High Absorption Characteristics Research Articles

Quantification of absorption contributions in microstructured silicon fabricated by femtosecond laser pulses

Microstructured silicon material, fabricated by femtosecond laser pulses, has a lot of crucial applications in silicon-based photovoltaics, photo-detectors, and super-hydrophobic devices etc., due mainly to the high absorption in both visible and infrared regions. However, the mechanisms attributed to its high-absorption characteristics have never been accurately quantified, which limits further the exploitation of this kind of material. Here, we experimentally quantify different absorption contributions in microstructured silicon fabricated by femtosecond laser pulses, which can be attributed to dopant impurities in the silicon substrate, doping impurities induced during the laser fabrication process, absorption enhancement from the light-trapping structure, and surface disordered material formed also during the laser fabrication process. From these analyses, we determine that with the assist of a light-trapping structure, dopant impurities in the silicon substrate contribute much more to the infrared absorption than those of the doping sulfur impurities induced during the fabrication process. Furthermore, the infrared absorption of material can be annealing-insensitive. These results have important implications for the design and fabrication of high-efficiency optoelectronic devices.

The impact of different multi-walled carbon nanotubes on the X-band microwave absorption of their epoxy nanocomposites.

BackgroundCarbon nanotube (CNT) characteristics, besides the processing conditions, can change significantly the microwave absorption behavior of CNT/polymer composites. In this study, we investigated the influence of three commercial multi-walled CNT materials with various diameters and length-to-diameter aspect ratios on the X-band microwave absorption of epoxy nanocomposites with CNT contents from 0.125 to 2 wt%, prepared by two dispersion methods, i.e. in solution with surfactant-aiding and via ball-milling.ResultsThe laser diffraction particle size and TEM analysis showed that both methods produced good dispersions at the microscopic level of CNTs. Both a high aspect ratio resulting in nanotube alignment trend and good infiltration of the matrix in the individual nanotubes, which was indicated by high Brookfield viscosities at low CNT contents of CNT/epoxy dispersions, are important factors to achieve composites with high microwave absorption characteristics. The multi-walled carbon nanotube (MWCNT) with the largest aspect ratio resulted in composites with the best X-band microwave absorption performance, which is considerably better than that of reported pristine CNT/polymer composites with similar or lower thicknesses and CNT loadings below 4 wt%.ConclusionsA high aspect ratio of CNTs resulting in microscopic alignment trend of nanotubes as well as a good level of micro-scale CNT dispersion resulting from good CNT-matrix interactions are crucial to obtain effective microwave absorption performance. This study demonstrated that effective radar absorbing MWCNT/epoxy nanocomposites having small matching thicknesses of 2–3 mm and very low filler contents of 0.25-0.5 wt%, with microwave energy absorption in the X-band region above 90% and maximum absorption peak values above 97%, could be obtained via simple processing methods, which is promising for mass production in industrial applications.Graphical Comparison of the X-band microwave reflection loss of epoxy composites of various commercial multi-walled carbon nanotube materials.

Perovskite solar cells: from materials to devices.

Perovskite solar cells based on organometal halide light absorbers have been considered a promising photovoltaic technology due to their superb power conversion efficiency (PCE) along with very low material costs. Since the first report on a long-term durable solid-state perovskite solar cell with a PCE of 9.7% in 2012, a PCE as high as 19.3% was demonstrated in 2014, and a certified PCE of 17.9% was shown in 2014. Such a high photovoltaic performance is attributed to optically high absorption characteristics and balanced charge transport properties with long diffusion lengths. Nevertheless, there are lots of puzzles to unravel the basis for such high photovoltaic performances. The working principle of perovskite solar cells has not been well established by far, which is the most important thing for understanding perovksite solar cells. In this review, basic fundamentals of perovskite materials including opto-electronic and dielectric properties are described to give a better understanding and insight into high-performing perovskite solar cells. In addition, various fabrication techniques and device structures are described toward the further improvement of perovskite solar cells.

