Porous Silicon Matrix Research Articles

Photodetector application of CuO nanoparticles on porous silicon fabricated by laser ablation in liquid at diverse laser energies

Abstract This paper describes the synthesis and analysis of a photodetector made of copper oxide nanoparticles (CuONPs) embedded in a porous silicon (PS) matrix. CuONPs were generated utilizing pulsed laser ablation in ethanol (PLAL), while a porous silicon-(PS) substrate was created via photo-assisted electrochemical etching. An investigation is conducted on the optical, structural, and electrical characteristics of CuONPs/PS devices, with a focus on their dependence on laser energy. The X-ray diffraction analysis reveals the presence of distinct peaks associated with a copper cubic structure, demonstrating the successful synthesis of CuONPs that have been deposited onto PS. The study using field emission scanning electron microscopy revealed that the particles exhibited spherical form. The CuO-nanocolloids exhibited a linear relationship between laser power and absorption, and their surface plasmon resonance peaks were clearly visible at 570–590 nm. Band gaps of 1.70, 1.61, 1.81, and 1.90 eV were found for CuONPs produced at 500, 600, 700, and 800 mJ of laser energy, respectively, according to the optical characteristics. The greatest responsivity of the CuO-NPs/PS photodetector, manufactured at an energy level of 700 mJ, was 0.135345 A/W at 450 nm, as determined by the optoelectronic characteristics. As a result of combining PS with CuONPs, the devices shown in this work have the ability to function as highly efficient photodetectors.

Molecular dynamics to model carbon infiltration into a porous silicon matrix: An experimental and computational approach

In this work, a porous silicon matrix (PSm) and its functionalization with carbon atoms are modeled by molecular dynamics (MD); the simulation is correlated experimentally to analyze the model results. Computationally, the Tersoff potential for the silicon carbon system is used to build a model by MD using Large-scale Atomic/Molecular Massively Parallel Simulator free-source code (LAMMPS). First, a model of a PSm with an aleatory distributed macroporous was built; then, C atoms were injected into the PSm model to functionalize the matrix; finally, the model shows the functionalization of the PSm, forming carbon-silicon composites, which are Si clusters surrounded by C atoms. Experimentally, PSm was fabricated using samples of a p-type crystalline silicon wafer by electrochemical etching. A colloidal suspension of graphene oxide (GOs) was used as a source of carbon atoms: the GOs was added to the electrolyte, during the etching process, to functionalize the PSm with C atoms. AFM images show that the PSm pores are not obstructed after functionalization. Carbon-silicon composites were formed into the PSm samples according to X-ray diffraction and EDS characterizations. The results of the modeling agree with the results of the experiments.

Synthesis of Al quantum dots on porous silicon as an effective radiation detector using extended gate technique

In this study, porous silicon (PS) and aluminum (Al) doped porous silicon were synthesized through an electrochemical method, utilizing carefully selected parameters. The etching procedure was calibrated with a 4:1 HF/ethanol ratio, maintaining a current of 20 mA for 20 min, and incorporating 0.05 g of doping powder. Comprehensive structural analysis using FESEM-EDX revealed the incorporation of Al into the porous silicon matrix. Subsequently, the samples were covered with a finger mask, which facilitated the creation of an interdigitated electrode using a sputtering deposition method. The I–V characteristics of the samples were systematically studied, showing an increase in bias voltage at the source correlated with the measured current. Remarkably, upon X-ray exposure, pulses were successfully measured, highlighting the potential of these materials for radiation detection. These pulses were evaluated under various X-ray irradiation parameters using a sample detector. The study successfully identified the optimal parameters for PS and Al-PS as (90 V, 100 mA, 1 s) and (100 V, 10 mA, 0.5 s), respectively. This research underscores the potential applications of these materials in advanced electronic devices and sensors. The unique properties of synthesized porous silicon, particularly when doped with aluminum, could be beneficial in areas such as photovoltaics, biosensors, and photonics. Additionally, the material's efficiency in detecting X-ray radiation suggests its suitability for medical imaging, security scanning, and radiation monitoring systems. Based on the I–V characteristic studies, these materials may be well-suited for use in electronic components requiring precise control of electrical properties. Overall, this study not only enhances our understanding of porous silicon and aluminum-doped porous silicon but also opens up new avenues for their application in a wide range of sensing technologies.

