Synthetic Method Development and Molecular Weight Control for Homo- and Co-Polysilynes, Silicon-Based Network-Backbone Polymers

Smith, D. A.; Joray, Scott J.; Bianconi, Patricia A.

doi:10.1007/s10965-005-1765-x

Cited by 6 publications

(5 citation statements)

References 23 publications

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“…Since the first reports of fairly efficient photoluminescence (PL) in the visible-near IR region from nanocrystalline Si ( nc -Si) − and porous Si, , much effort has been focused on creating Si with efficient, tunable UV−visible emission. To effectively confine a photoexcited electron−hole pair within Si’s Bohr radius of ∼5 nm, several low-dimensional Si-based materials have been theoretically ,, and experimentally explored: − zero-dimensional nc -Si and nanoparticles as visible−near IR emitters, − Si nanowire , and one-dimensional helical polysilane as an exitonic UV emitter and a two-dimensional (2D) skeleton as a visible emitter, such as Si−Si bonded network polysilyne (SNP), ,− , Wöhler Siloxene, and Si/SiO 2 superlattice . Although SNP was previously regarded as a soluble model polymer of amorphous Si ( a -Si) and 2D-Si nanosheet-like “saturated bonded sila-graphene”, ,,,, further studies on pyrolytic products of SNP derivatives and their inherent photophysical properties under a vacuum and low temperature have not yet been reported.…”

Section: Introductionmentioning

confidence: 99%

Full-Visible-Spectrum Emitters from Pyrolysis of Soluble Si−Si Bonded Network Polymers

et al. 2009

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Crystalline silicon is a poor UV-visible-near IR emitter because of its indirect, narrow band gap and low quantum yield of ∼1 × 10 -2 % at room temperature. To effectively confine a photoexcited electron-hole pair (exciton) within Si's Bohr radius of ∼5 nm, we have theoretically and experimentally explored several low-dimensional Si-based materials. Although Si-Si bonded network polysilyne was previously regarded as a soluble model polymer of amorphous Si and Si nanosheet-like "saturated silagraphene," further studies on pyrolytic products of polysilyne derivatives and their inherent photophysical properties under a vacuum have not yet been reported. The present paper demonstrated visible light emission from ten soluble polysilynes in the range 460 nm (2.70 eV) to 740 nm (1.68 eV) at both 77 K and room temperature by controlling temperature and time of the pyrolysis (200-500 °C, 10-90 min) under a vacuum. When very weakly deep-red emitting Si particles produced by the pyrolysis of poly(nbutylsilyne) at 500 °C for 90 min were exposed to air, the photoluminescence switched abruptly to an intense sky-blue color (λ ) 430 nm), with a quantum yield of 20-25% and a short lifetime of ∼5 ns in common organic solvents at room temperature because of the Siloxene-like, multilayered Si-sheet structures.

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Section: Introductionmentioning

confidence: 99%

Full-Visible-Spectrum Emitters from Pyrolysis of Soluble Si−Si Bonded Network Polymers

et al. 2009

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“…24 Absorption bands corresponding to Si-H (2072 cm À1 ) and Si-O-Si (1026 cm À1 ) are also noted. While their origin is described else-where, 24,29 these groups enhance the precursor's pyrophoric nature and siloxane content leading to reduced SiC purity during pyrolysis.…”

Section: Resultsmentioning

confidence: 99%

Polymer Precursor‐Based Preparation of Carbon Nanotube–Silicon Carbide Nanocomposites

et al. 2011

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Multiwalled carbon nanotubes were dispersed in a silicon carbide matrix to examine nanotube influence on mechanical properties of the resulting composite. The ceramic matrix was generated through high temperature conversion of poly(methylsilyne), a preceramic polymeric precursor. Nanotube alkylation was explored using two functionalization schemes: organic peroxide workup and alkyllithium displacement of fluorinated nanotubes, which promoted extensive mixing within precursor solutions, thereby ensuring nanotube dispersion within the polymer matrix while facilitating interfacial bonding. The former scheme was less effective at displacing inner nanotube shell bound fluorine and resulted in lower alkyl chain grafting density on the outer shell. Polymer nanocomposites were pyrolyzed and consolidated using an optimized spark plasma sintering scheme to generate fully densified ceramics. The pure polymer‐derived ceramic displayed exceptional Young's modulus and Vickers microhardness of 126 ± 12 and 9.6 ± 0.5 GPa, respectively, while maintaining a fracture toughness of 2.8 ± 0.3 MPa·m1/2. Increased sintering time further augmented the fracture toughness to 3.6 ± 0.4 MPa·m1/2, approaching the 4 MPa·m1/2 that characterizes pure silicon carbide, while maintaining both Young's modulus and microhardness. Nanotube addition resulted in some loss of the intrinsic mechanical properties, but enhanced monolith damage tolerance behavior, raising the Vickers indent force needed to induce cracks to an excess of 98.1 N in contrast to the pure polymer‐derived sample, which began crack propagation below 49.0 N.

