Effect of polarity of self-assembled monolayers on morphology and magnetic properties of a deposited magnetic material

Abstract

With the decreasing size of devices, the ability to organize materials and control their physical properties through spatial and morphology manipulation becomes critical. Here, we show that the nature of the organic functional group at the top surface of the self-assembled monolayers can strongly influence the growth of a metallic thin film on the monolayer, as a chemical reaction may occur at the interface. We have sputtered Permalloy (Ni79Fe21) on patterned templates of polar and nonpolar self-assembled monolayers. Uniform film formation is observed on polar regions, and cluster/dropletlike structures are formed on the nonpolar regions. A similar behavior in morphology is observed for the deposition of Permalloy on a substrate having single component self-assembled monolayers. Magnetic measurements reveal that Permalloy exhibits a superparamagnetic behavior when deposited on a nonpolar self-assembled monolayer substrate, whereas a ferromagnetic behavior is observed for Permalloy deposited on a polar self-assembled monolayer substrate. Thus, a systematic deposition of Permalloy on polar and nonpolar self-assembled monolayers allows a control on morphology and the magnetic properties due to the difference in wettability of the terminal organic functional groups of the self-assembled monolayers.

Study of thickness variation, morphology, and magnetic properties of Permalloy on organic monolayers

“…The stripe patterns of MHA/ODT were formed by using a microcontact printing technique as discussed earlier. 18 Finally, Py was sputtered on these patterned and unpatterned substrates of SAMs in a 3.5 mT argon atmosphere in a chamber with a base pressure of 3.5 ϫ 10 −7 Torr. AFM and MFM imaging was done by using a scanning electron microscopy ͑Digital Instruments Dimension 3000 SPM͒ in tapping mode.…”

“…16,17 Recently we have reported the sputtering of ϳ6 nm thick films of Permalloy ͑Py͒ on SAMs of 16-mercaptohexadecanoic acid ͑MHA͒ and 1-octadecanethiol ͑ODT͒ and have observed significant differences in morphology and magnetic behavior of the Py. 18,19 MHA has a polar ͑-COOH͒ OFG and ODT has a nonpolar ͑-CH3͒ OFG at the top surface. Sputtering of Py on a patterned SAM structure with -COOH and -CH 3 terminal groups results in the formation of uniform film on -COOH regions and clusters on -CH 3 regions.…”

Organic Spin‐Valves and Beyond: Spin Injection and Transport in Organic Semiconductors and the Effect of Interfacial Engineering

“…For example, MHA (16‐mercaptohexadeconic acid; HS(CH 2 ) 15 CO 2 H) and ODT (1‐Octadecanethiol; CH 3 (CH 2 ) 17 SH) are two widely used thiol SAMs with very different tail groups. As thiols, both ODT and MHA bond well to metallic surfaces such as Au . However, when they are assembled onto Au surfaces, they induce quite different physical and chemical properties due to the different tail groups.…”

“…However, when they are assembled onto Au surfaces, they induce quite different physical and chemical properties due to the different tail groups. MHA, with a carboxylate tail group, increases the Au work function and makes the Au surface hydrophilic . ODT, with a simple methyl tail group, decreases the Au work function and makes the Au surface hydrophobic .…”

“…MHA, with a carboxylate tail group, increases the Au work function and makes the Au surface hydrophilic . ODT, with a simple methyl tail group, decreases the Au work function and makes the Au surface hydrophobic . Because of these differences, the effects of the insertion of these SAMs (ODT and MHA) between Co and Alq 3 on the electronic structure hybridization, the energetics and band offset, and the spin‐dependent properties at the interface are thought‐provoking, and they have been investigated.…”