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  • 51.
    Gorbunov, Andrey V.
    et al.
    Eindhoven Univ Technol, Netherlands.
    Iglesias, Miguel Garcia
    Eindhoven Univ Technol, Netherlands.
    Guilleme, Julia
    Univ Autonoma Madrid, Spain.
    Cornelissen, Tim
    Linköping University, Department of Physics, Chemistry and Biology, Complex Materials and Devices. Linköping University, Faculty of Science & Engineering.
    Roelofs, W. S. Christian
    Eindhoven Univ Technol, Netherlands.
    Torres, Tomas
    Univ Autonoma Madrid, Spain; IM DEA Nanociencia, Spain.
    Gonzalez-Rodriguez, David
    Univ Autonoma Madrid, Spain.
    Meijer, E. W.
    Eindhoven Univ Technol, Netherlands.
    Kemerink, Martijn
    Linköping University, Department of Physics, Chemistry and Biology, Complex Materials and Devices. Linköping University, Faculty of Science & Engineering. Eindhoven Univ Technol, Netherlands.
    Ferroelectric self-assembled molecular materials showing both rectifying and switchable conductivity2017In: Science Advances, ISSN 0036-8156, E-ISSN 2375-2548, Vol. 3, no 9, article id e1701017Article in journal (Refereed)
    Abstract [en]

    Advanced molecular materials that combine two or more physical properties are typically constructed by combining different molecules, each being responsible for one of the properties required. Ideally, single molecules could take care of this combined functionality, provided they are self-assembled correctly and endowed with different functional subunits whose strong electronic coupling may lead to the emergence of unprecedented and exciting properties. We present a class of disc-like semiconducting organic molecules that are functionalized with strong dipolar side groups. Supramolecular organization of these materials provides long-range polar order that supports collective ferroelectric behavior of the side groups as well as charge transport through the stacked semiconducting cores. The ferroelectric polarization in these supramolecular polymers is found to couple to the charge transport and leads to a bulk conductivity that is both switchable and rectifying. An intuitive model is developed and found to quantitatively reproduce the experimental observations. In a larger perspective, these results highlight the possibility of modulating material properties using the large electric fields associated with ferroelectric polarization.

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  • 52.
    Gorbunov, AV
    et al.
    Eindhoven University of Technology, the Netherlands.
    Meng, X
    Eindhoven University of Technology, the Netherlands.
    Urbanaviciute, Indre
    Linköping University, Department of Physics, Chemistry and Biology, Complex Materials and Devices. Linköping University, Faculty of Science & Engineering.
    Putzeys, T
    KU Leuven, Heverlee, Belgium.
    Wübbenhorst, M
    KU Leuven, Heverlee, Belgium.
    Sijbesma, RP
    Eindhoven University of Technology, the Netherlands.
    Kemerink, Martijn
    Linköping University, Department of Physics, Chemistry and Biology, Complex Materials and Devices. Linköping University, Faculty of Science & Engineering. Eindhoven University of Technology, the Netherlands.
    Polarization loss in the organic ferroelectrictrialkylbenzene-1,3,5-tricarboxamide (BTA)2017In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 19, no 4, p. 3192-3200Article in journal (Refereed)
    Abstract [en]

    We investigate the polarization loss in the archetypical molecular organic ferroelectric trialkylbenzene-1,3,5-tricarboxamide (BTA). We prove that the polarization loss is due to thermally activated R-relaxation,which is a collective reversal of the amide dipole moments in ferroelectric domains. By applying a weakelectrostatic field both the polarization loss and the R-relaxation are suppressed, leading to anenhancement of the retention time by at least several orders of magnitude. Alternative loss mechanismsare discussed and ruled out. By operating the thin-film devices slightly above the crystalline to liquidcrystalline phase transition temperature the retention time of one compound becomes more than12 hours even in absence of supportive bias, which is among the longest reported so far for organicferroelectric materials.

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  • 53.
    Hallam, Toby
    et al.
    University of Cambridge, England.
    Lee, MiJung
    University of Cambridge, England.
    Zhao, Ni
    University of Cambridge, England.
    Nandhakumar, Iris
    University of Southampton, England.
    Kemerink, Martijn
    University of Cambridge, England; Eindhoven University of Technology, Netherlands.
    Heeney, Martin
    University of London Imperial Coll Science Technology and Med, England.
    McCulloch, Iain
    University of London Imperial Coll Science Technology and Med, England.
    Sirringhaus, Henning
    University of Cambridge, England.
    Local Charge Trapping in Conjugated Polymers Resolved by Scanning Kelvin Probe Microscopy2009In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 103, no 25, article id 256803Article in journal (Refereed)
    Abstract [en]

    The microstructure of conjugated polymers is heterogeneous on the length scale of individual polymer chains, but little is known about how this affects their electronic properties. Here we use scanning Kelvin probe microscopy with resolution-enhancing carbon nanotube tips to study charge transport on a 100 nm scale in a chain-extended, semicrystalline conjugated polymer. We show that the disordered grain boundaries between crystalline domains constitute preferential charge trapping sites and lead to variations on a 100 nm scale of the carrier concentration under accumulation conditions.

  • 54.
    Haverkort, JEM
    et al.
    Eindhoven University of Technology, Netherlands.
    Dorren, BHP
    Eindhoven University of Technology, Netherlands.
    Kemerink, Martijn
    Eindhoven University of Technology, Netherlands.
    Silov, AY
    Eindhoven University of Technology, Netherlands.
    Wolter, JH
    Eindhoven University of Technology, Netherlands.
    Design of a polarization independent SOA at 1.55 mu m using composite InAsP/InGaAs quantum wells.1999In: ECIO99: 9TH EUROPEAN CONFERENCE ON INTEGRATED OPTICS AND TECHNICAL EXHIBITION, IST INT COMUNICAZIONI , 1999, p. 483-486Conference paper (Refereed)
    Abstract [en]

    We aim to extend the polarization independent SOA reported by Tiemeijer(1) to 1550 nm. Conventional quantum wells (QW) do not allow TM-gain at 1550 nm without exceeding the critical layer thickness. Composite InAsP/InGaAs QWs show high TM-differential gain at 1550 nm while simultaneously providing strain compensation.

  • 55.
    Haverkort, JEM
    et al.
    Eindhoven University of Technology, Netherlands.
    Dorren, BHP
    Eindhoven University of Technology, Netherlands.
    Kemerink, Martijn
    Eindhoven University of Technology, Netherlands.
    Silov, AY
    Eindhoven University of Technology, Netherlands.
    Wolter, JH
    Eindhoven University of Technology, Netherlands.
    Design of composite InAsP/InGaAs quantum wells for a 1.55 mu m polarization independent semiconductor optical amplifier1999In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 75, no 18, p. 2782-2784Article in journal (Refereed)
    Abstract [en]

    We investigate a composite InAsP/InGaAs quantum well in which an 8 nm tensile strained InGaAs well is surrounded by two compressively strained InAsP layers which feature a 70:30 conduction band offset ratio. The composite quantum well is found to provide a high TM differential gain. The InAsP layers provide strain compensation while simultaneously shifting the band gap to the relevant 1.55 mu m wavelength region and increasing the electron confinement. Composite InAsP/InGaAs quantum wells are a promising candidate for realizing a polarization independent semiconductor optical amplifier at 1.55 mu m. (C) 1999 American Institute of Physics. [S0003-6951(99)01944-0].

  • 56.
    Howard, Ian A.
    et al.
    Max Planck Institute Polymer Research, Germany .
    Etzold, Fabian
    Max Planck Institute Polymer Research, Mainz, Germany.
    Laquai, Frederic
    Max Planck Institute Polymer Research, Mainz, Germany.
    Kemerink, Martijn
    Linköping University, Department of Physics, Chemistry and Biology, Complex Materials and Devices. Linköping University, The Institute of Technology. Eindhoven University of Technology, MB, Netherlands.
    Nonequilibrium Charge Dynamics in Organic Solar Cells2014In: Advanced Energy Materials, ISSN 1614-6832, Vol. 4, no 9, article id 1301743Article in journal (Refereed)
    Abstract [en]

    The dynamics of charge carriers after their creation at, or near, an interface play a critical role in determining the efficiency of organic solar cells as they dictate, via mechanisms that are not yet fully understood, the pathways for charge separation and recombination. Here, a combination of ultrafast transient spectroscopy and kinetic Monte Carlo simulations based on a minimalistic model are used to examine various aspects of these charge dynamics in a typical donor-acceptor copolymer:methanofullerene blend. The observed rates of charge carrier energetic relaxation and recombination for a sequence of charge densities can be all consistently described in terms of the extended Gaussian disorder model. The physical picture that arises is a) that initial charge motion is highly diffusive and boosted by energetic relaxation in the disordered density of states and b) that mobile charge carriers dissociate from and re-associate into Coulombically associated pairs faster than they recombine, especially at early times. A simple analytical calculation confirms this picture and can be used to identify sub-Langevin recombination as the cause for quantitative deviations between the Monte Carlo calculations and the measured concentration dependence of the charge recombination.

