Surface chemical disorder and lattice strain of GaN implanted by 3-MeV Fe10+ ions

Chemical disorder on the surface and lattice strain in GaN implanted by Fe¹⁰⁺ ions are investigated. In this study, 3-MeV Fe¹⁰⁺ ions fluence ranges from 1×10¹³ ions/cm² to 5×10¹⁵ ions/cm² at room temperature. X-ray photoelectron spectroscopy, high-resolution x-ray diffraction, and high-resolution transmission electron microscopy were used to characterize lattice disorder. The transition of Ga-N bonds to oxynitride bonding is caused by ion sputtering. The change of tensile strain out-of-plane with fluence was measured. Lattice disorder due to the formation of stacking faults prefers to occur on the basal plane.     

二维应变作用下超导薄膜LiFeAs的磁性和电子性质

基于密度泛函理论的第一性原理计算,研究了二维应变作用下LiFeAs超导薄膜的磁性结构、电子能带和态密度变化,分析了应变对其超导电性的作用.结果显示,对体系施加1%—6%的二维平面张、压应变均不改变其基态条形反铁磁性结构,费米面附近的电子态密度主要来自于Fe-3d轨道电子以及少量的As-4p电子.研究发现,与无应变情形相比,当施加压应变时,体系中Fe离子的反平行的电子自旋局域磁矩减小,薄膜反铁磁性受到抑制,费米面上电子态密度增加,超导电性来自于以反铁磁超交换耦合作用为媒介的空穴型费米面和电子型费米面间嵌套的Cooper电子对.而在张应变作用时,局域反铁磁性增强,费米面上电子态密度减小,金属性减弱,特别是张应变时费米面上空穴型能带消失, Cooper电子对出现概率显著降低,将抑制超导相变.     

Strain engineering of electronic and magnetic properties of Ga_2S_2 nanoribbons

Using first-principles calculations, we study the tailoring of the electronic and magnetic properties of gallium sulfide nanoribbons(Ga_2S_2NRs) by mechanical strain. Hydrogen-passivated armchair-and zigzag-edged NRs(ANRs and ZNRs)with different widths are investigated. Significant effects in band gap and magnetic properties are found and analyzed. First,the band gaps and their nature of ANRs can be largely tailored by a strain. The band gaps can be markedly reduced, and show an indirect-direct(I-D) transition under a tensile strain. While under an increasing compressive strain, they undergo a series transitions of I-D-I-D. Five strain zones with distinct band structures and their boundaries are identified. In addition,the carrier effective masses of ANRs are also tunable by the strain, showing jumps at the boundaries. Second, the magnetic moments of(ferromagnetic) ZNRs show jumps under an increasing compressive strain due to spin density redistribution,but are unresponsive to tensile strains. The rich tunable properties by stain suggest potential applications of Ga_2S_2 NRs in nanoelectronics and optoelectronics.     

Al2O3陶瓷衬底碳离子预注入对金刚石薄膜应力的影响研究

通过对Al2O3陶瓷衬底进行碳离子预注入，大大降低了Al2O3陶瓷衬底上金刚石薄膜的应力，且金刚石薄膜中的压应力随碳离子注入剂量的增加而线性下降.通过对Al2O3陶瓷衬底注入前后的对比分析表明，高能量的碳离子注入Al2O3陶瓷衬底以后，并没有产生过渡层性质的新相，而是大量累积在Al2O3晶格的间隙位，使Al2O3晶格发生畸变.而且，随着碳离子注入剂量的增加，Al2O3基体内晶格畸变加剧，注入层残余压应力也随之上升.当金刚石薄膜沉积以后，在降温的过程中衬底这部分残余应力得到释放，从而部分弛豫了金刚石薄膜中的 关键词： 金刚石薄膜 应力 离子注入 Al2O3陶瓷     

Phase transitions in epitaxial (-110) BiFeO3 films from first principles

The effect of misfit strain on properties of epitaxial BiFeO3 films that are grown along the pseudocubic [110] direction, rather than along the usual [001] direction, is predicted from density-functional theory. These films adopt the monoclinic Cc space group for compressive misfit strains smaller in magnitude than ?1.6% and for any investigated tensile strain. In this Cc phase, both polarization and the axis about which antiphase oxygen octahedra tilt rotate within the epitaxial plane as the strain varies. Surprisingly and unlike in (001) films, for compressive strain larger in magnitude than ?1.6%, the polarization vanishes and two orthorhombic phases of Pnma and P2(1)2(1)2(1) symmetry successively emerge via strain-induced transitions. The Pnma-to-P2(1)2(1)2(1) transition is a rare example of a so-called pure gyrotropic phase transition, and the P2(1)2(1)2(1) phase exhibits original interpenetrated arrays of ferroelectric vortices and antivortices.     

