Carbon-coated Nickel Research Articles

Novel 1–3 metal nanoparticle/polymer composites induced by hybrid external fields

We reported a novel 1–3 nanocomposite consisting of carbon-coated nickel (Ni@C) nanoparticles and epoxy resin matrix, in which nanoparticles were found one-dimensional-aligned by applying hybrid electric and magnetic fields during the curing of resin. The alignment was explained based on the dipole–dipole interaction between Ni@C nanoparticles under external fields. The dc resistivity, dielectric constant and dielectric loss of composites were tested as the function of the loading content and external fields. The results show the resistivity of aligned composites decreases by 3–4 orders of magnitude than that of random composites in the loading content range of 3–10 wt%, accompanied with an increase in dielectric constant and dielectric loss. Specially, it deserves to note that the synergistic effect of electric field and magnetic field was observed.

Field electron emission from sputter-induced carbon nanofibers grown at room temperature

Graphite, carbon-coated silicon, and carbon-coated nickel surfaces were bombarded with obliquely incident Ar+ ions at room temperature. The sputtered surfaces were covered with conical protrusions, ∼2.5×105mm−2 or higher in numerical density, and partially aligned single carbon nanofibers (CNFs), ∼20nm in diameter and 0.3-2μm in length, grew on the tips. They were characterized by the amorphous nature and the boundaryless structure between the CNF and the conical base. The field electron emission measurements for the CNFs thus grown on the carbon-coated silicon substrate showed the threshold field of 1.8V∕μm with a current density of 1μA∕cm2, and the field enhancement factor was estimated to be 1951 from the Fowler-Nordheim plot assuming the work function of 4.6eV for graphite. The morphological structure of CNFs grown on conical bases was thought to be effective to reduce the screening effect due to sufficient distance between adjacent CNFs. Thus, the sputter-induced CNFs were concluded to be quite promising as a field electron emission source.

Transmission Electron Microscopy and X-Ray Diffraction Analysis of Aluminum-Induced Crystallization of Amorphous Silicon in α-Si:H/Al and Al/α-Si:H Structures

Solid phase crystallization of plasma-enhanced chemical-vapor-deposited (PECVD) amorphous silicon (alpha-Si:H) in alpha-Si:H/Al and Al/alpha-Si:H structures has been investigated using transmission electron microscopy (TEM) and X-ray diffraction (XRD). Radiative heating has been used to anneal films deposited on carbon-coated nickel (Ni) grids at temperatures between 200 and 400 degrees C for TEM studies. alpha-Si:H films were deposited on c-Si substrates using high vacuum (HV) PECVD for the XRD studies. TEM studies show that crystallization of alpha-Si:H occurs at 200 degrees C when Al film is deposited on top of the alpha-Si:H film. Similar behavior was observed in the XRD studies. In the case of alpha-Si:H deposited on top of Al films, the crystallization could not be observed at 400 degrees C by TEM and even up to 500 degrees C as seen by XRD.

Electrical characterization of C-coated nickel silicide nanowires grown on Ni-loaded Si substrate

Carbon-coated nickel silicide nanowires (C-coated NiSi NWs) were grown in a home-made chemical vapor deposition (CVD) reactor. The coating of semiconductor or metal nanowires with nano-sized carbon layer is effective to prevent the oxidation of the nanowires, resulting in the stabilization of electrical properties of nanodevices. The growth of the NiSi nanowires and the coating of the NWs with carbon layers simultaneously took place in the reaction. The current-voltage curve of individual NiSi nanowire showed highly linear behavior, indicating the good ohmic contact without the insulating layer. The resistivity of the NiSi nanowire was about 370 ΜΩ-cm at room temperature, decreased monotonically as the temperature was lowered, and became saturated at low temperatures, indicating the growth of metallic NiSi nanowires. Field emission measurements showed that the C-coated NiSi nanowires were an excellent field emitter with large emission current densities at very low electric field.

Anomalous growth and characterization of carbon-coated nickel silicide nanowires

Carbon-coated nickel silicide nanowires (C-coated NiSi NWs) were prepared in a radio-frequency-induction heating chemical vapor deposition (RF-CVD) reactor. The growth of the NiSi nanowires and the coating of the NWs with carbon layers simultaneously took place in the reaction. The nanowires grew straight with the length of more than 10 μm and the average diameter ranging in 20–40 nm. The nanowires were coated with a carbon layer with thickness of 1.5–1.7 nm. The resistivity of individual NiSi nanowire was about 370 μΩ cm at room temperature and it decreased monotonically as the temperature was lowered and became saturated at low temperatures, indicating the growth of metallic NiSi nanowires.

