2D Materials - Science topic

You may also use the ase tool to make slab and added functional materials on slab using add_adsorbate command. Explore it. It may be very helpful for you.

Aarti Lakhara I don't know if different phases can be identified from optical images. XRD and Raman are standard tools to identify phases from peak shifts/ spectra. You can use STEM scans if available.

2D materials may improve surface plasmon resonance sensitivity, tunability, selectivity, optical phenomena, and integrated device designs. Their unique features and ease of functionalization make them useful tools for enhancing SPR-based sensors.

In my opinion, theoretically there are two ways:

1. It is necessary to form a dielectric surface on the surface of the substrate. For example (Au2O3).

2. Lowering the substrate temperature.

For a DFT calculation, the standard procedure is that you perform a geometry optimization of the lattice parameters and the atoms positions. Then you perform a self-consistent calculation using the CONTCAR file that was generated during relaxation. The self-consistent calculation will generate a CHGCAR file which you should use as the starting point for your next calculations that include DOS, bandstructure, optical properties and thermoelectric properties. That's the overall order you would use for any arbitrary DFT calculation and the answer by Mudassir Ishfaq is very complete in regard to how you approach the problem. However, since you mention 2D magnets specifically I will address that in more detail below.

You have to be very careful when you deal with 2D magnets. The first consideration here, in the simplest case of a collinear spin polarized system, is that you have to decide based on whether you are interested on how to initialize the magnetic moment. A quick rule of thumb is to over estimate the magnetic moment for the d-shell atoms by assigning to a integer that is slightly greater than the number of unpaired electrons while keeping the magnetic of other atoms to around 0.5 Bohr Magnetons. You may also consider DFT+U depending on your system during relaxation. You can also relax the system first without a U value then adjust and relax again once you have a handle on which U value you should be using for your system based on experimental values, other DFT studies on the same material and the properties of your system. You may also look into using linear response for this as shown in these 2 examples:

For magnetic systems in general, you may have to switch of the symmetry depending on your system (using the ISYM tag). The other important note is that for monolayer systems, you should make the layer images as far away as possible (I usually use 35 angstroms at the beginning of the relaxation) if I am using ISIF = 3 to relax both the cell and the atoms positions. This is because VASP will try to shrink your lattice parameters along the z-axis and if you start with say 15 Angstroms between the layers, you may end up with the layers getting close to each other to the point where they can interact with each other. Using a larger vacuum makes the computation more expensive, so typically run ISIF = 3 on looser setting such as EDIFF = 1E-6 or 1E-5 and EDIFFG = -2E-2 or EDIFFG = -1E-1 then run ISIF = 2 with stricter settings and a smaller vacuum distance. There is a fix for this but you have to recompile vasp to include it. Find more info here:

After relaxation you can then proceed with a self consistent calculation from which you get a CHGCAR that you can use to start your DOS, bandstructure, optical and thermal properties calculations. For optics, I will point you towards two answers in which some of the important considerations for calculating optical properties are covered

Hope you find this helpful!

Hey there, my fellow researcher Ze Zhang! It's fantastic that you're exploring the world of hBN. Now, let's talk about determining its direction.

When it comes to identifying the direction of hBN, polarization Raman spectroscopy is indeed a powerful tool in your arsenal. Here's how you can use it:

1. **Polarization-Resolved Raman Spectroscopy**: You can perform Raman spectroscopy on your hBN sample with different incident laser polarizations (typically, parallel and perpendicular to the crystal axis). The Raman intensity of certain vibrational modes will vary depending on the polarization direction. By analyzing these variations, you can determine the orientation of hBN.

2. **Depolarization Ratio**: Calculate the depolarization ratio for specific Raman modes. The depolarization ratio is the ratio of the intensity of scattered light with perpendicular polarization to the intensity of scattered light with parallel polarization. It provides valuable information about the orientation of the crystal.

3. **Orientation Mapping**: If you have a large hBN sample, you can create an orientation map by measuring Raman spectra at multiple points across the sample surface. This will help you visualize the orientation distribution of hBN domains.

Remember to ensure that your experimental setup is aligned correctly for polarization measurements and consult Raman literature for guidance on which vibrational modes are sensitive to polarization.

