Synchroton Radiation Research Articles

Angle-resolved photoemission study of Pd(110)

A clean Pd(110) surface has been studied with angle-resolved photoelectron spectroscopy using polarized synchroton radiation. Valence band dispersions were determined along the ΓKX symmetry line by assuming a free-electron final band with constant inner potential. The symmetries of the initial state valence bands were identified by the polarization selection rule. Normal emission spectra can be interpreted mainly in terms of free-electron primary cone emissions as well as secondary cone emission. Our experimental band plots agree with Christensen's calculation. However, there are some features which do not fit the free-electron final band approximation. Some possible interpretations are given for these features.

X-Ray CrKβ emission and K absorption spectra in mixed copper chromium oxides

The Kβ emission spectra of chromium in oxidic compounds were investigated by means of the fluorescent method. The origin of the main Kβ lines is discussed using MO theory and the dependence of the energy positions on the chemical bond is reported. The compounds studied include the oxides Cr 2O 3 CrO 2 and CrO 3, and the mixed copper chromium oxides CuCrO 2, CuCr 2O 4 and CuCrO 4. High-resolution chromium K-edge absorption spectra have been recorded using the synchroton radiation available at LURE (Orsay, France). The object of this investigation is to obtain further information about the chemical state analysis of chromium in catalysts: an evaluation of the atomic Cr(VI):Cr total ratio in Cu x Cr y O 4 catalysts is reported.

The secondary structure of turkey gizzard myosin light chain kinase and the nature of its interaction with calmodulin

The enzymatic activities of native myosin light chain kinases are subject to modification by interaction with Ca2(+)-calmodulin (CaM). The interaction between myosin light chain kinase isolated from turkey gizzard (tgMLCK) and calmodulin isolated from bovine testes (CaMbt) and wheat germ (CaMwg) has been examined by means of the intrinsic tryptophan fluorescence of tgMLCK and the fluorescence of extrinsic fluorescent labels located at Cys-27 and Tyr-139 of CaMwg and Tyr-99 of CaMbt. Static and dynamic fluorescence measurements provide evidence for the involvement of the former two sites in the zone of contact with lesser involvement of the site marked by the probe at Tyr-99. Complex formation protected the primary cleavage site in CaMbt (Lys-77) from proteolysis by trypsin. These results are consistent with involvement of the N- and C-terminal lobes of CaM in stabilization of the complex with tgMLCK, but cannot rule out participation of the connecting strand in the interaction. CD measurements extending to 175 nm, obtained using synchroton radiation, indicate the following secondary structure content for tgMLCK: 17 +/- 2% alpha-helix, 22 +/- 3% antiparallel beta-sheet, 3 +/- 1% parallel beta-sheet, 24 +/- 2% beta-turns, and 34 +/- 2% random coil. Similar measurements of the CD spectra of CaMbt and of the 1:1::CaMbt:tgMLCK complex presently indicate that neither protein undergoes major secondary structure rearrangement during their interaction, although subtle changes in the CD spectrum of tgMLCK appear to be correlated with the interaction with CaM.

A SUMMATION FORMULA FOR PRODUCTS OF ELECTRON RADIAL WAVE FUNCTION IN CONSTANT MAGNETIC FIELD

This paper generalizes the formula ∑nIns(v)Ins′(v)=δss′ to the case with two differentia v. Ins(v) is the radial wave function of an electron in a constant magnetic field. These results are very useful in synchroton radiation and astrophysics.

A Study of the Structural Stability of TiC, TiN and TiO in the Pressure Range up to 65 GPa Using Synchroton Radiation.

A Study of the Structural Stability of TiC, TiN and TiO in the Pressure Range up to 65 GPa Using Synchroton Radiation.

Photoelectron Spectroscopy of Solids ? VUV Band Structure Studies

The electronic band structure of solids, including states specific to the surface, may now be explored in very great detail by photoelectron spectroscopy. Variable energy photon sources (synchroton radiation sources) coupled with advanced angle resolving electron spectrometers permit access to emission from specific points within the complete Brillouin zone. The technique of band mapping has now reached a stage where the small k-dependent changes to individual valence bands due to the effects of introduced lattice strain can be observed, for example. The relative importance of emission from surface states, as opposed to bulk band states, can be demonstated dramatically using off-normal emission data. Angle resolved constant initial state spectroscopy has recently been shown to provide details of excited state bandstructure and has clarified the involvement of surface and bulk Umklapp scattering in the photoemission process. The above capabilities of photoelectron spectroscopy are discussed, using metallic and semiconducting examples, and are related to interface problems in general.

