Camptothecin (CPT), a quinoline indole alkaloid, is one of the important inhibitors of eukaryotic DNA topoisomerase I. The highest concentration of this alkaloid has been reported from the fruits of Pyrenacantha volubilis Hook. Here we report the spatial and temporal distribution pattern of CPT in seeds and fruits of P. volubilis. Temporally, CPT content was highest in mature but unripe fruits compared to ripened fruits. Spatially, cotyledonary tissues of the seed had the highest amount of CPT followed by seed coat and fruit coat. This pattern is best explained by selection to deter fruit predators during fruit development, but attracting the fruit dispersers when fruits are mature and ripe.

Vadlapudi R.Rajeev Kumar

Patel Mohana Kumara

Amitava Srimany

Thalappil Pradeep

Department Of Chemistry

Fulltext

Spatial and temporal distribution pattern of camptothecin in seeds and fruits of Pyrenacantha volubilis Hook. (Icacinaceae) during different fruit developmental stages

The built-in potential (Vbi) of an organic diode and solar cell is an important parameter that decides the rectification behavior of organic diodes and affects the open circuit voltage and thereby the efficiency of organic solar cells. In this paper, we propose a physics-based model and an experimental method to extract Vbi from current density-voltage(J-V) characteristics.The proposed model is developed by solving the carrier transport and the continuity equations to obtain the analytic equations for charge carrier profile and current density. The proposed method is thoroughly verified using numerical simulation results. Applicability of thismethod on experimental results is further validated for poly(3-hexylthiophene):phenyl-C61- butyric acid methyl ester solar cells. Finally,Vbi is extracted from dark J-V characteristics of fabricated devices. © 2017 IEEE.

Prashanth Kumar Manda

Saranya Ramaswamy

Soumya Dutta

Department of Electrical Engineering

Analytical models

butyric acid

Carrier transport

Current voltage characteristics

Diodes

Extraction of the built-in potential for organic solar cells from current-voltage characteristics

Luminescence quenching in the presence of polarons is one of the major challenges in organic light emitting devices. In this work, exciton quenching in the presence of polarons is studied using phase sensitive photocurrent measurements on pentacene field effect transistors. The enhancement of conduction in the organic field effect transistors on light illumination is studied using photocurrent spectral response measurements and corresponding optical simulations. The photocurrent is shown to be governed by the polaron mobility and the exciton quenching efficiency, both of which depend on the polaron density in the channel. Two models are proposed on the exciton dynamics in the presence of gate induced polarons in the transistor channel. The first model simulates the steady-state exciton concentration profile in the presence of exciton-polaron interaction. The second one is a three-dimensional steady state exciton-polaron interaction model, which supports the findings from the first model. It is shown that the excitons quench by transferring its energy to polarons, thereby promoting the latter to high energy states in the density of states manifold. The polarons move in the higher energy states with greater microscopic mobility before thermalizing, thereby leading to an enhancement of conduction. It is observed that for the present system, where charge carrier transport is by hopping, all polarons interact with excitons. This implies that for low mobility systems, the interaction is not limited to deep trapped polarons. © 2019 Author(s).

Haripriya Kesavan

Subhamoy Sahoo

Sanjoy Jena

Amogh Kumar Baranwal

Jayeeta Bhattacharyya

Debdutta Ray

Excitons

Light

Light emission

Organic field effect transistors

Study of exciton-polaron interaction in pentacene field effect transistors using high sensitive photocurrent measurements

In this paper, we present the operation principle of an organic metal-insulator-semiconductor (MIS) capacitor where the organic semiconductor is undoped. In spite of a low charge concentration within the semiconductor, this device exhibits a capacitance variation with respect to the applied gate voltage yielding the capacitance-voltage characteristics similar to that of a traditional MIS capacitor based on the doped semiconductor. A physics-based model is developed to derive the charge concentration, surface potential, and the capacitance of the organic MIS capacitor. The model is validated with TCAD simulation results as well as with experimental data obtained from the fabricated organic MIS capacitor consisting of poly(4-vinylphenol) and poly(3-hexylthiophene-2, 5-diyl) as an insulator and a semiconductor, respectively. © 1963-2012 IEEE.

