Nanofabrication Applications Research Articles

Self-Assembly of Hierarchical Silicon-Containing Block Copolymers with Cross-Linkable 3 nm Smectic Motifs for Nanopatterning and Osmotic Energy Conversion Membranes.

Highly-dense small-feature-size nanopatterns and nanoporous membranes are important in advanced microelectronics, nanofiltration, and biomimic device manufacturing. Here, we report the synthesis and self-assembly of a series of high-interaction-parameter (high-χ) silicon-containing hierarchical block copolymers (BCPs) with cross-linkable subordering chalcone motifs, which possess both an intrinsic native etching contrast for nanofabrication and cross-linkability under ultraviolet light for generating free-standing membranes. BCPs with a volume fraction of chalcone block of 55-74% form ordered primary nanostructures with period 15-22 nm including lamellae, double gyroid, hexagonally packed cylinders, and body-centered cubic spheres of the minority Si-containing block. The majority PChMA block self-assembles into a highly ordered 3 nm smectic sublattice, and cross-linking after self-assembly enables the formation of free-standing isoporous membranes. Both silicon oxide nanopatterns and free-standing nanoporous osmotic energy conversion membranes are generated by etching films of these BCPs. This work demonstrates that the combination of hierarchical ordering and cross-linkable motifs in a high-interaction parameter BCP enables applications in both nanofabrication and free-standing functional porous membranes.

Recycling Materials for Sustainable DNA Origami Manufacturing.

DNA origami nanotechnology has great potential in multiple fields including biomedical, biophysical, and nanofabrication applications. However, current production pipelines lead to single-use devices incorporating a small fraction of initial reactants, resulting in a wasteful manufacturing process. Here, we introduce two complementary approaches to overcome these limitations by recycling the strand components of DNA origami nanostructures (DONs). We demonstrate reprogramming entire DONs into new devices, reusing scaffold strands. We validate this approach by reprogramming DONs with complex geometries into each other, using their distinct geometries to verify successful scaffold recycling. We reprogram one DON into a dynamic structure and show both pristine and recycled structures display similar properties. Second, we demonstrate the recovery of excess staple strands postassembly and fold DONs with these recycled strands, showing these structures exhibit the expected geometry and dynamic properties. Finally, we demonstrate the combination of both approaches, successfully fabricating DONs solely from recycled DNA components.

Optically controllable deformation and phase change in VO2/Si3N4/Au hybrid nanostructures with polarization selectivity

Optically spatial displacement and material modification hold great potential for the appealing applications in nanofabrication and reconfiguration of functional optical devices. Here, we propose and demonstrate a scheme to achieve simultaneous deformation and phase change in vanadium dioxide (VO2)/Si3N4/Au hybrid nanostructures by laser stimuli. Low triggering threshold and significant deformation characteristics of VO2, based on controllable phase transition, are demonstrated in microscale cantilevers. The plasmonic properties of the nanostructure array are further utilized to achieve a polarization-selective dynamic response. The persistence of deformation and dynamical optical modulation are further demonstrated. Such high-precision fabrication methods and non-contact reconfiguration methods are useful for future applications in dynamic optical manipulation.

Investigations on tip-based large area nanofabrication and nanometrology using a planar nanopositioning machine (NFM-100)

This paper explores large area application of tip-based nanofabrication by field emission scanning probe lithography and showcases the simultaneous possibility of atomic force microscopy on macroscopic scales. This is made possible by the combination of tip-based technology and a planar nanopositioning and nanomeasuring machine. Using long range atomic force microscopy measurement of regular grating structures, the performance of the machine is thoroughly characterized over the full 100 mm range of motion of the positioning machine, which was confirmed by repeated measurements. After initially focussing on achieving the minimum line width of < 40 nm in microscopic areas, a grating with a pitch of 1 μm is additionally fabricated over a total length of 10 mm, whereby the dimensions and deviations are also considered.

Three-Point-Star Deoxyribonucleic Acid Tiles with the Core Arm Length at Three Half-Turns for Two-Dimensional Archimedean Tilings and Beyond.

