This dissertation primarily documents the quantification of the interfacial behavior of carbon based nanomaterials, which includes two categories, one is the nanofriction properties evaluation of aligned carbon nanotube carpets, few-layer graphene as well as three types of functionalized graphene nanoribbons, the second is the mechanical characterization of individual functionalized carbon nanofibers and the interfacial fracture toughness quantification in carbon nanotube/polymer derived ceramics nanocomposite. The aligned carbon nanotube carpets have a highly anisotropic friction behavior, which means the friction force are lower for transversely aligned CNTs side than for vertically aligned CNTs surface. We can also tune the friction properties of graphene ribbons by grafting different functional groups. In addition, two narrow angular regions with high friction, separated by a wide angular interval with low friction, were identified between graphene and highly oriented pyrolytic graphite. The distance between the two friction peaks is 61◦, which corresponds well with the 60◦ symmetry of individual atomic layers in the graphite lattice. The technique that involves the usage of mcirodevices and nanoidenter was used to conduct tensile tests on pristine, fluorinated and amino-functionalized carbon nanofibers, which were found to exhibit varied load-bearing abilities and unique fracture modes. The technique was also used to perform single fiber pullout experiments to study carbon nanotube/polymer derived ceramic interface.

Motivated by a desire to understand the basic concepts of one-dimensional nanostructure growth, the research described in this thesis aims at understanding the basic mechanisms controlling the synthesis and formation of a specific group of II-VI semiconducting nanostructures. In particular, this thesis examines one-dimensional nanostructures (such as nanobelts and nanowires) and different morphologies of ZnS that result from the interesting properties that the materials have at the nanoscale. In order to understand how to tune these properties in the nanostructure, it is necessary to have an understanding of the growth mechanism that dictates the morphology, structure, and rate of growth of the nanomaterial. It is necessary to understand what impact changes to the macroscopic setup in the experiment have on the nanoscopic scale of the nanomaterials. Having a larger understanding and exerting more precise control over the growth of nanomaterials will allow a higher level of selectivity, more control over dimensionality and the type of morphology, easier manipulation, and the simpler incorporation of these structures into a nanotechnological device. The main focus of the research was on CdSe and ZnS, with the bulk of the research being conducted on ZnS nanostructures. These materials were chosen for their potential for extensive research, their possible applications in optoelectronics, their potential to form the wurtzite crystal structure, and the potential generalization of results to other nanomaterials. The framework for the research is given first. Then a description of the experimental setup and a model for the growth of nanostructures is discussed. A brief overview of the synthesis of CdSe nanostructures is given and then a detailed analysis of the synthesis of specific ZnS one-dimensional morphologies is presented.

In this dissertation, I have investigated applying the laser ablation of microparticle aerosol (LAMA) process to the production of nanocomposite polymer membranes for olefin/paraffin separation. Experimental results for three major thrusts are presented: 1) an investigation into the scalability of the LAMA process, 2) a new laser ablation technique for nanoparticle production from aqueous feedstocks, and 3) characterization of olefin-selective polymer nanocomposite membranes produced using LAMA. The propensity for Ag nanoparticles to form agglomerates in LAMA is investigated. Nanoparticle samples were collected on TEM grids at several feedstock aerosol densities. As the density increased, the particle morphology shifted from single nanoparticles 5 nm in diameter to chained agglomerates of 20 nm diameter primary particles. The results are in agreement with a numerical model of Brownian agglomeration and diffusion. Factors influencing nanoparticle morphology, such as temperature, initial nanoparticle charge, and feedstock aerosol density are discussed. It is shown that agglomeration occurs on a much longer timescale than the other processes, and can be treated independently. A new nanoparticle synthesis technique is presented: laser ablation of aqueous aerosols. A Collison nebulizer is used to generate a mist of ~10 [mu]m diameter water droplets containing dissolved transition metal salts. Water from the droplets quickly evaporates, leaving solid particles which are ablated by an excimer laser. Ablation results in plasma breakdown and photothermal decomposition of the feedstock material. For AgNO₃ ablated in He gas, metallic Ag nanoparticles were produced. For Cu(NO₃)₂ ablated in He gas, crystalline Cu₂O nanoparticles were produced. For Ni(NO₃)₂ ablated in He gas, crystalline NiO nanoparticles were produced. A combination of AgNO₃ and Cu(NO₃)₂ ablated in a reducing atmosphere of 10%H₂/He yielded nonequilibrium Ag-Cu alloy nanoparticles. Membranes composed of poly(ethylene glycol diacrylate) (PEGDA) and Ag nanoparticles were produced by the LAMA process. Permeation and sorption measurements for the light olefins and paraffins were conducted for these membranes. The membranes showed very little improvement in olefin/paraffin selectivity compared with neat PEGDA membranes. Using the LAMA implementation described here, it was impossible to produce membranes with high Ag loading. Whether membranes containing more Ag would exhibit improved selectivity remains an open question. / text

