S e n i o r Supervisor ( D r . J . C . 1rwin) Examining Committee (~r . K . S . ~i s w a n a t h a n ) Examining Committee ( D r . M . Hercher) E x t e r n a l Examiner PARTTAL COPYRIGIIT LICENSE I h e r e b y g r a n t t o Simon F r a s e r U n i v e r s i t y t h e r i g h t t o lend my t h e s i s o r d i s s e r t a t i o n ( t h e t i t l e o f which i s shown b e l o w ) t o u s e r s o f t h e Simon F r a s e r U n i v e r s i t y L i b r a r y , and t o make p a r t i a l o r s i n g l e c o p i e s o n l y f o r s u c h u s e r s o r i n r e s p o n s e t o a r e q u e s t from t h e l i b r a r y o f a n y o t h e r u n i v e r s i t y , o r o t h e r e d u c a t i o n a l i n s t i t u t i o n , on i t s own b e h a l f o r f o r one of i t s u s e r s . I f u r t h e r a g r e e t h a t p e r m i s s i o n f o r m u l t i p l e c o p y i n g of t h i s t h e s i s f o r s c h o l a r l y p u r p o s e s may be g r a n t e d b y me o r t h e Dean of Graduate S t t l d i e s . I t is u n d e r s t o o d t h a t c o p y i n g o r p u b l i c a t i o n of t h i s t h e s i s f o r f i n a n c i a l g a i n s h a l l n o t b e a l l o w e d w i t h o u t my w r i t t e n p e r m i s s i o n . T i t l e of T h e s i s /~i s s e r t a t i o n :A u t h o r :( s i g n a t u r e ) (name ) ( d a t e ) ABSTRACT D i e l e c t r i c breakdown and mechanical damage i n s i l i c a t e g l a s s e s under h i g h i n t e n s i t y l a s e r r a d i a t i o n i s i n v e s t i g a t e d l a t i v e magnitude of t h e e f f e c t proves t h a t t h e p h o t o c o n d u c t i v i t y does n o t r e s u l t from i o n i z a t i o n of sodium i n g l a s s as e x t e n s i v e l y quoted i n l i t e r a t u r e . The l i f e t i m e of t h e charge c a r r i e r s produced i s e s t i m a t e d t o be 1 0 -~s . From t h e r m o e l a s t i c c o n s i d e r a t i o n s a c r i t e r i o n f o r t h e v a l i d i t y of p o s s i b l e damage mechanisms i s e s t a b l i s h e d . It i s shown t h a t s t i m u l a t e d B r i l l o u i n s c a t t e r i n g cannot g i v e r i s e t o a n e f f e c t i v e a b s o r p t i o n of 50 em-' i n t h e f o c a l volume as r e q u i r e d by t h e t h e r m o e l a s t i c c o n s i d e r a t i o n s . It i s proposed and e s t a b l i s h e d t h a t t h e mechanical damage i s caused by t h e a c c e l e r a t i o n of p r i m a r y e l e c t r o n s produced by m u l t i p h o t o n i o n i z a t i o n , l e a d i n g t o a f u l l y developed e l e c t r o n i c i n s t a b i l i t y i n few nanoseconds. A t t h i s e l e c t r o n d e n s i t y t h e a b s o r p t i o n6 -i n t h e f o c a l volume i s 10 cm ', and i s r e s p o n s i b l e f o r t h e complete a b s o r p t i o n of t h e l a s e r p u l s e a t i n t e n s i t i e s above t h e t h r e s h o l d f o r breakdown. The d i f f u s i o n and recombination of e l e c t r o n s a r e found t o be n e g l i g i b l e , t h e o n l y r a t e l i m i t i n g process being the l o s s of e l e c t r o n energy...
Photoconductive gains greater than unity can be obtained by illuminating a homogeneous photoconductor having blocking contacts with band gap radiation. A model is presented, which conceives such a possibility. Au contacts to CdSe form a Schottky barrier at the interface. Upon illumination the photogenerated holes are trapped in the Schottky barrier, shrinking the barrier and allowing injection of electrons in the CdSe. This gives rise to the possibility of gain greater than unity. Experimental evidence supporting the model is presented. Photoconductive gains as large as 300 have been measured when these films were illuminated with a photon flux of 2×1015 photons/cm2/sec.
Experiments were conducted to examine the relationship between the coefJicient of friction and the physical properties of magnetictape surfaces. Based on the experimental data, it was obserued that the coefficient of friction has a strong dependence on complex modulus rlf the materials i n contact. Sofiening of the polymer binder of the tape surface at elevated temperatures results i n a n increase i n friction. This demonstrates the need for a relatively hard binder with tz softening temperature (at the appropriate rate of deformation) above the maxzmum operating condition. Surface topography has a strong influence on friction. A rougher surface results i n higher contact stress at the contacting asperities, and, therefore, in less nu1 contact area and lower friction. A rougher surfnce, however, may result i n higher head wear and poorer magnetic signal amplitude. These observations demonstrate the need for optimization of the surface topography to maintain high performance of a magnetic-&ape product.
A ~e v i e w of f~iction theories relevant to the itzteracliorl between mag?retic-recording-device components (hard, inelastic materiuls) and viscoelastic, pol~lmeric materials wed i n the manufactz~re of fiexible, n~ag-netic tape is presented. Trtbor's cl(~ssica1 theo~y ofadhesion with appropriate deformcttion and shear-strain rates, m well m Hegmon's theo~y of hysteresis friction, adequately describes the ft-ictional behavior. Other sources of udhesionctl friction are stiction, menisc~ls, and niicrocapillary evacuation.For magtetic-recording-tope applications, the adhesion component oJ'frictio.n is responvible for the major part of the observed friction, except nenr the softening temperature for the magtleticcoating layer, where the loss tungenl becomes very high, or i n the case of rough surfaces for which hysteresis friction is sign6cant. Frott~ a magnetic-tape design standpoint, the real area of contact (which directly affech adhesional friction) can be minimized by increasing the complex modulus of elusticity of the magnetic layer over the operc~ting temperature range and by increusing the surface roughness. High surface roughness is undesirable from a wear and recording-petfor?rlance standpoint, therefore, optimization is essential. Creep co~t~plia~tce of the magnetic coating luyer, furthermore, shoz~ld be as low as possible in order to minimize deformation that leccds to a n increase i n lhe real area of contact for tapes subjected to comf~ressive stresses under tension wound on a reel or (g(~inst the recording-head surface. I n addition, the use of nonpolar materials (which i n general possess lower su+ce energy than polar materials) would lead to reduced friction.
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