Formation Of Silicon Nanoparticles Research Articles

Towards ZnO-Based Near-Infra-Red Radiation Detectors: Performance Improvement via Si Nanoclusters Embedment

Si nanoparticles embedded in a ZnO matrix were produced by a sequential deposition of ZnO/Si/ZnO layers, by radio frequency sputtering. Sample growth temperatures of 25 °C, 300 °C, and 500 °C were used to deposit ZnO/Si/ZnO layers on soda lime glass and p-type silicon substrates; ZnO layers were deposited by reactive radio-frequency sputtering employing a mixture of Ar/O2, with a ratio of 66/33, as working atmosphere. The type of substrate and the growth temperature affect the first ZnO layer roughness, promoting the formation of silicon nanoparticles, matrix characteristics, and as consequence, spectral response. The roughness of the initial ZnO layer is transferred to the top layer of ZnO, and it can be tailored between 65 and 370 Å, depending on the sample growth temperature. Transmission electron microscopy show that substrate temperature mainly affects the density of silicon nanoparticles rather than their size. ZnO/Si/ZnO films deposited on p-type silicon substrate were processed and photosensors were obtained, showing a selective response in the 950 to 1150 nm wavelength range, making them suitable candidates for near infrared detectors.

Designing a Hypoxia-Activated Sensing Platform Using an Azo Group-Triggered Reaction with the Formation of Silicon Nanoparticles.

Hypoxia is known as a specific signal of various diseases, such as liver fibrosis. We designed a hypoxia-sensitive fluorometric approach that cleaved the azo bond (N═N) in the presence of hypoxia-controlled agents (sodium dithionite and azoreductase). 4-(2-Pyridylazo) resorcinol (Py-N═N-RC) bears a desirable hypoxia-responsive linker (N═N), and its azo bond breakup can only occur in the presence of sodium dithionite and azoreductase and leads to the release of 2,4-dihydroxyaniline, which can react with 3-[2-(2-aminoethylamino)ethylamino]propyltrimethoxysilane to generate yellow fluorescent silicon nanoparticles. This approach exhibited high selectivity and sensitivity toward both sodium dithionite and azoreductase over other potential interferences. The mouse liver microsome, which is known to contain azoreductase, was applied and confirmed the feasibility of the designed platform. Py-N═N-RC is expected to be a practical substrate for hypoxia-related biological analyses. Furthermore, silicon nanoparticles were successfully applied for Hela cell imaging owing to their negligible cytotoxicity and superb biocompatibility.

β-Glucuronidase-triggered reaction for fluorometric and colorimetric dual-mode assay based on the in situ formation of silicon nanoparticles

Backgroundβ-Glucuronidase (GUS) is considered as a promising biomarker for primary cancer. Thus, the reliable detection of GUS has great practical significance in the discovery and diagnosis of cancer. Compared with traditional organic probes, silicon nanoparticles (Si NPs) have emerged as robust optical nanomaterials due to their facile preparation, superior photobleaching resistance and excellent biocompatibility. However, most nanomaterials-based methods only output a single signal which is easily influenced by external factors in complex systems. Hence, developing nanomaterial-based multi-signal optical assays for highly sensitive GUS determination is still urgently desired. ResultsIn this study, we developed a simple and efficient one-step method for the in situ preparation of yellow color and yellow-green fluorescent Si NPs. This was achieved by combining 3-[2-(2-aminoethylamino) ethylamino] propyl-trimethoxysilane with p-aminophenol (AP) in an aqueous solution. The obtained Si NPs showed yellow-green fluorescence at 535 nm when excited at 380 nm, while also exhibiting an absorption peak at a wavelength of 490 nm. Taking inspiration from the easy synthesis step regulated by AP, which is generated through the hydrolysis of 4-aminophenyl β-D-glucuronide catalyzed by GUS, we constructed a direct fluorometric and colorimetric dual-mode method to measure GUS activity. The developed fluorometric and colorimetric sensing platform showed high sensitivity and accuracy with detection limits for GUS determination as low as 0.0093 and 0.081 U/L, respectively. SignificanceThis study provides a facile dual-mode fluorometric and colorimetric approach for determination of GUS activity based on novel Si NPs for the first time. This designed sensing approach was successfully employed for the quantification of GUS in human serum samples and screening of GUS inhibitors, indicating the feasibility and potential applications in clinical cancer diagnosis and anti-cancer drug discovery.

