 In this module, we have been looking at the characterization techniques and the way we have faced understanding the characterization techniques and how we can learn from these instruments namely diffractions spectroscopy, microscopy methods, instead of learning each and every technique. It is better that we look at some case studies and then we will understand in a comprehensive way how we can use these techniques to elucidate structure and to correlate that with the property that we are seeing. So, in today's lecture, we are going to look at case study on zinc oxide which is doped with manganese. In the last 7 years, this particular study has brought in lot of research focus mainly because it address one of the very sensitive area called spin tronics. In fact, this lecture is aimed to show how simple techniques can be used to understand whether we are really hitting the bullseye because it is possible that we can prepare several compounds, but yet not knowing that we have not achieved the final product. So, in this connection, we will try to see how all the characterization techniques can be combined to get a comprehensive idea of a single system that is manganese doped zinc oxide. Why it is important because it shows room temperature ferromagnetism? As a result, it finds a potential spin tronic application, but what I am going to tell is the story that evolved around this one single system and how cautious as a chemist or a physicist or as technologies we need to be and how this characterization techniques can come handy to understand. This is a simple cartoon we can try to visualize which is typical of zinc oxide wood side structure and if we try to incorporate a magnetic ion with a spin or it could be any other ion which can induce a ferromagnetism how this ferromagnetic core can influence zinc oxide. Now, notably manganese is not a ferromagnetic compound. So, we are going to look at the origin of magnetic property in zinc oxide using a doping of a non-magnetic ion. So, it is a much simpler issue how to elucidate the ferromagnetic component that is present in zinc oxide because both zinc oxide as well as manganese that is doped there M n 2 plus both are not magnetic. So, it is much easier for us to evaluate what is really going on there. Now, what is the big hype about manganese zinc oxide? Since it is a case study I want to single out some of the importance of this before we go into a in-depth analysis. Manganese is doped zinc oxide has gained more intense research activity in the past few years as I told you and because zinc oxide is optically very potential candidate for photonic applications any doping would affect the photonic properties or optical properties specially if you doped it with a high band gap material that is M n o. So, if it is manganese which is going as M n 2 plus into zinc oxide then you would see a clear shift in the optical property. Manganese is also being anti ferromagnetic metal the doping of M n o we can call this M n o in zinc oxide lattice should not necessarily show a ferromagnetic property it should not show. So, it makes the case much more interesting for us to understand where is the magnetism coming from, but what is peculiar of this manganese doped zinc oxide is you observe this at room temperature any compound which gives trace of impurities is supposed to show T c below room temperature, but manganese doped zinc oxide shows above room temperature that makes it much more interesting to know where this comes from. So, the question of origin of room temperature ferromagnetism after 7 years of effort is still not a resolved picture although plenty of indication is there about what exactly is happening. The potential advantage of such spinteronic materials is that you can make a spinteronic device and that will be higher speed greater efficiency and better stability at a reduced power consumption this is the implication as far as spinteronic application is concerned. So, with this in perception let us see where it all started how the story evolved report started coming as early as 2003 with the breaking news in nature materials this is actually a Swedish group professor K. V. Rao's group which published that manganese tuples when it is substituted in zinc tuples sites that is Z n o it shows room temperature ferromagnetism and soon there was a report saying that the observed magnetism is not coming from manganese substituted in Z n o, but it is due to a metastable phase such as m n 2 minus x Z n x o 3 minus delta this is nothing but m n 2 o 3 seemingly substituted with Z n 2 plus. So, there are several related papers which has come out which further shows the implication of the impurity phases which can cause magnetic signal due to segregated magnetic clusters this magnetic signature can come which was published in P R L in 2004 and someone elucidated that there is presence of m n 3 plus and m n 4 plus which leads to a double exchange mediated ferromagnetism which appeared as lead