Pulsed Laser Evaporation Research Articles

Development of matrix-assisted pulsed laser evaporation (MAPLE) for deposition of disperse films of carbon nanoparticles and gold/nanoparticle composite films

Carbon nanopearls films were deposited onto silicon substrates using MAPLE. A 248 nm KrF excimer laser was directed onto a target consisting of ~ 150 nm-sized carbon nanopearls dispersed in a solvent solution and frozen in liquid nitrogen. The morphology of deposited carbon nanopearl films found to be influenced by matrix solvent, laser energy, repetition rate, background pressure, and substrate temperature. At ambient laboratory temperatures, the morphology of deposited films was characterized by highly concentrated areas of carbon nanopearls in the shape of hollow rings, caused by impingement of liquid droplets of the solvent/nanopearl suspension on the substrate surface followed by evaporation of the solvent. As the substrate temperature was increased, the size of the liquid droplets reaching the substrate surface decreased; however, the amount of material deposited via evaporation also decreased. The optimal deposition conditions were suggested and used for a hybrid process where laser ablation from frozen dispersion solution targets was combined with sputtering from gold targets. A nanocomposite coating consisting of carbon nanopearls encapsulated in a gold matrix was synthesized using MAPLE and magnetron sputtering simultaneously. This process makes it possible to synthesize nanocomposite films using a nanostructured dispersion solution.

MAPLE prepared polymeric thin films for non-linear optic applications

This paper presents a study of some functionalised copolymers thin films prepared on silicon and quartz substrates by matrix assisted pulsed laser evaporation (MAPLE) method. Two polymeric structures have been synthesised by the copolymerisation of maleic anhydride and methyl methacrylate, respectively, maleic anhydride and vinyl benzyl chloride and their subsequent functionalisation with 2,4-dinitroaniline. UV–Vis, FTIR, Raman and photoluminescence spectroscopy have been used to investigate the influence on the properties of the films of different substrate temperature (150 °C and 250 °C), background N 2 pressure (5–30 Pa) and polymer concentration in target (2% and 3%). We have evidenced that this deposition process does not damage the chemical structure of the polymers. SEM investigations revealed the droplets type morphology of the polymeric films with thickness between 41 nm and 105 nm calculated from ellipsometric measurements.

Multifunctional thin films of lactoferrin for biochemical use deposited by MAPLE technique

Lactoferrin (Lf) is an iron-binding glycoprotein present in almost all mammalian secretions which plays an important role in host defense against microbial and viral infections. The protein has been reported to also have anti-inflammatory activity and antitumoral effects in vitro and in vivo. Thin films of Lf were deposited on silicon, quartz and Thermanox plastic coverslip substrates by Matrix Assisted Pulsed Laser Evaporation (MAPLE) technique, using a Nd:YAG laser working at 266 nm, at different laser fluences (0.1–0.8 J cm −2). The deposited layers have been characterized by Fourier Transformed Infra-Red spectroscopy (FTIR), and the morphology of the various substrates was investigated by Atomic Force Microscopy (AFM). The biocompatibility of lactoferrin thin films was evaluated for each substrate, by in vitro biochemical tests.

Transforming a Laser Micromachiner into a Direct-Write Tool for Electronic Materials

A conventional laser micromachining system is configured for use as a matrix-assisted pulsed laser evaporation direct-write (MAPLE-DW) system in a straightforward and cost-effective manner. The simplicity of the method is illustrated by highlighting the process for MAPLE-DW of polymer composites used in chemical gas sensor arrays. Important aspects are considered, including ribbon preparation, ribbon aging, and computerized process control for rapid prototyping.

MAPLE deposition of methoxy Ge triphenylcorrole thin films

Methoxy Ge Triphenylcorrole [Ge(TPC)OCH3] has been recently synthesized and deposited as thin film by the Matrix Assisted Pulsed Laser Evaporation (MAPLE) technique. In the last few years, corroles have been the object of an increasing number of studies and MAPLE technique seems to be a very promising deposition method for organic and polymeric films, producing good results for applications in chemical gas sensing layers production. In this work Ge(TPC)OCH3 thin films were deposited by both spin coating and MAPLE techniques for comparison. The morphology of the films was investigated by Atomic Force Microscopy (AFM), while their optical properties were analyzed by photoluminescence (PL) and UV-vis absorption measurements and were compared with the ones of the starting solution. The film absorption spectrum presented the same peaks with the same relative intensities of that recorded in solution. The luminescence spectra were acquired periodically to evaluate the aging effects and no detectable variations were recorded over a period of 1 month.

