scholarly journals Mechanisms of Enhanced Ionic Conduction at Interfaces in Ceramics

1994 ◽  
Vol 357 ◽  
Author(s):  
D. Lubben ◽  
F. A. Modine
Keyword(s):  
Film Thickness ◽  
Ionic Conduction ◽  
Defect Density ◽  
Ionic Conductivities ◽  
Dislocation Motion ◽  
Extended Defects ◽  
Epitaxial Relationship ◽  
Extended Defect ◽  
Charge Layer ◽  
Fine Grained

AbstractA large enhancement in the ionic conductivity of certain compounds occurs when the compound is produced as a composite material containing a finely-dispersed non-conductor such as SiO2 or Al2O3 This effect has been reported on for more than 20 years, and it is well established that the enhancement is associated with the presence of interfaces. The popular explanation has been based on a model which contends that the enhancement is due to a space-charge layer which forms to compensate a net charge layer at an interface. A different model proposes that extended defects such as dislocations and grain boundaries, either resulting from or stabilized by the interface, are responsible for the enhancement. This paper describes recent experiments which strongly support the latter model. The ionic conductivities of LiI and CaF2 thin films grown on sapphire(0001) substrates were monitored in-situ during deposition as a function of film thickness and deposition conditions. LiI films grown at 27°C exhibited a region of enhanced conduction within 100 nm of the substrate and a lesser enhancement as the film thickness was increased further. This conduction enhancement was not stable but annealed out with a characteristic log(time) dependence. The observed annealing behavior was fit with a model based on dislocation motion which implies that the increase in conduction near the interface is due to extended defects generated during the growth process. LiI films grown at higher temperatures (100°C) in order to reduce the grown-in defects showed no interfacial conduction enhancement. X-ray diffraction measurements suggest that these high-temperature LiI films nucleate as faceted epitaxial islands with a stable misfit dislocation density defined by the epitaxial relationship between the substrate and film. CaF2 films grown at 200°C showed a behavior similar to the 27°C LiI films, with a region of thermally unstable enhanced conduction that occurs within 10 nm of the substrate. Amorphous Al2O3 films deposited over the CaF2 layers created no additional enhancement but did increase the stability of the conduction, consistent with an extended defect model. Simultaneous deposition of CaF2 and Al2O3 produced films consisting of very-fine-grained CaF2 and particles of amorphous Al2O23 (5-10 nm grain and particle size) and a high defect density which was stable even well above the growth temperature. Measured conduction in the composite at 200°C was approximately 360 times that of bulk CaF2.

scholarly journals Enhanced Ionic Conduction at the Film/Substrate Interface in LiI Thin Films Grown on Sapphire(0001)

1993 ◽  
Vol 318 ◽  
Author(s):  
D. Lubben ◽  
F. A. Modine
Keyword(s):  
Thin Films ◽  
Film Thickness ◽  
Ionic Conduction ◽  
High Vacuum ◽  
Dislocation Motion ◽  
Ultra High Vacuum ◽  
Vacuum System ◽  
Substrate Interface ◽  
Interdigital Electrodes ◽  
Film Substrate

ABSTRACTThe ionic conductivity of LiI thin films grown on sapphire(0001) substrates has been studied in situ during deposition as a function of film thickness and deposition conditions. LiI films were produced at room temperature by sublimation in an ultra-high-vacuum system. The conductivity of the Lil parallel to the film/substrate interface was determined from frequency-dependent impedance measurements as a function of film thickness using Au interdigital electrodes deposited on the sapphire surface. The measurements show a conduction of ∼5 times the bulk value at the interface which gradually decreases as the film thickness is increased beyond 100 nm. This interfacial enhancement is not stable but anneals out with a characteristic log of time dependence. Fully annealed films have an activation energy for conduction (σT) of ∼0.47 ± .03 eV, consistent with bulk measurements. The observed annealing behavior can be fit with a model based on dislocation motion which implies that the increase in conduction near the interface is not due to the formation of a space-charge layer as previously reported but to defects generated during the growth process. This explanation is consistent with the behavior exhibited by CaF2 films grown under similar conditions.

