High resolution SIMS depth profiling of nanolayers
  We report results of high-resolution TOF SIMS (time of flight secondary ion mass spectrometry) depth profiling experiments on a nanolayered structure, a stack of 16 alternating MgO and ZnO ~5.5 nm layers grown on a Si substrate by atomic layer deposition. The measurements were performed using a newly developed approach implementing a low energy direct current normally incident Ar+ ion beam for sample material removal by sputtering (250 eV and 500 eV energy), in combination with a pulsed 5 keV Ar+ ion beam at 60{\deg} incidence for TOF SIMS analysis. By this optimized arrangement, a noticeably improved version of known dual-beam (DB) approach to TOF SIMS depth profiling is introduced, which can be called gentleDB. We apply the mixing-roughness-information model to detailed analysis of experimental results. It reveals that the gentleDB approach allows ultimate depth resolution by confining the ion beam mixing length to about 2 monolayers. This corresponds to the escape depth of secondary ions, the fundamental depth resolution limitation in SIMS. Other parameters deduced from the measured depth profiles indicate that a single layer thickness equals to 6 nm so that "flat" layer thickness d is of 3 nm and interfacial roughness {\sigma} is of 1.5 nm thus yielding d+2\bullet{\sigma}=6 nm. In essence, we have demonstrated that the gentleDB TOF SIMS depth profiling with noble gas ion beams is capable of revealing structural features of a stack of nanolayers, resolving its original surface and estimating the roughness of interlayer interfaces, which is difficult to obtain by traditional approaches. 
S.V. Baryshev, A.V. Zinovev, C.E. Tripa, M.J. Pellin, Q. Peng, J.W.   Elam, and I.V. Veryovkin
cond-mat.mtrl-sci physics.chem-ph