Preparation and Photocurrent Generation of Silicon Nanosheets with Aromatic Substituents on the Surface

Ohshita, Joji; Yamamoto, Kazuki; Tanaka, Daiki; Nakashima, Makoto; Kunugi, Yoshihito; Ohashi, Masataka; Nakano, Hideyuki

doi:10.1021/acs.jpcc.6b03014

Cited by 30 publications

(23 citation statements)

References 27 publications

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“…Two-dimensional (2D) materials have recently gained interest for their potential in applications such as photodetectors, − energy storage, − photovoltaics, and as quantum materials. − Among the 2D materials, atomically thin hydrogen-terminated silicon nanosheetsoften referred to as “silicane”have garnered attention due to their optical properties, showing potential for direct bandgap-like behavior in a form of silicon, which has been a long-standing goal in the fields of materials science and computing. Atomically thin silicon (111) nanosheets (SiNSs) are interesting in their own right as an optoelectronic material, but the applicability of any gained knowledge of SiNSs provides additional value to the scientific community, as it also provides a deeper level of understanding for all silicon-based systems.…”

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confidence: 99%

Anisotropic Disorder and Thermal Stability of Silicane

2021

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Atomically thin silicon nanosheets (SiNSs), such as silicane, have potential for next-generation computing paradigms, such as integrated photonics, owing to their efficient photoluminescence emission and complementary-metal-oxidesemiconductor (CMOS) compatibility. To be considered as a viable material for next-generation photonics, the SiNSs must retain their structural and optical properties at operating temperatures. However, the intersheet disorder of SiNSs and their nanoscale structure makes structural characterization difficult. Here, we use synchrotron X-ray diffraction and atomic pair distribution function (PDF) analysis to characterize the anisotropic disorder within SiNSs, demonstrating they exhibit disorder within the intersheet spacing, but have little translational or rotational disorder among adjacent SiNSs. Furthermore, we identify changes in their structural, chemical, and optical properties after being heated in an inert atmosphere up to 475 °C. We characterized changes of the annealed SiNSs using synchrotron-based total X-ray scattering, infrared spectroscopy, X-ray photoelectron spectroscopy, scanning electron microscopy, electron paramagnetic resonance, absorbance, photoluminescence, and excited-state lifetime. We find that the silicon framework is robust, with an onset of amorphization at ∼300 °C, which is well above the required operating temperatures of photonic devices. Above ∼300 °C, we demonstrate that the SiNSs begin to coalesce while keeping their translational alignment to yield amorphous silicon nanosheets. In addition, our DFT results provide information on the structure, energetics, band structures, and vibrational properties of 11 distinct oxygen-containing SiNSs. Overall, these results provide critical information for the implementation of atomically thin silicon nanosheets in next-generation CMOScompatible integrated photonic devices.

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Anisotropic Disorder and Thermal Stability of Silicane

2021

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“…Silicon (Si) has been playing a dominant role in the modern electric industry owing to its unique band alignment, high carrier mobility, high natural abundance, and environmentally benign nature. ,, Apart from its great prospects in lithium-ion batteries and photovoltaic devices, 2D silicon with a narrow bandgap, a large surface area, a short electron migration path, and a high density of exposed active sites is also desirable as an attractive photocatalyst for photocatalytic hydrogen production. − Nevertheless, the current preparation techniques toward silicon nanosheets based on CVD deposition, magnesium-thermal reduction, or exfoliation from complex silicon-based compounds are relatively expensive and complicated, limiting their scale-up production and application. − Recently, researchers have proved the feasibility of direct exfoliation of nonlayered materials. , Thus, it is fairly charming to consider exfoliating ultrathin silicon nanosheets from the bulk Si crystal, which have already been obtained through mature industrial methods. In addition, uncovering the mechanism of exfoliation of nonlayered structural materials that compose the majority of the large crystal family is both fascinating and critical.…”

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Directly Exfoliated Ultrathin Silicon Nanosheets for Enhanced Photocatalytic Hydrogen Production

Wang

Cai

Zhang

et al. 2020

J. Phys. Chem. Lett.

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Here we present direct exfoliation of ultrathin silicon nanosheets from commercial silicon powders through an improved liquid phase exfoliation procedure. The feasibility of exfoliation was ascribed to the intrinsic anisotropic lattice structure, which allowed the oriented propagations of cryo-mediation-induced quenching cracks with the assistance of sonication. It was also revealed that the solid–solvent interface played a critical role in determining the morphology of exfoliated pieces as well as the exfoliation efficiency. Moreover, due to its superior morphology, enlarged surface area, and improved photon absorption, the resulting ultrathin silicon nanosheets presented enhanced and visible light responsive photocatalytic hydrogen generation performance, even without applying any co-catalyst.

