Scientists at the U.S. Naval Research Laboratory (NRL) have reported the first observation of spin precession of spin currents flowing in a silicon nanowire (NW) transport channel, and determined spin lifetimes and corresponding spin diffusion lengths in these nanoscale spintronic devices. The spin currents were electrically injected and detected using ferromagnetic metal contacts with a tunnel barrier consisting of single layer graphene between the metal and silicon NW. False color atomic force microscopy image of a silicon nanowire with the four contacts used in the spin measurements. The ferromagnetic metal / graphene tunnel barrier contacts used to inject and detect spin appear as blue, the gold ohmic reference contacts appear as yellow, and the green line is the silicon nanowire transport channel. The bright dot on the end of the nanowire is the gold nanoparticle used to seed the nanowire growth. (Photo: U.S. Naval Research Laboratory) False color atomic force microscopy image of a silicon nanowire with the four contacts used in the spin measurements. The ferromagnetic metal / graphene tunnel barrier contacts used to inject and detect spin appear as blue, the gold ohmic reference contacts appear as yellow, and the green line is the silicon nanowire transport channel. The bright dot on the end of the nanowire is the gold nanoparticle used to seed the nanowire growth. The NRL research team observed spin precession (the Hanle effect) for both the spin-polarized charge near the contact interface and for pure spin currents flowing in the NW channel. The latter unambiguously shows that spins have been injected and transported in the Si NW. The use of graphene as the tunnel barrier provides a low-resistance area product contact and clean magnetic switching characteristics, because it smoothly bridges the NW and minimizes complicated magnetic domains that otherwise compromise the magnetic behavior. The team's discovery is an essential step toward the realization of highly scaled semiconductor spintronic devices. The research results are reported in the 19 June 2015 issue of Nature Communications (DOI 10.1038/ncomms8541). Semiconductor nanowires provide an avenue to further reduce the ever-shrinking dimensions of transistors. Including electron spin as an additional state variable offers new prospects for information processing, enabling future non-volatile, reprogrammable devices beyond the current semiconductor technology roadmap. Silicon is an ideal host for such a spin-based technology because its intrinsic properties promote spin transport, explains principal investigator Dr. Olaf van't Erve. Realization of spin-based Si NW devices requires efficient electrical spin injection and detection, which depend critically on the interface resistance between a ferromagnetic metal contact and the NW. This is especially problematic with semiconducting NWs because of the exceedingly small contact area, which can be of order 100 nm2. Researchers have shown standard oxide tunnel barriers to provide good spin injection into planar Si structures, but such contacts grown on NWs are often too resistive to yield reliable and consistent results. The NRL team developed and used a graphene tunnel barrier contact that produces excellent spin injection and also satisfies several key technical criteria: it provides a low resistance-area product, a highly uniform tunnel layer with well-controlled thickness, clean magnetic switching characteristics for the magnetic contacts, and compatibility with both the ferromagnetic metal and silicon NW. Using intrinsic 2D layers such as graphene or hexagonal boron nitride as tunnel contacts on nanowires offers many advantages over conventional materials deposited by vapor deposition (such as Al O or MgO), enabling a path to highly scaled electronic and spintronic devices. The use of multilayer rather than single layer graphene in such structures may provide much higher values of the tunnel spin polarization because of band structure derived spin filtering effects predicted for selected ferromagnetic metal / multi-layer graphene structures. This increase would further improve the performance of nanowire spintronic devices by providing higher signal to noise ratios and corresponding operating speeds, advancing the techological applications of nanowire devices. The NRL research team includes Dr. Olaf van't Erve, Dr. Adam Friedman, Dr. Connie Li, and Dr. Berend Jonker from the Materials Science and Technology Division, and Dr. Jeremy Robinson from the Electronics Science and Technology Division. About the U.S. Naval Research Laboratory The U.S. Naval Research Laboratory provides the advanced scientific capabilities required to bolster our country's position of global naval leadership. The Laboratory, with a total complement of approximately 2,500 personnel, is located in southwest Washington, D.C., with other major sites at the Stennis Space Center, Miss., and Monterey, Calif. NRL has served the Navy and the nation for over 90 years and continues to advance research further than you can imagine. For more information, visit the NRL website or join the conversation on Twitter, Facebook, and YouTube.
