Scanning Probe Microscopy (SPM)
| The first scanning probe microscope was realized in 1981 by G. Binning and H. Rohrer at the IBM research labs in Rüschlikon as a scanning tunneling microscope (STM). The basic concept is the detection of an interaction between a sharp tip and a sample surface. In case of the STM the quantum tunnelling current between a metallic tip and the conductive sample is detected. The high, up to atomic-scale lateral resolution is due to both, a sharp tip and an exponential dependence of the quantum tunnelling current. |
| Since its invention, the concept of the SPM has been utilized in many ways, thereby detecting various interactions between the tip and the surface. The most prevalent realization is the scanning force microscope (SFM). Here the tip is mounted on the end of a cantilever, and the force between the tip and the sample surface allows for the feedback circuit. This instrument allows therefore also the investigation of dielectric samples. |
| The big success of scanning probe microscopy is also due to a powerful and ubiquitous device: the lock-in amplifier (LIA) invented by R.~H.~Dicke in the forties. Basically a LIA allows to extract a signal at a given frequency and phase from a noisy environment. The popular use of LIA in scanning probe microscopy relies on the fact that several interactions between tip and sample surface can be driven externally. Thus choosing an frequency-modulated driving scheme allows for a very sensitive readout. That is why it has become a standard to implement at least one LIA in any commercial SPM electronics. |
|
|
