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Dienstmaier J.F.,Deutsches Museum | Dienstmaier J.F.,TU Munich | Dienstmaier J.F.,Center for NanoScience | Dienstmaier J.F.,Ludwig Maximilians University of Munich | And 8 more authors.
ACS Nano | Year: 2011

Two different straightforward synthetic approaches are presented to fabricate long-range-ordered monolayers of a covalent organic framework (COF) on an inert, catalytically inactive graphite surface. Boronic acid condensation (dehydration) is employed as the polymerization reaction. In the first approach, the monomer is prepolymerized by a mere thermal treatment into nanocrystalline precursor COFs. The precursors are then deposited by drop-casting onto a graphite substrate and characterized by scanning tunneling microscopy (STM). While in the precursors monomers are already covalently interlinked into the final COF structure, the resulting domain size is still rather small. We show that a thermal treatment under reversible reaction conditions facilitates on-surface ripening associated with a striking increase of the domain size. Although this first approach allows studying different stages of the polymerization, the direct polymerization, that is, without the necessity of preceding reaction steps, is desirable. We demonstrate that even for a comparatively small diboronic acid monomer a direct thermally activated polymerization into extended COF monolayers is achievable. © 2011 American Chemical Society.


Petershans A.,Karlsruhe Institute of Technology | Lyapin A.,Physical Electronics GmbH | Reichlmaier S.,Physical Electronics GmbH | Kalinina S.,Karlsruhe Institute of Technology | And 2 more authors.
Journal of Colloid and Interface Science | Year: 2010

Time-of-Flight Secondary Ion Mass Spectrometry (TOF-SIMS) was applied to validate GRGDS peptide patterned surfaces. The structuring of the surfaces included several steps: micro contact printing (μCP), chemical etching and aminofunctionalization followed by chemical coupling of spacer-linked GRGDS peptides via an isothiocyanate anchor. TOF-SIMS analysis of characteristic ions and molecular fragments with a lateral resolution of 100 nm allowed proving the change in chemical properties of the surface with each step during the structuring process. We found that the application of polydimethylsiloxane as stamp material resulted in the contamination of the surface with this polymer. TOF-SIMS investigations, however, also showed that during the preparation process the contaminations were removed and do not influence the bio functionality of the surface patterns. The results of the surface analysis carried out with TOF-SIMS were confirmed by complementary cell adhesion experiments with murine fibroblasts. As a result, specific cell adhesion restricted to GRGDS peptide functionalized areas was obvious by the formation of focal adhesion contacts in the fibroblasts. Thus, TOF-SIMS is the method of choice in chemical characterization of surfaces in structuring and functionalization processes, because it offers the opportunity to follow surface contamination during the preparation process and to assess the influence of the contamination on the applicability of the final substrate. © 2009 Elsevier Inc. All rights reserved.


Montero-Pancera S.,Karlsruhe Institute of Technology | Trouillet V.,Karlsruhe Institute of Technology | Petershans A.,Karlsruhe Institute of Technology | Fichtner D.,Karlsruhe Institute of Technology | And 7 more authors.
Langmuir | Year: 2010

A novel method to produce sub-microwalled chemically activated, polymer microwells by one-step UV-lithography under ambient conditions which are selectively coated with gelatin is introduced. The dimensions as well as the shape of the resulting polystyrene structures are both tunable merely by the irradiation time through one and. the same mask. It is shown that the UV-irradiation initiates three effects at those surface areas which are not covered by the mask: (i) oxidation, (ii) cross-linking, and (iii) degradation of polystyrene. The superposition of those effects results in the formation of microscaled, oxidized polymer wells separated, by polymer walls, whereas the polymer walls are formed below the mask structures. Topographical changes induced by the UV-irradiation are investigated by atomic force microscopy after different irradiation times. It is shown by X-ray photoelectron spectroscopy and ellipsometric investigations that the chemical composition of the irradiated areas and the degradation of polystyrene reach an equilibrium state after an irradiation time of 10 min. The lateral distribution of the cross-linked and oxidized and of the nonmodified polystyrene after irradiation was determined by fluorescence microscopy and time-of-flight secondary ion mass spectrometry. After the irradiated samples were treated with gelatin solution, it was found that stem cells selectively attach to the irradiated areas. This is due to the selective immobilization of the gelatin on the irradiated polymer areas, which was proved by X-ray photoelectron spectroscopy experiments. © 2009 American Chemical Society.


