*Surface Analysis of Graphene and Graphite DOI: http://dx.doi.org/10.5772/intechopen.108203*

(PMMA) is commonly used as a membrane support to prevent folding or tearing of graphene [20, 21]. Studies have shown that there is still some residual PMMA remaining on the surface of graphene after cleaning by chemical or thermal treatment [22, 23]. When exposed in the air or during XPS and ToF-SIMS measurements at room temperature, the adsorption of hydrocarbon and oxygen contaminants on the graphene and graphite surfaces is very likely. Xie *et al.* developed a process to produce a very clean graphene surface through annealing a graphene sample at 500°C in an ultra-high vacuum chamber without creating any additional defects [24]. XPS was used to estimate the residual PMMA and hydrocarbon contaminants on the graphene surface before and after annealing at different temperatures based on the curve-fitting results. The XPS results indicate that a clean surface was produced after annealing the sample at 500°C for 45 min. A similar experiment was repeated, and the sample was analyzed by ToF-SIMS. After selecting representative ions of PMMA and hydrocarbons from ToF-SIMS spectra, such as C2H3O2 + and CH3O− for PMMA and C4H5 + for hydrocarbons, and calculating their normalized intensities under different annealing conditions, the results confirmed that the residual PMMA can be removed from the surface of graphene at 400°C, while hydrocarbon contaminants require a higher temperature of 500°C to remove.

Furthermore, by using deuterium isotope-labeled PMMA and ToF-SIMS, the residual PMMA on a graphene surface was identified, located, and quantified. **Figure 3** shows ToF-SIMS depth profiles and high lateral resolution maps of C3 − ion representing graphene and 2 H− ion representing deuterated-PMMA [25]. As shown in the depth profiles, the 2 H− ion is concentrated on the top surface and its intensity drops when penetrating into the graphene structure. The C3 − ion increases gradually and reaches a maximum at the depth of about 0.2 nm (2 H− ion with relatively low intensity), and then gradually decreases when going into the SiO2 substrate layer. The mapping results, as shown in **Figure 3b** and **c**, indicate that the 2 H− ion appears mainly in the same areas where the C3 − ion is present, confirming that the residual PMMA is present on the graphene surface.

In addition, metallic impurities introduced during the transfer process can lead to contamination of fabrication devices. The out-diffusing of these impurities toward the substrate during the device processing can result in degradation of the device parts located beneath graphene. ToF-SIMS was used to detect Cu and Fe residuals originating from the transfer process of graphene [26]. The ToF-SIMS images of transferred graphene showed the presence of Cu and Fe residuals on the areas covered with graphene. A comparison of ToF-SIMS mass spectra between the SiO2/Si

**Figure 3.** *(a) ToF-SIMS depth profiles of 2 H− , C3 − and SiO2 − ions. ToF-SIMS images of (b) C3 − and (c) 2 H− ions [25].* substrates with and without graphene confirmed that the presence of residual metals is related to the graphene transfer process. Combined with total reflection X-ray fluorescence, the residual metal (Cu and Fe) concentrations were calculated to be approximately 1013–1014 atoms cm−2 regardless of the transfer method.
