Nano-patterned Structures Research Articles

Engineered Sustainable Omniphobic Coatings to Control Liquid Spreading on Food-Contact Materials.

The adhesion of sticky liquid foods to a contacting surface can cause many technical challenges. The food manufacturing sector is confronted with many critical issues that can be overcome with long-lasting and highly nonwettable coatings. Nanoengineered biomimetic surfaces with distinct wettability and tunable interfaces have elicited increasing interest for their potential use in addressing a broad variety of scientific and technological applications, such as antifogging, anti-icing, antifouling, antiadhesion, and anticorrosion. Although a large number of nature-inspired surfaces have emerged, food-safe nonwetted surfaces are still in their infancy, and numerous structural design aspects remain unexplored. This Review summarizes the latest scientific research regarding the key principles, fabrication methods, and applications of three important categories of nonwettable surfaces: superhydrophobic, liquid-infused slippery, and re-entrant structured surfaces. The Review is particularly focused on new insights into the antiwetting mechanisms of these nanopatterned structures and discovering efficient platform methodologies to guide their rational design when in contact with food materials. A detailed description of the current opportunities, challenges, and future scale-up possibilities of these nanoengineered surfaces in the food industry is also provided.

Fabrication, characterization and numerical modeling of Sb2Se3 nano-patterned structures

There has been a renewed and strong interest in phase change materials (PCMs) in many fields beyond traditional memories, due to their optical and electrical tunability aspect. Given their unique characteristic of changing phase and refractive index on-demand from amorphous to crystalline and vice versa via optical or electrical switching, they can be employed in many applications ranging from optical filters to rewritable metasurfaces. Patterning PCMs into self-assembled nanorod structures much smaller than the wavelength in diameter could potentially lead to interesting applications such as controlled chirality, birefringence and anisotropy. Additionally, such nanorod geometries may potentially lead to robust switching over multiple cycles for films of thicknesses well beyond those that are switchable in bulk thin film geometries. In this work, we grow and characterize self-assembled nanorods of antimony selenide PCM, and we characterize the nanostrucutres using ellipsometry and X-ray diffraction. We additionally provide an effective medium approximation (EMA) fit that greatly simplifies future macroscopic devices based on the underlying PCM nanorod geometry.

3D-patterned inverse-designed mid-infrared metaoptics

Modern imaging systems can be enhanced in efficiency, compactness, and application through the introduction of multilayer nanopatterned structures for manipulation of light based on its fundamental properties. High transmission multispectral imaging is elusive due to the commonplace use of filter arrays which discard most of the incident light. Further, given the challenges of miniaturizing optical systems, most cameras do not leverage the wealth of information in polarization and spatial degrees of freedom. Optical metamaterials can respond to these electromagnetic properties but have been explored primarily in single-layer geometries, limiting their performance and multifunctional capacity. Here we use advanced two-photon lithography to realize multilayer scattering structures that achieve highly nontrivial optical transformations intended to process light just before it reaches a focal plane array. Computationally optimized multispectral and polarimetric sorting devices are fabricated with submicron feature sizes and experimentally validated in the mid-infrared. A final structure shown in simulation redirects light based on its angular momentum. These devices demonstrate that with precise 3-dimensional nanopatterning, one can directly modify the scattering properties of a sensor array to create advanced imaging systems.

In-situ X-ray tomographic imaging and controlled steering of microcracks in 3D nanopatterned structures

An experimental approach to control the fracture behavior of 3D nanopatterned structures in real time and to describe the microcrack propagation in solids quantitatively is presented. The three-dimensional details of the complicated failure mechanism are unveiled with high resolution using a method that integrates a micro-scale fracture mechanics test into a nano X-ray computed tomography system, to allow in-situ 3D imaging of the kinetics of damage mechanisms in integrated circuits. With the unique combination of a miniaturized micro-mechanical experiment and high-resolution X-ray imaging, the critical energy release rate at the crack tip of materials is determined quantitatively in sub-100 nm dimension, which allows to reveal scale-dependent mechanical properties. The ability of controlled microcrack steering in engineered materials and structures into regions with high fracture toughness is demonstrated. This unique characterization capability promises broad applications for design and manufacturing of robust microchips in future technology nodes, and it is applicable to the study of a broad variety of 3D nanostructured material systems.