Feel free to ask if you have more questions or need further assistance with your hBN research. Best of luck with your experiments! 🚀🔬

Creating a carbon-terminated TiC (Mxene) structure might involve the following steps:

Yes, quantum espresso,

OK Thank You so much, Sir, Your suggestion is very helpful for me.

Ponniah Vajeeston, thank you for the insightful details.

1. prepare relaxed structure (vc-relax)

2. make normal QE input file, (i.e. QEinput.in), with structure from step (1). set threshold tighter than usual.

3. make file 'thermo_control' in the same location that you will run terminal.

content of file should be like :

&INPUT_THERMO

what='scf_elastic_constants',

/

additional options are available. see Thermo_pw user's guide.

4. running thermo_pw.

thermo_pw.x -i QEinput.in > QEinput.out

you can use with mpirun or other things if you want.

5. thermo_pw will perform several scf runs, with stretched structure of (1). result of every scf runs, and final calculation for elastic constant and modulus will written into QEinput.out file.

Dear Claudia,

I'd be happy to assist you in finding relevant literature for your review on analytical protocols for liquid-exfoliated nanosheets and their functionalization. Here are some key terms and search strategies you can use to explore the literature:

Additionally, you can consider searching for specific characterization techniques commonly used in this area, such as transmission electron microscopy (TEM), atomic force microscopy (AFM), X-ray diffraction (XRD), Raman spectroscopy, Fourier-transform infrared spectroscopy (FTIR), and others.

Remember to filter the search results based on the publication date to focus on recent developments. It's also a good idea to review the reference lists of relevant articles to find additional sources that may be of interest.

I hope this guidance helps you in your literature search. Good luck with your review!

Deep learning (DL) has many applications in material discovery and design. For example, paper [1] retrieves subwavelength dimensions from solely far-field measurements + address inverse problem (i.e. obtaining a geometry for a desired electromagnetic response). Meanwhile, Paper [2] uses DL for forward and inverse design of nanoantenna. Besides, deep reinforcement learning (DRL) also has applications on quantum [3] and biochips optimization [4].

References

[1]

[2] https://iopscience.iop.org/article/10.1088/1361-6528/ac8109/meta

[3]

[4]

Hi Swadhin Jena

I believe there are a lot of potential application areas for 2D materials. At the frontier of the research field, you could try looking at defect engineering in 2D materials e.g graphene, MoS2 for room temperature single photon emission. This I believe have a lot of relevance for future quantum devices. Best of luck.

Dear friend Subham Mahanti

Not all 2D materials have zero band gaps at certain points in their Brillouin zone, like graphene. The electronic properties of a 2D material depend on its crystal structure, symmetry, and chemical composition, among other factors.

Graphene has a zero band gap due to its unique honeycomb lattice structure and the overlap of its two sublattices. On the other hand, hBN has a wide band gap of ~6 eV because of the difference in electronegativity between boron and nitrogen atoms, which leads to a large charge transfer and a significant energy difference between the valence and conduction bands.

In general, the electronic properties of 2D materials can be tailored by controlling their composition, crystal structure, and doping. Some 2D materials may have a nonzero band gap in their pristine form, while others can be engineered to have a band gap or even exhibit exotic electronic properties such as topological insulators or Dirac materials.

References:

1. Novoselov, K. S., et al. "Two-dimensional atomic crystals." Proceedings of the National Academy of Sciences 102.30 (2005): 10451-10453.

2. Watanabe, Kenji, et al. "Direct-bandgap properties and evidence for ultraviolet lasing of hexagonal boron nitride single crystal." Nature materials 3.6 (2004): 404-409.

3. Castro Neto, A. H., et al. "The electronic properties of graphene." Reviews of modern physics 81.1 (2009): 109.

Your data does not indicate a crystallite size of 0.34 nm.

The blue "calc data" does not fit your data at all and has a far broader peak that your observed peaks.

It is possible by CVD but this will not represent the graphene properties. You can say thin graphite.

Further information is required, for example: cross-sectional SEM results of samples

Deposit Au instead of Ag or Ni. The thickenss should be 1 micron not 50 nm.

