The influence of incidence angle on disorder production in Cl and Ar ion implanted Si

Abstract

Cl and Ar ions have been implanted, at 30 keV and at various incidence angles, into Si substrates maintained at room temperature during implantation. Implantation induced Si disorder was measured using RBS channelling. The effects upon disorder of various incidence angles were studied over a fluence range of 10¹²-6·10¹⁵ ions·cm^?2

The results show that, at low fluences Cl and Ar ion implantations generate a bimodal disorder-depth profile, whilst at higher fluences measurements of amorphised layer thickness as a function of ion incidence angle allow values of the standard deviation of the disorder profile parallel and transverse to the ion beam direction for each ion to be obtained with good agreement to theoretical predictions. The disorder-fluence behaviour under these conditions is ion species independent.     

中能高浓度氦离子注入对钨微观结构的影响

采用15 keV, 剂量1×10¹⁷/cm², 温度为600 ℃氦离子注入钨, 分别以块体钨研究氦离子对钨的表面损伤; 以超薄的钨透射电镜样品直接注入氦离子, 研究该条件下钨的微观结构变化, 以了解氦离子与钨的相互作用过程; 采用扫描电子显微镜、聚焦离子束扫描显微镜、透射电子显微镜、高分辨透射电子显微镜等分析手段研究氦离子注入对钨表面显微结构的影响及氦泡在钨微观结构演化中的作用.     

氦泡在bcc钨中晶界处成核长大的分子动力学模拟

钨(W)是潜在的聚变堆面向等离子体材料.聚变反应中产生的氦(He)不溶于金属W,并在其中易聚集形成He泡,使W基体发生脆化,从而导致W基体的性能发生退化.在前人工作的基础上,本文采用分子动力学研究了He泡在单晶bcc-W中以及bcc-W中∑3[211](110)和∑9[110](411)晶界处He泡形核长大初期的演化过程.结果发现,晶界处He泡的长大机制和单晶W中有所不同.单晶W中He泡通过挤出位错环促进长大.而He泡在∑3[211](110)晶界处的长大机制为:首先挤出并发射少量自间隙W原子,而后挤出1/2⟨111⟩位错线,随后,该位错线会沿晶界面上[111]方向迁移出去;在∑9[110](411)晶界处,He泡在我们的模拟时间尺度范围内没有观察到W自间隙子的发射和位错的挤出.     

The size of active bubbles for the production of hydrogen in sonochemical reaction field

The sonication of aqueous solution generates microscopic cavitation bubbles that may growth and violently collapse to produce highly reactive species (i.e. OH, HO₂ and H₂O₂), hydrogen and emit light, sonoluminescence. The bubble size is a key parameter that influences the chemical activity of the system. This wok aims to study theoretically the size of active bubbles for the production of hydrogen in ultrasonic cavitation field in water using a single bubble sonochemistry model. The effect of several parameters such as frequency of ultrasound, acoustic intensity and liquid temperature on the range of sonochemically active bubbles for the production of hydrogen was clarified. The numerical simulation results showed that the size of active bubbles is an interval which includes an optimum value at which the production rate of H₂ is maximal. It was shown that the range of ambient radius for an active bubble as well as the optimum bubble radius for the production of hydrogen increased with increasing acoustic intensity and decreased with increasing ultrasound frequency and bulk liquid temperature. It was found that the range of ambient bubble radius dependence of the operational conditions followed the same trend as those reported experimentally for sonoluminescing bubbles. Comparison with literature data showed a good agreement between the theoretical determined optimum bubble sizes for the production of hydrogen and the experimental reported sizes for sonoluminescing bubbles.     

Comparing cleaning effects of gas and vapor bubbles in ultrasonic fields

The dynamic actions of cavitation bubbles in ultrasonic fields can clean surfaces. Gas and vapor cavitation bubbles exhibit different dynamic behaviors in ultrasonic fields, yet little attention has been given to the distinctive cleaning effects of gas and vapor bubbles. We present an experimental investigation of surface cleaning by gas and vapor bubbles in an ultrasonic field. Using high-speed videography, we found that the primary motions of gas and vapor bubbles responsible for surface cleaning differ. Our cleaning tests under different contamination conditions in terms of contaminant adhesion strength and surface wettability reveal that vapor and gas bubbles are more effective at removing contaminants with strong and weak adhesion, respectively, and furthermore that hydrophobic substrates are better cleaned by vapor bubbles. Our study not only provides a better physical understanding of the ultrasonic cleaning process, but also proposes novel techniques to improve ultrasonic cleaning by selectively employing gas and vapor bubbles depending on the characteristics of the surface to be cleaned.     

