Optical Emission Studies Research Articles

Effect of dilution gas on SiCN films growth using methylamine

Methylamine (CH 3NH 2) was employed with SiH 4 to deposit amorphous silicon carbon nitride films due to its easy dissociation as well as containing both carbon and nitrogen elements. The effect of dilution gas, such as H 2, N 2, Ar and He on the film growth was studied in electron cyclotron resonance plasma chemical vapor deposition (CVD) reactor. At a microwave power of 250 W and a substrate temperature of 700 °C, ternary silicon carbon nitride film has been successfully deposited using He as dilution gas. However, only binary silicon nitride films were formed using dilution gases of Ar, N 2 and H 2 but otherwise similar conditions. Characterization of the films using FTIR, XPS and optical emission study of the plasma were employed to study the growth process. Possible explanations and discussion for the growth behaviors of the dilution gases are presented.

Optical absorption and emission studies of 2 MeV Cu-implanted silica glass

It has been found that the chemical state of implanted ions in SiO 2 depends on local concentration and on the transport process of the implanted element. In this work we report the optical properties of high-energy Cu-implanted silica glass. 2MeV Cu + ions were implanted at room temperature (RT) in silica glass at fluences of 0.7, 3.0 and 5.0×10 16 ions/cm 2. The absorption spectra of the as-implanted samples indicated the formation of B 2 centers, but no Cu nanoparticles were formed. The photoluminescence (PL) spectra for excitation at 280 nm exhibited broad bands at 410 and 550 nm, associated with the presence of Cu + ions in the as-implanted samples. We discuss the effect of thermal annealing in air on the absorption and the emission spectra of these Cu-implanted samples, as well as the formation of copper nanoclusters from original Cu + ions.

Characterisation of pulsed-laser-deposited organic electroluminescent compounds for organic light-emitting diodes

A new UV-photopolymerisable anthracene-based compound has been pulsed-laser-deposited and then photochemically crosslinked to form a stable organic network in an electroluminescent device for the first time. Current-voltage and optical emission studies of similar anthracene-based compounds have also been employed to evaluate the laser-deposition technique. Electroluminescence emission and charge transport characteristics are comparable with devices fabricated using conventional spin-coating techniques.

Wavelength Dependence of Femtosecond Pulsed Laser Deposition of Zinc Oxide Films

We used 130-fs, 790-nm and frequency-doubled 395-nm laser pulses to study the wavelength dependence of femtosecond pulsed laser deposition of Al-doped ZnO films. The short wavelength pulses helped to increase deposition rates, decrease electrical resistivity of the films, and reduce droplets mixed into deposits. The transmission property of the films in the visible range was unchanged by the frequency doubling. The optical emission study showed a reduction of ion emissions and increase of kinetic energy when the 395-nm pulses were used.

Remote-plasma-enhanced reaction between a silicon surface and trifluoro-acetyl-fluoride gas

We propose reactive gases, which can be easily decomposed, as the etching gas to avoid “greenhouse effects.” In this article, the etching reaction between silicon and the trifluoro-acetyl-fluoride (CF3COF) gas is demonstrated, using a remote plasma at room temperature. The etching reaction is significantly enhanced by the addition of oxygen and remote-plasma excitation. The etch rate of silicon and oxide by CF3COF/O2 is larger than that by CF4/O2 and C2F6/O2 at the same O2 content. According to the optical emission study, however, the density of excited fluorine decreases in the plasma by the added oxygen into the CF3COF system. Photoelectron studies indicate that the major role of the additional oxygen is to remove the deposited fluorocarbon films from the surfaces.

Optical emission studies and neutral stream characterization of a surface reflection materials processing source

We report optical emission studies of the plasma source and measurements using heat flux and momentum analyzers of the fast neutral flux and energy in a low-energy surface-reflection neutral source. Both optical emission and Langmuir probe studies indicate a mode transition from a capacitively coupled mode to an inductively coupled mode as the rf power is increased. Spectroscopic actinometry shows that the atomic species resulting from molecular dissociation increase with increasing rf power. Changing the reflector bias changes the neutral energy without changing the discharge composition. The measured heat flux and momentum carried by the fast neutrals are used to derive the flux-weighted average velocity and the particle flux of the neutral stream. The measured neutral stream energy is found to be 4–6 eV. The neutral flux increases with the rf power. The measured neutral energy increases less than linearly with the reflector bias. This might be caused by the decreasing reflection efficiency of the reflector plate or a large collisional loss as the neutrals traverse the process region. The etch rates and cleaning rates calculated from the measured neutral flux and previously reported measured ashing and cleaning rates are in good agreement.

