Nitrogen-doped Nanocrystalline Diamond Films Research Articles

Influences of Melamine Flow Rate on the Growth Behavior of Nanocrystalline Diamond Films by Direct Current Plasma Chemical Vapor Deposition Method

InCH4/H2 atmosphere, Nitrogen-doped nanocrystalline diamond films were prepared by direct current hot-cathode plasma chemical vapor deposition (PCVD) method on the conditions of different flow rate of Melamine. While the flow rate of Melamine is 2sccm, the grain refining effect on the diamond films is obvious and the nanocrystalline grains protrude from the basis of the film which shape rough surfaces. The films are incompact, due to its large gaps and holes as well as defects, however the conductivity of these films are increased. The increasing flow rate of Melamine promotes the growth of (111) oriented.

Comparison of S-band radio-frequency field emission performance of nitrogen-doped nanocrystalline diamond before and after O2/Ar plasma etching

The effect of surface nanostructuring via reactive O2/Ar plasma etching on the S-band radio-frequency (RF) field emission performance for nitrogen-doped nanocrystalline diamond (N-NCD) films was preliminarily investigated. A transition in terms of surface morphology, from dense flower-like aggregated shape having low roughness (∼41nm) to uniform porous structure with increased surface roughness (∼104nm), was observed after plasma etching. Raman spectra revealed there was no obvious change in the bonding characteristics between the pristine and nanostructured N-NCD films. At surface RF gradient of 72.1MV/m, maximum current density of 80.2mA/cm2 was reached for the nanostructured N-NCD cathode, increasing about 41% compared to that of the pristine N-NCD cathode. Furthermore, the mechanism in the enhanced RF field emission was tentatively discussed through the measured Fowler–Nordheim (F–N) features.

Tuneable anisotropic transport in nitrogen-doped nanocrystalline diamond films: Evidence of a graphite-diamond hybrid superlattice

We show strong evidence of superlattice-like carbon layered structures in heavily nitrogen-doped ultrananocrystalline diamond (UNCD) films through the experimental demonstration of temperature-dependent anisotropic diffusive transport. The superlattice periodicity, in the range of several nanometers, is derived from the analysis of both magneto-resistance and the temperature-dependent conductivity based on the generalized diffusive Fermi surface model. The effect of quasi–two-dimensionality on the magneto-transport of these films yields a weak temperature dependence of the electron dephasing length. These results explain a reasonably strong coupling between the conducting carbon layers separated by the insulating nanodiamond grains producing the anisotropic transport in UNCD films controlled by the level of nitrogen incorporation.

Fabrication and characteristics of nitrogen-doped nanocrystalline diamond/p-type silicon heterojunction

Nitrogen-doped nanocrystalline diamond films (N-NDFs) have been deposited on p-type silicon (Si) by microwave plasma chemical vapor deposition. The reaction gases are methane, hydrogen, and nitrogen without the conventional argon (Ar). The N-NDFs were characterized by X-ray diffraction, Raman spectroscopy, and scanning electron microscopy. The grain sizes are of 8∼10 nm in dimension. The N-NDF shows n-type behavior and the corresponding N-NDF/p-Si heterojunction diodes are realized with a high rectification ratio of 102 at ∼ 7.8 V, and the current density reaches to 1.35 A/cm2 at forward voltage of 8.5 V. The findings suggest that fabricated by CH4/H2/N2 without Ar, the N-NDFs and the related rectifying diodes are favorable for achieving high performance diamond-based optoelectronic devices.

Electrons diffusion study on the nitrogen-doped nanocrystalline diamond film grown by MPECVD method

Nitrogen-doped nanocrystalline diamond (NNCD) films were deposited onto p-type silicon substrates with three different layer structures: (i) directly onto the silicon substrate (NNCD/Si), (ii) silicon with undoped nanocrystalline diamond layer which was deposited in the same way as the above mentioned NNCD by the recipe Ar/CH 4/H 2 with a ratio of 98%/1%/1% (NNCD/NCD/Si), and (iii) silicon wafer with 100 nm thickness SiO 2 layer (NNCD/SiO 2/Si). Atomic force microscopy (AFM), X-ray diffraction (XRD) and Raman spectroscopy were employed to characterize the morphology and microstructure of the as-grown nitrogen-doped diamond films. Silver colloid/silver contacts were made at to measure the current–voltage ( I– V) characteristics for the three different structures. Electrons from a CVD reactor hydrogen plasma diffuse toward the p-type silicon substrate during a deposition process under the high temperature (∼800 °C). The study concluded that the SiO 2 layer could effectively prevents the diffusion of electrons.

