Identification of dislocations in synthetic Chemically Vapor Deposited. diamond single crystals: SUPPORTING ADDITIONAL INFORMATION

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1 Identification of dislocations in synthetic Chemically Vapor Deposited diamond single crystals: SUPPORTING ADDITIONAL INFORMATION A. Tallaire *, T. Ouisse, A. Lantreibecq, R. Cours, M. Legros, H. Bensallah, J. Barjon, V. Mille, O. Brinza, J. Achard LSPM-CNRS, Université Paris 13, 99 avenue JB Clément Villetaneuse, France LMGP-CNRS, Université Grenoble Alpes, 3 Parvis Louis Néel, Grenoble Cedex 1, France CEMES-CNRS, 29 rue Jeanne Marvig, Toulouse Cedex, France 1. Sample fabrication 2. Birefringence imaging 3. Plasma etching 4. TEM measurement 5. Cathodoluminescence measurement 6. Comparison of etch-pits and birefringence without ICP etching step

2 1. Sample fabrication A commercial High Pressure High Temperature (HPHT) (100)-oriented single crystal diamond purchased from Sumitomo was used as a substrate. A 500 µm-thick diamond layer was epitaxially grown by high-power plasma assisted CVD in a home-made growth system under optimized conditions reported elsewhere [1] (step S1). The gas mixture consisted of high-purity H 2 and CH 4 with no intentional addition of impurities such as nitrogen. The substrate was then laser cut away and the CVD film polished on both sides resulting in a 400 µm-thick, 4 4 mm² slab by the company Almax EasyLab (step S2). The UV PL image showed no evidence from nitrogen incorporation that usually leads to a red luminescence from NV centers but only a dim blue luminescence (Fig. 1). Figure 1. Images of the freestanding CVD diamond plate under (a) visible and (b) UV light acquired using the DiamondView TM equipment. The round shape feature in the centre is the substrate holder.

3 In order to remove the subsurface damage induced by polishing, dry etching was carried out using an Inductively Coupled Plasma (ICP Corial 200IL) with an Ar/O 2 mixture (1:1). A 500 W plasma power was used with a substrate bias of 280 W and a pressure of 4 mbar for 10 minutes [2]. This treatment aims at removing around 2 µm of material off the surface. These processes have already been reported using either oxygen or a chlorine-based chemistry [3] and are known to lead to a low roughness. The effectiveness of this treatment is also illustrated in Fig. 3 below and associated comments. To facilitate the spatial localization of dislocations and a comparison with different analysis techniques, a tungsten grid that consists of an array of µm² squares was deposited on the surface (step S3). To this end, standard electron lithography in a Scanning Electron microscope (ZEISS SupraVP45) and ion beam sputtering in a (Gatan PICS) were used. Tungsten was chosen as it is able to withstand several minutes of harsh H 2 /O 2 plasma etching. The thickness of the W film was around 20 nm. 2. Birefringence imaging Birefringence was used as a fast non-destructive technique to visualize dislocations. In this study, we used the rotating polarizer method using a green light source of wavelength λ = 546 nm and Zeiss Neofluar objectives with magnifications ranging from 2.5 to 100 [4]. All the birefringence images are plots of the absolute value of sin δ, where δ is the phase shift. From this measurement it is possible to get access to the stress field induced by a dislocation. In favorable cases [5], using an adapted model, a Burgers vector attribution can be proposed as a best fit of the observed pattern. A drawing of the experimental set-up is given as an illustration in Fig. 2.

