The Experts below are selected from a list of 10392 Experts worldwide ranked by ideXlab platform
Robert H Hauge - One of the best experts on this subject based on the ideXlab platform.
-
splitting of a vertical multiwalled carbon nanotube carpet to a graphene nanoribbon carpet and its use in supercapacitors
ACS Nano, 2013Co-Authors: Chenguang Zhang, Robert H Hauge, Zhiwei Peng, Jian Lin, Yu Zhu, Gedeng Ruan, Chihchau Hwang, James M TourAbstract:Potassium vapor was used to longitudinally split vertically aligned multiwalled carbon nanotubes Carpets (VA-CNTs). The resulting structures have a carpet of partially split MWCNTs and graphene nanoribbons (GNRs). The split structures were characterized by scanning electron microscopy, transmission electron microscopy, atomic force microscopy, Raman spectroscopy and X-ray photoelectron spectroscopy. When compared to the original VA-CNTs carpet, the split VA-CNTs carpet has enhanced electrochemical performance with better specific capacitance in a supercapacitor. Furthermore, the split VA-CNTs carpet has excellent cyclability as a supercapacitor electrode material. There is a measured maximum power density of 103 kW/kg at an energy density of 5.2 Wh/kg and a maximum energy density of 9.4 Wh/kg. The superior electrochemical performances of the split VA-CNTs can be attributed to the increased surface area for ion accessibility after splitting, and the lasting conductivity of the structure with their vertical...
-
role of water in super growth of single walled carbon nanotube Carpets
Nano Letters, 2009Co-Authors: Placidus B Amama, Cary L. Pint, Robert H Hauge, Laura Mcjilton, Seung Min Kim, Eric A Stach, Terry P Murray, Benji MaruyamaAbstract:The Ostwald ripening behavior of Fe catalyst films deposited on thin alumina supporting layers is demonstrated as a function of thermal annealing in H2 and H2/H2O. The addition of H2O in super growth of single-walled carbon nanotube Carpets is observed to inhibit Ostwald ripening due to the ability of oxygen and hydroxyl species to reduce diffusion rates of catalyst atoms. This work shows the impact of typical carpet growth environments on catalyst film evolution and the role Ostwald ripening may play in the termination of carpet growth.
-
Formation of highly dense aligned ribbons and transparent films of single-walled carbon nanotubes directly from Carpets
ACS Nano, 2008Co-Authors: Cary L. Pint, Ya-qiong Xu, Matteo Pasquali, Robert H HaugeAbstract:Utilizing aligned carbon nanotube arrays grown from chemical vapor deposition, we present a highly scalable route toward the formation of ribbons and ultrathin transparent films directly from vertically aligned single-walled carbon nanotube arrays (SWNT Carpets). To "lay-over" the aligned nanotubes to form a film, we use a roller which acts to compress the film and preserve the alignment of nanotubes within the film. As we demonstrate, we can control the nanotube-catalyst interaction, leading to highly efficient transfer of the film to virtually any host substrate by following growth with a controlled H(2)O vapor etch. In addition, we demonstrate our ability to grow Carpets on patterned substrates leading to upright carpet lines, which can be rolled over to form transparent films composed of ultralong carbon nanotubes. This work demonstrates a highly scalable technique to form homogeneous, transparent films of aligned SWNTs that can be ultralong with absolutely no need for liquid phase SWNT processing.
Cary L. Pint - One of the best experts on this subject based on the ideXlab platform.
-
role of water in super growth of single walled carbon nanotube Carpets
Nano Letters, 2009Co-Authors: Placidus B Amama, Cary L. Pint, Robert H Hauge, Laura Mcjilton, Seung Min Kim, Eric A Stach, Terry P Murray, Benji MaruyamaAbstract:The Ostwald ripening behavior of Fe catalyst films deposited on thin alumina supporting layers is demonstrated as a function of thermal annealing in H2 and H2/H2O. The addition of H2O in super growth of single-walled carbon nanotube Carpets is observed to inhibit Ostwald ripening due to the ability of oxygen and hydroxyl species to reduce diffusion rates of catalyst atoms. This work shows the impact of typical carpet growth environments on catalyst film evolution and the role Ostwald ripening may play in the termination of carpet growth.
-
Formation of highly dense aligned ribbons and transparent films of single-walled carbon nanotubes directly from Carpets
ACS Nano, 2008Co-Authors: Cary L. Pint, Ya-qiong Xu, Matteo Pasquali, Robert H HaugeAbstract:Utilizing aligned carbon nanotube arrays grown from chemical vapor deposition, we present a highly scalable route toward the formation of ribbons and ultrathin transparent films directly from vertically aligned single-walled carbon nanotube arrays (SWNT Carpets). To "lay-over" the aligned nanotubes to form a film, we use a roller which acts to compress the film and preserve the alignment of nanotubes within the film. As we demonstrate, we can control the nanotube-catalyst interaction, leading to highly efficient transfer of the film to virtually any host substrate by following growth with a controlled H(2)O vapor etch. In addition, we demonstrate our ability to grow Carpets on patterned substrates leading to upright carpet lines, which can be rolled over to form transparent films composed of ultralong carbon nanotubes. This work demonstrates a highly scalable technique to form homogeneous, transparent films of aligned SWNTs that can be ultralong with absolutely no need for liquid phase SWNT processing.
Shohei Watabe - One of the best experts on this subject based on the ideXlab platform.