Blood-contacting implantable medical devices, such as stents, heart valves, ventricular assist devices, and extracorporeal support systems, as well as vascular grafts and access catheters, are used worldwide to improve patients' lives. However, these devices are prone to failure due to the body's responses at the blood-material interface; clots can form and inflammatory reactions can prevent the device from performing as indicated. Currently, when this occurs, the only solution is to replace the device. In a paper published in the April 13 issue of Nature Communications, investigators from Harvard report on a novel biochemical method that enables the rapid and repeated regeneration of selected molecular constituents in situ after device implantation, which has the potential to substantially extend the lifetime of bioactive films without the need for device removal. Their approach could also be used to load and release a number of material-bound constituents for controlled drug loading and delivery. Newer implantable devices have thin films with bioactive molecules and/or drugs that help prevent clots and inflammation while also enhancing device integration and local tissue repair, as well as inhibiting microbe colonization. For example, the blood-thinner heparin has been coated on the surfaces of cardiovascular devices to prevent clot formation on or within the devices. However, the newer devices have limitations. "Not only do they have a finite reservoir of bioactive agents, but the surface components of the thin films also degrade or lose their effectiveness when exposed to the physiological environment over time. Presently the only solution is to replace the entire device," said lead author Elliot Chaikof, MD, PhD, Chair of Surgery at Beth Israel Deaconess Medical Center (BIDMC). Dr. Chaikof is also Professor of Surgery at Harvard Medical School, an associate faculty member of Harvard's Wyss Institute of Biologically Inspired Engineering, and a faculty member of the Harvard-Massachusetts Institute of Technology Division of Health Sciences and Technology. A number of approaches have been attempted to improve the stability and activity of thin-film constituents of implantable devices. But despite some progress, a surface coating that reliably retains its biological activity over extended, clinically relevant time periods has not been developed. The new approach relies on an enzyme, Staphylococcus aureus Sortase A, which catalyzes the linking of two peptide sequences. By inducing a series of mutations, David Liu, PhD, Professor of Chemistry and Chemical Biology at Harvard University and a Howard Hughes Medical Institute Investigator, developed a laboratory-evolved enzyme, Staphylococcus aureus Sortase A (eSrtA), which has an enhanced catalytic activity of approximately 120-fold over the non-mutated, wild-type enzyme. eSrtA catalyzes not only linking of peptides but also breaking them apart, which it can do repeatedly. "We found that through a two-step process of removing and replacing bioactive coatings, eSrtA enables rapid, repeated thin-film regeneration in the presence of whole blood in vitro and in vivo," said Liu. "We also developed a series of new enzymes that recognize a variety of distinct peptide sequences that could be put to work in a similar manner." "But, we know that there are many questions that only further research can answer," said Chaikof. "For instance, eSrtA is a bacterial enzyme, and while there is a precedent for the clinical use of such enzymes - for example, streptokinase, uricase, and asparaginase - studies must be done to determine how immunogenic this enzyme might be." Additionally, it is unknown how often a bioactive coating would need to be regenerated, how long it would last, or whether the bioactive constituents could become inaccessible over time due to biologic processes. "Many thousands of people depend on implantable devices with bioactive constituents for their health and well-being, so finding a strategy that will ensure the long-term efficacy of these devices is of paramount importance," said Chaikof. "While this research is relatively early stage, it opens the door to a new way of approaching and addressing this clinical challenge." Explore further: Team builds implantable piezoelectric nanoribbon devices strong enough to power pacemaker (w/ Video)
Scott and Fyfe has appointed RSM Lining Supplies Global Ltd, a supplier of CIPP products, as its distributor for the range of Alphashield products in the UK, Ireland, Australia and New Zealand. The Alphashield range of seamless glass textiles liners has been designed for rehabilitation of small diameter pipes with multiple bends of up to 90°. ‘We are delighted to have formed a partnership with RSM Lining Supplies Global Ltd,’ said Michelle Quadrelli, business director of the Pipe Fabric Technology Division at Scott & Fyfe Ltd ‘RSM has built a strong reputation for supplying quality products into the CIPP market and we feel that they have the necessary expertise and channels to effectively bring our Alphashield range of products to the UK, Irish, Australian and New Zealand markets.’ This story uses material from Scott and Fyfe, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier.
