High-precision X-ray Research Articles

High-precision soft x-ray polarimeter at Diamond Light Source

The development and performance of a high-precision polarimeter for the polarization analysis in the soft x-ray region is presented. This versatile, high-vacuum compatible instrument is supported on a hexapod to simplify the alignment with a resolution less than 5 μrad, and can be moved with its own independent control system easily between different beamlines and synchrotron facilities. The polarimeter can also be used for the characterization of reflection and transmission properties of optical elements. A W/B(4)C multilayer phase retarder was used to characterize the polarization state up to 1200 eV. A fast and accurate alignment procedure was developed, and complete polarization analysis of the APPLE II undulator at 712 eV has been performed.

Chemical composition of melanosomes, lipofuscin and melanolipofuscin granules of human RPE tissues

Energy-filtered analytical transmission electron microscopy was used to image the ultrastructure and determine quantitatively the chemical composition of pigment granules of the choroid and retinal pigment epithelium of two healthy human donors, aged 68 and 85 years. The electron microscopy preparation procedure did not affect the autofluorescence of melanolipofuscin and lipofuscin granules, since staining was omitted during sample preparation. Oval melanosomes, melanolipofuscin and lipofuscin granules were observed, having sizes of about 1.5 μm × 0.5 μm, and were analyzed using energy-dispersive X-ray microanalysis and electron energy loss spectroscopy. Up to now, these pigments could only be identified by scattering contrast in bright field images, with melanosomes having dark contrast and lipofuscin being much brighter. High-precision energy-dispersive X-ray microanalysis of pigment granules (>15,000 integrated counts in the oxygen K α peak) yielded minimum detectable mole fractions of about 0.02 at% for copper and zinc. For the first time, quantitative analytical electron microscopy yielded the chemical composition of the different pigments without prior isolation from the tissue. This is important to better understand physical and chemical properties of the pigments and their metabolism and turnover. The composition of melanosomes and lipofuscin can clearly be distinguished by the applied methods. Melanosomes were the pigments with largest oxygen (about 5 at%) and nitrogen (about 10 at%) mole fractions. The S/N ratio determination demonstrated a high pheomelanin content of the melanosomes. Lipofuscin had a significantly smaller oxygen mole fraction (about 4 at%) and nitrogen was found to be only slightly above the limit of detection (0.4 at%). For comparison, the cytoplasm contained oxygen and nitrogen mole fractions of 3 at% and 0.8 at%. Bright field images showed melanolipofuscin granules having a core-shell structure with a dark inner and a bright outer fraction. The dark fraction had a chemical composition close to the melanosomes and the composition of the bright fraction could be distinguished from that of lipofuscin due to a significantly increased nitrogen mole fraction in the melanolipofuscin granule. For all pigments observed the oxygen mole fraction yielded a positive correlation with the calcium mole fraction as previously established for melanosomes. Only lipofuscin contained measurable phosphorus mole fractions, which also correlated positively with oxygen. In lipofuscin, mole fractions of nitrogen were significantly smaller than in melanosomes and only indicated a small fraction of proteins. In contrast, the phosphorus mole fraction was significantly larger indicating the presence of significant amounts of phospholipids. Copper and zinc mole fractions were larger than 0.1 at% in the melanosomes, but were below the detection limit in the lipofuscin granules. Compared to melanosomes of monkeys and rats analyzed beforehand, human retinal pigment epithelium melanosomes contained the highest amount of zinc, which even exceeded the calcium mole fraction. Trace elements like zinc are of great importance for metabolism and anti-oxidative mechanisms and also play a role in the progression of age related macular degeneration. They can now be investigated by quantitative analytical electron microscopy.

