纳米Si3N4制备及光学特性研究

为了制备高纯度的非晶纳米氮化硅粉体,在传统的激光诱导化学气相沉积法反应装置的基础上,加入正交紫外光束以激励NH3分解,从而提高气相中n(N)/n(Si)比,减少产物中游离硅的摩尔浓度.利用TEM技术和光谱分析技术研究了粒子的形貌和特性.结果表明:在一定的工艺参数条件下,可制备出粒径超微(7～15 nm)、无团聚、理想化学剂量(n(N)/n(Si)=1.314)的非晶纳米氮化硅粉体;表面效应和量子尺寸效应导致粉体红外吸收光谱和拉曼光谱的"蓝移"和"宽化"现象;采用双光束激励的激光诱导化学气相沉积法是制备高纯度纳米氮化硅粉体的理想方法.     

改性纳米氮化硅填充氯磺化聚乙烯橡胶的动态性能研究

用低分子量氯磺化聚乙烯(LMCSM)对纳米氮化硅粉体进行表面改性,并将其添加到氯磺化聚乙烯(CSM)中制备橡胶纳米复合材料.利用橡胶加工分析仪(RPA- 8000),扫描电子显微镜(SEM)对其表征.结果表明:添加少量改性纳米氮化硅粉体对CSM基体起到一定的补强作用,能够有效地提高材料的动态力学性能,并且添加生胶重量分...     

纳米镍包覆氮化硅粉体的制备和磁性能研究

利用一种简单的无催化化学镀法制备了纳米镍晶粒包覆氮化硅陶瓷的复合粉体.通过不同的反应PH值和搅拌工艺对比获得了较为均匀的包覆.利用X射线衍射、扫描电镜和透射电镜对包覆粉体的物相及显微形貌进行表征分析.磁性能测量表明包覆粉体具有良好的铁磁性能和磁各向异性.     

液体羧基丁腈橡胶对纳米Si3N4粉体表面处理研究

用液体羧基丁腈橡胶作表面处理剂处理纳米氮化硅(Si3N4)粉体.结果表明:液体羧基丁腈橡胶包覆在纳米Si3N4粉体的表面,并与其发生了化学作用,有效地阻止了纳米Si3N4粉体的团聚;处理过的Si3N4粉体粒径明显减小,在有机溶剂中的分散性良好;亲水性减小,亲油性增加,表面自由能明显降低,处理后的纳米Si3N4粉体更容易在聚合物中分散.     

BA-MMA-GMTS共聚物的合成及对纳米Si_3N_4的表面处理

为了使纳米氮化硅粉体能够均匀地分散在聚合物中并与聚合物具有良好的相容性,必须对其进行表面改性。本文中用BA-MMA-GMTS三元共聚物作为纳米Si3N4粉体表面改性剂,对纳米Si3N4粉体进行湿法包覆反应改性。结果表明:BA-MMA-GMTS三元共聚物包覆在纳米Si3N4粉体的表面,并与其发生了化学作用,有效地阻止了纳米Si3N4粉体的团聚,当BA-MMA-GMTS三元共聚物相对纳米Si3N4粉体质量比为10%时包覆效果最好。改性后的Si3N4粉体粒径明显减小,在有机溶剂中的分散性良好,由于相似相容原理,可以推测改性后的纳米Si3N4粉体必能与聚合物具有良好的相容性并且能更加均匀地分散在其中。     

甲基丙烯酸锌原位聚合改性纳米氮化硅

采用实验室制备的纳米级甲基丙烯酸锌对纳米Si3N4进行表面原位聚合包覆改性,运用FTIR、TEM、SEM等方法对处理前后的纳米Si3N4粉末进行了表征和比较.结果表明:通过原位聚合的方法,使甲基丙烯酸锌与纳米Si3N4粉体表面的活性基团产生了化学键合,成功实现了对无机纳米粉体表面的有机化改性,有效地阻止了纳米Si3N4粉体的团聚;同时,讨论了改性剂用量对改性效果的影响,改性剂用量为5%时,纳米粒径较小,分布最窄.并对甲基丙烯酸锌在氮化硅表面原位聚合机理作初步探讨.     

氮化硅粉体的水基流延研究

本文采用国产的α-氮化硅粉(d50=1μm),测定了粉体的zeta电位.根据粉体的表面性质,选用聚丙烯酸钠作为分散剂,分析了pH值、分散剂对氮化硅粉体zeta电位以及浆料粘度的影响,确定了良好分散的Si3N4浆料的pH值和分散剂含量分别为10和1wt%.选用PVA为粘结剂,PEG为塑性剂,二者在浆料中的含量分别为5wt%和2.5wt%.最后,制备了氮化硅水基流延膜,并用SEM对得到的流延膜进行了表征.     

