| 1. |
- Bengtsson, Stefan, 1961, et al.
(author)
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Carbon-based nanoelectromechanical devices
- 2011
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In: International Journal of High Speed Electronics and Systems. - 1793-6438. ; 20:1, s. 195-204
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Journal article (peer-reviewed)abstract
- Carbon-based nanoelectromechanical devices are approaching applications in electronics. Switches based on individual carbon nanotubes deliver record low off-state leakage currents. Arrays of vertically aligned carbon nanotubes or nanofibers can be fabricated to constitute varactors. Very porous, low density arrays of quasi-vertically aligned arrays of carbon nanotubes behave mechanically as a single unit with very unusual material properties.
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| 2. |
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| 3. |
- Jackman, Henrik, 1984-
(author)
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Mechanical behaviour of carbon nanostructures
- 2014
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Doctoral thesis (other academic/artistic)abstract
- AbstractCarbon nanotubes (CNTs) have extraordinary mechanical and electrical properties. Together with their small dimensions and low density, they are attractive candidates for building blocks in future nanoelectromechanical systems and for many other applications. The extraordinary properties are however only attained by perfectly crystalline CNTs and quickly deteriorate when defects are introduced to the structure. The growth technique affects the crystallinity where in general CNTs grown by arc-discharge are close to perfectly crystalline, while CVD-grown CNTs have large defect densities. Mechanical deformation also affects these properties, even without introducing defects. When CNTs are bent they behave similarly to drinking straws, i.e. they buckle or ripple and their bending stiffness drops abruptly.In this thesis, the mechanical behaviour of individual CNTs and vertically aligned carbon nanofibers (VACNFs) has been studied by performing force measurements inside electron microscopes. Cantilevered CNTs, and VACNFs, were bent using a force sensor, yielding force-deflection curves while their structure was imaged simultaneously.We have found that CNTs grown by arc-discharge have a high enough crystallinity to possess a Young’s modulus close to the ideal value of 1 TPa. CVD-grown CNTs possess a Young’s modulus that is about one order of magnitude smaller, due to their large defect density. The VACNFs are yet another order of magnitude softer as a result of their cup-stacked internal structure. We also found that a high defect density will increase the critical strain for the rippling onset and the relative post-rippling stiffness. Multi-walled CNTs with a small inner diameter are less prone to ripple and have a larger relative post-rippling stiffness. Our findings show large variations in the onset of rippling and the bending stiffness before and after rippling. These variations open up possibilities of tailoring the mechanical properties for specific applications.
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| 4. |
- Johansson, J. O., et al.
(author)
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Anisotropic hot electron emission from fullerenes
- 2012
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In: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 136:16
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Journal article (peer-reviewed)abstract
- Photoelectron spectra for fullerenes C-60 and C-70 ionized using 800 nm laser pulses with pulse durations from 120 to 1000 fs show thermal electron kinetic energy distributions but they also exhibit angular anisotropy with respect to the laser light polarization. The effective temperature of electrons, measured along the laser polarization direction, is significantly higher than in the perpendicular direction. We explain this observation by considering that the emission of the thermal electrons is uncorrelated with the phase of the laser pulse, unlike directly ionized electrons, and, depending on the time of emission, they may experience an additional "kick" from the vector potential of the laser field when they are emitted from the molecule. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4704828]
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| 5. |
- Kaunisto, R., et al.
(author)
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Nanotube Device
- 2010
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Patent (other academic/artistic)
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| 6. |
- Kjellberg, Mikael, 1980, et al.
(author)
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Momentum map imaging photoelectron spectroscopy of fullerenes with femtosecond laser pulses
- 2010
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In: Physical Review A. - 1050-2947. ; 81:2
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Journal article (peer-reviewed)abstract
- Photoelectron spectra of C60 and C70, ionized with ultrashort laser pulses, are measured with a momentum-map-imaging electron spectrometer. Above the photon energy, 1.6 eV, the spectra are essentially structureless and well described by Boltzmann distributions, with temperatures on the order of 104 K. This result is similar to previous results for C60 using a time-of-flight electron spectrometer, which are confirmed in this study. Comparisons of electron energy distributions recorded for identical laser intensities but for different pulse durations demonstrate unambiguously that a significant fraction of the electrons are emitted in quasithermal processes and results argue strongly against a field ionization or direct multiphoton ionization mechanism. For electron energies above the photon energy, which account for about half the intensity, the whole signal is consistent with this quasithermal emission.
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| 7. |
- Lindahl, Niklas, 1981, et al.
(author)
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Determination of the Bending Rigidity of Graphene via Electrostatic Actuation of Buckled Membranes
- 2012
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In: Nano Letters. - : American Chemical Society (ACS). - 1530-6984 .- 1530-6992. ; 12:7, s. 3526-3531
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Journal article (peer-reviewed)abstract
- Classical continuum mechanics is used extensively to predict the properties of nanoscale materials such as graphene. The bending rigidity, kappa, is an important parameter that is used, for example, to predict the performance of graphene nanoelectromechanical devices and also ripple formation. Despite its importance, there is a large spread in the theoretical predictions of kappa for few-layer graphene. We have used the snap-through behavior of convex buckled graphene membranes under the application of electrostatic pressure to determine experimentally values of kappa for double-layer graphene membranes. We demonstrate how to prepare convex-buckled suspended graphene ribbons and fully clamped suspended membranes and show how the determination of the curvature of the membranes and the critical snap-through voltage, using AFM, allows us to extract kappa. The bending rigidity of bilayer graphene membranes under ambient conditions was determined to be 35.5(-15.0)(+20.0) eV. Monolayers are shown to have significantly lower kappa than bilayers.
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| 8. |
- Rehammar, Robert, 1980, et al.
(author)
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Diffraction from carbon nanofiber arrays
- 2012
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In: Optics Letters. - 0146-9592 .- 1539-4794. ; 37:1, s. 100-102
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Journal article (peer-reviewed)abstract
- We fabricate a square planar photonic crystal (PC) from carbon nanofibres (CNFs) using e-beam lithography and chemical vapour deposition and investigate the optical properties of this system. The system exhibit diffraction that is well described by diffraction theory. We measure the intensity of the (-1,0) and (-1,-1) diffraction spots as functions of angle of incidence. The radiation diagram obtained can be explained by interference between different diffraction beams. We observe a polarisation dependence of the intensity. In conclusion we suggest future applications of these structures.
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| 9. |
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| 10. |
- Svensson, Johannes, et al.
(author)
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Carbon Nanotube Field Effect Transistors with Suspended Graphene Gates
- 2011
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In: Nano Letters. - : American Chemical Society (ACS). - 1530-6992 .- 1530-6984. ; 11:9, s. 3569-3575
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Journal article (peer-reviewed)abstract
- Novel field effect transistors with suspended graphene gates are demonstrated. By incorporating mechanical motion of the gate electrode, it is possible to improve the switching characteristics compared to a static gate, as shown by a combination of experimental measurements and numerical simulations. The mechanical motion of the graphene gate is confirmed by using atomic force microscopy to directly measure the electrostatic deflection. The device geometry investigated here can also provide a sensitive measurement technique for detecting high-frequency motion of suspended membranes as required, e.g., for mass sensing.
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