Dual beam mode

In recent years TOF SIMS has also proved to he a very powerful tool for ultra-shallow depth profiling, having the advantage of simultaneously detecting all elements of interest. The dual beam mode [3.41], in particular, (see Sect. 3.2.2.1) enables optimized depth resolution, because sputtering conditions can be independently optimized. 

Absorption spectra of 2-nitroanisole in supercritical C02, N20, Freon-13, ammonia and C02-methanol mixtures were obtained on a Cary model 1605 spectrophotometer operated in the dual beam mode. The gases used as supercritical solvents were of the highest purity available from the supplier (Matheson) and were further filtered prior to use. The mixed solvent system of C02-methanol was obtained from Scott Speciality Gases (15.4 wt% methanol), and other mixtures were made in the laboratory. Spectra of 2-nitroanisole in n-pentane, methanol, tetrahydrofuran and acetonitrile (Burdick A Jackson) were obtained using quartz cells with a 1-cm light path and with a pure solvent blank in the reference beam. Vapor phase and supercritical fluid spectra were obtained using an air reference. 

The detector is a miniature, recording, dual-beam UV flow photometer operating continuously at two different wavelengths, 254 and 280 nm (Tl, T2). The dual-beam mode of operation provides a means of referencing the changing properties of the eluent stream by differentially comparing the eluent stream to the eluate stream. 

The probe molecule used for the studies on the solvatochromic behavior of supercritical fluids was 2-nitroanisole, which has an S value of -2.428 0.195 (15) and a reference absorbance maximum of 32,560 cm-1 in cyclohexane ( )o) Absorption spectra of 2-nitroanisole in the supercritical fluids were obtained with a Varian Model 2200 spectrophotometer operated in the dual beam mode with an air reference. The gases used as supercritical solvents were SFC grade C02 high purity grade N2O and NH3, and research grade for the other gases. 

Space filtering is a method of determining particle velocity with the spatial light distribution of a gratelike structure including interference fringes. Dual beam mode LDV is one type of space filter the others include a reticle type filter and a filter with gratinglike detectors. 

Abstract. A new infrared imaging polarimeter operating in dual-beam mode is described, together with some of the early results. 

TOF-SIMS was pioneered by Professor Benninghoven and his group in the early 1980s [109], originally developed in static mode and applied for the chemical analysis (elemental as well as molecular) of the uppermost monolayer of solid surfaces [110]. By the introduction and further development of the dual beam technique, the TOF-SIMS can... 

Various types of neutron scattering can be utilized to extract data on structure and dynamics for novel catalytic materials. By selectively deuterating an SSZ-13 zeolite, Cheetham and others" used ND performed on the Dual Beam Neutron Spectrometer (DUALSPEC) diffractometer at the Chalk River Laboratories and found that two acid sites are present in the unit cell of the zeohte. INS can be used to probe the mechanism of the catalytic reaction by looking at the change in the vibrational modes of the adsorbed molecules on the surface. Lennon et alP found that the interaction of HCl with a ]-alumina catalyst results in the dissociative adsorption of HCl, in which the hydroxyl groups terminally bound to A1 are replaced by chlorine. INS spectra reveal an in-plane deformation mode, 5 (OH), that can be resolved into two bands located at 990 and 1050 cm. ... 

Dual mode PDA combines a planar PDA with a standard PDA so that two-phase differences are measured per scattering event. These are validated against each other to see if the signal is acceptable or not. This permits the rejection of distorted events caused by multiple scattering due to poor surface quality [168]. Dual beam frequency biased LDV permits simultneous measurement of particle size and electric charge in a two-component developer [169]. 

The thermogravimetric analyser is a SDT-DTA from TA Instruments, supported by an HP PC and software for control and data handling. The system consists of a dual beam horizontal balance. Each arm holds one cup and there is one thermocouple under and in contact with each cup. One cup contains the char sample and the other cup is empty, used as a reference for temperature effects. Detailed description of the instrument can be found somewhere else. Ceramic cups were used for most of the experiments. The apparatus has been recently upgraded and it was possible to operate in a TGA-DSC mode. Therefore, not only the temperature and the weight have been registered but also the heat demand of the process. Table 2 and Table 3 show the experimental matrix for this work. 

Figure 10.2 Use of background correction to improve baseline stability in the analysis of a mixture containing metroprolol and some potential contaminants. A was measured using the single wavelength mode, X = 280 nm and B by the single-beam, dual-wavelength mode, Xi = 280 nm, X2 = 300 nm. [Reproduced with permission of the Elsevier Scientific Publishing Co. from Cheng and Poole (1983).]...

F. 2.4 Schematic diagram of a dual beam spectrophotometer operating in transmittance mode... 

Fig. 13.2 The Laser Dopier Anemometry (LDA) method. Practical LDV systems for dual-beam, reference-beam, and dual-scatter modes [73]. The figure is reproduced from Goldstein [74] (p. 181) with permission from Hemisphere Publishing Corporation...

Optical measurements of the films on silica substrates were performed using a Cary model 17 dual-beam ratio recording spectrophotometer in the range 200-1600 nm. Measurements were made in the transmission mode. The optical bandgap was deduced from the transmittance near the absorption edge. The thickness of each film was obtained from the fringes in the spectra. 

EM continues to provide valuable information about the morphology of beam-sensitive polymer and organic molecular materials. A wide variety of complimentary methods are now available, including SEM, TEM, HREM, STEM, FIB, STEM-in-SEM, Cryo-TEM, and LVEM. Active areas of research include the use of aberration-corrected instruments, dynamic imaging modes, and dual beam methods. As these methods continue to improve, it will be possible to have a more complete imderstanding of the relationship between the microstracture of these interesting materials and their maao-scopic properties. 

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