Periodic Nanostructures Research Articles

Investigation of Ti nanostructures via laboratory scanning-free GEXRF.

The ability to characterize periodic nanostructures in the laboratory gains more attention as nanotechnology is widely utilized in a variety of application fields. Scanning-free grazing-emission X-ray fluorescence spectroscopy (GEXRF) is a promising candidate to allow non-destructive, element-sensitive characterization of sample structures down to the nanometer range for process engineering. Adopting a complementary metal-oxide semiconductor (CMOS) detector to work energy-dispersively via single-photon detection, the whole range of emission angles of interest can be recorded at once. In this work, a setup based on a Cr X-ray tube and a CMOS detector is used to investigate two TiO2 nanogratings and a TiO2 layer sample in the tender X-ray range. The measurement results are compared to simulations of sample models based on known sample parameters. The fluorescence emission is simulated using the finite-element method together with a Maxwell-solver. In addition, a reconstruction of the sample model based on the measurement data is conducted to illustrate the feasibility of laboratory scanning-free GEXRF as a technique to non-destructively characterize periodic nanostructures in the tender X-ray range.

Energy and Cost Efficient Manufacturing of Uniform Periodic Nanostructures Enabled by an Adaptable Beam Flattening Device

Energy and Cost Efficient Manufacturing of Uniform Periodic Nanostructures Enabled by an Adaptable Beam Flattening Device

Retroreflective Multichrome Microdome Arrays Created by Single-Step Reflow.

Structural colors are known for their tunability, fade resistance, and eco-friendliness. Recent advancements have shown that such colors can be efficiently produced using total internal reflection (TIR) on high-refractive-index convex microstructures without the need for periodic nanostructures. However, a reproducible, fast, and programmable production strategy for these microstructures is essential for commercial applications. Here, a single-step method is reported for creating multicolor patterns by transforming photolithographically-patterned micropillars into microdomes through thermal reflow. These micropillars, uniform in height but varying in diameter, are converted into microdomes that differ in diameter and height, which display a full spectrum of structural colors, creating a versatile color palette. This process enables the production of high-resolution multicolor graphics using a rainbow color set, with high reproducibility. Additionally, by mixing distinct microdomes and adjusting their densities, a rich variety of color presentations can be achieved, enabling the recreation of arbitrary color images with microdome arrays. The variable heights of the microdomes also allow for dynamic discoloration or color changes through mechanical compression. The high reproducibility and scalability of this method hold significant commercial promise for various optical applications.

Self-assembly of MoTe2 nanostructures and nanocomposites over centimeter-large areas via femtosecond laser

The fabrication of patterned two-dimensional (2D) materials exhibits significant potential for advancing their electronic and optoelectronic applications. In this Letter, we demonstrate a rapid and scalable method for creating nanoscale periodic molybdenum ditelluride (MoTe2) nanostructures and mixed-dimensional heterostructures over a large area using direct femtosecond laser irradiation. Under intense femtosecond laser pulses, periodic energy deposition occurs in layered MoTe2 and subsequently induces the formation of MoTe2 periodic nanostructures. In addition, femtosecond laser ablation at a high repetition rate (1 MHz) results in the formation of numerous crystalline Te nanoparticles scattered on the surface of MoTe2 layers, creating mixed-dimensional Te/MoTe2 heterostructures. Notably, the fabrication of MoTe2 periodic nanostructures and mixed-dimensional heterostructures is driven by a self-assembled process. This technique enables the production of centimeter-scale MoTe2 periodic nanostructures and nanocomposites within 5 min, offering a cost-effective, lithography-free approach for fabricating periodically nanostructured 2D materials in large areas for practical applications in electronics, optoelectronics, catalysis, and sensing.

