bluuebunny/crossref_metadata_2025 huggingface dataset:
High Resolution Tem of Organic Aerogels and Inorganic Aerogels
Authors: Ruben George C. , Pekala Richard W.
Published: March 2011

A base catalyzed silica aerogel and three base catalyzed resorcinol-formaldehyde (RF) aerogels were imaged with a new vertical platinum-carbon (Pt-C) replication technique. In deep gels single molecular chains can be visualized with transmission electron microscopy (TEM) with 9–10 Å thick Pt-C replicas backed with 110–130 Å of carbon [2]. The three RF aerogels produced with [Resorcinol]/[Catalyst] ratios (R/C) of 50, 200, and 300 had densities of 0.103, 0.063, and 0.065 gm/cc and had surface areas of 905, 580, and 390 m2/gm, respectively. The gel connectors and junctions in RF 300 and RF 200 were composed of 210±30 Å and 140±10 Å beads which were joined by polymeric chains covering an area less than half the bead's diameter and within a bead diameter's distance. The gel connectors and junctions in RF 50 were frequently composed of beads of about 120±10 Å joined over an area larger than half the bead's diameter. Similar to the silica aerogel (0.065 gm/cc, 113±10 Å beads), the beads were frequently connected over several bead diameter's distance from each other.
A New Synthetic Route to Organic Aerogels
Authors: Pekala R.W. , Alviso C.T.
Published: March 2011

The aqueous, sol-gel polymerization of melamine with formaldehyde, followed by supercritical extraction, leads to the formation of a new type of organic aerogel. Synthetic conditions (e.g. reaction time, pH) affect the density, transparency, and microstructure of the resultant aerogels. Unlike previous organic aerogels based upon resorcinol-formaldehyde, the melamine-formaldehyde aerogels are both colorless and transparent. Low densities (0.1–0.8 g/cc), high surface areas (∼1000 m2/g), and optical clarity are only a few of the promising characteristics of this new material.
Pre-Resonance Raman Characterization of Metal-Organic Films from Titanium Alkoxide Carboxylate Complexes
Authors: Gagliardi Charles D. , Dunuwila Dilum , Berglund Kris A.
Published: March 2011

Metal-organic films were produced at ambient temperatures and pressures by the controlled hydrolysis of carboxylic acid and titanium isopropoxide mixtures. Pre-resonance Raman spectroscopy was used to study the effect of the organic acid chain length upon the nature of the resulting film. Propionic, butyric, valeric, hexanoic, and octanoic acids were studied, resulting in a proposed correlation between film quality and certain spectroscopic features of the alkoxide carboxylates. The choice of the carboxylic acid and the presence of an appropriate amount of water were shown to be critical in the development of a good film.
XPS Characterization of Mixed Carbides Obtained from Polymer Precursors
Authors: Granozzi Gaetano , Glisenti Antonella , Soraru Gian D.
Published: March 2011

Polymer precursors for Si-C, Si-Ti-C-O and Si-Al-C-O systems have been obtained from polycarbosilane and the corresponding metal alkoxides. X-ray Photoelectron Spectroscopy (XPS) has been used to follow the structural evolution of these preceramic compounds during the pyrolysis process.
Chemically Derived Yttria-Stabilized Zirconia for Plasma-Spraying
Authors: Sherif Fawzy G. , Herman H.
Published: March 2011

Yttria-stabilized zirconia powders were prepared by three chemical routes utilizing emulsion hydrolysis techniques. Metal alkoxides, acetates and mixtures of alkoxides and acetates were used as starting materials. Under controlled hydrolysis conditions, particles with different morphology and size were obtained. Spherical or granular particles in the range of 20–60u in diameter were formed. The grain size varied from 0.1–0.2u. The powders were applied successfully as plasma spray coatings. The chemical uniformity was demonstrated by the presence of 100% non-transformable tetragonal zirconia in the powder and in the coating.
Transpiration Cooled Porous Type Vi Silica Rocket Windows
Authors: Fosmoe II Albert G , Hench Larry L.
Published: March 2011

A novel use of sol-gel derived porous Type VI silica for high performance rocket guidance system windows is evaluated. The samples produced for this study were optically transparent hydrofluoric and/or nitric acid catalyzed tetramethylorthosilicate (TMOS) xerogel monoliths with average pore radii of 1.2, 5.0, and 8.Onm. Maximum He transpiration velocities of up to 3 cm/sec, 3 times the velocity needed for transpiration cooling, are measured for a 5.0 nm sample at 3.2 MPa. Transpiration velocities of 0.6 cm/sec result in cooling effects as large as 44°C from 160°C.
Morphology Control In Precursor Ceramic Powder Production By The Electrical Dispersion Reactor
Authors: Harris Michael T. , Scott Timothy C. , Basaran Osman A. , Byers Charles H.
Published: March 2011

