SiO2 Shell Research Articles

Hydrophobic SiO2 Armor: Stabilizing Cuδ+ to Enhance CO2 Electroreduction toward C2+ Products in Strong Acidic Environments.

Electroreduction of CO2 in highly acidic environments holds promise for enhancing CO2 utilization efficiency. Due to the HER interference and structural instability, however, challenges in improving the selectivity and stability toward multicarbon (C2+) products remain. In this study, we proposed an "armor protection" strategy involving the deposition of ultrathin, hydrophobic SiO2 onto the Cu surface (Cu/SiO2) through a simple one-step hydrolysis. Our results confirmed the effective inhibition of HER by a hydrophobic SiO2 layer, leading to a high Faradaic efficiency (FE) of up to 76.9% for C2+ products at a current density of 900 mA cm-2 under a strongly acidic condition with a pH of 1. The observed high performance surpassed the reported performance for most previously studied Cu-based catalysts in acidic CO2RR systems. Furthermore, the ultrathin hydrophobic SiO2 shell was demonstrated to effectively prevent the structural reconstruction of Cu and preserve the oxidation state of Cuδ+ active sites during CO2RR. Additionally, it hindered the accumulation of K+ ions on the catalyst surface and diffusion of in situ generated OH- ions away from the electrode, thereby favoring C2+ product generation. In situ Raman analyses coupled with DFT simulations further elucidated that the SiO2 shell proficiently modulated *CO adsorption behavior on the Cu/SiO2 catalyst by reducing *CO adsorption energy, facilitating the C-C coupling. This work offers a compelling strategy for rationally designing and exploiting highly stable and active Cu-based catalysts for CO2RR in highly acidic environments.

Growth of CsPbX3 nanocrystals using sol–gel SiO2 solid powders as reactors without capping agents towards anomalous stable emission membranes

To overcome the poor stability of metal halide perovskite nanocrystals (NCs) prepared in organic solvents, a solid reaction method at high temperature was developed using sol–gel porous SiO2 as a reactor. Sol-gel SiO2 powders were used to encapsulate CsPbX3 NCs at high temperatures (600–800 °C) in air to get SiO2/CsPbX3 glass by dispersing growth cites in advance and no ligands added. After NaOH etching, a thin dense SiO2 shell was remained on the surface of CsPbX3 NCs (named as CsPbX3@SiO2).The photoluminescence (PL) quantum yield of the CsPbX3@SiO2 was 86.7 %, in which their PL peak wavelengths were adjusted from 410-707 nm by changing halogen components. The dense SiO2 shell on CsPbX3 NCs blocked the connection of CsPbX3 cores with water and oxygen in the external environment, resulting in CsPbX3@SiO2 revealed extraordinary high stability. After immersing in water for half year, the PL intensity of CsPbX3@SiO2 composites was remained unchanged and the composites still revealed bright PL after heat-treating in boiling water for 14 h. These highly stable composites were used to fabricate a white light-emitting diode, in which the color coordinates are located at (0.36, 0.33), and the color temperature reaches 5169 K which belongs to the warm white light range.

Hollow SiO2 photonic crystal - graphene quantum dots composite and its application in multi-level intelligent anti-counterfeiting through regulation synergistic effect of structural color and fluorescence

