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Effect of nitridation temperature on formation and properties of GaN nanowall networks on sapphire (0001) grown by laser MBE
No full textVertical aligned GaN nanowall networks (NWN) have been grown on sapphire (0 0 0 1) substrates using laser assisted molecular beam epitaxy (LMBE) by tuning the sapphire pre-nitridation temperature (200-600 degrees C). Field emission scanning electron microscopy studies showed the formation of hexagonal shaped vertical GaN NWN with wall width of 8-20 nm on high temperature (600 degrees C) nitridated sapphire whereas flower shape granular GaN structure with grain size of 50-240 nm was obtained on low temperature (200 degrees C) nitridated sapphire. The crystalline properties of the GaN NWN have been studied using high resolution X-ray diffraction (HR-XRD). The results show that the full width at half maximum of the GaN(0 0 0 2) X-ray rocking curve has a relatively low value compared to previous reports of hetero-epitaxial grown GaN NWN on sapphire and other substrates. Raman spectroscopy measurements revealed the presence of compressive stress in film whereas tensile stress in GaN NWN structures which is also complimented by HR-XRD analysis. The room temperature photoluminescence spectroscopy measurement for NWN having tip width 8-20 nm showed a 94 meV blue-shift in near band edge emission, even though NWN experienced with tensile stress, which confirm the observation of quantum size effect. The hetero-epitaxial growth of porous GaN NWN with high crystalline quality holds promise for applications in field of nitride based sensors and the enhancement of light extraction efficiency in optoelectronics devices
Estimation of the ion-trap assisted electrical loads and resulting BBR shift
Get PDFCapacitive, inductive and resistive loads of an ion-trap system, which can be modelled as LCR circuits, are important to know for building a high accuracy experiment. Accurate estimation of these loads is necessary for delivering the desired radio frequency (RF) signal to an ion trap via an RF resonator. Of particular relevance to the trapped ion optical atomic clock, determination of these loads lead to accurate evaluation of the Black-Body Radiation (BBR) shift resulting from the inaccurate machining of the ion-trap itself. We have identified different sources of these loads and estimated their values using analytical and finite element analysis methods, which are found to be well in agreement with the experimentally measured values. For our trap geometry, we obtained values of the effective inductive, capacitive and resistive loads as: 3.1 mu H, 3.71 (1) mu H, 3.68 (6) mu H; 50.4 pF, 51.4 (7) pF, 40.7 (2) pF; and 1.373 Omega, 1.273 (3)Omega, 1.183 (9)Omega by using analytical, numerical and experimental methods, respectively. The BBR shift induced by the excess capacitive load arising due to machining inaccuracy in the RF carrying parts has been accurately estimated, which results to a fractional frequency shift of 6.6 x 10(-17) for an RF of 1 kV at 2 pi x 15 MHz and with +/- 10 mu m machining inaccuracy. This needs to be incorporated into the total systematic uncertainty budget of a frequency standard as it is about one order of magnitude higher than the present precision of the trapped ion optical clocks
Reduction of Rocksalt Phase in Ag-Doped Ge2Sb2Te5: A Potential Material for Reversible Near-Infrared Window
Get PDFhase-change materials are attracting much attention in the scientific and engineering communities owing to their applications and underlying basic phenomena. Ge2Sb2Te5 is reversible-phase-change material (amorphous to crystalline and vice versa) that is used for optical data storage and phase-change random-access memory and has recently been explored for use as a reversible near-infrared (NIR) window [Singh et al., Appl. Phys. Lett. 111, 261102 (2017)]. For a reversible NIR window, large transmission contrast between two phases and low phase-transition temperature are required to reduce the power consumption. In the present work, phase transition in thermally deposited (Ge2Sb2Te5)(100-x)Ag-x (x = 0, 1, 3, 5, and 10) thin films is achieved by vacuum thermal annealing. Transmission sharply decreases with phase transition in the NIR region. Ge2Sb2Te5 shows large transmission contrast (more than 50%) in the wavelength range from 1600 to 3200 nm with phase transition from an amorphous to a hexagonal-close-packed structure at 260 degrees C. In (Ge2Sb2Te5)(90)Ag-10 thin films, a similar transmission contrast is achieved at a comparatively lower temperature (160 degrees C) due to reduction of the rocksalt phase. Distortion of the host lattice with addition of 10% Ag is confirmed from the drastic change in the density of states in the valence band and the shift in core-level (3d) spectra of Ag, Sb, and Te. This distortion enables a hexagonal-close-packed phase in (Ge2Sb2Te5)(90)Ag-10 thin films to be obtained at 160 degrees C. (Ge2Sb2Te5)(90)Ag-10 could be a potential candidate for a reversible NIR window as it requires less power to achieve phase transition and high transmission contrast
