Electron tomography at 2.4-ångström resolution

An electron tomography method is demonstrated that can determine the three-dimensional structure of a gold nanoparticle at 2.4 Å resolution, including the locations of some of the individual atoms within the sample. Atomic-scale grain of truth Electron tomography, an extension of transmission electron microscopy that was developed in the late 1960s, is widely used to obtain three-dimensional images of samples in the biological and materials sciences. Advances in recent years mean that the method can be used to determine the internal structure of nanomaterials at atomic resolutions, as long as certain assumptions are made concerning the sample structure. Scott et al . now demonstrate an electron-tomography method that bypasses the need for such assumptions, enabling the authors to determine the three-dimensional structure of a gold nanoparticle at 2.4-ångström resolution, including the locations of some of the individual atoms in the sample. Transmission electron microscopy is a powerful imaging tool that has found broad application in materials science, nanoscience and biology 1 , 2 , 3 . With the introduction of aberration-corrected electron lenses, both the spatial resolution and the image quality in transmission electron microscopy have been significantly improved 4 , 5 and resolution below 0.5 ångströms has been demonstrated 6 . To reveal the three-dimensional (3D) structure of thin samples, electron tomography is the method of choice 7 , 8 , 9 , 10 , 11 , with cubic-nanometre resolution currently achievable 10 , 11 . Discrete tomography has recently been used to generate a 3D atomic reconstruction of a silver nanoparticle two to three nanometres in diameter 12 , but this statistical method assumes prior knowledge of the particle’s lattice structure and requires that the atoms fit rigidly on that lattice. Here we report the experimental demonstration of a general electron tomography method that achieves atomic-scale resolution without initial assumptions about the sample structure. By combining a novel projection alignment and tomographic reconstruction method with scanning transmission electron microscopy, we have determined the 3D structure of an approximately ten-nanometre gold nanoparticle at 2.4-ångström resolution. Although we cannot definitively locate all of the atoms inside the nanoparticle, individual atoms are observed in some regions of the particle and several grains are identified in three dimensions. The 3D surface morphology and interna