|
|
PROGRESS TOWARD THE DEVELOPMENT OF SINGLE NANOWIRE-BASED ARRAYS FOR GAS SENSING APPLICATIONS
Chmela, Ondřej ; Vrňata, Martin (oponent) ; Macák, Jan (oponent) ; Hubálek, Jaromír (vedoucí práce)
This thesis presents the development of silicon-based platforms for selective integration of semiconducting metal oxide (MOX) nanostructures and their use as highly sensitive and selective elements for the detection of gas analytes in prospective mobile devices. Semiconducting MOX nanostructures, for instance nanowires, have proved better gas sensing properties including sensitivity, stability and to a certain extent also selectivity as compared to their bulk counterparts. The use of single (or few) nanowire structures connected in parallel has also shown to be the ideal architecture to achieve well-defined conduction channel easy to modulate by the gas-solid interactions. However, yet current methods for the integration of single nanowire structures in functional devices represent a technological challenge, with most of the methods needing the assistance of techniques, such as focused-ion beam (FIB), which restricts the scalability of the process and increases the cost and time of fabrication. In this context, this work is focused on the search and optimization of technological processes to fabricate gas sensing systems based on arrays of single semiconducting nanowires. In this thesis, three versions of electrode platforms were developed for the selective integration of single gas-sensitive metal oxide nanowires. State-of-the-art multistep throughput fabrication techniques, as well as electron-beam lithography (nanofabrication), were used as crucial fabrication technologies allowing the development of arrays with faced nanoelectrodes and other functional nanostructures. Results show the fabrication of electrode platform with faced nanoelectrodes (100 – 300 nm width) framed in narrow dielectric windows close to the nanowire diameter (100 – 200 nm approx.). These nanoelectrodes were used as both mechanical support to align the single nanowire, and electrical contacts to measure the electrical change along the nanowire during gas detection. Results also include the optimization of techniques for removal and redeposition of nanowires to achieve single nanowire interconnections in the array of parallel electrodes using an alternating electric field as a simple and effective technique for nanowires alignment (dielectrophoresis). The validation of these systems toward various gaseous species (oxidizing and reducing gases) was performed using non-functionalized and Pt-functionalized WO3 nanowires synthesized by aerosol-assisted chemical vapor deposition (AACVD) and backside ceramic heaters (with the operating temperature at 250 °C) assembled on TO-8 package. The sensing parameters of such systems showed better sensing responses in resistive regime to nitrogen dioxide (NO2) and ethanol (EtOH) than their counterparts based on multiple nanowire-based films. The last version of gas sensing systems developed in this thesis (described as third chip generation) includes a third insulated electrode buried under the gas sensitive nanowire for enhanced gas sensing regime. Gas sensing tests of this system to hydrogen (H2) and nitrogen dioxide (NO2) corroborated the enhanced functionality of these systems and the modulation of sensor response by applying external electrical stimuli on the buried electrode.
|
|
|
Ultrarychlá laserová spektroskopie hybridních nanosystémů
Galář, Pavel ; Malý, Petr (vedoucí práce) ; Herynková, Kateřina (oponent) ; Vrňata, Martin (oponent)
Název práce: Ultrarychlá laserová spektroskopie hybridních nanosystémů Autor: RNDr. Pavel Galář Katedra / Ústav: Katedra chemické fyziky a optiky Vedoucí disertační práce: prof. RNDr. Petr Malý, DrSc. Abstrakt: Disertační práce se zabývá fyzikálními jevy na rozhraní hybridního nanosystému tvořeného polykrystalickým diamantem a polymerem polypyrrolem. Hlavní metodou experimentálního studia byla ultrarychlá laserová spektroskopie, která umožnila získat nové poznatky o elektronových rekombinačních procesech v polykrystalických diamantových vrstvách, polypyrrolu a v jejich hybridních strukturách. Výzkum se soustředil na vzájemné ovlivňování obou komponent, zejména na přenos energie a náboje. V prvém kroku výzkumu byla provedena optická charakterizace různých typů polypyrrolu a komplexní studie dynamik rekombinačních procesů fotoexcitovaných nosičů probíhajících v polykrystalickém diamantu. Měření byla realizována pomocí metod časově rozlišené luminiscenční a transmisní spektroskopie na časové škále od pikosekund do milisekund. Získané výsledky vedly k vytvoření modelu vysvětlujícího původ luminiscenčního signálu spojeného s různými typy elektronových rekombinačních procesů v nediamantové fázi a na povrchových defektech diamantových zrn v polykrystalických vrstvách. Práce obsahuje obdobnou experimentální studii...
