Diamond-like phase formation in an amorphous carbon films prepared by periodic pulsed laser deposition and laser irradiation method

Diamond-like carbon (DLC) films were fabricated by pulsed laser ablation of a liquid target. During deposition process the growing films were exited by a laser beam irradiation. The films were deposited onto the fused silica using 248 nm KrF eximer laser at room temperature and 10⁻³ mbar pressure. Film irradiation was carried out by the same KrF laser operating periodically between the deposition and excitation regimes. Deposited DLC films were characterized by Raman scattering spectroscopy. The results obtained suggested that laser irradiation intensity has noticeable influence on the structure and hybridization of carbon atoms deposited. For materials deposited at moderate irradiation intensities a very high and sharp peak appeared at 1332 cm⁻¹, characteristic of diamond crystals. At higher irradiation intensities the graphitization of the amorphous films was observed. Thus, at optimal energy density the individual sp³-hybridized carbon phase was deposited inside the amorphous carbon structure. Surface morphology for DLC has been analyzed using atomic force microscopy (AFM) indicating that more regular diamond cluster formation at optimal additional laser illumination conditions (∼20 mJ per impulse) is possible.     

Structure and elastic recovery of Cr-C:H films deposited by a reactive magnetron sputtering technique

Cr-containing hydrogenated amorphous carbon (Cr-C:H) films were deposited on silicon substrates using a DC reactive magnetron sputtering with Cr target in an Ar and C₂H₂ gas mixture. The composition, bond structure, mechanical hardness and elastic recovery of the films were characterized using energy dispersive X-ray spectroscopy, X-ray photoelectron spectroscopy, Raman spectroscopy and nano-indentation. The film tribological behavior was also studied by a ball-on-disc tribo-tester. The results showed that the films deposited at low C₂H₂ flow rate (<10 sccm) presented a feature of composite Cr-C:H structure, which consisted of hard brittle chromium carbide phases and amorphous hydrocarbon phase, and thus led to the observed low elastic recovery and poor wear resistance of the films. However, the film deposited at high C₂H₂ flow rate (40 sccm) was found to present a typical feature of polymer-like a-C:H structure containing a large amount of sp³ C-H bonds. As a result, the film revealed a high elastic recovery, and thus exhibited an excellent wear resistance.     

Structural and optical properties of Fe-doped hydrogenated amorphous carbon films prepared from trans-2-butene by plasma enhanced metal organic chemical vapor deposition

Fe-doped hydrogenated amorphous carbon (a-C:H:Fe) films were deposited from a gas mixture of trans-2-butene/ferrocene/H₂ by plasma enhanced metal organic chemical vapor deposition. X-ray photoelectron spectroscopy, Fourier transform infrared spectra and Raman spectra were used to characterize the composition and the bonding structure of the a-C:H:Fe and a-C:H films. Optical properties were investigated by the UV–visible spectroscopy and the photoluminescence (PL) spectra. The Fe-doped films contain more aromatic structures and C=C bonds than the undoped films. The sp ² carbon content and sp ² clustering of the films increase, and aromatic-like rings’ structures become richer after Fe-doping. The Tauc optical gap of the a-C:H:Fe films become narrower by 0.3 eV relative to the value of the a-C:H films. The PL peak shifts from 2.35 eV of the a-C:H films to 1.95 eV of the a-C:H:Fe films, and the PL intensity of the a-C:H:Fe films is greatly enhanced. A deep level emission peak around 2.04 eV of the a-C:H:Fe films is observed.     

辉光放电等离子体辅助XeCl准分子激光溅射沉积碳氮薄膜

利用直流辉光放电等离子体辅助的脉冲激光沉积技术在Si衬底上生长了碳氮薄膜.通过扫描电子显微镜、X射线衍射、X射线光电子能谱、俄歇电子能谱等多种手段,对薄膜的形貌、成分、晶体结构、价键状态等特性进行了分析和确定.结果表明,沉积薄膜为含有非晶SiN和晶态氮化碳颗粒结构,晶态成分呈多晶态,主要为α-C₃N₄相、β-C₃N₄相,晶粒大小为40—60nm.碳氮之间主要以C-N非极性共价键形式相结合. 关键词： 脉冲激光沉积 直流辉光放电 碳氮薄膜     

