Nanowires are potentially important constituents for nanoscale devices. Manipulation of nanowires in suspension in order to assemble them for device applications has been a formidable problem. Previously most methods have involved the use of external magnetic fields acting on magnetic nanowires. Using ac electric fields applied to strategically designed microelectrodes, we show how nanowires, both magnetic and nonmagnetic, in suspension can be driven to align, to chain, to accelerate in directions parallel and perpendicular to its orientation, to concentrate onto designated places, and to disperse in a controlled manner with high efficiency despite an extremely low Reynolds number (of the order of 10^-5). This method of manipulating nanowires can also be applied to other small elongated entities such as carbon nanotubes.

We present a novel nanotube-on-insulator (NOI) approach to produce high-yield nanotube devices based on aligned single-walled carbon nanotubes. First, we managed to grow aligned nanotube arrays with controlled density on crystalline, insulating sapphire substrates, which bear analogy to industry-adopted silicon-on-insulator substrates. Based on the nanotube arrays, we demonstrated registration-free fabrication of both top-gated and polymer-electrolyte-gated field-effect transistors with minimized parasitic capacitance. In addition, we have successfully developed a way to transfer these aligned nanotube arrays to flexible substrates. Our approach has great potential for high-density, largescale integrated systems based on carbon nanotubes for both micro- and flexible electronics.

The paper describes the fabrication, characterization and applications of novel luminescent quantum dots fluorescence resonance energy transfer (FRET) based enzymatic activity probes. The luminescent probes are based on FRET between luminescent quantum dots that serve as donors and rhodamine acceptors that are immobilized to the surface of the quantum dots through peptide linkers that contain selective enzymatic cleavage sites. Upon enzymatic cleavage of the peptide linkers the rhodamine molecules no longer provide an efficient energy transfer channel to the quantum dots, which lightes up the initially quenched the quantum dots. The quantum dots based probes were applied for detecting enzyme activity and screening enzyme inhibitors. They were also used for the measurement of extracellular matrix metallproteinases (MMPs) activity in normal and cancerous breast cells tissues.

We describe our recent results on the formation of catalyst-free III-V semiconductor nanowires and related nanostructures utilizing selective-area metalorganic vapor phase epitaxial (SA-MOVPE) growth. Array of vertically aligned nanowires are grown on partially masked GaAs and InP substrate along the [111]B or [111]A directions, respectively. The alignment and size of the nanowires are controlled by the mask patterning as well as growth conditions. Nanowires containing heterostructures in their radial direction have also been realized by controlling the growth mode during SA-MOVPE. Their optical and transport properties are also investigated and described.

Nanowires are interesting candidates for thermoelectric applications because of their potentially low thermal conductivity and high power factor. However, measurements at the single-wire level are challenging and tend to lack detailed information about the atomic-level structure of the sample and contacts. We are modifying a high-resolution transmission electron microscope (HRTEM) with integrated scanning tunneling microscope (STM) for in-situ measurements of the thermoelectric properties of individual nanowires and nanotubes. A slender hot-wire probe is used to make electrical and thermal contact to the free end of a nanowire or nanotube. The electrical conductance of the nanowire/nanotube can be measured with the usual STM mode of operation. The Seebeck coefficient can be extracted from the transient response to a step change in the joule heating of the hot-wire probe. The thermal conductance can be calculated from the temperature and heat leakage of the hot-wire probe. These measurements are combined with detailed HRTEM observations.

We first demonstrate efficient patterning of conductive and transparent single-walled carbon nanotube films by photo- and e-beam lithography and subsequent reactive ion etching in an ICP-RIE system. We then study the geometry dependent transport characteristics of the film patterned into four point probe structures. We find that resistivity is independent of film length, while increasing significantly when width and thickness of the film shrink. We explain this behavior by a geometrical argument. The ability to pattern the film could enable the integration of nanotube films into electronic devices; however, the strong resistivity scaling should be carefully taken into account when designing submicron devices.

