People

Dr Richard Hopkinson

Associate Professor of Organic Chemistry

Profile

My research focuses on the modification, characterization and imaging of surfaces, achieved through the use of electrochemical methods and processes, supported by a wide variety of physical and spectroscopic techniques.

Research

My research falls into three distinct but related topics: development of in situ techniques, electroactive materials, and forensic science. The first two of these have a fundamental theme and the last of these exploits their application to latent fingerprint recovery. My research involves active collaborations with Professors Ryder and Abbott.

Development of in situ techniques

During the deposition, dissolution and redox switching of electroactive films, it is necessary to monitor the amount, nature and structure of the interfacial components; this addresses the questions how much?, what?, and where? When the electroactive material comprises multiple components and is perfused with electrolyte, the spatial distributions of the components are critical, as illustrated for the case of metal films.

Neutron reflectivity (in collaboration with researchers at the ISIS and Institut Laue Langevin large scale facilities) allows one to penetrate the electrode and solution to probe the composition and structure of “buried” interfaces. Analysis of the reflectivity response yields the spatial profiles of the components, illustrated (below) for the case of sequentially electrodepositing silver and copper layers on a gold electrode. The scattering length density (SLD), which is characteristic for each component, reveals inter-penetration of the metal layers and isotopic labelling reveals the extent of solvent incorporation.  

Complementary spatial profiles of the solution species are provided by probe beam deflection (PBD), in which a laser beam is deflected by concentration gradients that create a refractive index gradient in solution (somewhat like a mirage effect). When combined with nanogravimetric acoustic wave measurements using the quartz crystal microbalance (QCM), one can resolve surface and solution population changes during electrochemical processes. This provides insight into polymerisation/deposition efficiency, dissolution and controlled release processes, ion (de-)insertion in energy storage materials, and solution speciation.

Electroactive materials

A single material seldom provides all the (electro)chemical, optical, electronic and physical properties required for practical devices. Composite materials offer the prospect of combining these characteristics. Polymers based on transition metal salen complexes can incorporate metal oxide particles to provide candidate electrochromic materials for display devices. The potential dependence of UV/visible spectra of  poly[Ni(salen)] films incorporating TiO2 nanoparticles illustrates this (see right). Analysis of the absorbance profiles provides insight into the contributions to the overall response of the different components of the composite.

Conducting polymers based on aromatic monomers (pyrrole, thiophene, aniline and derivatives) possess technologically useful electronic, optical and chemical characteristics. While electro-polymerisation and deposition of these materials as thin films on electrodes is simple, small variations in conditions can result in dramatic changes in properties. We have used neutron reflectivity to study the growth dynamics of such films, exemplified by polypyrrole (right). Multiple reflections from the inner and outer surfaces of the film result in interference, much as one sees optically for thin films on a liquid surface. Analysis of these fringes yields the film thickness. Coulometric assay of the charge passed (using Faraday’s law) yields the amount of polymer created. Comparison of these two data sets provides the fractions of the film that are polymer and solvent. This can be spatially resolved as a depth profile. Variations of these profiles with the deposition mode explain the variations in film characteristics.

Forensic science

Fingerprints remain the primary means of identification of individuals, whether in criminal or civil (e.g. natural disaster) investigations. Criminal investigations generally involve latent (non-visible) marks: the challenge is to use chemical treatments to make the mark visible. For paper exhibits (documents, contracts, letters, ransom notes, paper currency) the physical developer (PD) method is typically employed. This involves the generation of colloidal silver particles via a redox reaction between Fe(II) and Ag(I) ions. The silver particles then selectively deposit on traces of fingermark residue (see SEM image, right). The presence of the silver is shown by spatially selective X-ray analysis in combination with scanning electron microscopy (SEM). One of the components of the traditional PD formulation, a surfactant that stabilises the silver particulates, has recently been shown to degrade in the environment to an endocrine disruptor and consequently environmentally outlawed. In collaboration with UK governmental scientists, we have determined the mechanism of operation of the classical method and thereby designed a new formulation with equivalent performance that presents no environmental hazard.

Many objects of forensic importance (firearms, bullets, knives, tools) are metallic. We have studied and optimised redox reactions between oxidising metal ions in solution and reactive metal surfaces that result in galvanic deposition of the elemental metal from solution. The image (left) shows the result of an iron surface on which is deposited a fingermark being exposed to a solution containing copper ions. The copper ions oxidised a small amount of exposed iron, resulting in the deposition of an equivalent amount of copper. In this case, the fingermark acts as a template, resulting in a negative image of the fingerprint. A large number of small features (“minutiae”) can be seen within the basic pattern: these provide sufficient detail for a fingerprint examiner to identify the individual leaving the mark. Application of this approach to a range of metals is being studied.

Publications

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Activities

Awards

Winner of the Inorganic Biochemistry Discussion Group Young Investigator's Award, 2018.

Qualifications

  • MChem (Oxford)
  • DPhil (Oxford)
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