Welcome to the research website of Chris Howard, Associate Professor in the Department of Physics & Astronomy at University College London. We create new materials that have desirable functional properties or that exhibit interesting emergent phenomena and we study these materials with a wide range of experimental techniques. Outputs range from nano-textured electrodes for battery and fuel cells to the discovery of exotic electronic groundstates. A particular expertise of the group is the ability to controllably dope (add charge carriers to) materials, especially nanomaterials and layered materials, via the addition of guest ions. The doping can drastically modify the material's properties (e.g turning a semiconductor into a metal) and we have also shown can enable the thermodynamic dissolution of the materials in liquids, for example, to form true solutions of 2-dimensional materials.
Production of phosphorene nanoribbonsWatts et al. Nature (2019), 568, 216
Over the previous five years there have been over 100 publications predicting that nanoribbons made from the 2-dimensional material phosphorene would have extraordinary properties. These properties could offer transformative advantages in applications ranging from fast-charging batteries to flexible thermoelectric devices to nanoelectronics. There have also been predictions of spin desnity waves, tunable magnetism, half-metallicity and topological states. However, until this paper no one had made discrete phosphorene nanoribbons (PNRs), and there was no obvious modification of methods for producing graphene nanoribbons to phosphorene. We describe a novel method for creating quantities of high-quality, individual PNRs by ionic scissoring of macroscopic black phosphorus crystals, and characterise the ribbons in detail. The ribbons have typical widths of 4-50 nm, predominantly single-layer thickness, measured lengths of up to 75 μm and aspect ratios of up to 1,000. The nanoribbons are atomically flat single crystals, aligned exclusively in the zigzag crystallographic orientation with remarkably uniform widths along their entire lengths, and are extremely flexible. Gallery of ribbons.
Magnetic control of graphitic microparticles in aqueous solutionsNguyen et al. Proc. Natl. Acad. Sci. (USA) (2019), 116(7), 2425
This paper, led by Dr Llorente Garcia also at UCL, presents the first ever magnetic transport of diamagnetic graphite microparticles in water solutions. Given the dominance of viscous drag forces at the microscale, moving a microparticle that is submerged in liquid is comparably as hard as moving a macroparticle within dense honey. While diamagnetism is a weak magnetic property, for graphite it can be exploited to manipulate graphite flakes in a liquid using magnets (see figure for set up). The contactless magnetic control of biocompatible micrographite, together with graphite's unique physical properties, opens up new possibilities for applications in sensing, analysis, synthesis, and diagnosis in chemistry, biology, medicine, and physics.