Electron-hole recombination in PbCl 2 : Tl crystals

A correlated ESR and optical emission study on samples doped with different concentrations of Tl + impurity ions shows the involvement of paramagnetic Pb 3+ 2 self-trapped electron centers (STEL) and trapped hole A centers in the electron–hole recombination responsible for the 2.6 eV blue-green luminescence.

Time-resolved vibrational and rotational emission analysis of laser-produced plasma of carbon and polymers

Optical emission studies of the C2 molecule and the CN radical in the plasma obtained by Nd:YAG laser ablation of graphite and polymers in atmospheric nitrogen and argon are presented. For the vibrational temperature (Tvib) determination of the plasma, the simultaneously measured band intensities of CN (Δv=−1, 0) and C2 (Δv=−1, 0, −1) (which were determined by a Time-Resolved Laser-Induced Breakdown Spectrometer) were used. The Tvib is calculated to be 10–13×103K. The calculation procedures and the differences are discussed in detail.

Optical emission study of ablation plasma plume in the preparation of diamond-like carbon films by KrF excimer laser

Optical emission study of the laser ablation plasma plume during the preparation of diamond-like carbon (DLC) films using KrF excimer (248 nm) pulsed laser deposition (PLD) has been carried out by means of a monochromator equipped with an intensified optical multichannel analyzer. In high vacuum (1×10−7 Torr), the emission lines from carbon ions of C+, C2+, and C3+ are observed in addition to atomic carbon emission lines, while no emission from the diatomic carbon molecule (C2) is observed. With increasing background nitrogen pressure up to 500 mTorr, the emission intensities of the C2 Swan band and the carbon nitride (CN) violet band increase. The diamond-like character of deposited DLC film degrades with background nitrogen pressure. The vibrational temperature of C2 and CN molecules decreases with the increasing of nitrogen pressure. The CN vibrational temperature for the first 2 μs after the laser pulse is very high and in agreement with the kinetic energy of monatomic carbon ions. The C2 vibrational temperature is as low as 0.6 eV and is consistent with the electron temperature of about 0.8–3.0 eV. It is conjectured that CN molecules are formed directly in reactions involving energetic ionic monatomic carbon, and that the formation of excited C2 molecules is the result of molecular recombinations of C atoms and ions. From the emission intensity measurements and the estimation of the vibrational temperature, it is suggested that the C2 molecule in the ablated plasma plume is not important, but energetic species, such as C+, are very important for producing high quality DLC films using PLD.

Reactive laser ablation of graphite in a nitrogen atmosphere: optical emission studies

A reactive laser ablation of graphite in a nitrogen atmosphere was investigated by optical emission analysis of the laser-induced plasma. Two emission bands of C 2 ( d 3 ∏ g → a 3 ∏ u , Swan band) and CN ( B 2 Σ +→ X 2 Σ + , Violet band) were observed. The vibrational and rotational temperatures of C 2 and CN molecules were deduced by simulation of the emission spectra. We examined the dependence of vibrational and rotational temperatures on the laser fluence and distance from the target to elucidate the expansion dynamics of the plume and formation mechanisms of C 2 and CN molecules.

Optical emission studies of laser ablated carbon plasma in a curved magnetic field

The laser produced carbon plasma in different regions of a curved magnetic field has been studied by emission spectroscopy. In addition to the ionic transitions CII, CIII, CIV; C 2 Swan bands are observed. The intensity of the C 2 Swan band is greatly enhanced when the magnetic field lines are convex to the moving plasma with the positive field gradient. The observed change in emission characteristics is attributed to the recombination of electrons due to the curvature gradient drift of the magnetic field.