  • 57.
    Huijbregts, L. J.
    et al.
    Technical University of Eindhoven, Netherlands.
    Brom, H. B.
    Technical University of Eindhoven, Netherlands.
    Brokken-Zijp, J. C. M.
    Technical University of Eindhoven, Netherlands.
    Kemerink, M.
    Technical University of Eindhoven, Netherlands.
    Chen, Z.
    Technical University of Eindhoven, Netherlands.
    de Goeje, M. P.
    Technical University of Eindhoven, Netherlands.
    Yuan, M.
    Technical University of Eindhoven, Netherlands.
    Michels, M. A. J.
    Technical University of Eindhoven, Netherlands.
    The optimal structure-conductivity relation in epoxy-phthalocyanine nanocomposites2006In: Journal of Physical Chemistry B, ISSN 1520-6106, E-ISSN 1520-5207, Vol. 110, no 46, p. 23115-23122Article in journal (Refereed)
    Abstract [en]

    Phthalcon-11 (aquocyanophthalocyaninatocobalt (III)) forms semiconducting nanocrystals that can be dispersed in epoxy coatings to obtain a semiconducting material with a low percolation threshold. We investigated the structure-conductivity relation in this composite and the deviation from its optimal realization by combining two techniques. The real parts of the electrical conductivity of a Phthalcon-11/ epoxy coating and of Phthalcon-11 powder were measured by dielectric spectroscopy as a function of frequency and temperature. Conducting atomic force microscopy (C-AFM) was applied to quantify the conductivity through the coating locally along the surface. This combination gives an excellent tool to visualize the particle network. We found that a large fraction of the crystals is organized in conducting channels of fractal building blocks. In this picture, a low percolation threshold automatically leads to a conductivity that is much lower than that of the filler. Since the structure-conductivity relation for the found network is almost optimal, a drastic increase in the conductivity of the coating cannot be achieved by changing the particle network, but only by using a filler with a higher conductivity level.

  • 58.
    Hynynen, Jonna
    et al.
    Chalmers Univ Technol, Sweden.
    Jarsvall, Emmy
    Chalmers Univ Technol, Sweden.
    Kroon, Renee
    Chalmers Univ Technol, Sweden.
    Zhang, Yadong
    Georgia Inst Technol, GA 30332 USA; Georgia Inst Technol, GA 30332 USA.
    Barlow, Stephen
    Georgia Inst Technol, GA 30332 USA; Georgia Inst Technol, GA 30332 USA.
    Marder, Seth R.
    Georgia Inst Technol, GA 30332 USA; Georgia Inst Technol, GA 30332 USA.
    Kemerink, Martijn
    Linköping University, Department of Physics, Chemistry and Biology, Complex Materials and Devices. Linköping University, Faculty of Science & Engineering.
    Lund, Anja
    Chalmers Univ Technol, Sweden.
    Mueller, Christian
    Chalmers Univ Technol, Sweden.
    Enhanced Thermoelectric Power Factor of Tensile Drawn Poly(3-hexylthiophene)2019In: ACS Macro Letters, E-ISSN 2161-1653, Vol. 8, no 1, p. 70-76Article in journal (Refereed)
    Abstract [en]

    The thermoelectric power factor of a broad range of organic semiconductors scales with their electrical conductivity according to a widely obeyed power law, and therefore, strategies that permit this empirical trend to be surpassed are highly sought after. Here, tensile drawing of the conjugated polymer poly(3-hexylthiophene) (P3HT) is employed to create free-standing films with a high degree of uniaxial alignment. Along the direction of orientation, sequential doping with a molybdenum tris(dithiolene) complex leads to a 5-fold enhancement of the power factor beyond the predicted value, reaching up to 16 mu W m(-1) K-2 for a conductivity of about 13 S cm(-1). Neither stretching nor doping affect the glass transition temperature of P3HT, giving rise to robust free-standing materials that are of interest for the design of flexible thermoelectric devices.

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  • 59.
    Hynynen, Jonna
    et al.
    Chalmers University of Technology, Sweden.
    Kiefer, David
    Chalmers University of Technology, Sweden.
    Yu, Liyang
    Chalmers University of Technology, Sweden.
    Kroon, Renee
    Chalmers University of Technology, Sweden.
    Munir, Rahim
    King Abdullah University of Science and Technology KAUST, Saudi Arabia; King Abdullah University of Science and Technology KAUST, Saudi Arabia.
    Amassian, Aram
    King Abdullah University of Science and Technology KAUST, Saudi Arabia; King Abdullah University of Science and Technology KAUST, Saudi Arabia.
    Kemerink, Martijn
    Linköping University, Department of Physics, Chemistry and Biology, Complex Materials and Devices. Linköping University, Faculty of Science & Engineering.
    Mueller, Christian
    Chalmers University of Technology, Sweden.
    Enhanced Electrical Conductivity of Molecularly p-Doped Poly(3-hexylthiophene) through Understanding the Correlation with Solid-State Order2017In: Macromolecules, ISSN 0024-9297, E-ISSN 1520-5835, Vol. 50, no 20, p. 8140-8148Article in journal (Refereed)
    Abstract [en]

    Molecular p-doping of the conjugated polymer poly(3-hexylthiophene) (P3HT) with 2,3,5,6-tetrafluoro-7,7,8,8-tetracyano-quinodimethane (F4TCNQ) is a widely studied model system. Underlying structure property relationships are poorly understood because processing and doping are often carried out simultaneously. Here, we exploit doping from the vapor phase, which allows us to disentangle the influence of processing and doping. Through this approach, we are able to establish how the electrical conductivity varies with regard to a series of predefined structural parameters. We demonstrate that improving the degree of solid-state order, which we control through the choice of processing solvent and regioregularity, strongly increases the electrical conductivity. As a result, we achieve a value of up to 12.7 S cm(-2) for P3HT:F4TCNQ, We determine the F4TCNQ anion concentration and find that the number of (bound + mobile) charge carriers of about 10(-4) mol cm(-3) is not influenced by the degree of solid-state order. Thus, the observed increase in electrical conductivity by almost 2 orders of magnitude can be attributed to an increase in charge-carrier mobility to more than 10(-1) cm(2) V-1 s(-1). Surprisingly, in contrast to charge transport in undoped P3HT, we find that the molecular weight of the polymer does not strongly influence the electrical conductivity, which highlights the need for studies that elucidate structure property relationships of strongly doped conjugated polymers.

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  • 60.
    Jacobs, SEJ
    et al.
    Eindhoven University of Technology, England.
    Kemerink, Martijn
    Eindhoven University of Technology, England.
    Koenraad, PM
    Eindhoven University of Technology, England.
    Hopkinson, M
    Eindhoven University of Technology, England.
    Salemink, HWM
    Eindhoven University of Technology, England.
    Wolter, JH
    Eindhoven University of Technology, England.
    Spatially resolved scanning tunneling luminescence on self-assembled InGaAs/GaAs quantum dots2003In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 83, no 2, p. 290-292Article in journal (Refereed)
    Abstract [en]

    Scanning-tunneling microscope induced luminescence at low temperature has been used to study the carrier injection into single self-assembled InGaAs/GaAs quantum dots. Electrons are injected from the tip into the dots, which are located in the intrinsic region of a p-i-n junction, and contain excess holes under typical operational conditions. Only a fraction (similar to4%) of the dots is found to be optically active under local electrical excitation. Spatial dependent measurements indicate a highly nonhomogeneous electron diffusion towards the dots. By analyzing the spatial dependence of individual peaks in the measured spectra, the contributions of individual dots to the total, multidot spectrum can be disentangled. (C) 2003 American Institute of Physics.

  • 61.
    Jan Anton Koster, L.
    et al.
    Eindhoven University of Technology, Netherlands; University of Groningen, Netherlands.
    Kemerink, Martijn
    Eindhoven University of Technology, Netherlands.
    Wienk, Martijn M.
    Eindhoven University of Technology, Netherlands.
    Maturova, Klara
    Eindhoven University of Technology, Netherlands.
    Janssen, Rene A. J.
    Eindhoven University of Technology, Netherlands.
    Quantifying Bimolecular Recombination Losses in Organic Bulk Heterojunction Solar Cells2011In: Advanced Materials, ISSN 0935-9648, E-ISSN 1521-4095, Vol. 23, no 14, p. 1670-+Article in journal (Refereed)
    Abstract [en]

    We present a new experimental technique that affords direct quantification of the fraction of charge carriers lost in poly(3-hexylthiophene): fullerene solar cells by bimolecular recombination. Depending on annealing conditions up to 17% of carriers recombine bimolecularly under solar illumination. We explain our findings with a closed analytical expression for the photocurrent generated by an organic solar cell.

