Physics: Research Talks

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Using Phase Shift Interferometry to Measure the Topography of Thin Metal Films
(Houghton University, 2023-04-15) Zdunski, Jonathon; Hoffman, Brandon
A low-cost phase-shifting laser interferometer is being constructed at Houghton University to measure the thickness and topography of thin metal films produced with a variety of deposition parameters. The modified Twyman-Green Interferometer uses a 632 nm laser. Three piezoelectric ceramic stacks move a reference mirror up to 883 nm along the direction of the beam with a precision of <1 nm. The interference pattern is captured by a 2 MP camera. The system is suspended by springs and uses eddy current damping to decrease the movement of the system. A housing mounted to the outer frame blocks wind produced by the building’s air handling system. A LabVIEW program controls the mirror movement and fits a sine function to the intensity of each pixel vs. reference mirror position. An intensity plot of the fitted phase shifts represents the topography. Initial tests using two λ/10 flat mirrors indicate that the individual pixel height measurements are repeatable within about 1.6 nm. Assuming the film surface is smooth, the maximum repeatability of the overall topography should therefore be <1 nm.
XLI Annual Rochester Symposium for Physics Students, University of Rochester (Rochester, NY), April 15, 2023
An Ambient Air Scanning Tunneling Microscope to Study the Surface of Thin Metal Films
(Houghton University, 2023-04-15) Wilson, Joshua C.; Hoffman, Brandon
An ambient-air scanning tunneling microscope (STM) is being built at Houghton University to study the crystal growth and transformation of thin metal films. The STM operates by maintaining a constant current between a piezo-electrically controlled scanning probe and the thin metal film sample while recording the height of the probe relative to the sample stage. This current is produced when electrons from the sample quantum tunnel through the ~10-10 m air gap to the probe, aided by a small bias voltage of ~-1 V applied to the sample; in order to achieve a tunneling gap of this size, the STM utilizes stepper motors to perform a rough approach of the probe to the sample. The STM is suspended on a dual-stage vibration isolation system which utilizes springs with eddy current damping to protect the STM from background noise. The STM is controlled by a user interface via the Processing IDE software and a Teensy 4.1 microcontroller via the Arduino IDE, along with a control circuit. The data collected by the STM are used to create an intensity plot that will act as an atomic resolution “image” of the film surface. All hardware, electronics, and programs have been completely and successfully tested.
XLI Annual Rochester Symposium for Physics Students, University of Rochester (Rochester, NY), April 15, 2023
Automatic Control of an Inertial Electrostatic Confinement Device
(Houghton University, 2023-04-15) Condie, Micah K.; Yuly, Mark E.
The Houghton University Farnsworth-Hirsch fusor is an inertial electrostatic confinement device designed for the purpose of studying plasmas, D-D fusion, and as a source of x-rays and neutrons for other experiments. It operates via two concentrically arranged wire spheres with a voltage difference between them of up to 30 kV, ionizing a low-pressure gas to form and confine a plasma. The voltage across the two spheres is measured using a voltage divider circuit allowing the Arduino at the bottom of the chain to measure a lower proportional voltage. The current to the HV grid flows through an LED, floating at high voltage, the light from which is then measured at the end of a fiber optic cable using a phototransistor circuit. The previous fusor remote operating system used LabVIEW and Digi TS4 Port servers to communicate with the high voltage power supply, pressure gauge, and mass-flow controller via ethernet, RS-232, and RS-485. It was redesigned using python to communicate with the instrumentation directly over USB and RS-485. Furthermore, a PID controller was made so that the pressure in the chamber could be adjusted automatically, maintaining the plasma while raising the voltage. The fusor was successfully tested using air as the ionized gas with limited success using the PID controller. Future experiments will correct the automatic system and test the system with hydrogen then deuterium.
XLI Annual Rochester Symposium for Physics Students, University of Rochester (Rochester, NY), April 15, 2023
Thin Metal Film Physical Vapor Deposition System
(Houghton University, 2023-04-15) Bowman, Matthew; Hoffman, Brandon
A low-cost, thin film deposition system utilizing physical vapor deposition is being constructed at Houghton University. A mechanical and turbomolecular pump lower the chamber to a base pressure of 10-6 Torr. Three graphite crucibles are heated via thermionic emission from three corresponding tungsten filaments. Each filament floats at up to -4 kV with individually controlled currents of up to 3 A. The use of three separate crucibles and filaments allows for the deposition of up to three different materials either simultaneously or sequentially. The 10 cm Si substrate onto which the metals are deposited is mounted on a rotatable feedthrough behind a stepper motor-controlled linear shutter, which provides a method for depositing with a thickness gradient. A Giedd and Perkins evaporation rate monitor allows controlled deposition. The chamber is currently capable of producing films and is being retrofitted to use an Arduino to control the deposition process more easily.
XLI Annual Rochester Symposium for Physics Students, University of Rochester (Rochester, NY), April 15, 2023
Simulating Particle Transport within a Microcalorimeter to Unfold the Detector Response
(Houghton University, 2023-04-15) Brown, Adam E.; Koehler, Katrina E.
The measurement technique of Decay Energy Spectroscopy (DES) utilizes high-energy resolution (7.5 }0.2 eV FWHM at 6539 eV) [1] low temperature microcalorimeters to measure the total energy of a decay from an embedded radioactive source. DES spectra are histograms of the total decay energy thermalized in the absorber. Some of this energy is lost, largely due to decay products escaping the absorber or energy stored in metastable states (the latter depends on source preparation and is not considered in this work). This results in a measurement of energy that is lower than the decay energy. The escape probability is not constant as a function of initial decay energy but is dependent on the absorber material and the source’s energy, type, location, and distribution—all of which form what we call the detector response. In this work, the response matrix for a microcalorimeter is built using EGSnrc—a Monte Carlo particle transport software—to simulate the energy deposition of a point source of monoenergetic beta particles ranging from 10 keV to 2 MeV. This response matrix may be used to deconvolve the detector response from a DES measurement so systematic uncertainty can be reduced. This will result in a more precisely known beta decay shape, important for fields such as nuclear medicine and testing theoretical descriptions of beta decay at low energies.
XLI Annual Rochester Symposium for Physics Students, University of Rochester (Rochester, NY), April 15, 2023

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