Influence of nitrogen ion energy on the Raman spectroscopy of carbon nitride films

Carbon nitride films were deposited by filtered cathode vacuum arc combined with radio frequency nitrogen ion beam source. Both visible Raman spectroscopy and UV Raman spectroscopy are used to study the bonding type and the change of bonding structure in carbon nitride films with nitrogen ion energy. Both C–N bonds and CN bonds can be directly observed from the deconvolution results of visible and UV Raman spectra for carbon nitride films. Visible Raman spectroscopy is more sensitive to the disorder and clustering of sp² carbon. The UV (244 nm) Raman spectra clearly reveal the presence of the sp³ C atoms in carbon nitride films. Nitrogen ion energy is an important factor that affects the structure of carbon nitride films. At low nitrogen ion energy (below 400 eV), the increase of nitrogen ion energy leads to the drastic increase of sp²/sp³ ratio, sp² cluster size and C---N bonds fraction. At higher nitrogen ion energy, increase leads to the slight increase of CN bonds fraction and sp² cluster size, slight decrease of C---N bonds fraction and sp²/sp³ ratio.     

Deposition of carbon nitride films by filtered cathodic vacuum arc combined with radio frequency ion beam source

Atomically smooth carbon nitride films were deposited by an off-plane double bend filtered cathodic vacuum arc (FCVA) technique. A radio frequency nitrogen ion source was used to supply active nitrogen species during the deposition of carbon nitride films. The films were characterized by atomic force microscopy (AFM), XPS and Raman spectroscopy. The internal stress was measured by the substrate bending method. The influence of nitrogen ion energy (0–1000 eV) on the composition, structure and properties of the carbon nitride films was studied. The nitrogen ion source greatly improves the incorporation of nitrogen in the films. The ratio of N/C atoms in the films increases to 0.40 with an increase in the ion beam energy to 100 eV. Further increase in the ion beam energy leads to a slight decrease in the N/C ratio. XPS results show that nitrogen atoms in the films are chemically bonded to carbon atoms as C---N, C=N, and CN bonds, but most of nitrogen atoms are bonded to sp² carbon. The increase in nitrogen ion energy leads to a decrease in the content of nitrogen atoms bonded to sp² carbon, and an increase in the content of nitrogen atoms bonded to sp³ and sp¹ carbon. Raman spectra indicate an increase in the sp² carbon phase in carbon nitride films with an increase in nitrogen ion energy. The increase in sp² carbon fraction is attributed to the decrease in internal stress with increasing nitrogen ion energy.     

The carbon nitride films prepared at various substrate temperatures by vacuum cathodic arc method

Carbon nitride films have been grown by vacuum cathodic arc method in the substrate temperature range of 100–500 °C. The bonding structure of the films was investigated by X-ray photoelectron spectroscopy (XPS), Raman spectroscopy and infrared (IR) spectroscopy. With increasing substrate temperature, the films indicate various characteristics. At 100 °C, it can be described as a network similar to DLC in which aromatic sp²C phase is cross-linked by sp³C phase. Between 200 and 400 °C, with increasing substrate temperature the films become graphitized and the sp²CN phase increases, meanwhile the non-aromatic sp²CN phase appears at the edges of aromatic clusters in planar position as well as in out-of-planar regions. While at 500 °C the non-aromatic sp²CN phase almost comes to the same level as the aromatic sp²CN phase. So in the network of the film the aromatic sp²C phase is cross-linked by the non-aromatic sp²C phase. Based on the variation of the microstructure of the films, a comprehensive assignment pattern for the XPS C1s and N1s at different substrate temperature is proposed. In addition, the interpretation of p electron band in valence band spectra at various substrate temperatures is also discussed.     

Characteristics of carbon films prepared by plasma-based ion implantation

A series of carbon films have been prepared by plasma-based ion implantation (PBII) with C on pure Al and Si. Emphasis has been placed on the effect of implanting voltage on the characteristics of these films. The structures of the films were analyzed by X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy. The morphologies were observed by atomic force microscope (AFM). Surface hardness and electrical resistivity were also measured. The results indicate that the characteristics of these films are strongly dependent on the implanting voltage. An implanting voltage threshold value ranging from 3 to 5 kV starts to form a C-substrate transition layer owing to C⁺ ions implanted into the substrate. The transition layer exhibits a gradual change in composition and structure and effectively connects the carbon film and the substrate. Also, an implanting voltage threshold value ranging from 5 to 10 kV starts to form diamond-like carbon (DLC) films. An increasing voltage causes the resultant DLC films to be smoother and more compact. Moreover, Raman spectrum, chemical state of C1s, surface hardness and electrical resistivity all prove an optimum voltage of approximately 30 kV corresponding to the lowest ratio of sp²/sp³.     

