arXiv subjects

Matthew C. Sullivan

Publications and source records attributed to Matthew C. Sullivan.

3 recordsLinked to original sources

arXiv2025

Computational Physics in the Advanced Lab: Experiment and Simulation of Thermal Diffusion in Metal Rods

We present a simple experiment on thermal diffusion in metal rods that can be used to integrate computation into the advanced lab. An analytical solution exists for the transient heat conduction in an infinite rod with a delta function heat input, but no analytical solution exists for short rods or for long duration heat inputs. Our apparatus is a copper rod with a heater and thermometers attached to the rod. The temperature of the metal rod due to transient heat conduction can be modeled using a simple numerical simulation and the finite centered difference method. Using a 22 cm long copper rod with the ends thermally sunk in aluminum blocks, we show poor agreement between the experimental results and the infinite-rod analytical model, but excellent agreement between the experimental results and our numerical simulation. This experiment shows the power of a numerical simulation but also the limitations of the chosen model, which can be used as motivation for further exploration.

physics.ed-ph↗

arXiv2024

Measurement of the Crystallization and Phase Transition of Niobium Dioxide Thin-Films for Neuromorphic Computing Applications Using a Tube Furnace Optical Transmission System

Significant research has focused on low-power stochastic devices built from memristive materials. These devices foster neuromorphic approaches to computational efficiency enhancement in merged biomimetic and CMOS architectures due to their ability to phase transition from a dielectric to a metal at an increased temperature. Niobium dioxide has a volatile memristive phase change that occurs $\sim$800$^\circ$C~that makes it an ideal candidate for future neuromorphic electronics. A straightforward optical system has been developed on a horizontal tube furnace for \emph{in situ} spectral measurements as an as-grown \NbtOf\ film is annealed and ultimately crystallizes as \NbOt. The system measures the changing spectral transmissivity of \NbtOf\ as it undergoes both reduction and crystallization processes. We were also able to measure the transition from metallic-to-non-metallic \NbOt\ during the cooldown phase, which is shown to occur about 100$^\circ$C~ lower on a sapphire substrate than fused silica. After annealing, the material properties of the \NbtOf\ and \NbOt\ were assessed via X-ray photoelectron spectroscopy, X-ray diffraction, and 4-point resistivity, confirming that we have made crystalline \NbOt.

physics.app-ph↗

arXiv2014

Epitaxial growth of Bi$_2$Pt$_2$O$_7$ pyrochlore

Certain pyrochlore oxides are among the best oxygen catalysts in alkaline media. Hence, exploring epitaxial films of these materials is of great fundamental and technological interest. Unfortunately, direct film growth of one of the most promising pyrochlores, Bi$_2$Pt$_2$O$_7$, has not yet been achieved, owing to the difficulty of oxidizing platinum metal in the precursor material to Pt$^{4+}$. In this work, in order to induce oxidation of the platinum, we annealed pulsed laser deposited films consisting of epitaxial $δ$-Bi$_2$O$_3$ and co-deposited, comparatively disordered platinum. We present synchrotron x-ray diffraction results that show the annealed films are the first epitaxial crystals of Bi$_2$Pt$_2$O$_7$. We also visualized the pyrochlore structure by scanning transmission electron microscopy, and observed ordered cation vacancies in a bismuth-rich film but not in a platinum-rich film. The similarity between the $δ$-Bi$_2$O$_3$ and Bi$_2$Pt$_2$O$_7$ structures appears to facilitate the pyrochlore formation. These results constitute a new approach for synthesis of novel pyrochlore thin film oxygen catalysts.

cond-mat.mtrl-sci↗