Surface Modification Of Porous Silicon Research Articles

Near-infrared photodetector based on the surface modification of porous silicon with silver nanoparticles

This study describes the modification of Porous silicon (PS) by depositing commercial Ag powder on its surface and within its pores to improve its physical properties and performance as a near-infrared (NIR) photodetector. The incorporation of Ag-nanoparticles (Ag-NPs) into the PS structure increases the energy band gap from 1.74 eV to 2.46 eV and decreases the diffuse reflectance over a broad range of wavelengths. Afterward, NIR photodetectors of both structures are produced. The maximum current is measured at 850 nm for both photodetectors. In addition to a substantial decrease in the dark current of PS-Ag, PS-Ag's photo-excited current is 4.5 times greater than its dark current, whereas PS's photo-excited current is only 1.7 times greater. In addition, the I–V curves are used to determine the photodetector's sensitivity (S) and the current gain (G) at different incident light wavelengths. At wavelengths of 850 nm, the Au/PS-Ag/Au photodetector exhibits a greater sensitivity of 3.26 × 102 compared to the Au/PS/Au photodetector, which exhibits a sensitivity of 0.83 × 102. Based on the results, it is clear that modifying the PS with Ag-NPs is a strong candidate for excellent performance as a near-infrared photodetector in commercial photoelectronic device applications.

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.

Electrochemical and optical investigation of dental pulp stem cell adhesion on modified porous silicon scaffolds

Extensive use of porous silicon (PSi) for tissue engineering is due to its convenient properties as it is both nontoxic and bioresorbable. Moreover, PSi surface modification is an important step to enhance cell adhesion and proliferation. In this work, a combination of optical and electrochemical studies is performed to elaborate a suitable PSi multilayer substrate for cell culture. For this study, we modified PSi surface by silanization and antibody grafting (APTES-anti STRO1), the 12-mer specific peptide to silicon p + type coating and the peptide modified with the antibody recognition sequence. Electrochemical characterization of PSi multilayers is performed to investigate its electrical behavior, determine the optimal measuring conditions and reveal the most stable PSi surfaces. Then, the behavior of dental pulp stem cells (DPSC) was investigated on various modified PSi surfaces. An electrochemical method was applied for the first time monitoring the electrical behavior of stem cell adhesion. The cells electrochemical behavior depends on the nature of the surface coating and the peptide-anti STRO1 improved adhesion and cell spreading onto the PSi surface compared to bare surface and the one coated with the peptide. Fluorescent microscopy revealed that all surface modification methods enhance cell adhesion compared to the bare PSi surface. An increased cell number is observed on APTES-anti STRO1, peptide and peptide-anti STRO1 coated PSi. The peptide-anti STRO1 provided the best cell proliferation results suggesting the improved accessibility of the recognition fragment of the antibody anti-STRO1.

Spatially Controlled Surface Modification of Porous Silicon for Sustained Drug Delivery Applications

A new and facile approach to selectively functionalize the internal and external surfaces of porous silicon (pSi) for drug delivery applications is reported. To provide a surface that is suitable for sustained drug release of the hydrophobic cancer chemotherapy drug camptothecin (CPT), the internal surfaces of pSi films were first modified with 1-dodecene. To further modify the external surface of the pSi samples, an interlayer was applied by silanization with (3-aminopropyl)triethoxysilane (APTES) following air plasma treatment. In addition, copolymers of N-(2-hydroxypropyl) acrylamide (HPAm) and N-benzophenone acrylamide (BPAm) were grafted onto the external pSi surfaces by spin-coating and UV crosslinking. Each modification step was verified using attenuated total reflection-Fourier transform infrared (ATR-FTIR) spectroscopy, water contact angle (WCA) measurements, X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM). In order to confirm that the air plasma treatment and silanization step only occurred on the top surface of pSi samples, confocal microscopy was employed after fluorescein isothiocyanate (FITC) conjugation. Drug release studies carried out over 17 h in PBS demonstrated that the modified pSi reservoirs released CPT continuously, while showing excellent stability. Furthermore, protein adsorption and cell attachment studies demonstrated the ability of the graft polymer layer to reduce both significantly. In combination with the biocompatible pSi substrate material, the facile modification strategy described in this study provides access to new multifunctional drug delivery systems (DDS) for applications in cancer therapy.

