Hydrogen enhanced oxygen diffusion

The diffusion of oxygen impurities in Cz silicon is thought to occur by a single process over the temperature range 350–1250°C. Enhanced oxygen diffusion has been reported for samples which have been subjected to high temperature pre-anneals, deliberate metallic contamination or irradiation by high energy electrons. Recently, enhanced oxygen diffusion has also been observed for samples annealed in a hydrogen plasma and there are correlated enhancements in the rate of production of thermal donors. It seems likely that hydrogen is also responsible for the enhanced rates of oxygen diffusion previously observed and these findings may have important consequences for plasma processing.     

SiO2包覆对ZnS纳米材料发光的增强机制

为了明确团聚现象及表面性质对ZnS纳米材料发光性质的影响,采用SiO₂对ZnS材料进行了表面修饰,并对ZnS及ZnS/SiO₂复合材料的光学性质进行对比研究.采用吸收光谱分析了包覆前后光吸收性质的差异,发现SiO₂包覆后ZnS纳米材料的带边由333 nm红移至360 nm.为了研究ZnS纳米材料与ZnS/SiO₂纳米复合材料的光发射性质,分别对含纳米材料的水溶液样品及粉末样品的发光光谱进行了采集.对比研究的结果表明,SiO₂包覆后ZnS纳米材料在蓝紫光区的发光得到了明显增强.以氙灯作为激发光源所获得荧光光谱显示ZnS/SiO₂粉末样品发光的积分强度增大为原来的17.5倍,但相同条件下针对溶液样品的测试结果显示其发光强度只增大了1.1倍,这种增强可用SiO₂的存在抑制了ZnS纳米粒子间的团聚来解释,且这一推断由325 nm紫外激光激发下获得的光致发光数据进行了验证.     

Reactions and diffusion of water and oxygen molecules in amorphous SiO2

Water and oxygen molecules determine many of the properties of amorphous SiO2 used in several technologies, but the underlying atomic-scale processes remain unresolved. We report results of first-principles calculations showing that a wide range of behavior is possible in an amorphous environment, including diffusion of the molecule as a whole and various reactions with the network. Experimental data including oxygen exchange reaction and radiation sensitivity are accounted for. The possibility of H3O+ formation as a source of positive charge is discussed.     

Mechanism of interstitial oxygen diffusion in hafnia

We have performed density functional calculations of oxygen incorporation and diffusion in monoclinic hafnia (HfO2) for a range of oxygen charge states. The calculations demonstrate that oxygen favors atomic incorporation and that O2- is the most stable species. We find that oxygen interstitials diffuse via exchange with lattice oxygen sites in hafnia, and that O- species have the smallest diffusion barrier.     

Proton diffusion mechanism in amorphous SiO2

We study proton diffusion in amorphous SiO2 from the atomic scale to the long-range percolative regime. Ab initio molecular dynamics suggest that the dominant atomic process consists in cross-ring interoxygen hopping assisted by network vibrations. A statistical analysis accounting for the disorder in amorphous SiO2 yields relations between transition energies and interoxygen distances for both cross-ring and nearest-neighbor hopping. The percolative regime is then addressed through large-size model systems reproducing these relations. Cross-ring hopping is confirmed as the dominant diffusion mechanism and supported by a good agreement with experiment for the activation energy.     

Mechanisms of diffusion of boron impurities in SiO2

We report first-principle total-energy calculations that clarify mechanisms of boron diffusion in SiO2. We find that a B atom takes a variety of stable and metastable geometries depending on its charge state. We also find that atomic rearrangements during the diffusion manifest a wealth of bonding feasibility in SiO2 and that the calculated activation energy agrees with the experimental data available. Recombination enhanced diffusion is also proposed.     

O2 diffusion in SiO2: triplet versus singlet

We address the diffusion of the oxygen molecule in SiO2, using first-principles spin-polarized total-energy calculations. We find that the potential energy surfaces for the singlet and triplet states are very different in certain regions, and that the O2 molecule preserves its spin-triplet ground state not only at its most stable interstitial position inside the solid but also throughout its diffusion pathway. Therefore, the singlet state is not a good approximation to describe the behavior of O2 inside SiO2, and spin-polarization effects are fundamental to understand the properties of this system.     

Formation of singly charged selenium ions in e-Se2 collisions

The excitation of spectral lines of Se II in e-Se₂ collisions has been studied for the first time. Forty-eight excitation cross sections of Se II spectral lines have been measured at an electron energy of 50 eV. Three optical excitation functions have been recorded in an electron energy range of 0–100 eV. Possible reaction channels at low electron energies are discussed.     

Laser spectroscopy for QED tests in highly charged ions

An overview on laser spectroscopic work on highly charged ions (HCI) currently performed or in preparation at GSI is given. This includes laser spectroscopy on HCI in ion traps at the HITRAP facility and at the experimental storage ring (ESR).     

