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• 1.
Lund University, Lund, Sweden.
Tailoring the Optical Response of III-V Nanowire Arrays2017Doctoral thesis, comprehensive summary (Other academic)

Semiconductor nanowires show a great deal of promise for applications in a wide range of important fields, including photovoltaics, biomedicine, and information technology. Developing these exciting applications is strongly dependent on understanding the fundamental properties of nanowires, such as their optical resonances and absorption spectra. In this thesis we explore optical absorption spectra of arrays of vertical III-V nanowires with a special emphasis on structures optimized to enhance absorption in the solar spectrum. First, we analyze experimentally determined absorption spectra of both indium phosphide (InP) and gallium phosphide (GaP) nanowire arrays. The study provides an intuitive understanding of how the observed absorption resonances in the nanowires may be tuned as a function of their geometrical parameters and crystal structure. As a consequence, the spectral position of absorption resonances can be precisely controlled through the nanowire diameter. However, the results highlight how the blue-shift in the optical absorption resonances as the diameter of the nanowires decreases comes to a halt at low diameters. The stop point is related to the behavior of the refractive indices of the nanowires. The wavelength of the stop is different for nanowire polytypes of similar dimensions due to differences in their refractive indices. We then present a theoretical argument that it is important to consider symmetry properties when tailoring the optical modes excited in the nanowires for enhanced absorption. We show that absorption spectra may be enhanced compared to vertical nanowires at normal incidence by tilting the nanowires with normal incidence light, or by using off-normal incidence with vertical nanowires. This is because additional optical modes inside the nanowires are excited when the symmetry is broken. Looking forward to omnidirectional applications, we consider branched nanowires as a way to enhance the absorption spectra at normal incidence by taking advantage of simultaneous excitation of the spectrally different optical modes in the branches and the stems. Third, we describe in theoretical terms how integrating distributed Bragg reflectors (DBRs) with the nanowires can improve absorption spectra compared to conventional nanowires. DBRs provide a way to employ light trapping mechanisms which increases the optical path length of the excited modes and thereby improves the absorption of the excited modes. At normal incidence, DBR-nanowires improve the absorption efficiency to 78%, compared to 72% for conventional nanowires. We show that the efficiency is increased to 85% for an off-normal incident angle of 50˚. Overall, our results show that studies of optical resonances in nanowires that take the light-matter interaction into account provide opportunities to develop novel optical and optoelectronic functionalities in nanoscience and nanotechnology.

• 2.
Lund University, Lund, Sweden.
Halmstad University, School of Information Technology, Halmstad Embedded and Intelligent Systems Research (EIS), MPE-lab. Lund University, Lund, Sweden.
Enhanced broadband absorption in nanowire arrays with integrated Bragg reflectors2018In: Nanophotonics, E-ISSN 2192-8614, Vol. 7, no 5, p. 819-825Article in journal (Refereed)

A near-unity unselective absorption spectrum is desirable for high-performance photovoltaics. Nanowire arrays are promising candidates for efficient solar cells due to nanophotonic absorption resonances in the solar spectrum. The absorption spectra, however, display undesired dips between the resonance peaks. To achieve improved unselective broadband absorption, we propose to enclose distributed Bragg reflectors (DBRs) in the bottom and top parts of indium phosphide (InP) nanowires, respectively. We theoretically show that by enclosing only two periods of In0.56Ga0.44As/InPDBRs, an unselective 78% absorption efficiency (72% for nanowires without DBRs)is obtained at normal incidence in the spectral range from 300 nm to 920 nm. Under oblique light incidence, the absorption efficiency is enhanced up to about 85% at an incidence angle of 50º. By increasing the number of DBR periods from two to five, the absorption efficiency is further enhanced up to 95% at normal incidence. In this work we calculated optical spectra for InP nanowires, but the results are expected to be valid for other direct band gap III-V semiconductor materials. We believe that our proposed idea of integrating DBRs in nanowires offers great potential for high-performance photovoltaic applications. ©2018 Håkan Pettersson et al., published by De Gruyter, Berlin/Boston.

• 3.
Solid State Physics and NanoLund, Lund University, Lund, Sweden.
Halmstad University, School of Information Technology, Halmstad Embedded and Intelligent Systems Research (EIS).
Enhanced optical absorption in nanowires over a desire range of wavelengths2017In: MOC2017 : technical digest of the Twenty-Second Microoptics Conference: November 19-22, 2017, Institute of Industrial Science, The University of Tokyo, Japan, 2017, Vol. 2017-November, p. 360-361Conference paper (Refereed)

Engineering optical absorption in nanowires, over a desire range of wavelengths is of importance to design high-performance nanowire-based photovoltaics. To this end, we integrate the nanowires with distributed Bragg reflectors to enhance absorption spectra of the nanowires and relate the consequent enhancement to increasing the optical path lengths of the modes. © 2017 The Japan Society of Applied Physics.

• 4.
Lund University, Lund, Sweden.
Lund University, Lund, Sweden. Halmstad University, School of Information Technology, Halmstad Embedded and Intelligent Systems Research (EIS). Lund University, Lund, Sweden.
Comparative study of absorption efficiency of inclined and vertical InP nanowires2017In: Physics, Simulation, and Photonic Engineering of Photovoltaic Devices VI / [ed] A. Freundlich, L. Lombez, M. Sugiyama, Bellingham, WA: SPIE - International Society for Optical Engineering, 2017, Vol. 10099, article id UNSP 100990SConference paper (Refereed)

Geometrically designed III-V nanowire arrays are promising candidates for optoelectronics due to their possibility to excite nanophotonic resonances in absorption spectra. Strong absorption resonances can be obtained by proper tailoring of nanowire diameter, length and pitch. Such enhancement of the light absorption is, however, accompanied by undesired resonance dips at specific wavelengths. In this work, we theoretically show that tilting of the nanowires mitigates the absorption dips by exciting strong Mie resonances. In particular, we derive a theoretical optimum inclination angle of about 30 degrees at which the inclined nanowires gain 8% in absorption efficiency compared to vertically standing nanowires in a spectral region matching the intensity distribution of the sun. The enhancement is due to engineering the excited modes inside the nanowires regarding the symmetry properties of the nanowire/light system without increasing the absorbing material. We expect our results to be important for nanowire-based photovoltaic applications. © 2017 SPIE.

