Browsing by Author "Lin, D. -S."

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Atomic and electronic structures of thin NaCl films grown on a Ge(001) surface
(2009-07-01)
Tsay, Shiow-Fon
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Lin, D. -S.
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物理研究所
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Institute of Physics
Density functional theory (DFT) with LDA and GGA have been employed to study the interface and thin film properties of NaCl on a Ge(0 0 1) surface. The atomic and electronic structures of thin NaCl films from one to ten monolayers were analyzed. The layer adsorption energies show that a quasi-crystalline (0 0 1) fcc NaCl film is built up via a layer-by-layer growth mode with NaCl thickness above 2 ML. Simulated STM images show a well-resolved (1 x 1) NaCl atomic structure for sample bias voltage V(s) < -2.5 V and the bright protrusions should be assigned to the Cl(-) ions of the NaCl film. The Ge substrate dimer is reserved and buckled like a clean Ge(0 0 1)-p(2 x 2) surface as the result of weak interface interaction between the dangling bonds coming from valence pi states of the Ge substrate and the 3p states of the interfacial Cl(-) ion. These results are consistent with the experiments of STM, LEED and EELS. (C) 2009 Elsevier B.V. All rights reserved.
Electronic reconstruction at a buried ionic-covalent interface driven by surface reactions
(2009-11-01)
Lou, C. -T.
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Li, H. -D.
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Chung, J. -Y.
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Lin, D. -S.
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Chiang, T. -C.
Lattice-matched ionic NaCl films were grown layer by layer on covalent Ge(100) using cycles of two half reactions (HRs) that involved the alternative adsorption of Cl and Na. The Ge 3d photoemission spectra obtained after full cycles of growth resembled that of clean Ge(100), but came to resemble that of the polar Cl-terminated surface after the subsequent half reaction of Cl adsorption. Concurrently, the Na and Cl core levels of the nanofilms shifted by similar to 1.7 eV between these two interface configurations. Our results demonstrate that reactions on the NaCl surface drive periodic electronic reconstructions at the NaCl-Ge interface.
Systematic variations in apparent topographic height as measured by noncontact atomic force microscopy
(2006-11-01)
Yang, K. -M.
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Chung, J. Y.
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Hsieh, M. F.
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Ferng, S. -S.
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Lin, D. -S.
A flat Si(100) surface is prepared with neighboring n- and p-doped regions. The contact potential difference between the tip and the two well-defined regions of similar material is utilized to examine the effects and interplay of essential tip-sample forces in atomic force microscopy. Measurements with a frequency-modulated noncontact atomic force microscope (NCAFM) show large apparent topographic height variations across the differently doped regions. The height differences depend on the bias polarity, bias voltage, radius, and conducting state of the tip. The functional relationships are well explained by integrated model calculations. These findings provide a coherence scenario of NCAFM operation under these essential forces and facilitate quantitative understanding of the systematic errors in surface topographic height measurement commonly performed in nanoscience.