Matrix assisted pulsed laser evaporation of biomaterial thin films

In this paper, processing of biomaterial thin films using a novel physical vapor deposition process known as matrix assisted pulsed laser evaporation (MAPLE) is reviewed. The matrix assisted pulsed laser evaporation process provides excellent control over several film parameters, including thickness, roughness, homogeneity, and reliability. Deposition of dexamethasone thin films, poly (d, l) lactic acid/dexamethasone bilayer thin films, and chitosan thin films is reviewed. The results highlight the expanding role of matrix assisted pulsed laser evaporation process in biomaterials, drug delivery, and tissue engineering.     

Thermal, morphological and optical investigations of Cu(DAB)2 thin films produced by matrix-assisted pulsed laser evaporation and laser-induced forward transfer for sensor development

Many hybrid metal-organic complex materials which exhibit crystalline nature, nonlinear optical properties and chemoselective behavior generate interest as choice materials in various applications. In this paper we report results on Cu(II) 2,2′-dihydroxyazobenzene thin films deposited on silicon and quartz substrates by matrix assisted pulsed laser evaporation using a Nd:YAG laser, at 266 and 355 nm laser wavelengths. Thermal analysis, atomic force microscopy, scanning electron microscopy and spectroscopic ellipsometry were performed in order to investigate thin film properties. Micrometric pixels of the compound have been transferred on glass plates by laser-induced forward transfer for chemoselective sensor development purposes.     

Morphological, optical and electrical properties of samarium oxide thin films

We present here results on samarium oxide thin films, obtained by pulsed laser deposition and by radio frequency assisted pulsed laser deposition. Three different substrate types were used: silicon, platinum covered silicon and titanium covered silicon. The influence of the deposition parameters (oxygen pressure and laser fluence) on the structure and morphology of the thin films was studied. The substrate-thin film interface zone was investigated; the optical and electrical properties (the losses, dielectric constant and leakage currents) were also determined.     

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.     

Pulsed Laser Processing of Carbon and Silicon Clusters and Thin Films

Abstract

Several new processes have been developed for the preparation of fullerenes and thin films by using a pulsed excimer laser. The irradiation of a pulsed KrF excimer laser beam onto a C₆₀ powder target produced single phase C₆₀ thin films when the laser energy fluence was in the range between 40 and 50mJ/cm². By atomic force microscopy, the laser-deposited C₆₀ thin film was verified to have a surface far smoother that the surfaces of films produced by the conventional evaporation method. The stainless steel rods coated with this film exhibited an excellent tribological property. Cluster formation from SiC and other carbides MC_n(M=Ti,W,B) was investigated by laser desorption time-of-flight mass spectrometry. No clear indication was observed for the production of such clusters as (SiC)₆₀ and (M_xC_60-x) from the sintered targets directly as well as from the films laser deposited from the targets. However, C₆₀ and C₇₀ were found to exists in the laser-deposited films, indicating a new applicability of pulsed laser processing for segregative cluster synthesis from solid solution. Preliminiary results on thin film deposition via pulsed ablation of (Ba,Na)_xSi₄₆ clathrate were also presented.     

Optical properties of ZnO thin film on γ-LiAlO2 substrate grown by pulsed laser deposition

Optical properties were investigated of ZnO thin films grown on (100) γ-LiAlO₂ (LAO) substrates by pulsed laser deposition method. C-axis oriented ZnO film was grown on (100) LAO substrate at the substrate temperature of 550 °C. The transmittances of the films were over 85%. Peaks attributed to excitons were seen in the absorption spectra, indicating that the thin films have high crystallinity. Photoluminescence spectra were observed at room temperature; the peak at 550 nm is ascribed to oxygen vacancies in the ZnO films caused by the diffusion of Li from the substrate into the film during deposition.     

Fabrication of PDPhSM matrix nanocomposite thin films by pulsed laser ablation

We have developed a new method to fabricate poly(diphenylsilylenemethylene) (PDPhSM) matrix nanocomposite thin films containing copper nanoparticles produced by pulsed laser ablation in this paper. First of all, 1,1,3,3-tetraphenyl-1,3-disilacyclobutane (TPDC) films were deposited on 4 cm² silicon substrates cut from c-Si wafers by conventional vacuum evaporation under a pressure of 3.0 × 10⁻⁵ Torr; then copper nanoparticles were deposited onto the TPDC films by pulsed laser ablation; finally the TPDC films with copper nanoparticles were heated in an electric furnace in an air atmosphere at 553 K for 10 min to induce ring-opening polymerization of TPDC. The results indicated that it is possible to fabricate PDPhSM matrix nanocomposite thin films using copper nanoparticles produced by laser ablation. The morphology and size distribution of copper nanoparticles can be controlled by pulsed laser ablation conditions. Also, the polymerization efficiency depends on the size and chemical state of copper nanoparticles.     

