Pulsed Laser Evaporation Research Articles

Enhancement of the optically activated NO 2 gas sensing response of brookite TiO 2 nanorods/nanoparticles thin films deposited by matrix-assisted pulsed-laser evaporation

Brookite titanium dioxide (TiO 2) nanorods, synthesized by a surfactant-assisted aminolysis route, were used as precursors for the fabrication of thin films by using the matrix-assisted pulsed-laser deposition (MAPLE) technique. Thin films with controllable thickness were grown on a variety of substrates for different characterizations. High-resolution scanning and transmission electron microscopy investigations evidenced the formation of rough TiO 2 films incorporating individually distinguishable nanocrystals with different shapes. Suitable alumina substrates equipped with interdigitated electrical contacts (IDC) and heating elements were used to fabricate gas-sensing devices based on resistive transduction mechanism. Electrical characterization measurements in controlled environment were carried out. Typical gas sensor parameters (such as gas response, sensitivity, stability and detection limit) towards selected oxidizing and reducing gases, namely NO 2 and CO, respectively, were extracted in dark condition. Very interesting optically activated enhancement of the response towards NO 2 oxidizing gas was achieved in controlled atmosphere upon irradiating the sensing layer with UV light with low energy close to the TiO 2 sensing layer band-gap width.

Matrix-assisted pulsed laser methods for biofabrication

Abstract

Magnesium and strontium doped octacalcium phosphate thin films by matrix assisted pulsed laser evaporation

Octacalcium phosphate (OCP) is a promising alternative to hydroxyapatite as biomaterial for hard tissue repair. In this study we successfully applied Matrix Assisted Pulsed Laser Evaporation (MAPLE) to deposit Mg and Sr doped OCP (MgOCP and SrOCP), as well as OCP, thin films on titanium substrates. OCP, Mg-substituted and Sr-substituted OCP were synthesized in aqueous medium, then were suspended in deionised water, frozen at liquid nitrogen temperature and used as targets for MAPLE experiments. The depositions were carried out using a KrF* excimer laser source (λ = 248 nm, τ FWHM = 25 ns) in mild conditions of temperature and pressure. The results of X-ray diffraction, infrared spectroscopy, scanning electron microscopy and energy dispersive spectroscopy investigations revealed that the OCP thin films are deposited in the form of cauliflower-like aggregates and droplets, as well as crystal fragments, with a homogeneous distribution of magnesium and strontium on the surface of the coatings. Human osteoblast-like MG-63 cells were cultured on the different biomaterials up to 14 days. MgOCP and SrOCP coatings promote osteoblast proliferation and differentiation with respect to OCP. Under these experimental conditions, the production of procollagen-type I, transforming growth factor-β1, alkaline phosphatase and osteocalcin indicated that the level of differentiation of the cells grown on the different coatings increased in the order OCP < MgOCP < SrOCP.

Matrix assisted pulsed laser evaporation of Mn12(Propionate) thin films

Single molecule magnets are of great interest due to a multitude of potential applications for some of which thin films are required. Traditional physical vapor deposition techniques are not suitable for the deposition of these fragile materials with low decomposition temperatures. Matrix Assisted Pulsed Laser Evaporation technique has been employed for the growth of thin films of the single molecule magnet Mn12(Propionate) on Si and glass substrates. In this paper we report on the appropriate growth conditions and also the morphology, chemical composition and magnetic behavior of the films. Continuous Mn12(Propionate) films with properties similar to bulk materials have been obtained.

Hybrid dextran-iron oxide thin films deposited by laser techniques for biomedical applications

Iron oxide nanoparticles were prepared by chemical co-precipitation method. The nanoparticles were mixed with dextran in distilled water. The obtained solutions were frozen in liquid nitrogen and used as targets during matrix assisted pulsed laser evaporation for the growth of hybrid, iron oxide nanoparticles-dextran thin films. Fourier Transform Infrared Spectroscopy and X-ray diffraction investigations revealed that the obtained films preserve the structure and composition of the initial, non-irradiated iron oxide-dextran composite material. The biocompatibility of the iron oxide-dextran thin films was demonstrated by 3-(4.5 dimethylthiazol-2yl)-2.5-diphenyltetrazolium bromide-based colorimetric assay, using human liver hepatocellular carcinoma cells.

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.

