Microstructural observations of the “Wustite-Spinel” coexistence following quenching of cation-excess spinels, Ni2(1+x)Ti1-xO4

1990 ◽  
Vol 48 (4) ◽  
pp. 1058-1059
Author(s):  
Ian M. Anderson ◽  
Arnulf Muan ◽  
C. Barry Carter
Keyword(s):  
Film Growth ◽  
Spinel Phase ◽  
Model Systems ◽  
Ion Milling ◽  
Coexistence Of Phases ◽  
Nonequilibrium Conditions ◽  
Diffraction Patterns ◽  
Spinel Structures ◽  
Highly Porous ◽  
Standard Techniques

Oxide mixtures which feature a coexistence of phases with the wüstite and spinel structures are considered model systems for the study of solid-state reaction kinetics, phase boundaries, and thin-film growth, and such systems are especially suited to TEM studies. (In this paper, the terms “wüstite” and “spinel” will refer to phases of those structure types.) The study of wüstite-spinel coexistence has been limited mostly to systems near their equilibrium condition, where the assumptions of local thermodynamic equilibrium are valid. The cation-excess spinels of the type Ni2(1+x)Ti1-xO4, which reportedly exist only above 1375°C4, provide an excellent system for the study of wüstite-spinel coexistence under highly nonequilibrium conditions. The nature of these compounds has been debated in the literature. X-ray and neutron powder diffraction patterns have been used to advocate the existence of a single-phase, non- stoichiometric spinel. TEM studies of the microstructure have been used to suggest equilibrium coexistence of a stoichiometric spinel, Ni2TiO4, and a wüstite phase; this latter study has shown a coexistence of wüstite and spinel phases in specimens thought to have been composed of a single, non- stoichiometric spinel phase. The microstructure and nature of this phase coexistence is the focus of this study. Specimens were prepared by ball-milling a mixture of NiO and TiO2 powders with 10 wt.% TiO2. The mixture was fired in air at 1483°C for 5 days, and then quenched to room temperature. The aggregate thus produced was highly porous, and needed to be infiltrated prior to TEM sample preparation, which was performed using the standard techniques of lapping, dimpling, and ion milling.

Microstructural characterization of YBa2Cu3O7-x thin films formed by metalorganic CVD

1991 ◽  
Vol 49 ◽  
pp. 1080-1081
Author(s):  
P. Lu ◽  
W. Huang ◽  
C.S. Chern ◽  
Y.Q. Li ◽  
J. Zhao ◽  
...  
Keyword(s):  
Thin Film ◽  
Thin Films ◽  
Critical Current Density ◽  
Critical Current ◽  
Current Density ◽  
Film Growth ◽  
Chemical Vapor ◽  
Microstructural Characterization ◽  
Ion Milling ◽  
Conventional Grinding

The YBa2Cu3O7-x thin films formed by metalorganic chemical vapor deposition(MOCVD) have been reported to have excellent superconducting properties including a sharp zero resistance transition temperature (Tc) of 89 K and a high critical current density of 2.3x106 A/cm2 or higher. The origin of the high critical current in the thin film compared to bulk materials is attributed to its structural properties such as orientation, grain boundaries and defects on the scale of the coherent length. In this report, we present microstructural aspects of the thin films deposited on the (100) LaAlO3 substrate, which process the highest critical current density.Details of the thin film growth process have been reported elsewhere. The thin films were examined in both planar and cross-section view by electron microscopy. TEM sample preparation was carried out using conventional grinding, dimpling and ion milling techniques. Special care was taken to avoid exposure of the thin films to water during the preparation processes.

TEM study of lanthanum aluminate

1990 ◽  
Vol 48 (4) ◽  
pp. 1060-1061
Author(s):  
C.Y. Yang ◽  
Z.R. Huang ◽  
Y.Q. Zhou ◽  
C.Z. Li ◽  
W.H. Yang ◽  
...  
Keyword(s):  
Domain Boundary ◽  
Point Group ◽  
Optical Microscope ◽  
Dark Field ◽  
Zone Axis ◽  
Superconducting Film ◽  
Ion Milling ◽  
Lanthanum Aluminate ◽  
Ring Diameter ◽  
Diffraction Patterns

