National Physical Laboratory

Scanning Probe Microscopy

Scanned Probe Microscopy 

Scanning Probe Microscopy is a class of measurement methods for imaging surfaces by mechanically scanning a probe over the surface under study. It is a generic term that encompasses a wide number of techniques including AFM, SNOM, STM, etc.

However, there is no single technique that can provide complete information about a nanostructured material. Approaches combining different methods using optical, chemical and nanomechanical probes can bring insight into their structures and properties, but there are many immediate obstacles. This includes the measurement of small forces, calibration of tip-dimensions and tip-stiffness, understanding of the contact mechanics, reliable quantification of measured data, and traceability to the SI system.

At NPL we are addressing issues related to the following scanned probe techniques:

Atomic Force Microscopy is a popular method used to measure surface topography and materials properties with spatial resolutions of 5 - 20 nm and height dimensions in the range from 100 nm down to approx 5 nm. This provides a 3D image of the surface from which line profiles may be extracted. In addition, variations of AFM can provide a wide range of information, which includes the following techniques:

Lateral Force Microscopy (LFM), also called Frictional Force Microscopy (FFM), uses an AFM tip to image variations in surface friction measuring the lateral deflections of the cantilever as it scans across the sample.

Nanomechanics refers to measurements of mechanical properties, such as stiffness of a polymer, with nanometre resolution. This can be done using AFM in force spectroscopy mode.

Chemical Force Microscopy uses a functionalised AFM tip to measure the chemical force between atoms or molecular groups on the tip and those on the sample surface.

Dip Pen Nanolithography is powerful yet easy to tool for writing nanoscale structure with molecules and nanoparticles.

Scanning Near-field Optical Microscopy / Nanoscale Raman Spectroscopy offers optical imaging of surfaces at a resolution of between 50 and 90nm. SNOM is similar in operation to AFM, but with the added analytical potential of optical spectroscopy (such as Raman and IR) at nanoscale resolution.

We are particularly interested in Tip Enhanced Raman Spectroscopy (TERS), which uses a specially prepared AFM tip, kept in close proximity of the sample surface (few nm), utilising the massive enhancement factor of the Raman signal caused by the tip.


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Last Updated: 5 Mar 2012
Created: 24 Aug 2010


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