Crystalline Silicon Nanoparticles Research Articles

Validation of the silicon nanoparticle production on the pilot plant scale via long-term gas-phase synthesis using a microwave plasma reactor

The formation of crystalline silicon nanoparticles by homogeneous gas-phase reactions as a direct way to produce high-purity raw material is applied. For this purpose, a microwave-assisted plasma reactor is used. Goal of this paper is to show the scalability of our process technology from laboratory scale to pilot plant scale while maintaining the particle characteristics. This is demonstrated by producing and analyzing silicon nanoparticles during long-term synthesis in a pilot-scale microwave plasma reactor over a period of six hours. The focus is on a high production rate in conjunction with consistent particle characteristics. A continuous production of the mostly spherical crystalline silicon particles with a count median diameter (CMD) of 23.4 nm and a geometric standard deviation of 1.5 is shown using TEM analysis. The stability of the synthesis process is monitored by means of regular sampling and analyzing batch samples extracted from the process every 30 min. Here it is shown that the CMD varies statistically between 21 and 26 nm. Moreover, the decomposition rate of the precursor was determined to be 99%, while the energy supply remained constant. A constant production rate of about 200 g∙h−1 is shown.

Rice straw based silicon nanoparticles improve morphological and nutrient profile of rice plants under salinity stress by triggering physiological and genetic repair mechanisms

The agricultural sector is facing numerous challenges worldwide, owing to global climate change and limited resources. Crop production is limited by numerous abiotic constraints. Among them, salinity stress as a combination of osmotic and ionic stress adversely influences the physiological and biochemical processes of the plant. Nanotechnology facilitates the production of crops either directly by eradicating the losses due to challenging environmental conditions or indirectly by improving tolerance against salinity stress. In this study, the protective role of silicon nanoparticles (SiNPs) was determined in two rice genotypes, N-22 and Super-Bas, differing in salinity tolerance. The SiNPs were confirmed through standard material characterization techniques, which showed the production of spherical-shaped crystalline SiNPs with a size in the range of 14.98–23.74 nm, respectively. Salinity stress adversely affected the morphological and physiological parameters of both varieties, with Super-Bas being more affected. Salt stress disturbed the ionic balance by minimizing the uptake of K+ and Ca2+ contents and increased the uptake of Na+ in plants. Exogenous SiNPs alleviated the toxic effects of salt stress and promoted the growth of both N-22 and Super-Bas, chlorophyll contents (16% and 13%), carotenoids (15% and 11%), total soluble protein contents (21% and 18%), and the activities of antioxidant enzymes. Expression analysis from quantitative real-time PCR showed that SiNPs relieved plants from oxidative bursts by triggering the expression of HKT genes. Overall, these findings demonstrate that SiNPs significantly alleviated salinity stress by triggering physiological and genetic repair mechanisms, offering a potential solution for food security.

A Single-Step Bottom-up Approach for Synthesis of Highly Uniform Mie-Resonant Crystalline Semiconductor Particles at Visible Wavelengths.

Optically Mie-resonant crystalline silicon nanoparticles have long attracted interest for their unique scattering behaviors. Here, we report a bottom-up nonthermal plasma process that produces highly monodisperse particles, with diameters controllable between 60 and 214 nm, by temporarily electrostatically trapping nanoparticles inside a continuous-flow plasma reactor. The particle size is tuned by adjusting the gas residence time in the reactor. By dispersing the nanoparticles in water, optical extinction measurements indicate colloidal solutions of a particle-based metafluid in which particles support both strong magnetic and electric dipole resonances at visible wavelengths. The spectral overlap of the electric and magnetic resonances gives rise to directional Kerker scattering. The extinction measurements show excellent agreement with Mie theory, supporting the idea that the fabrication process enables particles with narrow distributions in size, shape, and composition. This single-step gas-phase process can also produce Mie-resonant nanoparticles of dielectric materials other than silicon and directly deposit them on the desired substrates.

