D.S. Choi

Atomic structures of Ag islands on Si(001)(2 × 1)

Abstract Atomic structures of the three-dimensional (3D) Ag islands and the growth mode of Ag grown on Si(001)(2 × 1) have been studied by coaxial impact collision ion scattering spectroscopy. At room temperature (RT), Ag grows in Stransky-Krastanov (SK) mode. Although the crystallinity is not good, the 3D Ag islands have a structure of Ag(001)//Si(001) with an interlayer spacing between the first and third layers of d 13 = 2.80 A . After the sample grown at RT was annealed at 600°C, the two-dimensional (2D) Ag layer disappeared and the 3D Ag islands are reconstructed to a structure of Ag(001)//Si(001) and Ag[100]//Si[100] with a good crystallinity. The interlayer spacing between the first and third layers was d 13 = 4.09 A . For deposition at a substrate temperature of 600°C, Ag also grows in SK mode and the 3D Ag islands have a structure of Ag(001)//Si(001) and Ag[100]//Si[100]. We found that our results on the 2D Ag layer support the surface unwetting due to the free energy difference between the 2D layer and the 3D islands, and the surface unwetting characterizes the behavior of the Ag on the Si(001) surface.

Atomic structure of ultrathin Co layer on Si(001)(2×1) at room temperature

Abstract The atomic structure of Co on the Si(001)(2×1) surface is investigated by coaxial impact collision ion scattering spectroscopy. When 0.6xa0ML Co atoms are deposited on the Si(001) at room temperature, the deposited Co atoms reside two-dimensionally on the Si(001) surface. The first preferential adsorption site is T4, and the next favorable site is HB, with a height of 2.72xa0A and 3.47xa0A from the second Si(001) layer, respectively. As the coverage increases up to 1.9xa0ML, Co atoms occupy the HB and T3 sites, of which the latter is at a height of 3.58xa0A from the second layer of the Si(001) surface.

Atomic structure of Ba layer on Si(001)-(2×1) surface studied by low energy ion scattering

Abstract The atomic structure of Ba layer on Si(0xa00xa01)-(2×1) surface is investigated by coaxial impact collision ion scattering spectroscopy. When 0.7 ML of Ba atoms are adsorbed on Si(0xa00xa01) at room temperature, the first preferential site of adsorption is T3 site with a height of 3.00±0.05 Axa0from the second layer of Si(0xa00xa01) even though the periodicity is poor. The next favorable site is HH site with a height of 3.50±0.05 Axa0from the second layer of Si(0xa00xa01).

Surface structure of Pt/Si(001)

Abstract We have investigated Pt adsorption on the Si(0xa00xa01) surface using LEED and low energy ion scattering spectroscopy (ISS). We observe a c(4×2) LEED image at annealing temperatures between 700 and 1150 °C. For annealing temperatures between 800 and 1000 °C, a c(4×6) LEED image is observed simultaneously with the c(4×2) LEED image. The Pt/Si(0xa00xa01) surface structure does not depend on the initial Pt coverage. We also measure the adsorption site at the c(4×2) surface using the ISS. We find that the Pt atoms are adsorbed at T3 sites and some Pt atoms diffuse into the bulk. The height of the adsorbed Pt atoms from the Si surface is determined to be 0.5 A.

Atomic structure of two-dimensional Ag layer grown on Si(001)-(2×1) at room temperature

Abstract Atomic structures of the two-dimensional Ag layer grown on Si(001)-(2×1) at room temperature have been studied by coaxial impact collision ion scattering spectroscopy. After several monolayers of Ag had been deposited on the Si(001)-(2×1) surface, the two-dimensional Ag layer was found to consist of Ag dimers. The bond length of the Ag dimer was 2.89±0.05xa0A. The heights of the Ag dimers from the second Si layer were 2.45 and 3.02xa0A. The Ag dimers were located in the hollow sites between two and among four neighbouring Si dimers, and the orientation of the Ag dimer row was perpendicular to that of the Si dimer. Thus, the Si substrate under the two-dimensional Ag layer still retained its initial dimer structure. Therefore, it was concluded that the two-dimensional Ag layer on Si(001)-(2×1) had a Ag(2×2) structure with a saturation coverage of 1xa0ML.

Atomic structure of Cs layer grown on Si(0 0 1)(2 × 1) surface at room temperature

Abstract The atomic structure of Cs atoms adsorbed on the Si(0xa00xa01)(2xa0×xa01) surface has been investigated by coaxial impact collision ion scattering spectroscopy. When 0.5 ML of Cs atoms are adsorbed on Si(0xa00xa01) at room temperature, it is found that Cs atoms occupy a single absorption site on T3 with a height of 3.18xa0±xa00.05 A from the second layer of Si(0xa00xa01)(2xa0×xa01) surface, and the bond length between Cs and the nearest Si atoms is 3.71xa0±xa00.05 A.

Atomic structure of Ag grown on Si(001) (2×1) at high temperature

Abstract Atomic structures of Ag grown on Si(001) (2×1) surface at an elevated substrate temperature of 600°C have been studied by coaxial impact collision ion scattering spectroscopy. At a substrate temperature of 600°C, the Ag grows in the Stranski–Krastanov mode. The three-dimensional Ag islands have the structure of Ag(001)//Si(001) and Ag[100]//Si[100] with a good crystallinity. The interlayer spacing between the first and third layers is d 13 =4.09±0.05xa0A. It is found that the Ag atoms in the two-dimensional layer are positioned on the cave site between Si dimers with different heights of 0.8 and 1.5xa0A from the Si(001) (2×1) surface.

Structural analysis of the reconstructed Si(001)-C surface

The atomic structure of reconstructed Si(001)c(4 x 4)-C surface has been studied by coaxial impact collision ion scattering spectroscopy. When the 100L of ethylene (C(2)H(4)) molecules have been exposed on Si(001)-(2 x 1) surface at 700 degrees C, it is found that C atoms cause the ordering of missing Si dimer defects and occupy the fourth layer of Si(001) directly below the bridge site. Our results provide the support for the previous model in which a missing dimer structure is accompanied by C incorporation into the subsurface.

Structural determination of the low-coverage phase of Al on Si(001) surface

The atomic structure of Al layer on Si(001)-(2 x 1) surface has been studied by coaxial impact collision ion scattering spectroscopy. When 0.5 monolayer (ML) of Al atoms are adsorbed on Si(001) at room temperature, it is found that Al adatoms are dimerized and Al ad-dimers are oriented parallel to the underlying Si dimers at the position of centering T3 site with a height of 1.02 Angstroms from the first layer of Si(001). The bond length of the Al dimer is 2.67 Angstroms. With increasing Al coverage up to one ML, Al ad-dimers still occupied near T3 site and the next favorable site is near HH site.

Hydrocarbon-associated Si(001) surface structure : CAICISS

The surface structure of C2H4 on Si(001) has been investigated by coaxial impact collision ion scattering spectroscopy (CAICISS). To determine the adsorption structure of the C2H4 molecules definitely, the computer simulation with the two-dimensional trajectory count method has been applied to the recently proposed most possible two single molecular adsorption configurations (di-σ on-top and di-σ end-bridge). The CAICISS spectra and simulation results show that the di-σ on-top structure is better fitted with the experimental results rather than the di-σ end-bridge.