生理盐水在经济上得到了日本促进科学促进会 (KAKENHI) 资助的资助 (26810126 号赠款)。黄感谢 Deanship 的科学研究, 通过科研椅副 Deanship 创建。
在纳米加工设备上进行了广角 XRD 测量, 由日本国家高级工业科学技术研究院 (AIST) (IBEC) 创新平台共同提供支持。堀场技术服务有限公司和日本材料科学技术促进基金会 (MST) 分别进行了多孔薄膜的拉曼光谱测量和透射电镜观察。MST 还对透射电镜图像中的应变进行了可视化。我们感谢 Edanz 集团 (www.edanzediting.com/ac) 博士的安德鲁. 杰克逊编辑这篇手稿的草稿。

1. 前体溶液的制备
<ol><li>溶出50毫克的两嵌段共聚物 PS (18000)-b-聚氧乙烯 (7500) 在1.5 毫升的四氢呋喃在40°c。冷却聚合物溶液室温 (RT)。</li>
	<li>将127.7 毫克醋酸钡溶于830µL 乙酸, 搅拌40摄氏度, 5 分钟. 将醋酸钡溶液冷却到 RT 中. 添加170毫克钛丁醇到醋酸钡溶液中, 搅拌反应混合物1分钟。</li>
	<li>将聚合物溶液加入醋酸钡溶液滴状。</li>
</ol>2. 介孔钛酸钡薄膜的合成
<ol><li>在自旋涂布机的舞台上设置 Si/x 型 x-/Ti/铂基板 (2 厘米 x 2 厘米), 并将准备好的前体溶液放在完全覆盖基体上。 注:x、Ti 和 Pt 层的薄膜厚度分别约为1.6、40和 150 nm。</li>
	<li>以 500 rpm 为5秒 (第一步), 然后依次为三十年代 (第二步) 的 3000 rpm 旋转 Si/正向x/Ti/Pt 衬底。</li>
	<li>将准备好的薄膜放在热板上, 加热到120摄氏度, 使其老化5分钟, 然后让它自然冷却室温 (RT)。</li>
	<li>将退火后的薄膜放在消音器炉内, 在空气中煅烧800摄氏度, 10 分钟, 斜坡速度为1摄氏度/分钟 (用于加热和冷却)。</li>
</ol>3. 表征
<ol><li>形态学和晶体表征
	<ol>
<li>
扫描电镜 (SEM) 测量
		<ol>
<li>把样品放在样品台上, 用碳胶带覆盖边角以修复样品。调整样品持有者的高度。</li>
			<li>将样品持有者设置在装货杆中, 并将其插入扫描电镜. 将样品持有者放置在工作距离为8毫米的家庭位置。</li>
			<li>将加速电压和发射电流设置为5伏和10毫安, 并生成电子束。在低放大率下显示示例的整个图像。移动舞台以显示感兴趣的区域 (ROI), 并将焦点放在图像上。</li>
			<li>将放大倍数提高到50,000X。关注毛孔, 观察多孔形态。当观察到合适的图像时, 保存图片。</li>
		</ol>
</li>
		<li>
透射电镜 (TEM) 测量
		<ol>
<li>按照步骤3.3.1 中的描述, 在 TEM 测量之前准备一个截面试样。</li>
			<li>在样品架上设置准备好的标本。将加速电压设置为300伏并生成电子束。将持有者插入 TEM。</li>
			<li>在低放大率下显示示例的整个图像。移动舞台以显示 ROI 并聚焦于图像。</li>
			<li>将放大倍数提高到250,000X。着重于样品, 观察合成薄膜的多孔形貌 (~200 纳米厚度)。当观察到合适的图像时, 保存图片。</li>
		</ol>
</li>
		<li>
广角 X 射线衍射 (XRD) 测量
		<ol>
<li>设置装有铜 Kα源的 x 射线衍射仪。</li>
			<li>把样品放在样品台上的中心。</li>
			<li>调整示例在其中阻止 X 射线的一半的 Z 轴 (i. e, 高度位置)。然后, 调整ω轴 (i. e, 放牧角度), 使样品表面平行于 X 射线。</li>
			<li>重复步骤 3.1.3.3, 直到采样阶段位置变得合适 (i. e), 样品表面位于 x 射线光束的中心, 并与 x 射线平行。</li>
			<li>将ω固定到一个小角度 (e. g, 0.5°), 然后将 2θ (i. e, 探测器角度) 从扫描到 70°, 其速率为 1°/分钟. 在测量后保存数据。 注: 为了抑制衬底上的背景信号, 在一个非常小的掠角照射到合成薄膜的表面时, 进入的 X 射线被辐照。</li>
		</ol>
</li>
	</ol></li>
	<li>铁电相热稳定性试验
	<ol>
<li>打开拉曼显微镜和操作计算机, 然后打开操作软件 LabSpec。单击自动校准以校准计算机。</li>
		<li>在加热阶段设置玻璃滑块, 然后将合成膜放在玻璃上。关闭舞台的封面。</li>
		<li>使用15°c/分钟的坡道比加热阶段来加热样品。当温度达到目标温度时, 设置加热阶段以保持温度, 等待几分钟。 注: 在本研究中, 我们选择了 RT 和 50, 75, 100, 110, 120, 125, 130, 135, 140, 和150°c 为散装 BT, 其中居里温度约130°c。我们选择了 RT 的温度和 75, 125, 175, 225, 275, 325, 375, 425, 475, 和525摄氏度为介孔 BT 薄膜, 居里温度被评估是大约470°c 从早先研究8。</li>
		<li>在温度稳定后, 用共焦拉曼显微镜测量不同温度下的拉曼光谱, 使用300µm 共焦孔和 532 nm 激光器 (样品10兆瓦) 进行励磁。单击视频图标以显示所观察到的图像, 然后将焦点放在图像上。分别将采集时间和累计设置为100s 和 3, 然后单击度量图标以开始测量。在测量后保存数据。</li>
		<li>继续测量直到频谱发生变化 (i. e, 可分配到铁电相的峰值消失)。 注: 测量值为三点, 得到的光谱平均值。</li>
	</ol></li>
	<li>应变的可视化
	<ol>
<li>用聚焦离子束对外周铣、底、微桥切割、试样细化等微抽样方法制备出合成薄膜中的横断面试样。试样的尺寸应约为20µm 长度和4µm 的厚度。</li>
		<li>测量高分辨率透射电镜 (2,000,000X) 在凸和凹面引起的孔隙度。</li>
		<li>选择一个面积 (512 x 512 像素) 的快速傅立叶变换 (fft), 并计算 fft 模式。从 FFT 模式估计晶格间距, 并将其除以无应变晶格间距, 计算出 "变形比"。</li>
		<li>将 FFT 分析区域移动32像素, 然后重复步骤3.3.3。继续这个过程, 直到所有的 HR-TEM 图像覆盖面积 (在本研究中, 5664 x 5664 像素 (162 x 162 点))。 注: 从最小失真的 FFT 图像估计无应变晶格间距。</li>
		<li>根据计算的变形比设置区域的颜色, 以可视化应变。通过计算变形比来制作直方图。 注: 通过软件 CryStMapp, 对 HR 图像的变形进行了分析。</li>
		<li>
创建一个详细的直方图使用软件伊戈尔 Pro 注: 由于步骤3.3.5 中获得的失真直方图是粗糙的, 因此创建了一个使用软件伊戈尔 Pro 的详细直方图。<ol>
<li>通过选择数据 |装载波浪 |加载常规文本并将其另存为波形且名称正确。 注意: 伊戈尔 Pro 定义的对象, 包括一个数字数组作为一个波。</li>
			<li>通过选择数据 | 将保存的波形更改为矩阵 (162 x 162) 更改波形缩放。</li>
			<li>通过选择图像 | 将波形显示为2D 图像|新 |图像端口。</li>
			<li>选择分析 |包装 |图像处理以显示图像菜单。</li>
			<li>选择图像 |roi显示 roi 面板。选择启动 roi 绘制以选择 roi。在图像的顶部绘制区域, 然后选择完成 ROI。</li>
			<li>选择保存 ROI 副本以创建掩码以选择要作为 ROI_M_Mask 波形分析的区域。</li>
			<li>在命令窗口的命令行中输入 "ImageHistogram = M_ROIMASK/秒waveneame" 以制作直方图。在 wavename 中使用步骤3.3.6.1 中设置的名称。</li>
			<li>在命令窗口的命令行中输入 "显示 W_ImageHist" 以显示直方图。如果需要, 修改图表。</li>
		</ol>
</li>
	</ol></li>
</ol>

