Carbon fractals grown from carbon nanotips by plasma-enhanced hot filament chemical vapor deposition

Carbon nanomaterials with different structures were prepared in a custom-designed plasma-enhanced hot filament chemical vapor deposition system using methane, hydrogen and nitrogen. They were investigated by scanning electron microscopy (SEM) and micro-Raman spectroscopy. The SEM images show that the smooth carbon nanotips are formed under a high bias current and the carbon fractals can grow from the tips of the carbon nanotips under a low bias current. The results of micro-Raman spectroscopy indicate that the graphitization of the carbon nanomaterials was improved by ion bombardment. Combined the ion bombardment, electric field enhancement and electron emission mechanisms, the formation model of the carbon fractals was suggested.     

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。     

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     

Study on the orientation of silver films by ion-beam assisted deposition

Low energy ion beam assisted deposition (IBAD) was employed to prepare Ag films on Mo/Si (100) substrate. It was found that Ag films deposited by sputtering method without ion beam bombardment were preferred (111) orientation. When the depositing film was simultaneously bombardment by Ar⁺ beam perpendicular to the film surface at ion/atom arrival ratio of 0.18, the prepared films exhibited weak (111) and (200) mixed orientations. When the direction of Ar⁺ beam was off-normal direction of the film surface, Ag films showed highly preferred (111) orientation. Monte Carlo method was used to calculate the sputtering yields of Ar⁺ ions at various incident and azimuth angles. The effects of channeling and surface free energy on the crystallographic orientation of Ag films were discussed.     

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     

On the possibility of synthesizing one-dimensional carbon during radiative carbonization of PVDF

The modification of x-ray photoelectron spectra (XPS) and C KVV spectra of a partially crystalline polyvinylidene fluoride (PVDF) film under the long action of soft x-rays and secondary electrons followed by argon ion bombardment of its surface is investigated. Deep radiative carbonization leads to the formation of carbynoid structures (chain carbon) on the PVDF surface. Hence, the carbon XPS of the carbonized sample differs from those obtained for graphite and PVDF. Ion bombardment shows the instability of the carbonized sample surface, giving rise to formation of sp ² hybrid bonds of carbon atoms. The obtained results are indirect experimental evidence that, before ion bombardment, sp-type bonds are dominant on the carbonized PVDF surface.     

Ripening of subsurface amorphous C clusters formed by low energy He ion bombardment of graphite

Surfaces of highly oriented pyrolytic graphite (HOPG) were bombarded with 100 eV and 500 eV He ions at ion doses of a few 10¹⁵ cm² and temperatures ranging from 300 K to 800 K. AFM images were recorded to investigate the topography of the surfaces after ion bombardment. Supplementary electron energy loss (EEL) and thermal desorption (TD) spectra were measured to determine the C sp² fraction of the bombarded surfaces and the amount of trapped He. The temperature at which He ion bombardment was performed had a drastic effect on the surface structure and topography of the targets on the angstrom-scale and micrometer-scale as well. At 300 K, limited defect atom transport revealed an amorphous but relatively flat HOPG surface. Bombardment at 400 K leads to a granular structure of small protrusions in micrometer-scale AFM images, however, without crystalline order on the surface. The protrusions are due to the formation of subsurface clusters of carbon formed by atoms displaced by ion irradiation. Towards higher temperatures during bombardment the clusters agglomerate and cause the surface layers to bend upwards in dome-like shapes. Simultaneously, the microscopic order of the graphite lattice recovers. At 800 K large areas of the top layer retain their order during bombardment, however, a small number of domes indicate that there still exist some subsurface C clusters. The cluster–cluster distance deduced from the dome distribution indicates that the clusters grow through a ripening process. Annealing of graphite at high temperatures subsequent to ion bombardment at low temperatures is much less effective for recovering the surface crystallinity than ion bombardment at high temperature.     

Mechanisms of nanoporous VN–Ar/He structure formation under high-energy ion bombardment

The initial stages of formation of VN–Ar/He nanocrystalline thin films that were obtained using ion beam-assisted deposition technology have been investigated. It has been shown that the vanadium deposition accompanied by mixed inert and reactive gas beam bombardment leads to the formation of a nanoporous structure. The electron microscopic data and computer simulation results prove that many different processes take place during film structure nucleation, in particular, metal atom deposition, gas–vacancy cluster formation, and their migration, growth and collapse with gas release. As a result, vacant and gas-filled pores with a diameter of 5–50 nm were created.     

