Synthesis and polarity driven alignment of ZnO crystallites

该项目的重点是制备具有固有取向极性的氧化锌晶体，以及基于其结晶度和取向的这种材料的特殊电气和机械性能。其目的是获得一种各向异性的微结构，使其能够在压应力下改变极化，从而调制跨结的电荷载流子传输。为此，将以受控方式合成纳米和微米尺寸的氧化锌微晶，并以定向方式沉积。将应用几种技术来在衬底上获得从薄膜到厚膜的各种对象，从而可以使用额外的处理或烧结步骤。如果合适的合成条件，可以得到具有中微米级氧化锌颗粒的多晶结构。首先，必须合成尺寸合适的氧化锌单晶，从而要求颗粒均匀，粒度分布窄。氧化锌微晶的可控取向是一个合成挑战，将使用三种不同的方法进行研究：(A)电场诱导(B)毛细管力(对流组装)或(C)有机模板(自组装单分子膜或逐层聚电解质堆叠)。建立了压电材料的电泳沉积(A)，用于沉积产生尺寸在微米到毫米范围内的自由站立的陶瓷体的压电材料。因此，本文将首次研究这种方法用于沉积具有交替取向极性的层。通过对流组装(B)的方法对准和堆积氧化锌小片提供了单层和多层的受控形成的路线。有机模板(C)可以与专门合成的颗粒的沉积以及从化学浴中原位形成的陶瓷氧化锌层相结合。该项目的两个中心任务和挑战性的目标是寻找最佳的合成沉积技术，使其能够控制合成氧化锌晶体，并将其组装成具有取向极性的所需沉积。该项目是压阻效应和电导率机械调制领域的联合研究工作的一部分。因此，与Klein、Albe、Rödel/Kleebe和Gjonaj/Xu等伙伴项目的互动至关重要。我们的工作本质上是对科学问题的贡献：化学成分、粒子取向及其在界面上的电子结构如何影响电导率和应变的相关性？我们的材料选择将是对Rödel/Kleebe项目处理的大尺寸氧化锌双晶体研究的理想补充。同样，这项提案将受益，但也将提供材料方面的专门知识，供PAK 928/1的其他小组使用。

The project focuses on the fabrication of zinc oxide crystals with an inherent oriented polarity as well as the particular electrical and mechanical properties of this material based on its crystallinity and orientation. The aim is to achieve an anisotropic microstructure which enables the alteration of the polarisation under compressive stress and thus the modulation of charge carrier transport across junctions. For this purpose nano- and micrometre sized crystallites of zinc oxide will be synthesized in a a controlled fashion and deposited in an oriented manner. Several techniques will be applied to obtain objects ranging from thin to thick films on substrates whereby additional processing or sintering steps can be used. If the synthetic conditions are suitably adapted, a polycrystalline structure with meso- and microsized ZnO grains will become accessible. First, ZnO single crystals of suitable size must be synthesized, whereby uniform particles with a narrow size distribution are required. The controlled alignment of the ZnO crystallites is a synthetic challenge and will be studied using three different approaches: (a) induced by electrical fields (b) by capillary forces (convective assembly) or (c) by organic templates (self-assembled monolayers or layer-by-layer stacks of polyelectrolytes). The electrophoretic deposition (a) of piezoelectric materials is established for the deposition of piezoelectric materials yielding free standing ceramic bodies with dimensions in the regime of micro to millimetres. This method will consequently be studied for the deposition of layers with alternating oriented polarity herein for the first time. The alignment and stacking of ZnO platelets by means of convective assembly (b) provides a route for a controlled formation of mono and multilayers. Organic templates (c) could be combined with the deposition of dedicatedly synthesized particles as well as with in-situ formed ceramic ZnO layers from chemical baths. Finding the optimum synthetic deposition techniques which allow a controlled synthesis of ZnO crystals and the assembly of those to yield their desired deposition with oriented polarity are the two central tasks and challenging goals of the project which is part of the joined research effort in the field of piezoresisitive effects and mechanical modulation of electrical conductivity. Therefore the interaction with the partner projects; Klein, Albe, Rödel/Kleebe and Gjonaj/Xu is essential. Our work contributes essentially towards scientific questions as: How do chemical composition, particle orientation and its electronic structure at interfaces affect the dependence of electrical conductivity and strain? Our materials choice will ideally supplement the studies of macroscaled ZnO bicrystals treated by the Rödel/Kleebe project. Likewise this proposal will benefit but will also provide materials expertise for use in the other groups of PAK 928/1.