Since the first demonstration of electroluminescence (EL) from a CNTFET about three year ago, significant progress has been achieved in CNT optoelectronics. We have developed semiclassical and quantum transport simulators for CNT optoelectronic devices. A self-consistent simulation, which couples a quantum treatment of the metal-CNT contacts to a semiclassical treatment of the channel, is performed to understand carrier transport and light emission in a CNT infrared emitter. The results show that when the channel is long, light emission significantly affects carrier transport, and reduces the source-drain current by a factor of 2 in ambipolar transport regime. The experimentally observed light-spot movement along the channel can be mostly understood and explained by a simple, semiclassical picture. The photoconductivity of carbon nanotube (CNT) Schottky barrier transistors is studied by solving the nonequilibrium Green's function transport equation. The model provides a detailed and coherent picture of electron-photon coupling and quantum transport effects. The photocurrent shows peaks at photon energies near the subband gaps, which can be engineered by controlling the CNT diameter. Electron-phonon coupling (i) slightly broadens the peaks, (ii) leads to phonon-assisted photocurrent at certain energy ranges, and (iii) changes the energy-resolved photocurrent. We also show that the metal/CNT barrier height has a much smaller effect on the photocurrent than on the dark current. We also show the important role of sub-bandgap impact ionization and excitation in CNT devices.

We have developed techniques to model electron dynamics in carbon nanotubes and hypothetical field effect devices that incorporate nanotubes into their structure. We use both Monte Carlo methods that are based on semiclassical transport, and distributed analyses that utilize quantum corrected semiconductor equations. The MC calculations predict velocity oscillations that are spatially distributed along the carbon nanotube. A quantum corrected semiconductor mathematical model is presented for CNT-MOSFET device simulation. Calculations predict improved performance of CNT-MOSFETs over conventional structures under certain conditions.

We develop rational chemical strategies to synthesize novel one-dimensional nanowire materials of transition metal silicides, investigate their physical properties, and use them as nanoscale building blocks for the bottom-up assembly of integrated photonic, electronic, and spintronic nanosystems. Transition metal silicides are extremely important to microelectronics because of the ohmic contact and interconnect many silicides (NiSi, CoSi₂, and TiSi₂) provide. Furthermore, many silicides are direct bandgap semiconductors (CrSi₂, β-FeSi₂) and are promising for silicon-based photonics. The recent discovery of Fe_xCo_1-xSi alloys as ferromagnetic semiconductors make them promising for spintronic applications as well. Herein, we describe the chemical synthesis of free standing single-crystal nanowires (NWs) of FeSi, the only transition metal Kondo insulator and isostructural CoSi, an important metallic silicide for CMOS electronics. Straight and smooth FeSi and CoSi nanowires are produced on silicon substrates covered with a thin layer of silicon oxide through the decomposition of the single source organometallic precursors trans-Fe(SiCl₃)₂(CO)₄ and Co(SiCl₃)(CO)₄, respectively, in a simple chemical vapor deposition (CVD) process. Unlike typical vapor-liquid-solid (VLS) NW growth, silicide NWs form without the addition of metal catalysts, have no catalyst tips, and depend strongly on the surface employed. The physical properties of these new FeSi and CoSi nanowires, including electrical transport and X-ray spectroscopy, are reported. This general approach to silicide nanowire growth is likely to yield other functional silicide nanosystems with significant applications in nanoelectronics and nanophotonics, and for Fe_xCo_1-xSi, silicon based spintronics.

The growth of single crystal InAs nanowire arrays on crystalline and amorphous substrates is described. This method is quite simple and fast, and uses only a bare InAs substrate as a source and a gold colloid on the growth substrate. High quality InAs nanowires can be produced by this technique, with the nanowire diameter controllable by the gold colloid size and the nanowire length controlled by the growth time and growth temperature. By a proper choice of substrate, parallel, non-interacting nanowire arrays can be formed, as well as arrays exhibiting a cross-over geometry. These geometries can have a significant impact on the plasmonic properties, specifically on surface enhanced Raman (SERS). Results indicate a significantly enhanced SERS signal for nanowire arrays which contain wire crossings, which is explained in terms of electric field "hot" spots.

