research

Optical Pulse Monitoring (OPM) is an emerging non-invasive approach to measuring the mechanical pulsations of the brain that arise from the cardiac cycle. Unlike conventional intracranial monitoring which requires surgically implanted probes or catheters to measure intracranial pressure (ICP) directly, OPM uses optical signals at the scalp to detect subtle volume changes in the underlying cerebrovascular system.

The technique sits at the intersection of photonics, neuroscience, and clinical engineering, and holds promise for continuous, bedside-safe monitoring of patients at risk of raised ICP.

Intracranial pressure (ICP) is the pressure exerted by cerebrospinal fluid and brain tissue within the skull, normally 7–15 mmHg in a supine adult. Sustained elevation above roughly 20–25 mmHg is associated with serious neurological injury, yet the gold-standard measurement method — inserting a pressure transducer or external ventricular drain directly into the brain — carries significant procedural risk. Developing reliable non-invasive alternatives is therefore a major clinical priority, particularly for patients who have suffered acute brain injury or subarachnoid haemorrhage.

The two case reports in this category apply a novel non-invasive brain pulse monitor to exactly these high-stakes scenarios. The 2023 Dove Press paper assesses the device’s ability to track ICP following acute brain injury, while the 2024 paper examines cerebrovascular responses, specifically Lundberg B waves, a recognised marker of impaired cerebrovascular autoregulation, in a patient recovering from subarachnoid haemorrhage. Together they provide early clinical evidence that optical brain pulse signals can capture haemodynamically meaningful ICP dynamics without the risks of invasive instrumentation.

Metal-organic frameworks (MOFs) are a class of coordination polymers in which metal ion clusters are linked by organic ligand “struts” to form highly ordered one-, two-, or three-dimensional porous structures. At the nanoscale, the nearly limitless combinatorial library of organic building blocks makes MOFs an attractive platform for engineering emergent electronic phenomena: by choosing the right metal centre and ligand geometry, researchers can in principle dial in specific band structures, magnetic interactions, or correlated-electron states. Two-dimensional MOFs grown on surfaces are particularly compelling because they can be interrogated and gated with scanning probe and electrostatic techniques unavailable to bulk crystals.

This body of work spans three publications that progressively deepen the understanding of electronic correlations in 2D MOFs. The 2021 Advanced Functional Materials paper identifies a manifestation of strongly correlated electrons in a 2D kagome-lattice MOF, attributing a measured Kondo resonance to the correlated electron state of the framework itself. The 2024 Nature Communications paper by Lowe, Field, Hellerstedt et al. demonstrates local electrostatic gate control of a Mott metal-insulator transition in a 2D MOF, a landmark result showing that the correlated insulating state can be switched on and off with a gate voltage. Most recently, the 2025 Small Structures paper explores how chirality at the MOF–substrate interface can be used to tune interfacial electronic properties, opening a further design axis for functional 2D MOF devices.

There’s plenty of room at the bottom

Richard Feynman

The invention of the scanning tunneling microscope (STM) by Binnig and Rohrer — recognised with the 1986 Nobel Prize in Physics — and the subsequent development of non-contact atomic force microscopy (nc-AFM) transformed surface science by making the imaging and manipulation of individual atoms and molecules a routine laboratory exercise. This body of work exploits both techniques to study what happens when organic molecules are deposited on atomically clean metal and insulator surfaces: how they self-assemble, how the substrate modifies their electronic structure, and how unexpected chemical reactions can be catalysed at the single-atom level. The research sits at the boundary of physics and chemistry, and a recurring theme is that even tightly controlled ingredients can produce surprising results.

