Norcada (Canada)

In liquid cell (LC) annular dark-field scanning transmission electron microscopy (ADF-STEM), the spatial resolution is limited by the low ratio of signals from samples to background signals from the silicon nitride window membranes and liquid. We report the development of a double-tilt LC holder for atomic-resolution LC-ADF-STEM imaging of single-crystal samples under zone-axis incidence conditions. A SrTiO3 <001> lamellar sample, approximately 100 nm thick, was prepared using the focused ion beam technique and transferred onto a silicon nitride window membrane of an LC chip via a glass probe pick-up method in air, which avoids Ga ion beam-induced damage to the window membrane. The sample adhered to the high-flatness window membrane and remained immobile, even when embedded in a water droplet. The sample and pure water were enclosed in an LC and observed under <001> zone-axis incidence conditions using aberration-corrected ADF-STEM. Electron channeling along the atomic columns enabled atomic-resolution LC-ADF-STEM imaging with high contrast, sufficiently overcoming background signals from window membranes and liquids. This high-contrast imaging technique could lower the probe current and is expected to mitigate electron-beam-induced radiolysis and minimize undesired sample damage, particularly under high-magnification imaging conditions.

Al-33wt%Cu eutectic droplets were rapidly solidified using Impulse Atomization, a drop tube technique. The samples were then processed in situ in an SEM using an HTN-0101 MEMS heating chip manufactured by Norcada. The temperature of the chip, as well as the heating and cooling rates, can be easily set using the chip’s control software, allowing for heating and cooling rates as fast as 1000°C/second. The droplets were heated above the eutectic melting temperature. Thanks to the oxide skin, the droplets retained their spherical shape, which allowed in situ solidification experiments. The live feed of the surface of the droplet obtained with the SEM was recorded during the experiments alongside the temperature-time profile. Various cooling rates were imposed and the liquid samples were shown to undercool prior to solidification. The resulting eutectic morphologies and spacings were then analyzed as a function of the cooling rates and undercoolings.

Under rapid solidification conditions, Al-33wt%Cu eutectic droplets develop a microstructure composed of two different eutectic morphologies: an undulated eutectic, assumed to grow during recalescence, followed by a lamellar eutectic growing post recalescence. In situ heat treatments are applied to Al-33wt%Cu droplets rapidly solidified using impulse atomization to investigate the dynamic effect of temperature and time on the two eutectic morphologies. The samples are aged in situ in an SEM using a heating stage developed by Norcada. The undulated region coarsens faster than the regular eutectic, with fine lamellae still visible at 500 °C. At 525 °C, and both regions are indistinguishable from each other. At 550 °C, the droplet is fully liquid, but retains its spherical shape due to the oxide skin. This technique enables observation and quantification of in situ aging, coarsening and solidification experiments.KeywordsAl–Cu eutecticIn situ processingCoarsening

Solid-state nanopores are powerful tools for sensing of single biomolecules in solution. Fabrication of solid-state nanopores is still challenging, however; in particular, new methods are needed to facilitate the integration of pores with larger nanofluidic and electronic device architectures. We have developed the tip-controlled local breakdown (TCLB) approach, in which an atomic force microscope (AFM) tip is brought into contact with a silicon nitride membrane that is placed onto an electrolyte reservoir. The application of a voltage bias at the AFM tip induces a dielectric breakdown that leads to the formation of a nanopore at the tip position. In this work, we report on the details of the apparatus used to fabricate nanopores using the TCLB method, and we demonstrate the formation of nanopores with smaller, more controlled diameters using a current limiting circuit that zeroes the voltage upon pore formation. Additionally, we demonstrate the capability of TCLB to fabricate pores aligned to embedded topographical features on the membranes.