J.J. Li

Resistive and capacitive response of nitrogen-doped TiO2 nanotubes film humidity sensor

Dielectric oxides are traditionally used to fabricate resistive surface humidity-sensing devices, as well as capacitive sandwich-structured sensors. In the present work, relative humidity (RH) sensors were fabricated by employing vertically aligned TiO(2) nanotubes array (TNA) film produced using electro-chemical anodization of Ti foil followed by a nitrogen-doping process, simultaneously showing resistive and capacitive humidity-sensing properties in the range of 11.3-93.6%. For the sample formed at optimized experimental conditions, the capacitance (C(S)) and resistance (R(S)) of the as-fabricated RH sensors made from nitrogen-doped TiO(2) nanotubes film could be simultaneously obtained. Both the resistive and capacitive sensitivity (K(R) and K(C)) of the as-fabricated TiO(2) nanotube RH sensors show distinct dependence on the frequency of alternating current (AC) voltage signal and RH. At higher water coverage, water-water interaction will result in lowering of the water dissociation barrier, leading to an increase of conductance. With the increase of RH, the polarization of as-adsorbed water molecules will also occur, causing a sharp increase of capacitance. For an explanation of the frequency response of both C(S) and R(S), ionic transport, as well as the polarization effect, should be comprehensively considered. The changes of capacitance and resistance at different temperatures are plausibly caused by thermal expansion and surface state modification by adsorption and desorption of oxygen and water.

Improving mechanical properties of amorphous carbon nitride films by titanium doping

Titanium doped amorphous carbon nitride (a-CNx) films with a nitrogen content of ∼24at.% were synthesized by radio frequency magnetron sputtering method. The effects of incorporating Ti on the mechanical properties of a-CNx films were investigated by nanoindentation, scanning electron microscope, x-ray diffraction spectra, and x-ray photoelectron spectroscopy, respectively. It was found that nanometer sized TiN crystallites were formed and embedded in the a-CNx matrix, causing an enhancement of hardness from ∼28to∼40GPa in the a-CNx films. The improved mechanical properties with addition of Ti are attributed to the densified microstructure due to the development of fine grain size of TiN and sp3 C–N bonds. These TiN nanocrystal grains are separated by an amorphous phase, preventing dislocation movement and hence enhancing the hardness of the film. The increased sp3 C–N bond fraction induced by incorporation of Ti also plays an important role in the enhancement of hardness.

Effect of grain boundary on local surface conductivity of diamond film

In this article, the direct experimental evidences to determine the effect of grain boundary on local surface conductivity (SC) of diamond films were provided by the measurement using double probe scanning electron microscopy (SEM) technology. Undoped diamond films with (001) orientation were first grown by microwave plasma enhanced chemical vapor deposition and were then hydrogenated at different conditions for SC measurement. In the SEM system, double probes with tiny tip radius severed as two leads were moved along and contacted with the diamond film surface to directly test the local SC of diamond film. The surface electrical property results indicate that for the same distance between the two probes, the local SC of the area across grain boundary is much higher than that of area without grain boundary for the same duration of hydrogenation degrees. In addition, local SC of the area between the two probes increases with the number of grain boundaries in this area, which demonstrates that the grain bou...

Evolution of dislocation loops in He ion irradiated nickel under different temperature

The effect of temperature on the evolution of loops in nickel was investigated under 30 keV He+ irradiation. The size, Burgers vector, and nature of loops were analyzed by a transmission electron microscope (TEM). In addition, the Weibull statistical analysis was introduced to analyze the size distributions of the loops. The TEM results indicate that the sizes of loops increase with increasing irradiation temperature, where they are mainly in the range of 10–30, 20–50, and 30–80 nm at 300, 400, and 500 °C, respectively. In the irradiation temperature range of 300–500 °C, the size distributions of loops fit Weibull distribution very well, which suggests that the loops tend to grow larger and/or be merged. In addition, almost all the loops formed under He+ irradiation are the interstitial loops with Burgers vectors b =   a2⟨110⟩, which is ascribed to the assistance of the He atom on the formation process of loops.

Domain wall scattering in the nanocontacts of ferromagnetic metals with different coercive forces

The electrical transport properties of nanocontact nanostructures of ferromagnetic metals with different coercive forces have been studied by the I-V measurements at room temperature without applied magnetic field. The result indicates that the nanocontact structure within the critical contact width for NiFe, Fe and Ni can pin a single domain wall at the nanocontact position. A sharp resistance drop will happen when the domain wall is depinned from the contact position by injecting the spin polarized current. Furthermore, we have found that the critical current density for depinning is constant for each ferromagnetic metal. They are 1.8 x 10(7) A cm(-2) for NiFe, 3.2 x 10(7) A cm(-2) for Ni and 3.8 x 10(7) A cm(-2) for Fe, respectively, which increases with the increase of the coercive force of ferromagnetic metal. Micromagnetic simulation results provided a detailed understanding on the magnetic configuration for ferromagnetic metals with different coercive forces.

Metallic electrical transport in inter-graphitic planes of an individual tubular carbon nanocone

Tubular carbon cones (TCCs) with a herring-bone-like graphitic structure are synthesized on gold wire via the bias-assisted hot filament chemical vapor deposition (HFCVD) method. The electrical transport properties of an individual TCC are studied in the temperature range from 300 to 500 K by using a double probe scanning electron microscopy (DPSEM) in situ electrical measurement system. The high-resistance I-V characteristics of W-TCC-Au back-to-back double junctions show that electrons tunnel through the W-TCC junction, while thermoionic transport through the Au-TCC junction contributes to low-resistance properties. Temperature dependence of the electrical characteristics indicates that inter-graphitic-plane electrical transport in TCC is metallic.

Local field emission characteristic of individual AIN cone fabricated by focused ion beam

In summary, an individual AlN cone with high aspect ratio was formed by FIB technique. And a nature field emission property of individual AlN cone was measured in a dual probe SEM system. The results indicated that as formed single AlN cone with high aspect ratio exhibits a good field emission ability without any field shielding effect although only has a tiny emission area. Compared with a single Si cone fabricated by the same method, a single AlN cone has a better electron emission ability and hence a good promising candidate of point electron source candidate for the application of vacuum electronic device field.

Growth and Filed Emission of Tubular Carbon Cones

A new tubular carbon cones (TCCs) were grown on the gold wires by hot filament chemical vapor deposition (HFCVD), having long-cone-shaped appearance with a herringbone hollow interior surrounded by helical sheets of graphite coiling around. It is considered to be a main result of TCCs formation that during growth the size of catalyst particle located in the top of TCCs is decreased continuously due to etching effect in the CVD plasma. In addition, these TCCs exhibited excellent field emission ability with a very low threshold field of 0.27 V/mum and a stable emitting current, which is attributed to its lower effective work function and the reduced screening effect