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WAVEVECTOR SELECTIVITY

One important enhanced sensitivity of DAFS is its wavevector selectivity. Wavevector selectivity can be obtained whenever different spatial regions, or components, of the sample produce Bragg diffraction peaks at separable locations in reciprocal space. Then, the local atomic structure of each region can be determined by using one of its characteristic diffraction peaks, even when the different regions contain identical atomic types. Wavevector selectivity is not possible with XAFS measurements in general, because there is often no way to separate the absorption signals of the different regions or components. Some applications where the wavevector selectivity of DAFS can provide information that cannot be obtained using XAFS include: (1) strained and/or compositionally modulated layers, (2) mixed phase powders or composite materials, (3) buried layers, and (4) buried monolayers or reconstructed interfaces. The example described in this section is for a buried layer system. Examples of wavevector selective DAFS for mixed phase powders [9] and for buried monolayers [8, 25] have been reported by several groups.