作者想感谢萨, 药剂师的药房在海德堡大学医院, 她对 MRI 幻影的贡献。此外, 我们还要感谢 NORAS MRI 产品有限公司 (Höchberg, 德国), 特别是丹尼尔 Gareis 提供了一个原型的16通道多用途线圈。此外, 我们感谢与西门子医疗有限公司 (埃尔兰根, 德国) 的友好合作, 特别是 Nittka 为他们的顺序设置协助。

1. 幻像准备
<ol><li>使用水驱方法确定种植体体积 (例如)。 注: CCT t 样品的容积和 Z t 样品分别测量了0.65 毫升和0.73 毫升。</li>
	<li>使用细螺纹固定在非铁磁、塑料、防水盒中间的植入位置。使用大于预期的 MRI 工件的框。 注: 如果没有对植入物和/或脉冲序列的工件体积进行粗略估计, 则通过将幻像放置在一个盒子中, 在大约10x 大于幻影的范围内填充水来进行测试扫描。本研究的工件体积范围从7.3 毫升 (CCT t 样本) 和0.09 毫升 (Z T 样品) 不等。</li>
	<li>
小心融化合成脂肪 (58.8%), 水 (40%) 和 macrogol-8-stearate (1.2%) 的混合物, 使用水浴在50°c。 注: 对于本研究中的样品, 我们使用了500毫升混合物来嵌入每个样品。<ol>
<li>当混合物变成液体时, 停止加热, 开始缓慢搅拌, 停止加热。确保不存在脂肪和水相的分离。</li>
	</ol>
</li>
	<li>一旦凝血开始, 慢慢开始植入与混合物。为此, 将嵌入的混合物慢慢倒入与植入物的幻框。 注: 浇注必须缓慢, 以避免空气夹杂。</li>
	<li>将幻框与嵌入的植入物放入冰箱, 在4摄氏度过夜, 以干燥。第二天, 通过迁去除任何残余流体部分。</li>
</ol>2. MRI 检查
<ol><li>将幻像 (带有嵌入植入物的框) 置于 MRI 中与体内情况相同的方向。在 MRI 的 isocenter 中定位幽灵的中间位置。</li>
	<li>对于测量, 使用线圈, 允许在成像体积内均匀的信号分布, 没有严重和明显的信号下降 (例如, 头线圈)。</li>
	<li>当在 mri 控制台上规划 mri 扫描时, 请确保幻像盒 (包括方框边缘的一些空气) 在成像量内。</li>
	<li>接下来, 进行 MRI 检查。</li>
</ol>3. 图像分析和后处理
<ol><li>从 MRI 控制台 (例如, 使用 DICOM 格式) 导出图像, 而不会造成任何质量损失 (例如压缩)。在 MRI 后处理软件中导入图像, 允许放置感兴趣的区域 (roi)、评估 ROI 信号强度、基于阈值的分割以及分割卷的量化 (请参见材料表)。</li>
	<li>
要定义堆积工件的阈值, 并检查成像卷内的均匀信号分布, 请将线条垂直放置, 并与切片上可见工件的外部边界相邻, 并将工件大小设置为最大值 (图 1a)。 注: 堆积工件是置换工件, 呈现具有人为高信号强度的区域。它们出现在切片方向和读出方向上。<ol>
<li>将背景 roi (roi背景) 置于四个相交点 (图 1a) 之外的直径10毫米。使用细分编辑器将感兴趣的线条和背景区域放在一起。</li>
		<li>分别测量这些 4 roi背景值和每个 roi背景中所有素的平均信号强度和标准偏差 (SD)。在 "项目" 视图中使用工具材料统计信息。</li>
		<li>确保每个 ROI背景的平均信号强度在其他3个对应的平均信号的 1.5 SD 范围内, 以保证均匀的信号分布。</li>
		<li>通过将 roi 的 3 SD背景添加到这些 4 ROI背景值的所有素的平均信号强度, 计算堆积工件的阈值。对堆积工件进行半自动阈值分割, 方法是选择所有素, 其信号强度大于每个切片中与信号丢失工件相邻的阈值。利用分割编辑器的掩蔽工具对预定义的信号强度范围进行可视化, 并对其进行分割。</li>
	</ol>
</li>
	<li>
要定义信号损耗工件的阈值, 请将4个感兴趣的区域 (ROIs) 放在包含空气的区域 (ROIair; 每10毫米直径) 在幻像框的拐角处, 测量这些 4 ROI 内所有素的平均信号强度和 SD。Air , 如步骤3.2 中所述, 分别使用分段编辑器和 "材料统计"。 注意: 信号损耗工件存在于具有人工低信号强度的素。它们是由 dephasing 和置换工件造成的。<ol>
<li>将 ROI 置于信号丢失工件 (roi核心) 的核心, 由低信号强度的最大连通区域 (图 1a) 定义。手动增加 ROI核心的大小, 直到信号丢失工件中最大可能的大小, 其平均信号强度低于平均 ROI空气+ 各自 SD 的3x。最后, 测量 ROI核心的平均信号强度和 SD。</li>
		<li>通过将 roi核心的 3 SD 添加到 roi核心的平均值, 计算信号损耗工件的信号强度阈值。通过选择所有连接到 ROI核心且信号强度低于阈值的素, 执行基于半自动阈值的信号丢失工件分割。</li>
		<li>利用分割编辑器的掩蔽工具对预定义的信号强度范围进行可视化, 并对其进行分割。如果可能, 请在细分编辑器的分路 "选择" 中使用 "填充" 函数, 以包括尚未选定的分割中的所有素。如果适用, 请手动将其他明确的信号丢失工件添加到分割中。</li>
	</ol>
</li>
	<li>从计算工件体积减去物理种植体体积, 以获得真正的工件体积。重复分析至少3x。至少两周的时间间隔应将多次读取分开, 以排除学习偏差。</li>
</ol>

