Optical Investigation of ZnS/GaAs and CuGaS2/GaP Systems

Microwave absorbing material (MAM) is a kind of functional material that can absorb electromagnetic wave effectively and convert electromagnetic energy into heat or make electromagnetic wave disappear by interference (Kimura et al., 2007). MAM is currently gaining much attention in the field of civil and military applications. For example, the materials have been widely applied to minimize the reflection of microwave darkrooms, airplanes, steamboats, tanks and so on (Zou et al., 2008). Generally, the electromagnetic absorbing performance of any MAM is linked to its intrinsic electromagnetic properties (i.e. conductivity, complex permittivity and permeability) as well as to extrinsic properties such as the thickness and working frequencies. It is clear that the microwave absorption properties can be improved by changing the above parameters. However, the traditional MAMs or novel nanomaterials still have some disadvantages such as high density, narrow band, and low absorptivity (Zou et al., 2006). Therefore, demands for developing more economical MAMs with “low density, wide band, thin thickness, and high absorptivity” are ever increasing. Wurtzite-structured ZnO is of great importance for its versatile applications in optoelectronics, piezoelectricity, electromagnetic wave absorption, laser, acous-optical divices, sensors, and so on (Wang et al., 2007). One-dimensional nanostructures of ZnO, such as nanowires, nanobelts, and nanotetrapods, have been a hot research topic in nanotechnology for their unique properties and potential applications. Moreover, several types of three-dimensional ZnO nanostructures have been synthesized. Because of the high surface/volume ratio and integrated platform, three-dimensional oxide networks have been demonstrated for building ultrasensitive and highly selective gas sensors and optoelectronics applications (Zhu et al., 2007). It is worth mentioning that the ZnO nanostructures have shown great attraction for microwave radiation absorption and shielding material in the high-frequency range due to their many unique chemical and physical properties (Zhuo et al., 2008). Some research works focused on nanoscaled ZnO as a vivid microwave absorption material due to their light weight, high surface/volume ratio, and semiconductive and piezoelectric properties (Wang & Song, 2008). On the other hand, carbon nanotubes (CNTs) as conductive filler have been widely studied in MAMs due to the unique spiral and tubular structure since the discovery of CNTs by Iijima in 1991 (Iijima, 1991). CNTs/polymer composites exhibit a strong microwave absorption in the frequency range of 2-18 GHz and have the potential application as broad

Sea surface temperature (SST) is one of the critical parameters in marine meteorology and oceanography. The SST datasets are incorporated as conditions for ocean and atmosphere models. The SST needs to be investigated for various scientific phenomenon such as salinity, potential fishing zone, sea level rise, upwelling, eddies, cyclone predictions. On the other hands, high spatial resolution SST maps can illustrate eddies and sea surface currents. Also, near real time producing of SST map is suitable for weather forecasting and fishery applications. Therefore satellite remote sensing with wide coverage of data acquisition capability can use as real time tools for producing SST dataset. Satellite sensor such as AVHRR, MODIS and SeaWIFS are capable of extracting brightness values at different thermal spectral bands. These brightness temperatures are the sole input for the SST retrieval algorithms. Recently, Landsat-8 successfully launched and accessible with two instruments on-board: (1) the Operational Land Imager (OLI) with nine spectral bands in the visual, near infrared, and the shortwave infrared spectral regions; and (2) the Thermal Infrared Sensor (TIRS) with two spectral bands in the long wavelength infrared. The two TIRS bands were selected to enable the atmospheric correction of the thermal data using a split window algorithm (SWA). The TIRS instrument is one of the major payloads aboard this satellite which can observe the sea surface by using the split-window thermal infrared channels (CH10: 10.6 μm to 11.2 μm; CH11: 11.5 μm to 12.5 μm) at a resolution of 30 m. The TIRS sensors have three main advantages comparing with other previous sensors. First, the TIRS has two thermal bands in the atmospheric window that provide a new SST retrieval opportunity using the widely used split-window (SW) algorithm rather than the single channel method. Second, the spectral filters of TIRS two bands present narrower bandwidth than that of the thermal band on board on previous Landsat sensors. Third, TIRS is one of the best space born and high spatial resolution with 30 m. in this regards, Landsat-8 can use the Split-Window (SW) algorithm for retrieving SST dataset. Although several SWs have been developed to use with other sensors, some adaptations are required in order to implement them for the TIRS spectral bands. Therefore, the objective of this paper is to develop a SW, adapted for use with Landsat-8 TIRS data, along with its accuracy assessment. In this research, that has been done for modelling SST using thermal Landsat 8-imagery of the Persian Gulf. Therefore, by incorporating contemporary in situ data and SST map estimated from other sensors like MODIS, we examine our proposed method with coefficient of determination (R2) and root mean square error (RMSE) on check point to model SST retrieval for Landsat-8 imagery. Extracted results for implementing different SW's clearly shows superiority of utilized method by R<sup>2</sup> = 0.95 and RMSE = 0.24.

