Hidetsugu Shiozawa

Direct observation of Tomonaga-Luttinger-liquid state in carbon nanotubes at low temperatures.

The electronic transport properties of conventional three-dimensional metals are successfully described by Fermi-liquid theory. But when the dimensionality of such a system is reduced to one, the Fermi-liquid state becomes unstable to Coulomb interactions, and the conduction electrons should instead behave according to Tomonaga–Luttinger-liquid (TLL) theory. Such a state reveals itself through interaction-dependent anomalous exponents in the correlation functions, density of states and momentum distribution of the electrons. Metallic single-walled carbon nanotubes (SWNTs) are considered to be ideal one-dimensional systems for realizing TLL states. Indeed, the results of transport measurements on metal–SWNT and SWNT–SWNT junctions have been attributed to the effects of tunnelling into or between TLLs, although there remains some ambiguity in these interpretations. Direct observations of the electronic states in SWNTs are therefore needed to resolve these uncertainties. Here we report angle-integrated photoemission measurements of SWNTs. Our results reveal an oscillation in the π-electron density of states owing to one-dimensional van Hove singularities, confirming the one-dimensional nature of the valence band. The spectral function and intensities at the Fermi level both exhibit power-law behaviour (with almost identical exponents) in good agreement with theoretical predictions for the TLL state in SWNTs.

Tight-binding description of the quasiparticle dispersion of graphite and few-layer graphene

A.G. acknowledges the Marie Curie Foundation COMTRANS from the European Union. A.R. and C.A. are supported in part by Spanish MEC Grant No. FIS2007-65702-C02-01 , Grupos Consolidados UPV/EHU of the Basque Country Government Grant No. IT-319-07 European Community e-I3 ETSF and SANES Grant No. NMP4- CT-2006-017310 projects. L.W. acknowledges support from the French national research agency Project PJC05_6741 . R.S. acknowledges MEXT Grants Nos. 20241023 and No. 16076201 .

Hybrid Carbon Nanotube Networks as Efficient Hole Extraction Layers for Organic Photovoltaics

Transparent, highly percolated networks of regioregular poly(3-hexylthiophene) (rr-P3HT)-wrapped semiconducting single-walled carbon nanotubes (s-SWNTs) are deposited, and the charge transfer processes of these nanohybrids are studied using spectroscopic and electrical measurements. The data disclose hole doping of s-SWNTs by the polymer, challenging the prevalent electron-doping hypothesis. Through controlled fabrication, high- to low-density nanohybrid networks are achieved, with low-density hybrid carbon nanotube networks tested as hole transport layers (HTLs) for bulk heterojunction (BHJ) organic photovoltaics (OPV). OPVs incorporating these rr-P3HT/s-SWNT networks as the HTL demonstrate the best large area (70 mm(2)) carbon nanotube incorporated organic solar cells to date with a power conversion efficiency of 7.6%. This signifies the strong capability of nanohybrids as an efficient hole extraction layer, and we believe that dense nanohybrid networks have the potential to replace expensive and material scarce inorganic transparent electrodes in large area electronics toward the realization of low-cost flexible electronics.

Fine tuning the charge transfer in carbon nanotubes via the interconversion of encapsulated molecules

Tweaking the properties of carbon nanotubes is a prerequisite for their practical applications. Here we demonstrate fine-tuning the electronic properties of single-wall carbon nanotubes via filling with ferrocene molecules. The evolution of the bonding and charge transfer within the tube is demonstrated via chemical reaction of the ferrocene filler ending up as secondary inner tube. The charge transfer nature is interpreted well within density functional theory. This work gives the first direct observation of a fine-tuned continuous amphoteric doping of single-wall carbon nanotubes.

Confined crystals of the smallest phase-change material.

The demand for high-density memory in tandem with limitations imposed by the minimum feature size of current storage devices has created a need for new materials that can store information in smaller volumes than currently possible. Successfully employed in commercial optical data storage products, phase-change materials, that can reversibly and rapidly change from an amorphous phase to a crystalline phase when subject to heating or cooling have been identified for the development of the next generation electronic memories. There are limitations to the miniaturization of these devices due to current synthesis and theoretical considerations that place a lower limit of 2 nm on the minimum bit size, below which the material does not transform in the structural phase. We show here that by using carbon nanotubes of less than 2 nm diameter as templates phase-change nanowires confined to their smallest conceivable scale are obtained. Contrary to previous experimental evidence and theoretical expectations, the nanowires are found to crystallize at this scale and display amorphous-to-crystalline phase changes, fulfilling an important prerequisite of a memory element. We show evidence for the smallest phase-change material, extending thus the size limit to explore phase-change memory devices at extreme scales.

Catalyst and Chirality Dependent Growth of Carbon Nanotubes Determined Through Nano‐Test Tube Chemistry

[*] Dr. Hidetsugu Shiozawa, Prof. S. Ravi P. Silva Advanced Technology Institute, University of Surrey, Guildford, GU2 7XH (UK) Email: h.shiozawa@surrey.ac.uk; s.silva@surrey.ac.uk Dr. Christian Kramberger, Dr. Rudolf Pfeiffer, Prof. Hans Kuzmany, Prof. Thomas Pichler Faculty of Physics, University of Vienna, Strudlhofgasse 4, 1090 Vienna (Austria) Dr. Zheng Liu, Dr. Kazu Suenaga Research Center for Advanced Carbon Materials, AIST, Tsukuba 305-8565 (Japan) Dr. Hiromichi Kataura Nanotechnology Research Institute, AIST, Tsukuba 305-8562 and JST, CREST (Japan)

Orbital and spin magnetic moments of transforming one-dimensional iron inside metallic and semiconducting carbon nanotubes

The orbital and spin magnetic properties of iron inside metallic and semiconducting carbon nanotubes are studied by means of local x-ray magnetic circular dichroism (XMCD) and bulk superconducting ...

Electronic structure of CeCoIn 5 from angle-resolved photoemission spectroscopy

We have investigated the low-energy electronic structure of the heavy-fermion superconductor

Hybridization effects in CeCoIn(5) observed by angle-resolved photoemission

{\text{CeCoIn}}_{5}

Microscopic insight into the bilateral formation of carbon spirals from a symmetric iron core

by angle-resolved photoemission and band-structure calculations. We measured the Fermi surface and energy distribution maps along the high-symmetry directions at