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蒂姆. Hilgenfeld, Schwindling 和亚历山大 Juerchott 从海德堡大学医学院的博士后奖学金中获得资金。该研究部分由 Dietmar-Hopp-基金会 (项目 23011228) 支持。作者明确指出, 与本条有关的没有利益冲突。

金属植入物患者的数量和 MRI 检查的数量目前正在增加1,2,3。在过去, 关节置换术后, MRI 检查被避免。然而今天, MRI 不仅被要求成像这样的病人, 但也应允许评估并发症直接毗邻关节置换术。因此, 植入物的 mri 安全性和 mri 适用性以及金属工件抑制的鲁棒脉冲序列正变得越来越重要13。为评价 MRI 在工件体积方面的适用性, 提出了一种综合、高效的实时协议。它允许对信号损耗和堆积工件进行可靠的三维评估, 作为抑制脂肪和非脂肪抑制 T1 和 T2-weighted 脉冲序列的切片畸变的指示器。
对于某些协议步骤, 必须特别注意以达到最佳的可能结果。熔化后的嵌入物质和植入之前, 它是非常重要的搅拌嵌入物质足够长, 而它开始降温, 其总状态变化 (流体到固体), 因为它的脂肪和水相容易分离, 即使在乳化剂的存在。此外, 用嵌入物质慢慢填充幻框是很重要的, 以避免气泡。这是至关重要的, 因为空气和信号损耗工件都导致零信号, 这将导致高估的工件。
一个高和均匀的信号是必要的, 以便对工件体积的准确评估。如果表面线圈达到最高的信噪比 (信噪比), 那么预先测试轮廓和线圈定位的灵敏度是否允许幻像中的齐次信号 (如上所述) 是至关重要的, 这样基于阈值的分割可以在没有任何分割错误的情况下运行。
与其他分析大型植入物 (例如、髋关节或膝关节置换或 spondylodesis) 的研究相比, 本协议使用的是小型植入物, 在某些情况下导致工件体积远低于1毫升。即使在如此具有挑战性的条件下, 我们也能发现不同样本和不同脉冲序列之间的工件体积存在显著的差异。因此, 可以假定该协议具有较高的测量精度, 从而能够准确地评估复杂植入物的 MRI 伪影体积和材料组成和形状。此外, 该协议可用于比较不同脉冲序列的脆弱性与金属诱发的工件所造成的特定种植体。
对金属工件的评价提出了多种不同复杂度的方法。为了比较不同的脉冲序列, 弗里茨et使用定性排名来评估每个序列11的漏洞。其他的, 例如 Zho et, 通过测量最大距离和通过平面工件来确定在平面工件 (信号丢失和堆积) 卷中, 通过计算受工件影响的切片数10。然而, 这两种方法都不考虑完整的工件体积, 这可能导致工件体积不足或高估。这也适用于一些使用手动分割11的研究。因为这是一个非常耗时的方法, 通常只有一个或两个中心切片在视觉基础上进行评估, 忽略剩余工件比例。
对于体外研究, 作者经常使用琼脂糖或明胶作为嵌入物质14,15。这两种材料都可以很容易地处理, 并保证足够的信号 T2 和 T1-weighted 图像。然而, 它们不允许对任何加权中的脂肪抑制序列进行评估。这是一个主要的缺点, 因为脂肪抑制对工件体积有深远的影响, 经常用于识别与植入物相关的并发症 (例如, 在感染病例中与种植体相邻的水肿和液体收集,微粒疾病, 或无菌淋巴细胞为主的血管炎-关联病变)13,16,17。
必须确认此协议的某些限制。首先, 它不允许对工件体积进行体内量化, 因为完整工件体积的差异需要一个均匀的背景信号。对于体内评估, 可以使用其他方法 (如测量磁性敏感度)。第二, 该协议允许检测堆积工件 (作为切片畸变的指示器), 仅与信号丢失工件直接相邻。但是, 除了信号丢失工件之外, 还可以预期额外的切片失真。这就是为什么可能低估了扭曲量的原因。
最后, 本协议有助于规范未来的研究, 评估植入物的 MRI 伪影体积和脉冲序列对金属工件的脆弱性。这可能有助于优化植入物和序列技术的 MRI 适用性, 最终改善病人护理。

