Adsorption dynamics of monoenergetic iodine monobromide (IBr) on the Si(111)-7×7 surface

Abstract

The adsorption of monoenergetic IBr molecules on the Si(111)-7×7 surface has been studied using scanning tunneling microscopy, mass spectrometry, Auger electron spectroscopy, and supersonic molecular beam techniques. The adsorption proceeds predominantly via the direct abstractive adsorption mechanism and preferentially occurs at the center Si adatoms. The IBr abstraction probabilities at the incident energies of 0.15 and 0.82 eV have been determined to be 0.90±0.03 and 0.77±0.03, respectively. The minor dissociative adsorption channel of IBr can be enhanced at the expense of the abstractive adsorption channels by raising the incident energy. Most importantly, no atomic selectivity for iodine or bromine was observed. A reaction mechanism involving two types of transition states, Si⋯I⋯Br(s) and Si⋯Br⋯I(s), has been proposed to interpret the experimental observations. The attractive interaction between the nearly symmetric highest occupied molecular orbitals (HOMO, π* antibond) of IBr and the partially-filled Si adatom dangling bonds governs the surface site selectivity and the atomic selectivity of IBr adsorption on Si(111). Comparison with the adsorption of ICl on the surface has also been made to clarify the role of the asymmetric molecular bonding in adsorption dynamics.

Adsorption of Diatomic Interhalogens on the Si(100) and Ge(100) Surfaces

“…Cl and Br to I ratios and Cl to H ratio vs total adsorbate coverage on the Si(100), Ge(100), and Si(111) surfaces calculated from the normalized intensities of Cl 2p, Br 3d, and I 4d core-level spectra. The data for the Si(111):ICl, Si(111):IBr, and Si(100):HCl systems are reproduced from refs , , and , respectively.…”

“…Simple model systems reduce complexity in chemisorption dynamics and kinetics. To this end, researchers have extensively studied the adsorption of halogen-contained diatomic molecules such as diatomic halogen molecules, hydrogen halides, and diatomic interhalogens on semiconductor surfaces. − Upon adsorption, both hydrogen and halogen atoms each form a single bond with a surface atom. − From an applied viewpoint, halogen-contained molecules are frequently employed in etching processes in semiconductor and nanodevice fabrication …”

“…Kummel et al studied the heterohalogen molecules of iodine monochloride (ICl) and iodine monobromide (IBr) on the Si(111)-(7 × 7) surface and reported that the two apparently similar systems exhibited very different adsorption processes at room temperature. , Their study shows that the adsorption of IBr is essentially dissociative, meaning that, upon cleavage of the I–Br bond, both I and Br radicals each, respectively, form a single Si–I and Si–Br bond. Thus, the coverage ratio of the two adsorbates (i.e., Br/I) is 1.0, in sharp contrast to the coverage ratio of Cl/I which is about 0.33.…”

Patterned Atomic Reaction at Surfaces

“…In a subsequent study IBr adsorption was dominated by abstraction (90% at 0.15 eV incident energy, 77% at 0.82 eV incident energy, as for ICl). A preference for abstraction to occur at middle adatoms was found.…”

On the viability of single atom abstraction in the dissociative chemisorption of O2 on the Al(111) surface

“…Experimental data from several other reactions reported in the literature are consistent with single atom abstraction as well. [21][22][23][24][25] In addition, Jarrold and Bower give evidence that when O 2 dissociates on large Al n ϩ clusters, a product is the cluster with a single O atom bound to it. 26 Single atom abstraction is one possible explanation of this observation.…”