title: Evaluation and optimization of quartz resonant-frequency retuned fork force sensors with high Q factors, and the associated electric circuits, for non-contact atomic force microscopy.
abstract: High-Q factor retuned fork (RTF) force sensors made from quartz tuning forks, and the electric circuits for the sensors, were evaluated and optimized to improve the performance of non-contact atomic force microscopy (nc-AFM) performed under ultrahigh vacuum (UHV) conditions. To exploit the high Q factor of the RTF sensor, the oscillation of the RTF sensor was excited at its resonant frequency, using a stray capacitance compensation circuit to cancel the excitation signal leaked through the stray capacitor of the sensor. To improve the signal-to-noise (S/N) ratio in the detected signal, a small capacitor was inserted before the input of an operational (OP) amplifier placed in an UHV chamber, which reduced the output noise from the amplifier. A low-noise, wideband OP amplifier produced a superior S/N ratio, compared with a precision OP amplifier. The thermal vibrational density spectra of the RTF sensors were evaluated using the circuit. The RTF sensor with an effective spring constant value as low as 1000 N/m provided a lower minimum detection limit for force differentiation. A nc-AFM image of a Si(111)-7 × 7 surface was produced with atomic resolution using the RTF sensor in a constant frequency shift mode; tunneling current and energy dissipation images with atomic resolution were also simultaneously produced. The high-Q factor RTF sensor showed potential for the high sensitivity of energy dissipation as small as 1 meV/cycle and the high-resolution analysis of non-conservative force interactions.
authors.affiliation: Natural Science and Technology, Kanazawa University, Kanazawa, Ishikawa 920-1192, Japan.
authors.forename: Hiroaki
authors.initials: H
authors.lastname: Ooe
authors.affiliation: Natural Science and Technology, Kanazawa University, Kanazawa, Ishikawa 920-1192, Japan.
authors.forename: Mikihiro
authors.initials: M
authors.lastname: Fujii
authors.affiliation: Japan Advanced Institute of Science and Technology, Nomi, Ishikawa 923-1292, Japan.
authors.forename: Masahiko
authors.initials: M
authors.lastname: Tomitori
authors.affiliation: Natural Science and Technology, Kanazawa University, Kanazawa, Ishikawa 920-1192, Japan.
authors.forename: Toyoko
authors.initials: T
authors.lastname: Arai