2D Archimedean tiling and complex tessellation patterns assembled from soft materials including modular DNA tiles have attracted great interest because of their specific structures and potential applications in nanofabrication, nanoelectronics, nanophotonics, biomedical sensing, drug delivery, therapeutics, etc. Traditional three- and four-point-star DNA tiles with the core arm length at two half-turns (specified as three- and four-point-star-E previously and abbreviated as 3PSE and 4PSE tiles here) have been applied to assemble intricate tessellations through tuning the size of inserted nT (n = 1-7, T is thymine) loops on helper strands at the tile center. Following our recent findings using a new type of four-point-star tiles with the core arm length at three half-turns (specified as four-point-star-O previously and abbreviated as 4PSO tiles here) to assemble DNA tubes and flat 2D arrays, we report here the cross-hybridization weaving architectures at the tile center to construct three new 3PSO tiles with circular DNA oligonucleotides of 96-nt (nucleotides) serving as the scaffolds, further the monotonous and combinatory E- and O-tilings on one type of 3PSO tiles to create 2D Archimedean tiling patterns (6.6.6) and (4.8.8), and finally, the combination of 3PSO with 4PSO as well as 2PSO tiles to tile into complex tessellation patterns. The easy realization of regular and intricate DNA tessellations with 2-4PSO tiles not only richens the fundamental DNA modules and complex DNA nanostructures in types but also broadens the potential application scopes of DNA nanostructures in nanofabrication, DNA computing, biomedicine, etc.

Selectivity and Growth Rate Modulations for Ruthenium Area‐selective Deposition by Co‐Reagent and Nanopattern Design

AbstractArea‐selective deposition (ASD) is a bottom‐up technique that provides numerous opportunities for nanoelectronic device fabrication. For example, advanced nano‐interconnect structures with barrierless metals like Ru in the contact holes can be created by Ru ASD with the bottom metals as growth surfaces and dielectrics as non‐growth surfaces. This work investigates Ru ASD by chemical vapor deposition (CVD) on industrially relevant substrates and nanopatterns and reveals how selectivity and growth rate are modulated by the CVD conditions and type of nanopattern. For low‐k dielectric/Cu substrate combinations, the selectivity reverses from metal‐on‐metal to metal‐on‐dielectric upon only changing the CVD co‐reagent from H2 to NH3. In contrast, NH3 is the preferred co‐reagent for SiO2‐TiN line patterns with critical dimension (CD) of 40 nm due to the more favorable adsorption and diffusion kinetics that cause growth rate and selectivity enhancement. Consistent with a diffusion‐mediated mechanism, the growth rate enhances even more for Ru CVD on nanoscale contact holes with CD of 10.5 nm, becoming 2.4 times higher as compared to unpatterned substrates. Thus, the ASD process changes drastically when pattern dimensions reach the nanoscale. The reported insights facilitate rational design of metal ASD processes for multiple applications in nanofabrication.

Acoustofluidic separation of prolate and spherical micro-objects

Most microfluidic separation techniques rely largely on object size as a separation marker. The ability to separate micro-objects based on their shape is crucial in various biomedical and chemical assays. Here, we develop an on-demand, label-free acoustofluidic method to separate prolate ellipsoids from spherical microparticles based on traveling surface acoustic wave-induced acoustic radiation force and torque. The freely rotating non-spherical micro-objects were aligned under the progressive acoustic field by the counterrotating radiation torque, and the major axis of the prolate ellipsoids was parallel to the progressive wave propagation. The specific alignment of the ellipsoidal particles resulted in a reduction in the cross-sectional area perpendicular to the wave propagation. As a consequence, the acoustic backscattering decreased, resulting in a decreased magnitude of the radiation force. Through the variation in radiation force, which depended on the micro-object morphology enabled the acoustofluidic shape-based separation. We conducted numerical simulations for the wave scattering of spherical and prolate objects to elucidate the working mechanism underlying the proposed method. A series of experiments with polystyrene microspheres, prolate ellipsoids, and peanut-shaped microparticles were performed for validation. Through quantitative analysis of the separation efficiency, we confirmed the high purity and high recovery rate of the proposed acoustofluidic shape-based separation of micro-objects. As a bioparticle, we utilize Thalassiosira eccentrica to perform shape-based separation, as the species has a variety of potential applications in drug delivery, biosensing, nanofabrication, bioencapsulation and immunoisolation.

Spreading Solution Additives Governs the Quality of Polystyrene Particle-Based Two-Dimensional Opals.

