| 1. |
- Klason, Peter, et al.
(författare)
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A speed of sound based feed water temperature sensor
- 2012
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Ingår i: 9th International Temperature Symposium on Temperature. - : AIP. ; , s. 925-930
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Konferensbidrag (refereegranskat)abstract
- Controlling thermal power in the feed water line of a power plant presupposes both accurate flow and temperature measurement. In this application the temperature measurement is usually a single Pt-100. This results in a measurement error of several kelvin. In this study we have investigated two different sensors based on the speed of sound (SoS) in the flowing medium for measuring the average temperature across a flow pipe cross-section. This is a task within the on-going European research project called ENG-06. The two SoS-based temperature measuring sensors were investigated under laboratory conditions. Investigations were done using both homogenous and non-homogenous temperature distributions with temperature differences up to 25 K. In addition the influence of pressure (50-200 kPa) and flow rates (0.5-2 m/s) on the SoS devices were also investigated. Our results show that the SoS-based temperature principle is working. Furthermore, depending on the measurement conditions a SoS temperature measurement device significantly can reduce the deviation to the reference sensor compared with a single Pt-100 sensor. Relative reductions in the deviation to the reference of 20-85 % were possible to achieve. This opens for the possibility of increasing the energy efficiency in power plants as aimed for in the ENG-06 project.
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| 2. |
- Klason, Peter, et al.
(författare)
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Measuring Temperature in Pipe Flow with Non-Homogeneous Temperature Distribution
- 2014
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Ingår i: International journal of thermophysics. - : Springer Science and Business Media LLC. - 0195-928X .- 1572-9567. ; 35:3-4, s. 712-724
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Tidskriftsartikel (refereegranskat)abstract
- Accurate temperature measurements in flow lines are critical for many industrial processes. It is normally more a rule than an exception in such applications to obtain water flows with inhomogeneous temperature distributions. In this paper, a number of comparisons were performed between different 100 ohm platinum resistance thermometer (Pt-100) configurations and a new speed-of-sound-based temperature sensor used to measure the average temperature of water flows with inhomogeneous temperature distributions. The aim was to achieve measurement deviations lower than 1 K for the temperature measurement of water flows with inhomogeneous temperature distributions. By using a custom-built flow injector, a water flow with a hot-water layer on top of a cold-water layer was created. The temperature difference between the two layers was up to 32 K. This study shows that the deviations to the temperature reference for the average temperature of four Pt-100s, the multisensor consisting of nine Pt-100s, and the new speed-of-sound sensors are remarkably lower than the deviation for a single Pt-100 under the same conditions. The aim of reaching a deviation lower than 1 K was achieved with the speed-of-sound sensors, the configuration with four Pt-100s, and the multisensor. The promising results from the speed-of sound temperature sensors open the possibility for an integrated flow and temperature sensor. In addition, the immersion depth of a single Pt-100 was also investigated at three different water temperatures.
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| 3. |
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| 4. |
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| 5. |
- Klason, Peter, et al.
(författare)
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Temperature measurement in flow pipes : Comparison with single Pt-100 and multisensors
- 2013
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Ingår i: AIP Conference Proceedings. - : AIP. - 0094-243X. - 9780735411784 ; , s. 987-992
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Konferensbidrag (refereegranskat)abstract
- Accurate temperature measurements in flow lines are critical for many industrial processes. It is normally more a rule than an exception in such applications to obtain water flows with in-homogenous temperature distributions. In this paper a number of comparisons between different Pt-100 configurations used to measure the average temperature of water flows with in-homogenous temperature distributions were studied. By using a custom-built flow injector a water flow with a hot water layer on top of a cold water layer was created. The temperature difference between the two layers was up to 32K. The average temperature from a custom-built multiple Pt-100 sensors (consisting of 9 Pt-100) was used as reference. Our study shows that for a 32 K temperature difference between the two layers the deviation to the references decreased from about 4 K to 1 K by taking the average temperature of 4 Pt-100 mounted in the same pipe plane (90° apart) instead of a single Pt-100. Overall the deviation to the temperature reference for the average temperature of 4 Pt-100 is remarkable lower than the deviation for a single Pt-100 under the same conditions. In addition the immersion depth of a single Pt-100 was also investigated at three different water temperatures.
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| 6. |
- Merlone, Andrea, et al.
(författare)
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A new challenge for meteorological measurements : The meteoMet project-Metrology for meteorology
- 2013
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Ingår i: AIP Conference Proceedings. - : AIP. - 0094-243X .- 1551-7616. - 9780735411784 ; , s. 1030-1035
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Konferensbidrag (refereegranskat)abstract
- Climate change and its consequences require immediate actions in order to safeguard the environment and economy in Europe and in the rest of world. Aiming to enhance data reliability and reduce uncertainties in climate observations, a joint research project called MeteoMet-Metrology for Meteorology started in October 2011 coordinated by the Italian Istituto Nazionale di Ricerca Metrologica (INRiM). The project is focused on the traceability of measurements involved in climate change: surface and upper air measurements of temperature, pressure, humidity, wind speed and direction, solar irradiance and reciprocal influences between measurands. This project will provide the first definition at the European level of validated climate parameters with associated uncertainty budgets and novel criteria for interpretation of historical data series. The big challenge is the propagation of a metrological measurement perspective to meteorological observations. When such an approach will be adopted the requirement of reliable data and robust datasets over wide scales and long terms could be better met.
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| 7. |
- Al-Hilli, Safaa, 1965, et al.
