Electronic modifications and surface reactivity of an ion bombarded graphite surface

The first steps of structural and electronic modifications of a graphite surface bombarded with argon, hydrogen and deuterium ions were investigated using high resolution electron energy loss spectroscopy (HREELS). The energy and the damping of the low energy plasmon mode of graphite (E//C mode) were studied with respect to the bombardment settings. We show that argon bombardment affects the energy of the plasmon mode, while no similar change is observed after hydrogen (deuterium) bombardments. This can be related to the variation of inter-planar distance between two graphene layers. Moreover, the damping of the plasmon mode can be correlated with the interstitial defect concentration. Concerning the reactivity of the bombarded surfaces, we demonstrate that deuterium bombardment produce a non-deuterated surface. This last is very reactive to a further atomic deuterium exposure, as it is shown by the formation of C-D bondings. The deuterated sites can be removed after thermal annealings between 473 and 783 K. The occurrence of a chemical erosion mechanism accompanying this deuteration is discussed.     

Charge compensation in an insulated target bombarded by a pulsed electron beam in the forevacuum pressure range

We report on the results of computation of the time dependence of the ion flux and the dielectric target potential at the initial stage of bombardment by an electron beam in forevacuum. It is shown that a satisfactory agreement with experimental data is attained with allowance for the possibility of the discharge between the target and the earthed walls of the vacuum chamber.     

A potential double layer formation by ion beam reflection at an ion-absorbing boundary in a non-magnetized plasma

A potential double layer is formed by injecting an ion beam into an ion-absorbing boundary with a large cross section from a low potential side in a non-magnetized plasma. An ion-density crest caused by the ion reflection is observed.     

Mathematical modeling of the heating of a fast ignition target by an ion beam

We develop a BIN computer code for simulating the interaction of a monochromatic ion beam with a plasma, which takes into account changes in the spatial distribution of the heated-plasma temperature. This enables us to calculate the heating of both homogeneous and inhomogeneous plasmas with parameters corresponding to their real spatial distributions at the time of maximum compression of the inertial confinement fusion (ICF) target. We present the results of a numerical simulation using the BIN code for the heating of a homogeneous deuterium–tritium plasma by a short pulse of monochromatic ions at various ion velocity and plasma–electron thermal velocity ratios. We also present the results of calculations for the heating of an inhomogeneous plasma of a non-cryogenic target formed as a beryllium deuteride–tritide shell by beams of light, medium, and heavy ions. As the initial distributions, we use the results of numerical simulations for such a target, precompressed by a laser pulse (carried out at the M. V. Keldysh Institute of Applied Mathematics using the DIANA code). We demonstrate the possibility of forming the central ignitor with the parameters sufficient for igniting the targets by beams of ions with energies E ~ 100 ? 400 MeV/u and specific energy densities of the beam Q ～ 5?20 GJ/cm². The required specific energy density drops with increase in the ion energy; however, due to the increased path length, larger-charge ions have to be used.     

强流脉冲电子束作用下钽金属靶膨胀的轴向约束

研究了强流脉冲电子束与钽金属靶相互作用后靶材流体动力学膨胀的轴向约束问题。由于电子束在金属钛和钽内的能量沉积存在差异,未完全气化的钛箔对气化膨胀的钽材能够起到约束作用,并且可以通过吸收钽的能量来降低钽的膨胀速度。通过分析比较电子束在靶上形成孔洞的形貌以及高速相机拍摄得到的不同时刻靶材喷射的图像,证实了钛箔能够对钽金属靶的轴向膨胀起到一定的约束作用。尤其是电子束打靶过后1 μs内的初始阶段,约束效果比较明显。     

强流脉冲电子束作用下钽金属靶膨胀的轴向约束

研究了强流脉冲电子束与钽金属靶相互作用后靶材流体动力学膨胀的轴向约束问题。由于电子束在金属钛和钽内的能量沉积存在差异,未完全气化的钛箔对气化膨胀的钽材能够起到约束作用,并且可以通过吸收钽的能量来降低钽的膨胀速度。通过分析比较电子束在靶上形成孔洞的形貌以及高速相机拍摄得到的不同时刻靶材喷射的图像,证实了钛箔能够对钽金属靶的轴向膨胀起到一定的约束作用。尤其是电子束打靶过后1μs内的初始阶段,约束效果比较明显。     