Matrix-assisted pulsed laser evaporation of chemoselective polymers

In this work, matrix-assisted pulsed laser evaporation was applied to achieve gentle deposition of polymer thin films onto surface acoustic wave resonators. Polyepichlorhydrin, polyisobutylene and polyethylenimine were deposited both onto rigid substrates e.g. Si wafers as well as surface acoustic wave devices using a Nd-YAG laser (266 nm, 355 nm, 10 Hz repetition rate). Morphological investigations (atomic force microscopy and optical microscopy) reveal continuous deposited polymer thin films, and in the case of polyethylenimine a very low surface roughness of 1.2 nm (measured on a 40×40 μm2 area). It was found that only for a narrow range of laser fluences (i.e. 0.1–0.3 J/cm2 in the case of polyisobutylene) the chemical structure of the deposited polymer thin layers resembles to the native polymer. In addition, in the case of polyisobutylene it was shown that the irradiation at 355-nm wavelength produces deviations in the chemical structure of the deposited polymer, as compared to its bulk structure. Following the morphological and structural characterization, only a set of well established conditions was used for polymer deposition on the sensor structures. The surface acoustic wave resonators have been tested using the Network Analyzer before and after polymer deposition. The polymer coated surface acoustic wave resonator responses have been measured upon exposure to various concentrations of dimethylmethylphosphonate analyte. All sensors coated with different polymer layers (polyethylenimine, polyisobutylene, and polyepichlorhydrin) show a clear response to the dimethylmethylphosphonate vapor. The strongest signal is obtained for polyisobutylene, followed by polyethylenimine and polyepichlorhydrin. The results obtained indicate that matrix-assisted pulsed laser evaporation is potentially useful for the fabrication of polymer thin films to be used in applications including microsensor industry.

Adsorption properties of Mg–Al layered double hydroxides thin films grown by laser based techniques

Powdered layered double hydroxides (LDHs) have been widely studied due to their applications as catalysts, anionic exchangers or host materials for inorganic and/or organic molecules. Assembling nano-sized LDHs onto flat solid substrates forming thin films is an expanding area of research due to the prospects of novel applications as sensors, corrosion-resistant coatings, components in optical and magnetic devices.Continuous and adherent thin films were grown by laser techniques (pulsed laser deposition – PLD and matrix assisted pulsed laser evaporation – MAPLE) starting from targets of Mg–Al LDHs. The capacity of the grown thin films to retain a metal (Ni) from contaminated water has been also explored. The thin films were immersed in an Ni(NO3)2 aqueous solutions with Ni concentrations of 10−3% (w/w) (1g/L) and 10−4% (w/w) (0.1g/L), respectively. X-ray diffraction (XRD), atomic force microscopy (AFM), scanning electron microscopy (SEM) combined with energy dispersive X-ray analysis (EDX) were the techniques used to characterize the prepared materials.

MAPLE deposition of PLGA:PEG films for controlled drug delivery: Influence of PEG molecular weight

Implantable devices consisting of indomethacin (INC) cores coated with poly(lactide-co-glycolide):polyethylene glycol films (i.e. PLGA:PEG films) deposited by Matrix Assisted Pulsed Laser Evaporation (MAPLE) were produced. To predict their behavior after implantation inside the body, the implants were studied in vitro, in media similar with those encountered inside the body (phosphate buffered saline (PBS) pH 7.4 and blood). The influence of the molecular weight of PEG (i.e. low (1450Da) versus high (10kDa) molecular weights) on the characteristics of the implants was investigated, in terms of morphology, blood compatibility and kinetics of the drug release. The use of PEG of high molecular weight resulted in larger pores on the implants surfaces, enhanced blood compatibility of the implants and higher drug delivery rates. For both molecular weights PEGs, sustained release of INC was maintained over a three weeks interval. Theoretical fitting of the drug release data with Higuchi's model indicated that the INC was released mainly by diffusion, most probably through the pores formed in PLGA:PEG films during PBS immersion.

Design challenges for matrix assisted pulsed laser evaporation and infrared resonant laser evaporation equipment

Design challenges for matrix assisted pulsed laser evaporation and infrared resonant laser evaporation equipment

Study of titania nanorod films deposited by matrix-assisted pulsed laser evaporation as a function of laser fluence

Chemically synthesized brookite titanium dioxide (TiO2) nanorods with average diameter and length dimensions of 3–4 nm and 35–50 nm, respectively, were deposited by the matrix-assisted pulsed laser evaporation technique. A toluene nanorod solution was frozen at the liquid-nitrogen temperature and irradiated with a KrF excimer laser (λ=248 nm, τ=20 ns) at the repetition rate of 10 Hz, at different fluences (25 to 350 mJ/cm2). The deposited films were structurally characterized by high-resolution scanning and transmission electron microscopy. 〈100〉 single-crystal Si wafers and carbon-coated Cu grids were used as substrates. Structural analyses evidenced the occurrence of brookite-phase crystalline nanospheres coexisting with individually distinguishable TiO2 nanorods in the films deposited at fluences varying from 50 to 350 mJ/cm2. Nanostructured TiO2 films comprising only nanorods were deposited by lowering the laser fluence to 25 mJ/cm2. The observed shape and phase transitions of the nanorods are discussed taking into account the laser-induced heating effects, reduced melting temperature and size-dependent thermodynamic stability of nanoscale TiO2.

