163 results on '"Ilkka Tittonen"'
Search Results
2. Direct GaAs Nanowire Growth and Monolithic Light‐Emitting Diode Fabrication on Flexible Plastic Substrates
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Vladislav Khayrudinov, Anastasiia Sorokina, Vidur Raj, Nikita Gagrani, Tomi Koskinen, Hua Jiang, Ilkka Tittonen, Chennupati Jagadish, Hark Hoe Tan, Harri Lipsanen, and Tuomas Haggren
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bendable ,flexible plastic substrates ,GaAs nanowires ,light-emitting diodes ,Applied optics. Photonics ,TA1501-1820 ,Optics. Light ,QC350-467 - Abstract
The growth of self‐catalyzed GaAs nanowires (NWs) and monolithic light‐emitting diode (LED) directly on flexible plastic substrates is reported. Dense GaAs NW forest is attained in self‐catalyzed mode using metalorganic vapor phase epitaxy. The NWs are shown to be crystalline with a zinc‐blende phase. The optical properties of the GaAs NWs are found to be promising in both photoluminescence emission and light‐trapping based on reflectance and transmittance measurements. The LED is fabricated from p‐type NWs by depositing Au as Ohmic contact and TiO2/ITO as an electron‐selective contact. The demonstrated NW growth and LED fabrication represent a significant step toward low‐cost, industrially feasible flexible III–V NW optoelectronic applications, as plastic is inexpensive, and the fabrication steps are compatible with roll‐to‐roll processing.
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- 2022
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3. Photodeposition of RuOx Nanostructures on TiO2 Films with a Controllable Morphology
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Erich Michael See, Camilla Tossi, Lassi Hällström, and Ilkka Tittonen
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Chemistry ,QD1-999 - Published
- 2020
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4. CuI p-type thin films for highly transparent thermoelectric p-n modules
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Bruno Miguel Morais Faustino, Diogo Gomes, Jaime Faria, Taneli Juntunen, Guilherme Gaspar, Catarina Bianchi, António Almeida, Ana Marques, Ilkka Tittonen, and Isabel Ferreira
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Medicine ,Science - Abstract
Abstract Developments in thermoelectric (TE) transparent p-type materials are scarce and do not follow the trend of the corresponding n-type materials – a limitation of the current transparent thermoelectric devices. P-type thermoelectric thin films of CuI have been developed by three different methods in order to maximise optical transparency (>70% in the visible range), electrical (σ = 1.1 × 104 Sm−1) and thermoelectric properties (ZT = 0.22 at 300 K). These have been applied in the first planar fully transparent p-n type TE modules where gallium-doped zinc oxide (GZO) thin films were used as the n-type element and indium thin oxide (ITO) thin films as electrodes. A thorough study of power output in single elements and p-n modules electrically connected in series and thermally connected in parallel is inclosed. This configuration allows for a whole range of highly transparent thermoelectric applications.
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- 2018
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5. Excitation-dependent fluorescence from atomic/molecular layer deposited sodium-uracil thin films
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Ville Pale, Zivile Giedraityte, Xi Chen, Olga Lopez-Acevedo, Ilkka Tittonen, and Maarit Karppinen
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Medicine ,Science - Abstract
Abstract Atomic/molecular layer deposition (ALD/MLD) offers unique possibilities in the fabrication of inorganic-organic thin films with novel functionalities. Especially, incorporating nucleobases in the thin-film structures could open new avenues in the development of bio-electronic and photonic devices. Here we report an intense blue and widely excitation-dependent fluorescence in the visible region for ALD/MLD fabricated sodium-uracil thin films, where the crystalline network is formed from hydrogen-bonded uracil molecules linked via Na atoms. The excitation-dependent fluorescence is caused by the red-edge excitation shift (REES) effect taking place in the red-edge of the absorption spectrum, where the spectral relaxation occurs in continuous manner as demonstrated by the time-resolved measurements.
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- 2017
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6. Effect of Synthesis Conditions of Nitrogen and Platinum Co-Doped Titania Films on the Photocatalytic Performance under Simulated Solar Light
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Daryna Ihnatiuk, Camilla Tossi, Ilkka Tittonen, and Oksana Linnik
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photocatalysis ,sol-gel ,titania ,platinum ,nitrogen ,XPS ,Chemical technology ,TP1-1185 ,Chemistry ,QD1-999 - Abstract
Platinum and nitrogen co-doped titania films of different surface morphologies obtained via a sol-gel process have been tested for tetracycline hydrochloride photocatalytic decomposition under simulated solar light. Titania crystallization to anatase is shown by XRD for all films. A shift of the bandgap edge toward the visible region in absorption spectra and, consequently, a narrowing of the bandgap is observed for some films doped with nitrogen and/or exposed to UV pretreatment. The surface peculiarities of the samples are presented by an SEM and TEM investigation. The surface saturation by Pt and N with a homogeneous distribution of Pt ions on the surface as well as bulk as established by XPS and EDS data can be achieved with a certain synthesis procedure. The influence of the platinum content and of the pretreatment procedure on the state and atomic surface concentration of incorporated nitrogen and platinum is studied by XPS analysis: substitutional and interstitial nitrogen, non-metal containing fragments, Pt0, Pt2+ and Pt4+ ions. The photocatalytic activity of the films is ruled by the presence of Pt2+ ions and N rather than Pt0. The formation of the polycrystalline titania structure and Pt0 nanoparticles (NPs) is confirmed by TEM and electron diffraction images. The mechanism of primary photocatalytic processes is proposed.
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- 2020
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7. Large-Area Thermal Distribution Sensor Based on Multilayer Graphene Ink
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Tomi Koskinen, Taneli Juntunen, and Ilkka Tittonen
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graphene ,thermoelectric ,sensor ,flexible ,Chemical technology ,TP1-1185 - Abstract
Emergent applications in wearable electronics require inexpensive sensors suited to scalable manufacturing. This work demonstrates a large-area thermal sensor based on distributed thermocouple architecture and ink-based multilayer graphene film. The proposed device combines the exceptional mechanical properties of multilayer graphene nanocomposite with the reliability and passive sensing performance enabled by thermoelectrics. The Seebeck coefficient of the spray-deposited films revealed an inverse thickness dependence with the largest value of 44.7 μV K−1 at 78 nm, which makes thinner films preferable for sensor applications. Device performance was demonstrated by touch sensing and thermal distribution mapping-based shape detection. Sensor output voltage in the latter application was on the order of 300 μV with a signal-to-noise ratio (SNR) of 35, thus enabling accurate detection of objects of different shapes and sizes. The results imply that films based on multilayer graphene ink are highly suitable to thermoelectric sensing applications, while the ink phase enables facile integration into existing fabrication processes.
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- 2020
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8. Printed Circuit-Based Thermoelectric Sensor Film for Temperature Distribution Measurements.
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Antti Immonen, Priyanka Goel, Tomi Koskinen, Matias Pekkanen, Ilkka Tittonen, Tommi Kärkkäinen, Pertti Silventoinen, and Mikko Kuisma
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- 2024
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9. Exploring the optimality of approximate state preparation quantum circuits with a genetic algorithm
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Tom Rindell, Berat Yenilen, Niklas Halonen, Arttu Pönni, Ilkka Tittonen, Matti Raasakka, Particle Physics and Astrophysics, Ilkka Tittonen Group, RWTH Aachen University, Aalto University, Department of Electronics and Nanoengineering, and Aalto-yliopisto
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noisy intermediate-scale quantum ,FOS: Computer and information sciences ,Quantum Physics ,Quantum state preparation ,Noisy intermediate-scale quantum ,Quantum circuit complexity ,Computer Science - Neural and Evolutionary Computing ,FOS: Physical sciences ,General Physics and Astronomy ,114 Physical sciences ,Genetic algorithm ,NISQ ,Nisq ,quantum circuit complexity ,genetic algorithm ,quantum state preparation ,Neural and Evolutionary Computing (cs.NE) ,Quantum Physics (quant-ph) - Abstract
We study the approximate state preparation problem on noisy intermediate-scale quantum (NISQ) computers by applying a genetic algorithm to generate quantum circuits for state preparation. The algorithm can account for the specific characteristics of the physical machine in the evaluation of circuits, such as the native gate set and qubit connectivity. We use our genetic algorithm to optimize the circuits provided by the low-rank state preparation algorithm introduced by Araujo et al., and find substantial improvements to the fidelity in preparing Haar random states with a limited number of CNOT gates. Moreover, we observe that already for a 5-qubit quantum processor with limited qubit connectivity and significant noise levels (IBM Falcon 5T), the maximal fidelity for Haar random states is achieved by a short approximate state preparation circuit instead of the exact preparation circuit. We also present a theoretical analysis of approximate state preparation circuit complexity to motivate our findings. Our genetic algorithm for quantum circuit discovery is freely available at https://github.com/beratyenilen/qc-ga ., Comment: 22 pages, 4 figures; version 2 changes: title changed, numerical analysis extended to 1000 random states, references added, other minor improvements, conclusions remain unaltered
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- 2023
10. Methodologies and Advanced Characterizations of Photoelectrochemical Processes
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Camilla Tossi, Ornella Laouadi, Ilkka Tittonen, and Aadesh P. Singh
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- 2022
11. Enhanced Thermoelectric Transport and Stability in Atomic Layer Deposited-HfO2/ZnO and TiO2/ZnO-Sandwiched Multilayer Thin Films
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Taneli Juntunen, Ilkka Tittonen, Yukiharu Uraoka, Mutsunori Uenuma, Camilla Tossi, Yasuaki Ishikawa, Jenichi Clairvaux Felizco, Jarkko Etula, Nara Institute of Science and Technology, Ilkka Tittonen Group, Physical Characteristics of Surfaces and Interfaces, Department of Electronics and Nanoengineering, Department of Chemistry and Materials Science, Aalto-yliopisto, and Aalto University
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Materials science ,Doping ,02 engineering and technology ,010402 general chemistry ,021001 nanoscience & nanotechnology ,01 natural sciences ,Bond-dissociation energy ,0104 chemical sciences ,Atomic layer deposition ,Chemical engineering ,Electrical resistivity and conductivity ,Thermoelectric effect ,General Materials Science ,Thermal stability ,Thin film ,0210 nano-technology ,Layer (electronics) - Abstract
Herein, enhancements in thermoelectric (TE) performance, both the power factor (PF) and thermal stability, are exhibited by sandwiching HfO2 and TiO2 layers onto atomic layer deposited-ZnO thin films. High-temperature TE measurements from 300 to 450 K revealed an almost two-fold improvement in electrical conductivity for TiO2/ZnO (TZO) samples, primarily owing to an increase in carrier concentration by Ti doping. On the other hand, HfO2/ZnO (HZO) achieved the highest PF values owing to maintaining Seebeck coefficients comparable to pure ZnO. HZO also exhibited excellent stability after multiple thermal cycles, which has not been previously observed for pure or doped ZnO thin films. Such improvement in both TE properties and thermal stability of HZO can be attributed to a shift in crystalline orientation from the a axis to c axis, as well as the high bond dissociation energy of Hf-O, stabilizing the ZnO structure. These unique properties exhibited by HZO and TZO thin films synthesized by atomic layer deposition pave the way for next-generation transparent TE devices.
