Light guides the evolution of graphene

Graphene is very promising for new electronics devices because of extraordinary electrical and optical properties. The standard routes for graphene patterning and processing are based on conventional microelectronics technology. This suggest covering the graphene by resist and patterning it by high-energy rays (UV, electron beam). This cause the impurities on the surface of graphene that alter the properties of graphene and demands for additional procedures of cleaning and restoration.

Group of scientist from Russia, Spain and Germany has suggested new route for graphene materials processing that can change the technology of graphene bases electronics. The researchers from National Research University of Electronic Technology – MIET (Russia), Technological Center AIMEN (Spain) and Forschungszentrum Jülich (Germany) have developed the technology for graphene physical and chemical modification avoiding the step of resist deposition. The technology based on high-energy photons from UV lamp or focused femtosecond laser pulses. Depending of initial graphene state and light source parameters the process provides cleaning, etching, doping, oxidation, reduction and 3D modification of materials and patterning for different applications in electronics, biology and optics.  

The researchers explore the use of focused laser beam for graphene processing. They discovered the photochemical and physical effect on graphene can be separated under femtosecond laser pulsed irradiation. That means the possibility to separate the chemical reactions induced in graphene from thermal effects from high energy laser pulses.

Scheme of physical (left) and chemical (right) patterning of graphene under femtosecond laser pulses

As recently published in IOPJournal of Physics D: Applied Physics (Photophysical and photochemical effects in ultrafast laser patterning of CVD graphene), the work of AIMEN and MIET researches demonstrates the mask-less and resist-free patterning of graphene by two different routes: thermal ablation or oxidative etching. That means that varying the parameters of laser pulses the chemical tuning (energy gap control) and isolation line patterning is possible for single process without any chemicals. The same group in Elsevier Materials Letters (Laser direct 3D patterning and reduction of graphene oxide film on polymer substrate) published the results of graphene oxide reduction by using thermal

and chemical effects from laser irradiation. Moreover the laser pulses provide 3D embossing of graphene that open the way for single processing of NEMS and microfluidic-based sensors in graphene.

Scheme of laser induced patterning and embossing of graphene oxide and micro-channel with resistive heater made by pulsed laser irradiation of graphene oxide

Authors claims the photochemical effect of femtosecond laser pulses is similar to UV effect even for green laser because of multiphoton absorption. In work published in AIP Applied Physics Letters (The effect of ultraviolet light on structural properties of exfoliated and CVD graphene), MIET and Forschungszentrum Jülich researches demonstrated the UV light effect on electrical and structural properties of graphene-based field effect transistors. Moreover, the authors demonstrated the effect of UV exposure is drastically differ for single and bi-layer graphene. While the UV light changes chemical and electrical properties of single layer graphene, the bi- and few layer graphene for the same time do not alter its properties. Thus, the UV exposure can be used for selective modification for totally graphene-based electronic devices.

Scheme of graphene UV oxidation process (left), graphene FET (center) and evolution of electrical characteristics of FET under UV treatment

The era of graphene and related materials is only rising. However, it is already obvious the molecular-based devices working on new principles must be processed with making use of novel techniques. The light-based technology provides mask-less, impurity free and ecology friendly routs for new device development and modification.

The work leading to these results was held within the European FAIERA project, funded by the European Union’s Seventh Framework Programme (GA 316161), under the Research Potential initiative REGPOT in the Capacities Programme and Russian Science Foundation Grant no.14–19-01308.

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