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Photoluminescence spectra of the Al-doped Si3N4 nanowires and undoped pure Si3N4 under excitation of a 325 nm HeCd laser at room temperature.
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Al-doped single-crystalline Si(3)N(4) nanowires were synthesized by catalyst-assisted pyrolysis of polymeric precursors. The doping levels can be controlled by tailoring the Al concentration in the precursors. It is found that the Al concentration has a significant effect on the shape, sizes, and phase compositions of the synthesized Si(3)N(4) low-...
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... similar measurement on the amorphous SiCN particles fails to record any light emission, confirming that the PL spectra are from the Si 3 N 4 nanowires. Figure 5 compares typical PL spectra of the samples with different Al-doping concentrations together with that of pure Si 3 N 4 nanobelts. 1,35 It is seen that the PL peaks of the Al-doped Si 3 N 4 nanowires show red shifts compared to that of the undoped sample, suggesting that the Al doping caused the decrease in band energies, consistent with a previous study. ...
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... Nanowires with different microstructural features have been reported to exhibit specific optical, electrical and mechanical properties, which have an important impact on their applications in many fields such as electronic components and optical parts [35]. In addition, the above two types of nanowires have an amorphous thin layer on the surface, which is a normal phenomenon for the synthesised Si 3 N 4 nanowires [36,37]. ...
?-Si3N4 nanowires with diameters of 100-180 nm (Si3N4-W1) and 420-510 nm (Si3N4-W2) were synthesized by a modified chemical vapour deposition (CVD) method and their microstructure changes after high-temperature oxidation were studied. The results showed that both Si3N4 nanowires were not significantly oxidized when the temperature was lower than 900?C. However, the Si3N4-W1 microstructure began to change significantly after oxidation at 1200?C, while the Si3N4-W2 microstructure remained almost unchanged. Moreover, the Si3N4- W1 and Si3N4-W2 nanowires oxidized significantly after treatment at 1400?C, with weight gain of 26.4% and 13.7%, respectively.
... Doping is used as an effective method to modulate and improve the luminescence properties of Si 3 N 4 nanowires. For example, Al doping in Si 3 N 4 nanowires had a profound effect on the emission behavior [15]. The Ga doped Si 3 N 4 nanowires showed ten emission peaks [16]. ...
Si3N4 nanowires doped with rare earth ions (such as Ce³⁺, Tb³⁺, Eu²⁺ and Eu³⁺) were synthesized by plasma assisted direct nitridation method using Si, rare earth oxides and N2 as raw materials. The prepared doped Si3N4 nanowires were characterized by XRD, EDS, XPS, SEM and TEM. The obtained single-crystal doped Si3N4 nanowires have uniform diameters of about 50-100 nm and lengths of more than 10 μm. The photoluminescence (PL), PL decay curves as well as thermal quenching behaviors of doped Si3N3 nanowires were systematically investigated. This work provides an effective strategy for doping large-size functional atoms in Si3N4 nanowires.
... In addition to adding Si source, N source, and catalyst to the polymer, it was also possible to introduce specific components into the polymer to dope the nanowires. In 2007, Yang et al. synthesized controlled aluminum (Al)-doped α-Si 3 N 4 nanowires via pyrolysis of polymer precursors containing Al [74]. They did not use the traditional doping method such as the addition of metal powders or compounds related to desired doping elements, and they pyrolyzed the polymeric precursors containing Al to realize the doping [74]. ...
... In 2007, Yang et al. synthesized controlled aluminum (Al)-doped α-Si 3 N 4 nanowires via pyrolysis of polymer precursors containing Al [74]. They did not use the traditional doping method such as the addition of metal powders or compounds related to desired doping elements, and they pyrolyzed the polymeric precursors containing Al to realize the doping [74]. The products had a diameter of 40-70 nm and a length of several millimeters, and the doping of Al significantly changed the photoelectric performance of nanowires, which would be introduced in detail in the properties section. ...
