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We investigate 29Si nuclear magnetic resonance (NMR) chemical shifts, δiso, of silicon nitride. Our goal is to relate the local structure to the NMR signal and, thus, provide the means to extract more information from the experimental 29Si NMR spectra in this family of compounds. We apply structural modeling and the gauge-included projector augmented wave (GIPAW) method within density functional theory (DFT) calculations. Our models comprise known and hypothetical crystalline Si3N4, as well as amorphous Si3N4 structures. We find good agreement with available experimental 29Si NMR data for tetrahedral Si[4] and octahedral Si[6] in crystalline Si3N4, predict the chemical shift of a trigonal-bipyramidal Si[5] to be about −120 ppm, and quantify the impact of Si-N bond lengths on 29Si δiso. We show through computations that experimental 29Si NMR data indicates that silicon dicarbodiimide, Si(NCN)2 exhibits bent Si-N-C units with angles of about 143° in its structure. A detailed investigation of amorphous silicon nitride shows that an observed peak asymmetry relates to the proximity of a fifth N neighbor in non-bonding distance between 2.5 and 2.8 Å to Si. We reveal the impact of both Si-N(H)-Si bond angle and Si-N bond length on 29Si δiso in hydrogenated silicon nitride structure, silicon diimide Si(NH)2.
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This content will become publicly available on December 1, 2026
Formation of silicon nitride by high-fluence femtosecond laser treatment
High-fluence femtosecond laser pulses can induce physical and chemical changes in materials that are unrealizable under standard laboratory conditions. The exact nature of these changes can depend strongly on the gaseous environment in which the material is irradiated since near-surface chemical reactions can occur between the two materials. Surface modifications of silicon are of particular interest due to its significance in semiconductor-based applications. Specifically, the formation of silicon nitride (Si3N4) structures is desirable for multiple applications due to its high stability and low dielectric constant. Herein, we report on femtosecond laser-induced morphological and chemical modifications of silicon in a nitrogen atmosphere. We observed an extremely fast chemical reaction in the silicon-nitrogen system. The presence of crystalline Si3N4 was confirmed using high-resolution transmission electron microscopy, representing the first reported synthesis of Si3N4 nanocrystals through femtosecond laser-based methods. In addition, the surface was found to contain alternating layers of amorphous and crystalline silicon. Provided are plausible mechanisms for the formation of each of these structures. Taken together, these findings on surface modification of silicon using femtosecond laser irradiation may provide new pathways for manufacturing of nanoscale devices.
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- Award ID(s):
- 2207664
- PAR ID:
- 10626446
- Publisher / Repository:
- Elsevier
- Date Published:
- Journal Name:
- Materials Science in Semiconductor Processing
- Volume:
- 200
- Issue:
- C
- ISSN:
- 1369-8001
- Page Range / eLocation ID:
- 109929
- Subject(s) / Keyword(s):
- Femtosecond laser Irradiation Silicon nitrogen system Silicon nitride formation
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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