Introduction

Point-contact methods

  • Soft Point-contact
  • Mechanical Point-contact

Difficult to operate when faced with samples shown in (c)

Different Sample Surfaces

Methods

Device & Apparatus Design

Assembly of Scanning Probe Device
Apparatus

Detection of Resonance Frequency

The electric properties of a tuning fork can be well described using simple RLC model.1

\[ \begin{gathered} \omega_{r}=2 \pi f_{r}=\frac{1}{\sqrt{L C}} \\ Y(\omega)=\frac{I(\omega)}{U(\pi)}=i \omega C_{S}+\frac{1}{R+\frac{1}{i \omega C}+i \omega L} \\ Y(f)=\frac{I(\omega)}{U(\pi)}=i 2 \pi f C_{S}+\frac{A_{0} \Delta f\left(\Delta f-2 i\left(f-f_{r}\right)\right)}{\Delta f^{2}+4\left(f-f_{r}\right)^{2}} \end{gathered} \]

Using these formula to fit the measurement curve, we can recover the quality factor of the tuning fork.

Engaging Detection

(a) shift on resonating frequency (b) the amplitude of voltage on versus steps of displacement in z direction

Controlling Strategy

Naive Controlling Strategy that performs retraction on each step
Labview block diagrams of the naive program

Improvement

  • Eliminate retracting
  • Change routing scheme to zig-zag
illustration of no retracting scheme

Avoid discontinuities in \(x, y\) direction.

Straight-Forward routing scheme (left) vs. Zig-Zag routing scheme (right)

Modular Design & Developping

Debugging interface on zig-zag routing scheme
Modular diagram of improved driver. Measuring has been packaged into subVI.

Results

We can recover the shape of a wire using the prototype scanning probe, indicating that the prototype has reached Micron-level resolution.

  1. 1.Kamra et al., “An All-Electrical Torque Differential Magnetometer Operating under Ambient Conditions.” ↩︎