Silicon nanocrystals (Si‐NCs) are emerging as an attractive class of quantum dots owing to the natural abundance of silicon in the Earth's crust, their low toxicity compared to many Group II–VI and ...III–V based quantum dots, compatibility with the existing semiconductor industry infrastructure, and their unique optoelectronic properties. Despite these favorable qualities, Si‐NCs have not received the same attention as Group II–VI and III–V quantum dots, because of their lower emission quantum yields, difficulties associated with synthesizing monodisperse particles, and oxidative instability. Recent advancements indicate the surface chemistry of Si‐NCs plays a key role in determining many of their properties. This Review summarizes new reports related to engineering Si‐NC surfaces, synthesis of Si‐NC/polymer hybrids, and their applications in sensing, diodes, catalysis, and batteries.
The grand old newcomer: Silicon may be the “grand old semiconductor”, however, it is a relative newcomer to the field of quantum dots. Silicon nanocrystals (Si‐NCs) are emerging as a promising, non‐toxic, and greener alternative to Group II–VI and III–V quantum dots. This Review highlights how surface chemistry can be used to engineer properties of Si‐NCs and adapt them towards modern applications, such as sensors, photovoltaics, and light‐emitting diodes.
The syntheses of colloidal silicon nanocrystals (Si-NCs) with dimensions in the 3–4 nm size regime as well as effective methodologies for their functionalization with alkyl, amine, phosphine, and ...acetal functional groups are reported. Through rational variation in the surface moieties we demonstrate that the photoluminescence of Si-NCs can be effectively tuned across the entire visible spectral region without changing particle size. The surface-state dependent emission exhibited short-lived excited-states and higher relative photoluminescence quantum yields compared to Si-NCs of equivalent size exhibiting emission originating from the band gap transition. The Si-NCs were exhaustively characterized using transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and Fourier transformed infrared spectroscopy (FTIR), and their optical properties were thoroughly investigated using fluorescence spectroscopy, excited-state lifetime measurements, photobleaching experiments, and solvatochromism studies.
Metal nitride nanostructures have been predicted to exhibit plasmonic responses in the UV to IR region, which can enable their potential use as low-cost, chemically, and thermally stable materials in ...several applications. In the case of photothermal applications, nitrides have been shown, both numerically and experimentally, to perform better than the noble metals. Additionally superior thermal stability of the metal nitride materials offers compatibility with high temperature device fabrication techniques. The plasmon frequency for transition metal nitride materials can be tuned from the UV to IR region by varying the type of metal in the nitride and metal/nitrogen ratio. Recently, studies have focused on developing and applying free-standing metal nitride nanostructures. Most investigations have focused on TiN, but as of late focus has been shifting to investigate other nanostructured nitrides such as ZrN and HfN. This Perspective will highlight recent key findings on the synthesis of plasmonic metal nitrides; associated thermal stability and photothermal properties; and application in photothermal therapy, solar-driven water evaporation, and chemical reactions. An outlook on current knowledge gaps and challenges and future directions to further this field is also presented.
In this study, the influence of metals (Mg, Al, and Ca) and reaction conditions (time, temperature, and metal grain size) on the metallothermic reduction of Stöber silica nanoparticles (NPs) to form ...porous Si has been explored. Mg metal was found to be an effective reducing agent even at temperatures below its melting point; however, it also induced a high degree of structural damage and morphology change. Al was effective in reducing silica NPs only at its melting point or above, but the resulting particles retained a higher degree of structural morphology as compared to those reduced using Mg. Ca was found to be ineffective in reducing silica. A new reductant, a mixture of 70 % Mg and 30 % Al, was found to induce the least amount of morphology change, and the reactions proceeded at a temperature (450 °C) lower than those required with Mg or Al individually. Furthermore, porous Si NPs obtained using Mg, Al, and the mixture of 70 % Mg and 30 % Al as reductants have been investigated as carriers for ibuprofen loading and release. Porous Si obtained from reductions with Mg and the Mg/Al mixture showed higher drug loading and a sustained drug release profile, whereas porous Si obtained from Al reduction had lower loading and showed a conventional release profile over 24 h.
Coming through: Silica nanoparticles have been reduced to silicon with different metals and combinations thereof (see graphic). The products thus obtained have been tested as nanocarriers for ibuprofen uptake and delivery.
