Figure 2.

Metal coating the polymer-film sample decreased frequency noise significantly. Spectrum of cantilever frequency fluctuations observed experimentally (right-hand axis) and the equivalent power spectral density of force fluctuations (left-hand axis, calculated using eq 1). (a) Force fluctuation spectrum over a gold-coated film prepared by lamination (blue, tip–sample separation $h=37\text{nm}$; see Figure 6) and over bare polystyrene (orange, $h=41\text{nm}$). (b) Force fluctuation spectrum over gold-coated film prepared by lamination (blue, $h=37\text{nm}$; see Figure 6) and by e-beam evaporation (orange, $h=40\text{nm}$). All data were taken at a temperature of $T=4.2\text{K}$ and an external magnetic field of $B_0=0\text{T}$. The gold thickness was 12 nm. The zero-to-peak cantilever amplitude was $x_{0_{\text{p}}}=164\text{nm}$. The data in (a) and the blue data in (b) were acquired using cantilever A (Table 1), while the orange data in (b) were acquired using cantilever B. The dashed lines are the thermomechanical force noise, eq 2, and the corresponding thermally limited frequency noise.