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     

Low-resistivity indium tantalum oxide films by magnetron sputtering

Low-resistivity Ta-doped In₂O₃ (InTaO) films from ceramic targets of In₂O₃ doped with 2, 5, and 10 wt% Ta₂O₅ were deposited on Corning glass # 1737 substrates by magnetron sputtering. The electrical and optical properties of these films were studied. The carrier type of InTaO films was found to be n-type. The resistivity, carrier density, and Hall mobility of InTaO films were in the range of 0.28–200.2×10^-4 cm, 0.2–7.4×10²⁰ cm^-3, and 3–31 cm²V^-1s^-1, respectively. A minimum resistivity of 2.8×10^-4 cm with a mobility of 31 cm²V^-1s^-1 and a high transparency of 85% in the visible were achieved for the InTaO thin films doped with 5 wt% Ta₂O₅. PACS 81.15.Cd; 81.40.Rs; 73.90.+f     

Crystalline growth of cubic (Eu, Nd):Y2O3 thin films on α -Al2O3 by pulsed laser deposition

In this paper we report on the growth of crystalline, europium- and neodymium-doped cubic yttria ((Eu,Nd):Y₂O₃) thin films on hexagonal corundum (-Al₂O₃ ) substrates using the pulsed laser deposition (PLD) technique. A KrF excimer laser was used to ablate material from ceramic (Eu, Nd):Y₂O₃ targets. The yttria films were deposited on the -Al₂O₃ (0001) substrates. X-ray diffractometry (XRD) revealed that the films grew in the Y₂O₃[111]-direction. The surface topography of the films was investigated using atomic force microscopy (AFM). PACS 81.15.Fg; 42.70.hj; 68.55.Jk     

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     

Fabrication of Nd:KGW film on a Si substrate with a CeO<Subscript>2</Subscript> buffer layer

Highly textured single-oriented (110)Nd-doped potassium gadolinium tungstate [Nd:KGd(WO₄)₂ or Nd:KGW] thin films were successfully fabricated on (100)Si substrate by introducing a (100)CeO₂ buffer layer using KrF-excimer-laser pulsed laser deposition (PLD) at precisely controlled experimental conditions. The CeO₂ buffer layer was also prepared by PLD. Home-made potassium-enriched ceramic targets were prepared and used in order to prevent K deficiency in the film during the deposition. Depositions were performed in both Ar and O₂ environments. The optimal growing conditions achieved from the viewpoint of best crystallinity, optical properties and surface morphology were: d_T–S=4 cm, P(O₂)=0.08 mbar and T_sub=700 °C, respectively. Improvement of the properties of the as-grown films was examined by post-deposition annealing between 700 °C and 900 °C in air. Optical waveguide loss and the photoluminescence spectrum in the 800–1400-nm range were measured. PACS 81.15.Fg; 42.79.Gn; 42.79.Hj     

Electroless deposition of Ag on Pd-activated TiN/p-Si(100) substrate

Nano-thick Ag films were electrolessly deposited on TiN/p-Si(100) substrates. The substrates were prepared by sputtering TiN on p-Si(100) wafers. An activation process of the substrates was performed by immersing the substrates in a solution of 0.0019 moLL^-1PdCl₂+0.45 moLL^-1HF+8.7 moLL^-1aceticacid+0.036 moLL^-1 HCl so as to obtain the Pd seed layer. The general composition of the electroless Ag bath was 0.0032 moLL^-1AgNO₃+2.24 moLL^-1NH₃+0.56 moLL^-1aceticacid+0.1 moLL^-1 NH₂NH₂ at pH 10.2. The morphologies of the Pd seed layer and the Ag films were characterized by atomic force microscopy (AFM). The effect of the Pd activation on electroless Ag deposition was tested by open circuit potential with time technology (OCP-t). For comparison, the morphology of the films deposited by electrochemical deposition on the substrates was also studied by AFM. PACS 82.45.Mp; 81.15.Pq; 81.10.Dn     

Q-switched mode-locking with Cr4+ : YAG in a diode pumped Nd : GdVO4 laser

We have demonstrated passively Q-switched mode-locking in a laser-diode-pumped Nd:GdVO₄ laser with an intracavity Cr⁴⁺:YAG saturable absorber. At a pump power of 19.4 W, the Q-switched mode-locked laser produced an average output power of 3.22 W, and the repetition rates of the Q-switched envelope and the mode-locked laser pulse were 227 kHz and 144 MHz, respectively. The duration of the mode-locked pulse was within the sub-nanosecond range. PACS 42.55.Xi; 42.60.Fc; 42.60.Gd; 42.55.Rz     

Preparation of single-crystal-like MgO films on Si and orientation control of platinum films on MgO/Si

