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113 results on '"Guha, Suchismita"'

6. Molecularly Engineered Quinoxaline-Pyridyl Pyrazine Polymers for Field-Effect Transistors and Complementary Circuits

Author

Barron, John, Attar, Salahuddin, Ghobadi, Arash, Gangopadhyay, Shubhra, Sredojević, Dušan, Al-Hashimi, Mohammed, Guha, Suchismita, Barron, John, Attar, Salahuddin, Ghobadi, Arash, Gangopadhyay, Shubhra, Sredojević, Dušan, Al-Hashimi, Mohammed, and Guha, Suchismita

Abstract

Regioregularity in conjugated polymers plays a significant role in enhancing the semiconducting properties and narrowing the optical band gap. Two donor–acceptor copolymers, specifically quinoxaline-thienylenevinylene (P1) and regioregular pyridyl pyrazine-thienylenevinylene (P2), were synthesized and characterized. Their potential applications in organic field-effect transistors (FETs) and complementary inverter circuits were explored. P2 exhibits a narrower absorption spectrum with distinct vibronic peaks compared to P1. In both top-gate and bottom-gate FET architectures, the copolymers display p-type behavior, with P2 demonstrating approximately an order of magnitude higher carrier mobility (∼10–3 cm2/(V s)) than P1. The performance of the FETs is further improved by the surface treatment of the source–drain contacts, which is particularly noticeable in P1. These p-type FETs, incorporating P1 and P2, were employed in complementary voltage inverter circuits along with thiazole-selenophene-linked fluorinated isoindigo (IID-TzSe) n-type organic FETs. The P1–IID-TzSe inverter, characterized by balanced p- and n-channels with similar threshold voltages, shows a gain >20 at a supply voltage of 50 V. Similar gains are also observed in the P2–IID-TzSe inverter circuits.

Published
2024

13. Weak magnetic field-dependent photoluminescence properties of lead bromide perovskites.

Author

Butler, Rory, Burns, Randy, Babaian, Dallar, Anderson, Matthew J., Ullrich, Carsten A., Morrell, Maria V., Xing, Yangchuan, Lee, Jaewon, Yu, Ping, and Guha, Suchismita

Subjects
PEROVSKITE, MAGNETIC field effects, RASHBA effect, PHOTOLUMINESCENCE, MAGNETIC fields, BAND gaps, SPIN-orbit interactions
Abstract

The strong spin–orbit coupling (SOC) in lead halide perovskites, when inversion symmetry is lifted, has provided opportunities for investigating the Rashba effect in these systems. Moreover, the strong orbital moment, which, in turn, impacts the spin-pair in singlet and triplet electronic states, plays a significant role in enhancing the optoelectronic properties in the presence of external magnetic fields in lead halide perovskites. Here, we investigate the effect of weak magnetic fields (<1 T) on the photoluminescence (PL) properties of CsPbBr 3 nanocrystals with and without Ruddlesden–Popper (RP) faults and single crystals of CH 3 NH 3 PbBr 3. Along with an enhancement in the PL intensity as a function of an external magnetic field, which is observed in both lead bromide perovskites, the PL emission red-shifts in CsPbBr 3 nanocrystals. Density-functional theory calculations of the electronic band-edge in CsPbBr 3 show almost no change in the energy gap as a function of the external magnetic field. The experimental results, thus, suggest the role of mixing of the triplet and singlet excitonic states under weak magnetic fields. This is further deduced from an enhancement in PL lifetimes as a function of the field in CsPbBr 3. In CH 3 NH 3 PbBr 3 , an increase in PL intensity is observed under weak magnetic fields; however, no changes in the peak energy or PL lifetimes are observed. The internal magnetic fields due to SOC are characterized for all three samples and found to be the highest for CsPbBr 3 nanocrystals with RP faults. [ABSTRACT FROM AUTHOR]

Published
2022
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22. Visualizing transport in thiazole flanked isoindigobased donor-acceptor polymer field-effect transistors.

