Emergent nano-structuring on diamond by two-photon UV etching
R.P. Mildren
MQ Photonics Research Centre, Department of Physics and Astronomy,
Macquarie University, NSW, Australia
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Diamond’s extreme properties are of intense interest in applications such as quantum information processing, spin sensing, and Raman lasers. However, there is a lack of effective techniques for creating structures with the required resolution and without simultaneously introducing collateral damage to the surrounding material. Recently, it has been shown that exposure of diamond surfaces to sub-ablation fluences of ultraviolet radiation desorbs carbon from the surface at well defined rates and without inducing damage to the crystal structure [1, 2]. The phenomenon forms the basis for a promising novel method manipulation of the surface shape and properties of this most challenging of materials to process. Also, it enables exploration of one of the few opportunities in nature in which an optical process is able to selectively remove atoms from a surface [3]. However, many of the details of the process have not been investigated including the nano-scale properties of the machined surface that are critical in many applications.
We review here the nano-scale properties of the UV etched single crystal diamond surfaces. From a scaife polished as-supplied surface, etching produces patterns that progressively exhibit defined nano-structures with long range order. Investigations on other surfaces show that pattern morphology and frequency depend strongly on the incident pump polarization. Periodic deep sub-wavelength patterns are produced with morphologies depending upon the orientation of the incident polarization with respect to the crystal axis. Facetted ridge, grid, and wave-like patterns, are obtained for polarizations parallel to low-miller index directions on {100} and {110} diamond surfaces.Some patterns show highly periodic behaviour with good long range order. For small etch depths, the smallest feature size visible using the SEM was approximately 30 nm.
This paper provides detailed characterization of etching patterns as a function of facet, etch beam fluence and polarization in order to underpin future development of models for the photo-selective UV carbon ejection.We show that the etching provides a rapid, controllable, and area-scalable method for nano-patterning diamond surfaces. Of more fundamental significance, these observations comprise mesoscopic evidence for polarization dependent coupling of photons with localized and directional surface states corresponding to the carbon bonds. We believe that this result has important implications for atom-scale surface manipulation of diamond as well as possibly other covalently bonded materials.
The author acknowledges the valuable contributions to this work from A. Lehmann, C. Baldwin, J. Downes and C. Bradac.
References
[1] V.V. Kononenko, M.S. Komlenok, S.M. Pimenov, V.I. Konov, Quantum Electron.37, 1043–1046. (2007)
[2]R.P. Mildren, J.E. Downes, J.D. Brown, B.F. Johnston, E. Granados, D.J. Spence, A. Lehmann, L. Weston, A. Bramble, Opt. Mater. Express1, 576–585. (2011)
[3]A. Lehmann, C. Bradac, and R. P. Mildren, Nat. Commun. 5, 3341, (2014)