National Nanomanufacturing Network

Large Area Growth of Single Layer Hexagonal Boron Nitride Films

National Nanomanufacturing Network - August 28, 2014 - 4:29am
Two-dimensional hexagonal boron nitride (h-BN) is a material of significant interest due to the strong ionic bonding of boron and nitrogen atoms that provides unique properties, including the thinnest insulating nanomaterial, exhibiting a bandgap of 5.9 eV, with superior chemical, mechanical, and thermal stability. In addition, h-BN provides an ideal substrate for improving the electrical properties of graphene since the surface is atomically smooth and free of dangling bonds, thereby reducing charge scattering effects resulting in an order of magnitude increase in graphene charge mobility over materials grown on silicon or silicon dioxide. Previously, the method to synthesize monolayer n-BN utilized ultra-high vacuum chemical vapor deposition (UHVCVD) using borazine as a precursor on single crystal transition metal substrates, such as nickel, platinum, or silver, but proved difficult to scale. Polycrystalline metal foils (Ni, Co, Cu, and Pt) were additionally used to grow h-BN using regular chemical vapor deposition (CVD), but the thickness and quality of the films critically depended on surface morphology and crystal orientation of the substrate. High quality h-BN has been synthesized on Pt foils using ammonia borane precursor, yet control of film thickness and domain size remains a challenge for scaling, and the specific growth mechanisms are not well understood. Recently, Park et.al., reported results from a systematic study for synthesis of large area single layer h-BN films on polycrystalline Pt foils using low pressure CVD comparing borazine and ammonia borane precursors. The authors’ goal was to study the effect of the Pt lattice orientation, the total pressure, and the different cooling rate in order to understand h-BN growth mechanisms. Since nitrogen is not soluble in Pt, the authors’ objective was to confirm the contributions to h-BN growth surface mediated and precipitation processes. The study included analysis of film properties dependence on cooling rate and crystal orientation of the substrate. Their findings demonstrated that film growth was by a surface mediated growth mechanism, facilitated by a catalytic reaction, that produced polycrystalline h-BN monolayers confined by the underlying Pt surface orientation. The thickness of the h-BN films exhibited a dependence on the Pt surface orientation, presumably determined by the available catalytic reaction sites that decompose the borazine precursor, which would exhibit a dependence on crystal orientation. Improved understanding of h-BN growth mechanisms will potentially lead to methods for controlling the growth of high-quality h-BN films. This further provides the basis for materials and substrates for application in quantum tunneling devices, novel heterostructures, and two-dimensional semiconductors such as molybdenum sulfide and graphene.Reference: Park J, Park JC, Yun SJ, Kim H, Luong DH, Kim SM, Choi SH, Yang W, Kong J, Kim KK, Lee YH. Large-Area Monolayer Hexagonal Boron Nitride on Pt Foil. ACS Nano. 2014; 8 (8): 8520-852 doi: 10.1021/nn503140y (http://pubs.acs.org/doi/full/10.1021/nn503140y#showRef) Image reprinted with permission from American Chemical Society.

Nanotechnology engineering produces a water splitter that runs on an ordinary AAA battery

