Eugen Aldea

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.

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.

Formation and Expansion Phases of an Atmospheric Pressure Glow Discharge in a PECVD Reactor via Fast ICCD Imaging

This paper reports on the experimental study of the dynamic evolution of a dielectric barrier discharge in an atmospheric-pressure plasma enhanced chemical vapor deposition reactor using a gated intensified charge coupled detector. It is observed that a diffuse atmospheric pressure glow is formed via transition from Townsend-like discharge or, alternatively, can be initiated by a filamentary discharge. The formation of the glow current spot is followed by the lateral expansion of the discharge.

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 + .

Influence of a-Si:H buffer layers on the properties of CNx materials

On the basis of ab initio calculations, the (alpha) , (beta) - C3N4 crystalline compounds have been proposed as promising materials for optical applications in ultraviolet and visible. However, these crystalline forms of carbon nitride have been hardly obtained, mostly the formation of amorphous material being noticed. Previously, deposition of amorphous carbon nitride from an RF plasma jet operating in nitrogen with graphite electrodes was reported. This work reports on the deposition and characterization of carbon nitride thin films by RF nitrogen plasma beam with graphite electrodes either on glass on crystalline Si or on intermediate a-Si:H buffer layers. The layers properties (composition, crystallinity and absorption in ultraviolet, visible and infrared) have been studied by x-ray photoelectron spectroscopy (XPS), FTIR (Fourier transform infrared spectroscopy) and UV-VIS absorption, energy dispersive x-ray analysis (EDX) and x-ray diffraction (XRD) techniques. It is shown that amorphous carbon nitride materials with variable optical bandgap in the range 1.2-3.5 eV can be obtained. Also, the formation of an intermediate SiCN interlayer and the promotion of crystallinity in CNx films, due to buffer layer presence, is proved.

Laser treatment of a-SiC:H thin films for optoelectronic applications

Amorphous and hydrogenated (a-SiC:H) as well as crystalline silicon carbide are widespread materials for optoelectronic applications. In this paper, we studied the effect of laser/RF plasma jet treatment of a-SiC:H thin films deposited by Plasma Enhanced Chemical Vapor Deposition, on Si wafers. A Nd:YAG laser ((lambda) equals 1.06 micrometers , tFWHM equals 14 ns, E0 equals 0.015 J/pulse) was used with a fluence of 4 mJ/cm2 incident on the sample, the number of pulses being varied. Plasma treatments were performed in a plasma jet generated by a capacity coupled RF discharge in N2. Different analysis techniques were used to investigate the films, before and after the irradiation: X-ray diffraction, X-ray photoelectron spectroscopy and transmission electron microscopy. We followed the modification of their structure and composition as an effect of the laser/plasma treatment. A comparison with the excimer and also with the RF treatments was performed.