Structural characterization of CdS thin film on quartz formed by femtosecond pulsed laser deposition at high temperature

CdS thin films have been grown on quartz substrates using femtosecond pulsed laser deposition. The structural and optical properties of the CdS thin films were characterized by X-ray diffraction, scanning electron microscopy, atomic force microscopy, X-ray photoelectron spectroscopy and Raman spectroscopy. The results indicate that the compositional segregation of the CdS films could be drawn from the selective evaporation of sulfur from the film surface as a result of heating up the substrates. Growth temperature played an important role on changing crystal structure and optical properties of the CdS films.     

Creatinine biomaterial thin films grown by laser techniques

Creatinine thin films were synthesised by matrix assisted pulsed laser deposition (PLD) techniques for enzyme-based biosensor applications. An UV KrF* (λ = 248 nm, τ∼10 ns) excimer laser source was used for the irradiation of the targets at incident fluence values in the 0.3–0.5 J/cm² range. For the matrix assisted PLD the targets consisted on a frozen composite obtained by dissolving the biomaterials in distilled water. The surface morphology, chemical composition and structure of the obtained biomaterial thin films were investigated by scanning electron microscopy, Fourier transform infrared spectroscopy, and electron dispersive X-ray spectroscopy as a function of the target preparation procedure and incident laser fluence.     

Biomolecular papain thin films growth by laser techniques

Papain thin films were synthesised by matrix assisted and conventional pulsed laser deposition (PLD) techniques. The targets submitted to laser radiation consisted on a frozen composite obtained by dissolving the biomaterials in distilled water. For the deposition of the thin films by conventional PLD pressed biomaterial powder targets were submitted to laser irradiation. An UV KrF* excimer laser source was used in the experiments at 0.5 J/cm² incident fluence value, diminished one order of magnitude as compared to irradiation of inorganic materials. The surface morphology of the obtained thin films was studied by atomic force profilometry and atomic force microscopy. The investigations showed that the growth mode and surface quality of the deposited biomaterial thin films is strongly influenced by the target preparation procedure.     

离子束辅助脉冲激光沉积硼碳氮薄膜

以烧结B4C为靶材料、在氮离子束辅助下用脉冲激光沉积方法制备了三元化合物硼碳氮（BCN）薄膜.用X光电子谱和傅立叶变换红外谱方法表征了制备的薄膜.结果表明,膜层中包含B-C、N-C、B-N键等复合结构,以B-C-N原子杂化的形式结合成键,而并非各种成分的简单混合.还探讨了成膜过程和相关机理,离子束中的活性氮有效地和脉冲激光对B4C靶烧蚀产生的硼和碳结合成键,氮离子束的辅助还能在一定程度上抑制氧杂质进入膜层,给衬底适当加温有利于提高氮的含量并影响薄膜的化学结构.     

The staying power of adhesion-associated antioxidant activity in Mytilus californianus

The California mussel, Mytilus californianus, adheres in the highly oxidizing intertidal zone with a fibrous holdfast called the byssus using 3, 4-dihydroxyphenyl-l-alanine (DOPA)-containing adhesive proteins. DOPA is susceptible to oxidation in seawater and, upon oxidation, loses adhesion. Successful mussel adhesion thus depends critically on controlling oxidation and reduction. To explore how mussels regulate redox during their functional adhesive lifetime, we tracked extractable protein concentration, DOPA content and antioxidant activity in byssal plaques over time. In seawater, DOPA content and antioxidant activity in the byssus persisted much longer than expected—50% of extractable DOPA and 30% of extractable antioxidant activity remained after 20 days. Antioxidant activity was located at the plaque–substrate interface, demonstrating that antioxidant activity keeps DOPA reduced for durable and dynamic adhesion. We also correlated antioxidant activity to cysteine and DOPA side chains of mussel foot proteins (mfps), suggesting that mussels use both cysteine and DOPA redox reservoirs for controlling interfacial chemistry. These data are discussed in the context of the biomaterial structure and properties of the marine mussel byssus.     

