Depth-profile

A sample collected from a pumping well provides average water properties and the detailed profile provides the fine structure, which is most important to the understanding of the dynamics of groundwater movement, as discussed in section 4.8. 

Depth profiles in observation wells, or nonpumped wells, are conducted by lowering sensors into the well. The depth is usually read from markings on the electrical cable. The lowering of sensors into the well agitates the water and mixes the water column in the well. For this reason, 

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Samples can be collected from a depth profile by carefully lowering a cylindrical sampling bottle (commercially available). It should be gradually lowered to deeper sections so that each bottle collects undisturbed water. The depths of perforated sections, and other details of the well construction, must be known for proper interpretation of the data obtained in each profile. 

Planning of a hydrochemical study has to take into account the need to measure depth profiles and to select the proper time to do them. 

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The reason for these results is that the intensity of the leakage field and the RMS error used depend strongly on the parameter c and the crack width, and to a lesser extent on the depth profile of the crack. Also, the distribution of the density of the leakage field is measured over the centre of the crack and correspondingly changes more by varying of dj and dj rather than of d, dj, dj and d . 

Table 2. Relative errors made in the computation of the depth profile, the width, and the parameter c for the cracks from Fig.4a, Fig.4b, and Fig.4c and orientation angles C>=0°, =30 and 0=45°.

Both the Monte Carlo and the molecular dynamics methods (see Section III-2B) have been used to obtain theoretical density-versus-depth profiles for a hypothetical liquid-vapor interface. Rice and co-workers (see Refs. 72 and 121) have found that density along the normal to the surface tends to be a... 

AES Auger electron spectroscopy After the ejection of an electron by absorption of a photon, an atom stays behind as an unstable Ion, which relaxes by filling the hole with an electron from a higher shell. The energy released by this transition Is taken up by another electron, the Auger electron, which leaves the sample with an element-specific kinetic energy. Surface composition, depth profiles... 

SIMS Secondary Ion mass spectroscopy A beam of low-energy Ions Impinges on a surface, penetrates the sample and loses energy In a series of Inelastic collisions with the target atoms leading to emission of secondary Ions. Surface composition, reaction mechanism, depth profiles... 

Secondary ion mass spectrometry (SIMS) is by far the most sensitive surface teclmique, but also the most difficult one to quantify. SIMS is very popular in materials research for making concentration depth profiles and chemical maps of the surface. For a more extensive treatment of SIMS the reader is referred to [3] and [14. 15 and 16]. The principle of SIMS is conceptually simple When a surface is exposed to a beam of ions... 

SIMS is, strictly speaking, a destructive teclmique, but not necessarily a damaging one. In the dynamic mode, used for making concentration depth profiles, several tens of monolayers are removed per minute. In static SIMS, however, the rate of removal corresponds to one monolayer per several hours, implying that the surface structure does not change during the measurement (between seconds and minutes). In this case one can be sure that the molecular ion fragments are truly indicative of the chemical structure on the surface. 

As in Auger spectroscopy, SIMS can be used to make concentration depth profiles and, by rastering the ion beam over the surface, to make chemical maps of certain elements. More recently, SIMS has become very popular in the characterization of polymer surfaces [14,15 and 16]. 

Ellipsometry measurements can provide infomiation about the thickness, microroughness and dielectric ftinction of thin films. It can also provide infomiation on the depth profile of multilayer stmctiires non-destmctively, including the thickness, the composition and the degree of crystallinity of each layer [39]. The measurement of the various components of a complex multilayered film is illustrated m figure Bl.26.17 [40]. 

A laser pulse strikes the surface of a specimen (a), removing material from the first layer, A. The mass spectrometer records the formation of A+ ions (b). As the laser pulses ablate more material, eventually layer B is reached, at which stage A ions begin to decrease in abundance and ions appear instead. The process is repeated when the B/C boundary is reached so that B+ ions disappear from the spectrum and C+ ions appear instead. This method is useful for depth profiling through a specimen, very little of which is needed. In (c), less power is used and the laser beam is directed at different spots across a specimen. Where there is no surface contamination, only B ions appear, but, where there is surface impurity, ions A from the impurity also appear in the spectrum (d). 

Some solid materials are very intractable to analysis by standard methods and cannot be easily vaporized or dissolved in common solvents. Glass, bone, dried paint, and archaeological samples are common examples. These materials would now be examined by laser ablation, a technique that produces an aerosol of particulate matter. The laser can be used in its defocused mode for surface profiling or in its focused mode for depth profiling. Interestingly, lasers can be used to vaporize even thermally labile materials through use of the matrix-assisted laser desorption ionization (MALDI) method variant. 

The laser can be used as a finely focused beam that, with each pulse, drills deeper and deeper into the specimen to give a depth profile. Alternatively, the beam can be defocused and moved over an area at lower power to explore only surface features of a specimen. 

Wilson, R.G., Stevie, F.A., and Magee, C.W., Secondary Ion Mass Spectrometry A Practical Handbook for Depth Profiling and Bulk Impurity Analysis, Wiley, Chichester, U.K., 1989. 

Fig. 18. Ideal and real sputter-depth profiles for thin film of A and substrate B.

Finally, it is difficult to caUbrate the depth scale in a depth profile. This situation is made more compHcated by different sputtering rates of materials. Despite these shortcomings, depth profiling by simultaneous ion sputtering/aes is commonly employed, because it is one of the few techniques that can provide information about buried interfaces, albeit in a destmctive manner. 

Ion Implantation Systems. An ion implantation system is used to accelerate ionized atomic or molecular species toward a target sample. The ionized species penetrates the surface of the sample with the resulting depth profile dependent on the implanted species mass, energy, and the sample target s tilt and rotation. An implanter s main components include an ionizer, mass separator, acceleration region, scanning system, and sample holder (168). 

For a given fixed flow rate Q = Vbh, and channel width profile b(x), Eq. (6-56) may be integrated to determine the liquid depth profile h(x). The dimensionless Fronde number is Fr = VVg/j. When Fr = 1, the flow is critical, when Fr < 1, the flow is subcritical, and when Fr > 1, the flow is supercritical. Surface disturbances move at a wave velocity c = V they cannot propagate upstream in supercritical flows. The specific energy Ejp is nearly constant. 

A depth profile is a record of the variation of a property (such as composition) as a function of depth. Some of the techniques in this volume have essentially no intrinsic depth profiling capabilities the signal is representative of the material integrated over a fixed probing depth. Most, however, can vary the depth probed by varying the condition of analysis, or by removing the surface, layer by layer, while collecting data. 

Destructive Chemical bonding Depth profiling Quantification Accuracy Detection limits Sampling depth Lateral resolution Imaging/mapping... 

Detection limits Depth probed Depth profiling... 

No, except to electron beam-sensitive materials and during depth profiling... 

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