Static laser light scattering (SLLS) investigations of the scattering parameters of a synthetic polymer

A laser light scattering system was built to study the scattering parameters of some materials in solution form. The light source used was an argon-ion laser at wavelength 488 nm (all lines). The investigated material was a synthetic polymer which has a wide range of applications in the field of teeth medicine applications. This is polymethyl-methacrylate (PMMA) which is used for the formation of artificial clamps. The PMMA was solved in both acetone and methyl-ethyl-ketone (MEK). The acetone solvent is chosen for its high specific refractive index increment dn/dc at the same wavelength 488 nm as the argon laser source. The angular distribution of the scattered laser light intensities of PMMA dissolved in acetone was measured at different scattering angles from 30 to 150° for each concentration. The angular distributions have a symmetrical behavior about the scattering angle π/2; by using the scattered intensities the Zimm plot was formed. The weight average molecular weight (WAMW) was determined, the two other scattering parameters like as radius of gyration, h, and the second verial coefficient, A₂ were determined.     

火灾烟雾颗粒532 nm光散射矩阵实验研究

基于自主研制的结合偏振调制和锁相检测技术的光散射实验装置,测量了两种典型火灾烟雾颗粒(棉绳阴燃烟雾和正庚烷池火烟雾)及超声雾化水滴颗粒的532 nm光散射矩阵元素随散射角的分布. 通过水滴颗粒测量结果与数值计算结果的比较验证了实验装置的可靠性. 对比分析了棉绳阴燃烟雾和正庚烷池火烟雾光散射矩阵元素随散射角的分布特征,讨论了该特征在颗粒区分上的应用. 研究了烟雾颗粒微观形貌特征对光散射矩阵的影响,发现可以利用Lorenz-Mie理论描述棉绳阴燃烟雾的光散射,表明其形貌为球形,并利用模拟退火拟合的方法得到了棉 关键词： 光散射 散射矩阵 烟雾     

Synthesis of wurtzite-phase ZnS nanocrystal and its optical properties

The wurtzite phase of ZnS nanocrystal has been prepared by annealing in 200–600 °C temperature range, its cubic phase of 2–3 nm size, prepared through soft chemical method. Results of isochronal experiments of 2 h at different temperatures indicate that visible transformation to wurtzite from cubic ZnS appears at a temperature of 400 °C, which is about three times smaller than that of bulk ZnS phase transition temperature. The phases, nanostructures, and optical absorption characteristics are obtained through X-ray diffraction, transmission electron microscopy, and UV–visible absorption spectroscopy. A stable and green photoluminescence emission peaked at 518 nm is observed from the 600 °C annealed samples, under ultraviolet light excitation.     

Development of scattering near-field optical microspectroscopy apparatus using an infrared synchrotron radiation source

We report the status of a scattering near-field microspectroscopy apparatus developed at SPring-8 using an infrared synchrotron radiation (IR-SR) source. It consists of a scattering type scanning near-field optical microscope and a Fourier transform infrared spectrometer. The IR-SR is used as a highly brilliant and broad-band IR source. This apparatus has potential for application in near-field spectroscopy with high spatial resolution beyond the diffraction limit. In order to eliminate background scatterings from the probe shaft and/or sample surface, we used higher harmonic demodulation method. The near-field spectra were observed by 2nd harmonic components using the lock-in detection. The spatial resolution of about 300 nm was achieved at around 1000 cm^? 1 (10 μm wavelength).     