as 2007 and defect structures were also contributing to the magnetic properties which was told in 2005. So, as you see here historically this is the first paper and the second paper that comes along is this. Now, in the next few slides I will try to show you what were the contradictions and how the analytical instruments or techniques that were used help us understand what really was going. This lecture is intended not to put any research group in darker side, but just to highlight based on the published reports how careful we need to be when we are preparing oxides and when we make assertion that there is a magnetism in a particular compound. So, with this as a disclaimer I would like to show some of the results. Now, in nature materials 2003 as you know Professor Rao's group published this article saying ferromagnetism is above room temperature both in bulk and transparent films which brought a curiosity among the scientific community because sometimes you can see ferromagnetism in bulk, but it need not actually transpose in the thin film form or sometimes it may be there in thin film it need not be in bulk, but when it goes hand in hand and when you see that the bulk pellets as well as transparent films of very thin order they show this sort of ferromagnetism then you are bound to believe that something is really happening. So, what was the abstract? The abstract said the search for ferromagnetism above room temperature in dilute magnetic semiconductors has been intense activity in recent years. We report the first observations of ferromagnetism above room temperature for dilute that is less than 4 atom percent manganese doped zinc oxide. The manganese is found to carry an average magnetic moment of 0.16 mu b per ion and what did they say? They also said the unique feature of our sample preparation is that it is a low temperature processing all the samples were prepared below 700 and they could do this pronouncing that there is a room temperature effect and they also said that this could be the new spinteronic device for magnetic optic devices. Now soon after this report there was a counter argument from this group. This is a professor Venkatesan's group in University of Maryland at college park and they came with another paper in the same magazine that is nature materials in a span of just 9 months where they said on the origin of high temperature ferromagnetism in the low temperature processed manganese oxide compound. I would not like to read through the whole thing but all I would like to pin point is direct low temperature thin film deposition shows ferromagnetism at low zinc concentration and for an optimum oxygen growth pressure our results strongly suggest that the observed ferromagnetic phase is oxygen vacancy stabilize m n 2 minus x z n x o 3 minus delta. If I have to sum up in the first place what exactly they are finding was this is the abstract that they showed and we will just see through few slides to see how they progressively elucidated this which will be a fundamental importance for our understanding about how to use this techniques and how handy it can be. Now this is the 2 percent manganese doped zinc oxide if you measure you will see a clear ferromagnetic loop and that magnetic loop is at 300 K. Now if you look at this ferromagnetic loop as clear as this one would blindly say I have a magnetic material and carefully if you try to run m versus t m versus t you see here there is a ferromagnetic transition down to 1000 Kelvin that means t c is somewhere around 700 above 700 degree centigrade. So because it is showing a t c above 700 degree centigrade you can be sure that at room temperature it has to be a room temperature ferromagnetic. So there is nothing wrong with this compound but we need to understand whether it is clearly a dilute magnetic semiconductor or not. So what this group did they took both zinc oxide plus 2 percent mn O 2 that is dope then mix it together and try to do a T g analysis. This is what they have to say to clarify the nature of inter diffusion reactions between mn O 2 and zinc oxide powders as a function of temperature we used thermogravimetric analysis. Thermogravimetry is not a very very astounding or a very costly instrument it is affordable and almost every lab or analytical centers would have it. But look at the way that the group has resorted to use a simple technique not much involved but to elucidate some primary features out of it. What did they do? They just took this mixture of 2 percent mn O 2 and then did the thermogravimetric analysis and also they took just mn O 2 which is the starting material and do the thermogravimetric analysis in air. So if you try to heat mn O 2 you can see this red graph which clearly shows 2 plateau first there is no change no loss of oxygen up to nearly 700 k and beyond 760 k you see a sharp fall and all these horizontal lines that you are seeing here is the calculated values for different composition of manganese namely mn 2 O 3 