Substrate Patterning Using Regular Macroporous Block Copolymer Monoliths as Sacrificial Templates and as Capillary Microstamps

Polystyrene‐block‐poly(2‐vinylpyridine) (PS‐b‐P2VP) monoliths containing regular arrays of macropores (diameter ≈1.1 µm, depth ≈0.7 µm) at their surfaces are used to pattern substrates by patterning modes going beyond the functionality of classical solid elastomer stamps. In a first exemplary application, the macroporous PS‐b‐P2VP monoliths are employed as sacrificial templates for the deposition of NaCl nanocrystals and topographically patterned iridium films. One NaCl nanocrystal per macropore is formed by evaporation of NaCl solutions filling the macropores followed by iridium coating. Thermal PS‐b‐P2VP decomposition yields topographically patterned iridium films consisting of ordered arrays of hexagonal cells, each of which contains one NaCl nanocrystal. For the second exemplary application, spongy‐continuous mesopore systems are generated in the macroporous PS‐b‐P2VP monoliths by selective‐swelling induced pore generation. Infiltrating the spongy‐continuous mesopore systems with ink allows capillary microstamping of continuous ink films with holes at the positions of the macropores onto glass slides compatible with advanced light microscopy. Capillary microstamping can be performed multiple times under ambient conditions without reinking and without quality deterioration of the stamped patterns. The macroporous PS‐b‐P2VP monoliths are prepared by double replication of primary macroporous silicon molds via secondary polydimethylsiloxane molds.     

Microfluidic Contact Lenses

Contact lens is a ubiquitous technology used for vision correction and cosmetics. Sensing in contact lenses has emerged as a potential platform for minimally invasive point‐of‐care diagnostics. Here, a microlithography method is developed to fabricate microconcavities and microchannels in a hydrogel‐based contact lens via a combination of laser patterning and embedded templating. Optical microlithography parameters influencing the formation of microconcavities including ablation power (4.3 W) and beam speed (50 mm s^?1) are optimized to control the microconcavity depth (100 µm) and diameter (1.5 mm). The fiber templating method allows the production of microchannels having a diameter range of 100–150 µm. Leak‐proof microchannel and microconcavity connections in contact lenses are validated through flow testing of artificial tear containing fluorescent microbeads (Ø = 1–2 µm). The microconcavities of contact lenses are functionalized with multiplexed fluorophores (2 µL) to demonstrate optical excitation and emission capability within the visible spectrum. The fabricated microfluidic contact lenses may have applications in ophthalmic monitoring of metabolic disorders at point‐of‐care settings and controlled drug release for therapeutics.     

Therapeutic Window of Ligand‐Free Silver Nanoparticles in Agar‐Embedded and Colloidal State: In Vitro Bactericidal Effects and Cytotoxicity

The inhibition of bacterial growth through effective non‐toxic antimicrobial substances is of great importance for the prevention and therapy of implant infections in various medical disciplines. For the evaluation of a therapeutic window of silver nanoparticles (AgNPs), their bactericidal properties were tested in agar composites and colloids on four medical relevant bacteria. Therefore, we produced AgNPs using high‐power nanosecond laser ablation in water showing a log‐normal particle diameter distribution centered at 17 nm. Bacteria were incubated with AgNP concentrations ranging from 5 to 70 µg · mL^?1 and the growth rate was recorded. Additionally, cytotoxic effects of AgNPs on human gingival fibroblasts were examined. The experiments demonstrated that laser‐synthesized AgNPs resulted in a significant bacterial growth inhibition of more than 80% at the indicated concentrations in a solid agar model (Pseudomonas aeruginosa 10 µg · mL^?1, Streptococcus salivarius 10 µg · mL^?1, Escherichia coli 20 µg · mL^?1, Staphylococcus aureus 70 µg · mL^?1). In a planktonic bacteria model, the growth of the tested bacteria was significantly delayed by the addition of AgNPs at a concentration of 35 µg · mL^?1. The cytotoxic assays showed limited adverse effects on human fibroblasts at concentrations of less than 20 µg · mL^?1. The present study illustrates the strong antibacterial effects of ligand‐free, laser‐generated AgNPs that exhibit moderate cytotoxic effects, resulting in a therapeutically applicable concentration of AgNPs for medical purposes between 10 and 20 µg · mL^?1.     

