Nanoscale confinement can be defined as a space confined by interfaces with at least one nanometer-scale dimension. Objects under nanoscale confinement have a large ratio of interfacial area to volume that makes interfacial properties have significant impact. This dissertation examines three cases in which liquids are confined between solids. The main focus (two papers) describes how electrostatic interactions between two interfaces affect ions confined within the liquid. Commonly, the charge distribution near an interface is described by electrical double layer model, where the characteristic decay length of the potential is the Debye length κ^(-1), which is typically 1–100 nm. In a nanoscale confinement, the electrostatic potential from both confining surfaces overlaps, and there is no bulk solution in the confined liquid. If the two surfaces have the same potential in isolation, the potential will increase throughout the liquid phase. I examine two hypotheses for ions under confinement in aqueous solution: (1) diffusion of ions will be hindered by the electrostatic potential; (2) surfactants will form surface aggregates (a form of micelles) that would not occur without the modified potential. To test the first hypothesis, I studied diffusion of fluorescein sodium salt in the nanoscale water confined between glass surfaces. The confining glass surfaces were fabricated by thermally bonding Borofloat glass wafers. Fluorescence microscopy was used to monitor the amount of fluorescein throughout the confined water, and thereby to understand the diffusion Measurements with done for a variety of different Debye lengths and water film thicknesses. I found that the time for fluorescein to reach equilibrium distribution in the nano-scale confinement could be 10× longer when there was no salt initially present compared to when salt was present. However, even a small amount of salt initially in the confined liquid led to a very weak effect of Debye length on diffusion. Thus, provided that the surface potential inside a thin film is initially screened by even a low concentration of electrolyte inside the confinement, diffusion is unhindered. A practical application of this result is delivery of dissolved species should not be preceded by infusion of pure water into pores if speedy delivery is desired. For the second hypothesis, I studied adsorption and aggregation of dodecyltrimethylammonium bromide (DTAB), a cationic surfactant, within the same type of nanoscale confinement by Borofloat glass. A fluorescent dye, Nile red, whose fluorescence depends on its solvent environment was used to indicate formation of surface aggregates by the surfactant. We found that surface aggregation of DTAB occurred at a very low surfactant concentration (<1 % of the critical micelle concentration) when the confinement was less than 30 nm, which was about one Debye length of the solution. This finding overturns a major assumption of many surface forces measurements and ideas of colloidal stability. It has been customary to assume that the state of surfactant aggregation is constant when two particles approach, whereas we find that aggregation changes with the solution is confined. The change in aggregation can lead to a change in electrical potential, which affects the surface forces and colloidal stability. Past work that used this assumption will need to be re-interpreted. The third topic was the study of the displacement of oil trapped in dead-end nanopores by water. This is a model of the process of tertiary oil recovery. Surfactants are used to assist with oil recovery, but the mechanism is not well studied. Three hypotheses were considered for the effect of surfactant on oil displacement: (1) Lowering of the oil–water interfacial tension; (2) Adsorption to the water–solid interface; and (3) Effects on transport rather than thermodynamics. Measurements of three different types of surfactants: sodium dodecyl sulfate (SDS), an anionic surfactant; Aerosol OT (AOT), an anionic surfactant; dodecyltrimethylammonium bromide (DTAB), a cationic surfactant; and no surfactant. Results show that AOT was the only surfactant that led to substantial spontaneous displacement of oil within 12 hours. The effect was attributed to AOT's ability for form reverse micelles in the oil phase that could deliver water to the hydrophilic solid walls, thereby displacing oil. No prior literature describing this mechanism has been found. / Doctor of Philosophy / Nanoscale confinement are domains contained by interfaces with at least one dimension on the nanometer scale level. This dissertation describes very thin (1–100 nm) layers of water between solids. Such thin layers of water are important in oil recovery, cellular processes, delivery of sham-poo to hair, drug delivery, etc. I studied the transport and adsorption of ions in these thin layers, particularly when the solid walls were charged. Results show that (1) Diffusion of ions could be se-verely hindered by unscreened electrostatic potential within the thin film of water. Diffusion times were increased by up to 10 times; (2) Surfactant aggregation occurred in the thin film, even when it did not occur in bulk solution at the same concentration; (3) Water could not displace oil in a thin film, even when assisted by a variety of surfactants. One particular surfactant, Aerosol OT could displace the oil, which I attribute to its ability to transport water through the oil and onto the solid.