The Electrical Dispersion Reactor (EDR) allows the continuous production of composite oxide ceramic precursor materials. Silica particles in the form of highly porous shells are produced by the hydrolysis of tetraethylorthosilicate as the continuous phase and water-ammonia as the disperse phase, reflecting the diffusion of the silicon moiety into the dispersed phase. Alternately, denser silica particles result when aqueous solutions of sodium metasilicate are dispersed in a continuous phase containing acetic acid in 2-ethyl-1-hexanol. Additionally, spherical particles in the size range 0.1 to 2 microns are produced from the dispersion of aqueous solutions containing cupric chloride or a mixture of cupric chloride, yttrium nitrate, and barium nitrate (3:1:2 molar ratio) into a continuous organic phase containing ammonia.
Effect of Nitrous Oxide Gas on Cvd Diamond Film Deposition
Authors: Koinuma H. , Yoshimoto M. , Takagi Y. , Sawaoka A. B. , HaHashimoto T. , Nagai T. , Shiraishi T.
Published: March 2011

The addition of nitrous oxide (N2O) gas in the hot-filament chemical vapor deposition of carbon film from mixtures of methane and hydrogen was found to increase remarkably the content of diamond structure in the film. Increased particle size and crystal orientation parallel to the (111) direction were also obtained by the N2O addition. Mass spectrometry revealed that the vapor phase reaction was scarcely affected by the N2O addition.
Synthesis of Superconducting Perovskite by Coprecipitation of Hydroxides
Authors: Valente-Campion I. , Barboux P. , Mazerolles L. , Michel D. , Morineau R. , Livage J.
Published: March 2011

The synthesis of the superconducting perovskite YBa2Cu3O7 using hydroxides as starting precursors has been investigated. Hydroxides are homogeneously coprecipitated from mixed alcohol-water solutions without loss of barium. Upon heat-treatment the perovskite phase rapidly forms around 750°C. However, it remains tetragonal even after long time annealing in oxygen ambient. This is related to an unusual microtwinning in the (ac) plane.
Preparation of Bi-Pb-Sr-Ca-Cu-O Superconductor By Thermal Decomposition of an Edta Colloid
Authors: Koo H.S. , Chiang C.K. , Huang Y.T. , Tu G.C.
Published: March 2011

High-Tc superconducting Bi-Pb-Sr-Ca-Cu oxide with zero resistance temperature at above lOOK has been synthesized via the use of ethylenediamine-tetra-acetate(EDTA) colloid and corresponding metal nitrates. Remarkable sinterability of the precursor requires shorter time to achieve superconducting phases than conventional solid-state reactions. Superconducting properties were measured electrically and magnetically. The thermal decomposition, X-ray diffraction and microstructural characteristics of the precursor and the sintered samples were also discussed.
Solution-Derived Yba2Cu,Sub3O7−Δ. Thin Films And Barrier Layers
Authors: Whitwell G. E. , Wandass J. H. , Cambria F. M. , Antezzo M. F.
Published: March 2011

Hydrolyzed metal alkoxide solutions were spin-coated on Si substrates with subsequent thermal processing. Barrier layers of alkaline earth oxides, perovskites, Y2O3, ZrO2 and others were produced. Characterization was performed via SEM, XRD, ESCA, Auger depth profiling and resistivity measurements. Barrier layer films were fairly smooth with some cracking and pitting present. Si migration was severe for alkaline earth thin films on Si wafers. Some perovskite films on Si showed formation of Ba-Si-O phases at the Si interface. Thin films of 1–2–3 on barrier layers of SrTiO3 or ZrO2 on Si showed Ba pileup at the Si interface and were not superconducting. 1–2–3 layers deposited on single crystal ZrO2 were superconducting and showed onset temperatures of 90 K with zero resistance reached at about 55 K.
Evaluation Of YBa2Cu3O7-δ Sol-Gel Derived Films On Sapphire Substrates Produced From Different Cu(Ii) Alkoxide Groups.
Authors: Kenzer D.S. , Teepe M.R. , Moore G.A. , Kordas G.
Published: March 2011

