AVS 46th International Symposium
    Thin Films Division Friday Sessions
       Session TF-FrM

Paper TF-FrM2
Ion Beam Induced Defects and Phonon Confinement in 2H-WS@sub 2@ by "In-situ/Real-Time" Raman Measurements

Friday, October 29, 1999, 8:40 am, Room 615

Session: In-situ Characterization and Material Process Imaging
Presenter: F.S. Ohuchi, University of Washington
Authors: F.S. Ohuchi, University of Washington
K. Ishioka, National Institute for Metals, Japan
M. Kitajima, National Institute for Metals, Japan
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Ion beam bombardment induces chemical and structural changes in the solid surface. This occurs because a large fraction of the incident ion energy goes into bulk processes like atomic mixing, dissociation and reduction, forming defects in the material. Ra man scattering is sensitive to small changes that occur in the lattice symmetry of a crystal, thus it has been used as a sensitive structure probe to study the defects in solids. In this paper, we report "in-situ" and "real-time" Raman measurements on tu n gsten disulfide (WS@sub 2@) single crystals during the bombardment of 5 keV He@super +@ ion beam. Changes in the peak intensity, energy and broadening for the E@sub 2g@ phonon mode were measured as a function of ion dose (1x10@super 12@-4x10@super 16@ i o n s/cm@super 2@), and the phonon correlation lengths were obtained using "spatial phonon correlation (SPC)" model. The phonon correlation length decreased with ion irradiation dose, and their changes were correlated with our previous investigation on t h e surface stoichiometry change with ion bombardment (JVST A12(4) 2451, 1994). Appearance of a new shoulder peak at around 416 cm@super -1@ to the A@sub 1g@ peak became evident when the dose exceeded more than 10@super 14@ions/cm@super 2@. This peak is considered as a forbidden mode originated from defect-induced coupling of the longitudinal acoustic (LA) and transverse acoustic (TA) phonons at the K point in the Brillouin zone of the WS@sub 2@ lattice. .