这项工作由国家自然科学基金授予号 2016YFA0300901 2016YFA0300903 和2017YFA0205003 在11634001、11290162/A040106 的资助下, 由全国重点研究 & 开发项目提供资金。Y.J. 承认国家科学基金对杰出青年学者和长江青年学者项目的支持。j.g. 承认国家博士后项目对创新人才的支持。

注: 实验是在 5 K 上吸附在 Au 支持的氯化钠 (001) 薄膜 (图 1a) 上的水分子, 并配有 Nanonis 电子控制器的超高真空 (特高压) 低温 STM。
1. 实验样品的制作
<ol><li>
清洁金 (111) 单晶
	<ol>
<li>将燃气线泵入 10-7毫巴的压力, 然后用 Ar 气体冲洗煤气线。把泵/冲洗循环三次。 注: 每个泵/冲洗周期约为30分钟。</li>
		<li>用 Ar 气体将气体管线填满2巴的压力, 从而禁止大气渗透到气体管线中。</li>
		<li>将 Au (111) 晶体放在加热器台上, 安装在特高压室的机械手上 (1.4×10-10毫巴的基压)。</li>
		<li>用 Ar+离子溅射周期的15分钟 (p (Ar) = 5×10−5毫巴、1.0 kV、6µA) 和随后的退火约 900 K (5 分钟) 来清洁 Au (111) 单晶。 注: 退火温度应缓慢降低, 否则在 Au 表面会形成高浓度的台阶边缘。通常使用 3-5 溅射/退火循环。</li>
		<li>将 Au (111) 样本转移到 stm 扫描阶段, 并使用 stm (图 1b的插入) 检查清洁度。</li>
	</ol>
</li>
	<li>
在 Au (111) 基板上的 NaCl 沉积
	<ol>
<li>加盐源。在努森细胞上慢慢增加电流, 直到源温度达到 670 k 加盐源数次, 直到腔室的压力低于 4×10-9毫巴。 注: 电流的增加率取决于 NaCl 源的出气率, 以维持 1×10-8毫巴下面的腔室的压力。</li>
		<li>将 au (111) 样品放在机械手上, 调整 au 试样的位置, 使样品面对努森细胞的快门。 注: 在室温下 (77-300 K) 的情况下, 非盟 (111) 基板的温度会降低, 并以连续流动的液氮冷却机械手头。</li>
		<li>增加努森电池的电流, 直到源温度达到 640 K, 并在打开快门前让蒸发通量稳定5分钟。</li>
		<li>打开快门, 将氯化钠沉积在非盟 (111) 样品上, 在 290 K 处保持2分钟。</li>
		<li>将 Au 支持的 NaCl 样品转移到 STM 扫描阶段。使用 STM (图 1b) 检查非盟 (111) 基板上双层 NaCl (001) 岛的覆盖范围和大小。</li>
	</ol>
</li>
	<li>用冷冻泵-解冻周期21清除真空中的水, 以除去剩余杂质。<ol>
<li>准备三封密封玻璃-特高压适配器。将水 H2o、d2o 和 D2o: 部门: H2o 同位素混合物溶液 (2 毫升) 分别转换为三个适配器, 并在煤气线上安装适配器 (图 2)。 注意: D2o: H2o 同位素混合物可通过混合超纯 H2o 和 D2o, 并在超声振荡下的10分钟内将其与相等的量进行混用来获得。</li>
		<li>用液氮冷冻液态水。请确保在冻结前将气体管线泵送至 10-7毫巴的压力。</li>
		<li>打开隔膜密封阀, 在空气中泵出15分钟。然后关闭隔膜密封阀, 解冻溶液。 注: 气体气泡在解冻时从溶液中演化而来。 警告:让冷冻溶剂自行解冻。用水浴解冻溶液会导致玻璃容器断裂。要快速冻结和解冻解决方案, 请用金属特高压适配器替换玻璃特高压适配器, 但金属容器中的溶液是隐形的。</li>
		<li>重复步骤 1.3. 2-1. 3.3, 直到溶液融化时没有气泡从溶液中演化出来。把冷冻泵解冻循环至少三次。</li>
		<li>关闭波纹管密封阀, 并使气体管线处于真空状态。然后打开隔膜密封阀, 让水蒸气填满煤气线。</li>
	</ol>
</li>
	<li>剂量水分子原位到样品表面<ol>
<li>将试样的温度降低到 5 k 缓慢打开泄漏阀, 使 STM 特高压室的压力增加到 2×10-10毫巴。 注: 水分子通过加药管流入特高压室, 它指向盾牌的快门。快门和样品之间的距离 (在盾牌中) 大约有6厘米。STM 室的基压力优于 7×10-11毫巴。沉积速率约为0.01 双层最小值-1。</li>
		<li>打开快门。将水分子放到 Au 支持的 NaCl 表面上1分钟。然后关闭快门和漏阀。</li>
		<li>用 STM 检查在 Au 支持的 NaCl (001) 表面上水分子的覆盖率。样本表面上的隔离水单体形式 (图 1c)。</li>
	</ol>
</li>
</ol>2. 氯终止尖端的制备
<ol><li>制造一个电化学蚀刻钨 (W) 尖端。<ol>
<li>将 0.3 mm 的电线放入3摩尔/L 氢氧化钠蚀刻溶液中, 浸泡长度约为2毫米。</li>
		<li>对插入到氢氧化钠溶液中的铂金环电极, 将5伏直流电位应用于 W 线。</li>
		<li>当悬挂的 W 导线脱落时, 停止蚀刻过程。用蒸馏水和乙醇清洗蚀刻的 W 尖。然后将 W 尖端传输到扫描仪中。 注: 电化学蚀刻 W 尖端可用于交换前一年。</li>
	</ol>
</li>
	<li>在 STM 尖端应用电压脉冲 (2-10 V) 和控制崩溃程序 (0.25-0. 4 nm), 直到氯化钠表面的原子 Cl 原子被解决。 注意: STM 尖端被戳在非盟 (111) 表面的清洁区域。</li>
	<li>将 STM 笔尖放置在一个 Cl 原子的中心 (图 3a) 中。将裸露的 STM 尖端靠近 NaCl 表面接近于 V = 5 mV 和 I = 5 n A (图 3b) 的设置点。</li>
	<li>将笔尖撤回到原始设置点 (图 3c) 并扫描同一区域。检查 Cl 尖端的获取是否通过改进的分辨率和在 NaCl (图 3d e) 的 STM 图像中丢失的 Cl 原子。 注: 不成功的病例有时可能发生, 例如, 当 Cl 原子不转移到 STM 或多个 Cl/Na 原子吸附在尖端。如果发生这种情况, 请重复步骤 2.2-2.5。</li>
</ol>3. 水单体的轨道成像
<ol><li>用电压脉冲 (2-10 V) 和控制崩溃 (0.25-0. 4 nm) 程序来形成 STM 尖端。</li>
	<li>扫描水分子吸附在 NaCl (001) 表面与 10 nm 10 毫微米帧在 5 K。</li>
	<li>集中在一个单独的水单体和放大。以系统的方式扫描水单体, 作为偏置 (-400-400 mV) 和隧穿电流 (50-300 pA) 的功能。 注: 用裸露的 STM 尖端, 最高被占领 (人) 和最低空置 (LUMO) 的水分子轨道出现在正和负偏倚, 分别为22。一旦尖端被 Cl 终止, 只有同性恋出现 (图 4a), 并且在可访问的偏置范围 (从-400 mv 到 400 mv) 中没有观察到 LUMO 特征。即使在较大的偏压电压下, 由于振动激发, 水分子也会不稳定。</li>
