In this work we present a new microscope based on Nano-illumination microscopy (NIM), i.e., an innovative technique based on a 2D array of nano-Light-Emitting Diodes (LEDs) used to illuminate a sample. The key point of this method is that the pitch of the LED array fixes the spatial resolution. So, potentially, with LED pitches lower than the diffraction limit, super resolution could be achieved. While nanometer sized LEDs are not available yet, we present a prototype based on optical downscaling of a single 5µm lateral size LED. Extended Field-of-View (FOV) is obtained by mechanical movement with nanopositioners. Aspects of NIM microscopy such as its size, its flexibility in the sensing hardware or its potential for fluorescence, make it a perfect candidate to enhance emerging sensing applications in different fields, but especially life science (medical imaging, genomics, ...). We demonstrate the possibilities of the NIM technique with patterns as well as with biological samples.
Proc. SPIE. 10246, Smart Sensors, Actuators, and MEMS VIII
KEYWORDS: Gas sensors, Cameras, Sensors, Calibration, Glasses, Chemical compounds, Gases, Sensor performance, Time metrology, Biological and chemical sensing, Arsenic, Industrial chemicals, RGB color model
Colorimetric sensors based on color-changing dyes offer a convenient approach for the quantitative measurement of gases. An integrated, mobile colorimetric sensor can be particularly helpful for occasional gas measurements, such as informal air quality checks for bad odors. In these situations, the main requirement is high availability, easy usage, and high specificity towards one single chemical compound, combined with cost-efficient production. In this contribution, we show how a well stablished colorimetric method can be adapted for easy operation and readout, making it suitable for the untrained end user.
As an example, we present the use of pH indicators for the selective and reversible detection of NH3 in air (one relevant gas contributing to bad odors) using gas-sensitive layers dip coated on glass substrates. Our results show that the method can be adapted to detect NH3 concentrations lower than 1 ppm, with measure-to-result times in the range of a few minutes. We demonstrate that the color measurements can be carried out with the optical signals of RGB sensors, without losing quantitative performance.
Nanosensors systems comprised of an array of parallel-connected single-nanowires across electrodes with finger-widths, closely related to the diameter of gas sensitive WO3 nanowire are developed. The processing steps for the fabrication of these systems include electron-beam lithography, direct writing laser lithography, metallization, etching, dielectrophoresis, and aerosol assisted chemical vapour deposition, among others. The functionality of these systems in resistive configuration towards ethanol and nitrogen dioxide is evaluated. Results indicate higher sensor responses at 250°C and less signal to noise by applying constant currents of 50 nA. For these conditions, the sensor systems demonstrate reproducible responses to each analyte, with higher response to low concentrations of nitrogen dioxide (0.2, 1, 2.5 ppm), as opposed to ethanol (2.5, 10, 100 ppm), and in line with the literature.
The development of an integrated gas chromatographic system using micro and nanotechnologies is presented in this
paper. For this purpose, the different components of the chromatographic system, namely the preconcentrator, the
chromatographic column and the gas sensors are being investigated and developed, and the actual state of this
investigation is presented. The proposed target application comes from the agrofood industry, in particular the
determination of the fish freshness. The structure of the preconcentrator has been fabricated using deep reactive ion
etching (DRIE). The same fabrication technique has been employed for the patterning of the silicon microcolumns,
which have been sealed with Pyrex glass. Inlet and outlets have been connected and initial experiments of
functionalization have been performed. Gas sensors have been obtained by microdeposition of doped WO3 or SnO2
nanomaterials on microhotplates and their responses to the gases of interest have been measured, proving that the target
gas concentrations can be detected.
Functional metal oxide micro and nanostructures for the detection of gas are a very promising candidate for future gas-sensors.
Due to reduced size and thus an increased surface to volume ratio nanosized sensitive structures offer a high
potential for increasing sensitivity. A top down sputtering approach for gas sensors with nano-sized gas sensitive metal
oxide areas is presented. Oxidised silicon wafer were used as substrates. The silicon dioxide film of 1 &mgr;m thickness was
prepared by thermal oxidation in order to insulate the gas sensing elements from the substrate. At the sensor chips (1.5 x
1.5 mm2) a Ta/Pt film (20/200 nm thickness) was deposited and patterned to act as interdigital electrodes, heater and
temperature sensor. In a second step nano-scaled tin oxide layers (60nm thick, 5 &mgr;m width) were deposited by sputtering
techniques and photolithographical pattering between the platinum micro-electrodes (4 &mgr;m gap). As the last step the
width of the stripes was reduced by using Focused Ion Beam (FIB) technology to obtain the desired size and structure.
