Frank Balzer

University of Duisburg-Essen | uni-due

Oriented, fluorescing organic nanoaggregates derived from 1,4```-dicyano-functionalized para-quaterphenylene (CNP4) are obtained upon vacuum deposition on muscovite mica. Two types of aggregates are observed with fiber- and wing-like shape, respectively, both growing along distinct substrate directions. The polarization of the emitted fluorescence,...

Structural diffraction analysis of an anilino squaraine with branched isobutyl side chains (SQIB) shows crystallization into two polymorphic structures in the bulk and in spin-casted thin films. We observe multi-peaked and pleochroic absorption spectra being blue-(red)-shifted for the monoclinic (orthorhombic) polymorph. We understand the packing a...

Molecular chirality and the inherently connected differential absorption of circular polarized light (CD) combined with semiconducting properties offers great potential for chiral opto-electronics. Here we discuss the temperature-controlled assembly of enantiopure prolinol functionalized squaraines with opposite handedness into intrinsically circul...

Organic semiconductors are emerging as promising candidates for novel electrically self‐sufficient photovoltaic prosthetics for neurostimulation, especially for restoration of light sensitivity in degenerate retina. Considering future applications, it is essential to gain fundamental insight into the signaling mechanisms at the organic photosensor–...

The use of polarized light for the analysis of organicmicro- and nanofibers from π-conjugated smallmolecules grown on or transferred to surfaces such as mica, alkali halides, graphite, and glass is explored. Often the fibers emit strongly polarized light after UV excitation. Via image processing the polarization of the fluorescence is used to deter...

Organic molecular beam deposition (OMBD) of para-hexaphenylene (p6P) on polycrystalline platinum results in the formation of unique nanoaggregates, predominantly as nanofibers and nanoribbons. These aggregates exhibit distinct morphological properties, as revealed by atomic force microscopy (AFM). Grazing incidence X-ray diffraction (GIXD) confirms...

ABSTRACT: This article presents a parameterized response model that enhances the Limit of Detection (LOD) of piezoelectrically driven microcantilever (PD-MC) based gas sensors by accounting for the adsorption-induced variations in elastic properties of the functionalization layer (binder) and the non-linear-motional-dynamics-of the PD-MC. The devel...

Prototypical n-alkyl-terminated anilino squaraines for photovoltaic applications show characteristic double-hump absorption features peaking in the green and deep-red spectral range. These signatures result from the coupling of an intramolecular Frenkel exciton and an intermolecular charge-transfer exciton. Crystalline, textured thin films suitable...

The impact on chiral aggregation in solution processed and thermally annealed thin films of two indolenine and one anilino squaraines with chiral (S)-citronellyl functionalization at the nitrogen of the squaraine backbone is investigated. A pseudo polymorphic crystal structure is obtained for one of the indolenine squaraines, but thin films of both...

Controlling the polymorph formation in organic semiconductor thin films by the choice of processing parameters is a key factor for targeted device performance. Small molecular semiconductors such as the prototypical anilino squaraine compound with branched butyl chains as terminal functionalization (SQIB) allow both solution and vapor phase deposit...

Controlling the polymorph formation in organic semiconductor thin films by the choice of substrate and deposition temperature is a key factor for targeted device performance. Small molecular semiconductors such as the quadrupolar donor-acceptor-donor (D-A-D) type squaraine compounds allow both solution and vapor phase deposition methods. A prototyp...

Prototypical n-alkyl terminated anilino squaraines for photovoltaic applications show characteristic double-hump absorption features peaking in the green and deep-red spectral range. These signatures result from coupling of an intramolecular Frenkel exciton and an intermolecular charge transfer exciton. Crystalline, textured thin films suitable for...

Polycrystalline textured thin films with distinct pleochroism and birefringence comprising oriented rotational domains of the orthorhombic polymorph of an anilino squaraine with isobutyl side chains (SQIB) are analyzed by imaging Mueller matrix ellipsometry to obtain the biaxial dielectric tensor. Simultaneous fitting of transmission and oblique in...

Solution-processed and thermally annealed thin films from a series of n-alkyl terminated anilino squaraines are systematically investigated regarding their structural and optical properties by means of X-ray diffraction (XRD) and spectroscopic ellipsometry (SE). Their characteristic intense double-hump-shaped absorbance spectra consisting of couple...

An enantiomerically pure (R)‐2‐methylpyrrolidine‐based anilino squaraine crystallizes in two chiral polymorphs adopting a monoclinic C2 and an orthorhombic P212121 structure, respectively. By various thin‐film preparation techniques, a control of the polymorph formation is targeted. The local texture of the resulting textured thin films is connecte...

