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The formation mechanisms of relief structure formed in situ on the surface of B4C–SiC ceramics were studied. The hardness difference between B4C and SiC is one of the formation conditions of relief structure. SiC grains are subjected to a preferential wearing owing to their lower hardness as compared to B4C grains, resulting in the difference of wear rates between B4C grains and SiC grains. Clean, no gap grain boundary in the B4C–SiC ceramics, which can make B4C grains and SiC grains bond firmly protecting them from pulling out, is another formation condition of relief structure.

The preparation processes of Co-Cu and Au-Ag electrodeposited films and electroless Au films, using high-density and highly orientated CNTs on a SiC substrate, were investigated. The attachment via electrochemical reduction of PVP to the CNTs/SiC resulted in a hydrophilic CNTs surface the water contact angle reduced from 110° to 70°. After Co-Cu electrodeposition, the D-band shifted to a lower wavenumber, that indicated an increase in the mass number as Co-Cu metals deposited on the CNTS/SiC. However, the morphology of this Co-Cu electrodeposited film was not related to its hydrophilicity. The CNTs worked well as cathode electrodes because of their high conductivity. During the Co-Cu electrodeposition process, high pH and a complex agent were used. This did not affect the nucleation generation rate, however, the diffusion velocity affected the reaction velocity. Meanwhile, the Au-Ag particle sizes formed with a Pt seed layer were smaller than with the CNTs/SiC substrate. The nucleation generation rates were also different since CNTs/SiC conductivity was smaller than that of Pt. The deposition bath constitution was also thought to be connected to the deposition mechanism. Therefore, to obtain small-sized particles, a higher conductivity of CNTs was needed. Lastly, to obtain more precise metal particles, electroless Au deposition was carried out. After oxygen plasma treatment, the oxidized surface and inner CNTs were displaced by deposited Au ions. The deposition of Au, with particle size approximately 5 nm, was confirmed by TEM analysis and EDS mapping. CNTs mixed electrodeposition and electroless deposition of metals were also investigated. It was confirmed that metal nanoparticles enhanced the deposition of well aligned and high-density CNTs/SiC, with a diameter of 5 nm.

We show that boron-doped epitaxial graphene can be successfully grown by thermal decomposition of a boron carbide thin film, which can also be epitaxially grown on a silicon carbide substrate. The interfaces of B

Acceleration of photocarrier relaxation in graphene results in the enhancement of its properties for graphene-based ultrafast optical devices. The acceleration can be achieved by utilizing the relaxation paths outside the graphene to avoid bottlenecks in the graphene for photocarrier relaxation. In this study, we investigate photocarrier relaxation in epitaxial and transferred monolayer graphene on SiC with a buffer layer at room temperature by means of time-resolved photoluminescence spectroscopy. The photoluminescence decay at 0.7 eV in the epitaxial monolayer graphene is faster than that in the transferred monolayer graphene. On the basis of the three-temperature model calculation, it is found that the carrier–phonon interaction with phonons of the buffer layer for the epitaxial monolayer graphene is 3 times stronger than that for the transferred monolayer graphene. This study demonstrates that ultrafast photocarrier relaxation can be achieved in graphene by epitaxial growth.

We report the complete set of dielectric breakdown strength (EBD) for h-BN, that is, ~12 MV/cm for out-of-plane EBD is four times higher than that for in-plane EBD and it is larger than that for diamond. The large anisotropy in dielectric constant (i.e., related with band gap) due to the layered structure causes this anisotropy.

We have performed low-temperature magnetotransport measurements on epitaxial graphene composed of domains of single-layer and bilayer areas simultaneously present on SiC(0 0 0 1). Positive magnetoresistance that tends to saturate at high magnetic fields is observed for longitudinal component , while the Hall resistance exhibits sublinear behaviour. The lineshapes for both and can be accounted for extremely well by the semiclassical magnetotransport model incorporating two types of carriers conducting in parallel. Two sets of mobilities and densities, corresponding to single-layer and bilayer regions, respectively, can be obtained by fitting the experimental traces to the two-carrier model formulae. From the carrier densities, in turn, the ratio of the single-layer to bilayer areas can be deduced, assuming the alignment of the Fermi levels in the two types of areas with differing dispersion relations and Dirac point energies. The ratio of areas thus obtained is consistent with the ratio directly ob...

