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ISO 27911-2011 pdf free download
ISO 27911-2011 pdf free download.Surface chemical analysis — Scanningprobe microscopy — Definition and calibration of the lateral resolution of a near-field optical microscope
Analyse chimique des surfaces — Microsco pie a sonde a balayage — Definition et etalonnage de Ia resolution latérale d’un microscope optique en champ proche.
compromise both resolution and contrast. The method of formation of the aperture in the metal coating is also important. For example, if it was by focused ion beam millingt121 or by the pounding method(13], it will produce a rather blunt-ended probe shape but a well-defined aperture, whilst the shadowing methodl14l will usually result in a sharper probe end but the aperture boundary might not be so clearly defined. In general, coatings that are smooth and homogeneous also offer electromagnetic fields that are more predictable and better confined and therefore provide better imaging qualities.
5.4.4 Vertical size of the specimen
This is particularly important because topographic change in the specimen surface has been known to contribute to the optical contrast of the NSOM Image. This phenomenon, caused by an effective crosstalk between the topographic-signal channel and the optical-signal channel, results in topographic artefacts in the optical imagel11l. Any change in the topography signal might induce modulation in the optical signal, so that one ends up with similar features in both the optical image and the topography image, even though no corresponding optical contrast exists in the specimen. This effect is more often observed if there is a strong background signal in the optical-signal channel that can be perturbed by the modulation of the topography signal. Therefore, transmission or reflection Images that have an intrinsic background optical signal throughout the whole area of the image are especially subject to this topographic artefact. The effect is also more likely when a blunt probe is used to image a surface with a rapidly varying topography. In this case, the variation (with changing tip-specimen separation) of the optical coupling between the NSOM probe and the specimen surface results in topographic artefacts.
In order to avoid the above artefacts, one should eliminate both topographic changes in the specimen and the optical background signal as far as possible. A test specimen that is topography-free but still provides optical contrast is a good way of eliminating topography changes in the specimen surface, even though the preparation of such a specimen could be technically challenging(31 The optical background could be effectively eliminated by using fluorescence imaging where Stokes-shifted luminescence is detected while incident laser light is blocked. This way, one can isolate the true optical signal from the background signal that can be affected by the crosstalk, because the background signal and the fluorescence signal are spectrally separated.(4) However, even using fluorescence imaging, if the whole or part of the surface to be imaged has a background fluorescence signal, any optical contrast riding on this background signal could be due to the topographic artefacts. Therefore, isolated fluorescent objects of nano-size on a non-luminescent substrate would be desirable as the test specimenj4i
5.4.5 Lateral size of the specimen
This is also important in measuring the lateral resolution of an NSOM When imaging a small object, the recorded NSOM image is the convolution of the object and the PSF of the NSOM. Therefore, the apparent size of the object is larger than the PSF of the NSOM. The PSF of the NSOM cannot be regarded as a simple Gaussian or Lorentzian distribution, but rather as having a complicated structure that depends on the aperture shape, the condition of the outer metal coating. the input polarization, the light-coupling conditions, etc., and it is virtually impossible to de-convolve the true PSF of the NSOM from the observed profile of the small object in the NSOM image. Therefore, it is recommended that the effect of the object size be minimized by using objects as small as possible, so that one can regard the FWHM of the observed profile of the small object, to a reasonable approximation, as the FWHM of the NSQM PSF (see 6.2).ISO 27911-2011 pdf free download.
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