Investigating SERS performance of controllable fabricated Ag periodic nanostructures with morphologies of nanoclaws and nanocones in detecting SARS-CoV-2 S protein

Surface-enhanced Raman scattering (SERS) spectroscopy plays an important role in enabling high-precision detection and non-invasive diagnostics. Periodic metallic nanostructures with strong electromagnetic fields and tunable localized surface plasmon resonance can achieve high SERS sensitivity, but fabricating such nanostructures remains a challenge. In this work, the anodic aluminum oxide (AAO) nanocavity template-assisted process of fabricating periodic nanostructures with modulating morphologies from Ag nanoclaws (AgNCWs) to Ag nanocones (AgNCEs) is proposed. The morphologies-related SERS performances of nanostructures are analyzed by using rhodamine 6 g (R6G) as a probe molecule and the optimized AgNCEs possess a limit of detection (LOD) of 1 × 10−9 M. A sandwich strategy is applied to detect SARS-CoV-2 S protein in phosphate-buffered saline (PBS) and pharyngeal swab solution (PSS). The ACE2-modified AgNCEs (ACE2/AgNCEs) structure is applied to bind to the SARS-CoV-2 S protein. The 4-MBA and SARS-CoV-2 S antibody functionalized Au nanoparticles (AuNPs) are used as nanotags. By forming the ACE2/AgNCEs-SARS-CoV-2 S protein-nanotags sandwich structure, characteristic peak intensities of 1580 cm−1 are used as the report signal, and the LOD for SARS-CoV-2 S protein in PBS and PSS solution are 10 fg/mL.

Formation of Periodic Nanostructures on Medical Polymer with Femtosecond Laser for Control of Cell Spreading

Formation of Periodic Nanostructures on Medical Polymer with Femtosecond Laser for Control of Cell Spreading

Molecular dynamics simulation to investigate effect of deformation of copper-based graphene for continuous/adjacent indentation

The fabrication of periodic nanostructures has garnered significant attention. Despite the investigation into the mechanical properties and deformation behaviors of graphene coated on metal surfaces during single indentation, there remains a dearth of research on the mechanical response and deformation behaviors of graphene/Cu systems, as well as the effects of different crystal orientations during continuous nanoindentation. The present study employed molecular dynamics simulations to investigate the effects of crystal orientation and coated graphene on surface morphology, elastic recovery, and dislocation evolution in Cu and graphene/Cu systems under continuous indentation-induced deformation. The results revealed that the force required for continuous indentation was approximately 1.36 times higher than that for initial indentation at the same depth on Gr/Cu, indicating a significant work hardening effect induced by the first indentation. Moreover, the continuous indentation enhances the surface pile-up effect and promotes the formation of more atoms in the overlap region between adjacent indentations. The presence of graphene coatings significantly influences the contact area, suppressing dislocation nucleation while increasing dislocation density. Furthermore, during continuous indentation, the depth at which dislocation nucleation occurs is shallower compared to that observed during initial indentation. The subsurface damage caused by the initial indentation was comparatively more severe than that induced during continuous indentation. Notably, the extent of dislocation propagation resulting from continuous indentation on graphene/Cu surpassed that observed on Cu alone. These findings significantly contribute to our comprehension of the metal-graphene interaction mechanism during continuous indentation and offer valuable insights for optimizing indentation quality.

Algorithm for Calculating the Coefficient of Electron Transmission through One- and Two-Dimensional Periodic Nanostructures

Algorithm for Calculating the Coefficient of Electron Transmission through One- and Two-Dimensional Periodic Nanostructures