Poster for the cancelled DPG spring conference in Dresden.

Local polarized surface photovoltage (SPV) spectroscopy is used to characterize an organic squaraine‐fullerene photovoltaic layer blend. The anisotropic optical response of the textured photoactive layer is dominated by the largely Davydov‐split absorption within the deep red of the crystallized donor compound. Through knowledge of the crystallogra...

We show a facile route to soft matter bulk heterojunction photodiode detectors sensitive to the circular polarization state of light. The device is based on the intrinsic excitonic circular dichroism of the photoactive layer. Within the green spectral range the photodiodes convert circular polarized light into a handedness-dependent photocurrent wi...

We intend to develop a minimal invasive implantable neurostimulating device based on organic photovoltaic compounds for restoration of light sensitivity in degenerated retina. The present study investigates whether single neuroblastoma (N2A) cells, grown on a photosensor based on a small molecular squaraine:fullerene photoactive layer blend, option...

A facile route to soft matter self-powered bulk heterojunction photodiode detectors sensitive to the circular polarization state of light is shown based on the intrinsic excitonic circular dichroism of the photoactive layer blend. As light detecting materials, enantiopure semiconducting small molecular squaraine derivates of opposite handedness are...

Sizable ex-chiral-pool synthesis of enantiopure prolinol functionalized squaraine small molecular compounds with opposite handedness has been achieved. Early stage aggregation in solution shows formation of H-aggregates with helical stacking. Thermal annealing of spin-casted thin films induces further supramolecular aggregation into J-aggregates wi...

The epitaxial growth of the mono-functionalized para-quaterphenylene molecule CNHP4 on muscovite mica is investigated. The vacuum deposited molecules aggregate into nanofibers of varying morphology. Due to muscovite’s cm symmetry, almost mutually parallel fibers grow. Polarized light microscopy together with X-ray diffraction resolves the projected...

As a step towards the realization of neuro-prosthetics for vision restoration, we follow an electrophysiological patch-clamp approach to study the fundamental photoelectrical stimulation mechanism of neuronal model cells by an organic semiconductor-electrolyte interface. Our photoactive layer consisting of an anilino-squaraine donor blended with a...

Thin films from conjugated small molecule semiconductors are important building blocks for organic electronics, but can also serve as active or passive templates for biological applications. Functionalization can control their electrical and optical properties, and even change the thin film morphology. Cyano-functionalization is of special interest...

Vacuum deposition of the methoxy-functionalized p-quaterphenylene MOP4 on muscovite mica at elevated temperatures led to the formation of several ten micrometer long nanofibers. As shown by X-ray diffraction and polarized optical microscopy, the fibers are formed by lying molecules which grow epitaxially (point-on-line coincidence) along two direct...

Semiconductor-electrolyte interfaces are of major importance for technologically relevant applications such as photoelectrochemical cells and batteries and, more recently, also for biomedical devices such as retinal implants. The latter benefit from implementing organic materials, which are able to form intimate contact with biological tissue. Besi...

The epitaxial growth of the methoxy functionalized para-quaterphenylene (MOP4) on the (001) faces of the alkali halides NaCl and KCl and on glass is investigated by a combination of low energy electron diffraction (LEED), polarized light microscopy (PLM), atomic force microscopy (AFM), and X-ray diffraction (XRD). Both domains from upright molecule...

Continuous and discontinuous thin films from small rod like conjugated organic molecules such as the acenes, the para-phenylenes, and the thiophenes have extensively been investigated in the past due to their potential in optoelectronic devices. Functionalization of the building blocks can selectively improve both the electrical as well as the opti...

Continuous and discontinuous thin films from small rod like conjugated organic molecules such as the acenes, the para-phenylenes, and the thiophenes have extensively been investigated in the past due to their potential in optoelectronic devices. Functionalization of the building blocks can selectively improve both the electrical as well as the opti...

Organic molecular beam grown α-sexithiophene (α-6 T) forms nanostructured thin films on buckminsterfullerene (C60) thin film layers. At substrate temperatures of 300 K during growth a rough continuous film is observed, which develops to larger elongated islands and dendritic- as well as needle like structures at temperatures around 390 K. X-ray dif...

Functionalization of small, rod like organic molecules can be used to optimize organic devices. Here we report on nanofiber formation and thin film growth of a methoxy-functionalized para-quaterphenylene (1,4'''-Dimethoxy- 4,1':4',1'':4'',1'''-quaterphenylene, MOP4) on prototypical dielectric substrates such as muscovite mica, phlogopite mica, high...

