Experimental energy band dispersions and lifetimes for valence and conduction bands of copper using angle-resolved photoemission

Knapp, J. A.; Himpsel, F. J.; East̀man, D. E.

doi:10.1103/physrevb.19.4952

Cited by 360 publications

(107 citation statements)

References 39 publications

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“…Assuming the lower initial-state (s, p) band given in Ref. 12, we obtain k Ќ ϳ0.77(2 /a) for 3.0 ML and k Ќ ϳ0.75(2 /a) for 6.0 ML, in fair agreement with the results obtained in Fig. 3.…”

supporting

confidence: 82%

“…⌬k Ќ, f in Table I is defined as the inverse of the photoelectron escape depth, which in turn is estimated from the experimental inelastic mean free path ͑IMFP͒ for bulk Cu. 12 At the higher-energy transition around ϳ80 eV ⌬k Ќ, f is similar to ⌫ m /(បv f ). Thus in this case the final-state broadening appears to shade the initial state broadening contribution.…”

mentioning

confidence: 77%

“…In contrast, ⌫ m /(បv f ) increases by 35% from 6 ML to 3 ML at the lower-energy resonance. At around 14 eV the IMFP goes up to 15 Å in Cu, 12 i.e., ⌬k f is reduced to 0.07 Å Ϫ1 , about half of the value of ⌫ m /(បv f ). Therefore ⌬k i must be brought in at low energy.…”

mentioning

confidence: 99%

“…11 The lower-energy band is taken from the experimental data of Ref. 12. With respect to k Ќ , the cross section is periodic, i.e., all transitions occur at the same value k Ќ ϳ0.75(2 /a) for 3.0 ML and k Ќ ϳ0.74(2 /a) for 6.0 ML.…”

mentioning

confidence: 99%

“…In order to fit the data in this case, v f (E) is obtained from the parabolic band given in Ref. 12 and it is already introduced as a correction to the experimental Lorentzian fit in Fig. 3.…”

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confidence: 99%

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Periodicity and thickness effects in the cross section of quantum well states

et al. 2000

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The photoemission cross section of quantum well states in very thin Cu films has been analyzed as a function of photon energy within a wide energy range. We show that this cross section is periodical in k space, peaking around vertical transitions of the respective Cu bulk band. The cross section peak width is analyzed in terms of final-and initial-state wave vector broadening. The latter can only be detected at low kinetic energies due to reduction of final state broadening. The initial state k Ќ broadening increases when the Cu film gets thinner, as simply expected from the uncertainty principle.In a thin metal film deposited on a solid substrate electrons are confined in the perpendicular direction by the surface and interface potentials, leading to the formation of quantum well ͑QW͒ states. These are known to be responsible of intriguing phenomena in layered systems, like the oscillatory magnetic coupling of two magnetic layers across a nonmagnetic spacer 1 or the giant magnetoresistance. 2 Their existence has been frequently probed in noble and transition metals by means of angle-resolved photoemission 3 ͑ARPES͒ where they display strong energy-dependent cross sections. In general the QW cross section is expected to be maximum near vertical transitions of the bulk crystal of the material comprising the thin film. This reflects the conservation of the perpendicular wave vector in transitions from thin film states to final states in the continuum. 4 Such behavior has been qualitatively observed in Cu/Co͑100͒ ͑Ref. 5͒ and Ag/ Cu͑111͒ ͑Ref. 6͒. Away from this vertical transition region one can also obtain periodic modulations of the QW intensity. They have been attributed to discretization of the photoemission final-state band, 6 but also to surface-interface coherent photoemission effects. 7,8 Furthermore, it has been claimed that at low energies and very thin films such emission dominates over the regular QW photoemission from inside the thin film. 8 Here we show that this is not true for Cu films on Co͑100͒, since the cross section displays clear peaks around vertical transitions to the lowest three bulk final-state bands. The cross-section peak width is analyzed in terms of perpendicular wave vector broadening (⌬k Ќ ) for both final and initial ͑i.e., QW͒ states. The results show that the finalstate ⌬k Ќ dominates at h ϳ80 eV, whereas at h ϳ14 eV initial-state effects are necessary to explain the width of the transition peak. The thickness dependence of the initial state ⌬k Ќ and its magnitude appears to be related to confinement within the QW via the uncertainty principle.High-resolution photoemission experiments were done at the Synchrotron Radiation Center in Stoughton, Wisconsin (h Ͻ16 eV) and at the VUV photoemission beam line of the synchrotron radiation laboratory Elettra at Trieste, Italy (h Ͼ40 eV). In both cases the polarization of the synchrotron light was set to p-like in order to enhance sensitivity to ⌬ 1 -symmetry initial states. The photoemission spectra were normalized to the photon flux. ...

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confidence: 82%

mentioning

confidence: 77%

mentioning

confidence: 99%

mentioning

confidence: 99%

mentioning

confidence: 99%

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Periodicity and thickness effects in the cross section of quantum well states

et al. 2000

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Ultraviolet Photoelectron Spectroscopy

Hill

2002

Characterization of Materials

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Ultraviolet photoelectron spectroscopy (UPS) probes electronic states in solids and at surfaces. It relies on the process of photoemission, in which an incident photon provides enough energy to bound valence electrons to release them into vacuum. Their energy E , momentum ℏ k , and spin σ provide the full information about the quantum numbers of the original valence electron using conservation laws. Depicts the process in an energy diagram. Essentially, the photon provides energy but negligible momentum (due to its long wavelength λ=2π/| k |), thus shifting all valence states up by a fixed energy (“vertical” or “direct” transitions). In addition, secondary processes, such as energy loss of a photoelectron by creating plasmons or electron‐hole pairs, produce a background of secondary electrons that increases toward lower kinetic energy. It is cut off at the vacuum level E V , where the kinetic energy goes to zero. The other important energy level is the Fermi level E F , which becomes the upper cutoff of the photoelectron spectrum when translated up by the photon energy. The difference ϕ = E V ‐ E F is the work function. It can be obtained by subtracting the energy width of the photoelectron spectrum from the photon energy. Photoemission is complemented by a sister technique that maps out unoccupied valence states, called inverse photoemission or bremsstrahlung isochromat spectroscopy (BIS). Inverse photoemission represents the reverse of the photoemission process, with an incoming electron and an outgoing photon. The electron drops into an unoccupied state and the energy is released by the photon emission. Both photoemission and inverse photoemission operate at photon energies in the ultraviolet (UV), starting with the work function threshold at ∼4 eV and reaching up to 50‐ to 100‐eV photon energy, where the cross‐section of valence states has fallen off by an order of magnitude and the momentum information begins to get blurred. At kinetic energies of 1 to 100 eV, the electron mean free path is only a few atomic layers, making it possible to detect surface states as well as bulk states.

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Ultraviolet Photoelectron Spectroscopy

Himpsel

2012

Characterization of Materials

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A brief overview of ultraviolet photoelectron spectroscopy (UPS) and related techniques is given. This technique measures the occupied electronic states in solids and at surfaces. In its angle‐resolved version, it provides the complete information about electrons in solids. After discussing the underlying physics, a variety of applications in materials science are illustrated. Practical questions are addressed as well.

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Experimental energy band dispersions and lifetimes for valence and conduction bands of copper using angle-resolved photoemission

Cited by 360 publications

References 39 publications

Periodicity and thickness effects in the cross section of quantum well states

Periodicity and thickness effects in the cross section of quantum well states

Ultraviolet Photoelectron Spectroscopy

Ultraviolet Photoelectron Spectroscopy

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