Meiners A.,HAWK University of Applied Sciences and Arts | Leck M.,HAWK University of Applied Sciences and Arts | Lyapin A.,Physical Electronics GmbH | Abel B.,University of Leipzig
Applied Physics A: Materials Science and Processing | Year: 2010

The adhesion of sealants to mortar or concrete is an important feature especially in building joints and the durability of the joints over a long period is an essential goal. In the present work, the surface of a cement mortar substrate is plasma treated by means of a dielectric barrier discharge. It is shown that the adhesion to a silicone sealant is improved by the plasma pretreatment. For this purpose, tensile strength tests were carried out. Furthermore, the molecular pictures behind this adhesive optimization are investigated. The plasma-treated surface was analyzed by Raman and X-ray photoelectron spectroscopy. It has been found that the plasma causes chemical modification of the substrate surface resulting in particular in a decrease of carbonate groups and a simultaneous increase of calcium oxide and probably calcium hydroxide. The improved adhesion is attributed to the formation of covalent bonds with the silanol groups of the silicone sealant and to an increase of hydrogen bonding. © 2010 Springer-Verlag.


News Article | August 30, 2016
Site: www.nanotech-now.com

Abstract: A newly discovered method for making two-dimensional materials could lead to new and extraordinary properties, particularly in a class of materials called nitrides, say the Penn State materials scientists who discovered the process. This first-ever growth of two-dimensional gallium nitride using graphene encapsulation could lead to applications in deep ultraviolet lasers, next-generation electronics and sensors. "These experimental results open up new avenues of research in 2D materials," says Joshua Robinson, associate professor of materials science and engineering. "This work focuses on making 2D gallium nitride, which has never been done before." Gallium nitride in its three-dimensional form is known to be a wide-bandgap semiconductor. Wide-bandgap semiconductors are important for high frequency, high power applications. When grown in its two-dimensional form, gallium nitride transforms from a wide-bandgap material to an ultrawide-bandgap material, effectively tripling the energy spectrum it can operate in, including the whole ultraviolet, visible and infrared spectrum. This work will have a particular impact on electro-optic devices that manipulate and transmit light. "This is a new way of thinking about synthesizing 2D materials," said Zak Al Balushi, a Ph.D. candidate coadvised by Robinson and Joan Redwing, professor of materials science and engineering and electrical engineering. Al Balushi is lead author on a paper appearing online today (Aug.29) in the journal Nature Materials titled "Two-Dimensional Gallium Nitride Realized via Graphene Encapsulation." "We have this palette of naturally occurring 2D materials," he continued. "But to expand beyond this, we have to synthesize materials that do not exist in nature. Typically, new material systems are highly unstable. But our growth method, called Migration Enhanced Encapsulated Growth (MEEG), uses a layer of graphene to assist the growth and stabilize a robust structure of 2D gallium nitride." The graphene is grown on a substrate of silicon carbide, which is a technologically important substrate used widely in industry for LEDs, radar and telecommunications. When heated, the silicon on the surface decomposes and leaves a carbon-rich surface that can reconstruct into graphene. The advantage of producing the graphene in this way is that the interface where the two materials meet is perfectly smooth. Robinson believes that in the case of two-dimensional gallium nitride, the addition of a layer of graphene makes all the difference. Graphene, a one-atom-thick layer of carbon atoms, is known for its remarkable electronic properties and strength. "It's the key," Robinson says. "If you try to grow these materials the traditional way, on silicon carbide, you normally just form islands. It doesn't grow in nice layers on the silicon carbide." When gallium atoms are added to the mix, they migrate through the graphene and form the middle layer of a sandwich, with graphene floating on top. When nitrogen atoms are added, a chemical reaction takes place that turns the gallium and nitrogen into gallium nitride. "The MEEG process not only produces ultra-thin sheets of gallium nitride but also changes the crystal structure of the material, which may lead to entirely new applications in electronics and optoelectronics," said Redwing. ### Additional coauthors include Ke Wang, Rafael Vila, Sarah Eichfield, Yu-Chuan Lin and Shruti Subramanian of Penn State, Ram Krishna Ghosh and Suman Datta of Notre Dame, Joshua Caldwell, U.S. Naval Research Laboratory, Xiaoye Qin and Robert Wallace The University of Texas at Dallas and Dennis Paul, Physical Electronics USA. The Asahi Glass Co., Ltd, Japan, and the U.S. National Science Foundation provided funding for this project. The NSF Materials Science and Engineering Center at Penn State provided funding for Al Balushi. Other funding was provided by the Alfred P. Sloan Foundation, the Penn State Materials Characterization Laboratory and the Center for Low Energy Systems Technology (LEAST), funded by the Semiconductor Research Corporation and DARPA. For more information, please click If you have a comment, please us. Issuers of news releases, not 7th Wave, Inc. or Nanotechnology Now, are solely responsible for the accuracy of the content.