The research on composite materials with rainbow color (structural color) and ultraviolet excitation characteristics (fluorescence) is the development direction of the new generation of functional photonic engineering materials. Herein, composite materials composed of hollow SiO2 photonic crystals (PCs) with nanometer thickness and PEGDA gel containing graphene quantum dots (GQDs) were prepared to achieve fluorescence regulation effect and thus apply in multi-level intelligent anti-counterfeiting. Due to the SiO2 shell thickness of 20–41 nm, the Bragg diffraction law explained that the material underwent secondary refraction, resulting in a wide photonic band gap (PBG). On the other hand, due to the comparison of refractive index between air (n = 1) and composite material (n = 1.46), the transmittance of the composite materials were only 21 %–26 %, indicating strong refractive ability. Therefore, we constructed a PC structure with a wide photonic bandgap (PBG) to provide better wavelength selectivity and coverage range, which would significantly increase the effect of structural color on fluorescence. Based on the unique quantum dot size effect of GQDs, we also investigated the fluorescence enhancement effect with 157 nm FWHM located on PC materials. Therefore, artificial design and control of both fluorescence enhancement and fluorescence suppression had been achieved through multi-level regulation of structural color. We further utilized these properties to create multi-level anti-counterfeiting verification patterns, such as a 3 × 3 digital encoding matrix. The authenticity of the product information must be verified through stepwise identification under specified conditions. This intelligent anti-counterfeiting technology offers a novel approach to safeguard information security.

Structural design of CA/SiO2 hybrid nanofiber membranes with semi-interpenetrating structure and switching wettability

The development of a stable structure separation membrane with adaptive switching wettability has positive significance for the expansion of membrane applications, especially in complex processing scenarios. Herein, a kind of core-shell cellulose acetate/silicon dioxide (CA/SiO2) hybrid nanofiber membrane with a semi-interpenetrating structure and switching wettability surface property was prepared via electrospinning process and subsequently in-situ hydrolysis, which integrated a superamphiphilicity SiO2 shell onto the porous CA nanofibers core to form an anchor embedding structure by vacuum forcing the silica precursor into the pores of CA nanofibers. The obtained CA/SiO2 hybrid nanofiber membrane exhibited superamphiphilicity in air with adaptive switching wettability, appearing non-stick to oil underwater or to water underoil, corresponded to superoleophobicity underwater and superhydrophobicity underoil, respectively. The CA/SiO2 hybrid nanofiber membrane with the hydrolysis time of 5 h demonstrated excellent properties. It achieved permeation fluxes of 19771 and 9104 L/m2·h with a separation efficiency exceeding 99.99% for immiscible light/heavy oil/water mixtures when pre-wetted by water and oil and subjected to gravity. Moreover, the semi-interpenetrating structure of SiO2 nanoparticles to CA nanofibers ensured the structural stability of the CA/SiO2 hybrid nanofiber membranes, which endowed it with excellent reusable performance.

A highly sensitive point-of-care detection platform for Salmonella typhimurium by integrating magnetic enrichment and fluorescent CsPbBr3@SiO2.

A platform was designed based on Fe3O4 and CsPbBr3@SiO2 for integrated magnetic enrichment-fluorescence detection of Salmonella typhimurium, which significantly simplifies the detection process and enhances the working efficiency. Fe3O4 served as a magnetic enrichment unit for the capture of S. typhimurium. CsPbBr3@SiO2 was employed as a fluorescence-sensing unit for quantitative signal output, where SiO2 was introduced to strengthen the stability of CsPbBr3, improve its biomodificability, and prevent lead leakage. More importantly, the SiO2 shell shows neglectable absorption or scattering towards fluorescence, making the CsPbBr3@SiO2 exhibit a high quantum yield of 74.4%. After magnetic enrichment, the decreasing rate of the fluorescence emission intensity of the CsPbBr3@SiO2 supernatant at 527 nm under excitation light at UV 365 nm showed a strong linear correlation with S. typhimurium concentration of 1 × 102~1 × 108 CFU∙mL-1, and the limit of detection (LOD) reached 12.72 CFU∙mL-1. This platform has demonstrated outstanding stability, reproducibility, and resistance to interference, which provides an alternative for convenient and quantitative detection of S. typhimurium.

