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Femtosecond micromachining offers a contact-free and mask-less technique formaterial patterning. With ultrafast laser irradiation, permanent modificationsto the properties of single layer graphene through material ablation or defectintroduction can be induced. Multiple femtosecond pulse interactions with asingle layer graphene are studied and a low laser ablation threshold ~9.2mJ/cm2 is reported for a 15 second illumination time. Clean ablated structuresare generated in such a multi pulse irradiation configuration at low pulseenergies as an attractive alternative to ablation with single femtosecond, highenergy pulses. For a fully ablated graphene hole, a radially symmetric regionextending around 2 um from the ablated edge is characterized by strong defectgeneration. Average distances between point-defects down to ~58 nm are derivedand Raman spectroscopy implies that overall there is a strong resemblance toamorphous structures. For fluence values around 75% of the ablation threshold,modification with defect generation down to ~48 nm average defects lengths isreported, while the underlying graphene structure is maintained. Thus,depending on the laser parameter choice, the same laser configuration can beused to ablate graphene or to primarily introduce defect states. The presentedfindings offer interesting insights into femtosecond induced structuralmodifications of graphene that can lead to improved precision ablation andpatterning of single-layer materials at the micro- and nano-scale. Further,this can be attractive for graphene or carbon-based device fabrication as wellas sensor and transistor applications, where regions of varying carrierconcentrations and different electrical, optical or physical properties aredesired.

Micro-Structuring, Ablation and Defect Generation in Graphene with Femtosecond Pulses