| 61. |
- Pettersson, Håkan, et al.
(författare)
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Friction measurements on InAs NWs by AFM manipulation
- 2008
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Konferensbidrag (refereegranskat)abstract
- We discuss a new approach to measure the friction force between elastically deformed nanowires and a surface. The wires are bent, using an AFM, into an equilibrium shape determined by elastic restoring forces within the wire and friction between the wire and the surface. From measurements of the radius of curvature of the bent wires, elasticity theory allows the friction force per unit length to be calculated. We have studied friction properties of InAs nanowires deposited on SiO2, silanized SiO2 and Si3N4 substrates. The wires were typically from 0.5 to a few microns long, with diameters varying between 20 and 80 nm. Manipulation is done in a `Retrace Lift' mode, where feedback is turned off for the reverse scan and the tip follows a nominal path. The effective manipulation force during the reverse scan can be changed by varying an offset in the height of the tip over the surface. We will report on interesting static- and sliding friction experiments with nanowires on the different substrates, including how the friction force per unit length varies with the diameter of the wires.
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| 62. |
- Pettersson, Håkan, et al.
(författare)
-
Infrared Photodetectors in Heterostructure Nanowires
- 2006
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Ingår i: Nano letters (Print). - Washington : American Chemical Society (ACS). - 1530-6984 .- 1530-6992. ; 6:2, s. 229-232
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Tidskriftsartikel (refereegranskat)abstract
- We report on spectrally resolved photocurrent measurements on single self-assembled nanowire heterostructures. The wires, typically 3 μm long with an average diameter of 85 nm, consist of InAs with a 1 μm central part of InAsP. Two different sets of wires were prepared with phosphorus contents of 15 ±3% and 35 ±3%, respectively, as determined by energy-dispersive spectroscopy measurements made in transmission electron microscopy. Ohmic contacts are fabricated to the InAs ends of the wire using e-beam lithography. The conduction band offset between the InAs and InAsP regions virtually removes the dark current through the wires at low temperature. In the optical experiments, interband excitation in the phosphorus-rich part of the wires results in a photocurrent with threshold energies of about 0.65 and 0.82 eV, respectively, in qualitative agreement with the expected band gap of the two compositions. Furthermore, a strong polarization dependence is observed with an order of magnitude larger photocurrent for light polarized parallel to the wire than for light polarized perpendicular to the wire. We believe that these wires form promising candidates as nanoscale infrared polarization-sensitive photodetectors.
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| 63. |
- Pettersson, Håkan, et al.
(författare)
-
Intersubband photoconductivity of self-assembled InAs quantum dots embedded in InP
- 2004
-
Ingår i: Journal of Applied Physics. - : American Institute of Physics (AIP). - 0021-8979 .- 1089-7550. ; 95:4, s. 1829-1831
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Tidskriftsartikel (refereegranskat)abstract
- The results from photoconductivity (PC) measurements on InAs dots embedded in InP are presented. The PC technique is recently applied to the study of InAs dots embedded in matrices of GaAs and Al0.3Ga0.7As matrix, respectively. It is demonstrated that this technique reveals important new physical insight into the electronic structure of the InAs/InP dots, information that cannot easily be obtained by other techniques.
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| 64. |
- Pettersson, Håkan, 1962-, et al.
(författare)
-
Nano-Schottky contacts realized by bottom-up technique
- 2010
-
Ingår i: Bulletin of American Physical Society. - : American Physical Society.
-
Konferensbidrag (refereegranskat)abstract
- Here we present a comprehensive study of a rectifying nano-Schottky contact formed at the interface between a gold catalytic particle and an epitaxially grown GaInAs/InAs nanowire. Selective electrical connections formed by electron beam lithography to the catalytic particle on one side, and to the InAs segment on the other side allowed electrical and optical characterization of the formed Schottky junction. From IV measurements taken at different temperatures we have deduced the Schottky barrier height and the height of the barrier formed in the graded GaInAs nanowire segment. The IV characteristics measured under laser stimulation showed that the device can be used as a unipolar photodetector with extremely small detection volume and potentially ultra fast response.
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| 65. |
- Pettersson, Håkan, 1962-, et al.
(författare)
-
Nanowire friction with an applied bias
- 2010
-
Ingår i: Bulletin of the American Physical Society. - : American Physical Society.
-
Konferensbidrag (refereegranskat)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.
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| 66. |
- Pettersson, Håkan, et al.
