Observation of Strong Resonant Behavior in the Inverse Photoelectron Spectroscopy of Ce Oxide
X-ray Emission Spectroscopy (XES) and Resonant Inverse Photoelectron Spectroscopy (RIPES) have been used to investigate the photon emission associated with the Ce3d5/2 and Ce3d3/2 thresholds. Strong resonant behavior has been observed in the RIPES of Ce Oxide near the 5/2 and 3/2 edges. Inverse Photoelectron Spectroscopy (IPES) and its high energy variant, Bremstrahlung Isochromat Spectroscopy (BIS), are powerful techniques that permit a direct interrogation of the low-lying unoccupied electronic structure of a variety of materials. Despite being handicapped by counting rates that are approximately four orders of magnitude less that the corresponding electron spectroscopies (Photoelectron Spectroscopy, PES, and X-ray Photoelectron Spectroscopy, XPS) both IPES and BIS have a long history of important contributions. Over time, an additional variant of this technique has appeared, where the kinetic energy (KE) of the incoming electron and photon energy (hv) of the emitted electron are roughly the same magnitude as the binding energy of a core level of the material in question. Under these circumstances and in analogy to Resonant Photoelectron Spectroscopy, a cross section resonance can occur, giving rise to Resonant Inverse Photoelectron Spectroscopy or RIPES. Here, we report the observation of RIPES in an f electron system, specifically the at the 3d{sub 5/2} and 3d{sub 3/2} thresholds of Ce Oxide. The resonant behavior of the Ce4f structure at the 3d thresholds has been addressed before, including studies of the utilization of the technique as a probe of electron correlation in a variety of Ce compounds. Interestingly, the first RIPES work on rare earths dates back to 1974, although under conditions which left the state of the surface and near surface regions undefined. Although they did not use the more modern terminology of 'RIPES,' it is clear that RIPES was actually first performed in 1974 by Liefeld, Burr and Chamberlain on both La and Ce based materials. In these experiments, the La and Ce metallic samples were attached to the anode of an x-ray tube and the x-ray emission characteristics were measured using a two crystal monochromator. The pressure in the x-ray tube was quoted as being below 2 x 10{sup -8} Torr. They did indeed observed resonant behavior at the M{alpha} (3d{sub 5/2}) and M{beta} (3d{sub 3/2}) thresholds. In fact, our results here will confirm the measurements made upon the Ce based sample used in by Liefeld et al. However, the state of the Ce sample surface and near surface regions are quite undefined in the study in Ref 9. For example, the authors suggest that they are probing Ce metal, since they cannot see any evidence of an OK{alpha} (1s) XES line. However, they do report the observation of FK{alpha} (1s) line, possibly due to the utilization of cerium fluoride in the sample preparation. Later, they tried to address these issues in a new ultrahigh vacuum system. Based upon our results, it is clear that their original sample surface was oxidized, using the word here in its more general context as in having lost electrons to the oxidizing agent, although whether the structure is an oxide or fluoride remains unclear. In any case, the primacy of Liefeld and coworkers in these measurements should be noted. Cerium and cerium oxide have been studied with a variety of spectroscopic techniques under UHV conditions. This includes Bremstrahlung Isochromat Spectroscopy or BIS, Photoelectron Spectroscopy, X-ray Absorption Spectroscopy, Electron Energy Loss Spectroscopy and Resonant XES, to name just a few. We will compare our results to those of other spectroscopies.
- Research Organization:
- Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
- Sponsoring Organization:
- USDOE
- DOE Contract Number:
- W-7405-ENG-48
- OSTI ID:
- 1020331
- Report Number(s):
- LLNL-JRNL-421685; TRN: US201116%%264
- Journal Information:
- Physical Review. B, Condensed Matter and Materials Physics, Vol. 83; ISSN 1098-0121
- Country of Publication:
- United States
- Language:
- English
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ABSORPTION SPECTROSCOPY
BINDING ENERGY
CERIUM
CERIUM FLUORIDES
CERIUM OXIDES
COUNTING RATES
CROSS SECTIONS
ELECTRON CORRELATION
ELECTRONIC STRUCTURE
EMISSION SPECTROSCOPY
ENERGY-LOSS SPECTROSCOPY
KINETIC ENERGY
OXIDES
OXIDIZERS
PHOTOELECTRON SPECTROSCOPY
PHOTON EMISSION
RARE EARTHS
SAMPLE PREPARATION
SPECTROSCOPY
X-RAY PHOTOELECTRON SPECTROSCOPY
X-RAY TUBES