March 21, 2008

Quantum dot–based memory structures potentially one thousand times faster than current memory

The concept of a memory device based on self-organized quantum dots (QDs) is presented, enabling extremely fast write times, limited only by the charge carrier relaxation time being in the picosecond range. (from Applied Physical letters) [potentially one thousand times faster than current computer memory] For a first device structure with embedded InAs/GaAs QDs, a write time of 6 ns is demonstrated. A similar structure containing GaSb/GaAs QDs shows a write time of 14 ns.

Other interesting news from Applied Physical Letters:
Re-examination of Casimir limit for phonon traveling in semiconductor nanostructures.

The effective mean free path MFP of nanofilms is found to be larger than that of nanowires, where the Casimir limit for nanofilms equals twice its thickness, or two times of the limit for nanowires. The theoretical formula agrees approximately with available experimental and computer simulation results for heat conduction along semiconducting nanowires, nanofilms, and superlattices.


Nanomechanical device powered by the lateral Casimir force

The coupling between corrugated surfaces due to the lateral Casimir force is employed to propose a nanoscale mechanical device composed of two racks and a pinion. The noncontact nature of the interaction allows for the system to be made frustrated by choosing the two racks to move in the same direction and forcing the pinion to choose between two opposite directions. This leads to a rich and sensitive phase behavior, which makes the device potentially useful as a mechanical sensor or amplifier. The device could also be used to make a mechanical clock signal of tunable frequency.


Excimer-based red/near-infrared organic light-emitting diodes with very high quantum efficiency

Various light output measures of red/near-infrared (NIR) excimer-based organic light-emitting diodes (LEDs) are reported for different cathodes (Al, Al/LiF, Ca, and Ca/PbO2). By using a selected phosphor (PtL2Cl) from a series of terdentate cyclometallated efficient phosphorescent Pt(II) complexes, PtLnCl, as the neat film emitting layer and a Ca/Pb(IV)O2 cathode, the authors achieve unusually high forward viewing external quantum efficiencies of up to 14.5% photons/electron and a power conversion efficiency of up to 6% at a high emission forward output of 25 mW/cm2. These are the highest efficiencies reported for a NIR organic LED.


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