K. Haenen

Hasselt University, Hasselt, Flemish, Belgium

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Publications (215)441.68 Total impact

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    ABSTRACT: Photoactive reaction centers (RCs) are protein complexes in bacteria able to convert sunlight into other forms of energy with a high quantum yield. The photo-stimulation of immobilized RCs on inorganic electrodes result in the generation of photocurrent that is of interest for bio-solar cell applications. This paper reports on the use of novel electrodes based on functional conductive nanocrystalline diamond onto which bacterial RCs are immobilized. A 3-dimensional conductive polymer scaffold grafted to the diamond electrodes enables an efficient entrapment of photoreactive proteins. The electron transfer in these functional diamond electrodes is optimized through the use of a ferrocene-based electron mediator, which provides significant advantages such as a rapid electron transfer as well as high generated photocurrent. A detailed discussion of the generated photocurrent as a function of time, bias voltage and mediators in solution unveils the mechanisms limiting the electron transfer in these functional electrodes. This work featuring diamond-based electrodes in bio-photovoltaics, offers general guidelines that can serve to improve the performance of similar devices based on different materials and geometries.
    ACS Applied Materials & Interfaces 04/2015; 7(15). DOI:10.1021/acsami.5b00711 · 5.90 Impact Factor
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    ABSTRACT: Lead phthalocyanine (PbPc) thin films of 5 and 50 nm have been deposited on hydrogen and oxygen terminated single crystal diamond (SCD) using organic molecular beam deposition. Atomic force microscopy and X-ray diffraction (XRD) studies showed that PbPc grown on the hydrogen terminated SCD forms layers with a high degree of crystallinity, dominated by the monoclinic (320) orientation parallel to the diamond surface. The oxygen terminated diamond led to a randomly oriented PbPc film. Absorption and photocurrent measurements indicated the presence of both polymorphs of PbPc, however, the ratio differed depending on the termination of the SCD. Finally, polarized Raman spectroscopy was used to determine the orientation of the molecules of the thin film. The results confirmed the random orientation on the O-terminated diamond. On SCD:H, the PbPc molecules are lying down in accordance with the XRD results.
    Physical Chemistry Chemical Physics 03/2015; 17(15). DOI:10.1039/c5cp00174a · 4.20 Impact Factor
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    ABSTRACT: Nanocrystalline diamond (NCD) is a promising material for electronic and mechanical micro- and nanodevices. Here we introduce a versatile pick-up and drop technique that makes it possible to investigate the electrical, optical and mechanical properties of as-grown NCD films. Using this technique, NCD nanosheets, as thin as 55 nm, can be picked-up from a growth substrate and positioned on another substrate. As a proof of concept, electronic devices and mechanical resonators are fabricated and their properties are characterized. In addition, the versatility of the method is further explored by transferring NCD nanosheets onto an optical fibre, which allows measuring its optical absorption. Finally, we show that NCD nanosheets can also be transferred onto 2D crystals, such as MoS2, to fabricate heterostructures. Pick-up and drop transfer enables the fabrication of a variety of NCD-based devices without requiring lithography or wet processing.
    Nanotechnology 03/2015; 26(12). DOI:10.1088/0957-4484/26/12/125706 · 3.67 Impact Factor
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    ABSTRACT: In this study we show an optical biosensor concept, based on elastic light scattering from sapphire microspheres. Transmitted and elastic scattering intensity of the microspheres (radius 500 μm, refractive index 1.77) on an optical fiber half coupler is analyzed at 1510 nm. The 0.43 nm angular mode spacing of the resonances is comparable to the angular mode spacing value estimated using the optical size of the microsphere. The spectral linewidths of the resonances are in the order of 0.01 nm, which corresponds to quality factors of approximately 105. A polydopamine layer is used as a functionalizing agent on sapphire microspherical resonators in view of biosensor implementation. The varying layer thickness on the microsphere is determined as a function of the resonance wavelength shift. It is shown that polymer functionalization has a minor effect on the quality factor. This is a promising step toward the development of an optical biosensor.
    Sensors and Actuators A Physical 02/2015; 222. DOI:10.1016/j.sna.2014.11.024 · 1.94 Impact Factor
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    ABSTRACT: Boron doped diamond layers have been grown on (110) single crystal diamond substrates with B/C ratios up to 20 ppm in the gas phase. The surface of the diamond layers observed by scanning electron microscopy consists of (100) and (113) micro-facets. Fourier Transform Photocurrent Spectroscopy indicates substitutional boron incorporation. Electrical properties were measured using Hall effect from 150 to 1000 K. Secondary ion mass spectrometry analyses are consistent with the high incorporation of boron determined by electrical measurements. A maximum mobility of 528 cm2.V- 1.s- 1 was measured at room temperature for a charge carrier concentration of 1.1 1013 cm- 3. Finally, properties of boron doped (110) diamond layers are compared with layers on (100) and (111) orientated substrates.