Microperforation of Three Common Plastic Films by Laser and Their Enhanced Oxygen Transmission for Fresh Produce Packaging

Three different plastic films of biaxially oriented polypropylene (BOPP), biaxially oriented polyethylene terephthalate (BOPET) and low‐density polyethylene (LDPE) were perforated using Nd‐YAG laser. Effects of laser pulse energy were examined by varying energies from 50 to 250 mJ where the pulse duration and pulse repetition were kept constant at 10 ns and 1 Hz, respectively. It was found that perforation diameters of all films increased with increasing pulse energies. Observed perforations were different among the three film types. Explanation was contributed to material inherent property and its interaction with laser. Incorporation of an inorganic filler (i.e. silica based anti‐blocking agent used in packaging film) of 0.5 wt% into the LDPE films (0.5Si‐LDPE) could improve perforation performance for LDPE. This was attributed to an increased thermal diffusivity of the 0.5Si‐LDPE film. Commercial BOPET and BOPP films containing 97 microholes/m² (hole diameter of ~100 µm) showed an improvement in oxygen transmission rates (OTR) of 18 and 5 times that of the neat films without perforation. In the case of perforated 0.5Si‐LDPE films having similar perforations of 97 microholes/m² and perforation diameter of 100 µm, a two‐fold increase of OTR was obtained. Gas transmission rates of the microperforated films were measured based on the static method. Measured OTR and CO₂TR values of the three films with varying perforation diameters in a range of ~40–300 µm were compared and discussed. Overall results clearly indicate that perforation by laser is an effective process in developing breathable films with tailored oxygen transmission property for fresh produce packaging. Copyright © 2014 John Wiley & Sons, Ltd.     

Anomalous and Polarization‐Sensitive Photoresponse of Td‐WTe2 from Visible to Infrared Light

Recently, an emergent layered material T_d‐WTe₂ was explored for its novel electron–hole overlapping band structure and anisotropic inplane crystal structure. Here, the photoresponse of mechanically exfoliated WTe₂ flakes is investigated. A large anomalous current decrease for visible (514.5 nm), and mid‐ and far‐infrared (3.8 and 10.6 µm) laser irradiation is observed, which can be attributed to light‐induced surface bandgap opening from the first‐principles calculations. The photocurrent and responsivity can be as large as 40 µA and 250 A W^?1 for a 3.8 µm laser at 77 K. Furthermore, the WTe₂ anomalous photocurrent matches its in‐plane crystal structure and exhibits light polarization dependence, maximal for linear laser polarization along the W atom chain a direction and minimal for the perpendicular b direction, with the anisotropic ratio of 4.9. Consistently, first‐principles calculations confirm the angle‐dependent bandgap opening of WTe₂ under polarized light irradiation. The anomalous and polarization‐sensitive photoresponses suggest that linearly polarized light can significantly tune the WTe₂ surface electronic structure, providing a potential approach to detect polarized and broadband lights up to far infrared range.     

Visually Imperceptible Liquid‐Metal Circuits for Transparent,Stretchable Electronics with Direct Laser Writing

A material architecture and laser‐based microfabrication technique is introduced to produce electrically conductive films (sheet resistance = 2.95 Ω sq^?1; resistivity = 1.77 × 10^?6 Ω m) that are soft, elastic (strain limit >100%), and optically transparent. The films are composed of a grid‐like array of visually imperceptible liquid‐metal (LM) lines on a clear elastomer. Unlike previous efforts in transparent LM circuitry, the current approach enables fully imperceptible electronics that have not only high optical transmittance (>85% at 550 nm) but are also invisible under typical lighting conditions and reading distances. This unique combination of properties is enabled with a laser writing technique that results in LM grid patterns with a line width and pitch as small as 4.5 and 100 µm, respectively—yielding grid‐like wiring that has adequate conductivity for digital functionality but is also well below the threshold for visual perception. The electrical, mechanical, electromechanical, and optomechanical properties of the films are characterized and it is found that high conductivity and transparency are preserved at tensile strains of ≈100%. To demonstrate their effectiveness for emerging applications in transparent displays and sensing electronics, the material architecture is incorporated into a couple of illustrative use cases related to chemical hazard warning.     

