professor Shahid Ali Yousafzai I've been working with material optical characterization for quite some time but I sometimes forget a detail here and there, and this video was exactly what I needed. I will recommend your channel to my colleagues and collaborators. May I ask what are you working on currently? Thank you very much
Many thanks for the appreciation Professor. Your words mean a lot to me. I hope that your colleagues and students will like the rich contents in the big playlist.
I hope you remember me SIR, your video on Tauc plot is a full complete explanation. It's simply WOW!! The clarity and depth of your explanation makes it evident how passionate and dedicated you are to your subject matter. Thank you for going above and beyond as a teacher and for sharing your expertise with a wider audience through your channel. Your commitment to education is inspiring, and I feel fortunate to have been your student.
Good morning sir. Two months before I was very depression, stress due to COVID 2 years waste in my research work.... I felt help less.. at the time I found your channel sir....all the characterization techniques I learnt from your channel 🙏🙏🙏🙏 yesterday I submitted one paper sir.... getting ready another paper .... looking journals Everything because of you sir 🙏🙏🙏🙏you are saved me....I never forget you in my life.... thank you so much sir..I salute you 🎊💐🙏 sir how to colour in EDS
Your beautiful words touched my heart. May you have a healthy life. I'm glad that my tutorials helped you. Every day I'm receiving prayers and best wishes from around the world and it boost my ego to do even more. Please share it with others to be benefitted. Thanks
It's very useful content. Thank you for your effort. A little but important correction is needed. Before estimating the bandgap value from intersection of straight line with x-axis, the y-axis scale should be adjusted to zero as the starting point.
Thanks for the appreciation dear 😊. Yes, you're right. In case, no offset or baseline correction is involved, it must be at y=0. The offset I have explained in the following video. ruclips.net/video/3gkcmp10uog/видео.html
Hi, thanks for this video. I have a question regarding the last part which you are determining bandgap energy. I am wondering why you chose that part of the graph for estimating Eg, why didn't you chose the part from energy 4 to 5 to draw the line?
@maliheghafari2979 when you are having multiple regions, you will have to draw for each region. Sometimes, you need a baseline correction. The following video tutorial will further guide you in this regard. Thanks ruclips.net/video/3gkcmp10uog/видео.html
Thank you for your comment! If (ahv)^1/2 provides a good interpolation, it suggests a linear relationship between the square root of absorbance and photon energy. To determine the band gap energy, you can extrapolate this linear relationship to the x-axis (photon energy axis) and find the point where absorbance becomes zero. This point corresponds to the band gap energy. However, it's crucial to validate this approach with additional methods or literature values to ensure accuracy.
Thank you for watching and your feedback! In the video, I discussed both the direct and indirect graphs, but focused on the direct graph as it had a matching profile, making it more applicable for the analysis presented. If you have any specific questions about the indirect graph, feel free to ask, and I'd be happy to explain it in more detail.
Hello sir proud on such like teacher. I have a decision .to start the remaining course content of quantum David j grifith and also start it's problem solution . Because the student have many problme in quantum no one is able to solve it's problme so I request to u kindly do it
Hi, thank you for your detailed explanation. I'm having a question to the last step in the video: you read the bandgap = 5.6eV at (ahv)2=-50, should we read it at (ahv)2= 0?
There's a formula for the Vicker's hardness in which you use the diagonal lengths of the microindentation. I'll try to include it in the tutorial series. Thanks
Thanks a lot for your video! I have one question: when you calculate the bandgap after extrapolating with the red line to the X axis, don't you have to rescale your graph so that Y axis start from 0? From your screen reader, you had something like Y = -47... Thanks once again!
Thanks for the appreciation dear. Yes, you're right. It is better to be at y=0 to calculate the x value. However, it's not a general rule. In some cases, we set an offset at some non-zero y values, like in composite type bandgap. The following article will help you understand it more. Thanks again for your input. pubs.acs.org/action/showCitFormats?doi=10.1021/acs.jpclett.8b02892
Thanks for a very clear explanation. Will the same method be applicable to determine the band gap of colloidal particles in a solution or we need to have a DRS data only.
@@SAYPhysics Understood, thank you! Meaning, this method may work in either case, right? We don't seem to have an accessory to measure DRS and my carbon/Ti composite does show desired red-shift on the UV-Vis spectra, so I am thinking to proceed with the band gap calculations using the method you described in this video. Hope I am headed in the right direction
Thank you for your video. In case that the absorption spectrum has more than one peak. the peak at a longer wavelength has lower intensity. which peak we will consider to calculate the optical bandgap energy.
9:45 You are mistaken. you should have determined the band gap at the intersection with the x-axis at the zero level absorptin ((alfaE)^2 = 0). (alfaE)^2 cannot take negative values
Yes, you're right. It is better to be at y=0 to calculate the x value. However, it's not a general rule. In some cases, we set an offset at some non-zero y values, like in composite type bandgap. The following article will help you understand it more. Thanks again for your input. pubs.acs.org/action/showCitFormats?doi=10.1021/acs.jpclett.8b02892
In Tauc plot analysis, gamma represents the nature of the transition and is usually assumed to be either 1/2, 1, or 2/3. Each value corresponds to a different type of transition, such as direct allowed transition, indirect allowed transition, or indirect forbidden transition, respectively. To determine the proper gamma for your data analysis, it is essential to consider the characteristics of your material and the available literature. Experimental techniques, material properties, and previous studies on similar materials can provide insights into the appropriate gamma value. Consulting relevant research papers, textbooks, or expert opinions in the field can help you determine the most suitable gamma value for your specific material and experimental setup. Additionally, discussing with colleagues or experts in the field may provide valuable guidance and insights for selecting the proper gamma during your data analysis. Thanks
very elaborative and comprehensible video, thanks for sharing. Could you please help me in determing the band gap energy of my hydrothermally synthesized MoS2 nanoparticles which is in powder form..May I make its slurry in water and get absorption at differnt wavelength and proceed as you shown in the video?....Thanks in advance.