Thermal transport properties of porous silicon filled by ionic liquid nanocomposite system

This paper investigates thermal transport in a nanocomposite system consisting of a porous silicon matrix filled with ionic liquid. Firstly, the thermal conductivity and heat capacity of two imidazolium and one ammonium ionic liquids were evaluated using the photoacoustic approach in piezoelectric configuration and differential scanning calorimetry, respectively. Then, the thermal transport properties of the composite system "ionic liquid confined inside porous silicon matrix" were investigated with the photoacoustic approach in gas-microphone configuration. The results demonstrated a significant enhancement of the thermal conductivity of the composite system when compared to the individual components, i.e. (i) more than two times for pristine porous silicon and (ii) more than eight times for ionic liquids. These results provide new paths for innovative solutions in the field of thermal management, particularly in the development of highly efficient energy storage devices.

RAMAN SPECTRА OF SILICON/GERMANIUM ALLOY THIN FILMS BASED ON POROUS SILICON

The regularities of composition changes of silicon/germanium alloy thin films formed on a monocrystalline silicon substrate by electrochemical deposition of germanium into a porous silicon matrix with subsequent rapid thermal annealing (RTA) at a temperature of 750–950°C are studied. An analysis of the samples by Raman spectroscopy showed that an increase of RTA temperature leads to a decrease in the germanium concentration in the formed film. A decrease of the RTA duration at a given temperature makes it possible to obtain films with a higher concentration of germanium and to control the composition of thin silicon/germanium alloy films formed by changing the temperature and duration of RTA. The obtained results on controlling the composition of silicon/germanium alloy films can be used to create functional electronic devices, thermoelectric power converters, and optoelectronic devices.

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.

Synthesis of organic–inorganic hybrids based on the conjugated polymer P3HT and mesoporous silicon

Organic–inorganic hybrids are a class of functional materials that combine favorable properties of their constituents to achieve an overall improved performance for a wide range of applications. This article presents the synthesis route for P3HT-porous silicon hybrids for thermoelectric applications. The conjugated polymer P3HT is incorporated into the porous silicon matrix by means of melt infiltration. Gravimetry, sorption isotherms and energy dispersive X-ray spectroscopy (EDX) mapping indicate that the organic molecules occupy more than 50% of the void space in the inorganic host. We demonstrate that subsequent diffusion-based doping of the confined polymer in a FeCl3 solution increases the electrical conductivity of the hybrid by five orders of magnitude compared to the empty porous silicon host.

Фотолюмінесценція нанокристалічного CdTe, впровадженого в пористий кремній

A method of colloidal synthesis of monodisperse nanocrystals (NC) with high stability, narrow bands of photoluminescence (PL) and high quantum yield has been developed. The process of colloidal synthesis took place at room temperature and for the passivation of NC used a variety of surfactants. The surface of NC CdTe was modified by introducing them into a matrix, organic or crystalline. In our case, the matrix was porous Silicon (PS), that is a composite structure was formed on the basis of the matrix and NC semiconductor. Nanocomposite structures of PS – NC CdTe were obtained by introducing colloidal solutions of NC CdTe into the solid matrix of PS and subsequent processing at a certain temperature regime. The photoluminescent properties of a composite system in which the matrix is microcrystalline PS and the second component is NC CdTe deposited from a colloidal solution of NC CdTe have been studied. The peculiarity of this system is that both components have PL of different intensities.The large difference in PL intensities and different positions of the radiation bands allowed, comparing the PL spectra of the colloidal solution of NC CdTe, PS and NC CdTe – PS at different stages of introduction of CdTe nanoparticles into the porous Silicon surface, to identify the interaction and mutual influence of the two constituent materials. The main disadvantages of the method are its relative novelty, which leads to the need for empirical selection of some parameters of the synthesis. The planned change of properties of PS and colloidal solutions of NC CdTe by variation of technological methods of synthesis and processing methods will allow to control the physical properties of this composite system and use it to develop new principles of design and creation of new generation sensor devices.

