Photo-induced electrochemical anodization of p-type silicon: achievement and demonstration of long term surface stability.
TL;DR: This study provides a route for preparing highly sensitive organic vapour sensors with a precise selection of the fabrication parameters and demonstrating their prolonged performance by fabrication using a photoluminescence quenching technique.
Abstract: Surface stability is achieved and demonstrated by porous silicon (PS) fabricated using a wavelength-dependent photo-electrochemical (PEC) anodization technique. During anodization, the photon flux for all wavelengths was kept constant while only the effect of light wavelength on the surface morphology of PS was investigated. PS optical sensors were realized, characterized and tested using a photoluminescence (PL) quenching technique. An aliphatic chain of alcohols (methanol to n-octanol) was detected in the range of 10?200?ppm. Long term surface stability was observed from samples prepared under red (750?620?nm) and green illumination (570?495 nm), where the PL quenching cycles evoke the possibility of using PS for stable sensor device applications. This study provides a route for preparing highly sensitive organic vapour sensors with a precise selection of the fabrication parameters and demonstrating their prolonged performance.
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TL;DR: The present review describes the fabrication of nano-porous silicon and its biosensing capabilities for detection of various analytes including, but not limited to, glucose, DNA, antibodies, bacteria and viruses.
163 citations
Journal Article•
TL;DR: In this paper, a relaxation in the q-vector selection rule for the excitation of the Raman active optical phonons was proposed to increase the red shift and broadening of the signal from microcrystalline silicon films.
Abstract: The red shift and the broadening of the Raman signal from microcrystalline silicon films is described in terms of a relaxation in the q-vector selection rule for the excitation of the Raman active optical phonons. The relationship between width and shift calculated from the known dispersion relation in c-Si is in good agreement with available data. An increase in the decay rate of the optical phonons predicted on the basis of the same model is confirmed experimentally.
105 citations
TL;DR: In this paper, the use of porous silicon (PS) as an electrochemical biosensor has been reviewed and the authors provide a critical assessment of the various factors which are actually responsible for enhanced performance of PS electrochemical sensors.
Abstract: The use of porous silicon (PS) as an electrochemical biosensor has been reviewed. For electrochemical biosensing, the enhanced surface area is not the only advantage of using PS. In fact, depending on the transduction mechanisms, various issues like modulation of electric field lines through the pores and its interface with the biomolecules and ions of the analytes, nature of PS–metal contacts, orientation of the molecules within the pores and modification of the effective spring constant of the structure leading to a change in the resonant frequency have significant impact on sensitivity, reproducibility and longevity. In this review, we provide a critical assessment of the various factors which are actually responsible for enhanced performance of PS electrochemical biosensors. Formation procedures of PS for electrochemical biosensing have been mentioned. The mechanism of surface modification and derivatization has been briefly discussed. The contact formation techniques have been outlined. Four different categories of electrochemical biosensors using PS have been analysed in details with emphasis on equivalent circuit models and the specific role of PS in the electrical transduction mechanisms. Finally the existing challenges and the future prospects of such devices for commercial use are highlighted.
63 citations
TL;DR: This paper presents the performance of a highly selective ethanol sensor based on MoS2-functionalized porous silicon (PSi), and an enhancement in sensitivity and a selective response for ethanol were observed, with a minimum detection limit of 1 ppm.
Abstract: This paper presents the performance of a highly selective ethanol sensor based on MoS2-functionalized porous silicon (PSi) The uniqueness of the sensor includes its method of fabrication, wafer scalability, affinity for ethanol, and high sensitivity MoS2 nanoflakes (NFs) were synthesized by sulfurization of oxidized radio-frequency (RF)-sputtered Mo thin films The MoS2 NFs synthesis technique is superior in comparison to other methods, because it is chip-scalable and low in cost Interdigitated electrodes (IDEs) were used to record resistive measurements from MoS2/PSi sensors in the presence of volatile organic compound (VOC) and moisture at room temperature With the effect of MoS2 on PSi, an enhancement in sensitivity and a selective response for ethanol were observed, with a minimum detection limit of 1 ppm The ethanol sensitivity was found to increase by a factor of 5, in comparison to the single-layer counterpart levels This impressive response is explained on the basis of an analytical resistiv
56 citations
TL;DR: In this paper, a miniaturized prototype sensor based on TiO2 nanotubes/porous silicon (PS) heterojunction is developed for selective ethanol sensing in sub-ppm range.
