Surface roughening under ion bombardment

Ion bombardment can cause roughening of a surface. Inadequate step coverage and poor adhesion of films on such surfaces are of concern. An extreme case of surface roughening results in cone formation under ion bombardment.The results of the investigation, using scanning electron microscopy, will be discussed in terms of the role of (a) embedded particles, (b) impurities and (c) surface migration in cone formation on the target surface.     

Nitrogen beam bombardment induce polarity of carbon nanotubes

The multiwalled carbon nanotubes (MWCNTs) were prepared on SiO₂ substrates using chemical vapor deposition (CVD). N ion beam bombardment to MWCNTs was performed at different beam currents of 5–15 mA in an ion-beam-assisted deposition (IBAD) system. Scanning electron microscope (SEM) and Transmission electron microscope (TEM) proved no significant crack and surface morphological change for MWCNTs after N ion beam bombardment. X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectrometry (FTIR), and Raman studies indicated that higher N ion beam current (15 mA) or N atomic concentration (8.6%) induced formation of polar N-containing functional groups of N–C and N–H bonds on the surfaces of MWCNTs. The content of N–C and N–H bonds increased with N ion beam current.     

Characteristic erosion of silica by oblique argon ion beam bombardment

Following previous work on the angular distribution of ejected particles, features of the oblique argon ion beam bombardment of fused silica were elucidated again but from a different aspect. Detailed observations were made of the erosion topographies of fused silica targets obliquely bombarded with partially neutralized argon ion beam at polar angles of 0°, 22.5°, 45° and 67.5° using scanning electron microscopy. The form of the erosion topography changed systematically from isolated circular etch pits at 0° to isolated crescent etch pits at 22.5° and continuous and homogeneous ripple structures at 45°. Scarcely any erosion pattern was found at 67.5°, except for rare band-like structures. Irrespective of the incidence angle of the beam these structures increased in size with total ion dose but their forms remained unchanged. Essentially the same phenomena were observed in the case of sintered SiO₂-5wt.%P₂O₅ and SiO₂-5wt.%B₂O₃ targets in spite of the fact that their surfaces were initially rougher than that of the fused silica target.     

The growth of amorphous and graphitic carbon layers under ion bombardment in an rf plasma

Methods of preparing C-films from energetic C-ions and from ion impact bombardment of hydrocarbon species are reviewed. It is shown that amorphous C-deposits resulting from impact damage can have dielectric properties and be exceptionally hard. The rf plasma technique used to grow a-C-films on a negatively biased target is described and the effects of temperature rise on structural change is followed using differential scanning calomimetry. The as-grown films contain absorbed hydrogen which produces compressive stress and is released to form gas bubbles at 400°C.     

Excited atom emission from metals under ion bombardment

In this paper the available models of excited atom emission from metals under ion bombardment are analysed and a new approach to solving the problem of finding the sputtered atom excitation probability is offered. At distances between a metal and an atom less than some critical distance the ‘metal-sputtered atom’ system is considered adiabatically. At the larger distances interaction between the metal and the atom is considered in terms of a weak perturbation which can excite the valence electron of the atom. The calculations of the probability of sputtered Al and Cu atom excitation and the radiation intensity for a number of spectral lines of these elements have been carried out.     

Study of the growth of carbon on targets during ion bombardment

The phenomenon of carbon growth on targets irradiated with MeV ions was studied as a function of various parameters: beam intensity, target temperature, nature of the target, nature of the incident ion. It is proposed that the observed phenomenon of carbon growth is due to the dissociation of hydrocarbons of the residual atmosphere, by thermal cracking and by the secondary electrons emitted by the targets. The dissociation is followed by polymerization at the beam spot and partial carbonization.     

A simple track structure model of ion beam radiotherapy

A simple radiotherapy ion beam calculation based on the cellular track structure model, using in vitro cell survival parameters fitted from recent experimental data, is presented. The calculation represents a single-fraction ion exposure (roughly corresponding to a 2 Gy fraction of megavolt X rays) and exploits concepts used in clinical radiotherapy, such as entrance, or 'skin' ion dose. The depth distribution of cells surviving their irradiation by a beam of 385 MeV amu(-1) carbon ions is calculated over the range of the stopping ions, as a sequence of track-segments, in the continuous slowing-down approximation. An interpretation of the 'clinical relative biological effectiveness' concept is suggested.     