</ol>4. 单分子振动光谱学
<ol><li>
数字锁定和偏置光谱学模块 (Nanonis 电子控制器) 的设置
	<ol>
<li>
偏置光谱学模块的设置:选择当前、LIX1 (dI/dv 光谱信号) 和 LIX2 (d2I/dv2频谱信号) 通道。将设置时间设置为50毫秒, 集成时间为300毫秒. 增加积分时间和扫描时间以获得平滑的光谱。调整 Z 偏移量以在不同尖端高度进行偏倚光谱学。确保 Z 控制器集保持和锁定在测量期间运行 注意:设置时间定义为: 在将偏倚更改为下一级和开始获取数据之前等待的时间, 以避免偏差变化引起的瞬态效应。集成时间定义为: 获取和平均数据的时间。</li>
		<li>
锁定模块的设置 注: 扫描隧穿光谱学、dI/dv 和 d2I/dv2谱, 分别通过解调隧道电流的第一和第二次谐波, 同时使用锁定放大器获得。<ol>
<li>调节偏置和解调电流。将调制频率设置为数以百赫兹和调制振幅为 5-7 mV。确保在设定点频率和相应的第二谐波频率上没有机械和电子噪声。</li>
			<li>
设置第一个谐波阶段:切换到 Z 控制器模块。将尖端升降机设置为 10 nm, 然后关闭反馈。切换到锁定模块并打开锁定按钮 (绿色)。单击第一个谐波自动相位并记录该阶段。重复该自动阶段至少五次, 并采取平均。然后从平均相位中减去90度以获得连接的相位。</li>
			<li>
设置第二个谐波阶段:将 STM 尖端放置在 Au (111) 基板上, 并开始从-1.5 V 到 1.5 v 的偏置光谱学扫描. 选择通道 LIX 1 和函数 dY/dX, 它们一起显示 dI/dV 光谱的导数。在光谱中找到一个突出的峰值特征, 并将相应的能量设置为偏置。打开锁定并将 STM 系统保留在隧道中。单击第二个谐波自动相位至少五次, 并取平均值。 注: 由于第二谐波信号通常非常微弱, 相位可以剧烈波动。当减小尖端高度以增加信号的强度时, 相位的波动将会小得多 (几度), 第二谐波相位会更准确。</li>
		</ol>
</li>
	</ol>
</li>
	<li>
尖端-增强的 D2O 单体的我们
	<ol>
<li>在 V=100 mV 和 I=50 pA 的设置点上扫描一个带有 Cl 尖端的水单体。</li>
		<li>将 Cl 尖端定位在 NaCl 表面, 以偏倚光谱学为背景信号。然后将 Cl 尖端定位在水单体上, 开始偏置光谱学扫描。</li>
		<li>如果 dI/dv 和 d2I/dv2光谱的水是无特征的, 只需跟随背景 NaCl 表面 (图 4c-d的蓝色曲线)。通过调整 Z 偏移量来减小尖端高度, 直到振动特征出现在光谱中 (图 4c d的红色曲线)。 注意: 对于我们测量, 需要一个长的集成时间 (1 秒) 和多个扫描。对于 D2O 水单体, 将偏差范围从-360 mv 设置为 360 mv。对于 H2的水单体, 将偏差从-475 mv 扫到 475 mv。与 D2o、H2o 和我们相比, 水单体更容易受到干扰, 甚至在测量过程中被扫走。</li>
	</ol>
</li>
	<li>
H 键强度
	<ol>
<li>重复步骤 4.2. 2-4. 2.3 和调整扫描偏差范围, 以集中在伸展模式的水单体。在23中介绍和讨论了水 D2o、H2o 和我们。</li>
		<li>利用这种经验公式, 从 h 粘结 oh 拉伸频率 (相对于自由 oh 伸展能量) 转换, 获得 h 键合能量: ΔH = 1.3 x √Δv (1) 注: ΔH 是 H 键合能量, 在焦/摩尔;Δv是 OH 拉伸模式的红移, 在 cm-1中。将 H 键合强度单位转换为兆伏特: 1 焦/摩尔 = 10.4 兆伏特/原子。将 Eq 1 应用于 OD 伸展模式, 数量Δv应该乘以一个因子: v(oh)/ v(od) = 1.3612, 其中v(oh) 和v(od) 是自由的部门分子的 OH 和 OD 舒展频率,分别。</li>
	</ol>
</li>
</ol>5. 分子操纵
<ol><li>
构建水聚丙烯 (图 5a)
	<ol>
<li>扫描含有四水单体的区域。在 V=100 mV 和 I=50 pA 的设置点上, 将 Cl 尖端放置在单体的顶端。降低 V=10 mV 和 I=150 pA 设置点的高度, 提高端水相互作用。</li>
		<li>沿预先设计的轨迹移动 Cl 尖端。然后将笔尖收回到初始设置点 (V=100 mV、I=50 pA), 再重新扫描同一区域以检查水的二聚体是否形成。</li>
		<li>重复步骤 5.1. 1-5. 1.2, 形成水三聚体和聚丙烯。 注意: 上述操作过程可以通过 Nanonis 控制器 (扫描控制-跟随我模块) 实现。扫描控制的设置-跟随我模块: 偏置:10 mV 速度: 500 pm/秒 Z-ctrl 设定: 150 pA 打开/关闭 Z-Ctrl: 绿色 等待时间: 1s 当前增益: in 10 ^ 9 路径: 单击 "记录" 按钮并在图像上绘制设计的轨迹, 然后单击 "停止" 按钮。 单击 "执行" 按钮, STM 提示将沿预先设计的轨迹移动, 并在 "跟随我" 模块中设定定义。如果水单体不移动, 在操作过程中降低尖端高度 (较小的偏置和较大的电流)。</li>
	</ol>
</li>
	<li>
水聚丙烯的手性切换 (图 6)
	<ol>
<li>用 Cl 尖扫描水聚丙烯。将设置点更改为 V=5 mV, I=5 pA, 并将笔尖稍稍从水聚丙烯的中心处定位。</li>
		<li>在 z 控制器模块中, 在关闭 z 控制器 (例如、笔尖提升:-230 pm) 时, 定义一个距离以提升笔尖。关闭 Z 控制器反馈。把尖端靠近水聚丙烯 (230 pm)。</li>
		<li>记录当前的痕迹, 显示两个不同的水平, 表明聚丙烯已经经历了可逆的换算之间的两个 H 键合手。</li>
		<li>将电流保持在高电平, 然后切换 Z 控制器反馈。收回笔尖到原来的设置点 (V=5 mV, I=5 pA)。然后用 V=10 mV 和 I=100 pA 的设置点对水聚丙烯进行扫描, 以检查水聚丙烯的手性状态。</li>
		<li>重复步骤 5.2. 1-5. 2.4 至少10次, 以确认在高电流水平的水聚丙烯的相应的手性状态。</li>
		<li>重复步骤 5.2.1-5.2.4 至少10次, 但将电流保持在较低的水平, 以检查相应的水聚丙烯的手性状态。</li>
		<li>记录隧道跟踪20分钟, 其中包含几个百开关事件</li>
		<li>分别绘制聚丙烯在当前跟踪的低和高级别上所花费的时间的分布。</li>
		<li>将分布调整为指数衰减 (图 7)。然后得到合适的时间常数。反转时间常数以产生切换速率。</li>
	</ol>
</li>
</ol>

