Search

Energy flux density for higher-order cylindrical vector vortex (HCVV) beam focused through a dielectric interface is analyzed numerically based on vector diffraction theory. Numerical results shows variation in the direction of the energy flux or Poynting vector distribution both in transverse and longitudinal plane upon suitably tuning the topological charge and polarization order of HCVV beam. We also note that the strong reverse flow of energy occur at the centre of the focal plane for certain values of the topological charge and polarization order. These results may find potential applications in optical trapping and optical manipulations.

This work was supported by RUSA, UGC-SAP, DST-FIST, DST-PURSE grants. The authors extend their appreciation to the Researchers supporting project number (RSP-2020/247) King Saud University, Riyadh, Saudi Arabia.

To improve the performance of PSCs, it is essential to prevent the carrier recombination losses at the interfaces of the transparent metal oxide electrode/electron transport layer (ETL)/active absorber perovskite layer. This present work reports on the green synthesis approach used for the preparation of flake like-ZnO nanostructure (GF-ZnO NS), naturally extracted from the leaf of Albizia Amara, used as a reducing cum capping agent. Herein, we have introduced an n-type GF-ZnO NS material as an efficient electron transport interfacial layer (bi-ETL) at the ETL/perovskite junction in the fabricated perovskite solar cells (PSCs). The structure of the fabricated PSC device is as follows: glass/ITO/bi-ETL (c-TiO2/GF-ZnO NSs)/CH3NH3PbI3−xClx/spiro-MeOTAD/Au. A comparative study has also been carried out by deploying electron transport materials such as c-TiO2 and GF-ZnO NSs separately. From this, it has been found that the bi-ETL perovskite solar cell devices achieved a maximum power conversion efficiency (PCE) of 7.83% with an open-circuit voltage (VOC) of 0.728 V, a short circuit current density (JSC) of 20.46 mA cm−2 and a fill factor (FF) of 52.61% whereas, the c-TiO2, GF-ZnO NSs and the chemically reduced CR-ZnO ETL based devices achieved a PCE of 4.84%, 5.82% and 6.81%, respectively. The better performance obtained for the bi-ETL based devices is ascribed to the enhanced carrier extraction and the reduced recombination losses at the interface between the ETL and the active perovskite layer.

The rapid increase in the efficiency of perovskite solar cells (PSCs) in last few decades have made them very attractive to the photovoltaic (PV) community. However, the serious challenge is related to the stability under various conditions and toxicity issues. A huge number of articles have been published in PSCs in the recent years focusing these issues by employing different strategies in the synthesis of electron transport layer (ETL), active perovskite layer, hole transport layer (HTL) and back contact counter electrodes. This article tends to focus on the role and classification of different materials used as HTL in influencing long-term stability, in improving the photovoltaic parameters and thereby enhancing the device efficiency. Hole Transport Materials (HTMs) are categorized by dividing into three primary types, namely; organic, inorganic and carbonaceous HTMs. To analyze the role of HTM in detail, we further divide these primary type of HTMs into different subgroups. The organic-based HTMs are subdivided into three categories, namely; long polymer HTMs, small molecule HTMs and cross-linked polymers and the inorganic HTMs have been classified into nickel (Ni) derivatives and copper (Cu) derivatives based HTMs, p-type semiconductor based HTMs and transition metal based HTMs. We further analyze the dual role of carbonaceous materials as HTM and counter electrode in the perovskite devices. In addition, in this review, an overview of the preparation methods, and the influence of the thickness of the HTM layers on the performance and stability of the perovskite devices are also provided. We have carried out a detailed comparison about the various classification of HTMs based on their cost-effectiveness and considering their role on effective device performance. This review further discusses the critical challenges involved in the synthesis and device engineering of HTMs. This will provide the reader a better insight into the state of the art of perovskite solar devices. Keywords: Perovskite solar cells, Hole transporting materials, Organic HTMs, Inorganic HTMs, Carbonaceous HTMs, Photovoltaic parameters

This study focuses on the fabrication and characterization of Cs2AgBiBr6 double perovskite thin film for field-effect transistor (FET) applications. The Cs2AgBiBr6 thin films were fabricated using a solution process technique and the observed XRD patterns demonstrate no diffraction peaks of secondary phases, which confirms the phase-pure crystalline nature. The average grain sizes of the spin-deposited film were also calculated by analysing the statistics of grain size in SEM image and was found to be around 412 (±44) nm the larger grain size was also confirmed by the XRD measurements. FETs with different channel lengths of Cs2AgBiBr6 thin films were fabricated on an electrode deposited heavily doped p-type Si substrate with a 300 nm thermally grown SiO2 dielectric under ideal conditions in air processing under ambient pressure and temperature. The Cs2AgBiBr6 FETs showed a p-type nature with a positive threshold voltage. The on current, threshold voltage and hole-mobility of the FETs decreased with increasing channel length. A high average hole mobility of 0.29 cm2s-1V-1 was obtained for the FETs with a channel length of 30 µm, and the hole mobility was reduced by an order of magnitude (0.012 cm2s-1V-1) when the channel length was doubled. The on current and hole-mobility of Cs2AgBiBr6 FETs followed a power fit, which confirmed the dominance of channel length in electrostatic gating in Cs2AgBiBr6 FETs. A very high-hole mobility observed in or FET that could be attributed to the much larger grain size of Cs2AgBiBr6 film made in this work.