Great question! When calculating the band gap from UV-Vis absorption data, the thickness of the film is typically used in centimeters (cm). However, it's important to be consistent with the units used in your calculations and to follow any specific guidelines or conventions relevant to your field of study. Thanks
...also. "A" you said is a constant (proporcionality, and in texts it says that is related with disorder and tail state). Why did you assume it like absorbance? Thank you so much
Thanks for the appreciation. I fear you can't, as we extrapolate the line onto the x-axis in relation to the y-axis. You can't change one (x-axis) while keeping the other the same (y-axis). However, in the following video, I have taken the x-axis as wavelength instead of energy. ruclips.net/video/x6rvyuAKiGI/видео.html
Yes, you're right that it is related to the disorder and tail state. However, for the materials which aren't modified, we have it as a constant. When its role is crucial, we'll have to put its value as per nature of our sample. Thanks
You may approximate is to 1. The value of A depends on several factors, including the nature of the semiconductor material, the size and shape of the nanoparticles, and the measurement conditions. A can be affected by factors such as the density of states in the conduction and valence bands, the bandgap energy, the effective mass of the charge carriers, and the dielectric constant of the material. In general, A is not directly related to the size or shape of the nanoparticles, but rather to the intrinsic properties of the material itself. However, the absorption coefficient can be influenced by the size and shape of the nanoparticles through the quantum confinement effect, which can cause changes in the bandgap energy and the density of states. Overall, the value of A in the Tauc equation is a material-dependent constant that is determined by the intrinsic properties of the semiconductor material and can be affected by various factors, including the size and shape of the nanoparticles. Thanks
I ve got a question. In this case, when you find x - intercept value, the y axis has a negative value. Should y axis value be zero? Maybe if you extrapolate the linear part which is parallel to x axis and find the point of intersection
@@SAYPhysics I am trying to get familiar with UV -Vis analysis so i have so many questions. What happens when tauc plot has 2 linear parts? So you dont know which one corresponds to band gap energy
Hello! thank you for the video. However, I am still confused; some papers suggest that the direct band gap is obtained y = 1/2 while the indirect one is y = 2, especially for DRS analysis.
@@SAYPhysics sorry for the mistake. You can also check this reference: "10.1021/acs.jpclett.8b02892". I am just trying to figure it out who is right in the scientific community 🥴
It seems you are confusing two different things i.e. y and the power of αhν. In a Tauc plot, which is a plot of (αhν)^2 versus the photon energy (hν), where α is the absorption coefficient and hν is the photon energy, a direct bandgap material exhibits a linear portion with a steep slope near the bandgap energy. Here y=(αhν)^2, to get α, we take square root of both sides so y become y^1/2 for direct bandgap and vice versa. Thanks
To convert transmittance into absorbance in the case of UV-Vis data, you can use the following equation: Absorbance (A) = -log10(T) where: A is the absorbance, T is the transmittance. The negative logarithm of the transmittance is taken to convert it into absorbance. The absorbance scale is logarithmic, which means that as the absorbance value increases, the sample absorbs more light. Here's a step-by-step guide on how to convert transmittance values into absorbance: Obtain the transmittance values from your UV-Vis spectrophotometer measurements for the desired wavelengths. Calculate the absorbance by applying the equation A = -log10(T) to each transmittance value. Repeat the calculation for all the transmittance values obtained from your UV-Vis data. Note: The equation assumes that the light path length and the solvent used are constant for all measurements. Also, it's important to keep in mind that absorbance values are often reported as positive numbers, even though the equation includes a negative sign. Thanks
sir as you explained at (8:48), if we are still not getting the best fit. Can we go further and take Cube (of Absorbance and energy) instead of Square and then we can plot...
Thanks for the appreciation dear. There are so many references, you may find some of them as below; www.sciencedirect.com/science/article/pii/0025540868900238 onlinelibrary.wiley.com/doi/abs/10.1002/pssb.201552007 www.nature.com/articles/s41598-019-47670-y
Assalam o alaikum sir! Sir if the material we have used for is amorphous and have indirect allowed transition so it is compulsory to plot energy vs 1/2?as 1/2 is for indirect
Wa Alaikum Assalam! Yes, for an amorphous material with an indirect allowed transition, it is important to plot \((\alpha h u)^{1/2}\) versus energy (\(h u\)) to determine the band gap accurately. This approach corresponds to the characteristic absorption edge of indirect transitions. Thanks
I plotted both the graphs for direct as well as indirect but as mentioned already that my material is having indirect band gap and I got perfect slope from the direct band gap graph...so what to do?? Should I opt for the direct or indirect??
Dear Sir, Hope you are doing well. Thank you for this one. I have measured the absorption spectra of my CdS QDs for solar applications. I have used a glass solid TiO2 substrate, on which CdS quantum dots have been deposited via a technique called the SILAR method. The glass substrates are cut to match the cuvet size. You mentioned that the l is the thickness of the liquid and at somewhere you substituted the value of l to the thickness of the cuvet which in your case will be the thickness of the fluid, but in my case (glass substrate) it would be the thickness of the glass slide, right? and not the cuvet thickness?.
As far as I understood your question, your thickness is the CdS QDs thickness. The absorption caused by the substrate is supposed to be subtracted as a reference. If you're using a dual beam spectrometer, put your undeposited glass slide in the reference slot, while the deposited in the measurement slot. Thanks
@@SAYPhysics Right Sir. I get it. I have used one glass substrate as a reference ( the undeposited one). You mean I should take the value of the difference between the deposited and undeposited one?.
First of all thanks a lot for this video... sir what if the band gap increases ?whether it is crt or not... bcoz.. I was plot my graph but I got more than 5ev ...
Thanks for the appreciation dear. It depends on the nature of the dopant, whether it narrow or widen the bangap. You'll have to check about the energy diagrams of your host and dopant materials. Thanks
hi thank you for the great video, but i couldnt understand why alpha = 0,4343 A cm^-1 become alpha = 2.302 cm^-1. looking forward for answer, thanks :)
Hello sir As I understood absorption coefficient formula is (2.302/d)*A per cm, but you did directly with formula 2.303*A per cm,please clarify which is right. Thank you
To assess the effects of concentration on bandgap determination, it is essential to carefully prepare and analyze samples, consider correction factors (for example, Concentration-Dependent Absorption Intensity, Exciton Interactions, Saturation Effects, and Multiple Absorption Processes), and, if possible, perform measurements at different concentrations. Additionally, modeling techniques that account for exciton interactions and other concentration-dependent phenomena can be employed for a more accurate interpretation of the UV-Vis spectrum. Thanks
Sir, the vedio is quite interesting, but you should adjust the Y axis in such a matter that it start from zero, other wise the band gap obtained is incorrect.
