 So we have been discussing about different advanced surface characterization techniques for the last 4 or 5 and more 7 lectures the last technique which I am going to discuss in detail is known as secondary ion mass spectroscopy. In the literature it is always written as sims being the acronym for secondary ion mass spectroscopy this is very advanced technique and very few laboratories in India have access to this technique as far as I know only the laboratories access to the atomic energy like BRC or IGC they have access to these facilities but still for the understanding of different students we need to discuss this technique in detail the literature is very well known in this topics the most important book on which literatures available I have listed at the bottom first one is by JC Vickerman second one is again encyclopedia of material characterization edited by bundle and events and Wilson these two books are easily available in different libraries so you can have access the outline of this presentation is as follows first I am going to discuss about historical background of sims but before I discuss about exclusive background of sims I must talk about the mass spectroscopy per se there I am going to talk about the difference between MS and the sims and most notably the what are these two techniques are so that you can get an feeling of mass spectroscopy and secondary ion mass spectroscopy obviously these two techniques are related followed by I will discuss the working principle of both the techniques and then I am going to talk about different measurements which can be done by sims also lastly the advantage disadvantage and some amount of instrumentation as you know it all started in about 100 10 years back by Sir JJ Thompson who first basically build the prototype of mass spectroscopy to measure the m by z of any electron mass by species charge and as you know he was awarded in old prize in 1906 for his discovery and for many other things which he has made but basically the first concept of mass spectroscopy came into practice by a gentleman known Francis Aston who was working in Cambridge in England and he actually first principle or concept of mass spectroscopy was put forward into practice by him and he was also awarded in old prize in year 1922 then it saw a huge effort to make the mass spectroscopy popular different kinds of mass spectroscopic techniques came into picture but the real problem in dealing with mass spectroscopy was the vacuum systems in early 9 20th century basically 1910 to 1930 and 1935 the vacuum technology was not so well known. Although the technique was not as not progress much only 1940 wave 8 to 4052 in the post second world war era the important time of flight mass analyzer came into picture and change the scenario it was followed by a major discovery again by Paul W. Paul which led to quadruple iron filters and this quadruple iron filters actually has allowed us to measure this this you know pcs of different mass by Z value M by Z values and because of this very famous discovery in 1955 W. Paul was awarded in old prize in 1989 actually he also invents iron trap in 1983 for informations in after that in 1968 it saw the development of tandem mass spectrometers and secondary arms spectroscopy came little later at about 1980s when the secondary arms production possible by different primary and sources to give you better idea of sims the most important problem in developing sims was the pumping technology vacuum technology as I told already and that is actually hindered the growth of the sims in fact only 1940s actually in 1948 or so the first exporter by experiments in sims was done at University of Vienna, Austria in 1960s two sims experiment was developed but not so good one was an American project for analyzing moon rocks other was of the University of Paris this first experiments were based on a magnetic double focusing selector field mass spectroscopy and used Argan as a primary ion beam obviously these things are not known to you I am going to discuss in detail and then this was followed by recent development and focusing this noble primary ion sources species is like C60 even ionized glasses of gold and bismuth and this followed lot of instrumentation and the comparison of the technique and now it is fully automated and comes at a cost of about few tens of clothes of the piece well what is actually mass spectroscopy that is you must know fast mass spectrometry or mass spectroscopy is basically an analytical technique as any spectroscopic technique but it measures a different thing it measures mass to charge ratio of any charge particle you must remember this any mass spectroscopy does not measure mass it measures mass to the charge ratio of any charge pieces so therefore in any sample whatever you material you think of there is no charge species the samples will be neutral you need to create the charge pieces first and then by using certain technique you can measure this mass to charge ratio this is a characteristics of any charge whether it is a single ion single atom ion charge or it is a multiple ion charge multiple pieces charge does not matter but this is a very characteristic things it have used in both quantitative and qualitative analysis to determine the composition of the structure of specific compounds not only that it allows us to be used as analytical method to measure the molecular and atomic plates of the sample so it has a versatility as you can see it gives a host of informations and I have listed only few of them in the slide first and foremost it allows us to determine the chemical and structural information of any molecule any molecule or any ionic pieces you see it gives us an understanding of chemical and structural nature of that molecule then it allows us to identify the unknown compounds start with it also allows us to quantify the known compounds we can actually determine the relative abundance of isotopes and measure that exact masses remember it is possible to measure the exact mass of the isotope those masses you see in the books reported are basically measured using sims and then it also allows us to measure the molecular mass of any sample correct now if you look at the uses it is used in wide spectrum irrespective of different branches of science engineering most important one it is used in geological problems basically in oil consumption or oil production units like you know in oil production unit there are different kinds of chemical pieces available organic and it allows us to detect them then comes a pharmaceutical industry that is pharmacokinetics dark discovery drug mechanism next one which uses this technique extensively space application like composition of the plasmas and the solar winds by the astrophysicist obviously it can be used for environmental technique like water quality food contamination biotechnology in fact it can be used in high vacuum system smug spectrometers to be used to measure even the serial gases present in a particular system if you look at this series I am not mentioned about materials science so obviously material science is involved in all these things we can use this particular spectroscopic experiment technique for analyzing our day-to-day materials or the materials which you are actually preparing in the labs in detail manner well so basically after knowing this mass spectroscopy and the advantage and that these things what actually