Radiation effect on the photoluminescence properties of Si/SiO2 thin films

Silicon ions were implanted into SiO₂ thin films with various doses and energies. For the films implanted with various ion doses the photoluminescence (PL) intensity of 470 nm firstly increased with the increase of Si ion dose, which is similar to the variation trend of displacement per atom (DPA) number during ion radiation. Further increasing Si ion dose the PL intensity of 470 nm decreased gradually since the neutral oxygen vacancy centers were destroyed. For the samples implanted with different energy the variation trend of PL intensity for 470 nm peak is similar to the result of DPA under different radiation energy according to SRIM2006 simulation. With the increase of radiation energy a new PL peak at 550 nm appeared because of the variation of defect type. Combining with the simulation results and PL spectra the radiation effect on Si/SiO₂ thin films were proposed.     

Nonlinear optical properties of MeV and keV ion beam synthesized Ag nanoclusters

Ag nanoclusters embedded in silica glass matrix have been synthesized by high fluence ion implantation using both keV and MeV ion beams. In keV implantation case, optical absorption shows an intense surface plasmon resonance (SPR) peak corresponding to the Ag clusters formed in the matrix. Transmission electron microscopy (TEM) measurements carried out on identically implanted SiO₂ thin films on a TEM catcher grid shows the presence of Ag nanoclusters of size around 4 nm in the matrix. However, for the MeV implantation case, the SPR peak appears in the optical absorption spectra only after air annealing the sample at 500 °C for one hour. For the annealed samples, TEM measurements show the presence of 6 nm sized Ag nanoclusters. On the other hand the as-implanted sample shows smaller nanoclusters with a lower particle density in the matrix. Interestingly, open aperture z-scan measurements carried out on keV implanted samples did not show any nonlinear absorption, while the MeV as-implanted as well as annealed samples showed nonlinear absorption. The nonlinear absorption coefficient of the MeV annealed sample is extracted from a fit to the z-scan data considering a three photon like absorption process.     

Mechanisms in the ion beam mixing of Al in Si

Ion beam mixing of Al in Si has been studied by implanting 100 keV ⁴⁰Ar⁺ ions into 300 Å Al overlayers on Si substrates. The mixing of the collisionally similar Al and Si atoms was studied with the nuclear resonance broadening technique. It is characterized to be proportional to the square root of ion fluence. The mixing is compared with that of Al in Si due to irradiation with 40 keV ²²Ne⁺ ions studied recently by us. Mechanisms which enhance the observed atomic mixings with about 5 times that expected for ballistic mixing have been studied by Monte Carlo simulation of the collisional cascades. The results indicate the need to revise the present model of the ballistic mixing by focusing more attention to the effect of low-energy impurity—matrix atom collisions.     

The excitation power density effect on the Si nanocrystals photoluminescence

In the present work we have studied the photoluminescence (PL) behavior from Si nanocrystals (NCs) as a function of the excitation power density and annealing time. The NCs were produced in a SiO₂ matrix by Si implantations from room temperature (RT) up to 700 °C, followed by post-annealing in N₂ atmosphere at high temperature. With this aim we have changed the excitation power density (from 2 × 10⁻³ W/cm² up to 15 W/cm²) and the annealing time (from 10 min up to 15 h). The strong PL signal, which at 15 W/cm² is composed by a single-peak structure (650–1000 nm) centered at around 780 nm, expands up to 1200 nm showing a two-peak structure when measured at 20 × 10⁻³ W/cm². The peak structure located at the short wavelength side is kept at 780 nm, while the second peak, starting at around 900 nm, redshifts and increases its intensity with the implantation temperature and annealing time. The effect of the annealing time on the PL spectra behavior measured at low excitation power agrees by the first time with the Si NC growth according to quantum confinement effects.     

Influence of annealing temperatures and time on the photoluminescence properties of Si nanocrystals embedded in SiO2

We report on the effects of annealing conditions on the photoluminescence from Si nanocrystal composites fabricated by implantation of Si ions into a SiO₂ matrix, followed by thermal treatment in a nitrogen atmosphere. The evolution of the photoluminescence under different annealing temperatures (900–1100 °C) and annealing time (0.5 up to 5 h) were systematically studied for the implanted samples. After annealing the spectra presented two photoluminescence bands: one centered at 610 nm and another around 800 nm. Combined with transmission electron microscopy, we conclude that the photoluminescence behavior of the two bands suggests different origins for their emissions. The 610 nm band has its origin related to matrix defects, while the 800 nm band can be explained by a model involving recombination via quantum confinement effects of excitons in the Si nanocrystals and the interfacial states recombination process confined in the interfacial region between nanocrystals and SiO₂ matrix.     

