Andrew Johnson – 2015

WEBJohnsonImpact of the Ferroelectric Polarization State on Conductivity Through Thin-film SrTiO3/Si Heterostructures

Research Advisor: Dr. Joshua Veazey

Certain thin-film ferroelectric oxide-semiconductor heterostructures allow for reversible, local changes in conductivity, with potential applications including non-volatile memory devices. Force microscopy techniques were used to investigate the impact of the ferroelectric polarization state on local conductive properties of ferroelectric SrTiO3 (STO) thin films deposited by molecular beam epitaxy onto both p- and n-type Si(001) substrates. Under certain conditions, local current voltage (I-V) curves exhibited pronounced hysteresis under forward bias. These characteristics are not, however, well-correlated with the polarization state of the ferroelectric STO. Alternative explanations for the current hysteresis are presented.

This work was generously supported by the Hope College Department of Physics Frissel Research Fund, and the National Science Foundation under NSF-MRI Grant No. CHE-1126462. Portions of this work were conducted in the CMP group facilities at Michigan State University; we would like to gratefully acknowledge R. Loloee and the MSU physics department for their support.

Margaret Dickinson – 2015

WEBDickinson2Development of a Novel Method to Measure Per- and Polyfluoralkyl Substances in Paper and Textiles

Research Advisor: Dr. Paul DeYoung and Dr. Graham Peaslee

Per- and polyfluoroalkyl substances (PFASs) are chemical compounds used as powerful, long-lived surfactants in many consumer products. Because of the environmental persistence of PFASs, their ability to bioaccumulate, and their suspected human toxicity, new methods to identify these chemicals in consumer products are needed. Current techniques to measure PFASs involve liquid chromatography-tandem mass spectrometry (LC-MS/MS) which requires significant time and expense per sample for analysis. Particle Induced gamma-ray emission (PIGE) spectroscopy is an established ion beam analysis method used to measure total fluorine concentrations in various objects, typically sediments and minerals. PIGE utilizes a beam of accelerated protons to excite 19F nuclei in a sample. As these nuclei return to their ground state, they emit characteristic gamma rays that can be used to identify and quantify the total fluorine content in a sample. In this study, paper and textile samples were analyzed with LC-MS/MS, paired with the total oxidizable precursor (TOP) assay, and with PIGE. A comparison of the results reveals that PIGE is an effective tool to determine the presence or absence of PFASs added to these consumer products. Limits of detection and the application of this method for rapid, non-destructive screening for certain consumer products were explored.

This work is made possible by funding from the National Science Foundation (NSF-RUI 1306074), the Department of Energy (DE-SC0007352), and the Hope College Department of Physics Guess Research Fund.

Jacob Pledger – 2015

Pledger
Crystalline Channeling of MeV ion beams

Research Advisor: Dr. Stephen Remillard

Thin film strontium titanate (SrTiO3) on single crystal MgO substrate, and thin film strontium manganese oxide (SrMnO3) also on single crystal MgO substrate, are being considered for use in engineered superlattices.  Crystal matching of the films to the substrates is indicated by channeling of an ion beam through the lattice.  With its ability to resolve depth in a sample, Rutherford backscattering of helium ions is used to determine layer thickness and the depth profile of the elemental composition of a sample.  Ion beam channeling occurs when the beam’s incident angle is parallel to crystal planes, or rather normal to the surface. Channeling can occur in well-ordered and pure crystals, providing an indication of sample quality.  Comparison of the backscattering yields at different incident angles will show a drop in yield as the optimum channeling angle is approached.  Channeling is seen with the bulk SrTiO3 sample as well as with the thin film samples.  Even though an 8% lattice mismatch exists between SrMnO3 and MgO, channeling was still evident, although in this case the yield suppression revealed structure around normal incidence.

This work was funded by a seed grant from the Michigan Space Grant Consortium and by the Hope College Natural and Applied Sciences Division.

Alec Nelson – 2015

AlecNelson

Inductive and Resistive Nonlinearities of a Superconductor Resonator

Research Advisor: Dr. Stephen Remillard

This experiment is designed to compare the feedback from an altered superconductor resonator with a conventional, unaltered superconductor resonator. Superconducting transmission lines are patterned on a lanthanum aluminium substrate chip with a geometry that resonates within the microwave range. Nonlinearities, distortion of the signals in the superconductor, can be engineered into the transmission line using an ion beam or other artificial source of radiation. The sample in this experiment, thin-film yttrium barium copper oxide: YBCO, was sent to a facility in Italy to be engineered with a nonlinearity and then characterised in a low temperature (77 K) cryostat. This means that the power dependence of a intrinsic resonator will differ greatly from this sample. Two key figures of merit of superconducting resonators are their critical power, where the power input to the resonator is most absorbed, and critical frequency of the sample, the frequency at which the critical power occurs. Both were found to vary with temperature, and at high incident power the frequency response of the resonator begins to experience deformation. The change of the power response as frequency is swept through (bending) and the hysteresis in the curve (bifurcation) form the core disparities between traditional superconducting resonators and those with engineered nonlinearities.

Funding for this project was provided by The Hope College Natural and Applied Sciences Division and Award number DMR-1206149 from the National Science Foundation.

Christina Sarosiek – 2015

WEBSarosiek

Differential PIXE Analysis of Multi-layer Auto Paint

Research Advisor: Dr. Paul DeYoung and Dr. Graham Peaslee

Differential Particle Induced X-ray Emission (DPIXE) is a technique developed to analyze multi-layered samples in a non-destructive manner. Analysis of auto paint, in particular, is beneficial in legal cases involving automobile crimes. Particle Induced X-ray Emission (PIXE) involves particle beams produced by an ion beam accelerator to analyze the concentration of elements present in one or more layers. As the beam penetrates into the sample, characteristic x rays of various energies are emitted which correspond to different elements in the sample. DPIXE involves varying the beam energy so the beam penetrates to different depths within the sample, emitting x rays only from the layers through which the beam has passed. Quantitative analysis is made easier by first taking measurements of the thickness of each layer. A Scanning Electron Microscope (SEM) with Energy Dispersive Spectroscopy (EDS) capabilities allows us to view a cross-section of paint and measure the thickness of each layer, as well as earn a better understanding of which layers hold the major elements within the sample. A careful combination of the SEM, EDS and DPIXE data is required to obtain accurate concentrations of elements in a sophisticated peak fitting program (GeoPIXE) with calculations of energy loss as the beam penetrates to different depths and reabsorption of x rays as they travel out of the sample towards the detector. This technique has shown to produce reasonable results when analyzing samples containing layers of uniform thickness.

his effort is based upon work supported by the National Science Foundation under grant No. PHY-1306074.