Loïk Gence

Structural and electrical characterization of hybrid metal-polypyrrole nanowires.

We present here the synthesis and structural characterization of hybrid Au-polypyrrole-Au and Pt-polypyrrole-Au nanowires together with a study of their electrical properties from room temperature down to very low temperature. A careful characterization of the metal-polymer interfaces by transmission electron microscopy revealed that the structure and mechanical strength of bottom and upper interfaces are very different. Variable temperature electrical transport measurements were performed on both multiple nanowires-contained within the polycarbonate template-and single nanowires. Our data show that the three-dimensional Mott variable-range-hopping model provides a complete framework for the understanding of transport in polypyrrole nanowires, including nonlinear current-voltage characteristics and magnetotransport at low temperatures.

Sign reversal and tunable rectification in a ballistic nanojunction

Low-temperature measurements show that an asymmetric mesoscopic junction patterned in a two-dimensional electron gas can exhibit tunable rectification, including sign reversal. Strikingly, we observe that the amplitude and sign of the effect are governed by the conductances of the channels and that rectification is reversed without reversing the asymmetry of the device. Based on the temperature dependence of the rectified voltage, we show that the effect is ballistic and exhibits unexpected features with respect to predictions of available models.

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.

Single spin-torque vortex oscillator using combined bottom-up approach and e-beam lithography

A combined bottom-up assembly of electrodeposited nanowires and electron beam lithography technique has been developed to investigate the spin transfer torque and microwave emission on specially designed nanowires containing a single Co/Cu/Co pseudo spin valve. Microwave signals have been obtained even at zero magnetic field. Interestingly, high frequency vs. magnetic field tunability was demonstrated, in the range 0.4–2 MHz/Oe, depending on the orientation of the applied magnetic field relative to the magnetic layers of the pseudo spin valve. The frequency values and the emitted signal frequency as a function of the external magnetic field are in good quantitative agreement with the analytical vortex model as well as with micromagnetic simulations.

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.

Analysis of Bandwidth and Nonlinear Effects in InAlAs/InGaAs/InP Based Ballistic Nanodevices for Applications up to THz Range

Analysis of nonlinear effects in InAlAs/InGaAs-based channels and three-terminal ballistic junctions (TBJs) is performed for applications up to THz range. Results show that InGaAs-based channels designed for ballistic operation exhibit high intrinsic cut-off frequency (fT ~ 10 THz). Nonlinear effects in TBJs, which result from device geometry and space charge distribution, show good qualitative agreement with published results.