这项工作得到JSS KAKENHI授权号16H06037的支持。衷心感谢北海道大学佐佐木博士对HR-DSC的技术支持。

1.将全氟聚合物的液晶对准层制备到玻璃基板上<ol><li> 制备全氟聚合物溶液 <ol><li>通过以1:2的比例将全氟聚合物溶液（9重量％聚合物）溶解在市售溶剂中来制备1mL全氟聚合物溶液;这样可以确保0.5-1μm厚的均匀的薄膜被旋涂。 注意:请参阅材料清单，了解所用溶液和溶剂。 </li></ol></li><li> 将全氟聚合物涂覆在干净的玻璃基板上 <ol><li>通过在38或42kHz的碱性洗涤剂中超声波处理玻璃基板（典型尺寸:1cm×1cm）。反复用蒸馏水冲洗。一般冲洗10次以上，每次超声处理5分钟。 </li><li>将基材用于UV-O 3清洁剂10分钟。 </li><li>将20μL从步骤1.1的溶液滴入清洁的玻璃基质上工商业污水附加费。立即将溶液以3500rpm和室温旋涂70秒。将膜在80℃下烘烤60分钟以除去溶剂，并在200℃下烘烤60分钟以固化。 </li></ol></li></ol> LC细胞的制备<ol><li>使用光固化树脂和波长为365nm（1.1W / cm 2 ）的LED灯将两片涂有薄膜的玻璃基板胶合。通过使用微米级玻璃颗粒或聚萘二甲酸乙二醇酯膜，将两个基板之间的间隙厚度调整在2-100μm的范围内。 </li><li>在高于各向同性液体（I）的温度下，使用刮刀在毛细管力下将LC物质4&#39;-丁基-4-庚基 - 双环己基-4-甲腈（CCN47;0.2-10μL） 9引入制备的LC细胞中， （N）相变温度。 注意:CCN47具有负介电各向异性，相序为Cry 298.6 K SmA 301.3 KN 331.3 KI，其中Cry和SmA代表晶体和近晶相。不要在N相或SmA相中引入CCN47，因为可以促进流动引导的对准。 </li></ol>样品表征<ol><li> 通过偏光光学显微镜（POM）进行纹理观察10 <ol><li>观察POM下的LC细胞与4-100X物镜结合热阶段，以±0.1-K的精度控制样品温度。将纹理记录在超过5帧，以开尔文为间隔。在291-343K范围内冷却和加热时，请依次使用数码彩色照相机。 </li></ol></li><li> 介电光谱（DS） 11 <ol><li>制备具有ITO电极的LC电池，其可以具有正方形或圆形并且可以在两种基板上商业购买。将引线焊接到每个基板。 注意:请参阅所用基材的材料清单。 </li><li>使用商用阻抗/增益相位分析仪测量LC单元的电容或介电常数，与POM一样。确保在每次测量之前均衡样品的状态。通过每5分钟手动测量LC电池的电容来测量电容的时间依赖性或LC单元的介电常数。 </li><li>仅当LC单元的电容或介电常数变得非时间依赖时才启动DS测量。 </li></ol></li><li> 高分辨率差示扫描量热法（HR-DSC） 12 <ol><li>将LC细胞置于自制的HR-DSC中，与POM（ 不使用DSC平底锅）完全相同。参考参考12设计和构建HR-DSC并学习如何使用它。以0.05-0.10 K / min的扫描速率进行测量，以提高最低温度解析度呃。 </li></ol></li><li> 放射X射线衍射（GI-XRD） 13 <ol><li>将LC单元（用于POM或DSC）或具有2至5μLCCN47液滴的样品放置在GI-XRD样品台上的涂覆基材上，该样品台应配备温度控制器。 </li><li>在冷却和加热下，在291-343 K范围内的所需温度下将样品平衡超过10分钟。 </li><li>在样品上使用入射的X射线束，以0.05-0.10°的微小入射角提取分子取向和排列/结构的表面信息。摆动X射线束的入射角，找到衍射强度最强的最佳入射角。以最佳入射角度进行测量。 注意:请注意，GI-XRD可以探测纳米尺度的界面特性，从而最大化来自薄层的信号同时尽量减少大量信号。注意，除了GI-XRD之外，正常的XRD几何不是表面敏感的方法，因为X射线辐射束具有大的材料穿透深度。 </li></ol></li></ol>

