Frozen n-Tetradecane Investigated by Cryo-Atom Probe Tomography

Abstract

Atom probe tomography (APT) has been established in the microscopic chemical and spatial analysis of metallic or semiconductors nanostructures. In recent years, and especially with the development of a transfer shuttle system and adapted preparation protocols, the field of frozen liquids has been opened up. Still, very limited knowledge is available about the evaporation and fragmentation behavior of frozen liquids in APT. In this work, efforts were made to extend the method toward organic and biological soft matter, which are mostly built from hydrocarbon chains, the evaporation and fragmentation behavior of simple alkane chains (n-tetradecanes). Tetradecane shows a very complex evaporation behavior whereby peaks of C1–C15 can be observed. Based on multihit events and the representation of these in correlation plots, more detailed information about the evaporation behavior and the decay of molecules into smaller fragments in the region near the tip can be studied. A variety of different dissociation tracks of larger molecules in their excited state and their subsequent decay in low-field regions, on the way to the detector, could be observed and the dissociation zone in the low-field region was calculated.

Nanoscale analysis of frozen honey by atom probe tomography

“…In general, the mechanism of field evaporation for organic species is more complex than for metals, leading to molecular fragments of C x H y /C x O y H z groups instead of single atoms. In our various APT experiments with soft matter and liquids and related DFT-based calculations 20 , 21 , 43 , 44 , 53 , we gathered increasing evidence that the field strength during the continuous field desorption is the decisive factor which in turn is mostly affected by the bonding strength of the matrix materials. For example, alkane chains strongly bonded by a thiol group to a metallic substrate evaporate in rather small hydrocarbons with one or two carbon atoms.…”

“…These measurements revealed that organic materials evaporate very differently from metals or semiconducting materials. Instead of individual atoms, the organic material evaporates in larger fragments or even as complete molecules, depending on the measurement conditions 21 . This evaporation behavior complicates peak identification due to mass peak overlap and leads to ambiguity in peak identification.…”

“…With the newly available cryo-transfer systems 33 – 36 it is now possible to transfer the samples between different instruments, which provides access to liquid specimens and opens a new era in APT. Since this development, several measurements of frozen liquids were reported 21 , 37 – 44 . This may enable the analysis of large volumes of frozen liquids, providing statistically reliable information on the evaporation and fragmentation behavior of liquids.…”

Atom Probe Study of 1-Octadecanethiol Self-Assembled Monolayers on Platinum (111) and (200) Surfaces

“…Loosely bound molecules, such as physiosorbed thiols or noncross-linked polymers can be expected to result in large ions, since they are easily removed from the surface and may only dissociate further during acceleration to the detector. In the extreme case, stable molecules (strong covalent intra-molecule bonds) but only weakly bonded to their environment can lead to the detection of the integer molecule unit as shown in the examples of physisorbed organic small molecules (Proudian et al, 2019) or, even more remarkably in direct comparison to the aliphatic SAM molecules, the field-desorption of complete tetradecane chains out of van der Waals bonded frozen liquid (Meng et al, 2021), In the case of a well-formed SAM on Pt, the molecules are however strongly bound via the S-Pt bond to the tip, therefore the chain cannot be easily evaporated as a whole unit and require in comparison higher fields for evaporation. SAMs are dielectrics and thus result in a shielding of the electric field.…”

Understanding the Underlying Field Evaporation Mechanism of Pure Water Tips in High Electrical Fields

“…More recently, and especially with overcoming the limitation by developing transfer shuttles, , “soft matter” and frozen liquids in general have become accessible for APT and may pioneer a new generation. However, only a few publications are available for aqueous solutions. − In previous work, some of us have demonstrated that it is generally possible to measure pure water and identify and localize dissolved biomolecules (glucose) in a water solvent . Nevertheless, the evaporation process and fragmentation behavior of organic matter or frozen liquids are still unknown and encourage further progress to better understand the underlying processes in high electrical fields. ,− …”