Laser vaporization (LV) is a remarkably versatile technique for the catalytically-aided synthesis of nanomaterials, such as single-wall carbon nanotubes (SWNT). SWNT show remarkable promise for future generations of electronics and structural materials, however their application and commercialization has been hampered by a lack of control over the synthesis process, and low production quantities. Time-resolved in situ spectroscopic investigations of the laser-vaporization SWNT-synthesis process are described which are yielding some of the first direct determinations of carbon nanotube growth mechanisms and rates necessary to evaluate strategies for controllable synthesis and large- scale production. Our measurements indicate that SWNT grow over extended annealing times during the LV process by the conversion of condensed phase nanoparticle feedstock. These measurements were extended to grow carbon nanotubes by CO₂-laser-annealing heat treatments of carbon and metal nanoparticle mixtures, offering an alternative synthesis approach to vapor-phase methods. These results present opportunities for scaled-up production of nanomaterials compatible with commercial high-power laser technology.

Catalytic activities of Fe, Pt, and Ni/Co metals were compared in the synthesis of single-wall carbon nanotubes (SWNTs) by using CO₂ laser vaporization. In room temperature laser vaporization in AR gas under pressures of 150-760 Torr, a small amount of SWNTs, forming thin bundles, were synthesized by Pt and Ni/Co catalysts. However, SWNTs were not synthesized by using an Fe catalyst. The central diameters of SWNTs were 1.51 and 1.33 nm for the Pt and Ni/Co catalysts, respectively. At 1200 degree(s)C, thick bundles of SWNTs with a central diameter of 1.39nm were synthesized for Ni/Co in high yield (>70%0. However, the increase in SWNT yield was not significant when using a Pt catalyst at 1200 degree(s)C. We discuss catalytic growth of SWNTs in terms of eutectic temperatures of Pt-C and Ni/Co-C phases.

It is demonstrated that coherent laser excitaton results in a selective modification of nanocrystals, results in the change of size, shape and crystal structure of nanocrystals.

Colloidal CdSe-ZnS semiconductor quantum dots (QDs) have tunable narrow-band luminescence emission and high resistance to photodegradation, properties that make them promising for use as fluorescent labels in biotechnological applications such as fluoro-immunoassays and in cellular imaging. We have developed efficient methods for conjugating these inorganic fluorophores to antibodies via the use of a molecular adaptor protein, the B2 domain of streptococcal protein G appended with an electrostatic interaction domain, which acts as a bridge between the QD fluorophore and antibodies. In this approach, coupling of the adaptor to the QD is driven by electrostatic self-assembly, while bridging to the antibody is driven by specific interactions. In the present study, we present fluoro-immunoassay studies employing QD-antibody conjugates for the detection of low levels of the explosive hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX). We will also explore the use of self-assembled QD-protein-receptor complexes in Foerster energy transfer assays, where the QD emission can be altered by a quenching dye receptor in a QD-protein-receptor conjugate.

We demonstrate that laser-based thermal processing of an ensemble of metal nanoparticles on a transparent substrate can be highly selective with regard to the dimensions of the particles. The selectivity originates from the resonant dependence of the absorption cross section for surface plasmon excitation of a metal nanoparticle on its size and shape. This makes possible resonant heating by selective absorption and subsequent rapid quenching of the deposited energy by electron-phonon coupling. As a result, the temperature rise of a nanoparticle is determined by the absorbed photon energy and by the thermal properties of the substrate rather than by the heat flow between the particles, provided their number density and the laser pulse duration are properly chosen. Finally, desoprtion and diffusion activated by the temperature rise cause substantial changes of the particle size and shape. These laser-induced modifications are even more selective than laser-stimulated heating due to a threshold-like dependence of the thermally activated processes on the temperature of an individual particle. Altogether this can be exploited in a novel technique to control the size and shape distribution of supported metal nanoparticles through laser illumination in a very precise manner. Here, we present a detailed theoretical treatment of all aspects of selective laser- induced thermal processing of nanoparticles.

