Pulsed Laser Evaporation Research Articles

Deposition of antibacterial of poly(1,3-bis-(p-carboxyphenoxy propane)-co-(sebacic anhydride)) 20:80/gentamicin sulfate composite coatings by MAPLE

We report on thin film deposition of poly(1,3-bis-(p-carboxyphenoxy propane)-co-sebacic anhydride)) 20:80 thin films containing several gentamicin concentrations by matrix assisted pulsed laser evaporation (MAPLE). A pulsed KrF* excimer laser was used to deposit the polymer–drug composite thin films. Release of gentamicin from these MAPLE-deposited polymer conjugate structures was assessed. Fourier transform infrared spectroscopy was used to demonstrate that the functional groups of the MAPLE-transferred materials were not changed by the deposition process nor were new functional groups formed. Scanning electron microscopy confirmed that MAPLE may be used to fabricate thin films of good morphological quality. The activity of gentamicin-doped films against Escherichia coli and Staphylococcus aureus bacteria was demonstrated using disk diffusion and antibacterial drop test. Our studies indicate that deposition of polymer–drug composite thin films prepared by MAPLE is a suitable technique for performing controlled drug delivery. Antimicrobial thin film coatings have several medical applications, including use for indwelling catheters and implanted medical devices.

Thin films of polymer blends deposited by matrix-assisted pulsed laser evaporation: Effects of blending ratios

In this work, we show successful use of matrix-assisted pulsed laser evaporation (MAPLE) for obtaining thin films of PEG:PLGA blends, in the view of their use for controlled drug delivery. In particular, we investigate the influence of the blending ratios on the characteristics of the films. We show that the roughness of the polymeric films is affected by the ratio of each polymer within the blend. In addition, we perform Fourier transformed infrared spectroscopy (FTIR) measurements and we find that the intensities ratios of the infrared absorption bands of the two polymers are consistent with the blending ratios. Finally, we assess the optical constants of the polymeric films by spectroscopic ellipsometry (SE). We point out that the blending ratios exert an influence on the optical characteristics of the films and we validate the SE results by atomic force microscopy and UV–vis spectrophotometry. In all, we stress that the ratios in which the two polymers are blended have significant impact on the morphology, chemical structure and optical characteristics of the polymeric films deposited by MAPLE.

Mg–Al layered double hydroxides (LDHs) and their derived mixed oxides grown by laser techniques

Layered double hydroxides (LDHs) have been widely studied due to their applications as multifunctional materials, catalysts, host materials, anionic exchangers, adsorbents for environmental contaminants and for the immobilization of biological materials. As thin films, LDHs are good candidates for novel applications as sensors, corrosion resistant coatings or components in electro optical devices. For these applications, lamellar orientation-controlled film has to be fabricated. In this work, the successful deposition of LDH and their derived mixed oxides thin films by laser techniques is reported. Pulsed laser deposition (PLD) and matrix assisted pulsed laser evaporation (MAPLE) were the methods used for thin films deposition. The ability of Mg–Al LDHs as a carrier for metallic particles (Ag) has been considered. Frozen targets containing 10% powder in water were used for MAPLE, while for PLD the targets consisted in dry-pressed pellets. The structure and the surface morphology of the deposited films were examined by X-ray Diffraction, Atomic Force Microscopy, Scanning Electron Microscopy and Secondary Ion Mass Spectrometry.

Microstructure of fluorite-like solid solutions in vacuum condensates

Transmission electron microscopy is used to study the microstructure of fluorite-like solid solutions formed in pulsed-laser evaporation vacuum condensates. The dependence of the shape and size of the crystallites on the condensate temperature and the type of stabilizing oxide is shown. The effect of the admixture cation is explained using the phase diagrams for the relevant binary oxide systems. The significance of the phase size effect for the stabilization of the fluorite-like solid solutions formed in fine vacuum condensates is ascertained.

Interface-controlled pulsed-laser deposited polymer films in organic devices

Matrix assisted pulsed laser evaporation (MAPLE) allows homogeneous film coverage of organic materials for layer-by-layer growth providing a tighter control of the polymer–dielectric interface in field-effect transistors (FETs) and metal–insulator–semiconductor (MIS) diodes. Electrical characteristics of FETs and MIS diodes using MAPLE and spin-coated grown fluorene copolymer films are compared. Current–voltage characteristics of MAPLE grown FETs without any surface modification show a better performance compared to the spin-coated FETs. Capacitance–voltage and conductance–voltage investigations of the MIS structures show that loss as well as accumulation capacitance and time constant dispersions are less in the MAPLE grown film compared to the spin-coated film.

