Role of silylene in the deposition of hydrogenated amorphous silicon

Abstract

95, 9302-93 I O IO ' -I 0 : * IO6 I-2 U Im z 0 0 W ta: u lo5 lo4 12 12 4 12 8 13.2 E N E R G Y , eV Figure 5. Comparison of calculated VTST k ( E ) curves (dashed) with experiment (continuous curve). The calculations are for a critical energy 2.83 eV (= 65.26 kcal/mol).The loosening parameters a = 2 and a = 1 correspond to early and late loosening of the transitional modes, respectively. Early loosening is basically the phase space theory (PST) result. The experimental curve RSP is from coincidence experimentszzb by Rosenstock, Stockbauer, and Parr.demonstrates that the present calculations for the J = 0 approximation may be compared with experiment. We compared calculated VTST time-resolved photoionization efficiency curves with experimental ones from ref 5. The method for calculating PIE curves has been de~cribed.~ We employed a critical energy Eo = 2.76 eV (= 63.65 kcal/mol) which originally gave agreement,5 on the basis of a fixed RRKM transition state with a 1000 K activation entropy AS* = +8.07 eu. The result for late loosening with a = 1 and Eo = 2.76 eV is seen to be in disagreement with experimental results (Figure 2). A slightly higher critical energy, Eo = 2.83 eV (= 65.26 kcal/mol), and early loosening ( a = 2), which is the PST result, are in excellent agreement with experiment ( Figure 3). Keeping Eo constant at 2.83 eV and assuming late loosening of the transitional modes ( a = 1) has a very minor effect on the agreement with experiment (Figure 4). We next compared the calculated microcanonical VTST rate coefficients with the photoelectron photoion coincidence (PEPICO) results of Rosenstock, Stockbauer, and Parr22b (RSP, Figure 5 ) . The coincidence data are the ones that were fittedub by an RRKM model with Eo = 2.76 eV and AS* = 8.07 eu. Figure 5 shows that the RSP results are in good agreement with early loosening PST results ( a = 2, Eo = 2.83 eV) between IO5 and IO6 s-l above and below which the curves diverge slightly, while the late loosening curve ( a = 1, Eo = 2.83 eV) is in fair agreement with the RSP result between IO4 and IO5 s-I and diverges considerably at energies higher than 12.4 eV ( E > 3.43 eV).Comparison of the VTST results with experiments is still incomplete. More accurate experiments giving k ( E ) over wider energy ranges, particularly in the range k(E) I IO7 s-', are desirable. The present data indicate best agreement for a totally loose OTS, Le., early loosening of the transitional modes.Pratt and C h~p k a~~ were the first to suggest the use of VTST for the halobenzene ions but have not actually performed the calculations. In agreement with their results, we find the OTS to fit experimental data and to give a slightly higher critical energy than a fixed TTS (Eo(OTS) = 2.83 eV versus Eo(TTS) = 2.76 eV) and as a result a slightly higher heat of formation for the phenyl cation,27 AHfoo(C,H5+) = 1148 kJ mol-'.The comparison of VTST calculations with microcanonical rate coefficients performed here demonstrates the necessity of more refined ab initio potential energy surfaces in...

Phosphorus- and boron-doped hydrogenated amorphous silicon films prepared using vaporized liquid cyclopentasilane

“…The thermal decomposition of silane compound initiates with formation of a silylene-type radical [16]. The generated radical reacts with CPS by inserting one into Si-H bonds in CPS to form a larger polysilane.…”

Properties of Phosphorus‐Doped Silicon‐Rich Amorphous Silicon Carbide Film Prepared by a Solution Process

“…Heating and optical irradiation of hydrosilane results in cleavage of the relatively weak intrachain Si–Si bond, thereby leading to silylene‐type radicals . The radicals are ground‐state singlets, and their characteristic reactions include insertion into Si–H bonds and π‐type addition across C=C and C≡C bonds .…”

Polymeric precursor for solution-processed amorphous silicon carbide

“…The relatively weak intrachain Si-Si bond in hydrosilane undergoes cleavage by heating, leading to a silylene-type radical. 19 Silylenes are important intermediates in the synthesis of hydrosilanes. They exist as ground-state singlets, and their characteristic reactions include insertion into Si-H and p-type addition across CQC and CRC bonds.…”