The Effects of Selenization Treatment Temperature on the Phase Formation and Properties of Ba-Doped LaCuOSe Thin Films

Comments

Revision

1. Please go through a final round of thorough proof reading. There are several typos still present in the manuscript (ex, LnCuOS’ in line 255, tower band gap’ in line 262).

We sincerely appreciate your valuable comments, which have been very helpful, and we have made the corresponding revisions accordingly.

2. I personally find the title of the paper to be slightly misleading. Are the authors sure that the Ba-doped LaCuSeO films have 10 at% Ba concentration? While the pellets used as sputter targets may have been designed the have such compositions, there is no guarantee that sputter yield is identical for each of the atoms, and there may be slight offsets in the final composition of the films. What is the composition of the films as determined by XPS? If it is exactly 10 at%, the authors should mention this in the manuscript. If it is slightly off, why not modify the title to read ‘~~Ba-doped LaCuOSe thin films’ rather than being so specific about concentration?

We sincerely appreciate your valuable suggestion and fully agree with your point. Although the sputtering target was designed with 10 at% Ba doping, it cannot be ensured that the sputtering yield of each atom is identical, and therefore the final film composition may present slight deviations. Accordingly, we have revised the title following your recommendation.

(Effects of Selenization Treatment Temperature on the Phase Formation and Properties of La₀.₉Ba₀.₁CuOSe Ba-doped LaCuOSe Thin Films)

3. One of the key importances of the data presented by the authors is that their samples were synthesized in thin film form, rather than powder form often reported in previous works. The authors should add a paragraph near the introduction that discusses the importance of preparing functional materials in thin film form, citing recent references such as APL Mater. 12, 120901 (2024), Processes 13(2), 587 (2025).

We sincerely appreciate your suggestion and fully recognize the importance of preparing materials in thin film form. We also thank you for providing the references, which are very helpful in supplementing our background knowledge.

These references have been cited and discussed in the revised manuscript.

1.The authors mention that Ba was chosen due to similar ionic radii with La³⁺, but provide limited evidence for actual Ba incorporation into the lattice.

We fully agree with your comment and have supplemented the manuscript with additional content accordingly.

The observed binding energy peaks are close to the Ba 3d_5/2 binding energy of Ba-O (779.9 eV) reported in Ref. [33], suggesting that Ba substitutes La and bonds with O.

 2.The XPS analysis of Ba 3d spectra (Figure 3) shows inconsistent results and the authors acknowledge insufficient Ba substitution.

We agree with your viewpoint, and note that similar concerns were also raised by other reviewers. Although the sputtering target was designed with 10 at% Ba doping, it cannot be ensured that the sputtering yield of each atom is completely identical. Therefore, the final film composition may exhibit slight deviations. Therefore, we have revised the title and the corresponding descriptions.

3.authors should provide more convincing evidence of Ba incorporation (e.g., EDX mapping, lattice parameter analysis) or acknowledge that the "doping" may be incomplete and discuss implications.

We greatly appreciate your valuable suggestion. For comparison, we also fabricated undoped LaCuOSe films and analyzed them alongside the Ba-doped LaCuOSe. The results reveal that the incorporation of Ba leads to a reduction in the lattice parameters of LaCuOSe.

4. Equation (1) is presented as the decomposition reaction, but the stoichiometry and thermodynamic feasibility should be discussed more thoroughly. Authors should provide thermodynamic analysis or cite literature supporting this reaction pathway.

We sincerely appreciate your comment, and we have included additional thermodynamic analysis to supplement the discussion.

Equation (15) is stoichiometrically balanced and reflects experimentally observed secondary phases under Se-rich, oxidizing conditions. The reaction's thermodynamic driving force principally derives from the formation and volatilization of gaseous SeO₂. Literature on LaCuOSe and tanalogous oxychalcogenides supports he overall reaction pathway and impurity phase evolution[23、24].

5.Figure 2 (SEM images) would benefit from scale bars and better contrast.