Because carbon nanotube forest formed by surface decomposition of silicon carbide (CNT forest on SiC) is densely packed and vertically aligned with no entangle parts, it is useful to investigate the electrical properties of dense CNT forest. CNTs atomically bond to SiC substrates, causing good electrical contact for SiC power devices, where the Schottky barrier height is considerably low as ~0.4 eV. CNTs contact with each other in dense CNT forest and contact conductance of CNT/CNT interface can be evaluated as ~108 S cm−2. This value corresponds to the tunneling conductance between electron clouds of adjacent graphene sheets.

The electrical contact properties of silicon carbide (SiC) and carbon nanotubes (CNTs) were measured by conductive atomic force microscopy (C-AFM). A CNT forest was synthesized by SiC surface decomposition. Trenches, which electrically separate the conduction area, were fabricated using a focused ion beam (FIB) without a cover layer, and the resistance of each island was measured by C-AFM. From the dependence of the resistance on the CNT forest island size, the contact resistance between the CNTs and the SiC substrate was measured. By varying the dopant density in the SiC substrate, the Schottky barrier height was evaluated to be ~0.5 eV. This is slightly higher than a previously reported result obtained from a similar setup with a metal covering the CNT forest. We assumed that the damaged region existed in the islands, which is due to the trench formation by the FIB. The commensurate barrier height was obtained with the length of the damaged region assumed to be ~3 μm. Here, we could estimate the resistivity of a CNT/SiC interface without a cover layer. This indicates that a CNT forest on SiC is useful as a brief contact electrode.

We report the thermoelectric properties of Nb-doped (Nd0.55Li0.36)TiO3 bulk ceramics prepared by the conventional sintering method. Superlattice structure present throughout the crystalline grain was observed and a glass-like thermal conductivity (∼2 W/m·K) was obtained. The electrical properties of (Nd0.55Li0.36)TiO3 were improved due to the Ti-site-Nb-doping. The low solid solubility of Nb and the distortion of TiO6 octahedron impaired the electrical performance of Nb-doped (Nd0.55Li0.36)TiO3. The sample with 5 at%Nb gave the maximum ZT value of 0.05 at 650 K. This work is helpful for the design of novel oxide thermoelectric materials.

Understanding of the contact conductivity of carbon nanotubes (CNTs) will contribute to the further application of CNTs for electronic devices, such as thin film transistors whose channel or electrode is made of dispersed CNTs. In this study, we estimated the contact conductivity of a CNT/CNT interface from the in-plane conductivity of an uncapped CNT forest on SiC. Investigation of the electrical properties of dense CNT forests is also important to enable their electrical application. The in-plane conductivity of a dense CNT forest on silicon carbide normalized by its thickness was measured to be 50 S/cm, which is two to three orders of magnitude lower than the conductivity of a CNT yarn. It was also found that both the CNT cap region and the CNT bulk region exhibit in-plane conductivity. The contact conductivity of CNTs was estimated from the in-plane conductivity in the bulk region. Dense and uncapped CNT forest can be approximated by a conductive mesh, in which each conductive branch corresponds to th...

We report the first in situ synthesis of copper nanoparticles (CuNPs) within the interlayer space of inorganic layered semiconductors (titania nanosheet films) through the following steps. A sintered titania nanosheet (s-TNS) film was synthesised, forming a transparent, layered semiconductor film (∼2 μm thick). A considerable amount of copper ions (ca. 68% relative to the cation exchange capacity of TNSs) was intercalated in the s-TNSs using the methyl viologen-containing s-TNSs as the intermediate. The resultant copper-containing s-TNS (TNS/Cu2+) film was treated with an aqueous solution of NaBH4, resulting in a colour change. Extinction spectra of NaBH4-treated films exhibited a wide extinction band at λmax (the extinction band maximum) = 683 nm. The spectral shapes and λmax were similar to those for copper nanoparticles on TiO2 surfaces. Transmission electron microscopy analysis demonstrated the wide distribution of electron dense particles on the titania sheet of NaBH4-treated TNS/Cu2+. XRD analysis and absorption/extinction analysis with different amounts of TNSs suggest that CuNPs were formed within the interlayer space rather than the surface of TNSs through NaBH4 treatment. Repeatable oxidation and reduction behaviour, i.e. colouration and decolouration cycles of the copper species within TNS films, was investigated.

