Using the Platinum-Iridium tips constructed using wire cutters,
the following images and analysis were obtained with a Burleigh
Instructional STM and accompanying software.
The first images collected were that of a graphite surface at magnifications of 100 by 100 angstroms, and 20 by 20 angstroms. (Click on image to magnify)
Information:100 by 100 angstroms, filtered with FFT, contour view, graphite
Information: 100 by 100 angstroms, filtered with FFT, 3d view, graphite
Information: 20 by 20 angstroms, unfiltered, contour view, graphite
Information: 20 by 20 angstroms, filtered with FFT, contour view, graphite
Information: 20 by 20 angstroms, unfiltered, 3d view, graphite
Information: 20 by 20 angstroms, filtered with FFT, graphite
This picture is the same as the previous one except it traces out the hexagonal structure the carbon atoms make in graphite. Using cross sectional analysis on the STM software were able to determine an approximate distance between carbon atoms in the hexagonal configuration. The graph below depicts the results from various cross sections analyzed. The peaks in the graph represent individual atoms. The approximated distance between carbon atoms was determined to be 2.45 angstroms.
The next substance analyzed with the STM was a Molybdenum Disulfide (MoS2).
Information: 120 by 120 angstroms, filtered with FFT, contour view, MoS2
Information: 120 by 120 angstrom, filtered with FFT, 3d view, MoS2
As seen in the pictures above the MoS2 has quite a different surface structure than graphite. In fact, the structure consists of two sulfur atoms (seen a humps on the images) bonded to a molybdenum atom beneath the surface (seen as tiny bright spots). The image below represents a cross section taken between two adjacent sulfur atoms.
The following analysis reveals two sulfur atoms (two large peaks), and one molybdenum atom (small peak) barely beneath the surface.
Using the cross sectional analysis, we determined the atomic spacings in the triangular structure. The spacing between sulfur atoms was determined to be 1.6 angstroms. This is about one-half the length of the accepted value of 3.16 angstroms.7 We found similar cross sections to be off by a factor of one-half as well, leading us to believe that a scaling error was made in data collection.
The image below provides a detailed images of the structure of MoS2.