A new route to grow single crystal semiconductor nanostructures was proposed and demonstrated on non-single crystal substrates. Hydrogenated silicon surfaces, amorphous silicon and microcrystalline silicon, were used to provide atomic short-range order required for epitaxial growth of nanostructures. Indium phosphide was chosen as a platform for semiconductor nanostructures. Indium phosphide was deposited on the hydrogenated silicon surfaces by low-pressure metalorganic chemical vapor deposition with a presence of colloidal gold nanoparticles. Under specific metal organic chemical vapor deposition growth conditions, the indium phosphide was found to grow into nanoneedles. Structural analysis reveals that the nanoneedles are single crystal and have either face-centered-cubic or hexagonal-closed-pack lattice when grown onto the hydrogenated microcrystalline silicon surfaces. Micro-photoluminescence measurements shows that the emission peak wavelength of an ensemble of the InP nanoneedles both on the hydrogenated amorphous silicon and hydrogenated microcrystalline silicon surfaces have a substantial blue-shift with respect to that of bulk indium phosphide. The unique shape of the emission spectra is attributed to different types of nanoneedles co-existing on the samples. The proposed route to grow semiconductor nanostructures on non-single crystal substrates would open new applications including photovoltaic, photo-detection, photo-emission and thermal energy-conversion, for which the usage of costly single crystal substrates is not preferred.

The photosynthetic reaction center (RC) is one of the most advanced light sensing and energy converting materials developed by Nature. Its coupling with inorganic surfaces is attractive for the identification of the mechanisms of interprotein electron transfer (ET) and for the possible applications for the construction of protein-based innovative photoelectronic and photovoltaic devices. Using genetically engineered bacterial RC proteins and specifically synthesized organic linkers, we were able to construct self-assembled and aligned biomolecular surfaces on various electrodes, including gold, carbon, indium tin oxide (ITO), highly ordered pyrrolytic graphite (HOPG) and carbon nanotube (CNT) arrays. Our results show that, after immobilization on the electrodes, the photosynthetic RC can operate as a highly efficient photosensor, optical switch, and photovoltaic device.

Metal oxides gas sensing properties particularly for In₂O₃ and ZnO nanostructures and nanostructured thin films are reviewed. Fabrication methods for these most commonly used metal oxides are presented, followed by a study on how growth techniques lead to nanostructures and nanostructured polycrystalline films with surface features of nanometer scale for film thickness bellow 1μm. The study continues with a discussion on how, a broad range of morphological parameters, affect the thin film response to various gases. After an overview, the study focus on thin films prepared by reactive dc magnetron sputtering and pulsed laser deposition in different growth conditions. In₂O₃ and ZnO thin films prepared for ozone sensing exhibit resistivity changes of five to eight orders of magnitude at room temperature after exposure to UV light and subsequent ozone treatment. Structural properties, i.e., crystallinity and microstructure investigated by X-ray diffraction (XRD) and Atomic Force Microscopy (AFM) are studied. The nanostructure and nanostructured surfaces are highly controlled by the deposition parameters, which, control the transport properties, and thus the sensing characteristics as measured by conductometric techniques. Analyses on the sensing response of nanostructures and nanostructured In₂O₃ and ZnO films for different gases are presented. Experiments on Surface Acoustic Wave (SAW) devices based on In₂O₃ and ZnO thin films fabricated on LiNbO3 substrates indicate the capability of achieving sensing levels in the low ppb range.

Antimony nanowire arrays have been fabricated by template assisted electro-deposition technique. Anodic aluminum oxide membranes with pore diameters around 60-90 nm are used to cast quasi-one dimensional Sb nanostructure. The as-grown Sb nanowires are characterized by electron microscopy and energy dispersive x-ray spectroscopy. Upon their remarkable linear response to hydrogen ion concentration, Sb nanowire arrays are utilized as nanoscale electrodes to determine solution pH value. They demonstrate promising potential for nanoscale solid state sensing device.

Quasi 1-D metal oxide single crystal chemiresistors are about to occupy their specific niche in the real world solid state sensorics. The major expected advantage of this kind of sensors with respect to available granular thin film sensors will be their smaller size and stable, reproducible and calculable performance within a wide range of operating conditions. To be able to compete in sensitivity with the best available nanocrystalline thin film sensors, one has to use very fine nanowires with the effective diameter of the order of ten nanometers. Fabrication of nanostructures reproducibly and controllably in this size domain remains a challenging task. The second challenge is a control of the selectivity of these nanosensors. In this report, a few exemplary approaches to grow and functionalize the prospective nanosensors are presented. Namely, in order to produce the nanostructures with the reduced diameter of the conducting channel, we grow nanowires with the oscillating morphologies where mesoscopic, several microns long segments are connected by the segments with much smaller diameters. In order to tune the sensitivity and selectivity of these sensors the influence of the surface sensitization with catalyst particles of Ni/NiO and Pd were examined.

