Advanced Nanofabrication Research Articles

A parylene-mediated plasmonic-photonic hybrid fiber-optic sensor and its instrumentation for miniaturized and self-referenced biosensing.

With the development of advanced nanofabrication techniques over the past decades, different nanostructure-based plasmonic fiber-optic sensors have been developed and have presented a low limit of detection for various biomolecules. However, owing to both the dependence on complex equipment and the trade-off between the fabrication cost and sensing performance, nanostructured plasmonic fiber-optic sensors are rarely used outside laboratories. To facilitate wider application of the plasmonic fiber-optic sensors, a parylene-mediated hybrid plasmonic-photonic cavity-based sensor was developed. Compared with a similar plasmonic sensor which only works in the plasmonic mode, the proposed hybrid sensor shows a higher reproducibility (CV < 2.5%) due to its resistance to fabrication variations. Meanwhile, a self-referenced detection mechanism and a novel miniaturized system were developed to adapt to the hybrid resonance sensor. The entire system only has a weight of 263 g, and a size of 12 cm × 10 cm × 8 cm, and is especially suitable for outdoor applications in a handheld manner. In experiments, a high refractive index sensitivity of 3.148 RIU-1 and real-time biomolecule monitoring at nanomolar concentrations were achieved by the proposed system, further confirming the potential of the miniaturized system as a candidate for point-of-care health diagnostics outside laboratories.

Advanced materials for bioresorbable stent for real-time health-care monitoring

Purpose: Heart failure, which has a mortality rate higher than most cancers, is among the most important public health issues. Because of this, the fields of medicine and bio-medical engineering have provided a lot of attention to cardiovascular disease. In this review, we present the recent bioresorbable stent technology in aspect of advanced materials to overcome health issues.&#x0D; Methodology: This study is based on reviews of Bioresorbable stent (BRS) technology from various technical resources.&#x0D; Main Findings: Bioresorbable stent (BRS) shows new class of medical devices in interventional cardiology for the treatment of coronary artery disease. The concept of the BRS is to provide temporal support to the vessel during healing before being degraded and absorbed by the body, eliminating the additional surgical process.&#x0D; Implications: With advances in nanofabrication, novel kinds of bioresorbable sensing/wireless component could be fabricated and integrated on the stent without failure when it expanded in the vessel. These technologies will significantly influence future diagnosis technology for future generations.&#x0D; Novelty: The technology was introduced to overcome limitations of current developed drug-eluting stents, which are fabricated with metallic materials. With development of medical strategies, we could response earlier for medical issues to prevent recurrence of disease.

Nanostructured Transition Metal Dichalcogenide Multilayers for Advanced Nanophotonics

AbstractTransition metal dichalcogenides (TMDs) attract significant attention due to their exceptional optical, excitonic, mechanical, and electronic properties. Nanostructured multilayer TMDs were recently shown to be highly promising for nanophotonic applications, as motivated by their exceptionally high refractive indices and optical anisotropy. Here, this vision is extended to more sophisticated structures, such as periodic arrays of nanodisks and nanoholes with ultra sharp walls, as well as proof‐of‐concept all‐TMD waveguides and resonators. Specific focus is given to various advanced nanofabrication strategies, including careful selection of resists for electron beam lithography and etching methods, especially for non‐conductiven but relevant for nanophotonic applications substrates, such as SiO2. The specific materials studied here include semiconducting WS2, in‐plane anisotropic ReS2, and metallic TaSe2, TaS2, and NbSe2. The resulting nanostructures can potentially impact several nanophotonic and optoelectronic areas, including high‐index nanophotonics, plasmonics and on‐chip optical circuits. The knowledge of TMD material‐dependent nanofabrication parameters developed here will help broaden the scope of future applications of all‐TMD nanophotonics.

Open-Source Computational Photonics with Auto Differentiable Topology Optimization

In recent years, technological advances in nanofabrication have opened up new applications in the field of nanophotonics. To engineer and develop novel functionalities, rigorous and efficient numerical methods are required. In parallel, tremendous advances in algorithmic differentiation, in part pushed by the intensive development of machine learning and artificial intelligence, has made possible large-scale optimization of devices with a few extra modifications of the underlying code. We present here our development of three different software libraries for solving Maxwell’s equations in various contexts: a finite element code with a high-level interface for problems commonly encountered in photonics, an implementation of the Fourier modal method for multilayered bi-periodic metasurfaces and a plane wave expansion method for the calculation of band diagrams in two-dimensional photonic crystals. All of them are endowed with automatic differentiation capabilities and we present typical inverse design examples.

