Silicon Oxide Shell Research Articles

Synthesis of silver nanoparticles with polyols under reflux and microwave irradiation conditions

Four polyols were used as stabilisers to synthesise silver nanospheres under reflux and microwave irradiation conditions. The nanoparticles were covered with a protective up to 10 nm silicon dioxide shell. The shell-isolated nanoparticle-enhanced Raman spectroscopy (SHINERS) technique was used to analyse the self-assembled monolayer of 4-mercaptobenzoic acid (4-MBA) by applying the produced silver core-silica shell nanoparticles. The article provides a detailed description of the synthesis, analysis and application of the nanoparticles based on UV/Vis, HR-TEM and SHINERS data.

Express test for NT-proBNP competitive detection based on lateral flow immunoassay using silanized fluorescent quantum dots

This paper describes the step-by-step development and the application of a lateral flow immunoassay (LFIA) for the detection of the N-terminal pro-brain natriuretic peptide (NT-proBNP). NT-proBNP is widely used as a biomarker for diagnosing heart failure and other cardiac dysfunctions, distinguishing patients with heart failure from patients without heart failure, and for risk assessment. CdSe/CdS fluorescent quantum dots (QDs) were synthesized as immunoassay labels, carefully coated with a silicon dioxide shell with a high fluorescence quantum yield of 51% for silanized QDs, and finally functionalized with carboxy- or epoxy groups. The conjugation pathways of the resulting silanized QDs with antibodies specific to amino acid residues 61-76 in NT-proBNP were optimized. The LFIA uses the principle of competitive detection with the test line containing proBNP precursor molecule as the cover antigen and the control line containing rabbit anti-mouse immunoglobulins. All components of the LFIA strip, including membrane type, blocking buffer composition, and QD-antibody conjugate composition, were optimized to reduce nonspecific interaction. The LFIA test was applied to determine NT-proBNP in human plasma. The optimal dilution of plasma for application of the test was found to be 10-fold. Under optimized conditions, the LFIA cut-off level was set as 0.5 ng/mL NT-proBNP in human plasma. The LFIA design ensures that the test line fluorescence disappears at the cut-off concentration.

Heat-Mediated Transformation of PMMA-SiO2 Core-Shell Particles into Hollow SiO2 Particles

Changes in the morphology and structure of the core-shell particles of polymethyl methacrylate-silicon dioxide and hollow SiO2 particles during their heat treatment were studied by electron microscopy, infrared spectroscopy, and X-ray diffraction. The polymeric core of the PMMA-SiO2 hybrid particle was found to undergo an unusual transformation when exposed to the electron microscope beam: its shrinkage occurs through the formation of a spherical cavity. It was shown that the process of silica-shell formation occurs in the temperature range of 200–600 °C and is accompanied by the loss of vinyl- and OH-groups. It was determined by the method of X-ray diffraction, that in the place of the interaction of PMMA and the shell, the degree of ordering of the polymer is higher than that in the volume of the polymer core. It was shown that the frequency of the TO3-vibrational mode (asymmetric stretching vibrations of the Si–O–Si bonds) increases with an increase in the annealing temperature, which is associated with the densification of the silicon dioxide shell.

Origin of photo-enhanced hysteretic electrical conductance in nanostructured silicon-based heterojunction

Photo-enhanced hysteretic I–V curves have been observed under reverse bias in a p-i-n structure containing electrochemically etched nanostructured silicon (Si) sandwiched between p-Si and n-type a-Si:H layers. These curves have been found to depend on intensity of incident illumination and structural morphology of the nanostructured Si layer. The conductance in trace path is lower than that in retrace path. Charge transport mechanism in this structure has been interpreted using microscopic description of charge trapping and detrapping in the defect states present at the interface of nanocrystalline silicon core and oxide shell in the active layer. An applied voltage dependent probability distribution of trapping and detrapping has been calculated in light of classical random walk problem. The trapping/detrapping of charges leading to development/destruction of potential barriers in the path of charge flow shows an analogy with the river bed deposition/erosion. The rate of trapping has been considered to depend on the empty defect states whereas the rate of detrapping depends on the already filled defects. Moreover, the rate of both trapping and detrapping is expected to depend on the charge flow rate. All these considerations lead the I–V relations for trace and retrace paths in reverse bias fitting nicely with experimental I–V loops. The observed peaks in the voltage dependent dynamic conductance in trace and retrace paths have been explained as a consequence of development and destruction of two barriers in the active layer for electrons and holes separately. Best fit values of the fitting parameters indicates that the trace path is dominated by holes whereas the retrace path is dominated by electronic transport. The difference in mobility of electron and hole leads to different trapping and detrapping rates in the two paths resulting in the observed hysteresis.

