Coulomb Blockade and Single Electron Effects in Arrays of Selforganized Ultrasmall Metal Clusters Observed at Room Temperature

Abstract

Operation of Single Electron Devices at room temperature is strongly correlated with the fabrication of ultrasmall conductive islands separated by well defined tunneling barriers. The requirements e 2 /2C >> k B T and R T >> h/e 2 ≃ 25.8kΩ force the capacitances to be in the sub aF range and hence the particle size to be only a few nm in diameter. In a first part we report on STM-studies of selforganized Pt clusters (1-4 nm in diameter) on top of a thin isolating Al 2 O 3 layer being supported by an underlying atomically flat Au-substrate. The complete sample structure has been. fabricated and measured in UHV without breaking the vacuum With the STM-tip as a second contact electrode, this system establishes a double-tunnel- junction, which exhibits Coulomb blockade effects at room temperature. The recorded I(U)-curves on individual clusters showed a variety of features like a Coulomb gap, Coulomb staircase, barrier suppression and asymmetric tunneling barrier effects, with the Coulomb gap (0.3-1.5 eV) being the most often observed feature. In a second part we present the results of measurements done on an 2-dimensional array of selforganized Pt dots being placed in a 30-120 nm wide gap between two microstructured electrodes on top of an oxidized Si-wafer (100 nm SiO 2 ). We demonstrated a clear Coulomb gap of 0.1 - I eV at room temperature. We were able to change the current through the array by applying a gate voltage to the silicon substrate and therefore demonstrated a transistor like device based on the single electron tunneling in a 2-dimensional array of selforganized metal dots. In some cases we could observe a gate- voltage induced oscillating behaviour of the current.