or mn 3 O 4 or mn O these are the components that can come if you take mn O 2 and heat it in air. So if mn 2 O 3 is forming then this should be in the first plateau if mn 3 O 4 is forming this should be in this plateau. So look at this there is some similarity between the 2 percent manganese oxide doped zinc oxide versus the standard mn O 2 what is happening you see the same sort of a fall and the first plateau is actually resembling that of mn 2 O 3 and then there is another plateau which is similar to mn 3 O 4. So you are almost getting a similar feature that of mn O 2 in zinc oxide but only thing the formation of mn 3 O 4 here is above 1000 Kelvin whereas that region is actually more favored even at low temperature as low as say 980. So there is a considerable shift in the formation of the second plateau that is mn 3 O 4 similarly you can see the mn 2 O 3 formation seems to be happening much below the standard. So there could be some thing that we can pick up as it is that in the presence of Z n O the formation of both mn 2 O 3 and mn 3 O 4 are favored at much lower temperature this is the first lesson that we can take. Another thing that the mn 2 O 3 mn 3 O 4 are still present in 2 percent mn O 2 doped zinc oxide therefore there is a clue that probably manganese is not exactly getting doped even at 700 900 K it is still remaining as a phase of mn 3 O 4 or mn 2 O 3. Now we can resort to the bulk x-ray pattern. So these are the bulk x-ray patterns this is for zinc oxide which shows the hexagonal structure and this is characterized by three intense peaks one around 35 one around 47 and one around 57 you see this three peaks and suppose you are going to take 2 percent of mn O 2 and you are going to mix it with this Z n O you would see for the unsintered sample there are some signatures here which is not present in the pure Z n O. So for example this feature and these are some of the features that are coming only if you physically mix mn O 2 with Z n O. So this is the feature number two if you start sintering this compound below 700 K you see still there are reflections of mn O 2 here there is one reflection of mn O 2 here there is a reflection of mn O 2 here there is another one here there is another one. In other words even at 700 K you do not seem to see this mn O 2 signature vanishing. Now why this was missed out mainly because the earlier group they studied the x-ray with a linear intensity scale but what we are showing here is the log intensity. When you try to plot the log intensity versus 2 theta value you always see all the impurities coming up which are more pronounced. Therefore as a thumb rule when we try to work with polycrystalline samples or bulk samples or even with thin film samples always it is a cardinal rule to look at the log intensity plot of x-ray because log intensity plot will bring this sort of small features to prominence mainly because relative to the intense peak of Z n O in linear intensity plot you would certainly miss out on these signatures. And this was the first clue that made the other group to believe that probably manganese is not getting doped in the Z n O lattice. So this is very crucial the first message that we should take as we go through a set of data is that never look at the x-ray pattern without taking a log intensity plot on the y axis. So if you get a log intensity plot and then you do not see any impurity feature you can satisfy yourself saying that there is no secondary phase which is causing any influence on the physical property that you are studying. So this is one of the message that we can take. Now this same group went about trying to elucidate if there is any way that they can clearly prove that this is not manganese doping but any other impurity phase. How did they do this? They resorted now not to bulk compound but to making thin films and what sort of thin films you can make take c axis oriented yield O 3 which is also called sapphire. Sapphire is titanium or iron doped alumina which can be easily grown as a single crystal material. So you try to take a single crystal of yield O 3 and then if we try to put zinc oxide if you try to put zinc oxide up to 700 angstrom and then over the zinc oxide you can try to put manganese oxide. So how does it go? It is almost like as depicted here you first take the alumina peak that is your sapphire substrate and then epitaxially grow this much of zinc oxide and after that you try to grow M n 3 O 4 layer which is marked in the with green circles. So this is the film that is grown it is called a bilayer deposition just to understand what is really happening as you try to anneal the substance. So these films are actually grown at higher temperature meaning below 700 k below the transition point. So what is the message that we can take? As you see here you have a intense peak for alumina somewhere here but along with that you also have the zinc oxide peak here and one would also observe even for 2 percent doped manganese oxide