Nanopatterned Films Research Articles

Sculpting the Electronic Nano-Terrain on a Perovskite Film for Efficient Charge Transport.

Nanopatterned halide perovskites have emerged to improve the performance of optoelectronic devices by controlling the crystallographic and optical properties via morphological modification. However, the correlation between the photophysical property and morphology transformation in nanopatterned perovskite films remains elusive, which hinders the rational design of nanopatterned halide perovskites for optoelectronic devices. In this study, we employed nanoimprinting lithography on a perovskite film to exert a precise control over grain growth and manipulate electronic structures at the level of individual grains. Surface-selective fluorescence lifetime imaging microscopy (FLIM) analyzes the spatiotemporally disentangled geometrical variations in carrier recombination rate and band structure modulation according to different pattern morphologies. Consequently, the stereoscopic mechanism of confined grain growth was unveiled, highlighting the quantitative grain size-based parameters that are crucial for nanoscale material engineering. Notably, the pattern-induced reduction of effective charge mass enabled exclusive control over the subdiffusive carrier transport dynamics on perovskite surfaces, ultimately realizing the surface-selective perovskite photodetectors. The implications of this study are expected to provide valuable guidelines, inspiring innovative design protocols for advancing the next-generation optoelectronic technologies.

Simulated Guidance in Interpreting Nano-Patterned Co70Fe30 Film Imaging with Differential Phase Contrast.

Our paper introduces a simulation-based framework designed to interpret differential phase contrast (DPC) magnetic imaging within the transmission electron microscope (TEM). We investigate patterned magnetic membranes, particularly focusing on nano-patterned Co70Fe30 thin-film membranes fabricated via focused ion beam (FIB) milling. Our direct magnetic imaging reveals regular magnetic domain patterns in these carefully prepared systems. Notably, the observed magnetic structure aligns precisely with micromagnetic simulations based on the dimensions of the underlying nanostructures. This agreement emphasizes the usefulness of micromagnetic simulations, not only for the interpretation of DPC data, but also for the prediction of possible microstructures in magnetic sensor systems with nano-patterns.

Replicated biopolymer pattern on PLLA-Ag basis with an excellent antibacterial response

The design of functional micro or nanostructured surfaces is undergoing extensive research for their intriguing multifunctional properties and for large variety of potential applications in biomedical field (tissue engineering or cell adhesion), electronics, optics or microfluidics. Such nanosized topographies can be easily fabricated by various lithography techniques and can be also further reinforced by synergic effect by combining aforementioned structures along materials with already outstanding antibacterial properties. In this work we fabricated novel micro/nanostructured substrates using soft lithography replication method and subsequent thermal nanoimprint lithography method, creating nanostructured films based on poly (l-lactic acid) (PLLA) fortified by thin silver films deposited by PVD. Main nanoscale patterns were fabricated by replicating surface patterns of optical discs (CDs and DVDs), which proved to be easy, fast and inexpensive method for creating relatively large area patterned surfaces. Their antimicrobial activity was examined in vitro against the bacteria Escherichia coli and Staphylococcus epidermidis strains. The results demonstrated that nanopatterned films actually improved the conditions for bacterial growth compared to pristine PLLA films, the novelty is based on formation of Ag nanoparticles on the surface/and in bulk, while silver nanoparticle enhanced and nanopatterned films exhibited excellent antibacterial activity against both bacterial strains, with circa 80 % efficacy in 4 h and complete bactericidal effect in span of 24 h.

Application of nano-patterned InGaN fabricated by self-assembled Ni nano-masks in green InGaN/GaN multiple quantum wells

The nano-patterned InGaN film was used in green InGaN/GaN multiple quantum wells (MQWs) structure, to relieve the unpleasantly existing mismatch between high indium content InGaN and GaN, as well as to enhance the light output. The different self-assembled nano-masks were formed on InGaN by annealing thin Ni layers of different thicknesses. Whereafter, the InGaN films were etched into nano-patterned films. Compared with the green MQWs structure grown on untreated InGaN film, which on nano-patterned InGaN had better luminous performance. Among them the MQWs performed best when 3 nm thick Ni film was used as mask, because that optimally balanced the effects of nano-patterned InGaN on the crystal quality and the light output.

