Formation,Dynamics, and Characterization of Nanostructures by Ion Beam Irradiation

Ion beam irradiation is a potential tool for phase formation and material modification as a non-equilibrium technique. Localized rise in temperature and ultra fast (～10^?12 s) dissipations of impinging energy make it an attractive tool for metastable phase formation. As a matter of fact, a major component of materials science is dominated by ion beam methods, either for synthesis of materials or for its characterization. The synthesis of nanostructures, and their modification by ion beam technique will be discussed in this review article. Formation of nanostructures using ion beam technique will be discussed first. Depending on species (e.g., mass and charge state) and energy range, there are various modes for an energetic ion to dissipate its energy. The role of the electron will also be covered in this article as a basic principle of its interaction with matter, which is same as for an ion. By using a simple reactive ion beam or electron induced deposition, a secondary phase can be nucleated by ion beam mixing techniques, either by using inert gas irradiation or reactive gas implantation on any desired substrate. Nucleation of secondary phase can also be executed by electron irradiation and direct implantation of either negative or positive ions. Post implantation annealing processes are required for the complete growth of clusters formed in most of these ion irradiation techniques. Implantation processes being inherently a non-equilibrium technique, defects always have a role to play in phase formation, amorphization, and beyond (blister formation). When implanted with large energy, even electrons, one of the lightest charged particles, also manifest these properties. Electronic and nuclear energy losses of the impinging charged particle play a crucial role in material modification. Doping a nanocluster, however, is still a controversial topic. Some light will be shed on this topic with a discussion of focused ion beam.     

Li3+ ion irradiation effects on ionic conduction in P(VDF–HFP)–(PC + DEC)–LiClO4 gel polymer electrolyte system

Swift heavy ion irradiation of P(VDF–HFP)–(PC + DEC)–LiClO₄ gel polymer electrolyte system with 48 MeV Li³⁺ ions having five different fluences was investigated with a view to increase the Li⁺ ion diffusivity in the electrolyte. Irradiation with swift heavy ion (SHI) shows enhancement of conductivity at lower fluences and decrease in conductivity at higher fluences with respect to unirradiated polymer electrolyte films. Maximum room temperature (303 K) ionic conductivity is found to be 2.2 × 10^− 2 S/cm after irradiation with fluence of 10¹¹ ions/cm². This interesting result could be ascribed to the fluence-dependent change in porosity and to the fact that for a particular ion beam with a given energy higher fluence provides critical activation energy for cross-linking and crystallization to occur, which results in the decrease in ionic conductivity. The XRD results show decrease in the degree of crystallinity upon ion irradiation at low fluences (≤ 10¹¹ ions/cm²) and increase in crystallinity at high fluences (> 10¹¹ ions/cm²). The scanning electron micrographs (SEM) exhibit increased porosity of the polymer electrolyte films after low fluence ion irradiation.     

Study of intermixing and Zr-silicide formation using swift heavy ion irradiation

Swift heavy ion (SHI) beam induced irradiation is an established technique for investigating structural modifications in thin films depending on the S _e sensitivity of material. Intermixing due to 120 MeV Au ion irradiation at different fluences from 10¹² to 10¹⁴ ions/cm² has been reported as a function of ion fluence in a-Si/Zr/a-Si thin films on Si substrate. The samples are characterized before (pristine) and after irradiation using Grazing Incident X-ray Diffraction (GIXRD) and Rutherford Backscattering Spectroscopy (RBS), which confirm the formation of ZrSi at thin film interface. It is suggested that mixing is mainly due to electronic energy loss since the energy transferred from high energy ions seems to create a transient molten zone along the ion track. It is found that the interface mixing increases linearly with the increase in ion fluence. The mixing effect explained in the framework of Thermal spike model. The irradiation effect on the surface roughness of the system is measured using Atomic Force Microscopy (AFM) technique. The current conduction mechanism and Schottky barrier height are also calculated by taking I–V curves across the Metal/Si junction.     

Investigation of the initial stages of defect formationin carbon nanotubes under irradiation with argon ions

The formation of defects in carbon nanotubes under irradiation with argon ions is investigated. The π plasmons generated in single-walled and multiwalled carbon nanotubes are examined using electron energy-loss spectroscopy. In the course of experiments, the supramolecular structure of nanotubes is stepwise modified by an argon ion beam (the maximum irradiation dose is 360 μC/cm²). The content of argon ions implanted into a nanotube structure is controlled using Auger electron spectroscopy. The effect of ion irradiation on the π-plasmon energy E_π and on the half-width at half-maximum δE of the π-plasmon spectrum is determined experimentally. An expression relating the above quantities and the concentration of implanted argon is derived. It is shown that the formation of defects under ion irradiation is a discontinuous process occurring in a stepwise manner. A qualitative phenomenological interpretation is proposed for the experimentally revealed decrease in the π-plasmon energy E_π and for its attendant broadening of the π-plasmon spectrum. The assumption is made that the microscopic mechanism of the observed phenomena is associated with the narrowing of the energy π subbands in the electric field of charged defects generated by ions.     

