Relevance of bibliometric indicators on scientific areas critically depends on the quality of their delineation. Macro-level studies, often based on a selection of list of journals, accept a high degree of fuzziness. Micro-level studies rely on sets of individual articles in order to reduce noise and enhance precision of retrieval. The most usual information retrieval process is based on lexical queries with various levels of sophistication. In the experiment on Nano-sciences reported here, this process was used in a first step, to delineate a 'seed' of literature. It has strong limitations, especially for emerging or transversal fields. In a second step, the alternative way of citation linkages, was used to expand the bibliography starting from lexical seed. The third step is a structuration of the field by factorial methods to allow expert decision on final delineation. First results on citations are shown.