SwePub - sökning: WFRF:(Isacsson Andreas 1975)

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1.	Eriksson, Anders, 1975, et al. (författare) Direct Transmission Detection of Tunable Mechanical Resonance in an Individual Carbon Nanofiber Relay 2008 Ingår i: Nano Letters. - : American Chemical Society (ACS). - 1530-6984 .- 1530-6992. ; 8 Tidskriftsartikel (refereegranskat)abstract A direct on-chip transmission measurement of the resonance frequency of an individual singly clamped carbon nanofiber relay is reported. The experimental results are in good agreement with a small signal model and show the expected tuning of the resonance frequency with changing bias voltage.
2.	Shiri, Daryoush, 1975, et al. (författare) An Electrically Controlled Heat Rectifier using Graphene Nanoribbons 2019 Ingår i: 2019 IEEE 14th Nanotechnology Materials and Devices Conference, NMDC 2019. - 2378-377X. - 9781728126371 ; October 2019, s. 1-4 Konferensbidrag (refereegranskat)abstract Using Molecular Dynamics (MD) simulations we propose that splitting a graphene nanoribbon into two unequal strained sections using external force leads to large asymmetry in the forward and reverse heat fluxes. We find that the corresponding rectification ratio (RR) is enhanced to 60% compared to previous proposals. More importantly, the polarity of the proposed heat diode is controllable on-the-fly i.e. by changing the position where force is applied. This technique obviates the complex nano-patterning and lithography required to pattern graphene every time a new rectification value or sign is sought for and opens a route to simpler fabrication of phononic devices in 2D materials.
3.	Shiri, Daryoush, 1975, et al. (författare) Gunn-Hilsum Effect in Mechanically Strained Silicon Nanowires: Tunable Negative Differential Resistance 2018 Ingår i: Scientific Reports. - : Springer Science and Business Media LLC. - 2045-2322 .- 2045-2322. ; 8:1 Tidskriftsartikel (refereegranskat)abstract Gunn (or Gunn-Hilsum) Effect and its associated negative differential resistivity (NDR) emanates from transfer of electrons between two different energy subbands. This effect was observed in semiconductors like GaAs which has a direct bandgap of very low effective mass and an indirect subband of high effective mass which lies ~300 meV above the former. In contrast to GaAs, bulk silicon has a very high energy spacing (~1 eV) which renders the initiation of transfer-induced NDR unobservable. Using Density Functional Theory (DFT), semi-empirical 10 orbital (sp 3 d 5 s ∗ ) Tight Binding and Ensemble Monte Carlo (EMC) methods we show for the first time that (a) Gunn Effect can be induced in silicon nanowires (SiNW) with diameters of 3.1 nm under +3% strain and an electric field of 5000 V/cm, (b) the onset of NDR in the I-V characteristics is reversibly adjustable by strain and (c) strain modulates the resistivity by a factor 2.3 for SiNWs of normal I-V characteristics i.e. those without NDR. These observations are promising for applications of SiNWs in electromechanical sensors and adjustable microwave oscillators. It is noteworthy that the observed NDC is different in principle from Esaki-Diode and Resonant Tunneling Diodes (RTD) in which NDR originates from tunneling effect.
4.	Shiri, Daryoush, 1975, et al. (författare) Heat-to-mechanical energy conversion in graphene: Manifestation of Umklapp enhancement with strain 2019 Ingår i: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 125:12 Tidskriftsartikel (refereegranskat)abstract Conversion of heat-flux from a steady state temperature difference to mechanical vibration is demonstrated in graphene nanoribbons using direct non-equilibrium molecular dynamics. We observe that this effect is independent of the method of imposing the temperature gradient, heat flux, as well as imposed boundary conditions. We propose that simply dividing the nanoribbon in long and short sections using a partially immobilized area will lead to excitation of long-wavelength vibrations into the long section of the nanoribbon. This results in simpler architectures for heat-to-vibration converter devices based on graphene. Furthermore, we observe that applying tensile axial strain to nanoribbons facilitates vibrational instability by reducing the required threshold heat flux or the temperature gradient. Finally, we discuss the role played by Umklapp scattering for physical mechanisms behind these observations.
5.	Ahlberg Helgee, Edit, 1986, et al. (författare) Adsorption of metal atoms at a buckled graphene grain boundary using model potentials 2016 Ingår i: AIP Advances. - : AIP Publishing. - 2158-3226 .- 2158-3226. ; 6:1 Tidskriftsartikel (refereegranskat)abstract Two model potentials have been evaluated with regard to their ability to model adsorption of single metal atoms on a buckled graphene grain boundary. One of the potentials is a Lennard-Jones potential parametrized for gold and carbon, while the other is a bond-order potential parametrized for the interaction between carbon and platinum. Metals are expected to adsorb more strongly to grain boundaries than to pristine graphene due to their enhanced adsorption at point defects resembling those that constitute the grain boundary. Of the two potentials considered here, only the bond-order potential reproduces this behavior and predicts the energy of the adsorbate to be about 0.8 eV lower at the grain boundary than on pristine graphene. The Lennard-Jones potential predicts no significant difference in energy between adsorbates at the boundary and on pristine graphene. These results indicate that the Lennard-Jones potential is not suitable for studies of metal adsorption on defects in graphene, and that bond-order potentials are preferable.
