Phase detection of electrostatic force by AFM with a conductive tip

Area of Science:

• Surface Science
• Scanning Probe Microscopy
• Condensed Matter Physics

Background:

• Surface potential is crucial for understanding material properties.
• Accurate measurement of surface potential is challenging.
• Kelvin probe force microscopy (KPFM) is a technique for surface potential mapping.

Purpose of the Study:

• To improve the accuracy of surface potential determination using KPFM.
• To evaluate work functions of metals and surface Fermi levels of InAs/GaAs.
• To demonstrate the benefit of complementary amplitude and phase signal analysis in KPFM.

Main Methods:

• Utilized Kelvin probe force microscopy (KPFM), integrating atomic force microscopy with a conductive tip.
• Applied AC bias with DC offset to induce electrostatic forces between sample and tip.
• Analyzed the amplitude and phase of the f(s) component of the electrostatic force for surface potential evaluation.

Main Results:

• Identified a 180-degree phase jump in the f(s) component when DC offset matches the surface potential difference.
• Demonstrated that complementary use of amplitude and phase signals significantly improves surface potential measurement accuracy.
• Successfully measured work functions of various metals and surface Fermi levels of InAs layers on GaAs substrates.

Conclusions:

• The phase detection method in KPFM, when combined with amplitude analysis, offers a more accurate approach to surface potential measurement.
• This enhanced KPFM technique is effective for characterizing electronic properties of materials like metals and semiconductors.
• The study validates the utility of KPFM for precise determination of work functions and surface Fermi levels.