a mass spectrometer needs to have what are the basic things it must have well basically it must obviously have a sample because that is what we are analyzing and then we have to have a you know source of ions so sample is ionized and we create different sources of ions this is what is done by these techniques which I am going to discuss and then this ions are actually analyzed based on you know mass to charge ratio by using either quadruples or time of flight measurements and this then they are detected either a photographic plate or electron multiplier or Faraday Cup a different kinds of detectors available and the whole system whole thing is kept this whole thing is has to be evacuated because the ions needs to move forward from the source to the detector so their movements would not be hindered by any kind of residual molecule gaseous molecule present in the system so vacuum systems to be of the order of you know create a vacuum of their tend to minus 900-10 Thor inside the chamber and these all actually leads to the cost of the instrument so this is the basically three models of any small spectroscopy in since both the analyzer detector remains same only thing which gets changed is the source we do create secondary ions using the primary ions okay but in a mass spectroscopy you use primary ions to analyze these masses so in a nutshell if I have to show you in a very chart what you need is to create ions and this can be done by ionizations you can do by electrospray you can do Maldi I will tell you you can do even you know other ionization techniques like you can use a primary source of ion as pattern and create ions and then after you created the answer to collect ions you collect the ions and then you separate them in a different mass to charge ratio that is what is done by mass analyzer it can be Maldi time of flight or it can be quadruple time of flight it can be quadruple time of flight only or you can be triple quadruple also and there are many others actually but these are the main ones after that we will detect the masses and that is done by mass spectrum analysis also you need to have a database like XID fraction has database and many others so this is the main thing of a mass spectroscopy only thing as I said was going to change in sims is basically this part these two parts other two parts will remain same so actually you create a ion source you can have a gas ion mass analyze and detector this is I have told so in a not in a basically pictorial things I can say there is an ionizer and there is a mass analyzer there is a detector that is how the ions actually move through this how do you analyze actually that is what we must know there are different ways of ionizing first one is known as first atom bombardment or fab if this is nothing but impact of five velocity atoms on a sample dissolves in liquid matrix if you have a high velocity atoms like argon or oxygen or cesium and these atoms actually are allowed to fall on a sample which is kept inside liquid matrix it can create ions of the atoms in a sample second one is secondary ion mass spectroscopics and this is the topics of today discussion it is nothing but impact of high velocity ions on a thin film of a sample of a metal sub on a metal substrate it can be also dissolved in liquid matrix so by this way these fast iron from bombardment and secondary ion mass specs actually the preparation of ions are almost similar what you need to have is impact of the high velocity ions in case of sims and in case of fast fab you need to have impact high velocity atoms then you can always have a plasma desorption is a nothing but impact of nuclear fission fragments nuclear fission fragments are always you know like alpha particle gamma particle or beta particles this fission fragments can lead to plasma desorption you can also have a technique known as so we have discussed this this this we can also have a technique known as metric assisted laser desorption and ionization which is known as Maldi that is what I have been I talked in the last slide so it does actually create ions by impact of high energy photons on a sample embedded in a solid organic matrix so you create a photon is nothing but you know h nu I would laser has lot of photon or quantum and this is basically allowed to fall at a high velocity on a sample which is embedded in a solid organic matrix and that is how you can ionize ions then one can do field desorption on electro spray field desorption is nothing but imposition of high electrical field gradient on a sample deposition special solid substrate those of you have some idea about atom probe in atom probe we do the same thing actually we have create a large impose a high electrical field between the sample and and the electrode and because of the creation of the high electric field the ions on the sample is just dislodged or the atom sample and dislodged and created comes as a ion. Electro spray is basically very simple much simpler than all these techniques it is nothing but a formation of charged liquid droplets from which ions are desolvated or dissolved you have a charged liquid doublet you could create that liquid droplets by using electrical field or just spray using electrical field and then you can dissolve it or dissolve so these are the bit different techniques of ionizations which is done so you see because Sims comes one of the techniques of ionizations not only seems there are many other techniques so that is why I want to discuss mass spectroscopy in togetherness now how do you then apricating the ions you have to analyze the masses how do you analyze the masses there are host of techniques available that is what the discovery is happened first and very simple one is single focusing magnetic deflection which I will tell you second one is double focusing magnetic analyzer third one which is widely used is quadruple mass analyzer then you have mass analyzer and the last one which is very popular one is known as time of flight mass analyzer let us look at them this particular is slide is on sickle focus mass spectrometer it is very simple technique this is this pictures schematic is taken from this one there is a presentation available on the website what is done here let me first explain the theory this is the most common type separator at any given accelerating voltage V suppose all the singly charged ions are provided some kinetic energy and that is given by is this electronic charge e multiplied by the accelerating voltage V must be equal to kinetic energy of the charge species that is half MV square now if you allow this charge accelerated species to pass through a magnetic field which is shown here this is the magnet you see the charge ions will experience a magnetic force and this magnetic force is given by H e V where H is the magnetic field strength so therefore this is balance this magnetic force is balance by the centrifugal force obviously so that means we can write down H e V must be equal to centrifugal force that is MV square by R so you get M by E is equal to H square R square by 2 V straight forward and this is what is the classical equation which allows us to separate different PCs with different values of M by E ratio as you can see depending on the different M by ratio if you keep H and V constant R will change so therefore lighter ones will come at us as a smaller and here ones come as a very larger so that is how actually you can