High-resolution Synchrotron Radiation Research Articles

A structural evidence of polar clusters in PLZT relaxor ceramics

ABSTRACTIn this paper, a quantification of the polar/non-polar phases of perovskite single-phase relaxor ferroelectric ceramics of lanthanum modified lead titanate zirconate (PLZT x/65/35, x = 5, 8, 9 and 10%) was performed by Rietveld refinement using measurements obtained with Cu kα radiation and with high-resolution synchrotron radiation. The refinements were performed concerning two crystalline phases, being one of them nonpolar (Pm-3m) and the other polar. The refinement results showed the relationship between the polar/nonpolar phases and the La content in PLZT, suggesting the existence of polar clusters of relaxor ferroelectric ceramics.

Monoclinic deformation of calcite crystals at ambient conditions

High resolution synchrotron radiation powder diffraction shows that the average crystal structure of calcite at ambient conditions is described with the trigonal space group R3¯c but there is a systematic hkl-dependent Bragg peak broadening. A modelling of this anisotropic peak broadening with the microstrain model from Stephens (1999) [15] is presented. The observed lattice parameters' correlations can be described by assuming a monoclinic-type deformation of calcite crystallites. A quantitative model of this monoclinic deformation observed at ambient conditions is described with the space group C2/c. The monoclinic unit cell suggested at ambient conditions is related with the monoclinic unit cell reported in calcite at high pressure (Merrill and Bassett (1975) [10]).

Research Update: Strain and composition effects on ferromagnetism of Mn0.05Ge0.95 quantum dots

Mn0.05Ge0.95 quantum dots (QDs) samples were grown by molecular beam epitaxy on Si substrates and 15-nm-thick fully strained Si0.8Ge0.2 virtual substrates, respectively. The QDs samples grown on the Si0.8Ge0.2 virtual substrates show a significant ferromagnetism with a Curie temperature of 227 K, while the QDs samples grown on the Si substrates are non-ferromagnetic. Microstructures of the QDs samples were characterized by high resolution transmission electron microscopy and synchrotron radiation X-ray diffraction. Interdependence between microstructure and ferromagnetism of Mn-doped Ge QDs was investigated. For the QDs sample grown on the strained Si0.8Ge0.2 virtual substrate, although the ferromagnetic phase Mn5Ge3 clusters were found to be formed in small dome-shaped dots, the significant ferromagnetism observed in that sample is attributed to ferromagnetic phase Mn-doped large dome-shaped Ge QDs, rather than to the ferromagnetic phase Mn5Ge3 clusters. The fully strained Si0.8Ge0.2 virtual substrates would result in a residual strain into the QDs and an increase in Ge composition in the QDs. Both consequences favor the formations of ferromagnetic phase Mn-doped Ge QDs from points of view of quantum confinement effect as well as Mn doping at substitutional sites.

Thermally assisted oxidation of GaSb(100) and the effect of initial oxide phases

The oxidation of GaSb(100) surface has been widely studied because it affects the functionality of various devices. However even initial stages of the oxygen incorporation are not completely understood. To clarify this issue, we have investigated the oxidized GaSb(100) surfaces, which have been recently probed by scanning tunneling microscopy and spectroscopy, with high resolution synchrotron radiation photoelectron spectroscopy, in order to interconnect these different measurements. The results give a clear support that the oxidation initiates through saturation of available Ga bonds with; i.e., replacing some of the SbGa bonds with OGa in the surface layers. Oxygen atoms have two different bonding environments in consistent with two dominating STM features. Also role of the plasmon features in the spectra have been elucidated.

Distortion of the crystal structure of MnO at ambient conditions

High resolution synchrotron radiation diffraction studies of polycrystalline powder MnO show a systematic distortion from the standard NaCl-type cubic structure (space group Fm3¯m). Two models of the distortion of MnO crystallites are presented: (i) anisotropic Bragg peak broadening due to a distribution of internal microstrains, and (ii) a model with tetragonal symmetry (space group I4/mmm) with at≈ac/√2, ct≈ac. Both models show good agreement with the experimental data which is significantly better than the cubic model with isotropic Bragg peak broadening. Both models imply a distortion of the cubic symmetry of the MnO crystal structure. The size of the tetragonal distortion is x=ct/(at√2)=1±Δ, where Δ≈2×10−4 at ambient conditions. Both tetragonal structures with elongation along ct (x=1+Δ) and shrinking along ct (x=1−Δ) give the same fit quality estimators. The distortion from cubic symmetry increases with milling time for powder MnO samples milled in a planetary mill. The proposed tetragonal space group I4/mmm has a group-subgroup relation with the monoclinic space group C2/m observed in MnO below TN.

