Large-scale Au nanoparticle cluster arrays with tunable particle numbers evolved from colloidal lithography.

The assembly of metal nanoparticles (NPs) can regulate their plasmon resonance properties to pursue the best properties for applications. However, the controllable assembly of large-scale metal NP cluster arrays remains a significant challenge. This paper presents a novel strategy to prepare large-scale Au NP cluster arrays based on colloidal lithography and template-guided self-assembly technique. The NPs arrays are fabricated by introducing Au NPs onto the quaternized poly(2-(dimethylamino)ethyl methacrylate) (PDMAEMA) brush templates via electrostatic interaction. The number of Au NPs in cluster can be arbitrarily tuned by changing the surface area of the polymer templates created by colloidal lithography, which resulted in tunable plasmonic properties. The prepared Au NP cluster arrays were used for surface enhanced Raman scattering (SERS) and the SERS properties of the Au NP cluster arrays were studied.

Polymer-Passivated Inorganic Cesium Lead Mixed-Halide Perovskites for Stable and Efficient Solar Cells with High Open-Circuit Voltage over 1.3 V.

Cesium-based trihalide perovskites have been demonstrated as promising light absorbers for photovoltaic applications due to their superb composition stability. However, the large energy losses (Eloss ) observed in inorganic perovskite solar cells has become a major hindrance impairing the ultimate efficiency. Here, an effective and reproducible method of modifying the interface between a CsPbI2 Br absorber and polythiophene hole-acceptor to minimize the Eloss is reported. It is demonstrated that polythiophene, deposited on the top of CsPbI2 Br, can significantly reduce electron-hole recombination within the perovskite, which is due to the electronic passivation of surface defect states. In addition, the interfacial properties are improved by a simple annealing process, leading to significantly reduced energy disorder in polythiophene and enhanced hole-injection into the hole-acceptor. Consequently, one of the highest power conversion efficiency (PCE) of 12.02% from a reverse scan in inorganic mixed-halide perovskite solar cells is obtained. Modifying the perovskite films with annealing polythiophene enables an open-circuit voltage (VOC ) of up to 1.32 V and Eloss of down to 0.5 eV, which both are the optimal values reported among cesium-lead mixed-halide perovskite solar cells to date. This method provides a new route to further improve the efficiency of perovskite solar cells by minimizing the Eloss .

Autonomous Control of Fluids in a Wide Surface Tension Range in Microfluidics.

In this paper, we report the preparation of anisotropic wetting surfaces that could control various wetting behaviors of liquids in a wide surface tension range (from water to oil), which could be employed as a platform for controlling the flow of liquids in microfluidics (MFs). The anisotropic wetting surfaces are chemistry-asymmetric "Janus" silicon cylinder arrays, which are fabricated via selecting and regulating the functional groups on the surface of each cylinder unit. Liquids (in a wide surface tension range) wet in a unidirectional manner along the direction that was modified by the group with large surface energy. Through introducing the Janus structure into a T-shaped pattern and integrating it with an identical T-shaped poly(dimethylsiloxane) microchannel, the as-prepared chips can be utilized to perform as a surface tension admeasuring apparatus or a one-way valve for liquids in a wide surface tension range, even oil. Furthermore, because of the excellent ability in controlling the flowing behavior of liquids in a wide surface tension range in an open system or a microchannel, the anisotropic wetting surfaces are potential candidates to be applied both in open MFs and conventional MFs, which would broaden the application fields of MFs.

Unidirectional Wetting of Liquids on "Janus" Nanostructure Arrays under Various Media.