Electric Field Sensor Based on High Q Fano Resonance of Nano-Patterned Electro-Optic Materials

This paper presents theoretical studies of Fano resonance based electric-field (E-field) sensors. E-field sensor based on two electro-optical (EO) materials i.e., barium titanate (BaTiO3, BTO) nanoparticles and relaxor ferroelectric material Pb(Mg1/3Nb2/3)O3-PbTiO3 (PMN-PT) combined with nanostructure are studied. As for the BTO based E-field sensor, a configuration of filling the BTO nanoparticles into a nano-patterned thin film silicon is proposed. The achieved resonance quality factor (Q) is 11,855 and a resonance induced electric field enhancement factor is of around 105. As for the design of PMN-PT based E-field sensor, a configuration by combining two square lattice air holes in PMN-PT thin film but with one offsetting hole left is chosen. The achieved resonance Q is of 9,273 and an electric field enhancement factor is of around 96. The resonance wavelength shift sensitivity of PMN-PT nanostructured can reach up to 4.768 pm/(V/m), while the BTO based nanostructure has a sensitivity of 0.1213 pm/(V/m). If a spectrum analyzer with 0.1 pm resolution is considered, then the minimum detection of the electric field Emin is 20 mV/m and 0.82 V/m for PMN-PT and BTO based nanostructures, respectively. The nano-patterned E-field sensor studied here are all dielectric, it has therefore the advantage of large measurement bandwidth, high measurement fidelity, high spatial resolution and high sensitivity.

Nano-Patterned Ionogel Film for High-Sensitivity and Recyclable Flexible Pressure Sensor

Flexible pressure sensors have drawn tremendous attention in the past decades due to their widely advanced applications in electronic skin, intelligent robots and wearable devices. Most existing pressure sensors are developed based on capacitive sensing mechanism, but the sensitivity of such sensors still need to be improved. Herein a high-sensitivity pressure sensor was developed based on the P(VDF-HFP)/[Emim][BF₄] ionogel film. The ionogel film has the characteristics of good mechanical flexibility, good ionic conductivity, high dielectric constant and uniformed nanocone array structure, so the flexible pressure sensor which incorporates it as the dielectric layer shows a high sensitivity (22.38 kPa^−1 within 0–3 kPa, and 15.17 kPa^−1 within 3–15 kPa), fast response (0.29 s) and relaxation (0.16 s) time and good long-term stability. The good solubility of the P(VDF-HFP) copolymer in acetone and the non-crosslinking of the [Emim]^+ and [BF₄]^− within the copolymer network give the ionogel the ability to be recycled, thus endowing the critical component of the pressure sensor with 100% recyclability of structure and function. In addition, the sensor was successfully applied to identify fingertip force and map the pressure distribution of different objects, demonstrating that the pressure sensor can be used as part of wearable devices and human–machine interfaces to sense pressure.

Solution-Driven Imprinting Lithography of Sol-Gel ZnO Thin Films for Liquid Crystal Display.

We present a simple and economically convenient method to fabricate nanopatterned ZnO films by imprinting lithography and use them for the layer alignment of liquid crystal (LC) displays. First, a one-dimensional nanopattern was obtained by laser interference lithography on a silicon wafer, and the silicon mold replica was transferred onto a flexible polydimethylsiloxane (PDMS) sheet for conformal patterning. The so-obtained PDMS mold was then applied on a ZnO film spin-coated on a glass substrate. During the imprinting process, the temperature was controlled from 100 to 250 °C to observe the transferring morphologies of the ZnO film; the nanopattern was successfully transferred at annealing temperatures of 200 and 250 °C because the ZnO film at the sol state filled the cavities of the PDMS nanopattern and solidified, forming a negative replica of the nanopattern. The direction of the nanopatterned ZnO film served as a guide for aligning the LC molecules on the LC surface at the centimeter scale and, due to their elastic characteristics and group behavior, propagating their directional states in the LC bulk. The resulting LC cell exhibited an enhanced electro-optical performance and high thermal endurance above 180 °C. The geometry of the alignment layer increased the electric field on the ZnO film and showed reduced threshold voltage. In addition, since flexible devices are generally based on polyimide, which imidized at around 200 °C, the relatively low annealing temperatures of our fabricated nanopatterned ZnO film allow it to be mounted on such devices without any deterioration of the underlying thermoplastic substrate. Therefore, nanopatterned ZnO has a considerable potential for advanced LC displays.

Phonon thermal transport in silicon thin films with nanoscale constrictions and expansions

In patterned thin film devices, abrupt geometric changes can introduce thermal constriction and expansion resistances whose magnitude and relative importance depends on the device's size and geometry as well as the dominant heat carrier mean free path spectra of the comprising material. Existing analytical models of thermal constriction and expansion resistances at the nanoscale have focused primarily on semi-infinite geometries or other situations which are quite different from those encountered in modern nanopatterned thin film devices. In this work, Monte Carlo methods are used to simulate phonon transport in silicon thin films patterned with a commonly utilized source-channel-drain geometry. The length, width, and thickness of the channel region were varied, and the dependence of the thermal constriction–expansion resistance on these parameters was determined. Results show that thin film source–drain reservoirs with diffuse boundary scattering do not behave as semi-infinite reservoirs for feature sizes smaller than approximately 100 nm in silicon near 300 K, and that existing analytical models cannot be readily applied to such systems. In addition, our results support the case that ballistic phonon effects in silicon nanowires at room temperature, if present, are small and not easily observable. Finally, we provide guidance and perspective for Si nanowire measurements near room temperature as to what scenarios may lead to a non-negligible amount of error if constriction–expansion geometry effects are ignored.

