Lithography-based Techniques Research Articles

Femtosecond laser-induced glass refractive index change in tellurite glass

Tellurite glass has excellent infrared optical properties and is widely used in lasers, optical communications, and sensing. Femtosecond laser direct writing is a preferred method for manufacturing tellurite photonic devices, which requires precise control of the variable of refractive index. However, accurate testing of the refractive index changes induced by femtosecond laser in tellurite glass is challenging due to the small magnitude of change and localized region. In this study, we present a novel approach to measure the refractive index change of tellurite glass through the utilization of volume phase grating (VPG) diffraction. We first investigated the laser-induced damage threshold (LIDT) of tellurite glass and then proceeded to prepare VPGs inside the glass by using femtosecond laser direct writing technology, ensuring that the laser energy remained below the LIDT. By measuring the thickness and diffraction efficiency of VPGs prepared under different laser energies, we determined the associated change in refractive index. In our experiment, when subjected to laser incidence with wavelengths of 632.8 and 808 nm, the maximum values of refractive index change in the laser-modified region are measured to be 1.97 × 10−3 and 1.61 × 10−3, respectively. This method offers a precise means of measuring refractive index change within the microregion of tellurite glass induced by femtosecond laser. This capability holds great significance for the fabrication of high-quality tellurite glass photonic devices using lithography-based techniques.

Digital light processing of high-strength hydroxyapatite ceramics: Role of particle size and printing parameters on microstructural defects and mechanical properties

Dense hydroxyapatite (HA) bars were fabricated using digital light processing. The roles of HA median particle size (MPS), curing depth-to-layer thickness ratio (CD/LT), and debinding process on the printing/debinding flaws and flexural strength of the sintered parts were investigated. Commercial HA was milled for different times to provide powders with an MPS ranging from 0.3 to 2.7 µm. Thermal debinding led to delamination and vertical cracks, which decreased with increasing MPS; the minimum value required to fabricate specimens with appreciable flexural strength was 0.9 µm. At a given MPS (2.7 µm), the CD/LT varied between 1.4 and 3.3, indicating a progressive disappearance of the above major flaws. Finally, the positive effect of water debinding prior to thermal debinding on reducing crack formation was demonstrated. After optimisation, the bars achieved a flexural strength greater than 100 MPa, which is the highest value among dense HA fabricated using lithography-based techniques.

Analysis of Nanoparticle-Embedded-Resin Printing Conditions for High-Aspect-Ratio Metasurfaces

Metasurfaces, composed of periodic nanostructures, have been attractive because of their extraordinary modulation of light propagation. However, conventional electron-beam lithography to fabricate metasurfaces is time-consuming and costly, which prevents commercialization of functional metasurfaces. We investigate nanoimprint lithography-based technique for single-step fabrication of metasurfaces. A high-refractive-index material is granulated and mixed with nanoimprint resin. This mixture results in higher effective refractive index, and thus can be utilized to directly fabricate metasurfaces. Besides, diverse processing conditions are investigated such as swelling effect for the successful replication of high-aspect-ratio nanostructures. Finally, we verify the optimized nanoparticle-embedded resin printing process through the replication of metasurfaces with various dimensions and an optimal design.

Nanoimprint lithography-based replication techniques for fabrication of metal and polymer biomimetic nanostructures for biosensor surface functionalization

Nanostructuring is a promising and successful approach to tailor functional layers and to improve the characteristics of biosensors such as signal transmission and tighter cell-surface coupling. One of the major objectives in biosensing and tissue engineering is the development of interfaces that mimic the natural environment of biosystems composed of extracellular matrix biomolecules. Nevertheless, effective techniques to reconstruct the random distribution of these biomolecules are still not well established. For this reason, the presented work demonstrates different methods based on nanoimprint lithography to replicate randomly distributed natural nanostructures with complex geometries into different polymers and metals. The fidelity of the replicated nanostructures has been evaluated by atomic force microscopy and the attributes of the fabrication processes have been discussed. Finally, different replication techniques have been combined for the biomimetic nanostructuring of the dielectric passivation layer as well the metal electrode surface to develop novel whole-surface-nanostructured microelectrode arrays.

Ag-Decorated Si Microspheres Produced by Laser Ablation in Liquid: All-in-One Temperature-Feedback SERS-Based Platform for Nanosensing.