Simulation of Iron Distribution after Crystallization of mc Silicon

2009 ◽  
Vol 156-158 ◽  
pp. 223-228 ◽  
Author(s):  
Jonas Schön ◽  
Holger Habenicht ◽  
Martin C. Schubert ◽  
Wilhelm Warta
Keyword(s):  
Defect Density ◽  
Iron Concentration ◽  
Experimental Studies ◽  
Total Iron ◽  
Extended Defects ◽  
Dimensional Model ◽  
Extended Defect ◽  
Recombination Lifetime ◽  
Block Height ◽  
Total Iron Concentration

Interstitial iron (Fei) and iron-boron pairs influence or even limit the recombination lifetime in industrial block cast multicrystalline (mc) silicon, though the proportions in the total iron concentration are generally small. Most of the iron in mc silicon is precipitated and less recombination active. This work aims for a better understanding of the distribution of iron in its different states (precipitated or dissolved) over the block height, as well as in regions of different crystal quality. In experimental studies several features of iron in mc silicon were observed, which occur due to the high extended defect density. In our 2-dimensional model for mc silicon, trapping of interstitial Fe at extended defects and precipitation at the extended defects are taken into account. The results are compared with NAA-data and spatial resolved measurements of the Fei concentration.

Study of the Effects of a Two-Step Anneal on the End of Range Defects in Silicon

2002 ◽  
Vol 717 ◽  
Author(s):  
Renata A. Camillo-Castillo ◽  
Kevin. S. Jones ◽  
Mark E. Law ◽  
Leonard M. Rubin
Keyword(s):  
Defect Density ◽  
Low Energy ◽  
Extended Defects ◽  
Dislocation Loops ◽  
Extended Defect ◽  
Enhanced Diffusion ◽  
Interstitial Concentration ◽  
Transmission Electron ◽  
Concentration Peak ◽  
Scale Down

AbstractTransient enhanced diffusion (TED) is a challenge that the semi-conductor industry has been faced with for more than two decades. Numerous investigations have been conducted to better understand the mechanisms that govern this phenomenon, so that scale down can be acheived. {311} type defects and dislocation loops are known interstitial sources that drive TED and dopants such as B utilize these interstitials to diffuse throughout the Si lattice. It has been reported that a two-step anneal on Ge preamorphized Si with ultra-low energy B implants has resulted in shallower junction depths. This study examines whether the pre-anneal step has a measurable effect on the end of range defects. Si wafers were preamorphized with Ge at 10, 12, 15, 20 and 30keV at a dose of 1x1015cm-2 and subsequently implanted with 1x1015cm-2 1keV B. Furnace anneals were performed at 450, 550, 650 and 750°C; the samples were then subjected to a spike RTA at 950°C. The implant damage was analyzed using Quantitative Transmission Electron Microscopy (QTEM). At the low energy Ge preamorphization, little damage is observed. However at the higher energies the microstructure is populated with extended defects. The defects evolve into elongated loops as the preanneal temperature increases. Both the extended defect density and the trapped interstitial concentration peak at a preanneal temperature of 550°C, suggesting that this may be an optimal condition for trapping interstitials.

Interactions of Point and Extended Defects in Structural Intermetallics: Real-Space Lmto-Recursion Calculations

1997 ◽  
Vol 491 ◽  
Author(s):  
O. Yu. Kontsevoi ◽  
O. N. Mryasov ◽  
Yu. N. Gornostyrev ◽  
A. J. Freeman
Keyword(s):  
Electronic Structure ◽  
Dislocation Core ◽  
Real Space ◽  
Dislocation Motion ◽  
Localized States ◽  
Extended Defects ◽  
Recursion Method ◽  
Extended Defect ◽  
Structure Changes ◽  
Ternary Additions

ABSTRACTA real-space TB-LMTO-recursion method for electronic structure calculations is applied to the study of interacting extended and point defects in NiAl. Results of calculations for the pure intermetallic and with ternary additions (within a supercell model) show good agreement with band structure results. Further, electronic structure and total energy calculations of point (single impurity, M=Ti, V, Cr, Mn, Fe and Co) and planar defects such as anti-phase boundaries (APB) were carried out and the interaction between them was determined. We found that for the ½〈111〉{110} APB in NiAl, ternary additions occupy exclusively the 3d-metal sublattice and decrease the APB energy (except for Co). Finally, we employ TB-LMTO-REC to study the electronic structure of the most complex extended defect, a dislocation. We demonstrate for the 〈100〉{010} edge dislocation in NiAl that: (i) quasi-localized states may exist as a result of specific lattice distortions in the dislocation core with a type of “broken” bonds; (ii) the electronic structure changes appreciably in the process of dislocation motion; (iii) van-Hove singularities present in the ideal crystal may be shifted to E;r as a result of the dipolar character of the deformations in the dislocation core.

