Infrared study of spin crossover Fe-picolylamine complex

Infrared (IR) absorption spectroscopy has been used to probe the evolution of microscopic vibrational states upon the temperature- and photo-induced spin crossovers in [Fe(2-picolylamine)3]Cl2EtOH (Fe-pic). To overcome the small sizes and the strong IR absorption of the crystal samples used, an IR synchrotron radiation source and an IR microscope have been used. The obtained IR spectra of Fe-pic show large changes between high-spin and low-spin states for both the temperature- and the photo- induced spin crossovers. Although the spectra in the temperature- and photo-induced high-spin states are relatively similar to each other, they show distinct differences below 750 cm-1. This demonstrates that the photo-induced high-spin state involves microscopically different characters from those of the temperature-induced high-spin state. The results are discussed in terms of local pressure and structural deformations within the picolylamine ligands, and in terms of their possible relevance to the development of macroscopic photo-induced phase in Fe-pic.Comment: 6 pages (text) and 6 figures,submitted to J. Phys. Soc. Jp

Phase Transition in a One-Dimensional Extended Peierls-Hubbard Model with a Pulse of Oscillating Electric Field: I. Threshold Behavior in Ionic-to-Neutral Transition

Photoinduced dynamics of charge density and lattice displacements is calculated by solving the time-dependent Schr\"odinger equation for a one-dimensional extended Peierls-Hubbard model with alternating potentials for the mixed-stack organic charge-transfer complex, TTF-CA. A pulse of oscillating electric field is incorporated into the Peierls phase of the transfer integral. The frequency, the amplitude, and the duration of the pulse are varied to study the nonlinear and cooperative character of the photoinduced transition. When the dimerized ionic phase is photoexcited, the threshold behavior is clearly observed by plotting the final ionicity as a function of the increment of the total energy. Above the threshold photoexcitation, the electronic state reaches the neutral one with equidistant molecules after the electric field is turned off. The transition is initiated by nucleation of a metastable neutral domain, for which an electric field with frequency below the linear absorption peak is more effective than that at the peak. When the pulse is strong and short, the charge transfer takes place on the same time scale with the disappearance of dimerization. As the pulse becomes weak and long, the dimerization-induced polarization is disordered to restore the inversion symmetry on average before the charge transfer takes place to bring the system neutral. Thus, a paraelectric ionic phase is transiently realized by a weak electric field. It is shown that infrared light also induces the ionic-to-neutral transition, which is characterized by the threshold behavior.Comment: 24 pages, 11 figure

Möglichkeiten und Grenzen der Metallisierung textiler Flächen mittels PVD-Technologien für multifunktionale Schutztextilien

Für leichte textile Flächengebilde zum Hitze- und Kälteschutz waren durch Applikation metallischer Schichten durch thermisches Verdampfen und Magnetron-Sputtern kombinierte Shielding-Funktionen zu entwickeln. Dabei richtete sich das Augenmerk auf die Haftungsproblematik der Metallschichten ohne merklichen Verlust der Oberflächenwiderstände. Zur Verbesserung der Schichthaftung wurden die Textilien verschiedenen Vorbehandlungen, einer Gasphasenfluorierung, einer 100 nm starken Hexamethyldisiloxan-Beschichtung (HMDSO) sowie einer Behandlung mit einem Haftvermittler der Firma Bolte unterzogen. Außerdem wurden die metallisierten Materialien mit verschiedenen Zweitausrüstungen aus Polyurethan-, Vinylacetat- und zwei Polysiloxanausrüstungen nach Herstellerangaben bzw. mit einer HMDSO-Schicht behandelt. Zur Bestimmung der Haftkräfte ausgewählter Schichten dienten der Peel-Test sowie ein Martindale-Schleudertest. Parallel dazu erfolgten bis zu vier Waschprüfungen je Probe. Zur Beurteilung der elektrischen Leitfähigkeiten der Muster wurden die Oberflächenwiderstände ausgewählter Proben nach DIN EN 1149-1 mit einer Ringelektrode gemessen. Die angestrebten Haftkräfte von 8 N/15mm wurden für bedampfte und besputterte Fallschirmseide, ohne Schichtpartikel mit dem Tape vom Substrat zu lösen, erreicht und übertroffen. Die Ergebnisse im Martindale-Scheuertest zeigen, dass mit dem thermischen Bedampfen und dem Magnetron-Sputtern auf textilen Substraten Schichten mit guten Hafteigenschaften gegenüber Scheuerbeanspruchung abgeschieden werden können. Vor allem die Sputter-Beschichtung ermöglicht die Generierung sehr haftfester Schichten. Eine zusätzliche Nachbehandlung der Metallschichten mit Polymerbeschichtungen und HMDSO ist empfehlenswert. Bei den Vliesstoffen kann die Verbundfestigkeit durch eine zusätzliche Polymerbeschichtung deutlich verbessert werden. Bei der parallel zum Abriebtest erfolgten Waschbehandlung mit bis zu 4 Wäschen je Probe wurde das anvisierte Ziel, Schichthaftungen bis zu 15 Wäschen ohne merklichen Verlust der funktionellen Eigenschaften wie die Leitfähigkeit zu erzielen, nicht erreicht

Correlations of the distribution of spin states in spin crossover compounds

Short range correlations of the distribution of high spin (HS) and low spin (LS) states show up in thermal spin transition curves, decay curves of the light induced metastable HS state (LIESST state), and in structural features during the spin transitions. Correlations are due to short range interactions between the spin crossover molecules. Short range interactions may compete with omnipresent long range interactions and give rise to interesting spin transition phenomena. In this paper, the effect of correlations on the thermal spin transition in the mixed crystal system [FexZn1−x(pic)3]Cl2·EtOH (pic=picolylamine) is discussed. In particular the step in the thermal transition curve is a direct consequence of such correlations. In addition, the decay of the metastable HS state of the pure iron compound at ca. 20 K can be significantly changed by preparing metastable HS states with a random distribution over the lattice sites. Both experiments could be well reproduced by Monte Carlo simulations. In the orthorhombic modification of the compound Fe[5NO2-sal-N(1,4,7,10)]([2,2'-(2,5,8,11-tetraazadodeca-1,11-diene-1,12-diyl)4-nitrophenolato] (2-)-N2, N2',N2'',N2''',O1, O1']Fe(II)) a commensurable superstructure has been found. This compound represents the first example of a stable infinite range correlation of the spin states over the lattice sites

Astrobiological instrumentation for Mars - the only way is down

In this paper, in this edition of the Journal commemorating the life and work of David Wynn-Williams, we consider approaches to the astrobiological investigation of Mars. We provide a brief account of the scientific rationale behind the approach presented here. In particular, we outline the capabilities of the Raman spectrometer for the detection of biomarkers. David Wynn-Williams was an active champion of this instrument who was keen to field-qualify a version in Antarctica with a view to flying a Raman instrument onboard a Mars-bound space mission. We examine a scenario for the deployment of such an instrument in conjunction with other instrumentation and argue that subsurface deployment of scientific instruments is essential if we are to succeed in detecting any evidence that may exist for former life on Mars. We outline a mission scenario – Vanguard – which represents a novel but low-risk, low-cost approach to Mars exploration that was conceived and developed jointly by one of the authors (Ellery) and the late David Wynn-Williams

ATHLET-Modellentwicklung fuer WWER 440 Reaktoranlagen Abschlussbericht

SIGLEAvailable from TIB Hannover: RN 7660(1899) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekBundesministerium fuer Forschung und Technologie (BMFT), Bonn (Germany)DEGerman