Self-assembled Polystyrene Spheres Research Articles

Rapid, non-contact identification of organic solvents: Monolithic GaN chips incorporating PDMS/PS photonic crystals

The prompt identification of organic solvents is essential in many practical scenarios. This work introduces a compact optical device for rapid, non-contact detection of organic solvents. The fabrication of the GaN chip employs a monolithic integration approach, enabling the simultaneous formation of on-chip components responsible for light emission and light detection. The self-assembled polystyrene (PS) spheres embedded in a polydimethylsiloxane (PDMS) layer as photonic crystals can effectively induce distinct optical changes when exposed to organic solvents. By analyzing the magnitude and recovery time of the photocurrent signals, up to seven types of organic samples can be distinguished. Different from traditional optical sensing systems, the proposed chip-level integration strategy eliminates the need for external assembly of optical components, resulting in an ultracompact millimeter-sized sensing unit. The developed device also offers features of simplicity of use and a short measurement time of less than 10 s, making it a feasible solution for quick detection in emergency scenarios.

Lead-free perovskite Cs2AgBiBr6 photodetector detecting NIR light driven by titanium nitride plasmonic hot holes

Lead-free perovskite Cs2AgBiBr6 manifests great potential in developing high-performance, environmentally friendly, solution-processable photodetectors (PDs). However, due to the relatively large energy bandgap, the spectrum responses of Cs2AgBiBr6 PDs are limited to the ultraviolet and visible region with wavelengths shorter than 560 nm. In this work, a broadband Cs2AgBiBr6 PD covering the ultraviolet, visible, and near infrared (NIR) range is demonstrated by incorporating titanium nitride (TiN) nanoparticles that are prepared with the assistance of self-assembled polystyrene sphere array. In addition, an atomically thick Al2O3 layer is introduced at the interface between the Cs2AgBiBr6 film and TiN nanoparticles to alleviate the dark current deterioration caused by nanoparticle incorporation. As a result, beyond the spectrum range where Cs2AgBiBr6 absorbs light, the external quantum efficiency (EQE) of the TiN nanoparticle incorporated Cs2AgBiBr6 PD is enhanced significantly compared with that of the control, displaying enhancement factors as high as 2000 over a broadband NIR wavelength range. The demonstrated enhancement in EQE arises from the photocurrent contribution of plasmonic hot holes injected from TiN nanoparticles into Cs2AgBiBr6. This work promotes the development of broadband solution-processable perovskite PDs, providing a promising strategy for realizing photodetection in the NIR region.

Highly ordered arrays of hat-shaped hierarchical nanostructures with different curvatures for sensitive SERS and plasmon-driven catalysis.

Regulation of hot spots exhibits excellent potential in many applications including nanolasers, energy harvesting, sensing, and subwavelength imaging. Here, hat-shaped hierarchical nanostructures with different space curvatures have been proposed to enhance hot spots for facilitating surface-enhanced Raman scattering (SERS) and plasmon-driven catalysis applications. These novel nanostructures comprise two layers of metal nanoparticles separated by hat-shaped MoS2 films. The fabrication of this hybrid structure is based on the thermal annealing and thermal evaporation of self-assembled polystyrene spheres, which are convenient to control the metal particle size and the curvature of hat-shaped nanostructures. Based on the narrow gaps produced by the MoS2 films and the curvature of space, the constructed platform exhibits superior SERS capability and achieves ultrasensitive detection for toxic molecules. Furthermore, the surface catalytic conversion of p-nitrothiophenol (PNTP) to p, p'-dimercaptobenzene (DMAB) was in situ monitored by the SERS substrate. The mechanism governing this regulation of hot spots is also investigated via theoretical simulations.

