| 1. |
- Abadei, S., et al.
(författare)
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DC field dependent properties of Na0.5K0.5NbO3/SiO2/Si structures at millimeter-wave frequencies
- 2001
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Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 78:13, s. 1900-1902
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Tidskriftsartikel (refereegranskat)abstract
- Dielectric properties of laser-ablated 0.5-mum-thick c-axis epitaxial Na0.5K0.5NbO3 films on high-resistivity (7.7 Omega cm) silicon SiO2/Si substrate are studied experimentally at frequencies up to 40 GHz. For measurements, planar 0.5-mum-thick gold electrodes (interdigital and straight slot) are photolithography defined on the top surface of Na0.5K0.5NbO3 films. The slot width between the electrodes is 2 or 4 mum. 13% capacitance change at 40 V dc bias and Q factor more than 15 are observed at 40 GHz, which makes the structure useful for applications in electrically tunable millimeter-wave devices.
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| 2. |
- Blomqvist, Mats, et al.
(författare)
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High-performance epitaxial Na0.5K0.5NbO3 thin films by magnetron sputtering
- 2002
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Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 81:2, s. 337-339
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Tidskriftsartikel (refereegranskat)abstract
- Epitaxial Na0.5K0.5NbO3 (NKN) thin films have been grown on LaAlO3 substrates by rf magnetron sputtering of a stoichiometric, high-density, ceramic target. X-ray diffraction analysis showed c-axis oriented cube-on-cube growth. Micrometer size interdigital capacitor (IDC) structures were defined on the surface of the NKN film using photolithography. The electrical characterization at 1 MHz showed dissipation factor tan delta of 0.010, tunability 16.5% at 200 kV/cm and dielectric permittivity epsilon(r)=470. The frequency dispersion of epsilon(r) between 1 kHz and 1 MHz was 8.5% and the IDCs showed very good insulating properties with leakage current density on the order of 30 nA/cm(2) at 400 kV/cm. The polarization loop exhibits weak ferroelectric hysteresis with maximum polarization 23.5 muC/cm(2) at 600 kV/cm. These results are promising for tunable microwave devices based on rf sputtered NKN thin films.
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| 3. |
- Cho, Coong-Rae, et al.
(författare)
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Na0.5K0.5NbO3/SiO2/Si Thin Film Varactor
- 2000
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Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 76, s. 1761-
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Tidskriftsartikel (refereegranskat)abstract
- Perfectly c-axis oriented micrometer thickNa 0.5 K 0.5 NbO 3 (NKN) films have been prepared on a thermally grown ultrathinSiO 2 template layer onto a Si(001) wafer by the pulsed laser deposition technique. A x-ray diffraction θ–2θ scan reveals multiple-cell structuring of single phase NKN film along the polar axis, while filmsgrown onto amorphous ceramic (Corning) glass show a mixture of slightly c-axis oriented NKN and pyrochlore phases. This implies a small amount ofSiO 2 crystallites distributed in an amorphous matrix inherit Si(001) orientation and promotes highly oriented NKN film growth. NKN filmdielectric permittivityε ′ was found to vary from 114.0 to 107.2 in the frequency range 1 kHz–1 MHz, while the resistivity was on the order of2.6×10 10 Ω cm @ 20 kV/cm. The planar interdigital variable reactance device (varactor) based on theNKN/SiO 2 /Si thin film structure possesses a dissipation factor of 0.8% at 1 MHz and zero bias, electrical tunability of 3.1%, and nA order leakage current at 20 V bias at room temperature.
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| 4. |
- Khartsev, Sergiy, et al.