We agree with your suggestion, which makes the SEM images clearer, and we have adjusted the figures accordingly.

Due to the addition of new data, the order of the figures has been adjusted. The original Figure 2 has now been updated and renumbered as Figure 3.

6. Figure 3 (XPS spectra) is quite dense and difficult to read. Consider separating into multiple figures or improving the layout.

We fully agree with your valuable comment that an excess of information in a single figure may hinder readability. Therefore, we have separated the XPS data into multiple figures and refined the layout to enhance clarity.

Due to the adjustment of figure arrangements, the original Figure 3 has now been divided and presented as Figures 5–9.

7.Language and Grammar:

   - Line 252: "whir or" should be "which"

   - Line 261: "tower bandgaps" should be "lower bandgaps"

   - Several instances of missing articles and minor grammatical errors throughout

We appreciate your valuable comments, which have been very helpful, and we have made the corresponding revisions accordingly.

7.The selenization duration is mentioned as "fixed duration" but the actual time is not specified.

We sincerely appreciate your valuable question. We have now included the exact selenization duration in the revised manuscript.

The selenization process was carried out at various annealing temperatures (750°C, 800°C, 850°C, and 900°C) for a fixed duration Selenization was conducted at annealing temperatures of 750 °C, 800 °C, 850 °C, and 900 °C for 2 hrs.

8.Film thickness measurements from SEM should be quantified and reported.

We sincerely appreciate your comment, and we have added the average film thickness measured by SEM to the manuscript.

The cross-sectional average film thicknesses were measured to be 106 nm, 107 nm, 123 nm, and 205 nm at Figure 3 (a) 750 °C, (b) 800 °C, (c) 850 °C, and (d) 900 °C, respectively.

9. Table 1 could include uncertainty values for the calculated parameters.

We sincerely appreciate your suggestion, and we have added the standard deviation of the grain size in Table 1.

10. The Hall effect data presentation in Figure 5 could be improved with error bars.

We fully agree with your valuable suggestion. We have now incorporated error bars into the presentation of the Hall effect data in the revised manuscript.

Due to the addition of new data, the order of the figures has been adjusted. The original Figure 5 has now been updated and renumbered as Figure 11.

11. While the authors compare their results with literature values, a more systematic comparison table would be helpful.

We sincerely appreciate your valuable suggestion and fully agree with your point. Accordingly, we have included a table(Table.2) that compares our results with those reported in other literature.

12. The novelty compared to previous Ba-doped systems should be better highlighted.

Thank you very much for your suggestion. To date, most reports on LaCuOSe doping have focused on divalent cations such as Ca, Sr, and Mg, while studies on Ba-doped LaCuOSe are scarcely available. However, we also compared LaCuOSe with Mg-doped LaCuOSe samples, as shown in Table 2 for reference.

13.The shift in preferred orientation from (102) to (200) and (110) planes at higher temperatures is interesting but deserves more discussion regarding its implications for properties.

We fully agree with your viewpoint. The change of preferred orientation at higher temperatures is indeed an interesting phenomenon, and we have provided additional explanations accordingly.

According to the JCPDS card data of LaCuOSe (PDF#49-1221) and Cu₂Se (PDF#65-2982), the (110) and (200) planes of LaCuOSe exhibit interplanar spacings close to those of the (200) and (220) planes of Cu₂Se. During the crystal growth process, elevated temperatures may facilitate preferential orientation, while the formation of secondary phases at high temperatures is likely to alter the properties of the films.

14.The two-bandgap behavior at higher temperatures is well-explained, but the authors should comment on whether this affects the material's suitability for TCO applications.

We sincerely appreciate your valuable suggestion. We have added further explanations in the revised manuscript accordingly.

The results indicate that, under different selenization annealing temperatures, Ba-doped LaCuOSe thin films exhibit an increased band gap and enhanced transmittance. Furthermore, the presence of an appropriate amount of Cu₂Se markedly improves the electrical properties of the films. In contrast, excessively high selenization annealing temperatures result in a reduction of transmittance in the LBCOSe thin films.

