Event
Ph.D. Research Proposal Exam: Jennifer DeMell
Thursday, April 25, 2024
9:00 a.m.
AVW 2328
Maria Hoo
301 405 3681
mch@umd.edu
ANNOUNCEMENT: Ph.D. Research Proposal Exam
Name: Jennifer DeMell
Committee:
Professor KEVIN DANIELS (Chair)
Professor EDO WAKS
Professor MOHAMMAD HAFEZI
Date/time: Thursday April 25, 2024 at 9 am
Location: AVW 2328
Title: NOVEL MATERIAL HETEROSTRUCTURES FOR SPINTRONIC DEVICE APPLICATIONS
Abstract:
As the role of big data continues to grow, computing power and resources cannot keep up. Modern integrated-circuit systems integrate logic operations by incorporating silicon transistors in a binary computing scheme using the charge of the electron as the state variable. To continue improvements in terms of scale and performance, something needs to change. Transitioning the state variable from the electron’s charge (electronics) to its intrinsic spin (spintronics) introduces several benefits including considerably lower energy operation, higher speeds, and greater device densities.
For the most part, device speed and power performance have further improved as the dimensions decrease by applying a scaling voltage to the device. However, as materials become thinner, there is an exponential increase in leakage current and energy loss due to thermionic effects. Unfortunately, as bulk materials are grown more and more thinly, the surface roughness and number of pinholes increase, destroying tunneling effects, increasing scattering, decreasing adhesion, and increasing interfacial effects. In addition to the effects plaguing tunnel barriers, as bulk ferromagnetic materials scale down in thickness, magnetic states lose stability, reducing device functionality and reliability. The current state-of-the-art material approach uses bulk, crystalline layers of stacked materials, heterostructures, which are victim to the above effects as the materials are thinned.
This research will focus on changing the state variable to the spin of the electron and changing the material to improve low-dimensional, non-volatile spintronic devices through the incorporation and growth of large-area films and heterostructures. To improve on the state-of-the-art devices, constituent materials and material heterostructures must improve in the following measurable areas: operating temperature, scale of material growth, spin polarization efficiency, and the spin diffusion length, cumulatively all of which inform on the versatility and functionality of the device.
Heterostructures of novel materials such as topological insulators and two-dimensional materials possess several unique characteristics, including spin momentum locking, high spin-orbit coupling, and susceptibility to proximity effects. In the case of a graphene/lead-tin-telluride heterostructure, a spin-split two-dimensional electron gas forms at the material interface and a quantum phase change is observed at 40 K, which can provide an additional low-power switching mode for novel electronic devices for future computing platforms. Measurements up to 500 K show a spin diffusion length of about 13 µm and spin polarization efficiencies up to 12 %. In the proposed research, the suitability of this material for incorporation in a spintronic device is studied.
Theory predicts that MnxSey is a strongly magnetic thin film with a high TC of nearly 250 K and stability in ambient conditions, unlike many other leading 2D ferromagnets. Despite the material’s suitability as a large-scale, high TC magnetic thin film, much is still unknown and the crystallographic phases of thin-film MnxSey and their properties are still not well understood. A distinct Raman peak is observed at 255 cm-1 in preliminary growths, using a 532 nm laser excitation source with a 14 mW spot power, previously reported in literature as the A1g Mn-Se stretching mode. A thorough investigation of optical, chemical, and electrical characterization, and susceptibility to proximity effects will inform on whether the predictions posed by theory calculations hold true experimentally. Suitability for inclusion in a functional, low-dimensional spintronic device will be determined by comparing the material performance metrics in operating temperature, scale of material growth, spin polarization efficiency, and spin diffusion length.