doped one. You can clearly see in thin sorry this is not M n 3 O 4. So over and above zinc oxide if you try to put M n 3 O 4 layer then you can see these signals coming here these are corresponding to M n 3 O 4 and if you try to heat the whole film that is Z n O M n O 4 M n 3 O 4 bilayer then you can see here that the annealed one and the unealed film both are showing the faces for zinc oxide and M n 3 O 4. But what you see here in the inset is there is a slight shift in the peak value for the Z n O peak and there is a slight shift in the peak value for M n 3 O 4 which means something has happened at the interface. You are still seeing the Z n O peak you are still seeing the M n 3 O 4 phase but on annealing you see a small shift there therefore something should be happening only at the interface not in the bulk and what happens at the interface will tell us what sort of evolution is happening with the phase. Now if you look at the R B S pattern this is R B S spectra nothing but Rutherford back scattering spectrum and this is called a channeling experiment which will tell us whether in a zinc oxide crystal if there is any impurity is doped whether that would give a good channel or a disturbed channel. If the channeling value is good then you say that there is clear doping if a secondary phase is forming then the channeling will be very bad which means you are not able to grow a epitaxial layer. So you can get variety of information from Rutherford back scattering. So this is the situation for a Z n O layer and then which is kept with the M n 3 O 4 layer. So this is as grown you have alumina then you put a thick Z n O and then on the top you put M n 3 O 4. Now channeling profile will be something like this the dotted one here is the simulated spectrum for 2 percent of manganese oxide doped Z n O the simulated spectrum has to be something like this. And what you see here for a as grown film this is the one which is showing that there is a substantial decrease in zinc because you have M n 3 O 4 on the top. But as you anneal the sample you can see here that suddenly there is a camel back that is coming and that camel back is actually due to M n 3 O 4. So what really happens between the as grown film and the annealed film you can see here as it is given in this cartoon the some of the zinc oxide zinc 2 plus ions are actually diffusing into the M n 3 O 4 layer and they are getting substituted in the interstitial sites. There are vacancies oxygens are also lost and zinc is getting incorporated here and there in the M n 3 O 4 matrix. This is the signature that we can get from Rutherford back scattering. Now what would happen if you take such a film and then you heat it this film is nothing but representation of this configuration. So you actually have a sapphire and then you have the zinc oxide and then over that you have manganese 3 O 4 layer. So if you try to take a BSM loop you can see here with more and more of annealing temperature the ferromagnetic loop is developing. So this could actually happen at the interface because of a inter diffusion across the layers rather than substitution. So more and more of zinc seemingly is getting incorporated into the lattice and as into the M n 3 O 4 lattice as a result you see the magnetic moment is picking up incidentally this signature is comparable to what is reported. So instead of a reverse engineering that is zinc manganese getting doped into zinc we seem to see zinc getting dispersed into the M n 3 O 4 matrix forming a secondary phase which is responsible for such a magnetic phase. Now you can try to reconfirm this by growing zinc oxide on M n 3 O 4 instead of growing M n 3 O 4 layer like this on Z n O we try to grow Z n O on M n 3 O 4. Now if you try to do the channeling studies as you can see here this is the as grown signature for Z n O on M n 3 O 4 which means there is considerable amount of zinc. Now if you try to anneal this compound for 9 hours you can see considerably the zinc proportion is going down what does it mean there it is not the reverse transport that is manganese going into zinc oxide it is the zinc which is diffusing into the manganese oxide layer. So this is a very handy proof and to support this this group also went above doing another experiment what is they do here again they took alumina substrate and over this alumina substrate they just deposited 2 percent zinc oxide incorporated M n 3 O 4. Take M n 3 O 4 take M n 3 O 4 and make it as a hard pellet so that you can grow films and in this M n 3 O 4 pellet you try to dope 2 percent zinc. Now if you deposit such a film this is what is the x-ray pattern what is it show you should you clearly see signature for M n 2 O 3 you see signature for M n 2 O 3 again you see signature for M n 2 O 3 here along with M n 2 O 3 you also see signature for M n 3 O 4 and you also see signature for M n 3 O 4 and now this film clearly shows there is a magnetic signal at 300 K. Magnetic signal is clear at room temperature