One dimensional carbon nanotubes (CNTs) and two-dimensional layered materials like graphene, MoS2, hexagonal boron nitride (hBN), etc. with different electrical and mechanical properties are great candidates for many applications in the future. In this study the synthesis and growth of carbon nanotubes on both conducting graphene and graphite substrates as well as insulating hBN substrate with precise crystallographic orientation is achieved. We show that the nanotubes have a clear preference to align to specific crystal directions of the underlying graphene or hBN substrate. On thicker flakes of graphite, the edges of these 2D materials can control the orientation of these carbon nanotubes. This integrated aligned growth of materials with similar lattices provides a promising route to achieving intricate nanoscale electrical circuits. Furthermore, short channel nanoscale devices consisting of the heterostructure of 1D and 2D materials are fabricated. In these nanoscale devices the nanogap is created due to etching of few layer graphene flake through hydrogenation and the channel is either carbon nanotubes or 2D materials like graphene and MoS2. Finally the transport properties of these nanoscale devices is studied.

Les nanomatériaux représentent un sujet de recherche en plein essor dans des domaines variés : D'une part, la miniaturisation augmente la vitesse de transmission et le stockage de l'information dans les technologies de la communication. D'autre part, la réduction en taille des matériaux révèle des propriétés physiques (optiques, électriques, etc.) nouvelles et étonnantes qui ouvrent la voie à de nombreuses applications (dispositifs nanoélectroniques, capteurs moléculaires etc.). Un grand défi consiste à fabriquer ou intégrer des nanostructures fonctionnelles afin d'exploiter leurs propriétés physiques intrinsèques. Dans ce contexte, nous avons développé une nouvelle approche de nanofabrication à partir de nanomatériaux colloïdaux basée sur l'assemblage par forces de capillarité. Cette technique consiste à contrôler l'évaporation en milieu confiné d'une suspension colloïdale sur un substrat lithographié grâce à un dispositif thermoélectrique associé à un système d'aspiration d'air. Les phénomènes physiques mis en jeu pendant l'assemblage ont été étudiés aussi bien à l'échelle macro- que nano-scopique. Ainsi, la température et le débit d'aspiration se sont révélés être des paramètres complémentaires pour le contrôle de l'évaporation, le déplacement de la ligne de contact, l'angle de contact et le mouvement colloïdal. De cette manière, des colloïdes de taille et nature (or et polystyrène allant de 50 nm à 1 μm) variées ont été assemblés dans des structures complexes. En particulier, des objets métalliques déterministes ont été crées afin d'étudier leurs interactions plasmoniques. Des dimères d'or de distance inter-particule variable ont démontré un fort couplage plasmonique.

The field of Information and Communication Technologies is witnessing a development speed unprecedented in history. Moore’s law proves that the processor speed and memory size are roughly doubling each 18 months, which is expected to continue in the next decade. If photonics is going to play a substantial role in the ICT market, it will have to follow the same dynamics. There are mainly two groups of components that need to be integrated. The active components, including light sources, electro-optic modulators, and detectors, are mostly fabricated in III-V semiconductors. The passive components, such as waveguides, resonators, couplers and splitters, need no power supply and can be realized in silicon-related semiconductors. The prospects of silicon photonics are particularly promising, the fabrication is mostly compatible with standard CMOS technology and the on-chip optical interconnects are expected to increase the speed of microprocessors to the next generation. This thesis starts with designs of various silicon-based devices using finite-difference time-domain simulations. Parallel computation is a powerful tool in the modeling of large-scale photonic circuits. High Q cavities and resonant channel drop filters are designed in photonic crystal platform. Different methods to couple light from a single mode fiber to silicon waveguides are studied by coupled-mode theory and verified using parallel simulations. The performance of waveguide grating coupler for vertical radiation is also studied. The fabrication of silicon-based photonic devices involves material deposition, E-beam or optical lithography for pattern defining, and plasma/wet-chemistry etching for pattern transfer. For nanometer-scaled structures, E-beam lithography is the most critical process. Depending on the structures of the devices, both positive resist (ZEP520A) and negative resist (maN2405) are used. The proximity and stitch issues are addressed by careful dose correction and patches exposure. Some examples are given including photonic crystal surface mode filter, micro-ring resonators and gold grating couplers. In particular, high Q (2.6×105), deep notch (40 dB) and resonance-splitting phenomenon are demonstrated for silicon ring resonators. It is challenging to couple light into photonic integrated circuits directly from a single-mode fiber. The butt-coupled light-injecting method usually causes large insertion loss due to small overlap of the mode profiles and large index mismatch. Practically it is not easy to cleave silicon sample with smooth facet where the waveguide exposes. By adding gold gratings to the waveguides, light can be injected and collected vertically from single-mode fiber. The coupling efficiency is much higher. There is no need to cleave the sample. The access waveguides are much shortened and the stitch problem in E-beam lithography is avoided. In summary, this thesis introduces parallel simulations for the design of modern large-scale photonic devices, addresses various issues with Si-based fabrication, and analyses the data from the characterization. Several novel devices using silicon nanowire waveguides and 2D photonic crystal structures have been demonstrated for the first time. / QC 20100923

