Silicon‐29 Solid‐State MAS NMR Investigation of Selective Area Laser Deposition Silicon Carbide Material

Abstract

The microstructure of silicon carbide fabricated from the gas‐phase‐based, laser‐driven selective area laser deposition (SALD) process has been characterized by X‐ray diffraction and solid‐state 29Si NMR techniques with magic angle spinning (MAS). X‐ray patterns reveal the characteristic spectrum of pure ß, cubic silicon carbide polytype while NMR shows a ß‐SiC pattern with additional peaks. To determine the source of the extra peaks, a comparative evaluation of commercially available silicon carbide powders, both alpha‐ and ß‐SiC, was undertaken with NMR. Spin‐lattice relaxation time measurements (T1) were also carried out to determine the polytype morphology of the SALD deposit. The results showed an NMR spectrum that appears to be a combination of alpha and ß polytypes. Microtwinning is advanced as a possible explanation for this phenomenon.

Phase Segregation in Silicon Carbide−Carbon Solid Solutions from XRD and NMR Studies

“…The plot of the intensity of the NMR signal at −18.5 ppm vs recovery delay τ shows an exponential-like dependence (Figure ) with the best fit obtained using a double exponential function of the form from which T 1 SiC and T 1 SiC-C , the spin−lattice relaxation times of the two different types of silicon sites, can be derived ( M 0 SiC and M 0 SiC-C are the corresponding amplitudes). The four parameter least-squares fit gives relaxation times T 1 SiC = 137 ± 20 s and T 1 SiC-C = 16 ± 3 s. The first value is in good agreement with the relaxation time of ∼130 s reported for β-SiC . Thus, both the relaxation time and the 29 Si chemical shift confirm that one of silicon sites in the as-synthesized compound corresponds closely to cubic silicon carbide.…”

Microstructure and thermal stabilities in various atmospheres of SiB0.5C1.5N0.5 nano-sized powders fabricated by mechanical alloying technique

“…To further investigate the polytypes of SiC in the SiBCN powders, 29 Si solid-state NMR studies were introduced. Previous 29 Si solid-state NMR studies have outlined the relationship of the spectra to phase properties of SiC [18][19][20][21][22]. Typically, a single resonance line is observed in the spectrum of b-SiC while up to three closely spaced resonances characterize the a-SiC materials.…”

“…In their experiments, broad 29 Si peaks, which were similar to our experiments, appeared for the Si-C mixture milled for 48 h and 72 h. The peaks have shoulders at À24.5 ppm, and the authors explained that they were formed by the stacking faults in 3C polymorph. Narisawa et al [19], Bouclé et al [21], Harrison et al [22], and Martin et al [56] have fabricated SiC by pyrolysis of polymers or selective area laser deposition. Similar broad 29 Si peaks, which were also had shoulders, were detected at about À20 ppm, furthermore the XRD patterns of those experiments [21,22,55] were similar to these for the ball milled SiC.…”

“…Narisawa et al [19], Bouclé et al [21], Harrison et al [22], and Martin et al [56] have fabricated SiC by pyrolysis of polymers or selective area laser deposition. Similar broad 29 Si peaks, which were also had shoulders, were detected at about À20 ppm, furthermore the XRD patterns of those experiments [21,22,55] were similar to these for the ball milled SiC. But a-SiC was proved to exist in these Si-C powders after the deconvolution of the peaks.…”

Structural and microstructural characterization of SiB0.5C1.5N0.8Al0.3 powders prepared by mechanical alloying using aluminum nitride as aluminum source

“…The broad peak at À18.3 ppm (as shown in Fig. 3(a)) indicates that amorphous SiC structure based on SiC 4 sites was formed in SiB 0.5 C 1.5-N 0.8 Al 0.3 powders [12]. A small peak at À90.3 ppm is attributed to the residual starting Si material due to insufficient milling [12].…”