Thermal Neutron damage in cadmium

The isochronal annealing of the damage produced by thermal neutron irradiation of cadmium at 3.6 °K has been studied for several initial doses which vary by a factor of 1000. The recovery results show a strong dependence upon initial dose. This effect, which is not seen to this extent in the fcc metals, cannot be accounted for by an irradiation annealing mechanism. In contrast to the observation of two processes involving long range defect migration for several fcc metals only one process, at high temperatures, is discernable from isochronal annealing of Cd. The presence of another process at low temperatures is clearly established by other means. Irradiation annealing effects observed during the production of damage at high defect concentrations indicate that the spontaneous annihilation volume between the defects of a new capture event and the defects from an earlier event is 80 atomic volumes. Other results suggest that damage production and recovery mechanisms may be associated with the anisotropic nature of the cadmium hexagonal lattice.     

Extremely low-energy projectiles for SIMS using size-selected gas cluster ions

A new cluster time-of-flight secondary ion mass spectrometry (TOF-SIMS) was developed using a size-selected gas cluster ion as a projectile. Since a large gas cluster ion can generate many low-energy constituent atoms in a collision with the surface, it causes multiple and ultra low-energy sputtering. The mean kinetic energy of constituent atoms is provided by dividing the acceleration energy of the gas cluster ion by the number of constituent atoms. Therefore, the sputtering can be controlled to minimize the decomposition of sample molecules and substrate material by precisely adjusting the number of constituent atoms (the cluster size) and/or acceleration energy of the gas cluster ion. The cluster size was selected on the basis of the time-of-flight method using two ion deflectors attached along the ion-beam line. A high resolution of 11.7 was achieved for the cluster size/size width (M/ΔM) of Ar-cluster ions.     

Photon emission from clean and oxygenated Si and SiO2 surfaces bombarded by 5 keV krypton ions

The effect of oxygen on the light emission from a Si (1 0 0) semiconductor bombarded by energetic Kr⁺ ions has been studied in the 200–300 nm wavelength range. The influence of oxygen was verified by studying the optical spectra of SiO₂ bombarded under similar experimental conditions. It has been found that the measured intensities of the emitted photons are always higher in the presence of oxygen, even higher than those obtained for SiO₂. The electron-transfer model can explain our experimental observations. We do believe that in the presence of oxygen, an intermediate structure of silicon sub-oxide SiO_X<2 is formed on silicon surface, which is responsible for the increase of photon emission. In addition, the radiative dissociation process and breaking of chemical bond seems contribute to the enhancement of emitted photons intensity.     

Critical energy for damage at silicon surfaces bombarded with low-energy argon ions

Positron-annihilation technique has been used to study the recovery of defects in -irradiated n-type GaAs specimens. The Doppler-broadened lineshape parameterS, shows a smooth recovery of defects over the temperature region 120–600° C. The lifetime measurements have also been performed to characterise the types of defects present. The positron mean lifetime _m follows the behaviour of the S parameter, indicating a rather complex defect structure recovery. The variation in the defect specific parameter,R, with temperature is also consistent with these observations.     

Exchange bias in bulk Ni-Mn-In-based Heusler alloys

The crystal structure and exchange bias of the bulk Heusler alloys Ni₅₀Mn_50−xIn_x with 14.5?x?15.2 have been investigated using X-ray diffraction and magnetization measurements, respectively. Magnetic measurements were performed with SQUID magnetometry after samples were zero-field cooled and field cooled (FC) in positive magnetic fields up to H=50 kOe, from a temperature T=380 K. Three temperatures of the phase transitions, T₁<T_M<T_C, and a shift of the FC (50 kOe) magnetic hysteresis loops up to 120 Oe at 5 K have been detected for all samples. The exchange bias field (H_E) was almost constant for intermediate In concentrations 14.8<x<15.2, and sharply decreased to about 20 Oe on the borders of this concentration interval (x?14.5; 15.2?x). The changes of H_E have been related to changes in the ratio of T₁ to T_M: the overlapping of transitions at T₁ and T_M (for x=14.8, and 15.2) results in a decrease in H_E.     

Influence of sample geometry on determination of magnetocaloric effect for Gd60Co30Al10 glassy ribbons using direct and indirect methods

Rare-earth based metallic glasses with high saturation magnetization show a sizeable magnetocaloric effect (MCE) and are subject of extensive research concerning magnetic refrigeration materials. In this work, the magnetic phase transition from paramagnetic to ferromagnetic of Gd₆₀Co₃₀Al₁₀ metallic glass has been characterized and three different methods were applied for the determination of its magnetocaloric specific parameters: (a) direct measurement of the adiabatic temperature change by exposing the material to an adiabatically applied magnetic field; (b) determination of the magnetization M(H,T) and calculation of the temperature dependent magnetic field induced entropy change ΔS_m by application of the Maxwell relation and (c) measuring the total heat capacity C_p(H,T) in zero and non-zero magnetic field. Gd₆₀Co₃₀Al₁₀ glassy ribbons were prepared by melt spinning, a technique that offers very high cooling rates due to the low dimensionality of the sample. Depending on the particular method of measurement, pieces of these glassy ribbons form samples with different appropriate total volume and dimensions. We show that the combination of the pronounced two-dimensionality of the ribbon pieces (aspect ratio ∼100) together with the very high magnetic permeability principally can cause strong internal demagnetizing fields that cannot be neglected when evaluating the intrinsic MCE parameters obtained from different methods.     

