Study on formation and shape of carbon nanotips depending on ion bombardment

Carbon nanotips were grown from carbon film deposited on silicon substrate by plasma-enhanced hot filament chemical vapor deposition. The carbon film and carbon nanotips were investigated by scanning electron microscopy and micro-Raman spectrometry, respectively. The results indicate that the carbon film is composed of amorphous carbon and the carbon nanotips are characteristic of nanographite, and their formation and shapes depend on ion bombardment strongly. Simultaneously, the number of forming the carbon nanotips is increased by the ion bombardment. Because there are ion deposition and sputtering-etching in the process of growing of the carbon nanotips, the theory related to ion deposition and sputtering was used to obtain their formation condition and analyze effects of the ion bombardment on their shapes and the number of forming them.     

等离子体增强热丝CVD生长碳纳米尖端的研究

用CH₄，NH₃和H₂为反应气体，利用等离子体增强热丝化学气相沉积系统在不同偏压电流的条件下制备了碳纳米尖端，并用扫描电子显微镜和显微Raman光谱仪对碳纳米尖端进行了研究.结果表明碳纳米尖端是石墨结构，随着偏压电流的增大，碳纳米尖端的顶角减小，生长速率增大.结合有关等离子体和溅射的理论，分析讨论了碳纳米尖端的形成和碳纳米尖端的生长随偏压电流的变化. 关键词： 碳纳米尖端 等离子体 化学气相沉积     

非晶碳氮纳米尖端的微结构和发光机理

利用等离子体增强热丝化学气相沉积系统,用CH₄、H₂和N₂为反应气体,在Si衬底上制备了碳氮纳米尖端。用扫描电子显微镜和显微Raman光谱仪对其进行了表征。在室温下测试了它的发光性能,发光谱由中心约为406 nm和506 nm的两条发光带组成。根据Raman散射谱,对其微结构进行了分析。结合非晶碳氮薄膜的结构和发光机理,分析了它的发光性能。     

a-C:N:H纳米尖端荧光产生的机理

用CH4,H2和NH3为反应气体,利用等离子体增强热丝化学气相沉积在沉积有碳膜的Si衬底上制备了a-C:N:H纳米尖端,并用扫描电子显微镜和微区Raman光谱仪对碳膜和纳米尖端进行了表征。结果表明:Raman谱中含有与碳和氮相关的峰,且纳米尖端的Raman谱比碳膜的Raman谱有很强的荧光背景。Raman谱中的峰说明沉积的碳膜和纳米尖端是a-C:N:H薄膜和a-C:N:H尖端。a-C:N:H纳米尖端的Raman谱中强荧光背景的产生表明其在激发光源照射的过程中发射了强荧光,对a-C:N:H纳米尖端产生强荧光的机理进行了探讨。     

电子回旋共振-射频双等离子体沉积氧化硅薄膜过程中的射频偏压效应

本文利用六甲基乙硅氧烷(HMDSO)和氧气(O2)为反应气体,利用微波电子回旋共振-射频双等离子体化学气相沉积法沉积氧化硅薄膜,并利用发射光谱对等离子体特性进行原位诊断.研究表明,RF偏压对氧化硅薄膜沉积速率和薄膜中的化学键结构产生有意义的影响.小的直流自偏压会略微提高沉积速率;但随着直流自偏压的增加,离子轰击效应及刻蚀作用加强,薄膜的沉积速率下降.在13.56MHz和400kHz两个不同射频频率条件下所沉积的薄膜中,O和Si的比例基本相同,均超过2∶1;但400kHz射频偏压下薄膜中的碳成分比例比13.56MHz条件下的要高得多.这可以归因为高的射频偏压的应用不仅可增强离子轰击效应,而且与体等离子体相互作用,使高活性的氧原子增多;而低频偏压的作用主要是增强离子轰击效应.     

