Secondary dynamic mode

Ions are also used to initiate secondary ion mass spectrometry (SIMS) [ ], as described in section BI.25.3. In SIMS, the ions sputtered from the surface are measured with a mass spectrometer. SIMS provides an accurate measure of the surface composition with extremely good sensitivity. SIMS can be collected in the static mode in which the surface is only minimally disrupted, or in the dynamic mode in which material is removed so that the composition can be detemiined as a fiinction of depth below the surface. SIMS has also been used along with a shadow and blocking cone analysis as a probe of surface structure [70]. 

In situ adsorption cells enable adsorption under gas flow (dynamic mode) or under pressure (static mode). The catalysts are generally studied afler pre-treatment, under specific gases or under secondary vacuum, at high temperature. Adsorption may be carried out between 450 C and liquid nitrogen temperature depending on the material used. 

Figure 3.31 Elastic and inelastic collisions leading to emission of secondary ions Static and dynamic modes...

Conceptually, SIMS can be considered a straightforward and direct technique. In practice, there are many complexities introduced as a result of the various methodologies that can be applied, whether in the static or in the dynamic mode of SIMS. This exists because there are numerous conditions under which SIMS can be carried out. Each condition is optimized to deal with the analysis of a different elemental or molecular species, from different solid matrices. In addition, relating the output to the compositional variations that may occur on or within the sohd being examined can be problematic. This stems, in part, from the complexities surrounding secondary ion generation, or more precisely, the matrix effect. As the term suggests, the matrix effect describes the effect of the matrix on the population of ions emitted. Matrix effects and their associated transient effects are discussed in Section 3.3.3.1.2. 

SIMS, whether used in static or dynamic mode, identifies the types of isotopes, elements, or molecules present on or within a substrate by the mass to charge ratio (m/q) of the emitted secondary ions. Identification is possible because ... 

A mass spectrum, derived by scanning the mass filter over some predefined m/q ratio range, constitutes all the secondary ions of the polarity of interest (only one polarity can be collected at a time). Such spectra are of interest when the sample type is unknown (this allows for the identification of the elemental and/or molecirlar constituents) and/or when information on the optimal signals for the acqirisition of images and/or depth profiles is required. This option is available and commonly used in all applications of SIMS, whether in Static or Dynamic modes. 

Although the concern is primarily for the response of the piping. system, the possibiliis of dynamic coupling with the containment structure should not be neglected. A concern is whether or not the secondary shield wall will withstand the dynamic interaction between the walls and the pump. This is answered by examining the mode shapes if there were no coupling between the walls and the pump. 

The measurement of ED intensities in a precession mode allows all ED intensities to be recorded under reduced influence from dynamical diffraction and secondary scattering contributions, therefore permitting structure analysis of improved precision. By processing a incident beam at a constant angle around a zone axis in combination with a similar precession of the ED pattern below the specimen the equivalent mechanism of the precession of the specimen is obtained. 

An interesting aspect of many structural phase transitions is the coupling of the primary order parameter to a secondary order parameter. In transitions of molecular crystals, the order parameter is coupled with reorientational or libration modes. In Jahn-Teller as well as ferroelastic transitions, an optical phonon or an electronic excitation is coupled with strain (acoustic phonon). In antiferrodistortive transitions, a zone-boundary phonon (primary order parameter) can induce spontaneous polarization (secondary order parameter). Magnetic resonance and vibrational spectroscopic methods provide valuable information on static as well as dynamic processes occurring during a transition (Owens et ai, 1979 Iqbal Owens, 1984 Rao, 1993). Complementary information is provided by diffraction methods. 

We should not forget that an appropriate detector, a Faraday cup or a secondary electron multiplier equipped with a conversion dynode, is needed for ion detection. Most commercial instruments are equipped with a secondary electron multiplier, which can be operated in a low amplification mode, the analogue mode, and with a high gain, the counting mode, where each ion is counted. With this dual mode, a linear dynamic range of up to nine orders of magnitude can be achieved, so that major and minor components of the sample can be measured in one run. 

To illustrate the potential of the hybrid method in describing the role of an intramolecular bath in the decay dynamics induced by a conical intersection, we consider the model of Ref. [7,8] for the S2-S1 Cl in pyrazine. Fig. 1 shows the wavepacket autocorrelation function C(t) = ( k(O)l (t) for an increasing number of bath modes. G-MCTDH hybrid calculations for 4 core (primary) modes plus nb bath (secondary) modes are compared with reference calculations by the standard MCTDH method. 

Recent applications of CPSA descriptors include QSAR investigations of the genotoxicity of thiophene derivatives (Mosier et al., 2003) as well as of secondary and aromatic amines (Mattioni et al., 2003) and a study to classify phenols with respect to toxic modes of action (Aptula et al., 2003). A somewhat different route has been explored with the concept of dynamic molecular surface areas (Lipkowitz et al., 1989) that represent Boltzmann-weighted means of surface areas of different conformations within a preset energy window (e.g., within an excess of 10.5 kJ/mol above the lowest energy found for the particular molecule). Following this strategy, so-called dynamic polar... 

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