Jan Pekárek

Sensing properties of multiwalled carbon nanotubes grown in MW plasma torch: electronic and electrochemical behavior, gas sensing, field emission, IR absorption.

Vertically aligned multi-walled carbon nanotubes (VA-MWCNTs) with an average diameter below 80 nm and a thickness of the uniform VA-MWCNT layer of about 16 μm were grown in microwave plasma torch and tested for selected functional properties. IR absorption important for a construction of bolometers was studied by Fourier transform infrared spectroscopy. Basic electrochemical characterization was performed by cyclic voltammetry. Comparing the obtained results with the standard or MWCNT‐modified screen-printed electrodes, the prepared VA-MWCNT electrodes indicated their high potential for the construction of electrochemical sensors. Resistive CNT gas sensor revealed a good sensitivity to ammonia taking into account room temperature operation. Field emission detected from CNTs was suitable for the pressure sensing application based on the measurement of emission current in the diode structure with bending diaphragm. The advantages of microwave plasma torch growth of CNTs, i.e., fast processing and versatility of the process, can be therefore fully exploited for the integration of surface-bound grown CNTs into various sensing structures.

Surface analysis of polymeric substrates used for inkjet printing technology

Purpose – This paper aims to find an optimal surface treatment of commonly used polymeric substrates for achieve the high adhesion of printed structures. For this reason, the investigation of substrates surfaces from different perspectives is presented in this paper. Design/methodology/approach – The contact angle measurements as well as the roughness measurements were realised for the analysis of surface properties of investigated substrates. The impact of applied chemical agents for surface treatment onto the wettability is analysed for polyimide, polyethylene terephthalate and polyethylene naphthalene substrates. Findings – The results prove the correlation among wettability, surface energy and work of adhesion with respect to the theoretical background. The surface treatment of polymeric substrates by chemical agents, such as acetone, toluene, ethanol, isopropyl and fluor silane polymer, has a significant impact onto the wettability of substrates which affects the final deposition process of nanoinks....

MEMS Carbon Nanotubes Field Emission Pressure Sensor With Simplified Design: Performance and Field Emission Properties Study

The pressure sensor application gained recently substantial interest in many fields of basic and applied research and applications. In this paper, microelectromechanical system (MEMS)-based pressure sensor contains nanostructured electrode consisting of carbon nanotube (CNT) array. CNTs are directly grown on such electrode by plasma-enhanced chemical vapor deposition method using microwave plasma torch at atmospheric pressure. This growth method enables us to use a simple electrode structure without need of buffer layer and time-consuming lithography process. Combination of CNTs field emission and MEMS membrane mechanical properties make possible to enhance sensitivity of the sensor. Field emission properties of CNTs are measured by newly developed system enabling us precise measurement of expecting properties, such as dependence on diaphragm (upper electrode) distance, applied voltage, and stability of the sensor. Measured values are compared with a numerical modeling of the membrane system in CoventorWare software by finite-element method. We also suggest encapsulating the sensor using glass frit bonding because such method is more suitable for high vacuum requirements of the field emission operation.

Electrodes modified by carbon nanotubes for pressure measuring

This paper describes a new approach to pressure sensors development using field emission and capacitive principles. Both sensors consist of two high doped silicon electrodes. Usually, for both pressure measurements, one electrode is anisotropic etched to obtain a sensitive membrane and the other one is solid with a carbon nanotubes (CNTs) array. The field emission sensor works on the principle that the field emission current is correlated with the electrical field intensity, i.e. the anode-emitter distance when the applied voltage is fixed. The capacitive sensor takes advantage of CNTs dimensions to increase the surface. This means that the CNTs array in the emission sensors serves as the emitter source of electrons between the cathode and the anode in the electric field and the CNTs arrays in the capacitive sensors increase the surface of the electrodes, which are similar to a plate capacitor.

Stress and charge transfer in uniaxially strained CVD graphene

Mechanical properties of graphene prepared by chemical vapor deposition (CVD) are not easily comparable to the properties of nearly perfect graphene prepared by mechanical cleavage. In this work, we attempt to investigate the mechanical performance of CVD graphene (simply supported or embedded in polymer matrix), transferred by two different techniques, under uniaxial loading with simultaneous in-situ monitoring by Raman microspectroscopy. The level of charge transfer doping and strain is assessed using the vector analysis modified for uniaxial strain. The strain distribution across the samples varies significantly, owing to the growth and transfer process, which induces wrinkles and faults in the CVD graphene. In simply supported specimens, the stress transfer efficiency is generally very low and the changes in Raman spectra are dominated by variations in the charge transfer originating from the realignment of the domains on the substrate upon the application of strain. In contrast, samples covered with an additional polymer layer exhibit an improved stress transfer efficiency, and the alterations of charge doping levels are negligible. In fully embedded specimens, the variations in stress transfer efficiencies are caused by the size of the effective graphene domains defined by cracks, folds and or/wrinkles.