In situ annealing of hydroxyapatite thin films

Hydroxyapatite is a bioactive ceramic that mimics the mineral composition of natural bone. Unfortunately, problems with adhesion, poor mechanical integrity, and incomplete bone ingrowth limit the use of many conventional hydroxyapatite surfaces. In this work, we have developed a novel technique to produce crystalline hydroxyapatite thin films involving pulsed laser deposition and postdeposition annealing. Hydroxyapatite films were deposited on Ti–6Al–4V alloy and Si (100) using pulsed laser deposition, and annealed within a high temperature X-ray diffraction system. The transformation from amorphous to crystalline hydroxyapatite was observed at 340 °C. Mechanical and adhesive properties were examined using nanoindentation and scratch adhesion testing, respectively. Nanohardness and Young's modulus values of 3.48 and 91.24 GPa were realized in unannealed hydroxyapatite films. Unannealed and 350 °C annealed hydroxyapatite films exhibited excellent adhesion to Ti–6Al–4V alloy substrates. We anticipate that the adhesion and biological properties of crystalline hydroxyapatite thin films may be enhanced by further consideration of deposition and annealing parameters.     

Investigation of ZnO films on Si<111> substrate grown by low energy O+ assisted pulse laser deposited technology

Zinc oxide thin films (ZnO) with different thickness were prepared on Si (111) substrates using low energy O⁺ assisted pulse laser deposition (PLD). The structural and morphological properties of the films were investigated by X-ray diffraction (XRD) and atomic force microscopy (AFM) measurements, respectively. The quality of ZnO films was also examined by using Rutherford backscattering spectroscopy/ion channeling (RBS/C) techniques. XRD showed that there was only one sharp diffraction peak at 2θ = 34.3° with the full width at the half maximum (FWHM) of around 0.34° for two ZnO samples, which also indicated that ZnO thin films had a good c-axis preferred orientation. Results of Rutherford backscattering and ion channeling clearly indicated that the Zn:O ratio in zinc oxide thin film approached to unity and the ZnO thin film grown by low energy O⁺ assisted pulse laser deposition had a polycrystalline structure. In the case of ZnO film fabricated by low energy O⁺ assisted pulse laser deposited under identical experimental conditions except growth time, AFM analysis has shown that the root mean square (RMS) roughness (2.37 nm) of thinner ZnO film (35 nm) was far below that (13.45 nm) of the thicker ZnO film (72 nm).     

Improved stability of organic light-emitting diode with aluminum cathodes prepared by ion beam assisted deposition

We have fabricated highly stable organic electroluminescent devices based on spin-coated poly-p-phenylene-vynylene (PPV) thin films. The electrical properties of aluminum cathode, prepared by ion beam assisted deposition, on PPV have been investigated and compared to those by thermal evaporation. Although energetic particles of Al assisted by Ar⁺ ion may damage the organic material, I–V–L characteristics are improved by applying thin Al buffer layer. In addition, a dense Al cathode inhibits the permeation of H₂O and O₂ into PPV film through pinhole defects, and thus retards dark spot growth. It may be deduced from highly packed structure of Al cathode with an increase in the contact area between Al and PPV that reduce the contact resistance. In conclusion, the lifetime of organic light-emitting device (OLED) has been extended effectively by dense Al film through ion beam assisted deposition process.     

Enhanced Flux Pinning Properties of BaZrO3-doped YBCO Films Grown by Pulsed Laser Deposition on LaAlO3(100) Substrates Decorated with Y2O3 Nanoislands

In this work, we intend to investigate the interaction between two types of nanoscaled artificial pinning centers and their pinning properties in YBCO thin films grown by pulsed laser deposition technique. The two types of artificial pinning centers were prepared in different processes, (1) Y₂O₃ nanoislands decorated on substrates prior to the deposition of YBCO thin film, and (2) BaZrO₃ nanoparticles self-assembled within YBCO matrix during the deposition of YBCO thin film. We compared the transport characteristics of the YBCO thin films containing these two types of artificial pinning centers with those of pure YBCO thin films grown on decorated substrates and BZO-doped YBCO thin films grown on undecorated substrates. It was found that these two types of artificial pinning centers, which are simultaneously present, acted constructively to enhance the pinning properties of YBCO thin films.     