Resonant elastic scattering of light from single quantum wells in semiconductor multilayers

A theory is developed for steady-state elastic scattering of light via quasi-2D excitons from a quantum well (QW) whose interfaces are randomly rough. The study is mainly focused on the angle dependences of radiation giving direct information about static disorder responsible for the elastic scattering. A nonlocal excitonic susceptibility is expressed in terms of random profile functions of QW interfaces. Treated is elastic scattering of light from a disordered QW in the following actual dielectric environments: (i) a uniform background, (ii) a Fabry–Perot film with rough boundaries, and (iii) a semiconductor microcavity. The cross-sections are derived analytically for scattering of linearly polarized light to the lowest (Born's) approximation with arbitrary roughness statistics. The spectral and angle dependencies of scattering intensity are analyzed numerically in the absolute-value scale with Gaussian correlation of interface roughness. The probability 10⁻² was found for the exciton-mediated scattering of a photon from a QW interface roughness whose root-mean-square height is on the level of 2×10⁻¹ nm. This probability is shown to exceed by two orders of magnitude that is typical of resonant scattering from either a single semiconductor surface or rough boundaries of a semiconductor Fabry–Perot film containing the QW. The scattering spectrum of a QW placed in a microcavity is predicted to have a doublet structure whose components are associated with the cavity exciton–polaritons.     

CCD-camera based high sensitivity TL/OSL-spectrometer

A high sensitivity TL/OSL-spectrometer has recently been built at the Freiberg Luminescence Dating Laboratory. It detects luminescence over a range of 200–800 nm simultaneously with a grating spectrograph and an attached liquid-nitrogen cooled CCD-array. The completely computer-controlled system allows free user defined measurement cycles in a temperature range of 20–700°C and optical stimulation from UV to IR with monochromatic light from a 200 W mercury lamp. The general construction of the apparatus and examples of spectra are presented.     

Investigations on the scattering of α-particles on Li

Excitation functions of α-scattering on ⁷Li leading to the ground and first excited states have been measured in the bombarding energy regions 8.6–12.5 MeV and 17.0–22.5 MeV at c.m. scattering angles of 54.2°, 72.4° and 89.8°. A systematic deviation from smooth behaviour is revealed which, because of its regularity, is attributed to the exchange of a triton cluster between two α-particles.     

Dimensional evolution of silicon nanowires synthesized by Au–Si island-catalyzed chemical vapor deposition

This study explores the nucleation and morphological evolution of silicon nanowires (Si-NWs) on Si (0 0 1) and (1 1 1) substrates synthesized using nanoscale Au–Si island-catalyzed rapid thermal chemical vapor deposition. The Au–Si islands are formed by Au thin film (1.2–3.0 nm) deposition at room temperature followed by annealing at 700 °C, which are employed as a liquid-droplet catalysis during the growth of the Si-NWs. The Si-NWs are grown by exposing the substrates with Au–Si islands to a mixture of gasses SiH₄ and H₂. The growth temperatures and the pressures are 500–600 °C and 0.1–1.0 Torr, respectively. We found a critical thickness of the Au film for Si-NWs nucleation at a given growth condition. Also, we observed that the dimensional evolution of the NWs significantly depends on the growth pressure and temperature. The resulting NWs are 30–100 nm in diameter and 0.4–12.0 μm in length. For Si (0 0 1) substrates 80% of the NWs are aligned along the 1 1 1 direction which are 30° and 60° with respect to the substrate surface while for Si (1 1 1) most of the NWs are aligned vertically along the 1 1 1 direction. In particular, we observed that there appears to be two types of NWs; one with a straight and another with a tapered shape. The morphological and dimensional evolution of the Si-NWs is significantly related to atomic diffusion kinetics and energetics in the vapor–liquid–solid processes.     

Modification of polycarbonate surface properties by nano-, micro-, and hierarchical micro–nanostructuring

Polycarbonate surfaces were patterned with nanopillars, microbumps, or nanopillars superimposed on microbumps. Patterning was achieved by applying nanoporous anodized aluminum oxide (AAO) membranes, microstructured aluminum foil, or anodic alumina on microstructured aluminum as mold inserts in injection molding. The effect of the different-sized structures on properties of the polycarbonate surface was investigated in contact angle measurements with water and oleic acid. The water contact angle increased from 82° on the smooth surface to 139° on the hierarchical micro–nanostructure. The transmittance of the polycarbonate increased with nanopatterning, while the reflection properties of the polycarbonate surface decreased. Reflection was lowest for the nanostructure with 53 nm pillar diameter and 77 nm interpillar distance. Values ranged from 0.6 to 1.1% over the whole wavelength range of visible light, which was 4–5% units lower than the corresponding values for the smooth polycarbonate.     

