Combining Nanoimprint Lithography Research Articles

Stretchable Metamaterials with Tamm/Fano Resonances for Tunable, Efficient Mechanochromic Color Shifting

AbstractNext‐generation wearable and optoelectronic technologies requires highly adaptable light manipulation capabilities for applications in sensors, displays, and optical switches on flexible substrates. Here, a cost‐effective approach is presented for realizing a Tamm Plasmon (TP) resonant device on a flexible platform by combining nanoimprint lithography with layer‐by‐layer assembly. The TP device incorporates a stretchable, 1D bragg (BRG) stack coupled with a gold (Au) and aluminum (Al) metasurface, whose dimensions are designed to enable tunability in the visible and near‐infrared (NIR) regions of the spectrum. The device exhibits substantial reflected intensities (≈75%) and a well‐defined, narrow TP minimum of approximately 30 nm. Both TP and Fano resonances can be clearly observed by incorporating symmetry‐broken metasurface features with the BRG stack. The integrated system is subjected to both uniaxial (up to 37% strain) and biaxial (up to 25% strain) stretching, demonstrating dynamic chromatic responses in both the visible and near‐infrared regimes with sensitivities of ≈6.2 nm/%. This work clearly demonstrates a cost‐effective route for the fabrication of multi‐plasmon resonant devices with tunable colors on a flexible platform.

Nanoimprint Lithography for Next-Generation Carbon Nanotube-Based Devices.

This research reports the development of 3D carbon nanostructures that can provide unique capabilities for manufacturing carbon nanotube (CNT) electronic components, electrochemical probes, biosensors, and tissue scaffolds. The shaped CNT arrays were grown on patterned catalytic substrate by chemical vapor deposition (CVD) method. The new fabrication process for catalyst patterning based on combination of nanoimprint lithography (NIL), magnetron sputtering, and reactive etching techniques was studied. The optimal process parameters for each technique were evaluated. The catalyst was made by deposition of Fe and Co nanoparticles over an alumina support layer on a Si/SiO2 substrate. The metal particles were deposited using direct current (DC) magnetron sputtering technique, with a particle ranging from 6 nm to 12 nm and density from 70 to 1000 particles/micron. The Alumina layer was deposited by radio frequency (RF) and reactive pulsed DC sputtering, and the effect of sputtering parameters on surface roughness was studied. The pattern was developed by thermal NIL using Si master-molds with PMMA and NRX1025 polymers as thermal resists. Catalyst patterns of lines, dots, and holes ranging from 70 nm to 500 nm were produced and characterized by scanning electron microscopy (SEM) and atomic force microscopy (AFM). Vertically aligned CNTs were successfully grown on patterned catalyst and their quality was evaluated by SEM and micro-Raman. The results confirm that the new fabrication process has the ability to control the size and shape of CNT arrays with superior quality.

Actively Tunable Spectral Filter for Compact Hyperspectral Camera Using Angle‐Sensitive Plasmonic Structures

AbstractHyperspectral imaging provides enhanced classification and identification of veiled features for diverse biomedical applications such as label‐free cancer detection or non‐invasive vascular disease diagnostics. However, hyperspectral cameras still have technical limitations in miniaturization due to the inherently complex and bulky configurations of conventional tunable filters. Herein, a compact hyperspectral camera using an active plasmonic tunable filter (APTF) with electrothermally driven spectral modulation for feature‐augmented imaging is reported. APTF consists of angle‐sensitive plasmonic structures (APS) over an electrothermal MEMS (Microelectromechanical systems) actuator, fabricated by combining nanoimprint lithography, and MEMS fabrication ona 6‐inch wafer. APS have a complementary configuration of Au nanohole and nanodisk arrays supported on asilicon nitride membrane. APTF shows a large angular motion at operational voltages of 5–9 VDC for continuous spectral modulation between 820 and 1000 nm (45 nm/V). The compact hyperspectral camera was fully packaged with a linear polarizer, APTF and amonochromatic camera, exhibiting asize of 16 mm (ϕ) × 9.5 mm (h). Feature‐augmented images of subcutaneous vein and a fresh fruit have been successfully demonstrated after the hyperspectral reconstruction and spectral feature extraction. This functional camera provides a new compact platform for point‐of‐care or in vivo hyperspectral imaging in biomedical applications.

