Nanoscopic molecular memories

Scanning probe microscopy (SPM) was utilized to form novel nanometer-scale memory units in organic molecular layers. One method is based on the conductivity changes induced in evaporated n-paraffin films by imposing electric pulses. The scanning tunneling microscope (STM) image revealed clearly the formation of high-conductive area, the spot size of which is as small as 1 nm, suggesting the creation of the extremely high-density molecular memory over 10¹⁴ bit/cm². Moreover, the analysis with the aid of a computer simulation demonstrated that the extraction of H atoms for n-paraffin molecules by applying electric pulses results in the changes in the electric states as well as geometric conformation. Next, ferroelectric organic materials were utilized to construct another type of reversible molecular memory. Here, the nanometer-scale polarization switching in ferroelectric (VDF/TrFE) films was achieved with the SPM technique by applying a positive or a negative electric voltage to the film spin-coated on Pt substrate, and actually, several local domains with different polarities could be formed even within a small crystalite of about 200 nm in length. Finally, the possibility of creating the novel molecular memories of the next generation is discussed.