Covalent grafting of organoalkoxysilanes on silica surfaces in water-rich medium as evidenced by <Superscript>29</Superscript>Si NMR

This paper addresses two questions related to functionalization of silica particles: (1) is the grafting of hydrophobic organoalkoxysilanes on a silica surface possible in water-rich medium and (2) how to prove the formation of covalent bonds with the surface? Trimethylethoxysilane, dimethyldiethoxysilane and methyltriethoxysilane have been reacted with precipitated silica in water-rich medium (water/ethanol 25/75 v/v) and ²⁹Si MAS NMR was used to answer both questions: ²⁹Si chemical shift values of the organosilicon units in the case of trimethylethoxysilane and dimethyldiethoxysilane clearly distinguished between self-condensation reactions and surface reactions through covalent bonds.     

Tunable in-plane spin orientation in Fe/Si(557) film by step-induced competing magnetic anisotropies

Although the spin-reorientation transition from out-of-plane to in-plane in Fe/Si film is widely reported, the tuning of in-plane spin orientation is not yet well developed. Here, we report the thickness-, temperature- and Cu-adsorptioninduced in-plane spin-reorientation transition processes in Fe/Si(557) film, which can be attributed to the coexistence of two competing step-induced uniaxial magnetic anisotropies, i.e., surface magnetic anisotropy with magnetization easy axis perpendicular to the step and volume magnetic anisotropy with magnetization easy axis parallel to the step. For Fe film thickness smaller than 32 monolayer(ML), the magnitudes of two effects under various temperatures are extracted from the thickness dependence of uniaxial magnetic anisotropy. For Fe film thickness larger than 32 ML, the deviation of experimental results from fitting results is understood by the strain-relief-induced reduction of volume magnetic anisotropy.Additionally, the surface and volume magnetic anisotropies are both greatly reduced after covering Cu capping layer on Fe/Si(557) film while no significant influence of Na Cl capping layer on step-induced magnetic anisotropies is observed.The experimental results reported here provide various practical methods for manipulating in-plane spin orientation of Fe/Si films and improve the understanding of step-induced magnetic anisotropies.     

基于RSM的单晶Si高速线锯切割力试验研究

采用Box-Behnken Design (BBD)设计实验,研究高速线锯切割过程中线锯速度、进给速度和工件转速三个工艺参数对单晶Si切割力的影响,通过曲面响应法(Response surface methodology,RSM)建立单晶Si片切割力的响应模型,并进行方差分析,获得了高速线锯切割单晶Si过程中不同工艺参数对切割力的影响规律和切割力最小时的工艺参数.试验结果表明该模型能实现单晶Si切割过程的切割力预测.     

原位退火温度对Mg_2Si薄膜结构及方块电阻的影响

采用磁控溅射法和原位退火工艺在钠钙玻璃衬底上制备Mg_2Si半导体薄膜.首先在钠钙玻璃衬底上依次溅射一定厚度的Si、Mg薄膜,冷却至室温后原位退火4h,在400~600℃退火温度下制备出一系列Mg_2Si薄膜样品.采用X射线衍射仪(XRD)、扫描电子显微镜(SEM)对Mg_2Si薄膜样品的晶体结构和表面形貌进行表征,利用四探针测试仪测试薄膜样品的方块电阻,讨论了原位退火温度对Mg_2Si薄膜结构、表面形貌及电学性能的影响.结果表明,采用原位退火方式成功在钠钙玻璃衬底上制备出单一相的Mg_2Si薄膜,退火温度为550℃时,结晶度最好,连续性和致密性最强,方块电阻最小.这对后续Mg_2Si薄膜器件的设计与制备提供了重要的参考.     

