Abstracts:Fitted with a field emission source, aberration-corrected optics and an energy-dispersive X-ray detector of large solid angle, a modern analytical TEM can generate a current density high enough to chemically identify a single metal atom within a fraction of a second, if the atom remains stationary within the electron probe. However, atom motion will occur if the atomic binding energy is too low, the specimen temperature too high, or the electron accelerating voltage above a certain threshold. We discuss such motion in terms of thermal diffusion, beam-induced sputtering and beam-assisted surface migration. Calculations based on a Rutherford-scattering approximation suggest that when atomic displacement is possible, it drastically reduces the analytical signal and signal/noise ratio. For certain elements, electron energy-loss spectroscopy (EELS) provides a higher detectability than energy-dispersive X-ray (EDX) but suffers from the same problem of atomic displacement.

Abstracts:Interlayer electrical transport between two-dimensional atomic crystals can be strongly modulated by the rotational misalignment between them. However, the experimental study on the interlayer electrical transport between rotated two-dimensional atomic crystals with variable rotation angles is challenging. Here, an in-situ scanning electron microscopy method is developed to study the interlayer electrical transport between rotated graphene layers. We employ nanoprobes installed in a scanning electron microscope to function as both “fingers” to induce interlayer rotation of a microfabricated metal-graphite-metal sandwiched island and also electrical probes to measure interlayer electrical resistivity of the rotated graphene layers. Interlayer electrical resistivity of the rotated graphene layers is found to increase monotonically by three orders of magnitude from ∼0.1 to ∼100 Ω cm when the rotational misalignment angle increases from 0° to 30°. This phenomenon can be well described by phonon-mediated electrical transport model. The large-magnitude tunability of interlayer electrical resistivity by mechanical rotation implies the potential applications of rotated graphene layers in nanoelectromechanical systems. Our results also provide a method for studying and tuning interlayer electrical transport between rotated two-dimensional atomic crystals.

Abstracts:Statistical noise, or shot noise, dominates experimental image quality in scanning transmission electron microscopy because efficiencies of recent detectors are close to ideal. We establish a general framework for the statistical noise taking into account two random processes in the electron incidence and the electron scattering. Using this framework, in terms of signal-to-noise ratio, we evaluate several STEM coherent imaging techniques: annular bright field, enhanced annular bright field, differential phase contrast, and ptychography and show that ptychography is the most efficient imaging for weak phase objects. Moreover, we find that normalizing annular-bright-field image by total electron count in the bright field significantly suppress the noise.

Abstracts:Tuning multiple strain and polar states of ferroelectrics by using strain engineering is an essential approach for designing multifunctional electric devices such as multiple state memories. However, integrating multiple strain states is still a challenge, and in addition, revealing such strains and the resultant polar behaviors on the atomic level remains difficult. In this work we prepare PbZr0.52Ti0.48O3/PbTiO3 (PZT/PTO) superlattices on SrRuO3-buffered SrTiO3(001) substrates. Aberration-corrected high angle annular dark field scanning transmission electron microscopy (HAADF-STEM) reveals that the superlattice is coherent in both c (out-of-plane polar direction) and a (in-plane polar direction) domains. We find that the strain states of both PZT and PTO in c and a domains are variant, leading to four special strain states. For example, the tetragonality for PTO in c and a domains is 1.061 and 1.045, respectively. In contrast, PZT in c domains displays a tetragonality as giant as 1.107, which corresponds to 110 µC cm⁻² spontaneous polarization, much larger than the bulk PZT; while PZT in a domains exhibits 1.010 tetragonality with about 70 µC cm⁻² polarization. This study reveals a practical way to integrate multiple strain states and enhanced polarizations in ferroelectric films, which could be used as multifunctional electric elements.

Abstracts:In this paper we present design and application of novel piezoresistive scanning thermal microscopy (SThM) probes. The proposed probe integrates a piezoresistive deflection sensor and thermally active, resistive nanosize tip. Manufacturing technology includes standard silicon MEMS/CMOS processing and sophisticated postprocessing using Focus Ion Beam milling. Authors also describe dedicated measurement technique in order to perform quantitative nanoscale thermal probing. Performance of the developed thermal probes is validated by test scans (topography and temperature distribution) of silicon nanoresistors supplied with current.

Abstracts:In-situ transmission electron microscopy experiments are of great interest to nanoscience and nanotechnology. However, it is known that the electron beam can have a significant impact on the structure of the sample which makes it important to carefully interpret in-situ data. In this work, we studied the thermal stability of CTAB-stabilized gold nanorods under different gaseous environments in an environmental transmission electron microscope and compared the outcome to ex-situ heating experiments. We observed a remarkable influence of the electron beam: While the nanorods were stable under inert conditions when exposed to the electron beam even at 400°C, the same nanorods reshaped at temperatures as low as 100°C under ex-situ conditions. We ascribe the stabilizing effect to the transformation of the CTAB bi-layer into a thin carbon layer under electron beam irradiation, preventing the nanorods from deforming. When exposed to an oxidizing environment in the environmental transmission electron microscope, this carbon layer was gradually removed and the gold atoms became mobile allowing for the deformation of the rod. This work highlights the importance of understanding the phenomena taking place under electron beam irradiation, which can greatly affect in-situ experiments and conclusions drawn from these. It stresses that in-situ electron microscopy data, taken on measuring the temperature dependence of nanoparticle properties, should be carefully assessed and accompanied by ex-situ experiments if possible.