Preparation of carbon-coated Co and Ni nanocrystallites by a modified AC arc discharge method

A modified AC arc discharge method was used to prepare carbon-coated cobalt and nickel nanocrystallites under He atmosphere. The metal content of the magnetic nanomaterials were remarkably enhanced by increasing metal loading ratio and modifying experimental apparatus. The powder was separated from the soot by magnetic separation and acid (HCl) treatment. Structure and morphology were examined by powder X-ray diffraction (XRD) and transmission electron microscopy (TEM). The metal content was determined by thermogravimetric analysis (TG). The magnetic properties of the powder were measured by a vibrating sample magnetometer (VSM). The size of the wrapped metal particles was between 10 and 100 nm. XRD profiles showed peaks associated with major peaks of graphite and single phase of fcc β-Co and cubic Ni with no evidence of metal carbides. With the Co metal content ranging from 28.8 to 57.5 wt.%, the corresponding B s ranged from 210.6 to 758.2 G. The B s of the carbon-coated Ni powder ranged from 90.7 to 205.0 G while the Ni metal content ranged from 34.6 to 64.5 wt.%.

Synthesis and characteristics of carbon-coated iron and nickel nanocapsules produced by arc discharge in ethanol vapor

Fe(C) and Ni(C) nanocapsules with low carbon content have been produced via an arc discharge process in ethanol vapor. It is clarified by X-ray diffraction that the core of the Fe(C) nanocapsules consists of γ-Fe, α-Fe and Fe 3C phase, while that of the Ni(C) nanocapsules contains only nickel. High-resolution transmission electron microscopy imaging confirms that these particles have a broad size distribution and the core/shell structure. Besides mutually independent nanocapsules with segregate graphitic shells, those with sharing shells are also observed in the Fe(C) nanocapsules. The remanence and the coercivity at room temperature of both the nanocapsules are higher than those of the corresponding microcrystallines, while the saturation magnetization is lower.

Aluminum-Induced Crystallization of Amorphous Silicon (α-Si:H) at 150°C

Thin amorphous silicon (α-Si:H) films (50 nm) were grown by plasma-enhanced chemical vapor deposition (PECVD) on carbon-coated nickel transmission electron microscope (TEM) grids. A thin layer (50 nm or less) of aluminum (Al) was then deposited on the α-Si:H films by vacuum evaporation. These structures were then annealed at temperatures between 140 and 200°C in vacuum using a lamp furnace to investigate the aluminum-induced crystallization (AIC) of PECVD grown α-Si:H. The process of crystallization was studied by TEM and electron diffraction (ED) and X-ray diffraction (XRD). For glancing angle XRD studies, 500 nm thick α-Si:H and 400 nm thick Al films were used, and in situ annealing was performed at temperatures between 100 and 250°C using a model TTK low temperature camera mounted on the omega shaft of the goniometer of a Philips X'Pert XRD system. The TEM results revealed complete crystallization of the α-Si:H film in 30 min at an annealing temperature of 150°C. The in situ XRD data also indicate conversion of the α-Si:H into a crystalline silicon phase at temperatures between 150 and 160°C. These results show for the first time that polycrystalline silicon with grain sizes as large as 0.2 to 0.5 μm can be obtained by AIC of PECVD α-Si:H at a temperature as low as 150°C. © 2001 The Electrochemical Society. All rights reserved.

Preparation and properties of ferromagnetic carbon-coated Fe, Co, and Ni nanoparticles

Carbon-coated iron, cobalt, and nickel particles were produced by an arc discharge process modified in the geometry of the anode and the flow pattern of helium gas. Field emission scanning electron microscopy shows that the resulting material consists of only carbon-coated metal particles without any nanotubes or other unwanted carbon formations present. The diameters of iron, cobalt, and nickel particles range predominantly from 32 to 81 nm, 22 to 64 nm, and 16 to 51 nm, respectively. X-ray diffraction analysis confirmed that the as-made particles are carbon-coated elements rather than metal carbides. High resolution transmission electron microscopy reveals that the as-made cobalt and nickel particles are covered by 1–2 graphitic layers, while iron particles are surrounded by amorphous carbon. When the samples were treated by annealing or immersion into nitric acid, particles completely coated by carbon resisted both postdeposition treatments. However, further graphitization of the carbon coating by either of the two treatments was observed. Particles only partially coated by carbon were not protected, but sintered by annealing or dissolved in the acid. The magnetic properties of the as-made particles were measured by a vibrating sample magnetometer. The values of the saturation magnetic moment per gram of each type of metal particle are 56.21, 114.13, and 34.9 emu/g representing 26%, 71%, and 64% of the saturation moments of the bulk ferromagnetic elements iron, cobalt, and nickel, respectively. All the metal particles were shown to be ferromagnetic with a ratio of remnant to saturation magnetization MR/MS∼0.3 at room temperature (25 °C). In this article the detailed preparation and the properties of these carbon-coated metal particles will be discussed.

A new procedure for quantitative measurements of virus particles in crude preparations.

A new method is described for the quantitative measurement of virus concentration in crude preparations by density gradient centrifugation and electron microscopy. The centrifugation is carried out in a specially designed centrifuge tube which permits separation and sedimentation of virus particles at different levels according to their sedimentation velocity. The gradient of a mixture of heavy and normal water (D(2)O-H(2)O) is designed to sediment the virus particles with constant velocity so that the optimal time of centrifugation can easily be calculated. The virus particles are collected on carbon-coated nickel grids floating on mercury at the bottom of the centrifuge tube and are counted by means of electron microscopy. The efficiency of the method is demonstrated with a crude plant extract of tobacco mosaic virus.