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作者没有什么可透露的。

在多孔 BT 薄膜 (图 3b) 的拉曼光谱中, A1(to) 模式的分裂来源于压缩应变。FFTM 方法 (图 4) 清楚地观察到了这个特性, 并且它在 [1-10] 方向上的各向异性都是从失真的直方图 (图 5) 中确定的。沿 [1-10] 方向的压缩应变与诱导 (001) 表面的双向压缩应变具有相似的效果, 增强了 BT1中的铁电性。多孔驱动的各向异性应变拉长晶格向c轴的方向, 导致 Ti4 +的进一步错位从晶格中心。这种位错预计会增加电偶极矩, 进而增强其铁 (压电) 电流。事实上, 介孔 BT 薄膜的压电性优于非多孔膜8。
在 BT 晶格中诱导的应变稳定了畸变的四方相。因此, 晶格的热稳定性有望得到增强。多孔 BT 薄膜的拉曼光谱表明, 四方相起源峰 (在710厘米−1) 保持可见, 直到375摄氏度, 虽然峰值逐渐变弱和更宽 (图 6b)。这种趋势类似于以前的研究中发现的情况, 其中Tc估计为470°c8。因此, 我们证实了在 BT 薄膜中的孔隙驱动应变有效地热稳定四方相的假设。
通过这项研究, 我们澄清了由一个简单而廉价的化学程序形成的孔隙诱导应变与由晶格不匹配引起的异质界面的应变有相似的影响。这些发现为应变工程提供了新的见解。

