Mid-infrared characterization of thiophene-based thin polymer films

AbstractOptical properties of seven regioregular poly(3-alkylthiophene) with different alkyl side chain lengths which are poly(3-butylthiophene-2,5-diyl) (P3BT), poly(3-pentylthiophene-2,5-diyl) (P3PT), poly(3-hexylthiophene-2,5-diyl) (P3HT), poly(3-heptylthiophene-2,5-diyl) (P3hept), poly(3-octylthiophene-2,5-diyl) (P3OT), poly(3-decylthiophene-2,5-diyl) (P3DT), and poly(3-dodecylthiophene-2,5-diyl) (P3DDT) have been studied in the mid-infrared (IR) spectral region by means of Fourier Transformation Infrared (FTIR) spectroscopy and IR spectroscopic ellipsometry (IRSE). Absorbance spectra obtained in this fingerprint region are potential to characterize the structures formed by organic molecules in thin films due to molecular vibrations in detail. In consequence, the vibrational absorption bands of these seven samples demonstrated that P3PT, P3HT, and P3hept exhibited very similar band profiles, in contrast, the stretching vibration of thiophene rings (≈1465cm−1: CC) underwent a blue shift in P3BT, P3OT, P3DT and P3DDT. The highest value of the real part (ɛ1) of the complex dielectric constant was obtained from P3HT on both indium thin oxide (ITO) and silicon (Si) substrates whereas the imaginary part (ε2) was directly affected by increasing in the alkyl side chain lengths in a frequency range around 3000cm−1. The optical properties of P3PT in the mid-IR region developed an affinity with those of P3HT. Thus, P3PT is particularly a suitable polymer active material candidate for high-performance devices

Динаміка збудження автоіонізаційних станів в атомі рубідію

З використанням методу електронної спектроскопії, нами досліджені функції збудження (ФЗ) деяких дублетних та квартетних автоіонізаційних станів (АІС), які представлені на рис.1. Похибка при визначенні ефективних перерізів збудження не перевищувала 30%

Non-stoichiometric amorphous magnesium-iron silicates in circumstellar dust shells. Dust growth in outflows from supergiants

We investigate the dust growth in oxygen-rich stellar outflows for a set of nine well-observed massive supergiants with optically thin dust shells. Models of the infrared emission from their circumstellar dust shells are compared to their observed infrared spectra so as to derive the essential parameters that govern dust formation in the extended envelope of these stars. The results obtained from the comparative study are also compared with the predictions of a model for silicate dust condensation solely based on laboratory data and basic stellar properties. The infrared emission in the wavelength range between 6 and 25 mu can be reproduced rather well by a mixture of non-stoichiometric iron-bearing silicates, alumina, and metallic iron dust particles for all nine objects. The observed spectra obtained from three objects, mu Cep, RW Cyg, and RS Per, can be reproduced by a stationary and (essentially) spherically symmetric outflow which enables a direct comparison with predictions from a theoretical dust growth model. The temperature at the onset of massive silicate dust growth is of the order of 920 K and the corresponding outflow velocity of the order of the sound velocity for these objects. The condensation temperature suggests that the silicate dust grows on the corundum dust grains that are formed well in the interior of the silicate dust shell at a much higher temperature. Our results propose that regarding the two major problems of dust formation in stellar outflows: (i) formation of seed nuclei; (ii) their growth to macroscopic dust grains, we are gradually coming close to a quantitative understanding of the second item.Comment: 29 pages, 9 figures, accepted by Astronomy & Astrophysic

A2BC-Type Porphyrin SAM on Gold Surface for Bacteria Detection Applications: Synthesis and Surface Functionalization

Currently used elaborate technologies for the detection of bacteria can be improved in regard to their time consumption, labor intensity, accuracy and reproducibility. Well-known electrical measurement methods might connect highly sensitive sensing systems with biological requirements. The development of modified sensor surfaces with self-assembled monolayers (SAMs) from functionalized porphyrin for bacteria trapping can lead to a highly sensitive sensor for bacteria detection. Different A2BC-type porphyrin structures were synthesized and examined regarding their optical behavior. We achieved the synthesis of a porphyrin for SAM formation on a gold surface as electrode material. Two possible bio linkers were attached on the opposite meso-position of the porphyrin, which allows the porphyrin to react as a linker on the surface for bacteria trapping. Different porphyrin structures were attached to a gold surface, the SAM formation and the respective coverage was investigated