Measurement of the absolute value of mean energy of particles in collider beams

A method for the measurement of the absolute value of the mean energy of particles in collider using the angular and energy dependences of the synchroton radiation intensity distribution in the direction vertical to the orbit plane is described. The resolution calculated by this method for some colliders, acting or under construction, is about 10 −7 when 10 12 particles are accummulated and ionization chambers are used. The proposed method may also be used for p p beam energy measurements in supercolliders by means of the visible light of SR. The realizability of the method is discussed.

Spin-polarized angle-resolved UV photoelectron spectroscopy (SP-ARUPS) study of the electronic structure of disordered ferromagnetic Fe 0.65 Ni 0.35 Invar alloy

We report the first study of the electronic structure of a disordered ferromagnetic Fe-35Ni Invar alloy, using a combination of angle-, energy- and spin-resolved photoemission with synchroton radiation and self-consistent and spin-polarised KKR-CPA calculations. Direct comparison between photoemission spectra and calculated Bloch spectral functions shows that the majority spin features at 2.5, 0.9 and 0.2eV binding energy correspond to emission from Γ ↑25', Γ ↑12 and X↑ states respectively. In minority — spin EDC, a rather broad feature between E F and 1.3 eV below it is identified with a similar broad peak in the Bloch spectral function near the Γ-point. In general, the agreement between theory and experiment is found to be good.

Synchrotron radiation studies of defect structure evolution in aluminium during creep

Results are reported of in situ observations (using synchroton radiation) of the nonmonotonic evolution of the structural parameters of polycrystalline aluminium deformed under creep at intermediate temperatures. As an explanation of the experimental data, a theoretical model is proposed of dislocation ensemble transformation: chaotically distributed (in subgrain interiors) dislocations → sub-boundary dislocations.

X-ray assisted nitridation of silicon surface at ambient temperature

The reaction of Si (111) surface with chemisorbed NH 3 assisted by Synchroton Radiation (SR) is studied in detail with photoemission spectroscopy. In-situ ambient temperature nitridation is achieved and the promoting role of SR is demonstrated. The analysis of core-level spectra indicates that the film is close to stoichiometric, while valence band and partial yield spectra show the widening of the band gap. These enable us to generate the interface energy band diagram. Experiments performed with different photon energies indicate that the softer part of the SR spectrum is more efficient in promoting the reaction.

Microradiography of creep damage in copper

Abstract New advances in the radiographic technique have been made using high intensity synchroton radiation as the X-ray source. A 100-fold improvement in the resolution of the technique was realized, and features on the order of micrometers in size can now be routinely observed using “microradiography”. The resolution which can be achieved and the factors influencing resolution and sensitivity are discussed. We have applied microradiography to a study of the development of creep damage in metals. Notched samples of copper were subjected to high temperature, slow strain rate tensile testing, and the resulting creep damage in these samples was recorded using microradiography. The density and distribution of creep damage was measured from the radiographs using an image analysis system. The results from the image analysis can be compared to damage predictions obtained from finite element models of the damage process to determine the applicability of these models.

High pressure–high temperature research using high energy synchrotron radiation at the TRISTAN accumulation ring (invited)

High energy synchrotron radiation emitted from the bending magnet of the TRISTAN accumulation ring (6.5 GeV) at the National Laboratory for High Energy Physics has been used for the high pressure–high temperature diffraction experiments using a multianvil press system, MAX80. Owing to the specific features of high energy synchroton radiation, significant improvements have been brought to the high pressure research. The wide energy range of diffraction spectrum leads to an increase in the number of observable diffraction peaks in an energy-dispersive method, resulting in an increase in the accuracy of the measurements of the lattice and thermal parameters. Due to the high penetrating power of radiation, diffraction patterns can be taken in a short time from materials containing heavy elements or materials surrounded by a metal foil. Typical examples of high pressure–high temperature experiments with high energy synchrotron radiation are also described.

Fully scaled 0.5 μm MOS circuits by synchrotron radiation X-ray lithography: Devices fabrication and overlay evaluation

Functional NMOS and CMOS circuits with fully-scaled 0.5 μm ground rules have been fabricated using synchroton radiation X-ray lithography for all device levels. The exposures were done at the VUV storage ring of the National Synchrotron Light Source at Brookhaven National Laboratory using a mask/wafer aligner developed at IBM Research. The performance of the aligner on both test wafers and device wafers is discussed, with emphasis on overlay. Characteristics of the fabricated circuits are also presented.

X-ray mask repair by electron beam induced metal deposition

The electron beam induced metal deposition is a powerful technique to repair clear X-ray mask defects in the sub-μm range. The initial growth rate of dots deposited at 10 keV e-beam energy and 3 nA/μm 2 current density was 10 nm/sec. Dots of different heights were exposed to synchroton radiation. Dot growth times of 150 sec gave sufficient X-ray contrast for pattern transfer into HPR 204 resist. Mask repair is demonstrated on a test structure by closing clear defects and adding lines. The spatial resolution of deposited structures is ⩽ 500 nm with aspect ratios up to 6.