Despite the progressive enhancement in the flexibility of Pb-based perovskites for optoelectronic applications, regrettably, they are facing two main challenges; (1) instability, which originates from using organic components in the perovskite structure, and (2) toxicity due to Pb. Therefore, new, stable non-toxic perovskite materials are demanded to overcome these drawbacks. The research community has been working on a wide variety of Pb-free perovskites with different molecular formulas and dimensionality. A variety of Pb-free halide double perovskites have been widely explored by different research groups in search for stable, non-toxic double perovskite material. Especially, Cs-based Pb-free halide double perovskite has been in focus recently. Herein, we present a review of theoretical and experimental research on Cs-based Pb-free double halide perovskites of structural formulas Cs2M+M3+X6 (M+ = Ag+, Na+, In+ etc.; M3+= Bi3+, In3+, Sb3+; X = Cl−, Br−, I¯) and Cs2M4+X6 (M4+ = Ti4+, Sn4+, Au4+ etc.). We also present the challenges faced by these perovskite compounds and their current applications especially in photovoltaics alongside the effect of metal dopants on their performance.

Hydrogen produced from water using photocatalysts driven by sunlight is a sustainable way to overcome the intermittency issues of solar power and provide a green alternative to fossil fuels. TiO2 has been used as a photocatalyst since the 1970s due to its low cost, earth abundance, and stability. There has been a wide range of research activities in order to enhance the use of TiO2 as a photocatalyst using dopants, modifying the surface, or depositing noble metals. However, the issues such as wide bandgap, high electron-hole recombination time, and a large overpotential for the hydrogen evolution reaction (HER) persist as a challenge. Here, we review state-of-the-art experimental and theoretical research on TiO2 based photocatalysts and identify challenges that have to be focused on to drive the field further. We conclude with a discussion of four challenges for TiO2 photocatalysts—non-standardized presentation of results, bandgap in the ultraviolet (UV) region, lack of collaboration between experimental and theoretical work, and lack of large/small scale production facilities. We also highlight the importance of combining computational modeling with experimental work to make further advances in this exciting field.

Contains fulltext : 238202.pdf (Publisher’s version ) (Open Access) Systemic sclerosis (SSc) is a rare complex disease, characterized by microvascular damage, auto-immunity, and fibrosis. Nailfold capillary microscopy (NCM), a safe and noninvasive imaging technique, can be used to visualize specific microvascular alterations in SSc. In this review, we discuss an interesting case of a patient with changes in microvascular pattern on NCM after pulmonary transplantation. We provide an overview of microvascular alterations in systemic sclerosis and the evidence in the literature about the effect of vasoactive and immunomodulation therapy on these vascular changes. We also outline the influence of pulmonal pathology, such as interstitial lung disease and pulmonary arterial hypertension, on the capillaroscopic pattern, and finally, we discuss how NCM could possibly serve as a biomarker of treatment.

The article investigates the potential of wearables and the Internet of Things (IoT) in the insurance business, especially regarding pricing and product design.

Molybdenum disulphide (MoS2) is a rising star among transition-metal dichalcogenides in photovoltaics, diodes, electronic circuits, transistors and as a photocatalyst for hydrogen evolution. A wide range of MoS2 polymorphs with varying electrical, optical and catalytic properties is of interest. However, in-depth studies on the structural stability of the various MoS2 polymorphs are still lacking. For the very first time, 14 different MoS2 polymorphs are proposed in this study and in-depth analysis of these polymorphs are carried out by employing first-principle calculations based on density functional theory (DFT). In order to investigate the feasibility of these polymorphs for practical applications, we employ wide range of analytical methods including band structure, phonon and elastic constant calculations. Three of the polymorphs were shown to be unstable based on the energy volume calculations. Among the remaining eleven polymorphs (1T1, 1T2, 1H, 2T, 2H, 2R1, 2R2, 3Ha, 3Hb, 3R and 4T), we confirm that the 1T1, 1T2, 2R2 and 3R polymorphs are not dynamically stable based on phonon calculations. Recent research suggests that stabilising dopants (e.g. Li) are needed if 1T polymorphs to be synthesised. Our study further shows that the remaining seven polymorphs are both dynamically and mechanically stable, which make them interesting candidates for optoelectronics applications. Due to high electron mobility and a bandgap of 1.95 eV, one of the MoS2 polymorphs (3Hb-MoS2) is proposed to be the most promising candidate for these applications.

The tight focusing properties of an azimuthally polarized Bessel Gaussian beam phase modulated by annular Walsh function filter is studied numerically by vector diffraction theory. It is observed that upon suitable optimization of order and annular obstruction ratio of an annular Walsh function filter, one can generate multiple sub wavelength scale optical tubes (optical holes) with super long focal depth. Such a focal system is usable for Nano-lithography, particle trapping and transportation, as well as confocal and STED microscopy, microstructure fabrication etc.

We demonstrate by means of first-principle calculations that the band structure of TlBiS2 characterizes this material as a promising candidate for photovoltaic applications. Two calculation hybrid functional models are used, one including the spin-orbit coupling and one neglecting it. These calculations show that TlBiS2 has a direct band gap of 1.10 eV in the absence of spin-orbit coupling and 0.67 eV for spin-orbit coupling. The absorption peaks appear in the visible region with a consequently high absorption intensity for both without and with spin-orbit coupling. We show how computational modeling of TlBiS2 can substantially enrich the understanding of photovoltaic properties.

Sol gel dip coating method has been used for preparing ZnO nanorods. ZnO nanorods have been sensitized using CdSe quantum dots by simple chemical method. Uniform coverage of quantum dots on ZnO nanorods is observed. The structural, optical and morphology of the ZnO nanorods, CdSe quantum dots and CdSe quantum dot sensitized ZnO nanorods have been studied. The presence of CdSe quantum dots in ZnO nanorods based film is clearly seen in FESEM and TEM image and the elements Zn, O, Cd and Se present in the film was confirmed by EDAX analysis. FTO/CdSe quantum dot-ZnO nanorods/electrolyte/platinum structure based solar cell has been fabricated and the cell efficiency has been found to be 2.1%.

