Preparation Of Porous Silicon Research Articles

Preparation of porous silicon using magnesiothermic reduction of porous silica glass and electrode characteristics for lithium-ion batteries

Preparation of porous silicon using magnesiothermic reduction of porous silica glass and electrode characteristics for lithium-ion batteries

Preparation of porous silicon by Ag-assisted chemical etching in non-filling type carbon shell for high performance lithium-ion batteries

Silicon is regarded as one of the most potential anode materials due to its high specific capacity (4200 mAh g−1), but some disadvantages such as low conductivity and large volume expansion effect cannot be ignored. Here, a silver etched and non-filling type carbon coating porous silicon (pSi/Ag@C) anode material is proposed to solve the problems. The porous structure can alleviate the volume change of the silicon material during charging and discharging process. It is worth mentioning that, compared with the traditional carbon coating, the novel non-filled carbon coating layer reserves space for the volume expansion of silicon, which can prevent the rupture of carbon layer. The pSi/Ag@C anode material maintains a high discharge specific capacity of 904 mAh g−1 after 200 cycles at a current density of 0.5 C (1 C = 4.2 A g−1), much better than the 333.1 mAh g−1 of Si-raw material.

Green utilization of silicon slime: recovery of Si and synergetic preparation of porous silicon as lithium-ion battery anode materials

Green utilization of silicon slime: recovery of Si and synergetic preparation of porous silicon as lithium-ion battery anode materials

Preparation of porous silicon by vacuum sublimation dealloying method

Porous silicon has many potential applications in lithium-ion battery anodes and medical sensors, owing to its high specific capacity and photoluminescence properties. In this work, porous silicon is prepared with vacuum sublimation dealloying method by heating Mg2Si precursor to 750 °C and holding it for 1 h under vacuum. The relationship between pressure and temperature, as well as the characteristics of the longitudinal section of condensation products show that the sublimation process of Mg in Mg2Si precursor can be divided into three stages. The aperture distribution curves of the Brunauer-Emmett-Teller (BET) and Mercury Intrusion Porosimetry (MIP) of porous silicon show that the pore size of mesopores is between 3.1 ± 0.2 and 6.3 ± 0.2 nm, and that of macropores is between 351.6 ± 1 and 2101.7 ± 1 nm. The prepared porous silicon has pores with frost flower shaped and shrub-shaped structures in the interior and polygonal contoured pores on the surface. This paper aims to investigate the reaction mechanism of vacuum sublimation dealloying method and provide a foundation for optimizing the performance of porous silicon in applications such as lithium-ion battery anodes and hydrogen generating materials by studying its unique pore structure.

High-performance silicon from quartz product waste as an anode material for Li-ion batteries

As the demand for quartz products increases year over year, the increase in the production of quartz waste has gradually contributed to increases in resource waste and environmental pollution. To recover quartz from spent quartz product waste and realize its high-value utilization, quartz waste ($0.15/kg) was used as the raw material to prepare high-performance porous silicon as an anode material for lithium ion batteries via a simple high-energy ball-milling method, followed by magnesiothermic reduction. The formation mechanism of silicon from quartz particles with different particle sizes during magnesiothermic reduction was investigated by X-ray diffraction, field-emission scanning electron microscopy, and other methods. The preparation of porous silicon without residual impurities was determined to be highly dependent on the size of the quartz particles after high-energy ball milling. When formed into an anode material for electrochemical measurements, the pure porous silicon (Si-4) anode delivered an initial specific charge capacity of 2712 mAh·g−1 with a high initial Coulombic efficiency of 81% at a current density of 200 mA g−1. The specific capacity was sustained at 923 mAh·g−1 for 300 cycles at a current density of 4000 mA g−1. The results reported herein highlight the feasibility of recovering spent quartz resources for harmless treatment and high-value utilization.