(Invited, Digital Presentation) Enhancement of Magnetic Dipole Transition of Molecules By Silicon Nanoparticle Nanoantenna

A nanoantenna is a nanodevice that manipulates light propagation and enhances light-matter interaction at the nanoscale. Integration of an emitter into a nanoantenna capable of increasing local density of photonic states at the emission wavelength results in the enhanced spontaneous emission rate (Purcell effect). The most widely studied nanoantennas for the Purcell enhancement are plasmonic nanoantennas made from gold or silver nanostructures supporting surface plasmon resonances. In most cases, nanoantennas have been used for the enhancement of electric dipole-allowed transition of a molecule. In addition, recently, nanoantennas capable of enhancing magnetic dipole transition of a molecule are attracting attention. For the magnetic Purcell enhancement, nanoantennas have to have magnetic resonances at the optical frequency. Although it is possible to achieve magnetic resonances at the optical frequency by plasmonic nanostructures, the inherent absorption loss of noble metals limits the magnetic Purcell enhancement. On the other hand, nanoparticles of high refractive index dielectrics inherently have low-loss magnetic-type Mie resonances at the optical frequency, and thus are potentially more attractive as a material to realize large magnetic Purcell enhancement.We have developed spherical nanoparticles of crystalline silicon (Si) having the magnetic dipole (MD) and quadrupole (MQ) Mie resonances at the optical frequency [1]. In this work, to demonstrate the potential of a Si nanoparticle as a nanoantenna for the magnetic Purcell enhancement, we develop a composite nanoparticle, that is, a Si nanosphere decorated with europium ion (Eu3+) complexes, in which magnetic dipole emission of Eu3+ is efficiently coupled to the magnetic Mie modes of the nanosphere [2]. We systematically investigate the light scattering and photoluminescence spectra of the coupled system by means of single particle spectroscopy. The results are shown in Figure 1. By tuning the MQ Mie resonance of a Si nanosphere to the 5D0-7F1 magnetic dipole transition of Eu3+, the branching ratio between the magnetic and electric dipole (5D0-7F2) transitions is enhanced up to 7 times. The observed large magnetic Purcell enhancement offers an opportunity to develop novel fluorophores with enhanced magnetic dipole emission. Furthermore, the enhanced magnetic field of dielectric Mie resonators enhances otherwise very weak absorption due to magnetic dipole transition, and makes direct excitation of triplet states of a molecule possible [3]. Direct excitation of triplet states reduces photon energy necessary for energy conversion and chemical reactions utilizing a triplet state compared to a conventional process involving singlet-singlet excitation and singlet-triplet intersystem crossing.[1] H. Sugimoto, et. al., "Mie Resonator Color Inks of Monodispersed and Perfectly Spherical Crystalline Silicon Nanoparticles" Advanced Optical Materials, 8 (2020) 2000033.[2] H. Sugimoto, and Minoru Fujii, "Magnetic Purcell Enhancement by Magnetic Quadrupole Resonance of Dielectric Nanosphere Antenna", ACS Photonics, 8 (2021) 1794.[3] H. Sugimoto, et. al., "Direct Excitation of Triplet State of Molecule by Enhanced Magnetic Field of Dielectric Metasurfaces", Small, 2021, DOI: 10.1002/smll.202104458.Figure 1: Photoluminescence (red curves) and scattering (black curves) spectra of single Si naosphere-Eu3+ complex composite nanoparticles with different Si nanosphere diameters. The diameters are shown at the right end of the figure. Figure 1

(De)Lithiation and Strain Mechanism in Crystalline Ge Nanoparticles.

Germanium is a promising active material for high energy density anodes in Li-ion batteries thanks to its good Li-ion conduction and mechanical properties. However, a deep understanding of the (de)lithiation mechanism of Ge requires advanced characterizations to correlate structural and chemical evolution during charge and discharge. Here we report a combined operando X-ray diffraction (XRD) and ex situ 7Li solid-state NMR investigation performed on crystalline germanium nanoparticles (c-Ge Nps) based anodes during partial and complete cycling at C/10 versus Li metal. High-resolution XRD data, acquired along three successive partial cycles, revealed the formation process of crystalline core-amorphous shell particles and their associated strain behavior, demonstrating the reversibility of the c-Ge lattice strain, unlike what is observed in the crystalline silicon nanoparticles. Moreover, the crystalline and amorphous lithiated phases formed during a complete lithiation cycle are identified. Amorphous Li7Ge3 and Li7Ge2 are formed successively, followed by the appearance of crystalline Li15Ge4 (c-Li15Ge4) at the end of lithiation. These results highlight the enhanced mechanical properties of germanium compared to silicon, which can mitigate pulverization and increase structural stability, in the perspective for developing high-performance anodes.