Yttrium methoxyethoxide, barium methoxyethoxide and various copper(II) alkoxide groups were used as precursors for the formation of YBa2Cu3O7-δ stable sols in a 2- methoxyethanol / methyl ethyl ketone / toluene / diisopropyl ketone solvent system. Sol fractal dimensions were varied with the sol concentration and with the addition of pyridine. Strong correlation was found between the wettability and the fractal dimensions of the various precursors as determined by contact angle measurements. YBa2Cu3O7-δ thin films were deposited on sapphire substrates using a dip-coating technique. The films were fired at 850°C under flowing oxygen or an ozone/oxygen mixture. Although the ozonetreatments helped in the formation of single YBa2Cu3O7-δ phase, they contributed to extensive cracking in the films. The different copper(II) alkoxide precursors had little effect on final film microstructure.
Aspects Of Chemistry and Chemical Processing Of Organically Modified Ceramics
Authors: Schmidt Helmut K.
Published: March 2011

For the synthesis of composites on a nano or molecular level, chemical or physical methods have to be used since mechanical procedures cannot be employed for these systems. If organics have to be included, low temperature processing has to be used for the synthesis of the inorganic component in order not to damage the organic component. Sol-gel techniques are an appropriate means to synthesize oxidic networks by soft chemistry, and various systems of organically modified ceramics (ORMOCERs) have been developed so far. It has been shown that the synthesis parameter can be used to tailor the material properties in a wide range. A review over the chemistry and chemical properties of ORMOCERs and several examples of material developments will be given.
Hydrolysis of Aluminum -Are All Gels Created Equal?
Authors: Wood T. E. , Siedle A. R. , Hill J. R. , Skarjune R. P. , Goodbrake C. J.
Published: March 2011

The nuclearity and structure of aluminum cations generated by the hydrolysis of aluminum salt solutions depends markedly on the method of preparation. This speciation affects not only the thermochemistry of processes leading to ceramics, but the microstructures of the ceramics themselves. A brief review of aluminum ion hydrolysis is presented along with a study of the thermal evolution of gels derived from aluminum salt solutions via several different hydrolysis methods. The observation of 5 - coordinate aluminum in a bulk transition alumina by MAS-NMR is reported. A new, high defect precursor of η-alumina dubbed “high-5 alumina” is described and the far reaching implications of this discovery are discussed.
Modelling Diffusion in and From Polysilicon Layers
Authors: Hill C. , Jones S.K.
Published: March 2011

The physical processes involved in dopant redistribution during heat treatments of polysilicon layers are described, and one and two—dimensional models based on these are presented. The quantitative effects of the physical parameters determining arsenic andboron distributions in bipolar VLSI emitter—base structures are demonstrated, andclose correspondence shown with available experimental data. Areas needing new models are outlined, and an approach to the modelling of epitaxial alignment is proposed.
In-Situ Doped Polycrystalline Silicon Deposited by Rapid Thermal Chemical Vapor Deposition Using Tertiarybutylphosphine
Authors: Liao Jimmy C. , Kim Ki-Bum , Maillot Philippe
Published: March 2011

The effects of using tertiarybutylphosphine (TBP) as a source of phosphorus dopants during polycrystalline silicon (polysilicon) deposition in a rapid thermal processor (RTP) was investigated using TEM, SIMS, spectrophotometry, and 4-point probe analysis. It was found that the introduction ot TBP significantly inhibited the deposition of polysilicon on silicon dioxide, but only slightly reduced the growth rate of polysilicon on polysilicon. The introduction of TBP during the last 20% of the deposition time formed a thin phosphorus-rich layer on the top surface. Adsorption of the phosphorus was found to be gas-transport-limited. Incorporation of the dopant into the rest of the polysilicon layer was accomplished with an in-situ anneal (RTA) in nitrogen, resulting in a resistivity as low as 720 μΩ-cm.

The grain size of the polysilicon was found to increase with deposition temperature, however was not affected by the introduction of the dopant, or any subsequent anneal. It ispostulated that unincorporated phosphorus, and oxygen and carbon in the grain boundariesprevent the combination and growth of silicon crystals.
Supersaturated P-Type Polycrystaline Films Produced by Rapid Thermal Annealing of High Dose Boron Ion Implants for Interconnects and Shallow Junction Diffusion Sources
Authors: Raicu B. , Current M.I. , Keenan W.A. , Mordo D. , Brennan R. , Holzworth R.
Published: March 2011

Highly conductive p+-polysilicon films were fabricated over Si(100) and SiO2 surfaces using high-dose ion implantation and rapid thermal annealing. Resistivities close to that of single crystal silicon were achieved. These films were characterized by a variety of electrical and optical techniques as well as SIMS and cross-section TEM.
Electrical and Optical Properties of Polysilicon Sheets for Photovoltaic Devices Grown From Powder
Authors: Urli Natko B.
Published: March 2011