Thanks for the appreciation dear. Yes, you're right. It is better to be at y=0 to calculate the x value. However, it's not a general rule. In some cases, we set an offset at some non-zero y values, like in composite type bandgap. The following article will help you understand it more. Thanks again for your input. pubs.acs.org/action/showCitFormats?doi=10.1021/acs.jpclett.8b02892
Yes dear. Thickness is being used in the formula. Thanks 😊 You may watch the following video for details of absorption coefficient calculation. ruclips.net/video/9UYAVZnJt9k/видео.html
Excuse me, we have (2601) in our scientific center. In respect to absorbance: 1) Should we substract the values of glass data from films data? or the instrument does it? 2) The maximum value is four, why not one? Should we divide data on four?
It seems that you are having 'UV 2601 UV-VIS Double Beam Spectrometer', then it means in one beam, you'd have placed the glass with thin film and in the other beam (reference), you'd have placed uncoated glass. 1) If this is the case, you don't need any subtraction of the glass as the machine would have done it. 2) Intensity doesn't matter, unless you're comparing with other samples. You can normalize your data to 1. Just keep y=0 when drawing the slope. Thanks
@@SAYPhysics Thank you very much, Maybe my colleague does it wrongly, she first puts the uncoated glass, then puts the coated one separately, not at the same time as I understood from your response.
@معتز سعدي بدري عبد الدليمي We usually do this method for a single beam equipment, thereby subtracting the uncoated from the coated one, which is not very accurate for critical samples but does the job. For a dual beam, we may follow the procedure, as I suggested earlier. Thanks
This is something not very straightforward but requires some literature overhauling. Sometimes, such regions do mean a bandgap and sometimes it's an offset. I'm referring to an article, which will help you understand it more. Thanks DOI: 10.1021/acs.jpclett.8b02892
In the start of the few minutes of this tutorial, I have explained about the thickness calculation. Let me know if it needs further clarification. Thanks
Yes, you're right. The y-axis must be selected from 0 while drawing the slope. However, the bandgap is right as it make a difference of 0.05 eV which again rounds up to 5.6 eV. Thanks for the input.
Thank you for your question! When working with thin films and calculating band gap energy from UV-Vis absorption, it's important to maintain consistent units for accurate results. In your case, if the thickness of the thin film is given in nanometers (nm), you should ensure that all other parameters in your calculations are also in the same unit.
Actually, the energy converted is the energy corresponding to the band gap. Rest of the photon energy is simply a waste in the solar cell as heat. Solar cells operate on the solar spectrum to extract energy. The Shockley-Queisser equation puts a theoretical limit on the efficiency of single-junction solar cells (meaning, a definite single value for the band gap energy). Detailed calculations yield a curve of limiting efficiency (single junction, AM=1.5), which show two peaks. The larger peak is at a band gap of 1.34 ev yielding a limiting efficiency of 33.7%. The smaller peak occurs for band gap energy of about 1.1 ev giving an efficiency limit of nearly 32%. That is close to the band gap of silicon, currently the most popular material. Thanks
Yes, you can use it. The thickness of film can be used as the thickness here. If the substrate will also be absorbing in that range then that thickness will also be added. For details, please see the following article. Thanks www.mdpi.com/1420-3049/17/9/10000/pdf
Thanks for great video! I have a one question. I've heard that UV-visible spectroscopy requires liquid sample, and actually Beer-Lambert law considers sample's concentration. Then, how can we use this for semiconductor sample?
Yes, you're right. We can find the concentration with BL law from a liquid sample only. This I have explained in the following video ruclips.net/video/s47xMoF9_xE/видео.html However, we can find the bandgap of both liquid or solid transparent samples. In the case of opaque/reflecting samples, we can utilize reflection mode or DRS for finding the bandgap. Thanks
(ahv)^1/n = A(hv-Eg) and (ahv)= A (hv-Eg)^n both are Tauc equation according to literature...but these equations are similar just if A = 1....I am confused about that....Tauc plot is used just for amorphous materials?? But why is used for TiO2 and other materials??
Yes Angelica, you're right that Tauc's eq. can be written in both forms, which are the same excluding A. A is a proportionality constant, which is playing its role in the equation (and depends on some geometrical/physical parameters). However, in calculation of the bandgap, it is not playing its role, as I have explained it in the start of the tutorial i.e. y=0 in the equation, and hence 0/A=0. You're again right that Tauc used this eq. for amorphous material. However, it can be used for disordered s/cs as well. Consult the this link and the references there in for more understanding. Thanks en.wikipedia.org/wiki/Tauc_plot
thanks a lot for the video! i don't understand one thing... like I used to apply Beer-Lambert law to figure out the concentration of the sample for instance, and here in the equation the concentration kinda neglected at all either in others videos about Tauc Plot. I have a feeling it's because the concentration is a constant during all the measurement, but I might be wrong. Please, could you make that thing clear for me? Thank you in advance.
Thanks for the appreciation dear. It's a single plot with one constant concentration. To measure concentration from the absorbance data, I'm about to upload the next video.
If you're talking wrt to this video, the best line will be to the one which has overlap with most of the linear portion of the curve. Generally, for the best fit, the linear regression R2 value close to 1 gives the best fit. Thanks
Yes, you're right, it's thickness of the sample, which I have mentioned. For a solution, the cuvette internal dimensions (sample thickness) is 1 cm. Thanks
@@SAYPhysics thanks for your answer. I have another question. Why do we use cm as a unit of tauc plot?(ie, cm-1 eV). If we use m not cm, slpoe of linear region of tauc plot gets bigger and X intersection(optical band gap) gets also bigger. So I wonder whether there is certain reason or meaning for using cm.
