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Singh C.B.,Samtel Center for Display Technologies | Singh C.B.,SSN College of Engineering | Biswas P.,Indian Institute of Technology Kanpur | Sarkar S.,Indian Institute of Technology Kanpur | And 3 more authors.
Proceedings of the International Conference on Nanoscience, Engineering and Technology, ICONSET 2011

Here, we report the study of growth of CNTs using pulsed DC Plasma Enhanced Chemical Deposition (PECVD) process. Pulsed DC PECVD is employed as it provides enhanced control on arcing and uniformity over large area and thus control on length, diameter and positioning of CNTs. High yields of Multi-Walled Carbon nanotubes with diameters ranging from 40 to 100 nanometers are synthesized by plasma enhanced chemical Vapour deposition system. A layer of Titanium (50 nm) is used as buffer layer and a layer of Nickel (∼10 nm) is used as catalyst layer. Effect of Temperature, growth pressure and acetylene (C 2H 2) concentration on the synthesis of CNTs is studied. CNTs are characterized by Secondary Electron Microscopy (SEM) and Raman spectroscopy. Uniform CNTs growth observed at growth temperature 700°C and 800°C. Raman spectroscopy of CNTs shows that the strength of D-band (Defect-induced band) relative to G-band (Graphite-related optical band) decreases as the growth temperature increases which indicates the crystalline, defects free, uniform diameter and length of aligned CNTs. From temperature 700°C to 800°C, Up-shift in D-band indicates the increase in diameter of CNTs while up-shift in G-band may because of chemical doping in tubes. Downshift in G-band. © 2011 IEEE. Source

Purohit G.,Samtel Center for Display Technologies | Shankar M.,Samtel Center for Display Technologies | Deepak,Samtel Center for Display Technologies | Damodaran S.,Indian Institute of Technology Kanpur | Katiyar M.,Samtel Center for Display Technologies
Proceedings of SPIE - The International Society for Optical Engineering

Molecular electronics, in which a molecule having some nanometers of conjugation length is used as an active element, requires the ability to interface the molecule to macroscopic electronic circuits. For this application, the focused ion beam (FIB) is proposed out of various nano-scale patterning techniques because of its simplicity, minimum time and efforts needed for fabrication of large number of devices. We patterned I-pads with bridge thickness (<10μm) using photolithography and used FIB milling to fabricate contact electrodes separated by hundreds of nanometer. The approach was tested by device fabrication with pentacene deposition on patterned gold pads. We were able to successfully fabricate and demonstrate saturation in large number of organic thin film transistors with channel length in order of 200-300nm by this approach. © 2012 SPIE. Source

Kumar N.,Samtel Center for Display Technologies | Tiwari A.P.,Samtel Center for Display Technologies | Panda S.,Samtel Center for Display Technologies | Panda S.,Indian Institute of Technology Kanpur
ISPTS 2015 - 2nd International Symposium on Physics and Technology of Sensors: Dive Deep Into Sensors, Proceedings

In this work, the annealing effects of e-beam deposited Ta2O5 films on the pH sensitivities of EIS based sensors are presented. XPS studies confirmed that the films annealed above 700 °C showed the best stoichiometry (Ta1.96O5.04) compared to the as deposited film and the films annealed till 600 °C. XRD spectra confirmed the amorphous nature of the as deposited film, which remained amorphous till 600 °C and became polycrystalline above 700 °C. The EIS device showed the maximum sensitivity of 51.4mV/pH for the film annealed at 700 °C, while the device with the as deposited film had a sensitivity of 44.3mV/pH. Further increase in annealing temperature above 700 °C resulted in reduced sensitivity (31.0mV/pH) because of increased interface states (indicated by C-V hysteresis in a MOS device) and enhanced cracks formation in the films (indicated by FESEM). Therefore, the annealing temperature of 700 °C was found to be the optimum annealing temperature for the e-beam deposited Ta2O5 films. © 2015 IEEE. Source

Sharma R.K.,Indian Institute of Technology Kanpur | Sharma R.K.,Samtel Center for Display Technologies | Katiyar M.,Indian Institute of Technology Kanpur | Katiyar M.,Samtel Center for Display Technologies | And 5 more authors.
Physical Chemistry Chemical Physics

If an organic light emitting diode is to be used as part of a matrix addressed array, it should exhibit low reverse leakage current. In this paper we present a method to improve the on/off ratio of such a diode by simultaneous application of heat and electric field post device fabrication. A green OLED with excellent current efficiency was seen to be suffering from a poor on/off ratio of 102. After examining several combinations of annealing along with the application of a reverse bias voltage, the on/off ratio of the same device could be increased by three orders of magnitude, specifically when the device was annealed at 80 °C under reverse bias (-15 V) followed by slow cooling also under the same bias. Simultaneously, the forward characteristics of the device were relatively unaffected. The reverse leakage in the OLED is mainly due to the injection of minority carriers in the hole transport layer (HTL) and the electron transport layer (ETL), in this case, of holes in tris-(8-hydroxyquinoline)aluminum(Alq3) and electrons in 4,4′,4″-tris(N-3-methylphenyl-N-phenylamino)triphenylamine (m-MTDATA). Hence, to investigate these layers adjacent to the electrodes, we fabricated their single layer devices. The possibility of bulk traps present adjacent to electrodes providing states for injection was ruled out after estimating the trap density both before and after the reverse biased annealing. The temperature independent current in reverse bias ruled out the possibility of thermionic injection. The origin of the reverse bias current is attributed to the availability of interfacial hole levels in Alq3 at the cathode work function level in the as-fabricated device; the suppression of the same being attributed to the fact that these levels in Alq3 are partly removed after annealing under an electric field. © the Owner Societies 2016. Source

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