We report a detailed theoretical and numerical investigation of the sensing mechanism and performance of plasmonic fiber-optic sensors using group IV transition metal nitrides. We first compared the ...plasmonic properties of hafnium nitride (HfN), zirconium nitride (ZrN), and titanium nitride (TiN) to gold (Au) as a conventional plasmonic material and designed two different plasmonic fiber-optic sensing platforms using side-polished single mode fibers and few mode fibers (FMFs). Using the finite element method, we demonstrated that the sensing mechanisms in the proposed sensors are based on the interplay between fiber and plasmonic modes and variation of resonance wavelength depending on analyte refractive index. We show that HfN and ZrN can considerably outperform Au in the visible region as alternative cost-effective plasmonic materials for the design of fiber-optic sensors with more than three times larger sensitivity and a sensing figure of merit of almost eight times that of Au. In particular, HfN-coated FMF sensors can demonstrate an average linear sensitivity of 6140 nm/RIU, a maximum sensitivity of 8200 nm/RIU, and an average (maximum) figure of merit of 133 (201) for analyte refractive indices between 1.33 and 1.38. We show that the figure of merit of the proposed simple side polished HfN coated FMF is more than four times larger than that of the previously reported similar fiber-optic sensors. The results show the potential of group IV transition metal nitrides, particularly HfN and ZrN, to replace Au in various fiber-optic applications including monitoring marine environments, medical diagnosis, and biosensing.
Graphic Abstract
Ceramic nanoparticles that exhibit a plasmonic response are promising next‐generation photonic materials. In this contribution, a solid‐state metathesis method has been reported for the synthesis of ...Group 4 nitride (TiN, ZrN, and HfN) nanocrystals. A high‐temperature (1000 °C) reaction between Group 4 metal oxide (TiO2, ZrO2, and HfO2) nanoparticles and magnesium nitride powder yielded nitride nanocrystals that were dispersible in water. A localized surface plasmonic resonance was observed in the near‐infrared region for TiN and in the visible region of light for ZrN and HfN nanocrystals. The frequency of the plasmon resonance was dependent on the refractive index of the solvent and the nanocrystal size.
Ready to plassemble: The synthesis of TiN, ZrN, and HfN nanocrystals using solid‐state metathesis is reported. The nanocrystals, which are dispersible in water, show localized surface plasmonic resonances in the near infrared (TiN) and visible region (ZrN, HfN) of light. This makes them ideal for applications like photothermal therapy or plasmon‐enhanced sensing.
Nitrogen reduction to ammonia under ambient conditions is an emerging area of research sparked by the increasing concerns over climate change which is driving the efforts to find alternatives to ...energy‐intensive Haber–Bosch process. Ammonia is a critical component in the manufacturing of fertilizers and is required to support the global food supply. It can also be used as a fuel source to generate electricity. Many strategies have been used to drive nitrogen reduction under milder conditions including incorporation of plasmonic nanomaterials. The ability of plasmonic nanomaterials to strongly interact with light, resulting in near‐field enhancement, hot charge‐carrier generation and injection, increase in local temperature, has made them attractive candidates for catalysis. This review provides a comprehensive survey of recent developments in photocatalytic, plasmon‐enhanced nitrogen conversion to ammonia and the proposed mechanisms for the increased catalytic activity. A brief outlook on the current challenges and future directions is also provided.
Plasmonic nanomaterials are attractive candidates for catalysis as they strongly interact with light, resulting in near‐field enhancement, hot charge‐carrier generation and injection, and increase in local temperature. This review provides a comprehensive survey of plasmonic nanomaterials used in a photocatalytic conversion of nitrogen to ammonia and the proposed mechanisms for the enhanced activity.
The origin of photoluminescence (PL) in silicon nanocrystals (SiNCs) remains a subject of considerable debate. Size-dependent PL that supports the quantum confinement model has been proposed by ...several researchers. On the other hand, SiNC PL arising from surface states that are independent of nanocrystal size has also been shown. This work addresses the origin of surface-functionalized SiNC PL as relating to surface states and the NC size. SiNCs of different sizes (3 and 5 nm diameters) were prepared with three distinct surface chemistries. Steady-state and time-resolved PL measurements were performed at temperatures ranging from 37 to 377 K. Temperature-dependent luminescence consistent with core emission was observed for alkyl-terminated SiNCs, while alkylamine-functionalized SiNCs displayed minimal temperature-dependent luminescence, consistent with a charge-transfer mechanism. Lightly oxidized alkyl SiNCs had similar emission profiles to alkyl SiNCs; however, they showed longer luminescence lifetimes and their luminescence spectrum was shifted to shorter wavelengths than their nonoxidized counterparts. A general mechanism is proposed to explain all three phenomena, suggesting that surface groups play a crucial role in SiNC optical response.
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