In-house synthesis and characterisation methods
Advances in materials synthesis and characterisation go hand in hand with a better understanding of fundamental physical processes as well as the discovery of new phenomena. Our division has unique expertise in both synthesis and characterisation of complex material systems. Our own labs complement larger infrastructures such as the Tandem Laboratory for ion-beam based methods and Super ADAM and other facilities for neutron scattering. We are also involved in common facilities at the Ångström Laboratory, such as Myfab, AM@Å and the X-ray laboratory.
Here you can find an overview of the set-ups situated in our own labs:
The synthesis of new materials is central to our research in order to be in control in all parts of the Materials research spiral (see figure on the right).
We use two techniques called magnetron sputter deposition and molecular beam epitaxy (MBE) to fabricate thin films, layers with thicknesses on the nanometre scale, of crystalline or amorphous materials. These thin films often have physical properties which differ significantly from those of thick bulk materials.
Layers of different materials can be deposited with thickness control down to a single layer of atoms. By simultaneous deposition of different materials from several sources we can produce alloys and phases that do not exist naturally. For sputter deposition it is also possible to admit a reactive gas into the sputtering chamber to produce compounds such as oxides or nitrides. These deposition processes are extremely versatile allowing us to tailor our samples to our research questions.
The Materials Design Spiral visualises the several steps and iterations necessary to develop new materials. The advanced synthesis and characterisation methods in our lab allow us to control this process from start to finish.
Example for the creation of magnetic nanopatterns by ion implantation through a mask. Adapted from https://doi.org/10.1063/5.0239106.
In addition to using samples with thicknesses on the nanoscale, it is also possible to create lateral nanostructures. These structures can be topographic or distinguished by a different chemical composition.
In our division we use electron beam lithography at Myfab to create (topographic) nanostructure arrays over extended areas. Different shapes and sizes of individual structures (often called islands) and the pattern in which they are arranged are possible. We study how the structure connects to materials properties, for example magnetic behaviour.
Energetic ions can be used to remove material (“sputtering”) and for example create pores or etchable tracks in membranes. This way nanopatterned graphene can be fabricated. By irradiating a material through a patterned mask, we can also selectively implant ions and create structures with different chemical composition creating for example magnetic nanoarrays.
Self-assembly is the spontaneous formation of structures on all length scales. Examples range from atoms forming galaxies containing millions of stars to cells growing into highly complex biological structures. The crucial parameter controlling self-assembly is the specific interaction between building blocks.
Self-assembly on intermediate length scales, tens of nanometres up to millimetres, allows to develop materials with new properties interesting for many applications. The most relevant interactions between building blocks for our research are van der Waals forces, hydrophobic, and magnetic and electrostatic interactions. The first two in particular are comparable to thermal excitations at room temperature, which might cause chemical bonds to break and reform resulting, for example in phase transitions.
In our group, we focus on fundamental understanding of self-assembly of colloids as well as viscoelastic properties. We study the first one by tuning magnetic and electrostatic interactions between nano- and micrometre sized particles. This way we control the self-assembly process and design materials in a bottom-up approach. We also drive self-assembled systems out of equilibrium and study the response. By combing stress-strain measurements with scattering methods we try to understand how elastic and flow properties of materials are related to the structure of the building blocks down to atomic length scales.
Self-assembled layers can for example convert a surface from a hydrophilic to a hydrophobic interface. The image shows a contact angle measurement of a droplet of water on a silicon wafer, which was coated with a self-assembled monolayer of a molecule called octadecyltrichlorosilane to turn it hydrophobic.
Our set-up for measuring pair distribution function of thin films. The coin in the centre visualises the size of the square sample next to it. The sample is held by air suction to avoid additional scattering from the sample holder.
Information about crystal structure (or lack thereof), layering and interfaces can be obtained through X-ray scattering experiments in a range of different scattering geometries. X-ray diffraction is the standard method for determination of crystal structure. We also have instrumentation for X-ray reflectometry to measure the thickness of thin films. For amorphous thin films, the pair distribution function is used to quantify the distance between atoms in a sample. Our division has developed a new lab-based instrument for measuring these pair distribution functions.
