Bioinspired structural color sensors based on responsive soft materials

Structural colors in nature have inspired the design of diverse photonic structures, which can interact with light via interference, diffraction or scattering. Among them, responsive soft material-involved photonic structures uniquely feature large volumetric changes upon external stimuli. The volumetric changes result in peak/valley shift of reflection spectra and perceptible color changes, providing responsive soft material-based structural color systems capability of serving as sensors for detecting chemical and biological analytes. Synthetic polymers and some natural materials are the most studied and utilized responsive soft materials for constructing structural color sensors, by tuning the thickness and morphology of formed films, or incorporating them into template structures, or their self-assembling. In this review article, structural colors in nature are firstly introduced, followed by discussing recent developments of promising responsive soft material-based structural color sensors, including the design of structural color sensors based on synthetic polymers and natural materials, as well as their applications for chemical sensing, biosensing, and multi-analyte sensing with sensor arrays. For specific sensing of chemicals and biomolecules, the sensing performance is evaluated in terms of detection range, sensitivity, response time, and selectivity. For multi-analyte sensing, cross-reactive structural sensor arrays based on simply a single soft material will be shown capable of discriminating various series of similar compounds. The future development of structural color sensors is also proposed and discussed.     

一种基于色彩处理的被动声呐宽带目标检测显示方法

针对被动声呐传统宽带能量检测方式难以解决强干扰存在时的弱目标检测问题,着眼于目标、干扰及背景噪声频谱特征差异,提出了一种划分子带,利用颜色合成理论进行宽带融合检测的显示方法。针对弱目标存在稳定线谱或在部分频点能量相对较强的情况,可有效提升对弱目标的检测能力,并增强不同目标方位历程的区分度。     

Material design and structural color inspired by biomimetic approach

Abstract

Generation of structural color is one of the essential functions realized by living organisms, and its industrial reproduction can result in numerous applications. From this viewpoint, the mechanisms, materials, analytical methods and fabrication technologies of the structural color are reviewed in this paper. In particular, the basic principles of natural photonic materials, the ideas developed from these principles, the directions of applications and practical industrial realizations are presented by summarizing the recent research results.     

Intrinsic optical and structural properties of SrS thin films

SrS thin films were deposited by electron beam evaporation on heated silica substrates. The optical properties of the layers – complex refractive index and optical band gap –were derived from optical transmission spectra, measured by means of UV-VIS-NIR spectrophotometry. The influence of post-deposition annealing by rapid thermal processing (RTP) was studied. X-ray powder diffraction (XRD) was used to study the film crystal structure and preferential orientation.     

Fabrication of hydrophobic inorganic coatings on natural lotus leaves for nanoimprint stamps

Hydrophobic inorganic films were obtained by direct deposition of copper or silicon onto natural lotus leaves by ion beam sputtering deposition technique. Scanning electron microscopy observations showed a lotus-leaf-like surface structure of the deposited inorganic films. Hydrophobic nature of the inorganic films on lotus leaves had been improved compared to the inorganic films deposited on flat silicon substrates. Water contact angles measured on the lotus-leaf-like copper and silicon films were 136.3 ± 8° and 117.8 ± 4.4°, respectively. The hydrophobic lotus-leaf-like inorganic films had been repeated used as nanoimprint stamps. Negative structures of lotus-leaf-like inorganic films were obtained on the polystyrene resist layers.     

光电经纬仪结构动态特性研究

光电经纬仪的结构动态特性是设计光电经纬仪的重要依据。用临界转速法建立了光电经纬仪的结构动态特性模型,讨论了光电经纬仪转速与轴系横向振动固有频率的关系:光电经纬仪的临界转速在数值上与经纬仪横向自由振动的固有频率相同,且光电经纬仪的固有频率只与其轴系挠度的平方根成反比。研究表明,提高光电经纬仪伺服控制系统带宽有4个途径:1) 增大光电经纬仪的固有频率;2) 对结构谐振进行补偿;3) 使用电流反馈;4) 使用加速度和速度反馈等。     

A model for the dynamic fracture toughness of ductile structural steel

We assume in this paper that the dynamic fracture toughness K_Id of ductile structural steels is dependent on void nucleation and void growth. The void nucleation-induced dynamic fracture toughness K_Id·n and the void growth-induced dynamic fracture toughness K_Id·g were obtained by modifying the void nucleation-induced and void growth-induced static fracture toughness models, respectively, considering the effect of strain rate and local temperature. By the relationship between the void nucleation-induced dynamic fracture toughness K_Id·n and the void growth-induced dynamic fracture toughness K_Id·g((K_Id)²=(K_Id·n)²+(K_Id·g)²) dynamic fracture toughness K_Id could be quantitatively evaluated. With this model the dynamic fracture toughness of two structural steels (X65 and SA440) was assessed, and the causes for the differences between the static and dynamic fracture toughness were also discussed.     

