Transnational citation, technological diversity and small world in global nanotechnology patenting

Despite the extensive studies conducted in the field of nanotechnology based on US patent data, the choice of a single database may impede a wider view of this technology frontier. Based on patent data from the Derwent Innovation Index database that covers the data of 41 major patent offices, we review the development of nanotechnology patenting from the dimensions of patenting authority and technological classification. We find that a small number of countries dominating the technology have similar technological diversity in terms of nanotechnology patents. After the discussion and summary of the citation modes and citation rate curve, we construct the patent citation networks at the patent document level and discuss the distinctive transnational citation patterns. We then use Search Path Count Method to extract the technological trajectory, where we find very high selectiveness. In the final section of this paper, we discover the small world phenomenon in the citation networks, which is widely investigated in undirected networks such as co-authorship networks, but rarely touched in citation networks due to the limitations of the presumptions. We propose the reachable path length and citation clustering in the revised small world model for acyclic directed networks and provide the realistic meaning of the new measures.