Stefano Piscanec - Academia.edu (original) (raw)
Papers by Stefano Piscanec
2004 IEEE International Conference on Semiconductor Electronics, 2004
... Wong Yuen Yee, Muhammad Yahaya, MIEEE, Muhamad Mat Salleh, MIEEE and Burhanuddin Yeop Majlis,... more ... Wong Yuen Yee, Muhammad Yahaya, MIEEE, Muhamad Mat Salleh, MIEEE and Burhanuddin Yeop Majlis, SMIEEE Institute of Microengineering and Nanoelectronics (IMEN ... [14] "X-ray studies of AuSi Eutectic Alloy" from the website of 0. Shpyrko: http://liquids.deas.harvard.edu ...
We present a detailed study of the vibrational properties of Single Wall Carbon Nanotubes (SWNTs)... more We present a detailed study of the vibrational properties of Single Wall Carbon Nanotubes (SWNTs). The phonon dispersions of SWNTs are strongly shaped by the effects of electron-phonon coupling. We analyze the separate contributions of curvature and confinement. Confinement plays a major role in modifying SWNT phonons and is often more relevant than curvature. Due to their one-dimensional character, metallic tubes are expected to undergo Peierls distortions (PD) at T=0K. At finite temperature, PD are no longer present, but phonons with atomic displacements similar to those of the PD are affected by strong Kohn anomalies (KA). We investigate by Density Functional Theory (DFT) KA and PD in metallic SWNTs with diameters up to 3 nm, in the electronic temperature range from 4K to 3000 K. We then derive a set of simple formulas accounting for all the DFT results. Finally, we prove that the static approach, commonly used for the evaluation of phonon frequencies in solids, fails because of ...
AIP Conference Proceedings, 2005
ABSTRACT
AIP Conference Proceedings, 2003
We calculate the effects of phonon confinement on the Raman spectra of Silicon nanowires. The the... more We calculate the effects of phonon confinement on the Raman spectra of Silicon nanowires. The theoretical predictions are checked by measuring the Raman spectra of SiNWs selectively grown by plasma enhanced chemical vapor deposition (PECVD) employing gold as a catalyst. In order to fully account for the measured spectra and their variation as a function of laser power, the standard confinement theory is extended to include anharmonic phonon processes.
Physical Review Letters, 2005
Physical Review Letters, 2005
We demonstrate the key role of phonon occupation in limiting the high-field ballistic transport i... more We demonstrate the key role of phonon occupation in limiting the high-field ballistic transport in metallic carbon nanotubes. In particular, we provide a simple analytic formula for the electron transport scattering length, that we validate by accurate first principles calculations on (6,6) and (11,11) nanotubes. The comparison of our results with the scattering lengths fitted from experimental I-V curves indicates the presence of a non-equilibrium optical phonon heating induced by electron transport. We predict an effective temperature for optical phonons of thousands Kelvin.
Physical Review B, 2006
We prove that Electron-phonon coupling (EPC) is the major source of broadening for the Raman G an... more We prove that Electron-phonon coupling (EPC) is the major source of broadening for the Raman G and G − peaks in graphite and metallic nanotubes. This allows us to directly measure the opticalphonon EPCs from the G and G − linewidths. The experimental EPCs compare extremely well with those from density functional theory. We show that the EPC explains the difference in the Raman spectra of metallic and semiconducting nanotubes and their dependence on tube diameter. We dismiss the common assignment of the G − peak in metallic nanotubes to a Fano resonance between phonons and plasmons. We assign the G + and G − peaks to TO (tangential) and LO (axial) modes.
Physical Review B, 2007
We present a detailed study of the vibrational properties of single wall carbon nanotubes ͑SWNTs͒... more We present a detailed study of the vibrational properties of single wall carbon nanotubes ͑SWNTs͒. The phonon dispersions of SWNTs are strongly shaped by the effects of electron-phonon coupling. We analyze the separate contributions of curvature and confinement. Confinement plays a major role in modifying SWNT phonons and is often more relevant than curvature. Due to their one-dimensional character, metallic tubes are expected to undergo Peierls distortions ͑PD͒ at T = 0 K. At finite temperature, PD are no longer present, but phonons with atomic displacements similar to those of the PD are affected by strong Kohn anomalies ͑KA͒. We investigate by density functional theory ͑DFT͒ KA and PD in metallic SWNTs with diameters up to 3 nm, in the electronic temperature range from 4 K to 3000 K. We then derive a set of simple formulas accounting for all the DFT results. Finally, we prove that the static approach, commonly used for the evaluation of phonon frequencies in solids, fails because of the SWNTs reduced dimensionality. The correct description of KA in metallic SWNTs can be obtained only by using a dynamical approach, beyond the adiabatic Born-Oppenheimer approximation, by taking into account nonadiabatic contributions. Dynamic effects induce significant changes in the occurrence and shape of Kohn anomalies. We show that the SWNT Raman G peak can only be interpreted considering the combined dynamic, curvature and confinement effects. We assign the G + and G − peaks of metallic SWNTs to TO ͑circumferential͒ and LO ͑axial͒ modes, respectively, the opposite of semiconducting SWNTs.
