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In this paper, a new method for pesticide detection based on porous silicon microcavities was proposed. First, the aptamer of acetamiprid was fixed in the functionalized porous silicon microcavity. Then, the complementary strand of the aptamer modified with graphene quantum dots was hybridized with the aptamer, and the effective refractive index of the porous silicon microcavity increased. When acetamiprid was added, it bound to the aptamer due to its stronger specificity. The aptamer separated from the complementary strand of the coupled graphene quantum dots and bound to acetamiprid, resulting in a decrease in the effective refractive index, and its central wavelength of reflection spectrum was blue shifted, and the blueshift increased with the increase of acetamiprid concentration. The relationship between the change in central wavelength and the concentration of acetamiprid was analysed, and the detection limit of acetamiprid was 151 nm.

In this study nano lithium oxide Li2O was prepared using simple chemical method SCM. Structural and optical invesitgations were executed such as X-ray diffraction XRD, Scanning Electron Microscopy SEM, Foriour Trandformation InfraRed FTIR and UV–Vis to know the characteristics of the nano material, then nano Li2O was deposited on p and n-types porous silicon substrates to fabricate the heterojunction after appliying Al drops on upper and lower side. Two applications of the manufactured heterojunction were carried out solar cell and measuring its characteristics and photodetector with its figures of merit.

In this study, porous silicon (PSi) was used to manufacture gas sensors for acetone and ethanol. Samples of PSi were successfully prepared by photoelectrochemical etching and applied as an acetone and ethanol gas sensor at room temperature at various current densities J= 12, 24 and 30 mA/cm2with an etching time of 10 min and hydrofluoric acid concentration of 40%. Well-ordered n-type PSi (100) was carefully studied for its chemical composition, surface structure and bond configuration of the surface via X-ray diffraction, atomic force microscopy, Fourier transform infrared spectroscopy and photoluminescence tests. Results showed that the best sensitivity of PSi was to acetone gas than to ethanol under the same conditions at an etching current density of 30 mA/cm2, reaching about 2.413 at a concentration of 500 parts per million. The PSi layers served as low-cost and high-quality acetone gas sensors. Thus, PSi can be used to replace expensive materials used in gas sensors that function at low temperatures, including room temperature. The material has an exceptionally high surface-to-volume ratio (increasing surface area) and demonstrates ease of fabrication and compatibility with manufacturing processes of silicon microelectronics.

In this paper, a grayscale variation of fluorescence Image based on porous silicon (PSi) Bragg mirrors (Bm) was proposed to detect pesticides quickly and easily. In this way, CdSe/ZnS quantum dots (QDs) were used as fluorescence labelling to weaken the fluorescence intensity, and a digital imaging method was used for detection. The QDs were coupled with complementary strand aptamers and interacted with aptamers immobilized on the PSi‘inner wall; thus, the fluorescence of the QDs produced by the PSi Bm was further enhanced. Acetamiprid would bind specifically to its corresponding aptamer, the complementary strand aptamers of the coupled QD would be replaced, and the fluorescence intensity would weaken. The fluorescence image of the PSi Bm surface was acquired by imaging device, and the acetamiprid pesticide was detected by computing the average grey value variation of the image. Experimental results presented that the variation in the average grey value increased with increasing pesticide concentration and presented a linear relationship within a certain range. The detection limit of acetamiprid pesticide with this type of way was 2.8 nM, indicating that this method achieved a low-cost, rapid and simple detection of pesticide.

