POLAR DISTRIBUTION OF ABLATED ATOMIC MATERIAL DURING THE PULSED-LASERDEPOSITION OF CU IN VACUUM - DEPENDENCE ON FOCUSED LASER SPOT SIZE AND POWER-DENSITY

Experiments have been carried out to investigate the polar distributio n of atomic material ablated during the pulsed laser deposition of Cu in vacuum. Data were obtained as functions of focused laser spot size and power density. Thin films were deposited onto flat glass substrate s and thickness profiles were transformed into polar atomic flux distr ibutions of the form f(theta)=cos(n) theta. At constant focused laser power density on target, I=4.7+/-0.3X10(8) W/cm(2), polar distribution s were found to broaden with a reduction in the focused laser spot siz e. The polar distribution exponent n varied from 15+/-2 to 7+/-1 for f ocused laser spot diameter variation from 2.5 to 1.4 mm, respectively, with the laser beam exhibiting a circular aspect on target. With the focused laser spot size held constant at phi=1.8 mm, polar distributio ns were observed to broaden with a reduction in the focused laser powe r density on target, with the associated polar distribution exponent n varying from 13+/-1.5 to 8+/-1 for focused laser power density variat ion from 8.3+/-0.3X10(8) to 2.2+/-0.1X10(8) W/cm(2) respectively. Data were compared with an analytical model available within the literatur e, which correctly predicts broadening of the polar distribution with a reduction in focused laser spot size and with a reduction in focused laser power density, although the experimentally observed magnitude w as greater than that predicted in both cases. (C) 1996 American Instit ute of Physics.