Simple and scalable growth of AgCl nanorods by plasma-assisted strain relaxation on flexible polymer substrates

Release of ions enhanced the antibacterial performance of laser-generated, uncoated Ag nanoparticles

Identifying the antibacterial mechanisms of elemental silver at the nanoscale remains a significant challenge due to the intertwining behaviors between the particles and their released ions. The open question is which of the above factor dominate the antibacterial behaviors when silver nanoparticles (Ag NPs) with different sizes. Considering the high reactivity of Ag NPs, prior research has primarily concentrated on coated particles, which inevitably hinder the release of Ag+ ions due to additional chemical agents. In this study, we synthesized various Ag NPs, both coated and uncoated, using the laser ablation in liquids (LAL) technique. By analyzing both the changes in particle size and Ag+ ions release, the impacts of various Ag NPs on the cellular activity and morphological changes of gram-negative (E. coil) and gram-positive (S. aureus) bacteria were evaluated. Our findings revealed that for uncoated Ag NPs, smaller particles exhibited greater ions release efficiency and enhanced antibacterial efficacy. Specifically, particles approximately 1.5 nm in size released up to 55 % of their Ag+ ions within 4 h, significantly inhibiting bacterial growth. Additionally, larger particles tended to aggregate on the bacterial cell membrane surface, whereas smaller particles were more likely to be internalized by the bacteria. Notably, treatment with smaller Ag NPs led to more pronounced bacterial morphological changes and elevated levels of intracellular reactive oxygen species (ROS). We proposed that the bactericidal activity of Ag NPs stems from the synergistic effect between particle-cell interaction and the ionic silver, which is dependent on the crucial parameter of particle size.

Menezes L, Tittl A, Ren H, Maier SA. Optical Metasurfaces for Energy Conversion

Nanostructured surfaces with designed optical functionalities, such as metasurfaces, allow efficient harvesting of light at the nanoscale, enhancing light-matter interactions for a wide variety of material combinations. Exploiting light-driven matter excitations in these artificial materials opens up a new dimension in the conversion and management of energy at the nanoscale. In this review, we outline the impact, opportunities, applications, and challenges of optical metasurfaces in converting the energy of incoming photons into frequency-shifted photons, phonons, and energetic charge carriers. A myriad of opportunities await for the utilization of the converted energy. Here we cover the most pertinent aspects from a fundamental nanoscopic viewpoint all the way to applications.

Development and comparison of various rod-shaped mini-reference electrode compositions based on Ag/AgCl for potentiometric applications

Several fundamentally similar, miniaturized solid-state reference electrode designs, and their fabrication and comparison are described in this article. All electrodes were based on Ag/AgCl as their reference element. The best electrode (a three-layer assembly with graphite oxide, epoxy, and hardener as the framework providers and with well-mixed micro-Ag particles in the bottom layer, AgCl in the middle layer, and fine KCl powder in the top layer) exhibited satisfactory short-term performance to replace a commercial reference electrode in many cases and was rigorously tested in terms of pH response, long-term leakage, and the effect of oxygen to better evaluate its characteristics. To assess the electrode's performance in medically important studies, cytotoxicity experiments and tests in artificial saliva were also conducted. All tests demonstrated that our best reference electrode was stable and had a long shelf life.

Completely Hazy and Transparent Films by Embedding Air Gaps for Elimination of Angular Color Shift in Organic Light-Emitting Diodes

Red, green, and blue top-emission organic light-emitting diodes (RGB TOLEDs) suffer from white color change with viewing angle due to the microcavity effect, called white angular dependence (WAD). Great efforts are devoted by applying various kinds of hazy films, but they suffer from poor mechanical stability and optical transmittance. Herein, we introduce an air-gap-embedded hazy film (AEHF) to solve these problems and suppress WAD in RGB TOLEDs. The AEHF is designed with optical simulation to realize high haze with transparency. By tuning geometries of the air gap inside the polymer, the AEHF realizes high haze of more than 90% in all RGB colors while maintaining high transparency. To experimentally demonstrate the AEHF, the O₂ plasma is treated on a polymer film with AgCl as an etching mask to fabricate microstructures with high aspect ratios. Afterward, PDMS is coated on the patterned surface; air gaps develop spontaneously in the valleys between microstructures during the coating process. Using these processes, an air gap with 1.2 μm size and 400 nm period is formed inside the film and ∼100% haze is achieved while maintaining a high transmittance of 88%; these results agree well with rigorous coupled wave analysis results. By utilizing the AEHF into TOLEDs, the WAD can be drastically suppressed by 95.2% compared with that of a device without AEHF.