Electrical conduction at the single molecule scale has been studied extensively with molecular nanojunctions. Measurements have revealed a wealth of interesting physics. I3owever; our understanding is hindered by a lack of methods for simultaneous local imaging or spectroscopy to determine the conformation and local environment of the molecule of interest. Optical molecular spectroscopies have made significant progress in recent years, with single molecule sensitivity achieved through the use of surface-enhanced spectroscopies. In particular surface-enhanced Raman spectroscopy (SERS) has been demonstrated to have single molecule sensitivity for specific plasmonic structures. Many unanswered quest ions remain about the SERS process, particularly the role of chemical enhancements of the Raman signal. The primary goal of the research presented here is to combine both electrical and optical characterization techniques to obtain a more complete picture of electrical conduction at the single or few molecule level. We have successfully demonstrated that nanojunctions are excellent SERS substrates with the ability to achieve single molecule sensitivity. This is a major accomplishment with practical applications in optical sensor design. We present a method for mass producing nanojunctions with SERS sensitivity optimized through computer modeling. We have demonstrated simultaneous optical and electrical measurements of molecular junctions with single molecule electrical and SERS sensitivity. Measurements show strong correlations between electrical conductance and changes to the SERS response of nanojunctions. These results allow for one of the most conclusive demonstrations of single molecule SERS to date. This measurement technique provides the framework for three additional studies discussed here as well as opening up the possibilities for numerous other experiments. One measurement examines heating in nanowires rather than nanojunctions. We observe that, the electromigration process used to turn Pt nanowires into nanojunctions heats the wires to temperatures in excess of 1000 K, indicating that thermal decomposition of molecules on the nanowire is a major problem. Another measurement studies optically driven currents in nanojunctions. The photocurrent is a result of rectification of the enhanced optical electric field in the nanogap. From low frequency electrical measurements we are able to infer the magnitude of the enhanced electric field, with inferred enhancements exceeding 1000. This work is significant to the field of plasmonics and shows the need for more complete quantum treatments of plasmonic structures. Finally we investigate electrical and optical heating in molecular nanojunctions. Our measurements show that molecular vibrations and conduction electrons in nano-junctions under electrical bias or laser illumination can be driven from equilibrium to temperatures greater than 600 K. We observe that individual vibrations are also not in thermal equilibrium with one another. Significant heating in the conduction electrons in the metal electrodes was observed which is not expected in the ballistic tunneling model for electrons in nanojunctions this indicates a need for a more completely energy dissipation theory for nanojunctions.

<p>The objective of this dissertation work is to examine light localization in semiconductors provided by a complete photonic bandgap via three-dimensional (3D) woodpile photonic crystals. A 3D photonic crystal is a periodic nanostructure that demonstrates omni-directional Bragg reflection. These materials are anticipated to become a powerful tool for engineering light propagation and localization within subwavelength scales due to their complete photonic bandgap and the distinctive dispersion relation. </p><p>The approach of realizing microcavities in this dissertation is to combine multi-directional etching fabrication methods with mode gap design. Modulation of unit cell size along a line-defect 3D waveguide could bring a guiding mode into the mode gap region of the waveguide and form a microcavity with a resonance inside the complete photonic bandgap. The designed microcavities could be fabricated by multi-directional etching methods because they can structurally be decomposed into two sets of connected and straight dielectric rods. </p><p>Ultra-high-quality factor microcavities and sub-wavelength-scale waveguides are designed without introduction of local disorders. Monopole, dipole, and quadrupole resonant modes are demonstrated with a small modal volume. The smallest modal volumes obtained are 0.36 cubic half-wavelengths for a resonance field in vacuum, and 2.88 cubic half-wavelengths for a resonance field in a dielectric. Direct metal contacts with the microcavities do not significantly deteriorate the quality factors because the resonant fields are located inside the microcavities. Single-mode woodpile waveguides are also designed in both lateral and vertical propagation directions. </p><p>The multi-directional etching method is a simple approach to the fabrication of woodpile photonic crystals and designed optical components with a variety of crystal orientations and surfaces, including (110), (001), (100), and (010) planes. An arbitrary surface plane (mn0) is obtained with this method, where m and n are integers. Moreover, it can also produce large area woodpile photonic crystals with high precision in silicon and GaAs materials.</p><p>These optical components in woodpile photonic crystals would be building blocks of high-density, low-loss 3D integrated optics, cavity quantum electrodynamics (QED), nonlinear optics, and enable the realization of current-injection optical devices.</p> / Dissertation

