Porous Silicon Surface Research Articles

Structure and composition of a composite of porous silicon with deposited copper

Porous silicon is a promising nanomaterial for optoelectronics and sensorics, as it has a large specific surface area and is photoluminescent under visible light. The deposition of copper particles on the surface of porous silicon will greatly expand the range of applications of the resulting nanocomposites. Copper was chosen due to its low electrical resistivity and high resistance to electromigration compared to other metals. The purpose of this research was to study changes in the structure and composition of porous silicon after the chemical deposition of copper. Porous silicon was obtained by the anodisation of monocrystalline silicon wafers KEF (100) (electronic-grade phosphorus-doped silicon) with an electrical resistivity of 0.2 Ohm·cm. An HF solution in isopropyl alcohol with the addition of H2O2 solution was used to etch the silicon wafers. The porosity of the samples was about 70 %. The porous silicon samples were immersed in copper sulphate solution (CuSO4·5H2O) for 7 days. We used scanning electron microscopy, IR spectroscopy, and ultrasoft X-ray emission spectroscopy to obtain data on the morphology and composition of the initial sample and the sample with deposited copper. The chemical deposition of copper on porous silicon showed a significant distortion of the pore shape as well as the formation of large cavities inside the porous layer. However, in the lower part the pore morphology remained the same as in the original sample. It was found that the chemical deposition of copper on porous silicon leads to copper penetrating into the porous layer, the formation of a composite structure, and it prevents the oxidation of the porous layer during storage. Thus, it was demonstrated that the chemical deposition of copper on a porous silicon surface leads to visible changes in the surface morphology and composition. Therefore, it should have a significant impact on the catalytic, electrical, and optical properties of the material.

Improved spectral responsivity of porous silicon after the deposition of palladium nanoparticles via laser ablation at different laser energies

In this work, palladium (Pd) nanoparticles (NPs) were synthesized using laser ablation in liquids (LAL) at laser energies of 360, 660, and 800[Formula: see text]mJ and a laser wavelength of 1064[Formula: see text]nm with 200 pulses per shot. The Pd nanoparticle suspension deposited on porous silicon (PS) was investigated. X-ray diffraction (XRD) was used to determine the crystal structure. Field emission-scanning electron microscopy (FE-SEM) revealed the sponge-like structure of the PS and spherical clusters of Pd NPs within it. The optical properties of the prepared solution samples were investigated by testing the absorbance between 250–850[Formula: see text]nm, and energy gap values of ∼2.35, 2.56, and 2.75[Formula: see text]eV were calculated for the laser energies 360, 660, and 800[Formula: see text]mJ, respectively. The electrical properties, including [Formula: see text] and [Formula: see text] of the Al/PS/Si/Al and Al/Pd NPs/PS/Si/Al heterojunctions were calculated from [Formula: see text] measurements. The observed enhancement of the fabricated Pd NPs/PS is shown by the broad spectral response in the visible to near-infrared (vis-NIR) range. The increased spectral responsivity due to coating the PS surface with Pd NPs promotes using these nanostructures in photodetectors.

Growth and optical properties of ZnO nanorods on the full surface of porous silicon by sol–gel method and oil bath method

A method for the preparation of composites that allow the growth of ZnO nanorod structures on the full surface of porous silicon (polished surface, pore walls, and pore bottoms) is presented. The porous silicon is obtained by electrochemical etching of P-type silicon (100). The nanorods were grown in two steps: a sol–gel method and an oil bath method. The morphology of ZnO nanorods at different concentrations of the growth solution was investigated using scanning electron microscopy. X-ray diffraction confirmed the formation of ZnO hexagonal fibrous zincite structures. UV–Vis absorption spectroscopy confirmed that the composites possess good light absorption in the broad spectral region. In the wavelength range of 300 to 400 nm, the light absorption value of the porous silicon/zinc oxide (porous Si/ZnO) nanorods was increased by ~25% compared to that of the porous Si/ZnO films. The photoluminescence spectra confirmed the luminescence performance of the composites. Finally, the optical properties of the composites were further verified by simulation calculations.

