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High-density samples of fluorescent quantum dots ͑QDs͒ were imaged using an apertureless near-field optical microscopy technique. QD fluorescence was modulated by oscillating a silicon atomic force microscope tip above an illuminated sample and a lock-in amplifier was used to suppress background from the excitation laser. Spatial resolution near 10 nm and a peak signal-to-noise ratio ͑SNR͒ of ϳ60 were achieved. Individual QDs within high-density ensembles were still easily resolved ͑SNRϾ 5͒ at a density of 14 QDs/ m 2. These results have favorable implications for the eventual nanoscale imaging of viable biological systems, such as cellular membranes.

We demonstrate a near-field tomography method for investigating the coupling between a nanoscopic probe and a fluorescent sample. By correlating the arrival of single fluorescence photons with the lateral and vertical position of an oscillating tip, a complete three-dimensional analysis of the near-field coupling is achieved. The technique is used to reveal a number of interesting three-dimensional near-field features and to improve image contrast in tip-enhanced fluorescence microscopy.

We investigate the limits of one-photon fluorescence as a contrast mechanism in nanoscale-resolution tip-enhanced optical microscopy. Specifically, we examine the magnitude of tip-induced signal enhancement needed to resolve individual fluorophores within densely-packed ensembles. Modulation of fluorescence signals induced by an oscillating tip followed by demodulation with a lock-in amplifier increases image contrast by nearly two orders of magnitude. A theoretical model of this simple modulation/ demodulation scheme predicts an optimal value for the tip-oscillation amplitude that agrees with experimental measurements. Further, as an important step toward the eventual application of tip-enhanced fluorescence microscopy to the nanoscale structural analysis of biomolecular systems, we show that requisite signal enhancement factors are within the capabilities of commercially available silicon tips.

Abstract-We demonstrate the first reported use of single-walled carbon nanotubes as nano-optical probes in apertureless nearfield fluorescence microscopy. We show that, in contrast to silicon probes, carbon nanotubes always cause strong fluorescence quenching when used to image dye-doped polystyrene spheres and Cd-Se quantum dots. For quantum dots, the carbon nanotubes induce very strong near-field contrast with a spatial resolution of ∼20 nm. Images of dye-doped spheres exhibit crescent-shaped artifacts caused by distortions in the surface water layer found in ambient conditions. Index Terms-Atomic force microscopy (AFM), carbon nanotubes, fluorescence microscopy, fluorescence quenching, nanooptics, near-field optics.

Cu has two advantages over Al for sub-quarter micron interconnect application: (1) higher conductivity and (2) improved electromigration reliability. However, Cu diffuses quickly in SiO2and Si, and must be encapsulated. Polycrystalline films of Physical Vapor Deposition (PVD) Ta, W, Mo, TiN, and Metal-Organo Chemical Vapor Deposition (MOCVD) TiN and Ti-Si-N have been evaluated as Cu diffusion barriers using electrically biased-thermal-stressing tests. Barrier effectiveness of these thin films were correlated with their physical properties from Atomic Force Microscopy (AFM), Transmission Electron Microscopy (TEM), Secondary Electron Microscopy (SEM), and Auger Electron Spectroscopy (AES) analysis. The barrier failure is dominated by “micro-defects” in the barrier film that serve as easy pathways for Cu diffusion. An ideal barrier system should be free of such micro-defects (e.g., amorphous Ti-Si-N and annealed Ta). The median-time-to-failure (MTTF) of a Ta barrier (30 nm) has been measured at different bias electrical fields and stressing temperatures, and the extrapolated MTTF of such a barrier is > 100 year at an operating condition of 200C and 0.1 MV/cm.

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