Kyoto University (京都大学) / 0048 / 新制・課程博士 / 博士(エネルギー科学) / 甲第19096号 / エネ博第320号 / 新制||エネ||65 / 32047 / 京都大学大学院エネルギー科学研究科エネルギー応用科学専攻 / (主査)教授 松田 一成, 教授 岸本 泰明, 教授 大垣 英明 / 学位規則第4条第1項該当

This thesis presents the design and synthesis of nanowires (NW) with targeted and tunable optical properties. Moreover, we show how single and assembled NW devices can enable new photovoltaic (PV) and photonic platforms. Beginning with an investigation of axially modulated p-i-n junction NWs, we established several fundamental parameters dictating solar cell performance at the nanoscale and demonstratred the first series integration of multiple solar cells on a single NW. Thereafter, implementation of the first silicon NW photovoltaic device with radially modulated p-n junctions showed that power conversion efficiencies of 3-4% are attainable from a nanoscale architecture, exceeding efficiencies for many organic and hybrid organic-inorganic solar cells. Despite these achievements, the poor electrical characteristics and insufficient control over absorption properties characterizing the aforementioned devices would limit the promise of silicon NWs for next generation solar cells. We overcome these limitations with a class of polymorphic core/multi-shell silicon NWs with highly-crystalline hexagonally-faceted shells and embedded coaxial p/i/n junctions. NW PV devices 200-300 nm in diameter exhibit open-circuit voltages of 0.5 V and fill-factors of 73% under one-sun solar illumination. Single-NW wavelength-dependent photocurrent measurements agree quantitatively with FDTD simulations. Synthetic manipulation of NW size and morphology drives tuning of optical resonances such that optimized structures can yield current densities double those for films of comparable thickness. Further optimized NW devices achieve current densities of 17 mA/cm2 and power conversion efficiencies of 6%. We also present steps toward rational assembly of larger-scale NW PV arrays. Parallel integration of NWs preserves PV metrics while assembly of vertically-stacked NWs yields current densities of \(25 mA/cm^2\) and projected efficiencies of ~15% for \(1 \mu m\) thick assemblies. Finally, we present the first ever NW material possessing 3 degrees of structural freedom, thus expanding the NW "structome." Such NWs were achieved through the first demonstration of facet selective growth of silicon and germanium in the gas phase. Photonic devices based on this new material present intriguing optical properties, including selective attenuation, enhancement, and wavelength tunability of resonant cavity modes. / Chemistry and Chemical Biology

