| 1. |
- Batili, Hazal, et al.
(författare)
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A comparative study on the surface chemistry and electronic transport properties of Bi2Te3 synthesized through hydrothermal and thermolysis routes
- 2024
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Ingår i: Colloids and Surfaces A. - : Elsevier BV. - 0927-7757 .- 1873-4359. ; 682
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Tidskriftsartikel (refereegranskat)abstract
- Bismuth telluride-Bi2Te3 is the most promising material for harvesting thermal energy near room temperature. There are numerous works on Bi2Te3 reporting significantly different transport properties, with no clear connection to the synthetic routes used and the resultant surface chemistry of the synthesized materials. It is of utmost importance to characterize the constituent particles’ surface and interfaces to get a better understanding of their influence on the transport properties, that will significantly improve the material design starting from the synthesis step. Electrophoretic deposition (EPD) is a promising technique, enabling the formation of thick films using colloidally stabilized suspensions of pre-made nanoparticles, which can enable the study of the effect of surface chemistry, in connection to the synthetic route, on the material's transport properties. In order to explore the differences in surface chemistry and the resultant transport properties in relation to the synthetic scheme used, here we report on Bi2Te3 synthesised through two wet-chemical routes in water (Hydro-) and oil (Thermo-) as the solvents. XRD analysis showed a high phase purity of the synthesized materials. SEM analysis revealed hexagonal platelet morphology of the synthesized materials, which were then used to fabricate EPD films. Characterization of the EPD films reveal significant differences between the Hydro- and Thermo-Bi2Te3 samples, leading to about 8 times better electrical conductivity values in the Thermo-Bi2Te3. XPS analysis revealed a higher metal oxides content in the Hydro-Bi2Te3 sample, contributing to the formation of a resistive layer, thus lowering the electrical conductivity. Arrhenius plots of electrical conductivity vs inverse temperature was used for the estimation of the activation energy for conduction, revealing a higher activation energy need for the Hydro-Bi2Te3 film, in agreement with the resistive barrier oxide content. Both the samples exhibited negative Seebeck coefficient (S) in the order of 160–170 mV/K. The small difference in S of Hydro- and Themo-Bi2Te3 films was explained by the effective medium theory, revealing that the magnitude of S is linearly correlated with the surface oxide content. Based on the findings, TE materials synthesized through thermolysis route is recommended for further studies using soft treatment/processing of pre-made TE materials. EPD platform presented here is shown to clearly expose the differences in the electronic transport in connection to nanoparticle surface chemistry, proving a promising methodology for the evaluation of morphology, size and surface chemistry dependence of electronic transport for a wide range of materials.
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| 2. |
- Batili, Hazal, et al.
(författare)
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Electrophoretic assembly and electronic transport properties of rapidly synthesized Sb2Te3 nanoparticles
- 2023
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Ingår i: Applied Surface Science. - : Elsevier BV. - 0169-4332 .- 1873-5584. ; 637
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Tidskriftsartikel (refereegranskat)abstract
- With the recent advances in thermoelectric (TE) technology, there is an increasing demand to develop thick films that would enable large-scale TE devices. Assembly of TE-films from size and morphology-controlled nano particles has been a challenging issue that can be addressed by the use of electrophoretic deposition (EPD) technique. In this work, morphology-controlled Sb2Te3 nanoparticles were synthesized through microwave assisted thermolysis, which were subsequently used for EPD of TE films on specially developed glass substrates. The electronic transport properties were measured in the temp-range of 22-45 degrees C. The as-made EPD films showed a high initial resistance, ascribed to high porosity and the presence of surface oxide/passivating layers. The impact of two types of small organic molecules-as hexanedithiol and dodecanethiol, on the electronic transport was investigated, resulting in a significant improvement in the electrical conductivity of the films. The XPS analysis suggests that the thiols bind to the surface of nanoparticles through formation of sulfides. Seebeck coefficient in the range of + 160 to + 190 & mu;V/K was measured, revealing the p-type transport through the deposited films. Finally, a power factor of about 2.5 & mu;W/K2.m was estimated the first time for p-type EPD films, revealing the potential of the developed nanoparticles and substrate, the small molecule additives and the EPD process presented in this work.