  • 62.
    Janssen, FJJ
    et al.
    Eindhoven University of Technology, Netherlands.
    Sturm, JM
    Eindhoven University of Technology, Netherlands.
    van der Gon, AWD
    Eindhoven University of Technology, Netherlands.
    van IJzendoorn, LJ
    Eindhoven University of Technology, Netherlands.
    Kemerink, Martijn
    Eindhoven University of Technology, Netherlands.
    Schoo, HFM
    Eindhoven University of Technology, Netherlands.
    de Voigt, MJA
    Eindhoven University of Technology, Netherlands.
    Brongersma, HH
    Eindhoven University of Technology, Netherlands.
    Interface instabilities in polymer light emitting diodes due to annealing2003In: Organic electronics, ISSN 1566-1199, E-ISSN 1878-5530, Vol. 4, no 4, p. 209-218Article in journal (Refereed)
    Abstract [en]

    In polymer light emitting diodes (PLEDS) with an (ITO/PPV/Ca) structure we observed a significant reduction of both the current and the light output at constant voltage after heat treatment for only 30 min at 65 degreesC. Electroluminescence spectroscopy experiments showed that the shape as well as the amplitude of the spectra were changed. The reduction of current and light output was investigated by measuring I-V and E-V (current-voltage and brightness-voltage) characteristics of PLEDs, I-V characteristics of single carrier devices, and by performing low energy ion scattering and X-ray photoelectron spectroscopy experiments on the Ca/PPV interface. It was concluded that the current and light output reduction could be ascribed to the degradation of the Ca/PPV and the ITO/PPV interfaces. The degradation of the ITO/PPV interface resulted in a reduction of the zero field hole mobility and a small increase of the field dependence of the mobility. The degradation of the Ca/PPV interface, probably by diffusion of calcium into the PPV, resulted in carrier traps and quenching sites, which influenced the field dependent electron mobility. (C) 2003 Elsevier B.V. All rights reserved.

  • 63.
    Janssen, P.
    et al.
    Eindhoven University of Technology, Netherlands.
    Cox, M.
    Eindhoven University of Technology, Netherlands.
    Wouters, S. H. W.
    Eindhoven University of Technology, Netherlands.
    Kemerink, M.
    Eindhoven University of Technology, Netherlands.
    Wienk, M. M.
    Eindhoven University of Technology, Netherlands.
    Koopmans, B.
    Eindhoven University of Technology, Netherlands.
    Tuning organic magnetoresistance in polymer-fullerene blends by controlling spin reaction pathways2013In: Nature Communications, ISSN 2041-1723, E-ISSN 2041-1723, Vol. 4, article id 2286Article in journal (Refereed)
    Abstract [en]

    Harnessing the spin degree of freedom in semiconductors is generally a challenging, yet rewarding task. In recent years, the large effect of a small magnetic field on the current in organic semiconductors has puzzled the young field of organic spintronics. Although the microscopic interaction mechanisms between spin-carrying particles in organic materials are well understood nowadays, there is no consensus as to which pairs of spin-carrying particles are actually influencing the current in such a drastic manner. Here we demonstrate that the spin-based particle reactions can be tuned in a blend of organic materials, and microscopic mechanisms are identified using magnetoresistance lineshapes and voltage dependencies as fingerprints. We find that different mechanisms can dominate, depending on the exact materials choice, morphology and operating conditions. Our improved understanding will contribute to the future control of magnetic field effects in organic semiconductors.

  • 64.
    Janssen, P.
    et al.
    Eindhoven University of Technology, Netherlands.
    Wagemans, W.
    Eindhoven University of Technology, Netherlands.
    Verhoeven, W.
    Eindhoven University of Technology, Netherlands.
    van der Heijden, E. H. M.
    Eindhoven University of Technology, Netherlands.
    Kemerink, M.
    Eindhoven University of Technology, Netherlands.
    Koopmans, B.
    Eindhoven University of Technology, Netherlands.
    On the role of minority carriers in the frequency dependence of organic magnetoresistance2011In: Synthetic metals, ISSN 0379-6779, E-ISSN 1879-3290, Vol. 161, no 7-8, p. 617-621Article in journal (Refereed)
    Abstract [en]

    In this work we investigate the frequency dependence of organic magnetoresistance (OMAR) both in small molecule-based (Alq3) and polymer (PPV derivative) materials, and investigate its thickness dependence. For all devices, we observed a strong decrease in magnetoconductance (MC) with increasing frequency of the ac component of the applied magnetic field. Moreover, we observed a strong reduction of the cut-off frequencies for increasing film thickness. By means of admittance spectroscopy and device simulations, we show that the cut-off frequency is related to the inverse transit time of the minority charge carriers. These observations confirm the important role of minority carriers in OMAR, and show that changes in OMAR are not only due to microscopic mechanisms, but also device physics is of significant relevance. (C) 2011 Elsevier B.V. All rights reserved.

  • 65.
    Jasiunas, Rokas
    et al.
    Ctr Phys Sci and Technol, Lithuania.
    Melianas, Armantas
    Linköping University, Department of Physics, Chemistry and Biology, Biomolecular and Organic Electronics. Linköping University, Faculty of Science & Engineering. Stanford Univ, CA 94305 USA.
    Xia, Yuxin
    Linköping University, Department of Physics, Chemistry and Biology, Biomolecular and Organic Electronics. Linköping University, Faculty of Science & Engineering.
    Felekidis, Nikolaos
    Linköping University, Department of Physics, Chemistry and Biology, Complex Materials and Devices. Linköping University, Faculty of Science & Engineering.
    Gulbinas, Vidmantas
    Ctr Phys Sci and Technol, Lithuania.
    Kemerink, Martijn
    Linköping University, Department of Physics, Chemistry and Biology, Complex Materials and Devices. Linköping University, Faculty of Science & Engineering.
    Dead Ends Limit Charge Carrier Extraction from All-Polymer Bulk Heterojunction Solar Cells2018In: ADVANCED ELECTRONIC MATERIALS, ISSN 2199-160X, Vol. 4, no 8, article id 1800144Article in journal (Refereed)
    Abstract [en]

    Extraction of photocreated charge carriers from a prototypical all-polymer organic solar cell is investigated by combining transient photocurrent and time-delayed collection field experiments with numerical simulations. It is found that extraction is significantly hampered by charges getting trapped in spatial traps that are tentatively attributed to dead ends in the intermixed polymer networkin photovoltaic devices based on the same donor polymer and a fullerene acceptor this effect is much weaker. The slow-down in charge extraction leads to enhanced recombination and associated performance losses. These effects are observed in addition to the dispersive behavior that is characteristic of charge motion in energetically disordered media. Upon annealing the effects of spatial traps diminish, rationalizing the doubling in device power conversion efficiency after annealing.

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  • 66.
    Jonkheijm, P
    et al.
    Eindhoven University of Technology, Netherlands.
    van Duren, JKJ
    Eindhoven University of Technology, Netherlands.
    Kemerink, Martijn
    Eindhoven University of Technology, Netherlands.
    Janssen, RAJ
    Eindhoven University of Technology, Netherlands.
    Schenning, APHJ
    Eindhoven University of Technology, Netherlands.
    Meijer, EW
    Eindhoven University of Technology, Netherlands.
    Control of film morphology by folding hydrogen-bonded oligo(p-phenylenevinylene) polymers in solution2006In: Macromolecules, ISSN 0024-9297, E-ISSN 1520-5835, Vol. 39, no 2, p. 784-788Article in journal (Refereed)
    Abstract [en]

    The film morphology of pi-conjugated oligomers has been controlled by self-assembly in solution. To this end supramolecular hydrogen-bonded systems of oligo(p-phenylenevinylene) (OPV) carrying ureido-s-triazine hydrogen-bonding groups are used. Neutron scattering experiments in dodecane solutions show that columnar stacks are formed. Films with thicknesses on the order of 100 nm are made that have a supramolecular organization resembling the organization present in solution. Uniform rodlike morphological domains range over several hundreds of nanometers as shown by atomic force microscopy. The rodlike morphology of the OPVs was also preserved when blended with a C-60 derivative, producing stable photovoltaic devices.

  • 67.
    Karuthedath, Safakath
    et al.
    KAUST, Saudi Arabia.
    Gorenflot, Julien
    KAUST, Saudi Arabia.
    Melianas, Armantas
    Linköping University, Department of Physics, Chemistry and Biology, Biomolecular and Organic Electronics. Linköping University, Faculty of Science & Engineering.
    Kan, Zhipeng
    KAUST, Saudi Arabia.
    Kemerink, Martijn
    Linköping University, Department of Physics, Chemistry and Biology, Biomolecular and Organic Electronics. Linköping University, Faculty of Science & Engineering.
    Laquai, Frederic
    KAUST, Saudi Arabia.
    Buildup of Triplet-State Population in Operating TQ1:PC71BM Devices Does Not Limit Their Performance2020In: Journal of Physical Chemistry Letters, ISSN 1948-7185, E-ISSN 1948-7185, Vol. 11, no 8, p. 2838-2845Article in journal (Refereed)
    Abstract [en]

    Triplet generation in organic solar cells has been considered a major loss channel. Determining the density of the triplet-state population in an operating device is challenging. Here, we employ transient absorption (TA) spectroscopy on the quinoxaline-thiophene copolymer TQ1 blended with PC71BM, quantify the transient charge and tripletstate densities, and parametrize their generation and recombination dynamics. The charge recombination parameters reproduce the experimentally measured current-voltage characteristics in charge carrier drift-diffusion simulations, and they yield the steady-state charge densities. We demonstrate that triplets are formed by both geminate and nongeminate recombination of charge carriers and decay primarily by triplet-triplet annihilation. Using the charge densities in the rate equations describing triplet-state dynamics, we find that triplet-state densities in devices are in the range of charge carrier densities. Despite this substantial triplet-state buildup, TQ1:PC71BM devices exhibit only moderate geminate recombination and significantly reduced nongeminate charge recombination, with reduction factors between 10(-4) and 10(-3) compared to Langevin recombination.

