Electrode-less plasma jet synthesis of core-shell iron/iron oxide nanoparticles

We report on core-shell iron and iron oxide nanoparticle prepared by plasma synthesis controlled by process gas mixture. The synthesis was carried out using an atmospheric pressure microwave electrodeless plasma jet. We focused on phase composition control and better passivation. We studied the influence of O2, H2 and N2 admixtures to the Ar process gas on the properties of the prepared nanomaterial. Similarly to thermal process, the oxygen admixture preferentially produced Fe2O3 nanoparticles whereas hydrogen admixture resulted in particles with higher metallic content. However, in contrast to thermal process, the addition of nitrogen did not produce iron nitride, but iron/iron-oxide core-shell nanoparticles with enhanced chemical stability

SYNTHESIS OF CARBON NANOSTRUCTURES BY PLASMA ENHANCED CHEMICAL VAPOUR DEPOSITION AT ATMOSPHERIC PRESSURE

Carbon nanostructures present the leading field in nanotechnology research. A wide range of chemical and physical methods was used for carbon nanostructures synthesis including arc discharges, laser ablation and chemical vapour deposition. Plasma enhanced chemical vapour deposition (PECVD) with its application in modern microelectronics industry became soon target of research in carbon nanostructures synthesis. Selection of the ideal growth process depends on the application. Most of PECVD techniques work at low pressure requiring vacuum systems. However for industrial applications it would be desirable to work at atmospheric pressure. In this article carbon nanostructures synthesis by plasma discharges working at atmospheric pressure will be reviewed.Uhlíkové nanostruktury patří mezi vedoucí nanotechnologický výzkum. K syntéze uhlíkových nanostruktur lze použít širokou škálu chemických a fyzikálních metod jako například obloukové výboje, laserovou ablaci a CVD. PECVD se svých uplatněním v mikroelektronice se brzy stalo cílem výzkumu i v této oblasti. Výběr metod úzce souvisí s aplikací dané technologie. Ačkoli mnoho metod pracuje při nízkém tlaku, z hlediska aplikací by bylo vhodné použít metodou pracující za atmosférického tlaku. V této publikaci jsou shrnuty metody syntézy uhlíkových nanostruktur za atmosférického tlaku.Carbon nanostructures present the leading field in nanotechnology research. A wide range of chemical and physical methods was used for carbon nanostructures synthesis including arc discharges, laser ablation and chemical vapour deposition. Plasma enhanced chemical vapour deposition (PECVD) with its application in modern microelectronics industry became soon target of research in carbon nanostructures synthesis. Selection of the ideal growth process depends on the application. Most of PECVD techniques work at low pressure requiring vacuum systems. However for industrial applications it would be desirable to work at atmospheric pressure. In this article carbon nanostructures synthesis by plasma discharges working at atmospheric pressure will be reviewed

SELF-ORGANIZATION IN MICROWAVE FILAMENTARY DISCHARGES

We studied the self organising phenomena im filamntary microwave discharge at various pressures and excitation types

Measurement of Mechanical Properties of Composite Materials

The aim of the present work was the study of mechani- cal properties of MWCNT/PU. Four types of coatings were compared. Two different concentrations of MWCNTs com- mercially functionalized with COOH group were prepared and studied. These composites showed improved mechanical properties compared to PU, and the modified nanotubes proved to be much better fillers than the unmodified MWCNTs due to stronger filler-to-matrix attachment. Be- cause the modified nanotubes seem to be much more conven- ient composite filler, the first experiments with nanotube modification have been carried out. Modification using induc- tively coupled discharge in argon and oxygen mixture was successful and the mechanical properties of the composite were increased at the same level as in case of the commer- cially COOH functionalized MWCNT fillers.V práci byly studovány mechanické vlastnosti vrstev MWCNT/PU a porovnávány čtyry různé typy jejich nanášení. Práce byla zaměřená zejména na studium vlivu funkcionalizace uhlíkových nanotrubek v plazmatu na mechanické vlastnosti výsledného kompozitu. Rovněž se zabývalo modelováním viskoelastických a viskoplastických vlastností kompozitů MWCNT/PU

Synthesis of Carbon Nanotubes in MW Plasma Torch with Different Methods of Catalyst Layer Preparation and their Applications

