Search

The carbon and nitrogen derived from ZIF-8 embedded in TiO2/Fe2O3 (i.e., C,N-ZIF/TiFe) nanostructures exhibit superior electrocatalytic performance toward oxygen evolution reactions (OER), hydrogen evolution reactions (HER), and overall H2O splitting. The results showed that the C,N-ZIF/TiFe nanostructure was the best catalyst in comparison to ZIF/TiFe and TiFe nanostructures toward HER and OER. These results revealed that combining the highly active carbon and nitrogen from ZIF-8 with a TiO2/Fe2O3 semiconductor enriched the overall H2O splitting. A possible OER mechanism is attributed to some groups that support the surface active site of the catalyst and adsorbent intermediate species. Finally, this inexpensive electrocatalyst was synthesized without noble metals and showed superior electrocatalytic activity and great stability with the potential to achieve ground-breaking and novel applications in fuel cells.

Europium-doped (0.01–0.04) Al[Formula: see text]La[Formula: see text]TiO3 (AELTO) nanoparticles (NPs) series were synthesized using a hydrothermal method. These NPs were investigated for structural, and morphological studies through XRD, FTIR, FESEM and TEM analysis. Scherrer’s formula and Williamson–Hall (W–H) analysis were employed to determine crystallite size and lattice strain. The crystallite size was decreased with an increase in Eu content up to 0.03 wt.%. The surface morphology and percentage of elementals of AELTO NPs were investigated using FESEM with EDX as well as TEM analysis. The vibrational modes of AELTO NPs were attained by employing FTIR spectra. These modes are deferred mainly on chemical composition, crystallinity, morphology and strain of the AELTO NPs. Optical bandgaps of AELTO NPs were calculated and found to be in the range of 3.40–3.37[Formula: see text]eV with the increase of Eu content. These NPs could find potential applications for solid state lighting and down-shifter for solar energy harvesting.

We report on the influence of incorporation of Ta2O5 thin film at the interface of Au/GaN by means of e-beam evaporation technique. The fabricated Au/Ta2O5/n-GaN MIS junctions have been analysed using I–V measurements and were extended to a voltage range of ± 20 V. The Schottky diode parameters for instance Φbo, n and RS values are evaluated using I–V curves at room temperature. The statistical distribution analysis provides the mean ‘Φbo’ value of 0.85 eV with deviation of 0.00181 eV and mean value from ‘n’ is 1.36 with a normal deviation of 0.00562. Two important electrical parameters such as RS and Rsh values are also extracted from I–V characteristics. Furthermore, Cheung, Norde, modified Norde, Hernandez and Chattopadhyay methods are used to evaluate the Schottky barrier parameters from I–V data. The comparison is made between the extracted electrical parameters such as n, Φbo and RS from I–V characteristics of Au/Ta2O5/n-GaN MIS junctions and are in well agreement with each other. Under forward-bias, the fabricated Au/Ta2O5/n-GaN MIS junction conduction mechanisms such as ohmic and SCL were found to be dominant at lower and higher voltage regimes, respectively. By fitting reverse-bias region of I–V curves, PF conduction mechanism was found to be dominant at the interfaces of Au/Ta2O5/n-GaN. In conclusion, the obtained superior rectification ratio of 6.06 × 104 and higher SBH of 0.87 eV was ascribed to the purposefully deposited undoped GaN buffer layer between epitaxial GaN and sapphire substrate.

Cost effective and highly sensitive Cr/Ni/Cu/n-GaN/Ti/Al asymmetric type metal-semiconductor-metal (MSM) Schottky barrier ultraviolet photodetector has been fabricated at room temperature. Surface morphological and oxidation states of Cr and Ni metal layers were investigated using atomic force microscopy and X-ray absorption spectroscopy, respectively. Current-voltage (I–V) measurements were performed in dark and at various wavelength illuminations in the range 350–370 nm indicated a very good rectification ratio of 1.5–4.6 × 104 (at ± 7 V) due to the utilisation of two metal stacks with different workfunctions. The Schottky diode parameters such as Schottky barrier height, ideality factor and series resistance were calculated at different wavelength illuminations using different reliable approaches. The spectral responses measured from the fabricated GaN based UV PD at several biases in the wavelength range 300–450 nm were found to be bias dependent due to the internal gain effect. Using time dependent photoresponses the rise/fall time values were evaluated at 5 V of different wavelengths and were found to be in the range 1.55–2.05 s and 2.92–3.35 s, respectively. Consequently, from current-voltage (I–V), photoresponsivity and time-dependent photoresponse studies, the 365 nm was found to be the optimum and reflects the high wavelength selectivity for the fabricated GaN based A-type MSM UV PD under study.