A transmission electron microscopic study of structural transitions in fast ionic conductors

1987 ◽  
Vol 45 ◽  
pp. 156-157
Author(s):  
R. B. Queenan ◽  
P. K. Davies
Keyword(s):  
Optical Properties ◽  
Ionic Conduction ◽  
Recent Observation ◽  
Ionic Conductivities ◽  
Sodium Aluminate ◽  
Two Dimensions ◽  
Ionic Conductors ◽  
Electron Microscopic ◽  
Transmission Electron ◽  
Trivalent Cations

Na ß“-alumina (Na1.67Mg67Al10.33O17) is a non-stoichiometric sodium aluminate which exhibits fast ionic conduction of the Na+ ions in two dimensions. The Na+ ions can be exchanged with a variety of mono-, di-, and trivalent cations. The resulting exchanged materials also show high ionic conductivities.Considerable interest in the Na+-Nd3+-ß“-aluminas has been generated as a result of the recent observation of lasing in the pulsed and cw modes. A recent TEM investigation on a 100% exchanged Nd ß“-alumina sample found evidence for the intergrowth of two different structure types. Microdiffraction revealed an ordered phase coexisting with an apparently disordered phase, in which the cations are completely randomized in two dimensions. If an order-disorder transition is present then the cooling rates would be expected to affect the microstructures of these materials which may in turn affect the optical properties. The purpose of this work was to investigate the affect of thermal treatments upon the micro-structural and optical properties of these materials.

scholarly journals Investigating the Factors Affecting the Ionic Conduction in Nanoconfined NaBH4

Inorganics ◽  
2021 ◽  
Vol 9 (1) ◽  
pp. 2
Author(s):  
Xiaoxuan Luo ◽  
Aditya Rawal ◽  
Kondo-Francois Aguey-Zinsou
Keyword(s):  
Ionic Conductivity ◽  
Ionic Conduction ◽  
Metal Hydrides ◽  
Ionic Conductivities ◽  
Effective Strategy ◽  
Li Ion Batteries ◽  
Large Cage ◽  
Factors Affecting ◽  
Li Ion ◽  
Mcm 41

Nanoconfinement is an effective strategy to tune the properties of the metal hydrides. It has been extensively employed to modify the ionic conductivity of LiBH4 as an electrolyte for Li-ion batteries. However, the approach does not seem to be applicable to other borohydrides such as NaBH4, which is found to reach a limited improvement in ionic conductivity of 10−7 S cm−1 at 115 °C upon nanoconfinement in Mobil Composition of Matter No. 41 (MCM-41) instead of 10−8 S cm−1. In comparison, introducing large cage anions in the form of Na2B12H12 naturally formed upon the nanoconfinement of NaBH4 was found to be more effective in leading to higher ionic conductivities of 10−4 S cm−1 at 110 °C.

Optoelectronic Properties of Plasma CVD a-Si:H Modified by Filament-Generated Atomic H

1992 ◽  
Vol 258 ◽  
Author(s):  
Y.M. Li ◽  
I. An ◽  
M. Gunes ◽  
R.M. Dawson ◽  
R.W. Collins ◽  
...  
Keyword(s):  
Film Thickness ◽  
Real Time ◽  
Chemical Potential ◽  
Defect Density ◽  
Plasma Deposition ◽  
Plasma Cvd ◽  
Near Surface ◽  
Optical Gap ◽  
New Material ◽  
Control Samples

ABSTRACTWe have studied a-Si:H prepared by alternating plasma deposition with atomic H treatments performed with a heated W filament. Real time spectroscopie ellipsometry provides the evolution of film thickness, optical gap, and a measure of the fraction of Si-Si bonds broken in the near-surface (200 Å) during H-exposure of single films. This information guided us to the desired parameters for the H-treatments. Here, we concentrate on a weak hydrogenation regime characterized by minimal etching, a higher H content by 2 at.%, and a larger optical gap by 0.02 eV for the growth/hydrogenation structures in comparison to continuously deposited control samples. This new material has shown an improvement in the defect density in the light-soaked state in comparison to the control samples. This may result from stabilization of the Si structure due to an increase in the H chemical potential in the a-Si:H.

