Controlled synthesis of high quality micro/nano-diamonds by microwave plasma chemical vapor deposition Alastair Stacey a , Igor Aharonovich a, ⁎, Steven Prawer a , James E. Butler b a School of Physics, University Of Melbourne, Melbourne, 3010, Australia b Gas/Surface Dynamics Section, Naval Research Laboratory, Washington DC 20375 USA abstract article info Article history: Received 18 April 2008 Received in revised form 4 August 2008 Accepted 20 September 2008 Available online 30 September 2008 Keywords: Diamond crystal Chemical vapor deposition Color center Diamond containing engineered color centers is rapidly becoming a medium of choice for quantum information applications. Many of the dramatic recent results in this field have been demonstrated in diamond nano-crystals. Here we demonstrate controlled synthesis of spatially isolated high quality micro- and nano-diamonds using a microwave plasma chemical vapor deposition technique (MPCVD). The growth from nano-seeds rather than other nucleation techniques allows improved control over the final size of the crystals and the density of the crystals on the substrate. The growth rate of the diamond crystals was found to be 22 nm/min. Various parameters of the growth sequence were studied and the microwave power density was found to have the major influence on the crystal morphology, with the best quality diamond formed under conditions of relatively high pressure and plasma density. Our ability to control size, dispersion and levels of perfection constitutes an enabler for future quantum information applications utilizing diamond color centers. © 2008 Elsevier B.V. All rights reserved. 1. Introduction Diamond is a unique platform for quantum information processing [1], possessing an unprecedented range of properties. For applications in Quantum Key Distribution, such as the use of diamond as a source of single photons, isolated high quality diamond crystals of subwave- length size are highly desirable because the emitted photons can be collected with higher efficiency than is possible from large single crystals or continuous films. Therefore, the demand for controlled synthesis of submicron size, individual diamond crystals containing color centers has increased dramatically in recent years [2–4]. A recent Coherent Population Trapping experiment using the NV color center in a bulk crystal [5] has highlighted the need for precise control over the attributes of the host diamond to successfully conduct quantum optical experiments. For the case of nano-diamond in particular, a number of factors may influence the quantum properties of the color centers used for QIP. These include the influence of surface states, the incorporation of impurities and the presence of defects and non- diamond bonding. While growth of high quality homoepitaxial single crystal has been demonstrated [6] and recipes for the growth of continuous nano-diamond and ultranano-diamond films on non- diamond substrates are well established [7–10], the production of high quality low impurity content and isolated individual nano- crystals remains a challenge. Furthermore, methods for the controlled growth of isolated nano-diamond particles using CVD techniques are far less developed than the growth of diamond films and large single crystals. Of particular interest is the ability to deposit particles with low defect density, with well defined morphology and size, which are well dispersed over the substrate, allowing individual addressing and manipulation. Despite advances in techniques such as biased enhanced nuclea- tion, the formation of dispersed, individual high quality micro- or nano-diamond crystals on a non-diamond substrate is still a challenge. Various groups have reported the formation of chemical vapor deposition (CVD) crystalline diamond using a variety of CVD methods including MPCVD [11–13] and hot filament CVD [14,15]. Seeding or treatment of the substrate is required to initiate or enhance diamond nucleation. Techniques include polishing of the substrate with diamond powder, ultrasonic treatment of the substrate in a slurry of micron or smaller sized diamond powder [16] or nucleation from energetic species [17]. However, it is expected that mechanical treatments would damage the surface of the substrate along with any topographical features which have been manufactured onto the surface. In particular formation of nano-diamond of optimum size and with optical and quantum properties approaching that of the best quality single crystal diamond has not yet been accomplished. We have begun to address the problem of controlling the growth of individual submicron diamond crystals by applying the high quality homoepitaxial techniques used on large samples to growth on tiny nano- diamond seeds, while also providing a technique for controlled dispersion of these seeds to promote the growth of isolated high quality nano- diamonds. We used a MPCVD technique to synthesize the diamonds and demonstrate that the use of a high microwave power density leads to the Diamond & Related Materials 18 (2009) 51–55 ⁎ Corresponding author. E-mail address: i.aharonovich@pgrad.unimelb.edu.au (I. Aharonovich). 0925-9635/$ – see front matter © 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.diamond.2008.09.020 Contents lists available at ScienceDirect Diamond & Related Materials journal homepage: www.elsevier.com/locate/diamond