  • 68.
    Karuthedath, Safakath
    et al.
    KAUST, Saudi Arabia.
    Melianas, Armantas
    Linköping University, Department of Physics, Chemistry and Biology, Biomolecular and Organic Electronics. Linköping University, Faculty of Science & Engineering. Stanford Univ, CA 94305 USA.
    Kan, Zhipeng
    KAUST, Saudi Arabia.
    Pranculis, Vytenis
    Ctr Phys Sci and Technol, Lithuania.
    Wohlfahrt, Markus
    KAUST, Saudi Arabia.
    Khan, Jafar I.
    KAUST, Saudi Arabia.
    Gorenflot, Julien
    KAUST, Saudi Arabia.
    Xia, Yuxin
    Linköping University, Department of Physics, Chemistry and Biology, Biomolecular and Organic Electronics. Linköping University, Faculty of Science & Engineering.
    Inganäs, Olle
    Linköping University, Department of Physics, Chemistry and Biology, Biomolecular and Organic Electronics. Linköping University, Faculty of Science & Engineering.
    Gulbinas, Vidmantas
    Ctr Phys Sci and Technol, Lithuania.
    Kemerink, Martijn
    Linköping University, Department of Physics, Chemistry and Biology, Complex Materials and Devices. Linköping University, Faculty of Science & Engineering.
    Laquai, Frederic
    KAUST, Saudi Arabia.
    Thermal annealing reduces geminate recombination in TQ1:N2200 all-polymer solar cells2018In: Journal of Materials Chemistry A, ISSN 2050-7488, Vol. 6, no 17, p. 7428-7438Article in journal (Refereed)
    Abstract [en]

    combination of steady-state and time-resolved spectroscopic measurements is used to investigate the photophysics of the all-polymer bulk heterojunction system TQ1:N2200. Upon thermal annealing a doubling of the external quantum efficiency and an improved fill factor (FF) is observed, resulting in an increase in the power conversion efficiency. Carrier extraction is similar for both blends, as demonstrated by time-resolved electric-field-induced second harmonic generation experiments in conjunction with transient photocurrent studies, spanning the ps-mu s time range. Complementary transient absorption spectroscopy measurements reveal that the different quantum efficiencies originate from differences in charge carrier separation and recombination at the polymer-polymer interface: in as-spun samples similar to 35% of the charges are bound in interfacial charge-transfer states and recombine geminately, while this pool is reduced to similar to 7% in thermally-annealed samples, resulting in higher short-circuit currents. Time-delayed collection field experiments demonstrate a field-dependent charge generation process in as-spun samples, which reduces the FF. In contrast, field-dependence of charge generation is weak in annealed films. While both devices exhibit significant non-geminate recombination competing with charge extraction, causing low FFs, our results demonstrate that the donor/acceptor interface in all-polymer solar cells can be favourably altered to enhance charge separation, without compromising charge transport and extraction.

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  • 69.
    Kemerink, M.
    et al.
    Eindhoven University of Technology, Netherlands.
    Charrier, D. S. H.
    Eindhoven University of Technology, Netherlands.
    Smits, E. C. P.
    Philips Research Labs, Netherlands; University of Groningen, Netherlands.
    Mathijssen, S. G. J.
    Eindhoven University of Technology, Netherlands; Philips Research Labs, Netherlands.
    de Leeuw, D. M.
    Philips Research Labs, Netherlands; University of Groningen, Netherlands.
    Janssen, R. A. J.
    Eindhoven University of Technology, Netherlands.
    On the width of the recombination zone in ambipolar organic field effect transistors2008In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 93, no 3, article id 033312Article in journal (Refereed)
    Abstract [en]

    The performance of organic light emitting field effect transistors is strongly influenced by the width of the recombination zone. We present an analytical model for the recombination profile. By assuming Langevin recombination, the recombination zone width W is found to be given by W = root 4.34d delta, with d and delta the gate dielectric and accumulation layer thicknesses, respectively. The model compares favorably to both numerical calculations and measured surface potential profiles of an actual ambipolar device. (C) 2008 American Institute of Physics.

  • 70.
    Kemerink, M.
    et al.
    University of Cambridge, England; Eindhoven University of Technology, Netherlands.
    Hallam, T.
    University of Cambridge, England.
    Lee, M. J.
    University of Cambridge, England.
    Zhao, N.
    University of Cambridge, England.
    Caironi, M.
    University of Cambridge, England.
    Sirringhaus, H.
    University of Cambridge, England.
    Temperature- and density-dependent channel potentials in high-mobility organic field-effect transistors2009In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 80, no 11, article id 115325Article in journal (Refereed)
    Abstract [en]

    The density-dependent charge-carrier mobility in high-mobility organic field-effect transistors is investigated by simultaneous measurements of the channel potential and the transfer characteristics. By working under ultrahigh-vacuum conditions extrinsic effects due to H(2)O traces could be eliminated. The shape of the channel potential is inconsistent with a density-independent mobility. We find that the variable range hopping model as derived by Vissenberg and Matters for an exponential density of states [Phys. Rev. B 57, 12964 (1998)] consistently describes the data.

  • 71.
    Kemerink, Martijn
    ; .
    Correction: Characteristics of a First-Generation X-Ray System (vol 259, pg 534, 2011)2011In: Radiology, ISSN 0033-8419, E-ISSN 1527-1315, Vol. 260, no 2, p. 612-612Article in journal (Refereed)
    Abstract [en]

    n/a

  • 72.
    Kemerink, Martijn
    Linköping University, Department of Physics, Chemistry and Biology, Biomolecular and Organic Electronics. Linköping University, Faculty of Science & Engineering.
    Peer review2019In: Legal History Review, ISSN 0040-7585, E-ISSN 1571-8190, Vol. 87, no 3, p. 291-298Article in journal (Refereed)
    Abstract [en]

    Over the years, peer review has developed into one of the fundaments of science as a means to provide feedback on scientific output in a relatively objective manner. While peer review is clone with the common good in mind, specifically to provide a quality check, a novelty and relevance check, fraud detection and general manuscript improvement, it has its weaknesses and faces threats that undermine both its effectiveness and even its goals. Herein, I address the role of the various actors in the peer reviewing process, the authors, the editors, the reviewers and the broader society. While the first three actors are active participants in the process, the role of society is indirect as it sets the boundary conditions for the process. I will argue that although authors, editors and reviewers all are in part to blame for the sub-optimal functioning of the system, it is the broader society that intentionally and unintentionally causes many of these problems by enforcing a publish-or-perish culture in academia.

    The full text will be freely available from 2020-12-12 14:48
  • 73.
    Kemerink, Martijn
    et al.
    Eindhoven University of Technology, Netherlands.
    Alvarado, SF
    Eindhoven University of Technology, Netherlands.
    Koenraad, PM
    Eindhoven University of Technology, Netherlands.
    Janssen, RAJ
    Eindhoven University of Technology, Netherlands.
    Salemink, HWM
    Eindhoven University of Technology, Netherlands.
    Wolter, JH
    Eindhoven University of Technology, Netherlands.
    Scanning-tunneling spectroscopy on conjugated polymer flims2003In: ORGANIC AND POLYMERIC MATERIALS AND DEVICES, MATERIALS RESEARCH SOCIETY , 2003, Vol. 771, p. 49-54Conference paper (Refereed)
    Abstract [en]

    Scanning-tunneling spectroscopy experiments have been performed on conjugated polymer films and have been compared to a three-dimensional numerical model for charge injection and transport. It is found that field enhancement near the tip apex leads to significant changes in the injected current, which can amount to more than an order of magnitude, and can even change the polarity of the dominant charge carrier. As a direct consequence, the single-particle band gap and band alignment of the organic material can be directly obtained from tip height-voltage (z-V) curves, provided that the tip has a sufficiently sharp apex.

  • 74.
    Kemerink, Martijn
    et al.
    Eindhoven University of Technology, Netherlands.
    Alvarado, SF
    Eindhoven University of Technology, Netherlands.
    Muller, P
    Eindhoven University of Technology, Netherlands.
    Koenraad, PM
    Eindhoven University of Technology, Netherlands.
    Salemink, HWM
    Eindhoven University of Technology, Netherlands.
    Wolter, JH
    Eindhoven University of Technology, Netherlands.
    Janssen, RAJ
    Eindhoven University of Technology, Netherlands.
    Scanning tunneling spectroscopy on organic semiconductors: Experiment and model2004In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 70, no 4, article id 045202Article in journal (Refereed)
    Abstract [en]

    Scanning-tunneling spectroscopy experiments performed on conjugated polymer films are compared with three-dimensional numerical model calculations for charge injection and transport. It is found that if a sufficiently sharp tip is used, the field enhancement near the tip apex leads to a significant increase in the injected current, which can amount to more than an order of magnitude and can even change the polarity of the predominant charge carrier. We show that when charge injection from the tip into the organic material predominates, it is possible to probe the electronic properties of the interface between the organic material and a metallic electrode directly by means of tip height versus bias voltage measurements. Thus, one can determine the alignment of the molecular orbital energy levels at the buried interface, as well as the single-particle band gap of the organic material. By comparing the single-particle energy gap and the optical absorption threshold, it is possible to obtain an estimate of the exciton binding energy. In addition, our calculations show that by using a one-dimensional model, reasonable parameters can only be extracted from z-V and I-V curves if the tip apex radius is much larger than the tip height. In all other cases, the full three-dimensional problem needs to be considered.

