November 2010 - Ifeffit - millenia.cars.aps.anl.gov

Re: [Ifeffit] Transmission EXAFS sample
by Scott Calvin 22 Nov '10

22 Nov '10

On Nov 22, 2010, at 7:09 AM, Jatinkumar Rana wrote: >> > Hi Scott, > > Sorry for mixing up the things. > > For the case, when i have very limited amount of sample that i can not > cover 1sq.cm area, you, Matt and others have given very very clear > explanation about possible solutions and the probable effects on data > quality. I am really very thankful to all of you for sharing your > experience and expertise. > > My last post was with reference to the case when i have enough powders > (i.e., reference oxide compounds). It is just to be ensured that i am > doing things 100% exactly in a same way it has to be done. > > With best regards, > Jatin > > -- > Jatinkumar Rana > Yes, Jatin, the procedure you described is fine. There is no "right" way to make samples, although there are many wrong ways. --Scott Calvin Faculty at Sarah Lawrence College Currently on sabbatical at Stanford Synchrotron Radiation Laboratory

1 0

Re: [Ifeffit] Transmission EXAFS sample
by Jatinkumar Rana 22 Nov '10

22 Nov '10

On 21.11.2010 19:00, ifeffit-request(a)millenia.cars.aps.anl.gov wrote: > Send Ifeffit mailing list submissions to > ifeffit(a)millenia.cars.aps.anl.gov > > To subscribe or unsubscribe via the World Wide Web, visit > http://millenia.cars.aps.anl.gov/mailman/listinfo/ifeffit > or, via email, send a message with subject or body 'help' to > ifeffit-request(a)millenia.cars.aps.anl.gov > > You can reach the person managing the list at > ifeffit-owner(a)millenia.cars.aps.anl.gov > > When replying, please edit your Subject line so it is more specific > than "Re: Contents of Ifeffit digest..." > > > Today's Topics: > > 1. Re: Transmission EXAFS sample (Jatinkumar Rana) > 2. Re: Transmission EXAFS sample (Scott Calvin) > > > ---------------------------------------------------------------------- > > Message: 1 > Date: Sun, 21 Nov 2010 11:44:25 +0100 > From: Jatinkumar Rana<jatinkumar.rana(a)helmholtz-berlin.de> > To:ifeffit@millenia.cars.aps.anl.gov > Subject: Re: [Ifeffit] Transmission EXAFS sample > Message-ID:<4CE8F809.3040208(a)helmholtz-berlin.de> > Content-Type: text/plain; charset=ISO-8859-1; format=flowed > > On 20.11.2010 19:00,ifeffit-request@millenia.cars.aps.anl.gov wrote: > >> Send Ifeffit mailing list submissions to >> ifeffit(a)millenia.cars.aps.anl.gov >> >> To subscribe or unsubscribe via the World Wide Web, visit >> http://millenia.cars.aps.anl.gov/mailman/listinfo/ifeffit >> or, via email, send a message with subject or body 'help' to >> ifeffit-request(a)millenia.cars.aps.anl.gov >> >> You can reach the person managing the list at >> ifeffit-owner(a)millenia.cars.aps.anl.gov >> >> When replying, please edit your Subject line so it is more specific >> than "Re: Contents of Ifeffit digest..." >> >> >> Today's Topics: >> >> 1. Re: Transmission EXAFS sample (Scott Calvin) >> 2. Re: Transmission EXAFS sample (Frenkel, Anatoly) >> >> >> ---------------------------------------------------------------------- >> >> Message: 1 >> Date: Fri, 19 Nov 2010 10:30:37 -0800 >> From: Scott Calvin<dr.scott.calvin(a)gmail.com> >> To: XAFS Analysis using Ifeffit<ifeffit(a)millenia.cars.aps.anl.gov> >> Subject: Re: [Ifeffit] Transmission EXAFS sample >> Message-ID:<DEC4127B-B536-4A85-BED3-2799D5B596C4(a)gmail.edu> >> Content-Type: text/plain; charset=US-ASCII; format=flowed; delsp=yes >> >> Hi Jatin, >> >> Matt covered most of what I would say, but I'll add a few comments of >> my own. >> >> I'm not sure how you arrived at the conclusion that you have only a >> few percent of what you need--you must be assuming a sample area >> somehow. I have frequently made transmission measurements on samples >> where I only had a few milligrams available. Generally, I did it by >> spreading it on a layer of tape as well as I could and then folding >> the tape over and over again--sometimes to make as many as 16 layers. >> (Of course, that many layers is not advisable if you're below 6 keV or >> so, as the absorption of the tape itself would kill the signal). Even >> if there are lots of pinholes because you can't cover the tape >> effectively, 16 layers from folding will make them cancel out fairly >> well. I can then narrow the beam a bit to match the size of my sample. >> Flux isn't really the issue here, so I don't even need a focussed >> beamline--I can just narrow the slits. >> >> Two other tips: >> >> 1) Realize that even with a tiny amount of sample that much of it >> won't end up on the tape. The process of brushing on tape is designed >> to separate the small grains from the big ones, with only the small >> ones ending up on tape. Allow that