News Article | December 18, 2013
LSI has been a 33-year survivor in the hot-and-cold storage networking semiconductor industry. Storage networking chip maker LSI Corp., which has been busy acquiring other companies the past few years to gain market share, itself has been acquired. Avago Technologies, a Singapore-based company that also makes processors that power both wireless and wired communications equipment, said Dec. 17 that it will acquire San Jose, Calif.-based LSI for $6.6 billion in cash. LSI has been a survivor in the hot-and-cold semiconductor industry. It was founded in 1980 by former executives of now-defunct Fairchild Semiconductor, which also had other executives who went on to start Intel in the 1970s. LSI is the No. 1 storage networking processor maker in the world by sales. Its main competitors have been China's Marvell Technology Group, NXP Semiconductor and ST Microelectronics. To a lesser extent, LSI competes against companies such as Nvidia and Intel.To bolster itself against all those worthy market opponents, LSI over the past few years has bought small but forward-thinking companies such as solid-state storage makers SandForce, ONStor, SiliconStor and StoreAge; semiconductor maker Aquantia; and Ethernet networker Chelsio Communications.Avago, which became public in 2009, is the former Hewlett-Packard semiconductor division that was part of the spinoff business that became Agilent Technologies in 1999. Agilent and Avago subsequently separated six years later , with Avago moving its headquarters to Singapore. In 2005, it employed about 6,800 and was responsible for about a quarter of Agilent's revenue; nonetheless, it was not considered central to Agilent's plans going forward. Avago now has a market cap of about $11 billion. LSI shareholders will receive $11.15 per share from the transaction, which equates to a premium of about 40 percent from the Dec. 13 closing share price of $7.94. Shares of Avago were up more than 16 percent, to $52.75, following news of the deal.
Abstract: Scientists at the U.S. Naval Research Laboratory (NRL) have devised a clever combination of materials -- when used during the thin-film growth process -- to reveal that particle atomic layer deposition, or p-ALD, deposits a uniform nanometer-thick shell on core particles regardless of core size, a discovery having significant impacts for many applications since most large scale powder production techniques form powder batches that are made up of a range of particles sizes. "Particle atomic layer deposition is highlighted as a technology that can create new and exciting designer core/shell particles to be used as building blocks for the next generation of complex multifunctional nanocomposites," said Dr. Boris Feygelson, research engineer, NRL Electronics Science and Technology Division. "Our work is important because shell-thickness is most often a crucial parameter in applications where core-shell materials can be used to enhance performance of future materials." Atomic layer deposition is a layer-by-layer chemical vapor deposition-based thin-film growth technique used extensively in the electronics industry to deposit nanometer-thick films of dielectric materials on devices. Combined with other deposition and shadowing masking techniques, ALD is an integral part of electronic chip and device manufacturing. The same gas-phase process can be applied in a rotary or fluidizing powder bed reactor to grow nanometer-thick films that are highly conformal and uniformly thick on individual particles. Previous research on p-ALD, patented by ALD NanoSolutions, Inc., has shown that growth of each layer during the deposition process varies with particle size, with the underlying assumption that larger particles will always have less growth. To observe this growth phenomenon, the NRL team grew alumina on nano- and micron-sized particles of tungsten and measured the shell thickness in a transmission electron microscope. Because of the huge mass/density difference of the two materials, this pairing provides maximum contrast in the electron microscope and delineation was easily distinguishable between the particle core and shell. In their research, the scientists created core and shell powders consisting of a tungsten particle core and thin alumina shell that were then synthesized using atomic layer deposition in a rotary reactor. Standard atomic layer deposition of trimethylaluminum and water was performed on varying batches of powder with different average particle sizes. "Amazingly, we found that the growth per cycle of the alumina film on an individual particle in a batch was shown to be independent of the size of an individual particle, and therefore, a powder batch -- which consists of particles sizes spanning orders of magnitude -- has constant shell thicknesses on all particles. This result upsets the current understanding of ALD on particles," said Dr. Kedar Manandhar, ASEE postdoc, NRL Electronics Science and Technology Division and leading author of the research paper. The work, published recently in the Journal of Vacuum Science and Technology A, suggests that water, a reactant in the ALD process, is reason for the same rate of growth on different particles. This uniformity of thickness on different particle sizes in a particular batch is determined to be due to the difficulty of removing residual water molecules from the powder during the purging cycle of the atomic layer deposition (ALD) process. "Water is very sticky and it is very difficult to remove the last mono-layer from surfaces," Feygelson says. "And when you have a tumbling bed of powders, the water sticks around between the particles and results in consistent shell growth in the tumbling powder. Applications for this research demonstrate implications for use in materials like abrasion resistant paints, high surface area catalyst, electron tunneling barriers, ultra-violet adsorption or capture in sunscreens or solar cells and even beyond when core-shell nanoparticles are used as buildings blocks for making new artificial nanostructured solids with unprecedented properties. ### This research is a cross-disciplinary effort at NRL between the Materials Science and Technology Division and Electronics Science and Technology Division. The authors of the paper gratefully acknowledge Drs. Dev Palmer (Defense Advanced Research Projects Agency), Baruch Levush (NRL), and Fritz Kub (NRL). For more information, please click If you have a comment, please us. Issuers of news releases, not 7th Wave, Inc. or Nanotechnology Now, are solely responsible for the accuracy of the content.