Mask-free and programmable patterning of graphene by ultrafast laser direct writing

doi:10.1016/j.chemphys.2013.12.005

Chemical Physics

Volume 430, 17 February 2014, Pages 13-17

https://doi.org/10.1016/j.chemphys.2013.12.005 Get rights and content

Highlights

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We present a mask-free and programmable patterning of graphene.
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Ultrafast laser can homogeneously reduce graphene oxides into micropatterns.
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Desired graphene micropatterns could be created on flexible substrates.
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Laser exposure duration shows influence on the conductivity of reduced graphene.
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The method holds promise for fabrication and integration of graphene electronics.

Abstract

Reported here is a mask-free and programmable patterning of graphene by using femtosecond laser direct writing on graphene oxide (GO) films. Take advantage of the ultrahigh instantaneous intensity of the femtosecond laser pulse, and especially its nonlinear interactions with materials, the GO could be efficiently reduced under atmospheric condition at room temperature. Moreover, the designability of femtosecond laser direct writing (FsLDW) technique allow making graphene micropatterns arbitrarily according to the preprogrammed structures, which provides the feasibility for rational design, flexible fabrication and integration of graphene-based micro-devices. Raman spectra show that the reduced and patterned region is very homogeneous, which is confirmed by the almost consistent I_D/I_G ratio. The novel graphene patterning technique would provide a technical support for the development of graphene-based micro-devices for future electronics.

Graphical abstract

Introduction

Recent years have witnessed a rapidly increased research interest in graphene and its related materials. Ever since the first discovery of this unique one-atom-thick carbon crystal, graphene has revealed a cornucopia of both fundamental research and potential applications due to its exceptional properties, such as ultrahigh electron mobilities [1], high thermal conductivity [2], mechanical strength [3], flexibility [4], excellent stability [5] and optical transparency [6]. All of these unique properties make graphene a promising candidate material for nanoscale electronic devices, such as electrodes [7], [8], sensors [9] and transistors [10]. Currently, graphene could be readily prepared by chemical vapor deposition (CVD) with Cu [11] or Ni [12] substrate as catalysts. However, the application of CVD graphene suffers from complex substrates transferring procedure, significantly limiting its practical use in electronic devices. Alternatively, graphene oxide (GO) prepared from chemical oxidation of raw graphite shows distinct advantages in mass production and solution processability [13], [14], [15], [16], [17], [18]. Generally, GO sheets consist of a graphitic carbon network bearing various types of oxygen-containing defects that render the sheets solubility in water, which allows the tractable processing and dispersion of isolated sheets or multilayer films from aqueous solutions. However, due to the high oxygen level in GO, there exist a lot of defects which seriously affect its electrical properties. And therefore, removal of oxygen containing groups of GO becomes necessary for its further application in electronics [17], [19], [20].

On the other hand, besides the reduction procedure, rational design and patterning of graphene is of considerable importance for the fabrication and integration of graphene-based devices [21], [22], [23]. However, the currently available patterning techniques including classical lithography [24], O₂ plasma etching [25], and flash reduction [26] usually need protected layer or a shadow mask to define the desired micropatterns. In the mask-defined pattering, different micropatterns usually need different masks. Moreover, the substrates should be very smooth and the tight contact between the graphene/RGO (reduced graphene oxide) and the mask layer would inevitably cause breakage or contamination of the graphene films. Therefore, mask-free methods that could be used for making graphene micropatterns are highly desired. In addition, novel patterning approaches such as reduction and patterning of GO by using a heated AFM-tip [27], and a combination of modulating the solution wettability of the substrates and spin-coating process [28] are also adopted for making graphene micropatterns. However, these methods depend on special instrument or precise treatment of substrate and suffer from low efficiency. Recently, photoreduction of GO by using various laser shows the feasibility for making graphene micropatterns in a non-contact manner, revealing great potential for fabrication and integration of graphene-based micro-devices [28], [29], [30], [31], [32], [33]. However, in order to achieve a relative high conductivity, the laser reduction should be carried out with the protection of inert gases, which not only limits the patterning area, but also brings considerable complexity for the device fabrication, and especially integration with other devices. Therefore, a mask-free and designable patterning of GO under atmospheric condition at room temperature is of critical importance to the development of graphene-based micro-devices, but obviously, it remains a technical challenge.

It is remarkable that, as an ultrafast laser, femtosecond laser pulse has been widely used for designable fabrication of three-dimensional (3D) microstructures with high spatial resolution due to its ultrashort pulse, ultrahigh instantaneous intensity and nonlinear interactions with various materials [34], [35], [36], [37], [38], [39], [40]. In this work, ultrafast laser pulse was adopted to fabricate reduced graphene micropatterns by direct writing on GO films according to the predetermined computer programs. In the case of femtosencond laser process, no mask is needed for the patterning, so hereafter, we called this method as “mask-free” patterning of graphene. Experimental results show that the reduced and patterned GO film is conductive, and exposure duration could be used to control its electrical conductivity. In addition, the laser reduction is also a chemical-free and “green” process, which means no chemical reagent is used during the reduction of GO. Thus, the mask-free, chemical-free and programmable patterning of GO films holds great promise for fabrication and integration of graphene-based micro-devices for future electronics.

Section snippets

Preparation of GO

Graphene oxide was synthesized using a modified Hummer’s method [41] from purified natural graphite. In typical procedure, 2 g of natural graphite flake, 2 g of NaNO₃, and 100 mL of concentrated H₂SO₄ (98%) were mixed at 0 °C under stirring. Then, 15 g of KMnO₄ was gradually added into the above mixture under stirring at 0 °C for 90 min, and at 35 °C for 2 h, respectively. After addition of 300 mL of distilled water slowly to the resulting solution, 10 mL of H₂O₂ (30%) was dropped into the mixture to

Results and discussion

Fig. 1 shows the schematic illustration of the femtosecond laser direct writing system that is used for the mask-free and programmable patterning of GO. A femtosecond laser with 80 MHz repetition rate, 120 fs pulse width and 800 nm central wavelength was focused by a 100 × oil immersion objective len to direct write various predesigned micropatterns on GO films. The laser scanning path was precisely controlled by computer according to the preprogrammed structures. During the fabrication, the entire

Conclusion

In conclusion, we have developed a mask-free, chemical-free and programmable approach to make graphene micropatterns towards flexible fabrication and integration of graphene-based micro-devices. By using the ultrafast laser direct writing on GO films, any desired micropatterns could be direct formed under atmosphere at room temperature due to the laser induced reduction of GO. A series of characterizations including AFM, XPS spectra, and Raman spectra show that after laser scanning, the oxygen

Acknowledgement

The authors acknowledge the financial support from NSFC under Grant no. 61008104, and no. 61376123. National Basic Research Program of China under Grant no. 2011CB013000.

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View full text

Mask-free and programmable patterning of graphene by ultrafast laser direct writing

Highlights

Abstract

Graphical abstract

Introduction

Section snippets

Preparation of GO

Results and discussion

Conclusion

Acknowledgement

Solid State Commun.

Carbon

Nano Today

Carbon

Nano Today

Nano Lett.

Science

Nature

Science

Nano Lett.

Appl. Phys. Lett.

Adv. Mater.

Nat. Mater.

Electron. Device Lett., IEEE

Nat. Nanotechnol.

Appl. Phys. Lett.

Nano Lett.

ACS Nano

Nano Lett.

Nat. Nanotechnol.

Nat. Nanotechnol.

J. Am. Chem. Soc.