Thermal transport across three-dimensional Lennard-Jones superlattices, two-dimensional heterostructures of graphene and hexagonal boron nitride (hBN), and in C60 molecular crystals is studied atomistically. The first two systems are studied as finite junctions placed between bulk leads, while the molecular crystal is studied as a bulk. Two computational methods are used: molecular dynamics (MD) simulations and harmonic lattice dynamics calculations in conjunction with the scattering boundary method (SBM). In Lennard-Jones superlattice junctions with a superlattice period of four atomic monolayers at low temperatures, those with mass-mismatched leads have a greater thermal conductance than those with mass-matched leads. We attribute this lead effect to interference between and the ballistic transport of emergent junction vibrational modes. The lead effect diminishes when the temperature is increased, when the superlattice period is increased, and when interfacial disorder is introduced, and is reversed in the harmonic limit. In graphene-hBN heterostructure junctions, the thermal conductance is dominated by acoustic phonon modes near the Brillouin zone center that have high group velocity, population, and transmission coefficient. Out-of-plane modes make their most significant contributions at low frequencies, whereas in-plane modes contribute across the frequency spectrum. Finite-length superlattice junctions between graphene and hBN leads have a lower thermal conductance than comparable junctions between two graphene leads due to lack of transmission in the hBN phonon band gap. The thermal conductances of bilayer systems differ by less that 10% from their single-layer counterparts on a per area basis, in contrast to the strong thermal conductivity reduction when moving to from single- to multi-layer graphene. We model C60 molecules using the polymer consistent force-field and compute the single molecule vibrational spectrum and heat capacity. In the face-center cubic C60 molecular crystal at a temperature of 300 K, we find three frequency peaks in the center-of-mass translations at 20, 30 and 38 cm􀀀1, agreeing with the average frequencies of the three acoustic branches of the frozen phonon model of the same system and suggesting that a phonon description of center-of-mass translations. We use both direct method and Green- Kubo MD simulations to predict the thermal conductivity of the molecular crystals at a temperature of 300 K. We find that the thermal conductivity of the molecular crystal is 20 to 50% lower than that of a reduced order model where only molecular center-ofmass translations are present, suggesting that molecular vibrations and rotations act as significant scattering sources for the center-of-mass phonons.

The objective of this dissertation is to analytically model a parallel plate electrostatic actuator operating in a liquid electrolyte and experimentally verify the analysis. The model assumes the system remains in thermodynamic equilibrium during actuation, which enables the ion mass balance equations and Guass’ Law to be combined into the Poisson-Boltzmann equation. The governing equations also include the linear momentum equation including the following forces: the electric force, the osmotic force, the spring force, the viscous damping force, and the van der Waals force. Equations are also derived for the energy stored in the actuator. The analytical results emphasize the stored energy at mechanical equilibrium and the voltage versus electrode separation behavior including the instability. The analytical results predict that the system may not be a good actuator because the displacement has a very limited stable range, although the actuator would be suitable for bistable applications. The experiment consisted of a fixed flat gold electrode and a movable gold electrode consisting of a gold sphere several micrometers in diameter mounted on the end of an Atomic Force Microscope (AFM) cantilever, which serves as the spring. The electrodes were separated by approximately 100nm of 1mM NaCl aqueous solution. The analytical results were not verified by the experiment. Relative to the analysis, the experiments did not show distinct critical points, and the experiments showed less electrode separation for a given applied electric potential. The experiments did show points at which the electrode separation versus electric potential rapidly changed slope, which may be instability points. It is suggested that this phenomenon may be due to coalesced gas bubbles on hydrophobic regions of the electrode surfaces, which are not included in the model. Although clean gold surfaces are hydrophilic, gold surfaces may become hydrophobic due to impurities.