to happen! >> >> 2) You can sometimes get a second piece of tape to have some sample on >> it by putting it sticky side down on your mortar and peeling it back. >> A thin layer of dust from the sample will stick to the tape, and give >> you a little more absorption and a bit more of a uniform distribution. >> If you stack that with the primary piece of tape and then fold a few >> times, you may end up in pretty good shape, as long as you're not >> operating at a low enough energy so that all the layers of tape are a >> problem.. >> >> This procedure doesn't give me the best data I've ever seen, but it's >> often not bad. >> >> --Scott Calvin >> Sarah Lawrence College >> >> On Nov 19, 2010, at 8:13 AM, Matt Newville wrote: >> >> >> >>> Dear Jatin, >>> >>> The idea that the optimum absorption length (mu*t) for transmission >>> experiments is 2.3 assumes that the errors in the measurement are due >>> to counting statistics of the x-rays. For any synchrotron experiment, >>> the number of x-rays in the transmission chamber is high enough that >>> the noise from counting statistics is rarely significant. This means >>> that using a value of 2.3 is really not that important. >>> >>> The more important issues are >>> a) having a uniform sample. >>> b) not having (mu*t) so high that higher-order harmonics dominate >>> the transmission measurement. >>> >>> For transmission measurements, it's difficult to overstate the >>> importance of a uniform sample. For an ideal thickness, I would say >>> that the better rules of thumb than mu*t = 2.3 are to aim for an edge >>> step of 0.1 to 1.0, and a total absorption less than 3.0. >>> >>> If you only have enough material for an edge step as low as 0.02 (as >>> you imply), then measuring in fluorescence or electron emission is >>> probably a better choice. Such a sample won't be severely affected by >>> "self-absorption" (or "over absorption" to use the term this mailing >>> list prefers) in the fluorescence measurement. I would recommend >>> simultaneously measuring transmission and florescence for such a >>> sample. >>> >>> My concern about a very thin sample is uniformity. Specifically, is >>> the grain size really well below mu/0.02 so that a collection of >>> particles can give a uniform thickness? Since you didn't give any >>> details of the system, it's hard to guess. >>> >>> Is it feasible to pack that material into a smaller area so that the >>> thickness is increased and use a smaller x-ray beam? >>> >>> >>> >>>> -- Can my sample be only few percentage of the "actual amount" (i.e. >>>> calculated based on above fact) required, and still i can perform >>>> transmission EXAFS ? How would this affect my data ? (I guess, it >>>> will be >>>> heavily dominated by noise) >>>> >>>> >>> I would guess that a sample with mu*t of 0.02 would be dominated by >>> pinholes. >>> >>> >>> >>>> -- What if, i have required amount of sample but since material's >>>> density is >>>> so high that it yields only small volume of powder (for a given >>>> weight), >>>> that it can not be covered up on multiple layers of Kapton tape to >>>> ensure >>>> pinhole-free sample ? >>>> >>>> >>> If you cannot get the grain size small enough to have many overlapping >>> grains in the sample, the sample won't be uniform enough for good >>> transmission data. The techniques of using multiple layers of mixing >>> with a low-Z binder don't solve this problem. These do help to make a >>> uniform collection of overlapping grains, but don't make the grains >>> smaller. >>> >>> I would recommend trying to increase the thickness at the expense of >>> cross-sectional area, and/or measuring in both transmission and >>> fluorescence. >>> >>> Hope that helps, >>> >>> --Matt >>> _______________________________________________ >>> Ifeffit mailing list >>> Ifeffit(a)millenia.cars.aps.anl.gov >>> http://millenia.cars.aps.anl.gov/mailman/listinfo/ifeffit >>> >>> >> ------------------------------ >> >> Message: 2 >> Date: Fri, 19 Nov 2010 23:21:43 -0500 >> From: "Frenkel, Anatoly"<frenkel(a)bnl.gov> >> To: "XAFS Analysis using Ifeffit"<ifeffit(a)millenia.cars.aps.anl.gov> >> Subject: Re: [Ifeffit] Transmission EXAFS sample >> Message-ID:<69bc35f1-e92c-426c-8786-e2a5c881fae8@blur> >> Content-Type: text/plain; charset="us-ascii"; Format="Flowed"; >> DelSp="Yes" >> >> That's probably how they discovered graphene, by trying to make exafs >> sample. >> Anatoly >> >> Sent from my mobile phone, please forgive typos. >> >> -----Original message----- >> From: Scott Calvin<dr.scott.calvin(a)gmail.com> >> To: XAFS Analysis using Ifeffit<ifeffit(a)millenia.cars.aps.anl.gov> >> Sent: Fri, Nov 19, 2010 18:30:37 GMT+00:00 >> Subject: Re: [Ifeffit] Transmission EXAFS sample >> >> >>