Structural properties of porous silicon obtained with laser photoetching assisted by computerized numeric control

This study presents the preparation of porous silicon (PS) using the photoetching technique. The light source was a laser with a 405 nm wavelength. Hydrofluoric acid, hydrogen peroxide, and ethanol were used in the process. An approach to forming PS in a selected area was also studied, in which a computational control of the laser movement was developed. A laser allows for the formation of PS in short period of time using n-type crystalline silicon (c-Si) as a substrate. Photosynthesized PS shows similar characteristics (physical and chemical) to anodized PS. Raman scattering showed a broadening of the peak centered at 525 cm−1, this behavior is related to the formation of PS. Micro-Fourier transform infrared spectroscopy showed bands related to Si-H wagging and SiH2 bending vibrations, these types of bonds were generated during the porosification process. The morphologic characteristics were defined by scanning electron microscopy (SEM) and revealed that the porous structures depend on the potency of the laser used. The topography of the surface confirms PS formation. SEM analysis demonstrated that pores with diameters of 60 and 300 nm can be obtained. Energy-dispersive x-ray spectroscopy showed an increase in oxygen in the PS due to the oxidation process following photoetching. The x-ray diffraction showed that this type of etching eliminates the induced tension in the c-Si grain edges due to PS formation.

Effect of current density on the porous silicon preparation as gas sensors**

AbstractIn this study, porous silicon (PSi) was used to manufacture gas sensors for acetone and ethanol. Samples of PSi were successfully prepared by photoelectrochemical etching and applied as an acetone and ethanol gas sensor at room temperature at various current densities J= 12, 24 and 30 mA/cm2with an etching time of 10 min and hydrofluoric acid concentration of 40%. Well-ordered n-type PSi (100) was carefully studied for its chemical composition, surface structure and bond configuration of the surface via X-ray diffraction, atomic force microscopy, Fourier transform infrared spectroscopy and photoluminescence tests. Results showed that the best sensitivity of PSi was to acetone gas than to ethanol under the same conditions at an etching current density of 30 mA/cm2, reaching about 2.413 at a concentration of 500 parts per million. The PSi layers served as low-cost and high-quality acetone gas sensors. Thus, PSi can be used to replace expensive materials used in gas sensors that function at low temperatures, including room temperature. The material has an exceptionally high surface-to-volume ratio (increasing surface area) and demonstrates ease of fabrication and compatibility with manufacturing processes of silicon microelectronics.

(Invited) In-Situ Monitoring of Luminescence and Oxidation of Porous Silicon in Liquid Electrolytes with Photoconduction

Silicon can be made porous by electrochemical (anodization) etching in hydrofluoric acid (HF). This is the most controlled and used technique for the preparation of porous silicon (PSi). The porous structure depends on several factors, such as silicon resistivity and type, as well as HF concentration and anodization current. In the case of lightly-doped p-type silicon, uniform sponge-like nano-structures can be formed. This type of PSi layer is characterized in particular by its porosity and thickness. PSi is interesting for a variety of properties, some related to quantum confinement in its nanostructure, such as luminescence and porosity-dependent optical absorption, refractive index and surface area. It has potential applications in optoelectronics, photovoltaics, medicine and sensing.Recently, we have made use of the particular behavior of PSi photoconduction in an electrolyte: when PSi is illuminated, only the charge carriers photogenerated in the Si substrate contribute to the measured photocurrent, and thus, the photocurrent is a measure of the optical transmission of PSi. This behavior allowed us to measure the PSi optical constants for various optical wavelengths and PSi porosities in situ in HF and thus for the most pristine form of PSi and avoiding all the problems related to the drying and handling of high-porosity PSi free-standing layers1. We have also used the photoconduction to study the chemical etching of PSi in HF. We could monitor the etching as it proceeded and developed a model that allowed us to derive the HF-dependent etching rates and the absorption coefficient of PSi for a large range of porosities not explored so far, from as-prepared to close to 100% porosity (PSi fully dissolved)2. Finally, we have also made use of the photoconduction technique to understand the photoetching of PSi in HF by monochromatic light.3 In this paper, we use the photoconduction technique to monitor the evolution of different types of oxidation processes of PSi in acid solutions. The photoluminescence is also acquired in-situ. The different oxidation processes studied here are: chemical oxidation in different solutions, photo-assisted oxidation by monochromatic light, and electrochemical oxidation. The photoconduction technique allowed for a good understanding of the oxidation progress and the evolution of the oxidation rates over reaction time. Moreover, the monitoring of the photoluminescence, coupled to the in-situ derivation of the optical absorption provides a way to optimize the reaction time for achieving maximum luminescence efficiency.An example is shown in Fig. 1. It shows the photocurrent (at 405 nm illumination)-time plot for a 5-μm thick PSi layer of initial porosity 68% oxidized in H2SO4 0.5M. The photocurrent, signature of the optical absorption, increases as the oxidation progresses since the formed oxide is transparent at the 405 nm light. Here, the oxidation does not proceed up to full PSi oxidation, therefore the photocurrent does not reach full saturation. The photoluminescence was also recorded and reached its maximum at ~ 65 h (blue star on the plot). 1 B. Gelloz, H. Fuwa, and L. H. Jin, Ecs Journal of Solid State Science and Technology 5 (3), P190 (2016). 2 B. Gelloz, K. Ichimura, H. Fuwa, E. Kondoh, and L. Jin, Ecs Journal of Solid State Science and Technology 6 (1), R1 (2017). 3 B. Gelloz, H. Fuwa, E. Kondoh, and L. Jin, Ecs Journal of Solid State Science and Technology 7 (12), P730 (2018). Figure 1

