Nano-materials are interesting material category with a single unit size between 1 and 1000 nanometers and possess unique mechanical, electrical, optical, and other physical properties that make them stand out from ordinary materials. With increasing demand for reduced size of electronic devices and integrated micro/nano-electro-mechanical systems (MEMS / NEMS), there is a high driving force in scientific research and technological advancement in nanotechnology. My research is about two popular novel nanomaterials: carbon nanotubes (1-dimensional material) and thin-layer transition metal dichalcogenides (2-dimensional materials). My first research direction is about the characterization of electrical properties of carbon nanotubes and using them as bio-sensors. Carbon nanotubes (CNTs), in general, are a material of great interest for many applications since their first discovery in 1991 [1], due to their unique structure, extraordinary electrical and mechanical properties, and unusual chemical properties. High-throughput fabrication of carbon nanotube field effect transistors (CNTFETs) with uniform properties has been a challenge since they were first fabricated in 1998. We invent a novel fabrication method to produce a 1×1 cm2 chip with over 700 CNTFETs fabricated around one single carbon nanotube. This large number of devices allows us to study the stability and uniformity of CNTFET properties. We grow flow-aligned CNTs on a SiO2/Si substrate by chemical vapor deposition and locate a single long CNT (as long as 1 cm) by scanning electron microscopy. Two photolithography steps are then used, first to pattern contacts and bonding pads, and next to define a mask to ‘burn’ away additional nanotubes by oxygen plasma etch. A fabrication yield of ~72% is achieved. The authors present statistics of the transport properties of these devices, which indicates that all the CNTFETs share the same threshold voltage, and similar on-state conductance. These devices are then used to measure DNA conductance by connecting DNA molecule of varying lengths to lithographically cut CNTFETs. While one single carbon nanotube is considered 1-dimensional material because it only has one side with “non-nano” length, the thin-layer transition metal dichalcogenides (TMDCs) are called the 2-dimensional materials since they have two sides of normal lengths and the other side of atomic size. Atomically thin materials such as graphene and semiconducting transition metal dichalcogenides have attracted extensive interests in recent years, motivating investigation into multiple properties. We use a refined version of the optothermal Raman technique [2][3] to measure the thermal transport properties of two TMDC materials, MoS2 and MoSe2, in single-layer (1L) and bi-layer (2L) forms. This new version incorporates two crucial improvements over previous implementations. First, we utilize more direct measurements of the optical absorption of the suspended samples under study and find values ~40% lower than previously assumed. Second, by comparing the response of fully supported and suspended samples using different laser spot sizes, we are able to independently measure the interfacial thermal conductance to the substrate and the lateral thermal conductivity of the supported and suspended materials. The approach is validated by examining the response of a suspended film illuminated in different positions in radial direction. For 1L MoS2 and MoSe2, the room-temperature thermal conductivities are (80±17) W/mK and (55±18) W/mK, respectively. For 2L MoS2 and MoSe2, we obtain values of (73±25) W/mK and (39±13) W/mK. Crucially, the interfacial thermal conductance is found to be of order 0.1-1 MW/m2K, substantially smaller than previously assumed, a finding that has important implications for design and modeling of electronic devices.

