Structural color in porous, superhydrophilic, and self-cleaning SiO2/TiO2 Bragg stacks

Thin-film Bragg stacks exhibiting structural color have been fabricated by a layer-by-layer (LbL) deposition process involving the sequential adsorption of nanoparticles and polymers. High- and low-refractive-index regions of quarter-wave stacks were generated by calcining LbL-assembled multilayers containing TiO(2) and SiO(2) nanoparticles, respectively. The physical attributes of each region were characterized by a recently developed ellipsometric method. The structural color characteristics of the resultant nanoporous Bragg stacks could be precisely tuned in the visible region by varying the number of stacks and the thickness of the high- and low-refractive-index stacks. These Bragg stacks also exhibited potentially useful superhydrophilicity and self-cleaning properties.     

Stacking the Nanochemistry Deck: Structural and Compositional Diversity in One‐Dimensional Photonic Crystals

One‐dimensional photonic structures, known as Bragg stacks or Bragg reflectors or Bragg mirrors, represent a well‐developed subject in the field of optical science. However, because of a lack of dynamic tunability and their dependence on complex top‐down techniques for their fabrication, they have received little attention from the materials science community. Herein, we present recent and ongoing developments on the way to functional one‐dimensional photonic structures obtained from simple bottom‐up techniques. We focus on the versatility of this new approach, which allows the incorporation of a wide range of materials into photonic structures.     

Experimental determination of refractive index of condensed reflectin in squid iridocytes

Loliginid squid dynamically tune the structural iridescence of cells in their skin for active camouflage and communication. Bragg reflectors in these cells consist of membrane-bound lamellae periodically alternating with low refractive index extracellular spaces; neuronal signalling induces condensation of the reflectin proteins that fill the lamellae, consequently triggering the expulsion of water. This causes an increase in refractive index within the lamellae, activating reflectance, with the change in lamellar thickness and spacing progressively shifting the wavelength of reflected light. We used micro-spectrophotometry to measure the functionally relevant refractive index of the high-index lamellae of the Bragg reflectors containing the condensed reflectins in chemically fixed dermal iridocytes of the squid, Doryteuthis opalescens. Our high-magnification imaging spectrometer allowed us to obtain normalized spectra of optically distinct sections of the individual, subcellular, multi-layer Bragg stacks. Replacement of the extracellular fluid with liquids of increasing refractive index allowed us to measure the reflectivity of the Bragg stacks as it decreased progressively to 0 when the refractive index of the extracellular medium exactly matched that of the reflectin-filled lamellae, thus allowing us to directly measure the refractive index of the reflectin-filled lamellae as n_{condensed lamellae} ≈ 1.44. The measured value of the physiologically relevant n_{condensed lamellae} from these bright iridocytes falls within the range of values that we recently determined by an independent optical method and is significantly lower than values previously reported for dehydrated and air-dried reflectin films. We propose that this directly measured value for the refractive index of the squid''s Bragg lamellae containing the condensed reflectins is most appropriate for calculations of reflectivity in similar reflectin-based high-index layers in other molluscs.     

Broad-wavelength-range chemically tunable block-copolymer photonic gels

Responsive photonic crystals have been developed for chemical sensing using the variation of optical properties due to interaction with their environment. Photonic crystals with tunability in the visible or near-infrared region are of interest for controlling and processing light for active components of display, sensory or telecommunication devices. Here, we report a hydrophobic block-hydrophilic polyelectrolyte block polymer that forms a simple one-dimensional periodic lamellar structure. This results in a responsive photonic crystal that can be tuned via swelling of the hydrophilic layers by contact with a fluid reservoir. The glassy hydrophobic layer forces expansion of the hydrophilic layer along the layer normal, yielding extremely large optical tunability through changes in both layer thickness and index of refraction. Polyelectrolyte polymers are known to be highly responsive to a range of stimuli. We show very large reversible optical changes due to variation of the salt concentration of a water reservoir. These one-dimensional Bragg stacks reflect incident light from the ultraviolet-visible region to the near-infrared region (lambda(peak)=350-1,600 nm) with over a 575% change in the position of the stop band. Our work demonstrates the extremely high responsivity possible for polyelectrolyte-based photonic materials.     

