Individual carbocyanine dye molecules in a sub-monolayer spread have been imaged with near-field scanning optical microscopy. Molecules can be repeatedly detected and spatially localized (to -X/50 where X is the wavelength of light) with a sensitivity of at least 0.005 molecules/(Hz)"12 and the orientation of each molecular dipole can be determined. This information is exploited to map the electric field distribution in the near-field aperture with molecular spatial resolution. Fig. iD) is consistent with the emission expected from a single diIC12(3) molecule under the known excitation conditions (21). Fourth, each structure in Fig. 1 has a well-defined dipole orientation as discussed below. Finally,
A single-electron transistor scanning electrometer (SETSE)-a scanned probe microscope capable of mapping static electric fields and charges with 100-nanometer spatial resolution and a charge sensitivity of a small fraction of an electron-has been developed. The active sensing element of the SETSE, a single-electron transistor fabricated at the end of a sharp glass tip, is scanned in close proximity across the sample surface. Images of the surface electric fields of a GaAs/AlxGa1-xAs heterostructure sample show individual photo-ionized charge sites and fluctuations in the dopant and surface-charge distribution on a length scale of 100 nanometers. The SETSE has been used to image and measure depleted regions, local capacitance, band bending, and contact potentials at submicrometer length scales on the surface of this semiconductor sample.
Using continuous-wave excitation to eliminate the problems inherent with pulsed laser measurements of nonlinear transitions, we have measured the 1^5'i-2^5'i interval in positronium (Ps) to be 1 233607216.4±3.2 MHz. The quoted 2.6 ppb (parts per 10^) uncertainty is primarily due to the determination of the Ps resonance relative to the Te2 reference line, with a 1.5 ppb contribution from a recent calibration of the Te2 line relative to the hydrogen 15-25' transition. The uncertainty corresponds to 3.5 X 10"^ of the a^Roo QED contribution to the 1^51-2^51 interval. Our measurement is sufficiently accurate to provide a test of the as yet uncalculated a^Roo QED corrections.
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