The electrical properties of metal-molecular nanoparticle networks are studied both theoretically and experimentally. Benzenedithiol-aluminum cluster linear chains, Y-shaped and H-shaped networks are modeled with semi-empirical methods to study the electronic properties of such structures. The HOMO (highest occupied molecular orbital)-LUMO (lowest unoccupied molecular orbital) gaps of the benzenedithiol-Al cluster networks decrease several eV compared to the isolated benzenedithiol molecule. Frontier energy levels become more closely spaced as the size of the molecular networks increase, accompanied with an increased HOMO energy and decreased LUMO energy, indicating a decreased energy barrier to electron transport. Delocalized spatial distribution of the frontier orbitals indicates a high probability for electron transmission and corresponds well with peaks near the HOMO-LUMO gap in the electronic density of states. Self-assembled molecular networks consisting of dithiol/thiol molecules and 30 nm colloidal gold nanoparticles are fabricated with a solution-based method. Electrical measurements performed on these nanostructures show a typically linear current-voltage characteristic while nonlinear I-V curves are also observed for networks built of benzenedithiol or hexane/octanethiol molecules. Further analysis with atomic force microscopy shows that the network’s conductance is determined by the molecule’s conductivity and network dimensions. Circuit model consisting of networked molecular resistors is applied to study the interconnections between the particles within the network and the simulated values of the network’s conductance is consistent with the measured values. Theoretical and experimental study on the electrical properties of metal-molecular nanoparticle networks reveals the influence of molecules and metallic particles on determining the network’s conductivity. Such self-assembled networks can be used to implement several circuit elements, such as resistors, diodes, etc., and more complicated computation components such as nanocells, memristors, etc. The electrical properties of the networks can be tuned by proper choice of molecules, metallic particles and network geometry making them promising for future molecular electronic circuits. / Graduate

Thesis advisor: Krzysztof Kempa / Thesis advisor: Zhifeng Ren / In the past few decades, accompanied by the fascinating development of micro- and nano-fabrication techniques, the successful integration of subwavelength optics and multilayer structures has led to a number of remarkable discoveries. In this work, I present both experimental and theoretical investigations of the optics of thin metallic films with micro-/nano-scale perforations in the UV-VIS-IR ranges. Different fabrication techniques are employed, including nanosphere lithography, grain boundary lithography, crack templates, and sintered nanoparticles. The optical properties these films are studied, revealing important relation between optical response and the film geometry. This includes the evolution of plasmonic resonances in a series of periodic arrays of holes in a metallic film, with hole sizes increasing gradually until an array of islands is achieved. This evolution is an analog of the percolation problem, and critical phenomena are observed at the percolation threshold. Multilayer broad-band electromagnetic absorbers are also designed and fabricated based on the study of these perforated films. Parallel with these observations, an analytical coherence model is proposed to bridge the subwavelength and superwavelength limits. Such a model also provides an alternative way to handle thin random structures, avoiding large quantity of numerical computation. These studies can find applications in the design of sensors, ultrathin solar cells and transparent electrodes, as well as in applications where random structures are widely used. / Thesis (PhD) — Boston College, 2014. / Submitted to: Boston College. Graduate School of Arts and Sciences. / Discipline: Physics.

The unique properties, such as large direct bandgap, excellent thermal stability, high μH × ns, of III-nitrides make them ideal candidates for both optoelectronic and high-speed electronic devices. In the past decades, great success has been achieved in commercialization of GaN based light emitting diodes (LEDs) and laser diodes (LDs). However, due to the lack of native substrates, thin films grown on sapphire or SiC substrates have high defect densities that degrade the device performance and reliability. Conventional epitaxy lateral overgrowth (ELO) can reduce dislocation densities down to ∼10-6 cm-2 in the lateral growth area, but requires ex situ photolithography steps. Hence, an in situ method using a SiNx interlayer (nano-scale ELOG) has emerged as a promising technique. The GaN templates prepared by this method exhibit a very low dislocation density (low-10-7 cm-2) and excellent optical and electrical properties. As a cost, such high quality GaN templates containing SiN, nanonetworks are not suitable for heterojunction field effect transistor (HFET) applications due to degenerate GaN:Si layer which serves as parallel conduction channel. This dissertation discusses the growth of low dislocation density GaN templates, by using the in situ SiNx nanonetwork for conductive templates, and the AIN buffer for semi-insulating templates. On SiN x nanonetwork templates, double-barrier RTD and superlattice (SL) exhibited negative differential resistances. Moreover, the injection current of Blue LEDs (450 nm) was improved ∼30%. On semi-insulating GaN templates, nearly lattice matched AlInN/AIN/GaN HFETs were successfully demonstrated and exhibited ∼ 1600 cm2/Vs and 17 600 cm2/Vs Hall mobilities at 300 K and 10 K, respectively. Those mobility values are much higher than literature reports and indicate that high quality HFETs can be realized in lattice matched AlInN/AIN/GaN, thereby solving the strain related issue. The attempt to use InGaN as the 2DEG channel has also been successfully implemented. A Hall mobility (1230 cm2/Vs) was achieved in a 12 nm InGaN channel HFET with AlInGaN barrier, which demonstrates the viability of InGaN channel HFETs.