HCl化学激光振转跃迁爱因斯坦自发辐射系数的计算

验证了用Level程序计算爱因斯坦自发辐射系数的可信性,选用精确的RKR势函数和最新的电偶极矩函数,计算得到了振动态量子数小于6的氯化氢激光基频振转跃迁的爱因斯坦自发辐射系数,更新了文献中的数据。结果表明Level是非常适合量子电子学同行使用的一个工具。     

HCl化学激光振转跃迁爱因斯坦自发辐射系数的计算

 验证了用Level程序计算爱因斯坦自发辐射系数的可信性,选用精确的RKR势函数和最新的电偶极矩函数,计算得到了振动态量子数小于6的氯化氢激光基频振转跃迁的爱因斯坦自发辐射系数,更新了文献中的数据。结果表明Level是非常适合量子电子学同行使用的一个工具。     

Electrostatic field effect on molecular structures at metal surfaces

We report on the structural transitions of molecules on metal surfaces by external electrostatic field. An electrode–molecule–electrode model is considered to quantify the effect of electrostatic forces at the molecule–electrode interface. Within a quasi-parallel-plate capacitor approach, this model reveals how external electrostatic fields change the delicate balance between molecule–substrate and molecule–molecule interactions, leading to substantial changes in the molecular conformation. The predictions are validated by scanning tunneling microscopy (STM) observations of four different molecules and electrode facets. In addition, first-principles simulations verify the results of our model calculations.     

Coumarinic fluorescent chemosensors for the detection of transition metal ions

Fluoroionophores consisting of coumarin-153 linked to mono- and diaza-crown ethers are able to complex transition metal cations (Ni²⁺, Zn²⁺, Cd²⁺) and Pb²⁺, with concomitant large changes in photophysical properties. The stability constants in acetonitrile are higher than 3×10⁶ M ^–1 except for Ni²⁺.     

Kinetic electron emission due to perpendicular impact of carbon ions on tungsten surfaces

Total electron yields for perpendicular impact of C⁺ ions on W have been measured for projectile energies from 0.2 keV to 7 keV. The data are compared with the data of C⁺ bombardment of gold and graphite in order to demonstrate general trends in kinetic electron yields at low projectile velocities. The total electron yields in the studied combinations of projectiles and substrates show a similar exponential dependence Γ ∝ (v/A) exp(−A/v), where A is a constant and v is the projectile velocity.     

Effect of heat treatment procedure on magnetic and magnetocaloric properties of Ni43Mn46In11 melt spun ribbons

The effect of heat treatment on the structural, magnetic and magnetocaloric properties of Ni₄₃Mn₄₆In₁₁ melt-spun ribbons was systematically investigated using X-ray powder diffraction (XRD), scanning electron microscope (SEM), atomic force microscope (AFM), magnetic force microscope (MFM) and magnetic measurements. From the XRD studies, tetragonal and cubic phases were detected at room temperature for as-spun, quenched and slow-cooled ribbons. Furthermore, it was observed, upon annealing martensite transition temperatures increased when compared to the as-spun ribbon. To avoid magnetic hysteresis losses in the vicinity of the structural transition region, the magnetic entropy changes-ΔS _m of the investigated ribbons were evaluated from temperature-dependent magnetisation-M(T) curves on cooling for different applied magnetic fields. The maximum ΔS _m value was found to be 6.79 J kg^?1 K^?1 for the quenched ribbon in the vicinity of structural transition region for a magnetic field change of 50 kOe.     

Adsorption of halogens on metal surfaces

This paper presents a review of the experimental and theoretical investigations of halogen interaction with metal surfaces. The emphasis was placed on the recent measurements performed with a scanning tunneling microscope in combination with density functional theory calculations. The surface structures formed on metal surface after halogen interaction are classified into three groups: chemisorbed monolayer, surface halide, bulk-like halide. Formation of monolayer structures is described in terms of surface phase transitions. Surface halide phases are considered to be intermediates between chemisorbed halogen and bulk halide. The modern theoretical approaches in studying the dynamics of metal halogenation reactions are also presented.     