physica status solidi (b), 2008
We compare the electronic properties of graphene nanoribbons, with either bulk or edge substituti... more We compare the electronic properties of graphene nanoribbons, with either bulk or edge substitutions, edge functionalization, or chemisorption. Chemical modifications can cause semiconductor-metal transitions, lifting of spin degeneracy, widening of bandgap, or appearance of non-dispersive impurity bands and doping. (Right) Ferromagnetic spin arrangement on N-bulk substituted+NH 2 edge functionalized zigzag ribbon 2070 F. Cervantes-Sodi et al.: Electronic properties of chemically modified graphene ribbons physica p s s status solidi b
We measure the temperature dependence of the Raman spectra of metallic and semiconducting nanotub... more We measure the temperature dependence of the Raman spectra of metallic and semiconducting nanotubes. We show that the different trend in metallic tubes is due to phonon re-normalization induced by the variation in electronic temperature, which is modeled including non-adiabatic contributions to account for the dynamic, time dependent nature of the phonons.
Diamond and Related Materials, 2005
Phys Rev Lett, Jun 12, 2006
Graphene is the two-dimensional (2d) building block for carbon allotropes of every other dimensio... more Graphene is the two-dimensional (2d) building block for carbon allotropes of every other dimensionality. It can be stacked into 3d graphite, rolled into 1d nanotubes, or wrapped into 0d fullerenes. Its recent discovery in free state has finally provided the possibility to study experimentally its electronic and phonon properties. Here we show that graphene's electronic structure is uniquely captured in its Raman spectrum that clearly evolves with increasing number of layers. Raman fingerprints for single-, bi- and few-layer graphene reflect changes in the electronic structure and electron-phonon interactions and allow unambiguous, high-throughput, non-destructive identification of graphene layers, which is critically lacking in this emerging research area.
Phys Rev Lett, Jun 12, 2006
Graphene is the two-dimensional (2d) building block for carbon allotropes of every other dimensio... more Graphene is the two-dimensional (2d) building block for carbon allotropes of every other dimensionality. It can be stacked into 3d graphite, rolled into 1d nanotubes, or wrapped into 0d fullerenes. Its recent discovery in free state has finally provided the possibility to study experimentally its electronic and phonon properties. Here we show that graphene's electronic structure is uniquely captured in its Raman spectrum that clearly evolves with increasing number of layers. Raman fingerprints for single-, bi- and few-layer graphene reflect changes in the electronic structure and electron-phonon interactions and allow unambiguous, high-throughput, non-destructive identification of graphene layers, which is critically lacking in this emerging research area.
We demonstrate that graphite phonon dispersions have two Kohn anomalies at the Gamma-E_2g and K-A... more We demonstrate that graphite phonon dispersions have two Kohn anomalies at the Gamma-E_2g and K-A'1 modes. The anomalies are revealed by two sharp kinks. By an exact analytic derivation, we show that the slope of these kinks is proportional to the square of the electron-phonon coupling (EPC). Thus, we can directly measure the EPC from the experimental dispersions. The Gamma-E_2g and K-A'1 EPCs are particularly large, whilst they are negligible for all the other modes at Gamma and K.
International Journal of Materials and Product Technology, Mar 20, 2015
The introduction of computer simulations has promoted significant design optimisation and cost re... more The introduction of computer simulations has promoted significant design optimisation and cost reduction in many fields of engineering. Nowadays, atomistic modelling of materials is becoming time and cost effective not only for pure research, but also for cutting-edge ...
