Racetrack micro-resonator (MR), made from partially or totally oxidized poroussilicon (PS) ridge waveguides fabricated with standard photolithography process, is reported. The design and the technological process are described including a study of waveguide dimensions that provide single mode propagation. Scanning electronic microscopy observations and optical characterizations clearly show that the MR based on PS ridge waveguides has been well implemented. As the MRs will be used for sensing application, we also present a preliminary theoretical study of the porous MRs sensitivity. A very promising theoretical sensitivity around 1200 nm/RIU (Refractive Index Unit) has been calculated for such porous racetrack MR.
Energy ( eV )
Figure 6 : PL spectra of PS and PS/Co samples with different immersion durations in CoCl 2
This behavior is quite similar to the effect of the iron incorporation in the poroussilicon matrix . These results would confirm that the presence of cobalt in PS matrix may modify the surface electronic structure by creating a new radiative recombination centers. While, for longer immersion durations, the large cobalt quantity deposited on the porous layer promotes the non-radiative energy transfer by creating excitation energy traps which induce the decrease of the PL intensity. This behavior is well known as autoextinction phenomenon [22- 23]. Furthermore, the large quantity of cobalt deposited on the nc-Si induced changes on their distribution and their sizes which explain the blue shift observed for a long t imm . Following
Fig.7. linearity of photodetector device as a function of incident photo energy density
Fig.8. Open circuit voltage as a function of the incident photo energy density
Figure 9 shows the spectral responsivity of Sb/PS/n-Si device under white illumination the higher light sensitivity (0.225A/W) is observed at shorter wavelength 400 nm than visible region 700nm which has of (0.15A/W) , because of the incident energy is higher than the excitation energy of electron-hole pairs and that mean , the wavelength in near UV region is absorbed in the depletion region of Sb/PS contact .The lower light sensitivity peak (0.15W/A) is a result of absorption of 700 nm in the depletion region of PS/n-Si heterojunction interface. The quantum confinement effects interpret this result.The direct band gab semiconductor offer much stronger absorption coefficient; therefore, the poroussilicon has better optoelectronic properties than bulk silicon.
A poroussilicon micro gas preconcentrator filled with Carbopack B has been implemented and successfully tested for the detection of explosives. The significant impact of the couple Carbopack-Poroussilicon on the preconcentration of explosives has also been demonstrated. We are currently focusing of the improvement of this µGP by using different PS substrates from micro to macro-PS and also by optimizing experimental parameters for shortening the detection duty cycle.
In this paper, we analyze the photoluminescence spectra (PL) of poroussilicon (PS) layer which is elaborated by electrochemical etching and passivated by Fe 3+ ions (PSF) via current density, electro-deposition and temperature measurements. We observe unusual surface morphology of PSF surface and anomalous emission behavior. The PSF surface shows regular distribution of cracks, leaving isolated regions or “platelets” of nearly uniform thickness. These cracks become more pronounced for high current densities. The temperature dependence of the PL peak energy (E PL ) presents anomalous behaviors ,i.e., the PL peak
band gap. This compound is also interesting for the production of blue and UV light emitters used in the optoelectronic devices, such as UV lasers , blue to UV light-emitting diodes[10-13] and UV sensors . Several methods are used for preparing ZnO films, such as magnetron sputtering [14-15], pulsed laser deposition(PLD), spray pyrolysis [17-20], sol–gel process [21-23] chemical bath deposition (CBD) [24-27] and chemical vapor deposition (CVD) [28,29],..etc. However, these methods are not well suited for large area coating, low temperature processing, and low cost. The electro-deposition technique has been proved to be one of the simplest and most effective way to prepare nicely crystallized ZnO at relatively low temperatures. This technique is widely used in order to growth and functionalize oxide materials with specific chemical and physical properties. The advantages offer by the electro-deposition technique for oxide films [30-34] are numerous as the easy preparation, rapid and simple, low cost, possibility of large-scale deposition, low temperature processing and direct control of film thickness, in comparison with other deposition techniques [14-23]. Generally, in literature [30, 33], the aqueous deposition was performed using either zinc chloride or zinc nitrate on a variety of seeded or seedless substrates. In this work, the nano composites of ZnO have been deposited on n type poroussilicon (PS) substrates. This later has been intensively studied since the discovery of its efficient photoluminescence at room temperature in the visible light region with the possibility to adjust its emitting wavelength from red to blue by managing the erosion process. In the present work, the electro-deposition technique was successfully used for the preparation of ZnO on nano-poroussilicon substrates with high porosity. Within this device topology, we expect to combine the particular properties of PS with the potential applications of ZnO. For this reason, structural, optical and electrical properties of the structure ZnO /PS were investigated using X-ray diffraction (DRX), Scanning Electro Microscopy (SEM) spectroscopy and FTIR
Laboratoire d’Optronique, FOTON, UMR-CNRS 6082, 22302 Lannion, France (Dated: November 8, 2005)
We present a neutron scattering analysis of the structure of the smectic liquid crystal octyl- cyanobiphenyl (8CB) confined in one-dimensional nanopores of poroussilicon films (PS). The smec- tic transition is completely suppressed, leading to the extension of a short-range ordered smectic phase aligned along the pore axis. It evolves reversibly over an extended temperature range, down to 50 K below the N-SmA transition in pure 8CB. This behavior strongly differs from previous obser- vations of smectics in different one-dimensional porous materials. A coherent picture of this striking behavior requires that quenched disorder effects are invoked. The strongly disordered nature of the inner surface of PS acts as random fields coupling to the smectic order. The one-dimensionality of PS nano-channels offers new perspectives on quenched disorder effects, which observation has been restricted to homogeneous random porous materials so far.