• 5.
Solid State Physics and NanoLund, Lund University, Lund, Sweden.
Solid State Physics and NanoLund, Lund University, Lund, Sweden. Halmstad University, School of Information Technology, Halmstad Embedded and Intelligent Systems Research (EIS). Solid State Physics and NanoLund, Lund University, Lund, Sweden.
Considering Symmetry Properties of InP Nanowire/Light Incidence Systems to Gain Broadband Absorption2017In: IEEE Photonics Journal, ISSN 1097-5764, E-ISSN 1943-0655, Vol. 9, no 3, article id 4501310Article in journal (Refereed)

Geometrically designed III-V nanowire arrays are promising candidates for disruptive optoelectronics due to the possibility of obtaining a strongly enhanced absorption resulting from nanophotonic resonance effects. With normally incident light on such vertical nanowire arrays, the absorption spectra exhibit peaks that originate from excitation of HE1m waveguide modes in the constituent nanowires. However, the absorption spectra typically show dips between the absorption peaks. Conventionally, such weak absorption has been counteracted by either making the nanowires longer or by decreasing the pitch of the array, both alternatives effectively increasing the volume of absorbing material in the array. Here, we first study two approaches for compensating the absorption dips by exciting additional Mie resonances: 1) oblique light incidence on vertical InP nanowire arrays and 2) normal light incidence on inclined InP nanowire arrays. We then show that branched nanowires offer a novel route to achieve broadband absorption by taking advantage of simultaneous excitations of Mie resonances in the branches and guided HE1m modes in the stem. Finite element method calculations show that the absorption efficiency is enhanced from 0.72 for vertical nanowires to 0.78 for branched nanowires under normal light incidence. Our work provides new insight for the development of novel efficient photovoltaics with high efficiency and reduced active material volume.

• 6.
Halmstad University, School of Information Science, Computer and Electrical Engineering (IDE).
Halmstad University, School of Information Science, Computer and Electrical Engineering (IDE).
Electrical and Optical Characteristics of InP Nanowires based p-i-n Photodetectors2010Independent thesis Advanced level (degree of Master (One Year)), 10 credits / 15 HE creditsStudent thesis

Photodetectors are a kind of semiconductor devices that convert incoming light to an electrical signal. Photodetectors are classified based on their different structure, fabrication technology, applications and different sensitivity. Infrared photodetectors are widely used in many applications such as night vision, thermal cameras, remote temperature sensing, and medical diagnosis etc.

All detectors have material inside that is sensitive to incoming light. It will absorb the photons and, if the incoming photons have enough energy, electrons will be excited to higher energy levels and if these electrons are free to move, under the effect of an external electric field, a photocurrent is generated.

In this project Fourier Transform Infrared (FT-IR) Spectroscopy is used to investigate a new kind of photodiodes that are based on self-assembled semiconductor nanowires (NWs) which are grown directly on the substrate without any epi-layer. The spectrally resolved photocurrent (at different applied biases) and IV curves (in darkness and illumination) for different temperatures have been studied respectively. Polarization effects (at low and high Temperatures) have been investigated.  The experiments are conducted for different samples with high concentration of NWs as well as with lower concentration of NWs in the temperature range from 78 K (-195ºC) to 300 (27ºC). These photodiodes are designed to work in near infrared (NIR) spectral range.

The results show that the NW photodetectors indeed are promising devices with fairly high break down voltage, change of photocurrent spectra with polarized light, low and constant reverse saturation current (Is). The impact of different polarized light on photocurrent spectra has been investigated and an attempt has been made to clarify the observed double peak of InP photocurrent spectrum. Our investigations also include a comparison to a conventional planar InP p-i-n photodetector.

• 7.
Onsala Space Observatory, Chalmers University of Technology, Gothenburg, Sweden.
Onsala Space Observatory, Chalmers University of Technology, Gothenburg, Sweden.
Combined-Array Imaging of Extra-Galactic Radio Sources1994In: Astronomy with Millimeter and Submillimeter Wave Interferometry: IAU Colloquium 140 : Meeting held 5-9 October 1992, Hakone, Japan / [ed] M. Ishiguro & Wm. J. Welch, San Francisco: Astronomical Society of the Pacific , 1994, p. 123-124Conference paper (Refereed)
• 8.
Laboratorio de Astrofísica Espacial y Física Fundamental, Madrid, Spain; Instituto de Astrofísica de Andalucía CSIC, Granada, Spain.
Max Planck Institut für Radioastronomie, Bonn, Germany. Max Planck Institut für Radioastronomie, Bonn, Germany. IRAM, Domaine Universitaire, Grenoble, France. IRAM, Domaine Universitaire, Grenoble, France. Departamento de Astronomía Universitat de Valéncia, Spain. Onsala Space Observatory. Onsala Space Observatory. Onsala Space Observatory; Observatorio de Yebes, Guadalajara, Spain. NEROC, Haystack Observatory, Westford, Massachusetts, USA. Boston University, Boston, MA, USA. NEROC, Haystack Observatory, Westford, Massachusetts, USA. IRAM, Domaine Universitaire, Grenoble, France; Institut für Weltraumsensorik (DLR), Berlin, Germany. Max Planck Institut für Radioastronomie, Bonn, Germany.
The high-frequency compact radio structure of the peculiar quasar 4C 39.251997In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 327, no 2, p. 513-521Article in journal (Refereed)

