Cryogenic Focused Ion Beam (Cryo-FIB)
Cryogenic Focused Ion-Beam (Cryo-FIB) microscopy is an upgraded version of the Cryogenic Scanning Electron Microscope (Cryo-SEM) technique where the electron microscope is able to produce 3D images of the cryogenic sample rather than the 2D images provided by normal SEM’s. Samples with inherent electron transparency can be rapidly frozen (vitrified) in amorphous ice and imaged directly on a cryogenic transmission electron microscopy (Cryo-TEM), but this is not valid for material systems, which can be layered structures, embedded architectures, or contained within device.
In this method, a tightly focused (5–10 nm) beam of ions, typically from a gallium ion source, hits the sample surface similar to the beam of electrons in conventional SEM. With the interaction of the sample and ion beam, secondary electrons are generated which forms an image and a large mass of gallium ion behaves as a tool for selectively removing material from the specimen resulting in a thin section of the specimen. An FIB which physically bombards the sample results in a lot of heat generation during the milling which can cause damage to sensitive materials and to avoid the same, Cryogenic Focused Ion Beam (Cryo-FIB) is used. This technique also uses the same FIB principle but with a sample stage that can be controlled at cryogenic temperatures. It is performed using dual-beam FIB/SEM that allows simultaneously processing and monitoring the sample.
Cryogenic Focused Ion Beam (Cryo-FIB) involves two types of electron microscopes; scanning electron microscopy (SEM) to understand the subsurface layers and transmission electron microscopy (TEM) for investigating thin electron transparent lamellae for high-resolution tomography. The third method combines scanning electron microscopy (SEM) with a focused ion beam (FIB) to form a Cryo-FIB-SEM. The electron beam produced by SEM scans the surface of samples whereas the ion beam mills into the surface to depict the core of the sample.
The accelerated and focused electron beam (primary electrons) provided by SEM scans across the surface are elastically and inelastically scattered due to the impact on the sample’s atom. As an outcome, few primary electrons escape from the lower surface, developing into a backscattered electron (BSE) which carries information on the density, atomic weight, and crystallographic orientation of the sample. The secondary electrons (<50 eV) can be produced from the collision connecting the between incoming electrons and the loosely bonded outermost electrons (K shell). Detectors are used to collect these interactions to visualize the sample’s surface morphological and topographical information.
MaTestLab offers this test to clients in the USA and across the world, utilizing its large testing laboratory network.
Common Uses of Cryogenic Focused Ion Beam (Cryo-FIB)
(1) Determination of the 3D structures of biomacromolecules Surface, porosity, and structural analysis of nanoparticles, biological species, and soft matter materials (2) semiconductor failure analysis and solid-state physics (3) It is an efficient tool for preparing TEM specimens for highly sensitive crystalline materials (4) Revealing complex unknown local structures at an atomic resolution.
Advantages of Cryogenic Focused Ion Beam (Cryo-FIB)
(1) Automation, 3D microscopic visualization, extended run time, and Cryo-lift-out lamella process (2) FIB imaging and milling with 5nm resolution at 30 kV (3) Minimizes the structural damage caused during the ion beam milling process (4) Reduces the contamination of the sample and hinders light element migration (5) A large area and high-quality sample can be produced with desired orientation from a bulk crystal (6) Allow the examination of hydrated samples and also control radiation damage to frozen samples at room temperature (7) Can observe a contrast between nucleic acids, proteins, and lipids to be distinguished (8) Good preservation of biological structures inside the vacuum chamber.
Limitations of Cryogenic Focused Ion Beam (Cryo-FIB)
(1) Very low signal-to-noise ratio (2) Difficult to measure images from tilted samples (3) The sample temperature should be below 135 degrees Celsius in Cryo-EM (4) More time-consuming to generate samples unless there is a good protocol and good samples.
Industrial Applications of Cryogenic Focused Ion Beam (Cryo-FIB-SEM)
(1) For processing and characterizing sensitive battery materials, used to characterize lithium dendrites with frozen liquid electrolyte (2) Preparation of perovskite-based solar cells for atom probe tomography (3) Used in the semiconductor industry for fabrication, modification, and ablation of chips and devices (4) Avoids undesired hydrogen pick-up and formation of hydride in Ti alloys preparation.
