Microanalysis of a ductile iron by microchip laser-induced breakdown spectroscopy

Laser beams with ns pulse width are generally employed as an excitation source in the process of detecting inclusions and elemental segregation on a workpiece surface by microanalysis of the laser-induced breakdown spectroscopy.In addition,the ablation crater interval of laser sampling on the sample surface is generally 20 μm or more.It is difficult to detect the morphology of inclusions smaller than 50 μm in diameter and the micro-segregation of elements.However,in this work,when the laser ablation crater is 10 μm and the sampling resolution of the laser on the sample surface is 5 μm,the morphology and distribution of spherical inclusions (20-60 μm) in ductile iron can be detected according to the difference of the Fe spectrum on the Fe matrix and the spheroidal inclusions.Moreover,the distribution of micro-segregation of Mg and Ti elements in ductile iron was also studied.     

Recovery of fused silica surface damage resistance by ion beam etching

An increase of photoluminescence induced by laser irradiation in vacuum was observed for the fused silica. The degradation of transmittance and damage resistance performance of fused silica surfaces may be due to substoichiometric silica and a sufficient defect population introduced in the near surface. When the laser-irradiated surface layers were removed by ion beam etching, the laser-induced damage threshold recovered to that of un-irradiated samples. The photoluminescence also decreased after ion beam etching. According to the calculated etching depth, the laser-induced defects formed in the surface layer of 10-20 nm when different parameters used during vacuum exposure. In addition, the evolution of surface root-mean-square microroughness as a function of ion beam etching time was studied by the optical interferometric technique and atomic force microscopy.     

Fabrication of hollow Ag nanoclusters in silica by irradiation with Ar ions

Ion irradiation is an effective method to control the morphology, size and distribution of metal nanoclusters in substrates. In this work, Ag nanoclusters embedded in silica by 200 keV Ag⁺ ion implantation were irradiated at room temperature with Ar⁺ ions at 200 keV and 500 keV to different fluences. After irradiation, a transmission electron microscopy (TEM) study revealed that nanovoids are formed in the larger Ag nanoclusters. With the increase of fluence and energy of the Ar⁺ ions, the number and average size of the nanovoids grow combining with increases in the average size of the larger Ag nanoclusters within a projected range. During the ion irradiation process, the electronic energy and nuclear energy loss of the Ar⁺ ions determine the size of the hollow Ag nanoclusters and the change of the size and distribution of Ag nanoclusters in silica, leading to changes in the optical absorption spectra.     

毛细管X光透镜聚焦的微束X射线荧光谱仪的研发及应用

针对不同样品的分析需求,本文设计了几种不同类型的微束X射线荧光谱仪。用高精度激光位移传感器实时校正样品表面被测量点与毛细管透镜出端之间的距离,以减少形状不规则的古陶瓷样品测量时带来的误差;利用毛细管X光透镜传输能量高于25 keV的X射线效率低的特点,将其应用于高铅釉瓷器彩料的无损分析中;采用大功率X射线源,扫描分析了大米中K、Ca等元素分布;以人民币5角硬币为例,研究了能量色散的微束X射线衍射方法。研究结果表明,本文研发的微束X射线荧光谱仪在生物样品和文物样品的分析研究中有广泛的应用前景。     

Structural modification in amorphous silica after exposure to low fluence 355 nm laser irradiation

