[Show abstract][Hide abstract] ABSTRACT: As the film becomes atomically thin, the on-site Coulomb interaction energy between two 3p holes of the NiO films on Ag(001) U (Ni 3p) significantly decreases as revealed by both X-ray photoelectron and Auger electron spectroscopies. The reduction of U (Ni 3p) for the ultrathin films is well accounted for by varied image potentials and polarization energies in the films from their bulk values. The present results confirm a previous model predicting the reduction of charge fluctuation energies in ultrathin oxide films on highly polarizable substrates due to the extra-atomic relaxations.
[Show abstract][Hide abstract] ABSTRACT: We achieved electron beam (e-beam) patterning without a photoresist on a Cl-terminated Si(0 0 1) surface. Synchrotron radiation photoemission spectroscopy and scanning photoelectron microscopy were employed to investigate the surface chemical state and pattern formation. The Cl-Si bonds were easily broken by the irradiation with an e-beam of 1 keV, leading to a pattern formation through the adsorption of residual molecules of water and hydrocarbon at the exposed Si dangling bond sites. In addition, we demonstrated the selective adsorption of desired molecules on the surface by e-beam irradiation in environments consisting of different gases, such as oxygen, ammonia, and 1-butanethiol.
[Show abstract][Hide abstract] ABSTRACT: We investigate on-site Coulomb interaction energy between two 3p holes U(Ni
3p) of ultrathin NiO films on Ag(001) by both x-ray photoelectron spectroscopy
and Auger electron spectroscopy. As the film becomes thin, U(Ni 3p)
monotonically decreases, and the difference of U(Ni 3p) for 1 monolayer (ML)
film from that of bulk-like thick film \delta U(Ni 3p) reaches ~ -2.2 eV. The
observed \delta U(Ni 3p) for 1 ML film is well reproduced by the differences of
both the image potential and polarization energies between 1 ML film and the
bulk-like thick film. Hence, the present results provide an evidence for the
picture originally proposed by Duffy et al. [J. Phys. C: Solid State Phys., 16,
4087 (1983)] and Altieri et al. [Phys. Rev. B 59, R2517 (1999)]
[Show abstract][Hide abstract] ABSTRACT: In-situ synchrotron radiation photoemission spectroscopy and X-ray photoemission spectroscopy have been used to investigate the initial stages of Al2O3 growth on a Si(001) substrate by atomic layer deposition (ALD). The core level spectra of Si 2p, O 1s, and Al 2p as well as the valence band spectra were measured at every half reaction in the trimethylaluminum (TMA)-H2O ALD process. The line shape changes and binding energy shifts of the core level spectra reveal that Al2O3 is predominantly formed with a small amount of Si oxide in the initial stages without the formation of Al silicate. All core level spectra were alternately shifted toward higher and lower binding energies sides at every half ALD reaction. This can be explained by the band bending effect induced by different chemical species on the surface during the TMA-H2O ALD reaction. The valence band spectra showed that four cycles of ALD reactions were necessary to complete the electronic structure of the Al2O3 film with a valence band offset of 3.73 eV.
Journal of Nanoscience and Nanotechnology 05/2011; 11(5):4328-32. DOI:10.1166/jnn.2011.3629 · 1.56 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: A peptide reaction of glycine on an amine-terminated Si(100) surface was investigated using C 1s, N 1s, O 1s, and Si 2p core-level spectroscopy, where the amine-terminated Si(100) surface was prepared using NH3. In-situ thermal treatments at a mild temperature of 50°C after the adsorption of glycine on a room-temperature amine-terminated Si(100) surface induced the peptide reaction between the carboxyl group of glycine and the amine group of the surface. This suggests that the amine-terminated Si(100) surface can be an excellent template for constructing a junction between a biomaterial and a Si surface using a dry process.