  • 75.
    Kemerink, Martijn
    et al.
    Eindhoven University of Technology, Netherlands.
    Asadi, Kamal
    University of Groningen, Netherlands; Philips Research Labs, Netherlands.
    Blom, Paul W. M.
    University of Groningen, Netherlands; Holst Centre, Netherlands.
    de Leeuw, Dago M.
    University of Groningen, Netherlands; Philips Research Labs, Netherlands.
    The operational mechanism of ferroelectric-driven organic resistive switches2012In: Organic electronics, ISSN 1566-1199, E-ISSN 1878-5530, Vol. 13, no 1, p. 147-152Article in journal (Refereed)
    Abstract [en]

    The availability of a reliable memory element is crucial for the fabrication of plastic logic circuits. We use numerical simulations to show that the switching mechanism of ferroelectric-driven organic resistive switches is the stray field of the polarized ferroelectric phase. The stray field modulates the charge injection from a metallic electrode into the organic semiconductor, switching the diode from injection limited to space charge limited. The modeling rationalizes the previously observed exponential dependence of the on/off ratio on injection barrier height. We find a lower limit of about 50 nm for the feature size that can be used in a crossbar array, translating into a rewritable memory with an information density of the order of 1 Gb/cm(2). (C) 2011 Elsevier B. V. All rights reserved.

  • 76.
    Kemerink, Martijn
    et al.
    Maastricht University, Netherlands.
    Dierichs, Tom J.
    Maastricht University, Netherlands.
    Dierichs, Julien
    Maastricht University, Netherlands.
    Huynen, Hubert J. M.
    Maastricht University, Netherlands.
    Wildberger, Joachim E.
    Maastricht University, Netherlands.
    van Engelshoven, Jos M. A.
    Maastricht University, Netherlands.
    Kemerink, Gerrit J.
    Maastricht University, Netherlands.
    Characteristics of a First-Generation X-Ray System2011In: Radiology, ISSN 0033-8419, E-ISSN 1527-1315, Vol. 259, no 2, p. 534-539Article in journal (Refereed)
    Abstract [en]

    Purpose: To compare the antiquated x-ray system of Hoffmans and van Kleef (circa 1896) with modern x-ray equipment in terms of radiation dose, x-ray beam properties, image quality, and electrical parameters. Materials and Methods: The antiquated x-ray system consisted of a Ruhmkorff inductor, battery, and Crookes tube. The radiation dose rate, x-ray beam properties, and electrical characteristics of this system were determined. A modern computed radiography plate was used to compare images of a hand specimen obtained by using the antiquated system with images obtained by using the modern system. Results: A peak voltage of 73 kV was obtained with an 8-V battery. With Crookes tube number 9, the half-value layer of the generated x-rays was 0.56 mm Al. Pinhole images showed that the x-rays originated from an extended area of the glass wall, causing image blurring. When measured on the skin of a hand specimen, the radiation dose of the antiquated system was about 10 times greater than that of the modern system for the same detector signal. The estimated skin dose was about 74 mGy for the antiquated system and 0.05 mGy for the modern system. The corresponding exposure times were 90 minutes and 21 msec. Conclusion: Radiation dose and exposure time of the antiquated system were greater than those of the modern system by about three and five orders of magnitude, respectively. Images of the hand specimen obtained with the antiquated system were severely blurred but were still awe inspiring, considering the simplicity of the system. (C)RSNA, 2011

  • 77.
    Kemerink, Martijn
    et al.
    Maastricht University, Netherlands.
    Dierichs, Tom J.
    Maastricht University, Netherlands.
    Dierichs, Julien
    Maastricht University, Netherlands.
    Huynen, Hubert J. M.
    Maastricht University, Netherlands.
    Wildberger, Joachim E.
    Maastricht University, Netherlands.
    van Engelshoven, Jos M. A.
    Maastricht University, Netherlands.
    Kemerink, Gerrit J.
    Maastricht University, Netherlands.
    Letter: First-Generation X-Ray System in RADIOLOGY, vol 260, issue 2, pp 611-6122011In: Radiology, ISSN 0033-8419, E-ISSN 1527-1315, Vol. 260, no 2, p. 611-612Article in journal (Other academic)
    Abstract [en]

    n/a

  • 78.
    Kemerink, Martijn
    et al.
    Maastricht University, Netherlands.
    Dierichs, Tom J.
    Maastricht University, Netherlands; Maastricht University, Netherlands.
    Dierichs, Julien
    Maastricht University, Netherlands; Maastricht University, Netherlands.
    Huynen, Hubert
    Maastricht University, Netherlands; Maastricht University, Netherlands.
    Wildberger, Joachim E.
    Maastricht University, Netherlands; Maastricht University, Netherlands.
    van Engelshoven, Jos M. A.
    Maastricht University, Netherlands; Maastricht University, Netherlands.
    Kemerink, Gerrit J.
    Maastricht University, Netherlands; Maastricht University, Netherlands.
    Editorial Material: The Application of X-Rays in Radiology: From Difficult and Dangerous to Simple and Safe in AMERICAN JOURNAL OF ROENTGENOLOGY, vol 198, issue 4, pp 754-7592012In: American Journal of Roentgenology, ISSN 0361-803X, E-ISSN 1546-3141, Vol. 198, no 4, p. 754-759Article in journal (Other academic)
    Abstract [en]

    OBJECTIVE. This article will provide an assessment of the application of x-rays in the early days of radiology, which is an excellent way to come to value the convenience and safety of modern x-ray systems. CONCLUSION. The gas tubes that were originally applied for x-ray production were very unstable because of variations in the tubes vacuum. In an effort to understand some of the problems of these tubes and the high occupational exposure that was indirectly caused by the tubes erratic behavior, we measured x-ray output rates as a function of the gas pressure inside the tube. The pressure range for the optimal production of x-rays, using an original Ruhmkorff inductor as a high-voltage generator, was found to be narrow. With the vacuum changing over time, this might explain the many photographs from the first years of radiology with operators watching their unshielded tube, either with bare eyes or with a fluoroscope, and their own hand as a test object. This practice often led to severe damage of the hands and to many early deaths due to cancer. Today, after a century of technologic development of x-ray tubes and associated equipment, the total average effective dose of workers in radiology can be close to natural background levels.

  • 79.
    Kemerink, Martijn
    et al.
    Eindhoven University of Technology, Netherlands.
    Gerritsen, JW
    Eindhoven University of Technology, Netherlands.
    Hermsen, JGH
    Eindhoven University of Technology, Netherlands.
    Koenraad, PM
    Eindhoven University of Technology, Netherlands.
    van Kempen, H
    Eindhoven University of Technology, Netherlands.
    Wolter, JH
    Eindhoven University of Technology, Netherlands.
    Low-temperature scanning-tunneling microscope for luminescence measurements in high magnetic fields2001In: Review of Scientific Instruments, ISSN 0034-6748, E-ISSN 1089-7623, Vol. 72, no 1, p. 132-135Article in journal (Refereed)
    Abstract [en]

    We have designed and built a low-temperature (1.3-4.2 K) scanning-tunneling microscope which is capable of collecting light that is generated in the tunneling region. Light collection is done by means of two fibers whose cleaved front is in close proximity (approximate to1 mm) to the tunneling region. The whole system can be operated in high magnetic fields (11 T) without loss of optical signal strength. As a demonstration, we measured the electroluminescence spectra of an InGaAs quantum well at various temperatures. At 4.2 K, we found an electron-to-photon conversion factor that is three orders of magnitude higher than at room temperature. (C) 2001 American Institute of Physics.

  • 80.
    Kemerink, Martijn
    et al.
    Eindhoven University of Technology, Netherlands.
    Gerritsen, JW
    Eindhoven University of Technology, Netherlands.
    Koenraad, PM
    Eindhoven University of Technology, Netherlands.
    van Kempen, H
    Eindhoven University of Technology, Netherlands.
    Wolter, JH
    Eindhoven University of Technology, Netherlands.
    Spectrally resolved luminescence from an InGaAs quantum well induced by an ambient scanning tunneling microscope1999In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 75, no 23, p. 3656-3658Article in journal (Refereed)
    Abstract [en]

    Spectrally resolved scanning tunneling microscope-induced luminescence has been obtained under ambient conditions, i.e., at room temperature, in air, by passivating the sample surface with sulfur. This passivation turned out to be essential to suppress the local anodic oxidation induced by the tunneling current. From the dependence of the luminescence signal on tunneling current and voltage, we find that the passivation solution and post-passivation annealing temperature strongly modify the surface density of states (SDOS). More specifically, we found evidence that, after annealing at 400 degrees C, no SDOS is left above the bottom of the conduction band. For annealing at 200 degrees C, the SDOS is found to be extended up to 1.0 +/- 0.2 eV above the bottom of the conduction band. In all cases, the passivated (001) surface appears to be completely pinned. (C) 1999 American Institute of Physics. [S0003-6951(99)01949-X].