高能通量脉冲电子束作用下钽靶破坏初步研究

 使用Monte-Carlo程序MCNP在2维情况下模拟得到了高能通量脉冲电子束在钽金属靶中的能量沉积。根据能量沉积的模拟结果以及实验后靶上穿孔的大小和形貌,提出了电子束对不同结构钽金属靶破坏的物理机制。由于能量沉积的差异,1 mm实心靶中的热激波在一定时间内沿径向和轴向持续对靶材进行压缩,而在叠靶中这种压缩效果并不明显,因此实验后1 mm实心靶上穿孔的大小几乎是叠靶上的两倍。根据理论模型分析得到的靶材熔融喷射和层裂现象与实验结果相吻合。     

平面上方二维介质目标对高斯波束的电磁散射研究

基于矩量法、互易性定理及镜像理论,提出了一种新的混合方法用于研究水平分界面上方二维介质目标对垂直入射高斯波束的差值散射场.应用镜像理论,介质水平分界面可被原始目标相对于该分界面的镜像目标所替代,从而给出散射问题的等效模型.在等效模型中,应用矩量法求解了原始目标及镜像目标对高斯波束的散射场,同时结合互易性定理得到了原目标与其镜像目标之间的耦合散射场.数值计算结果与相关文献方法及MoM所得结果进行了比较,验证了该混合方法的有效性. 关键词： 互易性定理 电磁散射 高斯波束 二维目标     

Erosion of the GaAs target under irradiation by a high-power pulsed ion beam

The results of examination of the GaAs-target erosion under irradiation by a high-power pulsed ion beam are reported. In the experiments, use was made of a high-power pulsed ion source with the following parameters: ion energy — 250 keV, target current density — 350 A/cm², pulse duration — 80 ns, target energy density — up to 7 J/cm². The target erosion coefficient and its dependence on the number of successive pulses are measured. It is found that the surface roughness parameter is increased with the number of successive beam pulses. A regular structure of surface relief is observed to form in the case where the number of pulses > 20–40. __________ Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 1, pp. 66–70, January, 2007.     

脉冲离子束作用下靶面次级电子的抑制

论述了离子束作用下固体表面次级电子产生的机制,介绍了特种真空器件中次级电子抑制的各种方法及其优缺点,提出了脉冲离子束作用下靶面次级电子抑制的自偏势法和曲面靶法等设计思路,并在实验上进行了初步验证。实验结果表明,自偏势电压大于80 V后,次级电子得到很好的抑制。在相同束流情况下,曲面靶较平面靶的次级电子产额少。利用实验结果进行估算得到了近似的次级电子产额约为0.67,比文献中的结果(0.58)偏大。对实验中自偏势法抑制反峰电子电流的效果进行了分析和讨论,结果表明:自偏势法不但能够有效抑制离子打靶产生的次级电子,还能抑制由功率源不稳定带来的入射反峰电子流。     

脉冲离子束作用下靶面次级电子的抑制

论述了离子束作用下固体表面次级电子产生的机制,介绍了特种真空器件中次级电子抑制的各种方法及其优缺点,提出了脉冲离子束作用下靶面次级电子抑制的自偏势法和曲面靶法等设计思路,并在实验上进行了初步验证。实验结果表明,自偏势电压大于80 V后,次级电子得到很好的抑制。在相同束流情况下,曲面靶较平面靶的次级电子产额少。利用实验结果进行估算得到了近似的次级电子产额约为0.67,比文献中的结果(0.58)偏大。对实验中自偏势法抑制反峰电子电流的效果进行了分析和讨论,结果表明：自偏势法不但能够有效抑制离子打靶产生的次级电子,还能抑制由功率源不稳定带来的入射反峰电子流。     

Formation of nanocavities in the surface layer of an aluminum target irradiated by a femtosecond laser pulse

It has been revealed experimentally that nanocavities remain inside a surface layer of aluminum after action of a femtosecond laser pulse. This result is in agreement with numerical simulation. A detailed picture of melting, formation of expansion and compression waves, and bubble nucleation in the stretched melt has been reconstructed through atomistic simulation. It has been shown that the bubbles do not fully collapse but remain as frozen disk-shaped nanocavities upon recrystallization of the melt. The formation of a porous metal with small voids is very important for understanding the physics of laser exposure and may have significant applications.     