Silica-assisted Pt1/CeO2 single-atom catalyst for enhancing the catalytic combustion performance of VOCs by inducing H2O activation

Due to the competitive adsorption of water and reactants at the active sites, especially the water toxicity of platinum-based single-atom catalysts, it is of great importance to improve the low-temperature activity and the water resistance of catalysts for the catalytic combustion of benzene. In this work, it was found that constructing a SiO2 shell layer on the catalyst not only "immobilized" the Pt single atoms, but also effectively weakened the adsorption of H2O on the Pt active sites, which resulted in excellent water resistance of the Pt single-atom catalysts. The comprehensive characterization results demonstrated that the participation of water molecules in the catalytic oxidation reaction of benzene could be effectively promoted by enhancing the strong metal-support interactions (SMSI) at the core-shell interface, which would change the electronic structure of the catalyst surface. As a result, the Pt1/CeO2@SiO2-4 catalyst with a Pt-O-Si active interface exhibits good activity (T = 190 °C) as well as excellent water resistance under the wet condition (10 vol%). This project provides a promising strategy for the design of Pt-based core-shell catalysts with excellent water resistance.

MOF-derived yolk-shell CoN/Co-NC@SiO2 nanozyme with oxidase mimetic activities for colorimetric detection of glutathione

The development of nanozymes has garnered significant attention in biosensing applications owing to their exceptional catalytic properties and structural tunability. Herein, we present a yolk-shell nanozyme derived from metal-organic frameworks (MOFs) featuring CoN/Co-NC@SiO2 architecture, exhibiting remarkable oxidase mimetic activities for colorimetric glutathione (GSH) detection. The synthesis involves a facile pyrolysis process of cobalt-based MOFs encapsulated within a silica shell, resulting in a unique yolk-shell nanostructure with CoN/Co-NC active sites. Yolk-shell CoN/Co-NC@SiO2 has been studied in detail as an oxidase and catalase-like nanozyme. In consideration of structural and composition modulation, including hydrophilic SiO2 shell, the unique cavity, a high specific surface area and dispersed active sites, the CoN/Co-NC@SiO2 was proposed for colorimetric detection of glutathione with its oxidase-like activities. Based on the oxidation of 3,3′,5,5′-tetramethylbenzidine (TMB) by CoN/Co-NC@SiO2, a wide linear detection range of 0.5–60 μM as well as a lower detection limit of 0.054 μM were obtained. Our research shows that optimizing structure and composition plays an important role in the construction of multiple-enzyme activity and offers bright potential applications of MOF-derived yolk-shell nanozymes in biosensing and medical diagnostics.

Inflammatory bowel disease alters in vivo distribution of orally administrated nanoparticles: Revealing via SERS tag labeling technique

Nanoparticles (NPs) could be uptake orally and exposed to digestive tract through various sources such as particulate pollutant, nanomedicine and food additive. Inflammatory bowel disease (IBD), as a global disease, induced disruption of the intestinal mucosal barrier and thus altered in vivo distribution of NPs as a possible consequence. However, related information was relatively scarce. Herein, in vivo distribution of typical silica (SiO2) and titania (TiO2) NPs was investigated in healthy and IBD models at cell and animal levels via a surface-enhanced Raman scattering (SERS) tag labeling technique. The labeled NPs were composed of gold SERS tag core and SiO2 (or TiO2) shell, demonstrating sensitive and characteristic SERS signals ideal to trace the NPs in vivo. Cell SERS mapping revealed that protein corona from IBD intestinal fluid decreased uptake of NPs by lipopolysaccharide-induced RAW264.7 cells compared with normal intestinal fluid protein corona. SERS signal detection combined with inductively coupled plasma mass spectrometry (ICP-MS) analysis of mouse tissues (heart, liver, spleen, lung and kidney) indicated that both NPs tended to accumulate in lung specifically after oral administration for IBD mouse (6 out of 20 mice for SiO2 and 4 out of 16 mice for TiO2 were detected in lung). Comparatively, no NP signals were detected in all tissues from healthy mice. These findings suggested that there might be a greater risk associated with the oral uptake of NPs in IBD patients due to altered in vivo distribution of NPs.

