Reverse Nanoimprint Lithography Research Articles

Biomimetic Transparent Nanoplasmonic Meshes by Reverse-Nanoimprinting for Bio-Interfaced Spatiotemporal Multimodal SERS Bioanalysis.

Multicellular systems, such as microbial biofilms and cancerous tumors, feature complex biological activities coordinated by cellular interactions mediated via different signaling and regulatory pathways, which are intrinsically heterogeneous, dynamic, and adaptive. However, due to their invasiveness or their inability to interface with native cellular networks, standard bioanalysis methods do not allow in situ spatiotemporal biochemical monitoring of multicellular systems to capture holistic spatiotemporal pictures of systems-level biology. Here, a high-throughput reverse nanoimprint lithography approach is reported to create biomimetic transparent nanoplasmonic microporous mesh (BTNMM) devices with ultrathin flexible microporous structures for spatiotemporal multimodal surface-enhanced Raman spectroscopy (SERS) measurements at the bio-interface. It is demonstrated that BTNMMs, supporting uniform and ultrasensitive SERS hotspots, can simultaneously enable spatiotemporal multimodal SERS measurements for targeted pH sensing and non-targeted molecular detection to resolve the diffusion dynamics for pH, adenine, and Rhodamine 6G molecules in agarose gel. Moreover, it is demonstrated that BTNMMs can act as multifunctional bio-interfaced SERS sensors to conduct in situ spatiotemporal pH mapping and molecular profiling of Escherichia coli biofilms. It is envisioned that the ultrasensitive multimodal SERS capability, transport permeability, and biomechanical compatibility of the BTNMMs can open exciting avenues for bio-interfaced multifunctional sensing applications both in vitro and in vivo.

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.

Design of mid-infrared filter array based on plasmonic metal nanodiscs array and its application to on-chip spectrometer

Mid-infrared wavelengths are called the molecular fingerprint region because it contains the fundamental vibrational modes inherent to the substances of interest. Since the mid-infrared spectrum can provide non-destructive identification and quantitative analysis of unknown substances, miniaturized mid-infrared spectrometers for on-site diagnosis have attained great concern. Filter-array based on-chip spectrometer has been regarded as a promising alternative. In this study, we explore a way of applying a pillar-type plasmonic nanodiscs array, which is advantageous not only for excellent tunability of resonance wavelength but also for 2-dimensional integration through a single layer process, to the multispectral filter array for the on-chip spectrometer. We theoretically and experimentally investigated the optical properties of multi-periodic triangular lattices of metal nanodiscs array that act as stopband filters in the mid-infrared region. Soft-mold reverse nanoimprint lithography with a subsequent lift-off process was employed to fabricate the multispectral filter array and its filter function was successfully extracted using a Fourier transform infrared microscope. With the measured filter function, we tested the feasibility of target spectrum reconstruction using a Tikhonov regularization method for an ill-posed linear problem and evaluated its applicability to the infrared spectroscopic sensor that monitors an oil condition. These results not only verify that the multispectral filter array composed of stopband filters based on the metal nanodiscs array when combined with the spectrum reconstruction technique, has great potential for use to a miniaturized mid-infrared on-chip spectrometer, but also provide effective guidance for the filter design.

3D Micro/Nanopatterning of a Vinylferrocene Copolymer.

In nanoimprint lithography (NIL), a pattern is created by mechanical deformation of an imprint resist via embossing with a stamp, where the adhesion behavior during the filling of the imprint stamp and its subsequent detachment may impose some practical challenges. Here we explored thermal and reverse NIL patterning of polyvinylferrocene and vinylferrocene-methyl methacrylate copolymers to prepare complex non-spherical objects and patterns. While neat polyvinylferrocene was found to be unsuitable for NIL, freshly-prepared vinylferrocene-methyl methacrylate copolymers, for which identity and purity were established, have been structured into 3D-micro/nano-patterns using NIL. The cross-, square-, and circle-shaped columnar structures form a 3 × 3 mm arrangement with periodicity of 3 µm, 1 µm, 542 nm, and 506 nm. According to our findings, vinylferrocene-methyl methacrylate copolymers can be imprinted without further additives in NIL processes, which opens the way for redox-responsive 3D-nano/micro-objects and patterns via NIL to be explored in the future.

Angle-dependent structural colors in a nanoscale-grating photonic crystal fabricated by reverse nanoimprint technology.