UV laser irradiation induced structural modification in amorphous silica was characterized using Fourier transform infrared and X-ray induced photoelectron spectroscopy. Laser irradiation experiment was conducted using a 3ω, 355 nm beam from a pulsed Nd-YAG laser with pulse length of 6.8 ns and laser repetition rate of 1 Hz at ambient conditions. The examined laser fluence was controlled at a relatively low level, ranging from 0 to 4 J/cm². The IR spectra revealed that the vibration frequency of the rocking mode of SiOSi covalent bond shifted to lower wave number, while the bending mode and asymmetric stretching mode of SiOSi covalent bond shifted to higher frequency. This result suggested that the length of SiOSi covalent bond was decreased, the bond angle was increased and the irradiation modified material was densified after irradiation. The high resolution XPS spectra of Si 2p and O 1s illustrated the chemical shift of silicon and oxygen ions after irradiation. The XPS chemical shift of the Si 2p peak about 1.1 eV revealed the existence of low valence silicon ions Si³⁺ species in silica glass after irradiation. The chemical shift of the O 1s peak about 0.9 eV illustrated the emergence of non-bridging oxygen ions during laser irradiation. The deconvoluted peak area and FWHM value of low valence silicon ions and non-bridging oxygen ions all exhibited exponentially growth as the linearly elevation of laser fluence. UV laser-induced photolysis of SiO covalent bond was suggested to be responsible for the formation and increase of low valence silicon ions and non-bridging oxygen ions. These FT-IR and XPS data revealed that short range structural modifications were important structure alterations in silica glass before the emergence of distinct and large size damage crater.     

Luminescent nanoclusters array fabricated by pulsed laser beam irradiation

Ordered luminescent nanoclusters array in the form of grating structures are fabricated on silicon (1 0 0) surface by Q-switched Nd:YAG laser beam irradiation of second harmonic wavelength (532 nm) in vacuum. Blue-green photoluminescence (PL) spectrum from the ordered nanoclusters array exhibits two asymmetrical peaks at 2.58 eV and 2.88 eV in the blue-green region corresponding to the bimodal distribution of nano size clusters. The size of the nanoclusters is estimated from the three dimensional quantum-confined model incorporating Gaussian size distribution. When subjected to rapid thermal annealing at 710 °C for 10 min in N₂ atmosphere there is an enhancement of the PL intensity without any change in the peak emission energy and broadening suggesting that the origin of PL is related to quantum confinement effect in Si nanocrystallite. The surface morphology of the irradiated surface varies considerable with the number of laser shots, laser fluence and ambient conditions.     

γ辐照对空间用光学玻璃透射率的影响

利用60Coγ射线对熔融石英、重火石和镧冕玻璃进行辐照,研究其光学透射率的变化及其在空间光学系统中的适用性。辐照后测试光学玻璃的透射率,光谱范围为400～1100nm。测量结果表明,除熔融石英玻璃外,其它玻璃的可见光透射率辐照后均下降。尽管重火石和镧冕玻璃光学透射率在辐照前相似,但辐照后的透射率损耗则不同,镧冕玻璃抗辐射能力更强。对于重火石和镧冕玻璃,未镀膜样品较镀防反射膜样品的抗辐射能力强。研究中观测到,当达到一定辐射剂量后,玻璃材料的透射率不再继续衰减而趋于稳定。这些结果为空间光学系统针对辐射进行冗余设计提供了依据。     

Removal of the deposition on JT-60 tile by nano-sec pulsed-laser irradiation

To clarify the property of tritium removal from carbon codeposition by using pulsed-laser induced desorption, hydrogen removal from co-deposits on JT-60 divertor tile using a fourth-harmonic emission (266 nm) of a nano-sec Nd:YAG laser was demonstrated. The threshold laser fluence for ablation was ∼0.3 J/cm², which was slightly higher compared to that of the pico-sec laser irradiation. The energy absorption coefficient for the nano-sec laser, which was obtained by fitting the removal rate by so-called Beer’s law, was larger than the pico-sec laser. Since the time constant of thermal wave propagation into the target is of the order of nano-sec, such differences between nano- and pico-sec lasers could be attributed to thermal effects. The ablation threshold of the deposited layer was lower than that of a pure graphite, which could be attributed to the difference of thermal conductivity between deposited layer and pure graphite. The removal rate of the nano-sec laser was higher than that of pico-sec laser in the fluence range of >∼0.5 J/cm². On the other hand, the production ratio [hydrocarbon species]/[H₂] continuously increased with the laser fluence, and no significant ionization of carbon was observed in this fluence range. This indicated that the fluence range in this study was “weak”-ablation range, which was still not sufficient to minimize the hydrocarbon production.     