A systematic structural study of epitaxial graphene samples on the SiC (0001) surface has been performed by the surface x-ray diffraction method, which is a non-contact technique. For samples with only a buffer layer, one layer graphene, and multilayer graphene, the distances between the buffer layer and the surface Si atoms were found to be 2.3 A. This value is the same as reported values. For quasi-free-standing graphene samples prepared by the rapid cooling method [Bao et al., Phys. Rev. Lett. 117, 205501 (2016)], there was no buffer layer and the distance between the quasi-free-standing graphene and the surface Si atoms was 3.5 A, which is significantly shorter than the value in hydrogen-intercalated graphene and slightly longer than the interplane distance in graphite. The Si occupancy deviated from unity within 1 nm of the SiC surface. The depth profile of the Si occupancy showed little sample dependence, and it was reproduced by a simple atomistic model based on random hopping of Si atoms.

We show that boron-doped epitaxial graphene can be successfully grown by thermal decomposition of a boron carbide thin film, which can also be epitaxially grown on a silicon carbide substrate. The interfaces of B4C on SiC and graphene on B4C had a fixed orientation relation, having a local stable structure with no dangling bonds. The first carbon layer on B4C acts as a buffer layer, and the overlaying carbon layers are graphene. Graphene on B4C was highly boron doped, and the hole concentration could be controlled over a wide range of 2 × 1013 to 2 × 1015 cm-2. Highly boron-doped graphene exhibited a spin-glass behavior, which suggests the presence of local antiferromagnetic ordering in the spin-frustration system. Thermal decomposition of carbides holds the promise of being a technique to obtain a new class of wafer-scale functional epitaxial graphene for various applications.

Because of unique plasmonic features, nanostructured graphene such as graphene nanoribbons (GNRs) and quantum dots (GQDs) is attracting much interests. In this work, we investigated real-space characterization of surface plasmon polariton (SPP) in GQDs on SiC substrate by utilizing a scattering-type scanning near-field optical microscope (s-SNOM) in the mid-infrared (MIR) band. Nanoscale near-field images revealed that the SPP in the GQDs was excited at the wavenumber of 929.02 cm−1, where the SPP in two-dimensional (2D) graphene has not been reported. The present findings provide not only a deeper understanding of the SPP in graphene nanostructures, but also a first step for exploring new plasmonic functionalities impossible with conventional 2D graphene.

The synthesis of silver nanoparticles (AgNPs) within the interlayer space of transparent layered titania nanosheet (TNS) films is investigated. A considerable number of silver ions (≈70% against the cation exchange capacity of the TNS) are intercalated in the TNS films using methyl‐viologen‐containing TNSs as a precursor. The silver ion (Ag+)‐containing TNS films are treated with aqueous sodium tetrahydroborate (NaBH4), resulting in a gradual color change to bright blue. Various structural analyses clearly show that crystalline AgNPs are generated within the interlayer space of the TNSs. The NaBH4‐treated films show intense and characteristic near‐infrared (NIR) extinction spectra up to 1800 nm. The stability of the AgNPs within the TNS against oxygen and moisture is also investigated, and 96% and 82% of the AgNPs remain after standing in air for 1 month and 1 year, respectively. The NIR extinctions of the AgNP‐containing TNS films are further extended by employing different preparation procedures, for example, using sintered TNS films as starting materials and irradiating the Ag+‐containing TNSs with ultraviolet (UV) light. The obtained AgNP‐containing TNS films exhibit photochemical activities in the production of hydrogen from ammonia borane under visible‐light irradiation and the decomposition of nitrogen monoxide under UV‐light irradiation.

