arXiv subjects

Adam Cronin

Publications and source records attributed to Adam Cronin.

3 recordsLinked to original sources

arXiv2023

Controlled catalyst transfer polymerization in graphene nanoribbon synthesis

Exercising direct control over the unusual electronic structures arising from quantum confinement effects in graphene nanoribbons (GNRs) - atomically defined quasi one-dimensional (1D) strips of graphene - is intimately linked to geometric boundary conditions imposed by the bonding within the ribbon. Besides composition and position of substitutional dopant atoms, the symmetry of the unit cell, the width, length, and termination of a GNR are integral factors that collectively can give rise to highly tuneable semiconductors, innate metallicity arising from topological zero-mode engineering, or magnetic ordering in spin-polarized lattices. Here we present a rational design that integrates each of these interdependent variables within a modular bottom-up synthesis. Our hybrid chemical approach relies on a catalyst transfer polymerization (CTP) that establishes uniform control over length, width, and end-groups. Complemented by a surface-assisted cyclodehydrogenation step, uniquely enabled by matrix-assisted direct (MAD) transfer protocols, geometry and functional handles encoded in a polymer template are faithfully mapped onto the structure of the corresponding GNR. Bond-resolved scanning tunnelling microscopy (BRSTM) and spectroscopy (STS) validate the robust correlation between polymer template design and GNR electronic structure and provide a universal and modular platform for the systematic exploration and seamless integration of functional GNRs with integrated circuit architectures.

cond-mat.mes-hall↗

arXiv2023

Low Energy Excitations in a [4]Triangulene Honeycomb Antiferromagnet

Carbon-based synthetic lattices offer a versatile platform for the realization and control of correlated quantum effects at the nanoscale. Advances in on-surface synthesis have facilitated the fabrication of increasingly complex molecular frameworks, opening new avenues for the exploration and engineering of custom tailored electronic and magnetic phases. Here, we report the design, on-surface synthesis, and characterization of a two-dimensional (2D) covalent organic framework (COF) assembled from D3h symmetric S = 3/2 [4]triangulene building blocks arranged in a honeycomb structure. Combined scanning probe microscopy and spectroscopy, corroborated by first-principles density functional theory (DFT) and GW calculations, establish an antiferromagnetic (AFM) insulating ground state. Low energy spectroscopy resolves spin excitations in both one-dimensional (1D) chains and extended 2D networks, providing direct insight into the emergent spin dynamics and establishing a modular platform to explore quantum magnetism in a pi-conjugated organic system.

cond-mat.str-el↗

arXiv2022

Room Temperature Optically and Magnetically Active Edges in Phosphorene Nanoribbons

Nanoribbons - nanometer wide strips of a two-dimensional material - are a unique system in condensed matter physics. They combine the exotic electronic structures of low-dimensional materials with an enhanced number of exposed edges, where phenomena including ultralong spin coherence times, quantum confinement and topologically protected states can emerge. An exciting prospect for this new material concept is the potential for both a tunable semiconducting electronic structure and magnetism along the nanoribbon edge. This combination of magnetism and semiconducting properties is the first step in unlocking spin-based electronics such as non-volatile transistors, a route to low-energy computing, and has thus far typically only been observed in doped semiconductor systems and/or at low temperatures. Here, we report the magnetic and semiconducting properties of phosphorene nanoribbons (PNRs). Static (SQUID) and dynamic (EPR) magnetization probes demonstrate that at room temperature, films of PNRs exhibit macroscopic magnetic properties, arising from their edge, with internal fields of ~ 250 to 800 mT. In solution, a giant magnetic anisotropy enables the alignment of PNRs at modest sub-1T fields. By leveraging this alignment effect, we discover that upon photoexcitation, energy is rapidly funneled to a dark-exciton state that is localized to the magnetic edge and coupled to a symmetry-forbidden edge phonon mode. Our results establish PNRs as a unique candidate system for studying the interplay of magnetism and semiconducting ground states at room temperature and provide a stepping-stone towards using low-dimensional nanomaterials in quantum electronics.

cond-mat.mes-hall↗