Freshly made PS is known to be unstable, showing considerable ageing effects that limit its use in practical applications. Poroussilicon (PS) layers with high porosity are of great interest; unfortunately, this material was found to be mechanically unstable during drying. Capillary forces have been invoked to explain such cracking .
R. Boukherroub, D.M. Wayner, and D.J. Lockwood National Research Council, Ottawa, Canada K1A 0R6
For practical applications of electroluminescence (EL) from nanocrystalline poroussilicon (nc-PS) diodes , the external power efficiency (EPE) should be improved beyond 1% at operating voltages below 10 V and the stability longer than 10,000 h under a cw operation. We recently developed a PS-EL device which offers the red band emission with an EPE of 0.4% at a voltage of 5 V , an external quantum efficiency (EQE) of 1.1% . The remaining subject to be pursued further is to enhance the EL stability. For this purpose, there are two possible approaches: (a) encapsulation of the device surface by a water-proof thin film and (b) passivation of luminescent nc-Si surfaces themselves by a stable termination. The effectiveness of the former was demonstrated in our previous paper . In this paper, it is reported that the latter is also very useful for stabilizing the EL emission.
The ability to tailor PorousSilicon (PSi) refractive index and layer thickness by controlling porosity and anodization time [1, 2] makes it especially attractive for optical applications. Optical multilayer devices such as Bragg reflectors or micro-cavities have already been formed from PSi layers notably for Visible and Near Infra-Red (NIR) wavelength ranges [3-10]. Two constant current densities are used for the high porosity (HP) and low porosity (LP) layers with low and high refractive
Fig.1 SEM cross section image of the porous silica ARROW structure (a) and refractive index profile (b)
Most of the used methods to elaborate ARROW waveguides are based on technologies using SiO2/Si/SiO2 (Shruti et al., 2009), SiO2/ TiO2/SiO2 (Chen et al., 2008), Polyimide/ Ta2O5/ Polyimide (Chu and Chuang, 2000) and SiO2/Si3N4/SiO2 (Prieto et al., 2001; Bernini et al., 2004). In our work, the ARROW structure is elaborated from the same material which is poroussilicon obtained by an electrochemical anodization method by varying the current density and the anodizing time.
The implementation of a Mid-IR silicon photonics transducer with broad Mid-IR transparency (up to 8 µm by taking into account Si transparency) is a challenge that could find applications in spectroscopic sensing and environmental monitoring. This paper demonstrates the fabrication of vertical PorousSilicon multilayer structures on Si substrates and their potential in the Mid-IR wavelength range notably near the cut-off band of Si due to its absorption at 8 µm. That is why the fabrication of Bragg reflector and vertical cavity on P + silicon substrate is investigated for applications in spectroscopic sensing in the (Mid-IR) wavelength range
UMR FOTON, CNRS, IMT Atlantique, F29238, Brest, France * Corresponding author: firstname.lastname@example.org
A micro-resonator based on poroussilicon ridge waveguides is implemented by a large scale standard photolithography process to obtain a low cost and sensitive sensor based on volume detection principle instead of the evanescent one usually used. The porous nature of the ridge waveguides allows the target molecules to be infiltrated in the core and to be detected by direct interaction with the propagated light. Racetrack resonator with radius of 100 µm and a coupling length of 70 µm is optically characterized for the volume detection of different concentrations of glucose. A high sensitivity of 560 nm/RIU is reached with only one micro-resonator and a limit of detection of 8.10 -5 RIU, equivalent to a glucose concentration of 0.7 g/L, is obtained.
obtained consists of oxidized poroussilicon (cap-layer), poroussilicon (inner-layer) and silicon substrate. The hardness curve has the typical “U shape” of low-dielectric-constant ﬁlms when the indentation depth rises: the early decrease in hardness, due to the soft inner layer, is followed by an increase, due to the hard substrate. A multilayer model is developed to account for hardness variation with respect to the applied load. This model considers the crumbling of the cap-layer and of the inner porous structure. As a result, it is shown that considering the minima in the U shape gives an over-estimated value when it comes to assessing the coating hardness. In our experiment, this minimum depends on both the hardness and the thickness of the oxidized cap layer, but not on the mechanical properties of the substrate, even for indentation depths slightly lower than the ﬁlm's thickness.
