The low-frequency 1/f noise in graphene transistors has been studied extensively owing to the proposed graphene applications in analog devices and communication systems [1-5]. The studies were motivated by the fact th...
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The low-frequency 1/f noise in graphene transistors has been studied extensively owing to the proposed graphene applications in analog devices and communication systems [1-5]. The studies were motivated by the fact that the low-frequency noise can be up-converted by device nonlinearity and contribute to the phase noise of the system. Similarly, the sensor sensitivity is often limited by the electronic low-frequency noise. Therefore, noise is usually considered as one of the main limiting factors for the device or overall system operation. However, the electronic noise spectrum itself can be used as a sensing parameter increasing the sensor sensitivity and selectivity. Here, we show that vapors of different chemicals produce distinguishably different effects on the low-frequency noise spectra of the graphene-on-Si transistor. Our study showed that some gases change the electrical resistance of pristine graphene devices without changing their low-frequency noise spectra while other gases modify the noise spectra by inducing Lorentzian components with distinctive features. The characteristic corner frequency f C of the Lorentzian noise bulges in graphene devices is different for different chemicals and varies from f C =10 - 20 Hz for tetrahydrofuran to f C =1300 - 1600 Hz for chloroform. We tested the selected set of chemicals vapors on different graphene device samples and alternated different vapors for the same samples. The obtained results indicate that 1/f noise in combination with other sensing parameters can allow one to achieve the selective gas sensing with a single pristine graphene transistor. Our method of gas sensing with graphene does not require graphene surface functionalization or fabrication of an array of the devices with each tuned to a certain chemical. The observation of the Lorentzian components in the vapor-exposed graphene can also help in developing an accurate theoretical description of the noise mechanism in graphene.
We studied cycle time （0.01-10 s with triangular input waves） and poling history （continuous versus fresh poling） dependent electric energy storage and discharge behaviors in poly（vinylidene fluoride-co-hexafluor...
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We studied cycle time （0.01-10 s with triangular input waves） and poling history （continuous versus fresh poling） dependent electric energy storage and discharge behaviors in poly（vinylidene fluoride-co-hexafluoropropylene） [P（VDF- HFP）] films using the electric displacement -- the electric field （D-E） hysteresis loop measurements. Since the permanent dipoles in PVDF are orientational in nature, it is generally considered that both charging and discharging processes should be time and poling history dependent. Intriguingly, our experimental results showed that the charging process depended heavily on the cycle time and the prior poling history, and thus the D-E hysteresis loops had different shapes accordingly. However, the discharged energy density did not change no matter how the D-E loop shape varied due to different measurements. This experimental result could be explained in terms of reversible and irreversible polarizations. The reversible polarization could be charged and discharged fairly quickly （〈 5 ms for each process）, while the irreversible polarization depended heavily on the poling time and the prior poling history. This study suggests that it is only meaningful to compare the discharged energy density for PVDF and its copolymer films when different cycle times and poling histories are used.
We present filling as a type of spatial subdivision problem similar to covering and packing. Filling addresses the optimal placement of overlapping objects lying entirely inside an arbitrary shape so as to cover the m...
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We present filling as a type of spatial subdivision problem similar to covering and packing. Filling addresses the optimal placement of overlapping objects lying entirely inside an arbitrary shape so as to cover the most interior volume. In n-dimensional space, if the objects are polydisperse n-balls, we show that solutions correspond to sets of maximal n-balls. For polygons, we provide a heuristic for finding solutions of maximal disks. We consider the properties of ideal distributions of N disks as N→∞. We note an analogy with energy landscapes.
It has been a long challenge to understand the equilibrium and the dynamic phenomena(*** reactions)at the electrode/electrolyte interface in a unified theoretical *** periodic first-principles calculations integrated ...
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It has been a long challenge to understand the equilibrium and the dynamic phenomena(*** reactions)at the electrode/electrolyte interface in a unified theoretical *** periodic first-principles calculations integrated with modified-Poisson-Boltzmann electrostatics are utilized to provide the atomic level insight into the nature of electrochemical double layer and the catalytic reaction at the interface.
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