| 1. |
- Chen, Jianing, et al.
(author)
-
Probing Strain in Bent Semiconductor Nanowires with Raman Spectroscopy.
- 2010
-
In: Nano Letters. - : American Chemical Society (ACS). - 1530-6992 .- 1530-6984. ; 10:4, s. 1280-1286
-
Journal article (peer-reviewed)abstract
- We present a noninvasive optical method to determine the local strain in individual semiconductor nanowires. InP nanowires were intentionally bent with an atomic force microscope and variations in the optical phonon frequency along the wires were mapped using Raman spectroscopy. Sections of the nanowires with a high curvature showed significantly broadened phonon lines. These observations together with deformation potential theory show that compressive and tensile strain inside the nanowires is the physical origin of the observed phonon energy variations.
|
|
| 2. |
- Conache, Gabriela, et al.
(author)
-
Bias-controlled friction of InAs nanowires on a silicon nitride layer studied by atomic force microscopy
- 2010
-
In: Physical Review B Condensed Matter. - College Park, Md. : American Physical Society. - 0163-1829 .- 1095-3795. ; 82:3
-
Journal article (peer-reviewed)abstract
- By studying how nanowires lying on a surface bend when pushed by an atomic force microscopy tip we are able to measure the friction between them and the substrate. Here, we show how the friction between InAs nanowires and an insulating silicon nitride layer varies when a dc voltage is applied to the tip during manipulation. The bias charges the capacitor formed by the wire and the grounded silicon back contact. Electrostatic forces increase the contact pressure and allow us to tune the friction between the wire and the silicon nitride surface. Using nanowires of about 40-70 nm diameter and a few microns in length we have applied biases in the range +12 to -12 V. A monotonic increase of the sliding friction with voltage was observed. This increase in friction with the normal force implies that the mesoscopic nanowire-surface system behaves like a macroscopic contact, despite the nanometer size of the contact in the direction of motion. The demonstrated bias-controlled friction has potential applications in MEMS/NEMS devices.
|
|
| 3. |
- Conache, Gabriela, et al.
(author)
-
Comparative friction measurements of InAs nanowires on three substrates
- 2010
-
In: Journal of Applied Physics. - College Park, MD : American Institute of Physics (AIP). - 0021-8979 .- 1089-7550. ; 108:9
-
Journal article (peer-reviewed)abstract
- We have investigated friction between InAs nanowires and three different substrates: SiO2, fluorosilanized SiO2, and Si3N4. The nanowires were pushed laterally with the tip of an atomic force microscope and the friction force per unit length for both static and sliding friction was deduced from the equilibrium shape of the bent wires. On all three substrates, thick wires showed a difference between sliding and static friction of up to three orders of magnitude. Furthermore, all substrates display a transition to stick-slip motion for nanowires with a diameter of less than about 40 nm. Hydrophobic and hydrophilic substrates display similar friction behavior suggesting that a condensed water layer does not strongly influence our results. The patterns and trends in the friction data are similar for all three substrates, which indicates that they are more fundamental in character and not specific to a single substrate. ©2010 American Institute of Physics.
|
|
| 4. |
- Conache, Gabriela
(author)
-
Studies of Nanowire Friction using AFM-based Manipulation
- 2010
-
Doctoral thesis (other academic/artistic)abstract
- In this thesis we present friction studies on InAs nanowires pushed laterally across surfaces by an AFM tip. The contact length in the direction of movement is of the order of a few tens of nanometers, and is thus comparable to that found in existing point-contact studies, but perpendicular to the motion the wire can be several microns in length. We are therefore able to investigate friction in the mesoscopic regime, with a geometry that closely models proposed MEMS structures and devices. The shape of the wire after manipulation is determined by an equilibrium between internal elastic restoring forces and friction with the substrate. We have developed a method to calculate the friction force per unit length by measuring the diameter and curvature of the bent nanowire and applying standard elasticity theory to calculate the stresses within the wire. We have studied InAs nanowires on three different substrates, silicon dioxide, fluoro-silanised silicon dioxide, and silicon nitride. We have measured the static and sliding friction force per unit length for a range of nanowire diameters on all three substrates. The system displays behaviors typical of friction studies at other scales, such as differentiated sliding and static friction and a transition to stick-slip motion, the details being an interesting mix of those from both atomic-scale and macroscopic regimes. We have also studied how the friction between InAs nanowires and an insulating silicon nitride layer on a Si substrate varies when a DC voltage is applied to the tip during a manipulation sequence. A monotonic increase of the sliding friction with the voltage applied to the tip was observed, caused by the electrostatic attraction of the wire to the substrate. The increase in friction with normal force implies that the mesoscopic nanowire-surface system behaves like a macroscopic interface, despite the nanometer size of the contact in the direction of motion. In the third part, we have investigated the friction between InAs nanowires and atomically-flat mica substrates. The dependence of the static friction force per unit length on the nanowire diameter is very different than the previously observed behavior on silicon nitride substrates and is consistent with models for atomically-smooth nanoscale friction. The results suggest that for the technologically relevant silicon-based surfaces the details of the surface roughness down to the atomic scale are important, and will affect the observed friction behavior.
|
|
| 5. |
- Pettersson, Håkan, 1962-, et al.
(author)
-
Nanowire friction with an applied bias
- 2010
-
In: Bulletin of the American Physical Society. - : American Physical Society.
-
Conference paper (peer-reviewed)abstract
- Recently, we have shown how the friction experienced by nanowires pushed by an AFM tip can be determined by measuring their radius of curvature after manipulation [1]. It is of fundamental interest to know whether the wires behave like macroscopic objects, or if they are more like true atomic-scale point contacts where friction becomes independent of the applied normal force. Here we study how the friction between InAs nanowires and a SiN layer on conductive silicon varies when a DC voltage is applied. The tip charges the capacitor formed by the wire and the silicon back contact, causing attractive Coulomb forces and so increasing the contact pressure. A monotonic increase of the sliding friction with voltage was observed. This implies that the friction increases with the normal force and that this mesoscopic system behaves more like a macroscopic contact, despite being only nanometers in size in the direction of motion.
|
|