Template‐Electrodeposited Plasmonic Metasurfaces for High‐Sensitivity Biomolecular Detection

AbstractBiomolecular detection is crucially significant for the medical and healthcare industries. The plasmonic metasurface is one of the ideal sensors that can be utilized for biomolecular detection. However, how to realize the more cost‐effective fabrication of plasmonic metasurfaces has always been a research hotspot. Herein, one combines nanoimprint lithography, electrodeposition, and nanotransfer printing to fabricate the electrodeposition template with nanoscale resolution. Centimeter‐scale plasmonic metasurfaces with uniform hexagonal gold nanopillar arrays are successfully fabricated via utilizing the electrodeposition template within several minutes. The plasmonic metasurfaces exhibit comparable performance with other reported metasurfaces fabricated through conventional approaches in refractometric sensing and immunoglobulin G (IgG) biomolecular detection. The electrodeposition template can be reused more than ten times, and the performance of successive plasmonic metasurfaces fabricated using the same template is highly consistent. Moreover, the novel fabrication of flexible metasurfaces may also be of interest to many other practical applications such as structural color, surface‐enhanced Raman spectroscopy (SERS), and fluorescence enhancement.

Introducing surface functionality on thermoformed polymeric films

We present a fabrication process for the production of 3-dimensional micro-structured polymeric films. The microstructures are fabricated in a single step using thermal nanoimprint lithography as patterning technique. The micro-structured polymer films are then transformed into a 3D shape by means of a plug-assisted thermoforming process, while keeping the functionality of the micro-patterned areas. The preserved functionality is characterized by water contact angle measurements, while the deformation of the micro-structured topographies due to the thermoforming process is analyzed using confocal microscopy and Digital Image Correlation (DIC) techniques. This combined fabrication process represents a promising solution to complement in-mold decoration approaches, enabling the production of new functional surfaces. As the microstructures are fabricated by means of a mechanical modification of the surface, without the need of chemical treatments or coatings, the presented technique represents a promising, simple and green solution, suitable for the industrial fabrication of 3D nonplanar shaped functional surfaces. • A method to produce 3-dimensional micro-structured polymeric films by combination of nanoimprint lithography and thermoforming is presented • The surface microstructures defined by Nanoimprint Lithography induce surface hydrophobicity which is maintained after the thermoforming process. The microstructures defined by nanoimprint induce surface hydrophobicity which is maintained after the thermoforming process. • The strain induced by the thermoforming process deforms the microstructure, affecting the functional properties. • This combined process complement in-mold decoration approaches with the introduction of new functional surfaces.

Controlled SOI nanopatterning for GaN pendeo-epitaxy

Nanopatterning of GaN/AlN layers on Silicon-On-Insulator (SOI) substrates is discussed with the aim of fabricating nanopillar arrays that can be used for subsequent GaN pendeo-epitaxy. The principle of the developed epitaxy process is that GaN crystallites are grown on deformable nano-pedestals able to rotate at GaN growth temperature. The objective is to control the complete pattern profile of GaN/AlN/Si/SiO 2 pillars, both in lateral and vertical directions. Since a smaller pillar diameter should enhance the pillar rotation at growth temperature, special emphasis will be given to nanometer-scale pillars. In this context, the control of GaN/AlN vertical sidewalls is still an issue for high-resolution nanopillars. In this paper, we report on the optimization of the plasma etching processes of GaN/AlN/Si/SiO 2 stacks to reduce the slope that widens the pillar base. Overall, we achieve near perfect arrays of 100 nm diameter nanopillars obtained by combining NanoImprint Lithography (NIL) and plasma etching, with bases of 150 nm in diameter. • Nanopatterning of GaN/AlN layers on SOI substrates • Controlled GaN/AlN etched sidewalls for high-resolution nanopillars • NIL Combined with ICP to achieve near perfect arrays of 100 nm diameter nanopillars

Nanoimprinted multifunctional nanoprobes for a homogeneous immunoassay in a top-down fabrication approach

Multifunctional nanoparticles are discussed as versatile probes for homogeneous immunoassays for in-vitro diagnostics. Top-down fabrication allows to combine and tailor magnetic and plasmonic anisotropic properties. The combination of nanoimprint lithography, thin film deposition, and lift-off processing provides a top-down fabrication platform, which is both flexible and reliable. Here, we discuss the material compositions and geometrical designs of monodisperse multicomponent nanoparticles and their consequences on optical and magnetic properties. The rotational hydrodynamics of nanoparticles is measured and considered under the influence of magnetic shape anisotropy in the framework of the Stoner-Wohlfarth theory. The plasmon-optical properties are explained by discrete-dipole finite-element simulations. Rotational dynamical measurements of imprinted nanoprobes for two test proteins demonstrate the applicability as highly sensitive biomolecular nanoprobes.

