离子在近电子能损阈值能区诱发云母表面小丘形成

利用0.65 MeV的He~+离子轰击白云母膜,并在大气环境下用原子力显微镜(AFM)的轻敲模式分析了辐照后的膜表面。实验结果显示,在不同温度下离子诱导的小丘高度在小于1 nm到几nm之间,且室温条件下能诱发小丘生成的He~+离子电子能损阈值在0.44 keV/nm以下。此外,升高温度至973 K并在其中选取不同温度进行表面辐照来验证观测到的小丘结构。实验发现,相比于室温,小丘直径和高度的统计分布在更高温度下表现出了更大的歧离。分别利用分析热峰模型和双温热峰模型计算了辐照过程中的核能损与电子能损,并选取了用能损在阈值附近的离子辐照所产生的小丘的实验数据与模拟结果相比较,发现实验结果与双温热峰模型吻合较好。     

He+离子辐照Inconel 718合金表面形貌改变及机理研究

研究了3种不同剂量He⁺离子辐照后Inconel 718合金的形貌变化规律及其形成机理。结果表明,He⁺离子辐照会在合金表面形成纳米多孔结构,其孔径会随辐照剂量的增加而增大。此外,He⁺离子辐照还会破坏合金表面δ相并导致碳化物的持续溅射损耗,且这一现象会随着辐照剂量的增加而愈发严重。由于辐照过程中氦泡间微观应力σ n作用会引起毗邻材料断裂及氦泡合并长大,且辐照溅射作用又会导致氦泡上层薄膜的损耗甚至破裂,因而这也是He⁺离子辐照Inconel 718合金表面纳米多孔结构的形成机制。     

高能136Xe离子辐照聚酰亚胺化学改性的电子能损效应

用1．755GeV^136Xe离子在真空室温环境下辐照叠层聚酰亚胺薄膜,通过红外和紫外光谱测量研究了高电子能损离子辐照引起的化学降解及炔基产生效应。红外测量结果表明,典型官能团随辐照注量的增加指数降解,且径迹芯中所有官能团均遭到破坏;对应8．8(最小能损,第一层)和11．5keV／nm(最大能损,第五层)电子能损,^136Xe辐照聚酰亚胺的平均降解半径分别为3．6和4．1nm。而相应能损条件下炔基的生成截面分别为5．6和5．9nm大于官能团的降解截面。紫外结果表明辐照引起的吸光度的改变随辐照注量线性增加,发色团的产生效率随电子能损的增大而增加。     

快重离子在聚合物潜径迹中引起的损伤效应研究

在室温和真空环境下利用不同的快重离子(1.158GeV Fe56、1.755GeV Xe136及2.636GeV U238)对多层堆叠的聚对苯二甲酸乙二醇酯(PET)、聚碳酸脂(PC)和聚酰亚胺(PI)进行了辐照,结合X射线衍射(XRD)、傅立叶红外光谱(FTIR)及紫外可见光谱测量技术,在较宽的电子能损(1.9-19.0 keV·nm-1)和注量范围(1×1010-6×1012 cm-2)研究了离子在不同聚合物潜径迹中引起的损伤过程,观测到了主要官能团的降解、炔基生成、非晶化及紫外吸收边缘的红移等现象随辐照注量及电子能损的变化趋势.通过对损伤过程的定量分析,应用径迹饱和模型假设,分别给出了Fe、Xe和U离子在不同电子能损下辐照PC时的平均非晶化径迹半径和炔基形成半径,并用热峰模型对实验结果进行了检验.     

高温He离子辐照引起的Hastelloy N合金微结构变化研究

本文采用30 keV的He离子辐照Hastelloy N合金,辐照温度为500C,剂量分别为:1×10¹⁵、×10¹⁵、1×10¹⁶He⁺/cm²。利用扫描电子显微镜（SEM）研究了辐照后块体样品的表面形貌。结果表明,辐照后的块体样品均观察到了表面起泡现象。利用透射电子显微镜（TEM）研究了辐照后TEM样品微结构的变化。结果表明,低剂量(1×10¹⁵ He⁺/cm²)辐照的样品中出现了黑斑缺陷;随着辐照剂量的增加,开始出现位错环及纳米级的氦泡,同时黑斑密度减少;当剂量增至1×10¹⁶He⁺/cm²,位错环以及氦泡的尺寸和密度明显增大,晶界处氦泡更加密集。     