1 0

Re: [Ifeffit] Ifeffit Digest, Vol 93, Issue 16
by Jatinkumar Rana 22 Nov '10

22 Nov '10

On 21.11.2010 19:00, ifeffit-request(a)millenia.cars.aps.anl.gov wrote: > Send Ifeffit mailing list submissions to > ifeffit(a)millenia.cars.aps.anl.gov > > To subscribe or unsubscribe via the World Wide Web, visit > http://millenia.cars.aps.anl.gov/mailman/listinfo/ifeffit > or, via email, send a message with subject or body 'help' to > ifeffit-request(a)millenia.cars.aps.anl.gov > > You can reach the person managing the list at > ifeffit-owner(a)millenia.cars.aps.anl.gov > > When replying, please edit your Subject line so it is more specific > than "Re: Contents of Ifeffit digest..." > > > Today's Topics: > > 1. Re: Transmission EXAFS sample (Jatinkumar Rana) > 2. Re: Transmission EXAFS sample (Scott Calvin) > > > ---------------------------------------------------------------------- > > Message: 1 > Date: Sun, 21 Nov 2010 11:44:25 +0100 > From: Jatinkumar Rana<jatinkumar.rana(a)helmholtz-berlin.de> > To: ifeffit(a)millenia.cars.aps.anl.gov > Subject: Re: [Ifeffit] Transmission EXAFS sample > Message-ID:<4CE8F809.3040208(a)helmholtz-berlin.de> > Content-Type: text/plain; charset=ISO-8859-1; format=flowed > > On 20.11.2010 19:00, ifeffit-request(a)millenia.cars.aps.anl.gov wrote: > >> Send Ifeffit mailing list submissions to >> ifeffit(a)millenia.cars.aps.anl.gov >> >> To subscribe or unsubscribe via the World Wide Web, visit >> http://millenia.cars.aps.anl.gov/mailman/listinfo/ifeffit >> or, via email, send a message with subject or body 'help' to >> ifeffit-request(a)millenia.cars.aps.anl.gov >> >> You can reach the person managing the list at >> ifeffit-owner(a)millenia.cars.aps.anl.gov >> >> When replying, please edit your Subject line so it is more specific >> than "Re: Contents of Ifeffit digest..." >> >> >> Today's Topics: >> >> 1. Re: Transmission EXAFS sample (Scott Calvin) >> 2. Re: Transmission EXAFS sample (Frenkel, Anatoly) >> >> >> ---------------------------------------------------------------------- >> >> Message: 1 >> Date: Fri, 19 Nov 2010 10:30:37 -0800 >> From: Scott Calvin<dr.scott.calvin(a)gmail.com> >> To: XAFS Analysis using Ifeffit<ifeffit(a)millenia.cars.aps.anl.gov> >> Subject: Re: [Ifeffit] Transmission EXAFS sample >> Message-ID:<DEC4127B-B536-4A85-BED3-2799D5B596C4(a)gmail.edu> >> Content-Type: text/plain; charset=US-ASCII; format=flowed; delsp=yes >> >> Hi Jatin, >> >> Matt covered most of what I would say, but I'll add a few comments of >> my own. >> >> I'm not sure how you arrived at the conclusion that you have only a >> few percent of what you need--you must be assuming a sample area >> somehow. I have frequently made transmission measurements on samples >> where I only had a few milligrams available. Generally, I did it by >> spreading it on a layer of tape as well as I could and then folding >> the tape over and over again--sometimes to make as many as 16 layers. >> (Of course, that many layers is not advisable if you're below 6 keV or >> so, as the absorption of the tape itself would kill the signal). Even >> if there are lots of pinholes because you can't cover the tape >> effectively, 16 layers from folding will make them cancel out fairly >> well. I can then narrow the beam a bit to match the size of my sample. >> Flux isn't really the issue here, so I don't even need a focussed >> beamline--I can just narrow the slits. >> >> Two other tips: >> >> 1) Realize that even with a tiny amount of sample that much of it >> won't end up on the tape. The process of brushing on tape is designed >> to separate the small grains from the big ones, with only the small >> ones ending up on tape. Allow that to happen! >> >> 2) You can sometimes get a second piece of tape to have some sample on >> it by putting it sticky side down on your mortar and peeling it back. >> A thin layer of dust from the sample will stick to the tape, and give >> you a little more absorption and a bit more of a uniform distribution. >> If you stack that with the primary piece of tape and then fold a few >> times, you may end up in pretty good shape, as long as you're not >> operating at a low enough energy so that all the layers of tape are a >> problem.. >> >> This procedure doesn't give me the best data I've ever seen, but it's >> often not bad. >> >> --Scott Calvin >> Sarah Lawrence College >> >> On Nov 19, 2010, at 8:13 AM, Matt Newville wrote: >> >> >> >>> Dear Jatin, >>> >>> The idea that the optimum absorption length (mu*t) for transmission >>> experiments is 2.3 assumes that the errors in the measurement are due >>> to counting statistics of the x-rays. For any synchrotron experiment, >>> the number of x-rays in the transmission chamber is high enough that >>> the noise from counting statistics is rarely significant. This means >>> that using a value of 2.3 is really not that important. >>> >>> The more important issues are >>> a) having a uniform sample. >>> b) not having (mu*t) so high that higher-order harmonics dominate >>> the transmission measurement. >>> >>> For transmission measurements, it's difficult to overstate the >>> importance of a uniform sample. For an ideal thickness, I would say >>> that the better rules of thumb than mu*t = 2.3 are to aim for an edge >>> step of 0.1 to 1.0, and a total absorption less than 3.0. >>> >>> If you only have enough material for an edge step as low as 0.02 (as >>> you imply), then measuring in fluorescence or electron emission is >>> probably a better choice. Such a sample won't be severely affected by >>> "self-absorption" (or "over absorption" to use the term this mailing >>> list prefers) in the fluorescence measurement. I would recommend >>> simultaneously measuring transmission and florescence for such a >>> sample. >>> >>> My concern about a very thin sample is uniformity. Specifically, is >>> the grain size really well below mu/0.02 so that a collection of >>> particles can give a uniform thickness? Since you didn't give any >>> details of the system, it's hard to guess. >>> >>> Is it feasible to pack that material into a smaller area so that the >>> thickness is increased and use a smaller x-ray beam? >>> >>> >>> >>>> -- Can my sample be only few percentage of the "actual amount" (i.e. >>>> calculated based on above fact) required, and still i can perform >>>> transmission EXAFS ? How would this affect my data ? (I guess, it >>>> will be >>>> heavily dominated by noise) >>>> >>>> >>> I would guess that a sample with mu*t of 0.02 would be dominated by >>> pinholes. >>> >>> >>> >>>> -- What if, i have required amount of sample but since material's >>>> density is >>>> so high that it yields only small volume of powder (for a given >>>> weight), >>>> that it can not be covered up on multiple layers of Kapton tape to >>>> ensure >>>> pinhole-free sample ? >>>> >>>> >>> If you cannot get the grain size small enough to have many overlapping >>> grains in the sample, the sample won't be uniform enough for good >>> transmission data. The techniques of using multiple layers of mixing >>> with a low-Z binder don't solve this problem. These do help to make a >>> uniform collection of overlapping grains, but don't make the grains >>> smaller. >>> >>> I would recommend trying to increase the thickness at the expense of >>> cross-sectional area, and/or measuring in both transmission and >>> fluorescence. >>> >>> Hope that helps, >>> >>> --Matt >>> _______________________________________________ >>> Ifeffit mailing list >>> Ifeffit(a)millenia.cars.aps.anl.gov >>> http://millenia.cars.aps.anl.gov/mailman/listinfo/ifeffit >>> >>> >> >> ------------------------------ >> >> Message: 2 >> Date: Fri, 19 Nov 2010 23:21:43 -0500 >> From: "Frenkel, Anatoly"<frenkel(a)bnl.gov> >> To: "XAFS Analysis using Ifeffit"<ifeffit(a)millenia.cars.aps.anl.gov> >> Subject: Re: [Ifeffit] Transmission EXAFS sample >> Message-ID:<69bc35f1-e92c-426c-8786-e2a5c881fae8@blur> >> Content-Type: text/plain; charset="us-ascii"; Format="Flowed"; >> DelSp="Yes" >> >> That's probably how they discovered graphene, by trying to make exafs >> sample. >> Anatoly >> >> Sent from my mobile phone, please forgive typos. >> >> -----Original message----- >> From: Scott Calvin<dr.scott.calvin(a)gmail.com> >> To: XAFS Analysis using Ifeffit<ifeffit(a)millenia.cars.aps.anl.gov> >> Sent: Fri, Nov 19, 2010 18:30:37 GMT+00:00 >> Subject: Re: [Ifeffit] Transmission EXAFS sample >> >> >>

