Scanning Auger microprobe

Not only is topographical information produced in the SEM, but information concerning the composition near surface regions of the material is provided as well. There are also a number of important instruments closely related to the SEM, notably the electron microprobe (EMP) and the scanning Auger microprobe (SAM). Both of these instruments, as well as the TEM, are described in detail elsewhere in this volume. 

XPS spectra were obtained using a Perkin-Elmer Physical Electronics (PHI) 555 electron spectrometer equipped with a double pass cylindrical mirror analyzer (CMA) and 04-500 dual anode x-ray source. The x-ray source used a combination magnesium-silicon anode, with collimation by a shotgun-type collimator (1.). AES/SAM spectra and photomicrographs were obtained with a Perkin-Elmer PHI 610 Scanning Auger Microprobe, which uses a single pass CMA with coaxial lanthanum hexaboride (LaBe) electron gun. 

The utility of a SiKa x-ray source in the study of catalyst systems, and especially its utility in the observation of previously undetected metal-support interactions has been demonstrated. Scanning Auger microprobe data were also useful in understanding the quantitative changes observed by XPS. Finally, the ability to treat materials in a controlled manner, and perform the subsequent analyses without exposure to the ambient atmosphere, made the experiment possible. 

Modern spectrometers only require electron beam currents in the range 0.1 lOnA and hence probe sizes of 20-200 nm may be readily achieved with thermionic sources and 5-15 nm with a FEG. Spatially resolved compositional information on heterogeneous samples may be obtained by means of the Scanning Auger Microprobe (SAM), which provides compositional maps of a surface by forming an image from the Auger electrons emitted by a particular element. 

Two-phase particles ranging from 10 to 20 microns in size, supported on a graphite substrate, were observed in-situ in the UHV chamber of a scanning Auger microprobe. Both surface composition analysis and imaging of the particles could be undertaken. The preparation of the samples has been described in detail elsewhere. ... 

An advantage of the scanning Auger microprobe (SAM) is that it can scan a surface and provide a map of each element in question. As such, these results are similar to an electron microprobe except the SAM is much more surface sensitive. 

This work was supported by the Division of Chemical Sciences, Office of Basic Energy Sciences, United States Department of Energy under Contract No. W-7405-ENG-48. The authors would like to thank Dr. John Wang for assistance with the scanning Auger microprobe and Dr. Phillip Ross for the use of his Auger apparatus. 

Better spatial definition can be attained using transmission microscopy but the opaqueness of the electrode support negates its effectiveness. The spatial distribution of elements on the surface can be resolved with a scanning Auger microprobe. The problem of electron beam damage to the modified surface has prevented widespread usage. 

The spatial resolution of scanning Auger microprobe systems Is now equivalent to most scanning electron microscopes. High magnification secondary electron Images or absorbed current images are a routine part of the data from such systems. Quantitative Aspects of AES... 

K IxlO 7 torr of oxygen was added to the vacuum system to remove carbon contamination and keep the particle clean. Sample cleanliness was examined by rcannealing the sample in a PHI 660 Scanning Auger Microprobe (SAM). The panicle starts out with a rounded shape and no distinct structure. When the sample is annealed in vacuum, the particle is convened to a nearly spherical shape with a series of flat facets. Electron channeling patterns taken in the scanning electron microscope indicate that the larger facets are oriented in the (100) direction while the smaller facets... 

Figure 17.3.2 Detection limits, sampling depth, and spot size for several surface spectroscopic techniques. XRP (x-ray fluorescence) EMP (electron microprobe) EEL (electron energy loss), SAM (scanning Auger microprobe) STEM (scanning transmission electron microscopy). Other abbreviations in Figure 17.3.1. This figure is meant to provide a graphic summary of the relative capabilities of different methods modem instmments have somewhat better quantitative performance characteristics than the 1986 values given here. [From A. J. Bard, Integrated Chemical Systems, Wiley, New York, 1994, pp. 103, with permission adapted from Texas Instmments Materials Characterizations Capabilities, Texas Instmments, Richardson, TX, 1986, with permission.]...

Some instruments, called scanning Auger microprobes (SAM) offer two-dimensional scan control (rastering) of the electron beam, so that analysis can be carried out as a function of surface position. The spatial resolution is controlled by the beam diameter, which can be as small as 50 nm. 

These two techniques demand fine spatial resolution which is achievable with AES but not with ESCA. In both cases, the compositional depth profile is then conveniently obtained using a narrow electron beam in a line scan instrument such as a scanning Auger microprobe, SAM [95]. 

The sulfation experiments were performed in a custom tractable high-pressure reaction cell [14] mounted in situ with a Perkin Elmer 545 Scanning Auger Microprobe. The effects of reaction conditions and catalyst composition were examined is a function of sulfur dioxide (SO2) exposure. Specifically, exposure to SO2 was examined as a function of sample composition (100 at.% cerium - Oat. % cerium), reaction pressure (1 Torr - 1000 Torr), and catalyst temperature (200 K - 1003 K), as outlined in Table 1. 

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