The effect of core-shell BaTiO3@SiO2 on the mechanical and dielectric properties of PVDF composites

ABSTRACT In this study, polymer composite films were prepared by the solution casting method using ceramic filler barium titanate (BT) to enhance the mechanical and dielectric properties of polyvinylidene fluoride (PVDF). A silicon dioxide (SiO2) shell was coated on BT surface by hydrolysis reaction of tetraethyl orthosilicate (TEOS) at different concentrations in order to provide a strong interface between PVDF and BT. The influence of SiO2 coating on morphology, structure, thermal, tensile and dielectric properties of composites were investigated compared to neat PVDF. The results of analyses show that SiO2 is successfully coated on BT and that the ceramic filler enhances the tensile and dielectric properties of the composites. At low BT concentrations (5 and 10 vol.%) the tensile strength and Young modulus are improved compared to neat PVDF. For films having a high content of SiO2, in particular, coated BT high values, such as 24.8 at 102 Hz are found for the dielectric constant, which is greatly improved by almost 2.3 times compared to neat PVDF. Properties, such as flexibility and thermal stability, are well retained in the prepared composites.

Innovative non-thermal plasma coating for “core–shell” CaCu3Ti4O12 material

Colossal permittivity of CaCu3Ti4O12 (CCTO) makes it a very interesting candidate for capacitor applications. To improve its properties, an innovative physical method based on a pulsed non-thermal micro-plasma treatment was set up to realize the coating of CCTO's grains (core) with silicon oxide (shell). This method is adapted to control the thickness and homogeneity of the shell, which will allow a better control of grain–grain boundary interfaces and improve the properties of this material. Best result is obtained for the set of gas mixture: Ar/O2/hexamethyldisiloxane (HMDSO) = 2028 N cm3 min−1/7.84 N cm3 min−1/523 mg h−1, respectively, in plasma with a shell thickness of 50 nm. This study offers a new opportunity to quickly synthetize core–shell materials with a dry technique and without almost no secondary product resulting from the chemical reaction because it is in the gaseous state. A complete analysis of the plasma by optical emission spectroscopy in the UV-visible range shows that HMDSO molecules are totally dissociated in atomic (Si, C, and O) or simple radical species (C2 and CH) in the plasma phase. In addition, several thermometer species (OH°, CH, CN, N2, and N2+) are used to estimate excitation temperatures of the plasma (Trot, Tvib, and Te = 300 K, 2400–3700 K, and 5.3 eV, respectively) that clearly shows the non-equilibrium character and the efficiency of this plasma.

The ROS-generating photosensitizer-free NaYF4:Yb,Tm@SiO2 upconverting nanoparticles for photodynamic therapy application

In this work we adapt rare-earth-ion-doped NaYF4 nanoparticles coated with a silicon oxide shell (NaYF4:20%Yb,0.2%Tm@SiO2) for biological and medical applications (for example, imaging of cancer cells and therapy at the nano level). The wide upconversion emission range under 980 nm excitation allows one to use the nanoparticles for cancer cell (4T1) photodynamic therapy (PDT) without a photosensitizer. The reactive oxygen species (ROS) are generated by Tm/Yb ion upconversion emission (blue and UV light). The in vitro PDT was tested on 4T1 cells incubated with NaYF4:20%Yb,0.2%Tm@SiO2 nanoparticles and irradiated with NIR light. After 24 h, cell viability decreased to below 10%, demonstrating very good treatment efficiency. High modification susceptibility of the SiO2 shell allows for attachment of biological molecules (specific antibodies). In this work we attached the anti-human IgG antibody to silane-PEG-NHS-modified NaYF4:20%Yb,0.2%Tm@SiO2 nanoparticles and a specifically marked membrane model by bio-conjugation. Thus, it was possible to perform a selective search (a high-quality optical method with a very low-level organic background) and eventually damage the targeted cancer cells. The study focuses on therapeutic properties of NaYF4:20%Yb,0.2%Tm@SiO2 nanoparticles and demonstrates, upon biological functionalization, their potential for targeted therapy.

Producing oxide free silicon nanocrystals – A novel & benign approach

A novel method of producing silicon nanocrystals (Si-NCs) having an indispensable oxide free surface is described. Construction of a cost-effective, robust & safe chemical laboratory setup is presented for the wet chemical etching of silicon oxide shell from Si-NCs using hydrofluoric acid (HF) solution followed by separation over a membrane filter by means of pressure filtration. Quantity of Si-NCs can range from milligrams to kilograms for processing at commercial scale.

