Monitoring carbon in electron and ion beam deposition within FIB-SEM

It is well known that carbon present in scanning electron microscopes (SEM), Focused ion beam (FIB) systems and FIB-SEMs, causes imaging artefacts and influences the quality of TEM lamellae or structures fabricated in FIB-SEMs. The severity of such effects depends not only on the quantity of carbon present but also on its bonding state. Despite this, the presence of carbon and its bonding state is not regularly monitored in FIB-SEMs. Here we demonstrated that Secondary Electron Hyperspectral Imaging (SEHI) can be implemented in different FIB-SEMs (ThermoFisher Helios G4-CXe PFIB and Helios Nanolab G3 UC) and used to observe carbon built up/removal and bonding changes resulting from electron/ion beam exposure. As well as the ability to monitor, this study also showed the capability of Plasma FIB Xe exposure to remove carbon contamination from the surface of a Ti6246 alloy without the requirement of chemical surface treatments

Gravitational waves from self-ordering scalar fields

Gravitational waves were copiously produced in the early Universe whenever the processes taking place were sufficiently violent. The spectra of several of these gravitational wave backgrounds on subhorizon scales have been extensively studied in the literature. In this paper we analyze the shape and amplitude of the gravitational wave spectrum on scales which are superhorizon at the time of production. Such gravitational waves are expected from the self ordering of randomly oriented scalar fields which can be present during a thermal phase transition or during preheating after hybrid inflation. We find that, if the gravitational wave source acts only during a small fraction of the Hubble time, the gravitational wave spectrum at frequencies lower than the expansion rate at the time of production behaves as $\Omega_{\rm GW}(f) \propto f^3$ with an amplitude much too small to be observable by gravitational wave observatories like LIGO, LISA or BBO. On the other hand, if the source is active for a much longer time, until a given mode which is initially superhorizon ($k\eta_* \ll 1$), enters the horizon, for $k\eta \gtrsim 1$, we find that the gravitational wave energy density is frequency independent, i.e. scale invariant. Moreover, its amplitude for a GUT scale scenario turns out to be within the range and sensitivity of BBO and marginally detectable by LIGO and LISA. This new gravitational wave background can compete with the one generated during inflation, and distinguishing both may require extra information.Comment: 21 pages, 2 figures, added discussion about numerical integration and a new figure to illustrate the scale-invariance of the GW power spectrum, conclusions unchange

Dynamical Stability of an Ion in a Linear Trap as a Solid-State Problem of Electron Localization

When an ion confined in a linear ion trap interacts with a coherent laser field, the internal degrees of freedom, related to the electron transitions, couple to the vibrational degree of freedom of the ion. As a result of this interaction, quantum dynamics of the vibrational degree of freedom becomes complicated, and in some ranges of parameters even chaotic. We analyze the vibrational ion dynamics using a formal analogy with the solid-state problem of electron localization. In particular, we show how the resonant approximation used in analysis of the ion dynamics, leads to a transition from a two-dimensional (2D) to a one-dimensional problem (1D) of electron localization. The localization length in the solid-state problem is estimated in cases of weak and strong interaction between the cites of the 2D cell by using the methods of resonance perturbation theory, common in analysis of 1D time-dependent dynamical systems.Comment: 18 pages RevTe

Number of distinct sites visited by N random walkers on a Euclidean lattice

The evaluation of the average number S_N(t) of distinct sites visited up to time t by N independent random walkers all starting from the same origin on an Euclidean lattice is addressed. We find that, for the nontrivial time regime and for large N, S_N(t) \approx \hat S_N(t) (1-\Delta), where \hat S_N(t) is the volume of a hypersphere of radius (4Dt \ln N)^{1/2}, \Delta={1/2}\sum_{n=1}^\infty \ln^{-n} N \sum_{m=0}^n s_m^{(n)} \ln^{m} \ln N, d is the dimension of the lattice, and the coefficients s_m^{(n)} depend on the dimension and time. The first three terms of these series are calculated explicitly and the resulting expressions are compared with other approximations and with simulation results for dimensions 1, 2, and 3. Some implications of these results on the geometry of the set of visited sites are discussed.Comment: 15 pages (RevTex), 4 figures (eps); to appear in Phys. Rev.

