Scanning Probes

Scanning ProbesBy allowing scientists to image surfaces at the scale of individual atoms, scanning probe microscopes have revolutionized nanotechnology research. The first scanning probe instrument was a scanning tunneling microscope, and although it was capable of obtaining atomic resolution it needed to be operated in ultra-high vacuum and could only work with metal or semiconducting sample. Soon, however, a variety of other scanning probe techniques were developed to allow for the analysis of a broad range of systems, including non-conducting systems as well as samples immersed in a liquid environment.

Research Poster PDFs
Atomic force microscopy
High-resolution atomic force microscopy by tracking the resonance frequency of small cantilevers in liquid
High Resolution Kelvin Probe Force Microscopy of Single Biomolecules
Scanning Tunnelling Microscopy Group
Structural Transitions in a Model Hydrophobic Boundary Layer under Water

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Figure:  Single Sb dopant in a Si(111)2x1 surface imaged using scanning tunnelling microscopy. [courtesy Philipp Studer and Neil Curson]

At the heart of a scanning tunneling microscope (STM), a sharp metal tip is held a few atomic diameters over the surface of a conducting material.  If a voltage is applied between the tip and the sample, quantum mechanics will allow electrons to tunnel from one side to the other, producing a current that is exponentially sensitive to the separation distance. This high sensitivity allows the STM to image surfaces with atomic resolution.  In addition, the STM can be used to move and precisely position atoms and molecules on some surfaces, and also to examine the electronic and magnetic structure of the system via elastic and inelastic spectroscopies.

Atomic force microscopy (AFM) or scanning force microscopy (SFM) is a very high-resolution type of scanning probe microscopy, with demonstrated resolution on the order of fractions of a nanometer, more than 1000 times better than the optical diffraction limit.

The AFM is one of the foremost tools for imaging, measuring, and manipulating matter at the nanoscale. The information is gathered by "feeling" the surface with a mechanical probe. Piezoelectric elements that facilitate tiny but accurate and precise movements on (electronic) command enable the very precise scanning.

Scanning near-field optical microscopy (SNOM) is a microscopy technique for nanostructure investigation that breaks the far field resolution limit by exploiting the properties of evanescent waves. This is done by placing the detector much closer to the specimen surface than the wavelength λ of the light. This allows for the surface inspection with high spatial, spectral and temporal resolving power.

With an electrochemical scanning tunneling microscope, or ECSTM, the structures of surfaces and electrochemical reactions in solid-liquid interfaces can be observed at atomic or molecular scales