Effect of the competition between relaxation and core hole decay on the Auger-photoelectron coincidence spectroscopy (APECS) spectrum of Ni metal

The valence hole created in Ni metal either by the L2-L3V Coster–Kronig (CK) transition or by the L3V shakeup/off becomes screened out prior to the L3-hole decay. We denote the atomic shell Lx (x = 2, 3) by LX. The metastable two-hole L3V state relaxes to the fully relaxed single L3-hole state before the L3-hole decays. Thus, the coincidence L2-L3(V)-VV(V) Auger-electron spectrum resembles closely the coincidence L3-VV Auger-electron spectrum. The final state of the CK transition preceded Auger transition is a two-hole state rather than a three-hole state. The four-hole satellite about 8 eV below the L3-VV main line in the singles (non-coincidence) Auger-electron spectrum is partly due to the L3VV-VVVV transition and the L2-L3VV-VVVV transition. The valence holes created either by the L2-L3VV transition or by the L3VV double shakeup/off remain localized during the L3-hole decay. The L3-hole lifetime widths of Fe, Co and Ni metals are determined from the APECS spectra. The agreement between experiment and theory (the independent-particle approximation) is poor.     

Significant influences of metal reactivity and oxide films at particle surfaces on coating microstructure in cold spraying

Based on large amount of experimental observations, the effects of metal reactivity and oxide films at particle surfaces on coating deposition behavior in cold spraying were presented and discussed. The oxygen contents in as-sprayed Ti, Ti-6Al-4V and Al coatings were higher than those in the corresponding starting powders. The obvious flashing jets outside nozzle exit during deposition of Ti and Ti-6Al-4V were caused by the reaction of the particles with oxygen in the entrained or the adopted air. For Ti and Ti-6Al-4V coatings, their porous structures are predominantly attributed to the surface reactivity (defined as reactivity with oxygen). This surface reaction could be helpful for formation of a metallurgical bonding between the deposited particles. For Al, even though it is more reactive than Ti, the oxide films at Al particle surfaces suppress the surface activity.     

Radioactive ions for solid-state investigations at magnetic surfaces and interfaces

Hyperfine interactions observed at isomeric states of radioactive probe nuclei are used as a tool for solid-state investigations. This method is sensitive to atomic-scale properties. In recent years surface and interface investigations using radioactive probes delivered many results which can hardly be achieved by any other method. Several groups, e.g., from Konstanz, Leuven, Groningen, Aarhus, Uppsala, Tel Aviv, Pennsylvania, contributed to this field. Our group studies magnetic properties at surfaces and interfaces performing perturbed angular correlation (PAC) measurements in the UHV chamber ASPIC (Apparatus for Surface Physics and Interfaces at CERN). We take advantage of the enhanced variety of PAC probes delivered by the on-line mass separator ISOLDE. First, we report on measurements of magnetic hyperfine fields ( B _hf) at Se adatoms on a ferromagnetic substrate using ⁷⁷Se as a PAC probe. The investigation of induced magnetic interactions in nonmagnetic materials is a further subject of our studies. Here the nonmagnetic 4d element Pd is investigated, when it is in contact with ferromagnetic nickel. An outlook will be given on studies to be done in the future. The experiments were performed at the HMI, Berlin, and at CERN, Geneva. Received: 1 May 2001 / Accepted: 4 December 2001     

铝对过渡金属离子掺杂的二氧化硅溶胶凝胶玻璃发光性质的影响

用溶胶凝胶法制备了过渡金属离子(Ni2+,Mn2+和Cu2+)单掺、铝共掺的二氧化硅玻璃,测量了荧光光谱、吸收光谱和红外光谱,研究了Al3+对过镀金属离子在二氧化硅玻璃中发光性质的影响。研究结果表明,Al3+对过渡金属离子的发光性质有着显著影响:Ni2+,Mn2+和Cu+的发光强度大幅度提高,Mn2+的发光峰峰位改变。     

Hydrogen dissociation on metal surfaces – a model system for reactions on surfaces

Received: 23 March 1998/Accepted: 21 August 1998     

金属Pt薄膜上二氧化钒的制备及其电致相变性能研究

通过引入SiO₂氧化物缓冲层, 在金属Pt电极上利用射频磁控溅射技术成功制备出高质量的VO₂薄膜. 详细研究了SiO₂厚度对VO₂薄膜的晶体结构、微观形貌和绝缘体–金属相变(MIT)性能的影响. 结果表明厚度0.2 μm以上的SiO₂缓冲层能够有效 消除VO₂薄膜与金属薄膜之间的巨大应力, 制备出具有明显相变特性的VO₂薄膜. 当缓冲层达到0.7 μm以上, 获得的薄膜具有明显的(011)晶面择优取向, 表面平整致密, 相变前后电阻率变化达到3个数量级以上. 基于该技术制备了Pt-SiO₂/VO₂-Au三明治结构, 通过在垂直膜面方向施加很小的驱动电压, 观察到明显的阶梯电流跳跃, 证实实现了电致绝缘体–金属相变过程. 该薄膜制备工艺简单, 性能稳定, 器件结构灵活可应用于集成式电控功能器件. 关键词： 二氧化钒薄膜 相变特性 电致相变 阈值电压