We report on catalyst-free growth of ZnO nanorods and their nano-scale electrical and optical device applications. Catalyst-free metalorganic vapor-phase epitaxy (MOVPE) enables fabrication of size-controlled high purity ZnO single crystal nanorods. Various high quality nanorod heterostructures and quantum structures based on ZnO nanorods were also prepared using the MOVPE method and characterized using scanning electron microscopy, transmission electron microscopy, and optical spectroscopy. From the photoluminescence spectra of ZnO/Zn_0.8Mg_0.2O nanorod multi-quantum-well structures, in particular, we observed a systematic blue-shift in their PL peak position due to quantum confinement effect of carriers in nanorod quantum structures. For ZnO/ZnMgO coaxial nanorod heterostructures, photoluminescence intensity was significantly increased presumably due to surface passivation and carrier confinement. In addition to the growth and characterizations of ZnO nanorods and their quantum structures, we fabricated nanoscale electronic devices based on ZnO nanorods. We report on fabrication and device characteristics of metal-oxidesemiconductor field effect transistors (MOSFETs), Schottky diodes, and metal-semiconductor field effect transistors (MESFETs) as examples of the nanodevices. In addition, electroluminescent devices were fabricated using vertically aligned ZnO nanorods grown p-type GaN substrates, exhibiting strong visible electroluminescence.

Modern CMOS transistors will not scale well in the next decade due to leakage currents, sources of variation, and platform requirements. To keep the cost per transistor decreasing, and to realize the feasibility of ultra-high density integrated circuits, low power techniques and efficiency optimization are being explored to counter these problems. Parallel to the development of electronic VLSI, using photons as a means of carrying information has been an appealing approach, due to the high speed and broad bandwidth of light, and the elimination of on-chip parasitic and electro-magnetic interference as its electronic counterpart. This paper focuses on photonic integrated circuits to solve the high-density problem, and presents a design for a nano-scale QD optical transducer (QDOT) that will function as a near-field photodetector and that can easily interface into a self- assembled QD integrated circuit (QDIC). The optical transducer consists of a QD between two metal electrodes. The tunneling current between the metal electrodes is mediated by the QD and can be gated by changing the optical signal intensity impinging on the QD. The device can be fabricated via self-assembly using QDs. In this method, a chemistry linker such as DNA or APTES is covalently bound to pre- defined zones on a substrate. The global location of these zones is defined via electron-beam lithography (EBL). Numerical simulations are discussed and ideal characteristics of the device are presented.

It is always inspiring to observe how nature effortlessly integrates a myriad of nanoparticles into very complex living and non-living structures. As we increase our engineering skills from making nanoparticles to integrating them into complex but more useful structures, we are tempted to mimic the approaches used in the nature. At first glance, the "natural way" appears to be particularly suited to handling of a very large number of nanoparticles whose local interaction with each other is dominated by their surface properties. Properly functionalized nanoparticles can therefore be expected to self-assemble into predetermined structures simply by providing the right environment. This approach has indeed been successfully employed to construct many interesting structures ranging from photonic bandgap crystals to solar cells. Can we continue to refine these approaches to make more complex structures? Or, is there an ultimate limitation? In a diverse field such as nanotechnology with much upside potential, it is difficult to predict limitations. Yet, not all technological approaches are equal in terms of achieving sustainable integration techniques for higher value products. We attempt to compare various integration approaches currently used as to their viability for continued progress. Since many self-assembly techniques have counterparts in natural processes, we examine the limitations and the prospects of nanoassembly processes by attempting to learn from the nature. More specifically, the "top-down" and "bottom-up" assembly approaches are examined for their applicability for nanostructure fabrication.

We report on single photon sources produced from photonic crystal - coupled InAs Quantum Dots (QDs). We observe large spontaneous emission rate modification of individual InAs Quantum Dots (QDs) in modified single defect cavities with large quality factor (Q). Compared to QDs in bulk semiconductor, QDs that are resonant with the cavity show an emission rate increase by up to a factor of 8. In contrast, off-resonant QDs indicate up to five-fold rate quenching as the local density of optical states (LDOS) is diminished in the photonic crystal. In both cases we demonstrate photon antibunching, showing that the structure represents an on-demand single photon source with pulse duration from 210 ps to 8 ns. We explain the suppression of QD emission rate using Finite Difference Time Domain (FDTD) simulations and find good agreement with experiment. High multiphoton suppression is achieved by resonant excitation. Finally, we discuss fabrication improvements based on FDTD analysis of already fabricated structures.

