The performances of a porous silicon nanorods / gold nanoparticle combination for high sensitivity plasmonic sensing was assessed. First, an innovative synthesis technique was developed in a view to obtain porous silicon particles (nanorods due to their elongated shape) with homogeneous size and shape. The porous silicon nanorods were then spin coated on a glass substrate covered with gold nanoparticles. The combination of the high specific surface area porous silicon nanorods and the plasmonic effect of the Au nanoparticles was tested to form a highly sensitive ellipsometric sensing device. The porous silicon nanorods could be attached to both the plane Au surface and the Au nanoparticles with a specific spectral shift in the reflected polarized light.
Materials in thin-film structures for optical sensing applications must have multiple features: (i) enhancing the optical signal providing high optical sensitivity for the measurement of the interface processes, (ii) having appropriate chemical properties for supporting the adsorption of the molecules to be detected, (iii) having stability and selectivity. Development of materials that meet all these requirements is an ever lasting process with a lot of opportunities. In this work we propose porous silicon nanoparticles for the detection of biomolecules in plasmonic and Bragg multilayer enhanced Kretschmann-Raether ellipsometry configurations.
A semi-cylindrical lens in Kretschmann geometry combined with a flow cell was designed for a commercial rotating compensator ellipsometer to perform internal reflection spectroscopic ellipsometry measurements, while allowing the use of multiple angles of incidence. A thin glass slide covered with a gold film was mounted between the half-cylindrical lens and a small-volume flow cell ensuring an improved sensitivity for protein adsorption experiments. The performance of the system was investigated depending on the angle of incidence, wavelength range and thickness of the gold films for surface plasmon resonance enhanced ellipsometric measurements, and a sensitivity increase was revealed compared to ellipsometric measurements with standard flow cells, depending on the measurement parameters and configuration. The sensitivity increase was demonstrated for fibrinogen adsorption.
Non-destructive analysing tools are needed at all stages of thin film process-development, especially photovoltaic (PV) development, and on production lines. In the case of thin films, layer thicknesses, micro-structure, composition, layer optical properties, and their uniformity are important parameters. An important focus is to express the dielectric functions of each component material in terms of a handful of wavelength independent parameters whose variation can cover all process variants of that material. With the resulting database, spectroscopic ellipsometry coupled with multilayer analysis can be developed for on-line point-by-point mapping and on-line line-by-line imaging. Off-line point-by-point mapping can be effective for characterization of non-uniformities in full scale PV panels or big area (even 450 mm diameter) Si-wafers in developing labs but it is slow in the on-line mode when only 15 points can be obtained (within 1 min) as a 120 cm long panel moves by the mapping station. Last years [M. Fried et al, Thin Solid Films 519, 2730 (2011)], a new instrumentation was developed that provides a line image of spectroscopic ellipsometry (wl=350- 1000 nm) data. Earlier a single 30 point line image could be collected in 10 s over a 15 cm width of PV material. Recent years we have built a 30, a 45 and a 60 cm width expanded beam ellipsometer which speed is increased by 10x. Now, 1800 points can be mapped in a 1 min traverse of a 60*120 cm PV panel or flexible roll-to-roll substrate.
Indirect optical methods like ellipsometry or scatterometry require an optical model to calculate the response of the system, and to fit the parameters in order to minimize the difference between the calculated and measured values. The most common problem of optical modeling is that the measured structures and materials turn out to be more complex in reality than the simplified optical models used as first attempts to fit the measurement. The complexity of the optical models can be increased by introducing additional parameters, if they (1) are physically relevant, (2) improve the fit quality, (3) don't correlate with other parameters. The sensitivity of the parameters can be determined by mathematical analysis, but the accuracy has to be validated by reference methods. In this work some modeling and verification aspects of ellipsometry and optical scatterometry will be discussed and shown for a range of materials (semiconductors, dielectrics, composite materials), structures (damage and porosity profiles, gratings and other photonic structures, surface roughness) and cross-checking methods (atomic force microscopy, electron microscopy, x-ray diffraction, ion beam analysis). The high-sensitivity, high-throughput, in situ or in line capabilities of the optical methods will be demonstrated by different applications.
Optical techniques have been intensively developed for many decades in terms of both experimental and modeling capabilities. In spectroscopy and scatterometry material structures can be measured and modeled from the atomic (binding configurations, electronic band structure) through nanometer (nanocrystals, long range order) to micron scales (photonic structures, gratings, critical dimension measurements). Using optical techniques, atomic scale structures, morphology, crystallinity, doping and a range of other properties that can be related to the changes of the electronic band structure can most sensitively be measured for materials having interband transition energies in the optical photon energy range. This will be demonstrated by different models for the dielectric function of ZnO, a key material in optoelectronics and in numerous other fields. Using polarimetry such as spectroscopic ellipsometry, sub-nanometer precision has long been revealed for the thickness of optical quality layers. The lateral resolution of spectroscopic ellipsometry is limited (> 50 μm) by the use of incoherent light sources, but using single-wavelength imaging ellipsometry, a sub-micron lateral resolution can be reached. In case of sub-wavelength structures, the morphology (of e.g. porous or nanocrystalline materials) can be characterized using the effective medium theory. For structure sizes comparable to the wavelength, scatterometry is applied in a broad versatility of configurations from specular to angle resolved, from coherent to incoherent, from monochromatic to spectroscopic, from reectometric to polarimetric. In this work, we also present an application of coherent Fourier scatterometry for the characterization of periodic lateral structures.
