Browsing by Author "Mojibpour, Ali"

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    Band structure dependent electronic localization in macroscopic films of single-chirality single-wall carbon nanotubes
    (Elsevier, 2021) Gao, Weilu; Adinehloo, Davoud; Li, Xinwei; Mojibpour, Ali; Yomogida, Yohei; Hirano, Atsushi; Tanaka, Takeshi; Kataura, Hiromichi; Zheng, Ming; Perebeinos, Vasili; Kono, Junichiro
    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.
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    Electroluminescence from Single-Chirality Single-Wall Carbon Nanotube Films
    (2022-04-22) Mojibpour, Ali; Kono, Junichiro
    Single-wall carbon nanotubes (SWCNTs) provide unique one-dimensional (1D) platforms for exploring nonintuitive many-body physics unique to 1D systems as well as for developing quantum devices for computation, sensing, and communication. There are semiconducting and metallic SWCNTs, and semiconducting SWCNTs, being direct-gapped, are promising for building revolutionary optoelectronic devices such as ultralow-threshold lasers and ultrahigh-efficiency solar cells. During the last decade, individual semiconducting SWCNTs have been extensively studied. However, optical properties of macroscopic assemblies and devices of SWCNTs have yet to be explored. In this work, we studied electroluminescence devices based on chirality-purified (6,5) SWCNT films, demonstrating intense near-infrared light emission with high efficiencies through the process of impact ionization. By eliminating residual carriers through annealing, we were able to achieve a more than 100% increase in efficiency for light emission per carrier. In addition, in films in which SWCNTs are well aligned, we made an unusual observation that the polarization of emitted photons depends on the direction of the current with respect to the SWCNT alignment direction. These results are not only fascinating but also important for developing unique macroscopically 1D optoelectronic devices based on aligned SCWNT films.
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    Multimode ultrastrong coupling in three-dimensional photonic-crystal cavities
    (Rice University, 2025) Tay, Fuyang; Mojibpour, Ali; Sanders, Stephen; Liang, Shuang; Xu, Hongjing; Gardner, Geoff C.; Baydin, Andrey; Manfra, Michael J.; Alabastri, Alessandro; Hagenmüller, David; Kono, Junichiro; U.S. Army Research Office;The Gordon and Betty Moore Foundation;The W. M. Keck Foundation;The Robert A. Welch Foundation; Applied Physics
    A work investigates multimode ultrastrong coupling between cavity modes of a three-dimensional photonic-crystal cavity and the cyclotron resonance of a Landau-quantized two-dimensional electron gas in gallium arsenide.
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    Phonon-Assisted Intertube Electronic Transport in an Armchair Carbon Nanotube Film
    (American Physical Society, 2023) Adinehloo, Davoud; Gao, Weilu; Mojibpour, Ali; Kono, Junichiro; Perebeinos, Vasili; The Smalley-Curl Institute
    The electrical conductivity of a macroscopic assembly of nanomaterials is determined through a complex interplay of electronic transport within and between constituent nano-objects. Phonons play dual roles in this situation: their increased populations tend to reduce the conductivity via electron scattering, while they can boost the conductivity by assisting electrons to propagate through the potential-energy landscape. We identified a phonon-assisted coherent electron transport process between neighboring nanotubes in temperature-dependent conductivity measurements on a macroscopic film of armchair single-wall carbon nanotubes. Through atomistic modeling of electronic states and calculations of both electronic and phonon-assisted junction conductances, we conclude that phonon-assisted conductance is the dominant mechanism for observed high-temperature transport in armchair carbon nanotubes. The unambiguous manifestation of coherent intertube dynamics proves a single-chirality armchair nanotube film to be a unique macroscopic solid-state ensemble of nano-objects promising for the development of room-temperature coherent electronic devices.
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    Single Plasmonic Nanoparticle Electroluminescence
    (2019-10-28) Mojibpour, Ali; Bharadwaj, Palash
    Plasmonic tunnel junctions perform the role of classical antennas in the visible. Due to their ultra-small footprint and their unique potential for being modulated at terahertz frequencies, they have gained much interest recently. Metal insulatormetal (M-I-M) junctions always have been the main component of plasmonic tunnel junctions due to their enhanced local density of optical states and increased inelastic electron tunneling probability. However, the presence of two few-nanometer apart plasmonic metals obscures the plasmonic resonance of each individual part. Here, in contrast to M-I-M junction, we use graphene to electrically contact a plasmonic nanoparticle. Since graphene is a dielectric in the optical frequencies, plasmon resonance of the nanoparticle is affected the least possible. This scheme has the benefit of increasing the spectral tunability of the emitted light above what is reported in M-I-M junctions.