Light–matter interaction in hybrid systems made of fluorophores embedded into a microcavity (MC) attracts much attention. Depending on the coupling strength between the components, either photoluminescence (PL) enhancement or hybridization of the luminophore energy levels with the MC eigenmode resulting in two hybrid energy states occurs in these systems. This effect can be used in various practical applications: enhancing Raman scattering, increasing conductivity, obtaining Bose–Einstein condensates at room temperature, etc. Hybrid structures emitting in the near-infrared (NIR) range can be used in biomedical applications for exciting and detecting radiation within the transparency window of biological tissues. Here, we have developed hybrid photoluminescent structures based on porous silicon photonic crystals (PhCs) and PbS quantum dots (QDs) emitting in the NIR range. The freestanding PhC-based MCs were obtained by electrochemical etching of monocrystalline Si. Comparison of the PhC reflectance spectra before and after exfoliation from the substrate, as well as after thermal oxidation, showed a 100-nm blue shift, other parameters being almost unchanged. After embedding QDs, we observed narrowing of their PL spectrum compared to the QD solution. We attribute this to the Purcell effect and weak coupling between the QD exciton and MC eigenmode. Thus, our hybrid structures exhibit weak light–matter coupling in the NIR range, which provides the basis for new nanophotonic biosensor systems. In addition, they are freestanding, thus offering prospects for designing sensors with the option of pumping analytes through the porous structure.

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.

To further improve the sensitivity of porous silicon-assembled microcavity biosensors, the detection of porous silicon assembled microcavity by angle spectrum method is also researched. This contribution uses CdSe/ZnS quantum dot-labelled probe DNA to amplify the refractive index and detect it by the angle spectrum method. The first layer is a microcavity layer, and the next is porous silicon with a Bragg structure. After functionalization, different concentrations of target DNA were coupled to construct quantum dot-labelled probe DNA to bind specifically to the target DNA. With the Bragg device based on quartz glass forming an assembled microcavity structure, using a He-Ne laser as the detection light and collimation beam, the angle spectrum method is used to detect different concentrations of target DNA before and after biological reaction with quantum dot-labelled probe DNA and reflect the angle of minimum light intensity. The experimental results show that with increasing target DNA concentration, probe DNA concentration and angle, the detection limit is 13.25 pM. The angle-spectrum method has been successfully used to detect the assembled porous silicon microcavity. The angle-spectrum method has the advantages of spectrometer free and low cost.

Label-free optical sensors are attractive candidates, for example, for detecting toxic substances and monitoring biomolecular interactions. Their performance can be pushed by the design of the sensor through clever material choices and integration of components. In this work, two porous materials, namely, porous silicon and plasmonic nanohole arrays, are combined in order to obtain increased sensitivity and dual-mode sensing capabilities. For this purpose, porous silicon monolayers are prepared by electrochemical etching and plasmonic nanohole arrays are obtained using a bottom-up strategy. Hybrid sensors of these two materials are realized by transferring the plasmonic nanohole array on top of the porous silicon. Reflectance spectra of the hybrid sensors are characterized by a fringe pattern resulting from the Fabry-Pérot interference at the porous silicon borders, which is overlaid with a broad dip based on surface plasmon resonance in the plasmonic nanohole array. In addition, the hybrid sensor shows a significant higher reflectance in comparison to the porous silicon monolayer. The sensitivities of the hybrid sensor to refractive index changes are separately determined for both components. A significant increase in sensitivity from 213 ± 12 to 386 ± 5 nm/RIU is determined for the transfer of the plasmonic nanohole array sensors from solid glass substrates to porous silicon monolayers. In contrast, the spectral position of the interference pattern of porous silicon monolayers in different media is not affected by the presence of the plasmonic nanohole array. However, the changes in fringe pattern reflectance of the hybrid sensor are increased 3.7-fold after being covered with plasmonic nanohole arrays and could be used for high-sensitivity sensing. Finally, the capability of the hybrid sensor for simultaneous and independent dual-mode sensing is demonstrated.

In order to solve this problem, a new biological detection method is proposed, which makes use of the characteristics of optical transmission at the edge of the spectral band gap and sensitive to refractive index variation. When the probe light with wavelength at the edge of the Bragg band gap of porous silicon is incident on the surface of porous silicon, the change of refractive index caused by deoxyribonucleic acid (DNA) reaction in porous silicon will affect the detection light intensity transmitted from the porous silicon sensor. By analyzing the change of the average gray value of the transmitted light image, the concentration of the DNA can be obtained.

