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We investigate the effect of the residual Doppler averaging on the susceptibility and optical switching of a weak probe field propagating through a four-level inverted-Y type atomic system driven by two strong coherent fields, namely the pump field (control field) and the repump field. A theoretical model of the inverted-Y type system is developed by using density matrix method and a set of sixteen optical Bloch equations (OBEs) are solved analytically under steady state condition to determine the probe coherence term. The imaginary part of susceptibility shows electromagnetically induced transparency (EIT) under Doppler free condition as well as under Doppler broadening. The line parameters of 5S1/2 → 5P3/2 → 5D5/2 and 5S1/2 → 5P3/2 → 7S1/2 transitions executed by 87Rb atoms are used to simulate the susceptibility and group index related to probe field propagation in order to show the effect of residual Doppler broadening due to wavelength mismatch between the pump field and the probe field. Under Doppler free condition the probe field propagation is subluminal on resonance while that under Doppler broadened condition is superluminal on resonance for both the transitions. [ABSTRACT FROM AUTHOR]

The absorption features of a probe field propagating through a six-level inverted-Y type atomic system in presence of two additional coherent fields are investigated under both Doppler-free and Doppler-broadened conditions resembling the 87Rb 5S1⁄2 → 5P3⁄2 → 44D5⁄2 (Tr-I) through numerical simulation. A comparative study in the probe absorption is also made with the 87Rb 5S1⁄2 → 5P3⁄2 → 7S1⁄2 transition (Tr-II). Under thermal averaging five velocity selective optically pumped absorption peaks (VSOPAP) appear for both the transitions (Tr-I and Tr-II). An interesting feature noticed in the simulated absorption profile is that under thermal averaging we get two extra electromagnetically induced transparency (EIT) dips for Tr-I compared to Tr-II where only two EIT dips are noticed. [ABSTRACT FROM AUTHOR]

Zinc oxide thin films were deposited by simple soft solution route at room temperature. The as grown thin films of ZnO were characterized for the structural, morphological and optical properties. X-ray diffraction (XRD) analysis reveals the polycrystalline nature of ZnO thin films with hexagonal structure. The films were highly oriented along (100) and (101) planes. The broad and low intense peaks in XRD pattern indicate the presence of coarsely fine, nano crystalline grains. Transmission Electron Microscopy (TEM) micrographs shows the formation of ZnO nanocrystallites. Atomic Force Microscopy (AFM) image shows uniform deposition of ZnO thin film on the substrate. The optical band gap was found to be 3.37 eV for as grown films. [ABSTRACT FROM AUTHOR]

We present a low-frequency electrical noise measurement in graphene based field effect transistors. For single layer graphene (SLG), the resistance fluctuations is governed by the screening of the charge impurities by the mobile charges. However, in case of Bilayer graphene (BLG), the electrical noise is strongly connected to its band structure, and unlike single layer graphene, displays a minimum when the gap between the conduction and valence band is zero. Using double gated BLG devices we have tuned the zero gap and charge neutrality points independently, which offers a versatile mechanism to investigate the low-energy band structure, charge localization and screening properties of bilayer graphene. [ABSTRACT FROM AUTHOR]

We focus on athermal phase transitions where in discrete and dissipative avalanches are observed in physical observables as the system jumps from one metastable state to another, when driven by an external field. Using higher order statistics of time dependent avalanches, or noise, in electrical resistivity during temperature-driven martensite transformation in thin nickel-titanium films, we demonstrate evidence suggesting the existence of a singular ‘global instability’ or divergence of the correlation length as a function of temperature at the transition. These results not only establish a mapping of non-equilibrium first order phase transition and equilibrium critical phenomena, but perhaps also call for a re-evaluation of many existing experimental claims of self-organized criticality. [ABSTRACT FROM AUTHOR]

By modifying the electrodeposition technique, we have stabilized the silver nanowires (AgNWs) in high-energy hexagonal closed packed (hcp) structure. The conductivity noise measurements show that the noise magnitude in hcp silver nanowires is several orders of magnitude smaller than that of face centered cubic (fcc) silver nanowires, which is obtained by standard over potential electrodeposition (OPD) technique. The reduction of noise can be attributed to the restricted dislocation dynamics in hcp AgNWs due to the presence of less number of slip systems. Temperature dependent noise measurements show that the noise magnitude in hcp AgNWs is weakly temperature dependent while in fcc AgNWs it is strong function of temperature. [ABSTRACT FROM AUTHOR]

