Interpretation of scanning tunneling microscopy images of graphite

Thesis/Dissertation · Fri Jan 01 04:00:00 EST 1988

OSTI ID:6106436

Mizes, H A

This dissertation analyzes scanning tunneling microscopy (STM) images of graphite. Graphite is an important substrate for molecular imaging and nanometer lithography. Because it is a layered structure with a simple unit cell, its electronic structure can be described simply using tight binding theory. More interestingly, the charge density at the Fermi level, which is the quantity that the STM probes, is well approximated by the six leading Fourier components. The effect of multiple atomic tips on the STM images of graphite can be predicted using the three sine wave description. Both the varying asymmetry between the two inequivalent atoms, and the loss of three fold symmetry observed in experimental images, can be attributed to differing tip configurations. The existence of multiple atomic tips is directly confirmed by the observation of moire' patterns occurring near grain boundaries. Physisorbed and intercalated atoms and molecules will produce weak perturbations in the electronic structure of the graphite. These perturbations can be measured with the STM as localized changes in the tunneling current, and appear as bright areas in STM gray-scale images. The dependence of the brightness with scanning height is calculated and can be used as a measure to help identify the atom or molecule. Chemisorbed atoms and molecules will produce a stronger long-range perturbation in the electronic structure of the graphite. It is shown that any strong perturbation should give rise to oscillations in the Fermi level charge density with a wavelength {radical}3 times that of the graphite lattice.

• Research Organization: Stanford Univ., CA (USA)
• OSTI ID: 6106436
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
360603* -- Materials-- Properties
ATOMS
CARBON
CHARGE DENSITY
CHEMICAL REACTIONS
CHEMISORPTION
COMPARATIVE EVALUATIONS
DEFECTS
ELECTRON MICROSCOPY
ELECTRONIC STRUCTURE
ELEMENTAL MINERALS
ELEMENTS
ENERGY LEVELS
FERMI LEVEL
GRAPHITE
IMAGES
MICROSCOPY
MINERALS
MOLECULES
NONMETALS
OSCILLATIONS
SCANNING ELECTRON MICROSCOPY
SEPARATION PROCESSES
SORPTION