Broadband, Angle- and Polarization-Invariant Antireflective and Absorbing Films by a Scalable Synthesis of Monodisperse Silicon Nanoparticles.

Optically induced magnetic resonances (OMRs) are highly tunable scattering states that cannot be reproduced in systems that only support electric resonances, such as in metals, lossy, or low-index materials. Despite offering unique scattering and coupling behavior, the study of OMRs in thin films has been limited by synthesis and simulation constraints. We report on the absorption and scattering response of OMR-based thin films composed of monodisperse crystalline silicon nanoparticles synthesized using a scalable nonthermal plasma growth technique and tractable simulation framework. The synthesis is solvent and ligand free, ensuring minimal contamination, and crystalline particles form with high yield and a narrow size distribution at close to room temperature. Using a scalable high-throughput deposition method, we deposit random particle films, without the need of a solid host matrix, showing near complete blackbody absorption at the collective OMR. This is achieved using 70% less material than an optimized antireflective-coated crystalline silicon thin film. The film exhibits strongly directional forward scattering with very low reflectivity, thus giving rise to angle- and polarization-insensitive antireflection properties across the visible spectrum. We find that, while commonly used effective medium models cannot capture the optical response, a modified effective medium accounting for multipole resonances and interparticle coupling shows excellent agreement with experiment. The effective permittivity and permeability are written in a mode and cluster resolved form, providing useful insight into how individual resonances and nanoparticle clusters affect the overall film response. Electric and magnetic-mode coupling show dramatically different behavior, resulting in uniquely different spectral broadening.

Characterization of iron-doped crystalline silicon nanoparticles and their modification with citrate anions for in vivo applications

Objectives. This paper presents data on the development and study of the structural properties of iron-doped crystalline silicon (nc-Si/SiOx/Fe) nanoparticles obtained using the plasma-chemical method for application in magnetic resonance imaging diagnostics and treatment of oncological diseases. This work aimed to use a variety of analytical methods to study the structural properties of nc-Si/SiOx/Fe and their colloidal stabilization with citrate anions for in vivo applications.Methods. Silicon nanoparticles obtained via the plasma-chemical synthesis method were characterized by laser spark emission spectroscopy, atomic emission spectroscopy, Fouriertransform infrared spectroscopy, and X-ray photoelectron spectroscopy. The hydrodynamic diameter of the nanoparticles was estimated using dynamic light scattering. The toxicity of the nanoparticles was investigated using a colorimetric MTT test for the cell metabolic activity. Elemental iron with different Fe/Si atomic ratios was added to the feedstock during loading.Results. The particles were shown to have a large silicon core covered by a relatively thin layer of intermediate oxides (interface) and an amorphous oxide shell, which is silicon oxide with different oxidation states SiOx (0 ≤ x ≤ 2). The samples had an iron content of 0.8–1.8 at %. Colloidal solutions of the nanoparticles stabilized by citrate anions were obtained and characterized. According to the analysis of the cytotoxicity of the modified nanosilicon particles using monoclonal K562 human erythroleukemia cells, no toxicity was found for cells in culture at particle concentrations of up to 5 µg/mL.Conclusions. Since the obtained modified particles are nontoxic, they can be used in in vivo theranostic applications.

