Formation Of Si Nanoparticles Research Articles

New aspects of femtosecond laser ablation of Si in water: a material perspective

We report a study of the role of material’s conductivity in determining the morphology of nanoparticles and nanostructures produced by ultrafast laser ablation of solids. Nanoparticles and textured surfaces formed by laser ablation display a wide variation in size and morphology depending on the material. In general, these qualities can be grouped as to material type, insulator, semiconductor, or metal; although each has many other different material properties that make it difficult to identify the critical material factor. In this report, we study these nanoparticle/surface structural characteristics as a function of silicon (Si) resistivity, thus honing-in on this critical parameter and its effects. The results show variations in morphology, optical, and nonlinear properties of Si nanoparticles. The yield of colloidal Si nanoparticles increased with an increase in the conductivity of Si. Laser-induced periodic surface structures formed on ablated substrates are also found to be sensitive to the initial conductivity of the material. Further, the laser ablation of Gamma-irradiated Si has been investigated to verify the influence of altered conductivity on the formation of Si nanoparticles. These observations are interpreted using the basic mechanisms of the laser ablation process in a liquid and its intricate relation with the initial density of states and thermal conductivities of the target material.

Formation of Si nanoparticles by pulsed discharge of Si strips in distilled water

Si nanoparticle features multiple excellent properties, such as high theoretical capacity of 4200 mAh/g and low volume expansion effect, and it is regarded as an outstanding anode electrode material for Li-ion batteries. In this study, we obtained Si nanoparticles through pulsed discharge of Si strips and analyzed the pulsed discharge process based on recorded current data. The recovered samples were characterized by various techniques, such as XRD, Raman spectroscopy, SEM, and TEM. The characterization results confirm that the recovered samples are smooth spherical Si nanoparticles smaller than 200 nm. Our investigation reveals that the charging voltage is a key factor to adjust the size distribution of recovered Si nanoparticles. In the charging voltage range of 4–7 kV, the increase of charging voltage value decreases D90 (the particle size at the 90% undersize point in the size distribution) of recovered Si nanoparticles from 48.7 to 24.9 nm. In the charging voltage range of 7–12 kV, the increase of charging voltage value increases D90 of recovered Si nanoparticles from 24.9 to 66.5 nm. Thus, the critical charging voltage value is 7 kV, at which condition D90 of formed Si nanoparticles is the minimum (24.9 nm). In addition, the analysis of discharge current curves indicates three discharge stages, including semiconductor joule heating, conductor joule heating, and plasma discharge, which possess correlation to the size distribution of formed Si nanoparticles.

Mechanisms of Si Nanoparticle Formation by Molten Salt Magnesiothermic Reduction of Silica for Lithium‐ion Battery Anodes

AbstractMolten salt methods enable the synthesis of Si nanostructures by moderating the thermal energy evolved in highly exothermic magnesiothermic reduction reactions (MRR) of silica. Due to their cost‐effectiveness and scalability, these techniques are well suited for producing nanoscale Si for a number of applications, including energy storage. To control the microstructure morphology and particle size, it is necessary to understand the formation mechanism of the Si produced. By evaluating the time‐resolved phase evolution, when NaCl moderates the thermal energy generated by MRR of SiO2, we elucidate 3 parallel interfacial reaction mechanisms yielding Si nanoparticles – via Mg vapor, Mg‐rich eutectic liquid, and Mg ions dissolved in molten NaCl. These individual Si nanoparticles offer a striking contrast to the typical by‐product of MRR of SiO2 with and without NaCl, which yields a 3‐dimensional (3‐D) porous network of sintered Si nanoparticles. Lithium‐ion battery half‐cells with electrodes composed of individual Si nanoparticles showed a greater first‐cycle irreversible discharge capacity and faster capacity loss over the first 5 cycles at a current density of 200 mA g−1 compared to half‐cells with electrodes of a porous 3‐D Si network–indicative due to thicker solid electrolyte interphase (SEI) formation on individual particles. At a higher current rate of 400 mA g−1, once SEI formation and activation of Si are established, both cells exhibit a similar capacity retention rate over 100 cycles.

