Electron Microscopy Nest:

Serving as a centralized resource, the Electron Microscopy Nest provides users with access to core principles of Electron Microscopy alongside cutting-edge developments in analysis and characterization techniques within the field 

Electron Microscopy in Materials Science and Engineering

Scanning Electron Microscopy

In basic scanning electron microscopy (SEM), a beam of highly energetic (0.1-50 keV) electrons is focused on a sample surface. This can produce several interactions including the emission of secondary electrons, backscattered electrons, photons, and X-rays; excitation of phonons; and diffraction under specific conditions.

Because the bombarding electron beam is scanned in the X-Y plane, an image for each of these different processes can be mapped with a suitable detector. A detector for secondary electrons, standard to all basic SEMs, records topography of the surface under observation with resolution on the order of 1-2 nm and magnification range from 10x to 500,000x. In addition, information on composition, phase, electrical, optical, thermal, and other properties can be mapped with excellent resolution with appropriate detectors. The basic SEM is probably the most versatile instrument in materials science. Beyond being an isolated instrument, it also represents a platform. When combined with other accessories, the electron microscope can be used to further control manipulation of nanostructures or select an area for observation with high precision. In situ phase transitions can be seen when cryogenic or heating stages are installed in the chamber. The combination with a focused ion beam is used for other applications such as sample preparation for transmission electron microscopy.

Focused-Ion-Beam

The Focused-Ion-Beam (FIB) workstation integrates a dual-beam setup comprising a FIB column and a scanning electron microscope (SEM) column on a single platform. Its functionalities encompass ion milling, metal deposition, ion and electron imaging at both micro and nanoscale levels, particularly applied to advanced photovoltaic materials and devices.

Furthermore, the dual-beam FIB facilitates the integration of other analytical tools such as Transmission Electron Microscopy (TEM) and enables precise, site-specific sample preparation for TEM, SEM, and complementary sample evaluations.

The FIB system also features capabilities for acquiring chemical spectra and elemental maps through energy-dispersive spectroscopy (EDS). Additionally, it enables the generation of three-dimensional chemical reconstructions by combining controlled ion milling with chemical mapping. The system is equipped with a gas injection system (GIS) for platinum metal deposition, which can be employed in conjunction with either ion-beam-assisted or electron-beam-assisted chemical vapor deposition techniques.

Moreover, utilizing a digital patterning generator enables the complete FIB milling or deposition of intricate structures, with parameters supplied by software or directly input via bitmap files.

🔬 Transmission and Scanning Transmission Electron Microscopy (TEM/STEM)

TEM/STEM are essential tools in materials science and biology that utilize a highly focused beam of electrons to analyze the structure, composition, and defects of materials at nanometer and even atomic scales. Both techniques require the sample to be extremely thin, typically less than 200 nm, to allow the electrons to pass through.

1. Transmission Electron Microscopy (TEM)

TEM works by bombarding a sample with a single-energy electron beam. The electrons that pass through are amplified by a sequence of electromagnetic lenses to produce an image or a diffraction pattern.

A. Data Collected in TEM

• Electron Diffraction Patterns: These patterns reveal the crystallographic structure of the material. By analyzing the symmetry and spacing of the spots or rings, scientists can determine the arrangement of atoms.

• Amplitude-Contrast Imaging (e.g., Diffraction Contrast): This imaging mode provides information about the material's microstructure, chemistry, and defects (like grain boundaries and dislocations). Contrast arises from differences in electron scattering due to local variations in density or crystal orientation.

• Phase-Contrast Imaging (HRTEM): High-Resolution TEM (HRTEM) offers detailed information about the microstructure and defects at an atomic scale. This technique can directly visualize the positions of atoms within the crystal lattice.

2. Scanning Transmission Electron Microscopy (STEM)

In STEM, a highly focused electron probe is used to systematically scan across the material. Various signals are collected at each point, allowing for sophisticated mapping and high-contrast imaging.

A. Key STEM Techniques

• Z-Contrast Imaging (HAADF): By collecting transmitted electrons scattered at high angles, STEM generates images where the contrast is strongly dependent on the atomic number (Z) of the elements. Areas containing heavier atoms (higher Z) appear brighter, making this a chemically sensitive, high-resolution imaging technique.

• Compositional Mapping (EDS): An Energy-Dispersive X-ray Spectroscopy (EDS) detector captures the characteristic X-rays generated when the electron beam interacts with the sample. This allows for the creation of high spatial resolution compositional maps, showing the distribution of specific elements.

• Electronic Property Mapping (EELS): An electron energy-loss detector, such as a Gatan Image Filter (GIF), measures the energy lost by the transmitted electrons. This loss is characteristic of the material's compositional and electronic properties (e.g., bonding states), enabling detailed mapping of these features.

Applications

Crystallography

Electron diffraction is used to determine the crystallographic structure of materials on a fine scale.

Microstructure

Diffraction-contrast and high-resolution TEM yields information on the composition, microstructure, and atomic structure of materials and defects. High-resolution STEM Z-contrast imaging provides directly interpretable, chemically sensitive images of the structure of materials, defects, and interfaces in samples with atomic resolution.

Composition

EDS and EELS provide quantitative and qualitative compositional analysis of materials to sub-nm spatial resolution for almost any element. STEM EDS and EELS enable elemental mapping with nm-scale resolution. EELS also provides information on the electronic properties of materials. A GIF enables elemental mapping by energy-filtered TEM with high-spatial resolution.

Cross-sectional Analysis

Investigates the structure, composition, and perfection of multilayer films and interfaces.

The following table is a condensed listing of equipment, techniques, applications, and properties of instrumentation for Transmission/Scanning Transmission Electron Microscopy.