Author

Barron, John, Attar, Salahuddin, Bhattacharya, Payal, Ping Yu, Al-Hashimi, Mohammed, and Guha, Suchismita

Abstract

Fluorination of donor-acceptor copolymers has been one strategy towards enhancing polymer coplanarity, increasing crystallinity, and improving charge transport mechanisms in organic devices. Herein, we report on the synthesis of thiazole flanked fluorinated isoindigo (IID) copolymers and demonstrate their field-effect transistor (FET) properties. The selenophene-substituted IID shows improved performance over the thiophene units. Different FET geometries were fabricated and tested. Top-gate FETs with varying dielectric layers showed n-type transport with electron carrier mobilities of the order of 10-2 cm² V-1 s-1 and on/off ratio of 105. Along with improving the electronic properties, fluorination is an effective means of enhancing the nonlinear optical properties. We exploit this feature by observing the semiconductor-dielectric polarization induced by the applied electric field and the injected carriers. Time-resolved electric field-induced second harmonic generation method is used to visualize the carrier motion within the FET channel region, which gives an alternate estimate of the electron carrier mobility, free from contact resistance issues. [ABSTRACT FROM AUTHOR]

Published
2022
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27. SERS active self-assembled diphenylalanine micro/nanostructures: A combined experimental and theoretical investigation.

Author

Kogikoski, Jr., Sergio, Khanra, Soma, Alves, Wendel A., and Guha, Suchismita

Subjects
SERS spectroscopy, DIPHENYLAMINE, NANOSTRUCTURED materials, GOLD nanoparticles, PHASE transitions, DENSITY functional theory, MOLECULAR structure
Abstract

Enhancing Raman signatures of molecules by self-assembled metal nanoparticles, nanolithography patterning, or by designing plasmonic nanostructures is widely used for detection of low abundance biological systems. Self-assembled peptide nanostructures provide a natural template for tethering Au and Ag nanoparticles due to its fractal surface. Here, we show the use of L,L-diphenylalanine micro-nanostructures (FF-MNSs) for the organization of Ag and Au nanoparticles (Nps) and its potential as surface-enhanced Raman scattering (SERS)-active substrates. The FF-MNSs undergo an irreversible phase transition from hexagonally packed (hex) micro-nanotubes to an orthorhombic (ort) structure at ~150 °C. The metal Nps form chains on hex FF-MNSs as inferred from transmission electron microscopy images and a uniform non-aggregated distribution in the ort phase. The high luminescence from the ort FF-MNS phase precludes SERS measurements with AgNps. The calculated Raman spectra using density-functional theory shows a higher intensity from rhodamine 6G (R6G) molecule in the presence of an Ag atom bound to ort FF compared with hex FF. The SERS spectra obtained from R6G bound to FF-MNSs with AuNps clearly show a higher enhancement for the ort phase compared with hex FF, corroborating our theoretical calculations. Our results indicate that FFMNSs both in the hex and ort phases can be used as substrates for the SERS analysis with different metal nanoparticles, opening up a novel class of optically active bio-based substrates. [ABSTRACT FROM AUTHOR]

Published
2017
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33. Measuring structural inhomogeneity of a helical conjugated polymer at high pressure and temperature

Author

Arge, Tummas Napoleon, Konôpková, Zuzana, Haase, Dörthe, Liermann, Hanns-Peter, Scherf, Ullrich, Guha, Suchismita, Knaapila, Matti, Arge, Tummas Napoleon, Konôpková, Zuzana, Haase, Dörthe, Liermann, Hanns-Peter, Scherf, Ullrich, Guha, Suchismita, and Knaapila, Matti

Abstract

We report on X-ray scattering measurements of helical poly[9,9-bis(2-ethylhexyl)-fluorene-2,7-diyl] by mapping the sample with 10μm spatial resolution from 0.3 GPa to 36 GPa. We follow the strongest 00/reflection, which moves toward higher scattering angles with pressure indicating planarization of helical polyfluorene. Lateral inhomogeneity is increased for >10 GPa concomitant with the solidification of the pressure transmitting medium (a 4:1 mixture of methanol and ethanol). We also follow the 00/reflection with increasing temperature at the constant pressure of 4.3 GPa in neon. We observe a sharp shift toward higher scattering angles indicative of a phase transition at 167–176 °C.

