Continuum supersonic gas jet enhanced focused electron beam induced deposition
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The unconventional approach of using a continuum, rather than molecular, gas jet to deliver precursor deposition molecules is applied toward the enhancement of focused electron beam induced deposition in terms of significantly increasing the precursor injection rate, enhancing surface diffusion, and increasing as-deposited deposition purity. These enhancements are carefully investigated by experiment, theory, and computational simulations and models. Use of argon as a carrier gas in the continuum flow regime is applied to achieve an organometallic deposition precursor injection rate that is four orders of magnitude greater than conventional molecular injection. The continuum flow regime also narrows the velocity distribution of impinging gas particles such that velocity may be tuned by nozzle temperature – either decreasing the temperature to increase sticking and prevent desorption, or increasing the temperature to increase surface diffusion (continuum jet induced 10x increase in surface diffusion) and deposition purity (heated continuum jet resulted in 95% as deposited tungsten purity). In order to analyze the effects of a continuum gas jet, a direct simulation monte carlo algorithm is developed to predict the complex flow structure developing due to a more localized and higher density flow emanating from a gas jet in the continuum flow regime. A novel adaptive algorithm is developed to allow the simulation to efficiently and accurately simulate flows with Knudsen numbers varying from O(0.01) (continuum flow) to O(10) (molecular flow) in a single simulation. Surface impingement data provided by the simulation is used in numeric integration of the hard-cube model to accurately predict the surface thermal responses to jet impingement as measured by a microscale resistance thermal detector and, for the first time, predict the spacial distribution of the effective temperature of the adsorption layer, which is in a highly non-equilibrium state relative to the surface. This adsorption layer effective temperature is the key to understanding and controlling the enhanced diffusion and enhanced deposition purity effects achieved via continuum flow gas jet enhanced deposition.