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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 [...]

A description of two metal/glass interfaces is provided.

The contrast due to a strain field at an amorphous silicon/crystalline silicon (a-Si/c-Si) interface relative to the bulk crystal is studied with a scanning transmission electron microscope equipped with a low angle annular dark field (LAADF) detector and a high angle ADF (HAADF) detector. Experimental observations suggest that strain contrast depends closely on sample thickness and collection angle. For a thin sample (<100 Å) strain contrast is negative in both the LAADF and HAADF images. For a thick sample (>150 Å) strain contrast is positive in the LAADF image and negative in the HAADF image. Theoretical calculations of the effect of a random strain field are carried out. First, a simple model based on atomic scattering with an extra Debye–Waller factor is employed. It predicts a positive strain contrast in the LAADF image and no contrast in the HAADF image. The simple model fails for the HAADF contrast because it does not consider the propagation process of the electron beam inside the sample. Therefore multislice simulations including propagation details are carried out. The multislice simulation results agree well with the experimental observations. A measure of the strain amplitude is attained by comparing the experimental data with multislice simulation results. Quantitative measurements of strain contrast are only possible if the sample thickness is known. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Electron irradiation induced phase decomposition in an alkaline earth multi-component oxide glass has been observed in a scanning transmission electron microscope. Separate regions that are rich and poor in alkaline earths form rapidly during the initial irradiation. In other words, alkaline earth multi-component oxide glasses are intolerant of high-energy (∼ 100 kV) electrons. This could result from the characteristics of a nonbridging O atom that bound to both Si (covalent) and alkaline earths (ionic). A modified Knotek-Feibelman model has been introduced to interpret the breakaway of cations from the glass network. Driven by electrostatic forces, the cations prefer to segregate, forming a cation rich region to reduce the amount of nonbridging O. [ABSTRACT FROM AUTHOR]

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.

Paul Leon Hartman, a professor emeritus of physics at Cornell University who made pioneering measurements of synchrotron radiation, died on May 20, 2005, in Ithaca, New York. He helped in developing the Cornell High Energy Synchrotron Source (CHESS) and his colleagues would miss a warm and enthusiastic person who loved experimental physics.

In a scanning transmission electron microscope, electron irradiation induced phase decomposition in an alkaline earth multi-component oxide glass is observed. During initial irradiation, separate regions that are rich and poor in alkaline earth form rapidly, which results in nonbridging O atom that bound to both Si and alkaline earths.

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 [...]