Absorption Of Incident Radiation Research Articles

Correlation between charge and current gain in LGADs treated with IR lasers

This study investigates the correlation between the gain, defined as the increase of measured charge generated from the absorption of incident radiation, and the gain measured as the increase of sensor leakage current in Low Gain Avalanche Detectors (LGAD) before and after neutron irradiations. LGADs exhibit high signal-to-noise ratios for minimum ionizing particles and will be used in high-energy physics experiments, mainly related to timing applications. Transient Current Technique (TCT) measurements were conducted with LGADs and PIN diodes. The electric field screening effect, caused by free and trapped carriers, is identified as the main reason for the differences measured in gain determined from the increase in leakage current and collected charge. These effects are more significant in irradiated LGAD sensors. The experimental results confirm expectations, demonstrating a growing spread between the two measured gains with fluence. The study enables the prediction of charge gain from the leakage current measurements, which are easier to conduct.

Determination of interparticle radiative heat transfer and radiation absorption for ellipsoidal particle beds using Monte Carlo ray tracing

The calculation of radiative heat transfer between particles in particle-based solar systems presents significant challenges in terms of computational cost and accuracy. This study addresses these challenges by employing the discrete element method to generate random particle packings and the Monte Carlo ray tracing method to investigate the influence of particle shape and volume fraction (ϕ) on interparticle radiation transfer and the absorption of incident radiation. The results reveal that, at low volume fractions, the shape and orientation of ellipsoidal particles have a pronounced impact on direct radiative transfer. Oblate particles exhibit the highest average radiation distribution factor (RDF), and the dispersion of RDF data is more prominent for oblate and elongated prolate particles compared to spheres. As ϕ increases to 0.35, the contribution of indirect transfer from neighboring particles becomes significant for oblate particles, resulting in a reduction in the dispersion of RDF data. Furthermore, when ϕ reaches 0.55, the decisive factor in determining RDF becomes the shielding effect of particles positioned between the emitting and receiving particles. The average RDF tends to converge among particles of different shapes, although oblate and elongated prolate particles still exhibit considerably larger RDF dispersion compared to spherical and near-spherical particles. Additionally, the effective absorptivity of the particle bed for incident radiation decreases as the aspect ratio of particles increases at all volume fractions. Moreover, the transmitted fraction demonstrates an exponential relationship with the depth, and beds composed of spherical particles exhibit better radiation transmittance compared to beds containing non-spherical particles.

THz properties of grating-gate plasmonic crystals

This study reviews recent advances in the modern field of terahertz plasmonics concerning the control of resonant properties of grating-gate plasmonic crystal structures. Particularly, we conducted both experimental and theoretical investigations of AlGaN/GaN grating-gate structures with a focus on investigations of the resonant structure of transmission spectra associated with plasmon excitations in two-dimensional electron gas at different modulation degree of concentration profiles. Two distinct resonant phases of the plasmonic crystal structure were analyzed. The first one, the delocalized phase, is observed in the case of a small modulation degree of electron gas. In this phase, we found that plasmonic resonant absorption of incident radiation occurs across the entire grating-gate structure, with domination in the gated regions of the electron gas. In contrast, the second phase, the localized one, is realized at a strong modulation of the electron concentration profiles when the gated regions of the electron gas are completely depleted. Here, plasmon resonances are characterized by the spatial localization of absorption of incident radiation exclusively within the ungated regions of the electron gas. Moreover, in the localized phase, we observed the unexpected blue shift of plasmon resonant frequency with an increase of gate voltage. This observation was explained by the result of ‘edge gating effect’ and additional shrinking of the concentration profile of the electron gas in the ungated region. We demonstrate that the correct description of both phases requires rigorous electrodynamic simulations and cannot be achieved solely in the frameworks of simplified single-mode or single-cavity models.

Dual-band plasmonic perfect absorber for refractive index sensing from mid- to near infrared region

A plasmonic perfect absorber (PA) utilizes high absorption of incident radiation and near-field enhancement which is so advantageous for many applications such as solar cell, infrared (IR) spectroscopy, and refractive index (RI) sensitivity. In this study, the numerically presented PA system has resonances from mid-infrared (MIR) to near-infrared (NIR) regions for different periodicities at 2.0, 2.4, and 2.8 µm. A fine-tuning mechanism is obtained to control the spectral response of PA through the geometrical parameters. Dual-band plasmonic resonances have nearly 98% absorption. Near-field intensity distributions are shown with the enhancement factor of 103 at the resonance frequencies. Refractive index sensitivity is also analyzed by embedding PA in different cladding mediums to show the sensing performance. Relationship between resonance wavelength and refractive index of the medium is observed for all resonant modes. The highest sensitivity value is 2382.48 nm/RIU and the figure of merit reaches as high as 28.29 RIU−1.