The luminescence arising from lanthanide cations offers several advantages over organic fluorescent molecules: sharp, distinctive emission bands allow for easy resolution between multiple lanthanide signals; long emission lifetimes (μs - ms) make them excellent candidates for time-resolved measurements; and high resistance to photo bleaching allow for long or repeated experiments. In order to obtain luminescence from lanthanide cations, the cation must be located at close distance to a suitable sensitizer ("antenna"). Two similar methods have been used in our group to develop more efficient lanthanide complexes based on a polymetallic approach to obtain lanthanide compounds with improved luminescence efficiency. The first method involves using dendrimers to combine multiple antennae groups and several lanthanide cations into the same discrete molecule. The second approach involves doping CdSe semiconductor nanocrystals with luminescent terbium cations to use the nanocrystal electronic structure as an antenna to sensitize lanthanide cations. Using nanocrystals as antennae provides a superior way to protect the lanthanide cations from non-radiative deactivations, while providing a variety of controlled donating energy levels. In both methods, it is possible to incorporate several lanthanide metal cations into each dendrimer or nanocrystal, thus increasing the number of emitters and the resulting luminescence intensity of the species.

Selective patterning of chemical functional groups on polymer surfaces is utilized for controlled placement of monodisperse noble metal nanoparticles. Self-assembled diblock copolymer films deposited on hydrophobic silicon substrates are used as a template for metal nanoparticle organization. By varying the processing conditions of polymer templates, micelle and cylindrical polystyrene-b-poly(methyl methacrylate) diblock copolymer templates were fabricated. Functional groups on the surface of poly(methyl methacrylate) domains in the diblock copolymer films were chemically modified from an ester group to a carboxylate using a base catalyzed hydrolysis step. Gold and silver nanoparticles were fabricated in solution in order to achieve size and shape control. After gold nanoparticle synthesis, a ligand exchange reaction was performed to produce nanoparticles with amine functional groups for chemical attachment on chemically modified poly(methyl methacrylate) surfaces. Atomic force microscopy and scanning electron microscopy images demonstrate that this fabrication route results in preferential attachment of metal nanoparticles on poly(methyl methacrylate) thin films and on poly(methyl methacrylate) domains in polystyrene-b-poly(methyl methacrylate) diblock copolymer thin films.

Zinc Oxide (ZnO) is a wide bandgap semiconductor that has been the subject of considerable research due to its potential applications in the areas of photonics, electronics and sensors. Nano-ZnO offers several advantages over existing biosensing platforms, most notably a large surface area for greater bio-functionalization and an inherent photoluminescence (PL) signal consisting of two emission peaks. One peak is in the UV, due to near band edge emission and the other is in the visible (green) region, due to oxygen vacancies caused by crystalline defects. Real-time detection of surface binding events may be possible if changes to the PL spectrum of a ZnO-based bio-sensor can be induced. Here we describe the surface modification of nanocrystalline zinc oxide (nano-ZnO) to introduce chemically reactive functionality for subsequent bio-functionalization. We have demonstrated through TEM-EDS that nano-ZnO powders have been surface modified with a heterobifunctional organosilane crosslinking agent that contains an amine-reactive aldehyde group. Furthermore, we have attached a fluorophore to the reactive aldehyde verifying the modified nano-ZnO surface is available for subsequent biomolecular covalent attachment. The introduction of a chemically reactive modifier to the surface of the nano-ZnO presents a template for the design of new, optically responsive bio-sensing platforms.

