Search results for: Andreas Pöppl

Items from 1 to 20 out of 51 results

article

Understanding MOF Flexibility: An Analysis Focused on Pillared Layer MOFs as a Model System

Irena Senkovska, Volodymyr Bon, Leila Abylgazina, Matthias Mendt, more

Angewandte Chemie International Edition > 62 > 33 > n/a - n/a

Flexible porous frameworks are at the forefront of materials research. A unique feature is their ability to open and close their pores in an adaptive manner induced by chemical and physical stimuli. Such enzyme‐like selective recognition offers a wide range of functions ranging from gas storage and separation to sensing, actuation, mechanical energy storage and catalysis. However, the factors affecting...

article

Understanding MOF Flexibility: An Analysis Focused on Pillared Layer MOFs as a Model System

Irena Senkovska, Volodymyr Bon, Leila Abylgazina, Matthias Mendt, more

Angewandte Chemie > 135 > 33 > n/a - n/a

article

Weak Electron Irradiation Suppresses the Anomalous Magnetization of N‐Doped Diamond Crystals

Annette Setzer, Pablo D. Esquinazi, Olesya Daikos, Tom Scherzer, more

physica status solidi (b) > 258 > 11 > n/a - n/a

Several diamond bulk crystals with a concentration of electrically neutral single substitutional nitrogen atoms of ≲80 ppm, the so‐called C or P1 centers, are irradiated with electrons at 10 MeV energy and low fluence. The results show a complete suppression of the irreversible behavior in field and temperature of the magnetization below 30 K, after a decrease in ≲40 ppm in the concentration of C...

article

Unraveling Structure and Dynamics in Porous Frameworks via Advanced In Situ Characterization Techniques

Volodymyr Bon, Eike Brunner, Andreas Pöppl, Stefan Kaskel

Advanced Functional Materials > 30 > 41 > n/a - n/a

Dynamic metal–organic frameworks (MOFs) represent a subgroup of frameworks featuring unique performance, as they are capable of adapting their pore size and/or the orientation of framework constituents in response to specific guest molecules such as gases or solutes and often outperform their rigid analogus in gas storage, sensing, or separation. In this review, the authors focus on recent methodical...

article

Dynamic Metal‐Organic Frameworks: Unraveling Structure and Dynamics in Porous Frameworks via Advanced In Situ Characterization Techniques (Adv. Funct. Mater. 41/2020)

Volodymyr Bon, Eike Brunner, Andreas Pöppl, Stefan Kaskel

Advanced Functional Materials > 30 > 41 > n/a - n/a

In article number 1907847, Volodymyr Bon, Stefan Kaskel, and co‐workers review recent advances in monitoring the structural dynamics of porous frameworks via in situ characterization techniques. The development of novel parallelized analytical methods enables a concise understanding of adaptive porous systems and their responsivity thermodynamics, a prerequisite for implementing adaptive solids into...

article

Experimental Evidence for the Incorporation of Two Metals at Equivalent Lattice Positions in Mixed‐Metal Metal–Organic Frameworks

Johannes Bitzer, Steffen Otterbach, Kavipriya Thangavel, Anastasia Kultaeva, more

Chemistry – A European Journal > 26 > 25 > 5667 - 5675

Metal–organic frameworks containing multiple metals distributed over crystallographically equivalent framework positions (mixed‐metal MOFs) represent an interesting class of materials, since the close vicinity of isolated metal centers often gives rise to synergistic effects. However, appropriate characterization techniques for detailed investigations of these mixed‐metal metal–organic framework materials,...

article

Negative‐U Properties of the Deep Level E3 in ZnO

Rainer Pickenhain, Matthias Schmidt, Holger von Wenckstern, Gabriele Benndorf, more

physica status solidi (b) > 255 > 7 > n/a - n/a

The deep level E3 is a commonly observed defect in bulk crystals and thin films of ZnO independently of the method of growth. Its chemical origin is still not finally understood. In this paper, previous research on the E3 level is reviewed and recent experimental results acquired by optical deep level transient spectroscopic (DLTS) methods are presented for the temperature range from 4 to 350 K,...

article

Iron incorporation in biosilica of the marine diatom Stephanopyxis turris: dispersed or clustered?

