| 1. |
- Bhatt, Pramod, et al.
(författare)
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Electronic structure of thin film iron-tetracyanoethylene : Fe(TCNE)x
- 2009
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Ingår i: Applied Physics A. - : Springer Science and Business Media LLC. - 0947-8396 .- 1432-0630. ; 95:1, s. 131-138
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Tidskriftsartikel (refereegranskat)abstract
- Thin film iron-tetracyanoethylene Fe(TCNE) x , x∼2, as determined by photoelectron spectroscopy, was grown in situ under ultra-high vacuum conditions using a recently developed physical vapor deposition-based technique for fabrication of oxygen- and precursor-free organic-based molecular magnets. Photoelectron spectroscopy results show no spurious trace elements in the films, and the iron is of Fe2+ valency. The highest occupied molecular orbital of Fe(TCNE) x is located at ∼1.7 eV vs. Fermi level and is derived mainly from the TCNE− singly occupied molecular orbital according to photoelectron spectroscopy and resonant photoelectron spectroscopy results. The Fe(3d)-derived states appear at higher binding energy, ∼4.5 eV, which is in contrast to V(TCNE)2 where the highest occupied molecular orbital is mainly derived from V(3d) states. Fitting ligand field multiplet and charge transfer multiplet calculations to the Fe L-edge near edge X-ray absorption fine structure spectrum yields a high-spin Fe2+ (3d6) configuration with a crystal field parameter 10Dq∼0.6 eV for the Fe(TCNE) x system. We propose that the significantly weaker Fe-TCNE ligand interaction as compared to the room temperature magnet V(TCNE)2 (10Dq∼2.3 eV) is a strongly contributing factor to the substantially lower magnetic ordering temperature (T C ) seen for Fe(TCNE) x -type magnets.
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| 2. |
- Blomqvist, M., et al.
(författare)
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Structural and tribological properties of cluster-assembled CNx films
- 2007
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Ingår i: Applied Physics A. - : Springer Science and Business Media LLC. - 0947-8396 .- 1432-0630. ; 87:4, s. 767-772
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Tidskriftsartikel (refereegranskat)abstract
- We report the structural and tribological characterization of nanostructured CNx thin films produced by the deposition of a supersonic carbon cluster beam assisted by nitrogen ion bombardment. The influence of the deposition parameters on the chemical composition and structure of the films has been systematically studied by X-ray photoelectron spectroscopy, elastic recoil detection analysis, transmission electron microscopy and atomic force microscopy. Depending on the deposition parameters, the films show a structure ranging from amorphous to disordered graphitic with interlinked planes. Nitrogen content depends on the nitrogen ion kinetic energy. The films have a very low density with a high surface roughness. Friction measurements at the nanoscale show a correlation between nitrogen content and mechanical properties of the system.
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| 3. |
- Bulgakova, Nadya, 1956, et al.
(författare)
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A general continuum approach to describe fast electronic transport in pulsed laser irradiated materials: the problem of Coulomb explosion
- 2005
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Ingår i: Applied Physics A. - : Springer Science and Business Media LLC. - 0947-8396 .- 1432-0630. ; 81, s. 345-356
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Tidskriftsartikel (refereegranskat)abstract
- We present a continuum model, based on a drift-diffusion approach, aimed at describing the dynamics of electronic excitation, heating, and charge-carrier transport in different materials (metals, semiconductors, and dielectrics) under femtosecond and nanosecond pulsed laser irradiation. The laser-induced charging of the targets is investigated at laser intensities above the material removal threshold. It is demonstrated that, for near-infrared femtosecond irradiation, charging of dielectric surfaces causes a sub-picosecond electrostatic rupture of the superficial layers, alternatively called Coulomb explosion (CE), while this effect is strongly inhibited for metals and semiconductors as a consequence of superior carrier transport properties. On the other hand, application of the model to UV nanosecond pulsed laser interaction with bulk silicon has pointed out the possibility of Coulomb explosion in semiconductors. For such regimes a simple analytical theory for the threshold laser fluence of CE has been developed, showing results in agreement with the experimental observations. Various related aspects concerning the possibility of CE depending on different irradiation parameters (fluence, wavelength and pulse duration) and material properties are discussed. This includes the temporal and spatial dynamics of charge-carrier generation in non-metallic targets and evolution of the reflection and absorption characteristics.
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| 4. |
- Bulgakova, Nadya, 1956, et al.
(författare)
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Possible role of charge transport in enhanced carbon nanotube growth
- 2006
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Ingår i: Applied Physics A. - : Springer Science and Business Media LLC. - 0947-8396 .- 1432-0630. ; 85, s. 109-116
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Tidskriftsartikel (refereegranskat)abstract
- We consider the role of electric fields during metal-catalysed thermal chemical vapour deposition growth of carbon nanotubes and show that enhanced growth occurs from a negatively biased electrode. An electric field, applied externally to the growing tubes and/or generated as a result of electron emission or self-biasing, may strongly affect the carbon supply through the catalyst nanoparticle, enhancing the growth rate. Different aspects of the growth process are analysed: the nature of the nanoparticle catalysis, carbon dissolution kinetics, electron emission from the nanotube tips, charge transport in the nanotube-catalytic nanoparticle system and carbon drift and diffusion through the catalyst under the action of the electric field. A fundamental tenet for modelling of charge-transport dynamics during the nanotube growth process is proposed.
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| 5. |
- Comini, E., et al.