Superconductivity in MgB2 films synthesized by ablation from high-power ion beam

MgB₂ thin films with T_c = 19 K were fabricated by the ion ablation technique utilizing a high-energy pulsed ion beam. A target remains pure MgB₂ after ablation, proving the excellent capability of ablation by the high-power ion beam. Chemical compositions of the deposited material, however, may vary with positions of the substrates from the beam axis. X-ray diffraction patterns exhibit only (0 0 1) and (0 0 2) peaks, which indicate a c-axis orientation of the films. Scanning electron microscopy images show a possible growth of single crystals with hexagonal shape and 1 μm size.     

强流脉冲离子束辐照对钛合金显微组织的影响

为研究强流辐照过程中钛合金微观组织结构和化学成分的变化,利用束流成分70%H+和30%C+的混合强脉冲离子束对钛合金进行了表面轰击,对离子束诱发的显微组织形貌和化学成分在扫描电子显微镜(SEM)上进行分析。结果表明,钛合金内部组织由α和β两相构成,为α+β型两相钛合金。试样不同区域组织类型存在明显差异,大部分区域组织类型一致,局部区域属于典型的魏氏组织。强流辐照钛合金表层组织和微观结构发生一定的变化,边缘β相结构遭到一定程度的破坏。显微组织结构的变化是由于表层温度梯度引起的热应力及其在靶材体内的传播造成的。     

Investigation of the ion acoustic effect during focused ion beam irradiation

Acoustic waves induced by an intensity modulated focused ion beam (FIB) have been measured. The experiments were performed with Ga⁺ ions of 35 keV at a current of 3 nA and variable chopping frequency up to 10 MHz. The acoustic signals were detected by means of a piezoelectric sensor with integrated pre-amplifier. A dependence on the sample material was found during line scan FIB motion. The results show that the ion-acoustic effect may be utilized for an alternative sample imaging and material analysis in FIB systems.     

Deposition of polycrystalline Si thin films on glass substrates by direct negative Si ion beam deposition

Polycrystalline Si (Poly-Si) thin films were deposited on a glass substrate by direct negative Si (Si⁻) ion beam deposition. The glass substrate temperature was kept constant at 500 °C for all depositions. Prior to deposition, the ion energy spread and ion-to-atom arrival ratio were evaluated as a function of the ion beam energy.The Si⁻ ion energy spread was less than 10% regardless of the ion energy, while the ion-to-atom arrival ratio increased proportionally from 1.3 to 1.6 according to the ion beam energy.Atomic force microscopy images showed that a relatively rough surface was obtained at 50 eV of Si⁻ ion energy and it is also concluded that the Si⁻ ion beam irradiation at 50 eV is effective to deposit Si thin film with small grains as shown in Fig. 3.     

Thermal and mechanical properties of polycrystalline U3Si2 synthesized by spark plasma sintering

U₃Si₂ has been explored as an alternative nuclear fuel material for increased accident tolerance. However, scatter has been reported in the thermal properties possibly because of the pores and impurities within the samples. In the present study, we prepared a polycrystalline U₃Si₂ bulk sample with high density and without impurity, and evaluated its thermal and mechanical properties. The sample was synthesized by arc melting and spark plasma sintering, followed by annealing. The density of the U₃Si₂ pellet was 96% of the theoretical density. The heat capacity was measured and compared with the calculation data. In addition, the measured data were used to evaluate thermal conductivity of U₃Si₂. The measurement data of elastic properties were compared with the theoretical calculation and agreed well. A high thermal conductivity and hardness compare to UO₂make it favorable to anticipated as alternative nuclear fuel.     

Diffusion inhibition against gold of ion beam synthesized buried silicon nitride layers in silicon

The ability of buried silicon nitride layers, produced by nitrogen implantation into silicon (330 keV, 1.2 × 10¹⁸ cm⁻²), to inhibit the diffusion of gold was tested. Buried amorphous layers characteristic for the as-implanted state as well as for postimplantation annealing at 1000°C show diffusion inhibition. This effect was not found for polycrystalline silicon nitride layers produced by annealing at 1200° C.     

