Conjugated Polymer and Hybrid Polymer-Metal Single Nanowires: Correlated Characterization and Device Integration

This book describes nanowires fabrication and their potential applications, both as standing alone or complementing carbon nanotubes and polymers. Understanding the design and working principles of nanowires described here, requires a multidisciplinary background of physics, chemistry, materials science, electrical and optoelectronics engineering, bioengineering, etc. This book is organized in eighteen chapters. In the first chapters, some considerations concerning the preparation of metallic and semiconductor nanowires are presented. Then, combinations of nanowires and carbon nanotubes are described and their properties connected with possible applications. After that, some polymer nanowires single or complementing metallic nanowires are reported. A new family of nanowires, the photoferroelectric ones, is presented in connection with their possible applications in non-volatile memory devices. Finally, some applications of nanowires in Magnetic Resonance Imaging, photoluminescence, light sensing and field-effect transistors are described. The book offers new insights, solutions and ideas for the design of efficient nanowires and applications. While not pretending to be comprehensive, its wide coverage might be appropriate not only for researchers but also for experienced technical professionals

Optical Characterization of a Single Quantum Emitter Based on Vanadium Phthalocyanine Molecules

Single quantum emitters play a fundamental role in the development of quantum technologies such as quantum repeaters, and quantum information processing. Isolating individual molecules with stable optical emission is an essential step for these applications, specially for those molecules that present large coherence times at room temperature. Among them, vanadium-oxide phthalocyanine (VOPc) molecules stand out as promising candidates due to their large coherence times measured in ensemble. However, the optical properties of individual molecules have not yet been reported. Here we show that single VOPc molecules with stable optical properties at room temperature can be isolated. We find that the optical response of the molecule under laser illumination of different polarization agrees well with a system having pyramidal C$_{4v}$ symmetry. Furthermore, the molecule reveals a non-radiative transition rate that depends on the excitation wavelength when its lifetime is interrogated. We provide theoretical calculations that support our experimental findings and provide insight to the role of phonons and internal electronic structure of the molecule. These results demonstrate that this single paramagnetic molecule can function as a single quantum emitter while displaying optical stability under ambient conditions to have their intrinsic properties investigated

Correlated characterization of hybrid metal-conjugated polymer nanowires

In recent years, investigators in industry and academia have increasingly tamed the structural and electronic properties of of low dimensional materials. Among them, nanowires (NWs) and nanotubes were intensely scrutinized because of their potential use in various applications requiring miniaturization. Besides the well-known CNT, many species of NWs-like nanomaterials can be synthesized from inorganic and/or organic materials and offer an impressive potential in applications ranging from bio-environmental sensing and energy harvesting to ultra-low power electronic devices and high density memories. Nevertheless, the use of single NW in real applications asks for identifying their intrinsic behavior and requires to manipulate and contact them properly. The aim of this thesis is to contribute to this active research area, focusing particularly on hybrid metal-polymer nanowires made of conjugated polymers (PPy, PEDOT, PANi) and metals (Au, Pt, Ni) with diameters ranging from 30 nm to 160 nm. In this experimental study, we investigated the electrical and structural properties of several classes of hybrid nanowires (HNW) and HNW arrays. The first part of this thesis, focuses on the structural and electrical characterization of several classes of HNW arrays. A careful characterization of the metal-polymer interfaces by transmission electron microscopy revealed that the structure and mechanical strength of the interfaces are very different. Variable temperature electrical transport measurements suggested that the three-dimensional Mott variablerange- hopping (VRH) model provides a complete framework for understanding charge transport, including nonlinear current-voltage characteristics and magnetotransport. The diameter dependence of the electrical properties of HNWs suggests that the transport mechanism changes for the 40 nm HNWs samples which exhibit a behavior indicative of the critical regime of disorder-induced metal-insulator transition. Then, because of the several limitations of the bulk characterization of HNWs (e.g. averaging effects on the measured properties, high contact resistance, no interactions with the environment, ...) we investigated the integration of single HNW in a planar electronic devices. Advantageously, single HNW measurements allow us to probe the responses of HNWs to different stimuli. Especially, we showed that the electrical properties of mutli-segmented HNWs can be switched chemically from a linear to a rectifying behavior. We proposed a simple model based on Schottky diodes to explain and reproduce the observed phenomenon. Finally, to gain further insight into the structure-property relationships of these nanomaterials, we developed, fabricated and characterized multipurpose platforms, fabricated via Si micromachining techniques. These microdevices enable the correlation between the structural properties -as observed, for instance, by transmission and scanning electron microscopies - the electrical and thermal properties obtained from the same sample. While these membrane-based microdevices were used for correlated studies of NWs, the extension to other nanomaterials (organic, inorganic, or hybrid films, nanoparticles) is straightforward.(FSA 3) -- UCL, 201

