2016 Undergraduate Research Symposium

Applied Physics undergraduate students participated in the Fifth Annual Undergraduate Research Symposium on October 6, 2016, in Carleton Commons. The event was hosted by SEAS Undergraduate Student Affairs and Global Programs, the Engineering Student Council, and the Columbia Undergraduate Scholars.

Betty Hu, SEAS '19, Applied Physics

"Device Fabrication for High Precision Electrical Transport Measurements on Complex Oxide Thin Films"

Supervising Faculty, Sponsor, and Location of Research:
Professor Kyle Shen, Cornell PARADIM REU, Cornell University

The open shell configuration of transition metal cations and quantum interactions between electrons can give rise to novel and unexpected electronic properties in transition-metal oxides (TMOs). For example, the Ruddlesden-Popper ruthenate family of materials (An+1RunO3n+1, where A is an alkaline earth element), are known to exhibit a wide array of electronic ground states in the bulk, ranging from ferromagnetic metals (SrRuO3, BaRuO3) in the three-dimensional limit (n = ∞) to unconventional superconductors (Sr2RuO4) in quasi-two-dimensional single-layer (n = 1). This sensitivity of electronic and magnetic properties to subtle changes in crystal structure suggests that the former can be artificially "tuned" in thin films grown by molecular-beam epitaxy (MBE) by adjusting parameters that couple to the film crystal structure, such as the structure and orientation of the substrate on which the film is deposited. Besides providing a useful platform for studying fundamental problems in solid-state physics, understanding how to exploit these structure-property relationships in TMOs is a crucial step towards the broader goal of realizing emergent properties of correlated electrons—e.g. metal-insulator transitions, magnetism, and superconductivity—in targeted materials by design. This project focused on using electrical transport measurements to characterize the interfacial electronic structure of both CaRuO3 and Ca2RuO4 samples grown on LaAlO3 substrates by MBE. LaAlO3 in particular was chosen because resistivity measurements of Ca2RuO4/LaAlO3 showed two metal-insulator transitions between 300 K and 4 K, suggesting this system is in close proximity to the electronic ordering instability observed in bulk Ca2RuO4, while the same measurements conducted on CaRuO3/LaAlO3 showed no metal-insulator transitions. Photolithography methods were used to fabricate gold devices—“Hall bars”—on the surfaces of the films to enable more directionally-precise transport measurements. Hall effect measurements on CaRuO3/LaAlO3 indicated a change from predominantly electrons as charge carriers below 80 K to predominantly holes as charge carriers above 80 K. In Ca2RuO4/LaAlO3 an “anomalous Hall effect”, which is often observed in magnetically ordered materials with appreciable spin-orbit coupling, was observed below the metal-insulator transition at 200 K. Based off this, it is very likely that this metal-insulator transition is accompanied by the formation of canted antiferromagnetic order.

Derek Tropf, SEAS '17, Applied Physics

"Development of Automated Batch Workflow and Real Time Large Data Processing for X-ray Fluorescence Tomography"

Supervising Faculty, Sponsor, and Location of Research:
Yong Chu, Science Undergraduate Laboratory Internship (SULI), National Synchrotron Light Source II (NSLS-II), Brookhaven National Laboratory, Upton, NY

The unprecedented spatial resolution of the Hard X-ray Nanoprobe (HXN) beamline at the National Synchrotron Light Source II (NSLS-II) allows for material characterization on the scale of 10 nanometers (nm). Such resolution enables new frontiers of advanced material characterization. One of the important techniques, currently being developed at the HXN beamline, is 3D x-ray fluorescence microscopy, or fluorescence tomography, which allows scientists to visualize internal structures and quantify elemental composition. When excited by the incidence x-ray beam, the atoms in a sample emit characteristic fluorescence x-rays providing a unique fingerprint of elemental composition. Tomographic reconstruction of a set of 2D projection fluorescence images can reveal the 3D distribution of elemental composition within a sample – however, this technique requires the processing of large amounts of data. Currently, raw data is processed and analyzed in the PyXRF software developed at HXN. Although PyXRF provides an intuitive graphical user interface and advanced plotting capabilities, the software does not support real time data processing or automated batch workflow. This inherent bottleneck makes large data processing a timely and impractical endeavor. During my summer research, I developed a new automated workflow that processes large quantities of data in real time. The software I produced utilizes key functionality from PyXRF to eliminate the need for manual data processing and allows for immediate data analysis upon completion of an experiment. With such improvements, future efforts with HXN will focus on the problem of self-absorption in fluorescence tomography.

Shangzhou Xia, SEAS '19, Applied Physics

"Measuring the Thermal Conductivity of Lithium-ion Battery Anodes Using a Simple Differential Steady-state Method"

Supervising Faculty, Sponsor, and Location of Research
Prof. Yuan Yang, Egleston Scholar Program, Yang Group, Material Science and Engineering, Columbia University

Measurement of thermal conductivity is crucial to various fields such as materials science and mechanical engineering. More specifically, measuring the thermal conductivity of electrodes in lithium-ion batteries gives us a clearer understanding of how heat is produced and transferred in the batteries, shedding light on some potential improvements of lithium-ion batteries’ performance and efficiency. While some adopt dynamic-state methods, steady-state methods are also a plausible approach to the problem. In this project, we reduce the problem to one-dimensional and measured the thermal conductivity using a steady-state method that is derived directly from the Fourier Law of thermal conduction. Temperatures are measured using the Ktype thermocouples and the control of temperatures is realized through adjusting the powers supplied onto a heater and a cooler with a LabView program according to the feedback of temperature. Moreover, we adjust the temperature of the heater side of the sample to be at the same level as the ambient in order to eliminate the heat loss from the heater that might have caused inaccuracy of the measurement. Thermal paste is also applied onto the surfaces to ensure uniform and good thermal conduct between surfaces. The experiment is conducted with a piece of common anode in lithium-ion batteries, i.e. graphite on a copper substrate as the sample. After repeated experiments and calculations, we obtain the result

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