晶面效應影響鍺、砷化鎵基板和鈦酸鍶奈米顆粒電性以及鈦酸鍶奈米顆粒光學與光催化活性研究

Facet-Dependent Electrical Conductivity Behaviors of Ge, GaAs Wafers and SrTiO3 Nanocrystals as well as Optical and Photocatalytic Properties of SrTiO3 Nanocrystals

謝沛倫(Pei-Lun. Hsieh)

指導教授 ： 陳力俊 ； 黃暄益

國立清華大學/工學院/材料科學工程學系/博士(2021年)

摘要

晶面效應在電性、光催化活性和光性質上具有相當顯著的影響，本研究首先在鍺和砷化鎵基板上進行了晶面效應的電性量測實驗。鍺基板的{111}和{112}面與砷化鎵的{111}面分別是具有較好的導電性的晶面。而在同時接觸量測較易導電和較不易導電的晶面時，則得到一不對稱具有整流現象的曲線。使用調整過的能帶結構圖呈現，可說明晶面效應在電性上的影響。
同時製造各式的可變形狀奈米顆粒已成為材料工程中相當重要且引人注目的目標之一。本研究成功的在3小時內從水相溶液中以攝氏70度的低溫析出合成擁有正立方體鈣鈦礦結構的鈦酸鍶奈米立方體顆粒，並可調控約160-290奈米顆粒大小。當溫度提高至攝氏200度並置換溶劑中的乙醇為其他醇類如乙二醇或正己醇時，分別可以合成出鈍邊立方體和{100}面鈍角菱形十二面體。
透過X射線繞射儀和穿透式電子顯微鏡的觀察並以Rietveld精算分析的輔佐計算下，發現了形狀的改變也造成了晶格常數的改變。而在紫外-可見光分析光譜上可發現，立方體形狀的鈦酸鍶顆粒展示了能帶大小會隨顆粒大小而變化，且立方體的吸收峰相較其他有{110}面的顆粒會有更多藍位移的現象。
{100}面鈍角菱形十二面體相較起立方體也在亞甲藍液的染料降解和光催化的水分解產氫兩種實驗上展現出了較高的效率。使用修飾過的能帶圖可以來解釋所觀察到的鈦酸鍶{100}和{110}表面的能帶彎曲的現象，並提出藉由控制表面晶面可成為提升光催化效率的一種有效策略。最後我們進一步利用表面電漿共振效應，合成金與鈦酸鍶的異質結構奈米顆粒來增進光催化產氫效率。在紫外光區段下，在含有乙二醇作為犧牲劑的水溶液中得到了約有25%的效率增長。
另一方面，使用腔體架設四點探針座的掃描式電子顯微鏡，藉由控制自製的鎢探針來接觸奈米顆粒的每個表面來研究觀察鈦酸鍶奈米顆粒的電性質。完美的立方體形狀鈦酸鍶其{100}面表現絕緣體性質，然而鈍角菱形十二面體的{110}面卻表現出相當好的導電性。且當同時接觸量測此鈍角菱形十二面體的{100}和{110}面時可得到一不對稱的I-V曲線圖，顯現出具有電流整流的現象，可以用一調整過的能帶結構圖來說明晶面效應在電性上的影響。

關鍵字

鈦酸鍶 ； 鍺 ； 砷化鎵 ； 晶面 ； 光催化 ； 產氫

並列摘要

Facet-dependent properties of semiconductors have been widely investigated in recent years. In the present research, electrical conductivity measurements were performed on intrinsic Ge and GaAs wafers. The {111} and {112} facets of Ge are highly conductive, while the {111} facet of GaAs also possess great conductivity. Current-rectifying asymmetric I‒V curves were also recorded when contacting a conductive facet and a less conductive facet simultaneously for Ge and GaAs wafers. A modified band diagram is presented to illustrate the concept of facet-dependent electrical conductivity properties.
Formation of semiconductor nanocrystals with tunable shapes is often synthetically challenging, but the particles are highly useful for facet-dependent electrical conductivity, photocatalytic activity, and optical property characterizations to advance our knowledge of semiconductor materials. In this dissertation, SrTiO3, a cubic perovskite oxide, cubes with tunable sizes of 160−290 nm have been synthesized in an aqueous ethanol solution at just 70 ºC for 3 h. Raising the temperature to 200 ºC, and replacing ethanol with various alcohols such as hexanol and ethylene glycol, resulted in the formation of edge-truncated cubes and {100}-truncated rhombic dodecahedra, respectively. X-ray diffraction and transmission electron microscopy characterization, supported by Rietveld refinement analysis, has revealed shape-dependent tuning in the SrTiO3 lattice parameters. The cubes display slight size-related optical band shifts in the UV-vis spectrum, and they show clearly more blue-shifted light absorption than the other particles exposing significant {110} faces.
The {100}-truncated rhombic dodecahedra also show a higher efficiency than cubes at both photodegradation of methylene blue and photocatalyzed hydrogen evolution from water in the presence of methanol. An adjusted band diagram was provided to explain the surface band bending for the {100} and {110} faces of SrTiO3, suggesting surface facet control as a strategy for enhancing photocatalytic activity. Furthermore, we have introduced localized surface plasmon resonance (LSPR) to enhance the photocatalyzed hydrogen evolution efficiency by making Au/SrTiO3 hybrid nanoparticles. Under ultra-violet light, significant increase in hydrogen production rate from 25% ethylene glycol solution was recorded.
To investigate electrical conductivity properties of these shaped-controlled SrTiO3 crystals, we have employed a four-point probe device in a scanning electron microscope chamber and operated tungsten probes to contact the crystal facets. {100} faces of a perfect SrTiO3 cube are insulating, but the {110} faces of a SrTiO3 truncated rhombic dodecahedron are considerably more conductive. And a current-rectifying asymmetric I‒V curves were recorded with electrodes contacting the {100} and {110} faces of a SrTiO3 {100}-truncated rhombic dodecahedron. A modified band diagram is presented to understand the observed facet-dependent electrical conductivity properties.

並列關鍵字

SrTiO3 ； Ge ； GaAs ； Facet ； Photocatalytic ； Hydrogen

參考文獻

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