F. Stratmann

Experimental Comparison of Four Differential Mobility Analyzers for Nanometer Aerosol Measurements

ABSTRACT The performance of four differential mobility analyzers (DMAs), namely the TSI-long, the TSI-short, the Hauke 3/150, and the Spectrometre de Mobillte Electrique Circulaire (SMEC) were evaluated under the same conditions of flow rates, flow ratio, input monodisperse aerosols, and transport-line lengths. The evaluations were performed under the conditions of 10 1/min sheath air and 1 1/min aerosol flow rates, and at a flow ratio of 10:1. Monodisperse aerosols in the size range of 6 nm to 50 nm were obtained by classifying condensation aerosols using a Hauke DMA operated at 20:1 flow ratio. The transfer functions of all four DMAs have been obtained by deconvoluting the scan results of the evaluated DMA (DMA2), and by using the empirical transfer function of the first DMA (DMA1, the Hauke DMA at 20:1 flow ratio). The half-width, height, and area of the transfer functions have been compared for the four DMAs tested. These results provide a quantitative comparison of the mobility resolution and diffusi...

Thermophoretical and diffusional particle transport in cooled laminar tube flow

Abstract A highly accurate dimensional and a less accurate non-dimensional model to describe particle transport due to combined convection, diffusion and thermophoresis in cooled laminar tube flows are presented. To verify the dimensional model, an experimental setup was built. Results determined by applying the model to describe the particle transport in the experimental setup are compared with the experimental data gained. The influences of different fluid mechanical and aerosol dynamical effects (e.g. temperature dependence of the material properties, particle diffusion, particle concentration profiles) on particle deposition are discussed. Applying the less accurate non-dimensional model a new thermophoretic parameter was found and a simple approximation formula to calculate the total thermophoretic deposition efficiency is suggested. Results for axial deposition profiles considering particle transport due to convection and thermophoresis as well as convection, diffusion and thermophoresis are presented.

Differential electrical mobility analysis : A theoretical study

ABSTRACT The subject of this work is the theoretical investigation of slowly scanning differential mobility analyzers (DMAs) which are, e.g., utilized to determine DMA transfer functions and to measure particle mobility distributions. A model to describe such systems is introduced and applied to investigate three different regimes of input mobility distributions: 1) a mobility distribution much narrower than the DMA transfer function, 2) a mobility distribution of about the same width as the DMA transfer function, and 3) a mobility distribution much wider than the DMA transfer function. Cases 1) and 2) are relevant for DMA transfer function measurements utilizing tandem differential mobility analyzer (TDMA) systems. For either regime, it is not possible to determine DMA transfer functions directly from the concentration distributions measured at the outlet of a DMA. For these cases, a deconvolution procedure is needed. Therefore, an iterative deconvolution procedure was developed. Determining DMA transfer...

Suppression of Particle Deposition to Surfaces by the Thermophoretic Force

Product contamination by particles is of major concern in the electronics industry. It has become increasingly important because of the decreasing size of the product elements. In a study of the feasibility of using the thermophoretic effect to reduce particle contamination of surfaces, a simple asymptotic formula has been derived for the thickness of the dust-free space in the boundary layer over a flat plate with a flow normal to the surface. This simple formula compares well with the results of a numerical solution. For a temperature difference between the surface and the surrounding gas of 10–30° K and face velocities between 0.3 and 1.0 m/s, the thickness of the dust-free space is between 0.1 and 0.4 mm, much larger than the particle size (0.1 μm ≥ Dp < 0.5 μm). The results indicate that, under conditions representative of clean-room applications, thermophoresis can be effective in protecting surfaces against particle deposition.

Numerical solution of aerosol dynamics for simultaneous convection, diffusion and external forces

Abstract An existing and widely used 2D computational fluid flow program has been modified to simulate dynamical aerosol processes affected by simultaneous convection, diffusion, and external forces.

Theoretical and experimental study of particle transport in vacuum chambers

Abstract Particle deposition models applicable to low pressure were developed by incorporating known pressure dependencies into well established atmospheric deposition models. Contributions by various particle deposition mechanisms such as sedimentation, diffusion, and other external forces are accounted for in the particle deposition model. Particle deposition experiments were conducted at both the University of Duisburg (UD) and the Research Triangle Institute (RTI). Each organization used its own customized vacuum chamber and differing methods of particle generation and detection. Results from both experimental setups are compared with the deposition models to assess the capability of the models in describing particle deposition in semiconductor vacuum processing equipments.