Microporous Silicon Research Articles

Luminescent Porous Silicon Filled with Nanoscopic Magnetic Structures – Assessment of the Optical and Magnetic Properties

Luminescent porous silicon which is denoted as microporous silicon (LPSi) offers a structure size of a few nanometers. The pores are arranged in a branched network-like morphology. These structures are filled with magnetic metals resulting in a composite system with specific optical and magnetic properties. In this work Ni and Co, respectively are used. The luminescence is observed in the red-orange region due to the small structure size. The photoluminescence spectra of initial LPSi offer a peak around 620 nm, which is blue-shifted after Ni-filling with increasing deposition time and the intensity of the luminescence is increased. In the case of Co deposition the spectrum is adequate but with increasing metal filling the luminescence intensity decreases. Magnetic field dependent measurements performed for easy and hard axis magnetization show a high magnetic anisotropy between these two magnetization directions, even more pronounced in the case of Co. The magnetic response of the samples is related to the interconnected pores and differs significantly to mesoporous silicon filled with magnetic nanostructures.

Silicon Nanoparticles Formed via Pulsed Laser Ablation of Porous Silicon in Liquids

Picosecond pulsed laser ablation of meso- and microporous silicon layers in water and ethanol leads to the formation of nanosilicon suspensions with particle diameters below 100 nm. It is established that the use of porous silicon targets allows the laser ablation threshold to be reduced and the nanoparticle concentration increased as compared to the ablation of crystalline silicon.

Magnetic Filling of Microporous Silicon: An Interlink Between Optical and Magnetic Behavior

In the frame of this work microporous silicon (mPSi) is filled with magnetic metals (Ni, Co) resulting in a composite system with specific magnetic properties corresponding to its branched morphology. The results are compared with mesoporous silicon (PSi) loaded with Ni nanoparticles (NPs) of comparable size. The two systems offer drastic differences in their magnetic response. Furthermore mPSi offers luminescence in the visible range, whereat this behavior is due to the small structure size in the range of a few nanometers (2 – 5 nm). The morphology of mesoporous silicon shows straight pores with a diameter up to 50 nm. Due to the different template morphology the responding magnetic behavior shows distinct properties related to the two systems, although the size of the metal deposits is in a similar size range. The Ni loaded mPSi system merges optical and magnetic properties leading to a nanocomposite appropriate for possible magneto-optical devices.

Magnetic Filling of Microporous Silicon: An Interlink of Optical and Magnetic Behavior

In the frame of this work microporous silicon (mPSi) is filled with magnetic metals (Ni, Co) resulting in a composite system with specific magnetic properties. The results are compared with mesoporous silicon (PSi) loaded with Ni nanoparticles (NPs) of comparable size. The mPSi offers luminescence in the visible, whereat this behavior is due to the small structure size in the range of a few nanometers (2 – 5 nm) [1]. The morphology of mesoporous silicon shows straight pores with a diameter up to 50 nm.The mPSi samples are fabricated by anodization of a moderately doped p-type silicon wafer in a 10 wt% hydrofluoric acid solution. The challenging metal filling of these pores is carried out under cathodic conditions by pulsed electrodeposition. As electrolytes aqueous NiSO4 and CoSO4 solutions are employed. The microporous silicon offers a branched morphology and thus also the deposited nanosized metal structures are interconnected. The structure size of the porous samples is estimated by photoluminescence measurements to 5 nm which also determines the size of the deposits. Mesoporous silicon is produced by anodization of a highly n-doped silicon wafer resulting in straight pores of about 50 nm in diameter [2]. The loading of these samples with Ni NPs is also performed by electrodeposition.Magnetic filling of meso- and microporous silicon, respectively means a change in the morphology as well as in the structure size of the magnetic precipitations and both influence the magnetic behavior of the composite system drastically. In the case of mPSi also the luminescence is influenced in its intensity and wavelength by the magnetic filling. The magnetic properties are investigated with a Vibrating Sample Magnetometer (VSM) and a SQUID, respectively. A luminescence spectrometer is used to measure the intensity and the peak position of the photoluminescence spectrum. The structure is investigated by SEM and TEM.Field dependent magnetization measurements show a distinct difference between Ni filled mPSi and PSi loaded with Ni NPs. Considering mPSi filled with Ni and Co a strong magnetic anisotropy between the two magnetization directions applying a magnetic field perpendicular and parallel to the surface, respectively is observed, whereas in the case of Co this behavior is even more pronounced. Figure 1 depicts the hysteresis of mPSi and mesoporous silicon filled with Ni. The coercivities do not vary in a broad range between Ni and Co samples but the saturation field differs drastically between the two materials. In contrast mesoporous silicon loaded with Ni NPs offers only a small magnetic anisotropy caused by weak magnetic interactions between the Ni deposits.Since the microporous silicon offers photoluminescence the huge magnetic anisotropy is of interest for magneto-optical applications.[1] Handbook of Porous Silicon, Ed. L. Canham, Springer Int. Publishing, 2018.[2] P. Granitzer, K. Rumpf, Semiconductor Science and Technology 31, 4004, 2016. Figure 1

