Post Doctoral Fellows

 

The MacDiarmid Institute currently supports 13 Post Doctoral Fellowships, allowing early career scientists to focus on developing their research with the support and collaboration of some of the top researchers in New Zealand. Three of these Post Doctoral Fellows are profiled here.

Suresh Narayanaswamy

IRL, Gracefield, Wellington (s.narayan@irl.cri.nz)

PhD in Shock wave research 2002 “Some Investigations Under shock pressure” work carried out at Bhabha Atomic Research Centre (BARC), Mumbai, and University of Mumbai, India. Research Advisor: Prof. S.K. Sikka, Homi Bhabha Chair, BARC.

My research interest is high-pressure science. High pressure research is important for both basic and applied sciences. The increasing use of pressure as a thermodynamic variable in materials research is due to the fact that the volume reduction is much more effective than other methods. The material behaviour which can be studied during this compression regime ranges from elastic, plastic, structural phase transitions and electron structure changes to the ionization of the inner electronic shell.

I began my first Post-Doc with the MacDiarmid Institute in 2004 developing high-pressure capability at IRL to study the pressure effects on high-temperature superconductors with Professor Jeff Tallon. I developed a non-magnetic pressure cell that can subject samples to 1.2 GPa to study their magnetic properties at low temperatures using the SQUID at IRL, diamond anvil cells (DAC) for Raman and X-ray diffraction for powder and single crystal samples up to 20 GPa., and assisted Prof Geoff Jameson at Massey University to acquire a high-pressure cell for the NMR spectrometer which is now operational.

Between 2008-10 I left New Zealand for another Post-Doc at the Centre for Science at Extreme Conditions at the University of Edinburgh, developing a high-pressure cell for neutron diffraction at ISIS pulsed neutron facility. After I returned to IRL I commissioned a Circular Dichroism spectrometer as part of the Prime Minister’s Science award and an infra-red pulsed laser micro-machining facility for drilling, cutting and liquid-phase pulsed laser ablation for nanomaterial synthesis. I designed and developed a ceramic anvil pressure cell for SQUID that can load samples up to 6 GPa. In collaboration with Australian Synchrotron Micro-crystallography beam line I performed the first exploratory high-pressure single-crystal diffraction study using a special DAC.

My long term ambition is to build a national high-pressure R&D facility at IRL for the benefit of NZ science and industry.

 

Michael Fraser

University of Otago, Department of Chemistry, Dunedin (mfraser@chemistry.otago.ac.nz)

PhD thesis “The Synthesis and Spectroscopic Properties of Some Rhenium(I) and Copper(I) Polypyridyl Complexes”, under the supervision of Prof. Keith Gordon and Assoc Prof. Allan Blackman at the University of Otago.

Part of our research in the “Gordon Group” includes the synthesis of metal polypyridyl complexes and the characterization of their excited state properties with spectroscopic and computational techniques. Our interests in metal polypyridyls lie in their potential application in molecular electronic devices such as dye-sensitized solar cells and light-emitting diodes.

My PhD involved the synthesis of polypyridyl ligands and complexes with interesting optical and physical properties. Earlier on in my PhD I made dipyridophenazine (dppz) ligands appended with sulfur-containing substituents and their rhenium tricarbonyl chloride complexes. Despite the fact the dppz systems have been studied for twenty years, the idea of appending a donor group like sulflur had never been done.  These complexes showed unique photophysical properties because they have a new type of electronic state in which there is a charge-transfer from each end of the molecule, the metal and the sulfur into an electron accepting ligand core.

With the help of PhD student Chris Larsen, I am currently building on these findings. We hope to use the sensitivity of these dppz ligands and complexes to design reporter molecules for dye-sensitized solar cells. By attaching these molecules to the surface of TiO2 in a solar cell, we hope to gain an insight into the chemical environment of a working dye-sensitized solar cell. Another advantage of using these types of rhenium complexes is the carbonyl co-ligands, which give a spectroscopic ‘handle’ on the complexes, allowing us to further utilize time-resolved Raman and infrared spectroscopic techniques, in collaboration with Prof. Michael George (Nottingham).

To make these molecules we need to develop some chemistry and, as part of the program, both Chris and I are co-supervised by Dr. Nigel Lucas (AI) who is an expert in coupling reactions (among other things).  We are currently synthesising a range of dppz-based ligands using coupling chemistry including the Suzuki and Sonogashira methods. By doing this we alter the electron donor-acceptor properties of ligands. Re(I) complexes will be synthesized with functional groups for attachment to TiO2.

Ultimately, device fabrication and characterization will be possible through collaboration with Dr. Justin Hodgkiss (Victoria University of Wellington) and Prof. Simon Hall (Massey University) and overseas collaborator Dr. Atilla Mozer (University of Wollongong, Australia). It is hoped much can be learned about the inner workings of dye-sensitized solar cells by using these types of molecules.

 

James Storey

Industrial Research Limited, Wellington (j.storey@irl.cri.nz)

PhD Physics 2007, “Electronic Structure and Thermodynamic Properties of High Temperature Superconductors”. Supervisors: Prof. Jeffery Tallon and Dr. Grant Williams.

The mechanism of superconductivity in high-temperature superconductors (HTS) remains an unresolved challenge in physics. In 2004 I joined the world-wide efforts to solve this problem when I decided to undertake an MSc, later extended into a PhD, with Jeff Tallon studying isotope effects in high-Tc cuprate superconductors. Although I didn’t have a great deal of success with the initial isotope effect work, I really began to hit my stride calculating thermodynamic and transport properties from the electronic structure and comparing the results with those found through experiments. The research allowed me to combine physics with programming – one of my hobbies. A particular highlight was explaining the variation of the superconducting transition temperature of different cuprates in terms of the variation in the electronic density of states combined with a universal electron pairing energy from spin fluctuations.

Last June I returned to NZ after leading efforts at Cambridge University in high precision differential specific heat measurements for the past three years. Measuring the difference in specific heat between two closely related samples eliminates most of the large phonon background from the raw data, allowing features of the electronic specific heat to be studied over the entire temperature range. During my time there I performed the first comprehensive study of the electronic specific heat of a recently discovered class of iron-arsenide HTS, Ba1-xKxFe2As2, totalling 11 samples and spanning the entire temperature, doping and magnetic field phase diagram – a mammoth task. The results from this research are currently being prepared for publication.

Since returning to Wellington I have been studying a phenomenological model that does a good job of describing several normal-state properties of high-Tc cuprates at low dopings. I have also been assisting the applied HTS conductors programme at IRL by developing a rig to measure the room-temperature thermopower of thin films. Thermopower provides a quick and reliable measure of the doped hole concentration in HTS. This is important because for optimal performance, HTS conductors must be doped to a particular hole concentration.