Nanoimprinting on Impregnated Fabric Substrates

The Carter and Crosby research groups have collaborated to develop new methods to overcome existing challenges in the use of nanoimprinting patterning on flexible substrates in a roll-to-roll configuration. One of the major challenges is the delamination of imprinted materials from flexible substrates, such as PET films. To overcome delamination, we have recently proposed and demonstrated the use of woven substrates, rather than films, to allow mechanical interlocking to help in preventing unwanted delamination. In our process, we impregnate a woven fabric, with a curable formulation, which can subsequently be imprinted with a nanostructured pattern (top schematic). Our initial results (bottom images) are encouraging, and we are currently determining the material and spatial limits of this approach, as well as the mechanical properties of imprinted samples

Research Challenges for Integrated Systems Nanomanufacturing

The emerging capabilities of nanotechnology today for systematic control and manufacturing across multiple length scales are evolving into the next generations of nanotechnology products. These products can be categorized as passive nanostructures, active nanostructures, multi-dimensional nanosystems, heterogeneous molecular nanosystems, and multiscale, integrated nanosystems. The improved understanding of interactive forces among nanostructures and materials, combined with the resulting collective behavior within integrated systems has enabled new methodologies for the controlled manipulation of nanocomponents and structures comprising a broader hierarchy. As such, this new understanding will become a central research topic for discoveries and innovations toward new commercial applications, along with new paradigms in manufacturing sciences to address the necessary economy of scale requirements for these new products. Integrated systems nanomanufacturing must combine the understanding that has evolved to achieve this controlled manipulation of materials and structures with emerging capabilities and methodologies to realize new collective functionality for next generation systems

Nanofabrication Technologies for Roll-to-Roll Processing

The roll-to-roll (R2R) platform is an industrial vetted way to handle solution-based processes and coatings for high volume manufacturing. R2R processes are implemented for applications as diverse as instant photographic film, separation membranes, filtration media, advance printing and holographic coatings, polymer anti-shatter films for car windshields, flexible solar panels, composite electrodes on metal foils for lithium-ion batteries, and macroscale patterning of metal interconnects for flexible packaging of electronic components. Currently, manufacturers are looking for new innovative continuous-feed processes for printing materials and structures onto roll-based flexible substrates. In particular there is considerable interest in adapting R2R technologies for the extreme miniaturization of critical feature sizes to the nanoscale. This intersection of nanofabrication with R2R processes has considerable potential to spur innovation and economic growth. Nanofabrication for R2R process platforms represents a disruptive manufacturing technology involving solution-processed, multi-layer precision coatings with functionalized nanostructures, materials, and patterning capability to realize unprecedented properties and functionalities for next generation consumer products. Commercial products and applications impacted by this approach include displays, lighting, energy storage, electronics, solar photovoltaics. These high-value consumer electronics predicted to see double-digit market growth beyond the next decade (IDTechEx 2009-2029 Market Report). Incorporation of emerging nanofabrication methods within R2R manufacturing processes will make it possible to economically generate high value-added technology products at meters-per-minute rates on plastic film, paper, or foil, achieving feature dimensions as small as ten nanometers over areas encompassing billions of identical devices. Meeting this challenge is a key to high-rate manufacturing of nano-enabled products and for establishing viable industrial-scale manufacturing platforms for continuous large-area roll-to-roll processing

MOCVD Growth of Multistack Compound Semiconductor Heterostructures and Nanomaterials for Printable Solar Cells, LEDs, & FETs

Defying the textbook definition of wet etching (isotropic in nature), metal assisted chemical etching (MacEtch), fundamentally a wet but directional etching method, can produce anisotropic high aspect ratio semiconductor micro and nanostructures without incurring lattice damage. Figure 7.5.1 illustrates the MacEtch process to form pillar arrays, where the metal mesh pattern descends into the semiconductor, removing the semiconductor along the way and leaving behind a 3D semiconductor pattern that is the inverse of the metal pattern. The metal catalyst can be chemically removed from the semiconductor surface after MacEtch. MacEtch of Si has been widely accepted and practiced as a method to produce high aspect ratio structures such as nanowire arrays. However, MacEtch of III-V materials to produce periodic nanostructures, especially in high aspect ratios, has hardly been explored until now. The main challenge of MacEtch of III-V is the inherently small differential etch rate with and without metal presence under common MacEtch conditions. Through the right combination of oxidant, acid, and temperature, our recent work3 successfully demonstrated that ordered arrays of high aspect ratio GaAs nanostructures can be formed using Au-MacEtch. Figure 7.5.2 shows an array of GaAs pillars formed by immersing a n+-type GaAs wafer coated with an Au-mesh pattern in an MacEtch solution consisting of KMnO4 and H2SO4 at 40°C for 5 minutes. Although only n-type GaAs MacEtch is demonstrated here, MacEtch should work for other III-V material types and dopings, as well as heterostructures, as long as the right condition for deferential etching with and without metal can be found. In summary, MacEtch is a simple and efficient semiconductor etching technique that is capable of producing high aspect ratio semiconductor nanostructures beyond just Si. These high aspect ratio structures can potentially transform the fabrication of device structures that are currently fabricated by dry etch or bottom-up growth and assembly techniques. Examples include periodic nanostructures for photonic crystals, light trapping structures for LEDs and solar cells, 3D transistors, thermoelectric devices with roughened sidewalls, and nanowire batteries with greater energy density. MacEtch also brings affordability and possibly new device concepts for nanostructure based photonic and electronic devices

Challenges Remain for Effective Growth of Nanotechnology Enabled Products

According to conclusions from the recent report by the President’s Council of Advisors on Science and Technology (PCAST) the $12B NNI investment in nanotechnology since 2001 has provided a “catalytic and substantial impact.” Yet, with this positive assessment, significant challenges remain in order to stimulate sustainable economic impact and growth through commercialization of nanotechnologies. These challenges include workforce training and education while further balancing key issues of societal impact and worker safety through regulatory oversight. Several issues have recently been cited by industry groups, government organizations, and the PCAST report regarding regulation, workforce training, and effective commercialization of nanoscience breakthroughs that suggest a critical balance must be struck during the second decade of the NNI in order to optimally reap the benefits of federal investments. Also: Understanding the Resistivity-Transparency Tradeoffs for Carbon Nanotube Electrodes on Flexible Substrates; NanoBusiness Alliance Interview with Ajay Malshe; and NIST Wins R&D100 Award for Through-focus Scanning Optical Microscopy