Substrate Si Atoms Research Articles

Adsorption of potassium on a Si(111) surface

The adsorption of potassium on several sites (T 1, T 4, H 3) of a Si(111) surface is studied using the extended Hückel method and cluster models. The results show that the chemisorption energy on the T 4 site is almost equal to that on the H 3 site for an ideal surface. However, the analysis of chemical bonding of adatoms on a Si surface suggests that the chemisorption of adatoms might induce a kind of reconstruction on the Si(111) surface. Rough calculations for the adsorption on this reconstructed surface are carried out. In this paper, charge transfer, density of states and characterization of the bonds between the adatom and substrate Si atoms are also investigated in detail.

Adsorption of potassium on a Si(111) surface

The adsorption of potassium on several sites (T 1, T 4, H 3) of a Si(111) surface is studied using the extended Hückel method and cluster models. The results show that the chemisorption energy on the T 4 site is almost equal to that on the H 3 site for an ideal surface. However, the analysis of chemical bonding of adatoms on a Si surface suggests that the chemisorption of adatoms might induce a kind of reconstruction on the Si(111) surface. Rough calculations for the adsorption on this reconstructed surface are carried out. In this paper, charge transfer, density of states and characterization of the bonds between the adatom and substrate Si atoms are also investigated in detail.

The chemisorption of chlorosilanes and chlorine on Si(111)7 × 7

The chemisorption of SiCl 4, Si 2Cl 6, and chlorine on Si(111)7 × 7 has been characterized using soft X-ray photoemission with synchrotron radiation, thermal desorption spectroscopy, and Auger electron spectroscopy. SiCl4 dissociatively chemisorbs on room temperature Si(111)7 × 7 with an extremely low sticking coefficient, with only SiCl remaining on the surface. In contrast, Si 2Cl 6 chemisorbs with ∼ 500 times greater probability and then partly dissociates into SiCl x ( x = 1, 2, 3) fragments. A monolayer of Cl deposited directly also contains SiCl, SiCl 2, and SiCl 3 surface species, but they are created via reaction with substrate Si atoms and have lower Si2p core level binding energies. Upon heating the surface all the adsorbed Cl is removed via desorption of silicon chlorides, primarily SiCl 2, indicating that SiCl 4, Si 2Cl 6, and chlorine will etch Si(111)7 × 7 if an additional reactant is not avail to remove the surface Cl. Interestingly, the different reactivities of SiCl 4 and Si 2Cl 6 upon adsorption can be explained by the dynamics of different adsorption mechanisms.

Electrical and structural properties of Insb (111) epitaxially grown on Al 2O 3 (0001)

The chemisorption of SiCl4, Si2Cl6, and chlorine on Si(111)7 × 7 has been characterized using soft X-ray photoemission with synchrotron radiation, thermal desorption spectroscopy, and Auger electron spectroscopy. SiCl4 dissociatively chemisorbs on room temperature Si(111)7 × 7 with an extremely low sticking coefficient, with only SiCl remaining on the surface. In contrast, Si2Cl6 chemisorbs with ∼ 500 times greater probability and then partly dissociates into SiClx (x = 1, 2, 3) fragments. A monolayer of Cl deposited directly also contains SiCl, SiCl2, and SiCl3 surface species, but they are created via reaction with substrate Si atoms and have lower Si2p core level binding energies. Upon heating the surface all the adsorbed Cl is removed via desorption of silicon chlorides, primarily SiCl2, indicating that SiCl4, Si2Cl6, and chlorine will etch Si(111)7 × 7 if an additional reactant is not avail to remove the surface Cl. Interestingly, the different reactivities of SiCl4 and Si2Cl6 upon adsorption can be explained by the dynamics of different adsorption mechanisms.

