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the atoms in a sample, but only on the surface. We, however, can also have a look through the object. We can see the positions of atoms and observe and measure them with a precision of around 50 picometres. This means we can observe how materials interact on the atomic scale, and deduce their macroscopic properties from their microscopic characteristics.”
The new electron microscopes are also useful in biology, to examine viruses for example. And they win out over conventional electron microscopes in being less aggressive with the biological samples.
Asked why they decided to persevere where many of their colleagues had given up, both Haider and Urban say they were convinced at the time that the problem could be cracked. The three scientists based at different institutions and exploring different directions within materials science, coincided at a conference in 1989 where Rose presented his theoretical approach. “Within five minutes I had an idea for a solution, but it took me another twenty years to catch up with these five minutes,” Rose recalls.
“And the idea was a good one,” remarks colleague Urban, himself by that time a reputed scientist. The three decided to collaborate and apply for a public grant, unaware that U.S. agencies had just decided to call off the search for a higher-resolution electron microscope. But Rose, who admits to a stubborn streak, was convinced that the goal could be achieved, in that “there was no physical law to prevent it.” Determined to press on in the face of rejection, Haider, Rose and Urban approached the Volkswagen Foundation, which, as Urban explains, funds research “that is not necessarily all that close to practical developments.”
Urban admits that this was a risky career move, given the dimensions of the challenge; “But if you don’t take risks, you don’t discover new things!” And he points out the paradox that a project that struggled to find funding “has produced industrial results extremely fast.”
Adamant that it is the science only that interests him, his name does not figure on many of the patents protecting the technique, though he is “totally on board” with basic research leading to industrial developments. “When I began working with Rose and Haider, all the equipment purchased by my laboratory came from Japan. European manufacturers had abandoned the sector, because there were no new products, no innovation.”
ZnTe augments broadband terahertz radiation
A THz emitter just 40 nm thick can perform as well as much thicker traditional emitters
Metamaterials scientists at the U.S. Department of Energy’s Ames Laboratory have demonstrated broadband terahertz (THz) wave generation using metamaterials.
The metamaterial is based on zinc telluride (ZnTe).
ZnTe can be easily doped, and for this reason it is one of the more common compound semiconducting materials used in optoelectronics.
The material is important for development of various semiconductor devices, including blue LEDs, laser diodes, solar cells, and components of microwave generators. It can be used for solar cells, for example, as a back-surface field layer and p-type semiconductor material for a CdTe/ZnTe structure or in PIN diode structures.
The material can also be used as a component of ternary semiconductor compounds, such as CdxZn(1-x) Te (conceptually a mixture composed from the end- members ZnTe and CdTe), which can be made with a varying composition x to allow the optical bandgap to be tuned as desired.
A THz spectrometer driven by femtosecond laser pulses was used to demonstrate THz emission from a split-ring resonator metamaterial of single nanometre thickness
The discovery may help develop non-invasive imaging and sensing, and make possible THz-speed information communication, processing and storage. The results appeared in the January 8th issue ofNature Communications.
Terahertz electromagnetic waves occupy a middle ground between electronics waves, like microwave and radio waves, and photonics waves, such as infrared and
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www.compoundsemiconductor.net January / February 2014
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