Fluoride Oligomer Research Articles

Structural and Electronic Characterization of Epitaxially-Grown Ferroelectric Vinylidene Fluoride Oligomer Thin Films

AbstractThe structural and electric properties of newly synthesized vinylidene fluoride (VDF) oligomer thin films evaporated on various substrate were investigated. The structural behavior of the VDF oligomer thin films strongly depended on the kinds of substrate and substrate temperature during film preparation. In particular, the VDF oligomers epitaxially grew on KBr(001), aligned their molecular chain along the <110> direction of substrate surface, and were similar to polar Form Itype crystals of poly(VDF). While, the thin films evaporated on NaCl(001), SiO2/Si were non-polar Form II-type or mixture of both Form I- and Form II-type crystals with their molecular chain normal to the surface. These facts indicated that crystal field of substrate, based on van der Waals and electrostatic interactions, strongly influenced to ferroelectric phase transition of the VDF oligomer. In addition, we demonstrate the formation of the local polarized domains in the epitaxial crystals by applying electric pulses from a conducting AFM probe used as a positionable topelectrode, and confirm their piezoelectricity of the VDF oligomers for the first time.

Chain Length Effects on Crystal Formation in Vinylidene Fluoride Oligomers

Crystal modifications in vinylidene fluoride (VDF) oligomers, such as α, β, and γ forms, were studied as a function of the molecular chain length. VDF oligomers were prepared by a telomerization method and the oligomers were fractionated by vacuum vapor deposition. The fractionated oligomers were crystallized from the melt. The crystal forms in VDF oligomers were characterized by IR, X-ray, and DSC methods. The β form was found in the degree of polymerization (N) less than 10, the α form consisted of N ranging from 10 to 16 and the γ form was observed in N above 16. The effect of molecular chain length on the crystal forms in VDF oligomers could be associated with change in the conformational energy accompanying the steric hindrance along the molecular chain for the β form and differences in the crystallization behavior from the melt for the α and γ forms.

Structure and stability of gaseous fluorine-bridged heterodimers and heteropolymers: (AF) n(MF 3) m, A′F 2MF 3 (A = H, Li, Na, K; M = B, Al, Fe; A′ =Be, Mg, Mn; n,m = 1, 2)

Starting from an overview of experimentally identified and quantum chemically calculated gaseous fluoride heterodimers and oligomers, it is the intention of the authors to survey the present knowledge on structures and stabilities of these complexes and to draw some consequences for experimental chemistry. General characteristics of gaseous halogen-bridged complexes are explained in Section 2. The present knowledge on experimentally identified and quantum chemically calculated fluorine-bridged heterocomplexes is summarized in Section 3. Finally, stabilities and structures of fluoroaluminate complexes in the vapour phase are discussed in Section 4. The discussion is focused on fluoroaluminate complexes containing mono-, di-and trivalent cations.

Effect of Substrate Temperature on Molecular Orientation in Evaporated Thin Films of Vinylidene Fluoride Oligomer

A newly synthesized vinylidene fluoride oligomer (OVDF), for which ferroelectric properties are expected when the electric dipoles with the molecules are all aligned, was employed as a prospective evaporation material. Particularly, the crystal structure and molecular orientation in evaporated thin films were examined by a total reflection X-ray diffractometer and reflection absorption infrared spectroscopy. Consequently, it was revealed that the crystal structure of the evaporated films was similar to the form II crystals of poly(vinylidene fluoride) which is a polymeric sample of OVDF, and that the molecular orientations are perpendicular to the substrate. Moreover, it was observed that the molecular orientation changed from perpendicular to parallel to the substrate at the substrate temperature between -30 and -50° C and the stable crystal structure was form II.

Effect of molecular weight and chain end groups on crystal forms of poly(vinylidene fluoride) oligomers

The micro-structure of poly(vinylidene fluoride) oligomers was characterized by 19F and 13C n.m.r. and the effects of molecular weight and the chain end groups on the crystal forms were studied by i.r. and X-ray methods. One of the oligomers terminated with -CH 3 and the fragment of an initiator at the chain ends. The other oligomers were terminated with -Cl and CCl 3- at their chain ends. The larger chain end groups tended to produce the conformational disorder in the molecules yielding the γ form. The smaller molecular weight of the oligomer gave rise to the β form.

Cooperativity in hydrogen bonded clusters: an improved ab initio SCF study on the structure and energetics of neutral, protonated and deprotonated chains and of neutral, cyclic hydrogen fluoride oligomers

The equilibrium structures and the stabilization energies of neutral ((HF) n ) protonated ([(HF) n H] +) and deprotonated ([(HF) n − 1 F] −) chain-like hydrogen fluoride oligomers and of neutral (HF) n rings were investigated at the ab initio SCF level applying medium-sized to extended basis sets. Neutral and charged hydrogen fluoride clusters with n = 1 to 13 were treated using a DZ + P basis, and those with n = 1 to 7 were treated with a TZ + 2P + diffuse functions basis set. In addition, the cyclic (HF) n clusters with n = 2 to 6 were investigated. In order to demonstrate the strongly non-additive behaviour in these oligomers, we monitored their properties as a function of the cluster size. We investigated the convergence of a number of ground-state properties to edge and bulk-like properties in an attempt to characterize the protonated and deprotonated defect sites in long chains of hydrogen fluoride. The results are compared with earlier, lower level ab initio results as obtained with a DZ type basis set on still longer chains.

High-resolution infrared spectroscopy of DF trimer: A cyclic ground state structure and DF stretch induced intramolecular vibrational coupling

We present high resolution, infrared laser absorption spectra of (DF)3 in a slit supersonic jet expansion. In contrast to previous structureless near IR spectra of (HF)3, the (DF)3 data reveal clear rotational structure characteristic of a cyclic, 6-membered ‘‘ring,’’ and therefore provide the first accurate experimental evidence for the equilibrium geometry of any hydrogen fluoride oligomer beyond the well-studied dimer. Furthermore, the spectra display homogeneous rotational fine structure 2–3 orders of magnitude in excess of what could be anticipated from a single vibrational band. Analysis of this fine structure elucidates a novel IVR mechanism which involves single hydrogen bond cleavage, and consequent opening of the (DF)3 ring on the 40 ps time scale.

Infrared absorbance of hydrogen fluoride oligomers

Infrared absorbance of hydrogen fluoride oligomers