W. Moritz

Humboldt University of Berlin, Berlin, Land Berlin, Germany

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Publications (55)86.31 Total impact

  • [Show abstract] [Hide abstract]
    ABSTRACT: Frequency-dependent capacitance–voltage (C–V) and impedance-spectroscopy characteristics of nanoplate capacitive field-effect electrolyte-insulator-silicon-on-insulator (EISOI) structures with various thicknesses (30, 60 and 350 nm) of the top p-Si layer are investigated for the first time. The frequency-dependent C–V curves of EISOI structures show an unusual behaviour, which significantly differs from that of conventional EIS structures. Due to the large series resistance of the nanoplate top Si, the C–V curves of the EISOI structures show stronger frequency dependence in the accumulation region. In addition, C–V curves show typical low-frequency behaviour even at higher frequencies (up to 8 kHz). An equivalent circuit of an EISOI structure is discussed taking into account the series resistance of the nanoplate top Si.
    Physica Status Solidi (A) Applications and Materials 05/2011; 208(6):1327 - 1332. · 1.53 Impact Factor
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    ABSTRACT: An array of individually addressable nanoplate field-effect capacitive (bio-)chemical sensors based on an SOI (silicon-on-insulator) structure has been developed. The isolation of the individual capacitors was achieved by forming a trench in the top Si layer with a thickness of 350 nm. The realized sensor array allows addressable biasing and electrical readout of multiple nanoplate EISOI (electrolyte-insulator-silicon-on-insulator) capacitive biosensors on the same SOI chip as well as differential-mode measurements. The feasibility of the proposed approach has been demonstrated by realizing sensors for the pH and penicillin concentration detection as well as for the label-free electrical monitoring of polyelectrolyte multilayers formation and DNA (deoxyribonucleic acid)-hybridization event. A potential change of ∼ 120 mV has been registered after the DNA hybridization for the sensor immobilized with perfectly matched single-strand DNA, while practically no signal changes have been observed for a sensor with fully mismatched DNA. The realized examples demonstrate the potential of the nanoplate SOI capacitors as a new basic structural element for the development of different types of field-effect biosensors.
    Biosensors & Bioelectronics 02/2011; 26(6):3023-8. · 6.45 Impact Factor
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    ABSTRACT: A thin-film amorphous silicon (a-Si) deposited on a glass substrate was employed as a semiconductor material for the chemical imaging sensor, which can visualize the distribution of ion concentration in a solution. The sensing properties and the spatial resolution of the a-Si sensors were investigated. Nearly-Nernstian pH sensitivities and submicron resolution were demonstrated, which suggests the superior performance of the chemical imaging sensor based on thin-film a-Si.
    MRS Online Proceeding Library 01/2011; 910.
  • Fred Lisdat, Werner Moritz, Lothar Müller
    Zeitschrift für Chemie. 08/2010; 30(12):427 - 433.
  • Jan Szeponik, Werner Moritz, Farid Sellam
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    ABSTRACT: A new kind of semiconductor based fluoride sensor was prepared by growing thin polycrystalline LaF3 films directly on silicon substrates using vacuum vapour deposition technique. The EICS (Electrolyte Ion Conductor Semiconductor) structure was investigated by means of impedance spectroscopy, CV measurements and exchange measurements with labeled ions (18F). Whereas charge and potential conditions at the LaF3/ electrolyte interface are governed by the fast fluoride exchange the LaF3 bulk and the blocked Si/LaF3 interface determine the electrical behavior. Although the Si/LaF3 contact is not reversible the potential stability of the EICS structure is surprisingly high. Additional results at epitaxial LaF3 layers, prepared by MBE, were taken into account for comparision with those at polycrystalline layers.
    Berichte der Bunsengesellschaft für physikalische Chemie. 05/2010; 95(11):1448 - 1453.
