Spatial and Quantum Confinement of Si Nanoparticles Deposited by Laser Electrodispersion onto Crystalline Si

C–V characteristics and DLTS spectra of heterostructures made up of layers of closely packed amorphous Si nanoparticles deposited by laser electrodispersion onto single-crystal p-Si substrates have been examined. The patterns observed in the behavior of the C–V characteristics and DLTS spectra measured in the dark and under illumination with white light at various bias pulse voltages U _b and filling pulse voltages U _f suggest that the spatially localized amorphous Si nanoparticles have an average size of less than 2 nm, which is comparable with the de Broglie electron wavelength, and are characterized by quantum confinement. The ground and excited states of quantum dots are formed and exhibit the Stark effect and effects of electricdipole and controllable metastable occupancy under illumination.     

Carbon Clusters Formation by Laser Irradiation of Carbonaceous Solids

Abstract

A laser ablation/Fourier‐transform ion cyclotron resonance mass spectrometry was used to generate fullerenes clusters from targets of carbonaceous material containing carbyne, C₆₀ photopolymer, graphite, diamond, C₆₀ fullerene crystals.     

激光蒸凝法制备氧化铜纳米粒子

以１５０Ｗ ＣＷ ＣＯ_２激光器为光源,Ｃｕ（ＡＣ）_２·Ｈ_２Ｏ为靶材,采用激光蒸凝法制备出了氧化铜纳米粒子．初步研究了反应参数对纳米粒子性能的影响,并用Ｘ射线衍射、电子衍射、透射电镜等技术对纳米粒子的性能进行了表征,同时对纳米粒子的形成机理进行了初步的探讨．实验结果表明;激光功率密度、反应压力、载气种类及流量等工艺参数对产品的粒度、晶型等性能均有影响．在惰性气氛下,产物主要是Ｃｕ和Ｃｕ_２Ｏ,粒径为１０～３０ｎｍ;在氧气气氛下,产物主要是Ｃｕ、Ｃｕ_２Ｏ和ＣｕＯ的混合物,粒径为１０～５０ｎｍ．     

Selective Formation of Metal Nanoparticles on the Sidewalls of Carbon Nanotubes

Pt and Au nanoparticles spontaneously form on the sidewalls of single-walled carbon nanotubes (SWNTs) and multiwall carbon nanotubes (MWNTs) in a selective manner. Scanning electron microscope (SEM) and transmission electron microscope (TEM) studies reveal that metal ions are first absorbed on the sidewalls of carbon nanotubes (CNTs) and then are reduced by ethanol. This mechanism is tentatively proposed and discussed.     

不同厚度四面体非晶碳薄膜的高通量制备及表征

材料基因组工程能大幅度提高材料研发速度, 降低材料研发成本, 近年来受到广泛关注。本研究采用高通量制备工艺, 结合碳等离子体束流和基片位置的调控, 利用自主设计研制的45°双弯曲磁过滤阴极真空电弧设备, 沉积了厚度为4.7~183 nm的系列四面体非晶碳(ta-C)薄膜, 使用椭偏仪、原子力显微镜、拉曼光谱仪和X射线光电子能谱仪(XPS)表征了厚度对ta-C薄膜表面粗糙度、微结构和原子键态的影响。结果表明：通过碳等离子体束流和基片位置的调控, 实现了不同厚度ta-C薄膜的高通量制备。尽管膜厚不同, 所制备的ta-C薄膜均具有几乎不变的光滑表面(R_a=(0.38±0.02) nm)和色散值(Disp(G)), 说明不同厚度ta-C薄膜的sp³含量、sp²团簇尺寸保持相对稳定。XPS结果进一步证实ta-C薄膜的sp³相对含量均维持在(55±5)%。此外, 不同厚度ta-C薄膜的光学带隙E_opt均保持在(1.02±0.08)eV。相关结果为设计制备结构和光学性能可控的不同厚度ta-C薄膜提供了一种新思路。     

Controllable Formation of Luminescent Carbon Quantum Dots Mediated by the Fano Resonances Formed in Oligomers of Gold Nanoparticles

Rapid and controllable formation of fluorescent carbon quantum dots (CQDs) is highly desirable in the fields of nanophotonics and biophotonics. Here, a novel strategy for creating CQDs, which emit white light efficiently under the excitation of either laser light or a mercury lamp, is proposed and demonstrated. The luminescent CQDs are generated by irradiating a poly(vinyl alcohol) (PVA) film doped with dense gold nanoparticles (AuNPs) with femtosecond laser pulses. The creation of CQDs from PVA is a two‐step dehydration process mediated by AuNPs which act not only as heat sources but also as catalytic agents. The formation of C?C, C? C, and C? O bonds is confirmed by infrared Fourier transformation spectroscopy and X‐ray photoelectron spectroscopy. It is revealed both numerically and experimentally that a spatially localized temperature distribution at the deep subwavelength scale can be achieved in oligomers of AuNPs by resonantly exciting the Fano resonances formed in the oligomers of AuNPs, enabling the generation of CQDs with small diameters. As one of the potential applications, it is demonstrated that optical display and optical data storage with ultralow energy can be realized by selectively introducing luminescent CQDs in the AuNP/PVA film.     

