University of Texas at Dallas, Richardson, Texas 75080, USA.
J Am Chem Soc. 2009 Dec 23;131(50):18159-67. doi: 10.1021/ja907003w.
Molecular electronics is an attractive option for low-cost devices because it involves highly uniform self-assembly of molecules with a variety of possible functional groups. However, the potential of molecular electronics can only be turned into practical applications if reliable contacts can be established without damaging the organic layer or contaminating its interfaces. Here, a method is described to prepare tightly packed carboxyl-terminated alkyl self-assembled monolayers (SAMs) that are covalently attached to silicon surfaces and to deposit thin metallic copper top contact electrodes without damage to this layer. This method is based on a two-step procedure for SAM preparation and the implementation of atomic layer deposition (ALD) using copper di-sec-butylacetamidinate Cu(sBu-amd). In situ and ex situ infrared spectroscopy (IRS), X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), and electrical measurements are used to characterize the chemical modification of the Si/SAM interface, the perturbation of the SAM layer itself, and the metal homogeneity and interaction with the SAM headgroups. This work shows that (i) carboxyl-terminated alkyl monolayers can be prepared with the same high density and quality as those achieved for less versatile methyl-terminated alkyl monolayers, as evidenced by electrical properties that are not dominated by interface defects; (ii) Cu is deposited with ALD, forming a bidentate complexation between the Cu and the COOH groups during the first half cycle of the ALD reaction; and (iii) the Si/SAM interface remains chemically intact after metal deposition. The nondamaging thin Cu film deposited by ALD protects the SAM layer, making it possible to deposit a thicker metal top contact leading ultimately to a controlled preparation of molecular electronic devices.
分子电子学是低成本器件的一个有吸引力的选择，因为它涉及具有各种可能的官能团的分子的高度均匀的自组装。然而，只有在能够建立可靠的接触而不损坏有机层或污染其界面的情况下，分子电子学的潜力才能转化为实际应用。在这里，描述了一种方法来制备紧密堆积的羧基末端烷基自组装单层（SAM），这些 SAM 通过共价键附着在硅表面上，并在不损坏该层的情况下沉积薄的金属铜顶接触电极。该方法基于两步法制备 SAM 和使用铜二仲丁基乙酰胺[Cu（sBu-amd）]（2）实施原子层沉积（ALD）。原位和非原位红外光谱（IRS）、X 射线光电子能谱（XPS）、原子力显微镜（AFM）和电测量用于表征 Si/SAM 界面的化学修饰、SAM 层本身的扰动以及金属的均匀性和与 SAM 头基的相互作用。这项工作表明：（i）可以用与不太通用的甲基末端烷基单层相同的高密度和高质量制备羧基末端烷基单层，这可以通过不被界面缺陷主导的电性能来证明；（ii）通过 ALD 沉积 Cu，在 ALD 反应的前半个循环中，Cu 与 COOH 基团形成双配位络合物；（iii）金属沉积后 Si/SAM 界面保持化学完整性。ALD 沉积的无损薄 Cu 膜保护了 SAM 层，使得能够沉积更厚的金属顶接触，最终实现分子电子器件的可控制备。