钛酸钡 (BaTiO3, 此后 BT) 是典型的钙钛矿型铁电材料。尽管其铁电性质在二十世纪四十年代被发现, 但由于其良好的铁电和压电反应以及良好的介电常数, 至今仍被广泛应用。此外, 由于 BT 是一种无铅, 环保的材料, 它已吸引了极大的兴趣, 以取代锆钛酸铅 (PZT)。在室温下, BT 的晶体相位为四方, 其中c和晶格参数 ( c/a) 的比率不等于1。在四方阶段, BT 晶格稍微拉长向c轴和阳离子 (Ba2 +, Ti4 +) 和阴离子 (O2−) 在相反方向偏移。这种位移导致 BT 的自发极化. 当温度上升到居里温度 (Tc) 时, 会发生相变到立方相。在 BT 的立方相, 它有c/a = 1, 晶格畸变是宽松的, 并且它的铁电性丢失由于电子中立地位起源于晶格的反演对称。近年来, 高温铁电材料的使用已经扩大。但是, bt 的Tc相对较低 (~130 °c), 而大宗 bt 不满足这些要求。
为了增加 BT 的Tc , 铁电 (四方) 相通过在异质界面上的应变的应用而得到稳定。例如, 崔et增强了外延定向生长在GdScO 3 (110) 和DyScO 3 (110) 基板上生长的 BT 薄膜的铁电性, 通过使用晶格不匹配1引起的双轴压缩应变。但是, Tc的增加仅限于非常薄的薄膜 (十纳米厚)2,3, 这对于设备应用程序来说是不切实际的。
为了提高 BT 膜厚度, 同时防止应变松弛, 开发了超晶格 (非常薄层的周期结构) 和三维 (3D) 的异纳米构造。哈林顿et合成了 BT 和 Sm2O3的垂直细观结构, 并获得了一微米级有序厚膜, 不需要应变松弛。在本例中, 由于 BT 单元细胞的单轴扩张, 自发极化取向与基底垂直;因此, 在高温下保持了大量的残余极化 (i. e, Tc大于800°c)4。所得性能满意;然而, 制造过程中需要一个复杂而昂贵的物理流程 (脉冲激光沉积), 这是实际应用的一个缺点。
作为一种替代性的简便和廉价的制造工艺, 我们提出了3D 纳米复合材料的化学合成, 通过引入一个前体溶液的 BT 成孔隙的多孔钛酸锶 (SrTiO3, 此后 ST) 薄膜5.本研究采用表面活性剂辅助溶胶-凝胶法制备了多孔 ST 薄膜, 其中双亲表面活性剂胶束自组装为有机模板6,7。该方法在图 1中以示意图的方式说明。由于所获得的 ST 薄膜具有复杂的3D 多孔结构, 具有较大的表面积, 因此将 bt/ST 异质界面上的应变引入到纳米复合材料中, 从而导致 bt 铁电相位的稳定化 ( Tc ST/BT 纳米复合材料达到230摄氏度)。
假设孔隙度可以直接引入 BT 的应变, 提高铁电性质的热稳定性。本研究采用表面活性剂辅助溶胶-凝胶法制备多孔 BT 材料, 并对孔隙诱导菌株进行检查。此外, 我们还比较了多孔 bt 和型无孔散 bt 的热稳定性. 我们发现, 引入的孔隙诱导了各向异性的应变, 延长了 bt 晶格。这种效应可能有利于稳定铁电相。因为这里使用的合成过程非常简单, 它比传统的物理过程对3D 异质纳米结构有优势。

<table><tbody><tr><td>Diblock Copolymer PS(18000)-&lt;em&gt;b&lt;/em&gt;-PEO(7500)</td><td>Polymer Source, Inc.</td><td>#8399-SEO</td><td></td></tr><tr><td>Acetic acid (37 wt.%)</td><td>Wako</td><td>017-00256</td><td></td></tr><tr><td>Tetrahydrofuran</td><td>Wako</td><td>204-08745</td><td></td></tr><tr><td>Barium acetate</td><td>Sigma-Aldrich</td><td>243671-100G</td><td></td></tr><tr><td>Titanium(IV) butoxide</td><td>Sigma-Aldrich</td><td>244112-100G</td><td></td></tr><tr><td>Reference bulk BT single crystal</td><td>Crystal Base Co., Ltd.</td><td></td><td></td></tr><tr><td>Balance</td><td>Sartorius</td><td></td><td></td></tr><tr><td>Hot stirrer</td><td>IKA</td><td>RCT basic</td><td></td></tr><tr><td>Spin coater</td><td>Active</td><td>ACT-300DII</td><td></td></tr><tr><td>Hot plate</td><td>As one</td><td>ND-1</td><td></td></tr><tr><td>Muffle Furnace</td><td>Yamato Scientific Co., Ltd.</td><td>FO series</td><td></td></tr><tr><td>Scanning electron microscopy</td><td>Hitachi</td><td>SU-8000</td><td></td></tr><tr><td>Transmission electron microscopy</td><td>Hitachi</td><td>H-9000NAR</td><td></td></tr><tr><td>Wide-angle X-ray diffraction</td><td>Rigaku</td><td>RINT-Ultima III</td><td></td></tr><tr><td>Raman microscope</td><td>Horiba</td><td>XploRA Plus</td><td></td></tr></tbody></table>

chemical synthesis of porous barium titanate thin film and thermal stabilization of ferroelectric phase by porosity-induced strain

