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Chemical vapour deposition of boron-carbon thin films from organoboron precursors
Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
2015 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

Boron-carbon (BxC) thin films enriched in 10B are potential neutron converting layers for 10Bbased solid-state neutron detectors given the good neutron absorption cross-section of 10B atoms in the thin film. Chemical Vapour Deposition (CVD) of such films faces the challenge that the maximum temperature tolerated by the aluminium substrate is 660 °C and low temperature CVD routes for BxC films are thus needed. This thesis presents the use of two different organoboron precursors, triethylboron –B(C2H5)3 (TEB) and trimethylboron – B(CH3)3 (TMB) as single-source precursors for CVD of BxC thin films.

The CVD behaviour of TEB in thermal CVD has been studied by both BxC thin film deposition and quantum chemical calculations of the gas phase chemistry at the corresponding CVD conditions. The calculations predict that the gas phase reactions are dominated by β-hydride eliminations of C2H4 to yield BH3. In addition, a complementary bimolecular reaction path based on H2-assisted C2H6 elimination to BH3 is also present at lower temperatures in the presence of hydrogen molecules. A temperature window of 600 – 1000 °C for deposition of X-ray amorphous BxC films with 2.5 ≤ x ≤ 4.5 is identified showing good film density (2.40 – 2.65 g/cm3) which is close to the bulk density of crystalline B4C, 2.52 g/cm3 and high hardness (29 – 39 GPa). The impurity level of H is lowered to < 1 at. % within the temperature window.

Plasma chemical vapour deposition has been studied using TMB as single-source precursor in Ar plasma for investigating BxC thin film deposition at lower temperature than allowed by thermal CVD and further understanding of thin film deposition process. The effect of plasma power, total pressure, TMB and Ar gas flow on film composition and morphology are investigated. The highest B/C ratio of 1.9 is obtained at highest plasma power of 2400 W and TMB flow of 7 sccm. The H content in the films seems constant at 15±5 at. %. The B-C bond is dominant in the films with small amount of C-C and B-O bonds, which are likely due to the formation of amorphous carbon and surface oxidation, respectively. The film density is determined as 2.16±0.01 g/cm3 and the internal compressive stresses are measured to be <400 MPa.

Place, publisher, year, edition, pages
Linköping: Linköping University Electronic Press, 2015. , 29 p.
Series
Linköping Studies in Science and Technology. Thesis, ISSN 0280-7971 ; 1741
National Category
Physical Sciences Chemical Sciences
Identifiers
URN: urn:nbn:se:liu:diva-123909DOI: 10.3384/lic.diva-123909ISBN: 978-91-7685-858-5 (print)OAI: oai:DiVA.org:liu-123909DiVA: diva2:893663
Presentation
2016-01-21, Jordan/ Fermi, Fysikhuset, Campus Valla, Linköpings universitet, Linköping, 13:15 (English)
Opponent
Supervisors
Available from: 2016-01-13 Created: 2016-01-13 Last updated: 2016-02-29Bibliographically approved
List of papers
1. Gas phase chemical vapor deposition chemistry of triethylboron probed by boron-carbon thin film deposition and quantum chemical calculations
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2015 (English)In: Journal of Materials Chemistry C, ISSN 2050-7526, E-ISSN 2050-7534, Vol. 3, no 41, 10898-10906 p.Article in journal (Refereed) Published
Abstract [en]

We present triethylboron (TEB) as a single-source precursor for chemical vapor deposition (CVD) of BxC thin films and study its gas phase chemistry under CVD conditions by quantum chemical calculations. A comprehensive thermochemical catalogue for the species of the gas phase chemistry of TEB is examined and found to be dominated by beta-hydride eliminations of C2H4 to yield BH3. A complementary bimolecular reaction path based on H-2 assisted C2H6 elimination to BH3 is also significant at lower temperatures in the presence of hydrogen. Furthermore, we find a temperature window of 600-1000 degrees C for the deposition of X-ray amorphous BxC films with 2.5 less than= x less than= 4.5 from TEB. Films grown at temperatures below 600 degrees C contain high amounts of H, while temperatures above 1000 degrees C result in C-rich films. The film density and hardness are determined to be in the range of 2.40-2.65 g cm(-3) and 29-39 GPa, respectively, within the determined temperature window.

Place, publisher, year, edition, pages
ROYAL SOC CHEMISTRY, 2015
National Category
Physical Sciences Chemical Sciences
Identifiers
urn:nbn:se:liu:diva-122673 (URN)10.1039/c5tc02293b (DOI)000363252200030 ()
Note

Funding Agencies|European Spallation Source ESS AB; Knut and Alice Wallenberg Foundation; German Science Foundation (Research Training Group 1782); Beilstein Foundation (Frankfurt/Germany)

Available from: 2015-11-16 Created: 2015-11-13 Last updated: 2017-09-29
2. Trimethylboron as single-source precursor for boron-carbonthin film synthesis by plasma chemical vapor deposition
Open this publication in new window or tab >>Trimethylboron as single-source precursor for boron-carbonthin film synthesis by plasma chemical vapor deposition
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2015 (English)Manuscript (preprint) (Other academic)
Abstract [en]

Boron-carbon (BxC) thin films are potential neutron converting layers for 10B-based neutron detectors. However, as common material choices for such detectors do not tolerate temperature above 500°C, a low temperature deposition route is required for this application. Here we study trimethylboron B(CH3)3 (TMB) as a single-source precursor for the deposition of BxC thin films by plasma CVD using Ar plasma. The effect of plasma power, TMB/Ar ratio and total pressure on the film composition, morphology and structure are investigated. The highest B/C ratio of 1.9 was achieved at high TMB flow in a low total pressure and high plasma power which rendered an approximate substrate temperature of ~ 300 °C. X-ray photoelectron spectroscopy shows that B-C bonds prevail in the films, although C-C and B-O bonds are also present. Raman spectroscopy confirms the presence of amorphous carbon phases in the films. The H content in the films is found to be 15±5 at. % by the time of flight elastic recoil detection analysis (Tof-ERDA). The film density as determined from X-ray reflectivity (XRR) measurements is 2. 16 ± 0.01  g/cm3 and the internal compressive stresses are measured to be less than 400 MPa.

National Category
Physical Sciences Chemical Sciences
Identifiers
urn:nbn:se:liu:diva-123908 (URN)
Available from: 2016-01-13 Created: 2016-01-13 Last updated: 2016-01-13Bibliographically approved

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Yimamu (Imam), Maiwulidan (Mewlude)

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