Fabricating vertically aligned ultrathin graphene nanosheets without any catalyst using rf sputtering deposition

Few-layer graphene (FLG) and carbon nanotube (CNT) hybrid is prepared by in situ growth of FLG on the walls of CNTs, using PECVD, without catalyst. The amount and size of FLG can be controlled by total gas pressure and growth time. The field emission (FE) characteristics of CNTs coated with different-density FLG were studied, and an FE phenomenon schematic and electrostatic field equipotential model of these FLG-CNTs were proposed. These results show that the geometrical morphology of FLG plays an important role in the FE property of hybrid FLG-CNTs. The medium-density FLG on the CNTs exhibits excellent FE properties, with a low turn-on electric field and threshold field, as well as large field enhancement factor, which are much better than those of the as-grown CNTs. The excellent FE properties of the FLG-CNT hybrids make them promising candidates for high-performance FE emitters.

Field emission from carbon nanotubes for displays

A comparison between field-emission properties of three one-dimensional carbon materials

Superior field emission properties of ZnO nanocones synthesized by pulsed laser deposition

Radial AlN nanotips on carbon fibers as flexible electron emitters

Growth of carbon nanotubes on spontaneously detached free standing diamond films and their field emission properties

Vertically oriented, densely packed Ni nanorod arrays have been fabricated on metal-coated Si substrate via cost-effective electrochemical technique. Directional growth of the nanorods is performed through the nanopores of anodic alumina membrane via electrodeposition process. Al2O3 membrane is removed at the final fabrication step by wet-etching process to get vertically-standing nanorods on Si wafer. Electron microscopic images depict the growth of highly ordered, uniformly grown Ni nanorods with diameter around 50 nm. These types of vertically aligned uniform nanorods supported by Si substrate have very good applications in sensors and field emission displays. Closer look of the electron microscopic images show very sharp tips, which provide large field enhancement and, therefore, are particularly suitable for field emission applications. Field emission studies of the nanorods are performed with standard diode configuration with sample as cathode and a stainless steel tip as anode under high vacuum. Field emission current as a function of applied field shows considerable electron emission with low threshold field around 5 V/μm. The field emission data are found to be well-fitted with linear Fowler–Nordheim plot, indicating the cold field emission mechanism in our samples. Calculation of the geometrical field enhancement factor (β) of the as-synthesized nanorod tip is found to be around 3690, which is sufficient to enhance the macroscopic field at the emitter tip and, hence, supplies the required barrier field (also called local field at the emitter-tip) to produce low-threshold cold field electron emission. Therefore, the cost-effective synthesis of vertically aligned Ni nanorods supported by Si substrate can be used as a field emission device for potential low power panel applications.

The lifetime of explosive emission cathodes is important for high power microwave generators operating in the repetitive regime. For normal metallic cathodes, micropoints on the cathode surface with large field enhancement factors may be gradually consumed in explosive electron emission, which will lead to a limited lifetime. In this paper, a metal-ferroelectric cathode made of stainless steel and BaTiO3 is manufactured. Under voltage close to 1 MV and current near 10 kA, this cathode presents a much longer lifetime than the normal stainless steel cathode, demonstrating the lifetime advantage of the metal-ferroelectric cathode. Nevertheless, in the lifetime experiment of 1.28 × 105 pulses, this metal-ferroelectric cathode also presents obvious lifetime phenomena, one of which is the microwave duration generated by a relativistic backward wave oscillator decreasing from 27 ns to 19 ns. Observation of the cathode surface morphology shows that the emission property deterioration of the metal-ferroelectric ca...

