Lithium tantalate photonic integrated circuits for volume manufacturing

Electro-optical photonic integrated circuits (PICs) based on lithium niobate (LiNbO3) have demonstrated the vast capabilities of materials with a high Pockels coefficient1,2. They enable linear and high-speed modulators operating at complementary metal-oxide-semiconductor voltage levels3 to be used in applications including data-centre communications4, high-performance computing and photonic accelerators for AI5. However, industrial use of this technology is hindered by the high cost per wafer and the limited wafer size. The high cost results from the lack of existing high-volume applications in other domains of the sort that accelerated the adoption of silicon-on-insulator (SOI) photonics, which was driven by vast investment in microelectronics. Here we report low-loss PICs made of lithium tantalate (LiTaO3), a material that has already been adopted commercially for 5G radiofrequency filters6 and therefore enables scalable manufacturing at low cost, and it has equal, and in some cases superior, properties to LiNbO3. We show that LiTaO3 can be etched to create low-loss (5.6 dB m-1) PICs using a deep ultraviolet (DUV) stepper-based manufacturing process7. We demonstrate a LiTaO3 Mach-Zehnder modulator (MZM) with a half-wave voltage-length product of 1.9 V cm and an electro-optic bandwidth of up to 40 GHz. In comparison with LiNbO3, LiTaO3 exhibits a much lower birefringence, enabling high-density circuits and broadband operation over all telecommunication bands. Moreover, the platform supports the generation of soliton microcombs. Our work paves the way for the scalable manufacture of low-cost and large-volume next-generation electro-optical PICs.

Optimizing Josephson Junction Reproducibility in 30 kV E-Beam Lithography: An Analysis of Backscattered Electron Distribution

This paper explores methods to enhance the reproducibility of Josephson junctions, which are crucial elements in superconducting quantum technologies, when employing the Dolan technique in 30 kV e-beam processes. The study explores the influence of dose distribution along the bridge area on reproducibility, addressing challenges related to fabrication sensitivity. Experimental methods include e-beam lithography, with electron trajectory simulations shedding light on the behavior of backscattered electrons. Wedescribe the fabrication of various Josephson junction geometries and analyze the correlation between the success rates of different lithography patterns and the simulated distribution of backscattered electrons. Our findings demonstrate a success rate of up to 96.3% for the double-resist 1-step low-energy e-beam lithography process. As a means of implementation strategy, we provide a geometric example that takes advantage of simulated stability regions to administer a controlled, uniform dose across the junction area, introducing novel features to overcome the difficulties associated with fabricating bridge-like structures.

Rapid In-Plane Pattern Growth for Large-Area Inverse Replication Through Electrohydrodynamic Instability of Polymer Films

Nanopatterning driven by electrohydrodynamic (EHD) instability can aid in the resolution of the drawbacks inherent in conventional imprinting or other molding methods. This is because EHD force negates the requirement of physical contact and is easily tuned. However, its potential has not examined owing to the limited size of the pattern replica (several to tens of micrometers). Thus, this study proposes a new route for large-area patterning through high-speed evolution of EHD-driven pattern growth along the in-plane axis. Through the acceleration of the in-plane growth, while selectively controlling a specific edge growth, the pattern replica area can be extended from the micro- to centimeter scale with high fidelity. Moreover, even in the case of nonuniform contact mode, the proposed rapid in-plane growth mode facilitates uniform large-scale replication, which is not possible in conventional imprinting or other molding methods.

On the reproducibility of electron-beam lithographic fabrication of photonic nanostructures

Photonic nanostructures such as gratings and ring resonators have become ubiquitous building blocks in Photonics. For example, they are used in filters, they resonantly enhance signals and act as grating couplers. Much research effort is invested in using such structures to create novel functionalities, which often employs electron-beam lithography. An intrinsic issue in this field is the ability to accurately achieve a specific operating wavelength, especially for resonant systems, because nanometer-scale variations in feature size may easily detune the device. Here, we examine some of the key fabrication steps and show how to improve the reproducibility of fabricating wavelength scale photonic nanostructures. We use guided mode resonance grating sensors as our exemplar and find that the exposure condition and the development process significantly affect the consistency of the resonance wavelength, amplitude, and sensitivity of the sensor. By having careful control over these factors, we can achieve consistent performance for all the sensors studied, with less than 10% variation in their resonance behaviors. These investigations provide useful guidelines for fabricating nanostructures more reliably and to achieve a higher success rate in exploratory experiments.

Achieving High-Precision, Low-Cost Microfluidic Chip Fabrication with Flexible PCB Technology

Soft lithography has long remained the state of the art to generate the necessary micropatterning for molded microfluidic (MF) chips. Previous attempts to use printed circuit boards (PCBs) as a cheap and accessible alternative to expensive lithographed molds for the production of PDMS MF chip prototypes have shown their limitations. A more in-depth exploration of using PCBs as a mold substrate and a novel methodology of using flexible PCBs to produce highly accurate MF chips is reported here for the first time. Cross sections highlight the improved accuracy of this method, and peel testing is performed to demonstrate suitable adhesion between the glass substrate and PDMS cast. Positive cell growth viability showcases this novel method as a high-accuracy, high-accessibility, low-cost prototyping method for microfluidic chips while still maintaining all favorable properties provided by the PDMS material.

Single-Atom Control of Arsenic Incorporation in Silicon for High-Yield Artificial Lattice Fabrication

Artificial lattices constructed from individual dopant atoms within a semiconductor crystal hold promise to provide novel materials with tailored electronic, magnetic, and optical properties. These custom-engineered lattices are anticipated to enable new, fundamental discoveries in condensed matter physics and lead to the creation of new semiconductor technologies including analog quantum simulators and universal solid-state quantum computers. This work reports precise and repeatable, substitutional incorporation of single arsenic atoms into a silicon lattice. A combination of scanning tunneling microscopy hydrogen resist lithography and a detailed statistical exploration of the chemistry of arsine on the hydrogen-terminated silicon (001) surface are employed to show that single arsenic dopants can be deterministically placed within four silicon lattice sites and incorporated with 97 ± 2% yield. These findings bring closer to the ultimate frontier in semiconductor technology: the deterministic assembly of atomically precise dopant and qubit arrays at arbitrarily large scales.

Crafting chirality in three dimensions via a novel fabrication technique for bound states in the continuum metasurfaces

An additional deposition step was added to a multi-step electron beam lithographic fabrication process to unlock the height dimension as an accessible parameter for resonators comprising unit cells of quasi-bound states in the continuum metasurfaces, which is essential for the geometric design of intrinsically chiral structures.

