Photoinduced plasmon excitations in alkali-metal overlayers

Barman, S. R.; Horn, Karsten; Häberle, Patricio; Ishida, Hiroshi; Liebsch, A.

doi:10.1103/physrevb.57.6662

Cited by 34 publications

(38 citation statements)

References 30 publications

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“…This is expected because as the Na adlayer becomes thicker it can support Na related modes, as observed in our earlier work on alkali metal adlayers on Al. 5,7 It should be noted that photoyield measurements in this photon energy range cannot be performed on Ag without decreasing its work function ͑4.3 eV͒ by alkali metal deposition. However, no interband transitions related to Na are expected at this photon energy and there are no features in the photoyield spectrum of Na at 3.7 eV.…”

Section: B Photoyieldmentioning

confidence: 99%

“…Theoretical work on the surface response of metals has been performed extensively, and there is reasonable agreement between the theory and experiment for free-electron-like metals. [1][2][3][4][5][6][7] However, in metals such as Ag, the optical properties of which have also been studied extensively, this agreement has not been reached; here the influence of occupied 4d bands on the surface collective excitations results in a remarkably different behavior compared to the free-electron-like metals. For example, the energies of the Ag bulk plasmon p and monopole surface plasmon s are drastically reduced due to the presence of the filled Ag 4d bands.…”

Section: Introductionmentioning

confidence: 99%

“…This is the multipole plasmon mode m which has been theoretically predicted, and identified on many metal surfaces. 2,[5][6][7][10][11][12][13][14][15] Parallel to the surface, both s and m propagate such as plane waves with alternate positive and negative regions. Thus, along the surface both the modes are dipolar in nature.…”

Section: Introductionmentioning

confidence: 99%

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Electronic excitations on silver surfaces

Barman¹,

Biswas²,

Horn

2004

Phys. Rev. B

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The surface electronic structure and optical response of Ag has been studied using angle-and energyresolved photoyield ͑AERPY͒ and angle-resolved photoemission spectroscopy ͑ARPES͒ using low energy photons ͑2.7-18 eV͒. ARPES data for Ag͑100͒ exhibit an unexpected dispersing feature which cannot be assigned to a direct transition peak in the ⌫X direction of the bulk Brillouin zone. The origin of this feature is found in the surface mediated indirect transitions related to the direct transition in the ⌫L direction. From the AERPY experiments, the adlayer standing-wave-like bulk plasmon mode is clearly observed in Ag͑100͒ and Ag͑111͒ thin films. The silver multipole plasmon is observed both on Ag adlayers and bulk single crystal surfaces at 3.7 eV. No signature of the multipole plasmon is observed around 6.7 eV, in disagreement with the prediction of the s-d polarization model.

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Section: B Photoyieldmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Electronic excitations on silver surfaces

Barman¹,

Biswas²,

Horn

2004

Phys. Rev. B

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“…Na deposition was done at a substrate temperature of 100 K. One monolayer (ML) is defined as a close-packed Na layer. Coverage calibration and other experimental details were discussed previously [11]. A (4͞3 3 4͞3) low energy electron diffraction pattern was observed between 0.5 and 1 ML [12] beyond which a sharp hexagonal (1 3 1) pattern, indicative of epitaxial fcc Na layer growth, was observed.…”

Section: (Received 4 December 2000)mentioning

confidence: 86%

“…For simplicity, we represent overlayer and substrate in terms of the jellium model [17] which, combined with the time dependent local density approximation [18], provides an excellent description of excitation spectra of adsorbed alkali metal films [11,15,19]. Figure 3 illustrates the ground state potential and the dynamical local potential, which includes the response of the electron density to the incident photon field.…”

Section: (Received 4 December 2000)mentioning

confidence: 99%

Quantum Well Behavior without Confining Barrier Observed via Dynamically Screened Photon Field

et al. 2001

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Angle-resolved photoemission spectra from Na adlayers on Al(111) reveal features which behave like quantum well resonances although the substrate provides no confining barrier. These features are observed in a narrow photon energy range where overlayer collective excitations cause resonant enhancement of the photoemission intensity. The quantum well behavior is shown to be due to surface resonances of the Na͞Al system. The resonances are observable using photoemission because of spatial confinement and dynamical enhancement of the local electric field within the Na films. DOI: 10.1103/PhysRevLett.86.5108 PACS numbers: 73.20.At, 73.21.-b, 79.60.Dp Quantum well states are a striking manifestation of elementary quantum mechanics. An electron confined in a one-dimensional potential well may occupy discrete energy levels whose quantum number n specifies the number of half-wavelengths spanning the well. Quantum well states have been observed experimentally in a variety of layered semiconductor and metallic films where potential barriers restrict the electron's motion in the direction normal to the film. They provide a conceptually simple means for studying electron confinement, but are also interesting for applications, e.g., in the giant magnetoresistance effect [1]. Angle-resolved photoemission is an ideal tool for studying the dependence of quantum well states on film thickness and on substrate and overlayer band structure [2][3][4][5][6][7][8]. Generally, the confining potential consists of the vacuum barrier, and a reflecting barrier due to a gap in the substrate band structure on the opposite side. The quantum states can thus be readily understood in terms of the discrete level structure of a one-dimensional potential well.Here we discuss a different mechanism, namely, quantum well behavior in the absence of a confining wall between adsorbed metal film and substrate. The resonances are observable since the screened photon field is dynamically enhanced and spatially confined to the overlayer. While the former mechanism had been invoked earlier by Lindgren and Walldén [9] to explain spectral features observed in inverse photoemission from a Na monolayer on Al(111) [10], the special role of the photon field distinguishes the present system from ordinary quantum wells. We demonstrate that angle-resolved photoemission for Na on Al(111) in a wide range of coverages reveals quantum well-like spectral features associated with virtual states induced by the large negative potential step between overlayer and substrate. To observe these resonances it is crucial to suppress emission from substrate bands in the same energy region. This is achieved by tuning the photon energy to the collective modes of the overlayer. The local electric field is then enhanced and confined to the overlayer so that the Na resonances can be observed. Thus, while in usual quantum well systems the photon field plays no special role, here it serves as a novel mechanism ensuring the confinement of the excitation region.The measurements were carri...

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Sensitive Linear Surface Optics with Metal–Insulator–Metal Tunnel Contacts

Otto

Diesing

Schatteburg

et al. 1999

phys. stat. sol. (a)

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Aluminium–aluminiumoxide–silver tunnel junctions allow to measure light emission by hot electrons and internal photoemission. Adsorption of potassium or oxygen on the silver electrode increases or quenches the light emission considerably. The light intensity increases at negative surface charge on the silver electrode and is suppressed at positive surface charge. Surprisingly, the light emission by hot electrons within the optical skin depth is negligible. The observed intensity is assigned to electron–photon coupling at the surface, especially to inverse photoemission by hot electrons via the time inverted threshold effect postulated by A. Liebsch. This is not in contradiction to time resolved two photon photoemission experiments. Internal photoemission experiments corroborate this interpretation.

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Photoinduced plasmon excitations in alkali-metal overlayers

Cited by 34 publications

References 30 publications

Electronic excitations on silver surfaces

Electronic excitations on silver surfaces

Quantum Well Behavior without Confining Barrier Observed via Dynamically Screened Photon Field

Sensitive Linear Surface Optics with Metal–Insulator–Metal Tunnel Contacts

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