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Electrically pumped distributed feedback (DFB) lasing in silicon nanocrystals (SiNCs) has been observed. The DFB SiNC laser was made based on a SiNC light-emitting diode (LED) by incorporating a second-order DFB grating. The light emission covered the visible regime. Optical gains in the order of 102 cm−1 were found in the light emitting regime. The DFB grating was so designed and fabricated that lasing wavelength in the red regime was selected. Signals emitting from the surface of the DFB SiNC laser were recorded. The laser was pumped by a pulsed direct-current power supply at room temperature. Four typical criteria of lasing were identified, i.e., 1) threshold behavior of the electroluminescence (EL) intensity versus pumping power density, 2) evident spectral narrowing of the EL spectrum, 3) well-recognized degree of polarization, and 4) small spread of light emitting angle. The latter three were for the pumping power density beyond the threshold one.

Abstract Unlike the single grating Czerny–Turner configuration spectrometers, a super-high spectral resolution optical spectrometer with zero coma aberration is first experimentally demonstrated by using a compound integrated diffraction grating module consisting of 44 high dispersion sub-gratings and a two-dimensional backside-illuminated charge-coupled device array photodetector. The demonstrated super-high resolution spectrometer gives 0.005 nm (5 pm) spectral resolution in ultra-violet range and 0.01 nm spectral resolution in the visible range, as well as a uniform efficiency of diffraction in a broad 200 nm to 1000 nm wavelength region. Our new zero-off-axis spectrometer configuration has the unique merit that enables it to be used for a wide range of spectral sensing and measurement applications.

A luminescent Si nanocrystal (SiNC) thin film with photoluminescence quantum yield (PLQY) > 70% was made by using hydrogen silsesquioxane (HSQ), followed by long-time high-pressure hydrogenation. A net optical gain of 524 ± 21 cm−1 was obtained by means of variable stripe length-shifting excitation spot (VSL-SES). A rectangularly shaped SiO2 Fabry-Perot (F-P) cavity with size of 1.5 μm (width) × 0.7 μm (height) × 2000 μm (length) was made on top of the SiNC thin film. The waveguide F-P device was pumped with a 400 nm femtosecond pulsed laser. A threshold behavior of the light emission intensity as a function of the pumping power was observed. Other lasing characteristics including spectral narrowing, polarization of the emission, and small emission angle were also observed beyond the threshold pumping power.

It is of great technological importance in the field of plasmonic color generation to establish and understand the relationship between optical responses and the reflectance of metallic nanoparticles. Previously, a series of indium nanoparticle ensembles were fabricated using electron beam evaporation and inspected using spectroscopic ellipsometry (SE). The multi-oscillator Lorentz–Drude model demonstrated the optical responses of indium nanoparticles with different sizes and size distributions. The reflectance spectra and colorimetry characteristics of indium nanoparticles with unimodal and bimodal size distributions were interpreted based on the SE analysis. The trends of reflectance spectra were explained by the transfer matrix method. The effects of optical constants n and k of indium on the reflectance were demonstrated by mapping the reflectance contour lines on the n-k plane. Using oscillator decomposition, the influence of different electron behaviors in various indium structures on the reflectance spectra was revealed intuitively. The contribution of each oscillator on the colorimetry characteristics, including hue, lightness and saturation, were determined and discussed from the reflectance spectral analysis.

Abstract The optical properties of aluminum-doped zinc oxide (AZO) thin films were calculated rapidly and accurately by point-by-point analysis from spectroscopic ellipsometry (SE) data. It was demonstrated that there were two different physical mechanisms, i.e., the interfacial effect and crystallinity, for the thickness-dependent permittivity in the visible and infrared regions. In addition, there was a blue shift for the effective plasma frequency of AZO when the thickness increased, and the effective plasma frequency did not exist for AZO ultrathin films (

In this work, we present a simple method to improve the thermoelectric performance of the RF sputtered bismuth telluride films by raising the power of deposition. The as-deposited samples synthesized under different powers were investigated and compared. It shows that the films prepared under relatively higher power conditions exhibit much higher electrical conductivity to result in a greater power factor accompanied with a minor drop in the Seebeck coefficients. A relationship is established between the improvement in thermoelectric performance and the decrease in crystallinity, which might also reduce the thermal conductivity. A maximum power factor of 5.65 × 10−4 W·m−1·K−2 at 470 K is obtained for the sample deposited under 50 W with its Seebeck coefficient being −105 μV/K. The temperature-dependent behaviors of the samples are also looked into and discussed. This work might offer an in-situ and cost-effective approach to improve the performance of thermoelectric materials.

As the key approach to enhance the efficient application of solar energy, solar selective absorbers have been extensively investigated in the past years. With great efforts contributed by scientists and engineers all around the world, new materials and excellent structures were achieved in solid progress to stimulate applications in broad fields. In this book, we will present an overview of both theory and experimental methods to fulfill the high-efficiency solar absorber devices. It begins with a historical description of the study and development for the spectrally selective solar absorber materials and structures based on the optical principles and methods in past decades. The optical properties of metals and dielectric materials are addressed to provide the background on how to realize high performance of the solar absorber devices applied in the solar energy field. In the following sections, different types of materials and structures, including the experimental methods, are discussed for practical construction and fabrication of the solar absorber devices, aiming at maximally harvest the solar energy, at the same time to suppress the heat-emission loss effectively. The optical principles and methods used to evaluate the performance of solar absorber devices with broad applications in different physical conditions are presented. The book will be suitable for graduate students in applied physics fields with valuables reference also for the researchers working actively in the solar energy fields. [ABSTRACT FROM AUTHOR]