EUV-induced hydrogen desorption as a step towards large-scale silicon quantum device patterning

Atomically precise hydrogen desorption lithography using scanning tunnelling microscopy (STM) has enabled the development of single-atom, quantum-electronic devices on a laboratory scale. Scaling up this technology to mass-produce these devices requires bridging the gap between the precision of STM and the processes used in next-generation semiconductor manufacturing. Here, we demonstrate the ability to remove hydrogen from a monohydride Si(001):H surface using extreme ultraviolet (EUV) light. We quantify the desorption characteristics using various techniques, including STM, X-ray photoelectron spectroscopy (XPS), and photoemission electron microscopy (XPEEM). Our results show that desorption is induced by secondary electrons from valence band excitations, consistent with an exactly solvable non-linear differential equation and compatible with the current 13.5 nm (~92 eV) EUV standard for photolithography; the data imply useful exposure times of order minutes for the 300 W sources characteristic of EUV infrastructure. This is an important step towards the EUV patterning of silicon surfaces without traditional resists, by offering the possibility for parallel processing in the fabrication of classical and quantum devices through deterministic doping.

Inert-Atmosphere Microfabrication Technology for 2D Materials and Heterostructures

Most 2D materials are unstable under ambient conditions. Assembly of van der Waals heterostructures in the inert atmosphere of the glove box with ex situ lithography partially solves the problem of device fabrication out of unstable materials. In our paper, we demonstrate an approach to the next-generation inert-atmosphere (nitrogen, <20 ppm oxygen content) fabrication setup, including optical contact mask lithography with a 2 μm resolution, metal evaporation, lift-off and placement of the sample to the cryostat for electric measurements in the same inert atmosphere environment. We consider basic construction principles, budget considerations, and showcase the fabrication and subsequent degradation of black-phosphorous-based structures within weeks. The proposed solutions are surprisingly compact and inexpensive, making them feasible for implementation in numerous 2D materials laboratories.

Chemical Patterning on Nanocarbons: Functionality Typewriting

Nanocarbon materials have become extraordinarily compelling for their significant potential in the cutting-edge science and technology. These materials exhibit exceptional physicochemical properties due to their distinctive low-dimensional structures and tailored surface characteristics. An attractive direction at the forefront of this field involves the spatially resolved chemical functionalization of a diverse range of nanocarbons, encompassing carbon nanotubes, graphene, and a myriad of derivative structures. In tandem with the technological leaps in lithography, these endeavors have fostered the creation of a novel class of nanocarbon materials with finely tunable physical and chemical attributes, and programmable multi-functionalities, paving the way for new applications in fields such as nanoelectronics, sensing, photonics, and quantum technologies. Our review examines the swift and dynamic advancements in nanocarbon chemical patterning. Key breakthroughs and future opportunities are highlighted. This review not only provides an in-depth understanding of this fast-paced field but also helps to catalyze the rational design of advanced next-generation nanocarbon-based materials and devices.

Mesostructured Materials with Controllable Long-Range Orientational Ordering and Anisotropic Properties

Inorganic-organic mesophase materials provide a wide range of tunable properties, which are often highly dependent on their nano-, micro-, or meso-scale compositions and structures. Among these are macroscopic orientational order and corresponding anisotropic material properties, the adjustability of which are difficult to achieve. This is due to the complicated transient and coupled transport, chemical reaction, and surface processes that occur during material syntheses. By understanding such processes, general criteria are established and used to prepare diverse mesostructured materials with highly aligned channels with uniform nanometer dimensions and controllable directionalities over macroscopic dimensions and thicknesses. This is achieved by using a micropatterned semipermeable poly(dimethylsiloxane) stamp to manage the rates, directions, and surfaces at which self-assembling phases nucleate and the directions that they grow. This enables mesostructured surfactant-directed silica and titania composites, including with functional guest species, and mesoporous carbons to be prepared with high degrees of hexagonal order, as well as controllable orthogonal macroscopic orientational order. The resulting materials exhibit novel anisotropic properties, as demonstrated by the example of direction-dependent photocurrent generation, and are promising for enhancing the functionality of inorganic-organic nanocomposite materials in separations, catalysis, and energy conversion applications.

Controlling Colloidal Crystal Nucleation and Growth with Photolithographically Defined Templates

Colloidal crystallization provides a means to synthesize hierarchical nanostructures by design and to use these complex structures for nanodevice fabrication. In particular, DNA provides a means to program interactions between particles with high specificity, thereby enabling the formation of particle superlattice crystallites with tailored unit cell geometries and surface faceting. However, while DNA provides precise control of particle-particle bonding interactions, it does not inherently present a means of controlling higher-level structural features such as the size, shape, position, or orientation of a colloidal crystallite. While altering assembly parameters such as temperature or concentration can enable limited control of crystallite size and geometry, integrating colloidal assemblies into nanodevices requires better tools to manipulate higher-order structuring and improved understanding of how these tools control the fundamental kinetics and mechanisms of colloidal crystal growth. In this work, photolithography is used to produce patterned substrates that can manipulate the placement, size, dispersity, and orientation of colloidal crystals. By adjusting aspects of the pattern, such as feature size and separation, we reveal a diffusion-limited mechanism governing crystal nucleation and growth. Leveraging this insight, patterns are designed that can produce wafer-scale substrates with arrays of nanoparticle superlattices of uniform size and shape. These design principles therefore bridge a gap between a fundamental understanding of nanoparticle assembly and the fabrication of nanostructures compatible with functional devices.

Enhanced Thermal Conductivity of Free-Standing Double-Walled Carbon Nanotube Networks

Nanomaterials are driving advances in technology due to their oftentimes superior properties over bulk materials. In particular, their thermal properties become increasingly important as efficient heat dissipation is required to realize high-performance electronic devices, reduce energy consumption, and prevent thermal damage. One application where nanomaterials can play a crucial role is extreme ultraviolet (EUV) lithography, where pellicles that protect the photomask from particle contamination have to be transparent to EUV light, mechanically strong, and thermally conductive in order to withstand the heat associated with high-power EUV radiation. Free-standing carbon nanotube (CNT) films have emerged as candidates due to their high EUV transparency and ability to withstand heat. However, the thermal transport properties of these films are not well understood beyond bulk emissivity measurements. Here, we measure the thermal conductivity of free-standing CNT films using all-optical Raman thermometry at temperatures between 300 and 700 K. We find thermal conductivities up to 50 W m-1 K-1 for films composed of double-walled CNTs, which rises to 257 W m-1 K-1 when considering the CNT network alone. These values are remarkably high for randomly oriented CNT networks, roughly seven times that of single-walled CNT films. The enhanced thermal conduction is due to the additional wall, which likely gives rise to additional heat-carrying phonon modes and provides a certain resilience to defects. Our results demonstrate that free-standing double-walled CNT films efficiently dissipate heat, enhancing our understanding of these promising films and how they are suited to applications in EUV lithography.