In this paper we show for the first time the possibility to direct grow and tune the size and optical properties of high quality InAs/GaAs quantum dots on transferable crystalline silicon nanomembranes. The transferable silicon nanomembranes have been grown via in-situ H2 prebake of porous silicon in Ultra High Vacuum Chemical vapour Deposition (UHV-CVD) reactor. Flat and continuous transferable crystalline nanomembranes with thicknesses below 30 nm have been obtained. The mechanical strain in the silicon nanomembranes has been tuned via sintering temperature between 900 and 1100 °C for the direct crystalline growth of transferable InAs/GaAs (QDs)/Si foils. The size and band gap energy of these InAs/GaAs quantum dots are tuned via strain engineering in silicon nanomembranes. Several advanced techniques such as Scanning Electron Microscopy (SEM), High-Resolution Transmission Electron Microscopy (HR-TEM), X-Ray Diffraction (XRD), Photoluminescence (PL) spectroscopy are used to investigate the structural and optical properties of transferable silicon nanomembranes and the grown InAs/GaAs QDs. High quality InAs/GaAs QDs with tuned sizes grown on flat and continuous transferable crystalline nanomembranes have been obtained. The obtained results have shown that this novel process allows the growth of well separated InAs/GaAs QDs with well defined shape, high density around 2 × 1010/cm2 and a well controlled size variation as function of the substrate strain between 2 and 10 nm. The high quality of the structural and optical properties of the InAs/GaAs QDs monolithically grown on a transferable Si nanomembranes and its compatibility with standard Si solar cells technologies offer a great opportunity for growing a cheap and high performance InAs/GaAs quantum dots/Si third generation solar cells and microelectronic devices.

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.

A heterostructure composed of TiO2 and macroporous silicon in this study may represent the simplest relaxation oscillator ever reported. It consisted of macroporous Si with TiO2 grown on its pore walls, and metallic contacts. This is also the first relaxation oscillator of its kind. Such oscillators are commonly formed by a capacitor or an inductor and a feedback loop with a switching device operating with a threshold voltage. The dielectric characteristics of TiO2 (capacitive behavior) in combination with the tunnel diode characteristics of the heterostructure (presenting a negative differential resistance, when activated at a threshold voltage) are shown to give rise to the relaxation oscillations.

To solve the problem of the limited depth of penetration of biomolecules into silicon biosensors, which affects the performance of porous silicon devices, a new biological detection device assembled with porous silicon and Bragg structures is proposed that allows the biomolecules to directly enter the porous silicon microcavity layer, thus greatly shifting the resonance peak and improving the sensitivity of the porous silicon. The fabricated porous silicon devices with microcavities and Bragg structures are functionalized and coupled with biomolecules and then assembled with Bragg devices based on quartz glass to form the microcavity. Using the reflection spectrometer to detect the defect peak redshifts of different concentrations of target DNA molecules before and after reaction with the probe DNA molecules, obtaining the difference between the refractive indices before and after reaction. With an increase in the molecular concentration of the DNA in the target and an increase in the defect peak difference, the detection limit is 22.5 nM. The assembled microcavity has the advantages of high detection sensitivity, free labelling, low costs and so on.

In this work, macro porous silicon layers were fabricated by Laser Assisted Etching. The morphology, structure and luminescence characteristics of the porous Si were examined as functions of the etching time using Field Emission-Scanning Electron Microscopy (FE-SEM), Atomic Force Microscopy (AFM) and Photoluminescence (PL). FE-SEM pictures revealed that the macro porous silicon surface layer has macro pores with a similar structure, also the thickness of this layer and the average pore diameter have increased with the increase of etching time. The specific surface area was measured by BET method and it was found in range of 152–213 m2/g. The AFM images manifested the high roughness and root mean square at low current density which can affect the porous silicon for the gas sensing applications. The PL spectra gave the luminescence energy in the orange–red region of the visible spectrum with the energy band gap of around (2.01 eV) for n-Si etched for 16 min. Two electrode configurations have been investigated for the sensing performance toward the NH3 gas; planar and sandwich, the former depicted a gas response of 1.85, while the latter revealed an efficient and ultra-gas response of 3.5 with the fast response and recovery times.