Effect of wafer resistivity and light intensity on the topography of porous silicon surfaces produced by photo chemical method

This study includes the effect of wafer resistivity and intensity of light on topography of porous silicon surfaces which produced by photo chemical etching method, the results showed that changing of the resistivity led to change the porosity, where it found the porous silicon layer be less of high value resistivity. 
 Once all the wafers have same resistivity's value that’s found the light intensity effect on porosity, the less value of porosity produced by the less value of intensity light focused.
 The production of Nano crystalline silicon structures and control of their production conditions is the first step to control the properties of the devices (detectors, diodes, solar cells, sensors) and their appropriate applications. Ultimately, this is important in promoting research and development of renewable energy.

Self-Organization Effects of Thin ZnO Layers on the Surface of Porous Silicon by Formation of Energetically Stable Nanostructures.

The formation of complex surface morphology of a multilayer structure, the processes of which are based on quantum phenomena, is a promising domain of the research. A hierarchy of pore of various sizes was determined in the initial sample of porous silicon by the atomic force microscopy. After film deposition by spray pyrolysis, ZnO nanoclusters regularly distributed over the sample surface were formed. Using the electron paramagnetic resonance (EPR) method it was determined that the localization of paramagnetic centers occurs more efficiently as a result of the ZnO deposition. An increase in the number of deposited layers, leads to a decrease in the paramagnetic center relaxation time, which is probably connected with the formation of ZnO nanocrystals with energetically stable properties. The nucleation and formation of nanocrystals is associated with the interaction of particles with an uncompensated charge. There is no single approach to determine the mechanism of this process. By the EPR method supplemented with the signal cyclic saturation, spectral manifestations from individual centers were effectively separated. Based on electron paramagnetic resonance and photoluminescence studies it was revealed that the main transitions between energy levels are due to oxygen vacancies and excitons.

Porous silicon decorated with Au/TiO2 nanocomposites for efficient photoinduced enhanced Raman spectroscopy.

In this study, we investigated the potential of porous silicon (PSi) modified with Au/TiO2 nanocomposites (NCPs) as a substrate for photoinduced enhanced Raman spectroscopy (PIERS). One-step pulsed laser-induced photolysis (PLIP) was used to embed Au/TiO2 NCPs in the surface of PSi. Scanning electron microscopy revealed that adding TiO2 nanoparticles (NPs) during PLIP led to the formation of predominantly spherical Au NPs with a diameter of approximately 20 nm. Furthermore, modifying the PSi substrate with Au/TiO2 NCPs considerably enhanced the Raman signal of rhodamine 6G (R6G) after 4 h of ultraviolet (UV) irradiation. Real-time monitoring of the Raman signals of R6G at different concentrations under UV irradiation revealed that the amplitude of the signals increased with the irradiation time for R6G concentrations ranging from 10-3 M to 10-5 M. PSi substrates decorated with Au/TiO2 NCPs may be used to develop materials for PIERS applications.

Locally resonant porous phononic crystal sensor for heavy metals detection: A new approach of highly sensitive liquid sensors

In this research, a novel and highly sensitive phononic crystal (PnC) sensor is presented for the detection of CdBr2 concentrations at a low scale (ppm) which is considered a highly toxic heavy metal ion in freshwater. The proposed sensor is composed of two thin layers of rubber covering both the top and bottom surfaces of a one-dimensional ternary porous silicon (PSi) PnC. As a result, the whole designed structure is arranged as {rubber/[PSi1/PSi2/PSi3]N/rubber}. The appearance of local resonant modes is due to the presence of two thin rubber layers as a cap layer of the PnC design. In particular, the spectral position of the modes is significantly tuned when filling the PSi layers with CdBr2 ions. It is worth mentioning that the novelty of this work is mainly focused on three axes. The first one is the use of locally resonant PnCs (not conventional defective ones) as highly sensitive biosensors. The second one, the liquid of interest here is considered a dangerous aqueous solution with a very low scale (ppm). The last promising point, we proposed the pores inside Si layers are filled with a liquid material in contrast to most of the micromechanics methods of composite materials that supposed the pores are empty (just voids are inside). To realize the best performance of this sensor, an optimization strategy of some related parameters such as the rubber layer thickness, the geometry of the PnC, and the unit cell number was conducted. In this regard, the proposed sensor provides promising values of sensitivity, quality factor, detection limit, and damping rate of 47.25 Hz/ppm, 2756.2, 82 ppm, and 0.00018, respectively. Therefore, the present design could be of serious contribution to liquid sensors and bio-sensing applications due to its simplicity, novelty, and high performance.