(författare)
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Comparative characteristics of Na0.5K0.5NbO 3 films on Pt by pulsed laser deposition and magnetron sputtering
- 2003
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Ingår i: Integrated Ferroelectrics. - : Informa UK Limited. - 1058-4587 .- 1607-8489. ; 55, s. 769-779
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Tidskriftsartikel (refereegranskat)abstract
- Ferroelectric Na0.5K0.5NbO3 (NKN) thin films were grown on the Pt80Ir20 polycrystalline substrates by pulsed laser deposition (PLD) and radio frequency-magnetron sputtering (RF) technique using the same stoichiometric Na0.5K 0.5NbO3 ceramic target. X-ray diffraction proved both PLD- and RF-made Na0.5K0.5NbOj/Pt80Ir20 films are single phase and have preferential c-axis orientation. Temperature dependence of dielectric permittivity reveals the presence of two phase transitions around 210 and 410°C. Capacitance vs. applied voltage C-V @ 100 kHz, I-V, and P-E hysteresis characteristics recorded for the vertical capacitive structures yielded loss tan δ = 0.026 and 0.016, tunability about 44.5 and 30% @ 100 kV/cm, Ohmic resistivity 6.7 × 1012 Ω·cm and 0.2 × 1012 Ω·cm, remnant polarization 11.7 and 9.7 μC/cm2, coercive field 28.0 and 94.6 kV/cm for PLD- and RF-films, respectively. Piezoelectric test carried out in hydrostatic conditions showed piezoelectric coefficient dH = 21 for PLD-NKN and 15 pC/N for RF-NKN film.
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| 5. |
- Abadei, Saeed, 1961, et al.
(författare)
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Low-frequency and microwave performances of laser-ablated epitaxialNa 0.5 K 0.5 NbO 3 films on high-resistivitySiO 2 /Si substrates
- 2002
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Ingår i: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 91, s. 2267-
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Tidskriftsartikel (refereegranskat)abstract
- The dielectric properties of laser-ablated 0.5-μm-thick c-axis epitaxialNa 0.5 K 0.5 NbO 3 (NKN) films on high-resistivity (>7.7 kΩ cm) siliconSiO 2 /Si substrates are studied experimentally in the temperature interval of 30–320 K and at frequencies of 1.0 MHz–40 GHz. The films are grown by laser ablation from a stoichiometric target. For the measurements, planar 0.5-μm-thick gold electrodes (interdigital and straight slot) are photolithography defined on the top surface of NKN films. The slot width between the electrodes is 2.0 or 4.0 μm. At low frequencies(f 1. At microwave frequencies(f>10 GHz), the voltage dependence of the capacitance is given by the NKN film. More than a 13% capacitance change at 40 V dc bias and a Q factor of more than 15 are observed at 40 GHz, which make the structure useful for applications in electrically tunable millimeter-wave devices
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| 6. |
- Abadei, Saeed, 1961, et al.
(författare)
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Low frequency characterisation of laser ablation deposited thin Na0.5K0.5NbO3 (NKN) films for microwave application
- 2001
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Ingår i: Integrated Ferroelectrics. - : Informa UK Limited. - 1058-4587 .- 1607-8489. ; 263:1, s. 173-179
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Tidskriftsartikel (refereegranskat)abstract
- Experimental results on three types of Na0.5K0.5NbO3 (NKN) film capacitor structures are presented. The epitaxial NKN thin films have been deposited on (100) Si (high resistivity), SiO2/Si (low resistivity) and Pt/Si (low resistivity) substrates using laser ablation deposition. Both straight slot and interdigital electrode have been deposited on top of the NKN films. The leakage current and low frequency dielectric properties (I-V, C-V, tanδ-V) of the structures have been measured at 1 MHz as a function of electric field at room temperature. In all three types of capacitor structures the leakage currents in a-b plane are very small, while along c-axis there are extremely large leakage currents. On low resistivity silicon substrates the tunability of the dielectric permittivity is about 12% and loss tangent is low also. On high resistivity (ρ>10 kOhm cm) silicon substrate the tunability at 1 MHz is extremely high, about 10 times, and the losses are also high. On the other hand at microwave frequencies the losses are small (tanδ
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| 7. |
- Cho, Chong-Rae, et al.