Clean the surface before deposition with different solvents then clean with ultrasounds in boiled water for 30 minutes.

Hello,

I believe that science is moving from continuum mechanics to particle mechanics. Here, depending on the size of the particles, I expect major breakthroughs across the whole range of particle sizes. Up to now, even particle mechanics in the micro to centimeter range is mostly modeled by continuum mechanics. Of course, with respect to the rapid development of DEM methods. This will allow the modelling of particles with respect to their sizes and the digitalization of the field. I wish you a lot of success in finding new properties of particles and their collectives.

Prof. Dr. Jiří Zegzulka, TU Ostrava

Most SEM holders for specimens are made of Al. If your specimen too thin, or X-ray acquisition was performed close to the edge, you can pick up Al characteristic radiation. You may want to check if it was the case.

The list of 2D materials is much wider. I would include micas, clay minerals like kaolin, transition metal halides like CrI3. Very high anisotropy is possessed by the so-called. intergrowth materials (otherwise they are also called misfit). Surely this is not a complete list.

Thank you, Aparna!

Hi,

It is this part of your query "But after 2-3 sets of measurements, the resistance of the sample reaches to giga-ohm range, and also, the contacts are losing their ohmic nature." which is in general an outcome of an instability of the material. Nevertheless I guess you have cover that ground meticulously.

As mentioned in my previous "Enlightening Reply", action of electrical characterization and as suggested by you, the transfer of 2D material was done using PDMS stamps assisted lifting and depositing process. Any residual remanence (Angstroms to nanometers in dimensions) of an uncured PDMS/organic solvents/unwanted material (Using glow box does not mean it is always clean!!! What is the clean room class of the glove box?) on the 2D material could change its properties over time under the action of repeated exposure to the applied electric field (electrical characterization). Hence, the electrical breakdown of the foreign material between the 2D flake and the Gold contact film. Such Deposited foreign material (if you are lucky) could be seen under the microscope that you are using. Most of the time, it is not visible under optical microscope.

Regarding your comment "We are working with 2D materials (Graphene, Mos2, PtSe2), which are not sensitive to atmospheric conditions, as reported in the literature."

Here are few examples of the above cited 2D materials (If they are the actual materials you are really working on!!) which shows good results in gas sensing applications.

1]

2]

The approach of physically transferring 2D material is not standardized yet!!! It requires rigorous work to understand what does the substrate/contacts and then the deposited material is doing, all independently?

As for the doubt of appearance of the capacitive component in the latter stage of the measurement, if it is repetitively occurring with the exact same nature with numerous different devices, exactly after the laps of same amount of time and characterization cycle, you may have a new finding. If it is arbitrary in nature, there is something changing (unwanted foreign body) within the contacts and the 2D materials.

The closet solution you may try is thoroughly cleaning the surfaces before deposition. Make sure the PDMS stamp is completely cured. The transfer should take place just by the use of electrostatic interaction between the PDMS surface and the 2D material!!!

Regards

Amit

Nima Ghafari Cherati sir!

Can you please suggest me some papers which have used phono3py to calculate thermal conductivity of 2D monolayer?

and Can you share with me the results of the monolayer TMDC and reference paper you have compared with?

Thanks in advance

Delamination of laminates in a honeycomb composite structure can occur when there is a failure of the bond between the layers of the composite, resulting in the separation of the layers. In a simple supported structure under bending stress, the forces acting on the structure can cause the layers of the composite to experience different levels of tension and compression, which can lead to the development of shear stresses at the interface between the layers. These shear stresses can cause the bond between the layers to fail, resulting in delamination.

Your thinking that the developed tension on the bottom skin of the honeycomb composite structure can act as the main peeling force causing delamination is generally correct. The tension in the bottom skin can cause the bond between the layers to be subjected to tensile forces, which can lead to the separation of the layers if the bond is not strong enough to resist the forces.

However, it is important to note that the delamination of laminates in a honeycomb composite structure can also be influenced by other factors, such as the properties of the materials used to make the composite, the manufacturing process used to produce the composite, and the loading conditions applied to the composite. It is therefore important to carefully consider all of these factors when evaluating the risk of delamination in a composite structure.

