Preparation of Ne, Mg, Si, S, and Ar targets by ion implantation into thin carbon foils

The preparation of isotopically pure targets of ²⁰Ne, ²⁴Mg, ²⁸Si, ³²S, and ³⁶Ar by the implantation of 25-70 keV ions into carbon foils is described.     

Equilibrium charge state distributions for boron and carbon ions emerging from carbon and aluminum targets

Equilibrium charge state distributions of boron and carbon ions through carbon and aluminum targets were measured with an energy range of 3-6 MeV. Comparisons of the data with relevant semi-empirical models for the equilibrium mean charge states and for the charge state distribution widths could provide valuable insight on the underlying mechanisms for a fast ion to lose or capture electrons. In-depth examinations of the experimental results in combination with semi-empirical models suggest that equilibrium charge state distributions are well represented by Gaussian distributions.     

Development of a low-level setup for gamma spectroscopy: Application for nuclear astrophysics using reverse kinematics

It is more and more necessary to improve the sensitivity of gamma-ray spectroscopy systems, especially in nuclear astrophysics. In the case of radiative proton capture reactions, one means is to avoid the reactions on the target impurities by using reverse kinematics. This technique is possible with the LARN accelerator and can provide very clean cross-section measurements. For that purpose, a hydrogen standard has been carried out by means of ion implantation in silicon. In addition, a low-level setup has been put in place on a new beam line of the accelerator. A high efficiency and high resolution germanium detector is used conjointly with a double shielding. A passive lead castle shielding system is used to reduce the natural radioactivity and an active shielding consisting of an anti-cosmic veto is provided by an anticoincidence between the plastic scintillator and the gamma-ray detector. The setup allows a reduction of 70% of the background interference and provides an approximately 200 fold sensitivity gain of between 600 and 3000 keV. Some other developments have also been carried out to optimize the setup. The entire setup and the reverse kinematics have been validated by measuring the cross-section of the ¹³C(p,γ)¹⁴N and ¹⁵N(p,γ)¹⁶O reactions that present some astrophysical interest.     

Raman scattering studies of oxygen implanted CdS thin films prepared by vacuum evaporation

CdS thin films prepared by vacuum evaporation method were implanted with oxygen ions at the energy of 80 keV to different doses. Raman scattering studies of the as-deposited and implanted films reveal the shift in the Raman peak position of A₁(LO) mode towards higher wave number on implantation. The area under the peak increases with dose initially, and then decreases at higher doses. The shift of the Raman peak to higher wave numbers has been attributed to the replacement of sulphur atoms by the lighter oxygen atoms.     

XPS and optical studies of Xe-implanted and annealed YSZ single crystals

Xe⁺ ion implantation with 200 keV was completed at room temperature up to a fluence of 1 × 10¹⁷ ion/cm² in yttria-stabilized zirconia (YSZ) single crystals. Optical absorption and X-ray photoelectron spectroscopy (XPS) were used to characterize the changes of optical properties and charge state in the as-implanted and annealed crystals. A broad absorption band centered at 522 or 497 nm was observed in the optical absorption spectra of samples implanted with fluences of 1 × 10¹⁶ ion/cm² and 1 × 10¹⁷ ion/cm², respectively. These two absorption bands both disappeared due to recombination of color centers after annealing at 250 °C. XPS measurements showed two Gaussian components of O_1s spectrum assigned to Zr–O and Y–O, respectively, in YSZ single crystals. After ion implantation, these two peaks merged into a single peak with the increasing etching depth. However, this single peak split into two Gaussian components again after annealing at 250 °C. The concentration of Xe decreased drastically after annealing at 900 °C. And the XPS measurement barely detected the Xe. There was no change in the photoluminescence of YSZ single crystals with a fluence of 1 × 10¹⁷ ion/cm² after annealing up to 900 °C.     

An empirical formula for calculation of range of charged particles with Z from 2 to 103 and energy from 2.5 MeV/nucleon to 500 MeV/nucleon in beryllium

A new empirical formula for quick estimation of range in beryllium material of charged particles with the charge number from 2 to 103 and with energy in the range from 2.5 to 500 MeV/nucleon has been given. This formula was found based on a table of ranges measured experimentally and calculated up to 1990. It is shown that the differences between the values calculated by our formula and the values tabulated in the table is less than about 2% for all ions in the whole energy range.     