Ion mixing in multilayer films and the doping of the near-surface layers of polycrystalline substrates under irradiation by ion beams with a wide energy spectrum

Various factors influencing ion mixing efficiency are considered. It is established that the energy transfer from ions and primary knocked-on atom films to subsequent displacement cascades underlies the penetration of atoms from multilayer films into a polycrystalline substrate. The penetration of implanted atoms to great depths is in this case determined by the defect density, the radiation induced migration of the implanted atoms, and their interaction with the atoms of the matrix. All of these factors can be described in terms of the isotropic mixing model. It is shown that when doped by atoms from multilayer films, gradient layers form that are determined by the range of radiation in the substrate of the atoms to be implanted and their migration under irradiation by an ion beam with a wide range of energies.     

Simulation of Ion Paths in the Target Material for the Injection Complex of the BELA Facility

To realize the simulation experiments with the use of two ion beams at the injection complex of the BELA accelerator (Based on ECR ion source Linear Accelerator), it is necessary to determine the energy and irradiation angle of the beam of light ions which will be implanted into the region of radiation damage induced by heavy-ion beam. The depth of light-ion implantation is determined by the energy and kind of particles initiating the damage, as well as by their incidence angle. It is supposed that the incidence direction of heavy ions will coincide with the normal to the specimen surface. In our work, the necessary implantation zone for the iron ion beam with an energy of 3.2 MeV is located at depths of 300–800 nm. The simulation of the hydrogen and helium ion paths in the material of the iron target in the energy range from 150 to 600 keV at the angle to the normal from 0° to 65° is performed. The range of energies and irradiation angles for the hydrogen and helium ions are determined for the implantation into the radiation-induced defect-formation zone.     

Ion beam mixing of Al/Fe binary systems

Ion beam mixing of Al layers on Fe and Fe layers on Al are studied by irradiation with 200 keV Xe⁺-ions at room temperature as a function of the thickness of the top layer and of the ion fluence from 5×10¹⁵ to 7.5×10¹⁶ions/cm². Deconvolution procedures are needed to separate the influence of the ion sputter profiling by AES from the ion beam induced mixing effects. Auger electron spectroscopy data reveal that the mixing induced diffusivity ought to be considered as a function of concentration. The diffusion coefficients are evaluated by the Boltzmann-Matano method. A strong dependence of the diffusion coefficients and also the mixing efficiencies from the ion dose, the depth of the interface and the nuclear energy deposition were observed. Results are discussed in terms of the diffusional and collisional mixing as well as chemical affinity of both Fe and Al.     

Electrical transport characteristic of carbon nanotube after mass-separated ultra-low-energy oxygen ion beams irradiation

Mass-separated ultra-low-energy oxygen ion beams were irradiated to the single-walled carbon nanotubes (SWCNTs) under an ultra-high-vacuum pressure of 10⁻⁷ Pa for the purpose of achieving n-type conduction of nanotubes. The ion beam energy was 25 eV, which was close to the displacement energy of graphite. The incident angle of the ion beam was normal to the target nanotube. The ion dose ranged from 3.3 × 10¹¹ to 3.8 × 10¹² ions/cm². The structure of SWCNTs after the ion irradiation was investigated. The CNTs still have a clear single-walled structure after the ion irradiation. The graphite structure is distorted and some defects are induced in the nanotube by the oxygen irradiation. The oxygen ions with the ion energy of 25 eV are irradiated to the field effect transistor (FET) device with the nanotube channel. The n-type characteristic appears upon the oxygen ion irradiation, and the device exhibits ambipolar behavior. The defects induced by the ion irradiation may act as the n-type dopants.     

Effect of ion velocity on SHI-induced mixing in Ti/Bi system

Energetic ion beams are proving to be versatile tools for modification and depth profiling of materials. The energy and ion species are the deciding factor in the ion-beam-induced materials modification. Among the various parameters such as electronic energy loss, fluence and heat of mixing, velocity of the ions used for irradiation plays an important role in mixing at the interface. The present study is carried out to find the effect of the velocity of swift heavy ions on interface mixing of a Ti/Bi bilayer system. Ti/Bi/C was deposited on Si substrate at room temperature by an electron gun in a high-vacuum deposition system. Carbon layer is deposited on top to avoid oxidation of the samples. Eighty mega electron volts Au ions and 100?MeV Ag ions with same value of S_e for Ti are used for the irradiation of samples at the fluences 1?×?10¹³–1?×?10¹⁴ ions/cm². Different techniques like Rutherford backscattering spectroscopy, atomic force microscopy and grazing incidence X-ray diffraction were used to characterize the pristine and irradiated samples. The mixing effect is explained in the framework of the thermal spike model. It has been found that the mixing rate is higher for low-velocity Au ions in comparison to high-velocity Ag ions. The result could be explained as due to less energy deposition in thermal spike by high-velocity ions.     

