Auger apparatus

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. 

The apparatuses used for the studies of both ammonia synthesis emd hydrodesulfurization were almost identical, consisting of a UHV chamber pumped by both ion and oil diffusion pumps to base pressures of 1 x10 " Torr. Each chamber was equipped with Low Energy Electron Diffraction optics used to determine the orientation of the surfaces and to ascertain that the surfaces were indeed well-ordered. The LEED optics doubled as retarding field analyzers used for Auger Electron Spectroscopy. In addition, each chamber was equipped with a UTI 100C quadrupole mass spectrometer used for analysis of background gases and for Thermal Desorption Spectroscopy studies. 

Over the past 10 years a multitude of new techniques has been developed to permit characterization of catalyst surfaces on the atomic scale. Low-energy electron diffraction (LEED) can determine the atomic surface structure of the topmost layer of the clean catalyst or of the adsorbed intermediate (7). Auger electron spectroscopy (2) (AES) and other electron spectroscopy techniques (X-ray photoelectron, ultraviolet photoelectron, electron loss spectroscopies, etc.) can be used to determine the chemical composition of the surface with the sensitivity of 1% of a monolayer (approximately 1013 atoms/cm2). In addition to qualitative and quantitative chemical analysis of the surface layer, electron spectroscopy can also be utilized to determine the valency of surface atoms and the nature of the surface chemical bond. These are static techniques, but by using a suitable apparatus, which will be described later, one can monitor the atomic structure and composition during catalytic reactions at low pressures (< 10-4 Torr). As a result, we can determine reaction rates and product distributions in catalytic surface reactions as a function of surface structure and surface chemical composition. These relations permit the exploration of the mechanistic details of catalysis on the molecular level to optimize catalyst preparation and to build new catalyst systems by employing the knowledge gained. 

In Part A the aims and the potential of electron spectrometry of free atoms have been discussed for the example of photoionization and subsequent Auger decay in neon. Now the apparatus details and the basic features of the technique of electron spectrometry will be considered. The discussion is restricted to electrostatic deflection analysers. However, the properties discussed can easily be adapted and transferred to other kinds of electron energy analysers. 

Characterization of the bearing surface film, and film formed in a lubricated cam/tappet friction apparatus have been analyzed by reflectance-absorption infrared, X-ray photoelectron (XPS) and Auger electron (AES) spectroscopies (Lindsay et al., 1993). The two lubricants used were similar to fully formulated engine oils. 

Auger electron spectroscopy (AES) is particularly suited for surface analysis (depth 0.5-1 nm). AES depth profile analysis was employed to determine the thickness and composition of surface reaction layers formed under test conditions in the Reichert wear apparatus in the presence of four different ZDDPs additives at different applied loads (Schumacher et al., 1980). Using elemental sensitivity factors the concentration of the four elements (S, P, O, C) was determined at three locations corresponding to a depth of 1.8, 4.3, and 17 nm. No significant correlation between wear behavior and carbon or oxygen content of the reaction layer was observed. A steady state sulfur concentration is reached after a very short friction path. Contrary to the behavior of sulfur, phosphorus concentration in the presence of ZDDPs increases steadily with friction path, and no plateau value is reached. 

Extrusion Stiff plastic particle mix is pushed through a die orifice to form a continuous compact which may be cut to desired length. Vacuum auger, screw extruder, plunger press, piston extrusion apparatus... 

Figure 15.4 A schematic of a typical continuous stirred tank pyrolysis process. Legend 1 pyrolysis vessel with internal agitator 2 catalyst chamber 3 plastic feedstock hopper 4 char auger to remove solid residue 5 agitator drive motor 6 lower temperature sensor 7 upper temperature sensor 8 burner for furnace 9 feed auger for plastic feedstock 10 condenser cooling jacket 11 condenser 12 oil recovery tank (adapted from Saito, K. and Nanba, M., United States Patent 4,584,421 (1986) Method for thermal decomposition of plastic scraps and apparatus for disposal of plastic scraps )...

The experimental techniques and apparatus have been described in detail elsewhere. (8, 9) Titania and niobia were deposited onto the clean metal foils by vaporizing either a Ti-Ta alloy wire or a niobium wire in 10-7 Torr H2 at 800K. Auger electron spectroscopy (AES) was used to determine the oxide coverages, and temperature programmed desorption (TPD) was used to determine the effect of the oxide layers on the adsorption of CO and H2. Methanation rates were measured in a side chamber which allowed the sample to be characterized by AES before and after rates were measured. All rates were measured with 100 Torr CO and 400 Torr H2, and conversion to methane was always kept less than 1%. 

Fig. 3. Ultrahigh vacuum apparatus for studying single-crystal catalysts before and after operation at high pressure in catalytic reactor. Position 1 crystal is in position for Auger electron spectroscopy study of surface composition or of ultraviolet photoemission spectrum of surface species. Position 2 crystal is in position for deposition of a known coverage of poisons or promoters for a study of their influence on the rate of a catalytic reaction. Position 3 crystal is in position for a study of catalytic reaction rate at elevated pressures (s2 atm). Gas at high pressure may be circulated by using a pump mass spectrometric-gas chromatographic analysis of the reactants and products is carried out by sampling the catalytic chamber. From Ref. 5.

The apparatus as shown in Figure 6 has been described in detail elsewhere (6,7). It consists of a diflEusion-pumped, ultrahigh vacuum bell jar (1 X 10" Torr) equipped with a retarding-grid. Auger electron spectroscopy (AES) system, a quadrupole gas anafyzer, and a 2-keV ion sputter gun. The unique feature of the apparatus is an internal sample isolation cell which operates as a microbatch reactor (100 cm internal... 

The composition of the films was determined by Auger electron spectrometry (AES) using PHI-660 Perkin Elmer apparatus. The film structure was analyzed with atomic force (AFM) and scanning electron microscopy (SEM). 

The apparatus required for AES studies comprises a radiation or particle beam source and an electron energy analyzer. For X-ray excited Auger spectra the same sources as in XPS may be used, whereas excitation by electrons is performed by means of electron guns designed for kinetic energies typically between 100 eV and 5 keV. Ion excitation is rarely used in surface studies because of the extensive radiation damage caused by heavy particles. 

---