A highly-sensitive remote temperature sensor based on Tamm resonance is proposed using a one-dimensional photonic crystal. The proposed structure is prism/Ag/Toluene/SiO2 /(PSi1/PSi2)N/Si. The transfer matrix method is used to discuss the interaction between the structure and the S-polarization of the incident radiation waves. We optimized the structure by studying the effect of the incident angle, the thickness of the first and second layers of the photonic crystal unit cell, the porosity of them, and the thickness of the toluene layer. High sensitivity, high signal-to-noise ratio, and very low resolution are achieved due to the coupling between the porous silicon photonic crystal properties and Tamm resonance that makes it very distinguished compared to previous works.

A device, supporting negative differential resistance, has been fabricated. Aluminum top contacts have been deposited on electrochemically synthesized porous silicon layer on p-type silicon substrate for this purpose. Top-bottom DC current vs. voltage (I-V) characteristics of the fabricated device have been recorded at room temperature under dark condition and injecting photons. Dark I-V characteristics of this device indicate the presence of negative differential resistance (NDR). Similar kind of I-V characteristics has been observed under illumination. At the same time, fabricated device shows photovoltaic effect after injecting photons. This may be due to some series and parallel combination of multiple junctions with photovoltaic nature.

Water sources are vulnerable to intentional and inadvertent human pollution with thousands of synthetic and geogenic trace contaminants, posing long-term effects on the aquatic ecosystem and human health. Thus, early and rapid detection of water pollutants followed by corrective and preventive actions can lead to the reduction of the overall polluting impact to safeguard public health. This study presents a generic sensing assay for the label-free detection of copper contaminants in environmental water samples using multilayered polyethylenimine (PEI) functionalized porous silicon Fabry-Pérot interferometers. The selective chelating activity of PEI thin-films was monitored in real-time by reflective interferometric Fourier transform spectroscopy (RIFTS) while assessing the improved optical responses. The optimized scaffold of two sequential PEI layers depicted a linear working range between 0.2 and 2 ppm while presenting a detection limit of 0.053 ppm (53 ppb). The specificity of the developed platform was cross-validated against various metallic pollutants and cations commonly found in water bodies (i.e., Cd2+, Pb2+, Cr3+, Fe3+, Mg2+, Ca2+, Zn2+, K+ and Al3+). Finally, as a proof of concept, the analytical performance of the porous interferometers for real-life scenarios was demonstrated in three water samples (tap, ground and irrigation), presenting sufficient adaptability to complex matrix analysis with recovery values of 85-106%. Overall, the developed sensing concept offers an efficient, rapid and label-free methodology that can be potentially adopted for routine on-site detection using a simple and portable device.

