Probing 2-dimensional quantum materials at the atomic scale with scanning transmission electron microscopy
Mentor: Elisabeth Bianco
Student: Lanette Espinosa
2D materials, including transition metal halides and chalcogenides, possess low temperature structural transformations with concomitant magnetic or electronic changes, such as charge density waves. While these transformations are promising for material design, the driving forces for their emergence and capacity for tunability are not fully understood. Unraveling the mechanisms behind such structure-property relationships requires visualizing the material at the atomic-scale across the phase transition. In this project, you will use state-of-the-art scanning transmission electron microscopy (STEM) combined with image simulations to understand crystal structures of 2D materials at the atomic scale. Furthermore, you will perform in situ experiments under external stimuli such as electrical biasing and temperature changes to explore quantum phase transitions in 2D materials. These studies will help to elucidate how emergent phases evolve as a function of thickness, ultimately allowing for tailoring of electronic and magnetic properties.
Design of in situ Shadow Mask for Molecular Beam Epitaxy
Mentor: Dr. Darrell Schlom
Student: Alex Kurland
Molecular-beam epitaxy (MBE) is a method for the deposition of thin single-crystal films. The current method creates a uniform layer of a single crystal in which the structure of each layer can be varied with atomic-layer precision. The shadow mask that is the subject of this project will restrict the region upon which a film is deposited to a specific shape, allowing for the deposition of patterned atomic layers. This is particularly useful for the deposition of top electrical contacts with clean interfaces to the underlying layer that will allow its properties to be probed. These shadow masks would function inside the MBE system, but would allow for easy replacement of differently shaped masks.
Determination of the influence of non-stoichiometry and disorder on superconductivity and spectral characteristics in a high-temperature superconductor
Mentor: Dr. Brendan Faeth
Student: Nathaniel Luis
The binary compound FeSe is an archetypical Iron-based superconductor hosting a modest Tc of ~8 K. Interestingly, when grown in thin film form on the ubiquitous oxide perovskite SrTiO3, FeSe films exhibit dramatically enhanced superconducting properties, with Tc >40 K. A better understanding of this enhancement effect could allow for the deliberate engineering of more efficient and high temperature superconductors in alternative chemical systems. Despite much effort, however, a more complete understanding of the enhancement effect in this system remains elusive.
One curious aspect of the FeSe/SrTiO3 system is that the synthesis process for high-Tc films requires a vacuum annealing procedure in order for superconductivity to emerge. Recent work by our group suggests that the variation in disorder strength in films as a function of vacuum annealing condition is critical to the emergence of superconductivity in single-layer thick films (https://arxiv.org/abs/2010.11984). It is not well understood, however, if the primary source of this intrinsic disorder is structural (non-ideal crystallinity) or chemical (non-ideal stoichiometry) in nature. This REU project will seek to explore and understand the relationship between elemental non-stoichiometry (as measured via x-ray photoemission spectroscopy (XPS)), disorder, and superconductivity (as measured via ARPES) in ultra-thin FeSe/SrTiO3 films.
Atomic Properties of Hexagonal Boron Nitride from First Principles
Mentor: Dr. Betül Pamuk
Student: Nimit Mishra
Recently, two-dimensional (2D) few-layer hexagonal Boron Nitride (hBN) nanosheets have been fabricated using laser plasma deposition technique. Experimentally, it has been observed that the interlayer spacing between few-layer hBN is different with the number of layers. We will explore the physics behind this effect using different approximations in density functional theory (DFT).
Probing structural and electronic phases in novel infinite-layer nickelate thin films with atomic resolution
Mentor: Berit Goodge
Student: Hanna Porter
The recent discovery of superconductivity in infinite-layer nickelates (RENiO2, RE = hole-doped rare earth) has spurred a flurry of research into understanding the structural and electronic nature of these materials, particularly in comparison to their nominally isostructural cousins, the high-Tc cuprates. The structural meta-stability of the infinite-layer cuprates has thus far limited their successful synthesis to the thin film (t ~ 10-20 nm) geometry, requiring highly localized probes to measure and understand the underlying materials physics. This project will involve the collection and analysis of high-resolution STEM and EELS data to explore the rich phase diagram of PARADIM-grown nickelate thin films.
