Design and fabrication of an indigenous molecular beam ultraviolet photoelectron spectrometer

An ultraviolet photoelectron spectrometer for the study of van der Waals molecules has been designed and fabricated indigenously. The spectrometer consists of an HeI discharge lamp, a molecular beam sample inlet system, an electrostatic lens, a 180-degrees hemispherical electrostatic analyser and a channeltron detector. Performance of the spectrometer is illustrated with an example.

Vacuum ultraviolet circular dichroism spectrum of β-turn in solution

The vacuum ultraviolet circular dichroism spectrum of an isolated 4 → 1 hydrogen bonded β-turn is reported. The observed spectrum of N-acetyl-Pro-Gly-Leu-OH at − 40°C in trifluoroethanol is in good agreement with the theoretically calculated CD spectrum of the β-turn conformation. This spectrum, particularly the presence of a strong negative band around 180 nm and a large ratio [θ]201/[θ]225, can be taken as a characteristic feature of the isolated β-turn conformation. These CD spectral features can thus be used to distinguish the β-turn conformation from the β-structure in solution.

Metal-insulator transitions in Cr-doped V2O3 by x-ray and ultraviolet photoelectron spectroscopy

X-ray and ultraviolet photoelectron spectroscopy have been employed to investigate the high temperature metal-insulator transitions in V2O3 and (V0.99Cr0.01)2O3. The high temperature transitions are associated with more gradual changes in the 3d bands compared to the low-temperature transitions

Dynamics of I-asterisk(P-2(1/2)) production inthe ultraviolet photodissociation of alkyn iodides

The relative quantum yields, phi*, for the production of I*(P-2(1/2)) at 266, 280, and similar to 305 nm are reported for a series of primary alkyl iodides using the technique of two-photon laser-induced fluorescence for the detection of I(P-2(3/2)) and I*(P-2(1/2)) atoms. Results are analyzed by invoking the impulsive energy disposal model, which summarizes the dynamics of dissociation as a single parameter. Comparison of our data with those calculated by a more sophisticated time-dependent quantum mechanical model is also made. Near the red edge of the alkyl iodide A band, absorption contribution from the (3)Q(1) state is important and the dynamics near the (3)Q(0)-(1)Q(1) curve-crossing region seem to be influenced by the kinematics of the dissociation process

Ultraviolet photoelectron spectroscopy of the hydrogen bonded heterodimer H2Scdots, three dots, centeredHCl

The HeI photoelectron spectrum of the hydrogen bonded hetero-dimer H2Scdots, three dots, centeredHCl shows two vertical ionization energies at 10.91 and 12.16 eV. Ab initio MO calculations reveal that these features are due to the sulphur and chlorine lone pair ionizations respectively. Results show that while the ground ionic state is repulsive the first excited ionic state is strongly bound. The photoelectron spectrum of the diethyl sulphidecdots, three dots, centeredHCl complex is similar to that of H2Scdots, three dots, centeredHCl.

Solution processed reduced graphene oxide ultraviolet detector

Electronic properties of graphene have been studied more extensively than its photonic applications, in spite of its exciting optical properties. Recent results on solar cells, light emitting diodes and photodetectors show its true potential in photonics and optoelectronics. Here, we have explored the use of reduced graphene oxide as a candidate for solution processed ultraviolet photodetectors. UV detection is demonstrated by reduced graphene oxide in terms of time resolved photocurrent as well as photoresponse. The responsivity of the detectors is found to be 0.12 A/W with an external quantum efficiency of 40%. (C) 2011 American Institute of Physics. [doi:10.1063/1.3640222]

Structural Characterization and Ultraviolet Photoresponse of GaN Nanodots Grown by Molecular Beam Epitaxy

The present work explores the electrical transport and UV photoresponse properties of GaN nanodots (NDs) grown by molecular beam epitaxy (MBE). Single-crystalline wurtzite structure of GaN NDs is verified by X-ray diffraction and transmission electron microscopy (TEM). The interdigitated electrode pattern was created and current-voltage (I-V) characteristics of GaN NDs were studied in a metal-semiconductor-metal configuration. Dark I-V characteristics of lateral grown GaN NDs obeyed the Frenkel-Poole emission model, and the UV response of the device was stable and reproducible with on/off. The responsivity of the detectors is found to be 330 A/W with an external quantum efficiency of 1100%. (C) 2012 The Japan Society of Applied Physics

ZnO/Poly(3,4-ethylenedioxythiophene) Poly(styrenesulfonate) Based Ultraviolet and Visible Photodetectors: Role of Defects

Here, we report the ZnO/poly(3,4-ethylenedioxythiophene) poly(styrenesulfonate) (PEDOT:PSS) based photodetectors that can response to ultraviolet as well as visible light. The temporal response of the heterostructures for various excitations in the ultraviolet (UV) and visible range are performed. The time constants are found to be excitation-dependent, the response to visible light is better as compared to UV. The reason behind the better response to UV light is the high level of defects present in ZnO as confirmed by the photoluminescence (PL) measurements. This is corroborated by the time resolved fluorescence (TRF) measurements which provides sufficient information behind the slow response time under the UV excitations. The possible explanation being the non-radiative recombinations occurring due to the traps or impurities present in the film which slows down the photoresponse.