which gives us a clue that zinc can also diffuse into M n 3 O 4 and it is not the manganese which is diffusing into Z N O. Now if you try to monitor what is exactly the mechanism this is for a x is equal to 2 percent zinc that is doped at 400 millitour. Suppose for the same zinc composition if I try to deposit at 100 millitour instead of 400 millitour of oxygen pressure now you can see here I am not able to observe any M n 2 O 3 here there is no M n 2 O 3 there is no M n 2 O 3 here and there is no M n 2 O 3 here when I deposit this films at 100 millitour that is at low partial pressure of oxygen. Now I can twist this again instead of keeping same 400 millitour I can try to substitute now 4 percent of zinc. Now if I try to increase zinc concentration at 400 millitour again I am seeing a nice magnetic loop this is a room temperature signal. So 2 percent or 4 percent zinc at 400 millitour of oxygen partial pressure I am getting a film which is ferromagnetic. Now the same 4 percent if I try to do at 2 percent I am losing the ferromagnetic signal. Now keep the 400 millitour constant and then try to substitute with 10 percent of zinc again you would see M n 2 O 3 is not there when M n 2 O 3 is not there then you can clearly see that there is no ferromagnetism. Now when you do it at low partial pressure you again see there is no ferromagnetism. So 2 things are happening higher than 4 percent Z n there is no ferromagnetism and less than 100 millitour of oxygen again there is no ferromagnetism. So 2 things are clearly proving that there is something happening between the zinc that is getting diffused into the M n 3 O 4 layer rather than M n getting diffused into Z n O. So this clearly proves that it is the 2 percent zinc oxide that is getting into M n 3 O 4 phase as a result it is the M n 2 minus x Z n x O 3 minus delta which is responsible for ferromagnetism. So whenever there is lack of M n 2 O 3 then there is no ferromagnetism M n 3 O 4 is not affected M n 2 O 3 seems to be the clue and when M n 2 O 3 is always present you see there is a clear ferromagnetic loop coming. So this group went about to propose that it is not zinc that is doped into sorry this is not manganese that is doped into Z n O rather it is a defect induced concentration in M n 2 minus x Z n x O 3 minus delta which is actually stabilizing a ferromagnetic signal above room temperature. Now this is a very classic example to show that the characterization techniques that we employ can be both useful and it can be risky because blindly when you look at a magnetic signature if anything that is coming that cannot substantiate that it is a true property of a material specially when you are trying to dope impurities of the order of 2 percent or 4 percent one has to be extremely careful to see what is the exact mechanism that underlies the magnetic property. Now the sort of characterization tools like RBS or thin film whatever thin film based studies these are all very costly it is not possible always for all the groups to afford such exclusive techniques to elucidate whether the physical properties are going with the structure. But at the same time I have told I have shown you in the previous slides how simple techniques like thermogravimetry can also be very handy to substantiate this view point. So, in the next few slides I am going to show to you from a chemistry point of view we can try to understand how the whole thing can be understood. In fact the understanding of magnetism now is clear but from the chemist point of view I would like to throw different routes by which we can prepare and yet we can draw very conclusive evidence whether manganese is really getting doped or not in bulk or in thin film form. So, for this reason I have chosen 4 techniques that one can employ to study one single property that is manganese doped ZnO to ZnO and we can employ the simple solid state synthesis for comparison already I have shown you some of the results from the other group. We can try to make a thin film out of pulse electron deposition or we can use microwave coupled polyol route which I would be also discussing this example in module 6 when we talk about optical properties in solids and I will also show you another example of microwave combustion route all this the physical picture or the mechanistic understanding about these preparation routes I have already discussed in the first module but nevertheless I will use these 4 techniques to show how this can be understood from a chemist point of view. Let us take the case of manganese doped ZnO prepared by solid state synthesis and here if you look at the x-ray pattern you can clearly see that all the x-ray patterns are looking very clean whether you dope with 2 percent or 4 percent it gives a convincingly clear x-ray pattern. Now as we already saw that log intensity plots are very very important than seeing the linear intensity plot as you would see this is a linear intensity plot and this is a log intensity plot of the