Metal Filled Nanostructured Silicon With Respect to Magnetic and Optical Properties

Within this work the utilization of nanostructured silicon as host material for filling with various magnetic nanostructures is reviewed whereas the magnetic and optical properties of the gained composite systems are elucidated. The metal filling of the pores is mainly performed by electroless deposition or by electrodeposition which is discussed by means of some examples. Furthermore two different types of porous silicon (PSi) morphology are used for the deposition procedure. On the one hand microporous silicon offering luminescence in the visible range is utilized as template material. It offers a branched morphology with a structure size between 2 and 5 nm. In this case not only the magnetic response is investigated but also the influence of the metal filling on the optical properties. On the other hand mesoporous and macroporous silicon in it’s low pore regime is employed which offers straight pores with diameters up to 90 nm. In this case the magnetic response strongly depends on the size, the geometry and the spatial distribution of the metal deposits within the pores. A crucial role plays also the morphology of the porous silicon, especially the distance between adjacent pores which is an important parameter regarding magnetic interactions.

High Purity Porous Silicon Powder Synthesis by Magnesiothermic Reduction of Tunisian Silica Sand

Crystalline metallurgical silicon nanopowder was successfully produced from Tunisian silica sand by magnesiothermic reduction. Silica sand was first transformed into silica powder via a specific chemical process. The produced silica powder was reduced by magnesium granules at a temperature range of 500–800 °C. Thermal analysis shows that a low-temperature ramp rate (5 °C min−1) allows the initiation of a solid-state reaction at around 528 °C. X-ray diffraction shows that the produced mixture is the result of a rather complex reaction leading to the formation of Si, and other by-products such as MgO, Mg2Si, and Mg2SiO4. In order to remove the by-products, a two-steps leaching approach was used. After leaching, Si with a rate exceeding 99% was obtained. SEM images show that the produced silicon powder is composed of macro and microporous silicon crystallites having an average size dimension of about 47 nm. The porosities of the produced metallurgical silicon particles are resulting from the nature of the magnesio-reduction process. Raman investigations confirm that the resulted metallurgical silicon powder is essentially composed of silicon nanoparticles–based porous matrix. A comparison of the Fourier Infrared Spectroscopy spectrum of the produced metallurgical silicon powder with slightly doped solar grade silicon shows that both products exhibit a bulk Si-Si stretching vibrational mode at around 619 cm−1. These results show that pure porous and crystalline silicon powder can be easily produced at low energy cost from an abundant local and low-cost raw material.

In English

One of the promising materials for the development of 2D photonic structures is macroporous silicon obtained using photoanodic etching. Presence of periodically located cylindrical pores divided by silicon columns provides large effective surface of samples and enhanced optical and photo-physical characteristics of macroporous silicon structures. In this paper, the near-IR light absorption oscillations of 2D macroporous silicon structures with microporous silicon layers, SiO 2 nanocoatings and CdTe, ZnO surface nanocrystals are studded taking into account the Wannier–Stark electro-optical effect. An analysis of the experimental absorption spectra was carried out within the model of the resonant electron scattering with infinite amplitude on impurity states in strong electric field, with difference between two resonant energies equaled to the step of Wannier–Stark ladder. The constant oscillation period specifies the realization of Wannier–Stark effect on the randomly distributed surface bonds on silicon-nanocoating interface. We compared the IR absorption oscillations in 2D macroporous silicon with surface nanocoatings, analyzed shifts and deviations of oscillation peaks. The coherence of the IR spectra oscillations increases with the decrease of surface state concentration and with the optimal area of contact of nanocrystals to the macropore surface. Thus, the shift of oscillations for ZnO nanoparticles with optimal size of nanocrystals (3.7–4.4 nm) leads to deviations of the oscillation peaks within 0.26–0.42 meV, the oscillation coherence reaches 0.25–0.4 %. The small broadening parameter of the Wannier–Stark ladder levels G = 0.3¸0.8 cm –1 equals to that for surface phonon polaritons measured in thin films of II-VI semiconductors. Controllability and coherence of the investigated system are determined by forming of coherent Wannier levels in a narrow triangular potential well formed by an electric field at the silicon-nanocoating interface. In addition, we have proposed a high coherent optical quantum computer based on the quantum Wannier-Stark electro-optical effect on a silicon matrix with macropores and a layer of nanocrystals on the macropore surface.

Common mechanism for helical nanotube formation by anodic polymerization and by cathodic deposition using helical pores on silicon electrodes

We report that platinum-assisted chemical etching formed self-organized helical pores in silicon substrates can be utilized as platforms for the electrochemical production of nanohelices of conducting polymers (polypyrrole) and metals (gold). Surprisingly, the nanohelices thus created are tubes although the polymerization and deposition were carried out by anodic and cathodic reactions, respectively. Based on our results, we propose a common mechanism for the formation of tubular nanohelices by both anodic polymerization and cathodic deposition through the accumulation of reactants in microporous silicon which covers the wall surface of the helical pores.

Simultaneous preparation of TiO2 and ammonium alum, and microporous SiO2 during the mineral carbonation of titanium-bearing blast furnace slag

Abstract In this study, a route for simultaneous mineralization of CO2 and production of titanium dioxide and ammonium alum, and microporous silicon dioxide from titanium-bearing blast furnace slag (TBBF slag) was proposed, which is comprised of (NH4)2SO4 roasting, acid leaching, ammonium alum crystallization, silicic acid flocculation and Ti hydrolysis. The effects of relevant process parameters were systematically investigated. The results showed that under the optimal roasting and leaching conditions about 85% of titanium and 84.6% of aluminum could be extracted while only 30% of silicon entered the leachate. 84% of Al3+ was crystallized from the leachate in the form of ammonium aluminum sulfate dodecahydrate with a purity up to 99.5 wt%. About 85% of the soluble silicic acid was flocculated with the aid of secondary alcohol polyoxyethylene ether 9 (AEO-9) to yield a microporous SiO2 material (97.4 wt%) from the crystallized mother liquor. The Al- and Si-depleted solution was then hydrolyzed to generate a titanium dioxide (99.1 wt%) with uniform particle size distribution. It was figured out that approximately 146 kg TiO2 could be produced from 1000 kg of TBBF slag. Therefore, the improved process is a promising method for industrial application.

Electrochemical Behavior and Detection of Diclofenac at a Microporous Si3N4 Membrane Modified Water–1,6-dichlorohexane Interface System

The electrochemical behavior when the liquid–liquid interface was modified by commercially available, microporous silicon nitride membrane, was achieved using cyclic voltammetry with tetramethyl ammonium. The transfer characteristics of the ionizable drug diclofenac ( DCF − ), as an anti-inflammatory, anti-rheumatic, antipyretic, and analgesic treatment in common use in biomedical applications, were also investigated across microporous silicon nitride-modified liquid interface. Thus, some thermodynamic variables for DCF − , such as the standard Gibbs energy of transfer, the standard transfer potential and lipophilicity were estimated. Furthermore, the influence of possible interfering substances (ascorbic acid, sugar, amino acid, urea, and metal ions) on the detection of DCF − was investigated. An electrochemical DCF sensor is investigated using differential pulse voltammetry (DPV) as the quantification technique, a linear range of 8–56 µM and a limit of detection of 1.5 µM was possible due to the miniaturized interfaces formed within silicon nitride.

Effect of polyethylene glycol on corrosion of fresh macroporous silicon in 1.0 M NaOH and application in determination of porosity and thickness by gravimetric measurement

This work presents on improvement in gravimetric measurement for determining the porosity and thickness of microporous silicon. Herein, the corrosion of fresh macroporous silicon (f-MPSi) in 1.0 M NaOH with different concentrations of polyethylene glycol (PEG 200/400/600) was studied by weight loss measurement and scanning electron microscopy (SEM). The results showed that the corrosion rate decreased with increasing polyethylene glycol concentration, and increased with an increase in temperature. Polyethylene glycol can inhibit the corrosion of f-MPSi in NaOH solution. Moreover, 1.0 M NaOH/PEG 600 (10%) can be used as the optimized solution to remove f-MPSi for measuring its porosity and thickness by gravimetric measurement.

Electrochemical Disposition of Titanium Dioxide Photocatalyst on Micropores Silicon Wafer for Water Treatment Application

Titanium dioxide (TiO2), due to wide band gap, has a limited use in water treatment process because of its low activity under visible light. Such drawback is usually associated with the inadequate solar spectrum that activates its surface, i.e., most of the photoexcited electron-hole pairs tend to recombine, leading to a reduction in the photocatalytic performance. Immobilization of TiO2 on the surface of silicon is considered as a useful approach to overcome this drawback. However, the immobilization methods require high temperature and pressure, which limit the numbers and types of materials that can be utilized as a substrate. The known electrochemical deposition procedures are usually conducted through two major steps, electrochemical oxidation and hydrolysis of Ti(III) precursor to form a thin layer on the surface of the substrate, followed by thermal annealing to form crystalline phase. The present work introduces the immobilization of titanium dioxide on a microporous silicon (MPSi) wafer through direct electrochemical deposition, where titanium dioxide P25 was used in the electrolyte solution. The photocatalyst surface morphology and composition were characterized using Scan Electron Microscope (SEM), Electron Dispersive X-ray (EDX), X-ray diffraction (XRD), and X-ray Photoemission Spectroscopy (XPS) techniques. The photocatalytic activities of the new composites were investigated, and the experimental results indicate that the fabricated TiO2–MPSi showed higher methylene blue degradation rate than that of the conventional P25 catalyst. This is due to the unique photosensitivity and porous structure of the new photocatalytic composites. with the advantages of using this method, it is believed that more efficient photocatalyst can be produced.

Формирование кремниевых наночастиц методом импульсной лазерной абляции пористого кремния в жидкостях

It was shown that the ablation of meso- and microporous silicon layers by picosecond laser pulses in water and ethanol leads to the formation of nanosilicon suspensions with a diameter of less than 100 nm. It has been demonstrated that the use of porous silicon allows to reduce the thresholds of laser ablation and increase the concentration of particles in suspensions in comparison with the case of crystalline silicon ablation.

(Invited) Phonon Engineering for Improved Seebeck Coefficient and Thermal Conductivity of Thermoelectric Nanolaminate Films Synthesized on Porous Templates

Recently promising advances have been achieved with phononic crystal (PnC) nanostructures in thermoelectric materials, because the thermal conductivity of PnC samples is lower compared to non-patterned thermoelectric samples due to phonon-boundary scattering. In this study we report on the successful synthesis of PbTe and PbSe thermoelectric layers on patterned porous silicon substrates by a thermal ALD system. PbTe/PbSe nanolaminates grown on porous silicon membranes have higher Seebeck coefficients than the ones grown on regular planar silicon wafers. The higher Seebeck values result from the lower thermal conductivity k in porous structures, which in turn lead to a higher figure of merit ZT. We demonstrate the feasibility to enhance the figure of merit ZT further by modulating the size and periodicity of the pattern and the thickness of the thermoelectric film in relation to the mean free path (MFP) of the phonons of the thermoelectric material. In our study PbTe and PbSe thin films and nanolaminates were synthesized by Atomic Layer Deposition (ALD) technology on regular planar silicon wafers and on macro-porous silicon templates. ALD is a surface saturating, self-limiting, absolutely conformal thin film synthesis technique reacting two pulsed precursors that enable film growth of one atomic layer per growth cycle. Lead bis(2,2,6,6-tetramethyl-3,5-heptanedionato) (Pb(C11H19O2)2), (trimethylsilyl) telluride ((Me3Si)2Te) and (trimethylsilyl) selenide ((Me3Si)2Se) were employed as the chemical ALD precursors for lead, tellurium and selenium, respectively. The surface morphology observations indicate Volmer–Weber growth mechanism of PbTe/PbSe nanolaminates during the thermal ALD deposition process rather than classic layer-by-layer growth. The ALD PbTe/PbSe nanolaminates exhibited complete surface coverage on planar bulk silicon wafers and also inside the pores of microporous silicon membranes. For the case of porous Si templates, the Seebeck measurements in both the horizontal and vertical directions revealed significant enhancement in Seebeck coefficients for PbTe/PbSe nanolaminates synthesized inside strictly periodic lithographically defined porous silicon membranes.

3D porous silicon (nanorods array, nanosheets, and nanoclusters) production

In this research, using powder technology manufacturing is as a pioneering, low cost, a simple and safe method for the fabrication of nano-porous silicon (NPS-powder). It's attractive carriers for targeted in several research fields. It's prepared using a combination of alkali chemical etching process and ultra-sonication technique; through the utilization of commercial silicon powder; with high yield efficiency (81.43%). Several 3D-NPS-shapes (nanorods array, nanosheets, and nanoclusters) are fabricated. It's a mixture of microporous and mesoporous silicon powder {pore size (28-140 nm)}. The main factors which affect the production of NPS-powder are (KOHconc.), sonication time, separation process and drying velocity.

Silicon Nanoparticles Produced by Two-Step Nanosecond Pulsed Laser Ablation in Ethanol for Enhanced Blue Emission Properties

In this work, we introduce a facile method of laser ablation to synthesize silicon rich oxide nanoparticles colloid with blue-green emissions. The method includes a two-step nanosecond pulsed laser ablation of silicon in ethanol. First, the micro-porous layer is formed on the silicon surface by laser ablation of the target, followed by ablating the oxidized micro-porous silicon to prepare the nanoparticles dispersed in ethanol. The nanoparticles interface structure exhibit the crystalline of quartz and non-stoichiometric oxide in suboxide phase of the SiO1.5 as examined by Fourier transform infrared spectroscopy, UV-vis spectrophotometry and X-ray diffraction pattern. Study of the colloid photoluminescence properties reveals that the coupling of silicon nanocrystals and interfacial states may play important role in the blue emission mechanism of the colloid. Our results support that the radiative recombination at the interfacial localized states of Si/SiO1.5 can easily occur in the colloid resulting the blue emission peak at the wavelength of 425 nm. In other words, a more effective pathway is provided for excited electrons in the colloid including occurrence of excitations in silicon nanocrystal states and emission in the interfacial states. This method avoids any toxic by-product during the synthesis of colloid and can be used for the commercial-scale production of silicon nanoparticles as the blue emission material.

Rapid absorption of ethylene oxide exhaust by catalytic hydration on acid zeolite catalysts

Abstract Using a mineral acid, such as sulfuric acid, as a catalyst would cause serious environmental contamination. The use of such an acid requires subsequent distillation despite its efficiency to catalyze the absorption of ethylene oxide (EO) exhaust by water. This paper reports an energy-saving and environmentally friendly strategy to replace mineral acid with solid acid. Microporous silicon–aluminum zeolites, such as H-ZSM-5, HY, and H β , were previously shown to be strong solid acid materials. In this study, we investigate the effect of the acidity of these materials on the catalytic absorption of EO exhaust. The H-ZSM-5 with strongest Bronsted acidity exhibited the best performance. Furthermore, the intrinsic reaction kinetics indicated that the reaction conducted with and without a catalyst follows a first-order irreversible reaction model in which the reaction rate and activation energy toward the consumption of EO was greatly changed (k rate constant improved by 0.145 g−1 s−1 and Ea activation energy decreased by 13 kJ/mol).

Evolution of nanocrystal size distribution in porous silicon nanoparticles during storage in aqueous media: X-ray diffraction analysis

X-ray diffraction studies of electrochemically prepared mesoporous and microporous silicon particles were carried out to monitor their dissolution in aqueous media. The dissolution process was found to result in either decreasing or an increasing of the mean size of silicon nanocrystallites in mesoporous and microporous samples, respectively. The evolution of nanocrystallite size was related by polydispersity of the initial size distribution and it was described by using a model of “shrinking spheres.” The proposed approach was used to confirm an effect of biopolymer surrounding of silicon nanocrystallites on their stability in aqueous medium. The obtained results and developed model can be useful for potential biomedical applications of porous silicon.

Comparative analysis of silicon nanostructures by x-ray diffraction technique

Silicon nanoparticles and nanowires prepared by using different methods were investigated by means of x-ray diffraction (XRD) technique. Broadening of the XRD lines of crystalline Si lattice allows us to estimate the mean size of nanoparticles. Silicon nanoparticles stored in aqueous suspensions for several days were found to decrease their sizes due to dissolution process. The kinetics of dissolution for different kinds of nanoparticles were found to be different. It was also shown that the most unstable nanoparticles (microporous silicon ones) could be protected from dissolution via interaction with the polysaccharide molecules (dextrane) into the solution.

Mass-producible microporous silicon membranes for specific leukocyte subset isolation, immunophenotyping, and personalized immunomodulatory drug screening in vitro.

Widespread commercial and clinical adaptation of biomedical microfluidic technology has been limited in large part due to the lack of mass producibility of polydimethylsiloxane (PDMS) and glass-based devices commonly as reported in the literature. Here, we present a batch-fabricated, robust, and mass-producible immunophenotyping microfluidic device using silicon micromachining processes. Our Si and glass-based microfluidic device, named the silicon microfluidic immunophenotyping assay (SiMIPA), consists of a highly porous (∼40%) silicon membrane that can selectively separate microparticles below a certain size threshold. The device is capable of isolating and stimulating specific leukocyte populations, and allows for measuring their secretion of cell signaling proteins by means of a no-wash homogeneous chemiluminescence-based immunoassay. The high manufacturing throughput (∼170 devices per wafer) makes a large quantity of SiMIPA chips readily available for clinically relevant applications, which normally require large dataset acquisitions for statistical accuracy. With 30 SiMIPA chips, we performed in vitro immunomodulatory drug screening on isolated leukocyte subsets, yielding 5 data points at 6 drug concentrations. Furthermore, the excellent structural integrity of the device allowed for samples and reagents to be loaded using a micropipette, greatly simplifying the experimental protocol.