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

Peer Review File - Reviewers' comments first round: 
Reviewer #1 (Remarks to the Author): 
 
The manuscript of Z. Jiang et al. on the 'Reconstruction of Evolving Nanostructures in Ultrathin 
Films with X-ray Waveguide Fluorescence Holography' is a very valuable contribution to the related 
research field of non-destructive nanoanalytics for several reasons: 
1. The qualification of x-ray characterisation techniques for in-situ and time-resolved studies of 
elemental depth profile at the nanoscale is crucial to correlate material properties with the 
underlying chemical and physical properties. 
2. The simultaneous use of independent techniques such as the mixed-mode XWFH and GISAXS 
allow for the identification of potential artefacts like the slight broadening of depth profiles by 
GISAXS 
3. It is necessary to clearly describe the need for a-priori Knowledge required by a method like 
GISAXS, i.e. the shape of nanoparticles and assumptions on the type of spatial distributions,when 
comparing two orthogonal methods. 
4. The literature, advantages and disadvantages of related techniques such as GIXRF and GEXRF 
have been well discussed. 
 
There are some minor points worthwhile to be corrected or added for a revised version of the 
manuscript: 
a. The impact of the energy dependence of the detection efficiency of the 2D fluorescence detector 
for the Au-L fluorescences lines used on the data evaluation. 
b. A qualitative (or perhaps even quantitative) comparison of the 
depth profiling capapility of GIXRF, GEXRF and mixed-mode XWFH 
for buried nanolayer (or equivalent elemental distributions); 
also a reference to additional literature may serve for this 
Purpose 
c. an estimated budget for the uncertainties related to the measurands accessible by mixed-mode 
XWFH 
d. a few terms used in the manuscript are related to specific communities (e.g. fluorescence yield 
= fluorescence intensity or elastic energy = excitation energy) ; there is no need to change the 
entire manuscript but as readers may be from different fields it would be wise to use both terms 
when introducing them for the first time. 
 
 
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. They make use of the optical reciprocity theorem in 
the form of the evanescent-wave emission effect, for which the authors should reference Becker, 
Golovchenko, Patel PRL 50 (1983). The other clever trick performed in this study is to use both the 
Au La and Lb XRF signals for self-validation and for adding constraints to their analysis. Their work 
is 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). To bring this up a notch it would help if the authors more clearly 
substantiated on page 13 the potential importance of this new technique over other competing 
techniques, such as GISAXS and conventional TER-XSW. 
 
 
 
Reviewer #3 (Remarks to the Author): 
 
The authors present a proof of principle experiment with a technique they label X-ray Waveguide 
Fluorescence Holography (XWFH). The principle is that a thin layer acts as a waveguide to form an 
X-ray standing wave field when illuminated at grazing incidence angles. By measuring X-ray 
fluorescence at grazing emission angles the authors analyze gold nanoparticle layers and their 
dynamics upon thermal annealing. They state, that the gold nanoparticles in this case act as the 
fluorescence emitters as well as scattering centers and therefore dynamic scattering theory must 
be used for the reconstruction of the gold distribution. 
The paper is well written and cites much of the relevant literature and the results are in large parts 
comprehensible. The problem with the work is that the novelty and significance of the paper is 
questionable. 
As early as 1999, the enhancement of GEXRF due to sandwiching was published (Spectrochimica 
Acta Part B: Atomic Spectroscopy 54 1999 1881-1888) and the idea proposed that this could also 
be performed under GI conditions. In 2000, the same authors published GEXRF under two GI 
angles (X-Ray Spectrom. 2000; 29: 155–160). Recently, a few more examples of combining 
grazing incidence and emission subsequently for detecting X-ray fluorescence have been published 
(e.g. J. Anal. At. Spectrom., 2012, 27, 1432-1438, J. Anal. At. Spectrom., 2015, 30, 1086-1099, 
J.SynchrotronRad.(2015).22, 1419–1425). In all these publications, a sample as measured by the 
authors would be possible to measure and quantify. 
Analytically, the authors do not compare or discuss thoroughly the uniqueness of their 
reconstruction compared to other published reconstruction algorithms. Additionally, the 
information on the simulations is very short and at least should have been elaborated in the SI. 
And last but not least, the authors neither show a significant scientific case as application, nor 
discuss what applications are only possible with their ‘new’ technique. In conclusion, while the 
work is interesting and scientifically sound, the lack of significance and novelty prevent a 
publication in nature communications.