Name: all-electronic nanosecond-resolved scanning tunneling microscopy: facilitating the investigation of single dopant charge dynamics
Uploaded: 2018-01-19T14:00:00.000+00:00
Duration: 11 min 33 s
Description: Watch this Scientific Journal Video about All-electronic Nanosecond-resolved Scanning Tunneling Microscopy: Facilitating the Investigation of Single Dopant Charge Dynamics at JoVE.com

我们要感谢马丁克卢捷和马克 Salomons 的技术专长。我们还感谢 NRC、NSERC 和 AITF 的财政支持。

1. 显微镜和实验的初步设置
<ol><li>首先是一个超高真空低温能力的 STM 和相关的控制软件。将 STM 冷却到低温温度。 注: 在本报告中, 超高真空指的是实现 < 10 x 10-10乇的系统。应将 STM 冷却到低温温度;这是特别重要的, 当调查掺杂的电荷动力学, 这是热活化在温和的温度。其他室可能在室温。</li>
	<li>确保 STM 尖端配备高频布线 (〜 500 MHz)。 注: 通过使用脉冲整形方法, Grosse et al.报告了与标准低温同轴电缆 (20 MHz) 的 STM 的时间响应的极大增加。31
</li>
	<li>将具有至少两个通道的任意函数生成器连接到 tip (图 2), 用于准备用于泵探针实验的电压脉冲对的循环。</li>
	<li>配置任意功能发生器, 使泵和探头电压脉冲独立生成, 并在送入尖端之前进行求和。</li>
	<li>将用于成像和常规光谱学的直流偏置电压应用于示例 (VDC)。</li>
	<li>将两个射频开关连接到任意函数发生器的输出通道。</li>
	<li>配置开关, 使尖端将在 STM 成像和常规光谱学的基础上, 有效的偏见是VDC + v提示在泵浦探针实验中 (图 4A)。</li>
	<li>通过连接到样品的前置放大器收集所有测量的隧道电流。</li>
</ol>2. H Si (100)-(2x1) 重建的准备
<ol><li>从 3-4 mΩ·cm n 型砷掺杂 Si (100) 晶圆片的背面用碳化硅划线, 用玻璃显微镜轻轻地把样品从晶片上掰下来。</li>
	<li>将样品贴在 stm 样品盒上, 并将其引入到与 stm 室相邻的超高真空室。</li>
	<li>通过电阻将样品加热到600° c (一个高温计可以用来监测样品的温度), 并在超高真空中将温度保持在至少6小时。 注: 压力将最初上升作为样品和样品持有德加, 但应稳定附近的基本压力 (< 10-10乇) 后几个小时。</li>
	<li>在继续之前, 让样品冷却到室温。</li>
	<li>用电阻将灯丝加热至1800° c, 并等待系统恢复至基压, 以在同一个腔室中的钨丝。在继续之前关闭灯丝。 注: 在这一步中, 样品可以留在腔内, 因为它是由其表面的氧化层钝化的, 因此这一步引起的样品表面的任何污染将随后被去除。灯丝的温度将被校准到一个特定的电流/电压应用于灯丝使用高温计。</li>
	<li>通过将样品从样品表面上闪到900° c, 在冷却到室温之前, 将其在十年代的温度下除去。在闪蒸过程中, 压力会从基本压力中增加几个数量级。在此过程中发现的每一个闪光后, 等待样品冷却到室温和系统恢复到基础压力, 然后继续。 注: 在本报告中, 闪烁是定义为加热和冷却的样品与高坡道率, 在100° c/秒的顺序。</li>
	<li>逐步闪光的样品, 以更高的温度, 而试图达到最后的闪光1250年° c。在 9x10-10乇上的压力升高时中止任何闪光, 以防止样品表面受到污染。记录用于实现1250° c 闪存的电压/电流 (在步骤2.6 中加热灯丝发出的光将防止高温计对样品的温度进行精确读数, 因此应使用此设定值)。在最后的闪光, 确定的电压/电流所需的加热样品到330° c, 因为晶体是冷却, 然后让样品冷却到室温, 并让系统恢复到基地的压力, 然后继续。</li>
	<li>泄漏 H2气体进入会议厅的压力 1x10-6乇和加热钨灯丝到1800° c。 注意: 这会使 H2 atmoic 氢32的效果。</li>
	<li>保持样品在这些情况下为2分钟在闪动样品之前到1250° c,拿着它在那温度为 5 s, 并且冷却它到330° c。</li>
	<li>在330° c 曝光1分钟后, 同时关闭 H2泄漏阀, 关闭钨灯丝, 让样品冷却到室温。 注: 这些高闪温会影响样品中掺杂的分布。加热到1250° c 已被发现诱导一个〜 60 nm 掺杂剂耗尽区附近的样品表面30。</li>
	<li>通过拍摄表面的 STM 图像来验证样品的质量。 注: 好的样品将有大 (> 30 nm x 30 nm) 的梯田与缺陷率 < 1% (悬空债券, 吸附分子, adatoms,等), 并将演示经典 Si (100)-(2x1) 重建32, 其中二聚体行跨步边运行平行 (图 3B)。</li>
</ol>3. 评估隧道交汇处的泵探头脉冲的质量
<ol><li>通过将电流设定为 50 pA, 并对-1.8 v 的样本偏差进行接触, 将 STM 尖端与样品表面接触。 注: 在这些条件下, 尖端估计是从样品表面 < 1 nm。本工作中使用的 STM 尖端是由化学蚀刻多晶钨产生的。它被削尖进一步使用氮气蚀刻做法, 在 Rezeq et al.中被很好描述33。</li>
