Spatial resolution :

A principal disadvantage of conventional XPS was lack of spatial resolution the spectral information came from an analyzed area of several square millimeters and was, therefore, an average of the compositional and chemical analysis of that area. Many technological samples are, on the other hand, inhomogeneous on a scale much smaller than that of conventional XPS analysis, and obtaining chemical information on the same scale as the inhomogeneities would be very desirable. 

The thrust of development is toward ever better spatial resolution, which means the smallest possible spot size on the sample compatible with adequate signal-to-noise ratio, for acquisition within a reasonable length of time. 

In EMP the cross section of the electron probe is often of the order of 2 nm, and with a section thickness approximately 100 nm a resolution at the subcellular level can be obtained. Considering the fact that physiologically interesting elements generally are freely dispersed in the cytosol, it is clear that local variations in concentration in biological tissues are to be expected. Therefore, analysis data are retrieved from sets of spots in regions of the tissue deemed to be representative of the structure under investigation. 

FIGURE 5.5 The secondary x-ray information will emerge from cellular structures in the depth of the section within volume of the proton beam volume of excitation. In addition, a probe diameter of 5 /im will result in lateral overlap of cellular compartments. Hence, the spatial resolution of the proton probe is restricted to strata rather than single cells. The resolution can be improved by diminishing the probe diameter ( 2 //m) and the section thickness ( 6 //m) at the cost of a substantial increase in acquisition time. 

Two objects are completely resolved if they are separated by 2r, and barely resolved if they are separated by r. The latter condition is sometimes known as the Rayleigh criterion of resolution. The largest numerical aperture that can generally be achieved for a Cassegrainian optic is approximately 0.6, so the diffraction-limited spatial resolution is approximately equal to the wavelength of the Hght when n = 1.0. 

Although it was stated that the spatial resolution of a microscope is ultimately limited by diffraction, aU modes of chemical imaging employ detector elements of finite size. When the image of the pixel at the sample plane becomes the limit- 

In practice, even though the size of the images of the pixels at the sample plane is smaller than the wavelengths of Hght being used to measured the sample, the finite thickness of the sample (typically 5-20 pm) can degrade the achievable spatial resoluHon significantly. This effect is discussed further in Section 1.4. 

Distance of Film Edge from Aperture Image (pm) 

The manufacturers of infrared microscopes are split almost evenly between those that produce infinity-corrected and those producing non-infinity-corrected microscopes. Infinity correction effectively refers to a coUimation of the beam throughout the microscope (other than at the condenser and objective outputs), and is frequently used in research-grade optical microscopes. Despite the added 

In the absense of object motion and in a time-invariant field gradient Gx, Equation (3) simplifies to  

FT-IR microscopes are designed to allow spectra of physically small samples, or regions of small samples, to be measured as quickly and easily as possible. On most microscopes, a video image of the sample is displayed on the monitor screen immediately adjacent to the sample, allowing the position of the sample and the jaws of the aperture to be optimized prior to the measurement of the spectrum. A motorized sample stage allows mapping to be readily accomplished. 

As noted above, the best spatial resolution of a microscope is ultimately determined by diffraction of the radiation. Thus, the spatial resolution is limited by the radius r of the Airy disk for the longest wavelength in the spectrum and hence depends on n, the refractive index of the medium in which the optics are immersed, for example, 1.0 for air and up to 1.56 for oils. Oil immersion is almost never used for infrared microspectroscopy because of absorption by the oil but has occasionally been used to improve the spatial resolution in Raman microspectroscopy. Immersion oils have been shown to be essential in order to obtain good depth resolution with confocal Raman microscopy [21]. Of greater importance from a practical standpoint for infrared microspectroscopy is the improvement in spatial resolution that is achieved in an attenuated total reflection (ATR) measurement with a hemispherical IRE, especially when the IRE is fabricated from germanium ( = 4.0) or silicon (n = 3.4.) 

1) Nicolet Corporation made its first FT-IR spectrometer in 1971 and became the market leader shortly afterwards. In 1995, Thermo Electron Corporation purchased Nicolet. In 2006, Thermo Electron purchased Fisher Scientific and the corporation is now known as Thermo-Fisher. 

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The systems of such type have been developed of all last 10 years. We shall bring some characteristics of one of the last development within the framework of European BRITE project, carried out in LETT This 3D cone-beam tomograph is referred to as EVA Bench or Equipment for Voludensimetry Analysis. It is oriented on NDT of industrial products from ceramics and other composites. One of the main task of this tomograph is achievement of high resolution at study of whole internal volume of researched object. For test sample of the size 10mm spatial resolution in 50mm was obtained [14]. 

In general, the performance of a radioscopic system should always be checked via test pieces with natural flaws. To ensure an additional comparability, standardized image quality indicators have to be used to control the essential image quality parameters such as spatial resolution (unsharpness) and contrast sensitivity. 

