ERL X-ray Science Workshop 6 Abstracts
ERL Overview and Charge to Workshop
Don Bilderback Cornell High Energy Synchrotron Source, Cornell University The principle of operation of an Energy Recover Linac (ERL) is explained. The status and goals of the Cornell ERL project are summarized. Relevant characteristics of a 5 GeV ERL of the type we hope to build are described and some example experiments are given.Local Ordering of Fluids and Other Nanobeam Application & Waveguides
J. Friso van der Veen1,2, A. Diaz1, C. Bergemann3, O. Bunk1, D.K. Satapathy1, F. Pfeiffer1, C. David1, H. Keymeulen1, Hua Guo4, G.H. Wegdam4 1Paul Scherrer Institut, Villigen, Switzerland2ETH-Zürich, Switzerland
3Cavendish Laboratory, University of Cambridge
4Van der Waals-Zeeman Institut, University of Amsterdam, The Netherlands Confinement of a fluid between two opposing surfaces induces ordering of the fluid. This is suggested by surface force measurements [1], showing oscillations in the normal force whenever an integer number of layers are confined. The question arises whether such discrete layering effects can directly be observed by direct structural probes such as x-ray scattering. Another question is whether the confinement induces lateral short-range correlations within the fluid which are different from those in the bulk. In general, knowledge of confinement-induced structural arrangements within fluids is important for understanding lubrication, rheological properties of fluids in narrow tubes and crystallization phenomena. We report on ordering phenomena within colloids confined within arrays of microcavities that have been lithographically etched in silicon (Fig. 1). The colloid consists of SiO2 particles (112 nm diameter) dissolved in 55% benzyl alcohol + 45% ethanol. Cavity sizes range from 350 to 800 nm. Each array, having a constant period and cavity size, acts as a grating for the x-rays. Scattering from the colloid- filled grating results in Bragg peaks, being the different grating diffraction orders, as well as diffuse intensity. From the Bragg peaks we directly determine the average colloid density profile across the cavity using a one-dimensional phase retrieval algorithm subject to known boundary conditions. The diffuse intensity reveals the short-range spatial variations in the colloid density. The advantage of using a cavity array instead of a single cavity is that the scattered intensity is much higher. De-ionized colloidal solutions, in which electrostatic interactions are present, reveal average layered density profiles with a period that tends to adjust itself to the cavity width, whereas hard-sphere solutions (with salt added) provide evidence of a 'fractional-integer' effect in the number of layers; as the cavity width increases, cycles of layering and disordering occur in succession. Figure: X-ray scattering setup for investigations of confinement-induced ordering phenomena within colloids. One would like to scale the confining space down to a width of a few nanometer or less, enabling studies of ordering phenomena down to the molecular scale. It will be very difficult to fabricate nanocavity arrays for this purpose. However, a single planar slit with adjustable gap can be made from two opposing mica surfaces [1]. X-ray scattering experiments in that case would be optimally performed using a beam focused down to less than 10 nm. Clearly, sub-10 nm beams are required for many applications, but they have not yet been realized. We have theoretically investigated the focusing properties of Fresnel zone plate optics [3]. In contrast with x-ray waveguides [2], zone plates possess no fundamental limit to the smallest spot size to which they can focus, provided the zone are tilted such that the x-rays reflect specularly from the zone boundaries. References: 1. J.N. Israelachvili; Intermolecular and Surface Forces; Academic Press, London (1991) 2. C. Bergemann, H. Keymeulen, and J.F. van der Veen; Focusing X-Ray Beams to Nanometer Dimensions, Phys. Rev. Lett. 91 204801(2003) 3. F. Pfeiffer, C. David, J.F. van der Veen, and C. Bergemann; Nanometer Focusing Properties of Fresnel Zone Plates described by Dynamical Diffraction Theory, Phys. Rev. B, in the press
Nanobeams for Nanoelectronice Devices - the Importance of ERL for Characterization of the Optoelectronic Device Structures
A.A. Sirenko1, A. Kazimirov2, D.H. Bilderback2, Z.-H. Cai3, and B. Lai3 1Department of Physics, New Jersey Institute of Technology2Cornell High Energy Synchrotron Source, Cornell University
3Advanced Photon Source, Argonne National Laboratory Modern nanoelectronics is progressing from the planar epitaxial growth-based technology towards monolithic integration of multifunctional structures with complementary optical and electronic properties. Nanoscale selective area growth (NSAG) is a powerful technique for such integration, which holds a promise to improve both the optical properties and structural quality of the grown materials, and GaN -based device compounds in particular. The driving force behind these qualitative improvements is a more efficient bandgap engineering supported by strain relaxation at the sidewalls of the selectively grown nanostructures. A detailed analysis of the fundamental growth mechanisms and how they affect the structural and optical properties of the GaN -based NSAG structures is an important step towards their industrial applications. The adequate