Browsing by Author "Hsieh, Ming-Feng"

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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
;
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
;
Chung, Jen-Yang
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Lin, Deng-Sung
;
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.
Determination of dissociative fragment-adsorbate interaction energy during chemisorption of the diatomic molecule HCl on Si(100)
(2010-01-15)
Hsieh, Ming-Feng
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Cheng, Jen-Yin
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Yang, Jenq-Cheng
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Lin, Deng-Sung
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Morgenstern, Karina
This study investigates the surface chemistry and the ordering characteristics of coadsorbed hydrogen and chlorine atoms, generated by the exposure of the Si(100) surface to gas-phase HCl molecules at various substrate temperatures, by scanning tunneling microscopy (STM), core-level photoemission spectroscopy, and Monte Carlo simulation. Experimental results show that saturation exposure to HCl causes all surface dangling bonds to be terminated by the two fragments H and Cl atoms and that the number of H-terminated sites exceeds that of Cl-terminated ones by more than 10%. This finding suggests that, in addition to the dominant dissociative chemisorption, atomically selective chemisorption or atom abstraction occurs. STM images reveal that some Cl-terminated sites form patches with a local 2 x 2 structure at 110 K and that the degree of ordering is reduced as the substrate temperature increases. Results of Monte Carlo simulations demonstrate the importance of including dissociative fragment-adsorbate interactions during the random adsorption of diatomic molecules. Comparing the correlations between Cl-terminated sites identified from STM images and those predicted by simulation reveals two effective interaction energies of 8.5 +/- 2.0 and 3.5 +/- 2.0 meV between a dissociative fragment Cl atom and a nearest neighboring Cl adsorbates in the same dimer row and in the adjacent row, respectively.
Formation, Binding, and Stability of O-Ag-CO(2)-Ag-O Compounds on Ag(100) Investigated by Low Temperature Scanning Tunneling Microscopy and Manipulation
(2010-08-26)
Hsieh, Ming-Feng
;
Li, Hong-Doa
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Lin, Deng-Sung
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Morgenstern, Karina
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物理研究所
The understanding of reaction intermediates in heterogeneous catalysis has important implications for the design of novel catalysts. We investigate the adsorption of CO(2) on oxygen precovered Ag(100) at low temperature (17 K) by scanning tunneling microscopy and inelastic electron tunneling manipulation at 5 K. On the terraces, the adsorption leads to O-Ag-CO(2)-Ag-O compounds with reduced binding of the oxygen to the surface as compared to the separately adsorbed molecules. The compound can be either dissociated into a bistable O-Ag-CO(2) compound at 1.6 V, dissociated into its constituents at 2.2 V, or reacted at 6.5 V into a species, which we tentatively attribute to CO(3). The thus obtained carbon trioxide or carbonate is an intriguing reaction intermediate, because it is not stable in the gas phase. Our detailed study of coadsorbed species outlines a possibility to investigate precursors of reactions that involve the substrate atoms.
Formation, Binding, and Stability of O-Ag-CO2-Ag-O Compounds on Ag(100) Investigated by Low Temperature Scanning Tunneling Microscopy and Manipulation
(2010-08-26)
Hsieh, Ming-Feng
;
Li, Hong-Doa
;
Lin, Deng-Sung
;
Morgenstern, Karina
;
物理研究所
The understanding of reaction intermediates in heterogeneous catalysis has important implications for the design of novel catalysts. We investigate the adsorption of CO2 on oxygen precovered Ag(100) at low temperature (17 K) by scanning tunneling microscopy and inelastic electron tunneling manipulation at 5 K. On the terraces, the adsorption leads to O-Ag-CO2-Ag-O compounds with reduced binding of the oxygen to the surface as compared to the separately adsorbed molecules. The compound can be either dissociated into a bistable O-Ag-CO2 compound at 1.6 V, dissociated into its constituents at 2.2 V, or reacted at 6.5 V into a species, which we tentatively attribute to CO3. The thus obtained carbon trioxide or carbonate is an intriguing reaction intermediate, because it is not stable in the gas phase. Our detailed study of coadsorbed species outlines a possibility to investigate precursors of reactions that involve the substrate atoms.
Growth behaviour of Ge nano-islands on the nanosized Si{111} facets bordering on two {100} planes
(2006-10-28)
Ferng, Shyh-Shin
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Yang, Tsung-Hsi
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Luo, Guangli
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Yang, Kai-Ming
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Hsieh, Ming-Feng
Si( 100) substrates were used to fabricate various nanosized {111} facets between the ( 100) planes using photolithography and anisotropic wet chemical etching. Following simultaneous Ge chemical vapour deposition on the neighbouring ( 100) and {111} facets, the Ge nano-island formation and distribution was observed on both the ( 100) terraces and the {111} side walls using a dynamical atomic force microscope. The nano-island formation on the nanosized {111} strip facets was found to be strongly suppressed upon reducing the strip width due primarily to the interaction of adatoms on the neighbouring facets. Specifically, the difference in the effective chemical potential of Ge adatoms on the two neighbouring facets leads to the depletion of nano-islands on the {111} strip with width < 500 nm under the growth condition used in this study.
