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.     

Growth of oxide thin films for optical gas sensor applications

Tungsten trioxide and titanium dioxide thin films were synthesised by pulsed laser deposition. We used for irradiations of oxide targets an UV KrF* (λ = 248 nm, τ_FWHM ≅ 20 ns, ν = 2 Hz) excimer laser source, at 2 J/cm² incident fluence value. The experiments were performed in low oxygen pressure. The (0 0 1) SiO₂ substrates were heated during the thin film deposition process at temperature values within the 300-500 °C range. The structure and crystalline status of the obtained oxide thin films were investigated by high resolution transmission electron microscopy. Our analyses show that the films are composed by nanoparticles with average diameters from a few to a few tens of nm. Moreover, the films deposited at substrate temperatures higher than 300 °C are crystalline. The tungsten trioxide films consist of a mixture of triclinic and monoclinic phases, while the titanium dioxide films structure corresponds to the tetragonal anatase phase. The oxide films average transmittance in the visible-infrared spectral range is higher than 80%, which makes them suitable for sensor applications.     

Effect of substrate temperature on structure and electrical resistivity of laser-ablated IrO2 thin films

IrO₂ thin films were prepared on Si(1 0 0) substrates by laser ablation. The effect of substrate temperature (T_sub) on the structure (crystal orientation and surface morphology) and property (electrical resistivity) of the laser-ablated IrO₂ thin films was investigated. Well crystallized and single-phase IrO₂ thin films were obtained at T_sub = 573-773 K in an oxygen partial pressure of 20 Pa. The preferred orientation of the laser-ablated IrO₂ thin films changed from (2 0 0) to (1 1 0) and (1 0 1) depending on T_sub. With the increasing of T_sub, both the surface roughness and crystallite size increased. The room-temperature electrical resistivity of IrO₂ thin films decreased with increasing T_sub, showing a low value of (42 ± 6) × 10⁻⁸ Ω m at T_sub = 773 K.     

Surface characterization and luminescent properties of SrAl2O4:Eu,Dy nano thin films

SrAl₂O₄:Eu²⁺, Dy³⁺ thin films were grown on Si (1 0 0) substrates in different atmospheres using the pulsed laser deposition (PLD) technique. The effects of vacuum, oxygen (O₂) and argon (Ar) deposition atmospheres on the structural, morphological and photoluminescence (PL) properties of the films were investigated. The films were ablated using a 248 nm KrF excimer laser. Improved PL intensities were obtained from the unannealed films prepared in Ar and O₂ atmospheres compared to those prepared in vacuum. A stable green emission peak at 520 nm, attributed to 4f⁶5d¹→4f⁷ Eu²⁺ transitions was obtained. After annealing the films prepared in vacuum at 800 °C for 2 h, the intensity of the green emission (520 nm) of the thin film increased considerably. The amorphous thin film was crystalline after the annealing process. The diffusion of adventitious C into the nanostructured layers deposited in the Ar and O₂ atmospheres was most probably responsible for the quenching of the PL intensity after annealing.     

Structural and optical characterization of undoped, doped, and clustered ZnO thin films obtained by PLD for gas sensing applications

The synthesis by pulsed laser deposition technique of zinc oxide thin films suitable for gas sensing applications is herein reported. The ZnO targets were irradiated by an UV KrF^* (λ = 248 nm, τ_FWHM ∼7 ns) excimer laser source, operated at 2.8 J/cm² incident fluence value, whilst the substrates consisted of SiO₂(0 0 1) wafers heated at 150 °C during the thin films growth process. The experiments were performed in an oxygen dynamic pressure of 10 Pa. Structural and optical properties of the thin films were investigated. The obtained results have demonstrated that the films are c-axis oriented. Their average transmission in the visible-infrared spectral region was found to be about 85%. The equivalent refractive indexes and extinction coefficients were very close to those of the tabulated reference values. Doping with 0.5% Au and coating with 100 pulses of Au clusters caused but a very slight decrease (with a few percent) of both transmission and refractive index values. The coatings with the most appropriate optical properties as waveguides have been selected and their behavior was tested for butane sensing.     

