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The photoluminescence from a variety of individual molecules (1) and nanometre-sized crystallites (2) is defined by large intensity fluctuations, known as 'blinking', whereby their photoluminescence turns 'on' and 'off' intermittently, even under continuous photo-excitation (2). For semiconductor nanocrystals, it was originally proposed (3) that these 'off' periods corresponded to a nanocrystal with an extra charge. A charged nanocrystal could have its photoluminescence temporarily quenched owing to the high efficiency of non-radiative (for example, Auger) recombination processes between the extra charge and a subsequently excited electron--hole pair; photoluminescence would resume only after the nanocrystal becomes neutralized again. Despite over a decade of research, completely non-blinking nanocrystals (4,5) have not been synthesized and an understanding of the blinking phenomenon (6) remains elusive. Here we report ternary core/shell CdZnSe/ZnSe semiconductor nanocrystals that individually exhibit continuous, non-blinking photoluminescence. Unexpectedly, these nanocrystals strongly photoluminesce despite being charged, as indicated by a multi-peaked photoluminescence spectral shape and short lifetime. To model the unusual photoluminescence properties of the CdZnSe/ZnSe nanocrystals, we softened the abrupt confinement potential of a typical core/shell nanocrystal, suggesting that the structure is a radially graded alloy of CdZnSe into ZnSe. As photoluminescence blinking severely limits the usefulness of nanocrystals in applications requiring a continuous output of single photons, these non-blinking nanocrystals may enable substantial advances in fields ranging from single-molecule biological labelling (7) to low-threshold lasers (8)., Semiconductor nanocrystals have size-tunable optical properties that open up possibilities for revolutionary advances in lasers (8), light-emitting diodes (9), solar cells (10) and biological imaging (11-13). However, the photoluminescence from [...]

Transmission electron energy-loss spectroscopy facilitated the study of the characteristic features of sp2 and sp3 carbon bonding by recording its electron density map at a spatial resolution less than one nanometre. Detailed information on the sp2 and sp3 carbon aids the understanding of the mechanism underlying diamond nucleation on an amorphous carbon layer. Results of and data obtained during the analysis of the scanning transmission electron microscope image of diamond deposited by chemical vapor deposition corroborate the occurrence of a transition from sp2 to sp3, within a region of one nanometre, during diamond nucleation.

Visualizing individual atoms is hard, not least because free atoms move rapidly at room temperature. The problem is finding a way to keep them motionless for long enough to observe [...]

Heavy atoms can be detected by electron microscopy, but lighter atoms, such as carbon or hydrogen, are more elusive. These bashful atoms can now be pinpointed if they are adsorbed to a single layer of graphite. Imaging atoms: 'Invisible' graphene brings electron microscopy to single carbons and hydrogens Scanning tunnelling microscopes made it possible to image atomic-scale features on a solid-state surface. But they have limitations in terms of sample conductivity, cleanliness and data acquisition rate. An older technology, the transmission electron microscope (TEM), meanwhile evolved to be able to image individual heavy atoms. But lighter atoms remained beyond its range because of their low contrast. Enter graphene, the one-atom-thick sheet of carbon atoms packed in a dense two-dimensional honeycomb lattice. Meyer et al. show that atoms as small as carbon and even hydrogen adsorbed onto graphene can be imaged using standard TEM technology. Ultrathin graphene is an ideal support, either invisible or, if the lattice is resolved at high resolution, its contribution to the imaging signal is easily removed. This approach brings atomic resolution to biomolecules as well as to graphene itself. The cover shows hydrogen atoms (purple) on a graphene sheet (red), with a carbon atom (yellow tipped) near left centre. Yellow peaks are amorphous carbon., Author(s): John Silcox [sup.1] Author Affiliations: (1) John Silcox is in the School of Applied and Engineering Physics, Clark Hall, Cornell University, Ithaca, New York 14853, USA. js97@cornell.edu , Visualizing [...]