Tb3+ and Eu3+ Doped Zinc Phosphate Glasses for Solid State Lighting Applications
No full textTb3+ and Eu3+ doped zinc phosphate (ZP) glasses were prepared by conventional melt-quenching technique and their photoluminescence properties were investigated in detail. For, Tb3+ doped glasses the intense emission was at 545 nm corresponding to D-5(4)-> F-7(5) transition under 377 nm n-UV excitation. The optimized concentration for Tb3+ doped zinc phosphate glass was 3 mol% and above this concentration quenching takes place. The Eu3+ doped zinc phosphate glass revealed intense emission at 613 nm attributed to the D-5(0)-> F-7(2) transition under intense 392 nm n-UV excitation. The concentration quenching phenomenon was not observed in the Eu3+ doped ZP glasses. The CIE chromaticity coordinates for 3 mol% Tb3+ and 5 mol% Eu3+ doped ZP glasses were found to (0.283, 0.615) and (0.652, 0.331) lying in the green and red regions, respectively. The above mentioned results indicate that the prepared glass are suitable for application in the field of lighting and display devices
Biofunctionalized graphene oxide wrapped carbon nanotubes enabled microfluidic immunochip for bacterial cells detection
No full textA sensitive and selective microfluidic immunochip was fabricated for detection ofSalmonella typhimurium (S. typhimurium) bacterial cells. In this sensor, graphene oxide (GO) nano sheets wrapped carboxylated multiwalled carbon nanotubes (cMWCNTs) composite acted as a transducer material. The colloidal solution of GO-cMWCNTs composite was selectively deposited onto patterned indium tin oxide (ITO) electrode and sealed with polydimethylsiloxane (PDMS) micro channels. The S. typhimurium antibodies (StAb) were in situ biofunctionalized followed by EDC-NHS covalent chemistry via amidation reaction. The presence of abundant functional groups at the GO-cMWCNTs composite improved the loading of antibodies (StAb) against S. typhimurium leading to improved biosensing characteristics. Wrapping of cMWCNTs with GO resulted in superior electron transfer behavior enhancing the sensitivity (162.47 mu A/CFU-1/mLcm(-2)) almost two folds as compared to that based on GO (89.16 mu A/CFU-1/mLcm(-2)) sheets for bacterial cells detection. Besides this, GO wrapped cMWCNTs integrated microfluidics biosensor offered low detection limit as 0.376 CFU/mL and negligible interference due to presence of Escherichia coli (E. coli ( 0157:H7)
Topological Insulator Based Dual State Photo-Switch Originating Through Bulk and Surface Conduction Channels
No full textTopological insulators are novel electronic materials, where time reversal symmetry protects the spin-polarized surface states from backscattering. Although, the bulk offers a trivial semiconducting response to incident light, but the metallic surface states exhibit interesting electrical response towards the incident radiation, such as polarization dependent surface photocurrent and topological phase transitions. Here, we study the temperature dependent near-infrared photoresponse in bismuth selenide (Bi2Se3) nano-flakes. A very good photo-sensitivity to near-infrared 800nm wavelength is observed for the temperature range 300-2K. Voltage responsivity at 2K (1.481x10(10)VW(-1)) is estimated to be four-order greater than at 300K (2.095x10(6)VW(-1)) and is comparatively much higher than the previously reported values of voltage responsivity in other materials. Interestingly, we also find the temperature dependent existence of both positive and negative photoresponse in our device. An anomalous photoresponse reversal is observed at 2K, where resistance of the nano-flake increases under light illumination. We propose that this phenomenon is due to the topological surface states, which have dominant transport contribution at very low temperatures. These observations establish the fact that topological insulators can be further engineered to develop a dual state photo-switch, by manipulating the bulk and surface state conduction contribution
Films and dispersions of reduced graphene oxide based Fe2O3 nanostructure composites: Synthesis, magnetic properties and electrochemical capacitance
No full textFilms and dispersions of reduced graphene oxide (rGO) composites with Fe2O3 nanostructures have been synthesized by liquid/liquid interface and co-precipitation methods, respectively. Gamma phase, Fe2O3 nanoparticles with rGO are obtained as aqueous dispersions by co-precipitation method while Fe2O3 nanostructures consisting of a mixture of alpha and gamma phases are obtained in the form of freestanding thin films at the liquid/liquid interface. Different morphologies of Fe2O3 such as nano particles and nanorods are obtained by employing a modified or bare liquid/liquid interface. The nucleation and growth in this case is controlled by the density of oxygen functional groups on rGO. A comparison of the magnetic properties of dispersion and films of nanocomposites and their constituents are presented. rGO-gamma Fe2O3 dispersions show superparamagnetic nature while films exhibit extremely low magnetic moments confirming the presence of mixed phases of Fe2O3. Electrochemical capacitance studies of nanocomposite films reveal contributions due to electrical double layer capacitance of rGO and pseudocapacitance of Fe2O3 nanostructures and a specific capacitance 64.5 Fig at 2 mV/s is estimated. These films in microgram quantities without the aid of any binders exhibit good adhesion on carbon electrodes with excellent recyclability and less internal resistance and are promising for applications as supercapacitors
