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Cattani-Scholz - Research Group leader: Dr. Anna Cattani-Scholz (Chair of Prof. Dr. Martin Stutzmann) HOME NEWS PEOPLE PUBLICATIONS RESEARCH TEACHING FUNDING Inorganic semiconductors combined with bio-organic systems offer the potential for the development of a wide range of novel hybrid devices. In particular in the emerging area of hybrid organic/inorganic semiconductor interfaces for bioelectronic devices, there is a continuous need of developing new functional materials with improved properties. In this context, wide band gap semiconductors have attained increased interest as particularly promising substrate materials for the development of novel biosensing devices. SiC in particular is mechanically robust, chemically inert, non toxic and biocompatible and, thanks to its transparency for the visible light, can be used for in situ observation of living cell growth. The different polytypes of SiC are quite well matched to organic systems in terms of band gap and band alignment. In this project we have focused our first investigations on the covalent immobilization on 6H-SiC surfaces of peptide nucleic acid oligonucleotides, which are receptors for DNA hybridization. In contrast to DNA, PNA does not have an anionic phosphate backbone, and is therefore uncharged at neutral pH. The lack of repulsion between PNA and DNA results in enhanced hybridization efficiency and increased melting temperatures, properties which make PNA an ideal receptor in many biosensing applications. Characterization by cyclic voltammetry shows that it is possible to detect electrochemically the attachment of a PNA single strand to 4H-SiC as well as the hybridization with a complementary DNA strand, because the oligonucleotides significantly influence the charge transfer characteristics across the interface. In the frame of this project we want to test further our platform to the designed immobilization of proteins on SiC trough aptamer hybridization. Aptamers are artificial nucleic acids with specific binding affinity and selectivity for amino acids, drugs, proteins, and other small molecules and have potential applications as a recognition element in analytical and diagnostic assays. Since aptamers can be synthesized at low cost via in vitro procedures, the easy modification of the aptamer sequence with a complementary tag for the specific binding to the PNA moieties can allow to regulate immobilization of different aptamer sequences on the device surface. In this sense preliminary studies, using a thrombin-aptamer complex immobilized on a 4H-SiC electrode, have shown the potentiality of this approach. Selected publications Auernhammer M.; Schoell S.J.; Sachsenhauser M.; Liao K.-C.; Schwartz J.; Sharp I. D.; Cattani-Scholz A. “Surface Functionalization of 6H-SiC Using Organophosphonate Monolayers”, Applied Physics Letters 2012, 100, 101601. Cattani-Scholz, A.; Pedone, D.; Blobner, F.; Abstreiter, G.; Schwartz, J.; Tornow, M.; Andruzzi, L. “PNA-PEG Modified Silicon Platforms as Functional Bio-interfaces for Applications in DNA Microarrays and Biosensors”, Biomacromolecules 2009, 10, 489-496. Back To Top Expanding the range of molecules that can be covalently grafted on diamond substrates is of increasing interest in many bio-applications. The possibility of surface termination makes diamond a promising platform for different functionalization methods. In particular, diamond surfaces can be modified with organophosphonate self-assembled monolayers (SAMs) and polymer brushes, creating suitable platforms for the immobilization of proteins without loosing their functionality. In particular biohybrid heterostructures based on bacterial reaction centers immobilized on carbon-based electrodes can be applied to realize hybrid systems able to convert sunlight into photocurrent with high efficiency. Surface analysis methods, such as atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS) are used to characterize the modified surfaces. Electrochemical characterization with cyclic voltammetry (CV), square wave voltammetry (SWV), and electrochemical impedance spectroscopy (EIS) can be applied to investigate the charge transfer mechanism in such complex hybrid systems. Selected publications Caterino R.; Csiki R.; Wiesinger M.; Sachsenhauser M.; Speranza G., Janssens S. D.; Haenen K.; Stutzmann M.; Garrido J. A.; Cattani-Scholz A. "Organophosphonate biofunctionalization of diamond electrodes", ACS Appl. Mater. Interfaces 2014, 6, 13909−13916. Caterino R.; Csiki R.; Lyuleeva