Synthesis and upscaling of silicon nanoparticles for lithium-ion batteries in a hot-wall reactor

Small amounts of silicon are currently used to partly replace graphite as anode material in lithium-ion batteries to increase their energy density and fast charging capability. Ensuring mechanical integrity during charging and discharging as well as the production of suitable silicon-based materials on a large scale at acceptable costs still remains a challenge. In this work, the formation of silicon nanoparticles from the gas phase is analyzed to understand the process, identify key parameters regarding a suitable process technology, and resolve upscaling issues for transfer to the industrial pilot scale. The experimental findings are supported by simulations of fluid dynamics. Process conditions regarding the formation of pure as well carbon containing nanoparticles are studied and a successful transfer to an industrial pilot plant reactor is demonstrated.

Laser - Produced Functional Surfaces of Silicon and Quartz

Fiber laser of 1064 nm wavelength was employed for micro/nano machining process of silicon and quartz substrates. The experimental data reveal formation of silicon nanoparticles by pulse laser ablation in liquid. Various characterization techniques were used such as UV-Visible absorption, SEM morphology to examine silicon nanoparticles. Moreover, generation of microbeams from micro lens array was created by direct writing of fiber laser on quartz. Theoretical calculations using COMSOL software were adopted to estimate the surface temperature distribution at silicon and quartz surface and underneath. It is found that maximum temperature of about (4600 K) and (2400 K) for silicon and quartz respectively when 15 W laser power, 127 ns pulse duration, 30 KHz frequency and 100 mm/sec laser speed was used. Potential applications of silicon nanoparticles and microbeams array in optoelectronics and biological imaging can be conducted due to the controllable laser micro/nano machining process.

Fluorometric assay based on the in situ formation of silicon nanoparticles for the determination of β-glucuronidase.

As a prodrug-converting enzyme, β-glucuronidase (β-GCase) is a lysosomal enzyme participating in the release of glucose from glucopyranosyl glycoside. In this work, for the first time, we have developed an analytical method exhibiting fluorometric signals for straightforward determination of β-GCase using silicon nanoparticles (Si NPs). Via hydrothermal treatment, in the water bath of 70°C for 50min, dopamine (DA) reacts with (3-[2-(2-aminoethylamino) ethylamino] propyltrimethoxysilane) (AEEA) to produce green fluorescent Si NPs. Enlightened by such easy reaction and β-GCase-triggered specific hydrolysis of dopamine-4-β-D-glucuronide (DA-GCU) into DA, we have designed an analytical method for β-GCase sensing through the production of Si NPs. Therefore, through the designed sensing platform, β-GCase activity was monitored, and the limit of detection (LOD) for this study was 0.02 U/L. Furthermore, the feasibility of the method was assessed by measuring β-GCase activity in human serum where recoveries and RSD were in the ranges 99-104% and 1.37-3.44, respectively.

The Effect of Oxidation Temperature on the (1000–1300) cm−1 Band in FT-IR Spectra of Silicon Oxide Synthesized by Thermal Oxidation of Silicon Wafers

In this work, silicon wafers were thermal treated in air at temperatures varied in the range 800—1200 °C. The annealed samples were investigated using FTIR, X-ray diffraction, FTIR and optical reflection spectroscopy. The effect of annealing temperature on the (1000–1300) cm−1 band in FT-IR spectra of the prepared samples was investigated. The results showed that thermal oxidation at temperatures less than 1200 °C leads to enhance the phenomenon of the splitting of longitudinal optical and transverse optical stretching motions. This phenomenon was verified by observing the appearance of two overlapping peaks in the region (1000–1300) cm−1 in FT-IR spectra. The results also showed that the splitting process leads to the formation of defects in the crystal structure of silicon, which in turn leads to the formation of silicon nanoparticles.