Combination of dissimilar materials such as noble metals and common semiconductors within unified nanomaterials holds promise for optoelectronics, catalysis and optical sensing. Meanwhile, difficulty of obtaining such hybrid nanomaterials using common lithography-based techniques stimulates an active search for advanced, inexpensive, and straightforward fabrication methods. Here, we report one-pot one-step synthesis of Ag-decorated Si microspheres via nanosecond laser ablation of monocrystalline silicon in isopropanol containing AgNO3. Laser ablation of bulk silicon creates the suspension of the Si microspheres that host further preferential growth of Ag nanoclusters on their surface upon thermal-induced decomposition of AgNO3 species by subsequently incident laser pulses. The amount of the AgNO3 in the working solution controls the density, morphology, and arrangement of the Ag nanoclusters allowing them to achieve strong and uniform decoration of the Si microsphere surface. Such unique morphology makes Ag-decorated Si microspheres promising for molecular identification based on the surface-enhanced Raman scattering (SERS) effect. In particular, the designed single-particles sensing platform was shown to offer temperature-feedback modality as well as SERS signal enhancement up to 106, allowing reliable detection of the adsorbed molecules and tracing their plasmon-driven catalytic transformations. Considering the ability to control the decoration degree of Si microspheres by Ag nanoclusters via amount of the AgNO3, the developed one-pot easy-to-implement PLAL synthesis holds promise for gram-scale production of high-quality hybrid nanomaterial for various nanophotonics and sensing applications.

Photosensitive binder jetting technique for the fabrication of alumina ceramic

The fabrication of ceramic using additive manufacturing has been a promising technique thanks to its abilities to form complex structures and customized shapes as well as to reduce wastes in comparison with conventional methods. Concerning the lithography-based technique, its limitation includes the deterioration of large-sized parts in fabrication process owing to the excessive amount of vaporized pressure caused by debinding of polymeric binder in ceramic slurries. Besides, the binder jetting technique involves more complexities due to the powder modification in preparation for the solidification by water-based binder. Photosensitive binder jetting techniques fabricate ceramic parts using an inkjet system to deposit photo-curable polymers onto ceramic powder bed with the shape of the parts. The binder is polymerized by the ultraviolet light to entrap the ceramic powder and form the three-dimensional object. The heat treatment process is then applied to remove the binder and sinter the part. In this research, the shrinkage, density, porosity, microstructures, mechanical properties, and printing patterns of ceramic alumina fabricated by the photosensitive binder jetting technique were investigated. The results reveal that the full printing sample exhibited the shrinkage of 11 %, the density of 39 %, the flexural strength of 1.04 MPa and the compressive strength of 1.78 MPa, whereas the checkerboard-patterned sample with 50 % reduction of printing area exhibited the density of 33 %, the flexural strength of 0.42 MPa and the compressive strength of 0.72 MPa. Through the medium of checkerboard-patterned printing with 50 % of binder’s quantity at core areas, this technique enables crack minimization in the fabrication of the large-sized part (60 mm in diameter and 30 mm in height). Furthermore, the additional modifications of ceramic powder are not required.

Fabrication of Metamaterial Building Blocks with Selective Photoreduction of Metal Ions Followed By Electroless Plating Onto DNA Origami Templates

There is a growing interest in using DNA origami templates to make complex and unique nanostructures which can be used in many applications such as in optical metamaterial fabrication. The unique properties of DNA make it possible to overcome the limitations of the top-down processes such as lithography-based techniques to create metamaterial building blocks for optical frequency. In this report, we have demonstrated a photochemical metallization technique to coat DNA origami structures with a thin layer of silver in solution as well as when supported on a surface. The uniformly coated DNA was further enhanced to a higher thickness using electroless deposition of gold. Triangular and U-shaped DNA origami structures served as photosensitizers in the presence of UV light (365 nm wavelength) to reduce the silver ions from the bulk solution onto the origami surfaces. The photochemical metallization was shown to coat the DNA uniformly with metallic silver following the conformal structure of DNA triangles and Us. Repeating photoreduction steps on the same DNA resulted in increasing silver thickness to a self-limiting value of ~5 nm, after which a selective electroless gold deposition technique was performed to gain an additional 15-20 nm in height. The photochemical silver coating technique preserved the overall structure of the DNA template, though the effective dimension of the triangles and Us were slightly reduced. The light-induced self-limiting silver deposition exhibits a defect filling growth on DNA, which facilitates the uniform enhancement of gold to a higher thickness while mapping the original shape of the DNA template. This two-step metallization technique provides a foundation to create an array of metal nanostructures using DNA origami templates to fabricate metamaterials.