Abstract. Sea surface temperature (SST) is one of the critical parameters in marine meteorology and oceanography. The SST datasets are incorporated as conditions for ocean and atmosphere models. The SST needs to be investigated for various scientific phenomenon such as salinity, potential fishing zone, sea level rise, upwelling, eddies, cyclone predictions. On the other hands, high spatial resolution SST maps can illustrate eddies and sea surface currents. Also, near real time producing of SST map is suitable for weather forecasting and fishery applications. Therefore satellite remote sensing with wide coverage of data acquisition capability can use as real time tools for producing SST dataset. Satellite sensor such as AVHRR, MODIS and SeaWIFS are capable of extracting brightness values at different thermal spectral bands. These brightness temperatures are the sole input for the SST retrieval algorithms. Recently, Landsat-8 successfully launched and accessible with two instruments on-board: (1) the Operational Land Imager (OLI) with nine spectral bands in the visual, near infrared, and the shortwave infrared spectral regions; and (2) the Thermal Infrared Sensor (TIRS) with two spectral bands in the long wavelength infrared. The two TIRS bands were selected to enable the atmospheric correction of the thermal data using a split window algorithm (SWA). The TIRS instrument is one of the major payloads aboard this satellite which can observe the sea surface by using the split-window thermal infrared channels (CH10: 10.6 μm to 11.2 μm; CH11: 11.5 μm to 12.5 μm) at a resolution of 30 m. The TIRS sensors have three main advantages comparing with other previous sensors. First, the TIRS has two thermal bands in the atmospheric window that provide a new SST retrieval opportunity using the widely used split-window (SW) algorithm rather than the single channel method. Second, the spectral filters of TIRS two bands present narrower bandwidth than that of the thermal band on board on previous Landsat sensors. Third, TIRS is one of the best space born and high spatial resolution with 30 m. in this regards, Landsat-8 can use the Split-Window (SW) algorithm for retrieving SST dataset. Although several SWs have been developed to use with other sensors, some adaptations are required in order to implement them for the TIRS spectral bands. Therefore, the objective of this paper is to develop a SW, adapted for use with Landsat-8 TIRS data, along with its accuracy assessment. In this research, that has been done for modelling SST using thermal Landsat 8-imagery of the Persian Gulf. Therefore, by incorporating contemporary in situ data and SST map estimated from other sensors like MODIS, we examine our proposed method with coefficient of determination (R2) and root mean square error (RMSE) on check point to model SST retrieval for Landsat-8 imagery. Extracted results for implementing different SW's clearly shows superiority of utilized method by R2 = 0.95 and RMSE = 0.24.

Modern optoelectronics needs development of new materials characterized not only by high optical transparency and electrical conductivity, but also by mechanical strength, and flexibility. Recent advances employ grids of metallic micro- and nanowires, but the overall performance of the resulting material composites remains unsatisfactory. In this work, we propose a new strategy: application of natural scaffoldings perfected by evolution. In this context, we study two bio-inspired networks for two specific optoelectronic applications. The first network, intended for solar cells, light sources and similar devices, has a quasi-fractal structure and is derived directly from a chemically extracted leaf venation system. The second network is intended for touch screens and flexible displays, and is obtained by metalizing a spider's silk web. We demonstrate that each of these networks attain an exceptional optoelectonic and mechanical performance for its intended purpose, providing a promising direction in the development of more efficient optoelectronic devices.

