我们感谢 m. 中山, s. Toyohisa, 福岛和石田支持实验装置。我们感激地认识到, 通过26287061号项目和青年科学家 (b) 通过15K17675 项目的 Grantin (b) 为科学研究提供的资助。这项工作也得到日本下个 (创新领域 "拓扑材料科学", "16H00979 号") 和 jsp KAKENHI (批准号 16H02209) 的支持。

1. 装载和安装示例
<ol><li>将 Bi2Se313的单晶样品切成 1 x 1 x 0.5 毫米3 , 并使用银基环氧树脂将样品粘附在样品架上。</li>
	<li>将透明胶带粘贴到样品表面上。 注: 该透明胶带用于在超高真空 (特高压) 腔内切割样品以获得原子清洁的表面。</li>
	<li>将样品安装到负载锁的样品杂志中, 启动泵直到负载锁的压力低于 1×10-5宾夕法尼亚州。</li>
</ol>2. 试样裂解
<ol><li>打开负载锁和特高压准备室之间的特高压阀。</li>
	<li>使用连接到负载锁室的线性/旋转馈将样品杂志从负载岩石移动到准备室。</li>
	<li>从样品杂志上提取样品, 并附上准备室的转移杆。</li>
	<li>把样品杂志放回负载锁中, 关闭特高压阀门。</li>
	<li>等待, 直到准备室的压力低于 5×10-7宾夕法尼亚州</li>
	<li>在制备室中使用摆动棒剥离透明胶带, 在特高压条件下对试样进行切割。</li>
</ol>3. 样品转移到测量位置
<ol><li>将样品转移到特高压测量室, 并将试样固定在主 gonio 阶段, 由装有测量室的螺钉驱动。</li>
	<li>将 gonio 阶段移动到测量位置, 并使用千分尺阶段精确地将取样位置移到光谱仪的焦点上。</li>
</ol>4. 7 ev 激光装置
<ol><li>打开 Nd:YVO4 激光器。 注: 激光产生355纳米激光光, 重复率高120兆赫。</li>
	<li>打开激光光束快门, 确保激光穿过 KBBF 晶体, 产生 177 nm (6.994 eV) 的第二谐波波。</li>
	<li>通过改变355纳米激光与可变衰减器的功率, 优化 7 ev 激光器的功率。</li>
</ol>5. ARPES 数据采集
<ol><li>在台式计算机上打开分析器控制软件。 注: 我们使用 "SES 软件", 这是一个通用的程序控制 ScientaOmicron 分析仪与电子偏转器。</li>
	<li>在菜单栏上选择 "设置......" (图 2, 第一步 2-1)。</li>
	<li>选择ARPES 配置(图 3, 步骤 i. 3-1) 和ARPES 映射在列表中 (图 3, 第一步 3-2) 执行费米表面映射与光电子偏转器。</li>
	<li>单击 "编辑" (图 3, 第一步 3-3) 并配置费米曲面映射, 范围从-12°到12°的发射角θy 与0.5°的步长 (图 3, 第一步 3-4)。 注意: 用电子偏转器的半球分析器使我们能够映射费米表面而不进行样本旋转。</li>
	<li>单击 "运行" (图 2, 第一步 2-3)。</li>
</ol>6. SARPES 数据采集
<ol><li>手动更改 SARPES 测量的机器设置, 包括分析仪入口狭缝和孔径大小 (图 1)。</li>
	<li>在菜单栏上选择 "设置......" (图 2, 第一步 2-2)。</li>
	<li>选择 "旋转配置" (图 4、步骤 4-1) 和列表中的正常(图 4, 第一步 4-2), 然后单击"确定" (图 4, 第一步. 4-3)。</li>
	<li>选择DA30 (图 5, 第一步. 5-1) 在菜单栏和控制θ..。(图 5, 第一步. 5-2) 打开设置面板的 DA30 角 (θx, θy) 配置。</li>
	<li>选择发射角 (θx, θy) = (-6°, 0°) 以 SARPES 光谱 (图 5, 第一步. 5-3)。</li>
	<li>通过控制双极电容器库, 应用磁场, 将 VLEED 目标沿特定轴 (α: x、 y或z) 的正方向磁化。 注意: 在我们的系统中, 这个过程可以通过命令提示符完成 [图 6 (a)]。</li>
	<li>单击 "运行" 以采取强度频谱 (图 2, 第一步 2-3)。</li>
	<li>应用磁场对 VLEED 目标沿α方向磁化, 开始扫描以达到强度谱。</li>
	<li>计算自旋极化和自旋分辨谱。</li>
</ol>7. 扫描光极化依赖性
<ol><li>改变由步进电机精确控制的λ/2-waveplate 的角度来调节 7 eV 激光器的光极化。 注意: 在我们的系统中, 这个过程可以通过命令提示符完成 [图 6 (b)]。</li>
	<li>取x、y和z轴的自旋分辨光谱。</li>
	<li>将自旋分辨光谱扫描为光极化函数, 并将102°的半 waveplate 角与3°的步长大小变化。</li>
</ol>