The well-known layer-by-layer (LbL) method can be used to prepare solid thin films with a controlled electron transfer direction by appropriately stacking metal oxide nanosheets and functional organic ions. In this study, we prepared thin solid films consisting of cobalt oxide nanosheets (CoNSs) as the electron transfer medium, α,β,γ,δ-tetrakis(1-methylpyridinium-4-yl)porphyrin (TMPyP) as the electron donor, and 1,1'-dimethyl-4,4'-bipyridinium or methyl viologen (MV) as the electron acceptor. We investigated the photoinduced electron transfer phenomenon in these films by irradiating them with 450 nm light. Irradiating the LbL thin solid films prepared with the CoNS/TMPyP/CoNS/MV/CoNS sequence under reduced pressure led to the production of a one-electron reduction compound of MV. Hence, photoinduced electron transfer from TMPyP to MV bound to CoNSs occurred in these LbL thin solid films. However, the conduction band of CoNSs, as determined by the photoabsorption spectral and photoelectrochemical measurements, was much higher than the lowest unoccupied molecular orbital level of TMPyP. Our findings indicate that the observed equipotential photoinduced electron transfer was caused by the metallic electron conductivity of CoNSs, which show a unique charge arrangement of Co3+ and Co4+. Moreover, it was also found that the observed photoinduced charge separation state has a longer life-time (>5 h) under the reduced conditions.

The feasibility of using vertically aligned carbon nanotubes (CNTs) on a burnishing slider in the cleaning process of a magnetic disk surface was studied. Vertically aligned CNTs on SiC flat sliders were grown by the SiC surface decomposition method. Burnishing sliders with different CNT lengths were prepared for friction measurement on magnetic disks and for the burnishing test. Non-lubricated vertically aligned CNTs sliding on non-lubricated magnetic disks resulted in large friction; however, coating the CNTs and the disks with a perfluoropolyether lubricant film dramatically decreased the friction force. In addition, it was found that a specific amount of lubricant was needed on the CNTs to decrease the friction force and that the friction force depended on the CNT length. The particle burnishing test indicated that the 34-nm-long CNT burnishing slider with a rinsed lubricant film showed good burnishing performance.

We have performed density-functional tight-binding simulations mimicking the thermal decomposition of the SiC ( 0 0 0 1 ¯ ) surface to reproduce the experimentally observed growth of either graphene or carbon nanotubes. A graphene-like network was obtained from a layer-by-layer decomposition of the SiC surface. The interaction between graphene and SiC was found to be relatively weak. Meanwhile, carbon nanotubes grew when a five-membered ring was initially formed together with a carbon chain. The simulation results suggest that growth selectivity depends on the overall carbon network connectivity and carbon aggregation speed at the very initial stage of the decomposition process.

Longitudinal strains in epitaxial monolayer graphene (EMG) grown on SiC substrates were evaluated by z-polarization Raman microscopy. Due to the covalent bonds formed at the interface between graphene and the substrate, strong compressive strains were loaded on the EMG, which were sensitively detected by Raman spectroscopy. Our polarization Raman microscope was specially designed for evaluating the longitudinal (z-polarization) strain, as well as the lateral (xy-polarization). Z-polarization Raman microscopy revealed the relationship between the fluctuation of the local strains and the sample morphology in the SiC-graphene through submicron spatial resolution mapping. The amount of strain estimated through Raman shift and its spatial inhomogeneity have critical influence on the mobility of electrons, which are essential for future device applications of EMG.

The misfit layer compounds (BiS)1.2(TiS2)2, with a natural superlattice structures, are of substantial interest as thermoelectric materials. In this work we doped the Ti sites of (BiS)1.2(TiS2)2 with a series of transition metal (TM) elements (V, Cr, Mn, Fe, Co, Ni, Cu, and Zn), to optimize its transport properties and thermoelectric performance. X-ray diffraction confirmed all the resulting compositions were single-phase. X-ray photoelectron spectroscopy revealed the valence states of the doping elements, indicating they behave as acceptors and reduce the carrier concentration; this was also apparent from Hall measurements. However, because of the non-parabolic band structure of (BiS)1.2(TiS2)2, reduction of carrier concentration by doping with most of the TM elements did not improve the Seebeck coefficient. Exceptions were V and Cr. For these elements, the effective mass of electrons was maintained, or even enhanced, resulting in improvement of the Seebeck coefficient. Furthermore, the stacking disorder present in undoped (BiS)1.2(TiS2)2 was not observed for the TM element-doped samples, resulting in increased lattice thermal conductivity. Although the power factor of these materials was not optimized, because of the large reduction in electronic thermal conductivity upon doping, the Cr-doped sample had a higher figure of merit than the undoped material.