铬,钽离子束表面冶金合金的抗腐蚀机制

根据离子束表面冶金的特点，从合金成分、结构、缺陷、元素性质以及表面污染等方面系统地讨论了Ｃｒ、Ｔａ元素加入对金属腐蚀行为的影响。在此基础上，提出它们抑制腐蚀的综合模式，较好地解释了这类表面合金抗腐蚀的机制。     

高剂量N^＋注入碳膜形成氮化碳CNx的研究

研究了利用高剂量的Ｎ＾＋注入碳膜形成氮化碳ＣＮｘ的可能性，对这种新材料进行了城叶变换红外吸收光谱、Ｘ射线光电子能说、Ｘ射线衍射和薄膜的维氏显微硬度等测量。结果表明，在１００ｋｅＶ高剂量Ｎ＾＋注入碳膜过程中形成了含有碳氮共价键成分的ＣＮｘ化合物。     

Magnetic force microscopy studies on the magnetic ordering in organic materials induced by high-energy proton irradiation

In this study, ferromagnetic microstructures in highly oriented pyrolytic graphite and superparamagnetic spots in polyimide foils were created by 2.25 MeV proton microbeam irradiation and characterized using atomic and magnetic force microscopy. For this purpose, graphite samples were irradiated with cross-like patterns of 15 μm × 15 μm size using ion fluences in the range of (0.003–2.5) × 10¹⁸ cm⁻². The irradiated crosses showed strong magnetic signals and a complex domain structure in the magnetic images depending on the geometrical dimensions of the crosses. Furthermore, polyimide foils were irradiated with microspots and fluences in the range of (0.016–3.1) × 10¹⁹ cm⁻². Magnetic force microscopy shows very strong phase shifts in these irradiated areas.     

An algorithm for fast calculation of ion range and damage distributions based on the boltzmann transport equation

Boltzmann transport equation (BTE) method using large energy intervals in ion scattering calculations can lead to significant errors in the calculation of ion and damage distributions. We pointed out that the inaccuracy is caused by the fact that the flux distribution in a transited energy state is not uniform. The flux is higher at its higher energy end because of a relatively higher cross section for a small energy transfer. Neglecting this difference and assuming an evenly distributed flux will lead to significant errors. The issue can be alleviated by using small energy intervals which inevitably increases computational times. We proposed to redistribute the flux among neighboring energy states around a transited energy state, with the redistribution weighted by their proximities to the mean value of transited energy. Therefore, ion range distributions can be calculated accurately with large energy intervals, thus significantly improving computational efficiency, i.e. by at least one order of magnitudes for 100 keV Si self ion irradiation.     

Ion implantation of rare earth ions for light emitters

We discuss the excitation and deexcitation processes for solid state optical emitters. At present, there is considerable interest in depositing a material system, which is compatible to silicon microelectronics processing and which emits electroluminescence (EL). We will compare the EL results of rare earth doped transistors in silicon with doped insulators and doped wide bandgap semiconductors, especially Er in Si (a source for 1.5 μm) as well as Er and Tb in SiO₂, Si₃N₄ and AIN, which are sources for infrared and visible light. The most impressive results are achieved by RE doped GaN film devices, which cover the entire visible spectrum.     

Surface modification of Natural Rubber by ion implantation: Evidence for implant doping

Ion implantation is one of the most powerful and well-known technique for surface modification in polymers. Thin films of Natural Rubber were modified by the implantation of 60 keV N⁺ ions to the fluences of 10¹¹–10¹⁵ cm⁻². The electrical conductivity measurements of irradiated sample show 10 orders of magnitude compared to pristine state. Along with conductivity change there was a noticeable change in color to a dense shiny black for the most highly conducting films. The analysis of temperature dependence of dc electrical conductivity data reveals a three-dimensional variable range hopping mechanism. The microstructural evolution of the virgin and ion-beam modified samples was investigated by spectroscopic analysis such as UV/Vis & FTIR. These spectral studies gave evidence for the production of conjugate double bonds, which is a clear cut indication of implant doping. This is an important result since ion implantation usually does not produce doping in polymeric materials and only a few reports about the possibility of implant doping in polymers are available. The significant aspect of this study is that this confirms, the Natural Rubber’s potential to be used as a microelectronic device material. Also an attempt has been made to compare the conductivity enhancement in Natural Rubber by chemical and implant doping.     