Formation of ncl-Si in the Amorphous Matrix a-SiOx:H Located near the Anode and on the Cathode, Using a Time-Modulated DC Plasma with the (SiH4–Ar–O2) Gas Phase ($${{{\text{C}}}_{{{{{\text{O}}}_{2}}}}}$$ = 21.5 mol %)

The formation of ncl-Si in the amorphous matrix a-SiOx:H using a time-modulated DC plasma at an elevated oxygen content of $${{C}_{{{{{\text{O}}}_{2}}}}}$$ = 21.5 mol % in a gas mixture of (SiH4–Ar–O2) is investigated. Plasma modulation implies the repeated (n = 180) switching on (for ton = 5, 10, 15 s) and switching off (for toff = 5, 10, 15 s) of the magnet coil of the DC magnetron. The effect of self-induction is used to enhance the processes of SiH4 dissociation, the formation of Si nanoparticles, and the ionization of oxygen and ncl-Si flows towards the electrodes. The samples are located both on an electrically isolated substrate holder near the anode and on the cathode (beyond its erosion zone). These experiments show that the shape of the dependences of the photoluminescence intensity $$I_{{{\text{PL}}}}^{{ncl - {\text{Si}}}}$$ on the wavelength Λ are identical for all pairs of samples on the anode and cathode. When the ton value is small (ton = 5 s), the difference in the sample location only slightly affects the infrared (IR) spectra. At longer times ton (≥10 s) and a short time toff (5 s), the amorphous matrix located on the cathode is enriched with oxygen (as compared with that near the anode). The optimal plasma-modulation parameters are found to be toff/ton = 5, 10, 15/10 and toff/ton = 5, 10/15; under these conditions, the amorphous matrix has a “perfect structure” and is transparent to radiation, and the $$I_{{{\text{PL}}}}^{{ncl - {\text{Si}}}}$$ value is the largest in the range λ ≈ 0.75–0.9 μm.

Swift heavy ion irradiation assisted Si nanoparticle formation in HfSiOx nano-composite thin films deposited by RF magnetron sputtering method

Silicon co-deposited HfOx thin films were prepared by RF magnetron sputtering method. The average size of Si co-deposited nanocomposites is around 10–12 nm. 100 MeV Ag ion irradiation induces the Si nano-crystal formation within the nanocomposite. The average grain size of the Si nano-crystals increases with the increase of ion fluence. The observed luminescence at 430 nm is due to oxygen related defect states and the luminescence at 530 nm may be attributed to the emission from Si nanoparticles. Red shift in emission wavelength indicates either the increase in the size of the nanoparticles or ion induced change in the dielectric constant of surrounding medium. The increase in the intensity of the luminescence peak at 440 nm indicates the creation of defect states by ion irradiation. Raman measurements further confirm the formation of Si NPs that are embedded in the composite medium.

Формирование ncl-Si в аморфной матрице a-SiO-=SUB=-x-=/SUB=- : H, расположенной вблизи анода и на катоде, с помощью модулированной по времени DC-плазмы с (SiH_4-Ar-O-=SUB=-2-=/SUB=-)-газовой фазой (C-=SUB=-O_2-=/SUB=-=21.5 мол%)

AbstractThe formation of ncl -Si in the amorphous matrix a -SiO_ x :H using a time-modulated DC plasma at an elevated oxygen content of $${{C}_{{{{{\text{O}}}_{2}}}}}$$ = 21.5 mol % in a gas mixture of (SiH_4–Ar–O_2) is investigated. Plasma modulation implies the repeated ( n = 180) switching on (for t _on = 5, 10, 15 s) and switching off (for t _off = 5, 10, 15 s) of the magnet coil of the DC magnetron. The effect of self-induction is used to enhance the processes of SiH_4 dissociation, the formation of Si nanoparticles, and the ionization of oxygen and ncl -Si flows towards the electrodes. The samples are located both on an electrically isolated substrate holder near the anode and on the cathode (beyond its erosion zone). These experiments show that the shape of the dependences of the photoluminescence intensity $$I_{{{\text{PL}}}}^{{ncl - {\text{Si}}}}$$ on the wavelength Λ are identical for all pairs of samples on the anode and cathode. When the t _on value is small ( t _on = 5 s), the difference in the sample location only slightly affects the infrared (IR) spectra. At longer times t _on (≥10 s) and a short time t _off (5 s), the amorphous matrix located on the cathode is enriched with oxygen (as compared with that near the anode). The optimal plasma-modulation parameters are found to be t _off/ t _on = 5, 10, 15/10 and t _off/ t _on = 5, 10/15; under these conditions, the amorphous matrix has a “perfect structure” and is transparent to radiation, and the $$I_{{{\text{PL}}}}^{{ncl - {\text{Si}}}}$$ value is the largest in the range λ ≈ 0.75–0.9 μm.