differentiate between different a PCs charge PCs with different M by E ratios is very simple actually in fact the first to charge then accelerate and then accelerate is charged are passed to the magnetic field and it separates out that is how it is done so we are focusing with a single magnets that is why it is called a single focus mass spectrometer remember this is actually how we can actually separate the ions very easily and subsequently what all techniques separate techniques you will see there actually modification of this one so it very high resolution its instrument keeps actually gives you quite substantially high resolutions in the sense of ppm level detection possible in this type of instrument to I am being from independent sources passes side by side to a common mass analyzer and detected by separate collectors this is to compare sample with a standard or a through different ionic condition resolving power is order of 3000 30,000 sorry such you will be capability enables high molecular weight fragments which differ only by one mass unit that means if there are two PCs with a mass unit difference of 3000 30,000 and 29,999 still we can detect by this that is what the resolution of this instrument next one which is also widely used quite sometime is known as double focus mass spectrometer what is double pass mass spectrometer well single focus mass spectrometer you have seen here we are using two focusing magnets so you have a you can see this is the lens and then basically ion sources come through this this is the ion source and then it passes through a lens there is a source slit and then there is magnetic field it just basically magnetic sector it just separate this ions out or filters the masses and then it passes through this single mass whichever is whichever is basically you know passing through this radius which is matching with the slit we will pass through a to go to the detector so if you change the slit little bit or if you change the magnetic moment as H value you can allow either this one or this one or this one to pass through the slit and be detected that is the advantage as compared to the first technique single focus mass spectrometer it has very much better resolution than the single focus mass spectrometer that is mainly because there is a extra element like this possible have that is why it is called a double focus because first you are focusing us a magnetic sector then you are focusing with the electrostatic sector and that is how actually you can detect very precisely each and every atom a charge species this is again taken from one of the websites which is available on the Internet next one and probably one of the best one is quadruple mass analyzer the reason I am saying this is the best one because it allows us even better measurement than single focus or double focus magnetic spectrometer well it makes uses use of a combination of direct current and their frequency electric field applied to four parallel rods remember it is applied to four parallel rods to separate ions according to their mass by charge ratio. So we are using direct current as well as their frequency electric field and using four parallel rods these are all that is why it is called quadruple to separate the ions what is done here it is taken from Wickerman's book so you have a sample you create ions by different analysis techniques and then you have one two these are actually filters okay post or pre-filters quadruple they are the four important ones and then it passes through this you know region where this quadruple actually separates the ions depending its mass to charge ratio and detected you can see here this is DC voltage is the RA voltage you can apply and repeat these are the four probes of different dimensions now if I plot the movement of the ions you can see here this is the two parameters a and q q is a charge and a is basically the distance between the quadruples so if you can see the plots you see here there are different regions this is u by v constant low resolution u by v constant high resolution okay u by v u and v this is u – ? u by v constant by constant solutions and this what is the region of stability so that means we can change u and v in such a way u is basically DC voltage and if he is the RA voltage magnitude so by playing around these two we can actually get into this region of stability and that is the region one which you need to work obviously if you want to work with u by v constant high resolution you can do that or you can want to work with constant listen you can do that depending on the systems on which you are working on so as you see here this gives us many many possibilities of changing the conditions and do the measurements third fourth technique which is important is iron trap mass spectrometer as the names are this is basically traps as you know Paul actually got no prize because of andra mass the technique availability I have told you that in 1983 and beam currents are normally of the order of 10 to – 15 to – 19 amperes are very small that because the number of ions present in the source beam is very small this thing is generally employed iron collectors and they are actually photographic plates or electron multiplier select what is done here you are basically filament and which actually creates ions a charged species and then we have this kind of ring electrodes which basically collects a traps this ions and after that we can actually use this mass spectroscopy as I use this kind of you know single focus or more double focus or quadruple and then we can actually analyze these ions by mass by charge issue and finally we can detect them using that is why we did so basically preparation wise is different distinctly difference from the other three techniques this is normally not used much except for few specific applications this one is also taken from this website well the last technique which I am talking about is what is known as time of flights mass spectrometer a schematic source the technique actually what is here you look at it very carefully you have a iron gun which creates our analysis the analysis analysis the pieces and then there is a pulsing action it can pulse actually I am going can obviously pulse like a laser beam and then you can focus this it comes also it also allows the iron gun also allows to raster like ACM the ions and then once it falls on the target it creates ions from a surface and then it passes through this extractor which extract the ions which are coming from this from because of this ionization due to iron gun that means we are creating a secondary ions actually and then basically iron mills which is nothing but quadrupole detector or may be a time of flight detector it basically separates the iron and detector detects and gives you the spectrum correct so many cases as you create more ions so you have to have a electron flight gun otherwise charge balance will not be there in a sample surface in a more sophisticated design the time of flight analyzers corrects for the mall differences in initial energy an angle in what to achieve high mass solutions it is a combination of linear dips pass electronic sectors or the iron mirrors which are used and results are actually comes with the mass resolutions of the above 10,000 can be achieved advantage of you of this technique about the quadrupole and the magnetic sector type is that extremely high transmission parallel