  • 81.
    Kemerink, Martijn
    et al.
    UNIV NIJMEGEN, ENGLAND.
    Koenraad, PM
    UNIV NIJMEGEN, ENGLAND.
    Christianen, PCM
    UNIV NIJMEGEN, ENGLAND.
    Geim, AK
    UNIV NIJMEGEN, ENGLAND.
    Maan, JC
    UNIV NIJMEGEN, ENGLAND.
    Wolter, JH
    UNIV NIJMEGEN, ENGLAND.
    Henini, M
    UNIV NIJMEGEN, ENGLAND.
    Enhancement of spin-dependent hole delocalization in degenerate asymmetric double quantum wells1996In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 53, no 15, p. 10000-10007Article in journal (Refereed)
    Abstract [en]

    Exact, self-consistently calculated eigenfunctions and eigenvalues of the valence band in degenerate asymmetric double quantum wells are obtained from the full 4x4 Luttinger Hamiltonian for different hole densities. We found the solutions to be extremely sensitive to the charge density. The charge induces an extra asymmetry in the confining potential and leads to a smaller separation of the hole levels in the adjacent wells. This strongly enhances the different leakage of wave functions with opposite magnetic moment, called spin-dependent hole delocalization (SDHD). Furthermore, it is shown that the SDHD of the heavy-holt: states can be enhanced by increasing the confinement of the Light-hole states through adjustment of the height of the confining barriers. The theoretical results are shown to be in excellent agreement with transport and optical experiments, which are proven to be largely determined by space-charge effects.

  • 82.
    Kemerink, Martijn
    et al.
    CATHOLIC UNIV NIJMEGEN, NETHERLANDS.
    Koenraad, PM
    CATHOLIC UNIV NIJMEGEN, NETHERLANDS.
    Christianen, PCM
    CATHOLIC UNIV NIJMEGEN, NETHERLANDS.
    vanSchaijk, R
    CATHOLIC UNIV NIJMEGEN, NETHERLANDS.
    Maan, JC
    CATHOLIC UNIV NIJMEGEN, NETHERLANDS.
    Wolter, JH
    CATHOLIC UNIV NIJMEGEN, NETHERLANDS.
    Magneto-optical study on exciton screening in p-type AlxGa1-xAs/InyGa1-yAs quantum wells1997In: Physical Review B Condensed Matter, ISSN 0163-1829, E-ISSN 1095-3795, Vol. 56, no 8, p. 4853-4862Article in journal (Refereed)
    Abstract [en]

    We have studied exciton unbinding in empty and p-doped quantum wells, using magnetophotoluminescence excitation measurements. The use of p-type quantum wells allows us to discriminate unambiguously between exciton bleaching by Coulomb screening and by the Pauli exclusion principle. We found that the ground-state heavy-hole exciton, which experiences both effects, is unbound at hole densities in the range (6-9) x 10(15) m(-2). In contrast, the ground-state light-hole and first excited heavy-hole excitons, which are only screened by the Coulomb interaction, still have a finite binding energy at these densities. However, for both bands, its Value is far below what is found in an undoped well. Furthermore, we found a strong indication that, in p-doped wells, the excitons of excited subbands are less efficiently screened than those of the Light-hole ground state, due to the lesser overlap of the screening ground-state heavy holes with the excited subbands than with the ground-state light holes.

  • 83.
    Kemerink, Martijn
    et al.
    Eindhoven University of Technology, Netherlands.
    Koenraad, PM
    Eindhoven University of Technology, Netherlands.
    Parlangeli, T
    Eindhoven University of Technology, Netherlands.
    Christianen, PCM
    Eindhoven University of Technology, Netherlands.
    Van Schaijk, R
    Eindhoven University of Technology, Netherlands.
    Maan, JC
    Eindhoven University of Technology, Netherlands.
    Wolter, JH
    Eindhoven University of Technology, Netherlands.
    Exciton bleaching in p-type single and double quantum wells: The effects of subband occupation and wave function overlap1997In: Physica status solidi. A, Applied research, ISSN 0031-8965, E-ISSN 1521-396X, Vol. 164, no 1, p. 73-76Article in journal (Refereed)
    Abstract [en]

    We have studied exciton unbinding in empty and p-doped single and double quantum wells, using magneto-photoluminescence excitation measurements. The use of p-type heterostructures allows to discriminate unambiguously between exciton bleaching by Coulomb screening and by the Pauli exclusion principle. The groundstate heavy-hole exciton, which experiences both effects, is unbound at hole densities in the range (6 to 11) x 10(15) m(-2). In contrast, the groundstate light-hole and first excited heavy-hole excitons: which only experience Coulomb screening, still have a finite binding energy at these densities. We found that the excitons of excited subbands are far less efficiently screened than those of the light-hole groundstate, due to the lesser overlap of the screening groundstate heavy holes with the excited subbands than with the groundstate light holes.

  • 84.
    Kemerink, Martijn
    et al.
    COBRA Interuniversity Research Institute, Eindhoven University of Technology, Eindhoven, The Netherlands.
    Koenraad, PM
    COBRA Interuniversity Research Institute, Eindhoven University of Technology, Eindhoven, The Netherlands.
    Wolter, JH
    COBRA Interuniversity Research Institute, Eindhoven University of Technology, Eindhoven, The Netherlands.
    Effect of strain on a second-order van Hove singularity in AlxGa1-xAs/InyGa1-yAs quantum wells1996In: Physical Review B Condensed Matter, ISSN 0163-1829, E-ISSN 1095-3795, Vol. 54, no 15, p. 10644-10651Article in journal (Refereed)
    Abstract [en]

    We have performed low-temperature photoluminescence and photoluminescence excitation (PLE) measurements on highly degenerate p-type GaAs and InyGa1-yAs quantum wells. In the PLE spectrum of the GaAs well, evidence of a second-order van Hove singularity in the joint density of states of the ground-state light-hole and electron bands is found. This singularity results from the equality of ground-state light-hole and electron effective masses near the Gamma point, being a much more restrictive demand than the usual condition for a van Hove singularity, which requires only the equality of first derivatives of the subband dispersions. The second-order van Hove singularity gives rise to a power-law divergence at the singular point, whereas the corresponding usual van Hove singularity results in a steplike discontinuity in the joint density of states. The observed singularity could be described extremely well by a simple analytical model. The increased energy gap between light- and heavy-hole ground states in the compressively strained InyGa1-yAs well enhances the valence-band parabolicity, resulting in the disappearance of the van Hove singularity. Furthermore, it is shown that the anisotropic character of the heavy-hole ground state in GaAs is strongly suppressed in the InyGa1-yAs system. All experiments are in good agreement with our numerical modeling, based on an exact solution of the 4 x 4 Luttinger Hamiltonian.

  • 85.
    Kemerink, Martijn
    et al.
    Eindhoven University of Technology, Netherlands.
    Koenraad, PM
    Eindhoven University of Technology, Netherlands.
    Wolter, JH
    Eindhoven University of Technology, Netherlands.
    Exchange interaction in degenerate p-type quantum wells1998In: Physica. B, Condensed matter, ISSN 0921-4526, E-ISSN 1873-2135, Vol. 256, p. 503-506Article in journal (Refereed)
    Abstract [en]

    A detailed comparison between a magneto-transport experiment on a p-type GaAs/AlGaAs quantum well and model calculations is presented. It is shown that for all magnetic fields the Shubnikov-de Haas (SdH) trace is strongly influenced by the exchange interaction, in contrast with n-type structures where this interaction is only important in high magnetic fields. As a consequence, the effective hole masses that are extracted from the temperature dependence of the SdH oscillations are not a good measure of the single-particle hole mass, and can be regarded as meaningless. (C) 1998 Elsevier Science B.V. All rights reserved.

  • 86.
    Kemerink, Martijn
    et al.
    Eindhoven University of Technology, Netherlands.
    Koenraad, PM
    Eindhoven University of Technology, Netherlands.
    Wolter, JH
    Eindhoven University of Technology, Netherlands.
    Exchange interaction in p-type GaAs/AlxGa1-xAs heterostructures studied by magnetotransport1998In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 57, no 11, p. 6629-6635Article in journal (Refereed)
    Abstract [en]

    Low-temperature magnetotransport experiments have been performed on a p-type GaAs/AlxGa1-xAs quantum well. From activation measurements on Shubnikov-de Haas conduction minima it was found that ex change interactions can be of great importance for both odd and even filling factors and strongly influence the observed periodicity. Furthermore, it was found that the temperature dependence of Shubnikov-de Haas oscillations in the low-magnetic-field regime could not be explained within a single-particle model based on a solution of the full Luttinger Hamiltonian in a magnetic field. Numerical simulations of Shubnikov-de Haas spectra, based on a model that treats hole exchange interactions in a simplified manner, show unambiguously that exchange driven enhancement of hole "spin" splittings are extremely important at magnetic fields as low as 1.5 T. Also, the inclusion of a valence-band warping in the calculations is shown to be essential. Qualitatively, most experimental observations could be described within the presented model. Our results imply that, in any hole system, the effective masses obtained from temperature-dependent SdH measurements are to be treated with extreme care as they can deviate from their single-particle value by as much as a factor of 2.

