Fabrication of surface magnetic nanoclusters using low energy ion implantation and electron beam annealing

Magnetic nanoclusters have novel applications as magnetic sensors, spintronic and biomedical devices, as well as applications in more traditional materials such as high-density magnetic storage media and high performance permanent magnets. We describe a new synthesis protocol which combines the advantages of ion implantation and electron beam annealing (EBA) to produce surface iron nanoclusters. We compare the structure, composition and magnetic properties of iron nanoclusters fabricated by low dose 15 keV Fe implantation into SiO(2) followed by 1000?°C EBA or furnace annealing. Atomic force microscopy (AFM) and high resolution transmission electron microscopy (HRTEM) images together with superconducting quantum interference device (SQUID) magnetometry measurements show that only EBA leads to the rapid formation of surface crystalline Fe spherical nanoclusters, showing magnetic moments per Fe atom comparable to that of bulk bcc Fe and superparamagnetic properties. We propose a fabrication mechanism which includes e-beam enhanced desorption of SiO(2). This method has potential for fabricating nanoscale magnetic sensors integrated in microelectronic devices.     

Atomic physics experiments with the Cornell electron beam ion source

Over the past three years, a superconducting solenoid, cryogenic electron beam ion source has been designed, constructed and tested at Cornell University. The source is designed for atomic physics experiments requiring low energy, very highly charged ion beams. The present status of the source is discussed and its use in some preliminary atomic physics experiments is described.     

Characterization of ion beam modified ceramic wear surfaces using Auger electron spectroscopy

An investigation of the surface chemistry and morphology of the wear surfaces of ceramic material surfaces modified by ion beam mixing has been conducted using Auger electron spectroscopy and secondary electron microscopy. Studies have been conducted on ceramic/ceramic friction and wear couples made up of TiC and NiMo-bonded TiC cermet pins run against Si₃N₄ and partially stabilized zirconia disc surfaces modified by the ion beam mixing of titanium and nickel, as well as unmodified ceramic/ceramic couples in order to determine the types of surface changes leading to the improved friction and wear behaviour of the surface modified ceramics in simulated diesel environments. The results of the surface analyses indicate that the formation of a lubricating oxide layer of titanium and nickel, is responsible for the improvement in ceramic friction and wear behaviour. The beneficial effect of this oxide layer depends on several factors, including the adherence of the surface modified layer or subsequently formed oxide layer to the disc substrate, the substrate materials, the conditions of ion beam mixing, and the environmental conditions.     

基于中能段电子束离子阱的杂质光谱研究平台的概念设计

电子束离子阱（Electron Beam Ion Trap,EBIT）是一种用于研究高电离态离子物理过程的实验装置。中能段紧凑型EBIT实验平台能够产生30 keV的电子束能量,电子束流达到20 mA,对于研究未来聚变堆杂质离子输运行为研究具有重要意义。为了产生单一高电荷态离子,中能段EBIT装置阱区需要工作在超高真空（10⁻⁸ Pa）环境下。低温超导磁体需工作在10⁻⁵ Pa真空环境下以维持超导状态,因此真空度直接影响着中能段EBIT的工作性能,有必要研制一套稳定高效的真空控制系统以提升中能段EBIT装置稳定性与可靠性。文章基于RS485总线结构和Python编程语言开发了一套中能段EBIT真空控制系统,实现了对中能段EBIT真空系统的远程控制、数据采集和系统联锁保护。可为中能段EBIT装置提供稳定可靠的超高真空的实验环境,对中能段EBIT装置的稳态运行具有重要意义。

     

Mechanism of electron current suppression in self-magnetically-insulated ion diode

The process of pulsed ion beam generation at a gigawatt output power level by a diode with an explosive-emission potential electrode operating in a self-magnetic-insulation regime has been studied. It is shown that a plasma is effectively formed in the diode and the condition of magnetic cutoff of electrons is satisfied along the entire diode length during ion beam generation. However, because of a high drift velocity, the residence time of electrons and protons in the anode-cathode gap is the same, 3–5 ns, while that for C⁺ carbon ions is greater than 8 ns. This is indicative of a low efficiency of self-magnetic insulation in the given diode. At the same time, it is experimentally established that, during generation of the ion current, the electron component of the total current in stripe diodes of both planar and focusing geometry is suppressed by a factor of 1.5–2. A new mechanism of electron emission suppression is proposed that explains the observed decrease in the electron component of the total current in self-magnetically-insulated ion diodes.     

Effect of the characteristic magnetic field of a high-current electron beam on energy release in targets

The character of the energy released by a high-current electron beam in metal targets is studied taking into account the self-action of the beam.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 52, No. 6, pp. 977–980, June, 1987.     