Yuan, Wenxiang = CCTO陶瓷材料的制备和性质研究 / 苑文香. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2007. / Includes bibliographical references (leaves 63-67). / Text in English; abstracts in English and Chinese. / Yuan, Wenxiang = CCTO tao ci cai liao de zhi bei he xing zhi yan jiu / Yuan Wenxiang. / Acknowledgement --- p.ii / Abstract --- p.iii / Contents --- p.v / Chapter Chapter 1 --- Introduction --- p.1 / Chapter 1.1 --- Background --- p.1 / Chapter 1.2 --- Structure --- p.1 / Chapter 1.3 --- Models --- p.3 / Chapter 1.3.1 --- Parallel RC --- p.3 / Chapter 1.3.2 --- Two parallel RCs in series --- p.5 / Chapter 1.4 --- Motivation --- p.7 / Chapter 1.5 --- Our work --- p.7 / Chapter Chapter 2 --- Experiment --- p.8 / Chapter 2.1 --- Sources and substrate --- p.8 / Chapter 2.2 --- Preparation of the CCTO samples --- p.8 / Chapter Chapter 3 --- Experimental equipment --- p.13 / Chapter 3.1 --- Furnace --- p.13 / Chapter 3.2 --- X-ray diffraction (XRD) --- p.13 / Chapter 3.3 --- Scanning electron microscopy (SEM) --- p.16 / Chapter 3.4 --- Impedance analyzers --- p.17 / Chapter Chapter 4 --- Selections of the experimental conditions --- p.18 / Chapter 4.1 --- Selection of calcining-process conditions --- p.18 / Chapter 4.1.1 --- Experimental results --- p.18 / Chapter 4.1.2 --- Comparison with the results of other research groups --- p.21 / Chapter 4.2 --- Selection of sintering-process conditions --- p.22 / Chapter 4.2.1 --- CuO volatilization --- p.22 / Chapter 4.2.2 --- CCTO decomposition --- p.24 / Chapter 4.3 --- Optimizing of the Cu/Ca ratio --- p.29 / Chapter Chapter 5 --- Results and discussion --- p.31 / Chapter 5.1 --- Properties of CCTO ceramics sintered at different temperatures for 10 h --- p.32 / Chapter 5.2 --- Properties of CCTO ceramics sintered for different durations at 1000°C --- p.43 / Chapter 5.3 --- Properties of CC3+ΧTO ceramics --- p.52 / Chapter 5.4 --- Discussion --- p.58 / Chapter Chapter 6 --- Conclusions --- p.61 / References --- p.63

The trend over the last 50 years of down-scaling the silicon transistor to achieve faster computations has led to doubling of the number of transistors and computation speed over about every two years. However, this trend cannot be maintained due to the fundamental limitations of silicon as the main material for the semiconducting industry. Therefore, there is an active search for exploration of alternate materials. Among the possible candidates that can may [sic] be able to replace silicon is graphene which has recently gained the most attention. Unique properties of graphene include exceedingly high carrier mobility, tunable band gap, huge optical density of a monolayer, anomalous quantum Hall effect, and many others. To be suitable for microelectronic applications the material should be semiconductive, i.e. have a non-zero band gap. Pristine graphene is a semimetal, but by the virtue of doping the graphene surface with different molecules and radicals a band gap can be opened. Because the electronic properties of all materials are intimately related to their atomic structure, characterization of molecular and electronic structure of functionalizing groups is of high interest. The ab-inito (from the first principles) calculations provide a unique opportunity to study the influence of the dopants and thus allow exploration of the physical phenomena in functionalized graphene structures. This ability paves the road to probe the properties based on the intuitive structural information only. A great advantage of this approach lies in the opportunity for quick screening of various atomic structures. We conducted a series of ab-inito investigations of graphene functionalized with covalently and hapticly bound groups, and demonstrated possible practical usage of functionalized graphene for microelectronic and optical applications. This investigation showed that it is possible [to] produce band gaps in graphene (i.e., produce semiconducting graphene) of about 1 eV, without degrading the carrier mobility. This was archived by considering the influence of those adducts on electronic band structure and conductivity properties.

