Browsing by Author "Sterin, N.S."

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Capacitance and impedance spectroscopy studies of polymer light emitting diodes based on MEH-PPV:BT blends
(2019) Nimith, K.M.; Sterin, N.S.; Das, P.P.; Umesh, G.; Satyanarayan, M.N.
Light emitting polymer poly [2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene] (MEH-PPV) is blended with a wide bandgap electron transport material benzothiadiazole (BT) and its effect on the electronic properties has been studied by capacitance and impedance spectroscopy (IS) in PLEDs. The impedance data is fitted using equivalent circuit models and the minimum parallel resistance (Rp) at zero bias have been obtained for 1:3 ratio of MEH-PPV:BT blended devices. The negative capacitance (NC) shows the occurrence of the trap-assisted non-radiative recombination mechanism at low frequencies in the unblended MEH-PPV PLEDs. Further, this behavior is seen to be reduced in PLEDs with MEH-PPV:BT blends. This clearly suggests that the blending of MEH-PPV and BT at different weight ratios results in the suppression of trap-assisted recombination. This can be attributed to the elimination of trap states due to the dilution of semiconductor material on account of the addition of wide bandgap host material. Moreover, the blended devices have shown a significant improvement in the conductivity at small bias voltages. 2019 Elsevier B.V.
Capacitance and impedance spectroscopy studies of polymer light emitting diodes based on MEH-PPV:BT blends
(Elsevier Ltd, 2019) K M, N.K.; Sterin, N.S.; Das, P.P.; Umesh, G.; Satyanarayan, M.N.
Light emitting polymer poly [2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene] (MEH-PPV) is blended with a wide bandgap electron transport material benzothiadiazole (BT) and its effect on the electronic properties has been studied by capacitance and impedance spectroscopy (IS) in PLEDs. The impedance data is fitted using equivalent circuit models and the minimum parallel resistance (Rp) at zero bias have been obtained for 1:3 ratio of MEH-PPV:BT blended devices. The negative capacitance (NC) shows the occurrence of the trap-assisted non-radiative recombination mechanism at low frequencies in the unblended MEH-PPV PLEDs. Further, this behavior is seen to be reduced in PLEDs with MEH-PPV:BT blends. This clearly suggests that the blending of MEH-PPV and BT at different weight ratios results in the suppression of trap-assisted recombination. This can be attributed to the elimination of trap states due to the dilution of semiconductor material on account of the addition of wide bandgap host material. Moreover, the blended devices have shown a significant improvement in the conductivity at small bias voltages. © 2019 Elsevier B.V.
Dependence of the 0.5 (2e2/h) conductance plateau on the aspect ratio of InAs quantum point contacts with in-plane side gates
(2017) Das, P.P.; Jones, A.; Cahay, M.; Kalita, S.; Mal, S.S.; Sterin, N.S.; Yadunath, T.R.; Advaitha, M.; Herbert, S.T.
The observation of a 0.5 (2e2/h) conductance plateau in asymmetrically biased quantum point contacts (QPCs) with in-plane side gates (SGs) has been attributed to the onset of spin-polarized current through these structures. For InAs QPCs with the same width but a longer channel length, there is roughly a fourfold increase in the range of common sweep voltage applied to the SGs over which the 0.5 (2e2/h) plateau is observed when the QPC aspect ratio (ratio of length over the width of the narrow portion of the structure) is increased by a factor 3. Non-equilibrium Green's function simulations indicate that the increase in the size of the 0.5 (2e2/h) plateau is due to an increased importance, over a larger range of common sweep voltage, of the effects of electron-electron interactions in QPC devices with a larger aspect ratio. The use of asymmetrically biased QPCs with in-plane SGs and large aspect ratio could therefore pave the way to build robust spin injectors and detectors for the successful implementation of spin field effect transistors. 2017 Author(s).
Dependence of the 0.5 × (2e2/h) conductance plateau on the aspect ratio of InAs quantum point contacts with in-plane side gates
(American Institute of Physics Inc. subs@aip.org, 2017) Das, P.P.; Jones, A.; Cahay, M.; Kalita, S.; Mal, S.S.; Sterin, N.S.; Yadunath, T.R.; Advaitha, M.; Herbert, S.T.