A two-dimensional (2D) image of magneto-optical Kerr effect measurement system has been designed and constructed. The magnetic field is provided by two cylindrical permanent magnets in the 0–8000 G range. To avoid beam deviation and other problems in the measurement, an electronically controlled liquid crystal retarder with a fixed polarizer was used to detect the polarization change of the light at the 546.1 nm wavelength. The Fourier transformation method was used to retrieve the Kerr signal in data analysis. The Kerr image signal was measured by using a 2D charge coupled diode (CCD) array detector with 1536×1024 pixels. In terms of a telescope with 1:1 optical magnification, the CCD pixel detects the Kerr signal that is produced by the microsurface of the sample with the area size equaling to that of the pixel. The image Kerr effect of GdFe film sample was measured with the results to show that the 2D Kerr pattern can map the in-plane distribution of the magnetic property of the sample surface. © 2003 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The sub-20 nm ultrathin titanium dioxide (TiO2) films with tunable thickness were deposited on Si substrates by atomic layer deposition (ALD). The structural and optical properties were acquired by transmission electron microscopy, atomic force microscopy and spectroscopic ellipsometry. Afterwards, a constructive and effective method of analyzing interfaces by applying two different optical models consisting of air/TiO2/TixSiyO2/Si and air/effective TiO2 layer/Si, respectively, was proposed to investigate the influence of interface layer (IL) on the analysis of optical constants and the determination of band gap of TiO2 ultrathin films. It was found that two factors including optical constants and changing components of the nonstoichiometric IL could contribute to the extent of the influence. Furthermore, the investigated TiO2 ultrathin films of 600 ALD cycles were selected and then annealed at the temperature range of 400–900 °C by rapid thermal annealing. Thicker IL and phase transition cause the variation of optical properties of TiO2 films after annealing and a shorter electron relaxation time reveals the strengthened electron–electron and electron–phonon interactions in the TiO2 ultrathin films at high temperature. The as-obtained results in this paper will play a role in other studies of high dielectric constants materials grown on Si substrates and in the applications of next generation metal-oxide-semiconductor devices. [ABSTRACT FROM AUTHOR]

A solar selective absorber with a multilayered SiO2 (87.0 nm)/Cr (8.3 nm)/SiO2 (96.3 nm) film structure was designed and fabricated by magnetron sputtering on a surface-roughened copper (Cu) substrate. The proposed structure can enhance solar absorption by combining both the typical solar absorption designs of the textured surface and metal–dielectric multilayer film structure. The measured solar absorptance is about 94%, which yields an enhancement of about 2% accompanied by a slightly higher thermal emittance than that observed for the surface-smoothed structure. The increasing thermal emittance of the surface-roughened film structure is expected to markedly cancel the advantage of absorptance enhancement as the temperature increases to 600 K, implying that the proposed film structure functions more efficiently at low or intermediate temperatures (<600 K). [ABSTRACT FROM AUTHOR]

Niobium pentoxide (Nb2O5) films with different thicknesses were prepared using the electron beam evaporation method and then annealed at temperatures from 300 °C to 800 °C before being characterized by variable-angle spectroscopic ellipsometry, x-ray diffraction, etc. The results showed that the optical constants and microstructures of Nb2O5 films exhibit a strong dependence on the annealing temperature. In the visible light region, the refractive indices show a positive correlation with the annealing temperature from 300 °C to 600 °C, but a negative correlation from 600 °C to 800 °C. The amorphous Nb2O5 film converts into TT- Nb2O5 (pseudo-hexagonal) after annealing at 500–600 °C, and into T-Nb2O5 (orthorhombic) after annealing at 700–800 °C. [ABSTRACT FROM AUTHOR]

Graph is an important and fundamental data structure that presents in a wide variety of practical scenarios.With the rapid development of the Internet in recent years,there has been a huge increase in social network graph data,and the analysis of this data can be of great help in practical scenarios such as public services and advertising and marketing.There are already quite a few graph neural network algorithms that can get good results in such problems,but they still have room for improvement,and in many scenarios where high accuracy is pursued,engineers still want to have algorithms with better performance to choose from.This paper improves personalized propagation of neural predictions and proposes a new graph neural network algorithm called degree of node based personalized propagation of neural predictions(DPPNP)that can be used in social graph networks.Compared to traditional graph neural network algorithms,when the information is propagated between nodes,the proposed algorithm will keep its own information for different nodes in different proportions according to the degree of nodes,so as to improve the accuracy.Experiments on real datasets show that the proposed algorithm has better performance compared to previous graph neural network algorithms.

A new type of incidence-angle-variable infrared spectroscopic ellipsometer working in the 2100-10 000 wave number range has been designed and constructed. For the system, the analyzer and polarizer were driven by two microstepping motors having hollow shafts and rotating synchronously with a speed ratio of 2:1, i.e., A=2P. The incidence angle can be varied from 30° to 90° with an accuracy of 0.01°. The doubled Fourier transforms as both functions of the wave number and the azimuthal angles of the polarizer and analyzer were carried out and integrated in the system. Two sets of ellipsometric parameters measured in the experiment have been used to test the data self-consistency of the system. In data reduction, the error arising from the slight anisotropy of the stray light was corrected. In application, the complex dielectric function of the Au film was measured with a data accuracy better that 1% in the entire spectral range. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]