Kesterite type CZTS (Cu2ZnSnS4) thin films were deposited on Indium Tin Oxide (ITO) coated glass substrates by simple sol-gel method. X-ray diffraction (XRD) pattern showed the presence of crystalline kesterite phase, whereas the electron microscopic (FESEM) analysis established the 1D morphology of the CZTS films. Electrical studies revealed the interesting bistability phenomena of CZTS films. The current-voltage (I-V) characteristics showed two distinct paths for forward and reverse sweep directions. Conducting AFM (C-AFM) studies also supported the bistability phenomena of the CZTS films. Present study on electrical bi-stability of the CZTS thin films will help to understand the defects in the absorber materials and the photovoltaic performance of the CZTS device.

Based on vector diffraction theory and inverse Faraday effect (IFE), the light induced magnetization distribution of a tightly focused azimuthally polarized doughnut Gaussian beam superimposed with a helical phase and modulated by an optimized multi belt complex phase filter (MBCPF) is analysed numerically. It is noted that by adjusting the radii of different rings of the complex phase filter, one can achieve many novel magnetization focal distribution such as sub wavelength scale (0.29λ) and super long (52.2λ) longitudinal magnetic probe suitable for all optical magnetic recording and the formation of multiple magnetization chain with four, six and eight sub-wavelength spherical magnetization spots suitable for multiple trapping of magnetic particles are achieved.

We present first-principle computational modelling of the perovskite CsSnxPb(1−x)I3 (x = 0, 0.5 and 1), aimed at increasing the efficiency of perovskite photovoltaics. Using density functional theory calculations with a hybrid functional, we predict that both CsPbI3 and CsSnI3 are stable structures with direct bandgaps, suitable for photovoltaic application. On the other hand, the stable structure of CsSn0.5Pb0.5I3 exhibits an indirect bandgap, which could work as a direct bandgap due to the short electron-hole distance. The results of this study demonstrates that through bandgap engineering, we can obtain larger photon absorption ranges and higher efficiencies for perovskite based photovoltaics.

The power conversion of perovskite solar cells has increased steadily and reached 22.1%, recently. This has led the researchers to study lead-free halide perovskite materials like Cs2SnI6 due to the toxic nature of lead used in the record-breaking organic-inorganic perovskite structures. Since the presence of an intermediate band in semiconductors leads to enhancement of efficiency of the solar cells, we have also investigated the electronic structure of Cs2SnI6, to find whether the intermediate band is likely to exist in the middle of the band gap. The computational results for the electronic band structure and density of states indicate that Cs2SnI6 contains an intermediate band (IB). Additional absorption peaks that appear in the optical spectra of this material presented in this paper explicitly confirm this. All these studies and the presence of an IB that we identified in Cs2SnI6 suggests that Cs2SnI6 may have high potential used as intermediate band solar cell material.

Here we studied the annealing induced shape transformation of 1D Cu2ZnSnS4 (CZTS) nanorods from nanospheres and nanocubes by simple sol–gel method without using any toxic chemicals or complicated vacuum based technology. X-ray diffraction pattern and Raman spectra reveal the formation of kesterite structure CZTS thin films. The energy dispersive X-ray analysis results indicate the presence of Cu, Zn, Sn, and S. The elemental distribution of all the CZTS samples was studied using elemental mapping. The Hall effect studies of the CZTS thin film composed of nanorods exhibits the lowest resistivity values which indicates efficient charge transfer for unidirectional structure. The obtained optical band gap energy of CZTS thin film is in the range of 1.46–1.54 eV, which is quite close to the optimum theoretical value required for solar cell applications.

The properties of circularly polarized double ring shaped beam tightly focused through a uniaxial birefringent crystal are studied numerically by the use vectorial diffraction theory for small birefringence. Novel focal structures such as splitting of single focal spot into multiple spots and the focal shift of maximum intensity can be obtained with the proper combination of the topological charge [n], birefringence [Δn], and the pupil to beam ratio [β] of the input circularly polarized double ring shaped beam.

Halide perovskites have recently emerged as a promising material for low cost and high efficiency solar cells. Dye Sensitized Solar Cells (DSSCs) are the forerunners of perovskite solar cells. In liquid based dye sensitized solar cell the power conversion efficiency is low and also it had some stability issues. In 2012, a long term stable and high efficiency perovskite solar cell emerged by replacing liquid electrolyte with the solid hole conductor. The attractiveness of organometal halide perovskites are having suitable direct bandgap with large absorption coefficients, low cost and solution based fabrication process. This review summarizes the basic concepts of perovskite, their fabrication and its eminent properties.

This study focuses on employing cuprous iodide (CuI) as a hole-transporting material (HTM) in fabricating highly efficient perovskite solar cells (PSCs). The PSCs were made in air with either CuI or 2,2&prime, 7,7&prime, Tetrakis[N,N-di(4-methoxyphenyl)amino]-9,9&prime, spirobifluorene (spiro-OMeTAD) as HTMs. A simple and novel pressing method was employed for incorporating CuI powder layer between perovskite layer and Pt top-contact to fabricate devices with CuI, while spiro-OMeTAD was spin-coated between perovskite layer and thermally evaporated Au top-contact to fabricate devices with spiro-OMeTAD. Under illuminations of 100 mW/cm2 with an air mass (AM) 1.5 filter in air, the average short-circuit current density (JSC) of the CuI devices was over 24 mA/cm2, which is marginally higher than that of spiro-OMeTAD devices. Higher JSC of the CuI devices can be attributed to high hole-mobility of CuI that minimizes the electron-hole recombination. However, the average power conversion efficiency (PCE) of the CuI devices were lower than that of spiro-OMeTAD devices due to slightly lower open-circuit voltage (VOC) and fill factor (FF). This is probably due to surface roughness of CuI powder. However, optimized devices with solvent-free powder pressed CuI as HTM show a promising efficiency of over 8.0 % under illuminations of 1 sun (100 mW/cm2) with an air mass 1.5 filter in air, which is the highest among the reported efficiency values for PSCs fabricated in an open environment with CuI as HTM.

