形状控制微波合成四方形纳米PbS

以Pb(NO3)2、硫代乙酰胺(TAA)为原料,通过改变十六烷基三甲基溴化铵(CTAB)的用量控制合成了四方形PbS纳米晶,并用XRD、TEM进行了表征。结果表明,当CTAB质量浓度达10g/L时,所获产品全为四方形纳米晶。形状控制微波合成四方形PbS纳米晶的机理可能为:首先CTAB和Pb2+结合形成R-N:Pb-Br白色前驱沉淀,然后该前驱沉淀与S2结合,在一定温度和时间热分解形成四方形PbS纳米晶。前驱体中的CTAB烷基长链存在阻碍作用,导致PbS小晶粒不能快速聚集而结晶生长,有利形成四方形的纳米PbS。     

前驱物[S2-]/[Pb2+]摩尔比对PbS纳米晶红外发光光谱的影响

采用水溶性前驱物在乙醇介质中制备了不同[S2-]/[Pb2+]摩尔比例的PbS纳米晶,利用X射线衍射（XRD）、透射电子显微镜（TEM）、紫外-可见吸收光谱（Abs）、光致发光谱（PL）对所制备PbS纳米晶的晶体结构、纳米晶粒径、形貌以及能带结构和发光特性进行了表征,结果表明:随着前驱物[S2-]/[Pb2+]摩尔比例的提高,PbS纳米晶颗粒尺寸从3.9 nm增大到5.9 nm,发光峰值位置从1 009 nm移动到1 486 nm。通过拟合[S2-]/[Pb2+]=0.5条件下PbS纳米晶平均粒径对时间变化曲线,发现该方法下PbS纳米晶所经历的生长机制为Ostwald成熟化。运用经典纳米晶扩散控制生长模型,解释了实验中随着[S2-]/[Pb2+]的提高对溶液中纳米晶生长速率的影响。     

NiO空心微球的规模化制备与表征

以氨水与硝酸镍为原料,在乙醇–水介质中,采用均匀沉淀法,85℃恒温条件下,无需模板的存在和水热处理,制备出前驱体α-Ni(OH)2沉淀。该沉淀经400℃煅烧后得到NiO纳米片自组装空心微球。采用XRD和SEM对微球物相与形貌进行了表征。结果表明:该微球具有六方相结构,纳米片竖直排列在球状壳层的表面,其中纳米片大小约为2μm×2μm,厚度小于100nm。研究了乙醇对于纳米片自组装空心微球形貌形成的作用,对空心微球的自组装机理做了初步探讨。     

微乳液法制备竹节状纳米管的机理研究

通过反相微乳液法制备不同形貌的CdSe纳米晶。利用X-射线衍射(XRD)和透射电子显微镜(TEM)技术对纳米晶的结构和形貌进行表征。结果表明,纳米晶主要由CdSe和Na2SO4组成,根据Sherrer公式计算得到CdSe(100)方向的晶粒尺寸D100=35nm;不同制备条件下,纳米晶的形貌有短链状CdSe纳米晶、项链状和竹节状CdSe纳米管。其形成机理是:由于界面膜处束缚水含量小于水核内部自由水含量,造成CdSe纳米球外层密度小于中心密度,浓度差驱使Se2-与Cd2+向外层扩散形成CdSe空心纳米球;最终在取向附生生长机制下,CdSe空心纳米球生长为项链状和竹节状纳米管。     

Ca0.4Sr0.6Bi4Ti4O15纳米晶粉体的溶胶-凝胶法制备

采用溶胶-凝胶法和预碳化处理工艺制备了层状钙钛矿结构的Ca0.4Sr0.6Bi4Ti4O15纳米晶粉体。借助DSC-TG、XRD和SEM等分析表征了Ca0.4Sr0.6Bi4Ti4O15纳米晶粉体前驱体的热反应过程、粉体的物相结构及微观形貌。结果表明,对前驱体进行预碳化处理得到纳米晶粉体,其分散性得到明显的改善,800~850℃热处理的纳米晶粉体呈单一的层状钙钛矿结构,粉体为球形颗粒,大小均匀,分散性良好,粒径约在100 nm。     

