Gandhi Darshan D, Lane Michael, Zhou Yu, Singh Amit P, Nayak Saroj, Tisch Ulrike, Eizenberg Moshe, Ramanath Ganapathiraman
Materials Science & Engineering Department, Rensselaer Polytechnic Institute, Troy, New York 12180, USA.
Nature. 2007 May 17;447(7142):299-302. doi: 10.1038/nature05826.
Self-assembled molecular nanolayers (MNLs) composed of short organic chains and terminated with desired functional groups are attractive for modifying surface properties for a variety of applications. For example, organosilane MNLs are used as lubricants, in nanolithography, for corrosion protection and in the crystallization of biominerals. Recent work has explored uses of MNLs at thin-film interfaces, both as active components in molecular devices, and as passive layers, inhibiting interfacial diffusion, promoting adhesion and toughening brittle nanoporous structures. The relatively low stability of MNLs on surfaces at temperatures above 350-400 degrees C (refs 12, 13), as a result of desorption or degradation, limits the use of surface MNLs in high-temperature applications. Here we harness MNLs at thin-film interfaces at temperatures higher than the MNL desorption temperature to fortify copper-dielectric interfaces relevant to wiring in micro- and nano-electronic devices. Annealing Cu/MNL/SiO2 structures at 400-700 degrees C results in interfaces that are five times tougher than pristine Cu/SiO2 structures, yielding values exceeding approximately 20 J m(-2). Previously, similarly high toughness values have only been obtained using micrometre-thick interfacial layers. Electron spectroscopy of fracture surfaces and density functional theory modelling of molecular stretching and fracture show that toughening arises from thermally activated interfacial siloxane bridging that enables the MNL to be strongly linked to both the adjacent layers at the interface, and suppresses MNL desorption. We anticipate that our findings will open up opportunities for molecular-level tailoring of a variety of interfacial properties, at processing temperatures higher than previously envisaged, for applications where microlayers are not a viable option-such as in nanodevices or in thermally resistant molecular-inorganic hybrid devices.
由短有机链组成并以所需官能团封端的自组装分子纳米层（MNLs），因其能够修饰表面性质而在各种应用中颇具吸引力。例如，有机硅烷MNLs可用作润滑剂、用于纳米光刻、防腐蚀以及生物矿物结晶。近期的研究探索了MNLs在薄膜界面的用途，既作为分子器件中的活性成分，也作为抑制界面扩散、促进粘附并增韧脆性纳米多孔结构的钝化层。由于解吸或降解，MNLs在高于350 - 400摄氏度的表面上稳定性相对较低（参考文献12、13），这限制了表面MNLs在高温应用中的使用。在此，我们在高于MNL解吸温度的温度下利用薄膜界面处的MNLs来强化与微电子和纳米电子器件布线相关的铜 - 电介质界面。在400 - 700摄氏度下对Cu/MNL/SiO₂结构进行退火处理，得到的界面韧性比原始Cu/SiO₂结构高五倍，产生的值超过约20 J m⁻²。此前，只有使用微米厚的界面层才能获得类似的高韧性值。断裂表面的电子能谱以及分子拉伸和断裂的密度泛函理论建模表明，增韧源于热激活的界面硅氧烷桥接，这使得MNL能够与界面处的相邻两层紧密相连，并抑制MNL解吸。我们预计，我们的发现将为在高于先前设想的加工温度下对各种界面性质进行分子水平的定制开辟机会，适用于微层不可行的应用，例如纳米器件或耐热分子 - 无机混合器件。
