The excellent shared research facilities and resources of the Center for Nano and Molecular Science and Technology (CNM) have allowed the center to foster leading research in a number of thrust areas. Foremost of these are “Nanotechnology for Energy Needs” and “Nanoelectronics”. In addition to the facilities, the CNM provides an open environment where collaboration between researchers from across the University is possible. Collaborations across Department and individual College boundaries allow researchers to work together to tackling the challenges of nanotechnology from all angles. Integrating fundamental studies in chemistry and physics (bottom-up) with ever shrinking engineered electro-mechanical devices (top-down) provides CNM researchers with the knowledge to expand the frontiers of nanoscience and nanotechnology.

NANOTECHNOLOGY FOR ENERGY NEEDS

Developing new methods to meet the world’s ever increasing energy demands will require radical solutions that nanoscience and nanotechnology have the potential to address. The CNM faculty members are tackling these new problems in two major areas of renewable energy research photovolataics and hydrogen fuel cells. The CNM efforts couple both basic science and engineering to develop new materials, understanding, and devices.

An excellent example of our approach is the research of Dr. Paul Barbara (Chemistry and Biochemistry) whose research lab has developed powerful single molecule spectroscopy tools to characterize individual conjugated polymers. [Barbara, 2005][Palacios, 2006] Because the properties of the polymer in a bulk film vary greatly due to conformation and interaction with neighboring chains, it is extremely difficult in bulk studies to fundamentally understand how charges transfer into and out of chains. With repeated measurements on the same individual molecule, the Barbara group is able to observe single electron transfer events at the single molecule level. This allows for direct study of properties that are otherwise masked by ensemble averaging in bulk observations. A fundamental understanding of how charges move in and out of polymers is critical to the development of new materials and devices for plastic photovoltaic devices.

Also working in the area of fundamental photovoltaics is David Vanden Bout’s (Chemistry and Biochemistry) group. His research team utilizes high-resolution optical microscopy techniques that are capable of mapping out fluorescence lifetimes on the nanoscale to probe charge separation in conjugated polymer thin films. [Bunz, 2005] This initial charge separation is critical to the success of any photovoltaic device. Also, crucial to the advancement of photovoltaic research are new materials. In particular, hybrid photovoltaics comprised of both organics and inorganics rely on high quality monodisperse nanoparticles. Keith Stevenson’s (Chemistry and Biochemistry) group is working on characterization of charge transport behavior in organic and metal oxide thin films. This project focuses on the development of high resolution optical
and scanning probe microscopy tools for evaluation of charge transport in heterogeneous, nanostructured materials. [McEvoy, 20006] Spatially resolved measurements obtained at nanoscopic length scales aids in the understanding of structure-property and materials performance
relationships crucial for the development of next-generation batteries, fuel cells, and solar cells.

Brian Korgel’s (Chemical Engineering) research group has developed a number of synthetic methods for the production of bulk quantities of high quality semiconductor nanowires with very low dispersion in size. [Lu, 2005] [Smith, 2006] These nanowires have a number of applications ranging from photovoltaics to low-energy emissive displays. Finally, low cost, flexible plastic photovoltaics will require new manufacturing technology coupled with new plastic electronics. Dr. Lynn Loo (Chemical Engineering) is leading this effort in the CNM with the development of solution processible organic and polymer conductors and semiconductors for a variety of applications. [Dickey, 2006]

Another area where nanoscience and technology have the potential to make big impacts in renewable energy is in the development of fuel cell technology. Allen Bard’s (Chemistry and Biochemistry) research group has been working on mixed metal nanoparticle catalysts for oxygen reduction, a key step in proton exchange membrane fuel cells. They have developed a rapid screening method for testing electrocatlysis of nanoparticle arrays utilizing scanning electrochemical microscopy. These efforts have lead to the discovery of several non-Pt materials with activities on par with standard Pt catalysts. [Walsh, 2006]

Nanoscale catalysts have shown promising properties for a number of critical applications related to renewable energy and green chemical synthesis, because of their high surface to volume ratio and the ability to produce nanoparticles of a wide variety of sizes and shape. The laboratory of Richard Crooks (Chemistry and Biochemistry) has developed a new method for the synthesis of monodisperse dendrimer-encapsulated metal nanoparticles with well-defined stoichiometry. These protected nanoparticles can be made from nearly any metal, but when made from platinum and palladium serve as highly selective catalysts. [Wilson, 2006] The group has recently demonstrated the effect of size and face selectivity for Pd Nanoparticles.

NANOELECTRONICS

A key emerging area in nanotechnology is nanoelectronics. The CNM has developed a working partnership with the Microelectronics Research Center (MRC) at the University of Texas’ Pickle Campus to jointly push forward the development of nanoscale electronics. These efforts include both fundamental research on materials as well as applied engineering and testing of new nanoscale devices.

One area of Nanoelectronics research is “quantum engineering” of metallic and magnetic structures. Ken Shih (Physics) investigates how quantum confinement of electronic states impacts the thermodynamic properties of metallic nanostructures and how such confinement influences the collective bulk electronic properties such as magnetism and superconductivity. [Jiang, 2004] [Eom, 2006]

Another area of research in the Shih lab is “quantum coherent control” of photonic properties of semiconductor nanostructures. Exploration of new possibilities to control the quantum optical properties of such nanostructures and to harness these quantum optical properties for novel optical device applications is underway in the lab. These studies are providing the basic fundamental knowledge necessary for fabrication of a quantum computing device and quantum information technology. [Wang, 2005]

Sanjay Banerjee (Electrical and Computer Engineering) has been working on a project that clearly illustrates the combination of top-down and bottom-up approach. His group utilizes the self-assembly of chaperonin proteins onto a silicon surface to pattern semiconductor quantum dots with nanometer precision and accuracy. Then, this method is combined with conventional lithographic techniques to create floating gate memory devices with increased speed improved leakage current (reference?)

