Fabrication Of 3D Nanostructures Research Articles

Controlling Vertical Asymmetry of Nanocrystals Through Anisotropic Etching‐Assisted Nanosphere Lithography

Nanosphere lithography, a low‐cost fabrication technique, depends on the self‐assembly of nanoscale features to create nanostructures in a hexagonally close‐packed structure. In this article, the fabrication of 3D nanostructures over a large surface‐area with anisotropy along the growth direction through the combination of chemical and physical plasma etching is reported. The anisotropy stems from etching the nanosphere mask and the substrate at different rates. Due to the dynamic masking effect, a systematic variation of etching time gives rise to intriguing nanostructures with sharp edges that have strong potential for plasmonic applications, with the possibility of manipulating electromagnetic radiation. The structures obtained include nanocylinders, truncated hexagon‐based pyramids, circular pads on a conical base, and nanocones from a single‐layer nanosphere mask. Simulations of the fabrication process offer further insight into the understanding of nanostructure formation. A good agreement between predicted results and experiments confirms the potential of our numerical design. In addition, the optical properties of the nanostructures are investigated by UV–vis and the experimental findings are consistent with simulations based on a finite‐difference time‐domain method. The nanostructures described in this study contribute to the emerging 3D plasmonics and 3D magnonics, with strong potential for a significant impact on biosensor applications.

Atomic Layer Assembly Based on Sacrificial Templates for 3D Nanofabrication.

Three-dimensional (3D) nanostructures have attracted widespread attention in physics, chemistry, engineering sciences, and biology devices due to excellent functionalities which planar nanostructures cannot achieve. However, the fabrication of 3D nanostructures is still challenging at present. Reliable fabrication, improved controllability, and multifunction integration are desired for further applications in commercial devices. In this review, a powerful fabrication method to realize 3D nanostructures is introduced and reviewed thoroughly, which is based on atomic layer deposition assisted 3D assembly through various sacrificial templates. The aim of this review is to provide a comprehensive overview of 3D nanofabrication based on atomic layer assembly (ALA) in multifarious sacrificial templates for 3D nanostructures and to present recent advancements, with the ultimate aim to further unlock more potential of this method for nanodevice applications.

Rapid Bending Origami in Micro/Nanoscale toward a Versatile 3D Metasurface

AbstractDevices consisting of 3D components are always desired for their far more controllable degrees of freedom compared with their planar counterparts; however, the limitations on the fabrication of 3D nanostructures have severely restricted their applications. Here, a focused ion beam (FIB) defined rapid bending origami method is reported to fabricate 3D micro/nanoscale architectures, by relying on ion irradiation induced 2D structure bending mechanism based on the residual stress formation in metal/dielectric film. Regulated by ions irradiation dose and energy, a large‐scale programmable 2D patterns can be controllably bended to configure versatile 3D micro/nanostructures with scalable bending capacity and feature sizes down to 175 nm. The benefit of this method is, a 3D bended metasurface is designed and fabricated as an asymmetric mirror, showing a very simple strategy to realize high‐efficiency unidirectional reflectionless effect. This FIB‐defined bending origami proves to be a rapid fabrication approach of varied 3D configuration in micro/nanoscale with extremely flexible controllability of spatial orientation, providing more opportunities and options for various functional devices based on 3D configurations, especially for 3D metasurfaces.

Highly conductive and pure gold nanostructures grown by electron beam induced deposition.

This work introduces an additive direct-write nanofabrication technique for producing extremely conductive gold nanostructures from a commercial metalorganic precursor. Gold content of 91 atomic % (at. %) was achieved by using water as an oxidative enhancer during direct-write deposition. A model was developed based on the deposition rate and the chemical composition, and it explains the surface processes that lead to the increases in gold purity and deposition yield. Co-injection of an oxidative enhancer enabled Focused Electron Beam Induced Deposition (FEBID)—a maskless, resistless deposition method for three dimensional (3D) nanostructures—to directly yield pure gold in a single process step, without post-deposition purification. Gold nanowires displayed resistivity down to 8.8 μΩ cm. This is the highest conductivity achieved so far from FEBID and it opens the possibility of applications in nanoelectronics, such as direct-write contacts to nanomaterials. The increased gold deposition yield and the ultralow carbon level will facilitate future applications such as the fabrication of 3D nanostructures in nanoplasmonics and biomolecule immobilization.