Solvothermal Crystallization of Ag/AgxO-AgCl Composites: Effect of Different Chloride Sources/Shape-Tailoring Agents

In the present work, AgCl microcrystals were obtained by solvothermal crystallization to investigate the effect of H+, Na+, K+, and different shape-tailoring agents (non-ionic: polyvinylpyrrolidone vs. anionic: sodium dodecyl sulfate) on the textural and photocatalytic properties of the samples. The crystallization process resulted in secondary products, such as AgxO or Ag, AgClO3, AgClO4, which were further transformed during the photocatalytic tests. The most efficient photocatalyst (assessed for methyl orange degradation) was synthesized using HCl, as a chloride source and polyvinylpyrrolidone, as a shape-tailoring agent. Therefore, the ability of polyvinylpyrrolidone to enhance the photocatalytic activity was also investigated, and it was found that the addition of 0.6 g polyvinylpyrrolidone resulted in the most efficient photocatalyst. Moreover, AgxO, being a charge separator, could play a critical role in the photocatalytic process, while reversibly transforming to Ag back and forth.

Anti-Reflective Coating Materials: A Holistic Review from PV Perspective

The solar photovoltaic (PV) cell is a prominent energy harvesting device that reduces the strain in the conventional energy generation approach and endorses the prospectiveness of renewable energy. Thus, the exploration in this ever-green field is worth the effort. From the power conversion efficiency standpoint of view, PVs are consistently improving, and when analyzing the potential areas that can be advanced, more and more exciting challenges are encountered. One such crucial challenge is to increase the photon availability for PV conversion. This challenge is solved using two ways. First, by suppressing the reflection at the interface of the solar cell, and the other way is to enhance the optical pathlength inside the cell for adequate absorption of the photons. Our review addresses this challenge by emphasizing the various strategies that aid in trapping the light in the solar cells. These strategies include the usage of antireflection coatings (ARCs) and light-trapping structures. The primary focus of this study is to review the ARCs from a PV application perspective based on various materials, and it highlights the development of ARCs from more than the past three decades covering the structure, fabrication techniques, optical performance, features, and research potential of ARCs reported. More importantly, various ARCs researched with different classes of PV cells, and their impact on its efficiency is given a special attention. To enhance the optical pathlength, and thus the absorption in solar PV devices, an insight about the advanced light-trapping techniques that deals with the concept of plasmonics, spectral modification, and other prevailing innovative light-trapping structures approaching the Yablonovitch limit is discussed. An extensive collection of information is presented as tables under each core review section. Further, we take a step forward to brief the effects of ageing on ARCs and their influence on the device performance. Finally, we summarize the review of ARCs on the basis of structures, materials, optical performance, multifunctionality, stability, and cost-effectiveness along with a master table comparing the selected high-performance ARCs with perfect AR coatings. Also, from the discussed significant challenges faced by ARCs and future outlook; this work directs the researchers to identify the area of expertise where further research analysis is needed in near future.

Air-gap-embedded robust hazy films to reduce the screen-door effect in virtual reality displays

We report a way to make an air-gap-embedded flexible film to reduce the screen-door effect (SDE) in virtual reality (VR) displays. Oxygen plasma was treated with a polyethylene terephthalate substrate to produce wavelength-scale micropatterns. These micropatterns induce an effective haze, but it is easily destroyed by a very small external scratch. Such a problem could be solved by coating the patterns with poly(dimethylsiloxane) (PDMS). The viscosity of PDMS, controlled by the ratio of the base and curing agents, plays a key role in determining the size of air-gaps at the valleys of micropatterns. As the ratio of base agent increases to 40, the average haze abruptly increased from 0.9% to 88.6% in visible wavelengths, while the average total transmittance maintained was between 89.8 and 91.7%. The origin of air-gap-induced haze is confirmed by numerical simulations. The hazy film remarkably reduced the SDE of the VR display from 30.27% to 4.83% for red color, from 21.82% to 2.58% for green, and from 26.02% to 3.38% for blue, as the size of air-gaps increases from 0 to 406 ± 91 nm. No defects were found after 10 000 bending cycles with a bending radius of 3 mm.