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| 3. |
- Batili, Hazal, et al.
(författare)
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Electrophoretic Deposition and Characterization of Bi2Te3 Synthesized through Hydrothermal and Thermolysis Routes
-
Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- Bismuth telluride-Bi2Te3 is a promising material for harvesting thermal energyfor applications near room temperature, where large-area applications requirenew methods of depositing pre-made particulate materials. Electrophoretic deposition(EPD) technique has the promise of enabling the formation of thickfilms using colloidally stabilized suspensions of pre-made nanoparticles. It isvery important to understand the thermoelectric (TE) materials’ performancein relation to the synthetic process, to enable promising and scalable materialstechnologies. EPD films allow to study the effect of surface chemistry, stronglylinked to the synthetic route, on the material’s physico-chemical and transportproperties. Here we report on the synthesis of Bi2Te3 through wet-chemicalreactions performed in two different media as water (hydrothermal-Hydro) andoil (thermolysis-Thermo). Synthesized materials possess platelet morphology,which were then used to fabricated EPD films on specially developed glass substrates. Characterization of the materials and films reveal significant differencesbetween the surface chemistry of the EPD films of Hydro- and Thermo-Bi2Te3samples, where a higher content of metal oxide phases are observed in the Hydro-Bi2Te3 sample. This has a big impact the electronic transport properties, asrevealed by about nine times higher resistance, confirmed by significantly higheractivation energy, of the Hydro-Bi2Te3 film as compared to the Thermo-Bi2Te3film. Slight difference in the Seebeck coefficient (S) was explained by the effectivemedium theory, revealing that the magnitude of S is linearly correlatedwith the surface oxide content. Based on the findings, TE materials synthesizedthrough thermolysis route is recommended for future studies focusing on EPD of TE materials.
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| 4. |
- Batili, Hazal, et al.
(författare)
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On the electrophoretic deposition of Bi2Te3 nanoparticles through electrolyte optimization and substrate design
- 2022
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Ingår i: Colloids and Surfaces A. - : Elsevier BV. - 0927-7757 .- 1873-4359. ; 649, s. 129537-
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Tidskriftsartikel (refereegranskat)abstract
- Assembly of thermoelectric nanostructures with pre-defined morphology and surface chemistry on solid sub-strates has been one of the challenges for in-plane TE devices. Electrophoretic deposition (EPD) has the potential to be used for this purpose, where the use of non-conductive substrates is required to enable a reliable evaluation of the transport property of electrically active films. Bi2Te3 nanoparticles, which were synthesized using microwave-assisted hydrothermal route, were used for the EPD of thermoelectric films on glass substrates. A special substrate was fabricated using maskless photolithography, to evaluate the electronic transport properties of the TE films without the interference of the substrate. Electrolyte composition was optimized for high mobility of the suspended nanoparticles, and Bi2Te3 EPD films were fabricated with a high deposition rate, reaching 10 mu m/min. Initial EPD films showed high resistivity, ascribed to the surface oxide layer and capping ligands. The resistance was significantly reduced by the addition of a dithiol molecular linker, capable of interconnecting the Bi2Te3 nanoparticles through ligand-exchange. Seebeck coefficient in the range-150 to-180 mu V/K was measured, revealing the transport through the deposited films. Finally, a power factor of 169 nW/K-2.m was estimated, revealing the potential for the application of this technology to large area TE films as active coatings using the developed EPD process.
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| 5. |
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| 6. |
- Ergül, Adem Björn, 1980-
(författare)
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Superconducting Nanowire Single-photon Detectors : WSi SNSPDs for Quantum Optics Applications
- 2018
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- In this study we have developed a new fabrication technique for Tungsten Silicide (WSi) Superconducting Nanowire Single-Photon Detectors (SNSPD). These detectors arespecifically designed to interact with the photons in the infra-red region of theelectro magnetic spectrum. Fabrication process is described in great detail with the intention of giving the readers a broad view about the facts or aspects of various situations they might face in the clean room processes. Ultimate goal for the project is to integrate these high temperature SNSPD detectors with the photonic circuits.