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作者声明他们没有竞争的财政利益。

ARPES 和 SARPES 技术已被广泛用于研究电子带结构通过波段映射和自旋检测1,2。除了上述一般优点之外, 基于光偶极子激发的轨道选择规则的激光 SARPES 可以作为一种新的技术, 用于可视化波函数和量子自旋干涉中的自旋轨道耦合效应。.如图 9 和 10所示, 激光的偏振可以很容易地通过 waveplates 在p和s-偏振19之间的倾斜线性偏振来操作。在原理上, 可以在激光 SAPRES 中获得和使用圆形甚至椭圆形偏振光。在传统光源中, 如惰性气体放电灯和同步辐射等, 很难得到这种可调谐极化的变化。因此, 将偏振变激光与 SARPES 3D 自旋分辨率相结合, 大大提高了光电子技术的性能。
要在最佳条件下进行激光 SARPES, 必须时刻注意空间电荷效应12, 因为在高强度激光发射的致密电子数据包中, 库仑斥力通常会增大光电子的能量。如果出现这个问题, 你需要优化 7 eV 激光器 (步骤 4.3) 的功率。第二, 如果样品的光电子强度较差, 分析仪入口狭缝, 孔径应该是开放的 (步骤 6.1), 然而, 在这种情况下, 能量的分辨率是牺牲的。因此, 我们需要仔细选择实验设置, 以适应激光 SARPES 实验。
激光 SARPES 与同步辐射标准光电子技术相比, 其主要缺点是激光 SAPRES 激光器的光子能量一般不可调谐。在光电子技术中, 可调谐光子是探测kz 色散的必要条件, 并识别3D 散带结构和二维表面状态1。此外, 本文所用的 7 eV 的光子能量可以扫描小k区, 与光子能量较高的区域相比。因此, 激光 SARPES 在布里渊区中心的二维表面状态的研究中可能受到限制。
但应注意的是, 激光 SARPES 技术的威力可以广泛地应用于自旋轨道耦合状态。最近, 通过使用本文所描述的协议, 我们进一步揭示了强自旋-轨道耦合效应及其对双薄膜22和 BiAg2/Ag (111) 表面合金23的显著k依赖性。此外, 值得注意的是, 高效的 SARPES 技术刚刚开始发展, 并逐渐成为一个标准的实验技术。该协议旨在帮助研究人员使用 SARPES 和了解所产生的数据。

角分辨光电子光谱学 (ARPES) 技术已发展成为研究固态1中准粒子带结构最有力的工具之一。ARPES 的最具吸引力的特征是在能量和动量空间中的电子态特征的波段映射能力。自旋解析 ARPES (SARPES), 这里装有自旋探测器, 即g。莫特探测器2,3, 进一步使我们能够解决的自旋特性的观测带结构4。由于莫特探测器可以测量两个轴 (x和z, 或y和z) 的旋转, 两个莫特探测器的组合进一步允许一个在三维度4,5 中获得旋转方向..然而, 几十年来, SARPES 实验的效率低 (通常是 1/10000, 与自旋集成 ARPES 测量相比)3,4,5,6 ,7, 它限制了能量和角分辨率。最近, SARPES 的能量分辨率增加了一个基于交换散射的高效自旋探测器, 所谓的极低能量电子衍射 (VLEED) 探测器7,8,9 ,10。利用该检测器, 数据质量得到了显著提高, 数据采集时间缩短。最近, SARPES 成功地解决了自旋极化电子态, 特别是自旋-轨道耦合效应, 导致了表面带7的自旋纹理。
在这里, 我们使用 SARPES 测量与偏振变真空紫外线激光 (激光 SARPES), 并证明了这一组合技术的巨大优势。通过对 Bi2Se3中自旋轨道耦合表面状态的研究, 提出了两种激光 SARPES 的能力。首先, 由于线性极化激光器在偶极过渡态中的轨道选择规律, p-和s-偏振光有选择地激发了不同轨道对称的特征波函数的一部分。这样的轨道选择性激发, 从而在 SARPES, 即轨道选择性 SARPES。其次, SARPES 中的三维 (3D) 自旋检测显示了自旋量子轴的方向, 直接显示了光极化依赖性的完整信息。在本议定书中, 我们简要描述了一种方法来执行这一最先进的激光 SARPES 技术来研究强自旋轨道耦合效应。
我们的激光 SARPES 系统位于11东京大学固体物理研究所。图 1显示了我们的激光 SAPRES 机的原理图。偏振变 7 eV 激光光12照亮样品表面, 光电子从样品中发出。激光偏振由 MgF2基λ/2-和λ/4 waveplates 自动控制, 选择性地使用线性和圆形偏振。半球电子分析仪纠正了光电子, 并分析了它们的动能 (E族) 和发射角 (θx 和θy)。在 CCD 摄像机监控的E型θx 屏幕上映射了光电子强度。该图像直接转化为互补空间的能量带结构。
对于 SARPES 测量, 通过电子分析仪分析的光电子具有特定的发射角和动能, 对两个具有90度光电子偏转器的 VLEED 型自旋探测器进行了导引, 光电子束聚焦在两个铁 (001)p(1×1) 薄膜的不同靶点由氧终止。通过在每个自旋探测器中使用一个 channeltron, 在单通道检测中检测到目标反射的光电子。VLEED 的目标可以磁化与亥姆霍兹型的电线圈, 这是安排与正交几何相互尊重。磁化方向由双极电容器库控制。双 VLEED 自旋探测器从而使我们能够分析三维光电子的自旋极化矢量。