Emerging Self-Emissive Technologies for Flexible Displays

Featuring a combination of ultrathin and lightweight properties, excellent mechanical flexibility, low power-consumption, and widely tunable saturated emission, flexible displays have opened up a new possibility for optoelectronics. The demands for flexible displays are growing on a continual basis due not only to their successful commercialization but, more importantly, their endless possibilities for wearable integrated systems. Up to now, self-emissive technologies for displays, flexible active-matrix organic light-emitting diodes (flex-AMOLED), flexible quantum dot light-emitting diodes (flex-QLEDs), and flexible perovskite light-emitting diodes (flex-PeLEDs) have been widely reported, but despite the significant progress made in these technologies, enormous obstacles and challenges remain for the vision of truly wearable applications, in particular with flex-QLEDs and flex-PeLEDs. Here, a review of the recent progress of all three self-emissive technologies for flexible displays is conducted, including the emissive active materials, device structures and approaches to manufacturing, the flexible substrates, and conductive electrodes, as well as the encapsulation techniques. The fast-paced improvement made to the efficiency of flexible devices in recent years is also summarized. The review concludes by making suggestions on the future development in this area, and is expected to help researchers in gaining a comprehensive understanding about the newly emerging technologies for flexible displays.

Subwavelength-scale nanorods implemented hexagonal pyramids structure as efficient light-extraction in Light-emitting diodes

Subwavelength-scale nanorods were implemented on the hexagonal pyramid of photochemically etched light-emitting diodes (LEDs) to improve light extraction efficiency (LEE). Sequential processes of Ag deposition and inductively coupled plasma etching successfully produce nanorods on both locally unetched flat surface and sidewall of hexagonal pyramids. The subwavelength-scale structures on flat surface offer gradually changed refractive index, and the structures on side wall of hexagonal pyramid reduce backward reflection, thereby enhancing further enhancement of the light extraction efficiency. Consequently, the nanorods implemented LED shows a remarkable enhancement in the light output power by 14% compared with that of the photochemically etched LEDs which is known to exhibit the highest light output power. Theoretical calculations using a rigorous coupled wave analysis method reveal that the subwavelength-scale nanorods are very effective in the elimination of TIR as well as backward reflections, thereby further enhancing LEE of the LEDs.

Fabrication of Nickel Oxide Nanopillar Arrays on Flexible Electrodes for Highly Efficient Perovskite Solar Cells

Semiconductor nanomaterials with controlled morphologies and architectures are of critical importance for high-performance optoelectronic devices. However, the fabrication of such nanomaterials on polymer-based flexible electrodes is particularly challenging due to degradation of the flexible electrodes at a high temperature. Here we report the fabrication of nickel oxide nanopillar arrays (NiO _x NaPAs) on a flexible electrode by vapor deposition, which enables highly efficient perovskite solar cells (PSCs). The NiO _x NaPAs exhibit an enhanced light transmittance for light harvesting, prohibit exciton recombination, promote irradiation-generated hole transport and collection, and facilitate the formation of large perovskite grains. These advantageous features result in a high efficiency of 20% and 17% for the rigid and flexible PSCs, respectively. Additionally, the NaPAs show no cracking after 500 times of bending, consistent with the mechanic simulation results. This robust fabrication opens a new opportunity for the fabrication of a large area of high-performance flexible optoelectronic devices.

A strain induced subwavelength-structure for a haze-free and highly transparent flexible plastic substrate

This paper presents a method to produce subwavelength-scale (<250 nm) AgCl nanostructures on a flexible plastic film, which is indispensable for highly efficient flexible displays. Using Cl2 plasma treatment on an Ag-coated plastic film, AgCl nanostructures were produced through the reaction of Ag atoms with Cl radicals. During the reaction, the volume of AgCl expands, leading to drastically changed surface morphology from a two-dimensional (2D) flat Ag surface to a 3D subwavelength-scale AgCl nanostructure. The optical properties of AgCl on the plastic film were remarkably enhanced from 89.6% to 93.4% and the average transmittance ranged between 400 and 800 nm, while the average haze was retained below 0.3%. Consequently, OLEDs based on the subwavelength-scale AgCl nanostructure had an enhanced luminance efficiency (88.6 cd A-1 at 1000 cd m-2) of up to 10.7% without modifying the angular emission pattern, superior to that of the as-received PI film (efficiency of 80.0 cd A-1). The nanostructure enhances the transmission of electromagnetic (EM) waves as well as prohibits the scattering of EM waves, which was confirmed by finite-difference time-domain simulation and rigorous coupled wave analysis.