This PDF file contains the front matter associated with SPIE Proceedings Volume 6768, including the Title Page, Copyright information, Table of Contents, and the Conference Committee listing.

Finite elements calculations have been performed of the surface enhanced Raman (SERS) activity of Ag coated dielectric nanowires. It is shown that the SERS fields and the angle of the peak field from intersecting nanowires can be changed through the angle of the nanowires. In addition, it is shown that the strength of the SERS enhancement and its spatial profile depend on whether the nanowires are in free space or on a substrate. Experimental data for benzene thiol on dielectric coated nanowires is shown to support the calculations. These results demonstrate the importance of geometry and local environment on electric field hot spots in the SERS process.

The ZnO nanostructures can be implemented in optoelectronic applications, piezoelectric pressure sensors, Spintronic devices, transducers and biomedical applications [1-8]. Use of these nanostructures, will also allow building of nanoscale nanosensors, nanocantilevers, field-effect transistors and nanoresonators for a variety of military, homeland security and, commercial applications. In this paper we review growth and characterization of ZnO nanowires on a variety of substrates. Experimental results on the ZnO nanowires grown on GaN and SiC are presented with growth morphology, structure analysis, and dimensionality control. We also discuss Raman and micro-Raman spectroscopy for characterization of ZnO nanostructures.

Low temperature metal catalyzed InP nanowires with diameters ranging from 50nm to 500nm using a single step MOCVD process at 450°C on (111)-oriented silicon substrates have been synthesized. The diameter range is much higher than the critical limit (~24nm for InP on silicon) reported by a recent theoretical work on coherent growth of nanowire heterostructures. This article presents the results of our investigation to highlight the possible factors that lead to the unusually large diameters and help realize stable nanowire heterostructures in a highly lattice mismatched material system. Our analysis finds dislocations formed at the interfacial plane of the heterostructure due to high lattice mismatch is the most influential factor contributing to very large diameters. We have simulation results which indicate that each added pair of orthogonal dislocation lines at the interfacial plane between InP and silicon supports ~12nm increase in the nanowire diameter. A maximum nanowire density of ~5×108 cm^-2 is estimated with growth rates ranging from 0.1 µm/min for the shortest nanowires and 10 μm/min for the longest ones.

In a combined approach toward the optimization of chemical gas sensors, Fourier transform infrared spectroscopy is used to investigate in situ the surface reactions taking place at the surface of semiconductor nanoparticles and to simultaneously monitor the variations of the free-carrier density. The correlation between the surface reactions and the changes in the infrared absorbance under gas adsorption/desorption cycles gives information on the chemical phenomena responsible for electrical conductivity variations and therefore for the gas detection. Interaction of CO and NO_X with tin oxide nanoparticles is presented and discussed. While the chemical reactions leading to the increase of the electrical conductivity under CO adsorption are relatively straightforward, the adsorption of NO_X is much more complex. It is demonstrated that, although generating a strong increase of the electrical conductivity, the NO_X adsorption on a fresh tin oxide surface is not fully reversible and actually poisons the surface. Subsequent NO_X adsorptions lead to reversible chemical reactions even though the electrical response of the sensor is weaker.

Nanoparticles, particles with a diameter of 1-100 nanometers (nm), are of interest in many applications including device fabrication, quantum computing, and sensing because their decreased size may give rise to certain properties that are very different from those exhibited by bulk materials. Further advancement of nanotechnology cannot be realized without an increased understanding of nanoparticle properties such as size (diameter) and size distribution. Frequently, these parameters are evaluated using numerous imaging modalities including transmission electron microscopy (TEM) and atomic force microscopy (AFM). In the past, these parameters have been obtained from digitized images by manually measuring and counting many of these nanoparticles, a task that is highly subjective and labor intensive. Recently, computer imaging particle analysis routines that count and measure objects in a binary image¹ have emerged as an objective and rapid alternative to manual techniques. In this paper a procedure is described that can be used to preprocess a set of gray scale images so that they are correctly thresholded into binary images prior to a particle analysis ultimately resulting in a more accurate assessment of the size and frequency (size distribution) of nanoparticles. Particle analysis was performed on two types of calibration samples imaged using AFM and TEM. Additionally, results of particle analysis can be used for identifying and removing small noise particles from the image. This filtering technique is based on identifying the location of small particles in the binary image, assessing their size, and removing them without affecting the size of other larger particles.