(författare)
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Zinc oxide nanorods grown on two-dimensional macroporous periodic structures and plane Si as a pH sensor
- 2008
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Ingår i: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 103:1, s. 014302-014309
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Tidskriftsartikel (refereegranskat)abstract
- pH determination is a strong prerequisite for many biochemical and biological processes. We used two methods, namely, the electrochemical potential method (experimental) and site binding method (theoretical), to study the sensitivity of zinc oxide (ZnO) nanorods grown on two-dimensional macroporous periodic structures (2DMPPS) (p-and n-type) and plane n-type Si substrates for use as an intracellular pH sensing device. The dimension of these nanorods varied in radius between 50 and 300 nm and lengths of 1–10 μm. We found that the sensitivity of ZnO nanorods increases with reductions in size, from 35 mV/pH for D = 300 nm and L = 10 μm, to 58 mV/pH for D = 50 nm and L = 1 μm, using the site binding model. The experimental electrochemical potential difference for the ZnO nanorods working electrode versus Ag/AgCl reference electrode showed a high sensitivity range for ZnO nanorods grown on 2DMPPS n-Si substrate as compared to plane n-Si at room temperature for pH ranging from 4 to 12 in buffer and NaCl solutions
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| 8. |
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| 9. |
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| 10. |
- Bano, Nargis, et al.
(författare)
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Study of Radiative Defects Using Current-Voltage Characteristics in ZnO Rods Catalytically Grown on 4H-p-SiC
- 2010
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Ingår i: JOURNAL OF NANOMATERIALS. - : Hindawi. - 1687-4110 .- 1687-4129. ; 2010
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Tidskriftsartikel (refereegranskat)abstract
- High-quality ZnO rods were grown by the vapour-liquid-solid (VLS) technique on 4H-p-SiC substrate. The current transport mechanisms of the diodes at room temperature (RT) have been explained in term of the space-charge-limited current model based on the energy band diagram of ZnO rods/4H-p-SiC heterostructure. The tunneling mechanism via deep-level states was found to be the main conduction process at low-applied voltage but at trap-filled limit voltage VTFL all traps are filled and the space-charge-limited current conduction dominated the current transport. From the RT current voltage measurements, the energy of the deep level trap and the trap concentration were obtained as ∼0.24±0.02eV and 4.4×1018cm−3, respectively. The deep level states observed correspond to zinc interstitial (Zni ), responsible for the violet emission.
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| 11. |
- Borseth, T.M., et al.
(författare)
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Identification of oxygen and zinc vacancy optical signals in ZnO
- 2006
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Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 89:26, s. 262112-262115
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Tidskriftsartikel (refereegranskat)abstract
- Photoluminescence spectroscopy has been used to study single crystalline ZnO samples systematically annealed in inert, Zn-rich and O-rich atmospheres. A striking correlation is observed between the choice of annealing ambient and the position of the deep band emission (DBE) often detected in ZnO. In particular, annealing in O2 results in a DBE at 2.35±0.05 eV, whereas annealing in the presence of metallic Zn results in DBE at 2.53±0.05 eV. The authors attribute the former band to zinc vacancy (VZn) related defects and the latter to oxygen vacancy (VO) related defects. Additional confirmation for the VO and VZn peak identification comes from the observation that the effect is reversible when O- and Zn-rich annealing conditions are switched. After annealing in the presence of ZnO powder, there is no indication for the VZn- or VO-related bands, but the authors observe a low intensity yellow luminescence band peaking at 2.17 eV, probably related to Li, a common impurity in hydrothermally grown ZnO.
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| 12. |
- Brechensbauer Brandin, Madeleine, et al.
(författare)
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Centralen : Studier i området kring Stockholms Centralstation
- 1989
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Rapport (populärvet., debatt m.m.)abstract
- Denna skrift handlar om Centralen i Stockholm och dess närmaste omgivningar, Centralplan, T-centralen, Vasagatan och Klarabergsgatan. Den är resultatet av Arkitekturskolans arbete läsåret 1983- 84 och innehåller förutom en rad projekt också historiska utblickar och samtidskritiska resonemang. En stor del av innehållet redovisades redan våren 1984 - det skedde genom en utställning på Arkitekturmuseet och en preliminär publikation. Materialet har sedan svällt ut med innehållsrika uppsatser om Centralen, om äldre och nyare insatser för att förena konst och arkitektur och om den föga kända, ännu obebyggda Blekholmen.
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| 13. |
- Cervantes, Michel, et al.
(författare)
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Flow measurements in low-head hydro power plants
- 2012
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- Hydropower stands for a large part of the energy production portfolio in Sweden and provides about 50% of the electricity needs. Most of the turbines were built some decades ago and are in a need of refurbishment. An important refurbishment period started some years ago and will be continuous. Substantial production gains and adaptation to new market demands may be achieved with such refurbishments. Refurbishments are also stimulated by the government through the electricity certificate system. Efficiency step-ups are thus of importance but challenging due to the presence of mainly low head (H<50 m) machines in Sweden. During the last decades, the Winter-Kennedy method has been used to verify improvements of the efficiency by measuring before and after a refurbishment. The results have for a number of cases shown unpredictable results. There is a need of development to measure accurately the efficiency in order to evaluate the outcome of different refurbishment projects. A workgroup within the Swedish Hydropower Centre (Svenskt Vattenkraftcentrum, SVC) has been formed together with representatives from the majority of the hydro turbine industry in Sweden to address the challenge of flow measurements in low head hydraulic turbines. The present report presents the different methods available with their actual development status and potential to meet low head hydraulic machines constraints. The working group suggests several actions for the development of flow measurements in low head machines. They are divided in 2 categories: long term and short term. The long term actions are typical SVC projects for PhD or/and senior researcher while short term actions are projects for consultant or/and senior researcher. The following actions are suggested in a hierarchical order:Long term projects1. Development of the pressure-time method as an absolute and relative method2. Evaluation of scale-up formula and influence of the parameters differing between model and prototype such spiral inlet boundary conditionsShort term projects1. Procedure/road book for implementation, evaluation and reporting of the Winter-Kennedy method. Continue working on the common guideline drafted in SEK-TK4.2. Systematic error analysis of the Winter-Kennedy method3. Testing of the volumetric method on a full-scale unit to investigate capabilities and evaluate necessary development for low head hydro power plants4. Testing of the tracer dilution method on a full-scale unit to investigate capabilities and evaluate necessary development for low head hydro power plants
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| 14. |
- Counter, S Allen, et al.