质量分离低能离子束沉积碳膜及离子轰击效应

用质量分离的低能离子束沉积技术得到了非晶碳薄膜,X射线衍射、Raman谱以及俄歇深度谱的线形表明,此种非晶碳膜中镶嵌着金刚石颗粒.碳离子的浅注入是该碳膜SP³形成的主要机理.从一个侧面说明了化学气相沉积法中偏压预处理增加金刚石成核的主要原因是因为离子轰击效应. 关键词： 非晶碳 离子轰击 质量分离低能离子束     

Effect of Bias Voltage on Microstructure and Mechanical Properties of Nanocomposite ZrCN Films Deposited by Filtered Cathodic Vacuum Arc

Nanocomposite ZrCN films consisting of nanocrystalline ZrCN grains embedded in nitrogen-doped amorphous carbon film are deposited by filtered cathodic vacuum arc technology under different bias voltages ranging from 50to 400 V.The influence of bias voltage on the characterization and the mechanical properties of the ZrCN films are investigated by x-ray diffraction,x-ray photoelectron spectroscopy,scanning electron microscopy,transmission electron microscopy,Raman spectroscopy and nano-indentation.The bias voltage has a subtle effect on the ZrCN grain size,which is around 9.5 nm and keeps almost constant.A slight increase of the bias voltage induces a relatively high sp~3 fraction about 40%in N-doped amorphous C films but leads to the graphitization of the films under a higher voltage.The best mechanical property of the ZrCN film with the hardness of 41 GPa is obtained under the bias voltage of 200 V,indicating the positive effect of slight increase of ion bombardment on the hardness of the films.     

Modified π-states in ion-irradiated carbon

CVD polycrystalline diamond film, pulse laser-deposited (PLD) carbon film and highly oriented pirolitical graphite (HOPG) as reference, were modified by means of Ar⁺ ion bombardment and characterized by means of Raman scattering, transmission electron microscopy, electron-diffraction (TEM), reflected electron energy loss specroscopy (REELS) and X-ray photoelectron spectroscopy (XPS) techniques. It was found that the diamond was transferred to a carbon with halo-like morphology and disordered stack of graphene segments. Instead of the well-known electron energy loss peak of graphite at 6.5 eV, a new REELS peak appeared at 4-5 eV energies. The observed effect was explained by the modification of π-system in carbon films as a consequence of the formation of non-planar, nanometer-sized graphitic planes.     

Effects of total CH4/Ar gas pressure on the structures and field electron emission properties of carbon nanomaterials grown by plasma-enhanced chemical vapor deposition

The effects of total CH₄/Ar gas pressure on the growth of carbon nanomaterials on Si (1 0 0) substrate covered with CoO nanoparticles, using plasma-enhanced chemical vapor deposition (PECVD), were investigated. The structures of obtained products were correlated with the total gas pressure and changed from pure carbon nanotubes (CNTs) through hybrid CNTs/graphene sheets (GSs), to pure GSs as the total gas pressure changed from 20 to 4 Torr. The total gas pressure influenced the density of hydrogen radicals and Ar ions in chamber, which in turn determined the degree of how CoO nanoparticles were deoxidized and ion bombardment energy that governed the final carbon nanomaterials. Moreover, the obtained hybrid CNTs/GSs exhibited a lower turn-on field (1.4 V/μm) emission, compared to either 2.7 V/μm for pure CNTs or 2.2 V/μm for pure GSs, at current density of 10 μA/cm².     

