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Dynamics of Shuttle Devices

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1.3. EXPERIMENTAL IMPLEMENTATIONS to the starting point; 2. Matching between electronic and mechanical characteristic times (non- adiabaticity); 3. Quantized current determined by the mechanical frequency; 4. Low current fluctuations: the stochasticity of the tunneling event is suppressed due to an interplay between mechanical and electrical prop- erties. The tunneling event is only probable at some particular short time periods fixed by the mechanical dynamics (i.e. when the oscillat- ing dot is close to a specific lead). 1.3 Experimental implementations An experimental realization of the shuttle device has been produced by Erbe et al. [17]. The structure consists of a cantilever with a quantum island at the top placed between source and drain leads. Two lateral gates can set the cantilever into motion via a capacitive coupling. An ac voltage applied at these gates makes the cantilever vibrating and brings the tip alternatively closer to the source or drain lead and thus allows the shuttling of electrons. The device (shown in Fig. 1.1) is built out of silicon-on-insulator (SOI) materials (using Au for the metallic parts) using etch mask techniques and optical and electron beam lithography. The cantilever is 1µm long and the corresponding resonant frequency is of the order of 100MHz. The source elec- trode and the cantilever are at an average distance of approximately 0.1µm. Shuttling experiments have been performed by Erbe et al. at different tem- peratures. For experiments at 4.2K and 12K they measured a pronounced peak in the current through the cantilever for a driving frequency of approx- imately 120MHz corresponding to the natural frequency of the first mode of the oscillator. The peak in the current corresponds to a rate of shuttle success of about one electron per 9 mechanical cycles. The Erbe experiment is very close to the original proposal by Gorelik. The only difference is in the external driving of the mechanical oscillations. In the original proposal the bias was time independent and the driving induced by the electrostatic force on the charged oscillating island. The initially stochastic tunneling events would eventually cause the shuttling instability and drive the system into a self-sustained mechanical oscillation combined with periodic charging and discharging events. Another experiment often mentioned in the context of quantum shuttles is the C60-experiment by Park et al. [18] In this experiment a C60 molecule is 13

Anteprima della Tesi di Andrea Donarini

Anteprima della tesi: Dynamics of Shuttle Devices, Pagina 3

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.