-
scaling hypothesis of a spatial search on fractal lattices using a quantum walk
Physical Review A, 2020Co-Authors: Rei Sato, Tetsuro Nikuni, Shohei WatabeAbstract:We investigate a quantum spatial search problem on fractal lattices, such as Sierpinski Carpets and Menger sponges. In earlier numerical studies of the Sierpinski gasket, the Sierpinski tetrahedron, and the Sierpinski carpet, conjectures have been proposed for the scaling of a quantum spatial search problem finding a specific target, which is given in terms of the characteristic quantities of a fractal geometry. We find that our simulation results for extended Sierpinski Carpets and Menger sponges support the conjecture for the ${\it optimal}$ number of the oracle calls, where the exponent is given by $1/2$ for $d_{\rm s} > 2$ and the inverse of the spectral dimension $d_{\rm s}$ for $d_{\rm s} < 2$. We also propose a scaling hypothesis for the ${\it effective}$ number of the oracle calls defined by the ratio of the ${\it optimal}$ number of oracle calls to a square root of the maximum finding probability. The form of the scaling hypothesis for extended Sierpinski Carpets is very similar but slightly different from the earlier conjecture for the Sierpinski gasket, the Sierpinski tetrahedron, and the conventional Sierpinski carpet.
Placidius B. Amama - One of the best experts on this subject based on the ideXlab platform.
-
catalytic cvd growth of millimeter tall single wall carbon nanotube Carpets using industrial gaseous waste as a feedstock
Carbon, 2017Co-Authors: Haider Almkhelfe, Xu Li, Placidius B. AmamaAbstract:Abstract A gaseous product mixture from Fischer-Tropsch synthesis (FTS-GP) was utilized as an efficient feedstock for growth of high-quality, well-aligned single-wall carbon nanotube (SWCNT) Carpets of millimeter-scale heights on Fe and (sub) millimeter-scale heights on Co catalysts via chemical vapor deposition (CVD). Although the SWCNT Carpets were grown over a wide temperature range (between 650 and 850 °C), growth conducted at optimal temperatures for Co (850 °C) and Fe (750 °C) yielded predominantly SWCNTs that were straight and clean, with sidewalls largely free of amorphous carbon. Growth on Fe is characterized by a relatively high growth rate (∼50 μm/min) and long catalyst lifetime (>90 min), with the catalyst showing no decay of activity, while growth on a Co catalyst shows a lifetime of ∼60 min, with a slower growth rate of ∼7 μm/min. The resulting area densities of SWCNT Carpets grown on Fe and Co, determined by the weight-gain method, were 1.0 × 1012 and 6.0 × 1012 cm−2, respectively — among the highest achieved for SWCNT Carpets on standard catalysts. Unlike SWCNT carpet growth involving conventional feedstocks, growth rate and density of SWCNTs on Fe are less sensitive to the FTS-GP fraction and thus allow for relatively easy optimization and scale-up.
Placidus B Amama - One of the best experts on this subject based on the ideXlab platform.
-
gaseous product mixture from fischer tropsch synthesis as an efficient carbon feedstock for low temperature cvd growth of carbon nanotube Carpets
Nanoscale, 2016Co-Authors: Haider Almkhelfe, Jennifer Carpenanunez, T C Back, Placidus B AmamaAbstract:Low-temperature chemical vapor deposition (CVD) growth of carbon nanotube (CNT) Carpets from Fe and Fe–Cu catalysts using a gaseous product mixture from Fischer–Tropsch synthesis (FTS-GP) as a superior carbon feedstock is demonstrated. This growth approach addresses a persistent issue of obtaining thick CNT Carpets on temperature-sensitive substrates at low temperatures using a non-plasma CVD approach without catalyst pretreatment and/or preheating of the carbon feedstock. The efficiency of the process is evidenced by the highly dense, vertically aligned CNT structures from both Fe and Fe–Cu catalysts even at temperatures as low as 400 °C – a record low growth temperature for CNT Carpets obtained via conventional thermal CVD. The grown CNTs exhibit a straight morphology with hollow interior and parallel graphitic planes along the tube walls. The apparent activation energies for CNT carpet growth on Fe and Fe–Cu catalysts are 0.71 and 0.54 eV, respectively. The synergistic effect of Fe and Cu show a strong dependence on the growth temperature, with Cu being more influential at temperatures higher than 450 °C. The low activation energies and long catalyst lifetimes observed are rationalized based on the unique composition of FTS-GP and Gibbs free energies for the decomposition reactions of the hydrocarbon components. The use of FTS-GP facilitates low-temperature growth of CNT Carpets on traditional (alumina film) and nontraditional substrates (aluminum foil) and has the potential of enhancing CNT quality, catalyst lifetime, and scalability.
-
role of water in super growth of single walled carbon nanotube Carpets
Nano Letters, 2009Co-Authors: Placidus B Amama, Cary L. Pint, Robert H Hauge, Laura Mcjilton, Seung Min Kim, Eric A Stach, Terry P Murray, Benji MaruyamaAbstract:The Ostwald ripening behavior of Fe catalyst films deposited on thin alumina supporting layers is demonstrated as a function of thermal annealing in H2 and H2/H2O. The addition of H2O in super growth of single-walled carbon nanotube Carpets is observed to inhibit Ostwald ripening due to the ability of oxygen and hydroxyl species to reduce diffusion rates of catalyst atoms. This work shows the impact of typical carpet growth environments on catalyst film evolution and the role Ostwald ripening may play in the termination of carpet growth.