Name: atomic layer deposition of vanadium dioxide and a temperature-dependent optical model
Uploaded: 2018-05-23T13:00:00.000+00:00
Duration: 11 min 10 s
Description: Watch this Scientific Journal Video about Atomic Layer Deposition of Vanadium Dioxide and a Temperature-dependent Optical Model at JoVE.com

这项工作得到了美国海军研究实验室的核心项目的支持。

注意: 使用前请查阅所有相关的材料安全数据表 (MSDS), 并遵循所有适当的安全操作规程和程序。二氧化钒的原子层沉积生长使用一个限期反应器。用于限期增长的前体为四 (ethylmethylamido) 钒 (IV) (TEMAV) 和臭氧 (由超高纯度, 高压, 99.999% 氧气体, 0.3 流动和 5 psi 支持压力产生)。此外, 超高压 (99.999%) 氮气用于净化反应堆室。对于随后的真空退火, 超高压氧气体用于退火和超高压氮气的排气。TEMAV 是易燃的, 应仅用于适当的工程控制。压缩氧气体是一种危险, 只应用于适当的工程控制。压缩氮气是一种危险, 只应用于适当的工程控制。所有气体 (TEMAV、氧气、臭氧和氮气) 都使用适当的工程安全控制与限期反应反应器连接。不锈钢管连接臭氧发生器到限期反应堆, 因为它是清洁和更可靠的然后塑料管材。分离的超高压氧和氮气源在开始过程前使用适当的工程安全控制连接到真空退火室。丙酮和2丙醇是刺激物, 只应用于适当的个人防护设备和安全程序 (例如, 手套, 油烟机,等)。
1. 蓝宝石基底上二氧化钒的原子层沉积
<ol><li>清洁 c Al2O3 (蓝宝石) 衬底, 如下所示: 溶剂清洁基体在丙酮在40°c 在 sonicator 为5分钟, 然后直接地转移它 (没有漂洗) 到2丙醇在40°c 和油脂实验为5分钟. 冲洗基体在跑去离子用水2分钟, 用氮气烘干。</li>
	<li>确保限期反应釜室为150摄氏度, 并用氮气排出限期反应釜。</li>
	<li>将蓝宝石基板加载到反应器中, 关闭反应堆, 泵至 < 17 Pa 真空。至少等待 300s, 以确保样品达到150摄氏度。</li>
	<li>将 20 sccm 超高压氮气注入室内 (基本压力不应超过 36 Pa), 然后将臭氧脉冲用于15个饱和循环, 其中一个周期为0.05 秒的脉冲, 随后是十五年代的清除。</li>
	<li>为了增加二氧化钒, 脉冲 TEMAV 为 0.03 s 跟随了三十年代清除, 然后脉冲臭氧为 0.075 s 跟随三十年代清除。重复这个脉冲和清除周期, 直到达到预期的增长。 注意: 这个过程几乎是线性的, 每周期的增长率为 0.7-0.9 Å。</li>
	<li>先用超高压氮气排出限期反应堆室, 从限期反应堆中取出样品。将样品放在金属板上 (散热片), 使其冷却到室温。关闭限期反应堆和泵至 < 17 Pa 真空。样品现在包含蓝宝石基体上的无定形钒氧化物膜。 注意: 仔细取出样品, 因为样品加热到150摄氏度。</li>
</ol>2. 退火
注意: 在步骤1中由 "限期" 技术生长的2胶片产生无定形的 vo2。要创建面向多晶硅的2薄膜, 样品在一个具有六路十字的自定义超高真空退火室中退火。为了保持退火室的清洁, 将创建一个负载锁来插入和移除样品。3英寸直径的耐氧加热器由自定义铂丝加热器组成。该加热器提供了一个氧化镍雪橇的辐射加热, 样品安装在其中。该雪橇具有较高的发射率, 良好的传热从加热器到样品。
<ol><li>确保雪橇处于负载锁定状态, 然后用超高压氮气排气, 并打开负载锁。把样品放在雪橇上的装载锁和关闭负载锁室。</li>
	<li>使用粗泵将负载锁泵入 ~ 0.1 Pa。接下来, 切换到涡轮泵和泵负载锁定 < 10-4宾夕法尼亚州打开闸阀, 把雪橇转到退火室, 并将退火室泵到 < 10-5宾夕法尼亚州。</li>
	<li>流 1.5 sccm 超高纯度 (高压, 99.999%) 氧气进入退火室。 注: 运行氧气通过 5 sccm 质量流量控制器, 以确保低流量。压力必须介于 1x10-4和 7x10-4宾夕法尼亚州之间。这种压力必须在样品达到150摄氏度之前达到。</li>