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- 2020
12. Photoelectrochemical, photocatalytic and electrocatalytic behavior of titania films modified by nitrogen and platinum species
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Ilkka Tittonen, Anna Eremenko, V. S. Vorobets, D. V. Ihnatiuk, N. P. Smirnova, G. Kolbasov, O. Linnik, Kamila Kočí, Marcel Šihor, Camilla Tossi, Department of Electronics and Nanoengineering, Vernadsky Institute General and Inorganic Chemistry, VŠB – Technical University of Ostrava, National Academy of Sciences of Ukraine, Aalto-yliopisto, and Aalto University
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Materials science ,Band gap ,Materials Science (miscellaneous) ,Nanochemistry ,chemistry.chemical_element ,Quantum yield ,02 engineering and technology ,Electronic structure ,010402 general chemistry ,Photochemistry ,01 natural sciences ,Electrocatalytic oxygen and hydrogen evolution ,Photocatalytic NO decomposition ,Pt ions ,Electrical and Electronic Engineering ,Physical and Theoretical Chemistry ,Titania films ,Doping ,Oxygen evolution ,Nitrogen incorporation ,Cell Biology ,021001 nanoscience & nanotechnology ,Atomic and Molecular Physics, and Optics ,0104 chemical sciences ,chemistry ,Photocatalysis ,0210 nano-technology ,Platinum ,Biotechnology - Abstract
Co-doping of titania by N and Pt species was employed to tune the electronic structure and enhance the electrocatalytic and photocatalytic activity of the films. Herein, the different approaches of synthesis procedure of Pt- and Pt,N–TiO2 films were used to investigate their effect on the platinum oxidation states. The resulting different species of Pt led to the changes in the electronic structure of TiO2, with consequent bandgap narrowing, anodic shift of the flat band potential, and cathodic shift of the valence band The quantum yield efficiency was correlated with Pt0 atomic content and the relative atomic content of Ptn+–O–Ti fragments, whereas its decrease for some samples can be caused by the presence of N and Ptn+. The highest response for N2O photocatalytic decomposition was observed over Pt,N–TiO2 films. The presence of metal and non-metal species in TiO2 structure resulted in synergistic effect including (1) inhibition of recombination of the electrons and holes and (2) narrowing of the bandgap. Electrocatalytic properties in hydrogen and oxygen evolution reactions were improved by Pt doping. The formed Pt2+–O–Ti bonds rather than Pt nanoparticles are suggested to be responsible for the highest electrocatalytic activity. The additional UV exposure of the electrodes led to Pt NPs aggregation as a result of photodeposition of Pt ions. The mechanism of the Pt2+ photoreduction in TiO2 structure is proposed.
- Published
- 2021
13. Hydrogen induced interface engineering in Fe2O3–TiO2 heterostructures for efficient charge separation for solar-driven water oxidation in photoelectrochemical cells
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Aadesh P. Singh, Anders Hellman, Björn Wickman, Richard Baochang Wang, Camilla Tossi, Ilkka Tittonen, Department of Electronics and Nanoengineering, Chalmers University of Technology, Aalto-yliopisto, and Aalto University
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Photocurrent ,Materials science ,Valence (chemistry) ,Hydrogen ,business.industry ,General Chemical Engineering ,Doping ,chemistry.chemical_element ,Heterojunction ,02 engineering and technology ,General Chemistry ,Photoelectrochemical cell ,010402 general chemistry ,021001 nanoscience & nanotechnology ,01 natural sciences ,0104 chemical sciences ,Semiconductor ,chemistry ,Optoelectronics ,Reversible hydrogen electrode ,0210 nano-technology ,business - Abstract
Semiconductor heterostructure junctions are known to improve the water oxidation performance in photoelectrochemical (PEC) cells. Depending on the semiconductor materials involved, different kinds of junctions can appear, for instance, type II band alignment where the conduction and valence bands of the semiconductor materials are staggered with respect to each other. This band alignment allows for a charge separation of the photogenerated electron-hole pairs, where the holes will go from low-to-high valance band levels and vice versa for the electrons. For this reason, interface engineering has attracted intensive attention in recent years. In this work, a simplified model of the Fe2O3-TiO2 heterostructure was investigated via first-principles calculations. The results show that Fe2O3-TiO2 produces a type I band alignment in the heterojunction, which is detrimental to the water oxidation reaction. However, the results also show that interstitial hydrogens are energetically allowed in TiO2 and that they introduce states above the valance band, which can assist in the transfer of holes through the TiO2 layer. In response, well-defined planar Fe2O3-TiO2 heterostructures were manufactured, and measurements confirm the formation of a type I band alignment in the case of Fe2O3-TiO2, with very low photocurrent density as a result. However, once TiO2 was subjected to hydrogen treatment, there was a nine times higher photocurrent density at 1.50 V vs. the reversible hydrogen electrode under 1 sun illumination as compared to the original heterostructured photoanode. Via optical absorption, XPS analysis, and (photo)electrochemical measurements, it is clear that hydrogen treated TiO2 results in a type II band alignment in the Fe2O3-H:TiO2 heterostructure. This work is an example of how hydrogen doping in TiO2 can tailor the band alignment in TiO2-Fe2O3 heterostructures. As such, it provides valuable insights for the further development of similar material combinations.
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- 2021
14. Computational Study Revealing the Influence of Surface Phenomena in p-GaAs Water-Splitting Cells
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Camilla Tossi, Lassi Hällström, Ilkka Tittonen, Ilkka Tittonen Group, Department of Electronics and Nanoengineering, Aalto-yliopisto, and Aalto University
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Surface (mathematics) ,Materials science ,02 engineering and technology ,010402 general chemistry ,021001 nanoscience & nanotechnology ,01 natural sciences ,7. Clean energy ,0104 chemical sciences ,Surfaces, Coatings and Films ,Electronic, Optical and Magnetic Materials ,General Energy ,Chemical physics ,Water splitting ,Physical and Theoretical Chemistry ,0210 nano-technology - Abstract
A computational model of a photoelectrochemical cell describing the influence of competing surface reactions to the operation of the cell is presented. The model combines an optical simulation for the incident light intensity with fully self-consistent solution of drift-diffusion equations to accurately calculate the electronic state of the semiconductor electrode in a photoelectrochemical cell under operation. The solution is calculated for the full thickness of a typical wafer, while simultaneously solving the thin surface charge region with sufficient precision. In addition to comparing the simulated current–voltage response with experimental data, the simulation is shown to replicate experimental results from electrochemical impedance spectroscopy (EIS) measurements. The results show that considering optical losses in the system is crucial for accurate simulation. The model is capable of selectively characterizing the impact of material parameters on both current–voltage response and interface capacitance, while revealing the internal dynamics of the quasi-Fermi levels that are inaccessible by experimental methods.
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- 2021
15. Size- and density-controlled photodeposition of metallic platinum nanoparticles on titanium dioxide for photocatalytic applications
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Lassi Hällström, Ilkka Tittonen, Marko Vaelma, Jorma Selin, Camilla Tossi, Jouko Lahtinen, Erich M. See, Ilkka Tittonen Group, Department of Electronics and Nanoengineering, Surface Science, Department of Applied Physics, Aalto-yliopisto, and Aalto University
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Fabrication ,Materials science ,ta114 ,Renewable Energy, Sustainability and the Environment ,Scanning electron microscope ,ta221 ,Nanoparticle ,02 engineering and technology ,General Chemistry ,021001 nanoscience & nanotechnology ,Platinum nanoparticles ,Metal ,chemistry.chemical_compound ,X-ray photoelectron spectroscopy ,Chemical engineering ,chemistry ,visual_art ,Titanium dioxide ,visual_art.visual_art_medium ,Photocatalysis ,General Materials Science ,ta216 ,0210 nano-technology - Abstract
Photodeposition has been demonstrated to be a reliable tool for the growth of co-catalyst nanoparticles on titanium dioxide. The current state of investigation on the technique, however, lacks a comprehensive study on the collective influence of different process parameters, preferring to confront the effect of a single parameter at a time. This paper presents a parametric study on photodeposition of platinum nanoparticles from liquid precursors on ALD-grown titanium dioxide, applicable to the fabrication of photocatalytic composite materials. In the described process, a systematic and rigorous statistical analysis of the photodeposition parameters is conducted, assessing the influential parameters that control and predict the size, density and loading of the deposited nanoparticles. The results are assessed by scanning electron microscopy, statistical analysis of micrographs, and X-ray photoelectron spectroscopy. This confirms the simplicity and the viability of photodeposition as a method for the self-assembly of metal nanoparticles from liquid precursors and provides all-round insight on the role of parameters such as the concentration of sacrificial reagents, the presence of H 2SO 4, and the concentration of the precursor solution, in the chemical and structural properties of the deposited nanoparticles.
