The Experts below are selected from a list of 360 Experts worldwide ranked by ideXlab platform
Thomas Pichler - One of the best experts on this subject based on the ideXlab platform.
-
high quality double wall carbon nanotubes with a defined Diameter Distribution by chemical vapor deposition from alcohol
Carbon, 2006Co-Authors: A Gruneis, Thomas Pichler, T Gemming, Mark H Rummeli, C Kramberger, Amelia Barreiro, R Pfeiffer, H Kuzmany, B BuchnerAbstract:Abstract We have synthesized double wall carbon nanotubes (DWNTs) with few defects and little amorphous carbon by hot wall chemical vapor deposition (CVD) of alcohol. Catalysts for the DWNT growth were made from cobalt and molybdenum acetates. Scanning electron microscopy, transmission electron microscopy, multi frequency resonance Raman spectroscopy and optical absorption spectroscopy were used for characterization of the product with regard to DWNT yield, the nanotube Diameter Distribution, defect concentration and amorphous carbon content. Base pressures lower than 1 × 10 −5 mbar in the CVD reactor considerably suppress defects in the DWNTs. Optimized growth conditions for DWNT formation are presented.
-
bulk synthesis of carbon filled silicon carbide nanotubes with a narrow Diameter Distribution
Journal of Applied Physics, 2005Co-Authors: Ewa Borowiakpalen, Thomas Pichler, M Knupfer, Mark H Ruemmeli, T Gemming, K Biedermann, A Leonhardt, Ryszard J KalenczukAbstract:We report on a simple and low-cost route to produce SiC nanotubes without the need for the more usual oxide based reactions using a high temperature substitution reaction between multiwall carbon nanotubes as a frame and Si powder. Local scale studies using transmission and scanning electron microscopy are also presented. The SiC nanotubes are carbon filled and open ended. Both their mean Diameter and Diameter Distribution are smaller than previously reported for SiC nanotubes. Bulk scale studies using Raman and infrared as a probe showed the sample to be comprised of multiple polytypes and that finite size effects are present.
-
reduced Diameter Distribution of single wall carbon nanotubes by selective oxidation
Chemical Physics Letters, 2002Co-Authors: E Borowiakpalen, Thomas Pichler, Xianjie Liu, M Knupfer, A Graff, O Jost, W Pompe, Ryszard J Kalenczuk, J FinkAbstract:We report an easy way to narrow the Diameter Distribution of single-walled carbon nanotubes (SWNT) by oxidization treatments. Both a chemical treatment in 2 M HNO3 as well as oxidation in a reduced O2 atmosphere lead to a selective burning of the narrower SWNT in bulk samples and to a Diameter Distribution which is smaller by a factor of two. This is a first important step towards a selective production of SWNT with a defined Diameter on a bulk scale.
-
Diameter selective charge transfer in p and n doped single wall carbon nanotubes synthesized by the hipco method
Chemical Communications, 2002Co-Authors: Akos Kukovecz, Thomas Pichler, R Pfeiffer, H KuzmanyAbstract:The unusually broad Diameter Distribution of single wall carbon nanotubes (SWCNTs) in a HiPCO derived sample made it possible to observe for the first time a selective loss of Raman resonances corresponding to large Diameter tubes upon both p- (FeCl3) and n-type (K) doping.
-
detailed analysis of the mean Diameter and Diameter Distribution of single wall carbon nanotubes from their optical response
Physical Review B, 2002Co-Authors: Xianjie Liu, Thomas Pichler, M Knupfer, J Fink, Hiromichi Kataura, M S Golden, Y AchibaAbstract:We report a detailed analysis of the optical properties of single-wall carbon nanotubes (SWCNT's) with different mean Diameters as produced by laser ablation. From a combined study of optical absorption, high-resolution electron energy-loss spectroscopy in transmission, and tight-binding calculations we were able to accurately determine the mean Diameter and Diameter Distribution in bulk SWCNT samples. In general, the absorption response can be well described assuming a Gaussian Distribution of nanotube Diameters and the predicted inverse proportionality between the nanotube Diameter and the energy of the absorption features. A detailed simulation enabled not only a determination of the mean Diameter of the nanotubes, but also gives insight into the chirality Distribution of the nanotubes. The best agreement between the simulation and experiment is observed when only nanotubes within $15\ifmmode^\circ\else\textdegree\fi{}$ of the armchair axis are considered. The mean Diameters and Diameter Distributions from the optical simulations are in very good agreement with the values derived from other bulk sensitive methods such as electron diffraction, x-ray diffraction, and Raman scattering.
Vincent Jourdain - One of the best experts on this subject based on the ideXlab platform.
