Fe_（73．5）Cu_1Nb_3Si_（13．5）B_9非晶合金化过程的X射线

采用Ｘ射线衍射和正电子湮没多普勒展宽测量相结合，研究了纳米晶态材料Ｆｅ７３．５Ｃｕ１Ｎｂ３Ｓｉ１３．５Ｂ９的结构随退火温度的变化。实验结果表明：急冷非品样品在４８０℃开始明显晶化，基体中析出体心立方结构的α－Ｆｅ（Ｓｉ）固溶体。随着退火温度的升高，非晶漫射峰不断减弱，而晶态相的衍射谱逐渐增强。进一步计算对衍射谱的分离，给出了品化分数和非晶相平均原子间距随退火温度的变化规律。正电子湮没实验证实了约５５０℃退火时样品内出现以Ｎｂ、Ｂ原子为主的晶界非晶相，Ｓ参数随退火温度的变化与非晶相平均原子间距随退火温度的变化规律一致。     

Preparation and characterization of graphene nanoribbons

Graphene nanoribbons(GNRs) have been synthesized by unzipping oxidized multiwalled carbon nanotubes.The thickness of the GNRs synthesized is ranged from mono-layer to four layers.The morphology of prepared GNRs is strongly dependent on structure and defects of the MWCNTs.The synchrotron radiation X-ray diffractions show the d(002) spacing of the GNRs decreases with the increase of the annealing temperature.This may be caused by the removing of water molecules and oxygen-containing functional groups in the GNRs.     

Translational and rotational energy measurements of desorbed water molecules in their vibrational ground state following 157 nm irradiation of amorphous solid water

Water ice is the major solid component in a variety of astrophysical environments, e.g., cold and dense molecular clouds. Photodesorption plays a dominant role in consuming ice in such cold regions. In this study, photodesorption of vibrationally ground-state H₂O(v = 0) from amorphous solid water has been investigated at 157 nm. Using a resonance-enhanced multiphoton ionization technique, the translational and rotational energy distributions of photodesorbed H₂O(v = 0) were measured, i.e., Boltzmann distributions at 1800 and 300 K, respectively. These energies are in good accordance with those predicted by classical molecular calculations for water photodesorption due to a kick-out mechanism following absorption of a single photon; hot H atom released by photodissociation of H₂O in ice transfers enough momentum to another H₂O molecule to kick it off the surface. Desorption of D₂O(v = 0) following 193 nm photoirradiation of a D₂O/H₂S mixed ice was investigated to provide further direct evidence for the operation of a kick-out mechanism. The other desorption mechanisms were also discussed in the context of possible photodesorption of vibrationally excited H₂O.     

Angular distributions of Diffracted Channeling Radiation from moderate energy axially channeled electrons in Si and LiF crystals

Numerical calculations of the Diffracted Channeling Radiation angular distributions from axially channeled electrons with relativistic factor γ = 20 in Si and LiF crystals are performed. The calculations are based on a newly developed effective quantum-mechanical calculations algorithm of the wave functions and electron energies at axial channeling in a crystal. The numerical results obtained exhibit some new features of the Diffracted Channeling Radiation from axially channeled electrons compared to that from planar channeled electrons, e.g. increase of the widths of peaks, which might be useful in future experiments on observation of Diffracted Channeling Radiation.     

Sputtering and surface state evolution of Bi under oblique incidence of 120 keV Ar ions

The sputtering and surface state evolution of Bi/Si targets under oblique incidence of 120 keV Ar⁺ ions have been investigated over the range of incidence angles 0° ? θ_i ? 60°. Increasing erosion of irradiated samples (whose surface thickness reduced by ∼3% at normal incidence up to ∼8% at θ = 60°) and their surface smoothing with reducing grain sizing were pointed out using Rutherford backscattering (RBS), atomic force (AFM) and X-ray diffraction (XRD) techniques. Measured sputtering yield data versus θ_i with fixed ion fluence to ∼1.5 × 10¹⁵ cm⁻² are well described by Yamamura et al. semi-empirical formula and Monte Carlo (MC) simulation using the SRIM-2008 computer code. The observed increase in sputter yield versus incidence angle is closely correlated to Bi surface topography and crystalline structure changes under ion irradiation.     

