Fabrication and Characterization of Floating Memory Devices Based on Thiolate-Protected Gold Nanoclusters

The floating memory properties of thiolate-protected gold (Au:SR) nanoclusters, Au₂₅(SR)₁₈, Au₃₈(SR)₂₄, Au₁₄₄(SR)₆₀, and Au₃₃₃(SR)₇₉ (R = C₁₂H₂₅), and Au colloids were investigated using four-probe measurements in vacuum. Uniform and monolayer films of Au:SR nanoclusters or Au colloids were formed as floating memory layers on p-type Si substrates by Langmuir-Blodgett method. The fluoropolymer (CYTOP, ∼15 nm thick) was spin-coated on top to form a hydrophobic insulating layer. Using Au dot (∼40 nm thick) as the anode electrode, the capacitance-voltage (C-V) measurements were performed using the Au and Cu plate electrodes as contact points for the two probes. Clockwise hysteresis curves originating from the Au:SR nanoclusters or Au colloids were observed, and the hysteresis width was dependent on the size of the Au:SR nanoclusters and the sample temperature. In particular, for the Au₃₈(SR)₂₄ nanocluster, multiple phases were observed in the C-V curve, implying their application in multivalued memory devices.