Effects of co-substitution on the electrical properties of BiFeO3 thin films prepared by chemical solution deposition

Ferroelectric BiFeO₃ thin films with Nd-Cr (or Sm-Cr) co-substitution (denoted by BNdFCr and BSmFCr, respectively) were deposited on the Pt(2 0 0)/TiO₂/SiO₂/Si(1 0 0) substrates by a chemical solution deposition method. X-ray diffraction patterns revealed the formation of BNdFCr and BSmFCr thin films without any secondary phases. The co-substituted BNdFCr (or BSmFCr) thin films, which were annealed at 550 °C for 30 min in N₂ atmosphere, exhibited enhanced electrical properties compared to BFO thin films with the remanent polarization (2P_r) and coercive electric field (2E_c) of 196, 188 μC/cm² and 600, 570 kV/cm with the electric field of 800 kV/cm, respectively. The leakage current densities of BNdFCr and BSmFCr thin films measured at room temperature were approximately three orders of magnitude lower than that of BFO thin film, and the leakage current at room temperature of the thin films exhibited three distinctive conduction behaviors. Furthermore, the values of pulse polarizations [i.e., +(P*-P^{^}) or −(P*-P^{^})] of BNdFCr and BSmFCr thin films were reasonably unchanged up to 1.4 × 10¹⁰ switching cycles.     

Pulsed laser deposition of polyhydroxybutyrate biodegradable polymer thin films using ArF excimer laser

We demonstrated the pulsed laser deposition (PLD) of high quality films of a biodegradable polymer, the polyhydroxybutyrate (PHB). Thin films of PHB were deposited on KBr substrates and fused silica plates using an ArF (λ = 193 nm, FWHM = 30 ns) excimer laser with fluences between 0.05 and 1.5 J cm⁻². FTIR spectroscopic measurements proved that at the appropriate fluence (0.05, 0.09 and 0.12 J cm⁻²), the films exhibited similar functional groups with no significant laser-produced modifications present. Optical microscopic images showed that the layers were contiguous with embedded micrometer-sized grains. Ellipsometric results determined the wavelength dependence (λ ∼ 245-1000 nm) of the refractive index and absorption coefficient which were new information about the material and were not published in the scientific literature. We believe that our deposited PHB thin films would have more possible applications. For example to our supposal the thin layers would be applicable in laser induced forward transfer (LIFT) of biological materials using them as absorbing thin films.     

Structure and refractive index dispersive behavior of potassium niobate tantalate films prepared by pulsed laser deposition

Pure perovskite phase and crack-free KTa_0.5Nb_0.5O₃ thin films were prepared on Pt/Ti/SiO₂/Si substrates by pulsed laser deposition. The structure and orientation were analyzed by X-ray diffraction. The optical properties were investigated by an ellipsometer. The relationship between the refractive index dispersive behavior and internal structure was analyzed by Sellmeier dispersion model and single electronic oscillator approximation. The parameters of room temperature monomial Sellmeier oscillator were calculated. And the refractive index dispersive parameter E₀/S₀ of KTa_0.5Nb_0.5O₃ thin films on Pt/Ti/SiO₂/Si substrates is (6.72 ± 0.04) × 10⁻¹⁴ eV m², which is consistent with those of KTN crystals and compounds with ABO₃ perovskite type structure.     

Photoluminescence spectra of thin films containing CdSe/ZnS quantum dots irradiated by 532-nm laser radiation and gamma-rays

We have investigated temporal behavior of the photoluminescence (PL) spectra of thin films containing CdSe/ZnS quantum dots irradiated by 532 nm laser radiation and gamma-rays. Under ∼100 W/cm² laser radiation, the PL intensity (I_PL) increases with irradiation time upto about 500 s and thereafter declines linearly. The wavelength of the PL emission (λ_peak) exhibits a blue-shift with exposure time. Upon simultaneous irradiation by 100 W/cm² 532-nm laser, as well as 0.57 and 1.06 MeV gamma-rays, the temporal behaviors of both I_PL and λ_peak are significantly different; I_PL increases to a saturation level, and the magnitude of the blue-shift in λ_peak is reduced. We discuss possible mechanisms underlying these results.     