We present new high angular resolution images of the compact non-thermal radio source 4C 39.25 obtained from VLBI observations at λ1.3cm, λ7mm, and λ3mm wavelengths. These maps and Gaussian model-fits show that the milli-arcsecond to sub-milliarcsecond structure of 4C 39.25 consists of a complex bent core-jet structure with embedded moving and stationary VLBI components. Facilitated by the small observing beams and high angular resolutions obtained at mm-wavelengths, we measured the relative positions of the jet components with an accuracy of a few hundred micro-arcseconds. This allows the detailed followup of the ongoing merging process of a westward superluminally moving component (b_) with a stationary component a_, located at ~2.9 mas east of the putative core d_. In contrast to the other components of the structure with steeper spectra, the westernmost component d_ exhibits an inverted spectrum peaking between λ7mm and λ3mm, thus further supporting its identification as the VLBI core, self-absorbed at longer wavelengths. From two VLBI maps obtained nearly simultaneously at λ7mm and λ1.3cm, we made the first spectral index map of 4C 39.25 in this wavelength regime. The main characteristics of the spectral index distribution of the jet are pronounced changes of the spectral index between orientations parallel and transverse to the jet axis. Near the merging components a_ and b_ the spectral index steepens with increasing separation from d_. However, in the bridge of emission c_, which connects d_ with a_ and b_, the spectral index gradient has a direction transverse to the jet axis, suggesting a frequency dependent jet curvature and edge-brightening. A brief discussion of this behaviour within current jet models is presented.

• 9.
Swiss Light Source, Paul Scherrer Institut, Villigen, Switzerland.
Swiss Light Source, Paul Scherrer Institut, Villigen, Switzerland. Swiss Light Source, Paul Scherrer Institut, Villigen, Switzerland. IBM Research, Zurich Research Laboratory, Rüschlikon, Switzerland.
Spatial distribution of oxygen vacancies in Cr-doped SrTiO3 during an electric-field-driven insulator-to-metal transition2009In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 94, no 1, p. Article number: 013513-Article in journal (Refereed)

Spatially resolved x-ray fluorescence maps are presented that show the introduction and the evolution of oxygen vacancies in chromium-doped strontium titanate during an electric-field-driven insulator-to-metal transition. The vacancies are introduced at the anode and diffuse through the crystal toward the cathode. The spatial distribution of vacancies is explained by a model describing the electrical breakdown as a percolation process. Strong differences in the vacancy distribution were found when the transition took place in air and in a hydrogen-enriched atmosphere. In air, the vacancies disappeared from the surface, whereas in the reducing hydrogen atmosphere, they remained at the surface. © 2009 American Institute of Physics.

• 10.
Swiss Light Source, Paul Scherrer Institut, Villigen, Switzerland.
Swiss Light Source, Paul Scherrer Institut, Villigen, Switzerland. Swiss Light Source, Paul Scherrer Institut, Villigen, Switzerland. IBM Research, Zurich Research Laboratory, Rüschlikon, Switzerland. Swiss Light Source, Paul Scherrer Institut, Villigen, Switzerland.
Resistive switching in Cr-doped SrTiO3: An X-ray absorption spectroscopy study2007In: Materials Science & Engineering: B. Solid-state Materials for Advanced Technology, ISSN 0921-5107, E-ISSN 1873-4944, Vol. 144, no 1-3, p. 60-63Article in journal (Refereed)

X-ray absorption spectroscopy was used to study the microscopic origin of conductance and resistive switching in chromium-doped strontium titanate (Cr:SrTiO3). Differences in the X-ray absorption near edge spectroscopy (XANES) at the Cr K-edge indicate that the valence of Cr changes from 3+ to 4+ underneath the anode of our sample device after the application of an electric field. Spatially resolved X-ray fluorescence microscopy (μ-XRF) maps show that the Cr4+ region retracts from the anode-Cr:SrTiO3 interface after a conducting state has been achieved. This interface region is studied with extended X-ray absorption fine structure (EXAFS) and the results are compared with structural parameters obtained from density functional theory (DFT) calculations. They confirm that oxygen vacancies which are localized at the octahedron with a Cr at its center are introduced at the interface. It is proposed that the switching state is not due to a valence change of chromium but caused by changes of oxygen vacancies at the interface. © 2007 Elsevier B.V. All rights reserved.

• 11.
Swiss Light Source, Paul Scherrer Institut, Villigen, Switzerland.
Swiss Light Source, Paul Scherrer Institut, Villigen, Switzerland. Swiss Light Source, Paul Scherrer Institut, Villigen, Switzerland. IBM Research, Zurich Research Laboratory, Rüschlikon, Switzerland. École Polytechnique Fédérale de Lausanne (EPFL), Centre de Recherche en Physique des Plasmas, Association Euratom-Confédération Suisse, Villigen, Switzerland & Center for Electron Nanoscopy, Technical University of Denmark, Lyngby, Denmark. École Polytechnique Fédérale de Lausanne (EPFL), Centre de Recherche en Physique des Plasmas, Association Euratom-Confédération Suisse, Villigen, Switzerland. École Polytechnique Fédérale de Lausanne (EPFL), Centre de Recherche en Physique des Plasmas, Association Euratom-Confédération Suisse, Villigen, Switzerland.
Origin of oxygen vacancies in resistive switching memory devices2009In: Journal of Physics, Conference Series, ISSN 1742-6588, E-ISSN 1742-6596, Vol. 190, p. Article number: 012074-Article in journal (Refereed)

The resistive switching state in Cr-doped SrTiO3 was induced by applying an electric field. This was done in ambient air and in an atmosphere of H2/Ar. The distribution of the thereby introduced oxygen vacancies was studied by spatially resolved X-ray fluorescence images. It was concluded that the oxygen vacancies were introduced in the interface between the SrTiO3 and the positively biased electrode. © 2009 IOP Publishing Ltd.