	<li>加热雪橇到560°c (测量与高温计和热电偶) 使用热化舷梯率 ~ 20 °c/分钟. 在560°c 举行雪橇为 2 h (为300Å影片)。 注: 退火时间与厚度相关。经验数据表明退火 1 h 为样品 < 250 Å厚, 2 h 为样品 > 250 Å但 < 500 Å厚, 3 h 为样品 > 500 Å厚。</li>
	<li>关闭加热器并从加热器组件中取下雪橇 (朝向负载锁), 使样品淬火。</li>
	<li>将样品保持在氧气环境中, 直到样品温度小于150摄氏度 (例如, 在负载锁中使用高温计来测量样品温度)。 注意: 更好的样品通过等待, 直到更低的温度。一旦样品 < 150 摄氏度, 关闭氧气流和关闭闸阀。</li>
	<li>排气与超高压氮气。去除样品在 < 50 °c 并且放置样品在金属板材 (散热器) 冷却到室温。使用粗泵, 用空雪橇和泵向 0.1 Pa 关闭负载锁。切换到涡轮泵和泵负载锁定 < 10-4宾夕法尼亚州</li>
</ol>3. 表征
<ol><li>用拉曼光谱与532纳米激光激发源检验样品。
	<ol>
<li>将样品装入显微镜并将其聚焦。验证软件中照相机图像的样本焦点。将扫描激光功率设置为4兆瓦, 曝光时间为0.125 秒, 扫描次数为 10, 预览大小为40µm。</li>
		<li>单击 "实时频谱" 以观察拉曼光谱。优化对焦、激光功率、曝光时间和扫描次数, 最大限度地提高信噪比。单击 "保存频谱" 以保存数据。 开放光谱在 OMNIC。单击 "查找 Pks" 按钮以识别峰值。确定结晶度、相位 (VO2 vs vo、V2O3、v2O5、等) 和应变通过比较峰值到参考数据的钒氧化物12,13。 注: 窄峰表示高结晶质量, 而拉曼声子模式193、222和612厘米-1和/或软化389厘米-1模式的硬化是在 VO2晶体中的拉伸应变指示器。</li>
	</ol></li>
	<li>用 X 射线衍射 (XRD) 确定方向、结晶度和相位。 注: XRD 谱中峰的出现表明了晶体结构的性质, 特别是晶体结构和取向。通过将 XRD 数据峰值的2Θ角与 ICSD 的不同平面上的无机晶体结构数据库 (2) 卡相匹配, 确定 vo2的方向。通过将数据峰值与不同的钒氧化物相卡相匹配来确定相位。在这项工作中进行了实验峰与标准数据库的手工比较。单个 vo2峰值以39.9 度为单位验证了 vo2晶体质量, 并说明了型单斜 (020) 方向。</li>
	<li>X 射线光电子能谱 (XPS) 测定化学计量学和杂质含量
	<ol>
<li>将样品装载到样品架上。打开软件并单击 "排气负荷锁定"。将样品夹插入到负载锁中, 然后单击 "向下泵"。等待压力 < 4x10-5宾夕法尼亚州单击 "转移" 按钮将样品持有者移动到会议厅中。验证室压力为 < 7x10-6宾夕法尼亚州</li>
		<li>将测量参数输入到实验树中。打开 X 光枪与400µm 的斑点大小, 然后打开洪水枪。为测量量添加一个点, 然后为前体元素 (C 和 N) 以及薄膜元素 (V 和 O) 的高分辨率扫描添加点。对于每一个测量, 增加通行证能量 (200 ev 为勘测和 20 ev 为高分辨率扫描) 和扫描次数 (2 或更多为调查和15为高分辨率)。</li>
		<li>在样品的所需位置放置十字叉以进行点测量。单击并突出显示实验树标题, 然后单击菜单栏上的 "实验运行" 以执行所有测量扫描。</li>
		<li>执行调查 ID 程序以识别和分析影片中的元素。选择手动峰值添加后跟峰值匹配按钮, 分析高分辨率数据扫描中的键合。根据 XPS 手册14, 以综合峰值强度的比值来确定化学计量。</li>
		<li>完成后, 关闭枪, 然后单击转移按钮, 将样本持有人移动到负载锁。在加载锁中的示例后, 单击 "排气负载锁定" 并卸载该示例。 注意: 这标识了调查中所有元素的存在, 从而识别出杂质。XPS 峰值在特定的结合能显示钒氧化物的价, 如图 1所示。例如, 这些结果显示了两个代表 XPS 测量获得的深度分析与簇离子枪蚀刻的 as 沉积样品。xps 测量的表面显示的峰值在 518 eV 表明存在的 V2O5, 而 xps 测量的蚀刻样品 (在影片的散装) 显示了一个峰值在 516 eV 证明存在的 VO2。全宽半 max 表示钒在薄膜中的粘结均匀性 (换言之, 相纯度)。另外, 对其他能量峰值的分析可以识别污染物 (> 1%)。</li>
	</ol></li>
	<li>用原子力显微镜测定形态学 (AFM)
	<ol>
<li>打开计算机和 AFM 电子。启动 Nanoscope 程序, 选择攻丝模式, 然后选择负载实验。初始化阶段。</li>
