Surface energy engineering of graphene (1103.4667v1)

Abstract: Contact angle goniometry is conducted for epitaxial graphene on SiC. Although only a single layer of epitaxial graphene exists on SiC, the contact angle drastically changes from 69{\deg} on SiC substrates to 92{\deg} with graphene. It is found that there is no thickness dependence of the contact angle from the measurements of single, bi, and multi layer graphene and highly ordered pyrolytic graphite (HOPG). After graphene is treated with oxygen plasma, the level of damage is investigated by Raman spectroscopy and correlation between the level of disorder and wettability is reported. By using low power oxygen plasma treatment, the wettability of graphene is improved without additional damage, which can solve the adhesion issues involved in the fabrication of graphene devices.

• The paper demonstrates that epitaxial graphene on SiC exhibits a wettability shift, with contact angles increasing from 69° on bare SiC to 92.5° on graphene-coated surfaces.
• The paper reveals that low-power oxygen plasma treatment effectively enhances graphene’s surface hydrophilicity by reducing the contact angle from 92.5° to 55.1°.
• The paper quantifies defect density using Raman spectroscopy, establishing a correlation between the I(D)/I(G) ratio and wettability, which informs improved device fabrication.

Review of "Surface Energy Engineering of Graphene"

The paper "Surface Energy Engineering of Graphene" presents a comprehensive investigation into the wettability properties of epitaxial graphene (EG) on silicon carbide (SiC) substrates. The authors focus on contact angle measurements to explore the surface characteristics of graphene, which is critical for its application in various electronic devices. This paper diverges from the common electrical property focus of graphene research and instead provides insights into the interactions between graphene and other materials through surface engineering.

Summary of Key Findings

1. Wettability of Graphene: The paper demonstrates a significant change in the contact angle when a single layer of EG is placed on SiC substrates. The contact angle shifts from 69° on bare SiC to 92.5° on graphene-coated SiC, indicating the hydrophobic nature of the latter. The contact angles for mechanically cleaved graphene (MCG) and highly ordered pyrolytic graphite (HOPG) were found to be consistent with these results. Notably, the wettability was found to be independent of the number of graphene layers.
2. Oxygen Plasma Treatment: By employing oxygen plasma treatment, the authors introduce a method to modify the surface properties of graphene. They discover that low-power oxygen plasma can enhance the wettability of graphene, thus improving adhesive qualities without significant structural damage. This treatment changes the contact angle from 92.5° to 55.1°, indicating an increased hydrophilic characteristic due to the induced defects.
3. Raman Spectroscopy Analysis: The level of damage induced by the oxygen plasma was quantified using Raman spectroscopy. The D band to G band intensity ratio, I(D)/I(G), was used as an indicator of defect density. The paper establishes a correlation between the defect density and the wettability of graphene, providing crucial insights into the physical interpretations of Raman spectroscopic features.

Implications and Future Directions

• Enhanced Device Fabrication: The findings have practical implications for the fabrication of graphene-based electronic devices. The ability to control the surface properties of graphene through oxygen plasma treatment offers a pathway to resolve adhesion issues commonly faced during metal contact deposition. This could lead to more reliable manufacturing processes for graphene transistors and other nanoscale devices.
• Further Research into Surface Interactions: Although the correlation between defects and surface energy is explored, the paper suggests further studies to elucidate the precise mechanisms of defect-mediated changes in surface interactions. Understanding these interactions at a fundamental level might unlock new strategies for graphene surface modification in various environments.
• Raman Spectroscopy as a Diagnostic Tool: The research reinforces the utility of Raman spectroscopy as a diagnostic tool to assess defect levels in graphene. This could be further expanded into a standard method for analyzing surface modifications in graphene research.

Conclusion

This paper provides critical insights into the surface energy characteristics of graphene, particularly highlighting the impacts of contact angle changes and oxygen plasma treatments. It presents a nuanced understanding of wettability control without compromising graphene’s intrinsic properties, paving the way for advanced applications in graphene electronics. The methodologies and findings outlined could inspire further exploration of graphene surface engineering, contributing significantly to the materials science and nanotechnology fields.