    Diamond and Related Materials 01/2015; 53. DOI:10.1016/j.diamond.2015.01.006 · 1.57 Impact Factor
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    ABSTRACT: In this study development of impedimetric sensor based on oxygen terminated boron-doped nanocrystalline diamond (B:NCD:O) modified with theophylline imprinted polypyrrole is described. Hydrogen peroxide induced chemical formation of polypyrrole molecularly imprinted by theophylline was applied for the modification of conducting silicon substrate covered by B:NCD:O film. Non-imprinted polypyrrole layer was formed on similar substrate in order to prove efficiency of imprinted polypyrrole. Electrochemical impedance spectroscopy was applied for the evaluation of analyte-induced changes in electrochemical capacitance/resistance. The impact of polymerization duration on the capacitance of impedimetric sensor was estimated. A different impedance behavior was observed at different ratio of polymerized monomer and template molecule in the polymerization media. The influence of ethanol as additive to polymerization media on registered changes in capacitance/resistance was evaluated. Degradation of sensor stored in buffer solution was evaluated.
    Electrochimica Acta 12/2014; 130:361-367. DOI:10.1016/j.electacta.2014.03.035 · 4.09 Impact Factor
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    ABSTRACT: Correction for ‘Diamond functionalization with light-harvesting molecular wires: improved surface coverage by optimized Suzuki cross-coupling conditions’ by W. S. Yeap et al., RSC Adv., 2014, 4, 42044–42053.
    RSC Advances 10/2014; 4(92). DOI:10.1039/C4RA90027H · 3.71 Impact Factor
  • Physica Status Solidi (A) Applications and Materials 10/2014; 211(10). DOI:10.1002/pssa.201470267 · 1.53 Impact Factor
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    ABSTRACT: A microcavity-based deoxyribonucleic acid (DNA) optical biosensor is demonstrated for the first time using synthetic sapphire for the optical cavity. Transmitted and elastic scattering intensity at 1510 nm are analyzed from a sapphire microsphere (radius 500 μm, refractive index 1.77) on an optical fiber half coupler. The 0.43 nm angular mode spacing of the resonances correlates well with the optical size of the sapphire sphere. Probe DNA consisting of a 36-mer fragment was covalently immobilized on a sapphire microsphere and hybridized with a 29-mer target DNA. Whispering gallery modes (WGMs) were monitored before the sapphire was functionalized with DNA and after it was functionalized with single-stranded DNA (ssDNA) and double-stranded DNA (dsDNA). The shift in WGMs from the surface modification with DNA was measured and correlated well with the estimated thickness of the add-on DNA layer. It is shown that ssDNA is more uniformly oriented on the sapphire surface than dsDNA. In addition, it is shown that functionalization of the sapphire spherical surface with DNA does not affect the quality factor (Q ≈ 10 4) of the sapphire microspheres. The use of sapphire is especially interesting because this material is chemically resilient, biocompatible, and widely used for medical implants. © 2014 Society of Photo-Optical Instrumentation Engineers (SPIE) [DOI: 10.1117/1.JBO.19.9.097006]
    Journal of Biomedical Optics 09/2014; 19(9):097006. DOI:10.1117/1.JBO.19.9.097006 · 2.75 Impact Factor
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    ABSTRACT: Surface conductivity in hydrogen-terminated single crystal diamond is an intriguing phenomenon for fundamental reasons as well as for application driven research. Surface conductivity is also observed in hydrogen-terminated nanocrystalline diamond although the electronic transport mechanisms remain unclear. In this work, the piezoresistive properties of intrinsic surface conductive nanocrystalline diamond are investigated. A gauge factor of 35 is calculated from bulging a diamond membrane of 350 nm thick, with a diameter of 656 μm and a sheet resistance of 1.45 MΩ/sq. The large piezoresistive effect is reasoned to originate directly from strain-induced changes in the resistivity of the grain boundaries. Additionally, we ascribe a small time-dependent fraction of the piezoresistive effect to charge trapping of charge carriers at grain boundaries. In conclusion, time-dependent piezoresistive effect measurements act as a tool for deeper understanding the complex electronic transport mechanisms induced by grain boundaries in a polycrystalline material or nanocomposite.
    Applied Physics Letters 09/2014; 105(10):101601-101601-4. DOI:10.1063/1.4895458 · 3.52 Impact Factor