Nanotechnology has a steadily increasing impact on worldwide research and business activities. This work explores advanced micro/nano patterning approaches for molecular manipulation. The objectives are to (1) build a proper bridge from a few microns to the 100-10 nm range and below as well as to (2) combine “top-down” precise design with the “bottom-up” size scale to create designed surfaces, areas and volumes that can interact with molecules in a designed way. Three studies were designed and studied accordingly. The first investigation demonstrates that “top-down” Inclined Nanoimprinting Lithography (INIL) is able to produce three-dimensional (3-D) nanopatterns of varying heights in a single step. INIL reduces pattern's feature size from microns to nanometers. The degree of resulting nanopattern's asymmetry can be controlled by the magnitude of the inclination angle. Various 3-D nanostructures are successfully demonstrated including nanolines, nanocircles and nanosquares. The underlying INIL mechanism is investigated, which is primarily due to the induced shear force when the inclination angle is not zero. This leads to the anisotropic dewetting of polymer fluid and consequently asymmetric 3D nanopatterns of varying heights. INIL removes the need of preparation of expensive 3D nanotemplates or multiple template-to-substrate alignments. In addition, such 3-D structures are successfully transferred to silicon, silicone rubber and metal gold. INIL enables 3D nano-scale devices including angle-resolved photonic and plasmonic crystals. The second investigation demonstrates the success of “bottom-up” molecular imprinting of X-ray contrast agent iodixanol in polymer matrix. The synthetic tailor-made molecularly imprinted polymers (MIPs) are poly(4-vinylpyridine-co-ethylene glycol dimethacrylate) which possess specific binding sites induced by the template molecules of X-ray contrast agent iodixanol. It leads the feature size reduction from macromolecules to molecular scale. The properly imprinted binding sites also leads MIPs to have improved absorption capacity and efficiency for X-ray contrast agent iodixanol relative to non-imprinted polymers. The best binding capacity achieved from the optimized MIPs was 284 mg/g in aqueous solution, 8.8 times higher than that of the non-imprinted polymers. The best binding capacity obtained in sheep plasma was 232 mg/g, 4.5 times higher than the non-imprinted polymers. The factors that may affect the binding performance of MIPs in aqueous media are studied. The optimized MIPs are encouraging for biomedical implementations including dialysis and nanosensors. The third investigation of nanolithography-based molecular manipulation (NMM) explores a hybrid approach by combining “top-down” electron-beam lithography (EBL) with “bottom-up” surface initiated polymerization (SIP). It reduces the nanopattern's feature size to sub-10 nm and simultaneously tunes its surface chemistry through functional polymer brushes. The process has reduced process complexity and cost. The demonstrated prototype molecular manipulation templates have 3D surface nanostructures with sub-10 nm feature size and anisotropic surface functionalities. They mimic biocatalyst enzymes to “bottom-up” assemble nanoparticle targets at specific locations producing 3D nanostructures in a designated way. Various 3D synthetic nanostructures have been demonstrated including polystyrene “nanomushrooms” “nanospikes”, “nanofibers” and polystyrene-iron oxide “nanoflowers”. Potential applications of these synthetic 3D nanostructures can be improved therapeutic agents. This hybrid strategy realizes the integration of “top-down” design with “bottom-up” molecular scale to create designed nanopatterned surfaces that can interact with molecules in a designated way.