		<li>按照屏幕左侧的实验顺序, 然后单击 "设置" 菜单。使用焦点控件将光学聚焦在悬臂上。单击 "优化激光位置" 将激光对准探头。单击 "Autoalign 检测器" 按钮, 然后单击 Autotune 悬臂。</li>
		<li>加载样品并打开真空。</li>
		<li>单击 "导航" 按钮, 使用轨迹球将样本置于头部下方。单击 "笔尖反射", 并使用轨迹球将头部降低到样品表面, 同时按住焦点按钮直到笔尖处于焦点。单击 "示例" 按钮并关闭 AFM 引擎盖。</li>
		<li>单击 "检查参数" 菜单。确保扫描大小为 < 1 µm, 并将样品/线设置为512。单击 "参与" 菜单按钮。等待二十年代。</li>
		<li>设置扫描大小为3µm, 并保持扫描速度在3.92 赫兹. 如果需要, 通过改变参数来优化图像: 驱动器振幅、振幅设定点、积分和比例增益。</li>
		<li>通过单击 "捕获" 按钮后面的 "下拉" 按钮来捕获所需的图像。在扫描之后, 单击 "提取" 按钮。</li>
		<li>双击所需的图像以在分析软件中打开它。要确定形态学, 请单击 "拼合" 按钮, 然后单击 "执行"。通过点击粗糙度计算表面粗糙度来提取统计参数, 然后单击粒子分析, 计算深度直方图和平均晶粒尺寸。</li>
		<li>单击 "导航" 菜单, 然后单击 "示例加载位置"。关闭真空并卸载样品。 注意: 为了从样品到样品的一致性, 保持相同的 AFM 扫描参数。</li>
	</ol></li>
	<li>确定光学透射率和反射率。
	<ol>
<li>使用可调谐光源, 测量近红外区域 (或接近) 正常入射时的光学透射率和反射率。校准系统无样品100% 透射率, 并与金镜近100% 的反射率。</li>
		<li>将 VO2示例加载到温度控制阶段。在所需温度下稳定试样。测量透射率和反射率在所需的光谱范围, 例如, 在整个近红外区域。 注: 为获得最佳结果, 温度应在20摄氏度以上和低于2 (通常为68摄氏度) 的过渡温度以下变化。</li>
	</ol></li>
</ol>4. 模拟光学常数 (介电常数和折射率)
<ol><li>将复介电常数 ( ε) 模型作为光子能量的函数, E, 使用以下等式 (其中ε∞ 是高频介电常数, 后跟n振荡器的总和, n是振荡器振幅, En 振荡器能量, 和Bn 振荡器阻尼): <img alt="Equation 1" src="/files/ftp_upload/57103/57103eq1.jpg"> 注意: 自定义 Matlab 程序对数据进行分析和建模。</li>
	<li>在步骤4.1 中输入蓝宝石衬底的已知参数, 并使用它们计算介质介电常数作为光波长的函数。然后计算折射率 (n = √ε), 并用折射率计算基体的反射率和透射率。</li>
	<li>将步骤4.2 的结果与实测数据进行比较, 然后使用优化技术 (如并用单纯形米德15) 来更新步骤4.2 的输入参数, 以减少测量结果和计算所得值之间的误差, 从而优化蓝宝石衬底的参数。</li>
	<li>在步骤4.1 中的等式中估计2的参数, 并使用它们计算介电介电常数。然后计算折射率 (n = √ε) 并使用该值, 连同 VO2厚度、衬底厚度、折射率 (从步骤 4.3)、光波长、光学极化和入射角度作为向传输16的输入, 以获得2涂层基底的反射率和透射率。使用优化技术 (如并用单纯形米德15) 来更新vo 2 输入参数, 并减少测量结果和计算所得值之间的误差, 从而优化了vo2 的参数。</li>
	<li>在若干温度下执行步骤4.2 至 4.4, 横跨二氧化钒的绝缘和金属状态 (温度从30到90°c)。对 VO2的折射率的温度依赖性进行建模, 如下所示: <img alt="Equation 3" src="/files/ftp_upload/57103/57103eq3.jpg"> 其中εVO2(t)是作为温度函数的 VO2的折射率, εins 和ε金属是绝缘和金属相的介电介电常数, f (t)是一种与温度相关的功能, 用于控制绝缘和金属光学特性的分布。对f (T)使用费米-狄拉克类似函数来控制绝缘和金属状态之间的过渡, 类似于有效中近似17、18、19, 所给出的: <img alt="Equation 4" src="/files/ftp_upload/57103/57103eq4.jpg"> 其中tt 是转换温度, W控制转换的宽度。</li>
	<li>采用优化技术对f (T)方程中的参数 (W 和 Tt) 进行更新, 以减少测量结果与计算所得值之间的误差, 从而优化过渡温度和宽度。这导致了温度和波长依赖模型的介电介电常数和折射率的 VO2。</li>
</ol>

