In this paper, the evolution of shot-noise micro-bunching in a SASE-FEL is investigated. First, a simple one-dimensional model for phase-space evolution of electrons is presented. Then, for an e-beam with random distribution of electrons (i.e. with shot-noise), the start-up and growth of micro-bunching is calculated. It is shown that shot-noise micro-bunching starts in random positions within the e-beam and grows in amplitude and extent. The final micro-bunching pattern contains distinct regions each with a coherent micro-bunching but with no phase relation with that of the others. Such distinct micro-bunched regions show themselves in the so-called spiky pattern of output radiation.
Evolution of bunching factor in different sections of an electron beam moving along an undulator is investigated. An averaging code is developed to calculate the average value of bunching in two different modes. In the first mode, the magnitude of bunching factor is averaged. In the second mode, the average of bunching factor is calculated taking into account its complex nature. The first averaging shows that all sections have similar trend of evolution; but, the result is completely different for the second averaging. The difference is attributed to the inherent phase cancellation present in the second mode of averaging.
Beryllium doping has been used to harden the inherently soft zinc-selenides semiconductor mixed alloys. Stoichiometric semiconductor ternary alloys of BexZn1-xSe have been synthesized by the Bridgeman technique. Extended X-ray absorption fine structure (EXAFS) spectroscopy — in a state-of-art synchrotron-based method — is performed by varying the dopant Be concentration of Be from 6% to 55% in the zinc–selenide host semiconductor. EXAFS analyses is carried out to study the next neighbor and next nearest neighbor atomic positions, nature of the substitutional doping, extent of bond length homogeneity, presence of involuntary contrast among the path distances, and the cross over from soft to hard character of the ternary on increasing Be concentration. Our results indicate the presence of an impulsive nature of hardening in the ternary with a disparity at the lower and the higher doping levels. The observation of impulsive hardening of the substitutional dopants in the semiconductor lattice is explained by the help of self-accommodative attributes of the host lattice.
Bi-harmonic undulators are designed and field integrals are measured in a pulsed wire bench. An analytical formula is given for the shim counting and positioning along the length of the undulator. It is observed that the wire rigidity and stiffness of the thick wire do not affect the bi-harmonic undulator field measurement and gives comparable results with hall probe data.
X-ray absorption spectroscopy (XAS) is an extremely valuable tool for the characterization of the electronic and geometric properties of nanoparticles. However, there are drawbacks when it comes, for example, to time-resolved in situ measurements of wet-chemical synthetic reactions or when X-ray absorption near edge structure (XANES) spectra are used for characterizing atoms that occupy different sites in a nanoparticle. In this paper, we report results of test experiments using resonant inelastic X-ray scattering (RIXS) for obtaining high-resolution spectra that allow in principle site- and/or valency-specific XANES measurements. For a detailed analysis of wet-chemical reactions, a microreactor system is used in which time resolution is obtained by spatial resolution, i.e., by measuring spectra at various points along the microreactor. This system provides significantly better resolution (in the order of milliseconds) compared to conventional techniques.
We present in situ and ex situ Laue micro-diffraction experiments on micron-sized single crystal pillars. We show that the focused ion beam technique introduces measurable damage in Si pillars. The dynamics of the Laue patterns of Au pillars demonstrate the occurrence of crystal rotation and strengthening is explained by plasticity starting on a slip system that is geometrically not predicted but selected because of the character of the pre-existing strain gradient.
SINS is a soft X-ray spectroscopy facility at SSLS, dedicated to Surface, Interface and Nanostructure Science of advanced materials. Developed over the past few years, the SINS end-station includes a photoemission spectroscopy analyzer, LEED, in situ STM/AFM, and a separate sample preparation chamber. Applications to such fields as molecular electronics, high density data storage, and nanonetwork templates are briefly reviewed.
This article highlights recent progress in the use of functionalized self-assembled monolayers for organic electronics, with particular emphasis on the investigation of the CuPc-SAMs interface properties, particularly the energy level alignment and molecular orientation. Synchrotron-based high-resolution photoemission spectroscopy (PES) and near-edge X-ray absorption fine structure measurements (NEXAFS) are used to address these issues. It is found that the energy level alignment at the CuPc-SAMs interface depends on the chain length of SAMs. Fermi level pinning occurs at the interface of CuPc with short chain SAMs of 4-trifluoromethyl-benzenethiol (CF3-SAM) and 4-methyl-benzenethiol (CH3-SAM), whereas the vacuum level aligns at the interface of CuPc with long chain SAMs including 1-(p-thiophenyl)-4-phenylbenzene (BBB), 4-(p-thiophenyl)-2, 2', 5, 5'-tetramethoxy-biphenyl (BOO), 1-(p-thiophenyl)-4-(2', 5'-dimethoxyphenyl)-tetrafluorobenzene (BFO) and 4-pentafluorophenyl-1-(p-thiophenyl)-2, 5-dimethoxybenzene (BOF). A significant reduction of the hole injection barrier (Δh) by up to 0.75 eV was observed after deposition of 5 nm CuPc on BOF/Au(111) as compared to the CuPc/Au(111) (Δh = 0.9 eV). Angular-dependent NEXAFS measurements reveal that CuPc molecules adopt a standing up configuration on all SAMs. This suggests that the interface charge transfer has negligible effect on the molecular orientation of CuPc on various SAMs.