PH-controlled synthesis of sustainable lauric acid/SiO2 phase change material for scalable thermal energy storage

Lauric acid (LA) has been recommended as economic, eco-friendly, and commercially viable materials to be used as phase change materials (PCMs). Nevertheless, there is lack of optimized parameters to produce microencapsulated PCMs with good performance. In this study, different amounts of LA have been chosen as core materials while tetraethyl orthosilicate (TEOS) as the precursor solution to form silicon dioxide (SiO2) shell. The pH of precursor solution was kept at 2.5 for all composition of microencapsulated LA. The synthesized microencapsulated LA/SiO2 has been characterized by Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), X-Ray photoelectron spectroscopy (XPS), Scanning electron microscopy (SEM), and Transmission electron microscopy (TEM). The SEM and TEM confirm the microencapsulation of LA with SiO2. Thermogravimetric analysis (TGA) revealed better thermal stability of microencapsulated LA/SiO2 compared to pure LA. PCM with 50% LA i.e. LAPC-6 exhibited the highest encapsulation efficiency (96.50%) and encapsulation ratio (96.15%) through Differential scanning calorimetry (DSC) as well as good thermal reliability even after 30th cycle of heating and cooling process.

SHINERS in cultural heritage: Can SHINERS spectra always be compared with normal Raman spectra? A study of alizarin and its adsorption in the silicon dioxide shell

AbstractRaman microspectroscopy is a powerful analytical technique in cultural heritage. However, results are often compromised by luminescence interference and poor sensitivity. Surface‐enhanced Raman spectroscopy (SERS) is an alternative that can enhance the Raman signal and quench luminescence, but the interaction of an analyte and metal substrate produces altered Raman spectra. Shell‐isolated nanoparticle‐enhanced Raman spectroscopy (SHINERS) is a promising modification of SERS that encases the metal nanoparticles in ultrathin inert shells. As a consequence, it is reported that SHINERS spectra can be directly compared with normal Raman spectra, but this is not always the case, as discussed in this work. SHINERS, SERS, and normal Raman spectra were obtained from alizarin. The resulting spectra showed that the SHINERS data are comparable with the normal Raman spectrum of alizarin adsorbed in silica, not that of isolated alizarin. The structure of alizarin adsorbed in silica is discussed. Luminescence quenching observed in the SHINERS spectra can be attributed both to LSPR of the metallic nanoparticle cores and to alizarin–silica shell chemisorption. Both silica‐encapsulated silver and gold nanoparticles were considered, and it is shown that SHINERS spectra are dependent on the interaction of alizarin with silica, rather than the specific metal core within, in contrast to our observations of Ag and Au SERS nanoparticles. The metal agnostic quality of SHINERS is a potential advantage for the collection and comparison of reference data. Additionally, SHINERS systems result in quite stable spectra in pHs ranging from, at least, 6.0 to 9.3. Future research directions for SHINERS in cultural heritage are also discussed.

Highly Selective Photocatalytic CO2 Reduction to CH4 by Ball-Milled Cubic Silicon Carbide Nanoparticles under Visible-Light Irradiation.

The ultimate goal of photocatalytic CO2 reduction is to achieve high selectivity for a single product with high efficiency. One of the most significant challenges is that expensive catalysts prepared through complex processes are usually used. Herein, gram-scale cubic silicon carbide (3C-SiC) nanoparticles are prepared through a top-down ball-milling approach from low-priced 3C-SiC powders. This facile mechanical milling strategy ensures large-scale production of 3C-SiC nanoparticles with an amorphous silicon oxide (SiOx) shell and simultaneously induces abundant surface states. The surface states are demonstrated to trap the photogenerated carriers, thus remarkably enhancing the charge separation, while the thin SiOx shell prevents 3C-SiC from corrosion under visible light. The unique electronic structure of 3C-SiC tackles the challenge associated with low selectivity of photocatalytic CO2 reduction to C1 compounds. In conjugation with efficient water oxidation, 3C-SiC nanoparticles can reduce CO2 into CH4 with selectivity over 90%.