The ten publications spanning 2018–2024 cover a wide range of phenomena. Early work characterised the structural and electronic properties of surface-supported single-molecule magnets (Tb₂Pc₃) and iron-based metal-organic nanostructures, revealing local charge accumulation effects. Subsequent papers examined aromatic azide transformations on Ag(111), the role of nuclear quantum effects in hydrogen-bonded molecular chains, and long-range surface-assisted molecule–molecule hybridisation. More recent contributions demonstrated room-temperature selective C–H bond activation catalysed by single gold atoms, direct observation of narrow electronic band formation in 2D molecular self-assemblies, mesoscopic self-assembly on insulators, and an upper-bound estimate of the electronic scattering potential of weakly interacting molecular films, collectively building a detailed picture of how molecule–substrate coupling shapes nanoscale electronic structure.

Sodium bismuthide (Na₃Bi) is a topological Dirac semimetal in which band inversion near the Fermi level produces linearly dispersing “Dirac cones” — a three-dimensional analogue of the dispersion relation that made graphene famous. In the ultrathin-film limit, a gap can be opened in these cones by quantum confinement or an applied electric field, driving the material into a topological insulating phase. This tunability makes Na₃Bi a compelling candidate for a topological transistor: a device that switches between topologically trivial and non-trivial states under electrostatic control, with potential applications in low-dissipation electronics.

Eight publications from 2016 to 2021 document the systematic development of Na₃Bi as a practical thin-film platform. Initial work established high-quality epitaxial growth and characterised the electronic properties of the resulting films. Subsequent studies demonstrated electrostatic modulation of carrier density, molecular doping across the charge neutrality point using F₄-TCNQ, and the observation of a temperature-dependent n–p transition. A landmark 2018 Nature paper reported electric-field-tuned topological phase transitions in ultrathin Na₃Bi, direct experimental proof-of-concept for the topological transistor concept. The programme was completed by demonstrating air-stable quantum transport using MgF₂ capping layers and publishing a 2021 Advanced Materials review of the field, opening the door to Na₃Bi device fabrication outside ultra-high-vacuum environments.

Bismuth selenide (Bi₂Se₃) is the canonical topological insulator: a material whose bulk behaves as an electrical insulator while its surface hosts topologically protected conducting states that are robust against local perturbations. Because these surface states are protected by time-reversal symmetry rather than by material purity, they are of intense interest for applications in spintronics and fault-tolerant quantum computing. Realising this potential in practice requires thin-film growth techniques that preserve the topological surface states and methods to control the carrier density — both of which are complicated by the strong tendency of Bi₂Se₃ to acquire unintentional bulk doping.

The three 2014 publications from this thesis research addressed these challenges directly. In-situ transport measurements revealed that significant electron doping is already present in Bi₂Se₃ immediately upon growth on a substrate, before any atmospheric exposure — a finding that shifted understanding of the doping mechanism. A companion study characterised how the surface reconstructs and degrades upon exposure to air. Most importantly, the work demonstrated that the strong electron acceptor molybdenum trioxide (MoO₃) can compensate the excess electrons and stabilise Bi₂Se₃ in the topological regime under ambient conditions, providing a practical route to air-stable topological insulator devices.

Advances in surface-science experiments increasingly depend on purpose-built software to automate tedious or time-sensitive measurement tasks and to extract quantitative information from large image datasets. The two software contributions in this category address both needs in the context of scanning tunneling microscopy (STM): one automates the instrument itself, the other automates the analysis of the images it produces. Both tools are published as open-source software with accompanying peer-reviewed papers, making them citable, reproducible, and reusable by the broader surface-science community.

Scanbot (Ceddia et al., Journal of Open Source Software, 2024) is an STM automation bot that handles routine but demanding tasks, namely tip conditioning, sample navigation, and spectroscopy acquisition, without continuous human supervision, dramatically increasing experimental throughput. The companion tool, Counting Molecules (Hellerstedt et al., Software Impacts, 2022), provides a Python-based pipeline for the automated enumeration and categorisation of individual molecules in STM images, replacing laborious manual counting with a reproducible algorithmic approach. Together these tools represent a step toward fully automated STM workflows, from data acquisition through to quantitative analysis.