The microwave plasma torch (2.45 GHz) was used for the synthesis of carbon nanotubes from the mixture of CH4/H2/Ar or C2H2/H2/Ar on different substrates with iron catalyst. Iron catalyst was prepared by vacuum evaporation of iron on Si, Si/SiOx or Si/AlxOy substrates or by deposition of iron oxide nanoparticles on Si/SiOx substrate by decomposion of Fe(CO)5 in gas feed. Such prepared substrates were used for growth of carbon nanotubes. Recostruction of the iron catalyst layer into nanoparticles was also studied in dependence on substrate buffer layer, gas atmosphere and temperature. Samples were studied by scanning and transmission electron microscopy and Raman spectroscopy. Synthesis resulted in rapid growth of MWNTs on all samples but the density, purity and nanotube diameter distribution varied. Such prepared carbon nanotube layers were used for sensing applications.Mikrovlnný plazmový hořák (2,45 GHz) byl použit pro syntézu uhlíkových nanotrubek ze směsi CH4/H2/Ar nebo C2H2/H2/Ar na různých substrátech s železnými katalyzátori. Železný katalyzátor byl připraven vakuovým odpařováním železa na Si, Si/SiOx nebo Si/AlxOy substráty nebo ukládáním nanočástic oxidu železitého Fe (CO) 5 z plynné fáze na Si/SiOx substrát. Takto připravené substráty byly použity pro růst uhlíkových nanotrubek. Vytváření vrstvy katalyzátoru na nanočástice železa byl také studován v závislosti na mezivrstvě , atmosféře a teplotě. Vzorky byly studovány skenovací a transmisní elektronovou mikroskopi a Ramanovskou spektroskopii.The microwave plasma torch (2.45 GHz) was used for the synthesis of carbon nanotubes from the mixture of CH4/H2/Ar or C2H2/H2/Ar on different substrates with iron catalyst. Iron catalyst was prepared by vacuum evaporation of iron on Si, Si/SiOx or Si/AlxOy substrates or by deposition of iron oxide nanoparticles on Si/SiOx substrate by decomposion of Fe(CO)5 in gas feed. Such prepared substrates were used for growth of carbon nanotubes. Recostruction of the iron catalyst layer into nanoparticles was also studied in dependence on substrate buffer layer, gas atmosphere and temperature. Samples were studied by scanning and transmission electron microscopy and Raman spectroscopy. Synthesis resulted in rapid growth of MWNTs on all samples but the density, purity and nanotube diameter distribution varied. Such prepared carbon nanotube layers were used for sensing applications

Atmospheric pressure microwave torch for synthesis of carbon nanotubes

The microwave (mw) plasma torch at atmospheric pressure has been studied for carbon nanotube (CNT) synthesis. The depositions were carried out on silicon substrates with 515 nm thin iron catalytic overlayers from the mixture of argon, hydrogen and methane. The optical emission spectroscopy of the torch showed the presence of C2 and CH radicals as well as carbon and hydrogen excited atoms. The vicinity of the substrate influenced the relative intensities and increased the emission of C2. For fixed mw power, the temperature of the substrate strongly depended on its position with respect to the nozzle electrode and on the gas mixture, particularly the amount of H2. The speed of the substrate heating during an early deposition phase had a significant effect on the CNT synthesis. An abrupt increase of the temperature at the beginning increased the efficiency of theCNTsynthesis. Areas of dense straight standing CNTs, 30 nm in average diameter, with approximately the same sized iron nanoparticles on their tops were found in accordance with the model of growth by plasma enhanced chemical vapour deposition. However, the deposit was not uniform and a place with only several nanometres thick CNTs grown on much larger iron particles was also found. Here, taking into account the gas temperature in the torch, 31003900 K, we can see similarities with the dissolutionprecipitation model of the CNT growth by high temperature methods, arc or laser ablation.Možnosti syntézy uhlíkových nanotrubek(CNTs) byly zkoumány v mikrovlnném výboji buzeném za atmosférického tlaku. Vrstvy byly deponovány na křemíkový substrát s vrstvou železa 5-15 nm sloužící jako katalyzátor ve směsi argonu,vodíku a metanu. Optická emisní spektroskopie výboje prokázala přítomnost radikálů C2 a CH a excitovaných stavů atomů uhlíku a vodíku. Přítomnost substrátu ovlivňovala intenzitu spekter a vedla k vzrůstu intenzity C2 pásu. Při konstantní hodnotě mikrovlnného výkonu byla teplota substrátu silně závislá na vzdálenosti substrátu vůči trysce a průtoku plynů, zejména vodíku. Rychlost zahřívání substrátu v počátení fázi depozice měla významný vliv na depozici CNTs. Prudké zvýšení teploty substrátu na začátku depozice mělo za důsledek zlepšení efektivity depozice CNTs. Na substrátech bylo možno nalézt oblasti hustě uspořádaných CNTs s průměrem okolo 30 nm, které byly na vrcholu ukončeny částicemi katalyzátoru o stejném průměru. Tento výsledek je v souladu s obecně příjmaným růstovým modelem CNTs při použití metody plasma enhanced chemical vapor deposition (PECVD). Deponována vrstva však není uniformní na celé ploše substrátu a byly nalezeny i místa s nanotrubkami, o průměru pouze několika nanometrů, rostoucími na částicích katalyzátoru s mnohem většími rozměry. Vezmeme-li v úvahu teplotu plynu ve výboji, 3100-3900 K, je možno v tomto výsledku spatřovat podobnost s modelem růstu CNTs "dissolution-precipitation" při vysokoteplotních metodách jako jsou obloukový výboj nebo laserová ablace