In a search for low-cost and high efficiency solar cell manufacturing, several techniques of growing thin silicon sheets from powder have been adopted, such as: plasma spraying on various substrates, zone-melting using incoherent focussed light as heat source, and low-angle horizontal pulling of thin ribbon over the melted tin-lead support. Undoped, and n- and p-type silicon powders of various grain sizes have been used as starting materials, with pure graphite, quartz, or low-cost ceramics serving as temporary or permanent substrates. N+/p +/n junctions, and back surface fields were formed by implanting PF 5 and BF 3+ ions in a glow discharge ion implanter at ultralow energies (less than 1 keg) and high total ion doses. Ion induced damage was annealed by RTP in the incoherent light furnace at temperatures as low as 700°C.

Structural and optoelectronic properties of as-grown and processed thin polysilicon sheets were determined by Raman spectroscopy, spectral response, and electrical transport measurements. A sharp peak at 520 cm−1 in the Raman spectra, associated with TO ((Г) phonons, indicated a good crystallinity of polysilicon sheets. High values of short-circuit currents, and an almost flat spectral response down to 400 nm, without intentionally applying a surface passivating oxide, illustrate the advantage of the applied novel technologies.
Depth Variation of Transport Parameters in Poly-Si Under Am1 Illumination
Authors: Chen Z. , Burton L.C.
Published: March 2011

Abstract; Grain boundary (GB) recombination is a controlling factor in the electronic properties of polycrystalline silicon. We would like to report computer modeling of the variation of electron transport parameters with depth, under illumination. The GB barrier height (Vg) versus photogeneration rate G and depth are presented, along with the resulting electron lifetime (π), mobility (µ) and diffusion length (L). Under AM1 illumination, Vg increases whereas -π, µ and L all decrease drastically with increasing depth. The GB trap density is used as a parameter, and strongly influences transport parameters in both dark and light cases.
Effects of Arsenic Segregation and Electron Trapping on the Capacitance-Voltage Behavior of Polysilicon and Polycide Gates
Authors: Lin J. , Batra S. , Park K. , Lee J. , Banerjee S. , Sun S. , Yeargain J. , Lux G.
Published: March 2011

This paper discusses the effects of dopant segregation and electron trapping on the capacitance-voltage characteristics of arsenic-implanted polysilicon and amorphous Si gate MOS structures fabricated with and without a TiSi2 layer. The effects of gate bias, annealing temperature, silicide formation and polysilicon grain microstructure on the C-V characteristics have also been studied. The results show that insufficient arsenic redistribution at 800°C, coupled with carrier trapping at polysilicon grain boundaries and dopant segregation in TiSi2 causes depletion effects in the polysilicon gate and in turn, an anomalous capacitance-voltage behavior. The depletion tends to increase the “effective” gate oxide thickness and thereby degrade MOS device performance. Higher temperature anneals (≥ 900°C) are sufficient to achieve degenerate doping in the polysilicon gates and avoid the depletion effects.
Application of Polysilicon in Advanced IC - Technologies
Authors: Kabza Herbert , Meister Thomas F. , Schaber Hans
Published: March 2011

The progress in IC technology is unthinkable without the extensive use of polysilicon for a wide variety of purposes. These range from simple passive components like resistors and contacts through more complex structures such as recrystallized layers for SOI and 3D techniques, poly-Si filled isolation trenches and electrodes of DRAM capacitors to active device applications, i.e. MOS gates and poly-Si emitters in bipolar transistors. As silicide or in combination with such polysilicon allows practical local interconnects.
Polycrystalline Silicon in ULSI Technologies: Challenges for Deep-Submicron Structures
Authors: Wong Catherine Y. , Ning Tak H.
Published: March 2011

Polysilicon is a key material widely used in MOSFET, bipolar, and BICMOS devices. As these technologies evolve into the deep submicron regime, several issues emerge in the applications of polysilicon that must be addressed. In sub-0.5µm MOSFET, fabrication and reliability of n + poly for NMOS and p + poly for PMOS should be studied. In bipolar technology, scaling limits of polysilicon emitter must be investigated. Understanding polysilicon, both in terms of its basic material and process characteristics and its characteristics in specific integrated process and/or integrated device structures, is definitely required in order to realize the full potential of ULSI technologies.
Polysiliodn Annealing and its Inflience on Floating Gate Eeprom Degation
Authors: Seim Rakesh B. , Andeion L. B.
Published: March 2011

Experimental results on the influence of prooessing on degradation of thin silicon dioxide films are reported. The high temperature polysilicon oxidation degrades the integrity and robustness of thermally grown dry oxide as shown by constant current charge to breakdown measuremeits.

