G Gheorghe Dinescu

Optical Emission Diagnostic of Laser-Induced Plasma during CNX Film Deposition

To investigate the characteristics of the plasma plume created by reactive laser ablation (RLA) of graphite, optical emission spectra (OES) of the ablated species were recorded for different distances from the target, for various laser fluences and for several N2 pressures. The spectra were dominated by the molecular bands of C2 and CN radical: C2 Swan and CN violet spectral systems. From the molecular band intensities the rotational and vibrational temperatures of CN radicals were derived though there is not a significant dependence of the temperature with fluence, a strong increase of intensity can be observed with the increase of the laser fluence.

Amorphous hydrogenated carbon nitride films deposited via an expanding thermal plasma at high growth rates

An expanding thermal plasma of argon and nitrogen into which acetylene is injected, was used to deposit amorphous hydrogenated carbon nitride (a-C:N:H) films. In the absence of an external bias high growth rates (up to 37 nm/s) were achieved. The growth rate and refractive index of the films were studied in situ with HeNe-ellipsometry. Fourier transform infrared (FTIR) absorption spectroscopy was used to investigate the different bondings. The changes observed in the infrared absorption spectrum with increasing N2/C2H2 ratio in the plasma indicate an increase in dehydrogenation of the films leading to polymerization, and possibly also to graphitization. The microhardness and Young’s modulus, as determined by nano-indentation measurements, show a strong respectively overall increase with increasing acetylene flow, and appear to decrease on addition of N2. This is attributed to the increase in the polymerization of the films on incorporation of nitrogen. Evaluation of the chemical composition by Rutherford back scattering (RBS) and elastic recoil detection analysis (ERDA) reveals that a deposition mechanism should be considered in which N and H are in competition with each other during growth.

Characterization of carbon nitride thin films deposited by a combined RF and DC plasma beam

Abstract Thin carbon nitride films have been deposited on silicon(100) substrates downstream of a nitrogen plasma beam generated in a combined RF (13.56 MHz, 40–50 W) and DC (voltage ±200 V, power 1–10 W) discharge between a graphite electrode and a graphite nozzle. By combining the RF and DC sources the capability of RF field to create extended plasmas is used together with the enhanced sputtering and biasing effect of the DC source. The plasma characteristics (electron temperature, presence of molecular species) have been studied by optical emission spectroscopy. Deposition rates of 2.5–3 nm/s are obtained at the centre of the plasma beam and at a few centimetres distance from the nozzle. The films have been investigated by X-ray photoelectron spectroscopy, spectroscopic ellipsometry, scanning and transmission electron microscopy, and microhardness measurements. The films have an overall N:C ratio of 0.28 but the distribution of different nitrogen bonds depends upon the DC bias conditions. In the spectral range 0.3–0.7 μm the refractive index increases slightly from 1.5 to 2.2. The films are amorphous, with morphology consisting of a columnar structure. The columns have a diameter of about 20 nm. A hardness of 24 GPa has been measured.

Carbon Nitride thin films prepared by a capacitively coupled RF plasma jet

Abstract Carbon nitride thin films have been downstream deposited from a nitrogen plasma beam sustained by a capacitively coupled discharge generated between a RF powered carbon electrode and a grounded carbon nozzle. The spectral emission of the plasma jet strongly exhibits the CN radical emission indicating that the deposition takes place via a mechanism involving the CN radical. The deposition process is enhanced by DC biasing the powered electrode. The films have been investigated by X-ray diffraction, infrared absorption spectroscopy and X-ray photoelectron spectroscopy. The results show that the films are amorphous and contain in a large extent carbon nitrogen bonds.

Investigation of processes in low-pressure expanding thermal plasmas used for carbon nitride deposition: I. Ar/N2/C2H2 plasma

The chemistry of argon, argon/nitrogen and argon/nitrogen/acetylene expanding thermal plasmas is investigated in order to unravel the role of plasma species in the fast deposition (up to 40 nm s-1) of hydrogenated amorphous carbon nitride (a-C:H:N) films. The precursor dissociation is determined and the emission from the different plasmas is compared in order to distinguish possible mechanisms for species production and excitation.

