Dipolar magnetism in assembled Co nanoparticles on graphene.

The magnetic properties of the assembled Co nanoparticles on graphene were studied using X-ray magnetic circular dichroism (XMCD), magneto-optical Kerr effects, and a modeling simulation. We demonstrate that the superparamagnetic nanoparticles reveal a ferromagnetic phase when they are assembled on graphene. The moderate increase of the XMCD asymmetry and magnetization with coverage for this assembly indicates a dipolar-mediated magnetism, which is further verified by a model simulation considering the dipolar interaction between neighboring nanoparticles. Furthermore, C K-edge spectra reveal visible dichroism at the π* state of graphene, which indicates the existence of a spin-polarized interface state, while the assembled Co nanoparticles reveal a ferromagnetic phase. These results suggest an efficient route to stabilize the ferromagnetic phase of nanostructures on graphene by tailoring dipolar interactions, which is essential to realize a higher efficiency of spin injection in graphene-based spintronics.

Magnetic coupling of porphyrin molecules through graphene.

X-ray magnetic circular dichroism (XMCD) measurements and density functional theory (DFT)+U calculations reveal an unexpected antiferromagnetic coupling between physisorbed paramagnetic Co-porphyrin molecules and a Ni surface, separated by a graphene layer. A positive magnetization at the Ni substrate atoms is mediated by graphene and induces a negative one at the Co site, despite only a very small overlap between macrocyclic π and graphene pz -orbitals.

In situ hydrolysis of imine derivatives on Au(111) for the formation of aromatic mixed self-assembled monolayers: multitechnique analysis of this tunable surface modification.

This paper presents a novel method for preparing aromatic, mixed self-assembled monolayers (SAMs) with a dilute surface fraction coverage of protonated amine via in situ hydrolysis of C═N double bond on gold surface. Two imine compounds, (4'-(4-(trifluoromethyl)benzylideneamino)biphenyl-4-yl)methanethiol (CF(3)-C(6)H(4)-CH═N-C(6)H(4)-C(6)H(4)-CH(2)-SH, TFBABPMT) and (4'-(4-cyanobenzylideneamino)biphenyl-4-yl)methanethiol (CN-C(6)H(4)-CH═N-C(6)H(4)-C(6)H(4)-CH(2)-SH, CBABPMT), self-assembled on Au(111) to form highly ordered monolayers, which was demonstrated by infrared reflection absorption spectroscopy (IRRAS) and X-ray photoelectron spectroscopy (XPS). A nearly upright molecular orientation for CF(3)- and CN-terminated SAM was detected by near edge X-ray absorption fine structure (NEXAFS) measurements. Afterward, the acidic catalyzed hydrolysis was carried out in chloroform or an aqueous solution of acetic acid (pH = 3). Systematic studies of this hydrolysis process for CN-terminated SAM in acetic acid at 25 °C were performed by NEXAFS measurements. It was found that about 30% of the imine double bonds gradually cleaved in the first 40 min. Subsequently, a larger hydrolysis rate was observed due to the freer penetration of acetic acid in the SAM and resultant more open molecular packing. Furthermore, the molecular orientation in mixed SAMs did not change during the whole hydrolysis process. This partially hydrolyzed surface contains a controlled amount of free amines/ammonium ions which can be used for further chemical modifications.