液相沉积类金刚石膜的沉积机理研究

根据电化学的相关理论,提出了钛合金表面液相沉积DLC膜的反应机理,给出了可能电极过程,认为膜是通过甲基阳离子的亲电取代反应而不断生长。讨论了氢原子对金刚石结构的稳定作用,并解释了实验条件对膜结构和性能的影响。     

两电极电化学沉积法制备FePt薄膜

采用电化学沉积法制备FePt薄膜。将氯铂酸、氯化亚铁按一定比例混合成溶液100 mL,调pH值为2.5,倒入三口烧瓶中,调节脉冲电源参数制备FePt薄膜,并通过XRD、SEM、VSM等研究薄膜的微观结构以及宏观磁性能。XRD分析表明,所制备的FePt薄膜具有面心立方(fcc)结构,在550℃热处理后转变为面心四方(fct)结构;SEM观察显示,薄膜表面颗粒呈类球形,其厚度约为5μm;VSM测试表明,所制备的FePt薄膜矫顽力趋近于0,呈现超顺磁性,热处理后其矫顽力为150 Oe,饱和磁化强度为30.78 emu/cm3。     

Structure and properties of ta-C films prepared by vacuum cathodic arc with an unbalanced external electromagnetic field

ta-C thin films were deposited by vacuum cathodic arc technology with an unbalanced external electromagnetic field. The intensity of the magnetic field was adjusted by changing coil current and its effect on structure and properties of ta-C films was studied. FEM simulation results showed that as coil currents increased, the transverse, normal magnetic field and the magnetic intensity from arc cathode to substrates holder gradually increased. The UBM system increases the magnetic field intensity of the entire vacuum chamber by mainly improving the normal magnetic flux density near the arc cathode. The surface morphology, microstructure, tribo-mechanical properties of ta-C films were analyzed by SEM, Raman spectrometer, XPS, 3D surface profiler, Nano-indentation and ball-on-disk tribometer. Results showed that as the coil current increased, the average target voltage increased from 21.14 V to 25.97 V and target power rose from 845 W to 1043 W. Changes of magnetic field affected the plasma in vacuum chamber and the number of ions reaching the substrates, which had significant influences on film structure and properties. With a proper magnetic field (at coil current of 4A), ta-C films perform the highest hardness of 58.8 GPa, and the highest sp³ content of about 71% with the lowest ratio of I_D/I_G (0.38). During the wear process, the transfer layer was formed by oxidation and graphitization of contact surfaces. High hardness provided good support for transfer film, which leads to a low wear rate.     

Field emission enhancement of amorphous carbon films by nitrogen-implantation

Effect of nitrogen-implantation on electron field emission properties of amorphous carbon films has been examined. Raman and X-ray photoelectron spectroscopy measurements reveal different types of C-N bonds formed upon nitrogen-implantation. The threshold field is lowered from 14 to 4 V/μm with increasing the dose of implantation from 0 to 5 × 10¹⁷ cm⁻² and the corresponding effective work function is estimated to be in the range of 0.01-0.1 eV. From the perspective of tetrahedron bond formation, a mechanism for the nitrogen-lowered work function is proposed, suggesting that both the nitrogen nonbonding (lone pair) and the lone-pair-induced carbon antiboding (dipole) states are responsible for lowering the work function and hence the threshold field.     

