Browsing by Author "Chung, J. Y."

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Growth mode and novel structure of ultra-thin KCl layers on the Si(100)-2 x 1 surface
(2009-01-15)
Tsay, S-F.
;
Chung, J. Y.
;
Hsieh, M-F.
;
Ferng, S-S.
;
Lou, C-T.
This study investigates ultra-thin potassium chloride (KCl) films on the Si(1 0 0)-2 x 1 surfaces at near room temperature. The atomic structure and growth mode of this ionic solid film on the covalent bonded semiconductor surface is examined by synchrotron radiation core level photoemission, scanning tunneling microscopy and ab initio calculations. The Si 2p, K 3p and Cl 2p core level spectra together indicate that adsorbed KCl molecules at submonolayer coverage partially dissociate and that KCl overlayers; above one monolayer (ML) have similar features in the valance band density of states as those of the bulk KCl crystal. STM results reveal a novel c(4 x 4) structure at 1 ML coverage. Ab initio calculations show that a model that comprises a periodic pyramidal geometry is consistent with experimental results. (C) 2009 Elsevier B.V. All rights reserved.
Growth mode and novel structure of ultra-thin KCl layers on the Si(100)-2 x 1 surface
(2009-01-15)
Tsay, S-F.
;
Chung, J. Y.
;
Hsieh, M-F.
;
Ferng, S-S.
;
Lou, C-T.
This study investigates ultra-thin potassium chloride (KCl) films on the Si(1 0 0)-2 x 1 surfaces at near room temperature. The atomic structure and growth mode of this ionic solid film on the covalent bonded semiconductor surface is examined by synchrotron radiation core level photoemission, scanning tunneling microscopy and ab initio calculations. The Si 2p, K 3p and Cl 2p core level spectra together indicate that adsorbed KCl molecules at submonolayer coverage partially dissociate and that KCl overlayers; above one monolayer (ML) have similar features in the valance band density of states as those of the bulk KCl crystal. STM results reveal a novel c(4 x 4) structure at 1 ML coverage. Ab initio calculations show that a model that comprises a periodic pyramidal geometry is consistent with experimental results. (C) 2009 Elsevier B.V. All rights reserved.
Systematic variations in apparent topographic height as measured by noncontact atomic force microscopy
(2006-11-01)
Yang, K. -M.
;
Chung, J. Y.
;
Hsieh, M. F.
;
Ferng, S. -S.
;
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.