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Today. 63 (2), 34-39 (2010).</li><li>Carrasco, J., Hodgson, A., Michaelides, A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+molecular+perspective+of+water+at+metal+interfaces.">A molecular perspective of water at metal interfaces.</a> Nat. Mater. 11 (8), 667-674 (2012).</li><li>Kumagai, T. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Direct+observation+and+control+of+hydrogen-bond+dynamics+using+low-temperature+scanning+tunneling+microscopy.">Direct observation and control of hydrogen-bond dynamics using low-temperature scanning tunneling microscopy.</a> Prog. Surf. Sci. 90 (3), 239-291 (2015).</li><li>Maier, S., Salmeron, M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=How+does+water+wet+a+surface.">How does water wet a surface.</a> Acc. Chem. Res. 48 (10), 2783-2790 (2015).</li><li>JoVE Science Education Database. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.+Essentials+of+Organic+Chemistry.+Degassing+Liquids+with+Freeze-Pump-Thaw+Cycling.">. Essentials of Organic Chemistry. Degassing Liquids with Freeze-Pump-Thaw Cycling.</a> JoVE. , (2017).</li><li>Guo, J., 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+imaging+of+interfacial+water+with+submolecular+resolution.">Real-space imaging of interfacial water with submolecular resolution.</a> Nat. Mater. 13 (2), 184-189 (2014).</li><li>Guo, J., 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=Nuclear+quantum+effects+of+hydrogen+bonds+probed+by+tip-enhanced+inelastic+electron+tunneling.">Nuclear quantum effects of hydrogen bonds probed by tip-enhanced inelastic electron tunneling.</a> Science. 352 (6283), 321-325 (2016).</li><li>Meng, X., 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=Direct+visualization+of+concerted+proton+tunnelling+in+a+water+nanocluster.">Direct visualization of concerted proton tunnelling in a water nanocluster.</a> Nat. Phys. 11 (3), 235-239 (2015).</li><li>Thuermer, K., Nie, S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Formation+of+hexagonal+and+cubic+ice+during+low-temperature+growth.">Formation of hexagonal and cubic ice during low-temperature growth.</a> Proc. Natl. Acad. Sci. U.S.A. 110 (29), 11757-11762 (2013).</li><li>Shiotari, A., Sugimoto, Y. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Ultrahigh-resolution+imaging+of+water+networks+by+atomic+force+microscopy.">Ultrahigh-resolution imaging of water networks by atomic force microscopy.</a> Nat. 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作者没有什么可透露的。

