Stabilization of Epitaxial NiO(001) Ultra-Thin Films on Body-Centered-Cubic Ni(001)-p(1x1)O

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

Submitted work is a study of ultrathin NiO films stabilized by reactive molecular beam epitaxy on the (001) surface of a metastable bcc Ni film. Work is interesting, systematic and conclusions are supported by the data obtained using modern techniques and rigorous methodology. Ni/NiO system is one of the fundamental models in magnetism and better understanding of it at nanoscale is always appreciated. It was previously often analyzed for the case of thin films formed onto the surface of nanoparticles. Here this system was obtained in systematic and controlled way using highest technological advances.

Manuscript does not provide keywords. They are necessary for better introduction of the work to international scientific community.

In addition, oxidation of such a thin sample may take place from the lateral surfaces. With this respect it would be important to describe the total size of the deposited samples and the way they prepared for different studies.

Authors propose these materials (on the basis electronics band gap of NiO variations as a function of film thickness) for applications in oxide electronics, spintronics and correlated electron systems. However, in order to convince audience, they could estimate the possibility to increase the production rate up to industrial conditions or move the technology toward the use of the sputtering technique being better accessible.

Author Response

Comment 1: Manuscript does not provide keywords. They are necessary for better introduction of the work to international scientific community.

Answer: we added the keywords

Comment 2: oxidation of such a thin sample may take place from the lateral surfaces. With this respect it would be important to describe the total size of the deposited samples and the way they prepared for different studies.

Answer: we specified in the experimental section that the sample is a square with a laterla side of 1 cm

Comment 3: Authors propose these materials (on the basis electronics band gap of NiO variations as a function of film thickness) for applications in oxide electronics, spintronics and correlated electron systems. However, in order to convince audience, they could estimate the possibility to increase the production rate up to industrial conditions or move the technology toward the use of the sputtering technique being better accessible.

Answer: we mentioned the possibility to use sputtering for enhancing the deposition rate at the end of the paper

Reviewer 2 Report

Comments and Suggestions for Authors

Dear Editor!

In the manuscript, the authors report on the synthesis of NiO films with different thickness on the surface on Ni film. Using the methods of Auger Electron Spectroscopy and Scanning tunneling microscopy the chemical composition, stoichiometry and morphology of the samples were studied. By scanning tunneling spectroscopy the electron band gap was determined. The manuscript contains new and useful information about NiO film synthesis. There are several clarifying questions for the authors:

1) Line 238. Authors note that synthesized NiO films exhibit typical p-type doping. In general, the p-conductivity in NiO is due to non-stoichiometry (nickel deficiency). For samples consisting of several layers, the non-stoichiometry is different (as indicated in Table 2). Did the authors evaluate the position of the Fermi level as a function of non-stoichiometry?

2) Line 233. Authors note that band gap increases with the film thickness. However, there is no explanation for this effect anywhere in the text. This is due to a change in the density of localized states near the bottom of the valence band and the top of the conduction band, associated with a change in the concentration of defects (primarily surface ones). The authors should provide an appropriate explanation in the text. They can also refer, for example, to work [10.48550/arXiv.1804.04493].

I think, this manuscript is of interest for Coatings readers, but cannot be accepted in the current form and requires revision.

Author Response

Comment 1: Line 238. Authors note that synthesized NiO films exhibit typical p-type doping. In general, the p-conductivity in NiO is due to non-stoichiometry (nickel deficiency). For samples consisting of several layers, the non-stoichiometry is different (as indicated in Table 2). Did the authors evaluate the position of the Fermi level as a function of non-stoichiometry?

Answer: we specified in the new version of the manuscript that the measurements reported in Table 1 show that the Ni deficiency remains approximately constant across the considered thicknesses, in agreement with the fact that the band gap offset is also constant. 

Comment 2 Line 233. Authors note that band gap increases with the film thickness. However, there is no explanation for this effect anywhere in the text. This is due to a change in the density of localized states near the bottom of the valence band and the top of the conduction band, associated with a change in the concentration of defects (primarily surface ones). The authors should provide an appropriate explanation in the text. They can also refer, for example, to work [10.48550/arXiv.1804.04493].

Answer We expanded the discussion obout the origin of the band gap dependence on the film thickness. We added, among others, the reference suggested by the referee

Reviewer 3 Report

Comments and Suggestions for Authors

The authors experimentally examined the process of NiO film growth on BCC Ni(001) sublayer. 
They used a complex of methods for structure, morphology, and electron structure analysis of NiO thin films with different numbers of monolayers. Authors have shown a thickness-dependent evolution of the electronic band structure of NiO thin films, where the band energy gap increases from 0.8 eV at 3 ML to 3.5 eV at 16 ML.

There is a comment:

Line 2. Please use the correct denomination in the manuscript title - "body-centered cubic".

I recommend to accept this manuscript with title correction.

Author Response

Comment Please use the correct denomination in the manuscript title - "body-centered cubic".

Answer we modified the title