This PDF file contains the front matter associated with SPIE Proceedings Volume 8969, including the Title Page, Copyright information, Table of Contents, and Conference Committee listing.

Carbon nanotube assemblies can be used for specific applications such as sensors and filters. We present a method and proof-of-concept to directly grow vertically-aligned carbon nanotube structures within sealed enclosures by means of a feedback-controlled laser-assisted chemical vapor deposition technique. The process is compatible with a variety of micro-fabrication processes and bypasses the need for post-process packaging. To further investigate the possibilities of small CNT structures we present a femtosecond laser patterning method. This laser is used to pattern either the catalyst before CNT growth, modifying the surface and catalytic conditions, or the CNT structures directly after growth.

Simple kinetic models of carbon nanotube growth have been able to successfully link together many experimental parameters involved in the growth of carbon nanotubes for practical applications including the prediction of growth rates, terminal lengths, number of walls, activation energies, and their dependences on the growth environment. The implications of recent experiments utilizing in situ monitoring of carbon nanotube growth on our past kinetic model are first reviewed. Then, sub-second pulsed feedstock gas introduction is discussed to explore the nucleation and initial growth of carbon nanotubes in the context of the kinetic model. Moreover, kinetic effects in "pulsed CVD" - using repeated pulsed gas introduction to stop and restart nanotube growth - are explored to understand renucleation, the origin of alignment in nanotube arrays, and incremental growth. Time-resolved reflectivity of the surface is used to remotely understand the kinetics of nucleation and the coordinated growth of arrays. This approach demonstrates that continuous vertically aligned single wall carbon nanotubes can be grown incrementally by pulsed CVD, and that the first exposure of fresh catalyst to feedstock gas is critical to nanotubes site density required for coordinated growth. Aligned nanotube arrays (as short as 60 nm) are shown to nucleate and grow within single, sub-second gas pulses. The multiple-pulse growth experiments (> 100 pulses) show that a high fraction of nanotubes renucleate on subsequent gas pulses.

Laser ablation (LA) is a unique tool for nanoparticle synthesis. The main advantages of this method are in its green character and in the possibility of a control over particle size. In this study, we examine nanoparticle formation by laser ablation under different experimental conditions and analyse the results based on the developed models. The dynamics of the laser plume expansion is examined revealing the role of the background pressure and laser pulse parameters. As a result, the ablated material is compressed and a part of it becomes supersaturated. The so-called "primary" nanoparticles are formed at this stage. Then, nanoparticle aggregation/fragmentation enters into play leading to the formation of the secondary particles. In addition, laser- assisted fragmentation of nanoparticles is also examined. Based on numerical modeling we shed light on the above mechanisms by using different numerical approaches, such as molecular dynamics, Monte Carlo, numerical hydrodynamics, and analytical analysis. Calculations are performed for metallic targets under different background conditions. The obtained results explain recent experimental findings and help to predict the role of the experimental parameters. The performed analysis thus indicates ways of a control over nanoparticle synthesis

The synthesis of metal nanoparticles by femtosecond laser vaporization of nm-thickness metal films is explored with the goal of comparing the salient features of femtosecond-based through thin film laser ablation (TTFA) to that of ns TTFA, and testing the feasibility of direct synthesis of clean nanoparticle alloys to explore the synthesis of carbon nanotubes by chemical vapor deposition. It is demonstrated that evaporated metal films are cleanly removed from quartz substrates using the technique, producing a highly forward-directed plume of nanoparticles (angle of divergence of ~2.5°) which were cleanly deposited onto different supports for analysis. TEM showed the nanoparticles were spherical with diameters that ranged from a few nm to hundreds of nm in a bimodal fashion. Unlike ns-TTFA, it was found that raising the pressure had no effect on the intensity of the smaller mode within the distribution, suggesting that nanoparticle formation by gas phase condensation was not at play under the present conditions. Close examination of size distributions from a 20 and 10nm Pt film revealed an 80nm downshift in the position of the large mode within the distribution, suggesting film thickness may provide a route to controlling the modal distribution of nanoparticles produced by this method. Lastly, particles sourced by a Fe/Mo bilayer film were found to be effective in growing single wall carbon nanotubes by atmospheric chemical vapor deposition, indicating sufficiently small and catalytically active particles were produced.

