Nitrogen-doped Diamond-like Carbon Research Articles

Solar cells based on DLC film – Si structures for space application

Significant increase in solar cell (SC) efficiency after the deposition of thin antireflection diamond-like carbon (DLC) films has been observed. Thick (1300–1500 nm) DLC films deposited on a working side of the SC allow us to increase their stability relating to the effect of proton and ultraviolet (UV) irradiation. So, one-stage ( E=50 keV) or multi-energy (50+100 keV) implantation of proton into protected SC (the SC+DLC films system) did not practically influence the SC parameters. Moreover, SC covered by DLC film after UV irradiation show improvement of efficiency both for implanted and unimplanted samples. At the same time the unprotected SC deteriorated after those treatments.The effects observed are connected with the decrease in reflection losses due to the deposition of DLC films and self-annealing of radiation damages in implanted DLC films due to light-induced hydrogen bonding. Re-emission by DLC film of the absorbed ultraviolet light in visible spectral range was observed and mechanism of the effect was proposed. Application of nitrogen-doped DLC film as a fluorescent layer allows us to improve Si SC efficiency in UV spectral range. The results obtained have opened up a wide variety of potential applications of DLC films, especially for space solar cells.

Infrared optical properties of amorphous hydrogenated carbon nitride film

The microstructure and optical properties of nitrogen-doped hydrogenated carbon DLC:N films deposited by the rf plasma-enhanced chemical vapor deposition (PECVD) method were studied by atomic force microscopy (AFM), Raman, Fourier-transform infrared (FTIR) and infrared ellipsometric (IRE) spectrometry. The absorption intensities of the peaks CNH (1600 cm −1), CN (2200 cm −1) and NH (3250 cm −1) in the IR spectra increase with the N 2/CH 4 flux ratio. Raman spectra show that the shape of the D and G bands of DLC:N film varies slightly with the increase of N content, which means that the main structures of N-doped films are still diamond-like carbon (DLC). However, four Gaussian decomposition results show that the peak of the G band widens and shifts to the low wavenumber with increased nitrogen content in Raman spectra due to amorphous C 3N 4 structure being formed in the nitrogen-doped DLC film. AFM topographies and lateral force microscopy (LFM) images of DLC:N film confirm that the amorphous C 3N 4 exists as particles several tens of nanometers in size in the film. IRE spectral analysis results show that the refractive index of the film in the infrared region (2–14 μm) decreases slightly from 1.8 to 1.6 with increased nitrogen content.

The effect of nitrogen addition on field emission of diamond-like carbon films

Diamond-like carbon (DLC) films and nitrogen-doped DLC (N-DLC) films were deposited on a molybdenum-coated ceramic substrate using the pulsed laser deposition technique. The structure and surface morphology of the films were examined using X-ray diffraction, Raman spectroscopy, Auger electron spectroscopy and scanning electron microscopy. Field emission measurements were carried out, with the DLC or the N-DLC films as the cathode and ITO-coated glass as the anode. The field emission measurements indicated that the nitrogen doping could lower the turn-on field and increase the current density. It was believed that the interface at the molybdenum–N-DLC film plays an important role in improving the field emission performance of the N-DLC film.

Electron emission performance of nitrogen-doped hydrogen-free diamond-like carbon coating on Mo-Tip field emitter arrays

Nitrogen gas phase doped diamond-like carbon (DLC) coating on molybdenum-tip field emitter arrays (FEAs) has been used to improve electron emission characteristics. The conventional plasma enhanced chemical vapor deposition method using a layer-by-layer technique was applied to deposit N-doped hydrogen-free DLC films. Electron emission characteristics were measured and the possibility of applying these type of emitters to high frequency field emission displays was reported. The turn-on voltage of Mo-tip FEAs was decreased from 75 to 55 V by DLC coating and emission current was more stable than that of conventional Mo-tip FEAs. The transconductance of Mo-tip FEAs was increased by N-doped hydrogen-free DLC coating with lowering effective work function of emitters.

EFFECT OF NITROGEN ON THE RESIDUAL STRESS AND ADHESION OF DIAMOND-LIKE AMORPHOUS CARBON NITRIDE FILMS

Microstructure and adhesion properties of nitrogen-doped diamond-like amorphous carbon (DLC) film deposited by r f plasma-enhanced chemical vapor deposition method is studied by atomic force microscope, Auger electron spectroscopy (AES) and micro-indentation analysis. Results show that, with the increase of nitrogen content, particles of tens of nanometer in size appear in the film. The atomic lateral force microscope and AES analyses show that these nano particles are nitrogen-rich amorphous carbon nitride CNx, where x is larger than 0.126. Micro-indentation measurement shows that this DLC/CNx nano-composite structure reduces the residual stress of the film and improves the adhesion between DLC film and Si substrate.

