Amplifier for scanning tunneling microscopy at MHz frequencies

Area of Science:

• Surface Science
• Low-Temperature Physics
• Electronic Instrumentation

Background:

• Conventional scanning tunneling microscopy (STM) is limited to a few kHz bandwidth, restricting its ability to probe fast electronic phenomena.
• Existing techniques struggle with high-impedance measurements and achieving high signal-to-noise ratios at higher frequencies.

Purpose of the Study:

• To develop and test a novel amplifier circuit for STM capable of MHz bandwidth operation.
• To enable simultaneous high-resolution STM imaging and advanced spectroscopic measurements.
• To integrate this technology into commercial low-temperature, ultra-high vacuum STM systems.

Main Methods:

• Designed and built an amplifier circuit featuring an LC tank with a quality factor > 600 and a low-noise high electron mobility transistor.
• Utilized superconducting cross-wound inductors and low heat load materials for high signal-to-noise ratio in cryogenic environments.
• Tested the amplifier's performance by mapping tunneling electron noise and performing differential conductance spectroscopy.

Main Results:

• The amplifier successfully operated in the MHz regime while maintaining atomic resolution and high junction resistances (giga-ohms).
• Spatially mapped Poissonian noise of tunneling electrons on an Au(111) surface.
• Demonstrated 3 MHz differential conductance spectroscopy with superior performance compared to conventional methods.

Conclusions:

• The novel MHz bandwidth amplifier significantly extends the capabilities of STM.
• This technology opens new avenues for advanced surface science investigations, including spin resonance and Majorana mode detection.
• The developed circuit is suitable for integration into commercial low-temperature STM systems.