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 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. Transforming Nanowires Into Nano-Tools Using Cation Exchange Reactions A team of engineers from the University of Pennsylvania has transformed simple nanowires into reconfigurable materials and circuits, demonstrating a novel, self-assembling method for chemically creating nanoscale structures that are not possible to grow or obtain otherwise. Caltech scientists first to trap light and sound vibrations together in nanocrystal Researchers at the California Institute of Technology (Caltech) have created a nanoscale crystal device that, for the first time, allows scientists to confine both light and sound vibrations in the same tiny space. Nanowire biocompatibility in the brain: So far so good The biological safety of nanotechnology, in other words, how the body reacts to nanoparticles, is a hot topic. Researchers at Lund University in Sweden have managed for the first time to carry out successful experiments involving the injection of so-called 'nanowires.' Caltech scientists solve decade-long mystery of nanopillar formations Scientists at the California Institute of Technology (Caltech) have uncovered the physical mechanism by which arrays of nanoscale (billionths-of-a-meter) pillars can be grown on polymer films with very high precision, in potentially limitless patterns. Harvard scientists bend nanowires into 2-D and 3-D structures Taking nanomaterials to a new level of structural complexity, scientists have determined how to introduce kinks into arrow-straight nanowires, transforming them into zigzagging two- and three-dimensional structures with correspondingly advanced functions. Smallest Nanoantennas for High-speed Data Networks More than 120 years after the discovery of the electromagnetic character of radio waves by Heinrich Hertz, wireless data transmission dominates information technology. 0.2 second test for explosive liquids Since a failed terrorist attack in 2006, plane passengers have not been able to carry bottles of liquid through security at airports, leaving some parched at the airport and others having expensive toiletries confiscated, but work by a group of physicists in Germany is paving the way to eliminate this necessary nuisance. More Nanoscale Current Events and Nanoscale News Articles |
|||||||||||||||||||||
|
|||||||||||||||||||||
|
|||||||||||||||||||||