Corrosion investigation of fire-gilded bronze involving high surface resolution spectroscopic imaging

Gilded bronzes are often affected by severe corrosion, due to defects in the Au layer and Au/Cu alloy galvanic coupling, stimulated by large cathodic area of the gilded layer. Galvanic corrosion, triggered by gilding defects, leads to products growth at the Au/bronze interface, inducing blistering or break-up of the Au layer. In this context, fire-gilded bronze replicas prepared by ancient methods (use of spreadable Au–Hg paste) was specifically characterised by compiling complementary spectroscopic and imaging information before/after accelerated ageing with synthetic rain. Fire-gilded bronze samples were chemically imaged in cross-section at nano-metric scale (<200nm) using high energy and lateral resolution synchrotron radiation photoemission (HR-SRPES) of core levels and valence band after conventional characterisation of the samples by Glow Discharge optical Emission Spectroscopy (GD-OES) and conventional X-ray photoelectron spectroscopy (XPS). We have found a net surface enrichment in Zn and Sn after fire-gilding and presence of metallic Hg, Pb and Cu within the Au layer. Moreover, the composition distribution of the elements together with their oxidation has been determined. It was also revealed that metallic phases including Hg and Pb remain in the gilding after corrosion. Moreover, selective dissolution of Zn and Cu occurs in the crater due to galvanic coupling, which locally induces relative Sn species enrichment (decuprification). The feasibility advantages and disadvantages of chemical imaging using HR-SRPES to study artworks have been investigated on representative replicas.

Unusual Strong Incommensurate Modulation in a Tungsten-Bronze-Type Relaxor PbBiNb5O15.

Pb- or Bi-based perovskite oxides have been widely studied and used because of their large ferroelectric polarization features induced by stereochemically active 6s(2) lone pair electrons. It is intriguing whether this effect could exist in other related systems. Herein, we designed and synthesized a mixed Pb and Bi A site polar compound, PbBiNb5O15, with the TTB framework. The as-synthesized material turns out to be a relaxor with weak macroscopic ferroelectricity but adopts strong local polarizations. What's more, unusual five orders of incommensurate satellite reflections with strong intensities were observed under the electron diffraction, suggesting that the modulation is highly developed with large amplitudes. The structural modulation was solved with a (3 + 1)D superspace group using high-resolution synchrotron radiation combined with anomalous dispersion X-ray diffraction technique to distinguish Pb from Bi. We show that the strong modulation mainly originates from lone-pair driven Pb(2+)-Bi(3+) ordering in the large pentagonal caves, which can suppress the local polarization in x-y plane in long ranges. Moreover, the as-synthesized ceramics display strong relaxor ferroelectric feature with transition temperature near room temperature and moderate dielectric properties, which could be functionalized to be electromechanical device materials.

Observation of unusual metal-semiconductor interaction and metal-induced gap states at an oxide-semiconductor interface: The case of epitaxial BaO/Ge(100) junction

Oxidation of semiconductor surfaces is known to cause defect states at oxide-semiconductor interfaces of various devices. In contrast, effects of the semiconductor interaction with non-oxygen elements at such junctions are still unclear. We present evidence for the interrelationship between a metal (non-oxygen)-semiconductor reaction and formation of the band-gap defect states at a buried oxide-semiconductor interface by investigating well-defined epitaxial $\mathrm{BaO}/\mathrm{Ge}\phantom{\rule{0.16em}{0ex}}(100)$ junctions with high-resolution synchrotron-radiation photoelectron spectroscopy. The states that arise from the Ba-Ge interaction lead to Fermi-level pinning at $0.40\phantom{\rule{0.16em}{0ex}}\mathrm{eV}$ above the valence band maximum, while the defect-free $\mathrm{BaO}/\mathrm{Ge}\phantom{\rule{0.16em}{0ex}}(100)$ interface has a flat band structure.