<table>
	<tbody>
		<tr>
			<td>DA30-L hemispherical analyzer</td>
			<td>ScientaOmicron</td>
			<td></td>
			<td>http://www.scientaomicron.com/en/products/353/1170</td>
		</tr>
		<tr>
			<td>Silver-based epoxy</td>
			<td>Epoxy Technology</td>
			<td>H20E</td>
			<td></td>
		</tr>
		<tr>
			<td>Sctoch tape</td>
			<td>3M</td>
			<td>801-1-18C</td>
			<td></td>
		</tr>
		<tr>
			<td>UHV valve</td>
			<td>VAT</td>
			<td>01034-KE01</td>
			<td></td>
		</tr>
		<tr>
			<td>linear/rotary feedthrough</td>
			<td>Ferrovac</td>
			<td>MD40</td>
			<td></td>
		</tr>
		<tr>
			<td>transfer rod</td>
			<td>UHV design</td>
			<td>PP series</td>
			<td></td>
		</tr>
		<tr>
			<td>wobble stick</td>
			<td>Ferrovac</td>
			<td>WM40</td>
			<td></td>
		</tr>
		<tr>
			<td>Paladin compact 355</td>
			<td>Coherent</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>half waveplate</td>
			<td>Kogakugiken</td>
			<td></td>
			<td>order made</td>
		</tr>
		<tr>
			<td>Bipolar condenser bank</td>
			<td>Tsuji electronics</td>
			<td></td>
			<td></td>
		</tr>
	</tbody>
</table>

experimental methods for spin- and angle-resolved photoemission spectroscopy combined with polarization-variable laser

本协议的目的是介绍如何执行自旋和角分辨光电子光谱与偏振-变 7-eV 激光器 (激光 SARPES), 并证明了这一技术的力量, 研究固体物理。激光 SARPES 达到两大功能。首先, 通过对线性极化激光器的轨道选择规律的研究, 可以在 SAPRES 实验中进行轨道选择性激励。其次, 该技术可以显示自旋量子轴作为光极化函数的变化的完整信息。为了演示这些能力在激光 SARPES 中的协作能力, 我们将此技术应用于对 Bi2Se3的自旋轨道耦合表面状态的研究。这种技术可以从自旋轨道耦合波函数中分解自旋和轨道元件。此外, 该技术作为利用直接自旋检测与偏振变量激光器协作的代表优势, 明确地直观地揭示了自旋量子轴在三维中的光极化依赖性。激光 SARPES 显著提高了光电子技术的能力。