Versatile fabrication method for multiscale hierarchical structured polymer masters using a combination of photo- and nanoimprint lithography

We present a versatile and scalable method for the preparation of microfluidic channels with incorporated nano patterns. Since our approach is highly industrial driven, all used methods and materials are available in common micro-fabrication environment and are available in large quantities, respectively. In comparison to other fabrication methods capable of realizing multi-level patterns, we combine nanoimprint lithography with standard photolithography, and thereby overcome the problems of limited pattern dimensions as well as fabrication time, pathing the way for a new class of microfluidic devices. • High aspect ratio (AR = 11) fabrication of polymer masters using negative photoresists • Combinatorial approach for the fabrication of 2.5D scaffolds with micron and nano pattern • Combination of nanoimprint lithography and photolithography for fast prototyping • Optimized replication via soft-UV NIL using highly compatible resists and stamp materials

Tailored Nanostructures for Light Management in Silicon Heterojunction Solar Cells

Efficient light management is key for optimal performance of silicon solar cells. For monocrystalline single‐junction devices, there is an established industrially viable technology using pyramidal micro‐structured silicon wafers. As the efficiencies of market‐dominating silicon single‐junction solar cells are approaching their physical limit, innovative cell concepts are required to further reduce the levelized cost of electricity. Tandem solar cells combining silicon and perovskite absorber layers are regarded as a promising technology to overcome this limit at low costs. However, the combination of micro‐structured silicon and solution‐processed sub‐micrometer perovskite layers is a challenge, calling for alternative texturing methods. Herein, a technology to implement tailored nanostructures into silicon heterojunction solar cells by combining nanoimprint lithography, reactive ion etching, and wet chemical etching is introduced. These structures have a height below 400 nm and are thus compatible with perovskite spin‐coating. Efficiencies above 20% and an equivalent optical performance at near infrared wavelengths compared with pyramidal micro‐structures are demonstrated. This technology not only enables a variety of tailored structures in both mono‐ and multicrystalline silicon solar cell devices, but also paves the way for optically improved solution‐processed monolithic perovskite–silicon tandem solar cells.

Superhydrophobic, antireflective, flexible hard coatings with mechanically ultra-resilient moth-eye structure for foldable displays

Biomimetic inspiration from the moth-eye structure has led to many studies combining nanoimprint lithography (NIL) to realize low cost and large area anti-reflection (AR) coatings. However, the scope of application is severely limited by poor mechanical performance due to the intrinsic properties of the coating materials and the nanosized patterns. In this work, we demonstrate a moth-eye structured epoxy-siloxane molecular hybrid (ME-ESMH) fabricated using single UV-based NIL (UV-NIL) on a colorless polyimide (CPI), to be utilized as a flexible cover window (FCW) for foldable displays. Low reflection, a superhydrophobicity and good inward foldability were achieved, together with excellent thermal and chemical resistance. Furthermore, in situ uniaxial compression tests revealed that the fabricated structure can be elastically deformed and nearly restored to its original shape even after a large degree of compression. Our findings provide an easy-to-integrate solution for flexible hard coatings with superhydrophobic and AR properties, applicable to foldable optoelectronics.

SERS Active Hierarchical Nanopillar-huddle Array Fabricated via the Combination of Nanoimprint Lithography and Anodization

SERS Active Hierarchical Nanopillar-huddle Array Fabricated via the Combination of Nanoimprint Lithography and Anodization

Controlling Catalyst-Free Formation and Hole Gas Accumulation by Fabricating Si/Ge Core-Shell and Si/Ge/Si Core-Double Shell Nanowires.

The catalyst-free formation of silicon (Si) and germanium (Ge) core-shell and core-double shell nanowires (NWs) was studied for use as building blocks of high electron (hole) mobility transistors (HEMTs). Vertically aligned p-type Si (p-Si)/intrinsic Ge (i-Ge) core-shell NWs and p-Si/i-Ge/p-Si core-double shell NWs with uniform diameters were formed by combining nanoimprint lithography, Bosch etching, and chemical vapor deposition. The boron (B) doping process was used to prepare p-Si NWs. The hole gas accumulation could be reliably detected from the i-Ge shell region in the p-Si/i-Ge core-shell NW and p-Si/i-Ge/p-Si core-double shell NW arrays through the Fano resonance effect, showing that core-shell NW heterostructures can suppress impurity scattering and act as high-mobility transistor channels. This provides the possibility for the future creation of vertical high-speed transistors.

