Photoluminescence Of Porous Silicon Research Articles

Porous silicon membrane for investigation of transmembrane proteins

This article presents the assembly and signal transduction of an artificial biological membrane suspended on a thin porous silicon template. The electrochemically-fabricated porous silicon membrane has average pore diameters in the range 0.50–2μm and dimensions of about 200×200×3μm3 and may be batch fabricated in large arrays for combinatorial testing. Biological membranes may be deposited on one or both sides of this template are fully accessible for studies using electrochemical impedance spectroscopy. Initial results using a two probe impedance measurement clearly show a significant impedance change between the porous silicon structure and the lipid bilayer. Furthermore, there is a clear reduction in the impedance of lipid bilayer when fused with a transmembrane ion channel protein. The photoluminescence and biodegradability properties of porous silicon in addition to lower cost and ease of fabrication make it superior over e-beam patterned silicon structures used in previous works, and thus suitable for in vivo monitoring.

Enhancement of porous silicon photoluminescence by chemical and electrochemical infiltration of conducting polymers

Novel nanocomposites of conducting polymers and mesoporous silicon with pore sizes <50 nm have been successfully fabricated by chemical and electrochemical techniques. The electrochemically infiltrated polymers (polypyrrole, polyaniline, polythiophene) are more homogeneously deposited deep into the nanopores compared to the spin-coated polymer poly(2-methoxy-5-(2-ethyl-hexyloxy)-1,4-phenylene-vinylene). The fluorescent light intensity of as-formed nanocomposites was significantly enhanced after polymer infiltration. The infiltrated polymers likely passivate existing nonradiative channels. Exciton transfer takes place from the porous silicon matrix to the conducting polymers.

Effect of Electrochemical Reaction Enviroment on the Surface Morphology and Photoluminescence of Porous Silicon

Porous silicon (p-Si) is a well-known silicon based material that can emit visible light at room temperature. The radiative recombination that originated from quantum confinement effect shows photoluminescence (PL) in red, while the defect on silicon oxide at the surface of p-Si shows in blue-green region. Porous silicon can be synthesized through two methods; wet-etching and electrochemical anodization using hydrofluoric acid as the main electrolyte. The electrochemical anodization is more favorable due to faster etching rate at the surface than the conventional wet-etching method. The objective of this research is to show that both of porous silicons can be synthesized using the same main electrolyte but by varying the reaction environment during anodization/etching process. Here, we shows the wet-etching method that enhanced by polarization concentration will produce porous silicon with silicon oxide defects by means blue-green emission, while direct electrochemical anodization will produce samples that emit red PL signal. The effect of introducing KOH into the electrolyte was also studied in the case of enhanced-wet-etching method. Surface morphology of porous silicon and their photoluminescence were observed by Scanning Electron Microscope and PL spectroscopy, respectively.

The Preparation of p-PS and its Photoluminescence Properties

In this research, p-type porous silicon was successfully fabricated with a typical electrochemical etching method. The mixed solution of HF and absolute ethyl alcohol with different volume ratio was used as the electrolyte in this experiment. The anodic current density was 20 mA/cm2～60 mA/cm2. The luminous intensity of the PS samples increased with the increasing of the current density, the peaks of PL first red shift (from 692.1nm to 727.9nm) then blue shift (from 727.9nm to719.6nm). With the increasing of the concentration of HF, PS luminous intensity gradually decreases, and the peaks of PL gradually occurs red shift. And possible mechanisms of the growth and the photoluminescence of porous silicon were proposed to explain the experimental result．

Anodization Current Density Independent Photoluminescence of Porous Silicon

Porous silicon (PS) is usually prepared by means of the anodization under constant current density, and fabrication of PS is a key step towards the realization of all-silicon electronic devices. It is a general belief that the photoluminescent properties of electrochemically etched PS depend on the anodization current density. In this work, we electrochemically prepared a series of PS films in the electrolyte of hydrofluoric acid by varying anodizing current density in the range of 1-70 mA/cm2. In spite of the different anodizing current density, the peak wavelength of the photoluminescence spectrum of the electrochemically anodized PS does not depend on the anodization current density. SEM has been utilized to characterize the morphology of the prepared PS films, and the mechanism is discussed for the anodization current independent photoluminescence of PS.