The dynamics of cavitation bubbles in a sealed vessel

A model of cavitation bubbles is derived in liquid confined in an elastic sealed vessel driven by ultrasound. In this model, an assumption that the pressure acting on the sealed vessel due to bubble pulsations is proportional to total volume change of bubbles is made. Numerical simulations are carried out for a single bubble and for bubbles. The results show that the pulsation of a single bubble can be suppressed to a large extent in sealed vessel, and that of two matched bubbles with same ambient radius can be further suppressed. However, when two mismatched bubbles have the same ambient radii, an interesting breathing phenomenon takes place, where one bubble pulsates inversely with the other one. Due to this breathing phenomenon the suppression effect becomes weak, so the maximum radii of two mismatched bubbles can be larger than that of a single bubble or that of two matched bubbles in sealed vessel. Besides that, for two mismatched bubbles with different ambient radii, the small one in sealed vessel under some certain parameters can pulsate as strong as or even stronger than that of a single bubble in an open vessel.     

Pulsed laser deposition of tungsten and tungsten oxide thin films with tailored structure at the nano- and mesoscale

Nanostructured thin films synthesized by assembling atoms or clusters present a structure characterized by a modulation at the nanoscale and by a large effective area, which can be exploited for the tailoring of specific structural or electronic properties. These systems are appealing for functional applications, e.g. in sensing and catalysis. We have investigated the deposition of tungsten and tungsten oxide thin films with a wide range of morphologies by exploiting nanosecond pulsed laser deposition (PLD) in an inert background atmosphere (He, Ar and Kr). We show that the non-dimensional ratio of the target-to-substrate distance to the time integrated visible plume length, which depends on the gas mass and pressure and on the substrate position, permits to select morphologies ranging from a compact structure with a density similar to bulk, to a film with an open, low density foam-like mesostructure and a high fraction of voids.     

H+辐照前后W涂层表面的XPS分析

对离子束混合技术在不锈钢基体上沉积的W膜进行了H+辐照前后的XPS分析,研究了H+辐照对W的结合能的影响.分析结果表明,沉积的W膜中除了单质钨外,还有部分钨的氧化物,H+辐照结果表明,H+的辐照使钨的结合能向低能方向偏移;钨的氧化物有所减少,说明污染的氧化物在一定程度上被择优溅射掉.     

Refractive index profiles of ion implanted waveguides in thulium sodium yttrium tungstate

Planar waveguides were first formed in thulium sodium yttrium tungstate (Tm:NaY(WO₄)₂) crystals by the implantation of MeV He, P and Ni ions with certain doses at room temperature, respectively. The refractive index profiles of the three ion implanted waveguides were found different to some extent. The present data show that He⁺ ion implanted waveguides in Tm:NaY(WO₄)₂ should be the typical barrier type one, while a combination of radiation damage and radiation enhanced diffusion may be responsible for the refractive index profiles of the MeV Ni⁺ and P⁺ ion implanted waveguides in Tm:NaY(WO₄)₂.     

Two-dimensional hydrogen negative ion in a magnetic field

Making use of the adiabatic hyperspherical approach, we report a calculation for the energy spectrum of the ground and low-excited states of a two-dimensional hydrogen negative ion H^{-} in a magnetic field. The results show that the ground and low-excited states of H^{-} in low-dimensional space are more stable than those in three-dimensional space and there may exist more bound states.     

Formation of negative hydrogen ion in positronium-hydrogen collisions

The importance of the excited states of Positronium (Ps) in the formation cross sections (both differential and total) of the negative hydrogen ion (H^-) are investigated theoretically for the charge transfer reaction, Ps (n = 1, 2) + H ↦ e⁺ + H^- for a wide range of incident energies (e.g., threshold – 500 eV). The calculations are performed in the frame work of a qualitative model, the post collisional Coulomb modified eikonal approximation (CMEA). A comparative study is also made between the capture from ground and excited states of the Ps. The present CMEA model takes account of higher order effects which is essential for a rearrangement process where the first Born type approximation (Coulomb Born for the ionic case) is not supposed to be adequate. At low incident energies, the excited states of Ps (2s, 2p) are found to play a dominant role in the H^- formation cross sections. Significant deviations are noted between the present CMEA and the Coulomb Born (CBA) results even at very high incident energies (e.g., E_i = 500 eV), indicating the importance of higher order effects. At high incident energies the present CMEA differential cross section (DCS) exhibits a double peak structure which is totally absent in the CBA and could again be attributed to higher order effects.     

