- The paper demonstrates a dry transfer technique that uses thermal release tape to transfer epitaxial graphene from SiC substrates to various target materials.
- Raman spectroscopy and XPS confirmed an 87% transfer efficiency with an optimal bonding force of approximately 5 N/mm² ensuring uniform, low-defect films.
- Despite some reduction in carrier mobility post-transfer, the process maintains high electrical performance, making it promising for flexible and transparent electronic applications.
Technique for the Dry Transfer of Epitaxial Graphene onto Arbitrary Substrates
The paper under review presents a detailed investigation into a novel dry transfer technique for transferring large-area epitaxial graphene (EG) from silicon carbide (SiC) substrates onto various arbitrary substrates, utilizing a thermal release tape method. This research addresses the critical need for graphene to be positioned on substrates suitable for a range of technological applications, particularly in flexible electronics and optically transparent contacts.
Graphene Transfer Methodology
Epitaxial Graphene (EG) films have been noted for their outstanding electrical properties, such as high Hall mobility, making them suitable for electronic applications. Traditionally, these properties have been accessed via mechanical exfoliation techniques that do not readily scale to large-area films. The current paper circumvents these limitations by employing a dry transfer method leveraging a Nitto Denko Revalpha thermal release tape.
EG is grown on C-face 4H-SiC substrates through epitaxial means, resulting in high-quality films with room temperature Hall mobilities ranging considerably, with specific cross-structures achieving up to 23,000 cm²/Vs. The transfer procedure involves placing the thermal release tape directly onto the EG/SiC structure. A calibrated pressure is applied to ensure substantial bonding force before peeling the tape, thus transferring the majority of the EG layer onto the tape. This EG-coated tape is then placed on the target 'handle' substrates (e.g., SiO₂ on Si), and the bonding force is again applied. The adhesive tape is then thermally released to leave the graphene on the handle substrate.
Results and Analysis
Raman spectroscopy and X-ray photoemission spectroscopy (XPS) were employed to verify the thickness, uniformity, and quality of the transferred EG films. The paper detailed a transfer efficiency of about 87%, confirming the method's effectiveness. Electrical properties post-transfer were evaluated through Hall effect measurements. These measurements revealed a considerable reduction in carrier mobility and density post-transfer, indicative of potential defects introduced during the procedure. Nevertheless, the post-transfer mobilities remained significantly higher than many existing flexible conductive materials. The research also suggested the presence of intercalated silicon atoms within the EG films, likely acting as an isoelectronic dopant.
The paper further identified that the bonding force significantly influenced the uniformity and defect densities of the transferred graphene films. An optimal bonding force of approximately 5 N/mm² was determined, yielding the most continuous and lowest-defect EG films.
Implications and Future Work
The dry transfer technique presented allows for the scalable integration of EG films onto a variety of substrate types, thus broadening the scope for the material's application in electronics. The methodology potentially paves the way for large-scale manufacturing processes, bypassing limitations seen in wet chemical approaches that are not suitable for EG on SiC due to the chemical resilience of SiC.
This paper provides a foundational technique that could be further refined through the exploration of different bonding pressures, substrate types, and adhesive materials. Future work can delve into the reduction of transfer-induced defects, enhancing the electrical performance of transferred films. Additionally, expanding the spectrum of substrate materials compatible with this transfer process could further integrate graphene technology in diverse electronic and optoelectronic industries.
Overall, the paper contributes essential insights into a scalable method for transferring high-quality graphene films while maintaining a significant proportion of the as-grown film properties, thus offering substantial potential for the advancement of flexible and transparent electronic applications.