(författare)
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MRI evidence of endolymphatic impermeability to the gadolinium molecule in the in vivo mouse inner ear at 9.4 tesla
- 2013
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Ingår i: The Open Neuroimaging Journal. - : Bentham Science Publishers Ltd.. - 1874-4400. ; 7, s. 27-31
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Tidskriftsartikel (refereegranskat)abstract
- OBJECTIVE:Previous in vivo experimental magnetic resonance imaging (MRI) investigations of the mammalian inner ear at 4.7 Tesla have indicated that intravenously injected gadolinium (Gd) penetrates the perilymphatic labyrinth, but not the endolymphatic membranous labyrinth. In the present study, high field MRI at 9.4T was used to visualize the in vivo mouse vestibulo-cochlea system, and to determine whether the endolymphatic system is permeable to a Gd complex.METHODS:A 9.4 T Varian magnet equipped with a 12 cm inner diameter gradient system with maximum gradient strength of 600 mT/m, a millipede coil (Varian design) and a Gd contrast agent were used for image acquisition in the normal C57 BL-6 mouse.RESULTS:High-resolution 2D and 3D images of the mouse cochlea were acquired within 80 minutes following intravenous injection of Gd. Gd initially permeated the perilymphatic scala tympani and scala vestibuli, and permitted visualization of both cochlear turns from base to apex. The superior, inferior and lateral semicircular canals were subsequently visualized in 3 planes. The membranous endolymphatic labyrinth was impermeable to intravenously injected Gd, and thus showed no apparent uptake of Gd at 9.4T.CONCLUSION:The 9.4T field strength MRI permitted acquisition of high resolution images of anatomical and physiological features of the normal, wild type mouse perilymphatic inner ear in vivo, and provided further evidence that the endolymphatic system is impermeable to intravenously injected Gd.
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| 15. |
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| 16. |
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| 17. |
- Ferreira da Silva, Antonio, et al.
(författare)
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Growth, Optical Characterization and Modelling of ZnO Nanorods on Si, SiC and Macroporous Si Structure
- 2009
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Ingår i: Nanotech 2009 Vol. 3Nanotechnology 2009: Biofuels, Renewable Energy, Coatings, Fluidics and Compact Modeling. - Austin, TX, USA : Nano Science and Technology Institute. - 9781439817841 ; , s. 206-209
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Zinc Oxide (ZnO) and 4H-SiC are prominent materials with large applicability such as optoelectronic nanodevices and for instance ultraviolet detectors. There is lack of more information about optical transitions beyond the indirect band gap energy (BGE) of 4H-SiC and even more for ZnO direct BGE grown on the former material. Using the vapor-liquid-solid and the aqueous chemical growth methods we have grown ZnO nanorods on different substrates, such as quartz, n- and p-type silicon porous silicon and n-type 4H-SiC. The Scanning electron microscopy (SEM) are shown and compared for all samples. We have calculated the absorption and energy gap by employing a first-principle and a full-potential linearized augmented plane-wave (FPLAPW) method within the local density approximation (LDA). The absorption of ZnO nanorods, on different substrates, is lower than that of quartz substrate when photon energy is low. It is shown the strong effect of 4H-SiC on ZnO nanorods. Experiment and theory show a good aggreement when the optical energy gap is considered for both materials.
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| 18. |
- Holmsten, Magnus, et al.
(författare)
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Development and Evaluation of a Co–C Eutectic-Point Cell for Thermocouple Calibration
- 2015
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Ingår i: International journal of thermophysics. - : Springer Science and Business Media LLC. - 0195-928X .- 1572-9567. ; 36:8, s. 1888-1894
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Tidskriftsartikel (refereegranskat)abstract
- The cobalt–carbon (Co–C) eutectic point at 1324∘C has in previous studies proved to be suitable as a reference for thermocouple calibration above 1100∘C. For types S, R, and B, it fills the gap between the copper point and the palladium point, and for Pt/Pd thermocouples, it extends the range from the copper point. This work describes the implementation of the Co–C reference point at the Technical Institute of Sweden (SP). A Co–C cell was developed and manufactured at SP in a collaboration project with the National Metrology Institute of Japan (NMIJ). The principle of the cell is a hybrid design with double walls, both for the outer crucible and the inner thermometer well, with graphite foil between the walls. To evaluate the performance of the developed cell (SP cell), a comparison between the SP cell and another cell, manufactured and provided from the National Physics Laboratory (NPL) in England, is performed using Pt/Pd thermocouples as transfer standards. The comparison showed very good agreement, with differences below 40 mK, using the same furnace and two different thermocouples. The expanded uncertainty (k=2) for the comparison was estimated to be 70 mK.
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| 19. |
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| 20. |
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| 21. |
- Klason, Peter, 1977, et al.
