A new surface pretreatment approach for enhancing diamond nucleation

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A new surface pretreatment approach for enhancing diamond nucleation Qi Hua Fan,a) A. Fernandes, E. Pereira Department of Physics, University of Aveiro, 3810 Aveiro, Portugal

J. Gra´cio Department of Mechanical Engineering, University of Aveiro, 3810 Aveiro, Portugal (Received 20 August 1999; accepted 29 September 1999)

In this paper we present a new approach of surface pretreatment for enhancing diamond nucleation. The copper substrates were fixed inside a plastic cylinder container with diamond powder diluted in water. This container was coupled to a vibration unit moving up and down at ∼300 cycles/min with a stroke of 15 mm. Finally, samples pretreated for 30 min were deposited with diamond. A high nucleation density comparable to that on substrate abraded with diamond powder was achieved. This method proved to be more effective than our ultrasonic treatment, keeping the advantages of surface preservation. Being simple and straightforward, this “shaking” pretreatment most fits the cases where a thin interlayer has to be used (like diamond coating on steel) and where the samples have a complex shape.

Chemical-vapor-deposited (CVD) diamond possesses many extreme properties that make it attractive in several applications.1–4 In most cases sufficient film/substrate adhesion is required. It has been realized that the coating adhesion results from both chemical bonds and mechanical interlock.5 Therefore, a high nucleation density and adequate surface roughness can promote the adhesion.6 One of the most common and effective approaches used for enhancing the diamond nucleation is abrading the substrate surface with diamond paste or diamond powder.7–14 Abrasion with smaller diamond particles results in higher nucleation density8,14 but it implies very smooth surfaces (low roughness) with possible decrease in the effect of the mechanical interlock. Moreover, some substrates can not withstand severe mechanical abrasion. For example, when a thin intermediate layer—like Ti or Si—has to be used to enhance the adhesion of diamond coatings on strong carbon dissolving materials (like steel), scratching the substrate can destroy the interlayer. An alternative to diamond nucleation enhancement is ultrasonic treatment, once it avoids severe surface damage.15–24 In this method, diamond powder is diluted in a solvent. The sample is immersed in the solvent inside a container and treated in an ultrasonic field. In order to obtain effective surface treatment, one needs to select carefully a set of parameters: (i) diamond particle size; (ii) frequency and power of the ultrasonic source; (iii)

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Address all correspondence to this author. e-mail: [email protected]

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http://journals.cambridge.org

J. Mater. Res., Vol. 14, No. 12, Dec 1999 Downloaded: 18 Mar 2015

solvent and the powder/solvent ratio. Obviously, such a complex procedure may require extensive experimental work. Therefore, results concerning the efficiency of ultrasonic treatment reported in literature are often confusing, pr