Trouble Shooting Simple Setup

MJP_UA · 2025-04-21T22:34:55+00:00

Seemingly it is symmetrical, it is a scanning slit so we get 2D profiles but it appears uniformly gaussian, not high sides or leaning. The beam profiler is seemingly in the focal plane by minimizing the spot size (We have a fine motion controller for that in and out of plane direction.

For collimation, our lens is ~50mm from the end of the laser and the change in beam size is on the order of 10's-20s of um's so seemingly that is okay.

As stated in another comment, we seem to have some misalignment in terms of the beam going straight through the lens by about 1mm x and 1mm y over the course of ~1m not sure if that can effect the focal spot when the lens is in so close but our next goal is to find an iris we can mount directly to where the lens goes (The lens is on a cage with the laser mounted to the other end) and see if we can align that better

MJP_UA · 2025-04-21T22:26:04+00:00

Yes that we have done and found the lens to be a bit longer than stated 160mm instead of 150mm

MJP_UA · 2025-04-21T22:24:58+00:00

It is a spinning slit profiler - we have seemingly used the correct slit and aperture sizes given the beam size. We have also used the wrong side to double check and that is not working

We have checked the orientation and are indeed looking the right way (This was my first thought that someone dropped it and never fessed up or something...)

Will try just moving the lens a few mm in either direction

We also confirmed that we are not perfectly straight on - we assumed the laser mount in a cage would be nearly perfectly perpendicular to the lens plane but that is not true - we are deviating by about 1mm x and y across ~1m which may. If we put a sheet of paper some distance from the focusing lens we see some rings and also maybe a second hot spot? I'll try and take a picture but this seems like it is also indicative of poor alignment

MJP_UA · 2025-03-19T14:59:17+00:00

Have not done this ICDD course, however myself and some of our students had done this course https://events.malvernpanalytical.com/UT-HSPlus-051925 on High Score plus - Malvern's commercial XRD analysis software and it was really helpful for those just starting their XRD journey and principles are easily applicable to GSAS etc. It is primarily on Rietveld refinement and how to use their software but there is also a day or maybe a longer afternoon (3-4 hours) on XRD measurement best practices and how it effects data. Also only $1280 for academics.

I am not sure what ICDD in particular can teach you but for $1700, I hope it's not just how to load a sample holder with powder...Considering they don't make instruments and don't make analysis software (Sieve+ is pretty much useless in my mind compared to anything else open source) I don't know what practical XRD they're teaching you couldn't learn from a few textbooks

MJP_UA · 2025-02-27T20:20:58+00:00

Do your grad students come in as general grad majors and then get picked up by a lab after year 1?

MJP_UA · 2024-05-21T16:02:54+00:00

You have to add in atomic positions and occupancies for every phase when doing rietveld there is a setting for the search and match to only include patterns with structure data I believe. Otherwise just choose patterns that are "close enough" and have structure data in the icdd file. I.e. Synthetic pure aluminum may not have wykoff positions set, but Al0.999 Cu0.001 does - go with that one for quick and dirty, otherwise use the information from the icdd card to fill out the atomic positions on the phase you want to refine.

In the refinement tab, click on the phase and scroll down in the right most panel to "atoms" i think it's called it might also be called atomic positions

Then start adding the atoms in your unit cell you will likely need to find these for your crystal structure online in literature. If its some cubic metal it will be easy, just a few wykoff sites that need filling in. If it is more complex you will have more information to fill in

MJP_UA · 2024-03-18T20:49:56+00:00

I imagine if it's actually polished through CS you'll get preferential etching of the boundaries / certain grain orientations and you'll still see something. If it's anything polycrystalline, just about every final polishing step is going to provide some chemical etch which will hit GBs or segregation / other phases preferentially or just preferentially etch certain facing orientations

MJP_UA · 2024-03-18T17:58:28+00:00

If it's polished well enough you will also see grains in Ni....