Adlayer formation and its local charge states of Li on Si(111)7 × 7 surface studied by Δφ, MDS and AES

Initial states of Li adlayer formation on a Si(111)7×7 surface have been investigated by work function change (Δø), metastable-atom de-excitation spectroscopy (MDS) and Auger electron spectroscopy (AES), for the first time. MDS spectra detected remaining valence electrons on the adsorbed Li atom even in the earliest stage of adsorption, which provides clear evidence of the partial occupancy of a Li resonance. The charge state of adsorbates did not change in a low coverage region. The electronic structure of the substrate surface is little disturbed by the Li adsorption according to AES spectra. We observed two types of Auger transition occurring between deposited Li and substrate Si atoms, but no pure Li Auger peaks. It is suggested that the Li-Si interface grows by the process of initial adsorption followed by diffusion of Li beneath the Si surface.

The localization and crystallographic dependence of Si suboxide species at the SiO2/Si interface

X-ray photoemission spectroscopy has been used to examine the localization and crystallographic dependence of Si+1, Si+2, and Si+3 suboxide states at the SiO2/Si interface for (100)- and (111)-oriented substrates with gate oxide quality thermal oxides. The Si+1 and Si+2 states are localized within 6–10 Å of the interface while the Si+3 state extends ∼30 Å into the bulk SiO2. The distribution of Si+1 and Si+2 states shows a strong crystallographic dependence with Si+2 dominating on (100) substrates and Si+1 dominating on (111) substrates. This crystallographic dependence is anticipated from consideration of ideal unreconstructed (100) and (111) Si surfaces, suggesting that (1) the Si+1 and Si+2 states are localized immediately within the first monolayer at the interface and (2) the first few monolayers of substrate Si atoms are not significantly displaced from the bulk. The total number of suboxide states observed at the SiO2/Si interface corresponds to 94% and 83% of a monolayer for these (100) and (111) substrates, respectively. We speculate that the remaining interfacial substrate Si atoms that are not associated with bonding to oxygen are bonded to impurity species.

Initial stage of Pd adsorption on Si(111)7 × 7 surface studied by AES and EELS

The initial stage of adsorption of Pd on a Si(111)7 × 7 surface has been studied by means of Auger electron spectroscopy (AES), electron energy loss spectroscopy (EELS) and surface work-function change. For Pd deposition at room temperature (RT) the Si(LVV) Auger signal intensity decays in a broken linear line. The structure factor, defined as the intensity ratio of the subpeak to the main one in Si(LVV) Auger spectra, increases up to a maximum around one monolayer coverages. In EELS spectra two peaks, characteristics of Pd, appear at the completion of the first Pd layer. Pd atoms deposited on Si(111) at RT form initially flat layers of a few monolayers height without mixing with substrate Si atoms. For Pd deposition at a moderately high temperature (MT) of about 300°C, however, the structure factor for Si(LVV) Auger spectra does not change. EELS peaks, characteristic of Si substrate, remain clearly even beyond one monolayer coverage. Pd atoms deposited at MT are unstable and easily diffuse into the bulk. We present evidences to support the “screening” model for the bond-breaking mechanism at the Pd/Si interface.

Single-crystal Ge films on SiO2-coated Si wafers by laterally seeded heteroepitaxy

Germanium film crystallization with W encapsulation has been performed by using rf zone-heating slider system. With the laterally seeded heteroepitaxy technique, (100) single-crystal Ge is obtained on SiO2 islands as large as 280×510 μm on Si(100) substrates. The Ge surface morphology represents growth-velocity anisotropy, indicating a {111}-faceted liquid-solid interface during crystallization. It has been shown that a mixture of Ge crystal and polycrystalline Si2W exists at the peripheral region of the SiO2 island and at the Si opening. Si2W formation is explained by diffusion of substrate Si atoms in Ge followed by reaction with the encapsulant W. The crystalline quality of Ge near the seed is poor because of the Ge lattice deformation due to Si2W. Lateral epitaxy, however, is successfully performed to provide a good-quality Ge single-crystal film on the SiO2 island.