Dissociation of fast HeH ions at glancing angle scattering from a crystal surface

Scattered H⁺ fragments resulting from glancing angle incidence of MeV HeH⁺ ions on the clean (001) surface of a SnTe crystal are distributed on an ellipse in the E-φ plane, where the angle φ is measured in the plane parallel to the surface and E is the energy of the fragment. The kinetic energies released upon dissociation derived from the diameters of the ellipses are smaller than those calculated from the explosion of fully ionized fragments.

Based on a simplified model, we have simulated the dissociative scattering of HeH⁺ ions at the surface, where the dissociation takes place via excitation of HeH⁺ ions and the charges of fragments change along the trajectory. It is concluded from the simulation that the cross section for dissociation in HeH⁺-electron collisions is of the order of 10⁻¹⁶ cm².     

O2在UC(001)表面吸附的第一性原理研究

本文使用GGA+U方法研究了O₂在UC(001)表面的吸附、解离过程。结果表明：U_eff=1.5 eV能很好地再现晶格常数a和内聚能E_coh的实验结果;经过离子弛豫,最表面的两个原子层出现分层现象,各自形成两个亚层;O₂分子的吸附构型对吸附过程影响较大,吸附能在2.21～8.55 eV之间变化。通过Bader电荷、差分电荷和态密度分析,可确定O₂分子的解离活化机理为U的5f/6d电子转移至O₂的π2p和π*2p轨道。     

Intermediate Gas Phase of CHa/[Si（CH3）2O]5 Plasma and Its Effect on Structure of SiCOH Film

This paper investigated the radical behaviour of the plasma of a mixture of methane （CH4） and decamethylcyclopentasiloxane （DMCPS） by optical emission spectroscopy. The plasma was generated by electron cyclotron resonance （ECR） discharge and was used for depositing porous SiCOH low dielectric-constant film. In the ECR discharge plasma, CH, H, H2, C2, Si, O and SiO radicals were obtained. The CH, H and C2 radicals were from the dissociation of CH4, while the SiO. Si and O radicals from the dissociation of the Si-O chain. CHx radicals absorbed in the film were thermally unstable and could be removed by annealing. The dissociation of the Si-O chain led to an increase in a ratio of the Si-Ocage to Si-Onetwork. The removed of CHx radicals and the increased Si-Ocage to Si-Onetwork ratio were beneficial for reducing the film density and dielectric constant.     

Heavy Ion Source with Pulsed Magnetic Field

A compact P.I.G. ion source with pulsed field and end extraction is described. The source produces multiply ionized N, C, Ne, A, Kr and Xe. Pulsed currents of C3+, N3+, Ne3+, A3+, Kr3+ , Xe6+ between a few tens of ?A and a few hundreds of ?A have been obtained. Small size and power consumption make it compatible with a Van de Graaff terminal where space and power are at a premium.     

Production of Negative Helium Ions by Nearly-Resonant Charge Exchange in Potassium

The design criteria for a source of 5-10?A of He- ions suitable for tandem accelerator application have been investigated. The process used is a nearly-resonant charge exchange between He+ ions, from a duoplasmatron, and potassium vapor. In the He+ energy range of 5-25 keV, the He-/He+ yield has been measured as a function of He+ energy. Yields of ~2%/ have been observed. A He- beam emittance of 1.2 × 10-2 cm rad eV1/2 has been measured. The potassium flux into the system was found to be ~1016 particles/s.     

Production of Multiply-Charged Ions of Ne, Ar, Kr and Xe by the Electron-Bonbarded Hot Cathode IoN Source of IPCR

