System Bits: March 22

How nanocrystal structures self assemble
Researchers at MIT and the Cornell High Energy Synchrotron Source (CHESS) have discovered some of the secrets to a long-hidden magic trick behind the self-assembly of nanocrystal structures, the understanding of which could be used to create more vivid display screens and optical sensory devices.

The transformation of simple colloidal particles — bits of matter suspended in solution — into tightly packed, beautiful lace-like meshes, or superlattices, has puzzled researchers for decades. These tiny superlattices — also called quantum dots — have the potential to make any surface into a smart screen or energy source hinges, in part, by understanding how they form.

Through a combination of techniques including controlled solvent evaporation and synchrotron X-ray scattering, the real time self-assembly of nanocrystal structures has now become observable in-situ, the researchers explained.

The team expect their findings will have implications for the direct manipulation of resulting superlattices, with the possibility of on-demand fabrication and the potential to generate principles for the formation of related soft materials such as proteins and polymers.

Developed by researchers at the Cornell High Energy Synchrotron Source (CHESS), a massive tunnel imaging facility that sits below athletics fields, an experimental apparatus measures simultaneous small-angle and wide-angle X-ray scattering during controlled solvent evaporation.
(Source: MIT)

Techniques including electron microscopy and dynamic light scattering have uncovered some aspects of the starting colloidal state and the final superlattice structure, but they have not illuminated the transition between these two states. In fact, such foundational work dates back to the mid-1990s with another group at MIT.

Farming at the nanoscale
University of Cambridge, IBM, and Lund University researchers have discovered how tiny ‘nanowires‘ of a widely-used semiconductor self-assemble that could lead to a new crop of nanodevices. 

At IBM’s T.J. Watson Research Center, and working with researchers from Lund University in Sweden and the University of Cambridge, the team uses a technique called self-assembly to grow and directly control nanostructures that could one day form parts of ICs.

As a reminder, self-assembly looks at chip building from the other end of the spectrum: a “bottom-up” approach that builds nanostructures in a way that is dictated by physics rather than by an imposed pattern. The researchers noted that in some ways it is like farming in that seeds are planted to grow a crop, and then the growth is supported with the right conditions.

Further, they said exploring self-assembly doesn’t mean today’s approaches will be thrown out, but instead, the top-down strategies learned over many years will be combined with new tricks that use self-assembly.

The more precisely self-assembly can be detected, the more versatility can be achieved: different materials can be chosen for our nanostructures, built with different sizes, and the chemical compositions controlled in ways that allow them to be tuned to have the properties needed.

Artistic rendering of self-assembled nanowires composed of different crystal structures that spontaneously grow with the help of a catalytic nanoparticle at the tip of each nanowire. (Source: University of Cambridge)

The properties of some nanomaterials could include the ability to do the job of a transistor but with less power, or at extreme temperatures beyond what silicon can handle.

Sonar enables smartwatch finger tracking
To alleviate the difficulty of interacting with wearable device screens the size of a matchbook, University of Washington researchers have developed a sonar technology that allows mobile device users to interact with them by writing or gesturing on any nearby surface — a tabletop, a sheet of paper or even in mid-air.

FingerIO tracks fine-grained finger movements by turning a smartphone or smartwatch into an active sonar system using the device’s own microphones and speakers. And, because sound waves travel through fabric and do not require a line of sight, users can even interact with a phone inside a front pocket or a smartwatch hidden under a sweater sleeve, they said.

In user testing with off-the-shelf smartphones, the finger location computed by FingerIO (in green) was accurate to within 8mm of the actual motion recorded on a separate touchscreen (shown in black). (Source: University of Washington)

The team has demonstrated that FingerIO can accurately track 2D finger movements to within 8mm, which is sufficiently accurate to interact with today’s mobile devices.