Analysis of the low-frequency noise spectrum in graphene-based biochemical sensors and its application in analyte recognition and quantification

In this study, we use the theoretical model of low-frequency noise in an adsorption-based sensor to analyze the possibility for the recognition and quantification of the analyte based on the measured fluctuations spectrum. We have developed an analytical expression for the spectral density of the fluctuations of the number of analyte particles adsorbed onto the sensing surface which takes into account the processes of mass transfer through the sensor reaction chamber, adsorption and desorption, and surface diffusion of adsorbed particles [1,2]. The numerical calculations performed using the derived theory are in agreement with the experimental data from the literature obtained for graphene-based gas sensors [3,4]. While analyzing the dependence of specific features in the fluctuation spectra of various parameters, we investigate which type of information about the analyte and its interaction with the graphene surface can be obtained from the experimentally obtained noise spectrum. References:1. Djurić, Z., Jokić, I., Peleš, A., Microel. Eng. 124, 81-85 (2014).2. Djurić, Z., Jokić, I., Peleš, A., “Highly sensitive graphene-based chemical and biological sensors with selectivity achievable through low-frequency noise measurement – Theoretical considerations“, in Proceedings - MIEL 2014, 29th Int. Conference on Microelectronics, IEEE, 2014, pp. 153-156.3. Rumyantsev, S., Liu, G., Shur, M.S., Potyrailo, R.A., and Balandin, A.A., NanoLetters 12, 2294-2295 (2012).4. Rumyantsev, S., Liu, G., Potyrailo, R.A., Balandin, A.A., and Shur, M.S., IEEE Sensors Journal 13, 2818-2822 (2013)

Measurement of dielectric permitivity using coaxial chambers and electromagnetic-modeling software

Our research group has developed a method for measurement of complex relative permittivity of various dielectric materials in the frequency range from around 1 kHz up to several GHz. Material samples have preferably a disk shape. The thicknesses of the samples can be in a wide range, from about 10 μm (thick films) up to several mm. We have designed and manufactured a set of coaxial chambers, which we use as test fixtures. We have also developed two numerical-simulation programs for the electromagnetic analysis of bodies with rotational symmetry. One program is suitable for the low-frequency analysis. It is based on an electrostatic approach. The other program is based on an electrodynamic approach and it is tailored for microwave frequencies. In measurements, we use impedance meters and network analyzers to obtain the input impedance of a chamber with a sample. Thereafter, we implement our software for the electromagnetic modeling to extract the relative permittivity of the measured sample. As examples of verification of our method, we present here results for the relative permittivities of two sets of samples whose sizes are on the extreme limits of the method. The first set comprises poly (vinylidene fluoride) and mechanically activated ZnO nanoparticle composite films, whose relative permittivities are around 1.8. The second set comprises large, high-density samples of spinel (aluminum magnesium oxide) ceramics, sintered under various conditions. The measured relative permittivities of these samples are around 7.5. In all cases, good agreement with other available data has been obtained

Spark plasma sintering of mechanically activated MGO-TiO2 system

MgTiO3 is a material often used in different types of high-frequency capacitors, temperature compensating capacitors, and chip capacitors, so the enhancement of this material is still the focus of many research groups due to its remarkable dielectric properties. Outstanding features can only be achieved when the ceramics are highly dense. Densification of magnesium titanate by Spark Plasma Sintering (SPS) was the aim of this work. Magnesium titanate ceramics were prepared by applying mechanical activation as the first step. Powders prepared in this way were SPS sintered, at 1200 °C with a heating rate of 100 °C/min. After reaching the desired temperature, a uniaxial pressure of 50 MPa was applied. The dwell time at this condition was 5 min, followed by cooling to room temperature at 5°C/min. X-ray diffraction was performed in order to establish the phase composition of milled powders and obtained ceramics. Differences between samples milled in various times intervals, as well as sintered ceramics were examined by means of scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). The presence of MgTiz0s phase was detected in XRD and was confirmed by EDS analysis for the non-milled ceramics. In the samples obtained from milled powders, no MgTi2O5 was detected in XRD patterns, but this phase was detected in EDS spectra in a lower amount. Dielectric measurements were performed at a wide range of frequencies, while the hardness of the SPS samples was measured at loads up to 10 N. The highest value of the hardness was obtained from powder milled for 15 min before SPS