Growth of GaN films with controlled out-of-plane texture on Si wafers

GaN films were deposited on Si (400) wafers by a pulsed laser deposition technique, and it was shown that out-of-plane texture of the film is controllable although the film and the substrate do not have any interface epitaxy. The texture of the film can be set either in c-axis or a-axis direction, thereby achieving polar or nonpolar film surfaces as desired. The GaN film and Si substrate were found to be separated by a thin amorphous interface layer consisting of Si, Ga, and O atoms, that can enhance the bonding between GaN and Si. This study shows the possibility of depositing GaN films on Si wafers at low cost and the potential of integrating Si based electronics with GaN based optoelectronics.     

Application of pulsed laser deposited zinc oxide films to thin film transistor device

Transparent zinc oxide (ZnO) thin films were deposited on various substrates using a pulsed laser deposition (PLD) technique. During the PLD, oxygen pressure and substrate temperature were varied in order to find an optimal preparation condition of ZnO for thin film transistor (TFT) application. Dependence of optical, electrical and crystalline properties on the deposition conditions was investigated. The ZnO thin films were then deposited on SiN/c-Si layer structures in order to fabricate a TFT device. The pulsed laser deposited ZnO films showed a remarkable TFT performance: field effect mobility (μ_FE) of 2.4-12.85 cm²/V s and ratio of on and off current (R_on/off) in 2-6 order range. Influence of ZnO preparation conditions on the resulting TFT performance was discussed.     

金属涂层SPR的单端面LPFG折射率传感器(英文)

提出了一种新型的单端面反射的镀有金属膜的长周期光纤光栅传感器.这种基于表面等离子体谐振的具有三层结构的传感器分为两个部分,光栅部分用连续CO2激光脉冲制作,金属膜是由真空镀膜制成.在光栅上镀上各种不同厚度的薄金属膜来激发表面等离子体波,用这种光纤光栅传感器来测量液体的折射率,并研究它的反射谐振谱的特性.在标准气压下,镀有80 nm银膜的光栅从水(ns=1.33)到酒精(ns=1.36)中光栅谐振波长改变了1.14nm,其敏感度达到折射率变化～5×10-4谐振波长改变20 pm.研究发现不同厚度的不同金属膜显示了不同的敏感度.通过比较光栅在空气,水,酒精,甘油,以及在它们的混合物溶液中的谐振波长,得到这种反射式的长周期光纤光栅传感器的敏感特性.为制作一种高性能的用来测量折射率的光纤光栅传感器提供了一个有益的参考.     

Matrix-Assisted Pulsed Laser Evaporation of polythiophene films

Organic poly-conjugated systems have recently attracted great interest as semi-conducting materials and, among poly-conjugated systems, substituted polythiophenes have given relevant results in PVs applications. The high conductivity required is affected by both the polymer conjugation length and the chain packing. Thus, highly region-regular polymers must be used and deposited as thin films with some technique which favours orientation and crystallization of the polymer chains.A deposition technique often used for its flexibility and high control over film characteristics is Pulsed Laser Deposition (PLD). In PLD, largely applied for inorganic thin film deposition, the material is ablated from a solid target by a focused pulsed laser beam and is deposited on the substrate placed at a small distance. Although some addition polymers have been successfully deposited the deposition seems to proceed via a “depolymerization-monomer ablation-repolymerization” mechanism, this is clearly not possible in general for organic molecules and condensation polymers.On the contrary MAPLE (Matrix-Assisted Pulsed Laser Evaporation) is a recently developed PLD based thin film deposition technique, particularly well suited for organic/polymer thin film deposition. Up to now MAPLE depositions have been carried out mainly by means of modified PLD systems, using excimer lasers operating in UV, but use of less energetic radiations can minimize the photochemical decomposition of the polymer molecules.We have used a deposition system explicitly designed for MAPLE technique connected to a Q-switched Ng:YAG pulsed laser which can be operated at different wavelength ranging from IR to UV in order to evaluate the effect of the choice of laser radiation on the deposition of POOPT thin films.From DRIFT-IR spectroscopy, all deposited films showed structural order; it was determined that the better wavelength for POOPT deposition is 532 nm. With this value of the laser wavelength the local chemical structure of the polymer was retained and the film appeared more homogeneous.