Aberrant Putamen Connectivity in Adolescent Bipolar Disorder Type II Revealed by fMRI Analysis

This chapter discusses the fundamentals of porous silicon (PSi) based DNA biosensors. Various surface functionalization approaches are introduced, including surface passivation techniques that can be used to prevent corrosion of the PSi matrix upon DNA hybridization. Several PSi DNA sensor configurations are presented, ranging from single-layer interferometers to on-chip ring resonators, with a focus on performance in terms of sensitivity and limit of detection. Challenges to real-world implementation of PSi DNA biosensors are addressed and important areas of progress in on-chip integration and incorporation of microfluidic channels are highlighted. The chapter ends with an outlook on future point-of-care diagnostic applications.

Optical Properties of Monocrystalline Silicon Nanowires

The paper presents the results of a study of the optical reflection and transmission spectra of a silicon single crystal p-Si (100) with silicon nanowires grown on both sides and porous silicon p-Si (100) on a single crystal substrate in the spectral range 0.2 ÷ 1.7 μm. The layers of nanowires had a thickness of 5.5 µm, 20 µm, 50 µm and a porosity of 60 %. The porous silicon layers had a thickness of 5 μm, 50 μm and a porosity of 45 %, 55 % and 65 %. The change in the energy band structure in single-crystal silicon nanowires and in a single-crystal matrix of porous silicon is shown.

Magnetic and Plasmonic Composite Nanostructures for Creating Optical Filters at Substance and Material Diagnostics Systems

Introduction. Porous silicon (PS) and materials on its basis are of interest for application in nanoelectronics, targeted drug delivery and advanced gas sensors. In addition, PS-based nanostructures are promising as filters in fibre-optic communication systems, since conventional thin-film deposition filters possess sidebands in their operating range thus requiring high vacuum for nanometer-thick coatings.Aim. To develop optical band-stop filter prototypes based on composite magnetic nanoparticles and the effect of localized surface plasmon resonance (LSPR) in an array of silver nanoparticles located on the PS surface. Materials and methods. The development and synthesis of nanostructures for the creation of filter prototypes. The double differentiation method in conjunction with Mie absorption theory was used for processing and analyzing the prototypes attenuation characteristics.Results. Two prototypes were developed. An analysis of the attenuation characteristics of a prototype based on SiO2 matrix functionalized by FemOn indicated that the parameters of the detected absorption bands depend on the size of FemOn nanoparticles. The attenuation characteristics of the LSPR-based prototype contain two absorption bands. The center wavelength value in the band caused by LSPR in the array of silver nanoparticles, close to spherical, is 367.5 nm. Excitation of LSPR in silver quantum clusters, manifested by the appearance of the corresponding band, occurs at a wavelength of 265.5 nm. The suppression in each of the bands can be controlled by changing the parameters of the PS matrix synthesis.Conclusion. Despite the disadvantages, e.g. a relatively low accuracy in setting the center wavelength, as well as certain difficulties concerned with reducing the unevenness in the absorption band, the obtained prototypes surpass existing analogues and are prospective for the development of compact analysis and diagnostics systems in a wide energy range.

Temperature and excitation power dependence of photoluminescence and electrical characterization of Ni‐passivated porous silicon

A porous silicon (PS) layer was obtained on p-Si (100) substrate by electrochemical anodization and Ni-porous silicon nanocomposites (Ni–PS) were elaborated by the electrodeposition method using nickel chloride aqueous solution. PS and Ni–PS samples were analyzed by X-ray diffraction (XRD). The XRD patterns revealed the presence of nickel elements in the PS matrix. The investigation by Photoluminescence spectroscopy (PL) enabled us to exam the evolutions of PL peak position, PL intensity, and full width at half maximum (FWHM) as a function of temperature and excitation power density. The modified Arrhenius formula, considering two activation energies, has been used to fit the temperature-dependent integration of PL intensities. PL investigations show that Ni ions cause changes in the recombination process of PS by the creation of new radiative centers as well as the reduction of non-radiative transitions. For Ni–PS nanocomposites, the laser power dependence of the integrated PL intensity shows that the most of transitions are free to bound or bound to bound where as the excitonic transitions are the most dominant in untreated PS. The current–voltage (I–V) characteristics of Ag/PS and Ag/Ni–PS Schottky diodes have been examined. The Cheung method was adopted to extract the parameters of the diode. Experimental results show that the values of ideality factor (n), resistance series (Rs), and barrier height (φb) are affected by the presence of nickel in the porous matrix.

