on the device performance was also examined. The excellent device performance was due to the following: (i) benefited from the V-grooved Si structure, GaN NRs significantly trapped the incident light, which promoted high photocurrent conversion efficiency and (ii) GaN NRs grown on V-grooved Si(100) with Si(111) facets increased the surface-to-volume ratio and thus improved the gas interaction with a better diffusion ratio and high light trapping, which resulted in increased response/recovery times. These results represent an important forward step in prototype devices for multiple applications in materials research.

Dataset on electro-optically tunable smart-supercapacitors based on oxygen-excess nanograin tungsten oxide thin film.

The dataset presented here is related to the research article entitled "Highly Efficient Electro-optically Tunable Smart-supercapacitors Using an Oxygen-excess Nanograin Tungsten Oxide Thin Film" (Akbar et al., 2017) [9] where we have presented a nanograin WO3 film as a bifunctional electrode for smart supercapacitor devices. In this article we provide additional information concerning nanograin tungsten oxide thin films such as atomic force microscopy, Raman spectroscopy, and X-ray diffraction spectroscopy. Moreover, their electrochemical properties such as cyclic voltammetry, electrochemical supercapacitor properties, and electrochromic properties including coloration efficiency, optical modulation and electrochemical impedance spectroscopy are presented.

Switching Power Universality in Unipolar Resistive Switching Memories.

We investigate the resistive switching power from unipolar resistive switching current-voltage characteristics in various binary metal oxide films sandwiched by different metal electrodes, and find a universal feature (the so-called universality) in the switching power among these devices. To experimentally derive the switching power universality, systematic measurements of the switching voltage and current are performed, and neither of these correlate with one another. As the switching resistance (R) increases, the switching power (P) decreases following a power law P ∝ R(-ß), regardless of the device configurations. The observed switching power universality is indicative of the existence of a commonly applicable switching mechanism. The origin of the power universality is discussed based on a metallic filament model and thermo-chemical reaction.

Effect of Electronegativity on Bipolar Resistive Switching in a WO3-Based Asymmetric Capacitor Structure.

This study investigates the transport and switching time of nonvolatile tungsten oxide based resistive-switching (RS) memory devices. These devices consist of a highly resistive tungsten oxide film sandwiched between metal electrodes, and their RS characteristics are bipolar in the counterclockwise direction. The switching voltage, retention, endurance, and switching time are strongly dependent on the type of electrodes used, and we also find quantitative and qualitative evidence that the electronegativity (χ) of the electrodes plays a key role in determining the RS properties and switching time. We also propose an RS model based on the role of the electronegativity at the interface.

Multi-functional reactively-sputtered copper oxide electrodes for supercapacitor and electro-catalyst in direct methanol fuel cell applications.

This work reports on the concurrent electrochemical energy storage and conversion characteristics of granular copper oxide electrode films prepared using reactive radio-frequency magnetron sputtering at room temperature under different oxygen environments. The obtained films are characterized in terms of their structural, morphological, and compositional properties. X-ray diffraction, X-ray photoelectron spectroscopy and scanning electron microscope studies reveal that granular, single-phase Cu2O and CuO can be obtained by controlling the oxygen flow rate. The electrochemical energy storage properties of the films are investigated by carrying out cyclic voltammetry, galvanostatic charge/discharge and electrochemical impedance spectroscopy tests. The electrochemical analysis reveals that the Cu2O and CuO electrodes have high specific capacitances of 215 and 272 F/g in 6 M KOH solution with a capacity retention of about 80% and 85% after 3000 cycles, respectively. Cyclic voltammetry and chronoamperometry are used to study the electrochemical energy conversion properties of the films via methanol electro-oxidation. The results show that the Cu2O and CuO electrodes are electro-catalytically active and highly stable.

Resistance switching mode transformation in SrRuO3/Cr-doped SrZrO3/Pt frameworks via a thermally activated Ti out-diffusion process.

This work reports on a mechanism for irreversible resistive switching (RS) transformation from bipolar to unipolar RS behavior in SrRuO3 (SRO)/Cr-doped SrZrO3 (SZO:Cr)/Pt capacitor structures prepared on a Ti/SiO2/Si substrate. Counter-clockwise bipolar RS memory current-voltage (I-V) characteristics are observed within the RS voltage window of -2.5 to +1.9 V, with good endurance and retention properties. As the bias voltage increases further beyond 4 V under a forward bias, a forming process occurs resulting in irreversible RS mode transformation from bipolar to unipolar mode. This switching mode transformation is a direct consequence of thermally activated Ti out-diffusion from a Ti adhesion layer. Transition metal Ti effectively out-diffuses through the loose Pt electrode layer at high substrate temperatures, leading to the unintended formation of a thin titanium oxide (TiO(x) where x < 2) layer between the Pt electrode and the SZO:Cr layer as well as additional Ti atoms in the SZO:Cr layer. Cross-sectional scanning electron microscopy, transmission electron microscopy and Auger electron spectroscopy depth-profile measurements provided apparent evidence of the Ti out-diffusion phenomenon. We propose that the out-diffusion-induced additional Ti atoms in the SZO:Cr layer contributes to the creation of the metallic filamentary channels.