高电荷态离子与SiO2表面相互作用的研究

高电荷态离子(Pbq ,Arq )由兰州近代物理研究所的ECR实验平台所产生,轰击非晶态SiO2表面.用微通道板测量溅射粒子产额的角分布.用公式拟合实验溅射角分布得到了较好的结果,并给出了初步的理论解释.由此得出了高电荷态离子与SiO2表面作用的微分溅射截面.实验结果表明高电荷态离子能够增加动能溅射;同时高电荷态离子入射能够引起势能溅射.在大角度入射时,溅射产额主要是由碰撞引起的;在小角入射时势能溅射所占比重会增大.     

Dissociative ionization of the H2O molecule bombarded by swift singly charged and slow highly charged ions

Fragment ion energy spectra of the water molecule have been measured in conventional crossed-beam experiments by the impact of 46 keV/u energy, singly charged ions (SCIs) and 4.3 keV/u energy, highly charged ions (HCIs). Double differential cross sections have been determined and a comparative analysis has been performed. We found that the fragmentation spectra for SCIs and HCIs are very similar, indicating that both collisions lead to the same fragmentation channels. This suggests that the Coulomb explosion of the water molecule is dominantly determined by the charge state of the transient molecular ions, and it is almost independent from the primary ionization mechanism. Differences were observed not only between the SCI and HCI impact-induced fragmentation cross sections, but between those obtained by the 60 keV N⁶⁺ and 70 keV O⁷⁺ projectiles. The differences were attributed to the selectivity of the electron capture process for HCIs. Multiple target ionization cross sections have been deduced from the fragment ion spectra. We found contributions of up to fivefold ionization for SCIs and up to sixfold ionization for HCIs.     

Mechanism of diffusion of positively charged dust particles in a photoemission cell under microgravity conditions

The decay of a dusty plasma in a photoemission cell under microgravity conditions is investigated on the basis of the method of nonlocal moments. It is founds that plasma decay in space experiments occurs in accordance with the mechanism of free electron diffusion followed by dust particle drift. An analytic solution is found for the evolution of radial distributions of the dust particle concentration and the electric field under the experimental conditions. The effect of abnormally high temperatures of dust particles is considered. The effect of axial magnetic fields on the decay of dusty plasma is investigated. It is shown that the plasma decay in a magnetic field is governed by the ambipolar diffusion mechanism, the decay being prolonged up to 10³ s in a magnetic field on the order of 10³–10⁴ G in strength.     

Beta decay of highly charged ions

Ion storage rings and ion traps provide the very first opportunity to address nuclear beta decay under conditions prevailing in hot stellar plasmas during nucleosynthesis, i.e. at high atomic charge states. Experiments are summarized that were performed in this field during the last decade at the ion storage-cooler ring ESR in Darmstadt. Special emphasis is given to the first observation of bound-state beta decay, where the created electron remains bound in an inner orbital of the daughter atom. The impact of this specific ‘stellar’ decay mode for s-process nucleosynthesis as well as for nuclear ‘eon clocks’ is outlined. Finally, a new technique, single-ion decay spectroscopy, is presented, where one observes two-body beta decay characteristics (i.e. orbital electron capture or bound-state beta decay) of highly charged, single ions for well-defined nuclear and atomic quantum states of both the mother – and the daughter – ion.     

Hyperfine structure of highly charged ions

¹⁹⁷Au Mössbauer spectra from Au/TM (TM = Fe, Co, Ni) multilayers consist mainly of two components. One component shows a large hyperfine magnetic field due to the hybridization at the interface between Au and ferromagnetic layers. The other component is nonmagnetic arising from the middle part of the Au layers. From the fractional area of the magnetic components in each spectrum, the Au atoms in 0.4 nm Au layers are perturbed by the Fe and Ni layers, and Co layers perturb 0.3 nm Au layers at the interface.     

Production of multiply charged xenon ions

A multiply charged ion source based on E.C.R. heating is described and abundances for xenon ions up to Xe¹³⁺ are given.     

A laser system for the spectroscopy of highly charged bismuth ions

We present and characterize a laser system for the spectroscopy on highly charged ²⁰⁹Bi⁸²⁺ ions at a wavelength of 243.87?nm. For absolute frequency stabilization, the laser system is locked to a near-infra-red laser stabilized to a rubidium transition line using a transfer cavity based locking scheme. Tuning of the output frequency with high precision is achieved via a tunable rf offset lock. A?sample-and-hold technique gives an extended tuning range of several THz in the UV. This scheme is universally applicable to the stabilization of laser systems at wavelengths not directly accessible to atomic or molecular resonances. We determine the frequency accuracy of the laser system using Doppler-free absorption spectroscopy of Te₂ vapor at 488?nm. Scaled to the target wavelength of 244 nm, we achieve a frequency uncertainty of σ _{244 nm}=6.14?MHz (one standard deviation) over six days of operation.