Reversible carrier-type transition in gas-sensing oxides and nanostructures

Despite many important applications of a-Fe2O3 and Fe doped SnO2 in semiconductors, catalysis, sensors, clinical diagnosis and treatments, one fundamental issue that is crucial to these applications remains theoretically equivocal- the reversible carrier-type transition between n- and p-type conductivities during gas-sensing operations. Here, we give unambiguous and rigorous theoretical analysis in order to explain why and how the oxygen vacancies affect the n-type semiconductors, a-Fe2O3 and Fe doped SnO2 in which they are both electronically and chemically transformed into a p-type semiconductor. Furthermore, this reversible transition also occurs on the oxide surfaces during gas-sensing operation due to physisorbed gas molecules (without any chemical reaction). We make use of the ionization energy theory and its renormalized ionic displacement polarizability functional to reclassify, generalize and to explain the concept of carrier-type transition in solids, and during gas-sensing operation. The origin of such a transition is associated to the change in ionic polarizability and the valence states of cations in the presence of (a) oxygen vacancies and (b) physisorped gas molecules.Comment: To be published in ChemPhysChe

A Fiber Optic Catalytic Sensor for Neutral Atom Measurements in Oxygen Plasma

The presented sensor for neutral oxygen atom measurement in oxygen plasma is a catalytic probe which uses fiber optics and infrared detection system to measure the gray body radiation of the catalyst. The density of neutral atoms can be determined from the temperature curve of the probe, because the catalyst is heated predominantly by the dissipation of energy caused by the heterogeneous surface recombination of neutral atoms. The advantages of this sensor are that it is simple, reliable, easy to use, noninvasive, quantitative and can be used in plasma discharge regions. By using different catalyst materials the sensor can also be applied for detection of neutral atoms in other plasmas. Sensor design, operation, example measurements and new measurement procedure for systematic characterization are presented

Utilization of various lignocellulosic biomass for the production of nanocellulose: a comparative study

Nanocellulose was successfully extracted from five different lignocellulosic biomass sources viz. banana rachis, sisal, kapok, pineapple leaf and coir using a combination of chemical treatments such as alkaline treatment, bleaching and acid hydrolysis. The shape, size and surface properties of the nanocellulose generally depend on the source and hydrolysis conditions. A comparative study of the fundamental properties of raw material, bleached and nanocellulose was carried out by means of Fourier transform infrared spectroscopy, scanning electron microscopy, atomic force microscopy, transmission electron microscopy, birefringence, X-ray diffraction, inverse gas chromatography and thermogravimetric analysis. Through the characterization of the nanocellulose obtained from different sources, the isolated nanocellulose showed an average diameter in the range of 10–25 nm, high crystallinity, high thermal stability and a great potential to be used with acid coupling agents due to a predominantly basic surface. This work provides an insight into the effective utilization of a variety of plant biomass as a potential source for nanocellulose extraction.info:eu-repo/semantics/publishedVersio

Plasma mediated chlorhexidine immobilization onto polylactic acid surface via carbodiimide chemistry: Antibacterial and cytocompatibility assessment

The development of antibacterial materials has great importance in avoiding bacterial contamination and the risk of infection for implantable biomaterials. An antibacterial thin film coating on the surface via chemical bonding is a promising technique to keep native bulk material properties unchanged. However, most of the polymeric materials are chemically inert and highly hydrophobic, which makes chemical agent coating challenging Herein, immobilization of chlorhexidine, a broad-spectrum bactericidal cationic compound, onto the polylactic acid surface was performed in a multistep physicochemical method. Direct current plasma was used for surface functionalization, followed by carbodiimide chemistry to link the coupling reagents of N-(3-Dimethylaminopropyl)-N′-ethylcarbodiimide hydrochloride (EDAC) and N-Hydroxysuccinimide (NHs) to create a free bonding site to anchor the chlorhexidine. Surface characterizations were performed by water contact angle test, X-ray photoelectron spectroscopy (XPS) and scanning electron microscope (SEM). X-ray photoelectron spectroscopy (XPS) and scanning electron microscope (SEM). The antibacterial activity was tested using Staphylococcus aureus and Escherichia coli. Finally, in vitro cytocompatibility of the samples was studied using primary mouse embryonic fibroblast cells. It was found that all samples were cytocompatible and the best antibacterial performance observed was the Chlorhexidine immobilized sample after NHs activation. © 2021 by the authors. Licensee MDPI, Basel, Switzerland.Czech Science FoundationGrant Agency of the Czech Republic [19-16861S]; Ministry of Education, Youth and Sports of the Czech Republic-DKRVO [RP/CPS/2020/001]; DKRVO [RP/CPS/2020/005]; Slovenian Research AgencySlovenian Research Agency - Slovenia [L2-2616]RP/CPS/2020/005; Ministerstvo Školství, Mládeže a Tělovýchovy, MŠMT: RP/CPS/2020/001; Grantová Agentura České Republiky, GA ČR: 19-16861S; Javna Agencija za Raziskovalno Dejavnost RS, ARRS: L2-261