Investigation of processes in low-pressure expanding thermal plasmas used for carbon nitride deposition: II. Ar/N2 plasma with graphite nozzle

The chemistry of an argon/nitrogen thermal plasma expanding through a graphite nozzle is investigated in order to unravel the role of plasma species in the deposition (1-3 nm s-1 rate) of non-hydrogenated amorphous carbon nitride (a-C:N) films. The spectral emission of plasma species is studied and is used in combination with mass spectrometry and nozzle temperature measurements to distinguish possible mechanisms of species production and excitation.

Evidence of charge exchange between N+ and N2(A3S+u) in a low-temperature nitrogen plasma

Abstract The emission from the first negative system, N 2 + ( B 2 Σ + u )→N 2 + ( X 2 Σ + g )+ hν , is studied in the flowing nitrogen afterglow of a DC arc plasma. Investigation of the spectrum shows overpopulation of the vibrational levels 6 and 7 of the excited molecular ion, N 2 + ( B 2 Σ + u ). Selective excitation of these levels is explained by a charge exchange reaction between atomic ions in the ground state and metastable molecules in the N 2 ( A 3 Σ + u ) state. The emitted intensity of the first negative system is shown to be linear with electron density n e for n e >2×10 16 m −3 , a higher-order dependence exists below this value. This is consistent with population of N 2 + ( B 2 Σ + u ) by atomic ions, N + .

On expanding recombining plasma for fast deposition of a-Si:H thin films

A high-density expanding recombining plasma is investigated for deposition of a-Si:H thin films. The deposition method allows high growth rates and it relies on separation of plasma production in a high-pressure thermal arc, and transport of fragments of injected SiH4 monomer to the substrate. Some characteristics of the plasma are discussed together with an explanation of the dominant chemical kinetics, which proceed mainly through heavy-particle interactions. The deposition results indeed show very high growth rates from 2-30 nm s-1 on areas of 30 cm2. The properties of the layers are characterized by measuring their refractive index (in the range 3.1-3.8) and bandgap 1.2-1.5 eV). Analysis of the oxygen content in the deposited films shows oxidation of the samples in air, which is probably associated with the microstructure of the layers.

Remote nitridation of silicon surface by Ar/N2-fed expanding thermal plasma

Low temperature nitridation of native oxidized silicon surface using Ar/N2-fed expanding thermal plasma was investigated. Samples were exposed to the plasma downstream the arc nozzle. X-Ray photoelectron spectroscopy analysis showed that the nitrogen is chemically bonded to silicon, resulting in the change of the native oxide layer into an oxynitride layer. Secondary ion mass spectrometry and low energy ion scattering analyses provided the in-depth distribution of elements, showing that the oxynitride layer approximately reaches a thickness of 5 nm for a treatment time of 30 min. The plasma nitridation process has a passivation effect and provides the surface with increased etching resistance against Ar/SF6-fed expanding thermal plasma.

Absolute and relative emission spectroscopy study of 3 cm wide planar radio frequency atmospheric pressure bio-plasma source

The dynamics of low power atmospheric pressure radio frequency discharge generated in Ar gas in long gap of 3 cm is investigated. This plasma source is characterized and analyzed for possible large scale biomedical applications where low gas temperature and potential-less effluent are required. The discharge forms a homogenous glow-like afterglow in ambient air at input power of 30 W with low gas temperature of 330 K, which is desirable in biomedical applications. With absolute calibrated spectroscopy of the discharge, electron density of 0.4 × 1018 m−3 and electron temperature of 1.5 eV are obtained from continuum Bremsstrahlung radiation of the source. Time and spatial resolved emission spectroscopy is used to analyze discharge generation mechanism and active species formation. It is found that discharge dynamics strongly correlates with the discharge current waveform. Strong Ar(2p) excited states emission is observed nearby the electrodes surface on a distance up to 200 μm in the plasma sheath region a...