A Self‐Assembly Method for Tunable and Scalable Nano‐Stamps: A Versatile Approach for Imprinting Nanostructures

AbstractIn nanoimprint lithography (NIL), the imprinting stamp's fabrication is still a significant cost factor among the consumables. Bottom‐up lithography approaches based on a phase‐separation of polymer blends can provide a cost‐effective route for fabricating these stamps. Today's polymers used to prepare phase‐separated nanostructures (PSN), however, exhibit low glass transition temperatures. As a result, the PSN are prone to in‐plane stamp distortions in the presence of high imprinting pressure and temperature, limiting their practical relevance for NIL. Here, the realization of mechanically and thermally stable PSN‐based imprinting stamps for NIL systems via a phase‐separation of a homopolymer/inorganic–organic hybrid polymer blend is reported. It is demonstrated that these imprinting stamps are easily tunable and scalable by adjusting the formulation of homopolymer/hybrid polymer mixture and deposition conditions. Feature sizes in PSN ranging from a few μm down to 100 nm are achieved through an interplay of these factors. As demonstrations of the envisioned applications, the developed imprinting stamps are integrated into a roll‐to‐roll NIL system for patterning a polystyrene thin‐film. Moreover, light management is demonstrated by nanopatterning of a perovskite semiconductor in plate‐to‐plate process. The nanopatterned perovskite film achieves an integrated absorption and a photoluminescence emission peak increase of 7%rel and 121%rel, respectively.

An investigation of the coupling of phonon-polaritons with plasmon-polaritons in hBN/nanopatterned Au layered devices

Thin hexagonal boron nitride layers have been shown to support highly confined hyperbolic phonon-polaritons, which are of interest for light guiding applications. Localized plasmon resonances in nanopatterned metal films can exhibit subwavelength-scale confinement as well as a high local field strength that is of importance to imaging and sensor applications. In this work, the interaction between hyperbolic phonon-polaritons in a hexagonal boron nitride thin film and plasmon-polaritons in a nanopatterned gold thin film is investigated by means of finite-difference time-domain simulations of a series of coupled and uncoupled layered devices. Both far-field and near-field properties are calculated and analyzed, enabling the features due to plasmon-polaritons and phonon-polaritons, individually, to be distinguished and the coupling between these excitations to be explored and characterized.

Impact of surface topography on the bacterial attachment to micro- and nano-patterned polymer films

The development of antimicrobial surfaces has become a high priority in recent times. There are two ongoing worldwide health crises: the COVID-19 pandemic provoked by the SARS-CoV-2 virus and the antibiotic-resistant diseases provoked by bacteria resistant to antibiotic-based treatments. The need for antimicrobial surfaces against bacteria and virus is a common factor to both crises.Most extended strategies to prevent bacterial associated infections rely on chemical based-approaches based on surface coatings or biocide encapsulated agents that release chemical agents. A critical limitation of these chemistry-based strategies is their limited effectiveness in time while grows the concerns about the long-term toxicity on human beings and environment pollution. An alternative strategy to prevent bacterial attachment consists in the introduction of physical modification to the surface. Pursuing this chemistry-independent strategy, we present a fabrication process of surface topographies [one-level (micro, nano) and hierarchical (micro+nano) structures] in polypropylene (PP) substrates and discuss how wettability, topography and patterns size influence on its antibacterial properties. Using nanoimprint lithography as patterning technique, we report as best results 82 and 86% reduction in the bacterial attachment of E. coli and S. aureus for hierarchically patterned samples compared to unpatterned reference surfaces. Furthermore, we benchmark the mechanical properties of the patterned PP surfaces against commercially available antimicrobial films and provide evidence for the patterned PP films to be suitable candidates for use as antibacterial functional surfaces in a hospital environment.