• 12.
Swiss Light Source, Paul Scherrer Institut, Villigen, Switzerland.
Swiss Light Source, Paul Scherrer Institut, Villigen, Switzerland. Swiss Light Source, Paul Scherrer Institut, Villigen, Switzerland. Condensed Matter Theory Group, Paul Scherrer Institut, Villigen, Switzerland. Condensed Matter Theory Group, Paul Scherrer Institut, Villigen, Switzerland. IBM Research, Zurich Research Laboratory, Rüschlikon, Switzerland. Laboratory for Developments and Methods, Paul Scherrer Institut, Villigen, Switzerland.
Detecting oxygen vacancies in SrTiO3 by 3d transition-metal tracer ions2009In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 80, no 21, p. Article number: 212103-Article in journal (Refereed)

X-ray absorption experiments on 3d transition-metal tracer ions in SrTiO3 are presented. The absorption spectra of the tracer-ion changed upon reduction in the SrTiO3. This change is due to an oxygen vacancy created at the tracer-ion site. This finding is supported by density-functional theory calculations, which prove that the oxygen vacancies preferentially are created at the tracer-ion sites. Using the chemical sensitivity of x-ray absorption spectroscopy, tracer ions can be used to detect oxygen vacancies in SrTiO3 and possibly in other oxide systems. © 2009 The American Physical Society.

• 13.
Avd. f. Fasta Tillståndets Fysik, Lunds Universitet, Lund, Sweden.
Avd. f. Fasta Tillståndets Fysik, Lunds Universitet, Lund, Sweden. Avd. f. Fasta Tillståndets Fysik, Lunds Universitet, Lund, Sweden. Avd. f. Fasta Tillståndets Fysik, Lunds Universitet, Lund, Sweden. Avd. f. Fasta Tillståndets Fysik, Lunds Universitet, Lund, Sweden. Halmstad University, School of Information Technology, Halmstad Embedded and Intelligent Systems Research (EIS), MPE-lab.
Metal-assisted chemical etching of Si for fabrication of nanoimprint stamps2011Conference paper (Refereed)
• 14.
Department of Earth and Planetary Sciences, Massachusetts Institute of Technology, Cambridge, MA, USA; Department of Physics, Massachusetts Institute of Technology, Cambridge, MA, USA & Harvard-Smithsonian Astrophysical Observatory, Cambridge, MA, USA.
Department of Earth and Planetary Sciences, Massachusetts Institute of Technology, Cambridge, MA, USA; Department of Physics, Massachusetts Institute of Technology, Cambridge, MA, USA & Harvard-Smithsonian Astrophysical Observatory, Cambridge, MA, USA. NEROC, Haystack Observatory, Westford, MA, USA. Department of Physics, Massachusetts Institute of Technology, Cambridge, MA, USA & Max-Planck-Institut für Radioastronomie, Bonn, Germany. NEROC, Haystack Observatory, Westford, MA, USA. NEROC, Haystack Observatory, Westford, MA, USA. NEROC, Haystack Observatory, Westford, MA, USA. Steward Observatory, Tucson, AZ, USA. Max-Planck-Institut für Radioastronomie, Bonn, Germany. Onsala Space Observatory, Chalmers University of Technology, Gothenburg, Sweden.
The Compact Radio Source 2021+614: Simultaneous 2.3 and 8.3 GHz Mark III VLBI Observations1984In: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 279, no 1, p. 116-121Article in journal (Refereed)

Second-epoch VLBI observations of the flat-spectrum radio source 2021+614 made simultaneously at 2.3 and 8.3 GHz with the Mark III system are reported. The maps derived from these observations reveal a complex, frequency-dependent radio structure on the milliarcsecond scale. The object has four nearly collinear components oriented at a position angle of about 35 degrees and embedded in an extended region. Two of these are optically thin, one has a flat spectrum, and the other appears to be synchrotron self-absorbed in the frequency range 2.3-8.3 GHz. No significant structural variation is found at either frequency between epochs separated by about three years. The formal estimate of the transverse velocity between two components, one with a flat and the other with an inverted spectrum, is v/c = 0.7 + or - 2.3. Remarkable similarities between 2021+614 and the unusual source 0316+413 are discussed.

• 15.
Lund University, Lund, Sweden.
Technical University of Denmark, Lyngby, Denmark. Lund University, Lund, Sweden. Lund University, Lund, Sweden. Halmstad University, School of Information Technology, Halmstad Embedded and Intelligent Systems Research (EIS), MPE-lab. Lund University, Lund, Sweden. Lund University, Lund, Sweden. Lund University, Lund, Sweden. Technical University of Denmark, Lyngby, Denmark. Lund University, Lund, Sweden.
Radial Nanowire Light-Emitting Diodes in the (AlxGa1-x)yIn1-yP Material System2016In: Nano letters (Print), ISSN 1530-6984, E-ISSN 1530-6992, Vol. 16, no 1, p. 656-662Article in journal (Refereed)

Nanowires have the potential to play an important role for next-generation light-emitting diodes. In this work, we present a growth scheme for radial nanowire quantum-well structures in the AlGaInP material system using a GaInP nanowire core as a template for radial growth with GaInP as the active layer for emission and AlGaInP as charge carrier barriers. The different layers were analyzed by X-ray diffraction to ensure lattice-matched radial structures. Furthermore, we evaluated the material composition and heterojunction interface sharpness by scanning transmission electron microscopy energy dispersive X-ray spectroscopy. The electro-optical properties were investigated by injection luminescence measurements. The presented results can be a valuable track toward radial nanowire light-emitting diodes in the AlGaInP material system in the red/orange/yellow color spectrum. © 2015 American Chemical Society.