Laser fragmentation of silicon microparticles in liquids for solution of biophotonics problems

The possibility of manufacturing silicon nanoparticles by picosecond laser fragmentation of silicon microparticles in water is analysed. It is shown that for fragmentation duration of 40 min, the dependence of the average sizes of particles on the initial mass concentration of the micropowder varied in the range of 0.5 – 12 mg mL−1 is nonmonotonic, with the maximum average size of 165 nm being achieved at a concentration of 5 mg mL−1. To explain the obtained result, the simulation of propagation of a focused laser beam in a scattering suspension of silicon microparticles is performed for their different mass concentrations. It is demonstrated that at concentrations not exceeding 5 mg mL−1, fragmentation occurs in the paraxial region of the beam when it propagates deep into the cuvette with a suspension, while at higher concentrations it occurs primarily in the superficial layer owing to strong extinction. Calculations results allow the experimental features of the formation of silicon nanoparticles to be explained. Spectrophotometry measurements on suspensions of nanoparticles obtained at the initial concentration of microparticles of 12 mg mL−1 are compared with the theoretical estimates of the absorption and scattering coefficients obtained in the framework of the Mie theory. Measured optical properties indicate the potential of using fragmented nanoparticles as scattering and/or absorbing contrast agents in optical imaging of biological objects.

Broad and nearly white photoluminescence induced by the nitrogen incorporation in Si/SiOxNy multilayers

This work focuses on the study of the photoluminescent (PL) properties of Si/SiOxNy multilayer (ML) structures as a function of the thickness of silicon and silicon oxynitride layers. MLs were thermally annealed to induce the formation of silicon nanoparticles (Si-NPs). Infra-red spectroscopy (IR) vibration bands related to SiON bonds were observed and their intensity was stronger as the thickness of SiOxNy layers increased, indicating a larger N content. X-ray photoelectron spectroscopy (XPS) shows that the N content grows from 2 to 4% when the thickness of the SiOxNy layers increases from 2 to 6 nm, respectively; while it remains almost at the same value when the Si layer thickness changes. The analysis of the XPS-Si2p spectra reveals the formation of Si-NPs surrounded by a SiOxNy matrix by the existence of oxidation states such as Si4+, Si1+ and elemental silicon (Si0), as well as oxidation states attributed to the incorporation of nitrogen (N). MLs with the lowest N content (2%, thinnest oxynitride layer) emit a PL band centered in the red region, associated to the presence of Si-NPs and O-related defects. Nevertheless, an additional blue-green PL band is obtained when the nitrogen content increases (4%, thickest oxynitride layers). The N content induce radiative centers related to transitions of K or N centers which activates the blue-green PL. The diversity of these radiative centers within these Si/SiOxNy MLs produce a broad nearly white PL band, which is important for the development fo a white light source.

Formation Mechanism of Amorphous Silicon Nanoparticles Synthesized by Induction Thermal Plasma

This study focus on the synthesis of amorphous silicon nanoparticles and understanding the formation mechanism. Counter-flow quenching gases with different flow rates were injected from downstream of the torch to understand the effect of quenching gas on the formation of silicon nanoparticles. Transmission electron microscopy show that nanoparticles with spherical shape and agglomerates consist of smaller particles were synthesized. X-ray diffraction analysis is used to calculate the amorphization degree, which is defined as fraction of amorphous silicon in the silicon nanoparticles including both crystal and amorphous. The obtained results show that higher quenching gas flow rate leads to smaller diameter with higher amorphization degree. Electron diffraction patterns reveal that nanoparticles with diameter less than 10 nm are amorphous and agglomerated together, while for the nanoparticles with diameter larger than 10 nm are crystal. The formation mechanism of amorphous silicon nanoparticles is explained by estimated nucleation temperature and experimental results. Consequently, silicon nucleates at about 2400 K and then silicon vapor condenses on the nucleus. Finally, smaller nanoparticles will keep amorphous phase, while nanoparticles with a larger diameter grow to form crystalline.

Crystalline silicon nanoparticle formation by tailored plasma irradiation: self-structurization, nucleation and growth acceleration, and size control.