characterization tools, such as synchrotron radiation based nanobeam high-resolution x-ray diffraction (HRXRD), are required to support the current trends in monolithic materials integration. Here we present our recent characterization results obtained with a nondestructive HRXRD technique and reciprocal-space-mapping (RSM) analysis with the spatial resolution on both micron and submicron scales. In particular, we have studied optoelectronic device structures produced in industrial fabrication facilities. Thickness, strain, composition variation, and details of the surface migration have been determined for various SAG ridge structures with active regions consisted of InGaAlAs /InP and InGaN /GaN multiple-quantum-wells (MQW) [1,2]. Our HRXRD experiments have been carried out at two synchrotron facilities: at A2 beamline at CHESS equipped with a one-bounce focusing capillary optics and at the APS 2ID-D microscope beamline equipped with a phase zone plate. The x-ray beamsize at CHESS was 10 mm and the beamsize at APS was 0.3 mm. High angular resolution for diffraction measurements was provided by a perfect crystal analyzer [e.g., Si(004) or Ge(111) ]. In our reciprocal-space-mapping (RSM) experiments at CHESS we have utilized a combination of the crystal-analyzer and a matching two-bounce channel cut crystal. The latter was positioned between the focusing capillary and the sample to condition the incident x-ray beam. In this presentation we will also discuss the requirements for the future generation of the nanofocusing x-ray synchrotron facilities using three important parameters of the beamline setup: the flux as a number of photons seen by the detector (F), the beam-size on the sample (S), and the angular resolution (A). The figure of merit is the max for the following expression: F/(S×A). For example, at the 2-ID-D beamline we have F/(S×A) = 7'106 photons/(240 nm × 350nm × 2arcsec) >> 50 photons/(nm2×arcsec). Efficient utilization of our experimental setup for RSM analysis of GaN-based nanostructures requires an increase of the photon flux by at least 1 order of magnitude and a decrease of the x-ray beamsize by another order of magnitude. It will allow us to combine RSM technique with real-space mapping of the next generation of nanoscale devices. This example highlights the importance of ERL for the development of the high resolution nanobeam diffraction techniques as adequate tools for characterization of the next generation of optoelectronic devices. References: [1] A. Kazimirov, A.A. Sirenko, D.H. Bilderback, Z-H. Cai, B. Lai, R. Huang, and A. Ougazzaden, J. Phys. D: Appl. Phys. 39, 1422-1426 (2006) [2] A. Sirenko, A. Kazimirov, A. Ougazzaden, S. O'Malley, D.H. Bilderback, Z.-H. Cai, B. Lai, R. Huang, V. Gupta, M. Chien, S.N.G. Chu, Appl. Phys. Lett., 88, 081111 (2006)
A Roadmap Towards Nanometre Size Hard X-Ray Focusing with Reflective Optics
Oliver Hignette European Synchrotron Radiation Facility Graded multilayers seem the most promising approach to achieve high numerical aperture and therefore small focused spot size with reflective optics. The theoretical limit with a classical Kirkpatrick Baez architecture is predicted at about 4 nanometre FWHM independently of the energy. This is assuming that the volume diffraction is behaving as a perfect stigmatic surface, and that the complex electromagnetic field interaction does not limit the final resolution. A proper theoretical description of all the phenomena involved is still lacking, but a multilayer focusing device has already been tested at ESRF with a 40-nanometre focus size. Despite a far from perfect mirror figure, the error budget analysis does not show experimentally any broadening due to volume interaction. Devices and experiments are planned at ESRF to further validate experimentally this behaviour. A review of the technologies and methods, which have to be developed in the short term to get a predictable supply of the needed devices in the coming years, is presented. This includes both fabrication and metrology processes, with a level of sophistication, which most likely justifies pooling resources at a continental or worldwide level. This platform could be the base allowing reaching the theoretical limits by continuous increments. Once the single reflection architecture is mastered, multiple reflection schemes can be used to further increase the numerical aperture and reduce accordingly the spot size.Multilayer-Laue-Lens Optics for nm X-Ray Beams
A. T. Macrander Advanced Photon Source, Argonne National Laboratory Hard x-rays can now be focused by transmitting x-rays through the "sides" of a lens sliced from a multilayer wafer [1,2]. A multilayer-Laue-lens (MLL) is obtained by cutting out a cross sectioned piece and thinning it to the desired optical depth. This x-ray lens technology developed at Argonne National Laboratory consists of many individual layers, or Fresnel zones, precisely sputtered onto a silicon wafer. The outer-most zone is the thinnest and is the first to be deposited. Many layers with gradually increasing thicknesses are then grown to form a linear Fresnel lens structure. An advantage over standard x-ray zone plates is that very thin outer-most zones combined with arbitrarily large optical depths are available; aspect ratios that are more than ~100 times larger are possible. This advantage makes MLLs particularly suitable for focusing of hard x-rays. A one sided