With the semiconductor industry racing toward a historic transition, nano chips with less than 45 nm features demand I/Os in excess of 20,000 with multi-core processors aggregately providing highest bandwidth at lowest power. On the other hand, emerging mixed signal systems are driving the need for 3D packaging with embedded active components and ultra-short interconnections. Being able to provide several fold increase in the chip-to-package vertical interconnect density is essential for garnering the true benefits of nanotechnology that will utilize nano-scale devices. Electrical interconnections are multi-functional materials that must also be able to withstand complex, sustained and cyclic thermo-mechanical loads. Device- to- system board interconnections are typically accomplished today with either wire bonding or solders. Both of these are incremental and run into either electrical or mechanical barriers as they are extended to higher interconnections densities. Downscaling traditional solder bump interconnect will not satisfy the thermo-mechanical reliability requirements at very fine pitches. Other approaches such as compliant interconnects require lengthy connections and are limited in terms of electrical properties. A novel chip-package interconnection technology is developed to address the IC packaging requirements and to introduce innovative design and fabrication concepts that will further advance the performance of the chip, the package, and the system board. The nano-structured interconnect technology simultaneously packages all the ICs intact in wafer form with quantum jump in the number of interconnections with the lowest electrical parasitics. The intrinsic properties of nano materials also enable several orders of magnitude higher interconnect densities with the best mechanical properties for the highest reliability and yet provide higher current and heat transfer densities. This thesis investigates the electrical and mechanical performance of nano-structured interconnections through modeling and test vehicle fabrication. Test vehicles with nano-interconnections were fabricated using low cost electro-deposition techniques and assembled with various bonding interfaces. Interconnections were fabricated at 200 micron pitch to compare with the existing solder joints and at 50 micron pitch to demonstrate fabrication processes at fine pitches. Experimental and modeling results show that the proposed nano-interconnections could enhance the reliability and potentially meet all the system performance requirements for the emerging micro/nano-systems.

Central to the practical use of nanoscale materials is the controlled growth in technologically meaningful quantities. Many of the proposed applications of the nanomaterials potentially require inexpensive production of the building blocks. Solution-based synthetic approach offers controllability, high throughput, and scalability, which make the process attractive for the potential scale-up. Growth kinetics could be readily influenced by chemical interactions between the precursor and the solvent. In order to fully utilize its benefits, it is therefore pivotal to understand the decomposition chemistry of the precursors used in the reactions. Supercritical fluids were used as solvent in which high temperature reactions could take place. Silicon nanowires with diameters of 20~30 nm was synthesized in supercritical fluids with metal nanocrystals as seeds for the nanowire growth. To unravel the effect of silicon precursors, several silicon precursors were reacted and the resulting products were investigated. The scalability of the system is discussed based on the experimental data. The nanowires were characterized with various characterization tools, including high-resolution transmission electron microscopy and electron energy loss spectroscopy. The crystallographic signatures were analyzed through the transmission electron microscopic study, and fundamental electrical and optical properties were probed by electron energy loss spectroscopy. Carbon nanotubes were prepared by reacting carbon-containing chemicals in supercritical fluids with organometallic compounds that form metal seed particles in-situ. A batch reaction, in which the temperature control was relatively poor, yielded a mixture of multiwall nanotubes and amorphous carbon nanofilaments with a low selectivity of nanotubes in the product. When reaction parameters were translated into a continuous flow-through reaction, nanotube selectivity as well as the throughput of the total product significantly improved. Magnetic properties of various metal nanocrystals were also studied. Colloidal synthesis enables the growth of FePt and MnPt3 nanocrystals with size uniformity. The as-synthesized nanocrystals, however, had compositionally disordered soft-magnetic phases. To obtain hard magnetic layered phase, the nanocrystals must be annealed at high temperatures, which led to sintering of the inorganic cores. To prevent sintering, the nanocrystals were encapsulated with silica layer prior to annealing. Interparticle magnetic interactions were also explored using particles with varying silica thickness. / text

Within recent years, allotropic structures of carbon have been produced in the forms of tubes and ribbons which offer the promise of extraordinary electronic and thermal properties. Here we present analyses of oligophenyl and oligoacene systems–infinite, one-dimensional chains of benzene rings linked along the armchair and zigzag directions. These one-dimensional structures, which are amenable to calculation by analytical means, exhibit features very similar to carbon nanotubes and nanoribbons. Using a tight-binding Hamiltonian we analytically determine the density of states, local density of states, and energy-band structure for the phenyl and the acene. We also examine the effect of disorder on the energies and the corresponding states. / Department of Physics and Astronomy

