EPR investigation of a-Si:H aerosol particles formed under silane thermal decomposition

Abstract

The dangling bond defects were investigated in a-Si:H particles formed under silane thermal decomposition in flow reactor. EPR together with hydrogen evolution method were used. The experimental results allowed us to conclude that there are two kinds of dangling bond defects in aSi:H aerosol particles. The defects of the first kind are localized on the surface of interconnected microvoids and microchannels (surface dangling bonds) and those of the second kind are embedded in amorphous silicon network (volume dangling bonds). The thermal equilibration of dangling bonds and temperature dependence of equilibrium dangling bond concentration were investigated. It was found that at temperatures >400 K the dangling bond concentration N reversibly depends on sample temperature. The volume dangling bond concentration increases with temperature increasing (the effective activation energy of dangling bond formation U> 0), and the surface dangling bond concentration decreases with temperature increasing (U < 0). It has been found that EPR line is considerably asymmetric for samples with high hydrogen content and for low hydrogen content the EPR line is weakly asymmetric. A conclusion was drawn that the asymmetry degree depends on amorphous silicon lattice distortions. This conclusion has been confirmed by EPR spectra simulations.

Mechanism of thermal decomposition of silanes

“…The hydrogen of the `dilute' phase is a constituent of monohydride groups with the vibration frequency 2100 m 71 . Experimental results suggest that the SiH groups of the `clustered' phase are localised inside the amorphous silicon network 206 as `hydrogen complexes', viz., extended defects stabilised by hydrogen. 207 ± 211 The monohydride groups of the `dilute' phase are localised on the surfaces of interconnected microvoids and microchannels.…”

Evidence for Long-Range Coulomb Effects during Formation of Nanoparticle Agglomerates from Pyrolysis and Combustion Routes

“…However, the hydrogen atoms are usually very mobile at high temperatures. As a consequence of this, they migrate intensively through the silicon networks, and therefore, the hydrogen concentration reaches equilibrium very quickly over the particles. The effect of equilibration of hydrogen contents is to force to zero the dipole moment of the particles (or agglomerates).…”

“…33,34 The hydrogen content in the particles was measured by the hydrogen evolution method. 33,35,36 To this end, the aerosol particles were sampled by a quartz filter. The deposited mass was determined by weighing.…”

“…Aerosol particles formed due to silane pyrolysis consist of amorphous hydrogenated silicon. , The hydrogen content in the particles was measured by the hydrogen evolution method. ,, To this end, the aerosol particles were sampled by a quartz filter. The deposited mass was determined by weighing.…”

Pulsed EPR hole-burning experiment on dangling bond centers in a-Si:H aerosol particles formed by thermal decomposition of silane

“…Aerosol particles examined in the present work were prepared by silane thermal decomposition in a flow reactor described in [16][17][18][19][20][21]. Mixture of gases consisting of 5% SiH4 + 95% Ar was used.…”