... In 2007, Yang et al. used SLGS mechanism to explain the generation of the Al-doped Si 3 N 4 nanowires via pyrolyzing the precursors with catalysts [74]. Firstly, the precursors were thermally decomposed into Si-Al-C-N ceramics. ...
With advances in nanotechnology, nanowires have gained worldwide attention because of their novel properties and promising applications. Among them, silicon nitride (Si3N4) nanowires have attracted increasing attention due to their excellent performance and huge application potential. In this review, various synthesis methods of Si3N4 nanowires are introduced in detail, and then the growth mechanisms are also stated. Subsequently, the novel properties of Si3N4 nanowires including mechanical, optical, electrical, thermal, and wetting performance are highlighted. Applications corresponding to performance are also summarized later, such as composites, field emitters, field-effect transistors (FETs), photodetectors, photocatalysts, and microwave absorbers. Finally, the contents of this article are concluded and outlooks of future research directions are stated. This article reviews the recent advances and provides the prospects and challenges of Si3N4 nanowires.
... F I G U R E 1 0 Al solubility as a function of Si 3 N 4 nanowire width. [54][55][56][57][58] Blue and red bullets stand for α-Si 3 N 4 and β-Si 3 N 4 , respectively ...
Al‐Si3N4 couples were heat‐treated at 850‐1150°C for 250 hours. The thickness of the interacted area was measured by scanning electron microscopy (SEM) and scanning/transmission electron microscopy (TEM/STEM). The interaction rate increases exponentially with inverse temperature, with an activation energy of 194.23 kJ/mol and diffusion pre‐coefficient of 5 × 10⁻⁹ m²/s, indicating that the interaction is diffusion‐dependent. As the results showed, the interfacial area is comprised of Al alloy channels, Si precipitates, and AlN grains. Al‐Si transfer through the solid solution (Si3‐xAlxN4‐y) at the interface of Al alloy and β‐Si3N4 grains controls the kinetic of the interaction. When concentration of Al in solid solution exceeds a certain amount, it undergoes a topotactic phase transformation to form Al1‐xSixN1+y (viz., AlN). Next, the Al1‐xSixN1+y grains detach from the β‐Si3N4 grains and subsequently new Al‐Si3N4 interfaces are established. These interfaces repeat the interaction process, continuing until all the reactant is depleted. Thus, the interaction kinetics consist of a sequence of associated parabolic stages, precluding the observation of parabolic kinetics.
... Simultaneously, various techniques have been developed to synthesize Al-doped Si 3 N 4 . These techniques include nitridation of the Si powders with additives [8], chemical vapor deposition (CVD) [12] and pyrolysis of polymer precursors [15,16]. It is well established that Si 3 N 4 has two stable polymorphs under atmospheric conditions, i.e., α-Si 3 N 4 (P31c) and β-Si 3 N 4 (P63) [17,18]. ...
... It is well established that Si 3 N 4 has two stable polymorphs under atmospheric conditions, i.e., α-Si 3 N 4 (P31c) and β-Si 3 N 4 (P63) [17,18]. As β-Si 3 N 4 is thermodynamically stable compared with α-Si 3 N 4 , most of the reported Al-doped Si 3 N 4 are β phase [19] or α and β mixed phases [15,16]. The impurity introduced by the additives is hard to eliminate, and this limits the investigations of Al-doped α-Si 3 N 4 . ...
The band structures and optical properties for Al-doped α-Si 3 N 4 have been studied combining theoretical calculations and experimental measurements. The geometry and band structures for substitutional and interstitial Al defective α-Si 3 N 4 models have been calculated based on density functional theory. The results indicate that the location and composition of the intermediate energy level in the band gap are affected by the partial atomic environment around the Al atoms and the characteristics of Al-N and Al-Si bonds. The maximum energy gap is observably decreased to 1.99 eV because of the appearance of intermediate energy levels in the band gap for interstitial Al defective α-Si 3 N 4. Moreover, the energy gaps deduced from the measured absorption and photoluminescence spectra of the as-prepared Al-doped α-Si 3 N 4 sample are in good agreement with the calculated results. The significant improvement in the optical properties by doping Al makes silicon nitride a potential visible light emitting material.