Si/SiO_x films were fabricated by Pulsed Laser Ablation from a silicon target in a residual gas. The films were crystalline with minimal grain size of 2-4 nm and had a porous morphology. The film structure was found to be extremely sensitive to deposition conditions with porosity depending on the gas pressure during the deposition. In particular, the increase of helium pressure from 0.2 to 4 Torr in different depositions led to a gradual porosity (P) increase from 10% to 95%. The porosity increase was accompanied by a slight increase of mean crystal size in the deposit. It has been established that photoluminescence (PL) properties were different for films with different porosities. For low porous films (P < 40 %), we observed PL signals with peak energies between 1.6 and 2.12 eV depending on helium deposition pressure. In contrast, PL properties of highly porous films (P > 40%) were mainly determined by post-deposition oxidation phenomena. They led to an enhancement of PL bands around 1.6-1.7 eV and 2.2-2.3 eV, which were independent of deposition conditions. Similar 2.2-2.3 eV signals were observed after strong film oxidation through a thermal annealing of films in air or through a silicon ablation in oxygen-containing atmosphere. Mechanisms of film formation and PL origin are discussed.

We review desorption and structural changes on Si(001)-(2x1) surfaces induced by nanosecond laser irradiation with fluences well below thresholds of melting and ablation. Atomic imaging of the irradiated surface by scanning tunneling microscopy (STM) has shown that bond breaking takes place at intrinsic lattice sites and at atomic sites neighboring vacancies, leading to newly generation of vacancies and sequential growth of vacancy clusters. The bond breaking selectively removes outermost Si-dimers, exposing 1x1 like new phase. Repeated irradiations with a fixed fluence enlarge the new phase region up to 80% of the total surface area with a constant. The major products by the bond breaking are Si atoms emitting with a fluence-independent translational energy distribution, indicating strongly that the bond breaking is a purely electronic. Both efficiencies of Si-desorption and vacancy formation follow a common superlinear function of excitation intensity and show strong photon energy dependence with a prominent peak at 2.7 eV. The electronic bond breaking is shown to originate from nonlinear localization of excited species in surface electronic states.

A novel dry, vacuum-free laser-assisted method for a fabrication of nanostructured Si/SiO_x layers on a silicon wafer is demonstrated. This method uses the phenomenon of air optical breakdown to modify a semiconductor surface. Pulsed radiation from a CO₂ laser was focused on a silicon wafer to initiate the optical breakdown in atmospheric pressure air. After several breakdown initiations near the threshold of plasma production, a gray-tint layer was formed under the radiation spot on the silicon surface. The size of the processed area could be controlled by varying the radiation focusing conditions. Properties of the layers were studied by optical and SEM microscopies, XPS, XRD, Specular X-ray Reflectivity and PL spectroscopy. It was found that the layers had the porosity of about 75-80% and contained nanoscale holes and channels. They consisted of silicon nanocrystals embedded in SiO₂ matrix and exhibited strong photoluminescence (PL) at 1.9-2.0 eV, which could be seen by naked eyes. Possible mechanisms of nanostructure formation and PL origin are discussed. The method can be used for a controlled local patterning of photoluminescent nanostructured materials.

Erbium (Er)- or phosphorus (P)-doped silicon nanocrystallites (nc-Si) buried in SiO₂ layer were fabricated by laser ablation and the subsequent thermal annealing; i.e. solid-phase growth. The doping effects have been studied by measurements of temperature-dependent photoluminescence (PL) of Er from 6 K to 300 K and PL measurements of nc-Si at room temperature, as well as electron-spin-resonance (ESR) measurements of P donors in nc-Si. The results demonstrates that the solid-phase growth method can realize an intense 1.5micrometers Er PL without thermal quenching and P-donor doping can be attained in nc-Si. These results suggest that impurity doping is useful for modifying furthermore quantized properties of Si nanostructures and making them more functionally active.