Published
2019

36. Peptide-Based Assemblies on Electrospun Polyamide-6/Chitosan Nanofibers for Detecting Visceral Leishmaniasis Antibodies

Author

Liberato, Michelle S., primary, Mancini, Rodrigo S. N., additional, Factori, Irina M., additional, Ferreira, Fabio F., additional, de Oliveira, Vivian L., additional, Carnielli, Juliana B. T., additional, Guha, Suchismita, additional, Peroni, Luis A., additional, Oliveira, Marcone A. L., additional, and Alves, Wendel A., additional

Published
2019
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40. Correlating charge transport to structure in deconstructed diketopyrrolopyrrole oligomers: A case study of a monomer in field-effect transistors

Author

Pickett, Alec, Torkkeli, Mika, Mukhopadhyay, Tushita, Puttaraju, Boregowda, Laudari, Amrit, Lauritzen, Andreas, Bikondoa, Oier, Kjelstrup-Hansen, Jakob, Knaapila, Matti, Patil, Satish, Guha, Suchismita, Pickett, Alec, Torkkeli, Mika, Mukhopadhyay, Tushita, Puttaraju, Boregowda, Laudari, Amrit, Lauritzen, Andreas, Bikondoa, Oier, Kjelstrup-Hansen, Jakob, Knaapila, Matti, Patil, Satish, and Guha, Suchismita

Abstract

Copolymers based on diketopyrrolopyrrole (DPP) cores have attracted a lot of attention due to their high p-type as well as n-type carrier mobilities in organic field-effect transistors (FETs) and high power conversion efficiencies in solar cell structures. We report the structural and charge transport properties of n-dialkyl side-chain substituted thiophene DPP end-capped with a phenyl group (Ph-TDPP-Ph) in FETs which were fabricated by vacuum deposition and solvent coating. Grazing incidence X-ray diffraction (GIXRD) from bottom-gate, bottom-contact FET architectures were measured with and without biasing. Ph-TDPP-Ph reveals polymorphic structure with π-conjugated stacking direction oriented in-plane. The unit cell comprises either one monomer with a=20.89 Å, b=13.02 Å, c=5.85 Å, α=101.4°, β=90.6°, and γ=94.7° for one phase (TR1), or two monomers with a=24.92 Å, b=25.59 Å, c=5.42 Å, α=80.3°, β=83.5°, and γ=111.8° for the second phase (TR2). The TR2 phase thus signals a shift from a coplanar to herringbone orientation of the molecules. The device performance is sensitive to the ratio of the two triclinic phases found in the film. Some of the best FET performances with p-type carrier mobilities of 0.1 cm2/Vs and on/off ratio of 106 are for films that comprise mainly the TR1 phase. GIXRD from in-operando FETs demonstrates the crystalline stability of Ph-TDPP-Ph.

Published
2018

41. Correlating Charge Transport with Structure in Deconstructed Diketopyrrolopyrrole Oligomers: A Case Study of a Monomer in Field-Effect Transistors

Author

Pickett, Alec, primary, Torkkeli, Mika, additional, Mukhopadhyay, Tushita, additional, Puttaraju, Boregowda, additional, Laudari, Amrit, additional, Lauritzen, Andreas E., additional, Bikondoa, Oier, additional, Kjelstrup-Hansen, Jakob, additional, Knaapila, Matti, additional, Patil, Satish, additional, and Guha, Suchismita, additional

Published
2018
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47. Pressure-Induced Phase Changes in Cesium Lead Bromide Perovskite Nanocrystals with and without Ruddlesden–Popper Faults

Author

Yesudhas, Sorb, Morrell, Maria V., Anderson, Matthew J., Ullrich, Carsten A., Kenney-Benson, Curtis, Xing, Yangchuan, and Guha, Suchismita

Abstract

Lead halide perovskites have a rich landscape of structural and optical properties, which can be explored and possibly controlled by applying high pressure. Despite several reports on high-pressure studies of CsPbBr3nanocrystals (NCs), there have so far been no studies under pressure that incorporate planar defects. CsPbBr3NCs with Ruddlesden–Popper (RP) faults, formed via post-synthetic fusion growth, are significantly larger in size than as-synthesized NCs and display exceptional emission stability. Here, we compare synchrotron-based high-pressure X-ray diffraction and photoluminescence (PL) properties of CsPbBr3(without RP) and RP-CsPbBr3(with RP) and resolve their crystal structure under pressure for the first time. CsPbBr3undergoes a phase transition from the orthorhombic Pnmaphase at ambient pressure to the cubic Pm3̅mphase at 1.7 GPa, and RP-CsPbBr3transforms from Pnmato the monoclinic P21/mphase at 0.74 GPa in addition to several isostructural transitions. Density-functional calculations predict a narrowing of the band gap with pressure, concomitant with the PL energies. The RP-CsPbBr3NCs exhibit enhanced PL intensity at 1 GPa and show band gap opening at high pressures. This study opens new strategies for not only tuning just the structural properties but also tuning planar defects in alkali halide lead crystals for improved optical properties.

Published
2020
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