Anjan Chakravorty

Capacitance

Electric charge

Metal insulator boundaries

MIS devices

Organic conductors

Modeling of Organic Metal-Insulator-Semiconductor Capacitor

Contact effect in organic thin film transistor (OTFT) with bottom contact configuration has been considered as a serious issue that renders inferior device performance. In this article, the contact between metal and semiconductor is unveiled to be responsible for hysteresis in bottom gate bottom contact OTFT, consisting of poly(3-hexylthiophene) as semiconductor and cross-linked poly(4-vinylphenol) as polymer dielectric. The correlation between the contact effect and hysteresis is demonstrated by comparing gold contact and silver contact devices with having low and high contact resistances respectively. Negligible hysteresis in gold contact devices in contrary to sizable hysteresis in silver contact devices ensures contact-assisted trapping of charge carriers as the origin of hysteresis. Variation of hysteresis on scaling down the channel length of silver contact devices validates the contact induced hysteresis. A simplistic analysis based on charge trapping in the vicinity of source terminal is proposed to explain the scaling behavior of hysteresis with channel length. © 2018 Elsevier B.V.

Charge trapping

Chemical sensors

Crosslinking

Dielectric devices

Field effect transistors

Scaling of contact metal induced hysteresis in solution processed organic thin film transistors

In this report we address the open circuit voltage (Voc) variation with temperature (T) in details by using TCAD numerical simulation and by developing physics based model. The proposed model is in good agreement with the TCAD simulation and is able to explain the experimentally observed (Voc) variation with different temperature and intensity. © Springer Nature Switzerland AG 2019.

Rajdeep Dhar

ELECTRONIC DESIGN AUTOMATION

organic solar cells

Semiconductor devices

Solar cells

Timing circuits

Temperature dependent open circuit voltage variation of organic solar cells

The application of Mott-Schottky (MS) relation in organic devices often leads to erroneous results. In particular, the doping density, extracted using this method found to vary with the thickness of semiconductor. We address the limitations in using MS relationship for organic metal-insulator-semiconductor (MIS) capacitors as a consequence of deviation from the depletion approximation. © Springer Nature Switzerland AG 2019.

Karunakaran Logesh

Semiconductor doping

DEPLETION APPROXIMATION

Limitations of mott-schottky analysis for organic metal-insulator-semiconductor capacitors

Using a sample of 448.1×106 ψ(3686) events collected with the BESIII detector, we perform a study of the decay ψ(3686)→φπ+π-η. The branching fraction of ψ(3686)→φη′ is determined to be (1.51±0.16±0.12)×10-5, which is consistent with the previous measurement but with significantly improved precision. The resonances f1(1285) and η(1405) are clearly observed in the π+π-η mass spectrum with statistical significances of 18σ and 9.7σ, respectively. The corresponding product branching fractions are measured to be B(ψ(3686)→φf1(1285), f1(1285)→π+π-η)=(1.03±0.10±0.09)×10-5 and B(ψ(3686)→φη(1405), η(1405)→π+π-η)=(8.46±1.37±0.92)×10-6. These results are used to test the perturbative QCD "12% rule." © 2019 authors. Published by the American Physical Society.

Jim Libby

Department Of Physics

K. Ravindran

Measurement of branching fractions of ψ (3686) →φη′, φf1 (1285) and φη (1405)

The four decay modes D0→ϕπ0, D0→ϕη, D+→ϕπ+, and D+→ϕK+ are studied by using a data sample taken at the centre-of-mass energy s=3.773 GeV with the BESIII detector, corresponding to an integrated luminosity of 2.93 fb−1. The branching fractions of the first three decay modes are measured to be B(D0→ϕπ0)=(1.168±0.028±0.028)×10−3, B(D0→ϕη)=(1.81±0.46±0.06)×10−4, and B(D+→ϕπ+)=(5.70±0.05±0.13)×10−3, respectively, where the first uncertainties are statistical and the second are systematic. In addition, the upper limit of the branching fraction for D+→ϕK+ is given to be 2.1×10−5 at the 90% confidence level. The ratio of B(D0→ϕπ0) to B(D+→ϕπ+) is calculated to be (20.49±0.50±0.45)%, which is consistent with the theoretical prediction based on isospin symmetry between these two decay modes. © 2019 The Author(s)

Measurement of branching fractions for D meson decaying into ϕ meson and a pseudoscalar meson

By analyzing 2.93 fb-1 of e+e- annihilation data taken at the center-of-mass energy s=3.773 GeV with the BESIII detector, we determine the branching fractions of the inclusive decays D+→φX and D0→φX to be (1.135±0.034±0.031)% and (1.091±0.027±0.035)%, respectively, where X denotes any possible particle combination. The first uncertainties are statistical, and the second are systematic. We also determine the branching fractions of the decays D→φX and their charge conjugate modes D→φX separately for the first time, and no significant CP asymmetry is observed. © 2019 authors. Published by the American Physical Society.

Improved measurements of the absolute branching fractions of the inclusive decays D+ (0) →φX

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