MRS Proceedings, 2004
ABSTRACT
Physical Review B, 2006
We show that electron-phonon coupling ͑EPC͒ is the major source of broadening for the Raman G and... more We show that electron-phonon coupling ͑EPC͒ is the major source of broadening for the Raman G and G − peaks in graphite and metallic nanotubes. This allows us to directly measure the optical-phonon EPCs from the G and G − linewidths. The experimental EPCs compare extremely well with those from the density functional theory. We show that the EPC explains the difference in the Raman spectra of metallic and semiconducting nanotubes and their dependence on tube diameter. We dismiss the common assignment of the G − peak in metallic nanotubes to a resonance between phonons and plasmons and we attribute it to a resonance between phonons and electron-hole pairs. For metallic tubes, we assign the G + and G − peaks to TO ͑circumferential͒ and LO ͑axial͒ modes, the opposite of what is commonly done in literature.
Physical Review B, 2008
Graphene nanoribbons are the counterpart of carbon nanotubes in graphene-based nanoelectronics. W... more Graphene nanoribbons are the counterpart of carbon nanotubes in graphene-based nanoelectronics. We investigate the electronic properties of chemically modified ribbons by means of density functional theory. We observe that chemical modifications of zigzag ribbons can break the spin degeneracy. This promotes the onset of a semiconducting-metal transition, or of a half-semiconducting state, with the two spin channels having a different band gap, or of a spin-polarized half-semiconducting state, where the spins in the valence and conduction bands are oppositely polarized. Edge functionalization of armchair ribbons gives electronic states a few eV away from the Fermi level and does not significantly affect their band gap. N and B produce different effects, depending on the position of the substitutional site. In particular, edge substitutions at low density do not significantly alter the band gap, while bulk substitution promotes the onset of semiconducting-metal transitions. Pyridinelike defects induce a semiconducting-metal transition.
Nano Letters, 2008
We demonstrate n-and p-type field-effect transistors based on Si nanowires (SiNWs) implanted with... more We demonstrate n-and p-type field-effect transistors based on Si nanowires (SiNWs) implanted with P and B at fluences as high as 10 15 cm -2 . Contrary to what would happen in bulk Si for similar fluences, in SiNWs this only induces a limited amount of amorphization and structural disorder, as shown by electrical transport and Raman measurements. We demonstrate that a fully crystalline structure can be recovered by thermal annealing at 800°C. For not-annealed, as-implanted NWs, we correlate the onset of amorphization with an increase of phonon confinement in the NW core. This is ion-dependent and detectable for P-implantation only. Hysteresis is observed following both P and B implantation.
2004 IEEE International Conference on Semiconductor Electronics, 2004
... Wong Yuen Yee, Muhammad Yahaya, MIEEE, Muhamad Mat Salleh, MIEEE and Burhanuddin Yeop Majlis,... more ... Wong Yuen Yee, Muhammad Yahaya, MIEEE, Muhamad Mat Salleh, MIEEE and Burhanuddin Yeop Majlis, SMIEEE Institute of Microengineering and Nanoelectronics (IMEN ... [14] "X-ray studies of AuSi Eutectic Alloy" from the website of 0. Shpyrko: http://liquids.deas.harvard.edu ...
We present a detailed study of the vibrational properties of Single Wall Carbon Nanotubes (SWNTs)... more We present a detailed study of the vibrational properties of Single Wall Carbon Nanotubes (SWNTs). The phonon dispersions of SWNTs are strongly shaped by the effects of electron-phonon coupling. We analyze the separate contributions of curvature and confinement. Confinement plays a major role in modifying SWNT phonons and is often more relevant than curvature. Due to their one-dimensional character, metallic tubes are expected to undergo Peierls distortions (PD) at T=0K. At finite temperature, PD are no longer present, but phonons with atomic displacements similar to those of the PD are affected by strong Kohn anomalies (KA). We investigate by Density Functional Theory (DFT) KA and PD in metallic SWNTs with diameters up to 3 nm, in the electronic temperature range from 4K to 3000 K. We then derive a set of simple formulas accounting for all the DFT results. Finally, we prove that the static approach, commonly used for the evaluation of phonon frequencies in solids, fails because of ...
AIP Conference Proceedings, 2005
ABSTRACT
AIP Conference Proceedings, 2003
We calculate the effects of phonon confinement on the Raman spectra of Silicon nanowires. The the... more We calculate the effects of phonon confinement on the Raman spectra of Silicon nanowires. The theoretical predictions are checked by measuring the Raman spectra of SiNWs selectively grown by plasma enhanced chemical vapor deposition (PECVD) employing gold as a catalyst. In order to fully account for the measured spectra and their variation as a function of laser power, the standard confinement theory is extended to include anharmonic phonon processes.
