Employing Synchrotron Radiation Research Articles

High-resolution X-ray mapping of CdZnTe detectors

Recently the use of micro-characterization techniques employing synchrotron radiation permitted identification of the deteriorating effects associated with tellurium (Te)-rich secondary phases existing in CdZnTe (CZT) radiation detectors. These randomly distributed microscopic defects behave as trapping regions, where an unpredictable number of charges are lost leading to significant fluctuations in the total collected charge. Consequently, they adversely affect the efficiency and energy resolution of CZT devices, and are found to be the dominant cause of performance degradation in thick detectors. Mapping of the detector response with synchrotron radiation can reveal the details of transport properties and charge collection efficiency in semiconductor detectors on a spatial scale never before realized. A new dedicated beam-line has been recently established at BNL's National Synchrotron Light Source (NSLS) for detector characterization; it will assist with systematic studies focused on improvement of detectors and crystal-growth techniques.

Characterization of residual stresses in turbine discs by neutron and high-energy X-ray diffraction and comparison to finite element modeling

Knowledge of the evolution of residual stresses developing during fabrication of industrial components is steadily gaining importance. In this paper, the prevailing residual stresses in hot-forged, water-quenched turbine discs made of the nickel-based superalloy IN718 have been studied by neutron diffraction. Simultaneously, independent simulations using a finite element model (FE) have been performed. For a deeper examination of the studied component, the material and the simulation, a smaller model plate of the same alloy was measured as well. Furthermore, an in situ tensile test, employing synchrotron radiation, has been carried out to study the deformation behavior of the different reflections. The results show that the simulation gives a good description of the residual stress distribution in the turbine disc while the agreement is less satisfactory for the smaller plate. The tensile tests confirm that the (3 1 1) reflection gives a good measure for the macrostress in the studied material.

Observation of perturbed3snpdouble photoexcited Ryberg series of beryllium atoms

We observed the $3snp$ autoionizing Rydberg series of the Be atom in order to investigate the double-photoexcitation processes in two-$s$-electron systems. We employed synchrotron radiation to photoexcite the Be atoms and measured the generated ${\mathrm{Be}}^{+}$ photoions by the time-of-flight method. The $3snp$ $(n=3\text{--9})$ photoexcitation resonance peaks with interloper state of $3p4s$ that converges to ${\mathrm{Be}}^{+}(3p)$ threshold were observed. We derived the resonance parameters of $3snp$ series from a fitting procedure and obtained the Fano parameter $q$, energy position ${E}_{0}$, and resonance width $\ensuremath{\Gamma}$. These parameters are in good agreement with theoretical values. In the vicinity of the $3s5p$ state these experimental results clearly revealed the influence of the interloper $3p4s$ state, and the comparison with the numerical calculations indicates that more detailed calculations might be required to fully explain this phenomenon.

Spectroscopic ellipsometry and reflectance anisotropy spectroscopy of biomolecular layers on silicon surfaces

AbstractThe optical properties of the DNA bases deposited on flat and vicinal, hydrogen passivated Si(111) substrates are studied using spectroscopic ellipsometry (SE) up to 9.5 eV photon energy employing synchrotron radiation and reflectance anisotropy spectroscopy (RAS). The results for the dielectric function reveal strong optical anisotropy for adenine and guanine while the other two molecules form layers with isotropic properties. The experimentally derived dielectric functions are compared to density functional theory calculations of the optical response. Particularly interesting is the RAS response of the DNA bases as a function of thickness when deposited on vicinal Si surfaces. Ordering in the layers is induced by the step and terrace structure of the vicinal Si substrates. Even though the molecular structure is not dramatically different the RAS response is very distinct and allows an unambiguous identification of the bases. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Non-isothermal crystallization of a vinyl alcohol–ethylene copolymer studied by DSC and real time WAXS/SAXS scattering

Time resolved SAXS/WAXS experiments, employing synchrotron radiation, together with DSC studies have been carried out on a vinyl alcohol–ethylene copolymer in order to clarify the morphological changes occurring during the non-isothermal crystallization of that copolymer from the melt. It was found that the SAXS long spacing and the WAXS diffraction peaks appear at the same temperature, revealing that the predominant growth mechanism of this process is nucleation and crystal growth but not density fluctuations. Moreover, the temperature variation of different structural parameters (peaks intensity, degree of crystallinity, long period, lamellar thickness) was comprehensively analyzed. Three temperature intervals are observed in this analysis, which have been interpreted as ‘high-temperature crystallization’, ‘low temperature crystallization’ and sub-glass region in order of decreasing temperatures.

