Browsing by Author "Chiang, T. -C."

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Electronic reconstruction at a buried ionic-covalent interface driven by surface reactions
(2009-11-01)
Lou, C. -T.
;
Li, H. -D.
;
Chung, J. -Y.
;
Lin, D. -S.
;
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.
Enhancement of subband effective mass in Ag/Ge(111) thin film quantum wells
(2008-12-01)
Tang, S. -J.
;
Chang, Wen-Kai
;
Chiu, Yu-Mei
;
Chen, Hsin-Yi
;
Cheng, Cheng-Maw
Subband dispersions of quantum-well states in Ag films on Ge(111) have been determined by angle-resolved photoemission. The effective masses of the subbands at the zone center increase substantially for decreasing film thicknesses. This peculiar behavior is attributed to a kinetic constraint for standing-wave formation governed by a momentum-dependent phase-shift function. No evidence is found for in-plane electron localization within the confined geometry.
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.