Lanthanum aluminate(LaAlO3) single crystal as a substrate for high Tc superconducting film has attracted attention recently. We report here a transmission electron microscopy(TEM) study of the crystal structure and phase transformation of LaAlO3 by using Philips EM420 and EM430 microscopes. Single crystals of LaAlO3 were investigated first by optical microscope. Stripe-shaped domains of mm size are clearly seen(Fig.1a), and 90° domain boundary is also obvious. TEM specimens were prepared by mechanical grinding and polishing followed by ion-milling.Fig.lb shows μm size stripe domains of LaAlO3. Convergent beam electron diffraction patterns (CBED) from single domain were taken.Fig. 2a and Fig. 2c are [001] zone axis patterns which show a 4mm symmetry, and the (200) dark field of this zone axis gives 2mm symmetry(fig.2b). Therefore the point group of this crystal is either 4/mmm or m3m. The projection of the first order Laue zone(FOLZ) reflections on zero layer (fig. 2c) shows that the unit cell is face centered. A tetragonal unit ceil is chosen, with a=0.532nm and c=0.753nm, c being determined from the FOLZ ring diameter.

scholarly journals PECHINI SYNTHESIS AND CHARACTERIZATION OF Eu3+ DOPED ZnCo2O4 SPINELS

2005 ◽  
Vol 03 (2) ◽  
pp. 24-29
Author(s):  
P.M. PIMENTEL ◽  
A.M.G. PEDROSA ◽  
H.K.S. SOUZA ◽  
C.N.S. JÚNIOR ◽  
R.C.A. PINTO ◽  
...  
Keyword(s):  
Spinel Structure ◽  
Pechini Method ◽  
Synthesis Temperature ◽  
X Ray Diffraction ◽  
X Ray ◽  
Spinel Oxides ◽  
Diffraction Patterns ◽  
Pechini Synthesis ◽  
Spinel Structures

Spinel oxides with the composition ZnCo2O4 and ZnCo2O4:Eu3+ have been synthesized by the Pechini method and characterized by X-ray diffraction, infrared spectroscopy, thermal analysis and scanning electron microscopy. IR spectroscopy revealed the presence of n1 and n2 bands, typical of spinel structures. The formation of monophase cubic spinel structure was confirmed by X-ray diffraction patterns. Extra lines corresponding to other phase has been observed in the powders calcined at 900 ºC. The results showed the extremely lower synthesis temperature than those presents in conventional methods.

Observation of the Wurtzite Phase in OMVPE Grown ZnSe/GaAs: Effect on Implantation and Rapid Thermal Annealing

1989 ◽  
Vol 147 ◽  
Author(s):  
K. S. Jones ◽  
J. Yu ◽  
P. D. Lowen ◽  
D. Kisker
Keyword(s):  
Thermal Annealing ◽  
Rapid Thermal Annealing ◽  
Electrical Transport ◽  
High Resistivity ◽  
Ion Milling ◽  
Electrical Transport Properties ◽  
Wurtzite Phase ◽  
Cross Sectional ◽  
Transmission Electron ◽  
Diffraction Patterns

AbstractTransmission electron diffraction patterns of cross-sectional TEM samples of OMVPE ZnSe on GaAs indicate the existence of the hexagonal wurtzite phase in the epitaxial layers. The orientation relationship is (0002)//(111); (1120)//(220). Etching studies indicate the phase is internal not ion milling induced. The average wurtzite particle size is 80Å-120Å. Because of interplanar spacing matches it is easily overlooked. Electrical property measurements show a high resistivity (1010ω/square) which drops by four orders of magnitude upon rapid thermal annealing between 700°C and 900 °C for 3 sec. Implantation of Li and N have little effect on the electrical transport properties. The Li is shown to have a high diffusivity, a solid solubility of ≈1016/cm3 at 800°C and getters to the ZnSeA/aAs interface.

Structure, bonding, and growth at a metal–organic interface in the weak chemisorption regime: Perylene–Ag(111)

2004 ◽  
Vol 19 (7) ◽  
pp. 2028-2039 ◽  
Author(s):  
M. Eremtchenko ◽  
D. Bauer ◽  
J.A. Schaefer ◽  
F.S. Tautz
Keyword(s):  
Scanning Tunneling Microscopy ◽  
Organic Semiconductors ◽  
Film Growth ◽  
Field Effect Transistors ◽  
Analytical Techniques ◽  
Model Systems ◽  
Scanning Tunneling ◽  
Tunneling Microscopy ◽  
Resolution Electron ◽  
Metal Organic

