Nanometer-scale Recording Research Articles

Structural and Conductance Transitions of Rotaxane Based Nanostructures and Application in Nanorecording

Rotaxane-based molecules have been intensively studied for use as functional molecular electronic devices and as a medium for nanorecording. By means of both I-V, Raman and conductive contact atomic force microscopic measurements of rotaxane H1 and H2 molecular thin films and scanning tunneling microscopy studies of individual H2 molecules, we demonstrate conclusively that the conductance transition originates from single molecules and correlates with changes in molecular conformation. This provides the best evidence to date that the conductance transition arises from motion of the cyclobis(paraquat-p-phenylene) ring along the molecular backbone. Taking advantage of the switching property, we have achieved reproducible nanometer-scale recording (dots) on rotaxane Langmuir-Blodgett (LB) films via voltage application using a scanning tunneling microscope (STM) probe. Stable, reversible conductance transitions and memory effects were observed in solid state rotaxane-based H1 LB thin films; while the thin films of rotaxane H2 molecule can be successfully written, erased, re-written, and re-erased. The stable and controllable conductance switching makes the rotaxane an attractive candidate for nanorecording. Furthermore, these results suggest that controlling the rotaxane conformation, its electronic structure, and decoration of the molecule, are strongly needed to strive the practical applications to the molecular electronic devices.

Nanometer-Scale Recording on a Superhard and Conductive Carbon Film Using an Atomic Force Microscope

Nanometer-scale recording on a carbon film deposited by electron cyclotron resonance plasma sputtering (ECR-C) is demonstrated by locally changing the electrical resistance using an atomic force microscope. The recording mechanism is thermal annealing of the film surface due to Joule heat generated by the probe current. Such a recording without apparent topographic changes is considered to be possible due to the higher electrical conductivity of the ECR-C than those of conventional amorphous carbons. Namely, it enables us to modify the surface at a lower application voltage than the voltage above which topographic changes due to field-induced oxidation occur. High-density probe storage is demonstrated by applying pulse voltage rows to the ECR-C. The minimum size of the data bit is about 70 nm.

A new organic complex thin film for ultra-high-density data storage with a scanning tunneling microscope

A new organic complex, tetrathiafulvalene/m-nitrobenzylidene propanedinitrile (TTF/m-NBP), was prepared to use as an ultra-high-density data-storage medium. A nanometer-scale recording technique was demonstrated with a scanning tunneling microscope (STM) under ambient conditions. The organic complex thin film was fabricated by using a vacuum thermal deposition method. The results of Fourier transform infrared spectra showed that the structure of the organic complex thin film was the same as that of a complex crystal. Data were recorded by applying voltage pulses between the tip and the substrate. Current–voltage (I–V) curves measured by the STM showed that the conductance of the recorded region is much higher than that of the unrecorded region, which indicated that the data were recorded by a local change of the electrical property of the film. The smallest recorded mark was 1.1 nm in diameter and the width of the pulse voltage has an influence upon the diameter of the recording marks.

Stable bit formation in polyimide Langmuir–Blodgett film using an atomic force microscope

Nanometer scale recording bits were stably fabricated in polyimide (PI) Langmuir–Blodgett (LB) films on atomically flat Au (111) surfaces using an atomic force microscope (AFM). The bits are written by voltage application through the AFM probe only until the conductance increases. This method eliminates the influence of the variation in the transition time and therefore the degradation of the tip of the probe. 1 Mbit stable writing can be realized. The overall error rate is less than 2×10−3. The results show that an AFM based memory system with PI LB films is a hopeful candidate to realize a scanning probe microscope based memory system.

Parallel molecular stacks of organic thin film with electrical bistability

A thin film of 1,1-dicyano-2,2-(4-dimethylaminophenyl) ethylene (DDME) has been grown by a modified vacuum deposition. The films were characterized by Fourier transform infrared spectroscopy, transmission electron microscopy, and scanning tunneling microscopy (STM). Highly ordered parallel molecular stacks were repeatedly observed with STM under ambient conditions. The dc current–voltage (I–V) characteristics of device Au/DDME/Au were measured, and the film was found to possess good electrical bistability and electrochromic properties. Nanometer-scale recording was realized on the film by applying pulse voltage between the STM tip and substrate. The possible switching mechanism is discussed.

Ultrahigh density data storage in an organic film with a scanning tunneling microscope

A nanometer-scale recording technique was demonstrated on N-(3-nitrobenzylidene)–p-phenylenediamine (NBPDA) organic thin films with a scanning tunneling microscope (STM). NBPDA thin films were fabricated by vacuum thermal deposition. The results of ultraviolet-visible absorption and infrared transmission spectra showed that the structure of the NBPDA film was the same as that of NBPDA crystal. An atomic force microscope was utilized to characterize the surface morphology of the NBPDA film. Data were recorded by applying voltage pulses between the tip and the substrate. The current–voltage characteristics measured by the STM indicated that the local electrical property changed from an insulating property into a metallic property after the data were written. Data marks, 1.4 nm in diameter, corresponded to a data storage density of 1012 bits/cm2. A preliminary calculation was presented to explain the recording mechanism.

Nanometer-Scale Erasable Recording Using Atomic Force Microscope on Phase Change Media

We have demonstrated a nanometer-scale recording technique using an atomic force microscope (AFM) with an amorphous GeSb2Te4 film as a phase change medium. Data are recorded by changing the local electric properties of the film using a conductive AFM probe. The conductance of the film can be increased by more than one hundred times by applying a pulse voltage between the probe and the film. The recorded data are read by detecting the change in the conductance using the probe. The smallest possible recording region is 10 nm in diameter, which corresponds to a data storage density of 1 Tbit/cm2. The data can be erased by applying a negative DC voltage to the probe while scanning the probe over the film. The mechanisms of the reversible conductance change in the film are also discussed.

Nanometer-scale recording, erasing, and reproducing using scanning tunneling microscopy

We demonstrate using a scanning tunneling microscope reproducible and reversible recording and erasing of marks about 10 nm in size. Studies on both data storage devices and nanometer fabrication using a scanning tunneling microscope have been carried out, involving a variety of techniques and materials. However, most studies neglect erasing, despite the fact that erasing is a major requisite, as well as recording and reading. Using a thin layer of a vanadate glass deposited on vanadium bronze, β-NaxV2O5, has made it possible to record, erase, and read 10 nm level marks at ambient temperature and pressure. The main mechanism for reversible recording is sodium ion migration between the vanadium bronze crystal phase and the vanadate amorphous phase along the electric field. The organic medium of a hemiquinone molecule was proposed for higher recording speed.

Nanometer-scale recording on chalcogenide films with an atomic force microscope

A nanometer-scale recording technique has been demonstrated on an amorphous GeSb2Te4 film with an atomic force microscope (AFM). Data are recorded by locally changing the electrical property of the film with a conductive AFM probe. The conductance of the film is able to be increased more than one hundred times by applying a pulse voltage between the probe and the film. The recorded data are read by detecting the change of the conductance with the probe. The simultaneous measurement of the topographic and conductance images with the AFM shows that the surface topography of the recorded regions is not changed during the recording process. The smallest recorded region is 10 nm in diameter, which corresponds to a data storage density of 1 Tbit/cm2.