Silicon nanotips formed by self-assembled Au nanoparticle mask

The Au nanoparticle monolayer is formed by self-assembly technology on the Si substrates terminated with different functional groups. Silicon nanotips were fabricated by a self-assembled gold colloidal particle monolayer as an etch mask. The silicon nanotips with high density and uniformity in height and shape were obtained using reactive ion etching (RIE). The Si nanotips on the surface of the 3-aminopropyltrimethoxysilane (APTMS)-treated Si substrate are less-ordered array and uniformity than 3-mercaptopropyltrimethoxysilane (MPTMS)-treated Si substrate at the same etching conditions. The ordered array and uniformity of Si nanotips on the APTMS-modified Si substrate was improved through heat-treatment. This result is implied the different functional groups on the Si surfaces could affect the formation of the Si nanostructures during RIE process. The uniformly nanotip pattern with height of >20 nm is obtained on the etched nanoparticle-coated Si substrate. This method can be applied to patterning a wide variety of thin film materials into tip arrays.     

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。     

Silicon enhanced carbon nanotube growth on nickel films by chemical vapor deposition

Silicon enhances carbon nanotube growth on nickel films by chemical vapor deposition using methane and hydrogen. Nanotube growth characteristic is significantly improved on nickel films patterned by argon plasma etching on silicon oxide layers. Auger electron spectroscopy shows that a reduced silicon phase forms in the surface silicon oxide layer by Ar ion bombardment used for patterning. The enhanced growth of carbon nanotubes could be ascribed to an oxygen removal effect by silicon in the process of synthesis.     

Room temperature deposition of amorphous SiC thin films using low energy ion bombardment

Silicon carbide (SiC) films are prepared by single- and dual-ion beam sputtering deposition at room temperature, respectively. An assisting argon ion beam (ion energy Ei=150 eV) bombards directly the substrate surface to modify the SiC film surface. The thin films are characterized by the Fourier transform infrared spectroscopy (FTIR) and the Raman spectra. With assisting ion beam bombardment, the density of the Si–C bond in the film increases. Meanwhile, the excess carbon or the size of the sp² bonded clusters and the amorphous Si (a-Si) phase decrease. These results indicate that the composition of the films is mainly Si–C bond. UV-vis transmission shows that the E_opt increases steadily from 1.85 eV for the amorphous SiC (a-SiC) films without bombardment to about 2.29 eV for those with assisting ion beam bombardment.     

Infrared spectra of carbon monoxide on evaporated nickel films: A low temperature thermal detection technique

A novel thermal detection scheme has been developed and combined with the techniques of rapid scan Fourier transform infrared spectroscopy to make sensitive, high resolution measurements of the vibrational spectrum of carbon monoxide molecules on evaporated nickel films. Adsorbed molecules are detected by attaching a germanium resistance thermometer to the sample, cooling the assembly to liquid helium temperatures, and measuring the temperature changes which occur when infrared radiation is absorbed. Spectra are presented for a range of CO coverages on an evaporated nickel film and a film damaged by ion bombardment. The positions, shapes, and intensities of the spectral lines from linear and bridge bonded CO molecules give information about the surface structure of the metal films and about the different ordered phases of the adsorbed molecules.     

K9和石英玻璃基片上Au膜真空紫外反射特性研究

采用离子束溅射法,分别在经过不同前期清洗方法处理过的K9及石英玻璃光学基片上,选择不同的镀膜参量,镀制了多种厚度的Au膜。对镀制的Au膜在真空紫外波段较宽波长范围内的反射率进行了连续测量。测试结果表明:辅助离子源的使用方式、Au膜厚度对反射镜的反射率有重大影响。基片材料、镀前基片表面清洗工艺等对反射率也有一定影响。采用镀前离子轰击,可显著提高Au膜反射率及膜与基底的粘合力;获得最高反射率时的最佳膜厚与基片材料、镀膜工艺密切相关。对经过离子清洗的石英基片,膜厚在30 nm左右反射率最高;比较而言,石英基片可获得更高的反射率;辅助离子源的使用还显著影响获得最高反射率时对应的最佳膜厚值,且对K9基片的影响更显著。     

Electron beam nanofabrication of ferromagnetic nanostructures in TEM

Electron beam (e-beam) fabrication of nanostructures by transmission electron microscopy (TEM) is rapidly developing into a top-down nanofabrication method for the sub-5 nm fabrication of structures that cannot usually be realised using resist based lithographic techniques or by the focused ion beam patterning methods. We describe the usage of a variety of e-beam shapes, including point and elliptical line focus, as well as a comparison of LaB₆ and field-emission guns (FEGs), to achieve versatile sculpting of nanodot arrays, nanobridges and nanotips. We operate our patterning on free-standing nickel (Ni) thin film laterally connected to a silicon (Si) substrate as well as to free-standing Ni nanotips, where we achieve a novel three-dimensional (3D) nano-sculpting methodology.     