Template-free electrodeposition of highly oriented and aspect-ratio controlled ZnO hexagonal columnar arrays

We report an easy one-step template-free electrodeposition method for preparing large arrays of ZnO hexagonal nanocolumns, vertically oriented on a Au-coated Si substrate. Systematic scanning electron microscopy investigations revealed the potential of this method for obtaining a high degree of verticality and orientation of the nanostructures and for controlling their aspect-ratio in an easy manner. Further structural studies demonstrated that the as-obtained ZnO nanocolumns present a well defined hexagonal symmetry exhibiting an excellent crystallinity

Engineering Nonlinear Electrical Behavior with Asymmetric Multisegmented Polymer–Metal Nanowires

In this paper, we report on novel hybrid nanowires as prototypical building blocks for nanocomponents. Multisegmented hybrid nanowires (HNWs) made of metallic and conjugated polymer (CP) segments were elaborated and the impact of metal/polymer interfaces on the rectifying behavior was determined. Using HNWs integrated into micromachined devices, the relationship between electronic properties and original structure is revealed. By combining transmission electron microscopy (TEM) directly on the symmetric and asymmetric HNWs structures studied by current–voltage (I–V) spectroscopy, we show that rectifying I–V characteristics are observed only for asymmetric HNWs. Moreover, it is shown that the rectification ratio can be improved up to 3 orders of magnitude by a proper selection of the HNW composition. While the rectifying behavior is observed in HNWs after oxidative or acid doping, the charge transport mechanism in as-synthesized HNWs is bulk-limited and independent from their structure. Both symmetric and asymmetric HNWs exhibit Ohmic and nonlinear I–V curves above and below TNL ≈ 120 K, respectively. These electrical behaviors are consistent with a progressive transition from an Ohmic to a non-Ohmic variable-range-hopping (VRH) mechanism. We discuss the origin of these nonlinearities, comparing the two- and four-probe measurements on single HNWs, and we propose a simple model based on dual back-to-back Schottky diodes to explain qualitatively the rectifying properties

Self-seeded electrochemical growth of ZnO nanorods using textured glass/Al-doped ZnO substrates

tIn this work, large and dense arrays of zinc oxide (ZnO) nanorods (NRs) were fabricated by an improvedtemplate-free electrodeposition (ECD) route on top of home-made Al-doped ZnO (AZO) thin filmsdeposited on glass. The AZO layer, acting as transparent conducting oxide, was found to display enhancedelectrical and morphological properties compared to other commercially available substrates, facilitat-ing the subsequent electrochemical growth of the ZnO nanostructures. In addition, its intrinsic columnarnature strengthened the vertical orientation of the obtained ZnO NRs. The one-step low-temperatureelectrochemical method did not require any additional seeding layer, being suitable for applications inwhich the process simplicity and substrate’s thermal toughness are essential requirements. The ECDprotocol was optimized as a function of the process temperature and duration, demonstrating the pos-sibility to yield reasonable aspect-ratio ZnO NRs in a relatively short time synthesis. Further structuralstudies confirmed the excellent orientation along c-axis of the ZnO Wurtzite phase and have shown apolycrystalline nature of the NRs, with a well-defined hexagonal symmetry of the crystallites