Physical Review Letters, 2005
Physical Review Letters, 2005
We demonstrate the key role of phonon occupation in limiting the high-field ballistic transport i... more We demonstrate the key role of phonon occupation in limiting the high-field ballistic transport in metallic carbon nanotubes. In particular, we provide a simple analytic formula for the electron transport scattering length, that we validate by accurate first principles calculations on (6,6) and (11,11) nanotubes. The comparison of our results with the scattering lengths fitted from experimental I-V curves indicates the presence of a non-equilibrium optical phonon heating induced by electron transport. We predict an effective temperature for optical phonons of thousands Kelvin.
Physical Review B, 2006
We prove that Electron-phonon coupling (EPC) is the major source of broadening for the Raman G an... more We prove that Electron-phonon coupling (EPC) is the major source of broadening for the Raman G and G − peaks in graphite and metallic nanotubes. This allows us to directly measure the opticalphonon EPCs from the G and G − linewidths. The experimental EPCs compare extremely well with those from density functional theory. We show that the EPC explains the difference in the Raman spectra of metallic and semiconducting nanotubes and their dependence on tube diameter. We dismiss the common assignment of the G − peak in metallic nanotubes to a Fano resonance between phonons and plasmons. We assign the G + and G − peaks to TO (tangential) and LO (axial) modes.
Physical Review B, 2007
We present a detailed study of the vibrational properties of single wall carbon nanotubes ͑SWNTs͒... more We present a detailed study of the vibrational properties of single wall carbon nanotubes ͑SWNTs͒. The phonon dispersions of SWNTs are strongly shaped by the effects of electron-phonon coupling. We analyze the separate contributions of curvature and confinement. Confinement plays a major role in modifying SWNT phonons and is often more relevant than curvature. Due to their one-dimensional character, metallic tubes are expected to undergo Peierls distortions ͑PD͒ at T = 0 K. At finite temperature, PD are no longer present, but phonons with atomic displacements similar to those of the PD are affected by strong Kohn anomalies ͑KA͒. We investigate by density functional theory ͑DFT͒ KA and PD in metallic SWNTs with diameters up to 3 nm, in the electronic temperature range from 4 K to 3000 K. We then derive a set of simple formulas accounting for all the DFT results. Finally, we prove that the static approach, commonly used for the evaluation of phonon frequencies in solids, fails because of the SWNTs reduced dimensionality. The correct description of KA in metallic SWNTs can be obtained only by using a dynamical approach, beyond the adiabatic Born-Oppenheimer approximation, by taking into account nonadiabatic contributions. Dynamic effects induce significant changes in the occurrence and shape of Kohn anomalies. We show that the SWNT Raman G peak can only be interpreted considering the combined dynamic, curvature and confinement effects. We assign the G + and G − peaks of metallic SWNTs to TO ͑circumferential͒ and LO ͑axial͒ modes, respectively, the opposite of semiconducting SWNTs.
physica status solidi (b), 2008
We compare the electronic properties of graphene nanoribbons, with either bulk or edge substituti... more We compare the electronic properties of graphene nanoribbons, with either bulk or edge substitutions, edge functionalization, or chemisorption. Chemical modifications can cause semiconductor-metal transitions, lifting of spin degeneracy, widening of bandgap, or appearance of non-dispersive impurity bands and doping. (Right) Ferromagnetic spin arrangement on N-bulk substituted+NH 2 edge functionalized zigzag ribbon 2070 F. Cervantes-Sodi et al.: Electronic properties of chemically modified graphene ribbons physica p s s status solidi b
We measure the temperature dependence of the Raman spectra of metallic and semiconducting nanotub... more We measure the temperature dependence of the Raman spectra of metallic and semiconducting nanotubes. We show that the different trend in metallic tubes is due to phonon re-normalization induced by the variation in electronic temperature, which is modeled including non-adiabatic contributions to account for the dynamic, time dependent nature of the phonons.
Diamond and Related Materials, 2005
Phys Rev Lett, Jun 12, 2006
Graphene is the two-dimensional (2d) building block for carbon allotropes of every other dimensio... more Graphene is the two-dimensional (2d) building block for carbon allotropes of every other dimensionality. It can be stacked into 3d graphite, rolled into 1d nanotubes, or wrapped into 0d fullerenes. Its recent discovery in free state has finally provided the possibility to study experimentally its electronic and phonon properties. Here we show that graphene's electronic structure is uniquely captured in its Raman spectrum that clearly evolves with increasing number of layers. Raman fingerprints for single-, bi- and few-layer graphene reflect changes in the electronic structure and electron-phonon interactions and allow unambiguous, high-throughput, non-destructive identification of graphene layers, which is critically lacking in this emerging research area.
