This PDF file contains the front matter associated with SPIE Proceedings Volume 7758, including the Title Page, Copyright information, Table of Contents, and the Conference Committee listing.

Direct molecule-semiconductor interfacial charge transfer interactions have received considerable research attention for their applications in various fields. In this study, the dynamics of molecule-TiO₂ interfacial charge transfer complexes is monitored with femtosecond fluorescence upconversion and transient absorption. Small molecules (catechol, dopamine, benzhydroxamic acid, acetyl acetonate and salicylate)-modified TiO₂ nanoparticles are prepared and the complexation is followed with optical absorption measurements. Although little visible luminescence is observed from these molecule- TiO₂ nanoparticles, ultrafast emission in broad range of wavelengths is detected with fluorescence upconversion which is ascribed to the interfacial charge transfer emission. The charge transfer emission arose out of the radiative recombination of the electrons in the conduction band of TiO₂ with holes in the molecule. Femtosecond fluorescence anisotropy measurements have shown that the interfacial charge-transfer excitation is mostly a localized one for catechol, dopamine and benzhydroxamate modified TiO₂ nanoparticles. However, the possibility of delocalized charge-transfer excitations is observed for salicylate and acetyl acetonate-TiO₂ nanoparticles. The decay of the charge transfer emission is ascribed to the relaxation of the localized states to delocalized states in the TiO₂ conduction band. Transient absorption measurements have shown long-lived charge separation in the case of surface-modified TiO₂ nanoparticles. Further measurements on the influence of charge-transfer excitations on the interfacial electron transfer in surface-modified TiO₂ nanoparticles are being carried out.

The metal-insulator transition (MIT) induced by magnetic field, in barely metallic and compensated n-type GaAs has been analyzed using a scale theory. The experiments were carried out at low temperature in the range (4.2 -0.066 K) and in magnetic field up to 4 T. We have determined the magnetic field for which the conductivity changes from the metallic behaviour to insulator regime. On the metallic side of the MIT, the electrical conductivity is found to obey σ = σ + mT^1/2 down to 66 mK. The zero-temperature conductivity can be described by scaling laws.

The manner in which polymer chains pack and organize in thin film structures is crucial to maximizing the efficiency of charge and energy transport processes in solar cell devices. We use new spectroscopic and electrical imaging tools to spatially map and correlate local structure (chain conformation, packing, morphology) to local photocurrent generation efficiency. Both Raman and photoluminescence approaches are used that provide unique insights into important structural attributes and how they vary with film morphology. Simultaneous electrical measurements are then used to establish the roles of specific structural features to photocurrent production.

We present density functional theory calculations on the effect of subsurface titanium interstitial defects on the adsorption of O₂ and water on the anatase (101) surface. Our calculations show that for O₂ the strength of the adsorption is largely determined by the availability of electronic charge at specific adsorption sites above the interstitial, whereas for water the adsorption is mainly influenced by defect induced surface distortions. In particular, we found that the presence of a shallow subsurface interstitial makes O₂ adsorption very favorable, especially at surface 5-fold Ti sites above the defect, where the computed adsorption energy is as large as 2.5 eV. Lower lying interstitials have a less pronounced effect, since the excess electrons from the defect localize further down below the surface. For the case of water, instead, the adsorption energy does not depend significantly on the depth of the interstitial.

It is shown how second-harmonic generation microscopy (SHGM) can be used to study the architecture of molecules adsorbed inside zeolites. More specifically, probe molecule para-nitroaniline (PNA) in the two-dimensional pore system of ZSM-5 crystals is visualized. Analysis of the polarization dependency of the second-harmonic allows us to deduce the organization of the molecules inside the pores, which is notably different in the two pore types. Hence, it is possible deduce the internal structure of the zeolite from the organization of the PNA molecules. The SHGM technique is qualitatively compared to two-photon fluorescence microscopy (2PFM) via experimental results.

Raman scattering enhancement was observed in systems where different metal oxide semiconductors (TiO₂, Fe₂O₃, ZrO₂ and CeO₂) were modified with enediol ligands. The intensity of Raman scattering was dependent on laser frequency and correlated with the extinction coefficient of the charge-transfer complex of the enediol ligands and nanoparticles. The intensity and frequency of the Raman bands was found to depend on the chemical composition of the enediol ligand and the chemical composition (and crystallinity) of the nanoparticles. The intensity of the Raman signal depends on the number of surface binding sites, electron density of the ligands and their dipole moment. We also found that Raman scattering is observed for the bioconjugated system, where a peptide is linked to the surface of the particle through a catechol linker. These studies are important since these bioconjugates can be used to form the basis of Raman-based, in vitro and importantly in vivo biodetection, cell labeling and imaging, and nanotherapeutic strategies.

The adsorption of cytochrome c (cyt c) to a silica surface has been studied by use of evanescent wave broadband cavityenhanced absorption spectroscopy (EW-BBCEAS). Visible radiation from a supercontinuum source is coupled into an optical cavity consisting of a pair of broadband high reflectivity mirrors, and a total internal reflection (TIR) event at the prism/water interface. Aqueous solutions of cyt c are placed onto the TIR footprint on the prism surface and the subsequent protein adsorption is probed by the resulting evanescent wave. The time integrated cavity output is directed into a spectrometer, where it is dispersed and analysed. The high spectral brilliance of the SC affords a baseline noise comparable to evanescent wave cavity ring-down spectroscopy (EW-CRDS), and the broadband nature of the source allows observation of a wide spectral range (ca 250 nm in the visible). The system is calibrated by measuring the absorption spectra of dyes of a known absorbance. Absorption spectra of cyt c are obtained for both S and P polarized radiation, allowing information about the orientation of the adsorbed protein to be extracted.

