MIT Models Bismuth-Antimony Properties

MIT researchers said thin films of bismuth-antimony have electronic properties that are highly desirable for next-generation ICs or thermoelectric generators and coolers.

The compound forms two-dimensional Dirac cones, the cone-shaped graph plotting energy versus momentum for electrons moving through the material.

Materials science and engineering PhD candidate Shuang Tang and Professor Mildred Dresselhaus (Source: MIT)

The research, carried out by materials science and engineering PhD candidate Shuang Tang and Professor Mildred Dresselhaus, appears in the journal Nano Letters. Dresselhaus said the initial analysis was based on theoretical modeling of the bismuth-antimony film’s properties, and it will take about a year to test samples.

Tang said models show that electrons “can travel like a beam of light” through the bismuth-antimony compound, in some cases hundreds of times faster than in silicon.  “In a thermoelectric application — where a temperature difference between two sides of a device creates a flow of electrical current — the much faster movement of electrons, coupled with strong thermal insulating properties, could enable much more efficient power production,” MIT said in a detailed report on the effort.

Self Assemby of Nanoparticles

Scientists based at the Lawrence Berkeley National Laboratory and the University of California Berkeley said they have directed the first self-assembly of nanoparticles into device-ready materials. A Berkeley Lab report said the researchers produced multiple-layers of thin films from highly ordered one-, two- and three-dimensional arrays of gold nanoparticles, using a relatively inexpensive technique based on blending nanoparticles with block co-polymer supramolecules.

A supramolecule is a group of molecules that act as a single molecule able to perform a specific set of functions, while block copolymers are long sequences or “blocks” of one type of monomer bound to blocks of another type of monomer that have an innate ability to self-assemble into well-defined arrays of nano-sized structures over macroscopic distances, the report said.

Berkeley Lab researchers have developed a relatively simple and inexpensive technique for directing the self-assembly of nanoparticles into device-ready thin films with microdomains of lamellar (left) or cylindrical morphologies. (Source: Ting Xu group)

“Block copolymer supramolecules self-assemble and form a wide range of morphologies that feature microdomains typically a few to tens of nanometers in size,” Berkeley Lab scientist Ting Xu said. “As their size is comparable to that of nanoparticles, the microdomains of block copolymer supramolecules provide an ideal structural framework for the co-self-assembly of nanoparticles.”

The inter-particle distance between gold nanoparticles in the 1-D chains and the 2-D sheets was 8 to 10 nanometers, which may create opportunities in plasmonics, the phenomenon by which a beam of light is confined in ultra-confined spaces.

“Our gold thin films display strong plasmonic coupling along the inter-particle spacing in the 1-D chains and 2-D sheets respectively,” Xu says. “We should therefore be able to use these films to investigate unique plasmonic properties for next-generation electronic and photonic devices. Our supramolecular technique might also be used to fabricate plasmonic metamaterials.”

– by David Lammers

Flexible carbon FET

Japanese researchers said they have fabricated flexible field-effect transistors (CNT-FETs) based on single-walled carbon nanotubes (SWNTs). The team – based at the University of Tokyo and the Tokyo University of Science − used a polymer-laminated, transparent, plastic substrate that is considerably thinner than substrates used in other flexible CNT-FETs. The polymer substrate “allowed our devices to be highly deformable without degradation of electrical properties,” the researchers said in a paper published by Applied Physics Letters.

The flexible, transparent CNT-FET devices are able to withstand a 1 mm bending radius, which is flexible and thin enough (~15 µm) to be used in wearable electronics. The team reported that all of the components of the FET, including the channel, electrodes, dielectric layer, and substrate, were based on carbon-based materials.

Nanofelt Delivers Power

Carbon nanotube/polymer composite thin films exhibit thermoelectric effects. Multiple layers would generate more power. (Source: Wake Forest University)

Researchers at the Wake Forest University Center for Nanotechnology and Molecular Materials said they have combined multi-walled carbon nanotubes and polyvinylidene fluoride (PVDF) to develop a fabric-like material with a thermoelectric effect, i.e. capable of the solid-state conversion between thermal and electrical energy. The research team leader, David Carroll, said the material can be layered into a felt-like fabric which could generate a thermoelectric voltage high enough to power some mobile electronic systems. The “Power Felt” material, as described in the journal Nano Letters, could have enough layers to power a cellphone, or an emergency flashlight, for example.

