Coherent Diffractive Imaging



Coherent Diffractive Imaging


Liberato De Caro
Cinzia Giannini


Commessa:  PM.P04.011 / Diffrazione e imaging a raggi x per l'ingegneria di materiali nanostrutturati e tessuti biologici e per la biodiagnostica
Modulo:  PM.P04.011.002 / Imaging a raggi X e algoritmi di ricostruzione della fase


Phase Retrieval, Coherent Diffractive Imaging, Nano crystals

Dr. E. Carlino, TASC-INFM, Trieste
Prof. A. Nikulin, Monash University - Australia
Dr. Ana Diaz, cSAXS beamline, SLS-Villigen, Zurich
Dr. L. Manna, Istituto Italiano di Tecnologia, Genova
Dr. P. D. Cozzoli, National Nanotechnology Laboratory, Lecce
Dr. L. Curri, Dr. M. Striccoli, IPCF-CNR, Bari

The in-depth study of nanoscale matter represents a burning issue in modern materials science. Along with development of tools enabling programmable material fabrication with nanometer-level compositional and geometric precision, the unfolding of the local structure of nanomaterials with atomic resolution is increasingly emerging as a fundamental transition pathway towards control of their unique size-dependent properties and realization of their technological potential.

Coherent diffractive imaging (CDI) accomplished with short-wavelength probes, such as hard X-ray photons or medium-energy electrons, represents a powerful technique for the two-/three-dimensional spatial reconstruction of nanoscale objects. It relies on recording the coherent diffraction pattern of an isolated object at a sampling frequency smaller than the reciprocal of twice the object size, on the basis of which the image of the object is deduced by computational phase retrieval. This allows one to obtain an image of an object instead of using a lens to back-transform the diffraction pattern. Sophisticated iterative projection algorithms have provided useful practical solutions to giga-element nonlinear phase-retrieval problems, producing phase-retrieved images with resolutions beyond the capabilities of lens-based optical methods. Major difficulties preventing extraction of the entire information encoded in experimentally recorded diffraction patterns are not only imposed by the limited coherence of the incident wavefields, but also by the background noise and missing intensities arising from detector artefacts. Therefore, it is being envisioned that future boost of the imaging potential of CDI techniques will ultimately depend on the ability to overcome the inherent limitations associated with any experimentally measured diffraction patterns.

It is worth noting that electron and X-ray probes offer complementary fields of applications: with electrons a spatial resolution below 1 Å have been already obtained although on quite thin samples (few tenths of nanometers); with X-rays resolutions are still in the nanometric range (~10nm)  but samples buried into a matrix can be studied as well as experiments can be performed in specific samples environments.

The present research activity deals with the development of novel phase retrieval algorithms which could allow to extract sample information encoded in the diffraction patter, and from it, determine important structural features at the origin of the peculiar size-dependent physical-chemical properties of the concerned material in the nanoscale regime.


Liberato De Caro
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Last Updated (Monday, 06 December 2010 10:35)