Abstracts:Owing to the excellent mixed-ionic and electronic conductivity and fast oxygen kinetics at reduced temperature (<800 °C), double-perovskite oxides such as PrBaCo2O5+δ exhibit excellent properties as an oxygen electrode for solid oxide fuel cells (SOFCs). Using transmission electron microscopy (TEM), we revealed high-density antiphase domain boundaries (APBs) and 90° domain walls in PrBaCo2O5+δ grains. Besides the regular lamellar 90° domain walls in {021} planes, irregular fine 90° domains are attached to the curved APBs. Electron energy-loss spectroscopy (EELS) reveals the composition variation across some of the 90° domain walls. There are fewer Co and more Ba ions approaching the 90° domain walls, while the changes in Pr and O ions are not detectable. We assume that the extra Ba²⁺ cations replace the Pr³⁺ cations, while the Pr³⁺ cations go to the Co site to form PrCo antisite point defects and become Pr⁴⁺. In this case, the Pr⁴⁺ cations will help to balance the local charges and have compatible ionic radius with that of Co³⁺. The local strain field around the 90° domain walls play a crucial role in the stabilization of such PrCo antisite point defects. The antisite point defects have been observed in our high-resolution TEM images and aberration-corrected high-angle annular dark-field (HAADF) scanning TEM images. After Ca²⁺ doped into PrBaCo2O5+δ to improve the structure stability, we observed tweed structures in the PrBa0.8Ca0.2Co2O5+δ grain. The tweed structure is composed of high-density intersected needle-shaped 90° domain walls, which is linked to a strong local strain field and composition variation. Even when the temperature is increased to 750 °C, the domain structures are still stable as revealed by our in situ TEM investigation. Therefore, the influence of the domain structures and the PrCo antisite defects on the ionic and electric conductivities must be considered.

Abstracts:In microelectronics, recently developed 3D integration offers the possibility to stack the dice or wafers vertically instead of putting their different parts next to one another, in order to save space. As this method becomes of greater interest, the need for 3D imaging techniques becomes higher. We here report a study about different 3D characterization techniques applied to copper pillars, which are used to stack different dice together. Destructive techniques such as FIB/SEM, FIB/FIB, and PFIB/PFIB slice and view protocols have been assessed, as well as non-destructive ones, such as laboratory-based and synchrotron-based computed tomographies. A comparison of those techniques in the specific case of copper pillars is given, taking into account the constraints linked to the microelectronics industry, mainly concerning resolution and sample throughput. Laboratory-based imaging techniques are shown to be relevant in the case of punctual analyses, while synchrotron based tomographies offer highly resolved volumes for larger batches of samples.

Abstracts:In this paper we discuss developments for Lorentz mode or “medium resolution” off-axis electron holography such that it is now routinely possible obtain very high sensitivity phase maps with high spatial resolution whilst maintaining a large field of view. Modifications of the usual Fourier reconstruction procedure have been used to combine series of holograms for sensitivity improvement with a phase-shifting method for doubling the spatial resolution. In the frame of these developments, specific attention is given to the phase standard deviation description and its interaction with the spatial resolution as well as the processing of reference holograms. An experimental study based on Dark-Field Electron Holography (DFEH), using a SiGe/Si multilayer epitaxy sample is compared with theory. The method’s efficiency of removing the autocorrelation term during hologram reconstruction is discussed. Software has been written in DigitalMicrograph that can be used to routinely perform these tasks. To illustrate the real improvements made using these methods we show that a strain measurement sensitivity of  ±  0.025 % can be achieved with a spatial resolution of 2 nm and  ±  0.13 % with a spatial resolution of 1 nm whilst maintaining a useful field of view of 300 nm. In the frame of these measurements a model of strain noise for DFEH has also been developed.

Abstracts:A general method to set illuminating conditions for selectable beam convergence and probe size is presented in this work for Transmission Electron Microscopes (TEM) fitted with µs/pixel fast beam scanning control, (S)TEM, and an annular dark field detector. The case of interest of beam convergence and probe size, which enables diffraction pattern indexation, is then used as a starting point in this work to add 100 Hz precession to the beam while imaging the specimen at a fast rate and keeping the projector system in diffraction mode. The described systematic alignment method for the adjustment of beam precession on the specimen plane while scanning at fast rates is mainly based on the sharpness of the precessed STEM image. The complete alignment method for parallel condition and precession, Quasi-Parallel PED-STEM, is presented in block diagram scheme, as it has been tested on a variety of instruments. The immediate application of this methodology is that it renders the TEM column ready for the acquisition of Precessed Electron Diffraction Tomographies (EDT) as well as for the acquisition of slow Precessed Scanning Nanometer Electron Diffraction (SNED). Examples of the quality of the Precessed Electron Diffraction (PED) patterns and PED-STEM alignment images are presented with corresponding probe sizes and convergence angles.