Fabrication of Large Area, Ordered Nanoporous Structures on Various Substrates for Potential Electro-Optic Applications

Nanoporous structures have attracted great attention in electronics, sensor and storage devices, and photonics because of their large surface area, large volume to surface ratio, and potential for high-sensitivity sensor applications. Normally, electron or ion beam patterning can be used for nanopores fabrication by direct writing. However, direct writing is a rather expensive and time-consuming method due to its serial nature. Therefore, it may not translate to a preferred manufacturing process. In this research, a perfectly ordered large-area periodic pattern in an area of approximately 1 cm2 has been successfully fabricated on various substrates including glass, silicon, and polydimethylsiloxane, using a two-step process comprising visible light-based multibeam interference lithography and subsequent pattern transfer processes of reactive ion etching and nanomolding. Additionally, the multibeam interference lithography templated anodized aluminum oxide process has been described. Since the fabrication area in multibeam interference lithography can be extended by using a larger beam size, it is highly cost effective and manufacturable. Furthermore, although not described here, an electrodeposition process can be utilized as a pattern transfer process. This large-area perfectly ordered nanopore array will be very useful for high-density electronic memory and photonic bandgap and metamaterial applications.

Inelastic Deformation of Copper Nanoparticle Based Joints and Bonds

The inelastic deformation properties of sintered metal nanoparticle joints are complicated by the inherent nanocrystalline and nanoporous structures as well as by dislocation networks formed in sintering or under cyclic loading. Creep rates of sintered nanocopper structures were found to be dominated by the diffusion of individual atoms or vacancies, while dislocation motion remained negligible up to stresses far above those of practical interest. Rapid sintering of one material led to unstable structures the creep of which could be strongly reduced by subsequent annealing or aging. Longer sintering of another material led to more stable structures, but creep rates could still be strongly enhanced by subsequent work hardening in mild cycling.

Optimization of Ultra-High Aspect Ratio Nanostructures Fabricated Using Glancing Angle Deposition

This paper presents the optimization for obtaining ultra-high aspect ratio nanostructures by GLancing Angle Deposition (GLAD). GLAD is a bottom-up, physical deposition process for creating nanometer-level features by shadows cast by seeds on the substrate at high incident angles. Based on the seeds used, GLAD can be categorized into two types: GLAD with natural seeds and pre-defined seeds (pre-seeds). When natural seeds are used, the seeds are randomly distributed with sub-100 nm feature sizes, and the percent coverage of the substrate is determined simply by the incident angle of the vapor. When the pre-seeds are used, the features can be redistributed and regrouped to generate new periodic nanostructures. This paper discusses how to obtain ultra-high aspect ratio nanopillars from natural seeds and nanoribbons from pre-defined line seeds by GLAD. In the discussion on GLAD with natural seeds, a study on the dependence of the aspect ratio on the incident angle is provided; resolvable nanopillars are obtained with aspect ratio over 1:20, and the growth mechanism is proposed for pillars with high deposition angles. Next, line seeds used in the GLAD process for creating high aspect ratio nanoribbons are discussed. Proper design and process parameters are discussed for controlling the morphologies of the nanoribbons. The ultra-high aspect ratio nanostructures are potentially used for applications including sensing, surface property alteration, and the creation of nanoporous structures.

Nucleation and Growth-Controlled Facile Fabrication of Gold Nanoporous Structures for Highly Sensitive Surface-Enhanced Raman Spectroscopy Applications

The fabrication of porous metal structures usually involves complicated processes such as lithography or etching. In this study, a facile and clean method based on thermal evaporation at high pressure is introduced, by which a highly porous, black colored structure of Au can be formed through the control of homogeneous nucleation and growth during evaporation. The deposited films have different morphologies, from columnar to nanoporous structures, depending on the working pressure. These porous structures consist of Au nanoparticle aggregates, and a large number of nano-gaps are found among the nanoparticles. Thus, these structures indicate a much higher intensity of surface-enhanced Raman spectroscopy (SERS) when compared with commercial SERS substrates. The SERS intensity depends on the working pressure and thickness. Even circumstances that can induce agglomeration of nanoparticle aggregates do not deteriorate the sensitivity of SERS. These nanoporous structures based on high-pressure thermal evaporation are expected to provide a new platform for the development of low-cost and highly sensitive chemical sensors.

Preparation of Graphene/N-Doped Carbon Nanohybrids and Their Application in Supercapacitors

Background: Nanocarbon hybrids have become an increasing interest in recent years because of their important role in energy storage and conversion device fabrication. Objective: The objective of this study is the preparation of low-cost graphene/N-doped carbon composites (G-NC) for supercapacitor applications. Method: G-NC samples were prepared with a two-step hydrothermal method and characterized with field emission scanning electron microscopy, 77K nitrogen adsorption and X-ray photoelectron spectroscopy. The electrochemical performance of samples was investigated with cyclic voltammetry and charge-discharge measurements in three-electrode configurations. Results: Samples showed a sheet-type morphology and nanoporous structures. The nanohybrids had specific surface area of 350 m2g-1, delivered maximum specific capacitance of 103 F g-1 at 0.5A g-1 in 6 M KOH with good cycle stability. Conclusion: Low-cost G-NC nanohybrids with good electrochemical performance are promising for supercapacitor applications.