[Show abstract][Hide abstract] ABSTRACT: Synchrotron radiation based photoemission spectroscopy (SRPES) and low energy electron diffraction (LEED) are used to study the interaction between Ag atoms and the Si(1 1 1)1 × 1–H surface. At an Ag coverage of 0.063 monolayers (ML) on the Si(1 1 1)1 × 1–H surface, the Si 2p component corresponding to Si–H bonds decreases, and an additional Si 2p component appears which shifts to a lower binding energy by 109 meV with respect to the Si bulk peak. The new Si 2p component is also observed for 0.25 ML Ag on the Si(1 1 1)7 × 7 surface. These findings suggest that Ag atoms replace the H atoms of the Si(1 1 1)1 × 1–H surface and form direct Ag–Si bonds. Contrary to the widely accepted view that there is no chemical interaction between Ag particles and the H-passivated Si surface, these results are in good agreement with recent first-principles calculations.
[Show abstract][Hide abstract] ABSTRACT: We have investigated atomic structure and electrical properties of the Au/Si(557)-1×2 surface by using scanning tunneling microscopy. We observe the doubled periodicity (×2) for the step-edge atoms even far away from defects at room temperature (RT), indicating no Peierls-type transition reported earlier. We further identify the Au atoms well resolved from Si atoms in the Au-Si-Au chain at RT, in good accord with the prevailing structural model. Our scanning tunneling spectroscopy data taken along the step-edge atoms unambiguously reveal that these step-edge Si atoms are metallic, and are buckled apparently with a charge transferred from down to up Si atoms. We find no significant thermal fluctuation of the buckled step edges at RT.
[Show abstract][Hide abstract] ABSTRACT: Electronic structure of the In-adsorbed Si(111)3×3-Au surface was investigated by core-level and angle-resolved photoelectron spectroscopy. On the Si(111)3×3-Au surface, In adsorbates were reported to remove the characteristic domain-wall network and produce a very well-ordered 3×3 surface phase. Detailed band dispersions and Fermi surfaces were mapped for the pristine and In-dosed Si(111)3×3-Au surfaces. After the In adsorption, the surface bands shift toward a higher binding energy, increasing substantially the electron filling of the metallic band along with a significant sharpening of the spectral features. The resulting Fermi surface indicates the formation of a perfect isotropic two-dimensional electron-gas system filled with 0.3 electrons. This band structure agrees well with that expected, in a recent density-functional theory calculation, for the conjugate-honeycomb trimer model of the pristine Si(111)3×3-Au surface. Core-level spectra indicate that In adsorbates interact mostly with Si surface atoms. The possible origins of the electronic structure modification by In adsorbates are discussed. The importance of the domain wall and the indirect role of In adsorbates are emphasized. This system provides an interesting playground for the study of two-dimensional electron gas on solid surfaces.
[Show abstract][Hide abstract] ABSTRACT: We studied the atomic and electronic structures of the reconstructed Si557 surface composed of one 111 facet and three 112 facets in its single unit cell by using first principles calculations, scanning tunneling microscopy, and angle-resolved photoemission spectroscopy. A variety of atomic structure models of the 112 facet were introduced to understand overall properties of the Si557 surface. Among the atomic structure models considered, an adatom-parallel dimer model with a missing dimer with the same bonding network as the Si111-7 7 surface was found to be the most stable model. The scanning tunneling microscopy images and photoemission spectra of the Si557 surface can be widely explained by the model. In addition, these results suggest that the 112 facet with a width of 0.9 nm can be used as a one-dimensional template, as the Si111-7 7 surface plays the role of a two-dimensional template for various quantum dot arrays.
[Show abstract][Hide abstract] ABSTRACT: A soft X-ray beamline has been constructed at the Pohang Accelerator Laboratory (PAL). This bending magnet beamline provides photon energy from 100 to 1800 eV, and high energy resolution. Various techniques, such as high resolution photoemission spectroscopy, near edge X-ray absorption fine structure, EUV and soft X-ray reflectivity, and soft X-ray scattering, can be used for wide applications to semiconductors, transition metals, thin films, self-assembled monolayers (SAMs), and organic molecules.