An efficient double template strategy to construct large-area and highly ordered silver “urchin-like” arrays for sensitive SERS analysis

Plasmonic metal nanostructures possessing plentiful gaps or tips have attracted great attention in surface enhanced Raman scattering (SERS) due to their superior performance. Herein, we present an efficient fabrication strategy to construct a large-area and highly ordered 3D silver “urchin-like” array (SULA) based on the ultra-thin alumina membrane (UTAM) mask and the self-assembled polystyrene spheres template. Numerical simulations reveal that the proposed SULA possesses enormous hotspots at the tips of Ag nanocones and in the crevice gaps between the adjacent Ag nanocaps responsible for high sensitivity with an enhancement factor of 1.8 × 106 and excellent reproducibility with a relative standard deviation of 8.3% in SERS analysis. Furthermore, the SULA substrate exhibits great SERS performance for detecting the contaminant crystal violet and thiram in real water environments and excellent linear intensity-concentration dependence relationships. The results indicate the proposed SULAs are promising to be developed as high-performance SERS platforms in qualitative and quantitative trace contaminants in complex water environments.

Superhydrophilic Coating of Pine Wood by Plasma Functionalization of Self-Assembled Polystyrene Spheres

Self-assembling films typically used for colloidal lithography have been applied to pine wood substrates to change the surface wettability. Therefore, monodisperse polystyrene (PS) spheres have been deposited onto a rough pine wood substrate via dip coating. The resulting PS sphere film resembled a polycrystalline face centered cubic (FCC)-like structure with typical domain sizes of 5–15 single spheres. This self-assembled coating was further functionalized via an O2 plasma. This plasma treatment strongly influenced the particle sizes in the outermost layer, and hydroxyl as well as carbonyl groups were introduced to the PS spheres’ surfaces, thus generating a superhydrophilic behavior.

Large-area crack-free Au–SiO2 2D inverse opal composite films: Fabrication and SERS applications

Plasmonic-photonic metallo-dielectric structures have attracted recent research interests due to their novel optical properties. Au–SiO2 based photonic structures have been built and have shown promising applications for example, as SERS substrates. However, due to the lack of control over the constraints in the various stages of conventional colloidal crystal templating approach, monolayer metallo-dielectric inverse opal structures have not been widely reported. In this work, a 2D hexagonal inverse opal (IO) photonic structure of Au nanoparticles (NP) embedded in a SiO2 matrix is constructed using a new strategy. Here in, a binary Au–SiO2 sol was infiltrated into the accommodative interstices of 2D self-assembled polystyrene (PS) spheres in an air-water interface. Effective removal of the PS spheres by chemical method resulted in Au–SiO2 IO structures. Optical properties of these structures show interesting plasmonic-photonic coupling. When they are used as substrates for Raman signal enhancement of crystal violet, they show better enhancement than either Au nanoparticles aggregates or Au–SiO2 non-photonic structures. The Au–SiO2 IO structures were also used to perform Raman spectroscopy analysis of astaxanthin rich shrimp oil, a novel value-added product extracted from the water used in shrimp processing. The surface enhanced Raman spectra showed the presence of favourable esterified form of astaxanthin in shrimp oil.

Realizing the Control of Electronic Energy Level Structure and Gas-Sensing Selectivity over Heteroatom-Doped In2O3 Spheres with an Inverse Opal Microstructure.

Understanding the effect of substitutional doping on gas-sensing performances is essential for designing high-activity sensing nanomaterials. Herein, formaldehyde sensors based on gallium-doped In2O3 inverse opal (IO-(Ga xIn1- x)2O3) microspheres were purposefully prepared by a simple ultrasonic spray pyrolysis method combined with self-assembled sulfonated polystyrene sphere templates. The well-aligned inverse opal structure, with three different-sized pores, plays the dual role of accelerating the diffusion of gas molecules and providing more active sites. The Ga substitutional doping can alter the electronic energy level structure of (Ga xIn1- x)2O3, leading to the elevation of the Fermi level and the modulation of the band gap close to a suitable value (3.90 eV), hence, effectively optimizing the oxidative catalytic activity for preferential CH2O oxidation and increasing the amount of adsorbed oxygen. More importantly, the gas selectivity could be controlled by varying the energy level of adsorbed oxygen. Accordingly, the IO-(Ga0.2In0.8)2O3 microsphere sensor showed a high response toward formaldehyde with fast response and recovery speeds, and ultralow detection limit (50 ppb). Our findings finally offer implications for designing Fermi level-tailorable semiconductor nanomaterials for the control of selectivity and monitoring indoor air pollutants.

