Si 2p Core-level Excitations Research Articles

Dissociation dynamics of anionic and excited neutral fragments of gaseous SiCl4 following Cl 2p and Si 2p core-level excitations

The state-selective dissociation dynamics for anionic and excited neutral fragments of gaseous SiCl4 following Cl 2p and Si 2p core-level excitations were characterized by combining measurements of the photon-induced anionic dissociation, x-ray absorption and UV/visible dispersed fluorescence. The transitions of core electrons to high Rydberg states/doubly excited states in the vicinity of both Si 2p and Cl 2p ionization thresholds of gaseous SiCl4 lead to a remarkably enhanced production of anionic, Si− and Cl−, fragments and excited neutral atomic, Si*, fragments. This enhancement via core-level excitation near the ionization threshold of gaseous SiCl4 is explained in terms of the contributions from the Auger decay of doubly excited states, shake-modified resonant Auger decay, or/and post-collision interaction. These complementary results provide insight into the state-selective anionic and excited neutral fragmentation of gaseous molecules via core-level excitation.

Enhanced production of ionic photofragments of Si(CH 3) 2Cl 2 following core-to-valence excitation

The state-selective positive-ion and negative-ion dissociation pathways for gaseous and condensed Si(CH 3) 2Cl 2 following the Cl 2p and Si 2p core-level excitations have been characterized using synchrotron radiation. The Si 2 p → 15 a 1 ∗ excitation of Si(CH 3) 2Cl 2 induces an enhancement of the Cl + desorption yield in the condensed phase and the Si ( CH 3 ) 2 + and SiCH 3 + yields in the gaseous-phase. The Cl −desorption yields are notably enhanced at the 15 a 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 an insight into the comprehensive understanding of the state-selective fragmentation of molecules via core-level excitation.

Dissociation dynamics of positive-ion and negative-ion fragments of gaseous and condensed Si(CH3)2Cl2 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.

Production of neutral fragments of gaseous SiCl 4 following Si 2p core-level excitation studied by dispersed fluorescence spectroscopy

State-specific dissociation dynamics for ionic fragments and excited fragments of gaseous SiCl 4 following Si 2p core-level excitation have been characterized by the dispersed UV/optical fluorescence spectroscopy and photionization mass spectroscopy. The Si 2p core-to-Rydberg excitation leads to a noteworthy production of excited atomic fragments, neutral and ionic (Si *, Si +*). In particular, the excited neutral atomic fragments Si * are significantly reinforced. The Si 2p core-to-valence excitation generates an enhancement of excited molecular-ion SiCl 4 +. The experimental results provide deeper insight into the dissociation dynamics for excited neutral fragments of molecules via core-level excitation.

Dissociation dynamics of excited neutral fragments of gaseousSiCl4following Si2pand Cl2pcore-level excitations

State-specific dissociation dynamics for excited fragments of gaseous SiCl{sub 4} following Cl 2p and Si 2p core-level excitations were characterized by the dispersed UV/optical fluorescence spectroscopy. The core-to-Rydberg excitations at both Si 2p and Cl 2p edges lead to a noteworthy production of excited atomic fragments, neutral and ionic (Si{sup *},Si{sup +*}). In particular, the excited neutral atomic fragments Si{sup *} are significantly reinforced. The core-to-valence excitation at the Si 2p edge generates an enhancement of excited molecular-ion SiCl{sub 4}{sup +}. The experimental results provide deeper insight into the dissociation dynamics for excited neutral fragments of molecules via core-level excitation.

Resonantly enhanced production of excited fragments of gaseous molecules following core-level excitation

State-selective dissociation dynamics for the excited fragments of gaseous Si(CH 3) 2Cl 2 following Cl 2p and Si 2p core-level excitations have been investigated by resonant photoemission spectroscopy and dispersed UV/optical fluorescence spectroscopy. The main features in the gaseous Si(CH 3) 2Cl 2 fluorescence spectrum are identified as the emission from excited Si*, Si +*, CH* and H*. The core-to-Rydberg excitations at both Si 2p and Cl 2p edges lead to a noteworthy production of not only the excited atomic fragments, neutral and ionic (Si*, Si +*) but also the excited diatomic fragments (CH*). In particular, the excited neutral atomic fragments Si* are significantly reinforced. The experimental results provide deeper insight into the state-selective dissociation dynamics for the excited fragments of molecules via core-level excitation.

State selective enhanced production of excited fragments and ionic fragments of gaseous Si(CH3)2Cl2 and solid-state analogs following core-level excitation.

State-selective fragmentation dynamics for excited fragments and ionic fragments of gaseous and condensed Si(CH3)2Cl2 following Cl 2p and Si 2p core-level excitations have been characterized. The Cl 2p-->15a1* excitation of Si(CH3)2Cl2 induces significant enhancement of the Cl+ desorption yield in the condensed phase and the Si(CH3)+2 and SiCH+3 yields in the gaseous phase. The core-to-Rydberg excitations at both Si 2p and Cl 2p edges lead to enhanced production of the excited fragments. These complementary results provide deeper insight into the origin of state-selective fragmentation of molecules via core-level excitation.

