Page 1. The reverse engineering of catalytically-grown carbon nanotubes V. Stolojan, Y. Tison, GY... more Page 1. The reverse engineering of catalytically-grown carbon nanotubes V. Stolojan, Y. Tison, GY Chen and SRP Silva ... ChemPhysChem 4, 1150 1169 (2003) 2. Ren ZF, Huang ZP, Xu JW, Wang JH, Bush P., Siegal MP, Provencio PN, ...
The scanning tunneling microscopy (STM) and atomic force microscopy (AFM) images of two model sys... more The scanning tunneling microscopy (STM) and atomic force microscopy (AFM) images of two model systems M 1=4 TiS 2 (M ¼ Fe, Ni) were interpreted on the basis of the partial electron density qðr; E F Þ and total electron density qðrÞ of a slab which consists of seven (0 0 1) M 1=4 TiS 2 atomic layers. The geometrical structure of the slabs investigated was optimized. Electronic structure calculations were performed using the ab initio periodic LCAO-DFT method. The top sulfur plane (0 0 1) imaged gives a different answer depending both of the compounds considered and the scanning probe microscopic instrument used. Theoretical calculations have then been carried out in order to improve our knowledge of the surface electronic structure of these inserted compounds and attempts are made to rationalize the experimental data. A specific behavior of the surface electronic structure in comparison with the 3D compounds (depending on the guest specie inserted) is shown. Ó 2003 Elsevier Science B...
Scanning Tunneling Microscopy and Spectroscopy have been used in an attempt to elucidate the elec... more Scanning Tunneling Microscopy and Spectroscopy have been used in an attempt to elucidate the electronic structure of nanotube systems containing two constituent shells. Evidence for modified electronic structure due to the inter-layer interaction in double-walled carbon nanotubes ...
Using model catalysts, we demonstrate that CO desorption from Ru surfaces can be switched from th... more Using model catalysts, we demonstrate that CO desorption from Ru surfaces can be switched from that typical of single crystal surfaces to one more characteristic of supported nanoparticles. First, the CO desorption behaviour from Ru nanoparticles supported on highly oriented pyrolytic graphite was studied. Both mass-selected and thermally evaporated nanoparticles were deposited. TPD spectra from the mass-selected nanoparticles exhibit a desorption peak located around 410 K with a broad shoulder extending from around 480 K to 600 K, while spectra obtained from thermally evaporated nanoparticles exhibit a single broad feature from ∼350 K to ∼450 K. A room temperature deposited 50 Å thick Ru film displays a characteristic nanoparticle-like spectrum with a broad desorption feature at ∼420 K and a shoulder extending from ∼450 K to ∼600 K. Subsequent annealing of this film at 900 K produced a polycrystalline morphology of flat Ru(001) terraces separated by monatomic steps. The CO desorption spectrum from this surface resembles that obtained on single crystal Ru(001) with two large desorption features located at 390 K and 450 K due to molecular desorption from terrace sites, and a much smaller peak at ∼530 K due to desorption of dissociatively adsorbed CO at step sites. In a second experiment, ion sputtering was used to create surface defects on a Ru(0 1 54) single crystal surface. A gradual shift away from the desorption spectrum typical of a Ru(001) surface towards one resembling desorption from supported Ru nanoparticles was observed with increasing sputter time.
The atomic and electronic structure of a twisted and collapsed double-walled carbon nanotube was ... more The atomic and electronic structure of a twisted and collapsed double-walled carbon nanotube was characterized using scanning tunneling microscopy and spectroscopy. It was found that the deformation opens an electronic band gap in an otherwise metallic nanotube, which has major ramifications on the use of carbon nanotubes for electronic applications. Fundamentally, the importance of the intershell interaction in this double-walled carbon nanotube points to the potential of a reversible metal-semiconductor junction, which can have device applications, as well as a caution in the design of semiconductor components based on carbon nanotubes. Lattice registry effects between the two neighboring walls evidenced by atomically resolved images confirm earlier first principle calculations indicating that the helicity influences the collapsed structure and show excellent agreement with the predicted twisted-collapse mode.
The growth of carbon nanotubes from Ni catalysts is reversed and observed in real time in a trans... more The growth of carbon nanotubes from Ni catalysts is reversed and observed in real time in a transmission electron microscope, at room temperature. The Ni catalyst is found to be Ni3C and remains attached to the nanotube throughout the irradiation sequence, indicating that C most likely diffuses on the surface of the catalyst to form nanotubes. We calculate the energy barrier for saturating the Ni3C (2-13) surface with C to be 0.14 eV, thus providing a low-energy surface for the formation of graphene planes.
Evidence for modified electronic structure in double-walled carbon nanotubes with respect to thei... more Evidence for modified electronic structure in double-walled carbon nanotubes with respect to their individual inner and outer constituent single-walled nanotubes is provided by scanning tunneling microscopy and spectroscopy experiments. The contribution originating from the inner tube to the local density of states of the double-walled system was identified in agreement with previous theoretical calculations. Consequently, the chiral index for the inner tube was extracted based on the additional van Hove singularities present in the experimental tunneling spectra.