@@박승원-x7h The peaks (like in FTIR) are very well resolved when we use the wavenumber in cm-1 on the x-axis. However, here on the y-axis, there are no technical reasons. But in Physics, whenever we deal with coefficients (length dependent), we usually use cm. Thanks
You have explained very systematically but you have made mistake in showing the band gap. When the slop intercepts at (Y=0) X-axis the true value of the band gap is obtained. 80-90% researchers do the same mistakes.
Thank you for your insightful comment on my tutorial. While I agree that intercepting the X-axis at (Y=0) is a common method for determining band gap, it's essential to note that this approach may not universally apply, especially in cases involving bandgaps with offsets. Material characteristics and experimental conditions can influence the interpretation of UV-Vis absorption spectra. You may watch my another tutorial on it as follows. Thanks ruclips.net/video/3gkcmp10uog/видео.html
professor Shahid Ali Yousafzai
I've been working with material optical characterization for quite some time but I sometimes forget a detail here and there, and this video was exactly what I needed.
I will recommend your channel to my colleagues and collaborators.
May I ask what are you working on currently?
Thank you very much
Many thanks for the appreciation Professor. Your words mean a lot to me. I hope that your colleagues and students will like the rich contents in the big playlist.
I hope you remember me SIR, your video on Tauc plot is a full complete explanation. It's simply WOW!!
The clarity and depth of your explanation makes it evident how passionate and dedicated you are to your subject matter.
Thank you for going above and beyond as a teacher and for sharing your expertise with a wider audience through your channel. Your commitment to education is inspiring, and I feel fortunate to have been your student.
Thanks for the appreciation Iqra Anjum. Your beautiful words encourages me to do even more. Stay blessed
Good morning sir. Two months before I was very depression, stress due to COVID 2 years waste in my research work.... I felt help less.. at the time I found your channel sir....all the characterization techniques I learnt from your channel 🙏🙏🙏🙏 yesterday I submitted one paper sir.... getting ready another paper .... looking journals
Everything because of you sir 🙏🙏🙏🙏you are saved me....I never forget you in my life.... thank you so much sir..I salute you 🎊💐🙏 sir how to colour in EDS
Your beautiful words touched my heart. May you have a healthy life.
I'm glad that my tutorials helped you. Every day I'm receiving prayers and best wishes from around the world and it boost my ego to do even more.
Please share it with others to be benefitted. Thanks
Thank you for a great explanation to measure the bandgap energy using Origin.
Thanks for the appreciation dear 😊
Hello sir, I really wanted to thank you for this video and all the explanations. You saved my master degree thesis! Thank you so much!!
Thanks for the appreciation dear 😊. I'm glad that it helped you. It'll be a favor now to share it with others. Thanks
It's very useful content. Thank you for your effort. A little but important correction is needed.
Before estimating the bandgap value from intersection of straight line with x-axis, the y-axis scale should be adjusted to zero as the starting point.
Thanks for the appreciation dear. Yes, you're right when there's no offset involved.
My dear Sir you are doing excellent job, God bless you.
Thanks for the appreciation dear 😊
Thank you, sir, for this video. It really helped me a lot. clearly explained.
Thanks for the appreciation dear. Please share it with your friends too.
thank you for the useful video, I learned a lot of issues.how much can I download this presentation of yours? for answer, thank you in advance.
Thanks for the appreciation dear. Please share it with others too. Do you need the presentation part of this video? Thanks 😊
Really a wonderful explanation sir. Thank you so much sir. It's a very very useful video fr students.
Thanks for the appreciation dear 😊
Dr SB ! Well explained.. Thank you
So nice of you. Thanks 👍
Thank you sir for your good explanation about band gap energy
You are most welcome. Thanks
Thank you for the great explanation. However, I am wondering if the extrapolation should only cross at y =0. Please check.
Thanks for the appreciation dear 😊. Yes, you're right. In case, no offset or baseline correction is involved, it must be at y=0. The offset I have explained in the following video.
ruclips.net/video/3gkcmp10uog/видео.html
Thank you for letting us understand
You're welcome dear
Thank you for this video. It will be useful for my research :)
Thanks for the appreciation dear 😊
Hi, thanks for this video.
I have a question regarding the last part which you are determining bandgap energy.
I am wondering why you chose that part of the graph for estimating Eg, why didn't you chose the part from energy 4 to 5 to draw the line?
Thanks for the appreciation dear 😊
We need to select the region of interest by looking at where the slope has a well defined shape.
@@SAYPhysics I really appreciate your reply. in my case I have two region that I can draw a line. i don't know which region is correct.
@maliheghafari2979 when you are having multiple regions, you will have to draw for each region. Sometimes, you need a baseline correction. The following video tutorial will further guide you in this regard. Thanks
ruclips.net/video/3gkcmp10uog/видео.html
Good tutorial video. Clearly and simply explained.
Thanks for the appreciation dear....
Thank you for the great explanation, what if the (ahv)^1/2 gives a great interpolation? how do you obtain the band gap?
Thank you for your comment! If (ahv)^1/2 provides a good interpolation, it suggests a linear relationship between the square root of absorbance and photon energy. To determine the band gap energy, you can extrapolate this linear relationship to the x-axis (photon energy axis) and find the point where absorbance becomes zero. This point corresponds to the band gap energy. However, it's crucial to validate this approach with additional methods or literature values to ensure accuracy.
Thank you@@SAYPhysics
@moses2061 welcome dear
thank you for the great video. I am new to this analysis. Why do you ignore the indirect graph? could you explain it more?
Thank you for watching and your feedback! In the video, I discussed both the direct and indirect graphs, but focused on the direct graph as it had a matching profile, making it more applicable for the analysis presented. If you have any specific questions about the indirect graph, feel free to ask, and I'd be happy to explain it in more detail.
Hello sir proud on such like teacher.
I have a decision .to start the remaining course content of quantum David j grifith and also start it's problem solution .
Because the student have many problme in quantum no one is able to solve it's problme so I request to u kindly do it
Thanks for the appreciation dear. Sure, may be when I'll start it the next time, I'll do its problems.