液相沉积类金刚石膜的结构与性能研究

探讨了液相沉积法制备类金刚石的新工艺,并采用XPS,Raman光谱和SEM等对所得膜的结构进行表征,证实所得的是类金刚石膜。液相沉积得到的类金刚石膜与钛合金基材之间具有较强的结合强度,并具有较低的摩擦系数和一定的耐磨损能力。     

High-efficient synthesis of double-walled carbon nanotubes by arc discharge method using chloride as a promoter

With trace halide as a promoter in an iron sulfide catalyst, relatively perfect structural integrity double-walled carbon nanotubes (DWNTs) have been synthesized in large quantity and high yield by arc discharge method. Scanning electron microscope (SEM), transmission electron microscopy (TEM), thermogravimetric analysis (TGA) and Raman spectroscopy were used for structural characterization and yield determination. The results revealed that halide was a crucial factor for selectively synthesizing high yield DWNTs. The detailed experimental parameters were systematically investigated. The possible role of halide in growth of DWNTs was discussed as well.     

Spectroscopic investigations of the microstructure changes induced by substrate temperature in nitrogen-substituted amorphous carbon thin films

The effect of substrate temperature (T_S) on the microstructure of amorphous nitrogen-substituted carbon thin films (a-C_1−xN_x) has been studied. The a-C_1−xN_x films were deposited on Si(1 0 0) using reactive radio-frequency (RF) magnetron sputtering of a high-purity graphite target in a pure nitrogen plasma using different RF powers and different substrate temperatures T_S. Combined Fourier transform infrared (FTIR), Raman spectroscopy and residual stress measurements are used to fully characterise the films in the as-deposited state. FTIR spectra showed the existence of NCsp² and CN triple bonding, and suggested the presence of N-Csp³ bonding in the deposited films. The analysis of the spectra versus T_S reveals two rearrangement mechanisms of the microstructure. Up to 150 °C, the reversion of NCsp² to N-Csp³ and CCsp²respectively, and the increase the connectivity of the C-C network for higher T_S. The Raman features reveals that this progressive graphitisation of the material, with increasing T_S, is accompanied by a high disorder form of Csp² sites. These results are used to describe the stress variation that accompanies nitrogen evolution within the deposited films.     

真空制冰过程中水滴动态特性

为研究真空制冰水滴温度影响因素并进行分析,搭建了真空制冰动态特性研究实验台,进行相关实验,采集了相关图像和实验数据。对采集的图像进行了定性分析。采集的实验数据主要是在不同环境温度、环境压力、供水水温、水质、粒径及水滴下落初速度等情况下水滴温度随时间的变化情况,并与模拟计算值一并进行了对比分析。分析得出环境温度、供水水温、下落初速度对其影响较小,而环境压力、水滴粒径对其影响较为明显,供水水质对其影响比较特殊,主要表现在液滴的最大过冷度上。     

Graphite particles in the diamond-like a-C films prepared with the pulsed arc-discharge method

Microparticle collection on the coating surface has been studied during the preparation of diamond-like amorphous carbon coatings with the pulsed arc-discharge method. The curved solenoid method was used for the particle filtering. The quality of the coatings was studied using profilometer, ESCA and SEM techniques and wear, friction and acid resistance tests. The coatings without and with filtering contained graphite particles (40% and less than 1% respectively) and the sp²/sp³-bonding ratios were 51% and 78% respectively. The acid resistance of the nonfiltered films was poor. On the contrary, in pin-on-disc experiments with both types of coating against polyethylene, steel and Al₂O₃ pins, no clear differences in the friction and wear measurements were observed.     

Quality optimization of Bi2212 films prepared by aqueous solvent sol-gel method with nonionic surfactants

In this paper, Bi2212 films were prepared on LaAlO₃(100) and SrTiO₃(100) substrates by the sol-gel method using Bi(NO₃)₃·5H₂O, Sr(NO₃)₂, Ca(NO₃)₂·4H₂O and Cu(NO₃)₂·3H₂O as raw materials. TritonX-100 (TX-100), fatty alcohol poly oxyethylene ether (AEO-9), poly (vinylpyrrolidone) (PVP) and poly (vinyl alcohol) (PVA) were used as surfactants, respectively, to improve the wettability between the sol and the substrate. When glycine and glycolic acid were used as complexing agents, these surfactants were stably miscible with the sols. The effects of different surfactant sol-gel systems on the wettability of substrates as well as the crystallinity, morphology, surface roughness and electrical transport properties of Bi2212 superconducting films were investigated. The results showed that flat and continuous c-axis epitaxial Bi2212 films were obtained using all these sol-gel systems. In particular, TX-100 and AEO-9 as surfactants showed stronger wettability of the sol-gel for both substrates. In addition, the films prepared using polymer surfactants PVP and PVA sol-gel systems showed less surface roughness. The same patterns were found in all the film samples prepared using precursor sols of different complexing agents, and all the films exhibited good electrical transport properties. This work lays a certain research foundation for the preparation of thin films by aqueous solvent sol-gel method. The method also shows great potential in terms of the stability of different sol-gel systems and the improvement of the wettability of different substrates.     