  • 87.
    Kemerink, Martijn
    et al.
    CATHOLIC UNIV NIJMEGEN, ENGLAND.
    Koenraad, PM
    CATHOLIC UNIV NIJMEGEN, ENGLAND.
    Wolter, JH
    CATHOLIC UNIV NIJMEGEN, ENGLAND.
    Christianen, PCM
    CATHOLIC UNIV NIJMEGEN, ENGLAND.
    Geim, AK
    CATHOLIC UNIV NIJMEGEN, ENGLAND.
    Parlangeli, A
    CATHOLIC UNIV NIJMEGEN, ENGLAND.
    Maan, JC
    CATHOLIC UNIV NIJMEGEN, ENGLAND.
    Henini, M
    CATHOLIC UNIV NIJMEGEN, ENGLAND.
    Spin-dependent holed delocalization enhancement by bandfilling effects in degenerate asymmetric double quantum wells1997In: Superlattices and Microstructures, ISSN 0749-6036, E-ISSN 1096-3677, Vol. 21, no 2, p. 217-222Article in journal (Refereed)
    Abstract [en]

    We studied the wavefunctions and energy positions of the confined states in the valance band in an asymmetric double quantum well. We found these to be extremely sensitive to both the carrier density and the height of the confining barriers, which allows us to control the so-called Spin Dependent Hole Delocalization. The theoretical results are shown to be in excellent agreement with experiments. (C) 1997 Academic Press Limited

  • 88.
    Kemerink, Martijn
    et al.
    Eindhoven University of Technology, Netherlands.
    Kramer, JM
    Eindhoven University of Technology, Netherlands.
    Gommans, HHP
    Eindhoven University of Technology, Netherlands.
    Janssen, RAJ
    Eindhoven University of Technology, Netherlands.
    Temperature-dependent built-in potential in organic semiconductor devices2006In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 88, no 19, article id 192108Article in journal (Refereed)
    Abstract [en]

    The temperature dependence of the built-in voltage of organic semiconductor devices is studied. The results are interpreted using a simple analytical model for the band bending at the electrodes. It is based on the notion that, even at zero current, diffusion may cause a significant charge density in the entire device, and hence a temperature dependent band bending. Both magnitude and temperature dependence of the built-in potential of various devices are consistently described by the model, as the effects of a thin LiF layer between cathode and active layer. (c) 2006 American Institute of Physics.

  • 89.
    KEMERINK, MARTIJN
    et al.
    PHILIPS RES LABS, NETHERLANDS.
    MOLENKAMP, LW
    PHILIPS RES LABS, NETHERLANDS.
    STOCHASTIC COULOMB-BLOCKADE IN A DOUBLE-QUANTUM DOT1994In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 65, no 8, p. 1012-1014Article in journal (Refereed)
    Abstract [en]

    The series resistance of two coupled quantum dots in a (Al,Ga)As heterostructure has been studied experimentally. At very low lattice temperatures conductance oscillations of irregular amplitude and spacing are observed. The irregularities decrease on raising the temperature. The observations are interpreted as resulting from the stochastic Coulomb blockade effect.

  • 90.
    Kemerink, Martijn
    et al.
    Eindhoven University of Technology, Netherlands.
    Offermans, P
    Eindhoven University of Technology, Netherlands.
    Koenraad, PM
    Eindhoven University of Technology, Netherlands.
    van Duren, JKJ
    Eindhoven University of Technology, Netherlands.
    Janssen, RAJ
    Eindhoven University of Technology, Netherlands.
    Salemink, HWM
    Eindhoven University of Technology, Netherlands.
    Wolter, JH
    Eindhoven University of Technology, Netherlands.
    Measuring the potential distribution inside soft organic semiconductors with a scanning-tunneling microscope2002In: Physica. E, Low-Dimensional systems and nanostructures, ISSN 1386-9477, E-ISSN 1873-1759, Vol. 13, no 2-4, p. 1247-1250Article in journal (Refereed)
    Abstract [en]

    For the first time, we directly measured the potential distribution inside organic semiconductors. Combined spectroscopic measurements are performed on MDMO-PPV layers on Au and Yb substrates, using a scanning-tunneling microscope. The results are analyzed with a model that treats both current injection and bulk transport in detail. It is found that tip height-bias curves, which are taken by following the height of the STM tip as a function of bias, while the STM feedback system is active, reflect the potential distribution between tip and sample electrode. (C) 2002 Elsevier Science B.V. All rights reserved.

  • 91.
    Kemerink, Martijn
    et al.
    Eindhoven University of Technology, Netherlands.
    Offermans, P
    Eindhoven University of Technology, Netherlands.
    van Duren, JKJ
    Eindhoven University of Technology, Netherlands.
    Koenraad, PM
    Eindhoven University of Technology, Netherlands.
    Janssen, RAJ
    Eindhoven University of Technology, Netherlands.
    Salemink, HWM
    Eindhoven University of Technology, Netherlands.
    Wolter, JH
    Eindhoven University of Technology, Netherlands.
    Real-space measurement of the potential distribution inside organic semiconductors2002In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 88, no 9, article id 096803Article in journal (Refereed)
    Abstract [en]

    We demonstrate that the soft nature of organic semiconductors can be exploited to directly measure the potential distribution inside such an organic layer by scanning-tunneling microscope (STM) based spectroscopy. Keeping the STM feedback system active while reducing the tip-sample bias forces the tip to penetrate the organic layer. From an analysis of the injection and bulk transport processes it follows that the tip height versus bias trace obtained in this way directly reflects the potential distribution in the organic layer.

  • 92.
    Kemerink, Martijn
    et al.
    Eindhoven University of Technology, Germany.
    Reusch, TCG
    Eindhoven University of Technology, Germany.
    Bruls, DM
    Eindhoven University of Technology, Germany.
    Koenraad, PM
    Eindhoven University of Technology, Germany.
    Salemink, HWM
    Eindhoven University of Technology, Germany.
    Wolter, JH
    Eindhoven University of Technology, Germany.
    Quantitative determination of the charge density on surface steps on semiconductors by high-resolution local scanning-tunneling spectroscopy2002In: Physica. E, Low-Dimensional systems and nanostructures, ISSN 1386-9477, E-ISSN 1873-1759, Vol. 13, no 2-4, p. 1159-1162Article in journal (Refereed)
    Abstract [en]

    A novel technique is developed to follow the energetic position of the conduction and valence bands with respect to the Fermi level as a function of the lateral position on semiconductor surfaces. By combining high-resolution scanning-tunneling spectroscopy measurements with model calculations it is possible to relate the apparent change in conduction and valence band position to their real counterparts. This method allows one to determine the charge on surface artifacts like steps or vacancies, For a single step on p-type GaAs we find a charge of 0.9+/-0.3q nm(-1). (C) 2002 Elsevier Science B.V. All rights reserved.

  • 93.
    Kemerink, Martijn
    et al.
    Eindhoven University of Technology, Netherlands.
    Sauthoff, K.
    University of Gottingen, Germany.
    Koenraad, P. M.
    Eindhoven University of Technology, Netherlands.
    Gerritsen, J. W.
    University of Nijmegen, Netherlands.
    van Kempen, H.
    University of Nijmegen, Netherlands.
    Fomin, V. M.
    Eindhoven University of Technology, Netherlands; University of Antwerp, Belgium.
    Wolter, J. H.
    Eindhoven University of Technology, Netherlands.
    Devreese, J. T.
    Eindhoven University of Technology, Netherlands; University of Antwerp, Belgium.
    Optical properties of a tip-induced quantum dot2001In: Applied Physics A: Materials Science & Processing, ISSN 0947-8396, E-ISSN 1432-0630, Vol. 72, p. S239-S242Article in journal (Refereed)
    Abstract [en]

    We have performed optical spectroscopy measurements on a STM-tip-induced quantum dot in a GaAs layer. The dominant confinement in the (hole) quantum dot is found to be in the direction parallel to the tip axis. Electron confinement is achieved by a sub-surface AlGaAs barrier. Current-dependent measurements indicate that many-body interactions can cause spectral blueshifts up to 75 meV for a tunneling current of 10 nA. Consequently, a full treatment of the many-body problem is required for an accurate description of this type of system.