Comparison between an Innovative Solarization System and Dazomet-Based Fumigation

An innovative soil solarization system based on biochar was recently proposed. The difference with traditional solarization lies in the use, after soil irrigation, of a biodegradable black liquid sprayed on the soil surface in order to obtain a black body capable of drastically increasing the absorption of incident radiation and, as a consequence, increasing temperatures at different depths. Due to these higher temperatures, it is possible to eliminate pathogens in shorter times than with traditional solarization. In recent years, this practice has been tested in various contexts by comparing traditional solarization with this innovative new practice through temperature measurement at different soil depths for two months. The experimental data confirm the validity of this new approach for soil treatment: higher temperatures were registered with the innovative system, up to 10 °C more than the traditional method. In this work, we report a comparison between the new solarization system and a fumigation method. Our experimental results demonstrate that it is possible to obtain a satisfying soil treatment with a natural and sustainable practice based on solar energy, overcoming the major limitation of traditional solarization: application time. The black layer on the soil allows for the attainment of temperatures as high as necessary to eliminate most pathogens in a shorter time (just 30 days) than traditional solarization (2 months).

Multilayer Plasmonic Nanostructures for Improved Sensing Activities Using a FEM and Neurocomputing-Based Approach.

In order to obtain optimized elementary devices (photovoltaic modules, power transistors for energy efficiency, high-efficiency sensors) it is necessary to increase the energy conversion efficiency of these devices. A very effective approach to achieving this goal is to increase the absorption of incident radiation. A promising strategy to increase this absorption is to use very thin regions of active material and trap photons near these surfaces. The most effective and cost-effective method of achieving such optical entrapment is the Raman scattering from excited nanoparticles at the plasmonic resonance. The field of plasmonics is the study of the exploitation of appropriate layers of metal nanoparticles to increase the intensity of radiation in the semiconductor by means of near-field effects produced by nanoparticles. In this paper, we focus on the use of metal nanoparticles as plasmonic nanosensors with extremely high sensitivity, even reaching single-molecule detection. The study conducted in this paper was used to optimize the performance of a prototype of a plasmonic photovoltaic cell made at the Institute for Microelectronics and Microsystems IMM of Catania, Italy. This prototype was based on a multilayer structure composed of the following layers: glass, AZO, metal and dielectric. In order to obtain good results, it is necessary to use geometries that orthogonalize the absorption of light, allowing better transport of the photocarriers—and therefore greater efficiency—or the use of less pure materials. For this reason, this study is focused on optimizing the geometries of these multilayer plasmonic structures. More specifically, in this paper, by means of a neurocomputing procedure and an electromagnetic fields analysis performed by the finite elements method (FEM), we established the relationship between the thicknesses of Aluminum-doped Zinc oxide (AZO), metal, dielectric and their main properties, characterizing the plasmonic propagation phenomena as the optimal wavelengths values at the main interfaces AZO/METAL and METAL/DIELECTRIC.

Structural and optoelectronic properties of the Cs2InMCl6 (M: Sb, Bi, Ag) double perovskite compounds: A first-principles study

In this work we implied density-functional theory (DFT) to study structural and optoelectronic properties of the double perovskite Cs2InSbCl6 (CISC), Cs2InBiCl6 (CIBC) and Cs2InAgCl6 (CIAC) compounds. We found that structural parameters such as lattice constant and bulk modules are in close agreement with other computational and experimental results. Bandstructure calculations with norm-conserving pseudopotentials show that these compounds are semiconductors with a direct band gap that stay at the Gamma point of the first Brillouin zone. Their band gap values vary from 1.47 to- 3.16 eV. The valence band maximum (VBM) is primarily composed of the Cl-p, In-s, Sb/Bi-s, and Ag-s states, and the conduction band minimum (CBM) is composed of the Cl-s/p, In/Sb/Bi-p orbitals. Optical studies include dielectric function, absorption, optical conductivity, reflectivity, and refractive and extinction indexes were performed in the photon energy range 0.0 up to 14.0 eV to investigate the optical response of these structures. These compounds have large optical absorption of incident radiation in the range of about 2–14 eV. Therefore, they can potentially be promising candidates for use in optoelectronic devices.