MRI 已成为不可缺少的诊断工具。因此, 常规诊断中使用的 MRI 系统的数量进一步增加了1。同时, 植入物的患者数量也在增加,2,3。例如, 在 2012年, 超过100万膝关节置换术在美国单独执行了4。在 2010年, 这种植入物的流行率约为 700万, 这相当于80-89 岁5年龄组中10% 以上的女性。因此, MRI 检查的图像质量和诊断意义往往因金属植入物造成的工件受损, 导致诊断准确性降低。因此, 植入物的 MRI 适用性和脉冲序列的工件易损性变得越来越重要。已经发表了许多方法来评估这些特点。然而, 由于使用的评价方法存在很强的差异, 因此很难对各自的结果进行比较。
通过计算其磁化率6, 可以对材料的 MRI 适用性进行评估。然而, 不同的脉冲序列对工件的脆弱性不能与给定植入物的方法相比。反之亦然, 给定脉冲序列的工件卷只能粗略估计不同的植入物. 此外, 分析通常使用人工成形的植入物7,8。由于材料体积和形状对工件大小有影响6, 因此也应考虑这些特性。作为磁易感性的替代品, 工件的尺寸可以被评估。通常, 研究只依赖于工件大小9的定性评估, 或者只关注二维工件大小, 仅覆盖种植工件的一个切片10,11。此外, 通常使用手动分割方法, 这不仅费时费力, 而且容易产生内部和读者之间的差异11。最后, 协议通常不允许在12的同时测试非 fat 饱和和饱和脂肪的序列。然而, 这是可取的, 因为应用脂肪抑制技术深刻影响工件的大小。
在这里, 我们提出一个协议, 它允许可靠的, 半自动的, 基于阈值的, 三维量化的信号丢失和堆积工件的整个植入物, 或所有切片包含可见植入物工件。此外, 它允许测试 T1 和 T2-weighted 图像有或不含脂肪饱和度。该协议可用于评估不同植入物的 MRI 适宜性, 或不同脉冲序列对特定种植体金属工件的易损性。

<table border="0" cellpadding="0" cellspacing="0" width="638">
	<tbody>
		<tr height="21">
			<td height="21" style="height:21px;width:151px;">Aqua B. Braun Ecotainer</td>
			<td style="width:288px;">B. Braun Melsungen AG, Melsungen, Germany</td>
			<td style="width:136px;"></td>
			<td style="width:64px;"></td>
		</tr>
		<tr height="33">
			<td height="33" style="height:33px;width:151px;">Semisynthetic fat: Witepsol W25</td>
			<td style="width:288px;">Caelo Caesar &#38; Loretz GmbH, Hilder, Germany</td>
			<td style="width:136px;">4051</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:151px;">Macrogol-8-stearate</td>
			<td style="width:288px;">Caelo Caesar &#38; Loretz GmbH, Hilder, Germany</td>
			<td style="width:136px;">3023</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:151px;">Plastic box: not specified</td>
			<td style="width:288px;"></td>
			<td style="width:136px;"></td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:151px;">Implants: Nobel Replace</td>
			<td>Nobel Biocare, Z&#252;rich, Switzerland</td>
			<td style="width:136px;"></td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:151px;">Water bath Haake S5P</td>
			<td style="width:288px;">Thermo Scientific, Waltham, MA, USA</td>
			<td style="width:136px;"></td>
			<td></td>
		</tr>
		<tr height="52">
			<td height="52" style="height:52px;width:151px;">Measuring cylinder Blaubrand Eterna, Class A, Boro 3.3</td>
			<td style="width:288px;">BRAND GmbH + Co Kg, Wertheim, Germany</td>
			<td style="width:136px;">32708</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:151px;">Coil: Variety</td>
			<td style="width:288px;">Noras MRI products GmbH, H&#246;chberg, Germany</td>
			<td style="width:136px;"></td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:151px;">MRI: Magnetom Trio</td>
			<td style="width:288px;">Siemens Healthcare GmbH, Erlangen, Germany</td>
			<td style="width:136px;"></td>
			<td></td>
		</tr>
		<tr height="35">
			<td height="35" style="height:35px;width:151px;">Postprocesing software: Amira 6.4</td>
			<td style="width:288px;">Thermo Scientific, Waltham, MA, USA</td>
			<td style="width:136px;"></td>
			<td></td>
		</tr>
	</tbody>
</table>

protocol for the evaluation of mri artifacts caused by metal implants to assess the suitability of implants and the vulnerability of pulse sequences