The manipulation of magnetic anisotropy in a Co/Pt nano- multilayer(nano-ML) system with particles being embedded is reported. The samples, fabricated by a newly-developed normal incidence pulsed laser deposition (NIPLD) method, have salient magnetic properties, different from particle- free samples of almost the same structure: (1) they exhibit bi-axial magnetic anisotropies and (2) there exists a critical field at which the change in easy direction from a parallel direction to a perpendicular direction and vice versa. The careful manipulation of particles and nano- layers has also allowed us to control the degree of magnetic anisotropy by embedding particles in a well-defined nano- multilayer system: uni-axial anisotropy to bi-axial one and vice versa. This work indeed clearly shows that the integration of nano-building blocks into nano-structures can tailor properties of nano-materials.

The potential of a novel silver-silver oxide system for optical data storage with fluorescent readout has been discovered and developed. These properties arise from photolytic production of highly fluorescent single Ag_n molecules (n = 2-6 atoms) from silver oxide. Optical experiments with a 514.5nm Ar⁺ laser and a 100W Hg lamp allow determination of single Ag_n nanocluster absorption cross- sections ((sigma) = 8 x 10^-15 cm²) and saturation intensities (I_sat = 200 W/cm² at 514.5 nm). Single molecule fluorescence experiments have elucidated the dynamics of AgO photoactivation and subsequent Ag_n nanocluster emission. Additionally, excitation, wavelength and intensity dependent dynamics are investigated. Results clearly show dependence on wavelength and intensity in Ag_n nanocluster creation and destruction.

High-energy ion implantation is one of the unique methods to fabricate nano-scale structures, taking advantage of the spatial controllability and the non-equilibrium atomic injection. Metal-ion implantation into a transparent insulator creates a metal nanoparticle composite, which is promising as a nonlinear optical material with ultrafast response. Radiation damage of substrates and/or nanoparticles, which is inherent in ion implantation, is a drawback for optical performance of the nanoparticle composites. It is desired to annihilate radiation damage without melting the matrix. We have applied laser irradiation of sub-gap energy during heavy-ion implantation. Copper ions of 3 MeV and laser of a sub-gap energy (2.3 eV) irradiated insulators of a-SiO₂ and spinel MgO•2.4(Al₂O₃). The dose rate varied up to 10 (mu) A/cm² for Cu ions of 3 MeV and up to 0.2 J/cm²•pulse at 10 Hz for YAG-SHG laser. Only when ions and photons were simultaneously irradiated at the higher photon intensity (> 0.1 J/cm²•pulse), the insulators were effectively bleached in the optical absorption spectra. As well as the bleaching, precipitation enhancement and atomic desorption took place. The results indicate importance of dynamical electronic excitation during ion irradiation and that the photon irradiation enhances atomic displacements either at the surface or in the bulk.

We have developed a novel codeposition process system for producing quantum nanostructures composed of monodispersed silicon (Si) nanoparticles and indium oxide (In₂O₃) thin films. The codeposition process system consists of a chamber for the formation of nanoparticles by pulsed laser ablation (PLA) using a Nd: YAG SHG laser beam in inert background gas, a low-pressure differential mobility analyzer (LP-DMA) for classifying Si nanoparticles, and a chamber for the deposition of Si nanoparticles and In₂O₃ thin films. The classified Si nanoparticles have sharp size distribution of which the geometrical standard deviation is 1.2; thus, we call the classified Si nanoparticles monodispersed. The monodispersed Si nanoparticles were deposited onto a substrate and In₂O₃ was codeposited by PLA using an ArF excimer laser beam in the deposition chamber. By controlling background gas pressures in PLA and gas flow rates in LP-DMA, the codeposition of monodispersed Si nanoparticles and In₂O₃ thin films was realized. Evaluation of the nanostructures was carried out using a high-resolution transmission electron microscope. From observation of the nanostructures by energy dispersive spectroscopy, we found that silicon, indium and oxygen were deposited homogeneously. Furthermore, we attempted to modify the surface of monodispersed Si nanoparticles by introducing oxygen gas in the deposition chamber.