2001 MRSEC Faculty-Student Team Participants

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Taiala Carvalho, Faculty: M Bader
Home Institution: Penn St
Current year: Freshman
MRSEC PI: Ward
Title of work: "Synthesis and Characterization of Rigid and Chiral Mono- and Disulfonates for Crystal Engineering"

The purpose of this research project is to synthesize a group of mono- and disulfonates with the general formula O3S - spacer - SO3. The spacer group will be designed in such a way that would allow us to control the rigidity, stereo-chemical, and sulfur-to-sulfur distance. These molecules will then be used to prepare host crystals with guanidinium salts. The resulting guanidinium sulfonates crystals will be used as hosts for organic guest molecules. The basic idea is to prepare polar host crystals capable of incorporating highly polar organic molecules to form asymmetric guest host crystals for use in second harmonic generation. Examples of target molecules include 4-stilbene sulfonic acid, and 4,4'-stilbene disulfonic acid. These molecules can be oxidized to produce chiral compounds, which will be used to prepare "chiral" crystals. Also, from chiral crystals, one can try to see if separation of racemic mixtures is possible. Other functional groups will also be explored; these include Bunte salts and phosphonates. Several other disulfonates will be synthesized with various spacer groups as well.

Christopher M. Clark, Faculty: H.J. Leary, Jr.
Home Institution: University of Louisiana Lafayette
Current year: Junior
MRSEC PI: Palmstrøm
Title of work: "Metal-Insulator-Metal Studies by In-Situ X-ray Photoelectron Spectroscopy"

The work is focused toward understanding the evolution of the interfacial chemistry required for magnetic tunnel barrier junction process development, and is conducted in collaboration with a graduate student and a post doctoral fellow. Aluminum layers 4-10-20-30 Å thick are vacuum evaporated using effusion cells at a chamber pressure of ~ 7.5 x 10-11 Torr on Fe substrates (~ 150 Å thick, e-beam deposited, held at low but non-cryogenic temperatures). X-ray Photoelectron Spectroscopy (XPS) is employed to ensure the character and uniformity of the Al coverage, and its cleanliness. Sequential, and carefully controlled exposures of the Al layer to oxygen under UHV conditions occurred to establish the thickness of the chemically self-limiting insulating layers of Al2 O3 formed employing the XPS peak intensity ratio IAl 2 O 3 / IAl approach in conjunction with published values for the inelastic mean free path of the Al electrons photoemitted from the overlayer and substrate. In-depth analysis of the surface spectral features present after oxygen exposures also occurred. The identical overlayer-substrate approach using quantitative XPS determinations was applied in the follow-on deposition of a counter-electrode material, i.e., Al in this study, to establish its thickness. Thus, the interfacial chemistry of the Fe/Al/Al2O3/Al system was studied in some detail during Summer 2001. Low Energy Electron Diffraction (LEED) and Reflection High-Energy Electron Diffraction (RHEED) studies are planned. By variation, and precise control of the temperature of the Fe layer (e.g., from -10 °C to +25 °C, or cooling it to liquid-nitrogen temperature) for Al depositions on Fe, a variety of other interfacial barrier structures may be fabricated for spin polarization measurement and XPS data correlation comparison to advance process development. Further, still other barrier junctions may be fabricated by use of alternate metals as counter-electrode materials.

Anna Gopher, Faculty: B Nagalingam
Home Institution: United Tribes
Current year: Sophomore
MRSEC PI: Stein
Title of work: "Assembly of Functional Porous Solids in Hybrid Materials"

Three-dimensionally ordered macroporous (3DOM) metal oxides are prepared by filling the voids of polymer colloidal crystal template with a fluid precursor capable of solidification, followed by calcination to remove the template and simultaneously convert the precursor to a solid in the desired phase. Macroporous titania and zirconia materials prepared in this manner typically have nanocrystalline walls, in which small grains are fused together to form the 3 DOM skeleton. Control of the grain growth and interconnection will strengthen these materials, which is important for ease of processing and use in device applications. Synthesis conditions, including the choice of template, thermal treatment, synthesis atmosphere, and use of chemical additives will be varied to optimize the mechanical stability of the porous titania and zirconia materials. Nanoindentation measurements will be performed to evaluate the strength of the porous materials.

Stephanie Johnson, Faculty: M Evans
Home Institution: UW - Eau Claire
Current year: Junior
MRSEC PI: Palmstrøm
Title of work: "The Growth of ErAs(100) on GaAs(100) (2 x 4)-c(2 x 8) Annealed to 535 C Determined by Scanning Tunneling Microscopy"

The scanning tunneling microscope (STM) will be used to study ErAs(100) and GaAs(100) (2 x 4)-c(2 x 8). Varying layers of ErAs will be grown on the GaAs substrate. By varying the surface reconstruction of the GaAs(100) from the 2 x 4 to the c(2 x 8) the initial growth of the ErAs layer on the GaAs(100) can be better understood. Previous STM studies of this surface has shown that ErAs deposited onto GaAs with a post deposition anneal ends up in a subsurface location. However, it is still unclear whether the ErAs has a tendency to burrow into the GaAs, or the GaAs percolates up to the surface. By using a combination of STM images and X-ray Photoelectron Spectroscopy (XPS) we hope to correlate the various surface reconstructions to the location of the Erbium and Gallium Arsenides when annealed to high temperatures.

Bradley Motl, Faculty: A Wolf
Home Institution: Augsburg College
Current year: Sophomore
MRSEC PI: Dahlberg
Title of work: "Setup of Magneto-Optical Kerr Effect System for the Study of Magnetic Coupling within Anti-ferromagnet - Ferromagnet Bi-layers"

A Magneto-Optical Kerr Effect (MOKE) setup will be built to investigate exchange-coupled samples. MOKE is achieved by reflecting linearly polarized light off of a magnetic sample. The reflected beam passes through an analyzer into a detector. The use of an external magnetic field to change the magnetic characteristics of the sample results in the plane of polarization of the reflected light being rotated. Only a certain plane of polarization can pass through the analyzer, thus the rotation produces a change in detected intensity. A plot of this intensity versus the external magnetic field yields a hysteresis loop that is characteristic of the magnetic sample. The anti-ferromagnetic / ferromagnetic thin film samples that will be studied are NiMn / Co and NiO / NiFe. The samples will be produced using the sputtering method where a target is bombarded with Ar ions, depositing the sputtered material on a substrate.