State-specific enhancement of Cl+ and Cl- desorption for SiCl4 adsorbed on a Si(100) surface following Cl 2 p and Si 2 p core-level excitations

Dissociation dynamics of positive-ion and negative-ion fragments of gaseous and condensed Si(CH(3))(2)Cl(2) via Si 2p, Cl 2p, and Cl 1s core-level excitations

The state-selective positive-ion and negative-ion dissociation pathways of gaseous and condensed Si(CH(3))(2)Cl(2) following Cl 2p, Cl 1s, and Si 2p core-level excitations have been characterized. The excitations to a specific antibonding state (15a(1) (*) state) of gaseous Si(CH(3))(2)Cl(2) at the Cl 2p, Cl 1s, and Si 2p edges produce significant enhancement of fragment ions. This ion enhancement at specific core-excited states correlates closely with the ion kinetic energy distribution. The results deduced from ion kinetic energy distribution are consistent with results of quantum-chemical calculations on Si(CH(3))(2)Cl(2) using the ADF package. The Cl(-) desorption yields for Si(CH(3))(2)Cl(2)Si(100) at approximately 90 K are notably enhanced at the 15a(1) (*) resonance at both Cl 2p and Si 2p edges. The resonant enhancement of Cl(-) yield occurs through the formation of highly excited states of the adsorbed molecules. These results provide insight into the state-selective ionic fragmentation of molecules via core-level excitation.

Low-energy electron stimulated desorption of neutrals from multilayers of SiCl4 on Si(111)

The interaction of low-energy electrons with multilayers of SiCl(4) adsorbed on Si(111) leads to production and desorption of Cl((2)P(32)), Cl((2)P(12)), Si, and SiCl. Resonant structure in the yield versus incident electron energy (E(i)) between 6 and 12 eV was seen in all neutral channels and assigned to dissociative electron attachment (DEA), unimolecular decay of excited products produced via autodetachment and direct dissociation. These processes yield Cl((2)P(32)) and Cl((2)P(12)) with nonthermal kinetic energies of 425 and 608 meV, respectively. The Cl((2)P(12)) is produced solely at the vacuum surface interface, whereas the formation of Cl((2)P(32)) likely involves subsurface dissociation, off-normal trajectories, and collisions with neighbors. Structure in the Cl((2)P(32)) yield near 14 and 25 eV can originate from excitation of electrons in the 2e, 7t(2) and 6t(2), 6a(1) levels, respectively. Although the 14 eV feature was not present in the Cl((2)P(12)) yield, the broad 25 eV feature, which involves complex Auger filling of holes in the 6t(2) and 6a(1) levels of SiCl(4), is observed. Direct ionization, exciton decay, and DEA from secondary electron scattering all occur at E(i)>14 eV. Si and SiCl were detected via nonresonant ionization of SiCl(x) precursors that are produced via the same states and mechanisms that yield Cl. The Si retains the kinetic energy profile of the desorbed precursors.

Mechanism of anion formation in C 1s→π*-excited carbon dioxide

The mechanism of anion formation from core-excited carbon dioxide is investigated in the C 1s-excitation regime (280-340 eV), where negative-ion-positive-ion coincidences and negative-ion-positive-ion-positive-ion coincidences experiments are performed. O(-) formation occurs efficiently upon C 1s-->pi(*)-excitation (290.7 eV) from the singly charged cation CO(2) (+). This anion is measured in coincidence with the singly charged atoms C(+) and O(+). The formation of atomic cations is accompanied by a substantial kinetic energy release. This suggests that an intermediate CO(++) is formed together with O(-), where the dication decays via fission. The results are discussed in terms of an anion formation mechanism from core-excited molecules considering previous experimental results.