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Dynamics of Shuttle Devices

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CHAPTER 1. INTRODUCTION 1.2 A new transport regime The shuttle devices are a particular kind of NEMS. The characteristic compo- nent that gives the name to these devices is an oscillating object of nanometer size that transfers electrons one-by-one between a source and a drain lead. The device represents the nano-scale analog of an electromechanical bell in which a metallic ball placed between the plates of a capacitor starts to os- cillate when a high voltage is applied to the plates. The oscillations are sustained by the external bias that pumps energy into the mechanical sys- tem: when the ball is in contact with the negatively biased plate it gets charged and the electrostatic field drives it towards the other capacitor plate where the ball releases the electrons and returns back due to the oscillator restoring forces1 and the cycle starts again. In the first proposal [1] of a shuttle device the movable carrier is a metallic grain confined into a harmonic potential by elastically deformable organic molecular links attached to the leads. The transfer of charge is governed by tunneling events, the tunneling amplitude being modulated by the position of the oscillating grain. The exponential dependence of the tunneling amplitude of the grain position leads to an alternating opening and closing of the left and right tunneling channels that resembles the charging and discharging dynamics of the macroscopic analog. Different models for shuttle devices have been proposed in the literature since this first seminal work by Gorelik et al. [1]. The mechanical degree of freedom has been treated classically (using harmonic [2, 3, 4, 5] or more realistic potentials [6]) and quantum mechanically [7, 8, 9]. Armour and MacKinnon proposed a model with the oscillating grain flanked by two static quantum dots [7, 10, 11, 12]. More generally the shuttling mechanism has been applied to Cooper pair transport [13, 14] and pumping of superconduct- ing phase [15] or magnetic polarization [16]. The essential feature of the nano-scale realization is the quantity trans- ferred per cycle (a charge up to 1010 electrons for a macroscopic bell) that is scaled down to 1 quantum unit (electron, spin, Cooper pair in the differ- ent realizations). We can already guess the basic properties of the shuttle transport: 1. Charge-position correlation: the shuttling dot loads the charge on one side and transfers it on the other side, it releases it and returns back 1Due to the large amount of electrons in this macroscopic realization the ball gets positively charged at the second plate by loosing some extra electrons and the restoring force contains also an electrostatic component. The system is perfectly symmetric under commutation of charge sign. 12

Anteprima della Tesi di Andrea Donarini

Anteprima della tesi: Dynamics of Shuttle Devices, Pagina 2

Tesi di Dottorato

Dipartimento: Department if Micro and Nanotechnologies

Autore: Andrea Donarini Contatta »

Composta da 158 pagine.


Questa tesi ha raggiunto 319 click dal 01/02/2005.

Disponibile in PDF, la consultazione è esclusivamente in formato digitale.