Tianqi Wang

In situ growth of DyBa2Cu3O7−x thin films by molecular beam epitaxy

Films of DyBa2Cu3O7−x with transition temperatures as high as 89 K and with nominal thicknesses down to 35 A have been grown in situ using molecular beam epitaxy employing ozone as a source of reactive oxygen. The process has been successful with a variety of substrates including SrTiO3(100), SrTiO3(110), LaAlO3(100), MgO(100), and yttria‐stabilized zirconia. The films could be imaged with a scanning tunneling microscope at 4.2 K, indicating a conducting surface even at low temperatures.

High-temperature superconducting microbolometer

A superconducting microbolometer employing a DyBaCuO film deposited upon a silicon microstructure was found to have a responsivity of 800 V/W at 89 K and a response time of 1 ms.

In situ growth of DyBa sub 2 Cu sub 3 O sub 7 minus x thin films by molecular beam epitaxy

Films of DyBa2Cu3O7−x with transition temperatures as high as 89 K and with nominal thicknesses down to 35 A have been grown in situ using molecular beam epitaxy employing ozone as a source of reactive oxygen. The process has been successful with a variety of substrates including SrTiO3(100), SrTiO3(110), LaAlO3(100), MgO(100), and yttria‐stabilized zirconia. The films could be imaged with a scanning tunneling microscope at 4.2 K, indicating a conducting surface even at low temperatures.

Techniques for the growth of superconducting oxide thin films using pure ozone vapor

A simple, inexpensive apparatus for the production of pure ozone vapor for use in the in situ growth of superconducting oxide thin films is described. Pure condensed ozone is distilled at 77 K from a dilute mixture of ozone in oxygen gas. The condensed ozone is subsequently heated, raising its vapor pressure to provide an adequate flow of ozone gas into the thin film growth chamber. Thin films of YBa2 Cu3 O7−x with zero resistance at temperatures as high as 85 K have been grown with a deposition chamber pressure of only 2×10−7 Torr and without a post‐deposition anneal processing step. Unlike most other commonly used forms of highly reactive oxygen, ozone can be made and stored in very pure form. This makes it very useful when a well‐characterized oxidizing gas is needed for systematic studies of the growth kinetics and oxidation of the films. Safety aspects of the ozone‐production process are discussed.

Critical thickness and strain relaxation in molecular beam epitaxy-grown SrTiO3 films

We report on the study of the critical thickness and the strain relaxation in epitaxial SrTiO3 film grown on (La0.3Sr0.7)(Al0.65Ta0.35)O3 (001) (LSAT) substrate using the hybrid molecular beam epitaxy approach. No change in the films lattice parameter (both the in-plane and the out-of-plane) was observed up to a film thickness of 180 nm, which is in sharp contrast to the theoretical critical thickness of ∼12 nm calculated using the equilibrium theory of strain relaxation. For film thicknesses greater than 180 nm, the out-of-plane lattice parameter was found to decrease hyperbolically in an excellent agreement with the relaxation via forming misfit dislocations. Possible mechanisms are discussed by which the elastic strain energy can be accommodated prior to forming misfit dislocations leading to such anomalously large critical thickness.

Molecular beam epitaxy growth of SnO2 using a tin chemical precursor

The authors report on the development of a molecular beam epitaxy approach for atomic layer controlled growth of phase-pure, single-crystalline epitaxial SnO2 films with scalable growth rates using a highly volatile precursor (tetraethyltin) for tin and rf-oxygen plasma for oxygen. Smooth, epitaxial SnO2 (101) films on r-sapphire (101¯2) substrates were grown as a function of tin precursor flux and substrate temperatures between 300 and 900 °C. Three distinct growth regimes were identified where SnO2 films grew in a reaction-, flux-, and desorption-limited mode, respectively, with increasing substrate temperature. In particular, with increasing tin flux, the growth rates were found to increase and then saturate indicating any excess tin precursor desorbs above a critical beam equivalent pressure of tin precursor. Important implications of growth kinetic behaviors on the self-regulating stoichiometric growth of perovskite stannates are discussed.

Barrier technology for DyBa/sub 2/Cu/sub 3/O/sub 7-x/ junctions and related structures

Layered structures which include the high-temperature superconductor DyBa/sub 2/Cu/sub 3/O/sub 7-x/ have been fabricated using molecular beam epitaxy with ozone as the activated oxygen source. A c-axis-oriented DyBa/sub 2/Cu/sub 3/O/sub 7-x/ thin film with a T/sub c/ of 74 K has been grown on a layer of the rare earth sesquioxide Dy/sub 2/O/sub 3/ on a

Chemistry, growth kinetics, and epitaxial stabilization of Sn2+ in Sn-doped SrTiO3 using (CH3)6Sn2 tin precursor

PbTiO3-based ferroelectrics have impressive electroactive properties, originating from the Pb2+ 6s2 electron lone-pair, which cause large elastic distortion and electric polarization due to cooperative pseudo Jahn-Teller effect. Recently, tin-based perovskite oxide (SnTiO3) containing Sn2+ and a chemistry similar to that of the 6s2 lone-pair has been identified as a thermally stable, environmentally friendly substitute for PbTiO3-based ferroelectrics. However experimental attempts to stabilize Sn2+ on the A-site of perovskite ATiO3 have so far failed. In this work, we report on the growth of atomically smooth, epitaxial, and coherent Sn-alloyed SrTiO3 films on SrTiO3 (001) substrates using a hybrid molecular beam epitaxy approach. With increasing Sn concentration, the out-of-plane lattice parameter first increases in accordance with the Vegard’s law and then decreases for Sn(Sr+Ti+Sn) at. % ratio > 0.1 due to the incorporation of Sn2+ at the A-site. Using a combination of high-resolution X-ray photoelectr...

Onset superconductivity in ultrathin DyBa2Cu3O7 films

The superconductor-insulator transition has been explored in the low temperature limit using ultra thin DyBa2Cu3O7 c-axis oriented films prepared by molecular beam epitaxy. The results are remarkably similar to those obtained for amorphous Bi films deposited onto amorphous Ge at low temperatures.

Low temperature scanning tunneling spectroscopy of a DyBa2Cu3O7−x film

A superconducting film of DyBa 2 Cu 3 O 7−x was examined below 30 K with a scanning tunneling spectroscopy, i.e. scanning tunneling microscope (STM) images and tunneling data were obtained over the same area. Images were observed and some I-Vs showed charging effects.