| 1. |
- Bläckberg, Lisa, et al.
(författare)
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Investigations of surface coatings to reduce memory effect in plastic scintillator detectors used for radioxenon detection
- 2011
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Ingår i: Nuclear Instruments and Methods in Physics Research Section A. - : Elsevier BV. - 0168-9002 .- 1872-9576. ; 656:1, s. 84-91
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Tidskriftsartikel (refereegranskat)abstract
- In this work Al(2)O(3) and SiO(2) coatings are tested as Xe diffusion barriers on plastic scintillator substrates. The motivation is improved beta-gamma coincidence detection systems, used to measure atmospheric radioxenon within the verification regime of the Comprehensive Nuclear-Test-Ban Treaty. One major drawback with the current setup of these systems is that the radioxenon tends to diffuse into the plastic scintillator material responsible for the beta detection, resulting in an unwanted memory effect. Here, coatings with thicknesses between 20 and 900 nm have been deposited onto plastic scintillators, and investigated using two different experimental techniques. The results show that all tested coatings reduce the Xe diffusion into the plastic. The reduction is observed to increase with coating thickness for both coating materials. The 425 nm Al(2)O(3) coating is the most successful one, presenting a diffusion reduction of a factor 100, compared to uncoated plastic. In terms of memory effect reduction this coating is thus a viable solution to the problem in question.
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| 2. |
- Jogi, Indrek, et al.
(författare)
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Atomic layer deposition of high capacitance density Ta2O5-ZrO2 based dielectrics for metal-insulator-metal structures
- 2010
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Ingår i: Microelectronic Engineering. - : Elsevier BV. - 0167-9317 .- 1873-5568. ; 87:2, s. 144-149
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Tidskriftsartikel (refereegranskat)abstract
- We have investigated electrical properties of laminated atomic layer deposited films: ZrO2-Ta2O5, ZrO2-Nb2O5-Ta2O5, ZrO2-TaxNb1-xO5 and Ta2O5-ZrxNbyOz. Even though the capacitances of laminates were often higher compared to films of constituent materials with similar thickness, considerably higher charge storage factors, Q were achieved only when tetragonal ZrO2 was stabilized in ZrO2-Ta2O5 laminate and when the laminate thickness exceeded 50 rim. The decreased Q values in the case of most laminates were the result of increased leakage currents. In the case of thinner films only Ta2O5-ZrxNbyOz, stack possessed capacitance density and Q value higher than reference HfO2. Concerning the conduction mechanisms, in the case of thinner films, the Ta2O5 or TaxNb1-xO5 apparently controlled the leakage either by Richardson-Schottky emission or Poole-Frenkel effect. (C) 2009 Elsevier B.V. All rights reserved
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| 3. |
- Jogi, Indrek, et al.
(författare)
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Investigation of ZrO2-Gd2O3 Based High-k Materials as Capacitor Dielectrics
- 2010
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Ingår i: Journal of the Electrochemical Society. - : The Electrochemical Society. - 0013-4651 .- 1945-7111. ; 157:10, s. G202-G210
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Tidskriftsartikel (refereegranskat)abstract
- Atomic layer deposition (ALD) of ZrO2-Gd2O3 nanolaminates and mixtures was investigated for the preparation of a high permittivity dielectric material. Variation in the relative number of ALD cycles for constituent oxides allowed one to obtain films with controlled composition. Pure ZrO2 films possessed monoclinic and higher permittivity cubic or tetragonal phases, whereas the inclusion of Gd2O3 resulted in the disappearance of the monoclinic phase. Changes in phase composition were accompanied with increased permittivity of mixtures and laminates with low Gd content. Further increase in the lower permittivity Gd2O3 content above 3.4 cat. % resulted in the decreased permittivity of the mixtures. Leakage currents generally decreased with increasing Gd content, whereby laminated structures demonstrated smaller leakage currents than mixed films at a comparable Gd content. Concerning the bottom electrode materials, the best results in terms of permittivity and leakage currents were achieved with Ru, allowing a capacitance equivalent oxide thickness of similar to 1 nm and a current density of 3 X 10(-8) A/cm(2) at 1 V. Charge storage values up to 60 nC/mm(2) were obtained for mixtures and laminates with thickness below 30 nm. In general, at electric fields below 2-3 MV/cm, normal and trap-compensated Poole-Frenkel conduction mechanisms were competing, whereas at higher fields, Fowler-Nordheim and/or trap-assisted tunneling started to dominate.
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| 4. |
- Jõgi, Indrek, et al.