(författare)
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Ferroelectroc Na0.5K0.5NbO3 films for voltabe tunable microwave devices
- 2000
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Ingår i: Materials Issues for Tunable RF and Microwave Devices II : MRS fall conference. - : Materials Research Society. ; , s. 19-24
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Konferensbidrag (refereegranskat)abstract
- Single phase Na0.5K0.5NbO3 (NKN) thin films have been pulsed laser deposited on Al2O3(01-12), LaAlO3(001), and MgO(001) single crystal substrates as well as onto SiO2/Si(001) wafers to demonstrate films feasibility for voltage tunable microwave device applications. NKN film texture has been found to be quite different on three different single crystals: highly c-axis oriented on Al2O3, "cube-on-cube" epitaxial quality on LaAlO3, bi-axial textures on MgO, while NKN films grown on Si substrate with various thickness of SiO2 buffer layer possess highly c-axis oriented quadrupled structure. NKN film interdigital capacitors fabricated onto single crystal oxide substrates showed tunability of 30-40 % and dissipation factor of 0.01-0.02 at 1 MHz and applied electric field of 100kV/cm. Microwave frequency measurements for NKN/Si varactors yield 13 % tunability and dielectric loss tan delta as low as 0.012 at 40 GHz under 200 kV/cm applied bias.
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| 8. |
- Dzibrou, Dzmitry, 1984-
(författare)
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Complex Oxide Photonic Crystals
- 2009
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Microphotonics has been offering a body of ideas to prospective applicationsin optics. Among those, the concept of photonic integrated circuits (PIC’s) has recently spurred a substantial excitement into the scientific community. Relisation of the PIC’s becomes feasible as the size shrinkage of the optical elements is accomplished. The elements based on photonic crystals (PCs) represent promising candidacy for manufacture of PIC’s. This thesis is devoted to tailoring of optical properties and advanced modelling of two types of photonic crystals: (Bi3Fe5O12/Sm3Ga5O12)m and (TiO2/Er2O3)m potentially applicable in the role optical isolators and optical amplifiers, respectively. Deposition conditions of titanium dioxide were first investigated to maximise refractive index and minimise absorption as well as surface roughness of titania films. It was done employing three routines: deposition at elevated substrate temperatures, regular annealing in thermodynamically equilibrium conditions and rapid thermal annealing (RTA). RTA at 500 oC was shown to provide the best optical performance giving a refractive index of 2.53, an absorption coefficient of 404 cm−1 and a root-mean-square surface roughness of 0.6 nm. Advanced modelling of transmittance and Faraday rotation for the PCs (Bi3Fe5O12/Sm3Ga5O12)5 and (TiO2/Er2O3)6 was done using the 4 × 4 matrix formalism of Višňovský. The simulations for the constituent materials in the forms of single films were performed using the Swanepoel and Višňovský formulae. This enabled generation of the dispersion relations for diagonal and off-diagonal elements of the permittivity tensors relating to the materials. These dispersion relations were utilised to produce dispersion relations for complex refractive indices of the materials. Integration of the complex refractive indices into the 4 × 4 matrix formalism allowed computation of transmittance and Faraday rotation of the PCs. The simulation results were found to be in a good agreement with the experimental ones proving such a simulation approach is an excellent means of engineering PCs.
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| 9. |
- Emelchenko, G., et al.
(författare)
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1.5 μm photoluminescence of Er3+ in opal based photonic crystals
- 2008
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Ingår i: Proc SPIE Int Soc Opt Eng. - : SPIE. - 9780819471871
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Konferensbidrag (refereegranskat)abstract
- The study of the emission properties of opal-erbium oxide nanocomposites in the wide range of erbium concentrations was carried out. Erbium oxide concentration was varied from 0.25 to 16%wt. Maximal output of the photoluminescence (PL) took place at 1%wt of erbium oxide concentration. It was shown that the annealing temperatures from 600 to 900°C were too low to exhibit sufficient emission properties of the erbium-opal composites. The presence of the erbium silicates Er2SiO5 and Er 2Si2O7 in the opal-erbium nanocomposites was revealed by X-ray phase analysis. Amorphous silica in opal matrix was not crystallized at the annealing during a few hours at 1000 - 1200°C. The case of the tens hours of annealing the crystoballite phase occurred. No angle dependence of the PL intensity was observed as a result of degradation of the photonic band gap (PBG) at the annealing of the opal-erbium oxide nanocomposites. Further modification of the material processing to achieve a strong photonic band gap reflection peak near 1550 nm with high PL intensity in the opal-Er2O3 composite is running.
