G. A. N. Connell

Technique for monolithic fabrication of microlens arrays.

A microlens fabrication process is described which can be used in applications requiring integration of optical elements (lenses) and microcircuits. The process is fully compatible with 1C fabrication technology and uses commercially available 1C processing materials. The obtained microlenses are of excellent quality and basically show diffraction-limited resolution with ~1-microm spot size. Extensions of the process to production of nonspherical lenses and use of alternative material packages are also discussed.

High critical currents in strained epitaxial YBa2Cu3O7-δ on Si

Epitaxial YBa{sub 2}Cu{sub 3}O{sub 7{minus}{delta}} (YBCO) films were grown on Si (100) using an intermediate buffer layer of yttria-stabilized zirconia. Both layers are grown via an entirely {ital in} {ital situ} process by pulsed laser deposition. All films consist of {ital c}-axis oriented grains as measured by x-ray diffraction. Strain results from the large difference in thermal expansion coefficients between Si and YBCO. Thin ({lt}500 A) YBCO films are unrelaxed and under tensile strain with a distorted unit cell. Rutherford backscattering spectroscopy indicates a high degree of crystalline perfection with a channeling minimum yield for Ba as low as 12%. The normal-state resistivity is 280 {mu}{Omega} cm at 300 K; the critical temperature {ital T}{sub {ital c}} ({ital R}=0) is 86--88 K with a transition width ({Delta}{Tc}) of 1 K. Critical current densities of 2{times}10{sup 7} A/cm{sup 2} at 4.2 K and 2.2{times}10{sup 6} A/cm{sup 2} at 77 K have been achieved.Epitaxial YBa2Cu3O7−δ (YBCO) films were grown on Siu2009(100) using an intermediate buffer layer of yttria‐stabilized zirconia. Both layers are grown via an entirely in situ process by pulsed laser deposition. All films consist of c‐axis oriented grains as measured by x‐ray diffraction. Strain results from the large difference in thermal expansion coefficients between Si and YBCO. Thin (<500 A) YBCO films are unrelaxed and under tensile strain with a distorted unit cell. Rutherford backscattering spectroscopy indicates a high degree of crystalline perfection with a channeling minimum yield for Ba as low as 12%. The normal‐state resistivity is 280 μΩu2009cm at 300 K; the critical temperature Tc (R=0) is 86–88 K with a transition width (ΔTc) of 1 K. Critical current densities of 2×107 A/cm2 at 4.2 K and 2.2×106 A/cm2 at 77 K have been achieved.

Epitaxial yttria‐stabilized zirconia on hydrogen‐terminated Si by pulsed laser deposition

Epitaxial yttria‐stabilized zirconia films were grown on Siu2009(100) and Siu2009(111) by pulsed laser deposition. Rutherford backscattering spectroscopy indicates a high degree of crystalline perfection with a channeling minimum yield of 5.3%. A necessary predeposition process is removal of native silicon oxide from the Si prior to film growth. This is done outside the deposition chamber at 23u2009°C using a wet‐chemical hydrogen‐termination procedure. Epitaxial YBa2Cu3O7−δ films have been grown on these films.

Interference enhanced Raman scattering from very thin absorbing films

A new method of obtaining Raman spectra from a very thin highly absorbing films (α≳105 cm−1) is described. The technique which is termed interference enhanced Raman scattering (IERS) is shown theoretically to produce a gain in the scattered intensity of 10–103 (depending on the optical constants of the material) over that expected from a thick sample using the conventional Raman backscattering configuration. The potential of the method is demonstrated experimentally using tellurium, and a gain of 20 is obtained.

Properties of epitaxial YBa2Cu3O7 thin films on Al2O3 {1̄012}

Epitaxial YBa2Cu3O7 films were grown on Al2O3u2009{1012} by a laser ablation technique. X‐ray diffraction shows that films are epitaxial with the c axis perpendicular to the substrate surface and ‘‘123’’ [110] aligned with sapphire [1011], although the full width at half maximum of the rocking curve is larger than those of epitaxial films on SrTiO3. Typical Tc’s are between 85 and 88 K with transition widths between 0.5 and 3 K. The normal‐state resistivity is 270 μΩu2009cm at 300 K and extrapolates to zero at zero temperature while the magnetization Jc is as high as 5×106 A/cm2 at 4.2 K. High‐frequency loss measurements show that 2000‐A‐thick epitaxial films on Al2O3u2009{1012} have a surface impedance about 1 mΩ at 13 GHz at 4.2 K.Epitaxial YBa{sub 2}Cu{sub 3}O{sub 7} films were grown on Al{sub 2}O{sub 3} {l brace}{bar 1}012{r brace} by a laser ablation technique. X-ray diffraction shows that films are epitaxial with the {ital c} axis perpendicular to the substrate surface and 123 (110) aligned with sapphire (10{bar 1}1), although the full width at half maximum of the rocking curve is larger than those of epitaxial films on SrTiO{sub 3}. Typical {ital T}{sub {ital c}}s are between 85 and 88 K with transition widths between 0.5 and 3 K. The normal-state resistivity is 270 {mu}{Omega} cm at 300 K and extrapolates to zero at zero temperature while the magnetization {ital J}{sub {ital c}} is as high as 5{times}10{sup 6} A/cm{sup 2} at 4.2 K. High-frequency loss measurements show that 2000-A-thick epitaxial films on Al{sub 2}O{sub 3} {l brace}{bar 1}012{r brace} have a surface impedance about 1 m{Omega} at 13 GHz at 4.2 K.