Detection of environmental nanoplastics via surface-enhanced Raman spectroscopy using high-density, ring-shaped nanogap arrays

Micro- and nano-plastics (MNPs) are global contaminants of growing concern to the ecosystem and human health. In-the-field detection and identification of environmental micro- and nano-plastics (e-MNPs) is critical for monitoring the spread and effects of e-MNPs but is challenging due to the dearth of suitable analytical techniques, especially in the sub-micron size range. Here we show that thin gold films patterned with a dense, hexagonal array of ring-shaped nanogaps (RSNs) can be used as active substrates for the sensitive detection of micro- and nano-plastics by surface-enhanced Raman spectroscopy (SERS), requiring only small sample volumes and no significant sample preparation. By drop-casting 0.2-μL aqueous test samples onto the SERS substrates, 50-nm polystyrene (PS) nanoparticles could be determined via Raman spectroscopy at concentrations down to 1 μg/mL. The substrates were successfully applied to the detection and identification of ∼100-nm polypropylene e-MNPs in filtered drinking water and ∼100-nm polyethylene terephthalate (PET) e-MNPs in filtered wash-water from a freshly cleaned PET-based infant feeding bottle.

Theoretical Insights into the Solubility Polarity Switch of Metal-Organic Nanoclusters for Nanoscale Patterning

Metal-organic nanoclusters(MOCs) are being increasingly used as prospective photoresist candidates for advanced nanoscale lithography technologies. However, insight into the irradiation-induced solubility switching process remains unclear. Hereby, the theoretical study employing density functional theory (DFT) calculations of the alkene-containing zirconium oxide MOC photoresists is reported, which is rationally synthesized accordingly, to disclose the mechanism of the nanoscale patterning driven by the switch of solubility from the acid-catalyzed or electron-triggered ligand dissociation. By evaluating the dependence of MOCs' imaging process on photoacid, lithographies of photoresists with and without photoacid generators after exposure to ultraviolet (UV), electron beam, and soft X-ray, it is revealed that photoacid is essential in UV lithography, but it demonstrates little effect on exposure dose in high-energy lithography. Furthermore, theoretical studies using DFT simulations to investigate the plausible photoacid-catalyzed, electron-triggered dissociation, and accompanying radical reaction are performed, and a mechanism is demonstrated that the nanoscale patterning of this type of MOCs is driven by the solubility switch resulting from dissociation-induced strong electrostatic interaction and low-energy barrier radical polymerization with other species. This study can give insights into the chemical mechanisms of patterning, and guide the rational design of photoresists to realize high resolution and high sensitivity.

Extended-Surface Thin-Film Platinum Electrocatalysts with Tunable Nanostructured Morphologies

Reducing platinum group metal (PGM) loadings in fuel cells and electrolyzers is paramount for cost reductions and getting hydrogen to scale to help decarbonize the global economy. Conventional PGM nanoparticle-based ink-cast electrocatalysts lose performance at high current densities owing to mass transport resistances that arise due to the use of ionomer binders. Herein, we report the development of binder-free extended-surface thin-film platinum electrocatalysts with tunable nanoscale morphology and periodic spacing. The electrocatalysts are prepared by sputtering various loadings of platinum on Al2O3 nanostructures templated from self-assembled block copolymer (BCP) thin films on glassy carbon substrates. Testing for oxygen reduction on a rotating disk electrode setup with ultralow PGM loadings (5.8 μgPt cm-2) demonstrates electrocatalyst performance that rivals commercial platinum electrocatalysts in terms of mass activity (380 mA mgPt-1 at 0.9 V vs RHE) while surpassing commercial catalysts in terms of stability (mass activity loss: 11-13% after 20,000 potential cycles). Moreover, catalyst performance probed as a function of nanoscale feature size and morphology reveals an inverse correlation between feature size and electroactivity, as well as the superiority of cylindrical morphologies over lamellae, presenting BCP templating as a fabrication pathway toward stable, tunable catalyst geometries.

Nanoimprint Lithography as a Route to Nanoscale Back-Contact Perovskite Solar Cells

Back-contact perovskite solar cells are of great interest because they could achieve higher performance than conventional designs while also eliminating the need for transparent conductors. Current research in this field has focused on making electrode structures with reduced widths to collect charges more efficiently, but current lift-off-based fabrication techniques have struggled to achieve electrode widths smaller than 1000 nm and are difficult to implement on large areas. We demonstrate nanoimprint lithography in an etch-down procedure as a simple and easily scalable method to produce honeycomb-shaped, quasi-interdigitated electrode structures with widths as small as 230 nm. We then use electrodeposition to selectively deposit conformal coatings of a range of different hole-selective layers and explore how the efficiency of back-contact perovskite solar cells changes as the feature sizes are pushed into the nanoscale. We find that the efficiency of the resulting devices remains almost unchanged as the electrode width is varied from 230 to 2000 nm, which differs from reported device simulations. Our results suggest that reducing recombination and improving the quality of the charge transport layers, rather than reducing the minimum feature size, are likely to be the best pathway to maximizing the performance of back-contact perovskite solar cells.

Deconvolution volumetric additive manufacturing

Volumetric additive manufacturing techniques are a promising pathway to ultra-rapid light-based 3D fabrication. Their widespread adoption, however, demands significant improvement in print fidelity. Currently, volumetric additive manufacturing prints suffer from systematic undercuring of fine features, making it impossible to print objects containing a wide range of feature sizes, precluding effective adoption in many applications. Here, we uncover the reason for this limitation: light dose spread in the resin due to chemical diffusion and optical blurring, which becomes significant for features ⪅0.5 mm. We develop a model that quantitatively predicts the variation of print time with feature size and demonstrate a deconvolution method to correct for this error. This enables prints previously beyond the capabilities of volumetric additive manufacturing, such as a complex gyroid structure with variable thickness and a fine-toothed gear. These results position volumetric additive manufacturing as a mature 3D printing method, all but eliminating the gap to industry-standard print fidelity.

Mean Free Path of Electrons in Organic Photoresists for Extreme Ultraviolet Lithography in the Kinetic Energy Range 20-450 eV

The blur caused by the nonzero mean free path of electrons in photoresists exposed by extreme ultraviolet lithography has detrimental consequences on patterning resolution, but its effect is difficult to quantify experimentally. So far, most mean free path calculations use the dielectric formalism, which is an approximation valid in the optical limit and fails at low kinetic energy. In this work, we used a modified substrate-overlayer technique that exploited the attenuation of the Si 2p core level originating specifically from the native silicon dioxide to evaluate the attenuation of electrons traveling through 2 and 4 nm of photoresist overlayers to provide a close estimation of the inelastic mean free path relevant for photoresist lithography patterning and for electron microscopy. The photoemission spectra were collected in the proximity of the Si 2p edge (binding energy ∼101 eV) using synchrotron light of energy ℏω ranging between 120 and 550 eV. The photoresist films were prototypical chemically amplified resists based on organic copolymer of poly hydroxystyrene and tertbutyl methacrylate with and without triphenyl sulfonium perfluoro-1-butanesufonate photoacid generator and trioctylamine quencher. The inelastic mean free path of electrons, in the range that is relevant for photoresist exposure in extreme ultraviolet lithography (20-92 eV), was found to be between 1 and 2 nm. At higher kinetic energy, the mean free path increased, consistently with the well-known behavior. The presence of the photoacid generator and quencher did not change the mean free path, within experimental error. Our results are discussed and compared with the existing literature on organic molecules measured via dielectric formalism and electron transmission experiments.