Novel Synthesis of Si/Rgo Anode Materials for Lithium-Ion Batteries Via Reactive Spray Drying

In recent years, lithium-ion batteries (LiB) with Si anodes attracted increasing attention, particularly due to their high specific energy density. An optimization of this characteristic is extremely important for their extended use as power source not only in portable devices but also in larger applications, such as electric vehicles.The main disadvantage of using silicon as anode material in LIBs is its high volume expansion during lithiation, which leads to various negative effects, such as pulverization, delamination, and an unstable solid electrolyte interface (SEI) [1]. This eventually results in a reduced cell performance, especially in terms of cycling stability. One promising approach to mitigate these issues is to wrap silicon nanoparticles in a graphene-like matrix via spray drying. A suitable starting material for this approach is graphite oxide (GO) [2, 3, 4].In all processes described so far, an additional time- and energy-intensive calcination step is necessary to obtain the graphene-like “reduced graphene oxide” (rGO) structure. Here, we present a new reactive spray drying process for a simplified one-step synthesis of Si/rGO composites using water as solvent. To design the reactor properly, it is necessary to understand the reaction kinetics. Therefore, the reaction is investigated by simultaneous thermal analysis (STA) in various atmospheres. We can describe the thermal decomposition of GO to rGO as a second-order reaction (Arrhenius behaviour). The STA data also show that the additional presence of water in the atmosphere due to the one-step synthesis is negligible at temperatures below 600 °C for both the reaction of GO and the unwanted additional oxidation of Si. We use crystalline silicon nanoparticles (dp ≈ 100 nm) and micrometer-sized graphite oxide prepared via modified hummers method as starting materials. Si and GO are dispersed in water and ultrasonically treated to obtain a stable dispersion. The prepared dispersion is sprayed continuously into a hot reactor (> 500 °C), where the droplets dry in the first reaction zone, forming a Si/GO composite, followed by a thermal decomposition reaction to Si/rGO in the second one. The Si/rGO particles are separated from the hot gas stream via a cyclone. To prevent oxidation, the entire system is operated in an inert atmosphere. To evaluate the electrochemical performance, the as-prepared composites are coated on a copper foil using a water-based binder mixture of styrene-butadiene rubber and caboxymethyl cellulose (SBR:CMC = 1:1). The electrodes are cycled against Li/Li+ in a half cell setup.The specific capacity after cell formation is raised from 275 mAh g-1 for GO to 335 mAh g-1 for rGO due to the reactive spray drying process. A Si/rGO composite with a Si content of 11.5 % shows a capacity of 505 mAh g-1 after the formation. Future studies will focus on further reduction of the oxygen content of rGO and an improved integration of silicon in the carbon matrix.[1] J.W. Choi, D. Aurbach, Nature Reviews Materials 2016, 1 (4), 16013.[2] M. Li et al., Journal of Power Sources 2014, 248, 721-728.[3] J. Lee, J.H. Moon, Korean Journal of Chemical Engineering 2017, 34 (12), 3195-3199.[4] Y. Huang et al., Energy Fuels 2020, 34 (6), 7639-7647. Figure 1

Formation and quantitative analysis of internal structure of Si nanoparticles developed via bead-milling

Amorphous silicon nanomaterial is isotropic on the macroscale and can effectively inhibit the expansion/contraction during lithiation/delithiation processes, which remarkably improves the cycle performance of Li-ion batteries. Bead-milling is a simple, cost-effective, and scalable method for manufacturing amorphous and/or crystalline silicon nanoparticles. In this work, the internal structure of Si nanoparticles prepared by bead-milling was found to consist of amorphous and nanocrystalline silicon as well as amorphous silicon oxide. X-ray diffraction patterns and Raman spectra are used to calculate the average crystallite size and estimate the degree of crystallization and amorphization of silicon. The quantitative analysis of amorphous silicon oxide is carried out through x-ray photoelectron spectroscopy characterization and oxygen content measuring. It was found that the average particle size (D50) and the crystallite size were reduced to 91 and 3.7 nm, respectively, from 4.06 μm and 50.6 nm before bead-milling, and the degree of amorphization and oxygen content increased to 85.7% and 7.38%, respectively, from 37.5% and 0.12% before bead-milling. It is demonstrated that the longer the milling time, the smaller the sizes of particles and crystals and the higher the ratio of the amorphous phase. However, it inversely causes side-effects such as the increase in oxidization of Si nanoparticles and the increase in content of ZrO2 impurity.

