Cryo-EM, which earned the Nobel Prize in Chemistry in 2017, revolutionized imaging by introducing methods to prepare and observe samples in a "frozen" but native state. This is especially useful for studying organic and delicate materials, as it prevents structural damage that can occur with conventional imaging techniques. The cryogenic preparation process typically involves plunge-freezing, where samples are rapidly cooled by direct contact with cryogens like liquid nitrogen or liquid ethane, or by placing samples in a temperature-controlled stage. The rapid cooling rate prevents ice crystallization, locking the water molecules in an amorphous solid phase that preserves fragile organic structures.
The adoption of cryo-preparation protocols into APT has enabled researchers to analyze both soft matter and other temperature-sensitive materials, thus overcoming the stringent requirements typically needed for APT sample preparation. Cryo-APT is now emerging as a novel technique with the potential to bridge research areas across different scientific fields by enabling the analysis of materials that were previously challenging to study at atomic resolutions under standard APT conditions.
The workflow for cryogenic atom probe tomography (cryo-APT) can be divided based on whether focused ion beam (FIB) milling is required for sample preparation. Each approach has specific adaptations to maintain cryogenic conditions and sample integrity for atom probe analysis.
For samples that do not need FIB preparation—such as pre-sharpened metallic samples—pre-shaped tips are directly subjected to treatments (e.g., corrosion, heat, chemical reactions, or gas adsorption). Following these treatments, the samples are plunge-frozen, cryo-transferred, and analyzed with APT.
For improved handling, samples can be processed in a glovebox environment to minimize exposure to moisture, which can lead to ice condensation that blunts the tip necessary for precise APT imaging. The glovebox can control humidity, pressure, and cooling, and it connects directly to the cryo-transfer suitcase to maintain cryogenic temperatures during transfer.
An alternative method involves encapsulating nanoscale samples in graphene on pre-sharpened tips, which can prevent water sublimation during transfer and preparation.
For complex samples requiring site-specific preparation (e.g., biological samples), cryo-FIB techniques are essential. Cryo-FIB setups often involve a modified FIB stage with a “cold finger” to maintain cryogenic conditions. The main challenge is securely attaching “lift-out” samples to manipulators and supporting stages, as conventional gas injection systems are impractical at cryogenic temperatures.
A solution developed by Schreiber et al. uses by-products from ion milling as a bonding material, creating “nano-welds” for attaching samples to manipulators and sample stages without the need for external adhesives. Illustrations of this approach show attachment techniques for cryo-manipulation and lift-out samples.
A recent advancement in plasma FIB (PFIB) technology eliminates the need for the complex lift-out process by directly milling around a region of interest to form a tip-shaped sample ready for APT analysis. PFIB’s high milling efficiency enables precise shaping of nano-porous materials, such as nano-porous gold (NPG) with D₂O ice, directly into APT-ready samples.
Cold-Chain Maintenance: In both workflows, a continuous “cold-chain” is crucial to keep samples at cryogenic temperatures from initial treatment through APT analysis. Samples are either transferred in a cryogenic vacuum suitcase or, where this is not feasible, undergo in-situ sublimation of ice within the APT vacuum chamber before analysis.
These advancements are enabling a broad range of materials to be prepared and analyzed with cryo-APT, extending its applications beyond traditional boundaries and opening up new possibilities for delicate and temperature-sensitive samples.
High-temperature materials designed to function effectively at temperatures exceeding 300°C (932°F) without significant degradation are of critical for industries that demand durability under extreme conditions. Key properties such as thermal stability, oxidation resistance, and creep resistance define their performance at elevated temperatures. Thermal stability allows these materials to maintain their structural integrity, while oxidation resistance helps them avoid surface deterioration in oxygen-rich environments. Creep resistance ensures that they can withstand prolonged mechanical stress without deforming, which is crucial for components like turbine blades in jet engines. Additionally, refractory materials, a subset of high-temperature materials, offer exceptional heat and wear resistance, making them suitable for use in furnaces and kilns. The performance of these materials is governed by principles such as phase stability, diffusion mechanisms, and thermal expansion, all of which help engineers design materials that can endure extreme thermal and mechanical demands.
Cobalt based Superalloys
Development of low density Cobalt based superalloys for gas turbine engines Influence of microstructure and chemistry on mechanical properties Determination of the structure and chemistry across gamma /gamma’ interfaces at atomistic length scales Studying the partitioning of alloying elements along gamma /gamma’ interfaces. Understanding chemical and structural width of gamma/gamma’ interfaces 3D characterization of the morphology and composition of nanoscale gamma’ precipitates by coupling TEM tomography with 3D atom probe Determination of the lattice parameters of gamma and gamma’ phases as well as the site occupancies of different alloying elements in g’ experimental characterization coupled with atomistic modeling
Aluminum based Superalloys
Development of coarsening resistant Al-alloys for temperatures > 200 °C.
Stabilizing the nanoprecipitates for creep resistance above 200 °C
3D characterization of the morphology and composition of nanoscale gamma’ precipitates by coupling TEM tomography with 3D atom probe