Inkjet-Printed High-Q Nanocrystalline Diamond Resonators.

Diamond is a highly desirable material for state-of-the-art micro-electromechanical (MEMS) devices, radio-frequency filters and mass sensors, due to its extreme properties and robustness. However, the fabrication/integration of diamond structures into Si-based components remain costly and complex. In this work, a lithography-free, low-cost method is introduced to fabricate diamond-based micro-resonators: a modified home/office desktop inkjet printer is used to locally deposit nanodiamond ink as ∅50-60 µm spots, which are grown into ≈1 µm thick nanocrystalline diamond film disks by chemical vapor deposition, and suspended by reactive ion etching. The frequency response of the fabricated structures is analyzed by laser interferometry, showing resonance frequencies in the range of ≈9-30 MHz, with Q-factors exceeding 104 , and (f0 × Q) figure of merit up to ≈2.5 × 1011 Hz in vacuum. Analysis in controlled atmospheres shows a clear dependence of the Q-factors on gas pressure up until 1 atm, with Q ∝ 1/P. When applied as mass sensors, the inkjet-printed diamond resonators yield mass responsivities up to 981 Hz fg-1 after Au deposition, and ultrahigh mass resolution up to 278 ± 48 zg, thus outperforming many similar devices produced by traditional top-down, lithography-based techniques. In summary, this work demonstrates the fabrication of functional high-performance diamond-based micro-sensors by direct inkjet printing.

Multifunctional self-assembled monolayers via microcontact printing and degas-driven flow guided patterning

Soft lithography-based patterning techniques have been developed to investigate biological and chemical phenomena. Until now, micropatterning with various materials required multiple procedural steps such as repeating layer-by-layer patterning, aligning of stamps, and incubating printed inks. Herein, we describe a facile micropatterning method for producing chemically well-defined surface architectures by combining microcontact (µCP) and microfluidic vacuum-assisted degas-driven flow guided patterning (DFGP) with a poly(dimethylsiloxane) (PDMS) stamp. To demonstrate our concept, we fabricated a bi-composite micropatterned surface with different functional molecular inks such as fluorescein isothiocyanate labelled bovine serum albumin (FITC-BSA) and polyethylene glycol (PEG)-silane for a biomolecule array, and 3-aminopropyltriethoxysilane (APTES) and PEG-silane pattern for a self-assembled colloid gold nanoparticle monolayer. With a certain composition of molecular inks for the patterning, bi-composite surface patterns could be produced by this µCP-DFGP approach without any supplementary process. This patterning approach can be used in microfabrication and highly applicable to biomolecules and nanoparticles that spread as a monolayer.

Leveraging Innate Piezoelectricity of Ultra-Smooth Silk Thin Films for Flexible and Wearable Sensor Applications

In this paper, the innate peizoelectricity of silk is utilized to demonstrate an optimized silk thin film-based pressure sensor. Furthermore, a novel approach to pattern silk films is proposed, which could potentially lead to the development of a variety of miniaturized, flexible, and wearable sensors. The key in this endeavor is to achieve a uniform thin film of silk. The preparation methodology was optimized to achieve an ultra-smooth, reproducible thin film. The surface quality of the optimized thin film was analyzed using atomic force microscopy and the RMS roughness was found to be 2.43 nm. The piezo-response of the silk film was measured using Piezo force microscopy and the average $d_{33}$ value of the silk piezoelectric thin film was estimated at 56.7 pm/V. A pressure sensor using silk piezoelectric thin film was developed with a simple process flow. This process is devoid of any silk patterning steps. Keeping in view the potentiality of piezoelectric silk films in MEMS, a novel lithography-based technique was developed to pattern the silk films. This patterning technique can easily be integrated with any standard MEMS/Post CMOS process flow, thus opening up a new avenue in developing a variety of sensors.

Nanoimprinted perovskite metasurface for enhanced photoluminescence.

Recently, solution-processed hybrid halide perovskite has emerged as promising materials for advanced optoelectronic devices such as photovoltaics, photodetectors, light emitting diodes and lasers. In the mean time, all-dielectric metasurfaces with high-index materials have attracted attention due to their low-loss and high-efficient optical resonances. Because of its tunable by composition band gap in the visible frequencies, organolead halide perovskite could serve as a powerful platform for realizing high-index, low-loss metasurfaces. However, direct patterning of perovskite by lithography-based technique is not feasible due to material instability under moisture. Here we report novel organolead halide perovskite metasurfaces created by the cost-effective thermal nanoimprint technology. The nanoimprinted perovskite metasurface showed improved surface morphology and enhanced optical absorption properties. Significantly enhanced optical emission with an eight-fold enhancement in photoluminescence (PL) intensity was observed under room temperature. Temperature-dependent PL of perovskite nanograting metasurface was also investigated. Based on our results, we believe that thermal nanoimprint is a simple and cost-effective technique to fabricate perovskite-based metasurfaces, which could have broad impact on optoelectronic and photonic applications.