• 16.
University of Manchester, Nuffield Radio Astronomy Laboratories, Jodrell Bank, Cheshire, United Kingdom.
University of Manchester, Nuffield Radio Astronomy Laboratories, Jodrell Bank, Cheshire, United Kingdom. University of Manchester, Nuffield Radio Astronomy Laboratories, Jodrell Bank, Cheshire, United Kingdom. Onsala Space Observatory, Chalmers University of Technology, Gothenburg, Sweden.
High-resolution observations of quasars from the Parkes +/- 4 deg. sample1979In: Monthly notices of the Royal Astronomical Society, ISSN 0035-8711, E-ISSN 1365-2966, Vol. 188, p. 159-163Article in journal (Refereed)

VLBI observations of 20 compact quasars have been made between Jodrell Bank and Onsala at a frequency of 1666 MHz. Twelve of the quasars have inverted or peaked spectra at centimetre wavelengths and these are all unresolved, having angular diameters of less than 0.015 arcsec. Two out of five quasars with overall flat spectra are partially resolved on this scale size, as are three steep-spectrum quasars.

• 17.
Halmstad University, School of Information Science, Computer and Electrical Engineering (IDE), Halmstad Embedded and Intelligent Systems Research (EIS), MPE-lab.
St. Petersburger State University.
Berechnungen der Gleichgewichtslage der Welle unterpräzisierten geometrischen Voraussetzungen der Druckfluidströmung in LHS 7502009Report (Other academic)
• 18.
Halmstad University, School of Information Science, Computer and Electrical Engineering (IDE), Halmstad Embedded and Intelligent Systems Research (EIS), MPE-lab.
St. Petersburg State University.
Präzisierte Berechnungender Druckfluidströmung in LHS 7502008Report (Other academic)
• 19.
Halmstad University, School of Information Science, Computer and Electrical Engineering (IDE), Halmstad Embedded and Intelligent Systems Research (EIS).
Interaction of a charge with a thin plasma sheet2007In: Physical Review D. Particles and fields, ISSN 0556-2821, E-ISSN 1089-4918, Vol. 76, no 6, p. 065011-Article in journal (Refereed)

The interaction of the electromagnetic field with a two-dimensional plasma sheet intended to describe the pi-electrons of a carbon nanotube or a C-60 molecule is investigated. By first integrating out the displacement field of the plasma or the electromagnetic field, different representations for quantities like the Casimir energy are derived which are shown to be consistent with one another. Starting from the covariant gauge for the electromagnetic field, it is shown that the matching conditions to which the presence of the plasma sheet can be reduced are different from the commonly used ones. The difference in the treatments does not show up in the Casimir force between two parallel sheets, but it is present in the Casimir-Polder force between a charge or a neutral atom and a sheet. At once, since the plasma sheet is a regularization of the conductor boundary conditions, this sheds light on the difference in physics found earlier in the realization of conductor boundary conditions as "thin" or "thick" boundary conditions in Phys. Rev. D 70, 085010 (2004).

• 20.
Leipzig University, Institute for Theoretical Physics, Leipzig, Germany.
Raith GmbH, Dortmund, Germany. Lunds University, Physics Department, Lund, Sweden. Halmstad University, School of Information Technology, Halmstad Embedded and Intelligent Systems Research (EIS), MPE-lab. University Rovira i Vergili, Taragona, Spain. University Rovira i Vergili, Taragona, Spain. Fraunhofer Institute for Factory Automation, Magdeburg, Germany.
Parallel nano-assembly directed by short-range field forces2006In: Proceedings of the 1st IEEE International Conference on Nano/Micro Engineered and Molecular Systems, Piscataway, United States: IEEE Press, 2006, p. 620-622, article id 4135031Conference paper (Refereed)

We present the ECs Sixth Framework Programme PARNASS project, which stands for 'Parallel nano assembling directed by short-range field forces' and represents a radical innovative approach to fabricating large volumes of hybrid nano electronic devices. The project combines in a synergy the 'top-down' and 'bottom-up' methods addressing one of the challenging physical and engineering problems of the very high accuracy over a large area. An array of specially designed nano-scale force field sources has to be a key part of this innovative approach to large-scale nano manufacturing. © 2006 IEEE.

• 21.
Halmstad University, School of Information Science, Computer and Electrical Engineering (IDE), Halmstad Embedded and Intelligent Systems Research (EIS), Applied Mathematics and Physics (CAMP).
Lund University. Halmstad University, School of Information Science, Computer and Electrical Engineering (IDE), Halmstad Embedded and Intelligent Systems Research (EIS), Applied Mathematics and Physics (CAMP). Lund University. Lund University. Lund University. Lund University. Halmstad University, School of Information Science, Computer and Electrical Engineering (IDE), Halmstad Embedded and Intelligent Systems Research (EIS), Applied Mathematics and Physics (CAMP).
Shear stress measurements on InAs nanowires by AFM manipulation2007In: Small, ISSN 1613-6810, Vol. 3, no 8, p. 1398-1401Article in journal (Refereed)

On an upward curve? The curvature of an elastically deformed nanowire pinned to a flat surface contains information about the maximum static friction force, and hence the shear stress, between the nanowire and the surface. Here, InAs nanowires are bent in a controlled manner using the tip of an atomic force microscope (see image). The shear stress can be obtained from a simple analysis according to the standard theory of elasticity.

• 22.
Institute for Solid State Physics, University of Jena, Jena, Germany.
Lund University, Lund, Sweden. Lund University, Lund, Sweden. Lund University, Lund, Sweden. Lund University, Lund, Sweden. Lund University, Lund, Sweden. Lund University, Lund, Sweden. Lund University, Lund, Sweden. Linnaeus University, Kalmar, Sweden. Halmstad University, School of Information Technology, Halmstad Embedded and Intelligent Systems Research (EIS), MPE-lab. Lund University, Lund, Sweden. Institute for Solid State Physics, University of Jena, Jena, Germany.
A New Route towards Semiconductor Nanospintronics: Highly Mn-Doped GaAs Nanowires Realized by Ion-Implantation under Dynamic Annealing Conditions2011Conference paper (Refereed)
• 23.
3-dimensional imaging of refractory material at Pilkington Halmstad1996Report (Refereed)
• 24.
Delivery test of the EISCAT Svalbard Radar Antenna1996Report (Refereed)
• 25.
Onsala Space Observatory, Onsala, Sweden.
mm VLBI1993In: VLBI Technology – Progress and Future Observational Possibilities: Proceedings of the International Symposium Held at Kyoto International Conference Hall on September 6-10, 1993 / [ed] Tetsuo Sasao, Seiji Manabe, Osamu Kameya & Makoto Inoue, Tokyo: Terra Scientific Publishing Company , 1993, p. 70-74Chapter in book (Refereed)

Very long Baseline Interferometry (VLBI) has now made its break-through into the mm wavelength regime. A global VLBI array has produced maps of radio sources at $\lambda$3 mm since 1988 and development is under way to improve the sensitivity for VLBI also at $\lambda$1 mm. This contribution discusses the present state of mm VLBI and the future developments.