Electronic structure of tris(8-hydroxyquinolato) aluminum at room temperature and during annealing

We have employed synchrotron radiation photoemission to investigate the electronic structure of tris(8-hydroxyquinolato) aluminum $({\mathrm{Alq}}_{3})$ at room temperature as well as at elevated temperatures. The dependence of the molecular state cross sections on the photon energy is demonstrated. Three chemical environments of carbon are resolved, accompanied with at least two shake-up satellite structures. Small loss structures are detected in other N $1s$, O $1s$, and Al $2p$ core-level spectra, but with various magnitudes. Annealing produces charge redistribution of the molecular states within ${\mathrm{Alq}}_{3}$ itself. ${\mathrm{Alq}}_{3}$ is stable at high temperature.

Sub-nanosecond resolution x-ray magnetic circular dichroism photoemission electronmicroscopy of magnetization processes in a permalloy ring

Fast magnetization processes in a microstructured permalloy ring with80 µm o.d. and 30 nm thickness have been observed by photoemission electron microscopyexploiting x-ray magnetic circular dichroism as the magnetic contrast mechanism.As a high speed probe we employed synchrotron radiation pulses at the ESRF(Grenoble) operated in 16-bunch mode, yielding photon pulses of 105 ps FWHM witha period of 176 ns. Fast magnetic field pulses have been generated by means ofcurrent pulses through coplanar waveguides with the magnetic structure beinglithographically prepared on their surface. A stroboscopic pump–probe set-up witha variable time delay between the field pulse and photon pulse allowed us totake snapshots of the dynamic response of the magnetic domain structure. Weobserved coherent magnetization rotation during the leading edge part of the fieldpulse, the formation of a characteristic domain pattern (‘onion state’) in theplateau region of the pulse and the fast formation of a striped domain pattern(incoherent magnetization rotation) during the trailing edge part of the field pulse. Anumerical simulation confirmed essential features of the stroboscopic image series.

Highly Ordered “Defect-Free” Self-Assembled Hybrid Films with a Tetragonal Mesostructure

One-pot self-assembled hybrid films were synthesized by the cohydrolysis of methyltriethoxysilane and tetraethoxysilane and deposited via dip-coating. The films show a high "defect-free" mesophase organization that extends throughout the film thickness and for domains of a micrometer scale, as shown by scanning transmission electron microscopy. We have defined these films defect-free to describe the high degree of order that is achieved without defects in the pore organization, such as dislocations of pores or stacking faults. A novel mesophase, which is tetragonal I4/mmm (space group), is observed in the films. This phase evolves but retains the same symmetry throughout a wide range of temperatures of calcination. The thermal stability and the structural changes as a function of the calcination temperature have been studied by small-angle X-ray scattering, scanning transmission electron microscopy, and Fourier transform infrared spectroscopy. In situ Fourier transform infrared spectroscopy employing synchrotron radiation has been used to study the kinetics of film formation during the deposition. The experiments have shown that the slower kinetics of silica species can explain the high degree of organization of the mesostructure.

Physics and chemistry during the deposition and oxidation of ultrathin Mg overlayer on GaAs(1 0 0) surface

The interaction of active Mg metal with GaAs(1 0 0) surface as well as the oxidation of Mg ultrathin film were studied employing synchrotron radiation photoemission (SRPES) technique. Interfacial reaction was obviously observed through the energy shifts of Mg2p, Ga3d and As3d levels. The resulted Mg ultrathin film was easily and completely oxidized on exposure of oxygen indicating its polycrystalline nature and high sensitivity to oxygen. A model of Mg/GaAs(1 0 0) interface is proposed and the physical and chemical phenomena during the deposition and oxidation of Mg ultrathin film were discussed.

Surface and interface structure of Nd 1.2Ba 1.8Cu 3O y epitaxial films studied by grazing incidence X-ray diffraction

High quality, very flat Nd 1.2Ba 1.8Cu 3O y thin films have been grown by sputtering on TiO 2 terminated SrTiO 3 (100) single crystals and their surface structure have been determined by using Grazing Incidence X-ray Diffraction (GIXD) technique, employing synchrotron radiation. A 52 unit cells film presents a double terminated surface composed by a complete and ordered Cu(1)–O plane and a disordered Cu(1)–O plane partially covered by a BaO layer, in full agreement with scanning tunneling microscopy data. A preliminary comparison between the structure of 8 and 52 u.c. NdBCO films will be presented.