Furthermore the influence of high temperature processing on the charge trapping properties of the tunnel oxide (silicon dioxide) are ascertained. The details of electron trapping its capture cross section, areal concentration and trapping efficiency as studied by high field dark current-voltage method is presented. Generally, the dominant −15 electron trap with a large capture cross section of 10 cm2 is observed and is believed to be due to phosphorus near polysilicon/thin oxide interface. In addition the QBD reduction is correlated to outdiffusion of water from the thin oxide as seen by reduction in the hysteretic instability of I-V curves.
Impact of Various Polysilicon Deposition Process on Thin Gate-Oxide Properties in Submicron CMOS Technology
Authors: Roy P. K. , Kook T. , Kannan V. C. , Felton G. J. , Powell R. A. , Velaga A. N.
Published: March 2011

The dielectric quality (defect density, Do and breakdown strength, Fbd) of 150Å SiO2 gate oxide (GOX) films grown by conventional or stacked oxidation scheme are discussed from the leakage measurements of polysilicon capacitors on test structure simulating our submicron CMOS process. Various polysilicon (poly) deposition processes from silane pyrolysis (570°C -620°C) were used by the low pressure chemical vapor deposition (LPCVD) technique. Both in situ and ex situ poly doping by phosphorus (P) were used to ascertain their impact on the GOX properties. The substructural characteristics of the poly/SiO2 and SiO2/Si interfaces generated by various combinations of GOX and poly deposition processes were done by the high resolution TEM lattice fringe technique under phase contrast mode.
Submicron P-Channel Mos Devices with Boron Doped Polysilicon Gates Fabricated by Rapid Thermal Processing
Authors: Kugelmass Sheldon M. , Krusius J. Peter
Published: March 2011

A low thermal budget process is demonstrated for the fabrication of submicron Boron doped polysilicon gate p-channel MOS devices with ultra thin gate insulators. All critical processing steps with temperatures above 700 °C, including gate oxide growth and shallow source/drain junction formation, were performed by Rapid Thermal Processing (RTP). In situ doped polysilicon was used to eliminate the need for a high temperature drive-in step. Surface channel p-channel enhancement mode devices with excellent characteristics were fabricated to demonstrate the feasibility of this process.
Poly-Si - A Most Important Material
Authors: Hammond Martin L.
Published: March 2011

The many advantages of polycrystalline Si (poly-Si) to semiconductor device manufacturing are reviewed, together with methods of deposition and new uses.
The Electrical Properties of Polyoxide Depending on the Polycrystalline-Si Formation Conditions
Authors: Yi Kyoung-Soo , Cho Deok-Ho , Lee Jeong Yong , Nam Kee-Soo , Kang Sang-Won , Lee Jin-Hyo
Published: March 2011

Prior to growth of polyoxide, amorphous-Si with a cap of low temperature oxide was annealed to improve the dielectric property of polyoxide. Current-electric field, critical electric field, critical electric field histogram, and Fowler-Nordheim conduction plot were evaluated. The interface of polyoxide and poly-Si was observed with a transmission electron microscope. The annealing of the amorphous-Si prior to oxidation was effective to improve the dielectric property of the polyoxide.
Thickness Effects on the Activation Energy of Source-Drain Current in P and N Channel Polycrystalline Silicon Thin Film Transistors
Authors: Khan Babar A. , Pandya Ranjana
Published: March 2011

We report activation energy measurements of the source-drain current of polysilicon thin film transistors (TFTs). We have shown earlier that measurements carried out on unhydrogenated TFTs can be explained by the presence of band tail states in addition to deep localized states. After hydrogenation, the density of band tail states is greatly reduced and the data can be fitted with only the deep states.

In the present work we have studied both n and p channel TFTs. This was done by measuring both type of devices on the same wafer so that differences due to processing conditions could be ruled out. Both type of devices had intentionally undoped channels and were identical except for the n or p type source-drain regions. The thinner TFTs discussed in this work have a sharper drop in the activation energy than would be expected from idealized calculations. This sharp drop in activation energy is also an indication of a sharp subthreshold slope. This decrease in subthreshold slope (Volts/decade) is due to the complete depletion of the channel polysilicon, which leads to a rapid increase (or decrease) in the surface potential as a function of the gate voltage.
Defect Passivation Kinetics and Small Geometry Effects in Polysilicon Thin Film Transistors
Authors: Wu I-Wei , Huang Tiao , Lewis Alan G. , Jackson Warren B. , Chiang Anne
Published: March 2011