He/H离子辐照损伤及其对ODS钢显微硬度的影响研究

为研究氧化物弥散强化铁素体钢(ODS钢)中的He/H离子协同辐照效应,本文开展了室温条件下ODS钢的He/H离子单一及复合辐照实验,并研究了辐照损伤对其显微硬度的影响。实验结果表明:He/H离子主要分布在损伤峰值附近;H离子辐照对ODS钢显微硬度的影响大于He离子;H离子的引入导致He离子低温解吸峰消失,而He离子的注量减半则使其热解吸起始温度升高;He、H离子与材料中缺陷相互作用不同是影响显微硬度及正电子寿命结果的主要因素。     

电子束辐照对锂镧锆钽氧(Li6.5La3Zr1.5Ta0.5O12)固体电解质结构的影响

通过固相反应法制备出室温下高离子电导率Ta掺杂的锂镧锆钽氧(Li_6.5La₃Zr_1.5Ta_0.5O₁₂,LLZTO)固体电解质,详细研究了电子束辐照对LLZTO固体电解质结构和性能的影响。结果表明：电子束(250 kGy、500 kGy)辐照后并未产生其他杂相,且晶格间距随着剂量的增加逐渐变大,这有利于降低离子在晶格中的扩散能垒。第一性原理的计算发现,低剂量电子束辐照样的Li⁺扩散能垒比未辐照样降低了0.07 eV,说明辐照产生的缺陷能促进Li⁺扩散。辐照前后的电解质交流阻抗测试进一步证实了低剂量的电子束辐照有利于提升电解质的离子电导率。利用电子束辐照探究其对LLZTO氧化物固体电解质结构和电导率的影响对固体电解质的研究具有重要意义。     

电子能损效应对材料辐照缺陷影响的理论模拟研究进展

高能粒子与靶材料相互作用主要通过核能损和电子能损两种方式损失能量。电子阻止效应和电子-声子耦合效应是体现电子能损的两种不同机制。准确模拟高能粒子的辐照损伤过程,亟须解决电子能损效应对粒子辐照损伤的影响这一关键科学问题。本文综述了几种关键结构材料在考虑电子能损效应下辐照损伤行为的最新研究进展,阐述了电子阻止效应、电子-声子耦合效应和电子热导率等对辐照缺陷的影响规律,总结了目前电子能损效应对靶材料辐照损伤的影响规律,归纳了高能粒子辐照靶材料研究中存在的问题,并对后续的研究方向进行了展望。     

高能铁离子辐照单晶氧化铝产生的色心研究

室温下利用紫外-可见吸收光谱和荧光光谱技术对1.157GeV的56Fe离子注入辐照的单晶三氧化二铝(α-Al2O3)进行了测量分析,研究了辐照产生的阴离子空位的形成和演化规律.测量结果显示,高能Fe离子辐照产生了多种阴离子空位型缺陷,其中包括F、F 、F2 、F22 和F2心.随入射离子剂量的增加,各类缺陷的数量逐渐增大,并在高剂量时趋于饱和,但各类缺陷间的相对数量存在一定的比例,不随剂量的增加而有明显变化.用单离子饱和损伤模型对实验结果进行了拟合,获得各类色心的产生截面在40-90 nm2之间.与TRIM程序计算结果比较后发现,室温下辐照时阴离子单空位的产生速率约是由核能损过程在低温下产生缺陷速率的一半.     

PET核孔膜蚀刻速率影响因素的研究

核孔膜是通过重离子照射薄膜后进行化学蚀刻所得到的高性能过滤材料,蚀刻速率是影响高质量核孔膜制备的重要因素。本文探讨了不同蚀刻液浓度、温度以及重离子辐照能量对蚀刻速率的影响。利用140 MeV的32S离子在室温和真空条件下对4层堆叠的PET(polyethylene terephthalate)薄膜进行了辐照。在对辐照样品进行化学蚀刻期间采用电导法确定了径迹蚀刻速率Vt。结果表明:蚀刻速率与蚀刻温度呈指数相关,随蚀刻液浓度增加而线性增大;径迹蚀刻速率随能量损失率(离子能损)增大。研究确定,在入射32S能量为1.6 MeV·u-1时,NaOH浓度为1mol·L-1、蚀刻温度为85°C时最有利于形成圆柱形微孔。     

Surface swelling of sapphire induced by MeV and GeV heavy ions

-Al₂O₃ single crystals were bombarded with MeV xenon ions from 10¹⁵ to 10¹⁷ ions cm⁻² and GeV uranium ions from 10¹¹ to 10¹³ ions cm⁻² to study the surface swelling of sapphire at 77 and 300 K due to atomic collision processes (Xe) and electronic energy loss processes in the 20–45 keV/nm regime (U). The induced damage was studied by channeling Rutherford backscattering. Surface swelling was measured with a profilometer. The step height induced by nuclear cascades of MeV xenon increases with the ion fluence and saturates. With GeV uranium, an electronic stopping power threshold for surface swelling was observed and the step height increased with the damage for dE/dx higher than this threshold.     

