氮团簇离子注入单晶硅的光致发光谱研究

氮团簇离子N⁺₁₀注入单晶硅直接诱发其表层转化为纳米晶结构, 导致光学性质发生显著变化. 在250—320nm波段的紫外光激励下,在330—500nm光区出现明显的光发射带,并在360nm附近产生强度极高、单色性良好的发射峰,其强度达到N⁺注入试样或基底的5倍,是N⁺₂注入试样的1.5倍. 在可见光区的730nm附近和近红外区的830nm附近也出现发光带. 所有上述发光都非常稳定,可长时间保持其发 关键词： 光致发光 团簇离子注入 硅单晶 纳米晶结构     

Defects formation in the dual B+ and N+ ions implanted silicon

Silicon wafers were implanted with 40 keV B⁺ ions (to doses of 1.2×10¹⁴ or 1.2×10¹⁵ cm^–2) and 50 or 100 keV N⁺ ions (to doses from 1.2×10¹⁴ to 1.2×10¹⁵ cm^–2). After implantations, the samples were furnace annealed at temperatures from 100 to 450 °C. The depth profiles of the radiation damages before and after annealing were obtained from random and channeled RBS spectra using standard procedures. Two damaged regions with different annealing behaviour were found for the silicon implanted with boron ions. Present investigations show that surface disordered layer conserves at the annealing temperatures up to 450 °C. The influence of preliminary boron implantation on the concentration of radiation defects created in subsequent nitrogen implantation was studied. It was shown that the annealing behaviour of the dual implanted silicon layers depends on the nitrogen implantation dose.The authors would like to thank the members of the INP accelerator staff for the help during the experiments. The work of two authors (V.H. and J.K.) was partially supported by the Internal Grant Agency of Academy of Science of Czech Republic under grant No. 14805.     

Short-laser-pulse-driven emission of energetic ions into a solid target from a surface layer spalled by a laser prepulse

An efficient emission of picosecond bunches of energetic protons and carbon ions from a thin layer spalled from a organic solid by a laser prepulse is demonstrated numerically. We combine the molecular dynamics technique and multi-component collisional particle-in-cell method with plasma ionization to simulate the laser spallation and ejection of a thin (∼20–30 nm) solid layer from an organic target and its further interaction with an intense femtosecond laser pulse. In spite of its small thickness, a layer produced by laser spallation efficiently absorbs ultrashort laser pulses with the generation of hot electrons that convert their energy to ion energy. The efficiency of the conversion of the laser energy to ions can be as high as 20%, and 10% to MeV ions. A transient electrostatic field created between the layer and surface of the target is up to 10 GV/cm. Received: 13 March 2001 / Accepted: 20 March 2001 / Published online: 20 June 2001     

X-ray emission and photoluminescence spectroscopy of nanostructured silica with implanted copper ions

Quartz glass samples and compacted SiO₂ nanopowders have been studied by x-ray emission (CuL _{2, 3} transition 3d4s → 2p _{1/2, 3/2}) and photoluminescence spectroscopy following pulsed Cu⁺ ion implantation (energy, 30 keV; pulse current up to 0.5 A; pulse duration, 400 μs; irradiation doses, 10¹⁵, 10¹⁶, and 2 × 10¹⁷ cm^?2). It has been established that ion irradiation gives rise to the formation of glassy and compacted SiO₂ samples of nanosized metallic and oxide phases in the structure. An analysis of CuL x-ray emission spectra has shown that copper nanoparticles are thermodynamically metastable and chemically active because ion beam bombardment transfers them readily to the oxide form. This results from the radiation-stimulated fracture of regular Si-O-Si bonds in amorphous SiO₂ and the formation of defective Si-Si bonds, followed by capture of oxygen by copper atoms. The enhanced degree of oxidation of copper ions in SiO₂ nanostructured pellets can be reduced by coimplantation and thermal annealing. Optical spectroscopy studies suggest that, in glasses and SiO₂ nanostructured pellets, there exist metallic Cu _n ⁰ nanoclusters, which at low temperatures exhibit quantum-confined photoluminescence with a characteristic stepped excitation spectrum.     