A.; Pfisterer J.; Wiesinger M.; Janssens S. D.; Haenen K.; Cattani-Scholz A.; Stutzmann M.; Garrido J. A.; “Photocurrent generation on diamond electrodes modified with reaction centers”, ACS Appl. Mater. Interfaces 2015, 7, 8099−8107. Collaborations Jose A. Garrido, ICN2 - Catalan Institute of Nanoscience and Nanotechnology, Barcelona, Spain Back To Top Controlling the properties of functional layers in direct contact to semiconductor surfaces at the nanoscale is of major importance for future applications in nanoelectronics, photovoltaics and sensing. Recently, it has been demonstrated that, starting from a library of self-assembled monolayer molecules (SAMs), it is possible to tailor the properties of carbon nanomembranes, for example, to produce ultrathin films. These membranes are synthesized by irradiation-induced cross-linking of aromatic thiols on gold. Following this approach, we are interested in tuning the properties at the nanoscale of aromatic organophosphonate SAMs directly grown on semiconductor, like silicon dioxide and silicon carbide. We are working with self-assembled monolayers of complex aromatic phosphonic acids containing at the distal ends different functional groups (nitro, carboxylic, phosphonic acid) , potentially ready to further modification. The electron-induced cross-linking of the aromatic SAM can be achieved by irradiating the samples with an electron source at 10-8 mbar and with variation of the dose from 5 mC/cm² to 80 mC/cm². The novel functional interfaces generated are characterized by a variety of surface analysis methods, including optical microscopy, atomic force microscopy (AFM), contact angle (CA), X-ray photoelectron spectroscopy (XPS) as well as electrochemical measurements (Impedance spectroscopy and cyclic Voltammetry). Current investigations are focusing on the optimization of the cross-linking process and on the investigation of the chemical mechanism which cause the covalent interactions on the surface. Selected publications Csiki R. Neumann C.; Schwarzwälder S.; Liao K-C.; Schwartz J.; Turchanin A.; Stutzmann M.; Cattani-Scholz A. “Effects of Electron Irradiation on Monolayers of 9,10-Di-(9-anthryl)-2,6-diphosphonoanthracene (“Trianthracene phosphonate”) Deposited on Silicon Dioxide and Silicon Carbide”, 2018, under submission. Collaborations Jeffrey Schwartz, Chemistry Department, Princeton University New Jersey, USA Andrey Turchanin, Institute of Physical Chemistry, Friedrich Schiller University Jena, Germany Back To Top Citrus huanglongbing (HLB, ex greening) is one of the most serious and destructive citrus diseases in the world, responsible for increasing economic losses worldwide in the recent years. The aim of this project consist in the realization of electrochemical biosensors based on ZnO nanostructure, for the detection of compounds emitted from HLB diseased citrus plants, achieving high speed of detection associated with the ability to perform first screening on the field. Our research focusses on: Stable and homogenous immobilization of ZnO nanostructures on gold: Stable immobilization and homogenous distribution of ZnO nanostructures on solid substrates can play a fundamental role in optimizing nanostructured devices based on this material. The stability of ZnO nanoparticles (NPs) deposited into different self-assembled monolayers on gold electrodes shows a dramatic dependence on the SAMs terminal group. 11-mercaptoundecylphosphonic acid can form uniform and conformal monolayers on gold through the thiol group and the phosphonic acid at the distal ends of the resulting monolayer can be used as anchoring group for covalently bound the ZnO nanoparticles. The application of this chemistry can be used as a powerful tool for the fabrication of designed architectures of ZnO nanostructures on gold. The improved stability of ZnO nanostructers on the SAM functionalized gold surface is proved via surface chemical analysis (X-ray photoelectron spectroscopy), and surface morphological structure analysis (atomic force microscopy and scanning tunnelling microscopy). Biofunctionalization of ZnO nanostructures: Nanostructured zinc oxide (ZnO) not only possesses a high surface area and good biocompatibility, but it also shows biomimetic and specific electron transport features, making it an interesting material for potential applications in biosensing. One of the primary drivers to enhance and tailor the function and performance of ZnO in biosensing applications is the capability to immobilize tailored molecular and biomolecular layers on ZnO surfaces. Interfaces