No abstract

A novel sensor that deploys opto-and electrochemical techniques for the rapid and highly sensitive separation and detection of metal ions in aqueous media is reported. The sensor comprises a porous membrane coated with an ultra-thin porous layer of highly ordered, hexagonally packed arrays of metal (Au and Pt) nanoparticles with ≤ 25 nm sub-gaps. This platform enables an integrated detection method that relies on in-situ surface enhanced Raman scattering. An additional scheme is utilised based on electrochemical impedance spectroscopy to increase both the selectivity and the sensitivity of the sensor. Electrochemical separation bolsters the effectiveness of the optical method through ion separation and pre-concentration. The latter are induced by forcing the liquid electrolyte through the membrane's nanopores through a new proposed method based on surface tension mismatch. The sensor demonstrates high selectivity for six different heavy metal ions (Hg 2+ , Cd 2+ , Pb 2+ , Cu 2+ , Co 2+ , Ni 2+) at concentrations that range from 1 to 20 ppb (1 × 10 −3-20 × 10 −3 μg/ml). The novelty of this sensor consists of the fact that the separation, pre-concentration and detection of the targeted ions are all performed in a single stage, eliminating the need for time-consuming and complex sample preparation steps.

No abstract

Please cite this article in press as: M. Serry, et al., Nanostructured graphene-Schottky junction low-bias radiation sensors, Sens. Actuators A: Phys. (2015), http://dx. a b s t r a c tWe present a key idea of using the graphene-based Schottky junction to achieve high sensitivity and wide detection range radiation sensors. Nanostructured Schottky junction is formed at the interface between a graphene, metal electrode, and a semiconductor. The current flowing through the junction is mainly controlled by the barrier's height and width. Therefore, the detection principle is based on Schottky barrier height (SBH) modulation in response to different materials and stimuli. We have illustrated the concept for gamma (␥) radiation sensors. It's demonstrated that the integration of graphene leads to a great enhancement in sensitivity of up to 11 times coupled with 5 times increase in the sensing range as compared to conventional Schottky junctions. Furthermore, it was demonstrated that for proposed sensors, that the change in SBH could be fairly linearized as a function in the radiation dose unlike the SBH of comparable conventional junctions. The new concept opens the door for a novel class of minitiuarized, low biased, nanoscale radiation sensors for wireless sensor networks. The devices are based on new nanostructured Schottky junctions made by growing graphene on ultrathin platinum catalytic layer grown on different silicon substrates. Graphene high uniformity film with small flakes size embedded with platinum particles was synthesized using two deposition steps. The integration of graphene layers on regular M-S junctions was only possible by using an ALD grown platinum thin film (10-40 nm) and then growing graphene in PECVD at temperatures lower than platinum silicide formation temperature. The radiation sensing behaviors were investigated using two different substrate types. The first substrate type is a moderately doped n-type (n ≈ 2 × 10 15 cm −3 ) silicon substrate in which a Schottky rectifier response with different threshold voltages was observed. A device that is based on Pt/n-Si conventional Schottky junction was used as a reference. The various devices were exposed to a range of ␥-irradiations (2-120 kGy) using Co 60 source, and a change in terminal voltages before and after radiation were measured accordingly. A sensitivity of 3.259 A/kGy cm 2 at 1 V bias over a wide detection range has been realized. The charge transport mechanisms are interpreted on the basis of testing the detectors at elevated temperatures and theoretical models, both of which both verified tunneling as the dominant charge transport in the device. Tunneling allowed the operation of the detectors at low bias voltages with good sensitivity. The detector's realized sensitivity at low bias voltage is a significant advantage, allowing the sensor to operate on a small battery or an energy-harvesting source. This is ideal for low-cost wireless sensor networks.The obtained responses, increase in sensitivity, and increase in detection range, wer...