Bioactive glass and hydroxyapatite thin films obtained by pulsed laser deposition

Bioactive glass (BG), calcium hydroxyapatite (HA), and ZrO₂ doped HA thin films were grown by pulsed laser deposition on Ti substrates. An UV KrF^* (λ = 248 nm, τ ≥ 7 ns) excimer laser was used for the multi-pulse irradiation of the targets. The substrates were kept at room temperature or heated during the film deposition at values within the (400-550 °C) range. The depositions were performed in oxygen and water vapor atmospheres, at pressure values in the range (5-40 Pa). The HA coatings were heat post-treated for 6 h in a flux of hot water vapors at the same temperature as applied during deposition. The surface morphology, chemical composition, and crystalline quality of the obtained thin films were studied by scanning electron microscopy, atomic force microscopy, and X-ray diffractometry. The films were seeded for in vitro tests with Hek293 (human embryonic kidney) cells that revealed a good adherence on the deposited layers. Biocompatibility tests showed that cell growth was better on HA than on BG thin films.     

The ferroelectric and ferromagnetic characterization of CoFe2O4/Pb(Mg1/3Nb2/3)O3-PbTiO3 multilayered thin films

The multiferroic (PMN-PT/CFO)_n (n = 1,2) multilayered thin films have been prepared on SiO₂/Si(1 0 0) substrate with LNO as buffer layer via a rf magnetron sputtering method. The structure and surface morphology of multilayered thin films were determined by X-ray diffraction (XRD) and atom force microscopy (AFM), respectively. The smooth, dense and crack-free surface shows the excellent crystal quality with root-mean-square (RMS) roughness only 2.9 nm, and average grain size of CFO thin films on the surface is about 44 nm. The influence of the thin films thickness size, periodicity n and crystallite orientation on their properties including ferroelectric, ferromagnetic properties in the (PMN-PT/CFO)_n multilayered thin films were investigated. For multilayered thin films with n = 1 and n = 2, the remanent polarization Pr are 17.9 μC/cm² and 9.9 μC/cm²; the coercivity H_c are 1044 Oe and 660 Oe, respectively. In addition, the relative mechanism are also discussed.     

Enhanced ferroelectric property of (Pb0.95Ca0.05)(Nb0.02Zr0.80Ti0.20)O3 thin films prepared by RF magnetron sputtering

(Pb_0.95Ca_0.05)(Nb_0.02Zr_0.80Ti_0.20)O₃ [PCNZT] thin films were deposited on the Pt(1 1 1)/Ti/SiO₂/Si(1 0 0) substrates by RF magnetron sputtering with and without a LaNiO₃ [LNO] buffer layer. Ca and Nb elements in PZT films enhance the ferroelectric property, LaNiO₃ buffer layer improves the crystal quality of the PCNZT thin films. PCNZT thin films possess better ferroelectric property than that of PZT films for Ca and Nb ion substitution, moreover, PCNZT thin films with a LNO buffer layer possess (1 0 0) orientation and good ferroelectric properties with high remnant polarization (P_r = 38.1 μC/cm²), and low coercive field (E_c = 65 kV/cm), which is also better than that of PCNZT thin films without a LNO buffer layer (P_r = 27.9 μC/cm², E_c = 74 kV/cm). The result shows that enhanced ferroelectric property of PZT films can be obtained by ion substitution and buffer layer.     