On the atomic structure of Zr–Ni and Zr–Ni–Al metallic glasses

Using real space pair distribution functions derived from high precision x-ray diffraction data, the local atomic structure of Zr–Ni and Zr–Ni–Al metallic glasses was investigated. Unlike Zr–Cu metallic glasses, the structure of Zr–Ni metallic glasses cannot be approached with an ideal solution model, due to strong attractive interactions between Zr and Ni atoms, which promote chemical short range order. Addition of Al can be beneficial for the glass forming ability of Zr–Ni metallic glasses. The atomic size of Al, being intermediate to those of Zr and Ni and the strongly attractive interactions between Zr–Al and Zr–Ni atoms can lead to highly negative volumes of mixing ΔVmix, and to denser atomic structures, reduced atomic mobility in the liquid and easier suppression of crystallization in the undercooled liquid state

Fabrication of high precision X-ray mask for X-ray grating of X-ray Talbot interferometer

X-ray imaging is used in many applications such as medical diagnosis and non-destructive inspection, and has become an essential technologies in these areas. In one image technique, X-ray phase information is obtained using X-ray Talbot interferometer, for which X-ray diffraction gratings are required; however, the manufacture of fine, highly accurate, and high aspect ratio gratings is very difficult. X-ray lithography could be used to fabricate structures with high precision since it uses highly directive syncrotron radiation. Therefore, we decided to fabricate X-ray gratings using X-ray lithography technique. The accuracy of the fabricated structure depends largely on the accuracy of the X-ray mask used. In our research, we combined deep silicon dry etching technology with ultraviolet lithography in order to fabricate untapered and high precision X-ray masks containing rectangular patterns. We succeeded in fabricating an X-ray mask with a pitch of 5.3 μm. The thickness of the Au absorber was about 5 μm, and the effective area was 60 × 60 mm2, which is a sufficient size for phase tomography imaging. We demonstrated the utility of the Si dry etching process for making high precision X-ray masks.

The system uranium–palladium–boron withU2.5Pd20.5B6, a new heavy fermion compound

Phase equilibria in the system U–Pd–B were established at850 °C by light optical microscopy (LOM) and x-ray powder and single crystaldiffraction. Whereas in as-cast alloys only one ternary compound,τ1-U2 + xPd21 − xB6, was found to format x ∼ 0.5, a furthercompound τ2 with hitherto unknown structure was observed in alloys annealed at850 °C.Due to the formation of suitable single crystals, the crystal structures of two binary compounds,UB12 andUPd3 have been redetermined from high precision x-ray data. Similarly, the crystal structure ofτ1-U2.5Pd20.5B6 was investigated by single crystal x-ray diffraction (XRD) revealing isotypism with theCr23C6-type, (space group ; a = 1.1687(5) nm; RF2 = Σ|F02 − Fc2|/ΣF02 = 0.021). τ1-U2 + xPd21 − xB6 is a partially orderedcompound where 0.37(1)U + 0.63Pd atoms randomly share the 4a site in (0, 0, 0). Whereas mutual solubility of U-borides and Pd-borides wasfound at 850 °C to be below 1.0 at.%, a large homogeneity region of fcc-Pd(U, B) extends into the ternary system.U2.5Pd20.5B6 has metallic behavior; the ground state properties are determined from a balance of theKondo effect and the Ruderman–Kittel–Kasuya–Yosida (RKKY) interaction, revealing longrange antiferromagnetic ordering below 6 K. An extraordinarily large Sommerfeld value (γ > 500 mJ mol − 1 K − 2) groupsU2.5Pd20.5B6 among heavy fermion materials.

Glass formation in the Nb–Si binary system

Nb 81.3Si 18.7 ribbons were prepared by rapid quenching of the liquid on a rotating copper wheel using various values of rotating speed. It was found that the melt spun ribbons consisted of an amorphous matrix; however the critical cooling rate for the formation of fully amorphous ribbons was achieved at rather high values of wheel speed. Crystallization occurs upon annealing above 971 K. The Vickers hardness of the amorphous ribbons was found to be 915 HV, an unusually high value for a binary alloy. The atomic structure of the amorphous Nb–Si alloy was studied using real space pair distribution (PDF)/radial distribution functions (RDF) derived from high precision X-ray diffraction data acquired with high-energy, monochromatic synchrotron light in transmission.