MAPLE deposition of biomaterial multilayers

Double layers of polyethylene glycol (PEG) and 3-(3,4-dihydroxyphenyl)-2-methyl- l-alanine (m-DOPA) thin films were obtained by matrix assisted pulsed laser evaporation (MAPLE) technique, by depositing a first layer of m-DOPA on Si substrate and a second layer of PEG on top of it. The films were characterized by low angle X-ray diffraction (LAXRD), X-ray reflectivity (XRR), atomic force microscopy (AFM), and micro-Raman spectroscopy. From these analyses it resulted that PEG was deposited without any relevant damage both in terms of chemical structure and molecular weight. Furthermore, PEG chains were mostly in the extended conformation, although PEG micelles appeared.

Generation of surface features in films deposited by matrix-assisted pulsed laser evaporation: the effects of the stress confinement and droplet landing velocity

Coarse-grained molecular dynamics simulations are applied to investigate the origins of the surface features observed in films deposited by the Matrix-Assisted Pulsed Laser Evaporation (MAPLE) technique. The formation of transient balloon-like structures with a polymer-rich surface layer enclosing matrix vapor, observed in earlier simulations of slow heating of polymer-matrix droplets, has been explored in this work at higher rates of thermal energy deposition. Tensile stresses generated in the regime of partial stress confinement are found to induce an internal boiling in the overheated droplets and associated generation of “molecular balloons” at thermal energy densities at which no homogeneous boiling takes place without the assistance of tensile stresses. Simulations of the dynamic processes occurring upon the collision of a polymer-matrix droplet with a substrate provide the molecular-level pictures of the droplet impact phenomenon and reveal the connections between the droplet landing velocity and the shapes of the polymer features observed in scanning electron microscopy images of films deposited in MAPLE experiments. The distinct types of surface features observed in MAPLE experiments, namely, wrinkled “deflated balloons,” localized arrangements of interconnected polymer filaments, and elongated “nanofibers,” are shown to emerge from different scenarios of droplet landing and/or disintegration observed in the simulations.

Immobilization of urease by laser techniques: Synthesis and application to urea biosensors

Urease thin films have been immobilized using matrix-assisted pulsed laser evaporation for biosensor applications in clinical diagnostics. The targets exposed to laser radiation were made of frozen composites that had been manufactured by dissolving urease in distilled water. An UV KrF* (lambda = 248 nm, tauFWHM congruent with 30 ns, nu = 10 Hz) excimer source was used for the multipulse laser irradiation of the targets that were cooled down to solidification using Peltier elements. The incident laser fluence was set at 0.4 J/cm2. The surface morphology and chemical bonding states of the laser immobilized urease thin films were investigated by atomic force microscopy and Fourier transform infrared spectroscopy. The enzymatic activity and kinetics of the immobilized urease were assayed by the Worthington method, which monitors urea hydrolysis by coupling ammonia production to a glutamate dehydrogenase reaction. Decreased absorbance was found at 340 nm and correlated with the enzymatic activity of urease.

Composites of Single-Walled Carbon Nanotubes and Polystyrene: Preparation and Electrical Conductivity

Composites of single-walled carbon nanotubes (SWNT) and polystyrene have been prepared using three different types of SWNT: HiPco, CoMoCat, and pulsed laser vaporization (PLV). Nanotubes were incorporated into the polystyrene matrix by two methods: (1) evaporation of chloroform solutions of SWNT noncovalently functionalized with poly[(m-phenylenevinylene)-co-(2,5-dioctoxy-p-phenylenevinylene)] (PmPV) and polystyrene; (2) coagulation in water of DMF solutions containing polystyrene and nitric acid oxidized SWNT. From measurements of the electrical conductivities of the composites over a range of concentration from 0.1 to 6 wt % SWNT, the percolation threshold of conductivity was 0.17−0.3% SWNT for the PmPV-coated materials and 0.4–0.5% for those made by coagulation. Of the three types of SWNT, composites made with HiPco tubes had the highest conductivity.

Thermal analysis and thin films deposition by matrix assisted pulsed laser evaporation of a 4CN type azomonoether

Abstract A new synthesized 4CN type azomonoether, exhibiting dying properties, crystalline nature and generating interest as a material for non-linear optical applications was investigated. Modern devices incorporating liquid crystals tend to use thin films of such materials because of their special characteristics. Thermal stability studies are indispensable before attempting any deposition experiment. We have investigated the thermal behaviour of 4-[(4-chlorobenzyl)oxy]-4′-cyano-azobenzene (TG, DTG, DTA and DSC) in inert flow atmosphere, under non-isothermal conditions. The phase transitions were studied by repeated heating-cooling regimes, with intercalated isothermal steps. The thin films were deposited on silicon and quartz substrates by matrix assisted pulsed laser evaporation (MAPLE) using a Nd:YAG laser working at 266 nm. FTIR spectroscopy of the obtained thin films confirmed the preservation of the compound’s structure.

