A non-invasive optical measurement system based on a broadband light source and color filters has been developed for determining pulse rate and arterial blood oxygen saturation (SaO2). In contrast to classical pulse oximetry using red and infrared LEDs to measure the peripheral capillary oxygen saturation (SpO2), we use color filters in our system. Spectral analysis of human tissue can be easily achieved by combining a tiny color filter matrix and a commercial CMOS/CCD image sensor. During system operation, white LED light illuminates our tissue (e.g., a finger), while a CCD sensor covered by filters detects the light transmitted through that tissue. The CCD sensor is controlled by a Field Programmable Gate Array (FPGA) and a microcontroller. The detected photoplethysmographic (PPG) signal is transferred to a host computer and analyzed with MATLAB. After sensor system calibration, pulse rate and SpO2 can be simply extracted from the PPG signal. The heart rate and SpO2 of different volunteers are then measured simultaneously by commercial pulse oximetry and the proposed sensor system, in which results from both devices show good agreement. To integrate more functions into system, nanostructured color filter matrix containing 15 filters for different wavelengths is designed and fabricated. This filter can be designed to provide transmission peaks over the visible and near-infrared range (i.e., the human tissue optical transparent window) and has a high potential to be fabricated directly on top of pixels of an image sensor.
KEYWORDS: Scanning probe microscopy, Calibration, Standards development, Metrology, Atomic force microscopy, Scanners, Scanning electron microscopy, Electronics, Nanotechnology, Control systems
The continuing miniaturization in many technologies - among them the optical systems - demands high-resolution measurements with uncertainties in the nanometre-range or even well below. A brief introduction of measurement methods used at the micro- & nanometre scale is therefore given as introduction. While a wide range of these methods are well established for the determination of various physical properties down to the nanometric scale, it is Scanning Probe Microscopy (SPM) that provides a unique direct access to topographic surface features in the size range from atomic diameters to some ten or hundred micrometres. With the increasing use of SPMs as quantitative measurement instruments, the demand for standardized calibration routines also for this type of instruments rises. However, except for a few specially designed set-ups mainly at National Metrology Institutes (e. g. PTB in Germany), measurements made with SPMs usually lack traceability to the metre definition. A number of physical transfer standards have therefore been developed and are already available commercially. While detailed knowledge of the standards' properties is a prerequisite for their practical applicability, the calibration procedure itself deserves careful consideration as well. As there is, up to now, no generally accepted concept how to perform SPM calibrations, guidelines are now being developed on various national and international levels, e. g. VDI/VDE-GMA in Germany and ISO. This papers discusses the draft of an SPM calibration guideline by focusing on several critical practical aspects of SPM calibration. The paper intends to invite the readers to take active part in guideline discussions.
KEYWORDS: Scanning electron microscopy, Atomic force microscopy, Calibration, Line edge roughness, Metrology, Interferometers, Microscopes, Phase shifts, Very large scale integration, Electron microscopes
We report on investigations including calibration of a 100 nm pitch structure, the NanoLattice by VLSI Standards, with a special metrological scanning electron microscope (SEM) and a scanning force microscope (SFM). The SEM used is called electron optical metrology system (EOMS) and basically consists of a dedicated low voltage e-beam column which is mounted on top of a large vacuum chamber with an integrated, laser-controlled precision 2D stage. The key feature of this instrument is the advantage to combine sub-nm-resolution object position measurement by vacuum laser interferometry with a high resolution e-beam probe of about 5-10 nm. Correlation methods combining the laser interferometer and secondary electron intensity profile data are used to analyze global pitch as well as local pitch deviations. The EOMS measurements confirm an excellent pitch uniformity. Preliminary estimations yield sub-nanometric mean pitch uncertainties for the 100 nm grating period over the whole active area of 1 mm x 1.2 mm. Additional SFM investigations were performed by a modified NanoStation III (SIS GmbH, Germany) which has been especially adapted for high stability measurements. In this way, the instrument allows to determine pitch homogeneity and line edge roughness (LER) of the structures with high reproducibility.
Preliminary results show a good agreement with EOMS measurements.
KEYWORDS: Near field, Near field scanning optical microscopy, Molecules, Near field optics, Microscopy, Energy transfer, Metals, Lithography, Photomasks, Diffraction
Contact imaging by energy transfer was the first application of the optical near-field for imaging beyond the diffraction limit. It is a method by which surface nanostructures can be copied onto a monomolecular layer of a dye. Near field microscopy using tapered metal coated fibers with an aperture at their tip as a submicron source of light can be used as a tool to write structures at a resolution of 80 nm. These near-field optical methods are well suited to create-- by local photochemical reactions--patterns of locally differing chemical composition and reactivity. Such structures serve as matrices for a site selective binding of colloidal particles. Unlike other methods, light microscopy and near-field microscopy have a sensitivity to detect photochemical processes at the single molecular level. Near- field microscopy is not limited to a resolution of 50 nm. As recently shown, the resolution can be extended to the 1 - 10 nm range using the tetrahedral tip as a probe. We expect, that a convergence of these recent developments should result in a very powerful near-field optical toolbox to read, write and copy information at the 10 nm scale.
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