Optical properties of synthetic diamond

(supervisor: Rachel Cross)

Nature of project: experimental, data analysis

Available to full-time physicists or joint students.

Project description and methodology

With its wide energy band gap, diamond has many applications that exploit its optical properties that need to be measured out over a wide wavelength range from the UV to the far IR. These applications include ultra-transparent optics, optics for extreme environments, radiation sensors and quantum computing. Synthetic diamonds, fabricated using Chemical Vapour Deposition (CVD) or High Pressure High Temperature (HPHT) synthesis, are becoming more available and widely used, and it is crucial to determine and control properties such as composition, structure and optical absorption. Trace concentrations of defects in the crystal can lead to measurable differences in the optical properties (e.g. absorption, emission) and the control of these defects enables the engineering of materials for specific applications based on the optical response. For example, nitrogen impurities are common in natural and synthetic diamond and can lead to changes in colour from transparent to dark brown and whose spin can be controlled to provide the elements for quantum computing. This project will apply photoluminescence spectroscopy to synthetic diamond using a range of excitation sources, such as LED's and lasers. Materials synthesized and treated using various methods will be investigated using high resolution spectroscopy. Suitable instrumentation will be applied to obtain spectra that will be analysed in intensity and energy and interpreted in terms of optically-active defects in diamond.

A successful project will develop beyond the above in one/some of the following directions:
This project could be developed by extending to other excitation sources, such as x-rays and electrons. It could also be extended to materials that can be processed in the same environment as the measurement. For example this could involve changing the optical properties of the near-surface region by annealing and irradiation in vacuum. This has relevance in particular for optical centres in diamond that are used in quantum computing and sensing. To be useful for such applications, the defect centre needs to emit efficiently in the visible spectrum at room temperature and have the correct charge and spin state. There may be opportunities to develop the instrument and also software for control and data analysis.

When considering where to take your project, please bear in mind the time available. It is preferable to do fewer things well than to try many and not get conclusive results on any of them. However, sometimes it is useful to have a couple of strands of investigation in parallel to work on in case delays occur.

Additional scope or challenge if taken as a Year-4 project: The MPhys/MEng project will focus on one particular defect in diamond that has been reported to have many of the essential properties required for an optical qubit - the nitrogen-vacancy (NV) defect. The spin state of this state can be changed by microwave excitation and its energy can also be modified by a magnetic field. This project will involve the design of a combined microwave excitation and luminescence detection system that can be used, for example, as a sensitive, solid-state magnetometer.

Initial literature for students:

  1. Theory of defects in solids : electronic structure of defects in insulators and semiconductors, A. M. Stoneham (Primo)
  2. Optical characterization of semiconductors : infrared, raman, and photoluminescence spectroscopy S. Perkowitz (Primo)
  3. Optical Properties of Solids, Mark Fox (Primo)

Novelty, degree of difficulty and amount of assistance required

Moderate difficulty that involves the use of research equipment. The MPhys is a particularly challenging instrumentation project.

Project milestones and deliverables (including timescale)

milestoneto be completed by
Identification of materials end of October
Interpretation of spectra on standard materialChristmas
First luminescence spectra recordedend of February
Instrumentation finalised and data collection Easter

Students taking this project will have to submit a full risk assessment form