detection of all masses and unlimited mass range is possible yes because it does not use because what we are doing is basically time of flight measurements how much time a mass takes to fly or move in a particular distance and depending on that we can difference it among different PCs we are not using the exactly my z ratio. So let us let me just give the mathematics of it pulses of secondary ions are accelerated as you know iron grant clear secondary ions and pulses of secondary ions are accelerated to give to a given potential which is of the order of certain kilo electron both you to it such that all the iron process the same kinetic energies then these ions are allowed to dip through a field P space remember after these ions are accelerated they are allowed to pass through a dip through a field P space we are not applying any magnetic electric static steel before each single detector and when it passes to because they are the same kinetic energy m by m v square but velocity this will be different so because of this masses are different velocity this will be different because of this the time it takes to move a length will be given by L m by 2 z v half L is basically the length path length flight path length m is the mass jd is the jd is the at the ionic charge and v is the accelerating voltage. So as you can see depending on m by z values before even a learn we are constant T will be different and by knowing the different times we can actually separate these ions very easily this is actually widely used now what the whole worldwide technique and it has many advantages if I go back to the previous slide that is what is done in the ion mirror between the extractor and ion beer what is done is that this secondary ions having a same kind of energy travels or dips to a path of certain lengths length may be this much and get separated out and then we can plot I will show you the plots also later we can plot and get idea of that so this is I am going to discuss in detail when I come to seems so but to give you some idea in a static seeming experiments it actually analyzes the original non-modified surface compositions uses time of flight measurements and it basically is a quattus quasi-tonstractive surface analysis because it is uses very low ion dose well as I have talked about lot of different magnetic focus like single mirror magnetic focus or double magnetic focus or even quadrupole let me just give you some idea about what a radio of curvature means how does the ions actually get curved radius of curvature all of any ions of distinct M by Z ratio traveling to a perpendicular magnetic field B after it has been accelerated by certain potential is nothing but 1 by B within back a 2 MV by Z to the power half so if B is constant B is constant it depends on the M by Z so the travel ions actually traveling as I go back I can so yeah ions which are traveling at different radius that will depend on M by V so that is what actually used in this technique now after giving a huge introduction lot of things I have talked about it about the mass spectroscopy let me just get into details of the secondary ion mass spectroscopy although there are many things which are similar but distinct things the things which are distinct in seems as compared to this MS or mass spectroscopy I is to be known to you very clearly seems per se is a surface analysis technique to remember this mass could copy may not be surface analysis technique sims is basically a specifically surface analysis technique it is used to characterize surface and sub surface regions of any material thus actually what makes seems very popular even if you have a thin film on the surface of any material you can analyze it to the position of sims it can give you PPM level position it effectively employs this mass spectrometry what I discussed of ionized particles which are emitted when a solid surface is bombarded by energetic particles the schematic diagram on the right side up to you is showing this picture we have a incident ion source it can be ion which I am going to discuss any ion in fact this is what is our one of the things which I discussed incident ions which can be either cesium ion or it can be oxygen ion or it can be other ions but mostly cesium and oxygen ions are used which are actually accelerated with a certain kinetic energies and then they are allowed to fall on the surface of a sample or a target and once it comes it creates a cascade of events in which emitted secondary ions from the samples are emitted so primary particles are mostly ions or either it can be protons also it can be neutral pieces also it can be charged pieces also but they are actually primary ions and they invade are there actually the sample surface and creates the ions nice if I have to tell you about that you know in a secondary I have sims the primary ion sources are actually created by instrument called duo plasmon plasmaton is known as duo plasmaton plasmaton it is the one which can create different ions and it can actually uses you can create ions like you know different gases oxygen is basically commonly used in the in the sims oxygen can comes as a O- or O2 plus or it can comes even O2- we are surprised what are these O- is basically when oxygen all the oxygens are tripped O2 plus is that one oxygen is tripped O2- is one extra idea oxy electron is added so that is why so that means we can have positive chart ion negative with charge ion and also heavier charge ion O2- and O- so we can create all kinds of chart pieces and then these primary ions are allowed to fall on the sample surface to create this so you know but this O2- is the most abundant pieces used while positive ions are also used if you have a insulating material then we have to use O- ion because otherwise they will be charged build up on the surface and the second type of sims also uses something known as cesium ion it is to be enhanced actually yield of this electro negative elements like carbon oxygen or even sulphur because they are very low atomic mass elements we use cesion Gaons actually operate in the positive modes to create the ces plus ions generally ces beams are smaller and then generated by do plus moton do plus moton creates oxygen ion basically and you can create others but mostly and so but this is Gaons are basically much finer and it can spatter basically this is nothing but sputtering process you are coming in primary ions and sputtering you can sputter actually more material effectively because of their greater mass and it is normally used to use to extensively measure the different isotopes and when you use insulating material you can always use ces plus beams as you know the most of these things are surface and as in process so therefore it leads to hitting of the samples and sometimes it can create other problems also so let me just give little bit give idea about what is the collision what does the collision happens this is nothing but a collision cascade sample is prepared in a vacuum and when you put a primary ions of this much energy 3 to 20 kilo volts it causes a collision cascade among the surface atoms and between 1 and 10 actually ions are created this is always sputtering but sputtering by using primary ions sputter you will depends on nature of the sample also now what is collision cascade if I incident primary beam coming at an angle theta with respect to surface normal this can create large you can see