In Situ Oxidation Synthesis of p‐Type Composite with Narrow‐Bandgap Small Organic Molecule Coating on Single‐Walled Carbon Nanotube: Flexible Film and Thermoelectric Performance

Although composites of organic polymers or n‐type small molecule/carbon nanotube (CNT) have achieved significant advances in thermoelectric (TE) applications, p‐type TE composites of small organic molecules as thick surface coating layers on the surfaces of inorganic nanoparticles still remain a great challenge. Taking advantage of in situ oxidation reaction of thieno[3,4‐b]pyrazine (TP) into TP di‐N‐oxide (TPNO) on single‐walled CNT (SWCNT) surface, a novel synthesis strategy is proposed to achieve flexible films of TE composites with narrow‐bandgap (1.19 eV) small molecule coating on SWCNT surface. The TE performance can be effectively enhanced and conveniently tuned by poly(sodium‐p‐styrenesulfonate) content, TPNO/SWCNT mass ratio, and posttreatment by various polar solvents. The maximum of the composite power factor at room temperature is 29.4 ± 1.0 µW m^?1 K^?2. The work presents a way to achieve flexible films of p‐type small organic molecule/inorganic composites with clear surface coating morphology for TE application.     

Laser treatment of optical Nb2O5‐ and HfO2‐films

Optical thin films have to fulfil high quality requirements, which can be achieved for example by reactive low voltage ion plating (RLVIP). But especially for applications in precision optics, additional treatments are necessary to reduce residual optical absorption and compressive stress arising in the coatings, and to enhance the stability of the coatings – specifically for laser applications. In practice, post deposition heat treatment and backside coatings are mostly used to overcome these problems. In order to provide alternative methods to handle the disadvantages of the RLVIP‐process, the idea was to replace the mentioned steps by a laser treatment. This means that a laser beam is directed onto the sample after deposition or even during the coating process. In this study, the influence of a high power CO²‐laser beam on thin Nb²O⁵‐ and HfO²‐films was investigated. The effects on the refractive index and the film thickness are presented for different energy densities of a TEA‐CO²‐laser beam (10.59μm). For Nb²O⁵‐films a thickness increase up to 12.2nm (6.4 %) and a refractive index decrease of 0.074 (3.1 %) were found. In case of HfO² the values were 2.3nm (1.2 %) in thickness and 0.007 (0.3 %) in refractive index. From the observed changes also distinct impacts on the film stress can be expected. One intention of this research was also to call attention to an alternative technique for enhancement of thin film properties.     

Vacuum‐Drying Processed Micrometer‐Thick Stable CsPbBr3 Perovskite Films with Efficient Blue‐To‐Green Photoconversion

Metal halide perovskite materials have attracted great attention owing to their fascinating optoelectronic characteristics and low cost fabrication via facile solution processing. One of the potential applications of these materials is to employ them as color‐conversion layers (CCLs) for visible blue light to achieve full‐color displays. However, obtaining thick perovskite films to realize complete color conversion is a key challenge. Here, the fabrication of micrometer‐level thick CsPbBr₃ perovskite films is presented through a facile vacuum drying approach. An efficient green photoconversion is realized in a 3.8 µm thick film from blue light @ 463 nm. For a back luminance of 1000 cd m^?2, the brightness of the resulting green emission can reach as high as 200 cd m^?2. Furthermore, only ≈2% of decay in brightness is observed when the films are tested after 18 days of exposure to ambient environment. In addition, a potential design is also proposed for full‐color displays with perovskite materials incorporated as CCLs.     