水热环境下PZT纳米晶的结晶与生长习性

采用TiO2,ZrOCl2.8H2O,Pb(NO3)2为原料,KOH为矿化剂,在200℃,KOH浓度分别为1 mol/L,3 mol/L,5 mol/L,7 mol/L时,水热合成锆钛酸铅纳米晶体。结果表明,KOH浓度严重影响了Pb(Zr0.52Ti0.48)O3(PZT)纳米晶的结晶、生长习性与晶体形貌。当KOH浓度较低时,合成了PZT纳米晶片;当KOH浓度较高时,合成了PZT纳米四方晶柱。合成的纳米晶晶粒度为30 nm,纳米晶粒间通过层叠方式进行生长,成为较大的PZT多晶颗粒。     

TiO_2对水热法制备钛酸锶钡的影响

以乙酸锶、乙酸钡、钛酸丁酯为原料,通过溶胶-凝胶法制备出钛酸锶钡(BST)前驱体。在前驱体中分别加入10%金红石TiO_2、锐钛矿TiO_2和用水热法制备的一维TiO_2,再进行水热合成,得到3种不同的水热产物。用傅里叶变换红外光谱仪(FTIR)、X线衍射仪(XRD)、扫描电子显微镜镜(SEM)对前驱体和3种水热产物进行物相和形貌的表征,并对水热产物的生长机理和形成原因进行探讨。结果表明,在前驱体中添加锐钛矿TiO_2能够制备出柱状晶结构的BST;添加一维TiO_2的前驱体生成了一维的BST晶体。     

水热法制备一维钛酸锶钡晶体

用钛酸丁酯为原料,通过溶胶-凝胶法制备钛酸锶钡前驱体,进行水热处理,得到钛酸锶钡纳米粉体;在凝胶前驱体中加入10%的纳米锐钛矿TiO2,再进行水热处理,水热产物中有大量的一维钛酸锶钡晶体生成。用傅里叶变换红外光谱仪(FTIR)、X线衍射仪(XRD)、场发射扫描电镜(FESEM)、透射电镜(TEM)以及电子衍射(SAED)对前驱体和其对应的水热产物进行物相和形貌的表征,并对一维钛酸锶钡的生长机理进行探讨。结果表明一维钛酸锶钡晶体的生长机理是原位生长。     

铌酸钾纳米棒的制备与表征

以柠檬酸(CA)为配位剂与金属离子配合,水作为溶剂,乙二醇(EG)为酯化剂,通过聚合物前驱体法制备铌酸钾(KNbO3)粉体。研究了CA和EG的用量和pH值对溶胶性能的影响。采用X-射线衍射(XRD)和热失重分析(TG-DTA)研究了KNbO3晶相的形成过程,用透射电子显微镜(TEM)对所制得粉体的表面形貌进行了分析。结果表明,当前驱体溶胶的pH值为7.5,n(CA)∶n(金属离子)=3∶1,n(CA)∶n(EG)=1∶2时,可获得稳定性好的溶胶。凝胶前驱体在加热过程中先反应生成K3Nb7O19和K4Nb6O17,然后二者反应生成KNbO3。凝胶前驱体以不同的升温速率加热至700℃,对所得粉体的形貌影响较大,升温速率快,有利于粒状产物的形成;升温速率慢,易形成棒状产物。同时讨论了不同的升温烧结机制影响KNbO3形貌的原因。     

sol-gel燃烧法合成MgFe_2O_4纳米颗粒及其气敏性

以Mg(NO3)2、Fe(NO3)3和柠檬酸为原料,采用sol-gel燃烧法,合成了MgFe2O4纳米颗粒。利用XRD、TEM和红外光谱对产物进行了结构、形貌的测量和表征。结果表明:MgFe2O4的前驱体燃烧后经过500℃下1h的热处理,得到平均粒径小于20nm的纳米颗粒。以MgFe2O4为原料,制备了气敏元件,发现元件在工作电压为4.5V时对50×10–6的Cl2的灵敏度达到177,响应时间达4s,而且对其它气体的抗干扰性很好,有望开发成为对Cl2检测的传感器材料。     

Effect of Pb:S molar ratio in precursor solution on the properties of lead sulphide thin films by ultrasonic spray pyrolysis