In this work, chemical bath-deposited cadmium sulfide (CdS) thin films were employed as an alternative hole-blocking layer for inverted poly(3-hexylthiophene) (P3HT) and phenyl-C61-butyric acid methyl ester (PCBM) bulk heterojunction solar cells. CdS films were deposited by chemical bath deposition and their thicknesses were successfully controlled by tailoring the deposition time. The influence of the CdS layer thickness on the performance of P3HT:PCBM solar cells was systematically studied. The short circuit current densities and power conversion efficiencies of P3HT:PCBM solar cells strongly increased until the thickness of the CdS layer was increased to ~70 nm. This was attributed to the suppression of the interfacial charge recombination by the CdS layer, which is consistent with the lower dark current found with the increased CdS layer thickness. A further increase of the CdS layer thickness resulted in a lower short circuit current density due to strong absorption of the CdS layer as evidenced by UV-Vis optical studies. Both the fill factor and open circuit voltage of the solar cells with a CdS layer thickness less than ~50 nm were comparatively lower, and this could be attributed to the effect of pin holes in the CdS film, which reduces the series resistance and increases the charge recombination. Under AM 1.5 illumination (100 mW/cm2) conditions, the optimized PCBM:P3HT solar cells with a chemical bath deposited a CdS layer of thickness 70 nm and showed 50% power conversion efficiency enhancement, in comparison with similar solar cells with optimized dense TiO2 of 50 nm thickness prepared by spray pyrolysis.

In this work, for the growth of ZnO (Zinc Oxide) nanorod thin films, the seed layer is prepared by sol-gel dip coating and spin coating methods. We studied the effect of seed layer on structural and optical properties of the ZnO nanorods. FESEM image revealed the difference between the growth of ZnO nanorods on spin and sol-gel dip coated seed layers. It has been observed that ZnO nanorods with uniform size and highly oriented along the c-axis have been grown on spin coated seed layer. HRTEM and Transmission electron microscopy study shows that the ZnO nanorods have an average length of 300 nm and the average diameter is 50 nm, the interplanner spacing is found to be d = 2.63 A. The X-ray diffraction pattern revealed that the ZnO nanorods are of hexagonal structure. Absorption spectra showed that the ZnO nanorods exhibit UV absorption with absorption peak at 365 nm and the optical band gap has been found to be 3.23 eV. PL spectra indicated the presence of UV and visible emission lying in the range of 380–550 nm. ZnO nanorods based solar cells have been constructed using CdSe quantum dots.

ZnO nanorods (NRs) have been grown by sol–gel dip-coating method on FTO glass plates. The CdS quantum dots (QDs) were deposited on the as-prepared ZnO NRs by successive ionic layer adsorption and reaction method. The structural characteristics of the ZnO NRs, CdS QD and CdS QD-sensitized ZnO NRs films have been studied using X-ray diffraction method. ZnO NRs exhibit hexagonal structure. CdS QD had a size of 2 nm. The FESEM image showed the presence of CdS quantum dots on the ZnO NRs. From the optical studies, the optical band gap energy of ZnO thin film was found to be 3.26 eV and the band gap energy of CdS quantum dot was observed to be 2.1 eV. The optical absorption edge was found at 370 nm for ZnO NRs and at 460 nm for the CdS QD. The PL spectra of the prepared ZnO NRs and CdS QDs sample exhibit a strong emission peak at 395 and 688 nm. Solar cells have been fabricated using the CdS quantum dot sensitized ZnO nanorods, and the efficiency of the cell was 1.3 %.

Due to the low absorption coefficients of crystalline silicon-based solar cells, researchers have focused on non-silicon semiconductors with direct band gaps for the development of novel photovoltaic devices. In this study, we use density functional theory to model the electronic structure of a large database of candidates to identify materials with ideal properties for photovoltaic applications. The first screening is operated at the GGA level to select only materials with a sufficiently small direct band gap. We extracted twenty-seven candidates from an initial population of thousands, exhibiting GGA band gap in the range 0.5&ndash, 1 eV. More accurate calculations using a hybrid functional were performed on this subset. Based on this, we present a detailed first-principle investigation of the four optimal compounds, namely, TlBiS2, Ba3BiN, Ag2BaS2, and ZrSO. The direct band gap of these materials is between 1.1 and 2.26 eV. In the visible region, the absorption peaks that appear in the optical spectra for these compounds indicate high absorption intensity. Furthermore, we have investigated the structural and mechanical stability of these compounds and calculated electron effective masses. Based on in-depth analysis, we have identified TlBiS2, Ba3BiN, Ag2BaS2, and ZrSO as very promising candidates for photovoltaic applications.

We investigate properties of MBE grown photoconductive terahertz (THz) antennas based on the InGaAs/InAlAs/InP material system aimed for an excitation wavelength of approx. 1060 nm. Therefore, we analyze several different approaches concerning growth parameters, layer and material compositions as well as doping. The carrier dynamics are probed via transient white-light pump-probe spectroscopy as well as THz Time Domain Spectroscopy (TDS) measurements. We find that the electron capture probability is reduced for higher electron energies. By adjusting the material band gap this can be resolved and lifetimes of 1.3 ps are obtained. These short lifetimes enable the detection of THz TDS spectra with a bandwidth exceeding 4 THz.