-
unveiling the evolutions of nanotube Diameter Distribution during the growth of single walled carbon nanotubes
ACS Nano, 2017Co-Authors: Hugo Navas, Matthieu Picher, Eric Anglaret, Amandine Andrieuxledier, F Fossard, Thierry Michel, Akinari Kozawa, Takahiro Maruyama, Annick Loiseau, Vincent JourdainAbstract:In situ and ex situ Raman measurements were used to study the dynamics of the populations of single-walled carbon nanotubes (SWCNTs) during their catalytic growth by chemical vapor deposition. Our study reveals that the nanotube Diameter Distribution strongly evolves during SWCNT growth but in dissimilar ways depending on the growth conditions. We notably show that high selectivity can be obtained using short or moderate growth times. High-resolution transmission electron microscopy observations support that Ostwald ripening is the key process driving these seemingly contradictory results by regulating the size Distribution and lifetime of the active catalyst particles. Ostwald ripening appears as the main termination mechanism for the smallest Diameter tubes, whereas carbon poisoning dominates for the largest ones. By unveiling the key concept of dynamic competition between nanotube growth and catalyst ripening, we show that time can be used as an active parameter to control the growth selectivity of car...
-
processes controlling the Diameter Distribution of single walled carbon nanotubes during catalytic chemical vapor deposition
ACS Nano, 2011Co-Authors: Matthieu Picher, Eric Anglaret, Raul Arenal, Vincent JourdainAbstract:Single-walled carbon nanotubes are grown by catalytic chemical vapor deposition in various conditions of temperature and carbon precursor pressure. Systematic analyses of the Raman radial breathing modes at two laser wavelengths are used to monitor the evolution of the Diameter Distribution. Two distinct domains with opposite influences of the temperature and the precursor pressure on the Diameter Distribution are evidenced. Thanks to specially designed experiments made of two successive growths, three processes are identified to influence the Diameter Distribution during the nanotube growth: (i) at too low precursor pressure, nanotube nucleation cannot occur on the smallest catalyst particles; (ii) at low temperature and high precursor pressure, small catalyst particles are preferably encapsulated by disordered carbon structures; (iii) at high temperature, catalyst coarsening causes the disappearance of the smallest catalyst particles.
H Kuzmany - One of the best experts on this subject based on the ideXlab platform.
-
high quality double wall carbon nanotubes with a defined Diameter Distribution by chemical vapor deposition from alcohol
Carbon, 2006Co-Authors: A Gruneis, Thomas Pichler, T Gemming, Mark H Rummeli, C Kramberger, Amelia Barreiro, R Pfeiffer, H Kuzmany, B BuchnerAbstract:Abstract We have synthesized double wall carbon nanotubes (DWNTs) with few defects and little amorphous carbon by hot wall chemical vapor deposition (CVD) of alcohol. Catalysts for the DWNT growth were made from cobalt and molybdenum acetates. Scanning electron microscopy, transmission electron microscopy, multi frequency resonance Raman spectroscopy and optical absorption spectroscopy were used for characterization of the product with regard to DWNT yield, the nanotube Diameter Distribution, defect concentration and amorphous carbon content. Base pressures lower than 1 × 10 −5 mbar in the CVD reactor considerably suppress defects in the DWNTs. Optimized growth conditions for DWNT formation are presented.
-
origin of the fine structure of the raman d band in single wall carbon nanotubes
Physical Review Letters, 2003Co-Authors: Viktor Zolyomi, A Gruneis, J Kurti, H KuzmanyAbstract:Experiments show that the $D$ bands of bundles of single wall carbon nanotubes have a fine structure, apparently consisting of more than one subband. Using the double resonance theory, we calculate for the first time the $D$ band for a sample of a given Diameter Distribution for seven different laser excitation energies in a wide range. In addition, a detailed theoretical explanation for the fine structure of the $D$ band is provided. The calculated results agree well with experiments and show that the main factors in determining the fine structure are an enhanced trigonal warping of the phonon dispersion, the presence of a Diameter Distribution in the sample, and\char22{}most importantly\char22{}the resonance from the Van Hove singularities.
-
Diameter selective charge transfer in p and n doped single wall carbon nanotubes synthesized by the hipco method
Chemical Communications, 2002Co-Authors: Akos Kukovecz, Thomas Pichler, R Pfeiffer, H KuzmanyAbstract:The unusually broad Diameter Distribution of single wall carbon nanotubes (SWCNTs) in a HiPCO derived sample made it possible to observe for the first time a selective loss of Raman resonances corresponding to large Diameter tubes upon both p- (FeCl3) and n-type (K) doping.
Antoni Trasobares - One of the best experts on this subject based on the ideXlab platform.
