Electrochemical corrosion behavior of amorphous carbon nitride thin films

The corrosion behavior along with biocompatibility and mechanical properties plays an important role in determining of biomedical implants feasibility. Diamond-like carbon seems to be the promising material in which all these three requirements can be achieved. In this study nitrogen doped amorphous carbon (a-C:N) films were deposited on silicon and medical CoCrMo alloy substrates by vacuum glow discharge sputtering technique using different deposition conditions from graphite target. Potentiodynamic polarization tests were employed to assess the corrosion performances of the films at room temperature in 0.89 wt. % NaCl solution. The influence of substrate bias on the electrochemical corrosion behavior was investigated. The highest value off E_corr for CoCrMo substrate was measured on the coating deposited with substrate bias around −0.6 kV. The shift of E_corr to more positive values was about 350 mV.     

CHN薄膜化学结构和成分分析

采用外置式电容耦合低压等离子化学气相沉积法制备非晶CHN薄膜.X射线光电子能谱仪分析表明薄膜表面C、N和O的相对含量比,同时随着N2/CH4比例增大,薄膜中N元素的含量逐渐增加;并且对薄膜中存在的C-N共价键进行了讨论;傅里叶红外透射光谱分析表明薄膜中存在C-N键和其他官能团;拉曼光谱分析表明随着N2/CH4比例增大,D峰和G峰的中心位置先远离然后靠近,并且D峰和G峰的面积比逐渐增加,源于薄膜无序度增加且逐渐趋于石墨化.     

Effects of oxygen annealing on gas sensing properties of carbon nanotube thin films

Carbon nanotubes (CNTs) thin films deposited by plasma enhanced chemical vapor deposition have been investigated as resistive gas sensors towards NO₂ oxidizing gas. Effects of air oxidative treatment dramatically influence the nanotubes’ electrical resistance as determined by volt-amperometric measurements. In particular the electrical measurements show that electrical behavior of the CNT films can be converted from semiconducting to metallic through thermal treatments in oxygen. The electrical response was then measured exposing the films to sub-ppm NO₂ concentrations (100 ppb in air) at 165 °C. Upon exposure to NO₂, the electrical resistance of CNTs was found to decrease. The obtained results demonstrate that nanotubes could find use as a sensitive chemical gas sensor for (a) the fast response accompanied by a high sensitivity to sub-ppm NO₂ exposure, and (b) the precise recover of the base resistance value in absence of NO₂ at a fixed operating temperature, likewise indicating that intrinsic properties measured on as prepared nanotubes may be severely changed by extrinsic oxidative treatment effects.     

过滤阴极真空电弧法制备四面体非晶碳薄膜

利用离面双弯曲过滤阴极其空电弧沉积系统，在Ф200mm单晶硅片上制备四面体非晶碳薄膜。利用Dectek3型表面轮廓仪检验膜厚均匀性(小于5％)，并利用扫描电子显微镜(SEM)、原子力显微镜(AFM)、激光拉曼光谱(Raman)、X射线光电子谱(XPS)以及纳米压痕(Nano—Indenter)仪器测试薄膜的性能和结构。结果表明：试验制备的薄膜是四面体非晶碳薄膜，其中sp^3键含量高达80％以上，薄膜表面纯净，几乎没有大颗粒的污染，表面粗糙度(Rq)小于0．3nm(取样面积1μm^2)，薄膜硬度可达50GPa，杨氏弹性模量高于550GPa。     

The deposition of amorphous carbon thin films for hard mask applications by reactive particle beam assisted sputtering process

In this work, amorphous carbon thin films for hard mask applications were deposited by a reactive particle beam (RPB) assisted sputtering system at room temperature. The deposition characteristics of the films were investigated as functions of operating parameters such as reflector bias voltage and RF plasma power. By spectroscopic ellipsometry, the decrease in the refractive index of films at the wavelengths of 633 and 248 nm was observed with the increasing plasma power. In Raman spectra, the positions of G line shifted to higher wavenumbers with increasing plasma power. When the reflector bias voltage increases, the deposition rate was increased but the positions of G line remained nearly unchanged.     