Structure modifications of vertically grown carbon nanotubes by plasma ion bombardment

We report the structural modifications of vertically grown carbon nanotubes (VCNT) by plasma ion bombardments. The VCNT were grown by thermal chemical vapor deposition (CVD) using acetylene feedstock with iron catalyst and alumina supporting layers on silicon substrate. The plasma ion bombardments were performed using DC plasma enhanced CVD with parallel electrodes configuration. As a result, the height of the as-grown VCNT decreased with increasing applied bias voltages, plasma powers and working pressures. In addition, we observed the aggregated morphologies of the VCNT top surface after the plasma treatments which would be useful for field emission display and energy storage applications.     

A mechanism of surface micro-roughening by ion bombardment

The spatial distribution of sputter-etch effects is analysed theoretically under the assumption of random slowing-down of the bombarding ions. When a surface is bombarded at locally oblique incidence the most pronounced sputtering effect is likely to be observed not at the very point of impact, but further downstream. This effect may cause a significant reduction of the local sputtering yield on top of a spike or a ridge, and an increase on the bottom of a groove or a crater. As a consequence, small irregularities on a relatively smooth surface may be enhanced during bombardment. It is concluded that a microscopically flat surface is unstable under high-dose ion bombardment unless atom migration acts as a dominating smoothing effect. Conversely, sharp cones appear to be surprisingly stable under bombardment. Even on a clean surface, cones erode more slowly than a plane surface, provided that their dimensions are of the order of, or less than, the penetration depth of the ions.     

Low-energy ion beam bombardment of human cancer cells in vacuum to induce DNA transfection

A process of low-energy ion-beam-induced gene transfection in human cancer cells was developed for non-viral DNA transfection. The whole process included maintenance of the cells in vacuum, ion beam bombardment of the cells with optimized ion beam condition leading to a medium cell viability, and DNA transfer. A method of using a specially designed liquid-nitrogen cooled sample holder to house the cells and frozen medium to cover and protect the cells was adopted to maintain the cells viable in the vacuum condition during ion beam bombardment. Nitrogen ion beams with energy in the range 7–28 keV were used to bombard human cancer cells (HEp-2, the human laryngeal epitheloid cancer cell line) to fluence orders of 10¹⁵–10¹⁶ ions/cm². After ion beam bombardment, the cell viability was studied. The ion beam condition which resulted in a relatively medium viability of the cells was chosen to operate ion bombardment to induce gene transfection. To the viable cells, DNA transfection using plasmid DNA pEGFPN2 was carried out. The experiment demonstrated that under appropriately controlled ion beam conditions and freezing environment, the human cells could survive and be transfected with exogenous DNA. This technique could be used as an alternative of non-viral gene transfections with a promising efficiency.     

Direct ion beam deposited carbon films and clusters

Carbon films and clusters have been formed by direct ion beam deposition. In all experiments crystalline n-Si 〈1 0 0〉 wafers with the 300 nm thermal SiO₂ film have been used as substrates. Effects of thermally microstructured Ni and substrate temperature were studied. Chemical structure of the carbon films was investigated using Raman spectroscopy. Surface morphology was studied by atomic force microscopy (AFM). Supplemental research on sheet resistance of the films has been performed. Rough diamond-like carbon film was grown onto the catalytic layer at 400 K temperature, and surface of the diamond-like carbon film deposited directly onto the SiO₂ layer at 400 K temperature was very smooth. At 750 K growth of the array of cylindrically shaped clusters was observed by AFM in the case of catalytically assisted deposition. Raman spectra of deposited films were typical for glassy carbon and/or carbon nanotubes with the carbonaceous deposits. Catalyticless deposition at 750 K temperature resulted in the formation of the conductive polymer-like carbon film with the graphite clusters in it.     

Development of ion beam sputtering techniques for actinide target preparation

Ion beam sputtering is a routine method for the preparation of thin films used as targets because it allows the use of a minimum quantity of starting material, and losses are much lower than most other vacuum deposition techniques. Work is underway in the Isotope Research Materials Laboratory (IRML) at ORNL to develop the techniques that will make the preparation of actinide targets up to 100 μg/cm² by ion beam sputtering a routinely available service from IRML. The preparation of the actinide material in a form suitable for sputtering is a key to this technique, as is designing a sputtering system that allows the flexibility required for custom-ordered target production. At present, development work is being conducted on low-activity actinides in a bench-top system. The system will then be installed in a hood or glove box approved for radioactive materials handling where processing of radium, actinium, and plutonium isotopes among others will be performed.     