In order to achieve waste heat recovery using thermoelectric systems, thermoelectric materials showing high conversion efficiency over wide temperature range and high resistance against oxidation are indispensable. A silicide material with good n-type thermoelectric properties and oxidation resistance has been discovered. The composition and crystal structure of the silicide are found out Mn3Si4Al2 (abbreviated as 342 phase) and hexagonal CrSi2 structure, respectively. Element substitution of Mn with 3d transition metals is succeeded. Enhancement of Seebeck coefficient is observed in a Cr-substituted sample. The maximum dimensionless thermoelectric figure of merit ZT is 0.3 at 573 K in air for the Mn2.7Cr0.3Si4Al2 sample. Electrical resistivity of the Mn3Si4Al2 bulk sample holds constant value for 48 h at 873 K in air. This is due to formation of oxide passive layer on the surface of the bulk sample. The 342 phase is a promising n-type material with a good oxidation resistance in the middle temperature range of 500-800 K.

The substitutional doping of magnesium into the host layers (TiS2), calcium and strontium into phonon barrier layers (BiS) was attempted to improve the thermoelectric performance of (BiS)1.2(TiS2)2 misfit layer sulfides by decreasing the carrier concentration. The substitutional doping did reduce the carrier concentration; however, the Seebeck coefficient decreased slightly due to the decrease in the effective mass of carrier electrons. Meanwhile, the lattice thermal conductivity was increased by the formation of an ordered or commensurate structure.

In this study, layered double hydroxide (LDH) consisting of Mg(II) and Fe(III) (Mg/Fe-LDH) was synthesized by using a combination of coprecipitation with hydrothermal aging, and its anion-exchange properties were investigated. Through various analyses, the chemical formula of the proposed Mg/Fe-LDH was determined to be [Mg(0.76)Fe(0.24)(OH)(2)](Cl(-))(0.21)(CO(3)(2-))(0.02)·0.76H(2)O. Furthermore, amorphous Fe(III) impurities were contained in the present Mg/Fe-LDH. The proposed Mg/Fe-LDH exhibited clear selectivity for nitrate ions dissolved in water. This selectivity for nitrate ions can be explained by an anion-sieve effect by the existence of amorphous Fe(III) impurities. Our findings suggest that it is possible to synthesize LDHs with high selectivity for various anions by effective hybridizing Fe(III) impurities.

A natural superlattice with composition (SnS)1.2(TiS2)2, built by intercalating a SnS layer into the van der Waals gap of layered TiS2, has been directly observed by high-resolution transmission electron microscopy (HRTEM). The thermoelectric performance is improved in the direction parallel to the layers because the electron mobility is maintained while simultaneously suppressing phonon transport, which is attributed to softening of the transverse sound velocities due to weakened interlayer bonding. In the direction perpendicular to the layers, the lattice thermal conductivity of (SnS)1.2(TiS2)2 is even lower than the predicted minimum thermal conductivity, which may be caused by phonon localization due to the translational disorder of the SnS layers parallel to the layers. Moreover, we propose a large family of misfit-layer compounds (MX)1+x(TX2)n (M = Pb, Bi, Sn, Sb, rare-earth elements; T = Ti, V, Cr, Nb, Ta; X = S, Se; n = 1, 2, 3) with a natural superlattice structure as possible candidate high-performance thermoelectric materials.

