The dark phases of the N2HDM

We discuss the dark phases of the Next-to-2-Higgs Doublet model. The model is an extension of the Standard Model with an extra doublet and an extra singlet that has four distinct CP-conserving phases, three of which provide dark matter candidates. We discuss in detail the vacuum structure of the different phases and the issue of stability at tree-level of each phase. Taking into account the most relevant experimental and theoretical constraints, we found that there are combinations of measurements at the Large Hadron Collider that could single out a specific phase. The measurement of h125 → γγ together with the discovery of a new scalar with specific rates to τ+τ− or γγ could exclude some phases and point to a specific phase

Role of carbon atoms in the remote plasma deposition of hydrogenated amorphous carbon

The aim of this article is to determine the role of carbon atoms in the growth of hydrogenated amorphous carbon (a-C:H) films by means of an argon/acetylene expanding thermal plasma. Cavity ring down absorption spectroscopy is used to detect metastable carbon atoms by probing the 1s2 2s2 2p 3s 1P11s2 2s2 2p2 1S0 electronic transition. In addition to absorption measurements, the emission of the same transition is monitored by means of optical emission spectroscopy. These two measurements provide information about the local production of the C atoms and about their reactivity in the gas phase. It will be shown that under growth conditions in an Ar/C2H2 expanding thermal plasma, the metastable carbon density is also representative for the ground state carbon density. From obtained results it is concluded that the carbon atoms react rapidly with acetylene in the gas phase and therefore their contribution to the growth of hard diamond-like a-C:H films can be neglected. Only at low acetylene flows, the condition when soft polymer-like films are deposited, carbon atoms are detected close to the substrate and can possibly contribute to the film growth

Finite-size scaling of the error threshold transition in finite population

The error threshold transition in a stochastic (i.e. finite population) version of the quasispecies model of molecular evolution is studied using finite-size scaling. For the single-sharp-peak replication landscape, the deterministic model exhibits a first-order transition at $Q=Q_c=1/a$, where $Q$ is the probability of exact replication of a molecule of length $L \to \infty$, and $a$ is the selective advantage of the master string. For sufficiently large population size, $N$, we show that in the critical region the characteristic time for the vanishing of the master strings from the population is described very well by the scaling assumption \tau = N^{1/2} f_a \left [ \left (Q - Q_c) N^{1/2} \right ] , where $f_a$ is an $a$-dependent scaling function.Comment: 8 pages, 3 ps figures. submitted to J. Phys.

B-spline parametrization of the dielectric function applied to spectroscopic ellipsometry on amorphous carbon

The remote plasma deposition of hydrogenated amorphous carbon (a-C:H) thin films is investigated by in situ spectroscopic ellipsometry (SE). The dielectric function of the a-C:H film is in this paper parametrized by means of B-splines. In contrast with the commonly used Tauc-Lorentz oscillator, B-splines are a purely mathematical description of the dielectric function. We will show that the B-spline parametrization, which requires no prior knowledge about the film or its interaction with light, is a fast and simple-to-apply method that accurately determines thickness, surface roughness, and the dielectric constants of hydrogenated amorphous carbon thin films. Analysis of the deposition process provides us with information about the high deposition rate, the nucleation stage, and the homogeneity in depth of the deposited film. Finally, we show that the B-spline parametrization can serve as a stepping stone to physics-based models, such as the Tauc-Lorentz oscillator. © 2009 American Institute of Physics. U7 - Export Date: 24 March 2010 U7 - Source: Scopus U7 - Art. No.: 12350

