Free-jet mass spectrometry of laser ablation plumes in thin film deposition

Conference · Wed Mar 01 04:00:00 EST 1995

OSTI ID:110848

Hastie, J W; Paul, A J; Bonnell, D W ^[1]

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1. National Institute of Stanfords and Technology, Gaithersburg, MD (United States)

Plumes generated by high-power pulsed (10-30 ns) laser vaporization or ablation of refractory materials can attain ultra-high temperatures (5,000-30,000 K) and relatively high pressures (> 1 bar). However, plume expansion into a vacuum is sufficiently rapid that the initial species information can be retained and representative sampling with molecular beam mass spectrometry (MBMS) can be achieved. In order to verify and supplement the MBMS results, complementary investigations using emission spectroscopy and real-time imaging, coupled with gasdynamic, thermodynamic, and gaskinetic models are also carried out. In addition to plume species identities and abundances, MBMS analysis also provides beam time-of-flight information, yielding velocity distributions and gas temperatures. MBMS applications are considered here for systems important in thin film processing, such as Al{sub 2}O{sub 3} and C. Attention is also given to the essential features required of a free-jet MBMS system for representative sampling of laser ablation plumes. Significant progress in defining the general nature of laser vaporization/ablation plumes, used for thin film deposition, has been made in recent years. The authors current understanding of the main plume features are summarized by the idealized schematic. The plume initiates at the laser focus spot on the target surface and moves away along an axis normal to the target. After a few ns time delay from the onset of the laser pulse, sufficient vapor density develops for collisional local equilibrium to become established, followed by a supersonic adiabatic expansion process. This expansion process is isentropic and rapidly leads to a free-flight, collision-free condition. In the present work, species are sampled from this free-flight region for MBMS analysis.

• Research Organization: National Renewable Energy Lab., Golden, CO (United States)
• OSTI ID: 110848
• Report Number(s): NREL/CP--433-7748; CONF-9410343--; ON: DE95004052
• Country of Publication: United States
• Language: English

Related Subjects

42 ENGINEERING
ALUMINIUM OXIDES
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EVAPORATION
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LASER RADIATION
MASS SPECTROSCOPY
MOLECULAR BEAMS
PLUMES