Crystalline silicon nanoparticles at the nanometer scale have been attracting great interest in many different optoelectronic applications such as photovoltaic and light-emitting-diode devices. Formation, crystallization, and size control of silicon nanoparticles in nonharsh and nontoxic environments are highly required to achieve outstanding optoelectronic characteristics. The existing methods require high temperature, use of HF solution, and an additional process for the uniform redistribution of nanoparticles on the substrate and there are difficulties in controlling the size. Herein, we report a new self-assembly method that applies the controlled extremely low plasma ion energy near the sputtering threshold energy in rare gas environments as nonharsh and nontoxic environments. This method produces silicon nanoparticles by crystallization nucleation directly at the surface of the amorphous film via plasma surface interactions. It is evidently observed that the nucleation and growth rates of the crystalline silicon nanoparticles are promoted by the enhanced plasma ion energy. The crystalline silicon nanoparticle size is tailored to the nanometer scale by the plasma ion energy control.

Effect of solvent on silicon nanoparticle formation and size: a mechanistic study.

Silicon has emerged as the most desirable material for optical dielectric metamaterials, however chemists struggle to obtain the required silicon nanoparticle dimensions. Here the average diameter of silicon nanoparticles is varied between 3 and 15 nm by changing the reaction solvent. Electrochemistry and NMR elucidate the role of solvent on the synthetic mechanism. Surprisingly the solvent does not stabilize the nanoparticles and there is no trend associated with chain length or open-chain versus cyclical solvent molecules. The solvent's main role is to stabilize the by-products, which prolongs the reaction lifetime.

Outlier analysis for a silicon nanoparticle population balance model

We assess the impact of individual experimental observations on a multivariate population balance model for the formation of silicon nanoparticles from the thermal decomposition of silane by means of basic regression influence diagnostics. The nanoparticle model is closely related to one which has been used to simulate soot formation in flames and includes morphological and compositional details which allow representation of primary particles within aggregates, and of coagulation, surface growth, and sintering processes. Predicted particle size distributions are optimised against 19 experiments across ranges of initial temperature, pressure, residence time, and initial silane mass fraction. The influence of each experimental observation on the model parameter estimates is then quantified using the Cook distance and DFBETA measures. Seven model parameters are included in the analysis, with five Arrhenius pre-exponential factors in the gas-phase kinetic rate expressions, and two kinetic rate constants in the population balance model. The analysis highlights certain experimental conditions and kinetic parameters which warrant closer inspection due to large influence, thus providing clues as to which aspects of the model require improvement. We find the insights provided can be useful for future model development and planning of experiments.

Structural properties of silicon nanoparticles obtained via femtosecond laser ablation in gases at different pressures

In this paper, we report on the effect of buffer gas on silicon nanoparticle formation in femtosecond laser ablation process. For the first time the nonmonotonic dependence of the silicon nanoparticle sizes on the gas pressure is obtained. Distributions of the particles on the size received by means of atomic-force microscopy indicate reducing the Si nanoparticle diameter with pressure increase from 50 to 700 mbar for helium and nitrogen atmospheres, with the minimal nanoparticle size up to 5 nm reaching in helium. At further increase in pressure there is a growth of the nanoparticles size and distribution becomes wider. Using argon as a buffer gas results in larger nanoparticle sizes than in helium and more complicated dependence of the size distribution on the argon pressure. The electron diffraction and Raman scattering in the formed silicon nanoparticles evidence their crystallinity.

Silicon nanoparticle formation depending on the discharge conditions of an atmospheric radio-frequency driven microplasma with argon/silane/hydrogen gases

