 So, this is a typical design of a reflector meter that is there at ICS-RL. I just show you one of them which we have used, this is called a crisp reflector, no not crisp. Yes, this is a crisp reflector meter, we use pole rays. So, basically you dip the beam onto the sample and then the detector catches and if it is a polychromatic beam, even if it is an end-on detector that means the detector cylinder is looking at the beam, you can get large Q information from the time of flight because this is a polychromatic beam and the time of flight dictates what is the Q value. So, the angle remains same for lambda 1 and lambda 2, so because Q is 4 pi by lambda sin theta, for the same angle based on the time of flight you have different Q values. So, lambda 1 give you Q1 and Q2 will be given by 4 pi by lambda 2 dot dot dot. So, you can get number of Q values for the same setting. So, this is the crisp reflector meter as you can see here most important generally all this magnetic crisp reflector meter, there will be a large cryostat which is still over here and the detector is here and the beam comes from the spallation source from this direction, this is just a photograph the schematic I showed you. This is NG1 reflector meter NISD, so again you can see as I told you that we have polarizers super mirrors and polarizers can be used for analyzing the reflectivity reflected beam for up and down neutrons. So, it comes from the guide there is a focusing geometry because you focus in vertical direction but to obtain the reflectivity pattern in horizontal direction, so this focusing in the vertical direction helps us to get higher intensity without sacrificing the resolution in the horizontal plane and there is a neutron spin flipper and the neutron spin flipper is nothing but DC flipper is a structure like this on which you wind solenoids like this. So, that is if this is the neutron spin polarization and this is the direction of the solenoid field and the thickness is given by the thickness of the solenoid on which you have wound the wires. So, this is the wires you have wound for the solenoid, the neutron tends to precis around this field, so neutron tends to precis around this field and if you choose the thickness appropriate given the wavelength of the neutron because depending on the wavelength the velocity changes, velocity changes at time it spins in the magnetic field and that tells you by what angle the neutron will be precising in the field and right choice of field and the thickness of the DC flipper from up beam you can flip the neutron to down beam. So, this is a DC flipper which we use, so but you can also have other kind of spin flippers like radio frequency spin flippers, so this is a neutron spin flipper. So, there is a sample and there is a polarization analyzer also which is an iron silicon super mirror and then you have got a detector. So, the general geometry is very similar to what we have in all the sources. The other point I would like to mention that in this case it is coupled to a liquid to hydrogen cold source, reason being as I discussed earlier also that the intensity versus lambda if this is a maxolene in the normal room temperature beam in a cold source the spectrum shifts to lower energy or longer lambda and reflectometry as well as small angle instruments they use lambda of longer wavelength because we are working in the region of smaller cube low cube and that is why here the NG1 reflectometer is coupled with the liquid hydrogen cold source from where the cold neutron beam comes, so there you get better intensity and then you have got an instrument in which we have got vertically focusing pyrolytic graphite monochromator, polarizer, then you have the sample, then you have a spin flipper and then again you have iron silicon super mirror polarization analysis. So, without flipping and with flipping you can get the intensity of two beams, so now in case of another analyzer crystal your measuring intensity or reflected intensity of up neutron scattered as up neutron or up neutrons scattered as down and down neutrons scattered as down and down neutrons scattered as up, so you measure four intensities instead of now it is clear that when we don't do the analysis we have measurement of R plus that means reflectivity of the up neutrons and R minus reflectivity of the down neutrons we have these two and when you measure R plus and R minus without any analysis of the reflected polarization then what we obtain is magnetic moment density, when we do analysis of the reflected beam we find out four intensities this is non-spin flip, non-spin flip, spin flip spin flip then we get magnetic structure, it will be clearer when later I discuss this issue with a with an example, so this is the schematic and this is the reflectimeter similar to Dhruva as I told you earlier that this is a guide on which the beam passes the beam is reflected into this into this polarized this reflectometer using silicon pyrolytic graph or not silicon pyrolytic graphite monochromators and this is the magrav reflectometer SNS-O-PRI very similar