Nanocrystalline Cd-doped TiO 2 thin films have been prepared by sol–gel method. X-ray diffraction analysis reveals that TiO 2 and Cd-doped TiO 2 nanocrystalline thin films are of anatase phase. The average grain size of TiO 2 and Cd-doped TiO 2 nanocrystalline thin films was found to lie in the range of 15–18 nm. Solar cells have been fabricated with a device structure of ITO / Cd-doped TiO 2 /P3HT:PC 71 BM/MoO 3 /Al configuration. The power conversion efficiency of the inverted organic solar cell with Cd-doped TiO 2 is 3.06% and is higher than that of TiO 2 based organic solar cell (2.64%).

Bundle like structured ZnO nanorods and vertically aligned ZnO nanorods have been prepared by simple sol–gel dip coating method on ITO substrate. The X-ray diffraction pattern shows that the prepared ZnO samples are of hexagonal phase, the scanning electron microscope images reveal the formation of bundle like ZnO nanorods and aligned ZnO nanorods. The high resolution transmission electron microscope images also show the presence of nanorods. The average diameter and length of the nanorods in the bundle of ZnO nanorods and vertically aligned ZnO nanorods are 200 nm, 1.5 μm and 100 nm, 1.8 μm respectively. Dye sensitized solar cells have been assembled using N719 dye as sensitizer and the conversion efficiencies of the vertically aligned ZnO nanorods and bundle like ZnO nanorods thin film based solar cells have been found to be 0.74% and 0.83%, respectively.

In the present work, a systematic study has been carried out to understand the effect of In doping on the various properties of the ZnO nanocrystalline thin films. In-doped ZnO nanocrystalline thin films with different indium concentrations (1.98%, 4.03%, 6.74%, 8.62% and 10.48% In) have been synthesized by sol–gel method. The grain size and surface roughness of the In-doped ZnO thin films are observed to be smaller than those of the ZnO thin films. 6.74% In-doped ZnO films with a low resistivity of 1.95 × 10−3 Ω cm and a high mobility of 2.19 cm2 V−1 S−1 have been prepared under optimal deposition conditions. Inverted organic solar cells containing In-doped ZnO as an electron extraction layer with the structure indium tin oxide (ITO)/In-doped ZnO/poly[N-9′-heptadecanyl-2,7-carbazole-alt-5,5-(4′,7′-di-2-thienyl-2′,1′,3′-benzothiadiazole)] (PCDTBT): [6,6]-phenyl C71-butyric acid methyl ester (PC71BM)/MoO3/Al have been fabricated. The inverted organic solar cell with 6.74% In-doped ZnO exhibited a power conversion efficiency of 5.58%, which is the best efficiency reported so far for these type of solar cells. The device performance has been optimized by varying the indium doping concentration. The results clearly demonstrate that significant improvement in power conversion efficiency can be obtained by incorporating In into the ZnO films.

Ag-doped titanium dioxide (TiO2) nanocrystalline thin films have been prepared by the sol–gel dip coating method and used as photoanode to fabricate quantum dot sensitized solar cells. The X-ray diffraction studies reveal the formation of anatase phase without any impurity phase. The surface morphology studied using scanning electron microscope shows uniform distribution of particles. The optical band gap was found to be 3.5 and 3.4 eV for CdS quantum dot sensitized TiO2 and CdS quantum dot sensitized Ag-doped TiO2 thin film respectively. The Ag-doped TiO2 based solar cell exhibited a power conversion efficiency of 1.48 % which is higher than that of TiO2 (0.9 %).

Nanocrystalline TiO2 dye-sensitized solar cells have been fabricated using TiO2 photoelectrode sensitized using the extracts of red rose and table rose as natural sensitizers and their characteristics have been studied. The extracts having anthocyanin pigment (pelargonidin, peonidin and cyanidin), which have hydroxyl and carboxylic groups in the molecule can attach effectively to the surface of TiO2 film. The solar cell constructed using the red rose sensitized TiO2 photo-electrode exhibited a short-circuit photocurrent of 4.57 mA/cm2 and a power conversion efficiency of 0.81 % and that of table rose sensitized TiO2 photo-electrode exhibited a short-circuit photocurrent of 4.23 mA/cm2 and a power conversion efficiency of 0.67 %. Natural dye sensitized TiO2 photo electrodes present the prospect to be used as an environment-friendly, low-cost alternative system.

Quaternary Cu2ZnSnS4 (CZTS) thin films, a promising absorber material for solar cells has been successfully deposited on glass substrates by cost effective simple dip-coating method without using either polluting chemicals or expensive vacuum facilities. X-ray diffraction pattern reveals the formation of CZTS films with tetragonal type kesterite structure. The Raman spectra of the prepared films exhibited resonance peaks corresponding to the CZTS phase. The scanning electron microscopic image shows the formation of films with smooth surface. The surface topography studied using atomic force microscope gives an rms roughness of 1.6 nm. The Hall effect studies indicate that the prepared films are p-type with a carrier concentration of 4.77 × 1020 cm−3. The energy dispersive X-ray analysis result indicate the presence of Cu, Zn, Sn and S in the film. The absorption coefficient was found to be the order of 104 cm−1 and the band gap has been found to be 1.5 eV.