number of secondary ions so one can create other other can create another one and then goes on that is what is called cascade calculation cascade and this leads to cascade mixing in the sample so initial depths will be transient one and then finally when the cascade is stabilized this kind of origin of the surface ions is called steady state steps so therefore measurements from the steady state depths are actually much better than the transient one so we have discussed about collision cascade in a in an interaction of primary ions with a for the sample surface to give you a better idea of that I am just showing you the schematic picture this one is showing you the atoms and the primary and the secondary ions as you see here the different primary different atoms in the sample surface is shown here like this sorry and these are known as target atoms these are known as target atoms these ones which I marked and then you have a surface atoms which are marked in blue and you will always have a whole air which contains contaminations so primary ions which are coming at a very high energy they come and hits a positive primary and comes hit this atom and this atom is rejected or moved this atom has many choices it can either go and hit this or hit this or this one and subsequently those atoms which are hit can also hit the other atoms and that's how this cascade is created and finally it hits the surface atoms and the secondary ions comes into picture and these are all secondary ions as shown there so of this ejected atom some are ionized usually less than 10% and these are all called secondary ions the matrix of a sample must be known to accurately determine the elemental concentrations as ionization yields can vary very much as much as order of three orders matching between nearly identical atomic sputtering yields secondary ions can then be analyzed using mass spectroscopy which I have discussed now there are many primary ions was in sims the most widely used as I discussed is oxygen and the cesium but one can use also electron as an ion source you can have high current density of electrons like to manage basically argon or genome you can always use plasma plasma is nothing but hyper you know this a ionic charge gas it is a high pressure gas high electron density of plasma is formed normally is formed in do plasma tone which I discussed you can always have a air frequency for oxygen argon you can also have something known as surface ionization ion emissions thermally simulated by warming an absorbed layer of cesium on a high working metal like iridium you can do that because the thermal simulation can always lead to surface ionization easiest part the best one is the speed emission field ionization you can strip up electrons from the source atoms very neatly by using a high local electric field for that you need a very fine tip and this is what done in atom probe or you can have a liquid metal typically gallium on a tungsten tip so these all can be any of these things can be used other than even in a also you can use cesium and oxygen as I said now what is basically this partnering process all this is a collision cascade but it is basically a sputtering the process of sputtering is described by the principle of s classical mechanics by binary collisions of primary ions with a single target atoms depending on the energy range of the primary particles of primary ions elastic and elastic elastic squattering both are possible the dominant interactions in the clear electron ball range are elastic collisions they can be described by a parameter which is well known as a nucleus stopping power in the literature and this is defined as the energy loss of the primary particles per path length see if an energy primary particles are a losing energy because of the sputtering process we can always take d by dx as a parameter to determine the interaction between the primary ions and secondary secondary ions and this is what is known as a nucleus stopping power the number of inlastic collision increases with the rising energy as is usual inlastic scattering normally dominates if you have energies in a million electron volts so that is why very high energy once actually leads to lot of elastic scattering which are not good in those cases corresponding value to describe the interaction is known as electronic stopping power and this is known as d by dx e nucleus stopping power actually contributes to the collision cascade these are the two effective ways of basically terming this sputtering process now it is also important to know the primary ion sputter yield where how many primary ions are actually when the sputtering how many secondary ions are created per unit primary ion this is taken from Vickerman's book you know this is a plot of yield versus energy as you see yields varies from 10-3 to 10-2 that means it varies from very low value to 1000 and these are the different data from helium genome argon or some theoretical calculation or argon theory calculation you see here sputtering will actually varies from 10-2 to 101 that is 10 it does not increases much yield means basically number of secondary ion created per primary ions so that means when it is 10 one primary ion creates 10 secondary ions when it is in the minus 2 that means to create one secondary ion you need 100 primary ions so as you see as the energy increases sputtering yield increases so if you normally we can use from 10 to 150 to 100 electron volts as the energy sometime people use 3 to 10 also this is also not bad you can see in this window also you have something like 5 to 6 secondary ions per unit per primary ions can be created well obviously as I said O2 plus O minus O2 minus ions are used if you use that we can actually create secondary ions if we use this as a primary ion so positive secondary and yields when you have O2 plus bombardment is plotted here as a function of atomic number if you see for elements like nitrogen or sulphur tellurium gold platinum very low log to the power actually 3 but if you go to this one magnesium calcium palladium manganese iron these sets it is very high plus is of the order into power 4 5 so therefore the amount of yield or amount of the secondary ions created when you have O2 plus bombardment is good for this kind of elements not for other ones if you see us plus bombardment what happens this is M minus plus M plus ions bus atomic number as you see this is taken from this paper in analytical chemistry from American come society if you see here 0 yield 0 log 0 is basically means one so is above this these are good so therefore cast called carbon oxygen sulphur silicon phosphorus arsenic celerium germanium to some extent silver antimony tellurium iridium platinum and gold cesium is good but for these models like iron aluminium magnesium zirconium tungsten probably oxygen 2 plus iron is better that is what is shown here so that is why CS and the O2 plus they can complement each other as a primary beam to create good yield of the secondary ions and this is what is I am showing in a predictable secondary iron yields when a primary beams like that the factor that between the secondary iron is in efficiency seems our oxygen bombardment increases with the yield of positive ions cesium bombardment yield of negative ions as you see the increases the increases can range after four order magnitudes the yellow ones basically are O2 positive secondary ions and green ones