Controlled Fluxes of Silicon Nanoparticles to a Substrate in Pulsed Radio-Frequency Argon–Silane Plasmas

It has been hypothesized that high-energy impact of very small silicon nanoparticles on a substrate may lead to epitaxial growth of silicon films at low substrate temperature. A possible means for producing such energetic nanoparticle fluxes involves pulsing an RF silane-containing plasma, and applying a positive DC bias to the substrate during the afterglow phase of each pulse so as to collect the negatively charged particles generated during the RF power on phase. We here report numerical modeling to provide a preliminary assessment of the feasibility of this scheme. The system modeled is a parallel-plate capacitively-coupled RF argon–silane plasma at pressures around 100 mTorr. Simulation results indicate that it is possible to achieve a periodic steady state in which each pulse delivers a controlled flux of nanoparticles to the biased substrate, that average particle sizes can be kept below 2–3 nm, that impact energies of the negatively-charged nanoparticles that are attracted by the applied bias can be maintained in the ~1 eV/atom range thought to be conducive to epitaxial growth without causing film damage, and that the volume fraction of neutral nanoparticles that deposit by low-velocity diffusion can be kept well below 1 %. The effects of several operating parameters are explored, including RF voltage, pressure, the value of the applied DC bias, and RF power on and off time during each pulse

A contribution to the amaranthine quarrel between true and average electrical mobility in the free molecular regime

Landau and Lipschitz's approach—termed here H&B due to the use of Happel and Brenner's slow rotation approximation—for calculating the average electrical mobility over all orientations of an ion in the free molecular regime is shown in this manuscript to be an invalid assumption for non-globular ions when a fixed electrical field is present. The reason behind the invalidity seems to be the confusion between average “settling” velocity (the calculation intended by H&B) and the average mobility (drag) in the direction of the field. When a missing orientation is taken into account by rotating the drag tensor, the average mobility obtained through Landau's approach coincides with well-known orientationally averaged Kinetic Theory Methods such as those of Mason and McDaniel (M&M). H&B's averaging approach, however, can be related to the true mobility displacement of the ion or, in other words, the displacement occurring in the direction of the velocity. This true mobility displacement only agrees with the average mobility displacement if ion velocity and electrical field have always the same direction, which only happens under special cases. Analytical and numerical calculations of collision cross-sections of linear and planar structures using a momentum transfer kinetic theory approach are chosen here as a means to prove that a single rotation of the drag tensor is sufficient to show agreement between both methods. A projected area approach is also used to prove the inadequacy of the H&B method

Modeling of an Inverted Drift Tube for Improved Mobility Analysis of Aerosol Particles

A new mobility particle analyzer, which has been termed Inverted Drift Tube, has been modeled analytically as well as numerically and proven to be a very capable instrument. The basis for the new design have been the shortcomings of the previous ion mobility spectrometers, in particular (a) diffusional broadening which leads to degradation of instrument resolution and (b) inadequate low and fixed resolution (not mobility dependent) for large sizes. To overcome the diffusional broadening and have a mobility based resolution, the IDT uses two varying controllable opposite forces, a flow of gas with velocity v gas , and a linearly increasing electric field that opposes the movement. A new parameter, the separation ratio Λ = v drift /v gas , is employed to determine the best possible separation for a given set of nanoparticles. Due to the system’s need to operate at room pressure, two methods of capturing the ions at the end of the drift tube have been developed, Intermittent Push Flow for a large range of mobilities, and Nearly-Stopping Potential Separation, with very high separation but limited only to a narrow mobility range. A chromatography existing concept of resolving power is used to differentiate between peak resolution in the IDT and acceptable separation between similar mobility sizes

The size-mobility relationship of ions, aerosols, and other charged particle matter