Growth of a Pt/MgO bilayer on Si(100) was investigated by pulsed-laser deposition. The growth modes of both MgO and platinum films are layer-by-layer growth, which were revealed by in situ reflection high energy electron diffraction observations. Two kinds of orientations of platinum films, viz. epitaxially (100) and (111)-oriented platinum films, were obtained on the same MgO(100)/Si(100) substrate only by varying the laser fluence. The effect of laser fluence on the orientation of platinum films is briefly discussed. The platinum films prepared in our experiments are epitaxially grown and exhibit atomic-scale surface flatness. It is believed that the improvement in the quality of platinum films can be attributed to the perfectly single-crystalline quality of the MgO buffer layer, which was further confirmed by the excellent dielectric properties. For a 150 nm thick MgO film, the leakage current density was found to be 10^-7 Acm^-2 with an electric field of 8×10⁵ Vcm^-1 and the relative dielectric constant (_r) was 10.6. PACS 68.55.Jk; 81.15.Fg; 85.50.Gk     

Size and Interface Control of Novel Nanocrystalline Materials Using Pulsed Laser Deposition

We have developed a novel method based upon pulsed laser deposition to produce nanocrystalline materials with an accurate grain size and interface control. Using this method, the grain size in the case of Cu thin films was controlled by introducing a few monolayers of insoluble elements having high surface energy such as W, which increases interfacial energy and provides more nucleation sites. The grain size is determined by the thickness of Cu layer and the substrate temperature at which it transforms into islands (nanocrystalline grains) of fairly uniform size which we desgnate as self-assembling approach. Using this approach, the grain size was reduced from 160nm (Cu or Si (100) substrate) to 70–80nm for a simple W layer (Cu/W/Si (100)) to 4nm for a multilayer (Cu/W/Cu/W/Si (100)) thin film. The hardness of these films was evaluated using a nanoindentation technique, a significant increase in hardness from 2.0GPa for coarse-grained 180nm to 12.5GPa for 7nm films was observed. However, there is decrease in hardness below 7nm for copper nanocrystals. The increase in hardness with the decrease in grain size can be rationalized by Hall–Petch model. However, the decrease in slope and eventually the decrease in hardness below a certain grain size can be explained by a new model based upon grain-boundary deformation (sliding). We also used a similar materials processing approach to produce quantum dots in semiconductor heterostructures consisting of Ge and ZnO dots or nanocrystals in AlN or Al₂O₃ matrix. The latter composites exhibit novel optoelectronic properties with quantum confinement of phonons, electrons, holes and excitons. Similarly, we incorporated metal nanocrystals in ceramics to produce improved mechanical and optical properties.     

Dielectric response of K(Ta,Nb)O3 thin films

The dielectric response of K(Nb,Ta)O₃ films grown on (001) MgAl₂O₄ (100) by pulsed laser deposition from a mosaic target of KTa_0.63Nb_0.37O₃ and KNO₃ has been examined. In particular, the effects of growth temperature (650–800 °C), growth pressure (1–100 mTorr O₂), and annealing conditions on the tunability, dielectric constant, and dielectric losses in interdigitated capacitor device structures fabricated with these films are described. Annealing treatments lead to a reduction in the loss tangents for most of the films considered. Figure of merit calculations indicate that the best dielectric response (tunability=37%, tan =0.022) is achieved for films grown at 750 °C in an oxygen pressure of 100 mTorr and then annealing at 1000 °C for 2 h in air.     

γ-Fe2O3 nanoparticles prepared by laser ablation of a tiny wire

A new method of preparing nanoparticles by pulsed laser ablation of a tiny wire is reported. A Nd:YAG pulsed laser with a wavelength of 1064 nm was used to ablate a 0.5-mm-diameter iron wire in a sealed chamber in a flowing mixed gas of N₂, O₂, and air to generate -Fe₂O₃ nanoparticles. In the meantime, a bulk Fe sample was ablated in the same chamber with the same laser processing parameters in order to compare the effect of the bulk sizes on the production rates and the sizes of the nanoparticles. The experimental results demonstrated that the production rate of nanoparticles prepared by laser ablation of tiny wires was about eight times that of laser ablation of bulk targets with the same composition, while the sizes of the nanoparticles were basically the same. With a higher power density and/or smaller diameters of the metal wires, it is possible to obtain smaller sizes of the nanoparticles with higher production rates. PACS 81.07.Wx     

Tailoring of the functional properties of sol–gel films on Pt/TiO2/SiO2/(100)Si substrates: (Pb,La)TiO3/(Pb,Ca)TiO3 multilayer heterostructures

