Tag: Ben McMorran

Fabrication of Diffraction Gratings Using Electron Beam Lithography

Presenter: Carly Wright

Mentor: Ben McMorran

Poster: 36

Major: Physics/Math 

Studying electron diffraction using transmission electron microscopy allows us to better understand many different phenomena in physics, particularly conservation of forces and wave-particle duality. To be able to make these observations, we require diffraction gratings on the nanoscale. This can be done with a variety of techniques, but our particular focus is electron beam lithography. EBL is a dynamic method for fabrication and can be used from the micro-scale down to the nanoscale, but for our particular purposes and scale it is somewhat difficult to achieve nicely resolved lines. This technique involves coating a sample with a photosensitive resist that breaks down at the molecular level from the bombardment of electrons and then developing the resist to create physical features. Using this process, we were able to create straight and forked gratings ranging from 100nm pitch to 50nm pitch that can be used to study the behavior of electrons inside of a transmission electron microscope. With some revisions to our technique, we hope to decrease this pitch down to 20nm while maintaining efficiency, which will provide clearer diffraction data.

Vacuum Airship Design With Finite Element Analysis

Presenter(s): Daniel Sellers—Physics

Faculty Mentor(s): Ben McMorran

Session: Prerecorded Poster Presentation

The ultimate expression of Archimedes’ principle of buoyancy would be to enclose a vacuum with some structure of less mass than the air displaced by that structure . So far such a craft has never been realized in prototype due to the daunting material and engineering challenges . We propose a novel design for such an airship, using inflatable supports and an Aramid fabric shell, and examine the physical constraints and material requirements using both SolidWorks (SW) Simulation Finite Element Analysis and principles of structural statics .

We develop a dynamic simulator (in python) to approximate the shapes formed by thin fabric shell sections under unbalanced pressure loads . The resulting geometries are converted to thin shell SolidWorks models and analyzed . Attempts are made to verify the results, including mesh independence and comparison to empirical stress/strain results performed on similar materials and configurations .

Deflection of thin shell sections using material properties of Kevlar Aramid fiber are found to agree qualitatively with the theoretical results of Timeshemko, though actual deflection predicted by SW is marginally smaller than predicted by theory, which in turn only very roughly agrees with the experimental results considered . The tensile stress within the shell models is found to be well within acceptable limits for typical Aramid fibers . Some models for the inflatable support structure currently under development are presented, without results . The advantages and challenges of the Finite Element Method for novel design concepts are briefly discussed .