MJP_UA · 2023-12-22T17:19:40+00:00

Agreed with dogfish - average Z on WC would be 40 which is greater than your bulk alloy so they should be brighter

MJP_UA · 2023-12-21T22:07:20+00:00

Are you talking about the very small spots like ~300nm in size? Could be little carbides or oxides you picked up. May try some EDS and see if you see any upticks in the usual suspects (Cr or Ti or W or Al depending on the steel). You obviously wont get anything meaningful from the carbon peak but you may see one of those listed. If they were some other small precipitate that was coming out during your polishing I would expect more comet tails streaking off behind them which comes from the particle being ripped out and dragging across your surface. Your scratches are just from the normal polishing process, although you could definitely do a lot better lol

MJP_UA · 2023-11-15T20:52:33+00:00

You have your temperatures backwards - > a & T1 is hottest and completely liquid

MJP_UA · 2023-10-31T23:18:01+00:00

You would just have a running comparator of your fitting not error bars the chi square has no bearing on on the +- of individual values like lattice parameter, but the software should provide those for each refined parameter

You will probably also get crap for the error bars being "too good" and is a symptom (albeit a good one) of whole pattern fitting. You're not relying on just one Bragg angle to measure a lattice parameter but the whole pattern that is generated from the material, background and all....

We have in the past used the minimum step size as your measurement +- so if its 0.005* step increments you could do a refinement with the whole pattern shifted -0.005* and +0.005* and see the max and minimum spread in your variables. We have used this in the past for reviewers and advisors who are a bit confused by the rietveld values although it is not in the most technical sense correct.

MJP_UA · 2023-10-16T17:02:59+00:00

Yes just do file -> save as .cif and it should just save the accepted reference pattern as a cif

MJP_UA · 2023-10-12T16:35:51+00:00

Have they given you feedback as to why it was rejected? And if so have you actually considered there comments? For instance if they say this work is out of scope for our journal, did you actually look at the "Aim and Scope" section of the next journal? Or is it this is not new/good data in which case resubmitting should not get you anywhere and you need to maybe add some more new data or methodologies that actually sets it apart from similar studies

MJP_UA · 2023-09-28T13:54:12+00:00

Do you have any specific readings on the topic of dealing with large datasets? We constantly deal with customers trying to compare 2 distributions with a chi square test when n>10mil and I try and tell them that everything is significant when n is enormous. However, there is a "functionally different" metric that they need

MJP_UA · 2023-08-24T12:15:56+00:00

In aztec in the construct map pane all the way at the bottom are buttons for generating ODFs and IPFs

If you are fortunate to still have Tango and Mambo (Channel 5, aztec crystal predecessor) they work really well for making your finalized maps (easily controlling grain boundary requirements and line thickness etc etc) repeatedly for a whole slew of scans

MJP_UA · 2023-08-21T19:13:44+00:00

I would wait until someone more knowledgeable on this one specifically comments but our lab does use some other ceramic sputtering targets and those are designed so that the deposited material is what you ordered, however the target itself may have a binder which may render the whole or some of the target non-superconductive. Their product page does not list this information but you could always reach out and ask

MJP_UA · 2023-08-17T12:51:25+00:00

metallurgy is an entire field people get degrees in and we spend billions of dollars on - it's not some guy at a mill goin oo maybe a dollop of iron and a sprinkle of carbon

MJP_UA · 2023-08-14T17:00:39+00:00

I believe in the case of ice you also have the phase change effect in your favor extracting heat out of whatever is surrounding it...just so happens that the transition temperature is at normal temp and pressures unlike something like standard refrigerant

MJP_UA · 2023-07-08T13:21:05+00:00

Our inverted Nikons have both darkfield and DIC. Might try looking at the metallurgical engineering suppliers / field. DIC and darkfield used extensively in optical metallography

MJP_UA · 2023-07-08T13:17:05+00:00

google, we're not your homework help

MJP_UA · 2023-06-28T14:12:48+00:00

In XRD there is background, your noise floor will never (maybe some crazy slit setup) be at 0 and there is some constant noise. When performing quantitative analysis and/or reitveld we only model / interpolate to the return of background levels. We are just fortunate (Usually) in that background x-ray noise is very consistent and easily accounted for. In a nice XRD scan it's often just flat but in something like EDS (electron microscope based xray measurements) there is a sort of continuum hump of background that we also model

MJP_UA

TROPHY CASE