Events at Physics
Events During the Week of October 16th through October 23rd, 2022
- No events scheduled
- Thesis Defense
- Characterizations of ultrathin interfacial atomic-layer-deposited oxides and nitrides for semiconductor grafting applications
- Time: 8:00 am
- Place: EH 4610 in Engineering Hall
- Speaker: Jiarui Gong, Physics Graduate Student
- Abstract: Lattice-mismatched heterogeneous semiconductor grafting technique has been developed recently to combine lattice-mismatched semiconductors and create innovative devices. An ultrathin oxide (UO) deposited by atomic layer deposition (ALD) at the grafted interface has been recognized as a passivation and tunneling layer, which plays an important role in improving the junction performance, such as achieving higher on/off ratio and lower ideality factor in a pn junction. To better understand the influence of the ALD UO, various experiments have been conducted to characterize some electrical properties of the ALD UO in various semiconductor systems. In the first part of the presentation, the history of semiconductor heterostructures and the development of semiconductor grafting technique are reviewed. In the second part, the interfaces between the UO and several semiconductors were characterized by X-ray photoelectron spectroscopy (XPS). Various electron states were observed through peak fitting. The correlation between the passivation effect and the electron states was established. In the third part, the surface band-bending of c-plane Ga-face GaN with various UO/UN layers was characterized by XPS measurements. The valence band offset (VBO) between GaN and the UO/UN was calculated from the GaN valence band spectra. The possibility of fabricating an AlGaAs/GaAs/GaN npn heterojunction bipolar transistor (HBT) was examined through simulation. In the last part, a novel releasing and transfer printing method of the single-crystalline AlN nanomembrane (NM) was introduced. The properties of the AlN were characterized both before and after the whole process and no degradation was observed. The possibility of obtaining high-quality single-crystalline AlN NM brings new potentials to the semiconductor grafting technique.
- Host: Zhenqiang Ma, Mark Rzchowski
- Theory Seminar (High Energy/Cosmology)
- Statistical significances and projections for proton decay experiments
- Time: 4:00 pm - 5:00 pm
- Place: Chamberlin 5280
- Speaker: Prudhvi Bhattiprolu, University of Michigan
- Abstract: The projected discovery and exclusion capabilities of particle physics and astrophysics/cosmology experiments are often quantified using the median expected significance. We argue that this criterion leads to flawed results, which for example can counterintuitively project lessened sensitivities if the experiment takes more data or reduces its background. We advocate for standard use of the “exact Asimov” criterion detailed in this talk. Various counterintuitive flaws associated with frequentist and modified frequentist statistical measures of significance for multi-channel counting experiments are discussed in a general context and illustrated with examples. We argue in favor of conservative Bayesian-motivated statistical measures, and as an application we employ these measures to obtain the current lower limits on proton partial lifetime at various confidence levels, based on Super-Kamiokande's data, generalizing the 90% CL published limits. Finally, we present projections for exclusion and discovery reaches for proton partial lifetimes in p → ν K+ and p → e+ π0 decay channels at Hyper-Kamiokande, DUNE and JUNO.
- Host: George Wojcik
- GREAT IDEAS DEI Reading Group
- GREAT IDEAS DEI coffee hour
- Time: 12:15 pm - 1:15 pm
- Place: Chamberlin 5280 or online at
- Abstract: We will be discussing this paper in physics education research: “How well-intentioned white male physicists maintain ignorance of inequity and justify inaction.” (url: ) This is a long paper, so we will ask people to focus on the following Sections: Introduction (p1-3), Summary of Findings, Discussion, and Recommendations (p33-37). (We will also go over an article summary and we welcome attendees who haven't had an opportunity to read the article.)
GREAT IDEAS stands for Group for Reading, Educating, And Talking about Inclusion, Diversity, Equity, & Advocacy in Science. It is a multimedia reading group dedicated to amplifying the experiences of underrepresented groups in science and academia in order to become better advocates for our peers. GREAT IDEAS is open to everyone (students/ faculty/ staff/ etc), and all are welcome and encouraged to engage with the material and contribute to the discussions. To keep a welcoming and safe environment for everyone, we ask that everyone understand and adhere to our community guidelines for the discussions. If you would like to submit an article for a future GREAT IDEAS discussion, you can do so on this form.
- Host: GMaWiP and Climate and Diversity Committee (contact Jessie Thwaites or R. Sassella with questions)
- Astronomy Colloquium
- Towards precision measurements of dark matter
- Time: 3:30 pm - 4:30 pm
- Place: Sterling Hall 4421
- Speaker: Sukanya Chakrabarti, University of Alabama, Huntsville
- Abstract: For more than a century now, our inference of the mass distributions (including dark matter) in galaxies has been based on modeling the positions and velocities of stars, i.e., using kinematic analyses, which assume equilibrium. These kinematic estimates can be inaccurate for a time-dependent potential, and there are now many lines of observational evidence that show that our Galaxy has had a highly dynamic history. Recent technological advances now make it possible for us to carry out extreme-precision time-series measurements of the acceleration of stars that live within the gravitational potential of our Galaxy. I will talk about several different methods of direct acceleration measurements that we have developed, including our recent analysis of compiled pulsar timing data from which we were able to measure the Galactic acceleration for the first time. Given the measured acceleration, we can straightforwardly use the Poisson equation to determine the total density, and the local dark matter density (given an accounting of the stellar density). There are testable differences between popular models of dark matter on small scales, i.e., in their sub-structure. I will discuss the potential for measuring dark matter sub-structure in the Milky Way with pulsar timing and eclipse timing, and for constraining theories of gravity by combining constraints from pulsar timing and extreme precision radial velocity measurements. I will end by discussing our recent work in developing an “acceleration ladder” by calibrating kinematic estimates of the acceleration to direct acceleration measurements.
- Host: Ke Zhang
- Physics Department Colloquium
- Barschall Lecture: Shocking New Insights into Novae
- Time: 3:30 pm - 4:30 pm
- Place: 2241 Chamberlin Hall or online:
- Speaker: Brian Metzger, Columbia University & CCA Flatiron Institute
- Abstract: "Novae" - thermonuclear outbursts from white dwarfs accreting from a binary star companion - have been observed since antiquity as "guest stars" to our ancestors. Despite their storied place in the history of Astronomy, our understanding of the physical processes that give rise to novae and their emission remains strikingly incomplete. Nothing illustrates this better than the unexpected discovery by NASA's Fermi satellite that GeV gamma-ray emission is common if not ubiquitous from novae. These gamma-rays are likely produced by relativistic ions accelerated at shock waves produced in the nova ejecta. I will review our understanding of the multi-wavelength picture of novae, and describe how these transients can be used testbeds for studying relativistic particle acceleration at non-relativistic shocks in the novel "radiative" regime (in which the post-shock gas radiates ~100% of the its thermal/non-thermal energy). Lessons gleaned from novae can be applied to other shock-powered transients, which are candidate high-energy neutrino sources for IceCube. Time permitting, I will describe implications of the recent H.E.S.S. and MAGIC discovery of TeV gamma-rays from the recurrent nova RS Oph.
- Host: Justin Vandenbroucke