Transient processes induced by heavy projectiles in silicon

The thermal spike model developed for the electronic stopping power regime is extended to consider both ionization and nuclear energy loss processes of the projectile as electronic and atomic heat distinct sources. The time and space dependencies of the lattice and electron temperatures near the projectile trajectory are calculated and discussed for different ions in silicon, at room and cryogenic temperatures, taking into account the peculiarities of electron-phonon interaction in both domains. The model developed contributes to the understanding of transient microscopic processes immediately after the projectile interaction in the target.     

Surface topography induced by swift heavy ion impacts

Classical molecular dynamics simulations have been carried out to investigate the development of surface topographies following irradiation by swift heavy ions. Two models were used: a thermal spike model in which atoms within a cylinder surrounding the path of the ion are given kinetic energy due to the electronic energy loss of the particle; and an electron stripping with recombination model. Both models give qualitatively similar results and show the formation of hillocks on the surface above the ion track and a less dense track core near to the surface.     

Characterization of swift heavy ion tracks in CaF2 by scanning force and transmission electron microscopy

Single crystals of fluorite (CaF₂) were exposed to various swift heavy ions (Ca up to U) of energy 1–11.1 MeV per nucleon, covering a large range of electronic stopping power S_e between 4.6 and 35.5 keV/nm. The irradiated (1 1 1) cleaved surfaces were investigated by means of scanning force microscopy in tapping mode. Nanometric hillocks produced by the ion projectiles were analyzed in terms of creation efficiency E_eff, diameter and height values, and diameter–height correlation. Hillock formation appears with a low efficiency above a S_e threshold of 5 keV/nm. The mean height of these hillocks is approximately constant (1 nm) between 5 and 10 keV/nm and increases linearly with S_e above 10 keV/nm reaching 12.5 nm for the largest S_e value investigated. Similarly, the efficiency grows versus S_e achieving 100% for S_e > 13 keV/nm where each projectile produces an individual hillock. Above 13 keV/nm, the hillock height and diameter are strongly correlated. The diameter was deduced by graphical deconvolution of the scanning-tip curvature that is determined experimentally for each set of measurements. In the entire S_e regime, the mean diameter exhibits a constant value of 13 nm, which is significantly larger than 6 nm wide tracks observed by transmission electron microscopy.     

Surface tracks by MeV C60 impacts on mica and PMMA

Muscovite mica has been bombarded by C₆₀ ions with energies between 2 and 15 MeV. The produced surface tracks have been analyzed by atomic force microscopy (AFM). The particle impacts formed hillocks with a height which increases with energy from 2 to 6 nm. For impacts of I, Ge₃, C₈, C₁₀, Cu₉, and Cu₁₀ MeV ions, hillocks smaller than 0.6 nm have been found. Irradiation with GeV monoatomic particles at similar energy loss performed by other research groups has only changed the frictional properties of the mica surface but did not produce any hillocks. The results can be understood qualitatively by taking into account the large difference in the velocity of the projectiles and the secondary particles along the track.PMMA irradiated with MeV C_n, Ge_n, and I ions exhibited holes with diameters between 18 and 45 nm after development. The measured track area as a function of energy loss shows an approximately linear behavior, pointing towards a diffusive spreading of energy.     