6.	Ahlberg Helgee, Edit, 1986, et al. (författare) Diffraction and near-zero transmission of flexural phonons at graphene grain boundaries 2015 Ingår i: Physical Review B - Condensed Matter and Materials Physics. - 2469-9950 .- 2469-9969. ; 91:20 Tidskriftsartikel (refereegranskat)abstract Graphene grain boundaries are known to affect phonon transport and thermal conductivity, suggesting that they may be used to engineer the phononic properties of graphene. Here, the effect of two buckled grain boundaries on long-wavelength flexural acoustic phonons has been investigated as a function of angle of incidence using molecular dynamics. The flexural acoustic mode has been chosen due to its importance to thermal transport. It is found that the transmission through the boundaries is strongly suppressed for incidence angles close to 35 degrees. Also, the grain boundaries are found to act as diffraction gratings for the phonons.
7.	Ahlberg Helgee, Edit, 1986, et al. (författare) Scattering of flexural acoustic phonons at grain boundaries in graphene 2014 Ingår i: Physical Review B - Condensed Matter and Materials Physics. - 2469-9950 .- 2469-9969. ; 90:4 Tidskriftsartikel (refereegranskat)abstract We investigate the scattering of long-wavelength flexural phonons against grain boundaries in graphene using molecular dynamics simulations. Three symmetric tilt grain boundaries are considered: one with a misorientation angle of 17.9 degrees displaying an out-of-plane buckling 1.5 nm high and 5 nm wide, one with a misorientation angle of 9.4 degrees and an out-of-plane buckling 0.6 nm high and 1.7 nm wide, and one with a misorientation angle of 32.2 degrees and no out-of-plane buckling. At the flat grain boundary, the phonon transmission exceeds 95% for wavelengths above 1 nm. The buckled boundaries have a substantially lower transmission in this wavelength range, with a minimum transmission of 20% for the 17.9 degrees boundary and 40% for the 9.4 degrees boundary. At the buckled boundaries, coupling between flexural and longitudinal phonon modes is also observed. The results indicate that scattering of long-wavelength flexural phonons at grain boundaries in graphene is mainly due to out-of-plane buckling. A continuum mechanical model of the scattering process has been developed, providing a deeper understanding of the scattering process as well as a way to calculate the effect of a grain boundary on long-wavelength flexural phonons based on the buckling size.
8.	Atalaya, Juan, 1981, et al. (författare) Continuum elastic modeling of graphene resonators 2008 Ingår i: Nano Letters. - 1530-6992 .- 1530-6984. ; 8:12, s. 4196-4200 Tidskriftsartikel (refereegranskat)abstract Starting from an atomistic approach, we have derived a hierarchy of successively more simplified continuum elasticity descriptions for modeling the mechanical properties of suspended graphene sheets. We find that already for deflections of the order of 0.5 Å a theory that correctly accounts for nonlinearities is necessary and that for many purposes a set of coupled Duffing-type equations may be used to accurately describe the dynamics of graphene membranes. The descriptions are validated by applying them to square graphene-based resonators with clamped edges and studying numerically their mechanical responses. Both static and dynamic responses are treated, and we find good agreement with recent experimental findings.
9.	Atalaya, Juan, 1981, et al. (författare) Diffusion-Induced Bistability of Driven Nanomechanical Resonators 2011 Ingår i: Physical Review Letters. - 1079-7114 .- 0031-9007. ; 106:22 Tidskriftsartikel (refereegranskat)abstract We study nanomechanical resonators with frequency fluctuations due to diffusion of absorbed particles. The diffusion depends on the vibration amplitude through inertial effect. We find that, if the diffusion coefficient D is sufficiently large, the resonator response to periodic driving displays bistability. The lifetime of the coexisting vibrational states exponentially increases with increasing D and displays a scaling dependence on the parameters close to bifurcation points.
10.	Atalaya, Juan, 1981, et al. (författare) Diffusion-induced dephasing in nanomechanical resonators 2011 Ingår i: Physical Review B - Condensed Matter and Materials Physics. - 2469-9950 .- 2469-9969. ; 83:4 Tidskriftsartikel (refereegranskat)abstract We study resonant response of an underdamped nanomechanical resonator with fluctuating frequency. The fluctuations are due to diffusion of molecules or microparticles along the resonator. They lead to broadening and change of shape of the oscillator spectrum. The spectrum is found for the diffusion confined to a small part of the resonator and where it occurs along the whole nanobeam. The analysis is based on extending to the continuous limit, and appropriately modifying, the method of interfering partial spectra. We establish the conditions of applicability of the fluctuation-dissipation relations between the susceptibility and the power spectrum. We also find where the effect of frequency fluctuations can be described by a convolution of the spectra without these fluctuations and with them as the only source of the spectral broadening.
11.	Atalaya, Juan, 1981, et al. (författare) Elasticity theory for graphene membranes 2010 Ingår i: Adsorption and Phase Behaviour in Nanochannels and Nanotubes. - Dordrecht : Springer Netherlands. - 9789048124800 ; , s. 273-290 Bokkapitel (övrigt vetenskapligt/konstnärligt)abstract Starting from an atomistic approach we have derived a hierarchy of successively more simplified continuum elasticity descriptions for modeling the mechanical properties of suspended graphene sheets. We find that already for deflections of the order of 0.5∈Å a theory that correctly accounts for nonlinearities is necessary and that for many purposes a set of coupled Duffing-type equations may be used to accurately describe the dynamics of graphene membranes. The descriptions are validated by applying them to square graphene-based resonators with clamped edges and studying numerically their mechanical responses. Both static and dynamic responses are treated, and we find good agreement with recent experimental findings. © 2010 Springer Science+Business Media B.V.