are basically CS positive these times need to send it to second nation is you see at this one this lithium sodium and also these set of atoms or this set of actually elements are good for oxygen plus positive ions to create secondary iron yields on the other and there are also good on the other hand there are set of atoms like this even carbon nitrogen all this group here oxygen fluorine chlorine silicon phosphorus all they are actually good for I mean it will be large amount of secondary yields will possible when you CS plus primary ions well so that means if I consider positive and negative ion yield processes then I need to tell you that oxygen enhancement process occurs as a result of metal oxygen bonds in an oxygen region so therefore those are metals which are which will form very good metal oxygen bonds they only they will form better secondary and yields when these bonds break in a ion emission process oxygen becomes negatively charged because of its high electron affinity which favors electron capture and its high ionization potential in units the positive charging so metal is left with the positive charge then so oxygen means parting increases the concentration of the oxygen in the surface layer that is possible because oxygen actually first bonds with metal and forms bond then it is bear bond breaks oxygen and remains they are metal and gets comes out enhancement in us negative ion yield normally produced by the cesium bombardment and this is can be explained by what function that are reduced that are reduced by implant implantation of cesium into the sample surface more secondary electrons are excited of the sample potential barrier and this needs to increase availability of electrons leading to increase negative ion formation so as you clearly understood now that oxygen bombardment will lead to positive ion creation cesium bombardment lead to negative ion creation so therefore the metals in which positive ion creations are easier all metals as the positive ion creation is here but oxygen absorption is here it is better use oxygen enhancement and other things metal oids are even you know some other metals specific metal like copper or things here I have shown you zinc sorry copper silver gold on the heavy metals like Bismuth metal oil like Bismuth antimony tin tell you them you can use cesium obviously secondary ion yields depends on elements type of elements you are dealing with secondary ions efficiency is very is a very well defined things it is nothing but a fraction of this pattern that become ionized you have large number of sputter atoms only 10 or 15% atoms becomes ionized so that fraction is known as secondary ion yield as you know iron yield vary over orders of magnitude for different various elements that means there is an elemental effect the most obvious influence is on the iron yields are basically ionization potential of the positive ions otherwise if the ion potential is very high it will create it is pattern atom not an ion and also electron affinity of the negatively charged ions for example this figure actually shows a logarithmic positive ion yield as a function of ionization potential iron yields are relative to the silicon in a silicon matrix with oxygen sputtering so what you see here cesium ruthenium and sodium potassium has a very high ionization yield whereas new denium neon and helium as a very low ion yield in fact free is also in a borderline case so ionization potential is high means less secondary ion yield higher than the potential low more secondary ion yields that is obvious because then only we can create more ions by removing the electrons so that is actually how the secondary ion yields depends on not only that secondary ion has will have a kind of different energies because we can create secondary ions but whether they will be able to be traveling to a detector or not whether we will be able to collect them or not depends on their energy distributions sputtering process produce secondary ions with a range of kinetic energies and distributions are distinctly different for atomic and molecular ions molecular ions have always relative narrow tensile energy distribution because the kinetic energies in the internal vibration and rotational modes whereas atoms atomic ions have kinetic energy in transitional modes so following this figure actually showing as mono die and triatomic ions as you see relative intensities of the mono atomic ions are much larger than by and triatomic ions die and diatomic atoms that is understandable because as the number of ions are increases number of actually charge increases it is you know they will have less probability to presence so as you see this is a plot of latency bus energy so only in a particular energy window between about 2 to 8 volts you have a relatively high intensity of all the different types of ions so I have given you a lot of idea about primary ions sputtering yield of secondary ions and also the factors which control the secondary ion let me just give you some idea about how a sim spectrum look like sim spectrum can be plotted in two ways first one is on the top which is nothing but a plot between intensity versus mass to charge issue one can actually scan in B and V that is magnetic field or voltage static electric field applied to saw the to see masses across single detector as you see here this is fluid ion this is fluent to ion this is CF3 ion this is C2F3 and we can distinctly difference between this negatively charged ions depending on this mass charge issue not only that we can even quantitatively calculate from this intensity is how much of 19 mass by charge mass actually fluent ions are you represent or the double ions are present CF3 or C3F3-ions are present or not this is one way of plotting the data other way of plotting the data is to plot the different masses into multiple cups without changing the B and V in this case we are changing B and V in the top picture so if we can sweep all the masses here we are not changing B and V we are basically have different masses as a cups this is relative ion current versus magnetic field strength that is B as you see here at any constant B value you have different relative ions for 80, 80, 87, 86 atomina species so you get a cup like picture whenever you plot for the whole magnetic fields for the values of large range of magnetic fields so you can basically get a cup and this cups gives you different charge species if you plot basically seems can measure turning from lithium to uranium so if you want to show the relative intensities of the peaks for different metals this is the best one here I am showing intensity versus mass to charge ratio what you see here is basically starting of lithium to uranium the M by Z values and intensities so as you see here certain the M by Z if M by Z is you know low lower than actually certain areas like this one you have a very high intensity of your 10 to the power 6 10 to the power 5 count per second whereas here if it is M by Z is very high lead thorium, ironium even higher numbers so you can see here the yield is sorry the intensity is low you can actually see even that intensity is low for even barium-barium compounds also so that means the intensity of the of these secondary ions which is detected by detector depends also on the mass by charge ratio so the secondary ion mass spectroscopy what all things are there or really I have discussed about the ion