Porous Silicon Bragg Reflectors Research Articles

Sandwich-like CuNPs@AgNPs@PSB SERS substrates for sensitive detection of R6G and Forchlorfenuron

The development of a highly sensitive, synthetically simple and economical SERS substrate is technically very important. A fast, economical, sensitive and reproducible CuNPs@AgNPs@ Porous silicon Bragg reflector (PSB) SERS substrate was prepared by electrochemical etching and in situ reduction method. The developed CuNPs@AgNPs@PSB has a large specific surface area and abundant “hot spot” region, which makes the SERS performance excellent. Meanwhile, the successful synthesis of CuNPs@AgNPs can not only modulate the plasmon resonance properties of nanoparticles, but also effectively prolong the time stability of Cu nanoparticles. The basic performance of the substrate was evaluated using rhodamine 6G (R6G). (Detection limit reached 10−15 M, R2 = 0.9882, RSD = 5.3 %) The detection limit of Forchlorfenuron was 10 μg/L. The standard curve with a regression coefficient of 0.979 was established in the low concentration range of 10 μg/L −100 μg/L. This indicates that the prepared substrates can accomplish the detection of pesticide residues in the low concentration range. The prepared high-performance and high-sensitivity SERS substrate have a very promising application in detection technology.

Application of serum SERS technology combined with deep learning algorithm in the rapid diagnosis of immune diseases and chronic kidney disease

Surface-enhanced Raman spectroscopy (SERS), as a rapid, non-invasive and reliable spectroscopic detection technique, has promising applications in disease screening and diagnosis. In this paper, an annealed silver nanoparticles/porous silicon Bragg reflector (AgNPs/PSB) composite SERS substrate with high sensitivity and strong stability was prepared by immersion plating and heat treatment using porous silicon Bragg reflector (PSB) as the substrate. The substrate combines the five deep learning algorithms of the improved AlexNet, ResNet, SqueezeNet, temporal convolutional network (TCN) and multiscale fusion convolutional neural network (MCNN). We constructed rapid screening models for patients with primary Sjögren’s syndrome (pSS) and healthy controls (HC), diabetic nephropathy patients (DN) and healthy controls (HC), respectively. The results showed that the annealed AgNPs/PSB composite SERS substrates performed well in diagnosing. Among them, the MCNN model had the best classification effect in the two groups of experiments, with an accuracy rate of 94.7% and 92.0%, respectively. Previous studies have indicated that the AgNPs/PSB composite SERS substrate, combined with machine learning algorithms, has achieved promising classification results in disease diagnosis. This study shows that SERS technology based on annealed AgNPs/PSB composite substrate combined with deep learning algorithm has a greater developmental prospect and research value in the early identification and screening of immune diseases and chronic kidney disease, providing reference ideas for non-invasive and rapid clinical medical diagnosis of patients.

Vertical multilayer structures based on porous silicon layers for mid-infrared applications

In this work, the fabrication of a porous silicon Bragg reflector and vertical cavity on P+ silicon substrate is investigated for applications in spectroscopic sensing in the mid-infrared (Mid-IR) wavelength range. The complex refractive index of porous silicon layers is measured. Optical vertical devices are then fabricated and characterized by Fourier transform infrared (FTIR) spectrophotometry. This work demonstrates the use of electrochemically prepared Bragg reflectors with reflectance as high as 99% and vertical cavity based on porous silicon layers operating in the mid-IR spectral region (up to 8 µm). Experimental reflectance spectra of the vertical cavity structures are recorded as a function of air exposure duration after thermal annealing under nitrogen flux (N2) and results demonstrate that these structures could be used for spectroscopic sensing applications in the mid-IR (2-8 µm) by grafting specific biomolecules on the porous silicon internal surface.

Detection of breast cancer based on novel porous silicon Bragg reflector surface-enhanced Raman spectroscopy-active structure

In this Letter, the surface-enhanced Raman scattering (SERS) signal of early breast cancer (BRC) patient serum is obtained by a composite silver nanoparticles (Ag NPs) PSi Bragg reflector SERS substrate. Based on these advantages, the serum SERS signals of 30 normal people and 30 early BRC patients were detected by this substrate. After a baseline correction of the experimental data, principal component analysis and linear discriminant analysis were used to complete the data processing. The results showed that the diagnostic accuracy, specificity, and sensitivity of the composite Ag NPs PSi Bragg reflector SERS substrate were 95%, 96.7%, and 93.3%, respectively. The results of this exploratory study prove that the detection of early BRC serum based on a composite Ag NPs PSi Bragg reflector SERS substrate is with a stable strong SERS signal, and an unmarked and noninvasive BRC diagnosis technology. In the future, this technology can serve as a noninvasive clinical tool to detect cancer diseases and have a considerable impact on clinical medical detection.

