Thickness Control and Targeting in Large Scale Automated XTEM Lamella Preparation

The automation of both, transmission electron microscopy (TEM) imaging and lamella preparation using focused ion beam (FIB) has gathered an enormous momentum in last few years, especially in the semiconductor industry. The process development of current and future microprocessors requires a precise control on the patterning of a multitude of ultrafine layers, several of which are in the order of nanometers. The statistical accuracy and reliability of TEM based metrology and failure analysis of such complex and refined structures across the wafer needs a large-scale sampling, which is feasible only with an automation. An inherent requirement of automating TEM sample preparation entails a need of a robust and repeatable methodology that provides both, a good thickness control and an accurate targeting, on the intended feature in the ultra-thin lamella. In this work, key factors that impact both these aspects of a TEM lamella preparation will be discussed. In addition, steps needed to ensure that FIB toolsets consistently and reliably produce high quality samples, will be highlighted.

Origin of the enhanced Nb3Sn performance by combined Hf and Ta doping

In recent years there has been an increasing effort in improving the performance of Nb3Sn for high-field applications, in particular for the fabrication of conductors suitable for the realization of the Future Circular Collider (FCC) at CERN. This challenging task has led to the investigation of new routes to advance the high-field pinning properties, the irreversibility and the upper critical fields (HIrr and Hc2, respectively). The effect of hafnium addition to the standard Nb-4Ta alloy has been recently demonstrated to be particularly promising and, in this paper, we investigate the origins of the observed improvements of the superconducting properties. Electron microscopy, Extended X-ray Absorption Fine Structure Spectroscopy (EXAFS) and Atom Probe Tomography (APT) characterization clearly show that, in presence of oxygen, both fine Nb3Sn grains and HfO2 nanoparticles form. Although EXAFS is unable to detect significant amounts of Hf in the A15 structure, APT does indeed reveal some residual intragrain metallic Hf. To investigate the layer properties in more detail, we created a microbridge from a thin lamella extracted by Focused Ion Beam (FIB) and measured the transport properties of Ta-Hf-doped Nb3Sn. Hc2(0) is enhanced to 30.8 T by the introduction of Hf, ~ 1 T higher than those of only Ta-doped Nb3Sn, and, even more importantly the position of the pinning force maximum exceeds 6 T, against the typical ~ 4.5–4.7 T of the only Ta-doped material. These results show that the improvements generated by Hf addition can significantly enhance the high-field performance, bringing Nb3Sn closer to the requirements necessary for FCC realization.

Tracking of the Growth Interface during PVT-Growth of SiC Boules Using a X-Ray Computed Tomography Setup

A crystal comprising various polytype switches was analyzed in detail. A very flat temperature profile together with an on axis seed are used to increase the probability for the nucleation of foreign polytypes during growth. Formation of foreign polytype occurred from thin lamella propagating from the edge of the main facet to the crystal rim as well as from 2D nucleation. The evolution of the crystal surface during the growth time is visualized using in-situ X-Ray computed tomography. Two concurrent growth centers are identified in the beginning of the growth process. Nucleation and lateral growth of foreign polytypes in the main facet area can be traced during the growth process.

Mind the gap: micro-expansion joints drastically decrease the bending of FIB-milled cryo-lamellae

Cryo-focussed ion beam (FIB)-milling of biological samples can be used to generate thin electron-transparent slices from cells grown or deposited on EM grids. These so called cryo-lamellae allow high-resolution structural studies of the natural cellular environment by in situ cryo-electron tomography. However, the cryo-lamella workflow is a low-throughput technique and can easily be obstructed by technical issues like the bending of the lamellae during the final cryo-FIB-milling steps. The severity of lamella bending seems to correlate with shrinkage of the EM grid support film at cryogenic temperatures, which could generate tensions that may be transferred onto the thin lamella, leading to its bending and breakage. To protect the lamellae from these forces, we milled “micro-expansion joints” alongside the lamellae, creating gaps in the support that can act as physical buffers to safely absorb material motion. We demonstrate that the presence of such micro-expansion joints drastically decreases lamella bending. Furthermore, we show that this adaptation does not create instabilities that could constrain subsequent parts of the cryo-lamella workflow, as we obtained high-quality Volta phase plate tomograms revealing macromolecules in their natural structural context. The minimal additional effort required to implement micro-expansion joints in the cryo-FIB-milling workflow makes them an easy solution against cryo-lamella bending in any biological sample milled on EM grids.

Machining protein microcrystals for structure determination by electron diffraction

We demonstrate that ion-beam milling of frozen, hydrated protein crystals to thin lamella preserves the crystal lattice to near-atomic resolution. This provides a vehicle for protein structure determination, bridging the crystal size gap between the nanometer scale of conventional electron diffraction and micron scale of synchrotron microfocus beamlines. The demonstration that atomic information can be retained suggests that milling could provide such detail on sections cut from vitrified cells.

Failure Analysis Work Flow for Dislocation Identification and Characterization by Electron Channeling Contrast Imaging Using SEM and FIB

A failure analysis work flow is presented demonstrating dislocation visualization, site isolation, TEM lamella preparation and defect characterization. A novel beam control technique allows visualizing dislocations with significantly improved spatial resolution in SEM using Electron Channeling Contrast Imaging. Site-specific TEM preparation on dislocations is therefore possible. The prepared thin lamella can be inspected in the SEM using STEM to study dislocations. This is a cost effective work flow without using TEM.

Numerical study of head-on droplet collisions at high Weber numbers

Head-on collisions of binary water droplets at high Weber numbers are studied by means of direct numerical simulations (DNS). We modify the lamella stabilization method of Focke & Bothe (J. Non-Newtonian Fluid Mech., vol. 166 (14), 2011, pp. 799–810), which avoids the artificial rupture of the thin lamella arising in high-energy collisions, and validate it in the regime of high Weber numbers. The simulations are conducted with and without initial disturbances and the results are compared with the experimental work of Pan et al. (Phys. Rev. E, vol. 80 (3), 2009, 036301). The influence of initial white noise disturbance on the collision dynamics is identified and good agreement between the simulation results and the experimental results is obtained when the initial noise disturbances are properly exerted. In order to include the stochastic nature of the disturbance, we conduct several simulations with white noise disturbance of same strength and average the spectrum diagram for the unstably developing rim of the collision complex. We show that the magnification of rim perturbation can be predicted by Plateau–Rayleigh theory over a long time span.

Stepwise assembly of a cross-linked free-standing nanoparticle sheet with controllable shape

We report the shape controlled synthesis of a crosslinked nanoparticle thin lamella based on a polymer single crystal template.