金属铝诱导法低温制备多晶硅薄膜

以氢气稀释的硅烷(SiH₄)和硼烷(B₂H₆)为气源,利用等离子体增强化学气相沉积法(PECVD)制备出p型a-Si薄膜.采用铝诱导晶化技术对不同厚度的铝膜对a-Si薄膜晶化的影响进行了研究.实验中发现,铝膜溅射为10 s的非晶硅薄膜样品在450℃下退火10 min后,p型a-Si结构仍为非晶态,铝膜溅射为20 s的非晶硅薄膜在450℃下退火20 min后,p型a-Si薄膜开始晶化为poly-Si薄膜,并且铝膜厚度越厚,则a-Si薄膜晶化程度越强.     

非晶态半导体中的分形结构

非晶态半导体硅(α-Si:H)薄膜作为新型的光电子材料,近年来备受关注,发展迅速。但其晶化机理有待深入探索。用分形理论所作的分析表明,在一定条件下,a-Si:H薄膜中形成的微结构具有分形性质。本文计算了分维值,讨论了a-Si:H薄膜结构弛豫(相变)与分形结构形成的关联,和非晶硅薄膜可能的晶化机理。并研究了在高真空中用透射电子显微镜(TEM)及动态方法跟踪观测a-Si:H薄膜原位(in situ)退火过程中发生的晶化现象,获得晶化形貌的显微图像。利用图像处理技术对显微像进行光电转换,A/D转换和数字计算,得到a-Si:H薄膜样品在不同退火条件下,显微象的Sandbox关系曲线。从而获得薄膜中形成不同分形结构的分维。文中给出应用分形理论对非晶态半导体薄膜进行分析的技术细节。     

宽带隙Cu(In,Al)Se2薄膜的制备及表征

以特殊脉冲电沉积方法制备CuInSe2(CIS)前驱体薄膜, 通过真空蒸镀法在CIS薄膜上沉积Al膜, 经硒化退火后在氧化铟锡(ITO)基底上制备了Cu(InAl)Se2(CIAS)薄膜. 采用扫描电子显微镜(SEM)、X射线能谱(EDS)、X射线衍射(XRD)、X射线光电子能谱(XPS)、紫外-可见吸收光谱(UV-Vis)对其形貌、结构、成分及光学吸收性质进行了表征. 结果表明, 制备的CIAS薄膜颗粒均匀, 表面平整致密, 呈黄铜矿结构. 薄膜在可见光区具有良好的吸收, 带隙约为1.65 eV.     

n型Cu2O薄膜的简易水热法制备及其光电化学性能

采用一种简单的水热法,通过控制反应时间,使用铜片在只含有Cl~-的非含铜前驱物的NaCl溶液中生长出了n型Cu_2O薄膜。对制备的样品进行了X射线衍射(XRD)、拉曼光谱(Raman)、扫描电子显微镜(SEM)、X射线光电子能谱(XPS)和光电化学等表征或测试。本水热法相对其他的水热法工艺更简单,成本更低且能进行快速大规模化的生产。且得到的n型Cu_2O薄膜晶化程度高,经过Cl~-掺杂后,载流子浓度高达9.75×10~(17) cm~(-3),在可见光照射下表现出较好的光电转换性能。光电化学和电化学阻抗谱表明在中等浓度(0.1 mol·L~(-1))NaCl溶液中90℃的条件下水热反应50 h制备的Cu_2O薄膜具有最好的光电性能。     