Laser-Stimulated Phase Transformations in Thin Layers of SiOx and CNx –Ni

We demonstrate the possibility of laser-assisted phase transformations in thin layers of SiOx from the amorphous nonstoichiometric phase into a nanocomposite layer with Si nanocrystals embedded in the silicon-oxide matrix. The formation of Si nanoparticles (NPs) in SiOx films occurs due to their irradiation with nanosecond pulses of a Nd+3:YAG laser with base wavelength λ = 1.064 μm and the second harmonic λ = 0.532 μm. The nanostructurization of the surface in the form of nanoparticles with mean sizes varying within the range 5–85 nm was detected with the help of atomic force microscopy and optical transmission spectra. The sizes of nanoparticles and their surface distribution depend on the intensity of the laser and its wavelength λ. We determined the mechanism of formation of Si nanocrystals by laser-induced thermal shocks. By analyzing the results of atomic force microscopy, as well as the data of Raman and polarization-modulation spectroscopies, we detected the increase in the amount of single-crystal phase in the film of CNx–Ni nanocomposite with simultaneous increase in the sizes of CNx–Ni nanoparticles caused by the action of laser pulses. The mechanism of laser-stimulated nanocrystallization is proposed. This mechanism is based on the local annealing of the CNx shell as a result of laser heating of the metallic Ni core of CNx–Ni nanoparticles and a more intense sublimation of the amorphous phase of CNx–Ni due to the lower temperature of dissociation of the CNx shell as compared with the Ni core.

Nanoscale control of Si nanoparticles within a 2D hexagonal array embedded in SiO2 thin films

In this work, we investigate the ability to control Si nanoparticles (NPs) spatially arranged in a hexagonal network of 20 nm wide nanovolumes at controlled depth within SiO2 thin films. To achieve this goal an unconventional lithographic technique was implemented based on a bottom-up approach, that is fully compatible with the existing semiconductor technology. The method combines ultra-low energy ion beam synthesis with nanostructured block-copolymer thin films that are self-assembled on the SiO2 substrates to form a nanoporous template with hexagonally packed pores. A systematic analytical investigation using time of flight-secondary ion mass spectroscopy and low-loss energy filtered transmission electron microscopy demonstrates that by adjusting few fabrication parameters, it is possible to narrow the size distribution of the NPs and to control the number of NPs per nanovolume. Experimental results are critically discussed on the basis of literature data, providing a description of the mechanism involved in the formation of Si NPs.

Numerical study of Si nanoparticle formation by SiCl4 hydrogenation in RF plasma

Nanocrystalline silicon (nc-Si) is a promising material for many applications related to electronics and optoelectronics. This work performs numerical simulations in order to understand a new process with high deposition rate production of nc-Si in a radio-frequency plasma reactor. Inductive plasma formation, reaction kinetics and nanoparticle formation have been considered in a sophisticated model. Results show that the plasma parameters could be adjusted in order to improve selectivity between nanoparticle and molecule formation and, thus, the deposition rate. Also, a parametric study helps to optimize the system with appropriate operating conditions.