Porous silicon surface modification via a microwave-induced in situ cyclic disulfide (S-S) cleavage and Si-S bond formation

Porous silicon (pSi) materials have gained a great deal of attention from various research fields, and their surface-functionalization is one of the critical points for their applications. In this study, a new surface modification method of Si-H-terminated pSi materials via microwave-induced Si-S bond formation is disclosed. The silicon hydride (Si−H) functionality on the pSi surface could react with the 5-membered cyclic disulfide (S-S) compound (DL-α-lipoic acid in this study) by microwave-induced in situ S-S bond cleavage and Si-S bond formation. This surface chemistry is fast responsive (<10 min) and more efficient than other methods such as vortexing, heating stirring, or ultrasonication. The reaction maintains the primary porous structure of pSi materials including pSi wafer, pSi rugate filer, and pSi nanoparticles. An additional functional group such as carboxylic acid is demonstrated to be readily introducible on the pSi surface for further applications. Overall, this study has successfully demonstrated the porous silicon surface modification via a microwave-induced in situ cyclic disulfide (S-S) cleavage and Si-S bond formation.

Wet Chemical Synthesis and Characterization of Au Coatings on Meso- and Macroporous Si for Molecular Analysis by SERS Spectroscopy

Porous silicon (PS) is a promising material for nanostructure fabrication providing a precise control over its size, shape, and spatial distribution. This makes it an excellent candidate for constructing highly sensitive, reproducible, and low-cost platforms for surface enhanced Raman scattering (SERS) spectroscopy. In this work, we connect the PS structural parameters with the morphology of the gold nanostructures fabricated on its surface, placing the emphasis on the SERS response. Two different types of PS are considered here, namely meso- and macro-PS. The former is prepared by Si electrochemical etching, applying three different current densities: 100 mA cm−2, 60 mA cm−2, and 30 mA cm−2, while the technological parameters for the latter are selected to mimic metal nanovoids’ (Me NVs) configuration. The gold-coated PS surfaces are produced via an electroless chemical deposition method for different time periods. By performing comprehensive structural, morphological, and optical characterization, we show the importance of the size and density of the PS pore openings, which govern the Au growth kinetics. The results presented in this work assure a simple yet flexible approach for the fabrication of large-area plasmonic gold nanostructures, which are not only suitable for advanced SERS spectroscopy studies but can also serve for a wider range of plasmonic applications.

Fabrication of Porous Silicon as a Gas Sensor: The Role of Porous Silicon Surface Morphology

Manufacture of an environmental polluting gas sensor with improved properties by controlling the preparation conditions of the photo-electrochemical etching technique (PECE). The amount of porosity, the diameter of the pores, and the thickness of the prepared layer of porous silicon (Psi) can be controlled by changing one or all of these conditions. In this paper, n-type Si with a crystalline orientation (100) was used, whereby PSi was prepared with the use of a red diode laser with a wavelength of 650 nm, using different radiation intensity, and with the constancy of etching time and current density. Through the results obtained, it was noted that: the porosity increases significantly up to 75% as well as the thickness of the PSi layer up to 1.45 µm with the increase in the intensity of the laser beam. Also, examining the morphology of the surface samples by field emission scanning electron microscope (FE-SEM) besides, the average pore diameters of the prepared samples were calculated. It is clear that the intensity of the laser beam used in the irradiation process is one of the important factors in determining the properties of the prepared PSi. PSi samples have been tested by FTIR to investigate chemical bonds on surfaces such as, (Si-Si, Si-H, Si-H2, Si-O-Si, Si-O-Si, Si-H, Si-O-Si). Samples tested as gas sensors and noticed that an increase in the sensing current to 5.3 µA has appeared with the increase of porosity value where methanol gas is used as background.

Porous Silicon Carrier Endowed with Photothermal and Therapeutic Effects for Synergistic Wound Disinfection.