10.1007/s11700-008-1014-0

The morphological features of palladium thin films deposited on different substrates are described. Film deposition has been performed by means of the pulsed laser evaporation method. It is shown that the grain structure of palladium films is formed independently of the substrate roughness. Particular emphasis is placed on the correlation between gas-sensitive metal-insulator-semiconductor (MIS) sensor properties and the nanostructure of palladium films used as metal electrodes in these sensors. It is concluded that a change in the morphology of palladium films has no direct influence on the degradation of the hydrogen sulphide sensitivity of MIS sensors that arises after sensor annealing in air enriched with hydrogen.

Pulsed laser deposition of organic and biological materials

We report on the deposition of soft matter thin films by Matrix Assisted Pulsed Laser Evaporation (MAPLE). In particular, thin layers of biological material (Bovine Serum Albumin) and polymers (polyfluorene) for medical and optoelectronic applications, were realized by laser irradiating a frozen solution containing a low amount of material diluted in a laser absorbing volatile solvent. The depositions were carried out varying different parameters as solvent–solute concentration, solvent nature, laser fluencies, etc. The optical, morphological, structural and spectroscopical properties were detected by means of different analyses as FTIR, photoluminescence, AFM and SDS.

IR Photodissociation Spectroscopy and Theory of Au+(CO)n Complexes: Nonclassical Carbonyls in the Gas Phase

Au+(CO)n complexes are produced in the gas phase via pulsed laser vaporization, expanded in a supersonic jet, and detected with a reflectron time-of-flight mass spectrometer. Complexes up to n = 12 are observed, with mass channels corresponding to the n = 2 and n = 4 showing enhanced intensity. To investigate coordination and structure, individual complexes are mass-selected and probed with infrared photodissociation spectroscopy. Spectra in the carbonyl stretching region are measured for the n = 3-7 species, but no photodissociation is observed for n = 1, 2 due to the strong metal cation-ligand binding. The carbonyl stretch in these systems is blue-shifted 50-100 cm-1 with respect to the free CO vibration (2143 cm-1), providing evidence that these species are so-called "nonclassical" metal carbonyls. Theory at the MP2 and CCSD(T) levels provides structures for these complexes and predicted spectra to compare to the experiment. Excellent agreement is obtained between experiment and theory, establishing that the n = 3 complex is trigonal planar and the n = 4 complex is tetrahedral.

Analytical model for polyatomic gas expansion under pulsed evaporation

Polyatomic gas expansion under pulsed evaporation is considered in one-dimensional plane approach. A system of balance equations is constructed for gas cloud expansion. The obtained analytical solution allows to predict temporal evolution of the spatially averaged gas dynamic parameters, such as density, temperature, and velocity. The obtained results are in good agreement with results of direct Monte Carlo simulation. Based on the cloud parameters, the number of collisions per molecule during expansion is calculated. This number is used for approximate estimation of gas dynamic parameters (including vibrational temperature) for the case of incomplete vibrational cooling. Based on analytical regularities, analysis of experimental data on pulsed laser evaporation of aniline is performed. The calculated aniline vibrational temperature correlates well with the experimentally measured one.

Matrix-assisted pulsed laser evaporation of poly(D,L-lactide) for biomedical applications: effect of near infrared radiation

The deposition of thin films of poly(D,L-lactide) (PDLLA) by using the matrix-assisted pulsed laser evaporation (MAPLE) technique is investigated. PDLLA is a highly biocompatible and biodegradable polymer, with wide applicability in the biomedical field. The laser wavelength used in the MAPLE process is optimized to obtain a good-quality deposition. The structure of the polymer film is analyzed by Fourier transform infrared spectroscopy (FTIR). It is found that the chemical structure of PDLLA undergoes little or no damage during deposition with near-infrared laser radiation (1064 nm). It is thus confirmed that at this wavelength, the MAPLE technique can be applied for fragile biopolymer molecules, which are easily damaged by other laser radiations (UV radiation). This method allows future development of tailored polymer coatings for biomedical applications.