Micro-Structural and Field Emission Characteristics of Nitrogen-Doped And Micro-Patterned Diamond-Like Carbon Films Prepared by Pulsed Laser Deposition

ABSTRACTEffect of nitrogen doping on field emission characteristics of patterned Diamond-like Carbon (DLC) films was studied. The patterned DLC films were fabricated by the method reported previously[1]. Nitrogen-doping in DLC film was carried out by introducing N2 gas into the vacuum chamber during deposition. Higher emission current density of 0.3∼0.4 mA/cm2 was observed for the films with 6 at % N than the undoped films but the emission current density decreased with further increase of N contents. Some changes in CN bonding characteristics with increasing N contents were observed. The CN bonding characteristics which seem to affect the electron emission properties of these films were studied by Raman spectroscopy, x-ray photoemission spectroscopy (XPS) and Fourier transform infrared spectroscopy (FT-IR). The electrical resistivity and the optical band gap measurements showed consistence with the above analyses. High-resolution transmission electron microscopic (HRTEM) results also support the formation of graphite-like phase in 9 at % N-doped DLC film.

Effect of N doping on the electron emission properties of diamondlike carbon film on a 2-in. Mo field emitter array panel

We have studied the enhancement of field-emission characteristics by hydrogen-free nitrogen-doped diamondlike carbon (DLC) coating on Mo-tip field emitter arrays by a layer-by-layer technique using plasma-enhanced chemical vapor deposition. The Spindt-type molybdenum tip is used as an emission source without a resistive layer on the silicon substrate. The maximum emission current for each pixel was increased from 160 to 1520 μA by a 20 nm N-doped DLC coating. Furthermore, the emission current from DLC-coated field emitter arrays (FEAs) is more stable than that of noncoated FEAs.

Conduction processes in boron- and nitrogen-doped diamond-like carbon films prepared by mass-separated ion beam deposition

Boron- and nitrogen-doped diamond-like amorphous carbon (DLC) films were prepared by alternating direct deposition of low energy mass-separated 12C+ and dopant ions. Concentration vs. depth profiles for N and B dopants were determined by neutron depth profiling. The measured current-voltage characteristics of these films, which were deposited on polished stainless steel, are explained best by Frenkel-Poole emission for high electric fields. Two different trap states Φ1 and Φ2 were found to contribute to the conduction process. At low electric fields our results suggest that conduction is due to variable-range hopping via localized states at the Fermi level. The doped DLC films show a higher electrical conductivity, indicative of an increased density of localized states, rather than a shift in the Fermi level. A diode-like device was prepared, but the measured I-V curves did not indicate that a p-n junction had formed. DLC/Si heterojunctions were also prepared and their current-voltage characteristics are presented and discussed.

Effects of nitrogen trifluoride on the growth and properties of plasma-enhanced chemical-vapor-deposited diamond-like carbon films

Nitrogen-doped diamond-like carbon (DLC) or amorphous hydrogenated carbon (a-C:H) films were grown by plasma enhanced chemical vapor deposition using methane and nitrogen gases as precursors. The effects of nitrogen trifluoride (NF3) on these nitrogen-doped DLC films were also investigated. The deposition rate decreases sharply with the addition of nitrogen in the absence of NFF3 due to dilution, while it increases in the presence of NFF3 due, presumably, to the reduction of activated hydrogen species by the fluorine radical (F϶. X-ray photoelectron spectra reveal a nitrogen concentration in the range of 9.3 to 13.8% in these DLC films with a C Is electron binding energy of 287-288 eV, indicating the diamond-like structure. Infrared spectra of DLC films indicate the presence of amino groups (N-H) and nitrile and/or isonitrile (C= N) groups giving strong evidence of sp carbon. Diamond like carbon films deposited in CHF4 +NF4 (with and without NFF3) have a lower refractive index, a lower bulk resistivity, and a lower optical bandgap than films deposited using CHF4 due to a lower hydrogen content in the films. Moreover, the bulk resistivity of these films decreases by over four orders of magnitude and the optical bandgap decreases from 2.65 eV to about 0.75 eV following annealing at a temperature of 500°C.