In this work, PbS thin films were deposited onto glass substrate at 225 °C by spraying precursor solution prepared with different molar ratio of lead acetate and thiourea as a source of Pb²⁺ and S^2- respectively in order to investigate the effect of Pb:S molar ratio in the precursor solution on the physical properties of PbS thin films. Structural investigations carried out by X-ray diffractometer have shown that all films have fcc cubic structure and the average crystal size increased from 11 nm to 25 nm with the increasing the thiourea ratio in the precursor solution. In order to analyze the surface morphology of PbS thin films, AFM and SEM images were taken and elemental analysis of the films was performed by EDS. Optical transmittance and absorption spectra show that all deposited films have fairly low transmittance and high absorbance in the visible region. Additionally, it was determined that optical band gap of the deposited films were varied between 1.18 eV and 1.37 eV. As a consequence of electrical investigations, it was seen that all films have p-type conductivity and electrical resistivity decreased by increasing thiourea molar ratio in the precursor solution. All examinations have revealed that the molar ratio of lead acetate and thiourea has a significant effect on the physical properties of PbS thin films.     

Auger analysis of the PbS-Si heterojunction

The chemical structure of the solution-grown PbS-Si hetero-junction was studied by Auger Electron Spectroscopy. Auger depth profiles indicate a PbS film of uniform composition. No major contaminants were observed in the bulk of the PbS film. At the PbS-Si interface the only impurity observed was an oxygen peak, corresponding to approximately 1% atomic concentration. Heating the growth solution enhances the chemical reaction and deposition rates without altering the profiles of the elements at the interface. Similar oxygen peaks were detected at the Au-PbS interface and at the interface between consecutive PbS films. The interface oxygen concentration in the PbS-Si (100) structure is roughly twice that present in the PbS-Si (111) structure. Heat treatment in air increased the interface and surface oxygen concentration by a factor of 2 to 5. The same treatment in N₂} ambient had only a slight effect on the surface oxygen concentration but enhanced the interface oxygen concentration. The oxygen at the Au-PbS interface showed similar sensitivity to heat treatment. Oxygen content at the interface of HJs formed on unpolished Si was double that in HJs formed on polished Si. The relative intensity of the S to Pb peaks in the bulk of the PbS film compares closely with that measured on the cleaved surface of natural single crystal galena. The Pb: S peak ratio was roughly constant throughout the PbS film and at the PbS-Si interface. Fe and Cl contaminants were observed at the surface of the PbS film, along with significant changes in the Pb:S ratio. The simultaneous detection of Pb, S and Si near the interface is attributed to the presence of surface irregularity caused by a secondary PbS macrostructure consisting of isolated chain-like clusters. This paper was presented in part at the Electronic Materials Conference, June 1979, Boulder, CO.     

基于PVK/PbS纳米晶有机无机复合薄膜电双稳器件性能研究

通过简单旋涂方法,制备了一种基于硫化铅（PbS）纳米晶与聚乙烯基咔唑（PVK）的有机/无机复合薄膜电双稳器件,并对所制备的器件进行性能测试及其电荷传输机制研究。首先采用热注入的方法制备了尺寸均一的立方形PbS纳米晶,然后将PbS纳米晶与PVK聚合物混合作为活性层材料,制备了有机/无机复合薄膜电双稳器件。该器件展示了良好的电双稳特性并且可以实现稳定的“读-写-读-擦”操作。器件的最大电流开关比能够达到10⁴。并进一步对器件在正向电压下的I-V曲线进行了理论拟合,发现在不同电流传导状态下,器件符合不同的电传导模型。进而分析了该电双稳器件中的电荷传输机制,认为在电场的作用下,发生在纳米晶与聚合物之间的电场诱导电荷转移是产生电双稳特性的主要原因。     

掺铒Al_2O_3/Si多层薄膜中纳米晶Si的形成和敏化效应

采用脉冲激光沉积制备了掺铒Al2O3/Si多层薄膜,在淀积过程中脉冲激光溅射产生的高能量Er原子渗透进入非晶硅层,并引入了额外的应力,在低退火温度下诱导形成纳米晶Si。利用纳米晶Si作为敏化剂有效地增强了Er3+在Al2O3中的光致发光。样品微观结构和发光强度的关系表明,获得高密度和小尺寸的纳米晶Si和Er3+处于良好的发光环境是实现优化发光的关键,最优化的Er3+发光强度在退火温度为600℃的条件下得到。     