Advances in Novel Low-Macroscopic Field Emission Electrode Design Based on Fullerene-Doped Porous Silicon

Perspective low-macroscopic field (LMF) emission prototype cathodes based on fullerene C60—doped porous silicon were realized via a two-stage technique comprising the electrochemical etching process of a monocrystalline silicon wafer and functionalization of the acquired porous silicon (PS) matrix with silver-doped fullerene-based carbon structures. The resulting LMF cathode prototypes were studied with SEM and EDS techniques. The formation of an amorphous silver-doped C60-based layer consisting of nanosized aggregates on the matrix surface was established. The emission characteristics of the prototypes were analyzed, crucial parameters including threshold field strength values, emission current density, and effective potential barrier height for electrons were considered. A novel LMF emission model is suggested. It was established that the emitter prototypes realized during this study are on par with or superior to modern and promising field cathodes.

PNA-Based Graphene Oxide/Porous Silicon Hybrid Biosensor: Towards a Label-Free Optical Assay for Brugada Syndrome.

Peptide nucleic acid (PNA) is a synthetic DNA mimic that outperforms the properties of traditional oligonucleotides (ONs). On account of its outstanding features, such as remarkable binding affinity towards complementary DNA or RNA as well as high thermal and chemical stability, PNA has been proposed as a valuable alternative to the ON probe in gene-sensor design. In this study, a hybrid transducer made-up of graphene oxide (GO) nano-sheets covalently grafted onto a porous silicon (PSi) matrix has been investigated for the early detection of a genetic cardiac disorder, the Brugada syndrome (BS). A functionalization strategy towards the realization of a potential PNA-based device is described. A PNA, able to detect the SCN5A gene associated with the BS, has been properly synthesized and used as a bioprobe for the realization of a proof-of-concept label-free optical PNA-biosensor. PSi reflectance and GO photoluminescence signals were simultaneously exploited for the monitoring of the device functionalization and response.

Weak Coupling between Light and Matter in Photonic Crystals Based on Porous Silicon Responsible for the Enhancement of Fluorescence of Quantum Dots under Two-Photon Excitation

The development of optical and, in particular, photoluminescent sensors is currently becoming more and more significant because of their universality, selectivity, and high sensitivity ensuring their wide applications in practice. The efficiency of existing photoluminescent sensors can be increased by using photoluminescent nanomaterials and hybrid nanostructures. For biological applications of photoluminescent sensors, it is extremely relevant to excite photoluminescence in the near infrared spectral range, which allows excluding the effect of autofluorescence of biomolecules and ensuring a deeper penetration of radiation into biological tissues. In this work, it has been studied how the spectral and kinetic parameters of photoluminescence change under two-photon excitation of semiconductor quantum dots incorporated into a one-dimensional photonic crystal, a porous silicon microcavity. It has been shown that the formation of a weak coupling between an exciton transition in quantum dots and an eigenmode of the microcavity enhances the photoluminescence of quantum dots. It is important that quantum dots placed in the porous silicon matrix hold a sufficiently large cross section for two-photon absorption, which makes it possible to efficiently excite their exciton states up to saturation without reaching powers leading to the photothermic destruction of the structure of porous silicon and to the disappearance of the weak coupling effect. It has been demonstrated that the radiative recombination rate under the two-photon excitation of the system consisting of quantum dots and the microcavity increases by a factor of 4.3; it has been shown that this increase is due to the Purcell effect. Thus, fabricated microcavities based on 1D porous silicon crystals allow controlling the quantum yield of photoluminescence of quantum dots under two-photon excitation, which opens prospects for the development of new photoluminescent sensors based on quantum dots operating in the near infrared spectral range.

Porous Silicon Capacitor Structures with Embedded Barium Strontium Titanates

The possibility of creating capacitor structures based on porous silicon with oxide ferroelectrics embedded in the pores—barium strontium titanates, which have a diffuse phase transition—is considered. In this case, thin films of barium strontium titanate are characterized as nanostructures with ferroelectric properties. To obtain such structures, the extraction-pyrolytic method is used. The dependences of the capacitance and permittivity of the structures on the ratio of barium and strontium components in barium strontium titanates are studied. The results of this work confirm the possibility of using the presented technologies—the production of porous silicon matrices and the extraction-pyrolytic method for producing a ferroelectric based on barium and strontium titanates—to create a capacitive-type structures with different dielectric characteristics due to the possibility of varying the obtained ferroelectric composition, dimension, and morphology of the porous silicon matrix.