The structural color of angle-sensitive photonic crystals has attracted great interest because of a possible application in visual sensors. The appearance of a photonic crystal is mainly influenced by the optical properties, structural parameters and the observation angle. In this work, an angle-sensitive photonic crystal with nanoscale gratings was fabricated through reverse nanoimprint lithography. The periodicity and the structural color were investigated through measuring reflection spectra. The structural color of the photonic crystal has a period of 90°. Distinctive colors spanning the entire visible spectrum can be seen when the crystal is rotated. In addition, there is a blue-shift of the peak wavelength when the observation angle is increased. An equation for the observed wavelength as a function of the observation angle is proposed.

Multifunctional guest–host particles engineered by reversal nanoimprint lithography

Particulate polymeric microfibers with incorporated europium(III)oxide (Eu2O3) nanoparticles were introduced as a magneto-photoluminescent multifunctional material fabricated via reversal nanoimprint lithography. To specifically address the volume properties of these guest–host particles, the guest, Eu2O3, was milled down to an average particle size of 350 nm in diameter and mixed with the host-polymer, AMONIL®, before in situ hardening in the imprint stamp. The variation of the fabrication process parameters, i.e. delay time, spin coating speed, as well as the concentration of Eu2O3 nanoparticles was proven to have a significant impact on both the structure quality and the stamp release of the microfibers with respect to the formation of a thinner residual layer. Structural characterization performed by SEM revealed optimum fabrication process parameters for a homogeneous spatial distribution of Eu2O3 nanoparticles within the microfibers while simultaneously avoiding the formation of undesired agglomerates. The magneto-photoluminescent properties of Eu2O3 nanoparticles, i.e. a red emission at 613 nm and a paramagnetic response, were found to be superimposed to the optic and the diamagnetic behaviors of AMONIL®. The results imply that guest–host interdependence of these properties can be excluded and that the suggested technique enables for specific tailoring of particulate multifunctional materials with focus on their volume properties.

Food Quality Monitor: Paper-Based Plasmonic Sensors Prepared Through Reversal Nanoimprinting for Rapid Detection of Biogenic Amine Odorants.

This paper describes the fabrication of paper-based plasmonic refractometric sensors through the embedding of metal nanoparticles (NPs) onto flexible papers using reversal nanoimprint lithography. The NP-embedded papers can serve as gas sensors for the detection of volatile biogenic amines (BAs) released from spoiled food. Commercial inkjet papers were employed as sensor substrates-their high reflectance (>80%) and smooth surfaces (roughness: ca. 4.9 nm) providing significant optical signals for reflection-mode plasmonic refractometric sensing and high particle transfer efficiency, respectively; in addition, because inkjet papers have lightweight and are burnable and flexible, they are especially suitable for developing portable, disposable, cost-effective, eco-friendly sensing platforms. Solid silver NPs (SNPs), solid gold NPs (GNPs), and hollow Au-Ag alloyed NPs (HGNs) were immobilized on a solid mold and then transferred directly onto the softened paper surfaces. The particle number density and exposure height of the embedded NPs were dependent on two imprinting parameters: applied pressure and temperature. The optimal samples exhibited high particle transfer efficiency (ca. 85%), a sufficient exposure surface area (ca. 50% of particle surface area) presented to the target molecules, and a strong resonance reflectance dip for detection. Moreover, the HGN-embedded paper displayed a significant wavelength dip shift upon the spontaneous adsorption of BA vapors (e.g., Δλ = 33 nm for putrescine; Δλ = 24 nm for spermidine), indicating high refractometric sensitivity; in contrast, no visible spectroscopic responses were observed with respect to other possibly coexisting gases (e.g., air, N2, CO2, water vapor) during the food storage process, indicating high selectivity. Finally, the plasmonic sensing papers were used to monitor the freshness of a food product (salmon).

Printable photonic crystals with high refractive index for applications in visible light

Nanoimprint lithography (NIL) of functional high-refractive index materials has proved to be a powerful candidate for the inexpensive manufacturing of high-resolution photonic devices. In this paper, we demonstrate the fabrication of printable photonic crystals (PhCs) with high refractive index working in the visible wavelengths. The PhCs are replicated on a titanium dioxide-based high-refractive index hybrid material by reverse NIL with almost zero shrinkage and high-fidelity reproducibility between mold and printed devices. The optical responses of the imprinted PhCs compare very well with those fabricated by conventional nanofabrication methods. This study opens the road for a low-cost manufacturing of PhCs and other nanophotonic devices for applications in visible light.

Ferroelectric polymer nanopillar arrays on flexible substrates by reverse nanoimprint lithography

Large area ferroelectric polymer nanopillar arrays were prepared directly on flexible substrates using soft-mold reverse nanoimprint lithography at low pressure.

