New fabrication technique for highly sensitive qPlus sensor with well-defined spring constant

TL;DR

This paper introduces a novel fabrication method for highly sensitive qPlus sensors using focused ion beam techniques, resulting in stable, well-defined spring constants suitable for atomic resolution AFM and STM at cryogenic temperatures.

Contribution

It presents a new fabrication process combining FIB cutting and welding for qPlus sensors, achieving high sensitivity, stability, and precise spring constant control.

Findings

High resonance frequency and quality factor achieved.

Sensor stability under UHV tip cleaning and in-situ treatments.

Successful atomic resolution imaging at 4.5 K.

Abstract

A new technique for the fabrication of highly sensitive qPlus sensor for atomic force microscopy (AFM) is described. Focused ion beam was used to cut then weld onto a bare quartz tuning fork a sharp micro-tip from an electrochemically etched tungsten wire. The resulting qPlus sensor exhibits high resonance frequency and quality factor allowing increased force gradient sensitivity. Its spring constant can be determined precisely which allows accurate quantitative AFM measurements. The sensor is shown to be very stable and could undergo usual UHV tip cleaning including e-beam and field evaporation as well as in-situ STM tip treatment. Preliminary results with STM and AFM atomic resolution imaging at $4.5\,K$ of the silicon $Si(111)-7\times 7$ surface are presented.