While Banjeree’s research is utilizing the self-assembly of soft materials to pattern nanoscale electronics, other research groups are using the resources of the CNM to push conventional materials to their limits. Prof. Ray Chen (Electrical and Computer Engineering) recently invented an ultracompact silicon-photonic-crystal electro-optic modulator silicon modulator fabricated by standard lithographic techniques. This photonic crystal slows the speed of light down sufficiently that the intensity can be modulated by a very small electric current. [Jiang, 2005] This design requires ten times less power consumption normally needed for silicon modulators. Once these modulators can be combined with semiconductor lasers on a silicon platform they will significantly increase interconnect speeds and efficiencies.

Li Shi (Mechanical Engineering) is creating nanowires of thermoelectric materials (materials capable of converting voltage differences into heat and vice versa). Based on theoretical calculations these nearly one-dimensional structures should have exceptional thermoelectric properties. After synthesis of a batch of nanowires, individual nanostructures are placed onto a micron-sized thermal test bed structure that was developed and fabricated in Shi’s laboratory. Once fastened to the MEMS heater with a small amount of platinum ‘glue’, the electrical and thermal properties of individual nanowires can be measured. [Zhou, 2005] [Shi, 2005]

The CNM nanoelectronic’s efforts are also branching out from traditional semiconductors and into emerging areas such as spintronics. Maxim Tsoi’s (Physics) research is focused on this new technological discipline that refers to studying the role played by an electron spin in solid-state physics. The main focus of his work is in current driven spin-transfer phenomena. [Beach, 2005] His research group has recently demonstrated transfer of spin-angular momentum across and interface between ferromagnetic and antiferromagnetic metals. The spin transfer is mediated by an electrical current and revealed by variation in the exchange bias at the ferromagnet/antiferromagnet interface. [Wei, 2006] Current-mediated variation of exchange bias can be used to control the magnetic state of spin-valve devices, e.g., in magnetic memory applications which create an entirely new class of high-density non volatile memory.

Ananth Dodabalapur (Electrical and Computer Engineering) specializes in organic circuits, especially thin film transistors. By careful choice of the organic channel, organic transistors responses are modulated by their chemical environment. This effect allows them to be used as chemical sensors. [Torsi, 2005]

REFERENCES

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G. S. D. Beach, C. Nistor, C. Knutson, M. Tsoi, and J. L. Erskine; “Dynamics of Field-Driven Domain Wall Propagation in Ferromagnetic Nanowires” Nature Mater. 2005, 4, 741–744.

U. H. F. Bunz, J. M. Imhof, R. K. Bly, C. G. Bangcuyo, L. Rozanski, D. A. Vanden Bout; “Photophysics of Poly[p-(2,5-didodecylphenylene)ethynylene] in Thin Films” Macromolecules 2005, 38, 5892-5896.

K. C. Dickey, J. E. Anthony, Y.-L. Loo; “Improving Organic Thin-Film Transistor Performance Through Solvent Vapor Annealing of Solution-Processable Triethylsilylethnyl Anthradithiophene”, Adv. Mater. 2006, 18, 1721–1726.

D. Eom, S. Qin, M.-Y. Chou, C.K. Shih “Persistent Superconductivity in Ultra-Thin Pb Films: A Scanning Tunneling Spectroscopy Study” Phys. Rev. Lett. 2006, 96, 027005.

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D. K. Smith, D. C. Lee, B. A. Korgel; “High Yield Multiwall Carbon Nanotube Synthesis in Supercritical Fluids” Chem. Mater. 2006, 18, 3356-3364.

L. Torsi, A. Dodabalapur; “Organic Thin-Film Transistors as Plastic Analytical Sensors” Anal. Chem. 2005, 77, 380A-387A.

D. A. Walsh, J. L. Fernandez, A. J. Bard; “Rapid Screening of Bimetallic Electrocatalysts for Oxygen Reduction in Acidic Media by Scanning Electrochemical Microscopy” J. Electrochem. Soc. 2006, 153, E99-E103.

Q. Q. Wang, A. Muller, M. T. Cheng, H. J. Zhou, P. Bianucci, C. K. Shih; “Coherent Control of a V-type Three-Level System in a Single Quantum Dot,” Phys. Rev. Lett. 2005, 95, 187404.

Z. Wei, A. Sharma, A. S. Nunez, P. M. Haney, R. A. Duine, J. Bass, A. H. MacDonald, M. Tsoi; “Spin Transfer in an Antiferromagnet” Los Alamos National Laboratory, Preprint Archive, Condensed Matter (2006), 1-5, arXiv:cond-mat/0606462.

O. M. Wilson, M. R. Knecht, J. C. Garcia-Martinez, R. M. Crooks; “Effect of Pd Nanoparticle Size on the Catalytic Hydrogenation of Allyl Alcohol” J. Am. Chem. Soc. 2006, 128, 4510-4511.

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