This
paper is devoted to an investigation on the methane sensing
properties of graphene (G), decorated with silver nanoparticles (AgNPs),
under ambient conditions. To do so, we first present an effective
modification in the standard manner of decorating graphene by AgNPs.
From structural analysis of the product (AgNPs/G), it is concluded
that graphene is indeed decorated by AgNPs of a mean size 29.3 nm,
free of aggregation, with a uniform distribution. The so-produced
material is then used, as a resistivity-based sensor, to examine its
response to the presence of methane gas. Our measurements are performed
at relatively low temperatures, for various silver-to-graphene mass
ratios (SGMRs) and methane concentrations. To account for the effects
of humidity, we have made the measurements, at room temperature, for
different levels of humidity. Our results demonstrate that an increase
in the SGMR enhances the response of AgNPs/G to methane with an optimum
value of SGMR ≅ 12%. It is also illustrated that for methane
concentrations less than 2000 ppm, the maximal response increases
linearly and rapidly, even at room temperature. Moreover, we demonstrate
that AgNPs/G is of low limit of detection, highly stable, selective,
reversible, repeatable, and sensor-to-sensor reproducible, for methane
sensing. The results thus promise a low-cost and simple-to-fabricate
methane sensing device.
In this paper we study the spin and subbands populations, as functions of time, for electrons in a quasi-1D quantum wire, with spin -orbit coupling (SOC), to which a perpendicular magnetic field is applied. The system is governed by the Hamiltonian which, in the strong magnetic field limit, resembles the JaynesCummings model (JCM) in quantum optics (QO). Using a procedure similar to that in QO, we explicitly present the time-evolution operator, thereby calculating the spin states and subbands populations as functions of time. We show that the populations exhibit oscillations, depending on the interaction parameters, scale lengths and, particularly, the initial states of the system. Specifically, if the electrons are initially prepared in a maximal coherent superposition of spin states, the expectation values periodically collapse and revive. The collapse-revivals are most profound for the spin along the magnetic field and subbands populations.
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