In this work, we present a novel optical imaging device that can be directly integrated into a microfluidic network, and can therefore enable on-chip imaging in a microfluidic system. This micro imaging device, termed optofluidic microscope (OFM) is free of bulk optics and is based on a nanohole array defined in a non-transmissive metallic layer that is patterned onto the floor of the microfluidic channel. The operation of the optofluidic microscope is explained in details and its performance is examined with Caenorhabditis elegans (C. elegans) of various genotypes. Images from a large population of worms have been efficiently acquired within a short time frame. The quality of the OFM images of C elegans and the morphological characteristics revealed by the images are evaluated. The experimental results support our claim that the methodology described therein promises to create a powerful tool for fulfilling high- resolution, high-throughput imaging task of the microscopic biological samples.

Beyond 65 nm node, the ultra-narrow channel memory device serves as a possible technology for further scaling. A self-assembled carbon nanotube (CNT) channel with self aligned metal nanocrystals is proposed as an alternative to Si based ultra-narrow channel memory. The device demonstrates large memory window and single-electron sensitivity. The analysis of the transport in the CNT channel using non-equilibrium Green's function (NEGF) formalism confirms single electron sensitivity quantitatively at room temperature. The CNT channel conductance exhibits sensitivity to position of the charge along the channel. The NEGF based analysis is easily extended to the application of CNTFET as a charge sensor. The electrostatics of the CNT-nanocrystal memory was analyzed for transport between nanocrystal and CNT. Despite the nanocrystal being in close proximity of the CNT, it is strongly coupled to the gate electrode electrostatically. This effect is not observed in the planar 2D Si- based nanocrystal memory. It obviates a major trade-off in memory design of scaling the control dielectric to decrease operational voltage, while ensuring low gate leakage and should allow ultra-low voltage operations. Large tunneling current should also enhance write times. Large electric field asymmetry should enable a better write/retention ratio.

Miniaturizing electronic devices to the molecular scale is the next major step in the electronics revolution. To do this, however, three major unsolved challenges must be overcome. These are: (1) Synthesis of new molecules with functionality that allows them to act as nonlinear electronic elements and to attach them in a specific orientation to contact structures (2) Bridging the molecular (created via bottom-up fabrication) with the lithographic (created via top- down fabrication) length scales for device construction and (3) definition of new lithographic approaches that accommodate molecular installation during processing. Here, an approach and its implementation will be discussed that addresses each of these issues. In addition, the approach is designed to facilitate the demonstration of gain at the molecular level which can result from a state change within the molecular architecture rather than as the response of a molecule to a change in bias of an underlying (macroscopic) gate electrode.

The steady decrease of the feature size of integrated circuits towards the nanometer scale leads to an increase in generated heat per unit area. Hence, efficient transfer of heat away from hotspots of integrated circuits becomes a crucial issue in the design of new generations of electronic devices. The importance of efficient thermal transport is even more pronounced in moving parts of nanoelectromechanical systems (NEMS). Recent research has shown that low-dimensional nanomaterials possess high thermal conductivity and hence are promising candidates for efficient heat reduction in nanodevices. In this talk, we present results of theoretical modeling of heat transport in one-dimensional (e.g. long chain molecules) and quasi-one-dimensional (e.g. carbon nanotubes) nanostructures. The study is performed under the assumption that the contribution of electrons to thermal conductivity is negligible and therefore the heat transfer is solely due to nonlinear interactions between vibrations of atoms in a nanostructure. We investigate the role of various lattice vibration modes in the heat transport with a particular focus on nonlinear localized vibration modes (breathers). These modes are highly localized and have properties qualitatively different from the linear phonon vibration modes. In particular, breathers are very stable and, at certain conditions, they move at a constant velocity which exceeds the speed of sound. This property of breathers suggests their potential use in efficient transfer of heat away from hotspots in a nanoscopic device.

Blood analysis provides vital information for health conditions. For instance, typical infection response is correlated to an elevated White Blood Cell (WBC) count, while low Red Blood Cell (RBC) count, hemoglobin and hematocrit are caused by anemia or internal bleeding. We are developing two essential modules, deionization (DI) chip and microfluidic cytometer with impedance spectroscopy flow, for enabling the realization of a single platform miniaturized blood analyzer. In the proposed analyzer, blood cells are preliminarily sorted by Dielectrophoretic (DEP) means into sub-groups, differentiated and counted by impedance spectroscopy in a flow cytometer. DEP techniques have been demonstrated to stretch DNA, align Carbon Nanotubes (CNT) and trap cells successfully. However, DEP manipulation does not function in biological media with high conductivity. The DI module is designed to account for this challenge. H Filter will serve as an ion extraction platform in a microchamber. Sample and buffer do not mix well in micro scale allowing the ions being extracted by diffusion without increasing the volume. This can keep the downstream processing time short. Micro scale hydrodynamic focusing is employed to place single cell passing along the central plane of the flow cytometer module. By applying an AC electrical field, suspended cells are polarized, membrane capacitance C_m, cytoplasm conductivity σ_c, and cytoplasm permittivity ε_c will vary as functions of frequency. Tracing back the monitored current, the numbers of individual cell species can be evaluated.

