Surface scattering efficiency

Light scattered off the disk surface is perhaps the best independent tracer of particle size distributions in disks. This is because particle size and structure not only affect the scattering efficiency, but also change the phase function and polarization of the scattered light. These extra sets of observables can often be exploited to... 

This uitrasonio-opticai technique (or haif-opticai technique [89]) was aiso a hyphenated technique in terms of energy sources viz. thermai and opticai for phonon and photon production, respectiveiy). Thermai surface phonons restrict practical application of the technique owing to their iow scattering efficiency, which results in overly long data collection times (typicaiiy severai hours for a singie spectrum, even with advanced multipass interferometers). Similar to active Raman spectroscopy, coherent acoustic phonons are assumed to be excited by two narrow-line frequency tunable laser beams at different frequencies or by laser pulses of short duration compared to the acoustic period. 

Enormous improvements in sensitivity for Raman spectroscopy can be achieved through surface-enhancement. The interaction of snrface plasmon modes of metal particles with target analytes can increase scattering efficiency by as much 14-orders of magnitude, although 6-orders of magnitude are more coimnon. Spencer, et al. used SERS to measure... 

Atomic and molecular-beam surface-scattering studies reveal efficient energy transfer between the translational, vibrational, and rotational energy modes of the incident molecules and.the surface atoms. 

The scattering efficiencies of different rare gas ions are different for different surfaces. Heavy surface atoms respond better to bombardment with a heavy ion such as argon rather than He. The ability of ISS to resolve atoms close in mass decreases as the difference between the bombarding ion and the target atom increases. Spatial resolution of ISS is limited to about 100 pm, so it is not as good as AES in this respect. 

For irregular isolated particles, numerical methods can be used to calculate the scattering efficiency. However, the SERS effect generally involves complex morphological substrates, such as electrochemicaUy roughened surfaces. In this case, collective effects between the particles play an important role in the SERS process, and the single particle models alluded to above are not very appropriate to simulate the scattering effect. 

The probability of a molecule producing Raman scattering is much less than the probability of IR absorption. However, advances in Raman instrumentation and lasers have narrowed the gap considerably, in some optimal cases, the sensitivity of normal Raman scattering compares favorably with IR absorption. In addition, the Raman scattering efficiency can be greatly increased by use of the surface enhanced and/or RR effects. 

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