Functional polyethylene glycol derivatives nanostructured thin films synthesized by matrix-assisted pulsed laser evaporation

We report the thin film deposition by matrix-assisted pulsed laser evaporation (MAPLE) of a polymer conjugate with an hydrophilic sequence between metronidazole molecules that was covalently attached to both oligomer ends of carboxylate poly(ethylene glycol) (PEG 1.5-metronidazole). A pulsed KrF* excimer laser was used to deposit the drug-polymer composite films. Fourier transform infrared spectroscopy was used to demonstrate that MAPLE-transferred materials exhibited chemical properties similar to the starting materials. The dependence of the surface morphology on incident laser fluence is given.     

High fluence deposition of polyethylene glycol films at 1064 nm by matrix assisted pulsed laser evaporation (MAPLE)

Matrix assisted pulsed laser evaporation (MAPLE) has been applied for deposition of thin polyethylene glycol (PEG) films with infrared laser light at 1064 nm. We have irradiated frozen targets (of 1 wt.% PEG dissolved in water) and measured the deposition rate in situ with a quartz crystal microbalance. The laser fluence needed to produce PEG films turned out to be unexpectedly high with a threshold of 9 J/cm², and the deposition rate was much lower than that with laser light at 355 nm. Results from matrix assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF-MS) analysis demonstrate that the chemistry, molecular weight and polydispersity of the PEG films were identical to the starting material. Studies of the film surface with scanning electron microscopy (SEM) indicate that the Si-substrate is covered by a relatively homogenous PEG film with few bare spots.     

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.     

Matrix assisted pulsed laser evaporation of poly(d,l-lactide) thin films for controlled-release drug systems

We report the successful deposition of the porous polymer poly(d,l-lactide) by matrix assisted pulsed laser evaporation (MAPLE) using a KrF* excimer laser (248 nm, τ = 7 ns) operated at 2 Hz repetition rate. The chemical structure of the starting materials was preserved in the resulting thin films. Fluence played a key role in optimizing our depositions of the polymer. We demonstrated MAPLE was able to improve current approaches to grow high quality thin films of poly(d,l-lactide), including a porosity control highly required in targeted drug delivery.     

Thin films of Cu(II)-o,o′-dihydroxy azobenzene nanoparticle-embedded polyacrylic acid (PAA) for nonlinear optical applications developed by matrix assisted pulsed laser evaporation (MAPLE)

Thin films based on two different metal-organic systems are developed by MAPLE and their nonlinear optical applications are explored. A complex of o,o′-dihydroxy azobenzene with Cu²⁺ cation is found to organize as a non-central symmetric crystallite. A simple protocol is developed for the in situ fabrication of highly monodisperse copper-complex nanoparticles in a polymer film matrix of polyacrylic acid. The thin films were deposited on quartz substrates by MAPLE (matrix assisted pulsed laser evaporation) using a Nd:YAG laser working at 355 nm. Atomic force microscopy (AFM), Fourier transform infrared (FTIR), X-ray photoelectron spectroscopy (XPS), and optical second harmonic generation (SHG) were performed on the samples. The optical limiting capability of the nanoparticle-embedded polymer film is investigated.     

Matrix assisted pulsed laser evaporation of cinnamate-pullulan and tosylate-pullulan polysaccharide derivative thin films for pharmaceutical applications

We have demonstrated the successful thin film growth of two pullulan derivatives (cinnamate-pullulan and tosylate-pullulan) using matrix assisted pulsed laser evaporation (MAPLE). Our MAPLE system consisted of a KrF* laser, a vacuum chamber, and a rotating target holder cooled with liquid nitrogen. Fused silica and silicon (1 1 1) wafers were used as substrates. The MAPLE-deposited thin films were characterized by transmission spectrometry, profilometry, atomic force microscopy (AFM), Fourier transform infrared (FTIR) spectroscopy and Raman spectroscopy. The deposited layers ranged from 250 nm to 16.5 μm in thickness, depending on the laser fluence (0.065-0.5 J cm⁻²) and number of pulses applied for the deposition of one structure (1500-13,300). Our results confirmed that MAPLE was well-suited for the transfer of cinnamate-pullulan and tosylate-pullulan.     

