The idea of mimicking natural formation of biology-inspired nanostructures based on controlled and guided self-assembly is quite appealing to scientists from different disciplines. I have been told by scientists from many different fields of nanoscience, be it in materials science or from a perspective of device or life-science applications, that our concept of "nanotree" formation has been a source of inspiration. I could also guess that the fact that this article was chosen as the press-release of the month by the journal may have contributed.

Our approach to creating complex 3D structures, in the shape of nanotrees and nanoforests, is quite novel and could directly be adopted by many scientists. Hence, it should be useful to others.

The methods which we describe for the first time in this paper demonstrate the possibility of bringing the concept of epitaxy, i.e., the possibility of forming a single-crystalline material on top of another crystal, to another dimension. We suggest, and we demonstrate, that it is possible to use a trunk-like nanowire, which is grown on and is standing out from, a single-crystalline substrate, as a second-level substrate. We do this by attracting catalytic gold nanoparticles in such a way that they assemble along the "trunk." In the next stage we nucleate a "branch" which will be a single-crystalline extension from the "trunk," which in turn was a single-crystalline extension from the substrate. Doing this in multiple stages, very complex tree-like structures can be created and huge "forests" of such nanotrees can be formed—all created into a complex but monolithic 3D structure.

I took the initiative to explore nanowire growth in our lab around 1995-1996, after visiting Dr. Kenji Hiruma at Hitachi Research Laboratories in Japan. It took until 1999 when we really got started and another two to three years until this field of research became quite the dominant one in our laboratory. Today, up to 30 scientists (Ph.D. students, post-docs and senior scientists) are involved in different aspects of the growth, analysis, processing, physics, and device studies of nanowires. I took the initiative to first consider the nanotree concepts when I was inspired by a telephone meeting (in late summer 2003) with a solar panel research effort in Sweden, in which I was involved as a physics consultant. During discussions of artificial and natural photosynthesis processes I suddenly got this idea of the creation of complex tree-like structures in which it would be possible to construct built-in charge separation mechanisms in the nanowire branches and with the ideal crystalline quality of the nanowires allowing perfect semiconductor behavior to be utilized, even for nanotrees and nanoforests created on inexpensive substrates. I suggested this project to a Masters student, Kimberly Dick, who had recently joined us from Canada, who immediately achieved significant progress—she is also first author of the paper in Nature Materials—and is now involved in related research as part of her Ph.D. education.