The motion of chemical bonds within molecules can be observed in real time, in the form of vibrational wavepackets prepared and interrogated through ultrafast nonlinear spectroscopy. Such nonlinear optical measurements are commonly performed on large ensembles of molecules, and as such, are limited to the extent that ensemble coherence can be maintained. Here, we describe vibrational wavepacket motion on single molecules, recorded through time-resolved, surface-enhanced, coherent anti-Stokes Raman scattering. The required sensitivity to detect the motion of a single molecule, under ambient conditions, is achieved by equipping the molecule with a dipolar nano-antenna (a gold dumbbell). In contrast with measurements in ensembles, the vibrational coherence on a single molecule does not dephase. It develops phase fluctuations with characteristic statistics. We present the time evolution of discretely sampled statistical states, and highlight the unique information content in the characteristic, early-time probability distribution function of the signal.

Surface enhanced Raman scattering (SERS) from bipyridyl ethylene adsorbed on gold dumbbells shows Fano-like spectra at high incident light intensity. This is accompanied by an increased electronic temperature, while no vibrational anti-Stokes (AS) scattering is observed. Theory indicates that interference between vibrational and electronic Raman scattering can yield such asymmetric scattering lineshapes. The best fit to observations is obtained by disregarding this coupling and accounting for the detailed lineshape of the continuous electronic component of the SERS.

We demonstrate ultrafast laser driven nonlinear scanning tunneling microscopy (STM), under ambient conditions. The design is an adaptation of the recently introduced cross-polarized double beat method, whereby z-polarized phase modulated fields are tightly focused at a tunneling junction consisting of a sharp tungsten tip and an optically transparent gold film as substrate. We demonstrate the prerequisites for ultrafast time-resolved STM through an operative mechanism of nonlinear laser field-driven tunneling. The spatial resolution of the nonlinear laser driven STM is determined by the local field intensity. Resolution of 0.3 nm-10 nm is demonstrated for the intensity dependent, exponential tunneling range. The demonstration is carried out on a junction consisting of tungsten tip and gold substrate. Nano-structured gold is used for imaging purposes, to highlight junction plasmon controlled tunneling in the conductivity limit.

a b s t r a c tDeposits of one dimensional nanowires of zinc with diameters of 90-120 nm have been obtained by means of dc sputtering within an electron cyclotron resonance plasma reactor. The sputtering has been made effective by using a negatively biased cylindrical target. The structure of the nanocrystalline wires deposited on glass substrates were investigated with scanning electron microscopy, transmission electron microscopy and scanning tunneling microscopy. STM revealed that the structure of the one dimensional nanowires are ensemble of nanoclusters and nanowires with diameter of 4-5 nm. The crystalline nature of the metallic nanowires was studied with X-ray and electron diffraction analysis. The native oxide present on the metallic wires was revealed by photoluminescent spectroscopy. Theoretical modeling has been used to explain the possible mechanisms operative inside the plasma which lead into deposition of zinc on the substrate starting from the precursor species.

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