Electrically Tunable Perfect Terahertz Absorber Using Embedded Combline Graphene Layer
Round 1
Reviewer 1 Report
The Authors report on the design of a graphene-based absorbers operating in the THz range. The possibility to achieve absorption peaks is promising for several applications and could be useful for novel graphene-based devices especially in the targeted range. However, there are several points that should be addressed in order to improve its clarity and readability:
- English should be revised (e.g. what does it mean “supernatural” in this context?);
- The Authors should give more details about the numerical model implemented in CST. Is graphene considered as a thin layer or a boundary condition? What about the spatial resolution?
- The Authors should explain how the chemical potential range (0.2-0.6 eV) has been optimized for the targeted device. Which type of dielectric is used to achieve +/-240V? Is this below the breakdown voltage?
- The Authors should introduce in the main text the materials that have been used in the simulation. Are these compatible with the fabrication process? The realization of the nanostrip could affect the realization of the nanoribbons.
- One of my main concerns is related to the complex geometry proposed in the paper. Which is the advantage to use this complex geometry with respect to the state of the art? Which is the role of the ribbons and graphene nanostrip? Can the ribbons be considered as a flat, reflecting surface due to the small pitch? What happens if the ribbons are substituted by a flat surface?
- Is the potential of the graphene ribbons controlled or is it “floating”? In line 145 two values of chemical potential are indicated. How is possible to have two distinct values with only one DC voltage as in Figure 1a?
- The relaxation time is set equal to 1ps. The Authors should add a proper reference to experiential data and also comment on what happens when different values are taken into account.
- Several tables report geometrical parameters in the order of few nm/tens of nm. Although the Authors claim in the Conclusion that these small features can be realized with photolithography and electron beam lithography, the Authors should discuss about fabrication tolerances and should verify numerically how robust is their design against fabrication tolerances. The numerical results show that the absorption peak is very sensitive to the geometrical parameters.
- The total length L and width W are not reported in the text. Which is the footprint of the device? For which applications is this useful? Why the Authors utilize a plane wave instead of a focused/Gaussian beam?
- The Authors should comment more on the difference between the two polarizations (e.g. Fig.3).
- Are the ACS values acceptable for some applications (e.g. near perfect absorbers)?
Last but not least, the introduction should be improved providing other tunable absorber configurations over the e.m. spectrum such as those in the following papers:
- Total Absorption in a Graphene Monolayer in the Optical Regime by Critical Coupling with a Photonic Crystal Guided Resonance, ACS Photonics 2014, 1, 4, 347-353 (2014)
- Graphene-enabled electrically switchable radar-absorbing surfaces. Nat. Commun. 6, 6628 (2015).
- Reconfigurable and optically transparent microwave absorbers based on deep eutectic solvent-gated graphene, Scientific Reports volume 9, Article number: 5463 (2019)
- Tuning of Graphene-Based Optical Devices Operating in the Near-Infrared, Appl. Sci. 2021, 11(18), 8367; https://doi.org/10.3390/app11188367.
In conclusion, I believe that the manuscript is worthy to be published after major revision.
Author Response
Hi
Please see the attachment.
My best regards,
Author Response File: 
Author Response.docx
Reviewer 2 Report
This work produced by Amir Maghoul et al. on “Electrically Tunable Perfect Terahertz Absorber Using …..” is interesting and timely because terahertz absorbers based on graphene are promised as possible candidates for a variety of applications. Specifically, as underlined by the authors themselves, the advantage of using graphene layer is that the “Fermi potential level of the combline graphene layer,….can be controlled through external DC voltages”. The major finding of their study is that they suggest an absorber structure whose modelling confirms the tuning of the frequency by applying an electrostatic gating to graphene. However, the authors should clarify some important conditions/data they use in the model. In particular, referring to the following two sentences reported in the manuscript:
- “the graphene layer’s thickness is 1nm in the model”.
Since the thickness of a single layer of graphene is 0.35 nm, this implies that a layer of 1 nm corresponds to approximately 3-layers of graphene. This means that the effectiveness of the electrostatic gating is strongly reduced. Therefore, the author should discuss/explain why they used 1nm graphene layer in their model.
- “a Fermi level is tuned between 0.2 eV to 0.6 eV by applying DC voltages between -240 V to 240 V”.
The back gating using 240 volts is very high and to some extent anomalous for this kind of device. Therefore, the authors should clarify what kind of dielectrics could be used to avoid electric breakdown.
The manuscript could be published after a careful review.
Author Response
Hi
Please see the attachment.
My best regards,
Author Response File: Author Response.docx
Reviewer 3 Report
- What are the boundary conditions? Since it's a manuscript purly based on results of simulations, without any experiements, it's more convincing by listing details beyond governing equestion, etc.
- Is there limitation of this design? What's possible applications? Can you add some discussions?
Author Response
Hi,
Please see the attachment.
My best regards,
Author Response File: Author Response.docx
Round 2
Reviewer 1 Report
The Authors improved the quality of the presentation of the paper. There are still some typos (e.g. "fermi" should be "Fermi" with capital "F". The Authors should also introduce in the text the definition of the TE and TM polarization (e.g. electric field along x- or y-axis).
Author Response
Dear Reviewer,
I recorrected the article based on the given comment. I add a short definition regarding TE and TM modes in lines(178-181) of the manuscript.
Best Regards,
Reviewer 2 Report
The authors improved the manuscript.
Author Response
Dear Reviewer,
Thanks for your recommendation.
Best regards,