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作者没有什么可以披露的。

使用5-μmLC单元（ 图1a和b ）拍摄的10x POM图像清楚地表明，当以一级方式温度变化时，本体LC分子的取向状态在P和V取向之间转变。这是由领域成核和生长过程标记的，其新方向与初始取向不同，为90°。冷却和加热时的转变温度分别为321.5K和325.3K。由于CCN47的双折射为〜0.02 9 ，当LC单元的厚度在5-20μm的范围内时，Schlieren纹理的可视性是好的。如果厚度小于该范围，则Schlieren纹理的透射率变得较低，这导致较差的可见度。另一方面，如果厚度大于该范围，则光的干涉和散射导致POM图像中的像差，降低vi灵敏度甚至有效的光学分辨率。 为了定量研究LC导向器相对于正常表面（ 即极角）的倾斜角，在1kHz（远离导电频率范围）的固定频率下的DS测量同时进行POM作为温度的函数（ 图1c ）。由于使用的LC的介电各向异性通过使用具有P和V取向层的电池预先测量为温度的函数，所以在取向转变时介电常数（ℇ）的变化可以转化为极性的变化散装角度的LC。在图1c中 ，冷却和加热两者之间的曲线明确表明，从P（V）到V（P）的取向转变突然发生，迹线跳跃很大。从ℇ的大不连续性可以看出，方向转型具有一级性质，与POM的观察一致。即使DS测量足够强大来估计各向异性材料的极角，它缺乏深度分辨率，也不能给出面内方位角方向上的任何信息。 在图2a中 ，25μmLC电池中的HR-DSC迹线确认了热流的逐步变化，在约318K（在〜328K加热）下冷却时在取向转变处交叉，此时体取向状态从P变为V状态。此外，在〜332K的体积IN相变和〜303K的体积N-SmA相变时的热异常。高于0.05-0.10K / min的扫描速率将导致较差的温度分辨能力和噪声在热流中，会使目标样品脱离平衡状态。方向转换时热流的准逐步变化不伴随可测量的潜热，其代表存储在分子之间的键中的势能。这不同于涉及大量潜热的正常LC和晶体相变。这意味着每单位体积的热流量d Q / d t d V与比热容C p （ 即 d Q / d t d V〜C p ）直接相关。这种结果使得有可能确定完成从P到V的取向转变的体分子（ X ）的分数。这反过来又提供了对通过Kolmogorov-Johnson-Johnson的取向转变的成核和生长过程的理解， Mehl-Avrami，（KJMA或Avrami）分析16,17,18。 图2b给出了基于方程的Avrami拟合<img alt="方程" src ="/ files / ftp_upload / 55729 / 55729eq1.jpg"/&gt;，其中X ， K ， t和n分别是新域的体积分数，温度相关的Avrami系数，时间和Avrami指数）。 n被证实是〜2.6，表明异质成核和随后的2D生长界面润湿过程。该结果与通常的大容量NLC中的各向同性向列转变（n≈3.6）的Avrami指数形成鲜明对比（参见参考文献8中的支持信息）。请注意，由于我们的HR-DSC具有出色的温度分辨能力和良好的信噪比，因此目前的KJMA分析是可行的。这不能通过传统的DSC仪器来实现。由于这种技术对热流的小变化敏感（ 例如，即使是纳米丝的成核/生长过程也是可检测的），它具有测量小an在从有机材料到金属的任何材料的结构和阶段。此外，我们强调，这种技术在样本几何中的限制较少（ 例如，常规DSC仪器无法测量的LC单元）。 具有全氟聚合物表面的样品的GI-XRD图（ 图3a ）确认SAD和WAD峰，在I相的332K以外的温度下具有方向性。代表沿着LC分子的长轴的顺序的前者平行于表面延伸。表示沿着LC分子的短轴的顺序的后者位于垂直于前者的位置。 SAD峰强度比WAD峰强，SAD峰的FWHM也比WAD峰更窄。由于衍射峰的FWHM是痣之间位置相关强度程度的主要测量证明，存在沿着LC分子的长轴而不是沿着短分子的较长的位置相关性。这表明在表面附近存在上述SSWS。 如图3b所示 ，几个分子长度的近晶相关长度为纳米级。这种在纳米尺度和介观尺度上的局限于界面区域的信息只能通过表面敏感的XRD几何提取，例如在GI-XRD中，但不能通过传统的透射和反射几何来提取。此外，如果GI-XRD的入射角太大（〜&gt; 0.1°），则全反射条件将被破坏，并且不能再探测到表面特异性结构。

近年来，人们越来越关心学习如何响应于外部刺激的表面分子的动态分子特征和结构可能影响LC状态下材料的体取向。一个例子是使用LC生物传感器作为LC1,2的新应用。为了量化检测到多少目标生物物种，重要的是要知道接触粘附目标分子的界面LC如何变化和演化，同时也检测它们如何将其性质转移到体内。 使用模型来追求这些答案，我们从具有表面分子取向和短程排序的系统开始，热力学变化。这些系统允许我们以系统的方式将表面取向和排序的变化与所得到的体积方向相关联。最近，我们发现了几个显示o的LC系统自发体积分子取向随温度变化。原则上，定向转换可以分为准二阶3,4或准一阶转换5,6,7,8。前者伴随着温度变化时的连续大分子重新取向，而后者则表现出不连续的。在本文中，我们描述了P和V定向状态之间的准一阶方向的取向转变。它通过改变温度在单向向（N）相中进行。详细情况将在代表结果和讨论中提供。 由于体积的取向变化应受表面分子取向的变化和短期的限制很明显的是，该系统可以潜在地了解表面分子取向和短程排序的热力学变化如何影响体取向。在本文中，为了理解上述问题，我们使用四种补充方法（ 即 POM，DS，HR-DSC和GI-XRD）解决了三个问题:（1）定向过渡是什么样的？ （2）取向转变是否可热？ （3）为什么和如何发生方向转变？

