Ladungstransport durch Graphenschichten und GaAs-Nanodrähte untersucht mit einem Multispitzen-Rastertunnelmikroskop

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This work explores the integration of a scanning electron microscope (SEM) and a multitip scanning tunneling microscope (STM) with four tips as a nanoprober for electrical measurements on graphene layers and freestanding gallium arsenide (GaAs) nanowires. Four-probe measurements are essential for assessing the resistivity of one- and two-dimensional conductors, necessitating additional contacts for current-free potential measurements. The multitip STM was enhanced with advanced electronics to function as a flexible nanoprober. Graphene layers on insulating SiO2 and hexagonal boron nitride (h-BN), prepared via mechanical exfoliation, were contacted using the multitip STM. Tunneling current could not serve as feedback initially; thus, a contrast change in the SEM image upon tip contact was utilized. Scanning and electrical measurements revealed bubbles, wrinkles, and contaminants on graphene transferred to h-BN, yet STM images of clean areas showed a moiré pattern, indicating the graphene's flatness on the h-BN surface. Four-point measurements indicated poor conductivity (1/σ = 16 kΩ) and low field effect mobility (μ = 300 cm²/Vs), likely due to transfer contamination and electron irradiation. For freestanding p-doped GaAs nanowires, four-point measurements showed that elastic deformation does not significantly affect conductivity. Resistance profiles along the nanowires revealed a resistivity of a few kΩ/m for segments grown at