低温熔盐中电沉积Sm-Co合金膜及其磁性能

在353 K的尿素-乙酰胺-NaBr-KBr熔体中, 用恒电位电解法在Cu基片上制备了Sm-Co合金膜. 利用循环伏安法研究了熔体的电化学行为. 电化学实验结果表明, 在Pt电极上, Co(II)+2e→Co(0)是一步完全的不可逆反应; 测得CoCl2-尿素-乙酰胺-NaBr-KBr熔体中, Co(II)在Pt电极上的传递系数α=0.31, 扩散系数D0=4.78×10^-5 cm2·s-1; Sm(III)难以单独沉积, 但能被Co(II)诱导共沉积, 在不同阴极电位下制备出不同Sm含量的非晶合金膜. 用等离子发射光谱仪(ICP)检测薄膜成分, 用SEM观察了薄膜的表面形貌结构, 用XRD和振动样品磁强计(VSM)分析样品退火前后的晶相和磁性能变化特征. 结果表明, 在923 K进行退火30 s后Sm-Co薄膜由非晶转变为多晶结构, 并以hcp晶相结构为主; 退火和Sm含量对Sm-Co合金膜的磁性能有重要的影响.     

溶胶-凝胶-水热晶化法制备锐钛矿TiO2纳米膜的耐蚀性能

以钛酸正丁酯为前驱体, 采用溶胶-凝胶-水热晶化法在不锈钢(SS)表面制备TiO₂纳米膜. 利用X射线衍射(XRD)、Raman光谱、场发射扫描电子显微镜(SEM)、原子力显微镜(AFM)和俄歇电子能谱(AES)表征了TiO₂纳米膜的晶型、表面形貌和表面化学组成. 通过极化曲线和电化学阻抗谱(EIS)研究了TiO₂纳米膜的耐蚀性能. 170 °C下水热晶化制备的锐钛矿TiO₂与450 °C焙烧制备的锐钛矿TiO₂的结晶度类似, 但两种TiO₂薄膜的表面结构存在明显差异, 水热晶化法制备的TiO₂纳米膜在3.5% (w) NaCl溶液中的耐蚀性能优于焙烧法制备的.     

退火对TiO2纳米管/线复合阵列表面光电性质的影响

采用阳极氧化法制备了TiO2纳米管/线复合阵列. 利用表面光电压谱(SPS)和场诱导表面光电压谱(FISPS)研究了退火对TiO2纳米管/线复合阵列表面光电性质的影响. 结果表明, TiO2纳米管/线复合阵列在晶化前后的导带边缘均出现了束缚激子态, 晶化前由于自建场较弱, 束缚激子态能在正负电场作用下发生不对称偏转; 晶化后, 晶体结构从非晶态变为晶态, 自建场增强, 束缚激子态对正电场敏感并表现出明显的光伏响应, 而在负电场作用下束缚激子态没有任何光伏响应.     

高钐含量SmCo磁记录薄膜材料的研究

SmCo合金具有极高的单轴磁晶各向异性,成为未来高密度磁记录介质的候选材料之一.本文采用磁控溅射方法,在玻璃基片上制备了Cr(100nm)/SmCo(50 nm)/Cr(20 nm)结构的Smco薄膜,SmCo层中Sm含量为35%(原子分数).利用综合物性测试系统(PPMS)和X射线衍射(XRD)对薄膜的磁性能和晶体学结构进行了测试.结果表明,通过550℃退火20 min可以获得很好的硬磁性能,矫顽力R.达到了3183kA·m-1,XRD结果表明薄膜中同时存在磁性相SmCo5和非磁性相SmCo2等.高Sm古量的SmCo薄膜在退火温度为450℃时开始晶化,退火温度达到550℃时,晶化进行的比较完全.     

Fe3O4纳米粒子的制备及耐盐性能研究

通过共沉淀法制备了Fe3O4纳米粒子,并采用十二烷基磺酸钠(SDS)对纳米粒子进行了表面修饰。FT IR显示SDS修饰到纳米粒子表面,XRD表明纳米粒子为立方晶相,从TEM照片中可看出纳米粒子粒径在10nm左右。纳米粒子耐盐性实验表明,在NaCl、MgCl2、Al2(SO4)3等盐溶液中,超声作用都有利于提高Fe3O4纳米粒子的分散稳定性能,但在不同盐溶液中,纳米粒子的优化超声时间不同。对于NaCl和Al2(SO4)3溶液,纳米粒子稳定分散的最佳超声时间是1h,而对于MgCl2溶液,纳米粒子稳定分散的最佳超声时间是2h。     