Preferentially oriented sol–gel (Pb,Ca)TiO₃/(Pb,La)TiO₃/(Pb,Ca)TiO₃ and (Pb,La)TiO₃/(Pb,Ca)TiO₃/(Pb,La)TiO₃ multilayer heterostructure thin films deposited on silicon-based substrates have been studied and compared with identically prepared (Pb,La)TiO₃ (PTL) and (Pb,Ca)TiO₃ (PTC) films. The existence in their texture of two components that contribute to the net polarization in the direction normal to the plane of the film, 001 and 111, results in significant ferroelectric and pyroelectric properties. P_r=26 Ccm^-2 and =28.5×10^-9 Ccm^-2K^-1, and P_r=17 Ccm^-2 and =22.8×10^-9 Ccm^-2K^-1, have been achieved, respectively, in the PTL/PTC/PTL and PTC/PTL/PTC heterostructures. The surface roughness of these films provides a high specific surface that can be interesting for infrared detectivity. An increase of the dielectric permittivity in the whole temperature interval up to the transition temperature has been observed for both heterostructures with respect to the PTL and PTC films. This effect is due to a release of stress in the heterostructures that is revealed by the increase of the tetragonal distortion, c/a, of these films. PACS 68.55.Jk; 77.80.-e; 77.84.Dy     

Investigations on novel XUV-laser schemes

Short pulse laser generated plasmas interacting with a pulsed gas jet are studied to aid the realization of novel XUV laser schemes based on recombination supported by charge exchange pumping. Interaction of C⁴⁺, O³⁺ and O⁴⁺ ions with hydrogen and nitrogen indicates strong charge exchange pumping of C³⁺(3p-2s, 3d-2p) lines at 31.2 and 38.4 nm, and O²⁺ (2p3s-2p²) and O³⁺ (2s3d-2s²2p) lines at 37.4 and 23.8 nm. PACS 52.50.Jm; 52.25.Nr     

Textured thin films grown at room temperature by laser ablation

Thin films of SrFe₁₂O₁₉, BaFe₁₂O₁₉, Pb_0.76La_{0.16 0.08}Zr_0.53Ti_0.47O₃and Sr_0.3Ba_0.7Nb₂O₆ were grown on monocrystalline silicon substrates by pulsed laser deposition using a 20-ns Nd:YAG laser (1064 nm). The deposited thin films were analyzed by X-ray diffraction in the grazing incidence configuration. The analysis showed evidence of textured growth even though the films were grown at room temperature. Emission spectroscopy was used to establish the time of flight of the species within the plasma plume. Velocities of the order of 10⁶ cm/s were obtained. The high kinetic energy of the species is thought to be responsible for the film texture, as it is released in the substrate–film system, favoring a preferential growth. For all the ablated ceramics, singly ionized species were shown to expand at higher velocities than neutrals. For ions, no consistency in the mass–speed relation was obtained, suggesting both the presence of electric fields during the plasma formation and an evaporation of the target that depends on the vapor pressure of the elements. In this way species that are firstly evaporated will be attracted strongly by fast electrons, allowing heavy ions to acquire higher velocities than lighter ones. PACS 81.15.Fg; 52.38.Mf; 68.55.Jk; 52.38.Kd; 52.70.Kz     

Degenerate electrical conductive and excitonic photoluminescence properties of epitaxial films of wide gap p-type layered oxychalcogenides, LnCuOCh (Ln=La, Pr and Nd; Ch=S or Se)

Electrical and photoluminescence properties were investigated for epitaxial films of layered oxychalcogenides, LnCuOCh (Ln=La, Pr, and Nd, Ch=S or Se). Epitaxial films of Mg 10 at.% doped LaCuOS_1-xSe_x are the first demonstration of degenerate conduction with high hole concentration >10²⁰ cm^-3 in wide gap p-type semiconductors. Ion substitution varied the excitonic emission energy from 3.21 eV to 2.89 eV while lanthanide and chalcogenide ion substitutions displayed the opposite tendency against cell volume. These unique properties are discussed with respect to the electronic structure originating from the layered crystal structure. PACS 72.20.-i; 73.50.-h; 78.55.Hx; 78.66.-w     

Chemistry and microstructure of PLD (Ti,Al)CxN1-x coatings deposited at room temperature

The aim of the present work was the improvement of titanium-aluminium nitride (TiAlN) coatings by the solid-solution hardening with carbon atoms leading to titanium-aluminium carbon-nitride (Ti,Al)C_xN_1-x coatings with varying carbon (x) and nitrogen contents. The request of low deposition temperatures necessary for the coating of heat sensitive materials like tool steels of high hardness and polymers was reached by the application of the room temperature pulsed laser deposition (PLD) technique. A Nd:YAG laser of 1064 nm wavelength operated at two different laser pulse energies was used in the ablation experiments of pure TiAl targets (50 at.% Al) in various C₂H₂-Ar gas mixtures. Different pulse energies of the laser resulted in changes of the ratio of Ti/Al atoms in the grown coatings. Furthermore, the results reveal a strong proportionality of the gas mixture to the C and N content of the coatings. In the coatings deposited at low C₂H₂ gas flows the XRD investigations showed crystalline phases with fcc TiN type lattices, whereas high acetylene flows during deposition resulted in the formation of fully amorphous coatings and carbon precipitation or cluster boundaries found in Raman investigations. PACS 81.15.Fg; 46.55.+d     