Atmospheric radio-frequency driven non-equilibrium microplasma jets in an argon/silane/hydrogen gas mixture are characterised and analysed with respect to the reaction pathway, which leads to the formation of silicon nanoparticles. Optical emission spectroscopy is used to obtain initial information about possible plasma chemistry processes and high-time-resolution images uncover the mode of operation of the discharge. It is demonstrated that the effect of the way the electric field is applied (parallel or perpendicular to the gas flow), the gas flow magnitude, and varying the gas mixture can result in three different operation modes—filamentary plasma with a stationary filament, diffuse-like plasma with the filament changing its position, and a diffuse non-filamentary plasma—being formed in the one millimetre inner diameter tube with ring electrodes, which apply an electric field parallel to the gas flow (a parallel-field plasma). An electric field applied perpendicular to the gas flow (a cross-field plasma) results only in a homogeneous diffuse discharge with low plasma density. The nanoparticles synthesised in the microplasma jet are studied by scanning electron microscopy and dynamic light scattering. The experimental results reveal that the silane precursor can very probably be fully dissociated in the parallel-field plasma and particles with sizes almost independent of silane concentration are generated. In contrast, silane is only weakly fragmented in the cross-field plasma and negative ions are formed. Particle size reacts very sensitively to silane concentration in this case and is a result of a condensation of radicals or ions on the particle surface.

Modeling of silicon nanoparticle formation in inductively coupled plasma using a modified collision frequency function

A model is presented to describe particle growth in inductively coupled plasma. The model consists of plasma chemistry and a coagulation module that adopts a modified collision frequency function. The modified collision frequency function is modified by a collision correlation factor that reflects the repulsive force of the particle charge in plasma in order to describe the reduction of coagulation among medium size particles (around 100 nm). In this model, plasma state and concentration of nuclei are determined by a spatially averaged global model in the plasma chemistry module. Particle growth is calculated by a coagulation module. To verify the validity of the model, comparison analysis is performed between experimental data obtained with PBMS and models, some of which are modified by a collision correlation factor. The analysis is performed with respect to dependencies on synthesis time, plasma source power and chamber pressure. From the analysis, we confirm the validity of the model that adopts a modified collision frequency function for the plasma condition.

Shape dependence of the band gaps in luminescent silicon quantum dots

Silicon nanoparticles exhibit quantum confinement and function as optoelectronic devices whose optical properties are known to depend strongly on size and surface termination. The effect of nanoparticle shape on optical properties, however, has not yet been investigated. In this work we use tight binding and density functional theory simulations to study the HOMO–LUMO gaps of hydrogen-terminated silicon nanoparticles as a function of shape and size. It is shown that optical properties are strongly dependent upon nanoparticle shape, and in particular that octahedral nanoparticles exhibit significantly (up to 0.2 eV) larger band gaps than cubic or pseudo-spherical nanoparticles of the same volume. Control of the shape of nanoparticles via the tuning of the thermodynamic conditions in which they are formed may allow the formation of silicon nanoparticles with emission wavelengths running across the full visible range.

Advanced Multiphase Silicon-Based Anodes for High-Energy-Density Li-Ion and Li-Air Batteries

Given that lithium-ion and lithium-air batteries are the preferred choice for EVs and plug-in applications for the next 10–15 years, the focus is on improving their safety and performance. New, higher-capacity materials are required in order to address the need for greater energy density, longer cycle life and safer high-power operation. Silicon offers the highest gravimetric and volumetric capacity as an anode material (e.g. Li22Si5: nearly 4,200mAh/g, 9,800mAh/mL). The lithium-rich silicon compounds have high melting points. Their higher working potentials (vs. Li) eliminate the possibility of metallic-lithium deposition due to overcharge. Silicon is the second-most abundant element in the earth’s crust, and it is environmentally benign. Unfortunately, Si-based electrodes typically suffer from large volume changes (up to 420%) during insertion and extraction of lithium. This is followed by cracking and pulverization of silicon, which in turn, leads to the loss of electrical contact, unstable SEI and eventual capacity fading.We have developed two synthetic routes for the preparation of core-shell silicon multiphase composite particles. We studied the process of formation of the protective SEI layer on the anode nanoparticles and tested small laboratory-prototype cells with advanced anodes. The methods of attachment of silicon nanoparticles to carbon nanotubes (multi-wall carbon nanotubes (MWCNT)) were developed with the purpose of creating silicon anodes supported by a strong, rigid and high-electrically-conducting matrix. The methods are based on the silanization process or pyrolysis. STEM analysis showed that silicon particles are dispersed uniformly on the surface of the MWCNT. ESEM images indicated the formation of silicon nanoparticles wrapped by carbon nanotubes and coated by nanometer thick amorphous carbon. TEM, EELS and XPS tests confirm the formation of a layer of carbon on top of the silicon nanoparticles and Si-C bonding (Fig.1). The feasibility of using electrophoretic deposition for the preparation of composite silicon anodes coated by a ceramic-in-polymer protective layer has been proven.Li/LiPF6 EC:DEC/Si-C-MWCNT cells with anodes composed of about 50% core-shell Si-C composite exhibited de-intercalation capacity of 1373mAh/gSi at the 50th cycle and 1021mAh/cm2 at the 410thcycle. Li/LiTFSI-Pyr14/Si-C-MWCNT cells ran for more than 30 cycles with capacity of 1500mAh/gSi. Doped Si-alloy nanoparticles were formed by electrochemical means. The anodes are being tested. Acknowledgments Research is funded by EU FP7, contract no. 265971 and by Israel Academy of Science