Present article reports distinct and enhanced ultraviolet to visible light sensing property of metal-semiconductor-metal (MSM) based ZnS-PS:p-Si hybrid heterostructure. PS:p-Si heterostructure is prepared using electrochemical anodization technique by alternate variation of etching current density within the limit of 17.2–22.1 mA cm−2. ZnS (99.99% purity) in powder form is deposited on PS:p-Si surface via thermal evaporation technique under a chamber pressure of 2 × 10−5 m bar. To achieve MSM configuration Au electrode of ∼8 nm and Al electrode of ∼22 nm thickness are successively coated on top of ZnS-PS:p-Si surface using a shadow mask with dimension of 6 × 6 mm. Morphological features of the heterostructure are observed and analysed using cross section FESEM. This gives thickness of the deposited ZnS layer as around ∼110 nm on ∼540 nm thick PS:p-Si structure. These also confirm uniform interface between the two i.e, ZnS and PS:p-Si layers. Cross sectional EDX analysis indicates diffusion of ZnS particles into the PS layer. Optical analysis observed via UV–Visible spectroscopy gives bandgap (obtained through Tauc plot) of the bare ZnS film to be 3.4 eV with 70–90% transparency in the visible region (390–700 nm). Optical reflectance spectrum of the prepared heterostructure shows decreased reflectivity compared to that of the bare PS:p-Si structure which is itself 20–30% less compared to bulk silicon. Spectral response measured for the wavelength range of 200–500 nm gives distinct and enhanced responsivity peak values of ∼0.94 and ∼1.12 AW−1 at 365 nm (UV) and 400 nm (visible) compared to ∼0.5 AW−1 (maximum at 400 nm) of bare PS:p-Si MSM structure for bias voltage of −4 V. The response and recovery times of the heterostructure are found to be 0.54 ± ( 4.3 × 10 - 4 ) s, 0.38 ± 9.5 × 10 - 5 s and 0.50 ± 2.8 × 10 - 4 s, 0.35 ± 6.5 × 10 - 5 s under UV and visible irradiations.

Present work reports fabrication of metal-semiconductor-metal (MSM) [1] devices based on CdS-PS: p-Si and ZnO-PS: p-Si heterostructures for photo sensing applications. Field Emission Scanning Electron Microscope (FESEM) analyses confirm growth of hierarchical flower like nanostructured CdS and spherical shaped nanostructured ZnO layers of uniform thicknesses ∼170 and 160 nm respectively on PS: p-Si substrate. UV–visible absorbance spectra for CdS and ZnO nanostructures provide optical band gap of 2.6 and 3.3 eV respectively. Photoluminescence (PL) spectra analyses of the heterostructures show near band edge (NBE) emissions of nanostructured CdS at ∼450–482 nm for CdS-PS: p-Si and at ∼378–398 nm of nanostructured ZnO for ZnO-PS: p-Si along with characteristic PL peaks of PS at ∼600 nm [2] and some trap/defect assisted luminescence bands. Dark current analyses of the heterostructures give values of ideality factors (n) of 3.4 and 4.4 respectively. Heterostructures under increasing illumination intensity (17–71 µW cm−2, 400 nm) show almost symmetric rectification enhancement for positive and negative bias condition with maximum photo to dark current ratio (Iph/Id) of 10.3 and 34.3 respectively at −2 V bias. ZnO-PS: p-Si heterostructure shows superiority for UV–Visible photo sensing application in terms of high responsivity ∼2.6 AW−1, high EQE ∼800% and response time of ∼1.12 sec compared to ∼0.6 AW−1, 180% and 0.16 sec of CdS-PS: p-Si respectively at biasing of −2 V.

At present, the study of complex electro-physical characteristics of semiconductor nanofilaments and nanofilms is of interest: the presence of non-monotonic oscillating characteristics with memory, areas of negative differential resistance. The aim of this work is to experimentally study both the volt-ampere and volt-farad characteristics of semiconductor nanoporous structures. The studied samples of porous silicon with the p-n structure were obtained by electrochemical etching. Single-crystal silicon with a p – n+ junction was used as the initial substrate. The NI EL VIS II+ educational platform and the Agilent E4980A instrument were used to study the electrophysical characteristics. To measure the dependence of current on voltage, as well as capacitance on voltage, Inga contacts with a thickness of 370 nm each were applied to nanoporous films. Thus, in this work, the phenomena of current switching, hysteresis behavior of current, and capacitance of porous silicon nanofilms are experimentally studied. It was found that these effects are amplified by a factor of 3-4 when the films are irradiated with an infrared laser. The results of this work can be used in the field of nanotechnology to improve memory and sensory elements. The established experimental facts can serve as a basis for constructing physical theories.

