Single-atom detection

The extreme sensitivity and high resolving power of trace analysis techniques encourage the quest for single atom detection. 

A quantification of the repertoire of analytical chemistry is shown in Fig. 1.6. The field of operation covers over 30 orders of magnitude and more when the amount of lots is included. On the other hand, the relative amounts (contents, concentrations) with which the analyst has to do covers 20 orders and more because single atom detection has become reality now. 

Key words HRTEM, STEM, resolution, precision, sensitivity, single atom detection. 

Finally, we mention the application of multistep laser photoionization to the detection of small numbers of atoms. Researchers at Oak Ridge National Laboratory and at the Institute of Spectroscopy, USSR, have published papers on single atom detection. In both methods, resonant... 

Bekov, G.I. Letokhov, V.S. Matveev, 0.1. and Mishin, V.I., "Single-atom detection of ytterbium by selective laser excitation and field ionization from Rydberg states,"... 

One of the most successful applications of the laser to chemistry and physics lies in the area of diagnostics. Thanks to its intensity, monochromaticity and its continually expanding tunability, the internal states of chemical species can be probed readily to the concentration level of —10 -10 particles/cm. For several metal atoms which have large optical cross-sections, single-atom detection with the laser was achieved a few years ago. ... 

Note 1. Analytical advances have led to the possibility of "single atom detection" (85) At the same time it is recognized that at concentrations of 1 part in 10 (in water) in principle "every known organic compound could be detected" (86.). These measurement realities mandate the setting of regulatory levels on bases other than either non-zero concentrations, or the inherent ability to detect. 

With T = 10 s and r = 10 s we can expect n = 500 fluorescence photons per atom This allows single atom detection. 

Another very sensitive detection scheme is based on resonant two- or three-photon ionization of atoms and molecules in the gas phase (Sect. 6.3). With this technique even liquid or solid samples can be monitored if they can be vaporized in a furnace or on a hot wire. If, for instance, a heated wire or plate in a vacuum system is covered by the sample, the atoms or molecules are evaporated during the pulsed heating period and fly through the superimposed laser beams L1+L2 (+L3) in front of the heated surface (Fig. 15.2). The laser LI is tuned to the resonance transition /> - k) of the wanted atom or molecule while L2 further excites the transition k) f). Ions are formed if Ef is above the ionization potential IP. The ions are accelerated toward an ion multiplier. If L2 has sufficient intensity, all excited particles in the level / ) can be ionized and all atoms in the level [/ flying through the laser beam during the laser pulse can be detected single-atom detection) [15.10-15.12]. If... 

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