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真的静奕

铜虫 (初入文坛)

应助: 0 (幼儿园)
金币: 71.7
帖子: 42
在线: 10.7小时
虫号: 3052161
注册: 2014-03-14
性别: GG
专业: 基础物理学

[求助] 论文翻译

Oriented single-crystalline thin films of NiO and Fe304, and Fe304/NiO superlattices have been
grown on cleaved and polished substrates of MgO(001), using oxygen-plasma-assisted molecular-beam
epitaxy. We report the growth mode and structural characterization of the grown films using in situ
reflection high-energy electron diffraction (RHEED) and ex situ scanning electron microscopy and x-ray
diffraction. The (001) surface of MgO provides an excellent template for the pseudomorphic growth of
these thin films and superlattices, for it has a very small lattice mismatch (0.3-0.9%) to the cubic rocksalt
structure of Ni0 and to the half unit-cell dimension of the spinel structure of Fe304. Superlattices
consisting of alternating layers of NiO and Fe304 have been grown with a repeat wavelength down to 20
0A
(approximately one Fe304 unit cell plus two NiO unit cells) thick. These superlattices exhibit strong
crystalline ordering and sharp interface formation. RHEED pattern evolution in situ during growth indicates
formation of the rocksalt NiO crystalline symmetry and then the spinel Fe304 crystalline symmetry
in a periodic sequence as each material is being deposited. Our data indicate single-phase crystal
growth in registry with the substrate, with films of overall cubic symmetry. Strain in the grown films exhibits
interesting effects that clearly do not follow a simple elastic model.
I. INTRODUCTION
Growth of high-quality single-crystalline thin films of
metal oxides has become increasingly important recently
for both technological and fundamental physical reasons.
Ceramic oxides such as the ferrite spinels and magnetic
garnets exhibit a rich complexity in magnetic coupling
and electronic bonding not found in pure metallic and alloy
materials. In addition, because of the strong anioncation
bonding in oxides, such films are often tribologically
and chemically significant more stable than films
with free metal or semiconducting surfaces. Oxide ferrites,
especially those in layered structures, can also have
superior magnetization and microwave resonance properties
for use in a variety of planar device structures and
other technological applications. Recently, the synthesis
of layered oxide materials has received enhanced notoriety
because of the discovery of high-temperature superconductivity
in the ceramic perovskite oxides. As a
result of this combination of factors, strong research interest
deals with issues involved in the growth and integration
of magnetic and superconducting oxide structures
into planar integrated devices. '
Special emphasis in the research community is being
focused on thin films and modulated structures of ferrite
materials. ' Magnetic spinels, for example, show great
promise in planar device applications because of their superiority
as high-density magnetic recording media, their
resistance to corrosion and wear, and the inherent advantage
non-"lossy" insulating ferrites have in microwave
resonant circuits. In addition, layered structures of such
ferrite materials allow controllable constraints to be
placed on stoichiometry, lattice spacing, and strain that
couple directly with their magnetic properties. As a result,
layered magnetic oxides are ideally suited to a study
of a number of fundamental issues dealing with magnetic
coupling, ordering and anisotropy in nonitinerant electron
magnetic systems. Using the preparation techniques
of molecular-beam epitaxy (MBE), Bando and coworkers
have recently grown Fe304 films and
Fe304lCoO superlattices, and, using reactive sputtering,
Ortiz et al. ' '" have grown Fe304 films and Yoshii
et al. ' have grown y-Fe203 films. The current investigation
extends these studies and demonstrates the ability to
produce constrained metal-oxide thin-film stoichiometries,
including modulated structures of highcrystalline
order and purity with controllable magnetic
ordering and properties.
In our work, highly oriented single-crystalline thin
films of NiO, Fe304 and Fe30~lNiO superlattices have
been grown using oxygen-plasma-assisted MBE. We will
discuss here the synthesis and characterization techniques
used, with special emphasis on the crystal-growth
techniques used and the structural characterization of the
resultant films using reflection high-energy electron
diffraction (RHEED), scanning electron microscopy
(SEM), and x-ray diffraction (XRD). We have found the
(001)-oriented surface of MgO single crystals to provide
an excellent template for the pseudomorphic growth of
both NiO and Fe30~, for it has a small (&1%) lattice
mismatch to the cubic rocksalt structure of the former
and to the half unit-cell dimension of the spinel structure
of the latter. We report the preparation of NiO and
Fe304 thin films, as well as superlattices consisting of al-ternating layers of Ni0 and Fe304. The Fe304/NiO superlattices
have been grown with modulation wavelength
A between 20 and 258 A (the lower limit being slightly
greater than one Fe304 unit cell plus two NiO unit cells
thick), with optimal crystalline order obtained at substrate
growth temperature of 240 C. These films exhibit
coherent single-crystalline ordering over several hundred
repeat wavelengths. Reported elsewhere in the literature
are studies we have made on the magnetization and electron
transport properties of these thin films and superlattices'
' which show such effects as an unusually large
in-plane versus out-of-plane anisotropy () 10 difFerence)
in electron transport as well as strong modulation
wavelength-dependent magnetic ordering effects.

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