High-performance anode of lithium ion batteries with plasma-prepared silicon nanoparticles and a three-component binder

The crystalline silicon nanoparticles coated with an amorphous silicon layer was prepared by continuously pyrolysing the mixture of silane and hydrogen in a non-thermal arc plasma reactor. The hydrogen in the gas mixture effectively controls the thickness of the amorphous silicon layer and further improves the electrochemical performance of the silicon anode. The mechanism of the hydrogen was investigated by experiments. At the same time, a three-component polymer binder was concocted and introduced to tolerate the volume expansion of silicon effectively. Combining the silicon nanoparticles prepared at the optimal conditions with the novel polymer binder, the resulting silicon anode exhibits excellent electrochemical performance of 2120 mAh g−1 at 400 mA g−1 after 100 cycles.

Silicon nanoparticles: a new and enhanced operational material for nitrophenol sensing

The environmental problem is a big issue in the current scenario because the human beings are affected via natural or manmade sources. Over a range of industrial pollutents, the nitrophenol (referred to as 4-NP) known as harmful industrial chemical for the environment and listed as a carcinogenic compound for human health. To keep this view the present manuscript describes the formation of highly crystalline silicon nanoparticles (Si-NPs) and applied for the electrochemical sensing of 4-NP. The Si-NPs exhibit numerous applications in various directions such as catalyst, solar cells, LEDs, batteries etc. The Si-NPs were formed from the physical approach with using argon-silane mixture in a gas chamber with impregnation of microwave plasma. The processed material was examined through various techniques such as X-ray diffraction pattern (XRD), field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM) and Fourier transform spectroscopy (FTIR). It reveals from the acquired analysis that the size of each NP is ~ 4 nm with good structural and chemical characteristics and applied as a film form against to check the sensing of 4-NP with three electrode system. The electrochemical studies were conducted through cyclic voltammetry (CV) in terms of their low to high concentration (7.8, 15.62, 31. 25, 62.25, 250, 500, 1000 μM in PBS), scan rate at variable potential was accessed from 5 to 100 mV with Si-NPs based electrode. The sustainability, reproducibility and efficacy of the formed sensor (Si-NPs/GCE) was examined in occurrence with 4-NP (62.25 μM) for seven consecutive cycles. Including to this, chronoamperometry (0 to 1500 s) and electrochemical impedance spectra (7.8–1000 μM in PBS) were also analyzed. On the basis of acquired results and discussion a probable mechanism was also described.

Stimulated Raman Scattering from Mie-Resonant Subwavelength Nanoparticles.

Resonant dielectric structures have emerged recently as a new platform for subwavelength nonplasmonic photonics. It was suggested and demonstrated that magnetic and electric Mie resonances can enhance substantially many effects at the nanoscale including spontaneous Raman scattering. Here, we demonstrate stimulated Raman scattering (SRS) for isolated crystalline silicon (c-Si) nanoparticles and observe experimentally a transition from spontaneous to stimulated scattering manifested in a nonlinear growth of the signal intensity above a certain pump threshold. At the Mie resonance, the light gets confined into a low volume of the resonant mode with enhanced electromagnetic fields inside the c-Si nanoparticle due to its high refractive index, which leads to an overall strong SRS signal at low pump intensities. Our finding paves the way for the development of efficient Raman nanolasers for multifunctional photonic metadevices.

Silicon Nanoparticle Films Infilled with Al2O3 Using Atomic Layer Deposition for Photosensor, Light Emission, and Photovoltaic Applications

Solution-processed thin films of crystalline silicon nanoparticles (Si NPs) have a great potential for a wide variety of electronic and optoelectronic applications. However, such films are inherent...