Improved broadband design of SiC/MWCNT absorbing materials through synergistic regulation of heterointerface structure and triple periodic minimal surface meta-structure

SiC/multi-walled carbon nanotube (MWCNT) composites are considered to be promising materials for high-temperature electromagnetic wave (EMW) absorption due to their strong thermal stability and tunable dielectric properties. However, the EMW absorption performance of these composites is limited by poor impedance matching. This study proposes a novel multiscale structure synergistic regulation approach to enhance EMW absorption performance, which involves constructing a heterointerface structure and a triple periodic minimal surface (TPMS) meta-structure. The addition of a SiO2 shell as an impedance layer to the SiC/MWCNT core to improve the intrinsic impedance. Meanwhile, the heterointerface between the core-shell structure leads to multiple interface polarization, significantly enhancing EMW energy dissipation. Consequently, the effective absorption bandwidth (EAB) of SiO2–SiC/MWCNT composites increased from 0.88 to 4.56 GHz. Furthermore, a TPMS meta-structure, fabricated by three-dimensional (3D) printing and sol infiltration technology, is developed to further improve impedance matching with the equivalent electromagnetic effect. Simulation and experimental results demonstrate that the SiO2–SiC/MWCNT TPMS meta-structure exhibits broadband EMW absorption performance, with the EAB reaching 7.2 GHz. This improvement is attributed to the synergistic regulation of the heterointerface structure and TPMS meta-structure, which provides a good balance between the requirements of electromagnetic loss and impedance matching. Additionally, the composites exhibit excellent oxidation resistance, as their EAB remains almost unchanged after exposure to 1000 °C for 6 h. This research offers a new design paradigm for ultrabroadband design of the nonmagnetic high-temperature absorbing materials.

Rational design of silica nanoreactor encapsulated Ni for reinforcing coke-resistance in dry reforming of methane

Dry reforming of methane (DRM) provides a desired approach to produce valuable syngas in tackling greenhouse gases. Yet it faces a formidable challenge in the design and synthesis of high coke-resistant Ni-based catalysts. Herein, we report a nanoreactor strategy to construct a supported Ni catalyst (Ni@SiO2@SiO2) for reinforcing coke-resistance during DRM, by effectively encapsulating small Ni nanoparticles into dendritic fibrous silica (SiO2) nanospheres and coating SiO2 shell layers. Taking advantage of chemical characteristics of citric acid (CA), CA-chelated Ni impregnation enables the uniform immobilization of Ni species into the radial SiO2 framework, then following carbonization produces protective carbon layers on the Ni nanoparticle surface during SiO2 coating, which can be removed via oxidizing calcination. The resultant pomegranate-like nanoreactor catalyst possesses outstanding coke-resistance, without any detectable coke deposition after 200 h of DRM reaction at 700 ℃, benefiting from effectively restricting metal sintering and fully preventing formation of inert carbon species.

Surface-Enhanced Raman Scattering for Probe Detection via Gold Nanorods and AuNRs@SiO2 Composites

In this paper, a self-assembly method was used to prepare gold nanorod composites, and a seed-growth method was used to adjust the amount of AgNO3 solution, enabling the preparation of gold nanorods with different aspect ratios. AuNRs@SiO2 nanocomposite particles were then prepared by using the Stöber method to coat the gold nanorod surface with silica. Transmission electron microscopy showed that the maximum aspect ratio of the gold nanorods was 4.53, which was achieved using 2 mL of 10 mM AgNO3 solution. The Raman-scattering intensity of the gold nanorods was studied using rhodamine 6G, thiram, melamine, and piroxicam, and detection limits of 10−8 M, 10−5 M, and 10−3 M were, respectively, achieved. As a substrate, these gold nanorods showed good repeatability and reproducibility, and trace detection was successfully achieved. A transmission electron microscopy analysis shows that the SiO2 shell became thicker with increasing tetraethyl orthosilicate addition. Using AuNRs@SiO2 as the base and R6G, thiram, and piroxicam as the probes, measurable detection limits of 10−9 M, 10−6 M, and 10−5 M were achieved, and this composite also showed excellent repeatability and reproducibility.