Thin Films of nanocrystalline cobalt oxide were formed by sol-gel method. Structure, optical properties and surface properties of these films were investigated by numerous characterization techniques. These films were successfully fabricated on glass substrates below 500°C. . Micropatterns of cobalt oxide thin films were also fabricated on glass and silicon substrates by employing a lift-off method. Crystal size of these nanocrystalline cobalt films could be successfully controllable by varying the amount of cobalt precursors and number of layers. These films were used as the seeding layers for carbon nanotube growth in a CVD process By changing the concentration of monomer precursors in the solgel coating solutions, different size nanoclusters hence different size carbon nanotubes could be synthesized in CVD process. This method can be used for controlled growth of carbon nanotubes for many different applications. In this paper, detail of these experimental results will be presented.

The growth of carbon nanotubes was investigated using a hot filament assisted CVD system. The silicon and glass substrates coated with catalyst were kept in a CVD furnace tube and the carbon nanotubes were grown by a hot filament assisted decomposition of methane (CH₄). Argon (Ar) was used as carrier for carbon. It was found that carbon nanotubes could be grown at as low as 400°C by the hot filament CVD system. The properties of carbon nanotubes were characterized by scanning electron microscopy (SEM), transmission electronic microscopy (TEM), and Raman spectroscopy. Those carbon nanotubes have similar properties as grown at high temperature. This method has high reproducibility and controlling capability of nanotube growth at low temperature region.

Although many groups have studied the initial growth stages of various metals, including indium, there is little information in literature on diameter distributions of indium in relation to film thickness or annealing conditions. This paper reports island size distributions of thermally evaporated In islands on Si (100) and Si (111) substrates for nominal film thicknesses ranging from 5 to 50 nm. Because indium has a low melting temperature, and therefore a high homologous temperature at room temperature, 3-dimensional islands form during deposition with no subsequent heat treatments needed. Island diameters were calculated using commercial image analysis software in conjunction with SEM images of the samples. It is found that there is a bimodal island diameter distribution for nominal indium thicknesses greater than 5 nm. While the diameters of the larger islands increase exponentially with nominal thickness, those of the smaller islands increase linearly, and therefore more slowly, with nominal thickness. For nominal thickness of 50 nm, the average diameters of the small and large islands differ by almost an order of magnitude. Anneal conditions were studied in an attempt to narrow diameter distributions. Samples of each nominal thickness were annealed at temperatures ranging from 360°C to 550°C and the diameters again measured. The range of island diameters become narrower with 360°C anneal and volume average island diameter increases by ~30-50%. This narrowing of the distribution occurs due to smaller islands being absorbed by the larger in a process akin to Ostwald ripening, which is facilitated by higher surface diffusivities at higher homologous temperatures.

We present finite-element calculations of the electrostatics of NWFETs and numerical simulations of band bending, charge distributions, and dopant ion diffusion in NWs. For NWFETs, we find that the semiconducting nature and finite length of the NW warrant sizeable corrections to capacitance calculations using the standard analytical formula and simulations that assume a metallic NW. We thus provide a comprehensive set of correction factors to these approximations. We also present a possible mechanism for explaining non-uniform dopant distributions involving electrodiffusion of charged dopant ions at high temperatures. We find that changes in the internal NW electrostatics due to non-uniform dopant distributions can have significant effects on the free carrier concentration and therefore conductivity of semiconductor NWs.

We have recently shown that dielectric/metal composite nanowires can exhibit very strong surface enhanced Raman (SERS) signals, when arranged in a random 3D geometry. Since we believe that the intersections of nanowires are critical in generating the high electric fields necessary for this enhancement, we are investigating this effect under more controlled conditions. Thus, we will discuss the formation of nanowire arrays by in-situ growth, achieved by the control of nanowire material/substrate combination, as well as ex-situ nanowire array formation involving e-beam lithography. The effects of nanowire geometry and the resulting SERS behavior show the importance of the dielectric/metal configuration, as well as the importance of nanowire geometry in the SERS effect.

InN is an attractive material for novel nanoscale optoelectronic devices due to its low band gap and superior transport characteristics. Recently, Chang et al. [J. Electron. Mater. 35, 738 (2006)] presented measurements showing an anomalous resistance observed for InN nanowires with diameters less than 90nm. We examine possible theories presented in literature to explain the extraordinary observation and propose a possible explanation for the reported observations based on the unique attribute of InN − high density surface electron accumulation layer. The presence of high density accumulation layer at the surface leads to two distinct conduction mechanisms in InN viz. surface and bulk. For large diameter InN nanowires, bulk conduction is proposed to be the dominant mechanism whereas in small diameter nanowires both surface and bulk conduction contribute to carrier transport.

