Story of ion milling webinar

Q&A

Story of ion milling webinar

Q&A

We are so glad that many of you came to the "Story of ion milling" webinar last week. Hopefully you got a lot of useful information from the presentation.

Here you can find all the questions raised during the Q&A session.

Q: For geology sample you have special type of sample holder?

A: The type of sample holder depends on the sample dimensions, shapes and states. In case the sample is sensitive to oxygen, then a special type of sample holder is required indeed, and this is the VTU, the vacuum transfer unit, which makes the transportation of the sample to the microscope or to a glove box possible under vacuum or in an inert gas environment.

Q: By LN2 how much temperature we can down at the time of operation?

A: Measuring the sample temperature during ion milling is a real challenge but we managed to do it. The minimum temperature depends on the cooling time. A reasonable cooling time that we usually suggest to our customers is 2 hours, when the stage temperature is down to -70°C in a SEMPrep2. To put this number in a perspective, during a 1-hour-long 90° slope cut, at the high-energy of 10 kV the sample temperature does not increase by more than 15 °C, an LN2 cooled sample temperature will be way below 0°C.

Q: How we can protect ours guns from contamination?

A: There is a flushing program in the control software which is recommended to be done each day before turning the ion source on. The process uses argon to flush the gas supply system and the ion sources.

Q: Recently you developed 16kv high energy guns, but high energy damage the surface? then what is the application of it?

A: The high-energy of 16 kV can cause beam damage to sensitive samples indeed. 16 kV is mainly for samples that can bear the introduced heatload (which is significantly reduced due to our sample holders special design) and if speed is an extremely important factor of the preparation. Also, for samples that are made of hard materials which have very low milling rates, like ceramics, diamond, gems, different steels, some superalloys and so on.

Q: I have resin imbedded soil sample. Round shape, 15 mm diameter. Mixture of minerals, bacteria and roots . How long (Roughly) will it take to polish the surface? Forgot to mention, my soil disks are for correlative microscopy involving Light microscopy, SEM/EDX, HIM, ToF-SIMS and NanoSIMS.

A: The polishing time depends on several factors, like accelerating voltage, beam current, the milling angle, the aimed measurement (EDS, EBSD, AES, etc.), pre-milling surface quality or even how deeply we would like to look at the sample. I would say in simple cases the polishing takes 10-20 minutes. In case your sample needs to be cooled, it will increase the preparation time.

Q: You showed a case with the diamond. This is an irregular sample. How do you managed the preparation? Do you put it in a resine? Or you glue it on the sample holder? In any case, how do you apply the mask on such sample?

A: The diamond sample was surface polished, where we are not using any kind of mask, the entire sample surface is milled. This is why the whole 3 mm sample was prepared, uniformly. The sample was simply and solely fixed on an SEM pin mount for the surface polishing.

Q: For very small metal samples, we prepare mecanically the surface through resine embedding, then we used ion milling. We encounter some troubles at the edges of the sample, due to different sputtering rate between the resine and the sample. How do you reduce this phenomenom?

A: The phenomenon you mentioned is very well know and can be annoying. Technoorg Linda has developed small tools for mechanical sample preparation of small SEM and TEM samples. Using these, the resin can be forgotten and the samples can be prepared directly (saving time, money and human resources).

Q: On irregular sample, how do you apply the mask for cross-section cut?

A: Tricky question. There are a few methods to make a slope cut on an irregular-shaped sample (in case of surface polishing, the shape is not a concern as long as the polished surface is flat). The easiest way is making the irragular shape mechanically flat. If it is not possible because of the nature of the sample, then we can ignore the irregularity and act like it is flat but this method comes with a price. At some parts, the edge of the slope cut will not be sharp and well-defined. Sometime the only solution is making a sandwhich-like structure and make some liquide glue to make the leading edge more even.

Q: Can Ion Milling replace FIB Milling, with the use of masking coatings (to isolate the regions not to be milled)?

A: FIB and (broad beam) ion milling are not competing but complementary techniques. If I had to name the biggest advantages over each other, then FIB has accuracy (according to out experience, an exact place of a slope cut in SEMPrep2 can be chosen with the accuracy of 3 um, repeatedly), broad beam ion milling has the huge treated area. For answering this question of masking the regions need to be isolated, we would need some additional information. We could discuss it in more detailes.

Q: Can you give more information about cross section of paper. Thikness of sample, time of cut, energy of cut.