Silicon nanoparticles with iron impurities for multifunctional applications

Crystalline silicon (Si) nanoparticles (NPs) doped with iron (Fe) in the range from 0.02 to 2.5 at.% were prepared by plasma-ablative synthesis and were investigated by means of the transmission electron microscopy, X-ray diffraction (XRD), dynamic light scattering (DLS), infrared spectroscopy and nuclear magnetic resonance relaxometry. While the nanocrystal size in Si:Fe NPs did not depend significantly on Fe content, the hydrodynamic diameter of NPs in aqueous suspensions increases from 50 to 180[Formula: see text]nm. Both the transverse and longitudinal proton relaxation time were found to decrease in the prepared suspensions of Si:Fe NPs. Maximal shortening of the transverse relaxion was observed for Si:Fe NPs with 0.2 at.% of Fe and the relaxation rate was almost linearly proportional to the NP concentration. Both these findings and in vivo tests indicate that Si:Fe NPs are promising for biomedical applications in magnetic resonance imaging (MRI) and therapy of cancer.

Assembly, Stability, and Electrical Properties of Sparse Crystalline Silicon Nanoparticle Networks Applied to Solution-Processed Field-Effect Transistors

Thin films of crystalline silicon nanoparticles (Si NPs) processed from liquid dispersions of NPs (NP inks) using printing-type deposition methods are currently being intensively investigated for t...

Opto-structural properties of Si-rich SiNx with different stoichiometry

This study deals with the fabrication and characterization of silicon nanoparticles in a SiNx dielectric matrix to have thin films of different gap energies, films essentially based on silicon. Hydrogenated silicon-rich nitride films SiNx:H with different stoichiometry X = N/Si were grown on Si substrate using industrial low-frequency plasma-enhanced chemical vapor deposition (LF-PECVD). Optical, electrical, and structural properties of the obtained films have been studied after rapid thermal annealing at 950 °C. The GIXRD and Raman analysis demonstrate that the films contain simultaneously the hexagonal β-Si3N4 phase and crystalline silicon nanoparticles and the average size of silicon nanocrystallites is within the range of 2.5–11 nm according to the stoichiometry. A strong visible photoluminescence (PL) can be observed in silicon nitride and the evolution of PL with the NH3/SiH4 ratio is correlated with the evolution of the structure. The layers having a luminescence in the visible region present a photocurrent (PC) in the high-energy region. PC spectroscopy has clearly demonstrated the existence of increased absorption on the high-energy side associated with Si-Ncs and confirms the potential of Si-Ncs for photovoltaic applications.

Large-Scale and Low-Cost Fabrication of Silicon Mie Resonators.

High index dielectric nanoparticles have been proposed for many different applications. However, widespread utilization in practice also requires large-scale production methods for crystalline silicon nanoparticles, with engineered optical properties in a low-cost manner. Here, we demonstrate a facile, low-cost, and large-scale fabrication method of crystalline silicon colloidal Mie resonators in water, using a blender. The obtained nanoparticles are polydisperse with an almost spherical shape and the diameters controlled in the range 100-200 nm by a centrifugation process. Then the size distribution of silicon nanoparticles enables broad extinction from UV to near-infrared, confirmed by Mie theory when considering the size distribution in the calculations. Thanks to photolithographic and drop-cast deposition techniques to locate the position on a substrate of the colloidal nanoparticles, we experimentally demonstrate that the individual silicon nanoresonators show strong electric and magnetic Mie resonances in the visible range.

Structural and optical properties of nc-Si in SiOxNy matrix deposited by laser ablation for optoelectronic applications

