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Environmentally sensitive equilibrium morphology phase mapping of nanoparticles/nanorods

A project of the Theoretical Chemical and Quantum Physics Group

Team

Chris Feigl and Salvy Russo

Collaborators

Dr. Amanda Barnard: CSIRO

Brief Project Outline 

The use of zinc sulphide nanoparticles offers a range of exciting applications in medical diagnostics, photovoltaics, catalysis and electroluminescent displays. Currently these applications are hampered by safety and stability issues, whereby changes in the morphology of the ZnS nanoparticles can lead to device malfunctions and produce eco- and cyto-toxic by-products. These challenges can be addressed through the development of a morphology phase map.

A morphology phase map provides a means of thermodynamically predicting and thus preserving the nanoparticle morphology and phase throughout the lifecycle of the material. The phase refers to the specific arrangement of atoms within the material and determines all chemical and physical properties. The morphology refers to the geometric shape of the nanoparticle and can have consequences on how individual nanoparticles interact with each other and their environment, thus determining such aspects as bio-availability, catalytic activity and toxicity. Therefore, producing and maintaining the correct phase/shape combination is critical for gaining safety and stability.

For bulk materials, assessing safety and stability involves constructing an experimental phase map, revealing the temperature and pressure phase transformation points. On the nano-scale, this task becomes monumental, owing to transformation points that are also dependent on particle size and chemical environment. In addition the extremely small size and time scales present considerable challenges for experimental characterisation and control. For this reason, theoretical studies provide critical and irreplaceable insight into nanoscale phenomena. We are using modern quantum mechanical theories and cutting edge thermodynamic modelling techniques to calculate the equilibrium morphologies of ZnS NPs as a function of their temperature, pressure, size and chemical environment.

Zinc Blende stacking

Zinc Blende structure showing (a) diagonal ABCABC stacking (top), and (b) the higher temperature Wurtzite structure showing horizontal ABAB stacking in the ZnS dimers (bottom).

Recent Publications 

C. Feigl, S.P. Russo, A.S. Barnard, Safe, Stable and Effective Nanotechnology: Phase mapping zinc sulfide nanoparticles, J. Mater. Chem., 20, 4971-4980 (2010)


For more information about this project, please contact Salvy Russo.

Computer Modelling of Ionic Liquids as Electrolytes and their Interaction with Electrode Surfaces

A project of the Theoretical Chemical and Quantum Physics Group

Team

Dr. Akin Budi, Prof. Salvy Russo

Brief Project Outline 

Current lithium and lithium-ion battery technology employs organic electrolyte coupled with graphite or alloyed anode. Upon initial charging of the battery, a passivating layer called the Solid-Electrolyte Interphase (SEI) is formed which acts as a barrier that prevents the formation of dendritic growth on the electrode. This dendritic growth is detrimental to the stability of a lithium and lithium-ion battery and can cause catastrophic short circuiting of the battery.

Room temperature ionic liquids (RTILs) are attractive to use as a replacement for the organic electrolyte due to its low vapour pressure, low melting point, and high ionic conductivity. These properties allow the next generation batteries to be safer and have higher energy densities. In addition, unlike organic electrolyte, RTIL prevents the formation of dendritic growth on pure lithium anode, which further increases the energy density. It is believed that RTIL is forming an SEI layer on the lithium anode, but to date identifying the SEI species has remain inconclusive.

This project explores the interactions between the N-methyl-N-propyl-pyrrolidinium (mpPy) cation and bis(fluorosulfonyl)imide (FSI) anion pairs and the lithium anode, studied using the density functional theory method implemented in the Vienna Ab-initio Simulation Package.

Atomic structure of a room temperature ionic liquid.

For more information about this project, please contact Salvy Russo.

Titanium Defects in α-Quartz With a Focus on Properties Relevant to Geo-Thermometers

A project of the Theoretical Chemical and Quantum Physics Group

Team

Mr. Tim DuBois, Prof. Salvy Russo

Collaborators

Dr Nick Wilson & Dr Colin McRae: Division of Minerals, CSIRO.

Brief Project Outline 

Geodynamic processes are extremely difficult to investigate with current technologies. Rheology in the lithosphere and asthenosphere is highly nonlinear and elasticity causes complications near the surface when the ambient temperature is less than approximately 600°C. The current contention between Geologists and Geophysicists is that the Earth's main geodynamic process is that of Mantle Convection; exerting plate tectonics to organise the system. Considering that plate tectonics is only a kinematic description of observations though, and not a fully dynamic description of plate motion, this and other approximations and assumptions continue to build upon one another yielding incomplete and inconsistent models. Geothermobarometry is the science of measuring temperature and pressure histories of intrusive igneous or metamorphic rock in an attempt to understand these processes in a limited fashion.

The recent work complied on a Titanium-in-Quartz geothermometer by Wark & Watson concluded with an empirical formula generated from the cathodoluminescence of a synthesised Quartz system in the presence of Rutile. The absence of a major pressure effect on the calibration is suggested, but could not be verified.

Generation of an ab initio model of a Ti defect in a SiO2 crystal was undertaken to assist in validating the Ti/Quartz relationship at pressure and temperature over ranges of 0 - 11 GPa and 0 - 1500 K respectively. A Molecular Mechanics model was also constructed due to issues pertaining to the construction of the former. An analysis and comparison of the two models conclude that the Titanium-in-Quartz defect investigated showed a pressure dependence of less than 0.2% over the pressure range.

Atomic structure of a titanium defect in a SiO2 crystal.

For more information about this project, please contact Salvy Russo.