  • 94.
    Kemerink, Martijn
    et al.
    Eindhoven University of Technology, Netherlands.
    Sauthoff, K.
    University of Gottingen, Germany.
    Koenraad, P. M.
    Eindhoven University of Technology, Netherlands.
    Gerritsen, J. W.
    University of Nijmegen, Netherlands.
    van Kempen, H.
    University of Nijmegen, Netherlands.
    Wolter, J. H.
    Eindhoven University of Technology, Netherlands.
    Optical detection of ballistically injected electrons in III/V heterostructures2001In: Applied Physics A: Materials Science & Processing, ISSN 0947-8396, E-ISSN 1432-0630, Vol. 72, p. S201-S204Article in journal (Refereed)
    Abstract [en]

    We present a novel spectroscopic technique that is based on the ballistic injection of minority carriers from the tip of a scanning-tunneling microscope into a semiconductor heterostructure. By analyzing the resulting electro-luminescence spectrum as a function of tip-sample bias, both the injection barrier height and the carrier relaxation rate Gamma(s) after injection can be determined. At 4.2 K we found Gamma(s) = 5 x 10(13) s(-1) and at 77 K we found Gamma(s) = 8 x 10(13) s(-1). From current-dependent measurements we find that, at room temperature, a large fraction of the carriers is trapped prior to radiative recombination. At high currents or low temperatures the traps become saturated. We tentatively identify the Be acceptors in the structure as trapping centers.

  • 95.
    Kemerink, Martijn
    et al.
    Eindhoven University of Technology, Netherlands.
    Sauthoff, K
    Eindhoven University of Technology, Netherlands.
    Koenraad, PM
    Eindhoven University of Technology, Netherlands.
    Gerritsen, JW
    Eindhoven University of Technology, Netherlands.
    van Kempen, H
    Eindhoven University of Technology, Netherlands.
    Fomin, VM
    Eindhoven University of Technology, Netherlands.
    Wolter, JH
    Eindhoven University of Technology, Netherlands.
    Devreese, JT
    Eindhoven University of Technology, Netherlands.
    Optical properties of a tip-induced quantum dot2001In: PROCEEDINGS OF THE 25TH INTERNATIONAL CONFERENCE ON THE PHYSICS OF SEMICONDUCTORS, PTS I AND II, SPRINGER-VERLAG BERLIN , 2001, Vol. 87, p. 1183-1184Conference paper (Refereed)
    Abstract [en]

    We have performed optical spectroscopy measurements on an STM-tip-induced quantum dot. The dominant confinement in the (hole) quantum dot is in the direction parallel to the tip axis. Electron confinement is achieved by a sub-surface AlGaAs barrier. Current dependent measurements indicate that many-body interactions can cause spectral blue-shifts up to 75 meV.

  • 96.
    Kemerink, Martijn
    et al.
    Eindhoven University of Technology, Netherlands.
    Sauthoff, K
    Eindhoven University of Technology, Netherlands.
    Koenraad, PM
    Eindhoven University of Technology, Netherlands.
    Gerritsen, JW
    Eindhoven University of Technology, Netherlands.
    van Kempen, H
    Eindhoven University of Technology, Netherlands.
    Wolter, JH
    Eindhoven University of Technology, Netherlands.
    Optical detection of ballistic electrons injected by a scanning-tunneling microscope2001In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 86, no 11, p. 2404-2407Article in journal (Refereed)
    Abstract [en]

    We demonstrate a spectroscopic technique which is based on ballistic injection of minority carriers from the lip of a scanning-tunneling microscope into a semiconductor heterostructure. Ey analyzing the resulting electroluminescence spectrum as a function of tip-sample bias, both the injection barrier height and the carrier scattering rate, in the semiconductor can be determined. This technique is complementary to ballistic electron emission spectroscopy since minority instead of majority carriers are injected, which give the opportunity to study the carrier trajectory after injection.

  • 97.
    Kemerink, Martijn
    et al.
    Eindhoven University of Technology, Netherlands.
    Sauthoff, K
    Eindhoven University of Technology, Netherlands.
    Koenraad, PM
    Eindhoven University of Technology, Netherlands.
    Gerritsen, JW
    Eindhoven University of Technology, Netherlands.
    van Kempen, H
    Eindhoven University of Technology, Netherlands.
    Wolter, JH
    Eindhoven University of Technology, Netherlands.
    Optical detection of ballistically injected electrons in III/V heterostructures2001In: PROCEEDINGS OF THE 25TH INTERNATIONAL CONFERENCE ON THE PHYSICS OF SEMICONDUCTORS, PTS I AND II, SPRINGER-VERLAG BERLIN , 2001, Vol. 87, p. 819-820Conference paper (Refereed)
    Abstract [en]

    We present a novel spectroscopic technique which is based on the ballistic injection of minority carriers from the tip of an STM into a semiconductor heterostructure. By analyzing the resulting electro-luminescence spectrum as a function of tip-sample bias, both the injection barrier height and the carrier relaxation rate Gamma (s) after injection can be determined. From current dependent measurements we find that carrier trapping by impurities causes a significant non-radiative recombination channel at room temperature.

  • 98.
    Kemerink, Martijn
    et al.
    Eindhoven University of Technology, Netherlands.
    Thomassen, PMM
    Eindhoven University of Technology, Netherlands.
    Koenraad, PM
    Eindhoven University of Technology, Netherlands.
    Bobbert, PA
    Eindhoven University of Technology, Netherlands.
    Henning, JCM
    Eindhoven University of Technology, Netherlands.
    Wolter, JH
    Eindhoven University of Technology, Netherlands.
    Many-particle effects in Be-delta-doped GaAs/AlxGa1-xAs quantum wells1998In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 58, no 3, p. 1424-1435Article in journal (Refereed)
    Abstract [en]

    We have performed photoluminescence (PL) and photoluminescence excitation measurements on two series of center-delta-doped p-type GaAs/AlxGa1-xAs quantum wells, with variable well width and doping concentration. The experimental data are compared with self-consistent field calculations. The effects of exchange and correlation were found to be extremely important and various models for the hole exchange and correlation are compared with the experimental data. It is found that the model recently proposed by Bobbert et al. [P. A. Bobbert rt al., Phys. Rev. B 56, 3664 (1997)] consistently describes our experimental observations. Furthermore, for well widths w greater than or equal to 600 Angstrom clear excitonic effects were observed, for hole densities as high as 12 X 10(12) cm(-2), which is explained in terms of small spatial overlap between the screening particles and the exciton along the growth direction. In contrast to earlier work on similar samples, we found no indication for a Fermi-edge singularity in the PL spectra of our samples. Peaked structures at the high-energy side of the PL spectra are shown to arise from bulk transitions. [S0163-1829(98)04324-0].

  • 99.
    Kemerink, Martijn
    et al.
    Eindhoven University of Technology, Netherlands.
    Timpanaro, S
    Eindhoven University of Technology, Netherlands.
    de Kok, MM
    Eindhoven University of Technology, Netherlands.
    Meulenkamp, EA
    Eindhoven University of Technology, Netherlands.
    Touwslager, FJ
    Eindhoven University of Technology, Netherlands.
    Three-dimensional inhomogeneities in PEDOT : PSS films2004In: Journal of Physical Chemistry B, ISSN 1520-6106, E-ISSN 1520-5207, Vol. 108, no 49, p. 18820-18825Article in journal (Refereed)
    Abstract [en]

    Spin-cast PEDOT/PSS film are investigated using scanning probe-based spectroscopic techniques. The films are found to consist of relatively well-conducting islands that are embedded in a less conductive matrix. A scanning-tunneling microscope-based method is developed to obtain three-dimensional conductivity images with nanometer resolution. Order-of-magnitude variations in the film conductivity are observed in all spatial directions. In addition, charge transport in the normal direction depends on the injection spot and is found to be ohmic or space-charge-limited. We found that both the morphology and the conductivity of the top layer differ substantially from those in the bulk, which is attributed to an enhanced PSS content in the top layer.

  • 100.
    Kemerink, Martijn
    et al.
    Eindhoven University of Technology, Netherlands.
    van Duren, JKJ
    Eindhoven University of Technology, Netherlands.
    Jonkheijm, P
    Eindhoven University of Technology, Netherlands.
    Koenraad, PM
    Eindhoven University of Technology, Netherlands.
    Janssen, RAJ
    Eindhoven University of Technology, Netherlands.
    Salemink, HWM
    Eindhoven University of Technology, Netherlands.
    Wolter, JH
    Eindhoven University of Technology, Netherlands.
    Imaging individual chains and aggregates on conjugated polymer films2003In: ORGANIC AND POLYMERIC MATERIALS AND DEVICES, MATERIALS RESEARCH SOCIETY , 2003, Vol. 771, p. 23-28Conference paper (Refereed)
    Abstract [en]

    We demonstrate a novel method to visualize individual molecular chains in the surface layer of organic semiconducting polymer films of arbitrary thickness. The method is based on scanning force microscopy and employs a combination of a sensitive phase detection system and metal coated tips with a low (similar to1 N/m) spring constant and a relatively high Q factor (similar to200). The molecularly resolved morphology is observed in phase images that are taken simultaneously with the topography. Surprisingly, we found that, when the tip apex radius exceeds the intermolecular spacing in the surface layer, surface aggregates -when present- are visualized. In both cases, the phase contrast is shown to result from van der Waals interaction between the conjugated backbone of the polymer chains and the metallic tip, and can quantitatively be described by a simple harmonic oscillator model. We have employed this method to study the morphology of poly(p-phenylene vinylene) (PPV) derivatives with different substitutions.

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