(Invited) Electrodeposition As a Versatile Method to Prepare Materials for the Storage and Conversion of Sustainable Energy

Sustainable energy carriers such as sun light, wind or biomass will play a crucial role in our future. After converting the energy, one should be able to store it and transport it to places where it is needed most. Therefore, the research on materials for storage systems, such as batteries, supercapacitors and fuel cells is an important aspect. Electrodeposition is a powerful technique for the preparation of such materials. As industry strives to produce smaller portable devices, one needs also smaller and lighter batteries with a high storage capacity per gram of active material. The commercial graphite anodes are limited to ca. 370 mAh/g, but silicon and C-Si composites have a theoretical storage capacity beyond 1000 mAh/g. Thus, nanostructured Si, such as nanoporous Si layers, ordered arrays of Si (porous) nanopillars produced by using a combination of nanoimprint lithography and metal-assisted chemical etching or silicon thin films deposited from ionic liquids could be used as high-capacity anodes in Li-ions batteries. Another interesting semiconductor material besides Si is Cu2O. Photo-cathodes from Cu2O can be used to produce hydrogen as a chemical fuel by utilizing direct solar energy and its narrow bandgap of 2.0-2.2 eV that can lead to the theoretical value of solar-to-hydrogen efficiency of 18 %. One can fabricate Cu/Cu2O porous electrodes using the hydrogen bubbles as a dynamic and effective template by electrochemical deposition. These foam electrodes can then be used as photocathodes for water electrolysis under visible light irradiation. This contribution will discuss recent results from the authors’ labs on developing new anode materials for Li-ion batteries (Si based), new electrodes for electrochemical water splitting (Cu2O based) and for electrocatalysis. Further, approaches using light induced plating for electrical front side contacts of solar cells will be presented.

Fabrication and temperature-dependent magnetic properties of large-area L10-FePt/Co exchange-spring magnet nanopatterns

Abstract Exchange-spring (ES) magnets L10-FePt/Co nanopatterns with out-of-plane texture have been fabricated by using nanoimprint lithography (NIL) in combination with inductively coupled plasma reactive etching process. The patterns are regularly arranged 60 nm diameter size nanomagnets, and different thickness of the Co soft magnet layers hysteresis loops of the different ratio of Co soft magnet addition on L10-FePt hard nanomagnet was measured by superconducting quantum interference device (SQUID) magnetometry in the temperature range from 50 K to 350 K. The influence of exchange-coupling between hard and soft magnet by thickness control on magnetic properties of these nanocomposite patterns was investigated. The magnetic property results have proved to be possible tuned magnetic properties of magnet nanopatterns. According to exchange-coupling between two-phase quantities, the magnetic properties and magnetization reversal mechanism depend significantly. The exchange-spring magnet nanopatterns have a smaller coercivity, remanence, and magnetic anisotropy, while a higher saturation polarization than pure hard magnet nanopattern due to the soft magnetic layer. The temperature dependence of the coercivity was analyzed by the universal relation within the framework of micromagnetism. The obtained microstructural parameters α and Neff give evidence for a reduction of the coercivity by the exchange coupling in the exchange-spring magnets.

Plasmon-Mediated Synthesis of Periodic Arrays of Gold Nanoplates Using Substrate-Immobilized Seeds Lined with Planar Defects.

The seed-mediated growth of noble metal nanostructures with planar geometries requires the use of seeds lined with parallel stacking faults so as to provide a break in symmetry in an otherwise isotropic metal. Although such seeds are now routinely synthesized using colloidal pathways, equivalent pathways have not yet been reported for the fabrication of substrate-based seeds with the same internal defect structures. The challenge is not merely to form seeds with planar defects but to do so in a deterministic manner so as to have stacking faults that only run parallel to the substrate surface while still allowing for the lithographic processes needed to regulate the placement of seeds. Here, we demonstrate substrate-imposed epitaxy as a viable synthetic control able to induce planar defects in Au seeds while simultaneously dictating nanostructure in-plane alignment and crystallographic orientation. The seeds, which are formed in periodic arrays using nanoimprint lithography in combination with a vapor-phase assembly process, are subjected to a liquid-phase plasmon-mediated synthesis that uses light as an external stimuli to drive a reaction yielding periodic arrays of hexagonal Au nanoplates. These achievements not only represent the first of their kind demonstrations but also advance the possibility of integrating wafer-based technologies with a rich and exciting nanoplate colloidal chemistry.

