Peer review of: Reconstruction of evolving nanostructures in ultrathin films with X-ray waveguide fluorescence ho (2020)


RR2
 Reviewers' comments second round: Reviewer #1 (Remarks to the Author):
  The revised version of the manuscript of Z. Jiang et al. on the 'Reconstruction of Evolving
 Nanostructures in Ultrathin Films with X-ray Waveguide Fluorescence Holography' contains
 valuable updates on the issues raised with respect to the original submission:
 a. The paragraph regarding the Pilatus detection efficieny added to the Experiment section in
 Methods is fine. One may add an estimate of the detector's spec uncertainty contribution to the
 overall uncertainty of the XWFH results.
 b. The uncertainties of GIXRF and GEXRF depth profiling are strongly dependent on the
 uncertainties of the optical constants used for the calculation of the X-ray Standing Wave (XSW)
 field intensity distribution in Parratt's recursion formulation. For more pronounced spatial
 distributions of the elemental mass depositions than is the case in stratified layers, one has to use
 2D- or 3D-Maxwell equation solvers to determine the correct XSW distribution in order to preserve
 the uncertainty of elemental depth profiles in the few percent range.
 However, it remains unclear to which extent the uncertainty of the XWFH depth profiles depends
 on the uncertainties of the optical constants employed and to which extent the dynamical
 approach used here reflects a 2D or 3D Maxwell equation solution.
 c. Although the convergence of the XWFH approach is impressive, it remains somewhat unclear
 which uncertainty is associated with the depth profiles derived. Only figure S6 indicates 95 %
 confidence intervals associated with the HMCMC calculation results. In view of the authors'
 statement to b. that in either GIXRF or GEXRF one would expect the data analysis to be less
 satisfactory, it would be worthwile to comment on this issue. In particular, several GIXRF or GEXRF
 studies have been validated by independent methods.
 d. The use of alternate terms for yields and energies is acknowledged.
After a minor revision regarding the points mentioned above the manuscript may be accepted.
Reviewer #2 (Remarks to the Author):
   The paper demonstrates X-ray waveguide fluorescence holography (XWFH) as a significant
 extension to X-ray fluorescence (XRF) holography by confining the XRF nano sources/scatterers
 within a thin film, which acts as a wave guide. This novel method makes use of the optical
 reciprocity theorem in the form of the evanescent-wave emission effect. The other clever trick is
 the use of both the Au La and Lb XRF signals for self-validation and for adding constraints to the
 analysis. The work is further validated by a comparison of the XWFH structural findings of the z-
 profile of the Au nanosphere layers to that found by the more established method of grazing
 incidence small angle X-ray scattering(GISAXS).
 Reviewer #3 (Remarks to the Author):
 The authors did a thorough job in replying to all comments and convincing me. The novelty and
 significance of the work has been highlighted and with the inclusion of the reconstruction details in
 the main text, the work is acceptable for publication.