Self-Assembling VO2 Nanonet with High Switching Performance at Wafer-Scale

Technologically controlling nanostructures is essential to tailoring the functionalities and properties of nanomaterials. Various methods free from lithography-based techniques have been employed to fabricate 2D nanostructures; however it is still hard to achieve a well interconnected 2D regular nanostructure. Here, we demonstrate a facile chemical solution method to self-assemble a regular and interconnected VO2 nanonet on the wafer scale. The nanonet shows a well-defined 2D truss network constructed by VO2 nanorods with twinning relationships. The growth direction and crystallographic orientation of nanorods are synchronously controlled, leading to horizontally epitaxial growth of nanorods along three symmetric directions of the (001) single-crystal sapphire substrate. The unique nanonets enable the acquisition of excellent resistance switching properties and dramatic fatigue endurance. A large resistance change of near 5 orders with a 1.7 °C width of the hysteresis loop is characterized comparably to t...

Simulations and experiments in punching spring-steel devices with sub-millimeter features

This work demonstrates the feasibility of meso-scale (100μm to mm) punching of multiple holes of intricate shapes in metals. Analytical modeling, finite element (FE) simulation, and experimentation are used in this work. Two-dimensional FE simulations in ABAQUS were done with an assumed material modeling and plane-strain condition. A known analytical model was used and compared with the ABAQUS simulation results to understand the effects of clearance between the punch and the die. FE simulation in ABAQUS was done for different clearances and corner radii of the punch, die, and holder. To complement modeling with real experiments and for the purpose of comparison, a set of punches and dies were made to punch out a miniature spring-steel gripper. Comparison of compliant grippers made by wire-cut electro discharge machining (EDM) and punching shows that realizing sharp interior and re-entrant corners by punching is not easy to achieve. However, the promise of realizing meso-scale parts with complicated shapes through punching is demonstrated in this work; and further work is identified and some strategies are suggested for improvement. The main contribution of this paper is in adapting the well-established punching and blanking operations to the meso-scale as a viable alternative to making miniature devices currently dominated by lithography-based techniques.

Fabrication of Transistors on Flexible Substrates: from Mass‐Printing to High‐Resolution Alternative Lithography Strategies

In this report, the development of conventional, mass-printing strategies into high-resolution, alternative patterning techniques is reviewed with the focus on large-area patterning of flexible thin-film transistors (TFTs) for display applications. In the first part, conventional and digital printing techniques are introduced and categorized as far as their development is relevant for this application area. The limitations of conventional printing guides the reader to the second part of the progress report: alternative-lithographic patterning on low-cost flexible foils for the fabrication of flexible TFTs. Soft and nanoimprint lithography-based patterning techniques and their limitations are surveyed with respect to patterning on low-cost flexible foils. These show a shift from fabricating simple microlense structures to more complicated, high-resolution electronic devices. The development of alternative, low-temperature processable materials and the introduction of high-resolution patterning strategies will lead to the low-cost, self-aligned fabrication of flexible displays and solar cells from cheaper but better performing organic materials.

Hydride formation in single palladium and magnesium nanoparticles studied by nanoplasmonic dark-field scattering spectroscopy.

Scrutinizing functional nanosystems and relating details in their size, chemistry, and geometry to functionality remains a significant experimental challenge. Following the concept of indirect nanoplasmonic sensing (INPS), the exploitation of truncated Au nanocones with functionalized tips, nanofabricated in a one step, are used as single nanoplasmonic sensors for dark-field scattering spectroscopy measurements of the hydride formation Au in single Pd and Mg nanoparticles.

Fabrication of nanoscale electrostatic lenses

The fabrication of cylindrical multi-element electrostatic lenses at the nanoscale presents a challenge; they are high-aspect-ratio structures that should be rotationally symmetric, well aligned and freestanding, with smooth edges and flat, clean surfaces. In this paper, we present the fabrication results of a non-conventional process, which uses a combination of focused gallium ion-beam milling and hydrofluoric acid vapor etching. This process makes it possible to fabricate nanoscale electrostatic lenses down to 140 nm in aperture diameter and 4.2 µm in column length, with a superior control of the geometry as compared to conventional lithography-based techniques.

