Three-dimensional scanning force/tunneling spectroscopy at room temperature

Area of Science:

• Surface Science
• Scanning Probe Microscopy
• Nanotechnology

Background:

• Simultaneous measurement of force and tunneling current is crucial for understanding surface interactions at the nanoscale.
• Previous techniques often lack the ability to map local electronic properties alongside mechanical forces.
• The Si(111)-(7 × 7) surface is a well-established model system for surface science studies.

Purpose of the Study:

• To develop and demonstrate a novel measurement technique for simultaneous 3D force and tunneling current mapping.
• To integrate local density of states (LDOS) imaging with force and current measurements using the same scanning probe microscopy (SPM) tip.
• To investigate the atomic composition of the SPM tip during imaging of the Si(111)-(7 × 7) surface.

Main Methods:

• Utilized a scanning force/tunneling microscope (SFM/STM) setup operating at room temperature.
• Converted measured observables (frequency shift, time-averaged tunneling current) into physical quantities (interaction force, instantaneous tunneling current).
• Performed LDOS mapping by measuring tunneling current as a function of bias voltage at constant height for each lateral position.

Main Results:

• Successfully demonstrated simultaneous 3D force and tunneling current measurements on the Si(111)-(7 × 7) surface.
• Acquired LDOS images that revealed the tip apex composition, indicating coverage with silicon atoms.
• Established consistency between LDOS imaging results and the proposed Si-Si covalent bonding mechanism for atomic force microscopy (AFM) imaging.

Conclusions:

• A versatile measurement technique for 3D force/current mapping and LDOS imaging on equivalent surface areas using a single tip has been established.
• The findings provide insights into tip-surface interactions and the mechanisms governing AFM imaging.
• This integrated approach offers a powerful tool for advanced nanoscale surface characterization.