PL and ESR study for defect centers in 4H-SiC induced by oxygen ion implantation

Radiation damage in 4H-SiC samples implanted by 70 keV oxygen ion beams was studied using photoluminescence and electron spin resonance techniques.ESR peak of g =2.0053 and two zero-phonon lines were observed with the implanted samples.Combined with theoretical calculations,we found that the main defect in the implanted 4H-SiC samples was oxygen-vacancy complex.The calculated defect formation energies showed that the oxygen-vacancy centers were stable in n-type 4H-SiC.Moreover,the VsiO0c and VsiO-1C centers were optically addressable.The results suggest promising spin coherence properties for quantum information science.     

氩离子注入模拟太阳风对月岩的作用

对玄武岩和斜长岩等多种岩石样品进行了低能、超高剂量氩离子注入。氩离子能量12 0keV ,注入剂量 5× 10 18 cm2 。用X射线荧光光谱仪分析了辐照样品和未辐照样品的表面元素组成 ;用分步加热法分析了注入气体释放模式及岩石对氩气的保留能力。初步探讨了岩石对氩气的保留能力和分步加热释气模式等问题     

Charge sharing in multi-electrode devices for deterministic doping studied by IBIC

Following a single ion strike in a semiconductor device the induced charge distribution changes rapidly with time and space. This phenomenon has important applications to the sensing of ionizing radiation with applications as diverse as deterministic doping in semiconductor devices to radiation dosimetry. We have developed a new method for the investigation of this phenomenon by using a nuclear microprobe and the technique of Ion Beam Induced Charge (IBIC) applied to a specially configured sub-100 μm scale silicon device fitted with two independent surface electrodes coupled to independent data acquisition systems. The separation between the electrodes is comparable to the range of the 2 MeV He ions used in our experiments. This system allows us to integrate the total charge induced in the device by summing the signals from the independent electrodes and to measure the sharing of charge between the electrodes as a function of the ion strike location as a nuclear microprobe beam is scanned over the sensitive region of the device. It was found that for a given ion strike location the charge sharing between the electrodes allowed the beam-strike location to be determined to higher precision than the probe resolution. This result has potential application to the development of a deterministic doping technique where counted ion implantation is used to fabricate devices that exploit the quantum mechanical attributes of the implanted ions.     

Rapid-relocation model for describing high-fluence retention of rare gases implanted in solids

It has been known for a long time that the maximum areal density of inert gases that can be retained in solids after ion implantation is significantly lower than expected if sputter erosion were the only limiting factor. The difference can be explained in terms of the idea that the trapped gas atoms migrate towards the surface in a series of detrapping–trapping events so that reemission takes place well before the receding surface has advanced to the original depth of implantation. Here it is shown that the fluence dependent shift and shape of implantation profiles, previously determined by Rutherford backscattering spectrometry (RBS), can be reproduced surprisingly well by extending a simple retention model originally developed to account only for the effect of surface recession by sputtering (‘sputter approximation’). The additional migration of inert gas atoms is formally included by introducing an effective shift parameter Y_eff as the sum of the sputtering yield Y and a relocation efficiency Ψ_rel. The approach is discussed in detail for 145 keV Xe⁺ implanted in Si at normal incidence. Y_eff was found to increase with increasing fluence, to arrive at a maximum equivalent to about twice the sputtering yield. At the surface one needs to account for Xe depletion and the limited depth resolution of RBS. The (high-fluence) effect of implanted Xe on the range distributions is discussed on the basis of SRIM calculations for different definitions of the mean target density, including the case of volume expansion (swelling). To identify a ‘range shortening’ effect, the implanted gas atoms must be excluded from the definition of the depth scale. The impact-energy dependence of the relocation efficiency was derived from measured stationary Xe concentrations. Above some characteristic energy (20 keV for Ar, 200 keV for Xe), Y exceeds Ψ_rel. With decreasing energy, however, Ψ_rel increases rapidly. Below 2–3 keV more than 90% of the reemission of Ar and Xe is estimated to be due to bombardment induced relocation and reemission, only the remaining 10% (or less) can be attributed to sputter erosion. The relocation efficiency is interpreted as the ‘speed’ of radiation enhanced diffusion towards the surface. The directionality of diffusion is attributed to the gradient of the defect density on the large-depth side of the damage distribution where most of the implanted rare gas atoms come to rest. Based on SRIM calculations, two representative parameters are defined, the peak number of lattice displacements, N_d,m, and the spacing, z_r,d, between the peaks of the range and the damage distributions. Support in favour of rapid rare gas relocation by radiation enhanced diffusion is provided by the finding that the relocation efficiencies for Ar and Xe, which vary by up to one order of magnitude, scale as Ψ_rel=kN_d,m/Δz_r,d, independent to the implantation energy (10–80 keV Ar, 10–500 keV Xe), within an error margin of only ± 15%. The parameter k contains the properties of the implanted rare gas atoms. A recently described computer simulation model, which assumed that the pressure established by the implanted gas drives reemission, is shown to reproduce measured Xe profiles quite well, but only at that energy at which the fitting parameter of the model was determined (140 keV). Using the same parameter at other energies, deviations by up to a factor of four are observed.     