Water structure at the multilayers of palladium deposited at nanostructured Au electrodes

In situ ATR-SEIRAS experiments were carried out to describe water structure at the surface of multilayers of Pd modified nanopatterned gold film electrodes in contact with aqueous 0.1 M HClO 4 solution. The results show that the surface water becomes more ordered when the thickness of the Pd film increases. The “ice-like water” band becomes stronger and for the electrode with 5 ML Pd@Au, the ratio of “ice-like water” to “liquid-like water” becomes larger than that in bulk water. Concomitantly, the population of “monomers” or small water clusters diminishes. All surface water bands increase when hydrogen adsorption takes place. The bending band corresponding to “monomers” or “multimers” water is observed chiefly at the potentials of hydrogen adsorption.

Preparation of multilayer periodic nanopatterned WO3-based photoanode by reverse nanoimprinting for water splitting

Photoelectrochemical (PEC) water splitting has been studied extensively as an environmentally friendly technology for hydrogen production using solar energy. WO3 is considered a promising semiconducting material for photoanodes due to its high electron mobility, good hole diffusion length, and chemical stability. Periodic nanostructures of WO3 have been investigated for enhancing the PEC performance of WO3-based photoanodes. In this study, facile fabrication of periodic nanostructures of WO3 was achieved using reverse nanoimprint lithography, and the multilayer stacking of nanopatterned WO3 film was also confirmed. The multilayer nanopatterned WO3 films were used as photoanodes for PEC water splitting. The performance of the fabricated photoanode in PEC was 2 times higher than that of planar WO3 film due to its higher light absorbance and lower charge transfer resistance.

Facile fabrication of ordered discontinuous nanotopography on photosensitive substrates for enhanced neuronal differentiation

Controlling the development and morphology of neurons is important for basic neuroscience research as well as for applications in nerve regeneration and neural interfaces. Various studies have shown that nanoscale topographies can promote the development of neuronal cells and the differentiation of neural stem cells; however, the fabrication of these nanotopographical features often involves expensive and sophisticated techniques. Here, we employ nanosphere lens lithography combined with UV-LED technology to create nanopatterns on an SU-8 photoresist. We develop a facile method to create a reusable polystyrene nanosphere (PS-NS) lens array by the spontaneous formation of a hexagonal close-packed array of PS-NSs at a water–air interface and its subsequent transfer to a polydimethylsiloxane carrier film without using any special equipment. We show that this simple technique can create ordered arrays of nanodots on an SU-8 film, the dimensions of which can be controlled by the size of the PS-NSs. When used as a substrate for the neuronal differentiation of pheochromocytoma (PC12) cells, the nanopatterned SU-8 films exhibit enhanced differentiation parameters with respect to conventional tissue culture plastic as compared with their flat counterparts. The method proposed here can greatly facilitate the nanopatterning of various photosensitive substrates for the development of implants for nerve regeneration and neural interfacing.

(Invited) Nanopatterned Perovskite Films for High Performance Photo-Electronics

Ordered nanostructured crystals of thin perovskites films are of great interest to researchers because of the dimensional-dependence of their photoelectronic properties for developing the perovskites with novel properties [1]. In this presentation, both top-down and bottom-up approaches for fabricating nanostructured perovskite films are demonstrated. First, a variety of micro/nanopatterns of a perovskite film are fabricated by either micro/nano-imprinting or transfer-printing a thin spin-coated precursor film in soft-gel state with a topographically pre-patterned polymer mold, followed by thermal treatment for complete conversion of the precursor film to a perovskite one [2]. Second, we also demonstrate a simple and robust route, involving the controlled crystallization of the perovskites templated with a self-assembled block copolymer (BCP), for fabricating nanopatterned perovskite films with various shapes and nanodomain sizes [3]. When the precursor ion solution of a perovskite and poly(styrene)-block-poly(2-vinylpyridine) (PS-b-P2VP) was spin-coated on the substrate, a nanostructured BCP was developed by microphase separation. Spontaneous crystallization of the precursor ions preferentially coordinated with the P2VP domains yielded ordered nanocrystals with various nanostructures. The nanopatterned perovskites showed significantly enhanced photoluminescence (PL) with high resistance to both humidity and heat due to geometrically confining crystals in and passivation with the P2VP chains. Finally, we demonstrate that the perovskite crystals are more precisely controlled by the combination of the BCP self-assembly with top-down nanoimprinting.

Nafion Thin Films: Fabrication of Micro‐ and Nanopatterned Nafion Thin Films with Tunable Mechanical and Electrical Properties Using Thermal Evaporation‐Induced Capillary Force Lithography (Adv. Mater. Interfaces 7/2021)

In article number 2002005, Hyung Jin Kim, Deok-Ho Kim, and co-workers describe a facile method for enhancing the pattern fidelity of Nafion thin films that utilizes a thermal evaporation-induced capillary force lithography with a swelling process. Mechanical and electrical properties of micro- and nano-patterned Nafion films can be controlled by adjusting curing temperature and Nafion concentration.

