Development of optical spin-resonance methods with advanced light sources

Lead Research Organisation: University of Manchester
Department Name: Electrical and Electronic Engineering

Abstract

The optical and electronic properties of semiconductors and insulators are strongly dependent on the presence of defects contained within them, and their study has profound influence on the development of new optoelectronic materials. Electron spin resonance (ESR) measurements are particularly valuable in determining the electronic and structural properties of the defects, but coupling of light excitation/detection capabilities within the ESR experiment provides extremely valuable additional information. Two traditional generic methods have been deployed in this respect. (i) Monitoring of the ESR defect signals during illumination with tuneable light sources can provide additional optical parameters of the defects concerned, such as trap depth and the location of excited states (essentially a marriage of optical absorption experiments and ESR). (ii) Where the luminescence of a material is spin dependent (e.g. in donor-acceptor pair recombination), ESR signals can be carried by the luminescence (Optical Detection of Magnetic Resonance, ODMR), and this provides direct and unequivocal attribution of particular defects with specific luminescence emission processes.ODMR has proved particularly successful in understanding the link between defects and luminescence in semiconductors of moderate band-gap energies (Eg<~3eV) where suitable laboratory light excitation sources are widely available. In contrast, virtually no comparable work has been undertaken on wider-gap materials such as Boron Nitride and Aluminium Nitride (Eg~6eV), yet these classes of materials are potentially of great future importance in developing UV optoelectronic devices (lasers, LEDs etc). The main obstacle to such studies is in the provision of suitable high-energy lab-based light excitation sources. However, appropriate light sources for these experiments are available both in this country and overseas; synchrotron light sources and more complex laser systems (both optical and free-electron) can potentially be exploited for the research. Furthermore, the possibilities for combing both ODMR and the associated Optical Detection of X-ray Absorption (ODXAS) is particularly attractive, since the combined measurement method would enable a direct link between the optical emission properties of a sample, and structure of both the lattice, and the defects contained within it. As this approach is completely unique, no suitable experimental capabilities exist worldwide at present that can undertake such science. A core goal of the proposed work is thus to develop such capabilities, and demonstrate the effectiveness by application to a number of wide band-gap materials of particular interest to the development of new UV optoelectronic devices (LEDs, lasers etc), and in the understanding of materials suitable for radiation monitoring deployed in the fields of cancer radiotherapy. The work will establish the UK at the forefront in developing such advanced analytical methods, and is a necessary pre-requisite to new experiments on the planned advanced light sources such as 4GLS and XFEL.
 
Description This work involved designing and demonstrating an electron spin resonance system that could be used for optical (luminescence) detection of x-ray excited structures. A key point to this research was to achieve a small size/mass system which could be transported and used at synchrotron radiation sources.
Exploitation Route This work was carried out in collaboration with UK based industry and the novel concepts of cryogenic design, microwave cavity design and optical/x-ray coupling were transferred to associated company.
Sectors Chemicals,Electronics

 
Description Development of Optical Spin Resonance Methods With Advanced Light Sources
Amount € 76,800 (EUR)
Funding ID EP/F045905/1 
Organisation Engineering and Physical Sciences Research Council (EPSRC) 
Sector Academic/University
Country United Kingdom
Start 09/2008 
End 04/2010
 
Title X-Ray excited AFM charge imaging 
Description We have developed scanning probe microscopy tools which can exploit synchrotron radiation excitation for imaging charge localisation on the nano-scale. 
Type Of Material Improvements to research infrastructure 
Year Produced 2006 
Provided To Others? Yes  
Impact This technology has been used at the Advanced Photon Source (Argonne labs) , the SRS and Diamond Light Sources. The technique has shown that charge localises at twisted regions of single walled carbon nanotubes and at step edges on Si surfaces. 
 
Title X-Ray excited optically detected spin resonance 
Description We have developed (in collaboration with Brucker UK) an x-ray pumped EPR system which can detct spin states in wide gap solids by luminescence d detection. 
Type Of Material Improvements to research infrastructure 
Year Produced 2011 
Provided To Others? Yes  
Impact This development is currently embedded within the EPSRC national EPR Facility in Manchester where it will be further developed. This tool is planeed for development commercially by Brucker Uk 
 
Description TU Delft 
Organisation Delft University of Technology (TU Delft)
Country Netherlands 
Sector Academic/University 
PI Contribution We have developed a process technology which has demonstrated large improvement in dosimetry sensitivity
Collaborator Contribution Background knowledge and measurement skill transfer.
Impact We are planning a joint research activity/funding bid.
Start Year 2008