• 26.
Halmstad University, School of Business, Engineering and Science, The Rydberg Laboratory for Applied Sciences (RLAS).
Istituto di Radioastronomia del C.N.R., Bologna, Italy. Istituto di Radioastronomia del C.N.R., Bologna, Italy.
High resolution interferometry of the QSO 1422+2021997In: Astronomy and Astrophysics. Supplement Series, ISSN 1286-4846, Vol. 125, no 1, p. 453-458Article in journal (Refereed)

We present VLA A-array observations at 8.4 and 15GHz and European VLBI Network (EVN) observations at 1.6GHz of the radio source 1422+202. It is suggested that 1422+202 is a Medium-size Object in the evolutionary sequence from Compact Steep-spectrum Sources to larger sized radio sources. The VLBI data were analysed with the phase referencing technique and we show that the EVN can work as a phase stable instrument for separations between the calibrator source and the target source up to ~ 10 degrees. With the VLA and VLBI observations we investigate some of the issues about the nucleus of 1422+202 and we discuss the possible cause for the low frequency variability detected while monitoring the source.

• 27.
Onsala Space Observatory, Chalmers University of Technology, Gothenburg, Sweden.
A closer look at active galactic nuclei — the great engines of the universe1992In: Physica scripta. T, ISSN 0281-1847, Vol. T43, p. 57-66Article in journal (Refereed)

The intensive radio emission from powerful radio galaxies and quasars Make these attractive candidates to become "standard candles" to probe the Universe. This paper discusses this possibility and the physics of the radio sources.

• 28.
Onsala Space Observatory, Onsala, Sweden.
AGN Variability and VLBI1994In: Multi-Wavelength Continuum Emission of Agn: Proceedings of the 159th Symposium of the International Astronomical Union, Held in Geneva, Switzerland, August 30 – September 3, 1993 / [ed] T.J.-L. Courvoisier & A. Blecha, Dordrecht: Kluwer Academic Publishers, 1994, p. 181-186Chapter in book (Refereed)

This contribution discusses the connection between variability in radio and optical with structural variations observed with VLBI. Structural changes do not have to start in the core, and intensity variations may be caused by components in the jet outside the core. The scenario is probably more complicated than present day theories assume.

• 29.
Onsala Space Observatory, Chalmers University of Technology, Gothenburg, Sweden.
Astrophysical global interferometry at Onsala Space Observatory1982In: Reports from the Observatory of Lund, ISSN 0349-4217, Vol. 18, p. 23-25Article in journal (Refereed)
• 30.
Onsala Space Observatory, Chalmers University of Technology, Gothenburg, Sweden.
Global Fringe Fitting Applied to 100 GHZ VLBI Data1991In: Frontiers of VLBI: Proceedings of the International VSOP Symposium held at the Institute of Space and Astronautical Science on December 5-7, 1989, and Proceedings of the mm-Wave VLBI Workshop held at the Nobeyama Radio Observatory on December 8-9, 1989 / [ed] H. Hirabayashi, M. Inoue & H. Kobayashi, Tokyo: Universal Academy Press , 1991, p. 353-359Chapter in book (Refereed)

Earlier epoches of mm VLBI observations relied on single baseline fit of delays and rates to find the fringes. This approach does not, however, make use of all available information and therefore is less sensitive than is necessary. Global fringe fitting makes use of all simultaneous data to find station related clock offsets and rates over a certain period of time. © Universal Academy Press, Inc.

• 31.
Onsala Space Observatory, Chalmers University of Technology, Gothenburg, Sweden.
Global fringe fitting applied to Mk3 VLBI data1991In: Radio Interferometry: Theory, Techniques, and Applications / [ed] T.J. Cornwell & R.A. Perley, San Francisco, USA: Astronomical Society of the Pacific , 1991, p. 321-325Conference paper (Refereed)

A system has been developed where data from a Mk3 VLBI processor can be read into the AIPS-package. Multiband and single-band delays can then be fitted globally by station. The technique has been used to phasereference a background to two radiogalaxies in the Abell cluster A2634.

• 32.
Onsala Space Observatory, Chalmers University of Technology, Gothenburg, Sweden.
High resolution images of Blazar cores1992In: Variability of Blazars: Proceedings of a conference in honour of the 100th anniversary of the birth of academician Yrjö Väisälä, held at Tuorla Observatory, University of Turku, Finland, January 6-10, 1991 / [ed] E. Valtaoja & M. Valtonen, Cambridge, UK: Cambridge University Press, 1992, p. 196-204Conference paper (Refereed)
• 33.
Onsala Space Observatory, Chalmers University of Technology, Gothenburg, Sweden.
High Resolution Observations of Low Frequency Variables at 932 MHz1987In: The Impact of VLBI on Astrophysics and Geophysics: Proceedings of the 129th Symposium of the International Astronomical Union held in Cambridge, Mass., U.S.A., May 10-15, 1987 / [ed] Reid, M. J. & Moran, J. M., Dordrecht: Kluwer Academic Publishers, 1987, p. 117-118Chapter in book (Refereed)

Fifteen sources known to be varying at low frequencies have been observed at six epochs during 1983–84 with a global VLBI array. Some of the sources show structural variations similar to the superluminals. Beaming effect may therefore play an important role at low as well as at higher frequencies.