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.

To realize rapid biological detection and real-time analysis, a porous silicon microcavity optical biosensor with a central wavelength of 1550 nm was designed in this study, and a detection method based on the change in the gray value of the transmitted light image was proposed. The proposed method uses a near-infrared laser at the low absorption band of porous silicon as the light source. The infrared light transmitted from the surface of the porous silicon microcavity is converted into visible light by the infrared upconversion card. The transmitted light image is recorded by the charge-coupled device, and the gray value of the image is calculated to achieve detection. The experimental results show a linear relationship between the change in the gray value and the increase in complementary DNA concentration. The limit of detection of the proposed method is approximately 4 nM. The proposed method is lable free and spectrometer free, achieves fast detection speed, and can be further applied to biological detection in porous silicon microarrays.

In this research, a one-dimensional photonic crystal sensor for detecting soybean biodiesel is presented theoretically. The proposed sensor is composed of two alternating layers of Si and SiO2 with a defect layer of porous silicon immersed in the middle of this photonic crystal structure. The complete configuration of the proposed soybean photonic crystal sensor will be as [(Si/SiO2)5 (PSi) (Si/SiO2)5]. Thereby, a resonant peak is generated within the photonic band gap. This peak could be shifted downwards or upwards shorter or longer wavelengths due to any change in the concentration of soybean biodiesel. Therefore, the detection process could be investigated based on such variation. Also, the effects of many parameters, such as thickness of the porous silicon layer and temperature on the performance of our design are considered. In this regard, numerical results investigated high sensitivity and efficiency as well for the proposed soybean photonic crystal sensor.

Nanostructured porous silicon (PS) shows varied tunable functions leading to diversification of silicon technology. Among these functions, the emissions of photon, electron, and sound relate to the optical, electrical, and thermal properties of PS, respectively, as a quantum-confined material [1]. Some topics on further usefulness based on the functional combination is presented here. PS is composed of thermally isolated Si quantum dots (Si QDs) with a very high packing density. Due to a strong phonon confinement and interfacial scattering in PS, the thermal conductivity of PS layers is drastically lowered in comparison to that of bulk single-crystalline Si (c-Si). At the same time, its volumetric heat capacity is also significantly decreased. When combined with the mechanically metastable nature, it becomes possible to produce Si QDs with a considerably low external thermal energy. Actually, PS layers prepared by a standard electrochemical anodization of c-Si wafers in ethanoic HF solutions followed by peeling off from the wafer were dipped into organic solvents mixed with HF aqueous solution, and then in-situ heat treatment was made. It has been confirmed that PS layers are almost completely transformed into colloidal Si QDs with a significantly high yield even at a moderate temperature. The surfaces of as-prepared colloidal Si QDs are autonomously and organically passivated and they exhibit brighter PL emission than original PS. The dispersibility of Si QDs in solvents can be controlled by using organic solutions with appropriate function groups. Being a practical, clean, and low-power approach, this process provides a way for the scalable use of colloidal Si QDs as a printable material in optoelectronic, photoelectric, and biological applications. The thermal stability of PS with a controlled mesoporous surface structure, on the other hand, is useful as a substrate for epitaxial deposition of Si, Ge, SiC, diamond films, GaN, ZnO, and other III–V and II–VI semiconductors. The study has been extended to thin film deposition of ceramics like ferroelectric and ferrite materials. Recently [2], thin films of spinel ferrite (ZnFe2O4) were deposited on PS layers by pulsed laser deposition with an Nd:YAG laser of 266 nm for application to gas sensing. According to the structural and compositional characterizations, deposited thin films were polycrystalline and stoichiometric. Its average grain size and resistivity were smaller and higher, respectively, than those in the case of deposition on c-Si wafers. Obviously, the density of nucleation sites on the PS surface is much higher than that on the c-Si substrate. The measured sensitivity of a PS based device for liquefied petroleum gas was two-times higher than that of the c-Si based one. The sensitivity at high temperatures was comparable to that of ZnFe2O4 nanotubes and powder. It is important from a technological viewpoint that a reducing gas was detected effectively using the thin-film device configuration on c-Si wafer. In the high-porosity PS layer, thermal constants become close to the lower limit of solid state materials. When a temperature fluctuation is produced by electrical input to the heater electrode formed on the PS layer, an acoustic wave is generated near the surface via the thermos-acoustic transfer effect. A significant sound pressure amplitude is produced without any mechanical vibrations. The PS thermos-acoustic emitter shows a sufficiently flat frequency response in a wide ultrasonic band. One possible application is to reproduce complicated ultrasonic vocalization (USV) calls for clarifying the mechanism of mice communication and male-female interactions. As previously demonstrated, mouse mothers were attracted by pup USVs reproduced by a PS emitter, while they did not respond to other synthesized sounds. It was also found that the response to pup USVs was enhanced by social experiences. Studies on mutual recognition between mother and infant suggest that pup USVs looks to have an individual signature used in pup differentiation by mouse mothers, similar to acoustic communication between human mothers and their infants. It has also been reported that female mice exhibit disassortative social preferences in response to male USVs, and that the acoustic features that affect these social preferences are different between mouse strains [3]. The author NK thank Prof. Wakiya, and Prof. Kikusui for their continuing cooperation. [1] N. Koshida and T. Nakamura, Frontiers in Chemistry “Advances in Porous Semiconductors Science and Technology” Vol. 7, 273 (2019). [2] H. Ishigami, T. Kawaguchi, N. Sakamoto, S. Che, N. Koshida, K. Shinozaki, H. Suzuki, and N. Wakiya, J. Ceramic Soc. of Japan 128, 2020. [3] K. Nomoto, A. Hashiguchi, A. Asaba, M. Kato, N. Koshida, K. Mogi, and T. Kikusui, Experimental Animals, Published online, Feb 26, 2020.