Periodic 1D Assembly of Diblock Hetero-Nanowires As Tandem Electrocatalysts

There has been a growing interest in tandem electrocatalysts with unique interfaces and synergetic functions, which have been reported to exhibit outstanding performance in activity[1], selectivity[2], and stability[3]. Besides the development of monolithic tandem nanostructures, nanoparticle (NP) assembly provides a more desirable and controllable strategy to elaborately design novel nanocatalysts for various applications. Compared with two-dimensional (2D) and 3D tandem nanostructures, 1D tandem nanostructures have attracted more interest due to their high electrochemical surface areas, great atomic utilization, and outstanding structural stability, all of which are highly favored to achieve better electrocatalytic activity and stability. However, controllable 1D NP assembly is still challenging to achieve due to its relatively high surface energy and anisotropy, not to mention the creation of periodic 1D heterogeneous nanostructures with intimate interfaces and clean surfaces.In this work, we report a strategy to obtain periodic Pt-Au nanowires (NWs) by the assembly of Pt-Au Janus NPs with the assistance of peptide T7 (Ac-TLTTLTN-CONH2). We further demonstrate that the Pt-Au NWs show highly improved catalytic performance in the methanol oxidation reaction (MOR), a 5.3 times higher specific activity and a 2.5 times higher mass activity than that of the current state-of-the-art commercial Pt/C catalyst. The charge transfer at the interfaces of adjacent Pt and Au regions could weaken the binding energy between Pt and CO or CO-like intermediates, contributing to the enhancement of activities in MOR. More importantly, the periodic Pt-Au NWs exhibit outstanding stability in MOR, where the mass activity of Pt-Au NWs after 1000 cycles retains 93.9%, much higher than that of the commercial Pt/C (30.6%). We believe that this strategy to design and obtain periodic NWs by the assembly of Janus NPs is universal and transformative to diverse electrocatalytic reactions to achieve synergistic effects and intimate interfaces with high catalytic activity.[4][5] In conclusion, we have obtained periodic Pt-Au NWs by the assembly of Pt-Au Janus NPs with the assistance of peptides and demonstrated their outstanding activities and stability in MOR. This research presents a strategy to develop periodic heterogeneous nanowires with intimate interfaces and synergistic effects by the 1D assembly of Janus NPs, which offers an opportunity to design and program periodic 1D tandem catalysts.References Liu, Huibing, et al. "Dual active site tandem catalysis of metal hydroxyl oxides and single atoms for boosting oxygen evolution reaction."Applied Catalysis B: Environmental 297 (2021): 120451.Morales-Guio, Carlos G., et al. "Improved CO2 reduction activity towards C2+ alcohols on a tandem gold on copper electrocatalyst."Nature Catalysis 10 (2018): 764-771.You, Xingchao, et al. "Ru-Ni alloy nanosheets as tandem catalysts for electrochemical reduction of nitrate to ammonia."Nano Research (2024): 1-10.Shao, Qi, Pengtang Wang, and Xiaoqing Huang. "Opportunities and challenges of interface engineering in bimetallic nanostructure for enhanced electrocatalysis."Advanced Functional Materials 3 (2019): 1806419.Ma, Jiamin, et al. "Recent advances in application of tandem catalyst for electrocatalytic CO2 reduction."Molecular Catalysis 551 (2023): 113632.

(Invited) Metal and Compound Nanostructures Fabricated Via Photoelectrochemical Reactions

Metal and compound nanoparticles or nanostructures have unique properties that are different from bulk materials. For instance, metal nanoparticles exhibit light absorption and scattering due to localized surface plasmon resonance (LSPR) while compound nanoparticles such as CdS emit photoluminescence because of quantum size effects. The optical and photoelectrochemical properties of nanomaterials are significantly dependent on their size, shape, orientation, periodicity, and combination with other materials. Therefore, nanofabrication methods to control these factors are of critical importance for photovoltaic, photocatalytic, and other applications.We have successfully demonstrated photoelectrochemical techniques to fabricate different nanostructures composed of metal and/or metal oxide. Au-PbO2[1,2] and Au-Ag[3] hetero-nanostructures were fabricated via plasmon-induced charge separation (PICS)[4,5] in the presence of Pb2+ and Ag+ ions, respectively. Site-selective oxidative or reductive deposition took place at the resonance sites under excitation of LSPR of Au nanoparticles, that are in contact with a semiconductor such as TiO2 or a potential-controlled electrode. The reaction site can be controlled only by changing the irradiation wavelength. PbO2 deposited on the Au nanoparticles was galvanically replaced with MnO2 as a cocatalyst of photocatalytic reaction based on PICS[6]. Recently, we fabricated PbO2 periodic nanostructures by irradiating incoherent linearly polarized visible light to a potential-controlled bare indium-tin oxide electrode in the presence of Pb2+ ions[7] (see the image below). These photoelectrochemical approaches allow us to fabricate a variety of nanostructures with sizes beyond or comparable to the diffraction limit of light.