... Simultaneously, various techniques have been developed to synthesize Al-doped Si 3 N 4 . These techniques include nitridation of the Si powders with additives [8], chemical vapor deposition (CVD) [12] and pyrolysis of polymer precursors [15,16]. It is well established that Si 3 N 4 has two stable polymorphs under atmospheric conditions, i.e., α-Si 3 N 4 (P31c) and β-Si 3 N 4 (P63) [17,18]. ...
... It is well established that Si 3 N 4 has two stable polymorphs under atmospheric conditions, i.e., α-Si 3 N 4 (P31c) and β-Si 3 N 4 (P63) [17,18]. As β-Si 3 N 4 is thermodynamically stable compared with α-Si 3 N 4 , most of the reported Al-doped Si 3 N 4 are β phase [19] or α and β mixed phases [15,16]. The impurity introduced by the additives is hard to eliminate, and this limits the investigations of Al-doped α-Si 3 N 4 . ...
... The surfaces of the nanowires were sometimes coated with thin amorphous layers. This can often be observed in many synthesized Si 3 N 4 nanowires [25]. The resistance of the Si 3 N 4 nanowires to oxidation at high temperatures was evaluated by TG-DSC in air. ...
Silicon nitride nanowires were synthesized using silicon monoxide as raw materials and an alumina plate as substrate at 1500°C. The obtained nanowires were characterized by X-ray diffraction, Fourier transform infrared spectrosco‐ py, scanning electron microscopy, high-resolution trans‐ mission electron microscopy and thermogravimetric-differential scanning calorimetry. The results revealed that silicon nitride nanowires possess a diameter of about 200 nm and a length of several hundred micrometres. The preferred growth direction of the nanowires was [100]. The chemical and structural composition of the silicon nitride nanowires were also studied and were shown to have a composition of primarily α-Si 3 N 4. The temperature for fierce oxidation in air was above 1135°C. The formation mecha‐ nism of silicon nitride nanowires was assumed to be a vapour-solid (VS) process.
As a novel type of additive manufacturing, three-dimensional (3D) printing can efficiently realize the manufacturing of ceramic devices with more sophisticated structures. In this study, the method combining digital light processing (DLP) 3D printing technology and modified ceramic precursor polysiloxane (PSO) was not only used to fabricate Al2O3 ceramic devices with a gradient impedance bilayer structure, which consist of a cross-twist/flat structure with a torsion angle of 60°, but also to prepare needle-like SiC nanowire absorbents grown in situ to further endow the ceramic functional characteristics. The microstructure was regulated by different times of impregnation, light-curing, and thermal treatment of ferrocene-modified PSO, and Al2O3/SiCnw/SiOC composites with different electromagnetic absorption properties were prepared. We found that the Al2O3/SiCnw/SiOC composite (sample 1400–2) exhibited the optimal microwave absorption performance when it was immersed and light-cured twice, which was ascribed to its comprehensive satisfaction of the impedance matching and attenuation characteristics. When the thickness of sample 1400–2 was as thin as 2.5 mm, the minimum reflection coefficient (RCmin) reached −44.35 dB, indicating that more than 99.9990% of the electromagnetic waves could be absorbed. As the thickness increased to 2.8 mm, the effective absorption bandwidth (EAB) in the X-band was 3.6 GHz, which indicated that the effective coverage rate was as high as 85.7%. The results indicate that the generation of the stacking fault, dipole and interfacial polarization of the Al2O3/SiCnw/SiOC composites, and increasing conductivity contribute to the promotion of dielectric loss. Thus, the Al2O3/SiCnw/SiOC composite with bilayer gradient impedance structures is a good candidate for stealth radar wave absorption.
