Alexandr Laposa

Gas sensing properties of nanocrystalline diamond at room temperature.

Summary This study describes an integrated NH3 sensor based on a hydrogenated nanocrystalline diamond (NCD)-sensitive layer coated on an interdigitated electrode structure. The gas sensing properties of the sensor structure were examined using a reducing gas (NH3) at room temperature and were found to be dependent on the electrode arrangement. A pronounced response of the sensor, which was comprised of dense electrode arrays (of 50 µm separation distance), was observed. The sensor functionality was explained by the surface transfer doping effect. Moreover, the three-dimensional model of the current density distribution of the hydrogenated NCD describes the transient flow of electrons between interdigitated electrodes and the hydrogenated NCD surface, that is, the formation of a closed current loop.

Fabrication of Diamond Based Quartz Crystal Microbalance Gas Sensor

Synthetic diamond has remarkable properties comparable with natural diamond and hence is a very promising material for many various applications (sensors, heat sink, optical mirrors, cold cathode, tissue engineering, etc.). Nowadays, deposition of diamond films is normally employed in chemical vapor deposition (CVD) usually at high temperatures (800900 °C), what limit its application to high melting substrates. Gravimetric (mass) sensors belong to the major categories of chemical sensors and the most common type of mass sensor is the bulk acoustic quartz crystal microbalance (QCM). This contribution deals with a nanocrystalline diamond (NCD) growth from the H2/CH4/CO2 gas mixture at low temperature (400 °C) by pulsed linear antenna microwave plasma system on 10 MHz circular AT-cut quartz resonators substrate. Gas sensor based on the NCD-coated QCM was developed for detection of ammonia (NH3) at room temperature. Measurements not only confirmed the functionality of this first published NCD-coated QCM sensor, but in addition its sensitivity was twofold to a virgin QCM sensor with a gold active layer.

Respiration monitoring during sleeping

The respiration belongs among basic vital functions and the knowledge of their parameters and quality is necessary in medicine. The research is leading to the methods, which are inconvenienced patients. These methods are important for monitoring respiration towards observation quality sleeping or The Sudden Infant Death Syndrome (SIDS). This paper contains an overview of the methods for the respiration monitoring used not only in practice of medicine but till now developed.

Gas-sensing behaviour of ZnO/diamond nanostructures

Microstructured single- and double-layered sensor devices based on p-type hydrogen-terminated nanocrystalline diamond (NCD) films and/or n-type ZnO nanorods (NRs) have been obtained via a facile microwave-plasma-enhanced chemical vapour deposition process or a hydrothermal growth procedure. The morphology and crystal structure of the synthesized materials was analysed with scanning electron microscopy, X-ray diffraction measurements and Raman spectroscopy. The gas sensing properties of the sensors based on i) NCD films, ii) ZnO nanorods, and iii) hybrid ZnO NRs/NCD structures were evaluated with respect to oxidizing (i.e., NO2, CO2) and reducing (i.e., NH3) gases at 150 °C. The hybrid ZnO NRs/NCD sensor showed a remarkably enhanced NO2 response compared to the ZnO NRs sensor. Further, inspired by this special hybrid structure, the simulation of interaction between the gas molecules (NO2 and CO2) and hybrid ZnO NRs/NCD sensor was studied using DFT calculations.

Acoustic wave sensor system design consideration

In this paper, we present the development and considerations of simple acoustic wave chemical sensors. These sensors can be used for identifying environmental contaminants in large applications scale. Various finite element models of a Acoustic Wave sensors are developed using CoventorWare and 3D analysis is performed on the devices to study the acoustic wave propagation and characterize the device. The effects of the various interdigital transducers (IDT) design; intermediate layer on the propagation characteristics is also investigated.

Temperature dependence of the pyroelectric behaviour in GaN/AlGaN

So far the dependence of the spontaneous polarization coefficient for GaN and AlN on temperature has been measured to be minimal, which corresponds with expectation that the spontaneous polarization is reduced at the elevated temperatures of interest. There are also no reports on the piezoelectric polarization at higher temperature. This paper is initial study on the influence of temperature related pyroelectric behaviour in GaN/AlGaN. Summarize recent findings and consideration.

Screen printed and laminated electrodes for low-cost capacitive level measurement systems

Abstract The fabrication procedure and characterization of low-cost electrodes for capacitive level sensors realized on a flexible substrate are presented in this paper. The aim was to prepare conductive electrodes by printing of silver and PEDOT:PSS pastes on coated PET foil. Individual interdigital capacitors and a system with embedded microcontroller readout were designed for a comparative study. Individual capacitors in the form of interdigital electrodes (IDT) were designed with different finger width/spacing dimensions from 300/300 μm to 800/800 μm, a finger length 10 mm and 15 mm and an overall length of 100 mm. A demonstrator device featuring an integrated microcontroller, sensing and reference capacitive sensors and a resistive temperature sensor was realized to proof a practical utilization. The microcontroller is used to calculate capacitances of IDT electrodes in terms of charging time proportional to the fluid level. The design with reference capacitor can be directly applied to different fluids with a wide range of conductivities and dielectric constants without recalibration. The printed structures were thermally laminated with covering PET foil. The sensitivity of the fabricated devices was characterized in liquids with different relative permittivity and conductivity (water and oil). The highest measured sensitivity was 0.7 pF/mm and 0.08 pF/mm for water and oil respectively, with resolution down to 0.1 mm.

Acoustic method for respiratory monitoring

This paper describes a method of the respiration monitoring based on the sensing of acoustic signals in trachea. Further, the article describes method for signal processing of the acoustic signals. The respiration belongs among basic vital functions and the knowledge of their parameters and quality is necessary in medicine. The research is leading to the methods, which are inconvenienced patients. Monitoring of respiration is important for monitoring respiration towards observation quality sleeping or The Sudden Infant Death Syndrome (SIDS).

Gas analyzer for quick indicative measurements

The article describes the design and realization of the gas analyzer using 4 types of gas sensors — catalytic, electrochemical, semiconductor and infrared sensor. The analyzer is intended for quick orientation measuring the presence of gas. The analyzer includes basic parts — the sensor part, the evaluation and control part, the display and the output actuator part. The analyzer is designed for easy modification of its connection to different types of chemical sensors. The sensor part includes a chemical sensor, an EEPROM and a temperature sensor. The type of the used sensor sets the operation mode of the both part — evaluation and control part. Actuators on the output are ready to control the security elements (ventilation, alarm, etc.). The display shows the basic information — gas concentration, temperature, and more. Evaluation and control part includes microprocessor, memory for long-term data, signaling LEDs, push buttons.

Quartz Crystal Micro–Balance Gas Sensor with Ink–Jet Printed Nano–Diamond Sensitive Layer

Abstract the paper presents fabrication and characterization of a Quartz Crystal Microbalance based gas sensor with a diamond powder sensitive layer deposited using the ink-jet printing technique. The sensor was exposed to a low concentration of ammonia, acetone vapors and different levels of humidity. Impedance characteristics close to the natural resonant frequency of 10 MHz were examined. The sensor exhibits significant shifts in serial resonant frequency under different gas environments.