Abstract
We describe the use of the laser ablation of microparticle aerosol process to deposit patterned thick films of Ag by impacting nanoparticles with a mean size of 6 nm at high velocities and systematically study the effects of varying the nanoparticle impact velocity, while fixing the nanoparticle size. A positive relationship between impact velocity and relative density of the deposits is observed, but it is shown that the geometry of the deposits also influences the deposit density, with taller, narrower deposits resulting in lower relative densities. Scanning electron microscopy of film cross-sections shows that there are spatial variations in the relative density, with lower densities near the deposit surfaces. Using molecular dynamics simulations of the impact process for 6 nm particles, it is shown that a critical normal impacting velocity of 600-750 m/s exists for obtaining dense deposits. Normal velocities less than the critical velocity do not result in sufficient plastic deformation to fill interstices between the impacted particles. A geometric model based on this critical normal velocity and the relative deposit height is developed to explain the influence of relative heights and impacting velocity on porosity. Good qualitative agreement between the geometric model and experiments is demonstrated.
Highlights
Patterned thick films are routinely produced by high velocity impact of particles using the cold spray process1 and the aerosol deposition method (ADM)
While all three deposition processes utilize similar impact velocities (400-1500 m/s), studies have shown that films produced from cold spray and the ADM processes result in significantly different microstructures and densities compared to films made using ultrafine nanoparticle with laser ablation of microparticle aerosols (LAMA) due to differences in particle sizedependent deformation mechanisms
A series of molecular dynamics simulations are performed under conditions that are scitation.org/journal/adv nominally similar to those used in experiments to study the effect of normal impact velocity and it is shown that a critical normal impact velocity is required to obtain high density deposits
Summary
Patterned thick films are routinely produced by high velocity impact of particles using the cold spray process and the aerosol deposition method (ADM). A third process, the laser ablation of microparticle aerosols (LAMA), utilizes smaller (6-20 nm) nanoparticles (NPs) produced in situ from affordable micron-sized particles. Patterned thick films are routinely produced by high velocity impact of particles using the cold spray process and the aerosol deposition method (ADM).. While all three deposition processes utilize similar impact velocities (400-1500 m/s), studies have shown that films produced from cold spray and the ADM processes result in significantly different microstructures and densities compared to films made using ultrafine nanoparticle with LAMA due to differences in particle sizedependent deformation mechanisms.. Few systematic experimental studies have been performed, on high velocity impact of NPs with diameters less than 20 nm and the causes of these differences in microstructures and densities with particle size are not yet fully understood. This paper incorporates a systematic experimental study of the effects of NP impact velocity and deposit geometry on film density and microstructure, while keeping the particle size distribution constant. Experimental results are compared to the predictions from this model
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