Functionalized tetrapodal diazatriptycenes for electrostatic dipole engineering in n-type organic thin film transistors

V.R., F.S.B., S.H., M.M., M.-M.B., S.H., J.F., W.K., W.J., A.K., A.P., U.H.F.B., and K.M. acknowledge the German Federal Ministry of Education and Research (BMBF) for financial support within the INTERPHASE project (nos. 13N13656, 13N13657, 13N13658, 13N13659). V.R. thanks the German Research Foundation for financial support within the SFB1249 project and the Heidelberg Graduate School of Fundamental research.The authors also appreciate financial support by the German Research Foundation (grant ZH 63/39-1) and by the DAAD-ACEH Scholarship of Excellence (A.A.).A diazatriptycene‐based tetrapodal scaffold with thiol anchors enforces a nearly upright orientation of functional groups, introduced to its quinoxaline subunit, with respect to the substrate upon formation of self‐assembled monolayers (SAMs). Substitution with electron‐withdrawing fluorine and cyano as well as electron‐rich dimethylamino substituents allows tuning of the molecular dipole and, consequently, of the work function of gold over a range of 1.0 eV (from 3.9 to 4.9 eV). The properties of the SAMs are comprehensively investigated by infrared reflection absorption spectroscopy, near edge X‐ray absorption fine structure spectroscopy, and X‐ray photoelectron spectroscopy. As prototypical examples for the high potential of the presented SAMs in devices, organic thin‐film transistors are fabricated.Publisher PDFPeer reviewe

Analytical Study of Solution‐Processed Tin Oxide as Electron Transport Layer in Printed Perovskite Solar Cells

Solution‐processed tin oxide (SnOₓ) electron transport layers demonstrate excellent performance in various optoelectronic devices and offer the ease of facile and low cost deposition by various printing techniques. The most common precursor solution for the preparation of SnOₓ thin films is SnCl₂ dissolved in ethanol. In order to elucidate the mechanism of the precursor conversion at different annealing temperatures and the optoelectronic performance of the SnOₓ electron transport layer, phonon and vibrational infrared and photoelectron spectroscopies as well as atomic force microscopy are used to probe the chemical, physical, and morphological properties of the SnOₓ thin films. The influence of two different solvents on the layer morphology of SnOₓ thin films is investigated. In both cases, an increasing annealing temperature not only improves the structural and chemical properties of solution‐processed SnOₓ, but also reduces the concentration of tin hydroxide species in the bulk and on the surface of these thin films. As a prototypical example for the high potential of printed SnOₓ layers for solar cells, high performance perovskite solar cells with a stabilized power conversion efficiency of over 15% are presented

n-type doping of organic semiconductors : immobilization via covalent anchoring

We gratefully acknowledge the German Federal Ministry of Education and Research (BMBF) for financial support within the InterPhase project (FKZ 13N13659, 13N13656, 13N13657, and 13N13658).Electrical doping is an important tool in the design of organic devices to modify charge carrier concentration in and Fermi level position of organic layers. The undesired diffusion of dopant molecules within common transport materials adversely affects both lifetime and device performance. To overcome this drawback, we developed a strategy to achieve immobilization of dopants through their covalent attachment to the semiconductor host molecules. Derivatization of the commonly employed n-type dopant 2-(2-methoxyphenyl)-1,3-dimethyl-2,3-dihydro-1H-benzoimidazole (ο-MeO-DMBI) with a phenylazide enables the resulting o-AzBnO-DMBI to photochemically generate a reactive nitrene, which subsequently binds covalently to the host material, 6,6-phenyl-C61-butyric acid methyl ester (PCBM). Both the activation and addition reactions are monitored by mass spectrometry as well as optical and photoelectron spectroscopy. A suppression of desorption and a decrease in volatility of the DMBI derivative in ultrahigh vacuum were observed after activation of a bilayer structure of PCBM and o-AzBnO-DMBI. Electrical measurements demonstrate that the immobilized o-AzBnO-DMBI can (i) dope the PCBM at conductivities comparable to values reported for o-MeO-DMBI in the literature and (ii) yield improved electrical stability measured in a lateral two terminal device geometry. Our immobilization strategy is not limited to the specific system presented herein but should also be applicable to other organic semiconductor–dopant combinations.Publisher PDFPeer reviewe