<table border="1" fo:keep-together.within-page="1" fo:keep-with-next.within-page="always">
	<tbody>
		<tr>
			<td>CYTOP</td>
			<td>Asahi Glass Co. Ltd.</td>
			<td>CTX-809A</td>
			<td></td>
		</tr>
		<tr>
			<td>Solvent for CYTOP</td>
			<td>Asahi Glass Co. Ltd.</td>
			<td>CT-180 Sol.</td>
			<td></td>
		</tr>
		<tr>
			<td>Alkaline detergent</td>
			<td>Merck KGaA</td>
			<td>Extran MA01</td>
			<td></td>
		</tr>
		<tr>
			<td>NOA61</td>
			<td>Norland Products, Inc.</td>
			<td>#37-322</td>
			<td>Purchasable from Edmund Optics</td>
		</tr>
		<tr>
			<td>AL1254</td>
			<td>JSR Corporation</td>
			<td></td>
			<td>Planar alignment material in self-made cells</td>
		</tr>
		<tr>
			<td>4&#8217;-butyl-4-heptyl-bicyclohexyl-4-carbonitrile</td>
			<td>Nematel GmbH &#38; Co. KG</td>
			<td></td>
			<td>Custom-made</td>
		</tr>
		<tr>
			<td>UV-O3 cleaner</td>
			<td>Technovision Inc.</td>
			<td>UV-208</td>
			<td></td>
		</tr>
		<tr>
			<td>Hot-stage system</td>
			<td>Mettler Toledo</td>
			<td>HS82</td>
			<td></td>
		</tr>
		<tr>
			<td>High-Definition Color Camera Head</td>
			<td>Nikon</td>
			<td>DS-Fi1</td>
			<td></td>
		</tr>
		<tr>
			<td>Impedance/gain-phase analyzer</td>
			<td>Solartron Analytical</td>
			<td>1260</td>
			<td></td>
		</tr>
		<tr>
			<td>Indium Tin Oxide (ITO)-coated substrate</td>
			<td>GEOMATEC Co. Ltd.</td>
			<td></td>
			<td>Custom-made</td>
		</tr>
	</tbody>
</table>

orientational transition in a liquid crystal triggered by the thermodynamic growth of interfacial wetting sheets

在液晶（LC）物理化学中，表面附近的分子在控制体取向方面起着很大的作用。到目前为止，主要是为了在LC显示器中实现期望的分子取向状态，已经深入研究了LC的"静态"表面性质，即所谓的表面锚定。根据经验，一旦LC的初始取向通过特定的表面处理（例如用特定取向层的摩擦或处理）"锁定"，则几乎不随温度变化。在这里，我们提出一个体现温度变化的方向转变的系统，与共识相冲突。在转换过程中，体积LC分子经历取向旋转，在高温下的平面（P）取向与低温下的垂直（V）取向之间呈90°，以一阶过渡方式。我们通过偏振光学显微镜跟踪热力学表面锚固行为（POM），介电光谱（DS），高分辨率差示扫描量热法（HR-DSC）和掠入射X射线衍射（GI-XRD），并达到合理的物理解释:转变由表面生长引发润湿片材，其在本体上局部抵抗P取向局部施加V取向。这种景观将提供一个通用的链接，说明在许多液相色谱系统中平衡体取向受到表面定向取向的影响。在我们的表征中，通过提供关于LC分子的取向的空间分布的信息，POM和DS是有利的。 HR-DSC提供关于转换的精确热力学信息的信息，由于分辨率有限，传统DSC仪器无法解决。 GI-XRD提供关于表面特异性分子取向和短程排序的信息。本文的目的是提出一种用于准备展示transi的样品的方案并演示如何通过上述方法分析体积和表面上的热力学结构变化。

