Exploring Nano-Crystalline Particles
- Chief Supervisor
- Dr. James Sullivan (ANU)
- Supervisors
- Prof. Yasuyoshi Nagai (Tohoku University)
- Prof. Stephen Buckman (ANU)
- Dr. Anita Hill (CSIRO)
- Centre Nodes
- CSIRO
- ANU
- Collaborators
- Tohoku University
The study of nano-crystalline embedded particles (NCEP) in materials is an attractive subject because of their application prospects as quantum devices. However, until recently, there have been no experimental tools available to probe them directly, due to the fact that probes employed in conventional methods have no site-selectivity. Conventional probes interact equally with both the NCEP and the host material, making it difficult to extract the weak interaction signal of the NCEP from the much stronger background of the host.
Recently, it has been found that positrons are excellent site-selective probes for NCEPs. It is well known that positrons are sensitive to vacancy-type defects and it has now been confirmed that positrons can be confined in NCEPs with positron affinities higher than that of the host, even if the NCEPs are free from defects. This affinity-induced confinement has been dubbed a "positron quantum-dot-like state". The positron in the quantum-dot-like state annihilates with an electron of the NCEP exclusively, and provides site-selective information on the electronic structure by analysis of the two emitted annihilation gamma rays. Using this phenomenon, the atomic and electronic structure of the NCEP can be directly revealed.
However, due to the lack of a high-resolution positron beam, there have been no experiments to measure the positron affinity, the basis of the positron quantum-dot-like state and the important physical quantity that determines the sensitivity of positrons to the NCEPs. Current analysis relies solely on theoretically calculated values of this property. We will utilize the positron beam facility at ANU, with an energy resolution as high as 0.01eV, to accurately measure the positron affinities of various materials of interest.
The successful candidate will have an aptitude for experimental physics, a capacity to learn how to operate complex experimental apparatus and an ability to work in a team with other students and scientific staff. She/He will be required to develop a new exerimental station for the positron beamline to make these world first scientific measurements. She/He will develop many general experimental and scientific skills including handling positron beams, clean surface preparation techniques, precision instrumentation, high vacuum technology, computer control of the experiment using LabView software, data analysis and interpretation, manuscript writing and scientific communication. Travel to Japan to collaborate with the Tohoku Unoversity team may also be required.
