PHYSICAL REVIEW B 83, 224206 (2011) Diamond membrane surface after ion-implantation-induced graphitization for graphite removal: Molecular dynamics simulation Amihai Silverman Taub Computer Center, Technion-IIT, Haifa32000, Israel Joan Adler Department of Physics, Technion-IIT, Haifa 32000, Israel Rafi Kalish Department of Physics and Solid State Institute, Technion-IIT, Haifa 32000, Israel (Received 14 February 2011; revised manuscript received 8 May 2011; published 28 June 2011) Fabrication of diamond membranes, wherein photonic crystals and other nanosized optical devices can be realized, is of great importance. Many spintronic devices are based on specific optically active atomic structures in diamond, such as the nitrogen-vacancy center, and rely on the membrane’s performance. One promising approach for realizing such membranes is by creating a heavily damaged layer (rich in broken bonds) in diamond by ion implantation. Following annealing, this layer converts to graphite, which can be chemically removed, leaving a free-standing diamond membrane. Unfortunately, the optical properties of the exposed diamond surface (the diamond-vacuum interface) of such membranes currently are insufficient for high-quality photonic devices. We present molecular dynamics studies of the atomic structure of the etchable graphite/diamond interface. Different implantation and annealing conditions are simulated. The results show that cold implantation, followed by high-temperature annealing (>1500 ◦ C) leads to the creation of the sharpest diamond-etchable graphite interface, which should exhibit optimal optical properties among diamond membranes created by the implantation/graphitization method. DOI: 10.1103/PhysRevB.83.224206 PACS number(s): 07.05.Tp, 31.15.xv, 81.05.uj, 68.35.Ct I. INTRODUCTION There is great interest in manipulating and guiding single photons in microsized diamond structures. This is because they are important for developing potential applications of single-photon emitters in diamond as qubits and other building blocks for various quantum devices. 1 The photons require an emission source. One of the most promising centers for emitting such photons, exhibiting the required properties, is the negatively charged nitrogen-vacancy defect center in diamond. 2 Obviously, the optimal material to transport these photons is diamond itself, since it has unsurpassed optical and mechanical properties and the emitting center is naturally embedded therein. In order to achieve this goal, diamond membranes need to be formed with submicrometer thicknesses wherein photonic crystals can be realized. Such a membrane should have optimal optical properties (high transparency and edge reflectivity) to allow undisrupted photon transfer through it and to be of some 200 nm thickness (comparable to the wavelength of the emitted photon in diamond). The diamond membranes are commonly realized by taking advantage of the fact that heavily damaged diamond, following annealing, tends to convert to etchable graphite. 3 A damaged diamond layer, rich in broken bonds, is created at the required depth by ion implantation. High-temperature annealing is then carried out to convert those regions of the damaged diamond, in which the density of broken bonds exceeds a certain value, to graphite. Regions in front (below in our figures) and beyond (above in our figures) the main damage peak (in which the majority of carbon atoms remain sp 3 bonded) will anneal back to diamond. 4 The graphitized layer can be etched away by applying chemical or electrochemical methods leaving a diamond membrane (the thickness of which is determined by the implantation conditions) that can be lifted off from the substrate and in which the desired optical structure, such as photonic crystals, can be realized. This procedure, when combined with focused ion-beam processing of selected spots in the membrane, has yielded promising optical devices. 5 Unfortunately, the performance of such devices is, as yet, unsatisfactory. This is possibly because the optical quality of the diamond-vacuum interface following ion-beam- induced graphitization and graphite removal is nonideal. Therefore, it appears that application of the current ion- implantation/graphitization methods do not yield the optical qualities that would enable the utilization of such lift-off meth- ods to obtain high-quality waveguides and other nanosized optical devices. Thus, understanding the properties of this interfacial layer and finding ways to minimize its detrimental effects on the reflectivity of photons impinging from within the membrane are of major importance. Some laboratory studies along these lines have recently been performed. 6 The structure of the exposed diamond surface following graphite etching has been measured by grazing-angle ion-channeling experiments. Information on the perfection of the very first atomic layers of the exposed diamond surface and which treatments to this surface can improve its quality has been obtained. We present results of computer simulations of the evolution of graphite and diamond in a diamond sample exposed to carbon-ion implantations resulting in damage to the sample. On annealing, some initially damaged regions regrow as diamond, whereas, the regions that contain a high density of broken bonds result in a graphitic layer within the diamond sample. Since graphite contains carbon atoms with a 224206-1 1098-0121/2011/83(22)/224206(9) ©2011 American Physical Society