|
|
|
PROGRESS TOWARD THE DEVELOPMENT OF SINGLE NANOWIRE-BASED ARRAYS FOR GAS SENSING APPLICATIONS
Chmela, Ondřej ; Vrňata, Martin (oponent) ; Macák, Jan (oponent) ; Hubálek, Jaromír (vedoucí práce)
This thesis presents the development of silicon-based platforms for selective integration of semiconducting metal oxide (MOX) nanostructures and their use as highly sensitive and selective elements for the detection of gas analytes in prospective mobile devices. Semiconducting MOX nanostructures, for instance nanowires, have proved better gas sensing properties including sensitivity, stability and to a certain extent also selectivity as compared to their bulk counterparts. The use of single (or few) nanowire structures connected in parallel has also shown to be the ideal architecture to achieve well-defined conduction channel easy to modulate by the gas-solid interactions. However, yet current methods for the integration of single nanowire structures in functional devices represent a technological challenge, with most of the methods needing the assistance of techniques, such as focused-ion beam (FIB), which restricts the scalability of the process and increases the cost and time of fabrication. In this context, this work is focused on the search and optimization of technological processes to fabricate gas sensing systems based on arrays of single semiconducting nanowires. In this thesis, three versions of electrode platforms were developed for the selective integration of single gas-sensitive metal oxide nanowires. State-of-the-art multistep throughput fabrication techniques, as well as electron-beam lithography (nanofabrication), were used as crucial fabrication technologies allowing the development of arrays with faced nanoelectrodes and other functional nanostructures. Results show the fabrication of electrode platform with faced nanoelectrodes (100 – 300 nm width) framed in narrow dielectric windows close to the nanowire diameter (100 – 200 nm approx.). These nanoelectrodes were used as both mechanical support to align the single nanowire, and electrical contacts to measure the electrical change along the nanowire during gas detection. Results also include the optimization of techniques for removal and redeposition of nanowires to achieve single nanowire interconnections in the array of parallel electrodes using an alternating electric field as a simple and effective technique for nanowires alignment (dielectrophoresis). The validation of these systems toward various gaseous species (oxidizing and reducing gases) was performed using non-functionalized and Pt-functionalized WO3 nanowires synthesized by aerosol-assisted chemical vapor deposition (AACVD) and backside ceramic heaters (with the operating temperature at 250 °C) assembled on TO-8 package. The sensing parameters of such systems showed better sensing responses in resistive regime to nitrogen dioxide (NO2) and ethanol (EtOH) than their counterparts based on multiple nanowire-based films. The last version of gas sensing systems developed in this thesis (described as third chip generation) includes a third insulated electrode buried under the gas sensitive nanowire for enhanced gas sensing regime. Gas sensing tests of this system to hydrogen (H2) and nitrogen dioxide (NO2) corroborated the enhanced functionality of these systems and the modulation of sensor response by applying external electrical stimuli on the buried electrode.
|
|
|
Závěrečná zpráva z projektu - Bezpečné mazání paměťových čipů pomocí elektromagnetického pulsu
Fitl, Přemysl ; Vrňata, M. ; Fišer, L. ; Novotný, Michal ; Scholtz, V. ; Vlček, J. ; Tomeček, D.