source primary ions you need a sample primary ions comes and hit the sample create secondary ions then you have a energy analyzer or other energy grabber which the secondary ion grabber which grabs and analyze the energy and these ions are then passed to the mass spectrometer and then either which separates the ions depending on M by Z values and you detect so you can actually have a mass spectrum which has shown you you can also have a depth profile which I am going to discuss it is very important material science and you can actually also create an image of two-dimensional image actually truly speaking you can create a three-dimensional image also in a sense is so powerful technique so this is the one I have shown you that is why I wanted to show you this before I show the basic of our view now I am going to show you how depth of pile quantification and image formation is done well as I said may this one these are different mass analyze use and the idea is to show you how they are relative behavior is if you have a quadruple mass spectrometer your resolution of 10 to the power 2 10 to the power 3 that means 100 to 1000 mass range is which can be detected is less than 1000 that mission is pretty low all the cases but it is lower in lowest in the quadruple mass detection is sequential me one by one sensitivity in a scale of 10,000 it is one if you use a magnetic sector that car mind sector I shown you it is reduced into power 4 at 10,000 mass ranges can be very high that means you can detect into power 4 and higher transmission is also quite high quite high means higher than the quadruple 0.1 to 0.5 again measurement sequential sensitivity is better than quadruple but not very high best one is that is what I said you in the lecture is time of flight time of flight has a high evolution 10 to the power 3 or higher it can scan mass ranges from 10 to the power 3 to the power 4 it has a very good transmission approximately close to 1 it can detect masses a parallel sequence not sequence in parallel together that is advantage and it has a very high relative sensitivity 10 to the power 4 10,000 so that means time of flight is very strong. So therefore you can clearly see that time of flight is the best option for us or for these sims and that is why it is widely used in the different machine now sims analysis can be done in different ways one the most widely used one is static sims which are used to determine the surface concentration of elements and molecules without significantly altering the sample then you can image sims that is what I said in life you means back like static sims does not alter the sample appreciably this mode used to generate images of maps based upon the concentration of secondary ions representing either an element or molecule you can have also a dynamic sims involving the use of a much higher energy beams primary beams but it is used to generate normally depth profiles not are these the two dimensional profiles so along the depth you can measure the concentrations in a static sims actually sorry static sims actually you can use static sims you can actually use low ion flux this means a small amount of primary ions are used or is used to bombard the sample bar unit time spatters it spatters have the approximately only 10th of an atomic monolayer very small flux so we use normally argon genome ions or argon genome and it has a diameter of very small like a truth in a meters analyzes typically analysis typically requires more than 15 minutes it generates a mass spectra data well suited for detection of the organic molecules to give you some results it is taken from polyethanil method let sims both positive and negative sims data see that you can detectually different I do not know that you can see C3H5 plus C3H5 C15H5 or this kind of DCOC C3H5 things positive ions positive ones and negative ions if you use like CGMR things which can create as a you can actually have these are different negative ions CH3O- C3OH- C2CH- are these ones so depending on the no different part of a negative ions you can actually detect all of them using this static sims fragmentation is subsequent ion formation of a sample can reveal the world structure to this mass spectroscopy is possible to do next one which I already discussed is time of flight time of flight is that most notable one here actually you have ion gun which can pulse in pulsed and actually raster also and falls on the primary and falls on a sample surface then secondary ions are generated you can extract the secondary ions by using extractor and then it passes through a long distance and during the they actually extract an axilla to the same voltage same kinetic energies different both and kind of energy means kind of energy each ions are same at the beginning and when they travel the long distance the time of flight varies by this way we can detect this is sophisticated instrument as I said and used for many many application and so this is the equation I showed you depending on the aim by Z values you can have a different time scale and you can detect that sims and time of flight operations actually very popular one it uses it is a best extractive technique you can remove the sample and measures they are intense at the secondary ions and then one by one layer was removed possible and measure the compositions one by one so that is why it is used so you have a spotter you know time of spotter ions and then time of flight and then all lines mass spectrometer well we should also know some aspect about the intensity of species of the secondary ions and this is basically equal to IPY aq CAT as you see is basically depends on primary current density total spotter yield of the primary current alpha is nothing but innocent probability of the charge state Q CA is the factional concentration of the element a in the matrix and T is the instrumental transmission function so transmission function is that is why I have shown you in the slides before so as you see at this is strong person of IP and why that is why you discussed about the primary current primary ions and this sputtering yield they actually determine along with alpha and other factors exactly secondary ion concentration species well there are problems in using this data because this is what is the total intensity this can be used to quantify and there are problems the problem is that why total depends moderately on CA not only that alpha also depends strongly on CA so is basically that means I I of the intensity of secondary ion is not linearly proportional to CA but there will be matrix effects that is why sometimes it is not possible to measure exactly the quantity they quantify this thing there will be always some error involved well seems can also be used to raster or getting and time applied it is done and if you have a different path this is the beam path you can see here beam path follows like this so this is nothing but electronically gated area you can actually create a cater and as you raster every point you can measure the seems profile by time of flight and once you do that every point to measure you can actually get the composition values and by this you can create a three dimensional map and the important thing which seems allows you to do is the depth profile what is it well one can actually do slowly remove the material from sample surface in the depth direction measure the concentrations well the important aspect