Spectroscopic study on the evolution of graphite ablation plume in ECR argon plasma during the deposition of diamond-like carbon films

A spectroscopic study of carbon plume produced by pulsed laser ablation of a graphite target in argon plasma generated by electron cyclotron resonance (ECR) microwave discharge has been carried out in an attempt to clarify the processes involved in ECR argon plasma assisted pulsed laser deposition of diamond-like carbon (DLC) films. Optical emission spectroscopy measurements show that the plume exhibits different behaviors in its space distribution and time evolution when produced and expanding in argon plasma compared with the plume in vacuum or low-pressure argon ambient. In vacuum or low-pressure argon ambient, lines from carbon atoms and ions dominate the plume emission. In argon plasma, the emission evolves from consisting of lines from carbon atoms and ions to being dominated by bands from dimer C₂, with the strong C₂ bands governing the plume emission at the later stages of the plume expansion. The differences in the plume emission reveal the different gaseous species composing the plumes expanding in different environments, suggesting the different gaseous precursors for film deposition by PLD with or without the assistance of argon plasma. It was also found that the emissions of C₂ Swan bands and C₂ Deslandres D'Azembuja bands exhibit different space distribution.     

Diamond-like carbon thin films prepared by ECR argon plasma assisted pulsed laser deposition

Diamond-like carbon films were prepared by pulsed laser ablation of graphite target in argon plasma produced from electron cyclotron resonance (ECR) microwave discharge and analyzed by Raman spectroscopy and Fourier transform infrared (FTIR) spectroscopy. The analysis shows that the films prepared with argon plasma assistance have different chemical structure compared with the films prepared in vacuum without plasma assistance. The structure of the films prepared with plasma assistance depends strongly on the bias voltages applied on the substrate. Surface morphology observation shows that the films prepared with argon plasma assistance have a smoother surface than the films prepared without plasma assistance. The re-sputtering of the growing film due to the bombardment of the plasma stream results in reduction of the deposition rate. The ablation plumes during film preparation with and without plasma assistance were examined through optical emission spectroscopy. In vacuum, emission lines from mono-atomic carbons and carbon ions dominate the plume emission. In argon plasma, the plume emission exhibits different behavior in its temporal and spatial evolution. It is initially dominated by strong lines from mono-atomic carbons and carbon ions and then evolves to consist mainly of emissions from C₂ molecules superposed on a featureless continuum. It is also found that the emission intensity of the C₂ molecules as well as the continuum varies with the bias voltages.     

Dependence of the composition and bonding structure of carbon nitride films deposited by direct current plasma assisted pulsed laser ablation on the deposition temperature

Carbon nitride films were deposited by direct current plasma assisted pulsed laser ablation of a graphite target under nitrogen atmosphere. Atomic force microscopy (AFM), Fourier transform infrared (FTIR), Raman, and X-ray photoelectron spectroscopy (XPS) were used to characterize the surface morphology, bonding structure, and composition of the deposited films. The influence of deposition temperature in the range 25–400 °C on the composition and bonding structure of carbon nitride films was systematically studied. AFM images show that surface roughness and cluster size increase monotonically with deposition temperature. XPS, FTIR, and Raman spectra indicate directly the existence of CN, CN, and CN bonds in the deposited films. The increase of deposition temperature results in a drastic decrease in the N/C ratio, the content of CN bond and N atoms bonded to sp³ C atoms, in addition to the increase in the content of disorder sp² C atoms and N atoms bonded to sp² C atoms in the deposited films. Raman spectra show that the intensity ratio of D peak over G peak increases with increasing deposition temperature to 200 °C, then decreases with the further increase of deposition temperature, which results from the continuous growth of sp² cluster in the films.     

Epitaxial aluminum nitride thin films grown by pulsed laser deposition in various nitrogen ambients

The effect of nitrogen ambient pressure on growth of AlN films has been examined. High-quality epitaxial AlN films were grown on (0001) sapphire substrates using pulsed laser deposition from a sintered AlN target in low nitrogen ambient of 9.0×10⁻⁵ Torr. The orientation of AlN films can be controlled by nitrogen pressure. AlN films are c-axis oriented when grown in a nitrogen pressure of 9.0×10⁻⁵ to 4.0×10⁻² Torr. Film orientation converted to a-axis as nitrogen pressure increased to 4.0×10⁻¹ Torr. The X-ray rocking curves of the AlN (0002) peak became narrower with decreasing ambient pressure and yielded a full width at half-maximum of 0.078°. The N/Al composition ratio increases with nitrogen pressure.     