Peculiarities of Photoluminescence in Porous Silicon Prepared by Metal-Assisted Chemical Etching

Photoluminescent (PL) porous layers were formed on p-type silicon by a metal-assisted chemical etching method using H2O2 as an oxidizing agent. Silver particles were deposited on the (100) Si surface prior to immersion in a solution of HF and H2O2. The morphology of the porous silicon (PS) layer formed by this method was investigated by atomic force microscopy (AFM). Depending on the metal-assisted chemical etching conditions, the macro- or microporous structures could be formed. Luminescence from metal-assisted chemically etched layers was measured. It was found that the PL intensity increases with increasing etching time. This behaviour is attributed to increase of the density of the silicon nanostructure. It was found the shift of PL peak to a green region with increasing of deposition time can be attributed to the change in porous morphology. Finally, the PL spectra of samples formed by high concentrated solution of AgNO3 showed two narrow peaks of emission at 520 and 550 nm. These peaks can be attributed to formation of AgF and AgF2 on a silicon surface.

Parts per Million Water in Gaseous Vapor Streams Dramatically Accelerates Porous Silicon Oxidation

Substantial research has focused on exploiting and understanding porous silicon (pSi) photoluminescence (PL) for applications in areas ranging from chemical sensing to solid-state lighting. At ambient temperature, pure H2O is well-known to slowly (over a time scale of hours to days) and irreversibly oxidize as-prepared pSi (ap-pSi) to form oxidized pSi (ox-pSi). In this paper, we report that the apparent ap-pSi to ox-pSi oxidation rates can be orders of magnitude faster in the presence of nonaqueous vapor streams that contain just ppm H2O levels. When H2O is removed from the nonaqueous vapor stream, ap-pSi oxidation ceases. The nonaqueous analyte vapors serve as a vehicle to transport H2O directly into the hydrophobic, ap-pSi matrix where the H2O then oxidizes the ap-pSi leading to ox-pSi, permanently changing the pSi PL and surface chemistry. The ap-pSi oxidation rate is much faster in the presence of nonaqueous vapors because H2O transport into the pSi matrix is no longer limited by H2O slowly percolating–oxidizing–percolating through the ap-pSi matrix.

Detection of nerve agent stimulants based on photoluminescent porous silicon interferometer

Porous silicon (PSi) exhibiting dual optical properties, both Fabry-Pérot fringe and photolumincence, was developed and used as chemical sensors. PSi samples were prepared by an electrochemical etch of p-type silicon under the illumination of 300-W tungsten lamp during the etch process. The surface of PSi was characterized by cold field-emission scanning electron microscope. PSi samples exhibited a strong visible orange photoluminescence at 610 nm with an excitation wavelength of 460 nm as well as Fabry-Pérot fringe with a tungsten light source. Both reflectivity and photoluminescence were simultaneously measured under the exposure of organophosphate vapors. An increase of optical thickness and quenching photoluminescences under the exposure of various organophosphate vapors were observed.

Enhancement and stabilization of the photoluminescence from porous silicon prepared by Ag‐assisted electrochemical etching

In this paper, we present the results of studies on the photoluminescence (PL) of porous silicon (PSi) samples obtained by etching with the assistance of silver metal in different ways. If the Si sample, after being coated with a layer of silver nanoparticles, is electrochemically etched, its PL intensity becomes hundreds of times stronger than the PL intensity when it is chemically etched in the similar conditions. The difference in the PL intensities is explained partly by the anodic oxidation of silicon which occurs during the electrochemical etching process. The most obvious evidence that silicon had been oxidized anodically in the electrochemical etching process is the disappearance of the PSi layer and the appearance of the silicon oxide layer with mosaic structure when the anodization current density is large enough. The anodic oxidation has the effect of PSi surface passivation. Because of that, the PL of obtained PSi becomes stronger and more stable with time. Copyright © 2012 John Wiley &amp; Sons, Ltd.

