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.
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
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?
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. ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-3gkcmp10uog.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 ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-3gkcmp10uog.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.
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 :)
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.
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
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
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
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.
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
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
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.
You will have to use the Kubelka Munk function. I have explained this in the following video. Thanks ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-YYVoG0O30cI.html
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
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
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
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
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
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
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
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.
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??
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
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
Somehow you are right. Please watch this video tutorial to have a deep understanding of this. Thanks ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-s47xMoF9_xE.html
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
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?.
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...
(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 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
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.
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
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 ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-3gkcmp10uog.html
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
Teacher I have a questions how we solve questions like that determine the attenuation light absorbed by silicon slab thickness of 0.01 absorption coefficient of Si is 1.5 cm_1 incidence intensity was about 175 watt/m^2
...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. ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-x6rvyuAKiGI.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
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'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.
@@user-gz5zy1ve3o 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
Yes. It's in 3 parts. Link to the first part is here ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-YJkK5neS620.html. See rest of the parts yourself. Thanks
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.
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 ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-s47xMoF9_xE.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
