C. E. Kuyatt

Electron Monochromator Design

A study has been made of all the known factors which limit the performance of high resolution (0.07 to 0.01 eV FWHM) monochromators. These limiting factors have been incorporated into design equations for the optimum (maximum current output) monochromator. The conclusions are tested by performance measurements on a prototype instrument. The results require the introduction into the design equation of a new limiting factor, an anomalous energy spread in dense electron beams, which is empirically determined.

The GaAs spin polarized electron source

The design, construction, operation, and performance of a spin polarized electron source utilizing photoemission from negative electron affinity (NEA) GaAs are presented in detail. A polarization of 43±2% is produced using NEA GaAs (100). The polarization can be easily modulated without affecting other characteristics of the electron beam. The electron beam intensity depends on the intensity of the exciting radiation at 1.6 eV; beam currents of 20 μA/mW are obtained. The source is electron optically bright; the emittance phase space (energy‐area‐solid angle product) is 0.043 eV mm2 sr. The light optics, electron optics, and cathode preparation including the GaAs cleaning and activation to NEA are discussed in depth. The origin of the spin polarization in the photoexcitation process is reviewed and new equations describing the depolarization of photoelectrons in the emission process are derived. Quantum yield and polarization measurements for both NEA and positive electron affinity surfaces are reported. T...

Comparison of the Spherical Deflector and the Cylindrical Mirror Analyzers

The calculated performance of electrostatic analyzers of the cylindrical and spherical deflection type are compared. It is shown that considering geometrical terms through the third order the cylindrical device is significantly superior.

Apparent Oscillator Strengths for Molecular Oxygen Derived from Electron Energy-Loss Measurements

Oscillator strengths for O2 from 6 to 14 eV are derived from the energy‐loss spectrum of 100 eV incident electrons. Integrated f values for the Schumann–Runge bands and continuum, which span four orders of magnitude in intensity, agree well with high‐resolution photoabsorption measurements. Vibrational structure superimposed on the Schumann–Runge continuum, previously assigned to the (3sσg)  3Πg Rydberg state, contributes less than 0.5% to the total oscillator strength determined for that region. These data also yield f values for discrete bands in the region between 9.5 and 14.0 eV, where line saturation problems complicate oscillator strength analysis of the optical data. An oscillator strength sum of 0.198 is obtained for all transitions below the ionization potential at 12.07 eV.

Electron energy loss spectroscopy of acetone vapor

High resolution, inelastic electron scattering data can provide new spectroscopic information on the electronic structure of polyatomic molecules. Features in the acetone energy loss spectrum from 0 to 15 eV obtained for 100 eV incident electrons correspond to vibrational, electronic discrete, and electronic continuum excitations. These data are compared with optical measurements in a wide spectral region extending from the infrared to the vacuum ultraviolet. A comprehensive interpretation of the energy loss spectra is attempted with the use of photochemical and photoelectron data, as well as quantum‐chemical calculations in the literature. Three Rydberg series with quantum defects of 1.03, 0.81, and 0.315 join onto bands previously discussed in terms of transitions to valence orbitals. These series converge to an ionization limit of 9.705 eV in good agreement with previous optical determinations. Dissociative continua underlie the Rydberg region and give rise to a variety of neutral products observed in ...

Inelastic Electron Scattering from Formaldehyde

The electron scattering spectrum of H2CO has been determined in the energy loss range between 0 and 16.0 eV. Three Rydberg series in the region 7–11 eV can be identified with the s, p, and d series reported in the literature by ultraviolet absorption studies. Oscillator strengths are determined for some of the Rydberg states and comparison is made with recent ultraviolet absorption work employing photoelectric methods of detection. A serious disagreement exists between the f values obtained by the two methods for the 3sa1 Rydberg. Another Rydberg series, probably converging to the third ionization potential of H2CO, is observed in the electron scattering spectrum in the region 12.4–14.0‐eV energy loss. Erratic behavior of the quantum defects of the first Rydberg series as well as failure to detect the π → π* transition in H2CO is discussed in the light of recent theories involving valence states which can seriously perturb members of a Rydberg series.

Resolution Determination in Field Emission Energy Analyzers

The influence of energy analyzer transmission function on measured field emission energy distributions has been evaluated by folding a Gaussian transmission function into the field emission total energy distribution. The resulting distributions at 0, 4.2, 20.3, 77, and 300 K are plotted as a function of the field‐ and work‐function‐dependent parameter d, and for the special case φ=4.40 eV, F=3.0×107 V/cm. A criterion is established for determining the width of an analyzer transmission function from distributions measured at the above temperatures. It is shown that the slope of the log of the energy distribution is changed by less than 1% when the analyzer width is changed from 0 to 100 mV.

Design of Low Voltage Electron Guns

It is shown that by use of a multistage technique in which electrons are drawn from a cathode by a high potential and decelerated to the required final energy, guns can be designed capable of forming beams in which the current is limited only by space charge in the beam itself. The design principles and procedures are given and illustrated by two examples of electron guns giving highly collimated beams and operating at energies of 30 and 500 eV. The measured currents obtained are somewhat greater than the space charge limited beam maximum because of ion neutralization.

Field Emission Deflection Energy Analyzer

A Simpson‐Kuyatt type spherical deflection energy analyzer has been adapted to a field emission source. A special decelerating lens allows the analyzer to be used over a wide range of electron energies and energy resolutions. For an electron energy of 2000 eV, a resolution of 20 meV has been demonstrated, while better resolution can be obtained for lower energies (∼10 meV at 1000 eV). Special techniques and new design features were employed to make the new analyzer compatible with ultrahigh vacuum (∼10−12 Torr).

Absorption Spectrum of SF6 in the Far Ultraviolet by Electron Impact

Measurements of forward inelastic scattering of 400‐eV electrons from SF6 were made and used to derive relative ultraviolet‐absorption cross sections. The relative values were normalized to an ultraviolet‐absorption measurement at 23.00 eV. Agreement with additional uv measurements at 21.2 and 17.6 eV was excellent. Oscillator strengths for three absorption bands between 10 and 15 eV, as derived from the electron‐scattering measurements, are in fair agreement with the corresponding values measured by uv absorption. The total oscillator strength for excitations up to 32 eV is found to be 15.3.