News Article | August 29, 2016
Site: www.cemag.us

A newly discovered method for making two-dimensional materials could lead to new and extraordinary properties, particularly in a class of materials called nitrides, say the Penn State materials scientists who discovered the process. This first-ever growth of two-dimensional gallium nitride using graphene encapsulation could lead to applications in deep ultraviolet lasers, next-generation electronics, and sensors. "These experimental results open up new avenues of research in 2D materials," says Joshua Robinson, associate professor of materials science and engineering. "This work focuses on making 2D gallium nitride, which has never been done before." Gallium nitride in its three-dimensional form is known to be a wide-bandgap semiconductor. Wide-bandgap semiconductors are important for high frequency, high power applications. When grown in its two-dimensional form, gallium nitride transforms from a wide-bandgap material to an ultrawide-bandgap material, effectively tripling the energy spectrum it can operate in, including the whole ultraviolet, visible and infrared spectrum. This work will have a particular impact on electro-optic devices that manipulate and transmit light. "This is a new way of thinking about synthesizing 2D materials," says Zak Al Balushi, a Ph.D. candidate coadvised by Robinson and Joan Redwing, professor of materials science and engineering and electrical engineering. Al Balushi is lead author on a paper appearing online in the journal Nature Materials titled "Two-Dimensional Gallium Nitride Realized via Graphene Encapsulation." "We have this palette of naturally occurring 2D materials," he continues. "But to expand beyond this, we have to synthesize materials that do not exist in nature. Typically, new material systems are highly unstable. But our growth method, called Migration Enhanced Encapsulated Growth (MEEG), uses a layer of graphene to assist the growth and stabilize a robust structure of 2D gallium nitride." The graphene is grown on a substrate of silicon carbide, which is a technologically important substrate used widely in industry for LEDs, radar and telecommunications. When heated, the silicon on the surface decomposes and leaves a carbon-rich surface that can reconstruct into graphene. The advantage of producing the graphene in this way is that the interface where the two materials meet is perfectly smooth. Robinson believes that in the case of two-dimensional gallium nitride, the addition of a layer of graphene makes all the difference. Graphene, a one-atom-thick layer of carbon atoms, is known for its remarkable electronic properties and strength. "It's the key," Robinson says. "If you try to grow these materials the traditional way, on silicon carbide, you normally just form islands. It doesn't grow in nice layers on the silicon carbide." When gallium atoms are added to the mix, they migrate through the graphene and form the middle layer of a sandwich, with graphene floating on top. When nitrogen atoms are added, a chemical reaction takes place that turns the gallium and nitrogen into gallium nitride. "The MEEG process not only produces ultra-thin sheets of gallium nitride but also changes the crystal structure of the material, which may lead to entirely new applications in electronics and optoelectronics," says Redwing. Additional coauthors include Ke Wang, Rafael Vila, Sarah Eichfield, Yu-Chuan Lin, and Shruti Subramanian of Penn State, Ram Krishna Ghosh and Suman Datta of Notre Dame, Joshua Caldwell, U.S. Naval Research Laboratory, Xiaoye Qin and Robert Wallace of The University of Texas at Dallas, and Dennis Paul, Physical Electronics USA. The Asahi Glass Co., Ltd, Japan, and the U.S. National Science Foundation provided funding for this project. The NSF Materials Science and Engineering Center at Penn State provided funding for Al Balushi. Other funding was provided by the Alfred P. Sloan Foundation, the Penn State Materials Characterization Laboratory and the Center for Low Energy Systems Technology (LEAST), funded by the Semiconductor Research Corporation and DARPA.