Irradiation of solid C60 films with pulsed UV-laser-light: Fabrication of a periodic submicron C60 structure and transformation of C60 into a different carbon phase

A thin solid C₆₀ film has been irradiated under a fix incident angle with pulsed UV light at the wavelength of 266 nm. With scanning electron microscopy and atomic force microscopy, a surface transformation of the irradiated films has been observed to a periodic surface structure at low laser fluences in air as well as in vacuum and to strong morphology changes at higher laser fluences only in air. For both structural transformations the occuring surface chemistry has been studied with Raman spectroscopy and X-ray photoelectron spectroscopy. In the case of the periodical lines, these results in addition to a detailed discussion of the existing models for laser induced surface structures have shown that the C₆₀ film remains a van der Waals solid but with much oxygen incorporation in the lattice and does not polymerize as it is known to happen during continuous wave irradiation. The case of strong morphology changes could be explained by detailed comparison of the obtained Raman and X-ray photoelectron spectroscopy data as the formation of a new carbon phase with diamond-like sp³ bondings through an oxygen-assisted fullerene cage opening.     

Raman characterization of the structural evolution in amorphous and partially nanocrystalline hydrogenated silicon thin films prepared by PECVD

Hydrogenated silicon (Si:H) thin films were obtained by plasma‐enhanced chemical vapor deposition (PECVD). Raman spectroscopy was used to investigate the structural evolution in phosphor‐doped n‐type amorphous hydrogenated silicon thin films, which were prepared under different substrate temperatures and gas pressures. Meanwhile, the effect of nitrogen doping on the structure of P‐doped thin films was also investigated by Raman spectroscopy. Moreover, the transition from the amorphous state to the nanocrystalline state of undoped Si:H films deposited through low argon dilution was studied by Raman spectroscopy, X‐ray diffraction, and transmission electron microscopy. The results show that Raman spectroscopy can sensitively detect the structural evolution in hydrogenated silicon thin films deposited under different conditions in a PECVD system. Copyright © 2010 John Wiley & Sons, Ltd.     

Effect of nickel on the structure and bond type in amorphous diamond-like carbon films

Experimental data are presented from studies of the structure and bond type of carbon atoms in amorphous carbon-nickel films deposited from pulsed vacuum-arc discharge plasma sources. X-ray photoelectron spectroscopy was used. The characteristics of the plasmon loss spectra depend significantly on the deposition parameters. Carbon exists in a mixed sp²+sp³ hybridized state in the carbon–nickel films. The ratio of sp³/sp² carbon bonds increases when the nickel content is reduced (from 5.5 to 1.0 atomic %) and the deposition angle is increased. The structure closest to that of diamond was with a substrate bias voltage of –80 to –100 V and a deposition angle of 90°.     

The influence of ion irradiation on the structure and properties of amorphous carbon films

Presented in this work are the results of investigation of the structure and electrophysical properties of amorphous carbon films. The films were produced by sputtering of graphite by ion beam and usin ion irradiation (E=0–200 eV) during condensation process. The structure of i-C films has been studied by means of transmission electron microscope. The electron diffraction data have been interpretated by employing the calculated interference function of carbon clusters. The structure of V-band was obtained from AES by deconvolution method. Experimental data shows that under ion irradiation the transformation of short range order and electron bonds is an oscillating function of ion energy E. This paper presents a theoretical calculation of tunneling neutralization cross-section of Ar⁺ ions on carbon surface. The process also has an oscillating dependence on ion energy. A significant importance of inelastic processes in carbon phase transformation has been revealed.     