Low-resistivity Pd nanopatterns created by a direct electron beam irradiation process free of post-treatment steps

The ability to create metallic patterned nanostructures with excellent control of size, shape and spatial orientation is of utmost importance in the construction of next-generation electronic and optical devices as well as in other applications such as (bio)sensors, reactive surfaces for catalysis, etc. Moreover, development of simple, rapid and low-cost fabrication processes of metallic patterned nanostructures is a challenging issue for the incorporation of such devices in real market applications. In this contribution, a direct-write method that results in highly conducting palladium-based nanopatterned structures without the need of applying subsequent curing processes is presented. Spin-coated films of palladium acetate were irradiated with an electron beam to produce palladium nanodeposits (PdNDs) with controlled size, shape and height. The use of different electron doses was investigated and its influence on the PdNDs features determined, namely: (1) thickness of the deposits, (2) atomic percentage of palladium content, (3) oxidation state of palladium in the deposit, (4) morphology of the sample and grain size of the Pd nanocrystals and (5) resistivity. It has been probed that the use of high electron doses, 30000 μC cm−2 results in the lowest resistivity reported to date for PdNDs, namely 145 μΩ cm, which is only one order of magnitude higher than bulk palladium. This result paves the way for development of simplified lithography processes of nanostructured deposits avoiding subsequent post-treatment steps.

Spherical Micro/Nano Hierarchical Structures for Energy and Water Harvesting Devices (Small Methods 7/2022)

Inside Front Cover In article number 2200248, Jeong, Park, and coworkers developed a new strategy for generating spherical micro/nano hierarchical structures (S-HS) by combining the nanopatterned structures and expandable microspheres. These S-HS, which enable the control of nanopatterns and the density of spherical microstructures, dramatically increase the surface area and roughness. Effective electrical energy and water harvesting devices are demonstrated through the fabricated hierarchical structures.

Nanopatterning Graphite Surface by Diazoniums Using Electrochemical Method

Molecular functionalization of graphitic surfaces with nanopatterned structures is regarded as one of the effective bottom-up techniques to tune their electronic properties towards electronics applications. Diazonium molecules have been often employed to covalently functionalize graphene and highly oriented pyrolytic graphite (HOPG) substrates. However, controlling the structure of the molecular adlayers is still challenging. In this contribution, we demonstrated an inconventional approach for covalent functionalization the HOPG surface by using mixture of 4-nitrobenzenediazonium (4-NBD) and 3,5-bis-tert-butylbenzenediazonium (3,5-TBD) molecules in which the former tends to polimezise and physisorb while the later chemically anchors on surface. The physisorbed features can be removed by washing with hot toluene and water. As a result, the HOPG surface is patterned in a quasi-periodic fashion. The efficiency of this development was verified by a combination of cyclic voltametry (CV) and atomic force microscopy (AFM) methods. This finding represents a convenient strategy for creating nanoconfined templates that might serve as nano-playgrounds for further supramolecular self-assembly and other on-surface reactions.

Growth of N-Heterocyclic Carbene Assemblies on Cu(100) and Cu(111): From Single Molecules to Magic-Number Islands.

N‐Heterocyclic carbenes (NHCs) have superior properties as building blocks of self‐assembled monolayers (SAMs). Understanding the influence of the substrate in the molecular arrangement is a fundamental step before employing these ligands in technological applications. Herein, we study the molecular arrangement of a model NHC on Cu(100) and Cu(111). While mostly disordered phases appear on Cu(100), on Cu(111) well‐defined structures are formed, evolving from magic‐number islands to molecular ribbons with coverage. This work presents the first example of magic‐number islands formed by NHC assemblies on flat surfaces. Diffusion and commensurability are key factors explaining the observed arrangements. These results shed light on the molecule‐substrate interaction and open the possibility of tuning nanopatterned structures based on NHC assemblies.

