InterNano Nanomanufacturing Repository
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Latest Nanotechnology Signature Initiative Provides for Intriguing Concepts Addressing Critical Challenges
No full textThe recently announced Nanotechnology Signature Initiative (NSI), Nanotechnology for Sensors and Sensors for Nanotechnology: Improving and Protecting Health, Safety, and the Environment, is the fifth NSI to be launched by agencies of the National Nanotechnology Initiative (NNI). Sensors incorporating nanostructures and nanomaterials have been under development for over 20 years now, and show the potential to provide significant societal impact through the deployment of inexpensive, simple to use, portable devices that can rapidly detect, identify, and quantify biological and chemical substances. Such sensors would ultimately impact consumer and military applications including medicine and healthcare, biological and chemical warfare threat detection, environmental monitoring, pharmaceuticals, food, and agriculture. Looking through the details of the this NSI, the descriptions of the thrusts and goals provide for some intriguing concepts, and address some critical challenges and barriers to the successful deployment, and ultimately commercialization, of nanosensor technologies. The key thrusts of this NSI include, in some sense, nanosensors monitoring nanomaterials. Rather than conjuring up images of self-monitoring nanomaterials that become self-aware and take over the world, one can focus on the key aspects of this initiative that will lead to the realization of nano-enabled sensing technologies, and improved understanding of nanomaterials and systems to benefit society.
Also included: Researchers Create Highly Conductive and Elastic Conductors Using Silver Nanowires, Nanotechnology...naturally delicious, Solution Processing of Transparent Polymer Solar Cell
Understanding Anomalous Current - Voltage Characteristics in Microchannel-Nanochannel Interconnect Devices
No full textRecent experiments revealed nonlinear current–voltage characteristics in a micro–nanochannel integrated system. The current characteristics were found to deviate from the classical−diffusion limited current transport theory, which predicts a saturation of the current density at higher applied voltages with an infinite differential resistance. Using a detailed 2−D nonlinear, nonideal ion–selective model, we capture and explain all the three regions observed in the experiments, by analyzing the behavior of the ionic concentration, near the depletion junction of the micro–nanochannel. Figure 7.6(a) shows the normalized nonlinear current–voltage characteristics in a highly ion–selective nanochannel integrated with a microchannel using our physical model. At low electric fields (region I in Figure 7.6(a)), the current increases linearly with the applied voltage, following the Ohm’s law. However, beyond the first critical voltage, the current deviates from the Ohmic behavior, but continues to increase with a slope smaller than that of the Ohmic region. This region (II) is often referred to as the limiting resistance region (LRR). Finally, beyond a second critical voltage, the slope of the current increases in comparison to the limiting regime and this region is typically referred to as the overlimiting current region (III). We attribute the limiting resistance region to the predominant propagation of induced space charges towards the microchannel. The overlimiting current characteristics is attributed to the redistribution of the space charges near the micro/nanochannel interface resulting in an anomalous enhancement in the ionic concentration of the electrolyte (predominantly anion concentration) in the induced space charge region (see Figure 7.6(b))
Making Diodes in the Classroom
No full textJon Scott, a teacher from our teacher’s workshop, with assistance from University of Illinois researchers Dane Sievers and others, has developed an engaging laboratory, using materials readily available in most K-12 school laboratories, which fills a hole in existing K-12 curriculum related to electronics and circuitry. In this laboratory, students create a basic component important to the semiconductor industry—a Schottky diode—by fusing pieces of gold and aluminum foil about 5 mm apart to an n-type silicon wafer. In this laboratory, students test their device and gain not only an understanding of the scientific method, but also a more complete understanding of how microelectronics fabrication processes result in functioning devices.
This activity has been under development for several years and is continuing to be refined. It has been tested successfully with multiple classes in several school districts and has become a standard part of the content presented at our summer institutes for teachers. This activity has also been disseminated to others outside the Nano-CEMMS teacher network through presentations at multiple professional education conferences, including the National Educators Workshop at NCA&T
Nanofabrication Technologies for Roll-to-Roll Processing
No full textThe 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
Improved Performance Information Needed for Environmental, Health, and Safety Research
No full textFrom fiscal years 2006 to 2010, the National Science and Technology Council (NSTC) reported more than a doubling of National Nanotechnology Initiative (NNI) member agencies’ funding for nanotechnology environmental, health, and safety (EHS) research––from approximately 90 million. Reported EHS research funding also rose as a percentage of total nanotechnology funding over the same period, ending at about 5 percent in 2010. However, GAO identified several reporting problems that raise concerns about the quality of EHS funding data reported. For example, for 18 percent of the 2010 projects GAO reviewed that were reported as EHS research, it was not clear that the projects were primarily directed at EHS risks. In addition, NNI member agencies did not always report funding using comparable data. The absence of detailed guidance on how agencies should report funding for their nanotechnology research has contributed to these problems, as GAO also reported in 2008 and made a related recommendation.