We have developed and first reported Au/Ni/Pr2O3/GaN broadband photodetector device with photoresponsivity from 205 nm to 750 nm under self-powered mode. Using the Tauc's plot, the direct optical bandgap was found to be 4.8, 2.45 and 2.35 eV for the as-deposited, 550 °C and 650 °C post annealed samples, respectively. XRD study revealed that the phase of the as-deposited and post-annealed Pr2O3 films on GaN was monoclinic in nature. Atomic force microscopy method was engaged in non-contact mode to investigate the surface morphology of Pr2O3 films on GaN and the rms surface roughness was improved for the 650 °C post-annealed sample as 1.1 nm compared to other samples. In XPS study, two main Pr3d well separated XPS peaks were noticed at 933.5 eV (m) and 953.9 eV (m′) which corresponds to spin-orbit doublets of 3d5/2 and 3d3/2, respectively. In addition, the transient response measurements of the fabricated 650 °C post annealed device confirmed good stability even for the applied bias voltage of 20 V in the entire UV region. Further, the 650 °C post annealed device at 20 V provided best rise and fall times of 0.57 s and 0.41 s at 360 nm, respectively. The responsivity of the fabricated BB PD device at 650 °C revealed the evidence of bias dependency because of photoconductive gain. The attained progress in the fabricated PD device performance was due to the improved light absorption as evidenced from the optical absorption study. This results the transport of photogenerated electron-hole pairs across the bandgap by limiting recombination/trap states and intentionally deposited LT GaN buffer layer at the interface of sapphire/GaN. These results suggest that the developed BB PD device could also have the potential usage in optoelectronic device applications.

Three-dimensional MoS2 (3D-MoS2) microflowers consisting electrode of few-layered nanoflakes synthesized via a hydrothermal approach is a promising material for ultrahigh-performance symmetric supercapacitors. A three-electrode configuration of the 3D-MoS2 microflowers exhibited a remarkable electrolytic specific capacitance of 243.31F g−1 at 0.5 A g−1 and 98.71% retention after 2000 charge/discharge sequences at 8 A g−1. The fabricated coin cell-type symmetric supercapacitor devices (SSDs) showed an ultrahigh power density (Pd) of 2412.15 W Kg−1 at an energy density (Ed) of 1.06 Wh Kg−1, exhibiting the high energy storage capability of the 3D-MoS2 microflowers, thus enabling their application to electrodes in hybrid energy storage devices.

Dysprosium-doped fluorophosphate glasses (P2O5–CaF2–BaF2–TiO2-Dy2O3) have been prepared using melt-quenching technique and characterized their optical, structural, thermal and photoluminescence properties. Thermal stability (128 °C) of 0.5 mol% Dy2O3-doped glass has been estimated using Differential thermal analysis. Functional groups for 0.5 mol% Dy2O3-doped glass have been studied by Fourier Transform Infrared spectrum. Absorption spectra have been utilized for estimating the Judd-Ofelt (JO) parameters and allied properties. Several excitation wavelengths (350, 365, 387, 425, 452 and 472 nm) have been used for pumping the Dy3+ ions and analyzed for white luminescence. Intense emission has been observed for 0.5 and 1.5mol% of Dy2O3-doped glasses under 387 nm excitation. The 4F9/2 → 6H13/2 transition at 573 nm has unveiled a high stimulated emission cross-section (σSE) of 41.52 × 10−22 cm2 for 0.5 mol% Dy2O3-doped glass. CIE coordinates fall close to the white region in CIE diagram, and hence these glasses are suitable for cold white light emitting diode applications.

GaN based metal-insulator-semiconductor (MIS) type ultraviolet photodetector was fabricated and investigated using high-k dielectric CeO2 as an insulating oxide layer. Using XRD analysis, the phase formation of the as-deposited CeO2 films on GaN was found to be cubic fluorite. Non-contact mode atomic force microscopy technique was utilized and explored the surface morphology of CeO2 films on GaN composed of prearranged clusters of spherical shape with an average rms surface roughness of 0.428 μm. XPS analysis has revealed the existence of two oxidation states such as Ce3+ and Ce4+ in the Ce3d spectral envelop. Using absorbance versus wavelength data, the Tauc's plot was plotted and calculated a direct optical bandgap of 3.52 eV. The current-voltage (I–V) characteristics extracted from the device revealed the symmetric behavior or formation of back-to-back Schottky barrier at the metal-semiconductor (MS) interface. Photoresponsivity of the device at +10 V bias was calculated as 28.99 A/W and it is higher compared to the values extracted from metal-semiconductor-metal (MSM) type UV PDs reported in the literature. Furthermore, the transient response characteristics of the prepared device showed good stability with almost same rise time and fall time of ~2.73 s and ~5.35 s, respectively. Based on the device performance, the proposed MIS type structure could be a suitable for the development of ultraviolet photodetectors.

Holmium (Ho3+)-doped fluorophosphate glasses (P2O5–BaF2–CaF2–TiO2–Ho2O3, PCfBfTiH) were fabricated by melt-quenching technique. The glass transition (548 °C) and crystallization (577 °C) temperatures and glass stability factor (161 °C) were obtained from DSC analysis. Judd-Ofelt (JO) intensity parameters (Ω2, Ω4 and Ω6) of PCfBfTiH15 glass were evaluated. Intense green (545 nm) emission was obtained for the 5S2 + 5F4 → 5I8 transition upon excitation of 451 nm. The stimulated emission cross-section (σem) of PCfBfTiH15 glass was found to be as high as 2.01 × 10−20 cm2. Decay curves of the 5S2 + 5F4 → 5I8 transition were analyzed by double exponential function. High lifetime of 11.29 μs for the 5S2 + 5F4 level was obtained. The CIE chromaticity coordinates for the emission spectra were professed that the green emission owing to the 5S2 + 5F4 → 5I8 transition may be useful for laser and display applications at around 545 nm.