Fluorescence microscopy is used to explore the efficacy of surface acoustic waves (SAWs), as generated by a pulsed laser “tapping” a surface, to enhance the surface mobility of molecular adsorbates. The candidate adsorbate system under investigation comprises a series of gold clusters that are directly prepared on a silicon (111) surface by laser ablation of nanoparticles. Within the debris field the gold cluster Au8 is tracked because the fluorescence spectrum is known. The gold cluster is distinguished by using band-pass filters and tracked by fluorescence. The SAW source is a pulsed UV (355nm) laser operating at a repetition rate of 100Hz, where the laser fluence is set below the damage threshold of silicon. The experiment measures the location of the emitted light for a particular cluster through a high magnification (100X) imaging microscope that is integrated with a water-cooled (512x512 pixel) EMCCD camera. Image processing algorithms are used to track the light emission. Initial results show that the cluster Au8 moves approximately 0.5 Angstroms/s (when the excitation source is approximately 0.65 cm away). Diffusion and displacement data of adsorbed atoms and molecules on surfaces is sparse, though this value is similar for displacements of gold clusters on polymer films at 440 K, some metal-on-metal adatoms at room temperatures, and other nonmetal-metal interactions. The experiment also includes a laser heterodyne probe which measures the frequency distribution of the surface displacement induced by the pulsed SAWs. Results show that even at a source-to-probe distance of 1.8cm, frequency components up to 120MHz are present. These results suggest that “growing”/synthesizing thin films via surface aggregation of cluster compounds may be feasible.

Two-photon polymerization (TPP) is a promising micro/nanofabrication technique, which is capable of fabricating 3D micro/nanostructures beyond the diffraction limit of light. However, the study of TPP process with a focus on the dependence of degree of conversion on TPP parameters using a non-destructive and efficient method is still lacking. We studied the quantitative relationships between the TPP parameters and the cross-linking of an acrylic-based IP-L 780 photoresist via systematic Raman characterization. The differences in the Raman spectra between the non-polymerized and the polymerized IP-L 780 photoresists were observed by probing the excitation of carbon-carbon double bond (C=C) vibrations. We obtained the relationship between the degree of conversion in TPP and the Raman spectra of the IP-L 780 resin, in which the intensity of the characteristic Raman peak of IP-L 780 at 1635 cm^-1 decreases with the increase of the TPP laser dose. A mathematic model of the degree of conversion with respective to the TPP parameters, including laser average power and writing speed, has been established. The method provides a simple and effective way to characterize and optimize the TPP micro/nanofabrication processes. The established model for the degree of conversion as the function of TPP parameters will contribute to the advanced 3D TPP micro/nanofabrication by providing a guidance to optimize the laser doses, voxel sizes, and the mechanical strength of the polymers.

Recently, laser irradiation (LI) of colloidal nanoparticles (NPs) using a non-focused laser beam at moderate fluence attracts much attention as a novel and simple technique to obtain submicron-sized spherical particles. In the present study, we applied this technique to prepare gold SMPs. It was revealed that agglomeration of the source nanoparticles prior to laser irradiation is necessary to produce SMPs. However, when the agglomeration occurred in too much extent, significant amount of the source particles remained as the sediment after LI, leading to the lowering of the formation efficiency of SMPs. Therefore, the control of the agglomeration conditions of the source NPs is necessary to obtain SMPs efficiently. In the present study, we tried to adjust the agglomeration conditions of the source NPs by adjusting the concentration of citrate that was used as the stabilizing reagent of the source NPs. It was revealed that SMPs were obtained efficiently while the sedimentation of the source NPs were suppressed when the concentration of citrate was adjusted around 0.01-0.005 mM. In addition, observation of the temporal change in the shape of the colloidal particles during LI revealed that there is an induction period in which no formation of SMPs is brought about by LI. This finding suggested that LI removes the citrate ligands from the source NPs and induces the agglomeration of the source NPs, i.e. the agglomeration condition of the source NPs is also controlled by LI.

