  Conformal Atomic Layer Deposition (ALD) of nanoparticles is an now an
established nanofabrication concept employed by many researchers for
applications such as creating diffusion barriers, tuning catalysis, or masking
a toxic particle core with a biocompatible shell. To conformally coat many
grams of nanoparticles with ALD, long precursor soaking steps, fluidized beds,
vibrating stages, or rotary feedthroughs are typically needed. While these
impressive advancements in ALD techniques dominate literature searches of
particle ALD coating, such methods may lead to a more time-intensive or
cost-prohibitive process than what is required by many typical academic
researchers. Thus we have performed this study to explore the limits of static
planar ALD particle coating, the simplest method to coat nanoparticles with an
ALD film. Using an Arradiance GEMStar6 ALD system, we have explored a fast and
simple static ALD particle coating process. Our protocol produces relatively
small, but still academically useful, quantities of uniformally ALD-coated
nanospheres. This process can be scaled up to nanoparticle samples in the tens
of milligram to gram range. We have demonstrated that we can achieve silica or
titania spherical particle synthesis, and then uniform ALD coating on the
nanoparticles, all within 8-10 hours. The diameter of the chemically
synthesized silica and titania nanoparticles is tunable from 50 nm up to
greater than a micron. The refractive index of the titania nanoparticles is
tunable from approximately 1.7 to 2.7. This report will be most useful for
researchers who are new to particle ALD, or who want to experiment with core
particles conformally covered with ALD shells before moving to a more
complicated, higher throughput ALD method. We provide details for particle
synthesis, storage, and ALD coating along with a comparison to more
conventional approaches.
