Carbon nanotube networks for thin film electronic applications

Scope of the thesis -- The advent of flexible organic macroelectronics -- Current challenges -- Carbon nanotubes : powering up orgnaics with nanotechnology -- Objectives of the present work -- Outline the thesis -- Overview of carbon nanotube networks -- Fabrication of carbon nanotube networks -- Electrical properties of carbon nanotube networks -- Applications of carbon nanotube networks -- Experimental procedures -- Carbon nanotubes and their purification -- Separation and suspension of carbon nanotubes in solutions -- Optical spectroscopy -- Protocols for fabricating carbon nanotube networks -- Imaging of carbon nanotube networks -- Atomic force microscopy (AFM) imaging -- Electrical contacts to carbon nanotubes -- Patterning carbon nanotube networks -- Deposition of organic semiconductors -- Electrical characterization -- Evaluating the performance limits of conducting and semicondcuting carbon nanotube networks for thin-film applications -- The fabrication and scaling characteristics of aligned and random carbon nanotube network thin film transistors -- Self-assembly of carbon nanotube networks -- Electrical properties of carbon nanotube network thin film transistors -- Substrate vs. environment- What suppresses electron conduction in field-effect transistor? -- Carbon nanotube sheets as electrodes in organic light emitting diodes -- Carbon nanotubes as injection electrodes in organic thin film transistor

Electronic And Optoelectronic Transport Properties Of Carbon Nanotube/organic Semiconductor Devices

Organic field effect transistors (OFETs) are of significant research interest due to their promising applications in large area, low-cost electronic devices such as flexible displays, sensor arrays, and radio-frequency identification tags. A major bottleneck in fabricating highperformance OFET is the large interfacial barrier between the metal electrodes and organic semiconductors (OSC) which results in an inefficient charge injection. Carbon nanotubes (CNTs) are considered to be a promising electrode material which can address this challenge. In this dissertation, we demonstrate fabrication of high-performance OFETs using aligned array CNT electrodes and investigate the detailed electronic transport properties of the fabricated devices. The OFETs with CNT electrodes show a remarkable enhancement in the device performance such as high mobility, high current on-off ratio, higher cutoff frequency, absence of short channel effect and better charge carrier injection than those OFETs with metal electrodes. From the low temperature transport measurements, we show that the charge injection barrier at CNT/OSC interface is smaller than that of the metal/OSC interface. A transition from direct tunneling to Fowler-Nordheim tunneling observed in CNT/OSC system shows further evidence of low injection barrier. A lower activation energy measured for the OFETs with CNT electrodes gives evidence of lower interfacial trap states. Finally, OFETs are demonstrated by directly growing crystalline organic nanowires on aligned array CNT electrodes. In addition to investigating the interfacial barrier at CNT/OSC interface, we also studied photoconduction mechanism of the CNT and CNT/OSC nanocomposite thin film devices. We found that the photoconduction is due to the exciton dissociations and charge carrier separation caused by a Schottky barrier at the metallic electrode/CNT interface and diffusion of the charge iv carrier through percolating CNT networks. In addition, it is found that photoresponse of the CNT/organic semiconductor can be tuned by changing the weight percentage of CNT into the organic semiconductors

Miniaturized Transistors, Volume II

In this book, we aim to address the ever-advancing progress in microelectronic device scaling. Complementary Metal-Oxide-Semiconductor (CMOS) devices continue to endure miniaturization, irrespective of the seeming physical limitations, helped by advancing fabrication techniques. We observe that miniaturization does not always refer to the latest technology node for digital transistors. Rather, by applying novel materials and device geometries, a significant reduction in the size of microelectronic devices for a broad set of applications can be achieved. The achievements made in the scaling of devices for applications beyond digital logic (e.g., high power, optoelectronics, and sensors) are taking the forefront in microelectronic miniaturization. Furthermore, all these achievements are assisted by improvements in the simulation and modeling of the involved materials and device structures. In particular, process and device technology computer-aided design (TCAD) has become indispensable in the design cycle of novel devices and technologies. It is our sincere hope that the results provided in this Special Issue prove useful to scientists and engineers who find themselves at the forefront of this rapidly evolving and broadening field. Now, more than ever, it is essential to look for solutions to find the next disrupting technologies which will allow for transistor miniaturization well beyond silicon’s physical limits and the current state-of-the-art. This requires a broad attack, including studies of novel and innovative designs as well as emerging materials which are becoming more application-specific than ever before