News Article | February 22, 2017
Site: www.eurekalert.org

Scientists obtained the support of the Russian Foundation for Basic Research for implementation of the project on creation of new materials for capacitor type accumulators. In mid-February 2017 researchers of Peter the Great St. Petersburg Polytechnic University (SPbPU) and the University of Madras obtained support of the Russian Foundation for Basic Research for implementation of the project to create new materials for accumulators of capacitor type. The project should be completed within three years. Storage of electrical energy in the accumulators of capacitor type is one of the most promising approaches when rapid, in particular pulsed, charge output is required. Such devices should maintain their functionality in conditions of significant temperature increase, combined with the high currents. The aim of the project is to develop approaches for creation of new dielectric materials to increase the efficiency of accumulators of capacitor type in a wide temperature range. The research focuses on new materials based on antiferroelectrics, having significantly different working mechanism from the widely used analogue. The principal novelty of the approach offered by scientists is a joint study of the antiferroelectric materials properties both in the form of single crystals, which allows to apply most informative experimental techniques, and in the form of ceramics, that has direct practical significance. "The opportunity to study monocrystalline antiferroelectrics appeared only in the last few years with the development of methods of this type of crystal growth. Joint influence of pressure and temperature will be studied by X-ray scattering using resistively heated diamond anvil cells. Previously, such approach has never been applied. X-ray scattering techniques are planned to be applied using both laboratory diffractometers, and experimental facilities of synchrotron sources ESRF (France) and CAT (India)", said Dr. Alexey Filimonov, Head of Physical Electronics department of the Institute of Physics, Nanotechnology and Telecommunications, SPbPU.


Zhang P.,Beijing University of Chemical Technology | Zhang P.,University of Duisburg - Essen | Unger M.,Physical Electronics GmbH | Pfeifer F.,University of Duisburg - Essen | Siesler H.W.,University of Duisburg - Essen
Journal of Molecular Structure | Year: 2016

Variable-temperature Fourier-transform infrared (FT-IR) spectra of a predominantly amorphous and a semi-crystalline poly(l-lactic acid) (PLLA) film were measured between 30 °C and 170 °C in order to investigate their temperature-dependent structural changes as a function of the initial state of order. For an in-depth analysis of the spectral variations in the carbonyl stretching band region (1803-1722 cm-1) two-dimensional correlation spectroscopy (2DCOS) and perturbation-correlation moving-window two-dimensional (PCMW2D) analyses were applied. Significant spectral changes were observed during heating of the amorphous PLLA sample whereas the semi-crystalline specimen showed only slight band shifts as a function of the external perturbation. The PCMW2D results suggested that for efficient 2DCOS analyses the heating process should be split up in two temperature intervals. These analyses then provided information on the recrystallization of the amorphous regions, the presence of an intermediate state of order and a sequence scenario for the observed spectral changes. © 2015 Elsevier B.V.


Unger M.,Physical Electronics GmbH | Unger M.,Anasys Instruments Corp. | Pfeifer F.,University of Duisburg - Essen | Siesler H.W.,University of Duisburg - Essen
Applied Spectroscopy | Year: 2016

The main objective of this communication is to compare the performance of a miniaturized handheld near-infrared (NIR) spectrometer with a benchtop Fourier transform near-infrared (FT-NIR) spectrometer. Generally, NIR spectroscopy is an extremely powerful analytical tool to study hydrogen-bonding changes of amide functionalities in solid and liquid materials and therefore variable temperature NIR measurements of polyamide II (PAII) have been selected as a case study. The information content of the measurement data has been further enhanced by exploiting the potential of two-dimensional correlation spectroscopy (2D-COS) and the perturbation correlation moving window two-dimensional (PCMW2D) evaluation technique. The data provide valuable insights not only into the changes of the hydrogen-bonding structure and the recrystallization of the hydrocarbon segments of the investigated PAII but also in their sequential order. Furthermore, it has been demonstrated that the 2D-COS and PCMW2D results derived from the spectra measured with the miniaturized NIR instrument are equivalent to the information extracted from the data obtained with the high-performance FT-NIR instrument. © The Author(s) 2016.


Berger S.,Friedrich - Alexander - University, Erlangen - Nuremberg | Albu S.P.,Friedrich - Alexander - University, Erlangen - Nuremberg | Schmidt-Stein F.,Friedrich - Alexander - University, Erlangen - Nuremberg | Hildebrand H.,Friedrich - Alexander - University, Erlangen - Nuremberg | And 4 more authors.
Surface Science | Year: 2011

High resolution Scanning Auger Electron Spectroscopy (AES) is used to demonstrate the compositional variation across self-organized TiO2 nanotube layers grown in fluoride containing ethylene glycol electrolytes. The analysis results show a distinct fluoride rich layer in between the TiO 2 nanotubes and particularly in the triple points of the hexagonally ordered nanotubular arrays. AES analysis further revealed that extended e-beam exposure leads to a decrease in the fluoride signal (electron beam induced decomposition of fluoride species). The proof of the existence of a fluoride rich layer located between the tube walls strongly supports fluoride dissolution as the reason for a transition from a porous to a tubular morphology. © 2011 Elsevier B.V. All rights reserved.

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