阳极氧化TiN薄膜制备N掺杂纳米TiO2薄膜及其可见光活性

室温下通过电泳沉积(EPD)的方法在Ti片表面制备TiN薄膜, 然后对TiN薄膜进行阳极氧化得到N掺杂多孔纳米结构的TiO2薄膜. 利用X射线衍射(XRD), X射线光电子能谱(XPS), 扫描电子显微镜(SEM)及光电化学方法对得到的薄膜进行表征. XRD测试结果表明, 经过阳极氧化并在350 ℃空气气氛中退火1 h的薄膜中存在锐钛矿晶型的TiO2. XPS的结果表明, 样品中的N元素取代部分O, 且N的摩尔分数为0.95%. SEM显示, 经阳极氧化后薄膜表面出现多孔纳米结构. 光电化学测试结果显示, 阳极氧化提高了N掺杂TiO2薄膜在可见光下的光电响应. 经阳极氧化并热处理的薄膜在0 V电位及可见光照射下光电流密度为2.325 μA·cm-2, 而单纯热处理的薄膜在相同条件下光电流密度仅为0.475 μA·cm-2. 阳极氧化得到纳米多孔结构提高了N掺杂纳米TiO2薄膜的表面积, 从而对可见光的响应增大.     

Positron/positronium annihilation in nanocrystalline silicon thin films

Positron and positronium annihilation investigations were applied to nanocrystalline silicon (nc-Si) thin films, for the first time. The nc-Si thin films with average grain diameters of 3–5 nm show intense blue luminescence at room temperature. The nanometer-sized Si crystallites formed in amorphous Si (a-Si) matrix give rise to this luminescence. Very highS-parameters up to 0.62 were observed in the as-grown a-Si thin film suggesting positronium formation in the a-Si layer. The average lifetime of the positrons in the a-Si was determined to be about 520 ps. TheS-parameters dropped significantly to 0.53 by crystallization of the thin film at 800 °C for 10 seconds, which was almost the same to the value observed in bulk Si (100) substrate. Further crystallization from 60 seconds to 1 hour showed smaller change in theS-parameters than that from the a-Si to 10 seconds. The large change in theS-parameters due to the annealing might be caused by the formation of Si nanocrystallites in a-Si matrix suggesting that positron is a sensitive probe for structural investigations of the nc-Si materials.     

Mechanisms and energetics of hydride dissociation reactions on surfaces of plasma-deposited silicon thin films

We report results from a detailed analysis of the fundamental silicon hydride dissociation processes on silicon surfaces and discuss their implications for the surface chemical composition of plasma-deposited hydrogenated amorphous silicon (a-Si:H) thin films. The analysis is based on a synergistic combination of first-principles density functional theory (DFT) calculations of hydride dissociation on the hydrogen-terminated Si(001)-(2x1) surface and molecular-dynamics (MD) simulations of adsorbed SiH(3) radical precursor dissociation on surfaces of MD-grown a-Si:H films. Our DFT calculations reveal that, in the presence of fivefold coordinated surface Si atoms, surface trihydride species dissociate sequentially to form surface dihydrides and surface monohydrides via thermally activated pathways with reaction barriers of 0.40-0.55 eV. The presence of dangling bonds (DBs) results in lowering the activation barrier for hydride dissociation to 0.15-0.20 eV, but such DB-mediated reactions are infrequent. Our MD simulations on a-Si:H film growth surfaces indicate that surface hydride dissociation reactions are predominantly mediated by fivefold coordinated surface Si atoms, with resulting activation barriers of 0.35-0.50 eV. The results are consistent with experimental measurements of a-Si:H film surface composition using in situ attenuated total reflection Fourier transform infrared spectroscopy, which indicate that the a-Si:H surface is predominantly covered with the higher hydrides at low temperatures, while the surface monohydride, SiH((s)), becomes increasingly more dominant as the temperature is increased.     