The continuous scaling down of the metal-oxide-semiconductor field-effect transistor (MOSFET) has improved the performance of electronic appliances. Unfortunately, it has come to a stage where further scaling of the MOSFET is no longer possible due to the physical and the fabrication limitations. This has motivated researchers towards designing and fabricating novel devices that can replace MOSFET technology. Carbon Nanotube Field-Effect Transistors, Single Electron Tunneling Junctions, Nano-Magnetic Devices, and Spin Field-Effect Transistors are some prospective candidates that could replace MOSFET devices. In this dissertation, we have studied the computational performance of Nano−Magnetic Devices due to their attractive features such as room temperature operation, high density, robustness towards thermal noise, radiation hardened nature and low static power dissipation. In this work, we have established that data can be propagated in a causal fashion from a driver cell to the driven cells. We have fabricated a ferromagnetic wire architecture and used a magnetic force microscopy (MFM) tip to provide localized magnetic inputs. This experiment validated two important phenomena; (1) a clocking field is essential to propagate data and (2) upon removal of the clocking field data can be propagated according to the input data. Next, we have fabricated and captured MFM images of a nano-magnetic logic architecture that has computed the majority of seven binary variables. The architecture was designed by interconnecting three three-input majority logic gates with ferromagnetic and antiferromagnetic wire architectures. This seven input majority logic architecture can potentially implement eight different logic functions that could be configured in real-time. All eight functions could be configured by three control parameters in real-time (by writing logic one or zero to them). Even though we observed error-free operations in nano-magnetic logic architectures, it became clear that we needed better control (write/read/clock) over individual single layer nano-magnetic devices for successful long-term operation. To address the write/clock/read problems, we designed and fabricated amultilayer nano-magnetic device. We fabricated and performed a set of experiments with patterned multilayer stacks of Co/Cu/Ni80Fe20 with a bottom layer having a perpendicular magnetization to realize neighbor interactions between adjacent top layers of devices. Based on the MFM images, we conclude that dipolar coupling between the top layers of the neighboring devices can be exploited to construct three-input majority logic gates, antiferromagnetic and ferromagnetic wire architectures. Finally, we have experimentally demonstrated a magnetic system that could be used to solve quadratic optimization problems that arise in computer vision applications. We have harnessed the energy minimization nature of a magnetic system to directly solve a quadratic optimization process. We have fabricated a magnetic system corresponding to a real world image and have identified salient features with true positive rate more than 85%. These experimental results feature the potentiality of this unconventional computing method to develop a magnetic processor which solves such complex problems in few clock cycles.

This dissertation describes methodology that significantly improves the state of femtosecond laser writing of metals. The developments address two major shortcomings: poor material quality, and limited 3D patterning capabilities. In two dimensions, we grow monocrystalline silver prisms through femtosecond laser irradiation. We thus demonstrate the ability to create high quality material (with limited number of domains), unlike published reports of 2D structures composed of nanoparticle aggregates. This development has broader implications beyond metal writing, as it demonstrates a one-step fabrication process to localize bottom-up growth of high quality monocrystalline material on a substrate. In three dimensions, we direct laser write fully disconnected 3D silver structures in a polymer matrix. Since the silver structures are embedded in a stable matrix, they are not required to be self-supported, enabling the one-step fabrication of 3D patterns of 3D metal structures that need-not be connected. We demonstrate sub-100-nm silver structures. This latter development addresses a broader limitation in fabrication technologies, where 3D patterning of metal structures is difficult. We demonstrate several 3D silver patterns that cannot be obtained through any other fabrication technique known to us. We expect these advances to contribute to the development of new devices in optics, plasmonics, and metamaterials. With further improvements in the fabrication methods, the list of potential applications broadens to include electronics (e.g. 3D microelectronic circuits), chemistry (e.g. catalysis), and biology (e.g. plasmonic biosensing). / Engineering and Applied Sciences

Low-dimensional systems in condensed matter physics exhibit a rich array of correlated electronic phases. One-dimensional systems stand out in this regard. Electrons cannot avoid each other in 1D, enhancing the effects of interactions. The resulting correlations leave distinct spatial imprints on the electronic density that can be imaged with scanning probes. Disorder, however, can destroy these delicate interacting states by breaking up the electron liquid into localized pieces. Thus, to generate fragile interacting quantum states, one requires an extremely clean system in which disorder does not overcome interactions, as well as a high degree of tunability to design potential landscapes. Furthermore, to directly measure the resulting spatial correlations, one requires an exceptionally sensitive scanning probe, but the most sensitive probes presently available are also invasive, perturbing the system and screening electron-electron interactions. / Engineering and Applied Sciences

This thesis addresses nanostructure fabrication techniques based on electron beam lithography, which is the most widely employed nanofabrication techniques for R&D and for the prototyping or production of photo-mask or imprint mold. The focus is on the study of novel resist and development process, as well as pattern transfer procedure after lithography. Specifically, this thesis investigates the following topics that are related to either electron beam resists, their development, or pattern transfer process after electron beam lithography: (1) The dry thermal development (contrary to conventional solvent development) of negative electron beam resists polystyrene (PS) to achieve reasonably high contrast and resolution. (2) The solvent development for polycarbonate electron beam resist, which is more desirable than the usual hot aqueous solution of NaOH developer, to achieve a low contrast that is ideal for grayscale lithography. (3) The fabrication of metal nanostructure by electron beam lithography and dry liftoff (contrary to the conventional liftoff using a strong solvent or aqueous solution), to achieved down to ~50 nm resolution. (4) The study a novel electron beam resist poly(sodium 4-styrenesulfonate) (sodium PSS) that is water soluble and water developable, to fabricate the feature size down to ~ 40 nm. And finally, (5) The fabrication of gold nanostructure on a thin membrane, which will be used as an object for novel x-ray imaging, where we developed the fabrication process for silicon nitride membrane, electroplating of gold, and pattern transfer after electron beam lithography using single layer resist and tri-layer resist stack.