Hard repulsive barrier in hot adatom motion during dissociative adsorption of oxygen on Ag(100)
(2009-11-07)
Hsieh, Ming-Feng
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Lin, Deng-Sung
;
Gawronski, Heiko
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Morgenstern, Karina
;
物理研究所
Random pairing simulation and low temperature scanning tunneling microscopy (STM) are used to investigate the detailed O(2) dissociative adsorption processes at 200 K for various coverages. The distribution of oxygen adatoms shows a strong repulsion between the adsorbates with a radius of similar to 0.8 nm. The comparison between STM results and simulation reveals two prominent pairing distances of 2 and 4 nm and their branching ratio is about 2:1. These findings shed new light on the origin of the large intrapair distances found and on the process behind the empirical "eight-site rule.".
Possibility of direct exchange diffusion of hydrogen on the Cl/Si(100)-2X1 surface
(2009-07-01)
Hsieh, Ming-Feng
;
Lin, Deng-Sung
;
Tsay, Shiow-Fon
;
物理研究所
;
Institute of Physics
The diffusion behavior of hydrogen substitutional sites on the chlorine-terminated Si(100) surface was investigated at elevated temperatures using time-lapse scanning tunneling microscopy (STM). STM movies show that each hydrogen atom undergoes Brownian motion within a monochloride dimer row. The position of a hydrogen substitutional site is exchanged directly with that of an immediate neighboring chlorine atom in either the same dimer (intradimer diffusion) or in one of the two adjacent dimers in the same row (intrarow diffusion). Accordingly, conceptual direct exchange diffusion (DED) in a two-dimensional lattice was experimentally observed. Analysis of STM movies at various temperatures yielded rather low attempt frequencies and energy barriers, leading to the suggestion that the diffusion mechanism involves an intermediate low-energy molecular state. Density-functional theory (DFT) calculations were also performed and provided partial support for the proposed diffusion mechanism.
Whole-genome sequencing and identification of Morganella morganii KT pathogenicity-related genes
(2012-12-13)
Chen, Yu-Tin
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Peng, Hwei-Ling
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Shia, Wei-Chung
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Hsu, Fang-Rong
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Ken, Chuian-Fu
Background: The opportunistic enterobacterium, Morganella morganii, which can cause bacteraemia, is the ninth most prevalent cause of clinical infections in patients at Changhua Christian Hospital, Taiwan. The KT strain of M. morganii was isolated during postoperative care of a cancer patient with a gallbladder stone who developed sepsis caused by bacteraemia. M. morganii is sometimes encountered in nosocomial settings and has been causally linked to catheter-associated bacteriuria, complex infections of the urinary and/or hepatobiliary tracts, wound infection, and septicaemia. M. morganii infection is associated with a high mortality rate, although most patients respond well to appropriate antibiotic therapy. To obtain insights into the genome biology of M. morganii and the mechanisms underlying its pathogenicity, we used Illumina technology to sequence the genome of the KT strain and compared its sequence with the genome sequences of related bacteria. Results: The 3,826,919-bp sequence contained in 58 contigs has a GC content of 51.15% and includes 3,565 protein-coding sequences, 72 tRNA genes, and 10 rRNA genes. The pathogenicity-related genes encode determinants of drug resistance, fimbrial adhesins, an IgA protease, haemolysins, ureases, and insecticidal and apoptotic toxins as well as proteins found in flagellae, the iron acquisition system, a type-3 secretion system (T3SS), and several two-component systems. Comparison with 14 genome sequences from other members of Enterobacteriaceae revealed different degrees of similarity to several systems found in M. morganii. The most striking similarities were found in the IS4 family of transposases, insecticidal toxins, T3SS components, and proteins required for ethanolamine use (eut operon) and cobalamin (vitamin B-12) biosynthesis. The eut operon and the gene cluster for cobalamin biosynthesis are not present in the other Proteeae genomes analysed. Moreover, organisation of the 19 genes of the eut operon differs from that found in the other non-Proteeae enterobacterial genomes. Conclusions: This is the first genome sequence of M. morganii, which is a clinically relevant pathogen. Comparative genome analysis revealed several pathogenicity-related genes and novel genes not found in the genomes of other members of Proteeae. Thus, the genome sequence of M. morganii provides important information concerning virulence and determinants of fitness in this pathogen.