M. Uda

Chemical effects in PIXE spectra

Abstract PIXE spectra were recorded with the aid of a crystal monochromator. The most prominent change of the X-ray spectra with fine structure was observed on the intensity distributions of satellite lines emitted from atoms embedded in different chemical environments. As the origin of such a change in the satellite structures, two fundamental causes can be considered. The first one is change in the ionization cross section of the atom of interest for the multiply ionized states. The second is reconstruction of the molecular orbitals, especially in the outermost electronic shell, after an inner-shell ionization but before a characteristic X-ray emission. PIXE is promising for studying bond natures of atoms, as well as for microanalysis.

Yellow, red and blue pigments from ancient Egyptian palace painted walls

Yellow, red and blue pigments from the painted walls of the Malqata palace, founded by Amenhotep III, 18th Dynasty, were analyzed using PIXE and X-ray diAraction (XRD). From most of the yellow, red and blue parts, goethite, hematite and Egyptian blue, respectively, were found on the basis of diAractometry results. From some yellow parts, As was detected together with Fe spectroscopically, suggesting the use of orpiment as a yellow pigment. The red pigment seems to be natural and not man-made. This assumption is deduced from the dehydration experiment of a synthesized goethite. ” 2000 Elsevier Science B.V. All rights reserved.

An attempt to diagnose cancer by PIXE

Abstract PIXE is suitable especially for trace elemental analysis for atoms with high atomic numbers, which are contained in matrices composed mainly of light elements such as biological materials. An attempt has been made to distinguish elemental concentrations of cancer tissues from those of normal ones. Kidney, testis and urinary bladder cancer tissues were examined by PIXE. Key elements to diagnose these cancers were Ca, Ti, Cr, Fe and Zn. Enrichment of Fe and Ti, and deficiency of Zn could be seen in the kidney cancer. An opposite tendency was observed in the testicular cancer. Imbalance of these elemental concentrations in characteristic organs might give us a possibility for cancer diagnosis.

Structural Correlation among Different Phases in the Initial Stage of Epitaxial Growth of Au on Si(111)

Structures created on the Si(111) substrate in the presence of Au atoms corresponding to coverages (θ; Au) of ~0.7–1.4 monolayers (ML) are discussed on the basis of the observed scanning tunneling microscopy images. At small θ; Aus ( ~0.7–1.0 ML), a √3×√3 phase and a less-ordered phase coexist, the fractional area of the latter being increased with increasing θ; Au, and at larger θ; Aus (\stackrel>~ 1.1 ML), a 6×6 phase appears as a single phase, in agreement with previous reports. It is shown that the less-ordered phase coexisting with the √3×√3 phase already has a close relation to the 6×6 phase in structure. The most fundamental structure of the 6×6 phase is seen at a large θ; Au of ~1.4 ML, in which a layer of Au atoms sits on the Si(111) substrate incommensurately. As θ; Au decreases, some Au atoms appears to be removed with a periodicity of 6×6. The Au coverage of the √3×√3 phase seems to be ~2/3 ML.

Amarna blue painted on ancient Egyptian pottery

Abstract “Amarna blue” pigments (18 Dynasty, c. 1400 BC) painted on pottery fragments were investigated using the PIXE, XRF and XRD methods in laboratories and also using a portable type of X-ray spectrometer at the sites of excavation. On the blue-colored part enrichment of Na, Al, S, Cl, Ca, Mn, Co, Ni and Zn was found using X-ray spectroscopy, and CaSO4, NaCl and Co(M)Al2O4, M denoting Mn, Fe, Ni and Zn, were found by the help of X-ray diffraction. This means that Amarna blue is a mixture of CaSO4 and Co(M)Al2O4, at least in part.