Synthesis, characterization, and application of ZnO@SiO2-APTES core-shell composite for selective electrochemical detection of Pb2+ ions

This study focuses on improving the electrochemical performances for the detection of heavy metals such as Pb2+ by using a silica-based nanomaterial. In order to do this, ZnO nanoparticles (core) were used as a seed for the chemical deposition of a SiO2 shell. The nanomaterial was synthesized according to a core-shell configuration and the obtained particles were subsequently functionalized with (3-aminopropyl) triethoxysilane APTES to enhance their electrochemical sensing capabilities. The unique physical and chemical properties of these particles, such as their uniform porosity and their ability to detect Pb2+, were exploited. The resulting composite was characterized by scanning electron microscopy, X-ray diffraction, and infrared spectroscopy to analyze its morphology and chemical composition. An electrochemical characterization was also performed to evaluate the change in electrode properties with a ZnO@SiO2-APTES-modified glassy carbon electrode. The differential pulse voltammetry technique was used to determine the Pb2+ ion concentration. After optimization, the electrochemical sensor based on ZnO@SiO2-APTES showed significant sensitivity and exceptional performance in the detection of Pb2+ with a limit of detection of 0.1 nM. Moreover, the proposed electrochemical sensor was successfully applied in the determination of trace metal ions in real environmental samples.

A smartphone-assisted sensing hydrogels based on UCNPs@SiO2-phenol red nanoprobes for detecting the pH of aquatic products

For some aquatic products, pH has been considered a useful index to reflect the changes in materials during the loss of freshness. Based on the inner filter effect (IFE) between deprotonated phenol red (PR) and upconversion nanoparticles (UCNPs), UCNPs coated with PR-doped SiO2 shell were embedded in agarose hydrogel to develop a smartphone-assisted method for pH sensing. With the enhancement of pH response using a phase transfer agent (i.e., tetra butyl ammonium hydroxide, TBAH), the proposed senor realized the colorimetric and fluorescence detection of pH in the range of pH 6.6–8 and pH 6–8, respectively. The sensor also showed satisfied reversibility when switched between pH 6 and 8 for at least 5 cycles. Moreover, this sensor displayed great sensitivity, stability, and portability in analyzing actual fish, shrimp, and shellfish samples, providing a new sight for evaluating the freshness of aquatic products.

Fluorescent solid-state strips based on SiO2 shell-stabilized perovskite nanocrystals applying for magnetic aptasensing detection of aflatoxin B1 toxin in food

In this work, the perovskite fluorescent nanocrystals (CsPbBr3) were successfully synthesized and wrapped with SiO2 shell, utilized for the assembly of solid-state detection strip capable of conveniently and specifically detection of aflatoxin B1 (AFB1). The SiO2 coating aimed to enhance the stability of CsPbBr3 nanocrystals. The resulting CsPbBr3@SiO2 material exhibited remarkable fluorescence properties, and further self-assembled onto solid-state plate, generating AFB1-specific quenched fluorescence at a specific wavelength of 515 nm. When combined with the capture of AFB1 by magnetic nanoparticles conjugated with aptamers (MNPs-Apt), it was achieved the good separation and specific detection of AFB1 toxin in food matrices. The constructed fluorescent solid-state detection strip based on CsPbBr3@SiO2 exhibited good response to AFB1 toxin within a linear range of 0.1–100 ng mL−1 and an impressive detection limit as low as 0.053 ng mL−1. This presents a new strategy for the rapid screening and convenient detection of highly toxic AFB1.

