Surface-Based Point Defect Manipulation in Semiconducting Oxides

非技术描述：尽管二氧化钛和氧化锌等陶瓷半导体经常用于消费防晒霜，但它们也有其他重要的应用，如紫外线发射光学设备和气体传感器。对于器件和传感器应用，材料的性能受到规则有序原子结构中缺陷的强烈影响。这些缺陷可以是可移动的，附近的表面可以将它们注入或从固体块体中取出。实验和计算相结合，以考察这种化学是如何受到表面积累过量正电荷或负电荷的固有倾向，以及水等液体的存在的影响。实验需要将二氧化钛或氧化锌暴露在含有按重量特别标记的同位素标记原子的气体或液体中，并随后测量标记在固体中的积累量。计算使用了一系列植根于量子计算的建模技术。该项目为处理应用程序中的缺陷行为提供了丰富的新可能性。在室温附近使用液体尤其令人兴奋，因为与通常使用气体并加热到数百度的传统方法相比，这种方法大大降低了成本，而且材料制造起来也很容易。该项目还为初中生和高中生开发教材。大量本科生研究人员参与了这项研究，并正在开展几项活动，以促进科学和工程中伦理道德的重要性。技术细节：陶瓷半导体表面与体点缺陷(如间隙原子)的反应显示出丰富的化学成分，尽管它有助于调节缺陷类型和浓度，但人们对此知之甚少。实验和计算相结合，以考察这种化学是如何受到表面极性的影响的，表面极性描述了表面积累过量正电荷或负电荷的趋势。该项目还研究了液体增强缺陷从表面注入到块体中。研究包括不同极性和非极性晶体取向的氧化锌以及非极性二氧化钛。实验需要将固体暴露在含有同位素标记原子的气体或液体中，并随后测量标记在固体中的空间分布。对于气态气氛，在氮、硫和氯等外来吸附物质存在的情况下，正在检查氧和钛或锌的间隙原子。对于含水液体，在不同的pH、光刺激强度和溶液添加剂下检查氧间隙缺陷。计算采用了植根于量子计算的数学建模的层次结构，以提供有用的原子论见解。该项目开辟了一个丰富的表面行为新领域，并为操纵缺陷行为以改进光催化剂、紫外线发射器和气体传感器提供了新的手段。

NON-TECHNICAL DESCRIPTION: Although ceramic semiconductors such as titanium dioxide and zinc oxide often find use in consumer sunscreens, they also have other important applications such as ultraviolet-emitting optical devices and gas sensors. For device and sensor applications, the material's performance is strongly influenced by defects in the regularly-ordered atomic structure. These defects can be mobile, and nearby surfaces can inject or withdraw them from the solid bulk. Experiments and computations are being combined to examine how this chemistry is affected by the inherent tendency of the surface to accumulate excess positive or negative charge, and by the presence of liquids such as water. Experiments entail the exposure of titanium dioxide or zinc oxide to a gas or liquid containing isotopically-labeled atoms specially by weight, and subsequent measurement of the buildup of the label within the solid. Computations employ a range of modeling techniques rooted in quantum calculations. The project opens rich new possibilities for manipulating defect behavior in applications. Using liquids near room temperature is especially exciting because of greatly reduced cost and ease of material manufacturing compared to conventional methods that often employ gases and heating to hundreds of degrees. The project also develops educational materials for middle school and high school students. A significant number of undergraduate researchers participate in the research, and several activities to promote the importance of ethics in science and engineering are being pursued. TECHNICAL DETAILS: Reactions of ceramic semiconductor surfaces with bulk point defects such as interstitial atoms exhibit rich chemistry that is poorly understood despite that it helps to regulate defect types and concentrations. Experiments and computations are combined to examine how that chemistry is affected by surface polarity, which describes the tendency of the surface to accumulate excess positive or negative charge. The project also examines liquid-enhanced defect injection from the surface into the bulk. Investigations include zinc oxide of varying polar and nonpolar crystallographic orientations as well as nonpolar titanium dioxide. Experiments entail exposure of the solid to a gas or liquid containing isotopically labeled atoms, and subsequent measurement of the spatial distribution of the label within the solid. For gaseous ambients, interstitial atoms of both oxygen and titanium or zinc are being examined in the presence of foreign adsorbates such as nitrogen, sulfur and chlorine. For aqueous liquids, oxygen interstitial defects are being examined under varying pH, photostimulation intensity and solution additives. Computations employ a hierarchy of mathematical modeling rooted in quantum calculations to provide useful atomistic insights. The project opens a rich new domain of surface behavior, and provides new means for manipulating defect behavior to improve photocatalysts, ultraviolet emitters and gas sensors.