Phys Rev Lett, Jun 12, 2006
Graphene is the two-dimensional (2d) building block for carbon allotropes of every other dimensio... more Graphene is the two-dimensional (2d) building block for carbon allotropes of every other dimensionality. It can be stacked into 3d graphite, rolled into 1d nanotubes, or wrapped into 0d fullerenes. Its recent discovery in free state has finally provided the possibility to study experimentally its electronic and phonon properties. Here we show that graphene's electronic structure is uniquely captured in its Raman spectrum that clearly evolves with increasing number of layers. Raman fingerprints for single-, bi- and few-layer graphene reflect changes in the electronic structure and electron-phonon interactions and allow unambiguous, high-throughput, non-destructive identification of graphene layers, which is critically lacking in this emerging research area.
We demonstrate that graphite phonon dispersions have two Kohn anomalies at the Gamma-E_2g and K-A... more We demonstrate that graphite phonon dispersions have two Kohn anomalies at the Gamma-E_2g and K-A'1 modes. The anomalies are revealed by two sharp kinks. By an exact analytic derivation, we show that the slope of these kinks is proportional to the square of the electron-phonon coupling (EPC). Thus, we can directly measure the EPC from the experimental dispersions. The Gamma-E_2g and K-A'1 EPCs are particularly large, whilst they are negligible for all the other modes at Gamma and K.
International Journal of Materials and Product Technology, Mar 20, 2015
The introduction of computer simulations has promoted significant design optimisation and cost re... more The introduction of computer simulations has promoted significant design optimisation and cost reduction in many fields of engineering. Nowadays, atomistic modelling of materials is becoming time and cost effective not only for pure research, but also for cutting-edge ...
MRS Proceedings, 2004
ABSTRACT
Physical Review B, 2006
We show that electron-phonon coupling ͑EPC͒ is the major source of broadening for the Raman G and... more We show that electron-phonon coupling ͑EPC͒ is the major source of broadening for the Raman G and G − peaks in graphite and metallic nanotubes. This allows us to directly measure the optical-phonon EPCs from the G and G − linewidths. The experimental EPCs compare extremely well with those from the density functional theory. We show that the EPC explains the difference in the Raman spectra of metallic and semiconducting nanotubes and their dependence on tube diameter. We dismiss the common assignment of the G − peak in metallic nanotubes to a resonance between phonons and plasmons and we attribute it to a resonance between phonons and electron-hole pairs. For metallic tubes, we assign the G + and G − peaks to TO ͑circumferential͒ and LO ͑axial͒ modes, the opposite of what is commonly done in literature.
Physical Review B, 2008
Graphene nanoribbons are the counterpart of carbon nanotubes in graphene-based nanoelectronics. W... more Graphene nanoribbons are the counterpart of carbon nanotubes in graphene-based nanoelectronics. We investigate the electronic properties of chemically modified ribbons by means of density functional theory. We observe that chemical modifications of zigzag ribbons can break the spin degeneracy. This promotes the onset of a semiconducting-metal transition, or of a half-semiconducting state, with the two spin channels having a different band gap, or of a spin-polarized half-semiconducting state, where the spins in the valence and conduction bands are oppositely polarized. Edge functionalization of armchair ribbons gives electronic states a few eV away from the Fermi level and does not significantly affect their band gap. N and B produce different effects, depending on the position of the substitutional site. In particular, edge substitutions at low density do not significantly alter the band gap, while bulk substitution promotes the onset of semiconducting-metal transitions. Pyridinelike defects induce a semiconducting-metal transition.
Nano Letters, 2008
We demonstrate n-and p-type field-effect transistors based on Si nanowires (SiNWs) implanted with... more We demonstrate n-and p-type field-effect transistors based on Si nanowires (SiNWs) implanted with P and B at fluences as high as 10 15 cm -2 . Contrary to what would happen in bulk Si for similar fluences, in SiNWs this only induces a limited amount of amorphization and structural disorder, as shown by electrical transport and Raman measurements. We demonstrate that a fully crystalline structure can be recovered by thermal annealing at 800°C. For not-annealed, as-implanted NWs, we correlate the onset of amorphization with an increase of phonon confinement in the NW core. This is ion-dependent and detectable for P-implantation only. Hysteresis is observed following both P and B implantation.