【作者】 邵根荣；

【导师】 杨晴；

【作者基本信息】 中国科学技术大学 ， 无机化学， 2014， 博士

【摘要】 本论文主要探索研究硒化铅、硫化铅及其固溶体PbSexS1-x的液相可控制备及其机理。通过设计新的反应路线,控制制备出六角星形等多种硒化铅纳米结构,并探讨了其生长机理和其形貌关联的结构特征。同时,将此方法拓展至硫化铅及其相应固溶体的制备。此外,还探讨了其固溶相PbSexS1-x纳米结构的光电响应性能及可能机理。本文主要研究内容归结如下：1.发展了一种简单的硒化铅纳米结构的液相制备方法,控制制备出具有六角星形、立方体、八面体和截边八面体等多种形貌的硒化铅纳米晶体。具体利用四苯基铅,三苯基膦硒为原料,以二苄胺、油酸和油胺为反应介质(起溶剂及表面活性剂作用),在220℃反应30min,成功地制备出具有六角星形形貌的岩盐相PbSe纳米颗粒。通过溶剂及其用量的选择还可控制制备出立方体、八面体和截边八面体等不同形貌PbSe内米晶体。由透射电子显微镜(TEM)、扫描电子显微镜(SEM)、X射线粉末衍射(XRD)、选区电子衍射(SAED)以及能量色散型X射线荧光光谱(EDX)等表征发现,虽然这些PbSe纳米颗粒的形貌不同,但其都具有相同的岩盐相结构。同时,产物均表现出富铅相结构特点,并且其富铅程度随着{111}面比例的增大而增大。实验研究显示,溶剂对PbSe纳米晶体具有重要影响,其中二苄胺、油酸和油胺对产物影响程度的顺序为油酸>二苄胺>油胺。通过利用全反射傅里叶变换红外光谱(ATR-FTIR)对产物进一步表征和分析显示溶剂的使用确实能够影响产物的形貌,并能改变其表面的结构特征。通过利用溶剂对PbSe纳米晶体{111}、{110}和{100}等不同晶面的选择吸附及反应条件的调节,可以得到包括六角星形、八面体、立方体以及截边八面体等多种不同形貌的PbSe纳米结构。该研究不仅为不同形貌PbSe纳米晶体的控制制备提供理论基础,还为那些与其结构相似的体系提供参考,并且为具有特定晶面／形貌-成分关联的纳米晶体的控制制备提供一种有效的合成途径。2.在PbSe纳米晶体制备研究基础上,将该液相合成方法拓展到硫化铅,及其与硒化铅形成的固溶体即PbSe纳米结构的控制制备,通过选择反应活性相近的Se、S反应前驱源制备出具有六角星形形貌的岩盐相三元PbSexS1-x固溶体纳米晶体。具体选择二苄胺和油酸为反应介质,以三水合醋酸铅为铅源,以三苯基膦硒和二苄基二硫分别作为硒源和硫源,在260℃制备出六角星形形貌的PbSexS1-x固溶体纳米晶体。通过XRD、SAED、EDX以及XPS等表征手段,研究显示所制备的固溶体具有明显富铅相结构特征,并可通过调整实验条件控制固溶体产物的成分。实验研究和分析表明,能够制备出具有成分可调的三元PbSexS1-x固溶体纳米晶体的一个重要原因在于所选择的硫属前驱源在反应体系中具有相近的反应活性,而PbSe和PbS之间的晶格失配度较小(小于3%)也有利于该固溶体的形成。所制备的PbSexS1-x固溶体纳米晶体的成分与其晶格参数呈较好的线性关系,符合Vegard规则。同时,文中还探讨了PbSexS1-x固溶体纳米晶体的生长机理。研究表明,尽管PbSexS1-x固溶体纳米晶体的形成在热力学上是可行的,但由于受到动力学因素的限制,所制备的固溶体纳米晶体仍具有一定程度的偏聚结构,且随固溶体中S含量的增高,其元素无序分布程度也随之增加。延长反应时间能够促使固溶体的晶体结构从偏聚结构向均匀固溶体结构转变。3.探讨了三元PbSexS1-x固溶体纳米晶体的光电响应性能,发现在白光照射下其光电流大小可达820nA,远大于其对应PbS和PbSe二元产物的光电流,同时其光电流与暗电流比值可达27倍。具体研究中,以PbSexS1-x (X=0.2,硒组分投料比)纳米晶体为例详细探讨了三元固溶体的光电响应性能,通过XRD、TEM、 SEM、SAED及EDX表征发现,该岩盐相PbSexS1-x (X=0.2)固溶体纳米晶体仍保持规整的六角星形形貌、尺寸分布窄。XRD、Raman、XPS、EDX等测试分析显示该三元PbSexS1-x (X=0.2)固溶体纳米晶体具有富铅相结构特征,且其中存在明显的元素无序分布或点缺陷,具有明显的偏聚结构,其支角中S的含量要明显高于中心区域。对其光电响应性能研究发现,其光电性能具有比其相对应的二元化物明显增强的特征。基于PbSeXS1-X固溶体纳米晶体的结构分析及其光电性能增强的分析,在三元PbSexS1-x (x=0.2)固溶体中,存在着大量的缺陷等微结构,这种微结构的存在大大增加了固溶体纳米结构内部载流子浓度,因此增强了其光电响应特性。更多还原