随着磁共振成像 (mri) 扫描仪和医用植入物的数量不断增加, 放射科医生在 MRI 中越来越多地遇到与金属植入相关的工件, 从而降低了图像质量。因此, 植入物体积的 MRI 适配性以及脉冲序列的发展对减少图像工件的作用越来越重要。在这里, 我们提出了一个全面的协议, 允许对植入物体积的 MRI 的标准化评估。此外, 该协议还可用于分析不同脉冲序列对工件的易损性。所提出的协议可以应用于 T1 和 T2-weighted 图像, 有或不含脂肪抑制和所有被动植入物。此外, 该程序还实现了信号丢失和堆积工件的分离和三维识别。由于以往的调查在评价方法上差异很大, 结果的可比性有限。因此, 必须对 MRI 工件体积进行标准化测量, 以提供更好的可比性。这可能会改善植入物 MRI 的适用性和更好的脉搏序列, 以最终改善病人的护理。

通过上述协议, 我们评估了2种不同牙种植体的工件体积 (T; 参见材料表) 支持不同的冠 [瓷熔化对金属非贵金属合金 (CCT t) 和整体氧化锆 (Z T);图 1b和1c]。CCT T 样品代表高度顺磁性材料组分预测大文物 (钴 61%, 铬21% 和钨 11%;CCT)。Z T 样品的冠材料代表低顺磁性材料 (氧化锆 92%;Z). 此外, 评估了四种不同的、非脂肪饱和的 T2-weighted 序列, 以比较它们对金属工件的易损性。具体来说, 基于抽样完美的多角度倾斜梯度技术, 利用不同的翻转角演化 (MSVAT 空间), 金属工件的切片编码, 采用优化的对比度。校正 (SEMAC), 和他们的传统对应空间和涡轮旋转回声 (谢) 被评估 (参见表 1为详细的序列参量)。mri 扫描是在 3T mri 系统上进行的 (见材料表), 使用16通道多用途表面线圈。脉冲序列参数的变化对工件尺寸有很大的影响。因此, 脉冲序列参数选择尽可能接近于体内牙科 MRI 扫描中使用的, 以增加结果的可转移性。这项分析是由两名独立评分人3x 完成的。对于多项比较, 使用了方差分析和自组后Tukey 测试。
数据分析揭示了样本和应用序列之间的差异。在所有序列中, 与 Z t 样本 (P < 0.001 相比, CCT t 样本的组合工件体积 (信号损耗和堆积的总和) 较大;图 2和图 3)。在同一序列中, CCT t 样本的工件体积为 19.3x (SEMAC) 到 39.6x (MSVAT 空间), 大于 Z T 对应件的工件体积。
脉冲序列的选择对工件体积也有显著影响 (图 2和图 3)。对于 CCT T 样例, 为谢和 SEMAC 观察到最小工件体积, 以及空间中最大的工件 (P < 0.001)。此外, 与空间相比, MSVAT 空间显著降低了工件体积 (P < 0.001; 3.8 vs 7.3 mL)。与此相反, MSVAT 空间、谢和 SEMAC 的 Z T 样本之间没有显著差异。Z T 的工件体积最大, MSVAT 空间 (P < 0.05; 0.26 vs 0.1 mL) 显著减少。
<img alt="Figure 1" class="xfigimg" src="/files/ftp_upload/57394/57394fig1v2.jpg"> 图 1: ROI 定位和植入样例.(a) 此面板显示了感兴趣区域的典型位置 (ROIs), 用于测量堆积工件和信号分布的阈值 (roiB = roi背景) 和信号丢失工件 (roi = roi 空气;roiC = roi核心)。蓝色轮廓类似于该切片中的信号丢失工件的半自动分割结果。小红区域对应于堆积物的结果。(b和c) 这些面板显示了用于支持不同单冠的旧牙种植体的图像。钴铬钨钛 (CCT T);氧化锆钛 (Z T)。<a href="/files/ftp_upload/57394/57394fig1v2large.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/57394/57394fig2v2.jpg"> 图 2: 工件体积测量.(a和b)这些条形图显示了在减去物理种植体体积后, 所有4个评估序列的三维工件体积的标准偏差的平均值。如果适用, 则为信号丢失和堆积工件提供单独的标准偏差误差条。* P ≤ 0.05;** P≤ 0.001<a href="/files/ftp_upload/57394/57394fig2v2large.jpg" target="_blank">请单击此处查看此图的更大版本.</a>
<img alt="Figure 3" class="xfigimg" src="/files/ftp_upload/57394/57394fig3.jpg"> 图 3: 工件的外观.这些面板渲染整个植入物的工件体积 (上部行)。蓝色区域代表信号丢失工件, 红色区域代表堆积工件。面板显示所有计算的 T2-weighted 序列的彩色源图像 (下一行)。面板 (a) 是钴铬钨钛 (CCT t) 样品, 面板 (b) 是氧化锆-钛 (Z T) 样品。<a href="/files/ftp_upload/57394/57394fig3large.jpg" target="_blank">请单击此处查看此图的较大版本.</a>
<table fo:font-size="7" fo:keep-together.within-page="1" fo:keep-with-next.within-page="always"><tbody>
<tr>
<td>序列</td>
			<td>TR/特 女士]</td>
			<td>体素尺寸 [mm3]</td>
			<td>FOV [mm2]</td>
			<td>矩阵</td>
			<td>读数 带宽 [Hz/Px]</td>
			<td>片</td>
			<td>
片 编码 步骤或 采样 [%]
</td>
			<td>增值税</td>
			<td>时间 [最少: 秒]</td>
		</tr>
<tr>
<td>空间</td>
			<td>2500/131</td>
			<td>0.55 x 0.55 x 0.55</td>
			<td>140 x 124</td>
			<td>256 x 256</td>
			<td>501</td>
			<td>72</td>
			<td>55。6</td>
			<td>不</td>
			<td>14:02</td>
		</tr>
<tr>
<td>MSVAT 空间</td>
			<td>2500/199</td>
			<td>0.55 x 0.55 x 0.55</td>
			<td>140 x 84</td>
			<td>256 x 256</td>
			<td>528</td>
			<td>72</td>
			<td>55。6</td>
			<td>是的</td>
			<td>6:04</td>
		</tr>
<tr>
<td>谢</td>
			<td>5100/44</td>
			<td>0.59 x 0.59 x 1。5</td>
			<td>150 x 150</td>
			<td>256 x 256</td>
			<td>592</td>
			<td>25</td>
			<td>不</td>
			<td>不</td>
			<td>3:36</td>
		</tr>
<tr>
<td>SEMAC</td>
			<td>5100/45</td>
			<td>0.59 x 0.59 x 1。5</td>
			<td>150 x 150</td>
			<td>256 x 256</td>
			<td>592</td>
			<td>25</td>
			<td>4</td>
			<td>是的</td>
			<td>6:19</td>
		</tr>
</tbody></table>表 1: 所有已用序列的参数。