that enable such attachment can permit conformational control of surface-bound receptors with high target molecule binding efficiencies. Collaborations Rossana E. Madrid, Lab. De Medios e Interfases (LAMEIN), Dpto. Bioingeniería, Universidad Nacional de Tucumán, and INSIBIO-CONICET, Argentina Back To Top Organophosphonate self-assembled monolayers (SAMPs) fabricated on SiO2 surfaces can influence crystallization of vapor-deposited pentacene, and thus can affect device performance of pentacene-based organic thin film transistors. Polarized Raman spectroscopy is demonstrated to be an effective technique to determine the degree of anisotropy in pentacene thin films deposited on structurally different, aromatic SAMPs grown on silicon oxide dielectrics. Grain sizes of pentacene crystallites grown on bare SiO2 dielectric are larger than those grown on SAMPs. However, the transport characteristics of pentacene thin film transistors based on inferior, commercial Si/SiO2 substrates are drastically improved by SAMP dielectric functionalization. Vibrational characterization of pentacene molecules in these films reveals that the molecular orientation of adjacent crystalline grains is strongly correlated on the SAMP-modified dielectric surface, which results in enhanced interconnectivity between the crystallite domains, well beyond the size of a single grain. Through AFM, X-ray analysis, Raman spectroscopy, and electrical characterization we can show that aromatic organophosphonate monolayers can act as effective nucleation sites for the crystallization of pentacene and can influence molecular microstructure and intermolecular interactions in the deposited pentacene thin films. Selected publications S.; Westermeier C.; Weinbrenner D.; Sachsenhauser M.; Liao K-C.; Noever S.; Postorino P.; Schwartz J.; Abstreiter G.; Nickel B.; Zardo I.; Cattani-Scholz A. " Surface-Directed Molecular Assembly of Pentacene on Aromatic Organophosphonate Self-Assembled Monolayers Explored by Polarized Raman Spectroscopy", J. Raman Spectrosc. 2016, 48, 235–242. Collaborations Ilaria Zardo, Department of Physics, University of Basel, Switzerland Andrey Turchanin, Institute of Physical Chemistry, Friedrich Schiller University Jena, Germany Back To Top Nanoparticles (NPs) of semiconductor materials are playing a prevalent role in nanotechnology by breaking new ground in e.g. electronics, photovoltaics, thermoelectric power, light emitting devices, and biomedicine. In particular, crystalline silicon nanoparticles (Si NPs) offer many advantages, compared to the mostly studied NPs so far, i.e. CdX, PbX, ZnX (X=Se,S,Te) NPs. Si NPs are made of an environmentally inert, biocompatible, and highly abundant element and are potentially compatible with well-established Si electronics. High quality and size-controlled Si NPs can now be mass-produced in a cost-efficient manner using non-thermal plasma methods. In this research program, we will explore a bottom-up approach based on the directed assembling of thin films of NPs bound to solid surfaces functionalized with molecular monolayers. We expect this method to provide a stable and patternable immobilization of very thin layers of NPs - in the limit a NP monolayer - which cannot be achieved with conventional solution-based deposition methods. Moreover, we expect that the combination of NPs with organic molecules will provide novel means of enhancing the properties of NPs or enabling new functionalities. We have started also to investigate the charge transport properties of the assembled NP networks by means of electrical measurements. Collaborations Rui N. Pereira, Walter Schottky Institut and Physics Departement, Technische Universität München, Germany Back To Top The central goal of this research project is the investigation and optimization of the structural, electronic and electrochemical properties of organophosphonate functionalized silicon-based nanowire field effect devices. The devices rely on detecting changes in the electrical surface potential that occur as a result of adsorbing charged DNA. This signal transduction mechanism is free from the need to modify the target DNA molecules by, for example, fluorescent dyes; hence it constitutes a label-free detection method. To minimize hampering electrolyte screening effects a suitable organic interface is needed to provide high density of receptor binding sites at a short distance to the semiconductor sensing surface. To this end, we focus our research on the biofunctionalization of silicon oxide-terminated surfaces with peptidic