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Study of growth of intrinsic and doped NCD layers on organic polymer based substrates

Andrew Taylor1, 2*, Vaclav Petrak1, 2 and Milos Nesladek3
  • 1 Nano6 s.r.o., Czechia
  • 2 Institute of Physics, ASCR, v. v. i, Czechia
  • 3 IMOMEC, IMEC, Institute for Materials Research, University Hasselt, Belgium

Abstract Growth of nano-crystalline diamond (NCD) based layers on plastic substrates has been demonstrated in [1]. In this article we aim to expand this work by the use of a pulsed microwave plasma enhanced chemical vapour deposition apparatus with linear antenna delivery system [2] leading to large area growth (50cm x 30cm) with controlled sp3 purity, and therefore enabling doping of these layers via the addition of boron (B) to the growth chemistry, on various polymer based substrates. We report on the systematic optimisation of growth conditions for preparation of intrinsic and B doped NCD layers on organic based polymer substrates, such as polyimide, polyphenylene sulphide (PPS) and polytetrafluoroethylene (PTFE), whose relatively low melting points (PPS: 281°C, PTFE: 327°C and Polyimide: ~400 °C) limit their use as substrates in conventional CVD growth processes. By using the apparatus described in [2] and H2/CH4/CO2 gas mixtures, with added trimethylboron as a dopant, deposition of NCD thin films has been achieved on these organic polymer based substrates. Prepared layers have been studied with Raman spectroscopy to ascertain sp3/sp2 ratio and indicate B incorporation. AFM and SEM techniques have been used to confirm coverage and crystalline quality of the layers in order to ascertain ideal growth conditions. Resistivity (van der Pauw method) measurements have been utilised to confirm layer conductivity. Experimental Conditions All experiments were carried out using a pulsed microwave plasma enhanced chemical vapour deposition apparatus with linear antenna delivery system [2]. Three temperature regions were studied i) “standard” >500°C, ii) “low” ~400°C and iii) “very low” <250°C. Within each temperature regime the following parameters were investigated to achieve optimal NCD growth: a) gas chemistry (H2, CH4 and CO2 with and without B doping), b) process pressure, c) growth time, d) active substrate temp control (heating / cooling) and e) MW conditions (power and pulsing frequency). Various polymers, including PPS (Tecatron™), PTFE (Teflon®) and Polyimide (Kapton®), were tested for their compatibility with MW PECVD growth conditions along with standard reference substrates such as silicon, soda-lime glass, Corning EagleXG® glass and quartz. All substrates were seeded with NanoAmando® detonation diamonds with some areas left un-seeded as a reference. Several samples were placed in the reactor to simulate large area deposition. Results and discussion Intrinsic and B doped growth at standard temperatures (>500°C) produced high quality NCD layers (see Raman spectra in Figures 1A and 1B) on reference substrates. Incorporation of B in NCD is evidenced in Raman spectra by related features at 500 cm-1, 1230 cm-1 and shifted sp3 position as well as a measured electrical conductivity of ~20 S.cm. However, these temperatures are too high to be used with polymer based substrates. At low deposition temperatures (400°C) growth of conductive B doped NCD was achieved on standard microscope soda-lime glass slides, which have a strain point at 511°C. Raman spectra from this film show reduced Fano related features and increased sp2 content, which is reflected in a 10x reduction in electrical conductivity compared with growth at standard temperatures (>500°C). Also noted in the Raman spectra from the intrinsic layers was a small contribution from graphitic related D and G bands. By further reduction of the deposition temperature to 250oC, intrinsic NCD layers were produced on all polymer based substrates. However, even at these conditions these substrates suffered from chemical etching due to the H rich plasma conditions used during growth. To further protect these types of substrates, Ti interlayers or thicker nanodiamond seeding was used. The use of both of these protection techniques enabled repeatable NCD growth on thin (6µm) Kapton® samples (see Figure 2B). Films produced on Kapton® exhibited characteristic NCD Raman with a contribution from graphitic related D and G bands (see Figure 2A) and a crystallographic morphology (see Figures 2C and 2D). Conclusions Conditions for large area extremely low temperature (250°C) intrinsic NCD growth have been investigated. Intrinsic NCD layers have been successfully produced on various polymer based substrates. Conducting B doped NCD layers have been produced at low temperatures in the range of 400°C. This reduction in the growth temperature window of NCD films opens up the possibility to integrate NCD and therefore its applicable properties (biocompatibility, thermal conductivity, electrical resistance and conductivity) into existing technologies based, for example, in the biomedical and electronics fields.

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Acknowledgements

Financial support from FP7-NMP-2011-SMALL-5; NMP.20011.1.4-4 (MERIDIAN) is gratefully acknowledged.

References

References
1. K Tsugawa et al: PHYSICAL REVIEW B 82, 125460 2010
2. A Taylor et al: Diamond & Related Materials 20 (2011) 613–615

Keywords: Diamond, Nanodiamonds, chemical vapor deposition (CVD), Polyimide, Boron doping

Conference: MERIDIAN 30M Workshop, Brixen, Italy, 25 Sep - 25 Sep, 2014.

Presentation Type: Oral Presentation

Topic: Neuroengineering

Citation: Taylor A, Petrak V and Nesladek M (2014). Study of growth of intrinsic and doped NCD layers on organic polymer based substrates. Front. Neuroeng. Conference Abstract: MERIDIAN 30M Workshop. doi: 10.3389/conf.fneng.2014.11.00006

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Received: 06 Nov 2014; Published Online: 06 Nov 2014.

* Correspondence: Mr. Andrew Taylor, Nano6 s.r.o., Kladno, Czechia, andy.taylor@nano6.eu