Multilayer architectures based on a-SiC:H material: tunable wavelength filters in optical processing devices.

The characteristics of tunable wavelength filters based on a-SiC:H multilayered stacked pin cells are studied both theoretically and experimentally. The optical transducers were produced by PECVD and tested for a proper fine tuning of the cyan and yellow fluorescent proteins emission. The active device consists of a p-i'(a-SiC:H)-n/p-i(a-Si:H)-n heterostructures sandwiched between two transparent contacts. Experimental data on spectral response analysis, current-voltage characteristics and color and transmission rate discrimination are reported. Cyan and yellow fluorescent input channels were transmitted together, each one with a specific transmission rate and different intensities. The multiplexed optical signal was analyzed by reading out, under positive and negative applied voltages, the generated photocurrents. Results show that the optimized optical transducer has the capability of combining the transient fluorescent signals onto a single output signal without losing any specificity (color and intensity). It acts as a voltage controlled optical filter: when the applied voltages are chosen appropriately the transducer can select separately the cyan and yellow channel emissions (wavelength and frequency) and also to quantify their relative intensities. A theoretical analysis supported by a numerical simulation is presented.

Semiconductor device as optical demultiplexer for short range optical communications.

In this paper we present results on the use of a multilayered a-SiC:H heterostructure as a wavelength-division demultiplexing device for the visible light spectrum. The proposed device is composed of two stacked p-i-n photodiodes with intrinsic absorber regions adjusted to short and long wavelength absorption and carrier collection. An optoelectronic characterisation of the device was performed in the visible spectrum. Demonstration of the device functionality for WDM applications was done with three different input channels covering the long, the medium and the short wavelengths in the visible range. The recovery of the input channels is explained using the photo-current spectral dependence on the applied voltage. An electrical model of the WDM device is proposed and supported by the solution of the respective circuit equations. Short range optical communications constitute the major application field, however other applications are also foreseen.

Detection of change in fluorescence between reactive cyan and the yellow fluorophores using a-SiC:H multilayer transducers.

Optical colour sensors based on multilayered a-SiC:H heterostructures can act as voltage controlled optical filters in the visible range. In this article we investigate the application of these structures for Fluorescence Resonance Energy Transfer (FRET) detection, The characteristics of a-SiC:H multilayered structure are studied both theoretically and experimentally in several wavelengths corresponding to different fluorophores. The tunable optical p-i'(a-SiC:H)-n/p-i(a-Si:H)-n heterostructures were produced by PECVD and tested for a proper fine tuning in the violet, cyan and yellow wavelengths. The devices were characterized through transmittance and spectral response measurements, under different electrical bias and frequencies. Violet, cyan and yellow signals were applied in simultaneous and results have shown that they can be recovered under suitable applied bias. A theoretical analysis supported by numerical simulation is presented.

Pinpi'n and pinpii'n multilayer devices with voltage controlled optical readout.

In this paper we present results on the optimization of a pinpii'n type a-Si:H based three color detector with voltage controlled spectral sensitivity. The sensor element consists on a glass/ITO/p-i-n a-SiC:H multilayer structure which faces the incident illumination, followed by a-SiC:H(-p)/a-SiC:H(-i)/Si:H(-i')/SiC:H(-n)/ITO heterostructure, that allows the optically addressed readout. Results show that this approach leads to regionally different collection parameters resulting in multispectral photodiodes, coding for red (R), blue (B), and two green (G) components. In the polychromatic operation mode different sensitivity ranges are selected by switching between different biases so that the basic colors can be resolved with a single device. Positive bias is needed under blue irradiation and moderate reverse bias under green. The threshold voltage between green and red sensitivity depends on the thickness of the bottom a-SiC:H (-i) layer, and corresponds to the complete confinement of the absorbed green photons across the pinpi sequence. As the thickness of the a-Si:H i'-layer increases, the self-reverse effect due to the front absorption will be balanced by the decrease of the self-forward effect due to the back absorption shifting the threshold voltage to lower reverse bias. The various design parameters are discussed and supported by a numerical simulation.

