Pulsed Laser Ablation Deposition Research Articles

In-situ plasma emission optical spectroscopy during pulsed laser ablation deposition of PZTN thin films

Optical spectroscopy of the plasma emission produced by pulsed laser irradiation of a Nb-doped PZT (PZTN) target during film deposition is reported, including both spectral analysis of the emission species at different positions inside the plasma and time resolved measurements. The laser ablation system uses the second and third harmonic wavelengths of a 7 ns Nd : YAG laser. Several species present in plasma emission spectra were identified at two positions inside the expanding plasma under vacuum pressure (10 −7 mbar). The pulsed laser grown orientated PZTN films were characterized by X-ray diffraction (XRD).

Growth of crystalline ZnSe : N thin films by pulsed laser ablation deposition

Crystalline ZnSe thin films doped with nitrogen have been grown on polished GaAs(1 0 0) and Si(1 0 0) substrates by pulsed laser ablation deposition (PLAD) in N 2 atmospheres. Atomic force microscopy (AFM) shows that the surface morphology of the PLAD-grown ZnSe thin films is flat and dense, and the roughness for best films grown on GaAs(1 0 0) in 2×10 −3 Torr N 2 ambient is about 1.3 nm. X-ray diffraction (XRD) results indicate that the ZnSe film grown on GaAs(1 0 0) at 2×10 −3 Torr is a single crystalline epitaxial layer. The full-width at half-maximum of ZnSe(4 0 0) peak for best film grown on GaAs(1 0 0) is 232 arcsec. XRD and AFM analyses indicate that the crystallographic quality of PLAD-grown ZnSe thin films largely depends on ambient pressure and lattice match. X-ray photoelectron spectroscopy demonstrates that Zn and Se atoms in the PLAD-grown ZnSe thin film on GaAs(1 0 0) at 2×10 −3 Torr bond each other, and the concentrations of [N] and [O] are 7% and less than 3%, respectively, and no other impurities exist. The concentration of doped nitrogen for the best ZnSe thin film grown on GaAs(1 0 0) was estimated to be over 10 21 1/cm 3.

Ferrimagnetic resonance linewidths of thick barium hexaferrite films on MgO [111

C-axis oriented barium hexaferrite films having thickness from 3-30 /spl mu/m were deposited onto 0.5 mm magnesium oxide (MgO) [111] substrates by pulsed laser ablation deposition, and were characterized by magnetometry and ferrimagnetic resonance (FMR) measurements. The FMR linewidth for as-produced 30 /spl mu/m films was 0.65-0.70 kOe, while those of thinner (3 /spl mu/m) films was near 0.50 kOe. The narrowest linewidth of /spl sim/0.06 kOe was obtained for a 3 /spl mu/m film after annealing for two hours. However, increased annealing time beyond two hours caused an increase in FMR linewidth. The FMR linewidth of 30 /spl mu/m films where from 55-77% of the MgO substrate was removed decreased by 0.15-0.20 kOe compared to as-produced films. Further improvement in the FMR linewidth to 0.20 kOe was obtained by a two hour annealing. These FMR results are discussed in terms of the homogeneity, planar stress, and stoichiometry of these thick pulsed laser deposited films.

Magnetoelastic properties of laser-ablated non-crystalline Co cylindrical films

Non-crystalline Co films have been deposited on the cylindrical surface of copper wires by pulsed laser ablation deposition. These films are magnetoelastic. In particular, they exhibit the inverse Wiedemann effect (IWE): when they are twisted and an electrical current flows through the wires, a longitudinal component of the magnetization is observed. The value of the spontaneous magnetization, M s, of these films is achieved by the measurement of this effect. The dependence of the IWE on the torsion as well as on the circular magnetic field has been measured. The magnetostriction constant, λ s, has been found to be negative and λ s≈−(9.5±0.8)×10 −6.

Influence of target composition on the quality of YBCO films fabricated by Nd:YAG pulsed laser deposition

The influence of target composition on the formation of surface particles and the crystallinity of YBCO epitaxial films is studied by pulsed laser ablation–deposition method using the fourth harmonic of a Nd:YAG laser and by X-ray diffraction, scanning electron microscope, atomic force microscope, and electron probe X-ray microanalyzer analysis. Six kinds of targets in which one of the atomic constituents is deviated by ±5% to ±1% from stoichiometry were used in addition to the stoichiometric target YBa 2Cu 3O y . All films deposited are highly c-axis oriented. Films fabricated from stoichiometric targets have a high transition temperature ( T c) of 90.0±0.5 K and a small number of surface particles (mainly droplets), as low as 1.5 particles/10 μm 2. By constrast, the films deposited from non-stoichiometric targets exhibit a large number of outgrowths (CuO and oxides mainly of Ba and Cu) in addition to droplets and a low T c in the range of 75–89 K. The number and the sort of the outgrowths do not depend largely on the kinds of the non-stoichiometric targets nor on the extent of deviation in the range of ±1% to ±5%. These results have been reasonably understood as mainly due to the targets inhomogeneity from the following experimental evidence. (1) The non-stoichiometry of the targets produces much more extent of segregation of impurity phases than that expected from the imbalance of ±5% to ±1%. (2) The extent of segregation is almost identical for every non-stoichiometric target. The present study indicates clearly that the target should have the stoichiometric ratio (1:2:3) in order to prepare high quality YBCO epitaxial films.

