A superlattice sieve for electron energies.A superlattice A superlattice is a material with periodically alternating layers of several substances. Such structures possess periodicity both on the scale of each layer's crystal lattice and on the scale of the alternating layers. sieve for electron energies The iridescent ir·i·des·cent adj. 1. Producing a display of lustrous, rainbowlike colors: an iridescent oil slick; iridescent plumage. 2. sheen of an oil slick is one example of light interference caused by reflections from the upper and lower surfaces of a thin film. The same principle can be applied in constructing thin-film optical filters that screen out all but a specified wavelength of light. Relying on the analogy that has been established between the passage of light waves through materials such as glass and the propagation of electrons as waves through semiconductors, researchers have now designed an interference filter Interference filter An optical filter in which the wavelengths that are not transmitted are removed by interference phenomena rather than by absorption or scattering. not for light of a specified wavelength but for electrons with a certain energy. "It is clear that a wide variety of electron-wave optical devices are possible using electron-wave propagation, and that these devices can be designed by directly using existing optical designs," says electrical engineer Thomas K. Gaylord of the Georgia Institute of Technology Georgia Institute of Technology, in Atlanta, Ga.; coeducational; state supported; chartered 1885, opened 1888. It is a member school in the university system of Georgia. Significant among its facilities and programs are the Frank H. in Atlanta. Gaylord and Kevin F. Brennan describe their novel filter in the Nov. 21 APPLIED PHYSICS LETTERS Applied Physics Letters is a weekly peer-reviewed scientific journal published by the American Institute of Physics devoted to the publication of new experimental and theoretical papers about applications of physics to science, engineering, and modern technology. . Under the right circumstances, electrons can act as waves, showing a characteristic wavelength depending on the electron's energy. Overlapping these waves produces an interference pattern interference pattern An overall pattern that results when two or more waves interfere with each other, generally showing regions of constructive and of destructive interference. similar to the dark and light areas seen when light waves happen to cancel or reinforce each other. Furthermore, when such electron waves pass through a carefully structured semiconductor superlattice made of extremely thin, alternating layers of gallium arsenide An alloy of gallium and arsenic compound (GaAs) that is used as the base material for chips. Several times faster than silicon, it is used in high frequency applications such as cellphones, DVD players and fiber optics. and aluminum gallium arsenide, the lattice acts like an energy filter, allowing only electrons with a certain energy through. In their theoretical analysis, Gaylord and Brennan consider a filter consisting of nine layers, each layer a quarter or a half of the electron wavelength in thickness. Only electrons with an energy of 0.139 electron-volts would pass through such a filter, with a spread of just 0.003 electron-volts. Such high-resolution energy filters could be incorporated into semiconductor devices, for example, providing electrons for injection into highspeed, ballistic transistors. They could also control electron-beam energies when such beams are used for creating the masks needed to fabricate microelectronics circuits. Researchers at Georgia Tech are now attempting to fabricate semiconductor energy filters and other electron-wave devices. |
|
||||||||||||||||||
Printer friendly
Cite/link
Email
Feedback
Reader Opinion