Production of multiply-charged ions of Ne, Ar, Kr and Xe has been studied by use of an electron-bombarded hot cathode type ion source of the IPCR 160cm cyclotron, which is similar to Morozov's source. These multiply-charged ions were accelerated by a 3rd harmonics acceleration mode in the cyclotron and detected with a beam probe fixed at the radius of 55cm. Observed multiply-charged ions are Ne2+, Ne3+, Ne4+, Ne5+, Ar3+, Ar4+ Ar5+, Ar6+, Ar7+, Ar8+, Kr6+, Kr7+, Kr8+, Kr9+, Xe9+, Xe10+ and Xe11+. Relative abundance of each charge state of four elements were measured. In case of Kr and Xe , the intensity of observed multiply-charged ions decreased to 1/3 or 1/4 when the charge number is increased by one. Intensities of Ar4+, Ar6+, Ar8+, Kr6+ and Kr8+ were measured as a function of the operation conditions of the ion source, such as arc voltage, arc power and gas flow rate. It was found that a smaller gas flow and a higher arc power brought about a higher yield in all the measured ions. Obtained current intensities of ion source output are 40?A Ar8+, 600?A Kr6+, 40?A Kr9+, 150?A Xe9+ and 10?A Xe11+ respectively.     

电喷雾串联质谱模拟天然单质铀的形成

采用三重四级杆质谱模拟并分析微观含铀分子化学键断裂形成新的物质的过程以探讨单质铀的产生机理。结果表明,含铀分子在质谱中离子化后经碰撞诱导解离可生成U⁺。研究还发现,硝酸铀酰溶液通过电喷雾可形成UO⁺₂(m/z 270)、UO₂OH⁺(m/z 287)、UO₂H₂OOH⁺(m/z 305)、UO₂NO⁺₃(m/z 332)、UO₂(H₂O)₃NO⁺₃(m/z 386)及双聚铀酰离子［(UO₂NO₃H₂O)₂NO₃］⁺(m/z 762),在具有一定动能N₂的碰撞下它们均可产生游离的U⁺。通过模拟实验推测,天然单质铀形成的微观机理为：在漫长地质年代中放射性核素持续衰变产生的能量粒子撞击含铀分子使其化学键断裂生成游离铀离子,在封闭或强还原性等特殊地质条件下形成单质铀并被保存下来。     

Pixel X-ray detectors in epitaxial gallium arsenide withhigh-energy resolution capabilities (Fano factor experimentaldetermination)

Gallium Arsenide pixel detectors with an area of 170×320 μm² and thickness of 5 μm, realized by molecular beam epitaxy, have been designed and tested with X- and γ rays. No significant charge trapping effects have been observed, and a charge collection efficiency of 100% has been measured. At room temperature an energy resolution of 671 eV full width at half maximum (FWHM) at 59.54 keV has been obtained, with an electronic noise of 532 eV FWHM. With the detector cooled to 243 K, the electronic noise is reduced to 373 eV FWHM, and the K_α and K_β lines of the ⁵⁵Fe spectrum can be resolved. The Fano factor for GaAs has been measured at room temperature with 59.5 keV photons yielding F=0.12±0.01     

A Source for Multiply-Charged Ions and Acceleration of C, N and O Ions by IPCR Cyclotron

The design and performance of the ion source which is now used in the IPCR variable energy cyclotron are described. The source is of the electron-bombarded hot cathode type having two cylindrical cathodes of tungsten and a water-cooled copper anode containing a replaceable molybdenum slit plate. The arc discharge is established continuously but not pulsed. The source is usually operated very stably under an arc power of 1.5 to 3kW with a gas flow rate of 1 to 2 cc/min. The lifetime of the source is mainly limited by the erosion of the upper tungsten cathode at about 24 hours. At present, C4+, N4+, O4+, N5+ and O5+ ions are accelerated up to 48~100, 56~1100, 70~95, 56~125 and 70~125 MeV respectively, and a few micro-amperes of these ions are extracted from the cyclotron. The vacuum obtainable in the accelerating chamber is usually 2 ~ 4 × 10-6 mHg, and the loss of ion beam by the charge exchange effect is comparatively small. Extracted ion beams are used in several experiments for about 1900 hours in a year.     