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    ABSTRACT: A novel strategy for enhanced field-effect biosensing using capacitive electrolyte–insulator–semiconductor (EIS) structures functionalised with pH-responsive weak polyelectrolyte/enzyme or dendrimer/enzyme multilayers is presented. The feasibility of the proposed approach is exemplarily demonstrated by realising a penicillin biosensor based on a capacitive p-Si–SiO2 EIS structure functionalised with a poly(allylamine hydrochloride) (PAH)/penicillinase and a poly(amidoamine) dendrimer/penicillinase multilayer. The developed sensors response to changes in both the local pH value near the gate surface and the charge of macromolecules induced via enzymatic reaction, resulting in a higher sensitivity. For comparison, an EIS penicillin biosensor with adsorptively immobilised penicillinase has been also studied. The highest penicillin sensitivity of 100 mV/dec has been observed for the EIS sensor functionalised with the PAH/penicillinase multilayer. The lower and upper detection limit was around 20 µM and 10 mM, respectively. In addition, an incorporation of enzymes in a multilayer prepared by layer-by-layer technique provides a larger amount of immobilised enzymes per sensor area, reduces enzyme leaching effects and thus, enhances the biosensor lifetime (the loss of penicillin sensitivity after 2 months was 10–12%).
    Physica Status Solidi (A) Applications and Materials 03/2010; 207(4):884 - 890. · 1.53 Impact Factor
  • 7th International Conference on Semiconductor Micro- and Nanoelectronics, TSAKHCADZOR, ARMENIA; 07/2009
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    ABSTRACT: A capacitive field-effect EDIS (electrolyte–diamond–insulator–semiconductor) sensor with improved pH and penicillin sensitivity has been realised using a nanocrystalline-diamond (NCD) film as sensitive gate material. The NCD growth process on SiO2 as well as an additional surface treatment in oxidising medium have been optimised to provide high pH-sensitive, non-porous O-terminated films without damage of the underlying SiO2 layer. The surface morphology of O-terminated NCD thin films and the layer structure of EDIS sensors have been studied by scanning electron microscopy (SEM) and transmission electron microscopy (TEM) methods. To establish the relative coverage of the surface functional groups generated by the oxidation of NCD surfaces, X-ray photoelectron spectroscopy analysis was carried out. The hydrophilicity of NCD thin films has been studied by water contact-angle measurements. A nearly Nernstian pH sensitivity of 54–57 mV/pH has been observed for O-terminated NCD films treated in an oxidising boiling mixture for 80 min and in oxygen plasma. The high pH-sensitive properties of O-terminated NCD have been used to develop an EDIS-based penicillin biosensor. A freshly prepared penicillin biosensor possesses a high sensitivity of 85 mV/decade in the concentration range of 0.1–2.5 mM penicillin G. The lower detection limit is 5 μM.
    Electrochimica Acta 01/2009; 54:5981-5985. · 4.09 Impact Factor
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    ABSTRACT: An array of individually addressable nanoplate field-effect capacitive (bio-)chemical sensors based on an SOI (silicon-on-insulator) structure has been developed for multi-parameter detection. An isolation of the individual capacitors was achieved by forming a trench in the top Si layer with various thicknesses of 30-350 nm. The feasibility of the proposed approach has been demonstrated by realising sensors for the detection of pH as well as for the label-free electrical monitoring of adsorption and binding of charged macromolecules.
    Procedia Chemistry. 01/2009; 1(1):670-673.
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    ABSTRACT: Application of solid electrolytes as undergate layers accelerates the response of a sensor at room temperature as compared with ordinary hydrogen sensors manufactured on the basis of the metal-insulator-semiconductor (MIS) structures with a palladium gate. The proton-conducting solid electrolytes under study include NAFION, zirconium hydrophosphate, and etherified polyvinyl alcohol (PVA) with heteropolyacids and phenoldisulfonic acid, which can be deposited under the platinum gate. Sensors based on the MIS structures with these solid electrolytes show a high sensitivity toward hydrogen (∼120 mV per concentration decade). The response time τ0.63 of a freshly manufactured sensor with a layer of zirconium hydrophosphate amounts to about 2 min. The maximum mechanical stability, especially at relative humidities in excess of 80% is intrinsic to sensors containing layers of PVA with heteropolyacids. The response time of such sensors is nearly 10 min.
    Russian Journal of Electrochemistry 04/2007; 43(5):561-569. · 0.50 Impact Factor
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    ABSTRACT: An increase in the number of gases detectable by sensors based on Pd-SiO<sub>2</sub>-Si (MIS) and Pt-LaF<sub>3</sub>-Si<sub>3</sub>N<sub>4 </sub>-SiO<sub>2</sub>-Si (MEIS) structures was achieved by the application of an external catalyst element (CE). It was shown that as a result of the decomposition of hydrocarbon and fluorocarbon molecules on a Ni coil (CE), the products detectable by metal-insulator-semiconductor (MIS) and metal-electrolyte-insulator-semiconductor (MEIS) sensors are formed. The simultaneous catalytic oxidation of hydrocarbons and their thermal decomposition result in an optimum CE temperature of about 1050 K for propane. The kinetics of the thermal decomposition of gases on Ni were investigated. The activation energy of the reaction for C<sub>3 </sub>H<sub>8</sub> and the enthalpy in the case of CF<sub>3</sub>-CCl were estimated