Exploitation of a pulsed neutron source for the structural study of anisotropic polymer films

A novel but simple time-of-flight neutron scattering geometry which allows structural anisotropy to be probed directly, simultaneously and thus unambiguously in polymeric and other materials is described. A particular advantage of the simultaneous data collection when coupled to the large area of the beam is that it enables thin films (< 10 m < 10 mg) to be studied with relative ease. The utility of the technique is illustrated by studies on both deformed poly(styrene) glasses and on thin films of electrical conducting polymers. In the latter case, the power of isotopic substitution is illustrated to great effect. The development of these procedures for use in other areas of materials science is briefly discussed.     

Tunable structural color in organisms and photonic materials for design of bioinspired materials

Abstract

In this paper, the key topics of tunable structural color in biology and material science are overviewed. Color in biology is considered for selected groups of tropical fish, octopus, squid and beetle. It is caused by nanoplates in iridophores and varies with their spacing, tilting angle and refractive index. These examples may provide valuable hints for the bioinspired design of photonic materials. 1D multilayer films and 3D colloidal crystals with tunable structural color are overviewed from the viewpoint of advanced materials. The tunability of structural color by swelling and strain is demonstrated on an example of opal composites.     

Tunable structural color in organisms and photonic materials for design of bioinspired materials

In this paper, the key topics of tunable structural color in biology and material science are overviewed. Color in biology is considered for selected groups of tropical fish, octopus, squid and beetle. It is caused by nanoplates in iridophores and varies with their spacing, tilting angle and refractive index. These examples may provide valuable hints for the bioinspired design of photonic materials. 1D multilayer films and 3D colloidal crystals with tunable structural color are overviewed from the viewpoint of advanced materials. The tunability of structural color by swelling and strain is demonstrated on an example of opal composites.     

Edge‐adaptive color interpolation for complementary color filter array

Complementary color filter array (CCFA) is widely used in consumer‐level digital video cameras, since it not only has high sensitivity and good signal‐to‐noise ratio in low‐light condition but also is compatible with the interlaced scanning used in broadcast systems. However, the full‐color images obtained from CCFA suffer from the color artifacts such as false color and zipper effects. These artifacts can be removed with edge‐adaptive color interpolation (ECI) approaches which are generally used in primary color filter array (PCFA). Unfortunately, the unique array pattern of CCFA makes it difficult that CCFA adopts ECI approaches. Therefore, to apply ECI approaches suitable for CCFA to color interpolation is one of the major issues to reconstruct the full‐color images. In this paper, we propose a new ECI algorithm for CCFA. To estimate an edge direction precisely and enhance the quality of the reconstructed image, a function of spatial variances is used as a weight, and new color conversion matrices are presented for considering various edge directions. Experimental results indicate that the proposed algorithm outperforms the conventional method with respect to both objective and subjective criteria. © 2006 Wiley Periodicals, Inc. Int J Imaging Syst Technol, 16, 92–102, 2006     

On the structural changes during thermal oxidation of evaporated Zn thin films

Metallic Zn thin films (d = 200 nm-500 nm) were deposited in vacuum onto unheated glass substrate by quasi-closed volume technique at a source temperature of 723 K. Sets of samples simultaneously deposited on horizontally and vertically arranged substrates were prepared. The as-deposited Zn films were heated under ambient atmosphere at various temperatures ranged between 300 K and 650 K. By XRD and AFM techniques, the microstructural characteristics and their changes during Zn films heating were investigated. The influence of the deposition conditions on the structural changes during the oxidation process is also discussed.     

Bioinspired photonic nanoarchitectures from graphitic thin films

Bioinspired, regular, rectangular (with periodicities of 600 nm and 700 nm), and random (with average characteristic distances of 600 nm and 750 nm) two dimensional (2D) photonic nanoarchitectures of 60 nm thickness were produced in graphite by Focused Ion Beam (FIB) nanomachining and subsequent controlled oxidation. The color of the nanoarchitectures was modified by the conformal deposition of 90 nm Al₂O₃. The regular patterns generate iridescent colors, while the random ones exhibit a remarkably constant color with the variation of the illumination and viewing conditions.     

