S. J. Pang

Nanometer‐scale recording on an organic‐complex thin film with a scanning tunneling microscope

Nanometer‐scale recording on an organic‐complex thin film with a scanning tunneling microscope (STM) under ambient conditions is demonstrated. The recording marks are made by applying external voltage pulses between the tip and the highly ordered pyrolytic graphite substrate. A 30×30 nm2 STM image with recorded marks is given. The average recorded mark is 1.3 nm in diameter, which corresponds to a data storage density of about 1013 bits/cm2. The current–voltage characteristics measured by the STM show an insulator behavior for the unrecorded regions, and a conductor behavior for the recorded regions, which indicates that the data are recorded by local change of the electrical property of the films.

Data storage with 0.7 nm recording marks on a crystalline organic thin film by a scanning tunneling microscope

Ultrahigh density data storage on a novel organic thin film by scanning tunneling microscope (STM) under ambient conditions is demonstrated. The material, N-(3-nitrobenzylidene)p-phenylenediamine (NBPDA), is used for preparing thin film by vacuum evaporation method. Crystalline NBPDA films with electrical bistability are obtained by this method. Recording experiment on the films is made by applying voltage pulses between the STM tip and substrate. The recorded marks are 0.7 nm in size, corresponding to a storage density of 1014u2009bit/cm2. Current–voltage characteristic measurement shows that the resistance of the unrecorded region of the NBPDA films is much higher than that of the recorded region. The mechanism of recording is discussed.

Fractal structure in the silver oxide thin film

Abstract The first two steps of the preparation of Ag–O–Cs photocathodes are the deposition of silver films and their oxidation with the glow discharge method. The fractal structure and texture structure in the silver oxide thin film have been characterized by transmission electron microscopy (TEM). The Hausdorf dimension D of the fractal structure is calculated to be 1.80±0.01. The formation mechanism of the fractal structure is also discussed.

Ultrahigh density data storage from local polymerization by a scanning tunneling microscope

Ultrahigh density data storage from local polymerization on an organic thin film is demonstrated by using a scanning tunneling microscope (STM) operating in air. An organic monomer material, which may become electrical conductive by polymerization, is selected as data storage material. Films prepared by the monomer material are used for data recording. By applying a high electric field with the STM tip to realize local polymerization, highly stable recorded patterns with molecule-sized recorded marks have been performed. One recorded mark corresponds to a polymeric molecule in the film. The marks are 0.8 nm in size. The nearest distance between two recorded marks is 1.2 nm. Having been read 2000 times the recorded patterns show no discernible change.

Formation of ordered Ge quantum dots on the Si(111)–(7×7) surface

We present a pathway for the formation of ordered Ge quantum dots on Si(111)–(7×7) substrate. Self-assembled growth of Ge quantum dots on the Si(111)–(7×7) surface has been investigated using scanning tunneling microscopy. The Ge is grown on the substrate by solid phase epitaxy at room temperature. It has been found that the deposited submonolayer Ge can aggregate and form ordered Ge quantum dots on the surface through controlling the annealing temperature. The formation of ordered Ge quantum dots is due to the preferential adsorption sites of Ge on Si(111)–(7×7). The formed Ge quantum dots may have a great potential in the application of nanodevices.

Ionized‐cluster‐beam deposition and electrical bistability of C60–tetracyanoquinodimethane thin films

We report an ionized‐cluster‐beam (ICB) deposition and the electrical bistability of C60–tetracyanoquinodimethane (TCNQ) thin films. The films are fabricated by using an ionized‐cluster‐beam deposition method in a high vacuum system. The as‐deposited films were characterized by transmission electron microscopy and optical absorption spectroscopy, which verified the formation of the charge‐transfer complex system in C60–TCNQ thin films and the microstructure of these thin films. The structure and the electrical property of the ICB deposited Ag‐TCNQ thin films are also presented. The possible conductive mechanism of these ICB deposited thin films is discussed in the letter.

2D fractal pattern in fullerene doped polymer

Abstract Fractals in C60 doped tetracyanoquinodimethane thin films are reported. The fractal patterns and their microscopic features have been characterized by transmission electron microscopy (TEM). The results indicate that the observed fractals can be compared to the cluster-diffusion-limited-aggregation model. The fractal dimension has been determined to be 1.69±0.04. In addition, the formation mechanism of the fractals is discussed.

Scanning tunneling microscopy investigation of carbon nitride thin films grown by microwave plasma chemical vapor deposition

Abstract The surface atomic structure of carbon nitride thin films deposited on both Si (100) and highly ordered pyrolytic graphite (HOPG) substrates by microwave plasma chemical vapor deposition technique is studied by scanning tunneling microscopy (STM). STM images of the surface of the films with atomic resolution are obtained. The microstructure of the surface of the film on Si (100) substrate is very complex and composed of various components as confirmed by other techniques. An atomic structure is observed in the complex surface of the film on Si substrate. The unit cell constant of the structure is 4.7xa0A along a and b directions with 120° angle between them. This structure is clearly observed in the film deposited on HOPG substrate at a larger scale. The structure is discussed. It is found that the observed structure is well in agreement with the G-C 3 N 4 structure.

Self-assembled growth of ordered Ge nanoclusters on the Si(1 1 1)-(7×7) surface

The self-assembled growth of submonolayer Ge on the Si(111)-(7 x 7) surface grown by solid phase epitaxy has been studied using scanning tunneling microscopy. Ordered Ge nanoclusters on the surface are formed by the deposition of the submonolayer of Ge at room temperature and subsequent annealing. It is proposed that adsorbate Ge atoms are trapped in the attractive potential wells on the faulted half of the (7 x 7) unit cell

A new type of organometallic system for high density data storage by scanning tunneling microscopy

Abstract We report a new type of organometallic system, Ag-toluylene 2,4-dicarbamidonitrite (TDCN) composite thin film, for ultrahigh density data storage devices by scanning tunneling microscopy (STM). The Ag-TDCN thin film was prepared on a highly oriented pyrolytic graphite (HOPG) substrate using an ionized-cluster-beam (ICB) deposition method. Marks can be created on the thin film by employing a voltage pulse between the STM tip and surface of the HOPG substrate. The size of the created marks is about 50 nm and the corresponding data storage density is about 10 11 bits/cm 2 . The mechanism for the data storage can be attributed to the conductance transition in the complex system. This result shows a great potential for this new kind of organometallic composite system to find application in ultrahigh density data storage.