	<li>通过进行大面积扫描 (例如, 50 nm x 50 nm), 在样品表面上寻找一个没有大表面缺陷的区域。</li>
	<li>将 stm 尖端置于表面上的 H Si 上, 在 stm 图像中显示为二聚体 (图 3B)。</li>
	<li>关闭当前反馈控制器</li>
	<li>将vDC设置为-1.0 v, v泵浦到-0.5 v, v探头到-0.5 v, 泵的宽度和探头脉冲到 200 ns, 脉冲的上升/下降时间为 2.5 ns (图 4A)。</li>
	<li>发送一系列的泵和探头脉冲的火车和探头的相对延迟从-900 ns 到 900 ns。</li>
	<li>将隧道电流绘制成泵与探头之间的延时函数。它可能会显示强振铃 (在隧道电流的振荡, 作为一个功能的相对延迟泵和探针脉冲,图 4B)。 注意: Python 和原始软件被用来绘制、分析和评估为这份手稿收集的数据。</li>
	<li>重复步骤 3.1–3.5, 但增加脉冲的上升/下降次数。随着上升/下降时间的增加, 铃声将会减少。 注意: 想要消除铃声以提供最精确的光谱结果, 但是, 这些技术的时间分辨率仅限于使用的脉冲宽度。25 ns 上升时间为这项工作使用了。</li>
</ol>4. 时间分辨扫描隧道光谱学 (TR STS)
<ol><li>将 STM 提示置于硅 DB 上, 在负尖端显示为亮凸起 (图 3B)。</li>
	<li>关闭 STM 电流反馈控制器。</li>
	<li>
发送一列仅由探头脉冲组成的列车, 其重复率为25赫。在一系列脉冲列车上, 扫描探头脉冲在 500 mV 范围内的偏差, 从直流偏置-1.8 v 注意: 这个简单的实验类似于传统的 STS, 在这种情况下, 电导是在一系列偏差中取样的。<ol>
<li>配置脉冲列车的持续时间 (每一个都有不同的偏差), 这样产生的光谱有一个信号的噪声比 > 10。</li>
	</ol>
</li>
	<li>发送一列由泵浦脉冲设置的固定偏置 (如VDC + V泵> V) 的列车, 其重复率为25赫。在这些实验中, 分别设置vDC、 v泵、 v和-1.8 伏、500毫伏和-2.0 v。 注: 泵浦脉冲可以具有任意长的持续时间 (1 µs 通常足够)。</li>
	<li>
发送一列由泵脉冲与探针脉冲, 然后延迟 10 ns。在这些实验中, 将泵浦脉冲的振幅设置为500毫伏, 探头脉冲扫掠从50到 500 mv。 注: 在本实验中, 探针脉冲是由泵浦脉冲所制备的状态进行采样, 而不是在常规 STS 中取样的平衡态。<ol>
<li>在显示/评估从该步骤收集的信号时, 仅应用泵浦脉冲时减去所获得的信号。</li>
	</ol>
</li>
	<li>比较探头和泵 + 探头信号, 通过在同一个图中绘制它们。在这两个信号中的任何滞后都是动态的指示, 可以用时间分辨的 STM 技术来探测。 注意: 通过保持探头脉冲的范围固定和粗略地扫描 DC 偏移量 (例如, 在 0.25 V 步骤中), 可以有效地映射样本的整个能量范围, 以识别技术可访问的动态。根据实验, 可以修改脉冲持续时间。泵浦脉冲的宽度需要比掺杂剂被电离的速率要长, 这样它才能持续电离掺杂剂。一般情况下, 探头的持续时间应与所研究的动力学过程相同, 这样就可以在不取样两个电导状态平均值的情况下测量最大信号。在寻找动力存在的能量时, 建议将探针的持续时间减到最小, 这样只测量系统的一个状态来增强迟滞。随着弛豫时间常数的增加, 探头脉冲的时间可以提高, 以改善信噪比。</li>
</ol>5. 时间分辨的 STM 测量松弛动力学
<ol><li>将 stm 提示置于硅 DB 上, 并关闭 stm 电流反馈控制器。</li>
	<li>发送一列由泵浦脉冲设置的固定偏置 (如VDC + V泵> V) 的列车, 其重复率为25赫。在这些实验中, 分别设置vDC、 v泵、 v和-1.8 伏、400毫伏和-2.0 v。 注: 泵浦脉冲可以具有任意长的持续时间 (1 µs 通常足够)。</li>
	<li>发送一列泵和探头脉冲。确保探头脉冲的振幅小于泵, 并与滞后发生的范围相媲美 (V探头< v泵, v探测器+ vDC≈V滞)。</li>
	<li>扫泵和探头脉冲之间的延迟多达几十个µs。</li>
	<li>减去仅在应用泵浦脉冲时获得的信号。在这些实验中, 分别将vDC、 v泵和 v探测器设置为-1.8 伏、400毫伏和 210 mv。将相对延迟扫描从-5 μ s 设置为35μ s。 注: 如果从前一步获得的信号是很好的 (R2 > 0.80) 由一个指数衰减函数, 那么由泵浦脉冲所准备的瞬态状态的寿命可以从合适的提取。</li>
</ol>6. 时间分辨的激励动力学的 STM 测量
<ol><li>发送由泵脉冲设置的一个固定的偏差 (如大于VDC + V泵> V) 的列车, 重复率为25赫。在这些实验中, 分别将vDC和v两个设置为-1.8 v 和-2.0 v. 将V泵设置为220到450毫伏。</li>
	<li>将泵浦脉冲的持续时间从几纳秒扫到几百纳秒。</li>
	<li>发送一列泵和探头脉冲。探头脉冲的振幅应小于泵, 且与滞后发生的范围相媲美 (V探头< v泵, v探测器+ vDC≈v滞)。在这些实验中, 将V探测设置为 210 mV。</li>
	<li>减去仅在应用探针脉冲时获得的信号。 注: 如果得到的信号是指数, 它表明泵浦脉冲是准备瞬态 (电离掺杂) 的速度, 可以从适合提取 (R2> 0.80)。上面所述的协议是特定于本文所描述的实验和设备的。有许多潜在的途径, 读者自定义自己的实验设置, 以研究其他系统。例如, 一般技术不限于低温冷却单元;任何尖端材料都可以使用, 它们不需要氮气蚀刻。此外, 可以使用一个适当编程的任意函数发生器产生双脉冲波形, 这就否定了对两个独立信道求和的需要。最后, 可以使用较低的带宽缆线连接31。</li>
</ol>

