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SURFACE ANALYSIS FACILITY

ESCA and Auger spectrometers are available for the quantitative or semiquantitative chemical analysis of surfaces and surface layers. Both spectrometers have a sensitivity of a small fraction of a monolayer to most elements. In the case of ESCA, the presence of a chemical shift is often used to determine the valence state of surface species.

Capability: Ambient pressure is 10-10 torr. Sample size about 1 cm2. Depth sensitivity is of the order of 10 Å. Depth profile measurement using Ar ion sputtering is possible.

Application: Wherever chemical analysis of surface layers is desirable. In most cases, special sample handling procedures are of importance to reduce contamination effects.

Availability: These instruments are research tools being used extensively in ongoing research programs. They are generally not available for analyses of samples. However, in certain situations, where our staff might become involved in a research problem, the instrument could be made available. Special training is necessary for operation of either instrument.

Contact: Dr. John T. Yates, Jr., Acting Chief, Surface Process and Catalysis Section, Chemistry Building, Room B250, Phone 301-921-2188.

Literature:

[1] S. H. and D. M. Hercules, Surface Characterization by Electron Spectroscopy for Chemical Analysis (ESCA), p. 307 in book Characterization of Solid Surfaces, Kane & Larrabee, Plenum Pr., New York, 1974.

[2] C. C. Chang, Chemical Analysis by Auger Electron Spectroscopy, ibid, p. 509.

[3] E. N. Sickafus, J. Vac. Sci. & Tech. 11, 299 (1974).

Capability: The system is capable of measuring active surface areas as low as 100 cm2/g. The reproducibility of the system using krypton is 3 percent for materials with surface areas of 200 cm2/g or greater, having a total sample area of 500 cm2 or greater. Using nitrogen, the reproducibility is 3 percent for a total sample area of 5 m2 or greater. Special sample holders are available, capable of accepting planar materials having dimensions 1.5 x 1.5 x .05 cm. Applications: The surface area and/or pore size distribution of materials such as catalysts, gasket material, paper, plastics, foams, etc., may be determined. The special sample holders for planar materials enable determination of surface properties and physical tests on the same specimen.

Availability: To an qualified research worker after an initial training period with Dr. E. L. Graminski. A. good knowledge of vacuum systems is necessary to operate the apparatus.

Contact: Dr. E. L. Graminski, Polymer Stability and Reactivity Section, Polymer Building, Room A369, Phone 301-921-2923.

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SURFACE AREA

ANALYZER

The Surface Area Analyzer provides a complete system for preconditioning and measuring both low and high values of surface area by the classic BrunauerEmmett-Teller technique, employing krypton and nitrogen as the absorbates in a metal system. In addition, pore size distribution can be obtained from complete adsorption or desorption isotherms. Calculations can be made manually or with available computer programs.

Scanning electron photomicrograph shows broken fibers and other characteristics of a paper specimen which affect the surface area of the specimen. A typical specimen measured by the SURFACE AREA ANALYZER.

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X-RAY FACILITIES

ROTATING

X-RAY ANODE DIFFRACTION UNIT

Stationary anode X-ray tubes have been used for most conventional X-ray diffraction generators. However, since a large amount of heat energy is generated by the electron beam bombardment on the anode, the X-ray intensity is limited. The rotating anode tube can give higher intensity X-rays because the water-cooled anode is rotated at a high speed to distribute the heat energy over the circumferential surface of the anode.

Capability: The maximum operating conditions for this unit are 60 kV and 100 mA. This produces X-rays whose brilliance is 10 to 20 times greater than that of the normal sealed X-ray tubes. This makes it possible to reduce the exposure time dramatically in the photographic method, to scan rapidly with a counter, or to study dynamic changes or transformations in the crystal structure.

Applications: Measurement of the long period in chain-folded polymer crystals. Crystallographic studies of paraffins; observations of phase changes in polymer and paraffin crystals; X-ray diffraction patterns from wet collagen; detection of small amounts of crystalline impurities.

