Improvements have been made to a commercial Linnik microscope in order to perform measurements in water for studying structures of transparent and non-transparent samples. One of the main goals of the present work is to study pollutants in colloidal layers immersed in liquid. The second reason to work in liquid is to increase the lateral resolution. The challenges to overcome include achieving stability in the complex Linnik design as well as the difficulty of balancing the optical distance of the two arms of the interferometer to obtain the interference fringes. The main problem is the path length compensation in the mirror arm which needs a complex mechanical design to allow a high enough number of degrees of freedom to correct alignment of the optical elements. In our system, the reference mirror arm is mounted horizontally, making liquid immersion tricky. In this work, we have investigated alternative solutions based on non-liquid elastic polymers placed between the end of the objective and the reference mirror using sodium polyacrylate (SPA) beads and PDMS (polydimethylsiloxane) slabs, with a refractive index very close to that of water. The results of the performance tests of the modified system are presented and demonstrated. The new design provides a workable system that is ready for the future study of colloidal and other samples directly in water.
Glass formation and glassy behavior remain areas of investigation in soft matter physics with many aspects which are still not completely understood, especially at the nanometer size-scale and close to the glass transition temperature. In the present work, we show an extension of the “nanobubble inflation” method developed by O’Connell and McKenna [Rev. Sci. Instrum. 78, 013901 (2007)] which uses an interferometric microscope (white light scanning interferometry method) to measure the surface topography of a large array of 5 μm sized nanometer thick films. These so-called free-standing films are subjected to constant inflation pressure during which the nanobubbles grow or creep with time. Measurements of multiple bubbles in real time are possible via the technique of Phase Shifting Microscopy (PSM) thanks to the fast acquisition and processing of interferometry. This has been implemented using in-house developed LabVIEW based software combined with the IMAQ Vision module. Moreover this technique has the advantage, over the AFM method of O’Connell and McKenna, to be a true non-contact technique. Using this optical configuration, there is no substrate interaction to affect the polymer chains. Here we demonstrate the method using ultra-thin films of both poly(vinyl acetate) (PVAc) and polystyrene (PS) and discuss the capabilities of the method in comparison to AFM, with its advantages and disadvantages. The viscoelastic responses of the nanobubbles are determined by measuring their time-dependent diameters and then by extracting both the stress and strain time-dependent components (here the history of the polymer films has to be taken into account). We show that the results from experiments on PVAc are consistent with the prior work on PVAc. However high stress results with PS show signs of a new non-linear response regime that could be related to the plasticity of the ultra-thin film. Our homemade setup used to apply stresses on the films is also described. This first allows the control of both temperature, using a Peltier ring which surrounds the sample, and pressure, using gas flow linked to a manometer. Then major improvements of our setup in order to solve small experimental issues are described. Finally, plans for further improvements to the cell are explained for future experiments.
The development of new nanomaterials, devices and systems is very much dependent on the availability of new techniques for nanometrology. There now exists many advanced optical imaging techniques capable of subwavelength resolution and detection, recently brought to the forefront through the 2014 Nobel Prize for chemistry for fluorescent STED and single molecule microscopy. Label-free nanoscopy techniques are particularly interesting for nanometrology since they have the advantages of being less intrusive and open to a wider number of structures that can be observed compared with fluorescent techniques. In view of the existence of many nanoscopy techniques, we present a practical classification scheme to help in their understanding. An important distinction is made between superresolution techniques that provide resolutions better than the classical λ/2 limit of diffraction and nanodetection techniques that are used to detect or characterize unresolved nanostructures or as nanoprobes to image sub-diffraction nanostructures. We then highlight some of the more important label-free techniques that can be used for nanometrology. Superresolution techniques displaying sub-100 nm resolution are demonstrated with tomographic diffractive microscopy (TDM) and submerged microsphere optical nanoscopy (SMON). Nanodetection techniques are separated into three categories depending on whether they use contrast, phase or deconvolution. The use of increased contrast is illustrated with ellipsometric contrast microscopy (SEEC) for measuring nanostructures. Very high sensitivity phase measurement using interference microscopy is then shown for characterizing nanometric surface roughness or internal structures. Finally, the use of through-focus scanning optical microscopy (TSOM) demonstrates the measurement and characterization of 60 nm linewidths in microelectronic devices.
Full-field optical coherence tomography (FF-OCT) based on white-light interference microscopy, is an emerging noninvasive imaging technique for characterizing biological tissue or optical scattering media with micrometer resolution. Tomographic images can be obtained by analyzing a sequence of interferograms acquired with a camera. This is achieved by scanning an interferometric microscope objectives along the optical axis and performing appropriate signal processing for fringe envelope extraction, leading to three-dimensional imaging over depth. However, noise contained in the images can hide some important details or induce errors in the size of these details. To firstly reduce temporal and spatial noise from the camera, it is possible to apply basic image post processing methods such as image averaging, dark frame subtraction or flat field division. It has been demonstrate that this can improve the quality of microscopy images by enhancing the signal to noise ratio. In addition, the dynamic range of images can be enhanced to improve the contrast by combining images acquired with different exposure times or light intensity. This can be made possible by applying a hybrid high dynamic range (HDR) technique, which is proposed in this paper. High resolution tomographic analysis is thus performed using a combination of the above-mentioned image processing techniques. As a result, the lateral resolution of the system can be improved so as to approach the diffraction limit of the microscope as well as to increase the power of detection, thus enabling new sub-diffraction sized structures contained in a transparent layer, initially hidden by the noise, to be detected.
