Citation analysis of nanotechnology at the field level: implications of R&D evaluation

This article addresses the question of how much time it takes for contributions to the nanotechnology literature to establish themselves in the field by analyzing the dynamics of the citations to several cohorts of its papers and the consequences this has for the use of citations in evaluation of R&D. It focuses on the first ten years of publications (cohorts 1991 to 2000) in the field of nanotechnology and eighteen years (1991-2008) worth of citations in windows of increasing length for each cohort to establish some of the basic features of the dynamics of citations in this emerging field. It offers a characterization of the citation distributions of these cohorts of papers and analyzes the time it takes for information contained in those papers to be absorbed by the field as reflected in citations. With a measure developed for that purpose and graphical representation of several dynamical characteristics it finds that there are significant delays in the absorption of information from papers in each cohort. Many papers have sustained growth of citations for many years, sometimes a decade or more, at all levels of the absolute number of citations, and the rank of papers by number of citations has many changes over long periods of time. This suggests that more refined tools for analysis of field level characteristics of impact should be developed to pick up not only the early signs of a potential opportunity in the short term but also recognize topics with older antecedents on their way to a deep and sustained influence.