Hybrid organic-dielectric thin film stacks for nonlinear optical applications

We propose an optical switching device that utilizes the third-order nonlinear optical effect in an organic material embedded into a superprism photonic crystal structure. A convenient way for the realization of the photonic crystal is using a multilayer thin film stack made of dielectrics. Following this approach, we face the challenge of building hybrid stacks containing both inorganic dielectric as well as organic materials. We evaluate strategies for the design and fabrication of hybrid thin film stacks to avoid the development of thin film cracking during the fabrication of hybrid PS-Ta₂O₅ (polystyrene-tantala) and PMMA-Ta₂O₅ (poly(methyl methacrylate)-tantala) stacks on glass substrates. Crack-free hybrid PS-Ta₂O₅ as well as PS-SiO₂ (polystyrene-silicon dioxide) and PMMA-SiO₂ (poly(methyl methacrylate)-silicon dioxide) samples on glass substrates were fabricated.     

Common-path interferometric detection of protein monolayer on the BioCD

The bio-optical compact disk (BioCD) is an optical biosensor that performs common-path molecular interferometry of patterned proteins on a disk spinning at high speed. The common-path configuration makes it ultrastable and allows surface height precision below 10 pm. In this paper we show that two complementary interferometric quadrature conditions exist simultaneously that convert the modulus and phase of the reflection coefficient, modulated by protein patterns on the disk surface, into intensity modulation at the detector. In the far field they separate into spatially symmetric and antisymmetric intensity modulation in response to the local distribution of protein. The antisymmetric response is equivalent to differential phase-contrast detection, and the symmetric response is equivalent to in-line (IL) common-path interferometry. We measure the relative sensitivities of these orthogonal channels to printed protein patterns on disk structures that include thermal oxide on silicon and Bragg dielectric stacks. The scaling mass sensitivity of the IL channel on oxide on silicon was measured to be 0.17 pg/mm.     

Selective adsorption and release of cationic organic dye molecules on mesoporous borosilicates

Mesoporous materials can play a pivotal role as a host material for delivery application to a specific part of a system. In this work we explore the selective adsorption and release of cationic organic dye molecules such as safranine T (ST) and malachite green (MG) on mesoporous borosilicate materials. The mesoporous silica SBA-15 and borosilicate materials (MBS) were prepared using non-ionic surfactant Pluronic P123 as template via evaporation induced self-assembly (EISA) method. After template removal the materials show high surface areas and in some cases ordered mesopores of dimensions ca. 6–7 nm. High surface area, mesoporosity and the presence of heteroatom (boron) help this mesoporous borosilicate material to adsorb high amount of cationic dye molecules at its surface from the respective aqueous solutions. Furthermore, the mesoporous borosilicate samples containing higher percentage adsorbed dyes show excellent release of ST or MG dye in simulated body fluid (SBF) solution at physiological pH = 7.4 and temperature 310 K. The adsorption and release efficiency of mesoporous borosilicate samples are compared with reference boron-free mesoporous pure silica material to understand the nature of adsorbate–adsorbent interaction at the surfaces.     

Advanced protection against environmental degradation of silver mirror stacks for space application

Protection of silver mirror stacks from environmental degradation before launching is crucial for space applications.Hereby,we report a comparative study of the advanced protection of silver mirror stacks for space telescopes provided by SiO₂and Al₂O₃coatings in conditions of accelerated aging by sulfida-tion.The model silver stack samples were deposited by cathodic magnetron sputtering on a reference silica substrate for optical applications and a surface-pretreated SiC substrate.Accelerated aging was per-formed in dry and more severe wet conditions.Optical micrographic observations,surface and interface analysis by Time-of Flight Secondary Ion Mass Spectrometry(ToF-SIMS)and reflectivity measurements were combined to comparatively study the effects of degradation.The results show a lower kinetics of degradation by accelerated aging of the stacks protected by the alumina coating in comparable test conditions.     

Engineering 2D Mesoporous Silica@MXene‐Integrated 3D‐Printing Scaffolds for Combinatory Osteosarcoma Therapy and NO‐Augmented Bone Regeneration

The rising concerns of the recurrence and bone deficiency in surgical treatment of malignant bone tumors have raised an urgent need of the advance of multifunctional therapeutic platforms for efficient tumor therapy and bone regeneration. Herein, the construction of a multifunctional biomaterial system is reported by the integration of 2D Nb₂C MXene wrapped with S‐nitrosothiol (R? SNO)‐grafted mesoporous silica with 3D‐printing bioactive glass (BG) scaffolds (MBS). The near infrared (NIR)‐triggered photonic hyperthermia of MXene in the NIR‐II biowindow and precisely controlled nitric oxide (NO) release are coordinated for multitarget ablation of bone tumors to enhance localized osteosarcoma treatment. The in situ formed phosphorus and calcium components degraded from BG scaffold promote bone‐regeneration bioactivity, augmented by sufficient blood supply triggered by on‐demand NO release. The tunable NO generation plays a crucial role in sequential adjuvant tumor ablation, combinatory promotion of coupled vascularization, and bone regeneration. This study demonstrates a combinatory osteosarcoma ablation and a full osseous regeneration as enabled by the implantation of MBS. The design of multifunctional scaffolds with the specific features of controllable NO release, highly efficient photothermal conversion, and stimulatory bone regeneration provides an intriguing biomaterial platform for the diversified treatment of bone tumors.     