在温度变化期间收集POM图像，DS数据，HR-DSC数据和GI-XRD图案，特别是在冷却和加热两者的取向过渡附近。 图1表示在冷却（加热）期间从P（V）到V（P）取向状态的取向转变的POM观察期间由POM和DS测量形成的纹理的演变。显示了基于POM观察的取向转换过程中的重新定向过程（ 图1a ）。在冷却时，体积中的P取向正好低于IN转变温度，由二维（大多数）和四刷Schlieren纹理的外观来区分。值得注意的是，两刷Schlieren（具有s =±1/2的拓扑强度的旋转）是resu具有线缺陷的光结构，其拓扑上不允许在表面导向器14中预倾斜。另一方面，四刷Schlieren（具有s =±1的拓扑强度的旋转）具有点奇点，其可以存在于表面上或大量存在。与两刷Schlieren不同，根据对称论证允许表面导向器的预倾斜。通过将温度降低至321.5K，暗域（V取向）主要从±1旋错点的奇异点成核并随时间扩散。通过将样品退火数分钟或通过进一步冷却，整个视野变得完全变暗，这表明在体内从P向V方向的转变完成。在加热时，体积中从V到P取向的反向取向转变与冷却的重要不同:在5K附近的滞后，建议发现了一个强大的一阶转型。请注意，LC-LC转换的典型滞后范围（ 例如， IN和N - 近晶相变）小于1 K. 图2显示了通过HR-DSC测量的表示通过样品的热流的HR-DSC数据作为温度的函数（ 图2a ）和时间（ 图2b的插图）。 图2b插图中的数据用于分析取向转变后的Avrami指数（ 图2b ）。 图3显示了在各种温度下的两个样品几何中的GI-XRD图案:液滴几何（ 图3a ，顶部）和原位 LC单元几何形状（ 图3a &lt;/ strong&gt;，底部）。两者都表现出准SmA润湿片的短程排序，其中在表面附近形成层结构（以下简称为SSWS）。由GI-XRD峰的半峰全宽（FWHM）计算SSWS的大小（ 图3b ）。有两个关键的观察证实，SSWS应该是表面特定的结构:（1）如XRD所证实的，在CCN47的大部分中没有SmA排序（这里未示出）。 （2）在常规的P取向层材料上证实了在SAD（比全氟聚合物表面更弱和更宽的）和WAD的各向同性衍射图，证实了全氟聚合物和CCN47之间的特殊的分子相互作用。由于关于分子相互作用的争论超出了本讨论范围，它们将在未来的其他地方报告。令人惊讶的是，即使在P定向状态的温度范围内（见GI在328和322 K处的-XRD图），SSWS持续存在，表明表面取向条件受挫。表面的一些部分处于SSWS的斗篷下，呈现体积LC分子的V对准能力，而其余部分暴露出P对准能力。如果SSWS的尺寸或覆盖范围随着温度而变化，我们预期体积LC取向状态可能会发生变化，因为V对准能力与P对准能力的比值会相应变化。为了证实这种可能性，从SAD峰的FWHM计算SSWS相关长度（ 即，与表面垂直的方向上的SmA短程顺序的平均持续长度）的温度依赖性。 图3b证实了预期的趋势，显示在N相上的SSWS相关长度的增加以及潜在的滞后。滞后是指在SSWS形成之后e表面，在热力学上稳定，即使在高温下也是耐用的。关键特征是滞后范围与POM和DS确认的滞后范围一致（ 图1 ）。这表明定向转型是由SSWS的增长引发的。 <img alt="图1" class="xfigimg" src="/files/ftp_upload/55729/55729fig1.jpg" /> 图1:在冷却和加热时从P向V取向状态的取向转变的演变。 （ a ）冷却（蓝色向下箭头）和（ b ）加热（红色向上箭头）的纹理变化。 （ a ）顶部:P方向出现在IN转换下方。 （ a ）中间:在T C （ 即冷却时的取向转变温度），V取向从点defec出现t主要是四刷Schlieren纹理（红色虚线圆）。 （ a ）底部:具有V方向的区域扩展并覆盖整个视野，由内窥镜图像的插图补充。请注意，十字形圆锥视野图像在低温下几乎没有变化。 （ b ）底部:在T H （ 即，加热时的取向转变温度），暗和明亮的施利伦纹理使其从V取向域出现，表明薄层和厚层与P取向共存。 （ b ）中间:暗域转换为明亮的域。 （ b ）顶部:整个领域的导演是P方向，展现出一个薄的四刷Schlieren纹理。 （ c ）在两个冷却（空心圆圈）和加热（十字标记）之间测量的介电常数的温度依赖性。蓝线是实验在垂直LC单元中测量的CCN47的介电常数的数据。这个数字经过参考文献15的许可修改和修改。版权所有2012，美国物理学会。 <a href="https://ecsource-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/55729/55729fig1large.jpg" target="_blank">请点击此处查看此图的较大版本。</a> <img alt="图2" class="xfigimg" src="/files/ftp_upload/55729/55729fig2.jpg" /> 图2:使用HR-DSC的取向转变的热追踪。 （ a ）冷却和加热后涂覆全氟聚合物的电池中的HR-DSC图。在冷却之后，用常规的平面取向层材料AL1254涂覆的LC单元的结果也显示为对照测量。三个HR-DSC图表的基线正确转移。双箭头比例尺对应于1 mW / g。虚线被强调V方向的热流量比在全氟聚合物表面的电池中的P取向和I相中的热流小。 （ b ）用于区域的成核生长过程的Avrami拟合，其中V取向从冷却后具有P取向的区域产生。热流随时间的变化在插图中显示，用于Avrami拟合。这个数字经过参考文献7,8的许可修改和修改。版权所有2012，美国物理学会，版权所有2016，美国化学学会。 <a href="https://ecsource-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/55729/55729fig2large.jpg" target="_blank">请点击此处查看此图的较大版本。</a> <img alt="图3" class="xfigimg" src="/files/ftp_upload/55729/55729fig3.jpg" /> 图3:界面LC结构的热力学变化分析。 </（ a ）使用CCN47液滴在全氟聚合物表面上的GI-XRD图案相对于温度的变化和全氟聚合物表面上的LC单元。在具有P取向层材料AL1254的表面上的CCN47液滴的GI-XRD图案被示出为参考。 （ b ）冷却和加热时的近晶相关长度ξ∥的温度依赖性，由GI-XRD的小角度衍射图的半峰全宽计算。这个数字经过参考文献7,8的许可修改和修改。版权所有2012，美国物理学会;版权所有2016，美国化学学会。 <a href="https://ecsource-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/55729/55729fig3large.jpg" target="_blank">请点击此处查看此图的较大版本。</a>