Nuclear Instruments and Methods in Physics Research Section A Accelerators Spectrometers Detectors and Associated Equipment 11/2007; 581(3):850-855. DOI:10.1016/j.nima.2007.07.148 · 1.22 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The use of extreme ultraviolet (EUV)-induced surface modification for synthesis of nanolayer patterning was investigated. Firstly, the Si (100) wafer was cleaned by heating it to 900°C. Then, the clean Si(100) surface was exposed to 10 Langmuir (L) Cl2 gas to make the Cl2 molecular layer. The clean and Cl2-absorbed surface were analyzed by synchrotron radiation PES, carried out on the 8Al and 7Bi beamlines. The Cl 2/Si(100) surface was irradiated using a finely focused EUV beam of 650 eV for 5 minute at each position after experimental chamber was filled with NH3 gas to a partial pressure of 1×10-6. A Fresnel zone plate was used to increase the photon flux per unit area by focusing the EUV to ca. 1μm. It was observed that wavelength of light affected surface modification of nanolayers. Result shows that a Cl nanolayer exhibiting a thickness less than 1 nm can be modified with EUV.
[Show abstract][Hide abstract] ABSTRACT: Benzenethiol- and 1,4-benzenedithiol-adsorbed Si(111)-7 × 7 surfaces were studied by using scanning tunneling microscopy and synchrotron radiation photoemission spectroscopy, which showed that benzenethiol molecules were adsorbed on Si adatoms with upright structures and 1,4-benzenedithiol molecules on two adjacent Si adatoms with a bridging structure. At the initial stage, the adsorptions can be understood by a dissociative process between sulfur and hydrogen on the Si atoms. Here, sulfur bonds to the electrophilic adatoms while hydrogen bonds to neighboring nucleophilic restatoms. On the other hand, this adsorption mechanism during the initial stage does not apply at higher exposures of molecules, as is noticed from the photoemission spectra.
Journal- Korean Physical Society 03/2007; 50(3):690-694. DOI:10.3938/jkps.50.690 · 0.42 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Using core level spectra, it has been observed previously that the oxidation of silver nanoparticles deposited on sputter-damaged highly ordered pyrolytic graphite (HOPG) surfaces is very different from that taking place on surfaces composed entirely of silver. It is generally accepted that the final stage of the oxidation of silver is the formation of Ag 2 O/AgO. However, in the case of silver nanoparticles on HOPG, Ag 2 O/AgO can be further oxidized to give a species of unknown composition. In the present work it has been demonstrated that under these oxidizing conditions silver nanoparticles deposited on HOPG form silver carbonate. This implies that strong metal support interactions are responsible for the different behavior of silver nanoparticles on HOPG compared to that of silver in bulk. Carbonate formation is further suggested to be responsible for the deactivation of silver catalysts. # 2007 Elsevier B.V. All rights reserved.
Applied Catalysis A General 02/2007; 320. DOI:10.1016/j.apcata.2007.01.026 · 3.94 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The annealing temperature (TA) dependence of capacitance-voltage (C-V) characteristics has been studied in metal-oxide-semiconductor structures containing Ge nanocrystals (NCs) produced by ion implantation and annealing. These structures are of interest for application as nonvolatile memory and TA is shown to have a strong influence on the C-V hysteresis. This behavior is shown to be correlated with structural changes of the Ge NCs which have been characterized by synchrotron-radiation photoemission spectroscopy. Specifically, well-defined C-V characteristics with large hysteresis were found only for annealing temperatures greater than 950 °C where Ge nanocrystals are known to form. In this temperature regime, transmission electron microcopy and energy dispersive x-ray spectroscopy demonstrate the existence of regularly arranged Ge NCs of approximately 3–5 nm diameter located around 6.7 nm from the interface.