Carbon nanotube bridges fabricated by laser comb.

Suspended bridge-shaped carbon nanotube (CNT) has great potential in nano-electromechanical systems, highly-sensitive sensors, various nanodevices and so on. However, complex processing largely restricts its practical applications. This work presents a novel laser comb (Laco) effect, stimulating a simple and effective fabrication strategy to achieve aligned suspended CNTs, which are bridge-shaped, direction-controlled, easily-patterned and all-carbon based. The Laco phenomenon is ascribed to different heat accumulations in two vertical directions under pulse laser-raster scanning (PLrS).

Nanoenvelopes: Wrapping a Single-Walled Carbon Nanotube with Graphene using an Atomic Force Microscope.

Engineering the morphology and structure of low-dimensional carbon nanomaterials is important to study their mechanical and electrical properties and even superconductivity. Herein, first the techniques that are used to engineer carbon nanotubes, including manipulation, morphology modification, and fabrication of complex nanostructures, are reviewed. This is followed by a summary of the methods applied to fabricate graphene nanostructures, such as heterostructures and nanoenvelopes of graphene. Lastly, an insight into the applications of low-dimensional-carbon-based electronics is given, such as carbon nanotube (CNT) transistors, graphene-based nanoenvelopes, and graphene-contacted CNT field-effect transistors (FETs), which are promising components in future electronics.

Molecular Magnets Based on Graphenes and Carbon Nanotubes.

Molecular magnets are demonstrated to provide a promising way to realize nanometer-scale structures with a stable spin orientation. Herein, first a description of conventional molecular magnets coupled with sp2 carbon materials, such as carbon nanotubes and graphenes, is given. Then, progress on ferromagnetism in sp2 carbon nanomaterials due to the existence of defects or topological structures as the spin units, which makes the sp2 materials themselves act as a novel class of molecular magnets, is reviewed, and a scheme of controllable synthesis of the molecular magnets at the sheared ends of carbon nanotubes is proposed. To conclude, remarks on some challenges and perspectives in the synthesis of carbon nanotube arrays with orderly sheared ends as integrated molecular magnets are provided.

Observation of Van Hove Singularities and Temperature Dependence of Electrical Characteristics in Suspended Carbon Nanotube Schottky Barrier Transistors.

A Van Hove singularity (VHS) is a singularity in the phonon or electronic density of states of a crystalline solid. When the Fermi energy is close to the VHS, instabilities will occur, which can give rise to new phases of matter with desirable properties. However, the position of the VHS in the band structure cannot be changed in most materials. In this work, we demonstrate that the carrier densities required to approach the VHS are reached by gating in a suspended carbon nanotube Schottky barrier transistor. Critical saddle points were observed in regions of both positive and negative gate voltage, and the conductance flattened out when the gate voltage exceeded the critical value. These novel physical phenomena were evident when the temperature is below 100 K. Further, the temperature dependence of the electrical characteristics was also investigated in this type of Schottky barrier transistor.

Nanogap-Engineerable Electromechanical System for Ultralow Power Memory.

Nanogap engineering of low-dimensional nanomaterials has received considerable interest in a variety of fields, ranging from molecular electronics to memories. Creating nanogaps at a certain position is of vital importance for the repeatable fabrication of the devices. Here, a rational design of nonvolatile memories based on sub-5 nm nanogaped single-walled carbon nanotubes (SWNTs) via the electromechanical motion is reported. The nanogaps are readily realized by electroburning in a partially suspended SWNT device with nanoscale region. The SWNT memory devices are applicable for both metallic and semiconducting SWNTs, resolving the challenge of separation of semiconducting SWNTs from metallic ones. Meanwhile, the memory devices exhibit excellent performance: ultralow writing energy (4.1 × 10-19 J bit-1), ON/OFF ratio of 105, stable switching ON operations, and over 30 h retention time in ambient conditions.

Ultraclean individual suspended single-walled carbon nanotube field effect transistor.

In this work, we report an effective technique of fabricating ultraclean individual suspended single-walled carbon nanotube (SWNT) transistors. The surface tension of molten silver is utilized to suspend an individual SWNT between a pair of Pd electrodes during annealing treatment. This approach avoids the usage and the residues of organic resist attached to SWNTs, resulting ultraclean SWNT devices. And the resistance per micrometer of suspended SWNTs is found to be smaller than that of non-suspended SWNTs, indicating the effect of the substrate on the electrical properties of SWNTs. The ON-state resistance (∼50 kΩ), mobility of 8600 cm2 V-1 s-1 and large on/off ratio (∼105) of semiconducting suspended SWNT devices indicate its advantages and potential applications.

Amplitude response of conical multiwalled carbon nanotube probes for atomic force microscopy.

Carbon nanotubes are considered as great candidates for atomic force microscopy (AFM) probes because of their high aspect ratio and outstanding mechanical properties. In this work, we report that a conical AFM probe can be fabricated with arc discharge prepared multiwalled carbon nanotubes (MWCNTs) with an individual MWCNT at the apex by dielectrophoresis. The amplitude-displacement curve of the conical MWCNT probe demonstrates that this structure can remain stable until the force exerted on it increases to 14.0 ± 1.5 nN (nanonewton). Meanwhile, the conical MWCNT probes are able to resolve complex structure with high aspect ratio compared to commercial AFM probes, suggesting great potential for various AFM applications.

Large positive magnetoresistance in semiconducting single-walled carbon nanotubes at room temperature.

We have investigated the effect of a magnetic field on the resistance (magnetoresistance, MR) of single-walled carbon nanotube (SWNT) arrays. The SWNT devices consist of a mixture of metallic and semiconducting SWNTs between palladium electrodes. The MR of the devices is studied at room temperature and in the presence of perpendicular magnetic fields up to 0.24 tesla. The resistance increases as the external magnetic field becomes higher, suggesting a positive MR of SWNTs. After etching the metallic SWNTs by electrical breakdown, the MR can be further enhanced. Large positive MR values about 15%, 20% and 25% were found in three different devices at 0.24 tesla for semiconducting SWNTs at room temperature. Our results show potential for the development of magneto-electronic devices that are operable at room temperature.

Wafer-Scale Fabrication of Suspended Single-Walled Carbon Nanotube Arrays by Silver Liquid Dynamics.

Suspended single-walled carbon nanotubes (SWNTs) have advantages in mechanical resonators and highly sensitive sensors. Large-scale fabrication of suspended SWNTs array devices and uniformity among SWNTs devices remain a great challenge. This study demonstrates an effective, fast, and wafer-scale technique to fabricate suspended SWNT arrays, which is based on a dynamic motion of silver liquid to suspend and align the SWNTs between the prefabricated palladium electrodes in high temperature annealing treatment. Suspended, strained, and aligned SWNTs are synthesized on a 2 × 2 cm2 substrate with an average density of 10 tubes per micrometer. Under the optimal conditions, almost all SWNTs become suspended. A promising formation model of suspended SWNTs is established. The Kelvin four-terminal resistance measurement shows that these SWNT array devices have extreme low contact resistance. Meanwhile, the suspended SWNT array field effect transistors are fabricated by selective etching of metallic SWNTs using electrical breakdown. This method of large-scale fabrication of suspended architectures pushes the study of nanoscale materials into a new stage related to the electrical physics and industrial applications.