Modification of Working Electrode Surface with Carbon Nanotubes as an Electrochemical Sensor for Estimation of Melting Points of DNA

Screen-printed with three electrode system was used in this study. A working electrode has been printed from carbon nanotubes based paste on silver layer modified with nano-patterned structures for the first case. In the second case, vertically aligned carbonnanotubes were grown on the Au working electrode. The process of the nanotubes growing was tested to create homogenous and high density carbon nanotubes layer directly on the thick-film silver layer. Based on the characterization of electrodes, we used Au based for detection of nucleic acids. Moreover, we were able to estimated melting points of DNA. © 2009

Výzkum čistého oxidu grafitu jako citlivého materiálu chemoresistivního sensoru pro stanovení amoniaku při pokojové teplotě

Graphite oxide has been investigated as a possible room-temperature chemiresistive sensor of ammonia in a gas phase. Graphite oxide was synthesized from high purity graphite using the modified Hummers method. The graphite oxide sample was investigated using scanning electron microscopy, energy dispersive X-ray spectroscopy, X-ray diffraction, thermogravimetry and differential scanning calorimetry. Sensing properties were tested in a wide range of ammonia concentrations in air (10–1000 ppm) and under different relative humidity levels (3%–65%). It was concluded that the graphite oxide–based sensor possessed a good response to NH3 in dry synthetic air (R/R0 ranged from 2.5% to 7.4% for concentrations of 100–500 ppm and 3% relative humidity) with negligible cross-sensitivity towards H2 and CH4. It was determined that the sensor recovery rate was improved with ammonia concentration growth. Increasing the ambient relative humidity led to an increase of the sensor response. The highest response of 22.2% for 100 ppm of ammonia was achieved at a 65% relative humidity level.Byl zkoumán oxid grafitu jako možný materiál pro chemiresistivní senzor amoniaku za pokojové teploty. Oxid grafitu byl syntetizován z vysoce čistého grafitu modifikovanou Hummers metodou. Vzorek oxidu grafitu byl analyzován pomocí skenovací elektronové mikroskopie, energiově disperzní rentgenové spektroskopie, rentgenové difrakce, thermogravimetrie a diferenční skenovací kalorimetrie. Senzorické vlastnosti byly testovány v širokém rozmezí koncentrací amoniaku ve vzduchu (10 – 1000 ppm) a za různé relativní vlhkosti (3-65 %). Byl učiněn závěr, že senzor na bázi oxidu grafitu má dobrou odezvu na NH3 v suchém syntetickém vzduchu (R/R0 se pohyboval od 2,5 % do 7,4 % pro koncentrace 100-500 ppm při relativní vlhkosti 3 %) se zanedbatelnou krossensitivitou na H2 a CH4. Bylo zjištěno, že se s růstem koncentrace amoniaku zkracovala doba zotavení senzoru. Zvyšení relativní vlhkosti prostředí vedlo k zvýšení odezvy senzoru. Při relativní vlhkost 65 % bylo dosaženo nejvyšší odezvy 22,2 % pro 100 ppm amoniaku