Desorption of water adsorbed on iron oxide by laser irradiation

Desorption of water adsorbed on iron oxide by laser irradiation was studied by means of a time-of-flight (TOF) technique. The wavelength of the laser for desorption was varied from 355 to 600 nm. The energy threshold of the water desorption ranged around 2.0-2.3 eV. Based on the fact that this energy threshold approximately corresponds to the bandgap of Fe₂O₃, the initial process of water desorption is considered to be the electronic excitation of the iron oxide from the valence band to the conduction band. Analysis of the velocity distribution of the desorbed water suggests that following the electronic excitation of the iron oxide the desorption is caused by both thermal and nonthermal processes. The thermal process is caused by the rise of the surface temperature that occurs after the scattering and de-excitation of the excited electron in the iron oxide. In the case of the laser at λ = 355 nm, the desorption was mainly caused by the thermal process. On the other hand, in the case of the laser at λ = 430 nm, the desorption was mainly caused by the nonthermal process. The desorption caused by the nonthermal process is attributed to the transfer of the electron excited in the iron oxide to the adsorbed hydroxyl.     

Anisotropic deformation of polystyrene particles by MeV Au ion irradiation

MeV Au irradiation leads to a shape change of polystyrene (PS) and SiO₂ particles from spherical to ellipsoidal, with an aspect ratio that can be precisely controlled by the ion fluence. Sub-micrometer PS and SiO₂ particles were deposited on copper substrates and irradiated with Au ions at 230 K, using an ion energy and fluence ranging from 2 to 10 MeV and 1 × 10¹⁴ ions/cm² to 1 × 10¹⁵ ions/cm². The mechanisms of anisotropic deformation of PS and SiO₂ particles are different because of their distinct physical and chemical properties. At the start of irradiation, the volume of PS particles decrease, then the aspect ratio increases with fluence, whereas for SiO₂ particles the volume remains constant.     

Barrier modification of Au/n-GaAs Schottky diode by swift heavy ion irradiation

The effect of swift heavy ion (72.5 MeV ⁵⁸Ni⁶⁺) irradiation on Au/n-GaAs Schottky barrier characteristics is studied using in situ current-voltage measurements. Diode parameters are found to vary as a function of ion irradiation fluence. The Schottky barrier height (SBH) is found to be 0.55(±0.01) eV for the as deposited diode, which decreases with ion irradiation fluence. The SBH decreases to a value of 0.49(±0.01) eV at the highest ion irradiation fluence of 5 × 10¹³ ions cm⁻². The ideality factor is found to be 2.48 for unirradiated diode, and it increases with irradiation to a value of 4.63 at the highest fluence. The modification in Schottky barrier characteristics is discussed considering the energy loss mechanism of swift heavy ion at the metal-semiconductor interface.     

高激光损伤阈值化学膜透射元件的研制

以K9和熔石英玻璃为基底结合溶胶-凝胶镀膜技术,制备了用于负载1 064 nm和355 nm激光辐射的高损伤阈值透射玻璃元件。综合考虑基底表面和亚表面质量及薄膜质量,系统分析了影响激光损伤阈值的因素,并通过基底加工与薄膜改性的结合大幅提高了元件的损伤阈值。在薄膜改性方面,采用溶胶内添加聚乙二醇和氨气氛处理相结合的方法,使薄膜的结构缺陷减少,孔径分布更合理,所得薄膜的抗激光损伤能力远大于未处理的基底的。在基底加工方面,采用超级抛光和化学腐蚀的方法获得了超光滑表面和低缺陷亚表面,使用于红外波段的K9玻璃和紫外波段的熔石英玻璃的激光损伤阈值分别提高到原来的1.3和4.1倍。将上述改性后的薄膜镀在改性后的基底上,所得透射元件的激光损伤阈值不小于相应基底的。     