12.	Atalaya, Juan, 1981, et al. (författare) Nanomechanical mass measurement using nonlinear response of a graphene membrane 2010 Ingår i: Europhysics Letters. - : IOP Publishing. - 0295-5075 .- 1286-4854. ; 91:4 Tidskriftsartikel (refereegranskat)abstract We propose a scheme to measure the mass of a single particle using the nonlinear response of a 2D nanoresonator with degenerate eigenmodes. Using numerical and analytical calculations, we show that by driving a square graphene nanoresonator into the nonlinear regime, simultaneous determination of the mass and position of an added particle is possible. Moreover, this scheme only requires measurements in a narrow frequency band near the fundamental resonance.
13.	Bengtsson, Stefan, 1961, et al. (författare) Carbon-based nanoelectromechanical devices 2009 Ingår i: Advanced workshop on Frontiers in Electronics (invited paper). Konferensbidrag (refereegranskat)
14.	Croy, Alexander, 1981, et al. (författare) Nonlinear damping in graphene resonators 2012 Ingår i: Physical Review B - Condensed Matter and Materials Physics. - 2469-9950 .- 2469-9969. ; 86:23, s. Article Number: 235435- Tidskriftsartikel (refereegranskat)abstract Based on a continuum mechanical model for single-layer graphene, we propose and analyze a microscopic mechanism for dissipation in nanoelectromechanical graphene resonators. We find that coupling between flexural modes and in-plane phonons leads to linear and nonlinear damping of out-of-plane vibrations. By tuning external parameters such as bias and ac voltages, one can cross over from a linear-to a nonlinear-damping dominated regime. We discuss the behavior of the effective quality factor in this context. DOI: 10.1103/PhysRevB.86.235435
15.	Edblom, Christin, 1985, et al. (författare) Diffusion-induced dissipation and mode coupling in nanomechanical resonators 2014 Ingår i: Physical Review B - Condensed Matter and Materials Physics. - 2469-9950 .- 2469-9969. ; 90:15, s. Art. no. 155425- Tidskriftsartikel (refereegranskat)abstract We study a system consisting of a particle adsorbed on a carbon nanotube resonator. The particle is allowed to diffuse along the resonator, in order to enable study of, e.g., room-temperature mass sensing devices. The system is initialized in a state where only the fundamental vibration mode is excited, and the ring-down of the system is studied by numerically and analytically solving the stochastic equations of motion. We find two mechanisms of dissipation, induced by the diffusing adsorbate. First, short-time correlations between particle and resonator motions means that the net effect of the former on the latter does not average out, but instead causes nonexponential dissipation of vibrational energy. For vibrational amplitudes that are much larger than the thermal energy this dissipation is linear; for small amplitudes the decay takes the same form as that of a nonlinearly damped oscillator. Second, the particle diffusion mediates a coupling between vibration modes that opens a new dissipation channel by enabling energy transfer from the fundamental mode to the excited modes, which rapidly reach thermal equilibrium.
16.	Eriksson, Martin, 1989, et al. (författare) Frequency tuning, nonlinearities and mode coupling in circular mechanical graphene resonators 2013 Ingår i: Nanotechnology. - : IOP Publishing. - 1361-6528 .- 0957-4484. ; 24:39, s. srt. no. 395702- Tidskriftsartikel (refereegranskat)abstract We study circular nanomechanical graphene resonators by means of continuum elasticity theory, treating them as membranes. We derive dynamic equations for the flexural mode amplitudes. Due to the geometrical nonlinearity the mode dynamics can be modeled by coupled Duffing equations. By solving the Airy stress problem we obtain analytic expressions for the eigenfrequencies and nonlinear coefficients as functions of the radius, suspension height, initial tension, back-gate voltage and elastic constants, which we compare with finite element simulations. Using perturbation theory, we show that it is necessary to include the effects of the non-uniform stress distribution for finite deflections. This correctly reproduces the spectrum and frequency tuning of the resonator, including frequency crossings.
17.	Güttinger, J., et al. (författare) Energy-dependent path of dissipation in nanomechanical resonators 2017 Ingår i: Nature Nanotechnology. - : Springer Science and Business Media LLC. - 1748-3387 .- 1748-3395. ; 12:7, s. 631-636 Tidskriftsartikel (refereegranskat)abstract Energy decay plays a central role in a wide range of phenomena, such as optical emission, nuclear fission, and dissipation in quantum systems. Energy decay is usually described as a system leaking energy irreversibly into an environmental bath. Here, we report on energy decay measurements in nanomechanical systems based on multilayer graphene that cannot be explained by the paradigm of a system directly coupled to a bath. As the energy of a vibrational mode freely decays, the rate of energy decay changes abruptly to a lower value. This finding can be explained by a model where the measured mode hybridizes with other modes of the resonator at high energy. Below a threshold energy, modes are decoupled, resulting in comparatively low decay rates and giant quality factors exceeding 1 million. Our work opens up new possibilities to manipulate vibrational states, engineer hybrid states with mechanical modes at completely different frequencies, and to study the collective motion of this highly tunable system.
18.	Hakkinen, P., et al. (författare) Charge Sensitivity Enhancement via Mechanical Oscillation in Suspended Carbon Nanotube Devices 2015 Ingår i: Nano Letters. - : American Chemical Society (ACS). - 1530-6992 .- 1530-6984. ; 15:3, s. 1667-1672 Tidskriftsartikel (refereegranskat)abstract Single electron transistors (SETs) fabricated from single-walled carbon nanotubes (SWNTs) can be operated as highly sensitive charge detectors reaching sensitivity levels comparable to metallic radio frequency SETs (rf-SETs). Here, we demonstrate how the charge sensitivity of the device can be improved by using the mechanical oscillations of a single-walled carbon nanotube quantum dot. To optimize the charge sensitivity dQ, we drive the mechanical resonator far into the nonlinear regime and bias it to an operating point where the mechanical third order nonlinearity is canceled out. This way we enhance dQ, from 6 mu e/(Hz)(1/2) for the static case to 0.97 mu e/(Hz)(1/2) at a probe frequency of similar to 1.3 kHz.
