Manuel F. M. Costa

Surface inspection by an optical triangulation method

A noncontact optical microtopographer based on an active, discrete triangulation procedure has been under development for some time at the physics department of the University of Minho. Our experi- ence has shown that this kind of triangulation-based surface inspection system can be applied, not only to long-distance range sensing, but also to smaller samples or other surfaces with height resolutions that can go down to the submicron range. In our system, the topographic information is obtained from the horizontal shift of the bright spot created by an oblique collimated light beam on a surface when it is displaced vertically. A laser beam is focused onto a small, diffraction-limited spot on the surface and is made to scan it over the desired region. The horizontal position of the bright spot is perpendicularly imaged onto a linescan cam- era and the information on the individual detectors that are activated, above a certain controllable intensity threshold level, is used to compute the corresponding horizontal spots shift on the reference plane. Thus we can compute the distance between the surface and a reference plane at each sampled point. A map of the surface topography can then be built and statistical surface characterization parameters may be calculated. Our versatile laboratory setups have been used for different inspection tasks such as thickness measurements and relief mapping of different kinds of films (polyethylene, thin sputtered copper, tin dioxide and silver films) and several kinds of fabrics, and roughness measure and topo- graphic inspection of polyethylene molds and graphite samples. In this communication we briefly describe our method. The current configura- tion of our laboratory setup is described. A hand-held version of our system and also the setup for long-distance dimensional assessments are briefly presented.

Electrochromic coatings for smart windows

Electrochromic coatings are finding interesting applications in a wide range of fields. The possibility of controlling the transparency of tungsten oxide (WO 3 ) thin films by the application of small electrical voltages in a reversible way is quite promising and was explored in the work herein reported. Multi-layer films based on WO 3 were mainly deposited by reactive dc magnetron sputtering onto glass substrates. The films were analyzed by spectroscopy from the near infrared to the ultraviolet, by the laser triangulation for microtopographic inspection, atomic force microscopy and X-ray diffraction.

Optical Triangulation-Based Microtopographic Inspection of Surfaces

The non-invasive inspection of surfaces is a major issue in a wide variety of industries and research laboratories. The vast and increasing range of surface types, tolerance requirements and measurement constraints demanded during the last decades represents a major research effort in the development of new methods, systems and metrological strategies. The discreet dimensional evaluation the rugometric characterization and the profilometric inspection seem to be insufficient in many instances. The full microtopographic inspection has became a common requirement. Among the different systems developed, optical methods have the most important role and among those triangulation-based ones have gained a major status thanks to their flexibility, reliability and robustness. In this communication we will provide a brief historical review on the development of optical triangulation application to the dimensional inspection of objects and surfaces and on the work done at the Microtopography Laboratory of the Physics Department of the University of Minho, Portugal, in the development of methods and systems of optical triangulation-based microtopographic inspection of surfaces.

Optical properties of PZT 65/35 thin films deposited by sol-gel

PZT 65/35 thin films were deposited on Pt-coated Si (100) and MgO (110) substrates using the sol-gel technique. The crystalline structure of the films was investigated by X-ray diffraction and Raman spectroscopy. Results of measurements and modeling of the optical spectra for the PZT films on MgO substrates are reported. The effective dielectric function is calculated versus frequency and Gaussian tail of the join density of states under the assumption of direct band to band transition.

X-ray detector based on a bulk micromachined photodiode combined with a scintillating crystal

In this paper we report on the design, fabrication, assembly and testing of an x-ray detector based on a bulk micromachined photodiode (BMMPD) with a cavity filled with a scintillating crystal. The x-ray photons that reach the detector are first converted to visible light by the scintillating crystal. The visible light is then detected by the BMMPD, producing an electric current with a value proportional to the incident x-ray intensity. Tests were performed using two x-ray setups: an experimental setup and a professional setup. The first was powered with a maximum voltage of 35 kV, and a current ranging to 1 mA, and the second was powered with voltages from 40 to 60 kV and currents ranging from 10 to 55 mA.

a-Si:H interface optimisation for thin film position sensitive detectors produced on polymeric substrates

Abstract In this paper we present results concerning the optimisation of the electronic and mechanical properties presented by amorphous silicon (a-Si:H) thin films produced on polyimide (Kapton® VN) substrates with different thicknesses (25, 50 and 75 μm ) by the plasma enhanced chemical vapour deposition (PECVD) technique. The purpose of this study is to obtain a low defect density as well as low residual stresses (specially at the interface) in order to provide good performances for large area (10 mm wide by 80 mm long) flexible position sensitive detectors. The electrical and optical properties presented by the films will be correlated to the sensor characteristics. The properties of samples have been measured by dark/photoconductivity, constant photocurrent measurements (CPM) and the results have been compared with films deposited on Corning 7059 glass substrates during the same run deposition. The residual stresses were measured using an active optical triangulation and angle resolved scattering. The preliminary results indicate that the thinner polymeric substrate with 25 μm presents the highest density of states, which is associated to the residual stresses and strains associated within the film.

Resonance energy transfer in self-organized organic/inorganic dendrite structures

Hybrid materials formed by semiconductor quantum dots and J-aggregates of cyanine dyes provide a unique combination of enhanced absorption in inorganic constituents with large oscillator strength and extremely narrow exciton bands of the organic component. The optical properties of dendrite structures with fractal dimension 1.7-1.8, formed from J-aggregates integrated with CdTe quantum dots (QDs), have been investigated by photoluminescence spectroscopy and fluorescence lifetime imaging microscopy. Our results demonstrate that (i) J-aggregates are coupled to QDs by Förster-type resonant energy transfer and (ii) there are energy fluxes from the periphery to the centre of the structure, where the QD density is higher than in the periphery of the dendrite. Such an anisotropic energy transport can be only observed when dendrites are formed from QDs integrated with J-aggregates. These QD/J-aggregate hybrid systems can have applications in light harvesting systems and optical sensors with extended absorption spectra.

System of optical noncontact microtopography

In this paper we describe a method of noncontact optical microtopography based on discrete triangulation. We show that a light beam with an oblique incidence on a surface can be used to assess the distance of the latter to a reference plane if the bright spot produced on the surface is imaged onto an array of detectors that tracks its lateral displacement. The light beam is swept over the surface so that large areas can be scanned. The authors have used their system with success for the topographic inspection of several surfaces, e.g., thin copper and silver films, polyethylene rough films and molds, graphite, machined metallic parts, and fabrics.

Microtopographic inspection of Cr-Cr2O3 cermet solar absorbers

The importance of renewable energy sources is currently attracting widespread attention due to the limited availability of fuels and major environmental impacts. A great deal of effort is put our days on the development of new efficient solar energy collectors either by quantum or thermal conversion. On this communication we will refers just to thermal converters focusing on the roughness and microtopographic inspection of surface thin films and spectrally selective coatings. Physically Vapor Deposited coatings like sputter deposited metal oxide and nitride thin multilayered and graded ones can be used in spectrally selective surfaces for thermal collectors and energy- efficient windows.

Dependence of the Strains and Residual Mechanical Stresses on the Performances Presented by a-Si:H Thin Film Position Sensors

The influence of residual stresses on the performances of large area position sensitive detectors produced on flexible substrates are presented here. For evaluating the residual stresses, two main techniques were used: An active optical triangulation and angle resolved scattering and the constant photocurrent method (CPM). From the results it was possible to correlate the stresses and the density of defects present in the films.