Electrical Mobility is arguably the property upon which some of the most successful classification criteria are based for aerosol particles and ions in the gas phase. Once the value of mobility is empirically obtained, it can be related to a geometrical descriptor of the charged entity through a size-mobility relationship. Given the multiscale range of sizes in the aerosol field, approaches that can provide accurate transformations from mobility to size are not straightforward, and many times rely on experimentally derived parameters. The most well-known size-mobility analytical expression covering the whole Knudsen range for spherical particles is the semi-empirical Stokes-Millikan correlation. This expression matches Stokes' drag friction coefficient in the continuum regime and the friction factor for a predominantly diffuse reemission of the gas molecule in the free molecular regime, as theorized by Epstein, with empirical slip coefficients chosen to agree with Millikan's oil drop experiments. Despite its success, the Stokes-Millikan correlation has its shortcomings. For example, it needs to be modified to predict the mobility of non-spherical entities and needs correction terms when potential interactions or reduced mass effects are non-negligible. The Stokes-Millikan asymptotic behavior also fails to predict the gradual transition from diffuse to specular reemission behavior that is observed for increasingly smaller ions within the free molecular regime. Here we make an attempt at providing a comprehensive account of the existing mass-mobility relations in the continuum, transition and free molecular regimes for both spherical and non-spherical particles. Epstein's diffuse interaction is critically explored experimentally and numerically for different gases in the free molecular regime with the observation that, as the size of the particle increases, a progression from specular to diffuse reemission occurs for all gases studied. The rate at which this variation happens seems to differ from gas to gas and to be related to the conditions for which diffuse reemission effects stem from a combination of scattering and potential interactions

Analysis of Ion Motion and Diffusion Confinement in Inverted Drift Tubes and Trapped Ion Mobility Spectrometry Devices

Ion motion in trapped ion mobility spectrometers (TIMS) and inverted drift tubes (IDT) has been investigated. The two-dimensional (2D) axisymmetric analytical solution to the Nernst–Planck equation for constant gas flows and opposed linearly increasing fields is presented for the first time and is used to study the dynamics of ion distributions in the ramp region. It is shown that axial diffusion confinement is possible and that broad packets of ions injected initially into the system can be contracted. This comes at the expense of the generation of a residual radial field that pushes the ions outward. This residual electric field is of significant importance as it hampers sensitivity and resolution when parabolic velocity profiles form. When radio frequency (RF) is employed at low pressures, this radial field affects the stability of ions inside the mobility cell. Trajectories and frequencies for stable motion are determined through the study of Mathieu’s equation. Finally, effective resolutions for the ramp and plateau regions of the TIMS instrument are provided. While resolution depends on the inverse of the square root of mobility, when proper parameters are used, resolutions in the thousands can be achieved theoretically for modest distances and large mobilities

Optimization of long range potential interaction parameters in ion mobility spectrometry

The problem of optimizing Lennard-Jones (L-J) potential parameters to perform collision cross section (CCS) calculations in ion mobility spectrometry has been undertaken. The experimental CCS of 16 small organic molecules containing carbon, hydrogen, oxygen, nitrogen, and fluoride in N2 was compared to numerical calculations using Density Functional Theory (DFT). CCS calculations were performed using the momentum transfer algorithm IMoS and a 4-6-12 potential without incorporating the ion-quadrupole potential. A ceteris paribus optimization method was used to optimize the intercept σ and potential well-depth ϵ for the given atoms. This method yields important information that otherwise would remain concealed. Results show that the optimized L-J parameters are not necessarily unique with intercept and well-depth following an exponential relation at an existing line of minimums. Similarly, the method shows that some molecules containing atoms of interest may be ill-conditioned candidates to perform optimizations of the L-J parameters. The final calculated CCSs for the chosen parameters differ 1% on average from their experimental counterparts. This result conveys the notion that DFT calculations can indeed be used as potential candidates for CCS calculations and that effects, such as the ion-quadrupole potential or diffuse scattering, can be embedded into the L-J parameters without loss of accuracy but with a large increase in computational efficiency

Análisis comparativo de las políticas de Responsabilidad Social Corporativa entre España y Bélgica