National Nanomanufacturing Network - August 27, 2014 - 4:56am
In 2015, American consumers will finally be able to purchase fuel cell cars from Toyota and other manufacturers. Although touted as zero-emissions vehicles, most of the cars will run on hydrogen made from natural gas, a fossil fuel that contributes to global warming. Now scientists at Stanford University have developed a low-cost, emissions-free device that uses an ordinary AAA battery to produce hydrogen by water electrolysis. The battery sends an electric current through two electrodes that split liquid water into hydrogen and oxygen gas. Unlike other water splitters that use precious-metal catalysts, the electrodes in the Stanford device are made of inexpensive and abundant nickel and iron. "Using nickel and iron, which are cheap materials, we were able to make the electrocatalysts active enough to split water at room temperature with a single 1.5-volt battery," said Hongjie Dai (http://dailab.stanford.edu/), a professor of chemistry at Stanford. "This is the first time anyone has used non-precious metal catalysts to split water at a voltage that low. It's quite remarkable, because normally you need expensive metals, like platinum or iridium, to achieve that voltage." In addition to producing hydrogen, the novel water splitter could be used to make chlorine gas and sodium hydroxide, an important industrial chemical, according to Dai. He and his colleagues describe the new device in a study (http://dx.doi.org/10.1038/ncomms5695) published in the Aug. 22 issue of the journal Nature Communications. The promise of hydrogen Automakers have long considered the hydrogen fuel cell a promising alternative to the gasoline engine. Fuel cell technology is essentially water splitting in reverse. A fuel cell combines stored hydrogen gas with oxygen from the air to produce electricity, which powers the car. The only byproduct is water – unlike gasoline combustion, which emits carbon dioxide, a greenhouse gas.Earlier this year, Hyundai began leasing fuel cell vehicles in Southern California. Toyota and Honda will begin selling fuel cell cars in 2015. Most of these vehicles will run on fuel (http://energy.gov/eere/fuelcells/natural-gas-reforming) manufactured at large industrial plants that produce hydrogen by combining very hot steam and natural gas, an energy-intensive process that releases carbon dioxide as a byproduct. Splitting water to make hydrogen requires no fossil fuels and emits no greenhouse gases. But scientists have yet to develop an affordable, active water splitter with catalysts capable of working at industrial scales. "It's been a constant pursuit for decades to make low-cost electrocatalysts with high activity and long durability," Dai said. "When we found out that a nickel-based catalyst is as effective as platinum, it came as a complete surprise." Saving energy and money The discovery was made by Stanford graduate student Ming Gong, co-lead author of the study. "Ming discovered a nickel-metal/nickel-oxide structure that turns out to be more active than pure nickel metal or pure nickel oxide alone," Dai said. "This novel structure favors hydrogen electrocatalysis, but we still don't fully understand the science behind it." The nickel/nickel-oxide catalyst significantly lowers the voltage required to split water, which could eventually save hydrogen producers billions of dollars in electricity costs, according to Gong. His next goal is to improve the durability of the device. "The electrodes are fairly stable, but they do slowly decay over time," he said. "The current device would probably run for days, but weeks or months would be preferable. That goal is achievable based on my most recent results" The researchers also plan to develop a water splitter than runs on electricity produced by solar energy. "Hydrogen is an ideal fuel for powering vehicles, buildings and storing renewable energy on the grid," said Dai. "We're very glad that we were able to make a catalyst that's very active and low cost. This shows that through nanoscale engineering of materials we can really make a difference in how we make fuels and consume energy."Source: Stanford University (http://news.stanford.edu/news/2014/august/splitter-clean-fuel-082014.html)

Optical Microscope Technique Confirmed as Valid Nano-Measurement Tool

National Nanomanufacturing Network - August 27, 2014 - 4:20am
Recent experiments have confirmed* that a technique developed several years ago at the National Institute of Standards and Technology (NIST) can enable optical microscopes to measure the three-dimensional (3-D) shape of objects at nanometer-scale resolution—far below the normal resolution limit for optical microscopy (about 250 nanometers for green light). The results could make the technique a useful quality control tool in the manufacture of nanoscale devices such as next-generation microchips. NIST’s experiments show that Through-focus Scanning Optical Microscopy (TSOM) is able to detect tiny differences in 3-D shapes, revealing variations of less than 1 nanometer in size among objects less than 50 nm across. Last year,** simulation studies at NIST indicated that TSOM should, in theory, be able to make such distinctions, and now the new measurements confirm it in practice. “Up until this point, we had simulations that encouraged us to believe that TSOM could allow us to measure the 3-D shape of structures that are part of many modern computer chips, for example,” says NIST’s Ravi Attota, who played a major role in TSOM’s development. “Now, we have proof. The findings should be helpful to anyone involved in manufacturing devices at the nanoscale.” Attota and his co-author, Ron Dixson, first measured the size of a number of nanoscale objects using atomic force microscopy (AFM), which can determine size at the nanoscale to high accuracy. However, the great expense and relatively slow speed of AFM means that it is not a cost-effective option for checking the size of large numbers of objects, as is necessary for industrial quality control. TSOM, which uses optical microscopes, is far less restrictive—and allowed the scientists to make the sort of size distinctions a manufacturer would need to make to ensure nanoscale components are constructed properly. Attota adds that TSOM can be used for 3-D shape analysis without needing complex optical simulations, making the process simple and usable even for low-cost nanomanufacturing applications. “Removing the need for these simulations is another way TSOM could reduce manufacturing costs,” he says. More details on the TSOM technique and its application to 3-D electronics manufacturing can be found in this story (http://www.nist.gov/public_affairs/tech-beat/tb20130625.cfm#tsom), which covers the 2013 simulation study. *R. Attota and R.G. Dixson. Resolving three-dimensional shape of sub-50 nm wide lines with nanometer-scale sensitivity using conventional optical microscopes. Applied Physics Letters, 105, 043101, July 29, 2014, http://dx.doi.org/10.1063/1.4891676 (http://dx.doi.org/10.1063/1.4891676). **See the June 2013 NIST Tech Beat story, “Microscopy Technique Could Help Computer Industry Develop 3-D Components (http://www.nist.gov/public_affairs/tech-beat/tb20130625.cfm#tsom)” at www.nist.gov/public_affairs/tech-beat/tb20130625.cfm#tsom (http://www.nist.gov/public_affairs/tech-beat/tb20130625.cfm#tsom). Source: NIST (http://www.nist.gov/pml/div683/tsom-082614.cfm)

Graphene rubber bands could stretch limits of current healthcare, new research finds

