Margus Kodu

Electromechanical model for a self-sensing ionic polymer–metal composite actuating device with patterned surface electrodes

This paper further discusses a concept of creating a self-sensing ionic polymer–metal composite (IPMC) actuating device with patterned surface electrodes where the actuator and sensor elements are separated by a grounded shielding electrode. Different patterning methods are discussed and compared in detail; the presented experimental data give an understanding of the qualitative properties of the patterns created. Finally, an electromechanical model of the device is proposed and validated.

Investigation of possible replacement of protective magnesium oxide layer in plasma display panels by barium ternary oxides

The firing voltage (FV) of gas discharge in a test cell of plasma display materials was investigated for standard protective layers of MgO deposited by electron beam, and ternary BaY2O4 and BaGa2O4 oxides grown by pulsed laser deposition on the special dielectric coated glass substrates. The determined FVs for MgO (160 V), BaY2O4 (210 V) and BaGa2O4 (257 V) lead to the conclusion that a replacement of MgO by these ternary oxides is not expedient for plasma display panels. Using results from luminescence spectroscopy, values for the energy gap Eg ≈ 6.2 and 5.8 eV were estimated for BaY2O4 and BaGa2O4, respectively. The main reason for the observed high FVs is attributed to strong electron affinities χ, where χ (BaY2O4) < χ (BaGa2O4).

Highly sensitive NO2 sensors by pulsed laser deposition on graphene

Graphene as a single-atomic-layer material is fully exposed to environment and has therefore a great potential for creating of sensitive gas sensors. However, in order to realize this potential for different polluting gases, graphene has to be functionalized - adsorption centers of different type and with high affinity to target gases have to be created at its surface. In this present work, modification of graphene by small amounts of laser ablated materials is introduced for this purpose as a versatile and precise tool. The approach was demonstrated with two very different materials chosen for pulsed laser deposition (PLD), a metal (Ag) and a dielectric oxide (ZrO2). It was shown that the gas response and its recovery rate can be significantly enhanced by choosing the PLD target material and deposition conditions. The response to NO2 gas in air was amplified up to 40 times in case of PLD-modified graphene in comparison with pristine graphene and reached 7-8% at 40 ppb of NO2 and 20-30% at 1 ppm of N2. These results were obtained after PLD in gas environment (5 x 10-2 mbar oxygen or nitrogen) and atomic areal densities of deposited materials of were about 10 15 cm-2. The ultimate level of NO2 detection in air, as extrapolated from the experimental data obtained at room temperature under mild UV-excitation, was below 1 ppb.

Graphene functionalised by laser-ablated V2O5 for a highly sensitive NH3 sensor

Graphene has been recognized as a promising gas sensing material. The response of graphene-based sensors can be radically improved by introducing defects in graphene using, for example, metal or metal oxide nanoparticles. We have functionalised CVD grown, single-layer graphene by applying pulsed laser deposition (PLD) of V2O5 which resulted in a thin V2O5 layer on graphene with average thickness of ≈0.6 nm. From Raman spectroscopy, it was concluded that the PLD process also induced defects in graphene. Compared to unmodified graphene, the obtained chemiresistive sensor showed considerable improvement of sensing ammonia at room temperature. In addition, the response time, sensitivity and reversibility were essentially enhanced due to graphene functionalisation by laser deposited V2O5. This can be explained by an increased surface density of gas adsorption sites introduced by high energy atoms in laser ablation plasma and formation of nanophase boundaries between deposited V2O5 and graphene.

Experiments with self-sensing IPMC actuating device

This paper presents a realization of a self-sensing ionic polymer-metal composite (IPMC) device by patterning its surface electrodes and thus creating separate actuator and sensor parts. The sensor and actuator elements of such device are still electrically coupled through the capacitance and/or conductivity of the ionic polymer. By creating a separate grounded shielding electrode between the two parts, it is possible to suppress significantly the undesired cross-talk from the actuator to the sensor. The paper at hand compares three different methods for separating sensor and actuator parts: manual scraping, machine milling, and laser ablation. The basis of comparison of the methods is the electrical characteristics of the device after realizing the surface patterns and the convenience of manufacturing.

Structure-Dependent CO2 Gas Sensitivity of La2O2CO3 Thin Films

Rare earth oxycarbonates are potential candidate materials for constructing simple and low-cost chemiresistive sensors for monitoring carbon dioxide (CO2) gas in the living and working environment for personal comfort and health reasons. Also, measurement of CO2 concentrations is needed in many industrial processes. Specifically, sol-gel made nanoparticles of Nd and La oxycarbonates have been studied previously as novel CO2 gas sensor materials. In this paper, pulsed laser deposition of La oxycarbonate (La2O2CO3) thin films was studied and structural properties of obtained thin films were characterized. Also, CO2 gas sensing ability of synthesized films was evaluated. The films deposited under CO2 partial pressure in various conditions were all Raman amorphous. In situ or ex situ annealing procedure at high CO2 partial pressure was needed for obtaining crystalline La2O2CO3 films, whereby hexagonal and monoclinic polymorphs were obtained in ex situ and in situ processes, respectively. Sensor structure, made using in situ process, was sensitive to CO2 gas and showed relatively fast response and recovery characteristics.

Synthesis and gas-sensing properties of phenylhydrazine-functionalized single wall carbon nanotubes in polymer matrix

AbstractGas sensor material was prepared by encapsulation of functionalized single-walled carbon nanotubes (SWCNT) into a gas-permeable polymer poly(1-trimethylsilyl-1-propyne) (PTMSP). A phenylhydrazino group was used for the functionalization of SWCNTs to improve their solubility and compatibility with polymers. Syntheses were carried out in aqueous surfactant solutions and in pure phenylhydrazine without surfactant. Two different temperatures (24 and 50°C) and two surfactants (sodium dodecyl sulfate and tricaprylmethylammonium chloride — Aliquat®336) were compared. Functionalized SWCNTs were characterized by X-ray photoelectron (XPS), Raman and Fourier transform infrared (FTIR) spectroscopy. Analyses showed that the synthesis at higher temperature in pure phenylhydrazine resulted in the highest functionalization yield. Phenylhydrazine itself proved to be a good solvent for SWCNTs. The functionalized nanotubes were soluble in organic solvents that under the same conditions were appropriate solvents for polymers. The sensitivity of functionalized SWCNT-PTMSP thin film composite to NO2 gas at room temperature was significantly higher than that of the similar sensor material containing the pristine SWCNTs.