A novel instrumentation design and operation to study ultrafast laser damage with atomic scale characterization by scanning tunneling microscopy is described here. The STM system operates in an ultrahigh vacuum chamber, fitted with an in situ objective allowing for tight focusing of laser excitation onto the sample. A combination of in situ and ex situ laser machining is used to define fiducial registry markers that help identify the overlap region for the optical excitation and STM scanning, aided by simultaneous confocal imaging and far-field cameras. We report initial measurements of laser damage on silicon in UHV with 10 pulses (77 fs compressed width, 0.67J/cm2 peak fluence) from a 1030nm Yb:KGW laser. STM imaging of damage sites show several characteristic regions with sharply defined boundaries determined by underlying damage thresholds, including an ablation crater and the beginnings of periodic surface structures.
Ultrafast lasers are very useful for surface engineering of semiconductors. Here we used a Scanning Tunneling Microscope (STM) to map in situ topography and spectra of hydrofluoric acid-etched silicon (100) damaged by an ultrafast pulsed Yb:KGW laser at 1030nm with 70fs duration in high vacuum. We observed absence and presence of laser induced periodic surface structures with single and multiple shot irradiation, respectively. Surface morphology were captured with atomic resolution, which can help understand the subtle changes to surface ultrafast lasers can cause near the laser induced damage threshold fluence. The results demonstrate the potential of STM for in-situ studies of laser damage on clean surfaces in ultra-high vacuum.
Laser processing is useful for topographical and band structure modification of semiconductors. We used a Scanning Tunneling Microscope (STM) to map topography and spectra around hydrofluoric acid etched silicon (100) damaged with an ultrafast pulsed Yb:KGW laser at 1030nm with duration of 70fs in high vacuum. STM uses an atomically sharp tip and feedback loop controlled piezoelectric crystals to characterize conductive surfaces with atomic resolution. With this, we have observed periodic surface structures. This information can then be used to understand the laser damage process better and eventually can be used to characterize defect formation without the presence of topographical change.
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