<ol>
	<li>Nunes, G., Freeman, M. R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> Picosecond resolution in scanning tunneling microscopy. 262 (5136), 1029-1032 (1993).</li><li>Khusnatdinov, N. N., Nagle, T. J., Nunes, G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Ultrafast+scanning+tunneling+microscopy+with+1+nm+resolution.">Ultrafast scanning tunneling microscopy with 1 nm resolution.</a> Appl. Phys. Lett. 77 (26), 4434-4436 (2000).</li><li>Takeuchi, O., Morita, R., Yamashita, M., Shigekawa, H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Development+of+time-resolved+scanning+tunneling+microscopy+in+femtosecond+range.">Development of time-resolved scanning tunneling microscopy in femtosecond range.</a> Jpn. J. Appl. Phys. 41 (7 B), 4994-4997 (2002).</li><li>Terada, Y., Yoshida, S., Takeuchi, O., Shigekawa, H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Real-space+imaging+of+transient+carrier+dynamics+by+nanoscale+pump-probe+microscopy.">Real-space imaging of transient carrier dynamics by nanoscale pump-probe microscopy.</a> Nat. Photon. 4 (12), 869-874 (2010).</li><li>Yoshida, S., Yokota, M., Takeuchi, O., Oigawa, H., Mera, Y., Shigekawa, H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Single-atomic-level+probe+of+transient+carrier+dynamics+by+laser-combined+scanning+tunneling+microscopy.">Single-atomic-level probe of transient carrier dynamics by laser-combined scanning tunneling microscopy.</a> Appl. Phys. Express. 6 (3), (2013).</li><li>Kloth, P., Wenderoth, M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=From+time-resolved+atomic-scale+imaging+of+individual+donors+to+their+cooperative+dynamics.">From time-resolved atomic-scale imaging of individual donors to their cooperative dynamics.</a> Science Ad. 3, (2017).</li><li>Cocker, T. L., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=An+ultrafast+terahertz+scanning+tunnelling+microscope.">An ultrafast terahertz scanning tunnelling microscope.</a> Nat. Photon. 7 (8), 620-625 (2013).</li><li>Yoshioka, K., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Real-space+coherent+manipulation+of+electrons+in+a+single+tunnel+junction+by+single-cycle+terahertz+electric+fields.">Real-space coherent manipulation of electrons in a single tunnel junction by single-cycle terahertz electric fields.</a> Nat. Photon. 10 (12), 762-765 (2016).</li><li>Jelic, V., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Ultrafast+terahertz+control+of+extreme+tunnel+currents+through+single+atoms+on+a+silicon+surface.">Ultrafast terahertz control of extreme tunnel currents through single atoms on a silicon surface.</a> Nat. Phys. 13, 591-598 (2017).</li><li>Cocker, T. L., Peller, D., Yu, P., Repp, J., Huber, R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Tracking+the+ultrafast+motion+of+a+single+molecule+by+femtosecond+orbital+imaging.">Tracking the ultrafast motion of a single molecule by femtosecond orbital imaging.</a> Nature. 539 (7628), 263-267 (2016).</li><li>Loth, S., Etzkorn, M., Lutz, C. P., Eigler, D. M., Heinrich, A. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Measurement+of+Fast+Electron+Spin+Relaxation+Times+with+Atomic+Resolution.">Measurement of Fast Electron Spin Relaxation Times with Atomic Resolution.</a> Science. 329 (5999), 1628-1630 (2010).</li><li>Loth, S., Baumann, S., Lutz, C. P., Eigler, D. M., Heinrich, A. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Bistability+in+Atomic-Scale+Antiferromagnets.">Bistability in Atomic-Scale Antiferromagnets.</a> Science. 335 (6065), (2012).</li><li>Baumann, S., Paul, W., Choi, T., Lutz, C. P., Ardavan, A., Heinrich, A. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Electron+paramagnetic+resonance+of+individual+atoms+on+a+surface.">Electron paramagnetic resonance of individual atoms on a surface.</a> Science. 350 (6259), 417-420 (2015).</li><li>Yan, S., Choi, D. -. J., Burgess, J. A. J., Rolf-Pissarczyk, S., Loth, S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Control+of+quantum+magnets+by+atomic+exchange+bias.">Control of quantum magnets by atomic exchange bias.</a> Nat. Nano. 10 (1), 40-45 (2014).</li><li>Rashidi, M., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Time-Resolved+Imaging+of+Negative+Differential+Resistance+on+the+Atomic+Scale.">Time-Resolved Imaging of Negative Differential Resistance on the Atomic Scale.</a> Phys. Rev. Lett. 117 (27), 276805 (2016).</li><li>Rashidi, M., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Time-resolved+single+dopant+charge+dynamics+in+silicon.">Time-resolved single dopant charge dynamics in silicon.</a> Nat. Comm. 7, 13258 (2016).</li><li>Koenraad, P. M., Flatt&#233;, M. E. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Single+dopants+in+semiconductors.">Single dopants in semiconductors.</a> Nat. Mat. 10 (2), 91-100 (2011).</li><li>Kane, B. E. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+silicon-based+nuclear+spin+quantum+computer.">A silicon-based nuclear spin quantum computer.</a> Nature. 393 (6681), 133-137 (1998).</li><li>Freer, S., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+single-atom+quantum+memory+in+silicon.">A single-atom quantum memory in silicon.</a> Quantum Science and Technology. 2, 3-14 (2016).</li><li>Fuechsle, M., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+single-atom+transistor.">A single-atom transistor.</a> Nat. Nano. 7 (4), 242-246 (2012).</li><li>Lyding, J. W., Shen, T. -. c., Hubacek, J. S., Tucker, J. R., Abeln, G. C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Nanoscale+patterning+and+oxidation+of+H-passivated+Si(100)-2&#215;1+surfaces+with+an+ultrahigh+vacuum+scanning+tunneling+microscope.">Nanoscale patterning and oxidation of H-passivated Si(100)-2&#215;1 surfaces with an ultrahigh vacuum scanning tunneling microscope.</a> Appl. Phys. Lett. 64 (118), 2010-2012 (1994).</li><li>Livadaru, L., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Dangling-bond+charge+qubit+on+a+silicon+surface.">Dangling-bond charge qubit on a silicon surface.</a> New J. Phys. 12 (8), 83018 (2010).</li><li>Haider, M. B., Pitters, J. L., DiLabio, G. A., Livadaru, L., Mutus, J. Y., Wolkow, R. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Controlled+Coupling+and+Occupation+of+Silicon+Atomic+Quantum+Dots+at+Room+Temperature.">Controlled Coupling and Occupation of Silicon Atomic Quantum Dots at Room Temperature.</a> Phys. Rev. Lett. 102 (4), 46805 (2009).</li><li>Taucer, M., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Single-Electron+Dynamics+of+an+Atomic+Silicon+Quantum+Dot+on+the+H+-+Si+(100)-(2x1)+Surface.">Single-Electron Dynamics of an Atomic Silicon Quantum Dot on the H - Si (100)-(2x1) Surface.</a> Phys. Rev. Lett. 112 (25), 256801 (2014).</li><li>Engelund, M., Papior, N., Brandimarte, P., Frederiksen, T., Garcia-Lekue, A., S&#225;nchez-Portal, D. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Search+for+a+Metallic+Dangling-Bond+Wire+on+n+-Doped+H-Passivated+Semiconductor+Surfaces.">Search for a Metallic Dangling-Bond Wire on n -Doped H-Passivated Semiconductor Surfaces.</a> J. Phys. Chem. C. 120 (36), 20303-20309 (2016).</li><li>Bohloul, S., Shi, Q., Wolkow, R. A., Guo, H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Quantum+Transport+in+Gated+Dangling-Bond+Atomic+Wires.">Quantum Transport in Gated Dangling-Bond Atomic Wires.</a> Nano Lett. 17, 322-327 (2017).</li><li>Kolmer, M., Zuzak, R., Dridi, G., Godlewski, S., Joachim, C., Szymonski, M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Realization+of+a+quantum+Hamiltonian+Boolean+logic+gate+on+the+Si(001):H+surface.">Realization of a quantum Hamiltonian Boolean logic gate on the Si(001):H surface.</a> Nanoscale. 7, 12325-12330 (2015).</li><li>Schofield, S. R., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Quantum+engineering+at+the+silicon+surface+using+dangling+bonds.">Quantum engineering at the silicon surface using dangling bonds.</a> Nat. Comm. 4, 1649 (2013).</li><li>Wood, J. A., Rashidi, M., Koleini, M., Pitters, J. L., Wolkow, R. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Multiple+Silicon+Atom+Artificial+Molecules.">Multiple Silicon Atom Artificial Molecules.</a> https://arxiv.org/abs/1607.06050. , (2016).</li><li>Pitters, J. L., Piva, P. G., Wolkow, R. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Dopant+depletion+in+the+near+surface+region+of+thermally+prepared+silicon+(100)+in+UHV.">Dopant depletion in the near surface region of thermally prepared silicon (100) in UHV.</a> J. Vac. Sci. Technol. 30 (2), 21806 (2012).</li><li>Grosse, C., Etzkorn, M., Kuhnke, K., Loth, S., Kern, K. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Quantitative+mapping+of+fast+voltage+pulses+in+tunnel+junctions+by+plasmonic+luminescence.">Quantitative mapping of fast voltage pulses in tunnel junctions by plasmonic luminescence.</a> Appl. Phys. Lett. 103 (18), (2013).</li><li>Boland, J. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Scanning+tunnelling+microscopy+of+the+interaction+of+hydrogen+with+silicon+surfaces.">Scanning tunnelling microscopy of the interaction of hydrogen with silicon surfaces.</a> Adv. Phys. 42, 129-171 (1993).</li><li>Rezeq, M., Pitters, J., Wolkow, R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Tungsten+nanotip+fabrication+by+spatially+controlled+field-assisted+reaction+with+nitrogen.">Tungsten nanotip fabrication by spatially controlled field-assisted reaction with nitrogen.</a> J. Chem. Phys. 124, 204716 (2006).</li><li>Saunus, C., Raphael Bindel, J., Pratzer, M., Morgenstern, M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Versatile+scanning+tunneling+microscopy+with+120+ps+time+resolution.">Versatile scanning tunneling microscopy with 120 ps time resolution.</a> Appl. Phys. Lett. 102 (5), (2013).</li></ol>