The Microstructure and Electrical Properties of Directly Deposited TiN Ohmic Contacts to Gallium Nitride.

1999 ◽  
Vol 595 ◽  
Author(s):  
P. Ruterana ◽  
G. Nouet ◽  
Th. Kehagias ◽  
Ph. Komninou ◽  
Th. Karakostas ◽  
...  
Keyword(s):  
Gallium Nitride ◽  
Electrical Properties ◽  
Film Thickness ◽  
Ohmic Contact ◽  
Ohmic Contacts ◽  
Epitaxial Relationship ◽  
Si Doped ◽  
P Type ◽  
20 Nm

AbstractWhen the stoichiometric TiN was deposited directly on GaN, we obtained columnar TiN grains of 5-20 nm section which cross the whole film thickness and are rotated mostly around the [111] axis. The conventional epitaxial relationship is obtained and no amorphous patches are observed at the interface. The deposition of TiN on Si doped GaN layers lead to the formation of an ohmic contact, whereas we obtain a rectifying contact on p type layers.

scholarly journals Annihilation Radii for Dislocations Intercepting a Free Surface with Application to Heteroepitaxial Thin Film Growth

1998 ◽  
Vol 535 ◽  
Author(s):  
M. Chang ◽  
S.K. Mathis ◽  
G.E. Beltz ◽  
C.M. Landis
Keyword(s):  
Free Surface ◽  
Film Thickness ◽  
Film Growth ◽  
Interaction Force ◽  
Critical Issue ◽  
Dislocation Motion ◽  
Threading Dislocations ◽  
Fusion Reactions ◽  
Gaas Films ◽  
Preliminary Experimental Data

AbstractOne critical issue in heteroepitaxial, lattice mismatched growth is the inevitable appearance of threading dislocations which reside in the relaxing film and degrade its semiconducting properties. It has been shown in previous work that threading dislocations interact with each other through a series of annihilation and fusion reactions to decrease their density as the film thickness increases and follow a 1/h decay, where h is the film thickness. A characteristic reaction radius is associated with these interactions. In previous simulations, the reaction radius was taken to be a constant value estimated using a simple approximation based on infinite, parallel dislocation lines. Here, a continuum-based elasticity approach is taken to more accurately quantify the reaction radius by comparing the Peach-Koehler force of one dislocation acting on another at a free surface with the lattice resistance to dislocation motion. The presence of the free surface gives rise to a moderate reduction of the interaction force. Results are compared with preliminary experimental data for GaAs films grown on InP.

Bulk Gan Crystal With Low Defect Density Grown By Hydride Vapor Phase Epitaxy

1997 ◽  
Vol 482 ◽  
Author(s):  
A. Usui
Keyword(s):  
Vapor Phase ◽  
Flat Surface ◽  
Defect Density ◽  
Vapor Phase Epitaxy ◽  
Hydride Vapor Phase Epitaxy ◽  
Extended Defect ◽  
New Approach ◽  
Bulk Gan ◽  
Gan Crystal ◽  
Reflectance Measurements

AbstractA new approach to grow thick GaN layers by hydride vapor phase epitaxy (HVPE) is described. Selective growth is carried out at the beginning of growth. The coalescence of selectively grown facet structures makes it possible to achieve a flat surface over the entire substrate. As a result, crack-free GaN films with mirror-like surfaces are successfully grown even to a thickness of about 100 μm on a 2-inch-diameter sapphire substrate. The extended defect density is as low as 6×107 cm−2. The reduction mechanism for dislocation is discussed based on TEM observation. The high optical properties of FIELO GaN are confirmed by 5 K photoluminescence and reflectance measurements.

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