ALBERT

Notes: Photoemission results demonstrate that atom deposition of Ti, Cr, and Cu at 20 K on the high-temperature superconductors (HTSs) dramatically reduces interfacial reaction relative to 300 K growth but does not completely eliminate it. Thin Ti-O or Cr-O layers are formed during atom deposition of ∼2 A(ring) of Ti or Cr on YBa2Cu3O7 or Bi2Sr2Ca1Cu2O8 because oxygen is withdrawn from the Bi-O and/or Cu-O layers. Interfacial reactions are diffusion limited at 20 K, and metal overlayers nucleate on the reacted layers. These metal layers are more uniform than those grown at 300 K because clustering is suppressed. There is no additional disruption for Cr/HTS interfaces when warmed to 300 K, but increased disruption is evident for Ti/HTS interfaces. The differences reflect the stabilities of Cr and Ti in contact with their own interfacial oxide. Cu atom deposition on Bi2Sr2Ca1Cu208(100) at 20 K also leads to much less disruption than observed for deposition at 300 K.

Notes: The interfacial chemical bonding has been investigated for GaF3 and CaF2 deposited on S passivated GaAs(111)A, 100, and (111)B surfaces. Synchrotron radiation excited photoelectron spectroscopy S 2p measurements indicate greater S surface segregation for the Ga terminated (111) A and (100) surfaces relative to the As terminated (111)B surface. This S surface segregation correlates well with the Ga—S bond strength as well as the S—Ga coordination number for the three different GaAs surfaces. X-ray photoelectron spectroscopy measurements indicate S may act as a catalyst in the reduction of Ca2+ to metallic Ca at the CaF2–S/GaAs(111)A interface. In contrast to island growth observed for the CaF2/S/GaAs system, more uniform growth is observed for the GaF3/S/GaAs system. In addition, in contrast to the CaF2/S/GaAs system, band bending is considerably reduced for all surfaces upon deposition and annealing for the GaF3/S/GaAs system.

Notes: A Cr-Ti underlayer is found to enhance the in-plane coercive forces of Co-Cr-Pt and Co-Cr-Ta films; the maximum coercive force was 3.5 kOe for (CoCr0.15)0.84Pt0.16/CrTi0.2. The crystallites of Cr-Ti grow in a more highly oriented and uniform manner than ones of Cr, and their lattice spacings are closer to those of Co alloys than Cr, improving the epitaxial growth of Co-alloy crystallites with c-axis in-plane oriented components on the Cr-Ti underlayer. The crystalline anisotropy constant of Co-Cr-Pt with a high Pt concentration is found by torque measurement to be larger than that of Co-Cr-Ta. These can produce extremely high coercive forces in Co-Cr-Pt/Cr-Ti. The C/Co-Cr-Pt/Cr-Ti thin film media with high coercive forces show excellent read/write characteristics; the linear densities at 50% signal drop are very high, 175 and 101 kFCI, for the C/Co-Cr-Pt/Cr-Ti media at head-to-magnetic layer spacings of 0.01 and 0.07 μm.

Notes: Microstructural changes that occur in a GeSbTe film during repetitious overwriting in phase-change optical recording were investigated. The GeSbTe active layer was melted by a focused laser diode (LD) beam during each overwriting process over amorphous mark formation. The repetitious solidification and liquefaction process in such a short time as 50–200 ns resulted in microstructural changes in the active layer: a segregation, sink, and void formations. The sink was formed in the low-density active layer due to the shrinking of the volume during the resolidification process. Sink formation could be suppressed when a high-density active layer, having more than 80% of the bulk density, was used. Such a high-density GeSbTe film, however, resulted in a void formation of the size of 0.1 μm. The voids were thought to be nucleated by residual vacancies and Ar precipitation, since the active layer contained a high concentration of Ar impurities, due to the atomic peening effect. The subsequent void coalescence and migration processes across the beam scanning direction could result in the formation of thermally discontinuous grooves at the edges of the written marks. The voids could also migrate along the LD beam scanning direction, accompanied by a material flow of the active layer in the opposite direction. These phenomena were also found to depend on the material used to fabricate the protective layers which sandwiched the active layer. A TaOx protective layer enhanced the void migration across the track, resulting in the removal of voids from the center of the track. Use of the ZnS:SiO2 compound protective layer confined voids to the center of the track. The ZnS:SiO2 protective layer also promoted the formation of thermally discontinuous grooves at the edges of amorphous marks. The material flow along the track resulted in a thicker active layer at the start of the consecutive LD irradiation, and also in a high void density region at the final edge of the irradiation having a length on the order of 10 μm. This tendency was found for both the ZnS:SiO2 and TaOx sandwiching media. © 1995 American Institute of Physics.