    IEEE Sensors Journal 03/2007; · 1.85 Impact Factor
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    ABSTRACT: An LaF<sub>3</sub> layer was shown to improve the characteristics of field-effect gas sensors for room-temperature hydrogen monitoring. The Pt/LaF<sub>3</sub> interface leads to a Nernst-type response and a detection limit of 10-ppm hydrogen in atmospheric air. The response time was shown to be about 110 s and was independent of hydrogen concentration. A method for the stabilization of a long-term behavior of the sensor was successfully demonstrated. The mechanism of the sensor's response to hydrogen was shown to be different from that of the metal/insulator/semiconductor (MIS)-type sensors
    IEEE Sensors Journal 11/2006; · 1.85 Impact Factor
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    ABSTRACT: A silicon based semiconductor sensor structure Pd/LaF 3 /Si 3 N 4 /SiO 2 /Si was prepared using thin layer technology. The sensor can be used for hydrogen detection at room temperature. Therefore, the power consumption is reduced by a factor 10 6 compared to the best low power consumption hydrogen sensors. In contrast to other sensors it can be used for measurements at very low and high hydrogen partial pressure. The limit of detection was determined to be 0.5 ppm. Measurements at high concentrations near to and above the Lower Explosion Level (LEL) of 4 % hydrogen in air are demonstrated. A method to achieve long lifetime of the sensor was developed.
    ECS Transactions 10/2006; 3(10).
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    ABSTRACT: Scanning Photo-Induced Impedance Microscopy (SPIM) is an impedance imaging technique that is based on photocurrent measurements at field-effect structures. The material under investigation is deposited onto a semiconductor–insulator substrate. A thin metal film or an electrolyte solution with an immersed electrode serves as the gate contact. A modulated light beam focused into the space charge region of the semiconductor produces a photocurrent, which is directly related to the local impedance of the material. The absolute impedance of a polymer film can be measured by calibrating photocurrents using a known impedance in series with the sample.Depending on the wavelength of light used, charge carriers are not only generated in the focus but also throughout the bulk of the semiconductor. This can have adverse effects on the lateral resolution. Two-photon experiments were carried out to confine charge carrier generation to the space charge layer. The lateral resolution of SPIM is also limited by the lateral diffusion of charge carriers in the semiconductor. This problem can be solved by using thin silicon layers as semiconductor substrates. A resolution of better than 1 μm was achieved using silicon on sapphire (SOS) substrates with a 1 μm thick silicon layer.
    Electrochimica Acta. 01/2006;
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    ABSTRACT: The lateral resolution of photocurrent techniques such as light-addressable potentiometric sensors (LAPS) or scanning photo-induced impedance microscopy (SPIM) is limited by the properties of the semiconductor material used. We investigated metal-insulator-semiconductor (MIS) structures based on amorphous silicon (a-Si) prepared as a thin layer on transparent glass substrates. It was shown that a sub-micrometer resolution can be achieved for this material, which is much better than the results for single crystalline Si. Some limitations caused by light scattering in the structure were observed.
    Sensors and Actuators B: Chemical. 01/2004;
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    ABSTRACT: A.C. impedance spectroscopy is a valuable tool in the characterisation of electrochemical systems and new materials. However, the results obtained using this method are always surface averaged. A new technique, which is suitable for imaging the complex impedance of electrochemical and solid-state systems with good spatial resolution, has been developed. It is based on photocurrent measurements at field effect structures. A semiconductor–insulator structure serves as the substrate for the film under investigation. A pulsed and focused light beam scanned across the sample surface results in photocurrents, which provide information about the local distribution of the dielectric properties of the film. Thin films of poly methyl methacrylate were investigated as a model system. Absolute values of the impedance could be calculated from the photocurrent measurements using a simple calibration procedure. Good spatial resolution was achieved by using a thin epitaxial film of silicon as the semiconductor substrate.
