Inside a quantum dot: Tracking electrons at trillionths of a secondNovember 28, 2005Researchers at the EPFL (Ecole Polytechnique Federale de Lausanne) have developed a new machine that can reveal how electrons behave inside a single nano-object. The results from initial tests on pyramidal gallium-arsenide quantum dots are presented in an article in the November 24 issue of Nature. Hiding in the lab behind a dramatic black curtain, the hardware setup is not particularly imposing. It doesn't look expensive. Nonetheless, this machine in EPFL's Laboratory of quantum optoelectronics took four years to perfect and represents an equipment investment of more than a million Swiss francs. It is an ingenious combination of technologies onto a single powerful platform. It will improve our understanding of the dynamics that rule the nanoscale world, perhaps opening doors to exploiting the physics of nanoscale phenomena for practical ends. Even the most sophisticated methods used to explore material properties and dynamics run into limits when applied at the nanoscale. Current techniques either have good spatial resolution (down to tens of nanometers or below) or an ultrafast time resolution (down to picoseconds), but not both. At least not until now. The machine developed by Professor Benoit Deveaud-Pledran and his EPFL colleagues is the first tool that can track the passage of an electron in a nanostructure - at a time scale of ten picoseconds and a spatial resolution of 50 nanometers. The EPFL researchers replaced the standard electron gun filament on an off-the-shelf electron microscope with a 20 nanometer-thick gold photocathode. The gold is illuminated by an ultraviolet mode-locked laser, generating an electron beam that pulses 80 million times per second. Each pulse contains fewer than 10 electrons. The electrons excite the sample, causing it to emit light. The spectroscopic information is collected and analyzed to recreate the surface morphology and to trace the path the electrons follow through the sample. Deveaud-Pledran and his colleagues tested their new machine on pyramidal quantum dots. These 2-micron-high nano-objects, specially synthesized in the lab of EPFL professor Eli Kapon, contain several different nanostructures, making them ideal test objects. When the electron beam impacts the pyramid, the electrons diffuse towards the closest nanostructure. From there, the diffusion continues until the point of lowest energy is reached - the quantum dot at the tip of the pyramid. The time traces corresponding to each of these nanostructures reveal just how critical that 10- picosecond time resolution is; with even a 100-picosecond resolution, important information would be lost. The machine will not only give us a glimpse into nanoscale dynamics, but because it will work on any semiconductor, it will also allow researchers to study previously intractable materials. The wide energy range of the electrons in the beam can excite materials that won't luminesce with laser techniques, explains Deveaud-Pledran. "With a laser, you can't get a short enough wavelength to excite diamond or silicon, for example. This machine will." Nanotechnology is widely heralded as the key to the technology of the future - everything from quantum computing to ultra-dense data storage to quantum cryptography depends on the behavior and control of materials at the nanoscale. "Remember the first portable CD-players?" says Deveaud. "They consumed 4 AA batteries reading a single disk. We improved our understanding of the physics of materials, and now they consume 50 times less energy. As far as the nanoworld is concerned, we still don't understand the dynamics of materials at the nanoscale. I can't tell you exactly what this machine will lead to because that depends on who uses it and what we find. But there's no question that it will help us make progress, and that the potential applications are exciting." Ecole Polytechnique Fédérale de Lausanne |
|||||||||||||||||||||
| Related Nanoscale Current Events and Nanoscale News Articles Small optical force can budge nanoscale objects With a bit of leverage, Cornell researchers have used a very tiny beam of light with as little as 1 milliwatt of power to move a silicon structure up to 12 nanometers. That's enough to completely switch the optical properties of the structure from opaque to transparent, they reported. Small nanoparticles bring big improvement to medical imaging If you're watching the complex processes in a living cell, it is easy to miss something important-especially if you are watching changes that take a long time to unfold and require high-spatial-resolution imaging. Pushing light beyond its known limits Scientists at the University of Adelaide have made a breakthrough that could change the world's thinking on what light is capable of. Nanotech in Space: Rensselaer Experiment To Weather the Trials of Orbit Novel nanomaterials developed at Rensselaer Polytechnic Institute are scheduled to blast off into orbit on November 16 aboard Space Shuttle Atlantis. Caltech scientists develop DNA origami nanoscale breadboards for carbon nanotube circuits In work that someday may lead to the development of novel types of nanoscale electronic devices, an interdisciplinary team of researchers at the California Institute of Technology (Caltech) has combined DNA's talent for self-assembly with the remarkable electronic properties of carbon nanotubes, thereby suggesting a solution to the long-standing problem of organizing carbon nanotubes into nanoscale electronic circuits. Engineers image nanostructure of a solid acid catalyst and boost its catalytic activity The catalytic processes that facilitate the production of many chemicals and fuels could become much more environmentally friendly thanks to a breakthrough achieved by researchers from Lehigh and Rice Universities. Findings show nanomedicine promising for treating spinal cord injuries Researchers at Purdue University have discovered a new approach for repairing damaged nerve fibers in spinal cord injuries using nano-spheres that could be injected into the blood shortly after an accident. Magnetic nanoparticles to simultaneously diagnose, monitor and treat Whether it's magnetic nanoparticles (mNPs) giving an army of 'therapeutically armed' white blood cells direction to invade a deadly tumour's territory, or the use of mNPs to target specific nerve channels and induce nerve-led behaviour (such as the life-dependant thumping of our hearts), mNPs have come a long way in the past decade. Breakthrough in industrial-scale nanotube processing Rice University scientists today unveiled a method for the industrial-scale processing of pure carbon-nanotube fibers that could lead to revolutionary advances in materials science, power distribution and nanoelectronics. LANL Roadrunner simulates nanoscale material failure Very tiny wires, called nanowires, made from such metals as silver and gold, may play a crucial role as electrical or mechanical switches in the development of future-generation ultrasmall nanodevices. More Nanoscale Current Events and Nanoscale News Articles |
|||||||||||||||||||||
|
|||||||||||||||||||||
|
|||||||||||||||||||||