Recently, Imina Technologies and Alemnis launched a fully integrated system for in-situ SEM electrical and mechanical testing.
Dr. Anya Grushina (AG) from Imina Technologies talked to Dr. Rajaprakash Ramachandramoorthy (RR) from Max Planck Institute for Sustainable Materials, the first user of this integrated nanoindentor and electrical nanoprobing solution, about his experience with the setup.
Nanoindentation combined with nanoprobing
AG: Dr. Ramachandramoorthy, thanks for joining me for this interview. Let’s start with a few words about the research direction in your group.
R.R: Thank you so much Anya. I run the Nanomechanical Instrumentation and Extreme Nanomechanics group. We focus on in-situ micro and nanoscale mechanics, which we study inside electron microscope, either a scanning electron microscope or a transmission electron microscope.
We look into how mechanical properties vary with at different environmental conditions like the mechanical stress speed or temperature. We are also working on micro- and nanoscale metallic samples that additively manufactured using localized electro deposition. In this project, we are interested both in the mechanical and electrical properties of such architectures.
We print these structures using a printing system from Exaddon, Switzerland. Then we bring the sample into the SEM and probe it with the integrated nanoprobing and mechanical testing system so that we can get the electrical properties as a function of the mechanical loading.
Primarily, we explore pure metallic samples and different alloys. But we also have interest in some oxide materials.
AG: Why did you want to combine a nanoindentor with electrical nano probers inside SEM?
RR: This idea was on a wish list for several people in the material science community. We want to have mechanical stimuli, and we want to study not just the mechanical response, but also how it affects the electrical properties.
One of the key motivations for this combination is to assess the electrical resistivity of micro- and nanoscale samples as a function of mechanical loading. The idea of putting the Imina nanoprobers together with the Alemnis Standard Assembly nanoprobing system inside the SEM looked like the perfect solution.
From the application perspective, it is something relevant for semiconductor chips and MEMS / NEMS technologies. This kind of measurements are critical right now and they will become even more vital as we scale the devices further down in size in the next years.
And the second motivation for me is that we also want to do nanowire mechanics. We investigate 1D materials, and to look at their mechanical properties, we need to manipulate them. Now we use the Imina system for nanomanipulation of these nanowires and then use the Alemnis nanoindentor to get the mechanical data from them.
AG: Are you manipulating the nanowires by electrostatics or are you FIB'ing them to the tip and then moving them around?
RR: That is where the novelty of the work that we are doing comes in. Typically, to manipulate small-scale objects, such as nano wires, we use e-beam-induced deposition or ion-beam-induced deposition. Unfortunately, whenever we do that, we contaminate the nanowire systems. We deposit carbonacious platinum, which affects the nanowires properties. Now, instead, we are taking a slightly different approach with an SEM glue. When expose this glue to high-intensity electron beam it polymerizes and becomes hardened. To pick the nanowires, simple mechanical force is already enough, sometimes they just stick by Van der Waals forces. Then we place them and use the glue as clamps for the mechanical testing.
AG: For how long have you been using the system?
RR: We had to make a few ad-hoc changes to tune the system for ourselves. After that, I would say we have had three to four months of experience using the system.
AG: And how is your experience so far?
RR: It is definitely a complex instrument to use because it combines two state-of-the-art instruments for mechanical and electrical testing. And both going to the SEM. So, of course the learning curve is quite steep. But previously this kind of measurements were not even possible. In case of nanowire manipulation, which I have worked with throughout my PhD for five years or so, the complexity level was so high that the time to learn manipulation was more in the order of five-six months. So comparatively speaking, this system is much easier to use, absolutely.
We use the system for two different projects. For the first one, we create small-scale metallic objects using localized electrodeposition-based printing. We vary the microstructure of the metals that we are printing. And then I want to see the combined effect of the microstructure and the mechanical loading on the electrical resistivity. I use the Alemnis nanomechanical testing system to apply a displacement and to measure the force. And while doing this, I also want to see what is the electrical resistivity and how that changes in different samples.
In the second project, we study nanowires. For now, we focus on the manipulation and mechanical testing separately. We use Imina nanoprobers to pick and bring the nanowires to a specific place where we want to put them. Then we glue them using the SEM glue, and once they are clamped we can test them. For all of these purposes, the Imina robots perfectly fit the bill .
AG: You mainly focus on the materials where small scale is the most relevant, but would you say that combined electrical nanoprobing and nanoindentation are also useful for larger scale systems?
RR: Absolutely. When it comes to the larger scale systems, one of the key advantages this system provides is the isolation of different defects. Let's say we go for a laser particle fusion and we create metallic samples that are big. What we could do then is isolate different boundaries, let's say a grain boundary or a twin boundary, and then look at their electrical resistivity, also as a function of mechanical stress. We can have the indentor come in and locally hit a grain boundary, for example, while measuring the electrical resistance. All this testing has practical applications.
The key novelty in terms of the in-situ mechanical testing setup itself is the way that we can isolate specific defects and different phases in the system and then look at the mechanical properties. And now we also have a way to measure the electrical properties at the same time. Which is a great advantage to have.
AG: That's great to hear because that's what we also have in mind, but it's always good to hear it from the users.
It looks like so far, you had a good experience with a setup. But if there was one thing you would change about it, what would it be?
RR: I would not change anything about it. But because I am a little bit greedy, I would love to have four of Imina probers in my setup. That way, we could do four-point electrical measurements, because so far we use two- point impedance measurements, which have their limitations and peculiarities. The nanoprobers have a small form factor, but still fitting four of them inside with the mechanical testing system could be challenging. But it is possible.
AG: I think nanoindentor and the sample holder can also be used as contacts. But I do not know if that still fits with your experiment.
RR: You are correct. Given the low forces involved, I need to have very specialized load cells connected. They need to have an isolated trace that I can then use for the four point measurements. So that becomes more complex. So definitely if I have four probes I have far more freedom to do mechanics and then, in combination, a four-point measurement.
AG: Did you get any interesting results that you can share?
RR: We have some preliminary results coming up, which are by themselves interesting. But we are learning a lot about how to do these tests better as well. As you can imagine, we have the system only for a few months now. There is a postdoc and a PhD student using the system, and they have been working quite hard to get systematic results from this.
I have had equipment which I could use to separately do four-point measurements and in-situ nanomechanical testing. Now we need to put these two measurements together.
AG: Dr. Ramachandramoorthy, thank you very much for sharing your experience and looking forward to learning about more results when they come. Thanks for your time and, good luck.
RR: Thank you so much Anya, and thanks to Imina and Alemnis teams for giving me this amazing setup.