Controlling pore morphology and properties of nanoporous silica films using the different architecture PS-b-P2VP as a template

Nanoporous silica films were prepared through the templating of amphiphilic block copolymer, poly(styrene-2-vinyl pyridine) (PS-b-P2VP), and monodispersed colloidal silica nanoparticles. The experimental and theoretical studies suggested that the intermolecular hydrogen bonding existes between the colloidal silica nanoparticles and PS-b-P2VP. The effects of the loading ratio and P2VP chain length on the morphology and properties of the prepared nanoporous silica films were investigated. TEM and AFM studies showed that the uniform pore size could be achieved and the pore size increased with increasing porogen loading. The refractive index and dielectric constant of the prepared nanoporous films decreased with an increase in PS-b-P2VP loading. On the other hand, the porosity increased with an increasing PS-b-P2VP loading. This study demonstrated a methodology to control pore morphology and properties of the nanoporous silica films through the templating of PS-b-P2VP.     

Thin film photodiodes fabricated by electrostatic self-assembly of aqueous colloidal quantum dots

We demonstrate a thin film photodiode structure consisting of multi layers of colloidal quantum dots (QDs) which has application in photovoltaics and photodetection. The CdTe QDs with either positively or negatively charged capping ligands are self-assembled layer-by-layer on an indium tin oxide (ITO) substrate by electrostatic attraction in aqueous solution. A photolithographically patterned photoresist window defines the device active area and an evaporated aluminum (Al) thin film serves as the top electrode. The built-in electric field due to the work function difference between Al and ITO separates photo-excited electron-hole pairs and generates photocurrent. Since the ligands used for QD synthesis are short (less than 0.5 nm), no additional steps of ligand exchange or annealing is needed for enhancing the thin film photoconductivity. Thiol passivation and self-assembly in an inert environment help reduce surface traps, leading to less fermi-level pinning which also improves the device performance.     

High‐Performance Near‐IR Photodetector Using Low‐Bandgap MA0.5FA0.5Pb0.5Sn0.5I3 Perovskite

Photodetectors with ultrafast response are explored using inorganic/organic hybrid perovskites. High responsivity and fast optoelectronic response are achieved due to the exceptional semiconducting properties of perovskite materials. However, most of the perovskite‐based photodetectors exploited to date are centered on Pb‐based perovskites, which only afford spectral response across the visible spectrum. This study demonstrates a high‐performance near‐IR (NIR) photodetector using a stable low‐bandgap Sn‐containing perovskite, (CH₃NH₃)_0.5(NH₂CHNH₂)_0.5Pb_0.5Sn_0.5I₃ (MA_0.5FA_0.5Pb_0.5Sn_0.5I₃), which is processed with an antioxidant additive, ascorbic acid (AA). The addition of AA effectively strengthens the stability of Sn‐containing perovskite against oxygen, thereby significantly inhibiting the leakage current. Consequently, the derived photodetector shows high responsivity with a detectivity of over 10¹² Jones ranging from 800 to 970 nm. Such low‐cost, solution processable NIR photodetectors with high performance show promising potential for future optoelectronic applications.     

Preparation and characterization of P3HT:CuInSe2:TiO2 thin film for hybrid solar cell applications

Improved efficiency of hybrid Al/Ca/P3HT:CISe:TiO₂/PEDOT:PSS/ITO thin film solar cells was obtained by optimizing P3HT/CISe ratio. This study also investigated the effects of TiO₂ content in the P3HT:CISe active layer, and altering annealing temperature conditions. The optimum TiO₂ content and annealing temperature for solar cell efficiency is 25 wt.% and 150 °C, respectively. The optimal results for the open circuit voltages (V_OC), short-circuit current density (J_SC), fill factor (FF), and efficiency (η) of the prepared hybrid thin film solar cell were V_OC = 0.335 V, J_SC = 8.07 mA/cm², FF = 52.75, and η = 1.425.     

A Lagrange‐Euler‐assumed modes approach to modeling flexible robotic manipulators

Abstract

This paper presents a general Lagrange‐Euler‐assumed modes dynamics formulation for lightweight flexible manipulators. The proposed explicit form formulation, not yet available in the existing literature, can be viewed as an extended version of the Lagrange‐Euler formulation for rigid manipulators. The deformation of a link from its rigid body position is modeled by a homogeneous 4×4 transformation matrix composed of summations of assumed link modes. The number of modes can be arbitrarily selected. The joint flexibility is modeled by a linear torsionai spring with known characteristics. The methodology presented can be easily used to derive the full nonlinear dynamic equations of flexible manipulators by computing only the dynamic coefficients using computer algebra such as MACSYMA. The resulting nonlinear dynamic equations are in a closed form and are especially suitable for advanced nonlinear control strategy synthesis. Taken as an illustrative example, a two‐link flexible manipulator is studied to demonstrate the effectiveness of the formulation.     

Pattern composed of two-dimensional diffusion dots for showing dynamic images

A new type of diffusion pattern is proposed. The proposed patterns are composed of 2D diffusion dots. The diffusion dots are created on a photoresist plate by recording the image of a local area of a piece of ground glass dot by dot. An imaging lens covered by a mask with a slit aperture is used to form the image. By changing the orientation of the slit aperture on the mask plane, the diffusion dots can have different microintensity distributions for the same incident light beam. Therefore the diffusion dots created by the same slit aperture orientation show the same brightness, and the diffusion dots created by different slit orientations show different brightness for the same illuminating and viewing conditions. Thus a proposed diffusion pattern can show dynamic images by changing its illuminating or viewing directions. By applying the double-exposure technique to the diffusion dots of a pattern, the pattern not only can show dynamic effects but also can possess several hidden features for identifying the pattern. Therefore the proposed patterns are dynamic and anticounterfeiting.     

Synthesis of soluble polyimide/silica–titania core–shell nanoparticle hybrid thin films for anti-reflective coatings

In this study, researchers prepared polyimide/silica–titania core–shell nanoparticle hybrid thin films (PI/SiO₂–TiO₂) from soluble fluorine-containing polyimide, colloidal silica, and titanium butoxide. The soluble polyimide with carboxylic acid end groups (6FDA–6FpDA–4ABA–COOH) could condense with titanium butoxide to provide organic–inorganic bonding, and thus prevent macrophase separation. TGA and DSC analysis showed that the decomposition temperature of hybrid materials increased with an increase in the content of silica–titania nanoparticles within the hybrid films. FTIR spectra indicated that the imidization was complete and the cross-linking Ti–O–Ti network formed. HRTEM and HRSEM images showed that the size of the core–shell nanoparticles were 18–20 nm. The thickness of titania shell on the silica is about 2.5 nm. The n&k and UV–Vis analysis showed that the prepared hybrid films had good optical properties and a high refractive index of 1.735. Researchers applied the prepared PI/SiO₂–TiO₂ hybrid thin films to develop a three layer antireflective (AR) coating on the glass and PMMA substrate. Results showed that the reflectance of the AR coating on the glass and PMMA substrate at 550 nm was 0.356 and 0.495%, respectively. The transparency was greater than 90% for both AR coatings on the glass and PMMA substrates.