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| 2. |
- Alcer, David, et al.
(författare)
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Processing and characterization of large area InP nanowire photovoltaic devices
- 2023
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Ingår i: Nanotechnology. - 0957-4484. ; 34:29
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Tidskriftsartikel (refereegranskat)abstract
- III−V nanowire (NW) photovoltaic devices promise high efficiencies at reduced materials usage. However, research has so far focused on small devices, mostly ≤1 mm2. In this study, the upscaling potential of axial junction InP NW photovoltaic devices is investigated. Device processing was carried out on a full 2″ wafer, with device sizes up to 1 cm2, which is a significant increase from the mm-scale III−V NW photovoltaic devices published previously. The short-circuit current density of the largest 1 cm2 devices, in which 460 million NWs are contacted in parallel, is on par with smaller devices. This enables a record power generation of 6.0 mW under AM1.5 G illumination, more than one order of magnitude higher than previous III−V NW photovoltaic devices. On the other hand, the fill factor of the larger devices is lower in comparison with smaller devices, which affects the device efficiency. By use of electroluminescence mapping, resistive losses in the indium tin oxide (ITO) front contact are found to limit the fill factor of the large devices. We use combined light-beam induced current (LBIC) and photoluminescence (PL) mapping as a powerful characterization tool for NW photovoltaic devices. From the LBIC and PL maps, local defects can be identified on the fully processed devices.
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| 3. |
- 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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| 6. |
- Hessman, Dan
(författare)
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Spectroscopic studies of III-V semiconductors in two, one and zero dimensions
- 1996
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- In this thesis, spectroscopic studies of quantum wells (QWs), quantum wires (QWRs) and quantum dots (QDs) in III-V semiconductors are presented. The electronic structure of these low-dimensional structures have been studied by absorption, photocurrent, electroreflectance, photoluminescence (PL), and photoluminescence excitation (PLE) spectroscopy. The band alignment of GaAs pseudomorphically grown on InP is investigated. The absorption of a single GaAs/InP QW is measured and compared to a calculated spectrum obtained with the effective mass theory (EMT). The results are consistent with a type II alignment. Both theory and experiment give an absorption of the order of 1%. The formation of interface layers during the growth of single bi-layers of GaAs and GaInAs in InP is studied by PL and EMT calculations. Incorporation of As gives a red- shift of the PL, interpreted as an increased effective QW width. The As adsorbed on the growing surface is shown to be the primary source for the As incorporation at the second interface. An AlGaAs/GaAs QWR structure grown on a V-grooved substrate is characterised using transmission electron microscopy (TEM) and cathodoluminescence (CL). The different quantum structures in the sample give spectrally separated luminescence peaks, which are identified by CL. This allows PLE and time-resolved PL studies of the carrier transfer involved in the excitation of the QWR. The vertical QW connected to the QWR is found to be the main channel for the excitation. QDs produced in the Stranski-Krastanow growth mode are studied in different materials systems : InAs in GaAs, InAs in InP and InP in GaInP. Controlled positioning of the QDs is achieved by selective nucleation on pre-growth patterned substrates. The electronic structure of one single InP QD is investigated by micro PL techniques: PL, PLE and TRPL. The single QD is shown to emit several PL lines, due to a reduced relaxation rate. The different spectral components have line widths of about 1 millielectronvolt, to be compared with the life time broadening which is 1 microelectronvolt.
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| 7. |
- 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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| 8. |
- 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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| 9. |
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| 10. |
- 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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