Crystalline Organic Molecular Thin Film with Electrical Switching Property:  Scanning Probe Microscopy and Optical Spectroscopy Study

Abstract

We report on the growth and characterization of crystalline 1,1-dicyano-2,2-(4-dimethylaminophenyl)ethylene (DDME) thin film with electrical switching property. X-ray diffraction analysis indicates that bulk single-crystal DDME belongs to monoclinic, space group P21, and Z = 2 structure. Optical spectroscopy shows that the film chemical structure is consistent with that of the powder material, suggesting that DDME material is very stable during the vacuum thermal deposition process. Scanning probe microscopy and transmission electron microscopy observations reveal that the as-deposited film has extended crystal structure and smooth surface morphology in micrometer scale. Parallel molecular stacking structure is repeatedly observed in the film surfaces with the axis of the molecular stack parallel to the substrate. The ac crystal plane is found to be one of the most stable surfaces of the DDME film in ambient conditions. Nanometer scale data storage is realized on the film by applying pulse voltage between the STM tip and the substrate. The switching mechanism is briefly discussed.

A non-planar organic molecule with non-volatile electrical bistability for nano-scale data storage

“…The stretch vibration of -CMN exhibits a red-shift (from 2233.4 cm 21 to 2231.0 cm 21 ), which indicates that the cyano group was changed from a neutral to a negatively charged state in the molecule. 12,21 Compared with the literature, the shift of the cyano stretch vibration in FTIR is minor, which suggests a minor change in the electron density of the cyano group. This phenomenon is attributed to the charge delocalization from the cyano group to its connected conjugation moiety.…”

“…The stable and ordered crystalline thin film paves the way for the application of the CPMAB molecule in electrical devices. 12,13,20 A CPMAB thin film with a thickness of ca. 50 nm was deposited on an indium tin oxide (ITO)-coated glass with the sandwich structure ITO/CPMAB(50 nm)/ Al(75 nm) and the macroscopic I-V characteristics were measured with a standard two-terminal system (see the Experimental part).…”

“…It is expected that the combination of organic molecules (one or several molecules as the functional unit) and SPM (manipulation on the nano/atom-scale) will throw light on driving the data storage to ultrahigh density stage. Our group [10][11][12][13] has employed a series of organic molecules for information storage with the size of recording marks below 5 nm by STM.…”

“…Taking the quality of the crystalline film into account, co-planar molecules were preferred for the application. 11,12 However, the intramolecular and intermolecular charge transfer may interfere with each other, which is related to the quality of the recording media in the aspect of both 'write' and 'read-many-times'. Furthermore, Bandhopadhyay and Pal verified that D-p-A molecules usually have lower on/off current ratio because of the electron conjugation in the molecule, which restrains the usage in high-frequency binary computation.…”

Nanoscale Data Storage

“…The molecular layer may be a SAM, LB layer, or even a thin film. Obviously, it will be difficult to use organic thin films as the active medium in nanostorage due to the large roughness and poor uniformity [66].…”