Dependence of surface nano-structural modifications of Ti implanted by N ions on temperature

The surface modification of titanium thin foil/sheet samples (0.5 mm) implanted by nitrogen ions of 30 keV energy and a fluence of 1 × 10¹⁸ N⁺ cm⁻² at different temperatures is studied using XRD, AFM, SEM, and SIMS. XRD patterns showed the development of titanium nitride with different compositions in the implanted samples, while the presence of different titanium compositions such as titanium oxides was also observed. AFM images at 654 K showed the formation of grains, that after initial sputtering of the grain boundary at 728 K temperature, the morphology of the surface changed from small grains to a bimodal distribution of grains at 793 K which consisted of larger grains with bright hillocks within them. This was considered to be due to phase transformation/compositional changes, explained by correlating XRD and SIMS results. The SIMS results showed a maximum at about 730 K and a minimum at about 790 K for both N⁺ density and depth of N⁺ penetration in the Ti sample. The variation of these results with temperature was explained on the basis of the residual gas, substrate temperature, dissociation of water in the chamber and the gettering property of titanium.     

Chemical surface composition of the polyethylene implanted by Ag ions studied by phase imaging atomic force microscopy

High density polyethylene (HDPE) has been modified by Ag⁺ ion implantation with the energy of 60 keV. The total amount of implanted silver ions was 1, 5 and 12 × 10¹⁵ ions/cm². The surface topography was observed by atomic force microscopy (AFM), while the surface composition changes were detected using phase imaging AFM. Surface topography changes were studied in detail using 3D surface parameters analyses. The average roughness decreased for the implanted HDPE indicating the flattening of the surface. Phase AFM images indicated the homogenization of the polyethylene during ion implantation, while histogram analyses confirmed the change in surface composition.     

Sputtering of solicon and germanium by middle-energy heavy ions

The angular and energy dependences of the sputtering ratios of silicon and germanium targets under bombardment by argon ions of ten-keV energy are studied.     

On the redistribution of6Li + ions implanted into polypropylene foils

⁶Li⁺ (150 keV) was implanted into thin polypropylene foils at fluences of 1 x 10¹³ to 1 x 1014 cm^–2. Subsequent neutron depth profiling measurements of the Li distributions revealed considerable deviations from the expected ballistic range profiles. This Li redistribution was simulated by a numerical computer calculation. The best fit between measurements and simulations was obtained by assuming that (i) Li redistributes immediately after its ballistic slowing-down, (ii) the Li mobility is enhanced in the radiation-damaged polymer region, the local diffusion enhancement being controlled by the target's electronic damage, (iii) mobile Li is readily trapped at radiation-induced defects, their density being proportional to the target's electronic damage, (iv) these traps are saturable ones, and (v) Li migration is not restricted to the ion track region, but proceeds also through the neighboring unirradiated bulk, though with slower speed.     

Antimony implanted silicon: A comparison between the total implanted concentration profile and the donor concentration profile

Abstract

The total concentration profiles of various doses of antimony, implanted into silicon at 100 keV, have been determined by a new technique, using Kr⁺ ions to detect selectively the antimony (as Sb-M X-rays) at the expense of the silicon. Since most of these X-rays arise from only a few tens of Angstroms below the surface of the silicon, this allows the X-ray generation to be used in conjunction with an anodic stripping technique to obtain the antimony depth distribution. These profiles are compared with others, obtained by measuring the donor concentration as a function of depth, using standard Hall effect and conductivity measurements. A significant difference between these profiles was observed, which is thought to be due to the suppression of electrical activity which occurs as the result of lattice damage. Confirmatory evidence is presented in the form of electron microscope observations of the implanted region at various depths below the silicon surface.     

Photoemission and luminescence properties of quartz glass implanted with Cu+ ions

The special features of optically stimulated electron emission and luminescence of defects in KV quartz glass after Cu⁺ ion pulse implantation are studied. It is shown that the ion-beam modification of the photoemission and luminescence properties of samples is due to the formation of radiation defects and by dimensional factors caused by the appearance of Cu nanoparticles.     

