E. Arenholz

Pulsed-laser deposition of crystalline Teflon (PTFE) films

Abstract Thin films of crystalline polytetrafluoroethylene (PTFE) were prepared by pulsed-laser deposition using 248 nm UV-excimer-laser radiation. Pressed powder pellets and bulk PTFE have been employed as target material. The films were analyzed by means of optical polarization microscopy, stylus profilometry, capacity measurements, XRD, and IR spectroscopy. The effect of substrate temperature T s on the morphology and crystallinity of the films was studied. Films deposited from pressed powder targets at sufficiently high T s consist mainly of spherulite-like microcrystallites. These films are continuous, pinhole-free, well adherent to the substrate, and have a composition which is similar to that of the target material. It is suggested that film formation is based on laser-assisted material transfer with subsequent melting and crystallization. They are superior to films deposited from PTFE bulk targets, cut from a solid rod, with respect to film morphology, deposition rate, film cohesion, and optical and electrical properties.

Structure formation in UV-laser ablated poly-ethylene-terephthalate (PET)

Structure formation observed in UV-laser ablated poly-ethylene-terephthalate (PET) foils can uniquely be assigned to mechanical and thermal pretreatments.

Charge stability of pulsed-laser deposited polytetrafluoroethylene film electrets

Pulsed-laser deposited (PLD) polytetrafluoroethylene (Teflon-PTFE) films from press-sintered powder targets are found to be highly crystalline, with spherulite sizes adjustable over more than one order of magnitude by suitable thermal annealing. Films with large spherulites show an excellent charge stability, comparable and even superior to commercially available Teflon-PTFE foils. PLD-PTFE enlarges the family of Teflon materials and may thus become interesting for potential miniaturized electret devices.

UV-laser-induced surface topology changes in polyimide

Surface topology changes in polyimide induced by single UV-laser pulses with pulse durations between 140 ns and 5 μs are investigated by means of atomic force microscopy. With increasing fluence three different regimes are found: (a) real material removal (ablation), (b) swelling of the irradiated area above the level of the untreated surface (hump formation) and (c) lowering of the irradiated area below the level of the untreated surface (dent formation). A detailed description of these topology changes is given and different formation processes are discussed.

Enhanced adhesion of metal films on PET after UV-laser treatment

The adhesion-force of thin metal films on PET foils can be significantly improved by UV excimer-laser irradiation of the polymer surface prior to metal deposition. The laser fluences required are well below the ablation threshold.

Femtosecond excimer-laser-induced structure formation on polymers

Structure formation upon 500 fs 248 nm KrF-laser irradiation of PolyEthylene Terephthalate (PET) and PolyImide (PI) has been investigated. The results obtained with fs pulses have been compared to those with ns pulses.

Laser-induced surface modification and structure formation of polymers

Abstract Different types of surface modifications and structure formation of PET (poly-ethylene-terephthalate) and PI (polyimide) foils induced by excimer-laser radiation are investigated.

Remediation of Cr(VI) by biogenic magnetic nanoparticles: An x-ray magnetic circular dichroism study

Remediation of Cr(VI) by biogenic magnetic nanoparticles: An x-ray magnetic circular dichroism study N. D. Telling 1 , V. S. Coker 1 , R. S. Cutting 1 , G. van der Laan 1,2 , C. I. Pearce 1 , R. A. D. Pattrick 1 , E. Arenholz 3 , and J. R. Lloyd 1 School of Earth, Atmospheric and Environmental Sciences, University of Manchester, Manchester M13 9PL, UK Magnetic Spectroscopy Group, Diamond Light Source, Didcot, Oxfordshire, OX11 0DE, UK Advanced Light Source, Lawrence Berkeley National Laboratory, Berkeley, CA, USA Biologically synthesized magnetite (Fe 3 O 4 ) nanoparticles are studied using x-ray absorption and x-ray magnetic circular dichroism following exposure to hexavalent Cr solution. By examining their magnetic state, Cr cations are shown to exist in trivalent form on octahedral sites within the magnetite spinel surface. The possibility of reducing toxic Cr(VI) into a stable, non-toxic form, such as a Cr 3+ -spinel layer, makes biogenic magnetite nanoparticles an attractive candidate for Cr remediation. PACS number(s): 91.25.fa; 87.64.kd; 89.60.-k; 91.62.Rt

Single-pulse ultraviolet laser-induced surface modification and ablation of polyimide

Single-pulse laser ablation of polyimide was investigated by using focused UV-Ar+-laser radiation (λ≈302 nm, 140 ns⩽τl⩽50 ms) and atomic force microscopy. The results clearly demonstrate that the ablation rates do not depend on the total dose only, but depend as well on the duration of the laser pulses, τl. The experimental results can be interpreted almost quantitatively on the basis of a purely thermal model.

Pulsed-laser–deposited and plasma-polymerized polytetrafluoroethylene (PTFE)-like thin films: A comparative study on PTFE-specific properties

Glass-like and structural first-order phase transitions are investigated in polytetrafluoroethylene (PTFE) foils and PTFE-like films prepared by pulsed-laser deposition (PLD) and plasma polymerization (PP). A structural comparison of the investigated polymers is performed by infrared spectroscopy and dielectric dilatometry. It is shown that dielectric dilatometry (the measurement of the susceptance vs. temperature) provides a simple and elegant means for detecting volumetric transitions in thin nonpolar polymer films. In conventional PTFE foils, the known glass-like and structural first-order phase transitions are identified. The structure of pulsed-laser deposited PTFE strongly depends on the target material, ranging from highly crystalline films showing only structural phase transitions to films strongly deviating from PTFE foils, with structural characteristics comparable to plasma-polymerized fluorocarbons. The dielectric loss of the highly crystalline PLD films compares favorably with conventional PTFE foils, making the films attractive for new applications in miniature electret devices.