Enhanced dielectric constant and concurrently suppressed dielectric loss of PVDF composites incorporating BaTiO3@SSCNT@SiO2 core@double-shell structured fillers

Dielectric capacitor is an important component of power systems, but its low dielectric polarization and undesirable dielectric loss have still held back the development of miniaturized microelectronic devices. Hence, we reported core@shell structured fillers with a conducting material@insulating material double-shell to improve the dielectric performance of the poly (vinylidene fluoride) (PVDF) composites. The hybrid fillers introducing ultra-short carbon nanotube (SSCNT) as an inner layer between BaTiO3 (BT) as a core and silica (SiO2) as an outer shell were synthesized. As the thickness of the insulating shell is enough thin, the BT@SSCNT@SiO2/PVDF composites exhibit an enhanced dielectric constant and a concurrently suppressed dielectric loss with the decreasing thickness. The composite incorporating the filler with the thinnest SiO2 shell has the highest dielectric constant of 12.27 and the lowest dielectric loss of 0.023 at 20 wt% filler loading where the breakdown strength is about 15 less than the maximum value of 192.5 kV/mm. Furthermore, the hybrid fillers endow the composites with impressively stable dependence on frequency in a wide range of 102∼105 Hz. The achievement can be ascribed to the conducting property of the SSCNT inner layer and the suitable thickness of the insulating outer layer. They can synergetically provide the composites with an optimized polarization effect at a broad frequency resulting from the improved electrical field. This work reveals that a proper structure of the core@conducting material@insulating material core@double-shell filler can be an approach to optimize the overall dielectric performance of the polymer-based composites with high energy storage density.

PEI-Mediated Assembly of Fe3O4 onto SiO2-Encapsulated CsPbBr3 for Highly Sensitive Fluorescent Lateral Flow Immunoassay.

The conventional lateral flow immunoassay (LFIA) method using colloidal gold nanoparticles (Au NPs) as labeling agents faces two inherent limitations, including restricted sensitivity and poor quantitative capability, which impede early viral infection detection. Herein, we designed and synthesized CsPbBr3 perovskite quantum dot-based composite nanoparticles, CsPbBr3@SiO2@Fe3O4 (CSF), which integrated fluorescence detection and magnetic enrichment properties into LFIA technology and achieved rapid, sensitive, and convenient quantitative detection of the SARS-CoV-2 virus N protein. In this study, CsPbBr3 served as a high-quantum-yield fluorescent signaling probe, while SiO2 significantly enhanced the stability and biomodifiability of CsPbBr3. Importantly, the SiO2 shell shows relatively low absorption or scattering toward fluorescence, maintaining a quantum yield of up to 74.4% in CsPbBr3@SiO2. Assembly of Fe3O4 nanoparticles mediated by PEI further enhanced the method's sensitivity and reduced matrix interference through magnetic enrichment. Consequently, the method achieved a fluorescent detection range of 1 × 102 to 5 × 106 pg·mL-1 after magnetic enrichment, with a limit of detection (LOD) of 58.8 pg·mL-1, representing a 13.3-fold improvement compared to nonenriched samples (7.58 × 102 pg·mL-1) and a 2-orders-of-magnitude improvement over commercial colloidal gold kits. Furthermore, the method exhibited 80% positive and 100% negative detection rates in clinical samples. This approach holds promise for on-site diagnosis, home-based quantitative tests, and disease procession evaluation.

Stability of core–shell structure CsPbX3@SiO2 (X = Cl,Br) perovskite quantum dots

In this paper, CsPbX3@SiO2 (X = Cl, Br) with cubic morphology and stable optical properties have been developed. The average thickness of the SiO2 shell is 2 ∼ 6 nm, which has the effect of protecting CsPbX3 and isolating the external environment, passivating the surface and reducing the defect density, thus greatly improving the stability of CsPbX3 PQDs. Based on this, the advantages of APTES as a preparation system CsPbX3@SiO2 is revealed, the mechanism diagram is drawn and the stability improvement mechanism CsPbX3@SiO2 is analyzed in detail, which provides a new idea for the stability improvement of CsPbX3 perovskite quantum dots.

Fabrication and Application of Ag@SiO2/Au Core-Shell SERS Composite in Detecting Cu2+ in Water Environment.