Novel Si nanostructures via Ag-assisted chemical etching route on single and polycrystalline substrates

Silicon is the most widely used semiconductor material for electronics and energy related applications. Herein, different Si nanostructures with various shapes, sizes and morphologies are fabricated by a simple, low-cost and versatile metal‐assisted chemical etching (MACE) technique using Ag nanoparticles as a catalyst, deposited on Si surface. The influence of etching time, temperature and intrinsic properties of the silicon substrate (e.g., orientation, crystallinity) on the basic process are studied. Fast preparation of porous silicon (PSi) was achieved on Si 〈100〉 at room temperature after only 30 s of exposure to etching solution. Meanwhile increased etching time led to increase the pore diameter and a well-aligned SiNWs was obtained after 10 min. However, the exposure of Si 〈100〉 to the etching solution at 60 °C for only 2 min produced a homogenous and dense SiNWs layer. Additionally, the orientation of Si wafer was found to play a key role during the MACE process. Particularly, the MACE has no effect on Si 〈111〉 before 30 min whereas a zigzage PSi was formed. PSi nanostructures with straight and zigzag structures were successfully fabricated for the first time in addition to well-aligned, uniform and vertical Si nanowires (SiNWs) with smooth and polygonal shapes. The as-prepared Si nanostructures are characterized by various techniques including field emission-scanning electron microscopy (FE-SEM), X-ray photoelectron spectroscopy (XPS), UV–vis. and photoluminescence spectroscopy (PL). The optical properties of as-prepared Si nanostructures are enhanced and the reasons for this improvement and its correlation with the morphology difference are presented and discussed.

Research on micro-cavity structure processing technology based on porous silicon

Aiming at the problem of heterogeneity of sealed cavity in silicon microstructure processing technology, the technology of preparing micro-cavity by using porous silicon sacrificial layer is proposed. The effect of current density on the preparation of porous silicon and the effect of porous silicon with different porosity on the formation of micro-cavity in the preparation process of porous silicon were studied. Different process parameters were selected for experiments and the prepared micro-cavities were tested and analyzed. According to the test results, the suitable electrochemical corrosion process parameters were selected to prepare porous silicon, and the micro-cavity was realized by changing the process parameters, which greatly increased the application fields of micro-sensors and micro-actuators.

