Nanoscale temperature measurement during temperature controlled in situ TEM using Al plasmon nanothermometry

Electrical, thermal and noise properties of platinum-carbon free-standing nanowires designed as nanoscale resistive thermal devices

Platinum-carbon (PtC) composite nanowires were fabricated using focused electron beam induced deposition and postprocessed, and their performance as a nanoscale resistive thermal device (RTD) was evaluated. Nanowires were free-standing and deposited on a dedicated substrate to eliminate the influence of the substrate itself and of the halo effect on the results. The PtC free-standing nanowires were postprocessed to lower their electrical resistance using electron beam irradiation and thermal annealing using Joule heat both separately and combined. Postprocessed PtC free-standing nanowires were characterized to evaluate their noise figure (NF) and thermal coefficients at the temperature range from 30 K to 80 °C. The thermal sensitivity of RTD was lowered with the reduced resistance but simultaneously the NF improved, especially with electron-beam irradiation. The temperature measurement resolution achievable with the PtC free-standing nanowires was 0.1 K in 1 kHz bandwidth.

In situ pulsed electrical biasing TEM observation of AA7075

Electrically assisted heat treatment is the process of applying an electric current to a sample during heat treatment. Literature has generally shown there to be a difference in the resulting effects of direct current (DC) current and highly transient current (i.e. electropulsing). However, these differences are poorly characterized. In situ transmission electron microscopy (TEM) observation of an AA7075 sample while DC and pulsed current were passed through it was performed herein to explore the effects of an electric current on precipitate development. Numerical simulation results indicate that the thermal response of the samples was very rapid, causing the sample to reach steady-state temperatures almost instantly. There does not appear to be any significant difference between the results of pulsed current application and DC current. Additionally, the failure mechanism of an electrical biasing TEM sample is explored.

Dynamic hetero-metallic bondings visualized by sequential atom imaging

Traditionally, chemistry has been developed to obtain thermodynamically stable and isolable compounds such as molecules and solids by chemical reactions. However, recent developments in computational chemistry have placed increased importance on studying the dynamic assembly and disassembly of atoms and molecules formed in situ. This study directly visualizes the formation and dissociation dynamics of labile dimers and trimers at atomic resolution with elemental identification. The video recordings of many homo- and hetero-metallic dimers are carried out by combining scanning transmission electron microscopy (STEM) with elemental identification based on the Z-contrast principle. Even short-lived molecules with low probability of existence such as AuAg, AgCu, and AuAgCu are directly visualized as a result of identifying moving atoms at low electron doses.

The dynamic assembly and disassembly of atoms and molecules is challenging to characterize in real time, with atomic resolution and elemental identification. Here, the authors report direct observation of more than twenty homo and hetero-metallic compounds, including labile Ag-Cu dimers and Au-Ag-Cu trimers.

A multiscale in situ high temperature high resolution transmission electron microscopy study of ThO2 sintering

Two-grain model systems formed by ThO₂ nanospheres have been used to experimentally study for the first time the initial stage of sintering from room temperature to 1050 °C using high temperature high resolution transmission electron microscopy. In each grain, oriented attachment drove the reorganization and growth of the crystallites up to 300 °C to form a pseudo single crystal. Crystallite size kept growing up to 950 °C. At this temperature, a fast transformation probably corresponding to the elimination of stacking faults or dislocation walls led to the formation of single-crystals. The contact formed at room temperature between the two grains was stabilized during heat treatment by a slight reorientation of the crystallographic planes (T≈ 400 °C), leading the neck to be formed by numerous boundaries between the crystallites. At higher temperatures, the neck evolved and stabilized in the form of a plane of crystallographic orientation mismatch between the grains, which corresponds to the usual definition of the grain boundary. The growth of the neck by the addition of atomic columns was further observed in real time and quantified. At T = 950 °C, the evolution of the microscopic sintering parameter λ was obtained from HT-HRTEM images and indicated that the neck formation mostly proceeded through volume diffusion.

Evaluation and application of a new scintillator-based heat-resistant back-scattered electron detector during heat treatment in the scanning electron microscope

A new high-temperature detector dedicated to the collection of backscattered electrons is used in combination with heating stages up to 1050°C, in high-vacuum and low-vacuum modes in order to evaluate its possibilities through signal-to-noise ration measurements and different applications. Four examples of material transformations occurring at high temperature are herein reported: grain growth during annealing of a rolled platinum foil, recrystallisation of a multiphased alloy, oxidation of a Ni-based alloy and complex phase transformations occurring during the annealing of an Al-Si coated boron steel. The detector could be potentially adapted to any type of SEM and it offers good opportunities to perform high-temperature experiments in various atmospheres.