Deposition of carbon nitride via hot filament assisted CVD and pulsed laser deposition

Bias-assisted hot filament chemical vapour deposition (HFCVD) and ion-assisted pulsed laser deposition (IA-PLD) have been employed to deposit carbon nitride films. Crystalline C-N films composed of - and β---C₃N₄, as well as some unpredicted C-N solids have been synthesized on Ni(100) substrates via HFCVD using a gas mixture of nitrogen and methane. The crystal constants of the - and β-C₃N₄ phases, obtained via X-ray diffraction, coincide well with those predicted theoretically; additionally, cone-shaped crystals are observed on the Si(100) substrates. Similarly, high density cone-shaped (Si)-C-N crystals have been obtained on Si(100) substrates via ion-assisted pulsed laser ablation of a carbon (graphite) target intersecting a nitrogen ion beam. Amorphous C-N films were also produced using this method.     

Temperature effect on the nitrogen insertion in carbon nitride films deposited by ECR

The impact of the temperature on the local structure of carbon nitride coating a-C_1-x N_x:H was investigated by spectroscopic analysis. A set of carbon nitride films were deposited at several substrate temperatures (77 K, 300 K, 673 K and 900 K) by electron cyclotron resonance (ECR) ion gun technique fed of CH₄/N₂ plasma.The films were in situ characterized by X-ray photoelectron spectroscopy (XPS). A drastic decrease of the nitrogen content was observed when increasing the deposition temperature from 77 K to 900 K. Qualitative structural and electronic changes were followed after air exposure by infrared (FTIR), near-edge X-ray absorption fine structure (NEXAFS) and Ultraviolet photoelectron (UPS) spectroscopy. Below 300 K, the films are hydrogenated with aliphatic structure and nitrogen is bonded to carbon in many kind of configuration. Between 300 K and 600 K, the nitrogen amount is reduced while both the aromatic and the aliphatic carbons increase. The local structure of the films radically changes at 900 K, whereas the nitrogen surrounding is the same at 673 K. In that case the hydrogen fraction into the films is reduced to zero. The increase of the sp³ carbon as well as the ratio π?/σ? on the nitrogen K edge can be observed. This behaviour may be explain by nitrogen substituted to sp² carbon which induces local changes in the distribution of the π? states.     

Optical properties of nickel-incorporated amorphous carbon film deposited by femtosecond pulsed laser ablation

The present study investigates the optical properties of Ni-incorporated amorphous carbon (a-C:Ni) films covering a wide range of Ni concentration from doping to alloys. The films are deposited by sequential femtosecond pulsed laser ablation of graphite and Ni targets. The optical properties are analyzed by means of the Maxwell-Garnett theory with separated metal and carbon phases. This analysis permits to investigate the change of the carbon phase with Ni concentration. It is shown that the microstructure of the carbon phase is affected by the Ni incorporation even at low Ni concentrations (1 at.%) where a local reorganization of the carbon matrix occurs affecting the aromatic clusters. At higher Ni concentrations the films become more disordered.     

Diamond-like carbon by pulsed laser deposition from a camphoric carbon target: effect of phosphorus incorporation

DLC thin films were grown by XeCl excimer pulsed-laser deposition (PLD) at room temperature using a camphoric carbon (CC) target. To carry out doping, CC soot was mixed with varying amounts (1–7% by mass) of phosphorus (P) powder. The resistivity was observed to increase initially for the films deposited from a target containing 1% P. The resistivity then decreased sharply at first, and gradually thereafter, for the films deposited from targets with a higher P content. Raman, optical gap and the electrical resistivity studies suggest that the P incorporation in carbon films results in controlled doping for the films deposited from targets containing up to 5% P, and a higher P content induces graphitization by narrowing the optical gap.     

Preparation and microstructure properties of tetrahedral amorphous carbon films by pulsed laser deposition using camphoric carbon target

The properties of tetrahedral amorphous carbon (ta-C) films grown by pulsed laser deposition (PLD) using camphoric carbon (CC) target and their respective effects of diamond percentages by weight in the target (Dwt.%) are discussed. Scanning electron microscopy (SEM), atomic force microscopy (AFM), Visible-Raman spectroscopy, Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS) analyses indicated that the Dwt.% noticeably modified the sp³ bonds content and the morphology of the ta-C films. The optical gap (E_g) and electrical resistivity (ρ) increase with Dwt.% up to 1.6 eV and 5.63×10⁷ (Ω cm), respectively, for the ta-C films deposited using target with higher of 50 Dwt.%. We found that the Dwt.% has modified the surface morphological, structural, bonding and physical properties of the camphoric carbon films.     

