Nano science and technology (Solid state gas sensors)

We 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≈2×1015 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 Co60 source, and a change in terminal voltages before and after radiation
were measured accordingly. A sensitivity of 3.259A/kGycm2 at 1V 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, were explained by
studying the band diagrams of the graphene–Schottky junction in comparison to that of the conventional
junction. Further, the fact that graphene layer was grown on the M–S junction adds to the uniqueness
of this research since exfoliated graphene will result in increased contact resistance and lower carrier
mobility which might not yield the desired sensing response.

Tin-oxide-based metal oxide nanoparticles synthesis method and characterization results are
reported. These tin-oxide nanoparticles have been synthesized using the ultrasonic probe method.
The morphology and surface characteristics of synthesized nanoparticles have been analyzed
through electron microscopy and X-ray diffraction technique. The sensitivity of carbon dioxide gas
detection has been tested using a sensing layer prototype.

In this work the recent advances on Pd nanoparticles deposition by electroless deposition technique (EDT) onto ZnO and WO3 nanowires applied to gas sensing applications is reported. The reported nano-structured materials have been synthesized using combinations of conventional CSVT, thermal oxidation and electroless techniques. The CSVT and thermal oxidation techniques were used to obtain ZnO and WO3 metal-oxide nanowires with excellent gas sensing properties. The sensibility was improved by the deposition of Pd nano-particles using a variant of the nobility of EDT. The metallic nature of Pd particle was corroborated by XRD and Raman Scattering (RS). Dynamical-responses to single hydrogen (H2), water vapor (H2O) and Carbon dioxide (CO2) gaseous species using a 4500 PPMv pulse were satisfactory tested by the measure of their electrical resistance change.