作者声明他们没有竞争的金融利益。

不应用泵浦脉冲的 TR sts 的变体与传统的 sts 相比较, 只是系统的采样频率较高, 而不是连续取样。如果探针脉冲的持续时间是适当的 (>ΓLH), 则在没有泵浦脉冲的情况下获得的 TR sts 信号可以乘以与实验的任务周期成正比的常数, 以便与常规 sts 完全一致。测量.这是唯一可能的, 因为测量没有使用锁在放大器, 否则将减弱信号的一个未知数部分由于使用的低通滤波。这是不情愿的et al...

扫描隧道显微镜 (STM) 已成为纳米的主要工具, 它能够解决原子尺度的地形和电子结构。然而, 传统 STM 的一个局限性是, 由于当前前置放大器1的带宽有限, 其时间分辨率仅限于毫秒级。长期以来, 将 STM 的时间分辨率扩展到通常发生原子过程的尺度, 一直是一个目标。时间分辨扫描隧道显微镜 (TR STM) 的先驱工作由弗里曼et. al.1利用样品上图案的光导开关和微带传输线将皮秒电压脉冲传送到隧道连接处。这种连接混合技术已被用于实现 1 nm 和 20 ps2的同时分辨率, 但由于使用专门的样本结构的要求, 它从未被广泛采用。幸运的是, 从这些作品中获得的基本洞察力可以推广到许多时间分辨技术;即使 stm 电路的带宽仅限于几个赫兹, stm 中的非线性 I (V) 响应也能通过测量在许多泵探头循环中获得的平均隧道电流来探测更快的动力学。在这些年中, 已经探讨了许多方法, 其中最受欢迎的是下文简要回顾。
震动脉冲对激发 (SPPX) STM 利用超快脉冲激光技术的进步, 通过直接照亮隧道连接点和激动人心的载体在示例3中实现亚皮秒分辨率。入射激光产生的自由载流子, 瞬时增强传导, 并调制的泵和探头之间的延迟 (td) 允许 dI/dtd , 以锁定放大器来测量。由于泵和探头之间的延迟是调制的, 而不是激光的强度, 因为在许多其他光学方法中, SPPX-STM 避免了照片照明引起的尖端3的热膨胀。此方法的最近扩展扩展了 SPPX-STM 可以利用脉冲拾取技术来研究动态的时间刻度, 从而增加了泵探头延迟次数4的范围。重要的是, 最近的开发还提供了直接测量I(td) 曲线的能力, 而不是通过数值积分来度量。SPPX-STM 的最新应用包括研究单 (锰, 铁)/gaas (110) 结构的载体重组5和在 gaas6中的施主动力学。SPPX-STM 的应用面临一些限制。信号 SPPX-STM 措施取决于自由载流子激发的光脉冲和最适合半导体。此外, 虽然隧道电流是本地化的尖端, 因为大面积是激发的光脉冲, 信号是一个卷积的地方属性和物质运输。最后, 在测量的时间点固定在接合处的偏置, 使研究的动力学必须是光诱导的。
更近的光学技术, 太赫兹 stm (太赫兹), 夫妇自由空间太赫兹脉冲集中在连接到 stm 尖端。与 SPPX-STM 不同的是, 耦合脉冲表现为快速的电压脉冲, 允许对电子驱动的激发的调查, 与亚皮秒分辨率7。有趣的是, 由太赫兹脉冲产生的整流电流导致了传统的 STM8,9无法访问的峰值电流密度。该技术最近用于研究 Si (111)-(7x7)9中的热电子, 并对单个苯分子的振动进行图像10。太赫兹-脉冲自然耦合到尖端, 然而, 有必要整合一个太赫兹源的 STM 实验可能是对许多实验者的挑战。这推动了其他广泛适用和易于实施的技术的发展。
在 2010年, 不情愿的et al.11开发了一种全电子技术, 其中纳秒电压脉冲应用于直流偏置电子泵的顶部, 并探测系统11。这项技术的引入, 提供了一个关键的示范, 明确和实际应用的时间分辨 STM 测量以前未观测到的物理。虽然它不是一样快的结混合 stm, 它在它之前, 应用微波脉冲到 stm 提示允许任意样品被调查。此技术不需要任何复杂的光学方法或对 STM 连接的光学访问。这使它成为最简单的技术, 以适应低温单元。这些技术的首次演示应用于自旋-极化 STM 被用来测量泵浦脉冲激发的弛豫动力学的研究11。直到最近, 它的应用仍然局限于磁性原子系统12,13,14 , 但后来被扩展到从离散中隙状态15和电荷动力学的载波捕获速率研究单砷掺杂在硅中的15,16。后一项研究是这项工作的重点。
由于互补金属氧化物半导体 (CMOS) 器件现在进入了单个掺杂可以影响设备属性的系统, 因此对半导体中单掺杂的性能的研究已经引起了人们的广泛关注17.此外, 一些研究表明, 单掺杂可以作为未来器件的基本组成部分, 例如作为量子计算18和量子存储器19的量子比特, 以及作为单原子晶体管20,15. 未来的设备也可能包括其他的原子尺度缺陷, 如硅悬空键 (DB), 它可以用具有原子精度的图案与 STM 光刻21。为此, 星展集团已提出作为电荷量子比特22, 量子点元胞自动机架构23,24, 和原子线25,26 , 并已被阵列创建量子哈密顿逻辑门27和人工分子2829。前进, 设备可能包括单一掺杂和 DBs。这是一个有吸引力的策略, 因为 DBs 是表面缺陷, 可以很容易地用 STM 的特点, 并作为一个手柄, 以表征单一的掺杂装置。作为这一策略的一个例子, 星展在这项工作中用作电荷传感器来推断近表面掺杂的充电动力学。这些动态被捕获与使用的全电子方法的 TR STM, 这是适应的技术开发的不情愿的et al.11
测量是在选定的 DBs 上进行的氢终止 Si (100)-(2x1) 表面。在表面下面延伸约 60 nm 的掺杂剂损耗区域, 通过晶体30的热处理创建, 将了 DB, 并从散带中的少量剩余的近表面掺杂。STM 的研究发现, 他们的电导依赖于全球样本参数, 如掺杂浓度和温度, 但个别 dbs 也显示出强烈的变化, 取决于他们的本地环境16。在对单个 db 进行 STM 测量期间, 当前流受电子可以从大容量隧道到 db (Γ批量) 和从 db 到 tip (Γ提示) (图 1) 的速率的控制。但是, 由于 db 的传导对其本地环境很敏感, 因此附近掺杂的电荷状态会影响Γ批量(图 1B), 这可以通过监视 db 的电导来推断。因此, DB 的电导可以用来感知附近掺杂的电荷状态, 并可用于确定掺杂从大容量 (ΓLH) 中提供电子的速率, 并将它们丢失到 STM 尖端 (γHL/c13>)。为了解决这些动态, TR STS 是围绕阈值电压 (V,) 进行的, 在这种情况下, 尖端会诱发近表面掺杂的电离.在这里提出的三时间分辨实验技术中, 泵和探针脉冲的作用是相同的。泵瞬态带来的偏差水平, 从下面的V, 这导致掺杂电离.这增加了 DB 的电导率, 这是由探针脉冲采样, 它跟随在较低的偏置。
本文所描述的技术将有益于那些希望用 STM 来描述毫秒到纳秒时间的动力学特征的人。虽然这些技术并不局限于研究电荷动力学, 但至关重要的是, 通过瞬态变化的状态电导, 可以通过 STM 探测 (即,在表面或附近的状态) 来表现动力学。如果瞬态状态的电导与平衡态没有很大的不同, 那么瞬态和平衡电流之间的差乘以探针脉冲占空比的系统噪声下限 (通常1 pA), 信号将在噪声中丢失, 不会被这种技术探测到。由于对商业上可用的 STM 系统进行的实验性修改, 以执行本白皮书中所描述的技术是适度的, 预计这些技术将会被广泛的应用于社区。