A Mini Review: Recent Advances in Surface Modification of Porous Silicon.

Porous silicon has been utilized within a wide spectrum of industries, as well as being used in basic research for engineering and biomedical fields. Recently, surface modification methods have been constantly coming under the spotlight, mostly in regard to maximizing its purpose of use. Within this review, we will introduce porous silicon, the experimentation preparatory methods, the properties of the surface of porous silicon, and both more conventional as well as newly developed surface modification methods that have assisted in attempting to overcome the many drawbacks we see in the existing methods. The main aim of this review is to highlight and give useful insight into improving the properties of porous silicon, and create a focused description of the surface modification methods.

Modifying and Fine Controlling of Silver Nanoparticle Nucleation Sites and SERS Performance by Double Silicon Etching Process

Different forms of modified and well-controlled plasmonic silver nanoparticles (AgNPs) were synthesized by silver ion reduction process of porous silicon (PS). Fine control of PS surface morphology was accomplished by employing two etching processes: light-induced etching (LIE) and photo electrochemical etching (PECE). The idea was to prepare excellent and reproducible surface-enhanced Raman scattering (SERS) substrates with high enhancement performance. PS surface modification was employed to create efficient and nearly uniformly distributed AgNP hotspot regions with very high specific surface areas. Reproducibility deviation of no more than 5% and enhancement factor of 1.2 × 1014 were obtained by SERS measurements at very low, rhodamine 6G (R6G) dye, concentration 10−15 M. The PS morphology SERS substrate was well discussed and analyzed using field emission scanning electron microscopy (FE-SEM), X-ray diffraction spectroscopy (XRD), and Raman measurements.

A study of the role of polyacrylic acid in the surface modification of porous silicon with the aim of enhancing and stabilizing silicon photoluminescence

The effect of the chemical treatment of porous silicon with polyacrylic acid on the composition and photoluminescence properties of silicon is studied by infrared spectroscopy and photoluminescence. A mechanism of interaction between polyacrylic acid and the surface of porous silicon, which leads to a significant increase in the photoluminescence intensity of the samples, is proposed.

Surface of porous silicon under hydrophilization and hydrolytic degradation

Analysis of the IR absorption spectra is used to trace changes in the chemical composition of surface layers of mesoporous silicon crystals during the course of their hydrophilization via oxidation in hydrogen-peroxide solutions and as a result of indirect, by intermediate bromination, and direct nucleophilic substitution of bound hydrogen with a hydroxyl. The spontaneous process of atomic rearrangement with the transfer of oxygen atoms from adsorbed OH groups to lower-lying atomic layers of the crystalline skeleton, which yields Si-H bonds on its surface: -Si-Si-OH→-Si-O-Si-H, is revealed. The sequence of elementary processes that facilitate the hydrolytic degradation of porous silicon in weakly alkaline media is considered. The role played by the deformation of chemical bonds in a porous crystal in promoting the hydrolysis of silicon is noted. It is shown that the surface modification of porous silicon via bromination and subsequent treatment in water makes it possible to substantially increase the rate of its hydrolytic degradation in weakly alkaline solutions that are similar in pH values to biological fluids.

Surface modification of porous silicon with mesogenic moieties

The liquid crystal monolayer was obtained on Si (100) wafer using a hydrosilylation reaction catalyzed by Pt compounds. The chemical modification of the surface of silicon wafer was characterized using the attenuated total reflection IR spectroscopy and X-ray photoelectron spectroscopy. The silicon surface texture was evaluated with atomic force spectroscopy and high-resolution scanning electron microscopy.

Photosensitive Structures of Conjugated Polymer - Porous Silicon

The photosensitive hybrid structures poly-3,4-ethylenedioxythiophene (PEDOT)– porous silicon (PS)–n-Si are fabricated. Current-voltage characteristics of the obtained structures are investigated. It is shown that PS surface modification by PEDOT conjugated polymer gives rise to the appearance of a pronounced rectifying effect on the current-voltage characteristics. Spectral characteristics of photoresponse in the 450–1100 nm wavelength range, its temperature dependence in the 125–325 K range, and energy characteristics of the hybrid photovoltaic structures are studied. We propose possible mechanisms of the photoelectric processes in the hybrid structures PEDOT–PS–n-Si.