Fabrication of 3D nanostructures by multidirectional UV lithography and predictive structural modeling

This paper presents the fabrication and modeling of three-dimensional (3D) nanostructures by automated multidirectional ultraviolet (UV) lithography, which is a fast, cost-effective, manufacturable fabrication method. Multidirectional UV exposure is performed using a static UV light source equipped with a tilt-rotational substrate holder. A glass substrate with a nanopatterned chrome layer is utilized as both a photomask and a substrate, for which a backside UV exposure scheme is used. For the analytical modeling of the shape of fabricated nanostructures, UV exposure dosage, diffraction and refraction effects, and absorption rate are taken into account. For more accurate process predictive models, a commercially available multiphysics simulation tool is used. The structural shapes predicted from analytical calculation and simulation are compared with the fabricated ones for which various 3D nanoscale test structures are fabricated such as an inclined nanopillar array and a vertical triangular slab. Also, nanostructures with multiple heights are successfully implemented from single layer photoresist by controlling the UV exposure dosage and tilt angles. A tripod embedded horn and a triangular-slab embedded horn are demonstrated.

Fabrication of 3D nano-structures using reverse imprint lithography

In spite of the fact that the fabrication process of three-dimensional nano-structures is complicated and expensive, it can be applied to a range of devices to increase their efficiency and sensitivity. Simple and inexpensive fabrication of three-dimensional nano-structures is necessary. In this study, reverse imprint lithography (RIL) with UV-curable benzylmethacrylate, methacryloxypropyl terminated poly-dimethylsiloxane (M-PDMS) resin and ZnO-nano-particle-dispersed resin was used to fabricate three-dimensional nano-structures. UV-curable resins were placed between a silicon stamp and a PVA transfer template, followed by a UV curing process. Then, the silicon stamp was detached and a 2D pattern layer was transferred to the substrate using diluted UV-curable glue. Consequently, three-dimensional nano-structures were formed by stacking the two-dimensional nano-patterned layers. RIL was applied to a light-emitting diode (LED) to evaluate the optical effects of a nano-patterned layer. As a result, the light extraction of the patterned LED was increased by about 12% compared to an unpatterned LED.

Growth characteristics evaluations on the 3D nanostructure fabrication by the high accuracy control of focused-ion-beam

Several evaluations of the growth characteristics of three-dimensional (3D) nanostructures, such as the dependence of the amount of adsorbed gas on vertical growth, dependence of focused-ion-beam (FIB) irradiation pitch on lateral growth, and the relationship between the number of irradiation pitches and vertical growth, fabricated by focused-ion-beam chemical vapor deposition (FIB-CVD) were carried out by controlling the Ga + FIB at a positional accuracy of less than 1 nm. The result of this study indicated that high resolution control of the vertically aligned nanostructure could be achieved by carrying out high speed scanning of FIB. And, we found that the growth reaction in FIB-CVD depended on the FIB irradiation pitch change of 0.1 nm. In addition, downward growth was achieved by FIB-CVD, in spite of its limitation in the maximum allowable growth angle (approximately −17°). Furthermore, a proximity effect was observed during the fabrication of 3D nanostructures by FIB-CVD.

Scanning Probe‐based Fabrication of 3D Nanostructures via Affinity Templates, Functional RNA, and Meniscus‐mediated Surface Remodeling

Developing generic platforms to organize discrete molecular elements and nanostructures into deterministic patterns on surfaces is one of the central challenges in the field of nanotechnology. Here we review three applications of the atomic force microscope (AFM) that address this challenge. In the first, we use two-step nanografting to create patterns of self-assembled monolayers (SAMs) to drive the organization of virus particles that have been either genetically or chemically modified to bind to the SAMs. Virus-SAM chemistries are described that provide irreversible and reversible binding, respectively. In the second, we use similar SAM patterns as affinity templates that have been designed to covalently bind oligonucleotides engineered to bind to the SAMs and selected for their ability to mediate the subsequent growth of metallic nanocrystals. In the final application, the liquid meniscus that condenses at the AFM tip-substrate contact is used as a physical tool to both modulate the surface topography of a water soluble substrate and guide the hierarchical assembly of Au nanoparticles into nanowires. All three approaches can be generalized to meet the requirements of a wide variety of materials systems and thereby provide a potential route toward development of a generic platform for molecular and materials organization.

Integration of Top-Down and Bottom-Up Nanofabrication Schemes

AbstractThe fabrication of 3D nanostructures, which have tunable, sub-100 nm dimensions in all three directions, is a key issue of nanotechnology. Here we describe the integration of top-down nanoimprint lithography (NIL) and bottom-up layer-by-layer (LBL) assembly for the preparation of 3D hybrid nanostructures. NIL provided down to sub-100 nm poly(methylmethacrylate) (PMMA) structures. These were employed to fabricate patterned self-assembled monolayers of cyclodextrin (CD) host molecules on silicon oxide . The consecutive LBL assembly with adamantyl guest-functionalized dendrimers and CD-modified gold nanoparticles resulted in patterned multilayer structures with thicknesses of 3-30 nm. The x,y control by NIL and the z control by LBL assembly ultimately allowed the fabrication of circular structures with a radius of 25 nm and a thickness of 20 nm. The integration of the two methods has thus yielded a versatile 3D nanofabrication methodology comprising of 10-40 process steps.