Single-Crystal Y2O3 Epitaxially on GaAs(001) and (111) Using Atomic Layer Deposition

Single-crystal atomic-layer-deposited (ALD) Y2O3 films 2 nm thick were epitaxially grown on molecular beam epitaxy (MBE) GaAs(001)-4 × 6 and GaAs(111)A-2 × 2 reconstructed surfaces. The in-plane epitaxy between the ALD-oxide films and GaAs was observed using in-situ reflection high-energy electron diffraction in our uniquely designed MBE/ALD multi-chamber system. More detailed studies on the crystallography of the hetero-structures were carried out using high-resolution synchrotron radiation X-ray diffraction. When deposited on GaAs(001), the Y2O3 films are of a cubic phase and have (110) as the film normal, with the orientation relationship being determined: Y2O3//GaAs. On GaAs(111)A, the Y2O3 films are also of a cubic phase with (111) as the film normal, having the orientation relationship of Y2O3//GaAs. The relevant orientation for the present/future integrated circuit platform is (001). The ALD-Y2O3/GaAs(001)-4 × 6 has shown excellent electrical properties. These include small frequency dispersion in the capacitance-voltage (CV) curves at accumulation of ~7% and ~14% for the respective p- and n-type samples with the measured frequencies of 1 MHz to 100 Hz. The interfacial trap density (Dit) is low of cm−2eV−1 as extracted from measured quasi-static CVs. The frequency dispersion at accumulation and the Dit are the lowest ever achieved among all the ALD-oxides on GaAs(001).

THREE-DIMENSIONAL IMAGING OF GAS PORES IN FUSION WELDED Al ALLOYS BY SYNCHROTRON RADIATION X-RAY MICROTOMOGRAPHY

Large numbers of complicatedly distributed gas pores are inevitably formed during the hybrid fusion welding of aluminum alloys because of the sharp reduction of supersaturated hydrogen. However, there is no consistent and explicit view on how these gas pores are distributed and influence the static and fatigue property of welded aluminum joints. In this work, pores in hybrid welded 7020-T651 were characterized by high-resolution synchrotron radiation X-ray computed microtomography. The volume, sphericity, flatness and distance of pores centroid to free surface of samples were statistically measured and fitted. From the 3D characterization, micropores inside hybrid welds are mainly metallurgical pores, which are symmetrically distributed about the seam centerline, giving a mean sphericity larger than 0.65. Moreover, pores inside upper welds appear to be larger in effective diame- ter and denser in heat affected zone and lower welds. Besides, there are numerous pores with diameter less than 20 pm, with a frequency of 65% and 85% in the upper and lower weld, respectively. It seems that hot cracks with complicated morphology form in the lower weld due to shrinkage and rapid solidification of the molten pool. Furthermore, it is found that the connections of a few pore-pore and pore-hot-crack together with the hot cracks result in the smaller sphericity of gas pores in the lower welds. Finally it can be indicated that the higher welding speed gives rise to the smaller pore volume fraction, but has little influence on the distribution of pore position and sphericity.

Photoelectron spectroscopy as an in situ contact-less method for studies of MOS properties of ultrathin oxides on Si

The electric field across an ultrathin and uniform Si-oxide layer on a Si (111) surface and the positions of the valence band edges at the Si-oxide/Si (111) interface have been probed by high-resolution synchrotron radiation induced photoemission spectroscopy, as an in situ contact-less method. Variation of the “gate bias” is achieved by depositing Sn nanoparticles on the ultrathin oxide surface. These nanoparticles, growing as isolated hemi-spherical islands, attract various quantities of negative charges from the substrate inducing a potential difference between the Sn islands/Si-oxide and Si-oxide/Si (111) interface. This method allows us to study and extract the locally varying electric field and changes in the positions of the edges of the valence bands by measuring the valence band spectra and the Si 2p and Sn 4d core-levels at different Sn coverages. The ultrathin (0.8nm thick) Si-oxide layer is grown in a simple and traceable self-limiting thermal process on a clean Si (111) surface. The oxide grown in this way creates flat bands. The properties of the system of Sn islands grown on this system are also determined. The induced electric field in the oxide varies linearly with the amount of Sn deposited per area.

