Abstract
GaN nanowires are potential candidates for use in scanning probe microscopy due to their well-defined, reproducible, geometric shapes, their hardness, and their light guiding properties. We have developed and investigated probes for high resolution atomic force microscopy and scanning tunneling microscopy utilizing GaN nanowires as probes. The nanowires are n-doped and the morphology of the nanowires has been tailored for scanning probe microscopy by growing them with a sharp tip for measurements and high thickness for robustness. The individual GaN nanowires were removed from their growth substrate and attached onto commercial atomic force microscopy cantilevers or etched tungsten wires for scanning tunneling microscopy. A standard scanning electron microscope equipped with a nanoprobe, a focused ion beam column and a gas injection system was used to locate, transfer, and attach the nanowires. We evaluated the properties of the GaN probes on different substrates including HOPG, Au, SiO2, InAs, and GaAs. We demonstrate both atomic force microscopy and scanning tunneling microscopy measurements with single atomic layer resolution and evaluate the robustness of the tips by monitoring them before and after scanning. Finally, we explore the use of the tips for scanning tunneling spectroscopy demonstrating that reliable results, which can reveal information on the electronic properties of the surface-tip system, are obtainable. The fundamental properties of these probes, which are demonstrated in this work, show promise for future use of the probes in exploring semiconductor-semiconductor tunneling junctions at the nanoscale as well as for other scanning probe techniques where high resolution is required.
Highlights
The development and use of scanning probe microscopy (SPM) methods have contributed to many important advances in surface science during the last three decades
The atomic force microscope (AFM) measurements were performed in intermittent contact mode where the cantilever is resonating close to its Eigen frequency in and out of contact with the sample
The width of the step would indicate a resolution of ∼10 nm which is consistent with the limitation of this AFM
Summary
The development and use of scanning probe microscopy (SPM) methods have contributed to many important advances in surface science during the last three decades. The most common probes today are either metallic (W, Pt/Ir) for STM or coated Si for AFM, recent efforts have been aimed toward developing probes with particular electronic, optical, mechanical, or magnetic properties. Semiconducting materials, such as GaP, doped diamond, ZnO nanowires as well as InAs nanowires, and cleaved wafers have been evaluated and used as alternatives. The advantages of an InAs semiconducting tip for tunneling spectroscopy was demonstrated and discussed In both cases, the more complicated and variable density of states of the semiconductor (around the Fermi level) is used to extend the spectroscopic probing capabilities of the technique. Demonstrate stable STS measurements that reflect the combined electronic structure of the semiconductor GaN tip and both metal and semiconductor substrates
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