arXiv subjects

Evan Tillotson

Publications and source records attributed to Evan Tillotson.

4 recordsLinked to original sources

arXiv2025

Phase engineering of 1T$'$ and 1T CrS2 and Cr2S3 by MOCVD

Layered Cr-chalcogenides compounds offer a rich range of crystal phases with different magnetic properties some of which have been predicted only but not experimentally verified. Here we demonstrate a previously unreported crystal phase of CrS2, namely the distorted octahedral (1T$'$) structure, synthesized via metal-organic chemical vapour deposition (MOCVD). We achieved the tuneable synthesis of either 1T$'$ or 1T phase CrS2. The structure were identified using polarized Raman spectroscopy, density functional perturbation theory (DFPT), as well as scanning electron diffraction (4D-STEM). 4D-STEM reveals that 1T$'$ crystals grow from an originally nucleated kinetically favoured 1T phase which then transform into the thermodynamically stable 1T$'$ phase. Magneto-optic Kerr imaging reveals that the 1T$'$ CrS2 crystals have soft ferromagnetic nature at low temperature. Our MOCVD growth of complex phases of 2D CrS2 with long-range magnetic order paves the way for the scalable synthesis of 2D magnets for ultrathin magnetic memories for logic-in-memory applications and spintronics.

cond-mat.mtrl-sci↗

arXiv2025

Isotopically Selected Single Antimony Molecule Doping

A reliable route to the deterministic fabrication of impurity ion donors in silicon is required to advance quantum computing architectures based upon such systems. This paper reports the ability to dope isotopically-defined unique (${}^{121}\mathrm{Sb}{}^{123}\mathrm{Sb}$) clusters into silicon with measured detection efficiencies of 94% being obtained. Atomically resolved imaging of the doped clusters reveals a Sb-to-Sb separation of ~2 nm post-implantation, thus indicating suitability to form coupled qudit systems. The method used is fully compatible with integration into processing that includes pre-enrichment of the silicon host to < 3ppm ${}^{29}\mathrm{Si}$ levels. As such, we present a potential pathway to the creation of scaled qudit arrays within silicon platforms for quantum computing.

cond-mat.mtrl-sci↗

arXiv2024

Electron Channelling Contrast SEM Imaging of Twist Domains in Transition Metal Dichalcogenide Heterostructures

Twisted 2D material heterostructures provide an exciting platform for investigating new fundamental physical phenomena. Many of the most interesting behaviours emerge at small twist angles, where the materials reconstruct to form areas of perfectly stacked crystal separated by partial dislocations. However, understanding the properties of these systems is often impossible without correlative imaging of their local reconstructed domain architecture, which exhibits random variations due to disorder and contamination. Here we demonstrate a simple and widely accessible route to visualise domains in as-produced twisted transition metal dichalcogenide (TMD) heterostructures using electron channelling contrast imaging (ECCI) in the scanning electron microscope (SEM). This non-destructive approach is compatible with conventional substrates and allows domains to be visualised even when sealed beneath an encapsulation layer. Complementary theoretical calculations reveal how a combination of elastic and inelastic scattering leads to contrast inversions at specified detector scattering angles and sample tilts. We demonstrate that optimal domain contrast is therefore achieved by maximising signal collection while avoiding contrast inversion conditions.

cond-mat.mtrl-sci↗

arXiv2023

Ultra-clean assembly of van der Waals heterostructures

Layer-by-layer assembly of van der Waals (vdW) heterostructures underpins new discoveries in solid state physics, material science and chemistry. Despite the successes, all current 2D material (2DM) transfer techniques rely on the use of polymers which limit the cleanliness, ultimate electronic performance, and potential for optoelectronic applications of the heterostructures. In this article, we present a novel polymer-free platform for rapid and facile heterostructure assembly which utilises re-usable flexible silicon nitride membranes. We demonstrate that this allows fast and reproducible production of 2D heterostructures using both exfoliated and CVD-grown materials with perfect interfaces free from interlayer contamination and correspondingly excellent electronic behaviour, limited only by the size and intrinsic quality of the crystals used. Furthermore, removing the need for polymeric carriers allows new possibilities for vdW heterostructure fabrication: assembly at high temperatures up to 600°C, and in different environments including ultra-high vacuum (UHV) and when the materials are fully submerged in liquids. We demonstrate UHV heterostructure assembly for the first time, and show the reliable creation of graphene moiré superlattices with more than an order of magnitude improvement in their structural homogeneity. We believe that broad adaptation of our novel inorganic 2D materials assembly strategy will allow realisation of the full potential of vdW heterostructures as a platform for new physics and advanced optoelectronic technologies.

physics.app-ph↗