Free space microwave measurements are reported for a split ring and post type metamaterial which exhibits negative refraction in a frequency band between 13.5 and 14.5 GHz. Varying azimuthal angles and magnitudes are achieved by changing the polarization of the transmitter and receiver relative to each other and to the anisotropic axes of the material. The amplitude of the cross- polarized transmission has been measured at 50% of the co- polarization level. The maximum amplitude was achieved at a polarization angle of 20 degrees relative to the initial polarization. This polarization conversion indicates there are other losses besides ohmic losses.

In the past few years, exciting developments in the synthesis and novel device demonstration of one-directional (1D) semiconductor nanowires have given rise to an enormous optimism. Interesting characteristics such as high surface to volume ratio, quantum confinement, and simple and low cost synthesis process are opening new frontiers in novel electronic and photonic devices. One much debated issue of interfacing and integrating such nano-structures in a massively large number of devices and systems has attracted the attention of research groups all over the world and various approaches were proposed. This talk will give an overview of the recent progress and future challenges in the construction of large and complex systems with 1D semiconductor nanowires.

We measure the dynamical conductance of electrically contacted single-walled carbon nanotubes at dc and ac as a function of source-drain voltage in both low and high dc bias voltage. We show a direct relationship between the ac conductance and dc conductance. We also measure the microwave conductance of 2 nanotubes in parallel and observe an anomalous frequency dependence.

The fabrication of high density arrays of semiconductor nanowires is of interest for nanoscale electronics, chemical and biological sensing and energy conversion applications. We have investigated the synthesis, intentional doping and electrical characterization of Si and Ge nanowires grown by the vapor-liquid-solid (VLS) method in nanoporous alumina membranes. Nanoporous membranes provide a convenient platform for nanowire growth and processing, enabling control of wire diameter via pore size and the integration of contact metals for electrical testing. For VLS growth in nanoporous materials, reduced pressures and temperatures are required in order to promote the diffusion of reactants into the pore without premature decomposition on the membrane surface or pore walls. The effect of growth conditions on the growth rate of Si and Ge nanowires from SiH₄ and GeH₄ sources, respectively, was investigated and compared. In both cases, the measured activation energies for nanowire growth were substantially lower than activation energies typically reported for Si and Ge thin film deposition under similar growth conditions, suggesting that gold plays a catalytic role in the VLS growth process. Intentionally doped SiNW arrays were also prepared using trimethylboron (TMB) and phosphine (PH₃) as p-type and n-type dopant sources, respectively. Nanowire resistivities were calculated from plots of the array resistance as a function of nanowire length. A decrease in resistivity was observed for both n-type and p-type doped SiNW arrays compared to those grown without the addition of a dopant source.

Vertically-aligned carbon nanotubes/nanofibers grown on various substrates by a direct-current plasma-enhanced chemical vapor deposition method have been shown experimentally to function as classical low-loss dipole antenna arrays at optical frequencies. Two fundamental antenna effects, e.g., the polarization effect and length matching effect, directly observed on large-scale CNT arrays in visible frequency range, hold them promising for industry-level fabrication of devices including linear/beam-splitting polarizers, solar energy converters, THz demodulators, etc., some of which will, however, require or prefer a flexible and/or transparent conducting substrate to be compatible for multi-level integration and low-cost manufacturing process. A low-energy dark discharge fabrication technique is therefore devised which successfully yields CNT antennas directly on polyimide films and transparent conducting oxides (ITO, ZnO) with the absence of a buffer layer.

We investigate a viable manufacture method of large area transmission only polarizers (TOPOL). A multilayer, mixed-scale (nanostructures and microstructrures) design is presented to accomplish the required functional integration. The effective domain of the device is less than 2 μm in thickness. Nanoimprint and UV lithography is combined to demonstrate the viable fabrication processes with 100 mm diameter wafers. The proposed structures can be further integrated. We also present detailed comparisons of the integrated devices with high-performance commercial-grade bulk optics.

Large-scale, two-dimensional arrays of periodic particles were prepared by nanosphere lithography. We modified the fabrication technique based on a self-assembly of latex particles on water surface in order to improve mask quality and size. Modifications of particles arrangement in an array were also practicable by using double-layered masks and mask transfer method. Such particle arrays were used for catalytic growth of aligned carbon nanotubes and ZnO nanorods with various configurations, length, and diameter. These exhibit interesting phenomena - antenna effects, photonic bandgap behavior, subwavelength lensing, and enhanced field emission. Therefore, they can be used in variety of future optoelectronic devices, such as THz and IR detectors.