Effect of substrate temperature on poly(methyl methacrylate) nanocomposite thin films deposited by matrix assisted pulsed laser evaporation

The effects of substrate heating on thin films deposited by matrix assisted pulsed laser evaporation (MAPLE) were investigated. Substrates were heated at temperatures ranging from 315 to 425 K during depositions of neat poly(methyl methacrylate) (PMMA) and PMMA–carbon nanotube (CNT) composite thin films. Scanning electron microscopy (SEM) was used to examine the surface morphology of deposited films, while gel permeation chromatography (GPC) was used to determine the extent of photon-induced degradation in the molecular weight of deposited polymer. Significant reductions in molecular weight were observed. Further information regarding the degradation behavior was obtained from differential scanning calorimetry (DSC), where the glass transition temperatures ( T g) of native and MAPLE deposited PMMA samples were measured. A decrease in the surface roughness of deposited films was observed with increasing substrate temperature for both neat PMMA and PMMA–CNT composite films. At temperatures significantly lower than the measured T g for the as-received PMMA, features in deposited films began to take on a disc-like structure. DSC analysis of the deposited species shows a decrease in T g relative to the as-received material. This reduction in T g is attributed to the degradation of the native polymer during the MAPLE process, as shown by GPC results. Surface roughness effects in both the neat polymer and composite films show a continuous decrease in roughness as a function of temperature, as observed by both profilometry and SEM. The final roughnesses of the composite films were significantly greater than those of the pure polymer films. It is speculated that this is the result of CNT agglomeration within the starting target solutions.

Biocompatibility evaluation of a novel hydroxyapatite-polymer coating for medical implants (in vitro tests)

Nanocomposites consisting of hydroxyapatite (HA) and a sodium maleate copolymer (maleic polyelectrolyte), synthesized by hydrothermal method and deposited on titanium substrates by Matrix Assisted Pulsed Laser Evaporation (MAPLE) technique were tested for the biological properties. Coating bioanalysis was carried out by triple staining of actin, microtubules and nuclei followed by immunofluorescence microscopy. Within 24 h cells that occupied the biomaterial surface displayed the morphology and cytoskeleton pattern similar to the controls. Cells grown on nanocomposite coated surfaces had a higher proliferation rate than their counterparts grown on Ti coated with HA alone, indicating that maleic polyelectrolyte improved surface bio-adhesive characteristics. The capacity to induce cell attachment, spreading and proliferation demonstrated the potential of Ti coated with HA-polymer nanocomposites to be used as scaffolds in dental or orthopedic implantology.

Vibrational and Photoelectron Investigation of Amorphous Fluorinated Carbon Films

sp/sp2 amorphous carbon mixtures have been deposited by pulsed jet cooled supersonic carbon beams using graphite and polytetrafluoroethylene (PTFE) as target materials in a pulsed laser vaporization source. The investigated structure and composition reveal the formation of hydrogenated and fluorinated carbons, with the latter embedded in a PTFE-like matrix. There is a relevant structural difference between the two classes of samples in both the sp and sp2 subsystems, but a similar behavior in the degradation kinetics performed by dry air exposure was observed by Raman spectroscopy. Kinetic results are discussed with relation to the separate degradation of double- and triple-bonded carbon sp chains in the films.

Effect of Mild Nitric Acid Oxidation on Dispersability, Size, and Structure of Single-Walled Carbon Nanotubes

Oxidation of single-walled carbon nanotubes (SWNTs) with nitric acid increases their dispersability in water, methanol, and N,N-dimethylformamide. Two oxidation protocols, sonication in 8 M HNO3 at 40 °C and reflux in 2.6 M HNO3, have been examined using SWNTs produced by the CoMoCat, HiPco, and pulsed laser vaporization (PLV) methods. The dispersability of all types of nanotubes increased substantially after 1 h of sonication and after 2−4 h of reflux. Longer treatments resulted in little further improvement in dispersability and at reflux degraded the SWNTs. Stable dispersions of CoMoCat SWNTs in DMF at concentrations as high as 0.4 g/L were achieved without the use of surfactants or polymers. Raman spectroscopy showed greater covalent functionalization of the SWNTs by the reflux procedure than by the sonication procedure. Concurrent with improved dispersability, oxidation resulted in smaller diameters and shorter lengths as determined from AFM images, which show mostly bundles rather than individual tubes. The lengths of SWNTs after oxidation decreased in the order PLV > HiPco > CoMoCat. Recommendations for the method of conditioning of the various types of SWNTs depend on their intended use.

The influence of solvent parameters upon the surface roughness of matrix assisted laser deposited thin polymer films

Matrix assisted pulsed laser evaporation utilizing an infrared laser has been used to deposit poly(methyl methacrylate) and polystyrene thin films. The surface morphology has been investigated by surface sensitive techniques and it was found that the ‘goodness’ of the solvent (as defined by solubility parameters) strongly influences the morphology of the deposited films.