The effects of hydrogen plasma passivation on n-channel polycrystalline silicon thin film transistors fabricated with a maximum temperature of 600°C are investigated. It is found that charge, sharing, avalanche multiplication, grain size, and gate edge in-situ passivation or even partial hydrogenation can all contribute to the small geometry effect. At low drain bias, the channel charges supported by the source and drain fringing fields cause threshold shifts for short channel devices; at high drain bias avalanche multiplication is the dominant effect. The charge sharing effect may be related to the unpassivated trap-states in the channel since thresholds of fully hydrogenated devices became independent of channel length at low drain bias. The threshold shifts of narrow width devices were also diminished with increasing hydrogenation time. An anomalous turnaround effect of the field effect mobility in saturation regime for the short channel devices is observed near saturated hydrogenation. This effect is probably due to the passivation of back-channel defects and the reduction in impact ionization rate by hydrogenation. Saturated hydrogenation not only improves device performance but also reduces small geometry effects. Avalanche multiplication remains the dominant mechanism for short channel effect in the saturated hydrogenated devices.
High Resolution Transmission Electron Microscope Study of UHV Deposited Titanium Thin Films on (001), (III) and (011)Si
Authors: Wang M. H. , Chen L. J.
Published: March 2011

High resolution transmission electron microscopy has been applied to study the formation of amorphous interlayers by solid-state diffusion in ultrahigh vacuum deposited Ti thin films on (001), (111) and (011)Si

The interface structures of as deposited and annealed samples were examined. The disordered regions at the a-interlayer/c-Si interfaces were found to be most and least extensive in (011) and (111) samples, respectively. Growth behaviors of a-interlayers are described. The amorphization appeared to be initiated at the grain boundaries of Ti thin films. Ti5 Si3 was identified to be the phase formed at the initial stage of the interfacial reactions by HREM in conjunction with the optical diffraction.
SiO2/Si Interfaces Studied by Stm and Hrtem
Authors: Niwa Masaaki , Onoda Minoru , Iwasaki Hiroshi , Sinclair Robert
Published: March 2011

The morphology of SiO2/Si interfaces in a semiconductor LOCOS active area grown by several oxidation conditions has been studied, to compare the roughness of the interfaces observed by STM and HRTEM in particular. Samples consisted of typical MOS structures with a polysilicon gate/SiO2/Si(100). Hydrogen terminated Si surfaces were prepared by means of HF dipping for STM observations. The interface roughness of a “dry” oxide observed by HRTEM was slightly larger than that of a “wet” oxide. Good agreement could be found between STM and HRTEM for the wet oxide interfaces. As for the dry oxide interface, it was more difficult to obtain a reproducible STM image than for the wet oxide interface, but the reverse was true for HRTEM. During the HRTEM, high energy electrons damage the sample and reduce the oxide thickness, especially in the wet oxide samples.
The Study of Defects in Metals Using High Resolution Transmission Electron Microscopy and Atomistic Calculations
Authors: Mills M. J. , Daw M. S.
Published: March 2011

The coupling of HRTEM with atomistic calculations is described for the study of grain boundaries and dislocations in aluminum. HRTEM images of the Σ9 (221) [110] grain boundary are compared with molecular statics calculations using both the Embedded Atom Method (EAM) and two pair potentials. Comparison between observed and simulated images are shown to serve as a stringent test of the theoretical methods. Atomistic calculations can in turn provide threedimensional information about the defect structure. Using the EAM, it is also possible to account for the effects of thin foil geometries on the minimim energy configuration of defects. While these effects are found to be minimal for grain boundary structures, the influence of the thin-foil geometries on the core structure of the 60° dislocation in aluminum is discussed. These comparisons indicate that the EAM function provides a good description of grain boundary structures, but fails to reproduce the observed dislocation core structure due to a low predicted value of the intrinsic stacking fault energy (SFE) on the (111). In contrast, the pair potentials used in this study provide reasonable SFE values, but appear to be less accurate for the prediction of the Σ9 (221) [110] grain boundary structures.
Anti-Site Bonds and the Structure of Interfaces in SiC
Authors: Pirouz P. , Yang J.
Published: March 2011

High resolution electron microscopy has been used to study the structure of the 3C/6H interface, Σ,=3 {111}and Σ.=3 {112}grain boundaries in 3C-SiC. In SiC, as in other compound semiconductors, anti-site bonds occur in a variety of defects. These are high energy bonds comparable to that of dangling bonds. But, while dangling bonds at the grain boundaries may be eliminated by reconstruction just as in elemental semiconductors, it may not be possible to avoid anti-site bonds.These problems are discussed for the Σ=3 {112} grain boundary, where the structures proposed for Ge and Si are used as starting models for SiC.
High Resolution Transmission Electron Microscopy of GaAs/AlAs Hetero-Structures in the <110> Projection
Authors: Ikarashi N. , Sakai A. , Baba T. , Ishida K. , Motohisa J. , Sakaki H.
Published: March 2011

