Detector configurations

FIGURE 3-22 Coimnon detector configurations (a) thin-layer (channel) and (b) wall-jet flow cells. WE = working electrode. 

FIGURE 3-26 Dual-electrode thin-layer detector configurations for operation in the series (a) and parallel (b) amperometric modes. 

The primary method for velocity cahbration is the internal reference channel with reference target and detector configured in transmission geometry (Fig. 3.16). 

With a thermionic electron source, and a foil thickness of 100 nm, the volume of specimen excited is of the order 10-5 pm3. With a FEG source in a dedicated STEM, however, with a foil of 1 nm thickness this specimen-beam interaction volume can be as small as 10 8pm3. Very small signal levels are thus to be expected in AEM, hence the importance of employing higher brightness sources and the need to modify the specimen-detector configuration to maximize the collection angle. 

Microhotplates, however, are not only used for metal-oxide-based gas sensor applications. In all cases, in which elevated temperatures are required, or thermal decoupling from the bulk substrate is necessary, microhotplate-like structures can be used with various materials and detector configurations [25]. Examples include polymer-based capacitive sensors [26], pellistors [27-29], GasFETs [30,31], sensors based on changes in thermal conductivity [32], or devices that rely on metal films [33,34]. Only microhotplates for chemoresistive metal-oxide materials will be further detailed here. The relevant design considerations will be addressed. 

Fig. 4.62. Detector configuration with conversion dynode. By courtesy of JEOL, Tokyo.

Several different detector configurations have been evaluated and are being used for low level y spectrometry. Various sizes of plastic beta... 

This latter feature must come from CD2CO, which barely recoils out of the beam and therefore misses the smaller beam block used in this detector configuration. 

Different detector configurations and working electrodes can be used in combination with polymer CE microchips. 

For both qualitative and quantitative elemental analyses using EDS detectors in an AEM it is essential that the analyst understands the limitations of a particular experimental configuration and that a consistent protocol which optimises all analyses in a given experiment is employed. There is such a variety of instrument and detector configurations currently in use that only a brief summary of important considerations for modern-day AEMs will be addressed here. In older TEMs which have been modified for quantitative thin-film analysis [23], instrument dependent parameters should be critically assessed before attempts are made to quantify X-ray spectra. 

Figure 3.25 Common detector configurations thin-layer (channel) (a) and wall-jet (b) flow cells.

Electrochemical detection offers also great promise for CZE microchips, and for other chip-based analytical microsystems (e.g., Lab-on-a-Chip) discussed in Section 6.3 (77-83). Particularly attractive for such microfluidic devices are the high sensitivity of electrochemical detection, its inherent miniaturization of both the detector and control instrumentation, low cost, low power demands, and compatibility with micromachining technologies. Various detector configurations, based on different capillary/working-electrode... 

Detector configuration arrangement of multiple detectors in series or in parallel can cause additional peak broadening, flow rate variations, back pressure variations,... 

Two detector configurations with flow cells with volumes of 5 and 16 xl were used for studies on optimizing detector sensitivity and resolution. In addition, the effect of column diameter with a 2mm and a 3.9mm ID columns were compared. The objective was to see if there is an optimal combination of column dimension and detector configuration that provides the highest sensitivity without seriously compromising the resolution of a complex map. 

Fig. 1 Hardware schematic for a typical SEC triple on-line detector configuration.

Numerous styles and brands of instruments and sample cells have been used for the analysis of tablets. The authors currently use several brands of instrumentation for tablet analysis, including filter-, diffraction grating-, and acousto-optic tunable filter-based instrumentation. Detector configurations are evolving slowly toward an optimal design however, the designs of most manufacturers are suitable for many applica-... 

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