Template Design for Complex Block Copolymer Patterns Using a Machine Learning Method

This study represents the first attempt to address the inverse design problem of the guiding template for directed self-assembly (DSA) patterns using solely machine learning methods. By formulating the problem as a multi-label classification task, the study shows that it is possible to predict templates without requiring any forward simulations. A series of neural network (NN) models, ranging from the basic two-layer convolutional neural network (CNN) to the large NN models (32-layer CNN with 8 residual blocks), have been trained using simulated pattern samples generated by thousands of self-consistent field theory (SCFT) calculations; a number of augmentation techniques, especially suitable for predicting morphologies, have been also proposed to enhance the performance of the NN model. The exact match accuracy of the model in predicting the template of simulated patterns was significantly improved from 59.8% for the baseline model to 97.1% for the best model of this study. The best model also demonstrates an excellent generalization ability in predicting the template for human-designed DSA patterns, while the simplest baseline model is ineffective in this task.

Direct laser writing of 3D electrodes on flexible substrates

This report describes a 3D microelectrode array integrated on a thin-film flexible cable for neural recording in small animals. The fabrication process combines traditional silicon thin-film processing techniques and direct laser writing of 3D structures at micron resolution via two-photon lithography. Direct laser-writing of 3D-printed electrodes has been described before, but this report is the first to provide a method for producing high-aspect-ratio structures. One prototype, a 16-channel array with 300 µm pitch, demonstrates successful electrophysiological signal capture from bird and mouse brains. Additional devices include 90 µm pitch arrays, biomimetic mosquito needles that penetrate through the dura of birds, and porous electrodes with enhanced surface area. The rapid 3D printing and wafer-scale methods described here will enable efficient device fabrication and new studies examining the relationship between electrode geometry and electrode performance. Applications include small animal models, nerve interfaces, retinal implants, and other devices requiring compact, high-density 3D electrodes.

Optimization of Surface-Engineered Micropatterns on Bacterial Cellulose for Guided Scar-Free Skin Wound Healing

Bacterial cellulose (BC) has been widely used in tissue engineering due to its unique spatial structure and suitable biological properties. In this study, a small biologically active Arginine-Glycine-Aspartic acid-Serine (RGDS) tetrapeptide was incorporated on the porous BC surface followed by a low-energy CO₂ laser etching operation. As a result, different micropatterns were established on the BC surface with RGDS only anchored on the raised platform surface of the micropatterned BC (MPBC). Material characterization showed that all micropatterned structures exhibited platforms with a width of ~150 μm and grooves with a width of ~100 μm and a depth of ~300 μm, which displayed distinct hydrophilic and hydrophobic properties. The resulting RGDS-MPBC could hold the material integrity, as well as the microstructure morphology under a humid environment. In-vitro and in-vivo assays on cell migration, collagen deposition, and histological analysis revealed that micropatterns led to significant impacts on wound healing progress compared to the BC without surface-engineered micropatterns. Specifically, the basket-woven micropattern etched on the BC surface exhibited the optimal wound healing outcome with the presence of fewer macrophages and the least scar formation. This study further addresses the potential of adopting surface micropatterning strategies to promote skin wounds towards scar-free outcomes.

Cracked Film Lithography with CuGaOx Buffers for Bifacial CdTe Photovoltaics

Bifacial CdTe solar cells with greater power density than the monofacial baselines are demonstrated by using a CuGaO_x rear interface buffer that passivates while reducing sheet resistance and contact resistance. Inserting CuGaO_x between the CdTe and Au increases mean power density from 18.0 ± 0.5 to 19.8 ± 0.4 mW cm^-2 for one sun front illumination. However, coupling CuGaO_x with a transparent conductive oxide leads to an electrical barrier. Instead, CuGaO_x is integrated with cracked film lithography (CFL)-patterned metal grids. CFL grid wires are spaced narrowly enough (≈10 µm) to alleviate semiconductor resistance while retaining enough passivation and transmittance for a bifacial power gain: bifacial CuGaO_x /CFL grids generate 19.1 ± 0.6 mW cm^-2 for 1 sun front + 0.08 sun rear illumination and 20.0 ± 0.6 mW cm^-2 at 1 sun front + 0.52 sun rear-the highest reported power density at field albedo conditions for a scaled polycrystalline absorber.

Synthesis of Acrylate Dual-Tone Resists and the Effect of Their Molecular Weight on Lithography Performance and Mechanism: An Investigation

Acrylate photoresists have gained considerable attention in recent years owing to their high resolution, high sensitivity, and versality. In this work, a series of thermally stable copolymers are synthesized by introducing an isobornyl group, and well characterized using Fourier transform infrared spectroscopy (FT-IR) and nuclear magnetic resonance spectra (¹H-NMR). The effects of polymerization conditions on the molecular weight and their further influence on lithography are explored. By analyzing the thermal properties, film-forming capabilities, and the patterning behavior of these copolymers, a direct correlation between lithography performance and polymerization conditions is established via the molecular weight. In addition, the baking temperature of lithography is also optimized by atomic force microscopy (AFM), after which a line resolution of 0.1 μm is observed under the exposure of a 248 nm UV light and electron beam. Notably, our synthesized photoresist displays dual-tone resist characteristics when different developers are applied, and the reaction mechanism of acid-catalyzed hydrolysis is finally proposed by comparing the structural changes before and after exposure.

One-step printable platform for high-efficiency metasurfaces down to the deep-ultraviolet region

A single-step printable platform for ultraviolet (UV) metasurfaces is introduced to overcome both the scarcity of low-loss UV materials and manufacturing limitations of high cost and low throughput. By dispersing zirconium dioxide (ZrO₂) nanoparticles in a UV-curable resin, ZrO₂ nanoparticle-embedded-resin (nano-PER) is developed as a printable material which has a high refractive index and low extinction coefficient from near-UV to deep-UV. In ZrO₂ nano-PER, the UV-curable resin enables direct pattern transfer and ZrO₂ nanoparticles increase the refractive index of the composite while maintaining a large bandgap. With this concept, UV metasurfaces can be fabricated in a single step by nanoimprint lithography. As a proof of concept, UV metaholograms operating in near-UV and deep-UV are experimentally demonstrated with vivid and clear holographic images. The proposed method enables repeat and rapid manufacturing of UV metasurfaces, and thus will bring UV metasurfaces more close to real life.

Lithographic Microneedle-Motors from Multimodal Microfluidics for Cargo Delivery

Micromotors have led to an unprecedented revolution in the field of cargo delivery. Attempts in this area trend toward enriching their structures and improving their functions to promote their further applications. Herein, novel microneedle-motors (MNMs) for active drug delivery through a flexible multimodal microfluidic lithographic approach are presented. The multimodal microfluidics is composed of a co-flow geometry-derived droplet fluid and an active cargo mixed laminar flow in a triangular microchannel. The MNMs with sharp tips and spherical fuel-loading cavities are obtained continuously from microfluidics with the assistance of flow lithography. The structural parameters of the MNMs could be precisely tailored by simply choosing the flow speed or the shape of the photomask. As the actives are mixed into the phase solution during the generation, the resultant MNMs are loaded with cargoes for direct applications without any extra complex operation. Based on these features, it is demonstrated that with sharp tips and autonomous movement, the MNMs can efficiently penetrate the tissue-like substrates, indicating the potential in overcoming physiological barriers for cargo release. These results indicate that the proposed multimodal microfluidic lithographic MNMs are valuable for practical active cargo delivery in biomedical and other relative areas.