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    ABSTRACT: In this article, we report on a label-free real-time method based on heat transfer resistivity for thermal monitoring of DNA denaturation and its potential to quantify DNA fragments with a specific sequence of interest. Probe DNA, consisting of a 36-mer fragment was covalently immobilized on a nanocrystalline diamond surface, created by chemical vapor deposition on a silicon substrate. Various concentrations of full matched 29-mer target DNA fragments were hybridized with this probe DNA. We observed that the change in heat transfer resistance upon denaturation depends on the concentration of target DNA used during the hybridization, which allowed to determine the dose response curve. Therefore, these results illustrate the potential of this technique to quantify the concentration of a specific DNA fragment and to quantify the hybridization efficiency to its probe.
    Diamond and Related Materials 09/2014; 48. DOI:10.1016/j.diamond.2014.06.008 · 1.57 Impact Factor
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    ABSTRACT: Graphene has potential for applications in solar cells. We show that the short circuit current density of P3HT (Poly(3-hexylthiophene-2,5-diyl):PCBM((6,6)-Phenyl C61 butyric acid methyl ester) solar cells is enhanced by 10% upon the addition of graphene, with a 15% increase in the photon to electric conversion efficiency. We discuss the performance enhancement by studying the crystallization of P3HT, as well as the electrical transport properties. We show that graphene improves the balance between electron and hole mobilities with respect to a standard P3HT:PCBM solar cell.
    Applied Physics Letters 08/2014; 105(8):083306-083306-5. DOI:10.1063/1.4893777 · 3.52 Impact Factor
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    ABSTRACT: Nanocrystalline diamond (NCD) thin films were produced by chemical vapor deposition (CVD) and doped by the addition of phosphine to the gas mixture. The characterization of the films focused on probing the incorporation and distribution of the phosphorus (P) dopants. Electron microscopy evaluated the overall film morphology and revealed the interior structure of the nanosized grains. The homogeneous films with distinct diamond grains featured a notably low sp2:sp3-ratio as confirmed by Raman spectroscopy. High resolution spectroscopy methods demonstrated a homogeneous P-incorporation, both in-depth and in-plane. The P concentration in the films was determined to be in the order of 1019 cm–3 with a significant fraction integrated at substitutional donor sites. (© 2014 WILEY-VCH Verlag GmbH &Co. KGaA, Weinheim)
    physica status solidi (RRL) - Rapid Research Letters 08/2014; 9999(8-9999):n/a-n/a. DOI:10.1002/pssr.201409235 · 2.34 Impact Factor
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    ABSTRACT: The modification of the diamond surface with organic molecules is a crucial aspect to be considered for any bio-application of this material. There is a great interest in broadening the range of linker molecules which can be covalently bound to the diamond surface. In the case of protein immobilization, the hydropathicity of the surface has a major influence on the protein conformation and, thus, on the functionality of proteins immobilized at surfaces. For electrochemical applications, particular attention has to be devoted to avoid that the charge transfer between the electrode and the redox center embedded in the protein is hindered by a thick insulating linker layer. This paper reports on the grafting of 6-phosphonohexanoic acid on OH-terminated diamond surfaces, serving as linkers to tether electro-active proteins onto diamond surfaces. X-ray photoelectron spectroscopy (XPS) confirms the formation of a stable layer on the surface. The charge transfer between electro-active molecules and the substrate is studied by electrochemical characterization of the redox activity of aminomethylferrocene and cytochrome c covalently bound to the substrate through this linker. Our work demonstrates that OH-terminated diamond functionalized with 6-phosphonohexanoic acid is a suitable platform to interface redox-proteins, which are fundamental building blocks for many bioelectronics applications.
    ACS Applied Materials & Interfaces 07/2014; 6(16). DOI:10.1021/am503305t · 5.90 Impact Factor
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    ABSTRACT: A straightforward protocol for the covalent functionalization of boron-doped diamond electrodes with either ferrocene or single-stranded deoxyribonucleic acid (DNA) is reported. The functionalization method is based on a combination of diazonium salt electrografting and click chemistry. An azide-terminated organic layer is first electrografted onto the diamond surface by electrochemical reduction of 4-azidophenyldiazonium chloride. The azidophenyl-modified surface then reacts rapidly and efficiently with molecules bearing a terminal alkyne moiety by means of CuI-catalyzed alkyne–azide cycloaddition. Covalent attachment of ferrocene moieties was analyzed by X-ray photoelectron spectroscopy and cyclic voltammetry, whereas impedance spectroscopy was applied for the characterization of the immobilized DNA.
    06/2014; 1(7). DOI:10.1002/celc.201402068