Renormalization of composite operators

The blocked composite operators are defined in the one-component Euclidean scalar field theory, and shown to generate a linear transformation of the operators, the operator mixing. This transformation allows us to introduce the parallel transport of the operators along the RG trajectory. The connection on this one-dimensional manifold governs the scale evolution of the operator mixing. It is shown that the solution of the eigenvalue problem of the connection gives the various scaling regimes and the relevant operators there. The relation to perturbative renormalization is also discussed in the framework of the $\phi^3$ theory in dimension $d=6$.Comment: 24 pages, revtex (accepted by Phys. Rev. D), changes in introduction and summar

Measurements of Ice Shelf Water beneath the front of the Ross Ice Shelf using gliders

Measurements made by an underwater glider deployed near the Ross Ice Shelf were used to identify the presence of Ice Shelf Water (ISW), which is defined as seawater with its potential temperature lower than its surface freezing point temperature. Properties logged by the glider included in situ temperature, electrical conductivity, pressure, GPS location at surfacings and time. For most of the first 30 recorded dives of its deployment, evidence suggests the glider was prevented from surfacing due to being under the ice shelf. For dives under the ice shelf, farthest from the ice shelf front, ISW layers of varying thicknesses and depth locations were observed; between 2 m thick (centred at 231 m depth) to >93 m thick (centred at >360 m). For dives under the ice shelf, close to the ice shelf front, either no ISW was observed or ISW layers were centred at shallower depths (116–127 m). Thicker ISW layers (e.g. up to 250 m thickness centred at 421 m) were observed for some glider dives in open water in front of the Ross Ice Shelf. No in situ supercooling (water colder than the pressure-dependent freezing point temperature) was observed

The extent and effectiveness of protected areas in the UK

The Convention on Biological Diversity (CBD), to which 196 countries including the UK are contracting parties, set out 20 Aichi Biodiversity Targets to be met by 2020. Elements of Aichi Target 11 call for at least 17% of terrestrial land and inland water to be protected and effectively managed by 2020. Each national government is requested to report progress against this goal in national reports submitted at intervals to the CBD, and these are used as the basis of reporting towards the 17% target. Figures reported for the UK’s protected area coverage are inclusive of a wide range of levels of designation, management and condition. Here, we examine the protection given to sites under UK legislation and designations as a case study. We find that although 28% of UK land is reported by the UK government to be protected, only 11.4% of land area falls within protected areas designated primarily for nature conservation. Condition monitoring indicates that at most 43–51% of protected areas in the UK are currently in favourable condition, which suggests as little as 4.9% of UK land area may be effectively protected for nature. However, estimates of protected area coverage vary greatly depending on the types of protected areas considered ‘effectively protected’ as measured by management category and site condition. Taking the UK as an example of a country that has reportedly met the target, we suggest that global progress may have been overestimated, and that future targets and indicators need to focus on the quality as well as quantity of protected areas

Low-voltage SEM of air-sensitive powders: from sample preparation to micro/nano analysis with secondary electron hyperspectral imaging

Powder materials are used in all corners of materials science, from additive manufacturing to energy storage. Scanning electron microscopy (SEM) has developed to meet morphological, microstructural and bulk chemical powder characterization requirements. These include nanoscale elemental analysis and high-throughput morphological assays. However, spatially localized powder surface chemical information with similar resolution to secondary electron (SE) imaging is not currently available in the SEM. Recently, energy filtered (EF-) SEM has been used for surface chemical characterization by secondary electron hyperspectral imaging (SEHI). This review provides a background to existing powder characterization capabilities in the low voltage SEM provided by SE imaging, EDX analysis and BSE imaging and sets out how these capabilities could be extended for surface chemical analysis by applying SEHI to powders, with particular emphasis on air and beam sensitive powder surfaces. Information accessible by SEHI, its advantages and limitations, is set into the context of other chemical characterization methods that are commonly used for assessing powder surface chemistry such as by Auger electron spectroscopy (AES) and X-ray photoelectron spectroscopy (XPS). The applicability of existing powder preparation methods for SEM to SEHI is also reviewed. An alternative preparation method is presented alongside first examples of SEHI characterization of powder surfaces. The commercial powder materials used as examples were carbon-fiber/polyamide composite powder feedstock (CarbonMide®) used in additive manufacturing and powders consisting of lithium nickel cobalt oxide (NMC). SEHI is shown to differentiate bonding present at carbonaceous material surfaces and extract information about the work function of metal oxide surfaces. The surface sensitivity of SEHI is indicated by comparison of pristine powders to those with surface material added in preparation. A minimum spatial localization of chemical information of 55 nm was achieved in differentiating regions of NMC surface chemistry by distinct SE spectra

The Muonium Atom as a Probe of Physics beyond the Standard Model

The observed interactions between particles are not fully explained in the successful theoretical description of the standard model to date. Due to the close confinement of the bound state muonium ($M = \mu^+ e^-$) can be used as an ideal probe of quantum electrodynamics and weak interaction and also for a search for additional interactions between leptons. Of special interest is the lepton number violating process of sponteanous conversion of muonium to antimuonium.Comment: 15 pages,6 figure