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作者没有什么可透露的。

这里描述的生长方法为均匀性、化学、结构和形态学提供了可重现的结果。钒前驱体对制备沉积的限期膜的正确化学计量是至关重要的。这个特殊的前驱体促进了 +4 钒价态, 不像其他许多在文献中列出的促进更普遍的 +5 价态。此外, 这个特殊的前驱体有相当低的蒸气压, 需要加热, 以提供足够的剂量在给定条件下饱和。由于这一前驱体开始下降约175摄氏度, 这对两种加热的前驱体和限期增长的温度上限。另一个关键方面, 以实现正确的化学计量是臭氧浓度 (125 毫克/升在这里) 在剂量。通常, 发电机在特定条件下产生的臭氧浓度会随着时间的推移而降低或漂移。如果发生这种情况, 则必须调整臭氧脉冲和清除时间, 以保持化学计量学、形貌和硅片的均匀性。这里所描述的是如何在 c 平面蓝宝石基底上生长2的限期, 其中包括原位臭氧预处理。清洁和成核的生长之前的步骤依赖于基体;但是, 此处描述的过程适用于大多数基板 (惰性、氧化物、金属、等)。为了确定最佳的终止清洗和对 VO2生长的准备, 应考虑物种终止与钒前驱体之间的反应性, 同时尽量减少基体上的任何本底氧化物。最后, 在高长宽比衬底上展示了这一过程 (高达 100), 但对于极端情况, 人们应该考虑暴露或静态的 conformality 方法, 以进一步提高。
实现高品质, 晶限期的能力,2薄膜是相当依赖于后沉积退火参数。最关键的方面是压力, 特别是氧气的分压。高氧压力导致小面和谷物的生长, 最终导致纳米线的形成, 以及结果在 V2O5阶段。如果氧气压力过低, 氧气会从薄膜中退火, 导致 V2O3阶段。因此, 为了保持正确的相位并尽量减少薄膜的粗糙度, 应在 1x10-4到 7x10-4宾夕法尼亚州的范围内保持氧气压力。同样, 温度对于能够结晶薄膜、保持化学计量和最小化薄膜的粗糙是至关重要的。虽然2胶片的温度难以测量, 但经验结果表明, 结晶要求温度大于500摄氏度。在较高的温度下, 很难保持正确的化学计量和相, 并产生针孔自由膜。在温度和退火时间之间也有权衡, 特别是较高的温度可以减少退火时间。此外, 退火持续时间直接与薄膜的厚度有关。较厚的薄膜需要较长的时间才能达到最大结晶。因此, 对上述方法中所描述的氧压力、退火温度和退火时间进行了优化, 以产生高品质的2薄膜, 在近理想的过渡温度下表现出最大的光学性能变化。最后, 在氧退火过程中的升温和冷却速率对粗糙度和形貌有影响;这些越慢, 电影越平滑。
2的限期沉积和随后的退火, 产生具有大面积均匀性的定向多晶薄膜。在几乎任何基质的三维纳米形貌上, 共形都提供了生长薄膜。这使 VO2集成成为新的应用程序, 尤其适合于光学设备。
在增长和光学测量之后, 建立了一个模型, 它为在近红外光谱区域 (R2 = 0.96-0. 99) 中, 在其金属和绝缘相位中的 VO2的透射率和反射率提供了一个良好的匹配数据。红外绝缘相的反射率是创建该模型最具挑战性的过程。增加了振荡条件, 但这增加了模型的复杂性, 只是略微改善了适合在这个地区。应该指出的是, 在这个模型中, 洛仑兹振荡器的叠加是一个共同的光学模型, 不一定对应于特定的电子转换。最初, 模型包括一个德鲁德术语, 但是, 在数学优化之后, 德鲁德术语基本上被消除了。因此, 对几种最小化技术进行了研究。然而, 这些不同的技术融合在不涉及德鲁德术语的类似解决方案上。在限期任用的2中缺少一个德鲁德术语可能是由于许多因素, 如 1) 掺杂半导体样电阻率, 或 2) 等离子体频率移到较低的能量和/或大碰撞率 (阻尼项), 与金属协议这些电影的性质。
在绝缘相、T < 60 °c 中, 限期的介电常数和折射率2与其他制造方法 (溅射4、20、21和脉冲激光沉积22 ) 很好地吻合.、23)。在金属状态, T > 70 °c, 这些限期的影片比其他方法制造的 VO2表现出更低的损失。值得注意的是, 虽然不同的制造方法对2的介电常数和折射率产生一些不同的值, 但所有的胶片都显示出相似的趋势。
本文的模型对光学介电常数和折射率的温度和波长依赖性与实验测量数据吻合较好。该模型能够产生良好的质量符合测量的光学数据表明, 它可以可靠地预测的光学性质的 VO2作为相变从绝缘体到金属。使用这些模型, 可以根据温度、厚度和波长, 可预见地调整 VO2的光学特性, 以设计实现静态和动态目标的光学系统。这些模型通过修改胶片的厚度和温度, 使光学系统能够在被动和主动系统中使用 VO2来设计和开发。

二氧化钒在68摄氏度附近进行结晶相变。这就产生了从型单斜到四方的结构晶体变化。此转换的起源仍然是有争议的1, 但是最近的研究帮助开发了对生成此转换的进程的理解2,3,4 。无论起源如何, 相变的光学特性, 从绝缘体 (透射光) 在室温到一个更金属材料 (反射和吸收光) 在过渡温度2上的2 。.
在过去 (溅射、物理气相沉积、化学气相沉积、分子束外延、溶液、等) 中, 已经使用了各种方法来制造2的 VO。5. VO2的属性在很大程度上取决于用于制造薄膜6的技术, 这在不同的生长技术和随后的退火之间产生了显著的变异性, 并导致不同的结晶度和薄膜性能。本文研究了原子层沉积 (限期) 生长薄膜的光学性质, 但该方法适用于各种类型的 VO2薄膜的建模。
最近, 小组正在构造光学器件, 将2的薄膜加入到光学基底上。作为一种快速增长的新的沉积方法, 埃可以帮助制造这些光学器件, 并具有比替代技术更大的优势, 如大型区域均匀性、级厚度控制和保角膜覆盖范围 7 ,8,9。对于要求采用自限逐层沉积方法的应用而言, "限期" 是一种首选技术, 它制造了各种基材 (e. g), 用于异构集成, 或3D 结构的保形涂层10.最后, 对3D 结构的适形涂层在光学应用中特别有用。
本文的实验结果表明, 在低温条件下, 用双侧抛光的 c 型蓝宝石基板, 在氧环境中退火, 制备出高质量的结晶膜, 可获得超薄、无定形的定型膜。使用实验测量, 为在 VO2中的温度和波长相关的光学变化创建一个模型, 以使其用作可调谐折射率材料11。

<table><tbody><tr><td>c-Al2O3</td><td></td><td></td><td></td></tr><tr><td>UHP Oxygen</td><td>Air Products</td><td></td><td></td></tr><tr><td>UHP Nitrogen</td><td>Air Products</td><td></td><td></td></tr><tr><td>Tetrakis (ethylmethylamido)vanadium(IV) (TEMAV)</td><td>Air Liquide</td><td></td><td></td></tr><tr><td>Acetone</td><td>Fischer Scientific</td><td>A18-4</td><td></td></tr><tr><td>2-propanol</td><td>Fischer Scientific</td><td>A416P-4</td><td></td></tr><tr><td>Savannah S200-G2</td><td>Veeco - CNT</td><td>Savannah S200-G2</td><td></td></tr><tr><td>ozone generator</td><td>Veeco - CNT</td><td>ozone generator</td><td></td></tr><tr><td>Platinum wire heater</td><td>HeatWave Labs</td><td>custom</td><td></td></tr></tbody></table>

atomic layer deposition of vanadium dioxide and a temperature-dependent optical model