<table><tbody><tr><td>Low Temperature Scanning Tunneling Microscope</td><td>Scientaomicron</td><td></td><td>Custom-made with 500MHz bandwidth wiring</td></tr><tr><td>Arbitarary Function Genorator</td><td>Tektronix</td><td>AFG3252C</td><td></td></tr><tr><td>RF Power Splitter/ Combiner</td><td>Mini-Circuits</td><td>ZFRSC-42-S +</td><td></td></tr><tr><td>RF Switch</td><td>Mini-Circuits</td><td>X80-DR230-S +</td><td></td></tr><tr><td>Non-Contact Infrared Pyrometers</td><td>Micron Infrared</td><td>MI 140</td><td></td></tr></tbody></table>

all-electronic nanosecond-resolved scanning tunneling microscopy: facilitating the investigation of single dopant charge dynamics

微型半导体器件的规模, 小数量的掺杂可以控制设备的性能需要开发新的技术能够表征其动力学。研究单掺杂需要亚纳米空间分辨率, 从而促使扫描隧道显微镜 (STM) 的使用。但是, 传统的 STM 仅限于毫秒时间分辨率。为了克服这一缺点, 我们开发了几种方法, 包括全电子时间分辨 STM, 这项研究使用纳秒分辨率来检测硅中的掺杂动力学。这里提出的方法是广泛的可访问的, 允许在原子尺度上对各种动力学进行局部测量。提出了一种新的时间分辨扫描隧道光谱学技术, 用于有效地搜索动力学。

文本的这一节中显示的结果以前已发布15,16。图 3说明了与常规 STM 一起选择的 DB 示例的行为。传统的 I (V) 测量 (图 3A) 清楚地描述了 DB 在V-2.0 v 的电导率的急剧变化. 在-2.1 v (图 3B、左面板)、-2.0 v (中间面板) 和-1.8 v (右面板) 的 STM 图像中也会出现...

Watch this Scientific Journal Video about All-electronic Nanosecond-resolved Scanning Tunneling Microscopy: Facilitating the Investigation of Single Dopant Charge Dynamics at JoVE.com

All-electronic Nanosecond-resolved Scanning Tunneling Microscopy: Facilitating the Investigation of Single Dopant Charge Dynamics

我们演示了一种全电子的方法, 以观察纳秒分辨电荷动力学的掺杂原子在硅与扫描隧道显微镜。

全电子纳秒分辨扫描隧道显微镜: 促进单一掺杂剂电荷动力学的研究

The miniaturization of semiconductor devices to scales where small numbers of dopants can control device properties requires the development of new ...

all-electronic-nanosecond-resolved-scanning-tunneling-microscopy

Research

JoVE Journal

Engineering

9.5K 次观看.  University of Alberta. 我们演示了一种全电子的方法, 以观察纳秒分辨电荷动力学的掺杂原子在硅与扫描隧道显微镜。

视频: All-electronic Nanosecond-resolved Scanning Tunneling Microscopy: Facilitating the Investigation of Single Dopant Charge Dynamics

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

Scanning-probe Single-electron Capacitance Spectroscopy

The integration of low-temperature scanning-probe techniques and single-electron capacitance spectroscopy represents a powerful tool to study the electronic quantum structure of small systems - including individual atomic dopants in semiconductors. Here we present a capacitance-based method, known as Subsurface Charge Accumulation (SCA) imaging, which is capable of resolving single-electron charging while achieving sufficient spatial resolution to image individual atomic dopants. The use of a capacitance technique enables observation of subsurface features, such as dopants buried many nanometers beneath the surface of a semiconductor material1,2,3. In principle, this technique can be applied to any system to resolve electron motion below an insulating surface.
As in other electric-field-sensitive scanned-probe techniques4, the lateral spatial resolution of the measurement depends in part on the radius of curvature of the probe tip. Using tips with a small radius of curvature can enable spatial resolution of a few tens of nanometers. This fine spatial resolution allows investigations of small numbers (down to one) of subsurface dopants1,2. The charge resolution depends greatly on the sensitivity of the charge detection circuitry; using high electron mobility transistors (HEMT) in such circuits at cryogenic temperatures enables a sensitivity of approximately 0.01 electrons/Hz&frac12; at 0.3 K 5.

Scanning-probe single-electron capacitance spectroscopy facilitates the study of single-electron motion in localized subsurface regions. A sensitive charge-detection circuit is incorporated into a cryogenic scanning probe microscope to investigate small systems of dopant atoms beneath the surface of semiconductor samples.