Magnetic behaviour of nanosized zinc ferrite under heavy ion irradiation

Present investigation reports the effect of 100 MeV oxygen beam on the magnetic properties of zinc ferrite nanoparticles. The nanoparticles for this study were synthesized by using the nitrates of zinc and iron in the matrix of citric acid and by sintering the precursor at 500 and 1000 °C. Both these samples were irradiated by 100 MeV oxygen beam with two different fluence 1 × 10¹³ and 5 × 10¹³ ions/cm². Besides the presence of cubic spinel phase, ZnO phase appears after the irradiation in both the samples. A decrease in average particle size was observed in the irradiated samples as estimated by X-ray diffraction pattern. The magnetization versus applied field curves show the decrease in magnetization with the fluence of the beam, which is attributed to the ZnO phase. The thermal magnetization curve for the sample ZF500 shows almost constant value of blocking temperature after irradiation whereas for ZF1000 it increases from 18 K to 32 K at a fluence of 5 × 10¹³ ions/cm².     

Laser-induced optical reflection and absorption of GaP

Changes in the optical absorption and reflection coefficients of GaP induced by irradiation with 600 ns laser pulses of the wavelenghts at the direct and indirect band gaps have been measured. It is found that a persistent increase in the absorption coefficient and a permanent decrease in the reflection coefficient, in addition to transient increases in the absorption and reflection coefficients, are induced, by irradiation at the band gap. The persistent component is found to be evolved with a surprisingly long time constant of about 10 ms. This component is ascribed to laser-induced modification of the surface layers or damage formation. The transient component is ascribed to temperature rise on the basis of time-resolved optical absorption measurements. It is found that the persistent changes are induced by irradiation with the indirect band gap photons at a fluence which induces only a little change in the transient reflectivity. The threshold laser fluence to create the surface modification by the indirect band-gap irradiation is found to be only four times that by direct band-gap irradiation. A delayed reflectivity change is found to be induced by irradiation at the indirect band gap and is ascribed to the modification of surface layers by photons at the surface layer, which enhances the absorption coefficient. We interpret these experimental results in terms of non-thermal laser-induced atomic processes.     

Effect of thermal spike energy created in CuFe2O4 by 150 MeV Ni swift heavy ion irradiation

Effects of 150 MeV Ni¹¹⁺ swift heavy ion (SHI) irradiation on copper ferrite nanoparticles have been studied at the fluences of 1 × 10¹¹, 1 × 10¹², 1 × 10¹³, 1 × 10¹⁴ and 5 × 10¹⁴ ions/cm². The XRD pattern shows the irradiation fluence dependant preferential orientation. Scanning electron microscope analysis displays fine blocks of material for pristine while partial agglomeration on irradiation. Notably, a large number of holes are present at the fluence of 5 × 10¹⁴ ions/cm². The magnetization measurements performed in these samples exposes that the coercivity and remanence magnetization value increases due to the magnetocrystalline anisotropy up to the fluence of 1 × 10¹³ ions/cm². At 1 × 10¹⁴ ions/cm² fluence, the induced thermal energy overcomes the magnetocrystalline anisotropy constant and causes a decrease in coercivity and remanence values. The saturation magnetization decreases up to the fluence of 1 × 10¹³ ions/cm² and then it increases for further irradiation. The change of crystalline orientation observed from XRD, the creation of holes from SEM and the change in magnetic properties are discussed on the basis of electro-phonon coupling and it invokes the thermal spike theory.     

Cluster Dynamics modelling of irradiation growth of zirconium single crystals

This paper aims at modelling irradiation growth of zirconium single crystals as a function of neutron fluence. The Cluster Dynamics approach is used, which makes it possible to describe the variation of irradiation microstructure (dislocation loops) with neutron fluence. From the irradiation microstructure, the strain can be calculated along the axes of the lattice structure. The model is applied to the growth of annealed zirconium single crystals at 553 K measured by Carpenter and Rogerson in 1981 and 1987. The model is found to fit the experimentally measured growth of Zr single crystals very nicely, even at large neutron fluence where the ‘breakaway growth’ occurs. This was made possible by considering in the model the growth of vacancy loops in the basal planes. This growth of vacancy loops in the basal planes could be modelled by taking into account that diffusion of self-interstitial atoms (SIA) is anisotropic and that there exist in the basal planes some nucleation sites for vacancy loops (iron clusters), the density of which is considered constant over time.     