γ射线总剂量辐照对单轴应变Si纳米n型金属氧化物半导体场效应晶体管栅隧穿电流的影响

基于γ射线辐照条件下单轴应变Si纳米n型金属氧化物半导体场效应晶体管(NMOSFET)载流子的微观输运机制,揭示了单轴应变Si纳米NMOSFET器件电学特性随总剂量辐照的变化规律,同时基于量子机制建立了小尺寸单轴应变Si NMOSFET在γ射线辐照条件下的栅隧穿电流模型,应用Matlab对该模型进行了数值模拟仿真,探究了总剂量、器件几何结构参数、材料物理参数等对栅隧穿电流的影响.此外,通过实验进行对比,该模型仿真结果和总剂量辐照实验测试结果基本符合,从而验证了模型的可行性.本文所建模型为研究纳米级单轴应变Si NMOSFET应变集成器件可靠性及电路的应用提供了有价值的理论指导与实践基础.     

单晶硅片负极界面形貌的原位AFM探测

利用原子力显微镜原位研究单晶硅片负极在首次充放电循环中的界面形貌变化。硅负极表面固体电解质界面(SEI)膜的形成过程为：初始SEI膜从1.5 V开始形成,在1.25–1.0 V之间生长快速,0.6 V左右生长缓慢。初始SEI膜具有层状结构的特征,表层薄膜较软,下层呈颗粒状,机械稳定性较好。在锂化电位下,硅负极表面的单晶结构逐渐变得颗粒化,发生不可逆的结构变化。经过首个充放电循环后,硅负极表面被厚度不均一的SEI膜所覆盖,SEI膜的厚度大约为10–40 nm。     

Heterogeneous integration of GaAs pHEMT and Si CMOS on the same chip

In this work,we demonstrate the technology of wafer-scale transistor-level heterogeneous integration of Ga As pseudomorphic high electron mobility transistors(p HEMTs) and Si complementary metal–oxide semiconductor(CMOS) on the same Silicon substrate.Ga As p HEMTs are vertical stacked at the top of the Si CMOS wafer using a wafer bonding technique,and the best alignment accuracy of 5 μm is obtained.As a circuit example,a wide band Ga As digital controlled switch is fabricated,which features the technologies of a digital control circuit in Si CMOS and a switch circuit in Ga As p HEMT,15% smaller than the area of normal Ga As and Si CMOS circuits.     

MoO2/C共包覆Si/石墨复合锂离子电池负极材料的研究

采用溶胶-凝胶法, 用二氧化钼(MoO₂)和C共同包覆Si/石墨粒子制备了Si/石墨/MoO₂/C锂离子电池负极材料. 利用X射线衍射(XRD)、 扫描电子显微镜(SEM)、 透射电子显微镜(TEM)、 循环伏安(CV)和电化学阻抗(EIS)等分析了材料的形貌和性质. 结果表明, MoO₂/C的共包覆在缓解材料体积膨胀的同时提高了材料的电子和离子电导率, 进而提高了材料的电化学性能. 复合材料的首次充电比容量为2494 mA·h/g, 首次库仑效率为72%, 经过100次循环后比容量为636.6 mA·h/g.     

Mg2Si的电子结构和热电输运性质的理论研究

利用全势线性缀加平面波法,对Mg₂Si的几何结构和电子结构进行了计算,得到了稳定的晶格参数以及能带和电子态密度.能带结构表明,Mg₂Si为间接带隙半导体,禁带宽度为020 eV.在此基础上利用玻尔兹曼输运理论和刚性带近似计算了材料的电导率、Seebeck系数和功率因子.结果表明,在温度为700 K时p型和n型掺杂的Mg₂Si功率因子达到最大时的最佳载流子浓度分别为7749×10¹⁹ cm^-3和 关键词： 2Si')" href="#">Mg₂Si 全势线性缀加平面波法 热电输运性质     

界面缺陷态密度与衬底电阻率取值对硅异质结光伏电池性能的影响

在异质结前界面缺陷态密度Dit1和异质结背界面缺陷态密度Dit2均取不同值时,对p型单晶硅(c-Si(p))为衬底的硅异质结太阳电池的衬底电阻率ρ与电池性能的关系进行了数值研究.结果表明:衬底电阻率的最优值ρop取决于前界面缺陷态密度Dit1,且ρop随着Dit1的增大而增大;当ρρop时,背界面缺陷态密度Dit2对衬底电阻率的可取值范围具有较大影响,Dit2越大衬底电阻率的可取值范围越小.