Ni 50Nb 50/C amorphous multilayers for “water window” soft X-rays – structure and stability

Amorphous Ni 50Nb 50/C multilayers with a period of 2.4 nm for the water window soft X-rays were prepared by pulsed laser ablation deposition. The structural stability of these multilayers was studied by grazing incidence X-ray scattering. The multilayers were found to be highly stable at room temperature for periods as long as 3 years. However, the Ni 50Nb 50 layer was found to undergo an amorphous – crystalline disorder – order transformation due to annealing while the carbon layer remained unchanged. The crystalline phase after transformation could be identified as the NiNb phase. The vertical layered structure, however, was found to be highly stable even after annealing the multilayers at 473 and 593 K under vacuum. The multilayer period remains unchanged till 473 K and increases by 7% on annealing at 593 K.

Laser ablated pure non-crystalline Co thin films for inductors for ultra-high frequencies

ABSTRACTNon-crystalline Co thin films have been prepared by pulsed laser ablation deposition. From the M-H hysteresis loops measurements, a soft magnetic behavior is observed. Néel type magnetic domain walls are observed in the as-deposited films. The spontaneous magnetization, Ms(T = 300 K), is ≍ 860 emu/cm3. After annealing at 500 oC, Ms(T = 300 K) is ≍ 1460 emu/cm3. The extrapolated to zero K resistance decreases almost two orders of magnitude from the as deposited samples to the crystallized heated at 500 °C ones. A trilayer Co/Cu/Co has shown a real part magnetic susceptibility of 120 at 100 MHz. In the 100 MHz to 1 GHz frequency range, a perpendicular bias magnetic field increased this value up to 270, remaining almost constant for all range.

Effect of oxygen annealing on the magnetoresistance inLa0.7Ca0.3MnO3 epitaxial films

Epitaxially c-axis oriented thin films of La0.7Ca0.3MnO3(LCMO) have been fabricated on (001) SrTiO3 and (001) LaAlO3substrates by pulsed laser-ablated deposition technique. The physicalproperties of as-grown films are correlated with the structural nature ofthe substrate. The O2-annealed films grown on both substrates exhibithigher metal-insulator (M-I) transition temperatures (TMI) andlarger magnetoresistance (MR) ratios than the corresponding as-grown films.On the other hand, the Ar-annealed films display enhanced MRwithout any noticeable change in TMI. We suggest that increase inTMI is mainly ascribed to oxygen incorporation whereas enhancementof MR is largely associated with microstructural change induced by thermalannealing. Structural and transport data reveal that post-annealing withO2 not only saturates the anion defect sites but also relieves structural strain,resulting in the enhancement of TMI and large MR.

Metal–insulator transition temperature dependence on lead and oxygen content in La1−xPbxMnO3±y thin films

Preparation of the manganese oxide films with high Curie temperature (TC) above room temperature (RT) is essential for developing multilayered devices that work at RT. We have fabricated La1−xPbxMnO3±y (LPMO) thin films on LaAlO3–Sr2AlTaO6 (001) single-crystal substrates using a pulsed-laser ablation deposition method. Their metal–insulator transition temperature (TRmax), which nearly equals TC, is investigated as a function of the lead (Pb) and oxygen contents contained. The results in the following were obtained. X-ray diffraction indicates growth of epitaxial films with (001) orientation. Samples with high TRmax∼370 K can be prepared in deposition conditions with a substrate temperature (TS) of 600 °C and an oxygen pressure (PO) not less than 0.4 Torr. The TRmax decreases with increasing TS or decreasing PO. The former decrease in the TRmax is shown by electron-probe microanalysis to be ascribed to evaporation of Pb from the films at high TS. On the other hand, it is inferred that the latter decrease is due to a reduction in oxygen content in the films. The reduction of Pb and oxygen contents in the LPMO films, respectively, leads to a decrease in the number of conduction electrons and, consequently, results in a TRmax decrease of the films.