Two-dimensional polystyrene sphere opals are important materials for nanotechnology applications and fundamental nanoscience research. They are a facile and inexpensive nanofabrication tool, but the quality factor of these opals has drastic differences between reports. Additives like ethanol, ions, and organic molecules in the aqueous particle spreading solution are known to affect the quality factor and growth efficiency of the produced opals. However, a systematic study on the effect and optimization of some of the most effective additives has not been reported until now. Here, we investigate the influence of additives on the growth efficiency and quality factor of such monolayers formed at the air-water interface without the use of a Langmuir-Blodgett trough. The additives induced large variations in the monolayer quality factor and growth efficiency, and we found that the ideal additive content of the spreading agents is 30 wt % < cethanol < 70 wt %, 0 < cH2SO4 < 30.5 mM, and 0 < csty < 255.0 mM. This study provides a guideline for the rational composition and additive content of the spreading solution to obtain high-quality two-dimensional opals for further applications in nanofabrication and photonics and will enable researchers and application engineers to produce standardized nanofabrication materials.

Single Layer Lift-Off of CSAR62 for Dense Nanostructured Patterns

Lift-off processing is a common method of pattern transfer for different nanofabrication applications. With the emergence of chemically amplified and semi-amplified resist systems, the possibilities for pattern definition via electron beam lithography has been widened. We report a reliable and simple lift-off process for dense nanostructured pattern in CSAR62. The pattern is defined in a single layer CSAR62 resist mask for gold nanostructures on silicon. The process offers a slimmed down pathway for pattern definition of dense nanostructures with varied feature size and an up to 10 nm thick gold layer. The resulting patterns from this process have been successfully used in metal assisted chemical etching applications.

Ketocoumarin-Based Photoinitiators for High-Sensitivity Two-Photon Lithography

Ketocoumarins are attractive and distinct photosensitizers due to their high molar extinction coefficients, high intersystem crossing coefficients, and high photochemical stability. As a classic commercial ketocoumarin-based two-photon initiator, 7-diethylamino-3-thenoylcoumarin (DETC) was widely used in two-photon lithography. However, the large fluorescence quantum yield and low two-photon absorption cross section value greatly limit its application in high-throughput nanofabrication. In this work, a series of DETC derivatives were developed by extending the length of the alkyl chain and integrating different donor and acceptor groups. These ketocoumarin-based initiators, namely, compounds 1–7, were designed, synthesized, and unambiguously characterized. Compared with DETC, these compounds exhibit higher molar extinction coefficient, lower fluorescence quantum yield, higher two-photon absorption cross section, and improved sensitivity in two-photon lithography. Among these molecules, compound 7 with expanded π-electron systems and structures with enhanced intramolecular charge transfer exhibits the best sensitivity in two-photon lithography. With compound 7-based photoresist, many kinds of complex three-dimensional patterns can be fabricated using two-photon lithography at a writing speed of up to 60 mm s–1. The high two-photon initiation sensitivity makes these compounds promising candidates for commercialization and provides a new design concept for the development of new initiators.

In Situ Domain-Confined Epitaxial Regrowth of Individual Nanoparticle: Implications for Nanofabrication

Electron beam irradiation has become a powerful tool for designing material structures and studying nanostructure growth down to the individual nanoparticle (NP) level; the method has important fundamental research implications and potential technological applications. However, controlling NP growth under high-energy bombardment is challenging owing to the rapid and unconstrained evolution of NPs during nanofabrication. Herein, a real-time in situ study of epitaxial regrowth of partially sublimated NPs was performed using an FEI Titan 80–300 transmission electron microscope operated at 300 kV. Hybrid NPs containing Ag, Cu, and CuAg with particle sizes of 2–20 nm were obtained via electron beam irradiation of large (35 nm) CuAg NPs at 500 °C. NPs sublimed with increased temperature. Interestingly, domain-confined layer-by-layer epitaxial regrowth on the Ag{111} and {100} facets was observed for partially sublimated NPs. The newly grown part was mostly Ag, as determined using energy-dispersive X-ray spectroscopy. Electron beam irradiation was a key activator for epitaxial regrowth. This study provides real-time regrowth dynamics information at an atomic level, providing new insights into nanostructure growth control in gaseous environments, finding promising applications in nanofabrication.

Interplay of Consolidation Fronts and Cracks in Drying Colloidal Coatings and Its Application in Controlling Crack Pattern Formation

Cracks are frequently observed in drying colloidal coatings. Although a rich collection of crack patterns has been reported, the systematic study on how cracks grow into the final morphology during the drying process remains elusive. In this work, we use directional drying channels with wedge-shaped edges of different angles to study the interplay of advancing consolidation fronts and propagating cracks. We found that although the shape of the advancing consolidation fronts is altered by the drying edge, the growth direction of the following cracks remains perpendicular to the consolidation fronts during the whole drying process, resulting in cracks with a large curvature. We rationalize the evolution of consolidation fronts with the distribution of capillary pressure revealed by a Laplace model. Further, the growth direction of cracks can be explained by the fracture mechanics mechanism that the main orientation of internal tensile stresses developed during the consolidation determines the crack growth direction. Utilizing this understanding, wavy crack patterns are generated in rectangular drying channels with an alternating temperature field, demonstrating a feasible method of designing and controlling drying-induced crack patterns for micro-/nano-fabrication applications.