Formation of silicon nanoparticles by a pressure induced nucleation mechanism

Formation of silicon nanoparticles (SiNPs) was achieved using excimer laser crystallization of an amorphous Si (a-Si) thin film using a SiO2 capping layer (C/L) with improved thin-film transistor (TFT) performance due to the enlarged grain size of polycrystalline Si (poly-Si). After laser irradiation of an a-Si thin film covered with C/L, fluctuation in the surface morphology of the C/L was observed above the critical laser energy density (Ecr) with the formation of SiNPs. The grain size of the poly-Si layer after crystallization increased abruptly at the same time. A non-uniform pressure distribution beneath the SiO2 C/L was proposed for the initiation of nucleation, which is named pressure induced nucleation (PIN) mechanism. Following nucleation, the release of latent heat made it difficult for the remnant liquid Si to solidify and the volume increased due to the density difference between the liquid and solid Si. Consequently, the pressure on the liquid Si caused SiNPs to sprout through the SiO2 C/L as grains grew from the low temperature to high temperature point. This study offers not only a simple method to fabricate SiNPs with controllable size/density but also larger grain size with lower laser energy density, which leads to higher TFT performance.

Crystallization Kinetics of Plasma-Produced Amorphous Silicon Nanoparticles

ABSTRACTThe use of a continuous flow non-thermal plasma reactor for the formation of silicon nanoparticles has attracted great interest because of the advantageous properties of the process [1]. Despite the short residence time in the plasma (around 10 milliseconds), a significant fraction of the precursor, silane, is converted and collected in the form of nanopowder. The structure of the produced powder can be tuned between amorphous and crystalline by adjusting the power of the radio-frequency excitation source, with higher power leading to the formation of crystalline particles. Numerical modeling suggests that higher excitation power results in a higher plasma density, which in turn increases the nanoparticle heating rate due to the interaction between ions, free radicals and the nanopowder suspended in the plasma [2]. While the experimental evidence suggests that plasma heating may be responsible for the formation of crystalline powder, an understanding of the mechanism that leads to the crystallization of the powder while in the plasma is lacking. In this work, we present an experimental investigation on the crystallization kinetic of plasma-produced amorphous powder. Silicon nanoparticles are nucleated and grown using a non-thermal plasma reactor similar to the one described in [1], but operated at low power to give amorphous nanoparticles in a 3-10 nm size range. The particles are then extracted from the reactor using an orifice and aerodynamically dragged into a low pressure reactor placed in a tube furnace capable of reaching temperatures up to 1000°C. Raman and TEM have been used to monitor the crystalline fraction of the material as a function of the residence time and temperature. It is expected that for a residence time in the annealing region of approximately ∼300 milliseconds, a temperature of at least 750 °C is needed to observe the onset of crystallization. A range of crystalline percentages can be observed from 750 °C to 830 °C. A discussion of particle growth and particle interaction, based on experimental evidence, will be presented with its relation to the overall effect on crystallization. Further data analysis allows extrapolating the crystallization rate for the case of this simple, purely thermal system. We conclude that thermal effects alone are not sufficient to explain the formation of crystalline powder in non-thermal plasma reactors.