Curie temperature control of La 1− xPb xMnO 3− y thin film by changing the pulsed laser deposition conditions

The pulsed laser ablation deposition (PLD) method has been used to fabricate epitaxial films of La 1− x Pb x MnO 3− y (LPMO) oxide and to control Curie temperature ( T C) of films by changing the deposition conditions. X-Ray diffraction indicated growth of epitaxial films with good crystallinity. All films prepared showed metal–insulator phase transition. The respective phase corresponds to ferromagnetic and paramagnetic one. The transition temperature T R max (nearly equivalent to T C) decreases from 324 to 246 K with increasing substrate temperature ( T S) during film deposition. Electron probe microanalysis showed that the lead (Pb) concentration in the films decreased (evaporated) with increasing T S, indicating that the decrease in T R max is mainly due to the decrease of Pb content in the film. The magnetoresistance ratio normalized to the zero-field of a film, whose T R max is near room temperature (RT), is 0.45% at magnetic field ( H)=21 kOe at RT. The MR ratio is small unfortunately, however, the present results indicate that the phase transition temperature can be controlled by changing T S and epitaxial films with T R max above RT can be prepared by the PLD method. These films are necessary for development of multilayered devices which are composed of ferromagnetic and non-magnetic substances.

Pulsed laser ablation deposition of yttrium iron garnet and cerium-substituted YIG films

Yttrium iron garnet (YIG) thin films were grown on gadolinium gallium garnet substrates using pulsed laser ablation deposition (PLAD) with a XeCl excimer laser. Films were grown up to over 2 μm thick, however cracking proved to be a problem for films over 1 μm thick. The lattice parameter(s) of the films and the substrates were measured and indicated that the film/substrate structure was bending to accommodate strain due to the lattice mismatch. The films had saturation magnetisation values close to that of bulk YIG and were isotropic in the film plane. The magnetisation data also indicate stress-induced uniaxial isotropy. The ablation conditions were varied to produce uncracked films with low droplet densities. YIG melts incongruently during the laser ablation process and cone-like structures form on the ablation target lowering the ablation rates. Cerium-substituted YIG films were also grown in both oxygen and argon atmospheres, substituting cerium into YIG increases the lattice parameter and hence reduces the strain. The Ce-YIG film grown in argon was greenish indicating that cerium was in the desired oxidation state.

Novel thin-film fabrication method combining pulsed laser ablation and catalytic chemical vapor deposition: application to preparation of Er-doped hydrogenated amorphous Si films

A novel thin-film fabrication method combining pulsed laser ablation and chemical vapor deposition (CVD) was proposed and applied to preparation of erbium (Er-)-doped hydrogenated amorphous silicon (a-Si : H) films. In this method, a matrix of a-Si : H films is formed by catalytic CVD using silane (SiH 4), and Er is simultaneously doped in the a-Si : H films by laser ablation. Er content increases with an increase in the gas pressure during deposition, which originates from the enhanced reaction between ablated Er species and decomposed SiH 4 species in the shock front of the plume in the laser ablation. It was confirmed that there is no increase in the dangling-bond density in the a-Si : H matrices accompanied with the Er doping, suggesting that Er-doped a-Si :H films prepared by the proposed method are promising for optical-communication devices.

PbFe 12O 19 thin films prepared by pulsed laser deposition on Si/SiO 2 substrates

Pulsed laser ablation deposition has been used to grow polycrystalline PbFe 12O 19 thin films with high coercivity on Si/SiO 2 substrates. The influence of the substrate temperature (550–775°C) and the oxygen pressure (1.0–3.0 mbar) on the magnetic properties during the deposition is reported. The crystallisation of PbFe 12O 19 thin films occurs in the temperature range of 600–750°C, which is somewhat lower than that for the Sr and Ba hexaferrites, which crystallise in the range of 750–850°C. M-type lead hexaferrite films with high saturation magnetisation (280 emu/cm 3) and high coercive field (3.8 kOe) were grown using a substrate temperature of 700°C and a pressure of 3.0 mbar of oxygen. These films were observed to be isotropic, with an M r/ M s ratio of ∼0.5.

Electric field dependence of ferroelectric phase transition in epitaxial SrTiO3 films on SrRuO3 and La0.5Sr0.5CoO3

We report on the electric field dependence of ferroelectric phase transition in epitaxial SrTiO3 (STO) thin films grown by the pulsed-laser ablation deposition method. Metallic oxides SrRuO3 (SRO) and La0.5Sr0.5CoO3 (LSCO) were used as the bottom electrodes, and the bottom electrodes influence the dielectric properties of STO films. The change in the dielectric properties originates from the different work functions and the lattice mismatches among STO film, the bottom electrode, and the substrate. However, the field-induced ferroelectric phase transition temperatures of the STO/SRO/(100) STO and the STO/LSCO/(100) LaAlO3 systems are proportional to the applied electric field, indicating a field-induced first-order ferroelectric phase transition.