Plasma-enhanced chemical vapor deposition of nanocrystalline diamond

Nanocrystalline diamond films have attracted considerable attention because they have a low coefficient of friction and a low electron emission threshold voltage. In this paper, the author reviews the plasma-enhanced chemical vapor deposition (PE-CVD) of nanocrystalline diamond and mainly focuses on the growth of nanocrystalline diamond by low-pressure PE-CVD. Nanocrystalline diamond particles of 200–700 nm diameter have been prepared in a 13.56 MHz low-pressure inductively coupled CH₄/CO/H₂ plasma. The bonding state of carbon atoms was investigated by ultraviolet-excited Raman spectroscopy. Electron energy loss spectroscopy identified sp²-bonded carbons around the 20–50 nm subgrains of nanocrystalline diamond particles. Plasma diagnostics using a Langmuir probe and the comparison with plasma simulation are also reviewed. The electron energy distribution functions are discussed by considering different inelastic interaction channels between electrons and heavy particles in a molecular CH₄/H₂ plasma.     

Raman characterization of boron doped tetrahedral amorphous carbon films

Boron doped tetrahedral amorphous carbon films, having boron content from 0.59 to 6.04 at.%, have been prepared by a filtered cathodic vacuum arc system using boron mixed graphite targets. The influence of boron on the surface morphologies and microstructures of the films was studied by atomic force microscopy and Raman spectroscopy. The surface images showed that the irregular tops on the surface of the films tended to form larger clusters as boron content increased. The Raman spectra of the films were, respectively, deconvoluted using Gaussian and Breit-Wigner-Fano line shapes. The Raman parameters, including the intensity ratios, peak positions, peak widths and coupling coefficients, obtained from both line shapes were described and compared. It was found that both line shapes could produce consistent results except the peak widths of G bands. The major effect of boron introduction was to increase the clustering of the sp² phase in the films.     

Spectroscopic ellipsometry characterization of amorphous carbon and amorphous, graphitic and fullerene-like carbon nitride thin films

Carbon nitride (CN_x) and amorphous carbon (a-C) thin films are deposited by reactive magnetron sputtering onto silicon (001) wafers under controlled conditions to achieve amorphous, graphitic and fullerene-like microstructures. As-deposited films are analyzed by Spectroscopic Ellipsometry in the UV-VIS-NIR and IR spectral ranges in order to get further insight into the bonding structure of the material. Additional characterization is performed by High Resolution Transmission Electron Microscopy, X-ray Photoelectron Spectroscopy, and Atomic Force Microscopy. Between eight and eleven resonances are observed and modeled in the ellipsometrically determined optical spectra of the films. The largest or the second largest resonance for all films is a feature associated with C-N or C-C modes. This feature is generally associated with sp³ C-N or sp³ C-C bonds, which for the nitrogen-containing films instead should be identified as a three-fold or two-fold sp² hybridization of N, either substituted in a graphite site or in a pyridine-like configuration, respectively. The π→π? electronic transition associated with sp² C bonds in carbon films and with sp² N bonds (as N bonded in pyridine-like manner) in CN_x films is also present, but not as strong. Another feature present in all CN_x films is a resonance associated with nitrile often observed in carbon nitrides. Additional resonances are identified and discussed and moreover, several new, unidentified resonances are observed in the ellipsometric spectra.     

掺氮类金刚石薄膜激光退火的Raman光谱研究

采用功率密度分别为300,750和1500W／mm^2的氩离子激光器,对由射频等离子化学气相沉积（RF－CVD）法制备的掺氮类金刚石薄膜进行了激光退火处理。并用傅立叶红外吸收光谱和显微Raman等手段,对所得样品进行研究。结果表明：C－N键比C－H键更为稳定,一方面氮原子的引入制约了C－H键的生成,在激光退火中减少了因C－H键分解而引起薄膜的石墨化;另一方面生成的C－N键不易受热分解;因此随着氮含量的增加,薄膜中C－N成分增加,从而提高了类金刚石薄膜的热稳定性。     

Plasma-enhanced chemical vapor deposition of nanocrystalline diamond

Nanocrystalline diamond films have attracted considerable attention because they have a low coefficient of friction and a low electron emission threshold voltage. In this paper, the author reviews the plasma-enhanced chemical vapor deposition (PE-CVD) of nanocrystalline diamond and mainly focuses on the growth of nanocrystalline diamond by low-pressure PE-CVD. Nanocrystalline diamond particles of 200–700 nm diameter have been prepared in a 13.56 MHz low-pressure inductively coupled CH₄/CO/H₂ plasma. The bonding state of carbon atoms was investigated by ultraviolet-excited Raman spectroscopy. Electron energy loss spectroscopy identified sp²-bonded carbons around the 20–50 nm subgrains of nanocrystalline diamond particles. Plasma diagnostics using a Langmuir probe and the comparison with plasma simulation are also reviewed. The electron energy distribution functions are discussed by considering different inelastic interaction channels between electrons and heavy particles in a molecular CH₄/H₂ plasma.     

