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.     

溶液法铝诱导晶化多晶硅薄膜

介绍了一种基于溶液的廉价制备Al诱导晶化多晶硅薄膜的方法. 先以低压化学气相沉积(LPCVD)方法制备50 nm厚的非晶硅(amorphous silicon, a-Si)薄膜作为前驱物, 通过旋涂的方法, 将含有Al的盐溶液涂覆在a-Si薄膜表面, 550-620 ℃下氮气氛围退火若干小时得到多晶硅薄膜. 文中针对化学诱导源的种类、前驱物表面状况对晶化效果的影响进行了研究. 发现只有反应生成物中含有偏铝酸根(AlO-2)的碱性溶液才能发生诱导晶化, 而若Al溶液浓度过低, 则不能得到连续的多晶硅薄膜. a-Si表面若附有薄氧化层会有利于Al盐溶液在表面上的粘附以及得到大尺寸的晶粒, 然而又会增高退火晶化所需要的温度. 同时溶液在薄膜表面的粘附状况还会受到溶液中存在的其它离子的影响. 因此必须选用合适的实验条件.     

电化学沉积CdSe纳晶薄膜的性能及沉积机理

电化学沉积是半导体薄膜制备的一种简便方法,常用于Ⅱ-族化合物半导体薄膜的制备.通过电沉积条件的适当改变可成功地在导电衬底上制备半导体纳晶薄膜^[1].CdSe薄膜作为一种透光性好、导电性好的半导体材料,可进行光学性能和光电性能方面的研究,而半导体纳晶多孔电极的光电化学特性与体材料之间有很大不同.本文采用电化学沉积法制备了CdSe纳晶薄膜并研究了其性能,通过扫描隧道显微镜(STM)形貌分形分析进一步研究其沉积机理.     

镨元素对(Nd,Pr)10.5(FeCoZr)83.5B6合金显微结构和磁性能的影响

研究了稀土元素Pr对快淬(Nd1-xPrx)10.5(FeCoZr)83.5B6(x=0,0.2,0.4,0.6,0.8,1.0)合金显微组织结构和粘结磁体磁性能的影响。通过部分过快淬获得由非晶和微晶共同组成的条屑,在实验优化的退火条件下晶化处理后,制备出最佳磁性能的系列粘结磁体。随Pr含量的增加,磁体的内禀矫顽力Hci单调上升,剩磁Br单调下降,(BH)m在x=0.6～0.8处达到最大值70.6kJ·m-3。Pr元素使合金非晶态的晶化转变温度和转化能降低,合金的显微组织结构变得较粗大和较不均匀,从而使快淬粘结磁体剩磁降低,但Pr2Fe14B化合物较高的磁晶各向异性场使磁体的内禀矫顽力提高。     

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.     

快速凝固AlNiCuNd纳米/非晶复合材料的制备及显微组织研究

采用熔体单辊旋淬法制备了快凝Al87Ni7Cu3Nd3合金条带,利用差热扫描热力学(DSC)分析、X射线衍射(XRD)分析等手段对比研究了快凝合金条带及其不同退火态材料的晶化行为.选择合适工艺条件,对快凝合金条带进行等温加热退火,采用高分辨透射电镜(HRTEM)观察分析了等温退火态材料显微组织特征.结果表明,快凝Al87Ni7Cu3Nd3合金薄带呈现出完全均匀的非晶态结构.随加热温度升高,非晶态薄带的晶化过程包括两个主要的相转变: α-Al晶体从非晶基体中析出的初始晶化以及有Al3Ni,Al11Nd3和Al8Cu3Nd形成的第二次晶化过程.在低于310 ℃下加热,快速凝固Al87Ni7Cu3Nd3金属玻璃中发生的主要相转变是富Al非晶的初始晶化.110 ℃等温退火态薄带主要是由α-Al加残余非晶相的两相组成,α-Al晶体纳米颗粒均匀弥散分布在残余非晶基体上.而在310 ℃热暴露后的退火试样中,在除α-Al晶体外的残留非晶相中开始出现极少量的Al3Ni金属间化合物.     