Watch this Scientific Journal Video about Protocol for the Evaluation of MRI Artifacts Caused by Metal Implants to Assess the Suitability of Implants and the Vulnerability of Pulse Sequences at JoVE.c

Protocol for the Evaluation of MRI Artifacts Caused by Metal Implants to Assess the Suitability of Implants and the Vulnerability of Pulse Sequences

我们描述了一种标准化的方法来评估植入物引起的磁共振成像工件, 以估计植入物对磁共振成像的适用性和/或不同脉冲序列对金属工件的易损性。同时。

评估植入物所引起的 MRI 伪影和脉冲序列易损性评估的协议

As the number of magnetic resonance imaging (MRI) scanners and patients with medical implants is constantly growing, radiologists increasingly encounter ...

protocol-for-evaluation-mri-artifacts-caused-metal-implants-to-assess

Nanyang Technological University

Research

JoVE Journal

Engineering

9.7K 次观看.  Heidelberg University Hospital. 我们描述了一种标准化的方法来评估植入物引起的磁共振成像工件, 以估计植入物对磁共振成像的适用性和/或不同脉冲序列对金属工件的易损性。同时。

视频: Protocol for the Evaluation of MRI Artifacts Caused by Metal Implants to Assess the Suitability of Implants and the Vulnerability of Pulse Sequences

Harvesting Solar Energy by Means of Charge-Separating Nanocrystals and Their Solids