二氧化钒是一种材料, 具有可逆的金属绝缘子相变近68摄氏度。为了在广泛的基板上生长2 , 用硅片的均匀度和埃水平控制厚度, 选择了原子层沉积方法。这一限期的过程, 使高品质, 低温 (≤150°c) 增长的超薄薄膜 (100-1000 Å) 的 VO2。在此演示中, 在蓝宝石衬底上生长了2的 VO。这种低温生长技术主要产生无定形的2薄膜。随后的退火在超高真空室与压力的 7x10-4 Pa 的超高纯度 (99.999%) 氧气生产定向, 多晶 VO2薄膜。用拉曼光谱和 x-射线衍射法测定了2的结晶度、相和应变, 并用 x 射线光电子能谱法测定了化学计量学和杂质含量, 最后由原子力显微镜。这些数据证明了这种技术所生长的薄膜的高质量。创建了一个模型, 以适应在近红外光谱区域中的金属和绝缘相位的 VO2的数据。该方法的介电常数和折射率为2在其绝缘相中与其他制造方式很好地一致, 但在其金属状态上表现出不同。最后, 对薄膜光学特性的分析, 使得建立了一个波长和温度相关的复杂光学折射率模型, 用于开发2作为可调谐折射率材料。

为了鉴别生长的氧化钒的质量, x 射线光电子能谱 (XPS) 是在沉积的, 主要是无定形的 vo2薄膜 (图 1), 以及退火的水晶 vo2电影 (不显示)。X 射线衍射 (XRD) 是在退火的 VO2薄膜 (图 2) 上进行的。此外, 为了帮助量化薄膜内部化学的垂直剖面, 用聚类离子源进行深度剖面分析, 以尽量减少阳离子/负离子种类的优先蚀刻。两个典型的跟踪显示在图 1中, 一个在曲面上, 一个在大容量中。深度剖面和随后的 XPS 测量结果表明, 由于过量的环境 (不定) 氧和碳, 而沉积膜的前 1 nm 不为2 , 但在低压氧更受控制的退火过程中, 甚至表面稳定到 VO2。x 射线衍射测量是用铜 K α x 射线能量源进行的, 并显示在图 2中, 在39.9˚的单个 VO2峰值。这一峰值的签名验证了符合限期增长的 VO2的质量, 以及 (020) 晶体方向与蓝宝石基底的峰值对齐。
为了分析结晶度、相和应变, 采用 532 nm 激光器进行了拉曼光谱的激发。图 3显示了 VO2胶片的拉曼光谱, 显示了具有高结晶质量的窄峰。此外, 在钒钒低频率声子 (193 和222厘米-1) 和612厘米-1模式下增加的能量, 以及 389 cm-1模式的能量减少, 建议在这些影片中的拉伸应变12, 13。
用原子力显微镜 (AFM) 观察形态学。图 4显示的是 20-40 nm 的晶粒尺寸和 1.4 nm 的根均方根 (RMS) 粗糙度 (图 4A) 和退火胶片的 2.6 nm 的 RMS 粗糙度 (图 4B)。
利用具有扫描单色仪和光电探测器的白光光源, 在可见光和近红外区域提供覆盖, 获得光学透射率和反射率数据。图 5显示了胶片从绝缘体过渡到金属的温度依赖性, 表明过渡温度为61摄氏度。通过对实验数据的分析, 可以对2的温度和波长依赖性介电常数进行建模, 因为它从绝缘体过渡到金属。图 5显示了在使用表 1中的参数时, 模型如何准确地预测光学行为。
<img alt="Figure 1" class="xfigimg" src="/files/ftp_upload/57103/57103fig1.jpg"> 图 1: 在 c-Al2O3上, 35 nm 厚的 VO2的代表性 XPS 测量.XPS 显示, 该胶片的大部分为2 , 而表面 (包含 C 和 O 污染) 则被更转向 V2O5。化学计量建议2。<a href="/files/ftp_upload/57103/57103fig1large.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/57103/57103fig2v3.jpg"> 图 2: 在 c Al2O3上, 35 nm 厚的 VO2的 XRD 测量。此 XRD 测量显示单个 VO2 39.9˚中的峰值, 独立验证晶体质量并说明型单斜 (020) 方向与底层蓝宝石峰值对齐。<a href="/files/ftp_upload/57103/57103fig2v3large.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/57103/57103fig3.jpg"> 图 3: VO 的拉曼光谱2在 c-Al2O3.这种拉曼光谱有很窄的峰值, 表明高结晶质量, 并显示轻微的拉伸应变。<a href="/files/ftp_upload/57103/57103fig3large.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/57103/57103fig4.jpg"> 图 4: c-Al2O3上的 VO2的形态学。AFM 图像显示一致, 连续影片以五谷大小在20-40 毫微米的顺序和 RMS roughnesses (A) 1.4 毫微米为生长的影片和 (B) 2.6 毫微米为退火的影片。<a href="/files/ftp_upload/57103/57103fig4large.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/57103/57103fig5.jpg"> 图 5: 在 c-Al2O3上, 35 nm 厚的 VO2的近红外光学透射率和反射率。二氧化钒薄膜的光透射率和反射率的温度依赖性表现为40、60、70和90°c。图中的开放圆圈是在不同温度下, 在蓝宝石结构上测量的透射率、反射率和计算出的吸收, 而实线是二维温度的预测值, 而2的波长依赖性模型。<a href="/files/ftp_upload/57103/57103fig5large.jpg" target="_blank">请单击此处查看此图的较大版本.</a>
<table border="1" fo:keep-together.within-page="1" fo:keep-with-next.within-page="always"><tbody>
<tr>
<td></td>
			<td>ε∞</td>
			<td></td>
			<td>osc.1</td>
			<td>osc.2</td>
		</tr>
<tr>
<td>绝缘 子</td>
			<td colspan="4"></td>
		</tr>
<tr>
<td rowspan="3"></td>
			<td rowspan="3">3。4</td>
			<td>En
</td>
			<td>3。8</td>
			<td>1。2</td>
		</tr>
<tr>
<td>n
</td>
			<td>33</td>
			<td>2。1</td>
		</tr>
<tr>
<td>Bn
</td>
			<td>1。4</td>
			<td>1。3</td>
		</tr>
<tr>
<td>金属</td>
			<td colspan="4"></td>
		</tr>
<tr>
<td rowspan="3"></td>
			<td rowspan="3">4。5</td>
			<td>En
</td>
			<td>3。2</td>
			<td>0。6</td>
		</tr>
<tr>
<td>n
</td>
			<td>13</td>
			<td>5。3</td>
		</tr>
<tr>
<td>Bn
</td>
			<td>1。1</td>
			<td>1</td>
		</tr>
</tbody></table>表 1: 用于 VO 的典型模型参数2. 这些参数代表了振荡器模型中用于估计在其金属和绝缘相中的 VO2的介电常数。

