We build sensors, capable of detecting and measuring ultraviolet (UV) light, by depositing zinc oxide (ZnO) powder from a solvent suspension over common white paper. Although these sensors are easy to fabricate and require inexpensive materials, they feature characteristics similar to those of UV sensors made with complex and expensive procedures. The good performance in terms of conductivity change of our simple devices can be attributed to the conductivity and porosity properties of paper, which effectively binds the ZnO crystals. We perform analyses using quantum chemistry methods to describe possible mechanisms that explain the conductivity changes observed on the ZnO surface due to doping interactions with interstitial hydrogen and doping depletion caused by oxygen adsorption.
In this work we report the development of an oxygen sensor using a simple device made from a film of ZnO crystals dispersed over a paper surface. Due to the high porosity of this kind of device made from paper and ZnO, a large photoconductive effect is observed as result of the fast absorption and desorption of oxygen from the ZnO surface. To detect oxygen we propose to use ultraviolet (UV) illumination over the photoconductive surface of the sensor, the applied UV light produces oxygen desorption causing current variations through the sensor that are proportional to the oxygen presence nearby the sensor surface. The sensor developed in this work is attractive because it is remarkably easy to fabricate, employs only very low cost materials for its construction and shows a better sensitivity at low concentration of oxygen at partial vacuum environments.
A multilayer graphene device performing as a chemistry-based signal mixer is shown by a theoretical–experimental approach. We find current fluctuations across a three-layer graphene cluster using a combination of density functional and Green’s function theories. We suggest that these current fluctuations are due to the effect of the external bias on plasmons created from electron delocalization in graphene plates. The bias potentials affect the intrinsic behavior of the electron density corresponding to the frontier orbitals and perhaps other energetically near orbitals. The theoretical finding suggests that if the sheets of graphene show a plasmon behavior they may be used to mix signals of different frequencies. We corroborate this suggestion performing a proof-of-concept experiment on a sample of few-layer graphene by introducing two signals of different frequencies. We find experimentally that the recovered output contains the input frequencies, their sum and differences, as well as their second- and third-order harmonics, among others. Thus, plasmons between graphene layers and their high sensitivity surface make the graphene layers a mixer device able to detect the frequency differences of the input signals. Eventually these input signals could come from vibrational modes of molecules, and such a mixer would be of strong importance for sensing science and engineering at terahertz frequencies.
We report sensitivity to infrared radiation from a simple paper-made device, which increases its conductivity when exposed to hot objects. We propose that the conductivity of this device is due to ionic currents involving electrolyte salts dissolved in thin film of liquid dispersed over the paper surface, thus the current increases because of heating caused by absorption of infrared light from hot sources. The fast response to stimulus exposure of this sensor suggests that the heating effect is related to a radiative interaction rather than to another kind of heat transfer such as convection or conduction.
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