Spectral estimation of soil water content in visible and near infra-red range

Soils can be examined on the basis of spectral data, using such methods with which the reflected radiation can be divided into a large number of (several hundreds) small spectral channel (some nm). Based on the spectral characteristics of the soils, or the different index numbers calculated from hyperspectral data water content of soils can be well characterized. The examined soil samples were coming from different apple orchards of which soils had different physical characteristics (sandy loamy and clay). The goals of my experiments were the evaluation of spectral measurement method for soil content detection, and to carry out algorithms for fast field scale spectral evaluation of different soil water content. The spectral measuring was carried out by laboratory scale AvaSpec 2048 spectrometer at 400 – 1000 nm wavelength interval with 0.6 nm spectral resolutions and by ASD FieldSpec Junior at 350 – 2500 nm. After drying, dry soil samples were watered by 2.5 m/m% till maximal saturation, and each wetting was measured spectrally. Based on spectral properties, reflectances were decreased in the whole spectral range within the continuous wetting due to the high absorption characteristics of water. The most water sensitive spectral ranges were selected by principal component, and such algorithms were created, with which the water content can be detectable in the certain soil. The algorithms can facilitate farmers for irrigation scheduling of their orchards. These results can also be utilizable in precision water management, since it can be a basis for such integrated active sensors with LED or laser light source, measuring reflectance at the certain spectral range, which can facilitate real time water status assessment of orchards.

Doping effect of Zr–Zn binary mixture on the structural and electrical properties of SrCo2-W type hexaferrites

SrCo2Fe16−2x(Zr–Zn)xO27 hexaferrite nanocrystallites of average crystallite sizes in the range of 38–43nm were synthesized by the chemical co-precipitation method and their structural and electrical properties were determined. Single hexaferrite phase was established by X-ray diffraction (XRD) analysis of the synthesized samples and various parameters have been calculated using XRD data. Doping Zr–Zn binary mixture in SrCo2Fe16O27 resulted in a considerable enhancement of the room temperature resistivity (109Ωcm), which make it suitable for applications at higher frequencies and for the minimizing eddy current losses in the transformers cores. Of all the synthesized samples, the lowest value of the reflection loss is obtained for the dopant contents of x=0.2 and x=0.8. Materials with high absorption characteristics may find their applications in the microwave and radar absorption as well as for the electromagnetic attenuations.

Direct Reduction of Carbon Dioxide to Formate in High‐Gas‐Capacity Ionic Liquids at Post‐Transition‐Metal Electrodes

As an approach to combat the increasing emissions of carbon dioxide in the last 50 years, the sequestration of carbon dioxide gas in ionic liquids has become an attractive research area. Ionic liquids can be made that possess incredibly high molar absorption and specificity characteristics for carbon dioxide. Their high carbon dioxide solubility and specificity combined with their high inherent electrical conductivity also creates an ideal medium for the electrochemical reduction of carbon dioxide. Herein, a lesser studied ionic liquid, 1-ethyl-3-methylimidazolium trifluoroacetate, was used as both an effective carbon dioxide capture material and subsequently as an electrochemical matrix with water for the direct reduction of carbon dioxide into formate at indium, tin, and lead electrodes in good yield (ca. 3 mg h(-1) cm(-2)).

Impact strength, microstructure, and water absorption properties of kenaf/polyethylene terephthalate (PET) fiber-reinforced polyoxymethylene (POM) hybrid composites

Abstract

Boreal forest conifer extracts: potential natural additives for acrylic polyurethane coatings for the protection of heat-treated jack pine

Among consumers, heat-treated wood recently gained more importance due its attractive darker color along with several other advantages such as improved biological resistance, dimensional stability, and thermal insulating properties. However, exposure to the exterior environment drastically changes the attractive darker color of this product. From dark brown, it becomes almost white. For this reason, development of a nontoxic transparent coating which can protect the heat-treated wood from photodegradation is very important. Addition of UV stabilizers (UV absorbers, HALS, antioxidant) is necessary for transparent coatings in order to filter the harmful UV/VIS radiation. In this present study, the effectiveness of natural antioxidants, extracted from conifer barks or needles from trees in protecting the color of wood, as additives to acrylic polyurethane coating is examined. Also, their UV/VIS absorption capacities and semi-quantitative component analyses have been presented. The toxicity of these new products was also evaluated on human normal skin cells due to ever increasing environmental legislation. The chemical modification of acrylic polyurethane coating containing conifer bark and needle extract were examined by ATR–FTIR analysis. Promising results were obtained for these natural antioxidants which showed very high UV absorption characteristics and antioxidant activity.