Magnetite (Fe3O4) nano particles have been synthesized via sol-gel auto-combustion method using citric acid as a fuel. Post preparation thermal treatment was done at: 220 °C, 270 °C and, 320 °C for 1 hour, to insure the formation of single phase Fe3O4 nano particles. X-Ray diffraction (XRD) results confirm the formation of Magnetite (Fe3O4), and also the presence of Hematite (α-Fe2O3) as secondary phase. Results reveal that with increasing annealing temperature lattice parameter (a), specific surface area (S), hopping lengths (LA, LB) for tetrahedral (A) and octahedral site (B) increases, whereas x-ray density (ρXRD) and, Scherer’s grain diameter (Ds) varies respectively range between 5286.2−5376.1 kg/m³, 37.2−43.5 nm. Study of Fe3O4 nano particles is of value, due to its prospective applications in medical science - treating metastatic cancer by injecting into the cells. [ABSTRACT FROM AUTHOR]

Amongst various semiconductors, Bi2S3 is one of the most widely used compounds, used for various types of applications like thermoelectric and optoelectronic applications as well as biological and chemical sensors due to its various types of properties. Bi2S3 is a challenging material because of its midway band gap (Eg=1.74eV) and absorption coefficient of the order of 104 cm-1. There are a lot of techniques have developed for synthesizing the Bi2S3 thin films. Amongst them, Zhehao Zhu et al have revealed that as annealing temperature increases in sulfurvapour atmosphere, the light absorption and charge separation efficiencies enhances by achieving carrier diffusion length that is comparable to the light absorption depth, leading to high solar energy conversion efficiencies in Bi2S3. R.S. Mane et al also have reported that, the Photoelectrochemical (PEC) performance of chemically grown Bi2S3 is improved with increase in film thickness and grain size. [ABSTRACT FROM AUTHOR]

Amongst various metal oxides, Zinc Oxide (ZnO) draws the attention of the scientific community for its various types of properties. For this study purpose, ZnO thin films were prepared by Modified Chemical Bath Deposition (MCBD) technique. To remove out the formation of excessive hydroxide, the bath temperature was maintained at 80°C.There was no change in crystallinity in case of pristine sample. As the annealing temperature increased, the crystallinity goes on improving and then after decreased as it was depicted in the structural morphologies and the variation in the optical properties were also in good correlation with the structural morphologies. [ABSTRACT FROM AUTHOR]

The Zinc oxide thin films were grown on the amorphous glass substrate using Successive Ionic Layer Adsorption and Reaction (SILAR) technique at room temperature. The various preparative parameters were optimized to obtain good quality films. The as-grown films were annealed at 350° C for 2 h in air. The comparative study of the annealed and the as-grown thin films of ZnO were done for structural, optical and electrical studies. Polycrystalline nature was depicted from the x-ray diffraction (XRD) patterns. The peak intensity of as-grown ZnO thin films enhances after annealing. The average grain size calculated from XRD patterns was 17.66 nm for as-grown, while it increased to 24.66 nm after annealing. The band gap of as-grown ZnO thin films was relatively higher and was found to be 3.80 eV. After air annealing, the band gap decrease to 3.58 eV. The current-voltage characteristics show nearly ohmic behavior with decrease in the film resistance, after annealing in air. N-type conductivity was confirmed from the TEP measurements. [ABSTRACT FROM AUTHOR]

Natural fibre composites are showing tremendous potential to be an alternative reinforcement for synthetic fibre in composites. This paper deals with natural fibres such as kenaf fibres and veldt grape plant which belongs to the grape family. These fibres are varied in their length and content and placed in random orientation for reinforcing with epoxy based composites. The veldt grape fibres are mixed with kenaf fibre in several composition and several composite laminates are fabricated. The fabricated epoxy based composite laminates are then investigated for its mechanical properties. It is concluded from the results that the composites reinforced with 20% kenaf fibre and 15% veldt grape fibre fibres produce higher tensile strength, compressive strength and flexural strength when compared to other combinations of composite laminates. [ABSTRACT FROM AUTHOR]