19.	Isacsson, Andreas, 1975, et al. (författare) Accelerating a car from rest : friction, power and forces 2023 Ingår i: Physics Education. - 0031-9120 .- 1361-6552. ; 58:5 Tidskriftsartikel (refereegranskat)abstract The directions of frictional forces for bodies in motion are conceptually challenging. Students may be able to provide a correct solution using only calculus without drawing free-body diagrams. This can make their misconceptions go unnoticed and put them at risk to become further reinforced. Here, we discuss first-year bachelor students’ responses to multiple-choice questions and an open-ended question regarding friction when they come fresh out of high school. We further look into student solutions submitted to a national competition in physics for high-school students involving a problem concerning the acceleration of an electric rear-wheel drive car. Finding that most students had avoided drawing figures, we discuss to what extent teachers’ grading practices contribute to students’ development of problem-solving habits.
20.	Isacsson, Andreas, 1975, et al. (författare) Electronic superlattices in corrugated graphene 2008 Ingår i: Physical Review B. - 1098-0121. ; 77:3, s. 035423- Tidskriftsartikel (refereegranskat)abstract We theoretically investigate electron transport through corrugated graphene ribbons and show how the ribbon curvature leads to an electronic superlattice with a period set by the corrugation wavelength. Transport through the ribbon depends sensitively on the superlattice band structure which, in turn, strongly depends on the geometry of the deformed sheet. In particular, we find that for ribbon widths where the transverse level separation is comparable to the band edge energy, a strong current switching occurs as a function of an applied back gate voltage. Thus, artificially corrugated graphene sheets or ribbons can be used for the study of Dirac fermions in periodic potentials. Furthermore, this provides an additional design degree of freedom for graphene-based electronics.
21.	Isacsson, Andreas, 1975, et al. (författare) Low-frequency current noise of the single-electron shuttle 2004 Ingår i: Europhysics Letters. - : IOP Publishing. - 0295-5075 .- 1286-4854. ; 66:5, s. 708-714 Tidskriftsartikel (refereegranskat)abstract Coupling between electronic and mechanical degrees of freedom in a single-electron shuttle system can cause a mechanical instability leading to shuttle transport of electrons between external leads. We predict that the resulting low-frequency current noise can be enhanced due to slow fluctuations of the shuttle oscillation energy. Moreover, at the onset of mechanical instability a pronounced peak in the low-frequency noise is expected.
22.	Isacsson, Andreas, 1975 (författare) Mechanically mediated charge transfer in nanostructures 2000 Licentiatavhandling (övrigt vetenskapligt/konstnärligt)
23.	Isacsson, Andreas, 1975 (författare) Nanomechanical displacement detection using coherent transport in graphene nanoribbon resonators 2011 Ingår i: Physical Review B - Condensed Matter and Materials Physics. - 2469-9950 .- 2469-9969. ; 84:12 Tidskriftsartikel (refereegranskat)abstract Graphene nanoribbons provide an opportunity to integrate phase-coherent transport phenomena with nanoelectromechanical systems (NEMS). Due to the strain induced by a deflection in a graphene nanoribbon resonator, coherent electron transport and mechanical deformations couple. This coupling can be used for sensitive displacement detection in both armchair and zigzag graphene nanoribbon NEMS. Here it is shown that for ordered as well as disordered ribbon systems of length L, a strain epsilon similar to (w/L)(2) due to a deflection w leads to a relative change in conductance delta G/G similar to (w(2)/a(0)L), where a(0) approximate to 1.4 angstrom.
24.	Isacsson, Andreas, 1975, et al. (författare) Nonlinear resonance in a three-terminal carbon nanotube resonator 2007 Ingår i: Nanotechnology. ; 18:19, s. 195203- Tidskriftsartikel (refereegranskat)
25.	Isacsson, Andreas, 1975, et al. (författare) Parametric resonances in electrostatically interacting carbon nanotube arrays 2009 Ingår i: Physical Review B - Condensed Matter and Materials Physics. - 2469-9950 .- 2469-9969. ; 79:16, s. 165418- Tidskriftsartikel (refereegranskat)abstract We study, numerically and analytically, a model of a one-dimensional array of carbon nanotube resonators in a two-terminal configuration. The system is brought into resonance upon application of an ac signal superimposed on a dc bias voltage. When the tubes in the array are close to each other, electrostatic interactions between tubes become important for the array dynamics. We show that both transverse and longitudinal parametric resonances can be excited in addition to primary resonances. The intertube electrostatic interactions couple modes in orthogonal directions and affect the mode stability.
26.	Isacsson, Andreas, 1975, et al. (författare) Reply to comment on ‘Accelerating a car from rest: friction, power and forces’ 2024 Ingår i: Physics Education. - 1361-6552 .- 0031-9120. ; 59:3 Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)
27.	Isacsson, Andreas, 1975, et al. (författare) Scaling properties of polycrystalline graphene: A review 2017 Ingår i: 2D Materials. - : IOP Publishing. - 2053-1583. ; 4:1 Forskningsöversikt (refereegranskat)abstract We present an overview of the electrical, mechanical, and thermal properties of polycrystalline graphene. Most global properties of this material, such as the charge mobility, thermal conductivity, or Young's modulus, are sensitive to its microstructure, for instance the grain size and the presence of line or point defects. Both the local and global features of polycrystalline graphene have been investigated by a variety of simulations and experimental measurements. In this review, we summarize the properties of polycrystalline graphene, and by establishing a perspective on how the microstructure impacts its large-scale physical properties, we aim to provide guidance for further optimization and improvement of applications based on this material, such as flexible and wearable electronics, and high-frequency or spintronic devices.
