We present a general model based on a time-dependent, reaction-diffusion equation to determine the dosing times and coverage profiles in structured substrates during atomic layer deposition (ALD). We first derive expressions comprising a nonlinear diffusion-reaction equation coupled to a surface kinetic equation. In their non-dimensional forms, these equations show that coverage dynamics during ALD in nanostructured substrates depend only on two non-dimensional parameters, the Damkoler and precursor excess (number of molecules per surface site in the nanostructure) numbers. Using the assumptions of molecular flow in a circular pore, we derive a general, analytic equation to predict saturation exposure times. To demonstrate the utility of our model, we derive additional expressions incorporating a precursor loss term relevant to predicting exposure times during ozone-based ALD. Because our model makes no assumptions about the diffusion coefficient or sample geometry, it can easily be adapted to describe a broad range of ALD systems such as trenches and vias, anodized alumina, or aerogels under almost any conditions including molecular, viscous, and transition flow regimes

The inactivation of bacteria and biomolecules using plasma discharges were investigated within the European project BIODECON. The goal of the project was to identify and isolate inactivation mechanisms by combining dedicated beam experiments with especially designed plasma reactors. The plasma reactors are based on a fully computer-controlled, low-pressure inductively-coupled plasma (ICP). Four of these reactors were built and distributed among the consortium, thereby ensuring comparability of the results between the teams. Based on this combined effort, the role of UV light, of chemical sputtering (i.e. the combined impact of neutrals and ions), and of thermal effects on bacteria such as Bacillus atrophaeus, Aspergillus niger, as well as on biomolecules such as LPS, Lipid A, BSA and prions have been evaluated. The particle fluxes emerging from the plasmas are quantified by using mass spectrometry, Langmuir probe measurements, retarding field measurements and optical emission spectroscopy. The effects of the plasma on the biological systems are evaluated using atomic force microscopy, ellipsometry, electrophoresis, specially-designed western blot tests, and animal models. A quantitative analysis of the plasma discharges and the thorough study of their effect on biological systems led to the identification of the different mechanisms operating during the decontamination process. Our results confirm the role of UV in the 200-250 nm range for the inactivation of microorganisms and a large variability of results observed between different strains of the same species. Moreover, we also demonstrate the role of chemical sputtering corresponding to the synergism between ion bombardment of a surface with the simultaneous reaction of active species such as O, O 2 or H. Finally, we show that plasma processes can be efficient against different micro-organisms, bacteria and fungi, pyrogens, model proteins and prions. The effect of matrices is described, and consequences for any future industrial implementation are discussed.

A simple robust method is presented to determine the densities of metastable and resonant species in low temperature, low pressure argon and argon-diluted plasmas. The ratios of spectral lines which correspond to transitions from common upper states to resonant or metastable lower states are measured with low resolution optical spectrographs. Photon reabsorption makes these ratios sensitive to the population densities of the lower states. The concept of escape factors is used to develop a set of nonlinear equations for the line ratios, which does not depend on the densities of the upper states. By means of a least squares method, the equations can be solved for metastable and resonant state population densities. The method does not depend on the nature of the excitation process, which makes it superior to other spectroscopic techniques in situations where the electron energy distribution is not known.

Sequential infiltration synthesis (SIS) is an emerging materials growth method by which inorganic metal oxides are nucleated and grown within the free volume of polymers in association with chemical functional groups in the polymer. SIS enables the growth of novel polymer-inorganic hybrid materials, porous inorganic materials, and spatially templated nanoscale devices of relevance to a host of technological applications. Although SIS borrows from the precursors and equipment of atomic layer deposition (ALD), the chemistry and physics of SIS differ in important ways. These differences arise from the permeable three-dimensional distribution of functional groups in polymers in SIS, which contrast to the typically impermeable two-dimensional distribution of active sites on solid surfaces in ALD. In SIS, metal-organic vapor-phase precursors dissolve and diffuse into polymers and interact with these functional groups through reversible complex formation and/or irreversible chemical reactions. In this perspective, we describe the thermodynamics and kinetics of SIS and attempt to disentangle the tightly coupled physical and chemical processes that underlie this method. We discuss the various experimental, computational, and theoretical efforts that provide insight into SIS mechanisms and identify approaches that may fill out current gaps in knowledge and expand the utilization of SIS.