The carbon nanotubes (CNTs) on 6H-SiC and Si-doped CNTs on 6H-SiC were analyzed by hard x-ray photoelectron spectroscopy to identify the chemical bonding character of the doped Si in the CNT layer. We performed the depth profiling of the sample by changing photoelectron's take-off-angle (TOA). The spectral component associated with the doped Si is clearly seen in the Si 1s photoelectron spectra of Si-doped CNTs on 6H-SiC. The Si 1s peak shifts toward lower kinetic energy side from TOA = 80° (bulk-sensitive) to 8° (surface-sensitive), which implies the formation of the sp2-like structure in Si-doped CNTs. [DOI: 10.1380/ejssnt.2011.54]

Understanding the electrical contact properties of carbon nanotube (CNT) ends is important to use the high conductance of CNTs in the CNT on-axis direction in applications such as through-silicon via structures. In this study, we experimentally evaluated the contact resistivity between single-/multi-walled CNT ends and a metal nanoprobe using conductive atomic force microscopy (C-AFM). To validate the measured end contact resistivity, we compared our experimentally determined value with that obtained from numerical calculations and reported values for side contact resistivity. The contact resistivity normalized by the length of the CNT ends was 0.6–2.4 × 106 Ω nm for single-walled CNTs. This range is 1–2 orders of magnitude higher than that determined theoretically. The contact resistivity of a single-walled CNT end with metal normalized by the contact area was 2–3 orders of magnitude lower than that reported for the resistivity of a CNT sidewall/metal contact. For multi-walled CNTs, the measured contact resistivity was one order of magnitude higher than that of a CNT forest grown by remote plasma-enhanced chemical vapor deposition, whereas the contact resistivity of a top metal electrode was similar to that obtained for a single-walled CNT forest.

High-resolution transmission electron microscopic cross-sectional observations of graphene-on-SiC(0001) were carried out to directly observe the interface structure. A first principles calculation allowed us to understand the interface structures and their electronic states. Our observations revealed a metastable transitional interface structure formed by decomposition of a single SiC bilayer as well as complete honeycomb graphene formed by the decomposition of three SiC bilayers. The calculations further showed that the differences in the interface structures should strongly influence the electronic states, producing either metallic or semiconducting behavior. These results may help to resolve the controversy over the electronic states of graphene-on-SiC, and promote more accurate band-gap engineering via surface decomposition.

We have measured low-temperature ac impedance of films of closely-packed, highly-aligned carbon nanotubes prepared by thermal decomposition of silicon carbide wafers. The measurement was performed on films with the thickness (the length of the nanotubes) ranging from 6.5 to 65 nm. We found that the impedance rapidly decreases with the frequency. This can be interpreted as resulting from the electric transport via capacitive coupling between adjacent nanotubes. We also found numbers of sharp spikes superposed on frequency vs. impedance curves, which presumably represent resonant frequencies seen in the calculated conductivity of random capacitance networks. Capacitive coupling between the nanotubes was reduced by the magnetic field perpendicular to the films at 8.2 mK, resulting in the transition from negative to positive magnetoresistance with an increase of the frequency.

Graphene is a single-layer carbon sheet with a honeycomb structure, and bilayer graphene consists of two graphene sheets with AB stacking. In trilayer graphene, the third graphene sheet has two possible stacking sequences, A or C, when it is overlaid on bilayer graphene. It has been theoretically predicted that trilayer graphene exhibits a variety of novel electronic properties with/without a Dirac-cone band, depending on the stacking sequence. In this regard, trilayer graphene has a high potential for widening the capability of graphene-based electronic devices. However, the difficulty of selective fabrication has hindered the progress of research. Here, we report the first success in the selective fabrication of quasi-free-standing trilayer graphene with ABA or ABC stacking grown epitaxially on hydrogen-terminated silicon carbide. Angle-resolved photoemission spectroscopy (ARPES) clearly demonstrated that our trilayer graphene with ABA stacking has a massless Dirac-like band near the Fermi level, while that with ABC stacking shows a parabolic non-Dirac-like band dispersion. Strict control of temperature and pressure during annealing is shown to be crucial for controllably stacking graphene by a team in Japan. Graphene is a single layer of carbon atoms in a hexagonal arrangement. When two graphene layers are stacked, some carbon atoms in the top layer sit above the center of each hexagon of the lower layer. A third layer either sits directly aligned with the bottom layer (ABA stacking) or is again displaced from the previous two (ABC stacking). These two arrangements exhibit very different properties. Takashi Takahashi from Tohoku University and colleagues deterministically created either ABA or ABC trilayer graphene by first annealing bilayer graphene on a hydrogen-terminated silicon carbide substrate. They found that the alignment of the third layer is determined by the temperature and pressure of this anneal. Quasi-free-standing trilayer graphene with ABA or ABC stacking was selectively synthesized on hydrogen-terminated silicon carbide. The electronic structure was investigated by angle-resolved photoemission spectroscopy. While ABA graphene exhibits a massless Dirac-cone-like band at the K point in the Brillouin zone, ABC graphene was found to show a parabolic non-Dirac-like band. The present success in selective fabrication of ABA and ABC graphene would open a pathway toward graphene-based nano electronic devices with variable layer number and stacking sequence such as high-speed transistor and photodetector.

