Browsing by Author "Chung, Jen-Yang"

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Apparent topographic height variations measured by noncontact atomic force microscopy
(2007-07-01)
Yang, Kai-Ming
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Chung, Jen-Yang
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Hsieh, Ming-Feng
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Lin, Deng-Sung
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物理研究所
The topographic height measurement on a sample consisting of domains of different materials in noncontact atomic force microscopy (NC-AFM) is typically incorrect owing to the variation in electrostatic force between a tip and a sample. The tip-sample electrostatic force is owing to the difference in effective contact potential between a tip and a sample. This study demonstrates that the error in height strongly depends on the bias applied between the tip and the sample, the radius of the tip apex. the work function difference, and the frequency shift. Experimental results are well explained by integrated model calculations and by including the van der Waals and electrostatic forces between the tip and the sample in the analysis. When the simultaneous compensation of contact potentials during imaging is not performed, the errors occurring in the height measurement can be estimated from the tip-sample distance vs the bias curves obtained in situ.
Correlation of reaction sites during the chlorine extraction by hydrogen atom from Cl/Si(100)-2X1
(2007-07-21)
Hsieh, Ming-Feng
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Chung, Jen-Yang
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Lin, Deng-Sung
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Tsay, Shiow-Fon
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物理研究所
The Cl abstraction by gas-phase H atoms from a Cl-terminated Si(100) surface was investigated by scanning tunneling microscopy (STM), high-resolution core level photoemission spectroscopy, and computer simulation. The core level measurements indicate that some additional reactions occur besides the removal of Cl. The STM images show that the Cl-extracted sites disperse randomly in the initial phase of the reaction, but form small clusters as more Cl is removed, indicating a correlation between Cl-extracted sites. These results suggest that the hot-atom process may occur during the atom-adatom collision. (C) 2007 American Institute of Physics.
Sodium chloride on Si(100) grown by molecular beam epitaxy
(2011-02-25)
Chung, Jen-Yang
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Li, Hong-Dao
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Chang, Wan-Heng
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Leung, T. C.
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Lin, Deng-Sung
Sodium chloride (NaCl) films were grown on an Si(100)-(2 x 1) surface at near room temperature by molecular beam epitaxy (MBE). The atomic structure and growth mode of the prototypical ionic materials on the covalent bonded semiconductor surface is examined by synchrotron core-level x-ray photoemission spectrum (XPS), scanning tunneling microscopy (STM), and first-principles calculations. The Si 2p, Na 2p, and Cl 2p core-level spectra together indicate that adsorbed NaCl molecules at submonolayer coverage [i.e., below 0.4 monolayer (ML)] partially dissociate and form Si-Cl species, and that a significant portion of the dangling-bond characteristics of the clean surface remains after NaCl deposition of 1.8 MLs. The deposition of 0.65-ML NaCl forms a partially ordered adlayer, which includes NaCl networks, Si-Cl species, adsorbed Na species, and isolated dangling bonds. The STM results revealed that the first adlayer consists of bright protrusions which form small c(2 x 4) and (2 x 2) patches. Above 0.65 ML, the two-dimensional NaCl double-layer growth proceeds on top of the first adlayer.