Jeong-Tak Ryu

Ag-induced structural transformations on Si(111): quantitative investigation of the Si mass transport

Abstract Using scanning tunneling microscopy, the Si mass transport taking place at the formation of the Si(111) 3 × 3 -Ag and Si(111)6×1-Ag surface phases has been studied. From the measurement of the area occupied by various structural domains and the quantitative consideration of the Si mass balance, the top Si atom density in the Si(111) 3 × 3 -Ag and Si(111)6×1-Ag phases has been evaluated to be 1 monolayer and 4/3 monolayers, respectively.

Structural Analysis of 6H–SiC(0001)√3×√3 Reconstructed Surface

Using coaxial impact-collision ion scattering spectroscopy (CAICISS), the structure of the 6H–SiC(0001)√3×√3 reconstructed surface was investigated. As a result of composition analysis, the topmost layer of this surface was found to be covered with Si adatoms. Moreover, from the incidence angle dependence of the scattering intensity due to C atoms, it was found that the √3×√3 periodicity was formed by a one-third monolayer of Si adatoms occupying T4 sites, and the height of the Si adatoms from the first substrate layer was determined to be 1.5±0.2 A.

Mg/Si(100) Reconstructions Studied by Scanning Tunneling Microscopy

Using scanning tunneling microscopy (STM), the behavior of Mg submonolayers on a Si(100)2×1 surface has been studied during deposition at room temperature (RT) and upon annealing at 250°C and 400°C. RT-deposited Mg forms meandering chains of features that run roughly perpendicular to the substrate Si dimer rows and, at saturation, tend to form the arrays of the 2×2 reconstruction. Annealing at 250°C transforms the chains to random groups of Mg clusters. Subsequent annealing at 400°C induces Si redistribution at the surface and results in the formation of straight chains of features that are again aligned perpendicular to the Si dimer rows. These high-temperature (HT) features are plausibly composed of 1 Si atom and 1–2 Mg atoms. The spacing of the HT features within the chain is 2a (a=3.84 A) and stacking of the chains produces the domains of 2×2, 2×3 and other 2×n reconstructions. At saturation, almost the entire surface is occupied by the 2×2 reconstruction. At higher Mg coverages, the growth of a silicide occurs both at RT deposition and upon annealing.

The effect of hydrogen termination on In growth on Si(100) surface

Abstract We have investigated the effect of hydrogen termination on the initial stage of In growth on Si(100) surface at room temperature using time-of-flight impact collision ion scattering spectroscopy (TOF-ICISS) and low-energy electron diffraction (LEED). In this study, we found that In thin films grown on both clean and hydrogen-terminated Si(100)1×1 surfaces showed quite different results. The In thin film on the clean Si(100)2×1 surface epitaxially grows with the orientation of In(100)[011]//Si(100)[011]. On the contrary, the In thin film on the hydrogen-terminated Si(100)1×1 surface grows as a polycrystalline film. In other words, epitaxial growth of In thin films is disrupted by the presence of hydrogen atoms residing at the interface between the films and Si substrate. The growth mode of In thin films grown on both surfaces is SK growth mode, which indicates that the growth mode is not changed by hydrogen termination.

The growth of indium thin films on clean and hydrogen-terminated Si(100) surfaces

Abstract Using scanning tunneling microscopy and low-energy electron diffraction techniques, we have investigated the growth of indium thin films on clean and hydrogen-terminated Si(100) surfaces at room temperature. In this study, we found the ‘ antisurfactant ’ effect of atomic hydrogen on indium thin-film growth on the Si(100) surface. On a clean Si(100) surface, indium atoms form the mixed reconstruction phases of ( n ×3)-In at low coverage. With increasing coverage, indium atoms start to form flat, two-dimensional islands preferentially at step edges of the substrate. In contrast, indium thin films grown on a hydrogen-terminated Si(100) surface do not form any reconstruction phase at low coverage and indium atoms form small clusters of spherical shape, indicating a modified indium growth mode mediated by the hydrogen adlayer.