Electrical and optical characteristics of porous silicon impregnated with LaF 3 by a novel chemical bath technique

The structural, electrical and optical characteristics of porous silicon (PS) due to the impregnation of LaF 3 into PS by a novel chemical-bath deposition (CBD) technique have been investigated in this article. Without removing the PS from the anodization chamber the impregnation with LaF 3 has been done by reacting LaCl 3 with HF in the same chamber at room temperature. The impregnation of LaF 3 was confirmed by the SEM on the cross-section of the LaF 3/PS/Si system and EDX. The modification of PS surface by LaF 3 had direct influence on the electrical and optical properties of PS. Electrical properties of Ag/LaF 3/PS/p-Si/Ag structures were studied through the current–voltage ( I– V) and capacitance–voltage ( C–V) characteristics. Formation of metal–insulator–semiconductor (MIS) diode was evident whose forward current increased with annealing. A diode factor of about 2.4 has been obtained for the annealed heterostructure indicating a high density of trap states. The C −2- V curves of all samples showed negative flat band voltage of around −2 V confirming a large number of fixed positive charges in the LaF 3. The photoluminescence (PL) intensity of the LaF 3-impregnated PS showed aging for the as-deposited samples, but when annealed PS structure recovered the PL intensity. Experimental results show that the optimized chemical bath passivation process for the LaF 3 on porous silicon could enable the porous silicon to be an important material for photonic application.

Surface modification of composites with metal nanoparticles

This work examines the possibility of using copper, nickel, and cobalt nanoparticles in the electrodeposition of nickel coatings and for surface modification of porous silicon, and also colloidal silver particles for surface modification of silver-containing polymer-matrix composites. It is shown that the deposition of metal nanoparticles may influence the morphology, electronic structure, and phase composition of the surface and the catalytic, electrical, and optical properties of the material.

Chemical surface modification of porous silicon with palladium and characterizations

Porous silicon (PS) was formed on p-type crystalline silicon of (1 0 0) orientation and 2–5 Ω cm resistivity by the electrochemical anodization method using HF and ethanol as the electrolyte. Adjusting the current density and the HF concentration in the electrolyte the porosity of the samples were varied from 40% to 60%. The porous silicon surface was modified with PdCl 2 solution by a low cost chemical method. Both the unmodified and the modified PS were thoroughly characterized by the EDAX analysis, the digital X-ray image mapping and the XPS study. Electrical characteristics were performed by the I– V measurements for both the lateral and the sandwich structures using Al metal contact. The I– V characteristics of the modified PS for all the porosity were more reproducible compared to the unmodified PS surfaces. It was further observed that the conductivity increased with the increasing porosity for the Pd-modified surfaces whereas it decreased for the unmodified PS.

Porous Silicon for Photosensitized Formation of Singlet Oxygen in Water and in Simulated Body Fluid: Two Methods of Modification by Undecylenic Acid

Initially H-terminated and therefore hydrophobic surface of electrochemically prepared luminescent porous silicon (PSi) powder was transformed to the hydrophilic one by means of surface modification by undecylenic acid. Physical adsorption of undecylenic acid as a non-ionic surfactant and its chemical binding through C[triple bond]C bond opening and Si-C bond formation were applied as two different methods of PSi surface modification, physical and chemical modification, respectively. Luminescence of aqueous suspensions of the both types of modified PSi powders in merely water and in simulated body fluid physiological electrolyte was measured as a function of time. Many-fold (up to 20 times) building-up of the luminescence intensity was observed for PSi aqueous suspensions during the first few days, the growth was followed by a slower (a week and more) luminescence intensity decay. As it is evidenced by FTIR spectra and SEM images, the effect of the luminescence growth and decay of PSi suspension in water can be in part attributed to the PSi surface oxidation accompanied by its dissolution and de-aggregation of large PSi particles. It is concluded also from the experiments on PSi luminescence reversible quenching by O2 that SiO-related surface states with the excitation energy about 2.2 eV are formed during water-assisted oxidation of Si nanocrystal surface. An appearance of a large number of such surface states can be also responsible for the observed PSi luminescence building-up.