Organic semiconductors on single-crystalline metal surfaces are model systems for injection contacts in organic field-effect transistors (OFET) and light-emitting diodes. They allow us to classify possible metal–organic interaction scenarios and to elucidate general tendencies, which most likely will also be found at metal–organic interfaces in real devices. In this contribution, we report a comprehensive investigation of the interface of perylene, a promising material for OFETs, with the close-packed noble metal surface Ag(111), using high-resolution electron energy loss spectroscopy, low-energy electron diffraction, and scanning tunneling microscopy as surface analytical techniques. The most important findings are: In the monolayer, molecules are oriented flat and form an incommensurate, most probably fluid overlayer. The molecules interact electronically with the substrate and become weakly metallic. Scanning tunneling microscopy reveals a propensity of perylene molecules toward a specific adsorption site on Ag(111), if the influence of intermolecular interactions is inhibited. Film growth at room temperature is similar to Stranski–Krastanov type. Finally, co-planar adsorption of perylene on Ag(111) is metastable, and annealing the monolayer at 420 K leads to a structural transformation of the film. The perylene–Ag(111) interface can therefore be classified as weakly interacting.

An X-ray diffraction study of semiconductor and metallic vanadium dioxide

1993 ◽  
Vol 8 (4) ◽  
pp. 240-244 ◽  
Author(s):  
K. D. Rogers
Keyword(s):  
Vanadium Dioxide ◽  
Room Temperature ◽  
Transition Process ◽  
X Ray Diffraction ◽  
Space Group ◽  
X Ray ◽  
Coexistence Of Phases ◽  
Diffraction Patterns ◽  
Tetragonal Cell ◽  
Monoclinic Cell

Powder diffraction data for semiconductor and metallic states of vanadium dioxide are presented. The structures are refined by Rietveld methods using a monoclinic cell (a = 5.7529Å, b = 4.5263Å, c = 5.3825Å, β = 122.61°) and space group P21/c for the room temperature data, and a tetragonal cell (a =4.5540Å, c = 2.8557Å) and space group P42/mnm for data collected at 400 K. The similarity between the corresponding X-ray diffraction patterns is discussed. The transition process from the monoclinic to tetragonal phase is investigated and initial evidence for the coexistence of phases over a small temperature range is presented.

Determination of the Si(111)-(√3x√3) Au surface structure using UHV TEM

1995 ◽  
Vol 53 ◽  
pp. 574-575
Author(s):  
R. Plass ◽  
L. D. Marks
Keyword(s):  
Electron Beam ◽  
Diffraction Spot ◽  
Ion Milling ◽  
Small Surface ◽  
The Past ◽  
Analysis Technique ◽  
Cross Correlation Analysis ◽  
Diffraction Patterns ◽  
Surface Domains

For the past few decades the Si(111)-(√3×√3) Au surface (denoted hereafter as √3-Au) has received considerable attention in the literature as one of the prototypical Si(111)-(√3×√3) Metal systems. The √3 -Au system appears for gold coverages from roughly 0.5 ML to 1.0 ML after annealing of the substrate over 280°C. Several authors have noted the small surface domains of this structure and several possible diffraction spot features associated with different coverages and annealing temperatures. The two dominant models which have been proposed for this surface are the missing top layer twisted trimer (MTLTT) and the conjugate honeycomb chained trimer (CHCT) models.The √3-Au surface was prepared on bulk Si(111) TEM samples thinned by mechanical polishing and HNO3/HF solution chemical etching. Under UHV conditions the samples were cleaned by cycles of Ar+ ion milling and electron beam annealing until well defined Si(111)-(7×7) diffraction patterns were visible. On these surfaces roughly 0.7 ML of gold was evaporated followed by light electron beam annealing to produce the √3-Au surface. Through exposure electron diffraction patterns from three different sample locations and crystal tilts were collected and the negatives quantified using a cross correlation analysis technique.

Elucidating Structural Mechanisms for Cordierite Ceramic Formation using Synchrotron Radiation

1993 ◽  
Vol 307 ◽  
Author(s):  
Menno Oversluizen ◽  
S. M. Clark ◽  
G. N. Greaves
Keyword(s):  
Synchrotron Radiation ◽  
Spinel Phase ◽  
Average Energy ◽  
Nucleating Agent ◽  
Lattice Parameter ◽  
Oxide Glasses ◽  
X Ray ◽  
Different Temperatures ◽  
Diffraction Patterns ◽  
Prolonged Heat