在开始 SARPES 实验之前, 需要用高能量和角分辨率 (5.1-5.5) 的高度统计自旋综合 ARPES 结果准确地确定k位置, 以获得自旋分辨谱。图 7展示了双2Se3单晶的 ARPES 结果。这种材料被称为一个典型的拓扑绝缘体与自旋极化表面状态14,15。ARPES 带图清楚地解析了二维表面状态16的非常陡峭的狄拉克锥状能量色散。结果表明, ARPES 的表面质量高, 样品定向。从带图和费米曲面映射的能量和动量信息, 现在可以选择 SARPES 实验的特定发射角。
图 8(a)代表不同磁化方向 (my 和-my) 的能量分布曲线 (EDCs) (θx, θy) = (-6°, 0°) 横跨kF的曲面带, 对应于图 7所示虚线的切割。从数据中可以获得自旋解析 EDCs。首先, 利用此关系估计自旋极化 (Py):
<img alt="Equation 1" src="/files/ftp_upload/57090/57090eq1.jpg">
其中α是被分辨的轴 (x、 y和z), 而我+m α (im α) 是光电子强度为 +m α (-m α), 并且的是谢尔曼函数, 通常是 0.311。得到的Py 曲线如图 8 (b)所示。然后通过以下方法获得自旋 (<img alt="Equation 2" src="/files/ftp_upload/57090/57090eq2.jpg">) 和自旋下 (<img alt="Equation 3" src="/files/ftp_upload/57090/57090eq3.jpg">) 的旋转解析谱:
<img alt="Equation 4" src="/files/ftp_upload/57090/57090eq4.jpg">
由此产生的自旋解析谱如 图 8(c)所示。
双 VLEED 旋转探测器允许我们获得3D 的自旋分辨率沿x, y和z轴。图 9(a)中演示了使用p-极化设置和相应的自旋极化 (px、 py 和pz) 的自旋分辨光谱是显示。在费米能量附近的明显峰值被分配到 Bi2Se3的表面状态。数据表明, py 是完全自旋极化〜 100%, 而其他组成部分, px 和pz, 是微乎其微小。3D 自旋解析谱从而说明了沿y固定的曲面状态的自旋量子轴, 它与带计算16、17、18相一致。
然后, 重点研究了p-和s-偏振激光器的轨道选择性激励问题。一般情况下, 在强自旋轨道耦合下, 不同的轨道对称性与相反的旋在单个本征函数17、18中混合。在我们的实验几何中, p极化 (s-极化) 光对自旋轨道耦合波函数中的px 和pz (py) 轨道分量敏感 (嵌入在图 9)。因此, 通过自旋轨道耦合, 轨道选择性激光 SARPES 应检测p-和s-极化的反旋极化。的确, 这一点在图 9(a)和9 (b)中得到了证明。我们清楚地看到Py在表面状态17,18中直接显示自旋轨道耦合效应的显著光极化依赖性。
此外, 激光 SARPES 还可以进一步研究 p x、 py 和pz 的线性极化演化, 即使是p-和s-偏振之间的倾斜光极化。19. 如图 10(a)所示, 激光 SARPES 与3D 旋转检测显示px, py 和pz 在 0.025 eV 的结合能作为一个函数的线性偏振。在这里, 结果包含102个数据点, 这是在6小时内获得的。py 的极化依赖性很容易解释为一个事实, 即由应用激光器的p和s分量激发的光电子的正负Py抵消掉。然而, 这不能解释px 和pz的演化。为了完全描述这一结果, 有必要考虑光电子中的相干自旋过程, 如图 10(b)所述。如果线性极化同时激发了自旋和自旋向下的状态, 这两个量子自旋基在光电子态中被相干叠加, 从而产生旋转旋转。事实上, 模型计算充分再现了所显示的极化依赖性, 并考虑了p-和s-偏振19激发的自旋和自旋下的相干干扰。类似的自旋效应也被 3D SARPES 观测到, 同步辐射20,21。
<img alt="Figure 1" class="xfigimg" src="/files/ftp_upload/57090/57090fig1.jpg"> 图 1: 激光 SARPES 检测系统示意图.采用正交几何的两个 VLEED 自旋探测器连接到半球光电子分析仪。这个数字已经从 Yaji, K. 11.<a href="https://cloudflare-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/57090/57090fig1large.jpg" target="_blank">请点击这里查看这个数字的更大版本.</a>
<img alt="Figure 2" class="xfigimg" src="/files/ftp_upload/57090/57090fig2.jpg"> 图 2: 分析器控制软件的截图.步骤2-1 到 i. 2-3 显示如何开始选择检测模式 (ARPES 或 SARPES) 和采集数据。<a href="https://cloudflare-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/57090/57090fig2large.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/57090/57090fig3.jpg"> 图 3: 用于选择检测模式的控制面板的屏幕截图.步骤3-1 到 i. 3-4 显示如何启动费米曲面映射。如果按下按钮编辑(第一步 3-3), 新面板将弹出以定义映射的属性 (第一步. 3-4)。
<img alt="Figure 4" class="xfigimg" src="/files/ftp_upload/57090/57090fig4.jpg"> 图 4: 用于选择检测模式的控制面板的屏幕截图.步骤4-1 到 i. 4-3 显示如何启动 SARPES 模式。如果选择了旋转区域 (第一步 4-1), 底部OK被按下 (第一步. 4-3), 面板将关闭, 整个分析器设置将变成 SARPES 模式。
<img alt="Figure 5" class="xfigimg" src="/files/ftp_upload/57090/57090fig5.jpg"> 图 5: 电子偏转器控制面板的屏幕截图.步骤5-1 到 i. 5-3 显示如何控制光电子偏转器。如果按下了区域控制θ (第一步 5-2), 新的面板将弹出以定义光电子偏转器 (第一步 5-3) 的属性。<a href="https://cloudflare-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/57090/57090fig5large.jpg" target="_blank">请单击此处查看此图的较大版本.</a>
<img alt="Figure 6" class="xfigimg" src="/files/ftp_upload/57090/57090fig6.jpg"> 图 6: 旋转靶和光极化磁场的面板截图.这些属性由系统中的命令行控制。(a) 控制旋转目标磁场的命令: "spin_coil X" 对应于 "应用程序文件的名称"、"字段的方向、+ 或-" 和 "坐标轴、 X、 y或z"。(B) 控制光极化的命令: "wave_plate 180" 对应于 "应用程序文件的名称" 和 " λ/2-waveplate 的角度"。
<img alt="Figure 7" class="xfigimg" src="/files/ftp_upload/57090/57090fig7.jpg"> 图 7: 使用 ARPES 对2Se3表面状态的费米曲面映射和E k波段映射.虚线表示采用自旋分辨光谱的k位置, 如图 8和图 9所示。<a href="https://cloudflare-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/57090/57090fig7large.jpg" target="_blank">请单击此处查看此图的较大版本.</a>
<img alt="Figure 8" class="xfigimg" src="/files/ftp_upload/57090/57090fig8.jpg"> 图 8: Bi2Se3的自旋和角度分辨的表面带光谱.(a) 在与图 7中的虚线切割相对应的固定发射角上测量不同磁化方向 +my 和-my 的能量分布曲线 (EDCs)。(b) 自旋解析分析获得的结合能量函数的旋转偏振。(c) 由此产生的 EDCs (红色三角形) 和自旋向下 (蓝色三角形) 通道。<a href="https://cloudflare-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/57090/57090fig8large.jpg" target="_blank">请单击此处查看此图的较大版本.</a>
<img alt="Figure 9" class="xfigimg" src="/files/ftp_upload/57090/57090fig9.jpg"> 图 9: 光电子自旋的p和s-极化依赖于 Bi2Se3的表面状态.(a) 和 (b)x、y 和 z 轴的3D 自旋分辨光谱, 以及相应的自旋偏振(px、 py 和pz) 作为由P和 s 获得的结合能的函数-偏振在与图 7中的虚线切割相对应的固定发射角度。在嵌入式中, 给出了p-和s-偏振的实验配置。这个数字已经从黑田 K. 19. p(s) 极化有选择地激发px 和pz (py) 象轨道波函数。px 和pz (py) 状态是耦合到y旋转 (−y旋转) 在自旋轨道耦合的表面状态16,17。<a href="https://cloudflare-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/57090/57090fig9large.jpg" target="_blank">请单击此处查看此图的较大版本.</a>
<img alt="Figure 10" class="xfigimg" src="/files/ftp_upload/57090/57090fig10.jpg"> 图 10: 由线性偏振光引起的三维自旋极化效应.一个2Se3表面状态的Px、y、z 的图, 与应用的线性偏振激光器有关。在嵌入式中, 显示了投射到x z平面上的激光的应用电场。总数据点在6小时之内被采取了。这一数字已从黑田、K等地修改。19. (b) 由于自旋和自旋自旋的干扰, 可视化的3D 旋转旋转。<a href="https://cloudflare-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/57090/57090fig10large.jpg" target="_blank">请单击此处查看此图的较大版本.</a>