聚乳酸/聚己二酸二甘醇酯/甲基丙烯酸甲酯-丁二烯-苯乙烯共聚物生物降解薄膜的制备及性能

采用甲基丙烯酸甲酯-丁二烯-苯乙烯共聚物(MBS)对聚乳酸(PLA)进行增韧改性,增韧后的PLA再与增塑剂聚己二酸二甘醇酯(PDEGA)熔融共混挤出并吹膜。将PDEGA的质量分数固定为8%,改变PLA和MBS的比例,探讨了不同含量的MBS对PLA/PDEGA/MBS薄膜力学性能、光学性能、流变性能以及结晶性能的影响,用扫描电镜观察薄膜撕裂断面形态,用偏光显微镜观察PLA的结晶形貌。结果表明,加入PDEGA后,薄膜的Tg下降了近8℃,Tcc下降了约17℃;随着MBS的不断加入,拉伸强度、撕裂强度分别在25MPa和120kN/m以上,PLA薄膜的断裂伸长率由PLA的3.5%提高到薄膜的40%以上,薄膜的模量、黏度都有所增加;随着MBS含量的增加,PLA球晶的边界逐渐变得模糊,球晶数量增加,球晶尺寸明显变小,但PLA的结晶类型没有改变;薄膜保持了良好的透明性和降解性。     

核壳改性剂结构对透明MBS树脂的力学与光学性能的影响

采用种子乳液聚合方法,改变苯乙烯和甲基丙烯酸甲酯在丁苯橡胶上的接枝次序合成控制粒径与折光指数的MBS核壳改性剂.用其与MMA-co-St熔融共混制备透明MBS树脂,研究了透明MBS树脂冲击强度及可见光的透过率,并用TEM观察体系中橡胶相的分散与微观结构.结果发现,混合单体接枝方式合成的MBS改性剂有利于提高透明MBS树脂的冲击强度及可见光透过率,且其中丁苯橡胶含量为15%以上时,波长为589.3 nm的光线透过率高于理论计算值.     

4.2 Monitoring of optical thin films using a quartz crystal monitor

Quartz crystal monitoring in the production of dielectric multilayer stacks is compared to optical monitoring. The stacks are calculated with the aid of an optimizing program. This yields optical thicknesses of the layers differing from multiples of a quarter of the wavelength. Optical monitoring is complicated in this case. Using quartz crystal monitoring, planning and execution of the process is earsier and yields stacks with satisfactory reflectance characteristics faster than with optical monitoring.The reproducibility of the optical thickness of MgF₂ layers is investigated. In general, both methods turn out to be equivalent in performance.     

Does photosensitivity pave the way towards the fabrication of miniature coherent light sources in inorganic glass waveguides?

Photosensitivity designates the ability to permanently change the refractive index of a glass by optical processing. The phenomenon allows the fabrication of numerous phase structures, the simplest of which is the Bragg grating obtained by photoimprinting a periodic index modulation within the material. Bragg gratings have changed the way in which optical fibre (or planar waveguide) lasers are now used. Distributed Bragg Reflector (DBR) or Distributed Feed Back (DFB) lasers, when intracore Bragg gratings are used for linear cavity feedback, are commonly fabricated in rare earth doped optical silica-based fibres. On the other hand, photosensitivity can also result in effects which can prove to be detrimental to the fabrication of miniature coherent light sources. The paper will cover some of the advances that have been made in improving the photosensitivity of inorganic glasses, in searching new photosensitive materials and in characterizing Bragg grating properties relevant to laser applications.     

Tunable Bragg filters based on polymer swelling

We report on the optical properties of Bragg mirrors and filters fabricated from photo-cross-linked standard optical polymers. The transmittance spectra of these devices in the visible to near-infrared spectral range were measured. We demonstrate efficient tuning of the filter peak of the polymer Bragg filters over several hundred nanometers by adding organic solvents to the surrounding atmosphere of the filter. This represents what we believe to be a novel tuning principle for Bragg filters relying on the use of polymeric materials.     