The incorporation of rare earth-V (RE-V) semimetallic nanoparticles embedded in III-V compound semiconductors is of great interest for applications in solid-state devices including multijunction tandem solar cells, thermoelectric devices, and fast photoconductors for terahertz radiation sources and receivers. With regard to those nanoparticle roles in device applications and material itself, electrical and thermal properties of embedded RE-V nanoparticles, including nanoscale morphology, electronic structure, and electrical and thermal conductivity of such nanoparticles are essential to be understood to engineer their properties to optimize their influence on device performance. To understand embedded RE-V semimetallic nanostructures in III-V compound semiconductors, nanoscale characterization tools are essential for analysis their properties incorporated in compound semiconductors. In this dissertation, we used atomic force microscopy (AFM) with other secondary detection tools to investigate nanoscale material properties of semimetallic RE-V and GaAs heterostructures, grown by molecular beam epitaxy. We used scanning capacitance microscopy and conductive AFM techniques to understand electronic and electrical properties of ErAs/GaAs heterostructures. For the electrical properties, this thesis investigates details of statistical analysis of scanning capacitance and local conductivity images contrast to provide insights into (i) nanoparticle structure at length scales smaller than the nominal spatial resolution of the scanned probe measurement, and (ii) both lateral and vertical nanoparticle morphology at nanometer to atomic length scales, and their influence on electrical conductivity. To understand thermal properties of ErAs nanoparticles, in-plane and cross-sectional plane of ErAs/GaAs superlattice structure were investigated with a scanning probe microscopy technique implemented with 3[omega] method for thermal measurement. By performing detailed numerical modeling of thermal transport between thermal probe tip and employed samples, and estimation of additional phonon scattering induced by ErAs nanoparticles, we could understand influences of ErAs nanoparticles on the host GaAs thermal conductivity. Investigation of ErAs semimetallic nanostructure embedded in GaAs matrix with scanned probe microscopy provided detailed understanding of their electronic, electrical and thermal properties. In addition, this dissertation also demonstrates that an atomic force microscope with secondary detection techniques is promising apparatus to understand and investigate intrinsic properties of nanostructure materials, nanoscale charge transports, when the system is combined with detailed modeling and simulations. / text

In this report, the feasibility of a massively parallel, nanoscale laser shock peening process is investigated. This report will give a fundamental background on laser shock peening processes in general. The background will include a description of the mechanisms associated with laser shock peening, and the theory behind laser shock peening. The experiments that were performed to develop a nanoscale laser shock peening process will also be described in detail. The problems associated with different experiments and the results will be presented. / text

Integrated circuit (IC) technology has evolved rapidly but the continual development of transistors and interconnects (the connection between the transistors) is facing greater and greater challenges, which require new materials and new processes. Research in nano-particles (or nanoscale clusters) creates possibilities for both new materials and new processes. This thesis explores the electrical properties of amorphous antimony clusters and develops a new copper cluster deposition technique for application to transistors and interconnects respectively. For amorphous antimony clusters, an electron diffraction technique was applied to identify the phase of the clusters prior to deposition on electrically contacted samples. The deposition process produced uniform cluster films suitable for electrical measurements. A consistent percolation exponent for conduction (t=1.85) was obtained. After deposition, the resistance of the films continued to increase because of coalescence. Although it was previously reported that amorphous antimony films were semiconducting, from linear I(V) curves, a low temperature coefficient of resistance (10⁻⁴ K⁻¹) and no observable gate effect, it was found that the antimony cluster films in this study were not semiconducting, possibly due to the effect of coalescence. The development of the copper clusters for the interconnects application was very successful. Trenches of sub-200 nm widths, with different diffusion barriers and seed layers, and up to 5:1 aspect ratios have been completely filled with copper clusters. Due to the propensity for reflection of clusters from the planar surfaces between trenches, the process results in selective deposition into the trenches and bottom up filling is demonstrated. After annealing in hydrogen or in vacuum, the clusters sinter into a copper seed layer. The resistivity measured by a thin film four-point probe (1.6 - 2.3 × 10⁻⁸ Ωm) meets the requirement by industry (2.2 × 10⁻⁸ Ωm). The process is therefore promising for industrial application, but further testing and investigation of integration issues is required.

No description available.