Versatile methods for the fabrication of polyvinylidene fluoride microstructures

Polyvinylidene fluoride (PVDF) microstructures are of interest for a number of BioMEMS applications both for their piezoelectric and biocompatible properties. In this work, simple soft lithography-based techniques were developed to fabricate PVDF microstructures with diverse geometries, including microarrays of pillars, lines, and wells. Four different microstructure configurations were created: freestanding, stamped discontinuous, stamped continuous and imprinted patterns. Features with lateral dimensions down to 1μm were consistently reproduced on 2.5cm diameter areas. Atomic force microscopy (AFM) measurements of poled PVDF microstructures confirmed a marked inverse piezoelectric behavior. The techniques presented here have a number of advantages over previously demonstrated PVDF micropatterning approaches.

Selective Deposition and Alignment of Single-Walled Carbon Nanotubes Assisted by Dielectrophoresis: From Thin Films to Individual Nanotubes

Dielectrophoresis has been used in the controlled deposition of single-walled carbon nanotubes (SWNTs) with the focus on the alignment of nanotube thin films and their applications in the last decade. In this paper, we extend the research from the selective deposition of SWNT thin films to the alignment of small nanotube bundles and individual nanotubes. Electrodes with “teeth”-like patterns are fabricated to study the influence of the electrode width on the deposition and alignment of SWNTs. The entire fabrication process is compatible with optical lithography-based techniques. Therefore, the fabrication cost is low, and the resulting devices are inexpensive. A series of SWNT solutions is prepared with concentrations ranging from 0.0125 to 0.2 mg/ml. The alignment of SWNT thin films, small bundles, and individual nanotubes is achieved under the optimized experimental conditions. The electrical properties of these samples are characterized; the linear current–voltage plots prove that the aligned SWNTs are mainly metallic nanotubes. The microscopy inspection of the samples demonstrates that the alignment of small nanotube bundles and individual nanotubes can only be achieved using narrow electrodes and low-concentration solutions. Our investigation shows that it is possible to deposit a controlled amount of SWNTs in desirable locations using dielectrophoresis.

Ultraviolet ZnO Nanorod Photosensors

This study fabricates and characterizes ultraviolet (UV) photosensors with ZnO nanorods (NRs). The NR arrays were selectively grown in the gap between interdigitated (IDT) electrodes of devices using hydrothermal solution processes and a lithography-based technique. Compared with a conventional ZnO photosensor without NRs, the proposed UV NR photosensors have much higher photoresponse in the UV region. Additionally, the photoconductive gain of an NR photosensor increased as UV illumination time increased; it varied at 34.45-5.32 x 10(2) under illumination by 18.28 mW/cm(2) optical power. Consequently, the substantial photoconductive gain can be attributed to high surface-to-volume ratio of ZnO NRs. The high density of hole-trap states on NR surfaces lead to a persistent photoconductivity (PPC) state, promoting the transport of carriers through devices.

Submerged Nanocontact Printing (SnCP) of Thiols

Biological patterned surfaces having sub-micron scale resolution are of great importance in many fields of life science and biomedicine. Different techniques have been proposed for surface patterning at the nanoscale. However, most of them present some limitations regarding the patterned area size or are time-consuming. Micro/nanocontact printing is the most representative soft lithography-based technique for surface patterning at the nanoscale. Unfortunately, conventional micro/nanocontact printing also suffers from problems such as diffusion and stamp collapsing that limit pattern resolution. To overcome these problems, a simple way of patterning thiols under liquid media using submerged nanocontact printing (SnCP) over large areas (approximately cm2) achieving nanosize resolution is presented. The technique is also low cost and any special equipment neither laboratory conditions are required. Nanostructured poly(dimethyl siloxane) stamps are replicated from commercially available digital video disks. SnCP is used to stamp patterns of 200 nm 1-octadecanethiol lines in liquid media, avoiding ink diffusion and stamp collapsing, over large areas on gold substrates compared with conventional procedures. Atomic force microscopy measurements reveal that the patterns have been successfully transferred with high fidelity. This is an easy, direct, effective and low cost methodology for molecule patterning immobilization which is of interest in those areas that require nanoscale structures over large areas, such as tissue engineering or biosensor applications.