Growth of diamond nanocrystals by pulsed laser ablation of graphite in liquid

Nanocrystalline diamond has been successfully synthesized at room temperature and pressure using the novel technique of pulsed laser ablation (Nd:YAG, 532 nm) of a graphite target in water. High-resolution transmission electron microscopy (HRTEM), selected area electron diffraction (SAED), and laser Raman spectroscopy have been used to characterise the nanocrystals and to confirm that they are diamond. Time-averaged optical emission spectroscopy showed the presence of H, C and O atoms in the ablation plume. Imaging of the light emitted from the plume showed that H atoms were formed in two regions, in the liquid above the graphite surface, and also in the air just above the water surface. The results are consistent with the idea that atomic H is a necessary requirement for the growth of diamond via this method.     

Morphology,structure and density evolution of carbon nano-structures deposited by N-IR pulsed laser ablation of graphite

Carbon films were deposited by pulsed laser ablation on Si <100> substrates, heated at temperatures increasing from RT to 800 °C, from a pure graphite target, operating in vacuum (~ 10^− 4 Pa). The laser ablation was performed by an Nd:YAG laser, operating in the near IR wavelength (λ = 1064 nm).Micro-Raman and grazing incidence X-ray diffraction analysis (GI-XRD) established the progressive formation of ordered nano-sized graphitic structures, increasing substrate temperature. The surface morphology is characterised by macroscopic roughness (SEM, AFM) while the low temperature samples are characterised by very smooth surface. The film density, evaluated by X-ray reflectivity measurements, is also affected by the substrate temperature. This structural property modification induces relevant variation on the emission properties of carbon films, as evidenced by Field Emission measurements. The film structure and texturing is also strongly related to laser wavelength: the low energy associated to the IR laser radiation (1.17 eV) causes an early aromatic cluster formation at T = 400 °C associated to a sensible increase in the aromatic plane stacking distance (d₀₀₂ ~ 0.39 nm), compared to graphite. These density decrease shows a direct correlation with the electron emission properties. Roughness and presence of voids play a negative role both on the threshold electric field E_th and enhancement factor (β) The density decreasing and graphitic layer widening are notably to be ascribed to the very fast out-of-equilibrium growth and to the presence of large activated carbon species in the “plume”.     

Effect of target materials on crystalline carbon nitride film preparation by ion beam sputtering

In order to provide abundant chemical information, two novel bio-molecular target materials, instead of the conventional graphite target, were successfully developed to determine the possible formation mechanisms of carbon nitride during ion beam deposition. The azaadenine and adenine targets consist of carbonitro bonding, high N/C ratio as well as a six-fold carbonitro ring structure similar to that in hypothetical C₃N₄. Mass spectroscopy was used to determine the possible mechanisms of these two target materials. A lower electron beam energy at 75 eV was adopted to generate as abundant fragmental ions during the decomposition of these targets. Mass spectroscopy study on these two different targets indicates that the adenine target exhibits a more complex decomposition mechanism than the azaadenine target. However, the seven common hydrogenated carbonitro-species may suggest the same predominant mechanism during the decomposition of these two targets under the present deposition condition. The good correlation is one reason why two different targets can make almost the same quality crystalline carbon nitride films, including bonding, composition and structure.     

Synthesis of BCN thin films by nitrogen ion beam assisted pulsed laser deposition from a B4C target

Using sintered B₄C as target material, ternary BCN thin films were synthesized on Si(100) substrates by means of reactive pulsed laser deposition assisted by nitrogen ion beam. The composition, bonding configuration and crystalline structure of the synthesized films were characterized by X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy and transmission electron microscopy. The prepared films contain several bonds including B–C, N–C, B–N with B–C–N atomic hybridization. The ablation of the B₄C target results in the deposition of a film with B:C ratio about 3:1, deficient in boron compared with the target material. Nitrogen provided by the ion beam is incorporated in the film and bonded to boron and carbon. Heating of the substrate enhances the incorporation of nitrogen and influences the bonding configuration and crystalline structure of the film as well.     