Wachstum von N‐heterocyclischen Carbenen auf Cu(100) und Cu(111): von einzelnen Molekülen bis hin zu Inseln mit magischen Zahlen

AbstractN‐Heterocyclische Carbene (NHCs) haben ausgezeichnete Eigenschaften als Bausteine von selbstorganisierten Monoschichten (SAMs). Bevor diese Moleküle in technologischen Anwendungen zum Einsatz kommen können, ist als grundlegender Schritt der Einfluss des Substrates auf molekulare Anordnungen zu verstehen. Hier untersuchen wir die molekulare Anordnung eines Modell‐NHC auf Cu(100) und Cu(111). Während auf Cu(100) meist ungeordnete Phasen auftreten, bilden sich auf Cu(111) wohldefinierte Strukturen, die abhängig von der Bedeckung Inseln mit bevorzugter Anzahl von Molekülen (magische Zahlen) bis hin zu Streifenanordnungen zeigen. Diese Arbeit präsentiert das erste Beispiel von aus NHC gebildeten Inseln mit magischen Zahlen auf ebenen Oberflächen. Diffusion und Kommensurabilität sind wesentliche Faktoren zur Aufklärung der beobachteten Anordnungen. Diese Ergebnisse geben Aufschluss über die Molekül‐Substrat‐Wechselwirkung und eröffnen die Möglichkeit, auf NHC‐Verbindungen basierte Nanostrukturen abzustimmen.

Thermal Characterization of Metal-Oxide Interfaces Using Time-Domain Thermoreflectance with Nanograting Transducers.

Metal-oxide thermal boundary conductance (TBC) strongly influences the temperature rise in nanostructured systems, such as dense interconnects, when its value is comparable to the thermal conductance of the amorphous dielectric oxide. However, the thermal characterization of metal-amorphous oxide TBC is often hampered by the measurement insensitivity of techniques such as time-domain thermoreflectance (TDTR). Here, we use metal nanograting structures as opto-thermal transducers in TDTR to measure the TBC of metal-oxide interfaces. Combined with an ultrafast pump-probe laser measurement approach, the nanopatterned structures amplify the contribution of the thermal boundary resistance (TBR), the inverse of TBC, over the thermal resistance of the adjacent material, thereby enhancing measurement sensitivity. For demonstration purposes, we report the TBC between Al and SiO2 films. We then compare the impact of Al grating dimensions on the measured TBC values, sensitivities, and uncertainties. The grating periods L used in this study range from 150 to 300 nm, and the bridge widths w range from 72 to 205 nm. With the narrowest grating transducers (72 nm), the TBC of Al-SiO2 interfaces is measured to be 159-48+61 MW m-2 K-1, with the experimental sensitivity being 5× higher than that of a blanket Al film. This improvement is attributed to the reduced contribution of the SiO2 film thermal resistance to the temperature signal from TDTR response. The nanograting measurement approach described here is promising for the thermal characterization of a variety of nanostructured metal-amorphous passivation systems and interfaces common in semiconductor technology.

High‐Efficiency Top‐Emitting Green Perovskite Light Emitting Diode with Quasi Lambertian Emission

AbstractMetal halide perovskite light‐emitting diodes (PeLEDs) are regarded as alternative candidates for next‐generation display technologies due to their high efficiency, superior color purity, tunable bandgap. However, the research on transparent and top‐emitting PeLED with Lambertian emission profile significantly lags behind due to optical microcavity effect, which has become one of the main obstacles for potential practical display applications. Here, strategies are developed to suppress the microcavity effect by enhancing the transmission of the semitransparent electrode and extending the optical cavity length. Besides, a nanopatterned structure is incorporated to suppress the surface plasma and waveguide mode effect. Based on the above combination strategies, a transparent PeLED yields a record total external quantum efficiency (EQE) of 16.1% with Lambertian emission by depositing high refractive index molybdenum oxide on the semitransparent cathode. Besides, a high EQE of 13.6% of a top‐emitting device with quasi‐Lambertian emission is achieved by stretching the optical distance between two reflective layers and enhancing the transmission of the semitransparent electrode. The nanopatterned structure enables suppressed waveguide mode and surface plasmon polariton dilapidation of top‐emitting PeLEDs. This work paves a path to design transparent and top‐emitting PeLEDs for potential applications in both traditional and novel transparent displays.

PHIDL: Python-based layout and geometry creation for nanolithography

Computer-aided design (CAD) has become a critical element in the creation of nanopatterned structures and devices. In particular, with the increased adoption of easy-to-learn programming languages like python, there has been a significant rise in the amount of lithographic geometries generated through scripting and programming. However, there are currently unaddressed gaps in usability for open-source CAD tools—especially those in the GDSII design space—that prevent wider adoption by scientists and students who might otherwise benefit from scripted design. For example, constructing relations between adjacent geometries is often much more difficult than necessary—spacing a resonator structure a few micrometers from a readout structure often requires manually coding the placement arithmetic. While inconveniences like these can be overcome by writing custom functions, they are often significant barriers to entry for new users or those less familiar with programming. To help streamline the design process and reduce barrier to entry for scripting designs, we have developed PHIDL, an open-source GDSII-based CAD tool for python.