Characterization of epitaxial oxides on fluorite substrates for novel electronic applications
Mentor: Dr. Felix Hensling
Student: Veronica Show
In the past decades oxide thin films have become one of the central research topics for the development and improvement of electronic devices. This is based on their manifold interesting properties, which are often easily tunable. Examples are their conductivity, ranging from highly insulating to metallic, or their magnetic state, ranging from diamagnetic to ferromagnetic. Fluorite substrates i.e., yttria-stabilized zirconia is of growing interest in this context for high crystal quality epitaxial bixbyites and pyrochlores. The interest in these films is in turn based on their interesting properties, partially unique to the respective crystal class. The best-known bixbyite is probably tin-doped Indium oxide, commonly referred to as ITO, which is an industry standard for transparent conducting oxides. In the case of pyrochlores a wide array of highly interesting physical properties has been reported, e.g. spin ice, quantum spin ice, and topological antiferromagnetism. To optimize such properties, also for eventual industry applications, it is important to understand their relation to structural film properties such as strain. The aim of this project will be to establish the growth of epitaxial films of materials with especially promising properties and to understand how these properties relate to growth parameter induced changes in the film.
Ab initio study of mismatch layered superconductors
Mentor: Dr. Tomás Arias
Student: Sarah Uttormark
The student will learn and master first principles calculation techniques by which we solve the many-body Schrödinger equation to determine the behavior of condensed matter systems. The student will then apply these methods to explore the family of superconducting mismatched layered materials BiX/NbY2, where X,Y=S,Se,Te, predicting properties relevant to superconducting performance.
Development High Pressure Floating Zone Materials
Mentor: Evan Crites
Student: Luc Capaldi
Synthesis in high pressure, supercritical fluids is a materials growth frontier. Utilizing PARADIMs flagship capabilities for high pressure research, we will develop the synthesis of novel single crystal quantum materials that are only stable under the extreme conditions in supercritical, high temperature, oxygen/nitrogen/argon. As PARADIMs new high pressure capabilities come online, we will continue to push the available materials frontiers.
Streaming by Design: A new paradigm to optimize the PARADIM data ecosystem
Mentor: David Elbert
Student: Avery Lenihan
The project will develop a new tool to probe, visualize and control PARADIM’s data infrastructure. The tool creates the basis of an analytical investigation of data about the data and forms the foundation of understanding required to optimize use and growth of materials data infrastructure in a distributed, diverse, multiuser facility.
Tunable spin splitting in the two-dimensional transition metal chalcogenides
Mentor: Dr. Mojammel Khan
Student: Megan Michaud
Manipulating the spin of the electron is at the forefront of the spintronic systems and materials with large spin-orbit coupling with unidirectional spin orientation in momentum space is crucial for the development of next generation of spintronic devices. The persistent spin texture (PST) is usually not found in materials with strong SOC due to the spin dephasing. The problem of the spin dephasing by the SOC can be eliminated by designing the materials to exhibit unidirectional spin orbit field. Here, the spin texture is enforced to be uniform and independent from the electron momentum, called as the PST arising when the linear Rashba and Dresselhauss (two spin orbit induced terms in materials) contributions compensate each other. This phenomenon has already been established in quantum well and interface of 2D materials. Our project will aim at developing bulk materials where the PST can be observed.
Taking theoretical predictions as guide, the student will be working with the mentor to grow single crystals of potential candidate materials such as transition metal chalcogenides and then will proceed to characterize the structure and physical properties.
Development of New High Pressure Laser Pedestal Synthesis Capabilities
Mentor: Ben Redemann
Student: Mishra Mbuqua
We will work on the development of the new high pressure laser pedestal growth furnace in PARADIM.
Characterizing lattice and electronic Structure in narrow gap semiconductors with cryogenic scanning transmission electron microscopy
Mentor: Noah Schnitzer
Student: Beatriz Avila-Rimer
Cryogenic scanning transmission electron microscopy allows distortions in the atomic lattice to be characterized to the picometer. Here, it will be used to study the nanoscale structure of novel technologically interesting materials to characterize an anticipated emergent electronic ordering. This project will include sample preparation, imaging, and in particular, careful computational analysis to quantify image data.
Synthesizing the high-temperature superconductor Bi-2212 at single monolayer thickness over a large area
Mentor: Y. Eren Suyolcu
Student: Sean Chang
(SURF Project) The high critical temperature of cuprate superconductors makes them ideal for many modern applications. One way to synthesize superconducting materials with precise structural control is to fabricate them in thin films, especially via oxide molecular beam epitaxy (MBE). In this project, we will focus on one of the cuprate superconductors, DyBa2Cu3O7-δ (DBCO) and we aim to fabricate high-quality high-temperature superconducting DBCO films utilizing oxide MBE. The DBCO films will be analyzed via X-ray reflection (XRR) and X-ray diffraction (XRD) techniques, followed by transport measurements after each growth. XRR will assist in determining the film thickness to be assessed for precise calibration and XRD will be used to analyze the structure of the films to optimize and improve the film quality. Finally, transport measurements will be conducted to measure the superconducting transition temperature of the films.