High-Resolution Total Internal Reflection-Based Structural Coloration by Electrohydrodynamic Jet Printing of Transparent Polyethylene Glycol Microdomes.

Total internal reflection (TIR)-based structural coloration is a brilliant strategy to overcome the need for periodic nanostructures and complex fabrication processes. Light entering the microdome structure undergoes TIR, and owing to varying reflection paths, it exhibits a color that changes with the microdome size. Although solution-based printing techniques have been proposed to achieve this effect, they fall short of full-color realization owing to resolution limitations. Herein, we achieved 3628 dpi of full-color and high-resolution structural color images by printing transparent microdome structures with 1.2-9.9 μm diameter using electrohydrodynamic (EHD) jet printing. Additionally, high-resolution EHD jet-printed structural color images display complex encoded information, enhancing the anticounterfeiting effectiveness through their fabrication simplicity and precise control over the microdome size. Because of these advantages, this TIR-based structural coloration technique with EHD jet printing is highly suitable for anticounterfeiting applications.

Fabrication of uniform, periodic arrays of exotic AlN nanoholes by combining dry etching and hot selective wet etching, accessing geometries unrealisable from wet etching of planar AlN

Aluminium nitride (AlN) is a wide bandgap semiconductor with far reaching realised and potential applications in electronics and optoelectronic technology. For example, gallium nitride (GaN) quantum dots (QDs) housed within an AlN matrix are attractive due to the large bandgap offsets. However, making suitable AlN sites to house GaN QDs is challenging due to the difficulty in fashioning 3D AlN structures. This results from AlN's strong bonds that are difficult to chemically etch.Whilst dry etching of AlN nanostructures has been explored, wet etching at the nanoscale has been limited by the common exposed facet of AlN being etch-resistant. Hence, wet etching of AlN to create uniform arrays of periodic nanohole nanostructures has, thus far, not been heavily explored.In this paper, an initial dry etching of a 2D AlN planar template is used to expose alternative wet-etchable facets so that periodic arrays of nanohole structures are revealed by wet-etching. Both a study of different initial dry etched structures, including tapered nanoholes, and wet etching time were performed. A model to describe the dynamics of wet etching on the different dry etched nanohole structures is proposed. Periodic arrays of uniform nanohole features are realised that hold promise for applications such as the housing of site-controlled quantum dots.

Quasi-visualizable detection of deep sub-wavelength defects in patterned wafers by breaking the optical form birefringence

Abstract In integrated circuit (IC) manufacturing, fast, nondestructive, and precise detection of defects in patterned wafers, realized by bright-field microscopy, is one of the critical factors for ensuring the final performance and yields of chips. With the critical dimensions of IC nanostructures continuing to shrink, directly imaging or classifying deep-subwavelength defects by bright-field microscopy is challenging due to the well-known diffraction barrier, the weak scattering effect, and the faint correlation between the scattering cross-section and the defect morphology. Herein, we propose an optical far-field inspection method based on the form-birefringence scattering imaging of the defective nanostructure, which can identify and classify various defects without requiring optical super-resolution. The technique is built upon the principle of breaking the optical form birefringence of the original periodic nanostructures by the defect perturbation under the anisotropic illumination modes, such as the orthogonally polarized plane waves, then combined with the high-order difference of far-field images. We validated the feasibility and effectiveness of the proposed method in detecting deep subwavelength defects through rigid vector imaging modeling and optical detection experiments of various defective nanostructures based on polarization microscopy. On this basis, an intelligent classification algorithm for typical patterned defects based on a dual-channel AlexNet neural network has been proposed, stabilizing the classification accuracy of λ/16-sized defects with highly similar features at more than 90%. The strong classification capability of the two-channel network on typical patterned defects can be attributed to the high-order difference image and its transverse gradient being used as the network’s input, which highlights the polarization modulation difference between different patterned defects more significantly than conventional bright-field microscopy results. This work will provide a new but easy-to-operate method for detecting and classifying deep-subwavelength defects in patterned wafers or photomasks, which thus endows current online inspection equipment with more missions in advanced IC manufacturing.

