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The line shape of the photoelectron spectrum emitted from the sp-derived surface state at I on Cu(111) is investigated. The line shape is Lorentzian, and the temperature dependence of the width is linear, varying from 30 meV at 30 K to 75 meV at 625 K. Less than 5-rneV variation with binding energy is observed. The temperature dependence is explained as the phonon contribution to the inverse hole lifetime, predicted to be 2~kkbT allowing the determination that the electron-phonon mass enhancement parameter X. = 0.14~0.02 for this surface state at I . This is compared to X =0.15 reported as an average over the bulk Fermi surface.In the standard picture of angle-resolved photoemission spectroscopy, the peak width observed from a perfect crystal with negligible dispersion of the hole state perpendicular to the surface is equal to the inverse hole lifetime fi, /r. ' A measurement of linewidth as a function of binding energy, temperature, and impurity concentration determines the dependence of the hole lifetime on these variables. If the measurements are done at hole energies relatively close to the Fermi energy EF then one can compare to determinations based on low-energy techniques, such as Fermi surface probes, conductivity, and specific-heat measurements. The photoemission measurement is in many ways superior to these other techniques. It is more direct, involves no Fermi surface averaging, and does not depend on assumptions about one-electron theory. Photoemission also has the unique advantage that the energy dependence of the lifetime is directly observable. Its well-known surface sensitivity of a few atomic layers is both an advantage and a disadvantage. On the one hand, surfaces can be studied, while, on the other hand, comparison with bulk sensitive techniques is complicated. Photoemission is also a complex many-body process, allowing some uncertainty about the degree to which the standard picture of identifying widths with inverse hole lifetimes is correct. ' To date, there has been very little successful comparison of valence photoemission linewidths and inverse hole lifetimes, some notable failures of this identity, and some controversy. ' ' ' We report here quantitative understanding of the temperature dependence of the linewidth of a Cu(111) surface state based on the phonon contribution to the hole lifetime. In addition, we describe a surface sensitive method of determining one of the most ubiquitous parameters of solid-state physics, P, the electron-phonon mass enhancement parameter.There are three processes that contribute to valence hole decay at zero temperature in metals. One is Auger decay, where one hole decays into two less tightly bound holes and an electron via the electron-electron interaction (electronhole pair creation). The second is phonon scattering, where one hole decays into a less tightly bound hole plus a phonon via the electron-phonon interaction (phonon creation). The third is scattering by an impurity or defect from one momentum to another at fixed energy. At finite temperature,...

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We have performed an angle-resolved photoemission investigation, using synchrotron radiation, of the surface electronic structure of Be(0001). At normal emission we observe a surface state in the I 3-I 4. band gap with a binding energy of 2.8+0.1 eV. Away from I it disperses parabolically towards EF with an effective mass of m*/m-1.5. For %co &40 eV, the energy dependence of the photoexcitation cross section for this state shows rapid variations caused by changes in the local electromagnetic field at the surface. For Ace &40 eV, it shows only weak structure. This highenergy behavior is quite different from the large resonances observed for surface states on other metals and is associated with the short penetration depth of the Be surface state. The dispersion of this state is measured along I~M and I~E in the two-dimensional surface Brillouin zone. For a small range of k~~a round M, there is evidence for ttvo surface states in the M2-M4 gap with binding energies of 1.8+0.1 eV and 3.0+0.1 eV.

Articles you may be interested inA versatile electron-ion coincidence spectrometer for photoelectron momentum imaging and threshold spectroscopy on mass selected ions using synchrotron radiation Rev. Sci. Instrum. 80, 023102 (2009); 10.1063/1.3079331 Threshold photoelectron spectroscopy using synchrotron radiation AIP Conf. Proc. 576, 703 (2001); 10.1063/1.1395405High-resolution pulsed field ionization photoelectron-photoion coincidence spectroscopy using synchrotron radiation Rev.A study on background subtraction in Auger and photoelectron time coincidence spectroscopy using third generation synchrotron radiation source Rev. Sci. Instrum. 70, 3529 (1999); 10.1063/1.1149955 Photoelectron microscopy and spectroscopy using synchrotron radiationThe technique of Auger photoelectron coincidence spectroscopy (APECS) using synchrotron radiation is discussed. Technical considerations and experimental details are emphasized. Results from Cu( lOO), Ta( lOO), and Al( 111) are presented to show the kinds of new information that APECS can provide. 3013

We present photoemission spectra from the 3p level of Cu(lOO) obtained in coincidence with the MiW Auger line. The 3p level is narrowed from its 2.2-eV core-lifetime-broadened width to 1.0 eV, representing the intrinsic width of the l G Auger final state. The core line changes its energy within the 2.2-eV envelope as the Auger coincidence energy is changed, conserving the sum of Auger-electron and photoelectron kinetic energies.PACS numbers: 79.60.Cn, 71.50.+t Auger-photoelectron coincidence spectra were first reported by Haak and co-workers. 1 Many potential enhancements of ordinary photoelectron and Augerelectron spectroscopies are described in the original papers. l Most are based on the extra discrimination provided by knowing which subpeak in the Auger spectrum is associated with which subpeak in the photoelectron spectrum. Also suggested was the possibility that corehole lifetime broadening could sometimes be eliminated from the photoelectron spectrum. This is an especially exciting possibility, because the short Auger decay lifetime of core holes in solids can lead to broadening of more than an eV, obscuring interesting structure associated with chemical shifts, surface shifts, many-body structure, line shape, etc. 2 Poor instrumental energy resolution has previously prevented an experimental verification of this suggestion. In this paper we present data from the Cu(lOO) 3p core line in coincidence with the M3W (3p3d3d) Auger line illustrating this effect. The 3p linewidth is narrowed from 2.2 to 1.0 ±0.2 eV. We believe that this 1.0 eV is the lifetime width of the l G Auger final state.In this technique two electron energy analyzers are focused on one x-ray or uv illuminated sample. One analyzer is tuned to the energy of a core photoelectron and the other is tuned to an appropriate Auger decay energy. An event is recorded only when electrons are received in each analyzer simultaneously. This is interpreted to mean that both electrons are associated with the same photoexcitation event. Experimental details will be provided in another paper. 3 Briefly, commercial double-pass cylindrical-mirror analyzers 4 were set to 60-eV pass energy with 1-mm (small) apertures. One was fixed at a characteristic Auger energy, and the other was swept through the photoelectron spectrum. The 150-eV light from the National Synchrotron Light Source vacuum ultraviolet ring, was monochromatized by the U14 plane-grating monochromator. 5 The energy resolution, electron plus photon, in each system was <0.5 eV. The Auger (photoelectron) analyzer pulses provided starts (stops) for a time to amplitude converter. The output from the converter was analyzed by a multichannel analyzer. This provided output pulses for zero time delay (coincidence) and 180-ns time delay, each ±10 ns. The 180-ns delay pulses (one revolution time in the storage ring) were used to subtract accidental coincidences from the spectra. The sample was sputtered and annealed once per day. No contamination was visible in electron stimulated Auger spectra. Each coincide...