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Lindefelt, Ulf
Publications (10 of 101) Show all publications
Thiagarajan, K. & Lindefelt, U. (2015). Effects of vacancies on the electron transport in semiconducting zigzag carbon nanotubes. JOURNAL OF COMPUTATIONAL AND THEORETICAL NANOSCIENCE, 12(3), 473-477
Open this publication in new window or tab >>Effects of vacancies on the electron transport in semiconducting zigzag carbon nanotubes
2015 (English)In: JOURNAL OF COMPUTATIONAL AND THEORETICAL NANOSCIENCE, ISSN 1546-1955, Vol. 12, no 3, p. 473-477Article in journal (Refereed) Published
Abstract [en]

The electron transport in semiconducting zigzag carbon nanotubes containing vacancies is studied using the Monte Carlo method. The electronic band structure is derived from that of graphene using the zone folding method, and the phonon spectrum is obtained using a fourth nearest-neighbour force constant model. The scattering rates describing the electron-phonon interaction and the electron-vacancy interaction are both derived within the tight-binding formalism, and are calculated using Fermi's Golden rule. The steady-state drift velocity and the mobility for (13,0) and (10,0) nanotubes are calculated as functions of the electric field strength, density of vacancies and lattice temperature. We find that, apart from an expected overall reduction of the drift velocity (mobility), the effects of the vacancies are-fold: (1) the degree of levelling-off of the drift velocity as a function of the electric field-strength can be altered substantially by a high concentration of vacancies, and (2) the negative differential resistance disappears if the vacancy concentration is sufficiently high.

Keywords
Carbon Nanotubes, Drift Velocity, Monte Carlo Simulation, Tight-Binding Approximation, Scattering Rates, Vacancies
National Category
Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:miun:diva-18865 (URN)10.1166/jctn.2015.3755 (DOI)000352288500022 ()2-s2.0-84925272852 (Scopus ID)STC (Local ID)STC (Archive number)STC (OAI)
Available from: 2013-04-29 Created: 2013-04-29 Last updated: 2017-08-28Bibliographically approved
Thiagarajan, K. & Lindefelt, U. (2012). Electron-Phonon and electron-defect Scattering Rates in Semiconducting Zig-Zag Carbon Nanotubes. Paper presented at 8th International Vacuum Electron Sources Conference (IVESC)/NANOcarbon; OCT 14-16, 2010; Nanjing, PEOPLES R CHINA. Physica Status Solidi. C, Current topics in solid state physics, 9(1), 22-25
Open this publication in new window or tab >>Electron-Phonon and electron-defect Scattering Rates in Semiconducting Zig-Zag Carbon Nanotubes
2012 (English)In: Physica Status Solidi. C, Current topics in solid state physics, ISSN 1610-1634, E-ISSN 1610-1642, Vol. 9, no 1, p. 22-25Article in journal (Refereed) Published
Abstract [en]

Electron-phonon and electron-defect scattering rates have been calculated within a tight-binding approach for semiconducting zigzag carbon nanotubes. The scattering rates for (5,0), (7,0), (10,0), (13,0) and (25,0) nanotubes have been investigated. The electron-phonon scattering rate shows both diameter and temperature dependence, and the dependence of the electron-defect scattering rate on nanotube diameter is similar to that of the electron-phonon scattering rate. Backscattering and forward scattering for electrons interacting with defects occur with equal probability at all energies. The importance of electron-defect scattering relative to electron-phonon scattering depends very much on the energy of the electron.

Keywords
carbon nanotubes; electron-phonon scattering; electron-defect scattering rate; tight-binding approximation
National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:miun:diva-14995 (URN)10.1002/pssc.201084156 (DOI)000301545800004 ()2-s2.0-83755224763 (Scopus ID)STC (Local ID)STC (Archive number)STC (OAI)
Conference
8th International Vacuum Electron Sources Conference (IVESC)/NANOcarbon; OCT 14-16, 2010; Nanjing, PEOPLES R CHINA
Available from: 2011-11-30 Created: 2011-11-30 Last updated: 2017-12-08Bibliographically approved
Thiagarajan, K. & Lindefelt, U. (2012). High-field electron transport in semiconducting zigzag carbon nanotubes. Nanotechnology, 23(26), 265703-265709
Open this publication in new window or tab >>High-field electron transport in semiconducting zigzag carbon nanotubes
2012 (English)In: Nanotechnology, ISSN 0957-4484, E-ISSN 1361-6528, Vol. 23, no 26, p. 265703-265709Article in journal (Refereed) Published
Abstract [en]