Design and fabrication of photonic crystal structures by single pulse laser interference lithography

Photonic crystal (PhC) structures formed by periodic surface nanostructuring have emerged as pivotal elements for controlling light-matter interactions. One important application is reducing losses due to the high surface reflectivity of semiconductor optoelectronic devices, such as enhancing light absorption in photovoltaic cells or improving light extraction in light-emitting diodes (LEDs). Although various methods for fabricating such structures have been documented, the utilization of single pulse laser interference lithography (LIL) using commercial photoresist and its subsequent effective use as an etch mask has not been previously reported. Rapid exposure of photoresists with single nanosecond pulses offers benefits for high throughput patterning and reduces the requirement for a stable optical platform. We have successfully employed single pulse LIL to fabricate antireflective PhC structures on GaAs substrates using a commercial photoresist. Exposure is performed with single 7 ns 355 nm pulses of relatively low energy (<10 mJ). High-quality nanohole arrays of pitch of approximately 365 nm are fabricated and depths up to 400 nm have been etched using inductively coupled plasma (ICP) through the exposed photoresist mask. Reflectivity analyses confirmed that these structures reduce the average reflectance of the GaAs to below 5 % across the 450 nm to 700 nm visible wavelength range. The fabrication of PhC structures using this approach has potential for low-cost wafer-level patterning to provide improved light extraction in LEDs and enhanced light trapping in solar cells.

Assembly and Bilayer Liftoff of Periodic Nanostructures with Sub-20 nm Resolution Using Thermal Scanning Probe Lithography

The demands for high resolution fabrication processes are ever-increasing, with new and optimized methodologies being highly relevant across several scientific fields. We systematically investigated thermal scanning probe lithography process and detailed how tuning temperature and probe contact time on the sample can optimize patterning and achieve 10 nm resolution. Additionally, we propose a novel fabrication methodology that integrates thermal scanning probe lithography and bilayer liftoff, achieving sub-20 nm resolution of the final metallized structures. Each step of the process, from sample preparation to the final liftoff, is described in detail. We also present a quantitative analysis comparing the accuracy of the lithography process to that of the bilayer liftoff. Finally, we show the feasibility of using thermal scanning probe lithography for the fabrication of photonic devices by validating our work with promising dipole geometries for this field.

Enhanced efficiency and stability of perovskite solar cells through nanoimprinting dual-functional nanostructured PEAI/2D/3D perovskite interface

Using 2D perovskite for interface passivation and micro-nanostructures for light harvesting have emerged as highly effective strategies to enhance the electronic and optical performance of perovskite solar cells (PSCs) respectively. However, simultaneously achieving electronic and optical manipulation remains a challenge that holds significant importance in improving the efficiency and stability of PSCs. Here, we employed thermal imprinting to fabricate dual-functional nanostructured PEAI/2D/3D interface, which effectively passivates perovskite surface imperfections by 2D perovskites and enhances light absorption by periodic nanostructures. The simultaneous electronic and optical manipulation leads to a significant improvement in both efficiency and long-term stability. The PSCs with the dual-functional interface show a high power conversion efficiency (PCE) of 22.45 % and retain 90 % of their initial PCE after exposure to an 85 °C N2 atmosphere for 550 h.

Enhanced photo-induced optical activity of crisscrossed self-organized gratings in photosensitive nanolayers by introducing bi-periodicity

In the present work, the enhancement of photoinduced optical activity in a photosensitive nanolayer of AgCl doped by Ag nanoparticles, using bi-periodic crisscrossed self-organized periodic nanostructures (C-SPNs) is achieved. We found that the formation of two non-identical SPNs (i.e., with different periods), which crisscrossed each other, enhances the rotation of the polarization plane of the linear polarized probe beam, compared to the case when the two nanostructures are identical (i.e., having the same period). The difference in periods of the two C-SPNs increases the anisotropy of the medium, which in turn boosts the optical chirality produced by the formation of complex crisscrossed gratings made of Ag nanoparticles. The angle between the two gratings can be a control parameter for the amount and sign of rotation of the polarization plane of the probe beam. The enhanced optical activity of the bi-periodic C-SPNs, compared to the identical C-SPNs, can be attributed to the formation of more intricate chiral building blocks at the intersections of the two gratings.