Page 1. The reverse engineering of catalytically-grown carbon nanotubes V. Stolojan, Y. Tison, GY... more Page 1. The reverse engineering of catalytically-grown carbon nanotubes V. Stolojan, Y. Tison, GY Chen and SRP Silva ... ChemPhysChem 4, 1150 1169 (2003) 2. Ren ZF, Huang ZP, Xu JW, Wang JH, Bush P., Siegal MP, Provencio PN, ...
The scanning tunneling microscopy (STM) and atomic force microscopy (AFM) images of two model sys... more The scanning tunneling microscopy (STM) and atomic force microscopy (AFM) images of two model systems M 1=4 TiS 2 (M ¼ Fe, Ni) were interpreted on the basis of the partial electron density qðr; E F Þ and total electron density qðrÞ of a slab which consists of seven (0 0 1) M 1=4 TiS 2 atomic layers. The geometrical structure of the slabs investigated was optimized. Electronic structure calculations were performed using the ab initio periodic LCAO-DFT method. The top sulfur plane (0 0 1) imaged gives a different answer depending both of the compounds considered and the scanning probe microscopic instrument used. Theoretical calculations have then been carried out in order to improve our knowledge of the surface electronic structure of these inserted compounds and attempts are made to rationalize the experimental data. A specific behavior of the surface electronic structure in comparison with the 3D compounds (depending on the guest specie inserted) is shown. Ó 2003 Elsevier Science B...
Scanning Tunneling Microscopy and Spectroscopy have been used in an attempt to elucidate the elec... more Scanning Tunneling Microscopy and Spectroscopy have been used in an attempt to elucidate the electronic structure of nanotube systems containing two constituent shells. Evidence for modified electronic structure due to the inter-layer interaction in double-walled carbon nanotubes ...
Using model catalysts, we demonstrate that CO desorption from Ru surfaces can be switched from th... more Using model catalysts, we demonstrate that CO desorption from Ru surfaces can be switched from that typical of single crystal surfaces to one more characteristic of supported nanoparticles. First, the CO desorption behaviour from Ru nanoparticles supported on highly oriented pyrolytic graphite was studied. Both mass-selected and thermally evaporated nanoparticles were deposited. TPD spectra from the mass-selected nanoparticles exhibit a desorption peak located around 410 K with a broad shoulder extending from around 480 K to 600 K, while spectra obtained from thermally evaporated nanoparticles exhibit a single broad feature from ∼350 K to ∼450 K. A room temperature deposited 50 Å thick Ru film displays a characteristic nanoparticle-like spectrum with a broad desorption feature at ∼420 K and a shoulder extending from ∼450 K to ∼600 K. Subsequent annealing of this film at 900 K produced a polycrystalline morphology of flat Ru(001) terraces separated by monatomic steps. The CO desorption spectrum from this surface resembles that obtained on single crystal Ru(001) with two large desorption features located at 390 K and 450 K due to molecular desorption from terrace sites, and a much smaller peak at ∼530 K due to desorption of dissociatively adsorbed CO at step sites. In a second experiment, ion sputtering was used to create surface defects on a Ru(0 1 54) single crystal surface. A gradual shift away from the desorption spectrum typical of a Ru(001) surface towards one resembling desorption from supported Ru nanoparticles was observed with increasing sputter time.
The atomic and electronic structure of a twisted and collapsed double-walled carbon nanotube was ... more The atomic and electronic structure of a twisted and collapsed double-walled carbon nanotube was characterized using scanning tunneling microscopy and spectroscopy. It was found that the deformation opens an electronic band gap in an otherwise metallic nanotube, which has major ramifications on the use of carbon nanotubes for electronic applications. Fundamentally, the importance of the intershell interaction in this double-walled carbon nanotube points to the potential of a reversible metal-semiconductor junction, which can have device applications, as well as a caution in the design of semiconductor components based on carbon nanotubes. Lattice registry effects between the two neighboring walls evidenced by atomically resolved images confirm earlier first principle calculations indicating that the helicity influences the collapsed structure and show excellent agreement with the predicted twisted-collapse mode.
The growth of carbon nanotubes from Ni catalysts is reversed and observed in real time in a trans... more The growth of carbon nanotubes from Ni catalysts is reversed and observed in real time in a transmission electron microscope, at room temperature. The Ni catalyst is found to be Ni3C and remains attached to the nanotube throughout the irradiation sequence, indicating that C most likely diffuses on the surface of the catalyst to form nanotubes. We calculate the energy barrier for saturating the Ni3C (2-13) surface with C to be 0.14 eV, thus providing a low-energy surface for the formation of graphene planes.
Evidence for modified electronic structure in double-walled carbon nanotubes with respect to thei... more Evidence for modified electronic structure in double-walled carbon nanotubes with respect to their individual inner and outer constituent single-walled nanotubes is provided by scanning tunneling microscopy and spectroscopy experiments. The contribution originating from the inner tube to the local density of states of the double-walled system was identified in agreement with previous theoretical calculations. Consequently, the chiral index for the inner tube was extracted based on the additional van Hove singularities present in the experimental tunneling spectra.
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