Supercapacitor is the best potential candidate of the energy storage system due to the superior charge or discharge efficiency, high power density (>10 kW kg-1), and long cycling life. Porous carbon materials as the promising electrode material have been widely used in supercapacitor. In fact, conventional porous carbon supercapacitor electrodes cannot fulfil the growing demand of high energy and power densities of supercapacitor. A large number of studies show that nitrogen doping can change the surface electronic structure of carbon materials, thus significantly improving the electrochemical properties. In addition to, the pore structure and morphology of carbon materials have great influence on the electrochemical performance. In this work, we firstly fabricated nitrogen-doped porous carbon nanotubes by using a simple mixed salts (NaCl/ZnCl2) activation strategy. The as-obtained porous carbon nanotubes exhibited excellent electrochemical performance in supercapacitor. Furthermore, two- dimension nitrogen-doping porous nanosheets were prepared by a salt template-assisted monomer deposition method. In this study, by optimizing the synthesis conditions, the as-obtained carbon nanosheets showed a high specific capacitance of 277 F g-1 at 1 A g-1 and excellent cycle stability retained 91 % after 10,000 cycles. / College of Engineering, Science and Technology / M. Tech.( Civil and Chemical Engineering

In this thesis we investigate concepts associated with aggregation. The basic idea of aggregation is that there exists a reduced order model such that, for an appropriate initial condition, the trajectories of the reduced-order model are linear combinations of the trajectories of the ful 1-order model. We study systems which do not aggregate exactly, but which "nearly aggregate". It is shown that for "nearly aggregable" systems there exists a reduced-order model such that, for an appropriate initial condition, the trajectories of the reduced-order model are near a linear combination of the trajectories of the full-order model. Under certain conditions it has also been shown that near-aggregation is equivalent to near-unobservability (roughly, an invariant subspace close to the null space of C). Here we establish a relationship between near-unobservability and modal measures of observability as suggested by Selective Modal Analysis. With this result we then obtain an upper bound on the norm of the transfer function residue using near-unobservability measures. The Generalized Hessenberg Representation (GHR) and Dual GHR are examined throughout this analysis. It is finally shown that for SISO systems, the residue norm may be expressed in terms of certain parameters of the Dual GHR. / M.S.

The use of aluminum nitride as a substrate material for microelectronics is examined. A brief look at thermal, mechanical, and electrical properties of aluminum nitride show that it is a viable alternative material for this use. A study of the interfaces between aluminum nitride and several thick film pastes (palladium silver conductor, ruthenium oxide resistor, and gold conductor) was performed with optical microscopy, scanning electron microscopy, and energy dispersive spectroscopy. Results of this investigation showed that the contaminants in the substrate material that affect thermal conductivity do not affect the adhesion of the thick film pastes. However, it was found that the lack of certain elements in the binder of the thick film paste could lead to weaker adhesion, and severe degradation of the thick film's adhesion during thermal cycling.