Design of the charge push-through electronics for fully implantable artificial cochlea

The artificial cochlear implant is the only way how to get lost hearing back in some cases. Existing artificial cochlear devices use two separated parts for this purpose: a signal processing unit with transmitter and an implantable receiver with electrodes. This approach is applicable but not fully implantable. A new complex approach to design of a fully implantable artificial cochlea is described in this article. The proposed artificial cochlea consists of many subcircuits which have to be designed in close context to reach optimal performance and the lowest power consumption. Power consumption should be decreased to a value which allows using cochlear implant as a zero-powered system. A combination of micro-mechanized diaphragm filter bank, possible energy harvesting power source and especially ultra-low power processing electronics is presented in this article. A unique technique for nerve stimulatory output signal generation is discussed. This new technique named charge push-through electronics should use the major part of energy generated by energy harvesting subcircuit for output useful signal generation with minimal undesirable current. Mechanical parts of the subcircuits were simulated as complex electro-mechanical simulation models in ANSYS, CoventorWare, Matlab and SPICE environment. First, the real energy harvesting power source (human motion and temperature) behavior was measured. The model of this behavior was created in simulation environment and then the whole electronics simulation model for energy harvesting circuits was estimated. Next, signal processing circuits powered from energy harvesting power source were designed and simulated. The new signal processing circuits were simulated in relation to the results of complex electro mechanical diaphragm and SPICE energy harvesting power source simulation.

Carbon nanostructures used in capacitive sensors as the surface increase element

This paper describes a new approach to pressure sensor development using the capacitive principle. The novel pressure sensor consists of an elastic electrode-sensing film fabricated by a wet anisotropic etching process and a solid electrode. The capacitive sensor comprises of two high-doped silicon electrodes with multi-wall carbon nanotube (MWCNT) arrays. Between both parts of the body of the sensor there is an insulating spacer made of SIMAX® glass. The capacitive sensor takes advantage of CNT dimensions to increase the surface. It means that the CNT arrays in the capacitive sensors increase the surface of the electrodes which are similar to a plate capacitor. The CNTs were grown by plasma enhanced chemical vapor deposition (PECVD) by using iron as a catalyst in an atmospheric pressure microwave torch.

In Situ Observation of Carbon Nanotube Layer Growth on Microbolometers with Substrates at Ambient Temperature

Carbon nanotubes (CNTs) have near unity infrared (IR) absorption efficiency, making them extremely attractive in IR imaging devices. Since CNT growth occurs at elevated temperatures, integration of CNTs with IR imaging devices is challenging and has not yet been achieved. Here we show a strategy for implementing CNTs as IR absorbers using differential heating of thermally-isolated microbolometer membranes in a C2H2 environment. During the process, CNTs were catalytically grown on the surface of a locally-heated membrane while the substrate was maintained at an ambient temperature. CNT growth was monitored in situ in real time using optical microscopy. During growth, we measured the intensity of light emission and the reflected light from the heated microbolometer. Our measurements of bolometer performance show that the CNT layer on the surface of the microbolometer membrane increases the IR response by a factor of (2.3 ± 0.1) (mean ± one standard deviation of the least-squares fit parameters). This work opens the door to integrating near unity IR absorption, CNT-based, IR absorbers with hybrid complementary metal-oxide-semiconductor focal plane array architectures.

Design of an Artificial Microelectromechanical Cochlea

The paper presents the first results of research on an artificial cochlea based on a mechanical filter bank that could be produced by MEMS (Micro Electro Mechanical Systems) technologies and power supplied by energy harvesting systems. First, the basic configuration of the artificial cochlea proposed by our team is described. Then, the configuration of mechanoelectrical transducers (polycrystalline diffused piezoresistors) displayed in the first experiment is offered. Finally, the eigenfrequencies of resonant membranes calculated employing finite element systems Ansys and CoventorWare are introduced.

Cu 2 O based electrochemical sensor for direct glucose detection

Two types of working electrodes of electrochemical sensors were fabricated using screen-printing and spray-coating deposition methods and previously synthetized Cu2O micro/nanoparticles and used for direct electrochemical glucose detection. Glucose was successfully electrochemically detected against conventional Ag/AgCl reference electrode and platinum auxiliary electrode at potential of 0.5 V and 0.75 V for spray-coated and screen-printed electrode, respectively. Better sensitivity was observed using spray-coated electrode. For both electrodes types we obtained linear calibration curve in physiological range of concentrations from 0.5 to 10 mmol/L. Furthermore, the limit of detection lower than 100 μmol/L was achieved.