Molecular communication (MC) is a new bio-inspired communication paradigm towards realizing the communication and networking at the nanoscale to microscale dimensions among a vast number of engineered natural and/or artificial nanomachines communicating with each other to form a nanonetwork. In this thesis, we investigate a concentration-encoded molecular communication (CEMC) system where the transmitting nanomachine (TN) and the receiving nanomachine (RN) communicate with a single type of information molecules by modulating the transmission rate of information molecules at the TN. The information molecules undergo ideal (i.e. free) diffusion in three dimensions and become available to the RN that observes the concentration of the received molecules at its receptors and thus decodes the message. Our research shows that it is possible to realize complex modulation methods, combat the intersymbol interference (ISI), determine the effective communication ranges based on available signal concentration, develop signal detection schemes, and apply simple channel codes in a CEMC system. It has been found that the performance of the CEMC system is influenced by communication ranges, transmission data rates, ISI, and detection schemes. It is possible to sense the concentration signal intensity and develop optimum receiver structures that can detect the transmitted symbols at the RN. It is also possible to develop optimum signal detection schemes based on the interactions between the information molecules and the receptors using stochastic chemical kinetics (SCK) of the reaction events. Applying simple channel codes at the TN shows that it is possible to increase effective communication range in the CEMC system, however, this increases the complexity of the RN in implementing the detection circuitry. Finally, potential applications of CEMC would be in materializing CEMC-based molecular nanonetworks for emerging areas, e.g. in cancer detection and treatment, targeted drug delivery, and environmental protection and pollution control.

Femtosecond laser interaction with dielectrics has unique characteristics for micromachining, notably non-thermal interaction with materials, precision and flexibility. The nature of this interaction is highly nonlinear due to multiphoton ionization, so the laser energy can be nonlinearly absorbed by the material, leading to permanent change in the material properties in a localized region of Mu-m3. This dissertation demonstrated the potential of these nonlinear interactions induced changes (index modification and ablation for machining) in the dielectrics and explored several practical applications. We studied femtosecond laser ablation of Poly-methayl methacrylate (PMMA) under single and multiple pulse irradiation regimes. We demonstrated that the onset of surface ablation in dielectric surface is associated with surface swelling, followed by material removal. Also, the shape of the ablation craters becomes polarization dependent with increasing fluence, except for circular polarization. The morphology of the damaged/ablated material was examined by optical and scanning electron microscopy. The dynamics of laser ablation of PMMA was simulated using a 2 dimensional Molecular Dynamics model and a 3 dimensional Finite Difference Time Domain model. The results from numerical simulations agreed well with experimental results presented in this thesis. We also demonstrated the formation of nano-pillar within the ablation crater when the surface of bulk-PMMA was irradiated by two femtosecond pulses at a certain delay with energies below single shot ablation threshold. With increasing fluence, the nano-pillar vanished and the structure within the ablation crater resembled volcanic eruption. At higher fluences we demonstrated nanoscale porosity in PMMA. For application, a novel in-line fiber micro-cantilever was fabricated in bend insensitive fiber, that provides details of in-line measurement of frequency and amplitude of vibration, and can be further extended to be used as chemical/bio and temperature sensors. By modifying the refractive index at random spacing within the single mode fiber core, a unique quasi-random micro-cavities fiber laser was fabricated, which exhibits comparable characteristics with a commercial fiber laser in terms of narrow linewidth and frequency stability.

Restoring both anterior and posterior teeth with resin-composite materials is now an established clinical procedure with almost universal acceptance. The clinical performance of these restorations in the patient’s mouth is determined by a number of factors including the clinical techniques involved in their placement, the patient’s oral habits, and the physical and mechanical properties of the restorative materials themselves. These materials are being increasingly used in load-bearing areas of the posterior dentition and are therefore inevitably subject to masticatory forces of varying magnitude. The success of different resin-composites in different applications is understood through their clinical performance and laboratory-based experimental evaluation.My research was divided into two parts; the first part was concerned with the examination of different types of contemporary restorative resin-composites and in the second part, I compared different methods of examination. In the first part, I investigated and compared different sets of varied types of resin-composites, such as flowable resin-composites, bulk-fill resin-composites and conventional resin-composites. Using different sets of these materials, I examined a number of properties that affect their clinical performance and durability.In the second part, I studied and compared the conventional (macroscopic) methods of investigation with nanoindentation method. Both methods were applied to examine and characterise different properties for some types of resin-composites.The flowable and the bulk-fill resin-composites exhibited satisfactory results comparable with conventional resin-composites. The properties investigated included strength properties, modulus of elasticity, hardness and viscoelastic time-dependent creep deformation. The results obtained by nanoindentation confirmed that this method of examination is a valuable experimental tool to investigate and characterise some mechanical properties of resin-composites.