Physics – Condensed Matter – Mesoscale and Nanoscale Physics
Scientific paper
2011-04-07
Physics
Condensed Matter
Mesoscale and Nanoscale Physics
13 pages, 14 figures, submitted to Phys. Rev. B
Scientific paper
Electron emission from hafnium carbide (HfC) field emission tips induced by a sub-10 fs, 150 MHz repetition rate Ti:sapphire laser is studied. Two-photon emission is observed at low power with a moderate electric bias field applied to the tips. As the bias field and/or laser power is increased, the average current becomes dominated by thermally-enhanced field emission due to laser heating: both the low thermal conductivity of HfC and the laser's high repetition rate can lead to a temperature rise of several hundred Kelvin at the tip apex. The time delay between each electron detection event and the previous optical pulse is measured with 30 ps time resolution, and the timing correlation reveals that a fraction of the emission decays with a time-constant of 470 ps following each laser pulse. This is consistent with a transient, thermally-enhanced field emission due to pulsed heating of the tip followed by cooling of the apex region via conduction. The contribution of current from such a thermal transient at times shorter than the electron-phonon coupling time is considered in the context of the two-temperature model. Under the conditions of this experiment, the integrated current from the thermal transient is shown to be negligible in comparison with the two-photon emission. A finite element model of the laser heating and thermal conduction supports these conclusions and is also used to compare the nature of thermal effects in HfC, tungsten, and gold tips.
Foreman Seth M.
Gerlich Stefan
Kasevich Mark A.
Kealhofer Catherine
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