Micropatterning of porous silicon Bragg reflectors with poly(ethylene glycol) to fabricate cell microarrays: Towards single cell sensing

The work presented here describes the development of an optical label-free biosensor based on a porous silicon (PSi) Bragg reflector to study heterogeneity in single cells. Photolithographic patterning of a poly(ethylene glycol) (PEG) hydrogel with a photoinitiator was employed on RGD peptide-modified PSi to create micropatterns with cell adhesive and cell repellent areas. Macrophage J774 cells were incubated to form cell microarrays and single cell arrays. Moreover, cells on the microarrays were lysed osmotically with Milli-Q™ water and the infiltration of cell lysate into the porous matrix was monitored by measuring the red shift in the reflectivity. On average, the magnitude of red shift increased with the increase in the number of cells on the micropatterns. The red shift from the spots with single cells varied from spot to spot emphasizing the heterogeneous nature of the individual cells.

Porous Silicon Bragg Reflector/Carbon Dot Hybrids: Synthesis, Nanostructure, and Optical Properties.

Carbon dots (C-dots) exhibit unique fluorescence properties, mostly depending upon their physical environments. Here we investigate the optical properties and nanostructure of Carbon dots (C-dots) which are synthesized in situ within different porous Silicon (PSi) Bragg reflectors. The resulting hybrids were characterized by photoluminescence, X-ray photoelectron, and Fourier Transform Infrared spectroscopies, as well as by confocal and transmission electron microscopy. We show that by tailoring the location of the PSi Bragg reflector photonic bandgap and its oxidation level, the C-dots emission spectral features can be tuned. Notably, their fluorescence emission can be significantly enhanced when the high reflection band of the PSi host overlaps with the confined C-dots' peak wavelength, and the PSi matrix is thermally oxidized at mild conditions. These phenomena are observed for multiple compositions of PSi Bragg reflectors/C-dots hybrids.

Optical performance of hybrid porous silicon–porous alumina multilayers

In this work, we study the optical response of structures involving porous silicon and porous alumina in a multi-layered hybrid structure. We performed a rational design of the optimal sequence necessary to produce a high transmission and selective filter, with potential applications in chemical and biosensors. The combination of these porous materials can be used to exploit its distinguishing features, i.e., high transparency of alumina and high refractive index of porous silicon. We assembled hybrid microcavities with a central porous alumina layer between two porous silicon Bragg reflectors. In this way, we constructed a Fabry-Perot resonator with high reflectivity and low absorption that improves the quality of the filter compared to a microcavity built only with porous silicon or porous alumina. We explored a simpler design in which one of the Bragg reflectors is replaced by the aluminium that remains bound to the alumina after its fabrication. We theoretically explored the potential of the proposal and its limitations when considering the roughness of the layers. We found that the quality of a microcavity made entirely with porous silicon shows a limit in the visible range due to light absorption. This limitation is overcome in the hybrid scheme, with the roughness of the layers determining the ultimate quality. Q-factors of 220 are experimentally obtained for microcavities supported on aluminium, while Q-factors around 600 are reached for microcavities with double Bragg reflectors, centred at 560 nm. This represents a four-fold increase with respect to the optimal porous silicon microcavity at this wavelength.

Porous silicon Bragg reflectors on multi-crystalline silicon wafer with p-n junction

Bragg reflectors consisting of the sequence of dielectric layers are considered to create p-n junction solar cells (SC) with improved efficiency in the longwave spectral range. Bragg mirrors (BM) based on porous silicon (PS) mutilayers at the backside of single crystalline and multicrystalline silicon wafer were formed by electrochemically etching. Maximal experimental reflectivity for BM on multicrystalline substrate achieves 62% due to the natural crystallites disorientation of multicrystalline substrate, whereas for single crystalline silicon the reflectivity in maximum is 87%. BM was formed also on rear side of multicrystalline silicon wafer with p-n junction.