structure you can see similar to what we showed earlier only heavier parts and the displacement part, so with this I will now switch on to examples to start with I will give an example in which XRR and PNR together was used to understand the interface alloying in a nickel aluminium multi-layer, so to bring you to the subject proper here we deposited a multi-layer sample of periodic bilayers of nickel and aluminium now when we anneal this multi-layer you will find alloy layers forming at the interface and our intention was composition composition of interface alloy and its magnetic properties and XRR PNR they are the close cousins were used together I will explain it shortly why they were used together the nickel and aluminium they form a number of alloys and in which the nickel aluminium ratio keeps changing for example a low-temperature alloy is Al3Ni then you have Al3Ni2 then we have AlNi you also AlNi3 especially this alloy is a very important alloy because it compiles the hardness of nickel with the ductility ductility of aluminium and this is used heavily in aeronautical industry so our interest was in ultra thin films in ultra thin films how the alloy forms as a function of annealing at the interfaces and can we determine its composition using XRR PNR together why together that I will come to quickly because if we do XRR we get electron scattering length density and that is nothing but in a unit volume we know we have talked about scattering length density with respect to small angle neutron scattering sands as well as reflectometry given by number of aluminium then R0 Z of aluminium which is the Z value of aluminium and this plus number of nickel and Z value of nickel and R0 is the classical electron radius 2.818 femtometer so this equation gives me what is the chemical density that is we have for the given sample and this we obtain from reflectometry experiment similarly for neutrons it is the number of aluminium but now it is B coherent of aluminium and number of nickel and B coherent of nickel now let's see this we get from a PNR experiment as nuclear scattering density and this we get from an XRR experiment as electron scattering density but in this actually everything is known classical electron radius Z value of aluminium Z value of nickel classical electron radius B coherent of nickel B coherent of everything is known except these two unknowns and I can consider that XRR and PNR as two independent equations two independent experiments giving two independent equations which we should be able to solve algebraically solve once you obtain the density profile in these samples from these two equations that was the main aim and let me just give you the results here so this is the XRR result for the nickel aluminium sample and this is the PNR result this was done in NG7 at the experiments at NISD the next error was on a tabletop machine and we alloy formed alloy by annealing for one hours to eight hours at a low temperature at 160 degree centigrade and this is how the polarized neutral reflector material vary with respect to annealing and this is how the XRR reflectivity pattern changes this is after I have just product two after eight hours of annealing now we use parrots formalism for both of these but not together separately independently and we fitted the nuclear scattering length density from the PNR data and from the electron scattering length density from the XRR data so these two these two values I obtained from the experiment and then I attempted to find out what is the aluminium to nickel ratio and this is what we obtained nickel to sorry number of aluminium to number of nickel ratio atomic ratios 2.91 that means it indicates that at the interface at this low temperature annealing we obtained the AL3-NI alloy and it is also commensurate with the fact that low temperature annealing this is the first alloy that forms for nickel and aluminium so this is an interesting result in which not the magnetic properties but we obtained the physical density of an alloy layer which is typically around 1 to 2 nanometer or 10 to 20 angstrom thick in a nickel aluminium multi-layer and the nature of the alloy so you can see that the excellent resolution we could obtain using this non-destructive reflectometry technique for the alloy formation at the interfaces of nickel and aluminium this is one example I showed where we can use XRR and PNR together for our samples usually whenever we do PNR XRR comes as a preamble that means usually whenever we make a sample we carry out the XRR experiments to obtain its density thickness roughness etc with XRR because you can see the XRR data has much higher intensity and we can get better fitted values and then we go ahead and carry out the PNR of course this will not be true for all the samples but for most samples this route is chosen so with this I stop today I will carry on further example I will provide more examples and more interesting results just to show you the kind of experiment that one can do using PNR or polarized neutral reflectometry to understand the structure of thin films