Determination of Conditions for the Suppression of CH₃ + Sb(CH₃)₂→Sb(CH₃)₃ and Evaluation of D[(CH₃)₂Sb—CH₃]

Abstract

The pyrolysis of trimethylantimony has been studied in a toluene carrier flow system over the temperature range 690-803 K (total pressures 3.6-173.4 mm, contact times 1.0-13.5 s, decomposition 3.9-89.5%). The progress of the reaction was followed by measuring the amount of methane, ethane, and ethylbenzene formed. In 23 runs the undecomposed alkyl was also determined. The quantity found was in agreement with that expected from the product analysis if three methyl radicals are released for each molecule undergoing reaction. No heterogeneous reaction was detected.Deuterium labeling led to the conclusion that regeneration of the parent alkyl occurred during the course of the decomposition. This regeneration reaction was effectively eliminated by working at toluene pressures above 150 mm. Least squares analysis of the results obtained under conditions where regeneration should not be important given log,, k1s-I = 15.33 -(55 900 + I 000)/2.3RT The activation energy should be a good approximation to D[(CH,),S&CH,]. Significant decomposition of SbCH, probably does not occur. It seems most likely that free Sb is formed via 2Sb(CH3) + Sb(CH,), + Sb.La pyrolyse du trimtthylantimoine a ete etudiie dans un systeme courant porteur de toluene sur la gamme de temperature de 690-803 "K (pressions totales 3.6-173.4 mm, temps de contact 1.0-13.5 s, decomposition 3.9-89.5%). La progression de la reaction est suivie en mesurant la quantite de methane, d'ethane et d'ethylbenzene formee. Dans 23 essais, le produit alkyle non decompose a ete tgalement determine. La quantitt trouvee etait en accord avec celle attendue Q partir de I'analyse du produit dans le cas ou les trois radicaux methyle sont liberts pour chaque molecule qui subit des changements. Aucune reaction hethogene n'a ete detectee.Le marquage au deuterium amene Q la conclusion que la regeneration du groupe alkyle d'origine se produit durant le temps de la decomposition. Cette reaction de regeneration a ete completement tlimine en travaillant B des pressions de toluene superieures Q 150 mm. L'analyse des resultats par la methode des moindres carres dans des conditions ou la regeneration ne serait pas importante, a donne: log,, k1s-l = 15.33 -(55 900 + 1 000)/2.3RT

Decomposition Mechanisms of Antimony Source Compounds for Organometallic Vapor-Phase Epitaxy

“…The addition of azomethane (CH 3 N) 2 as a "clean" source of methyl radicals retards the TMSb decomposition slightly. This supports a reversible step in TMSb pyrolysis (reaction 7) that was previously reported [18]. Overall, homolytic fission of the Sb-C bonds in TMSb followed by normal free-radical reactions appears to describe the pyrolysis of TMSb under these conditions.…”

“…The resulting rate constants for TVSb and TIPSb derived from the Arrhenius plots are shown in eq 2 and 3, respectively. The activation energy for TVSb decomposition derived from eq 2 (49.0 kcal/mol) is less than the reported Sb-C bond energy for TMSb (55.9 kcal/mol) [18]. The activation energy for TIPSb decomposition derived from eq 3 (30.8 kcal/mol), which may represent the Sb-C bond strength in TIPSb, is substantially lower than for TMSb and TVSb.…”

“…There are several reasons for suspecting this to be the operative mechanism. First, the activation energy for TVSb decomposition (eq 2) is less than that found for scission of the Sb-CH 3 bond in TMSb [16,18]. If Sb-C bond homolysis occurs, one would exl.ec-the Sb-vinyl bond strength to be higher than the Sb-methy, bond strength.…”

Growth behavior of GaSb by metal–organic vapor-phase epitaxy

“…This study indicates that the decomposition mechanism of TMSb is similar to that of TMG in that it proceeds via bond scission and subsequent radical reactions to yield monomethyl antimony (MMSb, SbCH 3 ) and methyl radicals with an apparent activation energy of 55.9 kcal/mol [11]. It was again concluded that the active species in the radical chain reactions carried out in a H 2 or D 2 carrier gas were atomic hydrogen or deuterium [11,12].…”

“…This discrepancy could be reconciled under conditions of low Ga species surface coverage (K Ga P Ga 51), an assumption not explicitly stated by the authors. Furthermore, other kinetic studies of the decomposition of TMSb under a variety of conditions show no evidence of gas-phase Sb 4 formation [10][11][12]. Additionally, studies of the decomposition of TMG indicate that it is highly unlikely that TMG will decompose to Ga in the gas phase under typical MOVPE reactor residence times, pressures and temperatures [10,13,14].…”