EUV spectroscopy of Sn5+-Sn(10+)ions in an electron beam ion trap and laser-produced plasmas

Emission spectra from multiply-charged Sn5+ –Sn10+ions are recorded from an electron beam ion trap (EBIT) and from laser-produced plasma (LPP) in the extreme ultraviolet range relevant for nanolithographic applications. Features in the wavelength regime between 12.6 and 20.8 nm are studied. Using the Cowan code, emission line features of the charge-state-resolved Sn ion spectra obtained from the EBIT are identified. Emission features from tin LPP either from a liquid micro-droplet or planar solid target are subsequently identified and assigned to specific charge states using the EBIT data. For the planar solid tin target, the 4d–5p transitions of Sn8+ –Sn10+ions are shown to dominate the long-wavelength part of the measured spectrum and transitions of type 4d–4f + 4p–4d are visible in absorption. For the droplet target case, a clear increase in the charge state distribution with increasing laser intensity is observed. This qualitatively demonstrates the potential of using long-wavelength out-of-band emission features to probe the charge states contributing to the strong unresolved transition array at 13.5 nm relevant for nanolithography

Detection of the 5p-4f orbital crossing and its optical clock transition in Pr9+

Recent theoretical works have proposed atomic clocks based on narrow optical transitions in highly charged ions. The most interesting candidates for searches of new physics are those which occur at rare orbital crossings where the shell structure of the periodic table is reordered. There are only three such crossings expected to be accessible in highly charged ions, and hitherto none have been observed as both experiment and theory have proven difficult. In this work we observe an orbital crossing in highly charged ions for the first time, in a system chosen to be tractable from both sides: Pr9+. We present electron beam ion trap measurements of its spectra, including the inter-configuration lines that reveal the sought-after crossing. The proposed nHz-wide clock line, found to be at 452.334(1) nm, proceeds through hyperfine admixture of its upper state with an E2-decaying level. With state-of-the-art calculations we show that it has a very high sensitivity to new physics and extremely low sensitivity to external perturbations, making it a unique candidate for proposed precision studies

Differential-Algebraic Integrability Analysis of the Generalized Riemann Type and Korteweg-de Vries Hydrodynamical Equations

A differential-algebraic approach to studying the Lax type integrability of the generalized Riemann type hydrodynamic equations at N = 3; 4 is devised. The approach is also applied to studying the Lax type integrability of the well known Korteweg-de Vries dynamical system.Comment: 11 page

Vacancy ordering and electronic structure of gamma-Fe2O3 (maghemite): a theoretical investigation

The crystal structure of the iron oxide gamma-Fe2O3 is usually reported in either the cubic system (space group P4332) with partial Fe vacancy disorder or in the tetragonal system (space group P41212) with full site ordering and c/a\approx 3. Using a supercell of the cubic structure, we obtain the spectrum of energies of all the ordered configurations which contribute to the partially disordered P4332 cubic structure. Our results show that the configuration with space group P41212 is indeed much more stable than the others, and that this stability arises from a favourable electrostatic contribution, as this configuration exhibits the maximum possible homogeneity in the distribution of iron cations and vacancies. Maghemite is therefore expected to be fully ordered in equilibrium, and deviations from this behaviour should be associated with metastable growth, extended anti-site defects and surface effects in the case of small nanoparticles. The confirmation of the ordered tetragonal structure allows us to investigate the electronic structure of the material using density functional theory (DFT) calculations. The inclusion of a Hubbard (DFT+U) correction allows the calculation of a band gap in good agreement with experiment. The value of the gap is dependent on the electron spin, which is the basis for the spin-filtering properties of maghemite.Comment: 19 pages, 2 tables, 5 figures. To appear in the Journal of Physics - Condensed Matter (2010)

Instabilities of Higher-Order Parametric Solitons. Filamentation versus Coalescence

We investigate stability and dynamics of higher-order solitary waves in quadratic media, which have a central peak and one or more surrounding rings. We show existence of two qualitatively different behaviours. For positive phase mismatch the rings break up into filaments which move radially to initial ring. For sufficient negative mismatches rings are found to coalesce with central peak, forming a single oscillating filament.Comment: 5 pages, 7 figure

Rotaxane Co-II Complexes as Field-Induced Single-Ion Magnets

Mechanically chelating ligands have untapped potential for the engineering of metal ion properties. Here we demonstrate this principle in the context of CoII-based single-ion magnets. Using multi-frequency EPR, susceptibility and magnetization measurements we found that these complexes show some of the highest zero field splittings reported for five-coordinate CoII complexes to date. The predictable coordination behaviour of the interlocked ligands allowed the magnetic properties of their CoII complexes to be evaluated computationally a priori and our combined experimental and theoretical approach enabled us to rationalize the observed trends. The predictable magnetic behaviour of the rotaxane CoII complexes demonstrates that interlocked ligands offer a new strategy to design metal complexes with interesting functionality

Stringent test of QED with hydrogenlike tin

Inner-shell electrons naturally sense the electric field close to the nucleus, which can reach extreme values beyond $10^{15}\,\text{V}/\text{cm}$ for the innermost electrons. Especially in few-electron highly charged ions, the interaction with the electromagnetic fields can be accurately calculated within quantum electrodynamics (QED), rendering these ions good candidates to test the validity of QED in strong fields. Consequently, their Lamb shifts were intensively studied in the last decades. Another approach is the measurement of $g$ factors in highly charged ions. However, so far, either experimental accuracy or small field strength in low-$Z$ ions limited the stringency of these QED tests. Here, we report on our high-precision, high-field test of QED in hydrogenlike $^{118}$Sn$^{49+}$. The highly charged ions were produced with the Heidelberg-EBIT (electron beam ion trap) and injected into the ALPHATRAP Penning-trap setup, where the bound-electron $g$ factor was measured with a precision of 0.5 parts-per-billion. For comparison, we present state-of-the-art theory calculations, which together test the underlying QED to about $0.012\,\%$, yielding a stringent test in the strong-field regime. With this measurement, we challenge the best tests via the Lamb shift and, with anticipated advances in the $g$-factor theory, surpass them by more than an order of magnitude