Near edge structures of Mg-, Co-, Cu- and Zn-tetraphenylporphyrins measured by PESA and calculated with DV-Xα

Abstract The near-edge electronic structures of several tetraphenylprophyrins (TPPs), modified by substituting the central metal atoms (M), were measured using photoelectron spectroscopy in air (PESA), and were estimated using the DV-Xα molecular orbital calculation method. The metal atoms used were Mg, Co, Cu and Zn. The ionization thresholds and the photoelectron emission yields of these TPPs changed significantly from compound to compound. The thresholds for ionization or photoemission can be divided into two groups, i.e. 1) less than 5.26 eV for Mg II TPP and Zn II TPP, and 2) more than 5.38 eV for Co II TPP and Cu II TPP. DV-Xα calculations demonstrated that the upper valence band primarily consists of C2p in Mg II TPP and Zn II TPP, M3d in Co II TPP, and M3d and N2p in Cu II TPP. Such valence band components can be used to explain the difference in observed photoemission threshold energies and to elucidate the change in photoemission yields for electrons with low kinetic energy.

Application of the external PIXE analysis to ancient Egyptian objects

Mural paintings with ∼20 × 25cm2 in size excavated in Egypt were analyzed by the external PIXE technique. Colored layers were stacked with white, yellow, red and black pigments in sequence, which were composed of Mg3Ca(CO3)4 (white), αFeO·OH and As2S3 (yellow), αFe2O3 (red) and soot (black), respectively. A single particle of As2S3 was also found from the yellow colored part, which glinted in the sun. A thin paraffin layer did not disturb the PIXE analysis, which was a part of reinforcement materials for ancient remains and was flowed out from a back side to a surface region.

Initial stage of room temperature reaction at Ni/Si(111)–H interfaces

Abstract The formation of the Ni/Si interface was investigated by using molecular beam epitaxy to deposit Ni on hydrogen-terminated Si(111) surfaces at room temperature. Reflection high-energy electron diffraction observations showed that a sample on which 0.8-nm-thick Ni had been deposited shows the same 1×1 streak pattern that the original hydrogen-terminated Si surface did. And X-ray photoelectron spectroscopy measurements of the Si 2 p core-level showed that all the hydrogen atoms terminating the original Si surface are still there after the Ni deposition. This indicated that the Ni atoms diffused beneath the Si surface without breaking the surface Si–Si bonds. It thus seems that hydrogen atoms terminating the Si surface dangling bonds suppress the silicide reaction at room temperature.

PIXE AND PIXE-INDUCED XRF FOR CHEMICAL SPECIFICATION

Abstract Wavelength dispersive X-ray spectra with fine structures in the PIXE and PIXE-induced XRF spectra have been proved to be very much useful for chemical specification of condensed matters. The fine structures have been reproduced theoretically by introducing molecular orbital calculations, the shake-off and resonant orbital rearrangement (ROR) processes, together with the direct Coulomb interaction between projectiles and target atoms, and the self-absorption of emitted X-rays through the targets. Comparison between observed and theoretical spectra is given here for F and S atoms.

Resonant Orbital Rearrangement During F 1s Ionization or Decay Process

Abstract A new concept, a resonant orbital rearrangement ROR, has been introduced to explain an anomalously weak intensity of F Kα X-ray emitted from a K 1 L 1 doubly ionized state and an unassigned M peak in KVV Auger spectra of KF. ROR has been used for explaining resonance between HOMO at K 0 L 0 and LUMO at K 1 L 0 states during F 1s ionization or X-ray and Auger decay processes, where K m L n denotes m and n vacancies on K and L shells, respectively. Molecular orbitals describing the K m L n state were calculated by the DV-X α method. Ionization cross sections, F Kα X-ray energies and X-ray transition probabilities were calculated using the semi-classical approximations (SCA), the Slaters transition state method and the dipole approximation, respectively. In the present study we found excellent linearities between ROR probabilities and the M line intensities, and between fluorescence yields for a K 1 L 1 doubly ionized state and relative X-ray intensities of (K 1 L 1 /K 1 L 0 ). Here X-ray and Auger emission spectra were studied, which were emitted from the alkali-metal fluorides, i.e. NaF, KF, RbF and CsF. All the intensities of F Kα X-rays and KVV Auger electrons have successfully been explained for the first time.