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- 2019
16. Large-area implementation and critical evaluation of the material and fabrication aspects of a thin-film thermoelectric generator based on aluminum-doped zinc oxide
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Riina Ritasalo, Kirsi Tappura, Mikko Ruoho, Marko Pudas, Taneli Juntunen, Kaarle Jaakkola, Ilkka Tittonen, VTT Technical Research Centre of Finland, Department of Electronics and Nanoengineering, Picosun Oy, Aalto-yliopisto, and Aalto University
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Aluminum-doped zinc oxide ,Finite element method ,Fabrication ,Materials science ,020209 energy ,finite element method ,thin-film TEG ,FOS: Physical sciences ,Thin-film TEG ,02 engineering and technology ,Applied Physics (physics.app-ph) ,7. Clean energy ,Atomic layer deposition ,Aluminum doped zinc oxide ,0202 electrical engineering, electronic engineering, information engineering ,0601 history and archaeology ,SDG 7 - Affordable and Clean Energy ,Thin film ,large-area thermoelectric generator ,060102 archaeology ,Renewable Energy, Sustainability and the Environment ,business.industry ,aluminum-doped zinc oxide ,Physics - Applied Physics ,06 humanities and the arts ,Thermoelectric generator ,13. Climate action ,atomic layer deposition ,Optoelectronics ,Large-area thermoelectric generator ,business - Abstract
A large-area thermoelectric generator (TEG) utilizing a folded thin-film concept is implemented and the performance evaluated for near room temperature applications having modest temperature gradients (< 50 K). The TEGs with the area of ~0.33 m^2 are shown capable of powering a wireless sensor node of multiple sensors suitable e.g. for monitoring environmental variables in buildings. The TEGs are based on a transparent, non-toxic and abundant thermoelectric material, i.e. aluminium-doped zinc oxide (AZO), deposited on flexible substrates. After folding, both the electrical current and heat flux are in the plane of the thermoelectric thin-film. Heat leakage in the folded TEG is shown to be minimal (close to that of air), enabling sufficient temperature gradients without efficient heat sinks, contrary to the conventional TEGs having the thermal flux and electrical current perpendicular to the plane of the thermoelectric films. The long-term stability studies reveal that there are no significant changes in the electrical or thermoelectric properties of AZO over several months, while the contact resistance between AZO and silver ink is an issue exhibiting a continuous increase over time. The performance of the TEGs and technological implications in relation to a state-of-the-art thermoelectric material are further assessed via a computational study., 15 pages, 5 figures, post-peer-review, pre-copyedit version of an article published in Renewable Energy
- Published
- 2020
17. Thermoelectric Characteristics of InAs Nanowire Networks Directly Grown on Flexible Plastic Substrates
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Tomi Koskinen, Ilkka Tittonen, Vladislav Khayrudinov, Harri Lipsanen, Tuomas Haggren, Hua Jiang, Fahimeh Emadi, Department of Electronics and Nanoengineering, Department of Electrical Engineering and Automation, NanoMaterials, Department of Applied Physics, Aalto-yliopisto, and Aalto University
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Materials science ,Fabrication ,business.industry ,Nanowire ,Energy Engineering and Power Technology ,indium arsenide ,thermoelectric ,MOVPE ,chemistry.chemical_compound ,Semiconductor ,chemistry ,nanowire ,Thermoelectric effect ,Hardware_INTEGRATEDCIRCUITS ,Materials Chemistry ,Electrochemistry ,Chemical Engineering (miscellaneous) ,Optoelectronics ,Metalorganic vapour phase epitaxy ,Electrical and Electronic Engineering ,Indium arsenide ,flexible ,business ,III-V - Abstract
Publisher Copyright: © III-V semiconductor nanowires have shown promise for thermoelectric applications, but their use in practical devices has conventionally been hindered by complex fabrication processes and device integration. Here, we characterize the thermoelectric properties of InAs nanowire networks directly grown on flexible polyimide plastic. The n-type nanowire networks achieve a high room-temperature Seebeck coefficient of -110.8 mu V K-1 and electrical conductivity of 41 S cm(-1), resulting in a thermoelectric power factor of 50.4 mu W m(-1) K-2. Moreover, the nanowire networks show remarkable mechanical flexibility with a relative change in resistance below 0.01 at bending radii below 5.2 mm. We further establish the thermoelectric performance of InAs nanowire networks on plastic using a facile proof-of-concept thermoelectric generator producing a maximum power of 0.44 nW at a temperature gradient of 5 K. The findings indicate that direct growth of III-V nanowire networks on plastic substrates shows promise for the development of flexible thermoelectrics applications.
- Published
- 2021
18. Atomic layer deposition of Zr-sandwiched ZnO thin films for transparent thermoelectrics
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Tomi Koskinen, Ulrika Volin, Camilla Tossi, Ramesh Raju, Ilkka Tittonen, Department of Electronics and Nanoengineering, Aalto-yliopisto, and Aalto University
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Mechanics of Materials ,Mechanical Engineering ,atomic layer deposition ,zinc oxide ,zirconium ,General Materials Science ,Bioengineering ,General Chemistry ,transparent ,Electrical and Electronic Engineering ,thermoelectric - Abstract
Funding Information: The authors acknowledge the financial support from the Academy of Finland projects 319018 eVapor and 329406 CarbonSurf as well as from the Photonics Flagship PREIN. T.K. acknowledges the doctoral school of Aalto University School of Electrical Engineering, Walter Ahlström foundation and Waldemar Von Frenckell foundation for financial support. C.T. acknowledges the financial support of the Yrjö, Vilho ja Kalle Väisälä Fund and of the Finnish Academy of Sciences and Letters. The experimental work was carried out in Micronova, the nanofabrication facility of Aalto University. Edgar Maiorov is acknowledged for ALD equipment support. Dr Vladimir Kornienko is acknowledged for helping with the transmission measurement. The characterization by XRD, TEM and FIB was carried out in the Nanomicroscopy Center of Aalto University. Funding Information: The authors acknowledge the financial support from the Academy of Finland projects 319018 eVapor and 329406 CarbonSurf as well as from the PhotonicsFlagship PREIN. T.K. acknowledges the doctoral school of Aalto University School of Electrical Engineering, Walter Ahlström foundation and Waldemar Von Frenckell foundation for financial support. C.T. acknowledges the financial support of the Yrjö, Vilho ja Kalle Väisälä Fund and of the Finnish Academy of Sciences and Letters. The experimental work was carried out in Micronova, the nanofabrication facility of Aalto University. Edgar Maiorov is acknowledged for ALD equipment support. Dr Vladimir Kornienko is acknowledged for helping with the transmission measurement. The characterization by XRD, TEM and FIB was carried out in the Nanomicroscopy Center of Aalto University. Publisher Copyright: © 2022 The Author(s). Published by IOP Publishing Ltd. Atomic layer deposited (ALD) transparent thermoelectric materials enable the introduction of energy harvesting and sensing devices onto surfaces of various shapes and sizes in imperceptible manner. Amongst these materials, ZnO has shown promising results in terms of both thermoelectric and optical characteristics. The thermoelectric performance of ZnO can be further optimized by introducing extrinsic doping, to the realization of which ALD provides excellent control. Here, we explore the effects of sandwiching of ZrO2 layers with ZnO on glass substrates. The room-temperature thermoelectric power factor is maximised at 116μW m−1 K−2 with samples containing a 2% nominal percentage of ZrO2. The addition of ZrO2 layers is further shown to reduce the thermal conductivity, resulting in a 20.2% decrease from the undoped ZnO at 2% doping. Our results contribute to increasing the understanding of the effects of Zr inclusion in structural properties and growth of ALD ZnO, as well as the thermal and thermoelectric properties of Zr-doped ZnO films in general.
- Published
- 2022
19. MOVPE growth of InSb nanowires directly on flexible plastic substrates
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Vladislav Khayrudinov, Krzysztof Murawski, Harri Lipsanen, Małgorzata Kopytko, Kacper Grodecki, Hua Jiang, Ilkka Tittonen, Tomi Koskinen, Lide Yao, and Tuomas Haggren
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Materials science ,Semiconductor ,business.industry ,Thermal resistance ,Nanowire ,Optoelectronics ,Light emission ,Substrate (electronics) ,Metalorganic vapour phase epitaxy ,Epitaxy ,business ,Polyimide - Abstract
Semiconductor nanowires are routinely grown on high-priced crystalline substrates as it is extremely challenging to grow directly on plastics and flexible substrates due to high temperature requirements and substrate preparation. At the same time, plastic substrates can offer many advantages such as extremely low price, light weight, mechanical flexibility, shock and thermal resistance, and biocompatibility. We explore the direct growth of InSb nanowires on flexible plastic substrates by metal-organic vapor phase epitaxy (MOVPE). We synthesize InSb nanowires on polyimide and show that the fabricated NWs are optically active with strong light emission even at RT. Overall, we demonstrate that InSb nanowires can be synthesized directly on flexible plastic substrates inside a MOVPE reactor, and we believe that our results will further advance the development of the nanowire-based flexible electronic devices.
- Published
- 2021
20. Thermal conductivity suppression in GaAs-AlAs core-shell nanowire arrays
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Vladislav Khayrudinov, Ilkka Tittonen, Harri Lipsanen, Taneli Juntunen, Hua Jiang, Tomi Koskinen, Tuomas Haggren, Department of Electronics and Nanoengineering, Ilkka Tittonen Group, Australian National University, Department of Applied Physics, Aalto-yliopisto, and Aalto University
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Materials science ,Phonon ,business.industry ,Nanowire ,Physics::Optics ,Heterojunction ,02 engineering and technology ,010402 general chemistry ,021001 nanoscience & nanotechnology ,Thermoelectric materials ,Condensed Matter::Mesoscopic Systems and Quantum Hall Effect ,01 natural sciences ,7. Clean energy ,0104 chemical sciences ,Condensed Matter::Materials Science ,Semiconductor ,Thermal conductivity ,Thermal ,Optoelectronics ,General Materials Science ,0210 nano-technology ,business ,Transport phenomena - Abstract
openaire: EC/H2020/645241/EU//TransFlexTeg Semiconductor nanowire heterostructures have been shown to provide appealing properties for optoelectronics and solid-state energy harvesting by thermoelectrics. Among these nanoarchitectures, coaxial core–shell nanowires have been of primary interest due to their electrical functionality, as well as intriguing phonon localization effects in the surface-dominated regime predicted via atomic simulations. However, experimental studies on the thermophysical properties of III–V semiconductor core–shell nanowires remain scarce regardless of the ubiquitous nature of these compounds in solid-state applications. Here, we present thermal conductivity measurements of the arrays of GaAs nanowires coated with AlAs shells. We unveil a strong suppression in thermal transport facilitated by the AlAs shells, up to ∼60%, producing a non-monotonous dependence of thermal conductivity on the shell thickness. Such translation of the novel heat transport phenomena to macroscopic nanowire arrays paves the way for rational thermal design in nanoscale applications.