Thin films of CdS were prepared by simple, cost effective chemical bath deposition (CBD) technique. As grown thin films were annealed from 100-400°C for 1 h and characterized to obtain optimized annealing temperature (300°C) for optoelectronic properties. Silver nanoparticles were then synthesized using AgNO3 as a source of Ag+ ions. These Ag nanoparticles were then ultrasonically intercalated into the 300°C annealed CdS thin films using different sonication time. The optoelectronic characteristics of these thin films were then studied. The optical spectra revealed, the absorption over a wide wavelength range was enhanced significantly in the near IR region. Resistivity of the thin films was measured using two probe method and it was found to be decreased. [ABSTRACT FROM AUTHOR]

Thin films of ZnO are synthesized on ITO substrate using successive ionic layer adsorption and reaction (SILAR) technique. The as-grown thin films were annealed at 250 °C (pristine) in vacuum atmosphere (10-2 Torr) for 1 h and further irradiated using 120 MeV Au9+ ions with different fluence 3×1012 and 5×1012 ions/cm2. These pristine and irradiated samples were studied for structural and optoelectronic properties. XRD study reveals better crystalline quality of film at 3×1012 ions/cm2 fluence. On the other hand, electrical resistivity of the films decreases from 13.44 Ω-cm to 3.74 Ω-cm with increase in irradiation fluence. Also it appears that irradiation does not affect absorption edge. [ABSTRACT FROM AUTHOR]

The stochasticity associated with domain wall nucleation and propagation in a cylinderical nanowire has been studied using time resolved resistance measurement in presence of magnetic field. We have shown that the propagation stochasticity of domain wall in a cylindrical nanowire is reflected in the magnetic field dependent velocity distribution whereas the stochasticity involved in the domain wall nucleation can be effectively tuned by varying the angle between the direction of applied magnetic field and the long axis of the cylinder. [ABSTRACT FROM AUTHOR]

Amongst various metal oxides, Zinc Oxide (ZnO) is widely used semiconducting material amongst various II-VI group materials due to its various properties like wide energy band gap (3.3 eV), strong binding energy of 60 meV, higher transparency,low electron affinity sensitivity and selectivity for device grade applications. For this study purpose, for this study purpose (ZnO) thin films have been deposited by Successive Ionic Layer Adsorption and Reaction (SILAR) technique on amorphous glass substrate at room temperature. These films were then annealed for about 2 hours in air atmosphere. The structural studies reveal the increase in grain size upto 400oC. The change in crystallite size were observed in the Atomic Force Microscopy ( AFM) images. The optical studies were also in well agreement with the structural analysis. [ABSTRACT FROM AUTHOR]

Optical materials exhibiting a large third-order optical nonlinearity are in great demands because of their functional applications in optical limiting, optical switching, optical data storage etc. A well-known single Z-scan technique is employed to determine third-order nonlinear optical properties of nonlinear optical materials. Z-scan is a simple experimental technique to measure intensity dependent nonlinear susceptibilities of third-order nonlinear optical materials. It was originally introduced by Sheik Bahae et.al. In this technique, the sample is translated in the z-direction along the axis of a focused Gaussian beam, and the far field intensity is measured as function of sample position. Consequently, increases and decreases in the maximum intensity incident on the sample produce wavefront distortions created by nonlinear optical effects. This is a simple and sensitive single beam technique to measure the sign and magnitude of both real and imaginary part of the third order nonlinear susceptibility χ(3) of nonlinear optical materials. [ABSTRACT FROM AUTHOR]

Heavy metal based oxide glass series of composition xMoO3.(40-x)M.60B2O3 (M= Bi2O3 and PbO) have been prepared by the standard melt-quenching technique. The amorphous nature of the present systems was estimated by XRD patterns. The SEM pattern has been used to study the microstructure of the sample. The effect of temperature on DC conductivity has been measured in the temperature range 523-623K for the compositions. In this temperature range, the DC conductivity increases in MoO3-Bi2O3-B2O3 glasses with increase in MoO3 content is due to small polaron hopping mechanism between Mo5+ and Mo6+ ions whereas it decreases in MoO3-PbO-B2O3 glasses with an increasing MoO3 content which is due to predominantly to Pb2+ ions. [ABSTRACT FROM AUTHOR]