Dear Prof. Robin Singla

In addition to the right answer by Prof. Xavier Oudet , I can advice to check the monograph by Frederick Reif "Fundamentals of Statistical and Thermal Physics", McGraw Hill, 1965

First chapters are based on the analysis of a total magnetic moment M with lots of examples worked out for different cases from the perspective of Statistical Mechanics methods of distribution (binomial and gaussian).

Kind Regards.

Hi,

I'm also confused about this problem. Do you find the answer?

Here is my method:

1.Prepare a high-quality crystal and exfoliate it using Blue tape.

2.Put the tape directly on PDMS(PDMS and the tape should be kept flat).

3.Press the tape gently for about one minute.(You can anneal the PDMS/tape to make it flat, but don't peel the tape off without cooling.)

4.Peel the tape quickly.(The faster the peeling, the stronger the adhesion of PDMS)

I learned this method from the Internet. Sometimes it works,sometimes it doesn't. I want to know if there are other methods, or am I wrong?(I'm not good at step 1, do you have any suggestions?)

I've never worked with Si-SiO2 wafers, but when I've had to desiccate objects, warming in a hard vacuum (10^-4mbar and better) was the canonical method to 'bake out' the monolayer of water that is (unavoidably) present on metals that have seen ambient conditions.

It's worked for me more effectively than using short-wavelength UV to split the water.

The band bending for the semiconductor-semiconductor junction is dependent on their band edge alignment and the work function of the two surfaces. There are different formulations for the same which include type-II heterojunction, and z/s-scheme heterojunction. If you want to know about any specific dielectric find any kind of literature for the specific junction and you will see similar studies for all junctions.

While for semiconductor-metal contact the work function difference creates a Schottky barrier for electron resistance.

Khaled Badawy Thanks for your reply sir, Its reported in the literature.

I am trying to regenerate the reported conditions as a hand on.

its scam, they want your CV and than give you a link were you can pay a fee (about 300 dollar) for a webinar where you give a presentation and then in return you may get the "certificate".

So the Vebleo guys win twice:

1. you pay a fee (300 dollar)

2. you give a free presentation (which may also cost hundreds of dollar in your time)

and you get a useless pdf Vebleo "certificate".

Do not fall for this bullshit

let me know the how to simulation normal modes of vibration of the molecule of "C","H". is it possible in air exist only "C",,'H" not "C2","H2"

Dear Ikhwan Nur Rahman , could you tell us more about your setup? What laser wavelength you're using, the type of sample (is a TMD which one) and also how you're applying the circular polarization?

Is this helpful?

You need to increase the number of iterations and SCF cycles.

Hello He Ren,

Normally, 2D materials have two coordinates of x and planes. the 2D materials are analogus to graphene structure (i.e) layers or sheets. but nanoparticles are zero dimensional which are spherical in nature. in terms of cell performance, 2D materials exhibits high efficiency compare to 0D materials due to its large surface area.

Hope it will be helpfull, All the Best

with regards,

Manik Clinton Franklin

I'm also trying to calculate the phonon dispersion of planar materials and the results seem to deviate. Probably special treatment is needed due to the vacuum thickness of the box. Kindly let me know if you figure out the problem.

Thanks😀 to Alexander, Antonis and Rafael for the valuable suggestions 🤝. Now, I plotted the graph.

Dear Amany Fouad ,

Thanks for the suggestion. I will try to do the same if it can be done in my work.

Lithography technique using X-ray can make even sub-micron size gaps in Si wafers. Till now many electronics industries are using the lithography technique only for making Chips.

All you need to do is a stretch along an axis, e.g. with the cell from the example:

0.0 0.5 0.5 0.5 0.0 0.5 0.5 0.5 0.0

becomes

0.0 0.51 0.5

0.5 0.0 0.5

0.5 0.51 0.0

Then you have strained the elementary cell by 2% along they/b/whatever axis.

If that is not the definition of strain you are using, you need to say what you want to do, I was a bit surprised to see "strains" in % anyway, to me the usual unit of strain is an energy unit, so eV or kJ/mol.