Monolithic integrated micro-supercapacitors with ultra-high systemic volumetric performance and areal output voltage

Monolithic integrated micro-supercapacitors (MIMSCs) with high systemic performance and cell-number density are important for miniaturized electronics to empower the Internet of Things. However, fabrication of customizable MIMSCs in an extremely small space remains a huge challenge considering key factors such as materials selection, electrolyte confinement, microfabrication and device-performance uniformity. Here, we develop a universal and large-throughput microfabrication strategy to address all these issues by combining multistep lithographic patterning, spray printing of MXene microelectrodes and controllable 3D printing of gel electrolytes. We achieve the monolithic integration of electrochemically isolated micro-supercapacitors in close proximity by leveraging high-resolution micropatterning techniques for microelectrode deposition and 3D printing for precise electrolyte deposition. Notably, the MIMSCs obtained demonstrate a high areal-number density of 28 cells cm^-2 (340 cells on 3.5 × 3.5 cm²), a record areal output voltage of 75.6 V cm^-2, an acceptable systemic volumetric energy density of 9.8 mWh cm^-3 and an unprecedentedly high capacitance retention of 92% after 4000 cycles at an extremely high output voltage of 162 V. This work paves the way for monolithic integrated and microscopic energy-storage assemblies for powering future microelectronics.

Self-organization and dewetting kinetics in sub-10 nm diblock copolymer line/space lithography

In this work, we investigated the self-assembly of a lamellar block copolymer (BCP) under different wetting conditions. We explored the influence of the chemical composition of under-layers and top-coats on the thin film stability, self-assembly kinetics and BCP domain orientation. Three different chemistries were chosen for these surface affinity modifiers and their composition was tuned in order to provide either neutral wetting (i.e. an out-of-plane lamellar structure), or affine wetting conditions (i.e. an in-plane lamellar structure) with respect to a sub-10 nm PS-b-PDMSB lamellar system. Using such controlled wetting configurations, the competition between the dewetting of the BCP layer and the self-organization kinetics was explored. We also evaluated the spreading parameter of the BCP films with respect to the configurations of surface-energy modifiers and demonstrated that BCP layers are intrinsically unstable to dewetting in a neutral configuration. Finally, the dewetting mechanisms were evaluated with respect to the different wetting configurations and we clearly observed that the rigidity of the top-coat is a key factor to delay BCP film instability.

Engineered substrates incapable of induction of chondrogenic differentiation compared to the chondrocyte imprinted substrates

It is well established that surface topography can affect cell functions. However, finding a reproducible and reliable method for regulating stem cell behavior is still under investigation. It has been shown that cell imprinted substrates contain micro- and nanoscale structures of the cell membrane that serve as hierarchical substrates, can successfully alter stem cell fate. This study investigated the effect of the overall cell shape by fabricating silicon wafers containing pit structure in the average size of spherical-like chondrocytes using photolithography technique. We also used chondrocyte cell line (C28/I2) with spindle-like shape to produce cell imprinted substrates. The effect of all substrates on the differentiation of adipose-derived mesenchymal stem cells (ADSCs) has been studied. The AFM and scanning electron microscopy images of the prepared substrates demonstrated that the desired shapes were successfully transferred to the substrates. Differentiation of ADSCs was investigated by immunostaining for mature chondrocyte marker, collagen II, and gene expression of collagen II, Sox9, and aggrecan markers. C28/I2 imprinted substrate could effectively enhanced chondrogenic differentiation compared to regular pit patterns on the wafer. It can be concluded that cell imprinted substrates can induce differentiation signals better than engineered lithographic substrates. The nanostructures on the cell-imprinted patterns play a crucial role in harnessing cell fate. Therefore, the patterns must include the nano-topographies to have reliable and reproducible engineered substrates.

Odor Discrimination by Lipid Membranes

Odor detection and discrimination in mammals is known to be initiated by membrane-bound G-protein-coupled receptors (GPCRs). The role that the lipid membrane may play in odor discrimination, however, is less well understood. Here, we used model membrane systems to test the hypothesis that phospholipid bilayer membranes may be capable of odor discrimination. The effect of S-carvone, R-carvone, and racemic lilial on the model membrane systems was investigated. The odorants were found to affect the fluidity of supported lipid bilayers as measured by fluorescence recovery after photobleaching (FRAP). The effect of odorants on surface-supported lipid multilayer microarrays of different dimensions was also investigated. The lipid multilayer micro- and nanostructure was highly sensitive to exposure to these odorants. Fluorescently-labeled lipid multilayer droplets of 5-micron diameter were more responsive to these odorants than ethanol controls. Arrays of lipid multilayer diffraction gratings distinguished S-carvone from R-carvone in an artificial nose assay. Our results suggest that lipid bilayer membranes may play a role in odorant discrimination and molecular recognition in general.

Optical Fiber Grating-Prism Fabrication by Imprint Patterning of Ionic-Liquid-Based Resist

We present a method of microstructure fabrication on the tip of the optical fiber using a UV soft-imprint process of polymerizable ionic liquid-based optical resist. Ionic liquid with two UV-sensitive vinylbenzyl groups in the structure was diluted in non-hazardous propylene glycol (PG) to obtain liquid material for imprinting. No additional organic solvent was required. The impact of propylene glycol amount and exposure dose on optical and mechanical properties was investigated. The final procedure of the UV imprint on the optical fiber tip was developed, including the mold preparation, setup building, UV exposure and post-laser cure. As the IL-containing vinylbenzyl groups can also be polymerized by the radical rearrangement of double bonds through thermal heating, the influence of the addition of 1-2% BHT polymerization inhibitor was verified. As a result, we present the fabricated diffraction gratings and the optical fiber spectrometer component-grism (grating-prism), which allows obtaining a dispersion spectrum at the output of an optical in line with the optical fiber long axis, as the main component in an optical fiber spectrometer. The process is very simple due to the fact that its optimization already starts in the process of molecule design, which is part of the trend of sustainable technologies. The final material can be designed by the tailoring of the anion and/or cation molecule, which in turn can lead to a more efficient fabrication procedure and additional functionalities of the final structure.

