Flexible of CH4/H2 gas mixture was optimized


Flexible transparent conductive films (TCFs) with high electrical conductivity and optical transparency has been greatly studied for use in many electronic and optoelectronic devices such as liquid crystal displays (LCD), OLEDs, smart interactive displays, touchscreens. Such devices which become more common in our lives can protect their original properties after bending or stretching under some special environmental conditions . The materials that emerged in recent years such as 1D metallic nanowires, conductive polymers and carbon nanomaterials have been examined as alternative materials for producing flexible TCFs. Among these alternative materials, conducting polymers are electrically unstable despite they have good electrical, optical and mechanical properties. Carbon materials such as graphite and carbon nanotubes with high chemical stability, high transmittance, and high conductivity have been used for TCFs.

However, the surface roughness and uniformity of these materials may lead to significant drawbacks and decrease the performances of the device. In contrast, graphene, the two-dimensional allotrope of carbon, has been attracting much attention as a good candidate material due to extraordinary electronic properties high optical transmittance and flexibility. In addition, the synthesis of low-defect graphene is crucial to develop large-area graphene-based TCFs. As explained in chapter 1.5, CVD is the most suitable approach for high-quality large-area graphene synthesis. After graphene synthesis by CVD, graphene film must be isolated from the metal catalyst and transferred onto a requested transparent substrate for TCFs applications.

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Various techniques are used for transferring the CVD graphene, among them the wet chemical method is the most common approach. In the standard chemical transfer procedure, graphene films should be protected from high stress. Generally, Poly(methylmethacrylate) (PMMA) is used as supporting layer owing to its low viscosity, flexibility, high transparency and good solubility in various organic solvents After etching the metal substrate, free PMMA/graphene layer is transferred onto the transparent dielectric substrate for the TCFs applications, lastly, the supporting layer is removed by dissolution in acetone. In this work, large area graphene was synthesized on prepared Cu foil by atmospheric pressure chemical vapor deposition (APCVD) process and successfully transferred. Graphene film on Cu was grown using methane gases (CH4) as a carbon precursor with a gas mixture of argon (Ar) and hydrogen (H2). The amount of CH4/H2 gas mixture was optimized in order to remove the amorphous carbon deposits and obtain large area graphene crystals with few defects. The growth time was also optimized to grow the layer of graphene and control of the film thickness.

The synthesized graphene film successfully transferred onto polyethylene terephthalate (PET) substrate which is transparent and flexible. The synthesized graphene film size is limited by the size of the Cu substrate and the chamber of the growth system. 

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