Study ofn-Alkanethiol Self-Assembly Behavior on Iron Particles: Effect of Alkyl Chain Length and Adsorption Solvent on Resulting Iron-Based Magnetorheological Fluids

Self-assembled monolayers (SAMs) of organic molecules on metal surfaces are a type of inexpensive surface coating often used to improve metal substrate properties for sensors, electrochemistry, and nanofabrication applications. Iron, specifically, is one of the most commonly used metals, both as a pure metal and as an alloy due to its high conductivity, strong ferromagnetism, and low cost. However, magnetorheological fluids, which have shown impressive energy dampening in fields from civil infrastructure to biomedical devices utilizing iron dispersions, have suffered from low reliability and efficiency due to iron particle oxidation, corrosion, and settling. To understand the effect of self-assembled monolayers on iron and both the adsorbed particle's resistance against aggregation and performance impact, this work performs an in-depth study on alkanethiol-based self-assembled monolayers on iron particles. Adsorption of alkanethiols and the generation of SAMs on micron-sized iron particles were evaluated as a function of adsorption solvent polarity and alkanethiol chain length. Maximum alkanethiol loading, determined from appropriate isotherms, was found to strongly be a function of both parameters. Alkanethiol adsorption increased with increasing alkyl chain length and increasing solvent log P values in polar solvents. With respect to magnetorheologically relevant parameters, alkanethiol adsorption did not show any significant effect on both the magnetic properties of iron (as particles) and fluid on-state yield stress. The colloidal stability of n-alkanethiol adsorbed iron-based magnetorheological fluids (MRFs) was a function of both n-alkanethiol chain length and the iron particle adsorption solvent. MRFs composed of hexadecanethiol adsorbed iron prepared in polar solvents like methanol and ethanol showed excellent sedimentation stability compared to all other MRFs prepared in this study.

Advancing the Utility of DNA Origami Technique through Enhanced Stability of DNA-Origami-Based Assemblies.

Since its discovery in 2006, the DNA origami technique has revolutionized bottom-up nanofabrication. This technique is simple yet versatile and enables the fabrication of nanostructures of almost arbitrary shapes. Furthermore, due to their intrinsic addressability, DNA origami structures can serve as templates for the arrangement of various nanoscale components (small molecules, proteins, nanoparticles, etc.) with controlled stoichiometry and nanometer-scale precision, which is often beyond the reach of other nanofabrication techniques. Despite the multiple benefits of the DNA origami technique, its applicability is often restricted by the limited stability in application-specific conditions. This Review provides an overview of the strategies that have been developed to improve the stability of DNA-origami-based assemblies for potential biomedical, nanofabrication, and other applications.

Probing the Mechanical Properties of DNA Nanostructures with Metadynamics.

Molecular dynamics simulations are often used to provide feedback in the design workflow of DNA nanostructures. However, even with coarse-grained models, the convergence of distributions from unbiased simulation is slow, limiting applications to equilibrium structural properties. Given the increasing interest in dynamic, reconfigurable, and deformable devices, methods that enable efficient quantification of large ranges of motion, conformational transitions, and mechanical deformation are critically needed. Metadynamics is an automated biasing technique that enables the rapid acquisition of molecular conformational distributions by flattening free energy landscapes. Here we leveraged this approach to sample the free energy landscapes of DNA nanostructures whose unbiased dynamics are nonergodic, including bistable Holliday junctions and part of a bistable DNA origami structure. Taking a DNA origami-compliant joint as a case study, we further demonstrate that metadynamics can predict the mechanical response of a full DNA origami device to an applied force, showing good agreement with experiments. Our results exemplify the efficient computation of free energy landscapes and force response in DNA nanodevices, which could be applied for rapid feedback in iterative design workflows and generally facilitate the integration of simulation and experiments. Metadynamics will be particularly useful to guide the design of dynamic devices for nanorobotics, biosensing, or nanomanufacturing applications.