CdS quantum dot sensitized Gd-doped TiO2 nanocrystalline thin films have been prepared by chemical method. X-ray diffraction analysis reveals that TiO2 and Gd-doped TiO2 nanocrystalline thin films are of anatase phase. The absorption spectra revealed that the absorption edge of CdS quantum dot sensitized Gd-doped TiO2 thin films shifted towards longer wavelength side (red shift) when compared to that of CdS quantum dot sensitized TiO2 films. CdS quantum dots with a size of 5 nm have been deposited onto Gd-doped TiO2 film surface by successive ionic layer adsorption and reaction method and the assembly of CdS quantum dot with Gd-doped TiO2 has been used as photo-electrode in quantum dot sensitized solar cells. CdS quantum dot sensitized Gd-doped TiO2 based solar cell exhibited a power conversion efficiency of 1.18 %, which is higher than that of CdS quantum dot sensitized TiO2 (0.91 %).

Nanocrystalline TiO2 thin films have been prepared by sol–gel dip coating method. The X-ray diffraction results showed that TiO2 thin films annealed at 400, 450 and 500 °C are of anatase phase and the peak corresponding to the (1 0 1) plane is present in all the samples. The grain size of TiO2 thin films was found to increase with increasing annealing temperature. The grain size is found to be 20, 26 and 38 nm for the films annealed at 400, 450 and 500 °C. TiO2 thin films were sensitized by natural dyes extract from red cabbage and blue pea. It was found that the absorption peak of red cabbage extract is at about 545 nm while that of blue pea extract is at around 576 and 622 nm respectively. The dye sensitized TiO2 based solar cell sensitized using red cabbage, exhibited a Jsc of 4.38 mA/cm2, Voc of 0.47 V, FF of 0.36 and η of 0.73 % and the solar cell sensitized using blue pea, exhibited a Jsc of 4.16 mA/cm2, Voc of 0.45 V, FF of 0.35 and η of 0.67 %. Natural dyes as sensitizers for dye sensitized solar cells are promising because of their environmental friendliness, low-cost production and designable polychrome modules.

We study properties of electromagnetic fields that are focused into thin dielectric slabs using an approach based on physical-optics or Kirchhoff’s approximation, making the results valid both for low and high Fresnel number focusing geometries. A variety of thin slab structures and focusing systems are studied with emphasis on the impact of the field that is due to the presence of the back interface of the slab which is critical in various fields such as optical recording, bio and material sciences. In particular, we investigate how the intensity of the focused field depends on variables such as aperture size, aperture-slab distance, slab refractive index, and slab thickness. Numerical results show that the contribution from the electric field due to the presence of the back interface of the slab is significant along the axis, which passes through the center of the spherical aperture and the focal point. With fixed focal length, the axial field inside the slab is found to increase and the focal ...

Purpose To evaluate efficacy of oral antioxidant treatment given to patients before radiologic procedures in reducing x-ray-induced DNA damage. Materials and Methods In a single-center prospective controlled trial, antioxidant treatment with 2 g ascorbate, 1.2 g N -acetylcysteine, 600 mg lipoic acid, and 30 mg beta carotene was given to 5 consecutive participants before undergoing clinically indicated technetium-99m methylene diphosphonate ( 99m Tc MDP) bone scans for cancer staging. These participants were compared with 5 participants without antioxidant treatment. DNA damage was visualized in peripheral blood mononuclear cells (PBMCs) before and after bone scans using three-dimensional microscopy and fluorescently labeled gamma-H2AX protein. Wilcoxon rank sum test was used to determine whether there was a statistically significant difference in the radiation received between the control and antioxidant groups, the number of foci/cell before and after bone scan within groups, and foci/cell after bone scan between groups. Results There was a significantly higher number of gamma-H2AX foci/cell after ionization radiation in the control group compared with the antioxidant group ( P = .009). There was no statistically significant difference in number of gamma-H2AX foci/cell before or after exposure in the antioxidant group; the number of gamma-H2AX foci/cell was statistically significantly higher ( P = .009) in the control group after exposure to 99m Tc MDP. Conclusions In patients undergoing 99m Tc MDP bone scans, treatment with oral antioxidants before scanning significantly prevented DNA damage in PBMCs. Antioxidants may provide an effective means to protect patients and health care professionals from radiation-induced DNA damage during imaging studies.

ZnO nanorods have been prepared on indium tin oxide (ITO) glass substrates coated with sol–gel based ZnO seed layer through chemical method. Natural dyes (Ixora coccinea, Mulberry and Beetroot) have been used for the fabrication of dye sensitized solar cells. The surface morphology studied using scanning electron microscope shows that the vertically aligned ZnO nanorods are of hexagonal shape. The solar cell efficiency has been calculated and is found to be 0.33, 0.41 and 0.28% for Ixora coccinea, Mulberry and Beetroot extract dye sensitized solar cells.

We present a comprehensive investigation of the structural, electronic, mechanical, and optical properties of four promising candidates, namely Au2Cs2I6, Ag2GeBaS4, Ag2ZnSnS4, and AgCuPO4, for application in photovoltaic devices based on intermediate band (IB) cells. We perform accurate density functional theory calculations by employing the hybrid functional of Heyd, Scuseria, and Erhzerhof (HSE06). Calculations reveal that IBs are present in all proposed compounds at unoccupied states in the range of 0.34⁻2.19 eV from the Fermi level. The structural and mechanical stability of these four materials are also systematically investigated. Additional peaks are present in the optical spectra of these compounds, as characterised by a broadened energy range and high intensity for light absorption. Our findings, as reported in this work, may provide a substantial breakthrough on the understanding of these materials, and thus help the design of more efficient IB solar devices.

