Advanced Materials Characterization Chapter 13 Scanning Tunneling Microscopy

Advanced Materials Characterization Chapter 13 - by Igor Bello

Scanning probe microscopy (SPM) is a very large group of analytical techniques that use stylus probes for analysis of surface properties. The first devices that used styluses in surface analyses were surface profilers. The surface profilers with stylus probe precede scanning tunneling microscopy (STM) and atomic force microscopy (AFM). Stylus surface profilers have been used to analyze surface topography, surface roughness, depth of trenches, and thickness of films.

In stylus surface profilers, a stylus is scanned linearly or in x- and y- directions (xy-plane) while the stylus is in physical contact with the material surface. Thus, the volume of a cavity or removed material by sputtering can be calculated, which is often used in calibration, for example, in SIMS analyses. The stylus is installed on a cantilever whose deflection is measured as topographic changes along scanning a stylus over the material surfaces. Force ranging from 0.03 mgf to 15 mgf is applied to the stylus with a radius of 20 nm. Repetition-accuracy measurement of 1 um-tall step is 0.5 nm and maximum thickness that can be measured is 1,200m. Thickness resolution of surface profilers approaches that of AFM, while linear scan can be greater than 200 mm. Long scans permit measuring the surface curvature developed by stress in the deposited films. Therefore, profiler systems may be provided by a software for stress calculation using the Stoney’ equation.

STM is considered to be an ancestor of all scanning probe microscopes. It was invented by Gerd Binnig and Heinrich Rohrer at the IBM Zurich in 1981. Five years later the authors were awarded the Nobel Prize in physics for their invention. STM was the first instrument to generate real-space images of surfaces with atomic resolution. Thus, STM overwhelmingly affected scientific study in nanoscience and material analyses on atomic scales.