Digital Numbers Constructed by Fine Patterned Polydopamine on DNA Templates.

Using DNA nanostructures as templates to synthesize shape-controlled polydopamine (PDA) is a promising strategy to realize the fabrication of exquisite PDA nanomaterials. However, previous studies using small DNA tiles as templates could only afford very simple structures such as lines and crosses due to the limited space on the template and the relatively low resolution of the PDA nanopatterns. Therefore, the best resolution of the PDA nanostructures that can be achieved by this technique is carefully investigated. And by connecting several DNA tiles together, larger DNA templates are built up and achieve the synthesis of complicated digital nanopatterned PDA structures.

Passive tunable and polarization-insensitive fan-like metamaterial absorber in the visible spectrum

We numerically study a fan-like metamaterial absorber (FMMA) composed of an A u - T i O 2 - A u multilayer with a 3-D finite-difference-time-domain method (FDTD) and verify it experimentally. Our proposed design shows high absorbance, > --> 98 % numerically, in the visible spectrum, which is due to the excitation of both localized surface plasmons (LSPs) and propagating surface plasmons (PSPs). In particular, the T i O 2 dielectric spacer sandwiched between the top fan-like nanopatterned structure and the bottom planar Au-film is identified as playing a crucial role in the spectral response of the FMMA. Its introduction excites the PSP mode, which first enhances the absorbance of the FMMA and subsequently redshifts the spectral absorbance with a further increase in the thickness. Moreover, the proposed FMMA, numerically and experimentally, also shows polarization and angle insensitivity in the visible spectrum under normal and selected oblique incidence. These results offer unique potential in sensing applications and devices requiring selective absorption in the visible spectral region.

Improved Copper-Epoxy Adhesion by Laser Micro- and Nano-Structuring of Copper Surface for Thermal Applications.

The objective of this work is the enhancement of metal-to-metal bonding to provide high thermal conductivity together with electrical insulation, to be used as heat sinks at room and cryogenic temperatures. High thermal conductive metal (copper) and epoxy resin (Stycast 2850FT) were used in this study, with the latter also providing the required electrical insulation. The copper surface was irradiated with laser to induce micro- and nano-patterned structures that result in an improvement of the adhesion between the epoxy and the copper. Thus, copper-to-copper bonding strength was characterized by means of mechanical tensile shear tests. The effect of the laser processing on the thermal conductivity properties of the Cu/epoxy/Cu joint at different temperatures, from 10 to 300 K, is also reported. Using adequate laser parameters, it is possible to obtain high bonding strength values limited by cohesive epoxy fracture, together with good thermal conductivity at ambient and cryogenic temperatures.

Lithography-free and Highly Angle Sensitive Structural Coloration Using Fabry\u2013Perot Resonance of Tin

Recently, there has been much interest in applying the color changes of nano-patterned structures to sensor technology. However, the lithographic nano-patterning process is not environmentally friendly, and it is difficult to fabricate large areas of color due to limitations associated with this approach. In this study, we realized a highly tunable structural coloration based on a Fabry–Perot interferometer design that does not require nano-patterning processes. To increase the reflected color change according to the angle, a color element using an asymmetric metal–insulator–metal structure was applied, fabricated using silver–silicon dioxide–tin (Sn), respectively. Using the optical properties of Sn, we maximized the change in reflection color and realized three primary colors of subtractive color of cyan, magenta and yellow according to the angle of designed MIM structure. Theoretical and experimental results revealed that the color and intensity of the reflectance depended strongly on the angle of the reflective surfaces. The manufacturing process is simple and yields large surfaces of high quality. Based on this premise, we fabricated a soft robot capable of color camouflage, and an angle-detecting color sensor for inspecting the three-dimensional shape quality of curved glass with a high sensitivity of 1.8 nm/degree. In addition, we propose a shape evaluation method by color, spectrometry, and monochromatic light.

Remarkable bactericidal traits of a metal-ceramic composite coating elated by hierarchically structured surface.