First-principles theoretical analysis of silyl radical diffusion on silicon surfaces

We report results from a detailed analysis of the fundamental radical precursor diffusion processes on silicon surfaces and discuss their implications for the surface smoothness of hydrogenated amorphous silicon (a-Si:H) thin films. The analysis is based on a synergistic combination of first-principles density functional theory (DFT) calculations of SiH(3) radical migration on the hydrogen-terminated Si(001)-(2 x 1) surface with molecular-dynamics (MD) simulations of SiH(3) radical precursor migration on surfaces of a-Si:H films. Our DFT calculations yield activation energies for SiH(3) migration that range from 0.18 to 0.89 eV depending on the local electronic environment on the Si(001)-(2 x 1):H surface. In particular, when no substantial surface relaxation (Si-Si bond breaking or formation) accompanies the hopping of the SiH(3) radical the activation barriers are highest, whereas hopping between nearest-neighbor overcoordinated surface Si atoms results in the lowest radical diffusion barrier of 0.18 eV; this low barrier is consistent with the activation barrier for SiH(3) migration through overcoordinated sites on the a-Si:H surface. Specifically, the analysis of the MD simulations of SiH(3) radical migration on a-Si:H surfaces yields an effective diffusion barrier of 0.16 eV, allowing for the rapid migration of the SiH(3) radical prior to its incorporation in surface valleys; rapid migration and subsequent incorporation constitute the two-step mechanism responsible for the smoothness of plasma deposited a-Si:H thin films.     

LiNbO3 and LiTaO3 thin films deposited by chemical and/or physical processes

Lithium niobate LiNbO₃ thin films were deposited onto silicon (111) Si and sapphire (001) AI₂O₃ single crystal substrates by the pyrosol and/or r.f. sputtering processes. A matrix of experiments was designed to determine the effects of several experimental parameters on the resulting film quality (stoichiometry, crystallization state) and properties. Under optimized conditions, requiring the combination of the two above-mentioned deposition techniques, <001 > oriented polycrystalline LiNbO₃ films were grown which exhibit homogeneous and columnar grain structures with the <c > -polar axis normal to the substrate surface.     

聚苯乙烯/聚二甲基硅氧烷嵌段共聚物的表面形态研究

采用原子力显微镜(AFM)和透射电镜(TEM)研究了聚苯乙烯/聚二甲基硅氧烷嵌段共聚物(PS-b-PDMS)薄膜的相形态.结果表明,当采用甲苯作为溶剂,旋转涂膜的薄膜样品呈现网络状的形态分布在表面,而样品所对应的透射电镜照片中,PDMS相作为球状分布在PS的连续相中.退火温度对共聚物表面形态有一定的影响,当退火温度高于PDMS的玻璃化温度,表面中PDMS相增多.PS-b-PDMS嵌段共聚物的表面形态随着所用溶剂的变化而有所不同,当采用甲苯作为溶剂时,样品的PS相形成凹坑分布在PDMS的相区之中,而采用环己烷作为溶剂时,PS相作为突起分布在PDMS相区之中.另外,基底对共聚物薄膜表面形态的有较大的影响,当采用硅晶片作为基底时,样品中的PDMS相和PS相呈现近似平行于表面的层状结构.     

Effect of ex situ hydrogenation on the structure and electrochemical properties of amorphous silicon thin film

Nickel-metal hydride (Ni-MH) batteries were widely used due to their various advantages, but its further application and development have been seriously hindered by the low electrochemical discharge capacity of conventional hydrogen storage alloy electrode. The hydrogenated amorphous silicon (a-Si:H) thin film electrode for Ni-MH battery has been proven to have a dramatic electrochemical capacity. We prepared a-Si:H thin films by a two-step process of rf-sputtering followed by hydrogenation, and investigated the effect of hydrogenation on the structure and electrochemical properties of which as an anode. The maximum discharge capacity of a-Si:H thin film electrode after hydrogenation increases from initial 180 mAh·g⁻¹to 1827 mAh·g⁻¹, which is over tenfold that of as-deposited hydrogen-less a-Si thin film electrode. Then, the preliminary relationships between hydrogen content and electrochemical performance of a-Si:H thin film electrode were analyzed, and several negative factors of electrochemical performance for a-Si:H thin film electrode were proposed.

