Nanometric metallic particles were prepared on top of a thin epitaxial oxide layer. Samples with the following structure: Fe electrode/MgO/Fe particles were fabricated and the arrangement of the Fe particles could be tuned from random to self-aligned by simply varying the thickness of the Fe electrode. Under appropriate deposition conditions, the particles were found to be self-aligned along the < 110 > directions of the underlying Fe electrode. Scanning tunneling microscope (STM) showed that their mean diameter and size distribution were then significantly reduced compared to randomly organized particles. Transmission electron microscope (TEM) images indicated that the self-alignment process originates from the strain relaxation of the Fe electrode which favors faceting of its surface and the formation of pyramidal structures. These self-aligned particles may be straightly used for applications based on a thin oxide tunnel barrier such as single-electron tunneling devices. (c) 2005 American Institute of Physics.