Drug carriers endowed with photothermal effects will allow the drug delivery system to release drugs in a thermal-stimuli manner. In addition, the photothermal therapy (PTT) will also interplay with therapeutic drugs loaded in the carrier to exhibit synergistic bioactivity for various disease treatment. However, endowing the drug carrier with photothermal and synergistic therapeutic effects still has challenge. Herein, we demonstrate that surface modification of porous silicon (PSi) with polydopamine (PDA) could endow the classical drug carrier with a significant photothermal effect for advanced antibacterial therapy and wound disinfection. Specifically, the PSi surface interacts with a Cu2+/PDA complex via a simple and fast surface reduction-induced deposition method, forming the unique CuPDA coated PSi microcarrier (CuPPSi) without blocking the mesoporous structure. The CuPPSi carrier generates a higher near-infrared (NIR) photothermal efficiency and improved drug loading capacity owing to the abundant functional groups of PDA. Stimuli-responsive release of antibacterial Cu2+ and loaded curcumin (Cur) from CuPPSi can be realized under multiple stimuli including pH, reactive oxygen species and NIR laser irradition. Benefited from the carrier's intrinsic multimodal therapy, the CuPPSi-Cur platform exhibits amplified, broad-spectrum, and synergistic antibacterial effect, killing more than 98% for both Staphylococcus aureus and Escherichia coli at a mild PTT temperature (∼45 °C). Notably, the combined therapy promotes migration of fibroblasts with no significant cytotoxicity as revealed through cell experiments in vitro. In bacteria-infected mice model, efficient bacterial ablation and wound healing are further demonstrated with negligible side effects in vivo. Overall, the rational design of a drug carrier with photothermal and therapeutic effects provides a novel intervention for amplifing wound disinfection clinically.

Nanostructured Silicon Enabled HR-MS for the Label-Free Detection of Biomarkers in Colorectal Cancer Plasma Small Extracellular Vesicles

Despite improvements in treatment options for advanced colorectal cancer (CRC), survival outcomes are still best for patients with non-metastasised disease. Diagnostic tools to identify blood-based biomarkers and assist in CRC subtype classification could afford a means to track CRC progression and treatment response. Cancer cell-derived small extracellular vesicles (EVs) circulating in blood carry an elevated cargo of lipids and proteins that could be used as a signature of tumour suppressor/promoting events or stages leading up to and including metastasis. Here, we used pre-characterised biobanked plasma samples from surgical units, typically with a low volume (~100 µL), to generate and discover signatures of CRC-derived EVs. We employed nanostructured porous silicon (pSi) surface assisted-laser desorption/ionisation (SALDI) coupled with high-resolution mass spectrometry (HR-MS), to allow sensitive detection of low abundant analytes in plasma EVs. When applied to CRC samples, SALDI-HR-MS enabled the detection of the peptide mass fingerprint of cancer suppressor proteins, including serine/threonine phosphatases and activating-transcription factor 3. SALDI-HR-MS also allowed the detection of a spectrum of glycerophospholipids and sphingolipid signatures in metastatic CRC. We observed that lithium chloride enhanced detection sensitivity to elucidate the structure of low abundant lipids in plasma EVs. pSi SALDI can be used as an effective system for label-free and high throughput analysis of low-volume patient samples, allowing rapid and sensitive analysis for CRC classification.

Spectral-Free Double Light Detection of DNA Based on a Porous Silicon Bragg Mirror.

To improve the detection sensitivity of a porous silicon optical biosensor in the real-time detection of biomolecules, a non-spectral porous silicon optical biosensor technology, based on dual-signal light detection, is proposed. Double-light detection is a combination of refractive index change detection and fluorescence change detection. It uses quantum dots to label probe molecules to detect target molecules. In the double-signal-light detection method, the first detection-signal light is the detection light that is reflected from the surface of the porous silicon Bragg mirror. The wavelength of the detection light is the same as the wavelength of the photonic band gap edge of the porous silicon Bragg mirror. CdSe/ZnS quantum dots are used to label the probe DNA and hybridize it with the target DNA molecules in the pores of porous silicon to improve its effective refractive index and enhance the detection-reflection light. The second detection-signal light is fluorescence, which is generated by the quantum dots in the reactant that are excited by light of a certain wavelength. The Bragg mirror structure further enhances the fluorescence signal. A digital microscope is used to simultaneously receive the digital image of two kinds of signal light superimposed on the surface of porous silicon, and the corresponding algorithm is used to calculate the change in the average grey value before and after the hybridization reaction to calculate the concentration of the DNA molecules. The detection limit of the DNA molecules was 0.42 pM. This method can not only detect target DNA by hybridization, but also detect antigen by immune reaction or parallel biochip detection for a porous silicon biosensor.