The authors review recent studies of charge transfer dynamics across molecule/metal interfaces by resonant photoemission spectroscopy done at the Surface, Interface and Nanostructure Science (SINS) beamline, Singapore Light Source Synchrotron. The interfacial charge transfer takes place in the femtosecond scale due to the strong coupling between molecules and metal substrate, indicating that the transport properties of the molecule/metal junction is dominated not only by the chemical nature of molecules but also the interfacial properties of molecule/metal. Resonant photoemission spectroscopy is demonstrated to be a powerful tool for the study of ultrafast charge transfer dynamics across molecule/metal interfaces.
Hiroshima Synchrotron Radiation Center (HSRC) is a common facility for research and education in the field of synchrotron radiation science in Japan. The major role of the facility is to promote nationwide SR research activities in materials science, especially in solid state physics, and education in the related fields simultaneously. HiSOR is a compact synchrotron radiation source of HSRC constructed in 1996 as a typical VUV — soft X-ray source (0.87 keV critical photon energy) similar to Helios in Singapore. Because of a compact racetrack-type ring, its natural emittance 400π nm · rad is not so small as the other standard-sized rings. There are two undulators, one linear for 26–300 eV range and the other helical/linear for 4–40 eV. The most outstanding feature of the facility lies in the good combination with beamlines to attain high-resolution (below 1 meV) for photoemission spectroscopy. It is routinely operated from 09:00 to 20:00 on weekdays at the stored current starting from 350 mA with 8 h lifetime at 300 mA. HiSOR has been running over 10 years, thus, it is time to think about the future improvements of the facility. The motivation is to pursue the leading position in the field of materials science (solid state physics) using SR for high-resolution photoemission spectroscopy. Some candidates for the upgraded HiSOR are presented.
Speciation of copper and zinc (1:1) in MCM-41 has been studied by X-ray absorption near edge structural (XANES) and X-ray absorption fine structural (EXAFS) spectroscopies in the present work. The least-square fitted XANES spectra show that Cu(II) and Zn(II) are the major copper and zinc species, respectively in the channels of MCM-41 during calcination at 573–1173 K. The EXAFS data indicate that copper in MCM-41 possesses a Cu–O bond distance of 1.97 A with a coordination number (CN) of 3.4. During calcination at 573–1173 K, about 3.8–4.2 nearest oxygen atoms are bonded to the central copper atoms with Cu–O bond distances of 1.95–1.96 A in MCM-41. A small amount of Cu–Zn alloy may be formed during calcination. Existence of Zn–O)–Si (3.05–3.11 A) with CNs of 1.7–2.3 is also observed by EXAFS, suggesting an interaction between zinc and the framework SiO2 of MCM-41 during calcination.
Ion implantation of Co into silica layers and subsequent thermal annealing were used to form Co nanoparticles. Structural characterization was performed using X-ray Absorption Spectroscopy and Small Angle X-ray Scattering to determine, respectively, the local atomic structure and size distribution of the Co nanoparticles as a function of annealing temperature. For decreasing nanoparticle size, a bond-length contraction, an increase in Debye–Waller factor and a reduction in coordination number were observed. The bond-length contraction was related to the capillary pressure in the nanoparticles while an increase in Debye–Waller factor reflected an increase in disorder attributed to the high surface-area-to-volume ratio of small nanoparticles. X-ray Absorption Near Edge Structure spectroscopy revealed that the annealing conditions had a significant effect on the nanoparticle crystal structure and oxidised Co fraction.
Zn1-xCoxAl0.01O (x = 0, 0.15, 0.2, 0.3) films were fabricated on Si(100) substrates by pulsed laser deposition (PLD). X-ray diffraction (XRD) studies showed that the Co-doped ZnO films are polycrystalline with c-axis orientated wurtzite structure. Photoemission revealed a valence state of 2+ and a tetrahedral coordination of Co in the Co-doped ZnO. Ar+ sputtering was performed to investigate the changes to the valence state and the chemical environment of Co at surface and bulk. After Ar+ sputtering, the film composition was found to be closer to the starting target material. This was confirmed by the results of X-ray fluorescence (XRF) measurements, indicating the Co-doped ZnO film surface is cobalt-rich.
