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A microwave plasma chemical vapor deposition system was used to synthesize cubic boron nitride (cBN) coatings on diamond seeded silicon substrates using direct current (DC) bias. Effects of the argon (Ar) flow rate and bias voltage on the growth of the cBN coatings were investigated. Hydrogen (H2), argon (Ar), a mixture of diborane in H2 (95% H2, 5% B2H6), and N2 were used in the feed gas. A DC bias system was used for external biasing of the sample, which facilitates the goal of achieving sp3 bonded cBN. Fourier Transform Infrared Spectroscopy (FTIR) and X-ray Photoelectron Spectroscopy (XPS) revealed the existence of sp3-bonded BN in the produced samples. With increasing Ar flow, the cBN content in the coating increases and reaches a maximum at the maximum Ar flow of 400 SCCM used in this study. High-resolution XPS scans for B1s and N1s indicate that the deposited coating contains more than 70% cBN. This study demonstrates that energetic argon ions generated in a microwave-induced plasma significantly increase cBN content in the coating.
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Effects of direct current bias on nucleation density of superhard boron-rich boron carbide films made by microwave plasma chemical vapor deposition
Abstract We report bias enhanced nucleation and growth of boron-rich deposits through systematic study of the effect of a negative direct current substrate bias during microwave plasma chemical vapor deposition. The current flowing through a silicon substrate with an applied bias of −250 V was investigated for a feedgas containing fixed hydrogen (H2) flow rate but with varying argon (Ar) flow rates for 1330, 2670, and 4000 Pa chamber pressure. For 1330 and 2670 Pa, the bias current goes through a maximum with increasing Ar flow rate. This maximum current also corresponds to a peak in substrate temperature. However, at 4000 Pa, no maximum in bias current or substrate temperature is observed for the range of argon flow rates tested. Using these results, substrate bias pre-treatment experiments were performed at 1330 Pa in an Ar/H2plasma, yielding the maximum bias current. Nucleation density of boron deposits were measured after subsequent exposure to B2H6in H2plasma and found to be a factor of 200 times higher than when no bias and no Ar was used. Experiments were repeated at 2670 and 4000 Pa (fixed bias voltage and Ar flow rate) in order to test the effect of chamber pressure on the nucleation density. Compared to 4000 Pa, we find nearly 7 times higher boron nucleation densities for both 1330 and 2670 Pa when the substrate was negatively biased in the Ar/H2plasma. Results are explained by incorporating measurements of plasma optical emission and by use of heterogeneous nucleation theory. The optimal conditions at 1330 Pa for nucleation were used to grow boron-rich amorphous films with measured hardness as high as 58 GPa, well above the 40 GPa threshold for superhardness.
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- Award ID(s):
- 1655280
- PAR ID:
- 10362417
- Publisher / Repository:
- IOP Publishing
- Date Published:
- Journal Name:
- Materials Research Express
- Volume:
- 8
- Issue:
- 4
- ISSN:
- 2053-1591
- Page Range / eLocation ID:
- Article No. 046401
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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