Watch this Scientific Journal Video about Atomic Layer Deposition of Vanadium Dioxide and a Temperature-dependent Optical Model at JoVE.com

Atomic Layer Deposition of Vanadium Dioxide and a Temperature-dependent Optical Model

利用蓝宝石基底上的原子层沉积 (Å) 制备了二氧化钒薄膜 (100-1000) (2)。在此之后, 光学性能的特点是通过2的 VO 的金属绝缘子转换。通过测量的光学特性, 建立了一个模型来描述2的可调谐折射率。

二氧化钒原子层沉积与温度依赖性光学模型

Vanadium dioxide is a material that has a reversible metal-insulator phase change near 68 &#176;C. To grow VO2 on a wide variety of substrates, with ...

atomic-layer-deposition-vanadium-dioxide-temperature-dependent

Research

JoVE Journal

Engineering

11.8K 次观看.  Naval Research Laboratory. 利用蓝宝石基底上的原子层沉积 (Å) 制备了二氧化钒薄膜 (100-1000) (2)。在此之后, 光学性能的特点是通过2的 VO 的金属绝缘子转换。通过测量的光学特性, 建立了一个模型来描述2的可调谐折射率。

视频: Atomic Layer Deposition of Vanadium Dioxide and a Temperature-dependent Optical Model

Chemical Vapor Deposition of an Organic Magnet, Vanadium Tetracyanoethylene

Recent progress in the field of organic materials has yielded devices such as organic light emitting diodes (OLEDs) which have advantages not found in traditional materials, including low cost and mechanical flexibility. In a similar vein, it would be advantageous to expand the use of organics into high frequency electronics and spin-based electronics. This work presents a synthetic process for the growth of thin films of the room temperature organic ferrimagnet, vanadium tetracyanoethylene (V[TCNE]x, x~2) by low temperature chemical vapor deposition (CVD). The thin film is grown at &#60;60 &#176;C, and can accommodate a wide variety of substrates including, but not limited to, silicon, glass, Teflon and flexible substrates. The conformal deposition is conducive to pre-patterned and three-dimensional structures as well. Additionally this technique can yield films with thicknesses ranging from 30 nm to several microns. Recent progress in optimization of film growth creates a film whose qualities, such as higher Curie temperature (600 K), improved magnetic homogeneity, and narrow ferromagnetic resonance line-width (1.5 G) show promise for a variety of applications in spintronics and microwave electronics.

We present the synthesis of the organic-based ferrimagnet vanadium tetracyanoethylene (V[TCNE]x, x~2) via low temperature chemical vapor deposition (CVD). This optimized recipe yields an increase in Curie temperature from 400 K to over 600 K and a dramatic improvement in magnetic resonance properties.

化学气相沉积的有机磁体，钒四氰

Recent progress in the field of organic materials has yielded devices such as organic light emitting diodes (OLEDs) which have advantages not found in ...

科研

化学

Formation of Thick Dense Yttrium Iron Garnet Films Using Aerosol Deposition

Aerosol deposition (AD) is a thick-film deposition process that can produce layers up to several hundred micrometers thick with densities greater than 95% of the bulk. The primary advantage of AD is that the deposition takes place entirely at ambient temperature; thereby enabling film growth in material systems with disparate melting temperatures. This report describes in detail the processing steps for preparing the powder and for performing AD using the custom-built system. Representative characterization results are presented from scanning electron microscopy, profilometry, and ferromagnetic resonance for films grown in this system. As a representative overview of the capabilities of the system, focus is given to a sample produced following the described protocol and system setup. Results indicate that this system can successfully deposit 11 &#181;m thick yttrium iron garnet films that are &#160;&#62; 90% of the bulk density during a single 5 min deposition run. A discussion of methods to afford better control of the aerosol and particle selection for improved thickness and roughness variations in the film is provided.

This report describes the use of a custom-built system to perform aerosol deposition of thick films of yttrium iron garnet onto sapphire substrates at RT. The deposited films are characterized using scanning electron microscopy, profilometry, and ferromagnetic resonance to give a representative overview of the capabilities of the technique.

浓稠钇铁石榴石薄膜的形成使用气溶胶沉积

Aerosol deposition (AD) is a thick-film deposition process that can produce layers up to several hundred micrometers thick with densities greater than 95% ...

工程学

Improved Heterojunction Quality in Cu2O-based Solar Cells Through the Optimization of Atmospheric Pressure Spatial Atomic Layer Deposited Zn1-xMgxO

Atmospheric pressure spatial atomic layer deposition (AP-SALD) was used to deposit n-type ZnO and Zn1-xMgxO thin films onto p-type thermally oxidized Cu2O substrates outside vacuum at low temperature. The performance of photovoltaic devices featuring atmospherically fabricated ZnO/Cu2O heterojunction was dependent on the conditions of AP-SALD film deposition, namely, the substrate temperature and deposition time, as well as on the Cu2O substrate exposure to oxidizing agents prior to and during the ZnO deposition. Superficial Cu2O to CuO oxidation was identified as a limiting factor to heterojunction quality due to recombination at the ZnO/Cu2O interface. Optimization of AP-SALD conditions as well as keeping Cu2O away from air and moisture in order to minimize Cu2O surface oxidation led to improved device performance. A three-fold increase in the open-circuit voltage (up to 0.65 V) and a two-fold increase in the short-circuit current density produced solar cells with a record 2.2% power conversion efficiency (PCE). This PCE is the highest reported for a Zn1-xMgxO/Cu2O heterojunction formed outside vacuum, which highlights atmospheric pressure spatial ALD as a promising technique for inexpensive and scalable fabrication of Cu2O-based photovoltaics.