An extremely broad lower 2θ peak adjacent to the major (002) rhombohedral peak has been frequently observed in standard XRD profiles of bulk PZN-PT single crystals at room temperature. To understand the original and nature of this lower 2θ peak, high-resolution synchrotron X-ray diffraction study was carried out. The synchrotron (002) mapping together with a fracturing technique confirmed that the lower 2θ peak arises from a polishing-induced surface layer of "highly stressed rhombohedral state of monoclinic symmetry" which, structurally, may be likened to one full of "incipient monoclinic nuclei" of a range of lattice parameters. These "incipient" monoclinic nuclei/phases are microscopic in dimensions and are placed under intense in-plane compressive stress in the surface layer. All these contribute to the extreme broadness of the lower 2θ peak. The present work shows that deformation of relaxor single crystals occurs readily by stress-induced phase transformation of the material from the rhombohedral state to other lower symmetry states. The lower 2θ peak, and hence the "incipient" monoclinic surface layer, is fairly resistant to annealing and low-field poling but can be largely eliminated when the as-polished sample was poled to sufficiently high field (i.e., 1.5 kV/mm) at room temperature. After annealing, however, the "incipient" monoclinic surface layer became more resistant to poling such that remnant of the lower 2θ peak persisted even after high-field poling.
In this paper, magnetic and structural properties as well as the interface morphology of a series of sputtered Co/Pd multilayer thin films have been investigated. Interface morphology has been studied from grazing incidence specular and off-specular X-ray measurements using synchrotron radiation. High-angle X-ray diffraction measurements indicate a modulated structure which is strongly textured grown along (111) direction. The relation between intensity and the number of bilayers for different peaks of high-angle X-ray diffraction measurements has been investigated and compared to the grazing incidence X-ray scattering results. Vibrating sample magnetometer measurements have shown perpendicular magnetic anisotropy for all samples with Keff reaching highest value for those samples with highest fractal parameter.
A new experimental method for determining elastic constants of thin films is proposed. The curvatures of the single crystal substrates before and after depositing thin film are first measured using high-resolution X-ray rocking curve technique with high quality monochromatic and high intensity synchrotron radiation. The residual stress in the film is then calculated from the change in substrate curvature based on the well-known modified Stoney's equation. The formulae for calculating thin film's Young's modulus and Poisson's ratio are deduced based on measured residual stress and the lattice spacing dψ versus sin2ψ curves of the film before and after an unknown mechanical loading. LaNiO3 film grown on single crystal silicon substrate using pulsed laser deposition is employed to demonstrate the measurement method.
Electromagnetic metamaterials are a new class of ordered composite materials made from metallic unit structures that exhibit an electric and magnetic response to an incident electromagnetic wavefield such that ∊ and μ become simultaneously negative. We review the recent progress made in manufacturing and characterizing micro- and nanostructured metamaterials from 1 to 216 THz (300 to 1.4 μm, respectively), at the Singapore Synchrotron Light Source, and discuss new developments towards three-dimensional and multilayered metamaterials structures by means of deep X-ray lithography.
Elongated Pt nanocrystals (NCs) formed in SiO2 by ion implantation, thermal annealing and swift heavy ion irradiation (SHII) were analyzed by small angle X-ray scattering (SAXS) and transmission electron microscopy (TEM) measurements. Transmission SAXS measurements were performed in samples aligned at different angles relative to the photon beam resulting in nonisotropic scattering and thus enabling the three-dimensional analysis of the NCs. Selected angular sectors of the detector were integrated and analyzed separately, leading to the individual evaluation of both the major and minor dimensions of the rod-shaped NCs. This method enables the use of well-established spherical models for the SAXS data analysis and yielded good agreement with TEM results. Corrections to the amplitude of the SAXS diameter distributions to overcome the disparities between the spherical models and the nonspherical particles are also presented.
Materials with nanoscale dimensions have unique optical properties, which have been extensively explored and implemented for a variety of functionalized photonic structures and devices. In this paper, the nanofabrication processes for photonic applications are reviewed. The nanofabrication methods can be divided into two major categories: top-down and bottom-up. The main techniques used in each method are discussed in terms of its process capabilities, advantages, limitations, and applications. The cases which involve the combination of top-down and bottom-up approaches are also illustrated.
We report a novel approach to X-ray diffraction data analysis for nondestructive determination of the shape of nanoscale particles and clusters in three dimensions with a spatial resolution of a few nanometers. The advantage of the proposed approach is that it does not require a coherent X-ray source and therefore is suitable for almost any synchrotron radiation beamline and many laboratory sources. The technique is insensitive to the coherence of the X-rays, and 3D reconstruction of a modal image is possible without tomographic synthesis, rendering the approach suitable for laboratory facilities. Successful application of the technique to the characterization of nanoparticulate in a range of dispersed-phase nanocomposite structures illustrates this novel approach.
