The propagation of laser ablation plumes from 248 nm laser‐irradiated YBCO into vacuum and 100 mTorr ambient oxygen has been photographed with a gated, intensified CCD array camera system. The thermalization of the laser plasma and onset of shock structures due to collisions with the background gas are investigated from two‐dimensional digitized images of the visible plume emission.

Fast intensified‐CCD photography of YBa2Cu3O7−x laser ablation in vacuum and ambient oxygen

Frequency‐doubled Nd:YAG laser (532 nm) pulses of 1.7 J/cm2 and 10 ns duration were used to deposit thin films of YBa2 Cu3 O7−δ by laser ablation on NdGaO3 , LaGaO3, and SrTiO3 substrates held at 725±5 °C in 0.2 Torr of O2 ambient. Electrical resistivities versus temperature of all films show normal metallic behavior and sharp superconducting transitions with Tc (R=0) at 92–93 K. Critical current densities in 0.3–0.6 μm thick, 200 μm long, and 10–30 μm wide strips were measured to be 106 A/cm2 at 60, 77, and 80 K in the films on LaGaO3, NdGaO3, and SrTiO3, respectively. X‐ray diffraction patterns show that all films grew epitaxially, with domains of only two crystalline orientations rotated 90° with respect to each other in the a‐b plane (consistent with twins), and the c axis perpendicular to the substrates. The closely matched lattice constants of the film and substrates (0.8–2.1%) result in epitaxial growth of the films.

Epitaxial films of YBa2Cu3O7−δ on NdGaO3, LaGaO3, and SrTiO3 substrates deposited by laser ablation

Superconducting thin films of Y1Ba2Cu3O7−x were fabricated using the process of plasma‐assisted laser deposition. The substrate temperature was as low as 400 °C and high‐temperature post‐annealing in an O2 atmosphere was not necessary. The as‐deposited films have a Tc of ∼85 K, and are oriented mostly with the c axis perpendicular to the substrate surface. The measured Jc at 80 K was 105 A/cm2.

Deposition of superconducting Y‐Ba‐Cu‐O films at 400 °C without post‐annealing

High quality vanadium dioxide (VO2) thin films have been successfully deposited by pulsed laser deposition without postannealing on (0001) and (1010) sapphire substrates. X‐ray diffraction reveals that the films are highly oriented with (010) planes parallel to the surface of the substrate. VO2 thin films on (0001) and (1010) substrates show semiconductor to metal transistions with electrical resistance changes as large as 4×104, 105, respectively. Thin films on (1010) substrate have a transition at as low as 55 °C with a hysteresis less than 1 °C. These transition properties are comparable with single crystal VO2.

Pulsed laser deposition of VO2 thin films

YBa2Cu3O7−δ thin films were deposited onto (100) SrTiO3 substrates using 1064, 532, 355, 248, and 193 nm laser ablation. Transport measurements show lower normal‐state resistivities and higher critical currents in films deposited by the shorter wavelength lasers. The surface morphology of the films was rough with large particulates when the 1064 nm laser was used whereas much smoother surfaces with fewer and smaller particulates were obtained with the UV lasers. It is suggested that the better film quality obtained when the UV lasers are used is due to a small absorption depth of the UV photons in the ceramic target and to higher absorption by the ablated fragments. This leads to smaller ablated species and further fragmentation in the hotter plume and, therefore, to smoother and denser films.

Laser wavelength dependent properties of YBa2Cu3O7−δ thin films deposited by laser ablation

An oxygen jet placed near the target during plasma‐assisted laser deposition produces a strong atomic oxygen beam with kinetic energies of 5.6 eV, simultaneous with the laser‐induced atomic beams of Ba, Cu, and Y from the target. All atomic beams can be well characterized by a supersonic expansion mechanism. The behavior of the velocity distributions was studied as a function of the distance from the target and laser energy fluence. A target‐substrate separation of 7 cm was found to be optimum in terms of producing the best as‐deposited films. At that distance, the velocity distributions of all atomic beams become nearly the same.

Role of the oxygen atomic beam in low-temperature growth of superconducting films by laser deposition

Separate fast and slow components were observed in the electrical response to optical excitation of an Y‐Ba‐Cu‐O thin film prepared by laser deposition. The temperature dependence of these two components indicated different thermal and nonthermal behavior. The speed of the nonthermal component is limited by the 6 ns laser pulse duration used in the excitation. It was also demonstrated that thin films that were optically semitransparent were crucial in the observation of the fast nonthermal response.

Nonthermal optical response of Y‐Ba‐Cu‐O thin films

We describe here the deposition of superconducting and dielectric thin films by the laser evaporation technique. The characterization of this process, and possible optimization with regards to wavelength and pulse duration of the laser will be discussed.

Laser evaporation deposition of superconducting and dielectric thin films

CdS films have been grown by laser‐evaporation deposition in a clean vacuum environment. The films are highly oriented with a c axis perpendicular to the surface, and are optically smooth and homogeneous. These high quality films should be useful in nonlinear integrated optics applications.

Growth of highly oriented CdS thin films by laser-evaporation deposition

Photoluminescence spectroscopy of the plasma plume during plasma‐assisted laser deposition of YBa2Cu3O7−x was performed. The spectrum in the range of 355–900 nm was measured at several spatial positions using an optical multichannel analyzer. It was found that both atomic and molecular components were present. Rich emission lines of O, O+, Y, Y+, Ba, Ba+, and Cu were observed, from which the plasma temperature could be estimated. Cu+ emission was conspicuously absent. The mechanism of the plasma process and its relevance to thin‐film formation is discussed.

Q.Y. Ying

Papers

Role of the oxygen atomic beam in low-temperature growth of superconducting films by laser deposition

Nonthermal optical response of Y‐Ba‐Cu‐O thin films

Laser evaporation deposition of superconducting and dielectric thin films

Growth of highly oriented CdS thin films by laser-evaporation deposition

Spectroscopic study of plasma-assisted laser deposition of Y-Ba-Cu-O