Gold Enhanced Graphene-Based Photodetector on Optical Fiber with Ultrasensitivity over Near-Infrared Bands

Graphene has been widely used in photodetectors; however its photoresponsivity is limited due to the intrinsic low absorption of graphene. To enhance the graphene absorption, a waveguide structure with an extended interaction length and plasmonic resonance with light field enhancement are often employed. However, the operation bandwidth is narrowed when this happens. Here, a novel graphene-based all-fiber photodetector (AFPD) was demonstrated with ultrahigh responsivity over a full near-infrared band. The AFPD benefits from the gold-enhanced absorption when an interdigitated Au electrode is fabricated onto a Graphene-PMMA film covered over a side-polished fiber (SFP). Interestingly, the AFPD shows a photoresponsivity of >1 × 104 A/W and an external quantum efficiency of >4.6 × 106% over a broadband region of 980–1620 nm. The proposed device provides a simple, low-cost, efficient, and robust way to detect optical fiber signals with intriguing capabilities in terms of distributed photodetection and on-line power monitoring, which is highly desirable for a fiber-optic communication system.

Burger Model as the Best Option for Modeling of Viscoelastic Behavior of Resists for Nanoimprint Lithography

In this study, Atomic Force Microscopy-based nanoindentation (AFM-NI) with diamond-like carbon (DLC) coated tip was used to analyze the mechanical response of poly(methyl methacrylate) (PMMA) thin films (thicknesses: 235 and 513 nm) on a silicon substrate. Then, Oliver and Pharr (OP) model was used to calculate hardness and Young’s modulus, while three different Static Linear Solid models were used to fit the creep curve and measure creep compliance, Young’s modulus, and viscosity. Values were compared with each other, and the best-suited method was suggested. The impact of four temperatures below the glass transition temperature and varied indentation depth on the mechanical properties has been analyzed. The results show high sensitivity on experiment parameters and there is a clear difference between thin and thick film. According to the requirements in the nanoimprint lithography (NIL), the ratio of hardness at demolding temperature to viscosity at molding temperature was introduced as a simple parameter for prediction of resist suitability for NIL. Finally, thinner PMMA film was tentatively attributed as more suitable for NIL.

Luminescent Hydrogel Based on Silver Nanocluster/Malic Acid and Its Composite Film for Highly Sensitive Detection of Fe3+

Metal nanoclusters (NCs) with excellent photoluminescence properties are an emerging functional material that have rich physical and chemical properties and broad application prospects. However, it is a challenging problem to construct such materials into complex ordered aggregates and cause aggregation-induced emission (AIE). In this article, we use the supramolecular self-assembly strategy to regulate a water-soluble, atomically precise Ag NCs (NH4)9[Ag9(C7H4SO2)9] (Ag9-NCs, [Ag9(mba)9], H2mba = 2-mercaptobenzoic acid) and L-malic acid (L–MA) to form a phosphorescent hydrogel with stable and bright luminescence, which is ascribed to AIE phenomenon. In this process, the AIE of Ag9-NCs could be attributed to the non-covalent interactions between L–MA and Ag9-NCs, which restrict the intramolecular vibration and rotation of ligands on the periphery of Ag9-NCs, thus inhibiting the ligand-related, non-radiative excited state relaxation and promoting radiation energy transfer. In addition, the fluorescent Ag9-NCs/L–MA xerogel was introduced into polymethylmethacrylate (PMMA) to form an excellently fluorescent film for sensing of Fe3+. Ag9-NCs/L–MA/PMMA film exhibits an excellent ability to recognize Fe3+ ion with high selectivity and a low detection limit of 0.3 μM. This research enriches self-assembly system for enhancing the AIE of metal NCs, and the prepared hybrid films will become good candidates for optical materials.

Material Modeling of PMMA Film for Hot Embossing Process

This study provides an analysis of the hot embossing process with poly methyl methacrylate (PMMA) film. The hot embossing process engraves a fine pattern on a flexible film using a stamp, applied heat and pressure. As the quality of the embossing pattern varies according to various process variables, the mechanism of making the embossed shape is complicated and difficult to analyze. Therefore, analysis takes much time and cost because it usually has to perform a lot of experiments to find an appropriate process condition. In this paper, the hot embossing process was analyzed using a computational analysis method to quickly find the optimal process. To do this, we analyzed the embossing phenomenon using the finite element method (FEM) and arbitrary Lagrangian–Eulerian (ALE) re-mesh technique. For this purpose, we developed a constitutive model considering the strain, strain rate, temperature-dependent stress and softening of the flexible film. Work hardening, strain softening, and temperature-softening behavior of PMMA materials were well described by the proposed method. The developed constitutive model were applied in the embossing analysis via user-subroutine. This proposed method allowed a precise analysis of the phenomenon of film change during the hot embossing process.

