Date

Talk

Thursday
April 10

Senior Thesis Talks

Paul Amy
Michael Gillin

Thursday
April 17

Ultracold atoms in optical lattices: quantum information and solid state physics with dilute-gas Bose-Einstein condensates

Nathan Lundblad
NIST

Bose-Einstein condensation burst onto the atomic physics stage 13 years ago, ushering in a new era of atomic physics and providing sources of coherent matter waves as well as a window into phenomena at the nanoKelvin scale. BECs have been put to particularly elegant use in recent experiments involving optical lattices: standing waves of laser light that confine the atoms of the BEC in a periodic array of traps in one, two, and three dimensions. The resulting system can be used as a stable and tunable analogue of crystal-lattice condensed-matter systems, allowing (for example) insight into the Mott-insulator/superfluid transition; the single-atom control also allows for the implementation of various quantum computing protocols. I will give an overview of recent experiments at NIST exploring these possibilities.

Thursday
April 24

The Physics of Mechanical Reinforcement in Nanofilled Polymer Melts and Elastomers

S. S. Sternstein
RPI

Carbon black reinforcement of rubber for use in automobile tires has been practiced for about 100 years, but the mechanism by which reinforcement occurs remains controversial. Curiously, one of the earliest theories used to explain reinforcement is based on Einstein's well-known theory of viscosity enhancement in particulate filled liquids. This seminar will provide a broad perspective of the reinforcement issue, which include aspects of mechanics of solids and composites, materials science, polymer physics, rheology and statistical thermodynamics, making reinforcement a rich subject for multidisciplinary exploration. It will be shown experimentally that the Einstein equation fails to predict the correct limiting behavior of reinforced polymer melts as zero filler concentration is approached. Additionally, it will be argued that the reinforcement mechanism is not due primarily to filler agglomeration and/or percolation, but rather is due to the intrinsic statistical conformational behavior of polymer chains in the presence of filler particles.

Thursday
May 1

The Lifetime of the Neutral Pion - Results from the PrimEx Experiment

Mark Ito
Jefferson Lab

The lifetime of the neutral pion has a long history from both the theoretical and experimental point of view. Since there are no hadronic states lighter than the &pi⁰ its strong decay is not allowed. Still its short lifetime (of order 10^-16 s) made direct observation of a finite decay distance impossible for 35 years after its discovery. The first theory of its decay emerged in the 1960's and concluded that it should be a stable particle. Currently, the most accurate experiment and most modern theoretical calculations are in marginal disagreement. The PrimEx experiment at Jefferson Lab uses an indirect method, the Primakoff effect, to infer the lifetime with unprecedented precision. Preliminary results from PrimEx will be presented and the experimental outlook discussed.

Friday
May 2

Steinmetz Symposium

Union Physics and Astronomy Students present their research

Thursday
May 8

Solid-State Lighting with Wide Bandgap Group III - Nitride Semiconductors

Christian Wetzel
RPI

Electric lighting is a sizeable factor in the world's energy consumption and human environmental impact. Solid-State lighting therefore aims to replace all incandescent and fluorescent lighting with highly efficient light emitting diode (LED) solutions. Alloys and heterostructures of group-III nitride semiconductors GaN, AlN, and InN can be tuned to cover the entire visible spectrum and the near UV. Yet, while blue LEDs already have achieved an efficiency as 60%, significantly lower values so far limit the performance in the green spectral region.

I have developed a model of the electronic bandstructure in such heterostructures that accounts for the unusually huge piezoelectric polarization inherent to the system. In contrast to earlier accounts emphasizing the role of alloy non-uniformity in the GaInN quantum well (QW) alloy, we find that LED performance is generally higher in highly uniform QWs.

I will report on our recent progress in the development of green and deep green LEDs in the GaInN/GaN QW system in metal organic vapor phase epitaxy using various approaches of piezoelectric polarization control. In particular, I will report on homoepitaxial growth along polar c-, and non-polar a-, and m-axes of the wurtzite crystal structure of GaN.

Thursday
May 15

Bringing the Excitement of Physics to the Public, or Fighting the War on Error

Jessica Clark
APS

Public Outreach helps introduce people of all ages to the wonders of physics. With this in mind, the American Physical Society develops programs that aim to increase public awareness and appreciation of how physics profoundly increases our understanding of the universe and improves the human condition. This talk will highlight the last eight years of APS Public Outreach and will offer ideas for broadening your department's impact on the local community and beyond through outreach.

Thursday
May 22

Block Copolymer Lithography: How to Convince Thermodynamics to Work for You

Kevin Cavicchi
University of Akron

With the growth of nanotechnology and the shrinking of device sizes in the microelectronics industry there has been growing interest in using the thermodynamically driven self-assembly of molecules to pattern surfaces. These "bottom-up" patterning techniques offer unique advantages when compared to traditional "top-down" methods, such as optical lithography. Block copolymers have attracted considerable attention for patterning due to their ability to form ordered nanostructures on length scales of tens of nanometers. This talk will give an overview of the physics of block copolymers with a focus on how solvents can be used to control the morphology of nanostructured block copolymer thin films.

Friday
May 30

Olin 115 12:55-1:45pm

Joint Colloquium with Mechanical Engineering and Chemistry

Combustion synthesis of tin dioxide nanocomposites for gas sensing applications

Smitesh Bakrania, '03
University of Michigan

The current work focuses on understanding the mechanisms controlling tin dioxide (SnO2) nanoparticle morphology in combustion synthesis systems and how nanoarchitecture affects performance of solid-state gas sensors. A range of analytical methods (including transmission and scanning electron microscopy, x-ray diffraction, nitrogen absorption, and XEDS) were used to characterize the materials properties as a function of the combustion synthesis conditions. The results suggest a relationship between the precursor crystallite size and the product nanoparticles. The combustion synthesis and sensor fabrication methods that are the results of these studies will dramatically accelerate the design of new sensors and sensor optimization.

Please note special date and time. Lunch will be provided starting at 12:30pm in the Olin Rotunda.