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“…The structureless, broad absorption bands in the range of 200 to 400 nm are due to Sis-Sis* transitions that are characteristic of a Si-Si network skeleton, as reported previously. [23][24][25][26][27][28][29] The absorption edges of the FSNP, BSNP and F x B 1Àx SNP commonly appear at $400 nm, and the edge wavelength is weakly dependent on the their skeleton elements.…”

Section: Photophysical Propertiesmentioning

confidence: 99%

“…[5][6][7][8][9][10][11][12][13] These outcomes prompted both theoretical and experimental studies of the rational design and production of several low-dimensional Si-based materials. The most prominent examples are zerodimensional (0D) nanocrystalline silicon (nc-Si) and nanoparticles (Si-NPs); 5,6,9,14,15,[18][19][20] one-dimensional (1D) polysilane and nanowires (SiNWs); [16][17][18] two-dimensional (2D) Si-skeletons and Si nanosheets (Si-NSs), 13,[23][24][25][26][27][28][29][30][31][32][33][34][35][36] which include the siloxene family [(Si 6 H 3 (OH) 3 ) n , (Si 6 H 3 (OCH 3 ) 3 ) n , and (Si 6 H 6 ) n ], [30][31][32][33][34][35] Si/SiO 2 superlattices, 36 and Si-Si bonded network-like polysilyne (SNP) as a polymeric model of siloxenes. [23][24][25][26]…”

Section: Introductionmentioning

confidence: 99%

“…The most prominent examples are zerodimensional (0D) nanocrystalline silicon (nc-Si) and nanoparticles (Si-NPs); 5,6,9,14,15,[18][19][20] one-dimensional (1D) polysilane and nanowires (SiNWs); [16][17][18] two-dimensional (2D) Si-skeletons and Si nanosheets (Si-NSs), 13,[23][24][25][26][27][28][29][30][31][32][33][34][35][36] which include the siloxene family [(Si 6 H 3 (OH) 3 ) n , (Si 6 H 3 (OCH 3 ) 3 ) n , and (Si 6 H 6 ) n ], [30][31][32][33][34][35] Si/SiO 2 superlattices, 36 and Si-Si bonded network-like polysilyne (SNP) as a polymeric model of siloxenes. [23][24][25][26][27][28][29] Among these low-dimensional Si materials, 2D-Si skeleton materials have received considerable interest because of potential applications as tunable visible PL emitters. In 1988, Bianconi and Weidman first reported the synthesis of SNP by reducing n-hexyltrichlorosilane with NaK alloy under ultrasound irradiation.…”

Section: Introductionmentioning

confidence: 99%

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Air-stable poly(3,3,3-trifluoropropylsilyne) homo- and copolymers

et al. 2012

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A soluble Si-Si bonded polymer (polysilyne, SNP) bearing n-butyl groups (BSNP) has been reported to exhibit a green photoluminescence (PL) at 540 nm (2.30 eV). However, BSNP gradually changed to a colorless solid because of auto-oxidation within a few weeks when the polymer was stored in the absence of light without special care. Herein, we demonstrate the photophysical properties of SNP carrying 3,3,3-trifluoropropyl (TFP) side groups (FSNP), which remains unaffected by autooxidation. This stability against oxidation may be possibly attributable to intra-and inter-molecular CF-Si interactions between the electron-donating Si-Si main chain and the electron withdrawing TFP side groups. FSNP in polar tetrahydrofuran (THF) exhibited an almost pure-blue PL peak at 450 nm (2.76 eV), whereas in non-polar n-octane, it emitted a near-UV peak at 337 nm (3.68 eV), possibly, because of the CF-Si interactions. Additionally, thin films of FSNP exposed to air and in THF exhibited excellent resistance to air oxidation for at least one month, as determined by the lack of any changes in its PL, IR, and Raman spectra. From Gaussian03 calculations (TD-DFT, 6-31G* basis set, B3LYP) of trans-perhydrosiladecaline partially substituted with TFP and n-butyl groups as models of FSNP and BSNP, the most essential roles of TFP groups suggested that (i) the lowest Sis-Sis* transition state becomes the allowed transition by introducing strong polarity to the SNP skeleton and (ii) both the HOMO and LUMO energy levels are significantly stabilized, which provides the observed stability toward air oxidation. The air stability was effective in copolymers carrying TFP and n-butyl groups (FBSNP). However, FSNP and FBSNP that had been pyrolysed at temperatures greater than 500 C exhibited no such air stability because of the loss of the TFP groups.

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Synthetic Method Development and Molecular Weight Control for Homo- and Co-Polysilynes, Silicon-Based Network-Backbone Polymers

Cited by 6 publications

References 23 publications

Full-Visible-Spectrum Emitters from Pyrolysis of Soluble Si−Si Bonded Network Polymers

Full-Visible-Spectrum Emitters from Pyrolysis of Soluble Si−Si Bonded Network Polymers

Polymer Precursor‐Based Preparation of Carbon Nanotube–Silicon Carbide Nanocomposites

Air-stable poly(3,3,3-trifluoropropylsilyne) homo- and copolymers

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