Optical Fourier Volumes: A Revisiting of Holographic Photopolymers and Photoaddressable Polymers

AbstractTo avoid mixing of the undesired frequencies in a free‐space, the point sources of gratings, defined by a spatially varying refractive index, should be sinusoidally rather than binarily arranged. This long‐lasting but gold standard lesson attainable from a classical Fourier optics, however, is underutilized in the practical materialization of gratings, mainly because most of the fabrication methods, developed thus far, are intrinsically compatible with a binary rather than sinusoidal grating. Recently, such design concept of optical Fourier elements has been implemented into the real surface gratings (referred to as optical Fourier surfaces) by taking advantage of advanced nanofabrication, whereas their volumetric equivalents (optical Fourier volumes, OFVs) have yet to be conceptually and experimentally elucidated. In this work, the key characteristics of OFVs and their structural requirements are systematically exploited with the assistance of analytical and numerical calculations. Especially, the dynamic range and thickness of volume gratings, required for OFVs, are newly defined. Given these theoretical blueprints, both the holographic photopolymers and photoaddressable polymers are then revisited and they are experimentally validated as easy‐to‐craft mediums of OFVs. The landscape of volume gratings is extended by providing an integrative pipeline of OFVs across their theoretical design and practical materialization.

Recent Progress on Optical Micro/Nanomanipulations: Structured Forces, Structured Particles, and Synergetic Applications.

Optical manipulation has achieved great success in the fields of biology, micro/nano robotics and physical sciences in the past few decades. To date, the optical manipulation is still witnessing substantial progress powered by the growing accessibility of the complex light field, advanced nanofabrication and developed understandings of light-matter interactions. In this perspective, we highlight recent advancements of optical micro/nanomanipulations in cutting-edge applications, which can be fostered by structured optical forces enabled with diverse auxiliary multiphysical field/forces and structured particles. We conclude with our vision of ongoing and futuristic directions, including heat-avoided and heat-utilized manipulation, nonlinearity-mediated trapping and manipulation, metasurface/two-dimensional material based optical manipulation, as well as interface-based optical manipulation.

Simultaneous optical resonances at visible and mid-infrared frequencies with epitaxial TiN/Al0.72Sc0.28N/TiN metal/polar-dielectric/metal multilayers

Traditionally, light-matter interactions in the visible spectral range utilize tailored plasmonic nanostructure in metals that often require advanced nanofabrication techniques. Concomitantly, polar lattice vibrations in dielectrics are used to achieve mid-to-long wavelength infrared (IR) light-matter coupling. Achieving optical resonances simultaneously in the visible and mid-to-long wavelength IR spectral range in one host medium has been challenging due to mutually conflicting material and optical property requirements. In this article, we show simultaneous light-matter coupling and development of super absorbers in the visible and mid-IR spectral ranges with a lithography-free planar wide-angle metal-(polar)-dielectric-metal (MDM) Fabry-Pérot cavity composed of ultrathin refractory metallic TiN as the top layer and polar dielectric Al0.72Sc0.28N as the spacer layer. Lattice-matched TiN/Al0.72Sc0.28N/TiN MDM cavities exhibit super absorption resonance with maximum absorptivity of ∼99%. The absorption maxima spectral position is tuned with changes in spacer layer thickness and by utilizing multiple cavity interactions. Al0.72Sc0.28N inside the MDM is also used for light coupling to the transverse optical phonon mode and to the Berremann mode near the longitudinal phonon frequency with strong selective absorption. Demonstration of refractory epitaxial TiN/Al0.72Sc0.28N/TiN MDM metamaterials mark significant progress towards developing compact optical meta-structures with on-demand optical resonances at different spectral ranges.

Drawing at the Nanoscale through Macroscopic Movement.

Nanopatterns are important for applications in various nanodevice fields. Existing nanopatterning techniques mainly directly manufacture the nanopatterns through various lithographic methods, which usually are laborious, time-consuming, and need expensive equipment. Here, an extremely simple drawing at the nanoscale (DAN) concept to indirectly fabricate rational nanopatterns through controlling the macroscopic movement of the substrate , is demonstrated. The structure of the nanopatterns is completely determined by and can be shrunk by millions of times from the moving track of the substrate. Multiple surface nanopatterns of different materials with accurately tailorable relative positions can be simply stacked together by moving the substrate by macroscopic distances during different DAN processes. In combination with sophisticated lithographic methods, the DAN method is anticipated to enable substantial advances in nanofabrication.

