The U.S. military’s research efforts in nanoscience are being hampered by social attitudes about foreign-born scientists and a continued shortage of U.S. citizens trained in physical sciences, experts and university officials said.

Throughout the 1990s, the number of U.S. citizens getting graduate degrees in physics and related physical science fields has been going down. The military doesn’t have a sufficiently large pool of postdoctoral students to meet the growing demands of nanoscience. Lavish salaries in a strong economy lure holders of bachelor’s degrees directly into the job market, but the recent dot-com bust could reverse the trend.