(författare)
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Electrical characteristics and stability of gold and palladium Schottky contacts on ZnO nanorods
- 2008
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Ingår i: Nanotechnology. - : IOP Publishing. - 0957-4484 .- 1361-6528. ; 19:47, s. 475202-
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Tidskriftsartikel (refereegranskat)abstract
- The electrical characteristics and stability of Pd and Au Schottky contacts on ZnO nanorods grown on glass substrate have been investigated. The nanorods were grown using the aqueous chemical growth method. The nanorods were characterized with scanning electron microscopy (SEM), x-ray diffraction (XRD) and photoluminescence (PL). Prior to the metal contact deposition, an insulating PMMA layer was deposited between the nanorods. The best-produced Schottky contact was an as-deposited Pd/ ZnO contact with an ideality factor of 1.7 +/- 0.43 and a barrier height of 0.67 +/- 0.09 eV. The relatively high ideality factor indicates that the current transport cannot be described by pure thermionic transport. The presence of surface states due to the high evaporation pressure is probably the reason for the high ideality factor. Post metal deposition annealing at 150 degrees C for 30 min in air lowered the barrier height and decreased the Au/ ZnO ideality factor but increased it for Pd/ ZnO. The current follows ohmic behavior when the applied forward bias, V-forward, is lower than 0.1 V, whereas for Vforward between 0.1 and 0.45 V the current follows I similar to exp(cV), and at higher forward biases the current-voltage characteristics follow the relation I similar to V-2, indicating that the space-charge current-limiting mechanism is dominating the current transport.
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| 22. |
- Klason, Peter, 1977, et al.
(författare)
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Fabrication and characterization of p-Si/n-ZnO heterostructured junctions
- 2008
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Ingår i: Microelectronics Journal.
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Tidskriftsartikel (refereegranskat)abstract
- In this paper ZnO nanorods and nanodots (with and without a SiO2 buffer layer) were grown on p-Si, forming p–n heterojunctions. The nanorod devices showed no visible electroluminescence (EL) emission but showed rectifying behavior. Covering around 60% of the length of the nanorods with PMMA produced an ideality factor of 3.91±0.11 together with a reverse saturation current of View the MathML source. Up to two orders of magnitude rectification was observed for the current at bias -3 and 3 V. The nanodot devices showed EL emission under forward bias conditions. It seems that the buffer layer increased both the stability and efficiency of the devices, since the buffer layer device could operate at larger applied voltage and showed EL emission under reverse bias.
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| 23. |
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| 24. |
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| 25. |
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| 26. |
- Klason, Peter, 1977, et al.
(författare)
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Synthesis and structural and optical properties of ZnO micro- and nanostructures grown by the vapour-liquid-solid method
- 2006
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Ingår i: Physica Scripta. - 0031-8949 .- 1402-4896. ; T126, s. 53-56
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Tidskriftsartikel (refereegranskat)abstract
- ZnO micro- and nanostructures have been grown by the catalytic vapour - liquid - solid method on silicon and silicon carbide. These micro- and nanostructures were characterized by scanning electron microscope, x-ray diffraction and photoluminescence measurements. The characterization shows that the ZnO nano- and microrods grown have diameters of around 200 nm on the Si substrates and 600 nm when using the SiC substrates. The length ranges from 0.5 to 10 mu m.
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| 27. |
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| 28. |
- Klason, Peter, 1977
(författare)
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Zinc Oxide Bulk and Nanorods
- 2008
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Zinc Oxide (ZnO) has many promising properties for optoelectronics, sensor applications, transparent electronics etc. To mention a few, ZnO has a large exciton binding energy (60 meV at room temperature) and a direct wide bandgap energy of 3.37 eV. In addition, ZnO is piezoelectric and shows more resistance to radiation damage than Si and GaN. The green luminescence band, or deep band emission (DBE), in ZnO has been studied for decades, but no clear consensus has been made. The first part of this thesis has been addressed to the issue of the origin of the DBE. Both an ion implantation and a systematic annealing study was performed. In the ion implantation study both Zn and O ions were implanted in different concentrations in bulk single crystal ZnO wafers. The photoluminescence (PL) intensity of the DBE decreased rapidly with increased concentration of implanted Zn ions, whereas the DBE intensity only slightly decreased with increased concentration of the implanted O ions. The comparison of DBE intensities together with PL measurements of the as-grown samples led to the conclusion that zinc vacancies (VZn) are involved in the DBE. In the annealing study single crystalline bulk ZnO wafers were annealed in different atmospheres, especially O- and Zn- rich atmospheres, in a systematic way. All samples were characterized with PL measurement performed from 27 K to room temperature. A striking correlation between the position of the DBE and the annealing condition was observed. In particular, for samples annealed in Zn-rich atmospheres the DBE peak position was located at 2.53 eV at room temperature, whereas annealing in O-rich conditions resulted in a DBE peak position located at 2.35 eV. The former peak position was attributed to VO and the later to VZn. Furthermore, both the VZn- and the VO-related PL band exhibited characteristic features when the measurement temperature was decreased. The peak position of the VZn-related band increased with decreased measurement temperature, while that of VO decreased. Secondly, phonon replicas were clearly observed in the DBE spectra in the sample containing VZn. Finally, for the VZn-enriched samples the decay curves showed strong wavelength dependence and generally slower decay components as compared to the sample enriched with VO. The results showed that the DBE is composed of at least two components, VZn and VO. Both of them have their own characteristic features promoting defect identification. In the second part of the thesis growth and properties of ZnO nanorods are discussed. Both the vapor-liquid-solid (VLS) and the aqueous chemical growth method were used. Laser action was observed at room temperature from vertically aligned nanorods under optical pumping. Secondly, Schottky contacts were demonstrated on ZnO nanorods grown on glass substrates. The best Schottky contact was the as deposited Pd/ZnO contact with an ideality factor of 1.74 pm 0.43 and a barrier height of 0.67 pm 0.09 eV. The presence of surface states due to the high evaporation pressure is probably the reason for the high ideality factor. Finally buckling of ZnO nanorods under uniaxial compression was studied. The critical load was found to be 477 μN. The Young’s modulus together with the critical buckling stress and strain for single nanorods was calculated using the Euler (for long nanorods) and Johnson (for intermediate nanorods) buckling models.
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| 29. |
- Lindahl, Anton, 1982, et al.
