Abstract
Intense short laser pulses are an intriguing tool for tailoring surface properties via ultra-fast melting of the surface layer of an irradiated target. Despite extensive studies on the interaction of femto-second laser interaction with matter, the initial steps of the morphological changes are not yet fully understood. Here, we reveal that substantial surface structure changes occur at energy densities far below the melting threshold. By using low-temperature scanning tunneling microscopy we resolve atomic-scale changes, i.e. the creation of nanosized adatom and vacancy clusters. The two cluster types have distinct non-linear fluence-dependencies. A theoretical analysis reveals their creation and motion to be non-thermal in nature. The formation of these atomistic changes, individually resolved here for the first time, recast our understanding of how surfaces respond to low-intensity ultra-short laser illumination. A visualization and control of the initial morphological changes upon laser illumination are not only of fundamental interest, but pave the way for the designing material properties through surface structuring.
Highlights
Intense short laser pulses are an intriguing tool for tailoring surface properties via ultra-fast melting of the surface layer of an irradiated target
A clear understanding of even the simplest morphological responses to ultra-fast laser illumination is still lacking because an atomistic visualization of the structural changes to a metal during ultra-fast structural dynamics has not yet been achieved experimentally
For an easier identification of the same spot of the surface, the surface is pre-structured by a sputter pulse at low temperature prior to the laser illumination
Summary
Intense short laser pulses are an intriguing tool for tailoring surface properties via ultra-fast melting of the surface layer of an irradiated target. A theoretical analysis reveals their creation and motion to be non-thermal in nature The formation of these atomistic changes, individually resolved here for the first time, recast our understanding of how surfaces respond to low-intensity ultra-short laser illumination. The investigation of a material’s response to femtosecond laser illumination provides unparalleled insight into material behavior far from equilibrium under the extreme conditions of ultra-high peak power and ultra-short pulse duration. These processes are well understood only for high laser fluences (=energy per pulse and unit area) above the melting and ablation thresholds, where the surface damage results from heat-induced stress c onfinement[2], amongst others. We reveal via low-temperature scanning tunneling microscopy the response of a Ag(100) surface to a train of ultra-short laser pulses at incoming (absorbed) single-pulse fluences below 5.4 (0.315) mJ/cm[2 ], i.e. far below reported ablation threshold for absorbed fluences in Ag between 85 mJ/cm[213] and ≈ 1.5 J/cm[2] for a single
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