LICVD纳米硅和纳米氮化硅的制备、结构与物性研究

从制备过程、结构表征和物理性能三个方面对激光诱导化学气相沉积(LICVD)纳米硅和纳米氮化硅进行了比较系统的研究,获得了一系列有意义的结果。 选择适当的制备工艺参数可以制得不同粒径的纳米硅和纳米氮化硅,粒度分布比较均匀。纳米硅是结晶的,粒度为14～100nm。纳米氮化硅是非晶的,粒度为7～18nm。利用光学二步法能够制备高纯的理想化学计量的纳米氮化硅粉末(Si59.80wt％,N39.49wt％,O0.69wt％),N/Si高达1.321,非常接近于理想值(1.333)。 纳米硅具有类似于c-Si的晶格和键合结构,存在Si—Si、Si—H、Si—O—Si、Si—OH等键和硅悬挂键(Si_3Si~0)。纳米氮化硅具有短程有序结构特征(SiN_4),并且存在Si—N、Si—Si、Si—H、N—H、Si—O—Si和Si—OH等键和硅悬键(N_3Si~0)。 纳米硅具有不同于c-Si和a-Si的介电特性,提出了界面极化对介电特性起着主要贡献的模型,解释了在低频端具有很大的介电常数。首次发现nc-Si粒子光学吸收特性发生显著变化的临界尺寸(粒径)为～30nm,小于该粒径时其光学带隙明显加宽;粒度为15nm时,出现明显的吸收峰(5.77eV、4.28eV、3.46eV)。 首次发现纳米氮化硅具有强压电性和介电性。界面极化在介电特性中起着主导作用,使得纳米氮化硅呈现出许多奇异的新特性。对纳米氮化硅介电特性的应     

液相法制备纳米ZrO2粉体的研究进展

ZrO2是结构陶瓷和功能陶瓷重要的原材料之一,有关纳米ZrO2粉体制备方法的研究有很多,本文介绍了近年来研究较多的液相制备纳米ZrO2粉体的方法,并对制备过程中粉体团聚的形成与控制做了简要论述.     

燃烧合成氮化硅粉体的性能一致性评价方法和应用

陶瓷粉体的批次稳定性是陶瓷制品生产商最关心的核心指标,却又长期无据可依。本研究以燃烧合成的氮化硅粉体为样本,量化评价不同批次生产的氮化硅粉体的相似程度。首先构建了涵盖静态理化指标、动态流动性指标的粉体性能评价参数体系,进而测试得到在该参数体系中氮化硅粉体的全部性能数据,随后对所得性能数据分别采用余弦相似度法和欧氏距离法进行计算,得到了粉体性能一致性评价数据。结果表明,基于该参数体系的余弦相似度和欧氏距离均能反映批次粉体间的相似程度,量化显示出不同批次粉体的差异,两种方法的计算结果相互验证。对判定为不相似的粉体,追溯工艺流程中的差异找到了控制氮化硅粉体一致性的关键环节—原料硅粉;对判定为高度相似的粉体划分为同类,为不同批次氮化硅粉体的类别划分提供了量化依据。该工作建立的“粉体性能一致性评价体系”为氮化硅粉体产品质量的批次稳定性(性能一致性)提供了有效的评价手段和量化依据。     

纳米γ-(Fe,Ni)合金粉开发及应用研究

以五羰基铁和四羰基镍为前驱体，通过高温气相热分解可以获得纳米级γ－（Ｆｅ，Ｎｉ）合金粉，这种纳米合金粉主要为面心立方的γ－（Ｆｅ，Ｎｉ）相，颗粒大小为１０～５０ｎｍ，呈非球形，具有优异的光、电、磁性能，可用于开发具有某些奇特功能的新材料。     

溶胶-凝胶法制备纳米氧化锡及其性能表征

以SnCl4·5H2O为原料,采用溶胶-凝胶法制备了纳米SnO2粒子,研究了焙烧温度、碱的种类及反应物浓度对纳米SnO2粒子大小和分散状态的影响。采用XRD、TEM、ED等技术对SnO2纳米粒子的性能进行了表征。实验结果表明:用氨水和尿素作为沉淀剂,控制反应结束时pH值为7,在600℃焙烧,制备得到粒子尺寸约为15nm、分散性良好的纳米SnO2粒子。     

纳米In_2O_3的制备与结构表征

介绍了以同纯精铟为原料,采用化学沉淀法在一定的实验条件下制备纳米级In2O3粉体的实验过程,通过XRD、TEM、BET及化学分析等多种检测及分析手段对所制得的粉体的性能进行了初步表征,结果表明:采用化学沉淀法制备的In2O3为高纯单相类球形的黄色粉末,其平均粒径小于30nm。     

Morphologies of Si phase and La-rich phase in as-cast hypereutectic Al–Si–xLa alloys

In the present study, the diversified morphologies of Si phase and La-rich phase in as-casted hypereutectic Al–Si–xLa alloys are presented and investigated. The morphological features were examined using conventional optical microscopy and SEM for observations conducted on the optical samples and deep-etched samples, respectively. The results show that primary Si crystals show several morphologies, such as feathery, star-shaped, faceted polygonal, platelet and so on. There are three types of fivefolded Si crystals existing in the present study, fivefold symmetry as radial growth alone: thin-branched, coarse-branched and well-defined star-shaped growing from the preferred growth from the tips of branches. The eutectic Si in unmodified Al–Si alloys appears only in fibrous morphology, while discrete and interconnected coral and rodlike eutectic Si particles were observed in alloys with the addition of La. The La-rich phase also grows into a variety of morphologies, such as needlelike, broken rodlike in pores, spherical, and flat platelet. In optical microscopy, La-rich phase is observed to envelope some small polygonal Si crystals.     