H+辐照前后W涂层表面的XPS分析

对离子束混合技术在不锈钢基体上沉积的W膜进行了H+辐照前后的XPS分析,研究了H+辐照对W的结合能的影响.分析结果表明,沉积的W膜中除了单质钨外,还有部分钨的氧化物,H+辐照结果表明,H+的辐照使钨的结合能向低能方向偏移;钨的氧化物有所减少,说明污染的氧化物在一定程度上被择优溅射掉.     

Effect of 100 MeV Ni ion irradiation on MOCVD grown n-GaN

Metal-organic chemical vapor deposition (MOCVD) grown n-type Gallium nitride (GaN) has been irradiated with 100 MeV Ni⁹⁺ ions at room temperature. Atomic force microscopy (AFM) images show the nano-clusters' formation upon irradiation and the irradiated GaN surface roughness increases with the increasing ion fluences. High-resolution X-ray diffraction (HR-XRD) analysis reveals the formation of Ga₂O₃ due to the interface mixing of GaN/Al₂O₃ upon irradiation. FWHM values of GaN (0 0 0 2) increases due to the lattice disorder. Photoluminescence studies show reduced band edge emission and yellow luminescence (YL) intensity with the increasing ion fluences. Change in the band gap energy between 3.38 and 3.04 eV was measured by UV-visible optical absorption spectrum on increasing the ion fluences.     

Swift heavy ion irradiation effects on structural,optical properties and ac conductivity of polypyrrole nanofibers

Polypyrrole (PPy) nanofibers have been synthesized by interfacial polymerization method and irradiated with 160?MeV Ni¹²⁺ ions under vacuum with fluences in the range of 10¹⁰–10¹²?ions/cm². High-resolution transmission electron microscopy results show that upon swift heavy ion (SHI) irradiation the PPy nanofibers become denser. The crystallinity of PPy nanofibers increases upon SHI irradiation, while their d-spacing decreases. Upon SHI irradiation, the polaron absorption band gets red-shifted indicating reduction in the optical band gap energy of the irradiated PPy nanofibers. The indirect optical band gap energy is decreased as compared to corresponding direct optical band gap energy. The number of carbon atoms per conjugation length (N) and carbon atoms per cluster (M) of the SHI-irradiated PPy nanofibers increase with increasing the irradiation fluence. Fourier transform infrared spectra reveal the enhancement in intensity of some characteristic vibration bands upon SHI irradiation. The thermal stability of the PPy nanofibers is enhanced on SHI irradiation. The charge carriers in both pristine and irradiated PPy nanofibers follow the correlated barrier hopping mechanism. Scaling of ac conductivity reveals that the conduction mechanism is independent of the SHI irradiation fluence.     

The influence of ion irradiation on the structure and properties of amorphous carbon films

Presented in this work are the results of investigation of the structure and electrophysical properties of amorphous carbon films. The films were produced by sputtering of graphite by ion beam and usin ion irradiation (E=0–200 eV) during condensation process. The structure of i-C films has been studied by means of transmission electron microscope. The electron diffraction data have been interpretated by employing the calculated interference function of carbon clusters. The structure of V-band was obtained from AES by deconvolution method. Experimental data shows that under ion irradiation the transformation of short range order and electron bonds is an oscillating function of ion energy E. This paper presents a theoretical calculation of tunneling neutralization cross-section of Ar⁺ ions on carbon surface. The process also has an oscillating dependence on ion energy. A significant importance of inelastic processes in carbon phase transformation has been revealed.     

The energy spectra of secondary ions emitted during ion bombardment

Secondary ion energy spectra have been measured for singly charged ions emitted from targets irradiated with 43 keV A⁺ ions. Targets studied include the 3d transition metals (Sc, Ti, V, Cr, Fe, Ni) Cu and Zn, Zr, Al and Si and the compounds SiO₂, Al₂O₃, NaCl, KCl. Energy spectra were measured in the energy range 1–600 eV. In several cases a peak in the energy spectrum in the region around 200 eV has been found. This is in addition to the usual low energy peaks in the region of 5–10 eV. In many cases the low energy peak was observed to decay steadily with irradiation time or to increase with oxygen pressure. In the case of the cleanest Zn spectrum, only the high energy peak can be detected. The data are discussed in relation to current models of secondary ion emission. We conclude that, in general, elemental metal targets which are clean are characterised by the high energy peak in the secondary ion energy spectrum. The slower ions emitted have been neutralised by electron exchange processes. The low energy peaks in unclean, partially clean, oxide coated or compound targets (NaCl, KCl) arise because the neutralisation of the slower ions is either not as efficient or is not possible. The secondary ion emission model of Blaise and Slodzian could account for the emission of ions from most targets.     