Damage of low-energy ion irradiation on copper nanowire: molecular dynamics simulation

Physical and chemical phenomena of low-energy ion irradiation on solid surfaces have been studied systematically for many years, due to the wide applications in surface modification, ion implantation and thin-film growth. Recently the bombardment of nano-scale materials with low-energy ions gained much attention. Comared to bulk materials, nano-scale materials show different physical and chemical properties. In this article, we employed molecular dynamics simulations to study the damage caused by low-energy ion irradiation on copper nanowires. By simulating the ion bombardment of 5 different incident energies, namely, 1~keV, 2~keV, 3~keV, 4~keV and 5~keV, we found that the sputtering yield of the incident ion is linearly proportional to the energies of incident ions. Low-energy impacts mainly induce surface damage to the nanowires, and only a few bulk defects were observed. Surface vacancies and adatoms accumulated to form defect clusters on the surface, and their distribution are related to the type of crystal plane, e.g. surface vacancies prefer to stay on (100) plane, while adatoms prefer (110) plane. These results reveal that the size effect will influence the interaction between low-energy ion and nanowire.     

Strain-induced insulator–metal transition in ferroelectric BaTiO_3(001) surface:First-principles study

The electronic properties of TiO_2-terminated BaTiO_3(001) surface subjected to biaxial strain have been studied using first-principles calculations based on density functional theory. The Ti ions are always inward shifted either at compressive or tension strains, while the inward shift of the Ba ions occurs only for high compressive strain, implying an enhanced electric dipole moment in the case of high compressive strain. In particular, an insulator–metal transition is predicted at a compressive biaxial strain of 0.0475. These changes present a very interesting possibility for engineering the electronic properties of ferroelectric BaTiO_3(001) surface.     

Effect of deposition condition on residual stress of iron nitride thin films prepared by magnetron sputtering and ion implantation

The surface roughness and residual stress development in Fe-N thin films prepared by compound technology—combining magnetron sputtering with plasma based ion implantation were investigated by means of atomic force microscope and synchrotron radiation. The results indicate that the grain size of the thin film increases with the increasing of nitrogen ion implantation time, and the state of residual stress is related closely to the formation mechanism of thin films. With the nitrogen ion implantation time increasing, the residual stress of the thin film changes into tensile stress from initial compressive stress, and the tensile stress decreases with the further increasing of ion implantation time.     

应力作用下GdTiO_3磁序相变的第一性原理研究

采用基于密度泛函理论的第一性原理方法,系统研究了GdTiO_3薄膜在压缩应力和拉伸应力作用下的磁序相变.计算结果表明:1)在LaAlO_3压缩衬底的作用下,GdTiO_3薄膜从铁磁基态转变为G型反铁磁基态.该结果不同于YTiO_3和LaTiO_3在LaAlO_3压缩衬底作用时都呈现A型反铁磁基态的情况.若进一步加大压缩应力,例如在(001)平面施加YTiO_3衬底,此时GdTiO_3薄膜基态才为A型反铁磁态.2)在LaScO_3和BaZrO_3拉伸衬底的作用下,GdTiO_3薄膜的基态仍是铁磁态,但是随着拉伸应力的增大,A型反铁磁态的能量和铁磁态的能量差逐渐缩小,即GdTiO_3薄膜的基态有转变为A型反铁磁态的趋势.3)在外加应力的作用下,GdTiO_3薄膜基态的磁序发生了相变,但是其绝缘性并没有变,说明GdTiO_3薄膜仍为Mott型绝缘体.     

聚合物物理属性对离子注入效应的影响

聚合物导电性能差, 表面电荷积聚所产生的电容效应致使其表面电位衰减, 采用等离子体浸没离子注入对其表面改性是非常困难的. 建立了绝缘材料等离子体浸没离子注入过程的粒子模拟(PIC)模型, 实时跟踪离子在等离子体鞘层中的运动形态及特性并进行统计分析. 并基于PIC模型, 将聚合物表面的二次电子发射系数直接与离子注入即时能量建立关联, 研究了聚合物厚度、介电常数和二次电子发射系数等物理量对鞘层演化、离子注入能量和剂量的影响规律. 研究结果表明: 当聚合物厚度小于200 μ m, 相对介电常数大于7, 二次电子发射系数小于0.5时, 离子注入剂量和高能离子所占的份额与导体离子注入情况相当. 通过对聚合物表面离子注入剂量和高能离子所占份额的研究, 为绝缘材料和半导体材料表面等离子体浸没离子注入的实现提供了理论和实验依据.     