nucleic acid (PNA), an analogue of DNA. Functionalizing via attachment groups at the γ-points along the PNA backbone allows for multidentate binding of the PNA receptor in a lying configuration on the device surface, with potential advantages towards tackling the counter-ion screening problem at the sensor interface. PNA is chosen because of its high biological stability and its significantly higher affinity for complementary DNA, allowing for a higher signal-to-noise ratio detection capabilities. Current investigations are based on a detailed surface characterization of these novel functional interfaces performed by atomic force microscopy (AFM), ellipsometry, X-ray photoelectron spectroscopy (XPS), Fourier-transform infrared spectroscopy (FTIR), and in particular by electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV). The DNA detection mechanism by hybridization with PNA is investigated by fluorescence spectroscopy. Future work will focus on reduction of nonspecific DNA adsorption effects and monolithic integration of these sensor structures into microfluidic systems for reliable molecular characterization of DNA/RNA detection in disease diagnostics. Selected publications Bartl, J. D.; Stutzmann, M.; Tornow, M; Cattani-Scholz, A; "Synthesis and optimization of organic sensing platforms for label-free DNA detection," IEEE NEMS 2017, Los Angeles, USA, 2017, 118-121. Cattani-Scholz, A.; Pedone, D.; Dubey, M.; Neppl, S.; Nickel, B.; Feulner, P.; Schwartz, J.; Abstreiter, G.; Tornow, M. “Organophosphonate-based PNA-functionalization of silicon nanowires for label-free DNA detection”, ACS Nano 2008, 2, (8), 1653-1660. Collaborations Luca Selmi, partimento di Ingegneria “Enzo Ferrari”, Università degli Studi di Modena e Reggio Emilia, Italy Marc Tornow, Molecular Electronics and Department of Electrical and Computer Engineering, Technische Universität München, Germany Back To Top Since the first discovery of graphene in 2004, 2-dimensional materials have shown great promise in numerous applications, due to their particular electrical and optical properties. With the field of application ranging from sensing and photodetection up to energy conversion - to name just a few, gaining control over the physical properties of 2-dimensional materials has proven to be of great importance. In this project we investigate the effect of organophosphonate interfacial chemistry on the intrinsic doping behavior of monolayer MoS2 (ML-MoS2). For this purpose we fabricate heterostructures based on (Si/SiO)2 substrate, functionalized with organophosphonate self-assembled monolayers (SAMPs) and decorated with ML-MoS2. Interfacial interaction of ML-MoS2 and different SAMPs results in a shift of the Raman-active out-of-plane mode A1???? of MoS2, indicating the effect of functionalization on the electronic properties of the 2-dimensional material. Selected publications Csiki, R.; Parzinger, E.; Schwartz, J.; Stutzmann, M.; Wurstbauer, U.; Cattani-Scholz, A. Tuning the Physical Properties of MoS2 Membranes through Organophosphonate Interfacial Chemistry, IEEE-Nano 2015, Rome, Italy 2015. Collaborations Ursula Wurstbauer, Walter Schottky Institut and Physics Departement, Technische Universität München, Germany Jeffrey Schwartz, Department of Chemistry, Princeton University, USA K. Larsson, Uppsala University, Sweden Back To Top Understanding the electronic transport through layered systems comprising organic functional layers in direct contact to semiconductor surfaces is of major importance for future applications in nanoelectronics, photovoltaics and sensors. In this project we are interested in creating new molecular architectures based on organized growth of surface-attached organic semiconductors on nanoscale devices through directed regular stacking of bifunctional oligoarenes. We focus on the deposition of self-assembled monolayers of alkyl and aryl phosphonates (SAMPs) onto silicon/silicon oxide substrates. These SAMs can serve as a basis for the preparation of novel three-dimensional, organized bilayers of anthracene diphophonates, using techniques of coordination chemistry under controlled conditions by deposition of organometallic linkers onto the monolayers. Duplex stacks of dense monolayers can be prepared by a simple sequence of SAMP formation followed first by distal surface activation through coordination chemistry and then by introduction of the second monolayer unit. Structural analysis by QCM, AFM, and XRR indicated homogeneous growth of the duplexes and not random multilayer formation. In particular, we can show that resistive and capacitive behaviors of these stacks can be analyzed using impedance spectroscopy, and data can be analyzed using basic equivalent resistance-capacitor circuit models to parse the contributions of the individual components to the capacitance of the overall ensemble. In the group of M. Tornow the electrical transport through the monolayered SAMPs is further investigated by measuring the current-voltage (I-V) characteristics using a two terminal configuration set-up (hanging Hg drop) or by studying the transport characteristics in Si nano-gap devices. Selected publications Bora A.; Pathak A.; Liao K.