Adsorption, manipulation and self-assembling of TBrPP-Co molecules on a Ag/Si(111) surface by scanning tunnelling microscopy

Individual adsorption and two-dimensional assembling of 5,10,15,20-tetrakis-(4-bromophenyl)-porphyrin-Co (TBrPP-Co) molecules on a Si(111)-[Formula: see text] Ag reconstructed surface have been studied using low-temperature scanning tunnelling microscopy (STM). All the isolated molecules are observed in a planar shape with slight distortion. The isolated molecules can be controllably rotated with an STM tip to the orientation along the trigonal lattice ([Formula: see text] direction) of the substrate. With an increased coverage (0.07?ML) and appropriate annealing, the molecules assemble to form three types of ordered phase. The long-range ordered structures, however, disappear at higher coverage (0.75?ML).     

The role of an amorphous carbon layer on a multi-wall carbon nanotube attached atomic force microscope tip in making good electrical contact to a gold electrode

Multi-wall carbon nanotube (MWNT) attached atomic force microscope (AFM) tips (MWNT tips) have good potential for use in AFM lithography. Good conducting MWNT tips are needed in such applications. However, characterizing the conductance of MWNT tips is nontrivial: making a good electrical contact between the MWNT and electrode is difficult. We observed that MWNT tips produced by hydrocarbon-deposition attachment usually do not make good electrical contacts to gold electrodes because of the thin and rough amorphous carbon layer on the MWNT that was unintentionally deposited during the attachment. We found that good contacts can be made if a more amorphous carbon layer is deposited to form a thick and smooth amorphous carbon layer on MWNTs. Good contact was made either by transformation of the amorphous carbon layer into a conducting or peel-off layer, exposing the bare MWNT surface. MWNT tips with an exposed MWNT surface showed the well-known high-current-flowing capacity and the stepped-cutting behavior of bare MWNTs. The peeling-off behavior of a thick amorphous carbon layer may be utilized in producing bare-surfaced MWNT tips that have good conductance and therefore are useful for applications.     

Thermal stability of multilayer graphene films synthesized by chemical vapor deposition and stained by metallic impurities

Thermal stability is an important property of graphene that requires thorough investigation. This study reports the thermal stability of graphene films synthesized by chemical vapor deposition (CVD) on catalytic nickel substrates in a reducing atmosphere. Electron microscopies, atomic force microscopy, and Raman spectroscopy, as well as electronic measurements, were used to determine that CVD-grown graphene films are stable up to 700?°C. At 800?°C, however, graphene films were etched by catalytic metal nanoparticles, and at 1000?°C many tortuous tubular structures were formed in the film and carbon nanotubes were formed at the film edges and at catalytic metal-contaminated sites. Furthermore, we applied our pristine and thermally treated graphene films as active channels in field-effect transistors and characterized their electrical properties. Our research shows that remnant catalytic metal impurities play a critical role in damaging graphene films at high temperatures in a reducing atmosphere: this damage should be considered in the quality control of large-area graphene films for high temperature applications.     

Forming mechanism of the bipolar resistance switching in double-layer memristive nanodevices

To initiate resistance switching phenomena, it is usually necessary to apply a strong electric field to a sample. This forming process poses very serious obstacles in real nanodevice applications. In unipolar resistance switching (URS), it is well known that the forming originates from soft dielectric breakdown. However, the forming in bipolar resistance switching (BRS) is poorly understood. In this study, we investigated the forming processes in Pt/Ta?O?/TaOx/Pt and Pt/TaOx/Pt nanodevices, which showed BRS and URS, respectively. By comparing the double- and single-layer systems, we were able to observe differences in the BRS and URS forming processes. Using computer simulations based on an 'interface-modified random circuit breaker network model', we could explain most of our experimental observations. This success suggests that the BRS forming in our Pt/Ta?O?/TaOx/Pt double-layer system can occur via two processes, i.e., polarity-dependent resistance switching in the Ta?O? layer and soft dielectric breakdown in the TaOx layer. This forming mechanism can be used to improve the performance of BRS devices. For example, we could improve the endurance properties of Pt/Ta?O?/TaOx/Pt cells by using a small forming voltage.     

The application of graphene as electrodes in electrical and optical devices

Graphene is a promising next-generation conducting material with the potential to replace traditional electrode materials such as indium tin oxide in electrical and optical devices. It combines several advantageous characteristics including low sheet resistance, high optical transparency and excellent mechanical properties. Recent research has coincided with increased interest in the application of graphene as an electrode material in transistors, light-emitting diodes, solar cells and flexible devices. However, for more practical applications, the performance of devices should be further improved by the engineering of graphene films, such as through their synthesis, transfer and doping. This article reviews several applications of graphene films as electrodes in electrical and optical devices and discusses the essential requirements for applications of graphene films as electrodes.     

Competitive Adsorption of 3He and 4He to Carbon Nanotube Bundles

No Heading We have studied the competitive adsorption of the two helium isotopes to single-walled carbon nanotube bundles. It is observed that the presence of ⁴He suppresses subsequent ³He adsorption while the presence of ³He has little influence on the subsequent adsorption of ⁴He. These observations are generally consistent with expectations based on the difference in the masses of the isotopes.PACS numbers: 68.35.Md, 68.43.Fg, 81.07.De     

Analysis of Electromagnetic Characteristics of a Grounded Slab and a Parallel‐Plate Structure Using the SDDI Technique

In this paper, the electromagnetic characteristics of a grounded slab and a parallel‐plate structure are analyzed by the Spline‐type Divided‐Difference Interpolation (SDDI) technique. The technique efficiently evaluates the MoM impedance matrix elements of the multifold spectral or spatial domain integrals or summation in integrodifferential equations. The numerical results of the proposed method agree well with those of the corresponding literatures.