We have investigated the length-dependence of the in-plane electrical resistivity of vertically aligned and highly dense carbon nanotube (CNT) films that were dense enough to conduct electrons. The in-plane conductivity is well accounted for by a combination of inter-tube hopping (variable range hopping, VRH) and graphitic conduction. VRH conduction was dominant in the thinner CNT films, and the films showed negative temperature dependence of resistivity. The dimension of the VRH component varied depending on the CNT length. In the thicker CNT films, the graphitic conduction appeared, and then, the localization length spread, leading to the positive temperature dependence of resistivity. This behavior can be explained by the presence of a labyrinthine arrangement of graphene walls among aligned CNTs, which was confirmed by transmission electron microscopy observations.

Direct cross-sectional observations of graphene-on-SiC (0 0 0 1) by high-resolution transmission electron microscopy have revealed the presence of a metastable transitional structure formed by decomposition of a single SiC bilayer as well as fully-packed honeycomb graphene as an interface structure between graphene and SiC. A first principles calculation studied in parallel has clarified that the metastable transitional state exhibits the metallic behavior, while the fully-packed honeycomb graphene exhibits the semiconducting behavior.

To encourage the recycling of spent SiC abrasive powders, we investigated the synthesis of CNTs from several types of powders. The surface decomposition method was applied to as-received powders, and graphite was observed on the SiC surface but CNTs were not. This could be caused by the turbulence of the crystal structure and Fe contaminants on the SiC surface. On the other hand, from TEM observations we found that particle covered of CNTs could be synthesized by applying the surface decomposition method to powders pretreated by acid and heat, because the turbulence of the crystal structure on the surface could be improved and Fe contaminants could be removed. Consequently, the spent SiC abrasive powders pretreated by acid and heat could be used as a resource for synthesizing CNT particles.

Atomic-scale structure of the interface between graphene and SiC(0001) has been investigated using high-resolution transmission electron microscope observation. Our analysis revealed the presence of two types of the interface structure ; one is formed by decomposition of three SiC bilayers, and the other is formed by that of one SiC bilayer. Formation process of graphene layers on SiC is also described.

The electronic system in the layered perovskite Sr2−xNdxMnO4 is characterized as a two-dimensional eg-electron system. In order to understand the stability of electronic states in the Nd-content region of 0 ⩽ x ⩽ 0.50, the crystallographic features of this manganite have been investigated by transmission electron microscopy. The increase in the Nd-content led to the orbital ordered state in 0.10 ⩽ x ⩽ 0.25 and the charge and orbital ordered state in 0.25 ⩽ x 0.35.

We report on a nitride interface structure formed between epitaxial graphene and SiC (0001). The nitride interface can be obtained by the pretreatment of SiC in an $\mathrm{Ar}/{\mathrm{N}}_{2}$ atmosphere at 1600 \ifmmode^\circ\else\textdegree\fi{}C, followed by graphene growth in Ar at 1700 \ifmmode^\circ\else\textdegree\fi{}C. Our detailed high-resolution transmission electron microscopy revealed a nitride atomic layer between the 0th carbon layer and the SiC substrate. Due to the nitride interface, the interface carrier scattering was reduced, which resulted in an improvement of the room temperature mobility of graphene, indicating that this is another technique to modify the electronic properties of graphene.