Observation of subtle dynamic transitions by a combination of neutron scattering, X-ray diffraction and DSC: A case study of the monoclinic l-cysteine

The paper illustrates the benefit of combining several experimental techniques (incoherent elastic and inelastic neutron scattering, DSC, and X-ray diffraction) to study subtle dynamic transitions in a biologically important system, probing a broad time (frequency) range of the molecular motions in a wide temperature interval of 2–300 K. As a case study the crystalline form (a monoclinic polymorph) of l-cysteine ( +NH 3–CH(CH 2SH)–COO −) — an essential amino acid — has been selected. Crystals of amino acids are widely used to mimic important structural and dynamic features of peptides. The conformational lability of cysteine and the dynamics of the thiol-side chains are known to account for various phase transitions in the crystalline state and for the conformational transitions important for the biological function in the peptides. The effect of temperature on the monoclinic polymorph of l-cysteine, metastable at ambient conditions, has been studied for the first time. A dynamical transition at about 150 K, marking a crossover of the molecular fluctuations between harmonic and non-harmonic dynamical regimes, was evidenced by evaluating the evolution of the mean-square displacement obtained from the elastic fixed window approach using the backscattering spectrometer IN10 located at the ILL. Although this transition does not manifest itself in the DSC, it was clearly observed by incoherent inelastic neutron scattering. By analyzing the dynamical susceptibility contribution ( χ″(ω)) obtained using IN6 also at ILL we were able to evidence another relaxation process at a different time scale. The disordered soft l-cysteine structure has an excess of inelastic scattering at about 3 meV, analogous to the “boson peak” observed in glass-like materials and proteins. High-precision X-ray diffraction has revealed an anomaly in the changes of selected unit cell parameters and volume at about 240 K.

Low-energy anti-kaon nucleon and nucleus interaction

Central importance for the physics of strong interaction has the dynamics driven by chiral symmetry breaking in low-energy QCD. Valuable information is provided by high precision x-ray studies of the strong interaction at threshold. In this context precision measurements of the strong interaction induced energy shift and width in kaonic atoms are conducted at LNF/Italy at present and at J-PARC/Japan in the future. New dedicated experimental search for bound systems with anti-kaons are under way at GSI and will be conducted at LNF and J-PARC. These studies will provide urgently needed data for theoretical studies and will open the way to a detailed insight in the low energy regime of the strong force with anti-kaons. Especially interesting are nuclear systems involving strangeness and bound by the strong force, called kaonic nuclear clusters. At present this topic is in intense discussion and the search for these systems is conducted in new experiments (e.g. FOPI at GSI). LEANNIS, an international scientific network in Hadronphysics2 within the European Framework Program FP7, will bring together experimentalists and theorists to perform joint research work on the anti-kaon interaction with nucleons and nuclei. This presentation gives an overview on the open problems and and will present the status and outlook of research activities in this challenging field which is inherently connected with few-body physics.

Upgrade of long trace profiler for characterization of high-precision X-ray mirrors at SPring-8

The long trace profiler (LTP) at SPring-8 has been upgraded to improve stability and resolution of slope measurement. The performances of the upgraded LTP at SPring-8 are presented by cross-checking measurements on a flat mirror with data obtained using Nanometer Optical Component Measuring Machine (NOM) at the Helmholtz Zentrum Berlin / BESSY-II.

Monoclinic MB phase and phase instability in [110] field cooled Pb(Zn1/3Nb2/3)O3–4.5%PbTiO3 single crystals

We report the finding of a monoclinic M(B) phase in Pb(Zn(13)Nb(23))O(3)-4.5%PbTiO(3) single crystals. High precision x-ray diffraction investigations of [110] field cooled crystals have shown a transformation sequence of cubic(C)-->tetragonal(T)-->orthorhombic(O)-->monoclinic(M(B)), which is different from that previously reported [A.-E. Renault et al., J. Appl. Phys. 97, 044105 (2005)]. Beginning in the zero-field-cooled condition at 383 K, a rhombohedral (R)-->M(B)-->O sequence was observed with increasing field. Coexisting M(B) and O phases were then found upon removal of field, which fully transformed to M(B) on cooling to room temperature.

Localization of an ultrathin buried Fe layer in a multilayer structure Nb/Fe/[Mo/Si]40/SiO2 by means of X-ray standing waves

An analysis of the influence of standing waves on the angular dependencies of the fluorescent yield from an ultrathin iron layer buried inside a multilayer structure of Nb(50 nm)/Fe(3.9 nm)/[Si/Mo(6.77 nm)]40/SiO2 is presented. These angular dependencies of reflectivity and FeKα-fluorescence yield were measured at the Station for high-precision X-ray optics (HPXO) of the Kurchatov Center for Synchrotron Radiation and Nanotechnology. The measured data was analyzed with the help of our FLUO software package. As a result of the complex treatment of reflectivity and Fe fluorescent yield data, the depth profile for iron atomic density was restored.