CdZnTe thin films were fabricated on glass substrates by sputtering and the potentiality of photoinduced electrical data storage was investigated. As deposited film was annealed to enhance the crystallization and both the as deposited and annealed films were characterized by XRD, RAMAN, UV–vis-NIR, PL, FESEM and EDAX analysis. Optical and electrical properties of the films were investigated in detail. The thin films show interesting photo induced electrical bistability. The electrical bistability was observed with symmetric lateral electrodes under illuminated condition only. In the dark, forward and reverse bias curves traced the same path but under light illumination condition there is a substantial difference in the I–V traces of the forward and reversed biased conditions. After annealing the crystallinity of the as deposited film improved and the ON-OFF ratio of electrical bistability increased considerably. This phenomenom could be useful for light sensitive RAM type devices.

We consider the inductive inference model of Gold [15]. Suppose we are given a set of functions that are learnable with certain number of mind changes and errors. What properties of these functions are learnable if we allow fewer number of mind changes or errors? In order to answer this question this paper extends the Inductive Inference model introduced by Gold [15]. Another motivation for this extension is to understand and characterize properties that are learnable for a given set of functions. Our extension considers a wide range of properties of function based on their input-output relationship. Two specific properties of functions are studied in this paper. The first property, which we call modality, explores how the output of a function fluctuates. For example, consider a function that predicts the price of a stock. A brokerage company buys and sells stocks very often in a day for its clients with the intent of maximizing their profit. If the company is able predict the trend of the stock market "reasonably" accurately then it is bound to be very successful. Identification criterion for this property of a function f is called PREX which predicts if f(x) is equal to, less than or greater than f(x+1) for each x. Next, as opposed to a constant tracking by a brokerage company, an individual investor does not often track dynamic changes in stock values. Instead, the investor would like to move the investment to a less risky option when the investment exceeds or falls below certain threshold. We capture this notion using an identification criterion called TREX that essentially predicts if a function value is at, above, or below a threshold value. Conceptually,modality prediction (i.e., PREX) and threshold prediction (i.e., TREX) are "easier" than EX learning. We show that neither the number of errors nor the number of mind-changes can be reduced when we ease the learning criterion from exact learning to learning modality or threshold. We also prove that PREX and TREX are totally different properties to predict. That is, the strategy for a brokerage company may not be a good strategy for individual investor and vice versa.

We derive explicit formulas for the focal shift, the intensity increase, and the axial zeros obtained on focusing at low Fresnel numbers through a plane interface between two isotropic media, and demonstrate their validity through comparisons with numerical plots of axial intensity distributions. Also, we show that for the special case in which the two isotropic media have the same refractive index, these formulas are in complete agreement with previous results presented for focusing in a single medium.

A metasurface with an ultrahigh angular sensitivity to the angle of incidence at a chosen frequency is presented. Strongly interacting metamolecules are arranged such that a novel functionality of a metamaterial structure with multiple Fano resonances arises. Tuning the lattice constant of the structure enables a precise control of the angular response. We experimentally demonstrate equal responses for changes in azimuthal and for altitude angles of incidence. The concept could be used to enhance angle of arrival measurements, to determine the direction of a propagating wave or enhance the sensitivity of detectors by shielding them from scattered or unwanted signals.

We present an automated measurement setup which employs a fiber-coupled THz time domain spectrometer for simultaneous monitoring of the change in leaf water content of several plants at once. Moreover, it combines the collected THz spectra with data from other sensors. While the strong absorption of THz radiation by polar liquids like water tends to a problem in most biological and medical applications, it is a reliable indicator for leaf water content. We take this well-known basic principle to a level where biological experiments which explore the physiological behavior of plants under different drought stress condition become possible.

The main aim of the thesis is to investigate the technical feasibility of a new concept in coal mine washery waste disposal, namely "INTEGRATED COAL MINE WASHERY WASTE DISPOSAL", and to establish a basis for the proper understanding of the physical phenomena involved in this method. The objective was achieved through various stages such as information gathering, small scale field trials, laboratory modelling and testing, and numerical modelling.Small scale field trials of tailings disposal within a coarse reject embankment conducted at New Hope Colliery, helped to identify the key areas for further laboratory modelling and investigation. The laboratory modelling and testing generated a large amount of information on the engineering behaviour of coal tailings, coarse reject and mixtures of tailings and coarse reject. Subsequent numerical studies illuminated the nature of the seepage of tailings through a coarse reject embankment, and the critical factors controlling it.The consolidation of conventional tailings deposits require excessively long period of time, delaying or prohibiting altogether land rehabilitation work of the tailings storage areas. On the other hand, loosely dumped coarse reject are sources of both air and water pollution, aided by their potential for spontaneous combustion and leaching by rain water infiltration, respectively. Integrated coal washery waste disposal has the potential to ease this situation by eliminating the need for separate disposal areas for tailings and coarse reject. The combined coal washery waste formed by this method is simply a mixture of tailings and coarse reject with many improved engineering properties.Limitations of the conventional laboratory permeability testing equipment with regard to coal mine washery rejects, led to the development of a large diameter constant head permeability testing equipment with additional facilities to consolidate samples to required stress levels. The permeability test carried out in this apparatus clearly demonstrated that, the chief advantage of mixing coarse reject with tailings is the increased permeability of the resultant mixture. An increase in permeability of three to four orders of magnitude (from 10-7 m.s-1 for tailings to 10-3 m.s-1 for mixtures) were recorded from these tests.Consolidation tests carried out in large diameter Rowe cell demonstrated an improved consolidation behaviour for the tailings/coarse reject mixtures. This improvement is mainly attributable to the increased permeability of the mixtures in comparison to tailings only. As the proportion of tailings in a mixture increased (beyond 60% by weight) the mixture started to behave more like tailings. However, the mixture clearly demonstrated improved behaviour over a wide range of tailings to coarse reject mixing ratios (e.g. 20:80 to 40:60).Laboratory seepage modelling tests conducted in a specially designed seepage tank provided sufficient information regarding the filter cake formation and its effect in limiting the seepage through a coarse reject embankment. The transient nature of the seepage, the decreasing solids concentration of the effluent with the passage of time, and the depression of the wetting up line were studied in detail during these model tests.Laboratory tailings/coarse reject mixing trials were conducted in purpose built mixing tank with pore water pressure monitoring facilities. The mixing trials indicated that, to achieve good mixing of tailings and coarse reject, the coarse reject should be introduced into tailings within a certain time period after the deposition of tailings. Early introduction of coarse reject results in segregation, by coarse reject sinking to the bottom of the tailings. Late introduction of the coarse reject again results in segregation, where coarse reject is supported by the tailings, which gain strength by consolidation. Tailings can also be introduced into loose coarse reject, but effective mixing will occur to only shallow depth (of the order of 0.3 m).Consolidated drained direct shear tests carried out on tailings, coarse reject and mixtures thereof clearly indicated that these are essentially frictional materials, and the angle of friction is not very sensitive to the mixing ratios. The angle of friction remained high (above 30°) in all the tests.An existing finite element transient seepage analysis program "TSEEP" was calibrated using results from the laboratory seepage model tests and soil suction tests. The calibrated program was used to predict the field tailings seepage rate through a coarse reject embankment, simulating the small scale field trials conducted at the initial stages of the thesis investigation. Close agreement was found between the numerical predictions and the field measurements. The effect of the preferred seepage paths on the tailings seepage rate was successfully accounted for in the numerical modelling.The effectiveness of integrated coal washery waste disposal in a full scale mining operation was checked by field investigation carried out on a co-disposal site at Jeebropilly Colliery. The field investigation identified a few problems and the possible means of correcting these shortcomings are discussed in the thesis.