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| 7. |
- Ergül, Adem, 1980-
(författare)
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Fabrication and Characterization of Superconductive Coplanar Waveguide Resonators : Fabrication and Characterization of Superconductive Coplanar Waveguide Resonators
- 2009
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The objective of this thesis is to evaluate a generic process for fabrication and characterization of the Superconductive coplanar waveguide (CPW) resonators. Superconductive CPW resonators with various lengths and shapes are designed to investigate their electrical and magnetic properties as well as resonance properties and sensitivities. In the first part of thesis, two different models are introduced in order to estimate the nonlinear kinetic inductance of a superconducting CPW resonator. The first model is based on Bean critical-state model and the second one is based on current dependence of London penetration depth. The existence of a shift in resonant frequency of Superconductive CPW resonator caused by a non-linear kinetic inductance is also shown experimentally. Simulations were carried out to estimate the nonlinear kinetic inductance due to the self- induced magnetic field penetration. The rest of the thesis is concerned with development of very smooth Aluminum (Al) thin films with RMS (Root Mean Square) roughness 1~nm and CAD (Computer Aid Design) of superconductive CPW resonators. Experimental investigation of a generic fabrication technique for superconductive CPW resonator is carried out. Many resonators are fabricated with different design parameters, such as centerline or gap width, film thickness and gap capacitors length. The fabrication process is described in detail. Electron Beam Lithography is used to fabricate Nb and Al CPW resonators which are coupled to outer conductors via gap capacitors. We have fabricated GHz frequency CPW resonators with quality factors, Q up 5X10^5.
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| 8. |
- Ergül, Adem, et al.
(författare)
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Localizing quantum phase slips in one-dimensional Josephson junction chains
- 2013
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Ingår i: New Journal of Physics. - : IOP Publishing. - 1367-2630. ; 15, s. 095014-
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Tidskriftsartikel (refereegranskat)abstract
- We studied quantum phase-slip (QPS) phenomena in long one-dimensional Josephson junction series arrays with tunable Josephson coupling. These chains were fabricated with as many as 2888 junctions, where one sample had a separately tunable link in the middle of the chain. Measurements were made of the zero-bias resistance, R-0, as well as current-voltage characteristics (IVC). The finite R-0 is explained by QPS and shows an exponential dependence on root E-J/E-C with a distinct change in the exponent at R-0 = R-Q = h/4e(2). When R-0 > R-Q, the IVC clearly shows a remnant of the Coulomb blockade, which evolves to a zero-current state with a sharp critical voltage as E-J is tuned to a smaller value. The zero-current state below the critical voltage is due to coherent QPSs and we show that these are enhanced when the central link is weaker than all other links. Above the critical voltage, a negative, differential resistance is observed, which nearly restores the zero-current state.