Resonant infrared matrix-assisted pulsed laser evaporation of TiO2 nanoparticle films

The successful development of flexible, high performance thin films that are competitive with silicon-based technology will likely require fabricating films of hybrid materials that incorporate nanomaterials, glasses, ceramics, polymers, and thin films. Resonant infrared matrix-assisted pulsed laser evaporation (RIR-MAPLE) is an ideal method for depositing organic materials and nanoparticles with minimal photochemical or photothermal damage to the deposited material. Furthermore, there are many nonhazardous solvents containing chemical functional groups with infrared absorption bands that are accessible using IR lasers. We report here results of recent work in which RIR-MAPLE has been employed successfully to deposit thin films of TiO₂ nanoparticles on Si substrates. Using an Er:YAG laser (λ=2.94 μm), we investigated a variety of MAPLE matrices containing –OH moieties, including water and all four isomers of butyl alcohol. The alcohol isomers are shown to provide effective and relatively nontoxic solvents for use in the RIR-MAPLE process. In addition, we examine the effects of varying concentration and laser fluence on film roughness and surface coverage.     

Solvent-related effects in MAPLE mechanism

To study the role of the solvent and of the laser fluence in the matrix-assisted pulsed laser evaporation (MAPLE) process, we used a soft polymer (polydimethylsiloxane—PDMS) as “sensing surface” and toluene as solvent. Thin films of the PDMS polymer were placed in the position of the growing film, while a frozen toluene target was irradiated with an ArF laser at the conventional fluences used in MAPLE depositions (60–250 mJ/cm²). Apart the absence of solute, the MAPLE typical experimental conditions for the deposition of thin organic layers were tested. The effects on the PDMS films of the toluene target ablation, at different fluences, were studied using atomic force microscopy and contact angles measurements. The results were compared with the effects produced on similar PDMS films by four different treatments (exposure to a drop of the solvent, to saturated toluene vapors and to plasma sources of two different powers). From this comparative study, it appears that depending on the MAPLE experimental conditions: (1) the MAPLE process may be “semidry” rather than purely dry (namely the solvent is likely to be present in the deposition environment near the growing film), (2) the solvent, if sufficiently volatile, is in form of vapor molecules (neutral, ionized and probably dissociated) rather than in liquid phase near the substrate and (3) at relatively high laser fluences (>150 mJ/cm²), the formation of an intense plasma plume results which can damage/affect a soft substrate as well as a growing polymer film.     

Surface morphology of thin lysozyme films produced by matrix-assisted pulsed laser evaporation (MAPLE)

Thin films of the protein, lysozyme, have been deposited by the matrix-assisted pulsed laser evaporation (MAPLE) technique. Frozen targets of 0.3-1.0 wt.% lysozyme dissolved in ultrapure water were irradiated by laser light at 355 nm with a fluence of 2 J/cm². The surface quality of the thin lysozyme films of different thickness deposited on 7 mm × 7 mm Si-〈1 0 0〉-wafers was investigated with scanning electron microscopy and atomic force microscopy. Already at comparatively low thickness, ∼20 nm, the substrate is covered by intact lysozyme molecules and fragments. The concentration of lysozyme in the ice matrix apparently does not play any significant role for the morphology of the film. The morphology obtained with MAPLE has been compared with results for direct laser irradiation of a pressed lysozyme sample (i.e. pulsed laser deposition (PLD)).     

Fabrication of ZnO thin films by femtosecond pulsed laser deposition

The growth of ZnO thin films on sapphire substrate using the femtosecond PLD technique is reported. The effect of substrate temperature and oxygen pressure on the structural properties of the films was studied. Highly c-axis oriented ZnO films can be grown on sapphire substrates under vacuum conditions using the femtosecond PLD process. There is an optimum substrate temperature for the pulsed laser deposition of ZnO film that enhances the thermodynamic stability and allows the formation of well-crystallized thin films. The crystal quality of the films can be further improved by increasing the deposition time and introducing oxygen during the pulsed laser deposition process.     

Laser deposition of cryoglobulin blood proteins thin films by matrix assisted pulsed laser evaporation

We report the first successful deposition of type II cryoglobulin blood protein thin films by matrix assisted pulsed laser evaporation (MAPLE) using a KrF^* excimer laser source (λ = 248 nm, τ_FWHM ≈ 20 ns) operated at a repetition rate of 10 Hz. We demonstrate by AFM and FTIR that MAPLE-deposited thin films consist of starting type II cryoglobulin only, maintaining its chemical structure and biological functionality, being properly collected and processed. The dependence on incident laser fluence of the induced surface morphology is presented. The presence of type II cryoglobulin was revealed as aggregates of globular material in the MAPLE-deposited thin films and confirmed by standard cryoglobulin tests.     