lenses, that is, half of a full linear zone plate, comprised of 1588 layers with an outer-most layer thickness of only 5 nm has recently been tested at the Advanced Photon Source with x-rays having a wavelength of 0.64 nm (19.5 keV). A focus of 19.3 nm was measured [3]. In the future the smallest possible focal spot will be explored by reducing the outer-most zone thickness in an ideal structure wherein each Fresnel zone is tilted to meet its separate Bragg condition. Presently only linear focusing has been demonstrated. However, a crossed configuration is envisioned in order to focus to a spot. Calculations have been made that predict that 1nm or less can be achieved with an ideal MLL. MLLs are well matched to the specifications of the Cornell ERL for three reasons: i) MLLs focus coherent photons, and a high coherent flux will obtain, ii) the ultimate focus will be a convolution of the ERL source size and the point-source focus of an MLL, and a small source size will obtain, iii) MLLs efficiently focus hard x-rays, and a hard x-ray spectrum will obtain. Initial applications with the so-far demonstrated resolution include visualizing buried features in sub-100 nm microelectronics, mapping trace metals in biological cell substructures, and detecting deeply buried nano-flaws in materials, that is, at the crystalline defect level. Besides allowing scientific study of the inside of samples, hard x-rays are useful for the study of samples inside chambers. Particularly attractive in this regard are high pressure studies inside diamond anvil cells, since in that case sample sizes are very small. Otherwise impossible experiments due to otherwise low count rates are envisioned. Below 1 nm focusing, atomic resolution becomes feasible which opens up many new vistas. Persons who have contributed heavily on multiple facets of this work are: Hyon Chol Kang, Jorg Maser, Chian Liu, Ray Conley, and Brian Stephenson. Other contributors are: for diffraction simulations, Stefan Vogt and Hanfei Yan; for lens fabrication, Ruben Khachatryan and Mike Wieczorek; for SEM measurements, J. Qian and Leo O'Cola . This work is supported by the U.S. Dept. of Energy, Basic Energy Sciences-Materials Science, under Contract No. W-31-109-ENG-38. References: [1] C. Liu, R. Conley, A.T. Macrander, J. Maser, H.C. Kang, M. Zurbuchen, and G.B.Stephenson; J. Appl. Phys. 98, 113519 (2005) [2] H.C. Kang, J. Maser, G.B.Stephenson, C. Liu, R.Conley, A.T. Macrander, and S. Vogt; Phys. Rev. Lett. 96, 127401 (2006) [3] H.C. Kang, J. Maser, B. Stephenson, C. Liu, R.Conley, A. Macrander, S. Vogt, and H. Yan, unpublishedNm Science Enabled by Waveguides
C. Fuhse, C. Ollinger, and T. Salditt Institut fuer Roentgenphysik, Universitaet Goettingen, 37077 Goettingen, Germany Two-dimensionally confining x-ray waveguides [1,2] can be used as very small sources providing highly-coherent beams with cross-sectional dimensions of only some tens of nanometers. They can be applied to various kinds of scanning microscopy, or they can serve as point-like sources for lensless projection microscopy. In the latter case, a magnified in-line hologram is recorded, from which an image of the sample can be calculated by a holographic reconstruction. A well-known problem of in-line holography is that the reconstructed image is severely disturbed by a so-called "twin image". This problem is overcome when two coherently illuminated waveguides are used to record a magnified off-axis hologram. In first proof-of-principle experiments, the phase part of the optical transmission function of a sample was reconstructed with a spatial resolution of about 100 nm. Spatial resolution is limited by the cross-sectional dimensions of the guiding core, which may approach a fundamental limit slightly below 10 nm [3]. References: [1] F. Pfeiffer, C. David, M. Burghammer, C. Riekel, and T. Salditt; Science 297 (2002), 230. [2] A. Jarre, C. Fuhse, C. Ollinger, J. Seeger, R. Tucoulou, and T. Salditt; Phys. Rev. Lett. 94, 074801(2005) [3] C. Bergemann, H. Keymeulen. and J. F. Van der Veen; Phys. Rev. Lett. 91, 204801 (2003)Diffraction-limited X-Ray Nanobeam with KB Mirrors
Kazuto Yamauchi1, Hidekazu Mimura1, Satoshi Matsuyama1, Hirokatsu Yumoto1, Soichiro han da1, Yasuhisa Sano1, Kazuya Yamamura1, Kenji Tamasaku2, Yoshinori Nishino2, Makina Yabashi3, Tetsuya Ishikawa2 1Osaka University2SPring-8/RIKEN
3SPring-8/JASRI X-ray focusing using a Kirkpatrick-Baez setup with two total reflection mirrors is a promising method, allowing highly efficient and energy-tunable focusing. Fabricated mirrors having a figure accuracy of 1 nm peak-to-valley height gave ideal diffraction-limited focusing of hard X-rays. The focal size, defined as the full width at half maximum of the intensity profile, was 36 nm × 48 nm at an X-ray energy of 15 keV. Recently, we have achieved a 25 nm focal size, using a short-focal-length mirror. Fluorescence X-ray microscopy with KB mirrors was also developed, targeting cell biological applications. The distribution of various elements in a single cell was successfully observed with high resolution. Our next main project is the realization of sub-10 nm level hard X-ray focusing. At-wavelength metrology is being developed, in which a phase-retrieval simulator is coded for the determination of phase errors on mirror surfaces from the only intensity profiles of a focused beam. A Multilayer deposition system is also being prepared.