Fe:Mg:LiNbO3晶体电子结构和吸收光谱的第一性原理研究

基于密度泛函理论的第一性原理, 研究了LiNbO₃晶体以及不同Mg浓度的Fe:Mg:LiNbO₃晶体的电子结构和吸收光谱. 研究结果显示: 掺铁铌酸锂晶体的杂质能级由Fe 的3d轨道和O的2p轨道贡献, 禁带宽度为2.845 eV; 对于Mg, Fe共掺样品, Mg的浓度小于或等于阈值时, 禁带宽度分别为2.901 和2.805 eV; 掺铁铌酸锂晶体的吸收谱在2.3和2.6 eV处分别存在一个吸收峰, 其强度因Mg的浓度不同而发生变化. 研究结果还表明, 不同浓度的Mg对晶体内Fe²⁺和Fe³⁺的浓度以及占位产生了不同的影响. 还提出了光电子的形成不应单独考虑铁的轨道电子态, 而应同时考虑与铁成键的氧的轨道电子态的观点.     

Surface defects,stress evolution,and laser damage enhancement mechanism of fused silica under oxygen-enriched condition

Oxygen ions (O⁺) were implanted into fused silica at a fixed fluence of 1×10¹⁷ ions/cm² with different ion energies ranging from 10 keV to 60 keV. The surface roughness, optical properties, mechanical properties and laser damage performance of fused silica were investigated to understand the effect of oxygen ion implantation on laser damage resistance of fused silica. The ion implantation accompanied with sputtering effect can passivate the sub-/surface defects to reduce the surface roughness and improve the surface quality slightly. The implanted oxygen ions can combine with the structural defects (ODCs and E' centers) to reduce the defect densities and compensate the loss of oxygen in fused silica surface under laser irradiation. Furthermore, oxygen ion implantation can reduce the Si-O-Si bond angle and densify the surface structure, thus introducing compressive stress in the surface to strengthen the surface of fused silica. Therefore, the laser induced damage threshold of fused silica increases and the damage growth coefficient decreases when ion energy up to 30 keV. However, at higher ion energy, the sputtering effect is weakened and implantation becomes dominant, which leads to the surface roughness increase slightly. In addition, excessive energy aggravates the breaking of Si-O bonds. At the same time, the density of structural defects increases and the compressive stress decreases. These will degrade the laser laser-damage resistance of fused silica. The results indicate that oxygen ion implantation with appropriate ion energy is helpful to improve the damage resistance capability of fused silica components.     

应力对硅烯上锂吸附的影响

本文采用基于密度泛函理论的第一性原理平面波赝势方法研究了双轴应力作用下锂原子吸附硅烯的结构及其稳定性. 计算结果表明,在拉应力和一定的压应力作用下,锂吸附的硅烯体系基本保持原有的结构. 而当更大的压应力作用时,硅烯产生了向锂原子方向凸起的结构变化,所得到的体系的总能也有明显地下降. 本文通过对各种应力下的硅烯声子谱的计算,分析了在压应力作用下锂吸附的硅烯结构不稳定的原因. 关键词： 硅烯 应力 第一性原理 声子谱     

Effect of tensile and compressive strain on the magnetic ordering of the ($$\hbox {LaMnO}_{3})_{1}/\hbox {(SrTiO}_{3})_{1}$$ superlattice

We study the effects of tensile and compressive strain on the \((\hbox {LaMnO}_{3})_{1}/(\hbox {SrTiO}_{3})_{1}\) superlattice from density functional theory using Quantum-Espresso open source code. In the unstrained superlattice, electron interactions in out-of-plane Mn–O–Ti chains are dominated by superexchange interactions, giving rise to ferromagnetic and half-metallic conducting characters. We found that the most stable magnetic configuration is G-type antiferromagnetic configuration for strong compressive strain and for strong tensile strain it is A-type antiferromagnetic configuration. The results are in accordance with the experimental observations which show that the superlattices can be grown on different substrates, and due to the difference in lattice parameters of the substrate and the main layer, there are also changes in the amount of strain applied to the superlattice.     

Optical waveguide with homogeneous refractive index profile in LiNbO3 by double-low-energy Oxygen ion implantation

We report on the formation of the planar waveguide by 550 keV O ion followed by 250 keV O ion implantation in lithium niobate (LiNbO₃), at fluences of 6 × 10¹⁴ ions/cm² and 3 × 10¹⁴ ions/cm², respectively. The Rutherford backscattering/channeling spectra have shown the atomic displacements in the damage region before and after annealing. A broad and nearly homogeneous damage layer has been formed by double-energy ion implantation after annealing. Both the dark mode spectra and the data of refractive index profile verified that the extraordinary refractive index was enhanced in the ion implanted region of LiNbO₃. A homogeneous near-field intensity profile was obtained by double-low-energy ion implantation. There is a reasonable agreement between the simulated modal intensity profile and the experimental data. The estimated propagation loss is about 0.5 dB/cm.     