Watch this Scientific Journal Video about Orientational Transition in a Liquid Crystal Triggered by the Thermodynamic Growth of Interfacial Wetting Sheets at JoVE.com

Orientational Transition in a Liquid Crystal Triggered by the Thermodynamic Growth of Interfacial Wetting Sheets

在这里，我们提出一种协议来触发液晶响应于温度的取向转变。描述了制备样品以观察转变和详细过渡演化的方法。

由界面润湿片的热力学生长触发的液晶中的定向转变

In liquid crystal (LC) physical chemistry, molecules near the surface play a great role in controlling bulk orientation. Thus far, mainly to achieve ...

orientational-transition-liquid-crystal-triggered-thermodynamic

Nanyang Technological University

Research

JoVE Journal

Engineering

7.1K 次观看.  RIKEN Center for Emergent Matter Science (CEMS). 在这里，我们提出一种协议来触发液晶响应于温度的取向转变。描述了制备样品以观察转变和详细过渡演化的方法。 

视频: Orientational Transition in a Liquid Crystal Triggered by the Thermodynamic Growth of Interfacial Wetting Sheets

Dry Oxidation and Vacuum Annealing Treatments for Tuning the Wetting Properties of Carbon Nanotube Arrays

In this article, we describe a simple method to reversibly tune the wetting properties of vertically aligned carbon nanotube (CNT) arrays. Here, CNT arrays are defined as densely packed multi-walled carbon nanotubes oriented perpendicular to the growth substrate as a result of a growth process by the standard thermal chemical vapor deposition (CVD) technique.1,2 These CNT arrays are then exposed to vacuum annealing treatment to make them more hydrophobic or to dry oxidation treatment to render them more hydrophilic. The hydrophobic CNT arrays can be turned hydrophilic by exposing them to dry oxidation treatment, while the hydrophilic CNT arrays can be turned hydrophobic by exposing them to vacuum annealing treatment. Using a combination of both treatments, CNT arrays can be repeatedly switched between hydrophilic and hydrophobic.2 Therefore, such combination show a very high potential in many industrial and consumer applications, including drug delivery system and high power density supercapacitors.3-5
The key to vary the wettability of CNT arrays is to control the surface concentration of oxygen adsorbates. Basically oxygen adsorbates can be introduced by exposing the CNT arrays to any oxidation treatment. Here we use dry oxidation treatments, such as oxygen plasma and UV/ozone, to functionalize the surface of CNT with oxygenated functional groups. These oxygenated functional groups allow hydrogen bond between the surface of CNT and water molecules to form, rendering the CNT hydrophilic. To turn them hydrophobic, adsorbed oxygen must be removed from the surface of CNT. Here we employ vacuum annealing treatment to induce oxygen desorption process. CNT arrays with extremely low surface concentration of oxygen adsorbates exhibit a superhydrophobic behavior.

This article describes a simple method to fabricate vertically aligned carbon nanotube arrays by CVD and to subsequently tune their wetting properties by exposing them to vacuum annealing or dry oxidation treatment.

干式氧化及真空退火处理调整的润湿性能的碳纳米管阵列

In this article, we describe a simple method to reversibly  tune the wetting properties of vertically aligned carbon nanotube (CNT) arrays.  Here, CNT ...

科研

工程学

Sputter Growth and Characterization of Metamagnetic B2-ordered FeRh Epilayers

Chemically ordered alloys are useful in a variety of magnetic nanotechnologies. They are most conveniently prepared at an industrial scale using sputtering techniques. Here we describe a method for preparing epitaxial thin films of B2-ordered FeRh by sputter deposition onto single crystal MgO substrates. Deposition at a slow rate onto a heated substrate allows time for the adatoms to both settle into a lattice with a well-defined epitaxial relationship with the substrate and also to find their proper places in the Fe and Rh sublattices of the B2 structure. The structure is conveniently characterized with X-ray reflectometry and diffraction and can be visualised directly using transmission electron micrograph cross-sections. B2-ordered FeRh exhibits an unusual metamagnetic phase transition: the ground state is antiferromagnetic but the alloy transforms into a ferromagnet on heating with a typical transition temperature of about 380 K. This is accompanied by a 1% volume expansion of the unit cell: isotropic in bulk, but laterally clamped in an epilayer. The presence of the antiferromagnetic ground state and the associated first order phase transition is very sensitive to the correct equiatomic stoichiometry and proper B2 ordering, and so is a convenient means to demonstrate the quality of the layers that can be deposited with this approach. We also give some examples of the various techniques by which the change in phase can be detected.