Bismuth germanate is a well known scintillator material. It is also used in nonlinear optics, e.g. for building Pockels cells, and can also be used in the fabrication of photorefractive devices. In the present work planar optical waveguides were designed and fabricated in eulytine (Bi4Ge3O12) and sillenite (Bi12GeO20) type bismuth germanate crystals using single- and double-energy irradiation with N+ ions in the 2.5 < E < 3.5 MeV range. Planar waveguides were fabricated via scanning a 2 mm × 2 mm beam over the waveguide area. Typical fluences were between 1 • 1015 and 2 • 1016 ions/cm2. Multi-wavelength m-line spectroscopy and spectroscopic ellipsometry were used for the characterization of the ion beam irradiated waveguides. Waveguide structures obtained from the ellipsometric data via simulation were compared to N+ ion distributions calculated using the Stopping and Range of Ions in Matter (SRIM) code. M-lines could be detected up to a wavelength of 1310 nm in the planar waveguide fabricated in sillenite type BGO, and up to 1550 nm in those fabricated in eulytine type BGO.
Ion implantation proved to be a universal technique for producing waveguides in most optical materials. Tellurite glasses
are good hosts of rare-earth elements for the development of fibre and integrated optical amplifiers and lasers covering
all the main telecommunication bands. Er3+- doped tellurite glasses are good candidates for the fabrication of broadband
amplifiers in wavelength division multiplexing around 1.55 μm, as they exhibit large stimulated cross sections and broad
emission bandwidth. Fabrication of channel waveguides in such a material via N+ ion implantation was reported recently.
Parameters of waveguide fabrication in an Er-doped tungsten-tellurite glass via implantation of N+ ions were optimized.
First single-energy implantation at 3.5 MeV with fluences between 1·1016 and 8·1016 ions/cm2 was applied. Waveguide
operation up to 1.5 μm was observed. Then double-energy implantations at a fixed upper energy of 3.5 MeV and lower
energies between 2.5 and 3.0 MeV were performed to suppress leaky modes by increasing barrier width. Improvement of
waveguide characteristics was found by m-line spectroscopy and spectroscopic ellipsometry.
Slab optical waveguides were fabricated in tung-sten-tellurite glass doped with Er3 + ions by means of nitrogen ion implantation at 1.5 MeV. A wide range of ion doses (from 5·1012 to 8·1016 ions/cm2) was used. Optical characterization, performed by dark-line spectroscopy, revealed that the waveguides were of optical barrier type: the implanted layer exhibited a decrease of the refractive index with respect to the virgin bulk glass, while the region comprised between the sample surface and the end of the ion track acted as an optical guiding structure. It was also demonstrated that a post-implantation annealing process, performed at various temperatures on the samples implanted at higher doses, contributes to the reduction of the barrier region.
Slab waveguides were fabricated in Er-doped tungsten-tellurite glass and CaF2 crystal samples via ion implantation.
Waveguides were fabricated by implantation of MeV energy N+ ions at the Van de Graaff accelerator of the Research
Institute for Particle and Nuclear Physics, Budapest, Hungary. Part of the samples was annealed. Implantations were
carried out at energies of 1.5 MeV (tungsten-tellurite glass) and 3.5 MeV (CaF2). The implanted doses were between 5 x
1012 and 8 x 1016 ions/cm2. Refractive index profile of the waveguides was measured using SOPRA ES4G and Woollam
M-2000DI spectroscopic ellipsometers at the Research Institute for Technical Physics and Materials Science, Budapest.
Functionality of the waveguides was tested using a home-made instrument (COMPASSO), based on m-line spectroscopy
and prism coupling technique, which was developed at the Materials and Photonics Devices Laboratory (MDF Lab.) of
the Institute of Applied Physics in Sesto Fiorentino, Italy. Results of both types of measurements were compared to
depth distributions of nuclear damage in the samples, calculated by SRIM 2007 code. Thicknesses of the guiding layer
and of the implanted barrier obtained by spectroscopic ellipsometry correspond well to SRIM simulations. Irradiationinduced
refractive index modulation saturated around a dose of 8 x 1016 ions/cm2
in tungsten-tellurite glass. Annealing of
the implanted waveguides resulted in a reduction of the propagation loss, but also reduced the number of supported
guiding modes at the lower doses. We report on the first working waveguides fabricated in an alkali earth halide crystal
implanted by MeV energy medium-mass ions.