Thank you from my deep my heart
Thanks for the appreciation dear from the core of my heart
Your videos are highly usefull, if you having videos kindly share, about Cyclic Voltmeter graph drawing, impedance
Thanks for the appreciation Sir. I don't have any specific video on these. However, you may check the playlist to find any relevant one.
شكراً على هذا الشرح الرائع
Thanks for the appreciation dear 😊
tks you a lot for your video. This video is really meaningful for me
Thanks for the appreciation dear 😊
Please share it with your friends as well. Thanks
Thank you so much sir...very helpful video
Thanks for the appreciation dear...
Hi, thank you for your detailed explanation. I'm having a question to the last step in the video: you read the bandgap = 5.6eV at (ahv)2=-50, should we read it at (ahv)2= 0?
Yes. You're right. It's to be as y=0. Thanks for the appreciation dear 😊
Thank You Sir! For such a nice and informative (video)lecture ....
So nice of you
Thank you alot sir. This helped me
Glad it helped. Thanks
Sir put up the video Vickers microhardness testing.how I calculated work hardening coefficient or Meyer index value
There's a formula for the Vicker's hardness in which you use the diagonal lengths of the microindentation. I'll try to include it in the tutorial series. Thanks
Thanku Sir Its A Nice Explanation ....
Thanks for liking
Thanks alot Sir for detailed explanation. Would you like to upload more vedios about UV-Vis?
Regards
Thanks for the appreciation dear. Let me suggest what remains, so that, I can work on them, if feasible.
Thanks a lot for your video! I have one question: when you calculate the bandgap after extrapolating with the red line to the X axis, don't you have to rescale your graph so that Y axis start from 0? From your screen reader, you had something like Y = -47... Thanks once again!
Thanks for the appreciation dear.
Yes, you're right. It is better to be at y=0 to calculate the x value. However, it's not a general rule. In some cases, we set an offset at some non-zero y values, like in composite type bandgap. The following article will help you understand it more. Thanks again for your input.
pubs.acs.org/action/showCitFormats?doi=10.1021/acs.jpclett.8b02892
Thanks for a very clear explanation.
Will the same method be applicable to determine the band gap of colloidal particles in a solution or we need to have a DRS data only.
It works well for simple colloidal NPs, while for the core shell or functionalized NPs, the DRS results may work well. Thanks for the appreciation 😊
@@SAYPhysics Understood, thank you! Meaning, this method may work in either case, right? We don't seem to have an accessory to measure DRS and my carbon/Ti composite does show desired red-shift on the UV-Vis spectra, so I am thinking to proceed with the band gap calculations using the method you described in this video. Hope I am headed in the right direction
Yes and I hope that you will find some comparison in the literature.
Thank you for your video. In case that the absorption spectrum has more than one peak. the peak at a longer wavelength has lower intensity. which peak we will consider to calculate the optical bandgap energy.
Thanks for the appreciation. Usually, the first peak is the band-edge. Thanks
@@SAYPhysics Sorry, you mean the shorter wavelength 0.0?. Thanks
Ótima explicação, Professor! Ajudou bastante!
obrigado pela apreciação
thank you for this explication
You are welcome dear
9:45 You are mistaken. you should have determined the band gap at the intersection with the x-axis at the zero level absorptin ((alfaE)^2 = 0). (alfaE)^2 cannot take negative values
Yes, you're right. It is better to be at y=0 to calculate the x value. However, it's not a general rule. In some cases, we set an offset at some non-zero y values, like in composite type bandgap. The following article will help you understand it more. Thanks again for your input.
pubs.acs.org/action/showCitFormats?doi=10.1021/acs.jpclett.8b02892
The gamma in some measurements is 1 or 1/3 or 2/3. How can we find the proper gamma during our data analysis?
In Tauc plot analysis, gamma represents the nature of the transition and is usually assumed to be either 1/2, 1, or 2/3. Each value corresponds to a different type of transition, such as direct allowed transition, indirect allowed transition, or indirect forbidden transition, respectively.
To determine the proper gamma for your data analysis, it is essential to consider the characteristics of your material and the available literature. Experimental techniques, material properties, and previous studies on similar materials can provide insights into the appropriate gamma value.
Consulting relevant research papers, textbooks, or expert opinions in the field can help you determine the most suitable gamma value for your specific material and experimental setup. Additionally, discussing with colleagues or experts in the field may provide valuable guidance and insights for selecting the proper gamma during your data analysis. Thanks
Awesome explanation Sir, Can we use this for gold or silver nanoclusters? Looking for kind response.🌹
Thanks for the appreciation. Yes, you can use it. Thanks
@@SAYPhysics Thank you Sir. Jazak ALLAH
very elaborative and comprehensible video, thanks for sharing. Could you please help me in determing the band gap energy of my hydrothermally synthesized MoS2 nanoparticles which is in powder form..May I make its slurry in water and get absorption at differnt wavelength and proceed as you shown in the video?....Thanks in advance.
Thanks for the appreciation dear. Yes, you can disperse your powder in water or other dispersing medium. Thanks
you can take UV for powder sample too.
Thanks for the input
May I ask a question? When we calculate the band gap, we need to divide thickness of the film, should the unit of thickness be cm or nm?
Great question! When calculating the band gap from UV-Vis absorption data, the thickness of the film is typically used in centimeters (cm). However, it's important to be consistent with the units used in your calculations and to follow any specific guidelines or conventions relevant to your field of study. Thanks
@@SAYPhysics Thanks for your reply!
@@XiZhang-ko3hb You're welcome dear
Good video! Would it be correct if I extrapolate the high band in the absorbance spectra and later convert nm to eV?
...also. "A" you said is a constant (proporcionality, and in texts it says that is related with disorder and tail state). Why did you assume it like absorbance? Thank you so much
Thanks for the appreciation. I fear you can't, as we extrapolate the line onto the x-axis in relation to the y-axis. You can't change one (x-axis) while keeping the other the same (y-axis). However, in the following video, I have taken the x-axis as wavelength instead of energy.
ruclips.net/video/x6rvyuAKiGI/видео.html
Yes, you're right that it is related to the disorder and tail state. However, for the materials which aren't modified, we have it as a constant. When its role is crucial, we'll have to put its value as per nature of our sample. Thanks
Thank you so much sir.