Adaptive high-resolution Linnik interferometry for 3D measurement of microparticles.

Tailored 3D microparticles and nanostructures lead to increasing possibilities in semiconductor industry or biomedical applications. In an interdisciplinary study we investigate the parallel production of such particles by using nanoimprint lithography in combination with their characterization based on interference microscopy. In this Letter we report on a metrological inspection, which tends to a universal measurement solution comparing the sample optically to a master object produced in the same way as the sample.

Fabrication of Fabry–Perot-cavity-based monolithic full-color filter arrays using a template-confined micro-reflow process

Transmissive color filters based on metal-dielectric-metal (MDM) Fabry–Perot (FP) resonators are of great interest for various applications due to their high stability, environmental friendliness and chemical inertia. However, it is still technically challenging to obtain a compact monolithic MDM-based color filter array (CFA) because of the difficulty in achieving microscale-pixelated stepwise dielectric films with designed thickness. In this work, we proposed a template-confined thermal reflow approach to fabricate monolithic CFA based on silver–polymethyl methacrylate–silver (Ag–PMMA–Ag) sandwich configuration. Via template-confined thermal reflow of periodic PMMA nanogratings with different filling density, the thickness of PMMA dielectric layer in each pixel can be independently controlled, enabling the spectral tunability across the whole visible light region with high transmission efficiency and narrow linewidth. Compared to conventional multiple deposition technique, the approach we proposed is able to control the thickness of dielectric film via a single exposure step and can be potentially applied in high-throughput production by combining nanoimprint lithography.

Fabrication of nano-patterned sapphire substrates by combining nanoimprint lithography with edge effects

A volcano-shaped nano-patterned sapphire substrate fabricated by combining nanoimprint lithography with edge effects.

Nanoimprinted Chiral Plasmonic Substrates with Three-Dimensional Nanostructures.

We report a large-area fabrication method to prepare chiral substrates patterned with arrays of multilayer, three-dimensional nanostructures using a combination of nanoimprint lithography and glancing angle deposition. Several structures are successfully fabricated using this method, including L-shaped, twisted arc and trilayer twisted Au nanorod structures, demonstrating its generality. As one typical example, arrays of L-shaped nanostructures, consisting of two layers of orthogonally oriented Au nanorods separated by a Ge dielectric layer in the thickness direction, exhibit giant optical chirality in the infrared region with an experimentally achieved g-factor as high as 0.38. Electromagnetic simulations show that the optical chirality results from plasmon hybridization between the two orthogonal Au segments. To demonstrate scalability, a 1 cm2 chiral substrate is fabricated with uniform chiral optical property. This method combines both high throughput and precise geometrical control and is therefore promising for applications of chiral metamaterials.

Arrays of highly complex noble metal nanostructures using nanoimprint lithography in combination with liquid-phase epitaxy.

Current best-practice lithographic techniques are unable to meet the functional requirements needed to enable on-chip plasmonic devices capable of fully exploiting nanostructure properties reliant on a tailored nanostructure size, composition, architecture, crystallinity, and placement. As a consequence, numerous nanofabrication methods have emerged that address various weaknesses, but none have, as of yet, demonstrated a large-area processing route capable of defining organized surfaces of nanostructures with the architectural diversity and complexity that is routinely displayed in colloidal syntheses. Here, a hybrid fabrication strategy is demonstrated in which nanoimprint lithography is combined with templated dewetting and liquid-phase syntheses that is able to realize periodic arrays of complex noble metal nanostructures over square centimeter areas. The process is inexpensive, can be carried out on a benchtop, and requires modest levels of instrumentation. Demonstrated are three fabrication schemes yielding arrays of core-shell, core-void-shell, and core-void-nanoframe structures using liquid-phase syntheses involving heteroepitaxial deposition, galvanic replacement, and dealloying. With the field of nanotechnology being increasingly reliant on the engineering of desirable physicochemical responses through architectural control, the fabrication strategy provides a platform for advancing devices reliant on addressable arrays or the collective response from an ensemble of identical nanostructures.