Optical and structural properties of CVD-grown single crystal SiO 2 using optically detected XAS

Using a new method of low-temperature CVD preparation, very high quality single-crystal quartz can be grown at rates of up to 3 μm h −1. By employing synchrotron radiation methods, the optical and structural properties of these crystals can be interlinked and they are compared with those of high quality hydrothermally grown material. The luminescence excitation spectra, which are very sensitive to the quality of the material, are assessed for both band edge (excitonic) and core level Si L-edge excitations. For the most part, the optical and structural properties of the two types of sample are indistinguishable, verifying the high quality of the material grown by the new method. The only source of difference arises from a weak red luminescence band, thought to originate from NBOHC defects: in CVD material, the L-edges derived from this band reveal some degree of local lattice disorder.

Analysis of the surface termination ofNd1+xBa2−xCu3Oythin films

High quality, very flat ${\mathrm{Nd}}_{1+x}{\mathrm{Ba}}_{2\ensuremath{-}x}{\mathrm{Cu}}_{3}{\mathrm{O}}_{y}$ films have been grown by sputtering and analyzed by low energy electron diffraction, scanning tunneling microscopy (STM) and grazing incidence x-ray diffraction (GIXD) employing synchrotron radiation, in order to investigate the surface structure and morphology. The refinement of the GIXD data has been performed on the basis of structural models sensitive to the nature of the terminating layer. The interpretation of the results provides a picture of the surface structure that is in full agreement with STM results. The surface is composed by two terraces with different termination, one of which is an ordered and complete Cu(1)-O layer and the other an incomplete BaO layer that partially covers a disordered Cu(1)-O layer. Atomic vacancies and steps bounding terraces with a height of about $0.4\phantom{\rule{0.3em}{0ex}}\mathrm{nm}$, are present on the surface.

Surface-charge polarization effect at an organic and inorganic contact: Case study of tris(8-hydroxyquinolato) aluminum on Si(001)-2×1

We have employed synchrotron radiation photoemission to investigate the tris(8-hydroxyquinolato) aluminum (Alq3) molecules adsorbed on an inorganic Si(001)-2×1 surface at room temperature. The surface-related valence states associated with the dimers and backbonds lying a couple of eV below the Fermi level reduce in strength upon Alq3 adsorption, indicating that the organic molecules not only passivate the dangling bonds but also rupture the dimer bonds. The wave function of the surface dangling bonds and of the pyridyl side of an 8-quinolinol ligand overlaps greatly so that charge is polarized toward the organic adlayer, resulting in the appearance of low-energy components in both N 1s and C 1s core-level spectra, which is similar to the case of Mg-doped Alq3. However, the polarization diminishes at greater coverage, in which case both 1s cores behave as in the nominal states.

THz near-field imaging employing synchrotron radiation

Terahertz scanning near-field infrared microscopy below 1 THz is demonstrated at an electron storage ring using coherent synchrotron radiation. Spatial resolution below the diffraction limit down to about λ/40 at 2 cm−1 is derived from the transmittance spectra of a conical aperture probe. The potential of the technique is exemplified by imaging wet biological samples. Strongly absorbing living leaves have been imaged in transmittance with a spatial resolution of 130 μm at about 12 cm−1. The THz near-field images reveal distinct structural differences in the mesophytic and xerophytic leaves investigated.

Structure and Phase Transitions of Poly(heptamethylene p,p‘-bibenzoate) As Studied by DSC and Real-Time SAXS/MAXS Employing Synchrotron Radiation

The structure and phase transitions of liquid-crystalline poly(heptamethylene p,p'bibenzoate) have been studied by DSC and variable-temperature real-time SAXS/MAXS employing synchrotron radiation. It was suggested that three-dimensional crystal order appeared within the smectic domains during cooling the sample because the crystal correlation length is nearly the same as that of the smectic domains. These estimated domain sizes are of the order of the average macromolecular chain length, so that it seems that no chain folding exists in the present case. It was found that SAXS intensity in Porod's region obeys the power law, and it deviates significantly from Porod's law. These deviations were explained by an assumption of anisotropic density fluctuations within the phases. It was supposed that the melting process is ruled by an increasing quantity of anisotropic fluctuations within the crystallites but not by surface melting.

