Pulsed laser deposited carbon electrodes for diamond radiation sensors

This project will explore and optimise pulsed laser deposition (PLD) low resistivity amorphous carbon coatings as electrode material for radiation sensors based on high purity, high resistivity synthetic diamond produced by chemical vapour deposition (CVD). It will be the first time that the PLD technique is used for this purpose and it offers flexible deposition parameters to optimise the amorphous carbon based electrode properties with a technology that is compatible with conventional lithography.Electronic grade synthetic single crystal diamond is of interest for a large variety of electronic devices, such as high frequency components, transistors, high power diodes and more. High quality diamond bulk properties are ideally suited for a wide range of radiation detector applications ranging from X-ray and neutron sensors to deep UV detection, particle timing and spectroscopy. However, the current limitation to diamond sensor technology is a lack of understanding and reproducibility of contact depositions to the bulk material. This project will focus on the characterisation and optimisation of diamond sensor performance in medical dosimetry and X-ray beam monitoring applications, where diamond with metal-free pure amorphous carbon electrodes uniquely fulfils the requirements placed on X-ray sensors by the current progress in these areas. The nature and quality of the electrical interface determines the stability and performance of diamond radiation detector devices. The project will exploit the flexibility of PLD which allows the investigators to deposit pure carbon layers under a variety of deposition conditions to control and adjust the structural and electronic contact layer properties. PLD will allow them to optimise the deposition parameters of the contact layers according to the radiation sensor performance during the first phase of the project. This will improve the understanding of the influence of the contact properties on the charge transport across the diamond/electrode interface.In the second phase, pad and position sensitive radiation sensors based on the results of the first phase of the investigation will be produced. The sensor performance, including the spatial variation of the response will be studied. The spatial resolution of the prototype position sensor will be investigated to estimate the potential of this development for future X-ray imaging and monitoring devices. The application of the contacting techniques developed is not limited to radiation sensing and every electronic application involving diamond, which can operate at temperatures up to several hundred Celsius and in challenging chemical environments, will benefit from an improved understanding of the processes affecting charge transport across electrode interfaces.

Element Six Ltd (e6) with its research facilities based in Ascot, is the world leader in the synthesis of high purity electronic grade bulk diamond. Diamond Detectors Limited (DDL) based in Poole(UK) was set up as an e6 venture in 2007, dedicated to the commercial exploitation of this material in radiation sensing applications. Since the end of 2008, BAE Systems has held 50% of the company investing up to 2M, which demonstrates the rising interest in diamond sensors in recent years. It is expected that the UK will continue to be world leading in diamond synthesis and fabrication for commercial diamond based radiation sensors. The experience and location of the Radiation and Medical Physics Group in Surrey, which has a good working relationship with DDL, is ideally suited to complement and support this commercial UK activity. DDL will support this project with technical input and access to their facilities. This connection will ensure timely and professional considerations of any potential commercial exploitations resulting from the project. The main two areas benefitting directly are: 1) X-ray beam diagnostics: There is a need for diamond sensors in the X-ray diagnostic community, particularly for high intensity sources (i.e. synchrotrons and free electron lasers). The Surrey group has a good relationship with synchrotron scientists involved in instrumentation and detector development in several laboratories, including the Diamond Light source (DLS), the European Synchrotron Radiation Facility (ESRF) and DESY - host to the European free electron laser (XFEL).The DLS is a world class national UK synchrotron facility that has been established during the last decade and demands a UK commitment to synchrotron science for the future in order to optimise the benefit of this large investment. This work will continue to develop in discussion and liaison with colleagues at the light sources who have expressed their support for this project in the attached letters. They have a direct interest in obtaining usable beam diagnostic devices to improve their facilities for the benefit of all users; in this way, our work will support research programmes carried out at synchrotrons that span a large variety of science and engineering topics. 2) Medical dosimetry: This project can lead to the development of medical dosimetry devices, particularly for treatment planning and quality control of radiotherapy treatment delivery, where the trend is increasingly moving to higher resolution spatially defined irradiation fields. These will improve the accuracy of cancer treatment, reduce unwanted side effects and thus benefit health care. Results will be discussed with colleagues in the Medical Physics department of the Royal Surrey County Hospital who support this project and significant progress will be presented at medical physics workshops and conferences. In particular, the Surrey Physics department is part of the Radiation Instrumentation Theme of the SEPnet (South East Physics Network) consortium that is planning to hold focused workshops on detector developments for medical applications. Amorphous carbon electrode diamond sensors also open avenues to additional detector applications that benefit from diamonds material properties: a) Single particle sensitive sensors for biological and medical research that require non-toxic devices: The EPSRC Ion Beam Centre hosted by the University of Surrey is a world leading facility in targeted single cell irradiation which can benefit from thin position sensitive transmission detectors. b) Solar blind UV imaging devices for deep UV photolithography: Deep UV sources and their characterisation are required to reduce feature and thus device sizes in semiconductor industry. c) Radiation hard neutron detectors with low gamma sensitivity: Neutron detectors with these characteristics will benefit security applications as well as the renaissance of power generation by nuclear fission in the UK.