Nanostructure and molecular interface have currently received the great attractions for highly efficient, simultaneously analysis of a number of important biomolecules from proteomics to genomics. Outstanding optical property of noble metal nanostructures, localized surface plasmon resonance (LSPR), is a powerful phenomenon used in many chemical and biological sensing experiments. This report described two types of gold-capped nanostructures: nanoparticle and nanopore which reveal the strong excitation of LSPR spectra in the UV-visible region. The optical absorbance properties of these nanostructures governing its sensitivity to local environment were studied. The flexibility in design of the goldcapped nanostructures was evidently displayed on the wide-range capacity to develop in many types, from single to multiple to microfluidic formats. Moreover, chemical modifications on the nanostructure surface were thoroughly exploited to archive a highly sensitive protein and gene sensors such as using Protein A linker for orientation antibody or using specific binding of streptavidin and biotinylated PNA or DNA probes... Lastly, we introduced a new form of optical sensor, involving the coupling between interferometry and LSPR properties on the surface of gold-capped nanopore structure. Our optical biosensing devices connecting with the gold-capped nanostructures including both nanoparticle and nanopore are applicable to highly sensitive monitoring the interactions of other biomolecules, such as proteins, whole cells, or receptors with a massively parallel detection capability in a highly miniaturized package.

A new type of nanoscale field emitter array, consisting of carbon nanonecklaces and nanotentacles, has been produced by a novel multi-level self assembly process employing flexible porous alumina films. The field emission characteristics of the carbon nanostructures were measured using a scanning field emission microscope (SAFEM) and they exhibited strong Fowler-Nordheim emission. This new synthetic approach could find potential applications in flexible and inexpensive arrays of nanoscale cold cathode emitters.

Electrical properties of individual Single-Walled Carbon Nanotube/rope in the configurations of 2-probe resistance, field effect transistor (FET), and thermopower have been measured. It is shown that oxygen adsorption in SWNTs is indeed a physisorption process. The p-type behavior of SWNTs in the ambient is believed to be due to the Fermi level pinning at impurity states of O^2- near the top of the valence band of the tube. Chemisorption processes involving ammonia and nitrous oxide have been explored by studying FET properties. The thermoelectric power of individual ropes of SWNTs is measured and related to the FET properties.

We fabricated a photo-conducting device with InP nanowires bridged between phosphorous-doped hydrogenated amorphous silicon electrodes. Photoresponse of the device with DC bias was characterized with a white light source and a 630nm He-Ne laser. Experimental results from a large number of devices demonstrate a persistent photoconductivity, a very unique feature of interest. After the light source is shut off, the photogenerated excess carriers recombine very slowly over time and the effect is manifested in the form of persistent photocurrent that takes hours to decay to the dark current level in the range of ~15 nA. Quasi exponential decay of the persistent photocurrent is observed with higher decay rate at the initial stage just after the light source is turned off. Persistent photocurrent magnitude varies with the magnitude of bias voltage, intensity and wavelength of the optical illumination. Experimental decay constant is determined from 0.237/min for -8V bias to 0.174/min for -2V bias. The long recombination time can be attributed to the carrier trapping in the light-induced traps, defects in nanowires and/or in the interface between the nanowires and the amorphous silicon electrodes. Slow recombination process may also originate from the spatial separation of photogenerated electrons and holes by built-in electric fields due to band bending at the heterostructure interfaces between InP nanowire and amorphous silicon electrodes.

The origins of the surface-enhanced Raman (SERS) effect have been widely studied and are generally accepted as understood. However, there is still a need to provide a satisfactorily complete model which addresses the well known phenomena in which some molecules exhibit weak or even no SERS response at all. The relative intensities of vibrational modes observed in SERS can depend strongly on the mechanism of surface adsorption, such as bond type (covalent/noncovalent) and number of covalent bonds. Thus, in this experimental study the role of surface adsorption in surface-enhanced Raman scattering is investigated. A simple group of Benzene thiols was chosen to facilitate comparison with theoretical models. Experimental results with consideration towards surface bond strengths and reduction in degrees of freedom due to single and multiple surface bonds is presented and their effect on the relative intensities and positions of observed vibrational modes observed in the SERS spectra are discussed. The relative stability of molecules in the presence of nanostructures exhibiting strong and weak local electric fields will also be presented and discussed.