Watch this Scientific Journal Video about Experimental Methods for Spin- and Angle-Resolved Photoemission Spectroscopy Combined with Polarization-Variable Laser at JoVE.com

Experimental Methods for Spin- and Angle-Resolved Photoemission Spectroscopy Combined with Polarization-Variable Laser

在这里, 我们将偏振变 7 eV 激光器与自旋-角分辨光电子技术相结合, 以可视化固态中的自旋轨道耦合效应。

自旋角分辨光电子光谱与偏振变激光相结合的实验方法

The goal of this protocol is to present how to perform spin- and angle-resolved photoemission spectroscopy combined with polarization-variable 7-eV laser ...

experimental-methods-for-spin-angle-resolved-photoemission

Nanyang Technological University

Research

JoVE Journal

Engineering

9.8K 次观看.  University of Tokyo. 在这里, 我们将偏振变 7 eV 激光器与自旋-角分辨光电子技术相结合, 以可视化固态中的自旋轨道耦合效应。

视频: Experimental Methods for Spin- and Angle-Resolved Photoemission Spectroscopy Combined with Polarization-Variable Laser

Angle-resolved Photoemission Spectroscopy At Ultra-low Temperatures

The physical properties of a material are defined by its electronic structure. Electrons in solids are characterized by energy (&omega;) and momentum (k) and the probability to find them in a particular state with given &omega; and k is described by the spectral function A(k, &omega;). This function can be directly measured in an experiment based on the well-known photoelectric effect, for the explanation of which Albert Einstein received the Nobel Prize back in 1921. In the photoelectric effect the light shone on a surface ejects electrons from the material. According to Einstein, energy conservation allows one to determine the energy of an electron inside the sample, provided the energy of the light photon and kinetic energy of the outgoing photoelectron are known. Momentum conservation makes it also possible to estimate k relating it to the momentum of the photoelectron by measuring the angle at which the photoelectron left the surface. The modern version of this technique is called Angle-Resolved Photoemission Spectroscopy (ARPES) and exploits both conservation laws in order to determine the electronic structure, i.e. energy and momentum of electrons inside the solid. In order to resolve the details crucial for understanding the topical problems of condensed matter physics, three quantities need to be minimized: uncertainty* in photon energy, uncertainty in kinetic energy of photoelectrons and temperature of the sample.
In our approach we combine three recent achievements in the field of synchrotron radiation, surface science and cryogenics. We use synchrotron radiation with tunable photon energy contributing an uncertainty of the order of 1 meV, an electron energy analyzer which detects the kinetic energies with a precision of the order of 1 meV and a He3 cryostat which allows us to keep the temperature of the sample below 1 K. We discuss the exemplary results obtained on single crystals of Sr2RuO4 and some other materials. The electronic structure of this material can be determined with an unprecedented clarity.

The overall goal of this method is to determine the low-energy electronic structure of solids at ultra-low temperatures using Angle-Resolved Photoemission Spectroscopy with synchrotron radiation.

在极低的温度下角分辨光电子能谱

The physical properties of a material are defined by its  electronic structure. Electrons in solids are characterized by energy (&omega;)  and momentum ...