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| 10. |
- Grishin, Alex M.
(författare)
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Multifunctional oxides on Si
- 2005
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Ingår i: Proc. Electrochem. Soc.. ; , s. 482-497
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Konferensbidrag (refereegranskat)abstract
- We review the projects ongoing at the Royal Institute of Technology on engineering and application of novel oxides on Si platform. Colossal magnetoresistance (CMR) in La 1-x(Sr,Ca,Pb) xMnO 3 films grown on Si has been tailored to room temperature to make a prototype of uncooled IR bolometer. Demonstrator of ferroelectric PZT/SiC field effect transistor operates at temperatures up to 300 °C. Ferroelectric niobate (Na,K)NbO 3 films have been sintered and found to be feasible for biomedical, microwave and electro-optical applications.
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| 11. |
- Kawasaki, Hiroharu, et al.
(författare)
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TiO2/TiN/TiO2 heat mirrors by laser ablation of single TiN target
- 2008
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Ingår i: Journal of Physics, Conference Series. - : IOP Publishing. - 1742-6588 .- 1742-6596. ; 100:1, s. 012038-
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Tidskriftsartikel (refereegranskat)abstract
- Titanium oxide (TiO2 ) and titanium nitride (TiN) multilayered films grown by pulsed laser deposition (PLD) technique have been tested as a heat mirror, which have a high transmittance in the visible region and a high reflectance in the infrared. Three layer TiO2 /TiN/TiO2 heat mirrors were grown on Corning glass substrates ablating single TiN target. Switching of TiO2 -to-TiN layers composition was achieved by changing gas atmosphere (oxygen-to-nitrogen). Grown TiO2 /TiN/TiO2 heat mirrors are highly transparent in visible (above 60% at 525nm), opaque in infrared (10% at 2600nm) and in the range from 400 nm to 2600 nm they possess almost the same properties as films prepared using two targets: TiO2 and TiN. XPS confirms similarity of chemical composition of multilayered TiO2 /TiN films prepared by single TiN and two TiO2 and TiN targets techniques. Furthermore, multifunctional self cleaning properties of TiO2 /TiN heat mirrors are expected through the precise control of the composition of the top TiO2 layer operating as a photocatalyst.
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| 12. |
- Kim, Jang-Yong
(författare)
-
Novel tantalate-niobate films for microwaves
- 2005
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Microwave materials have been widely used in a variety of applications ranging from communication devices to military satellite services, and the study of materials properties at microwave frequencies and the development of functional microwave materials have always been among the most active areas in solid-state physics, materials science, and electrical and electronic engineering. In recent years, the increasing requirements for the development of high speed, high frequency circuits and systems require complete understanding of the properties of materials function at microwave frequencies. Ferroelectric materials usually have high dielectric constants, and their dielectric properties are temperature and electric field dependent. The change in permittivity as a function of electric field is the key to a wide range of applications. Ferroelectric materials can be used in fabrication capacitors for electronic industry because of their high dielectric constants, and this is important in the trend toward miniaturization and high functionality of electronic products. The simple tunable passive component based on ferroelectric films is a varactor which can be made as a planar structure, and electrically tunable microwave integrated circuits using ferroelectric thin films can be developed. Therefore, it is very important to characterize the dielectric constant and tunability of ferroelectric thin films. This thesis shows experimental results for growth, crystalline properties and microwave characterization of Na0.5K0.5NbO3 (NKN), AgTa0.5Nb0.5O3 (ATN), Ba0.5Sr0.5TiO3 (BST) as well as AgTaO3 (ATO), AgNbO3 (ANO) thin films. The films were grown by Pulsed Laser Deposition (PLD) and rf-magnetron sputtering of a stoichiometric, high density, ceramic NKN, ATN, BST target onto single crystal