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MOVPE GaN/AlGaN HEMT nano-structures
Hulicius, Eduard; Kuldová, Karla; Hospodková, Alice; Pangrác, Jiří; Dominec, Filip; Humlíček, J.; Pelant, Ivan; Cibulka, Ondřej; Herynková, Kateřina
2019 - English
GaN/AlGaN-based high electron mobility transistors (HEMTs) attain better performance than their state-of-the-art full silicon-based counterparts do, offering higher power, higher frequency as well as higher temperature of operation and stability, although their voltage and current limits are somewhat lower than for the SiC-based HEMTs. GaN/AlGaN-based HEMTs are a potential choice for electric-powered vehicles, for which they are approved not only for their power parameters, but also for their good temperature stability, lifetime and reliability. It is important to optimize HEMT structures and their growth parameters to reach the optimum function for the real-world applications. HEMT structures were grown by MOVPE technology in AIXTRON apparatus on (111)-oriented single-surface polished Si substrates. Structural, optical and transport properties of the structures were measured by X-ray diffraction, optical reflectivity, time-resolved photoluminescence and micro-Raman spectroscopy.\n
Keywords:
GaN; MOVPE; HEMT
Available at various institutes of the ASCR
MOVPE GaN/AlGaN HEMT nano-structures
GaN/AlGaN-based high electron mobility transistors (HEMTs) attain better performance than their state-of-the-art full silicon-based counterparts do, offering higher power, higher frequency as well as ...
New binary refractory metal-Fe intermetallic compounds for hard magnet applications
Tchaplianka, Maxim; Shick, Alexander
2019 - English
We investigate theoretically the electronic and magnetic structure of Fe2Hf. The density functional theory is used to calculate the magnetic moments on individual atoms, the total and projected densities of states, and the magnetic anisotropy energy. The Fe2Hf is found to be metallic and ferrimagnetic, with the magnetic moments of Fe and Hf atoms pointing in the opposite directions. The negative magnetic anisotropy, and the “in-plane” preferential direction of the magnetization are found as a result of theoretical calculations. Our study suggests that the chemical control of the magnetic anisotropy has to be investigated in order to evaluate the potential of Fe2Hf for the permanent magnet applications.\n
Keywords:
electronic structure; magnetic anisotropy; permanent magnets
Available at various institutes of the ASCR
New binary refractory metal-Fe intermetallic compounds for hard magnet applications
We investigate theoretically the electronic and magnetic structure of Fe2Hf. The density functional theory is used to calculate the magnetic moments on individual atoms, the total and projected ...
Microstructure and mechanical properties of the potentially biodegradable ternary system Zn-Mg0. 8-Ca0.2
Pinc, Jan; Čapek, Jaroslav; Kubásek, J.; Veřtát, Petr; Hosová, K.
2019 - English
Zinc and zinc alloys exhibit suitable corrosion properties for biodegradable implants. Insufficient mechanical properties (for some applications) or low biocompatible Zn2+ concentrations can be modified by the alloying by essential elements like magnesium, calcium or strontium. The alloying elements also enhance the biocompatibility of zinc due to a decrease of Zn2+ release which could be toxic in a concentration exceeding 100 µM. In this study, the microstructure and hardness of a potentially biodegradable alloy ZnMg0.8Ca0.2 were observed in relation to different cooling rates. It was found that zinc dendrites, Mg2Zn11 (MgZn2) and CaZn13 phases occur in the material structure. The micro-hardness measurements revealed constant hardness of the particular phases, however, the macro-harness slightly decreased with the decreasing cooling rate due to changes in phase sizes and distribution.
Keywords:
biodegradable materia; zinc; microstructure; hardness; ternary system
Available at various institutes of the ASCR
Microstructure and mechanical properties of the potentially biodegradable ternary system Zn-Mg0. 8-Ca0.2
Zinc and zinc alloys exhibit suitable corrosion properties for biodegradable implants. Insufficient mechanical properties (for some applications) or low biocompatible Zn2+ concentrations can be ...
The photoluminescence and optical absorptance of plasma hydrogenated nanocrystalline ZnO thin films
Remeš, Zdeněk; Chang, Yu-Ying; Stuchlík, Jiří; Mičová, J.