Availability: The use of this instrument by NBS research workers on problems of mutual interest can be arranged. It must be operated only under the direct supervision of the scientist in charge of the instrument.

Contact: Dr. Darreli H. Reneker, Chief of Structural Analysis and Standards Section, Polymer Building, Room A209, Phone 301-921-3344.

SOFT X-RAY SPECTROMETER. A comparison of the soft x-ray M. spectrum (SXS) of Cu with ultraviolet (UPS) and x-ray (XPS) photoemission and ion neutralization (INS) spectra.

SOFT X-RAY SPECTROMETER

This spectrometer is a 2-meter, grazing incidence instrument with a ruled glass grating, 30,000 lines per inch. It is equipped with an electron multiplier detector and magnetic tape output for digital computer processing. Programs are available for data reduction and plotting of spectra. A spectral range of approximately 2.5 to 80 nm can be covered but as presently set, the grating cut-off is at about 4 nm. Capability: Optimum specimen shape is a rod about 1/4" dia. x 3" long but variations from this can be used. Electron excitation of 2500 volts is used which causes some heating of the specimen. The temperature can be controlled within limits and can be continuously monitored with a thermocouple on the specimen. The maximum effective skin depth of material being analyzed is of the order of 4 to 100 nm, depending on atomic number.

Applications: Chemical analysis for the light elements down to lithium in atomic number (except oxygen and nitrogen with the spectrometer as presently set); this application would be particularly useful when associated with surface and shallow skin depth phenomena, such as the identification of boride, carbide, and sulfide precipitates on a fracture surface, for example. Application to other types of metallurgical phenomena such as detection of dezincification in brass and the reduction of iron oxide in the aluminizing of steel sheet; in the case of the higher atomic number elements, transitions between outer electron levels, and transitions from the valence band to outer levels are observed. Valence band spectra as a function of the state of chemical combination; the bulk of the work that has been done on this instrument has been the study of valence band structure to obtain a better understanding of the principles of intermetallic compound formation and the electronic basis for their physical properties.

Availability: To any qualified NBS research worker. Also, in appropriate situations the facility can be made available to researchers from other government, education and industrial organizations. Literature:

[1] A Soft X-Ray Spectrometer with Improved Drive, J. R. Cuthill, Rev. Sci. Inst. 41, 422 (1970).

[2] Improved Drive for Soft X-Ray Spectrometer, NBS Tech. News Bull., October 1970, Vol. 54, No. 10, Page 231.

Contact: Dr. John R. Cuthill, Assistant Chief, Alloy Physics Section, Materials Building, Room B-148, Phone 301-921-2913.

materials scientists concerned with bonding, electronic configurations, lattice and atomic vibrations, coordination, valence states, and other properties.

Availability: On a selective basis when not required for Crystallography Section programs. The instrument must be operated by Section personnel and only work of mutual interest can be undertaken. Literature:

[1] Inorganic Chemistry, 9, 2228 (1970).

[2] Crystal Structure Communications, 1, 247 (1972).

Contact: Dr. Alan D. Mighell, Room B222, Materials Building, Phone 301-921-2950.

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THREE-CIRCLE

X-RAY DIFFRACTOMETER

Operating completely under computer control, the instrument orients a single crystal in the x-ray beam and records the diffracted intensity for each of several thousand reflections.

Capability: Data are collected at rates up to 1000 reflections per day. Accuracy is indicated by the final R value obtained after least squares refinement. Typical values are in the range 3 to 5%.

Applications: Structural parameters, including bond lengths, angles between bonds, and amplitudes of thermal vibrations are obtained. Precise three-dimensional diagrams can be drawn to scale. Diagrams of this type are used by physicists, chemists and other

THREE CIRCLE X-RAY DIFFRACTOMETER. Diagram of the cobalt imidizole complex cation in the compound Co (Im.) (NO). The ellipsoids represent the root-mean-square amplitude of thermal oscillations of atoms.

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