It has been shown in the past that methoxy functionalization of para-quaterphenylene substantially improves the formation of aligned nanofibers. Here the influence of methoxy functionalization on the growth of another class of small, semiconducting organic molecules is investigated, i.e. on the formation of nanoaggregates from naphthyl end-capped o...

Naphthyl end-capped oligothiophenes are a class of materials well suited for high-performance organics based devices. The formation of nanofibers on muscovite mica from 2,5-bis(naphth-2-yl)thiophene (NaT), 5,5'-bis(naphth-2-yl)-2,2'-bithiophene (NaT2), and 5,5''-bis(naphth-2-yl)-2,2':5',2''-terthiophene (NaT3) as well as of the methoxy-functionaliz...

We observe the formation of thin films of fibre-like aggregates from the prototypical organic semiconductor molecule para-hexaphenylene (p-6P) on graphite thin flakes and on monolayer graphene. Using atomic force microscopy, scanning electron microscopy, x-ray diffraction, polarized fluorescence microscopy, and bireflectance microscopy, the molecul...

Organic semiconductors from small molecules such as para-phenylenes or thiophenes promise a vast application potential as the active ingredient in electric and optoelectronic devices. Their growth and self-organization into organic nanowires adds a peculiar attribute, where mutually aligned entities are of interest. Different methods for nanowire f...

Organic semiconductors formed by epitaxial growth from small molecules such as the para-phenylenes or squaraines promise a vast application potential as the active ingredient in electric and optoelectronic devices. Their self-organization into organic nanowires or "nanofibers" adds a peculiar attribute, making them especially interesting for light...

Environmentally stable, non-toxic squarylium dyes with strong absorption maxima in the red and near infrared spectral region are known for almost fifty years. Despite the fact that their optoelectronic properties distinguish them as promising materials for organics based photovoltaic cells, they have regained attention only very recently. For their...

Results are presented from a direct comparison of 2,7-diphenylcarbazole (DPC) nanofibers fabricated in the form of parallel to the surface plane aligned arrays by means of organic molecular beam deposition (OMBD) and fabricated in the form of normal to the surface aligned arrays by solution-assisted wetting of porous anodic alumina (PAA) membranes....

The morphological stability of organic nanowires over time and under thermal load is of major importance for their use in any device. In this study the growth and stability of organic nanowires from a naphthyl end-capped thiophene grown by organic molecular beam deposition is investigated via atomic force microscopy (AFM). Aging experiments under a...

Nanoaggregates from a custom-made phenyl-carbazole oligomer, namely 2,7-diphenylcarbazole, are fabricated both by organic molecular beam deposition (OMBD) and solution assisted wetting of porous anodic alumina membranes. The former method leads to the formation of mutually aligned nanofibers lying on the mica substrates, while the latter method all...

We report on the growth and morphology of alpha-quaterthiophene and alpha-sexithiophene clusters, needles (or "fibers"), and flat islands on muscovite mica (001). Samples are prepared by organic molecular beam deposition, and characterized ex situ by polarized fluorescence microscopy and by atomic force microscopy. The growth mechanism of such thio...

Results of a systematic study of the growth of blue-green light-emitting 2,5-di-4-biphenylthiophene (PPTPP) molecules on the (001) faces of the sheet silicates muscovite an phlogopite mica are reported. This includes morphology, crystallography, and optical properties. It is shown that small changes in the choice of the substrate,lead to distinctly...

The epitaxial order of sexiphenyl crystals on muscovite(001) is investigated by x-ray diffraction, lattice misfit calculations and atomic force microscopy. Depending on the substrate temperature during the thin film growth process, different epitaxial orientations are formed. Sexiphenyl thin films prepared at 370 K preferentially form crystals with...

Nanofibers from light-emitting organic molecules such as para-phenylenes have already demonstrated a promising application potential in nanophotonic devices and can act as waveguides or nanolasers. Here, the basic mechanisms for self-assembly of three different green- and green/blue-light emitting thiophene/phenylene co-oligomers into nanofibers ar...

Discontinuous nanofiber films of para-hexaphenylene molecules can be routinely fabricated via vacuum deposition on muscovite mica. The fibers emit upon UV illumination blue fluorescence with excitonic spectral peaks. Their intense fluorescence makes them very attractive for the use in photonic devices, given that the spectra are reproducible for va...

