ARPES, UPS

Angle-Resolved Photoelectron Spectroscopy detects valence band electrons emitted by irradiation of a sample with UV light due to the photoelectric effect. Highest resolution detection of the energy and angle distribution of the photoelectrons allows to determine the electronic structure of solids.

Photoelectron spectroscopy (PES) is one of the most powerful and most frequently used spectroscopic techniques in solid state physics, physical chemistry and materials science. Using the photoelectric effect, PES provides a material sensitive and non-destructive probe for modern scientists to examine the chemical composition (XPS or ESCA ) and the electronic structure (UPS and ARPES) of matter. By illuminating a sample with light of a certain photon energy (hν), electrons are released from a solid, using the photon energy to overcome their binding energy (Eb) and work function (Φ). The remaining energy provided by the photons is transferred into the kinetic energy (Ekin) of the photoelectrons. Such a transition can only occur from occupied electronic states of an energy Ei into unoccupied states of energy Ef, when the energy is conserved.

On the other hand, also the wave vector (or momentum) k ( kx, ky, kz) has to be conserved. The surface breaks the geometry, not affecting the energy conservations rule, but affecting the momentum conservation such, that the parallel wave component kӀӀ is conserved after crossing the surface, but the component along the surface normal (k) is not conserved. Finally the electrons can be analyzed in an electron analyzer with respect to their Ekin (or recalculated to Eb) and to Θ (or recalculated to the parallel wave vector component (kӀӀ). On this basis, a 2D distribution of the electrons (number of electrons for given Eb and kӀӀ is measured, directly reflecting the electronic (or band) structure of the material.

Such experiments in laboratory environments equire intense, small spot UV light sources of high stability for optimum performance. The intensity of the light source is the key point for fast and efficient measurements, while small spot sizes ensure measurements with highest angle (or momentum) resolution. SPECS offers a series of UV sources fitted to various demands, starting from flexible and robust UV sources for economic application to highly sophisticated UV sources for different gases and photon energies with monochromators for highest performance and energy resolution.

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APPLICATION NOTES

Small Spot UV Source UVS300
High resolution photoemission measurements demand not only the highest performance electron spectrometer, but also a UV source with high flux density and small spot size, especially for experiments with angular resolved data. SPECS has developed a focused UV source on the basis of the proven technology of the UVS 300 source. The UVS 300 generates a high density plasma by guiding the electrons extracted from a hot cathode filament along the lines of a strongly inhomogeneous magnetic field towards the small discharge region (duo-plasmatronprinciple).
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Overlayer Quantum Well States
Angle-resolved one-photon photoemission was used to investigate angular resolved photoemission from Ag overlayers on Cu(111).
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Resolving Power of the PHOIBOS Energy Analyzer Series
The line width of Xe and other rare gas levels using the SPECS gas cell UGC 10 and the SPECS UV-light source UVS 10/35 has been measured. The special geometry of the cell includes space charge compensation electrodes to demonstrate the ultimate energy resolution of the PHOIBOS analyzers.
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Ultimate energy resolution of the PHOIBOS Energy Analyzer series
We have measured the line width of the Xe 5p3/2gas line using the SPECS gas cell UGC 10 and the SPECS UV-light source UVS 300. The special geometry of the cell includes space charge compensation electrodes to demonstrate the ultimate energy resolution of the PHOIBOS analyzers together with the 2D-CCD Imaging Detector.
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PHOIBOS 150 2D-CCD Wide Angle Mode in 2PPE
These notes describe the application of the angular resolving wide angle lens mode (WAM) in two-photon-photoemission spectroscopy (2PPE).
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Ultimate Energy Resolution of the PHOIBOS 100 CCD
We have measured the line width of the Xe 5p3/2gas line using the SPECS gas cell UGC 10 and the SPECS UV-light source UVS 300. The special geometry of the cell includes space charge compensation electrodes to demonstrate the ultimate energy resolution of the PHOIBOS 100 analyzer together with the 2D-CCD Imaging Detector.
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Spin-resolved photoelectron spectroscopy
Spin-resolved photoelectron spectroscopy experiments were performed in an experimental station consisting of an analysis and apreparation chamber. The preparation chamber is used for substrate cleaning, as well as for the preparation and magnetization of ferromagnetic thin films.
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Photoelectron spectroscopy with UVLS and TMM 304
Angle-integrated and angle-resolved photoelectron spectroscopy measurements were performed using the SPECS UVLS ultraviolet-light source in combination with the toroidal-mirror monochromator SPECS TMM304, which was equipped with two cassettes of optical elements in order utilize the HeI and XeI emission lines with photon energies of hν=21.22eV and hν=8.437eV,respectively.
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Small Spot UV Source
High resolution photoemission measurements demand not only a highest performance electron spectrometer, but also a UV source with high flux density and small spot size, especially for angular resolved studies. SPECS has developed a focused UV source on the basis of the proven technology of the UVS 300 source. Using a special capillary, this source can be focused down to a theoretical spot size of 500 micrometers.
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Cross Section through the Brillouin Zone of Pb 2D Quantum Well State Bands
Examining unexpected properties of Pb, a free electron metal
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High Angular Resolution Data from the Band Structure of Thin Layers of Indium on Si(111)
The band structure of thin layers of indium on Si(111) was measured with ARPES. Due to electron confinement in the direction perpendicular to the surface, quantum well states (QWS) are formed. The experiments were performed at the BESSY II 10 m NIM beamline at the U125/2 undulator, which has an energy resolution of less than 1 meV, and a small spot size.
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Band Structure of Crystalline Graphite Layers on SiC (0001)
The band structure of crystalline graphite layers on the (0001) surface of SiC was measured by high-resolution angle-resolved photoelectron spectroscopy. The experiments were performed using a SPECS UV source 10-35, which has an energy resolution of about 2 meV and a spot size of about 0.6 mm in diameter. The photon energy for all measurements were 40.81 eV (He II).
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Fermi-edge of a single crystal TiTe2 sample at low temperature
The Fermi-edge of a single crystal TiTe2sample was measured at low temperature. The diode closest to the sample read 12 K. A sample temperature of 17 K was estimated. The data was taken with a PHOIBOS 150 CCD analyzer at 3 eV pass energy and with 0.2 mm slit width.
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Measurements of the Surface State of Au (111)
The band structure of the (111) surface of Au was measured by high-resolution angle-resolved photoelectron spectroscopy. The experiments were performed using a SPECS UV 10/35 source, which has an energy resolution of about 2 meV and a spot size of about 1.5 mm diameter. The photon energy for all measurements was 21.23 eV (He I).
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Measurements of the Surface State of Cu (111)
The band structure of the (111) surface of Cu was measured by high-resolution angle-resolved photoelectron spectroscopy. The experiments were performed using a VG UV source, which has an energy resolution of about 2 meV and a spot size of about 1.5 mm diameter. The photon energy for all measurements was 21.23 eV (He I).
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Quantum Size Effects in uncoupled Al layers on graphitized SiC
track Quantum well states, measure 2D band structure, parallel component of wave vector, 2D spectrometer use
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Two-Photon-Photoemission
This Note shows the one- and two-photon photoemission signal of the Cu(111) surface state at 300 K for the different angular resolved lens modes of the PHOIBOS analyzer at different pass energies Ep. The surface has been analyzed using a PHOIBOS 150 analyzer with the 2D CCD Detector.
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