Abstract
Nano and femtosecond laser writing are becoming very popular techniques for patterning carbon-based materials, as they are single-step processes enabling the drawing of complex shapes without photoresist. However, pulsed laser writing requires costly laser sources and is known to cause damages to the surrounding material. By comparison, continuous-wave lasers are cheap, stable and provide energy at a more moderate rate. Here, we show that a continuous-wave laser may be used to pattern vertical nano-crystalline graphite thin films with very few macroscale defects. Moreover, a spatially resolved study of the impact of the annealing to the crystalline structure and to the oxygen ingress in the film is provided: amorphization, matter removal and high oxygen content at the center of the beam; sp2 clustering and low oxygen content at its periphery. These data strongly suggest that amorphization and matter removal are controlled by carbon oxidation. The simultaneous occurrence of oxidation and amorphization results in a unique evolution of the Raman spectra as a function of annealing time, with a decrease of the I(D)/I(G) values but an upshift of the G peak frequency.
Highlights
As silicon transistors can no longer follow Moore’s law[1], carbon is considered one of the most promising material for replacing or complementing silicon-based electronics[2,3]
We provide clear evidence that oxidation occurs during the CW-laser annealing of carbon, as we observe a strong correlation between the in-depth amorphization process and the spatial repartition of oxygen as measured by energy dispersive X-ray spectroscopy (EDX)
We have studied the annealing of vertical nano-crystalline graphite (vnC-G) via CW laser and demonstrated the potential of this technique for laser writing
Summary
As silicon transistors can no longer follow Moore’s law[1], carbon is considered one of the most promising material for replacing or complementing silicon-based electronics[2,3]. Though short-wavelength (13.5 nm) laser-based lithography will be one of the most critical processes for the mass fabrication of high-performance transistors[4] at resolutions below 10 nm[5], a wide range of applications of carbon materials do not require such small features (thin-film transistors[4] or sensors). They are being considered as an alternative to pulsed lasers for direct writing Despite these various studies, the literature on CW laser annealing of carbon does not provide a clear description of the mechanisms behind these phase change and matter removal processes.
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