Imaging mode

There are three basic regions of interaction between the probe and surface (i) free space, (ii) attractive region, and (iii) repulsive region. At short distances, the cantilever mainly senses interatomic forces the very short range ( 0.1 nm) repulsive forces, and the longer-range (up to 10 nm) van der Waals forces. Attractive forces near the surface ean arise from a layer of contamination present on all surfaces in ambient air. The eontamination is typically an aerosol composed of water vapor and hydrocarbons. On the other hand, the repulsive force occurs between any two atoms or molecules that approach so closely that 

In the contact mode, there are static modes (de-modes), and dynamic modes (ac-modes). In the former, a cantilever-type spring bends in response to the force which acts on the probing tip until a static equilibrium is established [1]. In the dynamic mode, the lever oscillates close to its resonance frequency. A distance-dependence force shifts the resonance curve. Another technique is to modulate the position of the sample at a frequency below the cantilever resonance but above the feedback-response frequency and send the response signal to a lock-in amplifier to measure the signal s amplitude and phase [4]. The lock-in output is connected to the auxiliary data acquisition channels to form an image - this approach is popularly known as force modulation (FM-mode). FM-mode imaging or force cmve is an AFM technique that identifies and maps differences in surface stiffness or elasticity. 

Vertical tip position Profiie Verticai tip position Profiie 

Lateral foree microscopy (LEM) is a variant of the dc-contact mode, specifieally the constant-force mode, in which the laser-beam detector is arranged so as to allow monitoring not only of the vertical component of the tip deflection (topography), but also the 

In 1997, Hayes et al. [28] reported the physical and electrochemical properties of two-component self-assembled monolayers (SAMs) composed of both electroactive (4-aminothiophenol, 4-ATP) and electroinactive (w-octadecanethiol, ODT) species. LFM images obtained at three points near the critical region of the isotherm indicated that these two-component SAMs display complex phase behavior at relatively low 4-ATP coverage, the surface consists of small islands of 4-ATP embedded in an ordered film of ODT at higher coverage of 4-ATP, however, evidence was found for both separation into distinct phases and mixing of the two components. 

Thin sections of polymer blends can give bright field images with little or no contrast between the components. Transmitted light phase contrast converts the refractive index differences in such a specimen to light and dark image regions. Small 

In interference microscopy the illumination is split into two beams. The beam splitter is a half silvered mirror in reflection, and one beam is reflected off the specimen, the other off a flat reference mirror [4-8]. Transmission is more complex as the beam splitter may be a doubly refracting crystal (Wollaston prism), and the two beams can be displaced vertically or horizontally [2-7]. In all cases the two beams are recombined so that they interfere. The interference pattern can be used to measure the specimen thickness in transmission, or the specimen roughness in reflection. The Leitz Mach-Zehnder interference 

Transmitted light is more complex as separate matched devices have to be used to split and then recombine the beams [3-8]. In early systems, the beam displacement was large so that the reference beam did not pass through the specimen. In the Jamin-Lebedeff system (Zeiss last produced in the 1980s) [1,4,6], the reference beam is displaced by more than its diameter but both reference and measuring beam can be seen in the same field of view. The reference beam is set to pass through a featureless area of the specimen. 

The modern version of interference microscopy is differential interference contrast (also called Nomarski contrast, or DIG). Here again, the illumination is split into two beams, one of which is displaced at the specimen plane [1,5,6, 21]. In DIG, the beam is displaced a very small distance, much smaller than the beam diameter. The beams remain independent because the beam-splitting device is a doubly refracting crystal, producing two beams in perpendicular polarization states (see Section 3.1.7). A region 

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Tdrdk P, Sheppard C J R and LaczikZ 1996 Dark field and differential phase contrast imaging modes in confocal microscopy using a half aperture stop Optik 103 101-6... 

Figure Bl.24.16. An example of the applieation of the PIXE teelmique using the NMP in the imaging mode. The figures show images of the eross seetion tlirough a root of the Phaseolus vulgaris L. plant. In this ease the material was seetioned, freeze-dried and mounted in vaeuiim for analysis. The seales on the right of the figures indieate the eoneentrations of the elements in ppm by weight. It is elear that the transports of the elements tlirough the root are very different, not only in the eases of the major elements Ca and K, but also in the ease of the traee element Zn.

Transmission electron microscopy (tern) is used to analyze the stmcture of crystals, such as distinguishing between amorphous siUcon dioxide and crystalline quartz. The technique is based on the phenomenon that crystalline materials are ordered arrays that scatter waves coherently. A crystalline material diffracts a beam in such a way that discrete spots can be detected on a photographic plate, whereas an amorphous substrate produces diffuse rings. Tern is also used in an imaging mode to produce images of substrate grain stmctures. Tern requires samples that are very thin (10—50 nm) sections, and is a destmctive as well as time-consuming method of analysis. 

Figure 2 Micrographs of the same region of a specimen in various imaging modes on a high-resolution SEM (a) and (b) SE micrographs taken at 25 and 5 keV, respectively (c) backscattered image taken at 25 keV (d) EDS spectrum taken from the Pb-rich phase of the Pb-Sn solder (e) and (f) elemental maps of the two elements taken by accepting only signals from the appropriate spectral energy regions.