In this work, we show the development of SiOxNy (silicon oxynitride) thin films using the laser ablation technique. Instead of commonly used precursor materials SiH4 and NH3 or N2, hereby, we report the deposition using crystalline silicon targets and N2 precursors. The experiment was carried out in such a way that we can eradicate the drawback of hydrogen concentration in the thin films (due to silane precursor) and finally, adequate deposition conditions were found which allowed obtaining the material with suitable optoelectronic properties. Numerous experiments varying the deposition pressure (0.4–6 Pa) were carried out making possible the formation of different kinds of the stoichiometry of the material. For one set of thin films (lower pressure), silicon rich silicon-oxynitride thin films (SRSON) were obtained, whereas, for the other half (higher pressure) it was oxygen-rich silicon oxynitride (ORSON) kind of stoichiometry. Fourier transform infrared spectroscopy (FTIR) shown the dominance of Si-N bonds for the samples deposited at lower pressure, whereas, for the samples deposited at higher pressure shift in the absorption bands towards Si-O bonds was observed. For the middle-pressure range ;(0.8–2 Pa) depending on the composition of SiOxNy thin films, a band gap variation from 2.08 eV to 4.36 eV was obtained. The same could be correlated with the Si, N and O ratios in the deposited thin films. From the XPS analysis, it was found that the Si content was found to be reduced, whereas, N content was found to be varying randomly as an effect of an increase in the pressure. Lately, it also shown an overall increase in the O concentration. For the same range of pressure value (0.8–2 Pa), Raman, X-ray diffraction (XRD) and HRTEM analysis illustrated the formation of crystalline silicon nanoparticles from the as-deposited thin films. Overall, confirmation of Si nanoparticles embedded in an amorphous matrix of SiOxNy can be established from these analyses. Photoluminescence (PL) spectra also demonstrated the visible emission which remarks the quality of material and its tendency for the optical applications. Intense and homogenous PL was observed for samples grown at 2 Pa. Using unique deposition method presented in this manuscript with a great control over the composition and hence, on the optoelectronic properties of Si related thin films can be used for the future optoelectronic applications.

Effect of Ni nickel coated porous Si buffers layer on the structural and opto-electronic properties of silicon thin films

In this paper we present an extensive investigation of the effect of Ni metallization on the structural and opto-electronic properties of a dual porous silicon layers elaborated by electrochemical etching. Amorphous silicon thin films were deposited by plasma-enhanced chemical vapor deposition on the metalized porous layer. The microstructure of porous silicon films was systematically studied by atomic force microscopy (AFM), X-ray diffraction (XRD), Raman spectroscopy and Fourier transform infrared spectroscopy (FTIR). It was found that the structure of the porous layer metalized Nickel (SipMNi) strongly depends on the porosity level and on the immersion time in the Ni solution. The optical constants (n and k as a function of wavelength) of the SipMNi were obtained using variable angle spectroscopic ellipsometry (SE) in the UV–vis–NIR regions. The SE spectrum of the SipMNi was modeled as a mixture of void, crystalline silicon and Ni nanoparticles using the Cauchy model approximation. The electrical conductivity, conduction mechanism, relaxation model of the SipMNi/Si samples were studied by means of the impedance spectroscopy technique at various temperatures (340–410 °C). At high frequency a semiconductor to metallic behavior transition has been observed. A full correlation between the microstructure and opto-electrical properties has been presented. It was found that this simple and easy method is effective to produce silicon thin films with high quality suitable for opto-electronic applications.

Silicon quantum dots for energetic material applications

In its history as an energetic material, porous silicon has demonstrated flame speeds in excess of 3 km s−1, tunable combustion behavior, and high energy output, which in theory makes it a very attractive energetic system. In practice, its application within the field is limited by porous silicon's typical substrate-adhered form and caustic chemical processing requirements that limit how and when porous silicon is made. In this work, we have relieved porous silicon of these constraints by creating reactive silicon quantum dots from free-standing porous silicon films. The resulting material is composed of crystalline silicon nanoparticles with diameters as small as 2 nm that retain the chemical properties of the original films including the SiH2 termination layer. The fabricated silicon particles were characterized using FTIR Spectroscopy, TEM, and EDS for determining the size and the chemical composition. For testing as an energetic material fuel, porous silicon was mixed with an oft used oxidizer, sodium perchlorate. During open-channel combustion tests, silicon quantum dots mixed with sodium perchlorate demonstrated flame speeds over 2.5 km s−1, while bomb calorimetry tests showed an average heat of combustion of 7.4 kJ g−1. These results demonstrate the ability to retain the porous silicon material properties that allow for highly energetic material reactions to occur, despite the additional processing steps to create silicon quantum dots. This opens the door for the use of porous silicon in the bulk of the energetic material application space, much of which was previously limited due to the substrate-attached nature of typical porous silicon.