Τα νανοϋλικά, τα υλικά δηλαδή που οι διαστάσεις τους είναι στην νανοκλίμακα, έχουν διαφορετικές ιδιότητες από τα αντίστοιχα υλικά σε μεγαλύτερη κλίμακα. Για αυτό το λόγο, τα νανοϋλικά παρουσιάζουν ιδιαίτερο ενδιαφέρον για περαιτέρω μελέτη και έρευνα. Σε αυτά τα υλικά ανήκει και το οξείδιο του ψευδαργύρου (ZnO). Το οξείδιο του ψευδαργύρου είναι ένας σύνθετος ημιαγωγός τύπου II-IV με άμεσο ενεργειακό χάσμα (Eg=3.37 eV) σε θερμοκρασία δωματίου και με μεγάλη ενέργεια σύνδεσης εξιτονίου (60 meV). Σκοπός της παρούσας διπλωματικής εργασίας είναι η σύνθεση, ο χαρακτηρισμός και η μελέτη ιδιοτήτων νανοσύνθετων υλικών οξειδίου του ψευδαργύρου-πολυμερικής μήτρας. Το υλικό που θα χρησιμοποιήσουμε ως πολυμερική μήτρα είναι η πολυβινυλική αλκοόλη (PVA). Αρχικά, θα δώσουμε τον ορισμό της νανοτεχνολογίας και των νανοϋλικών, και θα παρουσιάσουμε και διάφορους τρόπους παρασκευής νανοϋλικών. Στο δεύτερο κεφάλαιο, θα ασχοληθούμε με το οξείδιο του ψευδαργύρου (ZnO). Στο κεφάλαιο αυτό, γίνεται εκτενής περιγραφή της δομής, των ιδιοτήτων και των νανοδομών του οξειδίου του ψευδαργύρου. Στην συνέχεια, θα περιγράψουμε τις βασικές αρχές που αφορούν τις πειραματικές τεχνικές που θα χρησιμοποιήσουμε για τoν χαρακτηρισμό των δειγμάτων. Ενώ στο τέταρτο κεφάλαιο, θα παρουσιάσουμε την πειραματική διαδικασία που θα ακολουθήσουμε για την σύνθεση του οξειδίου του ψευδαργύρου, καθώς και για την παρασκευή των μεμβρανών PVA-ZnO. Στο ίδιο κεφάλαιο, θα παρουσιάσουμε τα αποτελέσματα από το χαρακτηρισμό των νανοσωματιδίων του ZnO και των μεμβρανών PVA-ZnO. Στο τελευταίο κεφάλαιο, θα αναφέρουμε τα συμπεράσματα μας σχετικά με την παρούσα διπλωματική εργασία. / Nanomaterials, materials on the scale of a few nanometers, have different properties in comparison with larger-scale materials. For this reason, nanomaterials are of particular interest for further study and research. Zinc Oxide (ZnO) belongs to these materials. ZnO is a complex II-VI semiconductor with a direct band-gap energy (Eg = 3.37 eV) at room temperature and a large exciton binding energy (60 meV). The aim of the present diploma thesis is the preparation, the characterisation and the study of properties of ZnO particles in a polymer matrix. A polyvinyl alcohol (PVA) matrix has been used. Firstly, nanotechnology and nanomaterials are defined and various synthetic methods of nanomaterials are presented. The second chapter deals with ZnO. This chapter comprehensively describes the structure, the properties and the nanostructures of zinc oxide particles. Thereafter, in chapter three, the basic principles concerning the experimental techniques of characterization which have been used are described. The forth chapter describes the experimental process followed for preparing ZnO nanoparticles and PVA-ZnO nanocomposites. The results from the characterization of the ZnO nanoparticles and PVA-ZnO membranes are then presented. In the last chapter, we make our conclusions about this diploma thesis.

This thesis presents investigations into the design and synthesis of nanomaterials in supercritical carbon dioxide (sc-CO₂) as well as novel experimental design methodologies. First, the process-structure-property relationships are studied for the deposition of materials from organometallic precursors in sc-CO₂. The materials that were investigated in these studies were: (1) the semiconductor material copper zinc tin sulfide (Cu₂ZnSnS₄, or CZTS), which has application in solar energy capture; (2) zinc sulfide nanoparticles deposited onto carbon nanotubes, which have application in optoelectronics; and (3) silver nanoparticles deposited on silicon and glass wafer surfaces, which find application as biosensors via surface enhanced Raman spectroscopy. Next, two novel experimental design methodologies were implemented. The first is termed layers of experiment with adaptive combined design (LoE/ACD), which efficiently optimizes a process that is expensive and time consuming to study by zooming in on the process optimum through successive layers. The mean silver nanoparticle size was optimized as a function of temperature in the sc-CO₂ system using the LoE/ACD approach. The second experimental design methodology is called initial experimental design (IED). The IED methodology was developed to choose the first round of experiments for a system that is expensive to study (in terms of time and money), poorly understood, and possesses a related, non-identical system that is well-studied. The IED approach was used to optimize the mean iridium nanoparticle size as a function of temperature given expert opinion, prior data, and an engineering model for silver nanoparticles synthesized in sc-CO₂.

