Optical depth profile and phase transitions investigation of NaNbO3 and Pb(Zr, Ti)O3 thin films

Optiskā gradienta un fāzu pāreju pētījumi NaNbO3 un Pb(Zr,Ti)O3 plānās kārtiĦās Anotācija NaNbO3 (NN) plānām kārtiĦām, izgatavotām ar lāzera ablācijas metodi, tika pētītas optiskās īpašības (spektrālais diapazons 250-1200 nm), to gradients, laušanas koeficienta n un aizliegtās zonas platuma Eg temperatūras atkarības (5-830 K), izmantojot spektrālo elipsometriju (SE). Pavisam tika novērotas piecas fāzu pārejas (FP). Optiskā gradienta aprēėini parādīja, ka n samazinās pamatnes tuvumā, kas var izskaidrot nelielo FP temperatūru nobīdi, kas tika novērotas termooptiskos pētījumos. Tika veikti optisko īpašību, pārejas slāĦa, Eg, virsmas raupjuma biezuma atkarībās, kā arī optiskā gradienta pētījumi sol-gela PbZrxTi1-xO3 (PZT, x = 30, 52, 95%) plānās kārtiĦās. SE pētījumi parādīja, ka sol-gela ėīmiskās sintēzes šėīdumi nav atbildīgi par gradienta veidošanos: tas veidojas no kristalizācijas procesa. Tika novērota lineāra n samazināšanās un Eg palielināšanas, palielinoties Zr/Ti attiecībai PZT kārtiĦās.Optical depth profile and phase transitions investigation of NaNbO3 and Pb(Zr,Ti)O3 thin films Abstract Optical properties (spectral range 250-1200 nm), depth profile of refractive index n, temperature (5-830 K) dependence of n and optical band gap Eg of NaNbO3 (NN) thin films, made by pulsed laser deposition, were investigated by means of spectroscopic ellipsometry (SE). Totally five phase transition (PT) were observed. More deep gradient calculations revealed n decrease near the substrate what can explain the slight shift of the PT temperatures observed in thermo-optical investigations. The thickness dependency of optical properties, interface, Eg, surface roughness, and depth profile of n were evaluated for sol-gel PbZrxTi1-xO3 (PZT, x = 30, 52, 95%) thin films. SE investigations evaluated that the sol-gel chemical synthesis routes are not responsible for the gradient appearance: it appears from the crystallization process. The linear decrease of n and linear increase of Eg with increase of the Zr/Ti ration in PZT thin films were detected

Effect of Nanotube Aspect Ratio on Chemical Vapour Sensing Properties of Polymer/MWCNT Composites

The main topic of this paper is the study of polyisoprene-multi wall carbon nanotubes (PiMWCNT) composite’s electrical conductivity and volatile organic compound sensing properties with respect to type of multi wall carbon nanotubes used. Electrical percolation parameters like percolation threshold and critical exponent of produced composites are determined and analyzed. PiMWCNT composites exhibit a promising sensitivity to the presence of volatile organic compounds. Therefore the composite’s sensing mechanism of volatile organic compounds are analyzed in more detail by applying an original measuring technique which enables simultaneous measurement of an electrical resistance, mass and length change measurement of the sample in the presence and subsequent absence of a vapour. Measurement results enabled the evaluation of both vapour diffusion behavior in the composite and electrical resistance change mechanism

Effect of Nanotube Aspect Ratio on Chemicals Vapour Sensing Properties of Polymer/MWCNT Composites

Recently we have reported that polyisoprene/high structured carbon black composites demonstrated excellent chemoresistivity effect [1]. In this study polyisoprene/multiwall carbon nanotube composites (PCNTC) have been elaborated and their electric resistance response to vapour of volatile organic compounds (VOC) was tested. PCNTC has been produced using 2 types of multiwall carbon nanotubes (MWCNT) with clearly different aspect ratio (η) - long MWCNT with η = 12500 and short MWCNT with η = 40 (purchased from « Cheap Tubes Inc »). Additionally to that measurements of electric resistivity temperature dependence showed semiconductor like properties for long MWCNT and metal like properties for short MWCNT. Producing PCNTC with gradually increasing MWCNT concentration, percolation curves of electric conductivity have been obtained and percolation thresholds determined (pc). Percolation threshold is pc = 3.15 and 5.8 for PCNTC with long and short MWCNT respectively. PCNTC response to chemicals stimuli was analyzed by complex measuring technique, which enables simultaneous measurements of electrical resistance, mass and dimensions change of the sample exposed to certain VOC vapour. From obtained results an increase mechanism of composite electrical resistance as well as VOC vapour diffusion behaviour and parameters were evaluated. The MWCNT aspect ratio contribution to the composite VOC vapour sensing was evaluated as well

Optiska reflektometrija un elipsometrija planu kartinu biezuma un lausanas koeficienta noteiksanai

