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A new generation of electron microscopes is able to explore the microscopic properties of materials and devices as diverse as transistors, turbine blades and interfacial superconductors. All of these systems are made up of dissimilar materials that, where they join at the atomic scale, display very different behaviour from what might be expected of the bulk materials. Advances in electron optics have enabled the imaging and spectroscopy of these buried interface states and other nanostructures with atomic resolution. Here I review the capabilities, prospects and ultimate limits for the measurement of physical and electronic properties of nanoscale structures with these new microscopes. [ABSTRACT FROM AUTHOR]

Electron energy loss fine structure near the threshold of inner-shell edges can potentially give valuable information on bonding on an atomic scale. To use near-edge structure it is essential to understand what factors influence both the occupied and unoccupied local density of states in the material of interest. Different techniques of electronic structure theory are suitable for metals, semiconductors, and ionic materials, although some methods can be applied to a wide range of systems. To extract quantitative information on bonding it is important to avoid those edges that are strongly affected by the presence of the core hole such as cations in ionic materials. [ABSTRACT FROM AUTHOR]

The article looks at possible ways to measure and control orbital angular momentum on the atomic scale with electron microscopes. A study conducted by Masaya Uchida and Akira Tonomura demonstrated the use of orbital angular momentum in an electron microscope. Meanwhile, Jo Verbeeck and He Tian of the University of Antwerp, and Peter Schattschneider of the Vienna University of Tecnhnology produced a hologram by digitally interfering a vortex beam with a reference plane wave in a computer.

Abstract: The optimal lens parameters for incoherent imaging using third and fifth-order aberration-corrected electron microscopes are derived analytically. We propose simple models for the point spread function (PSF) and transfer function that give analytic formulae for the lateral resolution and depth resolution. We also derive an analytic formula for the contrast transfer function (CTF) in three dimensions and show that depth sectioning has an information limit equivalent to tomography with a missing cone of minus the aperture angle. [Copyright &y& Elsevier]

The ability to detect individual impurity atoms has been greatly enhanced by the development of aberration-corrected electron microscopes. The reduced depth of focus potentially enables three-dimensional reconstructions of impurity atoms from through-focal series. We test the robustness of this depth-sectioning method for detecting impurity atoms in gate oxides using multislice simulations. For amorphous materials, dopants can be reliably imaged, and are accurately described by a simpler three-dimensional linear imaging model. For crystalline materials, however, channeling artifacts can render the signal uninterpretable. These artifacts can be eliminated by orienting the crystal slightly off the zone axis, which still preserves atomic resolution. [ABSTRACT FROM AUTHOR]

As integrated circuits have shrunk, conventional electron microscopies have proven inadequate for imaging complicated interconnect structures due to the overlap of features in projection. These techniques produce transmission functions with a nonmonotonic dependence of intensity on thickness for common microelectronic materials, making them unsuitable for tomography. We report the use of an incoherent bright field imaging technique in a scanning transmission electron microscope optimized for the three-dimensional reconstruction of thick copper microelectronic structures. Predictable behavior of the signal in samples up to ∼1 μm thick allows us to reconstruct and quantify the shape and volume of stress voids within Ta-lined interconnects. [ABSTRACT FROM AUTHOR]

Electron tomography (ET) has become a standard technique for 3D characterization of materials at the nano-scale. Traditional reconstruction algorithms such as weighted back projection suffer from disruptive artifacts with insufficient projections. Popularized by compressed sensing, sparsity-exploiting algorithms have been applied to experimental ET data and show promise for improving reconstruction quality or reducing the total beam dose applied to a specimen. Nevertheless, theoretical bounds for these methods have been less explored in the context of ET applications. Here, we perform numerical simulations to investigate performance of ℓ 1 -norm and total-variation (TV) minimization under various imaging conditions. From 36,100 different simulated structures, our results show specimens with more complex structures generally require more projections for exact reconstruction. However, once sufficient data is acquired, dividing the beam dose over more projections provides no improvements—analogous to the traditional dose-fraction theorem. Moreover, a limited tilt range of ±75° or less can result in distorting artifacts in sparsity-exploiting reconstructions. The influence of optimization parameters on reconstructions is also discussed. [ABSTRACT FROM AUTHOR]

Abstract: To date, high-resolution (<1nm) imaging of extended objects in three-dimensions (3D) has not been possible. A restriction known as the Crowther criterion forces a tradeoff between object size and resolution for 3D reconstructions by tomography. Further, the sub-Angstrom resolution of aberration-corrected electron microscopes is accompanied by a greatly diminished depth of field, causing regions of larger specimens (>6nm) to appear blurred or missing. Here we demonstrate a three-dimensional imaging method that overcomes both these limits by combining through-focal depth sectioning and traditional tilt-series tomography to reconstruct extended objects, with high-resolution, in all three dimensions. The large convergence angle in aberration corrected instruments now becomes a benefit and not a hindrance to higher quality reconstructions. A through-focal reconstruction over a 390nm 3D carbon support containing over 100 dealloyed and nanoporous PtCu catalyst particles revealed with sub-nanometer detail the extensive and connected interior pore structure that is created by the dealloying instability. [Copyright &y& Elsevier]