Energy exchange between the electrons and phonons is particularly important to electron transport, and understanding this process will be vital for the realization of future graphene-based electronics. Epitaxial growth is a very promising approach for practical applications, as it has the ability to prepare graphene on a large scale and supported on a substrate. However, epitaxially grown graphene is highly inhomogeneous, with variations in the sample thickness occurring over length scale of a few micrometers. To pave the road for electronic devices based on epitaxial graphene, characterization methods with high spatial resolution are required. In this paper, we describe transient absorption microscopy as a novel tool to characterize graphene, and to interrogate the charge carrier dynamics. The carrier cooling exhibited a biexponential decay that showed a significant dependence on carrier density. The fast and slow relaxation times were assigned to coupling between electrons and optical phonon modes and the hot phonon effect, respectively. The limiting value of the slow relaxation time at high pump intensity reflects the lifetime of the optical phonons. Significant spatial heterogeneity in the dynamics was observed due to differences in coupling between graphene layers and the substrate. This is attributed to differences in coupling between the graphene and the substrate. These results point to transient absorption microscopy as a potentially important tool for characterizing graphene.

Colloidal dispersion of bimodal particles were self-organized inside water-in-oil emulsion droplets by evaporationdriven self-assembly method. After droplet shrinkage by heating the complex fluid system, small numbers of microspheres were packed into minimal second moment clusters, which are partially coated with silica nanospheres, resulting in the generation of patchy particles. The patchy particles in this study possess potential applications for selfassembly of non-isotropic particles such as dimmers or tetramers for colloidal photonic crystals with diamond lattice structures. The composite micro-clusters of amidine polystyrene microspheres and titania nanoparticles were also generated by evaporation-driven self-assembly to fabricate nonspherical hollow micro-particles made of titania shell.

The structures, densities of electronic states, and HOMO-LUMO gaps of surface-passivated ZnSe and CdTe nanocrystals are calculated using a first principles density functional pseudopotential method. The calculations are performed in real space without an explicit basis. The surfaces of the nanocrystals are passivated using fictitious partially charged hydrogen atoms. The value of the fractional charge is selected according to the type of covalent bond. The results of these calculations show that the fractional charge approach effectively removes the electronic states associated with the surface hydrogen atoms from the gap of group II-VI semiconductor nanocrystals. At the same time, the energies of the other electronic states are not significantly affected by the presence of partially charged hydrogen atoms on the nanocrystalline surface.

The elementary excitation in semiconductor quantum dots is the exciton, an excited electron-hole pair. The size and geometry of the dot confines the exciton thereby yielding quantum confinement effects. The simplest examples of size quantization effects include the spectrum of single exciton states which dominate the linear absorption spectrum and the Stokes shift for the spontaneous photoluminescence spectrum. Here, we report on our recent results exploring the structure and dynamics of both single excitons and multi-excitons in colloidal CdSe quantum dots using femtosecond state-resolved pump/probe spectroscopy. These experiments have revealed tremendous insight into the relaxation pathways of hot excitons, new aspects of exciton-phonon interactions, and in the first observation of the electronic structure of multi-excitons.

Time-domain non-adiabatic ab initio simulations are performed to study the phonon-assisted hot electron relaxation dynamics in CdSe spherical quantum dots (QDs) and elongated quantum dots (EQDs). EQDs have a narrower band gap and denser electron and hole energy states than QDs. As temperature increases, band gap values will become smaller due to thermal expansion effect. Also more phonons are excited to scatter with electrons and thus result in a higher relaxation rate for hot electrons. Besides, it is also found in our simulation that hot electron relaxation rate in EQDs has a weaker temperature dependence than in QDs, which could be attributed to the larger thermal expansion in EQDs.

In this report we explore how the surrounding environments around a single semiconducting nancrystal affect the photoinduced electron transfer, charge trapping fluorescence lifetime and fluorescence blinking. Using the time-correlated single photon counting techniques combined with confocal microscopy, we investigated photoluminescence of single CdSe/ZnS quantum dots embedded in agarose gel and on conductive substrates as examples. Understanding of the underlying mechanisms would allow us to better control of the photoluminescence properties of nanoparticles and to improve their performance in biophotonics and optoelectronics applications such as fluorescence markers, single-photon sources, photovoltaics and quantum dot lasers.

The multiple resistances to treatment, developed by bacteria and malignant tumors require finding alternatives to the existing medicines and treatment procedures. One of them is strengthening the effects of cytostatics by improving the delivery method. Such a method is represented by the use of medicines as micro/nano-droplets. This method can reduce the substance consumption by generating drug micro-droplets incorporated in substances that can favour a faster localization, than the classical mode of medicine administration, to the tumor tissues. This paper contains the results concerning the generation and study of micro/nano-droplets and the generation of micro-droplets with an inner core (medicine) and a thin layer covering it. We have measured the surface tension at water/air interface and water/oil interface for a medicine (Vancomycin) and we have generated and measured droplets of medicine containing a layer of Vitamin A by using a double capillary system. The micro/nano-droplets may be produced by mixing of two immiscible solutions in particular conditions (high rotating speed and/or high pressure difference). For this we have studied the generation of emulsions of vitamin A diluted in sunflower oil and a solution of a surfactant Tween 80 in distilled water. The concentration of surfactant in water was typically 4*10^-5M. We have studied in a batch stirred tank system the dependence of the droplet dimensions in emulsion, function of the mixing rotation speed, agitation time and components ratio. The droplet diameters were measured using a Malvern light scattering instrument type Mastersizer Hydro 2000M. We have obtained droplets with diameters smaller than 100 nm; the diameters distribution exhibited a peak at 65 nm.