High-intensity X-ray Sources Research Articles

An X-Ray Photoelectron Spectrometer Designed for Surface Research

An x-ray photoelectron spectroscopy (ESCA) apparatus designed specifically for surface research is described. The features, included in one vacuum envelope, are ultrahigh vacuum, a high intensity x-ray source, a 10 cm mean radius hemispherical electron energy analyzer, sample cleaning by argon ion bombardment, sample heating by electron bombardment, and the facility for the collection of electron spectra as a function of angle relative to the surface plane of the sample. It is shown that (1) sample cleaning increases net signal strengths by factors as great as 14; (2) less than 2% of a monolayer of cesium on a clean molybdenum substrate can be readily detected; and (3) that ultrahigh vacuum is essential for investigation of well-defined surfaces. Surface sensitivity is increased by an order of magnitude when spectra are collected at low electron take-off angles relative to the surface plane, and the importance of measuring angular dependence of spectra for interpretation of data from surfaces is demonstrated.

Study of Structural Detail by X-rays of Wavelength Greater than 4Å

AbstractSome branches of structural research could benefit from supplemental information provided by “soft” x-rays. Little use is made of these wavelengths because they are difficult to generate at high intensity, hard to collimate, need vacuum for propagation, and are heavily absorbed in the sample. None of these difficulties is insurmountable, however, and it will be shown that the information to be gained is often worth the extra effort.A few theoretical and experimental examples with silver L-radiation (λ ≈ 4.15Å) and aluminum K-radiation (λ ≈ 8.34Å) demonstrate that valuable semiquantitative information on the size and number of aperiodic scatterers in solid samples can be extracted. Other examples show the superior sensitivity of these longer wavelengths to dimensional changes in periodic lattices. Applicability of long-wavelength diffraction is restricted to values of interplanar distance d > λ/2. Valuable information about lattice imperfection can be gained from broadening of the reflection at larger glancing angles. It is shown that the heavy absorption of these wavelengths in the sample is not necessarily prohibitive.The instrumentation used in these studies was designed for routine operation by laboratory personnel without special training. It consists of a demountable high-intensity x-ray source and a multipurpose highvacuum camera. Operation of the x-ray unit resembles that of commercial x-ray diffraction instruments. Because of its greater-flexibility, photographic recording has been practiced so far but could be replaced by electronic readout.