150 MeV Au ion induced modification of Si nanoparticles prepared by laser ablation

We have investigated in detail the effects of 150MeV Au ions irradiation on Si nanoparticles (NPs) synthesized by picosecond laser ablation of single crystal Si wafers in acetone. The formation of Si NPs was confirmed by Raman spectroscopy, transmission electron microscopy (TEM) and field emission scanning electron microscope (FESEM) measurements. The size distribution of synthesized NPs was found to be in the range of few nm to 80nm. These samples were then irradiated with 150MeV Au ions at various fluences ranging from 1×1013 to 1×1014ions/cm2. The effects of ion irradiation on the size and shape of Si NPs were further investigated using TEM, FESEM and micro Raman spectroscopy. From TEM data, we have noticed the reduction in size of NPs with increasing ion irradiation fluence. Furthermore with the increasing fluence we also observed the nucleation of 6–9nm NPs in the vicinity of bigger NPs where there were no such NPs before ion irradiation. The increase in the FWHM of the Raman peak and its shift towards lower wave number side also suggests that the decrease in NP size is a result of increase in the fluence of irradiation.

AES and XPS studies of a por-Si/SnOx nanocomposite formed using a powerful ion beam of nanosecond duration

The results of the X-ray photoelectron spectroscopy (XPS), Auger electron spectroscopy (AES), and scanning electron microscopy (SEM) investigations of tin-oxide nanolayers on samples of por-Si/SnO x composites with varying matrix porosity, formed using a powerful ion beam of nanosecond duration, are presented. It is shown that rapid melting and crystallization of the surface leads to the formation of Si nanoparticles with a maximal size of 200 nm. It is established that tin is included in the structure of the nanocomposite in an oxidized state with a small inclusion of metallic β tin. With increasing porosity, the phase composition of the tin nanolayers becomes closer to the state corresponding to the highest tin oxide (SnO2). It is also shown that, upon an increase in the porosity, the intensity of the tin 4d subvalent line increases, which is, apparently, associated with an enhanced degree of hybridization of tin and oxygen atoms. The changes in the elemental composition of the composite and the depth of tin penetration are estimated from the results of ion etching.

Formation of metallic Si and SiC nanoparticles from SiO2 particles by plasma-induced cathodic discharge electrolysis in chloride melt

Silicon nanoparticles are formed from SiO2 particles by conducting plasma-induced cathodic discharge electrolysis. In a LiCl–KCl melt in which SiO2 particles were suspended at 450°C, we obtained Si nanoparticles with diameters around 20nm. During the electrolysis period, SiO2 particles are directly reduced by discharge electrons on the surface of the melt just under the discharge, and the deposited Si atom clusters form Si nanoparticles, which leave the surface of the original SiO2 particle due to free spaces caused by a molar volume difference between SiO2 and Si. We also found that SiC nanoparticles can be obtained using carbon anode. Based on Faraday's law, the current efficiency for the formation of Si nanoparticles is 70%.