Nano-designing of Mg doped phosphate tungsten bronzes and SiO2 composite obtained by ultrasonic spray pyrolysis method

In this study, the structure and substructure of SiO₂–Mg phosphate tungsten bronzes, MgPTB, (MgHPW₁₂O₄₀ · 29H₂O) obtained by ultrasonic spray pyrolysis method from a silica sol, and a MgPTB solution, obtained by the ion exchange method, as precursors were investigated.The mechanism of the formation of aerosol droplets is discussed. Phase composition, structure and substructure of SiO₂–MgPTB particles were investigated by X-ray powder diffraction (XRPD) analysis, transmission electron microscopy (TEM), and scanning electron microscopy (SEM).Good agreement between the theoretically predicted values for the mean diameters of particles and subparticles (1.27 μm and 75.4 nm, respectively) and the experimentally obtained ones (1.17 μm and 65–90 nm) was found.This agreement confirms the applicability of the model to get a satisfactory prediction of the most important data related to the nano-structural design of SiO₂–MgPTB powders.     

Surface plasmon resonance in nano-gold antimony glass–ceramic dichroic nanocomposites: One-step synthesis and enhanced fluorescence application

A single-step melt-quench in situ thermochemical reduction technique has been used to synthesize a new series of Au° nanoparticles embedded antimony glass–ceramic (K₂O–B₂O₃–Sb₂O₃–ZnO) dichroic nanocomposites. X-ray and selected area electron diffractions manifest growth of Au° nanoparticles along (2 0 0) planes. The particle sizes obtained from X-ray diffraction patterns are found to vary in the range 4–21 nm. Dichroic behavior is attributed to the elliptical shape gold nanoparticles having aspect ratio 1.2, as observed from the transmission electron microscopy (TEM) images. The Au° nanoparticles exhibit surface plasmon resonance band (SPR) around 600 nm, which experiences red-shifts with increasing Au concentration. These nanocomposites when co-doped with Sm₂O₃ and excited at 949 nm, exhibit 2-fold intensification of 636 nm red emission transition (⁴G_5/2 → ⁶H_9/2) due to SPR induced local field enhancement of Au° nanoparticles and are promising materials for display applications.     

A high-speed particle-detection in a large area using line-laser light scattering

We study the optical characteristics of a home-built line-laser surface light scattering system that detects sub-micron scale irregularities on a large area in high speeds. The sensitivity of the detection system, i.e. signal to noise (STN) ratio, is found to depend strongly on the detection angle. We find an optimal detection angle at 30°, at which STN ratio is maximized for 2500 nm silica particles on wafer surface. Experimental results of scattering intensity measurements from a smooth surface and from surfaces with spherical irregularities are in excellent agreement with corresponding theoretical model calculations. The line scan speed can be as high as ∼17 mm/s, while identifying the presence of a particle as small as 700 nm in a pixel area (∼15 μm × ∼17 μm). The presence of irregularities found by the line scan system is confirmed by confocal laser-scanning microscopy imaging. Due to unique advantages such as non-disruptiveness, high-speed over large area, and high sensitivity, this line scan system may be used as a surface inspection system that meets the requirements of recent flat panel display manufacturing environments.     

Quantum Monte Carlo simulation of exciton–exciton scattering in a GaAs/AlGaAs quantum well

We present a computer simulation of exciton–exciton scattering in a quantum well. Specifically, we use quantum Monte Carlo techniques to study the bound and continuum states of two excitons in a 10 nm wide GaAs/Al_0.3Ga_0.7As quantum well. From these bound and continuum states we extract the momentum-dependent phase shifts for s-wave scattering. A surprising finding of this work is that a commonly studied effective-mass model for excitons in a 10 nm quantum well actually supports two bound biexciton states. The second, weakly bound state may dramatically enhance exciton–exciton interactions. We also fit our results to a hard-disk model and indicate directions for future work.     

