Non-Equilibrium Phenomena in Graphene

Graphene has displayed much promise as an electrical conductor and as a optical material. To date there is a large body of literature dedicated to the equilibrium properties of graphene. In this thesis the properties of graphene out of equilibrium are probed. Through combined optical and transport measurements the behaviour of hot electrons are probed at temperatures over five orders of magnitude from 50mK to 2000K. This wide range of temperatures allows access to the behaviour of quantum corrections at the lowest temperatures to the highest energy phonon modes. From ultrafast femtosecond laser pulses to steady state heating from an electric field the cooling of hot electron populations through coupling to various phonon modes in the graphene and the substrate are explored. Additionally the effect of an electric field on the weak localisation correction to the conductivity was separated from heating effects using applied magnetic fields combined with careful modelling of the heat transport properties of the graphene. Finally the desorption dynamics of oxygen bound to the surface are shown using a combination of transport and two pulse correlation technique using an ultrafast laser. Surprisingly the cooling of hot carriers in graphene at low energies shows substrate surface phonons as an important cooling mechanism, highlighting the importance of substrate choice in future graphene devices. In contrast at the very highest energy scales accessed only by photoexcitation the cooling is shown not to be influenced by the presence of a substrate, but out-of-plane phonon modes increase cooling of the hot optical phonons.EPSR

Optically induced oxygen desorption from graphene measured using femtosecond two-pulse correlation

Copyright © 2014 American Physical SocietyRecently, there has been a great deal of interest in the effect of atmospheric gases on the properties of graphene. We investigate the electrical and optical response of graphene-based field effect transistors that have been exposed to high purity oxygen gas using a combination of ultrafast two-pulse correlation (to give high temporal resolution) and low-frequency transport measurements (to monitor the photoinduced changes in the Fermi level). By measuring the Fermi level shifts, we are only sensitive to the oxygen atoms that interact directly with the surface. We compare our results to predictions of the empirical friction model for molecular desorption. We show the time scale of the relaxation associated with oxygen desorption to be ∼100 fs, suggesting the desorption proceeds through hot electron generation in the graphene rather than heating of the lattice through hot phonon generation.EPSRC (Engineering and Physical Sciences Research Council

Compressed sensing with near-field THz radiation

We demonstrate a form of near-field terahertz (THz) imaging that is compatible with compressed sensing algorithms. By spatially photomodulating THz pulses using a set of shaped binary optical patterns and employing a 6-μm-thick silicon wafer, we are able to reconstruct THz images of an object placed on the exit interface of the wafer. A single-element detector is used to measure the electric field amplitude of transmitted THz radiation for each projected pattern, with the ultra-thin wafer allowing us to access the THz evanescent near fields to achieve a spatial resolution of ∼9  μm∼9  μm

A pyrene-appended spiropyran for selective photo-switchable binding of Zn(II): UV-visible and fluorescence spectroscopy studies of binding and non-covalent attachment to graphene, graphene oxide and carbon nanotubes

PublishedArticleSynthesis of photo-switchable, Zn2+ sensitive hybrid materials was achieved by facile non-covalent functionalization of graphene, graphene oxide and carbon nanotubes with a pyrene-appended spiropyran. Solution phase binding studies, using UV–visible and fluorescence spectroscopy, indicated that the pyrene-spiropyran dyad was highly selective for Zn2+ over a range of potentially competitive cations and that binding occurred with 1:1 stoichiometry and a binding constant of K=1.4×104 mol−1 dm3 at 295 K. Zn2+ binding was promoted by UV irradiation or in darkness and reversed upon irradiation with visible light.Engineering & Physical Sciences Research Council (EPSRC

Erratum: “Cavity enhanced third harmonic generation in graphene” [Appl. Phys. Lett. 112, 011102 (2018)]

In the paper "Cavity enhanced third harmonic generation in graphene," we reported third harmonic generation from a graphene-dielectric-metal cavity. Since the original publication, it has come to light that a rather severe error was made in the calibration of the detector used in the experiments. Correcting this error (see corrected Figs. 1 and 2) leads to significantly lower absolute powers than previously reported, and power conversion efficiencies approaching ∼10-8 (for the largest powers used in the experiment) when resonant with the cavity and ∼10-10 when off resonance. The off resonance conversion efficiency is in line with previously reported values for planar graphene measured with comparable pulse fluence.1 Note that, due to a miscommunication between the authors, this error did not propagate into the numerical modeling results from the paper, i.e., our pW output powers are in line with v3 of order 10-17 m2=V2, as found in the analytical modeling of Ref. 2. It should also be noted that the main conclusion of our original paper, i.e., a two orders of magnitude enhancement in the harmonic generation due to the cavity, is unaffected by this error. (Figure Presented).</p

Investigating the nature of chiral near-field interactions (dataset)

The article associated with this dataset is located in ORE at: http://hdl.handle.net/10871/33246This is the dataset used for the Barr et al. (2018) article "Investigating the nature of chiral near-field interactions" published in Physical Review B.Engineering and Physical Sciences Research Council (EP/L015331/1 and EP/K041215/1)Defense Science and Technology LaboratoryRoyal Society and TATA (RPG-2016-186

The evolution of living beings started with prokaryotes and in interaction with prokaryotes

In natural world, no organism exists in absolute isolation, and thus every organism must interact with the environment and other organisms. Next-generation sequencing technologies are increasingly revealing that most of the cells in the environment resist cultivation in the laboratory and several prokaryotic divisions have no known cultivated representatives. Based on this, we hypothesize that species that live together in the same ecosystem are more or less dependent upon each other and are very large in diversity and number, outnumbering those that can be isolated in single-strain laboratory culture. In natural environments, bacteria and archaea interact with other organisms (viruses, protists, fungi, animals, plants, and human) in complex ecological networks, resulting in positive, negative, or no effect on one or another of the interacting partners. These interactions are sources of ecological forces such as competitive exclusion, niche partitioning, ecological adaptation, or horizontal gene transfers, which shape the biological evolution. In this chapter, we review the biological interactions involving prokaryotes in natural ecosystems, including plant, animal, and human microbiota, and give an overview of the insights into the evolution of living beings. We conclude that studies of biological interactions, including multipartite interactions, are sources of novel knowledge related to the biodiversity of living things, the functioning of ecosystems, the evolution of the cellular world, and the ecosystem services to the living beings