Conjoining different semiconductor materials in a single nano-composite provides synthetic means for the development of novel optoelectronic materials offering a superior control over the spatial distribution of charge carriers across material interfaces. As this study demonstrates, a combination of donor-acceptor nanocrystal (NC) domains in a single nanoparticle can lead to the realization of efficient photocatalytic1-5 materials, while a layered assembly of donor- and acceptor-like nanocrystals films gives rise to photovoltaic materials.
Initially the paper focuses on the synthesis of composite inorganic nanocrystals, comprising linearly stacked ZnSe, CdS, and Pt domains, which jointly promote photoinduced charge separation. These structures are used in aqueous solutions for the photocatalysis of water under solar radiation, resulting in the production of H2 gas. To enhance the photoinduced separation of charges, a nanorod morphology with a linear gradient originating from an intrinsic electric field is used5. The inter-domain energetics are then optimized to drive photogenerated electrons toward the Pt catalytic site while expelling the holes to the surface of ZnSe domains for sacrificial regeneration (via methanol). Here we show that the only efficient way to produce hydrogen is to use electron-donating ligands to passivate the surface states by tuning the energy level alignment at the semiconductor-ligand interface. Stable and efficient reduction of water is allowed by these ligands due to the fact that they fill vacancies in the valence band of the semiconductor domain, preventing energetic holes from degrading it. Specifically, we show that the energy of the hole is transferred to the ligand moiety, leaving the semiconductor domain functional. This enables us to return the entire nanocrystal-ligand system to a functional state, when the ligands are degraded, by simply adding fresh ligands to the system4.
To promote a photovoltaic charge separation, we use a composite two-layer solid of PbS and TiO2 films. In this configuration, photoinduced electrons are injected into TiO2 and are subsequently picked up by an FTO electrode, while holes are channeled to a Au electrode via PbS layer6. To develop the latter we introduce a Semiconductor Matrix Encapsulated Nanocrystal Arrays (SMENA) strategy, which allows bonding PbS NCs into the surrounding matrix of CdS semiconductor. As a result, fabricated solids exhibit excellent thermal stability, attributed to the heteroepitaxial structure of nanocrystal-matrix interfaces, and show compelling light-harvesting performance in prototype solar cells7.

A general strategy for the development of charge-separating semiconductor nanocrystal composites deployable for solar energy production is presented. We show that assembly of donor-acceptor nanocrystal domains in a single nanoparticle geometry gives rise to a photocatalytic function, while bulk-heterojunctions of donor-acceptor nanocrystal films can be used for photovoltaic energy conversion.

通过电荷分离纳米晶及其固体收获太阳能

Conjoining different semiconductor materials in a single nano-composite provides synthetic means for the development of novel optoelectronic materials ...

科研

工程学

Monolayer Contact Doping of Silicon Surfaces and Nanowires Using Organophosphorus Compounds

Monolayer Contact Doping (MLCD) is a simple method for doping of surfaces and nanostructures1. MLCD results in the formation of highly controlled, ultra shallow and sharp doping profiles at the nanometer scale. In MLCD process the dopant source is a monolayer containing dopant atoms.
In this article a detailed procedure for surface doping of silicon substrate as well as silicon nanowires is demonstrated. Phosphorus dopant source was formed using tetraethyl methylenediphosphonate monolayer on a silicon substrate. This monolayer containing substrate was brought to contact with a pristine intrinsic silicon target substrate and annealed while in contact. Sheet resistance of the target substrate was measured using 4 point probe. Intrinsic silicon nanowires were synthesized by chemical vapor deposition (CVD) process using a vapor-liquid-solid (VLS) mechanism; gold nanoparticles were used as catalyst for nanowire growth. The nanowires were suspended in ethanol by mild sonication. This suspension was used to dropcast the nanowires on silicon substrate with a silicon nitride dielectric top layer. These nanowires were doped with phosphorus in similar manner as used for the intrinsic silicon wafer. Standard photolithography process was used to fabricate metal electrodes for the formation of nanowire based field effect transistor (NW-FET). The electrical properties of a representative nanowire device were measured by a semiconductor device analyzer and a probe station.

A detailed procedure for surface doping of Silicon interfaces is provided. The ultra-shallow surface doping is demonstrated by using phosphorus containing monolayers and rapid annealing process. The method can be used for doping of macroscopic area surfaces as well as nanostructures.

Monolayer Contact Doping (MLCD) is a simple method for doping of surfaces and nanostructures1. MLCD results in the formation of highly controlled, ultra ...

Fast Imaging Technique to Study Drop Impact Dynamics of Non-Newtonian Fluids

In the field of fluid mechanics, many dynamical processes not only occur over a very short time interval but also require high spatial resolution for detailed observation, scenarios that make it challenging to observe with conventional imaging systems. One of these is the drop impact of liquids, which usually happens within one tenth of millisecond. To tackle this challenge, a fast imaging technique is introduced that combines a high-speed camera (capable of up to one million frames per second) with a macro lens with long working distance to bring the spatial resolution of the image down to 10 &#181;m/pixel. The imaging technique enables precise measurement of relevant fluid dynamic quantities, such as the flow field, the spreading distance and the splashing speed, from analysis of the recorded video. To demonstrate the capabilities of this visualization system, the impact dynamics when droplets of non-Newtonian fluids impinge on a flat hard surface are characterized. Two situations are considered: for oxidized liquid metal droplets we focus on the spreading behavior, and for densely packed suspensions we determine the onset of splashing. More generally, the combination of high temporal and spatial imaging resolution introduced here offers advantages for studying fast dynamics across a wide range of microscale phenomena.

