Magic-angle spinning<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:mmultiscripts><mml:mrow><mml:mi mathvariant="normal">Si</mml:mi></mml:mrow><mml:mprescripts /><mml:mrow /><mml:mrow><mml:mn>29</mml:mn></mml:mrow><mml:mrow /><mml:mrow /></mml:mmultiscripts></mml:mrow></mml:math>NMR study of short-range order in<i>a</i>-Si

Shao, Wenguang; Shinar, J.; Gerstein, B. C.; Li, F.; Lannin, J. S.

doi:10.1103/physrevb.41.9491

Cited by 53 publications

(54 citation statements)

References 27 publications

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“…Another allotrope is amorphous silicon ( a -Si), produced by condensing silicon vapor generated by RF-plasma-sputtering of a silicon wafer on a condensing target that is maintained in an ultra high vacuum (UHV) or an inert atmosphere, for example argon [18,19]. This allotrope is a non-crystalline solid that displays a high concentration of dangling bonds [18].…”

Section: Introductionmentioning

confidence: 99%

“…This allotrope is a non-crystalline solid that displays a high concentration of dangling bonds [18]. Hydrogenated amorphous silicon ( a -Si:H) can be synthesized using the same method by including hydrogen or silane gas in the blanketing atmosphere [18,19]. Hydrogenated amorphous silicon has a lower concentration of dangling bonds than in amorphous silicon, a -Si [19].…”

Section: Introductionmentioning

confidence: 99%

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The Surface of Nanoparticle Silicon as Studied by Solid-State NMR

et al. 2012

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The surface structure and adjacent interior of commercially available silicon nanopowder (np-Si) was studied using multinuclear, solid-state NMR spectroscopy. The results are consistent with an overall picture in which the bulk of the np-Si interior consists of highly ordered (“crystalline”) silicon atoms, each bound tetrahedrally to four other silicon atoms. From a combination of 1H, 29Si and 2H magic-angle-spinning (MAS) NMR results and quantum mechanical 29Si chemical shift calculations, silicon atoms on the surface of “as-received” np-Si were found to exist in a variety of chemical structures, with apparent populations in the order (a) (Si–O–)3Si–H > (b) (Si–O–)3SiOH > (c) (HO–)nSi(Si)m(–OSi)4−m−n ≈ (d) (Si–O–)2Si(H)OH > (e) (Si–O–)2Si(–OH)2 > (f) (Si–O–)4Si, where Si stands for a surface silicon atom and Si represents another silicon atom that is attached to Si by either a Si–Si bond or a Si–O–Si linkage. The relative populations of each of these structures can be modified by chemical treatment, including with O2 gas at elevated temperature. A deliberately oxidized sample displays an increased population of (Si–O–)3Si–H, as well as (Si–O–)3SiOH sites. Considerable heterogeneity of some surface structures was observed. A combination of 1H and 2H MAS experiments provide evidence for a substantial population of silanol (Si–OH) moieties, some of which are not readily H-exchangeable, along with the dominant Si–H sites, on the surface of “as-received” np-Si; the silanol moieties are enhanced by deliberate oxidation. An extension of the DEPTH background suppression method is also demonstrated that permits measurement of the T2 relaxation parameter simultaneously with background suppression.

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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

The Surface of Nanoparticle Silicon as Studied by Solid-State NMR

et al. 2012

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“…[22,23,24,25] Variation in both hydrogen content (-5-50 at.%) and local order contribute to the wide rate of 29 Si isotropic chemical shifts for a-Si:H. For example, the -38 ppm shift of as-deposited a-Si:H film becomes increasingly negative with annealing until a recrystallization peak was observed at -79.9 ppm. [25] Annealing reduces both hydrogen content and disorder in a-Si:H. In PS, the absence of Si-H peaks downfield from c-Si demonstrates PS does not contain amorphous hydrogenated silicon regions comparable to those found in deposited films. This is a significant observation, as the luminescence behavior of PS has been discussed in relationship to the optical behavior of a-Si:H. [ 14] In a-Si:H films, the 29 Si line widths are quite broad (30 to 100 ppm), even upon applying MAS.…”