Thickness dependent electronic structure of ultra-thin tetrahedral amorphous carbon (ta-C) films

Microstructural properties of ultrathin (1-10 nm) tetrahedral amorphous carbon (ta-C) films are investigated by Near Edge X-ray Absorption Fine Structure (NEXAFS) spectroscopy, X-ray Photoelectron Spectroscopy, Raman spectroscopy and Atomic Force Microscopy (AFM). The CK-edge NEXAFS spectra of 1 nm ta-C films provided evidence of surface defects (C―H bonds) which rapidly diminish with increasing film thickness. A critical thickness for stabilization of largely sp³ matrix structure distorted by sp² sites is observed via the change of π*C═C peak behavior. Meanwhile, an increase in the film thickness promotes an enhancement in sp³ content, the film roughness remains nearly constant as probed by spectroscopic techniques and AFM, respectively. The effect of thickness on local bonding states of ultrathin ta-C films proves to be the limiting factor for their potential use in magnetic and optical storage devices.     

氟化非晶碳薄膜的低频介电性质分析

研究了电子回旋共振等离子体技术沉积的氟化非晶碳(α-C：F)薄膜的低频(10^2～10^6Hz)介电性质。发现α-C：F薄膜的低频介电色散随源气体CHF3／C6H6的比例、微波入射功率而改变。结合薄膜键结构的红外分析,发现薄膜中C=C相对含量的增大是导致低频介电色散增强的原因,而C—F相对含量的增大则使低频介电色散减弱。     

Deposition of polymeric nitrogenated amorphous carbon films (a-C:H:N) using electron cyclotron resonance CVD

In this paper the deposition of polymeric nitrogenated amorphous carbon (a-C:H:N) films from a mixture of hydrogen, methane and nitrogen, using the electron cyclotron resonance chemical vapor deposition (ECR-CVD) system is reported. Rutherford backscattering spectroscopy (RBS) and elastic recoil detection analysis (ERDA) measurements were used to determine the actual amount of nitrogen, carbon and hydrogen in the films. The results showed that there is insignificant change in the atomic concentration of C but a slight decrease in the atomic concentration of H with increasing N incorporation. A slight decrease in the amount of bonded H and an increase in the C=N bond was also observed as deduced from infrared (IR) absorption measurements. The optical gap was found to decrease and the Urbach band tail width increase at larger N₂ flow ratio. The conductivity increased by three orders of magnitude compared to that of films prepared in the absence of N₂. The results suggest that the observed C=N double bond effectively bridges the aromatic rings resulting in a delocalization of carriers.     

Deposition of amorphous hydrogenated carbon films on Si and PMMA by pulsed direct-current plasma CVD

A pulse-modulated direct-current methane plasma is used to deposit amorphous hydrogenated carbon (a-C:H) films on Si and polymethyl methacrylate (PMMA) substrates. The structure and mechanical properties of the films are examined by applying a negative pulse bias voltage of 0.5 to 3 kV to the substrate at a pulse bias period of 100 to 200 μs. The deposition rate on both Si and PMMA increases with increasing the net input power, independent of the pulse period. The Raman spectra demonstrate that the films on Si are diamond-like carbon (DLC), while those on PMMA are polymer-like or soft amorphous carbon because of higher crystallinity of the sp² phase and lower nanoscale hardness. The residual compressive stress of the films on PMMA is constantly low ranging from 0 to 2 GPa due exclusively to high flexibility of PMMA, which causes the easy relief of the stress and thus the density decrease in the films.     

Correlations between substrate bias, microstructure and surface morphology of tetrahedral amorphous carbon films

The microstructure and surface morphology of ta-C films deposited on p-type (1 0 0) single crystal silicon with the substrate negative bias varying from 0 to 2000 V by the filtered cathodic vacuum arc technology have been investigated by means of Raman spectroscopy and atomic force microscope. The optimal deposition process of sp³-rich ta-C films can be confirmed in light of the relations between the coupling coefficients or full-width at half-maximum and the substrate negative bias. The surfaces of these films are uniform and smooth and RMS surface roughness is less than 0.4 nm. At the lower energetic grades, the more the content of sp³ is in the film, the smoother the surface of the film is. The dependence of the surface morphology and the impinging energy of the species can be illustrated according to the subimplantation growth mechanism. Nevertheless at the high energetic grade, the impinging ions with appropriate energy sputter and smoothen the surface so that the roughness might be even lower than the one of the films with the richest sp³ component.     