This enables the control of the dimensions of the structures down to the resolution limit of the FIB-system which is a
few tens of nm. The structural and electrical characterisation of the sensors and their responses during exposure to
several test gases including O2, CO, NO2 and H2O are presented as well.
The detailed microstructural characterization of CuInS2 (CIS) polycrystalline films is performed by combined in depth MicroRaman scattering/Auger Electron Spectroscopy measurements as a function of the chemical composition and temperature of processing. This has allowed to identify the main secondary phases in the layers as CuIn5S8 for Cu-poor samples and CuS for Cu-rich ones. The presence of such phases is strongly related to the temperature of processing, being secondary phase formation inhibited when the growing temperature decreases from 520°C to 370°C. This is also accompanied by a significant degradation of the structural CIS features, as reflected by the increase in both shift and broadening of the A1 CIS mode in the spectra, and by the decrease of the grain size estimated by cross-section TEM. Besides, Raman spectra measured from samples grown at lower temperatures are characterized by the presence of an additional mode at about 305 cm-1. The presence of this mode in the spectra from Cu-rich samples gives experimental support to its previously proposed structural origin. Finally, MoS2 secondary phase has also been identified at the CIS/Mo interface region, being its occurrence also inhibited at low growing temperatures.
Transformation of defects in hydrogen implanted silicon and silicon-on-insulator structures caused by external pressure of argon ambient at the stage of defect removal in implanted material and high temperature annealing SOI structures is reported. The results are compared to these for crystals annealed at argon atmosphere of ambient pressure. Formation of the new phase crystallites was found in SOI structures annealed at high temperature in conditions of high pressure. Small insulations were also observed in hydrogen implanted silicon, which can be patterns of the new phase. Two reasons can cause phase transformation in the top silicon layer of as-bonded SOI structures: high hydrogen concentration and high local strain.
Si and epitaxial SiGe strained and relaxed layers have been implanted with C+ ions to investigate the formation of SiCy and SiGexCy alloys (medium doses) as well as the ion beam synthesis of SiC in SiGe matrices (high doses). These layers have been analyzed by Raman scattering, in correlation with XRD, XPS and TEM. These data show that for implant temperature of 500 degree(s)C (crystalline target), carbon is not incorporated in substitutional sites, and (beta) -SiC precipitates aligned with the implanted matrix are formed. The residual strain and the degree of missorientation of these precipitates depend on the strain, defects and bond length of the implanted matrix. Moreover, precipitation of (beta) -SiC in the implanted region causes an enhanced Ge migration, mainly towards the surface. This determines a Ge enrichment and consequent relaxation of the Si1-xGex matrix. This contrasts with the room temperature implants performed in preamorphized Si layers, where carbon incorporation in substitutional sites (Cs) takes place after thermal annealing. The maximum amount of Cs is found for the implanted dose corresponding to a peak carbon concentration of 1.3%. For higher doses, there is a degradation of the crystal quality of the recrystallized layer.
The Raman scattering analysis of damaged and amorphous SiC layers obtained by ion beam processing has been performed as a function of the processing parameters. Two different sets of samples are investigated: (a) 6H-SiC samples implanted with Ge+ ions at different doses, and (b) SiC layers obtained by C+ ion implantation into amorphous Si. In the first case, damage accumulation and amorphization are analyzed as a function of the implanted dose. In the second case, deep in the analysis of the dependence of recrystallization processes on the amorphous structure, the ion beam induced epitaxial crystallization (IBIEC) of amorphous layers obtained by carbon implantation is also studied. The results show the strong ability of Raman scattering for the identification of amorphous phases in the layers, as well as for the evaluation of residual damage after thermal or IBIEC processes. Correlation of these data with IR, RBS and TEM allows us to determine the structural evolution of the samples under thermal or irradiation processes.