Here, the authors report on a novel shielding technique for the fabrication of electrical contacts on exfoliated graphene by sputtering and lift-off process. The technique solves this problem by removing unwanted gold film in patterning contacts and reduces the high contact resistivity typically found in sputtered devices ranging from 260 to 940 kΩ μm induced by sputtered Au on graphene. By using a shielding tube integrated into our sputtering machine and optimizing the sputtering parameters, contact resistivity as low as 1.04 kΩ μm has been achieved. Consequently, the total device resistivity is significantly reduced, and the yield rate of the devices fabrication has also increased from 17% to 90%.
In this work, solar cells were constructed based polymers prepared as n-type and p-type. Eight polymers were prepared from the reaction of P-phenylene-diamine with carbon disulfide and sulfur by polymerization. The IR, XDR, and thermal history of polymers were studied at room temperature, with thicknesses between (0.7-0.6) mm. Also, Hall factor, the mobility for electrons and holes before and after doping were studied. The polymer solar cells (PSC) were manufactured by depositing n-type polymers on Si/p-type substrate. And p-type polymers on the same area of Si/n-type substrate. The aluminium layer was deposition as an ohmic contact on Si by evaporation under the pressure of 3.5×10-6 Torre the upper electrode, copper metal, was deposited on the surface covered with the polymer film. The I-V characteristics were obtained using a light with a power of 100 mW/cm 2. From I-V curves, the value of the filling factor-FF and power conversion efficiency-Ƞ were calculated. Then to improve the efficiency, four n-type polymers were chosen with the highest electrical conductivity. A solution of 99.9% purity of multi-walled carbon nanotubes (mWCNT) was added by depositing the mixture on a Si/p-type substrate using the spin-coating method. The results of final four cells after improving showed an increasing in the short-circuit current density between J sc =(13.8-19.8) mA/cm 2 , the open-circuit voltage between V oc =(0.345-0.370)V, the FF=(~38%) where the efficiency improved significantly and increased between ŋ =(2.6-4.48)%. The best PSC obtained gave a ŋ =1.07% before improvement, where after adding the carbon nanotube solution, it become about ŋ = 4.48%, that is, an increase of 4.18%. Therefore, the incorporation of carbon nanotubes into the organic conductive polymers can significantly improve the performance of the PSC.
A single-stage amplifier circuits containing transistor as BJT or FET transistor were designed for the microwave application using S-parameters, and developed as a lumped circuit then converted to its equivalent microstrip distributed circuits on different substrates such as Alumina ( r =9.8) and Beryllia ( r =6.3). The output results as power gain G p , noise figure NF, and stability factor K were obtained. These results were compared with other published worked included circuits having the same conditions. The comparison shows that in case of the feedback applied to the circuit the G p achieved about (~1.5) dB for BJT circuits along (0.6-1) GHz and noise figure increased about double, where for FET circuit the increasing in G p about (7) dB along (2) GHz, and noise figure was less than BJT circuit. The physical characteristics are discussed with respect to substrate and show that the substrate with high permittivity was helpful to reach the higher operating frequency and good power gain values.
A pn-junction was successfully fabricated by depositing n-type CdSe thin films on p-type Si as a substrate using chemical bath deposition technique (CBD) at 70 o C. Time of deposition was 6 hours and the preparing solution was changed every 2 hours during the deposition. Sodium Selenosulfate (with different weights) is the source of Se -2 ions, cadmium nitrate is the source of Cd +2 ions. The (I-V) characteristics for the n-CdSe/p-Si junction show it behaves as a Zener diode in reverse bias, with Zener resistance (3 and 27×10 3 ). SEM also shows spherical-shape particles with difference grain size (3.8 and 19.8) nm.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.