(författare)
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The electron affinity of tungsten
- 2010
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Ingår i: The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics. - : Springer Science and Business Media LLC. - 1434-6060 .- 1434-6079. ; 60:2, s. 219-222
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Tidskriftsartikel (refereegranskat)abstract
- The electron affinity of tungsten has been measured using laser photodetachment threshold spectroscopy in a collinear geometry. The electron affinity was determined to 6583.6(6) cm-1 by observing the onset of the process when W- ions in the 6S5/2 ground state are photodetached producing neutral W atoms in the 5D0 ground state. The measured value is in agreement with previous measurements and improves the accuracy by almost two orders of magnitude. Further, a photodetachment signal below the ground state photodetachment threshold was found, which indicates the existence of a bound excited state in W-.
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| 30. |
- Muhammad, Riaz, et al.
(författare)
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Bending flexibility, kinking, and buckling characterization of ZnO nanorods/nanowires grown on different substrates by high and low temperature methods
- 2008
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Ingår i: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 104:10, s. 104306-
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Tidskriftsartikel (refereegranskat)abstract
- Nanomechanical tests of bending flexibility, kinking, and buckling failure characterization of vertically aligned single crystal ZnO nanorods/nanowires were performed quantitatively by nanoindentation technique. These nanostructures were grown by the vapor liquid solid (VLS) method, a relatively high temperature approach, and the aqueous chemical growth (ACG) method, a relatively low temperature approach on different substrates, including SiC and Si. The first critical load at the inflection point found for the ZnO nanorods/nanowires grown by ACG method was 105 mu N on the SiC substrates and 114 mu N on the Si substrates. The corresponding buckling energies calculated from the force-displacement curves were 3.15x10(-12) and 2.337x10(-12) J, respectively. Similarly, for the samples grown by the VLS method, the first critical load at the inflection point and the corresponding buckling energies were calculated from the force-displacement curves as 198 mu N and 7.03x10(-12) J on the SiC substrates, and 19 mu N and 1.805x10(-13) J on the Si substrates. Moreover, the critical buckling stress, strain, and strain energy were also calculated for all samples. The strain energy for all samples was much less than the corresponding buckling energy. This shows that our as-grown samples are elastic and flexible. The elasticity measurement was performed for all the samples before reaching the first critical and kinking inflection point, and we subsequently observed the bending flexibility, kinking, and buckling phenomena on the same nanorods/nanowires. We observed that the loading and unloading behaviors during the bending test of the as-grown samples were highly symmetrical, and also that the highest point on the bending curves and the first inflection and critical point were very close. ZnO nanorods/nanowires grown on SiC by the ACG method, and those grown by the VLS method on Si substrates, show a linear relation and high modulus of elasticity for the force and displacement up to the first inflection and critical point. The results also show that the elasticity of the ZnO single crystal is approximately linear up to the first inflection point, is independent of the growth method and is strongly dependent on the verticality on the surface of the substrates. In addition, the results show that after the first buckling point, the nanorods/nanowires have plasticity, and become more flexible to produce multiple kinks.
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| 31. |
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| 32. |
- Noor, Hadia, et al.
(författare)
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Influence of background concentration induced field on the emission rate signatures of an electron trap in zinc oxide Schottky devices
- 2010
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Ingår i: JOURNAL OF APPLIED PHYSICS. - : American Institute of Physics. - 0021-8979 .- 1089-7550. ; 107:10
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Tidskriftsartikel (refereegranskat)abstract
- Various well-known research groups have reported points defects in bulk zinc oxide (ZnO) [ND (intrinsic): 1014–1017cm−3] naming oxygen vacancy, zinc interstitial, and/or zinc antisite having activation energy in the range of 0.32–0.22 eV below conduction band. The attribution is probably based on activation energy of the level which seems not to be plausible in accordance with Vincent et al., [J. Appl. Phys. 50, 5484 (1979)] who suggested that it was necessary to become vigilant before interpreting the data attained for a carrier trap using capacitance transient measurement of diodes having ND greater than 1015cm−3. Accordingly the influence of background free-carrier concentration, ND induced field on the emission rate signatures of an electron point defect in ZnO Schottky devices has been investigated by means of deep level transient spectroscopy. A number of theoretical models were tried to correlate with the experimental data to ascertain the mechanism. Consequently Poole–Frenkel model based on Coulomb potential was found consistent. Based on these investigations the electron trap was attributed to Zn-related charged impurity. Qualitative measurements like current-voltage and capacitance-voltage measurements were also performed to support the results.
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| 33. |
- Noor, Hadia, et al.
(författare)
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Time-delayed transformation of defects in zinc oxide layers grown along the zinc-face using a hydrothermal technique
- 2009
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Ingår i: JOURNAL OF APPLIED PHYSICS. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 105:12, s. 123510-
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Tidskriftsartikel (refereegranskat)abstract
- A study of deep level defects in a hydrothermally grown, intrinsically n-type zinc oxide (ZnO) device has been carried out using conventional deep level transient spectroscopy (DLTS). Performed under variable measurement conditions, DLTS demonstrates two electron trap levels, E-1 (dominant) and E-2, with activation energies E-c-0.22 +/- 0.02 eV and E-c-0.47 +/- 0.05 eV, respectively. A time-delayed transformation of shallow donor defects zinc(interstitial) and vacancy(oxygen) (Zn-i-VO) into the E-1 level has been observed. While the x-ray diffraction measurements reveal that the preferred direction of ZnO growth is along the (10 (1) over bar0) plane, i.e., the (Zn-i-V-O) complex, it is assumed that the (Zn-i-V-O) complex is transformed into a zinc antisite (Zn-O) under favorable conditions. As a result, the free carrier concentration decreases with increasing trap concentration. Henceforth, the E-1 level exhibiting the increase in concentration is attributed to ZnO.