扫描探针单电子电容谱

The integration of low-temperature scanning-probe techniques and single-electron capacitance spectroscopy represents a powerful tool to study the ...

Fabrication of Gate-tunable Graphene Devices for Scanning Tunneling Microscopy Studies with Coulomb Impurities

Owing to its relativistic low-energy charge carriers, the interaction between graphene and various impurities leads to a wealth of new physics and degrees of freedom to control electronic devices. In particular, the behavior of graphene&#8217;s charge carriers in response to potentials from charged Coulomb impurities is predicted to differ significantly from that of most materials. Scanning tunneling microscopy (STM) and scanning tunneling spectroscopy (STS) can provide detailed information on both the spatial and energy dependence of graphene&#39;s electronic structure in the presence of a charged impurity.&#160;The design of a hybrid impurity-graphene device, fabricated using controlled deposition of impurities onto a back-gated graphene surface, has enabled several novel methods for controllably tuning graphene&#8217;s electronic properties.1-8 Electrostatic gating enables control of the charge carrier density in graphene and the ability to reversibly tune the charge2 and/or molecular5 states of an impurity. This paper outlines the process of fabricating a gate-tunable graphene device decorated with individual Coulomb impurities for combined STM/STS studies.2-5 These studies provide valuable insights into the underlying physics, as well as signposts for designing hybrid graphene devices.

This paper details the fabrication process of a gate-tunable graphene device, decorated with Coulomb impurities for scanning tunneling microscopy studies. Mapping the spatially dependent electronic structure of graphene in the presence of charged impurities unveils the unique behavior of its relativistic charge carriers in response to a local Coulomb potential.

对于扫描隧道显微学与库仑杂质制造门可调谐石墨烯器件

Owing to its relativistic low-energy charge carriers, the interaction between graphene and various impurities leads to a wealth of new physics and degrees ...

Silicon Metal-oxide-semiconductor Quantum Dots for Single-electron Pumping

As mass-produced silicon transistors have reached the nano-scale, their behavior and performances are increasingly affected, and often deteriorated, by quantum mechanical effects such as tunneling through single dopants, scattering via interface defects, and discrete trap charge states. However, progress in silicon technology has shown that these phenomena can be harnessed and exploited for a new class of quantum-based electronics. Among others, multi-layer-gated silicon metal-oxide-semiconductor (MOS) technology can be used to control single charge or spin confined in electrostatically-defined quantum dots (QD). These QD-based devices are an excellent platform for quantum computing applications and, recently, it has been demonstrated that they can also be used as single-electron pumps, which are accurate sources of quantized current for metrological purposes. Here, we discuss in detail the fabrication protocol for silicon MOS QDs which is relevant to both quantum computing and quantum metrology applications. Moreover, we describe characterization methods to test the integrity of the devices after fabrication. Finally, we give a brief description of the measurement set-up used for charge pumping experiments and show representative results of electric current quantization.

The fabrication process and experimental characterization techniques relevant to single-electron pumps based on silicon metal-oxide-semiconductor quantum dots are discussed.

硅金属 - 氧化物 - 半导体量子点单电子泵

As mass-produced silicon transistors have reached the nano-scale, their behavior and performances are increasingly affected, and often deteriorated, by ...

Recombination Dynamics in Thin-film Photovoltaic Materials via Time-resolved Microwave Conductivity

A method for investigating recombination dynamics of photo-induced charge carriers in thin film semiconductors, specifically in photovoltaic materials such as organo-lead halide perovskites is presented. The perovskite film thickness and absorption coefficient are initially characterized by profilometry and UV-VIS absorption spectroscopy. Calibration of both laser power and cavity sensitivity is described in detail. A protocol for performing Flash-photolysis Time Resolved Microwave Conductivity (TRMC) experiments, a non-contact method of determining the conductivity of a material, is presented. A process for identifying the real and imaginary components of the complex conductivity by performing TRMC as a function of microwave frequency is given. Charge carrier dynamics are determined under different excitation regimes (including both power and wavelength). Techniques for distinguishing between direct and trap-mediated decay processes are presented and discussed. Results are modelled and interpreted with reference to a general kinetic model of photoinduced charge carriers in a semiconductor. The techniques described are applicable to a wide range of optoelectronic materials, including organic and inorganic photovoltaic materials, nanoparticles, and conducting/semiconducting thin films.

A Time Resolved Microwave Conductivity technique for investigating direct and trap-mediated recombination dynamics and determining carrier mobilities of thin film semiconductors is presented here.

通过时间分辨微波电导率重组动力学薄膜光伏材料

A method for investigating recombination dynamics of photo-induced charge carriers in thin film semiconductors, specifically in photovoltaic materials ...

Probing the Structure and Dynamics of Interfacial Water with Scanning Tunneling Microscopy and Spectroscopy

Water/solid interfaces are ubiquitous and play a key role in many environmental, biophysical, and technological processes. Resolving the internal structure and probing the hydrogen-bond (H-bond) dynamics of the water molecules adsorbed on solid surfaces are fundamental issues of water science, which remains a great challenge owing to the light mass and small size of hydrogen. Scanning tunneling microscopy (STM) is a promising tool for attacking these problems, thanks to its capabilities of sub-&#197;ngstr&#246;m spatial resolution, single-bond vibrational sensitivity, and atomic/molecular manipulation. The designed experimental system consists of a Cl-terminated tip and a sample fabricated by dosing water molecules in situ onto the Au(111)-supported NaCl(001) surfaces. The insulating NaCl films electronically decouple the water from the metal substrates, so the intrinsic frontier orbitals of water molecules are preserved. The Cl-tip facilitates the manipulation of the single water molecules, as well as gating the orbitals of water to the proximity of Fermi level (EF) via tip-water coupling. This paper outlines the detailed methods of submolecular resolution imaging, molecular/atomic manipulation, and single-bond vibrational spectroscopy of interfacial water. These studies open up a new route for investigating the H-bonded systems at the atomic scale.

