First results from a second generation toroidal electron spectrometer

Broekman, L.; Tadich, Anton; Huwald, E.; Riley, J.D.; Leckey, Robert; Seyller, Thomas; Emtsev, K. V.; Ley, L.

doi:10.1016/j.elspec.2005.01.022

Cited by 62 publications

(47 citation statements)

References 9 publications

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“…Experiments were performed in situ in ultrahigh vacuum with the toroidal electron analyzer (19) attached to the U125/2-SGM beamline at the Helmholtz Zentrum Berlin -Electron Storage Ring BESSY II. A photon energy of 30 eV and a photon incidence angle of 40°with respect to the surface normal were used.…”

Section: Methodsmentioning

confidence: 99%

Imaging the wave functions of adsorbed molecules

Lüftner

Ules

Reinisch

et al. 2013

Proc. Natl. Acad. Sci. U.S.A.

103

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The basis for a quantum-mechanical description of matter is electron wave functions. For atoms and molecules, their spatial distributions and phases are known as orbitals. Although orbitals are very powerful concepts, experimentally only the electron densities and -energy levels are directly observable. Regardless whether orbitals are observed in real space with scanning probe experiments, or in reciprocal space by photoemission, the phase information of the orbital is lost. Here, we show that the experimental momentum maps of angle-resolved photoemission from molecular orbitals can be transformed to realspace orbitals via an iterative procedure which also retrieves the lost phase information. This is demonstrated with images obtained of a number of orbitals of the molecules pentacene (C 22 H 14 ) and perylene-3,4,9,10-tetracarboxylic dianhydride (C 24 H 8 O 6 ), adsorbed on silver, which are in excellent agreement with ab initio calculations. The procedure requires no a priori knowledge of the orbitals and is shown to be simple and robust.photoemission spectroscopy | surface science | organic molecules | density functional theory A s the electronic, optical, and chemical properties of nanostructures are defined by their electronic orbitals, in the last decades experimentalists have striven to image them. This is despite the fact that orbitals are not, strictly speaking, quantummechanical observables. Molecules are arguably the best-defined nanostructures, and for simple diatomic molecules, such as N 2 , both the amplitude and the phase of the highest occupied molecular orbital (HOMO) in three-dimensional space have been recovered (1). This tomographic reconstruction requires higher harmonics generated from intense femtosecond laser pulses, focused on a series of molecular alignments, together with theoretical modeling (1). Although offering the exciting prospect of imaging orbitals on the time scale of chemical reactions, being both complex and only appropriate for simple molecules and orbitals, the technique is not generally applicable for the task of orbital reconstruction. Alternatively, scanning probe techniques offer real-space imaging of large molecules with submolecular resolution on surfaces. Although great advances have been made with understanding and controlling scanning probe tips, so-called "tip functionalization" (2), tips are still a factor of uncertainty. With an appropriate tip, the correct nodal structure of orbitals can be directly observed. Moreover, with tip molecules of p-wave structure the relative phase of the sample wave function may be inferred (3). Unfortunately, as the wave functions of the substrate generally spill out beyond the adsorbed molecules, decoupling layers such as NaCl are necessary to avoid direct tunneling into the substrate.The full angle dependence of valence band UV photoelectron spectroscopy from molecular films has been shown to contain rich information on the orbital structure (4, 5). In the past few years a number of studies on molecular films have demonstrated a...

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Section: Methodsmentioning

confidence: 99%

Imaging the wave functions of adsorbed molecules

Lüftner

Ules

Reinisch

et al. 2013

Proc. Natl. Acad. Sci. U.S.A.

