Photonically excited electron emission from modified graphitic nanopetal arrays

Abstract

Efficient electron emission for energy conversion requires a low work function and a stable emitter material. The work function of graphene-based carbon materials can decrease significantly by intercalation with alkali metals, thus increasing their emission current. In this work, electron emission from potassium-intercalated carbon nanosheet extensions grown on electrode graphite is investigated. These petal-like structures, composed of 5-25 layers of graphene, are synthesized using microwave plasma chemical vapor deposition. Samples are intercalated with potassium, and a hemispherical energy analyzer is used to measure the emission intensity caused by both thermal and photonic excitation. The emission from the potassium-intercalated structures is found to consistently decrease the work function by 2.4 to 2.8 eV relative to non-intercalated samples. High emission intensity induced by photonic excitation from a solar simulator, with a narrow electron energy distribution relative to established theory, suggests that electron scattering decreases emitted electron energy as compared to surface photoemission. A modified photoemission theory is applied to account for electron scattering, and the sample work function and mean number of scattering events are used as parameters to fit theory to experimental data. The thermal stability of the intercalated nanopetals is investigated, and after an initial heating and cooling cycle, the samples are stable at low temperatures. V

Reduced work function of graphene by metal adatoms

“…Li-doped graphene, the saturation values of are 2.05, 2.18, 3.24, 2.42 and 2.49 eV respectively. In the case of K-doping, the present results agree well with experimentally reported values (2.2 eV) [45].…”

Thermally enhanced photoinduced electron emission from nitrogen-doped diamond films on silicon substrates

“…4). The diamond-metal samples have shown relatively constant photoinduced emission intensity [21,22], which is consistent with the conventional Fowler-DuBridge model [2,28] that only involves direct photoemission. These results are consistent with the model discussed here, since PETE is not expected from a metal substrate.…”

“…Photons have been employed to generate electron emission from novel materials through various physical mechanisms [1,2]. Notably, a new emission mechanism that combines photoexcitation and thermal excitation, namely, photon-enhanced thermionic emission (PETE), has been proposed to describe results for Cs-coated p-type GaN [3].…”

“…This calls for a separate analysis. This emission mechanism can be simulated by employing an internal photoemission model [26,27], which describes the quantum yield as a function of the energy of the illuminating photons: (2) where N c and N v are the conduction band and valence band density of states (DOS) in the absorbing substrate. T (E) and S(E,hν) are the electron emission function and optical absorption function, respectively.…”

Thermionic and Photo-Excited Electron Emission for Energy-Conversion Processes

“…Field-emission devices and applications have undergone extensive research and advancements over the last century. Readers interested in learning more about field-emission studies are encouraged to explore citations provided within this document, including but not limited to work on the fundamental theory of field emission by Fowler and Nordheim (Fowler and Nordheim, 1928;Fowler, 1931), reviews by Good et al (Good and Muller, 1956;Murphy and Good, 1956), and recent work by Jensen et al (Jensen, 2007a,b). The paper includes derivation of a general formulation for thermionic and photo-emission theory in both three-and two-dimensional emitters.…”