Optical coherence tomography measurement of capillary filling in porous silicon

The use of nanoporous structures with known morphology allows studying the properties of fluids in conditions of strong spatial confinement. Alternatively, the capillary filling of nanoporous structures with simple fluids provides information on their morphology. When a liquid enters the porous structure there is an increase in the optical path of the porous layer, and measuring this optical path as a function of position and time allows evaluating the filling dynamics of the pores. In this work, we determined the capillary filling dynamics of nanostructured porous silicon (PS) by optical coherence tomography. The high spatial resolution of this technique allows one not only to follow the position of the liquid front as a function of time but also to resolve in detail the filling fraction profile of the liquid front inside the PS matrix. Moreover, these profiles contain information about the pore size distribution in the PS structure. Therefore, we show how the determination and analysis of the filling fraction profile along the advancing liquid front can be used as a method to study the pore size distribution inside PS structures.

Hybrid porous silicon/green synthetized Ag microparticles as potential carries for Ag nanoparticles and drug delivery.

In the present work, the fabrication of hybrid porous silicon/green synthetized Ag microparticles was shown and the potential use as carriers for Ag nanoparticles and drug delivery was explored. Hybrid microparticles were fabricated by incorporating green synthetized Ag nanoparticles into porous silicon matrix. The main physicochemical characteristics of the hybrid systems were studied by several techniques including UV-vis spectroscopy, TEM, SEM, XRD and XPS. The toxicology of these hybrid systems was investigated by cell viability, MTT, and comet assays. In addition, the possibility to aggregate different drug to use as drug delivery system was demonstrated by using florfenicol as drug model, due to its importance in salmon industry. The experimental results showed the potential to use these hybrid systems as carries for drug delivery in salmon industry.

Nanostructures based on functionalized porous silicon for promising solar energy systems

The promising application of functionalized composite materials based on porous silicon (PS) for perspective solar energy conversion systems is considered in this paper. PS-based nanostructures are suggested for further realization of photon-enhanced thermionic emission for solar concentrators and thermionic electrodes due to the remarkable properties displayed by these materials. Nanostructured layers functionalized with silver (PS/Ag) are obtained via electrochemical etching and deposition processes. The investigation of acquired materials functionalized with fractal-like silver agglomerates is performed. Electronic absorption spectroscopy is utilized in order to characterize the surface structure of PS/Ag layers. Localized surface plasmon resonance phenomenon taking place within the array of silver nanoparticles is observed. Two distinct absorption bands located in the visible spectrum are detected; their emergence is related to the resonance effect taking place in the two nanoparticle arrays appearing during the synthesis process. The intensity of these bands can be manipulated with synthesis parameters of porous silicon matrix.

In Situ Growth of ZnO inside a Porous Silicon Matrix Obtained by Electrochemical Etching with a Hydrofluoric Acid-Formaldehyde Solution

We present zinc oxide (ZnO) particles obtained inside a porous silicon matrix in the same electrolytic process using a p-type silicon wafer in a hydrofluoric acid (HF) solution containing formaldehyde (CH2O) and hydrated zinc sulfate as additives. The X-ray diffraction pattern of the sample confirmed the presence of ZnO with a hexagonal-type wurtzite structure. Photoluminescence (PL) spectra of the samples, before and after the functionalization process, were measured to observe the effect of ZnO inside the porous silicon. The PL measurements of porous silicon functionalized with ZnO (ZnO/PS) revealed infrared, red, blue, and ultraviolet emission bands. The ultraviolet region corresponds to the band-band emission of ZnO, and the visible emission is attributed to defects. The results of the nitrogen adsorption/desorption isotherms of the PS and ZnO/PS samples revealed larger BET surface areas and pore diameters for the ZnO/PS sample. We conclude that ZnO/PS can be obtained in a one-step electrolytic process. These types of samples can be used in gas sensors and photocatalysis.