Improved Heterojunction Quality in Cu2O-based Solar Cells Through the Optimization of Atmospheric Pressure Spatial Atomic Layer Deposited Zn1-xMgxO

Here we present a protocol for synthesizing Zn1-xMgxO/Cu2O heterojunctions in open-air at low temperature via atmospheric pressure spatial atomic layer deposition (AP-SALD) of Zn1-xMgxO on cuprous oxide. Such high quality conformal metal oxides can be grown on a variety of substrates including plastics by this cheap and scalable method.

在铜改善异质结质量<sub&gt; 2</sub&gt; O型的太阳能电池通过大气压力的空间原子层沉积的优化<br /&gt;锌<sub&gt; 1-X</sub&gt;镁<sub系列&gt; X</sub&gt; 0

Atmospheric pressure spatial atomic layer deposition (AP-SALD) was used to deposit n-type ZnO and Zn1-xMgxO thin films onto p-type thermally oxidized Cu2O ...

Synthesis and Characterization of High c-axis ZnO Thin Film by Plasma Enhanced Chemical Vapor Deposition System and its UV Photodetector Application

In this study, zinc oxide (ZnO) thin films with high c-axis (0002) preferential orientation have been successfully and effectively synthesized onto silicon (Si) substrates via different synthesized temperatures by using plasma enhanced chemical vapor deposition (PECVD) system. The effects of different synthesized temperatures on the crystal structure, surface morphologies and optical properties have been investigated. The X-ray diffraction (XRD) patterns indicated that the intensity of (0002) diffraction peak became stronger with increasing synthesized temperature until 400 oC. The diffraction intensity of (0002) peak gradually became weaker accompanying with appearance of (10-10) diffraction peak as the synthesized temperature up to excess of 400 oC. The RT photoluminescence (PL) spectra exhibited a strong near-band-edge (NBE) emission observed at around 375 nm and a negligible deep-level (DL) emission located at around 575 nm under high c-axis ZnO thin films. Field emission scanning electron microscopy (FE-SEM) images revealed the homogeneous surface and with small grain size distribution. The ZnO thin films have also been synthesized onto glass substrates under the same parameters for measuring the transmittance.
For the purpose of ultraviolet (UV) photodetector application, the interdigitated platinum (Pt) thin film (thickness ~100 nm) fabricated via conventional optical lithography process and radio frequency (RF) magnetron sputtering. In order to reach Ohmic contact, the device was annealed in argon circumstances at 450 oC by rapid thermal annealing (RTA) system for 10 min. After the systematic measurements, the current-voltage (I-V) curve of photo and dark current and time-dependent photocurrent response results exhibited a good responsivity and reliability, indicating that the high c-axis ZnO thin film is a suitable sensing layer for UV photodetector application.

We offered a method to directly synthesize high c-axis (0002) ZnO thin film by plasma enhanced chemical vapor deposition. The as-synthesized ZnO thin film combined with Pt interdigitated electrode was used as sensing layer for ultraviolet photodetector, showing a high performance through a combination of its good responsivity and reliability.

合成和高c轴ZnO薄膜等离子体的特性增强化学气相沉积系统及其紫外探测器的应用

In this study, zinc oxide (ZnO) thin films with high c-axis (0002) preferential orientation have been successfully and effectively synthesized onto ...

Seedless Growth of Bismuth Nanowire Array via Vacuum Thermal Evaporation

Here a seedless and template-free technique is demonstrated to scalably grow bismuth nanowires, through thermal evaporation in high vacuum at RT. Conventionally reserved for the fabrication of metal thin films, thermal evaporation deposits bismuth into an array of vertical single crystalline nanowires over a flat thin film of vanadium held at RT, which is freshly deposited by magnetron sputtering or thermal evaporation. By controlling the temperature of the growth substrate the length and width of the nanowires can be tuned over a wide range. Responsible for this novel technique is a previously unknown nanowire growth mechanism that roots in the mild porosity of the vanadium thin film. Infiltrated into the vanadium pores, the bismuth domains (~ 1 nm) carry excessive surface energy that suppresses their melting point and continuously expels them out of the vanadium matrix to form nanowires. This discovery demonstrates the feasibility of scalable vapor phase synthesis of high purity nanomaterials without using any catalysts.

A protocol for seedless and high yield growth of bismuth nanowire arrays through vacuum thermal evaporation technique is presented.

铋纳米线阵列通过真空热蒸发无核增长

Here a seedless and template-free technique is demonstrated to scalably grow bismuth nanowires, through thermal evaporation in high vacuum at RT. ...