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| 34. |
- Oberg, Johanna, et al.
(författare)
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Age related changes in brain metabolites observed by 1H MRS in APP/PS1 mice
- 2008
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Ingår i: Neurobiology of Aging. - : Elsevier BV. - 0197-4580 .- 1558-1497. ; 29:9, s. 1423-1433
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Tidskriftsartikel (refereegranskat)abstract
- Translational biomarkers in Alzheimer's disease based on non-invasive in vivo methods are highly warranted. (1)H magnetic resonance spectroscopy (MRS) is non-invasive and applicable in vivo in both humans and experimental animals. In vivo(1)H MRS and 3D MRI were performed on brains of double transgenic (tg) mice expressing a double mutant human beta-amyloid precursor protein APP(K670N,M671L) and human mutated presenilin gene PS1M146L, and wild-type (wt) littermates at 2.5, 6.5 and 9 months of age using a 9.4T magnet. For quantification, LCModel was used, and the data were analyzed using multivariate data analysis (MVDA). MVDA evidenced a significant separation, which became more pronounced with age, between tg and wt mice at all time points. While myo-inositol and guanidoacetate were important for group separation in young mice, N-acetylaspartate, glutamate and macrolipids were important for separation of aged tg and wt mice. Volume segmentation revealed that brain and hippocampus were readily smaller in tg as compared to wt mice at the age of 2.5 months. Amyloid plaques were seen in 6.5 and 9 months, but not in 2.5 months old animals. In conclusion, differences in brain metabolites could be accurately depicted in tg and wt mice in vivo by combining MRS with MVDA. First differences in metabolite content were readily seen at 2.5 months, when volume defects in tg mice were present, but no amyloid plaques.
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| 35. |
- Ogura, Kiteki, et al.
(författare)
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Comparison of Co–C Eutectic-Point Cells for Thermocouple Calibration Between SP and NMIJ
- 2014
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Ingår i: International journal of thermophysics. - : Springer Science and Business Media LLC. - 0195-928X .- 1572-9567. ; 36:2-3, s. 399-412
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Tidskriftsartikel (refereegranskat)abstract
- As recently reported, the metal–carbon eutectic points seem to be useful as practical reference points for calibrating thermocouples. The melting temperature of the cobalt–carbon eutectic point (Co–C, 1324◦C) is an ideal solution for a reference point being at approximately the middle between the freezing point of copper (1084.62◦C) and the melting point of palladium (1554.8◦C). In this study, a comparison of reference Co–C cells used for thermocouple calibration service was performed between the Technical Institute of Sweden (SP) and the National Metrology Institute of Japan (NMIJ) by means of two circulating Pt/Pd thermocouples and one circulating Co–C cell in order to investigate the reliability of thermocouple calibration at the Co–C eutectic point. The reference Co–C cell at SP was designed and constructed in the National Physical Laboratory (NPL), and provided to SP, while the reference Co–C cell at NMIJ as well as the circulating cell was designed and constructed at NMIJ. The melting temperature of the reference Co–C cells at SP and NMIJ were evaluated by using the calibrated radiation thermometers at NPL and NMIJ, respectively, prior to the circulation of the thermocouples and the cell between SP and NMIJ. The temperature difference between the reference cells of SP and NMIJ, as measured by means of the circulating thermocouples, was found to be within 0.33◦C, while that measured by means of the circulating cell was found to be within 0.22◦C. The temperature of reference cells at SP and NMIJ was found to agree within an expanded uncertainty (k=2) in spite of different temperature traceability chains. This means that the calibration of thermocouples at the Co–C eutectic point was sufficiently reliable.
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| 36. |
- Rahman, M. M., et al.
(författare)
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Fabrication and characterization of white light emitting diode based on ZnO nanorods on p-Si
- 2008
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Ingår i: 8th IEEE Conference on Nanotechnology, 2008. NANO '08.. - Piscataway, NJ, USA : IEEE. - 9781424421039 - 9781424421046 ; , s. 51-54
-
Konferensbidrag (refereegranskat)abstract
- Recently zinc oxide (ZnO) has drawn attention as it exhibits promising properties for making optoelectronic devices, biosensors. In this paper we will present our recent results from research work on the fabrication of light emitting diodes (LEDs) based on n-ZnO nanorods grown on p-Si by a low temperature chemical approach. The ideality factor of the p- Si/n-ZnO junctions was found to be 5.47+0.67. The high value is probably due to the presence of surface state. Structural, electrical and optical characterization from different processed LEDs will be presented and analyzed.
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| 37. |
- Riaz, M., et al.
(författare)
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Buckling and mechanical instability of ZnO nanorods grown on different substrates under uniaxial compression
- 2008
-
Ingår i: Nanotechnology. - : IOP Publishing. - 0957-4484 .- 1361-6528. ; 19:41
-
Tidskriftsartikel (refereegranskat)abstract
- Mechanical instability and buckling characterization of vertically aligned single-crystal ZnO nanorods grown on different substrates including Si, SiC and sapphire (a-Al2O3) was done quantitatively by the nanoindentation technique. The nanorods were grown on these substrates by the vapor-liquid-solid (VLS) method. The critical load for the ZnO nanorods grown on the Si, SiC and Al2O3 substrates was found to be 188, 205 and 130 µN, respectively. These observed critical loads were for nanorods with 280 nm diameters and 900 nm length using Si as a substrate, while the corresponding values were 330 nm, 3300 nm, and 780 nm, 3000 nm in the case of SiC and Al2O3 substrates, respectively. The corresponding buckling energies calculated from the force displacement curves were 8.46 × 10-12, 1.158 × 10-11 and 1.092 × 10-11 J, respectively. Based on the Euler model for long nanorods and the J B Johnson model (which is an extension of the Euler model) for intermediate nanorods, the modulus of elasticity of a single rod was calculated for each sample. Finally, the critical buckling stress and strain were also calculated for all samples. We found that the buckling characteristic is strongly dependent on the quality, lattice mismatch and adhesion of the nanorods with the substrate. © IOP Publishing Ltd.