The effect of the target structure and composition on the ejection and transport of polymer molecules and carbon nanotubes in matrix-assisted pulsed laser evaporation

Matrix-assisted pulsed laser evaporation (MAPLE) is a prominent member of a broad and expanding class of laser-driven deposition techniques where a matrix of volatile molecules absorbs laser irradiation and provides the driving force for the ejection and transport of the material to be deposited. The mechanisms of MAPLE are investigated in coarse-grained molecular dynamic simulations focused on establishing the physical regimes and limits of the molecular transfer from targets with different structures and compositions. The systems considered in the simulations include dilute solutions of polymer molecules and individual carbon nanotubes (CNTs), as well as continuous networks of carbon nanotubes impregnated with solvent. The polymer molecules and nanotubes are found to be ejected only in the ablation regime and are incorporated into matrix-polymer droplets generated in the process of the explosive disintegration of the overheated matrix. The ejection and deposition of droplets explain the experimental observations of complex surface morphologies in films deposited by MAPLE. In simulations performed for MAPLE targets loaded with CNTs, the ejection of individual nanotubes, CNT bundles, and tangles with sizes comparable or even exceeding the laser penetration depth is observed. The ejected CNTs align along the flow direction in the matrix plume and tend to agglomerate into bundles at the initial stage of the ablation plume expansion. In a large-scale simulation performed for a target containing a network of interconnected CNT bundles, a large tangle of CNT bundles with the total mass of 50 MDa is separated from the continuous network and entrained with the matrix plume. No significant splitting and thinning of CNT bundles in the ejection process is observed in the simulations, suggesting that fragile structural elements or molecular agglomerates with complex secondary structures may be transferred and deposited to the substrate with the MAPLE technique.

Resonant infrared laser deposition of polymer-nanocomposite materials for optoelectronic applications

Polymers find a number of potentially useful applications in optoelectronic devices. These include both active layers, such as light-emitting polymers and hole-transport layers, and passive layers, such as polymer barrier coatings and light-management films. This paper reports the experimental results for polymer films deposited by resonant infrared matrix-assisted pulsed laser evaporation (RIR-MAPLE) and resonant infrared pulsed laser deposition (RIR-PLD) for commercial optoelectronic device applications. In particular, light-management films, such as anti-reflection coatings, require refractive-index engineering of a material. However, refractive indices of polymers fall within a relatively narrow range, leading to major efforts to develop both low- and high-refractive-index polymers. Polymer nanocomposites can expand the range of refractive indices by incorporating low- or high-refractive-index nanoscale materials. RIR-MAPLE is an excellent technique for depositing polymer-nanocomposite films in multilayer structures, which are essential to light-management coatings. In this paper, we report our efforts to engineer the refractive index of a barrier polymer by combining RIR-MAPLE of nanomaterials (for example, high refractive-index TiO2 nanoparticles) and RIR-PLD of host polymer. In addition, we report on the properties of organic and polymer films deposited by RIR-MAPLE and/or RIR-PLD, such as Alq3 [tris(8-hydroxyquinoline) aluminum] and PEDOT:PSS [poly(3,4-ethylenedioxythiophene): poly(styrenesulfonate)]. Finally, the challenges and potential for commercializing RIR-MAPLE/PLD, such as industrial scale-up issues, are discussed.

Matrix assisted growth of nanoparticles and nanoporous films

Since the inception of matrix assisted pulsed laser evaporation (MAPLE), a large body of research has focused on the structure and property preservation of soft materials. Departing from this precedent, a variation of MAPLE to grow complex inorganic nanoparticles and nanoporous thin films from acetate precursors is presented. While some aspects of MAPLE are retained, a weakly absorbing matrix solvent is used to promote absorption by the precursors, leading to photothermal decomposition. The diffusion of ions within the laser interaction volume results in the formation of nanoparticles, which are then ejected by subsequent pulses. The acetate precursors were processed into colloidal suspensions in deionized water and frozen to form solid targets, followed by irradiation with a pulsed excimer laser at fluences ranging from 0.25 to 0.75 J/cm2. Nanoparticles and nanoporous films of unary, binary, and ternary metallic and oxide systems were deposited at room temperature onto substrates of Si and electron-transparent grids. Size distributions varied between different material systems with negligible pressure and energy effects, with distribution extrema ranging from 2 to 100 nm in diameter. Characterization of the nanoparticles was performed by high resolution scanning and transmission electron microscopy, and energy dispersive x-ray spectroscopy.