Light emission by swift He+ ions after focusing and channeling interactions on a monocrystalline nickel surface

The light emission from 195 keV He⁺ ions excited in scattering at a (101) Ni surface is used to indicate anisotropy effects of beam steering at monocrystalline surfaces. Experiments and computer simulations give clear evidence of focusing by surface channels and of maximum and minimum critical angles for planar channeling.     

Increase of the blue upconversion emission in YAG:Tm3+ nanopowders by codoping with Yb3+ ions

The YAG nanopowders were prepared by a co-precipitation method using nitrate and ammonium hydrogen carbonate as raw materials. To obtain homogenous precipitate, reverse-strike (adding salt solutions to the precipitant solution) technique was adopted. Therefore, single (Tm³⁺) and codoped (Tm³⁺–Yb³⁺) YAG nanopowders with a size between 40–90 nm have been obtained.Blue upconversion emission at around 480 nm has been found in YAG: Tm³⁺ nanopowders under excitation to the ³H₄ level of Tm³⁺ at around 800 nm. However, this upconversion emission in nanopowders codoped with Tm³⁺–Yb³⁺ ions is increased by a factor of about 10. The analysis of the temporal evolution of the involved levels and the dependence of the upconversion intensity on the pump power at 800 nm allowed to distinguish the upconversion mechanism. In YAG: Tm³⁺ nanopowders the upconversion mechanism is due to excited state absorption processes. However, in the codoped samples, Yb³⁺ ions acts as the sensitizers; in consequence, the blue upconversion is strongly increased.     

Surface chemical disorder and lattice strain of GaN implanted by 3-MeV Fe10+ ions

Chemical disorder on the surface and lattice strain in GaN implanted by Fe¹⁰⁺ ions are investigated. In this study, 3-MeV Fe¹⁰⁺ ions fluence ranges from 1×10¹³ ions/cm² to 5×10¹⁵ ions/cm² at room temperature. X-ray photoelectron spectroscopy, high-resolution x-ray diffraction, and high-resolution transmission electron microscopy were used to characterize lattice disorder. The transition of Ga-N bonds to oxynitride bonding is caused by ion sputtering. The change of tensile strain out-of-plane with fluence was measured. Lattice disorder due to the formation of stacking faults prefers to occur on the basal plane.     

Surface nanostructural modifications of Ti implanted by N+ ions as a function of energy

The surface modification of titanium foil/sheet samples (0.5?mm thickness) implanted by nitrogen ions of different energy and fluence of 1?×?10^18?N^+?cm^?2 was studied using X-ray diffraction (XRD), atomic force microscopy (AFM), scanning electron microscopy and secondary-ion mass spectrometry (SIMS). XRD patterns showed the development of titanium nitride with different compositions in the implanted samples, and the presence of different titanium compositions such as titanium oxides was also observed. AFM images at 16 and 20?keV showed the formation of grains, which were attributed to the initial sputtering of grain boundaries. The morphology of the surface changed at 25?keV showing granular structure with an almost uniform background and lowest surface roughness relative to lower and higher implantation energies. A correlation was obtained between all results for XRD, SIMS and AFM except the titanium nitride maximum intensity at 25?keV N⁺ implantation. In order to achieve more detailed information about the role of N⁺ energy in this kind of work it is proposed that a further investigation is needed on both N⁺ energy and substrate temperature as well as some theoretical studies.     

Low-energy surface collision induced dissociation of Ge and Sn cluster ions

Fragmentation of germanium and tin cluster ions in the low-energy collisions with a Si surface has been investigated by means of a tandem time-of-flight mass spectrometer. At low incident energies, smaller clusters fragmented by an atom loss process, whereas larger clusters decayed by fission. The favored fragmentation paths for both cluster ions were similar to those for Si cluster ions. The results support the structural similarities among Si, Ge, and Sn clusters in the present size range. For tin cluster ions, low-energy fragmentation patterns were compared with those obtained from theoretical calculations using generalized gradient approximation (GGA) and the B3PW91 exchange-correlation functional. It has been found that the B3PW91 hybrid functional results are consistent with the experimental observations.