Structure and mechanical properties of low stress tetrahedral amorphous carbon films prepared by pulsed laser deposition

Tetrahedral amorphous carbon films have been produced by pulsed laser deposition, at a wavelength of 248 nm, ablating highly oriented pyrolytic graphite at room temperature, in a 10^-2 Pa vacuum, at fluences ranging between 0.5 and 35 Jcm^-2. Both (100) Si wafers and wafers covered with a SiC polycrystalline interlayer were used as substrates. Film structure was investigated by Raman spectroscopy at different excitation wavelength from 633 nm to 229 nm and by transmission Electron Energy Loss Spectroscopy. The films, which are hydrogen-free, as shown by Fourier Transform Infrared Spectroscopy, undergo a transition from mainly disordered graphitic to up to 80% tetrahedral amorphous carbon (ta-C) above a threshold laser fluence of 5 J cm^-2. By X-ray reflectivity roughness, density and cross-sectional layering of selected samples were studied. Film hardness as high as 70 GPa was obtained by nanoindentation on films deposited with the SiC interlayer. By scratch test film adhesion and friction coefficients between 0.06 and 0.11 were measured. By profilometry we obtained residual stress values not higher than 2 GPa in as-deposited 80% sp³ ta-C films. Received 25 June 2001     

Raman investigation of the electron-phonon interaction in n-type silicon nanocrystals

Silicon nanocrystals prepared in phosphorus-doped (at a concentration of 3.3 × 10²⁰ cm^?3) amorphous silicon films under pulsed irradiation with an excimer laser are studied using Raman spectroscopy and electron microscopy. The experimental data can be interpreted in terms of the Fano interference as a manifestation of the electron-phonon interaction effects in n-type silicon nanocrystals. It is assumed that a strong electron-phonon interaction (as compared to similar interactions in n-type bulk silicon) is due to the weakening of the momentum selection rules in nanocrystals.     

含氮氟化类金刚石(FN-DLC)薄膜的研究：(Ⅰ) sp结构与化学键分析

以CF₄，CH₄和N₂为源气体，利用射频等离子体增强化学气相沉积法，在不同功率下制备了含氮氟化类金刚石膜.用俄歇电子能谱、拉曼光谱、X射线光电子能谱和傅里叶变换红外光谱对薄膜的电子结构和化学键进行了表征，并结合高斯分峰拟合方法分析了薄膜中sp²，sp³结构比率.结果表明，制备的薄膜属于类金刚石结构，不同沉积功率下，薄膜内的sp²/sp³值在2.0—9.0之间，随着沉积功率的增加薄膜内sp²的相对含量增加.膜内主要有C—F_x(x=1，2)，C—C，C=C和C≡N等化学键.沉积功率增加，C—C基团增加，膜内F的浓度降低，C—F基团减少，薄膜的关联加强，稳定性提高. 关键词： 含氮氟化类金刚石膜 sp结构 化学键结构 射频功率     

Effect of ion bombardment on the phase composition and mechanical properties of diamond-like carbon films

It is established that the addition of hydrogen to methane in the reaction mixture upon the fabrication of diamond-like carbon films via the plasma-enhanced chemical vapor deposition method decreases residual stresses in the obtained films and significantly reduces their growth rate. The films were investigated via atomic force microscopy, Raman spectroscopy, and X-ray photoelectron spectroscopy. Irradiation of the prepared films with P⁺ and PF ₄ ⁺ ions results in strong sample swelling with increasing dose, as well as in a decrease in the compressive stress up to transition to tensile one reaching saturation. Moreover, the fraction of sp ³ bonds increases with increasing ion dose while the fraction of sp ² bonds decreases symmetrically with the processes proceeding faster upon irradiation with molecular ions. Qualitative mechanisms explaining the experimental results are proposed.     

脉冲偏压电弧离子镀CNx薄膜研究

用脉冲偏压电弧离子镀通过控制不同的氮流量在(100)单晶Si基片上制备了不同成分的CN_x薄膜.用光学显微镜,XPS,XRD,激光Raman和Nanoindenter等方法研究了薄膜的形貌、成分、结构和性能.结果表明,薄膜表面平整致密、氮含量随着氮流量的降低而降低、结构为非晶且为类金刚石薄膜;随着氮含量从18.9%降低到5.3%(摩尔百分比,全文同),薄膜的硬度和弹性模量单调增加而且增幅较大,其中硬度从15.0 GPa成倍增加到30.0 GPa;通过氮流量的调整能够敏感地改变薄膜中的sp³键的含量,是CN_x薄膜的硬度和弹性模量获得大幅度调整的本质原因. 关键词： x薄膜')" href="#">CN_x薄膜 脉冲偏压 电弧离子镀 硬度     