Effect of excimer laser annealing on the properties of ZnO thin film prepared by sol-gel method

Pristine ZnO thin films have been deposited with zinc acetate [Zn(CH₃COO)₂], mono-ethanolamine (stabilizer), and isopropanol solutions by sol-gel method. After deposition, pristine ZnO thin films have been irradiated by excimer laser (λ = 248, KrF) source with energy density of 50 mJ/cm² for 30 sec. The effect of excimer laser annealing on the optical and structural properties of ZnO thin films are investigated by photoluminescence and field emission scanning electron microscope. As-grown ZnO thin films show a huge peak of visible region and a wide full width at half maximum (FWHM) of UV region due to low quality with amorphous ZnO thin films. After KrF excimer laser annealing, ZnO thin films show intense near-band-edge (NBE) emission and weak deep-level emission. The optically improved pristine ZnO thin films have demonstrated that excimer laser annealing is novel treatment process at room temperature.     

Investigation on upconversion photoluminescence of Bi3TiNbO9:Er:Yb thin films

Bi₃TiNbO₉:Er³⁺:Yb³⁺ (BTNEY) thin films were fabricated on fused silica by pulsed laser deposition. It was demonstrated that different laser fluence and substrate temperature during growth of BTNEY upconversion photoluminescence (UC-PL) samples control the film’s grain size and hence influences the UC-PL properties. The average grain size of BTNEY thin films deposited on fused silica substrates with laser fluence 4, 5, 6, and 7 J/cm² are 30.8, 35.9, 40.6, and 43.4 nm, respectively. The 525 nm emission intensities increase with the deposition laser fluence and the emission intensities of BTNEY thin film deposited under 700 and 600 °C are almost 24 and 4 times, respectively, as strong as those of samples under 500 °C. The grain size of BTNEY thin film increases with the increasing temperature. UC-PL of BTNEY films is enhanced by increasing grain size of the films.     

Enhanced ferroelectric properties of (Pb0.90La0.10)Ti0.975O3 multilayered thin films prepared by RF magnetron sputtering

The (Pb_0.90La_0.10)Ti_0.975O₃/PbTiO₃ (PLT/PT), PbTiO₃/(Pb_0.90La_0.10)Ti_0.975O₃/PbTiO₃ (PT/PLT/PT) multilayered thin films with a PbO_x buffer layer were in situ deposited by RF magnetron sputtering at the substrate temperature of 600 °C. With this method, highly (1 0 0)-oriented PLT/PT and PT/PLT/PT multilayered thin films were obtained. The PbO_x buffer layer leads to the (1 0 0) orientation of the films. The dielectric, ferroelectric and pyroelectric properties of the PLT multilayered thin films were investigated. It is found that highly (1 0 0)-oriented PT/PLT/PT multilayered thin films possess higher remnant polarization 2P_r (44.1 μC/cm²) and better pyroelectric coefficient at room temperature p (p = 2.425 × 10⁻⁸ C/cm² K) than these of PLT and PLT/PT thin films. These results indicate that the design of the PT/PLT/PT multilayered thin films with a PbO_x buffer layer should be an effective way to enhance the dielectric, ferroelectric and pyroelectric properties. The mechanism of the enhanced ferroelectric properties was also discussed.     

Nonlinear optical properties in SrTiO3 thin films by pulsed laser deposition

Well-crystallized 250 nm-thick SrTiO₃ thin films on fused-quartz substrate were prepared by pulsed laser deposition. The band-gap of SrTiO₃ thin film by transmittance spectra is equal to 3.50 eV, larger than 3.22 eV for the bulk crystal. The nonlinear optical properties of the films were examined with picosecond pulses at 1.064 μm excitation. A large two-photon absorption (TPA) with absorption coefficient of 87.7 cm/GW was obtained, larger than 51.7 cm/GW for BaTiO₃ thin films. The nonlinear refractive index n₂ is equal to 5.7×10⁻¹⁰ esu with a negative sign, larger than 0.267×10⁻¹¹ esu for bulk SrTiO₃. The large TPA is attributed to intermediate energy levels introduced by the grain boundaries, and the optical limiting behaviors stemming from both TPA and negative nonlinear refraction were also discussed.     