Processing of C<Subscript>60</Subscript> thin films by Matrix-Assisted Pulsed Laser Evaporation (MAPLE)

Thin films of fullerenes (C₆₀) were deposited onto silicon using matrix-assisted pulsed laser evaporation (MAPLE). The deposition was carried out from a frozen homogeneous dilute solution of C₆₀ in anisole (0.67 wt%), and over a broad range of laser fluences, from 0.15 J/cm² up to 3.9 J/cm². MAPLE has been applied for deposition of fullerenes for the first time and we have studied the growth of thin films of solid C₆₀. The fragmentation of C₆₀ fullerene molecules induced by ns ablation in vacuum of a frozen anisole target with C₆₀ was investigated by matrix-assisted laser desorption/ionization (MALDI). Our findings show that intact fullerene films can be produced with laser fluences ranging from 0.15 J/cm² up to 1.5 J/cm².     

MAPLE activities and applications in gas sensors

During the last decade, many groups have grown thin films of various organic materials by the cryogenic Matrix Assisted Pulsed Laser Evaporation (MAPLE) technique with a wide range of applications. This contribution is focused on the summary of our results with deposition and characterization of thin films of fibrinogen, pullulan derivates, azo-polyurethane, cryoglobulin, polyvinyl alcohol, and bovine serum albumin dissolved in physiological serum, dimethyl sulfoxide, sanguine plasma, phosphate buffer solution, H₂O, ethylene glycol, and tert-butanol. MAPLE films were characterized using FTIR, AFM, Raman scattering, and SEM. For deposition, a special hardware was developed including a unique liquid nitrogen cooled target holder. Overview of MAPLE thin film applications is given. We studied SnAcAc, InAcAc, SnO₂, porphyrins, and polypyrrole MAPLE fabricated films as small resistive gas sensors. Sensors were tested with ozone, nitrogen dioxide, hydrogen, and water vapor gases. In the last years, our focus was on the study of fibrinogen-based scaffolds for application in tissue engineering, wound healing, and also as a part of layers for medical devices.     

Growth of b-axis oriented VO2 thin films on glass substrates using ZnO buffer layer

VO₂ thin films are grown on glass substrates by pulsed laser deposition using vanadium metal as a target. In this study, a ZnO thin film was used as a buffer layer for the growth of VO₂ thin films on glass substrates. X-ray diffraction studies showed that the VO₂ thin film had b-axis preferential orientation on a c-axis oriented ZnO buffer layer. The thickness of the ZnO buffer layer and the oxygen pressure during VO₂ deposition were optimized to grow highly b-axis oriented VO₂ thin films. The metal-insulator transition properties of the VO₂ film samples were investigated in terms of infrared reflectance and electrical resistance with varying temperatures.     

Characterization of lysozyme films produced by matrix assisted pulsed laser evaporation (MAPLE)

Thin lysozyme films of thickness up to more than 100 nm have been produced in a dry environment by MAPLE (matrix assisted pulsed laser evaporation) from a water ice matrix. Analysis of the films demonstrates that a significant part of the lysozyme molecules is transferred to the substrate without decomposition and that the protein activity is preserved. The film deposition rate for 1 wt% lysozyme has a maximum at 2 J/cm² of about 1 ng/cm² per laser shot. During the film production the deposition rate is constant without any sign of depletion or accumulation effects in the water ice target or in the growing film. Scanning electron microscopy (SEM) images demonstrate that the silicon substrate is completely covered by lysozyme films thicker than 100 nm. Deposition was also made from a target with pressed (100%) solid lysozyme, but the deposition was difficult to handle and with a much slower rate than that from a water ice matrix.     

