Toshihiko Fujimori

Raman spectroscopy of boron-doped single-layer graphene

The introduction of foreign atoms, such as nitrogen, into the hexagonal network of an sp(2)-hybridized carbon atom monolayer has been demonstrated and constitutes an effective tool for tailoring the intrinsic properties of graphene. Here, we report that boron atoms can be efficiently substituted for carbon in graphene. Single-layer graphene substitutionally doped with boron was prepared by the mechanical exfoliation of boron-doped graphite. X-ray photoelectron spectroscopy demonstrated that the amount of substitutional boron in graphite was ~0.22 atom %. Raman spectroscopy demonstrated that the boron atoms were spaced 4.76 nm apart in single-layer graphene. The 7-fold higher intensity of the D-band when compared to the G-band was explained by the elastically scattered photoexcited electrons by boron atoms before emitting a phonon. The frequency of the G-band in single-layer substitutionally boron-doped graphene was unchanged, which could be explained by the p-type boron doping (stiffening) counteracting the tensile strain effect of the larger carbon-boron bond length (softening). Boron-doped graphene appears to be a useful tool for engineering the physical and chemical properties of graphene.

Conducting linear chains of sulphur inside carbon nanotubes

Despite extensive research for more than 200 years, the experimental isolation of monatomic sulphur chains, which are believed to exhibit a conducting character, has eluded scientists. Here we report the synthesis of a previously unobserved composite material of elemental sulphur, consisting of monatomic chains stabilized in the constraining volume of a carbon nanotube. This one-dimensional phase is confirmed by high-resolution transmission electron microscopy and synchrotron X-ray diffraction. Interestingly, these one-dimensional sulphur chains exhibit long domain sizes of up to 160 nm and high thermal stability (~800 K). Synchrotron X-ray diffraction shows a sharp structural transition of the one-dimensional sulphur occurring at ~450–650 K. Our observations, and corresponding electronic structure and quantum transport calculations, indicate the conducting character of the one-dimensional sulphur chains under ambient pressure. This is in stark contrast to bulk sulphur that needs ultrahigh pressures exceeding ~90 GPa to become metallic.

Confinement in Carbon Nanospace-Induced Production of KI Nanocrystals of High-Pressure Phase

An outstanding compression function for materials preparation exhibited by nanospaces of single-walled carbon nanohorns (SWCNHs) was studied using the B1-to-B2 solid phase transition of KI crystals at 1.9 GPa. High-resolution transmission electron microscopy and synchrotron X-ray diffraction examinations provided evidence that KI nanocrystals doped in the nanotube spaces of SWCNHs at pressures below 0.1 MPa had the super-high-pressure B2 phase structure, which is induced at pressures above 1.9 GPa in bulk KI crystals. This finding of the supercompression function of the carbon nanotubular spaces can lead to the development of a new compression-free route to precious materials whose syntheses require the application of high pressure.

Effect of a quaternary ammonium salt on propylene carbonate structure in slit-shape carbon nanopores.

The effect of addition of tetraethylammonium tetrafluoroborate (Et(4)NBF(4)) on the structure of propylene carbonate (PC) confined in slit-shaped carbon nanopores of activated carbon fiber (pore width = 1.0 nm) was studied by synchrotron X-ray diffraction and reverse Monte Carlo simulation. PC molecules are randomly packed in the slit carbon nanopores of 1 nm in the absence of Et(4)NBF(4). Addition of Et(4)N(+) and BF(4)(-) ions promotes formation of considerably ordered double layers of PC molecules even in the highly restricted slit pore space. PC molecules can accept these ions efficiently. This structural modulation function of PC molecular assemblies should contribute to the evolution of supercapacitance in carbon nanopores.

Accumulation of regulatory T cells in sentinel lymph nodes is a prognostic predictor in patients with node-negative breast cancer.