A method to prepare epitaxial layers of ordered alloys by sputtering is described. The B2-ordered FeRh compound is used as an example, as it displays a metamagnetic transition that depends sensitively on the degree of chemical order and the exact composition of the alloy.

变磁B2有序化的FeRh外延层溅射生​​长和表征

Chemically ordered alloys are useful in a variety of magnetic nanotechnologies. They are most conveniently prepared at an industrial scale using ...

Characterization of Recombination Effects in a Liquid Ionization Chamber Used for the Dosimetry of a Radiosurgical Accelerator

Most modern radiation therapy devices allow the use of very small fields, either through beamlets in Intensity-Modulated Radiation Therapy (IMRT) or via stereotactic radiotherapy where positioning accuracy allows delivering very high doses per fraction in a small volume of the patient. Dosimetric measurements on medical accelerators are conventionally realized using air-filled ionization chambers. However, in small beams these are subject to nonnegligible perturbation effects. This study focuses on liquid ionization chambers, which offer advantages in terms of spatial resolution and low fluence perturbation. Ion recombination effects are investigated for the microLion detector (PTW) used with the Cyberknife system (Accuray). The method consists of performing a series of water tank measurements at different source-surface distances, and applying corrections to the liquid detector readings based on simultaneous gaseous detector measurements. This approach facilitates isolating the recombination effects arising from the high density of the liquid sensitive medium and obtaining correction factors to apply to the detector readings. The main difficulty resides in achieving a sufficient level of accuracy in the setup to be able to detect small changes in the chamber response.

A growing number of radiation therapy devices offer the advantage of delivering the dose through very small beams to the tumor, allowing for increased conformity and higher doses per fraction. Many different detectors can be used for the dosimetry of these small fields. In the present study, the effect of ion recombination is investigated for a liquid ionization chamber using a stereotactic radiation therapy system.

重组的影响在液体电离室表征用于一个电波加速器的剂量学

Most modern radiation therapy devices allow the use of very small fields, either through beamlets in Intensity-Modulated Radiation Therapy (IMRT) or via ...

Ultrasound Velocity Measurement in a Liquid Metal Electrode

A growing number of electrochemical technologies depend on fluid flow, and often that fluid is opaque. Measuring the flow of an opaque fluid is inherently more difficult than measuring the flow of a transparent fluid, since optical methods are not applicable. Ultrasound can be used to measure the velocity of an opaque fluid, not only at isolated points, but at hundreds or thousands of points arrayed along lines, with good temporal resolution. When applied to a liquid metal electrode, ultrasound velocimetry involves additional challenges: high temperature, chemical activity, and electrical conductivity. Here we describe the experimental apparatus and methods that overcome these challenges and allow the measurement of flow in a liquid metal electrode, as it conducts current, at operating temperature. Temperature is regulated within &#177;2 &#176;C using a Proportional-Integral-Derivative (PID) controller that powers a custom-built furnace. Chemical activity is managed by choosing vessel materials carefully and enclosing the experimental setup in an argon-filled glovebox. Finally, unintended electrical paths are carefully prevented. An automated system logs control settings and experimental measurements, using hardware trigger signals to synchronize devices. This apparatus and these methods can produce measurements that are impossible with other techniques, and allow optimization and control of electrochemical technologies like liquid metal batteries.

Ultrasound velocimetry is used to study mixing by fluid flow in liquid metal electrodes. The focus of this manuscript is to illustrate the methods used for making precise, spatially-resolved ultrasound measurements while limiting oxidation and controlling and monitoring temperature, applied current, and the heater power being supplied.

超声速度测量的液态金属电极

A growing number of electrochemical technologies depend on fluid flow, and often that fluid is opaque. Measuring the flow of an opaque fluid is inherently ...

Selective Area Modification of Silicon Surface Wettability by Pulsed UV Laser Irradiation in Liquid Environment

The wettability of silicon (Si) is one of the important parameters in the technology of surface functionalization of this material and fabrication of biosensing devices. We report on a protocol of using KrF and ArF lasers irradiating Si (001) samples immersed in a liquid environment with low number of pulses and operating at moderately low pulse fluences to induce Si wettability modification. Wafers immersed for up to 4 hr in a 0.01% H2O2/H2O solution did not show measurable change in their initial contact angle (CA) ~75&#176;. However, the 500-pulse KrF and ArF lasers irradiation of such wafers in a microchamber filled with 0.01% H2O2/H2O solution at 250 and 65 mJ/cm2, respectively, has decreased the CA to near 15&#176;, indicating the formation of a superhydrophilic surface. The formation of OH-terminated Si (001), with no measurable change of the wafer&#8217;s surface morphology, has been confirmed by X-ray photoelectron spectroscopy and atomic force microscopy measurements. The selective area irradiated samples were then immersed in a biotin-conjugated fluorescein-stained nanospheres solution for 2 hr, resulting in a successful immobilization of the nanospheres in the non-irradiated area. This illustrates the potential of&#160;the method for selective area biofunctionalization and fabrication of advanced Si-based biosensing architectures. We also describe a similar protocol of irradiation of wafers immersed in methanol (CH3OH) using ArF laser operating at pulse fluence of 65 mJ/cm2 and in situ formation of a strongly hydrophobic surface of Si (001) with the CA of 103&#176;. The XPS results indicate ArF laser induced formation of Si&#8211;(OCH3)x compounds responsible for the observed hydrophobicity. However, no such compounds were found by XPS on the Si surface irradiated by KrF laser in methanol, demonstrating the inability of the KrF laser to photodissociate methanol and create -OCH3 radicals.