Effect of substrate temperature on MAPLE deposition of synthetic eumelanin films

Eumelanin is an important pigment almost ubiquitous in animals and plants exhibiting interesting charge transport capabilities. Its poor solubility in common solvents represents a severe limitation for preparing thin films. It was recently demonstrated that eumelanin films can be successfully deposited with the MAPLE (Matrix Assisted Pulsed Laser Evaporation) technique starting from a frozen water suspension, using infrared laser radiation. The low laser absorption of ice together with the high absorption of eumelanin suggests that the target ablation is due to laser energy absorbed by the eumelanin molecules, followed by thermal energy transfer, and ejection of ice/water/vapor containing undamaged eumelanin molecules and supramolecular structures. Here, we report on the deposition of eumelanin thin films on substrates at different temperatures eventually followed by in-situ annealing. Structural characterization (UV-VIS, FTIR, AP-MALDI) confirms that the deposited films maintain the characteristics of the eumelanin biopolymer. Morphological characterization (AFM) shows that surface roughness increases with increasing substrate temperature during MAPLE deposition, but is not influenced by annealing. Preliminary electrical characterization shows that eumelanin films seem to obey Ohm’s law without evidence that charge injection from gold electrodes is affected by the presence of significant energy barriers. Moreover, charge transport is drastically reduced in vacuum, even if the phenomenon is at least partially reversible.

The Matrix-Assisted Pulsed Laser Evaporation (MAPLE) process: origins and future directions

This review discusses the origins and evolution of the MAPLE technique as it started as an alternative to spray coating of thin films for chemical vapor sensors. It describes its numerous applications for the deposition of thin films of polymeric, organic and biomaterials for various applications. This is followed by an overview of several new variations of the MAPLE technique. This review concludes with an outlook on the future of this highly versatile and successful vapor deposition process.

MAPLE-deposited polymer films for improved organic device performance

Matrix-assisted pulsed-laser evaporation (MAPLE) provides a mechanism for layer-by-layer growth to control the polymer–dielectric interface in organic metal–insulator–semiconductor (MIS) diodes and field-effect transistors (FETs). MAPLE-deposited copolymers of polyfluorene (PF) and polythiophene maintain their structural and optical properties, as determined by Raman spectroscopy, absorption, and photoluminescence. These films are further utilized in MIS and FET structures with SiO2 and other polymer dielectrics. Since common polymer dielectrics prevent spin coating of solution processable polymers due to solubility effects, MAPLE is one of the only deposition techniques for investigating all polymer semiconductor-insulator interfaces. In this paper we present optical and electrical studies of MAPLE-deposited PF and polythiophene films in FETs and MIS structures. The FET carrier mobilities of these devices compare well with spin-coated devices. Capacitance–voltage and conductance–voltage from MIS structures with MAPLE-deposited PF copolymer films yield interface trap densities in the low 1012 eV−1 cm−2 range.

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.

RIR-MAPLE deposition of conjugated polymers for application to optoelectronic devices

Resonant-infrared matrix-assisted pulsed laser evaporation (RIR-MAPLE) is a promising deposition technology for the fabrication of conjugated polymer-based optoelectronic devices for two primary reasons: (i) the ability to control film morphology, and (ii) the ability to deposit multi-layered heterostructures. This article reviews a variation of RIR-MAPLE that uses emulsified targets of organic solvents and water such that the incident laser wavelength (Er:YAG at 2.9 μm) is resonant with hydroxyl (O–H) bonds in the host matrix, which are absent from the guest material. The novelty of the approach lies in the fact that while most polymers of interest and many compatible solvents do not resonantly absorb the laser energy at 2.9 μm, the emulsion with water enables high-quality, thin-film deposition with minimal photochemical and structural degradation for almost any polymer of interest. In addition, the advantages of emulsion-based RIR-MAPLE for conjugated polymer-based optoelectronic devices are demonstrated by two important studies. First, conjugated polymer films deposited by RIR-MAPLE are shown to have higher hole drift mobilities than films deposited using traditional drop-casting and spin-casting techniques. Second, the unique capability of RIR-MAPLE to enable conjugated polymer-based optical heterostructures is demonstrated by the fabrication and characterization of a multi-layer, polymer distributed Bragg reflector.

Growth of thin films of low molecular weight proteins by matrix assisted pulsed laser evaporation (MAPLE)

Thin films of lysozyme and myoglobin grown by matrix assisted pulsed laser evaporation (MAPLE) from a water ice matrix have been investigated. The deposition rate of these two low molecular weight proteins (lysozyme: 14307 amu and myoglobin: 17083 amu) exhibits a maximum of about 1–2 ng/cm2 per pulse at a fluence of 1–2 J/cm2 and decreases slowly with increasing fluence. This rate is presumably determined by the matrix rather by the proteins. A significant fraction of the proteins are intact in the film as determined by MALDI (Matrix assisted laser desorption ionization) spectrometry. The results for lysozyme demonstrate that the fragmentation rate of the proteins during the MAPLE process is not influenced by the pH of the water solution prior to freezing.