No abstract

We combine in a unique approach two modern ultrathin film techniques for production of heterostructure films. These are plasma deposition (which permitted one to obtain thin 20-500-A well-defined layers on any solid surface with an active, in our case charged, surface) and layer-by-layer deposition of the polycation/polyanion self-assembly. The latter technique was recently developed in our group and is based on the electrostatic attraction between opposite charges. Alternating adsorption of anionic and cationic polyelectrolytes from their aqueous solution onto charged substrate leads to the formation of multilayer assemblies. The multilayer heterostructure film was monitored by small-angle X-ray reflectivity. Oxygen, methane, argon, and polysiloxane plasma coating were tested as a precursor treatment for polyion assembly. The procedure was successfully accomplished for methane plasma deposition onto a glass substrate with further oxidation and consequent alternate assembling of a layer of polyallylamine (PAH) and polystyrenesulfonate (PSS). The step size of growth for the deposited PAH/PSS pair was 50 f 1 A. Model fitting of the X-ray reflectivity data allowed us to calculate the electron density profiles of plasma-deposited plus polymer-assembled heterofilms and to characterize the thickness and roughness of its composite layers. Furthermore, the combination of methane plasma treatment and polyelectrolyte self-assembly opens a new approach for constructing inorganic/organic nanocomposite films.

Continuous change of the propagation direction of a classical control field in the process of its off-resonant Raman interaction with a weak signal field in a three-level atomic medium is suggested for quantum storage of a single-photon wave packet. It is shown that due to phase matching condition such an angular control allows one to reversibly map the single-photon wave packet to the Raman spatial coherence grating. Thus, quantum storage and retrieval can be realized without using inhomogeneous broadening of the atomic transitions or manipulating the amplitude of the control field. Under some conditions the proposed scheme proves to be mathematically analogous to the quantum storage scheme based on controlled reversible inhomogeneous broadening of the atomic states.

The absorption spectrum of Er3+ ions in YAG crystal in the range from 645 nm to 655 nm was measured with the resolution of 0.01 nm using the frequency-anticorrelated broadband photon pairs (biphotons) generated by spontaneous parametric down-conversion. The spectrum of the sample was measured by counting the coincidences when the impurity crystal was placed in front of the signal photon detector, whilst the wavelength of the idler photons was resolved by a monochromator which was placed in front of another photon detector. The results are in agreement with those obtained by the usual intensity measurements with a classical light source and a monochromator. It was shown experimentally that the biphoton spectroscopy, unlike the usual single photon spectroscopy, allows one to obtain the spectroscopic information in the presence of an external noise such as background thermal radiation.