Nano-structured materials, interfaces and surface science

Paul PigramDr Paul Pigram

Head of Department of Physics, Faculty of Science, Technology and Engineering

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Narelle BrackDr Narelle Brack

Senior Lecturer, Faculty of Science, Technology and Engineering

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The research activities of this group focus on creating, understanding and controlling materials on the scale of nanometres. We have a strong focus on surface science, in particular, exploring chemical and molecular properties and processes at surfaces and at interfaces. A selection of our current research themes is summarised below.

Modification of carbon nanotubes for the development of advanced multi-functional nano-composite systems

Ozone-treated carbon nanotubes.Carbon nanotubes (CNTs) represent an ideal candidate for the development of multifunctional material systems such as polymer matrix composites. If CNTs are to be utilized as effective reinforcements, a good chemical bond to the polymer matrix is essential. The interface between the CNT and the polymer plays a critical role in determining the mechanical, electrical and thermal performance of the material. The primary goal of our research is to gain a fundamental understanding of the CNT / polymer system with the aim of being able to manipulate atomic scale interactions for the development of advanced multi-functional composite materials. A range of chemical and physical modification treatments have been investigated to improve the solubility and dispersion of CNTs in solvents and polymers. Changes to the surface chemistry of the CNTs are monitored using a combination of XPS, TOF-SIMS and EXAFS, while changes to the morphology are examined using SEM and AFM analysis.

Interactions at surfaces and interfaces

X-ray photoelectron spectroscopyA major interest of the group is exploring molecular interactions at surfaces and interfaces associated with the formation, function and degradation of materials structures, devices, and delivery vehicles. This direction is an integrated with the world class nanofabrication facilities of the Melbourne Centre for Nanofabrication (MCN) and the outstanding surface analytical instrumentation suite hosted at La Trobe University. The group has initiated a key partnership with CSIRO Materials Science and Engineering, founded on a group of shared Ph.D. students, that is focused on the investigation of interactions at surfaces.

Examples of research activity in progress include understanding the thin film structure and interfacial morphology in organic solar cells. Solar cell technology based on inorganic semiconductors such as Si is well established. Organic photovoltaics (OPVs) are seen as an exciting alternative due to their many beneficial features such as mechanical flexibility, extremely light weight, and compatibility with low cost manufacturing routes (e.g. printing). In this project, unique OPV cells are fabricated MCN and at CSIRO’s Clayton laboratories. Australia’s first gas cluster ion source ToF-SIMS, to be installed at La Trobe in mid 2013, will be used to explore the structure, interfacial morphology and failure of the OPV cells. Well established surface characterisation techniques such as XPS, AFM and ToF-SIMS provide complementary information and reveal the relationship between device fabrication parameters and the optimum OPV efficiency and lifetime.

Our project directions include the development of polymer microfluidic chips for chemistry and biology, combinatorial design of porous metallic substrates for surface-enhanced Raman spectroscopy, development of hyperspectral imaging techniques for multi-modal chemical imaging applications, combinatorial environmental gas sensing arrays, the characterisation of multilayered oxides for the protection metals, the development of surface tension-confined microfluidics for point-of-care diagnostics, and investigation of the interaction of multifunctional inhibitors with metallic surfaces.

Delivering chemotherapy drugs using nanoparticles

Chitosan nanoparticles for drug delivery. Image credit: Mas Jaffri MasarudinThe group has a very successful multidisciplinary project in progress with Dr Suzi Cutts and Professor Don Phillips (La Trobe Biochemistry). Anthracyclines such as doxorubicin are among the most effective chemotherapy agents for the treatment of a wide variety of cancer types. Although many mechanisms of action have been proposed, it is broadly accepted that the primary mechanism of action in cancer cells involves DNA damage. However, doxorubicin also attaches covalently to DNA in a reaction that is mediated by formaldehyde.

The group has demonstrated that the delivery of formaldehyde via suitably designed pro-drugs greatly enhances the rate of cell death. This raises the possibility that efficient and specific delivery of pro-drug to cancer cells, for example using a nanoparticle delivery system, might allow lower doses of doxorubicin to be adminstered. This in turn has the potential reduce the incidence of cardiotoxicity associated with doxorubicin use and extend patients lives.

A class of size controlled chitosan nanoparticles has been designed which allow the delivery of either doxorubicin or pro-drug to target cells. Excellent results have been achieved in vitro with high efficacy demonstrated and low toxicity to cells. The initial phase of cell studies is in progress leading on to an in vivo investigation of the system and evaluation of clinical benefits.

Exploring minerals and materials at the nanoscale

Precious black opal from Lightning Ridge, Australia. Image credit: Alex Fink.The group undertakes a variety of projects looking at the composition, structure and behaviour of mineral materials in the natural state and during processing procedures. Surface sensitivity spectroscopies such as XPS and ToF-SIMS are used to reveal chemistry and composition. There is a particular focus on exploring the distribution of chemical and molecular species on length scales substantially shorter than conventional mineralogical mapping techniques. With the arrival of a state-of-the-art scanning auger nanoprobe in 2013, it is expected that compositional variation on the scale of tens to hundreds of nanometres will be studied routinely.

Secondary electron micrograph of etched precious black opal from Lightning Ridge, Australia. Image credit: Alex Fink.A significant project is in progress examining the nature and formation of precious Australian black opal from the Lightning Ridge region. Detailed studies of composition, trace elements, and structure have been undertaken using samples collected from carefully selected locations within the opal district. The Australian Synchrotron powder X-ray diffraction beamline has been used to examine the formation of mineral phases in the opal at elevated temperature at high precision.

A similar approach is used to explore the behaviour of ceramics, oxides and glasses used in the manufactured products subject to extreme operating conditions. Thermally induced segregation, crystallite growth and structural decomposition are correlated with performance merits to understand the potential lifetime of devices and to identify optimal operating windows.

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