Janine Kaden, Stephan I. Brückner, Susanne Machill, Christoph Krafft, more

BioMetals > 2017 > 30 > 1 > 71-82

Iron incorporation into diatom biosilica was investigated for the species Stephanopyxis turris. It is known that several “foreign” elements (e.g., germanium, titanium, aluminum, zinc, iron) can be incorporated into the siliceous cell walls of diatoms in addition to silicon dioxide (SiO₂). In order to examine the amount and form of iron incorporation, the iron content in the growth medium was varied...

article

Mit variablem Abstand gestapelte lineare Ketten magnetischer Ionen: ferromagnetische Ordnung mit einer Curie‐Temperatur von über 20 K

Stefan Friedländer, Jinxuan Liu, Matt Addicoat, Petko Petkov, more

Angewandte Chemie > 128 > 41 > 12874 - 12879

Die magnetischen Eigenschaften Metall‐organischer Gerüste (MOFs) der SURMOF‐2‐Serie wurden untersucht. Anders als bei Volumen‐MOF‐2‐Kristallen, bei denen Cu²⁺‐Ionen in einer Schaufelrad‐Anordnung vorliegen und antiferromagnetisch gekoppelt sind, zeigen die Carboxylatgruppen hier eine reißverschlussartige Anordnung. Eine theoretische Analyse ergibt, dass diese ungewöhnliche Kopplung der Spin‐

1 / 2

‐Ionen...

article

Linear Chains of Magnetic Ions Stacked with Variable Distance: Ferromagnetic Ordering with a Curie Temperature above 20 K

Stefan Friedländer, Jinxuan Liu, Matt Addicoat, Petko Petkov, more

Angewandte Chemie International Edition > 55 > 41 > 12683 - 12687

We have studied the magnetic properties of the SURMOF‐2 series of metal–organic frameworks (MOFs). Contrary to bulk MOF‐2 crystals, where Cu²⁺ ions form paddlewheels and are antiferromagnetically coupled, in this case the Cu²⁺ ions are connected via carboxylate groups in a zipper‐like fashion. This unusual coupling of the spin

1 / 2

ions within the resulting one‐dimensional chains is found to stabilize...

chapter

Paramagnetic Adsorption Complexes as Studied by Advanced Electron Paramagnetic Resonance Techniques

Andreas Pöppl, Marlen Gutjahr, Thomas Rudolf

Lecture Notes in Physics > Molecules in Interaction with Surfaces and Interfaces > 185-215

One major challenge in the research of microporous materials is the spectroscopic characterization of surface adsorption complexes. If the adsorbed molecules are paramagnetic the structure of the formed complexes, the dynamics of the adsorbed molecules, and the specific adsorption sites at the metaloxide surface can be accessed by electron spin resonance spectroscopy. Such studies may provide a unique...

chapter

Paramagnetic Adsorption Complexes as Studied by Advanced Electron Paramagnetic Resonance Techniques

Andreas Pöppl, Marlen Gutjahr, Thomas Rudolf

Lecture Notes in Physics > Molecules in Interaction with Surfaces and Interfaces > 185-215

book

Molecules in Interaction with Surfaces and Interfaces

Reinhold Haberlandt, Dieter Michel, Andreas Pöppl, Ralf Stannarius

Lecture Notes in Physics

The study of the interaction of molecules with surfaces and interfaces is of great importance for the understanding of adsorption and catalysis on solid surfaces, the complex properties of molecules on fluid interfaces and the relationship between structure and functionality in macromolecular biological systems. It is the aim of this volume to present and analyse in a comprehensive and accessible...

book

Molecules in Interaction with Surfaces and Interfaces

Reinhold Haberlandt, Dieter Michel, Andreas Pöppl, Ralf Stannarius

Lecture Notes in Physics

article

The influence of Mn doping on the properties of Ge4Sb2Te7

Simon Welzmiller, Frank Heinke, Paula Huth, Georg Bothmann, more

Journal of Alloys and Compounds > 2015 > 652 > Complete > 74-82

Ge₃MnSb₂Te₇ and Ge_3.5Mn_0.5Sb₂Te₇ are doped variants of Ge₄Sb₂Te₇, a material from the homologous series (GeTe)_nSb₂Te₃. Phase purity was confirmed by ICP-AES, EDX and quantitative yield according to powder X-ray diffraction. Quenched solid solutions are metastable and exhibit a rocksalt-type average structure and contain multiply twinned domains with superstructures. At ∼300 °C, a phase transition...

article

Adsorption of nitric oxide in metal-organic frameworks: Low temperature IR and EPR spectroscopic evaluation of the role of open metal sites

Benjamin Barth, Matthias Mendt, Andreas Pöppl, Martin Hartmann

Microporous and Mesoporous Materials > 2015 > 216 > Complete > 97-110

The metal-organic framework materials M-MIL-100 (M = Al, Fe) and M-CPO-27 (M = Co, Ni) have been studied with respect to the adsorption of nitric oxide employing low-temperature ESR and IR spectroscopy. Exposure of the previously desolvated Ni (II) and Co (II) sites in CPO-27 leads to the formation of metal nitrosyl complexes that are stable up to temperatures of 393 K. A weaker bond is formed between...

article

Doping GeSb₂Te₄ with Cr³⁺: Structure and Temperature‐Dependent Physical Properties