LaAlO3(LAO), Al2O3 (sapphire), and Nd:YAlO3, and amorphous glass substrates. By x-ray diffractometry, NKN, ATN, BST films on LAO substrates were found to grow epitaxially, whereas films on r-cut sapphire substrates were found to be preferentially (00l) oriented. Coplanar waveguide interdigital capacitor (CPWIDC) structures were fabricated by standard photolithography processing and metal lift-off technique. Microwave properties of the NKN/Sapphire and ATN/Sapphire with CPW structures were characterized using on-wafer microwave measurement technique. Measurement setup is composed of network analyzer, probe station, and microwave G-S-G probes. External electric field through the connection between network analyzer and power supply was applied to measure voltage tunability. Measured S-parameter were used for the calculation of capacitance, loss tanδ, tunability and K-factor. The NKN films interdigital capacitors with 2 μm finger gap on Nd:YAlO3 showed superior performance compared to ATN in the microwave range from 1 to 40 GHz. Within this range, the voltage tunability (40V, 200 kV/cm) was about 29%, loss tangent ∼ 0.13, K-factor = tunability/tanδ from 152% @ 10GHz to 46% @ 40GHz. The microwave performance of ATN film CPWIDC with 2 μm finger gap on sapphire substrate in the microwave range from 1 to 40 GHz showed that frequency dispersion is about 4.3%, voltage tunability was 4.7% @ 20GHz and 200 kV/cm, loss tangent ∼ 0.068 @ 20GHz, K-factor = tunability/tanδ is ranged from 124% @ 10GHz to 35% @ 40GHz. The BST films CPWIDC with 2μmfinger gap on Al2O3 substrate showed frequency dispersion of capacitance in the microwave range from 1 to 40 GHz about 17%, voltage tunability = 1 - C(40V)/C(0) ∼ 22.2%, loss tangent ∼ 0.137 @ 20GHz, and K-factor = tunability/tanδ from 281% @ 10GHz to 95% @ 40GHz.
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| 13. |
- Manuilov, Sergey, 1982-
(författare)
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Ferromagnetic resonance in films with growth induced anisotropy
- 2011
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis discusses two different magnetic materials: epitaxial yttrium iron garnet (YIG) and heteromorphous CoFeB-SiO2 films. YIG films were grown by pulse laser deposition (PLD) techniques onto gadolinium gallium garnet (GGG) substrates of (111) and (001) crystal orientations. Using stoichiometric and overstoichiometric ablative targets, we developed two types of YIG submicron films. The films grown from overstoichiometric targets have magnetic properties slightly different from standard liquid phase epitaxy (LPE) YIGs. They also demonstrate good substrate matching and approximately 6% nonstoichiometry. In contrary, films grown from stoichiometric targets posses surprisingly high values of uniaxial anisotropy, meanwhile cubic anisotropy is reduced several times. These films also reveal strong lattice distortions and nonstoichiometry around 17%. Employing Weiss molecular field theory and single-ion anisotropy model we determined the preferential occupancy of the octahedral [a] positions in the YIG cubic lattices by Fe3+ vacancies. The vacancies were found to be preferentially oriented along the growth direction perpendicular to the film surface. We called this effect “deformation blockade”. Different magnetostatic surface wave (MSSW) filters were also demonstrated. The filters employ high uniaxial anisotropy in YIG submicron films with magnetic losses ΔH ~ 1 Oe. Heteromorphous CoFeB-SiO2 films were deposited onto glass substrates employing carrousel magnetron sputtering. This novel technique allows amorphous films fabrication with record high in-plane anisotropy. The induced anisotropy fields here are approximately dozen times greater the values achieved using conventional growth technique when external bias field is applied during deposition process. Interesting observations were made studying CoFeB-SiO2 magnetization dynamics in the wide frequency range from 500 kHz up to 15 GHz. Two different anomalies of the magnetic susceptibility were found at the field of in-plane anisotropy Hp and critical field Hcr (0 < Hcr < Hp). We explained the anomalies appearance by sequence of the domain walls transformations so that Néel-Bloch-Néel domain wall transition stands for the instability at H = ±Hcr and transition from the uniformly magnetized state to the domain state with Néel domain wall and vice versa is responsible for the instability at H = ±Hp.