28.	Isacsson, Andreas, 1975 (författare) Shuttle Transport of Charge in Normal and Superconducting Nanostructures 2002 Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract In nanoscale systems, accumulation of charge is associated with large charging energies. If the forces arising due to the Coulomb interaction are comparable to the rigidity of the structures mechanical deformations can couple to the electronic degrees of freedom. Using analytical and numerical methods, the interplay between charge transfer and mechanical motion has been studied in both normal and superconducting double junction geometries. In the first part of this thesis, the dynamics of a Coulomb blockade double junction where the central island may execute one dimensional center-of-mass motion in a harmonic potential are considered. It is shown that, for sufficiently large bias voltages, a dynamical instability occurs. The instability leads to a new shuttle mechanism for charge transfer where the island executes periodic motion thereby transferring charge mechanically between the leads. This is reflected in the zero temperature I - V characteristics as steps of quantized current in units of the grain vibration frequency and the electron charge. It is also shown that the onset of the mechanical instability can be associated with hysteresis in the I - V curves. Further, by considering a similar system, a mechanically flexible three terminal device in the high temperature limit, an example of electromechanical coupling leading to chaotic behavior is demonstrated. Finally, coherent charge transport in a superconducting shuttle junction is considered. This junction, a movable single-Cooper-pair box, consists of an externally driven grain oscillating between two remote superconducting leads. Close to each lead gates ensure degeneracy between nearby charge states. The degeneracy allows for a coherent superposition of zero and one extra Cooper pair on the grain and, hence, mechanically assisted coherent charge transport between the leads. Two different limiting cases are treated here; strongly and weakly coupled leads. In the first case it is shown that the shuttle junction can support a nonzero super current between two phase biased leads. In the second case, it is demonstrated that shuttle junction operation can establish phase coherence between two initially disconnected leads.
29.	Kateb, Movaffaq, 1985, et al. (författare) Nanoscale Elasto-Capillarity in the Graphene-Water System under Tension: Revisiting the Assumption of a Constant Wetting Angle 2023 Ingår i: Langmuir. - 1520-5827 .- 0743-7463. ; 39, s. 12610-12617 Tidskriftsartikel (refereegranskat)abstract Wetting highly compliant surfaces can cause them to deform. Atomically thin materials, such as graphene, can have exceptionally small bending rigidities, leading to elasto-capillary lengths of a few nanometers. Using large-scale molecular dynamics (MD), we have studied the wetting and deformation of graphene due to nanometer-sized water droplets, focusing on the wetting angle near the vesicle transition. Recent continuum theories for wetting of flexible membranes reproduce our MD results qualitatively well. However, we find that when the curvature is large at the triple-phase contact line, the wetting angle increases with decreasing tension. This is in contrast to existing macroscopic theories but can be amended by allowing for a variable wetting angle.
30.	Kaunisto, R., et al. (författare) Nanotube Device 2010 Patent (övrigt vetenskapligt/konstnärligt)
31.	Laitinen, Antti, et al. (författare) A graphene resonator as an ultrasound detector for generalized Love waves in a polymer film with two level states 2019 Ingår i: Journal of Physics D: Applied Physics. - : IOP Publishing. - 1361-6463 .- 0022-3727. ; 52:24 Tidskriftsartikel (refereegranskat)abstract We have investigated surface shear waves at 22 MHz in a 0.5 micron thick polymer film on a SiO2/Si substrate at low temperatures using suspended and non-suspended graphene as detectors. By tracking ultrasound modes detected by oscillations of a trilayer graphene membrane both in vacuum and in helium superfluid, we assign the resonances to surface shear modes, generalized Love waves, in the resist/silicon-substrate system loaded with gold. The propagation velocity of these shear modes displays a logarithmic temperature dependence below 1 K, which is characteristic for modification of the elastic properties of a disordered solid owing to a large density of two level state systems. For the dissipation of the shear mode, we find a striking logarithmic temperature dependence, which indicates a basic relation between the speed of the surface wave propagation and the mode dissipation.
32.	Lindahl, Niklas, 1981, et al. (författare) Determination of the Bending Rigidity of Graphene via Electrostatic Actuation of Buckled Membranes 2012 Ingår i: Nano Letters. - : American Chemical Society (ACS). - 1530-6984 .- 1530-6992. ; 12:7, s. 3526-3531 Tidskriftsartikel (refereegranskat)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.