[EN] We propose a fast and cost-effective method for obtaining a miniaturized array-formatted sensor suitable for multiplexed detection. Our solution is based on the fabrication of multiple mu m-sized suspended porous silicon (PSi) membranes working as independent transducers. Our process can potentially integrate an array of up to 1000 sensing spots per cm(2). We also propose a simple and user-friendly optical platform to simultaneously interrogate each element of the array in real-time. The feasibility of this idea was proved performing several sensing experiments where we were able to detect refractive index (RI) variations with different transducers at the same time. An average experimental sensitivity of 685 nm/RIU (Refractive Index Unit) was achieved, with a theoretical limit of detection (LoD) of 2.10(-4) RIU. The analyzed sensing spots displayed similar behavior both in time and in magnitude. We believe that the high capabilities of the sensor presented in this work, along with the sensing mechanism, can be very useful for multi-parametric analysis and multi-target detection of biological samples., This work was supported in part by the Ministry of Economy and Competitiveness and Spanish National Research Council under Project TEC2015-63838-C3-1-R-OPTONANOSENS and in part by the Generalitat Valencia under Project AVANTI/2019/123.

Selectivity remains a challenge for rapid optical vapor sensing via light reflected from porous silicon photonic crystals. This work highlights a method to increase optical vapor selectivity of porous silicon rugate filters by analyzing additive spectra from two rugate filter substrates with different functionalities, an oxidized and carbonized surface. Individually, both porous silicon rugate filters demonstrated sensitivity but not selectivity toward the vapor analytes. However, differences in peak shift trends between the two substrates suggested differences in vapor affinities for the surfaces. By adding the two spectra, improvements to selectivity relative to the individual surfaces were observed even at low vapor pressures and for analytes of similar polarity, refractive index, and concentration. These results are expected to contribute toward optical vapor selectivity improvements in one-dimensional porous silicon photonic crystals.