The influence of laser wavelength on the structure,morphology, and photoluminescence properties of pulsed laser deposited CaS: Eu2+ thin films

Europium-doped calcium sulfide thin films were grown on Si (100) substrates using the pulsed laser deposition technique. The influence of the laser wavelength on the structure, morphology, and photoluminescent properties of the films was studied. The X-ray diffraction data showed that the films were amorphous, except for the (200) diffraction peak observed from the films deposited at the wavelengths of 266 and 355 nm. The atomic force microscopy and Rutherford backscattering spectroscopy data showed that the film deposited at 355 nm was rougher and thicker than those deposited at 266 and 532 nm. As a result, the highest photoluminescence emission intensity around 650 nm was observed from the film deposited at 355 nm. This emission was attributed to the 4f⁶5d¹ → 4f⁷Eu²⁺ transitions of Eu²⁺ observed. These films were evaluated for blue light-emitting diodes.     

Fabry–Pérot Oscillation and Room Temperature Lasing in Perovskite Cube‐Corner Pyramid Cavities

Recently, organometal halide perovskite‐based optoelectronics, particularly lasers, have attracted intensive attentions because of its outstanding spectral coherence, low threshold, and wideband tunability. In this work, high‐quality CH₃NH₃PbBr₃ single crystals with a unique shape of cube‐corner pyramids are synthesized on mica substrates using chemical vapor deposition method. These micropyramids naturally form cube‐corner cavities, which are eminent candidates for small‐sized resonators and retroreflectors. The as‐grown perovskites show strong emission ≈530 nm in the vertical direction at room temperature. A special Fabry–Pérot (F–P) mode is employed to interpret the light confinement in the cavity. Lasing from the perovskite pyramids is observed from 80 to 200 K, with threshold ranging from ≈92 µJ cm^?2 to 2.2 mJ cm^?2, yielding a characteristic temperature of T₀ = 35 K. By coating a thin layer of Ag film, the threshold is reduced from ≈92 to 26 µJ cm^?2, which is accompanied by room temperature lasing with a threshold of ≈75 µJ cm^?2. This work advocates the prospect of shape‐engineered perovskite crystals toward developing micro‐sized optoelectronic devices and potentially investigating light–matter coupling in quantum optics.     

Phase‐Engineered PtSe2‐Layered Films by a Plasma‐Assisted Selenization Process toward All PtSe2‐Based Field Effect Transistor to Highly Sensitive,Flexible, and Wide‐Spectrum Photoresponse Photodetectors

The formation of PtSe₂‐layered films is reported in a large area by the direct plasma‐assisted selenization of Pt films at a low temperature, where temperatures, as low as 100 °C at the applied plasma power of 400 W can be achieved. As the thickness of the Pt film exceeds 5 nm, the PtSe₂‐layered film (five monolayers) exhibits a metallic behavior. A clear p‐type semiconducting behavior of the PtSe₂‐layered film (≈trilayers) is observed with the average field effective mobility of 0.7 cm² V^?1 s^?1 from back‐gated transistor measurements as the thickness of the Pt film reaches below 2.5 nm. A full PtSe₂ field effect transistor is demonstrated where the thinner PtSe₂, exhibiting a semiconducting behavior, is used as the channel material, and the thicker PtSe₂, exhibiting a metallic behavior, is used as an electrode, yielding an ohmic contact. Furthermore, photodetectors using a few PtSe₂‐layered films as an adsorption layer synthesized at the low temperature on a flexible substrate exhibit a wide range of absorption and photoresponse with the highest photocurrent of 9 µA under the laser wavelength of 408 nm. In addition, the device can maintain a high photoresponse under a large bending stress and 1000 bending cycles.     

Ultrafast Processing of Hierarchical Nanotexture for a Transparent Superamphiphobic Coating with Extremely Low Roll‐Off Angle and High Impalement Pressure

Low roll‐off angle, high impalement pressure, and mechanical robustness are key requirements for super‐liquid‐repellent surfaces to realize their potential in applications ranging from gas exchange membranes to protective and self‐cleaning materials. Achieving these properties is still a challenge with superamphiphobic surfaces, which can repel both water and low‐surface‐tension liquids. In addition, fabrication procedures of superamphiphobic surfaces are typically slow and expensive. Here, by making use of liquid flame spray, a silicon dioxide–titanium dioxide nanostructured coating is fabricated at a high velocity up to 0.8 m s^?1. After fluorosilanization, the coating is superamphiphobic with excellent transparency and an extremely low roll‐off angle; 10 µL drops of n‐hexadecane roll off the surface at inclination angles even below 1°. Falling drops bounce off when impacting from a height of 50 cm, demonstrating the high impalement pressure of the coating. The extraordinary properties are due to a pronounced hierarchical nanotexture of the coating.     