New perspectives in silicon micro and nanophotonics

In the last two decades, there has been growing interest in silicon-based photonic devices for many optical applications: telecommunications, interconnects and biosensors. In this work, an advance overview of our results in this field is presented. Proposed devices allow overcoming silicon intrinsic drawbacks limiting its application as a photonic substrate. Taking advantages of both non-linear and linear effects, size reduction at nanometric scale and new two-dimensional emerging materials, we have obtained a progressive increase in device performance along the last years. In this work we show that a suitable design of a thin photonic crystal slab realized in silicon nitride can exhibit a very strong field enhancement. This result is very promising for all photonic silicon devices based on nonlinear phenomena. Moreover we report on the fabrication and characterization of silicon photodetectors working at near-infrared wavelengths based on the internal photoemission absorption in a Schottky junction. We show as an increase in device performance can be obtained by coupling light into both micro-resonant cavity and waveguiding structures. In addition, replacing metal with graphene in a Schottky junction, a further improve in PD performance can be achieved. Finally, silicon-based microarray for biomedical applications, are reported. Microarray of porous silicon Bragg reflectors on a crystalline silicon substrate have been realized using a technological process based on standard photolithography and electrochemical anodization of the silicon. Our insights show that silicon is a promising platform for the integration of various optical functionalities on the same chip opening new frontiers in the field of low-cost silicon micro and nanophotonics.

Enhancement of the R6G fluorescence by gold nanoparticle depositions in porous silicon Bragg reflectors

We report on the fluorescence enhancement induced by gold nanoparticles (Au NPs) deposited on porous silicon Bragg reflectors (Bragg PS). The rhodamine 6 G (R6G) fluorescence was studied on single-layer porous silicon films and porous silicon Bragg reflectors. By comparison, R6G fluorescence of porous silicon films with Au NPs infiltrated is about two times that of porous silicon films without Au NPs. The R6G fluorescence of this porous silicon Bragg reflectors with Au NPs infiltrated is also stronger than the single-layered porous silicon films (∼2.3-fold) with Au NPs infiltrated. Such substrates with a multiple enhancement of the fluorescence have great potential for applications in the fields of medical diagnostics and biotechnology.

Study of the Microstructural and Optical Properties of Porous Silicon Bragg Reflectors Obtained by Differential Photoacoustic Electrochemical Cell

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Kinetics of adsorption–desorption processes of alcohol molecules in porous silicon Bragg mirror

Abstract A porous silicon Bragg reflector was applied to analyze the time dependent parameters that characterize the ethanol adsorption and desorption processes. Time-dependent parameters – amplitude, FWHM and Bragg peak at the measurement of reflectivity show complex behavior at adsorption/desorption for pure ethanol and colloidal solution with SiC nanoparticles. Models of equivalent Bragg mirror with partially pores filling were considered. Effects of pores filling on spectral properties of Bragg mirror was simulated by matrix method and compare with experimental data.

Bragg reflector formed on oxidised porous silicon

The manufacturing of a porous silicon Bragg reflector on P+ silicon substrate is investigated and the effects of oxidation on the Bragg reflector parameters is studied, notably the shift of the central wavelength after oxidation. This Letter shows how to anticipate the changes due to oxidation rather than to endure them. First, the variations in the refractive index and thickness after oxidation were studied. Then, from these measurements, an oxidised porous silicon Bragg reflector centred at 1550 nm was formed by anticipating the shift of central wavelength during oxidation. There was a good correlation between the experimental and theoretical spectra of the Bragg reflector.

Structural and Optical Properties of Annealed Porous Silicon Bragg Reflector for Thin-Film Crystalline Silicon Solar Cells

Implementing an annealed porous silicon Bragg reflector between a crystalline silicon thin-film solar cell and its cheap silicon substrate improves greatly its performance. Such a multilayer features indeed a high reflectivity, allowing the optical confinement which is essential for these cells. Annealing the porous silicon above 900 °C under H2 modifies significantly the structure of the porous silicon. This phenomenon lowers its resistivity to avoid high cell series resistance and allows the subsequent epitaxial growth of the silicon cell. The different behaviors of porous silicon structure alteration are studied and rationalized. The pores shapes and sizes, the porosities and the thicknesses of layers are affected. These changes depend on the initial porosities and thicknesses and the annealing parameters. Pores can erupt at the surface when they are neighboring, thus causing a roughness of characteristic length according to the porosity of the layer. The pores sizes increase in all cases. Different multilayer reflectivities are presented, the highest ones being up to 98% over a wide wavelength range. It allows a better understanding of this annealing process and the optimization of the reflectivity of the Bragg reflector in order to apply it on solar cells.

Fabrication and characterization of a porous silicon based microarray for label-free optical monitoring of biomolecular interactions

We have fabricated a microarray of porous silicon Bragg reflectors on a crystalline silicon substrate using a technological process based on standard photolithography and electrochemical anodization of the silicon. The array density is of 170 elements/cm2 and each element has a diameter of 200 μm. The porous silicon structures have been used as platform to immobilize an amino terminated DNA single strand probe. All fabrication steps have been monitored by spectroscopic reflectometry, optical and electron microscopy, and Fourier transform infrared spectroscopy. A label-free detection method has been employed to investigate the hybridization between micromolar DNA probe and its complementary target. Due to fast and low cost production, good reproducibility, and high quality optical features, this platform could be adopted also for other different microarray applications such as proteomics and medical diagnostics.