钛酸钡 (BaTiO3, 此后 BT) 是二十世纪四十年代首次发现的铁电材料, 由于其平衡的铁电性、压电和介电常数, 它仍然被广泛使用。此外, BT 不含任何有毒成分。因此, 它被认为是一种生态友好的材料, 这已引起了相当大的兴趣作为替代锆钛酸铅 (PZT)。然而, 散装 BT 丢失它的铁电性在大约130°c, 因此, 它不可能在高温使用。由于对高温铁电材料的需求量越来越大, 提高铁电性在 BT 中的热稳定性具有重要的意义. 在前人研究中, 采用了基于异质界面晶格失配的应变。然而, 这种方法的样品准备需要复杂而昂贵的物理过程, 这是不可取的实际应用。
在本研究中, 我们提出了一种化学合成的多孔材料作为一种替代方法引入应变。采用表面活性剂辅助溶胶-凝胶法制备了多孔 BT 薄膜, 采用自组装双亲表面活性剂胶束作为有机模板。通过一系列的研究, 我们阐明了孔隙的引入对 BT 晶格的畸变具有类似的作用, 对异质界面的影响, 导致了铁电性的增强和稳定。由于其简单性和成本效益, 这一制造过程比传统方法有相当大的优势。

用电子显微镜对所获得的介孔 BT 薄膜的形貌进行了研究。一个顶级的 SEM 图像证实了合成 BT 薄膜的多孔特性 (图 2a)。用横断面 TEM 图像 (图 2b) 研究了深度方向的形态学特征。直径为几纳米的大晶粒垂直堆积, 这些晶粒之间的空隙是孔隙。估计的 BT 薄膜厚度约为200纳米。
采用广角 XRD 测量方法研究了 BT 骨架的结晶度。BaCO3和2的非常微弱的峰值是可检测的, 并清楚地观察到了可以分配给 BT 晶体的突出峰值 (图 3a)。然而, 很难区分 (铁电) 四方和 (顺电) 立方相。这是因为两个阶段的 XRD 模式相当相似。主要区别在于, 三次相的2个θ = 45°的峰值为四方相分裂。在这项研究中, 由于薄膜的多晶性质拓宽了峰值宽度, 所以这种分裂的检测是困难的。因此, 为了澄清薄膜的晶相, 测量了其拉曼光谱 (图 3b)。在室温下, 大体积单 BT 晶体的拉曼光谱显示峰中心为 275, 305、515和 720 cm−1, 它被分配给a1(to), B1+e(到 + LO), e(到) +a1(to) 和E(lo) +A1(四方) 模式, 该阶段9。在多孔 BT 薄膜的频谱中, 尽管发生了A1(to) 模式的分裂, 但频谱的主要特征仍然保留。从而四方了合成多孔 BT 薄膜。
用快速傅里叶变换映射 (FFTM) 方法10检验了薄膜 BT 框架中应变的空间分布。该方法对高分辨率 (HR) TEM 图像 FFT 模式的微小畸变进行了分析和可视化。图 4描述了具有凸和凹面的薄膜区域的 HR TEM 图像以及相应的 FFTM 图像。凸区 [1-10] 方向的 FFTM 图像表明, 最外层凸面略有扩张, 这一安排应引起晶格松弛, 减弱铁电性。相反, 在表面下方的区域被压缩, 并且压缩的区域在框架之内完全地被观察了。这一结果与以前的报告一致, 表明 BT 纳米粒子的表面具有顺电立方相, 而内芯是铁电四方相 11, 12.在 BT 框架内, 还发现了一些扩展的区域, 主要是在缺陷和/或晶界 (图 4c) 中。对于凹区, 虽然最外层表面的变形没有被清楚地观察到, 很可能是因为曲面是多边形而不是弯曲的, 所以检测到框架内的压缩 (图 4d)。相反, 凸和凹区域的 [11-1] 方向的 FFTM 图像不清楚 (图 4e, f), 这表明 BT 单元细胞在这个方向上的变形不大。
为了更定量地考察 BT 晶格的变形程度, 在直方图 (图 5) 中总结了变形度。从这些直方图中, 我们确定了 "变形比", 它被定义为在目标和参照区域中相邻晶格间距之间的距离, 作为变形的度量。在 [11-1] 方向上, 直方图以1.00 的变形比为中心, 在凸和凹区域上几乎是对称的。这一结果表明, [11-1] 方向的应变很少, 与上面提到的 FFTM 结果一致。反之, [1-10] 方向的直方图中包含有显著的峰值, 变形率约为 0.99, 显示了 BT 薄膜中压缩应变增加的区域。
从温度依赖性的拉曼光谱 (图 6) 考察了铁电四方相的热稳定性。在大容量 bt 单晶中, 305 和720厘米−1的尖峰消失在140摄氏度, 这与大容量 bt (~ 130 °c) 的TC 一致。反之, 在710厘米−1从四方阶段的峰值保持在更高的温度, 可检测到高达375摄氏度的合成多孔薄膜。
<img alt="Figure 1" class="xfigimg" src="/files/ftp_upload/57441/57441fig1.jpg"> 图 1: 表面活性剂辅助溶胶-凝胶法的示意图图象.采用双亲表面活性剂胶束自组装为模板。结合有机模板和无机溶胶, 建立了有机/无机混合体。最后, 通过去除有机模板, 结晶无机骨架, 进行煅烧, 形成孔隙。<a href="https://cloudflare.jove.com/files/ftp_upload/57441/57441fig1large.jpg" target="_blank">请单击此处查看此图的较大版本.</a>
<img alt="Figure 2" class="xfigimg" src="/files/ftp_upload/57441/57441fig2v3.jpg"> 图 2: 介孔 BT 薄膜的电子显微镜图像.(a) 顶部查看 SEM 和 (b) 横断面 TEM 图像。这一数字已从铃木, N.等等中修改。13按照 "创作共享" 属性 (CC) 许可证进行。<a href="https://cloudflare.jove.com/files/ftp_upload/57441/57441fig2v3large.jpg" target="_blank">请单击此处查看此图的较大版本.</a>
<img alt="Figure 3" class="xfigimg" src="/files/ftp_upload/57441/57441fig3.jpg"> 图 3: 介孔 BT 薄膜晶体相的光谱数据.(a) 宽角度 XRD 模式和 (b) 在室温下合成的多孔 BT 薄膜的拉曼光谱。同时还包括了大量 BT 单晶的光谱。这一数字已从铃木, N.等等中修改。13按照 "创作共享" 属性 (CC) 许可证进行。<a href="https://cloudflare.jove.com/files/ftp_upload/57441/57441fig3large.jpg" target="_blank">请单击此处查看此图的较大版本.</a>
<img alt="Figure 4" class="xfigimg" src="/files/ftp_upload/57441/57441fig4v2.jpg"> 图 4: 孔隙诱导应变的可视化.(a, b)高分辨率 TEM 图像和 (c f) 快速傅立叶变换映射 (FFTM) 图像 (a、c、e) 凸和 (b、d、f) 的 BT 薄膜凹区。FFTM 图像的方向为 (c、d) [1-10] 和 (e、f) [11-1]。在 FFTM 图像中, 绿色和红色区域代表分别应用压缩和拉伸应变的区域, 而黄色表示参照区域。用于分析的方向也包括 (左)。这一数字已从铃木, N.等等中修改。13按照 "创作共享" 属性 (CC) 许可证进行。<a href="https://cloudflare.jove.com/files/ftp_upload/57441/57441fig4v2large.jpg" target="_blank">请单击此处查看此图的较大版本.</a>
<img alt="Figure 5" class="xfigimg" src="/files/ftp_upload/57441/57441fig5.jpg"> 图 5: 孔隙诱导应变的分析.失真直方图分析 (a) 凸 (图 4a,图 4c,图 4e) 和 (b) 凹 (图 4b,图 4d,图 4f) 多孔 BT 薄膜的区域. 此数字已根据 "创作共享" 归属 (CC) 许可证, 从铃木、N. et . 13 修改。<a href="https://cloudflare.jove.com/files/ftp_upload/57441/57441fig5large.jpg" target="_blank">请单击此处查看此图的较大版本.</a>
<img alt="Figure 6" class="xfigimg" src="/files/ftp_upload/57441/57441fig6.jpg"> 图 6: 铁电相的热稳定性.温度依赖性的拉曼光谱 (a) 的大容量 bt 单晶和 (b) 合成多孔 bt 薄膜。这一数字已从铃木, N.等等中修改。13根据 "创作共享" 属性 (CC) 许可证.  <a href="https://cloudflare.jove.com/files/ftp_upload/57441/57441fig6large.jpg" target="_blank">请单击此处查看此图的较大版本.</a>