High resolution transmission electron microscopy (HRTEM) of GaAs/AlAs hetero-structures grown by molecular beam epitaxy (MBE) is carried out in the <110> projection. It is shown that GaAs and AlAs are distinguished clearly by the difference in their lattice images at the samples thicknesses of about 15–30 nm under near Scherzer focus condition. Under these imaging conditions, very thin films consist of single monolayer AlAs are observed. Vicinal interfaces of GaAs/AlAs which were grown on (001) substrate misoriented toward [110] are also examined in the [110] projection. The interfacial structures are imaged edgeon, so that the fluctuations of terrace width, and the roughness of step-edges at these interfaces are observed on an atomic scale.
Incoherent Imaging of Materials Structure and Composition by Z-Contrast Stem
Authors: Pennycook S. J. , Jesson D. E. , Chisholm M. F.
Published: March 2011

It is shown how the use of a high angle annular detector in a STEM provides images which show strong compositional sensitivity and almost perfect incoherent characteristics. No contrast reversals occur with defocus or sample thickness and the contribution of an atomic string is insensitive to the distribution and strength of neighboring strings. The image is best described in real space as a simple convolution of the incident probe intensity profile with an object function sharply peaked at the atomic strings having a strength dependent on composition. How the incoherent characteristics arise is described using a Bloch wave approach and examples are shown of interfaces in semiconductor and superconductor materials.
“Column-By-Column” Compositional Mapping At Semiconductor Interfaces Using Z-Contrast Stem
Authors: Jesson D. E. , Pennycook S. J. , Baribeau J. -M.
Published: March 2011

A new strategy for atomic resolution compositional mapping at semiconductor interfaces is presented. Images can be interpreted directly to within 10% to give column-by-column compositional information with a sensitivity approaching Rutherford scattering cross sections. We apply the method to obtain the first atomic resolution images of interfacial ordering in ultrathin (SimGen)p superlattices and attribute the results to growth on (2 × 1) and (1 × 2) reconstructed surfaces.
High-Resolution Electron Microscopy of Planar Defects in Ain.
Authors: Mckernan Stuart , Norton M. Grant , Carter C. Barry
Published: March 2011

The defects which occur in polycrystalline aluminum nitride are very detrimental to the beneficial physical and electrical properties. 'Dome-like' or 'D' defects, consisting of a flat basal fault joined to a curved planar fault, are examined by high-resolution electron microscopy. The basal segments are shown to contain a thin ∼5Å layer of a second phase and are associated with a stacking-fault and an antiphase boundary. A structural model is proposed for the defect which incorporates a layer of alumina at the basal segment of the 'D' defect. The formation of thisdefect is discussed.
High-Resolution Electron Microscopy Studies of Faults and Intergrowth in Nb3O7F
Authors: permér Lotta , Lundberg Monica
Published: March 2011

HREM studies of the low-pressure form of Nb3O7F, obtained by thermal decomposition of NbO2F or by reacting stoichiometric amounts of NbO2F and Nb2O5, confirmed that the crystals are built up of a shear-type structure in which slabs of ReO3 type, infinite in two dimensions and three octahedra wide, separate the shear planes. Most of the crystals were well-ordered, although faults could occasionally be detected. However, some crystals were found to be intergrown with a structure closely related to the high-pressure form of Nb3O7F. The latter structure is composed of wavy rows of edge-sharing NbX7 pentagonal bipyramids, joined to each other by NbX6 octahedra. The connection between the two atomic arrangements can be understood in terms of the common c-axes and a slight distortion of the polyhedra along the boundary.
Hrem of Defects in Oxide Superconductors
Authors: Zandbergen H. W. , van Tendeloo G.
Published: March 2011

A review is given of defects occurring in the superconducting oxides YBa2Cu3O7, (Bi,Tl)2(Sr,Ba)2CanCul+nO6+2n, and Pb2Sr2(Cal-xYx)nCu2+nO6+2n+∂. A number of these defect structures correspond to other thermodynamically stable phases. The observations of these defects have led in several cases to successful synthesis of new superconducting compounds. Defects can effect the superconducting properties, which they can either deteriorate (weak links) or improve (flux pinning). Both effects are considered.
HREM of Epitaxial YBa2Cu3O7 Thin Films
Authors: Mitchell T. E. , Basu S. N. , Nastasi M. , Roy T.
Published: March 2011