离子轰击控制准直碳纳米管生长的研究

用CH₄,H₂和NH₃作为反应气体，利用等离子体增强热丝化学汽相沉积制备出准直碳纳米管，并用扫描电子显微镜研究了不同负偏压对准直碳纳米管生长的影响. 结果表明，随着负偏压的增大，准直碳纳米管的平均直径减小、平均长度增大. 由于辉光放电的产生，在衬底表面附近形成阴极鞘层，并在阴极鞘层内形成大量的离子和在衬底表面附近形成很强的电场. 离子在电场的作用下对衬底表面的强烈轰击将对准直碳纳米管的生长产生影响. 结合有关理论，分析和讨论了离子的轰击对准 关键词： 准直碳纳米管 离子轰击 负偏压     

Bombardment-induced tunable superlattices in the growth of Au-Ni films

Highly ordered superlattices are typically created through the sequential deposition of two different materials. Here, we report our experimental observation of spontaneous formation of superlattices in coevaporation of Au and Ni under energetic ion bombardment. The superlattice periodicities are on the order of a few nanometers and can be adjusted through the energy and flux of ion beams. Such a self-organization process is a consequence of the bombardment-induced segregation and uphill diffusion within the advancing nanoscale subsurface zone in the film growth. Our observations suggest that ion beams can be employed to make tunable natural superlattices in the deposition of phase-separated systems with strong bombardment-induced segregation.     

Optical and mechanical properties of alumina films fabricated on Kapton polymer by plasma immersion ion implantation and deposition using different biases

Alumina films are fabricated on Kapton polymer by aluminum plasma immersion ion implantation and deposition in an oxidizing ambient and the effects of the bias voltage on the film properties are investigated. Rutherford backscattering spectrometry (RBS) reveals successful deposition of alumina films on the polymer surface and that the O to Al ratio is higher than that of stoichiometric Al₂O₃. The thickness of the modified layers decreases from 200 to 120 nm when the bias voltage is increased from 5 to 20 kV. Our results indicate that higher bombardment energy may lead to higher crack resistance and better film adhesion. However, a higher sample bias degrades the optical properties of the films as indicated by the higher absorbance and lower energy band gap. Therefore, the processing voltage must be optimized to yield a protective layer with the appropriate thickness, superior optical properties, as well as high crack resistance.     

Electron irradiation induced reduction of magnesium chloride thin films deposited on gold: XPS and ISS study

The ion and electron beam stimulated desorption from MgCl₂ ultra-thin films is reported. The films are prepared by gas phase deposition of MgCl₂ on a polycrystalline Au foil in ultra-high vacuum conditions. The MgCl₂ film, held at 330 K, is uniformly bombarded with Ar-ions or electrons of 1 keV of energy. The chemical composition of the film is monitored by XPS and ISS. The ionic film surface is terminated by Cl atoms, as shown by ISS. The ion bombardment sputters the MgCl₂ film, without changing the chemical composition of the film surface. In contrast, the electron beam damages markedly the film, with the reduction of Mg²⁺ to the metallic state. Only 10% of the original Cl is left in the film after 30 min of electron bombardment. The ISS analysis shows that Mg atoms appear on the film surface after electron irradiation.     

Note on the formation of surface carbides

Features of the effect of ion bombardment and its influence on the composition of solid surfaces are considered. During ion bombardment, not only does cleaning (sputtering) of the surface take place, but the formation of carbides through the implantation of carbon from contamination also occurs. Such species were recognized clearly from their chemical shifts of XPS on intermetallic compounds, namely LaNi₅, CaNi₅, TiFe, MgaNi and Mg₂Cu and on the hydride Mg₂NiH₄. These surface carbides, for example, can seriously restrict data analysis owing to their contribution to the core level alterations, and the rate of sputtering owing to their extreme hardness. However, ion bombardment would serve as an unusual method of preparation of some compounds which cannot be obtained by conventional means. Types of problems, methods and results of their investigation are described.