Finite-size and quantum effects in plasmonics: manifestations and theoretical modelling [Invited

The tremendous growth of the field of plasmonics in the past twenty years owes much to the pre-existence of solid theoretical foundations. Rather than calling for the introduction of radically new theory and computational techniques, plasmonics required, to a large extent, application of some of the most fundamental laws in physics, namely Maxwell’s equations, albeit adjusted to the nanoscale. The success of this description, which was triggered by the rapid advances in nanofabrication, makes a striking example of new effects and novel applications emerging by applying known physics to a different context. Nevertheless, the prosperous recipe of treating nanostructures within the framework of classical electrodynamics and with use of macroscopic, bulk material response functions (known as the local-response approximation, LRA) has its own limitations, and inevitably fails once the relevant length scales approach the few- to sub-nm regime, dominated by characteristic length scales such as the electron mean free path and the Fermi wavelength. Here we provide a review of the main non-classical effects that emerge when crossing the border between the macroscopic and atomistic worlds. We study the physical mechanisms involved, highlight experimental manifestations thereof and focus on the theoretical efforts developed in the quest for models that implement atomistic descriptions into otherwise classical-electrodynamic calculations for mesoscopic plasmonic nanostructures.

A Comprehensive Multipolar Theory for Periodic Metasurfaces

AbstractOptical metasurfaces consist of 2D arrangements of scatterers, and they control the amplitude, phase, and polarization of an incidence field on demand. Optical metasurfaces are the cornerstone for a future generation of flat optical devices in a wide range of applications. The rapid advances in nanofabrication have made the versatile design and analysis of these ultra‐thin surfaces an ever‐growing necessity. However, a comprehensive theory to describe the optical response of periodic metasurfaces in closed‐form and analytical expressions has not been formulated, and prior attempts are frequently approximate. Here, a theory is developed that analytically links the properties of the scatterer, from which a metasurface is made, to its response via the lattice coupling matrix. The scatterers are represented by their polarizability or T matrix. Explicit expressions for the optical response up to octupolar order in both spherical and Cartesian coordinates are provided, for normal or oblique incidence. Several examples demonstrate that the proposed theoretical approach is a powerful tool for exploring the physics of metasurfaces and designing novel flat optics devices. Novel fully‐diffracting metagratings and particle‐independent polarization filters are proposed, and novel insights into bound states in the continuum, collective lattice resonances, and the response of Huygens’ metasurfaces under oblique incidence are provided.

Proximity-field nanopatterning for high-performance chemical and mechanical sensor applications based on 3D nanostructures

In this era of the Internet of Things, the development of innovative sensors has rapidly accelerated with that of nanotechnology to accommodate various demands for smart applications. The practical use of three-dimensional (3D) nanostructured materials breaks several limitations of conventional sensors, including the large surface-to-volume ratio, precisely tunable pore size and porosity, and efficient signal transduction of 3D geometries. This review provides an in-depth discussion on recent advances in chemical and mechanical sensors based on 3D nanostructures, which are rationally designed and manufactured by advanced 3D nanofabrication techniques that consider structural factors (e.g., porosity, periodicity, and connectivity). In particular, we focus on a proximity-field nanopatterning technique that specializes in the production of periodic porous 3D nanostructures that satisfy the structural properties universally required to improve the performance of various sensor systems. State-of-the-art demonstrations of high-performance sensor devices such as supersensitive gas sensors and wearable strain sensors realized through designed 3D nanostructures are summarized. Finally, challenges and outlooks related to nanostructures and nanofabrication for the practical application of 3D nanostructure-based sensor systems are proposed.

Excitation and detection of acoustic phonons in nanoscale systems.

Phonons play a key role in the physical properties of materials, and have long been a topic of study in physics. While the effects of phonons had historically been considered to be a hindrance, modern research has shown that phonons can be exploited due to their ability to couple to other excitations and consequently affect the thermal, dielectric, and electronic properties of solid state systems, greatly motivating the engineering of phononic structures. Advances in nanofabrication have allowed for structuring and phonon confinement even down to the nanoscale, drastically changing material properties. Despite developments in fabricating such nanoscale devices, the proper manipulation and characterization of phonons continues to be challenging. However, a fundamental understanding of these processes could enable the realization of key applications in diverse fields such as topological phononics, information technologies, sensing, and quantum electrodynamics, especially when integrated with existing electronic and photonic devices. Here, we highlight seven of the available methods for the excitation and detection of acoustic phonons and vibrations in solid materials, as well as advantages, disadvantages, and additional considerations related to their application. We then provide perspectives towards open challenges in nanophononics and how the additional understanding granted by these techniques could serve to enable the next generation of phononic technological applications.