Direct β–FeSi2 film preparation from gaseous phase was examined using a radio-frequency (rf) sputtering deposition apparatus equipped with a composite target of iron and silicon. Films composed of only β–FeSi2 phase were formed at substrate temperatures above 573 K when the chemical composition of the film was very close to stoichiometric FeSi2. The β–FeSi2 films thus formed showed rather large positive Seebeck coefficient. When the chemical composition of the films were deviated to the Fe-rich side, ∈–FeSi phase was formed along with β–FeSi2. On the other hand, α–FeSi2 phase, which is stable above 1210 K in the equilibrium phase diagram, was formed at the substrate temperature as low as 723 K when the chemical composition was deviated to the Si-rich side. The formation of α–FeSi2 phase induced drastic changes in the morphology and thermoelectric properties of the films. The α–FeSi2 phase formed in the films was easily transformed to β–FeSi2 phase by a thermal treatment.

Pd/Cu bimetallic nanoparticles supported on graphene nanosheets: Facile synthesis and application as novel electrocatalyst for ethanol oxidation in alkaline media

SiGe heterostructures with their associated geometries and properties promise a novel generation of Si-based devices. Surface processing and, in particular, dry or plasma etching of semiconductors is a key technology for producing optoelectronic integrated circuits and high speed electronic devices. We have used deep-level transient spectroscopy (DLTS) in an investigation of the electronic properties of defects introduced in n-Si 1 −xGex (x = 0.00 to 0.25) during 1 keV helium-ion etching (fluence = 1 × 1012 cm²) prior to the deposition of gold Schottky barrier diodes (SBDs). Six electron defects (EHel-EHe6) were detected after this processing stage. The defects detected after etching are compared to those introduced by 5.4 MeV alpha-particle (α-) irradiation and, also, radio frequency (rf) sputter-deposition of Au SBDs on material from the same wafer. Four of the electron defects (EHel, EHe2, EHe4, and EHe6) are detected in Si. The remaining two defects (EHe3 and EHe5) are only detected in material containing germanium. It was noted that defects introduced during the He-ion etch process have the same DLTS “signatures” as defects after the sputter deposition process, but none were the same as those introduced during the α-particle irradiation. The influence of increased Ge content on DLTS peak shape and positions is also illustrated and discussed.

The electrical properties of thick amorphous carbon (a-C) films with sequential sp3-rich/sp2-rich layered structure, grown by magnetron sputtering on Si substrates at room temperature, were investigated. At low electric fields, the conduction is due to the variable range hopping mechanism. At high electric fields, thermally assisted band-to-band indirect tunneling is the dominant conduction mechanism, while the Arrhenius plots of the current show a deviation from straight lines in the form of continuous bending satisfying the Meyer–Nelder rule. Comparative studies of low-frequency noise in sp2-rich single layer and sp3-rich/sp2-rich layered a-C films indicate that the noise in the a-C layered originates from traps located mainly at the interfaces of the sp3-rich/sp2-rich bilayers.

Field emission from flat graphene sheets is a challenge due to fewer emission sites. Here, we have synthesized free-standing vertically oriented few-layer graphene (FLG) films directly on dielectric substrates by hot-filament chemical vapor deposition (HFCVD) without any catalyst or special substrate treatment. The fabricated FLGs with a large smooth surface topography, standing roughly vertical to the substrate are found to grow according to the Stranski–Krastanov growth mechanism. The ease of large-area preparation and the low turn-on field of 22 V µm−1 in addition to the large field enhancement factor of ≈6520 for electron field emission suggest that the vertically oriented FLGs could be used as a potential edge emitter. Scanning electron microscopy image of vertically oriented few-layer graphene on a SiO2/Si substrate with the schematic of field electron emission.

EBSD characterization of graphene nano sheet reinforced Sn–Ag solder alloy composites

Ultrathin BN sheets protruded from BN fibers were fabricated through a designated facile multi-zone CVD process using ZnS nanowires as templates. Their field-emission characteristics show a low turn-on field of 1.9 V µm−1, a low threshold field of 4.65 V µm−1, a very high field-enhancement factor (∼1600), and a high stability with a low fluctuation of the field-emission current (∼1%). It is believed that the ultrathin BN nanosheets are necessary for securing these extraordinary field-emission properties. These results suggest that ultrathin BN nanosheets can be excellent candidates for applications as field emitters or other device systems.