- Published
- 2019
21. Hydrogen induced interface engineering in Fe
- Author
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Aadesh P, Singh, Richard Baochang, Wang, Camilla, Tossi, Ilkka, Tittonen, Björn, Wickman, and Anders, Hellman
- Abstract
Semiconductor heterostructure junctions are known to improve the water oxidation performance in photoelectrochemical (PEC) cells. Depending on the semiconductor materials involved, different kinds of junctions can appear, for instance, type II band alignment where the conduction and valence bands of the semiconductor materials are staggered with respect to each other. This band alignment allows for a charge separation of the photogenerated electron-hole pairs, where the holes will go from low-to-high valance band levels and
- Published
- 2020
22. Enhanced Thermoelectric Transport and Stability in Atomic Layer Deposited-HfO
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Jenichi, Felizco, Taneli, Juntunen, Mutsunori, Uenuma, Jarkko, Etula, Camilla, Tossi, Yasuaki, Ishikawa, Ilkka, Tittonen, and Yukiharu, Uraoka
- Abstract
Herein, enhancements in thermoelectric (TE) performance, both the power factor (PF) and thermal stability, are exhibited by sandwiching HfO
- Published
- 2020
23. Synergies of co-doping in ultra-thin hematite photoanodes for solar water oxidation: In and Ti as representative case
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Aadesh P. Singh, Camilla Tossi, Ilkka Tittonen, Anders Hellman, Björn Wickman, Department of Neuroscience and Biomedical Engineering, Department of Electronics and Nanoengineering, Chalmers University of Technology, Aalto-yliopisto, and Aalto University
- Subjects
Photocurrent ,Materials science ,Dopant ,General Chemical Engineering ,Doping ,chemistry.chemical_element ,02 engineering and technology ,General Chemistry ,Substrate (electronics) ,010402 general chemistry ,021001 nanoscience & nanotechnology ,01 natural sciences ,7. Clean energy ,Evaporation (deposition) ,0104 chemical sciences ,chemistry ,Chemical engineering ,Water splitting ,Thin film ,0210 nano-technology ,Indium - Abstract
Solar energy induced water splitting in photoelectrochemical (PEC) cells is one of the most sustainable ways of hydrogen production. The challenge is to develop corrosion resistant and chemically stable semiconductors that absorb sunlight in the visible region and, at the same time, have the band edges matching with the redox level of water. In this work, hematite (α-Fe2O3) thin films were prepared onto an indium-doped tin oxide (ITO; In:SnO2) substrate by e-beam evaporation of Fe, followed by air annealing at two different temperatures: 350 and 500 °C. The samples annealed at 500 °C show an in situ diffusion of indium from the ITO substrate to the surface of α-Fe2O3, where it acts as a dopant and enhances the photoelectrochemical properties of hematite. Structural, optical, chemical and photoelectrochemical analysis reveal that the diffusion of In at 500 °C enhances the optical absorption, increases the electrode–electrolyte contact area by changing the surface topology, improves the carrier concentration and shifts the flat band potential in the cathodic direction. Further enhancement in photocurrent density was observed by ex situ diffusion of Ti, deposited in the form of nanodisks, from the top surface to the bulk. The in situ In diffused α-Fe2O3 photoanode exhibits an improved photoelectrochemical performance, with a photocurrent density of 145 μA cm−2 at 1.23 VRHE, compared to 37 μA cm−2 for the photoanode prepared at 350 °C; it also decreases the photocurrent onset potential from 1.13 V to 1.09 V. However, the In/Ti co-doped sample exhibits an even higher photocurrent density of 290 μA cm−2 at 1.23 VRHE and the photocurrent onset potential decreases to 0.93 VRHE, which is attributed to the additional doping and to the surface becoming more favorable to charge separation.
- Published
- 2020
24. List of contributors
- Author
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Timo Aalto, Veli-Matti Airaksinen, Stephan Gerhard Albert, Giorgio Allegato, Marco Amiotti, Olli Anttila, Juergen Auersperg, Antonio Bonucci, Indranil Ronnie Bose, Tanja Braun, Mikael Broas, J. Burggraf, Christopher Cameron, Rob N. Candler, Zhen Cao, André Cardoso, Kuo-Shen Chen, Andrea Conte, Adriana Cozma, Cristina E. Davis, Sophia Dempwolf, Pradeep Dixit, Michael Dost, Viorel Dragoi, Simo Eränen, Bruno Fain, B. Figeys, Andreas C. Fischer, Christoph Flötgen, Sami Franssila, Alois Friedberger, Marc Fueldner, Maria Ganchenkova, Pilar Gonzalez, Miguel A. Gosálvez, Michael Grimes, Atte Haapalinna, Paul Hagelin, Paul Hammond, Kimmo Henttinen, Vesa Henttonen, David Horsley, Takeo Hoshi, Satoshi Itoh, Henrik Jakobsen, R. Jansen, Kerstin Jonsson, Dirk Kähler, Harindra Kumar Kannojia, Hannu Kattelus, Gudrun Kissinger, Roy Knechtel, Kathrin Knese, Kai Kolari, Mika Koskenvuori, Heikki Kuisma, Amit Kulkarni, Franz Laermer, Christof Landesberger, Christina Leinenbach, Michael K. LeVasseur, Jue Li, Yuyuan Lin, Paul F. Lindner, K. Lodewijks, Fabian Lofink, Giorgio Longoni, Sebastian Markus Luber, M. Mahmud-ul-hasan, Jari Mäkinen, Matti Mäntysalo, Devin Martin, Federico Maspero, Toni T. Mattila, Luca Mauri, Peter Merz, Doug Meyer, Marco Moraja, Teruaki Motooka, Gerhard Müller, Paul Muralt, Risto M. Nieminen, Frank Niklaus, Laura Oggioni, Juuso Olkkonen, Elmeri Österlund, Kuang-Shun Ou, Jari Paloheimo, Toni P. Pasanen, Mervi Paulasto-Kröckel, Thomas Plach, Jean-Philippe Polizzi, Klaus Pressel, Matti Putkonen, Riikka L. Puurunen, Wolfgang Reinert, Enea Rizzi, V. Rochus, Glenn Ross, X. Rottenberg, Lauri Sainiemi, Hele Savin, Harald Schenk, Marc Schikowski, Matthias Schulze, S. Seema, S. Severi, Lasse Skogström, Tadatomo Suga, Scott Sullivan, Tommi Suni, Horst Theuss, Markku Tilli, H.A.C. Tilmans, Ilkka Tittonen, Hannah Tofteberg, Pekka Törmä, Santeri Tuomikoski, Frode Tyholdt, Tsuyoshi Uda, Örjan Vallin, Carlo Valzasina, Timo Veijola, Eeva Viinikka, Dietmar Vogel, Andreas Vogl, Vesa Vuorinen, W.J. Westervelde, Sebastian Wicht, Robert Wieland, Bernhard Winkler, Levent Yobas, Luca Zanotti, and I. Zubel
- Published
- 2020
25. Photodeposition of RuO
- Author
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Erich Michael, See, Camilla, Tossi, Lassi, Hällström, and Ilkka, Tittonen
- Subjects
Article - Abstract
RuO2/TiO2 catalysts have shown broad use in promoting a variety of photocatalytic phenomena, such as water splitting and the photodecomposition of organic dyes and pollutants. Most current methods of photodepositing ruthenium oxide species (RuOx) onto titanium dioxide (TiO2) films involve precursors that are either difficult to produce and prone to decomposition, such as RuO4, or require high-temperature oxidations, which can reduce the quality of the resulting catalyst and increase the risks and toxicity of the procedure. The present work demonstrates the photodeposition of RuOx onto TiO2 films, using potassium perruthenate (KRuO4) as a precursor, by improving substantially a procedure known to work on TiO2 nanopowders. In addition to demonstrating the applicability of this method of photodeposition to TiO2 films, this work also explores the importance of the material phase of the TiO2 substrate, outlines viable concentrations and photodeposition times at a given optical intensity, and demonstrates that the morphology of the photodeposited nanostructures changes from cauliflower-like spheroids to a matted, porous sponge-like structure with the addition of methanol to the precursor solution. This morphology change has not been documented previously. By providing an explanation for this difference in the morphology, this work provides both newer insights into the photodeposition process and provides an excellent foundation for future procedures, allowing a more targeted and controlled deposition based on the desired morphology.