Dependence of the surface roughness of MAPLE-deposited films on the solvent parameters

Matrix-assisted pulsed laser evaporation (MAPLE) was used to deposit layers of poly(9,9-dioctylfluorene) (PFO) to study the relation between the solvent properties (laser light absorption, boiling temperature and solubility parameters) and the morphology of the deposited films. To this end, the polymer was diluted (0.5 wt%) in tetrahydrofuran—THF, toluene and toluene/hexane mixtures. The thickness of the films was equal to 70±20 nm. The morphology and uniformity of the films was investigated by Atomic Force Microscopy and by the photoluminescence emission properties of the polymer films, respectively. It is shown that, although the solubility parameters of the solvents are important in controlling the film roughness and morphology, the optical absorption properties and boiling temperature play a very important role, too. In fact, for matrices characterized by the same total solubility parameter, lower roughness values are obtained for films prepared using solvents with lower penetration depth of the laser radiation and higher boiling temperatures.

Thermal and microstructural analysis of Cu(II) 2,2′-dihydroxy azobenzene and thin films deposition by MAPLE technique

A newly synthesized copper-complex exhibiting nonlinear optical properties, crystalline nature, and generating interest as a material for non-linear optical applications was investigated. As thermal stability studies are indispensable before attempting any laser-assisted processing experiments, the thermal behavior of 2,2′-dihydroxy azobenzene with Cu2+ cations that are found to organize themselves as non-central symmetric crystallites, was investigated. The thin films were deposited on silicon substrates by matrix-assisted pulsed laser evaporation using a Nd:YAG laser working at 266 and 355 nm. Thermal analysis of the bulk compound indicates a higher thermal stability in argon flow when compared to the air atmosphere; as well, since, the adhesion of the compound onto the substrate enhances the bonding, the thermal stability of the Cu complex increases. Fourier transform infrared spectroscopy, atomic force microscopy, scanning electron microscopy, spectroscopic ellipsometry, and ultraviolet–visible spectroscopy investigations were also performed.

Strong magnetism observed in carbon nanoparticles produced by the laser vaporization of acarbon pellet in hydrogen-containing Ar balance gas

Nanometer-scale carbon particles driven by the pulsed-laser vaporization of pelletized pure carbon powderat 1000 °C in a hydrogen-containing environment show anomalous magnetism like a superparamagnet,while the sample prepared in 100% of Ar does not show such magnetism. Theobserved magnetism was unchanged over months in the ambient. The structure ofthis nanomaterial resembles the foam of a laundry detergent and transmissionelectron microscopy indicates a clear corrugated line contrast. On the other hand, asample without strong magnetism does not give such an image contrast. The x-raydiffraction pattern coincides with that of graphite and no other peak is detected.Thermogravimetry indicates that all samples completely burn out up to approx. 820 °C and no material remains after combustion, indicating that the sampledoes not contain impurity metals. Magnetization is easily saturated by ∼ 10 000 G at 280 K with no hysteresis, but the hysteresis appears at 4.2 K. This phenomenon isexplained by introducing a crystalline anisotropy which restricts the motion of themagnetic moment and stabilizes the remnant magnetization at zero magneticfield. Magnitudes of the saturation magnetization are in the range of 1–5 emu G g − 1 at 4.2 K, which correspond to 0.002–0.01 Bohr magneton per carbon atom. Thisconcentration may be increased by ten times or more, because only about 4–10% ofparticles have a magnetic domain in the present samples.

An experimental investigation of inhomogeneities in resonant infrared matrix-assisted pulsed-laser deposited thin polymer films

Thin polymer films are deposited using matrix-assisted pulsed-laser evaporation and subsequently are characterized by scanning electron and atomic force microscopies. An Er : YAG laser (2937 nm, 350 μs) is used as a light source and the effect of the energy density supplied by the laser on the morphology of the deposited films is investigated. It is found that the appearance of undesirable non-uniform morphological features arises from either poor solubility of the guest molecules or insufficient energy density provided by the laser to vaporize the entire ejected volume. In addition, the surface roughness of two guest–host systems is found to depend linearly on the polymer concentration. These results allow us to better understand earlier work in the field and to establish a framework by which MAPLE films may be improved.

Phenylalanine detection using matrix assisted pulsed laser evaporation of molecularly imprinted amphiphilic block copolymer films

Matrix assisted pulsed laser evaporation was used to deposit molecularly imprinted polymer films of an amphiphilic block copolymer imprinted with an amino acid. This method avoids the need for a common solvent for host and template, and permits fabrication of layers with controlled thicknesses in the nanometer range. Polystyrene-block-polyethylene oxide copolymer and phenylalanine template were co-deposited onto surface plasmon resonance (SPR) sensors from a water/toluene emulsion. FTIR confirmed removal and reintroduction of phenylalanine, and SPR measurements were used for quantitative analysis. A binding ratio of more than 10 was obtained for phenylalanine on imprinted sensors vs. the non-imprinted control surfaces of the same polymer, and a detection limit of 0.5 mM phenylalanine was established. Exposure of sensors to alanine, glutamine, tryptophan, and tyrosine demonstrated that the sensors were highly specific.