ZnO inverse opals with deposited Ag nanoparticles: Fabrication, characterization and photocatalytic activity under visible light irradiation

Highly ordered porous ZnO inverse opal (ZnO-IO) was manufactured via an auto-forced impregnation approach using self-assembled polystyrene (PS) spheres as colloidal crystal templates. ZnO-IO with deposited silver nanoparticles (Ag/ZnO-IO) was successfully fabricated based on a simple yet efficient photoassisted reduction route using an AgNO3 ethanol-water mixed solution at room temperature and characterized properly by various analytical techniques. Upon visible-light irradiation, the Ag/ZnO-IO composite catalyst exhibited higher photocatalytic activity than pristine ZnO-IO regarding the decolorization of rhodamine B (RhB) in aqueous solution. Such a significant photoactivity improvement was predominantly attributed to surface plasmon resonance (SPR) effect of metallic silver nanoparticles, which could enhance the harvesting of visible light and improve the segregation and transfer of photoinduced charge carriers. The stability of the Ag/ZnO-IO photocatalyst was also investigated with respect to the decomposition of RhB. Furthermore, a plausible degradation mechanism of the Ag/ZnO-IO sample in the course of photocatalytic oxidation of organic pollutants was tentatively put forward from active species trapping experiments. The work reported here may help further progress in design and construction of promising visible-light-induced photocatalysts.

Resonant laser printing of bi-material metasurfaces: from plasmonic to photonic optical response.

Metasurfaces are nanostructured surfaces with engineered optical properties - currently impacting many branches of optics, from miniaturization of optical components to realizing high-resolution structural colors. The optical properties of metasurfaces can be traced to the individual meta-atoms, which set the nature of the optical response, e.g., plasmonic for metallic meta-atoms or photonic for dielectric meta-atoms. Combining multiple types of responses opens up new horizons in design of optical materials, but has so far been avoided due to the fabrication difficulties associated with constructing a metasurface composed of several meta-atom materials. Here, we present a multi-material design approach by optically post-processing a metasurface constructed from self-assembled polystyrene spheres coated with silver. Using our concept of resonant laser printing, we locally alter the initial plasmonic response of the meta-atoms to a pure photonic response. Our work constitutes a conceptually different way of designing metasurfaces and can pave the way for realizing multi-material metasurfaces on large areas while being cost effective.

Surface-enhanced Raman spectroscopy substrate based on Ag-coated self-assembled polystyrene spheres

The silver (Ag) films were deposited on the monodispersed polystyrene spheres that were drop-coated on hydrophilic glass substrates in order to form a self-assembled 2D monolayer. Thus prepared Ag films over polystyrene nanospheres (AgFONs) were used to record the surface-enhanced Raman scattering (SERS) spectra of rhodamine 6G (R6G) and pyridine (λex = 514.5 nm). AgFONs were prepared by depositing 120, 180 and 240 nm thick Ag layer on the 1000 nm polystyrene spheres and 80, 120, 160 and 200 nm thick Ag layer on the 350 nm spheres as well as on their mixture (350 + 1000 nm). The silver was deposited by electron beam evaporation technique. The best enhancement of the Raman signal for both test molecules was obtained using 180 nm Ag film deposited on the 1000 nm spheres and using 80 nm Ag film deposited on the 350 nm polystyrene spheres. The lowest detectable concentrations of R6G and pyridine were 10−9 mol L−1 and 1.2 × 10−3 mol L−1, respectively. This study has shown that AgFONs could be regarded as good and reproducible SERS substrate for analytical detection of various organic molecules.