Ultra-low detection limit chemoresistive NO2 gas sensor using single transferred MoS2 flake: an advanced nanofabrication.

In this work, a method of fabricating a NO2 nano-sensor working at room temperature with a low detectable concentration limit is proposed. A 2D-MoS2 flake is isolated by transferring a single MoS2 flake to SiO2/Si substrate, followed by applying an advanced e-beam lithography (EBL) to form a metal contact with Au/Cr electrodes. The resulting chemoresistive nano-sensor using a single MoS2 flake was applied to detect a very low concentration of NO2 at the part-per-billion (ppb) level. This result is obtained due to the ability to create microscopic nano-sized MoS2 gaps using e-beam lithography (300 nm-400 nm). Experimental results also show that the sensor can capture changes in concentration and send the information out extremely quickly. The response and recovery time of the sensor also reached the lowest point of 50 and 75 ms, outperforming other sensors with a similar concentration working range.

Asymmetric Spin Transport in Colloidal Quantum Dot Junctions

The study of charge and spin transport through semiconductor quantum dots is experiencing a renaissance due to recent advances in nanofabrication and the realization of quantum dots as candidates f...

Role of Thin Film Adhesion on Capillary Peeling.

The capillary force can peel off a substrate-attached film if the adhesion energy (Gw) is low. Capillary peeling has been used as a convenient, rapid, and nondestructive method for fabricating free-standing thin films. However, the critical value of Gw, which leads to the transition between peeling and sticking, remains largely unknown. As a result, capillary peeling remains empirical and applicable to a limited set of materials. Here, we investigate the critical value of Gw and experimentally show the critical adhesion (Gw,c) to scale with the water-film interfacial energy (≈0.7γfw), which corresponds well with our theoretical prediction of Gw,c = γfw. Based on the critical adhesion, we propose quantitative thermodynamic guidelines for designing thin film interfaces that enable successful capillary peeling. The outcomes of this work present a powerful technique for thin film transfer and advanced nanofabrication in flexible photovoltaics, battery materials, biosensing, translational medicine, and stretchable bioelectronics.

Bound states in the continuum in resonant nanostructures: an overview of engineered materials for tailored applications

Abstract From theoretical model to experimental realization, the bound state in the continuum (BIC) is an emerging area of research interest in the last decade. In the initial years, well-established theoretical frameworks explained the underlying physics for optical BIC modes excited in various symmetrical configurations. Eventually, in the last couple of years, optical-BICs were exploited as a promising tool for experimental realization with advanced nanofabrication techniques for numerous breakthrough applications. Here, we present a review of the evolution of BIC modes in various symmetry and functioning mediums along with their application. More specifically, depending upon the nature of the interacting medium, the excitations of BIC modes are classified into the pure dielectric and lossy plasmonic BICs. The dielectric constituents are again classified as photonic crystal functioning in the subwavelength regime, influenced by the diffraction modes and metasurfaces for interactions far from the diffraction regime. More importantly, engineered functional materials evolved with the pure dielectric medium are explored for hybrid-quasi-BIC modes with huge-quality factors, exhibiting a promising approach to trigger the nanoscale phenomena more efficiently. Similarly, hybrid modes instigated by the photonic and plasmonic constituents can replace the high dissipative losses of metallic components, sustaining the high localization of field and high figure of merit. Further, the discussions are based on the applications of the localized BIC modes and high-quality quasi-BIC resonance traits in the nonlinear harmonic generation, refractometric sensing, imaging, lasing, nanocavities, low loss on-chip communication, and as a photodetector. The topology-controlled beam steering and, chiral sensing has also been briefly discussed.

Femtosecond laser nano-structuring for surface plasmon resonance-based detection of uranium

Surface plasmon resonance (SPR) is a proven technique in sensorics. Wide application of the method is still limited by a necessity of a complex optical equipment using special dispersion elements like a prism or diffraction grating (DG). We have implemented a novel and inexpensive way for fabrication of the DG on a silicon substrate using femtosecond laser ablation (highly regular laser-induced periodic surface structures - HR-LIPSS) technique. The potential of the method has been illustrated for the case of detection of uranium in water. For this purpose, fabricated gratings were coated with thermally evaporated nanofilms of gold and then used as substrates for deposition of nanoparticles of bioinspired polymer polydopamine (PDA) highly selective to uranium under neutral pH. Synergistic combination of the advanced nanofabrication and SPR sensing techniques with advanced PDA ligand allowed preparation of sensing elements with a sub-microgram sensitivity to uranium (∼1.0 × 10−7g/cm2). Even though the results reported here are just a proof of concept, we believe the approach can be expanded to selective detection of various types of analytes (heavy metals, biomolecules, viruses etc.) under different environments (water, air, aerosols) in the future.