Direct observation of laser-induced crystallization of a-C:H films

The post-growth modification of diamond-like amorphous hydrogenated carbon a-C:H films by laser treatment has been studied by transmission electron microscopy and Raman spectroscopy. a-C:H films grown on Si substrates by benzene decomposition in a rf glow discharge were irradiated with 15 ns pulses of a KrF-excimer laser with fluences in the range of E=50–700 mJ/cm². At fluences below 100 mJ/cm² an increase in the number of graphitic clusters and in their ordering was evidenced from Raman spectra, while the film structure remained amorphous according to electron microscopy and electron diffraction observations. At higher fluences the appearance of diamond particles of 2–7 nm size, embedded into the lower crystallized graphitic matrix, was observed and simultaneously a progressive growth of graphite nanocrystals with dimensions from 2 nm to 4 nm was deduced from Raman measurements. The maximum thickness of the crystallized surface layer (400 nm) and the degree of laser annealing are limited by the film ablation which starts at E>250 mJ/cm². The laser-treated areas lose their chemical inertness. In particular, chemical etching in chromium acid becomes possible, which may be used for patterning the highly inert carbon films.     

Structure and tribological properties of amorphous carbon films deposited by electrochemical method on GCr15 steel substrate

Amorphous carbon films were deposited on GCr15 steel substrates by electrolysis of methanol, dimethylsulfoxide (DMSO) and the methanol-DMSO intermixture electrolytes, respectively, under high voltage and low temperature conditions. The microstructure and wear morphology of the deposited films were analyzed using X-ray diffraction (XRD), Raman spectroscopy and scanning electron microscopy (SEM) combined with energy dispersive X-ray fluorescence spectrometer (EDX), respectively. The tribological properties of the films were evaluated using a ball-on-disk rotating friction tester under dry friction condition. The results show that the films deposited by electrodeposition technique on GCr15 steel substrates are amorphous carbon films. It is also found that the electrolytes have an obvious influence on the tribological properties of the deposited films with the electrodeposition method. The tribological properties of the films deposited with the intermixture electrolyte are better than those of the films deposited by other pure electrolytes. The related growth mechanism of the films in the liquid-phase electrodeposition is discussed as well in this study. Via the reaction of the CH₃ groups with each other to form carbon network and reaction of the CH₃ and SO²⁺ groups to achieve the doping of sulfur atom in the carbon network, respectively, in other words, amorphous carbon films can be obtained on GCr15 steel substrates by electrodeposition technique.     

Synthesis of carbon nitride films by direct current plasma assisted pulsed laser deposition

Carbon nitride films were deposited by pulsed laser ablation of a graphite target under a nitrogen atmosphere at room temperature. A direct current discharge apparatus was used to supply active nitrogen species during the deposition of carbon nitride films. The composition and bonding structure of carbon nitride films were determined by Fourier-transform infrared (FTIR) spectroscopy and X-ray photoelectron spectroscopy. The incorporation of nitrogen atoms in the films is greatly improved by the using of a dc glow discharge. The ratio N/C can reach 0.34 at the discharge voltage of 400 V. Six peaks centered at 1025 cm^-1, 1226 cm^-1, 1381 cm^-1, 1534 cm^-1, 1629 cm^-1, and 2200 cm^-1 can be clearly distinguished from the FTIR spectra of the deposited films, which indicates the existence of C–N, C=N, and C≡N bonds. The fraction of sp² C, C≡N bonds, and C=N bonds in the deposited films increases with increasing discharge voltage. Deconvolution results of C 1s and N 1s spectra also indicate that nitrogen atoms in the films are chemically bonded to sp¹ C, sp² C, and sp³ C atoms. Most of the nitrogen atoms are bonded to sp² C atoms. Increasing the discharge voltage leads to a decrease of the fraction of nitrogen atoms bonded to sp² C and the fraction of amorphous carbon; however, it leads to an increase of the fraction of nitrogen atoms bonded to sp³ C and the fraction of sp² C and sp³ C atoms bonded to nitrogen atoms. Received: 7 June 2000 / Accepted: 19 February 2001 / Published online: 27 June 2001     

Optical and Structural Properties of Ammonia-Free Amorphous Silicon Nitride Thin Films for Photovoltaic Applications

