Paper TF-TuE7
Thin Film Synthesis via Nanogrinding

Tuesday, December 9, 2014, 7:40 pm, Room Makai

Thin films composed of nanoscale particles possess unique and varied electrical, optical and mechanical properties, which can be used to create advanced functional materials and nanostructured composites for devices. Such thin films find applications in electronics, optics, photovoltaics, energy storage, biomedicine, etc.

Here we describe a general approach to nanoparticle thin film synthesis based on colloidal or nanogrinding. Nanogrinding can produce large amounts of nanoscale particles in an appropriate solvent without the use of complex chemical or physical processing. The nanogrinding method typically employs planetary ball milling to grind a starting bulk powder into a nanoscale colloidal suspension suitable for thin film coating. Ball milling uses the rotary motion of a grinding jar containing the sample, grinding beads and a liquid medium, which is arranged eccentrically on a so-called sun wheel. The efficient energy transfer during planetary ball motion leads to nanogrinding being a fast and inexpensive process for the creation of nanostructured thin films. In addition, nanogrinding is very flexible allowing the formation of semiconducting, metallic or insulating particles and films. These unique advantages combine to create a general solution-based processing approach for thin film surface coatings and devices (including non-planar geometries).

Results of nanogrinding trials using high-purity bulk materials (Si, silicides, oxides) and characterization of the nanoparticles and films via electron microscopy, scanning probe methods, Raman spectroscopy and elemental analysis are presented. Zirconia grinding vessels and either zirconia or silicon nitride beads are used in a planetary ball mill to grind readily available high-purity powders initially consisting of ~10-50 micron particles dispersed in solvent. Grinding speeds and times are varied between 200-1000 rpm and 10-500 minutes, respectively. After milling, the resulting colloidal dispersions are optionally filtered and deposited on a substrate for further analysis. As grinding time is increased, the resulting particles and films display good uniformity with sizes below 100 nm. Atomic force microscopy of the particles showed that diameters down to ~2-4 nm could be achieved. Elemental analysis indicates that contamination from the grinding tools is minimal.

Nanogrinding is an efficient route to directly creating nanoparticles suitable for thin film deposition of various materials from solution. By adjusting the grinding parameters, the size and dispersion of the particles can be controlled and their properties optimized for applications, including thin film electronic and optical devices.