Fabrication of ferroelectric polymer nanostructures on flexible substrates by soft-mold reverse nanoimprint lithography

Conventional nanoimprint lithography with expensive rigid molds is used to pattern ferroelectric polymer nanostructures on hard substrate for use in, e.g., organic electronics. The main innovation here is the use of inexpensive soft polycarbonate molds derived from recordable DVDs and reverse nanoimprint lithography at low pressure, which is compatible with flexible substrates. This approach was implemented to produce regular stripe arrays with a spacing of 700 nm from vinylidene fluoride co trifluoroethylene ferroelectric copolymer on flexible polyethylene terephthalate substrates. The nanostructures have very stable and switchable piezoelectric response and good crystallinity, and are highly promising for use in organic electronics enhanced or complemented by the unique properties of the ferroelectric polymer, such as bistable polarization, piezoelectric response, pyroelectric response, or electrocaloric function. The soft-mold reverse nanoimprint lithography also leaves little or no residual layer, affording good isolation of the nanostructures. This approach reduces the cost and facilitates large-area, high-throughput production of isolated functional polymer nanostructures on flexible substrates for the increasing application of ferroelectric polymers in flexible electronics.

The variation of the enhanced PL efficiency of Y2O3:Eu3+ phosphor films with the height to the ZrO2 nanoparticle-assisted 2D PCL by reverse nano-imprint lithography

We developed a zirconium oxide (ZrO2) nanoparticle-assisted photonic structure for improving the light extraction efficiency of Y2O3:Eu3+ phosphor films by reverse nano-imprint lithography approach. The structural effect of a two-dimensional (2D) ZrO2 nanoparticle photonic crystal (PC) pattern on the extraction efficiency of photoluminescence (PL) from the underlying Y2O3:Eu3+ phosphor film was investigated. The 2D photonic crystal structure was fabricated using a reverse nano-imprint process with a ZrO2 nanoparticle solution as a nano-imprint resin and a patterned trimethylolpropane propoxylate triacrylate (TPT)/polydimethylsiloxane (PDMS) stamp as a mold. We controlled height of ZrO2 nanoparticle patterns in the range 190–370nm by varying the height of master mold. This simple process results in 6.9 times improvement of extraction efficiency for a 2D ZrO2 nanoparticle-assisted photonic crystal pattern (h=∼370nm) compared to the conventional Y2O3:Eu3+ thin-film phosphors.

Residual layer-free Reverse Nanoimprint Lithography on silicon and metal-coated substrates

In this work we demonstrate that Reverse Nanoimprint Lithography is a feasible and flexible lithography technique applicable to the transfer of micro and nano polymer structures with no residual layer over areas of cm2 areas on silicon, metal and non-planar substrates. We used a flexible polydimethylsiloxane stamp with hydrophobic features. We present residual layer-free patterns imprinted using a commercial poly(methylmethacrylate) thermoplastic polymer over silicon, nickel and pre-patterned substrates. Our versatile patterning technology is adaptable to free form nano structuring and has coupling to adhesion technologies.

Fabrication of Superhydrophobic and Oleophobic Surfaces with Overhang Structure by Reverse Nanoimprint Lithography

This work reports the fabrication of superhydrophobic and oleophobic surfaces with an overhang structure by reverse nanoimprint lithography. An overhang structure is difficult to fabricate by conventional lithography; however, it was conveniently formed by reverse imprint lithography, employed in conjunction with reactive ion etching. The obtained overhang structure was coated with a fluoroalkylsilane monolayer to reduce its surface energy. Further, four different types of nanopatterns were separately embedded on the surface of the obtained overhang structure by modified reverse imprint lithography to enhance its oil-repelling properties. The embedded nanopatterns resulted in different overhang angles, thereby enhancing the oil-repelling properties. The morphology and wetting characteristics of the overhang structure were investigated by scanning electron microscopy and contact angle measurements. This study demonstrates that an overhang structure can be successfully fabricated on a substrate by reverse n...

Reverse Nanoimprint Lithography for Fabrication of Nanostructures

Reverse Nanoimprint Lithography for Fabrication of Nanostructures

Biomimetic nanostructured antireflection coating and its application on crystalline silicon solar cells

In this report, we demonstrate the implementation of biomimetic nanostructured antireflection coatings with polymethyl methacrylate (PMMA) layer on the micro-textured surface of silicon crystalline solar cells. To reduce cost, the process combines colloidal lithography, cast molding method, and reversal nanoimprint lithography. The technique is simple, low cost, and does not cause damage to the thin and brittle conventional crystalline solar cells. The antireflection properties of this biomimetic nanostructure coating are considered as effective as those of a conventional single-layer SiNx thin film. The resultant structures alone could reduce the average reflectance of solar cell from 13.2% to 7.8% and enhance power conversion efficiency from 12.85% to 14.2%.