（001）应变对正交相Ca2P0.25Si0.75能带结构及光学性质的影响

为了研究(001)应变对正交相Ca2P0.25Si0.75能带结构及光学性质的影响,采用第一性原理贋势平面波方法对(001)应变下正交相Ca2P0.25Si0.75的能带结构及光学性质进行了模拟计算.计算结果表明:晶格(001)面发生100%~116%张应变时,带隙随着应变增加而减小;在晶格发生88%~100%压应变时,带隙随着张应变的增加而增加;84%~88%压应变时,带隙随着压应变的增加而减小.当施加应变后光学性质发生显著的变化:随着压应变的增加,静态介电常数、折射率逐渐减小,张应变则增大.施加压应变反射向高能方向偏移,施加张应变反射向低能方向偏移,但施加应变对反射区域的影响不显著.施压应变吸收谱、光电导率的变化与介电函数和折射率相反.综上所述,(001)应变改变了Ca2P0.25Si0.75的电子结构和光学常数,是调节Ca2P0.25Si0.75光电传输性能的有效手段.     

Fabrication and optical characterization of light trapping silicon nanopore and nanoscrew devices

We have fabricated nanotextured Si substrates that exhibit controllable optical reflection intensities and colors. Si nanopore has a photon trapping nanostructure but has abrupt changes in the index of refraction displaying a darkened specular reflection. Nanoscrew Si shows graded refractive-index photon trapping structures that enable diffuse reflection to be as low as 2.2% over the visible wavelengths. By tuning the 3D nanoscale silicon structure, the optical reflection peak wavelength and intensity are changed in the wavelength range of 300-800?nm, making the surface have different reflectivity and apparent colors. The relation between the surface optical properties with the spatial features of the photon trapping nanostructures is examined. Integration of photon trapping structures with planar Si structure on the same substrate is also demonstrated. The tunable photon trapping silicon structures have potential applications in enhancing the performance of semiconductor photoelectric devices.     

Ca2Si电子结构和光学性质的研究

采用第一性原理赝势平面波方法系统的计算了Ca2Si电子结构和光学性质，其中包括能带、态密度、介电函数、复折射率、吸收系数、光电导率和能量损失函数。计算结果显示Ca2Si是典型的半导体，正交相结构有一个直接的带隙，并且光学性质显示出各向异性。Ca2Si立方相的计算结果也显示是直接带隙半导体，并且有很高的振子强度。从能带和态密度的计算结果判断出它们的光学性质主要由Si的3p态电子向Ca的3d态的带间跃迁所决定。     

Focus on silicon photonics

Si photonics has attracted much interest over the last decade as it allows integration of photonic and electronic devices on a small Si chip, providing high-capacity, energy-efficient, and cost-effective optical interconnects. Active optical cables based on Si photonics are now commercially available for rack-to-rack interconnects in supercomputers and data centers. Shorter reach optical interconnects, i.e., inter- and intra-chip optical interconnects, have been studied as the next challenge for higher speed computing. Science and technology of advanced materials is essential for rapid development in this field, and therefore it is very appropriate to publish this focus issue in STAM.

This focus issue introduces state-of-the-art material and device technologies in Si photonics. The topics cover not only technologies for the optical interconnects but also optical sensing as a novel application.

We are grateful to the authors who contributed to this focus issue, and hope that it will help researchers understand the frontiers of Si photonics, stimulating novel concepts in material and device technologies, as well as novel developments in and applications of Si photonics.     

Influence of Si doping level on the Raman and IR reflectivity spectra and optical absorption spectrum of GaN

The optical absorption (hν) and Raman and Infra Red (IR) spectra of Si doped GaN layers deposited on sapphire through buffer layers have been recorded for electron concentrations from 5×10¹⁷ to 5×10¹⁹ cm⁻³. The (hν) values deduced from photothermal deflection spectroscopy (0.5–3.5 eV) and IR absorption (0.15–0.5 eV) vary between 50 and 10⁴ cm⁻¹ showing doping dependant free electron absorption at low energy, doping independant band gap at high energy, and slowly doping dependant defect absorption in the medium energy range. In our micro Raman geometry, maxima appear or can be deduced near the frequency expected for either the A₁(LO⁻) or the A₁(LO⁺) modes split from the A₁(LO) mode by plasmon phonon interaction. There is a large systematic evolution in the expected way for the IR reflectivity.