【Abstract】 This dissertation is intended to develop the controllable synthesis and growth mechanism of hexapod-like PbSe and PbS as well as its ternary PbSexS1-x nanostructures. By designing different reaction routes, well defined hexapod-like PbSe as well as its ternary PbSexS1-x nanostructures with various compositions and morphologies were fabricated, the related growth mechanism and morphologies based structural characters were discussed. Meanwhile, the photoconductivity of the ternary PbSexS1-x (x=0.2) had also been studied and a possible mechanism was also proposed. The details are summarized as follows:1. A facile organometallic synthetic route had been developed for the preparation of well-defined star-shaped PbSe nanostructures, different morphologies of PbSe, including star-shape, cube, octahedron and side-cut cube were produced. Lead selenide (PbSe) nanostructures with well-defined star-shaped morphology were successfully fabricated via a facile organometallic synthetic route from the reaction of Pr4Pb with Ph3PSe in DBA with the assistance of OA and OAm at220℃for30min. The structure and shape of the nanocrystals were investigated by TEM, SEM, XRD, SEAD and EDX and found that the obtained PbSe nanostars presented Pb-rich features although the PbSe nanostars were still in typical rock salt phase. Experimental investigations demonstrated that the media of DBA, OA and OAm played important role in the morphologies evolutions of different PbSe nanostructures and found an order of OA> DAB> OAm in the growth of the PbSe nanostars with well-defined shapes. ATR-FTIR studies also showed that the media could change their morphologies as well as their surface features. By manipulating the absorption on exposed{111} faces and other relevant reaction conditions, different morphologies with cubic, side-cut cubic, and octahedral shapes can be fabricated. This study not only provided an insight into the controllable growth mechanism of different morphologies of PbSe nanostructures, but also gave a feasible synthesis route for the materials with specific faces and morphology-related characters.2. On the basis of the preliminary work, we expanded this organometallic synthetic route to the synthesis of PbSe, PbS and their ternary PbSexS1-x nanostructures. By effective selection of Se-and S-sources of Ph3PSe and DBDS that had similar reactivity in the current reaction system, hexapod-like ternary PbSexS1-x had been fabricated from the reaction of PhsPSe and DBDS in DBA with the addition of OA at260℃for5min. The shape, structure and composition of the nano structured hexapods was investigated by XRD, SEAD, EDX and XPS and found that the obtained ternary nano structured hexapods were of typical rock salt phase with Pb-rich features and their compositions could be systematically regulated by facile variations of reaction parameters. Investigations revealed that the successful fabrication of the ternary hexapods with tunable compositions was resulted from the similar reactivity of Se-and S-sources along with small lattice mismatch between the two endmembers of PbSe and PbS. In general, the relations between the composition and lattice parameters for the ternaries obtained in DBA with varied addition of OA exhibited linear slops that were consistent well with Vegard’s law. Meanwhile, the growth mechanism and procedure were also discussed, and found that the as-grown ternary PbSexS1-x hexapods were mainly gradient alloyed nanostructures with somewhat chalcogen-element segregations or disorders rather than homogeneously alloyed solid-state solutions due to kinetic limitation for short reaction time even though thermodynamics was feasible in the system, and also, high concentration of S element in the feedstocks tended to relative high density of disorders in the ternaries. Based on the reveal of the growth mechanism for the ternary hexapods with varied micro structures, the ternary PbSexS1-x hexapods could be tuned from gradient alloys with segregations to approximately homogeneous nanostructures via enlongating reaction time.3. The photoconductivity of the ternary PbSexS1-x (x=0.2) had been investigated and found its photocurrents could reached820nA under light illumination of a typical hexapod-like ternary PbSexS1-x (x=0.2) nanostructure and its signal-to-noise ratio could reach27times, better than its two binary materials. Different technical methods, like XRD, TEM, SEM, SEAD and EDX, were carried out and found that the obtained ternary PbSexS1-x (x=0.2) nano structured hexapods were of typical rock salt phase and obviously gradiently nanostructures with relatively small size distribution. XRD, Raman, XPS and EDX presented the Pb-rich features of the as-grown ternary PbSexS1-x (x=0.2) hexapods and different degree of chalcogen-element segregations, disordered or defected microstructures existed in them, namely, the concentration of S decreased gradually from the tips of arms to its central region. The photodetectors of the ternary PbSexS1-x (x=0.2) nanocrystal and its two endmembers PbSe and PbS were also fabricated and found there was an obviously enhanced photoconductivity feature between the ternary nanostructure and its two endmembers. A mechanism related to defected and vacancy nanostructure in ternary was proposed which demonstrated that these disordered nanostructure greatly increased concentration of carrier density and the photoconductivity enhanced.更多还原