You have mentioned l =1 it's only thin film or nanoparticles
I want to calculate bg for NiO nanoparticles..can I use L value 1
You may approximate is to 1.
The value of A depends on several factors, including the nature of the semiconductor material, the size and shape of the nanoparticles, and the measurement conditions. A can be affected by factors such as the density of states in the conduction and valence bands, the bandgap energy, the effective mass of the charge carriers, and the dielectric constant of the material.
In general, A is not directly related to the size or shape of the nanoparticles, but rather to the intrinsic properties of the material itself. However, the absorption coefficient can be influenced by the size and shape of the nanoparticles through the quantum confinement effect, which can cause changes in the bandgap energy and the density of states.
Overall, the value of A in the Tauc equation is a material-dependent constant that is determined by the intrinsic properties of the semiconductor material and can be affected by various factors, including the size and shape of the nanoparticles.
Thanks
Thank you so much sir
You are saved many research scholars 🙏💐💐 Thank you so much sir 🙏
You're welcome dear
This is my motivation to do more when I hear such an appreciation. You may share it with others so that majority is benefitted. Thanks
I ve got a question. In this case, when you find x - intercept value, the y axis has a negative value. Should y axis value be zero? Maybe if you extrapolate the linear part which is parallel to x axis and find the point of intersection
Yes. The y-axis must be zero, as explained in the presentation section at the start. Thanks
@@SAYPhysics I am trying to get familiar with UV -Vis analysis so i have so many questions. What happens when tauc plot has 2 linear parts? So you dont know which one corresponds to band gap energy
@kostaskouvelis2280 in that case the bandgap will be of dual nature both direct and the indirect. Thanks
Thanks , can I use this to calculate for TiO2 too , It has indirect band gap
Yes. Thanks
Hello! thank you for the video.
However, I am still confused; some papers suggest that the direct band gap is obtained y = 1/2 while the indirect one is y = 2, especially for DRS analysis.
Thanks for the appreciation. You've written direct bandgap at both places. I have explained this in the start of the video.
@@SAYPhysics sorry for the mistake. You can also check this reference: "10.1021/acs.jpclett.8b02892". I am just trying to figure it out who is right in the scientific community 🥴
It seems you are confusing two different things i.e. y and the power of αhν. In a Tauc plot, which is a plot of (αhν)^2 versus the photon energy (hν), where α is the absorption coefficient and hν is the photon energy, a direct bandgap material exhibits a linear portion with a steep slope near the bandgap energy. Here y=(αhν)^2, to get α, we take square root of both sides so y become y^1/2 for direct bandgap and vice versa. Thanks
Gud evening sir, could you tell us, how to convert transmittance value to absorption value
To convert transmittance into absorbance in the case of UV-Vis data, you can use the following equation:
Absorbance (A) = -log10(T)
where:
A is the absorbance,
T is the transmittance.
The negative logarithm of the transmittance is taken to convert it into absorbance. The absorbance scale is logarithmic, which means that as the absorbance value increases, the sample absorbs more light.
Here's a step-by-step guide on how to convert transmittance values into absorbance:
Obtain the transmittance values from your UV-Vis spectrophotometer measurements for the desired wavelengths.
Calculate the absorbance by applying the equation A = -log10(T) to each transmittance value.
Repeat the calculation for all the transmittance values obtained from your UV-Vis data.
Note: The equation assumes that the light path length and the solvent used are constant for all measurements. Also, it's important to keep in mind that absorbance values are often reported as positive numbers, even though the equation includes a negative sign. Thanks
sir as you explained at (8:48), if we are still not getting the best fit. Can we go further and take Cube (of Absorbance and energy) instead of Square and then we can plot...
Yes. In the beginning of the presentation, I have explained this which powers are to be taken in different situation. Thanks
@@SAYPhysics Thanks
Thank you sir for the tutorial, very helpful :)
Is there any an article or book reference that I can cite for this?
Thanks for the appreciation dear. There are so many references, you may find some of them as below;
www.sciencedirect.com/science/article/pii/0025540868900238
onlinelibrary.wiley.com/doi/abs/10.1002/pssb.201552007
www.nature.com/articles/s41598-019-47670-y
Assalam o alaikum sir! Sir if the material we have used for is amorphous and have indirect allowed transition so it is compulsory to plot energy vs 1/2?as 1/2 is for indirect
Wa Alaikum Assalam! Yes, for an amorphous material with an indirect allowed transition, it is important to plot \((\alpha h
u)^{1/2}\) versus energy (\(h
u\)) to determine the band gap accurately. This approach corresponds to the characteristic absorption edge of indirect transitions. Thanks
I plotted both the graphs for direct as well as indirect but as mentioned already that my material is having indirect band gap and I got perfect slope from the direct band gap graph...so what to do?? Should I opt for the direct or indirect??
@@SAYPhysics JazakAllah sir! May you live long and happy life Ameeeen
I will suggest to first check your calculations and then relate it with a trustworthy literature. Thanks
Thanks and Aameen dear.
Dear Sir, Hope you are doing well. Thank you for this one. I have measured the absorption spectra of my CdS QDs for solar applications. I have used a glass solid TiO2 substrate, on which CdS quantum dots have been deposited via a technique called the SILAR method. The glass substrates are cut to match the cuvet size. You mentioned that the l is the thickness of the liquid and at somewhere you substituted the value of l to the thickness of the cuvet which in your case will be the thickness of the fluid, but in my case (glass substrate) it would be the thickness of the glass slide, right? and not the cuvet thickness?.
As far as I understood your question, your thickness is the CdS QDs thickness. The absorption caused by the substrate is supposed to be subtracted as a reference. If you're using a dual beam spectrometer, put your undeposited glass slide in the reference slot, while the deposited in the measurement slot. Thanks
@@SAYPhysics Right Sir. I get it. I have used one glass substrate as a reference ( the undeposited one). You mean I should take the value of the difference between the deposited and undeposited one?.
Yes. That'll be your sample absorption thickness.
