If graphene is a promising material in many respects, its remarkable properties may be impaired by unavoidable defects. Chemical vapor deposition-grown graphene samples are polycrystalline in nature, with many grain boundaries. Those extended defects influence the global electronic structure and the transport properties of graphene in a way that remains to be clarified. As a step forward in this direction, we have undertaken quantum mechanical calculations of electron wave-packet dynamics in a multigrain self-supported graphene layer. Our computer simulations show that a grain boundary may act as a reflector at some energies and for some incidences of the Bloch waves. In addition, our calculations reveal that when two grain boundaries run parallel to each other, the graphene ribbon confined between them may behave like a channel for the charge carriers. We emphasize therefore the possibility of creating nanoscale electronic waveguides and nanowires on the graphene surface by a controlled engineering of its grain boundaries.
Photonic band gap material type nanoarchitectures occurring in the wing scales of butterflies possessing structural color
were investigated as selective gas/vapor sensors. From 20 examined butterfly species all showed selective sensing when
various volatile organic compounds were introduced as additives in ambient air. Four butterflies species: <i>Chrysiridia
ripheus</i> (Geometridae), <i>Pseudolycena marsyas, Cyanophrys remus </i>(both Lycaenidae) and <i>Morpho aega </i>(Nymphalidae)
were selected to demonstrate the possibilities of selective sensing offered by these natural nanoarchitectures. Each
butterfly species gives characteristic response both for species, i.e., for its typical nanoarchitecture, and for the seven
test vapors used. Fast response time, reproducible and concentration dependent signals are demonstrated.
Individual, unsupported scales of two male butterflies with dorsal blue and ventral green color were compared by
microscpectrometric measurements, optical and electronic microscopy. All the scales are colored by photonic band gap
type materials built of chitin (n = 1.58) and air. The different scales are characterized by different degrees of order from
fully ordered single crystalline blue scales of the <i>Cyanophrys remus</i> butterfly through polycrystalline green scales on the
ventral side of the same butterfly, to the most disordered dorsal blue scales of the <i>Albulina metallica</i>, where only the
distance of the first neighbors is constant. The different scale nanoarchitectures and their properties are compared.
Periodicity implies the creation of discretely diffracted beams while various departures from periodicity lead to broadened scattering angles. This effect is investigated for disturbed lattices exhibiting randomly varying periods. In the Born approximation, the diffused reflection is shown to be related to a pair correlation function constructed from the distribution of the
film scattering power. The technique is first applied to a natural photonic crystal found on the ventral side of the wings of the butterfly <i>Cyanophrys remus</i>, where scanning electron microscopy reveals the formation of polycrystalline photonic structures. Second, the disorder in the distribution of the cross-ribs on the scales another butterfly, <i>Lycaena virgaureae</i>, is investigated. The irregular arrangement of scatterers found in chitin structure of this insect produces light reflection in the long-wavelength part of the visible range, with a quite unusual broad directionality. The use of the pair correlation function allows to propose estimates of the diffusive spreading in these very different systems.
A quite wide brunch of the carbon nanotube science, including the utilization of singlewall nanotube for production of nano-electronic devices has being continuously explored even nowadays. Tuning and modifying the synthesis procedures to obtain nanotube junctions of T, Y, H or X shapes lead to inappropriate results concerning the industrial or large scale production. However, the importance and the demand for these junctions are quite large, since these may be the secondary building units of carbon nanotubes based chips or even more complex nanoelectronic devices. Recently, some novel solutions of their preparation have been published. A Taiwanese group described a method to prepare multi-junctioned carbon nanotubes on mechanically pretreated silicon surface applying chemical vapor deposition (CVD) technology using decomposition of methane at 1373 K. The nanotubes were nucleated following the lines prepared by scratching the surface with 600-grit sand paper. Contrary to the physical pretreatment of a substrate surface, chemical reactions can also be used for the preparation of carbon nanotube junctions. P.W. Chu et al. reported interconnecting reactions between functionalized carbon nanotubes . By the described method, the carboxyl groups on the wall of singlewall carbon nanotubes are converted to carbonyl chloride groups by reaction with SOCl2 at room temperature. The formed COCl groups are very reactive on the outer surface and can be reacted easily with various amines, particularly diamines resulting in the formation of amide bonding. When two functionalized carbon nanotubes react with such an amine molecule interconnection of tubes is generated. The resulted carbon nanotube junctions have been investigated by AFM.
In this presentation, we report on the results obtained on the preparation of carbon nanotube junctions applying two different procedures. The first method is similar to Chu’s one, which was mentioned above, i.e. we used functionalized multiwall carbon nanotubes and the successful interconnection of them by propylene diamine has been proven by TEM and AFM. The second method demonstrates a novel principle: catalyst material has been deposited on the outer surface of carbon nanotubes and branches of nanotubes were produced at this contact point by catalytic chemical vapor deposition (CCVD) of acetylene. The product has been characterized by TEM.
Regularly coiled carbon nanotubes, their structure and formation mechanism are puzzling questions since many years. The first models were based on the very regular incorporation of a small fraction (of the order of 10%) of non-hexagonal (n-Hx) rings: (pentagons and heptagons) in a perfect hexagonal (Hx) lattice. It is difficult to understand by which mechanism takes place such a regular incorporation of isolated n-Hx rings. In the present work a new family of Haeckelite nanotubes is generated in a systematic way by rolling up a two-dimensional three-fold coordinated carbon network composed of pentagon-heptagon pairs and hexagons in proportion 2:3. In this model the n-Hx rings are treated like regular building blocks of the structure. Cohesion energy calculation shows that the stability of the generated 3D Haeckelite structures falls between that of straight carbon nanotubes and that of C<sub>60</sub>. Electronic density of states of the Haeckelite computed with a tight-binding Hamiltonian that includes the C-μ orbitals only shows that the structures are semiconductor. The relation of the structures with experimental observations is discussed.
The functionalization of carbon nanotubes (CNTs) is important both for composite - to improve load transfer between CNTs and matrix - and nanoelectronic applications - to interlink individual nanotubes in a network. Oposite to earlier results, complete coverage of CNT surface with functional groups was achieved. The distribution of functional groups on the nanotube surface was investigated using STM and TEM. The influence of functional groups on the electron density of states of the nanotubes was studied with scanning tunneling spectroscopy (STS).
We performed scanning tunneling microscopy (STM) measurements on few wall carbon nanotubes that exhibited changing diameter. Such change in the diameter may occur if non-hexagonal carbon ring configurations are introduced in the nanotube walls. A few-walled nanotube knee of 4 degrees, with different diameter values on the two sides of the knee was imaged by STM. Theoretical model structures  of single-wall carbon nanotubes show that a bend of 4 degrees may occur when a pentagonal and a heptagonal carbon ring is incorporated side by side in the hexagonal nanotube structure. Scanning tunneling spectroscopic (STS) measurements show that additional electronic states are present in the energy gap in the region where the bend occurs. We also performed STS measurements on a single-wall nanotube with conical tip. In agreement with theory, the results show that the energy gap in the tapered end is larger than in the nanotube.