2019 - English
We have developed the technology of the deposition of the nominally undoped ZnO nanocrystalline thin films by DC reactive magnetron sputtering of Zn target in the gas mixture of argon and oxygen plasma. We have optimized the photoluminescence spectroscopy for measuring optically scattering thin layers with the high sensitivity, precise sample positioning and very low influence of the scattered excitation light. Here we present the latest results on the enhancement of the photoluminescence of the nanocrystalline ZnO thin films after plasma hydrogenation. The photoluminescence in near UV region has been enhanced whereas the deep defect related photoluminescence has been significantly decreased. We found good room temperature stability of the plasma hydrogenated ZnO nanocrystals in air, but fast degradation at elevated temperature\n
Keywords:
nanomaterials; ZNO; photoluminescence; magnetron sputtering
Available at various institutes of the ASCR
The photoluminescence and optical absorptance of plasma hydrogenated nanocrystalline ZnO thin films
We have developed the technology of the deposition of the nominally undoped ZnO nanocrystalline thin films by DC reactive magnetron sputtering of Zn target in the gas mixture of argon and oxygen ...
Germanium and tin nanoparticles encapsulated in amorphous silicon matrix for optoelectronic application
Stuchlíková, The-Ha; Remeš, Zdeněk; Stuchlík, Jiří
2019 - English
The plasma enhanced chemical vapour deposition was combined with in situ deposition of Ge and Sn thin film by evaporation technique at surface temperature about 220 °C to form nanoparticles on the surface of hydrogenated silicon thin films to prepare diodes. Formation of nanoparticles was additionally stimulated by plasma treatment through a low pressure hydrogen glow discharge. The diodes based on PIN diode structures with and without the embedded Ge or Sn nanoparticles were characterized by temperature dependence of electrical conductivity, activation energy of conductivity, measurement of volt-ampere characteristics in dark and under solar illumination\n
Keywords:
Ge NPs; a-Si:H; Sn NPs; diode structures; I-V characteristics
Available at various institutes of the ASCR
Germanium and tin nanoparticles encapsulated in amorphous silicon matrix for optoelectronic application
The plasma enhanced chemical vapour deposition was combined with in situ deposition of Ge and Sn thin film by evaporation technique at surface temperature about 220 °C to form nanoparticles on the ...
The hydrogen plasma doping of ZnO thin films and nanoparticles
Remeš, Zdeněk; Neykova, Neda; Potocký, Štěpán; Chang, Yu-Ying; Hsu, H.S.
2018 - English
The optical absorptance and photoluminescence studies has been applied on the hydrogen and oxygen plasma treated, nominally undoped ZnO thin films and aligned nanocolumns grown on the nucleated glass substrate by the hydrothermal process in an oil bath containing a flask with ZnO nutrient solution. The localized defect states at 2.3 eV below the optical absorption edge were detected by photothermal deflection spectroscopy (PDS) in a broad spectral range from near UV to near IR. The optical absorptance spectroscopy shows that hydrogen doping increases free electron concentration changing ZnO to be electrically conductive (hydrogen doping).\n
Keywords:
ZnO; nanoparticles; hydrothermal growth; hotoluminescence spectroscopy; PDS
Available at various institutes of the ASCR
The hydrogen plasma doping of ZnO thin films and nanoparticles
The optical absorptance and photoluminescence studies has been applied on the hydrogen and oxygen plasma treated, nominally undoped ZnO thin films and aligned nanocolumns grown on the nucleated glass ...
Modeling of monocrystalline magnesium microbeam bending
Němeček, J.; Maňák, Jan; Němeček, J.
2018 - English
This paper presents a numerical simulation of a micro-scale experiment on a magnesium alloy. Three dimensional numerical FE model with elastoplastic behavior respecting crystal anisotropy was used to fit experimental load displacement curves.
Keywords:
magnesium; microbeams; crystal anisotropy; FE model
Available at various institutes of the ASCR
Modeling of monocrystalline magnesium microbeam bending
This paper presents a numerical simulation of a micro-scale experiment on a magnesium alloy. Three dimensional numerical FE model with elastoplastic behavior respecting crystal anisotropy was used to ...