Nature Allows High Sensitivity Thermal Imaging With Type-I Quantum Wells Without Optical Couplers: A Grating-Free Quantum Well Infrared Photodetector With High Conversion Efficiency

Quantum well infrared photodetectors (QWIPs) have facilitated thermal imagers with excellent pixel operability, uniformity and stability. The main disadvantage of the standard QWIP technology is the low conversion efficiency (CE) as a result of weak quantum efficiency (QE) and photoconductive gain inhibiting the utilization of the sensor for low background and/or high frame rate applications. The other problem is the requirement of an optical grating which loses its efficiency with decreasing pixel pitch, as well as limiting the performance of dual-band focal plane array (FPA) due to the wavelength dependence of the diffraction-grating coupling efficiency. The author reports a grating-free 15 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu \text{m}$ </tex-math></inline-formula> pixel pitch <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$640\times 512$ </tex-math></inline-formula> mid-wavelength infrared (MWIR) QWIP FPA constructed with the InP/GaInP/In <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.83</sub> Ga <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.17</sub> As material system with normal incident radiation absorption ability. The pixels yielded peak QE, CE and specific detectivity of 23%, ~40% and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$1\times 10 ^{11}$ </tex-math></inline-formula> cmHz <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1/2</sup> /W (at ~80 K with f/2 optics) in spite of the absence of diffraction grating, substantially high cut-off wavelength (5.8 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu \text{m}$ </tex-math></inline-formula> ) and broad spectral response ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\Delta \lambda /\lambda _{\mathbf {p}}=31$ </tex-math></inline-formula> %). Together with excellent (uncorrected) responsivity and noise equivalent temperature difference nonuniformities of 5.9% and 17%, the results illustrate tremendous improvement over the performance of the conventional MWIR QWIP FPA exhibiting great potential to revive the QWIP technology especially in dual-band imaging.

Non-similar solution of Casson nanofluid with variable viscosity and variable thermal conductivity

PurposeThe purpose of this study is to provide a numerical investigation of Casson nanofluid along a vertical nonlinear stretching sheet with variable thermal conductivity and viscosity.Design/methodology/approachThe boundary-layer equations are presented in the dimensionless form using proper non-similar transformations. The subsequent non-dimensional nonlinear partial differential equations are solved using the implicit finite difference technique. To linearize the nonlinear terms present in these equations, the quasilinearization technique is used.FindingsThe investigation showed graphically the temperature, velocity and nanoparticle volume fraction for particular included physical parameters. It is observed that the velocity profile decreases with an increase in the values of Casson fluid parameter while increases with an increase in the viscosity variation parameter. The temperature profile enhances for large values of velocity variation parameter and thermal conductivity parameter while it reduces for large values of thermal buoyancy parameter. Further, the Nusselt number and skin-friction coefficient are introduced which are helpful in determining the physical aspects of Casson nanofluid flow.Practical implicationsThe immediate control of heat transfer in the industrial system is crucial because of increasing energy prices. Recently, nanotechnology is proposed to control the heat transfer phenomenon. Ongoing research in complex nanofluid has been fruitful in various applications such as solar thermal collectors, nuclear reactors, electronic equipment and diesel–electric conductor. A reasonable amount of nanoparticle when added to the base fluid in solar thermal collectors serves to deeper absorption of incident radiation, and hence it upgrades the efficiency of the solar thermal collectors.Originality/valueThe non-similar solution of Casson nanofluid due to a vertical nonlinear stretching sheet with variable viscosity and thermal conductivity is discussed in this work.

Microscopic nonlinear quantum theory of absorption of coherent electromagnetic radiation in doped bilayer graphene

The microscopic quantum theory of nonlinear stimulated scattering of chiral particles in doped $AB$ stacked bilayer graphene on Coulomb field of charged impurities in the presence of strong coherent electromagnetic radiation is presented. The Liouville-von Neumann equation for the density matrix is solved analytically. Here the interaction of electrons with the scattering potential is taken into account as a perturbation. The absorption rate of nonlinear inverse-bremsstrahlung for a grand canonical ensemble of fermionic chiral particles is calculated using the obtained solution. The analysis of the obtained rate shows that in the terahertz and near-infrared range of frequencies there is significant absorption of incident radiation via multiphoton stimulated bremsstrahlung mechanism.

