Nongovernmental groups, scientists and industry are lining up for a major public relations battle over the good and evils of nanotechnology. One side says nanotech will fill the world with self-replicating microscopic ``nanobots'' -- 1,000 times smaller than the diameter of a human hair -- that will wipe out humanity. The other calls nano a silver bullet that promises a cure for cancer, an end to crop shortages and the solution to cleaning up pollution.