High temperature thermal stability studies of ultrathin Al2O3 layers deposited on native oxide and sulphur passivated InGaAs surfaces

High resolution synchrotron radiation core level photoemission measurements have been used to undertake a comparative study of the high temperature stability of ultrathin Al2O3 layers deposited by atomic layer deposition (ALD) on both sulphur passivated and native oxide covered InGaAs. The residual interfacial oxides between sulphur passivated InGaAs and the ultrathin Al2O3 layer can be substantially removed at high temperature (up to 700°C) without impacting on the InGaAs stoichiometry while significant loss of indium was recorded at this temperature on the native oxide InGaAs surface.

Single-crystal atomic layer deposited Y2O3 on GaAs(0 0 1) – growth, structural, and electrical characterization

In situ atomic layer deposited (ALD) Y2O3 films 1–5nm thick on GaAs(001)-4×6 reconstructed substrates were found to be single crystalline. The epitaxial growth between the oxide films and GaAs was first observed using reflective high energy electron diffraction (RHEED) and later studied using high-resolution synchrotron radiation X-ray diffraction. The Y2O3 films are of cubic phase and have (110) as the film normal; the orientation relationship between the Y2O3 films and the GaAs substrates was determined to be Y2O3(110)[001][1¯10]//GaAs(001)[110][11¯0]. The frequency dispersion of the measured capacitance–voltage (C–V) curves of the single crystal ALD-Y2O3/GaAs(001)-4×6 is ∼7% for p-GaAs and ∼14% for n-GaAs (1MHz to 100Hz), lowest ever achieved in the ALD-oxides on GaAs(001).

Comprehensive Investigation of the Na3V2(PO4)2F3–NaV2(PO4)2F3 System by Operando High Resolution Synchrotron X-ray Diffraction

Na3V2(PO4)2F3 is a positive electrode material for Na-ion batteries which is attracting strong interest due to its high capacity, rate capability, and long-term cycling stability. The sodium extraction mechanism from this material has been always described in the literature as a straightforward solid solution, but several hints point toward a more complicated phase diagram. In this work we performed high angular resolution synchrotron radiation diffraction measurements, realized operando on sodium batteries upon charge. We reveal an extremely interesting phase diagram, created by the successive crystallization of four intermediate phases before the end composition NaV2(PO4)2F3 is reached. Only one of these phases undergoes a solid solution reaction, in the interval between 1.8 and 1.3 Na per formula unit. The ability to resolve weak Bragg reflections allowed us to reveal differences in terms of symmetry among the phases, to determine their previously unknown space groups, and to correlate them with sodium...

Texture gradient in a copper tube at maximum and minimum wall thickness

Tube drawing is an inhomogeneous process with anisotropic flow. Quantitative texture analysis was used to get inside in eccentricity and ovality of a Cu-tube drawn without a plug. To obtain the texture gradient over the wall thickness high resolution synchrotron radiation was used. One obtains on one hand different textures at the surfaces than in the central region and the other hand a variation of the texture gradient at the maximum wall thickness of the tube compared to the minimum wall thickness.

In-situ atomic layer deposition of tri-methylaluminum and water on pristine single-crystal (In)GaAs surfaces: electronic and electric structures

The electronic structure of single-crystal (In)GaAs deposited with tri-methylaluminum (TMA) and water via atomic layer deposition (ALD) is presented with high-resolution synchrotron radiation core-level photoemission and capacitance-voltage (CV) characteristics. The interaction of the precursor atoms with (In)GaAs is confined at the topmost surface layer. The Ga-vacant site on the GaAs(111)A-2 × 2 surface is filled with Al, thereby effectively passivating the As dangling bonds. The As-As dimers on the GaAs(001)-2 × 4 surface are entirely passivated by one cycle of TMA and water. The presumed layerwise deposition fails to happen in GaAs(001)-4 × 6. In In0.20Ga0.80As(001)-2 × 4, the edge row As atoms are partially bonded with the Al, and one released methyl then bonds with the In. It is suggested that the unpassivated surface and subsurface atoms cause large frequency dispersions in CV characteristics under the gate bias. We also found that the (In)GaAs surface is immune to water in ALD. However, the momentary exposure of it to air (less than one minute) introduces significant signals of native oxides. This indicates the necessity of in situ works of high κ/(In)GaAs-related experiments in order to know the precise interfacial atomic bonding and thus know the electronic characteristics. The electric CV measurements of the ALD-Al2O3 on these (In)GaAs surfaces are correlated with their electronic properties.