INVESTIGATION OF PHOTOELECTRIC CONVERTERS WITH A BASE CADMIUM TELLURIDE LAYER WITH A DECREASE IN ITS THICKNESS FOR TANDEM AND TWO-SIDED SENSITIVE INSTRUMENT STRUCTURES

Photovoltaic cells with a base layer of cadmium telluride with a decrease in its thickness are studied. It is known that the widespread use of photovoltaic converters is constrained by their high price in the case of highly efficient instrument structures, or low efficiency. The creation of tandem and two-sided sensitive photoelectric converters will reduce their cost while increasing their efficiency. However, to create tandem and two-sided sensitive photoelectric converters, the necessary conditions are the use of transparent contacts and a decrease in the thickness of the base layer for efficient absorption of incident radiation by the converter, which is lower. In the research process, it was found that reducing the thickness of the base layer to 1 μm allows to increase the efficiency of the photoelectric transducer during irradiation from the back. An increase in the efficiency of the photoelectric converter occurs due to a decrease in the distance from the generation region of nonequilibrium charge carriers in the region of separation. If the thickness of the base layer is less than 1 μm, then regardless of which side of the irradiation is carried out, a decrease in the efficiency of the instrument structure is observed. Increase in the efficiency of photoconverters is associated with an increase in the negative influence of recombination processes on the back contact, a decrease in the number of charge carriers generated due to incomplete absorption of incident radiation, and a decrease in the volume of the built-in field of the separating barrier when it overlaps with the depletion region of the back contact. ITO/CdS/CdTe/Cu/ITO SCs with a base layer thickness of 1 μm demonstrates degradation stability. The highest value of efficiency in the case of illumination from the front side 8.1 % and with illumination from the back side 3.8 % received after a year of operation of the photovoltaic converter.

Subwavelength diffraction gratings in the visible spectral range

We report the results of computer calculations and measurements of subwavelength diffraction gratings in the visible range of the radiation spectrum. The influence of various grating parameters (duty cycle, microrelief shape and depth, material, angle of incidence, wavelength, and radiation polarisation) on the diffraction efficiency is studied. A distinctive feature of the subwavelength gratings in question is that the entire diffracted energy of the beam is redistributed into the zero and –1st orders. It is found that the zero order can be suppressed by choosing the depth and shape of the grating relief. The subwavelength gratings with a period of 400 nm are fabricated and measurements are performed using lasers and laser diodes emitting in the visible wavelength range. High diffraction efficiency into the –1st order (more than 70 %) is observed in a wide spectral range of 450 – 650 nm with an increase in the grating relief depth (at a depth of h = 80 nm). It is experimentally demonstrated that under certain conditions, the plasmon resonance effect arises, in which total absorption of incident radiation takes place. The optical elements considered can be used in image processing systems, projection displays, in the development of various sensors, etc.

Daily direct, diffuse and global irradiances modelling for an accurate estimate of daily solar radiation intensity at the city of El Jadida (Morocco)

In this work, we derive analytic expressions and calculate numerical values of incident daily solar radiation on horizontal, fixed tilted, single-axis and double-axis tracking apertures as functions of day number, collector latitude, tilt and azimuth angles. The effect of non-uniform atmospheric absorption of incident radiation throughout a day is taken into account and new models of direct normal Bn and diffuse horizontal Dh components of global horizontal (tilted) irradiance Gh (Gt) are proposed, tested and validated on local experimental measurements. This enables us to extract global irradiance model parameters for average day of each month and to predict, accurately, daily solar radiation (energy per unit area) effectively received by any collector placed on earth during the whole year.

Impact of carbon nanotube geometrical volume on nonlinear absorption and scattering properties

Nonlinear optical (NLO) properties of carbon nanostructures are of great interest due to their broadband spectral response. As carbon nanotubes (CNTs) can be synthesized with various lengths, thicknesses, and numbers of layers, their optical properties can also be different. We have performed side-by-side comparative studies of the relationship between the geometrical volume and NLO properties of CNTs. The real and imaginary components of the third order optical nonlinearity are obtained using well-known Z-scan technique. While the transmission and scattered light are detected using photodiodes, the generated photoacoustic signal is recorded simultaneously using an ultrasonic transducer. Results show an inverse relationship between the volume of CNTs and their NLO properties. This can be attributed to the availability of more nanoparticles within the laser beam profile and concurrent generation of scattering sites upon the absorption of incident radiation.