Estimation of polyethylene nanothin layer morphology by differential evanescent light intensity imaging

We investigated the morphology of polyethylene films by the Differential Evanescent Light Intensity (DELI) imaging method developed by us previously. The films were prepared by the Matrix Assisted Pulsed Laser Evaporation (MAPLE) technique. Rough or smooth organic layers were fabricated with thickness depending on the deposition conditions. We used the DELI imaging method here as a fast, low cost method for surface morphology diagnostics of large areas (i.e., hundreds of mm2) of nano layer polyethylene films.

A comparative study of DRL-lift and lift on integrated polyisobutylene polymer matrices

This paper presents a comparative study of polymer pixel on sensors obtained by Laser Induced Forward Transfer (LIFT) assisted by a triazene polymer as Dynamic Release Layer (DRL). Polyisobutylene (PIB) was selected as model for chemoselective polymers which could be used as hydrogen-bond acidic polymer for vapor sensors. PIB films deposited on fused silica, respectively, on triazene polymer coated fused silica substrates were used as targets. Both targets were prepared by Matrix Assisted Pulsed Laser Evaporation (MAPLE). The parameters related to a regular, well-defined transfer were analyzed and compared for the substrates with and without the DRL. The morphological characterization of the transferred PIB was performed by Atomic Force Microscopy (AFM), Optical Microscopy, and Scanning Electron Microscopy (SEM). It was found that a minimal thickness of the dynamic release layer, i.e. 100 nm is required to protect the sensitive PIB polymer in a clean laser transfer process.

Thin films of polymer blends for controlled drug delivery deposited by matrix-assisted pulsed laser evaporation

We demonstrate the use of matrix-assisted pulsed laser evaporation technique for incorporating drugs (indomethacin) within thin films of polymer blends, to be used as biodegradable implants that deliver drugs in a controlled manner. For irradiation at fluences up to 1 J/cm2, the films show excellent surface morphology and the chemical structure of all constituent polymers within the blend is well preserved. The optical characteristics of the films are assessed by spectroscopic ellipsometry. The presence of the drug within the polymeric films is confirmed by its specific absorption at 319 nm.

Polyisobutylene Thin Films Obtained by Matrix Assisted Pulsed Laser Evaporation for Sensors Applications

Polyisobutylene Thin Films Obtained by Matrix Assisted Pulsed Laser Evaporation for Sensors Applications

Effect of Vaporization Temperature on the Diameter and Chiral Angle Distributions of Single-Walled Carbon Nanotubes

Pulsed laser vaporization synthesis of single-wall carbon nanotubes on Co/Ni and Rh/Pd catalysts was explored with respect to variations in the production temperature. The nanotube type populations were determined via photoluminescence, UV-Vis-NIR absorption and Raman spectroscopy. It was found that lowered production temperature leads to smaller nanotube diameters and exceptionally narrow (n, m) type distributions, with marked preference towards large chiral angles for both catalysts. Interestingly, larger nanotube diameters tend to be associated with larger chiral angles. These results demonstrate that PLV production technique can provide at least partial control over the nanotube (n, m) populations. In addition, these results have implications for the understanding the nanotube nucleation mechanism in the laser oven. SWCNT synthesized at lower temperatures appear quite attractive as a starting material for nanotube type separation experiments.

Mathematical modeling of dynamics of fast phase transitions and overheated metastable states during nano- and femtosecond laser treatment of metal targets

For a mathematical description of pulsed laser heating, melting, and evaporation of an aluminium target in an ambient atmosphere, a one dimensional, multifront hydrodynamic Stephan problem was used, written for both phases (liquid and solid). On the boundary of solid and gaseous forms, the Stephan problem is combined with radiation gas-dynamic equations, with thermal conductivity, and describes processes in the evaporated material and surrounding gas. For the numerical solution, finite difference method of dynamic adaptation, which gives an opportunity of explicitly tracking interphase boundaries and shock waves, was applied. As a result, in the process of the solution, the problem had 6 computational regions and 7 boundaries, 6 of them were moving, including 2 shock waves and one free boundary in the atmosphere. We used this model to calculate the pulsed laser interaction with an aluminium target with the following parameters: λ = 0.8 μm, τ = 10−8–10−15 s, and G0 = 10−9–10−16 W/cm2. Modeling revealed that in the case of long ∼1 ns pulses, most of the energy is spent on melting and heating the liquid. The depth of the molten pool depth constitutes about 1.2 μm. In the case of femtosecond pulses, most of the energy is spent on heating the solid body and the formation of shock waves in it. The depth of the molten pool does not exceed 0.03 μm. Even though the evaporated layers were of almost the same thickness. For nanosecond laser pulses with fluence J less than 30 J/cm2, there is no plasma formation in the evaporated material. For the same fluence of femtosecond laser pulses, plasma is formed after the pulses and is thermal by nature.