NiB和NiP超细非晶合金的退火晶化行为及催化性能

 采用X射线吸收精细结构（XAFS）,X射线衍射（XRD）和差热分析（DTA）等方法研究了以化学还原法制备的NiB和NiP超细非晶态合金催化剂在退火过程中的结构变化．XRD结果表明,在300℃下退火时,NiB超细非晶态合金晶化生成纳米晶Ni3B亚稳物相,NiP超细非晶态合金则主要晶化生成金属Ni和部分晶态Ni3P的混合物相;在500℃退火且近于完全晶化的条件下,大部分超细非晶态合金都晶化为金属Ni．XAFS结果定量地说明,对于NiB和NiP初始样品,第一近邻Ni－Ni配位的平均键长Rj分别为0.274和0.271nm,其结构无序度σS很大,分别为0.033和0.028nm,其热无序度σT分别为0.0069和0.0060nm．300℃退火后,晶化生成的Ni3B的Ni－Ni配位的σS降低到初始样品的33％,仅为0.011nm．500℃退火后,NiB样品的结构参数与金属Ni基本一致,但NiP样品的Ni－Ni配位的σS还远大于σT,仍为0.0125nm,表明NiB和NiP超细非晶态合金的退火晶化行为有很大的差别．纳米晶Ni3B催化苯加氢反应的转化率比超细Ni－B非晶态合金或多晶金属Ni更高,表明纳米晶Ni3B中的Ni与B原子组成了苯加氢催化反应的活性中心．     

P3HT修饰一维有序壳核式CdS/ZnO纳米棒阵列复合膜的光电化学性能

采用电化学方法在铟锡氧化物(ITO)导电玻璃上制备了高度有序的ZnO纳米棒阵列, 在ZnO纳米棒阵列上先后电化学沉积CdS纳米晶膜及聚3-己基噻吩(P3HT)薄膜得到P3HT修饰的一维有序壳核式CdS/ZnO纳米阵列结构, 并通过扫描电镜(SEM)、透射电镜(TEM)、X射线衍射(XRD)、能量散射X射线(EDX)等表征手段证实了该结构的形成. 以此纳米结构薄膜为光阳极组装新型半导体敏化太阳电池, 研究了CdS纳米晶膜的厚度和P3HT薄膜的沉积对电池光伏性能的影响, 初步探讨了电荷在电池结构中的传输机理, 结果表明, CdS纳米晶膜和P3HT薄膜的沉积有效地拓宽了光阳极的光吸收范围, 实验中电池的光电转换效率最高达到1.08%.     

退火温度对Ti/IrO2-CeO2电极组织结构与电容性能的影响

采用热分解法制备了钛基IrO2-CeO2二元氧化物涂层电极(Ti/IrO2-CeO2)。通过X射线荧光衍射(XRD),(SEM),循环伏安和交流阻抗等方法研究了退火温度对Ti/IrO2-CeO2涂层电极组织结构与电容性能的影响。结果表明,随退火温度升高,IrO2-CeO2涂层由非晶态向晶态转变,晶化程度逐渐升高;在460~480℃高温退火,IrO2-CeO2涂层中仍含有约28%的非晶态组织,说明CeO2有抑制IrO2晶化的作用。当退火温度为380℃时,电极的晶化程度约为25%,比电容达到最大值,并具有良好的循环稳定性。电极的电荷转移电阻取决于电极的晶化程度,随退火温度升高呈阶梯下降趋势。     

OTS自组装单层膜诱导生长Sb_2S_3薄膜及其生长机理

在接近室温的水溶液中通过采用OTS-自组装单分子层制备了Sb2S3薄膜。利用X-射线粉末衍射(XRD)、扫描电子显微镜(SEM)、X-射线能量色散谱(EDS)和紫外-可见分光光度计(UV-Vis)对Sb2S3薄膜的结构、形貌和光学性能进行了表征。结果表明,低温下所制备的薄膜为非晶态结构,当薄膜在空气中200~300℃热处理1h时,非晶态薄膜转化成具有正交晶相结构的多晶结构。光学性能测试表明,沉积的Sb2S3薄膜和在空气中200℃热处理1h后Sb2S3薄膜的能带值分别为2.05和1.78eV。功能化OTS自组装单分子层(SAMs)在Sb2S3薄膜的生长过程中起到了诱导生长的作用。通过实验结果,进一步分析了Sb2S3薄膜的形成机理。     

