Previous Page
US Naval Research Laboratory electronics science and technology engineers demonstrate the ability of single walled carbon nanotube transistors (SWCNTs) to survive the harsh space environment, investigating the effects of ionizing radiation on the crystalline structures and further supporting the development of SWCNT-based nanoelectronics for use in harsh radiation environments.
By developing a SWCNT structure with a thin gate oxide made from thin silicon oxynitride, NRL researchers recently demonstrated SWCNT transistors that do not suffer from such radiation-induced performance changes. This hardened dielectric material and naturally isolated one-dimensional SWCNT structure makes them extremely radiation tolerant.
The team found that, in addition to the rate at which the strain is applied, the effect depends critically - and in a highly predictable way - on the temperature of the material. “People think they’re independent,” Fan says, but it turns out the effects of strain rate and temperature are strongly related.
A team in MIT’s Department of Nuclear Science and Engineering (NSE) that studied how materials react to stresses, including impacts. The findings could ultimately help explain phenomena as varied as the breakdown of concrete under sudden stress and the effects of corrosion on various metal surfaces. Using a combination of computer modeling and experimental tests, the researchers studied one specific type of stress – in a defect called a screw dislocation – in one kind of material, an iron crystal lattice. But the underlying explanation, the researchers say, may have broad implications for many kinds of stresses in many different materials.
Essentially, the team analyzed how the strength of a material can increase quite abruptly as the rate of strain applied to the material increases. This transition in the rate at which a material cracks or bends, called a flow-stress upturn, has been observed experimentally for many years, but its underlying mechanism has never been fully explained, the researchers say.
“The formulation is not specific to this particular defect,” Yildiz explains. Rather, she and her colleagues have figured out what they believe is a set of general principles. “We have proven that it works in this system,” she says.
The effects are quite dramatic, Yildiz says: The rate of change taking place within the material can suddenly change by orders of magnitude, transforming a slow erosion into a sudden catastrophic fracture. The analysis could potentially help predict the breakdown of structures as varied as concrete buildings, metal pressure vessels in powerplants, and the structural components of airplane bodies, but further work will be needed to show how these basic principles can be applied to these different materials.