Pattern transfer of nano-scale ferroelectric PZT gratings by a reversal nanoimprint lithography

Nanoscale PZT gratings are successfully transferred to a Pt substrate using reversal nanoimprint technique without any chemical etch processes. The transfer process is preliminarily studied by measuring the surface topography of PZT coated on templates before transferring as well as the transferred patterns on substrates. Piezoelectric force microscopy (PFM) and Raman spectroscopy are used to investigate the transferred PZT nanostructures after annealing. Good ferroelectric and structural properties have been demonstrated by the transferred PZT nanostructures, indicating that this reversal imprint technique is applicable for forming nanoscale PZT domains, which may lead to the manufactures of high density data storage devices at economic cost.

Use of Reversal Nanoimprinting of Nanoparticles to Prepare Flexible Waveguide Sensors Exhibiting Enhanced Scattering of the Surface Plasmon Resonance

A flexible surface plasmon resonance (SPR)-based scattering waveguide sensor is prepared by directly imprinting hollow gold nanoparticles (NPs) and solid gold NPs onto flexible polycarbonate (PC) plates—without any surface modification—using a modified reversal nanoimprint lithography technology. Controlling the imprinting conditions, including temperature and pressure, allows for the fine adjustment of the depths of the embedded metal NPs and their SPR properties. This patterning approach exhibits a resolution down to the submicrometer level. A 3D finite-difference time domain simulation is used to examine the optical behavior of light propagating parallel to the air/substrate interface within the near-field regime. Consistent with the simulations, almost an order of magnitude enhancement in the scattering signal after transferring the metal NPs from the glass mold to the PC substrate is obtained experimentally. The enhanced signal is attributed to the particles' strong scattering of the guiding-mode waves (within the waveguide) and the evanescent wave (above the waveguide) simultaneously. Finally, the imprinting conditions are optimized to obtain a strongly scattering bio/chemical waveguide sensor.

Evaluation of nanoimprint lithography as a fabrication method of distributed feedback laser diodes

We have succeeded in employing nanoimprint lithography (NIL) to form the diffraction gratings of distributed feedback laser diodes (DFB LDs) used in optical communication. Uniform gratings and phase-shifted gratings with periods of 232 nm have been formed by using a reverse NIL with a step-and-repeat imprint tool. Line edge roughness has been sufficiently low with the fabricated gratings. DFB LDs fabricated by NIL have indicated comparable characteristics with LDs fabricated by electron beam lithography. We have also demonstrated that phase-shifted DFB LDs show better uniformity in characteristics than uniform-grating DFB LDs. The results of this study indicate that NIL has high potential for the fabrication of DFB LDs.

Evaluation of nanoimprint lithography as a fabrication process of phase-shifted diffraction gratings of distributed feedback laser diodes

The authors have succeeded in employing nanoimprint lithography (NIL) to form diffraction gratings of distributed feedback laser diodes (DFB LDs) used in optical communication. Uniform gratings and phase-shifted gratings with periods of 232 nm have been formed by using a reversal NIL with a step-and-repeat imprint tool. Line edge roughness has been sufficiently low with the fabricated gratings. DFB LDs fabricated by NIL have indicated comparable characteristics with LDs fabricated by electron beam lithography. LDs show high long-term stability in threshold current. The authors have also demonstrated that phase-shifted DFB LDs show better uniformity in characteristics than uniform-grating DFB LDs. The results of this study indicate that NIL has high potential for fabricating DFB LDs.

Fabrication of complex nanoscale structures on various substrates

Polymer based complex nanoscale structures were fabricated and transferred to various substrates using reverse nanoimprint lithography. To facilitate the fabrication and transference of the large area of the nanostructured layer to the substrates, a water-soluble polyvinyl alcohol mold was used. After generation and transference of the nanostructured layer, the polyvinyl alcohol mold was removed by dissolving in water. A residue-free, UV-curable, glue layer was formulated and used to bond the nanostructured layer onto the substrates. As a result, nanometer scale patterned polymer layers were bonded to various substrates and three-dimensional nanostructures were also fabricated by stacking of the layers.