     

Al-induced crystallization of amorphous ge and formation of fractal ge micro-/nanoclusters

Results on Al-induced crystallization of amorphous Ge (a-Ge) deposited by vacuum thermal evaporation techniques under thermal annealing in N(2) atmosphere are presented in detail. The a-Ge crystallization and fractal Ge pattern formation on the free surface of annealed Al/Ge bilayer films deposited on single-crystal Si (100) substrates were investigated by using scanning electron microscopy (SEM), X-ray diffraction (XRD), atomic force microscopy (AFM), energy dispersive X-ray spectrometry (EDS), and Raman spectra. It is found that the temperature field effects play an extremely crucial role in a-Ge crystallization and fractal Ge formation process. The open branched structure of fractal Ge clusters in Al/Ge bilayer films was effectively prepared by Al-induced crystallization when they were annealed at 400 °C for 60 min. These films with fractal Ge clusters exhibit charming noninteger dimensional nanostructures, which differ from those of conventional integer dimensional materials such as one-dimensional nanowires/nanorods, nanotubes, nanobelts/nanoribbons, two-dimensional heterojunctions, thin films, and zero-dimensional nanoparticles. The SEM image shows that a big Al grain was found located near the center of a fractal Ge cluster after the films were annealed at 400 and 500 °C for 60 min. This suggests that the grain boundaries of polycrystalline Al films are the initial nucleation sites of a-Ge. It also validates the preferred nucleation theory of a-Ge at triple-point grain boundaries of polycrystalline Al at the interface. This discovery may be explained by the metal-induced nucleation (MIN) mechanism.     

掺硼p型非晶硅薄膜的制备及光学性能的表征

以高氢稀释的硅烷(SiH₄ )为反应气体,硼烷(B₂H₆)为掺杂气体,利用RF-PECVD方法,在玻璃衬底上制备出掺硼的氢化非晶硅(a-Si:H)薄膜,研究了硼掺杂量对氢化非晶硅(a-Si:H)薄膜的光学性能的影响.利用NKD-7000 W光学薄膜分析系统测试薄膜的透射谱和反射谱,并利用该系统的软件拟合得出薄膜的折射率、消光系数、吸收系数等光学性能参数,利用Tauc法计算掺硼的非晶硅薄膜的光学带隙.实验结果表明,随着硼掺杂量的增加,掺杂非晶硅薄膜样品在同一波长处的折射率先增大后减小,而且每一样品均随着入射光波长的增加而减小,在波长500 nm处的折射率均达到4.3以上;薄膜的消光系数和吸收系数随着硼掺杂量的增大而增大,在500 nm处的吸收系数可高达1.5×10⁵cm^-1.在实验的硼掺杂范围内,光学带隙从1.81 eV变化到1.71 eV.     

Evolution of Structure of the Precursor During Sol-Gel Processing of ZnO and Low Temperature Formation of Thin Films

ZnO thin films were prepared on silicon substrate with Pt electrode by the sol-gel processing using Zn alkoxide solution prepared from Zn(NO₃)₂·6H₂O and 2-methoxyethanol. FT-IR spectroscopy showed the presence of Zn species in the alkoxide, with methoxyethoxide and nitrato groups as coordination ligands, indicating formation of Zn(NO₃)(OCH₂CH₂OCH₃). Smooth and homogeneous thin films were obtained by heat treating coating gel films in the temperature range from 250 to 500°C. The ZnO thin films exhibited a preferred growth of crystals with c-axis perpendicular to the Si substrate surface when fired at 250°C. It was discussed that the presence of nitrogen atoms in precursors had affected the phase development of crystals and was the basis of the structural relaxation for crystallization at low temperature.