Влияние лазерного разрушения на нелинейно-оптические свойства core/shell наностержней Au/SiO-=SUB=-2-=/SUB=-

The mechanisms of nonlinear optical response from ensembles of gold nanorods coated with a silicon dioxide (Au / SiO2 NRs) shell are analyzed. The Z-scan method under the action of 10 ns pulses of the second harmonic of a YAG: Nd3 + laser (532 nm) was used to find dependences characteristic of nonlinear absorption and a negative dynamic lens. It is shown that the bleaching of the colloidal solution, which intensifies with increasing pulse energy, is caused by laser destruction of the Au / SiO2 NRs, which occurs due to melting, which is confirmed by theoretical estimates. Negative nonlinear refraction is attributed to the response from spherical nanoparticles (Au NPs) formed upon laser destruction of NRs.

Nonlinear optical properties of Ag nanoparticles with and without silicon dioxide shell

Abstract The features of a nonlinear optical response of the spherical silver nanoparticles with an average size of 20 nm and “core-shell” systems based on them (Ag@SiO2) synthesized using the citrate method in the field of nanosecond pulses of the second harmonic of Nd:YAG laser (532 nm) are studied. It is shown that the presence of a SiO2 shell blocks the saturable absorption that occurs due to the photodestruction of silver nanoparticles. The formation of a positive dynamic lens for the Ag@SiO2, which is not typical for the original silver nanoparticles, was detected. An assumption is made about the capture of photo-excited charge carriers by the SiO2 shell.

High-temperature nitrogen annealing induced bonding states and photoluminescence changes in inductively coupled plasma torch synthesized silicon nanostructures

In this work, we investigate the optical properties of self-standing Si nanostructures (SiNS) as-grown, by an inductively coupled plasma torch process, and after their annealing under N2 flux at 1200 °C. We show that as-grown SiNS are embedded in a silicon oxide shell while part of the annealed SiNS transforms into silicon nitrides or oxynitrides. The analysis of the photoluminescence spectra and maps of both as-grown and annealed SiNS enabled us to confirm the occurrence of quantum confinement effects in the ultra-small SiNS and to highlight the role played by the silicon oxide, silicon nitrides, and silicon oxynitrides nanophases in the photoluminescence emission.

Efficient chemiluminescent ZnO nanoparticles for cellular imaging

Abstracts Chemiluminescence (CL) induced by peroxalate fuel and hydrogen peroxide has been widely applied in chemical detection and bioimaging. Nevertheless, the chemiluminescent emitters in the CL are focused on organic small-molecular dyes, most of which encounter serious obstacles in practical application due to their potential biotoxicity and low photostability. Here, bright blue CL is observed when biocompatible zinc oxide nanoparticles (ZnO NPs) with yellow photoluminescence (PL) are added into peroxalate and hydrogen peroxide solution, which is originated from the interaction between the zinc interstitial of ZnO NPs and the energy-rich intermediate produced in the CL process. With the modification of silane coupler, the CL quantum yield of ZnO NPs presents two orders of magnitude increase from 6.2× 10−6 to record 3.7 × 10−4 E⋅mol−1 for inorganic NPs owing to the protective effect from silicon oxide shell layer. By virtual of excellent CL ability, ZnO NPs have been firstly used as CL probes in bioimaging, which opens the way to a new design freedom for biosensor or bioimaging in the future.

In-situ study of platinum reaction with oxygen contaminated silicon layer

This work reports the study of platinum silicide formation on reaction with an oxygen contaminated silicon layer. The observed results are potentially a novel approach to use silicide forming metals as a direct contact electrode to the crystalline core-amorphous silicon oxide shell structure of silicon nanowires without the need of hazardous acids, e.g. hydrofluoric acid, which is commonly used during lithography device preparation to remove the oxide shell. The simulation of the in-situ RBS spectra at temperatures above 250 °C showed the reaction of platinum with the oxygen contaminated silicon layer, forming a new layer with a stoichiometry corresponding to the silicide phase containing about 10–15 at.% oxygen (e.g. Pt0.55, Si0.3, O0.15). The presence of oxygen is attributed to the diffusion of its atoms through the silicide layer to the surface. The in-situ XPS data revealed the diffusion of oxygen towards the surface during the reaction of platinum and silicon while in-situ XRD results showed the sequential formation of the Pt2Si and PtSi phases. Therefore, these results present a simple and user-friendly approach applicable in the fabrication of contact structures in the core-shell silicon nanowire based devices.

