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[摘要]：In this research, variable wavelength photoelectron emission microscopy (PEEM) with tunable UV light from the Duke University free electron laser is applied to image single fibrinogen molecules adsorbed onto n-type silicon surfaces. High resolution PEEM images (similar to 10 nm) are obtained with photon energies from 4 to 6 eV. Wavelength-dependent image sequences are analyzed to determine the photoionization spectrum and the photoelectron emission threshold of individual molecules. The experimental data are fitted using temperature dependent Fowler law, square-root law, and cube-root law. The details of the theoretical models are discussed. The square-root and cube-root fittings reveal the ionization threshold of 5.0 eV for fibrinogen adsorbed onto n-type silicon, while temperature dependent Fowler law shows a threshold of 4.9 eV. The accuracy of the measurements is calculated to be +/- 0.2 eV. The authors conclude that no significant difference is observed from the three theoretical fitting approaches. (C) 2008 American Vacuum Society. |
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