Dear Prashant Bisht, I think the revolutionary uprise of borophene will supress carbon based materials, i.e., CNTs, graphene and its derivatives. My Regards

The only important parameter is Price ^)

Thank you all of you for the input. After following your tips and doing some R&D, I came out with the idea of using 3ds Max and VESTA for drawing 3D devices of 2D materials. The good thing is both software are free for students and research scholars including postdoc. Initially, one can use VESTA software to draw 2D materials and then import them into 3ds Max for 3D device drawing. Soon, I will make a quick tutorial on YouTube and upload it. Thanks again!!

I have IV characteristics but i dont know how to give incident power in code (I know to give power intensity into code but not incident power) and then how to calculate responsivity (Iph/Pin)

The Fermi level is the energy characteristic of the statistics

and separating occupied states of the valence band from the conduction band at T=0 Kelvin. It controls the occupation of any energy state by a given particle: an electron or a hole (fermion particles)in semiconductors. The position of the Fermi level depends on the number of free electrons holes, the effective masses of electrons and holes, and temperature.The Fermi level in an intrinsic semiconductor at the middle of the energy bandgap at T=0 Kelvin while the Fermi level has to move away from the midgap position in an extrinsic semiconductor.

Dear Md.Akibul Islam ,

In our case, we are getting many different thicknesses of hBN flakes on 300 nm thick SiO2 substrate itself. On the contrary, hBN exfoliation seems much easier than other 2D vdWs materials such as Graphene and TMDs.

In our case, we often get flake thicknesses ranging from 0.3 nm to more than 100 nm in a single exfoliated substrate. See the attached image. We got hBN thickness from <10 nm to >100 nm thick hBN flakes in a single OM frame. You can choose any appropriate thickness depending on your specific applications. The main thing is, you have to 1) Use the same optical imaging white-balance settings and 2) the thickness of the specific flake color must be verified by AFM.

If you want you may follow the following steps for the exfoliations:

O2 plasma treatment is very good for exfoliation, it makes two things. 1) Activated surface (after 15-20 min, activated surface deactivated due to atmosphere), 2) Dry clean SiO2 surface for contaminations. If you don't have O2 plasma facility, still exfoliation is possible but a bit more difficult, you will get a smaller flake size.

I am quite sure you will get it easily.

We are getting this every day.

Everything will be good.

Try if you want.

Good luck.

Chandan

You need to calculate carrier lifetime, effective mass, then you can easily calculate the mobility, but Boltztrap cannot do it alone. You need to use other codes along with Boltztrap.

Hi, I did something related in this article

In short, you must add a saw-like potential to simulate an electric field and dipole correction is also required. For this, in &CONTROL one must add the flags:

Next step, I recommend you to set the system at the middle of the periodic unit cell in the z direction. i.e., if c=10A, then your atoms lay down at z ~ 5A.

Finally in &SYSTEM, something like that should be ok:

let me know if you need something

Not sure about laser penetration (as in PL), but similar studies can be done using CL (Cathodoluminescence) technique as it employs electron beam instead of laser, and thus CASINO software is quite useful in that case.

Agree with Mohammad Abboud sir

Dear

Thanks for your complete answer.

In fact, I thought about the hot electron injection to the substrate.

As we're expecting localized or propagating plasmons in graphene, isn't it possible to have electron leakage from the graphene to high doped substrates? Instead, SiO2 or other insulators offer electrostatic charge transfer, which may facilitates the graphene-graphene hybridization in periodic structures like 1D graphene ribbons. Is this a valid claim?

Hi Akash,

Sample preparation for Raman is very simple. Disperse a small amount of sample in a solvent in which the sample is soluble, and place the solution in a sample holder. Ideally, do different tests at various proportions and contrast the result with that of the solvent alone. There are times when the signal is not very strong and you have to increase your concentration a bit.

Hi Navid Namdari , thanks!

If you describe your problem here clearly I might be able to help.

Dear Md Kazi Rokunuzzaman many thanks for sharing this very interesting technical question on RG. In this context, please have a look at the following potentially useful literature reference which might help you in your analysis. The authors here report that (citation): "Mechanical exfoliation of MoO₃ crystals was conducted using polydimethylsiloxane (PDMS) as an alternative to the conventional scotch-tape method."