Influence of NH beam bombarding energy on structural characterization and cell attachment of CNx coating

The carbon nitride (CN_x) coating with its novel properties will be excellent candidate for biomedical applications. CN_x coatings were prepared on the surface of Ti–6Al–4V by ion-beam-assisted deposition (IBAD) with different NHⁿ⁺ beam bombarding energies at low substrate temperature. The coatings were characterized by Scanning electron microscopy (SEM), Auger electron spectroscopy (AES), X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, and Fourier-transform infrared (FTIR) spectroscopy. The result showed that the wear-resistance of CN_x coatings was better at higher beam bombarding energy. The cell attachment tests also gave interesting results that CN_x coatings exhibited low macrophage attachment and provide desirable surface for the normal cellular growth and morphology of the fibroblasts. Structural analysis showed that NHⁿ⁺ beam bombardment at the energies of 300–400 eV could result in more nitrogen concentration and fraction of sp³CN bonds in the structure of CN_x coatings, which may be responsible for the improvement in the wear-resistance and the cell attachment.     

Lamp-assisted CVD of carbon micro/nano-structures using metal catalysts and CH2I2 precursor

Carbon micro/nanofibers and nanotubes were deposited via chemical vapor deposition (CVD) using CH₂I₂ precursor and different metal catalysts (Pd, Ni, Fe, Co and Mn) on Si (1 0 0) substrates. A versatile and low-cost IR lamp technique is employed to induce the deposition process. With this method carbon features could be obtained already at temperatures much lower than with common techniques. Palladium metal was deposited by laser-assisted CVD from a liquid solution of the ammine complex and the 3d metals by thermal evaporation. Large-scale periodicity of nano-sized metal catalysts, and subsequently of carbon deposits was obtained by using monolayers of polystyrene microspheres as mask. The carbon structures were analyzed by SEM and micro-Raman spectroscopy.     

C+2离子轰击聚乙烯合成C26晶体

C2^＋离子轰击聚乙烯合成了由C26分子六角形密堆积组成的一种新碳晶体对高分辨透射电子显微镜、电子衍射和飞行时间质谱的研究证实,构成晶体的C26分子具有笼状富勒烯结构。     

Composition and corrosion resistance of coatings on the basis of nitrides of titanium and chromium

Ti-Cr-N coatings were deposited on a low-carbon steel St3 substrate by overlapping of Ti and Cr plasma flows in residual nitrogen atmosphere using ion bombardment. Auger electron spectroscopy and X-ray diffraction were used to analyze the element and phase composition of the deposited coatings. It was established that, under constant deposition conditions (the arc current, gas pressure, bias voltage), coatings possess the fcc structure of a (Ti,Cr)N solid solution with uniform distribution of elements along the depth. The growth of the substrate bias voltage leads to an increase of titanium concentration in the coating due to changes in the interaction processes (condensation and sputtering) of the deposited materials with the substrate. Corrosion tests of the coatings and steel St3 were performed in acid (1 M H₂SO₄) and salt (3% NaCl) media. It was found that the corrosion processes progress less intensely in salt solution than in acid medium.     

ECR-PECVD制备SiO2薄膜中衬底射频偏压的作用

采用微波电子回旋共振等离子体增强化学气相沉积（ECR－PECVD）技术在单晶衬底上制备了SiO2薄膜,研究了射频偏压对薄膜特性的影响。通过X射线光电子能谱（XPS）、傅里叶变换红外线光谱（FTIR）、原子力显镜（AFM）和扫描隧道显微镜（STM）三维形貌图测量等手段,对成膜特性进行了分析。实验结果表明,通过改变射频偏压的参数来控制离子轰击能量,对ECR－PECVD成膜的内应力、溅射现象、微观结构和化学计量均有明显的影响。     

Raman-in-SEM,a multimodal and multiscale analytical tool: Performance for materials and expertise

