Revealing the nano-structures of low-dimensional germanium on Ag(1 1 0) using XPS and XPD

In this work, we present a structural investigation of sub-monolayer films of germanium on Ag(1 1 0) by means of photoelectron spectroscopy (XPS) and diffraction (XPD), as well as low-energy electron diffraction (LEED). Since the rising progress in the synthesis of various kinds of nanoribbons, also germanium nanoribbons (Ge-NR) have been synthesized on Ag(1 1 0), recently. Here, we focus on their structural evolution and found the formation of two different phases of germanium at coverages of 0.5ML and 0.7ML, differing fundamentally from predicted nanoribbon structures. By means of LEED measurements, we obtained evidence for germanium superstructures which are not aligned along the [1¯¯¯10]-direction, as expected for nanoribbon growth. Using synchrotron-based high-resolution XPS and XPD experiments of the Ge 3d and Ag 3d core-levels, we resolved the local chemical and atomic order of the germanium films. Thus, the strong internal bonding of the buckled germanium film and a weak Van-der-Waals interaction between silver and germanium were discovered. Moreover, XPD-simulations delivered a detailed model of the structural arrangement of the preliminary nanoribbon phase, which also provided an approach to identify the origin of the two chemically shifted components in the Ge 3d signal by applying a component-wise decomposition of the XPD data

Fine tuning and the ratio of tensor to scalar density fluctuations from cosmological inflation

The form of the inflationary potential is severely restricted if one requires that it be natural in the technical sense, i.e. terms of unrelated origin are not required to be correlated. We determine the constraints on observables that are implied in such natural inflationary models, in particular on $r$, the ratio of tensor to scalar perturbations. We find that the naturalness constraint does not require $r$ to be lare enough to be detectable by the forthcoming searches for B-mode polarisation in CMB maps. We show also that the value of $r$ is a sensitive discriminator between inflationary models.Comment: 8 pages LaTeX; clarifications and a reference added; to appear in JCA

Petrogenesis of diachronous mixed siliciclastic-carbonate megafacies in the cool-water Oligocene Tikorangi Formation, Taranaki Basin, New Zealand

The Oligocene (Whaingaroan-Waitakian) Tikorangi Formation is a totally subsurface, lithostratigraphically complex, mixed siliciclastic-limestone-rich sequence forming an important fracture reservoir within Taranaki Basin, New Zealand. Petrographically the formation comprises a spectrum of interbedded rock types ranging from calcareous mudstone to wackestone to packstone to clean sparry grainstone. Skeletal and textural varieties within these rock types have aided in the identification of three environmentally distinctive megafacies for the Tikorangi Formation rocks-shelfal, foredeep, and basinal. Data from these megafacies have been used to detail previous conclusions on the petrogenesis and to further refine depositional paleoenvironmental models for the Tikorangi Formation in the central eastern Taranaki Basin margin.Shelfal Megafacies 1 rocks (reference well Hu Road-1A) are latest Oligocene (early Waitakian) in age and formed on or proximal to the Patea-Tongaporutu-Herangi basement high. They are characterised by coarse, skeletal-rich, pure sparry grainstone comprising shallow water, high energy taxa (bryozoans, barnacles, red algae) and admixtures of coarse well-rounded lithic sand derived from Mesozoic basement greywacke. This facies type has previously gone unrecorded in the Tikorangi Formation. Megafacies 2 is a latest Oligocene (early Waitakian) foredeep megafacies (formerly named shelfal facies) formed immediately basinward and west of the shelfal basement platform. It accumulated relatively rapidly (>20 cm/ka) from redeposition of shelfal megafacies biota that became intermixed with bathyal taxa to produce a spectrum of typically mudstone through to sparry grainstone. The resulting skeletal mix (bivalve, echinoderm, planktic and benthic foraminiferal, red algal, bryozoan, nannofossil) is unlike that in any of the age-equivalent limestone units in neighbouring onland King Country Basin. Megafacies 3 is an Oligocene (Whaingaroan-Waitakian) offshore basinal megafacies (formerly termed bathyal facies) of planktic foraminiferal-nannofossil-siliciclastic wackestone and mudstone formed away from redepositional influences. The siliciclastic input in this distal basinal setting (sedimentation rates <7 mm/ka) was probably sourced mainly from oceanic currents carrying suspended sediment from South Island provenances exposed at this time.Tikorangi Formation rocks record the Taranaki Basin’s only period of carbonate-dominated sedimentation across a full range of shelfal, foredeep, and basinal settings. Depositional controls on the three contrasting megafacies were fundamentally the interplay of an evolving and complex plate tectonic setting, including development of a carbonate foredeep, changes in relative sea level within an overall transgressive regime, and changing availability, sources, and modes of deposition of both bioclastic and siliciclastic sediments. The mixed siliciclastic-carbonate nature of the formation, and its skeletal assemblages, low-Mg calcite mineralogy, and delayed deep burial diagenetic history, are features consistent with formation in temperate-latitude cool waters