Nanocrystals are an important field of study in the 21st century. Crystallites that are nanometers in size have very different properties from their bulk analogs because quantum mechanical effects become dominant at such small length scales. When a crystallite becomes small enough, the quantum confinement of electrons in the material manifests as a size-dependence of the nanocrystal's properties. Electrical and optical properties such as absorbance, surface plasmon resonance, and photoluminescence are sensitive to the size of the nanocrystal and proffer an array of technological applications for nanocrystals in such fields as biological imaging, laser technology, solar power enhancement, LED modification, chemical sensors, and quantum computation.The synthesis of size-controlled nanocrystals is critical to using nanocrystal in applications for their size-dependent properties. The development of nanocrystal synthesis techniques has been its own entire field of study for two decades or more, and several successes have established novel, utilitarian protocols for the mass-production of nanocrystals with controlled size and very low polydispersity. However, the experimental successes are generally poorly understood and no theoretical framework exists to explain the dynamics of these processes and how to better control or optimize them. It is the goal of this thesis to develop novel theories of nanocrystal synthesis processes to describe these phenomena in theoretical detail and extract meaningful correlations and driving forces that provide the necessary insight to improve the technology and enhance our understanding of nanocrystal growth. Chapter 4, 5 and 6 comprise all the novel research conducted for this thesis, with Chapters 1, 2 and 3 serving as necessary background to understanding the current state of the art. In Chapter 4, we develop a quantitative describe of the process of size focusing, in which a population of polydisperse nanocrystals, which are useless for applications, can be made more monodisperse by the injection of new crystallizable material. We derive mass balance equations that relate the rate of new-material generation to changes in the growth patterns of the nanocrystals. Specifically, we determine that only when the rate of crystal-material production is sustained at a high level can size focusing occur and a monodisperse sample of nanocrystals be produced. Quantitative criteria are provided for how high the rate of production must be, and the quantitative effects on the nanocrystal size distribution function for various magnitudes of the production rate. The effect of the production rate on every facet of the size distribution function is evaluated analytically and confirmed numerically. Furthermore, through comparison of the theory to experimental data, it is determined that a typical nanocrystal synthesis accidentally correlates two variables that are critical to the phenomenon of size focusing. The unknowingly correlated variables have frustrated experimental investigations of the same insights we provided with theory. We recommend a new synthesis protocol that decouples the critical variables, and thus permit the quantitative control of nanocrystal size and polydispersity through theoretical relations, which can also be generalized for the a priori design and optimization of nanocrystal synthesis techniques. In Chapter 5, a theoretical investigation of the growth of surfactant-coated nanocrystals is undertaken. The surfactants create a layer around the nanocrystal that has different transport properties than the bulk solution, and therefore has a strong effect on diffusion-limited growth of nanocrystals. This effect of a surfactant layer is investigated through the lens of the LSW theory of Ostwald ripening as well as through the lens of our own theory of size focusing from Chapter 4. The quantitative effect of a surfactant layer on the various growth processes of spherical nanocrystals is determined, with the result that size focusing can potentially be enhanced by the choice of an appropriate surfactant for a particular nanocrystal material. In addition to the kinetic studies of Chapter 4 and 5, a thermodynamic investigation of surfactant-coated nanocrystals is conducted in Chapter 6, with the goal of understanding the process known as "digestive ripening". In digestive ripening, a population of polydisperse gold nanocrystals is exposed to a strongly binding surfactant, at which point the nanocrystals spontaneously shrink and become highly monodisperse. Different surfactants and different crystal materials can exhibit digestive ripening. Those same materials also have the capacity to be digested further from nanocrystals into molecular clusters that eliminate all crystalline material in favor of surfactant-crystal coordination. The outstanding question is, why does the spontaneous digestive ripening process appear to make large nanocrystals shrink to small nanocrystals, but it does not force small nanocrystals to shrink further to molecular clusters? We construct a full Gibbs free energy model, which we minimize under multiple constraints to obtain quantitative relations for what thermodynamic properties (such as the surfactant binding energy and the crystal-solvent surface energy) govern the existence and size-dependence of a thermodynamically stable nanocrystal. Through our model, we determine that a finite-size nanocrystal is only stable under two possible conditions: either the surfactant-crystal binding is stronger than the crystal-crystal binding and the system contains too few surfactants to form molecular clusters and thus "surfactant-lean" nanocrystals are created, or the surfactantsurfactant intermolecular interactions are sufficiently strong that the nanocrystal core is treated as a swollen micelle in a microemulsion and is stabilized by the surfactant tails' interactions. Quantitative equations are provided that establish what trends and values are expected for experimental results. The results are inconclusive: there is no evidence supporting either conclusion because the available experimental data is insufficient. More accurately, many thermodynamically critical parameters (like the crystal surface energy) are unknown and are practically immeasurable in experimental systems. Speaking generally, the evidence for the surfactant-lean condition is moderately better than the evidence for the microemulsion condition, but in both cases the evidence is insufficient to make a solid conclusion. We therefore use our quantitative results of the thermodynamic investigation to make recommendations to experimentalists as to what trends and what nanocrystal growth processes we expect to observe in either thermodynamic case. While our results are inconclusive in and of themselves, they will be used to highlight the exact thermodynamic driving forces of the experimental systems. We conclude by giving an overview of two new fields of study for theoretical descriptions of nanocrystal growth, specifically the growth of anisotropic nanocrystals and a practical theory for nanocrystal nucleation. Preliminary relations are constructed, with comments on what directions we expect the research to take and how the results would be useful in enhancing our understanding of nanocrystal growth behavior.