arXiv subjects

Hiromichi Kataura

Publications and source records attributed to Hiromichi Kataura.

12 recordsLinked to original sources

arXiv2025

Broadband Solar Selective Absorber with Dallenbach-type Bilayer Structure Achieved Using Carbon Nanotube Membranes with Tailored Optical Spectra

Spectrally selective absorbers that maximize solar absorption and minimize thermal radiation loss are crucial for efficient solar thermal energy harvesting. However, limitations imposed by the intrinsic properties of conventional materials hinder the fabrication of interference-based absorbers with desired optical properties. Herein, a high-performance solar absorber with a Dallenbach-type dielectric-metal tandem structure was fabricated using an ultrathin, subquarter-wavelength thickness single-walled carbon nanotube (SWCNT) membrane with tailored optical spectra as the absorbing layer. By mixing multiple SWCNT chiral structures, the optical response of the absorbing layer was tailored to approximate a theoretical complex refractive index spectrum of dielectrics; therefore enabling high solar absorptance, low infrared emittance, and a low angular dependence with a simple bilayer structure. The fabricated proof-of-concept 1 cm$^2$ absorber exhibited excellent spectral selectivity (solar absorptance/infrared emittance of 0.84/0.03), and an equilibrium temperature of $\approx 190^\circ$C ($270^\circ$C) under nonconcentrated ($2\times$ concentrated) sunlight, considerably outperformed a blackbody-like absorber. This study presents a high-performance solar absorber with a simple planar structure and proposes a concept of designing dielectric with the desired optical properties by mixing various types of structure-sorted SWCNTs.

physics.optics↗

arXiv2021

Band Structure Dependent Electronic Localization in Macroscopic Films of Single-Chirality Single-Wall Carbon Nanotubes

Significant understanding has been achieved over the last few decades regarding chirality-dependent properties of single-wall carbon nanotubes (SWCNTs), primarily through single-tube studies. However, macroscopic manifestations of chirality dependence have been limited, especially in electronic transport, despite the fact that such distinct behaviors are needed for many applications of SWCNT-based devices. In addition, developing reliable transport theory is challenging since a description of localization phenomena in an assembly of nanoobjects requires precise knowledge of disorder on multiple spatial scales, particularly if the ensemble is heterogeneous. Here, we report an observation of pronounced chirality-dependent electronic localization in temperature and magnetic field dependent conductivity measurements on macroscopic films of single-chirality SWCNTs. The samples included large-gap semiconducting (6,5) and (10,3) films, narrow-gap semiconducting (7,4) and (8,5) films, and armchair metallic (6,6) films. Experimental data and theoretical calculations revealed Mott variable-range-hopping dominated transport in all samples, while localization lengths fall into three distinct categories depending on their band gaps. Armchair films have the largest localization length. Our detailed analyses on electronic transport properties of single-chirality SWCNT films provide significant new insight into electronic transport in ensembles of nanoobjects, offering foundations for designing and deploying macroscopic SWCNT solid-state devices.

cond-mat.mes-hall↗

arXiv2017

Experimental determination of the local optical conductivity of a semiconducting carbon nanotube and its modification at individual defects

Measurements of optical properties at nanometre-level are of central importance for characterization of optoelectronic device. It was, however, hardly possible for the conventional light-probe measurements to determine the local optical properties from single quantum object with nanometrical inhomogeneity. Here we demonstrate the first successful determination of the absolute optical constants, including the optical conductivity and absorption coefficient, for an individual carbon nanotube with defects by comparing energy loss spectroscopy and optical absorption. The optical conductivity obtained from a certain type of defects indeed presents a characteristic modification near the lowest excitation peak (E11) where excitons and non-radiative transitions as well as phonon-coupled excitations are strongly involved. Detailed line-shape analysis of the E11 peak clearly shows different degree of exciton lifetime shortening and electronic state modification which is variable to the defect type.

cond-mat.mtrl-sci↗

arXiv2014

Giant Seebeck coefficient in semiconducting single-wall carbon nanotube film

We found a giant Seebeck effect in semiconducting single-wall carbon nanotube (SWCNT) films, which exhibited a performance comparable to that of commercial Bi2Te3 alloys. Carrier doping of semiconducting SWCNT films further improved the thermoelectric performance. These results were reproduced well by first-principles transport simulations based on a simple SWCNT junction model. These findings suggest strategies that pave the way for emerging printed, all-carbon, flexible thermoelectric devices.

cond-mat.mes-hall↗

arXiv2013

Exciton-phonon Bound Complex in Single-walled Carbon Nanotubes Revealed by High-field Magneto-optical Spectroscopy

High-field magneto-optical spectroscopy was conducted on highly-selected chiral (6,5) specific single-walled carbon nanotubes. Spectra of phonon sidebands in both 1st and 2nd sub-bands were observed to be unchanged by the application of an external magnetic field up to 52 T. Our analyses led to the conclusion that both phonon sidebands in respective sub-band originate from the dark K-momentum singlet (D-K-S) excitons. Moreover, while the relative ordering between the bandedge bright exciton and its zero-momentum anti-bonding counterpart was found to be opposite for the 1st and 2nd sub-bands, the relative ordering between the D-K-S exciton and the band-edge bright exciton was clarified to be the same for both sub-bands. Energy of these D-K-S excitons was estimated to be ~ 21.5 and ~ 37.3 meV above the band-edge bright exciton for the 1st and 2nd sub-bands, respectively.