科研

工程学

Spatial Separation of Molecular Conformers and Clusters

Gas-phase molecular physics and physical chemistry experiments commonly use supersonic expansions through pulsed valves for the production of cold molecular beams. However, these beams often contain multiple conformers and clusters, even at low rotational temperatures. We present an experimental methodology that allows the spatial separation of these constituent parts of a molecular beam expansion. Using an electric deflector the beam is separated by its mass-to-dipole moment ratio, analogous to a bender or an electric sector mass spectrometer spatially dispersing charged molecules on the basis of their mass-to-charge ratio. This deflector exploits the Stark effect in an inhomogeneous electric field and allows the separation of individual species of polar neutral molecules and clusters. It furthermore allows the selection of the coldest part of a molecular beam, as low-energy rotational quantum states generally experience the largest deflection. Different structural isomers (conformers) of a species can be separated due to the different arrangement of functional groups, which leads to distinct dipole moments. These are exploited by the electrostatic deflector for the production of a conformationally pure sample from a molecular beam. Similarly, specific cluster stoichiometries can be selected, as the mass and dipole moment of a given cluster depends on the degree of solvation around the parent molecule. This allows experiments on specific cluster sizes and structures, enabling the systematic study of solvation of neutral molecules.

We present a technique that allows the spatial separation of different conformers or clusters present in a molecular beam. An electrostatic deflector is used to separate species by their mass-to-dipole moment ratio, leading to the production of gas-phase ensembles of a single conformer or cluster stoichiometry.

分子构象器和星团的空间分离

Gas-phase molecular physics and physical chemistry experiments commonly use supersonic expansions through pulsed valves for the production of cold ...

Quantum State Engineering of Light with Continuous-wave Optical Parametric Oscillators

Engineering non-classical states of the electromagnetic field is a central quest for quantum optics1,2. Beyond their fundamental significance, such states are indeed the resources for implementing various protocols, ranging from enhanced metrology to quantum communication and computing. A variety of devices can be used to generate non-classical states, such as single emitters, light-matter interfaces or non-linear systems3. We focus here on the use of a continuous-wave optical parametric oscillator3,4. This system is based on a non-linear &#967;2 crystal inserted inside an optical cavity and it is now well-known as a very efficient source of non-classical light, such as single-mode or two-mode squeezed vacuum depending on the crystal phase matching. 
Squeezed vacuum is a Gaussian state as its quadrature distributions follow a Gaussian statistics. However, it has been shown that number of protocols require non-Gaussian states5. Generating directly such states is a difficult task and would require strong &#967;3 non-linearities. Another procedure, probabilistic but heralded, consists in using a measurement-induced non-linearity via a conditional preparation technique operated on Gaussian states. Here, we detail this generation protocol for two non-Gaussian states, the single-photon state and a superposition of coherent states, using two differently phase-matched parametric oscillators as primary resources. This technique enables achievement of a high fidelity with the targeted state and generation of the state in a well-controlled spatiotemporal mode.

We describe the reliable generation of non-Gaussian states of traveling optical fields, including single-photon states and coherent state superpositions, using a conditional preparation method operated on the non-classical light emitted by optical parametric oscillators. Type-I and type-II phase-matched oscillators are considered and common procedures, such as the required frequency filtering or the high-efficiency quantum state characterization by homodyning, are detailed.

光与连续波光学参量振荡器的量子态工程

Engineering non-classical states of the electromagnetic field is a central quest for quantum optics1,2. Beyond their fundamental significance, such states ...

Laser-induced Breakdown Spectroscopy: A New Approach for Nanoparticle's Mapping and Quantification in Organ Tissue

Emission spectroscopy of laser-induced plasma was applied to elemental analysis of biological samples. Laser-induced breakdown spectroscopy (LIBS) performed on thin sections of rodent tissues: kidneys and tumor, allows the detection of inorganic elements such as (i) Na, Ca, Cu, Mg, P, and Fe, naturally present in the body and (ii) Si and Gd, detected after the injection of gadolinium-based nanoparticles. The animals were euthanized 1&#160;to 24 hr&#160;after intravenous injection of particles. A two-dimensional scan of the sample, performed using a motorized micrometric 3D-stage, allowed the infrared laser beam exploring the surface with a lateral resolution less than 100 &#956;m. Quantitative chemical images of Gd element inside the organ were obtained with sub-mM sensitivity. LIBS offers a simple and robust method to study the distribution of inorganic materials without any specific labeling. Moreover, the compatibility of the setup with standard optical microscopy emphasizes its potential to provide multiple images of the same biological tissue with different types of response:&#160;elemental, molecular, or cellular.

Laser-induced breakdown spectroscopy performed on thin organ and tumor tissue successfully detected natural elements and artificially injected gadolinium (Gd), issued from Gd-based nanoparticles. Images of chemical elements reached a resolution of 100 &#956;m and quantitative sub-mM sensitivity. The compatibility of the setup with standard optical microscopy emphasizes its potential to provide multiple images of a same biological tissue.

激光诱导击穿光谱:对于纳米粒子的映射和定量的器官组织的新方法

Emission spectroscopy of laser-induced plasma was applied to elemental analysis of biological samples. Laser-induced breakdown spectroscopy (LIBS) ...