Processing of poly(1,3-bis-(p-carboxyphenoxy propane)-co-(sebacic anhydride)) 20:80 (P(CPP:SA)20:80) by matrix-assisted pulsed laser evaporation for drug delivery systems

We have demonstrated successful thin film growth of poly(1,3-bis-(p-carboxyphenoxy, propane)-co-(sebacic anhydride)) (20:80) by matrix-assisted pulsed laser evaporation using a KrF* excimer laser (λ = 248 nm, τ = 25 ns, ν = 10 Hz). The deposited thin films have been investigated by Fourier transform infrared spectroscopy, and atomic force microscopy. We have demonstrated that the main functional groups of poly(1,3-bis-(p-carboxyphenoxy, propane)-co-(sebacic anhydride)) (20:80) are present in the deposited film. The effect of matrix on both thin film structure and surface morphology was also examined. The goal of this work is to explore laser processing of this material to create suitable constructs for drug delivery applications.     

Applications of the matrix-assisted pulsed laser evaporation method for the deposition of organic,biological and nanoparticle thin films: a review

The matrix-assisted pulsed laser evaporation (MAPLE) technique offers an efficient mechanism to transfer soft materials from the condensed to the vapor phase, preserving the versatility, ease of use and high deposition rates of the pulsed laser deposition (PLD) technique. The materials of interest (polymers, biological cells, proteins, …) are diluted in a volatile solvent. Then the solution is frozen and irradiated with a pulsed laser beam. Here, important results of MAPLE deposition of polymer, biomaterials and nanoparticle films are summarized. Finally, the MAPLE mechanism is discussed. A review of experimental and theoretical works points out that the simple model of individual molecule evaporation must be abandoned. Solute concentration, solubility, evaporation temperature of solvents, laser pulse power density and laser penetration depth emerge as important parameters to explain the morphology of the MAPLE-deposited films.     

CdS thin films obtained by thermal treatment of cadmium(II) complex precursor deposited by MAPLE technique

Thin films of [Cd{SSi(O-Bu^t)₃}(S₂CNEt₂)]₂, precursor for semiconducting CdS layers, were deposited on silicon substrates by Matrix-Assisted Pulsed Laser Evaporation (MAPLE) technique. Structural analysis of the obtained films by Fourier transform infrared spectroscopy (FTIR) confirmed the viability of the procedure. After the deposition of the coordination complex, the layers are manufactured by appropriate thermal treatment of the system (thin film and substrate), according to the thermal analysis of the compound. Surface morphology of the thin films was investigated by atomic force microscopy (AFM) and spectroscopic-ellipsometry (SE) measurements.     

Nickel-titanium alloy: Cytotoxicity evaluation on microorganism culture

High purity nickel (Ni) and titanium (Ti) targets have been used to form well-defined thin films of nitinol on Ti substrate by pulsed laser deposition (PLD) technique. Their chemical composition, crystalline structure and surface properties have been investigated using X-ray diffraction (XRD), scanning electron microscopy (SEM) and atomic force microscopy (AFM).We have shown that by varying the deposition parameters such as laser fluence and number of laser pulses, we are able to control the film thickness as well as film's uniformity and roughness.Cytocompatibility tests have been performed through in vitro assays using microorganisms culture cells such as yeasts (Saccharomyces cerevisiae) and bacteria (Escherichia coli), in order to determine the thin film's toxic potential at the in vitro cellular level. Microorganism's adhesion on the nitinol surface was observed and the biofilm formation has been analyzed and quantified.Our results have shown no reactivity detected in cell culture exposed to NiTi films in comparison with the negative controls and a low adherence of the microorganisms on the nitinol surface that is an important factor for biofilm prevention. We can, therefore, conclude that NiTi is a good candidate material to be used for implants and medical devices.     

KTN thin films prepared by pulsed laser deposition on transparent single crystal quartz(100)

Using the Sol-Gel method to produce the KTN ultrafine powder and the sintering technique with K2O atmosphere to prepare KTN ceramics as the targets instead of the KTN single crystal, highly oriented KTN thin films were produced on the transparent single crystal quartz (100) by the pulsed laser deposition (PLD). Since the thermal stress sustained by the quartz is relatively small, the limit temperature of the quartz substrates (300℃) is much lower than that of the P-Si substrates (560℃); the prepared thin film is at amorphous state. Increasing the pulsed laser energy density in the process incorporated with annealing the film after deposition at different temperatures converts the amorphous films into crystal. The optimal pulsed laser energy density and annealing temperature were 2.0 J/cm2 and 600℃, respectively. A discussion was made to understand the mechanism of film production at relatively low substrate temperature by PLD and effects of the annealing temperatures on the forming of the perovskite p