Homogeneously aligned liquid crystal display on silicon oxynitride thin film using ion beam bombardment

This paper introduces the homogeneously aligned liquid crystal (LC) display using ion beam (IB) bombardment of a new silicon oxynitride (SiON) alignment layer for the first time. The pretilt angle was shown to be a function of the IB incident energy, and possible mechanisms of LC alignment were investigated with physical and chemical methods. An X-ray photoelectron spectroscopy analysis showed that the LC alignment on the IB-bombarded SiON inorganic surface was due to the reformation of Si–O bonds as a major factor. The electro-optical characteristics were comparable to those of rubbed polyimide films.     

不同能量离子束辅助沉积对形成氮化钛薄膜性能的影响

用不同能量离子束辅助沉积方法在医用不锈钢317L和Si(100)基底上沉积TiN薄膜。通过X射线光电子能谱(XPS)、X射线衍射(XRD)和俄歇电子能谱(AES)分析研究了薄膜的结构特征;测试了薄膜与基底的附着力和耐磨性;用电化学腐蚀的方法检测了薄膜在Hank’s模拟体液中的耐腐蚀性能;最后采用成纤堆细胞、骨髓细胞体外培养试验考察了生长于不同薄膜表面的细胞粘附、增殖、展布情况及细胞的形态。研究结果表明：用高、低能氮离子兼用的IBAD方法制备的TiN多晶薄膜比只用高能或低能沉积的薄膜具有更强的附着力和耐磨性,在Hank’s模拟体液中显示出更强的抗腐蚀能力,并在细胞体外培养中显示出良好的细胞相容性。     

Metallurgical applications of ion implantation and ion bombardment

The physical background to the metallurgy of ion implantation is discussed. For instance, the fate of implanted atoms is considered in the content of the precipitation processes which occur as a consequence of exceeding the solubility limit during implantation.The Metallurgical applications of ion implantation and ion bombardment are discussed under the following headings: surface and interfacial energies, surface applications, superconductivity and void formation.     

Separate cobalt-copper interface smoothening under the action of low-energy argon ion bombardment

Multilayer film structures of the types “buffer gold layer (20 nm)-copper (x nm)-cobalt (y nm)-protective gold layer (10 nm)” and “buffer gold layer (20 nm)-cobalt (y nm)-copper (x nm)-protective gold layer (10 nm)” with x+y≈6 nm obtained by ion beam deposition in vacuum were studied. It was established that the smoothest surface is obtained for a structure of the second type in which the cobalt layer prior to copper deposition was additionally irradiated with a beam of argon ions at an energy below the threshold energy of sputtering in the common vacuum deposition cycle. Additional irradiation with a mixture of argon and helium ions under analogous conditions leads to the formation of a less smooth structure. It is concluded that the cobalt-copper interface is smoothened as a result of multiple collisions of the low-energy argon ion with cobalt atoms during the former ion stopping within two to three of uppermost atomic layers of the target.     

Physical model of the formation of a periodic structure on the surface of pyrolytic graphite under high-energy ion bombardment

A physical model is proposed for the formation of a structure consisting of “micropoints” and “cavities” on the surface of pyrolytic graphite bombarded by 210 MeV Kr⁺ ions. This structure may be explained in terms of the depth distribution of the energy deposited by the bombardment. Pis’ma Zh. Tekh. Fiz. 23, 89–93 (July 26, 1997)     

Properties of amorphous carbon films deposited by ion beam methods

Amorphous carbon films were prepared by the ion beam sputtering of graphite, by the ion beam sputtering of graphite with simultaneous ion bombardment of the growing film, and by primary ion beam deposition using a beam from a methane- argon plasma. The films are semiconducting in nature, having band gaps of the order of 1 eV. A nuclear reaction involving an energetic (2 MeV) beam of ¹¹B⁺ was used to obtain hydrogen profiles of the films. It was found that the electrical, optical and mechanical properties of the films could be correlated with the hydrogen content. The observed properties are explained qualitatively in terms of amorphous semiconductor theory.