1 0

Re: [Ifeffit] Transmission EXAFS sample
by Jatinkumar Rana 21 Nov '10

21 Nov '10

On 20.11.2010 19:00, ifeffit-request(a)millenia.cars.aps.anl.gov wrote: > Send Ifeffit mailing list submissions to > ifeffit(a)millenia.cars.aps.anl.gov > > To subscribe or unsubscribe via the World Wide Web, visit > http://millenia.cars.aps.anl.gov/mailman/listinfo/ifeffit > or, via email, send a message with subject or body 'help' to > ifeffit-request(a)millenia.cars.aps.anl.gov > > You can reach the person managing the list at > ifeffit-owner(a)millenia.cars.aps.anl.gov > > When replying, please edit your Subject line so it is more specific > than "Re: Contents of Ifeffit digest..." > > > Today's Topics: > > 1. Re: Transmission EXAFS sample (Scott Calvin) > 2. Re: Transmission EXAFS sample (Frenkel, Anatoly) > > > ---------------------------------------------------------------------- > > Message: 1 > Date: Fri, 19 Nov 2010 10:30:37 -0800 > From: Scott Calvin<dr.scott.calvin(a)gmail.com> > To: XAFS Analysis using Ifeffit<ifeffit(a)millenia.cars.aps.anl.gov> > Subject: Re: [Ifeffit] Transmission EXAFS sample > Message-ID:<DEC4127B-B536-4A85-BED3-2799D5B596C4(a)gmail.edu> > Content-Type: text/plain; charset=US-ASCII; format=flowed; delsp=yes > > Hi Jatin, > > Matt covered most of what I would say, but I'll add a few comments of > my own. > > I'm not sure how you arrived at the conclusion that you have only a > few percent of what you need--you must be assuming a sample area > somehow. I have frequently made transmission measurements on samples > where I only had a few milligrams available. Generally, I did it by > spreading it on a layer of tape as well as I could and then folding > the tape over and over again--sometimes to make as many as 16 layers. > (Of course, that many layers is not advisable if you're below 6 keV or > so, as the absorption of the tape itself would kill the signal). Even > if there are lots of pinholes because you can't cover the tape > effectively, 16 layers from folding will make them cancel out fairly > well. I can then narrow the beam a bit to match the size of my sample. > Flux isn't really the issue here, so I don't even need a focussed > beamline--I can just narrow the slits. > > Two other tips: > > 1) Realize that even with a tiny amount of sample that much of it > won't end up on the tape. The process of brushing on tape is designed > to separate the small grains from the big ones, with only the small > ones ending up on tape. Allow that to happen! > > 2) You can sometimes get a second piece of tape to have some sample on > it by putting it sticky side down on your mortar and peeling it back. > A thin layer of dust from the sample will stick to the tape, and give > you a little more absorption and a bit more of a uniform distribution. > If you stack that with the primary piece of tape and then fold a few > times, you may end up in pretty good shape, as long as you're not > operating at a low enough energy so that all the layers of tape are a > problem.. > > This procedure doesn't give me the best data I've ever seen, but it's > often not bad. > > --Scott Calvin > Sarah Lawrence College > > On Nov 19, 2010, at 8:13 AM, Matt Newville wrote: > > >> Dear Jatin, >> >> The idea that the optimum absorption length (mu*t) for transmission >> experiments is 2.3 assumes that the errors in the measurement are due >> to counting statistics of the x-rays. For any synchrotron experiment, >> the number of x-rays in the transmission chamber is high enough that >> the noise from counting