Simon Welzmiller, Robert Schlegel, Andreas Pöppl, Georg Bothmann, more

Zeitschrift für anorganische und allgemeine Chemie > 641 > 12‐13 > 2350 - 2356

The tellurides Ge_0.94Cr_0.04Sb₂Te₄ and Ge_0.88Cr_0.08Sb₂Te₄ were synthesized in sealed silica glass ampoules. Rietveld refinements show that they crystallize in the 21R‐In₃Te₄ structure type (R$\bar{3}$m), similar to undoped GeSb₂Te₄. The composition and phase purity were confirmed by ICP‐AES as well as by SEM and TEM, including EDX measurements. EPR spectroscopy reveals the valence state +III for the...

article

EPR, ESE, and pulsed ENDOR study of the nitrogen donors in 15R SiC grown under carbon‐rich conditions

Dariya Savchenko, Ekaterina Kalabukhova, Bela Shanina, Andreas Pöppl, more

physica status solidi (b) > 252 > 3 > 566 - 572

X‐band field‐sweep electron spin echo and pulsed electron nuclear double resonance (ENDOR) spectroscopy were used to study n‐type 15R SiC wafers grown under carbon (C)‐rich conditions with the aim to verify the recently proposed concept that nitrogen (N) donors substitute both carbon (C) and silicon (Si) sites and may occupy nonequivalent positions at Si sites. It was found that besides the ¹⁴N ENDOR...

article

The Line Width of the EPR Signal of Gaseous Nitric Oxide as Determined by Pressure and Temperature-Dependent X-band Continuous Wave Measurements

Matthias Mendt, Andreas Pöppl

Applied Magnetic Resonance > 2015 > 46 > 11 > 1249-1263

The electron paramagnetic resonance (EPR) signal of gaseous nitric oxide (NO) has been measured by continuous wave X-band experiments at room temperature at gas pressures between 1 mbar and 60 mbar and at a gas pressure of 48 mbar at different low temperatures. A phenomenological spin Hamiltonian approach allows simulating each EPR signal of NO by changing only a single line width parameter. At room...

article

Dielectric Ceramic EPR Resonators for Low Temperature Spectroscopy at X-band Frequencies

Stefan Friedländer, Oleg Ovchar, Horst Voigt, Rolf Böttcher, more

Applied Magnetic Resonance > 2015 > 46 > 1 > 33-48

The performance of new dielectric ceramic resonators (DRs) for continuous wave (cw) X-band electron paramagnetic resonance (EPR) spectroscopy is investigated at room temperature and low temperatures (77, 6 K). The DRs with high dielectric constants of about $$\varepsilon _r = 80$$ ε r = 80 , featuring low residual paramagnetic impurities, have been developed and produced on the basis of...

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INFONA - science communication portal

Search results for: Andreas Pöppl

Understanding MOF Flexibility: An Analysis Focused on Pillared Layer MOFs as a Model System

Understanding MOF Flexibility: An Analysis Focused on Pillared Layer MOFs as a Model System

Weak Electron Irradiation Suppresses the Anomalous Magnetization of N‐Doped Diamond Crystals

Unraveling Structure and Dynamics in Porous Frameworks via Advanced In Situ Characterization Techniques

Dynamic Metal‐Organic Frameworks: Unraveling Structure and Dynamics in Porous Frameworks via Advanced In Situ Characterization Techniques (Adv. Funct. Mater. 41/2020)

Experimental Evidence for the Incorporation of Two Metals at Equivalent Lattice Positions in Mixed‐Metal Metal–Organic Frameworks

Negative‐U Properties of the Deep Level E3 in ZnO

Iron incorporation in biosilica of the marine diatom Stephanopyxis turris: dispersed or clustered?

Mit variablem Abstand gestapelte lineare Ketten magnetischer Ionen: ferromagnetische Ordnung mit einer Curie‐Temperatur von über 20 K

Linear Chains of Magnetic Ions Stacked with Variable Distance: Ferromagnetic Ordering with a Curie Temperature above 20 K

Paramagnetic Adsorption Complexes as Studied by Advanced Electron Paramagnetic Resonance Techniques

Paramagnetic Adsorption Complexes as Studied by Advanced Electron Paramagnetic Resonance Techniques

Molecules in Interaction with Surfaces and Interfaces

Molecules in Interaction with Surfaces and Interfaces

The influence of Mn doping on the properties of Ge4Sb2Te7

Adsorption of nitric oxide in metal-organic frameworks: Low temperature IR and EPR spectroscopic evaluation of the role of open metal sites

Doping GeSb₂Te₄ with Cr³⁺: Structure and Temperature‐Dependent Physical Properties

EPR, ESE, and pulsed ENDOR study of the nitrogen donors in 15R SiC grown under carbon‐rich conditions

The Line Width of the EPR Signal of Gaseous Nitric Oxide as Determined by Pressure and Temperature-Dependent X-band Continuous Wave Measurements

Dielectric Ceramic EPR Resonators for Low Temperature Spectroscopy at X-band Frequencies

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