Engineering Silk Protein to Modulate Polymorphic Transitions for Green Lithography Resists

Silk protein is being increasingly introduced as a prospective material for biomedical devices. However, a limited locus to intervene in nature-oriented silk protein makes it challenging to implement on-demand functions to silk. Here, we report how polymorphic transitions are related with molecular structures of artificially synthesized silk protein and design principles to construct a green-lithographic and high-performative protein resist. The repetition number and ratio of two major building blocks in synthesized silk protein are essential to determine the size and content of β-sheet crystallites, and radicals resulting from tyrosine cleavages by the 193 nm laser irradiation induce the β-sheet to α-helix transition. Synthesized silk is designed to exclusively comprise homogeneous building blocks and exhibit high crystallization and tyrosine-richness, thus constituting an excellent basis for developing a high-performance deep-UV photoresist. Additionally, our findings can be conjugated to design an electron-beam resist governed by the different irradiation-protein interaction mechanisms. All synthesis and lithography processes are fully water-based, promising green lithography. Using the engineered silk, a nanopatterned planar color filter showing the reduced angle dependence can be obtained. Our study provides insights into the industrial scale production of silk protein with on-demand functions.

Humidity- tunable liquefaction of Cr thin-film and its application to patterning

Electric field induced liquefaction of chromium (Cr) thin-films, being a surface-based process, is affected by the moisture content in the surroundings. The said process is an electrochemical reaction, which takes place on an electrically stressed Cr thin-film. The reaction results in a liquid region, which appears to flow out radially from the tip of the cathode. A proper understanding of the phenomenon is warranted as it is applied for performing a nanolithography process, electrolithography (ELG). In this study we have focused on the effect of relative humidity (RH) on the material formation and transport on electrically stressed Cr thin-film. Varying the RH over a wide range, the phenomenon is studied using different levels of DC stress. The effect of the applied DC stress coupled with varying levels of RH showed trends which are explained qualitatively and quantitatively. The results indicate that RH could be a pivotal parameter affecting the above-mentioned phenomenon on electrically stressed Cr thin-films and could significantly alter the minimum feature size attainable by ELG. To demonstrate the effect of RH on ELG, lines are drawn at various humidity levels resulting in greater than 100% increase in the attainable line width when RH is increased by about 40%.

Chemical Composition and Flexural Strength Discrepancies Between Milled and Lithography-Based Additively Manufactured Zirconia

PURPOSE

To evaluate the chemical composition, flexural strength, and Weibull characteristics of milled and lithography-based additively manufactured (AM) zirconia.

MATERIALS AND METHODS

A virtual design of a bar (25×4×2 mm) was completed using a software program. The standard tessellation language file was used to manufacture all the specimens: 3Y-TZP zirconia (Priti multidisc ZrO₂ monochrome) milled (M group) and 3Y-TZP zirconia (LithaCon 3Y 210) lithography-based AM (CeraFab System S65 Medical) (AM group) bar specimens (n = 20). The chemical composition of the specimens was determined by using energy dispersive X-ray (EDAX) elemental analysis in a scanning electron microscope. Flexural strength was measured in all specimens using 3-point bend test according to ISO/CD 6872.2 with a universal testing machine (Instron Model 8501). Two-parameter Weibull distribution values were calculated. The Shapiro-Wilk test revealed that the data were normally distributed (p < 0.05). Flexural strength values were analyzed using independent Student's t-test (α = 0.05).

RESULTS

There were no major chemical composition differences observed between M and AM groups. The AM specimens (1518.9 ± 253.9 MPa) exhibited a significantly higher flexural strength mean value compared to the milled (980.5 ± 130.3 MPa) specimens (DF = 13, T-value = -5.97, p < 0.001). The Weibull distribution presented the highest shape for M specimens (11.49) compared to those of AM specimens (6.95).

CONCLUSIONS

There was no significant difference in the chemical composition of milled and AM zirconia material tested. AM zirconia tested exhibited significantly higher flexural strength compared with the milled zirconia evaluated.

Nanoscale View of Engineered Massive Dirac Quasiparticles in Lithographic Superstructures

Massive Dirac fermions are low-energy electronic excitations characterized by a hyperbolic band dispersion. They play a central role in several emerging physical phenomena such as topological phase transitions, anomalous Hall effects, and superconductivity. This work demonstrates that massive Dirac fermions can be controllably induced by lithographically patterning superstructures of nanoscale holes in a graphene device. Their band dispersion is systematically visualized using angle-resolved photoemission spectroscopy with nanoscale spatial resolution. A linear scaling of effective mass with feature sizes is reported, underlining the Dirac nature of the superstructures. In situ electrostatic doping dramatically enhances the effective hole mass and leads to the direct observation of an electronic band gap that results in a peak-to-peak band separation of 0.64 ± 0.03 eV, which is shown via first-principles calculations to be strongly renormalized by carrier-induced screening. The methodology demonstrates band structure engineering guided by directly viewing structurally and electrically tunable massive Dirac quasiparticles in lithographic superstructures at the nanoscale.

Lithographic SERS Aptasensor for Ultrasensitive Detection of SARS-CoV-2 in Biological Fluids

In this paper, we propose a technology for the rapid and sensitive detection of the whole viral particles of SARS-CoV-2 using double-labeled DNA aptamers as recognition elements together with the SERS method for detecting the optical response. We report on the development of a SERS-aptasensor based on a reproducible lithographic SERS substrate, featuring the combination of high speed, specificity, and ultrasensitive quantitative detection of SARS-CoV-2 virions. The sensor makes it possible to identify SARS-CoV-2 in very low concentrations (the limit of detection was 100 copies/mL), demonstrating a sensitivity level comparable to the existing diagnostic golden standard-the reverse transcription polymerase chain reaction.

High-speed, scanned laser structuring of multi-layered eco/bioresorbable materials for advanced electronic systems

Physically transient forms of electronics enable unique classes of technologies, ranging from biomedical implants that disappear through processes of bioresorption after serving a clinical need to internet-of-things devices that harmlessly dissolve into the environment following a relevant period of use. Here, we develop a sustainable manufacturing pathway, based on ultrafast pulsed laser ablation, that can support high-volume, cost-effective manipulation of a diverse collection of organic and inorganic materials, each designed to degrade by hydrolysis or enzymatic activity, into patterned, multi-layered architectures with high resolution and accurate overlay registration. The technology can operate in patterning, thinning and/or cutting modes with (ultra)thin eco/bioresorbable materials of different types of semiconductors, dielectrics, and conductors on flexible substrates. Component-level demonstrations span passive and active devices, including diodes and field-effect transistors. Patterning these devices into interconnected layouts yields functional systems, as illustrated in examples that range from wireless implants as monitors of neural and cardiac activity, to thermal probes of microvascular flow, and multi-electrode arrays for biopotential sensing. These advances create important processing options for eco/bioresorbable materials and associated electronic systems, with immediate applicability across nearly all types of bioelectronic studies.