Notes: Three different ways of forming oxide overlayers on GaAs(110) have been examined with x-ray photoemission. First, Cr atoms were deposited onto cleaved GaAs(110) at 300 K, producing a disrupted region over which Cr metal grew. Subsequent exposure to O2 resulted in an inhomogeneous overlayer with areas of thick Cr2O3-like oxides in addition to As and Ga oxides. GaAs oxidation was enhanced by Cr-induced surface disruption, but there was no evidence of a catalytic process. Second, metallic clusters of Cr containing hundreds of atoms were condensed onto GaAs(110). In this case, no substrate disruption was observed at low temperature. O2 exposure resulted in Cr2O3 formation with small amounts of Ga2O3 and no detectable As2O3. Third, Cr atoms and O2 molecules were condensed onto a Xe buffer layer on GaAs(110) to produce Cr2O3-like species out of contact with the semiconductor. Buffer layer desorption brought these Cr2O3 aggregates into contact with the substrate. The overlayer produced in this manner was abrupt, and there was no evidence of GaAs oxidation.

Notes: Photoemission studies of low-temperature deposition of ∼30-A(ring)-diam Ge clusters on single-crystal Bi2 Sr2−x Ca1+x Cu2 O8+y (100) show that an interface is produced with no evidence of substrate disruption. Analysis of the superconductor core level emission as a function of coverage indicates uniform overlayer growth and complete surface coverage. These cluster-assembled interfaces were stable when warmed to 300 K, with only a slight reduction of Cu 2p3/2 satellite emission characteristic of the superconductor. In contrast, conventional atom-by-atom Ge deposition produces a Ge oxide layer and surface disruption.

Notes: The orientational stability of stepped (vicinal) Si (111) surfaces during As exposure has been investigated using low-energy electron diffraction and Auger electron spectroscopy. When clean, Si (111) surfaces misoriented in the [2¯11] and [11¯0] directions are faceted, while those misoriented in the [21¯1¯] direction are step tripled. If these surfaces are equilibrated in an arsenic pressure, they all form orientationally stable step-doubled structures. However, exposure of the clean surfaces to As at temperatures〈∼750 °C results in metastable structures with mixed step heights and/or facets.

Notes: The magnetic properties and the c axis orientation of Co-Cr thin films deposited on various substrates with concentrations of 0–20 at. % Cr are investigated. The intermediate layer of C,5 nm thick, between the substrate and Co-Cr layer is found to bring a great improvement in the c-axis orientation toward the normal of the film plane, a situation suitable for perpendicular recording. On the other hand, the thicker the underlayer of Cr, the better the c-axis orientation and a higher coercivity in the film plane is realized; this is suitable for longitudinal recording.

Notes: The characteristics of deep hole traps in p-type ZnSe are studied by means of a transient capacitance spectroscopy technique. p-type ZnSe layers were grown by molecular beam epitaxy using radical N2 (nitrogen) doping. A major deep hole trap with a thermal hole activation energy of ΔE=720±30 meV is detected for two different sample structures: (a) n+-p ZnSe diodes and (b) Au-p ZnSe double-Schottky diodes. The trap concentration tends to increase as the net acceptor (N) concentration increases. The deep hole trap has revealed an exponential temperature dependence of hole capture rates, indicating a strong electron-lattice coupling in carrier capture/emission processes.