in such a case is the depth resolution what we are showing here is the intensity or concentrations of the certain pieces as a function of you know they you know sputtering time or the depth as you see here this is the 100 time intensity which is good till certain time then it falls off in the surface so that means this is good in this region not good in this region okay so that is what actually can be done in a sims depth resolution profile one can actually use seems for kind of imaging or surface imaging because you can raster so if you can raster you can actually image by rastering a finely focused and beams over a surface like this and one can actually create mass resolve secondary images is basically nothing but a scanning electron microscopic image but here we are getting mass resolve secondary images and as you see here if I have a beam primary beam which I can raster on the sample surface and then each point from each point we can generate secondary ions and measuring the secondary on types and the yield of that and quantifying the different elements we can actually create a map it just like elemental map in a SCM you have different peaks from different element comes and then for a particular point and then measuring the peak intensity you can measure the quantify the particular element and they can map this is exactly done it here same thing you can use instead of a electron microscopy using this in a secondary ion mass spectroscopy and this is what a picture you get colorful picture you see here it shows you concentration of the three different pieces one is green blue and little bit red so that means it is possible go ahead not only that as I said is possible to do depth profiling in constant static seems experiment the dynamic ones actually high primary dose densities can be applied in this and it can give you successive removal of the respective top surface layers and by occurring spectra during this partnering the in-depth distribution of elements and small clusters can be monitored so as you see here this is a volume which is parted slowly and raster also obviously so you just start from this part and then go then you come back then come back blow like the raster so one surface layer is removed and you measure the composition then you go to the depth direction and then do the same thing rastering and get the distribution of elements in a three-dimensional or otherwise you can actually keep the beam constant static do not do the beam and just partner along a certain directions and measure the constants of the elements obviously I have given a lot of examples different examples all sorts of examples are given as you see here one must know very clearly that there are a very advanced measurements can be done using sims is a technique which is used extensively in material sands and surface sands to analyze the composition of solid surfaces and also thin plumes by sputtering the surface of the specimen with a focused primary ion beam and collecting and analyzing the ejected secondary ions secondary ions are then measured using a small spectrometer you can do elemental isotropic molecular composition of the surfaces actually you can do I could measure elements from you know hydrogen to uranium not hydrogen actually you can do lithium to uranium very easily you can actually detect element down to concentration from 1 ppm to 1 ppb isotope ratios can be measured isotope ratios means if you oxygen as 3 or 4 isotopes what are the abundance of the isotopes can be determined normally the position of 0.5 to 0.05 % which cannot be done by using any other techniques you can actually do two-dimensional ionic image measurements the ionic images which I shown you a secondary ion leaves the surface at a point close to the original location these enables localized analysis of a sample to be undertaken and he said correction is a constant cornerstone of the images. So not only that you can actually have three-dimensional ion images can be acquired by scanning or rusting the primary beam and did it in that it requires very little sample version let me tell you very little separation unlike in a CM on the TM you do not require mass sample versions and you can actually do many other things you can actually material sputter actually as you can you might be thinking middle spot is a large and no sputtering is few you know few fractions of distance of atomic layer on the surface. So sputtering is small you do not damage very but only once you do dynamic seems you can damage the sample surface and but there are problems and as and so I have just given you the dimension image following the material sputter is small I told but it has some limitations it is not a full put technique the major limitation of this technique is that the material which is part of the sample surface in not only consist of mono atomic ions but also consist of molecular species that in places can actually dominate the smart spectra spectrum and making the analysis of this element impossible is very obvious because you have a high energy primary source and this high energy primary source can bombard and create you know molecular species like CH4 plus CS3 plus CS3 minus species can be created in organic things many others normally metals is not possible but it can get metal complexes because cascade of this primary ion events can lead to mixing and mixing can lead to even formation of metal complexes second important thing which is bad about this is this whole sputtering process which is the main thing in a Sims is very poorly understood we do not have any quantity model so far that can accurately predict the secondary ionization process there is no so that is actually makes us assume certain things for the secondary ion generation process because and that assumption actually makes the technique little bit less attractive in the sense that we do not know really how the secondary ions are actually created what is the process so we have no idea we can measure the yields and other things but we have no idea theoretically also we cannot model it third thing is that you know to obtain a quantity information of a suitable standard you have to have a quantity information suitable standard that is the case for everything you know in a CM also EDS also requires so measurements of these requires a standard third thing is the sensitivity of an element is strongly dependent the composition of the matrix remember you are putting the element in a matrix organic matrix liquid matrix so it depends on the matrix we have shown that they call even the density is also function of the matrix is not a linear with only the element present and also type of primary beams you do used six standards should therefore be close to the composition of the unknown this is particularly to for isotropic analysis lastly samples which we are doing must be compatible at high vacuum it should not degrade inside the vacuum system because you are using a very high vacuum system you know minus 6 minus so no minus 9 to minus 10 top under the vacuum it should not transform or should not degrade to other thing else that is basically big limitation for that otherwise it has many advantages and so with this I actually close this discussion on the sims and only thing I need to do is to compare these three techniques surface character technique like XPS odd year and the sims and tell you how this techniques can be used in the front end