Building the New Spin-ARPES Laboratory

Building the New Spin-ARPES Laboratory

– Article based on a Group Dialogue facilitated by Karen-Elisabeth Sødahl


Håkon Røst, Justin Wells and Frode Strand


Background and motivation

Over the last few years we have developed an ARPES laboratory at NTNU. We built a homemade preparation chamber, a detector upgrade and a 5-axis manipulator. This gave us good facilities for routine ARPES measurements, a wide range of preparation options, as well as supplementary techniques such as XPS, LEED and Auger analysis. Our existing instrumentation has mostly relied on established technological developments and has proven itself to be generally useful for a wide range of applications, from biophysics to photovoltaics, quantum computer architectures and more.

This year, we have constructed a new bespoke instrument. Unlike the existing equipment, which relied on well-established principles, we have jumped into the co-development of a new type of spin-resolved and spatial-resolved ARPES instrument. Using the combination of our existing knowledge and background, together with the utilization of the latest developments internationally, we have been able to design and build a state-of-the-art spin-ARPES instrument.


What is spin-ARPES?

ARPES (Angle Resolved Photo-Electron Spectroscopy) is a refinement of the photoelectric electric effect for which Einstein received the Nobel Prize. In fact, photoelectron spectroscopy was the topic of other Nobel Prizes since i.e. when Siegbahn demonstrated the application to material characterization.

By measuring the angle of a photoemitted electron, it is possible to extract the initial momentum vector of the electron before emission from a sample. Since we also measure the energy of the electron, this gives access to the spectral function.

Spin-ARPES goes one step further and also allows the spin non-degeneracy of the electronic band structure to be probed.


How did you know what was possible?

Justin was involved in some of the early developments in spin-ARPES and has kept in touch with developments in the field ever since. In the period 2006-2008, Justin was involved in the commissioning of the Swiss spin-ARPES beam line “COPHEE” and is responsible for one of the first paper from this facility [PRL 102:096802 (2019)]. Whilst the early instruments were extremely slow (a typical dataset taking ~24h to collect), and the spatial resolutions were poor, the technique proved its usefulness. This led to a number of interesting prototypes appearing in which the large improvements of the spin-detection efficiency are claimed.

In parallel, we have also been gaining experience with Photo-Emission Electron Microscopy (PEEM): a technique in which the spatial resolution of the method has been dramatically improved, but at the expense of energy, momentum and spin resolutions.

We therefore realized that the time was right to jump into the co-development of a spin-resolved instrument, in which we co-develop a state-of-the-art spin-filter and use it in conduction with the latest developments in ARPES and PEEM instrumentation, such that we can construct an energy, momentum, spin and spatially resolved instrument with unprecedented performance.


How did you get support for this investment?

The financial support for this investment was part of QuSpin’s application to the Research Council of Norway to be granted as a Center of Excellence (SFF). Our strong background in this area was also an important prerequisite. Having worked with different research groups and companies internationally gave us the necessary positioning in the field.


The group

The underlying idea for a spin-resolved instrument, and the original research group was already established prior to the commencement of QuSpin. Associate Professor Simon Cooil played a central role in making the technical drawings and evaluation of the technical feasibility. An earlier version of our versatile preparation chamber, and our variable temperature 5-axis manipulator was designed and built by him during his postdoctoral period.

After the commencement of QuSpin, Ph.D. candidate Frode Strand was hired, and he took a central role in liaising with the external suppliers, figuring out what was technically possible, and dealing with the legalities of the procurement. Ph.D. candidate Håkon Ivarssøn Røst came onboard after these decisions were made and has been more involved in setting it up and using it.

More recently, the group has expanded and all of the group members have been involved in site preparations and the construction, installation and testing of the new equipment. Everyone has contributed a lot of hard work.


People want to show their competence and share it. They want to see it work. It is not like a supplier and customer relationship, but more like a scientific collaboration. – Justin


The procurement process and suppliers

The spin detector which is at the heart of the new instrument could only be constructed by one company; Focus GmbH in Hünstetten, Germany. Focus were also able to supply several other key components (i.e. suitable light sources, PEEM lenses and hemispherical electron analysers), but not able to meet all of our demands. The additional components (vacuum system, sample manipulator, liquid helium cryostat,  water  and gas manifolds, etc) were supplied in a partnership with Scienta-Omicron in Uppsala, Sweden. The sample transfer system, preparation chamber, sample characterization components were acquired from a wide range of suppliers (UHV-design, LewVac, OCI, Argon Services, and others), and we also utilized many refurbished components and in-house fabrication from NTNU’s mechanical workshop. Co-ordinating this project with many suppliers and non- standard components has been challenging, but has ultimately worked extremely smoothly.

Contrary to the case of a standard purchase, this was a shared risk between us and the various suppliers. However, all parties also share an interest in seeing this instrument completed and performing to a high standard, and in it becoming a flagship of its generation. During
the process, the relationship with the suppliers becomes deeper and ultimately they become friends as well as partners.


The timeline

The procurement paperwork took about 16 months to complete. Although this was longer than we originally anticipated, after signing the contracts, the project went much faster. It took under one year from signing the contract for the purchase of the main components until   we had the equipment fully constructed, tested and up  and running. Ultimately, the project was completed on  time and on budget. This was only possible because of the detailed technical planning which we had done in advance.


Developing and sharing knowledge and competence

We believe this solution is in the forefront of the field and in the world. Furthermore, the research environment gains a lot from the competence of understanding, building and implementing this new equipment.


The best guys out there are the best because they learn from the best. - Håkon


This competence is shared by having visitors from all around the world. We already have had visitors from Germany and China, and will soon have visitors from Denmark, UK and USA to collaborate on measurements which can be facilitated with our new instrument. This is typical within our field: the papers we publish are normally the result of a collaborations with others who are experts in complementary fields. You can’t be the expert of everything.


What can you do with this instrument?

We will measure electronic band-structure with very good spatial resolution, energy resolution, momentum resolution and spin resolution. This allows us to measure all kinds of new materials and structures that otherwise would not be possible. A lot of exciting new materials
are coming, and we want to be able to measure their electronic structure even if they are very small or inhomogeneous. In addition, our conjoined custom-made preparation and characterization chamber allows us to grow, clean, dope and otherwise modify a wide range of materials and heterostructures.


Collaboration between theorists and experimentalists at QuSpin?

For example, one main topics within QuSpin is understanding the electrons’ interactions with magnon and phonons. This is something that we are working on together with our theorists.


I took a long time to read, grasp and understand, but in that process you learn a lot more than you think.  - Frode


The individual learning experiences

All of us have put a lot of extra hours into tasks that is not in our job description. However, the bigger picture is that we all gained a lot from this. When something goes wrong with the equipment, we are in a stronger position to fix it because we have been involved in every step of the design, construction and testing. If you buy something “off the shelf” you generally rely on the manufacturer to come and fix it.


All these tasks and experiences leads to a much better base of competence. It is a transferable skill that goes in your tool set for later. It builds both competence and confidence. The willingness to learn and having a leader who is mentoring and letting people dive into the process and testing, are personal qualities crucial in this learning process!