Interface driven magnetoelectric effects in granular CrO2

Antiferromagnetic and magnetoelectric Cr2O3-surfaces strongly affect the electronic properties in half metallic CrO2. We show the presence of a Cr2O3 surface layer on CrO3 grains by high-resolution transmission electron microscopy. The effect of these surface layers is demonstrated by measurements of the temperature variation of the magnetoelectric susceptibility. A major observation is a sign change at about 100 K followed by a monotonic rise as a function of temperature. These electric field induced moments in CrO3 are correlated with the magnetoelectric susceptibility of pure Cr2O3. This study indicates that it is important to take into account the magnetoelectric character of thin surface layers of Cr2O3 in granular CrO2 for better understanding the transport mechanism in this system. The observation of a finite magnetoelectric susceptibility near room temperature may find utility in device applications.Comment: Figure 1 with strongly reduced resolutio

Phase separation in Ni-Nb-Y metallic glasses

The ternary system Ni-Nb-Y exhibits an extended miscibility gap in the equilibrium liquid The decomposition of the liquid can be used to prepare phase-separated Ni-Nb-Y glasses by means of rapid quenching of the melt Phase separation and structure formation take place during quenching in the undercooled liquid The temperature dependence of the critical temperature of liquid-liquid phase separation T-C determines essentially the quenched in microstructures For Ni contents 60 at % early stages of decomposition are obtained with correlation lengths in the nanometer-range. In situ small angle X-ray scattering at elevated temperatures gives evidence of the spinodal character of the decomposition. (C) 2009 Elsevier B.V. All rights reserved

In situ observations of self-repairing single-walled carbon nanotubes

Single-walled carbon nanotubes are shown to have self-repairing capabilities exceeding that predicted by theory. Time-series aberration-corrected low-voltage transmission electron microscopy is used to study the defect dynamics of single-walled carbon nanotubes in situ. We confirm experimentally previous theoretical predictions for the agglomeration of adatoms forming protrusions and subsequent ejection. An explanation for the preferred destruction of smaller-diameter tubes is proposed. The complete healing of a ∼20 -atom multivacancy in a nanotube wall is shown while theory only predicts the healing of much smaller holes. © 2010 The American Physical Society

In situ observations of fullerene fusion and ejection in carbon nanotubes.

We present in situ experimental observations of fullerenes seamlessly fusing to single-walled carbon nanotubes. The morphing-entry of a fullerene to the interior of a nanotube is also captured. The confined (1D) motion of the newly-encapsulated fullerene within its host attests to the actual change from the exterior to interior

Enhanced pi-pi interactions between a C-60 fullerene and a buckle bend on a double-walled carbon nanotube

In situ low-voltage aberration corrected transmission electron microscopy (TEM) observations of the dynamic entrapment of a C60 molecule in the saddle of a bent double-walled carbon nanotube is presented. The fullerene interaction is non-covalent, suggesting that enhanced π-π interactions (van der Waals forces) are responsible. Classical molecular dynamics calculations confirm that the increased interaction area associated with a buckle is sufficient to trap a fullerene. Moreover, they show hopping behavior in agreement with our experimental observations. Our findings further our understanding of carbon nanostructure interactions, which are important in the rapidly developing field of low-voltage aberration corrected TEM and nano-carbon device fabrication. © The Author(s) 2010

Single-wall-carbon-nanotube/single-carbon-chain molecular junctions

Stable junctions between a single carbon chain and two single-wall carbon nanotubes were produced via coalescence of functionalized fullerenes filled into a single-wall carbon nanotube and directly imaged by in situ transmission electron microscopy. First principles quantum chemical calculations support the observed stability of such molecular junctions. They also show that short carbon chains bound to other carbon structures are cumulenes and stable semiconductors due to Peierls-like distortion. Junctions like this can be regarded as archetypical building blocks for all-carbon molecular electronics. © 2010 The American Physical Society