Effect of temperature on sulfur-doped diamond-like carbon films deposited by pulsed laser ablation

In this study, S-DLC films were deposited using pulsed laser ablation of a novel sulfur-graphite (SG) mixture target using an ArF excimer laser (193 nm). The SG targets were made by mixing sulfur and graphite powders at different sulfur molar percentages from 0% to 25%. The S-DLC films were deposited at room temperature, 150 °C and 250 °C. The optical and electronic properties of the doped films were studied. Laser Raman spectroscopy indicated increased graphitic behavior with temperature but decreased with higher sulfur content. Spectroscopic ellipsometry analyses found that the optical band-gap energy, extinction coefficient and reflective index, clearly depended on deposition temperature and sulfur content. Hall Effect measurements indicated n-type carrier with concentration in the range of 1 × 10¹⁴ to 2 × 10¹⁷ cm^− 3, strongly depended upon the deposition temperature and amount of sulfur.     

Effects of nitrogen flow rate on titanium nitride films deposition by DC facing target sputtering method

TiN films were deposited onto a glass substrate by DC facing target sputtering, and the effects of N₂ flow rate on the film properties were investigated. Prepared TiN films had a rock salt (NaCl-type) structure with a very low resistivity (∼30 μΩ·cm) and gold-like color. Increase in the N₂ flow rate played an important role in controlling the properties of TiN films, such as Ti/N ratio and growth orientation. The growth orientation changed from a (111) phase to (200), with the ratio of N/Ti becoming near stoichiometric. The change in the growth orientation was caused by the increase in the N₂ flow rate, which weakens the kinetic energy of the bombarding particles. The observed phenomenon is explained by an energy loss in the reactive plasma due to the difference in the inner degree of freedom of the molecular gas causing the reduction in the effective energy for radicals.     

Electrochemical properties of Si thin film prepared by pulsed laser deposition for lithium ion micro-batteries

Si thin films were deposited directly on stainless steel substrates that act as current collectors using the pulsed laser deposition (PLD) technique. Amorphous Si films of different thicknesses were obtained at the Ar gas pressure of 5 × 10⁻⁵ Torr and a temperature of 500 °C but different deposition times. The microstructure and morphology of the films were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD) and atomic force microscopy (AFM). The anodic electrochemical performance of the films was examined in the range of 0.005-1.5 V, which revealed excellent cyclic stability without any large capacity fade up to the 70th cycle. The PLD process was suitable for improving the density and adhesion behavior of the films.     

WB2 to WB3 phase change during reactive spark plasma sintering and pulsed laser ablation/deposition processes

Reactive spark plasma sintering (SPS) of WB₂/WB₃ ceramics from elements is studied; the sintering pressure dependence of the ratio of WB₃ to WB₂ in samples produced by SPS is discussed. Regardless of the sintering pressure, the obtained samples are very hard ~20 GPa. WB₃ superhard films prepared by pulsed laser deposition (PLD) from selected SPS targets are presented.WB3 coatings were prepared on Si (100) substrates using a nanosecond, Nd:YAG laser operating at a 355 nm wavelength. The phase analysis, crystallography, and orientations have been studied using X-ray diffraction (XRD). A WB₂ to WB₃ phase transformation from 8.2% WB₃ in a sintered target to 93.3% WB₃ in a deposited film was observed. Additionally, the surface of a SPS sintered WB_x target after the ablation process was examined. XRD studies show that already during the laser ablation there is a significant WB₂ to WB₃ phase transformation. Vickers hardness of sintered samples was measured in macro- and micro-scale, and PLD films in the nanoscale.     

Fabrication and electrochemical characterization of zinc selenide thin film by pulsed laser deposition

High-quality crystalline ZnSe thin film has been successfully fabricated by using pulsed laser ablation of mixed target of Zn and Se. The physical, electrochemical and spectroelectrochemical properties of the as-deposited thin film at different substrate temperatures have been investigated by scanning electron microscopy (SEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), the charge/discharge, cyclic voltammetry (CV) and in situ absorbance spectra measurements. The thin film deposited at room temperature consisted of a mixture of Zn and Se. When the substrate temperature was elevated to 300 °C, the as-deposited thin film was composed of crystallized ZnSe. The cycle performance of ZnSe/Li cell is well than that of Zn-Se/Li cell. A couple of reduction and oxidation peaks at 0.51 and 1.4 V from CV curves of ZnSe/Li cell was found, indicating the reversible formation and decomposition of Li₂Se. Both classical alloying/dealloying processes and the partially selenidation/reduction of nano-sized metal zinc were proposed in lithium electrochemical reaction of ZnSe. The high degree of crystallinity in the zinc alloys and the slow kinetics should be responsible for a large irreversible capacity loss and poor cyclability.