Effect of surfactant and etching time on p-type porous silicon formation through potentiostatic anodization

Electrochemical anodization provides the scalability required for structuring porous silicon (PSi) layers for mass production; hence, new and feasible processes are highly sought-after. We investigate the effect of surfactant (additive) and etching time on the morphology of PSi matrix in a simplistic two-electrode anodization cell using aqueous HF electrolyte. Instead of the conventional galvanostatic mode (constant current density), we use the rarely reported technique of potentiostatic anodization (constant applied potential) for engineering PSi surface morphology. We demonstrate that under a constant applied potential, channel-like morphology, pyramids or well-ordered macropores are easily achieved through either increasing the processing time or adding a small amount of surfactant into the electrolyte. Our results provide better understanding of the mechanism underlying the formation of PSi and propose a practical solution for obtaining application-specific macrostructure of PSi.

Magneto-optical properties of cobalt nanoparticles in porous silicon

We report on the magnetooptical response of cobalt nanoparticles deposited on porous silicon surface. The use of such unconventional surface leads to a random feature for crystal relaxation considerably different from those of the smoothed one. Interestingly, heat treatment of the silicon substrate shows a significant effect on the morphology of the cobalt nanoparticles. Annealing exhaustively changes the shape of the cobalt nanoparticles. The study of the magnetic properties of the elaborated samples shows a peculiar behavior. Noticeably, an asymmetric hysteresis loop of the deposited cobalt is obtained. This result is attributed to a quadratic magneto-optical Kerr effect (QMOKE) contribution which certainly finds its origins in the interaction between neighboring clusters.

Morphology and Optical Properties of Nanostructure Porous Silicon Prepared by Electrochemical Etching for Solar Cells Application

In this work, nanostructure porous silicon surface was prepared using electrochemical etching under different current densities. I have studied the surface morphology and photoluminsense of four samples prepared at current densities 5 , 10 , 15 and 20 mA/cm2at fixed etching time 10 min.photoluminsense study showed that the energy gap of the porous silicon samples are is 3.1eV,and it was higher than the energy gap of bulk silicon which was 1.08 eV. A scanning electron microscope (SEM) micrographs were used to estimate the surface area. The surface area of the porous layer is strongly dependent on the porous layer geometry and its depth. The optical reflectance measurements were obtained by using an optical reflectometer (UV) which is equipped with an integrating sphere in the (200-1100) nm wavelength range, which reveals that the textured cells with PS layer sources have lower reflectivity value compared to the textured cell without PS structure.

Change of Optical Properties of Carbon-Doped Silicon Nanostructures under the Influence of a Pulsed Electron Beam

In the work, porous silicon with observed photoluminescence was made from a p-type silicon substrate doped with boron and crystallographic orientation (100) using the method of electrochemical etching in a solution containing H2(SiF6) (silicon hydrofluoric acid) and ethyl alcohol. Thin carbon films were sprayed by high-frequency magnetron sputtering at room temperature onto the surface of porous silicon. The resulting carbon-doped thin films of porous silicon were irradiated on a pulsed electron booster and comparisons were made with nonirradiated films of porous silicon. To understand the effect of carbon on the properties of porous silicon films samples were analyzed by Raman spectroscopy, spectrophotometry, and scanning probe microscopy (SPM). The results of the SPM showed that the roughness of the samples increases after carbon doping on the surface of porous silicon. Thus, for the first time, experimental results were obtained on the effect of irradiation on carbon-doped porous silicon obtained in a solution containing hydrogen hexafluorosilicate H2(SiF6) and a significant change in its optical properties was shown. The results of the study showed that irradiated samples of carbon-doped porous silicon have better photoluminescence compared to nonirradiated samples.

