摘要:

High-quality (001) thin filmLa0.5Sr0.5CoO3−x(LSCO) has been prepared on (001)SrTiO3substrates by pulsed laser deposition under different oxygen pressures with and without postannealing.C-axis expansion of the LSCO with reducing oxygen pressure was revealed. The electrical resistivity increased over five orders of magnitude when oxygen pressure varied from 1.0 mbar (plus postannealing) to10−3mbar. The negative magnetoresistance (n-MR) property as a function of temperature and oxygen pressure was investigated. Linear dependence of then-MR ratio on magnetic field and temperature was found and significant effect of oxygen stoichiometry on then-MR was demonstrated. The film prepared at 650 °C and 0.1 mbar oxygen shows an-MR ratio of −16&percent; at 81 K under a field of only 0.2 T. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.122080

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

A nucleation method to form diamond on chemically pretreated silicon (111) surfaces is reported. The nucleation consisted of binding covalently 2,2-divinyladamantane molecules on the silicon substrate. Subsequently, low pressure diamond growth was performed via microwave plasma chemical vapor deposition in a tubular deposition system. The resulting diamond layers presented a good crystallinity and the Raman spectra showed a very sharp peak at1331 cm−1.©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.122081

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

Hut cluster formation during Ge orSi1−xGexsolid source molecular beam epitaxial growth on Si(001) is a well-known kinetic pathway for partial strain relief. It results in undulated morphologies with {105} facets allowinga∥lattice parameter relaxation on the island apexes. Here, we show how subsequent Si coverages, grown at 500 °C, avoid being tensile strained and impede further increase of stored elastic strain energy. Dominant inhomogeneous Si surface diffusions take place as proven by a Ge marker technique able to provide transmission electron microscopy or high-resolution transmission electron microscopy images of the initial Si morphology stages and by reflection high-energy electron diffraction examinations. This mechanism prevails for high enough Si growth rates, able to quench lateral Ge diffusion and limit chemical strain relief. Mediated by stress variations on the noncapped island curvatures, Si is depleted from the top of the islands and accumulates in the troughs of the ripples where it accommodates mostly unstrained. By this selective Si coverage, the surface undergoes a rapid smoothing anda∥recovery toward the Si bulk value. When the Ge containing islands are completely buried, their strain, dictated by the Si buffer and cap layers, ends by being mainly along the growth direction or tetragonal(&Dgr;a∥=0).©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.122082

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

A novel principle for cooling by adiabatic pressure application in the mixed crystalline compoundPr1−xLaxNiO3is described and experimentally verified. Cooling occurs in the vicinity of the structural phase transition where the electronic ground state of thePr3+ions changes from a singlet to a doublet state. By properly choosing the La concentrationx, the cooling effect can be achieved down to some 100 mK. Furthermore,Pr1−xLaxNiO3can be used for second and third stage cooling down to the &mgr;K region by classical paramagnetic and nuclear demagnetization techniques, respectively. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.122083

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

It is shown that the growth mode of cobalt on the Cu(110) surface at 350 K can be changed from three-dimensional to extended layer-by-layer growth by pre- and co-adsorption of oxygen. The shape and the intensity of the growth oscillations observed in thermal energy helium atom scattering experiments depends sensitively on the total oxygen coverage. Helium diffraction reveals that different oxygen induced surface reconstructions of the top-most Co layer are responsible for the presence or absence of layer-by-layer growth in an extended coverage range. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.122084

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

This letter reports on a novel liquid crystal (LC) display device capable of achromatic reflection in a twisted homeotropic configuration using a chiral nematic LC with negative dielectric anisotropy. Using the elastic continuum formalism, we arrived at simulated values for each parameter of interest, including external twist, cell gap, molecular chirality for the chiral pitch, and the surface anchoring energy. The experimental results correspond well with the calculated expectations, exhibiting EO properties that demonstrate excellent achromatic reflection, extinction, and a high contrast ratio. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.122085

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

The isotopic effect on the infrared spectra is used to determine the existence of nitrogen–hydrogen bonds in amorphous carbon–nitrogen alloys(a-CNx)prepared by dual-ion-beam-assisted deposition. The deuteration experiments and the evolution of the infrared spectra upon atmospheric exposure show that hydroxyls are incorporated from atmospheric moisture. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.122115

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

Dislocations are observed in germanium crystals (9° off axis toward the [011] direction) that have undergone plastic deformation. Optical microscopy reveals that the substrates exhibit a crosshatch pattern, consisting of ridges and trenches that extend in the [011] and [011¯] directions. Further characterization of these features with scanning tunneling microscopy shows that they consist of bands of steps. These bands are created when a group of dislocations emerge onto the crystal surface from the bulk. The dislocations are determined to be type(a/2)⟨011⟩.©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.122086

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

Sb nanocrystals were formed in thin, thermally grownSiO2layers using low-energy ion implantation followed by thermal annealing. These Sb nanocrystals have good size and position uniformity. Both the narrow as-implanted profile and the compressive strain that exists near theSiO2/Siinterface supposedly contribute to the uniformity. TheI–Vcharacteristics of the diode structure show a Coulomb blockade region around 0 V and a Coulomb staircase at 4.2 K. The Coulomb blockade region was observed up to a temperature of 100 K. The technique offers the possibility of developing practical Si-based single-electron devices. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.122087

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

We report on structural investigations of the plastic strain relief in the highly mismatched InAs/GaAs(001) system grown in the layer-by-layer growth mode. The misfit dislocation generation mechanism is observed to be anisotropic in the two perpendicular ⟨110⟩ directions. We explain this result by the interplay between the chemically inequivalent dislocation types present in compound semiconductors and the applied growth condition. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.122088

出版商:AIP    

年代:1998

数据来源: AIP