We also develop and maintain several publicly available software packages for data processing and analysis of X-ray, neutron and ion scattering data.
To characterise magnetic materials, we often study how they behave in an externally applied magnetic field. We measure for instance hysteresis loops and image magnetic domain. In our labs, we typically make use of the magneto-optical Kerr effect (MOKE) for such measurements. MOKE measures changes in polarized light, reflected from a sample, which can be done with tabletop-sized equipment. Because we study very different magnetic materials, we have a range of different set-ups operating in different magnetic field orientations as well as temperature ranges.
This polar MOKE instrument measures the out-of-plane, that is perpendicular to the sample surface, hysteresis. With its high magnetic field strength up to 2.1 T, the set-up is optimised for the study of magnetic materials with magnetization pointing perpendicular to the sample plane.
We have two longitudinal MOKE set-ups that can measure in-plane hysteresis curves, namely magnetisation parallel to the sample surface. The pictured instrument operates at room temperature at magnetic field strengths up to 600 mT. It is also equipped with a rotation stage allowing for automated measurements in several geometries. The second longitudinal MOKE is combined with a cryostat and a heater and samples can be studied at temperatures between 10 K and 400 K and magnetic field strengths up to 270 mT.
For investigations of, among others, magnetic phase transitions, a set-up with extremely low background field is used. Here, we can measure the AC susceptibility with and without applied field as well as hysteresis loops up to 5 mT at different temperatures at and below room temperature. The high sensitivity allows for studies of even just a few monolayers of magnetic material.
A Kerr microscope turns the MOKE signal into an image. This way, we can distinguish between different directions of the magnetisation and see magnetic domains with sizes between just 300 nanometres up to a few millimetres. Our Kerr microscope can also be combined with a cryostat to perform measurements in a temperature range between 10 K and 300 K.
With this system, an excitation magnetic field is applied as a short pulse. The behaviour of a magnetic material can then be studied in a time-resolved manner during 60 nanoseconds. The time resolution of the system is 0.3 nanoseconds. Since the system is equipped with a quadrupole magnet, it is possible to apply an external magnetic field in any in-plane direction. This set-up can be used to study very non-homogenous thin films, as the dynamics are measured locally in a spot with a diameter of 5 micrometres.
Atomic force microscopy where a sharp tip is scanned across a surface provides unique information about surface features on the nanometre scale. In our lab, we have an atomic force microscope to measure surface topography, from continuous and patterned surfaces to nanoparticles. Special tips coated in magnetic material are used for magnetic force microscopy to image nanoscale magnetic domains.
Our goal is to conduct advanced materials research leading to physics understanding of the whole life cycle of materials – from synthesis to recycling. One of the approaches we take to reach this goal are in-situ measurements, which do not take synthesis and characterisation as two separate steps as shown in the Materials research spiral but aim to characterise a sample during a specific process. In practice this can mean, that we keep a sample in the same controlled environment (for example a high vacuum) for synthesis and characterisation or that we expose it to a stimulus (for example temperature or gas pressure) and analyse induced changes at the same time.
In our specialised in-house set-up, samples can be exposed to a controlled hydrogen pressure during measurements. Crystallographic changes (rearrangements, phase transitions) can be followed in-situ at different selected pressures and a wide interval of temperatures during hydrogen uptake, even for nano-sized layers (> 50 Å), by measuring optical conductivity as well as resistivity.
Many characterisation techniques we are using can be combined with in-situ approaches. Ion beam analysis at the Tandem Laboratory can monitor depth resolved composition changes when a sample is exposed to elevated temperatures and/or different gases. Neutron scattering at Super Adam can be performed in a range of different environments, for example applied magnetic fields, a wide range of temperatures or at different gas pressures.
Our division is also one of the scientific leads of the LigHt project, which is a new multi-instrument platform for materials science with a specific focus on light-element characterisation and in-situ and in-operando experiments.
Contact
- Programme Professor
- Daniel Primetzhofer
- Head of Division
- Gabriella Andersson
- Visiting address: Ångström Laboratory, Regementsvägen 10, Uppsala, House 4, floor 1 and House 6, floor 1.