• 34.
Onsala Space Observatory, Chalmers University of Technology, Gothenburg, Sweden.
Mapping in Practice1989In: Very Long Baseline Interferometry: Techniques and Applications / [ed] Felli, Marcello & Spencer, Ralph E., Dordrecht: Kluwer Academic Publishers, 1989, p. 199-230Chapter in book (Refereed)

The purpose of this lecture is to introduce the VLBI user to the practical details of mapping radio sources. I will concentrate on data processing and mapping with the AIPS (Thompson and D’Addario, 1982)-package. Other data reduction systems do exist, e.g. the Caltech-package and OLAF. These differ from AIPS mostly in the strategy for reaching the final and “best” map. It is more important to know the method and to be careful than what reduction procedure is used.

• 35.
Onsala Space Observatory, Chalmers University of Technology, Gothenburg, Sweden.
Millimetre VLBI capability status1993In: Sub-arcsecond Radio Astronomy: Proceedings of the Nuffield Radio Astronomy Laboratories' conference, held in Manchester, July 20–24, 1992 / [ed] R. J. Davis & R. S. Booth, Cambridge: Cambridge University Press, 1993, p. 431-433Chapter in book (Refereed)

The development of new reveiver and data reduction techniques have now made VLBI at mm wavelengths possible. This contribution discusses the capability of the present and future VLBI networks at λ1 and 3mm and compares with radio interferometers at other wavelength regimes.

• 36.
Onsala Space Observatory, Chalmers University of Technology, Gothenburg, Sweden.
mm VLBI vs. VSOP1991In: Frontiers of VLBI: Proceedings of the International VSOP Symposium held at the Institute of Space and Astronautical Science on December 5-7, 1989, and Proceedings of the mm-Wave VLBI Workshop held at the Nobeyama Radio Observatory on December 8-9, 1989 / [ed] H. Hirabayashi, M. Inoue & H. Kobayashi, Tokyo: Universal Academy Press , 1991, p. 197-201Chapter in book (Refereed)

VSOP-to-ground VLBI and mm VLBI are both needed if we want to further increase our knowledge of quasars, radio galaxies and their radio jets, mm VLBI will be a better instrument to study the "central engine" while satellite VLBI will better show the structure of the jets. The two instruments complement each other, and it is important to have a close collaboration. © Universal Academy Press, Inc.

• 37.
Onsala Space Observatory, Chalmers University of Technology, Gothenburg, Sweden.
New millimetric VLBI results1992In: Extragalactic radio sources - from beams to jets: Proceedings of the 7th IAP Meeting held at the Institut d'Astrophysique de Paris, Paris, France 2-5 July 1991 / [ed] J. Roland, H. Sol and G. Pelletier, Cambridge: Cambridge University Press, 1992, p. 137-144Conference paper (Refereed)
• 38.
Onsala Space Observatory, Chalmers University of Technology, Gothenburg, Sweden.
Radiogalaxer och kvasarer1990In: Astronomisk årsbok 1991, Johanneshov: Inova , 1990, p. 71-77Chapter in book (Refereed)
• 39.
Institutionen för astronomi, Lunds universitet, Lund, Sverige.
Radiospår i galaxhopar1973In: Astronomisk tidsskrift, ISSN 0004-6345, Vol. 6, no 1, p. 18-24Article in journal (Other academic)
• 40.
Onsala Space Observatory, Chalmers University of Technology, Gothenburg, Sweden.
Results from 100 GHz VLBI1991In: Frontiers of VLBI: Proceedings of the International VSOP Symposium held at the Institute of Space and Astronautical Science on December 5-7, 1989, and Proceedings of the mm-Wave VLBI Workshop held at the Nobeyama Radio Observatory on December 8-9, 1989 / [ed] H. Hirabayashi, M. Inoue & H. Kobayashi, Tokyo: Universal Academy Press , 1991, p. 285-295Chapter in book (Refereed)

Development of receiver and data reduction techniques have now made it possible to produce hybrid maps from global VLBI experiments observing at 100 GHz. Maps are shown here of the compact radio sources 3C 273, 3C 345, 3C 84, BL Lac and OJ 287 with angular resolution of 50 μas. The component born during the 1988 outburst of 3C 273 is seen only 2 month after its birth. The jet of 3C 345 is seen to have a larger curvature than has previously been observed.A component is seen moving outwards from the core of 3C84 with a speed of ≈21000 km sec-1. © Universal Academy Press, Inc.

• 41.
Onsala Space Observatory, Chalmers University of Technology, Gothenburg, Sweden.
Superluminal Motion in CTA 1021987In: Superluminal Radio Sources: Proceedings of a Workshop in honor of Professor Marshall H. Cohen, held at Big Bear Solar Observatory, California, October 28-30, 1986 / [ed] Zensus, J. Anton & Pearson, Timothy J., Cambridge: Cambridge University Press, 1987, p. 206-210Chapter in book (Refereed)
• 42.
Onsala Space Observatory, Chalmers University of Technology, Gothenburg, Sweden.
The Milliarcsecond Structure of some Extragalactic Objects1980Doctoral thesis, comprehensive summary (Other academic)
• 43.
Onsala Space Observatory, Chalmers University of Technology, Gothenburg, Sweden.
Varying gamma in 3C2731992In: Variability of Blazars: Proceedings of a conference in honour of the 100th anniversary of the birth of academician Yrjö Väisälä, held at Tuorla Observatory, University of Turku, Finland, January 6-10, 1991 / [ed] E. Valtaoja & M. Valtonen, Cambridge: Cambridge University Press, 1992, p. 229-233Conference paper (Refereed)
• 44.
Onsala Space Observatory, Chalmers University of Technology, Gothenburg, Sweden.
VLBI monitoring of BL Lac objects1983In: Highlights of Astronomy: as presented at the ... General assembly of the IAU. Vol. 6, As presented at the XVIIIth General assembly of the IAU, 1982 [in Patras, Greece, 17-26 August] / [ed] Richard M. West, Dordrecht: D. Reidel Publishing Group, 1983, p. 742-742Chapter in book (Refereed)
• 45.
Onsala Space Observatory, Chalmers University of Technology, Gothenburg, Sweden.
VLBI Monitoring of Bl-Lacertae Objects1984In: VLBI and Compact Radio Sources: Symposium no. 110 held in Bologna, Italy, June 27-July 1, 1983 / [ed] R. Fanti, K. Kellermann & G. Setti, Dordrecht: D. Reidel Publishing Group, 1984, p. 127-130Conference paper (Refereed)

