Single nanoparticle alignment by atomic force microscopy indentation

Unavoidable bulge formation during an indentation process is a serious obstacle to trapping nanoparticles in dent holes or trenches. We found an easy method of removing polymethyl methacrylate (PMMA) bulges formed during atomic force microscopy indentation. The method allowed the creation of dent holes or trenches in PMMA without bulges, which, using capillary interaction, allowed us to place 40-nm-diameter Au particles at precise locations. Furthermore, we could adjust the gap distance (∼10 nm) between the nanoparticle and the bottom electrode. The method will be helpful in characterizing the nanoparticles and molecules and, ultimately, will help in the development of nanoparitcle- or molecule-attached devices.