Electromagnetic control of convective heat transfer during electron beam evaporation: model experiments

The present paper aims to demonstrate that melt-flow during electron beam evaporation can be effectively controlled by using external magnetic fields to considerably reduce the convective heat transfer. We discuss the various effects of a static magnetic field, a static field combined with an applied electrical current, and a rotating magnetic field. We perform model experiments using GaInSn in eutectic composition as a test liquid. The liquid metal is heated locally at its free surface by an electric resistance heater. The results of the measurements are compared to prediction of numerical simulations.     

Analysis of defect displacements in GaP film using convergent beam electron diffraction

Sensitivity of the convergent beam electron diffraction on three dimensional strain field was utilized to determine the Burgers Vector of 60° dislocations and the displacement vector of stacking faults in GaP crystal grown by molecular beam epitaxy. Analysis was accomplished from the observations of splitting of HOLZ lines in the convergent electron beam Bragg disc and from splitting of Kikuchi lines associated with the HOLZ Bragg reflection. A limited sucess of analysis was obtained by using the electron beam orientations other than [111]. The CBED method seems to be useful for the determination of non-ZOLZ fault vector components particularly in a specimen situated in a microscope with a limited tilt range.     

Selective activation of mechanosensitive ion channels using magnetic particles.

This study reports the preliminary development of a novel magnetic particle-based technique that permits the application of highly localized mechanical forces directly to specific regions of an ion-channel structure. We demonstrate that this approach can be used to directly and selectively activate a mechanosensitive ion channel of interest, namely TREK-1. It is shown that manipulation of particles targeted against the extended extracellular loop region of TREK-1 leads to changes in whole-cell currents consistent with changes in TREK-1 activity. Responses were absent when particles were coated with RGD (Arg-Gly-Asp) peptide or when magnetic fields were applied in the absence of magnetic particles. It is concluded that changes in whole-cell current are the result of direct force application to the extracellular loop region of TREK-1 and thus these results implicate this region of the channel structure in mechano-gating. It is hypothesized that the extended loop region of TREK-1 may act as a tension spring that acts to regulate sensitivity to mechanical forces, in a nature similar to that described for MscL. The development of a technique that permits the direct manipulation of mechanosensitive ion channels in real time without the need for pharmacological drugs has huge potential benefits not only for basic biological research of ion-channel gating mechanisms, but also potentially as a tool for the treatment of human diseases caused by ion-channel dysfunction.     

Direct metal fabrication of titanium implants with tailored materials and mechanical properties using electron beam melting technology

The design of custom or tailored implant components has been the subject of research and development for decades. However, the economic feasibility of fabricating such components has proven to be a challenge. New direct metal fabrication technologies such as Electron Beam Melting (EBM) have opened up new possibilities. This paper discusses the design and fabrication of titanium implant components having tailored mechanical properties that mimic the stiffness of bone to reduce stress shielding and bone remodeling. Finite Element Analysis was used to design the tailored structures, and results were verified using mechanical testing.     

Transport of a high-current relativistic electron beam by magnetic multipoles

With the aid of moments of the distribution function a system of differential equations is obtained to describe the dynamics of a Gaussian high-current electron beam in magnetic fields with quadrupole and octupole symmetries. Results of its numerical solution are reported. Research Institute for Nuclear Problems at the Belarusian State University, Minsk, Belarus; Institute of Mathematics of the Academy of Sciences of Belarus, Minsk, Belarus. Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 70, No. 5, pp. 776–782, September-October, 1997.     

Low energy focused ion beam milling of silicon and germanium nanostructures

In this paper focused ion beam milling of very shallow nanostructures in silicon and germanium by low energy Ga( + ) ions is studied with respect to ion beam and scanning parameters. It has been found that, using low energy ions, many scanning artefacts can be avoided and, additionally, some physical effects (e.g. redeposition and ion channelling) are significantly suppressed. The structures milled with low energy ions suffer less subsurface ion beam damage (amorphization, formation of voids) and are thus more suitable for selected applications in nanotechnology.     

Transmission electron microscopy study of carbon nanophases produced by ion beam implantation

The formation of carbon nanocrystals, produced by ion implantation of carbon ions into fused SiO₂ substrates, followed by 1 h thermal annealing at 1000 °C, in an Ar + 5% H atmosphere has been studied. Combined high-resolution transmission electron microscopy (HRTEM) and selected area electron diffraction (SAED) have been employed for structural characterization of carbon nanophases embedded in the quartz substrate. The dependence of grain size and sample morphology of the carbon nanophases on implantation dose was studied. The carbon nanocrystals formed by the implantation for a dose of 1 × 10¹⁶ C/cm² at 320 keV have been identified as a mixture of c-diamond nanophase and a modified diamond nanophase known as n-diamond. For a higher implantation dose, 5 × 10¹⁶ C/cm², besides n-diamond, another solid carbon nanophase was observed, with a structure known as i-carbon. Following the highest implantation dose 1 × 10¹⁷ C/cm² the sample contained the i-carbon nanophase only. A least-square refinement of SAED patterns was employed for the calculation of unit-cell parameters of identified carbon nanophases.     