激光晶化非晶硅薄膜的表面机理研究

采用PECVD工艺在普通玻璃衬底上制备非晶硅薄膜,用波长为532nm的倍频Nd:YAG激光对非晶硅薄膜的表层进行了晶化。研究了激光能量密度对非晶硅薄膜表面结晶度以及晶粒大小的影响,并对晶化后的非晶硅表面形貌进行了表征。研究结果表明:该非晶硅薄膜晶化的阈值能量密度为800 mJ/cm~2,当激光能量密度大于该值时,晶化效果反而变差。同时经过拉曼光谱表征,经由高斯拟合和数值计算得出薄膜结晶度在45%～60%之间,平均晶粒尺寸在30～50nm。     

金属催化非晶碳转化制备石墨烯方法的研究进展

石墨烯自2004年被首次发现以来, 以其独特、优异的结构和特性引起了广泛关注。目前, 石墨烯的制备已取得了众多进展, 但在大尺寸、高质量、宏量石墨烯可控制备上仍存在挑战, 对制备技术仍需要进行更广泛地探索。非晶碳与石墨烯互为碳的同素异形体, 也可作为制备石墨烯的前驱体, 近些年利用非晶碳制备石墨烯的新颖方法引起了研究学者的兴趣。本文系统论述了利用非晶碳作为固体碳源, 通过金属催化制备大尺寸高质量石墨烯的技术优势, 并着重从金属种类、退火温度、碳源及金属含量比例等方面对石墨烯生成质量的影响进行了阐述。最后, 总结了该方法生长石墨烯的机理, 并对未来的发展方向进行了展望。     

On the Structure of Amorphous Mesoporous Silica Nanoparticles by Aberration‐Corrected STEM

Mesoporous silica materials have demonstrated a vast spectrum of applications, stimulating an intensive field of study due to their potential use as nanocarriers. Nonetheless, when produced at the nanoscale, their structural characterization is hindered due to the re‐arrangement of the pores. To address this issue, this work combines molecular dynamics simulations with electron microscopy computer simulations and experimental results to provide an insight into the structure of amorphous mesoporous silica nanoparticles. The amorphous silica model is prepared using a simple melt‐quench molecular dynamics method, while the reconstruction of the mesoporous nanoparticles is carried out using a methodology to avoid false symmetry in the final model. Simulated scanning transmission electron microscopy images are compared with experimental images, revealing the existence of structural domains, created by the misalignment of the pores to compensate the surface tension of these spherical nanoparticles.     

机械合金化Fe－Ti合金非晶形成能力的研究

利用Ｘ光衍射和扫描电镜对机械合金化Ｆｅ－Ｔｉ非晶合金的形成过程进行了研究。试验表明，机械合金化非晶形成的过程可以分为二个阶段：粉末的破碎阶段和非晶的形成阶段。此外，对Ｆｅ－Ｔｉ合金形成非晶的成分范围进行了理论计算和试验测定。结果表明，ＦｅｘＴｉ１－ｘ可以在０．３０≤ｘ≤０．５０的范围内形成非晶，这与理论计算值基本一致。     

Fast Melting of Amorphous Silicon Carbide Induced by Nanosecond Laser Pulse

We report the first experimental detailed study of laser induced surface melting on the nanoscale time scale of amorphous silicon carbide layers produced by ion implantation. Time-resolved reflectivity has been used to observe the fast liquid–solid–liquid transition features, and transmission electron microscopy (TEM) was used in order to study the structure resulting after the fast solidification following the laser induced melting. By means of the evaluation of the laser fluences required to induce melting of amorphous layers of different thickness on top of a crystalline substrate, we evaluated the thermal diffusion coefficient and the melting point of the amorphous material which occurred much lower than for crystalline material. Moreover, we give evidence of amorphous-to-crystal transitions occurring in the solid phase on the nanosecond time scale, for laser irradiation at fluences below the melting threshold. A quite different crystalline structure is observed for crystallization from the liquid phase than from the solid phase.     