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| 38. |
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| 39. |
- Svensson, Bengt Gunnar, et al.
(författare)
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Hydrothermally Grown Single-Crystalline Zinc Oxide; Characterization and Modification
- 2007
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Ingår i: MRS Proceedings Volume 1035 / 2007. - Warrendale, PA, USA : Materials Research Society.
-
Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- An overview of our recent results on characterization and modification of high-resistivity n-type bulk zinc oxide samples, grown by hydrothermal techniques, is given. Three specific topics are addressed; (i) the role of lithium (Li) as an electrically compensating impurity, (ii) extrinsic n-type doping by hydrogen implantation, and (iii) influence of annealing conditions on deep band emission. In (i), furnace annealing of as-grown samples at temperatures above ∼800 °C is shown to cause out-diffusion of residual Li impurities and concurrently, the resistivity decreases. After annealing at 1400 °C, a resistivity close to 10−1 Ωcm is obtained and the Li content is reduced from above 1017 cm−3 to the mid 1015 cm−3 range, providing evidence for the crucial role of Li as an electrically compensating impurity. For ion-implanted samples, vacancy clusters evolve during post-implant flash lamp annealing (20 ms duration) and these clusters appear to trap and deactivate Li with a resulting improvement of the n-type conductivity. However, these clusters have a limited stability and start to dissociate already after 1h at 900 °C, accompanied by a decrease in the conductivity. For topic (ii), n-type doping by hydrogen implantation is shown to enhance the conductivity by about 5 orders of magnitude already in the as-implanted state. Despite substantial loss of hydrogen, the conductivity remains stable, or even increases, after annealing up to ≥600 °C, and necessary conditions for doping by hydrogen are discussed. In (iii), the origin of the commonly observed deep band emission from monocrystalline zinc oxide is investigated using a concept of annealing as-grown samples in different atmospheres. A strong influence by the atmosphere and temperature is observed and the results can be interpreted in terms of dominant effects on the emission by vacancy-related defects.
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| 40. |
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| 41. |
- Willander, Magnus, 1948-, et al.
(författare)
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Excitonic effects in ZnO nanowires and hollow nanotubes
- 2007
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Ingår i: Proceedings of SPIE, the International Society for Optical Engineering. - : SPIE. - 0277-786X .- 1996-756X. ; 6486:648614
-
Tidskriftsartikel (refereegranskat)abstract
- Energy levels and wave functions of ground and excited states of an exciton are calculated by the method of imaginary time. Energy levels as functions of radius of single and double wall nanotube are studied. Asymptotic behavior of energy levels at large and small values of the radius using perturbation theory and adiabatic approximation is considered. Spatially indirect exciton in semiconductor nanowire is also investigated. Experimental result from high quality reproducible ZnO nanowires grown by low temperature chemical engineering is presented. State of the art high brightness white light emitting diodes (HB-LEDs) are demonstrated from the grown ZnO nano-wires. The color temperature and color rendering index (CRI) of the HB-LEDs values was found to be (3250 K, 82), and (14000 K, 93), for the best LEDs, which means that the quality of light is superior to one obtained from GaN LEDs available on the market today. The role of VZn and Vo on the emission responsible for the white light band as well as the peak position of this important wide band is thoroughly investigated in a systematic way.
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| 42. |
- Willander, Magnus, 1948, et al.
(författare)
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Fundamentals and properties of zinc oxide nanostructures: optical and sensing applications
- 2008
-
Ingår i: Superlattices and Microstructures. - : Elsevier BV. - 0749-6036 .- 1096-3677. ; 43:4, s. 352-61
-
Tidskriftsartikel (refereegranskat)abstract
- In this paper we will give an overview of the status of catalytic growth and of low-temperature chemical growth of ZnO nanostructures performed in our laboratory. Particularly results employing different substrates will be discussed. The second part deals with structural and optical properties of ZnO nanorods. The results from high resolution transmission electron microscope (HRTEM), scanning electron microscope (SEM), photoluminescence (PL), Cathodoluminescence (CL), and Electroluminescence (EL), on single nanowires will be shown. Our results on surface morphology, bulk and the position of the catalyst as well as the optical properties including UV emission, lasing and white emission will all be presented and discussed. In the third part experimental results from electroluminescence of ZnO nanorods on different substrates in the UV in addition to excellent white light emission obtained from samples grown at low temperature are to be given and discussed. Finally the sensing of molecules in water by ZnO nanorods will be discussed from a theoretical point of view. Also fundamental properties of polaritons and excitons in ZnO nanostructures are to be highlighted.
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| 43. |
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| 44. |
- Willander, Magnus, et al.
(författare)
-
Light-emitting diodes based on n-ZnO nano-wires and p-type organic semiconductors
- 2008
-
Ingår i: Proc. SPIE 6895. - : SPIE - International Society for Optical Engineering. ; 6895, s. 68950O-1-10-
-
Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- After our recent successful demonstration of high brightness white light emitting diodes (HB-LEDs) based on high temperature grown n-ZnO nanowires on different p-type semiconductors, we present here LEDs fabricated on n-ZnO nano-wires and p-type organic semiconductors. By employing a low temperature chemical growth (≤ 90 °C) approach for ZnO synthesis combined together with organic p-type semiconductors, we demonstrate high quality LEDs fabricated on a variety of different substrates. The substrates include transparent glass, plastic, and conventional Si. Different multi-layers of p-type organic semiconductors with or without electron blocking layers have been demonstrated and characterized. The investigated p-type organic semiconductors include PEDOT:PSS, which was used as a anode in combination with other p-type polymers. Some of the heterojunction diodes also contain an electron blocking polymer sandwiched between the p-type polymer and the n-ZnO nano-wire. The insertion of electron blocking layer is necessary to engineer the device for the desired emission. Structural and electrical results will be presented. The preliminary I-V characteristics of the organic-inorganic hybrid heterojunction diodes show good rectifying properties. Finally we also present our findings on the origin of the green luminescence band which is responsible of the white light emission in ZnO is discussed.