We report the unidirectional wetting behavior of liquids (water and oil) on Janus silicon cylinder arrays (Si-CAs) under various media (air, water, and oil). The Janus cylinders were prepared by chemical modification of nanocylinders with different molecules on two sides. Through adjusting surface energies of the modified molecules, the as-prepared surfaces could control the wetting behavior of different types of liquids under various media. We discuss the regularity systematically and propose a strategy for preparing anisotropic wetting surfaces under arbitrary media. That is, to find two surface modification molecules with different surface energies, one of the molecules is easy to be wetted by the liquid under the corresponding media, while the other one is difficult. Additionally, by introducing thermal-responsive polymer brushes onto one part of Janus Si-CAs, the surfaces show thermal-responsive anisotropic wetting property under various media. We believe that due to the excellent unidirectional wettability under various media, the Janus surfaces could be applied in water/oil transportation, oil-repellent and self-cleaning coatings, water/oil separation, microfluidics, and so on.

Multifunctional Reversible Fluorescent Controller Based on a One-Dimensional Photonic Crystal.

With the aim to build a multifunctional solid fluorescent controller, a one-dimensional photonic crystal and CdSe fluorescent single layer were separated on the opposite sides of quartz substrates. The separation structure remarkably facilitates materials selection for the fluorescent controller, which allows one to freely choose the fluorescent substance and constituents of 1DPC from a wide range of available materials with the best desirable properties and without caring about the interactions between them. Fluorescent enhancement and weakened effect were successfully achieved when the excitation light was irradiated from different sides of the fluorescent device. In addition, the fluorescent intensity can be altered reversibly along with environmental pH values according to the change of a pH-responsive one-dimensional photonic crystal layer, which is quite different from a previously reported quenching mode. Meanwhile, the original position of the photonic stop band is essential for deciding what pH value would produce the best effect of fluorescent control. It provides a way to adjust the effect of fluorescent controller according to certain applied situations. The mechanism of fluorescent variation was confirmed by the assistance of a finite-difference time-domain simulation. Furthermore, this device is also able to modulate fluorescent wavelength and full width at half-maximum by overlapping the photonic stop band and the emission of CdSe. Therefore, this method offers a universal strategy for the fabrication of fluorescent controllers.

Morphology-Patterned Anisotropic Wetting Surface for Fluid Control and Gas-Liquid Separation in Microfluidics.

This article shows morphology-patterned stripes as a new platform for directing flow guidance of the fluid in microfluidic devices. Anisotropic (even unidirectional) spreading behavior due to anisotropic wetting of the underlying surface is observed after integrating morphology-patterned stripes with a Y-shaped microchannel. The anisotropic wetting flow of the fluid is influenced by the applied pressure, dimensions of the patterns, including the period and depth of the structure, and size of the channels. Fluids with different surface tensions show different flowing anisotropy in our microdevice. Moreover, the morphology-patterned surfaces could be used as a microvalve, and gas-water separation in the microchannel was realized using the unidirectional flow of water. Therefore, benefiting from their good performance and simple fabrication process, morphology-patterned surfaces are good candidates to be applied in controlling the fluid behavior in microfluidics.

Hierarchical-Multiplex DNA Patterns Mediated by Polymer Brush Nanocone Arrays That Possess Potential Application for Specific DNA Sensing.

This paper provides a facile and cost-efficient method to prepare single-strand DNA (ssDNA) nanocone arrays and hierarchical DNA patterns that were mediated by poly(2-hydroxyethyl methacrylate) (PHEMA) brush. The PHEMA brush nanocone arrays with different morphology and period were fabricated via colloidal lithography. The hierarchical structure was prepared through the combination of colloidal lithography and traditional photolithography. The DNA patterns were easily achieved via grafting the amino group modified ssDNA onto the side chain of polymer brush, and the anchored DNA maintained their reactivity. The as-prepared ssDNA nanocone arrays can be applied for target DNA sensing with the detection limit reaching 1.65 nM. Besides, with the help of introducing microfluidic ideology, the hierarchical-multiplex DNA patterns on the same substrate could be easily achieved with each kind of pattern possessing one kind of ssDNA, which are promising surfaces for the preparation of rapid, visible, and multiplex DNA sensors.