Fabrication and Characteristics of Amorphous Carbon Films Grown in Pure Methane Plasma by using Radio Frequency Plasma Enhanced Chemical Vapor Deposition

Amorphous carbon (a-C) films were fabricated in pure methane plasma by using the radio frequency plasma-enhanced chemical vapor deposition (RF PECVD) system. Surface morphology and roughness of the films were examined as a function of substrate temperature by atomic force microscopy (AFM). Field emission from the a-C films was examined as a function of substrate temperature. We found that the roughness and the emission current of the films were improved considerably when the substrate temperature was higher than 600°C. From the results obtained by Raman spectroscopy, growth of graphite crystallites was promoted at high substrate temperature. Moreover, the surface morphology was abruptly changed at high substrate temperatures over 600°C. We discuss the field emission characteristics of the a-C films with regard to the surface morphology and the structural features.

Development of New Apparatus for Field Emission Measurement.

A field emission measurement profiler, which not only can measure the field emission of the entire film as well as its local points but also can present a two-dimensional map of the current density distribution, is developed. This apparatus is operated under an ultrahigh vacuum condition to measure the field emission distribution of amorphous carbon (a-C) films deposited by a RF magnetron sputtering system. The results show that the film surface consists of strong and weak emission sites. We also obtain the field emission maps of micrometer order from strong and weak emission sites; these can help us understand the mechanism of field emission for improving the procedure for growing films.

Coaxial Impact-Collision Ion Scattering Spectroscopy and Time-of-Flight Elastic Recoil Detection Analysis for In Situ Monitoring of Surface Processes in Gas Phase Atmosphere

Based on conventional coaxial impact-collision ion scattering spectroscopy (CAICISS) and time-of-flight elastic recoil detection analysis (TOF-ERDA), we have developed a novel ion scattering and recoiling spectrometer equipped with a differential pumping system for in situ monitoring of surface processes in gas phase atmosphere in the pressure regime up to 10-4 Torr. In order to demonstrate the performance of this apparatus, we have applied it to real-time monitoring of Ge thin film growth on a Si(001) surface in atomic hydrogen (H) atmosphere. The morphology of Ge thin films and H coverage on the growth front during the growth in H atmosphere were successfully observed.

Ge thin film growth on Si(111) surface using hydrogen surfactant

Abstract We have investigated the atomic hydrogen (H)-surfactant mediated growth of Ge on Si(111) surface, using coaxial impact-collision ion scattering spectroscopy (CAICISS), time-of-flight elastic recoil detection analysis (TOF-ERDA) and scanning electron microscopy (SEM). It has been found that the Ge thin film on the Si(111)1×1-H surface is flattened by the H-surfactant, whilst on the Si(111)7×7 surface the flatness does not change in spite of supplying H. These results indicate that the flatness of the Ge thin film is strongly influenced by the structure of the Si(111) substrate surface at the initial stage of Ge thin film growth.

Green and Red Electrophosphorescent Devices Consisting of Cabazole/Triarylamine-Based Polymers Doped with Iridium Complexes

Two types of polymers were synthesized such as poly[N-(2-ethylhexyl)carbazole-alt-N-(4-aminophenyl)carbazole] (PECAC) and poly[N-(2-ethylhexyloxy-phenyl) carbazole-alt-N-(4-aminophenyl)carbazole] (PEPCAC). These polymers are designed to have carbazole groups with wide band gap and a triarylamine moiety with a hole transporting property. Green and red phosphorescent polymer light emitting diodes (PhPLEDs) were fabricated with an emitting layer consisting of either PECAC or PEPCAC as a host matrix with suitable iridium complexed, Ir(ppy)3 as a green or IR-PIQCH as a red dopant, respectively. Red PhPLEDs doped with IR-PIQCH exhibited maximum EL emission peaks at 620 nm with higher luminescence and lower driving voltage, due to effective energy transfer from host polymers to IR-PIQCH red dopant. Based on HOMO and LUMO levels of the polymers and Ir(ppy)3, however, the synthesized polymers could not be served as suitable host polymers for Ir(ppy)3 green dopant. Ir(ppy)3 doped PhPLEDs exhibited red shift and wide range of EL emission.