Heat Treatment at Different Temperatures and its Effect on the Optical Properties of Pure PMMA and PMMA-Coumarin

The effect of thermal treatment on optical constants of pure PMMA and with addition (15 and 35) ml of coumarin at different temperatures (100, 110 and 120) C0 for 1 hour were investigated. Cast method used to prepares films of pure PMMA and PMMA with (15 and 35) of coumarin. UV/VIS spectrometer technique used to measure the absorption spectra for these films. The optical constant (absorption spectra and absorption coefficient) don’t changes after applied temperatures in pure PMMA film but the optical constant (absorption spectra and absorption coefficient) in PMMA with (15 and 35) ml of coumarin increased with applied temperatures. The optical energy gap of pure PMMA and PMMA with (15 and 35) ml of coumarin slightly decreased after applied temperature up to 1200 C.

Coupled Superhydrophilic PMMA Film with Inverted Pyramid Microstructures for Antireflection and Antifogging Properties

Transparent substrates with antifogging and antireflection ability are of extreme significance for optical devices, because they alleviate performance loss and maintenance costs. Here, we reported that a multifunctional film, with excellent mechanical properties, can be fabricated on the PMMA surface via the micro-transfer printing method. In particular, the synergistic effect of the inverted pyramid microstructure and SiO2 nanoparticles gives the film excellent antireflective, superhydrophilic and antifogging properties, and the silica sol firmly adheres to the PMMA substrate via the silane coupling agent, which exhibits an encouraging prospect of practical applications from lenses for personal and sports eyewear to transparent displays and sensors, etc.

Photo-Switchable Aggregation-Induced Emission of Bisthienylethene-Dipyrimido[2,1-b][1,3]benzothiazole Triad

A bisthienylethene-dipyrimido[2,1-b][1,3]benzothiazole (BTE-2PBT) triad has been designed and synthesized based on our recent discovery of PBTs as atypical propeller-shaped novel AIEgens. The triad not only maintains the photochromic properties of BTE moiety in solution, film, and solid state but also exhibits remarkable AIE properties. Moreover, the fluorescence of BTE-2PBT PMMA film could be modulated with high contrast by alternate UV and visible light irradiation. Photoerasing, rewriting, and non-destructive readout of fluorescent images on BTE-2PBT PMMA film well demonstrate its potential application as optical memory media.

Spin-coating of micron-scale thick PMMA films with embedded Au nanoparticles formed by laser ablation in liquid.

Background: A Facile is a scalable approach to fabricating organic thin films with an embedded layer of nanoparticles in the ambient environment. The approach is based on step-by-step spin-coating of polymethylmethacrylate (PMMA) films and a nanoparticle layer. Objective: The goal of the present work is to fabricate a sandwich structure of the PMMA films for the top and bottom layers of a sandwich structure as well as a middle layer of nanoparticles formed in solution by the laser ablation in liquid (LAL) method. Methods: First, a PMMA thin film was fabricated by spin-casting of PMMA solution in ethyl acetate. Secondly, a solution of Au nanoparticles synthesized by laser ablation in ethanol was spin-cast on a prefabricated PMMA film. The distribution of Au nanoparticles and the morphology of the resulting film were analyzed using scanning electron microscopy (SEM), optical microscopy, and atomic microscopy (AFM). Finally, another PMMA layer was spin-cast on the nanoparticle-decorated film. Results: A hybrid organic film with the embedded layer of nanoparticles was fabricated using the spin-casting method for top and bottom layers and the middle layer of Au nanoparticles fabricated by laser ablation in ethanol by a pulsed UV laser. Statistical and fractal analysis shows uniform distribution of nanoparticles on a length scale above ten microns. Conclusion: Spin-cast-based layer-by-layer approach to fabricating sandwich structures of organic films with embedded nanoparticles is a facile and scalable method for hybrid organic – nanoparticle films. This approach can be extended for the fabrication of multi-layered hybrid structures.

Study of naphthopyran derivatives: structure and photochromic properties in solution and in polymer film

Four naphthopyran derivatives, namely, 3,3-bis(naphthalen-1-yl)-3H-naphtho[2,1-b]pyran, C33H22O, NP1, 3,3-bis([1,1′-biphenyl]-4-yl)-3H-naphtho[2,1-b]pyran, C37H26O, NP2, 3,3-bis(4-phenoxyphenyl)-3H-naphtho[2,1-b]pyran, C37H26O2, NP3, and 3,3-bis(4-methoxy-2-methylphenyl)-3H-naphtho[2,1-b]pyran, C29H26O3, NP4, were synthesized and their photochromic properties investigated. NP1–NP4 exhibited good photochromism in different solutions and in poly(methyl methacrylate) (PMMA) film under UV light irradiation. Solvatochromism and the electronic and steric effects of the substituent group on photochromism were analyzed and decolouration curves were found to fit a monoexponential kinetic decay in most cases. Single-crystal X-ray analysis of NP1 and NP2 revealed the structure–property relationships. Good fatigue resistance of NP1, both in solution and in the PMMA film, endows it with potential value for applications.