Methods in laboratory of el. microscopy


SEM-Quanta , SEM-Fera , TEM-Tecnai , TEM-Jeol – are microscopes which is available in the LEM.

ACOM – Automated Crystal Orientation Mapping (TEM-Tecnai)
ACOM is based on electron diffraction using a quasi-parallel nanobeam to scan a selected region of interest. It is used for nanometer resolution mapping of (1) phase distribution in the sample (combined with EDS to determine chemical composition), (2) crystallographic orientation, and (3) stress distribution in a single-phase sample.

BF / DF – Bright-Field / Dark-Field Imaging (TEM-Tecnai, TEM-Jeol)
BF/DF is a basic method of imaging crystalline materials in TEM based on diffraction contrast. By using an objective aperture, which selects only one electron beam for imaging, it strongly enhances the image contrast (BF). Using directed sample tilting, precipitates in the matrix can be highlighted or dislocations/defects in the material structure can be studied.

EBIC – Electron Beam Induced Current (SEM-Fera)
EBIC is a method in which an electron beam induces a current in the sample that can be used as a signal to create images describing the electrical characteristics of the sample, e.g. areas of PN transitions in the sample, presence of local defects, contaminations, inhomogeneity of impurities, or to investigate properties of minority charge carriers.

EBSD – Electron Back-Scatter Diffraction (SEM-Quanta, SEM-Fera)
EBSD uses diffraction of back-scattered electrons in the form of Kikuchi lines to obtain information about the structure of the sample. It is used in SEM to study phase composition, crystallographic orientation or stress in materials. For example, the phase composition and preferred orientation of crystals in 3D-printed samples of metallic materials can be studied.

ED – Electron Diffraction (TEM-Tecnai, TEM-Jeol)
ED is used to differentiate phases with different atomic structures, e.g. graphite (C - hexagonal system) and diamond (C - cubic system). Three basic types of electron diffraction are distinguished: (1) spot diffraction patterns for single crystal samples, (2) ring diffraction patterns for powder samples, and (3) diffraction halo for amorphous samples. To determine the unknown structure, a 3D ED technique is used in which the sample is sequentially tilted while the ED patterns are recorded.

EDX ( EDS ) – Energy Dispersive X-ray Spectroscopy (SEM-Quanta, SEM-Fera, TEM-Tecnai)
EDS is a method for determining the chemical composition of a sample that is used in both SEM and S/TEM. It allows for the detection of elements from B upwards with a detection limit of 0.x-0.0x wt% from regions of about a micrometre (in the case of SEM) and about a nanometer (in the case of S/TEM). Elemental maps can be generated in SEM and STEM, and in combination with SEM/FIB, the surface of the sample can be sequentially removed by ions to obtain 3D elemental maps.

EELS – Electron Energy Loss Spectrometry (TEM-Tecnai)
EELS is a method for determining the chemical composition of a sample that is used in S/TEM. It complements and extends the information obtained by EDS. It allows for the detection of light elements (H, He, Li) and is particularly useful in case of overlapping signals in EDS (e.g. Ti and N). Furthermore, it is possible to distinguish the same element in different structural modifications or with different valence. Elemental maps can also be created in STEM.

EFTEM – Energy Filtered Transmission Electron Microscopy (TEM-Tecnai)
EFTEM is used to display the distribution of elements in the sample. It is based on an EEL spectrum from which a selected signal (energy region) can be filtered out using a slit. In EFTEM, a broad parallel beam is used and the image is formed instantaneously, unlike in STEM/EELS where a convergent beam is used and the region of interest is scanned sequentially. However, at higher electron energy losses, the signal is often too weak for EFTEM.

FIB – Focused Ion Beam (SEM-Quanta, SEM-Fera)
FIB is very often used in combination with SEM (however, there are also single-beam instruments available using only FIB). FIB is used for: (1) sequential removal of sample surface in 3D methods (imaging, EBSD, EDS, EBIC), (2) creating cross-sections, (3) nano-machining - e.g. preparation of nanopillars, and (4) preparation of TEM lamellas. There are two types of FIB: (1) Liquid Metal Ion Source (LMIS) - more suitable for fine work, and (2) Plasma - more suitable for the removal of large  volumes while reducing the contamination.

HAADF – High Angle Annular Dark Field (TEM-Tecnai)
HAADF is used in STEM mode to detect electrons scattered to high angles. This is incoherent scattering on the atoms of the sample, which shows a dependence on the square of the atomic number. Therefore, elements with higher atomic number scatter at higher angles. Thus, it is easy to distinguish the parts of the sample with light elements from the parts with heavy elements, e.g. Pd catalyst particles on Al2O3 support. In state-of-the-art microscopes, it is possible to focus the beam below the size of an atom and therefore "map" individual atoms directly.

HRTEM – High Resolution Transmission Electron Microscopy (TEM-Tecnai)
HRTEM is an imaging method in the TEM using a wide parallel beam. The image is formed by interference of multiple diffracted beams. When the crystal sample is properly aligned (the atoms are aligned in columns parallel to the incident electron beam), the result is a periodic image with atomic resolution. The HRTEM has applications, for exmaple, in the study of dislocations/defects in the structure, imaging of twin lamellae or the study of thin films.

LTEM – Lorentz Transmission Electron Microscopy (TEM-Tecnai)
LTEM is used to observe magnetic domain structures. The trajectories of electrons flying through the sample region with magnetic induction are deflected by the Lorentz force. To visualize the domains, we mostly use the defocusing (Fresnel) method. Thus, if we focus on a plane close below or above the sample, light and dark fringes corresponding to the boundaries of the individual domains appear in the image due to the phase shift of the individual rays.

SEM – Scanning Electron Microscopy (SEM-Quanta, SEM-Fera)
SEM studies the surface of samples by scanning a focused electron beam. Electrons interact with the sample and a large number of types of signal are produced. The basic types of imaging are (1) in secondary electrons (SE), which are sensitive to the surface morphology, and (2) in backscattered electrons (BSE), which show contrast due to the average atomic number. In addition, techniques for determining chemical composition (EDS) and detecting crystallographic orientation (EBSD) are used in SEM. In materials science, coupling with FIB is often used due to extending the 2D analysis into 3D by sequentially removing the sample surface.

STEM – Scanning Transmission Electron Microscopy (TEM-Tecnai)
The image in STEM is created by scanning a focused beam over a thin sample (transparent to electrons) and detecting the transmitted electrons (BF, ADF, HAADF). In state-of-the-art microscopes, it is possible to focus the beam below the size of an atom and therefore directly "map" individual atoms. In our lab, STEM is mainly used for chemical composition mapping by EDS and EELS and imaging by HAADF.

TEM – Transmission Electron Microscopy (TEM-Tecnai, TEM-Jeol)
TEM studies thin samples with the electron beam that passes through the sample. The electrons interact with the sample and a large number of types of signals are produced, which allow for the study of not only the microstructure of samples down to atomic resolution (BF, DF, HRTEM), but also the chemical composition (EDS, EELS) or the crystallographic orientation of individual grains (ED, ACOM).