(författare)
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Functional nanowires of tin oxide
- 2007
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Ingår i: Applied Physics A. - : Springer Science and Business Media LLC. - 0947-8396 .- 1432-0630. ; 89:1, s. 73-76
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Tidskriftsartikel (refereegranskat)abstract
- Quasi-one-dimensional nanostructures of tin oxide were produced in controlled conditions through condensation from the vapor phase. The preparation was assisted by noble metal catalysts and uniform single-crystalline nanowires were produced. The nucleation of nanowires was achieved at 470 °C, owing to the vapor-liquid-solid growth mechanism activated by the catalytic Pt clusters. The peculiar microstructural properties of these semiconducting metal oxide nanostructures will be summarized. The high aspect ratio and the high degree of crystallinity achieved for the nanowires foresee their functional exploitation. © 2007 Springer-Verlag.
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| 6. |
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| 7. |
- Dittmer, Staffan, 1970, et al.
(författare)
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Low ambient temperature CVD growth of carbon nanotubes
- 2006
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Ingår i: Applied Physics A. - : Springer Science and Business Media LLC. - 0947-8396 .- 1432-0630. ; 84, s. 243-246
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Tidskriftsartikel (refereegranskat)abstract
- We show that good quality single-walled and multi-walled carbon nanotubes can be grown on CMOS-compatible metal electrodes at ambient room temperature using highly localised catalyst heating at nanostructured electrodes. The method is relatively straightforward and allows considerable flexibility in the kinds of devices that can be fabricated as well as allowing CVD nanotube growth to take place in the close vicinity of temperature-sensitive materials and devices.
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| 8. |
- Enculecu, I., et al.
(författare)
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Current perpendicular to plane single-nanowire GMR sensor
- 2007
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Ingår i: Applied Physics A. - : Springer Science and Business Media LLC. - 0947-8396 .- 1432-0630. ; 86:1, s. 43-47
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Tidskriftsartikel (refereegranskat)abstract
- By electrochemical deposition in a single nanopore membrane we fabricate Cu/Co layered single nanowires, that exhibit up to 10% magnetoresistance at room temperature. Single nanopore membranes are prepared by irradiating polycarbonate membranes with exactly one swift heavy ion, and by subsequent chemical etching of the single ion track. Both dc and pulsed electrodeposition of single wires consisting of Cu-Co alloy and Cu/Co multilayers respectively, are performed from a bath containing the two metal ions. By sputtering a gold electrode on the upper membrane surface, the single nanowire embedded in the flexible polymer foil is reliably contacted. While alloy wires exhibit anisotropic magnetoresistance (AMR), multilayer wires display current-perpendicular-to-plane giant magnetoresistance (CPP-GMR) behavior. This demonstrates that both the fabrication and contacting methods are very suitable for the investigation of transport properties, without the necessity of lithographic processes and without manipulation of the nanowires. In addition, the method opens up many new possibilities for single nanowire-based sensors.
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| 9. |
- Fu, Y, et al.
(författare)
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Peak response wavelengths of p- and n-type InxGa1-xAs-InP quantum well infrared photodetectors
- 2005
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Ingår i: Applied Physics A. - : Springer Science Business Media. - 0947-8396 .- 1432-0630. ; 80:3, s. 523-528
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Tidskriftsartikel (refereegranskat)abstract
- p- and n-type InxGa1-xAs-InP quantum wells are suitable for multi-color infrared photodetector applications in atmospheric windows due to improved barrier quality and carrier-transport properties. We apply the k . p method to study the energy band structures and optical transition properties, which show that the peak response wavelengths of p- and n-type InxGa1-xAs-InP quantum well infrared photodetectors (QWIPs) are determined not only by the energy distance from the ground sublevels in the quantum well to the energy band edges of extended states, but also by the characteristics of the extended states. The optical phonon scattering process converts the broad absorption spectrum of the p-QWIP from 0 to 16 mum into a short-wavelength spectrum centered at 4.5 mum. The transport of electrons in the extended states of the n-QWIP is characterized by running wave boundary conditions, resulting in a theoretically optimal absorption rate by a 8-nm-thick In0.53Ga0.47As quantum well. Moreover, a conduction-band offset of 0.5 for an InxGa1-xAs- InP (x = 0.53) heterostructure gives the best data fitting of theoretical and experimental response peaks, whereas 0.55 is generally recommended in the literature.
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| 10. |
- Fu, Ying, et al.
(författare)
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Surface-plasmon-assisted electromagnetic field enhancement in semiconductor quantum dots
- 2007
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Ingår i: Applied Physics A. - : Springer Science and Business Media LLC. - 0947-8396 .- 1432-0630. ; 87:2, s. 167-169
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Tidskriftsartikel (refereegranskat)abstract
- The temporal development of incident electromagnetic plane waves across semiconductor quantum dots (QDs) is analyzed by the finite-difference time-domain method. By coating the QDs using thin metal films, surface plasmon polaritons (SPPs) can be created. As illustration, our modeling approach is applied to fluorescent multiphoton quantum dots made of cadmium sulphide of particular size (3.7 nm) and energy band gap (2.67 eV). When such a QD is coated by a metal film, a dipole-formed SPP is generated at the external surface of the coated QD by the incident electromagnetic wave with a photon energy of 1.34 eV corresponding to a two-photon process. When the thickness of the metal film is 0.37 nm, the peak intensity of the SPP oscillates through both the thin metal film and the core QD, resulting in an electromagnetic field inside the QD enhanced by a factor of 10, and thus an increased two-photon excitation that can be useful for bioimaging applications. Further increasing the metal film thickness blockades the SPP initially generated at the external surface of the coated QD from penetrating through the metal film, reducing the electromagnetic field inside the QD.
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