26 research outputs found
Role of substrate on interaction of water molecules with graphene oxide and reduced graphene oxide
No full textWe study local electronic properties of graphene oxide (GO) and reduced graphene oxide (RGO) on metallic (Pt) and insulating (Si3N4) substrates in controlled humidity environment. We demonstrate that the supporting substrate plays a crucial role in interaction of these materials with water, with Pt making both GO and RGO insensitive to humidity variations and change in environment. On the other hand, in the case of Si3N4substrate a significant difference between GO and RGO with respect to humidity variations is demonstrated, indicating complete water coverage at â1⁄460% R.H for RGO and â1⁄430% R.H. for GO. Irrespective of the substrate, both GO and RGO demonstrate relative independence of their electronic properties on the material thickness, with similar trends observed for 1 and 2 layers when subject to humidity variations. This indicates a relatively minor role of material thickness in GO-based humidity sensors
Influence of Structural Defects on the Electronic Properties of Carbon Nanotubes Examined by Scanning Tunnelling Microscopy
No full textAbstractThe electronic properties of carbon nanotubes are quite often drastically affected by the presence of defects that can develop during nanotube growth, processing or characterization too. Some of these defects such as pentagon-heptagon rings, substitutional impurities, vacancies and dislocations are of topological nature, and can sometimes create on-tube intramolecular junctions, as found by previous scanning tunnelling microscopy studies.Our recent STM experiments reveal for the first time a much more complicated junction structure, a hybrid single-walled carbon nanotube consisting of a distinct coiled structure located between two straight segments, each of different helicity. We characterise the hybrid junction at the atomic level and describe its electronic behaviour that has important implications in the practical design of functional components for nanoelectronic applications.</jats:p
Silicon photonic waveguides for mid- and long-wave infrared region
No full textSilicon photonics is experiencing a dramatic increase in interest due to emerging application areas and several high profile successes in device and technology development (Liu et al Nature 427:615, 2004; Rong et al Nature 433:725, 2005; Almeida et al Nature 431:1081, 2004). Conventional waveguides in silicon photonics are designed for the telecom wavelengths. However, mid- and long-wave infrared regions are interesting for several application areas including sensing, communications, signal processing, missile detection and imaging (Soref et al J Opt A Pure Appl Opt 8:840, 2006). The most popular waveguide platform in silicon photonics is the Silicon-On-Insulator (SOI) structure, in the form of either a strip or a rib waveguide. This material structure, however, is not suitable for longer wavelengths (except in the 2.9-3.6 µm range) due to the absorption spectra of silicon dioxide (Soref et al J Opt A Pure Appl Opt 8:840, 2006). In this paper, we discuss the design and fabrication of two different waveguide structures, the freestanding (Yang et al Appl Phys Lett 90:241109, 2007) and hollow core waveguides (Stankovic et al Proceedings of 51th Conference ETRAN, 2007). The former is suitable for long-wave infrared applications as it has an air cladding, whilst the latter is a candidate for sensing in the mid-wave infrared wavelength region
INTER-LAYER INTERACTION IN DOUBLE-WALLED CARBON NANOTUBES EVIDENCED BY SCANNING TUNNELING MICROSCOPY AND SPECTROSCOPY
No full textScanning Tunneling Microscopy and Spectroscopy have been used in an attempt to elucidate the electronic structure of nanotube systems containing two constituent shells. Evidence for modified electronic structure due to the inter-layer interaction in double-walled carbon nanotubes is provided by the experimental tunneling spectra and the contribution of the inner tube to the local density of states of the "composite" double-walled system is identified in agreement with previous theoretical calculations. An explicit correlation between the chirality of the two constituent tubes, the inter-wall interaction and the overall electronic structure for double-walled carbon nanotubes, is demonstrated by our experiments, showing that the effect the inner tube has on the overall electronic structure of double-walled nanotubes cannot be neglected, and is key to the opto-electronic properties of the system. We postulate that previous analysis of the opto-electronic properties on multiple-walled carbon nanotubes based purely on the outer layer chirality of the tube needs significant modification based on new understanding brought forth with our analysis
Exploring graphene formation on the C-terminated face of SiC by structural, chemical and electrical methods