표면 알킬기를 갖는 실리콘 나노입자의 One-Pot 용액환원 합성

가시광 영역에서 강한 광루미네선스(photoluminescence, PL) 특성이 있는 실리콘 나노입자는, 생물학적 형광 이미징, RGB(red, green, blue) 디스플레이, 포토닉스, 광전소자 등의 응용소재로 개발될 수 있어 많은 연구가 수행되고 있다. 실리콘 나노입자의 광학적 및 물리화학적 특성을 이용한 실용적인 응용 및 개발을 위해서는 그 특성의 조절이 용이한 제조법 개발이 필수적이다. 본 연구에서는 Na(naphthalide)를 환원제로 사용한 용액환원법을 이용하여 한 단계로 입자표면이 알킬기로 안정화된 평균 <10 nm 크기의 실리콘 나노입자를 합성할 수 있는 방안을 시도하였다. 이를 위하여 실리콘 전구체로 알킬기를 포함하고 있는 (Octyl)<TEX>$SiCl_3$</TEX> 단독 또는 (Octyl)<TEX>$SiCl_3$</TEX>와 <TEX>$SiCl_4$</TEX>의 혼합물을 사용하여 Si-Cl 결합의 환원을 통한 입자의 형성과 동시에 반응물에 포함된 Octyl 기에 의한 표면 안정화를 한번에 달성할 수 있었다. 합성한 실리콘 입자의 TEM/EDS, FTIR 분석결과 입자의 크기는 <10 nm이며, 표면이 알킬기로 덮여있어 소수성 용제인 헥산에 쉽게 용해되었으며 입자표면은 소량의 산화된 Si-O-Si 그룹을 포함하고 있었다. UV-vis 및 PL 분석결과 표면 알킬기를 포함하는 실리콘 나노입자의 전형적인 광 특성을 보여 간단한 반응단계를 통하여 표면이 Octyl기로 덮인 실리콘 나노입자를 합성할 수 있음을 보였다. 본 연구에서 시도한 합성법을 응용할 경우, 향 후 실리콘 나노입자의 표면에 다양한 기능기를 one-pot으로 도입할 수 있을 것으로 기대된다. Silicon nanoparticles have attracted a great deal of scientific interests due to its intense photoluminescence in the visible spectral region and its potential applications in biological fluorescence maker, RGB (red, green, blue) display, photonics and photovoltaics etc. Practical applications making use of optical and physicochemical properties of Si nanoparticles requires an efficient synthetic method which allows easy modulation of their size, size distribution as well as surface functionalities etc. In this study, a one-pot solution reduction scheme is attempted to prepare alkyl-terminated Si nanoparticles (<10 nm) with Si precursors, (Octyl)<TEX>$SiCl_3$</TEX> or mixture of (Octyl)<TEX>$SiCl_3$</TEX> and <TEX>$SiCl_4$</TEX>, containing alkyl-groups using Na(naphthalide) as reducing agent. The surface capping of Si nanoparticles with octyl-groups as well as Si nanoparticle formation was achieved in one-pot reaction. The hexane soluble Si nanoparticles with octyl-termination were in the range of 2-10 nm by TEM and some oxide groups (Si-O-Si) was present on the surface by EDS/FTIR analyses. The optical properties of Si nanoparticles measured by UV-vis and PL evidenced that photoluminescent Si nanoparticles with alkyl-termination was successfully synthesized by solution reduction of alkyl-containing Si precursors in one-pot reaction.

Si nanoparticle formation in SiO 2 by Si ion implantation: Effect of energy and fluence on size distribution and on SiO 2 composition

The injection of current in electroluminescent devices based on silicon nanocrystals (Si-nc) embedded in SiO 2 matrix is facilitated by the use of very thin SiO 2 layer. Therefore, the production of Si-nc by implantation of excess Si ions in the SiO 2 substrate has to be performed at lower energy. We have hence studied the effect of the Si ion energy on the Si-nc size distribution as well as on the surrounding SiO 2 matrix. Si has been implanted into thermally grown oxide film on Si (100) substrate at 50 and 150 keV with 5 × 10 16 to 2.2 × 10 17 Si +/cm 2. TEM has shown that for low doses (where the photoluminescent signal is at maximum) the Si-nc size is nearly uniform around 3 nm, whereas at high doses there is a size distribution (1.8–20 nm). A good agreement in the Si-nc average size has been found between XRD and TEM characterizations. Measurement by TEM of the implanted SiO 2 thickness has revealed that the swelling is more important for low fluence implantation due to the formation of amorphous Si clusters. XPS has shown partial oxygen depletion near the surface as well as a production of non-stoichiometric oxides of varying composition with depth.

Growth peculiarities of silicon nanoparticles in an oxide matrix prepared by magnetron sputtering

AbstractThe process of thermal decomposition of SiOx layers prepared by magnetron sputtering is studied by photoluminescence, AFM, Auger and SIMS methods. The dependence of the depth distribution of the chemical composition on excess silicon content is obtained. It is shown that as‐sputtered SiOx layers are characterized by homogeneous enough chemical composition and do not exhibit photoluminescence. High‐temperature annealing in nitrogen atmosphere stimulates not only Si nanoparticle formation but also the appearance of a Si depleted region near layer‐substrate interface. This last process is found to be dependent on excess Si content. The decrease of silicon content in the depth of the annealed layers is accompanied by the decrease of Si particle sizes as proved by the blue shift of the photoluminescence maximum. The mechanisms of SiOx decomposition and possible reasons for the appearance of the Si depleted region are discussed. (© 2007 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