Differentiation of ceramic chemical element composition and vessel morphology at a pottery production center in Roman Galilee

Cooking pots and bowls from two production locations ca. 200 m from each other at the rural settlement of Kefar Hananya in Roman Galilee were compared employing chemical element composition and vessel-shape analyses. Splits of each pulverized sample, all of which were taken from ceramic wasters, were analyzed by both instrumental neutron activation and high-precision X-ray fluorescence analyses, and computerized vessel-shape analysis was employed for morphological analysis of the same vessel forms from each location. Several statistical techniques (bivariate plots, principal component analysis, cluster analysis and discriminant analysis) were used for analyzing the resultant data. It was found that both the cooking pots and bowls made at each location could be distinguished by employing either chemical composition or morphological analysis. The implications of this work, with regard to investigating both production and consumption sites, and for pottery provenance studies, are discussed. The findings suggest that these analytical techniques can be useful as an aid for chronological differentiations of archaeological pottery.

High-precision x-ray spectroscopy in few-electron ions

The experimental and spectrum analysis procedures that led to about 15 new, high-precision, relative x-ray line energy measurements are presented. The measured lines may be used as x-ray reference lines in the 2.4–3.1 keV range. Applications also include tests of the atomic theory, and in particular of quantum electrodynamics and of relativistic many-body theory calculations. The lines originate from 2- to 4-electron ions of sulfur (Z=16), chlorine (Z=17) and argon (Z=18). The precision reached for their energy ranges from a few parts per million (ppm) to about 50 ppm. This places the new measurements among the most precise performed in mid-Z highly charged ions (Z is the nuclear charge number). The elements of the experimental setup are described: the ion source (an electron cyclotron resonance ion trap), the spectrometer (a single, spherically bent crystal spectrometer), as well as the spectrum acquisition camera (low-noise, high-efficiency CCD). The spectrum analysis procedure, which is based on a full simulation of the spectrometer response function, is also presented.

ATOMIC PHYSICS RESEARCHES AT COOLER STORAGE RING IN LANZHOU

The commissioning of the cooler storage rings (CSR) was successful, and the facility provides new possibilities for atomic physics with highly charged ions. Bare carbon, argon ions, were successfully stored in the main ring CSRm, cooled by cold electron beam, and accelerated up to 1 GeV/u. Heavier ions as Xe 44+ and Kr 28+ were also successfully stored in the CSRs. Both of the rings are equipped with new generation of electron coolers which can provide different electron beam density distributions. Electron-ion interactions, high precision X-ray spectroscopy, complete kinematical measurements for relativistic ion-atom collisions will be performed at CSRs. Laser cooling of heavy ions are planned as well. The physics programs and the present status will be summarized.

Monoclinic MC phase in (001) field cooled BaTiO3 single crystals

We report here the finding of a new phase in BaTiO3 single crystals. High precision x-ray diffraction investigations of (001) field cooled crystals have shown the presence of a monoclinic MC phase for temperatures below 300 K. This MC phase is shown to be stable upon removal of the electric field. The results demonstrate the presence of structurally bridging low symmetry phases that lie between tetragonal and rhombohedral ones in this classic perovskite system: indicating a means to achieve high piezoelectricity in Pb-free systems via domain engineering.

UHV-type synchrotron radiation reflectometer

We designed a reflectometer for grazing-incidence X-ray measurements with a rotational feedthrough consisting of three welded bellows and a circle-type goniometer. This apparatus does not require differential pumping and is suitable for ultra-high-vacuum applications. With this reflectometer, we successfully performed high-precision synchrotron radiation X-ray reflectivity measurements on a thin iron-film under an ultra-high-vacuum condition.

