Abstract
Multi-probe scanning tunneling microscopy can play a role in various electrical measurements and characterization of nanoscale objects. The consistent close placement of multiple probes relies on very sharp apexes with no other interfering materials along the shank of the tip. Electrochemically etched tips can prepare very sharp apex tips; however, other asperities on the shank can cause interference and limit the close positioning of multiple tips to beyond the measured radii. Gallium focused ion beam (FIB) milling is used to remove any interfering material and allow closely spaced tips with a consistent yield. The tip apex radius is evaluated with field ion microscopy, and the probe spacing is evaluated with STM on hydrogen terminated silicon surfaces. FIB prepared tips can consistently achieve the measured probe to probe spacing distances of 25 nm–50 nm.
Highlights
Multi-probe scanning tunneling microscopy (M-STM) has advanced in recent years from custom built to commercially available systems as researchers strive for atom resolving multi-tip surface analysis with the ability to controllably contact and electrically probe surfaces
One issue in measuring small structures is the ability to consistently prepare closely spaced probes at distances less than 100 nm. This is because the close spacing is determined by the apex sharpness and by the geometry between the multiple tips and the shoulders/shanks of the probes themselves
We found that electrochemical etching can occasionally create closely spaced probes, and Field Ion Microscopy (FIM) measurement confirmed very sharp apexes, protrusions on the shoulders of the tips limited the close spacing
Summary
Multi-probe scanning tunneling microscopy (M-STM) has advanced in recent years from custom built to commercially available systems as researchers strive for atom resolving multi-tip surface analysis with the ability to controllably contact and electrically probe surfaces.1–10 Several studies have shown the advantages of M-STM on various types of samples such as semiconductors,11–18 graphene,19–21 carbon films,22 and topological insulators.23–26 Recently, the resistivity of an atomic step on a silicon surface was measured,12,16 and lithographically prepared dangling bond (DB) wires on a germanium surface were measured.14,15 one issue in measuring small structures is the ability to consistently prepare closely spaced probes at distances less than 100 nm. This is because the close spacing is determined by the apex sharpness and by the geometry between the multiple tips and the shoulders/shanks of the probes themselves. We consider various methods to prepare closely spaced probes including electrochemical etching of probes, Field Ion Microscopy (FIM) imaging of probe apexes, and focused ion beam (FIB) milling of probes.
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