Nanoparticles are boring…

Nanoparticles are boring SQUARE HOLES in our silicon wafers!
Etch_Hole_2Etch_Hole_3

The gold nanoplates from the O’Toole group enhance the etch rate in our usual silicon-etching process. Mysterious square pores appear when nanoparticles are present on the silicon. Others have made conical nanopores in a different etch chemistry and with different gold nanoparticles, and used them as channels for studying ion transport. But ours are coming out square. There is a well known process to etch square holes in silicon using potassium hydroxide (KOH) or similar etchants, but you have to define the edges of the holes first. At a much larger scale, it’s possible to make square holes using a drill!

 

Inflatable actuator with two stable states

Here is the latest iteration of the macro bistable actuator. We inflated two air pockets to make this 3-D printed plastic beam contort into an S-shape; this shape is an important step on the way to “snap-through” of our small and large bistable beams. The work continues Fidel Tewolde’s earlier project and makes good use of the materials and techniques in this excellent tutorial.

Watching the fins on the beam, you can see where we need to exert compressive stress (fins get farther apart) or tensile stress (fins get closer together) in order to make the beam bend. The visible fins provide some insight into our thermally-driven micro-beams, where it is a little harder to see what’s going on.

Selective heating with two types of nanoparticles

Image of triangular gold nanoplates and nanospheres with superposed absorbance spectra for two different populations of nanoplates.
Triangular gold nanoplates absorb at a peak wavelength that depends upon their size.
Our paper “Wavelength specific excitation of gold nanoparticle thin films” came out and is available online.
Working with gold nanoplates from our collaborators in the O’Toole group, we are looking at thermal expansion in thin films as a way to bend microscale beams. These nanoparticles can be highly wavelength selective. We found that we could achieve selective heating of surfaces coated with two different nanoparticle “species” using two different wavelengths. Meaning, one day you might be able to make your nanodevice do a complex dance by flashing two or more different lasers at it. No wires needed! Both wavelengths we used are in the biological “water window” of near-infrared that can go through tissue.

Nanoparticles such as these also have applications in strain sensing–potentially very useful for our shape-detection work– and in locally increasing the etch rate through materials. They were originally studied for their fascinating photonic properties, and a major motivation for their development is photothermal cancer therapy.

Both our IR sources came from Dragon Lasers (and safety glasses from noIR)

Bending some beams

Energy landscape of a bending beam on an inclined substrate
Energy landscape of a bending beam on an inclined substrate

We are looking at thin-film beams embedded in flexible surfaces. Not only can these beams act as micro-switches, but they can quickly jump to a new shape if the curvature of the surface changes. Their “snap-through” behavior is controlled by the amount of compression put into the beam at fabrication time. The concept works for the centimeter-scale inflatable actuators and multi-position laser-cut structures from summer 2013 as well as microscale beams. Because it is a MEMS (microelectromechanical systems) project, electrical engineers here are being forced to read mechanics textbooks but will get back to familiar territory when it’s time to do electronic readout of the beam position. We did the calculations for this plot in MATLAB; the code is located in the group’s hpcflip Github repository.