Piezo-semiconductive quasi-1D conical NWs for high performance nanodevices
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Piezo-semiconductive quasi-1D conical NWs for high performance nanodevices Rodolfo Araneo1*, Giampiero Lovat1, Andrea Notargiacomo2, Antonio Rinaldi3,4 1
DIAEE - Sapienza University of Rome, Via Eudossiana 18, 00184, Rome Department of Electronic Engineering, University of Rome “Tor Vergata”, Via del Politecnico 1, 00133, Rome 3 University of L'Aquila, International Research Center for Mathematics & Mechanics of Complex System (MEMOCS), Via S. Pasquale, 04012, Cisterna di Latina (LT), Italy 4 ENEA ,C.R. Casaccia, Via Anguillarese 301, Santa Maria di Galeria, 00123, Rome, Italy 2
ABSTRACT Conical nanowires appear to be very versatile nanostructures for fabricating high performance piezoelectric nanodevices, for possible applications in the fields of mechanical sensing, piezotronics or piezo-photo-tronics. The results discussed in the present work are aimed at providing useful guidelines for the design of such devices. INTRODUCTION In the last two decades researchers have demonstrated that ZnO nanowires (NWs) possess unique and novel functionalities paving the way for their future use as fundamental building blocks in a variety of applications [1-4]. ZnO has several relevant properties: it has a direct wide band gap, it exhibits both semiconducting and piezoelectric properties, and it can be grown in a variety of nanostructures which are attractive for many applications in nanotechnology [5,6]. At the nanoscale, ZnO, as many other materials, exhibits an enhancement of the material properties (e.g., mechanical size effects) which allows nanostructures to be significantly deformed by extremely small mechanical forces, to have higher piezoelectric coefficients, and to exhibit outstanding mechanical properties, including higher fracture strains [7]. Very recently [8] it has been shown that, in case of vertical compression, piezoelectric conical nanostructures may have important advantages over cylindrical nanostructures in terms of available open-circuit voltage (piezopotential) and energy conversion (mechanical energy to electrical energy and viceversa). If the tip of the NW is sharp enough, a much larger strain is generated at the tip and much higher piezopotentials can be generated. In fact, the piezopotential is almost the same that would be obtained in a thin cylindrical NW having the same diameter as the small tip of the truncated conical NW. However, the tapered NW offers superior mechanical robustness, including a much stronger adhesion to the substrate, and is less subject to buckling, thus allowing the application of higher strains, which is a key for efficient mechanical-toelectrical transduction. In the present work we compare the electrical and mechanical performance of cylindrical and conical ZnO NWs when accounting for both piezoelectric and semiconductive properties. Numerical simulations based a FEM model [8,9] consistently show that conical NWs may provide substantially higher piezopotentials due to the much higher strain at their tip. In addition, we compute and analyze the ratio between the stored el
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