Preparation of structured surfaces for full-spectrum photon management in photovoltaic-thermoelectric systems

Micro-structured surfaces for broadband and omnidirectional photon management in photovoltaic-thermoelectric systems are fabricated on the silicon wafer by inductively coupled plasma etching with self-assembly polystyrene spheres mask, KOH solution etching and magnetron sputtering method. The Si antireflection structure coated with SiO2 film is fabricated on the top surface of Si substrate to enhance the absorption of the photons with wavelengths of 0.3–1.1µm is increase the electron-hole pairs. The TiO2/SiO2 films as the back-antireflection coating are deposited at the back of Si wafer to improve the transmission of solar energy within the wavelength range of 1.1–2.5µm. The absorbed photons within the wavelength range of 0.3–1.1µm can directly be converted into electricity power by Si solar cells while the photons with wavelengths of 1.1–2.5µm transmit through the cells and are utilized by thermoelectric modules. The effects of etching parameters on the spectral features are investigated to get the optimal etching parameters. With the optimal etching parameters, the surface absorption for the wavelengths of 0.3–1.1µm is significantly increased to above 0.95 due to the effective graded refractive index and the transmission is obviously enhanced for the wavelengths of 1.1–2.5µm. The incident angle-sensitivity and polarization-sensitivity of the fabricated structured surfaces are analyzed. The results indicate that these surfaces can be selected for photovoltaic-thermoelectric systems due to their high omnidirectional absorption and transmission of the photons as well as the favorable polarization-insensitivity within the expected wavelength ranges.

The Influence of Inverse Opal Template and Substrate Type on Electrodeposited 3D Macroporous Oxides

The objective of this study is a detailed investigation into the preparation of V2O5 inverse opals using electrodeposition into preformed colloidal opal templates as a function of electrodeposition parameters (sphere size, voltage, time and substrate). Inverse opals have a range of applications(1-3) and many materials can now be formed into 3D macroporous IO structures.(4-6) Electrodeposition of a VOSO4 aqueous solution in to the inverse opal template is investigated on three different substrates; transparent conducting oxide glass, stainless steel, and thermally oxidized stainless steel. The electrodeposition follows a diffusion limited growth mode to form 3D porous crystalline V2O5 after removal of the colloid photonic crystal template of self-assembled polystyrene spheres. Inverse opals were grown using spheres ranging in diameter from 0.5 µm to 6 µm, and binary inverse opals are also electrodeposited using binary mixtures of sphere size. Analysis of the electrodeposition growth profiles show that IO growth in single and binary opal templates is diffusion limited and that pre-heating stainless steel forms an oxide coating that forces the initial current to increase to a steady state to overcome the resistive oxide, allowing IO to electrodeposit at relatively constant rate. Tortuosity is significantly increased when large sphere diameter templates are used, and especially pronounced when binary opal templates are used, because of interstitial void filling by small spheres in binary opal templates. Raman scattering and X-ray diffraction confirm phase pure, high crystalline quality V2O5 is generally formed in all cases (voltages and substrates). Electrodeposition ensures electrical interconnection within the 3D structured material by definition.

Switchable reflection/transmission utilizing polarization on a plasmonic structure consisting of self-assembly polystyrene spheres with silver patches.

We report a plasmonic structure for switchable reflection and transmission by polarization. The structure is composed of a hexagonal-packed polystyrene sphere array with silver patches on them. Simulations and experiments demonstrated that the conversions between reflected beams and transmitted ones can be performed when the polarization directions of incident beams vary from 0° to 90°. A switchable reflection and transmission at a given wavelength can be obtained, as long as sizes of PS spheres and azimuthal angles are properly chosen. Such a patchy plasmonic structure serving as a switch between reflection and transmission have potential applications in photoelectric control devices.

Magnetization Reversal of Three-Dimensional Nickel Anti-Sphere Arrays

Three-dimensional antisphere arrays (3DAAs) of Ni have been fabricated using electrochemical deposition into self-assembled polystyrene sphere templates, which offers the advantage of straightforward scalability. Using the first-order reversal curve (FORC) method, the magnetic reversal mechanism is identified from the characteristic features in the FORC distribution. A left-bending boomerang-like feature is observed in the thinnest sample, which transforms to a ridge oriented along the local coercivity $H_{c}$ axis with increasing sample thickness. This transformation identifies a change in the reversal process from an exchange dominated domain-growth reversal to a localized weakly interacting particle-like reversal. Micromagnetic simulations confirm the decrease in domain growth and increase of pinning behaviors as the thickness of the Ni 3DAAs structure increases, providing strong support to the FORC analysis and interpretation.