A sensitive and simple method for detecting Cu2+ in the water source was proposed by using surface-enhanced Raman scattering spectroscopy (SERS) based on the Ag@SiO2/Au core-shell composite. The Ag@SiO2 SERS tag was synthesized by a simple approach, in which Ag nanoparticles were first embedded with Raman reporter PATP and next coated with a SiO2 shell. The Ag@SiO2 nanoparticles had strong stability even in a high-concentration salty solution, and there were no changes to their properties and appearance within one month. The Ag@SiO2/Au composite was fabricated through a controllable self-assemble process. L-cysteine was decorated on the surface of a functionalized Ag@SiO2/Au composite, as the amino and carboxyl groups of it can form coordinate covalent bond with Cu2+, which shows that the Ag@SiO2/Au composite labelled with L-cysteine has excellent performance for the detection of Cu2+ in aqueous media. In this study, the SERS detection of Cu2+ was carried out using Ag@SiO2 nanoparticles, and the limit of detection (LOD) as low as 0.1 mg/L was achieved.

Optimization of plasmonic nanofluid filters for spectral splitting photovoltaic/thermal systems

There remains a scarcity of studies on the utilization and optimization of core–shell plasmonic nanofluid filter although it shows potential in solar energy exploitation. To fill this research gap, this paper introduces an optimization methodology founded on merit function (MF) to optimize the Au@SiO2-based nanofluid filters for enhancing the photovoltaic/photothermal (PV/T) system performance. Initially, the MF model of the nanofluid filtered-PV/T system was constructed based on a reliable optical model and validated by referenced experimental results. Using these models, the effect of nanofluid parameters on the system performance and the mechanism of optimization procedure were investigated. Results indicated that modifying SiO2 shell thickness is a cost-effective means of tailoring the transmittance of the nanofluids compared to adjusting the Au core diameter. The optimization mechanism can be summarized as enhancing electrical efficiency or improving thermal efficiency to offset electricity losses. Furthermore, the MF of the Au@SiO2/EG nanofluid increased from 1.3737 to 1.3844 with optical thickness decreasing from 44 mm to 40 mm by mixing with Ag@SiO2 nanoparticles, indicating the cost-effectivity of blended nanofluid. The MF of the optimized blended nanofluids are 0.007–0.084 higher than those of the referenced nanofluids. This work offers a feasible pathway toward achieving high-performance nanofluid optical filters.

Enhanced surface passivation of GaAs nanostructures via an optimized SiO2 sol-gel shell growth

Gallium arsenide (GaAs) is an important compound semiconductor for optoelectronic devices. However, the fast nonradiative recombination velocity of GaAs requires surface passivation for the nano-optoelectronic and nanophotonic applications. Despite strides have been made in GaAs surface passivation, chemical treatments like sulfidation and nitridation suffer from reproducibility and stability issues, thus requiring protective layer encapsulation. Traditional vacuum based film passivation exposes samples to high temperature plasma, causing surface damage, and is expensive. Here, we demonstrate an effective passivation method via sol-gel growth of SiO2 shell on both dry etched GaAs nanopillar and bottom-up grown GaAs nanowires at room temperature with uniform coating and controlled thickness from sub-10 nm to around 100 nm, showing advantages in low cost as well as suitability for different types of nano morphology. X-ray photoelectron spectroscopy analysis confirms that the SiO2 sol-gel method with the addition of (NH4)2S can significantly remove the native oxides on the surface. Under the optimized SiO2 coating procedure, the emission intensity of dry etched GaAs nanopillar with a diameter of 0.5 μm is enhanced about 29.6 times and the decay lifetime of the minority carriers with a diameter of 1.8 μm increased from 43.6 to 477.5 ps. Thus, the easy fabrication, broad suitability, as well as effective passivation effect turn sol-gel growth of SiO2 into a cost-effective surface passivation approach for III–V nanostructures.