Efficient Catalytic Plasma Activation of CO2, NO, and H2O

The activation of small molecules, such as CO2, NO, and H2O, has been achieved at atmospheric pressure via ac glow discharge methods in the presence of metal catalysts coated onto the electrode surfaces. A fan-type reactor having one rotating and one static electrode has been designed to diminish mass transfer effects. Time lapse photography of the emitting plasma intermediate species and optical emission studies have been used to monitor reaction pathways. Gas chromatography, mass spectrometry, and combined GC−MS methods have been used to monitor product distributions, selectivities, and activities. The effects of flow rate, input voltage, diluent gases, and metal coating have been systematically studied. Additionally, the mechanisms of CO2 decomposition and the role of the metal catalyst in that decomposition have been studied by optical emission spectroscopy.

Carbon nitride films deposited by reactive laser ablation

Carbon nitride films were deposited at 20, 250 and 500°C on 〈111〉 Si substrates by XeCl laser ablation of graphite in low pressure (1–50 Pa) N 2 atmosphere at fluences of 12 and 16 J/cm 2. Different diagnostic techniques (SEM, TEM, RBS, XPS, XRD) were used to characterize the deposited films. Films resulted plane and well adhesive to their substrates. N/C atomic ratios up to 0.7 were inferred from RBS measurements in films deposited at 20°C and 16 J/cm 2. Nitrogen concentration increases with increasing ambient pressure and laser fluence. The N 1s peak of the XPS spectra indicate two different bonding states of nitrogen atoms to C atoms, while the C 1s peak, apart from the two bonding states to nitrogen atoms, indicates one bonding state with regard to carbon atoms. XRD and TEM analyses point to an oriented microcrystalline structure of the films. Heating of the substrate results in a lower nitrogen concentration in respect of films deposited at 20°C in otherwise identical experimental conditions. Optical emission studies of the laser plasma plume indicate a correlation between the emission intensity of the CN radicals in the plume and the nitrogen atom concentration in the films.

Spatially resolved optical emission study of sputtering in reactive plasmas

The study of material sputtering under low-pressure reactive ion etching conditions in various gases (Cl2, SiCl4, O2) was performed using optical emission spectroscopy with high spatial resolution. Sputtering-induced secondary photon emission (atomic and molecular) from the processed materials (Si, Al2O3, GaAs) was found to be strongly localized near the target surface. A spatial distribution of atomic line emission intensity was shown to be essentially nonmonotonical with distance from the surface. This effect was explained by a cascade feeding from the upper lying atomic levels, which is enhanced in plasma (collisional) environment. A simplified model accounting for the cascading has been developed, and velocities of sputtered excited atoms (in the range of 2–7×106 cm/s) and molecules (about 2–5×105 cm/s) have been evaluated from the emission spatial decay parameters. The excited sputtered atoms and molecules are produced in different types of collisions. Fast excited atoms can be produced only in the first few collisions of the incident ion in the surface top layers, whereas excited molecules are knocked off by secondary (slow) atoms originated from a collision cascade inside the solid. Based on this concept of the process, simple expressions for atomic and molecular excitation yields as functions of the incident ion flux and surface coverage were deduced. The technique can be used for in situ surface probing during plasma processing.

Optical emission study of the laser plasma plume produced during diamondlike carbon thin film preparation

We have studied the application of the diamondlike carbon (DLC) film as a protective coating layer for high temperature superconducting thin films. Recently, the DLC film was proposed as an attractive material for field electron emitter device. We report on spectroscopic properties of the KrF laser plasma plume produced during the DLC thin film deposition. Optical emission measurements showed appearance of such neutral and ionic species as H, C, C +, CH, CH +, C 2H +. Strong emission from neutral and ionic molecules CH, C 2, C 2H + produced by the reaction in the gaseous phase has been observed with the ambient hydrogen gas pressure increase. The calculated velocities of CH and C 2H + molecules at the distances of 10–20 mm from the target are found to be 5.0×10 3 m/s and 9.1×10 3 m/s, correspondingly. The properties of the DLC thin films are strongly affected by the laser plasma plume dynamics. The DLC film deposited on MgO (100) at room temperature and 200 mTorr hydrogen pressure was almost transparent in the visible light range and had an optical band energy gap of 2.0 eV, which is about half of that of a diamond.

