Mechanical tuning of tunnel gaps for the assembly of single-electron transistors

We have fabricated gold single-electron transistors (SETs), operating up to 25 K, with tunnel gaps that could be individually tuned during fabrication . A combination of atomic-force-microscopy manipulation of nanodiscs and in situ electrical measurements was used to form statically stable tunnel gap s between the discs and lithographically defined electrodes. The gap resist ances could be tuned to predetermined values over three orders of magnitude between similar to 1 M Omega and similar to 2 G Omega, corresponding to ga p widths in the range of 3-10 Angstrom. We report on SETs with symmetricall y and asymmetrically coupled islands, i.e., with equal or different tunnel resistances. In the asymmetric SET a distinct Coulomb staircase was observe d. (C) 1999 American Institute of Physics. [S0003-6951(99)01036-0].