Perovskite Nanoparticle Composite Films by Size Exclusion Lithography

Perovskite nanoparticle composite films with capability of high‐resolution patterning (≥2 µm) and excellent resistance to various aqueous and organic solvents are prepared by in situ photosynthesis of acrylate polymers and formamidinium lead halide (FAPbX₃) nanoparticles. Both positive‐ and negative‐tone patterns of FAPbX₃ nanoparticles are created by controlling the size exclusive flow of nanoparticles in polymer networks. The position of nanoparticles is spatially controlled in both lateral and vertical directions. The composite films show high photoluminescence quantum yield (up to 44%) and broad color tunability in visible region (λ_peak = 465–630 nm).     

High‐Concentration Solvent Exfoliation of Graphene

A method is demonstrated to prepare graphene dispersions at high concentrations, up to 1.2 mg mL^?1, with yields of up to 4 wt% monolayers. This process relies on low‐power sonication for long times, up to 460 h. Transmission electron microscopy shows the sonication to reduce the flake size, with flake dimensions scaling as t^?1/2. However, the mean flake length remains above 1 µm for all sonication times studied. Raman spectroscopy shows defects are introduced by the sonication process. However, detailed analysis suggests that predominately edge, rather than basal‐plane, defects are introduced. These dispersions are used to prepare high‐quality free‐standing graphene films. The dispersions can be heavily diluted by water without sedimentation or aggregation. This method facilitates graphene processing for a range of applications.     

Dry Etching with Nanoparticles: Formation of High Aspect‐Ratio Pores and Channels Using Magnetic Gold Nanoclusters

Methods for generating nanopores in substrates typically involve one or more wet‐etching steps. Here a fundamentally different approach to produce nanopores in sheet substrates under dry, ambient conditions, using nanosecond‐pulsed laser irradiation and magnetic gold nanoclusters (MGNCs) as the etching agents is described. Thermoplastic films (50–75 µm thickness) are coated with MGNCs then exposed to laser pulses with a coaxial magnetic field gradient, resulting in high‐aspect ratio channels with tapered cross sections as characterized by confocal fluorescence tomography. The dry‐etching process is applicable to a wide variety of substrates ranging from fluoropolymers to borosilicate glass, with etch rates in excess of 1 µm s^–1. Finite‐element modeling suggests that the absorption of laser pulses by MGNCs can produce temperature spikes of nearly 1000 °C, which is sufficient for generating photoacoustic responses that can drive particles into the medium, guided by magnetomotive force.     

One‐Step Fabrication of Pillar and Crater‐Like Structures on Titanium Using Direct Laser Interference Patterning

Direct laser interference patterning (DLIP) is used to create periodic crater‐ and pillar‐like patterns on titanium surfaces. A Nd:YAG laser operating at 532 nm wavelength with a pulse duration of 8 ns and the ability to control the polarization of each individual beam is used for the laser patterning process. The generated periodic patterns with spatial periods of 5 and 10 μm are produced with energy densities between 0.3 and 5.1 J cm^?2 with a single laser pulse. By varying the polarization of each interfering beam and the energy density, various forms of the occurring topography are observed due to the different shape of the interference intensity pattern and the solidification front of the molten material at the maxima positions. The characterization of the surface chemistry shows that the laser treatment increases the relative content of alumina in the reactive layer from 36% to 51%. The structural analysis of pillar‐like patterned surface shows no changes in microstructure after the laser treatment. Contact angles of 47° ± 7° down to 6° ± 4° are measured on both, crater‐ and pillar‐like surfaces which are significantly lower compared to the untreated reference (79° ± 2°).