This is a report on an ongoing project designed to study structural variations on the milliarcsecond scale in four BL Lac-type objects. The observations are made at λ6 cm with a global VLBI network consisting of the combined US and European networks. Hybrid maps at three epochs are presented for each of the sources AO 0235+164,0735+178, Mk 421, and 1749+701.

• 46.
Onsala Space Observatory, Chalmers University of Technology, Gothenburg, Sweden.
VLBI observations at 100 GHz1990In: Parsec-Scale radio jets: proceedings of a Workshop held at the National Radio Astronomy Observatory, Socorro, New Mexico, October 17-18, 1989 / [ed] Zensus, J. Anton & Pearson, Timothy J., Cambridge: Cambridge University Press, 1990, p. 91-97Chapter in book (Refereed)

We present maps using VLBI at 100 GHz of three sources, 3C273, 3C345, and 3C84. The resolution is 50 μas, the highest yet achieved.

• 47.
Onsala Space Observatory, Chalmers University of Technology, Gothenburg, Sweden.
Onsala Space Observatory, Chalmers University of Technology, Gothenburg, Sweden.
MmVLBI - High resolution imaging1991In: Radio Interferometry: Theory, Techniques, and Applications / [ed] T.J. Cornwell & R.A. Perley, San Francisco, USA: Astronomical Society of the Pacific , 1991, p. 326-329Conference paper (Refereed)

Hybrid maps at 100 GHz have been produced using VLBI data obtained at 100 GHz. The observations and global fringe fitting technique used to produce the maps are briefly described.

• 48.
Onsala Space Observatory, Chalmers University of Technology, Gothenburg, Sweden.
Massachusetts Institute of Technology, Cambridge, MA, USA. Massachusetts Institute of Technology, Cambridge, MA, USA. Massachusetts Institute of Technology, Cambridge, MA, USA. Massachusetts Institute of Technology, Cambridge, MA, USA. Haystack Observatory, Westford, MA, USA. Haystack Observatory, Westford, MA, USA. Haystack Observatory, Westford, MA, USA. Haystack Observatory, Westford, MA, USA. Goddard Space Flight Center, Greenbelt, MD, USA. Goddard Space Flight Center, Greenbelt, MD, USA. Jet Propulsion Laboratory, Pasadena, CA, USA.
Time-Dependent Radio Fine Structure of the Compact Sources NRAO 150 and 4C 39.251980In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 86, no 3, p. 364-372Article in journal (Refereed)

Very long baseline interferometer observations at 7.85 GHz have been used to probe the milliarcsecond structure of the unidentified, very compact radio source NRAO 150 and QSO 4 C 39.25. NRAO 150 exhibited no structural variations from 1972 to the end of 1974. A model with two circular Gaussian components fits the data well. NRAO 150 had a flux density of 7.6 plus or minus 0.5 Jy in the compact component; 4 C 39.25 showed a two-component structure, the components having a separation of (2.02 plus or minus 0.05 arc sec) x 10 to the -3rd power. The upper bound on the speed of transverse separation is 0.0001 arc sec per year or less than 2.7 c. From the spectrum there are also indications of a third, larger component.

• 49.
Onsala Space Observatory, Chalmers University of Technology, Gothenburg, Sweden.
Onsala Space Observatory, Chalmers University of Technology, Gothenburg, Sweden. Onsala Space Observatory, Chalmers University of Technology, Gothenburg, Sweden. Max-Planck-Institut für Radioastronomie, Bonn, Germany. Max-Planck-Institut für Radioastronomie, Bonn, Germany. Owens Valley Radio Observatory, Big Pine, CA, USA. Helsinki University of Technology, Radio Laboratory, Espoo, Finland. Netherlands Foundation for Radio Astronomy, Dwingenloo, The Netherlands.
The Radio Fine Structure of the BL Lacertae Objects AO0235+164, 0735+178, BL Lac, 1749+701, Mk 421 and 3C 66 A at 5 GHz1981In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 96, no 1-2, p. 316-324Article in journal (Refereed)

Very long baseline interferometer observations at 4997 MHz (lambda = 6 cm) on European and intercontinental baselines with lengths up to 1.35 108lambda have been used to probe the milliarc s structure of the BL Lacertae objects AO 0235+164, 0735+178, BL Lac, 1749+701, Mk 421, and 3C 66A. Two sets of observations are reported, made in November 1978 and March 1979. AO 0235+164 and 0735+178 both showed structures consisting of a very bright, unresolved core and a jet-like component extending ˜5".4 10-3 along position angle ˜20° and ˜4".2 10-3 along position angle ˜45°, respectively. AO 0235+164 contained more than 98% of the total flux density within a diameter of ≲ 36" 10-3. BL Lac, 1749+701 and Mk 421 all showed evidence for a complex structure of several components, including an unresolved core. 3 C 66A was elongated along position angle ˜ -45°.

• 50.
Onsala Space Observatory, Chalmers University of Technology, Gothenburg, Sweden.
EVN as a phase stable interferometer1991In: Radio Interferometry: Theory, Techniques, and Applications / [ed] T. J. Cornwell & R.A. Perley, San Francisco, USA: Astronomical Society of the Pacific Conference , 1991, p. 298-301Conference paper (Refereed)
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