Electric field measurements in atmospheric-pressure plasma jets

Atmospheric pressure non-thermal plasmas are researched for many applications. They became popular with plasma medicine, where restrictions on the plasmas are rigorous - they have to be at room temperature and not transfer significant amount of charge to the target, while still providing a mixture of reactive species, charge, field, to be efficient in medical applications. The intended applications soon extended to the treatment of different types of targets, where it is either important to treat them at atmospheric pressure (e.g. water) or with a plasma at room temperature. Atomic layer deposition is a good example of a traditionally low pressure technology being extended into the atmospheric pressure, and so is plasma catalysis. Another family of applications is in food and agriculture, where plasmas present a promising technology applied to a wide range of surfaces, dielectrics of different permittivities, in atmospheric air but also in humid conditions.The discharges used in these developments very often belong to the family of non-thermal atmospheric pressure plasmas - these are transient discharges, highly non-uniform in both space and time, small-scale (sub-mm), low ionization level, low light output, and most importantly sensitive to their environment. For example, a He plasma jet working in a kHz bullet mode changes its properties when impinging on a target with respect to the case when it expands freely into the ambient atmosphere. This is an important aspect to be kept in mind when bringing non-thermal atmospheric pressure plasmas intoapplications. It is also the motivation for the research presented in this talk. This work focuses on the fundamental properties of non-thermal plasmas such as the electric field, charge density and electron temperature. The work was performed on a non-thermal atmospheric pressure He plasma jet working in a kHz-driven mode with one ionization wave produced per voltage period or pulse. These fundamental properties of the discharge were measured in a freely expanding jet as well as when impinging on targets of different types, from low-permittivity dielectrics such as glass, to water, to metal. The measurements were performed in the plasma plume, but also in a target when a high-permittivity dielectric (er = 56) was used.The results bring one of the first sets of data concerning the E field, electron density and electron temperature, which are relatable to each other through the fact that they were all obtained on the same discharge. The effect of the gas flow speed is significant in the freely expanding jet, showing that the increased flow extends not only the visible length of the plasma plume, but also its electric field profile. In addition, the electron density and temperature were shown to respectively fall and rise within the plasma plume with increasing the distance from the end of the glass capillary.The presence of the target influences the plasma plume in several different ways. For low-permittivity targets, such as plastic or glass, the presence of the target does not significantly influence the plasma properties in the plume, but it does initiate surface discharges belonging to the family of ionization waves. The electric field induced in the target material by those surface ionization waves were measured, both axially, in the direction through the material, and radially. When the permittivity of the target is increased, the surface ionization waves are replaced by one or several return strokes and a significantly altered electric field profile, along with increased electron density and temperature. In the extreme case of the metallic target, combined with much higher electron densities, the duration of the discharge on the metal surface is extended to a microsecond. The work shows not only that the presence of the target influences the plasma, but that the properties of the target determine the plasma parameters, also in the gas phase

Production of negative ions on graphite surface in H₂/D₂ plasmas: experiments and SRIM calculations

In previous works, surface-produced negative-ion distribution-functions have been measured in H2 and D2 plasmas using graphite surfaces (highly oriented pyrolitic graphite). In the present paper, we use the srim software to interpret the measured negative-ion distribution-functions. For this purpose, the distribution-functions of backscattered and sputtered atoms arising due to the impact of hydrogen ions on a-CH and a-CD surfaces are calculated. The srim calculations confirm the experimental deduction that backscattering and sputtering are the mechanisms of the origin of the creation of negative ions at the surface. It is shown that the srim calculations compare well with the experiments regarding the maximum energy of the negative ions and reproduce the experimentally observed isotopic effect. A discrepancy between calculations and measurements is found concerning the yields for backscattering and sputtering. An explanation is proposed based on a study of the emitted-particle angular-distributions as calculated by srim

Investigation of the effect of microstructural changes on thermal transport in semicrystalline polymer semiconductors

Great progress in the development of new semiconducting polymers over the last two decades alongside improved understanding of electron transport mechanisms have resulted in a dramatic increase in the electron mobility of these materials making them promising candidates for electronic and thermoelectric applications. Heat transport phenomena, on the other hand—which govern thermal conductivity—have not received as much attention up to date. In spite of the simplicity of the principle behind the measurement of thermoelectric properties, the combined uncertainty in thermoelectric figure of merit zT could easily reach 50% with the largest uncertainty coming from thermal conductivity measurements. Such a high measurement uncertainty, often comparable to relative variations in zT encountered when optimizing within a given class of materials, prevents the study of structure-thermal property relationships. Here we present a protocol for the measurement of the thermal conductivity of thin films with reduced measurement uncertainty, which allowed us to investigate the effect of microstructural changes on the thermal conductivity of the conjugated polymer P(NDI2OD-T2). We show that the enhancement of the thermal conductivity upon annealing is much less pronounced than the corresponding increase in the electron mobility that has been reported under the same annealing conditions in the literature. This suggests that semicrystalline conjugated polymers in which thermal transport remains limited by the amorphous domain boundaries in between crystalline grains could be a suitable system for realizing the electron-crystal phonon glass concept and enable higher performance thermoelectric materials.</jats:p