Laser-induced local heating of moving multilayer media

Earlier work on the local heating of stationary multilayer structures by focused laser light has been extended to deal with nonstationary situations. The numerical procedures described here are therefore applicable to many important technologies including optical recording, thermal marking, and laser annealing. We demonstrate this in two examples, namely, the effects of readout intensity on the readout signal from a quadrilayer magnetooptic disk and the writing threshold for ablative materials in single-layer and three-layer structures.

Preparation of oriented Bi-Ca-Sr-Cu-O thin films using pulsed laser deposition

Oriented c‐axis thin films of Bi‐Ca‐Sr‐Cu‐O on [100]u2009SrTiO3 substrates have been fabricated using the pulsed excimer laser evaporation technique. Deposition at room temperature in 1 mTorr oxygen followed by an 875u2009°C anneal in oxygen yields superconducting films with zero resistance at 80 K and a resistivity drop near 110 K, hinting at the presence of another superconducting phase. Transmission electron microscopy shows that the films are epitaxial with the substrate, with an abrupt and planar interface boundary. The observed crystal structure is consistent with diffraction results on bulk materials.

Properties of epitaxial YBa sub 2 Cu sub 3 O sub 7 thin films on Al sub 2 O sub 3 l brace 1 012 r brace

Epitaxial YBa2Cu3O7 films were grown on Al2O3u2009{1012} by a laser ablation technique. X‐ray diffraction shows that films are epitaxial with the c axis perpendicular to the substrate surface and ‘‘123’’ [110] aligned with sapphire [1011], although the full width at half maximum of the rocking curve is larger than those of epitaxial films on SrTiO3. Typical Tc’s are between 85 and 88 K with transition widths between 0.5 and 3 K. The normal‐state resistivity is 270 μΩu2009cm at 300 K and extrapolates to zero at zero temperature while the magnetization Jc is as high as 5×106 A/cm2 at 4.2 K. High‐frequency loss measurements show that 2000‐A‐thick epitaxial films on Al2O3u2009{1012} have a surface impedance about 1 mΩ at 13 GHz at 4.2 K.Epitaxial YBa{sub 2}Cu{sub 3}O{sub 7} films were grown on Al{sub 2}O{sub 3} {l brace}{bar 1}012{r brace} by a laser ablation technique. X-ray diffraction shows that films are epitaxial with the {ital c} axis perpendicular to the substrate surface and 123 (110) aligned with sapphire (10{bar 1}1), although the full width at half maximum of the rocking curve is larger than those of epitaxial films on SrTiO{sub 3}. Typical {ital T}{sub {ital c}}s are between 85 and 88 K with transition widths between 0.5 and 3 K. The normal-state resistivity is 270 {mu}{Omega} cm at 300 K and extrapolates to zero at zero temperature while the magnetization {ital J}{sub {ital c}} is as high as 5{times}10{sup 6} A/cm{sup 2} at 4.2 K. High-frequency loss measurements show that 2000-A-thick epitaxial films on Al{sub 2}O{sub 3} {l brace}{bar 1}012{r brace} have a surface impedance about 1 m{Omega} at 13 GHz at 4.2 K.

Energetics of domain formation in thermomagnetic recording

A new model for the distribution of perpendicular magnetization in thin magnetic films supporting a circular domain is proposed. The contributions of various sources to the magnetic energy are determined and the demagnetizing effect in particular is discussed at length. It is shown that a demagnetizing energy density per unit area of the domain wall can be defined which, unlike the domain wall energy density arising from exchange and anisotropy contributions, is a function of film thickness h. For domains of large radius and small wall thickness (compared with h), the demagnetizing energy density is found to be linearly increasing with h. A typical cycle of thermomagnetic recording on a thin ferrimagnetic film with room temperature compensation point is then studied, and the effect of various parameters on the formation process and stability of reverse magnetized domains is discussed.

Magneto-optics and amorphous metals: an optical storage revolution

Abstract In the last five years excitement has been developing about the realization of a magneto-optic storage technology, based on amorphous rare-earth transition metal alloys. The goal of this paper is to identify important physics and materials issues that arise out of the storage, erasure and readout processes. Particular attention is paid to the origin of the magneto-optic properties in highly disordered metal alloys.