Proton Transfer and Protein Conformation Dynamics in Photosensitive Proteins by Time-resolved Step-scan Fourier-transform Infrared Spectroscopy

Monitoring the dynamics of protonation and protein backbone conformation changes during the function of a protein is an essential step towards understanding its mechanism. Protonation and conformational changes affect the vibration pattern of amino acid side chains and of the peptide bond, respectively, both of which can be probed by infrared (IR) difference spectroscopy. For proteins whose function can be repetitively and reproducibly triggered by light, it is possible to obtain infrared difference spectra with (sub)microsecond resolution over a broad spectral range using the step-scan Fourier transform infrared technique. With ~102-103 repetitions of the photoreaction, the minimum number to complete a scan at reasonable spectral resolution and bandwidth, the noise level in the absorption difference spectra can be as low as ~10-4, sufficient to follow the kinetics of protonation changes from a single amino acid. Lower noise levels can be accomplished by more data averaging and/or mathematical processing. The amount of protein required for optimal results is between 5-100 &#181;g, depending on the sampling technique used. Regarding additional requirements, the protein needs to be first concentrated in a low ionic strength buffer and then dried to form a film. The protein film is hydrated prior to the experiment, either with little droplets of water or under controlled atmospheric humidity. The attained hydration level (g of water / g of protein) is gauged from an IR absorption spectrum. To showcase the technique, we studied the photocycle of the light-driven proton-pump bacteriorhodopsin in its native purple membrane environment, and of the light-gated ion channel channelrhodopsin-2 solubilized in detergent.

Key steps of protein function, in particular backbone conformational changes and proton transfer reactions, often take place in the microsecond to millisecond time scale. These dynamical processes can be studied by time-resolved step-scan Fourier-transform infrared spectroscopy, in particular for proteins whose function is triggered by light.

质子转移和蛋白质构象动力学的光敏蛋白的时间分辨步进扫描傅立叶变换红外光谱

Monitoring the dynamics of protonation and protein backbone conformation changes during the function of a protein is an essential step towards ...

Advanced Experimental Methods for Low-temperature Magnetotransport Measurement of Novel Materials

Novel electronic materials are often produced for the first time by synthesis processes that yield bulk crystals (in contrast to single crystal thin film synthesis) for the purpose of exploratory materials research. Certain materials pose a challenge wherein the traditional bulk Hall bar device fabrication method is insufficient to produce a measureable device for sample transport measurement, principally because the single crystal size is too small to attach wire leads to the sample in a Hall bar configuration. This can be, for example, because the first batch of a new material synthesized yields very small single crystals or because flakes of samples of one to very few monolayers are desired. In order to enable rapid characterization of materials that may be carried out in parallel with improvements to their growth methodology, a method of device fabrication for very small samples has been devised to permit the characterization of novel materials as soon as a preliminary batch has been produced. A slight variation of this methodology is applicable to producing devices using exfoliated samples of two-dimensional materials such as graphene, hexagonal boron nitride (hBN), and transition metal dichalcogenides (TMDs), as well as multilayer heterostructures of such materials. Here we present detailed protocols for the experimental device fabrication of fragments and flakes of novel materials with micron-sized dimensions onto substrate and subsequent measurement in a commercial superconducting magnet, dry helium close-cycle cryostat magnetotransport system at temperatures down to 0.300 K and magnetic fields up to 12 T.

We describe the methodology of mechanical exfoliation and deposition of flakes of novel materials with micron-sized dimensions onto substrate, fabrication of experimental device structures for transport experimentation, and the magnetotransport measurement in a dry helium close-cycle cryostat at temperatures down to 0.300 K and magnetic fields up to 12 T.

对于新材料的低温磁输运测量先进的实验方法

Novel electronic materials are often produced for the first time by synthesis processes that yield bulk crystals (in contrast to single crystal thin film ...

SSVEP-based Experimental Procedure for Brain-Robot Interaction with Humanoid Robots

Brain-Robot Interaction (BRI), which provides an innovative communication pathway between human and a robotic device via brain signals, is prospective in helping the disabled in their daily lives. The overall goal of our method is to establish an SSVEP-based experimental procedure by integrating multiple software programs, such as OpenViBE, Choregraph, and Central software as well as user developed programs written in C++ and MATLAB, to enable the study of brain-robot interaction with humanoid robots.
This is achieved by first placing EEG electrodes on a human subject to measure the brain responses through an EEG data acquisition system. A user interface is used to elicit SSVEP responses and to display video feedback in the closed-loop control experiments. The second step is to record the EEG signals of first-time subjects, to analyze their SSVEP features offline, and to train the classifier for each subject. Next, the Online Signal Processor and the Robot Controller are configured for the online control of a humanoid robot. As the final step, the subject completes three specific closed-loop control experiments within different environments to evaluate the brain-robot interaction performance.
The advantage of this approach is its reliability and flexibility because it is developed by integrating multiple software programs. The results show that using this approach, the subject is capable of interacting with the humanoid robot via brain signals. This allows the mind-controlled humanoid robot to perform typical tasks that are popular in robotic research and are helpful in assisting the disabled.

The overall goal of this method is to establish an SSVEP-based experimental procedure by integrating multiple software programs to enable the study of brain-robot interaction with humanoid robots, which is prospective in assisting the sick and elderly as well as performing unsanitary or dangerous jobs.

SSVEP基础实验步骤与人形机器人脑机器人互动

Brain-Robot Interaction (BRI), which provides an innovative communication pathway between human and a robotic device via brain signals, is prospective in ...