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“…For instance, (SiH) n modification via nucleophilic substitution with phenylmagnesium bromide, hydrosilylation with olefins, dehydrogenation coupled with primary amines, and alcohols was reported. We recently reported OMSs containing arylmethylamine derivatives; interestingly, their optical properties were significantly influenced by the aromatic units . The silicanes were kinetically stabilized against hydrolysis by atmospheric moisture and air oxidation by the organic substituents.…”

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Silicanes Modified by Conjugated Substituents for Optoelectronic Devices

Nakano

Tanaka

Yamamoto

et al. 2019

Advanced Optical Materials

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forming a σ-conjugated network (e.g., hydrogen-terminated silicane shown in Figure 1b), [12] unlike the conventional diamond structured silicon. On the other hand, many experimental scientists have attempted to synthesize these predicted 2D silicon materials, and various prototype applications have been demonstrated, including optoelectronic devices, catalysts, and energy storage devices. [13] Regarding carrier mobilities, silicene features a linear Fermi-Dirac dispersion from the half-filled p z orbitals, and the energy dispersion is similar to group IV graphene analogs (graphene, germanene, and stanene). Consequently, these carriers behave as if they have no effective mass, and in graphene, this can lead to high field effect mobility. We recently reported the Fermi velocity of electrons at the Dirac point of calcium intercalated silicene (CaSi 2 ) as 1 × 10 5 m s −1 , although it is one order smaller than that of graphene and graphite (1-2 × 10 6 m s −1 ). [14] Considering these features, silicene is predicted to exhibit extremely high electron mobility and appropriate band-gap energy [15] ; however, its surface is extremely reactive under ambient conditions. Thus, silicene has only been observed experimentally under high vacuum conditions. [1] Recently, Tao et al. fabricated a silicene transistor, although the device performance was moderate. [16] Meanwhile, some organo-modified silicanes (OMSs) were derived from layered polysilane (SiH) n . For instance, (SiH) n modification via nucleophilic substitution with phenylmagnesium bromide, [17] hydrosilylation with olefins, [18,19] dehydrogenation coupled with primary amines, [20,21] and alcohols [22] was reported. We recently reported OMSs containing arylmethylamine derivatives; interestingly, their optical properties were significantly influenced by the aromatic units. [23] The silicanes were kinetically stabilized against hydrolysis by atmospheric moisture and air oxidation by the organic substituents. Specifically, the OMSs were more stable than silicene under ambient conditions. Organic substituents also improve the solubility and dispersibility in organic solvents. Moreover, amine, hexyl, and phenyl modified OMSs were calculated to have direct band gaps of 1.7, 1.66, and 1.92 eV, respectively. [24,25] Based on these properties (e.g., optical properties, stability, solubility, and band gaps), as new materials, OMSs overcome issues Silicanes are predicted to be a candidate for next-generation (opto-)electronics nanomaterials. However, their low carrier or hole densities hinder their practical use in electronic materials. If conjugated substituents (e.g., electron donators or electron acceptors) could be attached to the surfaces of silicanes, these would be effective channel materials for phototransistors and exhibit the corresponding characteristic optoelectronic properties. Herein, the synthesis of silicanes modified by conjugated substituents is reported, and the performances of organo-modified silicanes/graphene hybrid phototransistors are also evaluated. Th...

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Preparation and Photocurrent Generation of Silicon Nanosheets with Aromatic Substituents on the Surface

Cited by 30 publications

References 27 publications

Anisotropic Disorder and Thermal Stability of Silicane

Anisotropic Disorder and Thermal Stability of Silicane

Directly Exfoliated Ultrathin Silicon Nanosheets for Enhanced Photocatalytic Hydrogen Production

Silicanes Modified by Conjugated Substituents for Optoelectronic Devices

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