We report on a process of in situ alteration of HF treated Si (001) surface into a hydrophilic or hydrophobic state by irradiating samples in microfluidic chambers filled with&#160;H2O2/H2O solution (0.01%-0.5%) or methanol solutions using pulsed UV laser of a relative low pulse fluence.

硅表面润湿性的选择区域改性脉冲紫外激光照射在液体环境

The wettability of silicon (Si) is one of the important parameters in the technology of surface functionalization of this material and fabrication of ...

How to Ignite an Atmospheric Pressure Microwave Plasma Torch without Any Additional Igniters

This movie shows how an atmospheric pressure plasma torch can be ignited by microwave power with no additional igniters. After ignition of the plasma, a stable and continuous operation of the plasma is possible and the plasma torch can be used for many different applications. On one hand, the hot (3,600 K gas temperature) plasma can be used for chemical processes and on the other hand the cold afterglow (temperatures down to almost RT) can be applied for surface processes. For example chemical syntheses are interesting volume processes. Here the microwave plasma torch can be used for the decomposition of waste gases which are harmful and contribute to the global warming but are needed as etching gases in growing industry sectors like the semiconductor branch. Another application is the dissociation of CO2. Surplus electrical energy from renewable energy sources can be used to dissociate CO2 to CO and O2. The CO can be further processed to gaseous or liquid higher hydrocarbons thereby providing chemical storage of the energy, synthetic fuels or platform chemicals for the chemical industry. Applications of the afterglow of the plasma torch are the treatment of surfaces to increase the adhesion of lacquer, glue or paint, and the sterilization or decontamination of different kind of surfaces. The movie will explain how to ignite the plasma solely by microwave power without any additional igniters, e.g., electric sparks. The microwave plasma torch is based on a combination of two resonators &#8212; a coaxial one which provides the ignition of the plasma and a cylindrical one which guarantees a continuous and stable operation of the plasma after ignition. The plasma can be operated in a long microwave transparent tube for volume processes or shaped by orifices for surface treatment purposes.

This movie shows how an atmospheric plasma torch can be ignited by microwaves with no additional igniters and provides a stable and continuous plasma operation suitable for plenty of applications.

如何点燃常压微波等离子体炬没有任何额外的点火器

This movie shows how an atmospheric pressure plasma torch can be ignited by microwave power with no additional igniters. After ignition of the plasma, a ...

How to Build a Vacuum Spring-transport Package for Spinning Rotor Gauges

The spinning rotor gauge (SRG) is a high-vacuum gauge often used as a secondary or transfer standard for vacuum pressures in the range of 1.0 x 10-4 Pa to 1.0 Pa. In this application, the SRGs are frequently transported to laboratories for calibration. Events can occur during transportation that change the rotor surface conditions, thus changing the calibration factor. To assure calibration stability, a spring-transport mechanism is often used to immobilize the rotor and keep it under vacuum during transport. It is also important to transport the spring-transport mechanism using packaging designed to minimize the risk of damage during shipping. In this manuscript, a detailed description is given on how to build a robust spring-transport mechanism and shipping container. Together these form a spring-transport package. The spring-transport package design was tested using drop-tests and the performance was found to be excellent. The present spring-transport mechanism design keeps the rotor immobilized when experiencing shocks of several hundred g (g = 9.8 m/sec2 and is the acceleration due to gravity), while the shipping container assures that the mechanism will not experience shocks greater than about 100 g during common shipping mishaps (as defined by industry standards).

Here we describe how to build a robust spring-transport mechanism for a spinning rotor gauge. This device securely immobilizes the rotor and keeps it under vacuum during transportation. We also describe packaging that minimizes the risk of damage during transport. Tests show our design works for typical shocks during transport.

如何建立一个真空Spring的运输包装为纺转子规

The spinning rotor gauge (SRG) is a high-vacuum gauge often used as a secondary or transfer standard for vacuum pressures in the range of 1.0 x 10-4 Pa to ...