VUV-optical oscillator strength distributions of molecules and their implications to early events in radiation chemistry

Absolute photoabsorption cross sections of C 6H 12 isomers, i.e. cyclohexane, l-hexene, and tetramethylene, in the VUV region have been measured using synchroton radiation. The obtained cross sections of C 6H 12 isomers in this experiment together with those of C 2H 6O and C 3H 8O isomers, i.e. alcohols and ethers, in our previous paper have been analyzed and found to almost satisfy the Thomas-Kuhn-Reiche sum rule. Common new features of the oscillator strength distributions obtained from the photoabsorption cross sections have been found in each isomer group. These experimental results have been discussed with emphasis on their implications to early events in radiation chemistry, such as estimation of the energy deposition spectra of these molecules and the G value of the dissociation of superexcited states.

Interparticle interactions and structural changes of nucleosome core particles in low-salt solution

The structural behavior of the nucleosome core particles in the range of solvent Na+ concentration from 10.45 to 0.45 mM has been studied by small-angle neutron and synchroton radiation X-ray scattering, sedimentation, atomic absorption spectroscopy, density measurements, and circular dichroism. With decreasing salt concentration, the appearance of a scattering peak that is assignable to interparticle interactions, an intraparticle structural transition, a decrease in the sedimentation velocity of the particle, and a release of bound Na+ ions from the particle are all observed concurrently when the ratio of solvent Na+ ions per particle is below approximately 1000. These observations are interpreted to indicate that a release of bound Na+ ions from the particle brings about structural rearrangements and weakens the electrostatic shielding of the particle, and this introduces long-range repulsive ordering of the particle in low-salt solution. Analyses of the scattering data indicate that the rearrangement within the core particle in low-salt solution is slight, changing the particle's shape slightly from cylindrical to a more spherical form by moving the center of the mass of the DNA somewhat inward with accompanying small decreases in the radii of gyration of both the DNA and the histones.

ChemInform Abstract: Synthesis of TiNF and Determination of Its Structure by Powder Diffraction Using Synchroton Radiation.

AbstractThe title compound is prepared by ammonolysis of activated (via formation of a NH4Cl adduct and subsequent thermal decomposition) of (NH4)2TiF6.

Determination of Ca-As bonding at the CaF 2/GaAs interface

Surface-sensitive core levels are measured with synchroton radiation photoelectron spectroscopy (SRPES) to determine bonding properties at the epitaxial CaF 2/GaAs interface. It is found that Ca bonds to As at the interface, and that the dissociation reaction of CaF 2 takes place only on the GaAs(100) substrate. A structural model with a non-abrupt CaF 2/GaAs(100) interface is proposed based on these SRPES results. Differences in interfacial bonding properties between GaAs(100), (110), and (111) substrates are also discussed.

Synchrotron radiation photoemission spectroscopy of Ga-insulator interfaces for GaAs lateral epitaxial growth

The GaAs lateral-epitaxial growth mechanism on insulators is studied synchroton radiation photoemission spectroscopy on Ga-insulator interfaces. Interfacial reaction is compared with surface migration of deposited atoms and clusters. Surface sensitive PES results indicate that only Ga deposited on TiO 2 among Sm 2O 3, MgO, Al 2O 3 TiO 2, SiO 2 and Ta 2O 5 is heavily oxidized, and that interfacial TiO 2 is strongly reduced to Ti metal. The growth model is also discussed based on the chemically shifted PES peaks and TEM images of Ga islands. In comparison with the MOCVD GaAs lateral growth rate on these insulators, a close correlation of the surface migration rate of GaAs precipitates with the interfacial reactivity is obtained. A special surface treatment to decrease the surface oxygen on insulators is useful to diminish the Ga-insulator interaction.

Local structure around Ga and As doped in InP studied by fluorescence-detected EXAFS

Local structure around isoelectronic impurities (Ga:1.2×10 19 cm -3 , As:7.3 ×10 19 cm -3 ) doped in InP has been studied by fluorescencedetected extended x-ray absorption fine structure (EXAFS) using synchroton radiation. We find that the bond lengths of impurities in the dilute limit take values close to those in pure binary compounds, deviating from the interatomic distance of host lattice. Local distortion along the <111> direction gives rise to internal expansion or compression around impurities. Resulting structural disorder is discussed in relation to the local structure in (In, Ga)(As, P) quaternary alloys lattice-matched to InP.