-C.; Vexler M. I.; Kuligk A.; Cattani-Scholz A.; Meinerzhagen B.; Abstreiter G.; Schwartz J.; Tornow M. “Organophosphonates as model system for studying electronic transport through monolayers on SiO2/Si surfaces”, Appl. Phys. Lett. 2013, 102, 241602. Cattani-Scholz A.; Liao K.-C.; Bora A.; Pathak A.; Hundschelld C.; Nickel B.; Schwartz J.; Abstreiter G.; Tornow M. “Molecular Architecture: Construction of Self-Assembled Organophosphonate Duplexes and Their Electrochemical Characterization”, Langmuir 2012, 28, 7889−7896. Cattani-Scholz A.; Liao K.-C.; Bora A.; Pathak A.; Krautloher M.; Nickel B.; Schwartz J.; Tornow M.; Abstreiter G. “A New Molecular Architecture for Molecular Electronics”, Special Insert from DFG in Angew. Chem. Ed. Int. Ed. Engl. 2011, 37, A11-A16. Collaborations Marc Tornow, Molecular Electronics and Department of Electrical and Computer Engineering, Technische Universität München, Germany Jeffrey Schwartz, Department of Chemistry, Princeton University, USA Back To Top Reintegration of C1-sources like CO2 and CH4 into chemical valuable chains is one of the major challenges of our time. Both molecules, although abundant and cheap, exhibit high thermodynamic stability, resulting in a high activation energy of associated refining processes. Existing well-investigated thermal conversion must be replaced by more efficient novel routes. A promising alternative is the photocatalytic reduction of CO2 mediated by rhenium(I) bipyridine complexes. However, these homogeneous approaches generally suffer from low catalyst stability due to either light- or radical-induced deactivation [1]. Surface grafting on semiconducting nanostructures acting as active supports can stabilize these molecular complexes against deactivation processes. This project combines fundamental research in Semiconductor Electronics (Stutzmann), Photocatalysis (Rieger), Coordination Chemistry (Hess/Rieger) and Interface Chemistry (Cattani-Scholz). We focus on the development and optimization of hybrid photosystems for CO2 reduction. In particular, we investigate the influence of new (nano-structured) GaN-based pulsed light sources [2] on the photostability and photocatalytic activity of different rhenium catalysts (Scheme 1). As a proof of concept, we have established direct and indirect surface immobilization protocols on planar GaN (0001) substrates to chemically anchor differently functionalized rhenium(I) bipyridine complexes. An in-depth surface characterization of the different hybrid photocatalytic systems carried out by water contact angle (CA) measurements, atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS) confirmed the formation of stable and densely packed catalytic centers on the planar GaN substrate. The electronic structure and electrochemical properties of theses hybrid systems are further probed by photoluminescence (PL) and cyclic voltammetry (CV) measurements. Finally, photocatalytic activity and stability is investigated by gas chromatographic methods and nuclear magnetic resonance (NMR). Interested students should contact Dr. Anna Cattani-Scholz (anna.cattani-scholz@wsi.tum.de). Selected publications Pschenitza, M.; Meister, S.; von Weber, A.; Kartouzian, A.; Heiz, U. & Rieger, B. Suppression of Deactivation Processes in Photocatalytic Reduction of CO2 Using Pulsed Light, ChemCatChem, 2016, 8, 2688-2695. Hetzl, M.; Schuster, F.; Winnerl, A., Weiszer, S. & Stutzmann, M. GaN nanowires on diamond, Mater. Sci. Semicond. Process., 2016, 48, 65-78. Collaborations Bernhard Rieger, WACKER-Lehrstuhl für Makromolekulare Chemie, Technische Universität München, Germany Corinna Hess, Bioanorganische Chemie, Technische Universität München, Germany Alessio Gagliardi, Simulation of Nanosystems for Energy Conversion, Technische Universität München, Germany Francesca Toma, Joint Center for Artificial Photosynthesis (JCAP), Lawrence Berkeley National Laboratory, USA Back To Top