An atmospheric pressure microplasma jet is developed for depositing homogeneous thin films from C2H2. The adjustment of the gas flow through the microplasma jet assures optimal flow conditions as well as minimizes deposition inside the jet. In addition, the formation of an argon boundary layer surrounding the emerging plasma beam separates the ambient atmosphere from the flow of growth precursor. Thereby the incorporation of nitrogen and oxygen from the ambient atmosphere into the deposited film is suppressed. Soft polymerlike hydrogenated amorphous carbon (a-C:H) films are deposited at the rate of a few nm/s on the area of a few square millimeters.

This paper proposes a coherent set of electron impact inelastic cross sections for argon, based on recent experimental measurements. The updated set is validated by comparing calculated swarm parameters and rate coefficients (obtained by solving the two-term approximation electron Boltzmann equation) with available experimental data. This validation procedure is usually adopted when the cross section set is to be later used in plasma discharge modelling. Simulation results for the electron drift velocity and characteristic energy are in very good agreement with experimental values of these quantities. Calculations, using cross section sets proposed by different authors, of the total (direct + cascade) excitation coefficients to the 4s and 4p states, and of the Townsend ionization coefficient, show that the present set ensures the best overall agreement with measured values. The agreement is particularly good for the excitation coefficient to metastable 4s′[1/2]0 and the Townsend ionization coefficient, which are probably the most relevant electron macroscopic coefficients in the modelling of discharge plasmas.

Characterization of the behavior of chemically reactive species in a nonequilibrium inductively coupled argonhydrogen thermal plasma under pulse-modulated operation A rf microplasma jet working at atmospheric pressure has been characterized for Ar, He, and Ar/ CH 4 and Ar/ C 2 H 2 mixtures. The microdischarge has a coaxial configuration, with a gap between the inner and outer electrodes of 250 m. The main flow runs through the gap of the coaxial structure, while the reactive gases are inserted through a capillary as inner electrode. The discharge is excited using a rf of 13.56 MHz, and rms voltages around 200-250 V and rms currents of 0.4-0.6 A are obtained. Electron densities around 8 ϫ 10 20 m −3 and gas temperatures lower than 400 K have been measured using optical emission spectroscopy for main flows of 3 slm and inner capillary flows of 160 SCCM. By adjusting the flows, the flow pattern prevents the mixing of the reactive species with the ambient air in the discharge region, so that no traces of air are found even when the microplasma is operated in an open atmosphere. This is shown in Ar/ CH 4 and Ar/ C 2 H 2 plasmas, where no CO and CN species are present and the optical emission spectroscopy spectra are mainly dominated by CH and C 2 bands. The ratio of these two species follows different trends with the amount of precursor for Ar/ CH 4 and Ar/ C 2 H 2 mixtures, showing the presence of distinct chemistries in each of them. In Ar/ C 2 H 2 plasmas, CH x species are produced mainly by electron impact dissociation of C 2 H 2 molecules, and the CH x /C 2 H x ratio is independent of the precursor amount. In Ar/ CH 4 mixtures, C 2 H x species are formed mainly by recombination of CH x species through three-body reactions, so that the CH x /C 2 H x ratio depends on the amount of CH 4 present in the mixture. All these properties make our microplasma design of great interest for applications such as thin film growth or surface treatment.

Precursor reaction and transport are both critical in determining the thickness uniformity and conformality of atomic layer deposition (ALD) thin films. However, it is sometimes difficult to predict how changes in conditions, such as mass flow rate or precursor reactivity, will affect the outcome of an ALD experiment. To provide some insight and guidance, we have developed a simple 1D model to describe precursor transport and reaction in a tubular viscous flow ALD reactor. After making some simplifying assumptions, we show that the transport problem depends only on three independent parameters, the Peclet number, the Damkoeler number, and the excess number, which can be easily calculated for most ALD processes. Despite its simplicity, we obtain very good agreement with experimental results for the thickness profiles of ALD Al2O3 films deposited using trimethyl aluminum and H2O. The authors have applied the model to study the impact of precursor properties and experimental conditions on the growth profiles and saturation curves obtained during ALD, including the presence of nonself-limited wall recombination.