Aerosol-assisted Chemical Vapor Deposition of Metal Oxide Structures: Zinc Oxide Rods

Whilst columnar zinc oxide (ZnO) structures in the form of rods or wires have been synthesized previously by different liquid- or vapor-phase routes, their high cost production and/or incompatibility with microfabrication technologies, due to the use of pre-deposited catalyst-seeds and/or high processing temperatures exceeding 900 &#176;C, represent a drawback for a widespread use of these methods. Here, however, we report the synthesis of ZnO rods via a non-catalyzed vapor-solid mechanism enabled by using an aerosol-assisted chemical vapor deposition (CVD) method at 400 &#176;C with zinc chloride (ZnCl2) as the precursor and ethanol as the carrier solvent. This method provides both single-step formation of ZnO rods and the possibility of their direct integration with various substrate types, including silicon, silicon-based micromachined platforms, quartz, or high heat resistant polymers. This potentially facilitates the use of this method at a large-scale, due to its compatibility with state-of-the-art microfabrication processes for device manufacture. This report also describes the properties of these structures (e.g., morphology, crystalline phase, optical band gap, chemical composition, electrical resistance) and validates its gas sensing functionality towards carbon monoxide.

Columnar zinc oxide structures in the form of rods are synthesized via aerosol-assisted chemical vapor deposition without the use of pre-deposited catalyst-seed particles. This method is scalable and compatible with various substrates based on either silicon, quartz or polymers.

金属氧化物结构的气溶胶辅助化学气相沉积: 氧化锌棒

Whilst columnar zinc oxide (ZnO) structures in the form of rods or wires have been synthesized previously by different liquid- or vapor-phase routes, ...

Growth and Electrostatic/chemical Properties of Metal/LaAlO3/SrTiO3 Heterostructures

The quasi 2D electron system (q2DES) that forms at the interface between LaAlO3 (LAO) and SrTiO3 (STO) has attracted much attention from the oxide electronics community. One of its hallmark features is the existence of a critical LAO thickness of 4 unit-cells (uc) for interfacial conductivity to emerge. Although electrostatic mechanisms have been proposed in the past to describe the existence of this critical thickness, the importance of chemical defects has been recently accentuated. Here, we describe the growth of metal/LAO/STO heterostructures in an ultra-high vacuum (UHV) cluster system combining pulsed laser deposition (to grow the LAO), magnetron sputtering (to grow the metal) and X-ray photoelectron spectroscopy (XPS). We study step by step the formation and evolution of the q2DES and the chemical interactions that occur between the metal and the LAO/STO. Additionally, magnetotransport experiments elucidate on the transport and electronic properties of the q2DES. This systematic work not only demonstrates a way to study the electrostatic and chemical interplay between the q2DES and its environment, but also unlocks the possibility to couple multifunctional capping layers with the rich physics observed in two-dimensional electron systems, allowing the fabrication of new types of devices.

Growth and Electrostatic/chemical Properties of Metal/LaAlO3/SrTiO3 Heterostructures

We fabricate metal/LaAlO3/SrTiO3 heterostructures using a combination of pulsed laser deposition and in situ magnetron sputtering. Through magnetotransport and in situ X-ray photoelectron spectroscopy experiments, we investigate the interplay between electrostatic and chemical phenomena of the quasi two-dimensional electron gas formed in this system.

金属/LaAlO 的生长和静电/化学性质3/SrTiO3异

The quasi 2D electron system (q2DES) that forms at the interface between LaAlO3 (LAO) and SrTiO3 (STO) has attracted much attention from the oxide ...

Production of Single Tracks of Ti-6Al-4V by Directed Energy Deposition to Determine the Layer Thickness for Multilayer Deposition

Directed Energy Deposition (DED), which is an additive manufacturing technique, involves the creation of a molten pool with a laser beam where metal powder is injected as particles. In general, this technique is employed to either fabricate or repair different components. In this technique, the final characteristics are affected by many factors. Indeed, one of the main tasks in building components by DED is the optimization of process parameters (such as laser power, laser speed, focus, etc.) which is usually carried out through an extensive experimental investigation. However, this sort of experiment is extremely lengthy and costly. Thus, in order to accelerate the optimization process, an investigation was conducted to develop a method based on the melt pool characterizations. In fact, in these experiments, single tracks of Ti-6Al-4V were deposited by a DED process with multiple combinations of laser power and laser speed. Surface morphology and dimensions of single tracks were analyzed, and geometrical characteristics of melt pools were evaluated after polishing and etching the cross-sections. Helpful information regarding the selection of optimal process parameters can be achieved by examining the melt pool features. These experiments are being extended to characterize the larger blocks with multiple layers. Indeed, this manuscript describes how it would be possible to quickly determine the layer thickness for the massive deposition, and avoid over or under-deposition according to the calculated energy density of the optimum parameters. Apart from the over or under-deposition, time and materials saving are the other great advantages of this approach in which the deposition of multilayer components can be started without any parameter optimization in terms of layer thickness.

In this research, a rapid method based on melt pool characterization is developed to estimate the layer thickness of Ti-6Al-4V components produced by directed energy deposition.

用定向能沉积法生产 Ti-6Al-4V 层厚度的单车道多层沉积

Directed Energy Deposition (DED), which is an additive manufacturing technique, involves the creation of a molten pool with a laser beam where metal ...

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 ...

Niobium Oxide Films Deposited by Reactive Sputtering: Effect of Oxygen Flow Rate

Reactive sputtering is a versatile technique used to form compact films with excellent homogeneity. In addition, it allows easy control over deposition parameters such as gas flow rate that results in changes on composition and thus in the film required properties. In this report, reactive sputtering is used to deposit niobium oxide films. A niobium target is used as metal source and different oxygen flow rates to deposit niobium oxide films. The oxygen flow rate was changed from 3 to 10 sccm. The films deposited under low oxygen flow rates show higher electrical conductivity and provide better perovskite solar cells when used as electron transport layer.

Here, we present a protocol for niobium oxide films deposition by reactive sputtering with different oxygen flow rates for use as an electron transport layer in perovskite solar cells.

活性溅射沉积的氧化氮薄膜:氧气流速效应

Reactive sputtering is a versatile technique used to form compact films with excellent homogeneity. In addition, it allows easy control over deposition ...

二氧化钒原子层沉积与温度依赖性光学模型

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