Experimental Methods for Investigation of Shape Memory Based Elastocaloric Cooling Processes and Model Validation

Shape Memory Alloys (SMA) using elastocaloric cooling processes have the potential to be an environmentally friendly alternative to the conventional vapor compression based cooling process. Nickel-Titanium (Ni-Ti) based alloy systems, especially, show large elastocaloric effects. Furthermore, exhibit large latent heats which is a necessary material property for the development of an efficient solid-state based cooling process. A scientific test rig has been designed to investigate these processes and the elastocaloric effects in SMAs. The realized test rig enables independent control of an SMA&#39;s mechanical loading and unloading cycles, as well as conductive heat transfer between SMA cooling elements and a heat source/sink. The test rig is equipped with a comprehensive monitoring system capable of synchronized measurements of mechanical and thermal parameters. In addition to determining the process-dependent mechanical work, the system also enables measurement of thermal caloric aspects of the elastocaloric cooling effect through use of a high-performance infrared camera. This combination is of particular interest, because it allows illustrations of localization and rate effects &#8212; both important for efficient heat transfer from the medium to be cooled.
The work presented describes an experimental method to identify elastocaloric material properties in different materials and sample geometries. Furthermore, the test rig is used to investigate different cooling process variations. The introduced analysis methods enable a differentiated consideration of material, process and related boundary condition influences on the process efficiency. The comparison of the experimental data with the simulation results (of a thermomechanically coupled finite element model) allows for better understanding of the underlying physics of the elastocaloric effect. In addition, the experimental results, as well as the findings based on the simulation results, are used to improve the material properties.

Experimental methods for investigation of solid state cooling processes and characterization of elastocaloric material properties of Shape Memory Alloys (SMA) are presented. A custom-built test rig has been designed for controlling and comprehensive monitoring of elastocaloric cooling processes. Furthermore, it provides a validation platform for thermomechanically coupled modeling approaches.

基于形状记忆调查Elastocaloric冷却过程和模型验证实验方法

Shape Memory Alloys (SMA) using elastocaloric cooling processes have the potential to be an environmentally friendly alternative to the conventional vapor ...

Compact Lens-less Digital Holographic Microscope for MEMS Inspection and Characterization

A micro-electro-mechanical-system (MEMS) is a widely used component in many industries, including energy, biotechnology, medical, communications, and automotive. However, effective inspection and characterization metrology systems are needed to ensure the functional reliability of MEMS. This study presents a system based on digital holography as a tool for MEMS metrology. Digital holography has gained increasing attention in the past 20 years. With the fast development and decreasing cost of sensor arrays, resolution of such systems has increased broadening potential applications. Thus, it has attracted attention from both research and industry sides as a potential reliable tool for industrial metrology. Indeed, by recording the interference pattern between an object beam (which contains sample height information) and a reference beam on a CCD camera, one can retrieve the quantitative phase information of an object. However, most of digital holographic systems are bulky and thus not easy to implement on industry production lines. The novelty of the system presented is that it is lens-less and thus very compact. In this study, it is shown that the Compact Digital Holographic Microscope (CDHM) can be used to evaluate several characteristics typically consider as criteria in MEMS inspections. The surface profiles of MEMS in both static and dynamic conditions are presented. Comparison with AFM is investigated to validate the accuracy of the CDHM.

We present a compact reflection digital holographic system (CDHM) for inspection and characterization of MEMS devices. A lens-less design using a diverging input wave providing natural geometrical magnification is demonstrated. Both static and dynamic studies are presented.

紧凑的镜头少数字全息显微镜的MEMS检测与表征

A micro-electro-mechanical-system (MEMS) is a widely used component in many industries, including energy, biotechnology, medical, communications, and ...

Free-form Light Actuators &#8212; Fabrication and Control of Actuation in Microscopic Scale

Liquid crystalline elastomers (LCEs) are smart materials capable of reversible shape-change in response to external stimuli, and have attracted researchers&#39; attention in many fields. Most of the studies focused on macroscopic LCE structures (films, fibers) and their miniaturization is still in its infancy. Recently developed lithography techniques, e.g., mask exposure and replica molding, only allow for creating 2D structures on LCE thin films. Direct laser writing (DLW) opens access to truly 3D fabrication in the microscopic scale. However, controlling the actuation topology and dynamics at the same length scale remains a challenge.
In this paper we report on a method to control the liquid crystal (LC) molecular alignment in the LCE microstructures of arbitrary three-dimensional shape. This was made possible by a combination of direct laser writing for both the LCE structures as well as for micrograting patterns inducing local LC alignment. Several types of grating patterns were used to introduce different LC alignments, which can be subsequently patterned into the LCE structures. This protocol allows one to obtain LCE microstructures with engineered alignments able to perform multiple opto-mechanical actuation, thus being capable of multiple functionalities. Applications can be foreseen in the fields of tunable photonics, micro-robotics, lab-on-chip technology and others.

Here, we fabricate 3D polymeric micro/nano structures in which both the shape and the molecular alignment can be engineered with nanometer scale accuracy by the use of direct laser writing. Light induced deformation of several types of liquid crystalline elastomer microstructures can be controlled in the microscopic scale.