cond-mat.mes-hall↗

arXiv2013

Band-edge Exciton States in a Single-walled Carbon Nanotube Revealed by Magneto-optical Spectroscopy in Ultra-high Magnetic Field

We report high field magneto-optical study on the first and second sub-band transitions of single-chirality single-walled carbon nanotubes. The ordering and relative energy splitting between bright and dark excitonic states were found to be inverse between the first and second subbands. We verified that the zero-momentum dark singlet exciton lies below the bright exciton for the first subband transitions, while for the second sub-band transitions, it was found to have higher energy than the bright excitonic state. Effect of this peculiar excitonic structure was found to manifest itself in distinctive Aharonov-Bohm splitting in ultra-high magnetic fields up to 190 T.

cond-mat.mes-hall↗

arXiv2013

Survey of Exciton-Phonon Sidebands by Magneto-optical Spectroscopy Using Highly Purified (6,5) Single-walled Carbon Nanotubes

We report the first high-field magneto-optical study on the exciton-phonon sideband of single-walled carbon nanotubes (SWNTs) consisting only of (6,5) species. Both energy and intensity of the observed phonon sideband were found to be independent of the external magnetic field. Comparing with theoretical calculations, we confirmed that these sidebands originate from the optically forbidden K-momentum singlet excitons. Energy of these K-momentum dark excitons was extracted to be ~ 21.5 meV above the bright zero-momentum singlet excitons, in close agreement with recent theoretical predictions and experimentally determined values.

cond-mat.mes-hall↗

arXiv2012

Orbital and spin magnetic moments of transforming 1D iron inside metallic and semiconducting carbon nanotubes

The orbital and spin magnetic properties of iron inside transforming metallic and semiconducting 1D carbon nanotube hybrids are studied by means of local x-ray magnetic circular dichroism (XMCD) and bulk superconducting quantum interference device (SQUID) measurements. Nanotube hybrids are initially ferrocene filled single-walled carbon nanotubes (SWCNT) of different metallicities. After a high temperature nanochemical reaction ferrocene molecules react with each other to form iron nano clusters. We show that the ferrocenes molecular orbitals interact differently with the SWCNT of different metallicities without significant XMCD response. This XMCD at various temperatures and magnetic fields reveals that the orbital and/or spin magnetic moments of the encapsulated iron are altered drastically as the transformation to 1D Fe nanoclusters takes place. The orbital and spin magnetic moments are both found to be larger in filled semiconducting nanotubes than in the metallic sample. This could mean that the magnetic polarizations of the encapsulated material is dependent on the metallicity of the tubes. From a comparison between the iron 3d magnetic moments and the bulk magnetism measured by SQUID, we conclude that the delocalized magnetisms dictate the magnetic properties of these 1D hybrid nanostructures.

cond-mat.mes-hall↗

arXiv2008

Logic Ciucuits Using Solution-processed Single-walled Carbon Nanotue Transistors

This letter reports on the realization of logic circuits employing solution-processed networks of single-walled carbon nanotubes. We constructed basic logic gates (inverter, NAND and NOR) with n- and p-type field-effect transistors fabricated by solution-based chemical doping. Complementary metal-oxide-semiconductor inverters exhibited voltage gains of up to 20, which illustrates the great potential of carbon nanotube networks for printable flexible electronics.

cond-mat.mtrl-sci↗

arXiv2005

Rietveld analysis and maximum entropy method of powder diffraction for bundles of single-walled carbon nanotubes

The structure of bundles of single-walled carbon nanotubes (SWNT) has been refined by Rietveld analysis using neutron and X-ray powder diffraction data. Based on previous simulation studies of powder diffraction data of SWNT and standard Rietveld analyses, we have developed a pattern fit technique for SWNT which provides precise structure parameters. We also show that the present technique can be used with the maximum entropy method (MEM), which is complementary to the Rietveld analysis. Using the neutron diffraction data of pristine SWNT, we have successfully reconstructed the density of carbon nuclei and zero density in the inner cavity of SWNT by MEM.

cond-mat.mtrl-sci↗

arXiv2005

Low frequency excitations of C60 chains inserted inside single-walled carbon nanotubes

The low frequency excitations of C60 chains inserted inside single-walled carbon nanotubes (SWNTs) have been studied by inelastic neutron scattering (INS) on a high quality sample of peapods. The comparison of the neutron-derived generalized phonon density of states (GDOS) of the peapods sample with that of a raw SWNTs allows the vibrational properties of the C60 chains encapsulated in the hollow core of the SWNTs to be probed. Lattice dynamical models are used to calculate the GDOS of chains of monomers, dimers and polymers inserted into SWNTs, which are compared to the experimental data. The presence of strong interactions between C60 cages inside the nanotube is clearly demonstrated by an excess of mode density in the frequency range around 10 meV. However, the presence of a quasi-elastic signal indicates that some of the C60ś undergo rotational motion. This suggests that peapods are made from a mixture of C60 monomers and C60 n-mer (dimer, trimer ... polymer) structures.

cond-mat.other↗

arXiv2004

On the diffraction pattern of C60 peapods

We present detailed calculations of the diffraction pattern of a powder of bundles of C$_{60}$ peapods. The influence of all pertinent structural parameters of the bundles on the diffraction diagram is discussed, which should lead to a better interpretation of X-ray and neutron diffraction diagrams. We illustrate our formalism for X-ray scattering experiments performed on peapod samples synthesized from 2 different technics, which present different structural parameters. We propose and test different criteria to solve the difficult problem of the filling rate determination.

cond-mat.other↗