By David Lammers

Semiconductor Research Corporation (SRC) has joined with the National Science Foundation (NSF) to fund $20 million for 12 four-year grants on nanoelectronics research to researchers working at 24 U.S. universities.

The researchers “will contribute to the goal of discovering a new switching mechanism using nanoelectronic innovations as a replacement for today’s transistor,” the SRC said in announcing the awards.

“The search for a new semiconductor device that will provide the U.S. with a leadership position in the global era of nanoelectronics relies on making discoveries at these kinds of advanced universities,” said Jeff Welser, director of the Nanoelectronics Research Initiative (NRI), part of the SRC.

“This competition, Nanoelectronics for 2020 and Beyond (NEB), is an important component of the National Nanotechnology Initiative Signature Initiative, whose goal is to accelerate the discovery and use of novel nanoscale fabrication processes and innovative concepts to produce revolutionary materials, devices, systems, and architectures to advance the field of nanoelectronics,” said Lawrence Goldberg, senior engineering advisor at the National Science Foundation.

The joint NSF-NRI grants were awarded to the following projects in nanoelectronics research and can be viewed in detail at the accompanying links:

• Scalable Sensing, Storage and Computation with a Rewritable Oxide Nanoelectronics Platform, directed by Jeremy Levy at University of Pittsburgh. http://nsf.gov/awardsearch/showAward.do?AwardNumber=1124131
• Integrated Biological and Electronic Computation at the Nanoscale, directed by Timothy Lu at MIT. http://nsf.gov/awardsearch/showAward.do?AwardNumber=1124247
• Developing a Graphene Spin Computer: Materials, Nano-Devices, Modeling, and Circuits, directed by Roland Kawakami at University of California at Riverside. http://nsf.gov/awardsearch/showAward.do?AwardNumber=1124601
• Meta-Capacitance and Spatially Periodic Electronic Excitation Devices (MC-SPEEDs), directed by Jonathan Spanier at Drexel University. http://nsf.gov/awardsearch/showAward.do?AwardNumber=1124696
• Hybrid Spintronics and Straintronics: New Technology for Ultra-Low Energy Computing and Signal Processing Beyond the Year 2020, directed by Supriyo Bandyopadhyay at Virginia Commonwealth University. http://nsf.gov/awardsearch/showAward.do?AwardNumber=1124714
• Charge-Density-Wave Computational Fabric: New State Variables and Alternative Material Implementation, directed by Alexander Balandin at University of California at Riverside. http://nsf.gov/awardsearch/showAward.do?AwardNumber=1124733
• Ultimate Electronic Device Scaling Using Structurally Precise Graphene Nanoribbons, directed by Paulette Clancy at Cornell University. http://nsf.gov/awardsearch/showAward.do?AwardNumber=1124754
• Nanoelectronics with Mixed-valence Molecular QCA, directed by Craig Lent at University of Notre Dame. http://nsf.gov/awardsearch/showAward.do?AwardNumber=1124762
• Scalable Perpendicular All-Spin Non-Volatile Logic Devices and Circuits with Hybrid Interconnection, directed by Jian-Ping Wang at University of Minnesota at Twin Cities. http://nsf.gov/awardsearch/showAward.do?AwardNumber=1124831
• Physics-Inspired Non-Boolean Computation Based on Spatial-Temporal Wave Excitations, directed by Wolfgang Porod at University of Notre Dame. http://nsf.gov/awardsearch/showAward.do?AwardNumber=1124850
• Novel Quantum Switches Using Heterogeneous Atomically Layered Nanostructures, directed by Philip Kim at Columbia University. http://nsf.gov/awardsearch/showAward.do?AwardNumber=1124894
• Superlattice-FETs, Gamma-L-FETs and Tunnel-FETs: Materials, Circuits and Devices for Fast, Ultra-Low Power, directed by Mark Rodwell at University of California at Santa Barbara. http://nsf.gov/awardsearch/showAward.do?AwardNumber=1125017

These 12 NSF-NRI joint grants expand and strengthen the commitment to this public-private partnership program, which is in its sixth year.

Companies participating in NRI are GlobalFoundries, IBM, Intel Corporation, Micron Technology and Texas Instruments. These companies assign researchers to interact with the university teams, with a goal of demonstrating the feasibility of novel computing devices in simple computer circuits during the next five to 10 years.