The growth of thiophene/phenylene cooligomers is investigated on the basal surface of muscovite mica. Both the phenyl end-capped 5,5'-di-4-biphenylyl-2,2'-bithiophene (PPTTPP) and the thienyl end-capped 4,4'-di-2,2'-bithienylbiphenyl (TTPPTT) co-oligomers form fiberlike nanostructures from molecules lying on the substrate surface after vacuum depos...

The growth of 2,5-Di-4-biphenyl-thiophene (PPTPP) on the dielectric substrates NaCl, KCl, KAP, muscovite mica, and phlogopite mica is investigated by atomic force microscopy (AFM) and fluorescence microscopy. In all cases fibers are formed with several ten nanometers height and several hundred nanometers width, respectively. Only for PPTPP on musco...

Owner: fbalzer, Added to JabRef: 2008.11.07

Owner: fbalzer, Added to JabRef: 2008.09.08

The results of a comparative study of nanowires grown on single crystalline substrates from para-hexaphenylene, alpha-sexithiophene, and 5,5(')-Di-4-biphenyl-2,2(')-bithiophene are presented. Due to their interesting optical properties such nanowires are of importance for future integrated optoelectronic devices. From atomic force microscopy and po...

All relevant steps of discontinuous thin film growth of para-hexaphenylene on muscovite mica (0 0 1) from wetting layer over small and large clusters to nanofibers are observed and investigated in detail by a combined polarized fluorescence and atomic force microscopy study. From a variation of film thickness and surface temperature, we determine e...

Aligned ensembles of nanoscopic nanofibers from organic molecules such as para-phenylenes for photonic applications can be fabricated by self-assembled molecular growth on a suited dielectric substrate. Epitaxy together with alignment due to electric surface fields determines the growth directions. In this paper we demonstrate how aligned growth al...

A new route to bottom-up organic nanotechnology is presented. Molecular building blocks with specific optoelectronic properties are designed and grown via directed self-assembly arrays of morphologically controlled light-emitting organic nanofibers on template surfaces. The fibers can be easily transferred from the growth substrate to device platfo...

Functionalized para-phenylenes are versatile building blocks for generating aligned fiber-like nanostructures by a self-assembly growth process on muscovite mica substrates upon controlled vapor deposition (molecule epitaxy). Functional groups were implemented at the 1,4-para-positions of p-quaterphenylenes (p4P) using a Suzuki cross-coupling strat...

The para-phenylenes are a class of conjugated rigid rod-like molecules, which have attracted a great amount of interest during the last couple of years. In a series of experiments, it has been shown that needle-like crystals can be grown on various substrates like, e.g., the alkali halides [1, 2], muscovite mica [3, 4], Au (1 1 1) and Au foil [5–7]...

Organic nanofibers from semiconducting conjugated molecules are well suited to meet refined demands for advanced applications in future optoelectronics and nanophotonics. In contrast to their inorganic counterparts, the properties of organic nanowires can be tailored at the molecular level by chemical synthesis. Recently we have demonstrated the co...

The synthesis of molecules consisting of various combinations of phenylene and thiophene groups and the subsequent vacuum growth of needle-shaped nanoaggregates on specific surfaces allows us a systematic investigation of the transition between single parallel and multiple aligned needle ('nanofiber') growth. The former growth mode is observed for...

Nanofibers from symmetrically and unsymmetrically functionalized p-quaterphenylenes are fabricated by a bottom-up process on muscovite mica. The symmetrically functionalized p-quaterphenylenes emit intense, polarized blue light after unpolarized UV-excitation. Upon implementing electron push-pull functional groups like chlor and methoxy groups to t...

The generation of long, mutually oriented nanofibers of functionalized phenylene oligomers is reported for the case of symmetrically 4,4' ''-functionalized p-quaterphenylene molecules with chloride groups. Two domains of up to 30 mu m long, oriented fibers with nanoscopic widths and heights grow along muscovite mica < 110 > directions. Their mutual...

Nanofibers grown in a sophisticated surface self assembly process from organic molecules are important key elements for future nanoscaled optoelectronic devices. They might serve both as passive elements such as waveguides and as active elements such as nanoscaled light sources or nanolasers. For both applications, structuring of the nanofibers by...

Nanofibers from semiconducting conjugated organic molecules are of huge interest for applications, as model systems in basic research, and in optoelectronic device development. They are believed to push forward today’s microelectronics and photonics, using a bottom-up process to assemble new or either even more miniaturized or less expensive device...

Degradation of nanofibers made from organic molecules such as para-hexaphenylene or functionalized quaterphenylene via photoexcitation or thermal irradiation is investigated by optical and morphological studies. Under ambient air conditions and in the limit of strong excitation, the degradation of luminescence intensity is accompanied by an increas...