- Published
- 2019
26. Highly transparent copper iodide thin film thermoelectric generator on a flexible substrate
- Author
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Catarina Bianchi, Ilkka Tittonen, Isabel M.P.L.V.O. Ferreira, Taneli Juntunen, Ana C. Marques, Tomi Koskinen, B. M. Morais Faustino, J. Coroa, NOVA University Lisbon, Department of Electronics and Nanoengineering, Aalto-yliopisto, and Aalto University
- Subjects
Materials science ,business.industry ,General Chemical Engineering ,02 engineering and technology ,General Chemistry ,Substrate (electronics) ,010402 general chemistry ,021001 nanoscience & nanotechnology ,Thermoelectric materials ,7. Clean energy ,01 natural sciences ,0104 chemical sciences ,Thermoelectric generator ,Electrical resistivity and conductivity ,Optoelectronics ,Thin film ,0210 nano-technology ,business ,Electrical conductor ,Short circuit ,Voltage - Abstract
openaire: EC/H2020/645241/EU//TransFlexTeg Simultaneously transparent and flexible conductive materials are in demand to follow the current trend in flexible technology. The search for materials with compliant optoelectronic properties, while simultaneously retaining their electric conductivity at high strain deformation, comprises promising opportunities in modern nanotechnology. Copper iodide (CuI) is not only the most transparent and highly conductive p-type material, but its optimization has contributed to improved ZT values in planar thin-film thermoelectrics. In this work, the readiness of CuI thin films to transparent, flexible technology is evidenced. A maximum ZT value of 0.29 for single CuI thin films of ca. 300 nm in thickness is reported. Values of open-circuit voltage Voc, short circuit current Isc and power output of p-n thermoelectric modules of Gallium-doped zinc oxide (GZO) and CuI thin films deposited on a transparent flexible Kapton® (type CS) substrate are reported, and a prototype of a flexible transparent thermoelectric generatorbased on 17 p-n modules was constructed. Bending analysis of CuI thin films reveals interesting, distinct results when submitted to compression and tension analysis-a behaviour not seen in conventional semiconducting thin films under equivalent strain conditions. A plausible account for such diversity is also included.
- Published
- 2019
27. Cast Monocrystalline Silicon: New Alternative for Micro- and Nano-electromechanical Systems
- Author
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Ville Vähänissi, Nikolai Chekurov, Ilkka Tittonen, Zhengjun Liu, Hele Savin, Hele Savin Group, Oxford Instruments Technologies Oy, Department of Electronics and Nanoengineering, Aalto-yliopisto, and Aalto University
- Subjects
focused ion beam ,Materials science ,Silicon ,ta221 ,chemistry.chemical_element ,02 engineering and technology ,010402 general chemistry ,01 natural sciences ,cast mono-Si ,Monocrystalline silicon ,NEMS ,Etching (microfabrication) ,Deep reactive-ion etching ,Wafer ,Electrical and Electronic Engineering ,Ingot ,ta216 ,Microelectromechanical systems ,Nanoelectromechanical systems ,Mechanical Engineering ,021001 nanoscience & nanotechnology ,Engineering physics ,0104 chemical sciences ,MEMS ,photovoltaics ,chemistry ,monolike silicon ,0210 nano-technology ,quasimono silicon - Abstract
Casted silicon wafers dominate the current photovoltaic (PV) market due to much lower fabrication costs as compared to well-known Czochralski (Cz) –growth. Traditionally casted silicon ingots have been multicrystalline, but recent developments in casting technology have enabled also the growth of single crystalline (sc) silicon ingots. While the resulting sc-Si ingot quality is naturally high enough for PV, it is not sufficient for the integrated circuit (IC) industry, mainly due to the increased amount of intrinsic point defects and dislocations in comparison to Cz-Si. However, many applications that do not have such stringent requirements for substrates, such as micro-and nano-electromechanical systems (MEMS and NEMS), could potentially find this material beneficial. Indeed, here we take the first step in studying the applicability of cast mono-Si for such applications. More specifically, we focus on advanced focused ion beam lithography combined with deep reactive ion etching for NEMS and wet etching for MEMS. Our results show that the quality of cast mono-Si is high enough for successful patterning in both micro- and nanoscale. Sub-micron resolution is achieved and the Ga+ doses required for successful patterning are comparable to conventional Cz-Si. The preliminary results presented here thus show great promise for cast mono-Si as a low-cost alternative for micro- and nano-electromechanical systems. [2019-0081]
- Published
- 2019
28. Anderson Localization Quenches Thermal Transport in Aperiodic Superlattices
- Author
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Osmo Vänskä, Ilkka Tittonen, Taneli Juntunen, Department of Electronics and Nanoengineering, Aalto-yliopisto, and Aalto University
- Subjects
Length scale ,Physics ,Anderson localization ,ta114 ,Condensed matter physics ,Phonon ,Superlattice ,General Physics and Astronomy ,02 engineering and technology ,021001 nanoscience & nanotechnology ,01 natural sciences ,Thermal conductivity ,Lattice (order) ,0103 physical sciences ,Thermoelectric effect ,ta216 ,010306 general physics ,0210 nano-technology ,Anisotropy - Abstract
We show that aperiodic superlattices exhibit intriguing interplay between phononic coherent wave interference effects and incoherent transport. In particular, broadband Anderson localization results in a drastic thermal conductivity reduction of 98% at room temperature, providing an ultralow value of $1.3\text{ }\text{ }\mathrm{W}\text{ }{\mathrm{m}}^{\ensuremath{-}1}\text{ }{\mathrm{K}}^{\ensuremath{-}1}$, and further yields an anomalously large thermal anisotropy ratio of $\ensuremath{\sim}{10}^{2}$ in aperiodic $\mathrm{Si}/\mathrm{Ge}$ superlattices. A maximum in the thermal conductivity emerges as an unambiguous consequence of phonon Anderson localization at a system length scale bridging the extended and localized transport regimes. The frequency-resolved picture, combined with our lattice dynamical description of Anderson localization, elucidates the rich transport characteristics in these systems and the potential of correlated disorder for sub- to few-THz phononic engineering of heat transport in thermoelectric applications.
- Published
- 2019
29. Fluorescence-enhancing plasmonic silver nanostructures using azopolymer lithography
- Author
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Markku Sopanen, Jorma Selin, Christoffer Kauppinen, Ilkka Tittonen, and Ville Pale
- Subjects
Fluorophore ,Materials science ,General Chemical Engineering ,ta221 ,Nanoparticle ,Quantum yield ,Nanotechnology ,02 engineering and technology ,fabrication ,Grating ,010402 general chemistry ,01 natural sciences ,plasmonics ,Rhodamine 6G ,chemistry.chemical_compound ,azopolymer films ,Lithography ,Plasmon ,business.industry ,General Chemistry ,021001 nanoscience & nanotechnology ,Fluorescence ,0104 chemical sciences ,chemistry ,Optoelectronics ,lithography ,fluorescence ,0210 nano-technology ,business - Abstract
The performance of fluorescence-based measurement techniques is fundamentally limited by the intrinsic quantum yield of a fluorophore. Radiative decay engineering using metallic nanostructures has significant potential to improve the fluorescence emission of a fluorophore. Especially, periodic arrays of metallic nanostructures have the advantage of exhibiting a strong optical response, which is beneficial for improving sensitivity in surface enhanced spectroscopic techniques. In this work, we present a cost-effective and large-scale fabrication scheme for creating periodic plasmonic nanoparticle arrays for fluorescence enhancement. The fabrication process uses an azopolymer mask that forms a two-dimensional surface relief grating when illuminated with two orthogonal exposures, which can directly be used as a soft etching mask to define the nanoparticle array. This approach allows the creation of periodic arrays of symmetrical metallic nanostructures that exhibit good long-range order. Furthermore, the dimensions of the array and the structures can be tuned by changing the exposure or process parameters. The plasmonic behaviour of the fabricated structures was studied both experimentally and by numerical simulations. The fluorescence enhancement performance for the blue and green wavelength regions was verified by using Rhodamine 6G and Cascade Blue as fluorophores. A significant 14-fold fluorescence intensity increase for Rhodamine 6G was observed, whereas the fluorescence intensity for Cascade Blue was roughly doubled. In addition, time-resolved measurements displayed a shortening of the fluorescence lifetime for both of the fluorophores when deposited on the nanoparticle grating. We expect that this approach could be advantageous for other application areas of plasmonics, such as SERS or sensing.
- Published
- 2016
30. Coherent Electron Transport in Metamaterials of Integrated Semiconductor Quantum Dots and Biomolecules for Medical Imaging Applications
- Author
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F. B. Bayramov, V. V. Toporov, Harri Lipsanen, B. H. Bairamov, O. B. Chakchir, Mackillo Kira, and Ilkka Tittonen
- Subjects
chemistry.chemical_classification ,Nanostructure ,Photoluminescence ,Materials science ,business.industry ,Biomolecule ,Physics::Optics ,Metamaterial ,Electron ,Resonance (particle physics) ,symbols.namesake ,chemistry ,Quantum dot ,symbols ,Optoelectronics ,business ,Raman scattering - Abstract
The fundamental research of many-body interactions and coherent transport of single particle elementary excitations exploiting strong-light matter interactions in artificial molecular metamaterials for sensing having practical technological relevance is addressed. Confinement and coherent transport of elementary electron-hole excitations are directly monitored by high-spectral-resolution micro-Raman and photoluminescence spectroscopes in isolated semiconductor quantum dots. Crystalline nanostructures of nc-Si/SiO2 quantum dots as well as their functionalization by biomolecules with fabrication of nano-metamaterials will be considered. It has been found that these complexes are unique objects for the elucidation of the specific features in the manifestation of new quantum-size effects in biomacromolecules. It has been demonstrated that the possibility exists of detecting and recording in such nano-biomacromolecule metamaterials spectrally selective resonance enhancement of Raman scattering intensity in fluctuations of nucleotide molecules due to coherent nonradiative transfer of a photoexcited electron and a hole at the interface of the complex. This dynamic optical imaging of spectral responses can be of applied interest for the development of nanobiophotonic technologies for development label-free probes in a broader perspective for vital applications including early diagnosis of diseases at the molecular level.