Modeling a-SiC:H tandem pinpin and pinip photodiodes for color sensor application.

The present paper reports the optical properties of multilayer structures composed by p-i-n cells based on a-SiC:H or a-Si:H material. Different structures are studied in order to obtain image sensors that accomplish color filtering in addition to image pattern recognition. A simple theoretical model is developed to explain sensors behavior and to derive the optical-readout experimental procedure. Electrical models for the sensors are established for simulation purposes and to compare photocurrent signals with experimental data. A numerical simulation of the JV characteristic and of the spectral response is also presented in order to show possible future optimization of the device. Two main structures are studied, namely p-i-n/p-i-n and p-i-n/n-i-p tandem cells.

Photocurrent and spectral response analysis of a-SiC:H pinip and pinpin photodiodes.

We present in this paper results about the analysis of photocurrent and spectral response in a-SiC:H/a-Si:H pinpin and pinip structures. Our experiments and analysis reveal the photocurrent profile to have a strong nonlinear dependence on the externally applied bias and on the light absorption profile, i.e., on the incident light wavelength and intensity. Our interpretation points out the cause of such effect to a self biasing of the junctions under certain unbalanced light generation of carriers and to an asymmetric reaction of the internal electric fields to the externally imposed bias. The possibility to relate such a behavior to the light intensity and wavelength indicates realistic hypothesis of using these structures and this effect for color recognition sensors. We present results about the experimental characterization of the structures and numerical simulations obtained with the program ASCA. Considerations about electrical field profiles and inversion layers will be taken into account to explain the optical and voltage bias dependence of the spectral response. Our results show that in both structures the application of an external electrical bias (forward or reverse) mainly influences the field distribution within the less photo excited sub-cell.

[Periodontal disease in pregnancy and low birth weight] / Doença periodontal na gravidez e baixo peso ao nascer.

OBJECTIVE: Recently, it has been suggested that periodontal disease during pregnancy could have a causal relationship with low weight at birth. Our objective was to evaluate the influence of periodontal disease during pregnancy on the birth weight of newborn infants. METHODS: Mothers who gave birth to low-birth-weight infants were randomly selected (Group 1 - G1; n=13). Immediately after inclusion of each mother in group 1, the mother of the next term newborn with birth weight of > 2,500 g (Group 2 - G2; n=13) was included as control. Mothers were examined by a periodontist who was not informed of the group the child belonged to. A probe was used to measure attachment loss of the alveolar bone. The extension index (EI) and severity index (SI) of the periodontal disease were determined. RESULTS: Both groups of mothers were similar in terms of maternal age, parity, color of skin, height, nutrition, smoking, drinking, socioeconomic status, prenatal examinations, premature rupture of membranes, chorioamnionitis, bacteriuria, placenta previa, abruptio placentae, previous hypertensive disease, preeclampsia, and heart disease. The characteristics of the newborns were: birth weight - G1 = 1,804 -/+ 675 g x G2 = 3,030 -/+ 516 g; gestational age - G1 = 33 -/+ 5 weeks x G2 = 39 -/+ 2 weeks; length of stay in the neonatal intensive care unit (NICU) - G1 = 128 days x G2 = 0 days. Average EI: G1 = 89.788 -/+ 18.355 x G2 = 72.420 -/+ 20.717; p=0.033. Average SI: G1 = 1.377 -/+ 0.626 x G2 = 0.754 -/+ 0.413 (OR=18.3; CI95%: 2.5-133.3; p = 0.006). After adjustment for risk factors for low birth weight, such as smoking, maternal height, bacteriuria, and previous hypertension, the odds ratio for SI dropped to 7.2 (CI95% = 0.4-125.4; P = 0.176). CONCLUSION: The multivariate analysis indicated a marked association between periodontal disease measured by SI score and low birth weight. Our data suggested that periodontal disease during pregnancy may be a risk factor for low weight at birth.