Here, we present a protocol to investigate the structure and dynamics of interfacial water at the atomic scale, in terms of submolecular resolution imaging, molecular manipulation, and single-bond vibrational spectroscopy.

用扫描隧穿显微镜和光谱法探讨界面水的结构和动力学

Water/solid interfaces are ubiquitous and play a key role in many environmental, biophysical, and technological processes. Resolving the internal ...

化学

Novel Techniques for Observing Structural Dynamics of Photoresponsive Liquid Crystals

We discuss in this article the experimental measurements of the molecules in liquid crystal (LC) phase using the time-resolved infrared (IR) vibrational spectroscopy and time-resolved electron diffraction. Liquid crystal phase is an important state of matter that exists between the solid and liquid phases and it is common in natural systems as well as in organic electronics. Liquid crystals are orientationally ordered but loosely packed, and therefore, the internal conformations and alignments of the molecular components of LCs can be modified by external stimuli. Although advanced time-resolved diffraction techniques have revealed picosecond-scale molecular dynamics of single crystals and polycrystals, direct observations of packing structures and ultrafast dynamics of soft materials have been hampered by blurry diffraction patterns. Here, we report time-resolved IR vibrational spectroscopy and electron diffractometry to acquire ultrafast snapshots of a columnar LC material bearing a photoactive core moiety. Differential-detection analyses of the combination of time-resolved IR vibrational spectroscopy and electron diffraction are powerful tools for characterizing structures and photoinduced dynamics of soft materials.

Here, we present the protocols of differential-detection analyses of time-resolved infrared vibrational spectroscopy and electron diffraction which enable observations of the deformations of local structures around photoexcited molecules in a columnar liquid crystal, giving an atomic perspective on the relationship between the structure and the dynamics of this photoactive material.

观测 Photoresponsive 液晶结构动力学的新方法

We discuss in this article the experimental measurements of the molecules in liquid crystal (LC) phase using the time-resolved infrared (IR) vibrational ...

Quantitative Atomic-Site Analysis of Functional Dopants/Point Defects in Crystalline Materials by Electron-Channeling-Enhanced Microanalysis

A novel elemental and chemical analysis scheme based on electron-channeling phenomena in crystalline materials is introduced, where the incident high-energy electron beam is rocked with the submicrometric pivot point fixed on a specimen. This method enables us to quantitatively derive the site occupancies and site-dependent chemical information of impurities or intentionally doped functional elements in a specimen, using energy-dispersive X-ray spectroscopy and electron energy-loss spectroscopy attached to a scanning transmission electron microscope, which is of significant interest to current materials science, particularly related to nanotechnologies. This scheme is applicable to any combination of elements even when the conventional Rietveld analysis by X-ray or neutron diffraction occasionally fails to provide the desired results because of limited sample sizes and close scattering factors of neighboring elements in the periodic table. In this methodological article, we demonstrate the basic experimental procedure and analysis method of the present beam-rocking microanalysis.

We provide a general outline of quantitative microanalysis methods for estimating the site occupancies of impurities and their chemical states by taking advantage of electron-channeling phenomena under incident electron beam-rocking conditions, which reliably extract information from minority species, light elements, oxygen vacancies, and other point/line/planar defects.

通过电子引导增强微分析对晶体材料中功能性多裤/点缺陷的定量原子场分析

A novel elemental and chemical analysis scheme based on electron-channeling phenomena in crystalline materials is introduced, where the incident ...

用电化学方法分析单个纳米颗粒的异质性能

Tracking Electrochemistry on Single Nanoparticles with Surface-Enhanced Raman Scattering Spectroscopy and Microscopy

Studying electrochemical reactions on single nanoparticles is important to understand the heterogeneous performance of individual nanoparticles. This nanoscale heterogeneity remains hidden during the ensemble-averaged characterization of nanoparticles. Electrochemical techniques have been developed to measure currents from single nanoparticles but do not provide information about the structure and identity of the molecules that undergo reactions at the electrode surface. Optical techniques such as surface-enhanced Raman scattering (SERS) microscopy and spectroscopy can detect electrochemical events on individual nanoparticles while simultaneously providing information on the vibrational modes of electrode surface species. In this paper, a protocol to track the electrochemical oxidation-reduction of Nile Blue (NB) on single Ag nanoparticles using SERS microscopy and spectroscopy is demonstrated. First, a detailed protocol for fabricating Ag nanoparticles on a smooth and semi-transparent Ag film is described. A dipolar plasmon mode aligned along the optical axis is formed between a single Ag nanoparticle and Ag film. The SERS emission from NB fixed between the nanoparticle and the film is coupled into the plasmon mode, and the high-angle emission is collected by a microscope objective to form a donut-shaped emission pattern. These donut-shaped SERS emission patterns allow for the unambiguous identification of single nanoparticles on the substrate, from which the SERS spectra can be collected. In this work, a method for employing the SERS substrate as a working electrode in an electrochemical cell compatible with an inverted optical microscope is provided. Finally, tracking the electrochemical oxidation-reduction of NB molecules on an individual Ag nanoparticle is shown. The setup and the protocol described here can be modified to study various electrochemical reactions on individual nanoparticles.

作者聚焦:使用表面增强拉曼散射光谱和显微镜跟踪单个纳米颗粒的电化学  

The protocol describes how to monitor electrochemical events on single nanoparticles using surface-enhanced Raman scattering spectroscopy and imaging.

用表面增强拉曼散射光谱和显微镜跟踪单个纳米颗粒的电化学

Studying electrochemical reactions on single nanoparticles is important to understand the heterogeneous performance of individual nanoparticles. This ...

全电子纳秒分辨扫描隧道显微镜: 促进单一掺杂剂电荷动力学的研究

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