Development of InSb dry etch for mid-IR applications
We present a new chlorine-free dry etching process which was used to successfully etch indium antimonide grown on gallium arsenide substrates while keeping the substrate temperature below 150°C. By use of a reflowed photoresist mask a sidewall with 60degree positive slope was achieved, whereas a nearly vertical one was obtained when hard masks were used. Long etch tests demonstrated the non-selectivity of the process by etching through the entire multi-layer epitaxial structure. Electrical and optical measurements on devices fabricated both by wet and dry etch techniques provided similar results, proving that the dry etch process does not cause damage to the material. This technique has a great potential to replace the standard wet etching techniques used for fabrication of indium antimonide devices with a non-damaging low temperature plasma process. Display Omitted Chlorine-free low-temperature dry etch of MBE grown InSb on GaAs60° positive sloped or nearly vertical etch depending on maskNon-selective process etching through Insb, GaSb and GaAsLow damage process with potential to replace standard InSb wet etch
Infrared Antireflection Moth ’ s Eye Nanostructures
Biomimicry, attempting to create nanostructures that simulate those found in nature, is a relatively new field of study that is generating interest. One such natural structure that is used for antireflection applications is the moth’s eye due to its excellent ability to absorb light in the visible spectra from a wide range of angles. These moth’s eye nanostructures are typically made with silicon due to its low cost and the ease with which it can be etched. Silicon’s bandgap of 1.3 eV makes it sufficient for solar cell applications in the visible spectra where decreasing the reflectance would improve solar cell efficiency. However, in the infrared (IR) where most wavelengths have an energy of greater than 1.3 eV, silicon becomes transparent. Because of this, materials with bandgaps higher than silicon such as indium antimonide (InSb), mercury cadmium telluride (HgCdTe), and germanium (Ge) are used for applications in the IR. Technologies such as forward looking infrared (FLIR) cameras, solar cells, and IR telescopes could benefit from having our antireflection moth’s eye nanostructure. In our project, we have created a cone-and-ball nanostructure design capable of significantly reducing reflection in the near to mid-wavelength IR. We constructed a 3D model of our nanostructure using Computer Software Technology (CST) and simulated normal incidence on our nanostructure at wavelengths between 0.75 μm and 3 μm. Initially, only silicon was used in the simulations to analyze the effectiveness of our design. Then the nanostructure was optimized for silicon in the visible spectrum and this optimized structure was simulated in the IR with satisfactory results. Next, the nanostructure was simulated and optimized for InSb, HgCdTe, and Ge in the near and short-wavelength IR. This project was completely simulation based as there was not enough time to fabricate the structure in the FabLab. Material Science & Engineering Aspects This project is a perfect example of the structure-processing properties relationship that is so important in the field of materials science. Specifically, the cone-and-ball design of our biomimetic moth’s eye nanostructure requires precise microprocessing synthesis methods which, if done correctly, can produce the anti-reflection properties we simulated in CST. This project also involves material engineering as it requires knowledge of microprocessing, wave physics, and photonics. The cone-and-ball nanostructure design is made possible by using a self-assembling block copolymer. The benefit of using a self-assembling material is that it dramatically cuts down on the number of microprocessing steps and on the chemical waste produced during processing. It also makes the nanostructure easily tunable as different shapes and dimensions can be created just by slight changes to the chemistry of the block copolymer. The shape of the block copolymer is what determines how the nanostructure interacts with light instead of the chemical composition of the block copolymer. Since the main goal of this project is optimization of a structure using frequency domain simulations, it is essential that all material properties such as the dielectric constant and refractive index are known and accurate to ensure that the simulations give accurate results.
Gender and History in Medieval English Romance and Chronicle
New York, Bern, Berlin, Bruxelles, Frankfurt/M., Oxford, Wien. This reading of canonical texts of medieval English literature - Sir Gawain and the Green Night and Chaucer's Man of Law's Tale - alongside Geoffrey of Monmouth's Historia regum Britanniae and other Anglo-Norman and English chronicles offers a broader context for reading the romance narratives and re-evaluates romance conventions in light of the genealogical priorities of these chronicles. By arguing that maternity is featured as a position of power, Gender and History in Medieval English Romance and Chronicle adds to our understanding of women and sovereignty, and the ways gender and authority were rhetorically linked to medieval texts.