N. Kresz

Absorbing film assisted laser induced forward transfer of fungi (Trichoderma conidia)

We present an investigation on absorbing film assisted laser induced forward transfer (AFA-LIFT) of fungus (Trichoderma) conidia. A KrF excimer laser beam [λ=248nm,FWHM=30ns (FWHM, full width at half maximum)] was directed through a quartz plate and focused onto its silver coated surface where conidia of the Trichoderma strain were uniformly spread. The laser fluence was varied in the range of 0–2600mJ∕cm2 and each laser pulse transferred a pixel of target material. The average irradiated area was 8×10−2mm2. After the transfer procedure, the yeast extract medium covered glass slide and the transferred conidia patterns were incubated for 20 h and then observed using an optical microscope. The transferred conidia pixels were germinated and the areas of the culture medium surfaces covered by the pixels were evaluated as a function of laser fluence. As the laser fluence was increased from 0 to 355mJ∕cm2 the transferred and germinated pixel area increased from 0 to 0.25mm2. Further increase in fluence resulted...

Pulsed laser deposition of compact high adhesion polytetrafluoroethylene thin films

Polytetrafluoroethylene (PTFE) thin films were prepared from pressed powder pellets via pulsed laser deposition by using ArF (193 nm) excimer laser. The applied laser fluences were in the 1.6-10 J cm-2 range, the substrate temperature was varied between 27°C and 250°C and post-annealing of the films was carried out in air at temperatures between 320°C and 500°C. Films deposited at 250°C substrate temperature were found to be stoichiometric while those prepared at lower temperatures were fluorine deficient. Morphological analyses proved that the film thickness did not significantly depend on the substrate temperature and the post annealing at 500°C resulted in a thickness reduction of approximately 50%. It was demonstrated that the films prepared at 8.2 J cm-2 fluence and annealed at 500°C followed by cooling at 1°C min-1 rate were compact, pinhole-free layers. The adherence of films to the substrates was determined by tensile strength measurements. Tensile strength values up to 2.4 MPa were obtained. These properties are of great significance when PTFE films are fabricated for the purpose of protecting coatings.

Investigation of incubation in ArF excimer laser irradiated poly(methyl-methacrylate) using pulsed force mode atomic force microscopy

An atomic force microscopic method to study the incubation states of UV laser irradiated polymer samples is presented. Targets were illuminated by different number of pulses at 5.8 and 8.9mJ∕cm2 fluences. The induced adhesive and morphological changes were investigated simultaneously by an atomic force microscope equipped with a pulsed force mode extension. Importantly, below 100 pulses morphological changes were not observable while significant changes in the adhesion were found as a result of the incubation at 8.9mJ∕cm2 fluence. This method allows the imaging and detection of the whole laser modified area with nanometer resolution.

ADHESION STRENGTH MEASUREMENTS OF EXCIMER LASER TREATED PTFE SURFACES USING LIQUID PHOTOREAGENTS

The most known feature of polytetrafluoroethylene (PTFE) is its adhesion behavior: it is hydrophobic and oleophobic at the same time. This can cause serious problems and obstacles during the surface treatment and fixing of PTFE objects. During our experiments Teflon films were irradiated by an ArF excimer laser beam in presence of liquid photoreagents containing amine groups (aminoethanol, 1,2-diaminoethane, triethylene-tetramine). In consequence of the treatment the adhesion of the modified surfaces significantly increased, the samples could be glued and moistened. The adhesion strength of the glued surfaces was measured in the function of the applied laser fluence. The adhesion strength increased drastically between 0 - 1 mJ/cm2 and showed saturation above 1 mJ/cm2 at approximately 5 - 9 MPa values depending on the applied photoreagents. On the basis of our experiments it was found that the treatment with triethylene-tetramine was the most effective. The surface chemical modifications of the treated Teflon samples can be due to the incorporation of amine groups into the surface layer.

Influence of particulate size on the formation of polytetrafluoroethylene thin films during pulsed laser deposition

The lowest thickness of contiguous polytetrafluoroethylene (PTFE) thin films prepared by pulsed laser deposition is influenced by the size of the particulates emitted from the target. Since the particulates reach the substrate at random, by the time a contiguous layer is formed its average thickness can be several times as much as the mean size of the particulates. During our experiments the size distribution of the particulates emitted during ArF excimer laser deposition from pressed PTFE pellets was studied as the function of the applied ablating fluence in the range of 1.1 - 6.2 J/cm2. The size distribution of the particulates could be described with a first order exponential decay function. The value of the decay constant varied between 3.94 and 6.15 depending on the laser fluence. With the knowledge of the size distribution of the depositing particulates a theoretical model was used for simulating the growth of the thin film. The minimum number of the pulses required to obtain a contiguous layer and its thickness could be estimated. The thinnest layer could be obtained at the lowest investigated fluence.