Gas incorporation in sputtered and evaporated metal films

The argon and nitrogen gas concentrations in thin films have been measured for seven different metals. Sputtered and evaporated films are deposited on glass and tungsten substrates in a stainless steel ultra high vacuum system, which is designed to operate at background pressures in the 10-8 torr region, and at argon pressures of about 6 10-4 torr. The discharge is maintained by a triode type system and the plasma is confined with the aid of two magnet coils in a helmholtz configuration. The vacuum system is evacuated with ion and liquid nitrogen-cooled sublimation pumps. A second vacuum system is connected to the main deposition chamber by means of a gate valve so that the film samples can be withdrawn for study, using a rack and pinion mechanism, under continuously maintained vacuum conditions. The films are analysed by thorough outgassing in the second system, using an induction coil heater over a glass section of the system, so that desorption from other parts of the system is kept to a minimum. Gas analysis is achieved using a quadrupole mass spectrometer and the results are displayed on an XY recorder. Film thicknesses are monitored using a previously calibrated quartz crystal oscillator and the dimensions of samples and systems are known from careful measurement. The argon and nitrogen concentrations are measured as a function of gas pressure, film thickness. target voltage. target and substrate species and substrate bias voltage. The sputtered films are always found to contain more argon than the evaporated ones. This may be accounted for partly by the additional process of ion reflection, which takes place at the sputtered target surface but not at the evaporated one. Increasing the bias voltage causes an increase in the argon concentration in most of the films. This can be related to the noble gas clean-up effect, where energetic ions embed themselves in the film and become trapped by the continuous flux of metal atoms arriving at the surface. The results are in reasonable agreement with a theoretical model proposed by WINTERS et al. A comparison of the theoretical and experimental results makes it possible to derive sputtering yields for the gas. For argon, typical sputtering yields of ~ 10-16 atoms/ion are obtained at high bias ion energies, indicating that the gas release is being brought about by a gas sputtering mechanism. Yields of the same order as those of the metal suggest that gas release by a target sputtering process predominates at lower ion energies. However, the division between mechanisms is not well defined and depends to a great extent on the target species. The results for nitrogen incorporation support Winters proposal that metals can be divided into three classes. The results show that the simple hypothesis that bias sputtering always brings about a reduction in the impurity gas contamination does not hold for all gas/metal combinations. It is shown for nitrogen, that the gas concentration can increase or decrease depending on the class of the metal and on the partial pressure of nitrogen present during deposition. Some of the films have been examined using an electron microscope. A significant change in the surface appearance is observed in some the outgassed sputtered films which is not apparent in either the nonoutgassed films or in the evaporated samples. The reasons for this are not clear at present

Ultra-short solitons and kinetic effects in nonlinear metamaterials

We present a stability analysis of a modified nonlinear Schroedinger equation describing the propagation of ultra-short pulses in negative refractive index media. Moreover, using methods of quantum statistics, we derive a kinetic equation for the pulses, making it possible to analyze and describe partial coherence in metamaterials. It is shown that a novel short pulse soliton, which is found analytically, can propagate in the medium.Comment: 6 pages, 2 figures, to appear in Phys. Rev.

Invariant manifolds and the geometry of front propagation in fluid flows

Recent theoretical and experimental work has demonstrated the existence of one-sided, invariant barriers to the propagation of reaction-diffusion fronts in quasi-two-dimensional periodically-driven fluid flows. These barriers were called burning invariant manifolds (BIMs). We provide a detailed theoretical analysis of BIMs, providing criteria for their existence, a classification of their stability, a formalization of their barrier property, and mechanisms by which the barriers can be circumvented. This analysis assumes the sharp front limit and negligible feedback of the front on the fluid velocity. A low-dimensional dynamical systems analysis provides the core of our results.Comment: 14 pages, 11 figures. To appear in Chaos Focus Issue: Chemo-Hydrodynamic Patterns and Instabilities (2012

