Preparation of the La0.8Sr0.2MnO3 films on STO and LAO substrates by excimer laser-assisted metal organic deposition using the KrF laser

La_0.8Sr_0.2MnO₃ films were prepared on SrTiO₃ (STO) and LaAlO₃ (LAO) substrates using excimer laser-assisted metal organic deposition (ELAMOD). For the LAO substrate, no epitaxial La_0.8Sr_0.2MnO₃ film was obtained by laser irradiation in the fluence range from 60 to 110 mJ/cm² with heating at 500 °C. On the other hand, an epitaxial La_0.8Sr_0.2MnO₃ film on the STO substrate was formed by laser irradiation in the fluence range from 60 to 100 mJ/cm² with heating at 500 °C. To optimize the electrical properties for an IR sensor, the effects of the laser fluence, the irradiation time and the film thickness on the temperature dependence of the resistance and temperature coefficient of resistance (TCR: defined as 1/R·(dR/dT)) of the LSMO films were investigated. An LSMO film on the STO substrate that showed the maximum TCR of 3.9% at 265 K was obtained by the ELAMOD process using the KrF laser.     

Low-temperature growth of SnO2 film prepared by XeCl excimer laser MOD process

A SnO₂ film has been prepared by an excimer laser metal organic deposition (ELMOD) process using an XeCl laser. The effects of the laser fluence, shot number, and the pretreatment temperature of the Sn acetylacetonate (Sn-acac) on the crystallization of the SnO₂ film were investigated by X-ray diffraction and infrared spectroscopy. When the MO spin-coated film preheated at room temperature on a Si substrate was irradiated by the laser at a fluence of 100 mJ/cm² and at a repetition rate of 10 Hz for 5 min, a crystallized SnO₂ film was successfully obtained without heat treatment. At a fluence of 260 mJ/cm², the highest crystalline film was formed. On the other hand, when the amorphous SnO₂ film was irradiated by the laser at 260 mJ/cm², the crystallinity of the SnO₂ film was improved. SnO₂ films were also prepared by conventional thermal MOD in a temperature range from 300 to 900 °C. The crystallinity of the SnO₂ films prepared by the ELMOD process at room temperature was higher than that of the films prepared by heating at 900 °C for 60 min. PACS 81.15.Fg; 81.15.-z; 81.16.Mk; 82.50.Hp; 73.61.Le     

Influence of the laser wavelength on the epitaxial growth and electrical properties of La0.8Sr0.2MnO3 films grown by excimer laser-assisted MOD

Epitaxial La_1−xSr_xMnO₃ (LSMO) films were prepared by excimer laser-assisted metal organic deposition (ELAMOD) at a low temperature using ArF, KrF, and XeCl excimer lasers. Cross-section transmission electron microscopy (XTEM) observations confirmed the epitaxial growth and homogeneity of the LSMO film on a SrTiO₃ (STO) substrate, which was prepared using ArF, KrF, and XeCl excimer lasers. It was found that uniform epitaxial films could be grown at 500 °C by laser irradiation. When an XeCl laser was used, an epitaxial film was formed on the STO substrate at a fluence range from 80 to 140 mJ/cm² of the laser fluence for the epitaxial growth of LSMO film on STO substrate was changed. When the LaAlO₃ (LAO) substrate was used, an epitaxial film was only obtained by ArF laser irradiation, and no epitaxial film was obtained using the KrF and XeCl lasers. When the back of the amorphous LSMO film on an LAO substrate was irradiated using a KrF laser, no epitaxial film formed. Based on the effect of the wavelength and substrate material on the epitaxial growth, formation of the epitaxial film would be found to be photo thermal reaction and photochemical reaction. The maximum temperature coefficient of resistance (TCR) of the epitaxial La_0.8Sr_0.2MnO₃ film on an STO substrate grown using an XeCl laser is 4.0%/K at 275 K. XeCl lasers that deliver stabilized pulse energies can be used to prepare LSMO films with good a TCR.     

