Excimer Laser Photofragmentation of TMA on Aluminum: Identification of Photoproduct Desorption Dynamics

1988 ◽  
Vol 131 ◽  
Author(s):  
T. E. Orlowski ◽  
D. A. Mantell
Keyword(s):  
Gas Phase ◽  
Excimer Laser ◽  
Direct Evidence ◽  
Hydrogen Abstraction ◽  
Sample Surface ◽  
Translational Energy ◽  
Quadrupole Mass ◽  
Gas Phase Reactions ◽  
Si Substrates ◽  
Site Binding

ABSTRACTNew mechanistic details regarding aluminum deposition by ArF excimer laser photodecomposition of trimethylaluminum (TMA) adsorbed on aluminum covered SiO 2/Si substrates have been obtained using a time-of-flight quadrupole mass spectrometer. CH3 radicals and Al-(CH3)n (n = 1,2,3) species are efficiently photoejected from the surface with up to 0.22 eV of translational energy. Experiments at various TMA dosing levels reveal differences in desorbed fragment translational energy presumably associated with variations in surface site binding energy. No direct evidence is found for desorption of A1 from the surface indicating that A1 is more tightly bound than methyl-aluminum fragments. By carefully monitoring changes in fragment translational energy as an A1 deposit forms on the clean SiO2/Si substrate, we examine how the surface influences the onset of A1 growth. No evidence of ethane or methane desorption from the sample surface is found implying that radical recombination and hydrogen abstraction are primarily secondary gas phase reactions which are not surface initiated.

Methylene. III. Gas phase reactions with 1-chloropropane

1969 ◽  
Vol 312 (1509) ◽  
pp. 141-161 ◽  
Keyword(s):  
Gas Phase ◽  
Rate Constants ◽  
Hydrogen Abstraction ◽  
The Other ◽  
Gas Phase Reactions ◽  
Other Hand ◽  
Chlorine Substituent ◽  
High Degree ◽  
Singlet Methylene

The work described in this and the following paper is a continuation of that in parts I and II, devoted to elucidation of the mechanism of the reactions of methylene with chloroalkanes, with particular reference to the reactivities of singlet and triplet methylene in abstraction and insertion processes. The products of the reaction between methylene, prepared by the photolysis of ketene, and 1-chloropropane have been identified and estimated and their dependence on reactant pressures, photolysing wavelength and presence of foreign gases (oxygen and carbon mon­oxide) has been investigated. Both insertion and abstraction mechanisms contribute significantly to the over-all reaction, insertion being relatively much more important than with chloroethane. This type of process appears to be confined to singlet methylene. If, as seems likely, there is no insertion into C—Cl bonds under our conditions (see part IV), insertion into C2—H and C3—H bonds occurs in statistical ratio, approximately. On the other hand, the chlorine substituent reduces the probability of insertion into C—H bonds in its vicinity. As in the chloroethane system, both species of methylene show a high degree of selectivity in their abstraction reactions. We find that k S Cl / k S H >7.7, k T Cl / k T H < 0.14, where the k ’s are rate constants for abstraction, and the super- and subscripts indicate the species of methylene and the type of atom abstracted, respectively. Triplet methylene is discriminating in hydrogen abstraction from 1-C 3 H 7 Cl, the overall rates for atoms attached to C1, C2, C3 being in the ratios 2.63:1:0.

Methylene II. Gas phase reactions with ethyl chloride

1968 ◽  
Vol 306 (1485) ◽  
pp. 135-158 ◽  
Keyword(s):  
Carbon Monoxide ◽  
Gas Phase ◽  
Energy Content ◽  
Incident Light ◽  
Hydrogen Abstraction ◽  
Relative Concentration ◽  
Radical Mechanism ◽  
Gas Phase Reactions ◽  
Free Radical Mechanism ◽  
Singlet Methylene