High-resolution X-ray imaging—a powerful nondestructive technique for applications in semiconductor industry

The availability of high-brilliance X-ray sources, high-precision X-ray focusing optics and very efficient CCD area detectors has contributed essentially to the development of transmission X-ray microscopy (TXM) and X-ray computed tomography (XCT) with sub-50 nm resolution. Particularly, the fabrication of high aspect ratio Fresnel zone plates with zone widths approaching 15 nm has contributed to the enormous improvement in spatial resolution during the previous years. Currently, Fresnel zone plates give the ability to reach spatial resolutions of 15 to 20 nm in the soft and of about 30 to 50 nm in the hard X-ray energy range. X-ray microscopes with rotating anode X-ray sources that can be installed in an analytical lab next to a semiconductor fab have been developed recently. These unique TXM/XCT systems provide an important new capability of nondestructive 3D imaging of internal circuit structures without destructive sample preparation such as cross sectioning. These lab systems can be used for failure localization in micro- and nanoelectronic structures and devices, e.g., to visualize voids and residuals in on-chip metal interconnects without physical modification of the chip. Synchrotron radiation experiments have been used to study new processes and materials that have to be introduced into the semiconductor industry. The potential of TXM using synchrotron radiation in the soft X-ray energy range is shown for the nondestructive in situ imaging of void evolution in embedded on-chip copper interconnect structures during electromigration and for the imaging of different types of insulating thin films between the on-chip interconnects (spectromicroscopy).

Preferential Distribution of Lamps from the Jerusalem Area in the Late Second Temple Period (Late First Century B.C.E.-70 C.E.)

This is a systematic, regional, analytical study on the origins of the lamp, the most common lamp in late Second Temple-period Judaea. The project included 176 Herodian lamps from the northern sites of Gamala, Iotapata, Sepphoris, Dora, and Scythopolis, as well as several hundred examples of non-cooking ware of this period from the Galilee and Colon, and from Jerusalem and nearby sites. All samples were measured using both instrumental neutron activation and high-precision X-ray fluorescence analyses, and three statistical approaches were employed to evaluate the chemical compositional data. Ninety-six samples were also analyzed micromorphologically. The study showed that Herodian lamps from the Jerusalem area were found at all of the sampled northern settlements, but such lamps were also made in the north from a variety of locally available raw materials. The latter accounted for most of the Herodian lamps at the predominantly gentile cities of Dora and Scythopolis. The Jewish sites, in contrast, even when located at considerably greater distances from Jerusalem than the predominantly gentile cities, obtained the large majority of their Herodian lamps from the Jerusalem area. Possible reasons for this pronounced preference of the northern Jewish settlements for lamps from the Jerusalem area are discussed.

Point defects in pure amorphous silicon and their role in structural relaxation: A tight-binding molecular-dynamics study

Structural relaxation in pure amorphous silicon a-Si produced by ion implantation has been attributed to the annihilation of point defects vacancies and interstitials introduced during the amorphization process. We have studied this problem by using tight-binding molecular-dynamics simulations. We find that structural defects can, indeed, be identified in a-Si— they manifest themselves through a strong correlation between the charge and the volume of nearby atoms. The relaxation of these defects proceeds via the recombination of the dangling bonds. This results in an increase in the coordination number at constant density; the relaxation of a-Si, therefore, results from local, rather than global, structural changes, in full agreement with the highprecision x-ray diffraction experiments of Laaziri et al. Phys. Rev. Lett. 82, 346

Fabrication of the X-Ray Mask using the Silicon Dry Etching

The X-ray lithography of uses synchrotron radiation is one of the microprocessing structure fabrication technology. In X-ray lithography, precision of the fabricated structure is influenced by precision of the X-ray mask considerably. Conventionally, the X-ray mask was fabricated with UV lithography. However, it is difficult to fabricate the highly precise X-ray mask because of the tapering X-ray absorber. We introduces the ability of Si dry etching technology into UV lithography in order to fabricate untapered, high precision X-ray masks containing rectangular patterns. This new X-ray mask fabrication method uses a high-precision microstructure pattern formed by Si dry etching, thereby fabricating high aspect ratio, narrow line width resist microstructures that cannot be achieved by any conventional technology. An Au for the X-ray absorber is made to the groove of the structure, and it is formed by electroplating. The silicon substrate itself is used as seed layer and the structure is fabricated with the photo resist whose resistance is higher than silicon. It can be expected the gilding growth from only the bottom layer. High-density Au functions sufficiently as an absorber. Au plating was formed only from the base of the structure ditch and could bury Au of thickness 3.5µm in a narrow place of 2.7µm in width well. The fabricated structure using X-ray lithography. Highly-precise rectangular structure could be fabricated.