为了探讨吸附在固体表面上的水分子的内部结构、动力学和振动光谱学, 特别注意氢的自由度, 一些实验步骤至关重要, 这将是在以下各段中讨论。
在两个关键步骤的基础上实现了水分子的轨道成像。首先, 绝缘 NaCl 膜以电子方式将水从金基底上解耦, 其次通过端-水耦合的 STM 尖端的轨道浇口效应。要在 au (111) 基板上生长双层 NaCl 膜, 金 (111) 基板的温度应保持在 290 K 左右。当?...

水与固体材料表面的相互作用涉及各种表面反应过程, 如异质催化、photoconversion、电化学、腐蚀和润滑等。1,2,3一般而言, 研究界面水、光谱和衍射技术是常用的, 如红外和拉曼光谱、总和频率生成 (SFG)、X 射线衍射 (XRD)、核磁共振 (NMR)、中子散射4,5,6,7,8。然而, 这些方法受到空间分辨率、光谱展宽和平均效应的限制。
STM 是一种很有希望的技术来克服这些限制, 它结合了亚Ångström 空间分辨率, 原子操作和单键振动灵敏度9,10,11,12,13,14. 自本世纪初以来, STM 已广泛应用于研究固体表面水的结构和动态3,15,16,17, 18,19,20。另外, 基于 STM 的振动光谱学可以从二阶导数差分隧穿电导 (d2I/dV2) 中获得, 也称为非弹性电子隧穿光谱学 (我们)。然而, 解决内部结构,即H 键方向性, 获得可靠的水振动光谱学仍然是一个挑战。主要的困难在于水是一个接近壳的分子, 其前沿轨道远离 EF, 因此 STM 尖端的电子几乎无法隧道到水的分子共振状态, 导致信噪比差。分子成像和振动光谱学。
水吸附在 Au 支持的 NaCl (001) 薄膜提供了一个理想的系统进行原子尺度调查的 STM 与 Cl 终止尖端 (图 1a), 这是执行在 5 K 在超高真空 (特高压) 环境中的基本压力优于 8×10-11毫巴。一方面, 绝缘 NaCl 薄膜以电子方式将水分子从 Au 基体中分离出来, 从而保留了水的原生边界轨道, 延长了驻留在分子共振状态中的电子的寿命。另一方面, STM 尖端可以通过尖端-水耦合有效地调节水的前沿轨道向 EF , 特别是当尖端与 Cl 原子功能化时。这些关键步骤使高分辨率的轨道成像和水单体和簇的振动光谱。此外 , 由于负电荷的 Cl 尖端与水之间的强静电相互作用 , 水分子可以以良好的控制方式纵。
本报告分别在1和2节详细概述了样品的制备程序和 STM 调查的 Cl 终止尖端。在3节中, 我们描述了轨道成像技术, 它解决了水单体和聚丙烯的 O H 方向性。在4节中引入了尖端增强我们, 它允许在单键极限下检测水分子的振动模式, 并从氧-氢拉伸中的红移中确定高精度的 H 键合强度。水的频率。在5节中, 我们展示了如何通过控制尖端操作来构造和切换水聚丙烯。基于轨道成像、光谱学和操作技术, 可以进行同位素替代实验, 对界面水中质子的量子性质进行探测, 如量子隧穿和零点运动。