15. The dramatic improvement in electrical properties at higher temperatures is attributed to Cu₂Se formation, but this raises questions about the stability and reproducibility of these properties.

We sincerely appreciate your valuable suggestion. We repeated the experiments multiple times, and all results were consistently similar, confirming the reliability of our findings.

16.Specific Suggestions

-Abstract: Add the optimal selenization time to the experimental conditions mentioned.

- Introduction:Consider discussing other doping strategies for LaCuOSe systems for completeness.

-Methods:Specify the selenization duration and provide more details about the target preparation (pressing pressure, pellet dimensions).

-Results Section 3.1: Expand the discussion on why certain crystallographic orientations are preferred at different temperatures.

-Conclusions:Add a brief discussion on the practical implications and potential applications of the optimized films.

 Minor Corrections

- Line 116: Remove "Bulleted lists look like this:"

- Line 336: Remove duplicate text "the work reported in this manuscript"

- Check all chemical formulas for proper subscript formatting

- Ensure consistent notation (e.g., at% vs atomic percent)

We are grateful for your constructive feedback, which has helped us improve the clarity of our manuscript. The manuscript has been revised accordingly to address your concern.

Comments

Revision

1.The materials and methods section needs to be expanded. Describe the diagnostic equipment used and provide detailed measurement procedures. Please describe the instruments used (XPS, XRD, etc.) and provide a detailed description of the measurements.

We fully agree with your comment and have supplemented the manuscript with additional content accordingly.

Next, the crystal structure of the LBCOSe thin films was examined using Glancing Incidence Angle X-ray Diffraction (GIXRD, PANalytical X’PERT PRO) with Cu Kα (λ = 1.5406 Å), operated at 45 kV and 20 mA. To further investigate the microstructural features, the surface and cross-sectional morphologies were observed by field-emission scanning electron microscopy (FE-SEM, Hitachi-4700). In addition, the chemical com-position and bonding states of the films were analyzed by X-ray photoelectron spec-troscopy (XPS, JEOL JAMP-9500F Auger Electron Spectroscopy).

After establishing the structural and compositional characteristics, the electrical properties of the films, including resistivity, carrier mobility, and carrier concentration, were measured using a Hall effect system. Complementary optical characterization was performed by measuring the optical transmittance with a UV–Visible spectropho-tometer (Thermo Scientific Evolution 201).

2.It is necessary to add a figure containing a scheme of the synthesis of the material.

We sincerely appreciate your valuable suggestion. In response, we have added a flowchart illustrating the material preparation process (Figure 1).

3.How was the instrumental error of the XRD method estimated and corrected? If possible, calculate crystallite sizes for the Cu₂Se and La₂O₂Se phases.

We sincerely appreciate your question. As our study focuses on thin-film samples, the data analysis was calibrated by subtracting the FWHM obtained from a single-crystal reference.

4.I recommend that the authors, based on the experimental data of scanning electron microscopy, construct histograms of the distribution of nanoparticles by size and draw appropriate conclusions.

We fully agree with your comment and have added a histogram of the nanoparticle size distribution (Figure 4). Corresponding explanations have also been incorporated into the revised manuscript.

5.Please provide overview XPS spectra for all samples and identify all characteristic peaks.

We sincerely appreciate your valuable comment. In response, we have added the relevant data to the revised manuscript (Figure 5).

6.How possible surface charging of samples was controlled within the XPS method? Whether binding energy correction was applied based on the sample work function (see for example DOI: 10.1063/5.0086359 and 10.3390/technologies13070277)?

We sincerely appreciate your valuable suggestion. However, we would like to clarify that in our manuscript we have already cited the relevant literature on LaCuOSe [34], which explicitly states that “charge neutralization was attempted but was concluded to be unnecessary.”