Laser direct writing of micro- and nano-scale medical devices

Laser-based direct writing of materials has undergone significant development in recent years. The ability to modify a variety of materials at small length scales and using short production times provides laser direct writing with unique capabilities for fabrication of medical devices. In many laser-based rapid prototyping methods, microscale and submicroscale structuring of materials is controlled by computer-generated models. Various laser-based direct write methods, including selective laser sintering/melting, laser machining, matrix-assisted pulsed-laser evaporation direct write, stereolithography and two-photon polymerization, are described. Their use in fabrication of microstructured and nanostructured medical devices is discussed. Laser direct writing may be used for processing a wide variety of advanced medical devices, including patient-specific prostheses, drug delivery devices, biosensors, stents and tissue-engineering scaffolds.

Morphology of polyethylene nanolayers: a study by evanescent light microscopy

Thin films morphology investigation of polyethylene by the differential evanescent light intensity (DELI) imaging method has been performed. The films of nanometer thickness were obtained by the matrix-assisted pulsed laser evaporation (MAPLE) technique. MAPLE was demonstrated to be suitable for the synthesis of organic materials in form of nanostructures. To prepare targets, 3% polyethylene powder was dissolved in toluene and frozen at liquid nitrogen temperature. In MAPLE, the organic material is protected by the frozen solvent against the direct laser and plasma action. Polyethylene thin films of various thicknesses, below 200 nm, were thus fabricated by varying the deposition conditions. We applied the DELI microscopy technique for fast and low cost morphology investigation of large polyethylene nanolayer zones. A phenomenological model for the interaction between the evanescent waves and the deposited material is presented.

Electrostatic quadrupole plasma mass spectrometer measurements during thin film depositions using simultaneous matrix assisted pulsed laser evaporation and magnetron sputtering

A hybrid plasma deposition process, combining matrix assisted pulsed laser evaporation (MAPLE) of carbon nanopearls (CNPs) with magnetron sputtering of gold was investigated for growth of composite films, where 100 nm sized CNPs were encapsulated into a gold matrix. Composition and morphology of such composite films was characterized with x-ray photoelectron spectroscopy, scanning electron microscopy, and transmission electron microscopy (TEM) analysis. Carbon deposits on a gold magnetron sputter target and carbon impurities in the gold matrices of deposited films were observed while codepositing from gold and frozen toluene-CNP MAPLE targets in pure argon. Electrostatic quadrupole plasma analysis was used to determine that a likely mechanism for generation of carbon impurities was a reaction between toluene vapor generated from the MAPLE target and the argon plasma originating from the magnetron sputtering process. Carbon impurities of codeposited films were significantly reduced by introducing argon-oxygen mixtures into the deposition chamber; reactive oxygen species such as O and O+ effectively removed carbon contamination of gold matrix during the codeposition processes. Increasing the oxygen to argon ratio decreased the magnetron target sputter rate, and hence hybrid process optimization to prevent gold matrix contamination and maintain a high sputter yield is needed. High resolution TEM with energy dispersive spectrometry elemental mapping was used to study carbon distribution throughout the gold matrix as well as embedded CNP clusters. This research has demonstrated that a hybrid MAPLE and magnetron sputtering codeposition process is a viable means for synthesis of composite thin films from premanufactured nanoscale constituents, and that cross-process contaminations can be overcome with understanding of hybrid plasma process interaction mechanisms.

Process-Induced Cell Injury in Laser Direct Writing of Human Colon Cancer Cells.

Matrix-assisted pulsed-laser evaporation direct-write has emerged as a promising technique for biological construct fabrication. The posttransfer cell viability in matrix-assisted pulsed-laser evaporation direct-write depends on various operating conditions such as the applied laser fluence. To date, the effects of operating conditions such as laser fluence, direct-writing height, and cell density on the posttransfer cell viability have not been well elucidated. This study investigates the effects of operating conditions on the posttransfer cell viability in laser direct writing of human colon cancer HT-29 cells. It has been observed that (1) the HT-29 cell viability decreases from 95% to 78% as the laser fluence increases from 258 to 1482 mJ/cm(2), and the posttransfer cell proliferation capacity does not vary significantly as the laser fluence changes; (2) the direct-writing height does not have noticeable effect on the posttransfer cell viability under low laser fluences (258 and 869 mJ/cm(2)). However, a larger height (such as 29.3 mm) led to an almost 8% viability improvement compared with that of 16.6 mm under a high laser fluence (1482 mJ/cm(2)); and (3) the posttransfer cell viability is not dependent on the cell density for a range from 1 × 10(6) to 1 × 10(7) cells/mL.