The influence of amorphous carbon on FePt catalyst particles under chemical vapor deposition conditions typically applied for CNT growth Is examined through two routes. In the first, FePt catalyst particles supported on alumina are exposed to a well-established cyclohexane thermal CVD reaction at various temperatures. At higher temperatures where self-pyrolysis leads to copious amorphous carbon and carbon tar formation, carbon nanotubes are still able to form. In the second route, an amorphous carbon film is first deposited over the catalyst particles prior to the CVD reaction. Even for reactions where further amorphous carbon is deposited due to self-pyrolysis, graphitization is still demonstrated. Our findings reveal that the presence of amorphous carbon does not prevent catalytic hydrocarbon decomposition and graphitization processes. We also show an additional catalytic-reaction to be present, catalytic hydrogenation, a process in which carbon in contact with the catalyst surface reacts with H-2 to form CH4.

Nanostructured graphene and graphene nanoribbons have been fabricated by catalytic hydrogenation, and the edge smoothness has been examined via direct imaging with atomic resolution. When abstaining from solvents during sample preparation, the prepared nanoribbons possess clean edges ready for inspection via transmission electron microscopy (TEM). Edges with subnanometer smoothness could be observed. A method has been developed to make catalytic hydrogenation experiments compatible with TEM, which enables monitoring of the nanoparticles prior to and after hydrogenation. In this way, etching of free-standing few-layer graphene could be demonstrated. Our results enable evaluation of the degree of edge control that can be achieved by means of catalytic hydrogenation.

Catalytic hydrogenation is considered to be a key technological approach to structure graphene nanoribbons with desired and specific edge termination. In the present study the hydrogenation was catalyzed utilizing pre-defined cobalt nanoparticles that act as knives to cut graphite substrates in a hydrogen atmosphere at elevated temperatures. Only catalyst particles that reside at an exposed graphite edge carve into the graphite thus leaving etch tracks behind. Particles lying on the flat graphite plane do not etch channels. Thorough morphological and structural characterization of the Co catalyst particles is carried out using aberration-corrected low voltage high resolution electron microscopy. Based on our findings conclusions on the underlying hydrogenation mechanism are drawn that support the previously proposed interfacial hydrogen mechanism. (C) 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

The advancement in carbon nanotube (CNT) technology includes significant interest in their functionalization to modify their chemical and physical properties. In particular, the selective functionalization of the CNT ends opens exciting opportunities to design nanoscale architectures and networks. The realization of hard-magnetically terminated CNT via plasma enhanced chemical vapor deposition from Fe–Pt thin films is reported. Although FePt is rarely used as a catalyst for CNT synthesis the said binary catalyst affords attractive hard magnetic properties when present in the chemically ordered L10 phase.

We report on experiments to elucidate the underlying mechanism of the recently observed template-directed organization of gas phase deposited FePt nanoparticles into regular two-dimensional (2D) arrays on the bacterial surface protein layer (S-layer) of Bacillus sphaericus NCTC 9602. To this end, the size and charge state of the particles have been tuned prior to their deposition onto the S-layer, and the preferred particle deposition sites have been identified and correlated to the protein template lattice by means of statistical analysis of transmission electron microscopy images of the obtained hybrid structures. The experiments reveal that the match between the nanoparticle geometry and the regularly patterned template surface morphology is most important to achieve a high degree of nanoparticle ordering. Deposited nanoparticles were preferentially located at those sites where the S-layer surface exhibits hollows of appropriate size, so that the particle can reduce its surface free energy by maximizing its contact area with the exposed S-layer surface. Particular sites at the protein layer possessed a bimodal occupation frequency distribution. This can be explained by characteristic differences in the morphologies of the inner and outer faces of the S-layer sheets immobilized at the substrate surface. Experiments with nanoparticles of different charge states did not show significant variations in the particle distribution, indicating that the occurrence of a periodic surface charge modulation at the 2D protein crystal, which is often claimed to be the origin for the self-organization of particles deposited from solution, was not the relevant driving force under the chosen experimental conditions.