- Published
- 2018
31. Inkjet Printed Large-Area Flexible Few-Layer Graphene Thermoelectrics
- Author
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Ilkka Tittonen, Richard C. T. Howe, Henri Jussila, Tawfique Hasan, Mikko Ruoho, Leonard W. T. Ng, Tom Albrow-Owen, Zhipei Sun, Guohua Hu, Shouhu Liu, Taneli Juntunen, Tittonen, I [0000-0002-2985-9789], Apollo - University of Cambridge Repository, Department of Electronics and Nanoengineering, University of Cambridge, Aalto-yliopisto, and Aalto University
- Subjects
Materials science ,ta221 ,Nanotechnology ,02 engineering and technology ,010402 general chemistry ,01 natural sciences ,7. Clean energy ,law.invention ,Biomaterials ,large-area thermoelectrics ,law ,Thermal ,Thermoelectric effect ,Electrochemistry ,Thin film ,ta216 ,inkjet printing ,Nanocomposite ,Inkwell ,Nanoporous ,Graphene ,graphene ,021001 nanoscience & nanotechnology ,Condensed Matter Physics ,Thermoelectric materials ,0104 chemical sciences ,Electronic, Optical and Magnetic Materials ,0210 nano-technology - Abstract
openaire: EC/H2020/645241/EU//TransFlexTeg | openaire: EC/FP7/631610/EU//GrabFast Graphene-based organic nanocomposites have ascended as promising candidates for thermoelectric energy conversion. In order to adopt existing scalable printing methods for developing thermostable graphene-based thermoelectric devices, optimization of both the material ink and the thermoelectric properties of the resulting films are required. Here, inkjet-printed large-area flexible graphene thin films with outstanding thermoelectric properties are reported. The thermal and electronic transport properties of the films reveal the so-called phonon-glass electron-crystal character (i.e., electrical transport behavior akin to that of few-layer graphene flakes with quenched thermal transport arising from the disordered nanoporous structure). As a result, the all-graphene films show a room-temperature thermoelectric power factor of 18.7 µW m−1 K−2, representing over a threefold improvement to previous solution-processed all-graphene structures. The demonstration of inkjet-printed thermoelectric devices underscores the potential for future flexible, scalable, and low-cost thermoelectric applications, such as harvesting energy from body heat in wearable applications.
- Published
- 2018
- Full Text
- View/download PDF
32. Thin-film thermoelectric devices for energy harvesting and material parameter extraction
- Author
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Kirsi Tappura, Kaarle Jaakkola, Taneli Juntunen, Ilkka Tittonen, and Riina Ritasalo
- Abstract
A major barrier for a wider use of thermoelectric devices for energy harvesting is their low efficiency, which tends lead to a high cost per converted power. The ability to use non-toxic and abundant materials has also become increasingly important in the recent years and enhanced the interest towards improving the thermoelectric properties of metal oxides. Tin-doped indium oxide (ITO) is one of the most commonly used transparent conductive oxides due to its high electrical conductivity and high transparency. However, aluminum-doped zinc oxide (AZO) provides an environmentally friendly alternative that is more abundant, has better thermoelectric properties and lower cost. In this work, we present selected results of our thermoelectric device development based on AZO aiming at flexible thin-film TEG applications. Thermodynamic modelling and performance simulations are conducted for selected designs in order to estimate the available thermal gradients, the performance of the thermoelectric elements and the power available from the thermoelectric modules consisting of various geometries and configurations [1]. In addition to the electrical properties, the heat transfer mechanisms over the modules are studied. In addition to the conventional material characterizations, the potential of the materials is also evaluated by constructing experimental test devices of the thin-films and building corresponding simulation models of the test devices. By combining the experimental and theoretical approaches through device evaluations, the optimization of the thin-film materials and device designs can be performed in parallel for constructing a large-area thermoelectric module for thermal energy harvesting applicable in various environments without elaborated heat sinks. The ultimate goal of the project is to build a distributed sensor network integrating large-area thin-film thermoelectric devices and sensors for multifunctional smart windows and flexible high impact volume applications.
- Published
- 2018
33. CuI p-type thin films for highly transparent thermoelectric p-n modules
- Author
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Guilherme Gaspar, Taneli Juntunen, Ilkka Tittonen, Catarina Bianchi, António B. A. Almeida, Isabel M.P.L.V.O. Ferreira, Diogo Cardoso Gomes, Bruno Miguel Morais Faustino, Ana C. Marques, Jaime Faria, NOVA University Lisbon, Department of Electronics and Nanoengineering, Aalto-yliopisto, Aalto University, CENIMAT-i3N - Centro de Investigação de Materiais (Lab. Associado I3N), and DCM - Departamento de Ciência dos Materiais
- Subjects
Materials science ,Science ,Oxide ,chemistry.chemical_element ,02 engineering and technology ,Zinc ,01 natural sciences ,Article ,chemistry.chemical_compound ,Planar ,0103 physical sciences ,Thermoelectric effect ,Power output ,Thin film ,010302 applied physics ,Multidisciplinary ,business.industry ,OXIDE ,021001 nanoscience & nanotechnology ,chemistry ,Electrode ,Medicine ,Optoelectronics ,0210 nano-technology ,business ,Indium - Abstract
This work was mainly funded by H2020-ICT-2014-1, RIA, TransFlexTeg-645241, and ERC-CoG-2014, CapTherPV, 647596, and partially funded by FEDER funds through the COMPETE 2020 Program and National Funds through FCT - Portuguese Foundation for Science and Technology under the project UID/CTM/50025/2013. Developments in thermoelectric (TE) transparent p-type materials are scarce and do not follow the trend of the corresponding n-type materials - a limitation of the current transparent thermoelectric devices. P-type thermoelectric thin films of CuI have been developed by three different methods in order to maximise optical transparency (>70% in the visible range), electrical (σ = 1.1 × 104 Sm-1) and thermoelectric properties (ZT = 0.22 at 300 K). These have been applied in the first planar fully transparent p-n type TE modules where gallium-doped zinc oxide (GZO) thin films were used as the n-type element and indium thin oxide (ITO) thin films as electrodes. A thorough study of power output in single elements and p-n modules electrically connected in series and thermally connected in parallel is inclosed. This configuration allows for a whole range of highly transparent thermoelectric applications. publishersversion published
- Published
- 2018
34. Broadband laser polarization control with aligned carbon nanotubes
- Author
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He Yang, Bo Fu, Diao Li, Ying Tian, Ya Chen, Marco Mattila, Zhenzhong Yong, Ru Li, Abdou Hassanien, Changxi Yang, Ilkka Tittonen, Zhaoyu Ren, Jintao Bai, Qingwen Li, Esko I. Kauppinen, Harri Lipsanen, Zhipei Sun, Department of Micro and Nanosciences, Tsinghua University, Department of Applied Physics, Aalto-yliopisto, and Aalto University
- Subjects
Materials science ,education ,ta221 ,FOS: Physical sciences ,Physics::Optics ,02 engineering and technology ,polarization control ,010402 general chemistry ,01 natural sciences ,aligned carbon nanotubes ,law.invention ,symbols.namesake ,fiber laser ,law ,Fiber laser ,General Materials Science ,ta216 ,ta218 ,ta214 ,Extinction ratio ,ta114 ,ta213 ,business.industry ,Linear polarization ,Polarizer ,021001 nanoscience & nanotechnology ,Laser ,Polarization (waves) ,0104 chemical sciences ,symbols ,Optoelectronics ,Photonics ,0210 nano-technology ,business ,Raman spectroscopy ,Optics (physics.optics) ,Physics - Optics - Abstract
We introduce a simple approach to fabricate aligned carbon nanotube (ACNT) device for broadband polarization control in fiber laser systems. The ACNT device was fabricated by pulling from as-fabricated vertically-aligned carbon nanotube arrays. Their anisotropic property is confirmed with optical and scanning electron microscopy, and with polarized Raman and absorption spectroscopy. The device was then integrated into fiber laser systems (at two technologically important wavelengths of 1 and 1.5 um) for polarization control. We obtained a linearly-polarized light output with the maximum extinction ratio of ~12 dB. The output polarization direction could be fully controlled by the ACNT alignment direction in both lasers. To the best of our knowledge, this is the first time that ACNT device is applied to polarization control in laser systems. Our results exhibit that the ACNT device is a simple, low-cost, and broadband polarizer to control laser polarization dynamics, for various photonic applications (such as material processing, polarization diversity detection in communications), where the linear polarization control is necessary., 5 pages, 6 figures
- Published
- 2015
35. Excitation-dependent fluorescence from atomic/molecular layer deposited sodium-uracil thin films
- Author
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Maarit Karppinen, Ville Pale, Ilkka Tittonen, Xi Chen, Olga Lopez-Acevedo, Zivile Giedraityte, Department of Electronics and Nanoengineering, Department of Chemistry and Materials Science, Department of Applied Physics, Aalto-yliopisto, and Aalto University
- Subjects
Multidisciplinary ,Fabrication ,Materials science ,Absorption spectroscopy ,Science ,02 engineering and technology ,010402 general chemistry ,021001 nanoscience & nanotechnology ,Photochemistry ,01 natural sciences ,Fluorescence ,Article ,0104 chemical sciences ,Medicine ,Molecule ,Thin film ,0210 nano-technology ,Layer (electronics) ,Excitation ,Deposition (law) - Abstract
Atomic/molecular layer deposition (ALD/MLD) offers unique possibilities in the fabrication of inorganic-organic thin films with novel functionalities. Especially, incorporating nucleobases in the thin-film structures could open new avenues in the development of bio-electronic and photonic devices. Here we report an intense blue and widely excitation-dependent fluorescence in the visible region for ALD/MLD fabricated sodium-uracil thin films, where the crystalline network is formed from hydrogen-bonded uracil molecules linked via Na atoms. The excitation-dependent fluorescence is caused by the red-edge excitation shift (REES) effect taking place in the red-edge of the absorption spectrum, where the spectral relaxation occurs in continuous manner as demonstrated by the time-resolved measurements.
