Texas Photovoltaic Symposium

Friday January 30, 2009, All Day, NST 1.104

Evan Ma, Johns Hopkins University

Wednesday February 25, 2009, 12:00pm, NST 1.104

Nanostructured Metals: Opportunities for New Mechanical Properties and Deformation Mechanisms

Metals and alloys are normally polycrystalline. In recent years, there has been a push to drive the grain size down into the submicron and nanometer regime (10 to 100 nm). Such nanostructured materials offer new opportunities with respect to their mechanical properties. In this talk, I will present an overview of recent findings regarding the new deformation behavior and unusual properties of nanocrystalline and nanostructured (including ultrafine-grained) metals. We discuss the roles of partial dislocation mediated processes and nanoscale (growth) twins, as well as their dependence on deformation conditions. Repeated stress relaxation tests to separately monitor the evolution of the velocity and density of mobile dislocations are reported, to shed light on the rate-controlling mechanisms. We also highlight the interesting mechanical properties and unusual deformation modes uncovered recently. Strategies currently employed to improve the ductility of nanostructured metals are summarized. By taking advantage of the nanoscale effects, one now has new “knobs to turn” to derive unprecedented strength and ductility from nanostructured metals for applications, including those at cryogenic temperatures or high strain rates. The plastic instabilities suffered by nanomaterials may be either circumvented, or turned into an advantage to meet certain critical military needs.

Robert Hull, Rensselaer Polytechnic Institute

Wednesday March 11, 2009, 12:00pm, NST 1.104

New Methods for Nanoscale Assembly, Functionalization and Characterization of Semiconductor Nanostructures Using the Focused Ion Beam

I will describe how the focused ion beam (FIB) can be used for controlled fabrication and doping of novel semiconductor nanostructures, with application to potential nanoelectronic architectures.  Specific examples include nanoscale templating of epitaxial Ge quantum dots and quantum dot molecules on Si(100) surfaces, and fabrication of metal and insulator core-shell structures on semiconductor nanowires.  We are also developing methods for electronic and magnetic functionalization of these nanostructures using a mass-selected FIB, where ions of different species can be separated from liquid metal alloy sources (e.g. Si from AuSi, B and As from PdAsB, and Mn and Ge from MnGe). It will also be shown how the FIB can elucidate the detailed geometrical and chemical relationships in three-dimensional nanostructure arrays using in-situ tomography techniques.

Work in collaboration with J. Floro, M. Gherasimova, J. Graham, L. He, J. Thorp (U. Virginia), J. Gray (U. Pittsburgh), F. Ross (IBM), A. Portavoce (CNRS-Marseilles), J. Jonasson (U. Lund)

Masahiro Ishigami, University of Central Florida

Wednesday March 25, 2009, 12:00pm, NST 1.104

Transport Properties of Atomically-Clean Graphene

Graphene, an individual atomic layer of graphite, is a semimetal with unique linear electronic dispersion and vanishing density of states at the charge neutrality point.  As a result, graphene possesses unusual transport properties.  It is important to note that graphene is composed solely of surface atoms and, due to large surface to volume ratios, atomic-scale features such as adsorbates and defects play a very important role in determining its transport properties.

Recent advances [1] have allowed transport measurements on graphene in experimental environment controlled down to atomic scale.   I will discuss the intrinsic transport properties of atomically-clean graphene and the impact of both charged [2], long-range, and uncharged, short-range, impurities.  The results explain the large variability reported for graphene experiments and indicate the ultimate performance limitations of graphene-based electronics.

Amanda Petford-Long, Argonne National Laboratory

Wednesday April 15, 2009, 12:00pm, NST 1.104

Structure property relationships in nanoscale magnetic heterostructures

The properties of nanoscale magnetic materials depend critically on their microstructure and composition, with variations on the atomic scale leading to variations in properties. Of particular interest for technological applications in information storage systems are magnetic structures composed of thin layers, such as spin tunnel junctions. In such devices the microstructure and chemical profile across the layers are critical in determining the magnetic and transport properties, and therefore need to be critically controlled. In order to analyze the microstructure and composition profile we have used a range of transmission electron microscopy (TEM) techniques such as HREM and EFTEM mapping, in addition to atom probe tomography (APT) analysis. 

However, these data are really only of interest in so far as they enable us to understand the origins of the magnetic and transport properties, and we have been using in-situ TEM to investigate these properties. We have used a combination of Lorentz TEM and in-situ magnetizing experiments, plus micromagnetic modeling to study the micromagnetic behavior at the sub-micron scale of magnetic nanostructures such as patterned exchange-biased magnetic disks. Quantitative analysis of the Lorentz TEM data has been carried out using the transport of intensity equation (TIE) approach. We have also developed in situ TEM capabilities that enable us to correlate the local tunneling properties of magnetic tunnel junctions with microstructure, and results of these studies will also be presented.

Portfolio Student Presentations

Wednesday April 22, 2009, 12:00pm, NST 1.104

12:00 - 12:20 - Li-Hsin Han - A Bridge between Top-down and Bottom-up Manufacturing: 3D, Heterogeneous Micro-structure based on Free-form Fabrication

12:25 - 12:45 - David Fozdar - Neurons on Topography of Various Size and Shape

12:50 – 1:10 - Scott Collins - Nanofiber influence on aortic tissue and microvascular formation

1:15 – 1:35 - Tony Hu - The next generation proteomic nanochips for biomarker discovery

1:40 – 2:00 - Cynthia Burham - Development of a Cost Effective Fabrication Method for n-MOS to p-MOS Tunable Single Metal Gate/High-k Insulator Devices for Multiple Threshold Voltage Applications

2:05 – 2:25 - Karthik Kumar - Blood test for early cancer detection using magnetic nanoparticles

2:30 – 2:50 - Brandon Rowe - Physical aging in ultra-thin glassy polymer films

2:55 – 3:15 - Srivalleesha Mallidi - Molecular specific photoacoustic imaging

3:15 – 3:30 - Refreshments and Judging

3:30 – 3:45 - Awards Ceremony

Nanoparticle Optics Symposium
With Nano Night Poster Session at Noon

Friday April 24, 2009, NST 1.104

9:45 - 10 AM "Welcome and introduction" by Dr. Kallie Willets

10 - 11 AM - Mostafa El-Sayed, Georgia Tech - "Interesting Optical and Photothermal properties and applications of Gold Nanoparticles"

11 - 12PM - David Ginger, University of Washington - "Plasmon-Enhanced Photonics"

12 - 1:30PM - Lunch and poster session

1:30 - 2:30PM - Naomi Halas, Rice University - "Plexcitonics: plasmon enhanced fluorescence, spectroscopy, and coherent effects"

Kuntheak Kheng, Universite de Joseph Fourier, Grenoble

Thursday May 7, 2009, 3:30pm, RLM 7.104

A high-temperature single photon Source from CdSe/ZnSe nanowires quantum dots

In the past decades, semiconductor quantum dots have become a manifold tool for the development of new light sources, such as lasers, LEDs and single-photon sources. Application of quantum dots as nano-emitters in quantum optical technologies requires control of the dots density and location as well as high temperature operation. Quantum dots based on nanowire are interesting candidates for the development of such nano-emitters.
In this talk, I will review the advantages offered by the catalyst assisted growth of semiconductor nanowires by molecular beam epitaxy and I will present our work on the development of the growth of CdSe/ZnSe nanowire-quantum dots and their optical studies. The high quality structures that we have been able to obtain has allowed us to optically study single nanowire-quantum dots and to demonstrate single photon emission up to 220 K [1], the highest reported temperature for non-classical light emission from a (non-blinking) semiconductor quantum dot system.