Liang-Sun Hung

Anode modification in organic light-emitting diodes by low-frequency plasma polymerization of CHF3

Plasma polymerization of CHF3 at low frequencies was utilized for anode modification in organic light-emitting diodes. The polymerized fluorocarbon films have a high ionization potential and a relatively low resistivity. The devices with a polymer-coated anode of indium–tin–oxide exhibited enhanced hole injection and superior operational stability.

Epitaxial growth of MgO on (100)GaAs using ultrahigh vacuum electron‐beam evaporation

Epitaxial layers of MgO grown on (NH4)xS‐treated (100)GaAs substrates were prepared by electron‐beam evaporation in an ultrahigh vacuum system without introducing additional oxygen. The films deposited at 500 °C were found to grow with stoichiometric composition and have (110) planar orientation. X‐ray pole‐figure analysis showed that the [110] direction in the MgO(110) plane is parallel to the [011] direction in the GaAs(100) plane with a 4: 3 coincident site lattice. The film surface was smooth with no signs of structural defects or microcracks.

Epitaxial nonlinear optical films of LiTaO3 grown on GaAs in waveguide form

Nonlinear optical films of LiTaO3 were epitaxially grown on (NH4)2Sx‐treated (111) GaAs using e‐beam evaporated MgO as intermediate layers. The MgO lattice was found to rotate by 180° about the [111] surface normal with respect to the GaAs substrate. The laser‐ablated LiTaO3 film grew epitaxially in the preferred [0001] direction and formed a waveguide with its underlying buffer layer of MgO.

Epitaxial growth of alkaline earth fluoride films on HF‐treated Si and (NH4)2Sx‐treated GaAs without in situ cleaning

HF‐treated Si and (NH4)2Sx‐treated GaAs were used as substrates for epitaxial growth of CaF2 and BaF2 films without in situ cleaning. The fluoride layers grown on the chemical‐treated substrates exhibit good crystalline quality and smooth surfaces. With fluorides on Si, minimum ion channeling yields are about 3%–5%, comparable with the best data reported in the literature using thermal etching or sputtering for substrate cleaning. CaF2 and BaF2 films grown on GaAs(100) exhibit the same (100)‐lattice orientation as the underlying GaAs substrate and no misoriented crystallites are observed. Pole figure measurements on BaF2 show that the crystallites are in close registry with the principal axes of the GaAs.

Growth of superconducting Bi2Sr2CaCu2O8+x films on alumina, silicon, and fused quartz

Interactions between superconducting Bi2Sr2CaCu2O8+x films and substrates were investigated by ion backscattering, x‐ray diffraction, and four‐point probe resistivity measurements. During annealing at temperatures above‐ 800 °C, Bi2Sr2CaCu2 oxide films rapidly reacted with alumina, Si, Si covered with SiO2, and quartz, resulting in catastrophic failure. Zr‐based barrier layers were used to minimize film‐substrate interactions. When a single ZrO2 layer was interposed between the superconducting oxide film and the underlying substrate, the Bi2Sr2CaCu2 oxide films showed a large‐grained polycrystalline microstructure and exhibited the orthorhombic structure. Films on sapphire showed transitions to the superconducting state beginning near 100 K with zero resistance achieved at 70 K. Films on Si and thermally grown SiO2 showed a similar drop in resistance around 95 K, whereas the transition was broad and the zero resistance state was not reached. For films on quartz, high thermal stress caused cracking of the ...

Microstructure of epitaxially oriented superconducting YBa2Cu3O7−x films grown on (100) MgO by metalorganic decomposition

The microstructure in epitaxially oriented thin films of YBa2Cu3O7−x grown on (100) MgO by metalorganic decomposition has been studied by transmission electron microscopy and ion channeling. The as‐prepared films consisted of single‐crystal platelets lying flat on the MgO surface. The majority of the crystallites showed perfect alignment of their c axis with the [100] axis of MgO, while some crystallites were found to have a misorientation of up to 7.5°. Images of the interfacial regions showed good epitaxial growth to within one lattice spacing of the MgO substrate. He++ channeling measurements as a function of energy from 1 to 4.5 MeV indicated a 0.51° spread in crystallite orientation. Extrapolation of the channeling measurements to the limit of zero crystallite spread gave a minimum yield of 0.20 for bulk YBa2Cu3O7−x , which is much larger than the value reported for single crystals. The large backscattering yield is attributed to the grain boundaries in the film. A relatively strain‐free interface wa...

Multilayer structure for epitaxial growth of oxide films on Si with an underlying electrode

Multilayers of CaF2 , Pd, and Pt were epitaxially grown on HF treated (100)Si by sequential deposition of the desired materials in ultrahigh vacuum. This structure is suitable for epitaxial growth of oxide films on Si with an underlying electrode. The epitaxial layer CaF2 effectively acts as a barrier to impede metal‐substrate reaction, and the metal bilayer Pd/Pt forms an epitaxial electrode with good adhesion to the underlying substrate and high resistance to oxidation. KNbO3 deposited on this multilayer structure showed epitaxial growth in a mixed (001)/(110) orientation.

Epitaxial growth of oxides on semiconductors using fluorides as a buffer layer

The success in epitaxial growth of oxides on Si using an intermediate fluoride layer largely depends on the reactivity of the fluoride with the oxide and the stability of the fluoride against oxidation. The fluoride‐oxide reaction was studied by Rutherford backscattering spectrometry and x‐ray diffractometry. It is found that a large number of oxides are stable on CaF2, while some containing K, Li, and Ba react with CaF2. The results are consistent with thermodynamic predictions, and correlate well with the equalized electronegativity of the oxides. The stability of bare CaF2 on Si is found to be strongly related to the ambient. The CaF2 surface remains intact after annealing at 650 °C in 25% O2/N2, although Ca‐silicate formation takes place at the Si‐CaF2 interface. When annealing is conducted in air, Ca‐carbonate is readily formed at the surface. The results provide guidelines for epitaxial growth of oxides on semiconductor/fluoride structures. The potential application of using fluorides as buffer laye...

Fine line structures of ceramic films formed by patterning of metalorganic precursors using photolithography and ion beams

Fine line structures of ceramic thin films were fabricated by patterning of metalorganic precursors using photolithography and ion beams. A trilevel structure was developed with an outer resist layer to transfer patterns, a silver delineated layer as an implantation mask, and a planar resist layer protecting the precursor film from chemical attacking and sputtering. Ion irradiation through the Ag stencil rendered metal carboxylates insoluble in 2‐ethylhexanoic acid, permitting patterning of the precursor film with patterning features on micron scales. The potential of this technique was demonstrated in patterning of Bi2Sr2CaCu2O8+x and Pb(Zr0.53Ti0.47) thin films.

UPCONVERTING TM-DOPED BAYYBF8 OPTICAL WAVEGUIDES EPITAXIALLY GROWN ON GAAS

TM‐doped BaYYbF8 films were epitaxially grown on both (100) and (111) GaAs substrates using CaF2 or LiF as intermediate layers. The BaYYbF8 phase was found to be a previously unreported cubic phase with a lattice constant of 0.5711 nm, which is different from a monoclinic phase reported for bulk crystals. The films produced UV and visible radiation with wavelengths at 360 nm (UV), 450–480 nm (blue), and 500–550 nm (green) when pumped by laser radiation at 647 nm.