Functional dielectric/semiconductor and metal/semiconductor interfaces in organic field-effect transistors

The work presented in this thesis focuses on the investigation of two interfaces which play a crucial role in the physics of organic electronic devices: the dielectric/organic semiconductor and the organic semiconductor/metal ones. Regarding the dielectric/OS interface, we have deeply investigated the relationship between the SiO2 cleaning protocol or treatment and the electrical response of OFETs based on two PPV semiconducting polymers (MEH-PPV and OC1C10-PPV) and on a quarterthiopene derivative small molecule (DHCO-4T). Regarding the OS/metal interface, we investigated the electrical performances of PPV and DHCO-4T based OFETs with different metal contacts

Localized surface plasmons: a powerful tool for sensing

Plasmonic nanoparticles (NPs) represent an outstanding class of nanomaterials that have the capability to localize light at the nanoscale by exploiting a phenomenon called "localized plasmon resonance." This book reviews recent efforts devoted to the utilization of NPs in many research fields, such as photonics, optics, and plasmonics. In this framework, a particular interest is devoted to "active plasmonics," a quite broad concept that indicates those applications in which NPs play an "active" role, such as the realization of gain-assisted means, utilization of NPs embedded in liquid crystalline and flexible materials, and exploitation of renewable solar energy. The book puts together contributions from outstanding international research groups in the field of plasmonic nanomaterials

Online distributed voltage stress minimization by optimal feedback reactive power control

A standard operational requirement in power systems is that the voltage magnitudes lie within prespecified bounds. Conventional engineering wisdom suggests that having a tightly regulated voltage profile should also guarantee that the system operates far from static bifurcation instabilities, such as voltage collapse. In general, however, these two objectives are distinct and must be separately enforced. We formulate an optimization problem that maximizes the distance to voltage collapse through injections of reactive power, subject to power flow and operational voltage constraints. By exploiting a linear approximation of the power flow equations, we arrive at a convex reformulation, which can be efficiently solved for the optimal injections. We then propose a distributed feedback controller, based on a dual-ascent algorithm, to solve for the prescribed optimization problem in real time. This is possible, thanks to a further manipulation of the problem into a form that is amenable for distributed implementation. We also address the planning problem of allocating control resources by recasting our problem in a sparsity-promoting framework. This allows us to choose a desired tradeoff between optimality of injections and the number of required actuators. We illustrate the performance of our results with the IEEE 30-bus network

Engineering of semiconductor nanocrystals for light emitting applications

Semiconductor nanocrystals are rapidly spreading into the display and lighting markets. Compared with liquid crystal and organic LED displays, nanocrystalline quantum dots (QDs) provide highly saturated colors, wide color gamut, resolution, rapid response time, optical efficiency, durability and low cost. This remarkable progress has been made possible by the rapid advances in the synthesis of colloidal QDs and by the progress in understanding the intriguing new physics exhibited by these nanoparticles. In this review, we provide support to the idea that suitably engineered core/graded-shell QDs exhibit exceptionally favorable optical properties, photoluminescence and optical gain, while keeping the synthesis facile and producing QDs well suited for light emitting applications. Solid-state laser emitters can greatly profit from QDs as efficient gain materials. Progress towards fabricating low threshold, solution processed DFB lasers that are optically pumped using one- and two-photon absorption is reviewed. In the field of display technologies, the exploitation of the exceptional photoluminescence properties of QDs for LCD backlighting has already advanced to commercial levels. The next big challenge is to develop the electroluminescence properties of QD to a similar state. We present an overview of QLED devices and of the great perspectives for next generation display and lighting technologies

Role of Core-Shell Interfaces on Exciton Recombination in CdSe-CdxZn1-xS Quantum Dots

The shell thickness and composition of CdSe-Cd(x)Zn(1-x)S core-shell quantum dots (QDs) are defining parameters for the efficiency of such materials as light emitters. In this work we present a detailed study into the optical absorption and fluorescence properties of CdSe-CdS, CdSe-Cd0.5Zn0.5S, and CdSe-ZnS QDs as a function of shell thickness. Moreover, the single-exciton recombination dynamics of these systems are analyzed by means of a time-correlated single-photon counting technique and directly related to the specific core-shell interfaces of the various QDs studied using a phenomenological kinetic model. The findings from this model highlight the strong role of the core-shell interface on both steady state photoluminescence and exciton recombination dynamics in these systems