The charge transport and quantum interference effects in low-dimensional mesoscopic carbon networks prepared using self-assembling were investigated.

The mechanism of conduction in low-dimensional carbon networks was found to depend on the annealing temperature of the nitrocellulose precursor. The charge transport mechanism for carbon networks obtained at Tann=750°C was found to be the hopping conductivity in the entire investigated temperature range. The Coulomb gap near the Fermi level in the density of states was observed in the investigated carbon networks. The width of the Coulomb gap was found to be decreased with the annealing temperature of the carbon structures. The crossover from the strong localization to the weak localization regime of the charge transport in the carbon structures, obtained at Tann=950°C and Tann=1150°C, was observed in the temperature range T>100 K and T>20 K, respectively.

The preparation of monodisperse Fe nanoparticles and self-assembly into hcp and fcc or fcc-like arrays is described. Here dipolar interactions dominate for the interparticle spacings studied (1.4-3.4 nm). Comparison of the low temperature magnetic properties of multilayer arrays with those of dilute suspensions of the same particles show increased coercivity and slower magnetic relaxation in the arrays. Mean field calculations of magnetic interaction fields suggest the type of ordered structures formed.

This paper describes the formation of cobalt and iron metal nanoclusters in various polymeric domains. The size of the particles, their size distribution and their geometry is controlled by the extent of the interfacial interactions between the polymeric phase and the growing metal fragments. Iron oxide particles are shown to exhibit various geometries as a function of the polymer medium and the temperature at which they are formed. The selective phase separation and particle confinement of cobalt clusters in the presence of PS25300-b-PMMA25900 block co-polymer was achieved due to the different reactivities of the functional groups in the blocks towards the metal fragments. Transmission electron micrographs showed that cobalt clusters aggregated primarily in the poly(methyl methacrylate) block, while no cobalt nanoclusters were observed in the polystyrene block, thus creating a patterned distribution that coincided with the morphology of the block copolymer.

Ionically self-assembled monolayers (ISAMs) have recently been shown to spontaneously exhibit a polar ordering that gives rise to substantial second order nonlinear optical response. The deposition of ISAMs has been studied in situ via second harmonic generation. This is a particularly sensitive probe of the growth of nanometer-thick films since the centrosymmetry of the immersion solutions, the substrate, and the container yields no SHG contribution from these bulk components. Upon immersion in the NLO-active polyelectrolyte solution, the SHG rises sharply over the first minute. When a film is immersed into salt water, the SHG decreases significantly only to be restored when the salt solution is replaced with deionized water.

Motivated by the work of Li et al. [1], we have studied the strain induced morphological instability at the submonolayer coverage stage of heteroepitaxial growth on a vicinal substrate with regularly spaced steps. We have performed a linear stability analysis and determined for which conditions of coverage a flat front is unstable and for which conditions it is stable. For low coverages the instability will cause the front to break in an array of islands. Assuming that the fastest growing mode of the instability determines t he properties of the array, we make an estimation of the islands sizes and aspect ratios as well as an estimation of the separation length between islands of the array formed when the dominant mechanism for transport of matter is diffusion of particles along the growing front. These estimations are given as functions of the terrace width and coverage. Since these ones are experimentally controllable parameters, our results could be used to tailor the spontaneous formation of quantum nanostructures.

This paper reports the fabrication of large diameter pores (> 150nm) in anodic alumina that can be used to create wire arrays with significant surface effects, but without significant quantum confinement. These wires, therefore, allow us to distinguish between optical absorption spectra features originationg from quantum effects and those from surface effects. The paper presents techniques towards fabrication these bismuth wire arrays, and presents optical absorption data from two bismuth namowire arrays in the semimetal-semiconductor transition diameter regime. The results from previous publications are summarized and future directions are outlined.

The phase characteristics of transmitted optical pulses in three-dimensional photonic crystals were investigated in the frequency and time domain by using the spectrally resolved cross-correlation technique. The temporal evolution of femtosecond pulses passing through polystyrene colloidal crystals exhibits a large phase distortion near the stop bands. The phase discontinuity around the band gap was observed in the frequency-domain. The phase of the transmitted pulses is found to change by p across the band gap. The dispersion curve estimated from the phase shift shows good correspondence with those calculated from a photonic band calculation. The group velocity significantly slows down near the stop bands. A large change of the group velocity dispersion is also observed near the band edges. These results are in good agreement with the band theory.

We construct a 3D model for coherent island formation by (i) using a novel 3D strain tensor to account for bulk strains and (ii) representing adatom diffusion as an external field that perturbs an otherwise flat strained layer. Equilibrium shapes of coherent islands and wetting layer thickness are obtained. Coherently compressed layers are typically unstable, but become stable in tension. Comparisons with Si1-xGex/Si(001) and Si0.5Ge0.5/Si1-xGex(001) layers are discussed.

Self assembled quantum dots of Ge were obtained by magnetron sputter epitaxy of seven monolayers of Ge on a 33nm thick undoped Si buffer grown on top of a p-doped (100) Si substrate. The samples obtained in this manner were then capped with an increasing number of silicon layers in order to study the effect of Si deposition on the strain and the morphology of the dots. They were characterized “ex situ” by spectroscopic ellipsometry and Raman spectroscopy. The optical experiments revealed well defined differences between the capped and uncapped samples and among samples with different cap thicknesses.

By monitoring the energy and the splitting of the E0', E1 and E2 interband optical transitions of Ge and the Ge-Si vibrational mode, the optical measurements evidence strain effects as well as the formation of SiGe alloy, in agreement with the “in situ” STM measurements.