Theoretical framework for performance evaluation of silicon quantum dot solar cell under low concentration illumination

This article describes a silicon quantum dot (Si QD) solar cell with absorption enhancement due to quantum-confinement in the front-side emitter region, which helps in the improvement of the short-circuit current density. The Si QD solar cell is theoretically mimicked using an equivalent circuit to account the possible recombination losses under low concentration illumination. The electrical output is estimated using proposed theoretical model by considering the fundamental properties of intrinsic Si reported in the literature. An increase of ∼7.5% in generated current density is observed due to extra absorption of incident radiation through Si QD, which is in accordance with the experimental findings. The performance of Si QD/c-Si solar cell has been studied with respect to low concentration illumination, wherein with increasing CR from 1 sun to 5 suns, the short circuit current density increases from 29.4 to 147.2 mA/cm2 and the open circuit voltage increases from 0.565 to 0.609 V. This study provides a theoretical framework for design optimization of a future Si QD solar cells to achieve better performance of the device.

Theoretical maximum performance evaluation of third generation silicon solar cell consisting of nc-Si:H/a-Si:H quantum wells

The maximum performance of nc-Si:H/a-Si:H quantum well solar cell is theoretically evaluated by studying the spectral absorption of incident radiation with respect to the number of inserted nc-Si:H quantum well layers. Fundamental intrinsic properties of a-Si:H and nc-Si:H materials reported in literature have been used to evaluate the performance parameters. Enhanced spectral absorption is recorded due to insertion of nc-Si:H quantum well layers in the intrinsic region of a-Si:H solar cell. By inserting 50 QW layers of nc-Si:H in the intrinsic region of the a-Si:H solar cell, the short-circuit current density (JSC) increases by ∼100% as compared to the baseline whereas the open-circuit voltage (VOC) decreases by ∼38%. The decrease in VOC is explained on the basis of quasi-Fermi level separation under the illuminated state of solar cell. Theoretical maximum efficiency, having the combined effect of the increase in JSC and decrease in VOC, has increased by ∼24% in comparison with the baseline due to the use of QW as calculated using ideal carrier lifetime value. With a realistic carrier lifetime of the state-of-the-art a-Si:H solar cells, the addition of QWs do not yield any significant gain. From this study, it is concluded that a high carrier lifetime is required to gain a noteworthy benefit from the nc-Si:H/a-Si:H QWs.

Energy Harvesting Through Optical Properties of TiO2 and C- TiO2 Nanofluid for Direct Absorption Solar Collectors

Nanofluids are tailored suspensions of nanoparticles in a suitable base fluid. The discovery of nanofluids by Stephen choi opened a new heat transfer mechanism. Since then several research has taken place to explore thermal, electrical and magnetic property of nanofluids. Nanofluids showed enhanced electrical and thermal conductivities. The nanofluids are also proved as a potential candidate for direct absorption solar collectors (DASC). The present work investigates the effect of nanoparticle volume fraction and the associated optical intensity attenuation with a semiconductor laser diode of wavelength 670 nm. Nanoparticles of Titanium dioxide (TiO 2 ) and Carbon doped Titanium dioxide (C-TiO 2 ) are prepared by sol gel and characterized by powder XRD, SEM and UV. Since carbon is a good absorption material, TiO 2 are doped with carbon (C-TiO 2 ) to increase the absorption of incident radiation. Nanoparticles of TiO 2 and C-TiO 2 with two weight fractions such as 0.04 and 0.08 are dispersed in water and ethylene glycol to obtain TiO 2 and C-TiO 2 nanofluids. The nanofluids are investigated for their sedimentation time. Stability of TiO 2 nanofluid is nine times more than C-TiO 2 nanofluid but C-TiO 2 nanofluid are found to be efficient absorbers than TiO 2 nanofluid. A low volume fraction of C-TiO 2 nanofluid can ensure high stability, low pumping power and good absorption for a DASC. Keywords- : Nanofluid, TiO 2 C-TiO 2, optical absorption, Laser.DASC 1. Introduction Increasing consumption and growing demands of electrical appliances across the globe have posed a threat on the non renewable energy resources and has made us exploit the maximum of renewable energy resources, in which solar energy is the ultimate choice. Solar energy has been investigated for photovoltaic and thermal applications (Duffie, 1980) [1]. A major thrust in materials development is to identify new materials in order to increase the efficiency of solar cells. Materials with ultra fine grain size and nanomaterials have provided an opportunity to tune the band gap and absorption of the existing solar energy. Conventional solar cells transfer the heat from the flat plate to the working fluid and it suffers from the large heat loss. The concept of direct absorption solar collectors in which working fluid acts as absorber and carrier of heat started replacing the conventional solar cells (Otanicar TP,2009) [2]. Since thermal conductivity of pure liquids are extremely less than solid particles, suspension of microparticles gained prominence. But micro-colloidal suspensions has drawbacks like abrasion and sedimentation. Nanofluids were substituted by Robert Taylor (2009) to overcome the above problems [3].The term Nanofluid was coined by Stephen Choi in 1995.[4] Nanofluids are suspensions of nanosized solid particles (1-100nm) in suitable base fluids. Since 1995, nanofluids have been explored as a heat transfer fluid and the best results have been reported by Eastman and Stephen Choi in ( 2001). In the past five years nanofluids have been also explored for their electrical (Suvankar Ganguly 2009)[5] and magnetic properties( John Philip,2009).[6] Nanofluids can be prepared by two ways, single step method (H Zhu 2004 )[7] or two step method (Eastman 1997) [8]. Single step method is based on simultaneous synthesis of nanoparticle and nanofluid and two step methods involve; the synthesis of nanoparticles in the first step followed by dispersion in a suitable base fluid in the second step. The success of nanofluid for DASC depends on suitable choice of base fluid and nanoparticles. The best nanofluids have high stability, high absorption of sun light and minimum abrasion. In the present work an attempt has been made to identify the best absorption nanofluid.