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| 45. |
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| 46. |
- Willander, Magnus, 1948, et al.
(författare)
-
Solid and soft nanostructured materials: fundamentals and applications
- 2005
-
Ingår i: Microelectronics Journal. - : Elsevier BV. - 0026-2692. ; 36:11, s. 940-949
-
Tidskriftsartikel (refereegranskat)abstract
- The scientific work worldwide on nanostructured materials is extensive as well as the work on the applications of nanostructured materials. We will review quasi two-, one- and zero-dimensional solid and soft materials and their applications. We will restrict ourselves to a few examples from partly fundamental aspects and partly from application aspects. We will start with trapping of excitons in semiconductor nanostructures. The subjects are: physical realizations, phase diagrams, traps, local density approximations, and mesoscopic condensates. From these fundamental questions in solid nanomaterials we will move to trapping of molecules in water using nanostructured electrodes. We will also discuss how to manipulate water (create vortices) by nanostructure materials. The second part deals with nanorods (nano-wires). Particularly we will exemplify with ZnO nanorods. The reason for this is that ZnO has: a very strong excitons binding energy (60 meV) and strong photon–excitons coupling energy, a strong tendency to create nanostructures, and properties which make the material of interest for both optoelectronics and for medical applications. We start with the growth of crystalline ZnO nanorods on different substrates, both crystalline (silicon, silicon carbide, sapphire, etc) and amorphous substrates (silicon dioxide, plastic materials, etc) for temperatures from 50 °C up to 900 °C. The optical properties and crystalline properties of the nanorods will be analyzed. Applications from optoelectronics (lasers, LEDs, lamps, and detectors) are analyzed and also medical applications like photodynamic cancer therapy are taken up. The third part deals with nano-particles in ZnO for sun screening. Skin cancer due to the exposure from the sun can be prevented by ZnO particles in a paste put on the exposed skin.
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| 47. |
- Willander, Magnus, 1948-, et al.
(författare)
-
ZnO nanowires : chemical growth, electro-deposition and application to intracellular nano-sensors
- 2008
-
Ingår i: Physica Status Solidi. C, Current topics in solid state physics. - : Wiley. - 1610-1634 .- 1610-1642 .- 1862-6351. ; 5:9, s. 3076-3083
-
Tidskriftsartikel (refereegranskat)abstract
- In this paper we present our results on growth, characterization, and nano-devices based on ZnO nano-structures. The ZnO nano-structures were grown by mainly two methods, the catalytic Vapor Liquid Solid (VLS) and the low temperature chemical growth. We show that by multiple coating combined with low temperature chemical growth, well aligned with size controlled ZnO nanowires on silicon substrates can be achieved. The dissolution, due to its important on the stability of ZnO nano-structures in aqueous medium, is then discussed and some preliminary experimental results are shown. Basic Optical characteristics of ZnO nano-rods are briefly discussed. Finally, electrochemical intracellular nano-sensors based on ZnO nano-wires are demonstrated as efficient nano-sensors for monitoring the human cell activity with minute pH changes. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
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| 48. |
- Zhao, QX, et al.
(författare)
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Deep-level emissions influenced by O and Zn implantations in ZnO
- 2005
-
Ingår i: Applied Physics Letters. - : American Institute of Physics. - 0003-6951 .- 1077-3118. ; 87:21
-
Tidskriftsartikel (refereegranskat)abstract
- A set of bulk ZnO samples implanted with O and Zn at various densities were investigated by photoluminescence. The implantation concentration of O and Zn is varied between 1x10(17)/cm(3) and 5x10(19)/cm(3). The samples were thermally treated in an oxygen gas environment after the implantation. The results clearly show the influence of O and Zn implantations on the deep-level emission. By comparing the photoluminescence spectra for the samples with different implantations, we can conclude that the V-Zn is responsible to the observed deep-level emission. In addition, a novel transition at the emission energy of 3.08 eV at 77 K appears in the O-implanted sample with 5x10(19)/cm(3) implantation concentration. The novel emission is tentatively identified as O-antisite O-Zn.
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| 49. |
- Zhao, Qingxiang, 1962, et al.
(författare)
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Growth of ZnO nanostructures by vapor-liquid-solid method
- 2007
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Ingår i: APPLIED PHYSICS A-MATERIALS SCIENCE & PROCESSING. - : Springer Science and Business Media LLC. - 0947-8396 .- 1432-0630. ; 88:1, s. 27-30
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Tidskriftsartikel (refereegranskat)
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| 50. |
- Zhao, Qingxiang, et al.
(författare)
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Synthesis and characterization of ZnO nanostructures grown on Si substrates
- 2006
-
Ingår i: Physica Scripta. - 0031-8949 .- 1402-4896. ; T126, s. 131-134
-
Tidskriftsartikel (refereegranskat)abstract
- ZnO nanostructures were grown by thermal evaporation technique on ( 001) Si substrate and were characterized by photoluminescence measurements, scanning electron microscope and x-ray measurements. The results show that the formation of ZnO nanostructures is strongly influenced by the growth conditions. By optimizing the growth conditions, orientated ZnO nanorods with a diameter of around 300 nm and lengths of 20 - 35 mu m have been achieved, and they show excellent optical properties. The laser action is observed at room temperature by using optical pumping.
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