Functionalized MoS2 nanosheets assembled microfluidic immunosensor for highly sensitive detection of food pathogen
No full textTwo dimensional nanomaterials such as molybdenum disulfide (MoS2) has gained significant interest in designing electrochemical devices for biosensing application. In this work, we have designed cetyltrimethyl ammonium bromide (CTAB) functionalized MoS2 nanosheets (CTAB-MoS2-NS) for conjugation of protein on the microfluidics electrode for Salmonella typhimurium (S.typhimurium) detection. MoS2 nanosheets from the bulk MoS2 were synthesized using CTAB assisted exfoliation methods resulting into positive charge on the CTAB-MoS2-NS. Further, optical and electron microscopic studies of CTAB-MoS2-NS reveal, its suitability for biosensing application. These CTAB-MoS2-NS were deposited onto the patterned hydrolyzed indium tin oxide (ITO) microelelctrode, utilizing the strong electrostatic interaction with the positively charged CTAB-MoS2-NS. Then microelectrode has been integrated with polydimethylsiloxane (PDMS) microfluidic device to design a Lab on a Chip platform for S.typhimurium detection. Detection of the S.typhimurium cells have been performed using electrochemical impedance spectroscopy (EIS) technique. The fabricated microfluidic immunosensor offers highly improved biosensing parameters, as sensitivity was found to be 1.79 k Omega/CFU-1/mL cm(-2) with the detection limit 1.56 CFU mL(-1) in the wide detection range of 10(1-)10(7) CFUmL(-1
Nanostructured Cu2ZnSnS4 (CZTS) thin film for self-powered broadband photodetection
No full textNanostructured materials exhibit broad spectral photodetection, strong light matter interaction and exotic optoelectronic properties compared to their bulk counterpart. To overcome the limitations of silicon based photodetectors, various nanomaterials have been investigated. Here we have used industrially viable stacked layer reactive sputtering method to grow rice-like nanostructured (rln) Cu2ZnSnS4 (CZTS) thin films. The rln-CZTS film showed optical absorption coefficient one order of magnitude greater than the plain thin films of CZTS. Further, even under zero bias condition, broad spectral response (in visible and near infrared range) was observed. The rise and decay time constants for visible (532 nm) and near infrared (NIR) (1064 nm) light incident were 208 ms, 175 ms and 681 ms, 778 ms, respectively (for 1 mV bias). The improvement in photocurrent has been attributed to enhanced light harvesting due to the presence of nanostructures in thin film. Detectivity of 4.48 x 10(8) Jones over a large area was observed indicating that rln-CZTS would be a potential material for other technical applications. Deposition of nanostructured CZTS using industrially viable reactive sputtering with short anneal and fabrication of self-powered broadband photodetection device with low rise and decay time constants are the novelties of this work
Simple Extraction Cum RP-HPLC Method for Estimation of Nanotized Quercetin in Serum and Tissues of Mice
No full textIn recent years, several studies have focused on antioxidant, anti-inflammatory, and anti-cancer activities of quercetin (3,3',4',5, -pentahydroxyflavone). The nanotization of quercetin was shown to enhance its therapeutic efficacy due to smaller particle size. In the present study, an additional step was added to simple extraction cum RP-HPLC method for the quantification of nanotized quercetin (nQ) in biological samples to understand the pharmacokinetics and biodistribution of nQ following intravenous administration. The proposed method involves extraction of nQ from blood serum and tissues of mice with 2N HCl in comparison to well-known DMSO:MeOH mix method. The HCl extraction was found to be 2 - 3 times more efficient than DMSO:MeOH mix method. Results showed that the amount of nQ at various time intervals in the serum and tissues was 2 - 3 fold greater for HCl extraction than for DMSO:MeOH mix method, suggesting that HCl extraction must take into account nQ bound with protein. The reversed-phase HPLC was used for nQ detection, which showed the nQ retention time of 3.2 min. The limit of detection of nQ in blood serum was found to be 0.1 mu g/mL. The proposed method was also validated in terms of linearity, precision, and accurac