Porous Silicon Preparation by Electrochemical Etching in Ionic Liquids

Anodic etching of n-type {111} silicon in ionic liquid (IL) systems ([RMIM][X], R = H, Bu; X = BF4–, PF6–), realized under galvanostatic conditions and at room temperature, allowed the formation of...

Preparation of Porous Silicon by Electrochemical Etching Methods and its Morphological and Optical Properties

Preparation of Porous Silicon by Electrochemical Etching Methods and its Morphological and Optical Properties

Facile preparation of porous silicon from cost-wise silicon powder as effective catalyst for reduction of p-nitrophenol

For the first time, a metalloid is used for the reduction of p-nitrophenol to p-aminophenol. The porous silicon (PS) was prepared via chemical etching technique using HF/HNO3/H2O with a ratio of (1/5/10 v/v) as the chemical etchant. The Si: etchant ratio and etching time was investigated. Higher Si: etchant ratios and longer etching times resulted in an increase in the surface area of the PS. The various PS and silicon powder samples were then tested for the reduction of p-nitrophenol. It was found that the reduction of p-nitrophenol occurs approximately 8 times faster when PS was employed in comparison to silicon. The reduction rates increased with increasing surface area of the PS. Similar trends were observed when the amount of catalyst was added. The PS also shows good reusability for the catalytic reduction of p-nitrophenol.

A Combined Process for the Degradation of Azo-Dyes and Efficient Removal of Aromatic Amines Using Porous Silicon Supported Porous Ruthenium Nanocatalyst

Herein, we present a facile route for the preparation of porous silicon supported porous ruthenium nanoparticle system (Si@p-RuNP) for efficient removal of azo-based dyes and aromatic amines from wastewater. The synthesized nanoparticles were characterized using different analytical techniques including high-resolution transmission electron microscopy, X-ray photoelectron spectroscopy, field-emission scanning electron microscopy, powder X-ray diffraction, Brunauer–Emmett–Teller analysis, etc. The Si@p-RuNP nanocatalytic system exhibits dual catalytic behavior for the reduction of –N═N– bond and oxidation of aromatic amines in aqueous solution. The porous nanostructured Si@p-RuNP exhibits excellent degradation efficacy for Congo red dye (44 cycles in 1 h) as compared to its solid analogue Si@RuNP (24 cycles in 1 h) in the presence of NaBH4. Also, the present nanocatalyst mimics the peroxidase-like activity toward oxidation of various aromatic amines to their corresponding polyamines at pH 5.0 in the presen...

(Invited) Photo-Assisted Etching of Porous Silicon Nanostructures in Hydrofluoric Acid Using Monochromatic Light