The availability of Raman spectroscopy in a powerful analytical scanning electron microscope (SEM) allows morphological, elemental, chemical, physical and electronic analysis without moving the sample between instruments. This paper documents the metrological performance of the SEMSCA commercial Raman interface operated in a low vacuum SEM. It provides multiscale and multimodal analyses as Raman/EDS, Raman/cathodoluminescence or Raman/STEM (STEM: scanning transmission electron microscopy) as well as Raman spectroscopy on nanomaterials. Since Raman spectroscopy in a SEM can be influenced by several SEM-related phenomena, this paper firstly presents a comparison of this new tool with a conventional micro-Raman spectrometer. Then, some possible artefacts are documented, which are due to the impact of electron beam-induced contamination or cathodoluminescence contribution to the Raman spectra, especially with geological samples. These effects are easily overcome by changing or adapting the Raman spectrometer and the SEM settings and methodology. The deletion of the adverse effect of cathodoluminescence is solved by using a SEM beam shutter during Raman acquisition. In contrast, this interface provides the ability to record the cathodoluminescence (CL) spectrum of a phase. In a second part, this study highlights the interest and efficiency of the coupling in characterizing micrometric phases at the same point. This multimodal approach is illustrated with various issues encountered in geosciences.     

Secondary electron spectroscopy of platinum and carbon surfaces

The surfaces of platinum single crystals, of carbon deposits on platinum and of pyrographite are examined by secondary electron spectroscopy under 100 eV electron excitation. The spectra contain characteristic peaks in the range 0–30 eV, which are interpreted as band-like in origin. The effects of gas adsorption, of the reconstruction at Pt(100), of the temperature and of ion bombardment induced disorder are reported. The secondary electron spectrum provides a criterion for distinguishing between amorphous and graphitic carbon surfaces. By contrast with the Auger spectrum, it is sensitive to the degree of crystalline order at the surface over distances of 10–100Å.     

Magnetic nanotips: the realisation of an atomic-scale beam-splitter

We present the first realisation of ferromagnetic Fe nanotips. Studies of the field emitted beams of electrons and metallic ions above and under the Curie temperature T_c were made. We have observed a reversible splitting of the electron beams when the temperature crossed through T_c and multiple spot patterns for the emitted metallic ion beams. These phenomena were not observed with Fe microtips or non-magnetic nanotips and thus were correlated to a strong magnetic interaction at the atomic scale apex of the nanotips. The Fe nanotips constitute an atomic scale beam-splitter.     

锥形碳氮结构的发光性能

利用偏压增强化学气相沉积系统,以CH4、H2和NH3为反应气体,分别在沉积有钛膜和碳膜的Si衬底上制备锥形碳结构,并用扫描电子显微镜、X射线能谱仪和显微Raman光谱仪对其进行表征,结果表明所制备的样品为锥形碳氮结构.用显微Raman光谱仪对锥形碳氮结构在室温下的发光性能进行了研究,发光谱显示出中心在621,643,7...     

Raman scattering characterization of a carbon coating after low-energy argon ion bombardment

The characteristic of Raman scattering spectra of a carbon coating, which was modified by radio frequency argon plasma, has been investigated. The argon ion bombardment causes changes in the microstructure and amount of stress in the coating. Raman scattering spectra are discussed in terms of intensity, bandwidth and wavenumber. The evolvement of Raman spectra shows the following behavior with increasing bombardment time: the intensity changes of the disordered D band, amorphous D″ band and graphite G band could be separated into several stages; low-energy argon ion bombardment over a short period can reduce the number of defects in the carbon coating, while a larger bombardment period can increase the number of defects; the widths of the D and G bands both increase, while that of the D″ band decreases; the wavenumbers of all the three bands fluctuate according to the changes in electronic configuration and amount of stress in the carbon coating.     

Synthesis of C26 Crystallite Polyethylene by C2+ Ion Bombardment

A new form solid Carbon has been synthesized consisting of a hexagonal close packing of a26 molecules under energetic C₂₆ ion 2.4 MeV bombardment of ultra high molecular weight polyethylene. The beam current was about 150 mA and the total dose was 1×10¹⁶ ions cm^－2. The residual gas pressure in the irradiation chamber was 1.3×10^－4Pa during bombardment High-resolu-tion transmission electron microscopy, electron diffraction, and time-of-flight mass spectroscopy studies of the molecular packing confirm that the C₂₆ molecules have the Caged fullerene structure.