Preparation of super-hard coatings by pulsed laser deposition

Amorphous diamond-like carbon (DLC) films and nanocrystalline cubic boron nitride (c-BN) films were prepared by pulsed laser deposition. DLC films with 80 to 85% sp³ bonds prepared at a laser fluence above 6 J/cm² and a substrate temperature below 100 °C show high compressive stresses in the range of 8 to 10 GPa. Those stresses can be completely removed by means of pulsed laser annealing, allowing the preparation of DLC films with several-micrometre thickness. c-BN films were prepared with additional ion-beam bombardment at a substrate temperature of 250 °C. The properties of DLC and c-BN films deposited at high growth rates up to 100 nm/min are presented . PACS 81.15.Fg; 68.60.Bs: 62.40.+i     

Bonding configurations in amorphous carbon and nitrogenated carbon films synthesised by femtosecond laser deposition

The effect of nitrogen addition and laser fluence on the atomic structure of amorphous carbon films (a-C) synthesized by femtosecond pulsed laser deposition has been studied. The chemical bonding in the films was investigated by means of X-ray photoelectron (XPS) and Raman spectroscopies. XPS studies revealed a decrease in the sp³ bonded carbon sites and an associated increase in the N-sp²C bonding sites with increasing nitrogen content in the CN_x films. An increase in laser fluence from 0.36 to 1.7 J/cm² led to a rise in sp³C sites. These results were further confirmed by Raman spectroscopy. The I_D/I_G ratio increased monotonically and G line-width decreased with the increase of nitrogen content in the films indicating a rise in either the number or the size of the sp² clusters. Furthermore a visible excitation wavelength dependence study established the resonant Raman process in a-C and CN_x films. PACS 81.05.Uw; 81.15.Fg; 82.80     

Microstructural evolution and electrical properties of La<Subscript>0.7</Subscript>Ca<Subscript>0.3</Subscript>MnO<Subscript>3</Subscript> thin films grown on SrTiO<Subscript>3</Subscript> substrates by excimer-laser assisted metal-organic deposition

Thin films of La_0.7Ca_0.3MnO₃ were successfully grown epitaxially on (100) single-crystal SrTiO₃ substrates by excimer-laser assisted metal-organic deposition. Initial amorphous LCMO thin films were obtained by metal-organic deposition at 500 °C. Crystallization and epitaxial growth of the films was achieved using a KrF pulsed laser irradiation while the film/substrate samples were kept at 500 °C. High resolution transmission electron microscopy observations on cross-sections demonstrate the formation mechanism of the epitaxial films. The crystallization process starts at the LCMO/STO interface and grows by increasing the number of laser shots. A fully crystallized film was obtained after 5 min of irradiation. The film/substrate interface was found to be sharp and abrupt. The temperature dependence of the resistance R(T) shows various behaviors, starting from insulating to semiconducting and metal–insulator transition material during the formation of the manganite film. The oxygen content was also improved by increasing the irradiation time. Promising values of the temperature coefficient of resistance were obtained from these manganite films for prospect integration in silicon based microbolometric devices. PACS 81.15.-z; 81.15.Np; 73.61.-r; 71.30.+h     

Fabrication of LiNbO3 thin films by pulsed laser deposition and investigation of nonlinear properties

Thin films of LiNbO₃ were deposited by pulsed-laser deposition (PLD). Crystalline and transparent films were deposited on a sapphire substrate at 400 °C, in 100 mTorr of oxygen, with a fluence lower than 1.2 J/cm². Droplet free films were deposited with low ablation laser fluence by the eclipse method, and waveguide losses were 15.9 dB/cm and 3.1 dB/cm. Subsequently, second-harmonic generation (SHG) was achieved by waveguide mode phase matching. The center wavelength of the matching spectrum was 853 nm, and the full width at half maximum (FWHM) was 19 nm. PACS 42.70.Mp; 52.38.Mf; 68.55.Jk; 77.84.Dy; 81.15.-z     

Pulsed-laser crystallization and epitaxial growth of metal-organic films of Ca-doped LaMnO3 on STO and LSAT substrates

Ca-doped LaMnO₃ (LCMO) thin films have been successfully prepared on SrTiO₃ (STO) and [(LaAlO₃)_0.3-(SrAlTaO₆)_0.7] (LSAT) substrates using the excimer laser assisted metal-organic deposition (ELAMOD) process. The crystallization and the epitaxial growth of the amorphous metal-organic LCMO thin films have been achieved using a KrF excimer laser irradiation while the substrates were kept at constant temperature of 500 °C. Epitaxial films were obtained using laser fluence in the interval of 50-120 mJ/cm². The microstructure of the LCMO films was studied using cross-section transmission electron microscopy. High quality of LCMO films having smooth surfaces and sharp interfaces were obtained on both the STO and the LSAT substrates. The effect of the laser fluence on the temperature coefficient of resistance (TCR) was investigated. The largest values of TCR of the LCMO grown on the LSAT and the STO substrates of 8.3% K⁻¹ and 7.46% K⁻¹ were obtained at different laser fluence of 80 mJ/cm² and 70 mJ/cm², respectively.     