State-specific photochemistry of SiCl4 condensed on Si(100) with synchrotron radiation

State-specific photochemistry for SiCl4 adsorbed on Si(100) at ∼90 K following the Cl 2p and Si 2p core-level excitations has been investigated by photon-stimulated ion desorption, resonant photoemission, ion energy distribution, and soft x-ray absorption spectral measurements. The Cl+ photon-stimulated ion desorption spectrum and Cl L-edge x-ray absorption spectrum for condensed SiCl4 exhibit a clear dissimilarity unlike the other fragments, viz. SiCl3+, SiCl2+, SiCl+, and Si+. The Cl+ desorption yield shows a significant enhancement following the Cl 2p→8a1* excitation, while the Si 2p→8a1* excitation leads to the scarce enhancement of the Cl+ yield. The Cl+ ion energy distributions via the Cl 2p→8a1* excitation are shifted to higher energy (0.3–0.4 eV) compared to those via the Cl 2p→9t2* and Si 2p→8a1* excitations. The enhancement of the Cl+ desorption yield at the Cl(2p)−18a1* resonance is attributed to the higher ion escape energy. These results provide an insight into the comprehensive understanding of the state-selective fragmentation of molecules via core-level excitation.

Resonant photoemission from Si(0 0 1)

The evolution of the silicon valence-band photoemission spectra is observed in the photon energy range from the threshold of Si 2p core-level excitation to about 50 eV above this threshold. Besides the Si 3s3p- and 3p-like features in the spectra, there exhibits a new peak which is significantly enhanced while the photon energy is in the neighborhood of 20 eV above the Si 2p core-level excitation threshold. This phenomenon is suggested to be a resonant photoemission caused by the interference between the primary photoexcitation of 3s3p and its autoionization due to direct recombination of the 2p3d excitation.

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.

State-specific desorption for SiCl4 adsorbed on a Si(100) surface at approximately 90 K with variable coverage following the Cl 2p and Si 2p core-level excitations has been investigated using synchrotron radiation. The Cl+ yields show a significant enhancement following the Cl 2p-->8a*1 excitation. The Cl- yields are notably enhanced at the 8a*1 resonance at both Cl 2p and Si 2p edges. The enhancement of the Cl- yield occurs through the formation of highly excited states of the adsorbed molecules. These results provide some new dissociation processes from adsorbates on surfaces via core-level excitation.

Electronic relaxation and ion desorption processes of solid Si(CH3)2Cl2 following Si 2p core-level excitation

High-resolution Si L23-edge x-ray absorption near-edge structure (XANES) total electron yield (TEY) spectrum and photon stimulated ion desorption (PSID) spectra of condensed Si(CH3)2Cl2 have been measured in the energy range of 102–115 eV using synchrotron radiation. Excitation from Si 2p to a Si–C antibonding orbital enhances the CH3+ formation, while excitation to the Si–Cl antibonding orbital gives rise to a pronounced Cl+ production. This indicates that the character of the bound terminating orbital has a significant influence on the fragmentation processes. The selective enhancement of H+ yield at a peak of ∼106.0 eV is interpreted in terms of the excited electron in the bound orbital with strong C–H antibonding character. Applying resonant photoemission spectroscopy, the spectator Auger process was found to be the dominant decay channel for the resonantly excited Si(2p) core hole of condensed Si(CH3)2Cl2. The close resemblance of the TEY and PSID spectra of solid Si(CH3)2Cl2 was attributable to spectator Auger decay of core excited states and subsequent Coulomb repulsion of multivalence hole final states as proposed by the Knotek and Fiebelman mechanism.

Observation of neutral products of a soft X-ray stimulated etching reaction in the SF 6/a-SiO 2 absorption system

Soft X-ray stimulated etching reactions in an SF 6/a-SiO 2 adsorption system have been studied by the direct detection of neutral products using quadrupole mass spectrometry. Various nascent products were observed by Si 2p core-level excitation. The observation of SO x F + y fragments in relatively high amounts suggests that active species contain not only F atoms but also the S atoms play an important role. The excitation energy dependence of the SiF + intensity has shown evidence that core-level excitation is more effective on the etch rate than valence-level excitation, and that the etching is caused by surface excitation.

Si 2p core-level excitation in condensed SiCl 4

Using monochromatized synchrotron radiation in the range 102 to 112 eV we have monitored the total electron yield resulting from excitation of a Si 2p electron in condensed SiCl 4. We find a one-to-one correspondence for the first two peaks observed in the gas phase with those in the solid. However, the higher-lying peaks are either broadened or missing in the solid phase. This behaviour is consistent with the assignment of the first two peaks to core—valence transitions and most of the higher lying structure to core-Rydberg transitions.

Photon-stimulated desorption study of a SiO2 film surface

Photon-stimulated desorption (PSD) experiments on thermal oxide films on Si have been performed using synchrotron radiation with photon energies in the Si 2p core-level excitation region, to investigate the chemical nature of the film surface. Mass analysis of the PSD ions is performed using a time-of-flight technique. H+ is found to be the dominant ion species that desorbs from the film surface. It is observed that the H+ PSD ion yield decreases exponentially with increasing the irradiation time of incident photons. The H+ PSD ion yield as a function of photon energy exhibits a close similarity in spectral shape to the photoabsorption spectrum of SiO2. The present experimental results confirm us that hydrogen atoms exists on the outermost layer of SiO2 film, and provide direct evidence for Si–OH and Si–H termination of SiO2 films.