Special Seminar: Friday 3rd August 2012 Hume-Rothery Lecture Theatre 2pm
Prof. Stefan K. Estreicher, Texas Tech University, USA.
Impurities in covalent materials introduce localized vibrational modes. The lifetimes of these modes sometimes exhibit surprisingly large isotope dependences. One example involves interstitial O in Si. The frequency of the asymmetric stretch of 29Si–16O–28Si is within 0.1% of that of 28Si–16O–28Si but its lifetime almost doubles. Yet, it is the same mode of the same impurity in the same material measured at the same temperature. How can that be?
Vibrational lifetimes can be calculated from first principles using non-equilibrium molecular-dynamics (MD) simulations if the supercell is properly ‘prepared’ slightly away from equilibrium. Theory mimics transient-bleaching spectroscopy, the experimental technique used to measure lifetimes. The results provide an explanation to these experimental data.
This theoretical approach has been extended to the calculation of the thermal conductivity of nanostructures containing impurities. Surprisingly, the calculations predict large impurity-isotope effects, which appear to be related to the vibrational lifetimes of impurity-related modes. This suggests that some impurities can trap energy in the form of phonons. These effects have yet to be measured.
My talk will begin with the measured temperature- and isotope-dependence of vibrational lifetimes, and the subsequent challenge to theorists. Then, I will discuss supercell preparation in (and slightly away from) thermal equilibrium, and temperature control in non-equilibrium MD simulations without thermostat. The calculations of thermal conductivities now lead to a challenge to experimentalists. An interesting bottle of wine awaits the first who confirms the predicted isotope effects, or proves us wrong.
Three academic appointments
The Materials Department is delighted to welcome 3 new members of academic staff - Professor Roger Reed, Dr Jamie Warner and Dr Harish Bhaskaran.
Manufacturing the future: endohedral fullerenes, small molecules, big challenges
Dr Kyriakos Porfyrakis has been awarded an EPSRC Fellowship to explore the manufacturing capacity and chemical functionalization of endohedral fullerenes. The grant, worth £1.5M over 5 years, will allow Kyriakos to develop manufacturing methods for large-scale production of a variety of endohedral fullerenes.
Interview about nuclear materials research in Oxford
James Marrow (James Martin Chair in Energy Materials) has been interviewed by James Martin (benefactor of the Oxford Martin School) on the nuclear materials research in Oxford, and its contribution towards solving the global energy challenges of the 21st Century.
Recent graphene publications
A team led by Dr Jamie Warner and student Alex Robertson have published three papers in high impact journals (Nano Letters, ACS Nano and Nanoscale) on the atomic structure of graphene.
How safe is that Nuclear Reactor?
Prof George Smith FRS has been awarded the IoM3 Materials World Publication Award for 2013
Catching Quantum Mechanics in the act
Proceedings of the National Academy of Sciences February 14, 2013. DOI:10.1073/pnas.1208374110
Controlling the Orientation, Edge Geometry and Thickness of Chemical Vapor Depostion Graphene
ACS Nano 24 Jan 2013 DOI: 10.1021/nn3049297
Outreach - Y9 Materials and Chemistry Day
4 June 2013
Oxford University Open Days
26th and 27th June 2013
Electronic excitations and photoelectron spectroscopy - Oxford PES 2013
23rd-24th July 2013
Oxford University Open Day
20th September 2013
Gettering and Defect Engineering in Semiconductor Technology - GADEST 2013
22nd to 27th September 2013
Tungsten for Nuclear Applications
23-25 September 2013