Spectral properties of enhanced-green fluorescent protein and monomeric red fluorescent protein in porous photonic structures have been studied. The fluorescent proteins were successfully infiltrated into porous silicon photonic structures with different positions of the photonic band gap in visible spectral range. The intensity of fluorescence is enhanced in the spectral regions of high photonic density of states. The possibility to control the fluorescence spectra by the structure with the photonic band gap is demonstrated.

Picosecond pulsed laser ablation of meso- and microporous silicon layers in water and ethanol leads to the formation of nanosilicon suspensions with particle diameters below 100 nm. It is established that the use of porous silicon targets allows the laser ablation threshold to be reduced and the nanoparticle concentration increased as compared to the ablation of crystalline silicon.

The surface region of the CdS/por-Si/p-Si heterostructure in which the porous layer was formed by metal-assisted etching of the single-crystal p-Si substrate is studied by scanning electron microscopy and Raman spectroscopy methods. Experimental results of the CdS film morphology study are processed using two-dimensional detrended fluctuation analysis and average mutual information methods. It is shown that the porous layer has a significant effect on structural features of the CdS film.

Gas sensors are important in many fields such as environmental monitoring, agricultural production, public safety, and medical diagnostics. Herein, Tamm plasmon resonance in a photonic bandgap is used to develop an optical gas sensor with high performance. The structure of the proposed sensor comprises a gas cavity sandwiched between a one-dimensional porous silicon photonic crystal and an Ag layer deposited on a prism. The optimised structure of the proposed sensor achieves ultra-high sensitivity (S = 1.9×105 nm/RIU) and a low detection limit (DL = 1.4×10−7 RIU) compared to the existing gas sensor. The brilliant sensing performance and simple design of the proposed structure make our device highly suitable for use as a sensor in a variety of biomedical and industrial applications.

For the first time, we obtained the photoreflectance spectra in single-layer samples of porous silicon with 13 μm thick in the 550–1000 nm spectral region. To describe the observed reflection and photoreflectance spectra, we use a theory of multiple-beam interference, taking into account the strong absorption of Si in this spectral region. We show that, under the action of a laser radiation with a wavelength 532 nm of 30 mW power and pulse duration 3 ms, the change in the refractive index δn reaches values of the order of 10−5, and this takes place due to the thermal nonlinearity of the refractive index. We show that photoreflectance spectroscopy can be used to measure the thermo-optic coefficients of porous silicon.

Silicon nanowires (SiNWs) were obtained on p-Si (100) substrate by Ag-assisted chemical etching method in two-step process. The influence of the etching duration on the morphological, optical and electrical properties of SiNWs samples was investigated. SEM images show clearly the presence of nanowires and the existence of porous silicon structure especially for low etching duration. Fourier Transformed Infrared spectroscopy (FTIR) measurements allow identifying several particles on the SiNWs surfaces such as oxygen and hydrogen elements. The optical properties of the SiNWs layer were investigated by Photoluminescence spectroscopy (PL). A strong broad PL band was observed at room temperature for an etching time of 30 s. The PL spectra exhibit multi-band profile in the red-green region. The luminescence of SiNWs is mainly attributed to Si-oxide interface states and oxygen deficient centers. Ag/SiNWs/Si Schottky diodes were analyzed by X-ray diffraction (XRD) and studied by current - voltage (I-V) measurements. Diode parameters such as ideality factor (n), series resistance (Rs), saturation current (Is) and energy barrier (φb) were determined by analyzing the I-V characteristics. Ag/SiNWs/Si diode for an etching duration of 30 s exhibits a rectifying behavior with a factor ideality of 2.8 and a low threshold voltage of about 0.44 V in forward bias. Space charge limited current (SCLC) model is the dominant transport mechanism through Ag/SiNWs/Si diode. The trap states, on the Ag/SiNWs interface, play in important role in the conduction phenomenon through these structures.