真空烘箱法测试肥料中游离水分的偏离分析及解决方法

采用真空烘箱法测定肥料中游离水分时,受箱体内水汽平衡的制约,测试结果易低于真实值。采用重设真空法能打破箱体内水汽平衡,降低真空烘箱箱体内空气相对湿度,当DZF6090真空烘箱样品水分总含量低于2.3 g时,重设真空3次,可保证结果的准确性。箱体内空气相对湿度23.5%可作为样品游离水分完全干燥的指示值。     

Boron doped amorphous carbon thin films grown by r.f. PECVD under different partial pressure

Boron doped hydrogenated amorphous carbon (a-C) thin films have been deposited by r.f.-plasma CVD with a frequency of 13.56 MHz at room temperature using pure methane as a precursor of carbon source mixed with hydrogen (H₂) as a carrier gas. The films were prepared by varying the r.f. power, different flow rates of CH₄, and partial pressure of mixed gas (CH₄/H₂) using solid boron as a target. The thickness, structural, bonding and optical properties of the as-deposited films were studied by Alpha step surface profiler, Raman, FT-IR, XPS and UV–visible spectroscopy. It was found that changing the deposition pressure in presence of solid boron dopant in the r.f. PECVD process has a profound effect on the properties of the deposited films, as evidenced from their Raman scattering and optical results. The grown p-C: B films were found very smooth and thickness in the range of 240 to 360 nm for 1 h deposition. Films deposited at lower pressure appear brownish color whereas those deposited at higher pressure appear pale yellowish. The as-deposited film is found to be dominated by sp² rather than sp³, which might be due to the formation of small crystallites. The optical band gap is found to be reduced from 2.601.58 eV as the partial pressure of CH₄/H₂ gas is reduced.     

Controlled glow to arc transition in sputtering for high rate deposition of carbon films

We achieve control over the transition from a magnetically confined (magnetron) glow discharge to an arc discharge operating on a carbon cathode by applying constant voltage square wave pulses. A power supply with rapid turn off at a chosen current set point is used to produce a mode with a high current magnetron discharge and no arc (the high power impulse magnetron sputtering or HIPIMS mode) or a high current magnetron discharge that includes a short lived cathodic arc with very high but controlled current density (mixed HIPIMS arc mode). The deposition rate in the mixed HIPIMS arc mode at a duty factor of less than 1% was found to be greater than for conventional r.f. sputtering. We have studied the properties of carbon films deposited using both modes. In the mixed mode, the films contain graphitic nanoclusters with a number density and a morphology that depends on the bias applied to the substrate. The nanoclusters in the films prepared with bias have a flattened shape with graphitic layers approximately parallel to the surface, consistent with energetic impact of a spherical cluster of graphitic material. The matrix of the films has a sp³ content of approximately 50%, significantly greater than that for a conventionally sputtered film, but with a much higher instantaneous deposition rate. For negative substrate bias values of greater than 80 V, the surface is smooth enough to make films of interest as wear resistant coatings.     

Large-scale synthesis and characterization of carbon spheres prepared by direct pyrolysis of hydrocarbons

Large-scale production of pure carbon spheres, with diameters from 50 nm to 1 μm, has been achieved via direct pyrolysis of a wide range of hydrocarbons, including styrene, toluene, benzene, hexane, cyclohexane and ethene, in the absence of catalyst. Specific systematic studies using styrene as the feedstock indicate that the sizes of the resulting of carbon nanospheres can be controlled quite well by adjusting the experimental conditions. The resulting materials have been fully characterized using SEM, TEM, AFM, HRTEM, EDX, elemental analysis, density measurement, XPS, FTIR, XRD, Raman, and TGA. The results show that the spheres, which are 99% carbon, consist of concentric incompletely closed graphitic shells. The dangling bonds on the edges of the shells result in high chemical reactivity.