<table><tbody><tr><td>Au(111) single crystal</td><td>MaTeck</td><td>NA</td><td></td></tr><tr><td>NaCl</td><td>Sigma Aldrich</td><td>450006</td><td></td></tr><tr><td>Water, deuterium-depleted&amp;nbsp;</td><td>Sigma Aldrich</td><td>195294</td><td></td></tr><tr><td>Deuterium oxide&amp;nbsp;</td><td>Sigma Aldrich</td><td>364312</td><td></td></tr><tr><td>Sealed-off glass-UHV adapters</td><td>MDC vacuum products</td><td>46300</td><td></td></tr><tr><td>Diaphragm-sealed valve</td><td>any</td><td>NA</td><td></td></tr><tr><td>Bellows-sealed valve</td><td>any</td><td>NA</td><td></td></tr><tr><td>Leak valve</td><td>Kurt J. Lesker&amp;nbsp;</td><td>NA</td><td></td></tr><tr><td>Scanning tunneling microscopy</td><td>CreaTec</td><td>NA</td><td></td></tr><tr><td>Electronic controller.</td><td>Nanonis&amp;nbsp;</td><td>NA</td><td></td></tr><tr><td>Tungsten wire</td><td>any</td><td></td><td>diameter:0.3 mm; purity: 99.95%</td></tr></tbody></table>

probing the structure and dynamics of interfacial water with scanning tunneling microscopy and spectroscopy

水/固体界面无处不在, 在许多环境、生物物理和技术过程中发挥着关键作用。在固体表面吸附的水分子的氢键 (H 键) 动力学的求解是水科学的基本问题, 由于氢的重量轻、体积小, 这仍然是一个巨大的挑战。扫描隧穿显微镜 (STM) 是一个有希望的工具, 以攻击这些问题, 由于其能力的亚Ångström 空间分辨率, 单键振动灵敏度, 原子/分子操作。所设计的实验系统包括一个 Cl 终止尖端和一个样本, 通过将水分子就地制备到 Au (111) 支持的 NaCl (001) 表面。绝缘 NaCl 膜以电子方式将水与金属基体分离, 从而保留了水分子的固有前沿轨道。Cl 尖端促进了单水分子的操作, 并通过尖端水耦合将水的轨道浇到费米水平 (EF) 附近。本文概述了 submolecular 分辨率成像、分子/原子操作和界面水单键振动光谱的详细方法。这些研究开辟了一个新的途径, 以调查在原子能规模的 H 保税系统。

图 1a阐释了 STM 实验设置的示意图。首先, 金 (111) 基板是清洁的溅射和退火周期在特高压室。清洁 Au (111) 样品显示22×√3重建表面, 其中表面的原子占据了结构和 fcc 的地方形成人字构造 (插入图 1b)。氯化钠在 Au (111) 基板上蒸发, 形成双层岛屿 (图 1b)。然后, 水分子在 A...

Watch this Scientific Journal Video about Probing the Structure and Dynamics of Interfacial Water with Scanning Tunneling Microscopy and Spectroscopy at JoVE.com

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

在这里, 我们提出了一个协议, 以研究在原子尺度上的界面水的结构和动力学, 在 submolecular 分辨率成像, 分子操作, 和单键振动光谱学。

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

probing-structure-dynamics-interfacial-water-with-scanning-tunneling

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Chemistry

Chemical Bonding: Molecular Geometry and Bonding Theories

SCIENTISTS IN ACTION

8.7K 次观看.  Peking University. 在这里, 我们提出了一个协议, 以研究在原子尺度上的界面水的结构和动力学, 在 submolecular 分辨率成像, 分子操作, 和单键振动光谱学。

