Ana Perez-Rodriguez, Esther Barrena*, Antón Fernández, Enrico Gnecco* and Carmen Ocal. Nanoscale, 2017, 9, 5589-5596. DOI: 10.1039/C7NR01116D
Progress in the general understanding of structure–property relationships in organic devices requires experimental tools capable of imaging structural details, such as molecular packing or domain attributes, on ultra-thin films. An operation mode of scanning force microscopy, related to friction force microscopy (FFM) and known as transverse shear microscopy (TSM), has demonstrated the ability to reveal the orientation of crystalline domains in organic surfaces with nanometer resolution. In spite of these promising results, numerous questions remain about the physical origin of the TSM domain imaging mechanism. Taking as a benchmark a PTCDI-C8 sub-monolayer, we demonstrate experimentally and theoretically that such a mechanism is the same atomic scale stick-slip ruling FFM leading to the angular dependence of both signals. Lattice-resolved images acquired on top of differently oriented PTCDI-C8 molecular domains are crucial to permit azimuthal sampling, without the need for sample rotation. The simulations reveal that, though the surface crystallography is the direct cause of the FFM and TSM signals, the manifestation of anisotropy will largely depend on the amplitude of the surface potential corrugation as well as on the temperature. This work provides a novel nanoscale strategy for the quantitative analysis of organic thin films based on their nanotribological response.
Oxides for new-generation electronics
A molecular-scale portrait of domain imaging in organic surfaces
Systematic studies on polycrystalline Hf1–xZrxO2 films with varying Zr contents show that HfO2 films are paraelectric (monoclinic). If the Zr content is increased, films become ferroelectric (orthorhombic) and then antiferroelectric (tetragonal). HfO2 shows very good insulating properties and it is used in metal-oxide-semiconductor field-effect devices, while ZrO2 shows good piezoelectric properties, but it is antiferroelectric. In between, Hf0.5Zr0.5O2 shows good ferroelectric properties at the expense of poorer insulating and piezoelectric properties than HfO2 and ZrO2, respectively.
About ten years after ferroelectricity was first reported in doped HfO2 polycrystalline films, there is tremendous interest in this material and ferroelectric oxides are once again in the spotlight of the memories industry. Great efforts are being made to understand and control ferroelectric properties. Epitaxial films, which have fewer defects and a more controlled microstructure than polycrystalline films, can be very useful for this purpose. Epitaxial films of ferroelectric HfO2 have been much less investigated, but after the first report in 2015 significant progress has been achieved.
We report here a structural study of RBaMn2O6 (R=La, Pr, and Nd) compounds by means of synchrotron radiation x-ray powder diffraction and Raman spectroscopy. The three compounds are A-site ordered perovskites adopting the prototypical tetragonal structure at high temperature. A ferromagnetic transition is observed in the LaBaMn2O6 sample and the lattice parameters undergo anisotropic changes at TC related to the orientation of the magnetic moments.
The layered perovskite YBaCuFeO5 (YBCFO) is considered one of the best candidates to high-temperature chiral multiferroics with strong magnetoelectric coupling. In RBaCuFeO5 perovskites (R: rare-earth or Y) A-site cations are fully ordered whereas their magnetic properties strongly depend on the preparation process. They exhibit partial cationic disorder at the B-site that generates a magnetic spiral stabilized through directionally assisted long range coupling between canted locally frustrated spins.
We report the synthesis and theoretical study of two new colorimetric chemosensors with special selectivity and sensitivity to Ni2+ and Cu2+ ions over other metal cations in the CH3CN/H2O solution. Compounds (E)-4-((2-nitrophenyl)diazenyl)-N,N-bis(pyridin-2-ylmethyl)aniline (A) and (E)-4-((3-nitrophenyl)diazenyl)-N,N-bis(pyridin-2-ylmethyl)aniline (B) exhibited a drastic color change from yellow to colorless, which allows the detection of the mentioned metal cations through different techniques.