This is a past event.

Please join physics graduate students, Kumar Neupane and Nilanjana Ghosh for their presentations on Thursday, January 29 at 4 PM - Fisher Hall 139.

Kumar Neupane (Advisor: Yoke Khin Yap)

FORMATION OF HIGH-DENSITY MOLYBDENUM DISULFIDE (MOS₂ ) MONOLAYERS FOR PHOTOVOLTAIC APPLICATION

Transition Metal Dichalcogenides (TMDs), such as MoS₂, are promising for next-generation solar devices, because thinning them to a monolayer changes their band structure from indirect to direct. However, growing uniform and high-density monolayers using conventional chemical vapor deposition (CVD) remains challenging. This is due to a persistent trade-off between nucleation density and lateral domain growth as well as sensitivity to factors such as precursor placement, temperature variations, and sulfur delivery. In this presentation, I will share a salt- assisted CVD approach that adds a small amount of alkali halide, such as KCl, along with the Mo precursor. This process enhances Mo transport by promoting the formation of more reactive intermediate species, leading to fewer nucleation sites and the formation of uniform monolayer domains. I will explain the fundamental growth chemistry involved, as well as key experimental factors such as salt type and quantity, temperature ramp profile, and carrier-gas flow rates, and how these affect film morphology and consistency. We characterize samples using SEM, AFM, and EDX. Finally, I will discuss ways to incorporate these monolayers into device stacks (for example, ITO/TiO₂/MoS₂ Monolayer/MoO₃/Au) and highlight why achieving uniform monolayers is crucial for reducing variability in scalable solar-cell manufacturing.

Nilanjana Ghosh (Advisor: Petra Huentemeyer)

SEARCH FOR TEV GAMMA- RAY EMISSION FROM STAR- FORMING GALAXIES USING HAWC OBSERVATORY 

Star-forming galaxies host elevated star-formation activity, with a subset known as starburst galaxies exhibiting even more rapid star formation and dense interstellar environments, making them efficient sites for cosmic-ray acceleration. Interactions between these cosmic rays and ambient gas and radiation fields produce gamma rays predominantly via neutral pion decay, placing these galaxies among the most promising extragalactic targets for TeV gamma-ray observations. Using data from the High Altitude Water Cherenkov (HAWC) Observatory, we perform a stacking analysis of nearby star-forming galaxies to search for cumulative TeV emission. The expected contribution from each galaxy is weighted by its distance and infrared luminosity. No significant excess is detected, and we derive 95% confidence upper limits on the total gamma-ray flux. We compare these limits with existing TeV measurements from H.E.S.S. for NGC 253, which is only marginally observable by HAWC, and from VERITAS for M82, which lies outside HAWC’s field of view. These results emphasize the complementary sky coverage of current gamma-ray observatories and highlight the strong potential of future wide-field facilities, such as the Southern Wide-field Gamma-ray Observatory (SWGO), to study populations of star-forming galaxies in the Southern Hemisphere.