We have explored the influence of predefined gas phase prepared catalyst particles on carbon nanotube (CNT) properties such as their diameter and number of walls. During the catalyst preparation particles are simultaneously deposited onto a substrate for chemical vapour deposition as well as on a witness grid for analysis in transmission electron microscopy. This allows us to obtain precise information on the starting catalyst material on one side and the CNT product on the other. Clear correlations between the catalyst's size and the CNT diameter and number of walls have been found. Our results indicate a dependence of the resultant CNT on the volume to surface area ratio of the catalyst particle and fit well with our understanding of cap formation at CNT nucleation. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

To achieve a regular quadratic particle arrangement, gas phase prepared FePt nanoparticles which were annealed in flight in order to obtain the highly anisotropic tetragonal L 1 0 structure are deposited onto the regular 2-D bacterial surface-protein layer (S layer) of Bacillus sphaericus NCTC 9602 which exhibits a four-fold lattice symmetry with a lattice constant of 12.5 nm. The degree of regularity is studied by the statistical evaluation of the particles positions observed by transmission electron microscopy. Although the obtained regularity for the annealed hard magnetic particles is less than for previously studied disordered fcc FePt nanoparticles, a template-directed transfer of both lattice symmetry and periodicity from the 2-D protein crystal to the particle arrangement is observed. In addition, particle agglomeration which has been shown to have a strong effect on the arrangement's regularity, is clearly reduced for the annealed particles because of the mutual magnetic repulsion of adjacent particles.

FePt nanoparticles from the gas phase are deposited onto regular two-dimensional bacterial surface layer proteins with a four-fold lattice symmetry and a lattice constant of 12.5 nm. Transmission electron microscopy shows that the particle arrangement adopts both, the symmetry and periodicity of the protein template. The influence of the particle density on both the degree of agglomeration and the regularity of the particle arrangement is studied. Depositing the particles in a magnetic field applied parallel to the substrate leads to a significant decrease in agglomeration and thereby to an increase in the fraction of regularly arranged particles at high particle densities.

FePt nanoparticles from the gas phase are deposited onto the two-dimensional crystalline surface layer protein from the bacterium Bacillus sphaericus NCTC 9602. The potential of this protein layer to facilitate the ordered spatial arrangement of the otherwise statistically distributed nanoparticles on the substrate is studied. Transmission electron microscopy reveals the particles positions to be directed by the regular protein template. (c) 2007 American Institute of Physics.

The correlation between rf-response and magnetic microstructure is addressed in this paper. Patterned arrays with rectangular elements of an amorphous Co 92 Zr 2 Ta 6 (CZT) alloy were fabricated from single layers (thickness 80 nm) and CZT (40 nm)/Al 2 O 3 (4 nm)/CZT(40 nm) trilayers. The elements have an induced uniaxial anisotropy along their short axis. The rf-response of the arrays was characterized by pulsed inductive microwave magnetometry and directly compared to the properties of un-patterned films. The corresponding magnetic domain structure was analyzed by quasi-static and picosecond time-resolved wide-field Kerr microscopy in the longitudinal mode.

The influence of domain wall density on the magnetization dynamics of amorphous CoZrTa thin-film elements was investigated by a combination of microwave magnetometry and quasistatic plus time-resolved wide-field Kerr microscopy. In addition to domain wall motion, permeability rolloff at low frequencies occurs due to rotational processes. The dominating ferromagnetic resonance modes depend on the domain wall density due to the formation of a zone of magnetization curling at the domain walls, which results from a phase lag of domain and domain wall response. Both the amount of permeability reduction and the increase in precessional frequency, can be varied with magnetic history. All effects are avoided by lamination of the ferromagnetic films. The results demonstrate the importance of detailed domain control for the optimization of patterned films for high-frequency applications, beyond the elementary adjustment of material’s high-frequency properties.

We describe a novel microfluidic perfusion system for high-resolution microscopes. Its modular design allows pre-coating of the coverslip surface with reagents, biomolecules, or cells. A poly(dimethylsiloxane) (PDMS) layer is cast in a special molding station, using masters made by photolithography and dry etching of silicon or by photoresist patterning on glass or silicon. This channel system can be reused while the coverslip is exchanged between experiments. As normal fluidic connectors are used, the link to external, computer-programmable syringe pumps is standardized and various fluidic channel networks can be used in the same setup. The system can house hydrogel microvalves and microelectrodes close to the imaging area to control the influx of reaction partners. We present a range of applications, including single-molecule analysis by fluorescence correlation spectroscopy (FCS), manipulation of single molecules for nanostructuring by hydrodynamic flow fields or the action of motor proteins, generation of concentration gradients, trapping and stretching of live cells using optical fibers precisely mounted in the PDMS layer, and the integration of microelectrodes for actuation and sensing.