6—30keVB^＋,C^＋,N^＋,O^＋与H2碰撞单电子剥离的实验研究

用增长率方法首次测量６－３０ｋｅＶＢ＾＋、Ｃ＾＋、Ｎ＾＋、Ｏ＾＋与Ｈ２碰撞的单了截面，给出的Ｂ＾＋和Ｃ＾＋和６－３０ｋｅＶ能区截面随离子能量的趋势与已有的１００－２５００ｋｅＶ能区截面的变化趋势衔接很好。根据截面随入射离子能量和核电荷数的变化，对碰撞机理作了分析，Ｂ＾＋、Ｎ＾＋、Ｏ＾＋与Ｈ２碰撞的单电子剥离截面的变化规律由分子轨道模型得到很好的解释。     

冠醚-1,2-二氯乙烷在苦味酸体系中对轻希土元素的萃取

本文在文献[1]的基础上,研究了二环己基-18-冠-6(DC18C6)和二环己基-15-冠-5(DC15C5)在苦味酸体系中对La~(3+),Ce~(3+),Pr~(3+),Nd~(3+),Sm~(3+),Eu~(3+),Gd~(3+)七个轻希土元素的萃取,求得了萃合常数和萃合物在有机相中的离解常数,并测定了苦味酸在水相对七个希土元素的一级络合常数。     

A numerical simulation study on active species production in dense methane-air plasma discharge

Recently, low-temperature atmospheric pressure plasmas have been proposed as a potential type of ‘reaction carrier' for the conversion of methane into value-added chemicals. In this paper, the multi-physics field coupling software of COMSOL is used to simulate the detailed discharge characteristics of atmospheric pressure methane-air plasma. A two-dimensional axisymmetric fluid model is constructed, in which 77 plasma chemical reactions and 32 different species are taken into account. The spatial density distributions of dominant charged ions and reactive radical species, such as CH_4~+CH_3~+N_2~+O_2~+H, O, CH_3, and CH_2, are presented, which is due to plasma chemical reactions of methane/air dissociation(or ionization) and reforming of small fragment radical species. The physicochemical mechanisms of methane dissociation and radical species recombination are also discussed and analyzed.     

氚化分子NH_2T,CH_3T,TCHO,C_2HT,C_2H_3T及TCN的β蜕变后子体离子的势能曲线

本文用量子化学从头计算法研究了被氚化的分子NH_2T,CH_3T,TCHO,C_2HT,C_2H_3T及TCN等经β蜕变后其子体离子的势能曲线,并研究了它们的分离规律。     

PIC-EDDY Simulation of Different Impurities Deposition in Gaps of Carbon Tiles

A 3D Monte Carlo （MC） code PIC- EDDY, based on EDDY （erosion and deposition dynamic simulation） code, was used to investigate the redeposition of different impurities in the gaps of C tiles. By incorporating the rate coefficients of beryllium （Be） and tungsten （W） into the code, we obtain deposition profiles of hydrocarbon, beryllium and tungsten particles in the toroidal and poloidal gaps, respectively. The redeposition rate of tungsten was found to be higher than those of other impurities in the gaps, except at the bottom, due to its easier local deposition within one gyroradius. Due to the effect of reflection coefficients of hydrocarbon fragments on graphite, fewer hydrocarbons were resided at the entrance while more were deposited on the sides of the gap. At elevated plasma temperatures （such as 30 eV）, asymmetric deposition distributions were observed between the toroidal and poloidal gaps due to the dominant ionized particles. Ions were mainly deposited within 1 mm depth inside gaps, and the bottom deposition particles were almost all neutrals.     

CMOS器件辐照后热退火过程中激发能分布的确定

对CNMOS晶体管辐照后的等温、等时退火特性进行讨论，给出辐照敏感参数在等温、等时退火过程中随退火时间、退火温度的变化关系。根据退火模型计算了CMOS器件辐照后25、100^oC等温和25～250℃等时退火过程中激发能的分布。结果表明：25、100℃等温退火激发能范围分别在0.65～0.76eV和0.75～0.95eV之间；25～250℃等时退火的激发能范围在0.5～1.1eV之间，峰值位于0.81eV。     

Motion and conversion energies of ad-atom, di-adatom and tri-adatoms on copper (0 0 1) surface

Beginning of epitaxial growth of vapor deposition on (0 0 1) surface has been studied by use of molecular dynamics. The activation energies of motion and conversion have been calculated using an embedded atom potential at all temperatures. The activation energy of the motion of an ad-atom on (0 0 1) of copper is calculated to be 0.48 eV. The activation energy of dissociation in the direction of a di-adatom is 0.83 eV, and 0.55 eV from the nearest neighbor to the next nearest neighbor. Tri-adatoms are classified by the angle between the two bonds in the ad-atoms and the lengths of the two bonds. The conversion energies of tri-adatoms have also been calculated. The activation energy for the motion of an ad-atom on (0 0 1) is much higher than those corresponding values of the motion on (1 1 1) planes.     