The generation,detection and measurement of laser-induced carbon plasma ions and their implantation effects on brass substrate

The generation, detection and measurement of laser-induced carbon plasma ions and their implantation effects on brass substrate have been investigated. Thomson parabola technique was employed to measure the energy and flux of carbon ions. The magnetic field of strength 80?mT was applied on the graphite plasma plume to provide an appropriate trajectory to the generated ions. The energy of carbon ions is 678?KeV for laser fluence of 5.1?J/cm² which was kept constant for all exposures. The flux of ions varies from 32?×?10¹¹ to 72?×?10¹⁴?ions/cm² for varying numbers of laser pulses from 3000 to 12,000. In order to explore the ion irradiation effects on brass, four brass substrates were irradiated by carbon ions of different flux. Scanning electron microscope (SEM) and X-ray diffractometer (XRD) are used to analyze the surface morphology and crystallographic structure of ion-implanted brass, respectively. SEM analysis reveals the formation and growth of nano-/micro-sized cavities, pores and pits for the various ion flux for varying numbers of laser pulses from 3000 to 12,000. By increasing ion flux by increasing the number of pulses up to 9000 shots, the dendritic structures initiate to grow along with cavities and pores. At the maximum ion flux for 12,000 shots, the unequiaxed dendritic structures become distinct and the distance between the dendrites is decreased, whereas cavities, pores and pits are completely finished. The XRD analysis reveals that a new phase of ZnC (0012) is formed in the brass substrate after ion implantation. Universal tensile testing machine and Vickers microhardness tester are used to explore the yield stress, ultimate tensile strength and microhardness of ion-implanted brass substrate. The mechanical properties monotonically increase by increasing the ion flux. Variations in mechanical properties are correlated with surface and structural modifications of brass.     

ICP与吸收光谱测定LiNbO3, Zn:LiNbO3晶体中Cr3+离子的分布及有效分凝系数

应用坩埚下降法生长了掺杂Cr与双掺杂Cr，Zn的LiNbO3晶体。测定了掺杂晶体不同部位的吸收系数。用电感耦合等离子体原子发射光谱(ICP)法测定了Cr离子在LN晶体中的浓度，并计算了Cr离子在LiNbO3晶体中的有效分凝系数。研究结果表明：在单掺杂Cr的LiNbO3晶体中，随着Cr^3 掺杂浓度从0．1增加到0．5mol％时，其有效分凝系数从3．75减少到2．49，Cr^3 离子在晶体中的浓度分布差异逐步减少；ZnO的掺入能有效地减少Cr^3 的分凝系数，然而ZnO掺杂浓度从3增加到6mol％时，其有效分凝系数且从1．85增加到2．25。可从ZnO组分对Cr离子的排斥作用及Zn离子在LN晶体中随掺杂数量变化的分凝现象解释了产生Cr离子浓度及有效分凝系数变化的原因。     

Electronic structure and optical properties of CuAlO2 under biaxial strain

An ab initio calculation has been carried out to investigate the biaxial strain ( - 10.71% < ε < 9.13%) effect on elastic, electronic and optical properties of CuAlO(2). All the elastic constants (c(11), c(12), c(13), c(33)) except c(44) decrease (increase) during tensile (compressive) strain. The band gap is found to decrease in the presence of tensile as well as compressive strain. The relative decrease of the band gap is asymmetric with respect to the sign of the strain. Significant differences between the parallel and perpendicular components of the dielectric constant and the optical properties have been observed due to anisotropic crystal structure. It is further noticed that these properties are easily tunable by strain. Importantly, the collective oscillation of the valence electrons has been identified for light polarized perpendicular to the c-axis. From calculations, it is clear that the tensile strain can enhance the hole mobility as well as the transparency of CuAlO(2).     

The enhancement of the anodization of ion implanted silicon and its novel application

The enhancement of the anodization of silicon due to ion implantation is observed to be significant in the case of heavy ion implant with doses more than 10¹⁴ ions/cm². The studies indicate that the chemical effect caused by the implanted ions is smaller, but the lattice defects introduced by the implantation play an important role in the enhancement of the oxidation rate. A novel application of this effect to investigate the depth profile of damage in heavy implanted silicon is shown.