The effect of the crystal lattice mismatch between single p-GaAs nanowire grown on p-Si substrate on the solar cell efficiency is studied. The study is performed by measuring the I-V curves under red (wavelength=650 nm) laser illumination. The measurement of the single nanowire was done by conductive atomic force microscopy (C-AFM). The measured curve was reproduced by numerical simulations accounting piezoresistance and piezoelectric effects. The analysis demonstrated the presence of the tensile (2%) zinc blend insert at the interface between nanowire and substrate induced by crystal lattices mismatch. Strained insert at the interface changes the polarity of the photogenerated current and increases the efficiency by 2 times.

Owning to their superior electronic and optical properties, silicon nanomembranes (NMs) have attracted considerable attention to be exploited as fundamental building blocks for the applications in electronics, photonics, and optoelectronics. Nevertheless, small photon traveling distance in such ultra‐thin silicon (UT‐Si) nanomembranes with nanoscale thicknesses (50 nm) induces low total light absorption, which is crucial for optoelectronic applications. Here, a convenient and controllable strategy, involving self‐assembly of dielectric polystyrene (PS) microsphere array on UT‐Si, was proposed to enhance optoelectronic responses of UT‐Si‐based photodetectors in broadband. Scattering effect of PS microspheres facilitates to couple incident light into UT‐Si layer, thus enhancing the light absorption. UT‐Si‐based metal‐semiconductor‐metal (MSM) photodetectors with a PS microspehere array demonstrate significant enhancement in optoelectronic response compared with the photodetector without PS microspeheres. Furthermore, the response spectrum can be controllably tuned by adjusting the size of paved microspeheres. This research may provide a practical and cost‐efficient approach for enhancing the optoelectronic responses of nanomaterials with nanoscale thicknesses, thus expediting their potential applications in optoelectronic devices.

The effect of lattice mismatch on the chemical ordering of epitaxial FePt films was studied. The results showed that the lattice constant (c) of the FePt films decreased with increasing lattice mismatch ε from about 2.23% to 6.33%. Upon further increase of ε to about 8.8%, c increased. On the other hand, the variation of the lattice constant (a) of the FePt films showed a reversal behavior to that of c with the increased lattice mismatch. The ratio c∕a of the FePt films held a minimum of about 0.9466, while the chemical ordering degree and magnetic anisotropy constant held maximum values for ε around 6.33%. These results indicated that the strain from the lattice mismatch favored the ordering of the FePt films.

III-V mixed crystals are interesting for their application in modern optoelectronics and microwave electronics. Two mixed systems, namely GaAs1-xSbx and GaAs1-x- ySbxPy, were chosen to investigate an influence of gallium phosphite and gallium antimonide added to gallium arsenide on band structure properties and crystal lattice structure.© (1996) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Photophysics and photoreactivity of cross-conjugated enediynyl aggregates: Applications to multi-parametric sensing of microheterogeneity and reversible fluorescence switching

New types of microlens arrays for the IR based on inorganic chalcogenide photoresists

Monolithic High Contrast Gratings (MHCGs) are a special type of high-contrast grating (HCGs). In MHCGs, the stripes and the substrate on which they are implemented are made of the same material. MHCGs provide up to 100% power reflectance and thus are expected to find numerous applications in modern optoelectronics. We present thorough experimental analysis of spectral properties of GaAs MHCG mirrors designed at the wavelength of 1000 nm. Our results show that MHCG mirrors can be high-reflectivity mirrors as well as efficient polarizer and their properties can be modified by variation of lateral parameters of MHCG stripes.

