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Nanometrology coordinate measurement machines uncertainties caused by frequency fluctuations of the laser
Hrabina, Jan ; Lazar, Josef ; Číp, Ondřej
One of considerable sources of displacement measurement uncertainty in nanometrology systems such as multidimensional interferometric positioning for local probe microscopy is the influence of amplitude and especially frequency noise of a laser source which powers the interferometers. We investigated the noise properties of several laser sources suitable for interferometry for micro- and nano-CMMs (coordinate measurement machines) and compared the results with the aim to find the best option. The influences of amplitude and frequency fluctuations were compared together with the noise and uncertainty contributions of other components of the whole measuring system. Frequency noise of investigated laser sources was measured by two approaches – at first with the help of frequency discriminator (Fabry-Perot resonator) converting the frequency (phase) noise into amplitude one and then directly through the measurement of displacement noise at the output of the interferometer fringe detection and position evaluation. Both frequency noise measurements and amplitude noise measurements were done simultaneously through fast and high dynamic range synchronous sampling to have the possibility to separate the frequency noise and to compare the recorded results.
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Differential interferometry with suppression of the influence of refractive index of air for nanometrology
Holá, Miroslava ; Číp, Ondřej ; Hrabina, Jan ; Buchta, Zdeněk ; Lazar, Josef
We present an interferometric technique based on differential interferometry setup for measurement in the subnanometer scale in atmospheric conditions. The motivation for development of this ultraprecise technique is coming from the field of nanometrology. The key limiting factor in any optical measurement are fluctuations of the refractive index of air representing a source of uncertainty on the 1*E-6 level when evaluated indirectly from the physical parameters of the atmosphere. Our proposal is based on the concept of overdetermined interferometric setup where a reference length is derived from a mechanical frame made from a material with very low thermal coefficient on the 1*E-8 level. The technique allows to track the variations of the refractive index of air on-line directly in the line of the measuring beam and to compensate for the fluctuations. The optical setup consists of three interferometers sharing the same beam path where two measure differentially the displacement while the third evaluates the changes in the measuring range acting as a tracking refractometer. The principle is demonstrated on an experimental setup and a set of measurements describing the performance is presented.
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Scanning Probe Microscopy: Measuring on Hard Surfaces
Matějka, Milan ; Urbánek, Michal ; Kolařík, Vladimír
During a measurement by scanning probe microscopy (SPM) an image artifacts can appear in a measurement data. The source of image artifacts during an SPM measurement could be in parts of the SPM tool: mechanical system, piezoelectric crystal, scanner electronic. However, the main source of image artifact is the probe tip geometry and properties of the sample. For example, probe wearing, which occurs during the contact measurement on a sample with a hard surface, could result in heavy probe shape change, causing probe-related image artifacts. Measurement could appear problematic on a sample with periodical relief structure (e.g. gratings with sub 10 μm periodicity) prepared in hard materials (e.g. silicon), when the structure height is greater than about 500 nm. In this case, probe can easily get struck during the scanning, on the hard surface as well as at the high aspect ratio relief structure, causing image artifact thus reducing measurement quality.
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SPM Nanoscratching in the Sub 100 nm Resolution
Urbánek, Michal ; Kolařík, Vladimír ; Matějka, Milan
Scanning probe microscopy (SPM) is tool basically used for surface characterization. Besides that, it offers several lithographic methods (e.g. nanoscratching) to prepare structures in the sub 100 nm resolution. The nanoscratching using SPM offers a method for patterning of surface with a very high resolution based on near field interaction. By this method some tiny marks or taggants could be prepared. Therefore we used the SPM nanoscratching for preparation of nanostructures in thin soft polymer films by various tips. Nanoscratching regime of SPM is possible to operate in contact and close contact modes. In the contact mode we prepared an array of stamps with a variable size, where dimensions and depth dependency on number of pixels were inspected. For writing of these structures we used polymer films with different softness (e.g. PMMA, SU-8) and various values of setpoint, which are responsible for structures deepness.
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Multiple Probe Photonic Force Microscopy
Jákl, Petr ; Šerý, Mojmír ; Zemánek, Pavel
Single beam optical trap (also known as optical tweezers) is created by a laser beam that is tightly focused by microscope objective with high numerical aperture. A dielectric particle in water medium is then dragged by optical forces to place of the highest optical intensity, i.e. to the laser beam focus. Photonic force microscopy (PFM) is a technique that utilizes optical tweezers for confining the local probe, usually a dielectric particle of a sub-micron diameter. I.e. PFM belongs to the of large family of scanning probe microscopy (SPM) techniques. We have used fluorescently labeled polymer sphere in order to conveniently measure the distance between the particle center and the focal point of the laser beam. To make the measurement more precise, we have measured two-photon-fluorescence, which is quickly decreasing with the probe-focus distance.
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