Simplified PFE scheme from metals: at high electric fields E = U/z, the work function Φ0 = Wvac − WF of electrons is reduced by the Schottky effect ΔΦSchottky = (e3E/4πɛ0)0.5and by photo excitation with hν to the effective barrier height Φeff. Relaxation of excited electrons can occur due to e−−e− collisions.
(a) Schematic of the PFES system. The spectrometer is installed in the center of the front flange, as indicated. (b) Schematic of a 180° hemispherical sector analyzer.
Photo of the cathode setup. The function of all visible parts is explained in the text.
Photos of the gate support structure (a) and the shell with a conical mesh gate (b).
(a) Top view on the cathode and gate in measurement position. (b) View through the quartz window onto the back of a mesh gate. The laser beam passes the spectrometer nozzle.
Calculated electrostatic field distributions between a flat cathode (U = −100 V) and a hole (left) or mesh gate (U = +1000V). The mesh is approximated by five concentric rings.
Schematic of the triode configuration with circuit diagram.
Field emission spectra of a tungsten needle measured for the largest and smallest slits and different pass energies. Please note the calculated spectral resolution values ΔW for comparison.
Temperature of the W-needle vs. emission current. Inset: spectrum at 144 ± 20 nA with Fermi-Dirac fit of the high energy tail resulting in 584 ± 31 K.
Spectrum of a W needle measured at Ugate = 2800 V (Icath = 3.45 μA) for d = 2 mm and Wpass = 10 eV (ΔW = 105 meV) with exponential fit of the low energy tail. Inset: FN-plot of the integral current (voltage up- and down-swing) with linear fit.
SEM images of a triangular Si-tip array (Ø = 200 μm) and a single tip.
Icath vs. Ugate of 91 Si-tips measured at a gap of δ z = 450 μm without and with laser illumination. Inset: corresponding FN-plot with two linear fit regions for the initial slope.
(a) Normalized FE-spectra of the array with 91 Si-tips at different currents. (b) Average resistance values of the Si tips as calculated from the spectra.
Comparison of electron spectra with and without illumination: (a) measured at Icath = 0.05 μA; (b) after correction of charging at Icath = 5 μA.
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