- Published
- 2017
36. Optimization of Cuprous Oxides Thin Films to be used as Thermoelectric Touch Detectors
- Author
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Joana Loureiro, Isabel M.P.L.V.O. Ferreira, Joana Figueira, José Marques, Ilkka Tittonen, Mikko Ruoho, P. Duarte, and Catarina Bianchi
- Subjects
Materials science ,Annealing (metallurgy) ,Analytical chemistry ,Oxide ,chemistry.chemical_element ,02 engineering and technology ,Conductivity ,010402 general chemistry ,01 natural sciences ,chemistry.chemical_compound ,thermal evaporation ,Seebeck coefficient ,Thermoelectric effect ,General Materials Science ,postdeposition annealing ,Thin film ,ta114 ,Detector ,021001 nanoscience & nanotechnology ,Copper ,copper oxide ,0104 chemical sciences ,thin films ,chemistry ,Seebeck ,0210 nano-technology - Abstract
The electronic and optical properties of p-type copper oxides (CO) strongly depend on the production technique as it influences the obtained phases: cuprous oxide (Cu2O) or cupric oxide (CuO), the most common ones. Cu films deposited by thermal evaporation have been annealed in air atmosphere, with temperature between 225 and 375 °C and time between 1 and 4 h. The resultant CO films have been studied to understand the influence of processing parameters in the thermoelectric, electrical, optical, morphological, and structural properties. Films with a Cu2O single phase are formed when annealing at 225 °C, while CuO single phase films can be obtained at 375 °C. In between, both phases are obtained in proportions that depend on the film thickness and annealing time. The positive sign of the Seebeck coefficient (S), measured at room temperature (RT), confirms the p-type behavior of both oxides, showing values up to 1.2 mV·°C–1 and conductivity up to 2.9 (Ω·m)−1. A simple detector using Cu2O have been fabricate...
- Published
- 2017
37. Flexible Electronics: Transparent, Flexible, and Passive Thermal Touch Panel (Adv. Mater. Technol. 9/2016)
- Author
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Taneli Juntunen, Tapani Alasaarela, Marko Pudas, Ilkka Tittonen, and Mikko Ruoho
- Subjects
Materials science ,Mechanics of Materials ,business.industry ,Thermal ,Optoelectronics ,Touch panel ,General Materials Science ,business ,Engineering physics ,Industrial and Manufacturing Engineering ,Flexible electronics - Published
- 2016
38. Measurement of thin film thermal conductivity using the laser flash method
- Author
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Terje G. Finstad, Mikko Ruoho, Ilkka Tittonen, Kjetil Valset, Ilkka Tittonen Group, Department of Micro and Nanosciences, Aalto-yliopisto, and Aalto University
- Subjects
Materials science ,Nanocomposite ,Mechanical Engineering ,Ion track ,education ,Analytical chemistry ,Bioengineering ,General Chemistry ,Substrate (electronics) ,Thermal diffusivity ,Laser flash analysis ,Atomic layer deposition ,Thermal conductivity ,Mechanics of Materials ,General Materials Science ,Electrical and Electronic Engineering ,Composite material ,Thin film - Abstract
We present a method to measure the in-plane thermal conductivity of thin films by the laser flash technique. The method uses a well-defined structure for the analysis. We have realized the structure by conformal deposition of ZnO films of different thicknesses using atomic layer deposition onto a 20 μm thick ion track etched polycarbonate membrane as substrate. By using this procedure we could determine the thermal conductivity of the deposited thin film from the total thermal diffusivity of the nanocomposite structures. The method has been used to obtain the in-plane thermal conductivity of the deposited ZnO layers within the thickness range of less than 100 nm.
- Published
- 2015
39. Coherent Terahertz Control of Vertical Transport in Semiconductor Heterostructures
- Author
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Ilkka Tittonen, Mackillo Kira, Osmo Vänskä, Stephan W. Koch, Ilkka Tittonen Group, Department of Micro and Nanosciences, Aalto-yliopisto, and Aalto University
- Subjects
terahertz technology ,Quantum optics ,Materials science ,nanotechnology ,Condensed Matter::Other ,Terahertz radiation ,Scattering ,business.industry ,Dephasing ,education ,General Physics and Astronomy ,semiconductors ,Condensed Matter::Mesoscopic Systems and Quantum Hall Effect ,Terahertz spectroscopy and technology ,Semiconductor ,heterostructures ,Coherent control ,Optoelectronics ,coherent control ,quantum optics ,Microscopic theory ,business - Abstract
Coherent-control protocols are introduced to selectively transport electrons, excitons, or pure two-particle correlations through semiconductor interfaces. The scheme is tested in a double-quantum-well structure where a sequence of terahertz pulses is applied to induce the vertical excitation transfer between the wells. Using a microscopic theory, it is shown that efficient and highly selective transfer can be realized even in the presence of the unavoidable scattering and dephasing processes.
- Published
- 2015
40. Accessing orbital angular momentum of quantum-ring excitons via directional semiconductor luminescence
- Author
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Stephan W. Koch, Mackillo Kira, Osmo Vänskä, Julius Nieminen, Ilkka Tittonen, Ilkka Tittonen Group, Department of Micro and Nanosciences, Aalto-yliopisto, and Aalto University
- Subjects
Physics ,Semiconductor luminescence equations ,semiconductor theory ,Condensed Matter::Other ,education ,Physics::Optics ,General Physics and Astronomy ,quantum ring ,Condensed Matter::Mesoscopic Systems and Quantum Hall Effect ,7. Clean energy ,Azimuthal quantum number ,Condensed Matter::Materials Science ,Total angular momentum quantum number ,orbital angular momentum ,Quantum mechanics ,Physics::Space Physics ,Angular momentum of light ,Orbital motion ,Angular momentum coupling ,Orbital angular momentum multiplexing ,Orbital angular momentum of light ,quantum optics ,Atomic physics - Abstract
A full quantum theory is developed for semiconductor quantum ring photoluminescence. The computations show that the orbital angular momentum (OAM) of individual excitons yields strong angle-dependent emission. The characteristic OAM signatures also survive significant amount of dephasing, suggesting efficient quantum-level coupling between quantum-ring excitons and the OAM of light.
- Published
- 2015
41. Analytical solutions for electronic states in three‐dimensional semiconductor quantum rings
- Author
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Stephan W. Koch, Ilkka Tittonen, Mackillo Kira, and Osmo Vänskä
- Subjects
Ring (mathematics) ,Particle properties ,Semiconductor ,Chemistry ,business.industry ,Quantum mechanics ,Semiconductor nanostructures ,Charge carrier ,Condensed Matter Physics ,Wave function ,business ,Quantum ,Electronic states - Abstract
We study single-particle electronic states of a threedimensional semiconductor quantum ring. Starting from the envelope-function theory, we formulate a fully analytical model for single-particle wave functions and confinement energies of charge carriers. The approximative harmonic-oscillator model is found to be in excellent agreement with numerical results. The model is a powerful tool in practical calculations when there is a need to go beyond single particle properties to more demanding many-body effects. (© 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
- Published
- 2013
42. Sensitivity-improved silicon cantilever microphone for acousto-optical detection
- Author
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Jussi Raittila, Nikolai Chekurov, Päivi Sievilä, and Ilkka Tittonen
- Subjects
Materials science ,Cantilever ,business.industry ,Microphone ,010401 analytical chemistry ,Metals and Alloys ,Analytical chemistry ,Silicon on insulator ,02 engineering and technology ,021001 nanoscience & nanotechnology ,Condensed Matter Physics ,01 natural sciences ,0104 chemical sciences ,Surfaces, Coatings and Films ,Electronic, Optical and Magnetic Materials ,Etching (microfabrication) ,Optoelectronics ,Wafer ,Electrical and Electronic Engineering ,0210 nano-technology ,business ,Instrumentation ,Sensitivity (electronics) ,Photoacoustic spectroscopy ,Microfabrication - Abstract
Silicon cantilever sensors have been designed, fabricated and tested in acoustic wave detection. The principal application of the components is photoacoustic spectroscopy (PAS) which is a highly sensitive method in solid, liquid and gas analysis. The developed microfabrication process of the sensors is based on silicon-on-insulator (SOI) wafer etching, in which the challenge is to control and minimize the residual stress related curving in thin (5 μm) but large-area (few mm 2 ) components. The sensitivity of the fabricated cantilevers is investigated in photoacoustic measurements of solid samples, and the signal strength is shown to increase tens of percent compared with the results obtained with previously reported cantilever microphones. Improvement of the signal-to-noise ratio (SNR) verifies the advantage of the presented cantilevers in photoacoustic sensing.
- Published
- 2013
43. Thermal conductivity of amorphous Al2O3/TiO2 nanolaminates deposited by atomic layer deposition
- Author
-
Riikka L. Puurunen, Taneli Juntunen, Ilkka Tittonen, Oili Ylivaara, Harri Lipsanen, Simo-Pekka Hannula, Saima Ali, and Sakari Sintonen
- Subjects
Materials science ,Kapitza resistance ,amorphous ,Bioengineering ,02 engineering and technology ,01 natural sciences ,Atomic layer deposition ,Thermal conductivity ,0103 physical sciences ,Thermal ,Interfacial thermal resistance ,General Materials Science ,thermal conductivity ,nanolaminates ,Electrical and Electronic Engineering ,Composite material ,Thin film ,Deposition (law) ,010302 applied physics ,Mechanical Engineering ,Bilayer ,General Chemistry ,021001 nanoscience & nanotechnology ,Amorphous solid ,Mechanics of Materials ,ALD ,0210 nano-technology - Abstract
The thermophysical properties of Al2O3/TiO2 nanolaminates deposited by atomic layer deposition (ALD) are studied as a function of bilayer thickness and relative TiO2 content (0%- 100%) while the total nominal thickness of the nanolaminates was kept at 100 nm. Cross-plane thermal conductivity of the nanolaminates is measured at room temperature using the nanosecond transient thermoreflectance method. Based on the measurements, the nanolaminates have reduced thermal conductivity as compared to the pure amorphous thin films, suggesting that interfaces have a non-negligible effect on thermal transport in amorphous nanolaminates. For a fixed number of interfaces, we find that approximately equal material content of Al2O3 and TiO2 produces the lowest value of thermal conductivity. The thermal conductivity reduces with increasing interface density up to 0.4 nm?1, above which the thermal conductivity is found to be constant. The value of thermal interface resistance approximated by the use of diffuse mismatch model was found to be 0.45 m2KGW?1, and a comparative study employing this value supports the interpretation of non-negligible interface resistance affecting the overall thermal conductivity also in the amorphous limit. Finally, no clear trend in thermal conductivity values was found for nanolaminates grown at different deposition temperatures, suggesting that the temperature in the ALD process has a non-trivial while modest effect on the overall thermal conductivity in amorphous nanolaminates.
