Ubiquitous van der Waals (vdW) forces are very important for nanostructures. Although the vdW forces between two surfaces (or two layers)
have been measured for several decades, a direct detection at the single-molecule level is still difficult. Herein, we report a novel method to solve
this problem in high vacuum by means of AFM-based single-molecule force spectroscopy (SMFS). Solvent molecules and surface adsorbed
water are removed thoroughly under high vacuum so that the situation is greatly simplified. A constant force plateau can be observed when a
polymer chain is peeled off from a substrate in high vacuum. Accordingly, the vdW forces between one polymer repeating unit and the substrates
can be obtained. The experimental results show that the vdW forces (typical range: 21–54 pN) are dependent on the species of substrates
and the size of polymer repeating unit, which is in good accordance with the theoretical results. It is expected that this novel method can be
applied to detect other non-covalent interactions (such as hydrogen bond and π-π stacking) at the single-molecule level in the future.