The Influence of Colloidal Opal Template and Substrate Type on 3D Macroporous Single and Binary Vanadium Oxide Inverse Opal Electrodeposition

We report on the electrodeposition of 3D macroporous vanadium oxide inverse opals and binary inverse opals on transparent conducting oxide substrates and stainless steel and thermally oxidized stainless steel substrates. The electrodeposition follows a diffusion limited growth mode to form 3D porous crystalline V2O5 after removal of a colloid photonic crystal template of self-assembled polystyrene spheres. Inverse opals were grown using spheres ranging in diameter from 0.5 μm to 6 μm, and binary inverse opals were also electrodeposited using binary mixtures of sphere sizes. We demonstrate that the ionic diffusion that leads to growth has charge-to-mass Coulombic efficiency ranging from 60–90%, depending on the voltage used. Additionally, the tortuosity in ionic diffusion through the opal to the substrate is significantly increased when large sphere diameter templates and binary opal templates are used. Analysis of the contribution of true substrate active area and the influence of template structure on ionic diffusivity confirms that inverse opal growth is dictated by the size of opal spheres, interstitial void clogging by smaller spheres in binary opals, and the conductivity of the substrate active area. The crystallinity of the inverse opal is consistent and a function of applied voltage, and attains phase pure orthorhombic V2O5.

Synthesis of ordered bowl-like Cu-Cu2O array film for non-enzymatic hydrogen peroxide sensor

Ordered bowl-like Cu-Cu2O array film was successfully fabricated based on a self-assembled monolayer polystyrene sphere template and electrodeposition. This composite product consists of two components: cubic structured Cu and Cu2O with the content rate of 73.6% and 26.4%, respectively. Morphology observation revealed that the prepared Cu-Cu2O film is arranged in an ordered hexagonal close-packed bowl-like pore array with the average pore diameter of about 460nm. The Cu-Cu2O array film combined with the gold layer sputtered on the glass substrate can be used directly as a non-enzymatic hydrogen peroxide sensor. It exhibited much higher sensitivity of 66.23mAmM−1cm−2 attributed to the synergistic effect of Cu-Cu2O array film and good conductivity of the generated Cu.

Sauna-like process prepared periodic molybdenum metal catalytic electrodes and their applications in water reduction

To verify that the molybdenum metals exhibit similar catalysis characteristics as the related molybdenum compounds, i.e. molybdenum selenide (MoSe2) and molybdenum sulfide (MoS2) which have been well known as the high-performing catalysts for hydrogen evolution reactions, we may thus seek a low-cost, process-simplified, scalable, and highly-catalytic counterpart. We have grown periodic molybdenum (Mo) metal catalytic electrodes by employing self-assembled polystyrene (PS) spheres prepared by a sauna-like method as templates, followed by a reactive ion etching (RIE) process with oxygen gas and a double-layer deposition by low-temperature magnetron sputtering. By controlling the etching time of oxygen gas on PS spheres during the RIE process, the lateral and vertical feature sizes of Mo catalytic electrodes can be efficiently controlled, thereby having various surface area ratios. According to surface morphologies from atomic force microscopy, electrochemical linear sweep voltammetry, Tafel, and impendency measurements, we have found that the surface roughness and surface area ratios of Mo metal catalytic electrodes can be enhanced by prolonging the etching times of PS spheres, thereby reducing the charge transfer resistances and Tafel slopes, and then improving the hydrogen evolution reactions at the catalysts/electrolyte interfaces. We attribute this improvement to the fact that the Mo metal catalytic electrodes can efficiently form beneficial Schottky junctions with the electrolyte to enhance the carrier transportation, and the increased surface area ratios can improve the effective area of the Schottky junctions, thereby enhancing the carrier transportation at the catalysts/electrolyte interfaces. Tafel slope of the periodic molybdenum (Mo) metal catalytic electrodes in our work is as low as about 53.9 mV/dec, equivalent to highly catalytic materials MoS2 (55 mV/dec) and MoSe2 (105-120 mV/dec). The proposed periodic Mo catalytic electrodes, which combine a simple sauna-like self-assembly process with a double-layer Mo architecture is scalable and simple; and the surface area of periodic molybdenum (Mo) metal catalytic electrodes can also be flexibly controlled, so that the low-temperature magnetron sputtered Mo metal catalytic electrodes are cost-effective and highly compatible with various photovoltaic devices, highlighting the great potential to form high efficient monolithic solar-water-splitting devices.

