| 1. |
- Fian, Alexander, et al.
(författare)
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New Flexible Toolbox for Nanomechanical Measurements with Extreme Precision and at Very High Frequencies.
- 2010
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Ingår i: Nano Letters. - : American Chemical Society (ACS). - 1530-6992 .- 1530-6984. ; 10:Online August 26, 2010, s. 3893-3898
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Tidskriftsartikel (refereegranskat)abstract
- We show that the principally two-dimensional (2D) scanning tunneling microscope (STM) can be used for imaging of 1D micrometer high free-standing nanowires. We can then determine nanowire megahertz resonance frequencies, image their top-view 2D resonance shapes, and investigate axial stress on the nanoscale. Importantly, we demonstrate the extreme sensitivity of electron tunneling even at very high frequencies by measuring resonances at hundreds of megahertz with a precision far below the angstrom scale.
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| 2. |
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| 3. |
- Hällström, Waldemar, et al.
(författare)
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Fifteen-Piconewton Force Detection from Neural Growth Cones Using Nanowire Arrays
- 2010
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Ingår i: Nano Letters. - : American Chemical Society (ACS). - 1530-6992 .- 1530-6984. ; 10:3, s. 782-787
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Tidskriftsartikel (refereegranskat)abstract
- We used epitaxially grown monodisperse nanowire arrays to measure cellular forces with a spatial resolution of 1 mu m. Nerve cells were cultured on the array and cellular forces were calculated from the displacement of the nanowire tips. The measurements were done in situ on live cells using confocal microscopy, Forces down to 15 pN were measured on neural growth cones, showing that this method can be used to study the Fine details of growth-cone dynamics.
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| 4. |
- Lexholm, Monica, et al.
(författare)
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Optical determination of Young's modulus of InAs nanowires
- 2009
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Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 95:11
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Tidskriftsartikel (refereegranskat)abstract
- We present a study of Young's modulus of epitaxially grown InAs nanowires with diameters from 40 to 95 nm. The dynamic behavior of the nanowires is investigated using optical stroboscopic imaging. The Young's modulus, evaluated using the eigenfrequencies of the fundamental and the first excited modes in air, decreases for smaller diameters. To avoid the influence of the electric field on the resonance frequency, we use the free ring-down response to a voltage step rather than driving with a harmonic voltage. (C) 2009 American Institute of Physics. [doi: 10.1063/1.3225150]
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| 5. |
- Lexholm, Monica
(författare)
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Optical Imaging for Nanowire Mechanics
- 2010
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- In this work, we present a stroboscopic detection technique for the study of oscillating nanoscale objects. This optical read-out gives a position accuracy better than 1 nm which is a fraction of both the diffraction limit and the pixel size. The advantage of this stroboscopic method compared to conventional time-averaging techniques, is the time-resolution it provides as well as being non-invasive. Another advantage is that it can be readily applied to different experimental situations, the only requirement being that the dynamic behavior is repeated. The versatility of our detection technique allows for different types of actuation of the nanowire oscillation. Moreover, both the steady-state response to a harmonic force and the free ring-down response from a deflected position can be studied. In addition, the nanowire can be mounted with a side view or a top view and the surrounding pressure can be varied. The frequency response, the modal shapes, and the higher modes of epitaxially grown nanowires can be very well modeled using Euler-Bernoulli theory. However, one observed difference between the studied nanowires and macroscopic objects, is the size dependent Young's modulus, which decreases as the diameter is scaled down. Although the trend is quite vague, the Young's modulus of nanowires clearly deviates from that of bulk material. The nanowires are heavily damped at atmospheric pressure, resulting in Q factors of about 1-10. For pressures down to about 1 mbar, the Q factors increase as the surrounding pressure is decreased. For even lower pressure, the Q factors are constant, revealing that the damping is no longer due to the surrounding gas, but instead originates from intrinsic losses. At lower pressures, the damping is low enough to reveal that all the studied nanowires have split resonance frequencies, probably due to an asymmetric cross section. To investigate the direction of the oscillation in detail, the set-up is modified to enable a top view of the nanowire motion. For sensor applications, the spring constant is determined using the dimensions, the resonance frequency and the modal shape. The advantage of this method is that it is valid also for tapered nanowires, as it does not employ the Young's modulus. As a first step towards a mass sensor, a thin layer of gold is evaporated onto the nanowires and the resulting shift in resonance frequency is measured. The nanowires have also been used as force sensors for cellular forces. Nerve cells can be grown on arrays of nanowires. The living cells exert forces on the nanowires, causing the nanowires to bend. To correlate the cellular forces to the deflections of the nanowires, the static spring constant is determined through resonance frequency measurements.
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| 6. |
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| 7. |
- Lexholm, Monica, et al.
(författare)
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Optical interference from pairs and arrays of nanowires
- 2006
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Ingår i: Nano Letters. - : American Chemical Society (ACS). - 1530-6992 .- 1530-6984. ; 6:4, s. 862-865
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Tidskriftsartikel (refereegranskat)abstract
- The angle dependence of the scattered light from pairs and one-dimensional arrays of nanowires was studied. The intensity of the scattered light varied distinctly during rotation of the structure. The results could be theoretically modeled by treating a pair of nanowires as a double slit and an array of nanowires as a grating. The correspondence between theory and experimental results conclusively proves that the variations are due to the proposed interference effects.
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