La nanocommunication est un nouveau paradigme qui permet de communiquer à l'échelle nanométrique, via des mécanismes moléculaires, électromagnétiques, acoustiques, ou nano-mécaniques. Le cadre général de cette thèse concerne les réseaux de nanocapteurs sans fil et les nanoréseaux sur puce. Plus précisément, il s'agit des architectures d'interconnexion et des protocoles de communication dans la bande de fréquence des Térahertz. En effet, les architectures réseaux et les protocoles de communication existants doivent être repensés en tenant compte des mécanismes de communication à l'échelle nanométrique.En premier lieu, nous nous sommes focalisés sur la nécessité de développer des approches de diffusion efficaces dans le contexte des réseaux de nanocapteurs sans fil. Une approche de diffusion efficace, issue d'une adaptation d'un protocole de la famille des protocoles d'inondation probabilistes, est présenté et son efficacité et validée par simulations à l'aide de Nano-Sim et NS3.En second lieu, une étude approfondie de l'impact des portées de transmission sur les performances du mécanisme de diffusion basé sur les ondes électromagnétiques à l'échelle nanométrique a été effectuée. Les résultats des simulations montrent que l'adaptation des portées des nano-noeuds permet de contrôler le mécanisme d'inondation et de réduire les redondances des paquets tout en augmentant les débits. Une approche adaptative de sélection de portées de transmission contrôlée au niveau des nano-noeuds est proposée. En dernier lieu, nous nous sommes attaqués à un troisième défi en examinant ce nouveau paradigme de nanocommunication dans le contexte de la conception des nanoréseaux sur puce (Network on Chip, NoC). / Nanocommunication is a new paradigm that enables connectivity at the nanoscale through molecular, electromagnetic, acoustic, or nanomechanical mechanisms. The general context of this thesis concerns wireless nanosensor networks and nanonetworks on chips. More precisely, the thesis deals with interconnection architectures and communication protocols in the terahertz band. The existing network architectures and communication protocols should be revisited taking into account the communication mechanisms at the nanoscale.First, dissemination approaches in the context of wireless nanosensor networks are addressed. An efficient broadcasting approach is presented and the simulation performance results with Nano-Sim and NS3 show that the proposed scheme is superior to flooding, especially in the cases of excessive broadcasts.Second, we investigated the impact of transmission ranges on the performance of broadcast mechanisms based on electromagnetic waves at the nanoscale. Adaptive transmission range of electromagnetic-based communication approaches are proposed. Simulations are conducted with fixed and adaptive transmission ranges to show the efficiency of the proposed approaches in terms of throughput and latency according to the network density.The third part addresses the hypothesis of using EM-based nanonetwok as an on-chip interconnect for SoCs.

A number of nanomachines that cooperatively communicate and share information in order to achieve specific tasks is envisioned as a nanonetwork. Due to size and capabilities of nanomachines, the traditional communication paradigms cannot be used for nanonetworks in which network nodes may be composed of just several atoms or molecules and scale on the orders of few nanometers. Instead, the molecular communication is a promising solution approach for nanoscale communication paradigm. However, molecular communication must be thoroughly investigated to realize the nanoscale communication and nanonetworks for many envisioned applications such as nanoscale body area networks, nanoscale molecular computers. In this thesis, a simulation framework (NanoSim) for nanoscale molecular communication networks is presented. The objective of the framework is to provide a simulation experimental tool in order to create a better understanding of nanonetworks and facilitate the development of new communication techniques and validation of theoretical results. The NanoSim framework is built on top of core components of widely used network simulator (ns-2). It incorporates the simulation modules for various nanoscale communication paradigms based on diffusive molecular, motor-based and gap junction-based molecular communication channels. The details of NanoSim are discussed and some functional scenarios are defined to validate NanoSim. In addition to this, the numerical analyses of these functional scenarios and the experimental results for them are presented. The validation of NanoSim is done by comparing these experimental and numerical results.