Watch this Scientific Journal Video about Chemical Synthesis of Porous Barium Titanate Thin Film and Thermal Stabilization of Ferroelectric Phase by Porosity-Induced Strain at JoVE.com

Chemical Synthesis of Porous Barium Titanate Thin Film and Thermal Stabilization of Ferroelectric Phase by Porosity-Induced Strain

在这里, 我们提出了一个通过表面活性剂辅助溶胶-凝胶法合成多孔钛酸钡 (BaTiO3) 薄膜的协议, 其中自组装双亲表面活性剂胶束用作有机模板。

孔隙诱导应变法合成多孔钛酸钡薄膜及铁电相热稳定性

Barium titanate (BaTiO3, hereafter BT) is an established ferroelectric material first discovered in the 1940s and still widely used because of its ...

chemical-synthesis-porous-barium-titanate-thin-film-thermal

Research

JoVE Journal

Chemistry

11.0K 次观看.  Tokyo University of Science (TUS). 在这里, 我们提出了一个通过表面活性剂辅助溶胶-凝胶法合成多孔钛酸钡 (BaTiO3) 薄膜的协议, 其中自组装双亲表面活性剂胶束用作有机模板。

视频: Chemical Synthesis of Porous Barium Titanate Thin Film and Thermal Stabilization of Ferroelectric Phase by Porosity-Induced Strain