Thermoelastic solutions for anisotropic cracked thin films

Thermal stress intensity factors for cracks in anisotropic thin films subjected to uniform heat fluxes are investigated. Based on the method of analytic continuation associated with the alternating technique, the general solution of an anisotropic thin film/substrate under thermal loading is derived. Rapidly convergent series solutions for both the temperature and stress fields are obtained in terms of the corresponding homogeneous potentials. Using the technique of superposition and the Cauchy integral, the solution of the crack problem with arbitrary locations and angles is solved. Some typically numerical results are discussed, showing that a stiffer substrate can efficiently reduce the thermal stress intensity factors of the cracked thin films. The result also shows that the solution is accurate and rapidly converges as the thin film/substrate degenerates to a homogeneous medium.     

Effects of methane flux on structural and transport properties of CVD-grown graphene films

Large area, single-layer graphene films were synthesized on copper foils by chemical vapor deposition. We have investigated the effects of methane flux on structural and transport properties of graphene. Raman spectra and electrical results reveal that methane flux has almost no influence on the thickness of graphene, but clearly influences the structural defects of graphene. In addition, graphene field effect transistors with a gate length of 10 μm were fabricated, exhibiting obvious field effects and p-type characteristics.     

Grain growth and structural transformation in ZnS nanocrystalline thin films

Fabrication of ZnS thin films having similar stoichiometry at different substrate temperatures (T_S) e.g. 200 °C, 300 °C and 400 °C by means of RF magnetron sputtering method is presented. The films grown at T_S of 200 °C are in cubic zinc-blende phase and textured along (111) plane. The films deposited at T_S of 300 °C and 400 °C are in hexagonal wurtzite phase. The surface roughness and grain size of the films increase with increasing T_S. The ultra-violet and visible absorption studies show that the bandgap of films can be tailored by varying T_S, taking advantage of the structural transformation.     

多彩结构色氧化铝薄膜氧化机制的研究

在草酸电解液中,球形碳点电极作为阴极,铝箔作为阳极,利用一次氧化工艺成功的制备出了单一色彩和虹彩环形结构色的氧化铝薄膜.实验结果显示,球形碳点电极下制备的氧化铝薄膜厚度由薄膜中心向外呈对称性递减.当薄膜的径向厚度差在某一波长光的覆盖范围内时,薄膜呈现单一结构色,而当径向厚度差超出某一波长光的覆盖范围时,薄膜呈现虹彩环形结构色.本文详细的讨论了电极间距、氧化电压和氧化时间对薄膜结构色的影响,并从理论上分析了球形碳点电极下多孔氧化铝薄膜的氧化机制.     

Correlation study between structural, magnetic and transport properties of annealed Co thin films

This paper presents structural, magnetization and transport properties measurements carried out on as-deposited Co (400 Å) thin film as well as samples annealed in the temperature range 100-500 °C in steps of 100 °C for 1 h. The samples used in this work were deposited on float glass substrates using ion beam sputtering technique. The magnetization measurements carried out using MOKE technique, clearly indicates that as-deposited as well as annealed samples up to 500 °C show well saturation magnetization with applied magnetic field. The as-deposited sample shows coercivity value (H_c) of 26 Oe, and it is increased to 94 Oe for 500 °C-annealed sample. A minimum coercivity value of 15 Oe is obtained for 200 °C annealed sample. The XRD measurements of as deposited films show microcrystalline nature of Co film, which becomes crystalline with increase in annealing temperature. The corresponding resistivity measurements show gradual decrease in resistivity. AFM technique was employed to study the surface morphology of as deposited film as well as annealed thin films. Observed magnetization, and resistivity behaviour is mainly attributed to the (i) change in crystal structure (ii) increase in grain size and (iii) stress relaxation due to the annealing treatment.     

基于肤色特征和动态聚类的彩色人脸检测

在人类视觉机制和肤色聚类特性的基础上,提出了一种复杂背景下人脸检测方法。该方法采用K-均值动态聚类分析算法,利用人类肤色特征在输入图像中检测包含人脸的似人脸区作为候选人脸,再用同样的方法对候选人脸区域进行扫描,得到真正的人脸。实验结果表明,该方法的正确检出率达到84%,受背景、光照、角度、姿态的影响很小,具有较好的鲁棒性。