Bilayer SiO2 Nanorod Arrays as Omnidirectional and Thermally Stable Antireflective Coating

Nature instigates researchers significantly in imitating to engender comparable properties using artificial methods, which unlocks developing trend in material science and engineering progress. Fabricating graded‐index nanostructures is an effective approach to tune and generate similar properties artificially such as the moth's eye antireflectance (AR) or lotus like superhydrophobicity. Herein, Bilayer AR coatings with periodically arranged SiO₂ hierarchical nanostructures resembling moth eyes are fabricated on dense SiO₂ matrix base layer using the versatile route of glancing angle deposition technique (GLAD). The refractive indices of monolayer SiO₂ are tuned from 1.46 to 1.08 by changing the deposition angle (α) from 0 to 88°. The fabricated bilayer SiO₂ AR (BSAR) film possess high optical omnidirectional broadband transparency and tunability at a desired wavelength range showing <1% reflectance. The present AR design is flexible and practically applicable to various supporting substrate materials (η varies from 1.45 to 1.9). Furthermore, the omnidirectional BSAR films show multiple functions including enhanced mechanical strength, the thermal stability (up to 300 °C), and hydrophobic capability with a water contact angle (CA) of 147° to withstand under humid environment. This multipurpose coating provides an intriguing route in optics field for imminent research.

     

Growth kinetics and surface properties of single-crystalline aluminum-doped zinc oxide nanowires on silicon substrates

We present here the results from a systematic investigation on the growth kinetics and surface properties of Al-doped ZnO (AZO) nanowires synthesized on (0 0 1)Si substrates under different hydrothermal conditions. The as-synthesized vertical AZO nanowires exhibited a hydrophilic characteristic and their crystal structures were determined to be perfectly single crystalline with the axis of the wire parallel to the [0 0 0 1] direction. TEM and EDS results revealed that the as-synthesized AZO nanowires have tapered tips, and the Al-doped concentration in the AZO nanowires was about 1.6 at%. After a series of SEM examinations, the average length of AZO nanowires synthesized at each temperature studied was found to follow a linear relationship with the reaction time, indicating that the hydrothermal growth of AZO nanowires was a reaction-controlled process. The activation energy for linear growth of AZO nanowires on Si substrate, as obtained from an Arrhenius plot, was found to be about 46 kJ/mol. From UV–vis spectroscopic measurements, it was found that the Si substrate coated with vertically-aligned AZO nanowire arrays exhibited remarkably reduced reflectance (10–12%) over a wide range of visible wavelengths (400–800 nm) and angles of light incidence (8–60°). The good broadband and omnidirectional antireflection characteristics can be attributed to the light trapping effect and the graded refractive index resulting from the tapered AZO nanowire structures.     

VO2-ZnO composite films with enhanced thermochromic properties for smart windows

VO₂ film is a promising thermochromic material in smart windows due to its reversible metal to insulator transition (MIT) accompanied with an abrupt change of transmittance in near-infrared region at around 68 °C (T>68 °C, translucent; T < 68 °C, transparent), but which has not been widely applied because its low luminous transmittance (<60%) and solar modulation efficiency (<10%) are difficult to be improved simultaneously. In order to solve this problem, the ZnO-VO₂ composite film was prepared by a facile method, in which commercial ZnO nanoparticles (NPs) and VO₂ micro-particles were mixed by ball milling method to form the composites. By introducing ZnO NPs into the composite film, the luminous transmittance (T_lum) of the composite film was increased by 16.9% (from 54.9% to 63.9%) and the solar modulation efficiency (ΔT_sol) was increased by 14.1% (from 9.9% to 11.3%) compared to the pure VO₂ composite film. This was because ZnO NPs not only played the role of antireflection, but also prevented VO₂ particles from agglomeration by dispersing around VO₂ particles. Furthermore, the two-layered film based on ZnO-VO₂ composites exhibited an astonishing ΔT_sol of 18.8%, while maintaining excellent T_lum of 54.3%. This work could provide a simple and novel idea for us to improve the thermochromic properties of VO₂ films and simultaneously to promote their practical application.     

a-Si:H/SiNW shell/core for SiNW solar cell applications

Vertically aligned silicon nanowires have been synthesized by the chemical etching of silicon wafers. The influence of a hydrogenated amorphous silicon (a-Si:H) layer (shell) on top of a silicon nanowire (SiNW) solar cell has been investigated. The optical properties of a-Si:H/SiNWs and SiNWs are examined in terms of optical reflection and absorption properties. In the presence of the a-Si:H shell, 5.2% reflection ratio in the spectral range (250 to 1,000 nm) is achieved with a superior absorption property with an average over 87% of the incident light. In addition, the characteristics of the solar cell have been significantly improved, which exhibits higher open-circuit voltage, short-circuit current, and efficiency by more than 15%, 12%, and 37%, respectively, compared with planar SiNW solar cells. Based on the current–voltage measurements and morphology results, we show that the a-Si:H shell can passivate the defects generated by wet etching processes.     

