Browsing by Author "Pint, Cary L."

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    Broadband, Polarization-Sensitive Photodetector Based on Optically-Thick Films of Macroscopically Long, Dense, and Aligned Carbon Nanotubes
    (Nature Publishing Group, 2013) Nanot, Sebastien; Cummings, Aron W.; Pint, Cary L.; Ikeuchi, Akira; Akiho, Takafumi; Sueoka, Kazuhisa; Hauge, Robert H.; Leonard, François; Kono, Junichiro
    Increasing performance demands on photodetectors and solar cells require the development of entirely new materials and technological approaches.Wereport on the fabrication and optoelectronic characterization of a photodetector based on optically-thick films of dense, aligned, and macroscopically long single-wall carbon nanotubes. The photodetector exhibits broadband response from the visible to the mid-infrared under global illumination, with a response time less than 32 ms. Scanning photocurrent microscopy indicates that the signal originates at the contact edges, with an amplitude and width that can be tailored by choosing different contact metals. A theoretical model demonstrates the photothermoelectric origin of the photoresponse due to gradients in the nanotube Seebeck coefficient near the contacts. The experimental and theoretical results open a new path for the realization of optoelectronic devices based on three-dimensionally organized nanotubes.
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    Carbon Nanotubes and Related Nanomaterials: Critical Advances and Challenges for Synthesis toward Mainstream Commercial Applications
    (American Chemical Society, 2018) Rao, Rahul; Pint, Cary L.; Islam, Ahmad E.; Weatherup, Robert S.; Hofmann, Stephan; Meshot, Eric R.; Wu, Fanqi; Zhou, Chongwu; Dee, Nicholas; Amama, Placidus B.; Carpena-Nuñez, Jennifer; Shi, Wenbo; Plata, Desiree L.; Penev, Evgeni S.; Yakobson, Boris I.; Balbuena, Perla B.; Bichara, Christophe; Futaba, Don N.; Noda, Suguru; Shin, Homin; Kim, Keun Su; Simard, Benoit; Mirri, Francesca; Pasquali, Matteo; Fornasiero, Francesco; Kauppinen, Esko I.; Arnold, Michael; Cola, Baratunde A.; Nikolaev, Pavel; Arepalli, Sivaram; Cheng, Hui-Ming; Zakharov, Dmitri N.; Stach, Eric A.; Zhang, Jin; Wei, Fei; Terrones, Mauricio; Geohegan, David B.; Maruyama, Benji; Maruyama, Shigeo; Li, Yan; Adams, W. Wade; Hart, A. John
    Advances in the synthesis and scalable manufacturing of single-walled carbon nanotubes (SWCNTs) remain critical to realizing many important commercial applications. Here we review recent breakthroughs in the synthesis of SWCNTs and highlight key ongoing research areas and challenges. A few key applications that capitalize on the properties of SWCNTs are also reviewed with respect to the recent synthesis breakthroughs and ways in which synthesis science can enable advances in these applications. While the primary focus of this review is on the science framework of SWCNT growth, we draw connections to mechanisms underlying the synthesis of other 1D and 2D materials such as boron nitride nanotubes and graphene.
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    Synthesis, transfer printing, electrical and optical properties, and applications of materials composed of self-assembled, aligned single-walled carbon nanotubes
    (2010) Pint, Cary L.; Hauge, Robert H.
    Super growth of single-walled carbon nanotubes (SWNTs) has emerged as a unique method for synthesizing self-assembled, pristine, aligned SWNT materials composed of ultra-long (millimeter-long) nanotubes. This thesis focuses on novel routes of synthesizing such self-assembled SWNTs and the challenges that arise in integrating this material into next-generation applications. First of all, this work provides unique insight into growth termination of aligned SWNTs, emphasizing the mechanism that inhibits the growth of infinitely long nanotubes. Exhaustive real-time growth studies, combined with ex-situ and in-situ TEM characterization emphasizes that Ostwald ripening and subsurface diffusion of catalyst particles play a key role in growth termination. As a result, rational steps to solving this problem can enhance growth, and may ultimately lead to the meter or kilometer-long SWNTs that are necessary for a number of applications. In addition, other novel synthesis routes are discussed, such as the ability to form macroscopic fibrils of SWNTs, called "flying carpets" from 40 nm thick substrates, and the ability to achieve supergrowth of SWNTs that are controllably doped with nitrogen. In the latter case, molecular heterojunctions of doped and undoped sections in a single strand of ultralong SWNTs are demonstrated Secondly, as supergrowth is conducted on alumina coated SiO2 substrates, any applications will require that one can transfer the SWNTs to host surfaces with minimal processing. This work demonstrates a unique contact transfer route by which both patterned arrays of SWNTs, or homogenous SWNT carpets, can be transferred to any host surface. In the first case, the SWNTs are grown vertically aligned, and transferred in patterns of horizontally aligned SWNT. This transfer process relies on simple water-vapor etching of amorphous carbons at the catalyst following growth, and strong van der Waals adhesion of the high surface-area SWNT to host surfaces (gecko effect). Next, as the SWNTs produced in supergrowth are notably large in diameter (2-5 nm), this work provides the first characterization of these SWNTs using combined microscopy and infrared polarized absorption studies. Perfectly aligned SWNTs are transferred to infrared optical windows and mounted in a rotatable vacuum cell in which polarization dependent characterization is carried out. By modeling features observed in absorption to expected optical excitonic transition energies, diameter distributions are rapidly extracted. In addition, other concepts of optical characterization in ultra-long aligned SWNTs are explored. For example, the concept of using polarized near-IR characterization for such SWNT samples is inadequate to characterize the bulk alignment due to the mismatch of the excitation wavelength and the SWNT length. Therefore, comparing anisotropy in polarized near-IR Raman or absorption gives substantially different results than anisotropic electrical transport measurements. In addition to optical characterization, this work uniquely finds that the electrical transport properties of SWNTs is ultimately limited by SWNT-SWNT junctions. This is evident in temperature-dependent DC and AC conductivity measurements that emphasize localization-induced transport characteristics. A number of non-classical electrical transport features are observed that can simply be related to the sensitivity of electrical transport to SWNT-SWNT junctions. This means that despite the incredible electrical properties of individual SWNTs, it is necessary to focus on the growth and processing of ultra-long SWNTs in order to realistically make nanotube-based materials comparable in transport characteristics to conventional materials. Finally, this work concludes by demonstrating progress on the fabrication of new SWNT-based applications. First of all, a new type of solid-state supercapacitor material is fabricated where vertically aligned SWNT are coated with metal-oxide dielectric and counterelectrode layers to form efficient supercapacitors. This design benefits from the ultra-high surface area available in SWNT arrays, the intrinsic ultra-high current carrying capacity of ultra-long SWNT (1000 times copper), the high breakdown voltages one can achieve using solid dielectric layers, and the lightweight and temperature insensitive design of this capacitor. As a result, performance comparable to current electric-double layer capacitor devices is reported, and energy densities significant larger are predicted by material optimization. In addition, progress on other applications are discussed, including devices utilizing self-assembled molecular heterojunction arrays, and terahertz polarizers made from perfectly aligned transferred SWNT films. This work demonstrates a bottom-up route toward the synthesis of new materials for novel characterization and applications.