Bandwidth limitations, resource greedy applications verbose mark-up languages and an increasing number of voice and data users are straining the air interface of wireless networks. Hence, novel approaches and new algorithms to manage wireless bandwidth are needed. In addition, usage based pricing is becoming increasingly prevalent (pre-paid cell phones, calling cards, non-contract minutes, etc.). This paper unlocks the potential to improving the performance of overall system behavior by allowing users to change service level and/or service provider for a (small) price. The ability to dynamically re-negotiate service gives the user the power to control QoS while minimizing usage cost. On the other hand, the ability to change service level pricing dynamically allows the service providers to manage traffic better, improve resource usage and most importantly maximize their profit. This provides a surprising win-win situation for BOTH the service providers AND the users. In this paper we present easy to implement on-line algorithms to minimize the overall usage cost to individual mobile users. This on-line algorithm continuously receives pricing information and evaluates minimum QoS requirements. The algorithm then determines appropriate service level, chooses a service provider and sets a time for re-negotiation dynamically. Our algorithm can handle many practical issues such as capacity limitations, arbitrary price fluctuations and loss/gain of service providers due to mobility. Our results do not assume any specific technologies and can be applied to any environment that can employ dynamic pricing, including wired networks. In fact, dynamic pricing is becoming increasingly desirable since service provider and capacity changes are a growing by-product of mobility. Arriving and departing users at/from a cell tower (or wireless LAN) can effectively reduce or increase the available bandwidth in a cell (or LAN transmission area) and represents a natural opportunity for a pricing change.

Tight focusing properties of an azimuthally polarized Gaussian beam with a pair of vortices through a dielectric interface is theoretically investigated by vector diffraction theory. For the incident beam with a pair of vortices of opposite topological charges, the vortices move toward each other, annihilate and revive in the vicinity of focal plane, which results in the generation of many novel focal patterns. The usable focal structures generated through the tight focusing of the double-vortex beams may find applications in micro-particle trapping, manipulation, and material processing, etc.

Nanocrystalline CdS thin films have been prepared using cadmium nitrate and thiourea as precursors using the solgel spin coating method. The structural studies carried out on the prepared films using X-ray diffraction and high resolution transmission electron microscopy revealed that the CdS films exhibit hexagonal structure and the grain size was observed to be 10 and 14 nm for the films annealed at 250°C and 450°C. The surface topography of the films was studied using atomic force microscopy and the roughness was found to be 32 nm. The optical absorbance studies showed a strong blue shift due to the quantum confinement effect present in the CdS films. The grain size calculated using the band gap energy and quantum confinement effect was found to be in agreement with the results obtained from structural studies.

We compare focusing properties of conventional lenses and diffractive lenses (DLs). To that end, we use a converging electric-dipole wave as a model of an optimal converging wavefront that emerges from a conventional lens system. Our numerical results show that DLs have better focusing properties than conventional lenses for f -numbers less than 1. Although both types of lenses give nearly indistinguishable co-polarized intensity components in the focal region at low f -numbers, DLs provide much lower longitudinally polarized components. However, at sufficiently low Fresnel numbers and high f -numbers DLs fail to provide a well-focused energy distribution.

We consider problems involving how to schedule broadcasts in a pulled-based data-disseminationservice, such as the DirecPC system, where data requested by the clients is delivered via broadcast. In particular, we consider the case where all the data items are of equal size and preemption is not allowed. We give an offline O(1)-speed O(1)-approximation algorithm for the problem of minimizing the average response time. We provide worst-case analysis, under various objective functions, of the online algorithms that have appeared in the literature, namely, Most Requests First, First Come First Served, and Longest Wait First. Copyright © 2001 John Wiley & Sons, Ltd.