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

In Situ Characterization of Hydrated Proteins in Water by SALVI and ToF-SIMS

This work demonstrates in situ characterization of protein biomolecules in the aqueous solution using the System for Analysis at the Liquid Vacuum Interface (SALVI) and time-of-flight secondary ion mass spectrometry (ToF-SIMS). The fibronectin protein film was immobilized on the silicon nitride (SiN) membrane that forms the SALVI detection area. During ToF-SIMS analysis, three modes of analysis were conducted including high spatial resolution mass spectrometry, two-dimensional (2D) imaging, and depth profiling. Mass spectra were acquired in both positive and negative modes. Deionized water was also analyzed as a reference sample. Our results show that the fibronectin film in water has more distinct and stronger water cluster peaks compared to water alone. Characteristic peaks of amino acid fragments are also observable in the hydrated protein ToF-SIMS spectra. These results illustrate that protein molecule adsorption on a surface can be studied dynamically using SALVI and ToF-SIMS in the liquid environment for the first time.

In Situ Characterization of Hydrated Proteins in Water by SALVI and ToF-SIMS

This work presents a protocol for liquid handling and sample introduction to a microchannel for in situ time-of-flight secondary ion mass spectrometry analysis of protein biomolecules in an aqueous solution.

在水中水合蛋白原位表征SALVI和TOF-SIMS

This work demonstrates in situ characterization of protein biomolecules in the aqueous solution using the System for Analysis at the Liquid Vacuum ...

科研

化学

Sub-nanometer Resolution Imaging with Amplitude-modulation Atomic Force Microscopy in Liquid

Atomic force microscopy (AFM) has become a well-established technique for nanoscale imaging of samples in air and in liquid. Recent studies have shown that when operated in amplitude-modulation (tapping) mode, atomic or molecular-level resolution images can be achieved over a wide range of soft and hard samples in liquid. In these situations, small oscillation amplitudes (SAM-AFM) enhance the resolution by exploiting the solvated liquid at the surface of the sample. Although the technique has been successfully applied across fields as diverse as materials science, biology and biophysics and surface chemistry, obtaining high-resolution images in liquid can still remain challenging for novice users. This is partly due to the large number of variables to control and optimize such as the choice of cantilever, the sample preparation, and the correct manipulation of the imaging parameters. Here, we present a protocol for achieving high-resolution images of hard and soft samples in fluid using SAM-AFM on a commercial instrument. Our goal is to provide a step-by-step practical guide to achieving high-resolution images, including the cleaning and preparation of the apparatus and the sample, the choice of cantilever and optimization of the imaging parameters. For each step, we explain the scientific rationale behind our choices to facilitate the adaptation of the methodology to every user's specific system.

We present a method for achieving sub-nanometer resolution images with amplitude-modulation (tapping mode) atomic force microscopy in liquid. The method is demonstrated on commercial atomic force microscopes. We explain the rationale behind our choices of parameters and suggest strategies for resolution optimization.

亚纳米级分辨率成像与调幅原子力显微镜在液体

Atomic force microscopy (AFM) has become a well-established technique for nanoscale imaging of samples in air and in liquid. Recent studies have shown ...

工程学

Studying Dynamic Processes of Nano-sized Objects in Liquid using Scanning Transmission Electron Microscopy

Samples fully embedded in liquid can be studied at a nanoscale spatial resolution with Scanning Transmission Electron Microscopy (STEM) using a microfluidic chamber assembled in the specimen holder for Transmission Electron Microscopy (TEM) and STEM. The microfluidic system consists of two silicon microchips supporting thin Silicon Nitride (SiN) membrane windows. This article describes the basic steps of sample loading and data acquisition. Most important of all is to ensure that the liquid compartment is correctly assembled, thus providing a thin liquid layer and a vacuum seal. This protocol also includes a number of tests necessary to perform during sample loading in order to ensure correct assembly. Once the sample is loaded in the electron microscope, the liquid thickness needs to be measured. Incorrect assembly may result in a too-thick liquid, while a too-thin liquid may indicate the absence of liquid, such as when a bubble is formed. Finally, the protocol explains how images are taken and how dynamic processes can be studied. A sample containing AuNPs is imaged both in pure water and in saline.

This protocol describes the operation of a liquid flow specimen holder for scanning transmission electron microscopy of AuNPs in water, as used for the observation of nanoscale dynamic processes.

使用扫描透射电子显微镜研究纳米大小的物体的动态过程中的液体

Samples fully embedded in liquid can be studied at a nanoscale spatial resolution with Scanning Transmission Electron Microscopy (STEM) using a ...

In Situ Characterization of Boehmite Particles in Water Using Liquid SEM

In situ imaging and elemental analysis of boehmite (AlOOH) particles in water is realized using the System for Analysis at the Liquid Vacuum Interface (SALVI) and Scanning Electron Microscopy (SEM). This paper describes the method and key steps in integrating the vacuum compatible SAVLI to SEM and obtaining secondary electron (SE) images of particles in liquid in high vacuum. Energy dispersive x-ray spectroscopy (EDX) is used to obtain elemental analysis of particles in liquid and control samples including deionized (DI) water only and an empty channel as well. Synthesized boehmite (AlOOH) particles suspended in liquid are used as a model in the liquid SEM illustration. The results demonstrate that the particles can be imaged in the SE mode with good resolution (i.e., 400 nm). The AlOOH EDX spectrum shows significant signal from the aluminum (Al) when compared with the DI water and the empty channel control. In situ liquid SEM is a powerful technique to study particles in liquid with many exciting applications. This procedure aims to provide technical know-how in order to conduct liquid SEM imaging and EDX analysis using SALVI and to reduce potential pitfalls when using this approach.