激光空泡溃灭及其产生的声波

强激光脉冲在水中的自聚焦传输、成丝、击穿及击穿后产生的声波,近年来成为强激光脉冲传输应用研究领域的一个热点。强激光脉冲电离产生的空泡在溃灭过程中,对周围水体产生压缩,从而在水下产生声波。在现有理论基础上,考虑空泡含气量、水的粘滞系数和水的表面张力系数对空泡运动及其产生声波的影响。给出双空泡运动方程,分析空泡间距对空泡溃灭和其产生声压关系。根据实际情况,计算不同温度情况下单空泡和双空泡运动过程及其产生的声压,并进行相互比较。计算结果表明： 水温越高,空泡运动时达到的最小半径越小,空泡振荡周期和溃灭时间延长,产生声压越高。随双空泡间距减小,空泡溃灭时达到的最小半径线性减小,而其产生的最大声压则单调增大。     

Raman scattering study of ion implanted and C.W.-Laser annealed polycrystalline silicon

Recovery of crystallinity in ion-implanted and c.w.-laser annealed polycrystalline silicon films has been examined by the Raman spectroscopy. The variation of the Raman frequency and width with laser annealing and thermal annealing shows the presence of uniform strain in the laser annealed polysilicon. It is found that the subsequent thermal annealing releases the strain.     

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.     

Optical and paramagnetic properties of natural diamonds implanted with hydrogen ions

We used IR spectroscopy and electron spin resonance (ESR) to investigate defect reconstruction processes occurring in diamond crystals due to their implantation with H⁺ ions with energies of 65–350 keV and subsequent isochronous annealing in the temperature range 250–1550°C. We found that most of the hydrogen in diamonds implanted with protons is in an IR-inactive state. Magnetic hysteresis related to radiation defects in diamond is observed for the first time at room temperature using ESR. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 74, No. 4, pp. 485–490, July–August, 2007.     

声场中空化气泡的耦合振动及形状不稳定性的研究

计算了两个具有非球形扰动的气泡所组成系统的能量,并基于Lagrange方程得到了有声相互作用的非球形气泡的动力学方程和形状稳定性方程,研究了声场中非球形气泡间相互作用力对非球形气泡的形状不稳定性和气泡形状模态振幅的影响.研究结果表明声场中具有非球形扰动的气泡之间的耦合方式有两种:形状耦合模式和径向耦合模式,气泡之间的耦合方式取决于气泡形状扰动模态.由形状耦合及径向耦合产生的气泡之间的相互作用力能够改变单个气泡的形状不稳定及形状模态振幅,具体影响因素取决于声场驱动条件、气泡形状模态、相邻气泡的初始半径.     

三氧化钨表面氢吸附机理的第一性原理研究

采用基于密度泛函理论的第一性原理平面波超软赝势方法,在广义梯度近似下,研究了立方WO_3,WO_3(001)表面结构及其氢吸附机理.计算结果表明立方晶体WO_3理论带隙宽度为0.587 eV.WO_3(001)表面有WO终止(001)表面和O终止(001)表面两种结构,表面结构优化后W—O键长和W—O—W键角改变,从而实现表面弛豫;WO终止(001)表面和O终止(001)表面分别呈现n型半导体特征和p型半导体特征.分别计算了H原子吸附在WO终止(001)表面和O终止(001)表面的H—O_(2c)—H,H—O_(2c)…H—O_(2c),H—O_(1c)—H和H—O_(1c)…H—O_(1c)四种吸附构型,其中H—O_(1c)—H吸附构型的吸附能最小,H—O键最短,H失去电子数最多,分别为-3.684 eV,0.0968 nm和0.55e,此吸附构型最稳定.分析其吸附前后的态密度,带隙从吸附前的0.624 eV增加到1.004 eV,价带宽度基本不变.H的1s轨道电子与O的2p,2s轨道电子相互作用,在-8和-20 eV附近各形成了一个较强的孤立电子峰,两个H原子分别与一个O_(1c)原子形成化学键,最终吸附反应生成了一个H_2O分子,同时产生了一个表面氧空位.     

The effect of incidence angle on disorder production in ion implanted Si

Abstract

Ne, Ar, Sb, and Xe ions have been implanted, at 30 keV or 80 keV and at various incidence angles, into Si substrates maintained at room temperature during implantation. Implantation-induced Si disorder was measured using RBS-channelling. The effects upon disorder of various incidence angles were studied over a fluence range of 10¹²-10¹⁶ ions·cm^?2.

The results show that, at low fluences the lighter (Ne) and slightly heavier (Ar) ion implantations generate a bimodal disorder-depth profile, whilst at higher fluences measurements of amorphised layer thickness as a function of ion incidence angle allow values of the standard deviation of the disorder profile parallel and transverse to the ion beam direction for each ion to be obtained with good agreement to theoretical predictions.     

Current-driven dynamics of skyrmion bubbles in achiral uniaxial magnets

We report dynamics of skyrmion bubbles driven by spin-transfer torque in achiral ferromagnetic nanostripes using micromagnetic simulations. In a three-dimensional uniaxial ferromagnet with a quality factor that is smaller than 1, the skyrmion bubble is forced to stay at the central nanostripe by a repulsive force from the geometry border. The coherent motion of skyrmion bubbles in the nanostripe can be realized by increasing the quality factor to ～ 3.8. Our results should propel the design for future spintronic devices such as artificial neural computing and racetrack memory based on dipole-stabilized skyrmion bubbles.