Tunable polymer brush/Au NPs hybrid plasmonic arrays based on host-guest interaction.

The fabrication of versatile gold nanoparticle (Au NP) arrays with tunable optical properties by a novel host-guest interaction are presented. The gold nanoparticles were incorporated into polymer brushes by host-guest interaction between ß-cyclodextrin (ß-CD) ligand of gold nanoparticles and dimethylamino group of poly(2-(dimethylamino)ethyl methacrylate) (PDMAEMA). The gold nanoparticle arrays were prepared through the template of PDMAEMA brush patterns which were fabricated combining colloidal lithography and surface-initiated atom-transfer radical polymerization (SI-ATRP). The structure parameters of gold nanoparticle patterns mediated by polymer brushes such as height, diameters, periods and distances, could be easily tuned by tailoring the etching time or size of colloidal spheres in the process of colloidal lithography. The change of optical properties induced by different gold nanoparticle structures was demonstrated. The direct utilization of PDMAEMA brushes as guest avoids a series of complicated modification process and the PDMAEMA brushes can be grafted on various substrates, which broaden its applications. The prepared gold naoparticle arrays are promising in applications of nanosensors, memory storage and surface enhanced spectroscopy.

Bioinspired polyethylene terephthalate nanocone arrays with underwater superoleophobicity and anti-bioadhesion properties.

This paper presents a facile method to fabricate bioinspired polyethylene terephthalate (PET) nanocone arrays via colloidal lithography. The aspect ratio (AR) of the nanocones can be finely modulated ranging from 1 to 6 by regulating the etching time. The samples with the AR value of 6 can present underwater superoleophobicity with the underwater oil contact angle (OCA) of 171.8°. The as-prepared PET nanocone arrays perform anti-bioadhesion behavior, which inhibits the formation of the actin cytoskeleton when it used as the substrate for cell culture. Moreover, the oil wettability is temperature controlled after modifying the PET nanocone arrays with PNIPAAm film, and the oil wettability of the functionalized nanocone arrays can be transformed from the superoleophobic state with OCA about 151° to the oleophilic state with OCA about 25° reversibly. Due to the high-throughput, parallel fabrication and cost-efficiency of this method, it will be favourable for researchers to introduce oleophobic properties to various substrate and device surfaces. Due to the superoleophobicity and simple functionalizing properties, the PET nanocone arrays are very promising surfaces for anti-adhesion, self-cleaning and have potential applications in material, medical, and biological fields.

Elliptical polymer brush ring array mediated protein patterning and cell adhesion on patterned protein surfaces.

This paper presents a novel method to fabricate elliptical ring arrays of proteins. The protein arrays are prepared by covalently grafting proteins to the polymer brush ring arrays which are prepared by the techniques combining colloidal lithography dewetting and surface initiated atom-transfer radical polymerization (SI-ATRP). Through this method, the parameters of protein patterns, such as height, wall thickness, periods, and distances between two elliptical rings, can be finely regulated. In addition, the sample which contains the elliptical protein ring arrays can be prepared over a large area up to 1 cm(2), and the protein on the ring maintains its biological activity. The as-prepared ring and elliptical ring arrays (ERAs) of fibronectin can promote cell adhesion and may have an active effect on the formation of the actin cytoskeleton.

Patterning organic/inorganic hybrid Bragg stacks by integrating one-dimensional photonic crystals and macrocavities through photolithography: toward tunable colorful patterns as highly selective sensors.

Herein, we report a simple method to fabricate patterned organic/inorganic hybrid 1DPCs by top-down assisted photolithography. Versatile colorful pattern with different size and shape can be produced by selectively exposing the 1DPCs under UV light with predesigned photomask directly. The period change, especially the thickness variation of the top polymer layer, is the main reason for the colorful pattern generation. Because of the swelling property of the polymer layers, the pattern color can be modulated by introducing or taking off organic solvents, leading the as-prepared patterned 1DPCs to be effective sensors with high selectivity.