Electron transport in semiconducting zigzag carbon nanotubes is studied by solving the Boltzmann transport equation using the single-particle Monte Carlo technique. The electronic band structure is based on a standard nearest-neighbour tight-binding parameterisation, and the phonon spectrum is calculated using a fourth nearest-neighbour force constant model. The electron-phonon scattering probabilities are calculated within a tight-binding formalism. The steady-state drift velocities for the semiconducting zigzag nanotubes (8,0), (10,0), (11,0), (13,0), and (25,0) are computed as functions of electric field strength and temperature, and the results are analysed here. The results show the presence of negative differential resistance at high electric fields for some of the nanotubes. The drift velocity and the low field mobility reach a maximum value of and, respectively, for a (25,0) nanotube.

Place, publisher, year, edition, pages
Bristol, England: , 2012
Keywords
Carbon nanotubes, electron-phonon scattering, drift velocity, mobility, Monte Carlo simulation
National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:miun:diva-16551 (URN)10.1088/0957-4484/23/26/265703 (DOI)000305411400015 ()2-s2.0-84862657954 (Scopus ID)STC (Local ID)STC (Archive number)STC (OAI)
Note

Correction: Source: NANOTECHNOLOGY  Volume: 24  Issue: 39  Article Number: 399502  DOI: 10.1088/0957-4484/24/39/399502  Published: OCT 4 2013

Available from: 2012-06-25 Created: 2012-06-25 Last updated: 2017-12-07Bibliographically approved
Thiagarajan, K. & Lindefelt, U. (2011). Electron-phonon scattering rates in semiconducting zigzag carbon nanotubes. Journal of Computational and Theoretical Nanoscience, 8(9), 1694-1702
Open this publication in new window or tab >>Electron-phonon scattering rates in semiconducting zigzag carbon nanotubes
2011 (English)In: Journal of Computational and Theoretical Nanoscience, ISSN 1546-1955, Vol. 8, no 9, p. 1694-1702Article in journal (Refereed) Published
Abstract [en]

The energy dependence of the scattering rate for electrons interacting with phonons in semiconducting zig-zag carbon nanotubes has been investigated using a tight-binding method. Apart from the scattering rates, their components in terms of phonon emission, phonon absorption, backscattering and forward scattering have been determined. Results for (7, 0), (10, 0), (13, 0) and (25, 0) nanotubes at both room temperature and at 10K are presented and discussed. It is demonstrated that backscattering of the electron generally is more likely than forward scattering, and that phonon absorption can be comparable to, or even more important than, phonon emission in limited energy intervals. Furthermore, the phonons responsible for the main features in the scattering rates have been identified, and the similarities in the scattering rates between different nanotubes are clarified.

Keywords
Carbon Nanotubes; Electron-Phonon Scattering; Scattering Rates; Backscattering
National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:miun:diva-12152 (URN)10.1166/jctn.2011.1868 (DOI)000298514100009 ()2-s2.0-84856886654 (Scopus ID)STC (Local ID)STC (Archive number)STC (OAI)
Available from: 2010-10-22 Created: 2010-10-22 Last updated: 2016-10-14Bibliographically approved
Thiagarajan, K. & Lindefelt, U. (2010). Electron-phonon and electron-defect scattering rates in semiconducting zigzag carbon nanotubes. In: Proceedings - 2010 8th International Vacuum Electron Sources Conference and Nanocarbon, IVESC 2010 and NANOcarbon 2010. Paper presented at 8th International Vacuum Electron Sources Conference, IVESC 2010 and NANOcarbon 2010; Nanjing; 14 October 2010 through 16 October 2010 (pp. 282-283). IEEE conference proceedings
Open this publication in new window or tab >>Electron-phonon and electron-defect scattering rates in semiconducting zigzag carbon nanotubes
2010 (English)In: Proceedings - 2010 8th International Vacuum Electron Sources Conference and Nanocarbon, IVESC 2010 and NANOcarbon 2010, IEEE conference proceedings, 2010, p. 282-283Conference paper, Published paper (Refereed)
Abstract [en]

The electron transport properties of single walled carbon nanotubes are of fundamental importance for the development of carbon based nanotechnology. Carbon nanotubes can display both chemical and structural defects, which affect electronic states near the Fermi level. This is further complicated by the fact that the concentration of defects depends upon the method of synthesis. In this work, we have investigated both electron-phonon and electron-defect scattering in semiconducting zigzag carbon nanotubes by calculating and analyzing the quantum-mechanical scattering rates for these processes. One objective of this work is to give a theoretical limit for the concentration of defects at which electron-defect scattering rates would be comparable to the electron-phonon scattering rates.