Nanofibrous Resonant Membrane for Acoustic Applications

Because the absorption of lower-frequency sound is problematic with fibrous material made up of coarser fibers, highly efficient sound absorption materials must be developed. The focus of this paper is on the development of a new material with high acoustic absorption characteristics. For low-frequency absorption, structures based upon the resonance principle of nanofibrous layers are employed in which the resonance of some elements allows acoustic energy to be converted into thermal energy. A nanofibrous membrane was produced by an electrostatic spinning process from an aqueous solution of polyvinyl alcohol and the acoustic characteristics of the material measured. The resonant frequency prediction for the nanofibrous membrane is based on research into its production parameters. The distance between electrodes during the electrostatic spinning process determines the average diameter of the nanofibers, and the outlet velocity of the material determines its area density. The average diameter of nanofibers was measured using the Lucia software package directly from an electron microscope image. The resonant frequency of nanofibrous membranes was determined from the sound absorption coefficient and transmission loss measurement.

Reflectance of Micro-Structural Material on Au

The high absorption characteristics, the complex mechanism and the great potential application in detectors of micro-structural material aroused extensive attention. In order to understand the impact of the micro-structure, the optical simulation method based on Monte Carlo is used for reflection characteristics of micro-structural material with the cell of pyramid construction. In this simulation, the body material is made of gold, which can avoid the effect of tranmittance, with a number of 400 cells. The bottom square of each structure is 50×50 µm, and the height of cells is adjustable. Then the relationship between the height and reflectance can be built up. However, a very complex relationship between the reflectance and the input parameters, including refractive index, extinction coefficient and the structure of the material is showed from simulation result. Generally, the reflectance decreases while the height increases.

A parallel adaptive finite element simplified spherical harmonics approximation solver for frequency domain fluorescence molecular imaging

Fluorescence molecular imaging/tomography may play an important future role in preclinical research and clinical diagnostics. Time- and frequency-domain fluorescence imaging can acquire more measurement information than the continuous wave (CW) counterpart, improving the image quality of fluorescence molecular tomography. Although diffusion approximation (DA) theory has been extensively applied in optical molecular imaging, high-order photon migration models need to be further investigated to match quantitation provided by nuclear imaging. In this paper, a frequency-domain parallel adaptive finite element solver is developed with simplified spherical harmonics (SPN) approximations. To fully evaluate the performance of the SPN approximations, a fast time-resolved tetrahedron-based Monte Carlo fluorescence simulator suitable for complex heterogeneous geometries is developed using a convolution strategy to realize the simulation of the fluorescence excitation and emission. The validation results show that high-order SPN can effectively correct the modeling errors of the diffusion equation, especially when the tissues have high absorption characteristics or when high modulation frequency measurements are used. Furthermore, the parallel adaptive mesh evolution strategy improves the modeling precision and the simulation speed significantly on a realistic digital mouse phantom. This solver is a promising platform for fluorescence molecular tomography using high-order approximations to the radiative transfer equation.

P‐78: DOE Approach to Elimination of Display Mura Induced by LGP Warpage in HTHH Environment

AbstractIn this article, the mura issue of LCD panel induced by LGP warpage in high temperature and high humidity (HTHH) environment is discussed. From experiments, it is validated that insufficient gap between LGP and plastic mold frame, housing, will lead to deform the LGP. Due to the LGP has high moisture absorption and low thermal stability characteristics, it is easy to have volume expansion occurred. Obviously, the elongation of LGP will compress housing, thus LGP warping causes mura while panel in display mode. Experimental design (DOE) method is thus performed to generate a mathematical model to predict the displacement of LGP caused by hygrothermal effect. Finally, from experiment results, it is approved that the mura phenomenon has been eliminated. Furthermore, the mathematical construction model can provide the suitable design tolerance in module design phase.

Hydrothermal synthesis of titanate nanostructures with high UV absorption characteristics

The titanate nanostructures with high UV absorption characteristics could be fabricated by hydrothermal method within a temperature range of 90–150 °C. TEM, XRD, BET analyses, and UV–vis spectroscopy were employed to elucidate the synthesized titanate nanostructure characteristics which were microstructure, phase transformation, specific surface area, and band gap energy, respectively. With an increase in the hydrothermal treating temperature from 90 to 120 °C, the specific surface area of titanate nanostructures was increased from 83 to 258 m 2/g, while the band gap energy of titanate nanostructures was increased from 3.44 to 3.84 eV and then slightly decreased to 3.81 eV at 150 °C. The fabricated titanate nanostructures could exhibit higher UV adsorption capability but lower photocatalytic activity when compared with that of commercial TiO 2 powders.