Silicon can be made porous by electrochemical (anodization) etching in hydrofluoric acid (HF). This is the most controlled and used technique for the preparation of porous silicon (PSi). The porous structure depends on several factors, such as silicon resistivity and type, as well as HF concentration and anodization current. In the case of lightly-doped p-type silicon, uniform sponge-like nano-structures can be formed. This type of PSi layer is characterized in particular by its porosity and thickness. PSi is interesting for a variety of properties, some related to quantum confinement in its nanostructure, such as luminescence and porosity-dependent refractive index and surface area. It has potential applications in optoelectronics, photovoltaics, medicine and sensing. The post-anodization behavior of PSi in various environments is of interest for stability and degradation evaluation. The evolution of PSi is sometimes made intentional in order to further tailor the PSi properties after anodization. Typically, the effects of PSi oxidation (mainly for stabilization purposes), etching (to increase the porosity) or degradation in various environments (typically for biotechnology) are sometimes studied. Recently, we have made use of a particular behavior of the PSi photoconduction in HF: when PSi is illuminated in HF, only the charge carriers photogenerated in the Si substrate contribute to the measured photocurrent, and thus, the photocurrent is a measure of the optical transmission of PSi. This behavior allowed us to measure the PSi optical constants for various optical wavelengths and PSi porosities in situ and thus for the most pristine form of PSi and avoiding all the problems related to the drying and handling of high-porosity PSi free-standing layers1. We have also used the photoconduction to study the chemical etching of PSi in HF. We could monitor the etching as it proceeded and developed a model that allowed us to derive the HF-dependent etching rates and the absorption coefficient of PSi for a large range of porosities not explored so far, from as-prepared to close to 100% porosity (PSi fully dissolved)2. A small degree of tuning of the photoluminescence (PL) band of PSi may be achieved by adjusting anodization conditions, but fine tuning remains difficult. A few attempts aiming at controlling the PL or understanding PSi PL in HF have been attempted by using post-anodization photo-assisted etching in HF. The photoetching process itself was not studied in much detail, and were focusing on as-formed luminescent PSi. A better understanding of the photoetching process would be welcome to get better control and understanding of the effects. In this paper, we show how the photoetching of PSi (initially luminescent or not) can be monitored and its rate evaluated using the photoconduction technique that we have used previously in other studies1 , 2. The photocurrent was continuously measured during the illumination of PSi by monochromatic light, which was inducing photoetching. As PSi was etched, the PSi absorption was decreasing, more light was transmitted to the substrate and, as a result, the photocurrent was increasing. Figure 1 shows results for an initial porosity of 62%, an illumination wavelength of 450 nm, and different PSi thicknesses. A saturation state is reached when the PSi layer does not absorb anymore at the illumination wavelength. The waves observed for 1 μm and 2 μm-thick layers were attributed to thin film optical interference. The curve for 16 μm-thick PSi was affected by reproducibility problems because of instabilities in the diffusion of species and hydrogen bubbles inside the pores. For clean photoetching study, 4-μm thick PSi layers were used. Figure 2 shows the time evolution of the photocurrent for 4 μm-thick PSi layers, with different illumination powers at 450 nm. As expected, the photocurrent at saturation is proportional to the incident illumination power. Solid lines are fits obtained using a model that will be presented. Two regimes were characterized, one in which the photoetch rate is limited by the supply of photo-generated holes at the Si surface, and another one where it is limited by the photoetching reaction. The maximum photoetch rate was derived. The evolution of the in depth porosity profile can be obtained from the model as well. The effects of a range of parameters will be presented. 1 B. Gelloz, H. Fuwa, and L. H. Jin, Ecs Journal of Solid State Science and Technology 5 (3), P190 (2016). 2 B. Gelloz, K. Ichimura, H. Fuwa, E. Kondoh, and L. Jin, Ecs Journal of Solid State Science and Technology 6 (1), R1 (2017). Figure 1

Study on Silicon Microstructure Processing Technology Based on Porous Silicon

Aiming at the heterogeneity of micro - sealed cavity in silicon microstructure processing technology, the technique of preparing micro - sealed cavity of porous silicon is proposed. The effects of different solutions, different substrate doping concentrations, different current densities, and different etching times on the rate, porosity, thickness and morphology of the prepared porous silicon were studied. The porous silicon was prepared by different process parameters and the prepared porous silicon was tested and analyzed. For the test results, optimize the process parameters and experiments. The experimental results show that the porous silicon can be controlled by optimizing the parameters of the etching solution and the doping concentration of the substrate, and the preparation of porous silicon with different porosity can be realized by different doping concentration, so as to realize the preparation of silicon micro-sealed cavity, to solve the sensor sensitive micro-sealed cavity structure heterogeneous problem, greatly increasing the application of the sensor.

Room-Temperature Solution Synthesis of Mesoporous Silicon for Lithium Ion Battery Anodes.

As an important optoelectronic and energy-storage material, porous silicon (PSi) has attracted great interest in various fields. The preparation of PSi, however, usually suffers from low yields and/or complicated syntheses. Herein, we report a facile solution method to prepare PSi with controllable high specific surface area. Commercial Zintl compound Mg2Si readily reacts with HSiCl3 in the presence of amines at room temperature to produce amorphous PSi in high yields, where in situ formed salt byproducts serve as templates to generate uniform mesopores of ca. 3.8 nm in diameter. After crystallization treatment at 700 °C in flow Ar gas for 40 min, the obtained crystalline PSi coated with carbon layers shows excellent electrochemical performance when served as lithium ion battery anodes. The reversible specific capacity is about 2250 mA h g-1 at 0.1 A g-1 and the capacity retention is maintained at 90% after cycling at high current density of 2 A g-1 for 320 times. This simple, facile preparation method is very promising and paves the way for massive production of porous Si as high-performance anodes in Li-ion battery industry or for other applications, such as drug delivery systems and catalysis.