Drop impact of non-Newtonian fluids is a complex process since different physical parameters influence the dynamics over a very short time (less than one tenth of a millisecond). A fast imaging technique is introduced in order to characterize the impact behaviors of different non-Newtonian fluids.

快速成像技术来研究非牛顿流体的跌落冲击动力学

In the field of fluid mechanics, many dynamical processes not only occur over a very short time interval but also require high spatial resolution for ...

Analyzing the Movement of the Nauplius 'Artemia salina' by Optical Tracking of Plasmonic Nanoparticles

We demonstrate how optical tweezers may provide a sensitive tool to analyze the fluidic vibrations generated by the movement of small aquatic organisms. A single gold nanoparticle held by an optical tweezer is used as a sensor to quantify the rhythmic motion of a Nauplius larva (Artemia salina) in a water sample. This is achieved by monitoring the time dependent displacement of the trapped nanoparticle as a consequence of the Nauplius activity. A Fourier analysis of the nanoparticle&#39;s position then yields a frequency spectrum that is characteristic to the motion of the observed species. This experiment demonstrates the capability of this method to measure and characterize the activity of small aquatic larvae without the requirement to observe them directly and to gain information about the position of the larvae with respect to the trapped particle. Overall, this approach could give an insight on the vitality of certain species found in an aquatic ecosystem and could expand the range of conventional methods for analyzing water samples.

Analyzing the Movement of the Nauplius 'Artemia salina' by Optical Tracking of Plasmonic Nanoparticles

We use optical tracking of plasmonic nanoparticles to probe and characterize the frequency movements of aquatic organisms.

分析无节幼体的运动"<em&gt;卤虫</em&gt;&#39;由电浆纳米粒子的光学跟踪

We demonstrate how optical tweezers may provide a sensitive tool to analyze the fluidic vibrations generated by the movement of small aquatic organisms. A ...

Integrating a Triplet-triplet Annihilation Up-conversion System to Enhance Dye-sensitized Solar Cell Response to Sub-bandgap Light

The poor response of dye-sensitized solar cells (DSCs) to red and infrared light is a significant impediment to the realization of higher photocurrents and hence higher efficiencies. Photon up-conversion by way of triplet-triplet annihilation (TTA-UC) is an attractive technique for using these otherwise wasted low energy photons to produce photocurrent, while not interfering with the photoanodic performance in a deleterious manner. Further to this, TTA-UC has a number of features, distinct from other reported photon up-conversion technologies, which renders it particularly suitable for coupling with DSC technology. In this work, a proven high performance TTA-UC system, comprising a palladium porphyrin sensitizer and rubrene emitter, is combined with a high performance DSC (utilizing the organic dye D149) in an integrated device. The device shows an enhanced response to sub-bandgap light over the absorption range of the TTA-UC sub-unit resulting in the highest figure of merit for up-conversion assisted DSC performance to date.

An integrated device, incorporating a dye-sensitized solar cell and triplet-triplet annihilation up-conversion unit was produced, affording enhanced light harvesting, from a wider section of the solar spectrum. Under modest irradiation levels a significantly enhanced response to low energy photons was demonstrated, yielding a record figure of merit for dye-sensitized solar cells.

集成的三重态 - 三重态湮灭上转换系统，提高染料敏化太阳能电池的响应子带隙光

The poor response of dye-sensitized solar cells (DSCs) to red and infrared light is a significant impediment to the realization of higher photocurrents ...

Casting Protocols for the Production of Open Cell Aluminum Foams by the Replication Technique and the Effect on Porosity

Metal foams are interesting materials from both a fundamental understanding and practical applications point of view. Uses have been proposed, and in many cases validated experimentally, for light weight or impact energy absorbing structures, as high surface area heat exchangers or electrodes, as implants to the body, and many more. Although great progress has been made in understanding their structure-properties relationships, the large number of different processing techniques, each producing material with different characteristics and structure, means that understanding of the individual effects of all aspects of structure is not complete. The replication process, where molten metal is infiltrated between grains of a removable preform material, allows a markedly high degree of control and has been used to good effect to elucidate some of these relationships. Nevertheless, the process has many steps that are dependent on individual &#8220;know-how&#8221;, and this paper aims to provide a detailed description of all stages of one embodiment of this processing method, using materials and equipment that would be relatively easy to set up in a research environment. The goal of this protocol and its variants is to produce metal foams in an effective and simple way, giving the possibility to tailor the outcome of the samples by modifying certain steps within the process. By following this, open cell aluminum foams with pore sizes of 1&#8211;2.36 mm diameter and 61% to 77% porosity can be obtained.