Fabrication of Spatially Confined Complex Oxides

Complex materials such as high Tc superconductors, multiferroics, and colossal magnetoresistors have electronic and magnetic properties that arise from the inherent strong electron correlations that reside within them. These materials can also possess electronic phase separation in which regions of vastly different resistive and magnetic behavior can coexist within a single crystal alloy material. By reducing the scale of these materials to length scales at and below the inherent size of the electronic domains, novel behaviors can be exposed. Because of this and the fact that spin-charge-lattice-orbital order parameters each involve correlation lengths, spatially reducing these materials for transport measurements is a critical step in understanding the fundamental physics that drives complex behaviors. These materials also offer great potential to become the next generation of electronic devices 1-3. Thus, the fabrication of low dimensional nano- or micro-structures is extremely important to achieve new functionality. This involves multiple controllable processes from high quality thin film growth to accurate electronic property characterization. Here, we present fabrication protocols of high quality microstructures for complex oxide manganite devices. Detailed descriptions and required equipment of thin film growth, photo-lithography, and wire-bonding are presented.

We describe the use of pulsed laser deposition (PLD), photolithography and wire-bonding techniques to create micrometer scale complex oxides devices. The PLD is utilized to grow epitaxial thin films. Photolithography and wire-bonding techniques are introduced to create practical devices for measurement purposes.

空间密闭的复合氧化物制备

Complex materials such as high Tc superconductors, multiferroics, and colossal magnetoresistors have electronic and magnetic properties that arise from ...

科研

工程学

Synthesis of Non-uniformly Pr-doped SrTiO3 Ceramics and Their Thermoelectric Properties

We demonstrate a novel synthesis strategy for the preparation of Pr-doped SrTiO3 ceramics via a combination of solid state reaction and spark plasma sintering techniques. Polycrystalline ceramics possessing a unique morphology can be achieved by optimizing the process parameters, particularly spark plasma sintering heating rate. The phase and morphology of the synthesized ceramics were investigated in detail using X-ray diffraction, scanning electron microcopy and energy-dispersive X-ray spectroscopy. It was observed that the grains of these bulk Pr-doped SrTiO3 ceramics were enhanced with Pr-rich grain boundaries. Electronic and thermal transport properties were also investigated as a function of temperature and doping concentration. Such a microstructure was found to give rise to improved thermoelectric properties. Specifically, it resulted in a significant improvement in carrier mobility and the thermoelectric power factor. Simultaneously, it also led to a marked reduction in the thermal conductivity. As a result, a significant improvement (> 30%) in the thermoelectric figure of merit was achieved for the whole temperature range over all previously reported maximum values for SrTiO3-based ceramics. This synthesis demonstrates the steps for the preparation of bulk polycrystalline ceramics of non-uniformly Pr-doped SrTiO3.

Synthesis of Non-uniformly Pr-doped SrTiO3 Ceramics and Their Thermoelectric Properties

A protocol for the synthesis and processing of polycrystalline SrTiO3 ceramics doped non-uniformly with Pr is presented along with the investigation of their thermoelectric properties.

非均匀掺Pr的SrTiO的合成<sub&gt; 3</sub&gt;陶瓷及其热电性能

We demonstrate a novel synthesis strategy for the preparation of Pr-doped SrTiO3 ceramics via a combination of solid state reaction and spark plasma ...

化学

Preparation of Macroporous Epitaxial Quartz Films on Silicon by Chemical Solution Deposition

This work describes the detailed protocol for preparing piezoelectric macroporous epitaxial quartz films on silicon(100) substrates. This is a three-step process based on the preparation of a sol in a one-pot synthesis which is followed by the deposition of a gel film on Si(100) substrates by evaporation induced self-assembly using the dip-coating technique and ends with a thermal treatment of the material to induce the gel crystallization and the growth of the quartz film. The formation of a silica gel is based on the reaction of a tetraethyl orthosilicate and water, catalyzed by HCl, in ethanol. However, the solution contains two additional components that are essential for preparing mesoporous epitaxial quartz films from these silica gels dip-coated on Si. Alkaline earth ions, like Sr2+ act as glass melting agents that facilitate the crystallization of silica and in combination with cetyl trimethylammonium bromide (CTAB) amphiphilic template form a phase separation responsible of the macroporosity of the films. The good matching between the quartz and silicon cell parameters is also essential in the stabilization of quartz over other SiO2 polymorphs and is at the origin of the epitaxial growth.

A protocol is presented for the preparation of piezoelectric macroporous epitaxial films of quartz on silicon by solution chemistry using dip-coating and thermal treatments in air.

化学溶液沉积在硅外延大孔石英薄膜的制备

This work describes the detailed protocol for preparing piezoelectric macroporous epitaxial quartz films on silicon(100) substrates. This is a three-step ...