Acousto-optic superlattice modulation in fiber Bragg gratings

The superposition of a long-period grating and a fiber Bragg grating, which we call an optical superlattice, causes high-efficiency narrow-band reflections to be induced on either side of the Bragg wavelength. This effect was recently observed experimentally in a fiber-based acousto-optic superlattice modulator. We develop in detail the theory of optical superlattices in fiber Bragg gratings, treating both the acousto-optic and the fixed-grating cases. Applications include reconfigurable wavelength division multiplexers, fiber lasers and sensors, tunable filters, modulators, and frequency shifters.     

Fibre bragg gratings optical sensing technology

Fibre optic technology is a well established field in the world of smart structures. While optical communications systems date back as far as the late 1700s when the French engineer Claude Chappe invented the ‘optical telegraph’, advances in optical fibres did not really take off until Corning Glass Works (now Corning, Inc.) developed single-mode fibres with attenuation below 20 dB/km in 1970¹. Now fibre optics are widely used in the telecommunications industry. This breakthrough also led the way for the development of fibre optic sensors. While there are many types of optical sensors, the focus of this article is on the fibre Bragg grating sensor. In-line fibre Bragg gratings (FBGs) were developed as narrow band optical filters for the telecommunications industry². Television commercials by the major telephone companies describe the capability of transmitting as many as 16 telephone calls on the same optical fibre link, a capability made possible with wavelength division multiplexing using Bragg grating or equivalent spectral filtering technology. This intrinsic multiplexing capability and their sensitivity to thermo-mechanical loads also render in-fibre Bragg gratings one of the most promising distributed sensor technologies for structural systems. There are many other applications of FBGs including shape, moisture and corrosion sensing.     

Sol–gel derived photonic bandgap coatings for solar control

Sol–gel derived photonic bandgap films have been investigated as possible multilayer coatings for solar control glass applications. Multilayer Bragg mirrors, in particular, have been modelled by the Transfer Matrix method, designed to have either near-UV or near-IR reflectivity, but visible transparency, based on alternating aluminosilicate glass/titania quarter-wave stacks. Such composite multilayer structures have been deposited by sol–gel processing on selected glasses and other types of substrates and their optical characteristics have been measured by optical absorption and reflection spectroscopies, as well as spectroscopic ellipsometry to determine the single layer refractive index and thickness. The UV–visible-IR absorption and reflection characteristics of these multilayer coatings revealed solar control properties, due to the presence of peaks near ∼350–400 nm and ∼900–1000 nm, with reflectivities of the order of 70%, which appear promising for solar control application.     

Effective optical properties of highly ordered mesoporous thin films

This paper expands our previous numerical studies predicting the optical properties of highly ordered mesoporous thin films from two-dimensional (2D) nanostructures with cylindrical pores to three-dimensional (3D) structures with spherical pores. Simple, face centered, and body centered cubic lattices of spherical pores and hexagonal lattice of cylindrical pores were considered along with various pore diameters and porosities. The transmittance and reflectance were numerically computed by solving 3D Maxwell's equations for transverse electric and transverse magnetic polarized waves normally incident on the mesoporous thin films. The effective optical properties of the films were determined by an inverse method. Reflectance of 3D cubic mesoporous thin films was found to be independent of polarization, pore diameter, and film morphology and depended only on film thickness and porosity. By contrast, reflectance of 2D hexagonal mesoporous films with cylindrical pores depended on pore shape and polarization. The unpolarized reflectance of 2D hexagonal mesoporous films with cylindrical pores was identical to that of 3D cubic mesoporous films with the same porosity and thickness. The effective refractive and absorption indices of 3D films show good agreement with predictions by the 3D Maxwell-Garnett and nonsymmetric Bruggeman effective medium approximations, respectively.     

Embossed Bragg Gratings Based on Organically Modified Silane Waveguides in InP

Considering the large variety of applications for optical glass waveguide gratings, the effective production method of embossing for micropatterning, and the unique advantages of InP-based materials, we expect that hybridization of embossed optical glass waveguide gratings and InP substrates will inevitably lead to new applications in integrated optics. We present our preliminary results of research toward the development of solgel-derived glass waveguide gratings made by embossing on InP. Theoretically, the dependence of the stop-band FWHM and transmission contrast of the grating filter on the grating length, and the relationship between the Bragg grating's reflective wavelength and the dopant concentration in the solgel waveguide, are obtained. Experimentally, using organically modified silane, we solve the problem of mismatching of SiO(2) and InP, and successfully fabricate an embossed glass grating with a second-order Bragg reflection wavelength of 1580 nm and a FWHM of 0.7 nm fabricated upon a solgel waveguide on an InP substrate.