Analysis of Porous Silicon Formation on N-type Si (100) using Laser-Assisted Electrochemical Anodization Method

Porous silicon (PSi) was formed on n-type Si (100) substrates using the laser-assisted electrochemical anodization method. The silicon surface was anodized in the solution of HF (40%) and ethanol (99%) in a ratio of 3:1 at a current density of 20 mA/cm2 for 15 min. The laser was illuminated on a silicon surface during the etching process. PSi surface morphology was characterized by SEM and identification of chemical bonds using FTIR. The highest number of pores, the best pore size homogeneity, and the smallest pore diameter in PSi were formed in Si which was illuminated by a green laser (2.33 eV). In contrast to red (1.91 eV) and purple (3.06 eV) formed irregular pores because of their small number and inhomogeneous size. On the PSi surface, Si-H and Si-O-Si bonds are formed. The number of Si-Hn and Si-O-Si bonds is directly proportional to the number of pores formed in PSi.

Functionalized nanoporous silicon for extraction of Sc from a leach solution

Production of scandium (Sc) is a complicated process largely because the Sc concentration in ores is typically low in comparison to other types of metals. Therefore, typical extraction processes, such as solvent extraction and precipitation, that are used for separation and purification of leach liquors are inefficient. Adsorption/desorption is a good alternative method for extraction, but it is challenging to prepare affordable adsorbents with high stability, good selectivity, and high adsorption capacity. Most Sc sources are currently unexploited, and new, efficient, and environmentally sustainable methods for Sc extraction are needed. In the present study, bisphosphonates (BPs) immobilized on the surface of nanoporous silicon were used as metal ion chelators. Thermal carbonization was used to passivate the porous silicon surfaces with silicon carbide, on which the BP molecules were grafted. The BP grafted thermally carbonized porous silicon (BP-TCPSi) was used to extract Sc from a leach solution of Sc ore obtained from Rautalampi, Finland. First, Sc was leached from the ore using sulfuric acid. An oxidative precipitation method was employed to reduce the concentrations of the interfering metal ions; this treatment decreased the Fe, Ti, Al, and Mn concentrations by 99 ± 2%, 100 ± 14%, 35 ± 1%, and 76 ± 2%, respectively, while only 12 ± 1% of Sc was lost. The selectivity of BP-TCPSi was studied in a flow-through setup to adsorb Sc from the treated leach solution; then, in a two-step desorption process, Sc was separated from the other metal ions with a separation factor of 440 ± 13. The reusability of BP-TCPSi was examined in a flow-through setup with 10 adsorption/desorption cycles using a treated leach solution showing good stability of the adsorbent. The developed method provides a fast and convenient way to extract, purify, and enrich Sc with total recovery of 69 ± 1% in one cycle of adsorption/desorption of Sc from the leach solution with a low Sc concentration and a relatively high concentration of the other metal ions.

Preparation high quality ethanol gas sensor by modifying porous silicon (PS) surface with carbon nanotube (CNTs)

In the study, the high-quality gas sensor for ethanol was prepared by modified porous silicon (PS) with a thin layer of carbon nanotube. The PSi samples have been prepared by using the photoelectrochemical etching (PECE) process at various current densities J = 12, 24, and 30 mA/cm2 with 10 min etching time and Hydrofluoric acid concentration (HFC) of 40%. All samples (PSi and MWCNTs/PSi) were analyzed using X-ray diffraction (XRD), field emission Scanning electron microscopy (FE-SEM), Fourier Transform Infrared Spectroscopy (FTIR), and Atomic Force Microscopic (AFM), to determine the structural, morphological, and surface bond configuration. As a result, the Photoluminescence (PL) test was performed on all samples using the PL system in order to calculate the energy band gap for all samples. Then the PSi and MWCNTs/PSi samples were applied as ethanol gas sensor at room temperature (RT). The results showed that the best sensitivity of ethanol gas was about (2.1912349) at a concentration of 500 parts per million (ppm) for MWCNTs/PSi sample compared to PSi surface, it was about (1.709) under the same used conditions at etching current density 30 mA/cm2. The MWCNTs/PSi layers serve as low-cost and high-quality ethanol gas sensors. The carbon nanotube used to replace expensive materials used in gas sensors that function at low temperatures, including room temperature. The materials have an exceptionally high surface-to-volume ratio (increasing surface area), ease of fabrication, and compatibility with silicon microelectronics manufacturing processes.