X-Ray Diffraction

Atomic Layer Deposition (ALD) is similar to CVD except that the ALD reaction occurs at lower temperature and it is broken into two half-reactions, keeping the precursor materials separated during the reaction. The separation of the precursors is important to achieve a self-limiting surface reaction to enable precise thickness control and ensure uniform coatings and compactness even in complicated 3D structures.

The present implementation of the technique is suitable for mm to cm-size samples as those typically studied by spectroscopy and microscopy.

ALD has a rich history in microelectronics. It is studied as a potential technique to deposit high-k (high permittivity) gate oxides, high-k memory capacitor dielectrics, ferroelectrics, and metals and nitrides for electrodes and interconnects.

The number of materials that can be prepared by ALD has tremendously increased in the past decade. Notably, it can deposit a wider variety of materials, including important functional oxides like Al₂O₃, MoO₃, SiO₂ and HfO₂.

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.

Transmission Electron Microscopes (TEM) and Scanning Transmission Electron Microscopes (STEM)  are designed for high-resolution imaging and analysis.
In both cases, high energy electrons, incident on ultra-thin samples called TEM lamella (typically <100nm), travel through the specimen.
Depending on the density, crystallinity, orientation, etc. of the material present, electrons are scattered differently, giving rise to an image of the sample with different contrast features according to specimen properties and to the microscope setup.
Usually, the magnified image of the sample is focused on a CCD or CMOS camera. On the same system is also possible to acquire the electron diffraction produced by a specific area of the sample.

Modern TEM are equipped with a Cold Field Emission Gun (FEG) or with a Schottky FEG, making them suitable for materials science, nanotechnology, and various fields requiring detailed structural and compositional analysis in a local nanoscale. Indeed, point resolution below 0.3 nm at 200kV in TEM mode can be reached, according to the
instrument configuration.

In the STEM mode, electrons pass through the specimen, but, the electron optics focus the beam into a narrow spot which is scanned over the sample in a raster. The rastering of the beam across the sample makes these microscopes suitable for analysis techniques.

According to the specific configuration (see details and the specific availability below, referred to each instrument and facility), the microscope can be equipped with a selection of multiple detectors enabling different techniques, such as Energy-Dispersive x-ray Spectroscopy analysis (EDS), electron energy loss spectroscopy (EELS), STEM detectors in bright field (BF), annular bright field (ABF), annular dark field (ADF) for diffraction contrast, high-angle annular dark field (HAADF) for Z-contrast.

EELS/EDS system control software enables point-by-point signal acquisitions, for the analysis of spectra and maps.
Sample preparation (see details and the specific availability below, referred to each instrument and facility) is a crucial part in TEM experiments.

High quality TEM specimens have a thickness that is comparable to the mean free path of the electrons that travel through the samples, which may be only a few tens of nanometres. Preparation of TEM specimens is specific to the material under analysis and the desired information to obtain from the specimen. Sample preparation laboratories are equipped with the basic tools (diamond saw, polisher, dimpler, ultrasonic cutter, precision ion polishing system, plasma cleaner) commonly used in conventional thinning procedures.

X-ray Reflectivity (XRR) is a grazing incidence X-ray elastic scattering technique sensitive to surface electron densities. In the X-ray range, the index of refraction is slightly less than one and indeed, as a surface is illuminated with a collimated X-ray beam, total external reflection occurs up to the critical angle, which depends on the wavelength of the X-ray beam and the electron density of the material.

Above the critical angle, the intensity of the reflected X-ray beam decreases exponentially with increasing the incidence angle. The intensity of the beam entering the material likewise increases with the incidence angle and decreases with depth according to the Beer-Lambert law. If the beam crosses interfaces between materials having different electron densities, interference effects are detected that modulate the overall reflected intensity and produce oscillations known as Kiessig fringes. The thickness of the various layers impact on the periodicity of these fringes while surface/interface roughness reduces the overall reflected intensity.