Irreversible and reversible structural deformation and electromechanical behavior of carbon nanohorns probed by conductive AFM.
Irreversible and reversible structural deformation and electromechanical behavior of carbon nanohorns probed by conductive AFM.
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DOI：
10.1002/smll.201002148
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发表时间：
2011-05
期刊：
影响因子：
13.3
通讯作者：
Jianxun Xu;Y. Shingaya;H. Tomimoto;O. Kubo;T. Nakayama
中科院分区：
文献类型：
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作者：
Jianxun Xu;Y. Shingaya;H. Tomimoto;O. Kubo;T. Nakayama
由CNH聚集体在高压下压制形成的CNH小球的电导率由两组独立测量。然而，作者研究了宏观CNH小球(尺寸为几毫米)的电导率。这些结果有助于理解包含大量CNH聚集体的体系，其中CNH聚集体之间的电子跃迁是决定电导率的主要因素，这是作者得出的结论。不能获得单一CNH聚集体的本征电学性质。在这项工作中，利用导电原子力显微镜(c-AFM)直接测量了单个CNH聚集体在Au衬底上的电学行为，这表明CNH聚集体具有很高的电导率。此外，在c-AFM探针的作用下，CNH聚集体表现出了有趣的机电特性。研究发现，聚集体外表面突出的纳米角发生了不可逆的变形，导致电导率下降。在塑性变形后，同一骨料在100 NN以上的力都有弹性响应，电导随力的增大而增大。导电原子力显微镜悬臂梁与铂(铂)或铑(Rh)涂层用于成像和电气测量。图1a显示了割胶模式下单个CNH集料的地形图.聚集体的高度约为100 nm，与CNH聚集体的典型直径一致。图1b中还给出了单个CNH聚集体的扫描电子显微镜(SEM)图像以供参考。图1c显示了通过扫描电子显微镜获得的具有铂涂层的硅探针的俯视图。针尖的半径约为20-25 nm，导致AFM图像的空间分辨率较低。铂涂层的厚度在顶端约为10 nm，侧壁约为∼30-40 nm，根据断头的扫描电子显微镜图像(支持信息(SI)中的图S1)进行评估。较厚的金属涂层有利于提高电导测量的稳定性和耐磨性。如图1d中的测量方案所示，AFM探针在轻敲模式下定位聚集体后被放置在CNH聚集体的表面上。为此，选择了具有合适弹性常数的AFM悬臂梁，以在轻敲模式下提供稳定的图像，但在尖端加载期间不移动CNH聚集体。弹簧常数约为0.15，1.5，
The electrical conductivity of CNH pellets formed by pressing CNH aggregates under high pressure was measured by two groups independently.[17, 18] However, the authors studied the conductivity of macroscopic CNH pellets (with a size of several millimeters). These results are useful for understanding systems containing a large amount of CNH aggregates with close contact among them, in which conductivity is dominated by electron hopping between CNH aggregates, as concluded by the authors. The intrinsic electrical properties of a single CNH aggregate could not be obtained. In this work, the electrical behavior of a single CNH aggregate on Au substrate was measured directly using a conductive atomic force microscopy (c-AFM), which indicated the very high conductivity of CNH aggregates. In addition, CNH aggregates exhibited interesting electromechanical characteristics while pressed by the c-AFM probe. It was found that the protruding nanohorns on the outer surface of the aggregate undergo irreversible deformation, resulting in a drop in conductance. After the plastic deformation, elastic responses of the same aggregate were observed at forces over 100 nN, showing increased conductance with increasing force. Conductive AFM cantilevers with a platinum (Pt) or rhodium (Rh) coating were used for both imaging and electrical measurements. Figure 1 a shows the topographic image of a single CNH aggregate under the tapping mode. The height of the aggregate is approximately 100 nm, consistent with the typical diameter of CNH aggregates. A scanning electron microscopy (SEM) image of a single CNH aggregate is also given for reference in Figure 1 b. Figure 1 c shows a top view of a Si probe with a Pt coating obtained by SEM. The radius of the tip apex is approximately 20–25 nm, resulting in the relatively low spatial resolution of the AFM images. The thickness of the Pt coating is approximately 10 nm at the apex and∼ 30–40 nm at the side walls, evaluated from the SEM image of a broken tip (Figure S1 in the Supporting Information (SI)). The thick metal coating is helpful for increasing the wear resistance and the stability of conductance measurements. As shown in the measurement scheme in Figure 1 d, the AFM probe was positioned onto the surface of the CNH aggregate after locating the aggregate under tapping mode. For this purpose, an AFM cantilever with a suitable spring constant was chosen to provide stable images under tapping mode but not to move the CNH aggregate during tip loading. Cantilevers with spring constants of approximately 0.15, 1.5,