Preparation of Liquid-exfoliated Transition Metal Dichalcogenide Nanosheets with Controlled Size and Thickness: A State of the Art Protocol

We summarize recent advances in the production of liquid-exfoliated transition metal dichalcogenide (TMD) nanosheets with controlled size and thickness. Layered crystals of molybdenum disulphide (MoS2) and tungsten disulphide (WS2) are exfoliated in aqueous surfactant solution by sonication. This yields highly polydisperse mixtures containing nanosheets with broad size and thickness distributions. However, for most purposes, specific sizes (in terms of both lateral dimension and thickness) are required. For example, large and thin nanosheets are desired for (opto) electronic applications, while laterally small nanosheets are interesting for catalytic applications. Therefore, post-exfoliation size selection is an important step that we address here. We provide a detailed protocol on the efficient size selection in large quantities by liquid cascade centrifugation and the size and thickness quantification by statistical microscopic analysis (atomic force microscopy and transmission electron microscopy). The comparison of MoS2 and WS2 shows that both materials are size-selected in a similar way by the same procedure. Importantly, the dispersions of size-selected nanosheets show systematic changes in their optical extinction spectra with size due to edge and confinement effects. We show how these optical changes are related quantitatively to the nanosheets dimensions and describe how mean nanosheets length and layer number can be extracted reliably from the extinction spectra. The exfoliation and size selection protocol can be applied to a broad range of layered crystals as we have previously demonstrated for graphene, gallium sulphide (GaS) and black phosphorus.

A protocol for the liquid exfoliation of layered materials to nanosheets, their size selection and size measurement by microscopic and spectroscopic techniques is presented.

与尺寸可控液体剥离的过渡金属二硫属化物纳米片和厚度的制备:艺术议定书的国家

We summarize recent advances in the production of liquid-exfoliated transition metal dichalcogenide (TMD) nanosheets with controlled size and thickness. ...

Preparation of Liquid Crystal Networks for Macroscopic Oscillatory Motion Induced by Light

A strategy based on doped liquid crystalline networks is described to create mechanical self-sustained oscillations of plastic films under continuous light irradiation. The photo-excitation of dopants that can quickly dissipate light into heat, coupled with anisotropic thermal expansion and self-shadowing of the film, gives rise to the self-sustained deformation. The oscillations observed are influenced by the dimensions and the modulus of the film, and by the directionality and intensity of the light. The system developed offers applications in energy conversion and harvesting for soft-robotics and automated systems.
The general method described here consists of creating free-standing liquid crystalline films and characterizing the mechanical and thermal effects observed. The molecular alignment is achieved using alignment layers (rubbed polyimide), commonly used in the display manufacturing industry. To obtain actuators with large deformation, the mesogens are aligned and polymerized in a splay/bend configuration, i.e., with the director of the liquid crystals (LCs) going gradually from planar to homeotropic through the film thickness. Upon irradiation, the mechanical and thermal oscillations obtained are monitored with a high-speed camera. The results are further quantified by image analysis using an image processing program.

The goal of the protocol is to create liquid crystalline polymer films that can mechanically oscillate under continuous light irradiation. We describe in great detail the conception of free-standing films, from the liquid crystal alignment method to the photo-actuation. The experimental protocol applied to prepare this material is broadly applicable.

光诱导的宏观振荡运动液晶网络的制备

A strategy based on doped liquid crystalline networks is described to create mechanical self-sustained oscillations of plastic films under continuous ...

Preparation of Large-area Vertical 2D Crystal Hetero-structures Through the Sulfurization of Transition Metal Films for Device Fabrication

We have demonstrated that through the sulfurization of transition metal films such as molybdenum (Mo) and tungsten (W), large-area and uniform transition metal dichalcogenides (TMDs) MoS2 and WS2 can be prepared on sapphire substrates. By controlling the metal film thicknesses, good layer number controllability, down to a single layer of TMDs, can be obtained using this growth technique. Based on the results obtained from the Mo film sulfurized under the sulfur deficient condition, there are two mechanisms of (a) planar MoS2 growth and (b) Mo oxide segregation observed during the sulfurization procedure. When the background sulfur is sufficient, planar TMD growth is the dominant growth mechanism, which will result in a uniform MoS2 film after the sulfurization procedure. If the background sulfur is deficient, Mo oxide segregation will be the dominant growth mechanism at the initial stage of the sulfurization procedure. In this case, the sample with Mo oxide clusters covered with few-layer MoS2 will be obtained. After sequential Mo deposition/sulfurization and W deposition/sulfurization procedures, vertical WS2/MoS2 hetero-structures are established using this growth technique. Raman peaks corresponding to WS2 and MoS2, respectively, and the identical layer number of the hetero-structure with the summation of individual 2D materials have confirmed the successful establishment of the vertical 2D crystal hetero-structure. After transferring the WS2/MoS2 film onto a SiO2/Si substrate with pre-patterned source/drain electrodes, a bottom-gate transistor is fabricated. Compared with the transistor with only MoS2 channels, the higher drain currents of the device with the WS2/MoS2 hetero-structure have exhibited that with the introduction of 2D crystal hetero-structures, superior device performance can be obtained. The results have revealed the potential of this growth technique for the practical application of 2D crystals.

Through the sulfurization of pre-deposited transition metals, large-area and vertical 2D crystal hetero-structures can be fabricated. The film transferring and device fabrication procedures are also demonstrated in this report.

硫化过渡金属膜制备大面积垂直2D 晶体杂化结构

We have demonstrated that through the sulfurization of transition metal films such as molybdenum (Mo) and tungsten (W), large-area and uniform transition ...