Fabrication of channel waveguides in Er-doped tungsten-tellurite glasses was recently demonstrated. In order to get a
deeper understanding of the process and to optimize the characteristics of the waveguides, we fabricated a set of planar
waveguides, each of 7 mm × 7 mm lateral dimensions, in an Er-doped tellurite glass sample by implantation of 1.5 MeV
nitrogen ions. Doses of the implanting ions ranged from 1 · 1016 to 8 · 1016 ions/cm2. The samples were studied using
interference phase contrast microscopy (Interphako), m-line spectroscopy and spectroscopic ellipsometry. The results
show that a barrier layer of reduced refractive index was created around the range of the implanted ions at every dose. It
is hoped that combination of the results obtained in these experiments with simulations for channel waveguides will
make it possible to optimize ion-implanted fabrication of integrated optical components in this tellurite glass.
Tellurite glasses are known to be highly promising materials for broadening the amplification bandwidth of Er3+-doped
waveguide amplifiers, as they have large stimulated emission cross sections and broad emission bandwidth around the
1.55 micron wavelength. Furthermore, they exhibit a wide transmission range, the lowest vibrational energy among oxide
glass formers, and good non linear properties. Nevertheless fabrication of waveguides in tellurite glasses appears to be a
challenging task and so far it has been reported only in a few papers. Here we report on the development of a method
based on high-energy ion beam irradiation to create active channel waveguides in a tungsten-tellurite glass doped with
Er2O3. The waveguide stripes have been realized by 1.5 MeV N+ irradiation of the glass sample through a silicon mask
with doses of 1.0 x 1016 ions/cm2 using a 5 MeV Van de Graaff accelerator. Multimode light propagation has indeed been
observed in these channels, confirming the effectiveness of this technique.
Transmission phase gratings have been designed and fabricated in glass samples via implantation of helium and nitrogen ions of energies in the 500 keV - 1.6 MeV range, through photoresist masks. Both mono- and multienergy implantations have been applied. Diffraction efficiencies of the gratings as function of the energy and dose of the ion implantation were measured.The phase profiles of the lines of the gratings have also been measured directly via interference and phase contrast-microscopy and scanning electron microscopy. Diffraction efficiencies up to 20 % have been obtained.
The development of a special optical multichannel analyzer (OMA) has been finished in the frames of a COPERNICUS project. The aim of our present work is to recall the attention to some of the unique benefits of 2D CCD detector matrices in OMAs in contrast to the usual line detectors. We demonstrate the relatively simple hardware and software reconfiguration possibilities of our new OMA system to achieve the establishment of a problem oriented, neural network evaluated, low cost multichannel analyzer.
We have built a modular, PC controlled ellipsometer with variable angle of incidence measuring possibility. We used a HeNe laser, PIN-diode detector and film polarizer in the analyzer and polarizer elements at first. The analyzer, polarizer and goniometer unit of the ellipsometer are moved by a computer controlled mechanism. The data processing program developed by us makes it possible to evaluate measurements with several angles of incidence, too, which are used to measure samples with complex layer structure. The units of the equipment are easily replaceable in consequence of modularity. It has been developed further to a spectroscopic ellipsometer in the spectral range of 400 to 641 nm by using a xenon lamp and a CCD array detector with optical grating as a diffraction element in spite of a laser and a PIN-diode detector. The analyzer was rotated by a step-motor (quasi-stationary method) or a DC-motor (dynamic method). These two methods allow the choice of a faster but less accurate (dynamic method) or a slower but very precise (quasi-stationary) measurements. Further development of the quasi-stationary arrangement will provide a speed comparable with the dynamic method together with a high accuracy.
A hardware implementation of a Backpropagation feedforward neural network has been designed. The tool was proposed for reflectometric measurements integrated together with photosensor arrays. The intelligent reflectometric sensor is being implemented in a multi-chip-module approach. A logarithmic input transformation is applied for easing the misalignment and parameter scatter correction. It also allows for easy ratio calculation by subtraction for normalization with the reference value. The neural network was designed for complexities up to 100 inputs, 30 hidden neurons and 5 outputs. The digital building blocks (neurons) utilize a logic approximation of the sigmoid nonlinearity and the possibility of weight scaling. These hardware solutions result in a simultaneous area reduction and speed gain, at the cost of slightly decreased performance. Simulations of the proposed neural system prove applicability for evaluation of optical measurements were performed for reflectometric and ellipsometric data thin porous layers. Hardware simulations showed good correspondence to the optimum-case neural software simulations.
Transmission phase gratings of grating constants of 4, 6, 8 and 12 micrometers have been designed and fabricated in glass samples via implantation of helium and nitrogen ions of energies in the 500 keV - 1.6 MeV range, through photoresist masks of thickness of 3.3 micrometers . Both mono- and multienergy implantations have been applied. The gratings have been studied by measuring the diffraction efficiencies. The phase profiles of the lines of the gratings have also been measured directly via interference and phase contrast microscopy and scanning electron microscopy. It was found that the profile of the implanted gratings differed significantly from the quasi rectangular profile of the mask, especially in case of the two finest gratings. The highest first order diffraction efficiencies were around 20%. The dependence of the efficiencies of the gratings on the energy and dose of the implantation have been measured.
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