@@SAYPhysics Thanks a million sir. It was really helpful and its always a pleasure to learn from you . Stay bless. More power to you.
First of all thanks a lot for this video... sir what if the band gap increases ?whether it is crt or not... bcoz.. I was plot my graph but I got more than 5ev ...
Thanks for the appreciation dear. It depends on the nature of the dopant, whether it narrow or widen the bangap. You'll have to check about the energy diagrams of your host and dopant materials. Thanks
hi thank you for the great video, but i couldnt understand why alpha = 0,4343 A cm^-1 become alpha = 2.302 cm^-1. looking forward for answer, thanks :)
Thanks for the appreciation dear. I have explained it at 3:14 that 0.4343 is the value of log(e). Thanks
Hello i have some questions, I follow your step but the data isn’t as pretty as yours what can i do?
In the same playlist, I've some more videos on the bandgap, watch them please. Thanks
Hello sir
As I understood absorption coefficient formula is (2.302/d)*A per cm, but you did directly with formula 2.303*A per cm,please clarify which is right.
Thank you
d is 1 cm here. In the previous video of band gap energy calculation, I have done it in detail. Thanks
@@SAYPhysics Hi, I'm also confuse with this. Shouldn't it be multiply with column A instead of B?
d is 1 cm here. In the previous video of band gap energy calculation, I have done it in detail. Thanks
How does concentration affect the result of the bandgap?
To assess the effects of concentration on bandgap determination, it is essential to carefully prepare and analyze samples, consider correction factors (for example, Concentration-Dependent Absorption Intensity, Exciton Interactions, Saturation Effects, and Multiple Absorption Processes), and, if possible, perform measurements at different concentrations. Additionally, modeling techniques that account for exciton interactions and other concentration-dependent phenomena can be employed for a more accurate interpretation of the UV-Vis spectrum. Thanks
how you got to know which one is fitting better i.e. 2 or 1/2
The edge or slope can give us the idea. Thanks
How we can find bad gap of a powder sample using uv vis spectroscopy please give the formula
In this playlist, there's a video on DRS data calculations. Thanks
Thank you so much 👍
You're welcome dear
Hello my friend, Thank you for your useful video. Could you please provide the reference for the absorption-wavelength data? Thanks
Please check the video description for the references. Thanks for the appreciation dear
Sir, the vedio is quite interesting, but you should adjust the Y axis in such a matter that it start from zero, other wise the band gap obtained is incorrect.
Thanks for the appreciation dear.
Yes, you're right. It is better to be at y=0 to calculate the x value. However, it's not a general rule. In some cases, we set an offset at some non-zero y values, like in composite type bandgap. The following article will help you understand it more. Thanks again for your input.
pubs.acs.org/action/showCitFormats?doi=10.1021/acs.jpclett.8b02892
Hi sir, does thickness of material matter in calculating the absorption coefficient?
Yes dear. Thickness is being used in the formula. Thanks 😊
You may watch the following video for details of absorption coefficient calculation.
ruclips.net/video/9UYAVZnJt9k/видео.html
Excuse me, we have (2601) in our scientific center.
In respect to absorbance:
1) Should we substract the values of glass data from films data? or the instrument does it?
2) The maximum value is four, why not one? Should we divide data on four?
It seems that you are having 'UV 2601 UV-VIS Double Beam Spectrometer', then it means in one beam, you'd have placed the glass with thin film and in the other beam (reference), you'd have placed uncoated glass. 1) If this is the case, you don't need any subtraction of the glass as the machine would have done it. 2) Intensity doesn't matter, unless you're comparing with other samples. You can normalize your data to 1. Just keep y=0 when drawing the slope. Thanks
@@SAYPhysics
Thank you very much,
Maybe my colleague does it wrongly, she first puts the uncoated glass, then puts the coated one separately, not at the same time as I understood from your response.
@معتز سعدي بدري عبد الدليمي We usually do this method for a single beam equipment, thereby subtracting the uncoated from the coated one, which is not very accurate for critical samples but does the job. For a dual beam, we may follow the procedure, as I suggested earlier. Thanks
@@SAYPhysics ❤❤❤
Sir if the curve has two or three linear parts, then how to decide which linear part is suitable for calculating band gap.
This is something not very straightforward but requires some literature overhauling. Sometimes, such regions do mean a bandgap and sometimes it's an offset. I'm referring to an article, which will help you understand it more. Thanks
DOI: 10.1021/acs.jpclett.8b02892
@@SAYPhysics Thanks
Where is the thickness in calculating absorption coefficient?!
Absorption coefficient= (2.302*Absorption/thickness)
In the start of the few minutes of this tutorial, I have explained about the thickness calculation. Let me know if it needs further clarification. Thanks
Awesome sir awsome
Thanks for the appreciation dear 😊
Thanks a lot! This was really useful:D
Thanks for the appreciation dear
you are a legend
Thanks dear
Gravitational waves per ap k vedio hay YT may?
Yes. It's in 3 parts. Link to the first part is here ruclips.net/video/YJkK5neS620/видео.html. See rest of the parts yourself. Thanks
It's very useful , thank you !!!
You are welcome!
many thanks
Welcome dear
This sheet is not working for my data and can't calculate the alpha and energy for my data . Please check ✅ so thankful to you !
I rechecked. It is fine. May be you have problem with your Origin. Thanks
you have wrong bandgap on the graph, y-axis starts at 0, meanwhile you make y-axis negative, because y=0 then E=hv
Yes, you're right. The y-axis must be selected from 0 while drawing the slope. However, the bandgap is right as it make a difference of 0.05 eV which again rounds up to 5.6 eV. Thanks for the input.
I wanted to point out the same thing. The band gap should be read from y=0. Here it does not make a big difference but many could be misleaded.
Yes, you're right. In other such videos, I've explained this in more details. Thanks for your input. Thanks
informative content
Thanks dear.
what if I have a thin film which is 100 nm? Should I convert it to cm or I can make the calculations using nm?
Thank you for your question! When working with thin films and calculating band gap energy from UV-Vis absorption, it's important to maintain consistent units for accurate results. In your case, if the thickness of the thin film is given in nanometers (nm), you should ensure that all other parameters in your calculations are also in the same unit.