statistics is rarely significant. This means >> that using a value of 2.3 is really not that important. >> >> The more important issues are >> a) having a uniform sample. >> b) not having (mu*t) so high that higher-order harmonics dominate >> the transmission measurement. >> >> For transmission measurements, it's difficult to overstate the >> importance of a uniform sample. For an ideal thickness, I would say >> that the better rules of thumb than mu*t = 2.3 are to aim for an edge >> step of 0.1 to 1.0, and a total absorption less than 3.0. >> >> If you only have enough material for an edge step as low as 0.02 (as >> you imply), then measuring in fluorescence or electron emission is >> probably a better choice. Such a sample won't be severely affected by >> "self-absorption" (or "over absorption" to use the term this mailing >> list prefers) in the fluorescence measurement. I would recommend >> simultaneously measuring transmission and florescence for such a >> sample. >> >> My concern about a very thin sample is uniformity. Specifically, is >> the grain size really well below mu/0.02 so that a collection of >> particles can give a uniform thickness? Since you didn't give any >> details of the system, it's hard to guess. >> >> Is it feasible to pack that material into a smaller area so that the >> thickness is increased and use a smaller x-ray beam? >> >> >>> -- Can my sample be only few percentage of the "actual amount" (i.e. >>> calculated based on above fact) required, and still i can perform >>> transmission EXAFS ? How would this affect my data ? (I guess, it >>> will be >>> heavily dominated by noise) >>> >> I would guess that a sample with mu*t of 0.02 would be dominated by >> pinholes. >> >> >>> -- What if, i have required amount of sample but since material's >>> density is >>> so high that it yields only small volume of powder (for a given >>> weight), >>> that it can not be covered up on multiple layers of Kapton tape to >>> ensure >>> pinhole-free sample ? >>> >> If you cannot get the grain size small enough to have many overlapping >> grains in the sample, the sample won't be uniform enough for good >> transmission data. The techniques of using multiple layers of mixing >> with a low-Z binder don't solve this problem. These do help to make a >> uniform collection of overlapping grains, but don't make the grains >> smaller. >> >> I would recommend trying to increase the thickness at the expense of >> cross-sectional area, and/or measuring in both transmission and >> fluorescence. >> >> Hope that helps, >> >> --Matt >> _______________________________________________ >> Ifeffit mailing list >> Ifeffit(a)millenia.cars.aps.anl.gov >> http://millenia.cars.aps.anl.gov/mailman/listinfo/ifeffit >> > > > ------------------------------ > > Message: 2 > Date: Fri, 19 Nov 2010 23:21:43 -0500 > From: "Frenkel, Anatoly"<frenkel(a)bnl.gov> > To: "XAFS Analysis using Ifeffit"<ifeffit(a)millenia.cars.aps.anl.gov> > Subject: Re: [Ifeffit] Transmission EXAFS sample > Message-ID:<69bc35f1-e92c-426c-8786-e2a5c881fae8@blur> > Content-Type: text/plain; charset="us-ascii"; Format="Flowed"; > DelSp="Yes" > > That's probably how they discovered graphene, by trying to make exafs > sample. > Anatoly > > Sent from my mobile phone, please forgive typos. > > -----Original message----- > From: Scott Calvin<dr.scott.calvin(a)gmail.com> > To: XAFS Analysis using Ifeffit<ifeffit(a)millenia.cars.aps.anl.gov> > Sent: Fri, Nov 19, 2010 18:30:37 GMT+00:00 > Subject: Re: [Ifeffit] Transmission EXAFS sample > > >

