Chemical State Mapping of p/n-Controlled SrB6 Bulk Specimens by Soft X-ray Emission Electron Microscope
Round 1
Reviewer 1 Report
The manuscript describes soft X-ray emission spectroscopy work on SrB compounds with the aim of performing a chemical mapping. The work performed is well described with sufficient details. The sensitivity of the B K emission line to changes induced in the electronic configuration was profited from to perform chemical speciation and identify regions with different composition attributed to different Sr doping concentration. Comments on the manuscript for providing a revised version before a possible publication are as follows. The main concern is that not the main emission line is selected for making conclusions on the chemical state of B, but a featureless region on the high energy side and that the statistical significance of the results is not discussed.
Regarding the presentation of the gratings: are those commercially available gratings such that a part number as provided is necessary?
The statement that EDS has an energy resolution which is more than two orders of magnitude worse than that of the X-ray emission spectrometer used is not absolutely correct. Silicon drift detectors (SDDs) do have an energy resolution better than 100 eV for the energies used. For example, literature that C and N K X-ray fluorescence lines can be well discriminated with SDDs can be found.
In Figure 2: it is not obvious why the N K emission line measured in 2nd order is so prominent in the figure. Please provide more details.
While X-rays certainly have a larger penetration depth than electrons, the information depth of SXES is limited by the penetration depth of the exciting electrons used. Thus, this value should be compared against the one of BSE for evaluating the difference in the penetration depth (page 4, line 154).
The intensity axis on the different spectra are not labelled (Figs. 2, 4 and 5).
Why is a normalization to the maximum intensity chosen and not a normalization to the peak area? Like this integral area differences (sum of the absolute value of differences at each emission energy) could be calculated, which could provide a better sensitivity than just looking at the difference on the high energy side of the peak.
It is difficult to assess the significance of the difference at the peak shoulder since no measurements statistics are shown. Are the differences significantly above the measurement statistics?
The area to identify the difference is close to the background level. Thus, differences observed could as well have different origins. Can these be excluded from data treatment? Is this area a satellite region which can be attributed to the emission from B aside from the main peak described? Why are the differences not considered in the peak region or with the integral area difference mentioned?
Since about 50% of the references are self-references, the question arises if literature on this topic is so scarce or if a more balanced survey of the field can be realized.
Different typos should be corrected.
- A few times: high special resolution -> high spatial resolution
- Valid-line-spacing gratings -> variable line spacing gratings
- Several times: chemical bonding state -> chemical binding state
- Sr-dedicient -> Sr-deficient
- hoe-doping -> hole-doping
Author Response
Please see the attached pdf file.
Author Response File: 
Author Response.pdf
Reviewer 2 Report
Comment on paper “ Chemical state mapping of p/n-controlled SrB6 bulk specimens by soft X-ray emission electron microscope” #applsci-1396097
This paper is interesting and I think worth publishing in Appled Sciences as it given (another) demonstration of the use of x-ray emission spectroscopy in the soft x-ray range performed on electron microscopes. However I think that in its present form the conclusions paper are not convincing owing to a lack of clear discussion and also perhaps another presentation of some figures. I detail below my remarks.
Section 2.1. The authors want to give an explanation on the way chemical information can be obtained from x-ray spectra. This is welcome for readers not familiar with x-ray spectroscopy, but I find the discussion (the three first paragraphs) rather confusing. Indeed, they introduce EDS and never mention WDS which is their spectroscopy technique. Their discussion suggest that elemental analysis can only be performed with EDS, while this done in WDS mode since a long time (1950’s) on electron microprobes and scanning electron microscopes. From the cited references it seems that there is only the presented kind of spectrometer which can be used to obtain high resolution spectra on electron microscopes. I think that the authors should also cite the work of Alexei ERKO from Berlin who published in the recent years in Optics Express (22, 16897 and 23, 29476 for example) his results regarding another spectrometer. There is no mention of atomic lines and valence bands which are only presented as “c” and “d” in the text. It could be explained that the B K emission is an emission band sensitive to the chemical state of the boron atoms, whereas the Sr Mzeta emission is an atomic line not very sensitive to the chemical state of the strontium atoms.
I would suggest the authors to first present their figure 1 explaining which transitions are chemically sensitive and that this requires spectral resolution that EDS cannot provide but WDS can, particularly with the spectrometer developed by Pr. Terauchi.
While I understand the expression “first order line”(which is used in many places) I am not sure this would be the case for a reader not familar with x-ray spectroscopy. This is “line observed at the first order of diffraction”. I understand that the notation is longer, but at least explain the meaning of the expression when used for the first time in the text.
I think that the sentence “The combination of the two VLS gratings of JS50XL and JS200N covers 50-210 eV for 1st order lies and 100-420 eV for the 2nd order lines.” needs some details. Indicate separately what are the range of JS50 and the one of JS200.