Aiming at the fabrication of nano-structured materials and hybrid aggregates we synthesize and characterize nanoscopic objects from polymers, noble metals, and semiconducting materials. As an example for the preparation of mesoscopic functional assemblies we first describe the layer-by-layer deposition of dendritic building blocks to the walls of nanometric pores in an anodized alumina (Al₂O₃) substrate used as template. After dissolution of the matrix hollow nano-tubes are obtained with an outer diameter that corresponds to the pore diameter and with a wall thickness that is determined by the number of layers deposited. The tube length is given by the pore depth of the template and reaches in our examples up to 80 micrometers. Next, a single colloid particle-based templating protocol for the fabrication of non-trivial Au nanostructures is described. The obtained nano-crescents can be varied in terms of their size and shape over a wide range (at the hundreds of nanometers scale). Their plasmonic resonance behavior, e.g., the spectral position of their (multipole) absorbance peaks shows a characteristic dependence on the polarization of the exciting laser light. Finally, the optical properties of colloidal semiconductor (quantum dots) are analyzed. In particular, the spectral photoluminescence properties are described for nanotube assemblies that are fabricated by the deposition of (positively charged) dendrimers alternating with (negatively charged) quantum dots of different emission wavelength (energy transfer cascades). The last example of a hybrid assembly concerns the electronic coupling of (the HOMO/LUMO levels of) semiconducting nanoparticles to (the Fermi level of) a gold electrode.

A new route to grow single-crystal semiconductor nanostructures is reviewed. Unlike conventional epitaxial growth of single-crystal semiconductor films, the proposed route for growing semiconductor nanostructures does not require a single-crystal semiconductor substrate. In the proposed route, instead of using single-crystal semiconductor substrates that are characterized by their long-range atomic order, a non-single-crystal template layer that possesses short-range atomic order prepared on a non-single-crystal substrate is employed, providing epitaxial information required for singlecrystal semiconductor nanostructures. On the template layer, epitaxial information associated with its short-range atomic order is available within the size of area that is comparable to that of a nanostructure in the early stage of evolution. In this particular demonstration, hydrogenated silicon was utilized to provide short-range atomic order required for epitaxial growth of indium phosphide nanowires. Indium phosphide nanowires were grown on the hydrogenated silicon surfaces by low-pressure metalorganic chemical vapor deposition with the presence of colloidal gold nanoparticles. The hydrogenated silicon used as a template layer and the resulting indium phosphide nanowires were systematically studied.

Ion channels are one of the most important categories of proteins in animal and plant physiology. Their function dictates activities as far reaching as controlling transmembrane potential in the nervous system to regulating plant cell volumes in extreme environments. The functionality of these proteins is notoriously difficult to assess, and there is a great demand for high throughput measurement systems which can monitor channel activity in cellular systems. There have been significant recent advances in the field of chip-based electrophysiology, especially microfabricated patch-clamp systems. Our research group is currently pursuing research in this area, and here we provide a tutorial that summarizes all of the relevant work in the field to date. We have also noted areas where we feel that future research in the field is likely to provide improvements in device design, manufacturability and testing of these interesting and important devices.

We discuss our recently developed method to selectively functionalize mixed ligand gold nanoparticles at two specific defect points in the ligand shell and to join the nanoparticles together into chains by placing reactive molecules at those two points. Here we use infrared spectroscopy to confirm that the process of functionalizing those defect points rapidly reaches equilibrium. In addition, we demonstrate the quantitative reproducibility of the chaining reaction, and we discuss the case in which we perform the same functionalization procedure on homoligand nanoparticles.

A scheme for programmable nanoscale self-assembly that allows the precise arrangement of components in 2D or 3D geometries would have a wide range of applications. The ultrasmall size and programmability of the nucleotide subunits in DNA offer a versatile basis for such a scheme. In this paper, I discuss recent steps toward nanocomponent assembly by 2D DNA scaffolding, including 1) incorporation of 1.6-nm Au nanoparticles in a 2D DNA scaffolding, 2) in situ assembly of 5-nm metallic nanoparticle arrays with precisely controlled dimensions and 3) sequence-encoded assembly of different sized nanocomponents in a common scaffolding. In the near term, this ability to precisely assemble nanocomponent arrays could enable the study of electronic, magnetic and plasmonic interactions among particles in a regime where quantum confinement, Coulomb blockade, and magnetic effects play important roles. Eventually, such self-assembly techniques could lead to a manufacturing technology for nanoelectronics, nanophotonics, and nanosensing.