用于高效率电子能量转换器的低work function薄膜生长：耦合开尔文探针和氧化钾的光电发射研究
Low work function thin film growth for high efficiency thermionic energy converter: Coupled Kelvin probe and photoemission study of potassium oxide
摘要：
最近在热能收集方面的研究已经揭示了包括非常低功函数电极的超声波能量转换器的显著效率。从室温及以上温度，这种转换器可以提供低功耗的设备，如自主传感器网络。在这种类型的热电转换器中，电流注入主要由热电极处的电子发射机制控制，这解释了对低功函数涂层材料的兴趣。特别地，碱金属氧化物已被确定为用于涂覆转换器电极的优异候选物。本文主要研究了过氧化钾K_2O_2在硅表面的合成和表征。为了确定最佳的合成条件K2 O2，我们提出的图表显示不同的氧化物作为温度和氧气压力的函数，从中可以确定相稳定性特性。从实验的角度来看，我们目前的结果在超高真空和控制温度下合成氧化钾。所得表面的特征在于原位通过光电子能谱（PES）和接触电势差（CPD）测量。测量了1.35 eV的功函数，并讨论了相应转换器的预期效率。一般认为，碱金属/氧/硅体系中功函数的降低归因于碱金属和氧之间的电荷转移导致的表面偶极子的产生。
英文摘要：
Recent researches in thermal energy harvesting have revealed the remarkable efficiency of thermionic energy converters comprising very low work function electrodes. From room temperature and above, this kind of converter could supply low power devices such as autonomous sensor networks. In this type of thermoelectric converters, current injection is mainly governed by a mechanism of thermionic emission at the hot electrode which explains the interest for low work function coating materials. In particular, alkali metal oxides have been identified as excellent candidates for coating converter electrodes. This paper is devoted to the synthesis and characterization of potassium peroxide K2O2 onto silicon surfaces. To determine optimal synthesis conditions of K2O2, we present diagrams showing the different oxides as a function of temperature and oxygen pressure from which phase stability characteristics can be determined. From the experimental standpoint, we present results on the synthesis of potassium oxide under ultra high vacuum and controlled temperature. The resulting surface is characterized in situ by means of photoemission spectroscopy (PES) and contact potential difference (CPD) measurements. A work function of 1.35 eV is measured which and the expected efficiency of the corresponding converter is discussed. It is generally assumed that the decrease of the work function in the alkali/oxygen/ silicon system, is attributed to the creation of a surface dipole resulting from a charge transfer between the alkali metal and oxygen.
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