Structural characterization of swift heavy ion irradiated polycarbonate

Makrofol-N polycarbonate thin films were irradiated with copper (50 MeV) and nickel (86 MeV) ions. The modified films were analyzed by UV-VIS, FTIR and XRD techniques. The experimental data was used to evaluate the formation of chromophore groups (conjugated system of bonds), degradation cross-section of the special functional groups, the alkyne formation and the amorphization cross-section. The investigation of UV-VIS spectra shows that the formation of chromophore groups is reduced at larger wavelength, however its value increases with the increase of ion fluence. Degradation cross-section for the different chemical groups present in the polycarbonate chains was evaluated from the FTIR data. It was found that there was an increase of degradation cross-section of chemical groups with the increase of electronic energy loss in polycarbonate. The alkyne and alkene groups were found to be induced due to swift heavy ion irradiation in polycarbonate. The radii of the alkyne production of about 2.74 and 2.90 nm were deduced for nickel (86 MeV) and copper (50 MeV) ions respectively. XRD analysis shows the decrease of the main XRD peak intensity. Progressive amorphization process of Makrofol-N with increasing fluence was traced by XRD measurements.     

Copper precipitate hardening of irradiated RPV materials and implications on the superposition law and re-irradiation kinetics

Copper is known to play an important role in irradiation hardening and embrittlement of RPV materials. This is particularly true for old vessels. Indeed, while the Cu-content is low (<0.1%) in modern RPV materials, it often exceeded 0.15% in older vessels. Within the RADAMO irradiation program aiming to provide a reliable and extensive (chemistry, heat treatments, fluence, irradiation temperature) databank to investigate irradiation-induced hardening of RPV materials, we irradiated steels and welds with copper contents ranging from 0.06 to 0.31% at 300 and 265 °C. Experiments on re-irradiation after annealing were also performed to investigate the re-irradiation kinetics. It is found that copper plays a role in the very early stage of irradiation but saturates quite rapidly. The peak hardening is in agreement with the ageing data. Considering a two-component model, the linear superposition law provides the most appropriate one to rationalize the experimental data including re-irradiation path.     

Characterization of Carbon Plasma Evolution Using Laser Ablation TOF Mass Spectrometry

In this work, a time-of-flight (TOF) mass spectrometer has been used to investigate the distribution of intermediate species and formation process of carbon clusters. The graphite sample was ablated by Nd:YAG laser (532 nm and 1064 nm). The results indicate that the maximum size distribution shifted towards small cluster ions as the laser fluence increased, which happened because of the fragmentation of larger clusters in the hot plume. The temporal evolution of ions was measured by varying the delay time of the ion extraction pulse with respect to the laser irradiation, which was used to provide distribution information of the species in the ablated plasma plume. When the laser fluence decreased, the yield of all of the clusters obviously dropped.     

Detailed studies of photocathodes based on Y thin films grown by PLD technique

The effects of laser fluence on the morphology of Y films in the regime characteristic of multiple-pulse laser deposition were investigated. Y thin films were deposited on silicon and copper substrates. The samples deposited on silicon substrate were used to deduce the morphology and the thickness of the deposited films. On the contrary, the samples deposited on copper were tested as photocathodes in a DC photodiode cell. The interest to produce Y-based photocathodes is due to the low work function of this metal with the possibility to drive such photocathodes with a visible radiation in the radio-frequency photo-injector. In this way it is possible to reduce the thermal emittance of the photoelectron beam and to increase the photocurrent intensity by utilizing the second harmonic of Ti:Sa driver laser. The quantum efficiency was measured for the first time by using a visible CW laser diode emitting at 406 nm.