Grazing-angle scattering of electromagnetic waves in periodic Bragg arrays

A new powerful approximate approach for the theoretical analysis of Bragg scattering in oblique strip-like periodic arrays with the scattered wave propagating almost parallel to the array boundaries – grazing-angle scattering (GAS) – is introduced and justified. This approach is based on allowance for the diffractional divergence of the scattered wave by means of the parabolic equation of diffraction and Fourier analysis. The divergence is demonstrated to be an intrinsic physical cause of GAS. Detailed theoretical analysis of steady-state GAS is carried out for bulk and guided optical modes. It is demonstrated that the most interesting feature of GAS in arrays of width that is greater than a critical width is a unique combination of two strong simultaneous resonances with respect to frequency and angle of scattering. In such wide arrays, GAS is demonstrated to be not only unusually sensitive to angle of scattering, but also to small variations of array width and grating amplitude. Entire concentration of the resonantly strong scattered wave inside the array is shown to be possible. A relationship between GAS, conventional Bragg scattering, and extremely asymmetrical scattering (i.e. where the scattered wave propagates parallel to the array boundaries) is analysed. Applicability conditions for the used approximations and obtained results are derived and discussed.     

Collimating of diverging laser diode beam using graded-index optical fiber

This paper presents a technique for collimating a diverging beam from a laser diode using graded-index optical fiber. The optical set-up is relatively simple and easy to operate. The results show that laser beam of large divergent angle in the range of 10–35° can be reduced to a fully collimated beam with a divergent angle of less than 0.05°. The theory of the method as well as some experimental results is presented.     

Influence of interfaces density and thermal processes on mechanical stress of PECVD silicon nitride

The paper focuses on a particular silicon nitride thin film (SiN_x) produced by plasma enahanced chemical vapor deposition (PECVD) technique with high deposition rate (26 nm/min) and low values of mechanical stress (<100 MPa). This was perfomed with mixed frequency procedure varying the modulation of high frequency at 13.56 MHz and low frequency at 308 kHz of RF power supply during the deposition, without changing the ratio of reaction gases. Low stress silicon nitride is commonly obtained by tailoring the thickness ratio of high frequency vs. low frequency silicon nitride layers.The attention of this work was directed to the influence of the number of interfaces per thickness unit on the stress characteristics of the deposited material. Two sets of wafer samples were deposited with low stress silicon nitride, with a thickness of 260 nm and 2 μm, respectively. Thermal annealing processes at 380 and 520 °C in a inert enviroment were also performed on the wafers.The Stoney–Hoffman model was used to estimate the stress values by wafer curvature measurement with a mechanical surface profilometer: the stress was calculated for the as-deposited layer, and after each annealing process.The thickness and the refractive index of the SiN_x were also measured and charaterized by variable angle spectra elliposometry (VASE) techinique.The experimental measurements were performed at the MT-LAB, IRST (Istituto per la Ricerca Scientifica e Tecnologica) of Bruno Kessler Foundation for Research in Trento.     

Investigation of self-assembled fractal porous-silica over a wide range of length scales using a combined small-angle scattering method

The unique structure of a set of self-assembled porous silica materials was characterized through a combined small-angle scattering (CSAS) method using small- and ultra-small angle neutron scattering as well as small-angle X-ray scattering. The porous silica specimens investigated were prepared by a sol-gel method under the presence of alkylketene dimer (AKD) template particles and through calcination, which leads to the development of porous silica having a mass-fractal structure over length scales from ~ 100 nm to ~ 10 μm. Furthermore, the specimens posses a hierarchical structure, which consist of a fractal porous structure, and also contain primary silica particles less than 10 nm in size, which form a continuous silica matrix. To characterize these complex structures, observation over a broad range of length scales is indispensable. We propose a CSAS technique that serves this purpose well.     