Ni/Si体系离子束混合及相变研究

注入参量变化引起不同的混合结果,在宽温区中得到Ni_2Si、NiSi、NiSi_2多种化合物相,进而探讨了Xe离子诱导的Ni/Si体系界面原子混合机理及诱发相变的动力学过程。     

快重离子束引起的Cu-Si膜系的两种不同类型的增强附着效应

对沉积在N型半导体硅上的Cu薄膜用几MeV的Cl离子进行了不同剂量的辐照实验以观测其增强附着行为。结果表明,Cu-Si膜系存在两种不同类型的增强附着效应。用扫描电镜对低剂量轰击出现附着增强区域的硅基底表面进行观察,未发现任何微裂现象。这与人们在解释Au-SiO_2膜系出现类似增强附着时提出的微裂观点不相符合。     

Instrumentation and application of the ion beam analysis line of the in situ ion beam system

An ion beam analysis system was established on a 1.7 MV tandem accelerator, enabling Rutherford backscattering(RBS), elastic recoil detection(ERD), nuclear reaction analysis(NRA) and channeling measurements. The system was tested by performing qualitative and quantitative analysis of Si, Ni/Si, Bi Fe O3:La/Si,Mo C/Mo/Si and Ti BN/Si samples. RBS of a Bi Fe O3:La film was used as system calibration. Tested by ion beam channeling, a Si(100) is of good crystallinity(χmin= 3.01%). For thin film samples, the measured thickness agrees well with simulation results by SIMNRA. In particular, composition of a Mo C/Mo/Si and Ti BN film samples were analyzed by RBS and non-Rutherford elastic backscattering.     

Effect of crystallinity on the memory effect of Ge nanocrystals synthesized by atom beam sputtering

The effect of crystallinity of Ge nanocrystals on the charge storage properties of the metal oxide semiconductor (MOS) structure has been investigated. MOS structure with Ge nanocrystals embedded in the oxide has been fabricated by using atom beam sputtering technique. After annealing at 600 °C in Ar + H₂ atmosphere, capacitance-voltage (C-V) measurements show flat band voltage shift of ∼0.9 V. It which is a clear indication of the memory effect of Ge nanocrystals, while unannealed structure doesnot show any hysteresis in the C-V curve. Micro Raman spectroscopy and X-ray diffraction (XRD) analyses show that crystalline content of Ge nanoparticles in the MOS structure has increased after annealing.     

Modeling of ion beam induced damage in Si during channeling Rutherford backscattering spectrometry analysis

We have modeled damage creation by an analyzing beam during channeling Rutherford backscattering spectrometry (RBS) analysis. Based on classic scattering theory and the assumption that only a dechanneled ion beam can cause displacements, a chi-square approach is used to fit the modeled spectra with experimental profiles, to extract the dechanneling cross section and the displacement creation efficiency. The study has shown that, for a 2.0 MeV He beam channeled along a Si(1 0 0) axis, the efficiency of defect creation by dechanneled beams is about 8% of the value predicted from the Kichin-Pease model. This suggests a significant dynamic annealing of point defects. The modeling procedure in this work can be used to predict the displacement creation during channeling RBS analysis.     

Effect of different ion beam energy on properties of amorphous carbon film fabricated by ion beam sputtering deposition (IBSD)

Amorphous carbon (a-C) films were fabricated by ion beam sputtering technique. The influence of sputtering ion beam energy on bonding structure, morphologic, mechanical properties, tribological properties and corrosion resistance of a-C films are investigated systematically. Morphology study shows that lowest surface roughness exists for mid-ion beam energy. Improved adhesion is observed for the films that are prepared under high ion beam energy, attributed to film graphitization, low residual stress and mixed interface. Relatively, a-C films prepared with ion beam energy of 2 keV exhibits optimum sp³ bond content, mechanical properties and corrosion resistance. It is found that the wear rate of DLC films decrease with increased ion beam energy in general, consistent with the varied trend of the H/E value which has been regarded as a suitable parameter for predicting wear resistance of the coatings. The correlation of the sp³ bond fraction in the films estimated from Raman spectroscopy with residual stress, nanohardness and corrosion resistance has been established.     

The effect of MeV ion irradiation on the hydrogen content and resistivity of direct ion beam deposited diamondlike carbon

Diamondlike carbon films fabricated by direct ion beam deposition have been irradiated with 6.4 MeV fluorine and 1 MeV gold ions. Both beams reduce the hydrogen content with the fluorine beam being much more efficient than the gold beam. The resistivity of the materials is also reduced by both beams with the fluorine beam producing a much larger drop in resistivity and a lower fluence than the gold beam. It is concluded that defects produced by electronic energy loss of the bombarding ions are responsible for both the loss of hydrogen and the change in resistivity. The magnitude of both of these effects is reduced with increasing ion mass as the proportion of nuclear to electronic energy loss is increased. This is due to the production of retrapping centers in the case of hydrogen and ion induced annealing in the case of resistivity. There is a threshold in fluence for both effects and this may be associated with fluctuations in the rate of deposition of the electronic energy loss along an individual ion track.