3D angioarchitecture changes after spinal cord injury in rats using synchrotron radiation phase-contrast tomography.

A basic experiment study. An understanding of the three-dimensional (3D) angioarchitecture changes that occur after SCI will improve our knowledge of the pathogenesis of SCI and aid in the development of valuable therapeutic strategies to improve its poor outcomes. Our aim was to visualize the normal and traumatized spinal angioarchitecture in 3D using a high-resolution synchrotron radiation phase-contrast tomography (SR-PCT) and evaluate its diagnostic capability. SCI Center of Xiangya Hospital of Central South University in China. SR-PCT was used as novel high-resolution imaging tool to detect 3D morphological alterations in spinal cord microvasculature after injury. In a rat model, the morphology of the microvasculature on 2D digital slices was matched with histological findings in both the normal and injured spinal cord. 3D angioarchitecture changes after SCI were successfully obtained via SR-PCT without the use of a contrast agent. Quantitative analysis on 3D images of the injured spinal cord revealed a significant decrease in the number and volume of vascular networks. This was especially relevant to vessels with a diameter <50 μm. The 3D local blood supply to the spinal cord was severely disrupted after the acute violent injury. Our results indicate that the use of SR-PCT may improve our understanding of the pathogenesis of SCI and provide a new approach to the morphological investigation of neurovascular diseases in preclinical research.

Application of high resolution synchrotron micro-CT radiation in dental implant osseointegration

The purpose of this study was to describe a refined method using high-resolution synchrotron radiation microtomography (SRmicro-CT) to evaluate osseointegration and peri-implant bone volume fraction after titanium dental implant insertion. SRmicro-CT is considered gold standard evaluating bone microarchitecture. Its high resolution, high contrast, and excellent high signal-to-noise-ratio all contribute to the highest spatial resolutions achievable today. Using SRmicro-CT at a voxel size of 5 μm in an experimental goat mandible model, the peri-implant bone volume fraction was found to quickly increase to 50% as the radial distance from the implant surface increased, and levelled out to approximately 80% at a distance of 400 μm. This method has been successful in depicting the bone and cavities in three dimensions thereby enabling us to give a more precise answer to the fraction of the bone-to-implant contact compared to previous methods.

Temperature effect on the electronic structure of Nb:SrTiO3 (100) surface**Project supported by the Funds from the Chinese Academy of Sciences (Grant No. 1G2009312311750101) and the National Natural Science Foundation of China (Grant No. 11375228).

The effect of temperature on the electronic structure of Nb-doped SrTiO3 (100) surface is investigated by high-resolution synchrotron radiation photoemission spectroscopy. According to the x-ray photoemission spectroscopy (XPS) results, at an annealing temperature of less than 700 °C, the adsorbed carbon and hydroxyl on the STO surface could be removed, to expose the fresh intrinsic surface with a constant ratio of Ti/O. It is obvious that the STO would be doped by Ca+ impurities of bulks and O vacancies in the surface after annealing at 920 °C for one hour.

Porosity induced fatigue damage of laser welded 7075-T6 joints investigated via synchrotron X-ray microtomography

The interaction between the pores and the fatigue damage in 7075-T6 joints was characterised via high resolution synchrotron radiation X-ray microcomputed tomography. The spatial distribution and growth behaviour of the pores were investigated and quantified. The gas porosity inside 7075-T6 hybrid welds was found to play a significant role in the fatigue crack nucleation and propagation process. The volume fraction and the total number of pores increased slightly with increasing number of fatigue cycles, which provides a key indicator for the damage evolution. Experimental results indicate that the micropores grew and distorted during fatigue cyclic loading, eventually resulting in fatigue cracks. Under cyclic loads, the maximum micropore is usually not a favourable site, in terms of physical suitability, for fatigue crack initiation and propagation, and the diameter of the cracked pores is in the range of 10–100 μm.