Structure and properties of transparent conductive doped ZnO films by pulsed laser deposition

High quality transparent conductive ZnO thin films were deposited on quartz glass substrates using pulsed laser deposition (PLD). We varied the growth conditions such as the substrate temperature and oxygen pressure. X-ray diffraction (XRD), X-ray photoelectron spectrometer (XPS), and atomic force microscopy (AFM) measurements were done on the samples. All films show n-type conduction, the best transparent conductive oxide (TCO) performance (Al-doped ZnO = 1.33 × 10⁻⁴ Ω cm, Ga-doped ZnO = 8.12 × 10⁻⁵ Ω cm) was obtained on the ZnO film prepared at pO₂ = 5 mTorr and T_s = 300 °C.     

Influence of the substrate material on the properties of pulsed laser deposited thin Li1+xMn2O4−δ films

Thin Li_1+xMn₂O_4−δ films were deposited on several substrate materials (stainless steel, p-doped silicon and glassy carbon) by pulsed laser deposition. To obtain the correct thin film stoichiometries, targets with a different amount of excess lithium were required (Li_1.03Mn₂O₄ + xLi₂O; x = 2.5 and 7.5 mol%). The resulting polycrystalline thin films were characterized with respect to their morphology and electrochemical activity. It was found that only thin Li_1+xMn₂O_4−δ films deposited on stainless steel and glassy carbon showed the typical insertion and deinsertion peaks of Li⁺ during cycling.     

Laser synthesis of nanostructures based on transition metal oxides

Nanostructures based on iron oxides in the form of thin films were synthesized while laser chemical vapor deposition (LCVD) of elements from iron carbonyl vapors (Fe(CO)₅) under the action of Ar⁺ laser radiation (λ_L = 488 nm) on the Si substrate surface with power density about 10² W/cm² and vapor pressure 666 Pa. Analysis of surface morphology and relief of the deposited films was carried out with scanning electron microscopy (SEM) and atomic force microscopy (AFM). This analysis demonstrated their cluster structure with average size no more than 100 nm. It was found out that the thicker the deposited film, the larger sizes of clusters with more oxides of higher oxidized phases were formed. The film thickness (d) was 10 and 28 nm. The deposited films exhibited semiconductor properties in the range 170-340 K which were stipulated by oxide content with different oxidized phases. The width of the band gap E_g depends on oxide content in the deposited film and was varied in the range 0.30-0.64 eV at an electrical field of 1.6 × 10³ V/m. The band gap E_g was varied in the range 0.46-0.58 eV at an electrical field of 45 V/m. The band gap which is stipulated by impurities in iron oxides E_i was varied in the range 0.009-0.026 eV at an electrical field of 1.6 × 10³ V/m and was varied in the range 0-0.16 eV at an electrical field 45 V/m. These narrow band gap semiconductor thin films displayed of the quantum dimensional effect.     

Preparation and the optical nonlinearity of surface chemistry improved titania nanoparticles in poly(methyl methacrylate)-titania hybrid thin films

With 800-nm, 120-fs laser pulses, optical nonlinearity has been studied in a series of thin films containing poly(methyl methacrylate) (PMMA), filled with surfactant acetylacetone (Acac) capped TiO₂ nanoparticles, which were synthesized by a simple in situ sol-gel/polymerization process, assisted by spin coating and multi-step baking. The resulting nanohybrid thin films have highly optical transparency and demonstrate a unique nonlinear optical (NLO) response. The highest nonlinear refractive index (n₂) is observed up to 6.55 × 10⁻² cm² GW⁻¹ in the nanohybrid thin film of 60 wt% Ti(OBu)₄ in PMMA, with a negligible two-photon absorption (TPA), as confirmed by the Z-scan technique. The titanium precursor loading combined with the nature of the capping molecules are used to influence the ability of nanoparticles to nonlinear optical response. Indeed, the ligands at the nanoparticles’ surface can not only control the extent of the interaction between the organic molecules and the embedded nanoparticles but also influence the optical nonlinearities of nanoparticles.