Isothermal crystallisation of iPP/Vectra blends by DSC and simultaneous SAXS and WAXS measurements employing synchrotron radiation

The isothermal crystallisation behaviour and morphology of blends of isotactic polypropylene, iPP, and a liquid crystal polymer, Vectra A950, has been studied using differential scanning calorimetry, optical microscopy and simultaneous WAXS and SAXS in real-time measurements using synchrotron radiation. It has been observed that Vectra domains act as sites for the nucleation of iPP, and the rate of crystallisation is enhanced with increasing Vectra content in the blend. The presence of the α crystalline form in pure iPP, and both α and β forms for iPP in iPP/Vectra blends has been found. The SAXS patterns for iPP/Vectra blends containing β iPP are characterized by two different long period values that were related to the α and β lamellae. The secondary crystallisation mechanism has been investigated by SAXS/WAXS experiments. It is shown that, in contrast to primary crystallisation, secondary crystallisation of iPP is not affected by the presence of the thermotropic liquid crystalline polymer. As already known from pure iPP, the main process of secondary crystallisation is the growth of new lamellar stacks within remaining amorphous regions in the iPP spherulites.

A Novel Instrumentation for Contamination and Deposition Control on 300 mm Silicon Wafers Employing Synchrotron Radiation Based TXRF and EDXRF Analysis

A Novel Instrumentation for Contamination and Deposition Control on 300 mm Silicon Wafers Employing Synchrotron Radiation Based TXRF and EDXRF Analysis

Valence states of poly(3-hexyl-thiophene) as probed by photoelectron spectra at resonant excitation

Photoelectron spectroscopy employing synchrotron radiation is applied to learn about the electronic structure of regio-regular poly(3-hexyl-thiophene) (P3hT). We study the valence band photoelectron spectra around the carbon 1s threshold. This technique is equivalent to resonant excitation of core electrons into empty valence states. We probe the properties of these carriers in the conduction band and also learn about valence band states involved in the carbon (K L L) Auger transitions. The data give evidence that monomeric orbital energies are dominating in such processes. We conclude that poly(3-hexyl-thiophene) is a polymer with a rather short conjugation length.

Photoemission study of CaF2 on Si(001)-2×1 during annealing

We have employed synchrotron radiation photoemission to investigate calcium fluoride deposited on Si(001)-2×1 annealed at 700°C. The valence band spectra reveal that the initial molecules are dissociated to single Ca atoms resting on the surface. Si 2p core-level spectra manifest a negatively shifted Ca-induced line at 0.35eV. The dissociated Ca atoms occupy only half of the surface, on top of which the CaF2 molecules commence growth. This is in contrast to the Si(111)-7×7 counterpart, which exhibits a CaF layer in the interface. Strong elastic scattering due to the absorbed Ca atoms is evident in the photoemission spectra, thus averaging out the angle-dependent features.

Crystallization kinetics of copoly(ester imide)s derived from PBT, trimellitic anhydride, and aliphatic diamines

The crystallization kinetics of copoly(ester imide)s based on poly(butylene terephthalate) (PBT), trimellitic anhydride, and diaminobutane (PEI-4), resp. diaminohexane (PEI-6) or diaminoethane (PEI-2) are investigated by means of time-resolved x-ray scattering employing synchrotron radiation. The PEI-4 and PEI-6 copolymers exhibit a remarkably high degree of crystallinity, which can be attributed to the formation of mixed crystals in the co-PEI-4 and to blockiness in the case of co-PEI-6. Whereas the pure PEI-4 forms large negatively birefringent spherulites, the co-PEI-4 and the PEI-6 homo- and copolymers form much smaller superstructures like axialites or ellipsoids. In the co-PEI-4 and co-PEI-6, the rate of crystallization is slower compared to the homopolymers due to the incorporation of the respective comonomer unit. The PEI-4 forms a second crystal modification upon drawing and subsequent crystallization, probably with a monoclinic unit cell. The PEI-6 crystallizes faster than PEI-4 due to the improved flexibility of the longer diamine component. In contrast, the crystallization of PEI-2 and its copolymers takes several hours and the equimolar co-PEI-2 remains completely amorphous.