TEM offers two methods of specimen observation, diffraction mode and image mode. In diffraction mode, an electron diffraction pattern is obtained on the fluorescent screen, originating from the sample area illuminated by the electron beam. The diffraction pattern is entirely equivalent to an X-ray diffraction pattern a single crystal will produce a spot pattern on the screen, a polycrystal will produce a powder or ring pattern (assuming the illuminated area includes a sufficient quantity of crystallites), and a glassy or amorphous material will produce a series of diffuse halos. 

The former procedure is the method of choice during operation in the image mode, while the latter condition is desirable for maximizing source coherency in the diffraction mode. 

In image mode, the post-specimen lenses are set to examine the information in the transmitted signal at the image plane of the objective lens. Here, the scattered electron waves finally recombine, forming an image with recognizable details related to the sample microstructure (or atomic structure). 

There are three primary image modes that are used in conventional TEM work, bright-field microscopy, dark-field microscopy, and high-resolution electron microscopy. In practice, the three image modes differ in the way in which an objective diaphragm is used as a filter in the back focal plane. 

The annular dark-field detector of the field-emission STEM (see Figure 2) provides a powerful high-resolution imaging mode that is not available in the conventional TEM or TEM/STEM. In this mode, images of individual atoms may be obtained, as shown in Figure 4 (see Isaacson, Ohtsuki, and Utlaut ). Some annular dark-field... 

Static SIMS is labeled a trace analytical technique because of the very small volume of material (top monolayer) on which the analysis is performed. Static SIMS can also be used to perform chemical mapping by measuring characteristic molecules and fiagment ions in imaging mode. Unlike dynamic SIMS, static SIMS is not used to depth profile or to measure elemental impurities at trace levels. 

The imaging mode is used to determine the lateral distribution (xand ) of specific preselected elements. In certain circumstances, an imaging depth profile is acquired, combining the use of both depth profiling and imagii. ... 

SSIMS has been used in the TOP SSIMS imaging mode to study very thin layers of organic materials [3.32-3.36], polymeric insulating materials [3.37], and carbon fiber and composite fracture surfaces [3.38]. In these studies a spatial resolution of ca. 80 nm in mass-resolved images was achieved. 

For measurement of local ion intensities in the direct imaging mode (see Fig. 3.19), amplification ensuring laterally uniform-single ion detection is necessary. Depending on the sensitivity of the detector a single or double channel plate is used. Two imaging devices are in use ... 

Fig. 3.24. Di rect-imaging mode SIMS image of a passivation layer on a niobium alloy [3.54], Boron enrichment at the interface is not visible with EPMA. Measurement time 10 s image diameter 150 pm primary ions OJ primary energy 5.5 keV.

The advantage of the imaging mode is fast data acquisition. Because all pixels are projected and detected simultaneously the measurement time for one distribution is extremely low. 

As in the case of STEM, the main benefit arising from the use of the scanning mode is that the incident electron probe can be stopped or controlled in its motion and a variety of detector types and configurations can be used to obtain particular signals, giving information beyond that obtained in the normal Imaging modes. 

The dynamic imaging mode can be further classified into two subcategories intermittent contact mode (also known as tapping mode) and noncontact mode. In both techniques, the AFM tip is attached to the end of an oscillating cantilever. For the intermittent contact technique, the cantilever is vibrated near its resonance frequency. The amplitude of the oscillation is typically 100-200 nm with the tip intermittently contacting... 

Raman spectroscopy allows chemical identification of single phases and in the imaging mode a description of the morphology. Raman bands characteristic of the two main components PA and PTFE are easily distinguishable, as shown in Figure 6, where pure materials have been used from which to record reference spectra. To identify PTFE in the spectra of the bearing the symmetric C-F... 

ToF-SIMS is one of the most sensitive and interesting methods for surface analysis, but intricate and expensive. It can be operated in imaging mode, with resolutions below 1 pm (though usually not with polymers). 

The corrections and calibration of filterFRET differ significantly for CCD microscopes and confocal microscopes. This is because in confocal experiments, channel sensitivities are adjusted at will by the experimenter, and because relative excitation intensities show intended-as well as unintended variations (adjustments and drift, respectively). Confocal filterFRET therefore requires frequent, if not in-line, recalibration however, if properly streamlined this should not take more than 15 min a day. It also slightly complicates the mathematical framework, as compared to CCD imaging filterFRET. We aimed to arrive at a comprehensive theory that is equally applicable to both imaging modes. We also proposed mathematical jargon that is a compromise between the widely differing terminologies used in the various publications on this topic. 

Thus, AFM does not provide subsurface structure in contrast to TEM. AFM can employ a contact-imaging mode, i.e., the tip s end comes in close contact with the sample s surface. The tip may touch the sample. 

Figure 1 Diagrams showing the essential electron-optical configurations used for various imaging modes in CTEM and STEM as seen by two points A and B on the sample, (a) CTEM axial bright field, (b) CTEM tilted dark field, (c) CTEM hollow cone dark field, and (d) STEM with bright field and annular dark field detectors.

It should be noted that the various CTEM imaging modes are acquired simultaneously in the STEM. Furthermore, because samples are examined on a point-by-point basis, microanalytical information is potentially available with higher spatial resolution than is normally permissible in the CTEM. Thus the great attraction of the STEM over the CTEM is that it increases the information available, particularly from heterogeneous specimens. 

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