What do I need to major in if I want to go into the field of nanotechnology?

I am a senior right now and plan to go into engineering, particularly physical science. My teacher was suggesting about nanotechnology, which sparked my interest. I live in California, and I was browsing several good engineering schools (caltech, harvey mudd, ucla, uc berkeley, etc.), but none of them has nanotechnology as a separate major. So what do I need to major in if I want to work in that field? I know nanotech can be used in many areas. But I prefer those of mechanical or electrical engineerings.