This paper reports progress in an approach to create a general purpose platform to be used in the reproducible assembly of molecular electronic devices. We describe a method in which DNA molecules were immobilized on patterned neutravidin surfaces. First, a silicon wafer was functionalized with (3- aminopropyl)triethoxysilane (APTES) to produce an amine-terminated surface. The primary amine group was then reacted with the heterobifunctional linker molecule succinimidyl-6-(biotinamido)hexanoate which placed an active biotin group at the surface interface. These biotinylated surfaces were then patterned with the tetrameric protein neutravidin using microcontact printing (μCP) with relief features in polydimethylsiloxane (PDMS) stamps. The neutravidin proteins adsorb onto the surface and bind nearly irreversibly to one or two biotin groups leaving at least two biotin binding sites on each protein available for conjugation. Following neutravidin stamping, 1 μm long DNA molecules functionalized on one end with biotin were attached to the patterned areas. Water contact angle (WCA) measurements were used to characterize wettability changes of the silicon surfaces for amine and biotin functionalization. Atomic force microscopy (AFM) was used to image the patterns of immobilized neutravidin and DNA.

The extinction maximum of the localized surface plasmon resonance (LSPR) of noble metal nanoparticles is highly dependent upon the refractive index of the nanoparticles' surrounding environment. In this study, the effect that molecular resonances have on the intensity, LSPR peak width, and LSPR shift of the LSPR of Ag nanoparticles is monitored. By systematically tuning the LSPR extinction maxima of Ag nanoparticles versus molecular resonances, new phenomena are revealed. First, the LSPR peak shift induced by a resonant molecule varies with wavelength. In most instances, the trends in this data qualitatively track with the Kramer's-Kronig transformation of the molecular resonance spectrum; however, the magnitude of the response is severely underestimated. This was verified from both experimental data and theoretical calculations. Because this phenomenon is revealed to be electronic transition dependent, it is hypothesized that the coupling between the molecular and plasmon resonances is responsible for this wavelength dependent observation. These results will have implications in molecular enhanced LSPR sensing and in the understanding of surface-enhanced spectroscopy.

We have developed an ultra-high vacuum technique for the fabrication of complex nanosystems incorporating nonlithographic nanoparticles, ohmic contact metals and isolation dielectrics. It is believed that such a multi-component structure is a necessary prerequisite for the realization of practical photonic and electronic devices based on nanoparticles. The technique is compatible with silicon integrated circuit technology, thus making it suitable for volume manufacturing. The technique is also versatile, and allows the deposition of nanoparticles of any metal, semiconductor or insulator with diameters as small as 2 nm with less than 5% size variation. In addition, the technique allows the creation of multi-layered structures of nanoparticles of different dimensions separated by metal or dielectric layers. The technique also has the potential for creating patterned layers of nanopartciles. We have demonstrated the versatility of the equipment by depositing Si-nanoparticles with pre-selected narrow size-distributions as well as multi-layered structures of such nanoparticles.

The characteristics of surface plasmon wave (SPW) modes supported by multiple layer configurations are analysed in this paper. The transmission-line analysis based on the transverse resonance condition is implemented to describe SPW excitation via a prism coupler. This accurate yet convenient modeling technique is also applied to investigate the characteristics of SPWs in multilayer media with optical gain as a means of reducing/overcoming the typical, undesirably large loss associated with SPWs in conventional structures. The paper will also present experimental and theoretical results to quantify the operational characteristics to be expected from prism coupled SPW sensors that use semiconductor optical sources.

Integration of nanowires onto foreign substrates, and in functional devices, is widely recognized as a significant hurdle to further development of nanosystems based on quasi-one dimensional nanostructures. We describe methods for directly integrating relevant nanostructures on technologically relevant Si substrates using vapor phase synthesis of the nanowires. It is shown that ZnO nanowires may be directly integrated onto Si substrates containing patterned metal lines. Preferential growth from the edge of the metal lines has been achieved. We also show that growth of refractory transition metal carbides is also possible using catalytic growth. The electrical properties of such systems are also discussed. Finally, methods of integrating nanowires vertically on a Si substrate are also described.

The crystallographic phase and morphology of many materials change with the crystal size so that new needs arise to determine the crystallography of nanocrystals. Direct space high-resolution phase-contrast transmission electron microscopy (HRTEM) and atomic resolution scanning TEM (STEM) when combined with tools for image-based nanocrystallography in two (2D) and three (3D) dimensions possess the capacity to meet these needs. After a concise discussion of lattice-fringe visibility spheres and maps, this paper discusses lattice-fringe fingerprinting in 2D and tilt protocol applications. On-line database developments at Portland State University (PSU) that support image-based nanocrystallography are also mentioned.