An Investigation of Chemical Species and Electrical Property of Nitrogen-Doped Nanocrystalline Diamond Films Grown by Microwave Plasma Jet Chemical Vapor Deposition

This study investigated chemical species in the plasma while synthesizing nitrogen-doped nanocrystalline diamond (NCD) films using microwave plasma jet chemical vapor deposition (MPJCVD) system. The investigation is done by using in-situ plasma optical emission spectroscopy (OES). The electrical resistivity of the nitrogen-doped NCD films increases by 6 orders of magnitude (up to 6.7×10-4 Ω cm) with increasing nitrogen content. This approach also helps us in further understanding of the plasma species during depositing NCD films and also the electronic structure of grown conductive diamond phase through analysis of as-doped nitrogen contents.

Low-temperature thermionic emission from nitrogen-doped nanocrystalline diamond films on n-type Si grown by MPCVD

Temperature-dependent emission current–voltage measurements were carried out for nitrogen (N)-doped nanocrystalline diamond (NCD) films grown on n-type Si substrates by microwave plasma-assisted chemical vapor deposition (MP-CVD). Low threshold temperature (~ 260 °C) and low threshold electric field (~ 5 × 10 − 5 V/µm) were observed. Both the temperature dependence and the electric field dependence have shown that the obtained emission current was based on electron thermionic emission from N-doped NCD films. We have also studied the relation between nitrogen concentration and the saturation emission current. The saturation current obtained was as high as 1.4 mA at 5.6 × 10 − 3 V/µm at 670 °C when the nitrogen concentration was 2.4 × 10 20 cm − 3 . Low value of effective work function (1.99 eV) and relatively high value of Richardson constant (~ 70) were estimated by well fitting to Richardson–Dushman equation. The results of smaller φ and larger A′ suggest that N-doped NCD has great possibility of being a highly efficient thermionic emitter material.

Structural and electrical characteristics of nitrogen-doped nanocrystalline diamond films prepared by CVD

Nitrogen-doped nanocrystalline diamond (N-NCD) films were grown using microwave plasma enhanced chemical vapour deposition method. Films were characterized by Raman spectroscopy, x-ray diffraction and scanning electron microscopy. Perfectly ohmic contacts for the N-doped NCD film and p-type Si substrate were obtained using silver (Ag). Silver deposited at a temperature of 250 °C with the pulsed laser deposition method was found to show ohmic behaviour with a high degree of reproducibility. Current–voltage (I–V) characteristics are presented for various Ag/N-NCD and Ag–Si. Rectifying I–V behaviour for the interface N-NCD/p-Si suggests that the majority carriers for N-NCD are electrons.

Effect of the sp2 carbon phase on n-type conduction in nanodiamond films

Structural and electrical conduction properties of nitrogen-doped nanocrystalline diamond films are studied as a function of deposition temperature (TD) in a microwave Ar-rich/CH4 plasma with 30%N2 addition. Hall- and Seebeck-effect measurements confirm n-type conduction for TD above 1100 K. For TD from 1100 and 1220 K, the electron concentration increases up to 1020 cm−3 and the electron mobility is in the range of 4–8 cm2 V−1 s−1. For TD above 1250 K, the mobility decreases to ∼1 cm2 V−1 s−1. Low conductivity films deposited at low TD exhibit semiconductorlike thermal activation in the Arrhenius plots, while high conductivity films deposited at high TD are almost temperature independent, indicative of quasimetallic conduction. The nitrogen concentration in the films is about 0.3 at. %, independent of TD. As TD is increased, the sp2 content and order increase. This is responsible for the appearance of midgap states, their delocalization, and the larger distance between diamond grains. The high conductivity at high TD is due to the amount and crystallinity of sp2 carbon, rather than the nitrogen concentration.

Competition of nitrogen doping and graphitization effect for field electron emission from nanocrystalline diamond films

Field electron emission properties were investigated for nitrogen-doped nanocrystalline diamond films grown on Si substrates from CH4/Ar/N2 gas mixtures by direct current arc plasma chemical vapor deposition (CVD). Different nitrogen content in the gas mixtures and different deposition temperatures were used for the growth to get the films with different nitrogen content, microstructure, and field emission properties. In addition, higher growth temperature for some of the films assists to partial graphitization of the diamond films that can improve the emission too. The film surface and microstructure was studied using atomic force microscopy, scanning electron microscopy, Raman spectroscopy, x-ray photoelectron spectroscopy, Auger electron spectroscopy, and electron energy-loss spectra to find correlations between the field emission and other film properties. The field electron emission was studied using both a macroscopic phosphor screen setup and a microprobe setup. It was found that nitrogenated CVD diamond films show different microstructure than the films prepared without nitrogen. The field electron emission for the nitrogenated films was typically better than for the “pure” diamond films. On the other hand, partially graphitized films grown at higher temperatures (with or without nitrogen in the gas mixtures) typically show the best field emission properties with emission threshold fields of as low as 1–2 V/μm, higher density of emission sites, and higher working limit of the emission current.