@@SAYPhysics Thank you for your answer
@fluffybirb4758 you're welcome dear
Excellent video!
Thank you very much!
Excellent
Thanks
thank you so much!!!
You're welcome dear
Sir
Effect of band gap on power conversion efficiency ?
Actually, the energy converted is the energy corresponding to the band gap. Rest of the photon energy is simply a waste in the solar cell as heat. Solar cells operate on the solar spectrum to extract energy. The Shockley-Queisser equation puts a theoretical limit on the efficiency of single-junction solar cells (meaning, a definite single value for the band gap energy). Detailed calculations yield a curve of limiting efficiency (single junction, AM=1.5), which show two peaks. The larger peak is at a band gap of 1.34 ev yielding a limiting efficiency of 33.7%. The smaller peak occurs for band gap energy of about 1.1 ev giving an efficiency limit of nearly 32%. That is close to the band gap of silicon, currently the most popular material. Thanks
alpha=2.302A(cm) work for thin films if we need to calculate band gap of semiconductor thin films
Yes, you can use it. The thickness of film can be used as the thickness here. If the substrate will also be absorbing in that range then that thickness will also be added. For details, please see the following article. Thanks
www.mdpi.com/1420-3049/17/9/10000/pdf
Thanks for great video! I have a one question. I've heard that UV-visible spectroscopy requires liquid sample, and actually Beer-Lambert law considers sample's concentration. Then, how can we use this for semiconductor sample?
Yes, you're right. We can find the concentration with BL law from a liquid sample only. This I have explained in the following video
ruclips.net/video/s47xMoF9_xE/видео.html
However, we can find the bandgap of both liquid or solid transparent samples. In the case of opaque/reflecting samples, we can utilize reflection mode or DRS for finding the bandgap. Thanks
(ahv)^1/n = A(hv-Eg) and (ahv)= A (hv-Eg)^n both are Tauc equation according to literature...but these equations are similar just if A = 1....I am confused about that....Tauc plot is used just for amorphous materials?? But why is used for TiO2 and other materials??
Yes Angelica, you're right that Tauc's eq. can be written in both forms, which are the same excluding A. A is a proportionality constant, which is playing its role in the equation (and depends on some geometrical/physical parameters). However, in calculation of the bandgap, it is not playing its role, as I have explained it in the start of the tutorial i.e. y=0 in the equation, and hence 0/A=0.
You're again right that Tauc used this eq. for amorphous material. However, it can be used for disordered s/cs as well.
Consult the this link and the references there in for more understanding. Thanks
en.wikipedia.org/wiki/Tauc_plot
@@SAYPhysics Thanks for explanation!!!!
What is the range of bandgap any reference sir
Please check the video description of this video, there you will find many relevant references. Thanks
Thanks a lot!
You're welcome dear
Sir plz make a video on Psi and Delta graph of from ellipsometer data.. Plz ❤️
Noted. Thanks
How to find absorbance using reflectance
You will have to use the Kubelka Munk function. I have explained this in the following video. Thanks
ruclips.net/video/YYVoG0O30cI/видео.html
thanks a lot for the video! i don't understand one thing... like I used to apply Beer-Lambert law to figure out the concentration of the sample for instance, and here in the equation the concentration kinda neglected at all either in others videos about Tauc Plot. I have a feeling it's because the concentration is a constant during all the measurement, but I might be wrong. Please, could you make that thing clear for me? Thank you in advance.
Thanks for the appreciation dear. It's a single plot with one constant concentration. To measure concentration from the absorbance data, I'm about to upload the next video.
How can we guess which is good fit , to go through
If you're talking wrt to this video, the best line will be to the one which has overlap with most of the linear portion of the curve. Generally, for the best fit, the linear regression R2 value close to 1 gives the best fit. Thanks
Thank you so much sir
Most welcome dear.
How to determine "l" if the sample is powder in nature?
In case of an opaque sample, DRS is utilized which I'll cover in the forthcoming video. Thanks
Nice.
Thanks
why did you put 1cm as l? I think it should be thickness of sample not 1cm
Yes, you're right, it's thickness of the sample, which I have mentioned. For a solution, the cuvette internal dimensions (sample thickness) is 1 cm. Thanks
@@SAYPhysics thanks for your answer. I have another question. Why do we use cm as a unit of tauc plot?(ie, cm-1 eV). If we use m not cm, slpoe of linear region of tauc plot gets bigger and X intersection(optical band gap) gets also bigger. So I wonder whether there is certain reason or meaning for using cm.
@@박승원-x7h The peaks (like in FTIR) are very well resolved when we use the wavenumber in cm-1 on the x-axis. However, here on the y-axis, there are no technical reasons. But in Physics, whenever we deal with coefficients (length dependent), we usually use cm. Thanks
@@SAYPhysics thank you Sir 😊
how to calculate I and Io values sir
You don't need to. They're already in A or R values. Thanks
sir why we draw the tangent.
Inorder to find the x-intercept for the energy value. Thanks
is the value 2.3 fixed?
Yes, if you're using a standard cuvette. Thanks
@@SAYPhysics irrespective of the concentration too?
Yes, it's based on the geometry as I explained in the start of the tutorial. Thanks 👍
From the hypothesis, the thickness of the membrane enters the alpha calculations
Somehow you are right. Please watch this video tutorial to have a deep understanding of this. Thanks
ruclips.net/video/s47xMoF9_xE/видео.html
You have explained very systematically but you have made mistake in showing the band gap. When the slop intercepts at (Y=0) X-axis the true value of the band gap is obtained. 80-90% researchers do the same mistakes.
Thank you for your insightful comment on my tutorial. While I agree that intercepting the X-axis at (Y=0) is a common method for determining band gap, it's essential to note that this approach may not universally apply, especially in cases involving bandgaps with offsets. Material characteristics and experimental conditions can influence the interpretation of UV-Vis absorption spectra. You may watch my another tutorial on it as follows. Thanks ruclips.net/video/3gkcmp10uog/видео.html
THANKS
Welcome dear
how to insert f(x)?
I'm not getting your question. What's f(x)? Thanks
thanks
Welcome dear