ABSTRACTCr2O3 is a common nucleating agent useful for forming ceramics from oxide glasses. In this study we have used a variety of synchrotron radiation techniques to examine the atomic structure, crystallinity and microstructure of a magnesium alumino-silicate glass ceramic whose composition is close to that of the mineral cordierite, Mg2Al4Si5O13. X-ray Absorption spectra on the Cr K-edge have been performed with samples that were heat treated at different temperatures and times to examine the metamorphosis of the nucleating site. This study reveals that Cr3+ is always octahedrally coordinated with oxygen. In addition, the second nearest neighbour environment changes from an amorphous, single shell of Al/Si, but upon crystallisation, develops into a well ordered Al/Mg shell indicative of the formation of a dilute Cr spinel phase. Powder X-ray Diffraction (XRD) patterns, however, reveal that the major phase initially precipitated (˜900°C) is a stuffed quartz and from the lattice parameters that the composition is SiO2 -rich. With prolonged heat treatment a small quantity of a spinel phase emerges whose composition from its lattice parameter is close to MgAl2O4. Combined Small Angle X-ray Scattering (SAXS) and XRD establish that devitrification at these temperatures is associated with particles about 250 Å in size, on average. Energy dispersive powder diffraction patterns were collected in situ to observe changes in crystallinity with temperature and time. From these measurements the stuffed quartz phase identified at 900°C is found to be intermediate, being eventually replaced at higher temperatures by cordierite with a small quantity of spinel.

Design and Initial Performance of an Ultrahigh Vacuum Sample Preparation Evaluation Analysis and Reaction (SPEAR) System

1995 ◽  
Vol 1 (6) ◽  
pp. 267-279 ◽  
Author(s):  
C. Collazo-Davila ◽  
E. Landree ◽  
D. Grozea ◽  
G. Jayaram ◽  
R. Plass ◽  
...  
Keyword(s):  
Electron Microscopy ◽  
Sample Preparation ◽  
Photoelectron Spectroscopy ◽  
Film Growth ◽  
Ultrahigh Vacuum ◽  
Surface Preparation ◽  
Ion Milling ◽  
Structure Information ◽  
Analysis System ◽  
Analytical Tools

Results concerning the calibration and use of a new ultrahigh vacuum (UHV) surface preparation and analysis system are reported. This Sample Preparation Evaluation Analysis and Reaction (SPEAR) side chamber system replaces an older surface side chamber that was attached to a Hitachi UHV H-9000 microscope. The system combines the ability to prepare clean surfaces using sample heating, cooling, ion milling, or thin film growth with surface analytical tools such as Auger electron spectroscopy (AES), X-ray photoelectron spectroscopy (XPS), and scanning electron microscopy (SEM), along with atomic surface structure information available from high-resolution transmission electron microscopy (HREM). The chemical sensitivity of the XPS and AES are demonstrated in preliminary studies of catalytic and semiconductor samples. In addition, the surface preparation capabilities are also demonstrated for the Si(100) and Ge(100) surfaces, including the ability to acquire secondary electron images during milling. During operation, the entire system is capable of maintaining the UHV conditions necessary for surface studies.

Distortion of the oxygen sublattice in pure cubic-ZrO2

2004 ◽  
Vol 19 (5) ◽  
pp. 1315-1319 ◽  
Author(s):  
C.M. Wang ◽  
S. Azad ◽  
S. Thevuthasan ◽  
V. Shutthanandan ◽  
D.E. McCready ◽  
...  
Keyword(s):  
Electron Diffraction ◽  
Molecular Beam ◽  
Film Growth ◽  
Dark Field ◽  
Oxygen Sublattice ◽  
Dark Field Imaging ◽  
Selected Area Electron Diffraction ◽  
Diffraction Patterns ◽  
Field Imaging ◽  
The Ideal

Multilayer films of pure ZrO2 and CeO2 were grown using molecular beam epitaxy on a yttria-stabilized zirconia (YSZ) substrate. Distinctive forbidden diffraction spots of (odd, odd, even) type were observed on the selected-area electron-diffraction patterns of the film. Dark-field imaging clearly revealed that these forbidden diffraction spots were solely due to the ZrO2 layers. Comparison of the electron diffraction pattern with that simulated by dynamical calculations suggest that the pure ZrO2 layers possess a cubic structure of space with the group P4 3m oxygen sublattice being displaced diagonally, rather than along the c axis as suggested for YSZ. Our results further suggest that the displacement of the oxygen from the ideal (¼, ¼, ¼) position might have been introduced during the film growth process.

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