Structural and compositional characterization of LiNbO3 crystals implanted with high energy iron ions

Iron ions were implanted with a total fluence of 6 × 10¹⁷ ions/m² into lithium niobate crystals by way of a sequential implantation at different energies of 95, 100 and 105 MeV respectively through an energy retarder Fe foil to get a uniform Fe doping of about few microns from the surface. The implanted crystals were then annealed in air in the range 200-400 °C for different durations to promote the crystalline quality that was damaged by implantation. In order to understand the basic phenomena underlying the implantation process, compositional in-depth profiles obtained by the secondary ion mass spectrometry were correlated to the structural properties of the implanted region measured by the high resolution X-ray diffraction depending on the process parameters. The optimised preparation conditions are outlined in order to recover the crystalline quality, essential for integrated photorefractive applications.     

Effect of irradiation by 140 Mev Ag ions on the optical and electrical properties of polypropylene/TiO2 composite

Changes in the optical, structural, dielectric properties and surface morphology of a polypropylene/TiO₂ composite due to swift heavy ion irradiation were studied by means of UV–visible spectroscopy, X-ray diffraction, impedance gain phase analyzer and atomic force microscopy. Samples were irradiated with 140 MeV Ag¹¹⁺ ions at fluences of 1 × 10¹¹ and 5 × 10¹² ions/cm². UV–visible absorption analysis reveals a decrease in optical direct band gap from 2.62 to 2.42 eV after a fluence of 5 × 10¹² ions/cm². X-ray diffractograms show an increase in crystallinity of the composite due to irradiation. The dielectric constants obey the Universal law given by ε α f ⁿ⁻¹, where n varies from 0.38 to 0.91. The dielectric constant and loss are observed to change significantly due to irradiation. Cole–cole diagrams have shown the frequency dependence of the complex impedance at different fluences. The average surface roughness of the composite decreases upon irradiation.     

Deduction of the He–Fe interaction potential in eV-range from experimental data by computer simulation in grazing ion-surface scattering: Row-model

In glancing-angle scattering of keV-ions from a crystal surface, the ion reflection takes place in the eV-part of the interaction potentials. The elastic interactions are determined by the energy transverse to atomic rows, which can be of the order of 10 eV. A row-model using averaged potentials according to the Lindhard cylindrical potential has been developed using step-by-step integration of Newton's equations of motion. Previously [D. Danailov, K. Gärtner, A. Caro, Nucl. Instr. and Meth. B 153 (1999) 191; presented on COSIRES, Okayama, 1998] we reported that zig–zag trajectories within surface channels and the corresponding multimode azimuthal angular distributions of reflected ions are very sensitive to the interaction potential used in the simulation. Here we simulate the scattering of 15 keV He-atoms from Fe(1 0 0) surfaces at different angles of incidence comparable with previously published experimental results [D. Danailov, T. Igel, R. Pfandzelter, H. Winter, Nucl. Instr. and Meth. B 164–165 (2000) 583]. Our results show that for interaction energies below about 4 eV the well-known “universal” potential works well. However, for energies between 4 and 13 eV the “individual” He–Fe potential (D. Danailov, K. Gärtner, A. Caro, Nucl. Instr. and Meth. B 153 (1999) 191; presented on COSIRES, Okayama, 1998) gives a better agreement with the experimental data. For interaction energies above 13 eV both potentials are similar. We have constructed a mixed He–Fe potential, which describes the experimental observations well. The row-model enables us to deduce the He–Fe interaction potential in the eV-range. In addition, a shift in the experimental angular spectra compared with the calculated spectra indicates that the atomistic rows undergo an elastic horizontal bend due to the scattering and an order of magnitude smaller vertical displacement.     

Mössbauer study and structural characterization of UO2–Gd2O3 sintered compounds

Samples of UO₂and up to 10 wt% of Gd₂O₃ were prepared by solid-state reaction under a reducing atmosphere, in a thermal path comprising ramps and dwell times in the temperature range of 900–1750 °C. The sintered material was analyzed by X-ray diffraction and ¹⁵⁵Gd Mössbauer spectroscopy. The results showed that for samples annealed up to 900 °C, the gadolinium sesquioxide remained unreacted. However, when the temperature was increased to 1300 °C, a solid-state reaction took place forming mixed oxides. For the more severe sintering condition, at 1750 °C, gadolinia left urania partially unreacted producing a material consisting of two compositions, UO₂ (with no dissolved gadolinium) and (U, Gd)O₂. The proposed heating cycle provided pellets free from Gd₂O₃ phase and may be used by the nuclear fuel industry as a suitable sintering process.