El título del trabajo es «Análisis comparativo de las políticas de Responsabilidad Social Corporativa entre España y Bélgica» y ha sido realizado por Carlos Montori Larriba. La directora del TFG es Isabel Acero Fraile, profesora Departamento de Dirección y Organización de Empresas y la titulación a la que está vinculada es el Grado en Administración y Dirección de empresas en la Universidad de Zaragoza. Puesto que, por motivos de estudios en primer lugar y laborales más adelante, mi lugar de residencia se encuentra en Lovaina la Nueva (Bélgica), y ya que el año pasado tuve la oportunidad de cursar una asignatura cuyo objeto central era la responsabilidad social corporativa (RSC de aquí en adelante) en la universidad Católica de Lovaina. El trabajo estará enfocado de modo que se pueda establecer una comparativa entre España y Bélgica con el objeto de poder estudiar el desarrollo de esta filosofía empresarial en ambos países. Para ello, el trabajo consta de tres partes fundamentales. La primera de ellas es introductoria y se hará referencia tanto al concepto como a los objetivos perseguidos por la RSC así como a las diferentes formas de medirla y publicitaria, sin olvidar las críticas de las que no está exenta. En la parte troncal se realizará una comparativa entre ambos países así como una encuesta entre parte de la población que nos permitirá elaborar un estudio acerca de la opinión de los ciudadanos en los diversos aspectos planteados en la misma. Para acabar, se expondrán las conclusiones y posibles ideas de mejora de esta filosofía empresarial. Además, se analizará el futuro y la capacidad de desarrollo y crecimiento de la responsabilidad social en los años venideros

El comportamiento simbólico en las poblaciones neandertales: entre mito y realidad.

El origen del comportamiento simbólico centra uno de los temas de debate más intensos e interesantes en el panorama actual de la investigación prehistórica. Tradicionalmente, este comportamiento se ha asociado casi en exclusiva a los Humanos Anatómicamente Modernos. Si bien es cierto que las pruebas de una conducta simbólica en otras especies homínidas son escasas y poco firmes, en los últimos años, con el avance de los descubrimientos arqueológicos y las técnicas de investigación, las pruebas que asocian el origen de este comportamiento al Hombre de Neandertal se multiplican dando fuerza a la hipótesis de la existencia de un comportamiento simbólico anterior a nuestra especie

Contabilización de subvenciones, donaciones y legados

Last March 26 was issued the Order EHA/733/2010 25 March, approving the accounting aspects of public companies operating in certain circumstances, within which additional provision includes a standard about the criteria for designation as a non-refundable grant. This provision, together with the Statement No. 18, Grants, donations and legacies received, and, to some extent, the answer to the query number 11 included in the BOICAC number 75, governing the problem accounting of these operations, establishing the different points of time in which operations are to be recorded for this grant basis to accrual as defined in the Spanish Conceptual Framework.El pasado 26 de marzo se publicó la Orden EHA/733/2010, de 25 de marzo, por la que se aprueban aspectos contables de empresas públicas que operan en determinadas circunstancias, dentro de la cual, en su disposición adicional única, incluye una norma contable acerca de los criterios para calificar una subvención como no reintegrable, que es aplicable a todos los sujetos contables, con independencia de su carácter público o privado. Esta disposición, junto con la Norma de Registro y Valoración número 18, Subvenciones, donaciones y legados recibidos, del Plan General de Contabilidad y, en cierta medida, con la contestación a la Consulta número 11 incluida en el BOICAC número 75, regulan la problemática contable de estas operaciones, estableciendo los diferentes momentos del tiempo en los que se deben registrar las operaciones de subvención atendiendo para ello al Principio del Devengo definido en el Marco Conceptual del Plan General de Contabilidad

El nuevo Plan General de Contabilidad

Ejemplar dedicado a: Plan General de Contabilidad 90En el presente artículo los autores trazan una panorámica ordenada del conjunto de novedades que ha introducido el Plan General de Contabilidad de 1990 sobre el hasta ahora vigente de 1973.Publicad