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| 9. |
- Ergül, Adem, 1980-
(författare)
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Nonlinear dynamics of Josephson Junction Chains and Superconducting Resonators
- 2013
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis presents the results of the experimental studies on two kindof Superconducting circuits: one-dimensional Josephson junction chains andsuperconducting coplanar waveguide (CPW) resonators. One-dimensionalJosephson junction chains are constructed by connecting many Superconducting quantum interference devices (SQUIDs) in series. We have studied DC transport properties of the SQUID chains and model their nonlineardynamics with Thermally Activated Phase-Slips (TAPS). Experimental andsimulated results showed qualitative agreement revealing the existence of auniform phase-slipping and phase-sticking process which results in a voltage-independent current on the dissipative branch of the current-voltage char-acteristics (IVC). By modulating the effective Josephson coupling energy ofthe SQUIDs (EJ ) with an external magnetic field, we found that the ratio EJ /EC is a decisive factor in determining the qualitative shape of theIVC. A quantum phase transition between incoherent Quantum Phase Slip, QPS (supercurrent branch with a finite slope) to coherent QPS (IVC withwell-developed Coulomb blockade) via an intermediate state (supercurrentbranch with a remnant of Coulomb blockade) is observed as the EJ /EC ratio is tuned. This transition from incoherent QPS to the intermediate-statehappens around R0 ∼ RQ (RQ = h/4e^2 = 6.45kΩ). We also fabricated structured chains where a SQUID at the middle of the chain (central SQUID) has different junction size and loop area compared to other SQUIDs in the chain. Results showed that with these structured chains it is possible to localize andtune the amplitude of both TAPS and QPS at the central SQUID.The second part of the thesis describes the fabrication process and themeasurement results of superconducting CPW resonators. Resonators withdifferent design parameters were fabricated and measured. The transmissionspectra showed quality factors up to, Q ∼ 5 × 10^5 . We have observed bendingof the resonance curves to the lower frequencies due to existence of a nonlinear kinetic inductance. The origin of the nonlinear kinetic inductance isthe nonlinear relation between supercurrent density, Js, and superfluid veloc-ity, vs , of the charge carriers on the center line of the resonators. A simplemodel based on the Ginzburg-Landau theory is used in order to explain ob-served nonlinear kinetic inductance and estimates using this model showedgood agreement with the experimental results.
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| 10. |
- Ergül, Adem, et al.
(författare)
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Phase sticking in one-dimensional Josephson junction chains
- 2013
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 88:10, s. 104501-
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Tidskriftsartikel (refereegranskat)abstract
- We studied current-voltage characteristics of long one-dimensional Josephson junction chains with Josephson energy much larger than charging energy, E-J >> E-C. In this regime, typical I-V curves of the samples consist of a supercurrent-like branch at low-bias voltages followed by a voltage-independent chain current branch, I-chain at high bias. Our experiments showed that I-chain is not only voltage-independent but it is also practically temperature-independent up to T = 0.7T(C). We have successfully model the transport properties in these chains using a capacitively shunted junction model with nonlinear damping.
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| 11. |
- Ergül, Adem, et al.
(författare)
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Spatial and temporal distribution of phase slips in Josephson junction chains
- 2017
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Ingår i: Scientific Reports. - : Nature Publishing Group. - 2045-2322. ; 7
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Tidskriftsartikel (refereegranskat)abstract
- The Josephson effect, tunnelling of a supercurrent through a thin insulator layer between two superconducting islands, is a phenomena characterized by a spatially distributed phase of the superconducting condensate. In recent years, there has been a growing focus on Josephson junction devices particularly for the applications of quantum metrology and superconducting qubits. In this study, we report the development of Josephson junction circuit formed by serially connecting many Superconducting Quantum Interference Devices, SQUIDs. We present experimental measurements as well as numerical simulations of a phase-slip center, a SQUID with weaker junctions, embedded in a Josephson junction chain. The DC transport properties of the chain are the result of phase slips which we simulate using a classical model that includes linear external damping, terminating impedance, as well as internal nonlinear quasiparticle damping. We find good agreement between the simulated and the experimental current voltage characteristics. The simulations allow us to examine the spatial and temporal distribution of phase-slip events occurring across the chains and also the existence of travelling voltage pulses which reflect at the chain edges.
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| 12. |
- Hamawandi, Bejan, et al.
(författare)
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Electrical properties of sub-100 nm SiGe nanowires
- 2016
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Ingår i: Journal of semiconductors. - : Institute of Physics (IOP). - 1674-4926. ; 37:10
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Tidskriftsartikel (refereegranskat)abstract
- In this study, the electrical properties of SiGe nanowires in terms of process and fabrication integrity, measurement reliability, width scaling, and doping levels were investigated. Nanowires were fabricated on SiGe-on oxide (SGOI) wafers with thickness of 52 nm and Ge content of 47%. The first group of SiGe wires was initially formed by using conventional I-line lithography and then their size was longitudinally reduced by cutting with a focused ion beam (FIB) to any desired nanometer range down to 60 nm. The other nanowires group was manufactured directly to a chosen nanometer level by using sidewall transfer lithography (STL). It has been shown that the FIB fabrication process allows manipulation of the line width and doping level of nanowires using Ga atoms. The resistance of wires thinned by FIB was 10 times lower than STL wires which shows the possible dependency of electrical behavior on fabrication method.
