2017 Senior Design Expo
APAM seniors participated in the 2017 SEAS Senior Design Expo on May 3 in Roone Arledge Auditorium in Lerner Hall and presented posters on their senior research projects. (Left-right) Derek Tropf, Erica Yee, Kevin Tang, Sean Mbogo, and Michael Berkson
“Microstructural Characterization of Thin Metallic Films
Advisor: Prof. Katayun Barmak
The grain size and grain boundary character distribution (GBCD) of three Al thin film samples were measured using transmission electron microscopy (TEM)-based crystal orientation mapping. The GBCD of the films was compared to that of bulk Al. The GBCD is the relative length fraction (2D) or area fraction (3D) of boundaries as a function of the five crystallographic parameters (three for misorientation of one grain relative to its neighbor and two for the grain boundary plane orientation). Once the films are deposited on thermally oxidized Si wafers, they must be mechanically or chemically thinned so that they are electron transparent. The method of sample preparation I used to prepare several practice samples for TEM involves mechanical grinding and polishing on a lap wheel followed by dimple grinding and Ar ion milling. The crystal orientation data were analyzed to obtain both grain size and the GBCD. My work in this analysis involved using crystal orientation and image analysis software to gather grain size data that could be used to calculate the mean size and the grain size distribution of the sample. The film grain sizes were found to be 109, 152 and 157 nm, for the as-deposited film and films annealed at 400 °C for 30 and 150 minutes, respectively. We also found that the grain size distribution of the thin films was in agreement with the lognormal grain size distributions that have been determined using prior, slower image-based methods. Furthermore, the GBCD of the thin films differed from bulk Al in that the films exhibited a higher frequency of Σ3 boundaries, or twin boundaries, which as twist boundaries have a misorientation of 60° about the  axis. The length fraction of Σ3 boundaries was 0.245 for the as-deposited film compared to 0.016 in the bulk material. Annealing at 400 °C resulted in a decrease of the twin boundary length fraction.
“Quantitative Analysis of Excimer Laser-Induced Liftoff of Polyimide Bulk Material from Glass Substrate”
Advisor: Prof. James S. Im
An investigation of the lowest possible energy required to induce complete liftoff of polyimide (PI) bulk material from a glass substrate utilizing a 308 nm XeF laser was conducted. Polyimide can be used as a plastic substrate for flexible organic electroluminescent devices which are desired in high quality display materials commonly found, but not limited to, portable devices. PI bulk samples deposited on a SiO2 substrate were provided by a reputable company, and testing was performed by incrementally adjusting the energy deposited on the polyimide material until the lowest energy deposition required for complete separation of the polyimide film from the glass substrate was determined. A lower required deposited energy is ideal for large-scale processing of PI films by reducing overall cost. The minimum energy required for complete laser lift-off of this particular polyimide sample set utilizing the XeF 308nm Coherent laser was determined to be 219 mj/cm2 for an array of 30 PI squares.
“Design of an Anomalous Hall Resistivity Measurement System for Characterization of Magnetic Thin Films”
Advisor: William Bailey
The Hall effect produces a transverse voltage when a magnetic field is applied transverse to an electric current in a conductive material. In a normal conductor, this can be explained simply by the Lorentz force. In ferromagnetic materials, the Hall voltage is larger than expected and not simply proportional to the external magnetic field; the voltage also depends on the magnetization. This is known as the Anomalous Hall effect (AHE); the mechanism has eluded theorists and experimentalists for decades. Recently, it has been proposed that the AHE arises from two mechanisms: an intrinsic (spin-orbit coupling effects), and extrinsic (scattering and side jumping mechanisms). By controlling the magnetization of the ferromagnetic material, identification of the Anomalous Hall term is possible at high fields. Using Python and SCPI commands, we wrote a code which creates an interface to communicate with multiple GPIB instruments to control an external field. The thin film sample is placed upon a wooden base. Using a square Van der Pauw setup, contacts are made at the corners of the film with indium solder. The sample is centered out of plane with respect to the magnet and stabilized with wood supports. The applied magnetic field plane sweeps up to 1.3T; sufficient to saturate film magnetization out of plane. Efforts to measure the AHE and resistivity of thin-film magnetic materials are ongoing.
"Development of Quantitative Spectromicroscopy Tool for the Hard X-ray Nanoprobe Beamline at NSLS-II”
Advisors: Prof. I. Cevdet Noyan, Columbia University, &
Yong Chu, NSLS-II HXN Beamline Group Leader, Photon Division
The Hard X-ray Nanoprobe (HXN) beamline at the National Synchrotron Light Source II (NSLS-II) is an undulator beamline capable of material characterization on the scale of 10 nanometers (nm). One of the important techniques utilized at HXN, x-ray fluorescence microscopy, 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. The analysis of fluorescence data is currently done in a python based package called PyXRF. Although PyXRF offers a GUI design and high level fitting engine, spectromicroscopy data used to investigate reactions at the nanoscale is not currently implemented. To quantify spectromicroscopy data, a python based tool that utilizes PyXRF functionality has been created with the goal of real time analysis by HXN beamline users. The tool is tested by quantifying the oxidation states of Ni via fluorescence data taken of LiNi0.6Mn0.2Co0.2O2 material while subject to an applied voltage. By fitting to a linear combination of X-ray Absorption at Near Edge Structure (XANES) data, results show a fit that lies within the statistical error of experimental data. Further, chemical mapping of oxidation states reveal high intensity areas to be composed primarily of Ni2+ followed by Ni4+ in quantity. Further tests need to be conducted using data from experiments with more data points for more statistically reliable conclusions. Future improvements will be devoted to improving calculation speed and GUI framework, incorporating analysis of x-ray diffraction data, and integration of tool into HXN beamline structure.
“Fundamentals of X-Ray Fluorescence”
Advisor: Prof. I. Cevdet Noyan
X-ray fluorescence (XRF) is a prevalent technique to quantitatively and qualitatively analyze the elemental composition of materials, used in fields ranging from materials science to archeology to art history. Because XRF is less time- and energy-intensive than x-ray diffraction (XRD), it is a quick and useful tool to confirm and supplement XRD elemental analysis. The objective of this project was to assemble and implement an XRF detector into the lab’s x-ray chamber. Successful detector operation was verified by testing various materials samples and comparing characteristic XRF energies to analytical results derived from Moseley’s Law, an empirical formula that relates x-ray frequency to atomic number.