103

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“…ARPES measurements of the p-band dispersion near E F and also the Fermi surface were performed using the toroidal angleresolving endstation at the U125-2/SGM beamline at BESSY II, Berlin, Germany. 13 The energy distribution curve (EDC) measurements of the p-band were performed along the C À K surface direction at room temperature, using linearly polarised undulator radiation (h ¼ 50 eV) at normal incidence to the sample. The sample was introduced into vacuum and then annealed at 350-400 C for 3 h to remove hydrocarbon and airborne contamination.…”

Section: à2mentioning

confidence: 99%

“…In situ angle-resolved photoemission is used to measure an upward shift of (0.6 6 0.05) eV in the Dirac point from À0.43 eV to þ0.17 eV relative to the Fermi level. The carrier density is observed to change from n $ (1 Â 10 13 6 0.1 Â 10…”

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confidence: 99%

Tuning the charge carriers in epitaxial graphene on SiC(0001) from electron to hole via molecular doping with C60F48

Tadich

Edmonds

Ley

et al. 2013

Applied Physics Letters

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We demonstrate that the intrinsic electron doping of monolayer epitaxial graphene on SiC(0001) can be tuned in a controlled fashion to holes via molecular doping with the fluorinated fullerene C60F48. In situ angle-resolved photoemission is used to measure an upward shift of (0.6 ± 0.05) eV in the Dirac point from −0.43 eV to +0.17 eV relative to the Fermi level. The carrier density is observed to change from n ∼ (1 × 1013 ± 0.1 × 1013) cm−2 to p ∼ (2 × 1012 ± 1 × 1012) cm−2. We introduce a doping model employing Fermi-Dirac statistics which explicitly takes temperature and the highly correlated nature of molecular orbitals into account. The model describes the observed doping behaviour in our experiment and readily explains why net p-type doping was not achieved in a previous study [Coletti et al., Phys. Rev. B 81, 8 (2010)] which used tetrafluorotetra-cyanoquinodimethane (F4-TCNQ).

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“…The sample was post-growth annealed in air, at 190 °C for 100 h. The sample was cut into several pieces which were prepared by etching in concentrated HCl and transferred within 10 min into vacuum. The experiment was performed with a second-generation toroidal energy analyzer [28] at the TGM 4 dipole beamline of BESSY II. Spectra are normalized through a simultaneous recording of the photocurrent of the refocussing mirror of TGM 4.…”

Section: Introductionmentioning

confidence: 99%

Photoemission of Ga_1–xMn_x As with high Curie temperature and transformation into MnAs of zincblende structure

Rader

València

Gudat

et al. 2009

Physica Status Solidi (b)

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Epitaxial films of Ga1–x Mnx As, x = 0.08, with a high ferromagnetic ordering temperature (TC = 160 K) grown and post‐growth annealed at low temperature (LT) have been studied in a photoemission experiment. The (100) surfaces were prepared by wet etching to remove surface segregated interstitials. By resonant photoemission at the Mn M‐edge, the appearence of a Mn induced main peak at 4.5 eV binding energy and an intense satellite at ∼7.2 eV are observed in full agreement with our previous work on Ga1–x Mnx As with TC ∼50 K. Mn induced states are also observed around 1 eV to 2 eV but are of weaker intensity than in our previous work which may indicate a depletion of interstitial Mn. In no stage of surface preparation, emission from the gap region was observed where, according to recent local‐density calculations, interstitial Mn would contribute to the spectra. Additional annealing in situ changes the photoemission spectra strongly: The Mn 3d spectral weight increases altogether and the satellite decreases in intensity relative to the Mn 3d main peak and shifts to ∼6.5 eV. Comparison to the literature indicates that zincblende‐type MnAs is formed. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

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First results from a second generation toroidal electron spectrometer

Cited by 62 publications

References 9 publications

Imaging the wave functions of adsorbed molecules

Imaging the wave functions of adsorbed molecules

Tuning the charge carriers in epitaxial graphene on SiC(0001) from electron to hole via molecular doping with C60F48

Photoemission of Ga_1–xMn_x As with high Curie temperature and transformation into MnAs of zincblende structure

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First results from a second generation toroidal electron spectrometer

Cited by 62 publications

References 9 publications

Imaging the wave functions of adsorbed molecules

Imaging the wave functions of adsorbed molecules

Tuning the charge carriers in epitaxial graphene on SiC(0001) from electron to hole via molecular doping with C60F48

Photoemission of Ga1–xMnx As with high Curie temperature and transformation into MnAs of zincblende structure

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Product

Resources

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Photoemission of Ga_1–xMn_x As with high Curie temperature and transformation into MnAs of zincblende structure