Non-square-well potential profile and non-blinking effect in graded CdZnSe/ZnSe nanocrystals: An ionization-energy theoretic study

Randomly blinking nanocrystals have given rise to numerous and intense theoretical and experimental investigations recently. An experimental breakthrough was finally made by fabricating the non-blinking Cd$_{1-x}$Zn$_x$Se/ZnSe graded nanocrystal [Nature 459 (2009) 686]. Here, we report (1) an unequivocal and detailed theoretical investigation to understand the properties of the potential-well and the distribution of Zn content with respect to the nanocrystal radius and (2) develop a strategy to find the relationship between the photoluminescence (PL) energy peaks and the potential-well due to Zn distribution in nanocrystals. We found that the non-square-well potential can be varied in such a way that one can indeed control the PL intensity and the energy-level difference (PL energy peaks) in any non-free-electron nanocrystals accurately. This implies that we can either suppress the blinking altogether, or alternatively, manipulate the PL energy peaks and intensities systematically to give non-random blinking. Our theoretical strategy developed here is generic and can be applied to any non-free-electron nanocrystals.Comment: Published online in Nanoscale (2010). Different from published versio

MIRAN MOZETI^: CHARACTERIZATION OF EXTREMELY WEAKLY IONIZED HYDROGEN PLASMA ... CHARACTERIZATION OF EXTREMELY WEAKLY IONIZED HYDROGEN PLASMA WITH A DOUBLE LANGMUIR PROBE KARAKTERIZACIJA [IBKO IONIZIRANE VODIKOVE PLAZME Z DVOJNO LANGMUIRJEVO SONDO

Basic parameters of hydrogen plasma created in a large discharge chamber were determined using a double Langmuir probe. Plasma was created in a Pyrex cylinder with the diameter of 25 cm and the height of 80 cm by an antenna connected to a RF generator operating at the frequency of 27.12 MHz and the power of about 200 W. The antenna was a copper coil of 4 turns. The discharge chamber was pumped with an oil diffusion pump with the nominal pumping speed of 600 L/s backed by a two stage rotary pump with the pumping speed of 4.4 × 10 -3 m 3 s -1 . The ultimate pressure of about 2 × 10 -3 Pa was obtained in the vacuum system after pumping for few hours. A double Langmuir probe was galvanic separated from the mains and placed into the centre of the discharge chamber. The probe was made from 2 tungsten rods with a diameter of 1.2 mm and separated for 2 cm. The length of un-insulated part of the rods was 17.5 mm. Plasma parameters were measured at different pressures between 0.4 and 7.2 Pa. The electron temperature reached the maximum of about kTe = 3.5 eV at the pressure of 1 Pa. The plasma density was slowly decreasing with increasing pressure and was of the order of 10 15 m -3 , and the Debye length was rather constant at about 2 × 10 -4 m. The results were explained by characteristics of an electrode less RF discharge in the E mode. Keywords: plasma, hydrogen, double Langmuir probe, electron temperature, plasma density, Debye length Z Langmuirjevo sondo smo dolo~ali parametre vodikove plazme, ustvarjene v velikem plazemskem reaktorju. Ta je bil narejen iz cilindri~ne cevi iz stekla pyrex premera 25 cm in vi{ine 80 cm. Plazmo smo vzbujali z anteno, povezano z RF-generatorjem s frekvenco 27,12 MHz in mo~jo 200 W. Antena je bila narejena iz bakrene tuljave s 4 ovoji. Razelektritveno komoro smo~rpali z difuzijsko~rpalko z nazivno~rpalno hitrostjo 600 L/s in povezano z dvostopenjsko rotacijsko pred~rpalko s~rpalno hitrostjo 4,4 × 10 -3 m 3 s -1 . Po nekajurnem~rpanju smo dosegli kon~ni tlak 2 × 10 -3 Pa. Dvojna Langmuirjeva sonda je bila galvansko lo~ena od omre`ja in vstavljena v sredino razelektritvene komore. Sonda je bila narejena iz dveh volframovih palic premera 1,2 mm, ki sta bili med seboj oddaljeni 2 cm. Dol`ina neizoliranega dela palic je bila 17,5 mm. Parametre plazme smo merili pri tlakih med 0,4 Pa in 7,2 Pa. Temperatura elektronov je dosegla maksimum okoli kTe = 3,5 eV pri tlaku 1 Pa. Gostota plazme je po~asi padala z nara{~ajo~im tlakom in je bila reda 10 15 m -3 . Debyeva dol`ina je bila dokaj konstantna okoli 2 × 10 -4 m. Rezultate smo razlo`ili z zna~ilnostmi brezelektrodne RF-razelektritve v E-na~inu