A Giant Sample of Giant Pulses from the Crab Pulsar

We observed the Crab pulsar with the 43-m telescope in Green Bank, WV over a timespan of 15 months. In total we obtained 100 hours of data at 1.2 GHz and seven hours at 330 MHz, resulting in a sample of about 95000 giant pulses (GPs). This is the largest sample, to date, of GPs from the Crab pulsar taken with the same telescope and backend and analyzed as one data set. We calculated power-law fits to amplitude distributions for main pulse (MP) and interpulse (IP) GPs, resulting in indices in the range of 2.1-3.1 for MP GPs at 1.2 GHz and in the range of 2.5-3.0 and 2.4-3.1 for MP and IP GPs at 330 MHz. We also correlated the GPs at 1.2 GHz with GPs from the Robert C. Byrd Green Bank Telescope (GBT), which were obtained simultaneously at a higher frequency (8.9 GHz) over a span of 26 hours. In total, 7933 GPs from the 43-m telescope at 1.2 GHz and 39900 GPs from the GBT were recorded during these contemporaneous observations. At 1.2 GHz, 236 (3%) MP GPs and 23 (5%) IP GPs were detected at 8.9 GHz, both with zero chance probability. Another 15 (4%) low-frequency IP GPs were detected within one spin period of high-frequency IP GPs, with a chance probability of 9%. This indicates that the emission processes at high and low radio frequencies are related, despite significant pulse profile shape differences. The 43-m GPs were also correlated with Fermi gamma-ray photons to see if increased pair production in the magnetosphere is the mechanism responsible for GP emission. A total of 92022 GPs and 393 gamma-ray photons were used in this correlation analysis. No significant correlations were found between GPs and gamma-ray photons. This indicates that increased pair production in the magnetosphere is likely not the dominant cause of GPs. Possible methods of GP production may be increased coherence of synchrotron emission or changes in beaming direction.Comment: 33 pages, 10 figures, 6 tables, accepted for publication in Ap

Analysis and optimization of a free-electron laser with an irregular waveguide

Using a time-dependent approach the analysis and optimization of a planar FEL-amplifier with an axial magnetic field and an irregular waveguide is performed. By applying methods of nonlinear dynamics three-dimensional equations of motion and the excitation equation are partly integrated in an analytical way. As a result, a self-consistent reduced model of the FEL is built in special phase space. The reduced model is the generalization of the Colson-Bonifacio model and takes into account the intricate dynamics of electrons in the pump magnetic field and the intramode scattering in the irregular waveguide. The reduced model and concepts of evolutionary computation are used to find optimal waveguide profiles. The numerical simulation of the original non-simplified model is performed to check the effectiveness of found optimal profiles. The FEL parameters are chosen to be close to the parameters of the experiment (S. Cheng et al. IEEE Trans. Plasma Sci. 1996, vol. 24, p. 750), in which a sheet electron beam with the moderate thickness interacts with the TE01 mode of a rectangular waveguide. The results strongly indicate that one can improve the efficiency by a factor of five or six if the FEL operates in the magnetoresonance regime and if the irregular waveguide with the optimized profile is used

The influence of parents versus peers on Generation Y internet ethical attitudes

We examine the role of parental style versus peer influence on Generation Y's attitudes towards online unethical activities using a survey of a matched parent-child sample. Results suggest that a protective parental style has the greatest impact on Generation Y's online ethical attitudes, while a strict discipline style has no significant influence. Peers are more influential, but not as influential as when there is agreement between parents and their children on a specific activity. Methodologically, the research highlights the necessity to measure family dyads and assess whether or not parents and their children's perceptions are the same

A search for J^{PC}=1^{-+} exotic mesons in the pi- pi- pi+ and pi- pi0 pi0 systems

A partial wave analysis (PWA) of the pi-pi-pi+ and pi-pi0pi0 systems produced in the reaction pi- p -> (3pi)-p at 18 GeV/c was carried out using an isobar model assumption. This analysis is based on 3.0M pi-pi0pi0 events and 2.6M pi-pi-pi+ events and shows production of the a2(1320), pi2(1670) and \pi(1800) mesons. An earlier analysis of 250K pi-pi-pi+ events from the same experiment showed possible evidence for a J^{PC}=1^{-+}$ exotic meson with a mass of 1.6 GeV/c^2 decaying into rho pi. In this analysis of a higher statistics sample of the (3pi)- system in two charged modes we find no evidence of an exotic meson.Comment: 4 pages, 5 figures, added comment about the negative reflectivity exotic wave

Falling Incapacity Benefit claims in a former industrial city: policy impacts or labour market improvement?