Owing to its unique and interesting optical and electrical properties, poroussilicon (abbreviated as pSi) is one of the most extensively studied semiconductors [ 1 ]. In the 1990s, the discovery of visible photoluminescence (PL) [ 2 , 3 ] from pSi at room temperature has motivated extensive studies. In recent years, a large effort has been made to study both the light emission origin and engineering technology of silicon micro-particles (abbreviated as SimPs). In particu- lar, pSi micro-particles (abbreviated as pSimPs) were explored in diverse domains, such as in photovoltaic applications as a gettering layer, which traps undesirable impurities from metallurgical grade silicon by using different methods [ 4 ]. Chemically-modi ﬁed pSimPs have been used for sensitive and rapid humidity detection [ 5 ]. Furthermore, this porous material was used for broader applications in chemical [ 6 ] and biological sensors [ 7 ], drug delivery [ 8 ] and biomedical applications [ 9 , 10 ]. Moreover, many reports show that SimPs extract hydrogen, bonded to pSi, for ef ﬁcient hydrogen storage and production [ 11 , 12 ]. In addition, owing to its high theoretical capacity, it has been recognized as the most attractive and promising anode material for lithiumion batteries, (more than
whereas a sensitivity of 200 nm/RIU (Refractive Index Unit)  for a polymer MR sensor and a LOD of 7. 6.10 - 7 RIU  for a SOI MR sensor has been obtained for homogeneous sensing.
To improve the sensor performance, the interaction between the propagated light and the analytes can be further enhanced using a porous material such as poroussilicon (PSi) for the MR waveguide. PSi layer is a three dimensional porous material which optimizes molecules interactions with the guided EM-field and increases the binding sites for surface functionalization because of its high specific internal surface .
for electrochemically methylated 22 and methoxylated 20 PSi surfaces with a slight blue shift in the maximum intensity. The methoxylated surface lost the PL after aging in air for several days. Buriak et al. 55 have studied the aging effect on the PL fatigue of a PSi surfaces modified with 1-dodecene (prepared by a hydrosilylation reaction catalyzed by EtAlCl 2 ), soaked in HF/EtOH (30 min at room temperature), and boiled in aerated KOH/ EtOH solutions (pH ) 10, 2 h). They found that the PLs of both samples irradiated with a mercury lamp in air decay faster than freshly prepared H-terminated PSi. Raman spectroscopy is particularly informative in understanding the effect of the aggressive steam oxida- tion on H-terminated poroussilicon. The spectra given in Figure 10a shows that the first- and second-order silicon Raman features are considerably modified after steam treatment: the 630-cm -1 line disappears and the 516- and 960-cm - 1 lines shift up to 520 and 970 cm - 1 . Also, the SiH x line at 2115 cm -1 is no longer visible. The Si line at 520 cm - 1 is now sharp and symmetric, Figure 10b, and is typical of crystalline Si. The Raman
relaxation regimes is considered as a general feature of the influence from an attractive rigid wall. 32
Conversely, QENS studies concerning the fast dynamics of confined LC’s are scarce in the literature. In the present paper, we have studied the local short time dynamics of the model LC 4-n-octyl-4-cyanobiphenyl (8CB) by incoherent QENS. We have compared bulk 8CB to 8CB confined in poroussilicon (PSi). The columnar form of PSi provides a model nanoporous geometry for confinement studies, which corresponds to straight one-dimensional channels. 33 This situation presents some similarity with previous studies of molecular liquids confined in porous materials. It allows for a comparison between nanoconfined normal (or supercooled) liquids and nanoconfined LC’s in their isotropic phase. 6 In addition, we can consider additional features that occur specifically in LC’s at lower temperature and are related to mesomorphic properties. We have recently studied the thermodynamical and structural behavior of 8CB in PSi by neutron diffraction. 34 The smectic transition is completely suppressed, leading to the extension of a short-range ordered smectic phase. It evolves reversibly over an extended temperature range, down to 50 K below the N-SmA transition of bulk 8CB. In the present paper, the molecular dynamics related to this exceptional behavior has been tracked as a function of temperature.
Glycerol and trehalose-glycerol binary solutions are glass-forming liquids with remarkable bioprotectant properties. Incoherent quasielastic neutron scattering (QENS) is used to reveal the different effects of nanoconfinement and addition of trehalose on the molecular dynamics in the normal liquid and supercooled liquid phases, on a nanosecond timescale. Confinement has been realized in straight channels of diameter D=8 nm formed by poroussilicon. It leads to a faster and more inhomogeneous relaxation dynamics deep in the liquid phase. This confinement effect remains at lower temperature where it affects the glassy dynamics. The glass transitions of the confined systems are shifted to low temperature with respect to the bulk ones. Adding trehalose tends to slow down the overall glassy dynamics and increases the non-exponential character of the structural relaxation. Unprecedented results are obtained for the binary bioprotectant solution, which exhibits an extremely non-Debye relaxation dynamics as a result of the combination of the effects of confinement and mixing of two constituents.