Photoelectrochemical Behaviour of Hydrogenated Amorphous Silicon(a-Si:H) Films

Photoelectrochemical techniques have been employed in the investigation of p-type, n-type and intrinsic hydrogenated amorphous silicon(a-Si:H) films. The results show that the photocurrent response of the films strongly depends on the doped type electrolyte solution and the redox potential of the redox couples. Intrinsic a-Si:H film yields a stable photocurrent much higher than the p- and n-type ones. Based on the measurements, the energy levels and flatband potential of the intrinsic a-Si:H film are given, and the mechanisms of charge transfer in photoelectrochemical cell (PEC) are discussed.     

Modelling the dielectric function of thin films measured by spectroscopic ellipsometry: determination of microstructure and density

The dielectric function of thin-film amorphous hydrogenated silicon (a-Si:H) deposited by the glow discharge and hot wire technique has been investigated by spectroscopic ellipsometry. An improved interpretation of the ellipsometric data taking into account the influence of hydrogen incorporation into the amorphous network enables to determine the film density and the void volume fraction of the material. Thus ellipsometry provides a convenient and contactless means of characterizing the structural properties of thin films. The film density varies considerably with substrate temperature and hydrogen content depending on the individual deposition technique. A reduction of film density is mainly caused by the formation of voids in the amorphous network. The influence of the substrate temperature on the growth of dense a-Si: H films is pointed out.     

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.

     

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.     

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.     

Structural evolution in amorphous silicon and germanium thin films.

The structural evolution in amorphous silicon and germanium thin films has been investigated by high-resolution transmission electron microscopy (HRTEM) in conjunction with autocorrelation function (ACF) analysis. The results established that the structure of as-deposited semiconductor films is of a high density of nanocrystallites embedded in the amorphous matrix. In addition, from ACF analysis, the structure of a-Ge is more ordered than that of a-Si. The density of embedded nanocrystallites in amorphous films was found to diminish with annealing temperature first, then to increase. The conclusions also corroborate well with the results of diminished medium-range order in annealed amorphous films determined previously by a variable coherence microscopy method.     

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.     

Simulation of the electronic and vibrational structure of hydrogenated amorphous silicon using cluster models

A set of simple models of hydrogenated amorphous silicon (a-Si:H) consisting of hypothetical silane molecules with diamond or similar lattices was studied by the semiempirical AM1 method. Densities of states and infrared spectra were calculated for the silane molecules and similar molecules with dangling bonds disorder, and with boron or phosphorus substitution to simulate doping. Some examples are presented, and a comparison is made with experimental properties of a-Si:H. It is proposed to use these models in a study of the Staebler–Wronski photodegradation of a-Si:H and other aspects of amorphous silicon technology. © John Wiley & Sons, Inc.     

Synthesis of amorphous silicon colloids by trisilane thermolysis in high temperature supercritical solvents

Colloidal submicrometer-diameter amorphous silicon (a-Si) particles are synthesized with >90% yield by thermal decomposition of trisilane (Si3H8) in supercritical hexane at temperatures ranging from 400 to 500 degrees C and pressures up to 345 bar. A range of synthetic conditions was explored to optimize the quality of the product. Under the appropriate synthetic conditions, the colloids are spherical and unagglomerated. The colloids can be produced with average diameters ranging from 50 to 500 nm by manipulating the precursor concentration, temperature, and pressure. Relatively narrow particle size distributions, as measured by transmission electron microscopy (TEM), with standard deviations about the mean as low as approximately +/-10% could be obtained in some cases. We explored the thermal annealing of the amorphous silicon particles after isolation from the reactor and found that crystallization to diamond structure silicon occurred at temperatures as low as 650 degrees C. The amorphous and crystalline materials were characterized by X-ray diffraction and high resolution scanning and transmission electron microscopy.