Optical gas sensing properties of thermally hydrocarbonized porous silicon Bragg reflectors

In the present work, porous silicon (PS) based Bragg reflectors are fabricated, and the reactive PS surface is passivated by means of thermal carbonization (TC) by acetylene decomposition. The gas sensing properties of the reflectors are studied with different gas compositions and concentrations. Based on the results it can be concluded that thermally carbonized Bragg reflectors provide an easy and inexpensive means to produce chemically stable high quality PS reflectors with good gas sensing properties, which differ from those of unpassivated PS reflectors.

Fabrication of large-area patterned porous silicon distributed Bragg reflectors

A process to fabricate porous silicon Bragg reflectors patterned on a micrometer lateral scale over wafer areas of several square centimeters is described. This process is based on a new type of projection system involving a megavolt accelerator and a quadrupole lens system to project a uniform distribution of MeV ions over a wafer surface, which is coated with a multilevel mask. In conjunction with electrochemical anodisation, this enables the rapid production of high-density arrays of a variety of optical and photonic components in silicon such as waveguides and optical microcavities for applications in high-definition reflective displays and optical communications.

Porous silicon optical filters for biosensing applications

The surface of nanostructured silicon (porous silicon) was biofunctionalized by the deposition of 3-aminopropyltriethoxysilane from solution, leading to high density of amine groups covering the surface which would promote the further immobilization of biomolecules. In addition, porous silicon Bragg reflectors were developed for their use in the visible range. The optical behavior of these structures was previously designed by the use of a computational program, from which the optical constants and thickness of the individual porous silicon layers were determined. The possibility of using these structures as biosensors has been explored, based on the significant changes in the reflectance spectra before and after exposing the porous silicon optical structures to biomolecules. In particular, it is shown that there is a notable shift of the reflectance maximum associated to the Bragg reflector after immobilization of polyclonal mouse antibodies. Thus, the experimental results open the possibility of developing biosensors based on the variation of the position of the optical spectrum of porous silicon based devices.

Enhanced chromaticity of organic electroluminescence from siliconbased organic microcavity

Electroluminescence (EL) from Sibased organic microcavity has firstly been reported in the literature. The microcavity is made up of the central active multilayers sandwiched between a silver film and a porous silicon Bragg reflector (PSDBR), formed by electrochemical etching of p+Si substrate in the electrolyte of HF: C2H5OH:H2O. The central active multilayers consist of Al (1 nm) / LiF (05 nm) / Alq3 / Alq3: DCJTB / NPB / CuPc / ITO / SiO2． The reflectivity (relative to an Al mirror) of the PSDBR is up to 99%, and the stopband is about 160 nm wide. Resonant cavity mode appears as a tip in the reflectivity spectrum of the Sibased organic multilayer films, indicating that the Sibased organic multilayer structure is indeed a microcavity. The peak widths of the EL spetra are greatly reduced from 70 nm to 12 nm as compared with those measured from noncavity structures. Note that the EL emission from the cavity devices is singlemode, and the offresonant optical modes are highly suppressed. Moreover, an increase of a factor of about 4 of the resonant peak intensity is observed. In addition, the currentbrightnessvoltage characteristics and the effect of parameters on the lifetime of the cavity devices are also discussed. The present technique for obtaining enhanced EL emission from Sibased organic microcavity may also be another novel effective method for realizing allSibased photonic devices and optoelectronics device integration.

Infrared ellipsometry characterization of porous silicon Bragg reflectors

We investigate porous silicon Bragg reflectors in a nondestructive manner using variable angle-of-incidence infrared spectroscopic ellipsometry. In addition to the thickness, volume porosity, inhomogeneity, and optical anisotropy, properties of the solid content of the porous material are investigated in terms of dielectric function and surface chemistry. The material was found to have positive birefringence. The high sensitivity of the technique is employed to detect and identify infrared resonant absorptions related to different Si-H as well as Si-O-Si vibrational modes. The average electrical resistivity of the solid content of the porous material is determined to be 0.03 Omega cm, which is larger than the corresponding bulk value of 0.019 Omega cm. Furthermore the average carrier concentration in the porous material shows a decrease from 6.2 x 10(18) cm(-3) to 4 x 10(18) cm(-3).