Properties and dynamics of the image potential states on graphite investigated by multiphoton photoemission spectroscopy

Lehmann, Jörg; Merschdorf, M.; Thon, A.; Voll, Sabine; Pfeiffer, Walter

doi:10.1103/physrevb.60.17037

Cited by 54 publications

(49 citation statements)

References 39 publications

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“…How the IPS is populated is yet unclear, but it is detected by absorbing one additional photon; hence, E ¼ E IP þ hν. The IPS energy E IP ¼ 3.6 eV with respect to E F and the corresponding binding energy of 0.8 eV with respect to E v conform with the previous reports for graphite [40,42,49,50]. According to IPS wave-function symmetry, only the surface-normal Fig.…”

Section: Resultssupporting

confidence: 63%

“…3(c) which m ¼ 2 of hν > 3 eV for the TES and hν > 3.6 eV for the IPS [40,42]. As hν decreases, however, m increases markedly up to about 8 for the lowest energy hν ¼ 1.41 eV.…”

Section: Resultsmentioning

confidence: 99%

“…It has been assigned to a 2PP process that is initiated by resonant excitation from the initial π to intermediate π Ã bands [ Fig. 1(a)] [40,42]. Further excitation of the primary hot electron in the π Ã band is unlikely because there are no vertical bands above it within about 6 eV, where such transitions could terminate.…”

Section: Resultsmentioning

confidence: 99%

“…Hot electron dynamics in graphene and graphite have been investigated by optical, THz, photoemission, and theoretical methods [1][2][3][4][5][6][7][8][9]23,34,[39][40][41][42][43][44][45][46]. Xu et al [39] first applied ultrafast time-resolved two-photon photoemission (TR-2PP) spectroscopy to excite a hot electron population and monitor its energy-dependent decay in graphite.…”

Section: Introductionmentioning

confidence: 99%

“…Another focus has been the image potential states (IPSs) of graphite, which are the only band-structure features at the Γ point to appear in 2PP spectra [ Fig. 1(a)], but the mechanism for their excitation remains controversial because apposite initial states for vertical excitation do not exist [40,42,[49][50][51]. Also at the Γ point, there is a σ-symmetry interlayer band (ILB) with uniquely 3D free-electron character and band minimum at about 4.0 eV above the Fermi level (E F ; all electron energy levels are reported with respect to E F unless otherwise stated).…”

Section: Introductionmentioning

confidence: 99%

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Ultrafast Multiphoton Thermionic Photoemission from Graphite

et al. 2017

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Electronic heating of cold crystal lattices in nonlinear multiphoton excitation can transiently alter their physical and chemical properties. In metals where free electron densities are high and the relative fraction of photoexcited hot electrons is low, the effects are small, but in semimetals, where the free electron densities are low and the photoexcited densities can overwhelm them, the intense femtosecond laser excitation can induce profound changes. In semimetal graphite and its derivatives, strong optical absorption, weak screening of the Coulomb potential, and high cohesive energy enable extreme hot electron generation and thermalization to be realized under femtosecond laser excitation. We investigate the nonlinear interactions within a hot electron gas in graphite through multiphoton-induced thermionic emission. Unlike the conventional photoelectric effect, within about 25 fs, the memory of the excitation process, where resonant dipole transitions absorb up to eight quanta of light, is erased to produce statistical Boltzmann electron distributions with temperatures exceeding 5000 K; this ultrafast electronic heating causes thermionic emission to occur from the interlayer band of graphite. The nearly instantaneous thermalization of the photoexcited carriers through Coulomb scattering to extreme electronic temperatures characterized by separate electron and hole chemical potentials can enhance hot electron surface femtochemistry, photovoltaic energy conversion, and incandescence, and drive graphite-to-diamond electronic phase transition.

