This doctoral thesis focuses on exploring the possibilities of using techniques based on Atomic Force Microscopy (AFM), namely Kelvin Probe Force Microscopy (KPFM) and Conductive AFM (CAFM), for electrical characterization of nanoscale materials. The most significant work was done on characterization of electrical properties of dislocations in AlGaN/GaN. The main results are following: CAFM characterization of dislocations in GaN and AlGaN was optimized to provide reliable data for further correlation with different techniques. The correlation with electron channeling contrast imaging is shown. The measurement on AlGaN required careful sample and tip cleaning by multiple cycles of oxygen and etching treatments to reach stable and reliable measurement. Without the cleaning procedure, the tip conductivity was quickly lost. Therefore, additional surface-sensitive chemical analysis was performed to better understand the processes occurring on the GaN surface. Additionally, a modification of the CAFM technique that operates at constant current (cc-CAFM) was developed, further improving the stability of the measurement. Moreover, the cc-CAFM allows to easily visualize all conductive dislocations irrespective of their threshold voltage, increasing bias at low-conductivity areas and decresing the bias at high-coductivity areas to protect the tip from current-induced damage. Next, the application of KPFM is shown in a study on how electron irradiation changes the electrical properties of nanotube devices. KPFM was used to visualize the trapped charge in the underlying substrate and confirm that this trapped charge was the cause of the change in the resistance of the nanotubes after electron irradiation. Moreover, a simple electrostatic model that allows quantitative estimation of the amount of trapped charge directly
from KPFM images is presented. This thesis also tackles other applications that include visualization of grain boundaries on graphene by KPFM and CAFM, analysis of the graphene-substrate interaction by KPFM and detection of grain boundaries and chiral lines on a WS2 nanotubes by KPFM.