Lawrence Berkeley National Laboratory
Towards half-Angstrom resolution: From One Angstrom Microscope to TEAM
- Author(s): O'Keefe, Michael A.
- et al.
Sub-angstrom resolution is important for nanotechnology. Metal atoms can be routinely imaged in TEM specimens at resolutions from 2angstrom to 1.5angstrom. Better resolutions (~1angstrom) are required to "see" lighter atoms such as carbon, nitrogen and lithium. Once Cs is corrected, microscope information limit controls resolution. The one-angstrom microscope project at LBNL has demonstrated the capability of 0.78angsrom resolution at 300keV. The Transmission Electron Achromatic Microscope (TEAM) is proposed to reach resolutions of 0.5angstrom using hardware correction of Cs, a monochromator (to reduce electron-beam energy spread and improve its information limit beyond that of the One-angstrom microscope), and chromatic aberration correction to allow a range of electron energies to be focussed together. Methods employed in design and implementation of the successful One-Angstrom microscope project can be used to determine appropriate parameters for the TEAM. Calculations show that a Cc corrector is not required for TEAM to reach 0. 5angstrom at 300keV or 200keV, provided that energy spreads can be reduced to 0.4eV and 0.2eV respectively. These values allow substantial beam current. At lower voltages, TEAM would require stricter limits on energy spread to reach the targeted 0.5angstrom resolution. No improvement in HT stability is required to improve the information limit per se since the monochromator determines the energy spread in the beam. However, improved HT will improve the beam current statistics (number of electrons passing through the monochromator) by placing more of the electrons closer to the center of the energy-spread distribution.