Gas-Phase Reaction Pathways from SiH4 to Si2H6, Si2H4 and Si2H2: A Theoretical Study

Modelling the non-local thermodynamic equilibrium spectra of silylene (SiH2)

This paper sets out a robust methodology for modelling spectra of polyatomic molecules produced in reactive or dissociative environments, with vibrational populations outside local thermal equilibrium (LTE). The methodology is based on accurate, extensive ro-vibrational line lists containing transitions with high vibrational excitations and relies on the detailed ro-vibrational assignments. The developed methodology is applied to model non-LTE IR and visible spectra of silylene (SiH2) produced in a decomposition of disilane (Si2H6), a reaction of technological importance. Two approaches for non-LTE vibrational populations of the product SiH2 are introduced: a simplistic 1D approach based on the Harmonic approximation and a full 3D model incorporating accurate vibrational wavefunctions of SiH2 computed variationally with the TROVE (Theoretical ROVibrational Energy) program. We show how their non-LTE spectral signatures can be used to trace different reaction channels of molecular dissociations.

Data-Driven Investigation of Monosilane and Ammonia Co-Pyrolysis to Silicon-Nitride-Based Ceramic Nanomaterials

With its high strength, high thermal stability, low density, and high electrical resistance, silicon-nitride-based ceramics have been widely used as gate insulating layers, oxidation masks, and passivation layers. Employing SiN nanomaterials in anode applications also improves rate performances and cycling stability of the lithium-ion batteries. However, a fundamental understanding of the SiN synthetic process remains elusive. SiN gas-phase synthesis can be tailored with a comprehensive understanding of the underlying thermodynamics. In comparison to the characterization data available for solid-state SiN materials, high-level theoretical studies on gas-phase materials possessing Si-N bonds and comprehensive investigation of the SiN chemistry, particularly for nanoclusters, are very uncommon. Thus, we performed a theoretical study of Si and SiN alloy acyclic hydrides and polycyclic clusters to predict electronic structures and thermochemistry using quantum chemical calculation and statistical thermodynamics. Electronic properties by way of highest and lowest occupied molecular orbital energy gap and natural bonding orbitals analysis were calculated to explore the influence of elemental composition and geometry on the stability. Our studies provide characteristic data of SiN species for a data-driven approach to map the design space for discovery of novel silicon-nitride-based ceramic materials for advanced electronic and coating applications.

The role of multifunctional kinetics during early-stage silicon hydride pyrolysis: reactivity of Si2H2 isomers with SiH4 and Si2H6

Kinetic parameters for the dominant pathways during the addition of the four Si(2)H(2) isomers, i.e., trans-HSiSiH, SiSiH(2), Si(H)SiH, and Si(H(2))Si, to monosilane, SiH(4), and disilane, Si(2)H(6), have been calculated using G3//B3LYP, statistical thermodynamics, conventional and variational transition state theory, and internal rotation corrections. The direct addition products of the multifunctional Si(2)H(2) isomers were monofunctional substituted silylenes, hydrogen-bridged species, and silenes. During addition to monosilane and disilane, the SiSiH(2) isomer was found to be most reactive over the temperature range of 800 to 1200 K. Revised parameters for the Evans-Polanyi correlation and a representative pre-exponential factor for multifunctional silicon hydride addition and elimination reaction families under pyrolysis conditions were regressed from the reactions in this study. This revised kinetic correlation was found to capture the activation energies and rate coefficients better than the current literature methods.

Thermal decomposition mechanism of disilane

Thermal decomposition of disilane was investigated using time-of-flight (TOF) mass spectrometry coupled with vacuum ultraviolet single-photon ionization (VUV-SPI) at a temperature range of 675-740 K and total pressure of 20-40 Torr. Si(n)H(m) species were photoionized by VUV radiation at 10.5 eV (118 nm). Concentrations of disilane and trisilane during thermal decomposition of disilane were quantitatively measured using the VUV-SPI method. Formation of Si(2)H(4) species was also examined. On the basis of pressure-dependent rate constants of disilane dissociation reported by Matsumoto et al. [J. Phys. Chem. A 2005, 109, 4911], kinetic simulation including gas-phase and surface reactions was performed to analyze thermal decomposition mechanisms of disilane. The branching ratio for (R1) Si(2)H(6) --> SiH(4) + SiH(2)/(R2) Si(2)H(6) --> H(2) + H(3)SiSiH was derived by the pressure-dependent rate constants. Temperature and reaction time dependences of disilane loss and formation of trisilane were well represented by the kinetic simulation. Comparison between the experimental results and the kinetic simulation results suggested that about 70% of consumed disilane was converted to trisilane, which was observed as one of the main reaction products under the present experimental conditions.