Development of triboelectric-enabled tunable Fabry-Pérot photonic-crystal-slab filter towards wearable mid-infrared computational spectrometer

Miniaturized optical spectrometers have been realized by exploiting conventional working principles and advanced nanofabrication technology. Especially in the mid-infrared (MIR) range, chip-scale optical spectrometers enable fast and on-site detection of molecular fingerprints for selective chemical sensing in healthcare and environmental monitoring. This miniaturization is also highly desirable for the wearable devices where the tiny functional parts remain on rigid substrates but the electronics are flexible. In the last decade, the triboelectric nanogenerator (TENG) technology has been proven as an indispensable and enabling technology for wearable self-powered sensors, energy harvesters and voltage sources, etc. Although a few TENG based gas sensors have been demonstrated, each of these sensors can detect a particular gas other than diversified gases. Infrared spectrometer is known as an instrument which can investigate the infrared absorption characteristics of gas molecules. It is the best generic technology to sense multiple gases on the same instrument, or device. In this study, we demonstrate a TENG enabled tunable Fabry-Pérot (FP) photonic-crystal-slab filter aiming for the computational spectrometer in the MIR range. The textile-triboelectric nanogenerator (T-TENG) provides high open-circuit voltage to shift the resonance wavelengths of the electrostatically actuated FP-filter, where this feature provides the sampling bases required for the computational spectrometer. Furthermore, the FP-filter is fabricated by a new transfer-printing method and shows a large wavelength tunability. As a proof of concept, the transmission spectrum of acetone vapor is reconstructed from 5 to 6.5 µm using this TENG enabled FP-filter. The molecular fingerprint of acetone is identified at 5.75 µm. This work paves the way towards the wearable MIR miniaturized optical spectrometer. • A MEMS tunable Fabry-Perot (FP) photonic-crystal-slab filter is fabricated by transfer-printing method. • The computational optical spectrometer is demonstrated for the first time with a single MEMS tunable device. • A textile-TENG is incorporated to tune the resonance of FP filter, forming the sampling bases for computational spectrometer. • The transmission spectra of CO 2 and acetone are reconstructed with their molecular fingerprints identified.

Simple Fabrication of Solid-State Nanopores on a Carbon Film.

Solid-state nanopores are widely used as a platform for stochastic nanopore sensing because they can provide better robustness, controllable pore size, and higher integrability than biological nanopores. However, the fabrication procedures, including thin film preparation and nanopore formation, require advanced micro-and nano-fabrication techniques. Here, we describe the simple fabrication of solid-state nanopores in a commercially available material: a flat thin carbon film-coated micro-grid for a transmission electron microscope (TEM). We attempted two general methods for nanopore fabrication in the carbon film. The first method was a scanning TEM (STEM) electron beam method. Nanopores were fabricated by irradiating a focused electron beam on the carbon membrane on micro-grids, resulting in the production of nanopores with pore diameters ranging from 2 to 135 nm. The second attempt was a dielectric breakdown method. In this method, nanopores were fabricated by applying a transmembrane voltage of 10 or 30 V through the carbon film on micro-grids. As a result, nanopores with pore diameters ranging from 3.7 to 1345 nm were obtained. Since these nanopores were successfully fabricated in the commercially available carbon thin film using readily available devices, we believe that these solid-state nanopores offer great utility in the field of nanopore research.

Dynamics of thin precursor film in wetting of nanopatterned surfaces

The spreading of a liquid droplet on flat surfaces is a well-understood phenomenon, but little is known about how liquids spread on a rough surface. When the surface roughness is of the nanoscopic length scale, the capillary forces dominate and the liquid droplet spreads by wetting the nanoscale textures that act as capillaries. Here, using a combination of advanced nanofabrication and liquid-phase transmission electron microscopy, we image the wetting of a surface patterned with a dense array of nanopillars of varying heights. Our real-time, high-speed observations reveal that water wets the surface in two stages: 1) an ultrathin precursor water film forms on the surface, and then 2) the capillary action by nanopillars pulls the water, increasing the overall thickness of water film. These direct nanoscale observations capture the previously elusive precursor film, which is a critical intermediate step in wetting of rough surfaces.