Evaluation of crystallographic and electromagnetic defects in the superconducting crystals and films by analysis of magneto-microwave response

Magnetic-flux trapping in crystals and films of high- T c superconductors is investigated from the microwave (MW) response detected by electron spin resonance (ESR) spectrometer. For Bi2212 single crystals, the periodic MW spectra were observed at external magnetic fluxes Φ X =( k±1/2) Φ 0; where k is an integer, along with the surface impedance signal. The periodic spectrum is a clear evidence for the stepwise transitions ( k→ k+1) between the energy states of Josephson-junction (JJ) links by MW absorption, which follows the stepwise penetration of quantized flux Φ 0. Their analysis provided information on the phase shift Δ ϕ=0 or π of the vortex current along the link in addition to the link size, link-surface orientation, and the number of the penetrated quanta. The YBCO epitaxial films, which were fabricated by pulsed laser ablation–deposition (PLD), showed the three kinds of MW responses or their superimposed spectra: (1) surface impedance, (2) periodic spectra due to intra-crystal JJ, and (3) a complex spectrum characteristic of the flux dynamics at inter-granular JJ defects. They are discussed in comparison with the film-crystallinity studied by X-ray diffraction and scanning electron microscope (SEM) and have made it possible to evaluate the degree of epitaxy and the defects that work as flux-trapping sites.

Growth and characterization of thick oriented barium hexaferrite films on MgO (111) substrates

Highly oriented films of BaFe12O19 have been deposited onto MgO (111) substrates by pulsed laser ablation deposition. In contrast to epitaxial BaFe12O19 films grown on Al2O3 (001) substrates, these films experience an in-plane biaxial compressive stress, and do not crack or delaminate to thicknesses of at least 28 μm. X-ray diffraction, magnetometry, torque magnetometry, and ferrimagnetic resonance results all indicate excellent c-axis orientation normal to the film plane, and magnetic properties comparable to bulk values. The thickness and properties of these films approach those required for applications in low-loss self-biased nonreciprocal microwave devices.

Structure and magnetic properties of barium hexaferrite films deposited at low oxygen pressures

Barium hexaferrite films were grown by pulsed laser ablation deposition onto c-plane sapphire at oxygen pressures from 1 to 200mTorr to evaluate their structural and magnetic properties. Films deposited at pressures above 1mTorr showed excellent c-axis orientation normal to the film plane, and good surface morphologies. The c-axis lattice constant of films deposited at and above 50mTorr was reduced compared to bulk values. Film saturation magnetization values were slightly lower than bulk values, while anisotropy field values were comparable. Ferrimagnetic resonance measurements showed distinct absorption peaks, with the narrowest linewidth of 0.20kOe being measured for a 10mTorr film. The 1mTorr film had a significantly different texture wherein the c-axis laid down into the film plane, and also showed in-plane six-fold magnetic anisotropy. These results may indicate that highly c-axis oriented barium hexaferrite films can be grown to greater thicknesses using reduced oxygen pressures.

Growth of ZnSe:N epilayers by pulsed laser ablation deposition

Epilayers of nitrogen doped ZnSe have been grown on GaAs(100) substrates by pulsed laser ablation deposition assisted by a nitrogen beam produced by a supersonic nozzle beam source. X-ray photoelectron spectroscopy (XPS) shows that the epilayers are composed of 83.8% Zn and Se, 10.4% N and 5.8% O, and other kinds of impurity are rare. XPS spectra of Zn(2p3/2) and N(1s) core levels indicate that doped nitrogen with an estimated concentration of over 1021 cm-3 exists in the as-grown epilayer. Atomic force microscopy indicates that the surface of an as-grown ZnSe epilayer on GaAs(100) is flat with roughness of about 1.2 nm, which is less than that of some good-quality metalorganic vapour phase epitaxy grown layers. X-ray diffraction results show that these ZnSe epilayers are a characteristic of single crystallinity.

ＰＬＤ法により作製したＬａＰｂＭｎＯ系薄膜のキュリー温度

ＰＬＤ法により作製したＬａＰｂＭｎＯ系薄膜のキュリー温度

Pulsed laser ablation deposition of thin films on large substrates

We have designed and built an ultra-high vacuum chamber which allows thin film deposition on large area (up to 100 mm diameter) flat substrates and on three-dimensional substrates (e.g. 100 mm long, 50 mm diameter cylinders) by the pulsed laser deposition and reactive pulsed laser deposition techniques. Heating of substrates during and after film deposition is possible using either resistive heaters or a lamp array. Metal (Cu) and metal nitride (TiN) and carbide (TiC) films were deposited on Si wafers (60 and 100 mm diameter), three-dimensional steel substrates (steel cylinders and screws), Teflon plates, and paper sheets.