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    ABSTRACT: Hydrogen and oxygen surface-terminated nanocrystalline diamond (NCD) films are studied by the contactless time-resolved microwave conductivity (TRMC) technique and X-ray photoelectron spectroscopy (XPS). The opto-electronic properties of undoped NCD films are strongly affected by the type of surface termination. Upon changing the surface termination from oxygen to hydrogen, the TRMC signal rises dramatically. For an estimated quantum yield of 1 for sub-bandgap optical excitation the hole mobility of the hydrogen-terminated undoped NCD was found to be ~0.27 cm2/Vs with a lifetime exceeding 1 µs. Assuming a similar mobility for the oxygen-terminated undoped NCD a lifetime of ~100 ps was derived. Analysis of the valence band spectra obtained by XPS suggests that upon oxidation of undoped NCD the surface Fermi level shifts (towards an increased work function). This shift originates from the size and direction of the electronic dipole moment of the surface atoms, and leads to different types of band bending at the diamond/air interface in the presence of a water film. In the case of boron-doped NCD no shift of the work function is observed, which can be rationalized by pinning of the Fermi level. This is confirmed by TRMC results of boron-doped NCD, which show no dependency on the surface termination. We suggest that photo-excited electrons in boron-doped NCD occupy non-ionized boron dopants, leaving relatively long-lived mobile holes in the valence band.
    ACS Applied Materials & Interfaces 06/2014; 6(14). DOI:10.1021/am501907q · 5.90 Impact Factor
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    ABSTRACT: N3 dye molecules [cis-bis(isothiocyanato)-bis(2,2'-bipyridyl-4,4'-dicarboxylato)-ruthenium(II)] are covalently attached onto boron-doped nanocrystalline diamond (B:NCD) thin films through a combination of coupling chemistries, i.e. diazonium, Suzuki and EDC-NHS. X-ray and ultraviolet photoelectron spectroscopy (XPS and UPS), and near-edge X-ray absorption fine structure spectroscopy (NEXAFS) are used to verify the covalent bonding of the dye on the B:NCD surface (as compared to a hydrogen-terminated reference). The spectroscopic results confirm the presence of a dense N3 chromophore layer and the positions of the frontier orbitals of the dye relative to the band edge of the B:NCD thin film are inferred as well. Proof of concept photoelectrochemical measurements show a strong increase in photocurrent as compared to non-dye-functionalized B:NCD films. This study opens up the possibility to apply N3-sensitized B:NCD thin films as hole conductors in dye-sensitized solar cells.
    ACS Applied Materials & Interfaces 06/2014; 6(13). DOI:10.1021/am501783b · 5.90 Impact Factor
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    ABSTRACT: Diamond is a unique material that often exhibits extreme properties compared to other materials. Discovered about 30 years ago, the use of hydrogen in plasma-enhanced chemical vapor deposition (CVD) has enabled the growth and coating of diamond in film form on various substrate materials. CVD diamond research has been actively continued subsequently to develop new understanding and approaches for the growth and processing of this fascinating material. Currently, the study and development of diamond films has enabled a wide range of applications based on the combination of unique and extreme properties of diamond and the variety of film properties obtainable through tuning the microstructure, morphology, impurities, and surfaces. This issue of MRS Bulletin introduces the latest research, recent applications, and the challenges ahead for CVD diamond films.
    MRS Bulletin 06/2014; 39(06):490-494. DOI:10.1557/mrs.2014.97 · 5.07 Impact Factor
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    ABSTRACT: In this contribution we report on a novel method for the growth of laterally patterned synthetic diamond films with submicron feature sizes. The lateral patterning is induced by depositing a nanodiamond-based seeding layer prior to the chemical vapor deposition of the diamond films. The seeding layer is prepared by a microfluidic approach, based on soft lithography with PDMS moulds, used in the microcontact printing. These moulds are prepared by electron-beam lithography of photoresist on silicon substrates. The master moulds are reusable, allowing for cheap, high-throughput manufacturing, and the resulting diamond microstructures exhibit an outstanding smoothness and structural reproducibility. Possible applications are expected in the fields of diamond electronics, micro-electro-mechanical systems (MEMS) as well as bio- and chemosensors. The abstract figure shows the SU-8 master mould (left). The resulting diamond structure (right) is shown, after chemical vapor deposition. The purple color originates from the settings of the optical microscope, used to get a high-contrast image.
    Physica Status Solidi (A) Applications and Materials 06/2014; 211(6). DOI:10.1002/pssa.201330665 · 1.53 Impact Factor

Publication Stats

2k Citations
441.68 Total Impact Points

Institutions

  • 2005–2015
    • Hasselt University
      • Institute for Materials Research (IMO)
      Hasselt, Flemish, Belgium
  • 2012
    • Friedrich-Schiller-University Jena
      • Department of Solid State Physics
      Jena, Thuringia, Germany
  • 2006–2009
    • Transnationale Universiteit Limburg
      Belgium, Wisconsin, United States
  • 2008
    • imec Belgium
      Louvain, Flemish, Belgium