Comparison of the electronic structure of two polymers with strong dipole ordering

Abstract

Two different polymers, with large local electric dipoles, are compared: copolymers of polyvinylidene fluoride with trifluoroethylene [P(VDF-TrFE, 70%:30%)] and polymethylvinylidenecyanide (PMVC). While the different local point group symmetries play a key role, both crystalline polymers exhibit intra-molecular band structure, though the Brillouin zone critical points differ.

Different approaches to adjusting band offsets at intermolecular interfaces

“…The thin films thickness was dictated by a need to ensure layers free of pin-holes while still as thin as possible to diminish contributions of final state photoemission effects. Throughout, the P(VDF-TrFE) thin films were made on Al, Au and graphite substrates using the Langmuir-Blodgett (LB) technique, as described elsewhere [11,12], and are seen to be highly crystalline on graphite substrates [32][33][34].…”

“…The angle-resolved photoemission spectra reproduced here were taken with photon energy of 70 eV, unless otherwise stated, the photon incident angle was 40° from the surface normal and the photoelectrons were collected normal to the surface. While P(VDF-TrFE) does exhibit band structure of the unoccupied bands [32,36,37], the occupied bands exhibit only a small band width and little dispersion with wave vector (k || ) [38], so that the angle-resolved photoemission studies were primarily undertaken to determine molecular orientation as described elsewhere [39]. The He I (21.2 eV) ultraviolet photoemission (UPS), angle-resolved inverse photoemission, and XPS were undertaken in a single UHV chamber [12,13,21].…”

Energetics of the dipole flip-flop motion in a ferroelectric polymer chain

“…The P͑VDF͒ polymer is modeled by a chain consisting of four or five -͑CH 2 -CF 2 ͒-monomers, as has been successfully done elsewhere with semiempirical model calculations of P͑VDF-TrFE͒. 23,27 The carbon atoms at the two ends of the chain are capped with hydrogen atoms. This is a typical technique used in other calculations 23,[26][27][28] in order to correct the finite size effect and to compensate the loss of covalent bonding.…”

Changing band offsets in copper phthalocyanine to copolymer poly(vinylidene fluoride with trifluoroethylene) heterojunctions

“…The P͑VDF-TrFE͒ thin films were made on Au and graphite substrate surface by using the Langmuir-Blodgett technique, as described elsewhere, 8 and are seen to be highly crystalline on graphite substrates. 19 The CuPc thin films, of 2 nm thickness and greater, were evaporated onto Au and P͑VDF-TrFE͒ substrates in a preparation chamber, vacuum continuous with the spectroscopy ultrahigh vacuum ͑UHV͒ chamber, 9,18,19 at a rate of about 0.2 nm/ min. The photoemission spectra were taken with He I radiation of 21.2 eV, and the photoelectrons are collected along the surface normal.…”