Pulsed Laser Deposition

In a scanning electron microscope (SEM), an electron beam is scanned over the sample surface in a raster pattern while signals from secondary electrons (SE) or Back-scattered electrons (BSE) are recorded by specific electron detectors. The electron beam, typically with an energy ranging from a few hundred eV up to 30 keV, is focused to a spot of about 0.4 nm to 5 nm in diameter. The latest generation of SEMs can achieve a resolution of 0.4 nm at 30 kV and 0.9 nm at 1 kV.

Beyond the ability to image a comparatively large area of the specimen, SEM can be equipped with a variety of analytical techniques for measuring the specimen's composition. Chemical composition analysis can be performed by Energy Dispersive X-ray Spectroscopy (EDS), which relies on generating an X-ray spectrum from the entire scan area of the SEM. An EDS detector mounted in the SEM chamber collects and separates the characteristic X-rays of different elements into an energy spectrum. The EDS system software then analyzes this energy spectrum to determine the abundance of specific elements. EDS can identify the chemical composition of materials down to a spot size and create elemental composition maps over a much broader raster area.

By employing a suitable polarimeter, such as a Mott analyzer, the spin polarization of secondary electrons can be detected, thus revealing the magnetization orientation in a ferromagnetic sample with high spatial resolution. This technique is known as Scanning Electron Microscopy with Polarization Analysis (SEMPA).

Scanning transmission electron microscopy (STEM) can be also performed in a SEM. It provides high-resolution images and detailed information about the composition and structure of samples, making it an essential tool in various scientific fields. STEM Images can be of different types: Bright-Field (BF) images formed by transmitted electrons that pass through the sample without significant scattering; Annular Dark-Field (ADF) images formed by high-angle scattered electrons, providing information about the atomic number distribution in the sample, and; High-Angle Annular Dark-Field (HAADF) images formed by very high-angle scattered electrons, revealing the heaviest elements in the sample with high contrast.

AFM is a surface sensitive technique permitting to obtain a microscopic image of the topography of a material surface. Typical lateral image sizes are within a range of only a few Nanometers to several 10 Micrometers, whereas height changes of less than a Nanometer may be resolved.

A fine tip attached to a cantilever is scanned across the material surface and enables to measure height changes exploiting an optical beam deflection system (a laser that is reflected from the rear side of the cantilever onto a segmented photodiode). The position of a laser spot on the photodiode permits to track height changes as e.g. due to a nano-particle on the surface or an atomic terrace of a single crystal surface. A feedback loop controls the tip-surface distance and therefore ensures stable imaging conditions.

Different operation modes like contact or non-contact mode can be used to optimize the imaging conditions with highest lateral resolution on one hand and least sample interaction on the other hand. Measurements in different environmental conditions (liquid, gas,...) on a broad class of samples (smooth, rough, insulating, conductive, soft, stiff, wet, dry...) can be performed.

Choosing suitable tips and imaging modes, additional surface properties can be mapped together with the topography, with similar spatial resolution, like friction force, magnetization and surface potential, surface charge density and electrical resistance, as well as elastic modulus and adhesion of heterogeneous sample surfaces can be obtained. 

When linearly polarized light is reflected from a magnetic film, its polarization becomes elliptic (Kerr ellipticity) and the polarization principal axis is rotated (Kerr rotation). This rotation is proportional to a component (depending on the geometry of experiment) of the magnetization of the film. For this reason the MOKE magnetometry is a very popular tool for the characterization of the magnetic properties of materials.

Since the laser spot can be focused down to a few microns, the magnetic properties (e.g. coercivity, squareness ratio) of single micrometer or submicrometer structures can be evaluated. With a suitable set-up the sensitivity of the MOKE apparatus can be pushed to detect the signal coming from very thin films (ideally down to the atomic plane) making the technique suitable for the study of magnetic structure of thin films, interfaces and nanostructures.

Note that although this technique can be very sensitive, no quantitative measure of the magnetization is provided. Nevertheless, from the shape of the hysteresis loop, both static and dynamic magnetization reversal processes can be investigated in detail. Longitudinal and polar configurations are used routinely to detect the in-plane or the out-of-plane magnetization components, respectively. This technique is well suited to characterize either flat or micron- and submicron-patterned films.

The facility consists of a magneto-transport equipment for electrical characterization integrated in a cryogen-free measurement system at variable temperature and magnetic fields. It has capabilities for 2-point or 4-point measurements, for Hall effect measurements in the Van der Pauw and Hall bar geometries, as well as I-V and C-V characteristics in DC and AC modes. This allows study of electrical transport (both semiclassical, i.e. conductivity and electric carrier density and mobility, and quantum transport effects in nano- and mesoscopic devices) on material systems such as semiconductor low-D structures (2DEGs, nanowires…), 2D and 1D materials (graphene and graphene-like nanomaterials, nanotubes, transition metal dichalcogenides, ultrathin 2D-oxides…), topological insulators and superconductors.  Additional electrical contacts allow application of gate biases for sample polarization. Electric Transport-Optical measurements in Electro-Optical and Magneto-optical configurations are possible through a tuneable Xenon light source and fibre-optic sample illumination.

Samples are fitted in a 16-pin dual-in-line socket, which can be placed perpendicular or parallel to the magnetic field. All 16 electrical connections can be independently and automatically switched through a matrix switch unit under software control. Samples with a wide range of resistivities can be measured, ranging from diluted 2D electron gases in semiconductors to metals. It is possible to record sweeps of gate voltages and magnetic fields (for, e.g., the observation of Shubnikov–de Haas oscillations / Quantum Hall effect in semiconductor 2D systems), as well as of temperature.