Photoemission studies of organic semiconducting materials using open Geiger-Müller counter
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We investigated an open ionization cell based on the Geiger-Müller counter principle in a gas mixture at atmospheric pressure and demonstrated that the photoemission signals as weak as 1 electron per second are detectable. This finding allowed us to investigate more accurately the photoemission spectrums, especially in the vicinity of the photoemission threshold. Using such a cell, we investigated a number of organic semiconductor materials, tested various ways to analyze the results of the measurements of photoemission spectrums, and demonstrated an efficient way to determine ionization potential by using the square root of the derivative of the yield dependence on the light quanta energy (dY1/d(hν))1/2. This method leads to more evident graphical representation of the measurement results and better Ip estimation in comparison to the results estimated by using the traditional method of plotting Y1/n dependence on the quanta energy hν.Keywords:
Inverse photoemission spectroscopy
Geiger counter
We report the observation of anomalous bands in graphite valence band structure in angle-resolved photoemission spectroscopy (ARPES) experiments. The photon energy dependence of these bands shows a constant kinetic energy nature. Our results are supported by the very low energy electron diffraction data reported on graphite surfaces which essentially map the unoccupied states representing the photoemission final states. This suggests that the ARPES technique is capable of probing the unoccupied electronic states governed by the secondary electron emission process, along with the occupied bands of solids.
Inverse photoemission spectroscopy
Photon energy
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High resolution photoemission spectroscopy (HPES) has mostly been performed so far at energies below slightly higher than 100 eV. This is due to the necessity for the high enough resolution of photons. Nowadays high resolution better than a few me V is feasible by use of the state of art electron energy analyzers and very bright He I, II light sources. For angle resolved photoemission spectroscopy (ARPES), even angular resolution of better than ± 0.1 degree is feasible. Thus the low photon energy (hν) PES and ARPES are very popular in many laboratories. However, these measurements are relatively surface sensitive. In many cases of strongly correlated electron systems such as 4 f rare earth and 3 d transition metal systems, the surface electronic structures are much different from the bulk. Therefore bulk sensitive HPES is strongly required for bulk studies. The difference of the surface and bulk electronic states is reviewed by showing recent results of bulk sensitive soft X-ray HPES and ARPES measurements.
Inverse photoemission spectroscopy
Photon energy
Surface States
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In this review we describe the development of photoemission spectroscopy (PES) from the first historic observations of the photoelectric effect by Hertz and Hallwachs to state-of-the-art experiments. We present several examples for the application of PES for chemical analysis of solids (ESCA), the determination of the valence band structure by angle-resolved photoemission (ARUPS), and the investigation of many-body effects, in particular by high-resolution PES on the meV-scale. Furthermore, we give a brief overview about the wide spectrum of experimental methods based on PES.
Photoelectric effect
Inverse photoemission spectroscopy
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Abstract The valence band photoemission spectra of epitaxially grown film and bulk single crystal of magnetite were measured by the angle‐resolved ultraviolet photoemission spectroscopy (ARUPS) at 300 K and 120 K. Four main features of the electron photoemission were observed at about –1.0 eV, –3.5 eV, –5.0 eV and –6.5 eV below the chemical potential; they are rather strongly dependant on structure and preparation of surface. The three higher‐energy features showed significant energy dispersion. The ARUPS spectra were compared to the accessible band structure calculations. Special attention was paid to the leading edge of the emission at –1.0 eV of the low‐temperature spectrum where an insulating gap should be observed. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Inverse photoemission spectroscopy
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Inverse photoemission spectroscopy
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Angle Resolved Photo Emission Spectroscopy (ARPES) has been a very effective tool to study the electronic states of solids, from simple metals to complex systems like cuprate superconductors. For photon energy in the range of 10 - 100 eV, it is a surface sensitive process as the free path of the photo emitted electrons is of the order of a few lattice parameters. However to interpret the experimental data one needs to have a theoretical foundation for the photoemission process. From the theory of photoemission it may be seen that one can get information about the state from which the electron has been excited. As the translational periodicity is broken normal to the surface, a new type of electron state in the forbidden energy gap can exist localized in the surface region. ARPES can reveal the existence and the property of such surface states. We shall also discuss briefly how the electromagnetic field of the photons are influenced by the presence of the surface and how one can try to take that into account in photoemission theory.
Inverse photoemission spectroscopy
Surface States
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Inverse photoemission spectroscopy
Electron spectroscopy
Photon energy
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We review angle resolved photoemission spectroscopy (ARPES) results on the high Tc superconductors, focusing primarily on results obtained on the quasi-two dimensional cuprate Bi2Sr2CaCu2O8 and its single layer counterpart Bi2Sr2CuO6. The topics treated include the basics of photoemission and methodologies for analyzing spectra, normal state electronic structure including the Fermi surface, the superconducting energy gap, the normal state pseudogap, and the electron self-energy as determined from photoemission lineshapes.
Pseudogap
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Inverse photoemission spectroscopy
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The electronic structure of the V(100) surface has been studied by means of angularly resolved photoelectron spectroscopy (ARUPS) and momentum- ( k-) resolved inverse photoemission spectroscopy (KRIPES). A narrow peak in the photoemission spectrum which is seen at the Fermi level is attributed to a transition from a surface resonance. The existence of this surface resonance at the Fermi level of the V(100) surface is potentially very important for the occurrence of the expected magnetic ordering of this surface. The energy of the critical point , which defines the top of the unoccupied part of the 3d band, has been determined to be within 3.0 - 3.2 eV above from the normal incidence KRIPES spectra.
Inverse photoemission spectroscopy
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