STM study ofC2H2adsorption on Si(001)

Abstract

We present here a scanning tunneling microscope study of the initial bonding structure and subsequent reaction mechanism of C 2 H 2 with the Si͑001͒ surface. Upon exposure of the sample at room temperature to 0.2 L of C 2 H 2 ͑approximately 20% coverage͒ adsorption of the molecule on alternate dimer pairs is observed, leading to either a local 2ϫ2 or c(2ϫ4) structure. In the filled-state image, a local minimum is observed in the center of the reacted dimer pairs, while the unreacted dimer pairs maintain the normal bean-shaped contour of the clean surface. The molecule forms an overlayer with either local 2ϫ2 or c(4ϫ2) order, leading to a saturation coverage of 0.5 monolayers. Upon annealing the substrate at 775 K the surface becomes disordered and the steps are no longer visible. After further annealing at 875 K, SiC clusters are formed and the 2ϫ1 structure is again seen between the clusters. For a starting coverage of 20%, annealing to higher temperatures around 1100 K leads to pinning of the step movement by the SiC clusters. For a starting coverage of 0.5 monolayer, annealing at 1100 K results in faceting of the surface. Further annealing at 1275 K creates anisotropic facets that are oriented along the ͓110͔ direction with a typical aspect ratio of approximately 4 to 5. These facets act as nucleation sites for subsequent carbonization and SiC growth. ͓S0163-1829͑97͒05032-7͔

First-principles study of the adsorption ofC2H2andCho1, Kleinman2, Chan3 et al. 2001Phys. Rev. B51250View full textAdd to dashboardCite

“…For both adsorbed molecules the dimerized model is found to be more stable than the dimercleaved model as well as the tetra-model, showing that the carbon atoms of adsorbed C 2 H 2 and C 2 H 4 form sp 2 and sp 3 bonding, respectively. This result supports the majority of the experimental data [3][4][5][6][7][8] except that of a recent photoelctron imaging experiment, 7 where the tetra-model was proposed for adsorbed C 2 H 2 . Moreover, C 2 H 4 molecules favor adsorption on alternate Si dimers rather than on neighboring dimers along a dimer row, because of the repulsive hydrogenhydrogen interaction between adsorbed C 2 H 4 .…”

“…The saturation coverages of C 2 H 2 and C 2 H 4 on Si͑100͒ are still controversial. STM studies 4,8 observed the adsorption of the C 2 H 2 and C 2 H 4 molecules on alternate Si dimer sites, and therefore an overlayer with p(2ϫ2) or c(4ϫ2) order was locally formed, leading to the saturation coverage of ϭ0.5 ML. However, an ultraviolet photoemission spectroscopy study with the kinetic uptake method determined the saturation coverage to be ϭ1 ML.…”

“…On the other hand, a STM study for adsorbed C 2 H 2 observed either a local p(2ϫ2) structure or a c(2ϫ4) structure. 4 Although this ordering in adsorbed C 2 H 2 has not been explained by the present total-energy calculations, its origin may be explained by a dipole interaction between the gas-phase C 2 H 2 and adsorbed C 2 H 2 molecules via a mobile precursor mechanism, 27 as suggested by Li et al 4 In conclusion, our first-principles calculations showed that both C 2 H 2 and C 2 H 4 molecules adsorb identically on top of a Si dimer, forming two bonds between C and Si atoms.…”

“…1,2 Despite a wealth of experimental [3][4][5][6][7][8] and theoretical 9-11 studies on both adsorbed molecules, several basic issues on the adsorption site, bonding characteristics, and saturation coverage are still controversial.…”

Morphology Change of C60 Islands on Organic Crystals Observed by Atomic Force Microscopy

“…Within the past years, a large panel of organic/inorganic interfaces has been investigated by means of scanning probe microscopy (SPM), such as organic molecules adsorbed on metals, [5][6][7] semiconductors [8][9][10][11] and insulators. [12][13][14] However, fundamental studies of organic-organic interfaces are still scarce despite of their great interest for molecular electronic applications.…”