same pattern and you can see although this looks noisy this will give you clear evidence whether any impurities are hiding here so it is always careful for people working on bulk to probe the log intensity plot of x-ray than to simply be gratified by a linear intensity plot and all these plots what you are see here on the left side and right side is the same plot but plotted in different scale. So you can clearly see there is no evidence of any secondary phase coming here but what can we say now if you try to look at ESR spectra ESR spectra clearly gives you clue about whether it is Mn 2 plus or not in fact Mn 2 plus is possible doping Mn 2 plus in solid state method is possible but the ESR spectra does not give a clue that these are isolated Mn 2 plus core which is sitting in ZnO matrix why because if it is a isolated if it is a isolated Mn 2 plus then the ESR signal has to be a 6 line it should be a 6 line spectra but what we see here is a gross broad ESR spectra showing that there is a cumulative effect or there is manganese-manganese interaction in the ZnO it may be substituted but these manganese are not isolated as a result you do not get the splitting 6 line spectra rather you are getting a broad spectra. So there is a limitation in the solid state feature that you are effectively able to grow or substitute manganese yet the compound suffers from manganese-manganese interaction therefore the magnetic property is limited by this Mn 2 plus 2 plus interaction that is what you exactly see because you clearly see that your ZnO bulk is non-magnetic and it does not show any loop but with increasing concentration of manganese from 2 percent to 4 to 10 percent you clearly see that the moment is increasing. So this magnetic property is actually coming from Mn-Mn interaction rather than coming from a pure doped situation we will see other examples in the next few slides. In the same sample we can also get clue whether manganese is really getting doped if you take the photo luminescent spectra of manganese doped in zinc oxide you can clearly see that this is the peak for undoped ZnO powder which is synthesized by solid state all we can see here is defect induced PL emission that is characteristic of this 550 broad peak if it is really band to band age as I have discussed earlier in the other lectures the band to band age should actually come here at 380 but one thing we can be clear that when manganese is getting doped you can clearly see that this surface or defect induced emission is suppressed and the band to band age emission is getting favored although still there is considerable defects one can say that manganese is getting substituted in some form but not necessarily to affect the magnetic property but there is a corporate effect and manganese seems to be suppressing the oxygen deficiency because manganese is able to bring in oxygen while zinc is actually losing oxygen in the lattice. So this is one of the view point from the solid state prepared sample now let us go to same manganese 2 percent or 4 percent doped zinc oxide system but this time instead of solid state we will use pulse electron deposition because pulse electron deposition is also complementary to PLD as I have already discussed in module 2. So this is a simple setup of PED which we can use for making such samples and look at the x-ray pattern of this manganese doped zinc oxide films these are the zinc oxide films which is plotted in log intensity and the same films which are deposited on quartz plate in this case if you grow this zinc oxide you can clearly see they show very clean feature and you would not expect any sort of manganese impurity in this ZNO films therefore one can clearly walk out walk away with the understanding that manganese is getting doped and in this case you can also see that you can dope even 10 percent of manganese without any trace impurity for manganese here. So having said that look at the microstructure this is how the ZNO films are when you deposit using PED now this is for the 2 percent manganese this is for 4 percent manganese and when you go to 10 percent you do not see the same sort of a feature there is something else happening therefore compositionally it may be 10 percent doped sample but there could be something else happening so it need not necessarily be a doped zinc oxide film. So let us look at the PL spectra and the ESR spectra as you would see here compared to the solid state grown films you still see a very nice 380 nanometer peak for manganese doped ones and here again the same story as that of solid state where you see the zinc oxide shows a very low 380 nanometer peak mainly because it is losing much on the defect induced concentration whereas manganese doped ones are suppressing the 550 nanometer peak but it is showing the 380 nanometer peak. And when you go to the ESR spectra for 2 percent or 4 percent peak and this is what the cartoon says that there is no signature of isolated MN 2 plus signal rather