Anisotropic growth of Ag nanonails induced by plasmon-mediated chemical reactions in cross-shaped nanocavity array

The Ag nanonail rooted in Au cross-channel nanocavity is fabricated by plasmon-mediated chemical reactions (PMCRs). The Au cross-channel nanocavity is prepared based on two-dimensional polystyrene (PS) nanosphere template through wet etching, and the shape of Au cross-channel nanocavity changes from trapezoidal to triangular, depending on the wet etching time. The growth of Ag nanostructures in Au channels by PMCRs indicates the morphology of Ag nanostructures has changed from Ag nanoparticles to nanonails, which is regulated by the shape of Au nanocavities and the exciting light polarization. The hotspots distributions results in the anisotropic growth of Ag nanostructures induced by PMCRs, which leading to the different Ag nanostructures depending on the shape of Au nanocavity and light polarization, as confirmed by FDTD simulations. In comparison with others reports, our nanocavity provide more parameters to control the shapes of Ag nanostructures, the nanocavity shape, the light polarization and the growth time. Our work provides a profound insight into the construction of periodic nanostructures and reconstruction of hotspots.

Laboratory-based 3D X-ray standing-wave analysis of nanometre-scale gratings.

The increasing structural complexity and downscaling of modern nanodevices require continuous development of structural characterization techniques that support R&D and manufacturing processes. This work explores the capability of laboratory characterization of periodic planar nanostructures using 3D X-ray standing waves as a promising method for reconstructing atomic profiles of planar nanostructures. The non-destructive nature of this metrology technique makes it highly versatile and particularly suitable for studying various types of samples. Moreover, it eliminates the need for additional sample preparation before use and can achieve sub-nanometre reconstruction resolution using widely available laboratory setups, as demonstrated on a diffractometer equipped with a microfocus X-ray tube with a copper anode.

Development of Novel Surface-Enhanced Raman Spectroscopy-Based Biosensors by Controlling the Roughness of Gold/Alumina Platforms for Highly Sensitive Detection of Pyocyanin Secreted from Pseudomonas aeruginosa.

Pyocyanin is considered a maker of Pseudomonas aeruginosa (P. aeruginosa) infection. Pyocyanin is among the toxins released by the P. aeruginosa bacteria. Therefore, the development of a direct detection of PYO is crucial due to its importance. Among the different optical techniques, the Raman technique showed unique advantages because of its fingerprint data, no sample preparation, and high sensitivity besides its ease of use. Noble metal nanostructures were used to improve the Raman response based on the surface-enhanced Raman scattering (SERS) technique. Anodic metal oxide attracts much interest due to its unique morphology and applications. The porous metal structure provides a large surface area that could be used as a hard template for periodic nanostructure array fabrication. Porous shapes and sizes could be controlled by controlling the anodization parameters, including the anodization voltage, current, temperature, and time, besides the metal purity and the electrolyte type/concentration. The anodization of aluminum foil results in anodic aluminum oxide (AAO) formation with different roughness. Here, we will use the roughness as hotspot centers to enhance the Raman signals. Firstly, a thin film of gold was deposited to develop gold/alumina (Au/AAO) platforms and then applied as SERS-active surfaces. The morphology and roughness of the developed substrates were investigated using scanning electron microscopy (SEM) and atomic force microscopy (AFM) techniques. The Au/AAO substrates were used for monitoring pyocyanin secreted from Pseudomonas aeruginosa microorganisms based on the SERS technique. The results showed that the roughness degree affects the enhancement efficiency of this sensor. The high enhancement was obtained in the case of depositing a 30 nm layer of gold onto the second anodized substrates. The developed sensor showed high sensitivity toward pyocyanin with a limit of detection of 96 nM with a linear response over a dynamic range from 1 µM to 9 µM.