Room temperature synthesis of Mn2+ doped ZnS d-dots and observation of tunable dual emission: Effects of doping concentration, temperature, and ultraviolet light illumination

Mn2+ doped (0-50.0 molar %) ZnS d-dots have been synthesized in water medium by using an environment friendly low cost chemical technique. Tunable dual emission in UV and yellow-orange regions is achieved by tailoring the Mn2+ doping concentration in the host ZnS nanocrystal. The optimum doping concentration for achieving efficient photoluminescence (PL) emission is determined to be similar to 1.10 (at. %) corresponding to 40.0 (molar %) of Mn2+ doping concentration used during synthesis. The mechanism of charge transfer from the host to the dopant leading to the intensity modulated tunable (594-610 nm) yellow-orange PL emission is straightforwardly understood as no capping agent is used. The temperature dependent PL emission measurements are carried out, viz., in 1.10 at. % Mn2+ doped sample and the experimental results are explained by using a theoretical PL emission model. It is found that the ratio of non-radiative to radiative recombination rates is temperature dependent and this phenomenon has not been reported, so far, in Mn2+ doped ZnS system. The colour tuning of the emitted light from the samples are evident from the calculated chromaticity coordinates. UV light irradiation for 150 min in 40.0 (molar %) Mn2+ doped sample shows an enhancement of 33% in PL emission intensity. (C) 2013 American Institute of Physics. http://dx.doi.org/10.1063/1.4795779]

Surfactant free, non-aqueous method, for the deposition of ZnO nanoparticle thin films on Si(100) substrate with tunable ultraviolet (UV) emission

We report, strong ultraviolet (UV) emission from ZnO nanoparticle thin film obtained by a green synthesis, where the film is formed by the microwave irradiation of the alcohol solution of the precursor. The deposition is carried out in non-aqueous medium without the use of any surfactant, and the film formation is quick (5 min). The film is uniform comprising of mono-disperse nanoparticles having a narrow size distribution (15-22 nm), and that cover over an entire area (625 mm(2)) of the substrate. The growth rate is comparatively high (30-70 nm/min). It is possible to tune the morphology of the films and the UV emission by varying the process parameters. The growth mechanism is discussed precisely and schematic of the growth process is provided.

Monitoring of ultraviolet pulse rate dependent photomechanical actuation in carbon nanotubes using fiber Bragg gratings

In this Letter, we present a non-contact method of controlling and monitoring photomechanical actuation in carbon nanotubes (CNT) by exposing it to ultra-violet radiation at different pulse rates (10 to 200 Hz). This is accomplished by imparting a reversible photo induced strain (5-330 mu epsilon) on CNT coated fibre Bragg gratings; CNT undergoes an internal reversible structural change due to cyclic photon absorption that leads to the development of mechanical strain, which in turn allows reversible switching of the Bragg wavelength. The results also reveal an interesting pulse rate dependent rise and fall times of photomechanical actuation in CNT. (C) 2014 AIP Publishing LLC.

Simple chemical aqueous synthesis of dahlia nanoflower consisting of finger-like ZnO nanorods and observation of stable ultraviolet photoluminescence emission

In this work, we have reported the synthesis of dahlia flower-like ZnO nanostructures consisting of human finger-like nanorods by the hydrothermal method at 120 degrees C and without using any capping agent. Optical properties of the samples, including UV-vis absorption and photoluminescence (PL) emission characteristics are determined by dispersing the samples in water as well as in ethanol media. The quenching of PL emission intensity along-with the red shifting of the PL emission peak are observed when the samples are dispersed in water in comparison to those obtained after dispersing the samples in ethanol. It has been found that PL emission characteristic, particularly the spectral nature of PL emission, of the samples remains almost unaltered (except some improvement in UV PL emission) even after thermally annealing it for 2 h at the temperature of 300 degrees C. Also the synthesized powder samples, kept in a plastic container, showed a very stable PL emission even after 15 months of synthesis. Therefore, the synthesized samples might be useful for their applications in future optoelectronics devices. (C) 2014 Elsevier Ltd. All rights reserved.

Highly Dense ZnO Nanowires Grown on Graphene Foam for Ultraviolet Photodetection

Growth of highly dense ZnO nanowires (ZnO NWs) is demonstrated on three-dimensional graphene foam (GF) using resistive thermal evaporation technique. Photoresponse of the as-grown hybrid structure of ZnO NWs on GF (ZnO NWs/GF) is evaluated for ultraviolet (UV) detection. Excellent photoresponse with fast response and recovery times of 9.5 and 38 s with external quantum efficiency of 2490.8% is demonstrated at low illumination power density of 1.3 mW/cm(2). In addition, due to excellent charge carrier transport, mobility of graphene reduces the recombination rate of photogenerated charge carriers, hence the lifetime of photogenerated free charge carriers enhances in the photodetectors.