Place, publisher, year, edition, pages
IEEE conference proceedings, 2010
Keywords
carbon nanotubes; electron-phonon scattering; electron-defect scattering rate; tight-binding approximation
National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:miun:diva-12153 (URN)10.1109/IVESC.2010.5644235 (DOI)2-s2.0-78650663872 (Scopus ID)978-142446642-9 (ISBN)
Conference
8th International Vacuum Electron Sources Conference, IVESC 2010 and NANOcarbon 2010; Nanjing; 14 October 2010 through 16 October 2010
Available from: 2010-10-22 Created: 2010-10-22 Last updated: 2013-03-20Bibliographically approved
Olsen, M., Gradin, P., Lindefelt, U. & Olin, H. (2010). Nonharmonic oscillations of nanosized cantilevers due to quantum-size effects. Physical Review B Condensed Matter, 81(5), 054304
Open this publication in new window or tab >>Nonharmonic oscillations of nanosized cantilevers due to quantum-size effects
2010 (English)In: Physical Review B Condensed Matter, ISSN 0163-1829, E-ISSN 1095-3795, Vol. 81, no 5, p. 054304-Article in journal (Refereed) Published
Abstract [en]

Using a one-dimensional jellium model and standard beam theory we calculate the spring constant of a vibrating nanowire cantilever. By using the asymptotic energy eigenvalues of the standing electron waves over the nanometer-sized cross-section area, the change in the grand canonical potential is calculated and hence the force and the spring constant. As the wire is bent more electron states fits in its cross section. This has an impact on the spring "constant" which oscillates slightly with the bending of the wire. In this way we obtain an amplitude-dependent resonans frequency that should be detectable.

Abstract [sv]

Genom att använda en endimensionell fri elektronmodell där vi bortser från atomstrukturen i metallen (eng jellium model) och vanlig balkteori beräknar vi fjäderkonstanten hos en vibrerande nanotråd inspänd i ena änden. Vi använder de asymptotiska egenvärdena hos de stående elektronvågorna med vilkas hjälp vi beräknar den storkanoniska (dvs med variabelt elektronantal) potentialen hos elektrongasen. Från denna potential beräknar vi kraften vi måste använda för att böja tråden och därmed fjäderkonstanten. När nanotråden böjs ökar dess tvärsnittyta enligt den vanliga balkteorin och fler elektrontillstånd passar i ytan. Detta påverkar "fjäderkonstanten" vilken oscillerar något med hur mycket tråden är böjd. På detta sätt erhåller vi en amplitudberoende egensvängningsfrekvens hos tråden vilken borde vara mätbar.

National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:miun:diva-12287 (URN)10.1103/PhysRevB.81.054304 (DOI)000274998000046 ()2-s2.0-77954802785 (Scopus ID)
Available from: 2010-11-25 Created: 2010-11-25 Last updated: 2017-12-12Bibliographically approved
Hjelm, M., Martinez, A., Nilsson, H.-E. & Lindefelt, U. (2007). Interband tunneling description of holes in Wurtzite GaN at high electric fields. Journal of Computational Electronics, 6(1-3), 163-166
Open this publication in new window or tab >>Interband tunneling description of holes in Wurtzite GaN at high electric fields
2007 (English)In: Journal of Computational Electronics, ISSN 1569-8025, E-ISSN 1572-8137, Vol. 6, no 1-3, p. 163-166Article in journal (Refereed) Published
Abstract [en]

We have studied the time evolution of an ensemble of holes in Wurtzite GaN under the effect of a high electric field. The density matrix equation used as a foundation in the study includes band-to-band tunneling, but disregards collisions. In the description of the ensemble dynamics the full band structure is used. The average energy and group velocity for the ensemble is calculated, as well as velocity components corresponding to the non-diagonal elements of the velocity operator (interference). The calculations have been carried out for the electric field strengths 0.4 and 4 MV/cm. A comparison is presented of the results with and without inclusion of band tunneling in the ensemble dynamics. There is also a comparison of the velocity with and without the non-diagonal elements of the velocity operator terms. A conclusion is that Monte Carlo simulations considering band tunneling, but not interference, can give accurate results.

