X-ray diffraction of permalloy nanoparticles fabricated by laser ablation in water

Permalloy (NiFeMo) nanoparticles were fabricated by laser ablation of bulk material in water with a UV pulsed laser. Transmission electron microscope images showed that approximately spherical particles about 50 nm in diameter were formed in the ablation process. All diffraction peaks corresponding to the bulk material were present in the nanoparticles. In addition to these peaks several new peaks were observed in the nanoparticles, which were attributed to nickel oxide.     

硅、锗材料在Si(100)表面的生长研究

利用扫描隧道显微镜和超高真空实验装置系统进行了Si(10 0 )表面生长Si,Ge的实验研究。分析了所生成表面的形貌、结构等物理性质。研究表明 :Si在Si(10 0 )表面的同质生长可以形成纳米结构薄膜。Ge在Si(10 0 )表面生长形成规则的三维小岛。而在Si/Ge/Si(10 0 )多层膜上生长则形成大小二种三维岛。研究表明大岛具有Ge/Si/Ge的壳层结构     

Preparation of LiMn2O4 nanoparticles for Li ion secondary batteries by laser ablation in water

The laser ablation technique in liquids was applied for preparing LiMn₂O₄ nanoparticles for Li ion secondary batteries. A new optical configuration for laser irradiation was also developed to increase irradiation intensity. SEM observation proved that the amount of nanoparticles obtained drastically increased with an increase in laser intensity. On the other hand, the composition change caused by laser ablation was very small. The improvement in the rate capacity of the electrodes composed of the nanoparticles could be explained in terms of particle size reduction.     

离子束溅射制备Si／Ge多层膜研究

采用离子束溅射方法在Si衬底上制备Si／Ge多层膜，通过改变生长温度、溅射速率等因素得到一系列Si／Ge多层膜样品；通过X射线衍射、Raman散射等表征方法研究薄膜结构与生长条件的关系。在小束流（10mA）、室温条件下制备出界面清晰、周期完整的Si／Ge多层膜。     

Ge／Si纳米多层膜的光致发红光研究

采用磁控溅射设备，当衬底温度为500℃时，在Si（100）基片上磁控溅射生长Ge／Si多层膜样品，使用Raman和低角X射线技术对样品进行检测和研究。在红光波段对样品的光致发光进行了研究，结果表明在红光波段发光峰位来源于薄膜的非晶结构及其薄膜所产生的缺陷；发光峰的强度和峰形受Ge子层和Si子层厚度的影响。     

Preparation and characterization of Ge epitaxially grown on nano-structured periodic Si pillars and bars on Si(001) substrate

The selective epitaxial growth of germanium on nano-structured periodic silicon pillars and bars with 360 nm periodicity on Si(001) substrate is studied to evaluate the applicability of nano-heteroepitaxy on the Ge-Si system for different fields of application. It is found that SiO₂ used as masking material plays the key role to influence the strain situation in the Si nano-islands. To analyze this in detail, X-ray diffraction techniques in combination with theoretical simulations based on the kinematical X-ray scattering from laterally strained nano-structures and finite element method (FEM) calculations of the strain field are applied. The oxide related strain in the Si scales about linearly with the thickness of the SiO₂ mask, but FEM simulations supposing a homogeneous stress distribution in the oxide are not sufficient to describe the local strain distribution in the nano-structures. It is demonstrated that the Ge lattice relaxes completely during growth on the Si nano-islands by generation of misfit dislocations at the interface, but a high structural quality of Ge can be achieved by suited growth conditions.     

Ge/Si多层膜热稳定性的Raman光谱研究

用Raman光散射的方法，观察了磁控溅射技术制备的Ge/Si系列多层膜退火处理后的各Raman峰的变化，对其峰形、峰位及峰强的变化进行讨论分析。实验结果显示：Ge/Si多层膜经700℃热处理10min后，能改善各层的晶体质量，得到较完整的多层膜的结构。     

Si_3N_4/Si表面Ge生长过程的STM研究

利用STM和LEED分析了Ge在Si3 N4 /Si(111)和Si3 N4 /Si(10 0 )表面生长过程的结构演变。在生长早期 ,Ge在两种衬底表面上都形成高密度的三维纳米团簇 ,这些团簇的大小均在几个纳米范围内 ,并在高温退火时体积增大。当生长继续时 ,Ge的晶体小面开始显现。在晶态的Si3 N4 (0 0 0 1) /Si(111)表面 ,Ge的 (111)晶向的小面生长比其他方向优先。最后在大范围内形成以 (111)方向为主的晶面。相反 ,在非晶的Si3 N4 表面 ,即Si3 N4 /Si(10 0 ) ,Ge晶体的高指数侧面生长较顶面快 ,最终形成金字塔形的岛结构。对这样的表面生长过程进行了探讨并给出了合理的物理解释     

Island formation in Ge/Si epitaxy

We review current understanding of the island formation process, and outline some of the remaining problems. The initial island formation is coherent, with islands stabilised by the elastic relaxation associated with deformation of the substrate. We use finite element analysis to demonstrate the degree of relaxation associated with these deformations. The islands then relax further by introduction of dislocations. The first dislocations introduced in the large coherent islands are shown to be inclined burgers vectors (about 60°) adopting a nearly semicircular path around the island perimeter. The outstanding anomaly in Ge/Si growth is the temperature dependence of islanding, with slower relaxation rates and greater metastability associated with higher temperatures. We describe various possible explanations for this problem.     