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| 13. |
- Noroozi, Mohammad, et al.
(författare)
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Fabrications of size-controlled SiGe nanowires using I-line lithography and focused ion beam technique
- 2014
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Ingår i: ECS Transactions. - : The Electrochemical Society. - 1938-5862 .- 1938-6737. ; , s. 167-174
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Konferensbidrag (refereegranskat)abstract
- In this study, a novel method using Focus Ion Beam (FIB) technique was applied to scale down Si1-xGex wires (x=0.27-0.57) to 20 nm width. Originally, the wires were processed by using Iline lithography and dry etching of SiGe on oxide (SGOI) substrates. The SGOI wafers were processed through condensation method where a SiGe/Si layer was grown in the beginning on SOI wafers and oxidized at 850-1050 °C. The shape of the nanowires (NWs) during the successive FIB cutting was examined by scanning electron microscopy (SEM) and the carrier transport through the NWs was checked by resistivity measurements. The contact resistance was reduced by Ni-silicide prior to metallization. The fabricated NWs were also suspended by tilting FIB. The results present the limitations and challenges of FIB technique to create NWs for advanced sensors and transistors.
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| 14. |
- Noroozi, Mohammad, 1979-, et al.
(författare)
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Significant Improvement of Thermoelectric Efficiency in SiGe Nanowires
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Tidskriftsartikel (refereegranskat)abstract
- The thermoelectric (TE) properties of SiGe nanowires (NWs) with width of 60 nm in a back-gate configuration have been studied experimentally and theoretically. The carrier transport in NWs was modified by biasing voltage to the gate for different temperatures. The original wafers were SiGe-on-oxide (SGOI), which were formed through condensation of SiGe on Si-on-oxide wafers (SOI). The power factor of SiGe NWs was enhanced by a factor of >2 in comparison with SiGe bulk material over a temperature range of 273 K to 450 K. This enhancement is mainly attributed to the energy filtering of carriers in SiGe NWs which were introduced by the roughness in the shape of NWs, non-uniform SiGe composition and the induced defects during the manufacturing of SGOI wafers or processing of NWs. These defects create potential barriers which may significantly enhance the Seebeck coefficient, while the conductivity can be boosted by tuning the back-gate bias.
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| 15. |
- Noroozi, Mohammad, et al.
(författare)
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Unprecedented thermoelectric power factor in SiGe nanowires field-effect transistors
- 2017
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Ingår i: ECS Journal of Solid State Science and Technology. - : Electrochemical Society. - 2162-8769 .- 2162-8777. ; 6:9, s. Q114-Q119
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Tidskriftsartikel (refereegranskat)abstract
- In this work, a novel CMOS compatible process for Si-based materials has been presented to form SiGe nanowires (NWs) on SiGe On Insulator (SGOI) wafers with unprecedented thermoelectric (TE) power factor (PF). The TE properties of SiGe NWs were characterized in a back-gate configuration and a physical model was applied to explain the experimental data. The carrier transport in NWs was modified by biasing voltage to the gate at different temperatures. The PF of SiGe NWs was enhanced by a factor of >2 in comparison with bulk SiGe over the temperature range of 273 K to 450 K. This enhancement is mainly attributed to the energy filtering of carriers in SiGe NWs, which were introduced by imperfections and defects created during condensation process to form SiGe layer or in NWs during the processing of NWs.
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| 16. |
- Serrano-Claumarchirant, José F., et al.