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| 14. |
- Timopheev, A. A., et al.
(författare)
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Effect of interaction in the magnetization reversal relaxation of superparamagnetic granulaR CoFeB -SiO2 FILMS
- 2009
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Ingår i: Magnetism and Magnetic Materials. - : Scientific.Net. ; , s. 213-216
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Konferensbidrag (refereegranskat)abstract
- In order to study the magnetic interactions influence on the relaxation processes in superparamagnetic media, the magnetostatic measurements were carried out for the granular (CoFeB)x-(SiO2)1-x films with x values near percolation threshold. The observed temperature dependences of the coercivity for the samples magnetized along in-plane easy axis have shown two parts linear on √T with different inclination angles, which cross each other at the blocking temperature (Tb). The first part of the curve, which corresponds to the temperature range below T b, depends on the measuring time and is related to the thermal activation nature of magnetization reversal process in the blocked superparamagnetic state. Second part of the curve, which corresponds to the temperature range above Tb, is practically independent on the measuring time and is related to existence of correlated state of superparamagnetic grains moments, i.e. to superferromagnetic state. The method of the magnetization reversal curves simulation based on the numerical solving of kinetic equation has been applied to explain the experimental results.
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| 15. |
- Tkatch, V. I., et al.
(författare)
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Estimation of the heat transfer coefficient in melt spinning process
- 2009
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Ingår i: Journal of Physics, Conference Series. - : IOP Publishing. - 1742-6588 .- 1742-6596. ; 144, s. 012104-
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Tidskriftsartikel (refereegranskat)abstract
- Effect of the quenching wheel velocity in the range 20.7-26.5 m/s on the cooling rate as well as on the structure and microtopology of the contact surfaces of the glass-forming FeNiPB melt-spun ribbons has been experimentally studied. Both the values of the cooling rate and heat transfer coefficient at the wheel-ribbon interface estimated from the temperature vs. time curves recorded during melt spinning runs are in the ranges (1.6-5.2)×10 6 K/s and (2.8-5.2)×10 5 Wm -2K -1, respectively, for ribbon thicknesses of 31.4-22.0 μm. It was found that the density of the air pockets at the underside surface of ribbons decreases while its average depth remains essentially unchanged with the wheel velocity. Using the surface quality parameters the values of the heat transfer coefficient in the areas of direct ribbon-wheel contact were evaluated to be ranging from 5.75 to 6.65×10 5 Wm -2K -1.
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| 16. |
- Östling, Mikael, et al.
(författare)
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Thin films in silicon carbide semiconductor devices
- 2004
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Ingår i: Proceedings of SPIE, the International Society for Optical Engineering. - : SPIE. - 0277-786X .- 1996-756X. ; 5774, s. 5-10
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Tidskriftsartikel (refereegranskat)abstract
- Silicon carbide (SiC) semiconductor devices have been established during the last decade as very useful high power, high speed and high temperature devices because of their inherent outstanding semiconductor materials properties. Due to its large band gap, SiC possesses a very high breakdown field and low intrinsic carrier concentration which according makes A high voltage and high temperature operation possible. SiC is also suitable for high frequency device applications, because of the high saturation drift velocity and low permittivity. Thin film technology for various functions in the devices has been heavily researched. Suitable thin film technologies for Ohmic and low-resistive contact formation, passivation and new functionality utilizing ferroelectric materials have been developed. In ferroelectrics, the spontaneous polarization can be switched by an externally applied electric field, and thus are attractive for non-volatile memory and sensor applications. A novel integration of Junction-MOSFETs (JMOSFETs) and Nonvolatile FETs (NVFETs) on a single 4H-SiC substrate is realized. SiC JMOSFET controls the drain current effectively from the buried junction Late thereby allowing for a constant current level at elevated temperatures. SiC NVFET has similar functions with non-volatile memory capability due to ferroelectric gate stack. which operated up to 300degreesC with memory function retained up to 200degreesC.
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