Abstract: A miniaturized prototype sensor based on TiO2 nanotubes/porous silicon (PS) heterojunction is developed for selective ethanol sensing in sub-ppm range. Titanium (Ti) of thickness ∼ 200 nm was deposited on PS using RF sputtering technique. Both silicon and Ti were sequentially anodized to form PS and nanotubes respectively. Electrical contacts for testing of resistive sensors were fabricated using lift off process. The sensor was packaged onto a 12-pin header and tested in presence of different VOCs with concentration ranging from 0.5 to 100 ppm. The selective ethanol sensing at around 150 °C stems from the formation of TiO2 nanotubes/PS heterojunction. The sensitivity of such a sensor, improved manifold in comparison to the response of pure PS and pure TiO2 based sensors. The formation of heterojunction, selective response to ethanol, sub-ppm level sensing at comparatively low operating temperature is discussed. The study unfolds the collective properties of TiO2/PS heterojunction and demonstrates the potential of wafer scale integrated repeatable ethanol sensor tested at sub-ppm level.
44 citations
References
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TL;DR: In this paper, free standing Si quantum wires can be fabricated without the use of epitaxial deposition or lithography using electrochemical and chemical dissolution steps to define networks of isolated wires out of bulk wafers.
Abstract: Indirect evidence is presented that free‐standing Si quantum wires can be fabricated without the use of epitaxial deposition or lithography. The novel approach uses electrochemical and chemical dissolution steps to define networks of isolated wires out of bulk wafers. Mesoporous Si layers of high porosity exhibit visible (red) photoluminescence at room temperature, observable with the naked eye under <1 mW unfocused (<0.1 W cm−2) green or blue laser line excitation. This is attributed to dramatic two‐dimensional quantum size effects which can produce emission far above the band gap of bulk crystalline Si.
7,393 citations
TL;DR: In this paper, the pseudodielectric functions of spectroscopic ellipsometry and refractive indices were measured using the real-time capability of the spectro-optical ellipsometer.
Abstract: We report values of pseudodielectric functions $〈\ensuremath{\epsilon}〉=〈{\ensuremath{\epsilon}}_{1}〉+i〈{\ensuremath{\epsilon}}_{2}〉$ measured by spectroscopic ellipsometry and refractive indices $\stackrel{\ifmmode \tilde{}\else \~{}\fi{}}{n}=n+ik$, reflectivities $R$, and absorption coefficients $\ensuremath{\alpha}$ calculated from these data. Rather than correct ellipsometric results for the presence of overlayers, we have removed these layers as far as possible using the real-time capability of the spectroscopic ellipsometer to assess surface quality during cleaning. Our results are compared with previous data. In general, there is good agreement among optical parameters measured on smooth, clean, and undamaged samples maintained in an inert atmosphere regardless of the technique used to obtain the data. Differences among our data and previous results can generally be understood in terms of inadequate sample preparation, although results obtained by Kramers-Kronig analysis of reflectance measurements often show effects due to improper extrapolations. The present results illustrate the importance of proper sample preparation and of the capability of separately determining both ${\ensuremath{\epsilon}}_{1}$ and ${\ensuremath{\epsilon}}_{2}$ in optical measurements.
3,094 citations
TL;DR: In this paper, a relaxation in the q-vector selection rule for the excitation of the Raman active optical phonons was proposed to increase the red shift and broadening of the signal from microcrystalline silicon films.
2,059 citations
"Photo-induced electrochemical anodi..." refers methods in this paper
...7 nm for samples A, B, C and D, respectively, by using phonon confinement models [10, 11] (figure 2)....
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TL;DR: In this article, the effect of the exact shape of the microcrystal and the relationship between the width, shift and asymmetry of the Raman line is calculated and is in good agreement with available experimental data.
1,957 citations
TL;DR: The photoluminescence properties of porous silicon have attracted considerable research interest since their discovery in 1990 as discussed by the authors, which is due to excitonic recombination quantum confined in Si nanocrystals which remain after the partial electrochemical dissolution of silicon.
1,261 citations