Passive-performance, analysis, and upgrades of a 1-ton seismic attenuation system

The 10m Prototype facility at the Albert-Einstein-Institute (AEI) in Hanover, Germany, employs three large seismic attenuation systems to reduce mechanical motion. The AEI Seismic-Attenuation-System (AEI-SAS) uses mechanical anti-springs in order to achieve resonance frequencies below 0.5Hz. This system provides passive isolation from ground motion by a factor of about 400 in the horizontal direction at 4Hz and in the vertical direction at 9Hz. The presented isolation performance is measured under vacuum conditions using a combination of commercial and custom-made inertial sensors. Detailed analysis of this performance led to the design and implementation of tuned dampers to mitigate the effect of the unavoidable higher order modes of the system. These dampers reduce RMS motion substantially in the frequency range between 10 and 100Hz in 6 degrees of freedom. The results presented here demonstrate that the AEI-SAS provides substantial passive isolation at all the fundamental mirror-suspension resonances

Study of the neutron quantum states in the gravity field

We have studied neutron quantum states in the potential well formed by the earth's gravitational field and a horizontal mirror. The estimated characteristic sizes of the neutron wave functions in the two lowest quantum states correspond to expectations with an experimental accuracy. A position-sensitive neutron detector with an extra-high spatial resolution of ~2 microns was developed and tested for this particular experiment, to be used to measure the spatial density distribution in a standing neutron wave above a mirror for a set of some of the lowest quantum states. The present experiment can be used to set an upper limit for an additional short-range fundamental force. We studied methodological uncertainties as well as the feasibility of improving further the accuracy of this experiment

Laser interferometry with translucent and absorbing mechanical oscillators

The sensitivity of laser interferometers can be pushed into regimes that enable the direct observation of quantum behaviour of mechanical oscillators. In the past, membranes with subwavelength thickness (thin films) have been proposed as high-mechanical-quality, low-thermal-noise oscillators. Thin films from a homogenous material, however, generally show considerable light transmission accompanied by heating due to light absorption, which typically reduces the mechanical quality and limits quantum opto-mechanical experiments in particular at low temperatures. In this work, we experimentally analyze a Michelson-Sagnac interferometer including a translucent silicon nitride (SiN) membrane with subwavelength thickness. We find that such an interferometer provides an operational point being optimally suited for quantum opto-mechanical experiments with translucent oscillators. In case of a balanced beam splitter of the interferometer, the membrane can be placed at a node of the electro-magnetic field, which simultaneously provides lowest absorption and optimum laser noise rejection at the signal port. We compare the optical and mechanical model of our interferometer with experimental data and confirm that the SiN membrane can be coupled to a laser power of the order of one Watt at 1064 nm without significantly degrading the membrane's quality factor of the order 10^6, at room temperature

Soft Phonon Anomalies in the Relaxor Ferroelectric Pb(Zn_1/3Nb_2/3)_0.92Ti_0.08O_3

Neutron inelastic scattering measurements of the polar TO phonon mode dispersion in the cubic relaxor Pb(Zn_1/3Nb_2/3)_0.92Ti_0.08O_3 at 500K reveal anomalous behavior in which the optic branch appears to drop precipitously into the acoustic branch at a finite value of the momentum transfer q=0.2 inverse Angstroms, measured from the zone center. We speculate this behavior is the result of nanometer-sized polar regions in the crystal.Comment: 4 pages, 4 figure