The observation of a 0.5 × (2e2/h) conductance plateau in asymmetrically biased quantum point contacts (QPCs) with in-plane side gates (SGs) has been attributed to the onset of spin-polarized current through these structures. For InAs QPCs with the same width but a longer channel length, there is roughly a fourfold increase in the range of common sweep voltage applied to the SGs over which the 0.5 × (2e2/h) plateau is observed when the QPC aspect ratio (ratio of length over the width of the narrow portion of the structure) is increased by a factor 3. Non-equilibrium Green's function simulations indicate that the increase in the size of the 0.5 × (2e2/h) plateau is due to an increased importance, over a larger range of common sweep voltage, of the effects of electron-electron interactions in QPC devices with a larger aspect ratio. The use of asymmetrically biased QPCs with in-plane SGs and large aspect ratio could therefore pave the way to build robust spin injectors and detectors for the successful implementation of spin field effect transistors. © 2017 Author(s).
Redox-Active Vanadium-Based Polyoxometalate as an Active Element in Resistive Switching Based Nonvolatile Molecular Memory
(Wiley-VCH Verlag info@wiley-vch.de, 2020) Sterin, N.S.; Basu, N.; Cahay, M.; Satyanarayan, M.N.; Mal, S.S.; Das, P.P.
Resistive switching (RS)-based random access memory has been envisaged as a viable alternative to existing memory technology due to its nonvolatility, high switching speed, high endurance/retention, and considerably low operating voltage. Herein, a new uniform, repetitive, and stable RS phenomenon is demonstrated based on very low-cost two-terminal metal–insulator–metal stack fabricated using a highly redox-active vanadium-based polyoxometalate (POM) molecular clusters, [V10O28]6?—belonging to polyoxovanadate (POV) family. The RS is observed to be unipolar and nonvolatile in nature, and occur at a fairly low operating bias voltage (less than 2 V), making it suitable for low-power operations. The switching event is attributed to the cycling between formation and rupture of tiny conductive nanofilaments formed due to trapping and detrapping of positively charged ionized oxygen vacancy sites present in the active switching layer of [V10O28]6?. POMs, in their rich abundance, are highly stable early transition-metal oxide nanosized clusters, capable of storing as well as releasing a large number of electrons. In addition, they can undergo fast and reversible redox reactions (both in solid and liquid electrolyte media) in “stepwise” manner—a property that makes them a promising candidate for ultrafast and multi-level nonvolatile molecular memory for high-density data storage. Preliminary investigations on the POV-based memory cells result in device resistance ratio ?25, endurance for more than 200 cycles, and stable retention time around 2200 s, in fully open air condition. © 2020 Wiley-VCH GmbH
Understanding the coexistence of two bipolar resistive switching modes with opposite polarity in CuxO (1 ≤ x ≤ 2)-based two-terminal devices
(Springer, 2022) Sterin, N.S.; Thathron, T.; Mal, S.S.; Das, P.P.
In this work, we have fabricated and tested the resistive switching behavior of non-volatile nature in a number of devices with mainly two architectures: (1) W tip/CuxO/Pt/Ti/SiO2/Si and (2) Cu contact pad/CuxO/Pt/Ti/SiO2/Si. The device type (1) showed coexistence of two bipolar resistive switching modes, commonly known as eight-wise (8w) and counter-eight-wise (c8w), in their current–voltage (I-V) characteristics. We report considerably high ON/OFF ratio of 105 and stable retention time 15 × 103 s. The formation and annihilation of metallic Cu nanofilaments were argued as the plausible reason behind the observed resistive switching events. The onset of quantized conductance steps in the typical conductance plots (in units of quanta of conductance 2e2/h, where e and h are electronic charge and Planck’s constant, respectively) – a phenomenon usually observed in narrow conductive channel – was exploited to provide an “indirect” proof for formation of metallic Cu-based filaments or channels during switching. On the contrary, in device type (2), we observed only “regular” bipolar switching. The operating voltage was less than 1 V in both the devices – suggesting its potential low-power applications. We assessed the underlying conduction mechanism in depth and also theoretically estimated the lateral size of the tiny conductive nanofilaments formed during the switching events. Copper being a cost-effective and widely available substance, our results indicate that CuxO-based cells can be a feasible and useful route for non-volatile resistive memories. © 2021, The Author(s), under exclusive licence to Springer Science+Business Media, LLC, part of Springer Nature.