1 0

Re: [Ifeffit] Transmission EXAFS sample
by Scott Calvin 19 Nov '10

19 Nov '10

Hi Jatin, Matt covered most of what I would say, but I'll add a few comments of my own. I'm not sure how you arrived at the conclusion that you have only a few percent of what you need--you must be assuming a sample area somehow. I have frequently made transmission measurements on samples where I only had a few milligrams available. Generally, I did it by spreading it on a layer of tape as well as I could and then folding the tape over and over again--sometimes to make as many as 16 layers. (Of course, that many layers is not advisable if you're below 6 keV or so, as the absorption of the tape itself would kill the signal). Even if there are lots of pinholes because you can't cover the tape effectively, 16 layers from folding will make them cancel out fairly well. I can then narrow the beam a bit to match the size of my sample. Flux isn't really the issue here, so I don't even need a focussed beamline--I can just narrow the slits. Two other tips: 1) Realize that even with a tiny amount of sample that much of it won't end up on the tape. The process of brushing on tape is designed to separate the small grains from the big ones, with only the small ones ending up on tape. Allow that to happen! 2) You can sometimes get a second piece of tape to have some sample on it by putting it sticky side down on your mortar and peeling it back. A thin layer of dust from the sample will stick to the tape, and give you a little more absorption and a bit more of a uniform distribution. If you stack that with the primary piece of tape and then fold a few times, you may end up in pretty good shape, as long as you're not operating at a low enough energy so that all the layers of tape are a problem.. This procedure doesn't give me the best data I've ever seen, but it's often not bad. --Scott Calvin Sarah Lawrence College On Nov 19, 2010, at 8:13 AM, Matt Newville wrote: > Dear Jatin, > > The idea that the optimum absorption length (mu*t) for transmission > experiments is 2.3 assumes that the errors in the measurement are due > to counting statistics of the x-rays. For any synchrotron experiment, > the number of x-rays in the transmission chamber is high enough that > the noise from counting statistics is rarely significant. This means > that using a value of 2.3 is really not that important. > > The more important issues are > a) having a uniform sample. > b) not having (mu*t) so high that higher-order harmonics dominate > the transmission measurement. > > For transmission measurements, it's difficult to overstate the > importance of a uniform sample. For an ideal thickness, I would say > that the better rules of thumb than mu*t = 2.3 are to aim for an edge > step of 0.1 to 1.0, and a total absorption less than 3.0. > > If you only have enough material for an edge step as low as 0.02 (as > you imply), then measuring in fluorescence or electron emission is > probably a better choice. Such a sample won't be severely affected by > "self-absorption" (or "over absorption" to use the term this mailing > list prefers) in the fluorescence measurement. I would recommend > simultaneously measuring transmission and florescence for such a > sample. > > My concern about a very thin sample is uniformity. Specifically, is > the grain size really well below mu/0.02 so that a collection of > particles can give a uniform thickness? Since you didn't give any > details of the system, it's hard to guess. > > Is it feasible to pack that material into a smaller area so that the > thickness is increased and use a smaller x-ray beam? > >> -- Can my sample be only few percentage of the "actual amount" (i.e. >> calculated based on above fact) required, and still i can perform >> transmission EXAFS ? How would this affect my data ? (I guess, it >> will be >> heavily dominated by noise) > > I would guess that a sample with mu*t of 0.02 would be dominated by > pinholes. > >> -- What if, i have required amount of sample but since material's >> density is >> so high that it yields only small volume of powder (for a given >> weight), >> that it can not be covered up on multiple layers of Kapton tape to >> ensure >> pinhole-free sample ? > > If you cannot get the grain size small enough to have many overlapping > grains in the sample, the sample won't be uniform enough for good > transmission data. The techniques of using multiple layers of mixing > with a low-Z binder don't solve this problem. These do help to make a > uniform collection of overlapping grains, but don't make the grains > smaller. > > I would recommend trying to increase the thickness at the expense of > cross-sectional area, and/or measuring in both transmission and > fluorescence. > > Hope that helps, > > --Matt > _______________________________________________ > Ifeffit mailing list > Ifeffit(a)millenia.cars.aps.anl.gov > http://millenia.cars.aps.anl.gov/mailman/listinfo/ifeffit

2 1

Transmission EXAFS sample
by Jatinkumar Rana 19 Nov '10

19 Nov '10

Dear all, I have very basic question about the sample preparation for EXAFS. It is well understood and proven by several researchers that the optimum amount of sample (per unit area) required for EXAFS is determined by the fact that the total absorbtion of the entire sample above the absorption edge (of interest) should be between 2 to 2.5, more precisely, it should be 2.3. The reason which forces me to put this question to a mailing list is that, i treat my sample through a process which yields only few percentage of the total amount of sample required for EXAFS. I would prefer to measure EXAFS in transmission mode with samples prepared on several layers of Kapton tape which are bound together to ensure pinhole free sample. My questions are : -- Can my sample be only few percentage of the "actual amount" (i.e. calculated based on above fact) required, and still i can perform transmission EXAFS ? How would this affect my data ? (I guess, it will be heavily dominated by noise) -- What if, i have required amount of sample but since material's density is so high that it yields only small volume of powder (for a given weight), that it can not be covered up on multiple layers of Kapton tape to ensure pinhole-free sample ? I look forward to any comments or suggestions as this would help me improvise the quality of my data. With best regards, Jatin -- Jatinkumar Rana Helmholtz-Zentrum Berlin für Materialien und Energie GmbH Institut für angewandte Materialforschung FI-1 Mikrostruktur Hahn-Meitner-Platz 1 D-14109 Berlin Germany Tel: +49 30 8062-43217 Fax: +49 30 8062-43059 eMail: jatinkumar.rana(a)helmholtz-berlin.de **************************************************************************************** Mitglied der Hermann von Helmholtz-Gemeinschaft Deutscher Forschungszentren e.V. Vorsitzender des Aufsichtsrats: Prof. Dr. Dr. h.c. mult. Joachim Treusch Stellvertretende Vorsitzende: Dr. Beatrix Vierkorn-Rudolph Geschäftsführer: Prof. Dr. Anke Rita Kaysser-Pyzalla, Prof. Dr. Dr. h.c. Wolfgang Eberhardt, Dr. Ulrich Breuer Sitz der Gesellschaft: Berlin Handelsregister: AG Charlottenburg, 89 HRB 5583