It has been revealed that sentinel lymph nodes (SLNs) from patients with node-negative breast cancer involve RT-PCR detected micrometastases and isolated tumour cells. However, the prognostic significance of the pathologically undetectable micrometastases is still controversial. In this study, we evaluated Foxp3 positive regulatory T cells (Treg) in SLNs as host-side immune marker that has the potential to detect these micrometastases. In the analyses of training set (n=30), elevated Treg was strongly associated with the pathologically undetectable micrometastases. In the analyses of validation set (n=129) in patients with node-negative, relapse-free survival in patients with elevated Treg was significantly shorter than those with lower Treg (p=0.005). Furthermore, in multivariate analyses, elevated Treg was correlated with relapse-free survival (p=0.012). Our data indicate that Treg may increase in the microenvironment of SLNs along with pathologically undetectable micrometastases and is a prognostic predictor in patients with node-negative breast cancer.

Dynamic Quantum Molecular Sieving Separation of D2 from H2–D2 Mixture with Nanoporous Materials

Quantum molecular sieving separability of D(2) from an H(2)-D(2) mixture was measured at 77 K for activated carbon fiber, carbon molecular sieve, zeolite and single wall carbon nanotube using a flow method. The amount of adsorbed D(2) was evidently larger than H(2) for all samples. The maximum adsorption ratio difference between D(2) and H(2) was 40% for zeolite (MS13X), yielding a selectivity for D(2) with respect to H(2) of 3.05.

Evidence of Dynamic Pentagon−Heptagon Pairs in Single-Wall Carbon Nanotubes using Surface-Enhanced Raman Scattering

Surface-enhanced Raman scattering (SERS) was applied to detecting pentagon-heptagon pairs, the so-called Stone-Wales defect, in single-wall carbon nanotubes (SWCNTs). When a probing laser light was scanned over a SWCNT-dispersed silver surface, two distinct SERS spectra were obtained: (1) temporally stable spectra similar to that of resonance Raman spectra of bulk SWCNTs and (2) temporally fluctuating spectra with additional peaks which were not observed in the non-SERS spectra. The fluctuations in the SERS spectra are discussed in association with dynamic reconstruction of defective structures of SWCNTs (nonhexagonal arrangements of carbon atoms) in the vicinity of SERS-active sites under irradiation of the laser light.

Enhanced hydrogen adsorptivity of single-wall carbon nanotube bundles by one-step c60-pillaring method.

Single-wall carbon nanotube (SWCNT) bundles were pillared by fullerene (C60) by the cosonication of C60 and SWCNT in toluene to utilize the interstitial pores for hydrogen storage. C60-pillared SWCNTs were confirmed by the shift in the X-ray diffraction peak and the expanded hexagonal and distorted tetragonal bundles revealed by high-resolution transmission electron microscopy. The H2 adsorptivity of the C60-pillared SWCNT bundles was twice that of the original SWCNT bundles, indicating a design route for SWCNT hydrogen storage.

Anomaly of CH4 Molecular Assembly Confined in Single-Wall Carbon Nanohorn Spaces

Vibrational-rotational properties of CH(4) adsorbed on the nanopores of single-wall carbon nanohorns (SWCNHs) at 105-140 K were investigated using IR spectroscopy. The difference vibrational-rotational bands of the ν(3) and ν(4) modes below 130 K show suppression of the P and R branches, while the Q branches remain. The widths of the Q branches are much narrower than in the bulk gas phase due to suppression of the Doppler effect. These results indicate that the rotation of CH(4) confined in the nanospaces of SWCNHs is highly restricted, resulting in a rigid assembly structure, which is an anomaly in contrast to that in the bulk liquid phase.

Formation and properties of selenium double-helices inside double-wall carbon nanotubes: Experiment and theory

We report the production of covalently bonded selenium double-helices within the narrow cavity inside double-wall carbon nanotubes. The double-helix structure, characterized by high-resolution transmission electron microscopy and X-ray diffraction, is completely different from the bulk atomic arrangement and may be considered a new structural phase of Se. Supporting ab initio calculations indicate that the observed encapsulated Se double-helices are radially compressed and have formed from free Se atoms or short chains contained inside carbon nanotubes. The calculated electronic structure of Se double-helices is very different from the bulk system, indicating the possibility to develop a new branch of Se chemistry.