Spatial Resolution or Unsharpness The total resolution of the system is to be established via a platinum duplex wire penetrameter according to EN 462-5. The resolution limit that has been determined by this IQI can be directly converted to the system unsharpness. 

The sensitivity of the luminescence IP s in the systems employed here decreases with increasing x-ray energy more strongly than in the case of x-ray film. Therefore, this phenomenon must be compensated by using thicker lead front and back screens. The specific contrast c,p [1,3] is an appropriate parameter for a comparison between IP s and film, since it may be measured independently of the spatial resolution. Since the absorption coefficient p remains roughly constant for constant tube voltage and the same material, it suffices to measure and compare the scatter ratio k. Fig. 2 shows k as a function of the front and back screen thickness for the IP s for 400 keV and different wall thicknesses. The corresponding measured scatter ratios for x-ray films with 0,1 mm front and back screens of lead are likewise shown. The equivalent value for the front and back screen thicknesses is found from the intersection of the curves for the IP s and the film value. 

To evaluate the image quality of the processing system, one can determine classical parameters like spatial resolution, contrast resolution, dynamic range, local and global distortion. Guidelines for film digitization procedures have been well described now. Furthermore, a physical standard film for both equipment assessment and digitization calibration and control, will be available in a next future (4). 

Concerning the spatial resolution of NR images the present IP are not adequate to the best film based direct neutron imaging techniques. However, with time-and the development of new IP technology there are good possibilities to improve the inherent unsharpness of the IP systems to the level even better than with Gd/film combination ... 

Recently commercially available X-ray systems for laminography have a spatial resolution limited to hundred microns, which is not enough for modem multilayer electronic devices and assembles. Modem PCBs, flip-chips, BGA-connections etc. can contain contacts and soldering points of 10 to 20 microns. The classical approach for industrial laminography in electronic applications is shown in Fig.2. 

This approach is more close to X-ray stereo imaging and caimot reach enough depth resolution. There are also several systems with linear movement (1-dimensional) through the conical beam [5] as shown in Fig.4. In this case usable depth and spatial resolution can be achieved for specifically oriented parts of the object only. 

Other limitation for the spatial resolution can be found in the detector. A limited number of pixels in the camera array can be a reason for pure resolution in the case of a big field of view. For example, if field of view should be 10 by 10 nun with camera division 512x512 pixels the pixel size will be approximately 20 microns. To improve the relation of the field of view and the spatial resolution a mega-pixel sensor can be used. One more limitation for the spatial resolution is in mechanical movement (rotation) of the object, camera and source. In the case of a mechanical movement all displacements and rotations should be done with accuracy better than the spatial resolution in any tested place of the object. In the case of big-size assemblies and PCB s it is difficult to avoid vibrations, axle play and object non-planarity during testing. 

To reach enough good spatial resolution a new microlaminography approach has been developed. To avoid most errors from mechanical movements we use minimum movable parts (Fig.5). 

During testing a depth resolution of 50-80 micron and a lateral resolution of 20-40 micron was achieved. The spatial resolution was limited not mainly hy source or camera properties, but by the accuracy of compensation of the instrumental errors in the object movements and misalignments. According to this results a mote precision object rotation system and mote stable specimen holding can do further improvements in the space resolution of microlaminography. 

Laminographical approaches can be used for layer-by-layer visualization of the internal microstructure for the flat objects (multilayers, PCBs etc.), that caimot be reconstructed by computerized tomography because of the limited possibilities in rotation. Depth and lateral spatial resolutions are limited by the tube, camera and rotation accuracy. Microfocus X-ray tubes and digital registration techniques with static cameras allow improving resolution. Precision object manipulations and more effective distortion corrections can do further improvement. 

The AC-3 common industrial radionuclide tomograph have following technical characteristics diameter of tested articles from 5 to 250 mm, time of information registering -5-25 min, spatial resolution - 1%/... 

One of the more recent advances in XPS is the development of photoelectron microscopy [ ]. By either focusing the incident x-ray beam, or by using electrostatic lenses to image a small spot on the sample, spatially-resolved XPS has become feasible. The limits to the spatial resolution are currently of the order of 1 pm, but are expected to improve. This teclmique has many teclmological applications. For example, the chemical makeup of micromechanical and microelectronic devices can be monitored on the scale of the device dimensions. 

Plenary 8. J Grave et al, e-mail address J.Greve tn.utwente.nl (RS). Confocal direct unaging Raman microscope (CDIRM) for probing of the human eye lens. High spatial resolution of the distribution of water and cholesterol in lenses. 

The aehievable spatial resolution is limited by several eflfeets. The first is the maximum gradient strength and eneoding times available. Bearing in mind equation B1.14.1 and = l/A/n, the pixel size resulting from... 

The echo phase does not depend on the initial position of the nuclei, only on their displacement, vA, occurring in the interval between the gradient pulses. Analysis of the phase of the echo yields a measure of flow velocity in a bulk sample. Spatial resolution is easily obtained by the incorporation of additional imaging gradients. 

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