    Electrochimica Acta 01/2002; · 4.09 Impact Factor
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    ABSTRACT: The silicon based semiconductor structure Si/SiO2/Si3N4/LaF3/Pt can be used as a potentiometric oxygen sensor working at room temperature. A thermal re-activation can be applied to overcome the earlier disadvantage of an increase in response time with continuous use. Using the Pt gate electrode as a resistive heater, very short electrical high-power pulses can be applied. A heating time as short as 300 ns was sufficient for the re-activation of the sensor. This way, only the sensitive thin layer system LaF3/Pt was heated, and the whole sensor was at room temperature immediately after heating. Impedance spectroscopy, X-ray photoelectron spectroscopy (XPS) and quadruple mass spectrometric (QMS)–thermogravimetry (TG) were used to investigate the mechanism of deterioration in dynamic sensor behaviour and re-activation. The formation of hydrated carbonate and the desorption of CO2 and H2O have been shown to be the causes.
    Analytica Chimica Acta 06/2001; 437(2):183-190. · 4.39 Impact Factor
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    ABSTRACT: A method for submicrosecond heating of sensor surfaces and simultaneous detection of the surface temperature was developed enabling accurate and fast reactivation of a semiconductor based oxygen sensor. High power electrical pulses with current densities of more than 107 A/cm2 were applied to the 60-nm-thick Pt layer of a chemical semiconductor sensor structure resulting in surface temperatures as high as 700 K maintained in the nanosecond to microsecond range. Temperature measurement was carried out using the temperature dependent electrical resistance of the Pt film. Electrical power pulses of defined shape allowed accurate control of the surface temperature with ns time resolution. The high reactivation surface temperatures required high current densities, eventually leading to fatal destruction of the sensor structure. Comparative numerical simulations of the thermal impact as well as photo thermal and scanning force microscopy measurements were performed to optimize the heating process and to investigate the destruction mechanism.
    Thin Solid Films 01/2001; 391(1):143-148. · 1.87 Impact Factor
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    ABSTRACT: The spatial resolution of the light-addressable potentiometric sensor (LAPS) is investigated both theoretically and experimentally. For a theoretical analysis, the diffusion equation for minority charge carriers in the semiconductor was solved. The results suggest that by thinning the semiconductor wafer, the spatial resolution of the LAPS is no longer limited by the bulk minority charge carrier diffusion length. Spatial resolution in the micrometer range should thus be possible. For an experimental analysis, the effective diffusion length of light-generated charge carriers parallel to the sensor surface was measured. The results show that by increasing the doping density and by thinning the semiconductor substrate, spatial resolution of about 15 μm is obtained.
    Sensors and Actuators A Physical 11/2000; 86(3):187-196. · 1.84 Impact Factor
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    ABSTRACT: A miniaturized optical set-up based on a CD-ROM player optic was developed for LAPS (light addressable potentiometric sensors). A focus of 2.6 microm was achieved using this easy to handle device. The lateral resolution of LAPS measurements can be improved by using GaAs as the semiconductor material instead of Si. The diffusion length of the minority charge carriers was determined to be smaller than 3.1 microm. A new method called SPIM (scanning photo-induced impedance microscopy) is described. Using this technique, the impedance of thin films can be measured with lateral resolution.
    Fresenius Journal of Analytical Chemistry 07/2000; 367(4):329-33.

Publication Stats

225 Citations
86.31 Total Impact Points

Institutions

  • 1990–2010
    • Humboldt University of Berlin
      • Department of Chemistry
      Berlin, Land Berlin, Germany
    • Humboldt State University
      Arcata, California, United States
  • 2009
    • Universiteit Hasselt
      • Institute for Materials Research (IMO)
      Flanders, Belgium
  • 2006
    • Universitat Rovira i Virgili
      Tarraco, Catalonia, Spain
  • 1999
    • Kurchatov Institute
      Moskva, Moscow, Russia
  • 1993
    • Bundesanstalt für Materialforschung und -prüfung
      Berlín, Berlin, Germany
  • 1992
    • Institute of Molecular Biology
      Mayence, Rheinland-Pfalz, Germany