SiO2 films fabricated by F2 laser-induced chemical deposition using silicone rubber

Silicon dioxide (SiO₂) films were selectively fabricated on a Si substrate at room temperature by illuminating both the silicone rubber target and the substrate with an F₂ laser (157 nm). The laser fluence was much less than the ablation threshold. Absorption due to absorbed water (H₂O) and hydrogen-bonded silanol (SiOH) groups were observed in addition to absorption due to Si-O-Si stretching mode in the Fourier transform infrared spectroscopy (FT-IR) spectra of the films. The illumination with higher laser fluence caused an increase of Si-O-Si/OH peak ratio in the FT-IR spectra, a decrease of etching rate in hydrofluoric acid (HF) solution, and an increase in the refractive index close to the value of a thermal SiO₂ film. These results indicate that the quality of the grown SiO₂ films was improved. The high photon energy of F₂ laser induced photodissociation of main chains and side chains of silicone and oxygen (O₂), and bonds between the ejected gaseous molecules including Si and O(¹D) to form SiO₂ films. PACS 61.80.Ba; 81.15.Fg; 82.50.Hp     

Growth of polycrystalline La0.5Sr0.5CoO3 films by femtosecond pulsed laser deposition

In this paper we present the growth of La_0.5Sr_0.5CoO₃ (LSCO) films on MgO, quartz, and silicon substrates by pulsed laser deposition (PLD) using a Ti:sapphire laser (50 fs, 800 nm wavelength). The morphology and the structure of the films were studied by X-ray diffraction, atomic force microscopy, and scanning electron microscopy. The films were polycrystalline and exhibit a good adherence to the Si substrate. Different deposition parameters such as substrate temperature, oxygen pressure, and laser fluence were varied to achieve good surface quality and low resistivity crystalline films. We also defined the optimum conditions in which the deposited film surface is particulate free. The best films (droplets free) were grown at 625 °C, in an ambient oxygen pressure of 6 mbar, with an incident laser fluence of 0.19 J/cm². This is a mandatory step in the complex work of fabricating La_0.5Sr_0.5CoO₃/BaTiO₃/La_0.5Sr_0.5CoO₃ heterostructures for the development of thin film capacitors for non-volatile ferroelectric access memory devices. PACS 81.15 Fg; 42.62-b; 68.65.Ac     

Fabrication of diamond-like carbon thin films by femtosecond laser ablation of frozen acetone

Diamond-like carbon (DLC) thin films were fabricated by the ablation of frozen acetone with a 790 nm, 130 fs Ti:sapphire laser. Compared to a solid carbon target, frozen acetone could significantly reduce the number of fragments mixed into the films. The optical and mechanical properties of the fabricated DLC films were determined when the laser fluence was varied from 3 to 470 J/cm². With the increase in laser fluence, the films tinged with brown and the optical bandgap of the films decreased from 2.0 to 1.2 eV. Also, the refractive index and hardness of the films increased from 1.75 to 1.99 and from 10 to 16 GPa, respectively. The sp³ content was not changed even if the laser fluence was varied. The change in properties resulted from the hydrogen content of the films. PACS 81.05.Uw; 81.15.Fg     

La<Subscript>0.7</Subscript>Sr<Subscript>0.3</Subscript>MnO<Subscript>3</Subscript> thin films on SrTiO<Subscript>3</Subscript> and CaTiO<Subscript>3</Subscript> buffered Si substrates: structural,static, and dynamic magnetic properties

