Sunday, May 01, 2011

How small is small? the pico, femto, atto world

Man continues to master the manipulation of matter and timescales further up and down the chain from observable quotidian life. Regarding time, ultrafast materials is the area of science that deals with phenomena occurring in picoseconds and faster.

The familiar time scale is one second, easily measurable with a stop watch. A picsecond is 10-12 of a second or 0.000000000001 seconds, a timescale used in high speed electronics. A femtosecond is 10-15 of a second, the timescale of molecular vibrations and carrier interactions in solids. An attosecond is 10-18 of a second, the timescale of electron motion at atomic levels.

Scientists are now finding in nature that most energy transfer and charge transfer transactions are typically taking place at the vibrational range, at the femtosecond timescale. A prominent example is the rhodopsin photoreceptor for vision. Traditional models for describing these dynamics, e.g.; Bloch’s single-electron band structure model, work for condensed matter but not for regular matter.

New models are needed to understand the interplay between atomic structure and electronic structure. Atomic structural dynamics deal with ultrafast chemical reactions,
ultrafast phase transitions, and ultrafast biological processes. Electronic structural dynamics deal with bond dynamics, valence charge flow, charge transfer, and electronic phase transitions.

One new tool being applied is the femtosecond X-ray. Since femtosecond X-rays interact with atomic cores, they are useful for obtaining direct information about atomic positions as compared with traditional optical measurements which only provide indirect information. This has immediately transferable implications in electronics manufacturing and biological applications.

Moving beyond the femtosecond scale, a next-generation light source at the attosecond time scale is being planned for the 2020 timeframe at Lawrence Berkeley Lab.

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