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Positron annihilation spectroscopy of sputtered boron carbide films
Materials Science and Technology Division, Los Alamos National Laboratory.
Materials Science and Technology Division, Los Alamos National Laboratory.
Manuel Lujan Jr. Neutron Scattering Center, Los Alamos National Laboratory.
Stockholm University, Faculty of Science, Department of Physics.
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2005 (English)In: Diamond and related materials, ISSN 0925-9635, Vol. 14, no 2, 201-205 p.Article in journal (Refereed) Published
Abstract [en]

Positron annihilation spectroscopy (PAS) was carried out on boron carbide films deposited by sputtering and the results correlated to the bombardment conditions during film growth. Films were deposited with substrate bias voltages in the range of 0 to −200 V with a working pressure of 5 mTorr of Ar. Films deposited with bias voltages from −100 to −200 V present the same type of defect and the defect concentration increased linearly with the bias voltage. This defect was ascribed to vacancies in agreement with Monte Carlo simulations of Ar+ bombardment of boron carbide. On the other hand, films deposited with 0 V bias presented a higher S parameter values, whose origin was tentatively attributed to a relatively more open nanosized columnar structure, as suggested by the structure zone model. Annealing up to 800 °C for 30 min did not change the defect content.

Place, publisher, year, edition, pages
2005. Vol. 14, no 2, 201-205 p.
National Category
Condensed Matter Physics
Research subject
Materials Science
Identifiers
URN: urn:nbn:se:su:diva-27415DOI: 10.1016/j.diamond.2004.11.003OAI: oai:DiVA.org:su-27415DiVA: diva2:214098
Available from: 2009-05-02 Created: 2009-05-02 Last updated: 2009-05-03Bibliographically approved
In thesis
1. Experimental investigation of molecular solids and vanadium at high pressure and temperature
Open this publication in new window or tab >>Experimental investigation of molecular solids and vanadium at high pressure and temperature
2009 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Understanding high pressure effects on simple molecular system is of great interest for condensed matter science and geophysics. Accessing the static pressure and temperature regions found in planetary interiors is made possible by the development of the Diamond Anvil Cell technique. We developed a double sided resistive heating method for the membrane DAC operating in low pressure (<0.5 mTorr) pressure environment requiring only 175 W input power to reach sample temperatures up to 1300 K. We applied this technique successfully to study molecular solids at high temperatures, such as H2, N2 and CO2. We made an attempt to determine the melting line of hydrogen and present data up to 26 GPa in agreement with literature. Raman spectroscopy of Nitrogen indicates a high stability of the ε molecular phase, while θ phase is only accessible via certain P, T paths. Studies of solid CO2 at high pressure and temperature lead to the discovery of a six-fold coordinated stishovite-like phase VI, obtained by isothermal compression of associated CO2-II above 50 GPa at 530-650 K, or by isobaric heating of CO2-III above 55 GPa. From our X-ray diffraction experiment on isothermally compressed H2O we report a coexistence of ice VII and symmetric ice X from the start of the transition pressure 40GPa to just below 100 GPa and a volume change of 4% across the transition.

Vanadium, a transition metal undergoes a phase transition upon compression unlike other elements (Nb, Ta) from its group. We confirm the bcc phase transition to rhombohedral structure at 62 GPa under quasi hydrostatic compression in Ne pressure medium. Compression without pressure medium results in a much lower 30 GPa transition pressure at room temperature and 37 GPa at 425 K, pointing to a positive phase line between the bcc and rhombohedral crystalline phases.

 

Place, publisher, year, edition, pages
Stockholm: Department of Physics, Stockholm University, 2009. 71 p.
Keyword
molecular solid, high pressure, vanadium, phase transition
National Category
Physical Sciences
Research subject
Physics Of Matter
Identifiers
urn:nbn:se:su:diva-26917 (URN)978-91-7155-868-8 (ISBN)
Public defence
2009-05-26, sal FB53, AlbaNova Universitetscentrum, Roslagstullsbacken 21, Stockholm, 10:00 (English)
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Available from: 2009-05-05 Created: 2009-04-17 Last updated: 2009-05-04Bibliographically approved

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