Thesis:

Graphene-coated nanoprobes for conductive atomic force microscopy

Atomic force microscopy (AFM) is a powerful technique that enables the study of surface topography at the nanoscale and, depending on the operating mode, the characterization of local electrical properties. However, electrical measurements require AFM probes with conductive coatings. These coatings present several limitations, including reduced conductivity stability, limited mechanical robustness, and relatively high fabrication costs. In this context, this research evaluates the feasibility of graphene (Gr) as an alternative coating material for AFM probes. Silicon nanoprobe tips coated with graphene are proposed as an additional option for conductive AFM probes, expanding the range of materials that can be used to provide electrical conductivity to AFM tips. Graphene is first synthesized using chemical vapor deposition (CVD), producing a suspended two-dimensional graphene sheet at a water–air interface. The graphene film is then transferred from this interface onto the apex of an AFM probe using a hydraulic micromanipulator coupled to the AFM system through a polymer-free transfer approach. In this work, mono-, bi-, and multilayer graphene were successfully synthesized and transferred onto eight AFM probes. Scanning electron microscopy (SEM) was employed to analyze the morphology of the probes and verify the presence of the graphene coating on the tip apex. The synthesized graphene was further characterized using Raman spectroscopy. The structural quality and number of graphene layers were evaluated through the intensity ratios ID/IG and I2D/IG, respectively. Optical microscopy was additionally used to analyze the graphene coverage on the AFM chip, allowing the evaluation of its suitability for establishing electrical contacts required for conductive atomic force microscopy (C-AFM) measurements. Finally, the performance of the Gr-coated probes was evaluated through local topographic and conductivity measurements using C-AFM on a floppy disk test sample. This sample consists of Fe2O3 particles mixed with carbon black embedded in a polyurethane matrix, providing a surface with electrical heterogeneity ideal for conduction testing. The results show that(...).