Self-referenced nanometric displacement sensing assisted by optical anapole mode

Long range optical rulers measuring distance greater than 10 nm have important applications in monitoring biological processes, nanolithography, and nanometrology. In this work, we show that lateral displacement over 120 nm can be determined by measuring two reflection peaks of the proposed nanostructure. The optical anapole in the nanostructure is excited, resulting from interactions of plasmonic resonance modes of nanoholes perforated in metal films and an array of nanoblocks. Results show that a 120 nm relative displacement between the nanoblocks and nanoholes induces a negative correlated 90% variation of reflection spectrum which can be used for self-referenced measurement. The proposed design could find applications in nanometrology, biosensing, and nanofabrication.

Near-Field Electrospinning: Crucial Parameters, Challenges, and Applications.

Near-field electrospinning (NFES) is a micro- or nanofiber production technology based on jetting molten polymer or polymer solution. Thanks to the programmable collector and nozzle movement, it can generate designed patterns in the presence of an electric field. Despite a few shortcomings of NFES, its high resolution, simplicity, precision, high throughput, reproducibility, and low costs have convinced researchers to employ it for various purposes. Furthermore, as the paradigm of fiber-based structures shifts from random textures toward delicate designs, NFES can bridge the gap between existing inefficient processes and aspired technologies for precise patterning. NFES facilitates the production of ultrafine nanofibers because it can be used to fabricate them in every laboratory. These robust fibers are convenient tools for small and additive manufacturing. As such, NFES is considered a potent additive fabrication technology that facilitates the production of complicated patterns as well. It is suggested that near-field electrospun fibers exhibit outstanding results in various applications, owing to their precise and controllable positioning. Meanwhile, the ongoing development of NFES has yet to reach its climax, making it attractive for further research. In this review, the basic principles of NFES, derivatives, limitations, and applications in nanomanufacturing, tissue engineering, microscale electronics, biosensors, and optics are presented.

Generation of transversely oriented optical polarization Möbius strips.

We report a time-reversal method based on the Richards-Wolf vectorial diffraction theory to generate a prescribed polarization topology on a defined trajectory within areas of relatively high intensity. An example is given to generate transversely oriented optical Möbius strips that wander around an axis perpendicular to the beam propagation direction. A number of sets of dipole antennae are purposefully positioned on a defined trajectory in the y = 0 plane and the radiation fields are collected by one high-NA objective lens. By sending the complex conjugate of the radiation fields in a time-reversed manner, the focal fields are calculated and the optical polarization topology on the trajectory can be tailored to form prescribed Möbius strips. The ability to control optical polarization topologies may find applications in nanofabrication, quantum communication, and light-matter interaction.

Biomimicry of Blue Morpho butterfly wings: An introduction to nanotechnology through an interdisciplinary science education module

AbstractBiomimicry is the practice of imitating naturally occurring bio‐designs through engineering and invention. For instance, Blue Morpho butterfly wing colors are a result of the reflection and refraction of nanostructures embedded in the wing and have inspired practical applications in nanofabrication and photonics. Interdisciplinary science educational materials have been developed that demonstrate the cross‐disciplinary aspects and biomimetic properties used in designing nano‐based devices. The unique optical properties of the Blue Morpho wing provides an excellent source of demonstrating how aspects of chemistry, biology, physics, and nanotechnology relate. Specifically, these educational tools demonstrate concepts including natural selection, chemical and physical properties, structure at the nanoscale, optical, and electromagnetic design. In addition, the engaging activities are correlated to how nanotechnology drives invention and provides students a mechanism to be introduced to the possibilities nanotechnology provides. A comprehensive combination of lab, cleanroom, and classroom activities are suggested to promote remote learning.

Plasmonic metal‐organic frameworks

AbstractPlasmonic metal‐organic frameworks are composite nanoparticles comprising plasmonic metal nanoparticles (NPs) embedded within a metal‐organic framework (MOF) matrix. As a result, not only the functionalities of the individual components are retained, but synergistic effects additionally provide improved chemical and physical properties. Recent progress in plasmonic MOFs has demonstrated the potential for nanofabrication and various nanotechnology applications. Synthetic challenges toward plasmonic MOFs have been recently addressed, resulting in new opportunities toward practical applications, such as surface‐enhanced Raman scattering, therapy, and catalysis. The impact of key parameters (thermodynamic vs. kinetic) on the synthetic pathways of plasmonic MOFs is reviewed, while providing insight into related progress toward structure‐derived applications.