33.	Mahendran, Srinivasan, 1989, et al. (författare) Quantitative Predictions of the Thermal Conductivity in Transition Metal Dichalcogenides: Impact of Point Defects in MoS 2 and WS 2 Monolayers 2024 Ingår i: Journal of Physical Chemistry C. - 1932-7447 .- 1932-7455. ; 128:4, s. 1709-1716 Tidskriftsartikel (refereegranskat)abstract Transition metal dichalcogenides are investigated for various applications at the nanoscale because of their unique combination of properties and dimensionality. For many of the anticipated applications, heat conduction plays an important role. At the same time, these materials often contain relatively large amounts of point defects. Here, we provide a systematic analysis of the impact of intrinsic and selected extrinsic defects on the lattice thermal conductivity of MoS2 and WS2 monolayers. We combine Boltzmann transport theory and Green’s function-based T-matrix approach for the calculation of scattering rates. The force constants for the defect configurations are obtained from density functional theory calculations via a regression approach, which allows us to sample a rather large number of defects at a moderate computational cost and to systematically enforce both the translational and rotational acoustic sum rules. The calculated lattice thermal conductivity is in quantitative agreement with the experimental data for heat transport and defect concentrations for both MoS2 and WS2. Crucially, this demonstrates that the strong deviation from a 1/T temperature dependence of the lattice thermal conductivity observed experimentally can be fully explained by the presence of point defects. We furthermore predict the scattering strengths of the intrinsic defects to decrease in the sequence VMo ≈ V2S= > V2S⊥ > VS > Sad in both materials, while the scattering rates for the extrinsic (adatom) defects decrease with increasing mass such that Liad > Naad > Kad. Compared with earlier work, we find that both intrinsic and extrinsic adatoms are relatively weak scatterers. We attribute this difference to the treatment of the translational and rotational acoustic sum rules, which, if not enforced, can lead to spurious contributions in the zero-frequency limit.
34.	McDermott, Thomas, et al. (författare) Strong mechanically induced effects in DC current-biased suspended Josephson junctions 2018 Ingår i: Physical Review B. - 2469-9969 .- 2469-9950. ; 97:1 Tidskriftsartikel (refereegranskat)abstract Superconductivity is a result of quantum coherence at macroscopic scales. Two superconductors separated by a metallic or insulating weak link exhibit the AC Josephson effect: the conversion of a DC voltage bias into an AC supercurrent. This current may be used to activate mechanical oscillations in a suspended weak link. As the DC-voltage bias condition is remarkably difficult to achieve in experiments, here we analyze theoretically how the Josephson effect can be exploited to activate and detect mechanical oscillations in the experimentally relevant condition with purely DC current bias. We unveil how changing the strength of the electromechanical coupling results in two qualitatively different regimes showing dramatic effects of the oscillations on the DC-voltage characteristic of the device. These include the appearance of Shapiro-type plateaus for weak coupling and a sudden mechanically induced retrapping for strong coupling. Our predictions, measurable in state-of-the-art experimental setups, allow the determination of the frequency and quality factor of the resonator using DC only techniques.
35.	Midtvedt, Daniel, 1988, et al. (författare) Fermi-Pasta-Ulam Physics with Nanomechanical Graphene Resonators: Intrinsic Relaxation and Thermalization from Flexural Mode Coupling 2014 Ingår i: Physical Review Letters. - 1079-7114 .- 0031-9007. ; 112:14 Tidskriftsartikel (refereegranskat)abstract Thermalization in nonlinear systems is a central concept in statistical mechanics and has been extensively studied theoretically since the seminal work of Fermi, Pasta, and Ulam. Using molecular dynamics and continuum modeling of a ring-down setup, we show that thermalization due to nonlinear mode coupling intrinsically limits the quality factor of nanomechanical graphene drums and turns them into potential test beds for Fermi-Pasta-Ulam physics. We find the thermalization rate Gamma to be independent of radius and scaling as Gamma similar to T* /is an element of(2)(pre), where T* and is an element of(pre) are effective resonator temperature and prestrain.
36.	Midtvedt, Daniel, 1988, et al. (författare) Nonlinear phononics using atomically thin membranes 2014 Ingår i: Nature Communications. - : Springer Science and Business Media LLC. - 2041-1723 .- 2041-1723. ; 5, s. Article No. 4838 - Tidskriftsartikel (refereegranskat)abstract Phononic crystals and acoustic metamaterials are used to tailor phonon and sound propagation properties by utilizing artificial, periodic structures. Analogous to photonic crystals, phononic band gaps can be created, which influence wave propagation and, more generally, allow engineering of the acoustic properties of a system. Beyond that, nonlinear phenomena in periodic structures have been extensively studied in photonic crystals and atomic Bose-Einstein condensates in optical lattices. However, creating nonlinear phononic crystals or nonlinear acoustic metamaterials remains challenging and only few examples have been demonstrated. Here, we show that atomically thin and periodically pinned membranes support coupled localized modes with nonlinear dynamics. The proposed system provides a platform for investigating nonlinear phononics.
37.	Morell, Nicolas, et al. (författare) Optomechanical Measurement of Thermal Transport in Two-Dimensional MoSe2 Lattices 2019 Ingår i: Nano Letters. - : American Chemical Society (ACS). - 1530-6992 .- 1530-6984. ; 19:5, s. 3143-3150 Tidskriftsartikel (refereegranskat)abstract Nanomechanical resonators have emerged as sensors with exceptional sensitivities. These sensing capabilities open new possibilities in the studies of the thermodynamic properties in condensed matter. Here, we use mechanical sensing as a novel approach to measure the thermal properties of low-dimensional materials. We measure the temperature dependence of both the thermal conductivity and the specific heat capacity of a transition metal dichalcogenide monolayer down to cryogenic temperature, something that has not been achieved thus far with a single nanoscale object. These measurements show how heat is transported by phonons in two-dimensional systems. Both the thermal conductivity and the specific heat capacity measurements are consistent with predictions based on first-principles.