(författare)
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Thermoelectric Inks and Power Factor Tunability in Hybrid Films through All Solution Process
- 2022
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Ingår i: ACS Applied Materials and Interfaces. - : American Chemical Society (ACS). - 1944-8244 .- 1944-8252. ; 14:17, s. 19295-19303
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Tidskriftsartikel (refereegranskat)abstract
- Thermoelectric (TE) materials can have a strong benefit to harvest thermal energy if they can be applied to large areas without losing their performance over time. One way of achieving large-area films is through hybrid materials, where a blend of TE materials with polymers can be applied as coating. Here, we present the development of all solution-processed TE ink and hybrid films with varying contents of TE Sb2Te3 and Bi2Te3 nanomaterials, along with their characterization. Using (1-methoxy-2-propyl) acetate (MPA) as the solvent and poly (methyl methacrylate) as the durable polymer, large-area homogeneous hybrid TE films have been fabricated. The conductivity and TE power factor improve with nanoparticle volume fraction, peaking around 60-70% solid material fill factor. For larger fill factors, the conductivity drops, possibly because of an increase in the interface resistance through interface defects and reduced connectivity between the platelets in the medium. The use of dodecanethiol (DDT) as an additive in the ink formulation enabled an improvement in the electrical conductivity through modification of interfaces and the compactness of the resultant films, leading to a 4-5 times increase in the power factor for both p- and n-type hybrid TE films, respectively. The observed trends were captured by combining percolation theory with analytical resistive theory, with the above assumption of increasing interface resistance and connectivity with polymer volume reduction. The results obtained on these hybrid films open a new low-cost route to produce and implement TE coatings on a large scale, which can be ideal for driving flexible, large-area energy scavenging technologies such as personal medical devices and the IoT.
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| 17. |
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| 18. |
- Tholén, E., et al.
(författare)
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Gain, noise and intermodulation in a nonlinear superconducting resonator
- 2014
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Ingår i: EPJ Quantum Technology. - : SpringerOpen. - 2196-0763. ; 1:1
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Tidskriftsartikel (refereegranskat)abstract
- A superconducting microwave resonator is modified with several weak links to make it nonlinear and operated as a phase-insensitive microwave amplifier. Signal gain is demonstrated by intermodulation with a strong pump. The gain is sharply frequency dependent, and we demonstrate phase dependence by examining correlations between the signal and one idler which is a 3rd order intermodulation product of the pump and signal tones. A calibration procedure is described which is based on measurement of both thermal and quantum noise, revealing that the following HEMT amplifier adds noise at 15 times the quantum limit. When operated as a phase-insensitive amplifier the nonlinear resonator added noise at 2.5 times the quantum limit. Significant power is found at intermodulation products beyond 3rd order, which may be responsible for the inability to reach the quantum limit
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| 19. |
- Tholén, Erik, 1979-, et al.
(författare)
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Nonlinearities and parametric amplification in superconducting coplanar waveguide resonators
- 2007
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Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 90:25, s. 253509-
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Tidskriftsartikel (refereegranskat)abstract
- Experimental investigations of the nonlinear properties of superconducting niobium coplanarwaveguide resonators are reported. The nonlinearity due to a current dependent kinetic inductanceof the center conductor is strong enough to realize bifurcation of the nonlinear oscillator. Whendriven with two frequencies near the threshold for bifurcation, parametric amplification with a gainof +22.4 dB is observed.
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| 20. |
- Tholén, Erik, 1979-, et al.
(författare)
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Parametric amplification with weak-link nonlinearity in superconducting microresonators
- 2009
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Ingår i: Nobel Symposium 141: Qubits for Future Quantum Information; Gothenburg; 25 May 2009 through 28 May 2009.
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Konferensbidrag (refereegranskat)abstract
- Nonlinear kinetic inductance in a high Q superconducting coplanarwaveguide microresonator can cause a bifurcation of the resonance curve. Near thecritical pumping power and frequency for bifurcation, large parametric gain is observedfor signals in the frequency band near resonance. We show experimental results onsignal and intermodulation gain which are well described by a theory of the parametricamplification based on a Kerr nonlinearity. Phase dependent gain, or signal squeezing,is verified with a homodyne detection scheme.
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