In 2010, EHS research at the NNI member agencies GAO reviewed most frequently focused on carbon nanotubes, nanosilver, and nanoscale titanium dioxide. NNI has not prioritized nanomaterials for EHS research, but NNI’s 2011 EHS research strategy outlines criteria for NNI member agencies to use in doing so. It is too soon to tell how these criteria will influence NNI member agencies’ decisions about which nanomaterials to prioritize, and it is unclear if information needed to use the NNI criteria is available.
The NNI member agencies have collaborated extensively on EHS research and strategies. They have collaborated through the NSTC to develop joint EHS research strategies and have initiated numerous formal collaborative EHS research projects. Nonfederal stakeholders who responded to GAO’s web-based questionnaire on nanotechnology EHS research told GAO that they benefited from collaboration with the NNI member agencies but identified some challenges, including a lack of funding and limited awareness of collaboration opportunities, among others. Most respondents rated the 2011 NNI EHS research strategy as somewhat or very effective at addressing nanotechnology EHS research needs.
NNI strategy documents for EHS research issued by the NSTC address two and partially address the other four of the six desirable characteristics of national strategies identified by GAO that offer a management tool to help ensure accountability and more effective results. For example, the NNI strategy documents provide a clear statement of purpose, define key terms, and discuss the quality of currently available data, among others. However, they do not include performance information—such as performance measures, targets, and time frames for meeting those measures—that would allow stakeholders to evaluate progress towards the goals and research needs of the NNI. In addition, the documents do not include, or sufficiently describe, estimates of the costs and resources needed for the strategy. Without this information, it may be difficult for agencies and stakeholders to implement the strategy and report on progress toward achieving the research needs and assess if investments are commensurate with costs of the identified needs
A Natural Route to Nanowires and Energy Storage
No full textOrganic electronics is a burgeoning area, with a growing range of applications. This new research – in which nanowires are grown naturally rather then synthesized chemically – may provide new methods for biologically-produced or biologically-inspired materials for sustainable nanomanufacturing. Pilin nanofilaments (pili) — known now as microbial nanowires — are a class of fibrous proteins found in the sediment bacteria Geobacter. Temperature studies find metallic characteristics. The conductivity can be modulated by doping or by using an applied voltage in an electrochemical transistor configuration, showing the potential for device applications, including supercapacitors for energy storage
MOCVD Growth of Multistack Compound Semiconductor Heterostructures and Nanomaterials for Printable Solar Cells, LEDs, & FETs
No full textDefying 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
Heterogeneous Integration of Epitaxial Nanostructures: Strategies and Application Drivers
No full textIn order to sustain the historic progress in information processing, transmission, and storage, concurrent integration of heterogeneous functionality and materials with fine granularity is clearly imperative for the best connectivity, system performance, and density metrics. In this paper, we review recent developments in heterogeneous integration of epitaxial nanostructures for their applications toward our envisioned device-level heterogeneity using computing nanofabrics. We first identify the unmet need for heterogeneous integration in modern nanoelectronics and review state-of-the-art assembly approaches for nanoscale computing fabrics. We also discuss the novel circuit application driver, known as Nanoscale Application Specific Integrated Circuits (NASICs), which promises an overall performance-power-density advantage over CMOS and embeds built-in defect and parameter variation resilience. At the device-level, we propose an innovative cross-nanowire field-effect transistor (xnwFET) structure that simultaneously offers high performance, low parasitics, good electrostatic control, ease-of-manufacturability, and resilience to process variation. In addition, we specify technology requirements for heterogeneous integration and present two wafer-scale strategies. The first strategy is based on ex situ assembly and stamping transfer of pre-synthesized epitaxial nanostructures that allows tight control over key nanofabric parameters. The second strategy is based on lithographic definition of epitaxial nanostructures on native substrates followed by their stamping transfer using VLSI foundry processes. Finally, we demonstrate the successful concurrent heterogeneous co-integration of silicon and III-V compound semiconductor epitaxial nanowire arrays onto the same hosting substrate over large area, at multiple locations, with fine granularity, close proximity and high yield