Effects of focused electron beam irradiation parameters on direct nanostructure formation on Ag surfaces

Metallic nanostructures are applied in many fields, including photonics and plasmonics, due to their ability to absorb or emit light at frequencies which depend on their size and shape. It was recently shown that irradiation by a focused electron beam can promote the growth of nanostructures on metal surfaces and the height of these structures depends on the duration of the irradiation and the material of the surface. However, the effects on growth dynamics of numerous irradiation parameters, such as beam current or angle of incidence, have not yet been studied in detail. We explore the effects of focusing, angle of incidence, and current of the electron beam on the size and shape of the resulting structures on an Ag surface. In addition, we investigate how the nitrogen plasma cleaning procedure of a vacuum chamber can affect the growth of these structures. A beam current of around 40 pA resulted in the fastest structure growth rate. By increasing the beam diameter and angle of incidence the growth rate decreased; however, by raising the beam focus up to 5-6 μm above the surface the growth rate increased. Vacuum chamber cleaning reduced structure growth rate for a few hours. These findings can help to better control and optimise the growth of nanostructures on metal surfaces undergoing irradiation by a focused electron beam.

Edge-Contact MoS2 Transistors Fabricated Using Thermal Scanning Probe Lithography

The science and engineering of two-dimensional materials (2DMs), in particular, of 2D semiconductors, is advancing at a thriving pace. It is well known that these delicate few-atoms thick materials can be damaged during the processing toward their integration into final devices. Thermal scanning probe lithography (t-SPL) is a gentle alternative to the typically used electron beam lithography to fabricate these devices avoiding the use of electrons, which are well known to deteriorate the 2DMs' properties. Here, t-SPL is used for the fabrication of MoS₂-based field effect transistors (FETs). In particular, the use of t-SPL is demonstrated for the first time for the fabrication of edge-contact MoS₂ FETs, combining the hot-tip patterning and Ar⁺ milling to etch the 2DM. To avoid contamination of the contact interface by atmospheric gas molecules, etching and metal deposition are performed without breaking the vacuum conditions in between. With this process, edge-contact MoS₂ FETs are successfully fabricated and characterized. On/off ratios up to 10⁸ and 10⁹ are obtained at room temperature in air and vacuum, respectively, i.e., comparable with the best values reported in the literature.

Fabrication of Concave Microwells and Their Applications in Micro-Tissue Engineering: A Review

At present, there is an increasing need to mimic the in vivo micro-environment in the culture of cells and tissues in micro-tissue engineering. Concave microwells are becoming increasingly popular since they can provide a micro-environment that is closer to the in vivo environment compared to traditional microwells, which can facilitate the culture of cells and tissues. Here, we will summarize the fabrication methods of concave microwells, as well as their applications in micro-tissue engineering. The fabrication methods of concave microwells include traditional methods, such as lithography and etching, thermal reflow of photoresist, laser ablation, precision-computerized numerical control (CNC) milling, and emerging technologies, such as surface tension methods, the deformation of soft membranes, 3D printing, the molding of microbeads, air bubbles, and frozen droplets. The fabrication of concave microwells is transferring from professional microfabrication labs to common biochemical labs to facilitate their applications and provide convenience for users. Concave microwells have mostly been used in organ-on-a-chip models, including the formation and culture of 3D cell aggregates (spheroids, organoids, and embryoids). Researchers have also used microwells to study the influence of substrate topology on cellular behaviors. We will briefly review their applications in different aspects of micro-tissue engineering and discuss the further applications of concave microwells. We believe that building multiorgan-on-a-chip by 3D cell aggregates of different cell lines will be a popular application of concave microwells, while integrating physiologically relevant molecular analyses with the 3D culture platform will be another popular application in the near future. Furthermore, 3D cell aggregates from these biosystems will find more applications in drug screening and xenogeneic implantation.

Evolution in Lithography Techniques: Microlithography to Nanolithography

In this era, electronic devices such as mobile phones, computers, laptops, sensors, and many more have become a necessity in healthcare, for a pleasant lifestyle, and for carrying out tasks quickly and easily. Different types of temperature sensors, biosensors, photosensors, etc., have been developed to meet the necessities of people. All these devices have chips inside them fabricated using diodes, transistors, logic gates, and ICs. The patterning of the substrate which is used for the further development of these devices is done with the help of a technique known as lithography. In the present work, we have carried out a review on different types of lithographic techniques such as optical lithography, extreme ultraviolet lithography, electron beam lithography, X-ray lithography, and ion beam lithography. The evolution of these techniques with time and their application in device fabrication are discussed. The different exposure tools developed in the past decade to enhance the resolution of these devices are also discussed. Chemically amplified and non-chemically amplified resists with their bonding and thickness are discussed. Mask and maskless lithography techniques are discussed along with their merits and demerits. Device fabrication at micro and nano scale has been discussed. Advancements that can be made to improve the performance of these techniques are also suggested.

In Situ Time-of-Flight Mass Spectrometry of Ionic Fragments Induced by Focused Electron Beam Irradiation: Investigation of Electron Driven Surface Chemistry inside an SEM under High Vacuum

Recent developments in nanoprinting using focused electron beams have created a need to develop analysis methods for the products of electron-induced fragmentation of different metalorganic compounds. The original approach used here is termed focused-electron-beam-induced mass spectrometry (FEBiMS). FEBiMS enables the investigation of the fragmentation of electron-sensitive materials during irradiation within the typical primary electron beam energy range of a scanning electron microscope (0.5 to 30 keV) and high vacuum range. The method combines a typical scanning electron microscope with an ion-extractor-coupled mass spectrometer setup collecting the charged fragments generated by the focused electron beam when impinging on the substrate material. The FEBiMS of fragments obtained during 10 keV electron irradiation of grains of silver and copper carboxylates and shows that the carboxylate ligand dissociates into many smaller volatile fragments. Furthermore, in situ FEBiMS was performed on carbonyls of ruthenium (solid) and during electron-beam-induced deposition, using tungsten carbonyl (inserted via a gas injection system). Loss of carbonyl ligands was identified as the main channel of dissociation for electron irradiation of these carbonyl compounds. The presented results clearly indicate that FEBiMS analysis can be expanded to organic, inorganic, and metal organic materials used in resist lithography, ice (cryo-)lithography, and focused-electron-beam-induced deposition and becomes, thus, a valuable versatile analysis tool to study both fundamental and process parameters in these nanotechnology fields.

Designing Rewritable Dual-Mode Patterns using a Stretchable Photoresponsive Polymer via Orthogonal Photopatterning

The fabrication of dual-mode patterns in the same region of a material is a promising approach for high-density information storage, new anti-counterfeiting technologies, and highly secure encryption. However, dual-mode patterns are difficult to achieve because the two patterns in one material may interfere with each other during fabrication and usage. The development of noninterfering dual-mode patterns requires new materials and patterning techniques. Herein, a novel orthogonal photopatterning technique is reported for the fabrication of noninterfering dual-mode patterns on an azopolymer P1. P1 is a unique material that exhibits both photoinduced reversible solid-to-liquid transitions and good stretchability. In the first step of orthogonal photopatterning, patterned photonic structures are fabricated on a P1 film via masked nanoimprinting controlled by photoinduced reversible solid-to-liquid transitions. In the second step, the P1 film is stretched and irradiated with polarized light through a photomask, which generates a chromatic polarization pattern. In particular, the photonic structures and chromatic polarization in the dual-mode pattern are noninterfering. Another feature of dual-mode patterns is that they are rewritable via photo-, thermal, or solution reprocessing, which are useful for recycling and reprogramming. This study opens an avenue for the development of novel materials and techniques for photopatterning.

