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Curiosity Driven Science with Impact

The ability to control matter at the fundamental length scale of individual atoms will enable the fabrication of entirely new classes of functional devices, from sensors to quantum computers.Ìý We conduct fundamental, exploratory reseach that is directed toward developing new understanding of matter at the atomic scale, as well as developing methods for atomic-scale assembly and construction.ÌýÌý

Below you will find some examples of research from our group together with information about our laboratory.Ìý More detailed information on our published work can be found by accessing the papers in the Publications section of this web page.

Atomic-scale quantum dots

Atomic-scale quantum dots in silicon

The hydrogen-terminated silicon (001) surface is a model system for exploring the properties of atomic-scale quantum dots, which can be fabricated by removing individual hydrogen atoms one at a time with the STM tip.Ìý The absence of a single hydrogen atom produces a "dangling bond", which can be considered as a deep-level atomic-point defect.Ìý Creating assemblies of closely-spaced dangling bonds leads to the formation of artificial molecular orbitals.

Two-dimensional (2D) MaterialsÌý

Charge Density Waves on the Graphene Sheets of the Superconductor CaC6

Systems of reduced dimensionality, e.g., two-dimensional (2D) crystals,Ìýcan exhibitÌýspontaneous reorganisation of their free charge density, forming what are often referred to as charge density waves (CDWs).Ìý CDWs are usually the result of electron-phonon coupling (i.e., coupling of the electrons with the vibrational modes of the crystal) or electron-electron coupling (i.e., coupling of the electrons with themselves).Ìý The signature of CDWs are a long range modulationÌýof the charge density, which can be commensurate or incommensurate with crystal lattice, and the opening of an energy gap at the Fermi energy.Ìý The ability of the scanning tunnelling microscope to map the density of states with both atomic-scale spatial resolution and meV energy resolution makes it the ideal tool with which to explore CDWs in 2D materials.ÌýÌý

Mapping dopant wave functions in silicon

Imaging Donor and Acceptor States in SiliconÌý

Atoms from group V of the periodic table, e.g., phosphorus, arsenic, or antimony, can substitute for a silicon atom in a crystal of silicon.Ìý Since silicon is a group IV element, this results in a localised positive charge of +1e at the impurity site.Ìý This charge can localise an electron from the conduction band and in doing so forms a hydrogenic state.Ìý The orbitals of this hydrogenic defect are analogous to those of the hydrogen atom with some perturbation due to the effects of the crystal lattice.Ìý Using the scanning tunnelling microscope we can image the probability densities of these long-ranged quantum states (see above) produce energy-resolved spatial maps of their density of states.Ìý Hydrogenic defect states are currently being explored for their potential use as quantum bits ("qubits") in variousÌýsolid-state quantum computer architectures.Ìý The details understanding of their properties that can be gained from STM/STS measurements of individual defects and their interactions provides detailed information on these states that cannot be determined by any other method.Ìý

Organic functionalisation of semiconductor surfaces

Organic functionalisation of semiconductors

One of the focuses of the group is developing methods to incorporate molecular functionality with traditional semiconductor electronics. We approach this by depositing organic molecules onto the technologically ubiquitous (001) crystal face of silicon under ultrahigh vacuum. ÌýThe functionalised surfaces we investigate using both scanning tunnelling microscopy (STM), and synchrotron-basedÌýphotoelectron spectroscopy techniques, including x-ray photoelectron spectroscopy (XPS) and near edge x-ray adsorption find structure (NEXAFS) spectroscopy. ÌýWe have performed synchrotron experiments at the Swiss Light Source, the Australian Synchrotron, the National Synchrotron Radiation Research Centre (NSCCR; Taiwan), and have collaborated with scientists from the Diamond Light Source (UK).Ìý

Methoxyacetophenone adsorption to Si(001)

We have investigated the coverage-dependent behavior of p-methoxyacetophenone adsorption to atomically-cleanÌýSi(001)Ìýusing X-ray photoelectron spectroscopy andÌýdensity functional theory calculations. This compound exhibits a highÌýselectivity of adsorbate species formation by forming only twoÌýdistinct adsorbate structures at low coverage, with a thirdÌýconfiguration forming at high coverages. This coverage-dependent but well-defined behavior is promising in designing functional organic−inorganic interfaces on silicon. This work resulted in our second publication in our collaboration with the . Ìý

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Low-temperature Scanning Tunnelling Microscope Laboratory

Scanning Tunnelling Microscopy

We have threeÌýultrahigh vacuum (UHV) scanning tunnelling microscope (STM) systems that are run by two principal investigations, Steven Schofield and Neil CursonÌý.

(Left): 4-Kelvin UHV-STMÌýoptimised for spatially resolved tunnelling spectroscopy and the creation of atomic-scale structures. (Middle): 6-Tesla vector magnet field, 1.5-Kelvin UHV STM system.Ìý Optimised for tunnelling spectroscopy of magnetic systems. (Right): Variable temperatureÌýUHV STM.Ìý This system is used solely for the fabrication of atomic-scale dopant structures in silicon.Ìý

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