Simple Ultrasonic-Assisted Clean Graphene Transfer

Clean graphene transfer has received widespread research attention, where most methods are focused on cleaning the upper surface of graphene to improve the transfer technique. However, the residue formation on the bottom surface of graphene is also inevitable;therefore, cleaning the bottom surface is crucial. In this study, we proposed an improved graphene wet transfer method using an ultrasonic processing(UP) step for etching copper(Cu). Using this method, the bottom surface can be cleaned efficiently. The results of atomic force microscopy(AFM)and Raman spectroscopy mapping revealed that the graphene films transferred with UP had smoother and cleaner surfaces, less contamination, and higher quality than those transferred without UP.

Ultraclean transfer of graphene by mechanically exfoliating polymer with modified crosslink density

The transfer of graphene from metallic substrates onto application-specific substrates is usually inevitable for the applications of high-quality graphene films derived from chemical vapour deposition(CVD)approaches.Commonly used to support the graphene films during the transfer,the coating of the polymer would produce the surface contaminations and hinder the industrially compatible transfer.In this work,through the thermal imidization of polyamide acid(PAA)to polyimide(PI)and tuning of the concentration of dangling chains,we achieved the ultraclean and crack-free transfer of graphene wafers with high electronic quality.The resulting contamination-free and hydrophilic surface also enabled the observed improved cell viability in a biomedical applications.By avoiding aqueous etching or the usage of strong bases,our proposed transfer method is industrially compatible for batch transfer of graphene films towards the real applications.

Clean transfer of graphene on Pt foils mediated by a carbon monoxide intercalation process

Noble metals such as Pt are a perfect substrate for the catalytic growth of monolayer graphene. However, the requirements of the subsequent transfer process are not compatible with the traditional etching method. In this work, we find that the interaction of graphene with Pt foil can be weakened through the intercalation of carbon monoxide （CO） under ambient pressure. This intercalation process occurs on both hexagonal-shape graphene islands and irregular graphene patches on changing the CO partial pressure from 0 to 0.6 MPa, as observed by scanning electron microscopy （SEM）, Raman spectroscopy and X-ray photoemission spectroscopy. We demonstrate that, on a practical timescale, the intercalation ratio is proportional to the partial pressure of CO. Furthermore, we develop a clean transfer method of CO-intercalated graphene with water as a peeling agent. We show that this method enables the transfer of tens of micrometer-scale graphene patches onto SiO2/Si, which are free from metal or oxide particle contamination. This transfer method should be a significant step towards the dean transfer of graphene, as well as the recydable use of noble metal substrates.

Triboelectricity-assisted transfer of graphene for flexible optoelectronic applications

In this work, we developed a novel triboelectricity-assisted polymer-free method for the transfer of large-area chemical vapor deposited graphene films. With the assistance of electrostatic forces from friction-generated charges, graphene sheets were successfully transferred from copper foils to flexible polymer substrates. Characterization results confirmed the presence of high quality graphene with less defects and contaminations, compared to graphene transferred by conventional poly（methyl rnethacrylate）-mediated processes. In addition, the graphene samples possessed outstanding electrical transport capabilities and mechanical stability, when studied as electron transfer matrixes in graphene/ZnO hybrid flexible photodetectors. Our results showed a broad application potential for this transfer method in future flexible electronics and optoelectronics.

Thermoacoustic theory of graphene films considering heat transfer of substrate materials

Based on thermoacoustic theory, a coupled thermal-mechanical model for graphene films is established, and the analytical solutions for thermal-acoustic radiation from a graphene thin film are obtained. The sound pressure of the graphene film generator on different substrates is measured, and the measurement data is compared with the theoretical results. The frequency response from the experimental results is consistent with the theoretical ones, while the measured values are slightly lower than the theoretical ones. Therefore, the accuracy of the proposed theoretical model is verified. It is shown that thermal-acoustic radiation from a graphene thin film reveals a wide frequency response. The sound pressure level increases with the frequency in the low frequency range, while the sound pressure varies smoothly with frequency in the high frequency range. Thus it can be used as excellent thermal generator. When the thermal effusivity of the substrate is smaller, then the sound pressure of grapheme films will be higher. Furthermore, the sound pressure decreases with the increase of heat capacity per unit area of grapheme films. Results will contribute to the mechanism of graphene films generator and its applications in the design of loudspeaker and other related areas.