In Situ Characterization of Boehmite Particles in Water Using Liquid SEM

We present a procedure for real-time imaging and elemental composition analysis of boehmite particles in deionized water by in situ liquid Scanning Electron Microscopy.

原位水中石粒子的液体扫描电镜表征

In situ imaging and elemental analysis of boehmite (AlOOH) particles in water is realized using the System for Analysis at the Liquid Vacuum Interface ...

Interfacial Molecular-level Structures of Polymers and Biomacromolecules Revealed via Sum Frequency Generation Vibrational Spectroscopy

As a second-order nonlinear optical spectroscopy, sum frequency generation (SFG) vibrational spectroscopy has widely been used in investigating various surfaces and interfaces. This non-invasive optical technique can provide the local molecular-level information with monolayer or submonolayer sensitivity. We here are providing experimental methodology on how to selectively detect the buried interface for both macromolecules and biomacromolecules. With this in mind, interfacial secondary structures of silk fibroin and water structures around model short-chain oligonucleotide duplex are discussed. The former shows a chain-chain overlap or spatial confinement effect and the latter shows a protection function against the Ca2+ ions resulting from the chiral spine superstructure of water.

Being comprehensively utilized, sum frequency generation (SFG) vibrational spectroscopy can help to reveal chain conformational order and secondary structural change happening at polymer and biomacromolecule interfaces.

通过相频生成振动光谱揭示聚合物和生物大分子的界面分子级结构

As a second-order nonlinear optical spectroscopy, sum frequency generation (SFG) vibrational spectroscopy has widely been used in investigating various ...

生物化学

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

The miniaturization of semiconductor devices to scales where small numbers of dopants can control device properties requires the development of new techniques capable of characterizing their dynamics. Investigating single dopants requires sub-nanometer spatial resolution, which motivates the use of scanning tunneling microscopy (STM). However, conventional STM is limited to millisecond temporal resolution. Several methods have been developed to overcome this shortcoming, including all-electronic time-resolved STM, which is used in this study to examine dopant dynamics in silicon with nanosecond resolution. The methods presented here are widely accessible and allow for local measurement of a wide variety of dynamics at the atomic scale. A novel time-resolved scanning tunneling spectroscopy technique is presented and used to efficiently search for dynamics.

We demonstrate an all-electronic method to observe nanosecond-resolved charge dynamics of dopant atoms in silicon with a scanning tunneling microscope.

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 ...

Multiscale Sampling of a Heterogeneous Water/Metal Catalyst Interface using Density Functional Theory and Force-Field Molecular Dynamics

A significant number of heterogeneously-catalyzed chemical processes occur under liquid conditions, but simulating catalyst function under such conditions is challenging when it is necessary to include the solvent molecules. The bond breaking and forming processes modeled in these systems necessitate the use of quantum chemical methods. Since molecules in the liquid phase are under constant thermal motion, simulations must also include configurational sampling. This means that multiple configurations of liquid molecules must be simulated for each catalytic species of interest. The goal of the protocol presented here is to generate and sample trajectories of configurations of liquid water molecules around catalytic species on flat transition metal surfaces in a way that balances chemical accuracy with computational expense. Specifically, force field molecular dynamics (FFMD) simulations are used to generate configurations of liquid molecules that can subsequently be used in quantum mechanics-based methods such as density functional theory or ab initio molecular dynamics. To illustrate this, in this manuscript, the protocol is used for catalytic intermediates that could be involved in the pathway for the decomposition of glycerol (C3H8O3). The structures that are generated using FFMD are modeled in DFT in order to estimate the enthalpies of solvation of the catalytic species and to identify how H2O molecules participate in catalytic decompositions.

The goal of the protocol presented here is to generate and sample trajectories of configurations of liquid water molecules around catalytic species on a flat transition metal surface. The sampled configurations can be used as starting structures in quantum mechanics-based methods.

利用密度泛函理论和力场分子动力学对多相水-金属催化剂接口进行多尺度采样

A significant number of heterogeneously-catalyzed chemical processes occur under liquid conditions, but simulating catalyst function under such conditions ...

