Abstract
The induction of surface cleavage along the crystalline structure of a zinc oxide substrate (plane orientation: 0001) by femtosecond laser pulses (wavelength: 1030 nm) has been reported; a scanning electron microscope image of the one-pulse (pulse energy: 6–60 μJ) irradiated surface shows very clear marks from broken hexagons. This cleavage process differs from the general laser-induced melt process observed on the surfaces of narrower-bandgap semiconductors and other metal materials. This phenomenon is discussed using a multi-photon absorption model, and the pulse-energy dependence of the cleavage depth (less than 3 μm) is quantitatively analyzed. Laser-induced cleavage is found not to occur under multi-pulse irradiation; when more than four pulses are irradiated upon the same spot, the general laser-induced melt process becomes dominant. This cleavage–melt shift is considered to be caused by the enhancement of absorption due to the initial pulses, which is supported by our measurement of cathodoluminescence.
Highlights
Zinc oxide (ZnO)-based thin films fabricated by pulsed laser deposition have been widely reported by a vast number of researchers [2]; in most of these reports, a UV laser with a nanosecond order pulse duration was used
ZnO-based functional surface structures fabricated by direct laser irradiation upon a ZnO substrate occur seldom, despite the appearance of cheaper lasers with extremely high outputs [16,17]
Femtosecond laser-induced nano-ripples on ZnO surfaces have been separately reported by Hang et al [18] and Liu et al [19]
Summary
The emission of terahertz waves from ZnO-based devices is very strong evidence that ZnO has potential uses for terahertz components [8,10] In both the UV–visible and terahertz regions, laser processing is an efficient method for realizing thin-film-based devices or nano/microstructure-based functional surfaces [11,12,13,14,15]. No melting was observed from the one-pulse irradiated spot of the ZnO substrate; instead, corners with a 120◦ angle (pieces from broken hexagon patterns) are observed. To study these marvelous cleavage phenomena in detail, we performed one-pulse irradiation (pulse energy: 6–60 μJ) on the surface of the ZnO substrate, as well as multipulse (1–11 pulses) irradiation with the same pulse energy of 30 μJ. This shift is attributed to the enhancement of absorption due to the initial pulses, and the mechanism is supported by our measurement of cathodoluminescence
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