3 2

Re: [Ifeffit] Origin of terminology "self-absorption"
by Scott Calvin 17 Nov '10

17 Nov '10

I tried a few searches, but rapidly get lost in other uses of the term. My guess is we borrowed it from some other spectroscopy, much the way we borrowed "Debye-Waller factor" from XRD, and then proceeded to change its meaning. But it would be nice to be able to track that down. --Scott Calvin Faculty at Sarah Lawrence College Currently on sabbatical at Stanford Synchrotron Radiation Laboratory On Nov 16, 2010, at 10:54 AM, Matthew Marcus wrote: > It's definitely a misnomer. I use "overabsorption" and encourage > others to do so. I suppose to track it down would require going > back over the seminal papers on the subject. > mam > > On 11/16/2010 10:19 AM, Scott Calvin wrote: >> Hi all, >> >> As some of you know, I'm currently working on a textbook on XAFS >> analysis. Because of that, I'm going to occasionally pose some >> questions for the list that may seem a bit random. I hope none of >> you mind me using the list in this way; the questions may seem to >> come out of left field, but I think they will still be of interest >> to many. >> >> With that said, here's my question for today: >> >> What is the origin of the use of "self-absorption" to describe the >> suppression of fine-structure observed in thick, concentrated >> samples measured in fluorescence? I understand the physics of the >> effect itself, my question is the curious wording. Compared to a >> thin concentrated sample, the effect might better be described as >> "saturation," while compared to a thick dilute sample, it's >> actually related to a lack of absorption by other elements. >> >> --Scott Calvin >> Faculty at Sarah Lawrence College >> Currently on sabbatical at Stanford Synchrotron Radiation Laboratory >> _______________________________________________ >> Ifeffit mailing list >> Ifeffit(a)millenia.cars.aps.anl.gov >> http://millenia.cars.aps.anl.gov/mailman/listinfo/ifeffit > _______________________________________________ > Ifeffit mailing list > Ifeffit(a)millenia.cars.aps.anl.gov > http://millenia.cars.aps.anl.gov/mailman/listinfo/ifeffit

4 3

UO2 thin films on STO
by mohamed sobhy 16 Nov '10

16 Nov '10

Dear All I would like to grow UO2 thin films on STO (SrTiO3) substrate but I found that Sr K-edge 16105 and U L3-edge is 17166. Do you think there will be any interference? Best, Mohamed

4 3

Origin of terminology "self-absorption"
by Scott Calvin 16 Nov '10

16 Nov '10

Hi all, As some of you know, I'm currently working on a textbook on XAFS analysis. Because of that, I'm going to occasionally pose some questions for the list that may seem a bit random. I hope none of you mind me using the list in this way; the questions may seem to come out of left field, but I think they will still be of interest to many. With that said, here's my question for today: What is the origin of the use of "self-absorption" to describe the suppression of fine-structure observed in thick, concentrated samples measured in fluorescence? I understand the physics of the effect itself, my question is the curious wording. Compared to a thin concentrated sample, the effect might better be described as "saturation," while compared to a thick dilute sample, it's actually related to a lack of absorption by other elements. --Scott Calvin Faculty at Sarah Lawrence College Currently on sabbatical at Stanford Synchrotron Radiation Laboratory

3 2

help
by Aaron Yevick 11 Nov '10

11 Nov '10

Hi all, I downloaded Artemis twice, from both cars.uchicago and sourceforge. Both times I downloaded the latest, 1.2.11.exe. When it installed, I opened Artemis and was prompted to install several updates. I clicked Install Updates, and both times it says: downloading fetching update 10 (iff_010.zip).... downloaded iff_010.zip OK. expanding file iff_010.zip and goes no further in an hour. I quit. When it runs, along the bottom it says the version is 0.8.012 (c) 2002-2008, which I was told is not the latest version (is that true?) My operating system is Windows 7 Professional. Can anybody offer suggestions as to why this happens? Does it matter if I don't have these updates? Aaron

5 4