离子束增强沉积碳膜及其在抑制电子发射中的应用

栅电子发射是影响行波管工作性能和制约其使用寿命的主要因素。国内研制的导弹雷达制导用行波管因存在严重的栅电子发射现象,寿命只有70h,不能付诸军事应用。采用离子束增强沉积的方法在栅网表面沉积一层碳膜后,可有效地抑制栅电子发射,使行波管寿命超过了1000h,在军事和航天领域获得了成功应用。报导了低能离子束增强沉积类金刚石薄膜和高能离子束增强沉积类石墨碳膜的制备技术、结构性能及其在抑制栅电子发射中的应用和机理研究的结果。     

应用于离子注入的RFQ加速器

射频四极场(Radio frequency quodrupole,RFQ)加速器是一种非常适于用作MeV级能量离子注入的加速器.它具有束流强、体积小、使用方便、离子源处在地电位,还可同时加速正、负两种离子等优点.本文介绍了RFQ加速器在国际上的发展状况及其基本原理、北京大学研制的1 MeV RFQ加速器的具体结构、性能以及一种新型RFQ-SFRFQ组合加速器的特点.     

强脉冲离子注入中的脉冲能量效应研究

在脉冲离子束流密度为15120A/cm2、脉宽为50150ns、加速电压为150260kV范围内,在11014cm-2的低注量水平上, 研究了高功率Cn++H+混合离子束注入45号钢样品的强脉冲能量效应。摩擦磨损和微观硬度测量以及SEM和X射线衍射分析表明,上述低注量强脉冲离子束注入可以改变材料 表面的微观结构和力学特性,而且强烈依赖于单个脉冲离子束的功率密度和能量密度。在相同离子注量条件下,普通C++H+离子注入对45号钢样品表面微硬度和摩擦系数未 见明显影响。直接证明了强脉冲能量效应在离子注入中是相对独立于注入元素掺杂效应的又一可利用的重要效应。基于一维导热模型,讨论了强脉冲能量效应以及脉冲离 子束功率密度对离子束材料表面改性的作用。     

C、Co及C+Co双注入对高速钢机械性能影响的研究

采用ＭＥＶＶＡ源离子注入机对高速工具钢进行了Ｃ,Ｃｏ及Ｃ＋Ｃｏ注入,并做了硬度,摩擦系数测量和磨损实验,Ｃ离子注入剂量３×１０＾１７ｃｍ＾－２能量６０ｋｅＶ,Ｃｏ离子注入剂量为２×１０＾１７,４×１０＾１７,６×１０＾１７ｃｎ＾－２能量１０２ｋｅＶ。结果表明,不同元素,不同剂量的离子注入均能有效地改善ＨＳＳ的硬度和摩擦磨损特性,从而极大延长ＨＳＳ的工作寿命,且随着注入剂量的增加,改善的效果有所增强