Solution assisted laser ablation synthesis of discrete aluminum nanoparticles

Discrete aluminum nanoparticles with an average particle size of 21 nm have been prepared by laser ablation of a metallic aluminum target submerged in dry tetrahydrofuran in the presence of 0.001 M oleic acid as a stabilizing ligand. The particles display high solubility and minimal aggregation while the absence of oleic acid leads to highly aggregated particles and a broader particle size distribution. O/Al ratios obtained from EDS analysis suggest that the particles produced are primarily metallic aluminum with minimal oxide content.     

离子束溅射Si／Ge多层膜的界面结构研究

采用离子束溅射技术，在玻璃衬底上制备了不同周期数的Si／Ge多层膜样品。通过Raman光谱和X射线小角衍射对薄膜进行了表征和分析，发现随着生长周期数的增加，层与层之间的互扩散效应逐渐减弱，界面结构逐渐清晰，生长周期为25的样品界面最平整。     

Laser power effect on morphology and photoluminescence of ZnO nanostructures by laser ablation in water

The morphology and photoluminescence of ZnO nanostructures formed by laser ablation in water were found to be susceptible to the applied laser power. The products varied from nanoflakes to nanoparticles, then to short nanorods with the increase of laser power. Correspondingly, the relative intensity of violet emission decreased and that of green emission increased. The morphology formation mechanism and defect relaxation were analyzed from a view of laser power effect on the induced plasma states, which includes plasma intensity, lifetime, distribution, and thus on defect type. These results would be of great importance for understanding the growth dynamics of nanomaterials under extreme conditions.     

Formation of silver nanoparticles by through thin film ablation

Well dispersed Ag nanoparticles have been formed by a process denoted Through Thin Film Ablation. The nanoparticles were deposited on room temperature substrates, had a most probable size of 1 nm, and were not agglomerated. The nanoparticle deposit produced by this process showed no evidence of the larger particles commonly observed from conventional pulsed laser ablation that uses a bulk target. Synthesis of nanoparticles by Through Thin Film Ablation should be possible for any material that can be made as a thin film target and may enable the unique properties of isolated, non-agglomerated nanoparticles to be exploited more fully.     

Thermal and tensile properties of Si/Ge core-shell and superlattice nanowires

The Stillinger-Weber potential-based MD (Molecular dynamics) method is used to simulate the heating-up and axial tension of Si/Ge core-shell and superlattice nanowires; according to the simulative results, the differences in their thermal and mechanical properties are discussed. The results show the following: (1) The Si/Ge superlattice nanowire is more thermally stable than the core-shell one, and their melting points are 1160 and 1320 K, respectively. (2) The Si/Ge core-shell nanowire has higher elastic module than the super-lattice one. (3) Under tension, the super-lattice nanowire has better antideformation capability than the core-shell one but has comparative antiloading capability.     

Synthesis of Si-C nanostructures by laser ablation of silicon target in n-heptane vapor

Controllable synthesis of Si-C nanostructures was realized in a laser ablation system by adopting solid silicon target and n-heptane vapor as starting materials. Ultrafine SiC nanocrystals and graphite-coated SiC nanocrystals were synthesized with the laser frequency of 1 Hz and 20 Hz, respectively. According to the real-time observation on the plasma evolvement, we proposed a formation mechanism of Si-C nanostructure related to vapor-phase reaction. Our method can be extended to other material systems for diverse novel nanostructures.     

溅射气压对Ge/Si纳米点表面形貌的影响

利用磁控溅射技术在Si(100)衬底上直接外延生长一系列不同压强下的Ge纳米点样品,并利用AFM、Raman和XRF对Ge纳米点样品形貌和结构进行了研究。结果表明Ge薄膜表面粗糙度在某一临界压强下发生突变,高能粒子热化的临界值与这种转变密切相联;分析讨论了Ge岛在不同溅射气压下的生长过程,在一定范围随着压强的增大会显示典型生长阶段的特征。     

束流密度对Ge/Si量子点溅射生长的影响

采用离子束溅射技术在Si基底上自组织生长了一系列Ge量子点样品,研究了束流密度对Ge/Si量子点的尺寸分布和形貌演变的影响。原子力显微镜测试结果表明,随着束流密度的增加,量子点的面密度持续增大,其尺寸不断减小,量子点的形貌由圆顶形转变为过渡圆顶形。计算直径标准偏差的结果表明,当束流密度为0.86mA/cm2时,量子点的尺寸均匀性最佳。束流密度与沉积速率成正比,影响着表面吸附原子与其它原子相遇而形成晶核的能力。     

Energetics of Ge addimers on the Si(1 0 0) and Ge(1 0 0) surfaces: a comparative study

The adsorption energetics of Ge dimers on the (1 0 0) surfaces of Ge and Si has been investigated using the first-principles molecular dynamics method. Four high-symmetry configurations have been considered and fully relaxed. The most stable configuration for Ge dimers on Si(1 0 0) is found to be in the trough between two surface dimer rows, oriented parallel to the substrate Si dimers. These results are consistent with recent experimental studies of the system using the scanning tunneling microscopy (STM), and help to clarify some existing controversies on the interpretation of the STM images. In contrast, for Ge dimers on Ge(1 0 0), the most stable configuration is on top of the substrate dimer row.