Broadband light trapping based on periodically textured ZnO thin films.

Transparent conductive front electrodes (TCFEs) deployed in photovoltaic devices have been extensively studied for their significance in transporting carriers, coupling and trapping the incident photons in high-performing solar cells. The trade-off between the light-transmission, electrical, and scattering properties for TCFEs to achieve a broadband improvement in light absorption in solar cells while maintaining a high electrical performance has become the key issue to be tackled. In this paper, we employ self-assembled polystyrene (PS) spheres based on a sauna-like method as a template, followed by a double-layer deposition and then successfully fabricate highly-transparent, well-conductive, and large-scale periodically-textured ZnO TCFEs with broadband light trapping properties. A sheet resistance below 15 Ω sq(-1) was achieved for the periodically-textured ZnO TCFEs, with a concomitant average transmission of 81% (including the glass substrate) in the 400-1100 nm spectral range, a haze improvement in a broadband spectral range, and a wider scattering angular domain. The proposed approach affords a promising alternative method to prepare periodically-textured TCFEs, which are essential for many optoelectronic device semiconductors, such as photovoltaic and display applications.

Template-assisted self-assembly method to prepare three-dimensional reduced graphene oxide for dopamine sensing

Three-dimensional reduced graphene oxide (3D-rGO) materials have been successfully prepared by a template-assisted self-assembly method using polystyrene spheres (PSs) as sacrificial templates. PSs-rGO hybrids were prepared by self-assembly of PSs and GO through the π–π interaction, followed by reduction of such hybrids using hydrazine as reducing agent. 3D-rGO materials were obtained after removal of PSs in PSs-rGO hybrids by toluene. The combined characterizations of field emission scanning electron microscope (FE-SEM), transmission electron microscope (TEM), X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD) indicate the successful preparation of 3D-rGO materials. More importantly, 3D-rGO materials thus obtained exhibit good sensing performances for electrochemical detection of dopamine (DA), leading to a high-performance DA sensor. The DA sensor based on 3D-rGO materials has been evidenced to exhibit a better sensing performances than that of rGO and poly-(vinylpyrrolidone) (PVP)-stabilizing rGO. Furthermore, differential pulse voltammetry (DPV) indicates that the 3D-rGO-based DA sensor could be effectively used for DA sensing in the presence of ascorbic acid (AA) and uric acid (UA), indicating high selectivity of the DA sensor based on 3D-rGO materials.

Synthesis and photoluminescence properties of ZnS nanobowl arrays via colloidal monolayer template.

Two-dimensional Zinc sulfide (ZnS) nanobowl arrays were synthesized via self-assembled monolayer polystyrene sphere template floating on precursor solution surface. A facile approach was proposed to investigate the morphology evolution of nanobowl arrays by post-annealing procedure. Photoluminescence (PL) measurement of as-grown nanoarrays shows that the spectrum mainly includes two parts: a purple emission peak at 382 nm and a broad blue emission band centering at 410 nm with a shoulder around 459 nm, and a blue emission band at 440 nm was obtained after the annealing procedure. ZnS nanoarrays with special morphologies and PL emission are benefits to their promising application in novel photoluminescence nanodevice.