In this chapter, we study the effective electron mass (EEM), the Einstein relation for the diffusivity–mobility ratio (ER), the Einstein’s photoemission (EP), the field emission (FE) and the thermo-electric power (TP) in heavily doped nanowires (HDNWs) of different biosensing materials together with the relative comparison of the said transport features with that of the HDNW compounds. The EEM is an important transport quantity which is used in the analysis of different devices of low-dimensional electronics. The ER is useful in the characterizations of various types of hetero-structures and occupies a central position in the field of materials science. The EP is a physical phenomenon which finds extensive application in modern opto-electronics, and the FE is a quantum mechanical process. Besides, with the advent of quantum Hall effect, there has been considerable interest in studying the TP for various low-dimensional compounds. Although biosensing materials find wide applications and many physical properties have already been studied, nevertheless the investigations of the said electronic quantities for nanowires (NWs) of heavily doped (HD) biosensing materials are becoming increasingly important. Keeping this in mind in this chapter, an attempt is made to study the aforesaid quantities, talking HDNWs of various biosensing materials. We observe that the EEM is quantum number dependent. The ER oscillates with the electron statistics (n0) and the magnitude and nature of oscillations are totally different as compared with the ER in HDNWs of other materials talking HDNW of InSb as an example. The Einstein’s photo current from HDNWs of different biosensing materials also oscillates with n0 in radically different fashion as found from HDNWs of other materials. The field emitted current oscillates with increase in electric field due to van Hove singularities and the TP increases with increasing n0 in oscillatory ways. The most important realization is that the quantum signatures in all the cases are not only totally different, but also the variations of the said electronic quantities as compared with that of HDNWs different compounds excluding biomaterials are also different.KeywordsEffective Electron MassEinstein RelationEinstein’s PhotoemissionHeavily Doped NanowiresBiosensing MaterialsField EmissionThermoelectric Power

Quasi-collinear geometry is a special configuration of acousto-optic (AO) diffraction that provides an extremely large AO interaction length for achieving extremely high spectral resolution of AO tunable filters (AOTFs). Large AO interaction length also makes it possible to implement multifrequency diffraction in quasi-collinear AOTFs, which has found multiple applications in modern optoelectronics. The most widespread of them being ultrashort laser pulse shaping when the pulse shape and spectral composition is controlled by the spectral composition of the ultrasound pulse aroused in the AO crystal. The operation of quasi-collinear AOTFs is accompanied by the appearance of the temperature gradients in the AO device mainly due to the acoustic power absorption by the material. We experimentally assessed the influence of these gradients on the AOTF spectral characteristics. A theoretical model based on the Raman-Nath equations was proposed, which allows to consider the influence of ultrasound attenuation and temperature gradients on the AOTF transmission. This model is valid for transmission simulations both in single- and modulated-frequency AOTF operation modes. The study includes the effects of acoustic wave attenuation and AO phase matching shift caused by inhomogeneous crystal temperature along the optical beam path. The compensation strategy based on ultrasound frequency and magnitude adjustment is proposed for minimizing the effect of temperature gradients and acoustic field attenuation on AOTF spectral transmission for broadband operation in ultrashort laser pulse shaping.

The mechanism of formation of silicon nanoclusters in layers of nonstoichiometric composition is studied by Monte Carlo simulation. Interest in silicon nanoclusters (Si-nc) coated with an oxide layer is due to their applications in modern optoelectronics and nanoelectronics. A lattice Monte Carlo model is proposed to study atomic processes in the Si-SiO2 system. The formation of silicon nanoclusters during annealing of single SiO layers and SiO2-SiO-SiO2 layered structures is studied. Along with the diffusive motion of particles, the model takes into account the formation and collapse of mobile molecules of silicon monoxide. It is shown that accounting for transport of silicon under high-temperature annealing due to the motion of SiO accelerates the formation of Si-nc. Dependences of the size of nanoclusters on temperature, annealing time, and the composition of the SiO x layer are obtained. It is found that annealing of silica films containing layers of nonstoichiometric composition can lead to the formation of silicon nanoclusters or cavities.

The exciton and phonon strong coupling in functional materials is rich of physics and has promising applications in modern optoelectronics and photonics. However, the direct realization of strong exciton–phonon coupling without complex and well‐designed resonator at room temperature is still a challenge in this topic associated with the Born–Oppenheimer approximation and constrained by the thermalized noise. Here, the enhancement of exciton–phonon coupling in 2D MoSi2N4 material is demonstrated by the near exciton resonance technique and first realization of the strong‐coupling states of exciton and phonon in MoSi2N4 at room temperature. With the involving of three‐band terms transition processes, the phonon scattering transition probability and exciton–phonon interaction are significantly enhanced. Then the strong coupling is reached which maintains high energy transfer efficiency between exciton and phonon supporting over ten phonon replicas at room temperature without introducing harsh resonant cavity. This work identifies that the 2D MoSi2N4 should be a promising strong‐coupling system for exploring many‐body quantum states with strong correlations and further applications in quantum systems, especially for exciton tailoring and room‐temperature tunable exciton lasers.