Hydrogenated amorphous silicon nitride (a-SiN_x:H) thin films have been deposited through the green chemistry route using silane (SiH₄) and nitrogen (N₂) as process gases with SiH₄ flow being variable and N₂ flow being constant without the use of pollutant and corrosive ammonia (NH₃) by the plasma-enhanced chemical vapor deposition technique at 13.56 MHz. Fourier transform infrared spectroscopy analysis shows various possible vibrational modes of Si-H, Si-N, and N-H bonds present in the film. Raman spectroscopy is performed on these samples to calculate volume fractions corresponding to amorphous phases present in the a-SiN_x:H films. The refractive index (η) values are calculated using Swanepoel's method, which are in the range of 2.89 to 3.17. The thickness of the deposited films has been evaluated using transmission spectra. Absorption coefficient and band gap (E _g) values are obtained from optical absorption studies. An increase in the E _g and a decrease in the η value have been observed for the samples grown with decreasing SiH₄ flow.     

氮离子轰击能量对ta-C:N薄膜结构的影响

利用磁过滤真空阴极电弧技术制备了sp³键含量不小于80%的四面体非晶碳薄膜(ta-C), 然后通过氮离子束改性技术制备了氮掺杂的四面体非晶碳(ta-C:N)薄膜. 利用Raman光谱和X射线光电子能谱对薄膜结构的分析,研究了氮离子轰击能量对ta-C:N薄膜结构的影响. 氮离子对ta-C薄膜的轰击,形成了氮掺杂的ta-C:N薄膜. 氮离子轰击诱导了薄膜中sp³键向sp²键转化, 以及CN键的形成.在ta-C:N薄膜中,氮掺杂的深度和浓度随着氮离子能量的增大而增大. ta-C:N薄膜中sp²键的含量和sp²键团簇的尺寸随着氮离子轰击能量的增大而增加; 在ta-C:N薄膜中, CN键主要由C-N键和C＝N键构成, C-N 键的含量随着氮离子轰击能量的增大而减小,但是C＝N 键含量随着氮离子轰击能量的增大而增大.在ta-C:N薄膜中不含有C≡N键结构.     

Effect of concurrent electron irradiation on the structure of deposited carbon films

Carbon films 110–180 nm thick are fabricated on nickel substrates by the ion sputtering of graphite with simultaneous electron irradiation and subsequent ion irradiation. Irradiation leads to the formation of bonds in the films in various proportions due to the sp and sp ³ hybridization of orbitals (sp-and sp ³-bonds). Ion irradiation induces, to a greater extent, the formation of sp bonds, while concurrent electron irradiation increases the portion of sp ³ bonds. Electron and ion irradiation increases the film microhardness which reaches a value of 12 GPa. A model of the kinetics of creating carbon allotropes in a deposited film is proposed, which is based on the competition between the formation and breakage of carbon bonds during hybridization of different types. Electron and ion irradiation influence the probabilities of the formation and breakage of carbon bonds in the deposited film. The model provides a qualitative interpretation of the observed content ratios of carbon phases in the deposited film.     

Effect of phosphorus content on structural properties of phosphorus incorporated tetrahedral amorphous carbon films

With phosphorus incorporated tetrahedral amorphous carbon (ta-C:P) films prepared using filtered cathodic vacuum arc technique with PH₃ as the dopant source, we investigate the effect of phosphorus content on the structural properties of the films by X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy. XPS analysis indicates that a function is established between the atomic fraction of phosphorus in the samples and the flow rate of PH₃ during deposition, and that phosphorus implantation increases the graphite-like trihedral sp² bonds deduced from fitted C 1s and P 2p core level spectra. Raman spectra of a broad range show that there are two notable features for all ta-C:P films: the first-order band centered at about 1560 cm^-1 and the second-order band between 2400 and 3400 cm^-1. The broad first-order band demonstrates that the amorphous structure of all samples does not remarkably change when a lower flow rate of PH₃ is implanted, while a higher concentration of phosphorus impurity enhances the clustering of sp² sites dispersed in sp³ skeleton and the evolution of structural ordering. Furthermore, the second-order Raman spectra confirm the formation of small graphitic crystallites in size due to a finite-crystal-size effect. PACS 81.05.Uw; 81.15.Ef; 63.50.+x