When discussing figure 4(b) and (c) I do not understand how the authors can write that “the intensities of Sr Mzeta-emission of those areas in Fig4(c) are almost the same, suggesting the inhomogeniety is very small”. From the intensity map of 4(b) and the corresponding color scale (which can be hardly seen) I observe a factor two or three between the blue and red regions. So it is surprising that the Sr Mzeta spectra of 4(c) are of the same magnitude. The authors should clarify this point because it will be difficult to believe them when considering the sample homogeneous in this case.
I cannot understand the discussion of figure 4(d). First, it is written that some regions correspons to a smaller (lower?) intensity of the Sr Mzeta emission and a few line below that the intensity is almost the same. Second, the explanation why the tail of the peak is chosen instead of the maximum to obtain B K map is unclear. The intensity in the tail is quite low is this leads to weak differences in intensity on the map 4(d): from the color scale I can see (hardly because it is too small and mixed in the figure itself) that the intensity differences are very small. What is the uncertainty of these intensities? Using the maximum would have lead to a much contrasted map. I do not understand also the relationship between the chemical shift and this procedure. It is clear from figure 5(e) that if there is a chemcial shift of the emission band it is very small (0.1 eV) and that cannot be evidenced in the 187-188 eV region. Two references, 20 and 21, are cited to support this procedure but unfortunately, one is in Japanese and the other difficult to find. So the conclusion of this paragraph are hazardous for me and it seems that this is also the case for the authors who use the conditionnal form.
Perhaps woult it be better to plot the spectra of Figure 4(e) (this is the same for Figure 5) without shifting them vertically. Indeed, if the authors want to show that there is some intensity present in the 187-188 eV range for one spectrum and not for the other, this will be seen. Else with the current presentation with shifter spectra this is impossible to see for the reader.
L125: “The crystallinity of those specimens was examined by X-ray diffraction.” This is not at all discussed in the text. So the sentence must be suppressed or some short discussioon should be added. Do the authors mean that their samples are not amoprhous?
L151: indicate the energy of the Sr Mzeta line. “divided by an averaged value”: what is this avera value? Please explain the same also L182).
Ref 32: the reference is correct but quite old; it would be nice to add a more recent refrence of x-ray data table.
Many minor comments. It is a pity that the authors do not read carefully their paper before sending it!
L12-13: “Elemental and chemical state maps of p/n-controlled SrB6 bulk specimens are presented by using a soft X-ray emission spectroscopy electron microscope.”
L16 : “ a local Sr-deficiency”
L19: “This mixed nature originates presumably from …”
L31: “those characters of materials”, I do not understand; consider rewriting
L45: “characteristics” instead of “characters”?
L46: “chemical species
L52: “which placed at” whithout “which”
L65-66: “.. mapping … gives …”
Caption of figure 1: “chemical bonding”
Figure 1: some letters of a label at the bottom left are missing
L101: is it really “valid-line-spacing gratings”? I would have expected “variable-line-spacing gratings”
L104: “1st order lines”
L122-123: “The obtained powder materials were sintered by pulsed electric current sintering method”; it is not very informative to know that samples were sintered by sintering. Consider rewriting.
In section 3 and in other locations, there is at least three different ways to write “backscattered electron”, with a blank space, with “ing”, … Only one will be enough. It is the same with the acronym: BSE, BES, BSI!
L133: “clearly”
L134: “bright and rather homogeneous regions”
L140: “chemical”
L144: “probe”
L161: “Fig 4(c)”
L171: “emission”
L174: “larger”
L207-209: “One is the region”; “The other is the region”
Ref 27: the year is 2018 and not 2017
Author Response
Please see the attached pdf file.
Author Response File: Author Response.pdf
Round 2
Reviewer 1 Report
The authors provide satisfactory replies to most of the points raised, except for the questions on the data analysis and the citations on the instrumentation.
Indeed, I still do not understand why the authors do not attempt a more evolved data analysis: they are working on raw data and, while convinced of the long term stability which can certainly be claimed, use only a small part of the spectrum which is most sensitive to any changes in experimental conditions to draw conclusions. The approach presented is a valid approach during experiments for quick verification, but publishable work deserves certainly more intricate analysis and evaluation. The data quality is, despite the good spectral signal, difficult to evaluate as no numbers on the differences in the area considered are provided and apparently no background correction is being performed. The contour plots show again normalized data.
Regarding the spectrometer described I understand that the combination of a wavelength dispersive spectrometer with electron excitation is not common, but yet such spectrometers are very widespread in combination with X-ray sources. Exchanging the source, which is not an implicit part of the spectrometer and where spectrometers have great versatility with respect to the type of source used for performing spectroscopic measurements, does in my opinion not justify referencing primarly own work while disregarding literature on spectrometer developments. At least the authors could attempt to classify the differences between existing instruments.
In general, the axis and labels of the plots provided are barely readable, especially those of the colors scales provided for the contour plots.
Author Response
Please see the attachment.
Author Response File: Author Response.pdf
Reviewer 2 Report
The authors have improved the quality of their manuscript and I recommend its publication.
Author Response
I'm happy our corrections and rewritings were corresponded to your valuable comments and suggestions.