38.	Rhen, Christin, 1985, et al. (författare) Noise-tunable nonlinearity in a dispersively coupled diffusion-resonator system using superconducting circuits 2017 Ingår i: Scientific Reports. - : Springer Science and Business Media LLC. - 2045-2322 .- 2045-2322. ; 7, s. 41313- Tidskriftsartikel (refereegranskat)abstract The harmonic oscillator is one of the most widely used model systems in physics: an indispensable theoretical tool in a variety of fields. It is well known that an otherwise linear oscillator can attain novel and nonlinear features through interaction with another dynamical system. We investigate such an interacting system: a superconducting LC-circuit dispersively coupled to a superconducting quantum interference device (SQUID). We find that the SQUID phase behaves as a classical two-level system, whose two states correspond to one linear and one nonlinear regime for the LC-resonator. As a result, the circuit's response to forcing can become multistable. The strength of the nonlinearity is tuned by the level of noise in the system, and increases with decreasing noise. This tunable nonlinearity could potentially find application in the field of sensitive detection, whereas increased understanding of the classical harmonic oscillator is relevant for studies of the quantum-to-classical crossover of JaynesCummings systems. DO B, 2009
39.	Rhen, Christin, 1985, et al. (författare) Particle number scaling for diffusion-induced dissipation in graphene and carbon nanotube nanomechanical resonators 2016 Ingår i: Physical Review B. - 2469-9969 .- 2469-9950. ; 93:12 Tidskriftsartikel (refereegranskat)abstract When a contaminant diffuses on the surface of a nanomechanical resonator, the motions of the two become correlated. Despite being a high-order effect in the resonator-particle coupling, such correlations affect the system dynamics by inducing dissipation of the resonator energy. Here, we consider this diffusion-induced dissipation in the cases of multiple particles adsorbed on carbon nanotube and graphene resonators. By solving the stochastic equations of motion, we simulate the ringdown of the resonator, in order to determine the resonator energy decay rate. We find two different scalings with the number of adsorbed particles K and particle mass m. In the regime where the adsorbates are inertially trapped at an antinode of vibration, the dissipation rate Gamma scales with the total adsorbed mass Gamma alpha Km. In contrast, in the regime where particles diffuse freely over the resonator, the dissipation rate scales as the product of the total adsorbed mass and the individual particle mass: Gamma alpha Km(2).
40.	Rhen, Christin, 1985, et al. (författare) Stepwise relaxation and stochastic precession in degenerate oscillators dispersively coupled to particles 2017 Ingår i: Physical Review B - Condensed Matter and Materials Physics. - 2469-9950 .- 2469-9969. ; 96, s. 104302- Tidskriftsartikel (refereegranskat)abstract By numerical integration, we study the relaxation dynamics of degenerate harmonic oscillator modes dispersively coupled to particle positions. Depending on whether the effective inertial potential induced by the oscillators keeps the particles confined or if the particle trajectories traverse the system, the local oscillator energy dissipation rate changes drastically. The inertial trapping, release, and retrapping of particles result in a characteristic stepwise relaxation process, with alternating regions of fast and slow dissipation. To demonstrate this phenomenon we consider first a one-dimensional minimal prototype model which displays these characteristics. We then treat the effect of dispersive interaction in a model corresponding to an adsorbate diffusing on a circular membrane interacting with its three lowest vibrational modes. In the latter model, stepwise relaxation appears only in the presence of thermal noise, which also causes a slow-in-time stochastic precession of the mixing angle between the degenerate eigenmodes.
41.	Rieger, J., et al. (författare) Energy losses of nanomechanical resonators induced by atomic force microscopy- controlled mechanical impedance mismatching 2014 Ingår i: Nature Communications. - : Springer Science and Business Media LLC. - 2041-1723 .- 2041-1723. ; 5 Tidskriftsartikel (refereegranskat)abstract Clamping losses are a widely discussed damping mechanism in nanoelectromechanical systems, limiting the performance of these devices. Here we present a method to investigate this dissipation channel. Using an atomic force microscope tip as a local perturbation in the clamping region of a nanoelectromechanical resonator, we increase the energy loss of its flexural modes by at least one order of magnitude. We explain this by a transfer of vibrational energy into the cantilever, which is theoretically described by a reduced mechanical impedance mismatch between the resonator and its environment. A theoretical model for this mismatch, in conjunction with finite element simulations of the evanescent strain field of the mechanical modes in the clamping region, allows us to quantitatively analyse data on position and force dependence of the tip-induced damping. Our experiments yield insights into the damping of nanoelectromechanical systems with the prospect of engineering the energy exchange in resonator networks.
42.	Samadikhah, Kaveh, 1982, et al. (författare) General elasticity theory for graphene membranes based on molecular dynamics 2007 Ingår i: Materials Research Society Symposium Proceedings. - 0272-9172. - 9781605608266 ; 1057, s. 109-114 Konferensbidrag (refereegranskat)abstract We have studied the mechanical properties of suspended graphene membranes using molecular dynamics (MD) and generalized continuum elasticity theory (GE) in order to develop and assess a continuum description for graphene. The MD simulations are based on a valence force field model which is used to determine the deformation and the elastic energy of the membrane (EMD) as a function of external forces. For the continuum description, we use the expression Econt = Estretching + Ebending for the elastic energy functional. The elastic parameters (tensile rigidity and Poisson ratio) entering Econt are determined by requiring that E cont = EMD for a set of deformations. Comparisons with the MD results show excellent agreement. We find that the elastic energy of a supported graphene sheets is typically dominated by the nonlinear stretching terms whereas a linear description is valid only for very small deflections. This implies that in some applications, i.e. NEMS, a linear description is of limited applicability.
43.	Tassin, Philippe, 1982, et al. (författare) Multifunctional Teaching Studios for Virtual Classrooms during the Pandemic and Beyuond 2021 Ingår i: Optics InfoBase Conference Papers. Konferensbidrag (refereegranskat)abstract We will discuss the studios that we have built to livestream diffrent learning activites for virtual classrooms. We will show how to optimize the experience for both students and instructors and bring back interactivity.