Selective thermal terahertz emission from GaAs and AlGaAs

The selective thermally stimulated terahertz (THz) radiation emission from GaAs and AlGaAs alloys are experimentally observed at frequencies of coupled oscillations of free electron plasma and different branches of interface AlGaAs optical phonons. The effect of strong absorption of incident radiation with large oblique angle (26°) by heated GaAs and AlGaAs is revealed. The coherent THz radiation emission with the frequency of 7.6 THz from the heated high conductivity GaAs (n = 4 × 1018 cm−3) layer is observed. The results are highly relevant to application in optoelectronic THz devices.

Electric and Magnetic Field Enhancement with Ultralow Heat Radiation Dielectric Nanoantennas: Considerations for Surface-Enhanced Spectroscopies

Plasmonic structures are known to offer strong local enhancements of the electric field for interaction with molecules and materials in their vicinity. However, they inherently suffer from high losses and absorption, which can occur in both surface plasmon polaritons and localized plasmons in particles, on which we shall focus. An effect of those losses, and an aspect often neglected, is the local heating of the nanoparticle due to the absorption of incident radiation and the transduction into thermal energy. This increase in the nanoparticle temperature, and in turn in the surrounding medium, can directly disrupt the response of the system due to changes in the optical properties of the medium and nanoparticle itself. This is especially a problem in the spectroscopic analysis of matter, where the advantage of field enhancement due to the plasmonic effect can be obstructed (or hampered) by a local temperature increase affecting the pure electromagnetic response of the sample. Here we investigate the use of subwavelength structures made of high refractive index dielectrics with ultralow losses in the optical and near-IR regime, gallium phosphide (GaP) in this case, as a novel way to approach applications that require near- and far-field enhancement, such as surface-enhanced Raman spectroscopy, but with the peculiarity of not perturbing the response of the sample under evaluation due to local heating. In particular, we show a comparison of the near- and far-field enhancing performance of plasmonic dimers with the one obtained from similar structures made of GaP. This study opens new possibilities to overcome losses and heat generation issues associated with plasmonic nanostructures in a range of applications in nanophotonics and metamaterials.

Metal Assisted Synthesis of Single Crystalline Silicon Nanowires at Room Temperature for Photovoltaic Application

Synthesis of single crystalline silicon nanowires (SiNWs) array at room temperature by metal assisted chemical etching and its optical absorption measurements have been reported in this article. It has been confirmed that, SiNWs were formed uniformly on p-type silicon substrate by electroless deposition of Cu and Ag nanoparticles followed by wet chemical etching in (Hydrogen Fluoride) HF based Fe(NO3)3 solution. Synthesized SiNW structures were analyzed and investigated by Scanning Electron Microscopy (SEM) and Ultraviolet-Visible (UV-VIS) spectrophotometer. Formation of SiNWs is evident from the SEM images and morphology of the structures depends upon the concentration of chemical solution and etching time. The synthesized SiNWs have shown strong broadband optical absorption exhibited from UVspectroscopy. More than 82% absorption of incident radiation is found for Cu treated samples and a maximum of 83% absorption of incident radiation is measured for Ag synthesized samples which is considerably enhanced than that of silicon substrate as they absorbed maximum of 43% of incoming radiation only.