基于工业合金激光熔覆制备Fe基非晶涂层

以FeCoCrMoCBY块体合金为熔覆材料,采用激光熔覆在低碳钢表面制备非晶涂层,探讨不同激光功率对涂层成形及组织的影响,通过显微硬度仪、电化学工作站测试涂层显微硬度及耐腐蚀性能。研究结果表明,其他参数不变,激光功率为17.6~20.8 W时,涂层成形良好,与基材呈典型冶金结合。随激光功率增加,涂层稀释率升高,裂纹倾向增大,非晶化程度降低。激光功率为17.6 W时,涂层主要由非晶组成,稀释率低于24.2%,结构致密,包括热影响区、熔合区和熔覆区;涂层平均显微硬度为1 330HV,约高于基材9倍,在3.5%NaCl溶液中的耐腐蚀性能明显优于316L不锈钢。     

超声波机械法在纳米粒子制备中的实验研究

以SiO2为原料,探讨了超声波机械法制备纳米粉体粒子的实验情况,考察了搅拌棒齿间距、作用时间、原料浓度、分散剂浓度、转速等因素对超声波机械法制备纳米粉体的影响,探索了实验过程中纳米SiO2粒子的粉碎平衡。实验结果表明,超声波与机械搅拌技术的协同作用制备的纳米粒子,粒度更小、分散稳定性更好。两轮正交实验结果分析得出了显著性因素,影响因子以作用时间为最大,搅拌棒齿间距次之。     

Structure of Diamondlike Carbon Films Synthesized by the Method of Laser Evaporation of Graphite in a Vacuum

Using the methods of transmission electron diffraction, transmission electron microscopy, and electron paramagnetic resonance, we have analyzed the structure of thin carbon layers deposited on glass substrates, heated to a temperature of T 473 K, in a vacuum as a result of the exposure of a graphite target to a pulsed laser radiation of nanosecond duration and energy 2–8 J. It is shown that carbon films with an amorphous diamond structure undergo not only graphitization but also crystallization: polycrystalline diamond- and diamond-graphite concretions are formed on their surface.     

氢化非晶硅激光诱导结晶膜微结构的椭偏谱分析

用ＸｅＣｌ准分子激光器对氢化非晶硅（ａ－Ｓｉ：Ｈ）薄膜进行了诱导晶化处理。测定了结晶膜的椭偏谱。利用多层膜模型与Ｂｒｕｇｇｅｍａｎ有效介质近似（Ｂ－ＥＭＡ）分析了结晶膜的微结构特性。研究表明：低能量密度辐照形成的结晶层需用含有ａ－Ｓｉ：Ｈ的ＥＭＡ混合物表征，说明其结晶度相对较低；而高能量密度辐照形成的结晶层，因基结晶度较高，可用不含ａ－Ｓｉ：Ｈ的ＥＭＡ混合物表征。在结晶膜与衬底之是形成了互混层，其     

Toughening Mechanisms in Carbon Nanotube-Reinforced Amorphous Carbon Matrix Composites

Crack deflection and penetration at the interface of multi-wall carbon nanotube/amorphous carbon composites were studied via molecular dynamics simulations. In-situ strength of double-wall nanotubes bridging a matrix crack was calculated under various interfacial conditions. The structure of the nanotube reinforcement -ideal multi-wall vs. multi-wall with interwall sp³ bonding - influences the interfacial sliding and crack penetration. When the nanotube/matrix interface is strong, matrix crack penetrates the outermost layer of nanotubes but it deflects within the nanotubes with certain sp³ interwall bond density, resulting in inner wall pullout. With increasing the sp³ interwall bond density, the fracture mode becomes brittle; the fracture energy decrease while the bridging strength increases and then decreases. Our results suggest that the outermost nanotube wall can serve as a sacrificial layer such that the interface may be designed by effectively putting it inside the nanotubes. Controlling the density of sp³ interwall bond within the multiwall carbon nanotube makes the transition from brittle to tough failure modes in the composites even when the matrix/nanotube interface is strong.     

Spatially-Resolved Crystallization of Amorphous Silicon Films on the Glass Substrate by Multi-beam Laser Interference

Laser interference induced crystallization of amorphous silicon （a-Si） on the glass substrate was performed using a Q-switched Nd：YAG （yttrium aluminum garnet） laser. White light interferometer （WLI） and atomic force microscope （AFM） were used to characterize the morphology of the structured films, while X-ray diffraction （XRD）, combined with the AFM, was used to analyse the crystalline structure of the film. The experimental results show that the laser energy density above a certain threshold, in the range of 400-500 mJ/cm2,triggers the patterned crystallizations which take the form similar to the laser intensity distribution. For the patterned crystallization under multipulse exposure, a definite polycrystalline structure with individual phases was observed by XRD. The difference in feature form, e.g., deepened craters or heightened lines, is related to the laser energy density relative to the threshold of evaporation of the material.