Nanoscale Characterization of Liquid-Solid Interfaces by Coupling Cryo-Focused Ion Beam Milling with Scanning Electron Microscopy and Spectroscopy

Physical and chemical processes at solid-liquid interfaces play a crucial role in many natural and technological phenomena, including catalysis, solar energy and fuel generation, and electrochemical energy storage. Nanoscale characterization of such interfaces has recently been achieved using cryogenic electron microscopy, thereby providing a new path to advancing our fundamental understanding of interface processes.
This contribution provides a practical guide to mapping the structure and chemistry of solid-liquid interfaces in materials and devices using an integrated cryogenic electron microscopy approach. In this approach, we pair cryogenic sample preparation which allows stabilization of solid-liquid interfaces with cryogenic focused ion beam (cryo-FIB) milling to create cross-sections through these complex buried structures. Cryogenic scanning electron microscopy (cryo-SEM) techniques performed in a dual-beam FIB/SEM enable direct imaging as well as chemical mapping at the nanoscale. We discuss practical challenges, strategies to overcome them, as well as protocols for obtaining optimal results. While we focus in our discussion on interfaces in energy storage devices, the methods outlined are broadly applicable to a range of fields where solid-liquid interface play a key role.

Cryogenic Focused Ion Beam (FIB) and Scanning Electron Microscopy (SEM) techniques can provide key insights into the chemistry and morphology of intact solid-liquid interfaces. Methods for preparing high quality Energy Dispersive X-ray (EDX) spectroscopic maps of such interfaces are detailed, with a focus on energy storage devices.

通过冷冻聚焦离子束铣削与扫描电子显微镜和光谱学耦合，对液固界面进行纳米级表征

Physical and chemical processes at solid-liquid interfaces play a crucial role in many natural and technological phenomena, including catalysis, solar ...

Visualizing Solution Structure at Solid-Liquid Interfaces using Three-Dimensional Fast Force Mapping

Amongst the challenges for a variety of research fields are the visualization of solid-liquid interfaces and understanding how they are affected by the solution conditions such as ion concentrations, pH, ligands, and trace additives, as well as the underlying crystallography and chemistry. In this context, three-dimensional fast force mapping (3D FFM) has emerged as a promising tool for investigating solution structure at interfaces. This capability is based on atomic force microscopy (AFM) and allows the direct visualization of interfacial regions in three spatial dimensions with sub-nanometer resolution. Here we provide a detailed description of the experimental protocol for acquiring 3D FFM data. The main considerations for optimizing the operating parameters depending on the sample and application are discussed. Moreover, the basic methods for data processing and analysis are discussed, including the transformation of the measured instrument observables into tip-sample force maps that can be linked to the local solution structure. Finally, we shed light on some of the outstanding questions related to 3D FFM data interpretation and how this technique can become a central tool in the repertoire of surface science.

Here, we present a protocol for using three-dimensional fast force mapping - an atomic force microscopy technique - for visualizing solution structure at solid-liquid interfaces with the subnanometer resolution by mapping the tip-sample interactions within the interfacial region.

Amongst the challenges for a variety of research fields are the visualization of solid-liquid interfaces and understanding how they are affected by the ...

Microtensiometer for Confocal Microscopy Visualization of Dynamic Interfaces

Adsorption of surface-active molecules to fluid-fluid interfaces is ubiquitous in nature. Characterizing these interfaces requires measuring surfactant adsorption rates, evaluating equilibrium surface tensions as a function of bulk surfactant concentration, and relating how surface tension changes with changes in the interfacial area following equilibration. Simultaneous visualization of the interface using fluorescence imaging with a high-speed confocal microscope allows the direct evaluation of structure-function relationships. In the capillary pressure microtensiometer (CPM), a hemispherical air bubble is pinned at the end of the capillary in a 1 mL volume liquid reservoir. The capillary pressure across the bubble interface is controlled via a commercial microfluidic flow controller that allows for model-based pressure, bubble curvature, or bubble area control based on the Laplace equation. Compared to previous techniques such as the Langmuir trough and pendant drop, the measurement and control precision and response time are greatly enhanced; capillary pressure variations can be applied and controlled in milliseconds. The dynamic response of the bubble interface is visualized via a second optical lens as the bubble expands and contracts. The bubble contour is fit to a circular profile to determine the bubble curvature radius, R, as well as any deviations from circularity that would invalidate the results. The Laplace equation is used to determine the dynamic surface tension of the interface. Following equilibration, small pressure oscillations can be imposed by the computer-controlled microfluidic pump to oscillate the bubble radius (frequencies of 0.001-100 cycles/min) to determine the dilatational modulus The overall dimensions of the system are sufficiently small that the microtensiometer fits under the lens of a high-speed confocal microscope allowing fluorescently tagged chemical species to be quantitatively tracked with submicron lateral resolution.

This manuscript describes the design and operation of a microtensiometer/confocal microscope to do simultaneous measurements of interfacial tension and surface dilatational rheology while visualizing the interfacial morphology. This provides the real-time construction of structure-property relationships of interfaces important in technology and physiology.

用于动态界面共聚焦显微镜可视化的微量天体测量仪

Adsorption of surface-active molecules to fluid-fluid interfaces is ubiquitous in nature. Characterizing these interfaces requires measuring surfactant ...