System Bits: June 17

Smartphone for good: Adapted to reduce falls
Purdue University researchers have shown how to modify a smartphone so that it can be used to measure a person’s walking gait to prevent falls in people with compromised balance, such as the elderly or those with Parkinson’s disease.

The technology is being commercialized as SmartGait, and was designed as a tool to aid health care officials in assessing a person’s risk of falling and identifying ways to avoid injury.

The system captures the gait length – the distance from the tip of the front foot to the tip of the back foot – and the gait width, the distance between each foot, and walking speed. Until now, there has been no portable user-friendly system that could be worn for a period of time to record a person’s gait.

The researchers adapted a conventional smartphone with a downward-looking wide-angle lens and a special app that allows the phone to record and calculate gait measurements. The smartphone is worn on the waist, and the system records a person’s gait by measuring the distance between colored “foot markers” attached to the tip of each shoe.

The researchers compared SmartGait’s performance with that of a laboratory system that uses sensors and infrared-emitting diodes to measure gait. Compared to this gold standard, findings indicate the system calculates step length with an accuracy of about 95 percent. The method was shown to have a step width accuracy of about 90 percent.

Reimagining silicon
Silicon is ubiquitous in modern semiconductor manufacturing. Well-established procedures for its processing, perfected over more than five decades of industrial use, enable a diverse array of electronic devices that pervade everyday life. The highly evolved supply chain that accompanies Si’s dominance also enables very low manufacturing costs. In fact, it is far cheaper to fabricate a Si-based transistor than print a single letter in a newspaper, according to researchers at Georgia Tech.

The specific form of Si that fuels the ongoing semiconductor revolution is known as “diamond cubic.” This particular structure – the arrangement of atoms – readily forms during traditional processing. It is this structure that imparts Si with the properties that have been exploited in devices ranging from integrated circuits to solar cells. Importantly, because the properties of bulk diamond cubic Si are fixed, most think its long-term usefulness is limited. Yet this narrow view of a material’s capabilities, Si or otherwise, and thus its utility in specific applications, assumes that rearranging the atoms into new structures is exceedingly difficult or impossible.

What if techniques were available to program alternative structures? What new properties would arise? What applications might these reimagined materials enable? Dr. Michael A. Filler, an assistant professor in the School of Chemical & Biomolecular Engineering, and his research group are asking these questions about nanomaterials in general, and Si nanowires in particular.

The promise of designing materials with entirely programmable atomic arrangements, specifically the extensive property tunability that would accompany it, is what motivates his research team. Such a capability would allow the rethinking of the structure of new and old materials alike, so that they can conduct electricity, transport heat, or absorb light in distinct ways.

This research is inspired by the work of organic chemists, who apply a suite of synthetic methods, born from a basic knowledge of chemical bond breaking and forming, to create remarkably intricate functional molecules. “But unlike organic chemistry, the synthesis of most nanoscale materials is poorly understood, cannot be adequately controlled, and, as a result, yield low quality materials,” he commented.

Researchers frequently probe a material only after it has been made and, consequently, are unable to retrieve detailed information about the synthesis itself. “We watch the synthesis while it’s taking place. Once we have a better understanding of what’s going on, we can precisely engineer the structure we want,” Filler explained.

The researcher team showed for the first time that the stacking of atoms in a Si nanowire could be rationally manipulated. To do this, they controlled when and where special “structure directing” species attached to and covered the nanowire surface. This molecular coating forced the next layer of Si atoms to position themselves differently from the prior layer. “The rapid addition and removal of these species, whose chemical signatures we can observe in real time, allowed us to control the arrangement of Si atoms in the nanowire from one layer to the next,” he said. His group continues to refine their approach and will begin testing the properties of this new form of Si in the near future. Filler foresees that this work will find use in fields ranging from electronics and photonics to energy conversion and catalysis.

However, directing individual layers of Si atoms is just the first step, and as science and research continue to advance, Filler said there will be much more control over atomic placement in many materials. “The chemical engineers and materials scientists of the future will be able to choose the placement of every atom in a material.”