Applications of scattering-type scanning near-field optical microscopy in the infrared

This thesis is split into two broad sections. These are defined by the various applications of scattering-type near-field optical microscopy (s-SNOM) in different parts of the electromagnetic spectrum; the near-infrared (700 - 1000nm) and the mid-infrared (6 - 10um). S-SNOM is a means of imaging surfaces at resolutions well below the diffraction limit - the level of recorded detail does not depend on the wavelength of light (as it does with traditional optical microscopy), but instead on the sharpness of a probe (usually around 10nm), meaning an image resolution approaching a thousandth of a wavelength in the mid-infrared. For the work presented in the near-infrared, the focus lies with the modelling and mapping of various plasmonic resonances supported by metallic nanostructures. These resonances have the ability to "squeeze" light into substantially sub-wavelength volumes which is useful for a variety of applications ranging from cancer treatments to molecular sensing. The mid-infrared section starts with the implementation of a pulsed quantum cascade laser (QCL) as the system's light source. This presents some instrumentation challenges as all s-SNOM imaging to date has been conducted with continuous-wave (CW) lasers. Using a pulsed laser also raises some significant signal-to-noise implications which are quantified and discussed. In terms of the experimental applications of such a setup, the first steps towards ultra-high resolution infrared chemical spectroscopy are made by studying the epithelial cells of an oesophageal biopsy. The thesis concludes with an examination of the major noise sources faced by s-SNOM, and makes a number of recommendations on how their effects can be mitigated.Open Acces

Oxide Nanoelectronics

This thesis describes research performed on two types of complex oxide heterostructures. The first consists of ultrathin LaAlO3 films grown on SrTiO3 substrates. At the interface between these two insulating oxides, a quasi two dimensional electron gas may form under proper conditions. This interface has remarkable properties such as interfacial superconductivity, interfacial magnetism and a hysteretic voltage-controlled metal-insulator transition. We developed an Atomic Force Microscope (AFM) lithography technique which is capable of switching reversibly at room temperature this metal-insulator transition with nanometer scale spatial resolution. Based on this technique, conducting nanowires as thin as 2 nm and nanodots array with density up to 1014 inch-2 were written, probed and erased. Sketch-defined field effect transistors (SketchFET) with channel lengths as short as 2 nm were fabricated. These structures were characterized over a temperature range 15 K-300 K, revealing a complex energy landscape. Magnetotransport measurements performed at temperatures at and below 1 K reveal a variety of intriguing quantum phenomena, including integer and fractional quantum Hall states. The second material system consists of thin films of SrTiO3 grown directly on silicon. Although SrTiO3 is not ferroelectric at any temperature in bulk form, when strained to the silicon lattice it can become ferroelectric at and above room temperature. Temperature-dependent piezo force microscopy was performed to verify that those strain engineered films with certain thickness are indeed ferroelectric. Ultrafast optical experiments were carried out to measure lattice dynamics in these strained films. A coherent acoustic phonon mode was observed and studied as a function of film thickness and laser polarization. Using SrTiO3 grown on silicon-on-insulator structures, ferroelectric field effect transistors (FeFET) were fabricated and characterized at room temperature

Application of hydroxyapatite granules in posterolateral intertransverse lumbar spinal fusion

In many clinical disciplines used of bone graft is unavoidable such as to replace bone loss due to trauma, to fill in bone defect after tumour excision, for reconstructive surgery or spinal fusion. Calcium phosphate based hydroxyapatite is widely used bone graft substitute due to its similarity with the mineral components of bone matrix. This study was conducted to evaluate bone formation effect of this biomaterial in posterolateral intertransverse lumbar fusion, a novel site for its application. Twelve adult New Zealand white rabbits underwent bilateral intertransverse lumbar spinal fusion at L5-L6 vertebrae. One site of the animals was implanted with hydroxyapatite granules (HA group) while the contralateral sides received autograft and served as the control (AUTO group). Bone formation was assessed at 6 and 16 weeks by undecalcified histology and scanning electron microscopy. New bone was formed on the surface of hydroxyapatite granules and continually formed even at 16 weeks. Close contact between new bone and hydroxyapatite granules was demonstrated by scanning electron microscopy