This article provides an in-depth study of Incapacity Benefit (IB) claims in a major city and of the factors behind their changing level. It relates to the regime prior to the introduction of the Employment and Support Allowance (ESA) in 2008. Glasgow has had one of the highest levels of IB in Britain with a peak of almost one fifth of the working age population on IB or Severe Disablement Allowance (SDA). However, over the past decade the number of IB claimants in Glasgow, as in other high claiming areas, has fallen at a faster rate than elsewhere, and Glasgow now has twice the national proportion of working-age people on IB/SDA rather than its peak of three times. The rise in IB in Glasgow can be attributed primarily to deindustrialisation; between 1971 and 1991, over 100,000 manufacturing jobs were lost in the city. Policy response was belated. Lack of local statistics on IB led to a lengthy delay in official recognition of the scale of the issue, and targeted programmes to divert or return IB claimants to work did not begin on any scale until around 2004. Evidence presented in the article suggests that the reduction in claims, which has mainly occurred since about 2003, has been due more to a strengthening labour market than to national policy changes or local programmes. This gives strong support to the view that excess IB claims are a form of disguised unemployment. Further detailed evaluation of ongoing programmes is required to develop the evidence base for this complex area. However, the study casts some doubt on the need for the post-2006 round of IB reforms in high-claim areas, since rapid decline in the number of claimants was already occurring in these areas. The article also indicates the importance of close joint working between national and local agencies, and further development of local level statistics on IB claimants

Nematic-Isotropic Transition with Quenched Disorder

Nematic elastomers do not show the discontinuous, first-order, phase transition that the Landau-De Gennes mean field theory predicts for a quadrupolar ordering in 3D. We attribute this behavior to the presence of network crosslinks, which act as sources of quenched orientational disorder. We show that the addition of weak random anisotropy results in a singular renormalization of the Landau-De Gennes expression, adding an energy term proportional to the inverse quartic power of order parameter Q. This reduces the first-order discontinuity in Q. For sufficiently high disorder strength the jump disappears altogether and the phase transition becomes continuous, in some ways resembling the supercritical transitions in external field.Comment: 12 pages, 4 figures, to be published on PR

Structure of 8B from elastic and inelastic 7Be+p scattering

Motivation: Detailed experimental knowledge of the level structure of light weakly bound nuclei is necessary to guide the development of new theoretical approaches that combine nuclear structure with reaction dynamics. Purpose: The resonant structure of 8B is studied in this work. Method: Excitation functions for elastic and inelastic 7Be+p scattering were measured using a 7Be rare isotope beam. Excitation energies ranging between 1.6 and 3.4 MeV were investigated. An R-matrix analysis of the excitation functions was performed. Results: New low-lying resonances at 1.9, 2.5, and 3.3 MeV in 8B are reported with spin-parity assignment 0+, 2+, and 1+, respectively. Comparison to the Time Dependent Continuum Shell (TDCSM) model and ab initio no-core shell model/resonating-group method (NCSM/RGM) calculations is performed. This work is a more detailed analysis of the data first published as a Rapid Communication. [J.P. Mitchell, et al, Phys. Rev. C 82, 011601(R) (2010)] Conclusions: Identification of the 0+, 2+, 1+ states that were predicted by some models at relatively low energy but never observed experimentally is an important step toward understanding the structure of 8B. Their identification was aided by having both elastic and inelastic scattering data. Direct comparison of the cross sections and phase shifts predicted by the TDCSM and ab initio No Core Shell Model coupled with the resonating group method is of particular interest and provides a good test for these theoretical approaches.Comment: 15 pages, 19 figures, 3 tables, submitted to PR