Polytetrafluoroethylene Thin Films Research Articles

Pulsed-laser deposition of polytetrafluoroethylene

Thin films of polytetrafluoroethylene have been deposited on amorphous substrates by the pulsed-laser deposition technique. By transmission electron microscopy, the polymer films were shown to consist of both amorphous and crystalline components. The data for the crystalline component are consistent with it being highly ordered with the long helical molecular chains aligned parallel to the film substrate interface plane. The fraction of crystalline material in the films was found to be related to the substrate temperature during deposition with the maximum amount of crystalline material occurring when the substrate temperature was close to the melting temperature of the polymer.

F/sub 2/ laser deposition of CdTe microcrystallites-doped fluoropolymer thin films

Crystalline thin films of polytetrafluoroethylene (PTFE) were deposited by F/sub 2/ laser (157 nm) ablation in 200 mTorr Ar gas atmosphere. Combining this PTFE thin-film process with CdTe microcrystallites synthesis in sizes of 3-7 nm via KrF laser (248 nm) ablation, CdTe microcrystallites-doped PTFE thin films were fabricated. The X-ray photoemission spectra show that the main architecture of PTFE and CdTe are maintained in the doped films. CdTe microcrystallites doped in PTFE matrix show an absorption edge shift toward higher energy and a third-order optical nonlinearity, which are induced by the quantum size effect. >

The Morphology of Polytetrafluoroethylene (PTFE) Thin Films Formed by Pulsed-Laser Deposition

ABSTRACTThin films of polytetrafluoroethylene have been formed by the pulsed-laser deposition technique. The structure of the films was found to be dependent upon the substrate temperature during deposition. At substrate temperatures from room temperature to 200°C the films were determined, by transmission electron microscopy and X-ray diffraction techniques, to be amorphous. Films formed at higher substrate temperatures were found to contain both amorphous and crystalline components. The data for the crystalline component is consistent with it being highly ordered with the long helical molecular chains aligned parallel to the film-substrate interface plane. The maximum amount of crystalline material occurred when the substrate temperature was close to the melting temperature of the polymer.

Evidence for unzipping reactions in the laser ablation of polytetrafluoroethylene (PTFE)

We have characterized the neutral and charged species emitted by pulsed-laser irradiation of polytetrafluoroethylene (PTFE) in vacuum at 248 nm in fluence regimes appropriate for the pulsed-laser deposition of PTFE thin films. The time-of-flight behavior of the major neutral species is consistent with thermal emission at temperatures where PTFE is known to decompose thermally. The laser fluence dependence of the intensity of the most intense neutral component (the C2F4 monomer) is analyzed in terms of a thermally activated decomposition process. Under isothermal conditions, thermal decomposition is believed to be rate limited by radical formation, with an activation energy of a few eV. In contrast, the fluence dependence of the monomer intensity indicates an activation energy of about 0.9 eV — appropriate to an unzipping reaction rate limited by radical transport along the polymer chain.

Crystal Growth and Molecular Orientation of Organic Materials Vapor-deposited on Highly-oriented Polytetrafluoroethylene Thin Film

Polytetrafluoroethylene (PTFE) thin film used as substrates was rubbed mechanically on a glass plate. PTFE thin film was composed of a highly oriented thin layer containing a few grooves along the sliding direction. The chain axis of the PTFE macromolecules corresponding to the crystal c-axis was oriented parallel to the glass surface. Diacetylene molecules such as 4,6- decadiyn- 1,10-diol-bis-(n-butoxycarbonyl-methyl-urethane) deposited on a PTFE-coated glass plate formed disk-like or rectangular crystallites along the grooves of the PTFE film. Diacetylene molecules adsorbed their side chains almost perpendicular to the substrate surface and were aligned along the chain axis of the PTFE macromolecules

Neutral and ion emissions accompanying pulsed excimer laser irradiation of polytetrafluoroethylene

The neutral and charged species emitted by pulsed-laser irradiation of polytetrafluoroethylene (PTFE) at 248 nm in vacuum have been examined. In particular, the species and properties of the emission products produced at typical fluence regimes used in the pulsed-laser deposition of PTFE thin films have been characterized. The relative intensities of the major products as well as their dependence on laser fluence are presented, and a simple model is used to fit the observed fluence dependence. Evidence that the major neutral component, the monomer (C2F4), is formed from a thermally activated unzipping reaction is presented. The ionic species are derived from the neutral decomposition products, apparently ionized by electron collisions in the weak plasma generated at the target surface.

Energy conversion transducer using pyroelectric mylar and teflon thin films

Abstract It has been earlier reported1 by us that the ferroelectric polymer PVF2 has a good potential for thermodielectric energy conversion. Since PVF2 is costly, the study was extended to other commercially available and cheaper pyroelectric polymer films like Mylar and Teflon. Direct conversion by pumping solar thermal to electrical energy using the capacitance change is examined for their energy conversion characterisation. It has been also reported that the plastic films are superior to ferroelectric thin films.

Surface and guided polaritons in films of polytetrafluoroethylene

Multiple-internal-reflection spectra of thick and thin films of polytetrafluoroethylene have been measured. In the region of the C-F stretching vibrations, surface polaritons were observed, and for very thin films guided polaritons were observed. They had been suggested from our earlier work and are now confirmed with this recent investigation. This constitutes the first observation of the phenomena in polymeric materials.

Diffusion phenomena at the interface of CdSe and PTFE thin films

Previous research on CdSe thin film transistors and polytetrafluoroethylene (PTFE) thin film capacitors justify the study of PTFE as the insulator in a thin film active device. In a metal-insulator-semiconductor (MIS) structure, the interface of PTFE and CdSe was investigated. A slowly growing depletion layer in the CdSe was detected. This is explained as caused by a diffusion process of an impurity which acts as an acceptor. The diffusor could not be identified but is believed to be fluorine.

Pervaporation a travers des films de polytetrafluoroethylene modifies par greffage radiochimique de N-vinylpyrrolidone

An equimolar mixture of water and dioxane (composition close to the azeotrope) can be separated by pervaporation. Useful membranes are obtained by radiation grafting of N-vinylpyrrolidone on thin films of polytetrafluoroethylene. The characteristics of the films so formed depend on the method of preparation. Films modified by irradiation in a pyridine solution of the monomer are more selective than those obtained using a benzene solution but they give rise to slightly lower rates.

A note on the use of polytetrafluoroethylene in vacuum seals

BS>The method of preparing very thin films of polytetrafluoroethylene for use as vacuum seals is described. Cutting techaiques are included along with cleaning methods and the heating process which forms the seal. (J.R.D.)