Effect of high energy ball milling on sintering of MgO-TiO2 system

Perovskite ceramic material based on MgTiO3 is used in various types of electronic devices owing to its dielectric properties, high dielectric constant, and low losses. These features can be tailored by setting preparation conditions. Densification of magnesium titanate by Spark Plasma Sintering (SPS) was the aim of this work. First, the mechanical activation in the highenergy ball mill was applied on the powder of MgO-TiO2 mixed in mole ratio 1:1. Prepared powder mixtures, activated for different times, were SPS sintered, at 1200 oC with a heating rate of 100oC/min. After reaching the desired temperature, a uniaxial pressure of 50 MPa was applied, and dwelled at this condition for 5 min, followed by cooling to room temperature at 5oC/min. The starting powders, activated mixtures, and sintered ceramics bodies were investigated by X-ray diffraction, scanning electron microscopy (SEM), and energy dispersive spectroscopy (EDS). The presence of the MgTi2O5 phase was noticed for the nonmilled ceramics. In the samples obtained from milled powders, MgTi2O5 was detected in EDS spectra in a lower amount, below the threshold of the XRD method. Dielectric measurements were performed at a wide range of frequencies and temperatures. The highest value of the hardness was obtained from powder milled for 15 min before SPS

Structural investigation of mechanically activated ZnO powder

Commercially available ZnO powder was mechanically activated in a planetary ball mill. In order to investigate the specific surface area, pore volume and microstructure of non-activated and mechanically activated ZnO powders the authors performed N-2 physisorption, SEM and TEM. Crystallite size and lattice microstrain were analyzed by X-ray diffraction method. XRD patterns indicate that peak intensities are getting lower and expend with activation time. The reduction in crystallite size and increasing of lattice microstrain with prolonged milling time were determined applying the Rietveld's method. The difference between non-activated and the activated powder has been also observed by X-ray photoelectron spectroscopy (XPS). XPS is used for investigating the chemical bonding of ZnO powder by analyzing the energy of photoelectrons. The lattice vibration spectra were obtained using Raman spectroscopy. In Raman spectra some changes along with atypical resonant scattering were noticed, which were caused by mechanical activation

Markovian Dynamics on Complex Reaction Networks

Complex networks, comprised of individual elements that interact with each other through reaction channels, are ubiquitous across many scientific and engineering disciplines. Examples include biochemical, pharmacokinetic, epidemiological, ecological, social, neural, and multi-agent networks. A common approach to modeling such networks is by a master equation that governs the dynamic evolution of the joint probability mass function of the underling population process and naturally leads to Markovian dynamics for such process. Due however to the nonlinear nature of most reactions, the computation and analysis of the resulting stochastic population dynamics is a difficult task. This review article provides a coherent and comprehensive coverage of recently developed approaches and methods to tackle this problem. After reviewing a general framework for modeling Markovian reaction networks and giving specific examples, the authors present numerical and computational techniques capable of evaluating or approximating the solution of the master equation, discuss a recently developed approach for studying the stationary behavior of Markovian reaction networks using a potential energy landscape perspective, and provide an introduction to the emerging theory of thermodynamic analysis of such networks. Three representative problems of opinion formation, transcription regulation, and neural network dynamics are used as illustrative examples.Comment: 52 pages, 11 figures, for freely available MATLAB software, see http://www.cis.jhu.edu/~goutsias/CSS%20lab/software.htm

Structural investigation of mechanically activated ZnO powder

Commercially available ZnO powder was mechanically activated in a planetary ball mill. In order to investigate the specific surface area, pore volume and microstructure of non-activated and mechanically activated ZnO powders the authors performed N2 physisorption, SEM and TEM. Crystallite size and lattice microstrain were analyzed by X-ray diffraction method. XRD patterns indicate that peak intensities are getting lower and expend with activation time. The reduction in crystallite size and increasing of lattice microstrain with prolonged milling time were determined applying the Rietveld's method. The difference between non-activated and the activated powder has been also observed by X-ray photoelectron spectroscopy (XPS). XPS is used for investigating the chemical bonding of ZnO powder by analyzing the energy of photoelectrons. The lattice vibration spectra were obtained using Raman spectroscopy. In Raman spectra some changes along with atypical resonant scattering were noticed, which were caused by mechanical activation.Peer reviewed version of the paper: [https://machinery.mas.bg.ac.rs/handle/123456789/3948