Sol–gel derived ZnO/porous silicon composites for tunable photoluminescence

ZnO/porous silicon nanocomposites were fabricated by spin-coating the sol–gels of zinc acetate onto the top surface of porous silicon films. The photoluminescent properties of ZnO/porous silicon nanocomposites were investigated as a function of the concentration of zinc cations in the sol–gels. Characterizations with scanning electron microscopy, X-ray diffractometry and photospectroscopy indicated that ZnO nanocrystals were embedded into the spongy nanostructures of porous silicon after heat treatment at 245 °C for 20 min in air. The recorded photoluminescence exhibited that orange to green–blue emissions were achieved for the ZnO/porous silicon nanocomposites as the concentration of zinc cations in the sol–gels increased from 4 to 260 mM. The mechanisms on the tunability of the photoluminescence were discussed for the ZnO/porous silicon nanocomposites. Our results have demonstrated that the incorporation of green–blue phosphors into the porous matrix of porous silicon represents one endeavor to tune the photoluminescence of porous silicon across the visible spectral region.

Electrochromic effect in photoluminescent porous silicon–polyaniline hybrid structures

Changes in the intensity of light transmitted through polyaniline films caused by an external voltage are used to control the photoluminescence spectrum of nanoporous silicon. A study of the optical-luminescence properties of hybrid porous silicon-polyaniline structures under the influence of an applied external potential shows that polyaniline films deposited on a porous silicon surface can serve as an optical filter for the photoluminescence of porous silicon with an electrically controlled transmission band.

Detection of Nitroaromatic Compounds Based on Phenylethylene-Derivatized Porous Silicon

Nanocrystalline porous silicon (PSi) surfaces have been used to detect nitroaromatic compounds in vapor phase. The mode of photoluminescence (PL) is emphasized as a sensing attitude or detection technique. Quenching of PL from nanocrystalline porous surfaces as a transduction mode is measured upon the exposure of nitroaromatic compounds. To verify the detection of explosives, the surface of PSi is functionalized with different groups. The quenching mechanism of PL is attributed to the electron transfer behaviors of quantum-sized nano-crystallites in the PSi matrix to the analytes (nitroaromatics). An attempt has been done to prove that the surface-derivatized photoluminescent PSi surfaces can act as versatile substrates for sensing behaviors due to having a large surface area and highly sensitive transduction mode.

Photoluminescence of oxidized porous silicon treated by sodium borohydride aqueous solution

Alkaline solutions are usually used to remove porous layer from porous silicon. However, novel star-like photoluminescent oxidized porous silicon (PS) particles have been successfully fabricated in sodium borohydride (NaBH4) solution in this work. It is interesting that porous layer has been oxidized in NaBH4 alkaline solution, rather than being removed. Silicon oxide is formed due to the constant reactions of silicon nanocrystals and NaOH. Then these oxides are adjusted to star-like morphology by the pressure of H2. Both NaOH and H2 are generated from the hydrolysis of NaBH4. Oxidized PS shows bright orange photoluminescence (PL) at 550nm. This emission can be simply tuned into red or blue by illumination of high pressure mercury lamp or high temperature treatment. The PL of NaBH4-treated PS is originated from quantum confinement and surface state of silicon nanocrystallites.

Photoluminescence of porous silicon saturated with tungsten-tellurite glass with rare-earth metal impurities

It has been shown that the presence of silicon nanoparticles in a layer of porous silicon saturated with tungsten-tellurite glass causes an increase in the photoluminescence quantum efficiency of erbium (1530 nm) by an order of magnitude in the case of long-wavelength excitation and an enhancement of the ytterbium photoluminescence (980 nm) by almost 50 times and erbium photoluminescence by 25 times in the case of short-wavelength pumping. This luminescence enhancement is explained by the formation of additional channels of transfer of external excitation by silicon nanocrystallites in porous silicon to impurity ytterbium and erbium ions in tungsten-tellurite glass.