Creating the conditions so that matter naturally self-arranges at the nanoscale under a homogeneous excitation is an exciting challenge for the development of efficient and cost-effective processes. Sub-micrometer periodic templates can be formed spontaneously on materials by low-energy ion sputtering or with lasers. In the latter case, the formation of self-organized grating-like structures requires a high temperature rise and generally results from interactions with ultrashort laser pulses. Recently, a few studies have dealt with self-formed periodic patterns of metal nanoparticle assemblies, but they only reported changes in the spatial and size distributions of metal nanoparticles deposited on surfaces prior to interaction with femtosecond lasers. Here, we show that metal nanoparticles can grow in a selforganized manner within a waveguide illuminated from free-space by a continuous wave visible laser. We report the conditions that give rise to the generation of such 1D nanoparticle gratings and describe the parameters that influence the grating characteristics. We explain the mechanisms involved in the formation of such nanostructures on the basis of interference phenomena between the incident wave and guided modes.

Recent progress in modified Surface Enhanced Raman Scattering (SERS) using Ag nanoparticles makes them promising optical technique for direct gas sensing of interest. However, SERS has been shown to provide sub ppb level detection of the compounds in the vapor phase. The major problem with the sensitivity scaling-up was in the development of fabrication technology for stability and reproducibility of SERS substrates. We report an optimization of 1-propanethiol coated multiple Ag nanoparticle layers on SiO₂ substrate as well as new records of real-time, simultaneous vapor phase detection of toluene and 1-2 dichlorobenzene by the radiation of fiber optic coupled 785 nm diode laser and spectrograph. Multiple depositions of Ag NPs were loaded on SiO₂ and soaked in 1-propanethiol solution for 24 hours to modify the surface into hydrophobic due to the characteristics of vapor phase of our interests. Raman bands at 1003 cm^-1 and 1130 cm^-1 for toluene and 12DCB, respectively were compared to 1089 cm^-1 and each gas concentration in 1000 mL flask were calculated as a function of each vapor phase ratio. The saturation of toluene and 12DCB were limited only by 800 ppm and the detectable range was 0.6-800 ppm.

Titanium (Ti) is one of the most used biomaterials in metals. However, Ti is typically artificial materials. Thus, it is necessary for improving the biocompatibility of Ti. Recently, coating of the titanium dioxides (TiO₂) film on Ti plate has been proposed to improve biocompatibility of Ti. We have developed coating method of the film on Ti plate with an aerosol beam. Periodic structures formation on biomaterials was also a useful method for improving the biocompatibility. Direction of cell spreading might be controlled along the grooves of periodic microstructures. In our previous study, periodic nanostructures were formed on the film by femtosecond laser irradiation at fundamental wave (775 nm). Period of the periodic nanostructures was about 230 nm. In cell test, cell spreading along the grooves of the periodic nanostructures was observed although it was not done for the film without the periodic nanostructures. Then, influence of the period of the periodic nanostructures on cell spreading has not been investigated yet. The period might be changed by changing the laser wavelength. In this study, the periodic nanostructures were created on the film with femtosecond laser at 775nm and 388 nm, respectively. After cell test, cell spreading along the grooves of the periodic nanostructures was observed on 775 nm and 388nm laser irradiated areas. Distribution of direction of cell spreading on laser irradiated area was also examined. These results suggested that controlling the cell spreading on periodic nanostructures with period of 230 nm was better than that with period of 130 nm.