Nanoscale electrodeposition of metals and semiconductors from ionic liquids
Nanoscale electrodeposition of metals and semiconductors from ionic liquids
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DOI：
10.1016/s0013-4686(03)00378-5
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发表时间：
2003-09
影响因子：
6.6
通讯作者：
W. Freyland;C. Zell;S. Abedin;F. Endres
中科院分区：
文献类型：
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作者：
W. Freyland;C. Zell;S. Abedin;F. Endres
在欠电位（UPD）和过电位（OPD）范围内研究了Ni、Co及其合金与Al的电结晶以及Ge在Au（111）和Si(111):H上的电沉积。为此，在离子电解质、室温熔盐或离子液体AlCl3 - [BMIm]+Cl−和[BMIm]+PF6−中进行了原位电化学STM和STS测量。与水介质相比，这些离子电解质具有更大的电化学窗口，可以在纳米尺度上研究这些元素和化合物的电沉积。我们提出并比较了Ni和Co电沉积的二维和三维相形成的最新结果。在二维相形成中观察到明显的差异- ni单层与Co岛形成-根据这两种金属的界面自由能的不同值进行了讨论。在过电位（OPD）范围内，Ni的沉积是由三维Ni团簇沿台阶边缘柱状生长进行的，而Co团簇在低于- 0.17 V的电位下均匀生长。发现NixAl1−xx和CoxAl1−xx的电沉积非常相似。在这两种情况下，共沉积开始于明显正的Al/Al(III)-Nernst电位，随着Al含量的增加，观察到更小的晶粒。利用STS光谱原位探测了各合金簇的组成，发现不同电位E尺度下的有效隧道势垒与独立的常规电化学和光谱测量确定的簇组成有关。最后，我们首次报道了在Au（111）和Si(111):H上电沉积不同厚度的超薄Ge膜的研究。利用原位STS光谱探测这些薄膜的电子结构表明，随着薄膜厚度的增加，金属-半导体转变在2-3 nm以上。并与外延气相沉积法生长的超薄锗膜进行了比较。
The electrocrystallization of Ni, Co and their respective alloys with Al and the electrodeposition of Ge on Au(111) and Si(111):H have been studied in the underpotential (UPD) and overpotential (OPD) range. To this end, in situ electrochemical STM and STS measurements have been performed in ionic electrolytes, the room temperature molten salts or ionic liquids AlCl3–[BMIm]+Cl−and [BMIm]+PF6−. The larger electrochemical windows of these ionic electrolytes in comparison to aqueous media enables the investigation of electrodeposition of these elements and compounds on a nanometer scale. We present and compare recent results of 2D and 3D phase formation of Ni and Co electrodeposition. Clear differences are observed in the 2D phase formation—Ni monolayer vs. Co island formation—which are discussed in the light of the distinct values of the interfacial free energies of these two metals. In the overpotential (OPD) range, Ni deposition proceeds by a columnar growth of 3D Ni clusters along step edges, whereas Co clusters grow homogeneously at potentials below −0.17 V vs. Co/Co(II). Electrodeposition of NixAl1−xand CoxAl1−xis found to be very similar. In both cases, codeposition starts at a potential clearly positive of the Al/Al(III)-Nernst potential and with increasing Al content smaller grains are observed. The composition of the respective alloy clusters has been probed in situ by STS spectra and it is found that the effective tunneling barriers at different potentials E scale with the cluster composition determined from independent conventional electrochemical and spectroscopic measurements. Finally, we report first investigations of electrodeposition of ultrathin Ge films with varying thickness on Au(111) and Si(111):H. Probing the electronic structure of these films by in situ STS spectra a metal–semiconductor transition is indicated with increasing film thickness above 2–3 nm. This is discussed in comparison with ultrathin Ge films grown by expitaxial vapour deposition.