Transparent layers such as polymers are complex and can contain defects which are not detectable with classical optical inspection techniques. With an interference microscope, tomographic analysis can be used to obtain initial structural information over the depth of the sample by scanning the fringes along the Z axis and performing appropriate signal processing to extract the fringe envelope. By observing the resulting XZ section, low contrast, sub-μm sized defects can be lost in the noise which is present in images acquired with a CCD camera. It is possible to reduce temporal and spatial noise from the camera by applying image processing methods such as image averaging, dark frame subtraction or flat field division. In this paper, we present some first results obtained by this means with a white light scanning interferometer on a Mylar polymer, used currently as an insulator in electronics and micro-electronics. We show that sub-μm sized structures contained in the layer, initially lost in noise and barely observable, can be detected by applying a combination of image processing methods to each of the scanned XY images along the Z-axis. In addition, errors from optical imperfections such as dust particles on the lenses or components of the system can be compensated for with this method. We thus demonstrate that XZ section images of a transparent sample can be denoised by improving each of the XY acquisition images. A quantitative study of the noise reduction is presented in order to validate the performance of this technique.
KEYWORDS: 3D image processing, 3D acquisition, 3D metrology, Image processing, Field programmable gate arrays, Microscopy, Image resolution, Time metrology, Image acquisition, Modulation
Achieving real time 3D measurement of microscopic surfaces is difficult, mainly because of the high bandwidths
required for the data acquisition by the probe or camera, the transfer to the processor and the processing. In this paper we
present the results of our second prototype on-line measurement system that we have developed using continuous
scanning white light interference microscopy, a high speed CMOS camera and parallel processing with an FPGA that
enables data processing rates of up to 160 Mb/s. Two fringe detection algorithms have been implemented, one based on
the detection of the maximum fringe intensity and the other on the maximum of the fringe modulation function. The
practical performance is demonstrated on the measurement of laterally translating samples, with 3D image rates of up to
20 i/s being achieved for an image size of 256 x 320 pixels, and 2.96 i/s for an image size of 640 x 1024 pixels over a
depth of 5 μm. Depths of up to 20 μm can be measured. On-line 4D microscopy opens up new applications for
characterizing surfaces that are moving or changing in a non-periodic way with time, such as in MEMS, soft materials,
layer growth or chemical reactions.
KEYWORDS: 3D metrology, 3D image processing, Field programmable gate arrays, Microscopy, Image processing, Cameras, Imaging systems, High speed cameras, Digital signal processing, Modulation
White light scanning interference microscopy is used for measuring the surface morphology of materials and devices
more and more widely in many areas of research and industry. However, a limiting requirement is that the surface to be
analysed be kept static during measurement, which can typically take from several seconds to several minutes. As
industries such as MEMS manufacturing mature and create more complex dynamic devices, it becomes increasingly
important to be able to characterize structures that undergo periodic or transitory motion.
In this paper we present the architecture of a 4D (3D + time) interference microscopy system that is being developed
based on continuous fringe scanning over the depth of the sample. The simulation of results using real time detection of
the peak fringe intensity (PFSM, Peak Fringe Scanning Microscopy) or the maximum of the fringe visibility (FSA, Five
Sample Adaptative non linear algorithm) is discussed.
During scanning, a high speed CMOS camera provides images at a rate of 500 i/s (1280x1024 pixels) that are processed
using a FPGA (Field Programmable Gate Array) to extract the 4D measurements. At a bit stream rate of 625
Mbyte/second, it is reasonable to expect a measurement rate of nearly 1 i/s at full frame size over a 20 &mgr;m depth and 9 i/s
over a depth of 2 &mgr;m. By reducing the image size to 128x128 pixels, the rate is increased to 16 i/s over a 20 &mgr;m depth
and 600 i/s over 2 &mgr;m. These values could be increased further using under sampling or by means of higher speed reference mirror scanning.
We present a VLSI digital-analog readout electronic chain for silicon microstrip detectors. The characteristics of this circuit have been optimized for the high resolution tracker of the CERN CMS experiment. This chip consists of 128 channels at 50 micrometers pitch. Each channel is composed of a charge amplifier, a CR-RC shaper, an analog memory, an analog processor, an output FIFO which is read out serially by a multiplexer. This chip has been processed in the radiation hard technology DMILL. This paper describes briefly the architecture of the circuit and presents test results of the 128 channel full chain chip before and after irradiation up to 10 Mrad.
S. Gardien, P. Pangaud, J.-P. Walder, U. Goerlach, C. Hoffmann, C. Hu, A. Lounis, C. Maazouzi, P. Schmitt, G. Hall, M. Raymond, Freddy Anstotz, J.-D. Berst, G. Deptuch, Y. Hu, J.-L. Sohler, Renato Turchetta, Pierre Borgeaud, D. Lachartre, Marcus French, R. Robert
The silicon microstrips tracker for CMS at LHC demands fast, radiation-hard electronics. An original solution was proposed for the processing of signals from silicon detectors. This technique allows precise reconstruction of the arrival time of the particles, even with a 'slow' shaping time and a limited power budget. This idea was already implemented in the APV6 circuit, designed in a bulk CMOS technology from Harris.In this paper, we present the version (APVD) designed in the CMOS SOI radiation hard technology DMILL by a French-British collaboration. The APVD is a 128-channel mixed analogue-digital: each channel includes a low-noise charge preamplifier, a CR-RC shaper with a peaking time of 50 ns, an analogue pipeline where the signal is sampled at 40 MHz, an analogue pulse shape processor and a current output multiplexer. The circuit integrates an 12C interface for easy control of the operating parameters. All the control current and voltages as well as a calibration pulse are generated internally by dedicated blocks. The design and first experimental results from the first version of the 128-channel APVD, will be presented in this paper. They show the circuit is fully functional and can be used for the CMS experiment.
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