Cure depth control for complex 3D microstructure fabrication in dynamic mask projection microstereolithography

PurposeThe paper's aim is to explore a method using light absorption for improving manufacturing of complex, three‐dimensional (3D) micro‐parts with a previously developed dynamic mask projection microstereolithography (MSL) system. A common issue with stereolithography systems and especially important in MSL is uncontrolled penetration of the ultraviolet light source into the photocrosslinkable resin when fabricating down‐facing surfaces. To accurately fabricate complex 3D parts with down‐facing surfaces, a chemical light absorber, Tinuvin 327™ was mixed in different concentrations into an acrylate‐based photocurable resin, and the solutions were tested for cure depths and successful micro‐part fabrication.Design/methodology/approachTinuvin 327 was selected as the light absorber based on its high absorption characteristics (∼0.4) at 365 nm (the filtered light wavelength used in the MSL system). Four concentrations of Tinuvin 327 in resin were used (0.00, 0.05, 0.10, and 0.15 percent (w/w)), and cure depth experiments were performed. To investigate the effects of different concentrations of Tinuvin 327 on complex 3D microstructure fabrication, several microstructures with overhanging features such as a fan and spring were fabricated.FindingsResults showed that higher concentrations of Tinuvin 327 reduced penetration depths and thus cure depths. For the resin with 0.15 percent (w/w) of the Tinuvin 327, a cure depth of ∼30 μm was achieved as compared to ∼200 μm without the light absorber. The four resin solutions were used to fabricate complex 3D microstructures, and different concentrations of Tinuvin 327 at a given irradiance and exposure energy were required for successful fabrication depending on the geometry of the micro‐part (concentrations of 0.05 and 0.1 percent (w/w) provided the most accurate builds for the fan and spring, respectively).Research limitations/implicationsAlthough two different concentrations of light absorber in solution were required to demonstrate successful fabrication for two different micro‐part geometries (a fan and spring), the experiments were performed using a single irradiance and exposure energy. A single solution with the light absorber could have possibly been used to fabricate these micro‐parts by varying irradiance and/or exposure energy, although the effects of varying these parameters on geometric accuracy, mechanical strength, overall manufacturing time, and other variables were not explored.Originality/valueThis work systematically investigated 3D microstructure fabrication using different concentrations of a light absorber in solution, and demonstrated that different light absorption characteristics were required for different down‐facing micro‐features.

一からわかるレーザー歯科治療

Laser therapy is currently applied in various dental fields. Lasers are used not only in oral surgery such as soft tissue incision and coagulation, but also for periodontal therapy, pulp treatment including pulpectomy and infected root canal treatment, tooth preparation, dental caries prevention, and pain relief and acceleration of wound healing for stomatitis, dentin hypersensitivity, and temporomandibular disorder. The laser systems used in dental treatment are mainly divided into two types based on the characteristics of the wavelength: the surface absorption type and the tissue penetration type. The absorption characteristics vary depending on the laser wavelength, and the influence of laser irradiation on body tissues is especially dependent on absorption by water, which accounts for approximately 70% of the body. The Er: YAG and carbon dioxide (CO2) lasers have particularly high water absorption characteristics, and almost all the laser energy is absorbed in the most superfi cial tissue layer and the irradiation does not penetrate into deep tissues. In contrast, lasers with a wavelength in the visible to near-infrared range reach deep tissues, since this energy is unlikely to be absorbed by water. Therefore, Er: YAG and CO2 lasers are superior in terms of vaporization efficiency, whereas visible to near-infrared lasers have stronger coagulation effects. Power density and oscillation mode are also key factors that determine laser characteristics, and the clinical effects of lasers are characterized by a combination of these factors and wavelength.

Fiberoptic Confocal Microscopy Using a 1.55-$\mu$m Fiber Laser for Multimodal Biophotonics Applications

We have experimentally demonstrated a fiberoptic confocal microscope using a 1.55-mum laser source. A compact and efficient Er-doped fiber laser source and conventional single-mode fiber components were used to construct a near-infrared fiberoptic confocal microscope system with 3-D scanning capability. A broadband 1.55-mum light source was used to reduce fringe patterns and interferences that occur when a highly coherent source is used. Our system showed a lateral resolution as high as 1.1 mum with a 60times objective lens, which is close to the theoretical limit. The system can be used in various multimodal biophotonics platforms including precise 3D imaging, biosensing, and laser tissue ablation due to its high water absorption characteristics while maintaining low thermomechanical and self-focusing damage from high-power lasers.