(författare)
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On the Structural and Optical Properties of Ultrathin Iron Oxide
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- Nanostructured iron oxides and especially hematite are interesting for a wide range of applications ranging from gas sensors to renewable solar hydrogen production. A promising method for deposition of low dimensional films is atomic layer deposition, ALD. Although a potent technique, ALD of ultrathin films is sensitive to the substrate and temperature conditions where initial formation of islands and crystallites influences the properties of the films. In this work the optical and structural properties of iron oxide films in the thickness range of 6 nm to 50 nm have been investigated. Below 10 nm nominal film thickness we find island formation and phase dependent particle crystallization that impose difficulties for ALD deposition of phase pure iron oxides on non-lattice matching substrates. For films between 10-20 nm, post-annealing steps were found to be needed to recrystallize iron polymorphs to hematite whereas for films thicker than 20 nm, phase pure hematite can be formed directly with ALD with very low influence of the substrate. Analysis of the indirect and direct band gaps of the thinnest films show a quantum confined blue shift of the absorption edge.
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| 5. |
- Jogi, Indrek, et al.
(författare)
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Phase Formation Behavior in Ultrathin Iron Oxide
- 2015
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Ingår i: Langmuir. - : American Chemical Society (ACS). - 0743-7463 .- 1520-5827. ; 31:45, s. 12372-12381
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Tidskriftsartikel (refereegranskat)abstract
- Nanostructured iron oxides, and especially hematite, are interesting for a wide range of applications ranging from gas sensors to renewable solar hydrogen production. A promising method for deposition of low-dimensional films is atomic layer deposition (ALD). Although a potent technique, ALD of ultrathin films is critically sensitive to the substrate and temperature conditions where initial formation of islands and crystallites influences the properties of the films. In this work, deposition at the border of the ALD window forming a hybrid ALD/pulsed CVD (pCVD) deposition is utilized to obtain a deposition less sensitive to the substrate. A thorough analysis of iron oxide phases formation on two different substrates, Si(100) and SiO2, was performed. Films between 3 and SO rim were deposited and analyzed with diffraction techniques, high-resolution Raman spectroscopy, and optical spectroscopy. Below 10 nm nominal film thickness, island formation and phase dependent particle crystallization impose constraints for deposition of phase pure iron oxides on non-lattice-matching substrates. Films between 10 and 20 nm thickness on SiO2 could effectively be recrystallized into hematite whereas for the corresponding films on Si(100), no recrystallization occurred. For films thicker than 20 nm, phase pure hematite can be formed directly with ALD/pCVD with very low influence of the substrate on either Si or SiO2. For more lattice matched substrates such as SnO2:F, Raman spectroscopy indicated formation of the hematite phase already for films with 3 rim nominal thickness and clearly for 6 nm films. Analysis of the optical properties corroborated the analysis and showed a quantum confined blue-shift of the absorption edge for the thinnest films.
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| 6. |
- Jogi, Indrek, et al.
(författare)
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Precursor-dependent structural and electrical characteristics of atomic layer deposited films : Case study on titanium oxide
- 2006
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Ingår i: Materials Science in Semiconductor Processing. - : Elsevier BV. - 1369-8001 .- 1873-4081. ; 9:6, s. 1084-1089
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Tidskriftsartikel (refereegranskat)abstract
- Thin (10-20 nm) TiO2 films were atomic layer deposited from TiCl4, Ti(OC2H5)(4), H2O and H2O2 in the substrate temperature range 125-350 degrees C. The structure, chemical composition and electrical properties were correlated to the process temperature and nature of precursors, whereas the effect of precursors on conduction mechanisms was considerable only in the films grown at 125 degrees C, otherwise controlled by oxide-electrode interfaces. The use of chloride resulted in films with highest permittivity while the use of hydrogen peroxide resulted in lowest permittivity but also in lowest leakage. The post-deposition (pre-metallization) annealing resulted in densification and (re)crystallization of TiO2 layer but also in thickening of low-permittivity interface layers.
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| 7. |
- Karlsson, Martin, 1982-, et al.
(författare)
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Dye-sensitized solar cells employing a SnO2-TiO2 core-shell structure made by atomic layer deposition
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Ingår i: Advanced Energy Materials.
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Tidskriftsartikel (refereegranskat)abstract
- This paper describes the synthesis and characterization of core-shell structures, based on a SnO2 and TiO2 for use in dye-sensitized solar cells (DSC). Atomic layer deposition is employed to control and vary the thickness of the TiO2 shell. Increasing the TiO2 shell thickness to 2 nm improves the device performance of liquid electrolyte DSC from 0.7 % to 3.5 %. The increase in efficiency originates from a higher open-circuit potential and a higher short-circuit current as well as an improvement in the electron lifetime. SnO2-TiO2 core-shell DSC devices retain their photo-voltage in darkness for longer than 500 seconds showing that electrons are contained in the core material. Finally core-shell structures were used for solid-state DSC applications using the hole transporting material 2,2’,7,7’,-tetrakis(N,N-di-p-methoxyphenyl-amine)-9,9’,-spirofluorene. Similar increases in devices performance are seen for these solid-state DSC devices.
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| 8. |
- Karlsson, Martin, et al.