     

Dimension‐Controllable Microtube Arrays by Dynamic Holographic Processing as 3D Yeast Culture Scaffolds for Asymmetrical Growth Regulation

Transparent microtubes can function as unique cell culture scaffolds, because the tubular 3D microenvironment they provide is very similar to the narrow space of capillaries in vivo. However, how to realize the fabrication of microtube‐arrays with variable cross‐section dynamically remains challenging. Here, a dynamic holographic processing method for producing high aspect ratio (≈20) microtubes with tunable outside diameter (6–16 µm) and inside diameter (1–10 µm) as yeast culture scaffolds is reported. A ring‐structure Bessel beam is modulated from a typical Gaussian‐distributed femtosecond laser beam by a spatial light modulator. By combining the axial scanning of the focused beam and the dynamic display of holograms, dimension‐controllable microtube arrays (straight, conical, and drum‐shape) are rapidly produced by two‐photon polymerization. The outside and inside diameters, tube heights, and spatial arrangements are readily tuned by loading different computer‐generated holograms and changing the processing parameters. The transparent microtube array as a nontrivial tool for capturing and culturing the budding yeasts reveals the significant effect of tube diameter on budding characteristics. In particular, the conical tube with the inside diameter varying from 5 to 10 µm has remarkable asymmetrical regulation on the growth trend of captured yeasts.     

Aligning Solution‐Derived Carbon Nanotube Film with Full Surface Coverage for High‐Performance Electronics Applications

The main challenge for application of solution‐derived carbon nanotubes (CNTs) in high performance field‐effect transistor (FET) is how to align CNTs into an array with high density and full surface coverage. A directional shrinking transfer method is developed to realize high density aligned array based on randomly orientated CNT network film. Through transferring a solution‐derived CNT network film onto a stretched retractable film followed by a shrinking process, alignment degree and density of CNT film increase with the shrinking multiple. The quadruply shrunk CNT films present well alignment, which is identified by the polarized Raman spectroscopy and electrical transport measurements. Based on the high quality and high density aligned CNT array, the fabricated FETs with channel length of 300 nm present ultrahigh performance including on‐state current I_on of 290 µA µm^?1 (V_ds = ?1.5 V and V_gs = ?2 V) and peak transconductance g_m of 150 µS µm^?1, which are, respectively, among the highest corresponding values in the reported CNT array FETs. High quality and high semiconducting purity CNT arrays with high density and full coverage obtained through this method promote the development of high performance CNT‐based electronics.     

Surface Dependence of Protein Nanocrystal Formation

The self‐assembly kinetics and nanocrystal formation of the bacterial surface‐layer‐protein SbpA are studied with a combination of quartz crystal microbalance with dissipation monitoring (QCM‐D) and atomic force microscopy (AFM). Silane coupling agents, aminopropyltriethoxysilane (APTS) and octadecyltrichlorosilane (OTS), are used to vary the protein–surface interaction in order to induce new recrystallization pathways. The results show that the final S‐layer crystal lattice parameters (a = b = 14 nm, γ = 90°), the layer thickness (15 nm), and the adsorbed mass density (1700 ng cm^?2) are independent of the surface chemistry. Nevertheless, the adsorption rate is five times faster on APTS and OTS than on SiO_2, strongly affecting protein nucleation and growth. As a consequence, protein crystalline domains of 0.02 µm² for APTS and 0.05 µm² for OTS are formed, while for silicon dioxide the protein domains have a typical size of about 32 µm². In addition, more‐rigid crystalline protein layers are formed on hydrophobic substrates. In situ AFM experiments reveal three different kinetic steps: adsorption, self‐assembly, and crystalline‐domain reorganization. These steps are corroborated by frequency–dissipation curves. Finally, it is shown that protein adsorption is a diffusion‐driven process. Experiments at different protein concentrations demonstrate that protein adsorption saturates at 0.05 mg mL^?1 on silane‐coated substrates and at 0.07 mg mL^?1 on hydrophilic silicon dioxide.