Emission mechanisms in stabilized iron-passivated porous silicon: Temperature and laser power dependences

Photoluminescence (PL) measurements of porous silicon (PS) and iron-porous silicon nanocomposites (PS/Fe) with stable optical properties versus temperature and laser power density have been investigated. The presence of iron in PS matrix is confirmed by Raman spectroscopy. The PL intensity of PS and PS/Fe increases at low temperature, the evolution of integrated PL intensity follows the modified Arrhenius model. The incorporation of iron in PS matrix reduces the activation energy traducing the existence of shallow levels related to iron atoms. Also, the temperature dependence of the porous silicon PL peak position follows a linear evolution at high temperature and a quadratic one at low temperature. Such evolution is due to the thermal carriers' redistribution and an energy transfer. Similarly, we have compared the laser power dependence of the PL in PS and PS/Fe layers. The results prove that the recombination process in PS is realised through the lower energy traps localised in the electronic gap. However, the observed emission in PS/Fe is essentially due to direct transitions. So, we can conclude that the presence of iron in PS matrix induces a strong modification of the PL mechanisms.

Effect of natural aging on photoluminescence of porous silicon

The influence of natural aging on the intensity and position of the photoluminescence (PL) peak in n-type porous silicon (por-Si) has been studied. Changes in the phase composition and relative content of the amorphous and oxide phases in por-Si during aging were determined by simulating the spectra of Si L2,3 ultrasoft X-ray emission based on the reference spectra of the corresponding phases.

Quenching influence of cell culture medium on photoluminescence and morphological structure of porous silicon

In this work, the degradation of visible photoluminescence of porous silicon (PSi) under the influential actions of cell culture medium has been mainly studied in order to comprehend the quenching mechanisms necessitating the cell growth on spongy-like-silicon structures, which could form either micro- and/or nano-dimensional morphologies after stain-etching of the poly- or single-crystalline Si surfaces. Quenching effect of the neuron culture medium on visibly luminescent and non-luminescent porous silicon is found to be quite obvious so that this step of the culture process, especially, over nanostructured silicon is extremely essential for a variety of bionanotechnological applications.

GAS ADSORPTION SENSORS ON THE BASIS OF POROUS SILICON

The influence of hydrogen and methane adsorption on high frequency (1 MHz) conductivity and capacity of sensor structures based on porous silicon has been studied. An essential changing in electric parameters was registered as a function of partial gas pressure. It was calculated the adsorption sensitivity of porous silicon and multilayer structures with catalytic films. Sensor selectivity to hydrogen and methane may be improved by deposition on porous silicon surface the catalytic films of palladium or poly(epoxypropylcarbazole). It observed a marked sensitivity of porous silicon photoluminescence to adsorption of ammonia and ethanol. The obtained results make it possible to optimize the fabrication of selective sensors based on porous silicon.

Photoluminescence of monocrystalline and stain-etched porous silicon doped with high temperature annealed europium

In this work, for the first time, the photoluminescent emission and excitation spectra of non-textured layers and stain-etched porous silicon layers (PSLs) doped with high temperature annealed europium (Eu) are evaluated. The PSLs are evaluated as a host for rare earth ions and as an antireflection coating. The applied doping process, which consists in a simple impregnation method followed by a high-temperature annealing step, is compatible with the standard processes in the fabrication of solar cells. The results show down-shifting processes with a maximum photoluminescent intensity at 615 nm, related to the transition 5D0 → 7F2. Different initial concentrations of Eu(NO3)3 are evaluated to study the influence of the rare earth concentration on the photoluminescent intensity. The chemical composition and the morphology of Eu-doped PSLs are examined by means of x-ray dispersion spectroscopy, Fourier-transform infrared spectroscopy and scanning electron microscopy. These Eu-doped layers are considered to be applied as energy converters in silicon-based third generation solar cells.

Tunable photoluminescence of porous silicon by liquid crystal infiltration

The photoluminescence (PL) of porous silicon films has been investigated as a function of the amount of liquid crystal molecules that are infiltrated into the constricted geometry of the porous silicon films. A typical nematic liquid crystal 4-pentyl-4′-cyanobiphenyl was employed in our experiment as the filler to modify the PL of porous silicon. It is found that the originally red PL of porous silicon films can be tuned to blue by simply adjusting the amount of liquid crystal molecules in the microchannels of the porous films. The chromaticity coordinates are calculated for the recorded PL spectra. The mechanism of the tunable PL is discussed. Our results have demonstrated that the luminescent properties of porous silicon films can be efficiently tuned by liquid crystal infiltration.