see a very broad signal and this broad signal is suggesting that MN 2 plus are having some sort of clustering if it is MN interaction then you would expect something like this and there is also another signature here which is typical for MN 304 phase which although you do not see in the bulk form but yet you see there is a clear signal for something other than MN 2 plus there is a signal it could actually come from MN 3 plus or MN 4 plus concentration. So this is the situation if you try to look at the PED grown thin films now what is more convincing when you look at it is the magnetic property unless you see a unlike the other case where you see a faint magnetic signature if you grow PED grown films then you can see for 2 to 10 percent you can clearly see the signal changing for 2 percent you see a negative slope this is coming mainly because you are using a quartz plate and therefore the diamagnetic contribution is more. So you can actually do a diamagnetically corrected compound and in that case a clear loop is found this is at room temperature now if you increase the concentration you see the green curve and then the blue curve which on diamagnetic correction shows a clear loop. So if you do not probe into ESR and just look at the x-ray and then the magnetic property you can clearly say that I have doped manganese because there is a monotonic increase in the magnetic moment with respect to substitution therefore you would clearly convince yourself that it is a manganese doped zinc oxide film but this need not be mainly because we see that these are not isolated manganese in these ZNO matrix. So ESR in this situation comes out very handy now let us go to microwave combustion synthesis, microwave combustion synthesis is like a brute force method because you are providing enough of flame temperature in this reaction for the reaction to occur therefore you can quickly doped manganese into ZNO lattice not only that it is a fast quenching reaction as I discussed already in the first module. So you are actually using a rapid synthesis and a fast quenching method therefore you can stabilize metastable phase for example if manganese can clearly be doped at high temperature then you can suddenly cool it and stabilize the metastable phase and look at the x-ray pattern you can clearly see the ZNO peak and the microwave combustion stuff but what is interesting here to find is that at 10 percent you can clearly see another feature that is coming close to the ZNO peak and if you plot the whole thing in log intensity plot you can see this impurity much more pronounced even at 4 percent you can see the signature there therefore it is very important for us to carefully look at the signature that is coming out note for example these are all the signatures for MNO which is coming out of the zinc oxide lattice. So microwave combustion seemingly is able to doped manganese but there is also a residual impurity that is seen and the PL spectra is completely plagued with defect concentration therefore you do not see any band to band emission age emission but you see defect induced or oxygen deficient PL behavior. Now if you take the ESR spectra of this manganese doped compounds prepared by microwave combustion route you see that you can you do not exactly see a 6 line spectra but you are seeing a 16 line spectra and this 16 line spectra suggest that this is not exactly MN 2 plus but these are signatures for both MN 3 and MN 4 plus concentration it is for 2 percent it is for 4 percent it is for 10 percent therefore one can clearly say that in microwave combustion what is happening is the MN 2 plus is also getting converted to higher oxidation states which are MN 3 plus and MN 4 plus and therefore it is very very important that we try to look at the ESR spectra when you are specially studying the manganese system. Look at the magnetic signatures as seen here ZnO is clearly giving a negative slope so there is no problem the moment you put 2 percent it is turning positive and then for 4 percent and then for 10 percent you can clearly see a loop therefore it gives a very convincing signature that it is indeed a doped situation but actually what we see here is it is not just manganese doping it is something more than that you seem to end up with different oxidation states of manganese so a rapid combustion route clearly gives evidence for something other than manganese 2 plus which is present in the ZnO lattice. Now let us go to another soft route this is not a rapid route like thin film or the microwave combustion route this is a kinetically controlled one which I have already discussed in the first module again on microwave polyul synthesis. Now look at the X-ray pattern here again it is very clear that you have a clean phase there is nothing there but you can see it is bit noisy there are some small peaks which are emerging here when you do this plot in log intensity. So in log intensity plot you see there are some disturbing or mild impurity