44.	Tomi, M., et al. (författare) Buckled diamond-like carbon nanomechanical resonators 2015 Ingår i: Nanoscale. - : Royal Society of Chemistry (RSC). - 2040-3372 .- 2040-3364. ; 7:35, s. 14747-14751 Tidskriftsartikel (refereegranskat)abstract We have developed capacitively-transduced nanomechanical resonators using sp(2)-rich diamond-like carbon (DLC) thin films as conducting membranes. The electrically conducting DLC films were grown by physical vapor deposition at a temperature of 500 degrees C. Characterizing the resonant response, we find a larger than expected frequency tuning that we attribute to the membrane being buckled upwards, away from the bottom electrode. The possibility of using buckled resonators to increase frequency tuning can be of advantage in rf applications such as tunable GHz filters and voltage-controlled oscillators.
45.	Voje, Aurora, 1985, et al. (författare) Entanglement dynamics of quantum oscillators nonlinearly coupled to thermal environments 2015 Ingår i: Physical Review A - Atomic, Molecular, and Optical Physics. - 2469-9926 .- 2469-9934. ; 92:1 Tidskriftsartikel (refereegranskat)abstract We study the asymptotic entanglement of two quantum harmonic oscillators nonlinearly coupled to an environment. Coupling to independent baths and a common bath are investigated. Numerical results obtained using the Wangsness-Bloch-Redfield method are supplemented by analytical results in the rotating wave approximation. The asymptotic negativity as function of temperature, initial squeezing, and coupling strength, is compared to results for systems with linear system-reservoir coupling. We find that, due to the parity-conserving nature of the coupling, the asymptotic entanglement is considerably more robust than for the linearly damped cases. In contrast to linearly damped systems, the asymptotic behavior of entanglement is similar for the two bath configurations in the nonlinearly damped case. This is due to the two-phonon system-bath exchange causing a suppression of information exchange between the oscillators via the bath in the common-bath configuration at low temperatures.
46.	Voje, Aurora, 1985, et al. (författare) Entanglement Dynamics of Quantum Oscillators Nonlinearly Coupled to Thermal Environments 2014 Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract We study the asymptotic entanglement of two quantum harmonic oscillators nonlinearly coupledto an environment. Coupling to independent baths and a common bath are investigated. Numericalresults obtained using the Wangsness-Bloch-Redeld method are supplemented by analytical resultsin the rotating wave approximation. The asymptotic negativity as function of temperature, initialsqueezing and coupling strength, is compared to results for systems with linear system-reservoir coupling.We nd that due to the parity conserving nature of the coupling, the asymptotic entanglementis considerably more robust than for the linearly damped cases. In contrast to linearly damped systems,the asymptotic behavior of entanglement is similar for the two bath congurations in thenonlinearly damped case. This is due to the two-phonon system-bath exchange causing a supressionof information exchange between the oscillators via the bath in the common bath conguration at low temperatures.
47.	Voje, Aurora, 1985, et al. (författare) Generating macroscopic superposition states in nanomechanical graphene resonators 2012 Ingår i: Physical Review B - Condensed Matter and Materials Physics. - 2469-9950 .- 2469-9969. ; 85:20 Tidskriftsartikel (refereegranskat)abstract A theoretical study of the quantum dynamics of a symmetric nanomechanical graphene resonator with degenerate flexural modes is presented. Applying voltage pulses to two back gates, flexural vibrations of the membrane can be selectively actuated and manipulated. For graphene, nonlinear response becomes important for amplitudes comparable to the magnitude of zero-point fluctuations. We show, using analytical and numerical methods, that this allows for creation of catlike superpositions of coherent states as well as superpositions of coherent catlike nonproduct states.
48.	Voje, Aurora, 1985, et al. (författare) Multi-phonon relaxation and generation of quantum states in a nonlinear mechanical oscillator 2013 Ingår i: New Journal of Physics. - : IOP Publishing. - 1367-2630. ; 15 Tidskriftsartikel (refereegranskat)abstract The dissipative quantum dynamics of an anharmonic oscillator is investigated theoretically in the context of carbon-based nano-mechanical systems. In the short-time limit, it is known that macroscopic superposition states appear for such oscillators. In the long-time limit, single- and multi-phonon dissipation lead to decoherence of the non-classical states. However, at zero temperature, as a result of two-phonon losses the quantum oscillator eventually evolves into a non-classical steady state. The relaxation of this state due to thermal excitations and one-phonon losses is numerically and analytically studied. The possibility of verifying the occurrence of the non-classical state is investigated and signatures of the quantum features arising in a ring-down setup are presented. The feasibility of the verification scheme is discussed in the context of quantum nano-mechanical systems.
49.	Voje, Aurora, 1985, et al. (författare) Nonlinear-dissipation-induced entanglement of coupled nonlinear oscillators 2013 Ingår i: Physical Review A - Atomic, Molecular, and Optical Physics. - 2469-9926 .- 2469-9934. ; 88:2 Tidskriftsartikel (refereegranskat)abstract The quantum dynamics of two weakly coupled nonlinear oscillators is analytically and numerically investigated in the context of nonlinear dissipation. The latter facilitates the creation and preservation of nonclassical steady states. Starting from a microscopic description of two oscillators individually interacting with their dissipative environments, it is found that in addition to energy relaxation, dephasing arises due to the mutual coupling. Using the negativity as an entanglement measure, it is shown that the coupling entangles the oscillators in the long-time limit. For finite temperatures, entanglement sudden death and rebirth are observed.

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