-
comparison of beta johnson s sb weibull and truncated weibull functions for modeling the Diameter Distribution of forest stands in catalonia north east of spain
European Journal of Forest Research, 2007Co-Authors: Marc Palahi, Timo Pukkala, Elena Blasco, Antoni TrasobaresAbstract:The purpose of this study was to compare the beta, Johnson SB, Weibull and truncated Weibull functions in describing the Diameter Distributions of forest stands in Catalonia. The data consisted of permanent sample plots from the Spanish National Forest Inventory in Catalonia. The empirical data represent left-truncated Distributions, as the smallest Diameter measured in the field was 7.5 cm. A total of 1,242 plots were used to fit the functions and analyze their performance. The Distribution functions were fitted to the Diameter Distributions of the number of stems (DDN) and stand basal area (DDG). The performance of the candidate functions was compared by means of their bias and RMSE for different Diameter sums measuring the difference between the empirical and fitted Distributions. The leftmost part (from 0 to 7.5 cm) of the non-truncated functions was ignored in this analysis. Sensitivity analyses were conducted to check whether the results depended on the number of trees measured in the stand, or the main species of the stand. The truncated Weibull function for the Diameter Distribution of stand basal area appeared to be in all cases the most accurate and consistent function. Generally, functions describing the Distribution of stand basal area performed better than functions that described the Distribution of the number of trees. Of the basal area Distributions, beta and Johnson’s SB were the second best and nearly equally good with each other. The order of precision of the tested functions was: truncated Weibull for DDG, truncated Weibull for DDN, Johnson’s SB for DDG, beta for DDG, beta for DDN and Weibull for DDG, Weibull for DDN, and Johnson’s SB for DDN.
-
modelling the Diameter Distribution of pinus sylvestris pinus nigra and pinus halepensis forest stands in catalonia using the truncated weibull function
Forestry, 2006Co-Authors: Marc Palahi, Timo Pukkala, Antoni TrasobaresAbstract:Summary Parameter prediction models for the Diameter Distribution of Pinus sylvestris L., Pinus nigra Arn. and Pinus halepensis Mill. in Catalonia were developed using the truncated Weibull function as the theoretical Distribution. The parameter models allow one to use individual-tree models in the simulation of stand development when only stand-level data are collected in forest inventories. Parameter models for the Diameter Distribution of stand basal area were developed. The data consisted of permanent sample plots from the Spanish National Forest Inventory in Catalonia. A total of 1780 empirical Distributions of P. sylvestris , 1204 Distributions of P. nigra and 1535 Distributions of P. halepensis were used as modelling data. The empirical data represent lefttruncated Distributions, as the smallest Diameter measured in the fi eld was 7.5 cm. Two different approaches, namely, regression (two-step method) and optimization approach (one-step method), were used to fi nd the coeffi cients of the parameter models. In the two-step modelling method, the Weibull parameters were fi rst estimated separately for every empirical Distribution by maximizing the log-likelihood function of the Weibull density function. In the second-step, regression analysis was used to fi nd the relationship between Weibull parameters and stand basal area, number of trees per hectare and elevation of the site. The one-step method used optimization to fi nd such coeffi cients for the parameter models, which minimized the mean of the squared differences between empirical and predicted cumulative tree frequencies in the whole modelling data. The one-step optimization method performed better than the two-step regression method for all tree species. The parameter prediction models developed in this study enable the prediction of the Diameter Distribution of P. sylvestris , P. nigra and P. halepensis in Catalonia from limited stand information.
Sumio Iijima - One of the best experts on this subject based on the ideXlab platform.
-
single walled carbon nanotube growth with narrow Diameter Distribution from pt catalysts by alcohol gas source method
MRS Proceedings, 2014Co-Authors: Hiroki Kondo, Takahiro Maruyama, Sumio Iijima, R Ghosh, Shigeya NaritsukaAbstract:Single-walled carbon nanotube (SWCNT) growth were carried out on SiO2/Si substrates using Pt catalysts at different temperatures, from 400°C to 700°C, under various ethanol pressures by an alcohol gas source method, a type of cold-wall chemical vapor deposition (CVD). Raman measurements showed that the optimal ethanol pressure decreased as the growth temperature was reduced, and that SWCNTs grew even at 400°C by optimizing the ethanol pressure to 1× 10-5 Pa in a high vacuum system. Compared to the SWCNTs grown from Co catalysts, the Diameters of SWCNTs grown from Pt were smaller, irrespective of the growth temperature. In addition, both the SWCNT Diameter and the Distribution became narrower by reducing the growth temperature and we obtained small-Diameter SWCNTs of which the Diameters were less than 1 nm using Pt catalysts.
-
change of tube Diameter Distribution of single wall carbon nanotubes induced by changing the bimetallic ratio of ni and y catalysts
Chemical Physics Letters, 2000Co-Authors: M Takizawa, Yoshinori Ando, Shunji Bandow, Masako Yudasaka, Hiroshi Shimoyama, Sumio IijimaAbstract:Abstract The effect of Ni and Y concentrations in bimetallic Ni–Y catalyst on single-wall carbon nanotube (SWNT) generation is studied. When we added small amount of Y with the order of 0.1 atomic % (at%) against C, the generation rate of soot in arc discharge was enhanced by a factor of 2–3 as compared with that of only C. Addition of Ni well enhanced the generation of SWNTs. The tube Diameter Distribution was controlled by changing Y concentration (0–9.0 at%), but was not sensitive to Ni concentration (0.2–3.0 at%). The mean tube Diameter was increased with increasing Y concentration.