Silicon is a promising negative electrode material for lithium-ion (Li-ion) batteries, with volumetric and gravimetric capacities much higher than those in current commercial batteries. Implementation of Si as a negative electrode is halted, however, by a large irreversible capacity and declining reversible capacity over cycle life. These problems are linked to the large volume expansion that Si undergoes when reacted with lithium, and overcoming them is the focus of this thesis. To overcome this expansion, in the first part titanium silicides were proposed to buffer the volume expansion problem as Ti does not react with Li and is robust. A pure phase of the targeted TiSi and TiSi2 was not achieved, however one product mixture containing TiSi2 and Ti5Si3 was cycled against Li at C/20. A capacity of 715 mAh g-1 was achieved, however rapid capacity fade occurred over the first 10 cycles. The second part of the thesis focused on heterostructured Si-Ge and Ge-Si core- shell nanowires. The morphology of the nanowires allows for better accommodation of strain due to lithiation, and Ge functions as an active matrix, as it can store Li in a similar manner as Si. The specific capacities of the nanowires were good at 1346 mAh g-1 and 1276 mAh g-1, however after 50 cycles the Si-Ge nanowires had a capacity retention of 72.4 % and the Ge-Si retained 62.4 %. The diffusion coefficient of Li was determined from GITT and EIS to be within the range of 10-16 to 10-13 cm2s-1 and was slightly lower than other reported values, attributed to the dense structure of the nanowires slowing diffusion.

The linear and nonlinear optical response of plasmon hybridized systems is the subject of study of this thesis. Plasmonic silver nanoprisms are able to confine light to a sub-wavelength volume, which provides local field enhancement. This confined field is promising for achieving an enhanced nonlinear optical response. For many of plasmon nanoparticles, however, the plasmonic resonance is not at the near-infrared wavelengths of a Ti:Sapphire laser, the most common source used for ultra-fast measurements. To achieve resonance at these wavelengths, a tuning mechanism is required. The plasmon hybridization between silver nanoprisms and a thin gold film provides this tuning mechanism, which allows for enhanced optical second harmonic generation. Overlapping the plasmon resonance of the system with excitation source, by varying the spacer layer between the nanoprisms and the gold film, enhances the second harmonic counts by approximately three orders of magnitude. The finite-difference time-domain calculations agree to within a factor of two with the experimental findings in terms of the predicted enhancement factor. This plasmon hybridization approach is promising for future applications, including enhanced multi-photon lithography and nonlinear sensing using metal nanoparticles. / Graduate

This work presents a novel means of producing thin-film light-emitting devices, functioning according to the principle of electroluminescence, using an inkjet printing technique. This study represents the first report of a light-emitting device deposited completely by inkjet printing. An electroluminescent species, doped zinc sulfide, was incorporated into a polymeric matrix and deposited by piezoelectric inkjet printing. The layer was printed over other printed layers including electrodes composed of the conductive polymer poly(3,4-ethylenedioxythiophene), doped with poly(styrenesulfonate) (PEDOT:PSS) and single-walled carbon nanotubes, and in certain device structures, an insulating species, barium titanate, in an insulating polymer binder. The materials used were all suitable for deposition and curing at low to moderate (<150°C) temperatures and atmospheric pressure, allowing for the use of polymers or paper as supportive substrates for the devices, and greatly facilitating the fabrication process. The deposition of a completely inkjet-printed light-emitting device has hitherto been unreported. When ZnS has been used as the emitter, solution-processed layers have been prepared by spin-coating, and never by inkjet printing. Furthermore, the utilization of the low-temperature-processed PEDOT:PSS/nanotube composite for both electrodes has not yet been reported. Device performance was compromised compared to conventionally prepared devices. This was partially due to the relatively high roughness of the printed films. It was also caused by energy level misalignment due to quantization (bandgap widening) of the small (<10 nm) nanoparticles, and the use of high work function cathode materials (Al and PEDOT:PSS). Regardless of their reduced performance, inkjet printing as a deposition technique for these devices presents unique advantages, the most notable of which are rapidity of fabrication and patterning, substrate flexibility, avoidance of material wastage by using drop-on-demand technology, and the need for only one main unit operation to produce an entire device.