A: The thickness was approximately 350 microns, the sample was cut at 8 kV for 8 hours with LN2 cooling. The sample was cut through after 5 hours, but we were looking for a wide completely cut sample, so we continued for an additional 3 hours.

Q: Is there a typical level of flatness achieved by the cutting method and is there hard limit to the surface finish?

A: The level of flatness depends on a few parameters. Most importantly, the surface quality of the sample before slope cutting but also depends on the milling parameters and a little bit on the composition of the sample. Hardness is not an issue, especially if 16 kV can be applied. Basically everything can be slope cut in SEMPrep2 that can bear the high-vacuum.

Q: Why Ar instead of Xe? Is Ar better than Xe?

A: Xe does not give you significant advantages in most of the cases but very expensive. Argon is easily available to anyone and cheap which makes it a more ideal noble gas for ion milling.

Q: Can we have details about the Li ion battery preparation.

A: Great question! Today the goal was to give a broad picture about the possibilities, but in the next several months we will have dedicated webinars with deep content of different topic, like FIB lamella cleaning, heat sensitive samples, so on. We can also have a personal discussion.

Q: Do you have application specified sample holders or the user should decide which they use?

A: We don’t have dedicated holders for a specific application, but all types of samples have an ideal approach and you can choose the right sample holder for that.

Q: What are the cooling options and what are the samples temperatures with each options during the milling?

A: Peltier, LN2, Aut LN2, Temperature is hard to be measured, but we managed it and there is a very detailed data base of temperatures for different ion energies and cooling options. What I can tell now is Peltier cooling can protect your samples against over-heating and keep it around room temperature, but LN2 keeps all samples way below 0 degree during the high energy milling.

Q: What kind of pre-preparation is needed before ion milling?

A: Most of the cases – if the sample allows – a good quality mechanical polishing is needed or increases the chance for the ultimate result with ion milling. Deep topic, we organize trainings and have some training materials. Let me know if interested and we send.

Q: I have metal wire SEM samples with different diameters from 20 um to 300 um. Can they be prepared?

A: The short answer is YES. Easily, if you know the right approach. We prepared such samples recently with 17,7 um diameter, so we can share some detailed materials about that. That sample was PtW coated with a polymer coating. That was quite a routin job.

Q: You mentioned the High energy ion milling makes some damage on the surface. In case of EBSD the low energy is the solution?

A: In case of SEM samples the high energy ion milling is gentle enough if you use the right recipe. The low energy makes a significant difference on the TEM samples where you need to clean the last nanometers of amorphous material

Q: What are the exact maximum sample sizes in case of each sample holder?

A: For TEM is easy. they can accommodate the 3 mm samples or the similar grids. For SEM we have different types. Some of them were designs for handling large samples, others not.

Q: Why is the low angle important in case of ion milling?

A: The surface quality depends on it, the higher the angle, the rougher the surface.

Q: So ion milling is creating a damaged and amorphous layer, is that correct?

A: Yes! Just like mechanical sample preparations, high-energy ion milling also creates damaged and amorphous layers. As we reduce the energy, the damaged layer becomes thinner and thinner. This is why the possibility of low-energy treatment is crucial for achieving atomic resolution.

Q: What is the reason that so many different types of sample holder are needed?

A: In order to make sure that the widest range of applications is covered, various sample holders are provided for different sample shapes, states and sizes.

Q: What is the difference between the Single-sided and the double-sided TEM sample holders?

A: They both have their pros and cons. The double-sided is much more convenient and safer, as there is no need to remove the sample from the ion mill and turn it upside-down before the treatment of the other side because the ion mill does it for us. In case of the single-sided sample holder, the lowest, 0° milling angle can be achieved.

Q: Why did the sample motion make a real difference?

A: The properly chosen motion helps to eliminate several types of artefacts, like curtaining. The wide range of tilting, including low angles helps to form extremely flat and smooth surfaces.

Q: Can we have detailed information about the Li ion battery preparation.

A: Great question! Today we gave you a broad picture about the possibilities, but we are organizing dedicated webinars about different topics, like FIB lamella cleaning, heat sensitive samples and Li ion batteries and the preparation of the polymer membranes will be on of those topics. Please use the Survey to let us know which other topics would you be interested.

Q: Do you have application specific sample holders or the user should decide which they use?

A: We don’t have dedicated holders for a specific application, but all types of samples have an ideal approach and you can choose the right sample holder for that. We have experience and help you.