features propping up for 4 percent and 10 percent peak but seemingly the undoped ones are very clear. So with this in view we can try to see what is exactly happening as I told you earlier that you can do this using microwave polyul which is the chamber that is used here and if you take the ESR spectra of this manganese oxide powders you can see that there are interesting features coming up for 2 percent and 4 percent doped manganese oxide you clearly see a 6 line spectra if you amplify this you clearly see that this is a 6 line spectra and this is another 6 line spectra for your manganese core but the moment you go to higher percentage you see a very broad peak what does this mean in a soft route soft chemical route which is kinetically controlled not thermodynamically controlled you can essentially dope manganese in a better way that is a definite way that you can dope manganese into zinc oxide it is not impossible and that is seen from a 6 line spectra. Now having said that look at the PL, PL seems to be also again a defect induced PL emission so with this in background if we look at the magnetic property you see again there is a clear evidence for substitution for zinc oxide there is a clear loop coming whereas the loops are showing a hysteresis but then it is not as clear like the way the PED films are made or the microwave combustion route prepared samples. So, if you look at the magnetic property you can clearly say that even though I have a clear evidence for manganese substitution in zinc oxide but the magnetic property is not convincing because when there is manganese-manganese interaction and a broad zinc oxide spectra the magnetic feature is nearly come in comparison but when you have a 6 line spectra in all those cases you still see a diamagnetic contribution more pronounced therefore we need to be very cautious to say whether manganese is clearly doped or not if it is clearly doped we do not see a strong magnetic feature as we have seen in other cases but when there is a manganese-manganese interaction then you again see something as what is reported. Now if you look at the SEM features also you can clearly see that 2 percent and 4 percent manganese are clearly substituted in zinc oxide for example you take a macroscopic view of this 50 micron region you can take this is another view graph of 50 micron region if you try to blow up any sort of regions you can see these are all nano parts of zinc oxide you do not see any secondary phase whether in backscattered or secondary electron image you do not see any secondary phase in this compound so we can clearly say that manganese is doped whereas if you take 4 percent you see almost the same feature and you do not seem to see any secondary phase that is prominently seen so you can have a variety of view graphs whether now go to 10 percent doped one you can see there are regions which are significantly different from these regions that means when you go to higher percentage of manganese there can be chances for two different things to happen you know you can have both manganese doped one as well as manganese segregated one and this is what we see from the x-ray also that some impurity peaks keep propping up about 10 percent so what do we take lesson from here of all the techniques that we have adopted to prepare this manganese doped zinc oxide the most favored one where we can be clearly sure that 2 percent or 4 percent is exactly getting substituted we can go for the polyol route polyol route is the best for low doping concentration but what happens the magnetic property is not convincing whereas in the other cases where we have seen clear evidence for other phases of manganese you get very arresting magnetic signature for example in the case of microwave combustion route we get signature for balances other than m n 2 plus and in solid state synthesis I have shown you that the magnetic property is very convincing but then we see this as a case where m n o phase other phases are segregating and same way in p d films you can clearly dope manganese but the mechanism of manganese doping does not seem to be clear although the magnetic features are same so I have shown you one is a milder approach one is a brute force approach one is a thin film approach one is the conventional solid state approach we need to be extremely careful because each of this preparatory features seemingly throws a variety of magnetic information so this is a very candid study by which we can try to incorporate as many characterization techniques as possible to understand the physical properties therefore it is important for every chemist or physicists or anyone in this field who is trying to look at the physical property to look more carefully into the structural property so structure property correlation is very important and we will see in the next slides other case studies where we can use multi characterization techniques to elicited the structure and correlate with the properties.