Single Plant Derived Nanotechnology for Synergistic Antibacterial Therapies.

Multiple new approaches to tackle multidrug resistant infections are urgently needed and under evaluation. One nanotechnology-based approach to delivering new relevant therapeutics involves silicon accumulator plants serving as a viable silicon source in green routes for the fabrication of the nanoscale drug delivery carrier porous silicon (pSi). If the selected plant leaf components contain medicinally-active species as well, then a single substance can provide not only the nanoscale high surface area drug delivery carrier, but the drug itself. With this idea in mind, porous silicon was fabricated from joints of the silicon accumulator plant Bambuseae (Tabasheer) and loaded with an antibacterial extract originating from leaves of the same type of plant (Bambuseae arundinacea). Preparation of porous silicon from Tabasheer includes extraction of biogenic silica from the ground plant by calcination, followed by reduction with magnesium in the presence of sodium chloride, thereby acting as a thermal moderator that helps to retain the mesoporous structure of the feedstock. The purified product was characterized by a combination of scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDX), X-ray diffraction (XRD), Raman spectroscopy, transmission electron microscopy (TEM), and low temperature nitrogen gas adsorption measurements. Antimicrobial activity and minimum inhibitory concentration of a leaf extract of Bambuseae arundinacea was tested against the bacteria Escherichia Coli (E. Coli) and Staphylococcus aureus (S. Aureus), along with the fungus Candida albicans (C. Albicans). A S. aureus active ethanolic leaf extract was loaded into the above Tabasheer-derived porous silicon. Initial studies indicate sustained in vitro antibacterial activity of the extract-loaded plant derived pSi (25 wt %, TGA), as measured by disk diffusion inhibitory zone assays. Subsequent chromatographic separation of this extract revealed that the active antimicrobial species present include stigmasterol and 2,6-dimethoxy-p-benzoquinone.

Preparation of Porous Silicon from Porous Silica Glass via Magnesiothermic Reduction

We applied magnesiothermic reduction for porous silica glass, which was prepared from sodium borosilicate glass. The powdered porous silica glass was reduced to silicon and magnesium silicide at temperatures higher than 600 °C. The silicon was isolated by the hydrochloric acid treatment and the subsequent hydrofluoric acid treatment for the reduction products. The SEM observation revealed that the prepared silicon had a porous structure. The pore size distribution measured with a porosimeter was similar to that of the stating porous silica glass in the region less than several tens nanometers.

Enhanced quantum yield of photoluminescent porous silicon prepared by supercritical drying

The effect of supercritical drying (SCD) on the preparation of porous silicon (pSi) powders has been investigated in terms of photoluminescence (PL) efficiency. Since the pSi contains closely spaced and possibly interconnected Si nanocrystals (<5 nm), pore collapse and morphological changes within the nanocrystalline structure after common drying processes can affect PL efficiency. We report the highly beneficial effects of using SCD for preparation of photoluminescent pSi powders. Significantly higher surface areas and pore volumes have been realized by utilizing SCD (with CO2 solvent) instead of air-drying. Correspondingly, the pSi powders better retain the porous structure and the nano-sized silicon grains, thus minimizing the formation of non-radiative defects during liquid evaporation (air drying). The SCD process also minimizes capillary-stress induced contact of neighboring nanocrystals, resulting in lower exciton migration levels within the network. A significant enhancement of the PL quantum yield (>32% at room temperature) has been achieved, prompting the need for further detailed studies to establish the dominant causes of such an improvement.