National Nanomanufacturing Network - August 20, 2014 - 8:26am
New research published today in the journal ACS Nano ("Sensitive, High-Strain, High-Rate Bodily Motion Sensors Based on Graphene–Rubber Composites" (http://dx.doi.org/doi:10.1021/nn503454h)) identifies a new type of sensor that can monitor body movements and could help revolutionise healthcare. Although body motion sensors already exist in different forms, they have not been widely used due to their complexity and cost of production. Now researchers from the University of Surrey and Trinity College Dublin have for the first time treated common elastic bands with graphene, to create a flexible sensor that is sensitive enough for medical use and can be made cheaply. Once treated, the rubber bands remain highly pliable. By fusing this material with graphene - which imparts an electromechanical response on movement – the team discovered that the material can be used as a sensor to measure a patient's breathing, heart rate or movement, alerting doctors to any irregularities. "Until now, no such sensor has been produced that meets needs and that can be easily made. It sounds like a simple concept, but our graphene-infused rubber bands could really help to revolutionise remote healthcare," said Dr Alan Dalton from the University of Surrey. Co-author, Professor Jonathan Coleman from Trinity College, Dublin commented, "This stretchy material senses motion such as breathing, pulse and joint movement and could be used to create lightweight sensor suits for vulnerable patients such as premature babies, making it possible to remotely monitor their subtle movements and alert a doctor to any worrying behaviours. "These sensors are extraordinarily cheap compared to existing technologies. Each device would probably cost pennies instead of pounds, making it ideal technology for use in developing countries where there are not enough medically trained staff to effectively monitor and treat patients quickly." Source: University of Surrey (https://www.surrey.ac.uk/features/could-elastic-bands-monitor-patients%E2%80%99-breathing)

NSF Workshop for a Future Nanotechnology Infrastructure Support Program Webcast

National Nanomanufacturing Network - August 13, 2014 - 7:53am
On August 18 and 19, 2014 the NSF will conduct a Workshop for a Future Nanotechnology Infrastructure Support Program.The workshop is a next step in NSF's preparation for developing a program to succeed the National Nanotechnology Infrastructure Network (NNIN (http://nnin.org/)), after having received community input in response to a recent Dear Colleague Letter (DCL 14-068 (http://www.nsf.gov/pubs/2014/nsf14068/nsf14068.jsp?org=ENG)). To broaden engagement, portions of the Workshop for a Future Nanotechnology Infrastructure Support Program will be webcast. (The approximate webcast times shown below are Eastern Daylight Time.) The workshop will convene a panel of experts from academe, industry, and government to: develop a vision of how a future nanotechnology infrastructure support program could be structured, and determine the key needs for the broad user communities over the coming decade. The workshop is co-chaired by Dr. Thomas Theis (IBM Research, on assignment to the Semiconductor Research Corporation) and Dr. Mark Tuominen (University of Massachusetts, Amherst). More details are in the workshop agenda (http://www.nsf.gov/attachments/132127/public/Workshop_Future_Nanotechnology_Infrastructure_Support_Program.pdf). Webcast: August 18, 2014 8:00 AM to 12:00 PM and August 19, 2014 8:00 AM to 12:00 PM Morning sessions of the workshop will be broadcast via WebEx; afternoon breakout sessions will not be broadcast. If you have never used WebEx before or if you want to test your computer's compatibility with WebEx, please go to http://www.webex.com/lp/jointest/ (http://www.webex.com/lp/jointest/), enter the session information and click "Join". Please feel free to contact WebEx Support if you are having trouble joining the test meeting.Session number: 643 345 106 Session password: This session does not require a password. ------------------------------------------------------- To join the session ------------------------------------------------------- 1. Go to https://src.webex.com/src/k2/j.php?MTID=tb5710cac7d8b81a0e0e5c436b48545bc (https://src.webex.com/src/k2/j.php?MTID=tb5710cac7d8b81a0e0e5c436b48545bc) 2. Enter your name and email address. 3. Click "Join Now". 4. Follow the instructions that appear on your screen. 5. To receive a call back, provide your phone number when you join the session.------------------------------------------------------- To join the session by phone only ------------------------------------------------------- Call the number below and enter the access code. Toll-free number (US/Canada): 1-877-668-4490 Access code: 643 345 106 Meeting TypeWebcast Contacts Allison Hilbert, 919-941-9433, Allison.Hilbert@src.org (mailto:Allison.Hilbert@src.org)Preferred Contact Method: Email NSF Related Organizations NSF-Wide Directorate for Engineering Core Attachments Workshop Future Nanotechnology Infrastructure Support Program (http://www.nsf.gov/attachments/132127/public/Workshop_Future_Nanotechnology_Infrastructure_Support_Program.pdf)Source: NSF (http://www.nsf.gov/events/event_summ.jsp?cntn_id=132127 WT.mc_id=USNSF_13 WT.mc_ev=click)