Glasses with compositions xM.(40-x)PbO.60B2O3 (M= Fe2O3 and MoO3) have been synthesized by standard melt-quenching technique. The amorphous nature of the each sample was ascertained by XRD patterns. The absorption edge (λcut-off) shifts toward longer wavelengths with an increase in Fe2O3 as well as MoO3 content in the glass matrix. The Urbach’s energy is used to characterize the degree of disorder in amorphous solids. The values of optical band gap energy for indirect allowed and forbidden transitions have been determined and it was found that it decreases faster in Fe2O3 based samples than the samples containing MoO3 Content. From these results, it was observed that Fe2O3 to be a better probe to generate non-bridging oxygens (NBOs) than MoO3 content in the present study. [ABSTRACT FROM AUTHOR]

We present electrical transport and low frequency (1/f) noise measurements on mechanically exfoliated single, bi and trilayer MoS2 -based FET devices on Si/SiO2 substrate. We find that the electronic states in MoS2 are localized at low temperatures (T) and conduction happens through variable range hopping (VRH). A steep increase of 1/f noise with decreasing T, typical for localized regime was observed in all of our devices. From gate voltage dependence of noise, we find that the noise power is inversely proportional to square of the number density (∝ 1/n²) for a wide range of T, indicating number density fluctuations to be the dominant source of 1/f noise in these MoS2 FET [ABSTRACT FROM AUTHOR]

We demonstrate that the universal conductance fluctuations (UCF) can be used as a direct probe to study the valley quantum states in disordered graphene. The UCF magnitude in graphene is suppressed by a factor of four at high carrier densities where the short-range disorder essentially breaks the valley degeneracy of the K and K' valleys, leading to a density dependent crossover of symmetry class from symplectic near the Dirac point to orthogonal at high densities. [ABSTRACT FROM AUTHOR]

This paper describes the optimization of conductor size and the voltage regulator location & magnitude of long rural distribution lines. The optimization minimizes the lifetime cost of the lines, including capital costs and losses while observing voltage drop and operational constraints using a Genetic Algorithm (GA). The GA optimization is applied to a real Single Wire Earth Return (SWER) network in regional Queensland and results are presented. [ABSTRACT FROM AUTHOR]

We present the study of low-frequency noise, or 1/f noise, in degenerately doped Si:P and Ge:P δ-layers at low temperatures. For the Si:P δ-layers we find that the noise is several orders of magnitude lower than that of bulk Si:P systems in the metallic regime and is one of the lowest values reported for doped semiconductors. Ge:P δ-layers as a function of perpendicular magnetic field, shows a factor of two reduction in noise magnitude at the scale of Bφ, where Bφ is phase breaking field. We show that this is a characteristic feature of universal conductance fluctuations [ABSTRACT FROM AUTHOR]

Topological defects play an important role in the melting phenomena in two-dimensions. In this work, we report experimental observation of topological defect induced melting in two-dimensional electron systems (2DES) in the presence of strong Coulomb interaction and disorder. The phenomenon is characterised by measurement of conductivity which goes to zero in a Berezinskii- Kosterlitz-Thouless like transition. Further evidence is provided via low-frequency conductivity noise measurements. [ABSTRACT FROM AUTHOR]

We use a dual gated device structure to introduce a gate-tuneable periodic potential in a GaAs/AlGaAs two dimensional electron gas (2DEG). Using only a suitable choice of gate voltages we can controllably alter the potential landscape of the bare 2DEG, inducing either a periodic array of antidots or quantum dots. Antidots are artificial scattering centers, and therefore allow for a study of electron dynamics. In particular, we show that the thermovoltage of an antidot lattice is particularly sensitive to the relative positions of the Fermi level and the antidot potential. A quantum dot lattice, on the other hand, provides the opportunity to study correlated electron physics. We find that its current-voltage characteristics display a voltage threshold, as well as a power law scaling, indicative of collective Coulomb blockade in a disordered background. [ABSTRACT FROM AUTHOR]

We report non-saturating linear magnetoresistance (MR) in a two-dimensional electron system (2DES) at a GaAs/AlGaAs heterointerface in the strongly insulating regime. We achieve this by driving the gate voltage below the pinch-off point of the device and operating it in the non-equilibrium regime with high source-drain bias. Remarkably, the magnitude of MR is as large as 500% per Tesla with respect to resistance at zero magnetic field, thus dwarfing most non-magnetic materials which exhibit this linearity. Its primary advantage over most other materials is that both linearity and the enormous magnitude are retained over a broad temperature range (0.3 K to 10 K), thus making it an attractive candidate for cryogenic sensor applications. [ABSTRACT FROM AUTHOR]