33 research outputs found
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Progress in Nanoporous Templates: Beyond Anodic Aluminum Oxide and Towards Functional Complex Materials
Successful synthesis of ordered porous, multi-component complex materials requires a series of coordinated processes, typically including fabrication of a master template, deposition of materials within the pores to form a negative structure, and a third deposition or etching process to create the final, functional template. Translating the utility and the simplicity of the ordered nanoporous geometry of binary oxide templates to those comprising complex functional oxides used in energy, electronic, and biology applications has been met with numerous critical challenges. This review surveys the current state of commonly used complex material nanoporous template synthesis techniques derived from the base anodic aluminum oxide (AAO) geometry
Resist-free nanoimprinting on optical fibers for plasmonic optrodes
Nanostructure patterning on optical fibers enables miniaturized optrodes for photonic and plasmonic applications. Here we report a direct nanoimprint technique to produce high-quality nanostructure arrays on optical fiber endfaces. It has only one single step: imprinting optical fiber tips against a mold with nanostructures at the elevated temperature. This new method abandons resist used in traditional fiber-imprinting methods. Hundreds of fibers can be shaped simultaneously with one mold within minutes. The imprinted nanostructure arrays on optical fibers are transformed into plasmonic optrodes through metal deposition. Variation of imprint depths and mold patterns allows tailoring of the plasmonic resonances of these nanostructure arrays for high-performance refractometric sensing and on-fiber polarization. The sensitivity of 690 nm/RIU and figure of merit of 50 are both among the highest values for similar plasmonic nanostructure arrays. This resist-free nanoimprint paves the way towards a low-cost and high-throughput realization of plasmonic optrodes and their wide applications.Peipei Jia, Depeng Kong, Heike Ebendorff-Heideprie
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RESISTIVE SWITCHING CHARACTERISTICS OF NANOSTRUCTURED AND SOLUTION-PROCESSED COMPLEX OXIDE ASSEMBLIES
Miniaturization of conventional nonvolatile (NVM) memory devices is rapidly approaching the physical limitations of the constituent materials. An emerging random access memory (RAM), nanoscale resistive RAM (RRAM), has the potential to replace conventional nonvolatile memory and could foster novel type of computing due to its fast switching speed, high scalability, and low power consumption. RRAM, or memristors, represent a class of two terminal devices comprising an insulating layer, such as a metal oxide, sandwiched between two terminal electrodes that exhibits two or more distinct resistance states that depend on the history of the applied bias. While the sudden resistance reduction into a conductive state in metal oxide insulators has been known for almost 50 years, the fundamental resistive switching mechanism is a complex phenomenon that is still long-debated, complex process. Further improvements to existing memristor performance require a complete understanding of memristive properties under various operation conditions. Additional technical issues also remain, such as the development of facile, low-cost fabrication methods as an alternative to expensive, ultra-high vacuum (UHV) deposition methods.
This collection of work explores resistive switching within metal oxide-based memristive material assemblies by analyzing the fundamental physical insulating material properties. Chapter 3 aims to translate the utility and simplicity of the highly ordered anodic aluminum oxide (AAO) template structure to complex, yet more functional (memristive) materials. Functional oxides possessing ordered, scalable nanoporous arrays and nanocapacitor arrays over a large area is of interest to both the fields of next-generation electronics and energy storing/harvesting devices. Here their switching performance will be evaluated using conductive atomic force microscopy (C-AFM). Chapter 4 demonstrates a convective self-assembly fabrication method that effectively enables the synthesis of a low-cost solution processed memristor comprising binary oxide and perovskite ABO3 nanocrystals of varying diameter. Chapter 5 systematically compares the influence of inter-nanoparticle distance on the threshold switching SET voltage of hafnium oxide (HfO2) memristors. Utilizing shorter phosphonic acid ligands with higher binding affinity on the nanocrystal surface enabled a record-low SET voltage to be achieved. Chapter 6 extends the scope to the fine tuning of solution processed memristors with two types of perovskites nanocrystals. The primary advantage of nanocrystal memristors is the ability to draw from additional degrees of freedom by tuning the constituent nanocrystal material properties. Recent advancement of solution phase techniques enables a high degree of controllability over the nanocrystal size and structure. Thus, this work found in this dissertation aims to understand and decouple the effects of the geometric size and substitutional nanocrystal parameters on resistive switching
Anti-Reflective and Anti-Bacterial Properties of Biomimetic Nanostructures
In this thesis artificial nanostructured surfaces inspired by the moth eye were developed on both inorganic and organic substrates. Two properties, i.e. anti-reflective (AR) and anti-bacterial (AB) were studied in detail.
On inorganic fused silica (Suprasil®) substrates, nanopillar arrays were fabricated by combining block copolymer micellar lithography (BCML) and reactive ion etching (RIE) techniques. The nanopillar arrays were fabricated on a large area and the parameters of the pillars were controlled. The substrates were used as molds to create nanostructures in organic substrates using two methods: replica molding and nanoimprinting. The first method transferred the pillar structure into a polyurethane substrate creating nanoholes. However, it was shown that this method was limited due to the low aspect ratio and difficulties in mold removal. Using nanoimprinting methods instead solved these problems. Both nanohole and nanopillar structures were homogeneously imprinted in a large area of the intermediate polymer stamp (IPS®) and polymethylmethacrylate (PMMA) materials.
The AR properties of both organic and inorganic substrates were characterized using optical spectrometry. On Suprasil® surfaces, the transmittance was increased over a wide wavelength range of 200-1000 nm, with a maximum of 99.5% transmission per interface. Nanoimprinted IPS® and PMMA also depicted highly improved transmittance, with an increase from 91.5% to 95% with a single-sided nanohole array on IPS® and from 91.5% to 97.5% with a double-sided nanopillar array on PMMA. Excellent AR performance was achieved to a high incident angle of 60°, which significantly outperformed traditional thin-film AR coatings. A theoretical model was also set up matching the experimental results very well.
The AB properties of the moth eye inspired structures were investigated on the nanostructured Suprasil®. The surface coverage of Staphylococcus sciuri (S. sciuri) bacteria was statistically analyzed by optical microscopy and the attachment sites between the bacteria and the nanostructures were observed by scanning electron microscopy (SEM). Although the surface coverage showed no significant difference between the nanostructured and planar surfaces, SEM images clearly revealed a different interaction of the bacteria and the nanostructures compared to plain surfaces. Nanofibers most likely fimbriae connecting the bacteria and the nanopillar tips were observed. Therefore, it was shown that the bacterium is able to sense the nano-scale features and respond with cell morphological alterations
ULTRAVIOLET ROLL-TO-ROLL NANOIMPRINT LITHOGRAPHIC FABRICATION OF FLEXIBLE POLYMER MOULDS
Ph.DDOCTOR OF PHILOSOPH
Molding and Replication of Ceramic Surfaces with Nanoscale Resolution
The design of reproducible and more efficient nanofabrication routes has become a very active research field in recent years. In particular, the development of new methods for micro- and nanopatterning materials surfaces has attracted the attention of many researchers in industry and academia as a consequence of the growing relevance of patterned surfaces in many technological fields, ranging from optoelectronics to biotechnology. In this work we explore, discuss, and demonstrate the possibility of extending the well-known molding and replication strategy for patterning ceramic materials with nanoscale resolution. To achieve this goal we have combined physical deposition methods, molecule-thick antisticking coatings, and nanostructured substrates as master surfaces. This new perspective on an “old technology”, as molding is, provides an interesting alternative for high-resolution, direct surface-relief patterning of materials that currently requires expensive and time-consuming lithographic approaches.Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicada