Nanocrystalline Porous Silicon Research Articles

Synthesis of Porous Silicon by Electrochemical Etching for Gas Sensor Application

In the present study, the layers of porous Silicon (PS) have been produced from the p-type Silicon with a (100) orientation using the approach of electrochemical etching. The samples were anodized in a solution of HF concentration 18% and 99% C2H2OH. Samples characteristics of PS were studied by etching time constant (15 min). In addition, the alteration of the current density value into (5, 10,15,20, and 25) mA/ cm2 was also studied. Samples were characterized by nanocrystalline porous Silicon via X-Ray Diffraction (XRD). The AFM (Atomic force microscope) analysis of PS shows the sponge-like structure. Also, a 39.76 nm average diameter was coordinated in the rod-like temperature variation, fabricated from prepared samples on the sensor's sensitivity, recovery time, and response time. The maximal level of the sensitivity has been approximately (20,11)% for porous Silicon of gas NO2 and NH3, respectively.

Technological Characteristics of Vanadyl Sulfate – Porous Silicon Heterojunction

Near nano limit of [vanadium sulfate hydrate / porous silicon] heterojunction using zinc sulfide as a window for solar cell applications were investigated. Nanoparticles of vanadium sulfate hydrate were prepared by the electrochemical method followed by deposited in the form of thin films on bases of conductive glass and porous silicon to study the structural properties. The transmittance, absorbance and energy gap for the active material and the nanolayer window were performed. Grain size and roughness rate were determined via the surface topography test. The electrical parameters were measured, including the electrical conductivity. Nano crystalline porous silicon (PSi) films from p-type silicon (p - Si) wafer are synthesized using electrochemical etching (ECE) process of p-silicon wafer. Effective reflectance was obtained by (ZnS/VOSO₄.H₂O/PSi/p-Si) thin film that display excellent light-trapping at wavelengths ranging from (200 – 900) nm. The energy band gap of (VOSO4.H2O) NPs was calculated and found (4.2 - 5) eV. The average grain size ranged (67.7 – 82.9) nm. The electrical measurements current – voltage (I-V) were examined in dark and illumination conditions, for the heterojunctions fabricated. The efficiency of solar cell was reached (12.96%) while the power conversion efficiency was reached (51.8%).

On the Question of the Possibility of Using Nanocrystalline Porous Silicon in Silicon-Based Solar Cells

On the Question of the Possibility of Using Nanocrystalline Porous Silicon in Silicon-Based Solar Cells

Enhancing Photovoltaic Performance of Porous Silicon Solar Cells with Al2O3 Nanoparticles prepared by electrolysis method

In this work nanocrystalline porous silicon (PSi) prepared by electrochemical etching of p type silicon wafers. PSi is characterised by means of XRD, FTIR and AFM. Crystallites length become expected with the aid of X-Ray diffraction. Atomic Force microscopy confirmed the nanometric size. Colloidal Al2O3 nanoparticles prepared via electrolysis method and deposited using drop-casting method as a thin film. The structural, morphological, optical homes of Al2O3 NPs were investigated. The effect of Al2O3 NPs diffusion at the holes of PSi sun mobile have stated which exhibits an improvement in (Ag/Al2O3/PSi/Si/Al) solar cell performance.

Al2O3 NPs/porous silicon/silicon photovoltaic device

Alumina nanoparticles or (Al2O3 NPs) have been prepared by electrolysis method and deposited using drop casting method on glass and porous silicon (PS) substrates as thin films. Electrochemical etching of p-type silicon wafers was used to prepare nanocrystalline porous silicon. The structural and morphological properties of Al2O3 NPs were investigated by XRD, AFM and SEM techniques, respectively. The optical energy band gap of Al2O3 nanostructure (NSs) has been determined from its optical properties and it was around 3.6 eV. TEM has been used to investigate the nanoscale morphology of Al2O3NPs and showed the grains had a spherical shape and it confirmed the nanometric size of the prepared NPs. PS’s XRD pattern revealed that it had a single crystalline structure, whereas it was amorphous for the Al2O3 NSs. The nanometric scale of both Al2O3 NSs and PS was calculated by XRD patterns, it was about 34nm for Al2O3 NPs and about 90 nm for PS. The diffusion effect of the Al2O3NPs on the electrical properties of heterojunctions PS/Si was studied. Photovoltaic characteristics have been reported for Al2O3NPs/PS/Si Photovoltaic device. Ag/Al2O3/PS/Si/Al solar cell parameters were reported the efficiency of solar cell was 11.8% and F.F is 32.08 %. Ag/Al2O3/PS/Si/Al Photodetector heterojunctions have two peaks of response the first one located at 350 nm and the second at 850 nm with maximum responsivity of 0.8A/W.

Mechanical Strength Enhancement of Porous Nanocrystalline-Silicon (pnc-Si) Membrane via Titanium-oxide (Ti-O) Coating

Porous nanocrystalline silicon (pnc-Si) membrane is mainly studied as a blood filtration membrane, mimicking the glomerulus filtration membrane of a human kidney. However, the pnc-Si material itself is not hemocompatible and enormous membrane area to thickness ratio makes the membrane to be easily fractured. Silicon surface modification via titanium-oxide (Ti-O) thin film layer deposition has been proven to be hemocompatible and the presence of Ti-O layer has been numerically studied to give higher membrane flexural strength. In this work, square pnc-Si membranes of 2 mm × 2 mm × 20 nm size have been fabricated with and without Ti-O layer. Point loading-unloading nanoindentation method has been performed and the membranes’ displacement behaviour subjected to point loads is studied. The pnc-Si membranes with Ti-O layer were found to attain higher fracture strength, membrane bending stiffness and average hardness with the increase of ~20, ~11 and ~24%, respectively, compared to bare pnc-Si membranes. The mechanical strength of a free-standing pnc-Si membrane is improved by depositing a Ti-O thin film layer on the membrane structure.

Design and Numerical Investigation of Porous Nanocrystalline Silicon Membrane Filtration Device for Artificial Kidney

Design and Numerical Investigation of Porous Nanocrystalline Silicon Membrane Filtration Device for Artificial Kidney

Porous silicon prepared by photo electrochemical etching assisted by laser

Porous silicon (PS) layers are prepared by anodization fordifferent etching current densities. The samples are thencharacterized the nanocrystalline porous silicon layer by X-RayDiffraction (XRD), Atomic Force Microscopy (AFM), FourierTransform Infrared (FTIR). PS layers were formed on n-type Siwafer. Anodized electrically with a 20, 30, 40, 50 and 60 mA/cm2current density for fixed 10 min etching times. XRD confirms theformation of porous silicon, the crystal size is reduced towardnanometric scale of the face centered cubic structure, and peakbecomes a broader with increasing the current density. The AFMinvestigation shows the sponge like structure of PS at the lowercurrent density porous begin to form on the crystalline silicon, whenthe current density increases, pores with maximum diameter areformed as observed all over the surface. FTIR spectroscopy shows ahigh density of silicon bonds, it is very sensitive to the surroundingambient air, and it is possible to oxidation spontaneously.

Facile and Efficient Gas-Phase Pressure-Controlled Thermal Functionalization of Nanocrystalline Porous Silicon with 1-Hexene

Substitution of hydrogen at porous silicon (PSi) surface by organic groups can be done via thermally activated hydrosilylation reactions in which PSi is left for several hours into liquid alkenes at temperatures typically over 100°C. For alkenes whose boiling points are below 100°C (e.g. 1-heptene and shorter molecules), the process suffers from high reagent boiling and evaporation. Gas-phase hydrosilylation is an alternative when using short molecules. It has not been as extensively studied, and was mainly done in plasma reactors with silicon nanocrystals. Here we present a new method for facile gas-phase thermally-activated hydrosilylation in PSi, but using liquid solutions as reagent (1-hexene was used here). PSi and liquid alkene are loaded at room temperature into a chamber which is then closed and heated up to a temperature greater than the alkene boiling point. The effects of process temperature, time and pressure were investigated by means of Fourier transform infrared spectroscopy. The maximum theoretical derivatization efficiency was achieved with optimized parameters. The derivatization was uniform across the PSi layer depth. PSi luminescence was effectively stabilized by the process. The new gas-phase method presented here is facile, requires very small amount of liquid reagent, and is useful for attachment of short molecules to PSi or other materials surface.

Porous Nanocrystalline Silicon Supported Bimetallic Pd-Au Catalysts: Preparation, Characterization, and Direct Hydrogen Peroxide Synthesis.

Bimetallic Pd-Au catalysts were prepared on the porous nanocrystalline silicon (PSi) for the first time. The catalysts were tested in the reaction of direct hydrogen peroxide synthesis and characterized by standard structural and chemical techniques. It was shown that the Pd-Au/PSi catalyst prepared from conventional H2[PdCl4] and H[AuCl4] precursors contains monometallic Pd and a range of different Pd-Au alloy nanoparticles over the oxidized PSi surface. The PdAu2/PSi catalyst prepared from the [Pd(NH3)4][AuCl4]2 double complex salt (DCS) single-source precursor predominantly contains bimetallic Pd-Au alloy nanoparticles. For both catalysts the surface of bimetallic nanoparticles is Pd-enriched and contains palladium in Pd0 and Pd2+ states. Among the catalysts studied, the PdAu2/PSi catalyst was the most active and selective in the direct H2O2 synthesis with H2O2 productivity of 0.5 at selectivity of 50% and H2O2 concentration of 0.023 M in 0.03 M H2SO4-methanol solution after 5 h on stream at −10°C and atmospheric pressure. This performance is due to high activity in the H2O2 synthesis reaction and low activities in the undesirable H2O2 decomposition and hydrogenation reactions. Good performance of the PdAu2/PSi catalyst was associated with the major part of Pd in the catalyst being in the form of the bimetallic Pd-Au nanoparticles. Porous silicon was concluded to be a promising catalytic support for direct hydrogen peroxide synthesis due to its inertness with respect to undesirable side reactions, high thermal stability, and conductivity, possibility of safe operation at high temperatures and pressures and a well-established manufacturing process.

Improved quasiballistic electron emission from a nanocrystalline Si cold cathode with a monolayer-graphene surface electrode

The quasiballistic electron emission from a nanocrystalline porous silicon (nc-Si) diode is drastically enhanced by using a monolayer-graphene film as the surface electrode. Due to little scattering losses in monolayer-graphene, the electron emission efficiency at room temperature is increased up to 6.3% that is considerably higher than that in the case of conventional thin metal films. The peak energy of emitted electrons can be tuned by the applied voltage while keeping narrow energy dispersion. The energy distribution becomes more monochromatic at a low temperature of around 150 K. Monolayer-graphene acts as a highly transparent nanogrid for quasiballistic hot electrons.

IMPROVING THE PHOTORESPONSE OF POROUS SILICON FOR SOLAR CELL APPLICATIONS BY EMBEDDING OF CdTe NANOPARTICLES

The present work is concerned with the preparation of thin films of nanocrystalline porous silicon (PSi) by the method of electrochemical etching. CdTe nanoparticles (NPs) have been prepared by utilizing the pulsed laser ablation in liquid. The measurements of tunneling microscopy, X-ray diffraction (XRD), Fourier transformation infrared spectroscopy (FTIR) and atomic force microscopy (AFE) were carried out and revealed that the PSi was nanostructured and the produced CdTe NPs were ball shaped, having good disposability. The diffusion of CdTe NPs on the properties of PSi solar cell assures that there was an improvement upon their properties. The relationship between [Formula: see text] and the reverse bias voltage was observed to be linear. Values of the built-in potential were observed to be dependent on the laser fluence, current density and the etching time.

Vibration analysis of multi-phase nanocrystalline material nanoshells using strain gradient elasticity

This paper studies the free vibrational behavior of porous nanocrystalline silicon nanoshells using strain gradient theory. Nanocrystalline materials are multi-phase composites with the contribution of nanopores, nanograins and interface phase. Because of experimental observation of strain gradients near the interface phase, the nanoshell is modeled via strain gradient theory. A micromechanical model based on the Mori–Tanaka scheme is employed to incorporate the size of nanograins/nanopores and their surface energies. The nanoshell is modeled via first order shear deformation theory and Galerkin’s method is implemented to obtain vibration frequencies. Shape functions that satisfy available classical and non-classical boundary conditions in strain gradient theory are proposed. It is shown that the vibrational behavior of the nanoshell is influenced by the porosity percentage, nanograin size, strain gradient coefficient, boundary conditions, and the surface phase of nanograins/nanopores.

Dynamic modeling and vibration analysis of double-layered multi-phase porous nanocrystalline silicon nanoplate systems

Abstract Nanocrystalline materials (NcMs) are multi-phase composites containing nanograins, nanovoids and interface. A softening mechanism due to the interface phase and nanovoids is observed in NcMs. For the first time, vibration behavior of double-layered nanocrystalline silicon nanoplates on elastic substrate is analyzed based on a two-variable refined plate model. Due to the experimentally observation of grains micro-rotation and strain gradients near interfaces, the strain gradient based couple stress theory is employed to describe the size-dependent behavior of the nanocrystalline nanoplate. A micromechanical model is employed to incorporate the effects of inclusions and their surface energies. Galerkin's method is implemented to obtain the natural frequencies of nanocrystalline nanoplate with different boundary conditions. One can see that the nanograins size, nanograins surface energy, nanovoids size, void percentage, interface region, scale parameter, foundation constants and boundary conditions have a great influence on the vibration behavior of a double-layered nanocrystalline nanoplate.

Photosensitive heterostructures based on porous nanocrystalline silicon

The features of the manufacturing process, as well as the results of studies on the morphology, electrophysical, and photoelectric properties of photosensitive structures based on silicon containing siliconcarbide and porous silicon layers, are considered. A porous layer is created on the surface of a monocrystalline silicon substrate via electrolytic etching in fluorine-containing solutions. Wafers with a different surface microrelief such as a ground, polished, and textured one, has been used. The carbonization of the samples resulting in the formation of SiC/Si heterostructures has been carried out via gas transport endotaxy in a hydrogen flow using a vertical reactor with cold walls and a graphite container. The structure and composition of the manufactured SiC/Si heterostructures formed on different types of structured surfaces on polycrystalline and monocrystalline silicon, including the surface porous silicon layer, are investigated. It is shown that the process of endotaxy on all the types of surfaces leads to the formation of a single-crystal phase of silicon carbide by cubic modification. Using scanning and transmission electron microscopy, the morphology of the produced structures is investigated. Filiform entities with a different structure have been revealed on nonporous surfaces identified as silicon carbide, whereas the cylindrical or conical structures, whose nature is uncertain, have been observed on porous surfaces. The current-voltage and current-power curves are plotted for all types of manufactured structures, the general form of which indicates the presence of several potential barriers there. The photoelectric properties of the structures and the prospects of their use in photoelectric converters of solar cells are analyzed.

Visible Luminescence of Nanoporous Silicon Using Alternating Current Photo-Assisted Electrochemical Etching for Potential MSM Photodetector

The formation of nanocrystalline porous silicon (PS) was successfully prepared under a novel alternating current (sine-wave a.c. (50 Hz)) photo-assisted electrochemical (ACPEC) etching condition of an n-type (100) silicon (Si) substrate under the illumination of an incandescent white light. As grown Si and PS through conventional direct current(DC) anodization were also included for comparison. The ACPEC formed porous Silicon (PS) with excellent structural and surface morphological characteristic. According to the field emission scanning electron microscope (FESEM) micrographs, the nanoporous structures exhibited pores with uniform circular structure with estimated sizes, ranging between 20.5 nm and 30.5 nm. The atomic force microscopy (AFM) revealed an increase in the surface roughness induced by porosification. As compared to the as-grown Si, PS by AC method exhibited a substantial visible photoluminescence (PL) intensity enhancement with blue-shift associated with the quantum confinement effect of the nanostructure Si. Thermally treated nickel (Ni) finger contact was deposited on the PS to form MSM photodetector. Ni/PS MSM photodetector showed lower dark and higher photocurrent compared to the as grown Si device.

POROUS SILICON SOLAR CELL WITH ANTI-REFLECTION COATING LAYER FOR EFFICIENCY IMPROVED

Ponte Academic JournalMay 2016, Volume 72, Issue 5 POROUS SILICON SOLAR CELL WITH ANTI-REFLECTION COATING LAYER FOR EFFICIENCY IMPROVEDAuthor(s): Khalid Omar ,Khaldun A. SalmanJ. Ponte - May 2016 - Volume 72 - Issue 5 doi: 10.21506/j.ponte.2016.5.32 Abstract:A porous silicon layer was prepared by electrochemical etching and a zinc oxide film was deposited on a porous silicon layer using a radio frequency sputtering system. The surface morphology of the porous silicon and zinc oxide/porous silicon layers was characterized using scanning electron microscopy. Nano-pores were produced in the porous silicon layer with an average diameter of 5.8 nm, which increased the porosity to 83%. The photoluminescence emission spectra of the zinc oxide/porous silicon layers present three emission peaks, two peaks located at 385 and 603 nm due to the zinc oxide nanocrystalline film and a third located at 638 nm due to nanocrystalline porous silicon. Optical reflectance for all the layers was obtained using an optical reflectometer. The lowest effective reflectance was obtained for the zinc oxide/porous silicon layers. The fabrication of crystalline silicon solar cells based on the zinc oxide/porous silicon anti-reflection coating layers was performed. The I-V characteristics of the solar cells were studied. The zinc oxide/porous silicon layers were found to be an excellent anti-reflection coating and to exhibit exceptional light-trapping at wavelengths ranging from 400 to 1000 nm, which led to a high efficiency of the crystalline silicon solar cell of 15.49 % compared to 12.35% efficiency for the crystalline silicon solar cell with a porous silicon anti-reflection coating layer. The zinc oxide/porous silicon anti-reflection coating layers enhance and increase the efficiency of the crystalline silicon solar cell. Download full text:Check if you have access through your login credentials or your institution Username Password

Fabrication of Gas Sensor Device for H2 and NO2 from Porous Silicon

A nanocrystalline porous silicon (PS) layer was prepared by electrochemical etching method of p–type silicon wafer in hydrofluoric acid (HF). The properties of porous silicon structure under various etching times (10–50 min), HF concentrations, and current density were studied. The study included photoluminescence (PL), morphology, x–ray, and gas sensor. The results (PL) spectra (peak wavelength) can be shifted from (505 to 625) nm. PL analysis indicated that the energy band gap can be tuned from (1.984–2.455) eV with respect to etched time. Atomic Force Microscopy (AFM) analysis showed that the PS layer had a sponge–like structure. Surface roughness and the pyramid–like hillocks on the entire surface play an important role in variation visible luminescence. The AFM images shows that the average diameter of the PS layer pore and thickness the Silicon decreased when etching time increase and the average diameter particleboard ranged from (80.8–35.4) nm. PS X–ray topography studies that the skeleton maintained its silicon crystalline structure after anodization. PS Sensors were fabricated and tested successfully on H 2 and No 2 gas.

Influence of silicon dioxide capping layers on pore characteristics in nanocrystalline silicon membranes

Porous nanocrystalline silicon (pnc-Si) membranes are a new class of membrane material with promising applications in biological separations. Pores are formed in a silicon film sandwiched between nm thick silicon dioxide layers during rapid thermal annealing. Controlling pore size is critical in the size-dependent separation applications. In this work, we systematically studied the influence of the silicon dioxide capping layers on pnc-Si membranes. Even a single nm thick top oxide layer is enough to switch from agglomeration to pore formation after annealing. Both the pore size and porosity increase with the thickness of the top oxide, but quickly reach a plateau after 10 nm of oxide. The bottom oxide layer acts as a barrier layer to prevent the a-Si film from undergoing homo-epitaxial growth during annealing. Both the pore size and porosity decrease as the thickness of the bottom oxide layer increases to 100 nm. The decrease of the pore size and porosity is correlated with the increased roughness of the bottom oxide layer, which hinders nanocrystal nucleation and nanopore formation.

Giant and Tunable Mechanical Impulse of Energetic Nanocrystalline Porous Silicon

In this paper, a nanocrystalline porous silicon-based propulsion system is designed, and its explosion impulse is tuned by varying the propulsion design parameters and etching duration. The porous silicon is ignited by an electrical current passed through 100-nm-thick aluminum film deposited on the unpolished side of the wafer and the ignited porous silicon caused strong explosion, which destroys the chip into tiny fragments. The explosion impulse in the system can reach about at optimal conditions, which is two orders stronger than the impulse produced by conventional propellants (ZakarE., “Technology Challenges in Solid Energetic Materials for Micro Propulsion Applications” U.S. Army Research Lab. Rept. ARL-TR-5035, Nov. 2009). It is also shown that, by varying the etching time, which is an important factor that determines the porous layer thickness and the volume of nanocrystallite, the strength of the impulse can be tuned. Furthermore, a linear increasing trend of the explosion impulse with etching time is observed, which can be explained as the results of heat trapping, materials confinement, and the increasing number of reaction centers.