Optical Evaluation of Silicon Nanoparticles Prepared by Arc Discharge Method in Liquid Nitrogen

We have prepared silicon nanoparticles by an arc discharge method in liquid nitrogen. This system is easily adoptable in the preparation of large quantities of Si nanoparticles and has the potential for low-cost production. Etching Si nanoparticles with hydrofluoric acid reduced their size and passivated their surface such that they exhibited bright visible luminescence under UV illumination. The slow HF etching allows the formation of Si nanoparticles with a narrow size distribution. After etching, nanoparticles as small as 3–6 nm in diameter were obtained. Raman spectroscopy was used to determine the average diameter of Si nanoparticles during etching. The photoluminescence of Si nanoparticle was measured as a function of size and could be associated with a quantum confinement model.

Initial Stages of Electrochemical Anodization of Silicon Surface in Transient Regime: Monolayer Formation of Si Nanoparticles

not Available.

Understanding of the Synthesis and Structure of Si Nanocrystals in an Oxide Matrix from First Principles Based Atomistic Modeling

ABSTRACTKinetic Monte Carlo simulations were performed to examine mechanisms underlying the formation of Si nanoparticles in Si-rich SiO2. We have determined two important features of the embedded Si nanoparticle growth: “coalescence-like” and “pseudo Ostwald ripening”. The former is mainly responsible for fast Si particle growth at the early stage of annealing where the particles are close to each other, while the latter becomes important when the density of particles is low such that they are separated by large distances. The pseudo ripening process takes place several orders of magnitude slower than the “coalescence-like” growth. The predominance of “coalescence-like” behavior in the growth of Si nanoparticles results in a big variation in the particle size in terms of the Si:O ratio. Overall the predicted growth behavior based on our Monte Carlo simulations agrees well with experiments.

Formation of Si-nanoparticles in a microwave reactor: Comparison between experiments and modelling

The formation and growth of silicon-nanoparticles from silane in a microwave reactor was investigated. Experiments were performed for the following conditions: precursor concentration 380–2530 ppm, pressures of 20–30 mbar, microwave powers 120–300 W. The formed particles were examined in-situ with a particle mass spectrometer. Additionally, particles were collected on grids and analyzed by transmission electron microscopy, X-ray diffraction, and by determining the specific surface area by BET. The particle size was found to be in the range of 5–8 nm in diameter. A simple model was used to simulate the particle formation processes taking place inside the reactor. The microwave energy coupled into the reactor flow was treated as a spatially distributed energy source resulting in a local temperature increase. The particles were assumed to have a monodisperse size distribution. To allow an approximation of their shape they were characterized by their volume and surface area. The model takes nucleation, convection, coagulation, and coalescence into account. The fluid flow inside the microwave reactor was simulated with the commercial CFD-code Fluent.

Kinetics of Structural and Phase Transformations in Thin SiO[sub x] Films in the Course of a Rapid Thermal Annealing

Infrared spectroscopy and analysis of photoluminescence spectra have been used to study variations in the composition of the oxide phase in a SiOx film and the precipitation of the Si phase in the course of a rapid thermal annealing for 1–40 s at temperatures of 500–1000°C. Kinetics of phase segregation has been observed for the first time at temperatures of 600–700°C: an increase in the amount of precipitated silicon as the annealing duration increases followed by an eventual leveling off. The phase separation is brought to completion in a time as short as 1 s at temperatures higher than 900°C. The diffusion coefficient is estimated in the context of a model of the diffusion-controlled formation of Si nanoparticles. The obtained values of the diffusion coefficient exceed, by five to ten orders of magnitude, those of the silicon diffusion coefficients in SiO2 and Si and are comparable to the diffusion coefficients of the oxygen contained in these structures. It is assumed that oxygen mobility forms the basis for the mechanism of structural and phase transformations in the SiOx layers and for the formation of Si nanoparticles in the course of annealing.