Chemical vapor deposition of amorphous ruthenium-phosphorus alloy films

Chemical vapor deposition growth of amorphous ruthenium-phosphorus films on SiO₂ containing ∼ 15% phosphorus is reported. cis-Ruthenium(II)dihydridotetrakis-(trimethylphosphine), cis-RuH₂(PMe₃)₄ (Me = CH₃) was used at growth temperatures ranging from 525 to 575 K. Both Ru and P are zero-valent. The films are metastable, becoming increasingly more polycrystalline upon annealing to 775 and 975 K. Surface studies illustrate that demethylation is quite efficient near 560 K. Precursor adsorption at 135 K or 210 K and heating reveal the precursor undergoes a complex decomposition process in which the hydride and trimethylphosphine ligands are lost at temperatures as low at 280 K. Phosphorus and its manner of incorporation appear responsible for the amorphous-like character. Molecular dynamics simulations are presented to suggest the local structure in the films and the causes for phosphorus stabilizing the amorphous phase.     

Surface and bioproperties of nanocrystalline diamond/amorphous carbon nanocomposite films

Nanocrystalline diamond/amorphous carbon (NCD/a-C) nanocomposite films have been deposited by microwave plasma chemical vapour deposition from CH₄/N₂ mixtures. In order to investigate their suitability as templates for the immobilization of biomolecules, e.g. for applications in biosensors, four differently prepared surfaces, namely as-grown, hydrogen plasma treated, oxygen plasma treated, and chemically treated with aqua regia, have been thoroughly characterized by methods such as XPS, TOF-SIMS, AFM, and contact angle measurements. In addition, in order to investigate the affinity of these surface to non-specific bonding of biomolecules, they have been exposed to bovine serum albumin (BSA). It turned out that already the as-grown surface is hydrogen terminated; the degree of the termination is even slightly improved by the hydrogen plasma treatment. Reaction with aqua regia, on the other hand, led to a partial destruction of the H-termination. The oxygen plasma treatment, finally, causes a termination by O and OH, rather than by carboxylic acid groups. In addition, an increase of sp² bonded carbon is observed. All surfaces were found to be susceptible to attachment of BSA proteins, but the coverage of the hydrogen terminated was lower than that of the O-terminated film. The highest BSA concentrations were found for the aqua regia sample where the H-termination has been removed partially. Finally, our results show that even minor surface contaminations have a great influence on the BSA coverage.     

Structural and optical properties of Er implanted AlN thin films: Green and infrared photoluminescence at room temperature

In this work erbium ions were implanted into AlN films grown on sapphire with fluence range: (0.5-2) × 10¹⁵ at/cm⁻², ion energy range: 150-350 keV and tilt angle: 0°, 10°, 20°, 30°. The optical and structural properties of the films are studied by means of photoluminescence and Raman spectroscopy in combination with Rutherford backscattering/channeling (RBS/C) measurements. The photoluminescence spectra of the Er³⁺ were recorded in the visible and infrared region between 9 and 300 K after thermal annealing treatments of the samples. The emission spectrum of the AlN:Er films consists of two series of green lines centered at 538 and 558 nm with typical Er³⁺ emission in the infrared at 1.54 μm. The green lines have been identified as Er³⁺ transitions from the ²H_11/2 and ⁴S_3/2 levels to the ⁴I_15/2 ground state. Different erbium centers in the matrix are suggested by the change of infrared photoluminescence relative intensity of some of the emission lines when different excitation wavelengths are used. The relative abundances of these centers can be varied by using different implantation parameters. The Raman and RBS/C measurements show good crystalline quality for all the studied films.     

Optical properties of amorphous, erbium-doped yttrium alumino-borate thin films

In this paper, we report on the optical characterizations of erbium-doped yttrium alumino-borate glassy thin films prepared by the polymeric precursor and sol-gel routes and the spin-coating technique. High quality planar waveguides were produced by a multilayer processing of Y_1−xEr_xAl₃(BO₃)₄ compositions with x = 0.02, 0.05, 0.10, 0.30, and 0.50. Their optical properties were investigated using transmission, photoluminescence, and m-lines spectroscopy, whereas high resolution scanning electron microscopy (HR-SEM) was applied to check film thickness and surface homogeneity. The refractive indices determined from transmission and m-lines spectroscopy are in good agreement just like the film thickness measured by HR-SEM and transmission spectroscopy. We observed low propagation losses, together with efficient photoluminescence emission for polymeric precursor thin films, involving low cost and environment friendly reactants.