(författare)
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Dye-sensitized Solar Cells Employing a SnO2-TiO2 Core-shell Structure Made by Atomic Layer Deposition
- 2013
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Ingår i: CHIMIA. - : Swiss Chemical Society. - 0009-4293 .- 2673-2424. ; 67:3, s. 142-148
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Tidskriftsartikel (refereegranskat)abstract
- This paper describes the synthesis and characterization of core-shell structures, based on SnO2 and TiO2, for use in dye-sensitized solar cells (DSc). Atomic layer deposition is employed to control and vary the thickness of the TiO2 shell. Increasing the TiO2 shell thickness to 2 nm improved the device performance of liquid electrolyte-based DSC from 0.7% to 3.5%. The increase in efficiency originates from a higher open-circuit potential and a higher short-circuit current, as well as from an improvement in the electron. lifetime. SnO2-TiO2 core-shell DSC devices retain their photovoltage in darkness for longer than 500 seconds, demonstrating that the electrons are contained in the core material. Finally core-shell structures were used for solid-state DSC applications using the hole transporting material 2,2',7,7',-tetrakis(N,N-di-p-methoxyphenyl-amine)-9,9',-spirofluorene. Similar improvements in device performance were obtained for solid-state DSC devices.
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| 9. |
- Kukli, Kaupo, et al.
(författare)
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Atomic layer deposition of Ru films from bis(2,5-dimethylpyrrolyl)ruthenium and oxygen
- 2012
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Ingår i: Thin Solid Films. - : Elsevier BV. - 0040-6090 .- 1879-2731. ; 520:7, s. 2756-2763
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Tidskriftsartikel (refereegranskat)abstract
- Ru thin films were grown on hydrogen terminated Si, SiO2, Al2O3, HfO2, and TiO2 surfaces by atomic layer deposition from bis(2,5-dimethylpyrrolyl)ruthenium precursor and oxygen. The 4-20 nm thick films on these surfaces consisted of nanocrystalline hexagonal metallic ruthenium, regardless of the deposition temperature. At the lowest temperatures examined, 250-255 degrees C, the growth of the Ru films was favored on silicon, compared to the growth on Al2O3, TiO2 and HfO2. At higher temperatures the nucleation and growth of Ru became enhanced in particular on HfO2, compared to the process on silicon. At 320-325 degrees C, no growth occurred on Si-H and SiO2-covered silicon. Resistivity values down to 18 mu Omega.cm were obtained for ca. 10 nm thick Ru films.
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| 10. |
- Kukli, Kaupo, et al.
(författare)
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Structure and morphology of Ru films grown by atomic layer deposition from 1-ethyl-1 '-methyl-ruthenocene
- 2010
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Ingår i: Journal of Crystal Growth. - : Elsevier BV. - 0022-0248 .- 1873-5002. ; 312:12-13, s. 2025-2032
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Tidskriftsartikel (refereegranskat)abstract
- Ru thin films were grown on TiO2, Al2O3, HfO2, and ZrO2 films as well as on HF-etched silicon and SiO2-covered silicon by atomic layer deposition from 1-ethyl-1'-methyl-ruthenocene, (CH3C5H4) (C2H5C5H4)Ru, and oxygen. The growth of Ru was obtained and characterized at temperatures ranging from 250 to 325 degrees C. On epitaxial rutile, highly oriented growth of Ru with hexagonal structure was achieved, while on other substrates the films possessed nonoriented hexagonal structure. Ruthenium oxide was not detected in the films. The lowest resistivity value obtained for 5.0-6.6 nm thick films was 26 mu Omega cm. The conductivity of the films depended somewhat on the deposition cycle time parameters and, expectedly, more strongly on the amount of deposition cycles. Increase in the deposition temperature of underlying metal oxide films increased the conductivity of Ru layers.
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| 11. |
- Li, Jiantong, et al.
(författare)
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Ink-jet printed thin-film transistors with carbon nanotube channels shaped in long strips
- 2011
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Ingår i: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 109:8, s. 084915-
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Tidskriftsartikel (refereegranskat)abstract
- The present work reports on the development of a class of sophisticated thin-film transistors (TFTs) based on ink-jet printing of pristine single-walled carbon nanotubes (SWCNTs) for the channel formation. The transistors are manufactured on oxidized silicon wafers and flexible plastic substrates at ambient conditions. For this purpose, ink-jet printing techniques are developed with the aim of high-throughput production of SWCNT thin-film channels shaped in long strips. Stable SWCNT inks with proper fluidic characteristics are formulated by polymer addition. The present work unveils, through Monte Carlo simulations and in light of heterogeneous percolation, the underlying physics of the superiority of long-strip channels for SWCNT TFTs. It further predicts the compatibility of such a channel structure with ink-jet printing, taking into account the minimum dimensions achievable by commercially available printers. The printed devices exhibit improved electrical performance and scalability as compared to previously reported ink-jet printed SWCNT TFTs. The present work demonstrates that ink-jet printed SWCNT TFTs of long-strip channels are promising building blocks for flexible electronics.
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