Deposition of biopolymer thin films by matrix assisted pulsed laser evaporation

We report on the successful deposition of high quality type I fibrilar collagen thin films by Matrix assisted pulsed laser evaporation (MAPLE). Thin films deposition was performed in a N₂ ambient (20 Pa) using a KrF* laser source (=248 nm,20 ns) operated at a repetition rate of 3 Hz, the incident laser energy at a value within the range (20-35)mJ , and the laser spot area was (3.5-18.5)±0.1 mm². The collagen films were deposited on double face polished 100 single crystalline Si wafers and characterized by Fourier transform infrared spectroscopy, atomic force microscopy and high-resolution transmission electron microscopy. We demonstrate that our thin films are composed of collagen, with no impurities and the roughness can be controlled by the deposition conditions. PACS 52.38.Mf; 82.35.Pq; 83.80.Lz     

Pulsed laser deposition of magnetic films by ablation of Co- and Fe-based amorphous alloys

Magnetic films were prepared by pulsed laser ablation of amorphous magnetic ribbons (composition Co₆₇Cr₇Fe₄Si₈B₁₄, Fe_73.5Nb₃Cu₁Si_13.5B₉, and Fe₄₀Ni₄₀B₂₀) and permalloy foils (composition Fe_xNi_1-x with x=22,50). Depositions were performed in a vacuum of (2–4)×10^-5 Pa by KrF excimer laser pulses at fluences of between 2 and 7 Jcm². Films were deposited on oxidized silicon wafers, placed 60–80 mm apart from the target. Films were analyzed by SEM, XRD, RBS, and EDS. Ferromagnetic resonance (FMR) spectra were studied at GHz frequencies. From RBS and EDS measurements it follows that the stoichiometry of the targets is preserved in the films to a large extent. The films deposited from amorphous targets remain amorphous. From FMR studies it follows that Fe and Fe-Ni rich films exhibit properties close to those of bulk alloys, having very low magnetization motion damping parameter () of 7.0–7.8×10⁷ rad/s, which are appropriate for fast magnetic sensors. PACS 79.20.Ds; 75.50.Kj; 75.70.-i     

Pulsed laser deposition of oriented barium ferrite (BaFe<Subscript>12</Subscript>O<Subscript>19</Subscript>) thin films

Barium ferrite (BaFe₁₂O₁₉) thin films have been deposited by pulsed laser deposition at 900 °C in 250 mTorr oxygen on Si substrates with Pt(111) underlayers. The barium ferrite films contained platelet grains and a small amount of acicular grains, with sizes of 300 nm and 80×300 nm, respectively, and had a surface roughness of 11 nm. Vibrating-sample magnetometer measurements indicated that the BaFe₁₂O₁₉ films have some perpendicular orientation, with a perpendicular squareness of 0.64 and an in-plane squareness of 0.28. The saturation magnetization is about 190 emu/cc. The perpendicular and in-plane coercivities are 2.1 kOe and 1.6 kOe, respectively. PACS 75.50.Ss; 75.60.Ej; 75.70.Ak; 68.55.Ik     

Growth of polycrystalline LaNi<Subscript>1-x</Subscript>Co<Subscript>x</Subscript>O<Subscript>3</Subscript> (<Emphasis Type="BoldItalic">x</Emphasis> =0.3,0.5) thin films on Si(100) by pulsed laser deposition

Polycrystalline LaNi_1-xCo_xO₃ (x=0.5,0.3) thin films have been deposited on polished Si(100) substrates by pulsed laser deposition. The films are grown at 650 °C in ambient oxygen pressure of 0.4 mbar with an incident laser fluence of 1.5 J/cm² delivered by a KrF excimer laser. The lattice parameters of the as-grown films are slightly larger (0.05–0.4%) than those of the powders used to prepare the targets. The films exhibit weak texturing along the (012) direction. The low-temperature magnetic properties of the films, i.e. the coercive force, the remanence and the saturation magnetization, are enhanced compared to the powders. Furthermore, the x=0.3 film exhibits a low, almost temperature-independent resistivity above 200 K [(300 K)30 cm] and thus we propose it as a potential candidate material for electrode applications, e.g. in ferroelectric devices. PACS 68.55.-a; 73.61.-r; 81.15.Fg