SummaryA ceramic-based coating with a hierarchical surface structure was synthesized via solid-state reaction enabled by a double cathode glow discharge technique. This innovative coating comprises two distinct layers, specifically an outer layer with a well-aligned micro-pillar array and a dense inner layer. Both are composed of a face-centered cubic Cu(Co,Ni,Fe) solid solution phase together with a spinel-type Fe(Al,Cr)2O4 oxide. This coating exhibits superhydrophobicity and, yet, a very strong adhesion to water, i.e., the so-called “rose petal effect”. This coating also exhibits highly efficient antibacterial ability against both Staphylococcus aureus and Escherichia coli bacteria under both dark and visible light conditions. The excellent antibacterial property originates from the synergistic effects through the release of Cu ions coupled with photothermal activity upon light activation.

Application of co-culture technology of epithelial type cells and mesenchymal type cells using nanopatterned structures.

Various nanopatterning techniques have been developed to improve cell proliferation and differentiation efficiency. As we previously reported, nanopillars and pores are able to sustain human pluripotent stem cells and differentiate pancreatic cells. From this, the nanoscale patterns would be effective environment for the co-culturing of epithelial and mesenchymal cell types. Interestingly, the nanopatterning selectively reduced the proliferative rate of mesenchymal cells while increasing the expression of adhesion protein in epithelial type cells. Additionally, co-cultured cells on the nanopatterning were not negatively affected in terms of cell function metabolic ability or cell survival. This is in contrast to conventional co-culturing methods such as ultraviolet or chemical treatments. The nanopatterning appears to be an effective environment for mesenchymal co-cultures with typically low proliferative rates cells such as astrocytes, neurons, melanocytes, and fibroblasts without using potentially damaging treatments.

Parameters optimization of nanopatterned sapphire substrates for enhancing light extraction efficiency of GaN-based LEDs

The nanopatterned structures play an important role in enhancing the light extraction efficiency (LEE) of GaN-based light-emitting diodes (LEDs). Three-dimensional finite-difference time-domain (3D-FDTD) method was carried out to calculate the LEE enhancement of GaN-based LEDs designed on periodic nanostructures with different geometries. Orthogonal experiment method was employed to obtain the optimal structure parameters and analyze the weighting factor of critical parameters affecting the LEE enhancement. The results of orthogonal experiment showed that the height/depth of the periodic nanostructures is the dominated factor to influence the LEE enhancement, followed by the diameter and the spacing of the periodic nanostructures. It was also found that the far-field intensities of LEDs with periodic convex nanostructures were stronger than those with periodic concave nanostructures. The critical parameters of periodic convex nanostructures were further optimized by single factor method, and their optimal parameters were obtained. The optimal LEE enhancement of GaN-based LEDs grown on cone-shaped nanopillar and column-shaped nanopillar array patterned sapphire substrates are 1.95 and 1.97, respectively. This means the cone-shaped and column-shaped nanopillar structures have almost identical LEE enhancement of GaN-based LEDs.

Novel nano-patterned structures of mixed hairy nanoparticles in single layer

Tethering mixed homo/diblock polymer chains on the nanoparticles (NPs) imposes simultaneous enthalpic and entropic influences on their self-assembly. In the aggregation of these NPs, the chain distribution is strongly influenced by the neighboring NPs. Therefore, the so-called mutual templating of the NPs is the main reason for the formation of the exotic self-assembly structures of grafted chains. In this study, by using dissipative particle dynamics simulations, we design three representative mixed hairy nanoparticles (MHNPs) systems and investigate their microphase separation process during solvent evaporation. The minimal model for the MHNP is grafting two types of incompatible (A and B) homopolymer chains on the same graft-site with uniform distribution on the NP surface. Based on the minimal model, adding a C block at the free end of both A and B blocks facilitates the investigation of the influence of chain composition on microphase separation structures. In the third model, we change the B chain in the minimal model into a BC diblock copolymer chain to study the influence of chain mismatch on the formation of nano-patterns. By comparing the microphase structures and their formation processes, we can find that wedge-shaped nanostructures appear in specific range of interparticle distances (D) due to mutual templating; adding another block will terminate the mutual templating effect and results in the wedge-shaped nanostructures attaching to the NP surface surrounded by the ring structure formed by outer block C; for the systems with chain mismatch, apertures with six-fold symmetry appear in the monolayer film formed by MHNPs when D is large enough. These findings facilitate the design and fabrication of advanced functional materials with ordered structures on the nanoparticle level.