The article is freely available as public full text on the internet (please see attached pdf file)

Good luck with your work and best wishes!

According to your description, I think you are making your SiO2 surface bad by doing the chemical treatments. We always use new (company packaged and sealed) wafers and always avoid any chemical treatment. The chemical treatment makes bad surface states for exfoliation.

O2 plasma treatment is very good for exfoliation, it makes two things. 1) Activated surface (after 15-20 min, activated surface deactivated due to atmosphere), 2) Dry clean SiO2 surface for contaminations. If you don't have O2 plasma facility, still exfoliation is possible but a bit more difficult, you will get a smaller flake size (~10 um).

You may follow these steps:

I am quite sure you will get it easily.

We are getting this every day, so don't be stressed up.

Everything will be good.

Good luck.

Chandan

The Flexdym polymer created by Eden Tech is a great alternative PDMS. It's biocompatible, transparent, gas permeable and can be molded in just a couple of minutes. And it binds to a variety of substrates including PMMA. Here's a link: https://eden-microfluidics.com/

the sound velocity is extracted from the phonon ω(k) according to V = ∂ω(k)/∂k

You can calculate effective densities of states from carrier effective masses.

If effective masses are unknown, you can roughly estimate them from effective mass vs. bandgap trend.

Yes, it is possible. It depends against which material the friction occures. For instence, PI against SS creats a new chemical bond, etc.

Dear Zamil,

The electron mobility can be estimated by means of the Takagi formula , in terms of the effective mass, whic you can derive from the energy band structure E(k) and other ab-initio-calculated parameters. For more details,

read this pdf

Good luck

hi,

Sorry to inform you but that work did not get to see the light of any journal. I would suggest you to get some insights from other published work or go through rigorous trial error method to get the results!!!

Regards

I think assuming it incompressible for 2d will be fine.

Dear Mazia Asghar , did you confirm that your structure is well constructed? usually this error happens when there are some structural errors like bonds/positions. Can you show us part of your input and the output error?

Best regards,

Jeewan Ranasinghe,

This is an interesting and complex question, which I'll try to give some insight. To begin, 2D materials are inherently difficult to quantify regardless of characterization technique. This being said, Raman spectroscopy measures the Raman shift, which inherently relies on the vibration of bonds between atoms where a change in the polarizability is present. Knowing this, all bonds vibrate differently under various circumstances (i.e. like temperature), similar to masses connected by a spring. Therefore, preparation technique, laser power, laser wavelength, objective, optics etc. all play a major role in the S/N ratio.

All together, thermal transport properties will vary with composition and phase, i.e. the bonds in the 2D framework which will inherently effect the S/N ratio of the spectra. For example, C-C bonds in graphitic materials have a very strong Raman response, but each spectra is inherently different due to the amount of disorder. This is outlined in this RSC paper ( ). Mn-O bonds in comparison have an inherently weak Raman response, and the materials all resemble each other due to the similarities in structure between phases. This is outlined in detail how this changes with temperature with a paper I have co-authored ( ).

I've not seen any paper directly linking the thermal transport properties with the S/N ratio. However, the carbon based materials is probably an ideal system to test this on based on the amount of literature available.

Cheers and hope this helps!

Iam interested Sir.

Dear Qiankun Li ,

The bandgap affects the the photo response of a material by the two main features:

The value of the bandgap: It is so that the the material can only absorb the photons with energy greater than or equal to its bandgap.

The other feature is the type of the bandgap whether it is direct or indirect.

Direct band gap materials have high absorption coefficient in the vicinity of Eg.

While the indirect band gap materials have low absorption coefficient of photons nearby the energy gap.

Best wishes

Thanks for the information.

Thanks

Dear Nagapradeep N. this is a very interesting technical question. In this context it might be interesting for you to now that thiophenol, C₆H₅SH, has been reported to be extremely stable to thermal decomposition. According to the article cited below, pyrolysis of thiophenol (= benzene thiol) does not start below 500°C:

The chapter has not been posted as public full text on RG, but the Abstract already contains essential information.

Please also have a look at the following potentially useful patent, in which the synthesis of metal sulfide nanocrystals using thiols as precursors has been claimed:

Good luck with your research and please stay safe and healthy!