Nearly 50-nm thick La_0.7Sr_0.3MnO₃ (LSMO) films were grown on Si substrates using molecular beam epitaxy on (001) Si substrates over-layered by a 20 nm thick SrTiO₃ (STO) or by a 20 nm thick CaTiO₃ (CTO) film. In addition, a reference LSMO film was directly deposited on a (001) STO substrate by pulsed laser deposition. For all the samples, X-ray diffraction revealed an excellent epitaxy of the LSMO film and small mosaicity around (001), with in-plane [100] and [010] cubic axes. The LSMO/CTO films are in-plane compressed while the LSMO/STO ones are in-plane extended. The temperature dependence of their static magnetic properties was studied using a SQUID, showing a Curie temperature overpassing 315 K for all the samples. Hysteresis loops performed at room temperature (294 K) with the help of a vibrating sample magnetometer (VSM) are also discussed. At 294 K Micro-strip ferromagnetic resonance (MS-FMR) was used to investigate the dynamic magnetic properties. It allows concluding to a strong anisotropy perpendicular to the films and to a weak fourfold in-plane anisotropy with easy axes along the [110] and [1[`1]0 1\bar{1}0 ] directions. Their values strongly depend on the studied sample and are presumably related to the strains suffered by the films.     

The role of the temperature and laser fluence on the properties of PLD bioactive glass films

The effect of the deposition temperature and laser fluence on the bonding configuration, morphology and mechanical properties of the PLD bioactive glass thin films in the system SiO₂P₂O₅CaONa₂OK₂OMgO is presented.Information on the IR active Si-O groups was obtained by Fourier Transform Infrared (FTIR) spectroscopy. Surface morphology changes were followed by Atomic Force Microscopy (AFM) and the film thickness was measured by profilometry. Hardness and elastic modulus were determined by nano-indentation.The frequency shifting and intensity variations of the IR absorption bands indicate that the substrate temperature plays an important role on the bonding configuration of the films. This effect is associated with a network rearrangement and the surface chemistry that occurs during the film growth.The main effects of the laser fluence on the film properties are the linear dependence on it of the growth rate and the changes induced on the surface morphology. Both results are discussed in terms of beam–matter interaction and plume–substrate interaction in the PLD process. Finally, the hardness and the elastic modulus of the films are in agreement with the values reported in the literature for the bulk material. PACS 81.15.Fg; 87.68.+z; 68.60.Bs; 68.37.Ps; 61.43.F1; 67.70.+n     

Characteristics of Ba xSr 1–xTiO 3 thin films grown by pulsed laser ablation of rotating split targets of BaTiO 3 and SrTiO 3

We have grown heterostructures of Ba_xSr_1-xTiO₃(BST)/La_0.7Sr_0.3MnO₃(LSMO) on LaAlO₃(LAO) substrates by the pulsed laser deposition method. BST films with x=0.2,0.5,0.7 and 0.8 have been prepared using a novel rotating split-target arrangement. The lattice constant of the BST films is found to vary linearly with Ba/Sr ratio. An excellent cube-on-cube epitaxial relationship of (100)_BST||(100)_LSMO||(100)_LAO has also been obtained. Scanning electron microscopy studies have revealed smooth and crack-free BST films with a uniform grain size of about 100 nm. Dielectric measurements, made with patterned Au top electrodes and conducting LSMO bottom layers, have shown a maximum permittivity of approximately 280 at 5 kHz in BST films with x=0.7. P–E loop analyses of the Ba_0.7Sr_0.3TiO₃ and Ba_0.8Sr_0.2TiO₃ films have yielded remnant polarization values of 1.66 and 1.81C/cm², respectively. PACS 81.15Fg; 68.55Jk; 77.55+f     

Microstructural investigation of CaxCo4Sb12 films prepared by pulsed laser deposition

Ca_xCo₄Sb₁₂ skutterudite thin films have been synthesized by pulsed laser deposition from a Nd:YAG laser working at 532 or 355 nm. The influence of deposition temperature, laser fluence and working atmosphere on the structure and morphology of the films has been studied. The characterization has been carried out by X-ray diffraction, atomic force microscopy and scanning electron microscopy. Laser wavelength proved to be the most significant parameter to produce the skutterudite phase. PACS 81.15.Fg; 68.55.Jk; 81.05.Bx     

Effect of magnetic film thickness on rectifying properties of La0.8Sr0.2MnO3/TiO2 heterostructures

The La_0.8Sr_0.2MnO₃ (LSMO)/ TiO₂ heterostructures with different thicknesses of the LSMO films were successfully synthesized using the RF magnetron sputtering technique. Excellent rectifying characteristics are presented in all heterostructures in a wide temperature range. The differences of the diffusive potentials for three heterojunctions are very little at 300 K. The samples exhibit a high resistance that plays an important role on their rectifying properties. The diffusive potential decreases with increasing temperature. The result is attributed to both the reduction of the thickness of the deletion layer due to the thermal diffusion and the modulation of the interfacial electronic structure of the heterostructures. The metal-insulator (M-I) transition is observed clearly from the single LSMO layers and the LSMO/ TiO₂ p-n heterojunctions.     