Abstract in Latvian, EnglishAvailable from Latvian Academic Library / LAL - Latvian Academic LibrarySIGLELVLatvi

Complex Method for Describing Polyisoprene/Conductive Nanotube Composite Gas Sensing Properties

Polymer/conductive filler composites are widely studied with a purpose to evaluate a composite suitability for gas sensing. Conductive filler within polymer matrix material forms electroconductive grid, where two filler particles are not geometrically connected. Therefore, chemoresistive polymer film gas sensitivity is based on charge tunneling through insolator layers between conductive nanostructures. When diffusion of analyte into a composite occurs, the isolator layer swells and conductive particle distance increases, in turn the composite electrical resistance also increases. Here a method is presented which enables simultaneous mass, length and electrical resistance measurements. Data about a sample mass change give information about analyte diffusion rate and diffusion mechanism into the composite. Diffusion mechanism (Fickian, anomalous, Case II, Supercase II) evaluation is critically important for gas sensor material, because it says much about composite matrix material macromolecule mobility, that remarkably influence the sensor material response rate to the presence of gas. A sample length and electrical resistance evaluation give data about existing electrical resistance increase mechanism (tunneling; tunneling + conductive channel destruction) and response long-term stability. The developed method and home made setup has been demonstrated for investigation of polyisoprene/multi wall carbon nanotubes (MWCNT) composites with varying MWCNT content

Distributed Array of Polymeric Piezo-nanowires through Hard-Templating Method into Porous Alumina

We report on the preparation of ferroelectric polymeric nanowires through hard-templating strategy. Wet-impregnation of poly(vinylidene fluoride) (PVDF) and its copolymer poly(vinylidene fluoride-tri fluoro ethylene) [P(VDF TrFE)] was performed into commercially available porous Anodic Alumina Membrane (AAM). The polymeric nanowires show a diameter ranging from 144 to 166 nm, a length of tenth of micron and a high filling ratio of the alumina pores. X-ray diffraction pattern and infrared spectroscopy show the crystallization of both polymers into the ferroelectric β phase. In addition, Curie temperature (Tc) tests show an increase to higher Tc for the PVDF-TrFE polymeric nanowires with respect to the bulk polymeric material, thus revealing the importance of confined crystallization into mono-dimensional structures. A piezoelectric behavior was also observed by a voltage generation upon mechanical pressure, without pre-poling or mechanically orienting the polymer. These crystalline piezoelectric nanowires distributed in a vertical array would potentially address applications like mechanical pressure sensors, e.g., in robotics

Dynamic Mechanical Analysis of Organic and Inorganic Nanotubes – Elastomer Composites

Polymer-electro-conductive nanostructured composites have gained much interest, due to their potential use as flexible large size sensors with superior mechanical and electrical properties. We use TMA (thermo mechanical analysis) and DMA (dynamic mechanical analysis) to study the thermal expansion as well as the temperature and frequency dependence of the dynamic elastic susceptibility of various nanostructured composite materials. In this work we present a brief description of the method, the sample geometries used, etc. In the second part we present results of recent TMA and DMA measurements of polyisoprene/multiwall carbon nanotube (PMWCNT) composites (Fig.1) and Elastomer/MoS2 (2d) and Elastomer/Mo6S2I8 (nanowire) composites. For PMWCNT composites above the glass transition temperature Tg the composites with phr values above the electric percolation threshold [red (12 phr) and blue (16 phr) curves in Fig.1] show a ca. 30% higher thermal expansion coefficient than those with phr below the percolation threshold. Below Tg this difference disappears. This strong influence of filler concentration on thermal expansivity and its relation to the glass transition is discussed

Elastomer/Nanographite Composites for Mechanical and Chemical Sensing

black composites we can achieve excellent piezoresistivity effect [1] as well as chemoresistivity effect [2] for these composites. In this study we attempt to design polyisoprene matrix composites with promising more sophisticated fillers – thermoexfoliated graphite (TEG) as well as multiwall carbon nanotubes with high (LMWCNT) and low (SMWCNT) aspect ratio for their application in design of new sensitive polymer composites. TEG has been synthesized in Department of Physics of Kyiv National Taras Shevchenko University. Powders of LMWCNT and SMWCNT have been bought from Cheap Tubes Inc. Polyisoprene/TEG and polyisoprene /MWCNT composites were prepared in Institute of Technical Physics of Riga Technical University. Firstly each filler party was dispersed in chloroform in one vessel by ultrasonic homogenizer. Secondly polyisoprene and necessary additives, zinc oxide and sulphur were dissolved in chloroform in another vessel by magnetic stirring. After the definite filler dispersion was added to polyisoprene solution and the mixture was mixed by magnetic stirring for 24 hours. From the obtained raw mixture chloroform was evaporated. Finally the mixture was vulcanized under pressure of 30 atm at 150oC for 15 minutes. The acquired nanocomposite samples were electrically conductive and showed the ability to change the electrical resistance under the influence of mechanical force and volatile compound vapours as well