Plasma optical emission studies of high- Tc superconducting and buffer thin film physical vapour deposition

The non-intrusive technique of optical emission spectroscopy was used to identify the plasma species active in two different physical vapour deposition techniques: sputtering and laser ablation, when applied for high T c superconducting (HTSC) and buffer thin film deposition. Peak identification of the plasma optical emission spectra taken for targets of YBa 2Cu 3O 7 − x (YBCO), BiSrCaCu 2O 7 − x (BiSCCO 1112), Bi 2Sr 3Ca 3Cu 4O 7 −x( BiSCCO 2334), SrTiO 3, BaTiO 3, Y 2O 3-stabilized ZrO 2 (YSZ) and CeO 2 was made from published values and measured results for the constituting elements (Cu) and elemental oxides (Y 2O 3, BaCO 3, CuO). Aiming at determination of an appropriate criterion for in situ assessment of ambient oxygen sufficiency, the plasma optical emission was related to the deposited HTSC film characteristics. During YBCO RF single target off-axis sputtering and pulsed laser ablation the gas-phase preoxidation, witnessed by YO-optical emission, could be used as a qualitative criterion ensuring high quality film deposition. During dc magnetron sputtering with two-opposedtargets, the oxygen-to-argon peak actinometric ratio was used as a criterion instead. SEM investigation of the ablation-induced surface modification of targets of HTSC and buffer materials revealed specific topography for different target structure and density, which can influence the deposited film thickness uniformity. An extensive table is presented of the plasma emission lines and band heads for YBCO compiled from this work and that of other authors.

Optical emission studies of species in laser-produced plasma from carbon

Optical emission studies of molecules in plasma obtained by Nd:YAG laser ablation of graphite in a helium atmosphere are reported for irradiances in the range (1 - . The characteristics of the spectral emission intensity from the (Swan band) species have been investigated as functions of the distance from the target, ambient pressure and laser irradiance. Estimates of vibrational temperatures of species under various irradiance conditions are made. Results of measurements performed under different ambient helium gas pressures are also discussed.

Optical emission spectroscopy of the nitrogen arc in an arc-heated beam source used for synthesis of carbon nitride films

An exhaustive study of optical emission from a nitrogen arc produced by an arc-heated beam source is reported. Atomic nitrogen emission lines in the spectral region provide unequivocal evidence that the arc-heated beam source generates an appreciable flux of nitrogen atoms. Experimental results show that the ratio of [N] to increased as the arc pressure decreased. It is believed that this is because of the reduced probability of recombination of [N] atoms. Using this arc-heated beam source for pulsed laser deposition (PLD) film growth, we have synthesized carbon nitride and other nitride films with a high nitrogen content. AES and XPS results indicate that composition ratios ([N]/[C]) in the deposited films were between 0.2 and 0.6. It has been considered that [N] atoms, rather than molecules in the arc, are the most likely species responsible for the synthesis of nitride films.

Role of Ag in the Epitaxial Growth of Oxide Thin Films

ABSTRACTIn this paper, we have reported our investigations related to the growth of high temperature superconducting YBa2Cu3O7-δ (YBCO) and colossal magnetoresistive La0.7MnxO3-δ (LMO) thin films in presence of silver. The films were grown using pulsed laser deposition (PLD) techniques and characterized using x-ray diffraction, scanning electron microscopy, Squid magnetometer. The focus of our work is on the realization of significant improvement in microstructural and physical properties of these films by the addition of a common material (silver) to the films during their in-situ formation. Optical emission studies of plumes emanating from Ag target have been carried out to find the role of Ag acting as additional source of oxygen-supply to oxide lattices during film-growth.

Spatial and Temporal Behavior of a Laser Generated Titanium Plasma

Optical emission studies have been performed on the laser ablation of Titanium metallic targets. The high intensity radiation of a pulsed N2 laser (337.1 nm; 8 J/cm2) was focused onto the target to generate a short living (150 ns) plasma cloud that expands away from the surface into vacuum at high velocities. Time resolved measurements were taken as a function of the distance from the studied surface with a spatial rsolution of 20 µm, by collecting the emitted light in a direction perpendicular to the plasma expansion axis. A simple diffusion model with a “source” term is proposed to demonstrate the interaction of the laser beam with the plasma plume, as derived from analysis of the space-time behavior of several UV and visible atomic transitions.