Gallium nitride (GaN) nanowires (NW) and various nanostructures were grown by thermal reaction of gallium oxide and ammonia. The interplay between Ga/N reactant ratio and characteristic lengths of polar surfaces explained morphology variation. Field effect transistors were patterned on 40~185 nm diameter NWs by Ga⁺ focused ion beam (FIB) direct Pt deposition. The devices exhibited no gate responses with liner I-V for "small" diameter NWs. Linear I-V was unexpected since Pt forms Schottky barriers on n-GaN. I-V-T characteristics of the FIB-Pt contacts evolved from ohmic to rectifying with increasing NW diameter with strongly nonmetallic T-dependence. For small diameters, two-dimensional variable range hopping explained the contact conduction, the disorder being associated with ion-beam-induced sputtering and amorphization in the GaN under the FIB-Pt, as corroborated by transmission electron microscopy (TEM). For large diameters, back-to-back Schottky barriers explained the nonlinear I-V. High carrier concentration was confirmed explaining the absence of gate responses. Finally, Young's modulus E and quality factor Q of GaN NW were measured using in-situ TEM electromechanical resonance analysis. For large diameters, E was ~300 GPa but decreased for smaller diameters. Q was greater than was obtained from micromachined Si resonators with comparable surface-to-volume ratio, implying significant advantages of GaN NW for nanoelectromechanical applications.

To demonstrate the potential of the Wigner function in the processing of signals with very low SNR such as those generated by nanostructures, we present the results from two preliminary studies: visualization of the frequency content of a simulated signal of SNR as low as 0.2, and the recovery of the current density from the simulated magnetic field at a separation of z=10μm.

Subwavelength structures (SWS), a form of diffractive optic, are well-known for their ability to function as polarizers and anti-reflection coatings. They can also be used to create narrowband optical filters whose surface reflectance spectra exhibit resonant peaks that are highly wavelength dependent, especially as the surface index is modified by the deposition or adsorption of biomaterials such as molecules or cells. In this study, we report on the design and fabrication of SWS structures in silicon that are suitable for use as biosensors in sensitive molecular detection. The structures combine a two-dimensional dielectric grating and Si/SiO₂ optical waveguide to create a surface that can function as a narrowband optical filter. The SWS structures were fabricated using a combination of three-beam interference lithography and reactive-ion etching in a CBrF₃ plasma. This produced a two-dimensional periodic nanostructure grating array, having a period of ~450 nm and air pores of ~265 nm, within a 300 nm thick silicon layer that serves as the core waveguide region of the filter. The ability to achieve sensitive molecular detection (< nm) is expected by virtue of working with high-index silicon-based structures, but may be practically limited by the need to detect the reflectance at near-infrared, rather than visible, wavelengths.

In this paper, we present the simulation results on the absorption modification in photonic crystal (PC) structures. For one-dimensional (1D) PC, using transfer matrix method (TMM), we obtained enhanced absorption in both defect-free and defect based PC structures. High absorption (>60%) and small bandwidth (< 0.1 λ₀) at defect level were observed with optimal absorption layers of 10-15 for structures with single defect. We also present the modified infrared absorption in two-dimensional photonic crystal slabs (2D PCS), based on the three-dimensional finite-difference time-domain method (3D FDTD). The normalized absorption power spectral density in single defect based 2D PCS structures increased by a factor of 18 at the PC defect mode level. This enhancement factor is largely dependent upon the spectral overlap between the absorption material and the defect mode cavity. Complete absorption suppression within the photonic bandgap region was also observed in defect-free cavities, and in single defect cavities when the absorption spectral band has no overlap with the photonic bandgap.

It were performed light scattering measurements of barium sodium niobate crystals from 20 to 800°C and connected these results to studies of x-ray and transmission electron microscop with emphasis upon behavior of nanodomain structure (S. Mori et al. and J. M. Kiat et al.). Using of the 90°- elastic light scattering investigation and far field observation it were clarified the relation between behavior anomalies of light scattering and evolution of the microdomain structures of BSN. It is correlation between temperature transformations of microdomains and anomalies on the temperatures curves of the elastic light scattering intensity at about 200, 240 and 300°C. The phase transition near 500°C could be explained by appearance of a new incommensurate phase. It is the consistent with the structural investigation Pan Xiao-qing et al. by means transmission electron microscopy method.