离子束修形中光学元件表面热量沉积数值模拟

根据Sigmund溅射能量沉积理论建立了低能离子入射光学元件引起的能量扰动层厚度模型．理论推导了离子束倾斜入射时光学元件表面的束流密度,并建立了低能离子束对光学元件的热量沉积模型．采用MonteCarlo方法模拟了低能离子与熔石英光学表面的相互作用．分析了离子能量、离子类型、入射角度等参数对光学元件热量沉积和扰动层深度的影响规律．以离子束沉积在工件的能量作为热源,采用有限元分析软件ANSYS模拟了离子束入射工件的温度场分布、温度梯度场分布和温度应力分布．入射表面温度和热梯度呈高斯分布,束斑中心最高并向工件边缘逐渐减小．入射表面束斑区域受热膨胀,其膨胀受到外环区域的制约,从中心区域到大约束斑半峰值半径的区域,所受环向应力为压应力,在大致束斑半峰值半径以外区域为拉应力．     

Highly ordered Ga nanodroplets on a GaAs surface formed by a focused ion beam

The morphological evolution of a GaAs surface induced by a focused ion beam (FIB) has been investigated by in situ electron microscopy. Under off-normal bombardment without sample rotation, Ga droplets with sizes from 70 to 25 nm in diameter on the GaAs surface can self-assemble into a highly ordered hexagonal pattern instead of Ostwald ripening or coalescence. The mechanism relies on a balance between anisotropic loss of atoms on the surface of droplets due to sputtering and an anisotropic supply of atoms on the substrate surface due to preferential sputtering of As. The ratio of wavelength to the droplet diameter predicted by this model is in excellent agreement with experimental observations.     

High-intensity Si cluster ion emission from a silicon target bombarded with large Ar cluster ions

Secondary ions emitted from Si targets were measured with a quadrupole mass spectrometer under large Ar cluster and monomer ion bombardment. Incident ion beams with energies from 7.5 to 25 keV were used and the mean size of the Ar cluster ion was about 1000 atoms/cluster. Si_n⁺ ions with n values up to n = 8 were detected under Ar cluster ion bombardment, whereas Si cluster ions were scarcely detected under Ar monomer ion bombardment. These cluster ion yields showed the power law dependence on the cluster size.     

Analysis of the outermost atomic layer of a surface by low-energy ion scattering

Noble gas ion scattering is used to study the surface of solid targets. It is shown that this technique can be used to obtain a mass spectrum of the first atomic layer of the surface. Since the outermost atoms will largely determine the chemical reactivity and physical properties of the surface, this is an important property for an analytic tool to have. In addition to reflected ions, high-energy recoil ions are sometimes observed.Both the reflected and the recoil ions provide information about the atomic structure of the surface. The various possibilities of ion scattering are demonstrated for bromine, oxygen, sodium and potassium adsorbed on a Si(111) surface, for halogens adsorbed on Ni(100) and for GaP (110), (111) ($\text{111}$) surfaces. The influence of thermal vibrations of surface atoms and of electronic excitation on the spectra is discussed.     

Sputtering of the magnetron diode target in the presence of an external ion beam

The effect of an external ion beam on the plasma and target of a dc magnetron sputtering system in the course of reactive deposition of films is investigated. A combined experimental setup consisting of a magnetron diode and a hall-current ion source is constructed. The influence of a fast ion beam on the discharge current formation, the target emission characteristics, and the target etching rate is considered. It is shown that the ion assistance expands the operating range of the magnetron diode, increases the deposition rate, and substantially shortens the target training time. At the same time, it practically does not affect the ionization processes in the plasma.     

强流脉冲离子束辐照靶材烧蚀效应二维数值研究

对强流脉冲离子束(IPIB)辐照Ti靶的烧蚀效应进行了二维数值研究.得到了表面烧蚀物质随脉冲时间的变化关系.得出TEMP Ⅱ 型加速器产生的脉冲束流辐照靶材时引起的汽、液化均是从表面开始、并且汽化过程中表面物质被层层烧蚀的结论.同时，得到中心区的平均烧蚀速度为10m/s 数量级，它远小于产生的烧蚀等离子体的喷发速度.得到脉冲期间靶材内部不同位置烧蚀斑痕形状的时间演化过程，以及束流中含有的离子种类分额不同时IPIB辐照过程产生的不同效果. 关键词： 强流脉冲离子束 靶 烧蚀过程 二维数值模拟