Experimental study of the influence of the processes in the ion-beam drift space on beam current measurements

A method is proposed for separate measurements of the current produced by slow charge-exchange ions and that produced by the ions generated due to gas ionization by the beam ions and fast secondary electrons in the beam drift space. The method is based on an analysis of the current distribution over the electrodes of a modified Faraday cup with nonequipotential electrodes and allows one to determine the coefficient of ion-induced electron emission from the ion collector and the charge-exchange cross section of the accelerated ions. The method has been employed to measure the current of an argon ion beam with an ion energy from a few electronvolts to several tens of kiloelectronvolts and to study the processes in the beam drift space at pressures of 0.03–0.15 Pa.     

超强激光与固体气体复合靶作用产生高能氦离子

激光氦离子源产生的MeV能量的氦离子因有望用于聚变反应堆材料辐照损伤的模拟研究而得到关注.目前激光驱动氦离子源的主要方案是采用相对论激光与氦气射流作用加速高能氦离子,但这种方案在实验上难以产生具有前向性和准单能性、数MeV能量、高产额的氦离子束,而这些氦离子束特性是材料辐照损伤研究中十分关注的.不同于上述激光氦离子产生方法,我们提出了一种利用超强激光与固体-气体复合靶作用产生氦离子的新方法.利用这种方法,在实验上,采用功率密度5×10~(18)W/cm~2的皮秒脉宽的激光脉冲与铜-氦气复合靶作用,产生了前向发射的2.7 MeV的准单能氦离子束,能量超过0.5 MeV的氦离子产额约为10~(13)/sr.二维粒子模拟显示,氦离子在靶背鞘场加速和类无碰撞冲击波加速两种加速机理共同作用下得到加速.同时粒子模拟还显示氦离子截止能量与超热电子温度成正比.     

Ion beam mixing of AG on glass

A series of Ag-glass samples have been studied. They were irradiated as a function of bombarding ion species, dose, temperature, and energy. The results by RBS indicate that ion beam mixing of Ag-glass takes place not only at higher energy irradiation (I. OMeV Xe+), but also at lower energy irradiation (120KeV Ar+ and Kr+). The effective diffusion lengths squared, Dt, were introduced for comparison. It is found that Dt is dependent on the nuclear stopping power, dose and irradiation temperature.     

New monochromator of mass-spectrometric sources

A model of a new type of a monochromator for the ion beam emitted by mass-spectrometric ion sources with a broad energy distribution is considered. The ion beam monochromation was carried out by transforming the energy spectrum of particles in high vacuum by the shock effect produced by electric pulses on ions in a spatially nonuniform field followed by the formation of an ion beam in the electrostatic field of the immersion lens. Numerical simulation of the operation of the monochromator proves its performability as a compact and effective instrument for solving the problem of monochromation in mass-spectrometry.     

Investigation of the binary model of scattering of 1 keV to 25 eV Ar+ ions from a Cu surface 1

The validity of the binary collision approximation for describing the scattering of low energy Ar ions from a polycrystalline Cu surface was investigated. The Ar ions were incident upon the target surface at an angle of 45° (with respect of the plane of the surface). The range of primary ion energy studied was 1000–25 eV. An ultra-high vacuum magnetic sector mass spectrometer was used to analyze those secondary ions emitted from the specimen surface at an angle of 90° with respect to the primary ion beam. The scattered ions were identified and their energies measured. No significant deviation from the prediction of the binary collision model was found throughout the range of energy studied.     

Generation of a fast-ion beam upon the interaction of a multiterawatt picosecond laser pulse with a solid target

The parameters of fast particles generated upon the interaction of 10¹⁹ W/cm² laser pulses with solid targets are studied. The spatial and energy parameters of fast ions are investigated. It is found that approximately 1–3% of the laser energy is transformed to the energy of mega-and submegaelectronvolt ions at laser pulse intensities ≥10¹⁸ W/cm². It is shown experimentally that an ion beam is directed perpendicular to the target surface. The analytic and numerical simulations agree with experimental results and predict the propagation of fast electrons in the mirror direction with respect to the incident laser beam and of ions perpendicular to the target. The theoretical calculations are compared with the experimental output and spectra of fast electrons and ions.