Novel two-dimensional lead sulfide quadrangular pyramid-aggregated arrays with self-supporting structure prepared at room temperature

Two dimensional (2D) self-supporting lead sulfide (PbS) arrays composed of ordered quadrangular nanopyramids were successfully fabricated through a convenient wet-chemical route at room temperature. The as-synthesized products were characterized by X-ray diffraction, field emission scanning electron microscopy, transmission electron microscopy, UV–vis–NIR absorption and photoluminescence spectroscopy. The as-prepared highly ordered self-supporting superstructures are stable under ultrasonic conditions. A “template-mediated in situ growth” mechanism is proposed for the formation of 2D PbS superstructures. With the prolongation of reaction time, the morphology evolution of PbS is clearly observed, which could be changed from nanopyramid-aggregated arrays into nanocube-aggregated arrays at original position. The optical properties of PbS self-supporting superstructures are investigated in detail.     

配体链长对PbS量子点薄膜/Al肖特基结整流特性的影响

利用热注入法合成带有油酸配体的PbS量子点, 用短链乙醇胺替代长链油酸做为PbS量 子点的配体。 对比了由两种材料制得的量子点薄膜与Al形成的肖特基结的J-V特性,采用热 电子发射理论对其J-V特 性进行分析,结果发现,接有短链乙醇胺的PbS量子点薄膜具有更优的整流特 性,理想因子n为3.8,明显低 于采用油酸配体的PbS量子点(n=4.6)。 研究表明,短链配体有利于提高PbS薄膜表面的均匀性并形成较好的肖 特基接触;短链置换过程提高了量子点薄膜与Al电极的接触势垒高度,使肖特基结反向 漏电流降低。     

Unveiling the Nanoparticle‐Seeded Catalytic Nucleation Kinetics of Perovskite Solar Cells by Time‐Resolved GIXS

Recently, a new seeding growth approach for perovskite thin films is reported to significantly enhance the device performance of perovskite solar cells. This work unveils the intermediate structures and the corresponding growth kinetics during conversion to perovskite crystal thin films assisted by seeding PbS nanocrystals (NCs), using time‐resolved grazing‐incidence X‐ray scattering. Through analyses of time‐resolved crystal formation kinetics obtained from synchrotron X‐rays with a fast subsecond probing time resolution, an important “catalytic” role of the seed‐like PbS NCs is clearly elucidated. The perovskite precursor‐capped PbS NCs are found to not only accelerate the nucleation of a highly oriented intermediate phase, but also catalyze the conversion of the intermediate phase into perovskite crystals with a reduced activation energy E_a = 47 (±5) kJ mol^?1, compared to 145 (±38) kJ mol^?1 for the pristine perovskite thin film. The reduced E_a is attributed to a designated crystal lattice alignment of the perovskite nanocrystals with perovskite cubic crystals; the pivotal heterointerface alignment of the perovskite crystals coordinated by the Pb NCs leads to an improved film surface morphology with less pinholes and enhanced crystal texture and thermal stability. These together contribute to the significantly improved photovoltaic performance of the corresponding devices.     

Silicon nanocrystal formation upon annealing of SiO2 layers implanted with Si ions

The formation of silicon nanocrystals in SiO₂ layers implanted with Si ions was investigated by Raman scattering, X-ray photoelectron spectroscopy, and photoluminescence. The excess Si concentration was varied between 3 and 14 at. %. It was found that Si clusters are formed immediately after implantation. As the temperature of the subsequent annealing was raised, the segregation of Si accompanied by the formation of Si-Si₄ bonds was enhanced but the scattering by clusters was reduced. This effect is attributed to the transformation of loosely packed clusters into compact, separate-phase nanoscale Si precipitates, with the Raman peak observed at 490 cm^?1 being related to surface scattering. The process of Si segregation was completed at 1000°C. Nevertheless, characteristic nanocrystal photoluminescence was observed only after annealing at 1100°C. Simultaneously, scattering in the range 495–520 cm^?1, typical of nanocrystals, appeared; however, the “surface-related” peak at 490 cm^?1 persisted. It is argued that nanocrystals are composed of an inside region and a surface layer, which is responsible for their increased formation temperature.