2-Step self-assembly method to fabricate broadband omnidirectional antireflection coating in large scale

We have developed a simple and reproducible 2-step self-assembly method for the fabrication of broadband, omnidirectional antireflection coating on glass substrate with 4 in. size. The glass surface has been modified to be positively charged, then the negatively charged nano silica is self-assembled to the glass substrate by electrostatic attraction. The nanostructure on the glass substrate reduces the reflection significantly, which results in enhanced transmittance. Transmittance as high as 97.7% at 499 nm has been obtained for a double-side coated glass substrate. Obvious reduction in weighted reflectance is still observed up to 60° incident angle.     

具有激光二极管结构的1.3μm侧面发光二极管（Ⅰ）：理论分析

讨论了用某些参数不合格的激光二有管管芯制作侧面发光二极管的可能性，并给出了超辐射发光二极管和侧面发光二极管的定量判定依据。     

Design, fabrication and optical characterization of cerium oxide-magnesium fluoride double layer antireflection coatings on monocrystalline silicon substrates

Theoretical and experimental studies of a double layer antireflection coating deposited onto silicon wafers have been carried out. Magnesium oxide and cerium oxide fabricated by physical vapor deposition method have been applied as low- and high-refractive index materials. MgF₂–CeO₂–Si structures exhibited the reflectivity below 3% in the wavelength window from 0.5 μm to 1.2 μm. Theoretical simulations of spectral characteristics of the reflectivity of these coatings have been performed. A good correlation between experimental data and theoretical curves has been observed with the assumption that a thin SiO₂ layer of a thickness of 16 nm is formed onto Si substrates.     

Fabrication of evacuated glazing at low temperature

An indium-based seal augmented with an adhesive, developed to maintain a vacuum between two sheets of glass, avoids the high temperatures required to produce a seal in evacuated glazings to date. An experimentally-validated three-dimensional transient model has been used to predict heat transfer for an indium/adhesive sealed 1 m² area evacuated window with a highly insulating frame. An overall heat loss coefficient of 0.9 W m⁻² K⁻¹, with a midplane value of 0.36 W m⁻² K⁻¹, can be achieved with 0.72 visible transmittance for two 6 mm panes separated by 0.2 mm diameter pillars 40 mm apart. The conduction through a 3 mm edge-seal was 1.14 W m⁻² K⁻¹. Detailed three-dimensional isothermal contour plots through the system are presented.     

Enhancement of antireflection property of silicon using nanostructured surface combined with a polymer deposition

Silicon (Si) nanostructures that exhibit a significantly low reflectance in ultraviolet (UV) and visible light wavelength regions are fabricated using a hydrogen etching process. The fabricated Si nanostructures have aperiodic subwavelength structures with pyramid-like morphologies. The detailed morphologies of the nanostructures can be controlled by changing the etching condition. The nanostructured Si exhibited much more reduced reflectance than a flat Si surface: an average reflectance of the nanostructured Si was approximately 6.8% in visible light region and a slight high reflectance of approximately 17% in UV region. The reflectance was further reduced in both UV and visible light region through the deposition of a poly(dimethylsiloxane) layer with a rough surface on the Si nanostructure: the reflectance can be decreased down to 2.5%. The enhancement of the antireflection properties was analyzed with a finite difference time domain simulation method.     

Tuning the peak position of subwavelength silica nanosphere broadband antireflection coatings

Subwavelength nanostructures are considered as promising building blocks for antireflection and light trapping applications. In this study, we demonstrate excellent broadband antireflection effect from thin films of monolayer silica nanospheres with a diameter of 100 nm prepared by Langmuir-Blodgett method on glass substrates. With a single layer of compact silica nanosphere thin film coated on both sides of a glass, we achieved maximum transmittance of 99% at 560 nm. Furthermore, the optical transmission peak of the nanosphere thin films can be tuned over the UV-visible range by changing processing parameters during Langmuir-Blodgett deposition. The tunable optical transmission peaks of the Langmuir-Blodgett films were correlated with deposition parameters such as surface pressure, surfactant concentration, ageing of suspensions and annealing effect. Such peak-tunable broadband antireflection coating has wide applications in diversified industries such as solar cells, windows, displays and lenses.