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2017  Nov 1 - Dec 21
2017  Proposal/BTR deadline: 9/1/17

The Winter07 G-Line Symposium was held on

Tuesday, January 23, 2007
6:00 p.m.

Wilson Commons (3rd floor)

After beginning with Pizza and soft drinks (a blatant bribe), this symposium will feature a series of scientific presentations by graduate students and Post-docs whose research is based at CHESS/G-line and a brief overview of the G-line facility.

Determining Growth Mode of SrTIO3 (001) Homoepitaxy via Pulsed Laser Deposition Using In Situ X-ray Reflectivity
Presented by:  John Ferguson, Brock Group, Cornell

Homoepitaxial SrTiO3 thin films were grown on single-crystal SrTiO3 (001) via Pulsed Laser Deposition. The growth was monitored in real time by in situ x-ray reflectivity measurements at the specular anti-Bragg position. The growth process  can be separated into an initial transient  followed by a steady state growth. Considering only data obtained from the first 15 monolayers, a transition from layer by layer to step flow growth occurs as the surface miscut is increased at constant temperature. This transition is due to distance between atomic steps on the growth surface becoming shorter than the diffusion length of the adatoms. During late times, a transition from step flow to 3D occurs observed as the laser repetition rate is increased while maintaining a constant surface temperature and miscut. This crossover is attributed to the ability of adatom diffusion to smooth out the thickness variation due to differential deposition rates in the plume. A similar transition at a constant laser repetition rate occurs as the surface temperature is decreased.

Silicon Nanostructures from Block Copolymer Derived Thin Films
Presented by:  Hitesh Arora, Wiesner Group, Cornell

In this presentation organic-inorganic hybrid thin films and their application towards silicon nanostructures are discussed. Monolayer films are prepared using Evaporation Induced Self Assembly (EISA) of a mixture of PI-b-PEO block copolymers and an aluminosilicate sol, spin coated on a Silicon substrate. The hydrophobic phase (PI) forms hexagonally packed cylinders standing up on the substrate and surrounded by the hydrophilic phase (PEO and aluminosilicate). The calcined (organic free) aluminosilicate films are typically 15-20 nm thick, over a 4” (~100mm) Si substrate and can be characterized using AFM, SEM and GISAXS to obtain information on both, local and global scale order.

More recently we have discovered a method to use these inorganic films as a template to make Si nanostructures. This is achieved by LASER annealing of the calcined films inducing selective melting of the silicon substrate. The porous aluminosilicate film acts as a template for the silicon melt which fills the cylindrical pores and crystallizes epitaxially from the substrate into nanopillars. This method may allow the cost-effective and rapid formation of Si nanostructures down to the tens of nanometer regime without the use of traditional lithographic techniques.

Co-authors: Jerome Hyun, Phong Du and Uli Wiesner

Suggested reading:
1)  M. Templin, U. Wiesner et al., Science 278 (1997) 1795 2)  P. Du, U. Wiesner, C. K. Ober et al., Adv. mater. 16 (2004), 953

Anomalous Small-angle X-ray Scattering (ASAXS) Study of Multivalent Ion-DNA Interactions
Presented by:  Kurt Andreson, Pollack Group, Cornell

Multivalent ion-DNA interactions are important for biological function. The condensation and aggregation of DNA by multivalent ions has been extensively studied theoretically and (to a lesser extent) experimentally.  We report on the related, but largely unexplored, interactions between DNA and multivalent ions below the critical concentration for condensation/aggregation. Using ASAXS, a technique used for previous studies of monovalent and divalent atmospheres around DNA, we have investigated the competition of monovalent and trivalent ions around the biopolymer. These data should prove vital for modeling DNA-trivalent ion interactions and the mechanisms of DNA condensation and aggregation.

Surface Characterization of Novel Electrocatalysts for Fuel Cell Applications
Presented by:  Yi Liu, Abruña Group, Cornell

Ordered intermetallic compounds (e.g. PtBi, PtPb) are very promising candidate electrocatalyst for the oxidation of small organic molecules and have great potential applications for fuel cells. Because these reactions take place at the electrode/solution interface, probing and understanding electrode surface structure and its change is of great importance in order to establish structure-reactivity relationships which is the key to improve catalytic performance. In-situ experiment set-up was built up and preliminary data was consistent with ex-situ result in our group. Non-precious metal was leaching out from electrode surface when the electrode was subjected to cleaning/activation treatment at high upper limit potential in acidic supporting electrolyte. For singe crystal electrode surface, patterned Pt domains, which were dependent on the orientations, were formed when the electrode was subjected to 0.8V (vs.Ag/AgCl). When these electrodes were exposing to fuel solution (e.g. formic acid), the non-precious metal leaching-out procedure was precluded. These results provide valuable information for us to understand reaction mechanisms and improve the design for new electrocatalysts.

References:

  1. Electrocatalytic Activity of Ordered Intermetallic Phases for Fuel Cell Application, J. Am. Chem. Soc., 2004, 126, 4043-4049
  2. Surface composition of ordered intermetallic compounds PtBi and PtPb, Surf. Sci., 2006, 600, 2670-2680