Surface barrier resonances on a simple metal

Yang, Shuai; Bartynski, Robert; Papadia, S.; Fondén, T.; Persson, Mats

doi:10.1103/physrevlett.70.849

Cited by 33 publications

(16 citation statements)

References 30 publications

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“…Previous inverse photoemission and 2PPE experiments of aluminum surfaces lacked the energy resolution to distinguish resonances beyond n ¼ 2. For Al (100), a peak 0.2-0.5 eV below vacuum level was observed by Veyan et al [24], somewhat weaker but similar to that reported earlier for Al(111) [25][26][27]. Tentatively, this feature has been interpreted in terms of the ðn ¼ 1Þ imagepotential resonance or the superposition of a broadened full series of resonances [17,28,29].…”

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confidence: 58%

Trapping of Image-Potential Resonances on a Free-Electron-like Surface

2011

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Image-potential states have been studied by two-photon photoemission for the surface of Al(100) where the whole series is energetically degenerate with free-electron-like bulk states. In contrast with expectations, the series of resonances is not smeared out to one broad structure as a result of a strong coupling to the bulk continuum. Instead, the first resonance (n ¼ 1) is found to be suppressed, and the resonances with quantum numbers n ¼ 2; 3; 4; 5 are resolved as individual peaks in the time-resolved spectra. Both effects are suggested to be a consequence of resonance trapping. DOI: 10.1103/PhysRevLett.107.236801 PACS numbers: 73.20.Àr, 78.47.Àp, 79.60.Bm Electron transfer processes at solid surfaces and interfaces play a decisive role in many fields of research, such as surface chemistry or nanoscience. In the past decade, experimental and theoretical studies of the electronic decay at metal surfaces have considerably advanced the microscopic understanding of those inelastic scattering phenomena that drive the transfer in the case of states located in the forbidden energy gap of the solid [1,2]. Many practical situations, however, involve energy levels, e.g., of adatoms, molecules, clusters, or small islands, that are resonant with bulk bands. Then, elastic transfer channels are expected to dominate over the inelastic ones [3][4][5]. Interestingly, this rather basic, resonant electron transfer appears to be less well-understood than some of the inelastic electron-electron or electron-phonon many-body decay processes. Generally, when a quantum system is embedded in a continuum, the coupling can lead to striking effects like Fano-type interference phenomena in the case of a single level or avoided overlap and trapping in the case of two or more adjacent levels. Whereas such phenomena that go far beyond a simple resonance broadening have long been investigated intensively in atomic and nuclear physics [6-9], they are usually not taken into account in the discussion of electron decay at surfaces.The investigation of image-potential resonances of Al (100) by time-resolved two-photon photoemission (2PPE), reported in this Letter, clearly demonstrates the importance of such effects in surface physics. Like the well-known image-potential states in the projected band gap [10][11][12][13][14], image-potential resonances form a Rydberg series of hydrogenlike states below the vacuum level [15,16]. In contrast to gap states, electrons excited into these resonances are not confined to the surface, but can propagate into the metal without the need to undergo collisions. Even for surfaces with a wide projected band gap close to the vacuum level, such as Cu(111) or Ag(111), it has been suggested that they delocalize faster in this way than they decay by electron-hole-pair excitation [12][13][14]16]. In the case of the Al(100) surface investigated here, the corresponding energy gap is relatively narrow and located far below the vacuum level [ Fig. 1(a)]. In such a situation, one expects the coupling of the hydrogenic le...

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Trapping of Image-Potential Resonances on a Free-Electron-like Surface

2011

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“…[7][8][9][10] IPI states are present in systems where a bulk band gap provides a barrier, trapping electrons in the image tail of the surface potential. If no gap is present at the IPI energies, an electron is not reflected completely at the bulk barrier, and hybridization with surface truncated bulk states becomes possible.…”

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confidence: 99%

Image resonance in the many-body density of states at a metal surface

et al. 2003

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The electronic properties of a semi-infinite metal surface without a bulk gap are studied by a formalism that is able to account for the continuous spectrum of the system. The density of states at the surface is calculated within the GW approximation of many-body perturbation theory. We demonstrate the presence of an unoccupied surface resonance peaked at the position of the first image state. The resonance encompasses the whole Rydberg series of image states and cannot be resolved into individual peaks. Its origin is the shift in spectral weight when many-body correlation effects are taken into account.

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“…Image potential states are Rydberg series of bound states whose binding energy is given by E n = 0.85/n 2 eV, where n= 1, 2, 3,... and have been reported in many metal surfaces. 23,24,[30][31][32][33] They are pinned to the vacuum level (E vac ) and thus the energy of n= 1 image potential state is 0.85 eV below E vac . The work function of i-Al-Pd-Mn turns out to be 5± 0.15 eV, and the resulting E vac is shown by an arrow in Fig.…”

Section: Resultsmentioning

confidence: 99%

Unoccupied electronic states of icosahedral Al-Pd-Mn quasicrystals: Evidence of image potential resonance and pseudogap

et al. 2014

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We study the unoccupied region of the electronic structure of the fivefold symmetric surface of an icosahedral (i) Al-Pd-Mn quasicrystal. A feature that exhibits parabolic dispersion with an effective mass of (1.15±0.1)me and tracks the change in the work function is assigned to an image potential resonance because our density functional calculation shows absence of band gap in the respective energy region. We show that Sn grows pseudomorphically on i-Al-Pd-Mn as predicted by density functional theory calculations and the energy of the image potential resonance tracks the change in the work function with Sn coverage. The image potential resonance appears much weaker in the spectrum from the related crystalline Al-Pd-Mn surface, demonstrating that its strength is related to the compatibility of the quasiperiodic wave functions in i-Al-Pd-Mn with the free electron like image potential states. Our investigation of the energy region immediately above EF provides unambiguous evidence for the presence of a pseudogap, in agreement with our density functional theory calculations.

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Surface barrier resonances on a simple metal

Cited by 33 publications

References 30 publications

Trapping of Image-Potential Resonances on a Free-Electron-like Surface

Trapping of Image-Potential Resonances on a Free-Electron-like Surface

Image resonance in the many-body density of states at a metal surface

Unoccupied electronic states of icosahedral Al-Pd-Mn quasicrystals: Evidence of image potential resonance and pseudogap

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