Section: Resultsmentioning

confidence: 95%

“…In addition, considerable charge transfer can arise from disorder. [25] A distribution of bond angles and bond lengths will cause the chemical shift to be distributed over a range of values. While fast MAS spinning can average many line broadening interactions, it does not reduce chemical shift dispersion arising from disorder.…”

Section: Resultsmentioning

confidence: 99%

Nuclear Magnetic Resonance (NMR) of Porous Silicon

1996

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Porous silicon (PS) was characterized by 1H, 19F and 29Si solid-state nuclear magnetic resonance (NMR). On freshly prepared samples, hydrogen contents were between 3 × 1014 and 3 × 1015 per cm2 of PS surface area, while fluorine concentrations were below the detection limit. Cross-polarization (CP) was used to selectively observe the 29Si near the hydrogen passivation. The features of the 29Si NMR spectra are assigned as (O)2(Si)Si-H (-50 ppm), (O)3Si-H (-84 ppm), (Si)3Si-H (-91 ppm), (Si)2Si-H2 (-102 ppm) and (O)4Si (-109 ppm). Changes resulting from low temperature annealing in air and an HF soak were observed by both NMR and infrared spectroscopy. The 29Si NMR line widths for PS fall between those for crystalline silicon and those for amorphous hydrogenated silicon films (a-Si:H), suggesting disorder near the PS surface is intermediate between these extremes. However, comparison of the isotropie chemical shift values shows that the bonding in the disordered regions of PS differs from that found in a-Si:H. In addition, the sharp 29Si NMR resonance observed in the bulk single crystal starting material can not be resolved in the spectra of PS. Thus, well-ordered silicon nanocrystallites in the PS are either several bond-lengths removed from hydrogen or comprise only a small fraction of the PS layer.

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“…The 29 Si T 1 was reported to be 12,000 s for crystalline silicon nanoparticles. 32 Therefore, in the DP experiment, an excitation pulse of 30 o and a recovery time of 120 s were used to give us a qualitative but not quantitative signal, especially between the bulk and the surface silicon atoms. The DP MAS spectrum of SiNPs suspended in isopropanol ( Figure 8) reveals a distribution of peaks between -30 and -70 ppm and centered around -50 ppm and largely unaffected by the removal of 1 H decoupling.…”

Section: Methodsmentioning

confidence: 99%

Room-Temperature Reactivity Of Silicon Nanocrystals With Solvents: The Case Of Ketone And Hydrogen Production From Secondary Alcohols: Catalysis?

El‐Demellawi

Holt

Abou-Hamad

et al. 2015

ACS Appl. Mater. Interfaces

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Although silicon nanoparticles dispersed in liquids are used in various applications ranging from bio-labeling to hydrogen production, their reactivities with their solvents and their catalytic properties remain still unexplored. Here, we discovered that, because of their surface structures and mechanical strain, silicon nanoparticles react strongly with their solvents and may act as catalysts for the dehydrogenation, at room temperature, of secondary alcohols (e.g. isopropanol)into ketones and hydrogen. This catalytic reaction was monitored by gas chromatography, pH measurements, mass spectroscopy and solid-state NMR. This discovery provides new understanding of the role played by silicon nanoparticles, and nanosilicon in general, in their reactivity in solvents in general as well as being candidates in catalysis.

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Magic-angle spinningSi29NMR study of short-range order ina-Si

Cited by 53 publications

References 27 publications

The Surface of Nanoparticle Silicon as Studied by Solid-State NMR

The Surface of Nanoparticle Silicon as Studied by Solid-State NMR

Nuclear Magnetic Resonance (NMR) of Porous Silicon

Room-Temperature Reactivity Of Silicon Nanocrystals With Solvents: The Case Of Ketone And Hydrogen Production From Secondary Alcohols: Catalysis?

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