No full textThe properties of epitaxial graphene on the C-face of SiC are investigated using comprehensive structural, chemical and electrical analyses. By matching similar nanoscale features on the surface potential and Raman spectroscopy maps, individual domains have been assigned to graphene patches of 1-5 monolayers thick, as well as bare SiC substrate. Furthermore, these studies revealed that the growth proceeds in an island-like fashion, consistent with the Volmer-Weber growth mode, illustrating also the presence of nucleation sites for graphene domain growth. Raman spectroscopy data shows evidence of large area crystallites (up to 620 nm) and high quality graphene on the C-face of SiC. A comprehensive chemical analysis of the sample has been provided by X-ray photoelectron spectroscopy investigations, further supporting surface potential mapping observations on the thickness of graphene layers. It is shown that for the growth conditions used in this study, 5 monolayer thick graphene does not form a continuous layer, so such thickness is not sufficient to completely cover the substrate
Registry-Induced Electronic Superstructure in Double-Walled Carbon Nanotubes, Associated with the Interaction between Two Graphene-Like Monolayers
No full textPrior to the implementation of multi-walled carbon nanotubes in microelectronic devices, investigating their electronic structure down to the nanometer scale is necessary. In that prospect, we used scanning tunneling microscopy (STM) to study the detailed atomic scale structure of double-walled carbon nanotubes, each comprising two rolled monolayers of graphene. Atomically resolved STM images usually displayed a motif and periodicity similar to that found in graphite but, on selected regions, atomically resolved motifs with a clearly defined superstructure were observed. This phenomenon has been reported previously but without a suitable explanation. We discuss the origin of this behavior in terms of modified stacking sequences due to the mismatch in registry between the chiral angles of the inner and the outer shells, associated with the interaction between the two carbon monolayers. These phenomena must be taken into account for the realization of lateral interference devices based on carbon nanotubes or graphene layers
Structural, optical and electrostatic properties of single and fewlayers MoS2 : effect of substrate
No full textWe have decoupled the intrinsic electrostatic effects arising in monolayer and few-layer MoS2 from those influenced by the flake-substrate interaction. Using ultrasonic force microscopy nanomechanical mapping, we identify the change from supported to suspended flake regions on a trenched substrate. These regions are correlated with the surface potential as measured by scanning Kelvin probe microscopy. Relative to the supported region, we observe an increase in surface potential contrast due to suppressed charge transfer for the suspended monolayer. Using Raman spectroscopy we observe a red shift of the E12g mode for monolayer MoS2 deposited on Si, consistent with a more strained MoS2 on the Si substrate compared to the Au substrate
Interfacial Energy Level Alignment at Acid Oxidized Carbon Nanotube - Triphenyldiamine Contacts
No full textAbstractWe report an ultraviolet photoelectron spectroscopy study of the energetics at the interface between acid oxidised carbon nanotubes and the archetypical molecular N,N'-diphenyl-N,N'-bis(3-methylphenyl)-1,1'biphenyl-4,4'diamine(TPD). Electrical equilibrium is achieved across both interfaces within the experiment time frame due to the formation of an interfacial dipole layer which abruptly shifts the vacuum level at the interface. To the authors knowledge this is the first reported measurement of the electronic structure of a carbon nanotube / organic semiconductor interface; a system in which the magnitude of the dipole layer formed at the interface upon contact formation is proportional to the difference in work function between the substrate and organic semiconductor overlayer.</jats:p
Exploring graphene formation on the C- terminated face of SiC by structural, chemical and electrical methods Exploring graphene formation on the C-terminated face of SiC by structural, chemical and electrical methods
No full text2 the growth conditions used in this study, 5 monolayer thick graphene does not form a continuous layer, so such thickness is not sufficient to completely cover the substrate
GeTe-filled Carbon Nanotubes for Data Storage Applications
No full textAbstractBy virtue of their unique electronic properties, nanometer-diameter sized single-walled carbon nanotubes represent ideal candidates to function as active parts of nanoelectronic memory storage devices. We show for the first time that GeTe, a phase change material, currently considered to be one of the most promising materials for data-storage applications, can efficiently be encapsulated within single-walled carbon nanontubes of 1.4 nm diameter. Structural investigations on the encapsulated GeTe nanowires have been carried out by high resolution transmission electron microscopy. The electronic interactions between the filling material and the host nanotube have been examined using ultraviolet photoelectron spectroscopy experiments and show that the electronic structure of the encapsulating nanotube and that of the encased filling are not perturbed by the presence of each of the other component.The newly formed hybrids offer potential to operate as active elements in non-volatile electronic memory storage devices.</jats:p