Electrochemical Fabrication and Surface Modification of Porous Silicon

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Nanostructured Porous Silicon – Optical Properties, Surface Modification and Sensor Applications

Porous silicon is a very attractive material due to its intense visible photoluminescence at room temperature. Its unique physical and chemical properties are determined by the porous structure where a nanosized silicon layer is formed during the electrochemical etching of crystalline silicon. So far, the high chemical reactivity of the porous silicon surface has prevented its extensive application in optoelectronics. Considerable effort has been put into the development of suitable techniques of stabilization. On the other hand, high chemical reactivity and sorption capacity of porous silicon represent the principal advantage for the construction of sensitive sensors of chemical species. This article provides a brief overview of the ongoing activities in the development of porous-silicon-based chemical sensors at the Charles University and at the Institute of Chemical Technology. So far, the detection of chemical species is based on the measurement of the changes in photoluminescence intensity and photoluminescence decay time, other complementary electrochemical and optical detection methods will follow in order to increase the selectivity of the detection. Another approach resulting in increased selectivity of sensor response utilizes the modification of porous silicon surface – either by physical adsorption or chemical derivatization – by various molecules with recognition properties. Due to the interdisciplinary nature of the research the involved scientists have built a network of collaborating laboratories specialized in various fields – material research, surface chemistry, design and synthesis of the molecules with recognition properties and sensor development.

Transition metal mediated surface modification of porous silicon

Porous silicon has received considerable attention lately due to its unique optical properties and use in sensor applications. The utility of this material can be further advanced with the aid of new surface chemical modification methods. Here we describe two transition metal mediated reactions that allow for the mild and chemoselective functionalization of porous silicon. The first method utilizes rhodium carbene chemistry to modify porous silicon surfaces with esters and amides. The second technique exploits a pt-based Karstedt's catalyst to affect the hydrosilylation of porous silicon with alkenes. The mildness and selectivity of the hydrosilylation is highlighted by modification of n-type porous silicon matrix with an 8-residue cyclic peptide.

Surface Modification of Porous Silicon by Electrochemical Reduction of Organo Halides.

Functionalization of hydride-terminated porous and single-crystal silicon surfaces with organic species is accomplished by electrochemical reduction of organo iodides and organo bromides (see scheme). This new method is fast and efficient, and achieves high surface coverage with functionalized and nonfunctionalized alkyl and benzyl groups within minutes.

Surface Modification of Porous Silicon by Aluminum Isopropoxide and Its Impact on Electroluminescence

Dilute solutions of aluminum isopropoxide have been used to modify the surface of porous Si in an attempt to find simple chemical approaches to stabilize its electroluminescent response and simultaneously provide additional details concerning the mechanism of electroluminescence degradation. Both infrared and energy dispersive x‐ray spectroscopies confirm that aluminum is incorporated onto the porous Si surface. The modified porous Si has much more stable electroluminescence at lower bias voltages, and the rate of electroluminescence degradation is very sensitive to the surface temperature. The surface temperature, in turn, is clearly a function of applied bias voltage. Transmission electron microscopy and infrared spectroscopic measurements clearly demonstrate that the degradation is related to Si nanoparticle oxidation. By investigating the degradation rate of porous Si electroluminescence at different temperatures, the activation energy of porous Si oxidation can be estimated.

The effect of surface modification on the luminescence of porous silicon

The role of the surface in the optical properties of porous silicon remains a key issue. Although the burden of evidence points toward some intrinsic radiative mechanism in small silicon particles, the influence of the surface and ways of controlling surface interactions will always be important. We present here the results of surface modification of porous silicon using annealing and rapid oxidation steps. By comparing new results with existing published data we conclude that hydrogen passivation of the surface is not unique in its ability to saturate dangling bonds and hence promote strong luminescence; oxidation, especially at high temperatures, can play a similar role. Oxidation also produces an additional, low energy band which is linked to residual dangling bond related defects at the Si-SiO2 interface. Furthermore, this band suffers a blue shift with increasing porosity in similar fashion to that observed for the visible emission.