- Published
- 2016
44. Transparent, Flexible, and Passive Thermal Touch Panel
- Author
-
Taneli Juntunen, Mikko Ruoho, Tapani Alasaarela, Ilkka Tittonen, Marko Pudas, Sähkötekniikan korkeakoulu, School of Electrical Engineering, Mikro- ja nanotekniikan laitos, Department of Micro and Nanosciences, Aalto-yliopisto, and Aalto University
- Subjects
Technology ,Materials science ,02 engineering and technology ,010402 general chemistry ,01 natural sciences ,flexible electronics ,Industrial and Manufacturing Engineering ,thermal ,Thermocouple ,Thermoelectric effect ,Electronic engineering ,General Materials Science ,Thin film ,Electrical conductor ,Sheet resistance ,Energy ,touch sensors ,ta114 ,business.industry ,Physics ,large-area ,Electrical engineering ,021001 nanoscience & nanotechnology ,Flexible electronics ,0104 chemical sciences ,Indium tin oxide ,Mechanics of Materials ,Rise time ,transparent ,0210 nano-technology ,business - Abstract
This work presents a touch panel concept, which is enabled by a novel designof thin film thermocouples. The design offers a simple implementation byutilizing a single thin film to function as an array of thermocouples. Theconcept is demonstrated as a flexible, passive, and highly transparent touchpanel. The passive nature of the thermoelectric touch recognition allows theperformance of the presented sensor to be optimal at moderate sheet resistancevalues of the transparent conductive layers. Hence, the concept is highlypotential for low-cost large-area applications and does not rely on costlylow sheet resistance materials such as indium tin oxide. The demonstratorpresented in this work achieves a signal-to-noise ratio of 20 with a rise timeof 90 ms and is able to distinguish individual touches, sweeping with finger,as well as touching by multiple fingers at the same time. In addition, the conceptmay also be used in other thermal distribution mapping applications. Not
- Published
- 2016
45. ALD-assisted multi-order dispersion engineering of nanophotonic strip waveguides
- Author
-
Mikhail Erdmanis, Lasse Karvonen, Ari Tervonen, Ilkka Tittonen, Seppo Honkanen, Ville Pale, Mikko Ruoho, and Muhammad Saleem
- Subjects
Fabrication ,Materials science ,ta213 ,ta114 ,business.industry ,ta221 ,Nanophotonics ,Silicon on insulator ,coatings ,optical waveguides ,Atomic and Molecular Physics, and Optics ,Compensation (engineering) ,Atomic layer deposition ,Optics ,thin films ,Dispersion (optics) ,Hardware_INTEGRATEDCIRCUITS ,Wafer ,ta318 ,business ,Self-phase modulation ,ta216 ,ta116 ,silicon-on-insulator (SOI) technology ,Chromatic dispersion - Abstract
We propose a new technique for the multiorder dispersion engineering of nanophotonic strip waveguides. Unlike other techniques, the method does not require wafers with customized parameters and is fully compatible with standard wafers used in nanophotonics. The dispersion management is based on the application of nanometer-thick TiO2 layer formed by atomic layer deposition. The method is simple and reliable and allows good control of dispersion up to the fourth-order terms. The additional advantages are the reduction of propagation losses and partial compensation of fabrication tolerances.
- Published
- 2012
46. Passively Q-switched Nd:YAG pumped UV lasers at 280 and 374nm
- Author
-
Ilkka Tittonen and Ossi Kimmelma
- Subjects
Materials science ,Sum-frequency generation ,business.industry ,Single-mode optical fiber ,Second-harmonic generation ,Nonlinear optics ,Laser ,Q-switching ,Atomic and Molecular Physics, and Optics ,Electronic, Optical and Magnetic Materials ,law.invention ,symbols.namesake ,Optics ,law ,symbols ,Optoelectronics ,Electrical and Electronic Engineering ,Physical and Theoretical Chemistry ,business ,Raman scattering ,Doppler broadening - Abstract
Pulsed UV lasers at the wavelengths of 374 and 280 nm are realized by cascaded second harmonic generation (SHG) and sum frequency generation (SFG) processes using a Nd:YAG laser at 1123 nm. The Nd:YAG laser is longitudinally pumped and passively Q-switched, and it has a high peak power of 3.2 kW. The UV peak powers at 280 and 374 nm are 100 and 310 W, with pulse lengths of 6 and 8 ns, respectively. Spectral broadening of 374 nm laser by stimulated Raman scattering is studied in single mode pure silica core UV fiber. Realizations of UV lasers enabling compact design at 280 and 374 nm wavelengths are demonstrated.
- Published
- 2009
47. Towards Micromechanical Radio: Overtone Excitations of a Microresonator Through the Nonlinearities of the Second and Third Order
- Author
-
Mika Koskenvuori and Ilkka Tittonen
- Subjects
Physics ,Third order ,Resonator ,Mechanical Engineering ,Overtone ,Acoustics ,Capacitive sensing ,Electronic engineering ,Resonance ,Electrical and Electronic Engineering ,Electrical impedance ,Signal ,Excitation - Abstract
A micromechanical resonator with eigenfrequencies in the megahertz-range is excited by signals having frequencies from tens of megahertz to gigahertz. The high-frequency excitation voltage is downconverted to mechanical force at the lower resonance frequency by the second-order force-voltage nonlinearity. The conversion is either assisted by additional local-oscillator signal or it is intrinsic due to an amplitude-modulated (AM) input signal. A circuit-simulator model is tested against measurements and an excellent agreement and thorough interpretation of the results is found. The third-order intercept point is measured and simulated to study the strength of the capacitive third-order nonlinearity. Finally, various nonlinear contributions are compared and further improvements for the device are suggested based on the simulations.
- Published
- 2008
48. GHz-range FSK-reception with microelectromechanical resonators
- Author
-
Mika Koskenvuori and Ilkka Tittonen
- Subjects
Microelectromechanical systems ,Physics ,Frequency-shift keying ,Acoustics ,Metals and Alloys ,Fundamental frequency ,Condensed Matter Physics ,Surfaces, Coatings and Films ,Electronic, Optical and Magnetic Materials ,Resonator ,Excited state ,Electrical and Electronic Engineering ,Electromechanical transducer ,Instrumentation ,Excitation ,Helical resonator - Abstract
A micromechanical resonator with eigenfrequencies in the MHz-region is excited by using an AM-modulated GHz-range signal. The excitation voltage is down-converted to a force at the fundamental frequency of the resonator by voltage-force-non-linearity of the electromechanical transducer. Measurements are verified by simulations with excellent agreement. Finally, a method of coding information bits is presented and tested.
- Published
- 2008
49. Atomic layer deposition enhanced rapid dry fabrication of micromechanical devices with cryogenic deep reactive ion etching
- Author
-
Ilkka Tittonen, Mika Koskenvuori, V.M. Airaksinen, and Nikolai Chekurov
- Subjects
Materials science ,Silicon ,business.industry ,Mechanical Engineering ,chemistry.chemical_element ,Nanotechnology ,Electronic, Optical and Magnetic Materials ,Atomic layer deposition ,chemistry ,Mechanics of Materials ,Etching (microfabrication) ,Deep reactive-ion etching ,Optoelectronics ,Dry etching ,Electrical and Electronic Engineering ,Reactive-ion etching ,business ,Electron-beam lithography ,Microfabrication - Abstract
A fast, dry microfabrication process combining atomic layer deposition, electron beam lithography and cryogenic deep reactive ion etching is presented. The process exploits the extremely high selectivity of atomic layer deposited amorphous Al2O3 (alumina) to silicon in cryogenic etching by using an ultra-thin (t � 5n m) Al2O3 film as am ask. The process rules and limitations are carefully analyzed and a thorough understanding of the limiting factors is reached, and the effect of the limitations on the critical output current of a dc-biased clamped–clamped beam is studied. To test the process, multiresonant tuning fork resonators are fabricated and found to exhibit Q ≈ 8000 at fr ≈ 11.4 MHz. Both values are the highest reported for resonators fabricated with the dry process and comparable with values achieved with existing silicon micromachining processes. (Some figures in this article are in colour only in the electronic version)
- Published
- 2007
50. Non-tilting out-of-plane mode high-Q mechanical silicon oscillator as a moving cavity mirror
- Author
-
Ilkka Tittonen and Ossi Hahtela
- Subjects
Quantum optics ,Physics ,Physics and Astronomy (miscellaneous) ,Silicon ,business.industry ,Q value ,Quantum limit ,General Engineering ,Physics::Optics ,General Physics and Astronomy ,chemistry.chemical_element ,law.invention ,Finesse ,Interferometry ,Optics ,chemistry ,law ,Optical cavity ,business ,Free spectral range - Abstract
A very sensitive optomechanical sensor to detect femtometer-level displacements in the position of one of the cavity mirrors in a Fabry–Perot interferometer was constructed and characterized. We use a high-reflectivity coated, non-tilting out-of-plane mode high-Q mechanical silicon oscillator as a rear mirror in the Fabry–Perot interferometer. The benefit of our novel oscillator, if compared to traditional torsional, flexural and many bulk acoustic mode oscillators, is that the action of weak forces is observed to cause only pure linear translation of the moving mirror without any tilting or deformation of the mirror surface. This non-tilting behavior allows, in principle, more precise optical mode stabilization, use of very short optical cavities and studies of short-range interactions between parallel surfaces. The resonance frequency and Q value of the high-reflectivity coated silicon oscillator are f0=27.5 kHz and Q=19000 at low pressure (p=0.1 mbar) and at room temperature. The finesse of the optical cavity is $\mathcal{F}=2600$ . The sensitivity of the displacement measurement is Δxmin=5 fm with a 1 Hz bandwidth. The prospects of reaching the standard quantum limit in an interferometric displacement measurement using a macroscopic oscillator are discussed.
- Published
- 2007
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