Low atomic number silicon nitride films for transmission electron microscopy

Low stress silicon (Si)-rich silicon nitride (SiNx) films are usually used as membranes of microcapsules for transmission electron microscopy (TEM). Their relatively high atomic number has a negative impact on resolution, which is a key factor that affects imaging performance. To improve resolution, reducing Si content in films is an effective approach. However, the non-Si-rich SiNx films have large tensile stress and are ease to crack. In this study, ion implantation is utilized to adjust the stress of nearly stoichiometric (NS) SiNx films. The effects of ion implantation and thermal annealing on film properties are carefully analyzed. It is found that the NS SiNx films implanted with nitrogen (N) and annealed at low anneal temperature have both low atomic number and low stress, and their properties are very close to low stress Si-rich SiNx films. Moreover, a simple microcapsule is fabricated using the low atomic number SiNx films, and performs a TEM observation of water-soluble polypeptides growth. Polypeptides much smaller than 100 nm in size are observed.