Ferromagnetic Cobalt Nanoparticles and Their Immobilization on Monomolecular Films and Chemical Templates

Abstract

Monodisperse Co nanoparticles (NPs), stabilized by organic coating have been synthesized, and their immobilization on a variety of self-assembled monolayers (SAMs) bearing different terminal groups and on SAM-based chemical templates has been studied. The NPs had an average diameter of ∼ 10 nm and consisted of hcp cobalt covered by a thin ( ∼ 1 nm) oxide fi lm.They exhibited pronounced ferromagnetic properties with a blocking temperature above 380 K, which is unusual for the given NP size and is presumably related to the high magnetocrystalline anisotropy associated with the crystallographic perfection of the NPs. The NPs were found to attach selectively to the SAMs bearing the thiol tail group, whereas no stable immobilization to other SAMs, over the electrostatic forces, could be achieved. Finally, based on the results for the individual SAMs, high-contrast 2D structures of the Co NPs were fabricated on SAM-based chemical templates on both microand nanometer length scales. The templates were prepared by irradiationpromoted exchange reaction lithography, taking an OH-terminated aliphatic SAMs as the primary template and thiol-bearing aromatic molecules as the substituents.

Electron‐Irradiation Promoted Exchange Reaction as a Tool for Surface Engineering and Chemical Lithography

“…[56][57][58][59][60][61][62][63][64] As primary SAMs we mostly used those of the chemically inert, non-substituted alkanethiols on Au(111), with a preference for the dodecanethiolate (DDT) monolayer. [56][57][58][59][60][61][62][63][64] The basic experiments were performed with the primary SAM of either DDT or hexadecanethiolate (HDT) and mercaptoundecanoic acid (MUDA) or mercaptohexadecanoic acid (MHDA) as the substituents. [56,57] As the latter molecules carry carboxyl groups (COOH), their presence and concentration can be determined by X-ray photoelectron spectroscopy (XPS) and X-ray absorption spectroscopy (XAS).…”

“…The molecules shown in Figure 3 were tested for IPER, with the outcome of this procedure monitored preferably by WCA goniometry and XPS, in combination with some other complementary techniques. [56][57][58][59][60][61][62][63][64] In nearly all cases, IPER worked quite well, with the ultimate extent of the promoted exchange depending on the specific combination of the primary SAM and the substituent. Interestingly, to a certain extent IPER could also be applied to aromatic SAMs, as was demonstrated using the biphenylthiolate/MUDA combination.…”

“…[61,62] Interestingly, the Co NP used for the creation of the lithographic patterns (Figure 5c) exhibited exceptional magnetic properties with the so-called blocking temperature exceeding 380 K, which is unusual for the given NP size (an average diameter of ≈10 nm) and stems presumably from the high magnetocrystalline anisotropy due to the crystallographic perfection of these NPs. [62] The advantages of the approach could however be best visualized by the fabrication of polymer brush patterns, formed from such broadly used biopolymers as poly(N-isopropylacrylamide) (pNIPAAM) and poly(2-hydroxyethyl methacrylate) (pHEMA). These brushes were grown either on the DDT/ AUDT templates, following the attachment of a suitable initiator, such as a bromoisobutyryl group (BIB), to the terminal NH 2 groups of 12-aminododecanthiolate (AUDT), [59] or on the DDT/DTBUD templates, following the cleavage of the disulfide bond of DTBUD and subsequent adsorption of both BIB-terminated parts.…”

Synthesis of PtCo3 polyhedral nanoparticles and evolution to Pt3Co nanoframes

“…In addition, oleylamine acted as a solvent, reducing agent, and surfactant [43,44], while oleic acid also aided as a surfactant. Oleic acid was introduced into the synthesis to enhance the shape control as it has been shown that oleic acid has a particularly strong affinity for cobalt in many cobalt-based NP syntheses [7,[45][46][47][48][49]. Oleic acid has also been found to improve the effectiveness of oleylamine [49] and their synergistic effect was expected based on the slight temperature increase of their solution upon simple mixing of the two surfactants.…”

Selective Nanotrench Filling by One-Pot Electroclick Self-Constructed Nanoparticle Films

“…For instance, ferrimagnetic NPs will lead to next generation of high density magnetic storage media and magnetite NP films will find applications in spintronics . Surface functionalization by layer‐by‐layer, self‐assembled monolayers, Langmuir–Blodgett, or dip‐coating deposition were used to assemble NP platforms whose stability was recently improved by covalent reticulation . However, these techniques are still difficult to implement in electronic or photonic nanodevices, due to structural defects and high sensitivity to chemical and electromagnetic environment .…”