An investigation into the role of the optical detection set-up in the recording of cardiac optical mapping signals: A Monte Carlo simulation study

Photon scattering is known to distort the fluorescence signals recorded from optically mapped cardiac tissue. However, the contribution of the parameters which define the optical detection set-up has not been assessed. In this study, Monte Carlo (MC) simulations of photon scattering within ventricular tissue are combined with a detailed model of a tandem-lens optical detection apparatus to characterise (i) the spatial origin upon emission of photons recorded in voltage-sensitive fluorescence measurements of cardiac electrical activity (using the fluorescent dye di-4-ANEPPS) and how this affects signal distortion, and (ii) the role the detector characteristics could play in modulating signal distortion during uniform illumination and photon emission from tissue depth. Results show that, for the particular excitation/emission wavelengths considered (488 nm and 669 nm, respectively), the dimensions of the scattering volume during uniform illumination extend around 3 times further in the surface recording plane than in depth. As a result, fluorescence recordings during electrical propagation are more distorted when transmembrane potential levels differ predominantly in the surface plane than in depth. In addition, MC simulation results show that the spatial accuracy of the fluorescence signal is significantly limited due to photon scattering, with only a small fraction of the recorded signal intensity originating from tissue beneath the pixel (approximately 11% for a 0.25×0.25 mm pixel). Increasing pixel size increases this fraction, however, it also results in an increase in the scattering volume dimensions, thus reducing the spatial resolution of the optical system, and increasing signal distortion. MC simulations also demonstrate that photon scattering in cardiac tissue limits the ability of optical detection system tuning in accurately locating fluorescent emission from depth. Specifically, our results prove that the focal plane depth that yields maximum signal intensity provides an underestimation of the emission depth. In conclusion, our study demonstrates the potential of MC simulations of photon scattering in guiding the design of optical mapping set-ups to optimise performance under diverse experimental conditions.     

Measurement of soot morphology by integrated LII and elastic light scattering

A compact experimental setup that integrates laser-induced incandescence (LII) and one-angle elastic light scattering (1A-ELS) to measure the size of polydisperse soot aggregates is described. A 532 nm laser and a detection angle of 35 degrees were employed, which provided sensitivity for aggregate radius of gyrations (R _g) of R _g≤200 nm. Both lognormal and self-preserving distribution functions are compared with width parameters derived from both aggregation theory and transmission electron microscopy (TEM) measurements. Using these distributions, mean aggregate sizes derived from the scattering measurements are compared. The LII+1A-ELS technique is validated with a two-angle elastic light scattering (2A-ELS) approach with an additional detection angle at 145 deg. Unlike LII+1A-ELS, the 2A-ELS technique has the advantage of not requiring knowledge of soot optical properties. Good agreement is found between the two techniques for a given distribution. A fundamental discrepancy exists between distributions derived from TEM and those according to aggregation theory, limiting the accuracy of both 2A-ELS and LII+1A-ELS. The dependence of both techniques on laser fluence and hence soot temperature is examined and discussed.     

Microstructural characterization and optical polarization of glass with needle-like micro–nano silver oriented arrangement

Homogeneous glasses in the Na₂O–B₂O₃–Al₂O₃–SiO₂ system doped with proper amount of AgCl were obtained by melting at a temperature of 1450 °C. Then, with several steps of treatment, including crystallization, elongation and reduction, the glass with oriented arrangement of needle-like micro–nano silver particles was produced. The microstructure and the optical properties of the glass samples in different stages were studied by SEM-EDAX, FE-SEM and UV–Vis spectrum. The results showed that the glass after elongation and reduction exhibits excellent polarization performance in the wavelength range from 600 nm to 900 nm, with an extinction ratio larger than 45 dB. The glass only elongated shows also slight polarizing performance, which may result from the formation of filament structure of Ag during elongation processing.