Millimeter- and Submillimeter-Wave Dielectric Measurements of Household Powders Using Fourier Transform Spectroscopy

<para xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> This paper presents the first step in characterizing and detecting common household powders as hoax materials by investigating their broadband dielectric characteristics. Pesticide is also studied due to its similarities to anthrax. A modified two-beam polarizing interferometer and custom-made sample holders were utilized to obtain the refractive index (RFI), absorption coefficient, complex real and imaginary permittivity, and loss tangent of flour, dry milk, cornstarch, pesticide, baking soda, and talc as a continuous function of frequency in the range of 400–1200 GHz. Dispersive Fourier transform spectroscopy was employed to provide phase and amplitude information, leading to the accurate and direct acquisition of the complex RFI and complex dielectric permittivity spectra. It is the first time that such measurements were carried out over such an extended frequency range for common powders to reveal marked variation in absorption and RFI values for different powders. The powders exhibit high-absorption characteristics, and the RFI values lie between 2.4 and 3.4 in this spectral range. A unique resonance signature for talc was detected at 1135 GHz with an associated anomalous dispersion. Parameters such as grain size and orientation were analyzed for their effect on the dielectric properties of powders. Relationships between density, permittivity, and RFI are explored to provide the ability to extrapolate results for other densities. The RFI and the real part of the dielectric permittivity were found to be the most reliable for identification and detection purposes. </para>

Application of recycled waste aggregate to lean concrete subbase in highway pavement

As aggregates recycled from various types of construction waste are continuously being produced, interest has focused on how to apply them for use in highway pavement. This paper considers the application of waste aggregates to lean concrete, based on basic mechanical property tests and environmental toxicity. Compared with natural aggregates, waste aggregates derived mainly from recycled concrete have low specific gravity and high water absorption characteristics. After testing their environmental toxicity, it was found that waste aggregates do not release any metallic ions when introduced to alkaline conditions but do release a small but seemingly harmless amount of metallic ions when introduced to acidic solutions. Concrete made with waste aggregates has significant limitations in strength, particularly flexural strength, which is the main parameter of quality control and design for concrete pavement. It is therefore not practical to use waste aggregates for the surface layer of concrete without using additives or special treatments. It is possible, however, to apply concrete with waste aggregates for lean bases. In testing, lumps of asphalt, cement paste, bricks, and glass were classified as impurities and were observed for changes in strength based on the percentage of impurities used. If the amount of impurities is greater than 25%, the 7-d compressive strength does not meet the strength requirements specified for lean concrete.Key words: recycled waste aggregates, lean concrete, impurity content, concrete pavement.

Insight into the development of non-adherent, absorbent dressings.

This study aimed to develop a variety of wound dressing materials, made from standard natural fibres, that have high absorption and non-adherent characteristics. A total of 21 dressings were made using knitted and crochet technologies and their absorbency was tested. Five non-adherent recipes were selected from a range of chemical formulations and the optimised non-adherent finishes were applied to the four best dressings. Their absorbency and non-adherent properties were evaluated. The study demonstrated that rib cotton (RC), rib viscose (RV), crochet cotton medium (CCM) and crochet viscose medium (CVM) dressings possess high absorption and that five finishing recipes, C + D, A + G, I, I + N and I + G, impart high absorption as well as non-adherent properties. The finish I + G is superior in imparting non-adherence to RV dressing, both in dry and moist conditions. This means that irrigation with water, saline or sodium citrate solution before removing the dressing from a wound is not needed. A number of novel knitted and crochet structures with enhanced absorbency have been designed for wound management using standard bleached fibres. Novel non-adherent finishes for the developed structures have been formulated for the developed dressings, and offer an alternative to existing non-adherent dressings.

Retention of the high optical absorptance in thermally aged black chrome on variably sensitized Cu

The chemical composition, morphology, selective absorber characteristics, and degradation of selective absorber characteristics at high temperatures of black chrome solar selective coating are influenced by various substrate pre-treatments like mechanical polishing, chemical etching, and electropolishing prior to film deposition. The major oxide content in the deposit is formed as Cu 2(OH) 2CrO 4 (JCPDS 38-0230), which on high temperature annealing decomposes to CuCrO 4 (JCPDS 34-0507), CuO (JCPDS 41-0254), and Cu 2O (JCPDS 5-0667). Formation of the oxides of Cu at high temperatures retains the high optical absorption characteristics of the coating even after high temperature degradation.