In this work methylene was prepared by the photolysis of ketene, and the experiments include observations of the effects of changing the wavelength of the photolysing light and of introducing foreign gases. Results are consistent with a free-radical mechanism in which CH 2 abstracts a chlorine or a hydrogen atom from C 2 H 5 Cl: CH 2 +CH 3 CH 2 Cl→ k cl ĊH 2 Cl+CH 3 ĊH 2 , CH 2 +CH 3 CH 2 Cl→ k h1 ĊH 3 +ĊH 3 CH 3 Cl, } CH 2 +CH 3 CH 2 Cl→ k H2 ĊH 3 +CH 3 ċHCl. } ( k H ) All the fourteen products of the radical recombinations have been identified. Disproportionation of radicals and decomposition of excited molecules formed by recombinations yield additional products. Methylene insertion does not appear to play a significant role. When the incident light contains wavelengths in the region 2450 to 4000Å we find that k Cl / k H =1·62, k H1 / k H2 =0·098. If shorter wavelengths are excluded, or if nitrogen is added, lower values of k Cl / k H are obtained. On the other hand, in the presence of carbon monoxide the value of k Cl / k H may be greatly increased. It is suggested that these findings are attributable to differences in reactivity between singlet and triplet methylene. At longer wavelengths, or when nitrogen is present, the relative concentration of the singlet is reduced, but in the presence of carbon monoxide the triplet is removed preferentially (De Graff & Kistiakowsky 1967). Singlet methylene appears to be highly discriminating in its reactions, abstracting chlorine preferentially, while the triplet discriminates in favour of hydrogen abstraction. A kinetic analysis based on these ideas and consistent with the experimental observations shows that k S Cl / k S H >16·3, k T Cl / k T H <0·14. The selectivities shown by the two species of methylene are thought to be a result of differences in electronic structure rather than energy content.

ChemInform Abstract: Gas-Phase Reactions of F- with Phenyl Acetates. Translational Energy and Substituent Effects on Product Distribution

ChemInform ◽  
2010 ◽  
Vol 23 (13) ◽  
pp. no-no
Author(s):  
J. M. RIVEROS ◽  
S. INGEMANN ◽  
N. M. M. NIBBERING
Keyword(s):  
Gas Phase ◽  
Substituent Effects ◽  
Product Distribution ◽  
Translational Energy ◽  
Gas Phase Reactions

Translational energy dependence of gas-phase reactions of halides with halogenated alkanes

1991 ◽  
Vol 95 (26) ◽  
pp. 10582-10586 ◽  
Author(s):  
C. E. C. A. Hop ◽  
T. B. McMahon
Keyword(s):  
Gas Phase ◽  
Energy Dependence ◽  
Translational Energy ◽  
Gas Phase Reactions ◽  
Halogenated Alkanes

scholarly journals Crossed-beam chemical reaction dynamics probed with universal and state resolved ion imaging

2018 ◽  
Author(s):  
◽  
Alexander Kamasah
Keyword(s):  
Gas Phase ◽  
Chemical Reactions ◽  
Chemical Reaction ◽  
Reaction Dynamics ◽  
Reaction Cross ◽  
Translational Energy ◽  
Gas Phase Reactions ◽  
Chemical Reaction Dynamics ◽  
Products Of Reaction ◽  
State Selection

The main goal of chemical reaction dynamics is to unravel the intimate motions of individual atoms during a chemical transformation. This information must generally be inferred from indirect macroscopic measurement. Very important information such as translational energy dependence of the reaction cross-section, vibrational mode-specific promotion of reactivity, product angular and velocity distributions are normally extracted. Understanding how these chemical reactions occur at the microscopic level gives us a better insight in understanding reactive intermediates and products of reaction. For a better understanding of the elementary chemical reactions, it is imperative that the studies are performed under well-defined laboratory conditions. Over the last few decades, the field has witnessed unprecedented advances in both experiment and theory. Advancements in generating reactants, state selection, improvement of crossed-molecular beam machines and products detection have gone a long way to improve our ability in studying chemical reactions in the gas phase. In 1986, Hershbach,[1] Lee[2] , and Polayni[3] together shared the Nobel Prize in Chemistry for their work on the dynamics of gas phase reactions.