Molecular dynamics simulation of fluorine ion etching of silicon

Formation of precursors and desorption of etching products by fluorine ion irradiation were studied using molecular dynamics (MD) simulation. When F atoms impact sequentially on a Si substrate, a mixed layer of F and Si atoms is formed on the surface. When the incident energy is below 30 eV, the fluorine coverage reaches steady state after 1.0×10¹⁶ atoms/cm² irradiation. The ratio of F to Si in the mixed layer is about 1:1. At an incident energy of 15 eV, the mixed layer at steady state consists of 4.5 ML of fluorine with a depth of 20 Å and the main etching products are SiF₃ and SiF₄. At 30 eV incident energy, the mixed layer at steady state is 6.5 ML with a depth of 40 Å and the main etching products are SiF₂ and SiF₃. When F atoms were irradiated onto a Si substrate heated at 1000 K, a significant reduction of F coverage was observed due to diffusion of F atoms.     

Detection of Low Energy Heavy Particles with Silicon Barrier Detectors

The performance characteristics of silicon surface barrier detectors have been investigated for detecting H+, He+, N+, Ne+ and Ar+ in the energy interval 6-100 keV. For a cryogenically cooled, 50 mm2, 1325? depletion depth detector the resolution for protons was 1.65 keV (FWHM). The resolution decreased as the particle mass increased being 6.5 keV for 40 keV Ar+. All particles exhibit pulse height linearity throughout the energy range.     

铀铌合金表面热氧化膜结构研究

采用X射线光电谱分析技术、结合Ar离子枪溅射,研究了大气环境、不同温度(室温、100、200和300℃)条件下铀铌合金样品表面氧化膜结构的变化情况。实验结果表明:随温度升高,氧化膜厚度增大,氧化膜结构发生明显变化。不同温度热氧化处理后,铀铌合金初始表面Nb主要以Nb2O5形式存在,在Nb2O5与金属Nb之间,总存在一定厚度的NbO及少量其他价态氧化物NbOx(0x1,1x2)的混合层。室温～200℃热氧化合金样品表面铀均以含间隙氧的UO2+x(P型)存在,其U4f7/2结合能较UO2低约0.7eV。室温条件下,氧化膜成分主要为UO2;100、200℃热氧化后,氧化膜中除UO2外,还含有少量P型UO2+x,其U4f5/2卫星峰的结合能为396.6eV。300℃热氧化后的合金样品表面为铀的高价氧化物(U3O8或UOx,2x3),U4f特征峰的结合能分别为381.8和392.2eV;氧化层为UO2和金属铀的混合物。热氧化过程中,温度对铀氧化的影响较对Nb的明显得多。     

Low energy nitrogen ion doping into GaAs using combined ion-beam and molecular-beam epitaxy method

Low energy nitrogen (N) ions were irradiated during the epitaxial growth of GaAs using combined ion beam and molecular beam epitaxy (CIBMBE) method as a function of N⁺ ion acceleration energy (E_a) and N⁺ ion beam current density (I_N). E_a was varied from 70 to 170 eV I_N from 900 pA/cm² to 75 nA/cm². GaAs growth rate was fixed to 1 μm/h. In 2 K photoluminescence (PL) spectra of the samples with I_N = 3 nA/cm² and E_a = 70–100 eV, two sharp emissions at 1.508 eV (X₁) and 1.495 eV (X₂), which have been attributed to the emissions of excitons bound to isolated N atoms, and another one at 1.443 eV (X₅) were observed. These results show that nitrogen (N) atom in GaAs becomes optically active as an isoelectronic impurity at least in as-grown condition. For N⁺ ion-irradiated samples with rather high I_N, e.g., with I_N = 75 nA/cm² and E_a = 100 eV, a broad emission together with multiple sharp ones were observed after furnace annealing at 750°C which were ascribed to emissions of excitons bound to nitrogen-nitrogen (N---N) pairs.