Intrinsic Instability of Aberration-Corrected Electron Microscopes
  Aberration-corrected microscopes with sub-atomic resolution will impact broad areas of science and technology. However, the experimentally observed lifetime of the corrected state is just a few minutes. Here we show that the corrected state is intrinsically unstable; the higher its quality, the more unstable it is. Analyzing the Contrast Transfer Function near optimum correction, we define an 'instability budget' which allows a rational trade-off between resolution and stability. Unless control systems are developed to overcome these challenges, intrinsic instability poses a fundamental limit to the resolution practically achievable in the electron microscope. 
S. M. Schramm, S. J. van der Molen, R. M. Tromp
physics.ins-det cond-mat.mtrl-sci cond-mat.other