Keywords
band-to-band tunneling, density matrix, GaN, high-field simulation
National Category
Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:miun:diva-4224 (URN)10.1007/s10825-006-0081-y (DOI)000208473600039 ()2-s2.0-34247381937 (Scopus ID)4956 (Local ID)4956 (Archive number)4956 (OAI)
Available from: 2008-09-30 Created: 2008-09-30 Last updated: 2017-12-12Bibliographically approved
Lindefelt, U. (2005). Resonances and rotation symmetries in the conductance of armchair carbon nanotubes with extended defect pairs. Physical Review B Condensed Matter, 72(15), 153405-1
Open this publication in new window or tab >>Resonances and rotation symmetries in the conductance of armchair carbon nanotubes with extended defect pairs
2005 (English)In: Physical Review B Condensed Matter, ISSN 0163-1829, E-ISSN 1095-3795, Vol. 72, no 15, p. 153405-1Article in journal (Refereed) Published
Abstract [en]

The influence on the conductance of armchair carbon nanotubes due to the presence of extended vacancy pairs has been investigated using a conventional pi-electron tight-binding model. It is found that the conductance in the linear band region around the Fermi energy contains resonance peaks and dips, which can be understood as double-barrier scattering resonances and Fano antiresonances and whose number depends on the longitudinal intervacancy separation. Furthermore, for a given longitudinal intervacancy separation, only two distinctly different conductance spectra appear in this energy region as the second vacancy in the pair assumes all different lateral positions around the tube circumference. It is also found that the conductance can be very sensitive to minimal changes in the relative intervacancy positions.

Keywords
nanotubes, coherent transport
National Category
Natural Sciences
Identifiers
urn:nbn:se:miun:diva-3457 (URN)10.1103/PhysRevB.72.153405 (DOI)000232934400030 ()3522 (Local ID)3522 (Archive number)3522 (OAI)
Available from: 2008-09-30 Created: 2009-07-13 Last updated: 2017-12-12Bibliographically approved
Lindefelt, U., Nilsson, H.-E. & Hjelm, M. (2004). Choice of wavefunction phases in the equations for electric-field-induced interband transitions. Semiconductor Science and Technology, 19(8), 1061-1066
Open this publication in new window or tab >>Choice of wavefunction phases in the equations for electric-field-induced interband transitions
2004 (English)In: Semiconductor Science and Technology, ISSN 0268-1242, E-ISSN 1361-6641, Vol. 19, no 8, p. 1061-1066Article in journal (Refereed) Published
Abstract [en]

A set of equations for calculating the probability for electric-field-induced interband transitions in periodic crystals (Krieger and Iafrate 1986 Phys. Rev. B 33 5494) can be used in combination with the full band Monte Carlo method to study high-field electronic transport properties in semiconductors. However, when the equations are applied to realistic cases in which the underlying band structure is obtained from numerical band structure programmes, the equations are not directly solvable because of the indeterminacy of the phases of the band structure Bloch wavefunctions. Here we discuss this problem and present a method for choosing the phases of the Bloch functions in such a way that the equations yield physically correct interband transition probabilities.

Keywords
High-field transport
National Category
Natural Sciences
Identifiers
urn:nbn:se:miun:diva-2836 (URN)10.1088/0268-1242/19/8/018 (DOI)000224975600021 ()2-s2.0-4043098243 (Scopus ID)2505 (Local ID)2505 (Archive number)2505 (OAI)
Available from: 2008-09-30 Created: 2008-09-30 Last updated: 2017-12-12Bibliographically approved
Son, N., Persson, C., Lindefelt, U., Chen, W., Janzén, E., Meyer, B. & Hofmann, D. (2004). Cyclotron Resonance Studies of Effective Masses and Band Structure in SiC. In: Silicon Carbide: Recent Major Advances (pp. 437-460). Berlin: Springer
Open this publication in new window or tab >>Cyclotron Resonance Studies of Effective Masses and Band Structure in SiC
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2004 (English)In: Silicon Carbide: Recent Major Advances, Berlin: Springer, 2004, p. 437-460Chapter in book (Other academic)
Place, publisher, year, edition, pages
Berlin: Springer, 2004
National Category
Natural Sciences
Identifiers
urn:nbn:se:miun:diva-3478 (URN)3590 (Local ID)9783540404583 (ISBN)3590 (Archive number)3590 (OAI)
Available from: 2008-09-30 Created: 2008-09-30 Last updated: 2012-01-17Bibliographically approved
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