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Using state of the art scanning transmission electron microscopy (STEM) it is nowadays possible to directly image single atomic columns at sub-Å resolution. In standard (high angle) annular dark field STEM ((HA)ADF-STEM), however, light elements are usually invisible when imaged together with heavier elements in one image. Here we demonstrate the capability of the recently introduced Integrated Differential Phase Contrast STEM (iDPC-STEM) technique to image both light and heavy atoms in a thin sample at sub-Å resolution. We use the technique to resolve both the Gallium and Nitrogen dumbbells in a GaN crystal in [] orientation, which each have a separation of only 63 pm. Reaching this ultimate resolution even for light elements is possible due to the fact that iDPC-STEM is a direct phase imaging technique that allows fine-tuning the microscope while imaging. Apart from this qualitative imaging result, we also demonstrate a quantitative match of ratios of the measured intensities with theoretical predictions based on simulations.

We show that by operating a scanning transmission electron microscope (STEM) with a 0.1 nm 300 kV electron beam, one can sculpt free-standing monolayer graphene with close-to-atomic precision at 600 °C. The same electron beam that is used for destructive sculpting can be used to image the sculpted monolayer graphene nondestructively. For imaging, a scanning dwell time is used that is about 1000 times shorter than for the sculpting. This approach allows for instantaneous switching between sculpting and imaging and thus fine-tuning the shape of the sculpted lattice. Furthermore, the sculpting process can be automated using a script. In this way, free-standing monolayer graphene can be controllably sculpted into patterns that are predefined in position, size, and orientation while maintaining defect-free crystallinity of the adjacent lattice. The sculpting and imaging processes can be fully computer-controlled to fabricate complex assemblies of ribbons or other shapes.

Starting from the gas phase, small clusters can be produced and deposited with huge flexibility with regard to composition, materials choice and cluster size. Despite many advances in experimental characterization, a detailed morphology of such clusters is still lacking. Here we present an atomic scale observation as well as the dynamical behaviour of ultrasmall germanium clusters. Using quantitative scanning transmission electron microscopy in combination with ab initio calculations, we are able to characterize the transition between different equilibrium geometries of a germanium cluster consisting of less than 25 atoms. Seven-membered rings, trigonal prisms and some smaller subunits are identified as possible building blocks that stabilize the structure.

Using a combination of high-angle annular dark-field scanning transmission electron microscopy and atomically resolved electron energy-loss spectroscopy in an aberration-corrected transmission electron microscope we demonstrate the possibility of 2D atom by atom valence mapping in the mixed valence compound Mn 3 O 4 . The Mn L 2;3 energy-loss near-edge structures from Mn 2þ and Mn 3þ cation sites are similar to those of MnO and Mn 2 O 3 references. Comparison with simulations shows that even though a local interpretation is valid here, intermixing of the inelastic signal plays a significant role. This type of experiment should be applicable to challenging topics in materials science, such as the investigation of charge ordering or single atom column oxidation states in, e.g., dislocations. DOI: 10.1103/PhysRevLett.107.107602 PACS numbers: 79.20.Uv, 68.37.Ma, 75.25.Dk In transition metal oxides, the oxidation state of the transition metal cations is of fundamental importance as the physical properties of many oxides are determined by the occupancy of the cation d bands. Multiferroicity, for example, can be driven by charge ordering of these cations, as in Fe 3 O 4 and Pr 1Àx Ca x MnO 3 [1-3]. However, the exact mechanism of multiferroic behavior is not fully understood to date. A method allowing for direct mapping of cation valence states in these materials at atomic resolution should therefore provide further insight into the origin of multiferroicity.Recently, atomic resolution elemental mapping has become feasible by means of spatially resolved electron energy-loss spectroscopy and energy dispersive x-ray spectroscopy in a scanning transmission electron microscope (STEM-EELS and STEM-EDX) [4][5][6][7][8][9]. At the same time, tremendous effort is being invested into the identification of the oxidation states of cations using electron energy-loss spectroscopy (EELS). The shape of the L 2;3 edge [10], the chemical shift [11,12] and the L 3 =L 2 ratio [13] have all been used as a fingerprint for the transition metal valence. In fact, the correlation between the energy-loss near-edge structure (ELNES) and valence in different transition metal oxides was confirmed by several experiments in literature [10,[14][15][16][17][18][19][20][21]. The higher the energy resolution, the more convincing this link between valence and ELNES features becomes. Combining the atomic resolution capabilities of a STEM with bonding and valence information from EELS is a highly attractive prospect. While bonding information has been obtained at atomic resolution [7,17,22], 2D oxidation state mapping at the atomic level in, e.g., metaloxide materials has remained challenging due to poor EELS signal-to-noise ratio and the need for simultaneous high spatial and energy resolution of the instrument [10,17,23].Mn 3 O 4 is known to be a mixed valence compound, containing both Mn 2þ and Mn 3þ ions at room temperature [24]. It has a spinel structure with lattice parameters a ¼ 5:762 A and c ¼ 9:4696 A and space group I41=amd. Many interesting...