Předmětem smluvního výzkumu byl teoretický rozbor a matematický model problematiky průniku elektromagnetického pulzu. Popis přípravy experimentu obsahující odpájení a odpouzdřování paměťových čipů, metodiky testování paměťových médií, stínění experimentu, stínění zkoumaného paměťového čipu, generování EMP, měření intenzity EMP. \nShrnutí výsledků provedeného experimentu.\nSouhrnná výzkumná zpráva byla předána zástupcům NUKIB dne 31.5.2018. \nZástupci NUKIB potvrdili převzetí zprávy. Oponentura výsledků projektu proběhla 27.6.2018 v budově NUKIB. Projekt byl splněn. Za vypracování této zprávy byla fakturována sjednaná částka.\n\n\n
|
|
| |
|
|
Ultrarychlá laserová spektroskopie hybridních nanosystémů
Galář, Pavel ; Malý, Petr (vedoucí práce) ; Herynková, Kateřina (oponent) ; Vrňata, Martin (oponent)
Název práce: Ultrarychlá laserová spektroskopie hybridních nanosystémů Autor: RNDr. Pavel Galář Katedra / Ústav: Katedra chemické fyziky a optiky Vedoucí disertační práce: prof. RNDr. Petr Malý, DrSc. Abstrakt: Disertační práce se zabývá fyzikálními jevy na rozhraní hybridního nanosystému tvořeného polykrystalickým diamantem a polymerem polypyrrolem. Hlavní metodou experimentálního studia byla ultrarychlá laserová spektroskopie, která umožnila získat nové poznatky o elektronových rekombinačních procesech v polykrystalických diamantových vrstvách, polypyrrolu a v jejich hybridních strukturách. Výzkum se soustředil na vzájemné ovlivňování obou komponent, zejména na přenos energie a náboje. V prvém kroku výzkumu byla provedena optická charakterizace různých typů polypyrrolu a komplexní studie dynamik rekombinačních procesů fotoexcitovaných nosičů probíhajících v polykrystalickém diamantu. Měření byla realizována pomocí metod časově rozlišené luminiscenční a transmisní spektroskopie na časové škále od pikosekund do milisekund. Získané výsledky vedly k vytvoření modelu vysvětlujícího původ luminiscenčního signálu spojeného s různými typy elektronových rekombinačních procesů v nediamantové fázi a na povrchových defektech diamantových zrn v polykrystalických vrstvách. Práce obsahuje obdobnou experimentální studii...
|
|
|
IMPEDANCE MEASUREMENT OF GAS SENSORS WITH NICKEL(II)-AND COPPER(II)-OXIDE ACTIVE LAYERS
Horák, Pavel ; Khun, J. ; Vrňata, M. ; Bejšovec, Václav ; Lavrentiev, Vasyl ; Vacík, Jiří
Thin layers (90 nm) of nickel(II)- and copper(II)- oxide were deposited onto ceramic sensor substrates equipped with interdigital electrodes for signal reading. The deposition was carried out in two or three steps: (i) sputtering by means of Ar ion beam from pure (99.99%) metal targets, (ii) following thermal oxidation (400 degrees C for 5 h) in air, (iii) in some cases - sputtering of Pd catalyst to the surface. Then the impedance response of produced sensors (NiO, NiO+Pd, CuO, CuO+Pd) to 1000 ppm of hydrogen and 1000 ppm of methanol vapor was measured. Impedance measurements were performed in the frequency range from 40 Hz to 100 MHz. The obtained data were depicted in Nyquist representation (i.e. imaginary vs. real part of complex impedance). These diagrams have a character of one complete and one incomplete semicircle, each of them corresponding to a parallel RC-element. It was proved, that both NiO and CuO behave like p-type semiconductors; the sensor impedance increases on exposure to reducing gases. The best sensitivity was achieved on NiO+Pd sensor - during detection of hydrogen (1000 ppm) the real part of complex impedance measured at 40 Hz increased from 120 to 350 Omega.
|
|
|
Characterization of the Nanostructured Nickel Oxide Layers Prepared by Ion Beam Sputtering
Horák, Pavel ; Bejšovec, Václav ; Lavrentiev, Vasyl ; Khun, J. ; Vrňata, M.
Nanostructured nickel oxide layers (thickness cca 100 nm) were prepared by bombardment of nickel foil with ion beam created from a mixture of argon and oxygen. Different volume ratios of argon:oxygen mixture were used, ranging from 4:1 to 1:3. Composition of the resulting layers was analyzed by RBS, morphology by AFM and main crystal orientation of the sample by XRD. The electrophysical properties (resistivity, concentration of charge carriers) were measured by four point Van der Pauw technique and Hall measurement respectively. Prepared samples were characterized in as-deposited state and after annealing with varying temperature of treatment. Chemical composition (i.e. stoichiometry) of the as-deposited samples with different argon: oxygen ratio was related to their electrophysical parameters. Hall measurements are showing majority charge carriers to be electrons - surface concentration (0.5 - 2.3) x 10(21) m(-2) - suggesting prevailing metallic conductivity. Resistivity of the sample is increasing with higher amount of oxygen in gas mixture. The as-deposited layer is almost amorphous with no visible grains on AFM.
|
|
| |
|
| |
host ::
RSS.