Characterisation of molecular orientation in organic nanomaterials by X-ray Linear Dichroism Microscopy

Soft X-ray spectromicroscopy is emerging as a powerful method for the chemical and structural analysis of nanostructured organic materials. X-ray spectromicroscopy combines the chemical and structural sensitivity of Near Edge X-ray Absorption Fine Structure (NEXAFS) spectroscopy with the high spatial resolution of X-ray microscopy. Linear Dichroism (LD), the anisotropic absorption of linearly polarised radiation by an oriented molecule, is observed in NEXAFS spectra. LD-NEXAFS offers excellent sensitivity to molecular orientation, and can be used to characterise molecular order in materials at high spatial resolution. Technical developments in X-ray microscopy and synchrotron undulator sources have enhanced X-ray Linear Dichroism Microscopy (XLDM) studies of organic materials. This paper will review the state of XLDM for studies of oriented organic materials, its relationship to other techniques, and the prospects for the study of nanoscale organic materials with new spectromicroscopy facilities, such as those at the Canadian Light Source.