Characterization of hydrogenated silicon thin films and diode structures with integrated germanium nanoparticles
Stuchlík, Jiří; Fajgar, Radek; Kupčík, Jaroslav; Remeš, Zdeněk; Stuchlíková, The-Ha
2018 - English
Substrates with ZnO (or ITO) conductive layers were covered by thin film of a-Si:H deposited by PECVD technique. Under a turbo-molecular vacuum (10-4 Pa) the reactive laser ablation (RLA) was used to cover this a-Si:H thin film by germanium NPs. The RLA was performed using focused excimer ArF laser beam (193 nm, 100 mJ/pulse) under SiH4 background atmosphere (0.5 Pa). As a target the elemental germanium was used. Reaction between ablated Ge and silane led to formation of Ge NPs covered by thin SiGe layer. Then the deposited NPs were covered and stabilized by a-Si:H layer by PECVD. Those two deposition processes was alternated and applied a few times. The Si:H thin films with integrated Ge NPs were characterized by microscopic, spectroscopic and diffraction techniques. I-V characteristics of final diode structures without and under illumination were measured as well as their electroluminescence behaviour.
Keywords:
PECVD; a-Si:H diode structures; Ge; nanoparticles
Available at various institutes of the ASCR
Characterization of hydrogenated silicon thin films and diode structures with integrated germanium nanoparticles
Substrates with ZnO (or ITO) conductive layers were covered by thin film of a-Si:H deposited by PECVD technique. Under a turbo-molecular vacuum (10-4 Pa) the reactive laser ablation (RLA) was used to ...
Characterization of hydrogenated silicon thin films and diode structures with integrated silicon and germanium nanoparticles
Stuchlík, Jiří; Fajgar, R.; Remeš, Zdeněk; Kupčík, Jaroslav; Stuchlíková, Hana
2018 - English
P-I-N diode structures based on the thin films of amorphous hydrogenated silicon (a-Si:H) deposited by Plasma Enhanced Chemical Vapor Deposition (PECVD) technique were prepared with embedded Si and Ge nanoparticles. The Reactive Laser Ablation (RLA) of germanium target was used to cover the intrinsic a-Si:H layer by Ge NPs under a low pressure of the silane. The RLA was performed using focused excimer ArF laser beam under SiH4 background atmosphere. Reaction between ablated Ge NPs and SiH4 led to formation of Ge NPs covered by thin GeSi:H layer. The deposited NPs were covered and stabilized by a-Si:H layer by PECVD. Those two deposition processes were alternated repeatedly. Volt-ampere characteristics of final diode structures were measured in dark and under illumination as well as their electroluminescence spectra.
Keywords:
a-Si:H; PIN diode; thin films; reactive laser ablation; nanoparticles
Available at various institutes of the ASCR
Characterization of hydrogenated silicon thin films and diode structures with integrated silicon and germanium nanoparticles
P-I-N diode structures based on the thin films of amorphous hydrogenated silicon (a-Si:H) deposited by Plasma Enhanced Chemical Vapor Deposition (PECVD) technique were prepared with embedded Si and Ge ...
Histology and micro-CT study of diamond-coated metal bone implants in rabbit femurs
Potocký, Štěpán; Ižák, Tibor; Dragounová, Kateřina; Kromka, Alexander; Rezek, Bohuslav; Mandys, V.; Bartoš, M.; Bačáková, Lucie; Sedmera, David
2018 - English
A conformal coating of a thin diamond layer on three-dimensional metal bone implants was shown directly on stainless steel and TiAl6V4 cortical screw implant using ultrasonic and composite polymer pretreatment method. The best conformation coverage was achieved in the case of the WO3 interlayer for both stainless steel and TiAl6V4 screws. The process of osteointegration of the screw implants into rabbit femurs is evidenced by the formation of a bone edge via desmogenous ossification around the screws in less than six months after implantation. A detailed evaluation of the tissue reaction around the implanted screws shows good biocompatibility of diamond-coated metal bone implants.
Keywords:
screw implant; diamond coating; osteointegration; histology
Available at various institutes of the ASCR
Histology and micro-CT study of diamond-coated metal bone implants in rabbit femurs
A conformal coating of a thin diamond layer on three-dimensional metal bone implants was shown directly on stainless steel and TiAl6V4 cortical screw implant using ultrasonic and composite polymer ...
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