Ion beam enhanced etching of LiNbO3

Single crystals of z- and x-cut LiNbO₃ were irradiated at room temperature and 15 K using He⁺- and Ar⁺-ions with energies of 40 and 350 keV and ion fluences between 5 × 10¹² and 5 × 10¹⁶ cm⁻². The damage formation investigated with Rutherford backscattering spectrometry (RBS) channeling analysis depends on the irradiation temperature as well as the ion species. For instance, He⁺-irradiation of z-cut material at 300 K provokes complete amorphization at 2.0 dpa (displacements per target atom). In contrast, 0.4 dpa is sufficient to amorphize the LiNbO₃ in the case of Ar⁺-irradiation. Irradiation at 15 K reduces the number of displacements per atom necessary for amorphization. To study the etching behavior, 400 nm thick amorphous layers were generated via multiple irradiation with He⁺- and Ar⁺-ions of different energies and fluences. Etching was performed in a 3.6% hydrofluoric (HF) solution at 40 °C. Although the etching rate of the perfect crystal is negligible, that of the amorphized regions amounts to 80 nm min⁻¹. The influence of the ion species, the fluence, the irradiation temperature and subsequent thermal treatment on damage and etching of LiNbO₃ are discussed.     

Bubbles in SiC crystals formed by helium ion irradiation at high temperatures

Helium bubbles were found to be formed in SiC crystals by irradiation with He⁺ ions at 1000 to 1200° C. The size of bubbles increased with increasing irradiation temperatures.

The density of helium atoms in the bubbles was measured to be about 10²⁸ atoms/m³ by EELS measurement in combination with electron microscopic observation in the same selected areas, and the internal pressure of the bubbles was estimated therefrom to be on the order of 10⁸ Pa at room temperature.     

Kinetic electron emission yield induced by H and He ions versus stopping power for Al, Cu, Ag and Au

For H⁺ and He²⁺ ions impinging on Al, Cu, Ag and Au targets we measured simultaneously the yield, γ, of emitted electrons and the electronic energy loss, S_e, in the energy range 0.5 to 4.8 MeV. The targets were prepared under high-vacuum conditions before they were transferred to an ultra-high-vacuum chamber without breaking the vacuum. The targets were sputter cleaned and their composition was examined by Auger electron spectrometry. The values of γ were obtained by current integration and S_e was determined from the energy width of Rutherford backscattering spectra. For H⁺ ions impinging on Cu, Ag or Au and He²⁺ on Al and Cu, the expected proportionality between γ and S_e was found within the experimental errors of 2%. For H⁺ ions on Al and He²⁺ ions on Ag and Au targets, significant deviations were observed.     

Atomic force microscopy and Raman scattering studies of femtosecond laser-induced nanohillocks on CR-39

The phenomenon of nanohillock-like defect formation on the surfaces of CR-39 by ultra-short laser irradiation is investigated using an Atomic Force Microscope (AFM) and Raman Scattering. A polymer CR-39 target was exposed to Ti:sapphire 25-fs laser pulses with a central wavelength at 800 nm. Samples were irradiated for different laser fluences both in air and vacuum. Detailed surface topographical features of the bombarded samples were characterized by atomic force microscopy in contact mode in air at room temperature. AFM reveals that the growth of nanohillocks and their features are strongly dependent on the ambient condition, target position from focus, and irradiation fluence. The appearance of these nanohillocks in the range 1–20 nm in height and 10–90 nm in diameter are regarded as typical features for fast electronic processes (correlated with existence of hot electrons) and are explained on the basis of Coulomb explosion. These nanostructures due to localization of laser energy deposition in small areas provide a possible pathway from dense electronic excitation to atomic motion causing permanent structural modification which are well correlated to structural alterations, like crosslinking and chain scissions, inferred from Raman spectroscopy.     

Resonant ion stimulated desorption of O from the TiO2(1 1 0) surface: Effects of oxygenation and ion bombardment

The O⁺ desorption from reduced, oxygenated, and ion-bombarded TiO₂(1 1 0) surfaces has been investigated during He⁺ irradiation. The O⁺ desorption is initiated by creation of an antibonding O 2s core hole state via quasi-resonant charge exchange with the He⁺ 1s state, followed by the intra-atomic Auger decay of the O 2s hole. Upon oxygenation of the reduced TiO₂(1 1 0) surface, the O⁺ yield increases by one order of magnitude. The O₂ molecule is dissociated at the vacancy site of bridging oxygen and the oxygen atoms either fill a vacancy site or chemisorb at a fivefold-coordinated Ti⁴⁺ site as an adatom. The latter is detected with much higher efficiency than the former. The O⁺ yield is increased during He⁺ bombardment of the reduced TiO₂(1 1 0) surface due to formation of lower coordinated oxygen atoms. The oxygen species thus formed by ion bombardment or oxygenation are unstable on the surface and tend to diffuse into bulk vacancy sites or higher coordination surface sites even at room temperature.