Theoretical Study on Gas Phase Reactions of OH Hydrogen-Abstraction from Formyl Fluoride with Different Catalysts

2016 ◽  
Vol 29 (3) ◽  
pp. 325-334 ◽  
Author(s):  
Ding-mei Wang ◽  
Zheng-wen Long ◽  
Xing-feng Tan ◽  
Bo Long ◽  
Wei-jun Zhang
Keyword(s):  
Gas Phase ◽  
Theoretical Study ◽  
Hydrogen Abstraction ◽  
Gas Phase Reactions

Modeling of Silicon Deposition Yield at Low Temperature by ArF Excimer Laser Photolysis of Disilane

1992 ◽  
Vol 263 ◽  
Author(s):  
B. Fowler ◽  
S. Lian ◽  
S. Krishnan ◽  
C. Li ◽  
L. Jung ◽  
...  
Keyword(s):  
Gas Phase ◽  
Excimer Laser ◽  
Substrate Surface ◽  
Chemical Vapor ◽  
Film Deposition ◽  
Growth Surface ◽  
Phase Reaction ◽  
Gas Phase Reactions ◽  
Arf Excimer Laser ◽  
193 Nm

ABSTRACTNon-thermal Chemical Vapor Deposition (CVD) such as laser-enhanced photo-CVD of Si at low temperatures is important for Si-based heterostructures and doping superlattices. Growth kinetic models must be developed to allow these processes to be fully exploited. Intrinsic Si epitaxial layers were deposited at low substrate temperatures of 250-350ºC using the 193 nm output of an ArF excimer laser to directly dissociate Si2H6. The intrinsic film deposition rate can be described by a kinetic model that considers the gas phase reactions of the primary photolysis products and diffusion ofsilicon-bearing molecules to the growth surface. With the laser beam tangential to the substrate surface, growth rates as a function of beam-to-substrate distance have been characterized and indicate that very little gas phase reaction occurs for the dominant Si growth precursor. In order for intrinsic film deposition to result solely from Si2H6 photolysis products, a sticking coefficient ≥ 0.6 must be assigned to the dominant growth precursor in order to fit the observed yield of Si deposited in the films, indicating that the dominant growth precursor in 193 nm Si2H6 photolysis is perhaps H2SiSiH2.

Different routes to the formation of C54 TiSi2 in the presence of surface and interface molybdenum: A transmission electron microscopy study

2002 ◽  
Vol 17 (4) ◽  
pp. 784-789 ◽  
Author(s):  
Z-B. Zhang ◽  
S-L. Zhang ◽  
D-Z. Zhu ◽  
H-J. Xu ◽  
Y. Chen
Keyword(s):  
Electron Microscopy ◽  
Transmission Electron Microscopy ◽  
Direct Evidence ◽  
Sample Surface ◽  
Microscopy Study ◽  
Electron Microscopy Study ◽  
Cross Sectional ◽  
Surface And Interface ◽  
Si Substrates ◽  
Transmission Electron

Direct evidence revealing fundamental differences in sequence of phase formation during the growth of TiSi2 in the presence of an ultrathin surface or interface Mo layer is presented. Results of cross-sectional transmission electron microscopy showed that when the Mo layer was present at the interface between Ti films and Si substrates, C40 (Mo,Ti)Si2 formed at the interface, and Ti5Si3 grew on top after annealing at 550 °C. Additionally, both C54 and C40 TiSi2 were found in the close vicinity of the C40 (Mo,Ti)Si2 grains. No C49 grains were detected. Raising the annealing temperature to 600 °C led to the formation of C54 TiSi2 at the expense of Ti5Si3, and the interfacial C40 (Mo,Ti)Si2 also began to transform into C54 (Mo,Ti)Si2 at 600 °C. When the Mo was deposited on top of Ti, the silicide film was almost solely composed of C49 TiSi2 at 600 °C. However, a small amount of (Mo,Ti)5Si3 was still present in the vicinity of the sample surface. Upon annealing at 650 °C, only the C54 phase was found throughout the entire TiSi2 layer with a surface (Mo,Ti)Si2 on top of TiSi2. Hence, it was unambiguously shown that in the presence of surface versus interface Mo, different routes were taken to the formation of C54 TiSi2.

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