Standing waves have node locations that do not move. This principle was used in a demonstrative example to align nanowires into a square array. Alternating current was delivered to four piezoelectric transducers oriented in a square.
Typically becoming popular for micro-structures, oragami type assembly of connected template-like objects could be carried out in several ways. One instance is where silicon could be folded and unfolded with the introduction of water droplets to the wafer.
At the nanoscale, it is difficult to manually manipulate and arrange certain entities of interest. Therefore, in most cases, we rely on physics and chemistry to do the work for us. In the more simple case of nanoparticles, we can functionalize their surface and in essence create tethers or molecular links. These links can interact to bring the nanoparticles closer together in a determined manner.
||Self Assembly – Light Induced
Some molecules may greatly absorb incident electromagnetic energy. Upon doing so, the energy level of the molecule may change and cause a subsequent isomer transformation. In the case of a gold single-nanoparticle chain, the dicyanide trimer was directly observed to be responsible for the bent-to-linear transformation as well as linking into longer oligomers.
A tweezer effect may also be used to position nanostructures and quantum dots. The action is related to the accumulated recoil of incident photon momentum. Biologists, for example, use this effect in optical tweezers to fix cells and rotate them at the focus of a microscope. Physicists can also use the tweezer effect to isolate and collide Rb atoms at a velocity of about 1m/s and temperatures of one millionth of a degree above absolute zero.
Furthermore, gold nanorods may be positioned more regularly outside of their normal bonding symmetry by light induced plasmonic vibration. This process was found to occur in aqueous solutions although could readily explain ablation-generated plasmonic nanostructure.
||Self Assembly – DNA Mediated
DNA is composed of two complementary strands which are attracted to each other through matching base pairs. This attraction between the two strands can be used for the DNA-mediated self-assembly of two different nanoparticles into large-scale nanocomposite arrays. Synthetic DNA strands are attached to the nanoparticles of interest and the strands are allowed to naturally pair up, causing the nanoparticles to self-assemble into 3-D superlattices. This technique makes it possible to mix nanoparticles with different magnetic, optical or chemical properties and their self-assembly can be controlled to produce new enhanced or multifunctional materials.