#BESSYbeamlinePortraits: Roberto Felix Duarte

What’s the name of your beamline and what’s it like?

Our beamline is called KMC-1. The letters come from the German “Kristall-Monochromator”, and it is the first one out of three beamlines with a similar monochromator. Its energy range is from 2000 eV to about 12000 eV, so it produces light in the often called “tender x-rays” range.

I should say that, officially, I’m not the beamline scientist, but the endstation manager of the HIKE endstation (High Kinetic Energy Photoelectron Spectroscopy). Until very recently HIKE used to take most of the time at the beamline. KMC-1 is a very sturdy and reliable beamline. Compared to other beamlines, it’s a fairly straightforward setup, so there are fewer “moving parts” that can break down or cause trouble. However, KMC-1 is a beamline in very high demand in the user community.

For which research applications is this beamline especially suitable?

What we do at HIKE is called hard x-ray photoelectron spectroscopy.
You can do a  similar technique in the lab instead of at a light source like BESSY II, but in the lab you usually work with lower excitation energies, making the lab-based technique much more surface sensitive. The measurements take much longer because of the lower photon flux of lab-based x-ray sources compared to that of synchrotron light sources.
With our setup of HIKE and the KMC-1 beamline, we can measure surfaces, but by using higher excitation energies we can also probe deeper and deeper into the sample, not just one or two nanometers as before, but up to tens of nanometers. At first glance, this might not seem significant, but when you have a sample that consists of very thin layers of different materials you want to see what goes on at the interface of those layers. At HIKE we can do that and that’s interesting for quite a few research applications.

For example, there are a lot of energy related materials like thin film solar cell devices, or batteries, where each layer plays a different role. In a solar cell for instance, there is a layer called the absorber. It receives the sunlight and is responsible for exciting electrons and producing charge carriers (i.e., electrons and holes). But these charges then have to be separated to produce the electricity.
For example, electrons are transported through another layer next to the absorber that is called the buffer layer. And if the properties between the buffer and the absorber are not optimized there can be big losses that reduce the efficiency of the device. That’s why it’s important to know what is going on between the two.

What’s your background, scientifically? How did you get to be a beamline scientist?

I studied physical chemistry and then I did my PhD work in physics here at HZB. During this time, my group and I were frequent users at HIKE, the endstation that I actually manage now, so I gained a lot of experience at HIKE. As I finished my PhD there was an opening to manage the endstation so I started my postdoc as the endstation manager. I still do my own research at HIKE, mostly on perovskites.

It turns out that KMC-1 is a beamline very well suited for studying perovskites.
Typically, one tries to get the highest intensity in a beam to be able to measure faster and with lower signal noise. Because of its design/components, KMC-1 generates a lower photon flux, so the light density is lower. This can be an advantage when you are measuring samples that are easily damaged by the beam – like perovskites are, because they are based on organic components. At KMC-1 we can minimize these destructive effects. I mean, you still have to be careful, but it’s not as pronounced as on other higher photon flux beamlines.

This is a very nice feature that, let’s say, we were lucky with. Because when the beamline was designed perovskites weren’t the hot thing they are today in photovoltaic research. But now it’s a very nice application.

What is your work as a beamline scientist? (Or: What are you doing “all day”?)

In a typical week, if there ever exists one, on Mondays and Tuesdays we would do maintenance work at the beamline and the endstation. On Tuesdays, the new groups arrive, and depending on how experienced they are, I give them an introduction or a refresher on the operation of the beamline and endstation, help them to introduce their samples, and then have them on their way to do their measurements.

For the rest of the week, I will continue to help them with the system if needed, which again depends on the experience level of the users. Otherwise, I can turn to evaluating my own data.

Ideally, my workweek ends on Friday, but if there is a situation and the users are having trouble at the beamline I might need to come back in on the weekend. Most surprises are covered by the team from the “Hallendienst”, though. They are like our first responders at the instruments outside office hours, and they are on call all the time during user operation time. So I would usually try to coordinate with them first to solve an issue. When I do have to come in on a weekend, then the problem is probably more serious.

“I feel responsible for the users and I want to help them get the most out of their time at BESSY II. They went through a lot of effort to be able to have that beamtime.”

What is your biggest challenge in working with the beamline?

For me personally the biggest challenge is to maintain a good work-life balance. I rarely work on a fixed schedule, so it’s difficult to make plans. On the other hand, I feel responsible for the users and I want to help them get the most out of their time at BESSY II. They went through a lot of effort to be able to have that beamtime, as only about one third of the proposals for HIKE are currently accepted, so there is a lot riding on it, and I want to make sure that they can make optimal use of it.

I also assist other groups who are applying for beamtime. I can’t tell them exactly what to write, of course, but I can provide guidelines on what experiments are feasible or not.

What is the most rewarding part?

As beamline or instrument scientist, you get to be involved in a lot of very cool stuff that other people do. This way, you get a feeling for other types of research, different from your own, which is usually not so easy to achieve. I get to meet a lot of people, too, and I very much enjoy the different collaborations. I also have the opportunity of upgrading the HIKE setup, which allows to conduct more complex and challenging experiments that better represent the studied material systems in “real-life” devices.