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Section: Resultssupporting

confidence: 63%

“…3(c) which m ¼ 2 of hν > 3 eV for the TES and hν > 3.6 eV for the IPS [40,42]. As hν decreases, however, m increases markedly up to about 8 for the lowest energy hν ¼ 1.41 eV.…”

Section: Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Ultrafast Multiphoton Thermionic Photoemission from Graphite

et al. 2017

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Time‐resolved two‐photon photoemission

Fauster¹

2003

Solid‐State Photoemission and Related Methods

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In this chapter time resolution will be introduced to photoemission experiments. This means not just a series of regular photoemission measurements to monitor the changes of a sample with time. In two-photon photoemission the time delay between the two photons is an additional experimental parameter which can be controlled with femtosecond resolution, i.e., on a time scale relevant for electronic processes. At the same time, the introduction of the second photon leads to the participation of an additional electronic state in the energy diagram for photoemission. Energy diagramIn Figure 8.1 the transition from initial state |1 to an intermediate state |2 after the absorption of the photon with energy hν a is shown. The second photon of energy hν b excites the electron out of the intermediate state into the final state |3 . If the final state energy E 3 is above the vacuum energy E vac , the electron might leave the surface and its kinetic energy E kin is measured with an electron energy analyzer. Obviously, the initial state has to be occupied, i.e., its energy E 1 should be below the Fermi energy E F . The intermediate state on the other hand has to be empty at first. In most cases it is desirable to keep the photon energy hν a below the work function Φ = E vac − E F , because this constitutes the threshold for one-photon photoemission. This applies also to the other photon, because processes with the role of the two photons interchanged are possible as well. Energy-resolved spectroscopyThe spectrum sketched at the right of Fig. 8.1 shows a peak at the final state energy E 3 . The cutoff at kinetic energy zero corresponds to the vacuum level E vac of the sample. Electrons with the highest energy after the absorption of the photons with energies hν a and hν b appear at kinetic energy E max − E vac = hν a + hν b − Φ. These limits are familiar from regular photoemission spectroscopy and can be used to determine the work function from the width of the spectrum. Similarly, the momentum k of the electron parallel to the surface is conserved for single-crystal surfaces. For electrons emitted at an angle ϑ with respect to the surface normal one obtainshk = √ 2mE kin sin ϑ. Umklapp processes would add reciprocal lattice vectors of the surface to the momentum conservation, but play usually no role in twophoton photoemission. One has to keep in mind that the kinetic energies are generally quite

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Higher Order Photoemission from Metal Surfaces

Winkelmann

Chiang

Bisio

et al. 2010

Dynamics at Solid State Surfaces and Interfaces

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Photoemission spectroscopy (PES) is a widely employed method for mapping the electronic structure of solids [1,2]. In the simplest picture, the incident radiation induces transitions of electrons from occupied to unoccupied single-particle states separated by the photon energy. By invoking the laws of energy and momentum conservation, the photoemission process can be applied to map the occupied band structure of solids by detecting the photoelectrons in final states above the vacuum barrier.A generalization of the linear one-photon photoelectric effect can be realized by nonlinear multiphoton processes induced by ultrashort laser pulses of high intensity, where the occupied initial states, the unoccupied intermediate states, and the coupling between them play a central role. The unique power of these effects stems from the fact that the dynamical processes in the intermediate excited states become directly accessible in the time domain when using delayed excitation pulses. Especially the technique of time-resolved two-photon photoemission (2PPE) has been used to gain information on the decay rates of electronic populations and their dephasing times [3][4][5].Compared to 2PPE, higher order multiphoton photoemission processes (mPPE) in solids, which can extend the energy range of the studied unoccupied states and provide further information on photoexcitation processes, have received only little attention. This is mainly because their observation requires very intense optical fields and their considerably reduced photoelectron yields can be overwhelmed by space charge effects from the lower order processes [6][7][8][9][10][11][12][13][14][15]. Moreover, nonphotoelectric effect emission through the surface plasmon excitation and possibly tunneling, leading to ponderomotive acceleration of photoelectrons up to 0.4 keV energy [9,16], has been reported with comparatively low external fields. Therefore, the mechanisms for high-order photoelectric excitations at solid surfaces, in particular to what extent they are governed by the band structure of metals, are largely unexplored.

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Properties and dynamics of the image potential states on graphite investigated by multiphoton photoemission spectroscopy

Cited by 54 publications

References 39 publications

Ultrafast Multiphoton Thermionic Photoemission from Graphite

Ultrafast Multiphoton Thermionic Photoemission from Graphite

Time‐resolved two‐photon photoemission

Higher Order Photoemission from Metal Surfaces

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