Electron spectrometers

The teclmologies of die various electron spectroscopies are similar in many ways. The teclmiques for measuring electron energies and the devices used to detect electrons are the same. All electron spectrometers... 

The two essential elements of an electron spectrometer are the electrodes that accelerate electrons and focus them into a beam and the dispersive elements that sort electrons according to their energies. These serve the fimctions of lenses and prisms in an optical spectrometer. The same parameters are used to describe these elements in an electron spectrometer as in an optical spectrometer the teclmology is referred to as electron optics. 

Handschuh H, Gantefor G and Eberhardt W 1995 Vibrational spectroscopy of clusters using a magnetic bottle electron spectrometer Rev. Sci. Instnim. 66 3838... 

Neff H, Foditsch W and Kdtz R 1984 An electrochemical preparation chamber for the Kratos ES 300 electron spectrometer J. Electron. Spectrosc. Relat. Phenom. 33 171-4... 

Edx is based on the emission of x-rays with energies characteristic of the atom from which they originate in Heu of secondary electron emission. Thus, this technique can be used to provide elemental information about the sample. In the sem, this process is stimulated by the incident primary beam of electrons. As will be discussed below, this process is also the basis of essentially the same technique but performed in an electron spectrometer. When carried out this way, the technique is known as electron microprobe analysis (ema). 

Xps ndAes Instrumentation. The instmmentation required to perform xps and aes analyses is generally sophisticated and expensive (19). The need for UHV conditions in order to retain surface cleanliness for a tractable period of time was mentioned above. Beyond this requirement (and the hardware that accompanies it), the most important components of an electron spectrometer system are the source, the electron energy analyzer, and the electron detector. These will be discussed in turn below. 

SAM) and TEM. An Auger electron spectrometer with high spatial resolution imaging capability was developed especially for the detection of small particles and defects which might be present in the ULSI regime this enabled the inspection of wafers up to 200 mm in diameter [2.150]. 

FIGURE 7 Scientific research today often requires sophisticated equipment and computers. This chemist is using an Auger electron spectrometer to probe the surface of a crystal. The data collected will allow the chemist to determine which elements are present in the surface. 

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 irradiating X-ray beam cannot be focussed upon and scanned across the specimen surface as is possible with an electron beam. Practical methods of small-spot XPS imaging rely on restriction of the source size or the analysed area. By using a focussing crystal monochromator for the X-rays, beam sizes of less than 10 pm may be achieved. This must in turn correspond with the acceptance area and alignment on the sample of the electron spectrometer, which involves the use of an electron lens of low aberration. The practically achievable spatial resolution is rarely better than 100 pm. A spatial resolution value of 200 pm might be regarded as typical, and it must also be remembered that areas of up to several millimetres in diameter can readily be analysed. 

The total contribution to the Auger electron signal is then dependent upon the attenuation length (kM) in the matrix before being inelastically scattered, and upon the transmission efficiency of the electron spectrometer as well as the efficiency of the electron detector. Calculated intensities of Auger peaks rarely give an accuracy better than 50%, and it is more reliable to adopt an approach which utilises standards, preferably obtained in the same instrument. 

After several decades of systematic electron spectroscopy in ion-atom collisions by many groups (for recent reviews see Refs. 13 and 51), there are only two data sets of doubly differential experimental cross sections cfa/dE dfl for the emission of electrons with < 1 eV. It has been only recently that, with entirely new and extremely efficient electron spectrometers combined with recoil-ion momentum spectroscopy [52], doubly differential cross sections for ultralow -and low-energy electrons (1.5 meV < < 100 eV) have been obtained by... 

J.M. Thomas The energy resolution attainable with the electron spectrometers that have been available up to the present is inadequate to detect the fine structure that may be expected from phonon or local modes. With continued improvements, one may reasonably expect some progress in this direction but, at present, more information is retrievable from the fine structure, discussed in the text, that arises from causes other than vibrational modes. 

Fig. 9.1. Spectrum of the energetic electrons in the collimated beam as obtained in the experiment described in [16]. Black dots represent the experimental data. Also shown is the detection threshold of the electron spectrometer. The solid line is the spectrum of the electrons in the collimated beam as obtained from the PIC simulation...

The work of Siegbahn s group who, in the 1950s, improved the energy resolution of electron spectrometers and combined it with X-ray sources. This led to a technique called electron spectroscopy for chemical analysis (ESCA), nowadays more commonly referred to as X-ray photoelectron spectroscopy (XPS) [6]. Siegbahn received the Nobel Prize for his work in 1981. Commercial instruments have been available since the early seventies. 

Dedicated SEM instruments have resolutions of about 5 nm. Simple versions of SEM with micron resolution are often available on Auger electron spectrometers, for the purpose of sample positioning. The main difference between SEM and TEM is that SEM sees contrast due to the topology and composition of a surface, whereas the electron beam in TEM projects all information on the mass it encounters in a two-dimensional image, which, however, is of subnanometer resolution. 

Fowler-Nordheim tunneling of, 22 258 in HBTs, 22 167-168 Moore s law and device scaling and, 22 254 in RTDs, 22 170-171 in semiconducting silicon, 22 485-486 in semiconductors, 22 233, 237-239 in SETs, 22 171-172 in single layer OLEDs, 22 215-216 in spinel ferrites, 11 60-61 in the superconducting state, 23 804 Electron spectrometer system, components of, 24 100-101... 

Fig. 3. Schematic drawing of the high pressure electron spectrometer. A, Argon ion gun D, differentially pumped region EL, electron lens G, gas cell HSEA, hemispherical electron analyzer LO, two-grid LEED optics LV, leak valve M, long travel rotatable manipulator P, pirani gauge S, sample TSP titanium sublimation pump W, window X, twin anode x-ray source.

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