Replication is one of the processing techniques used for the production of porous metal sponges. In this paper one implementation of the method for the production of open celled porous aluminum is shown in detail.

铸造协议的开孔泡沫铝通过复制技术的生产和孔隙率的影响

Metal foams are interesting materials from both a fundamental understanding and practical applications point of view. Uses have been proposed, and in many ...

Electron Channeling Contrast Imaging for Rapid III-V Heteroepitaxial Characterization

Misfit dislocations in heteroepitaxial layers of GaP grown on Si(001) substrates are characterized through use of electron channeling contrast imaging (ECCI) in a scanning electron microscope (SEM). ECCI allows for imaging of defects and crystallographic features under specific diffraction conditions, similar to that possible via plan-view transmission electron microscopy (PV-TEM). A particular advantage of the ECCI technique is that it requires little to no sample preparation, and indeed can use large area, as-produced samples, making it a considerably higher throughput characterization method than TEM. Similar to TEM, different diffraction conditions can be obtained with ECCI by tilting and rotating the sample in the SEM. This capability enables the selective imaging of specific defects, such as misfit dislocations at the GaP/Si interface, with high contrast levels, which are determined by the standard invisibility criteria. An example application of this technique is described wherein ECCI imaging is used to determine the critical thickness for dislocation nucleation for GaP-on-Si by imaging a range of samples with various GaP epilayer thicknesses. Examples of ECCI micrographs of additional defect types, including threading dislocations and a stacking fault, are provided as demonstration of its broad, TEM-like applicability. Ultimately, the combination of TEM-like capabilities &#8211; high spatial resolution and richness of microstructural data &#8211; with the convenience and speed of SEM, position ECCI as a powerful tool for the rapid characterization of crystalline materials.

The use of electron channeling contrast imaging in a scanning electron microscope to characterize defects in III-V/Si heteroexpitaxial thin films is described. This method yields similar results to plan-view transmission electron microscopy, but in significantly less time due to lack of required sample preparation.

电子通道造影的快速III-V异质特征

Misfit dislocations in heteroepitaxial layers of GaP grown on Si(001) substrates are characterized through use of electron channeling contrast imaging ...

Quantification of Hydrogen Concentrations in Surface and Interface Layers and Bulk Materials through Depth Profiling with Nuclear Reaction Analysis

Nuclear reaction analysis (NRA) via the resonant 1H(15N,&#945;&#947;)12C reaction is a highly effective method of depth profiling that quantitatively and non-destructively reveals the hydrogen density distribution at surfaces, at interfaces, and in the volume of solid materials with high depth resolution. The technique applies a 15N ion beam of 6.385 MeV provided by an electrostatic accelerator and specifically detects the 1H isotope in depths up to about 2 &#956;m from the target surface. Surface H coverages are measured with a sensitivity in the order of ~1013 cm-2 (~1% of a typical atomic monolayer density) and H volume concentrations with a detection limit of ~1018 cm-3 (~100 at. ppm). The near-surface depth resolution is 2-5 nm for surface-normal 15N ion incidence onto the target and can be enhanced to values below 1 nm for very flat targets by adopting a surface-grazing incidence geometry. The method is versatile and readily applied to any high vacuum compatible homogeneous material with a smooth surface (no pores). Electrically conductive targets usually tolerate the ion beam irradiation with negligible degradation. Hydrogen quantitation and correct depth analysis require knowledge of the elementary composition (besides hydrogen) and mass density of the target material. Especially in combination with ultra-high vacuum methods for in-situ target preparation and characterization, 1H(15N,&#945;&#947;)12C NRA is ideally suited for hydrogen analysis at atomically controlled surfaces and nanostructured interfaces. We exemplarily demonstrate here the application of 15N NRA at the MALT Tandem accelerator facility of the University of Tokyo to (1) quantitatively measure the surface coverage and the bulk concentration of hydrogen in the near-surface region of a H2 exposed Pd(110) single crystal, and (2) to determine the depth location and layer density of hydrogen near the interfaces of thin SiO2 films on Si(100).

We illustrate the application of 1H(15N,&#945;&#947;)12C resonant nuclear reaction analysis (NRA) to quantitatively evaluate the density of hydrogen atoms on the surface, in the volume, and at an interfacial layer of solid materials. The near-surface hydrogen depth profiling of a Pd(110) single crystal and of SiO2/Si(100) stacks is described.

通过与核反应分析深度剖面的表面和界面层和颗粒材料氢含量的定量

Nuclear reaction analysis (NRA) via the resonant 1H(15N,&#945;&#947;)12C reaction is a highly effective method of depth profiling that quantitatively and ...

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 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 ...