Light absorption and nanofocusing on a tapered magnetic metasurface

A type of metasurface was constructed on a silicon wafer using a nanopatterned magnetic film to achieve ideal light absorption within a wide wavelength range of 3 μm–15 μm. Using the metasurface, the surface electrons could be localized efficiently into an arrayed planar magnetic nanotip and then modulated by configuring the surface architecture to produce remarkable infrared reflectivity variation. A theoretical analysis showed that the excited surface plasmon exhibit stronger electric field components at the common metal-to-air interface. The Tb14Fe68Co18 nanotip array provided more powerful nanofocusing and a lower infrared reflectivity than an array shaped on a traditional aluminum film. By adjusting the structural parameters of the nanorhombus array formed on the TbCo film system, the convergent light spot could be modulated to improve light absorption markedly.

Self-powered flexible pressure sensors based on nanopatterned polymer films

Purpose The pressure sensors can convert external pressure or mechanical deformation into electrical power and signal, which cannot only detect pressure or strain changes but also harvest energy as a self-powered sensor. This study aims to develop a self-powered flexible pressure sensor based on regular nanopatterned polymer films. Design/methodology/approach In this paper, the self-powered flexible pressure sensor is mainly composed of two nanopatterned polymer films and one conductive electrode layer between them, which is a sandwich structure. The regular nanostructures increase the film roughness and contact area to enhance the friction effect. To enhance the performance of the pressure sensor, different nanostructures on soft polymer sensitive layers are fabricated using UV nanoimprint lithography to generate more triboelectric charges. Findings Finally, the self-powered flexible pressure sensor is prepared, which consists of sub-200 nm resolution regular nanostructures on the surface of the elastic layer and an indium tin oxide electrode thin film. By converting the friction mechanical energy into electrical power, a maximum power of 423.8 mW/m2 and the sensitivity of 0.8 V/kPa at a frequency of 5 Hz are obtained, which proves the excellent sensing performance of the sensor. Originality/value The acquired electrical power and pressure signal by the sensor would be processed in the signal process circuit, which is capable of immediately and sustainably driving the highly integrated self-powered sensor system. Results of the experiments show that this new pressure sensor is a potential method for personal pressure monitoring, featured as being wearable, cost-effective, non-invasive and user-friendly.

Solubility of water in perfluoroalkylalkanes surfactants: Evidence of specific interaction between water and the surfactant molecule

The solubility of water in five liquid perfluoroalkylalkanes was measured as a function of temperature (283 K–313 K) and the thermodynamic functions of solution and solvation were calculated. The studied perfluoroalkylalkanes cover a range of relative lengths of the hydrogenated and perfluorinated segments.This is the first time the solubility of water in these substances has been measured, which is surprising given their pharmaceutical and medical relevance. The new data thus fills an important gap in the literature.The liquid organization of the water-in-PFAAs solutions was further investigated using atomistic molecular dynamics simulations, providing structural and energetic evidence about the solvation shell of water within the different solvents.The results indicate the existence of a specific interaction between the water molecule and the dipole located at the centre of the surfactant molecules, which explains the increased solubility of water in these solvents, relatively to alkanes and perfluoroalkanes. These findings also help to interpret the formation of nano-patterned molecular films of PFAA at the surface of water and of wet silicon wafers.

Liquid–liquid interfaces: Water–perfluoroalkanes and water–perfluoroalkylalkanes, experimental interfacial tensions and molecular simulation

The liquid-liquid interfacial tension of water with four liquid perfluoroalkanes (perfluoropentane, perfluorohexane, perfluorooctane and perfluorononane) and four liquid perfluoroalkylalkanes (perfluorobutylpentane, perfluorobutylhexane, perfluorohexylhexane and perfluorohexyloctane) was measured as a function of temperature in the 273 K–340 K range. The studied perfluoroalkylalkanes cover a range of relative lengths of the hydrogenated and perfluorinated segments.This is the first time the liquid-liquid interfacial tension with water has been measured for these substances, which is surprising given their pharmaceutical and medical relevance. The new data thus fills an important gap in the literature.The organization and interactions of the liquid-liquid interfaces was further investigated using atomistic molecular dynamics simulations, providing structural and energetic information of the systems. The results demonstrate the contribution of the interaction between the water molecule and the dipole located at the center of the perfluoroalkylalkane molecules, which explains the lower interfacial tension of these solvents with water, relatively to alkanes and perfluoroalkanes. Ultimately, these findings will help to interpret the formation of nano-patterned molecular films of PFAA at the surface of water and of wet silicon wafers.