4 Figure 2. Illustration of the experimental set-up used for measuring birefringence of the CVD diamond plate. 3. Plasma etching Plasma etching (step S4) was performed in-situ in a CVD diamond growth reactor (Plassys BJS150) using a mixture of 2 % O 2 in H 2. A pressure of 200 mbar and an injected microwave power of 3 kw were used for 10 minutes (step S3). TDs were preferentially etched leaving a typical pattern of inverted pyramids with varying sizes. Images of each region of the grid were then acquired using a Keyence VK9700 3D laser microscope. This technique allows assessing the depth of etch features with a nanometer accuracy. 4. TEM measurement For TEM analysis, thick slabs (1-2 µm thick, µm long) were cut around selected etchpits in a Focused Ion Beam (FIB) FEI Helios 600i SEM-FIB, using Ga ions with intensities ranging from 21 to 0.08 na so that the centre of the etch-pits was included (step S5). The slabs were then thinned down to nm by ion etching at angles ranging from 15 to 30 angles with respect to the surface normal to ensure that the slab contained the apex of the etch pit (Step S5). TEM observations and measurements were both performed on a JEOL 2010

5 and Philips CM20FEG operated at 160 kv to avoid radiation damages. The burgers vectors of dislocations were identified using the g.b=0 technique [6] by varying the diffraction vector either with a simple tilt or a tilt-rotation sample holder. 5. Cathodoluminescence measurement Prior to CL analysis, the sample was re-polished on a rotating scaife wheel (Coborn Engineering) in order to remove etch-pits, until the surface remained optically smooth. The wheel was conditioned with 1 µm-size diamond powder. An ICP treatment identical to that described in section 1 was carried out so as to remove subsurface mechanical damage. CL imaging was then performed with a Horiba Jobin Yvon optical system using a 10 kv electron beam produced in a JEOL7001F scanning electron microscope equipped with a field-emission-gun. The diamond film was coated with a semi-transparent gold layer in order to conduct away electrical charges and cooled down to 80 K thanks to a liquid helium cold stage. The luminescence was collected by a parabolic mirror and focused on a monochromator equipped with a 600 grooves/mm diffraction grating. Monochromatic CL images were taken by filtering the near-band-edge diamond emission (excitonic recombination at 235 nm) through the monochromator equipped with a UV photomultiplier detector synchronized with the beam scanning. 6. Comparison of etch-pits and birefringence without ICP etching step The effectiveness of the ICP treatment used prior to revealing dislocations can be evidenced when comparing birefringence patterns and etch-pits without using this step. It can be seen in Figure 3 that no correspondence can be made. The density of etch-pits is very high as compared with cross-shape features. Moreover some etch-pits are aligned along lines indicating that they result from subsurface damage due to mechanical polishing.

6 Figure 3. (a) Laser microscope and (b) birefringence images of the same region of the sample when no ICP treatment was used prior to H 2 /O 2 plasma etching. The red arrow indicates the position of a unit dislocation. The tungsten grid used as a reference mark is visible on both images. [1] J. Achard, F. Silva, A. Tallaire, X. Bonnin, G. Lombardi, K. Hassouni, A. Gicquel, High quality MPACVD diamond single crystal growth: high microwave power density regime. J. Phys. D, 40 (2007) [2] J. Achard, A. Tallaire, V. Mille, M. Naamoun, O. Brinza, A. Boussadi, L. William, A. Gicquel, Improvement of dislocation density in thick CVD single crystal diamond films by coupling H2/O2 plasma etching and chemo-mechanical or ICP treatment of HPHT substrates. physica status solidi (a), 211 (2014) [3] C.L. Lee, E. Gu, M.D. Dawson, I. Friel, G.A. Scarsbrook, Etching and micro-optics fabrication in diamond using chlorine-based inductively-coupled plasma. Diam. & Relat. Mat., 17 (2008)

7 [4] H.T.M. Le, T. Ouisse, D. Chaussende, M. Naamoun, A. Tallaire, J. Achard, Birefringence microscopy of unit dislocations in diamond. Crystal Growth & Design 14 (2014) [5] H.T.M. Le, T. Ouisse, D. Chaussende, Critical assessment of birefringence imaging of dislocations in 6H silicon carbide. Journal of Crystal Growth 2012, 354, (1), [6] D.B. Williams, C.B. Carter, Transmission Electron Microscopy, A Textbook for Materials Science, Springer 2009