(författare)
-
Optically induced charge storage and current generation in InAs quantum dots
- 2002
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - : American Physical Society. - 1098-0121 .- 1550-235X. ; 65:7, s. 0733041-0733044
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Tidskriftsartikel (refereegranskat)abstract
- We report on optically induced charge storage effects and current generation in self-assembled InAs quantum dots embedded in an InP matrix. Illumination with photons of energy higher than about 0.86 eV efficiently loads the dots with a maximum of about 1 hole/dot. The spectral response at lower photon energy is strongly enhanced at elevated temperatures. We present a detailed balance model for the dots and discuss the thermally assisted optical excitation processes pertinent to hole accumulation. We also show that these processes make the dots act as nanometer-scaled temperature-dependent current generators.
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| 67. |
- Pettersson, Håkan, et al.
(författare)
-
Photocurrent spectroscopy on self-assembled InAs quantum dots embedded in InP
- 2005
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Ingår i: Microelectronics Journal. - Amsterdam : Elsevier. - 0026-2692. ; 36:3-6, s. 227-230
-
Tidskriftsartikel (refereegranskat)abstract
- In this work, we report on an overview of recent results from Fourier transform photocurrent (FTPC) measurements in the infrared spectral region on ensembles of self-assembled InAs quantum dots embedded in a matrix of InP. In interband PC, clear signals related to the dots are observed. Comparing the PC- and PL spectra, we observe that the fundamental transition is absent in the PC spectra, which we interpret in terms of Pauliblocking due to a filled electron ground state of the dots. Our results furthermore suggest that an Auger process is involved in forming the interband PC signal. In intersubband PC, peaks related to transitions from the dots' ground- and first excited states to the conduction band of the matrix are observed. Using a novel approach of combining FTPC with illumination from an additional external non-modulated light source, we have measured the spectral distribution of photoionization of excitons in quantum dots and found an exciton binding energy in good agreement with theoretical calculations.
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| 68. |
- Pettersson, Håkan, et al.
(författare)
-
Photoexcitation of excitons in self-assembled quantum dots
- 2004
-
Ingår i: Applied Physics Letters. - : American Institute of Physics (AIP). - 0003-6951 .- 1077-3118. ; 85:21, s. 5046-5048
-
Tidskriftsartikel (refereegranskat)abstract
- Using an approach of combining Fourier transform infrared spectroscopy with resonant illumination from a secondary external light source, we have measured the photocurrent (PC) for multiple layers of self-assembled InAs dots embedded in a matrix of InP. Without external illumination, we observe photoexcitation of electrons from bound states in the dots to the InP barrier. By additional illumination from the external light source, a strong broadening of the PC signal is observed. We interpret this broadening in terms of photoexcitation of electrons in the presence of additional holes in the dots created by the external light source. We extract the spectral distribution of the photoexcitation process at 6 and 77 K, respectively, and show by comparison with theoretical calculations that it is consistent with an exciton binding energy of 20 meV.
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| 69. |
- Pettersson, Håkan, 1962-, et al.
(författare)
-
Shear stress measurements on InAs nanowires by AFM manipulation
- 2007
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Ingår i: Bulletin of the American Physical Society. - New York : American Physical Society. - 0003-0503. ; 52:1
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Tidskriftsartikel (refereegranskat)abstract
- In this paper, we report on a novel approach to measure shear stress between elastic nanowires and a SiO2 surface. The method is based on the fact that the curvature of an elastically deformed nanowire pinned to a flat surface contains information about the maximal static friction force, i.e., the shear stress between the wire and the surface. At rest, the deformed wire is kept in equilibrium by counterbalancing static friction forces and restoring elastic forces. In the present work, InAs nanowires are bent in a controlled manner using the tip of an atomic force microscope (AFM). After the manipulation, the curvature of the most bent state can be determined from AFM micrographs. Assuming bulk values for the Young’s modulus, the shear stress can be obtained from straight- forward analyses according to standard theory of elasticity.
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| 70. |
- Prinz, Christelle, et al.
(författare)
-
Axonal guidance on patterned free-standing nanowire surfaces
- 2008
-
Ingår i: Nanotechnology. - : IOP Publishing. - 0957-4484 .- 1361-6528. ; 19:34
-
Tidskriftsartikel (refereegranskat)abstract
- We demonstrate high-fidelity guidance of axons using rows of nanowires. The axons are prevented from crossing the rows, making it possible to guide and sort a large number of axons as opposed to when chemical patterns are used. Focal adhesion forms at the nanowires establishing a possible site of information transfer between the surface and the cells. Rows of gallium phosphide (GaP) nanowires were epitaxially grown on GaP(111) substrates in patterns defined by electron beam lithography.
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