7.In most cases, the interpretation of O1s spectra components with binding energy 530.5-531.5 eV as oxygen vacancy is incorrect (for example DOI: 10.1021/acs.chemmater.3c00801). The indicated binding energy is often characteristic of OH groups adsorbed on the surface of oxides.

Thank you very much for your helpful suggestion and for providing relevant references. We have revised the manuscript accordingly, and the suggested references have been cited and discussed in the revised version.

8.The authors should consider quantitatively the atomic composition of the surface based on the experimental XPS data. Does it correspond to La₀.₉Ba₀.₁CuOSe, i.e. do the films contain 10 at.% barium?

We sincerely appreciate your valuable suggestion and fully agree with your point of view. Although the sputtering target was designed with 10 at% Ba doping, it is not guaranteed that each atom has exactly the same sputtering yield, and thus the final film composition may slightly deviate from the nominal value. Therefore, we have revised the title of the manuscript accordingly.

9.What is the reason for the high noise level in the spectral range of 800-1000 nm (Figure 4) for the LaCuOSe sample obtained at 850°C?

We sincerely appreciate your question. To clarify this issue, we performed additional measurements for confirmation and found that the discrepancy originated from an instrumental calibration problem.

10.Tauc plot for samples is unreliable, detail the approach used to determine the optical band gap. Improve the quality of the plots and estimate the energy of the Urbach tail.

We sincerely appreciate your question. In response, we have improved the quality of the figure and included the calculation method of the energy levels in the revised manuscript.

11.The authors should clarify equation (4), when calculating it, Optical transmission is used in arb. units or in %. How was the specific electrical resistance Ω·cm converted to electrical sheet resistance Ω?

We sincerely appreciate your question. The optical transmission is expressed in arbitrary units (e.g., 90% is represented as 0.9). The resistivity of the thin films was determined using the film thickness, which was obtained from SEM cross-sectional measurements, multiplied by the sheet resistance measured experimentally.

Comments

Revision

1.The authors have presented in Figure 5 La 3d spectra of LBCOSe thin films annealed at various selenization temperatures. However, in addition to individual components, it is advisable to analyze the survey XPS spectra.

We agree with the reviewer’s suggestion and have included the analysis of the survey spectra of the thin films in the revised manuscript.

Figure 5 shows the survey spectra of LBCOSe thin films annealed at different selenization temperatures: (a) 750 °C, (b) 800 °C, (c) 850 °C, and (d) 900 °C. The spectra reveal characteristic peaks of La 3d (La 3d₅/₂ and La 3d₃/₂), O 1s, Cu 2p₃/₂, Se 3p, and Ba 3d. In addition, a C 1s peak is observed, which is likely attributed to the adsorption of carbon-containing compounds. The binding energies of these peaks are consistent with those reported in the literature [32,33].

2.It is impossible to answer the question of the need or lack of need for charge neutralization without a generalized analysis of survey XPS spectra. Additional complications come from differential charging, which means that different parts of the sample are not at the same electrical potential. This can be the case for inhomogeneous samples, especially if various phases have different conductivity. In particular, do the samples contain carbon and can the charge be calibrated against it, or are the samples free of other impurities?

We sincerely appreciate your suggestion. We have incorporated the analysis and description of the survey spectra of the thin films into the revised manuscript. During the XPS analysis, surface charging effects may occur. In the spectra, an adventitious carbon (AdC) C 1s peak was detected; however, calibration based on the C 1s peak is not reliable. Therefore, we adopted an alternative approach by calibrating the C 1s binding energy (BE) using the sample work function (ΦSA), according to the relation BE = 289.58 – ΦSA [21,22].

 The calculated energy shift was then applied to all core levels. We calibrated using the work function (∼6.0 eV) of divalent ion–doped LaCuOSe thin films reported in [23].

3.Reference 33 is missing, authors should correct references.

We appreciate your valuable comments, which have been very helpful, and we have made the corresponding revisions accordingly.