Impact of 532 nm 6 ns laser pulses on (104) oriented zinc single crystal: surface morphology, phase transformation, and structure hardness relationship

Specimens of (104) oriented Zn single crystal were irradiated in vacuum similar to 10(-3) Torr with pulsed Nd: YAGlaser (lambda= 532 nm, E= 50 mJ, tau = 6 ns) at a repetition rate 10 Hz. The number of laser shots was varied from 1 to 100. The laser fluence and laser intensity at the one laser shot irradiation spot on the target surface were 97.2 J cm(-2) and 1.6. x 10(10) Wcm(-2), respectively. Crater geometry of laser-irradiated specimens was examined by optical microscope. Crater area was found to increase with the increase in number of laser shots. The data points were encompassed by sigmoidal (Boltzmann) fit showing that crater area increases rapidly to begin with up to 50 laser shots and later on rather slowly till 100 laser shots. Surface morphology was examined by SEM and AFM, which revealed ripple patterns, cavities, trenches, ridges, nanohillocks, microcones, droplets, and solid flakes etc. Structural parameters, namely crystallite size and lattice strain were evaluated by Williamson-Hall analysis of x-ray diffraction patterns. Surface hardness was found to increase up to 50 laser shots and later on it decreased progressively till 100 laser shots. Correlation between surface hardness and crystallite size was also examined, and was found to obey inverse Hall-Petch relation.