Characterization and antibacterial functions of Ag–TiO<Subscript>2</Subscript> and W–TiO<Subscript>2</Subscript> nanostructured thin films prepared by sol-gel/laser-induced technique

A novel sol-gel/laser-induced technique (SGLIT) has been developed to form nanocrystalline titanium dioxide (TiO₂) based thin films with an improved antibacterial performance. TiO₂ precursor films loaded with W⁺⁶ and Ag⁺² ions (W–TiO₂, Ag–TiO₂) were prepared separately by sol-gel method and spin-coated on microscopic glass slides. As-dried films were subjected to KrF excimer laser pulses at optimized parameters to generate mesoporous anatase and rutile phases at room temperature. The anatase phase was obtained after irradiation with 10 laser pulses only at 75–85 mJ/cm² fluence in W–TiO₂ films. However, higher number of laser pulses and higher W⁺⁶ content favored the formation of rutile. Whereas Ag–TiO₂ films exhibited anatase up to 200 laser pulses at the same fluence. The films were characterized by using XRD, FEG-SEM, TEM and UV-Vis spectrophotometer to investigate the crystallographic structure, phase transformation, surface morphology, film thickness and the optical properties. A crystallite size of approximately 20 nm was achieved from the anatase prepared by SGLIT. The films exhibited an enhanced antibacterial function against E-Coli cells under the UV excitation.     

Finite size effect and phase diagram of ultra-thin La0.7Sr0.3MnO3

La_0.7Sr_0.3MnO₃ (LSMO) ultra-thin films have been grown by pulsed laser deposition in conditions optimized for cation stoichiometry and bulk-like physical properties in the thick limit. Through electrical transport and magnetic measurements, a phase diagram is constructed as a function of film thickness. With decreasing thickness, the LSMO films cross over at high temperatures from a paramagnetic metal to a paramagnetic insulator, and at low temperatures from a ferromagnetic metal to a ferromagnetic insulator, in close similarity to that observed for varying the electronic bandwidth in bulk manganites.     

Interfacial spin interactions of ferromagnetic and antiferromagnetic manganite bilayers

A pulsed laser deposition technique was used to grow ferromagnetic La_0.7Sr_0.3MnO₃ (LSMO) films on antiferromagnetic La_0.33Ca_0.67MnO₃ (LCMO) and Pr_0.7Ca_0.3MnO₃ (PCMO) films in bilayer forms. The LSMO film on the PCMO layer had a more elongated out-of-plane lattice than that on the LCMO layer. The former had a lower ferromagnetic transition temperature (320 K) than the latter (350 K). The enhanced low-temperature magnetoresistance of the LSMO/PCMO bilayer suggests that the spin frustration is stronger at this bilayer than in the LSMO/LCMO bilayer. These differences indicate that strain state and defect concentration play important roles in governing interfacial spin interactions.     

Matrix assisted pulsed laser deposition of light emitting polymer thin films

Matrix assisted laser processing allows for the deposition of functional and fragile materials with a minimum of breakdown and decomposition. In this communication we report on light emitting thin films of ruthenium tris(bipyridine)-centered star-shaped poly(methyl methacrylate), Ru(bpyPMMA₂)₃(PF₆)₂, grown by matrix assisted pulsed laser deposition. A pulsed excimer laser (KrF) operating at 248 nm was used for all experiments. Due to the absorption at 248 nm and the solubility characteristics of [Ru(bpyPMMA₂)₃](PF₆)₂, dimethoxy-ethane (DME) was used as a solvent [1]. Dilute solutions (2 wt.%) of [Ru(bpyPMMA₂)₃](PF₆)₂ and DME were flash frozen in liquid nitrogen producing a solid target. Thin films ranging from 20 to 100 nm were grown on Si in an Ar atmosphere at 200 mTorr at a laser fluence of 0.04 J/cm². The deposited materials were characterized by proton nuclear magnetic resonance (¹H NMR) and gel permeation chromatography (GPC) equipped with refractive index (RI), and ultraviolet/visible (UV/vis) detection. PACS 81.15.Fg; 79.20.Ds; 78.66.Qn; 42.70.Jk