Weiss

Developing on-chip functional devices requires reliable fabrication methods with high resolution for miniaturization, desired components for enhanced performance, and high throughput for fast prototyping and mass production. Recently, laser-based bubble-pen lithography (BPL) has been developed to enable sub-micron linewidths, in situ synthesis of custom materials, and on-demand patterning for various functional components and devices. BPL exploits Marangoni convection induced by a laser-controlled microbubble to attract, accumulate, and immobilize particles, ions, and molecules onto different substrates. Recent years have witnessed tremendous progress in theory, engineering, and application of BPL, which motivated us to write this review. First, an overview of experimental demonstrations and theoretical understandings of BPL is presented. Next, we discuss the advantages of BPL and its diverse applications in quantum dot displays, biological and chemical sensing, clinical diagnosis, nanoalloy synthesis, and microrobotics. We conclude this review with our perspective on the challenges and future directions of BPL.

Molecular Layer Deposition of a Hafnium-Based Hybrid Thin Film as an Electron Beam Resist

The development of new resist materials is vital to fabrication techniques for next-generation microelectronics. Inorganic resists are promising candidates because they have higher etch resistance, are more impervious to pattern collapse, and are more absorbing of extreme ultraviolet (EUV) radiation than organic resists. However, there is limited understanding about how they behave under irradiation. In this work, a Hf-based hybrid thin film resist, known as "hafnicone", is deposited from the vapor-phase via molecular layer deposition (MLD), and its electron-beam and deep-ultraviolet (DUV)-induced patterning mechanism is explored. The hafnicone thin films are deposited at 100 °C by using the Hf precursor tetrakis(dimethylamido)hafnium(IV) and the organic precursor ethylene glycol. E-beam lithography, scanning electron microscopy, and profilometry are used to investigate the resist performance of hafnicone. With 3 M HCl as the developer, hafnicone behaves as a negative tone resist which exhibits a sensitivity of 400 μC/cm2 and the ability to resolve 50 nm line widths. The resist is characterized via X-ray photoelectron spectroscopy (XPS) and infrared spectroscopy (IR) to investigate the patterning mechanism, which is described in the context of classical nucleation theory. This study of hafnicone hybrid MLD demonstrates the ability for the bottom-up vapor deposition of inorganic resists to be utilized in advanced e-beam and DUV lithographic techniques.

Hierarchical, Self-Assembled Metasurfaces via Exposure-Controlled Reflow of Block Copolymer-Derived Nanopatterns

Nanopatterning for the fabrication of optical metasurfaces entails a need for high-resolution approaches like electron beam lithography that cannot be readily scaled beyond prototyping demonstrations. Block copolymer thin film self-assembly offers an attractive alternative for producing periodic nanopatterns across large areas, yet the pattern feature sizes are fixed by the polymer molecular weight and composition. Here, a general strategy is reported which overcomes the limitation of the fixed feature size by treating the copolymer thin film as a hierarchical resist, in which the nanoscale pattern motif is defined by self-assembly. Feature sizes can then be tuned by thermal reflow controlled locally by irradiative cross-linking or chemical alteration using lithographic ultraviolet light or electron beam exposure. Using blends of polystyrene-block-poly(methylmethacrylate) (PS-b-PMMA) with PS and PMMA homopolymers, we demonstrate both self-assembled PS grating and hexagonal hole patterns; exposure-controlled reflow is then used to reduce the hole diameter by as much as 50% or increase the PS grating linewidth by more than 180%. Transferring these nanopatterns, or their inverse obtained by a lift-off approach, into silicon yields structural colors that may be prescriptively controlled based on the nanoscale feature size. Furthermore, patterned exposure enables area-selective feature size control, yielding uniform structural color patterns across centimeter square areas. Electron beam lithography is also used to show that the lithographic resolution of this selective-area control can be extended to the nanoscale dimensions of the self-assembled features. The exposure-controlled reflow approach demonstrated here takes a pivotal step toward fabricating complex, hierarchical optical metasurfaces using scalable self-assembly methods.

Gentle Patterning Approaches toward Compatibility with Bio-Organic Materials and Their Environmental Aspects

Advances in material science, bioelectronic, and implantable medicine combined with recent requests for eco-friendly materials and technologies inevitably formulate new challenges for nano- and micropatterning techniques. Overall, the importance of creating micro- and nanostructures is motivated by a large manifold of fundamental and applied properties accessible only at the nanoscale. Lithography is a crucial family of fabrication methods to create prototypes and produce devices on an industrial scale. The pure trend in the miniaturization of critical electronic semiconducting components has been recently enhanced by implementing bio-organic systems in electronics. So far, significant efforts have been made to find novel lithographic approaches and develop old ones to reach compatibility with delicate bio-organic systems and minimize the impact on the environment. Herein, such delicate materials and sophisticated patterning techniques are briefly reviewed.

Ionic Liquid Gating of SrTiO3 Lamellas Fabricated with a Focused Ion Beam

In this work, we combine two previously incompatible techniques for defining electronic devices: shaping three-dimensional crystals by focused ion beam (FIB), and two-dimensional electrostatic accumulation of charge carriers. The principal challenge for this integration is nanometer-scale surface damage inherent to any FIB-based fabrication. We address this by using a sacrificial protective layer to preserve a selected pristine surface. The test case presented here is accumulation of 2D carriers by ionic liquid gating at the surface of a micron-scale SrTiO₃ lamella. Preservation of surface quality is reflected in superconductivity of the accumulated carriers. This technique opens new avenues for realizing electrostatic charge tuning in materials that are not available as large or exfoliatable single crystals, and for patterning the geometry of the accumulated carriers.

High-Throughput Fabrication of Triangular Nanogap Arrays for Surface-Enhanced Raman Spectroscopy

Squeezing light into nanometer-sized metallic nanogaps can generate extremely high near-field intensities, resulting in dramatically enhanced absorption, emission, and Raman scattering of target molecules embedded within the gaps. However, the scarcity of low-cost, high-throughput, and reproducible nanogap fabrication methods offering precise control over the gap size is a continuing obstacle to practical applications. Using a combination of molecular self-assembly, colloidal nanosphere lithography, and physical peeling, we report here a high-throughput method for fabricating large-area arrays of triangular nanogaps that allow the gap width to be tuned from ∼10 to ∼3 nm. The nanogap arrays function as high-performance substrates for surface-enhanced Raman spectroscopy (SERS), with measured enhancement factors as high as 10⁸ relative to a thin gold film. Using the nanogap arrays, methylene blue dye molecules can be detected at concentrations as low as 1 pM, while adenine biomolecules can be detected down to 100 pM. We further show that it is possible to achieve sensitive SERS detection on binary-metal nanogap arrays containing gold and platinum, potentially extending SERS detection to the investigation of reactive species at platinum-based catalytic and electrochemical surfaces.