Preparation and thermal properties of microencapsulated stearyl alcohol with silicon dioxide shell as thermal energy storage materials

Microencapsulation of stearyl alcohol (SAL) with silica shell using sol-gel method has been attempted to obtain microencapsulated phase change materials (MPCM). Tetraethoxysilane (TEOS) was used as silica precursor to form silica shell. In order to inveatigate thermal properties of the MPCM, some tests were carried out. The results of Fourier transformation infrared spectroscope (FT–IR) indicated that the combination of the SAL with silica by sol-gel method is a physical action. X–ray diffractometer (XRD) was used to confirm PCM maintains stable crystal structure. Scanning electronic microscope (SEM) was employed to determine the MPCM has relatively stable physical structure. Thermal properties of MPCM were measured by Differential scanning calorimeter (DSC), where melting temperature and latent heat of MPCM1 (made from 10 g SAL, 10 g TEOS) is 55.89 °C and 229.73 J/g, respectively. Liquid–solid phase change has latent heat of 112.05 J/g at 56.74 °C while solid-solid phase change has latent heat of 72.01 J/g at 49.75 °C. Thermogravimetric analyzer (TGA) analysis confirms that MPCM has good thermal stability. After 100 thermal cycles of the MPCM1, there was no change in phase transition temperature and latent heat, which confirms that the MPCM has good reliability. The thermal conductivity of MPCM1 was measured to be 0.1508 W/m·K over melting point of MPCM1 and 0.1412 W/m·K at room temperature. Therefore, MPCM1 is found to be a promising candidate for thermal energy storage applications.

The shell matters: one step synthesis of core-shell silicon nanoparticles with room temperature ultranarrow emission linewidth.

Here we present a one-step synthesis that provides silicon nanocrystals with a thin shell composed of a ceramic-like carbonyl based compound, embedded in a porous organosilicon film. The silicon nanocrystals were synthesised from hydrogen silsesquioxane molecules, modified with organic molecules containing carbonyl groups, which were annealed at 1000 °C in a slightly reducing 5% H2 : 95% Ar atmosphere. The organic character of the shell was preserved after annealing due to trapping of organic molecules inside the HSQ-derived oxide matrix that forms during the annealing. The individual silicon nanocrystals, studied by single dot spectroscopy, exhibited a significantly narrower emission peak at room temperature (lowest linewidth ∼ 17 meV) compared to silicon nanocrystals embedded in a silicon oxide shell (150 meV). Their emission linewidths are even significantly narrower than those of single CdSe quantum dots (>50 meV). It is hypothesized that the Si-core-thin shell structure of the nanoparticle is responsible for the unique optical properties. Its formation within one synthesis step opens new opportunities for silicon-based quantum dots. The luminescence from the produced nanocrystals covers a broad spectral range from 530-720 nm (1.7-2.3 eV) suggesting strong application potential for solar cells and LEDs, following the development of a suitable mass-fabrication protocol.

A multiple scattering algorithm for three dimensional phase contrast atomic electron tomography

Electron tomography is used in both materials science and structural biology to image features well below the optical resolution limit. Here, we present a new method for high-resolution 3D transmission electron microscopy (TEM) which approximately reconstructs the electrostatic potential of a sample at atomic resolution in all three dimensions. We use phase contrast images captured through-focus and at varying tilt angles, along with an implicit phase retrieval algorithm that accounts for dynamical and strong scattering, providing more accurate results with much lower electron doses than current atomic electron tomography methods. We test our algorithm using simulated images of a synthetic needle geometry dataset composed of an amorphous silicon dioxide shell around a silicon core. By simulating various levels of electron dose, tilt and defocus, missing projections, and regularization methods, we identify a configuration that allows us to accurately determine both atomic positions and species. We also test the ability of our method to recover randomly positioned vacancies in light elements such as silicon, and to accurately reconstruct strongly-scattering elements such as tungsten.

Influence of solvent electron affinity on paramagnetic defects in hybrid Si/SiOx luminescent nanoparticles

Luminescence of 1-octadecene-coated silicon nanoparticles with 8 nm crystalline core in hexane and CCl4 colloidal solutions and its reversible photobleaching were examined. In agreement with previous reports, anti-correlation of luminescence intensity and the number of paramagnetic defects were found in hexane. Luminescence intensity is decreased by 75% during 30 min of 405 nm laser irradiation while the number of paramagnetic defects is increased by 65%. Paramagnetic defects were supposed to be silicon dangling bonds. In CCl4 colloidal solution, this correlation is lost: photobleaching is similar to hexane colloidal solution, while the number of paramagnetic defects is not changed during irradiation. Electron trapping and subsequent breaking of weak Si-Si bonds are proposed to be the reason of formation of silicon dangling bonds during irradiation. DFT calculation of geometry and g-tensor of Si-vacancy on the boundary of crystalline silicon core and oxide shell was performed. Formation of paramagnetic defects is supposed to be a by-process responsible only for a minor effect on luminescence intensity.