Stratégie innovante pour la mise en forme de nanostructures TiO2/Au à propriétés synergétiques pour le photovoltaïque

Actuellement, le secteur des nanotechnologies est en développement intense. Les nanoparticules de dioxyde de titane et d¿or occupent une part importante de ce secteur, avec des applications utilisant principalement leurs propriétés optiques et catalytiques. Les synergies pouvant exister entre les nanoparticules d¿or et leur support, en particulier via l¿effet plasmon, permettent de modifier la réponse optique de dispositifs catalytiques ou photovoltaïques. Une nouvelle technique polyvalente de mise en forme de film mésoporeux à base de nanoparticules de dioxyde de titane et d¿or a été développée. L¿utilisation de différentes méthodes de synthèse des nanoparticules a permis le contrôle de la morphologie et des propriétés physiques des films déposés par centrifugation. Finalement, l¿adéquation de ces films à leur utilisation en tant qu¿anode de cellules solaires à colorant a été évaluée.Nanotechnologies represent a fast growing market. Gold and titanium dioxide nanoparticles are an important part of this market, thanks to their optical and catalytic properties. Existing synergies between gold nanoparticles and their substrate, mainly via the plasmonic effect, allow modifying the optical response of catalytic and photovoltaic systems. A new versatile approach is proposed to form mesoporous nanostructures composed of gold and titanium dioxide nanoparticles. The use of various syntheses allowed the formation of nanoparticles leading to a good control upon aggregation morphology and physical properties of centrifuged films. Finally, appropriateness of these films for a use as dye sensitized solar cell anodes was evaluated.PARIS-JUSSIEU-Bib.électronique (751059901) / SudocSudocFranceF

Scanning probe and electron spectroscopy studies of adsorbed inorganic systems

The field of nanoscience is a rapidly expanding area of research with numerous applications for technology. The development of this field has been largely helped by the invention of the atomic force microscope, as well as other surface analytical techniques such as photoelectron spectroscopy. The studies described in this thesis cover a varied range of topics. These include polymeric systems, carbon nanotube and an organostannoxane cluster system. The common theme within these studies is in improving understanding of the fundamental processes that may occur in the self assembly of these systems on substrates. Chapter 1 is an introductory chapter in that the basic concepts regarding the field of nanotechnology are introduced. In Chapter 2 the important analytical probes used in this thesis are described i.e. atomic force microscopy and photoelectron spectroscopy. The ‘parent’ complex of the systems explored in Chapter 3 and Chapter 4, [Ru(bpy)3]2+, is introduced in Chapter 3. This is followed by an exploration of the self-assembly and the morphology observed for the redox polymer [Ru(bpy)2PVPioCl]Cl on a Si02/Si(l 11) substrate. The electronic structure of this polymer is also described using synchrotron radiation photoemission. Chapter 4 describes the modification of multi-wall carbon nanotubes with the inorganic ruthenium complex [&zs-(2,2 ’-bipyridine)-(4,4’-dicarboxy-2,2’-bipyridine) ruthenium (II)]. The resulting assembly is characterised using spectroscopic and atomic force microscopy techniques. An introduction to carbon nanotubes with a discussion on some of their potential applications is also given. In Chapter 5 atomic force microscopy imaging with subsequent statistical crystallographic analysis is used to investigate the morphology observed when an organostannoxane cluster is deposited onto a Si02/Si(lll) substrate. Advanced image analysis techniques based on Minkowski functionals is also used to provide a detailed quantitative analysis of the morphology of the organostannoxane overlayers. Variations in both the surface roughness and the in-plane correlation length are followed as a function of annealing time in order to probe the surface dewetting dynamics. The solid state electronic structure of the cluster is described using synchrotron radiation photoemission and resonant photoemission. Finally, in Chapter 6 the results of the work undertaken are summarised with suggestions on further possible research directions