Epitaxial Growth of Perovskite Strontium Titanate on Germanium via Atomic Layer Deposition

Atomic layer deposition (ALD) is a commercially utilized deposition method for electronic materials. ALD growth of thin films offers thickness control and conformality by taking advantage of self-limiting reactions between vapor-phase precursors and the growing film. Perovskite oxides present potential for next-generation electronic materials, but to-date have mostly been deposited by physical methods. This work outlines a method for depositing SrTiO3 (STO) on germanium using ALD. Germanium has higher carrier mobilities than silicon and therefore offers an alternative semiconductor material with faster device operation. This method takes advantage of the instability of germanium's native oxide by using thermal deoxidation to clean and reconstruct the Ge (001) surface to the 2&#215;1 structure. 2-nm thick, amorphous STO is then deposited by ALD. The STO film is annealed under ultra-high vacuum and crystallizes on the reconstructed Ge surface. Reflection high-energy electron diffraction (RHEED) is used during this annealing step to monitor the STO crystallization. The thin, crystalline layer of STO acts as a template for subsequent growth of STO that is crystalline as-grown, as confirmed by RHEED. In situ X-ray photoelectron spectroscopy is used to verify film stoichiometry before and after the annealing step, as well as after subsequent STO growth. This procedure provides framework for additional perovskite oxides to be deposited on semiconductors via chemical methods in addition to the integration of more sophisticated heterostructures already achievable by physical methods.

This work details the procedures for the growth and characterization of crystalline SrTiO3 directly on germanium substrates by atomic layer deposition. The procedure illustrates the ability of an all-chemical growth method to integrate oxides monolithically onto semiconductors for metal-oxide semiconductor devices.

锗通过原子层沉积钙钛矿型钛酸锶的外延生长

Atomic layer deposition (ALD) is a commercially utilized deposition method for electronic materials. ALD growth of thin films offers thickness control and ...

Spark Plasma Sintering Apparatus Used for the Formation of Strontium Titanate Bicrystals

A spark plasma sintering apparatus was used as a novel method for diffusion bonding of two single crystals of strontium titanate to form bicrystals with one twist grain boundary. This apparatus utilizes high uniaxial pressure and a pulsed direct current for rapid consolidation of material. Diffusion bonding of strontium titanate bicrystals without fracture, in a spark plasma sintering apparatus, is possible at high pressures due to the unusual temperature dependent plasticity behavior of strontium titanate. We demonstrate a method for the successful formation of bicrystals at accelerated time scales and lower temperatures in a spark plasma sintering apparatus compared to bicrystals formed by conventional diffusion bonding parameters. Bond quality was verified by scanning electron microscopy. A clean and atomically abrupt interface containing no secondary phases was observed using transmission electron microscopy techniques. Local changes in bonding across the boundary was characterized by simultaneous scanning transmission electron microscopy and spatially resolved electron energy-loss spectroscopy.

A viable technique for the formation of strontium titanate bicrystals at high pressure and fast heating rate via the spark plasma sintering apparatus is developed.

放电等离子烧结设备中使用的钛酸锶双晶体的形成

A spark plasma sintering apparatus was used as a novel method for diffusion bonding of two single crystals of strontium titanate to form bicrystals with ...

A Fabrication and Measurement Method for a Flexible Ferroelectric Element Based on Van Der Waals Heteroepitaxy

Flexible non-volatile memories have received much attention as they are applicable for portable smart electronic device in the future, relying on high-density data storage and low-power consumption capabilities. However, the high-quality oxide based nonvolatile memory on flexible substrates is often constrained by the material characteristics and the inevitable high-temperature fabrication process. In this paper, a protocol is proposed to directly grow an epitaxial yet flexible lead zirconium titanate memory element on muscovite mica. The versatile deposition technique and measurement method enable the fabrication of flexible yet single-crystalline non-volatile memory elements necessary for the next generation of smart devices.

In this paper, we present a protocol to directly grow an epitaxial yet flexible lead zirconium titanate memory element on muscovite mica.

基于范德华 Heteroepitaxy 的柔性铁电元件制备及测量方法

Flexible non-volatile memories have received much attention as they are applicable for portable smart electronic device in the future, relying on ...

Bulk and Thin Film Synthesis of Compositionally Variant Entropy-stabilized Oxides

Here, we present a procedure for the synthesis of bulk and thin film multicomponent (Mg0.25(1-x)CoxNi0.25(1-x)Cu0.25(1-x)Zn0.25(1-x))O (Co variant) and (Mg0.25(1-x)Co0.25(1-x)Ni0.25(1-x)CuxZn0.25(1-x))O (Cu variant) entropy-stabilized oxides. Phase pure and chemically homogeneous (Mg0.25(1-x)CoxNi0.25(1-x)Cu0.25(1-x)Zn0.25(1-x))O (x = 0.20, 0.27, 0.33) and (Mg0.25(1-x)Co0.25(1-x)Ni0.25(1-x)CuxZn0.25(1-x))O (x = 0.11, 0.27) ceramic pellets are synthesized and used in the deposition of ultra-high quality, phase pure, single crystalline thin films of the target stoichiometry. A detailed methodology for the deposition of smooth, chemically homogeneous, entropy-stabilized oxide thin films by pulsed laser deposition on (001)-oriented MgO substrates is described. The phase and crystallinity of bulk and thin film materials are confirmed using X-ray diffraction. Composition and chemical homogeneity are confirmed by X-ray photoelectron spectroscopy and energy dispersive X-ray spectroscopy. The surface topography of thin films is measured with scanning probe microscopy. The synthesis of high quality, single crystalline, entropy-stabilized oxide thin films enables the study of interface, size, strain, and disorder effects on the properties in this new class of highly disordered oxide materials.

