Silicon periphery (see section 2.1) provide easy laser beam

Silicon substrates with graphene transistors were
diced to 10´10 mm2
chips containing 32 GFETs in a 1´1 mm2 working area in the center. The
64 gold contact feedlines that were sputtered on chip’s periphery (see section
2.1) provide easy laser beam access to graphene channel. Samples were placed on
motorized stage under the optical system of femtosecond laser processing tool (see
Fig. S1). To process graphene we used a fiber-rod amplified femtosecond second
harmonic laser of 515 nm wavelength with 280 fs pulse duration, 2 nJ pulse energy,
500 kHz repetition rate and different photon flux, produced by varying the
number of pulses per ?m (Satsuma HP2, Amplitude Systems, France). A high-speed
galvanometer scanner (Newson, Belgium) with high numerical aperture optics with
a focal length of 35 mm (Sill Optics, Germany) was used. The scanner allows maximizing
the speed up to 2 m s-1 with a focal spot down to 500 nm in these
conditions. The process was controlled by changing the pulse frequency and
scanning speed i.e. pulse overlapping. More detailed description of ultrafast
laser-induced oxidation of graphene can be found elsewhere.Optical profilometry was
used to monitor the laser processing by a non-contact 3D optical profiler S
neox (Sensofar-Tech, Spain). Raman spectra were measured through an x100
objective at 532 nm (Cobolt, Sweden) with a beam spot of 0.5 ?m and laser power
of 1 mW on a micro-Raman spectrometer Centaur HR (Nanoscan Technology, Russia).
Atomic force microscopy (AFM) using Solver-Pro (NT-MDT, Russia) with standard
silicon cantilevers NSG03 series in semi-contact mode with fres = 90
kHz was used to characterize the topography of graphene surface. Spectroscopy
measurements through scanning tunneling microscopy (STM) with Pt/Rh tip were
carried out on CVD graphene samples after femtoseconds laser processing the
same way as GFETs.

Electrical
characterization was performed on Agilent U2741A during fs laser measurements and
semiconductor device analyzer (MNIPI, Belarus) otherwise. Transfer I-V curves
were measured using backgate (p Si) or liquid gate (Ag/AgCl)
electrode. Photocurrent measurements were performed using the previously mentioned
fs and continues wave lasers with lower power provided.

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