Direct observation of microscopic plastic deformation of stainless steel using lattice drawn by focused ion beam of Ga+

Abstract

Visualisation of the microscopic deformation of a stainless steel was attempted. A mirror polished, flat surface specimen was subjected to a simple tension test, and the deformation of a fine lattice drawn by a focused ion beam (FIB) of Ga⁺ was observed. The depth of the lattice was of the order of a few tens of nanometres. The penetration depth of Ga⁺ was estimated using SRIM software, and the result indicated that the use of a FIB might not cause serious detriment to the mechanical properties of the lattice surface. After testing, lattices were examined by field emission scanning electron microscopy (FESEM). The results showed that displacement was continuous in the grain as well as across the grain boundary, and the microscopic deformation was categorised into three patterns: (a) a clear thin layer of shear deformation which was discontinuous across the grain boundary, (b) an area of uniform deformation inside this thin layer and (c) microscopic shear bands appearing sporadically in the grains.     

Features of accelerated electron beam formation in LHCD experiments on FT-2 tokamak

In experiments with lower hybrid current drive (LHCD) on the FT-2 tokamak, lower hybrid (LH) waves have been successfully used for the first time to ensure effective additional heating of plasma electrons from 450 to 600 eV (I _Pl = 32 kA, Δt _RF = 14 ms, P _RF = 100 kW, F = 920 MHz). Several factors influencing the efficiency of plasma heating have been discovered. In particular, significant growth of radiation losses in the LHCD regime has been found, which is probably related to an increase in the intensity of synchrotron radiation from accelerated electrons. The increase in this intensity in the 53–156 GHz frequency range was accompanied by short spikes of microwave radiation, which were observed only in a narrower frequency range (53–78 GHz) and apparently resulted from interaction of a runaway electron beam with significant local mirrors of toroidal magnetic field. A model of the additional heating of plasma electrons due to absorption of the microwave radiation generated by a beam of accelerated electrons is proposed.     

Characterization of magnetic domain walls using electron magnetic chiral dichroism

Domain walls and spin states of permalloy were investigated by electron magnetic chiral dichroism (EMCD) technique in Lorentz imaging mode using a JEM-2100F transmission electron microscope. EMCD signals from both Fe and Ni L_3,2 edges were detected from the Bloch lines but not from the adjacent main wall. The magnetic polarity orientation of the circular Bloch line is opposite to that of the cross Bloch line. The orientations of Fe and Ni spins are parallel rather than antiparallel, both at the cross Bloch line and circular Bloch line.     

Characterization of magnetic domain walls using electron magnetic chiral dichroism

Abstract

Domain walls and spin states of permalloy were investigated by electron magnetic chiral dichroism (EMCD) technique in Lorentz imaging mode using a JEM-2100F transmission electron microscope. EMCD signals from both Fe and Ni L_3,2 edges were detected from the Bloch lines but not from the adjacent main wall. The magnetic polarity orientation of the circular Bloch line is opposite to that of the cross Bloch line. The orientations of Fe and Ni spins are parallel rather than antiparallel, both at the cross Bloch line and circular Bloch line.     

离子束辅助沉积铂碳混合膜及其抑制栅电子发射性能

采用离子束辅助沉积技术,在硅、钼衬底上分别制备铂碳混合膜.XRD的分析结果表明,当铂碳混合膜中铂的组份较多时,有较强的铂(111)面衍射峰和较弱的铂(200)面衍射峰,铂的组份呈(111)择优取向.Raman谱的分析结果表明,碳基本上呈非晶状态.模拟二极管的实验表明,在纯钼阳极上镀覆铂碳混合膜,其抑制热电子发射的性能明显优于纯钼阳极.     

The role of electronic energy loss in ion beam modification of materials

The interaction of energetic ions with solids results in energy loss to both atomic nuclei and electrons in the solid. In this article, recent advances in understanding and modeling the additive and competitive effects of nuclear and electronic energy loss on the response of materials to ion irradiation are reviewed. Experimental methods and large-scale atomistic simulations are used to study the separate and combined effects of nuclear and electronic energy loss on ion beam modification of materials. The results demonstrate that nuclear and electronic energy loss can lead to additive effects on irradiation damage production in some materials; while in other materials, the competitive effects of electronic energy loss leads to recovery of damage induced by elastic collision cascades. These results have significant implications for ion beam modification of materials, non-thermal recovery of ion implantation damage, and the response of materials to extreme radiation environments.