The synthesis of high quality bulk and thin film (Mg0.25(1-x)CoxNi0.25(1-x)Cu0.25(1-x)Zn0.25(1-x))O and (Mg0.25(1-x)Co0.25(1-x)Ni0.25(1-x)CuxZn0.25(1-x))O entropy-stabilized oxides is presented.

组分变熵稳定氧化物的体积和薄膜合成

Here, we present a procedure for the synthesis of bulk and thin film multicomponent (Mg0.25(1-x)CoxNi0.25(1-x)Cu0.25(1-x)Zn0.25(1-x))O (Co variant) and ...

Fabrication of Mechanically Tunable and Bioactive Metal Scaffolds for Biomedical Applications

Biometal systems have been widely used for biomedical applications, in particular, as load-bearing materials. However, major challenges are high stiffness and low bioactivity of metals. In this study, we have developed a new method towards fabricating a new type of bioactive and mechanically reliable porous metal scaffolds-densified porous Ti scaffolds. The method consists of two fabrication processes, 1) the fabrication of porous Ti scaffolds by dynamic freeze casting, and 2) coating and densification of the porous scaffolds. The dynamic freeze casting method to fabricate porous Ti scaffolds allowed the densification of porous scaffolds by minimizing the chemical contamination and structural defects. The densification process is distinctive for three reasons. First, the densification process is simple, because it requires a control of only one parameter (degree of densification). Second, it is effective, as it achieves mechanical enhancement and sustainable release of biomolecules from porous scaffolds. Third, it has broad applications, as it is also applicable to the fabrication of functionally graded porous scaffolds by spatially varied strain during densification.

Bioactive and mechanically reliable metal scaffolds have been fabricated through a method which consists of two processes, dynamic freeze casting for the fabrication of porous Ti, and coating and densification of the Ti scaffolds. The densification process is simple, effective and applicable to the fabrication of functionally graded scaffolds.

加工机械可调和生物活性金属支架的生物医学应用

Biometal systems have been widely used for biomedical applications, in particular, as load-bearing materials. However, major challenges are high stiffness ...

生物工程

Visualizing Uniaxial-strain Manipulation of Antiferromagnetic Domains in Fe1+YTe Using a Spin-polarized Scanning Tunneling Microscope

The quest to understand correlated electronic systems has pushed the frontiers of experimental measurements toward the development of new experimental techniques and methodologies. Here we use a novel home-built uniaxial-strain device integrated into our variable temperature scanning tunneling microscope that enables us to controllably manipulate in-plane uniaxial strain in samples and probe their electronic response at the atomic scale. Using scanning tunneling microscopy (STM) with spin-polarization techniques, we visualize antiferromagnetic (AFM) domains and their atomic structure in Fe1+yTe samples, the parent compound of iron-based superconductors, and demonstrate how these domains respond to applied uniaxial strain. We observe the bidirectional AFM domains in the unstrained sample, with an average domain size of ~50-150 nm, to transition into a single unidirectional domain under applied uniaxial strain. The findings presented here open a new direction to utilize a valuable tuning parameter in STM, as well as other spectroscopic techniques, both for tuning the electronic properties as for inducing symmetry breaking in quantum material systems.

Visualizing Uniaxial-strain Manipulation of Antiferromagnetic Domains in Fe1+YTe Using a Spin-polarized Scanning Tunneling Microscope

Using uniaxial strain combined with spin-polarized scanning tunneling microscopy, we visualize and manipulate the antiferromagnetic domain structure of Fe1+yTe, the parent compound of iron-based superconductors.

利用自旋偏振扫描隧道显微镜对 fe 1+yTe 中的反铁磁领域进行单轴应变操作

The quest to understand correlated electronic systems has pushed the frontiers of experimental measurements toward the development of new experimental ...

Applying Dynamic Strain on Thin Oxide Films Immobilized on a Pseudoelastic Nickel-Titanium Alloy

Direct alteration of material structure/function through strain is a growing area of research that has allowed for novel properties of materials to emerge. Tuning material structure can be achieved by controlling an external force imposed on materials and inducing stress-strain responses (i.e., applying dynamic strain). Electroactive thin films are typically deposited on shape or volume tunable elastic substrates, where mechanical loading (i.e., compression or tension) can affect film structure and function through imposed strain. Here, we summarize methods for straining n-type doped titanium dioxide (TiO2) films prepared by a thermal treatment of a pseudo-elastic nickel-titanium alloy (Nitinol). The main purpose of the described methods is to study how strain affects electrocatalytic activities of metal oxide, specifically hydrogen evolution and oxygen evolution reactions. The same system can be adapted to study the effect of strain more broadly. Strain engineering can be applied for optimization of a material function, as well as for design of adjustable, multifunctional (photo)electrocatalytic materials under external stress control.

Dynamic, tensile strain is applied on TiO2 thin films to study the effects of strain on electrocatalysis, specifically proton reduction and water oxidation. TiO2 films are prepared by thermal treatment of the pseudo-elastic NiTi alloy (Nitinol).

将动态应变应用于固定在伪弹性镍钛合金上的薄氧化物薄膜

Direct alteration of material structure/function through strain is a growing area of research that has allowed for novel properties of materials to ...

孔隙诱导应变法合成多孔钛酸钡薄膜及铁电相热稳定性

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