Thin films of YBa2Cu3O7 have been prepared by evaporation of Cu, Y and BaF2 onto (001) SrTiO3, LaGaO3. and LaAlO3 and subsequent annealing. Their microstructures have been examined by HREM of cross-sectional specimens. Epitaxial (001) grains of YBa2Cu3O7 form near the substrate interface in thin films but (001) and (010) grains tend to nucleate as the film thickens. 90° grain boundaries are therefore common, as well as other defects such as small-angle boundaries, dislocations and stacking faults. HREM of the substrate/superconductor interface indicates regions of perfect epitaxy, highly distorted areas, amorphous regions and areas showing evidence of interdiffusion. The relationship of these microstructural features to critical current density is discussed.
Morphology and Defect Structure of Sputtered High-Quality In-Situ YBa2Cu3O7−δ Films
Authors: Streiffer S. K. , Lairson B. M. , Eom C. B. , Marshallt A. F. , Bravman J. C. , Geballe T. H.
Published: March 2011

Transmission Electron Microscopy has been used to study the morphology and defect structure of sharp superconducting transition, high (2-6 ×107 A/cm2) critical current YBa2Cu3O7−δ films on MgO substrates. These were oriented such that the unit cell axes of the film aligned with those of the substrate, with some domains obeying a second orientation relationship rotated by 45° in the plane of the film, i.e. film <110> parallel to substrate <100>. The latter is not expected from simple lattice matching considerations. A strong influence of substrate surface topography on film microstructure was noted, leading to a high density of out-of-phase, low-angle tilt, and other boundaries near the substrate-film interface, which decreased with increasing distance from the substrate. Finally, the effects on film microstructure of two variables of specific interest in our sputtering system were investigated: the thickness of the deposited film, and the temperature at which a high oxygen pressure (500 torr) is introduced after deposition is complete. Increases in film thickness resulted in longer, more widely spaced twins, whereas lower oxygenation temperatures resulted in shorter twins.
Determination of the Formation of the 1/6[031] Extrinsic Stacking Faults in Deformed YBa2Cu3O7−δ
Authors: Kramer M. J. , Kvam E. P. , Chumbley L. S.
Published: March 2011

Mechanial deformation of the YBa2Cu3O7−δ high temperature superconductor under a number of different processing conditions resulted in the formation of <100> and <110> edge dislocations, both having a (001) slip plane. Subsequent high temperature annealing at 900°C resulted in the formation of extrinsic stacking faults with a large separation of the partial dislocations, up to 0.35 μm, suggesting a very low minimum stacking fault energy of 1.2 × 10−2 J/m2. High resolution transmission electron microscopy (HRTEM) in conjunction with image simulations revealed that the stacking faults were comprised of an extra CuO plane between the Ba layers with an offset of b/2. The stacking fault vector of 1/6[031] requires some separation of the <010> Burgers vectors into the c-axis direction. A model in which [010] separates into 1/6[031] + 1/[031] is consistent with the observed stacking faults.
Structure and Defects of Shock-Processed Ti and Y-Based Copper Oxide Superconductors
Authors: Sharma R. , Ramakrishna B. L. , Iqbal Z. , Thadhani N. N. , Chawla N.
Published: March 2011

We have studied the micro-structure of shock synthesized Tl2Ba2CuO6, shockprocessed YBa2Cu3O7 and 10% Ag-YBa2Cu3O7. The structural interpretation of the defects observed in these materials is discussed and compared with computer simulated images. Two planar defects with a stacking sequence of Cu-Ba-Tl-Ba-Cu and Cu-Ba-Tl-Tl-Ba-Cu-Tl-Cu-Ba-Tl-Tl-Ba-Cu in the Tl based oxide and a new defect sequence of Cu-Ba-Cu-Y-Y-Cu-Ba-Cu in the Y based oxides are reported here. An attempt is made to relate the change in superconducting properties observed to the defect structure present.
Relation between Leakage Current in PIN Photodiodes and Defects in InGaAs(P)/InP Heterostructures Grown Low Pressure MOCVD
Authors: Knight D. G. , Miner C. J. , Springthorpe A. J.
Published: March 2011

High resolution maps of the InGaAs photoluminescence intensity over whole 50mm diameter PIN detector wafers grown by low pressure MOCVD were obtained using a scanning photoluminescence (PL) system. The leakage current of PIN detectors was found to decrease exponentially with increased PL intensity. This correlation was quantitatively valid for both variation on a given wafer and for wafer-to-wafer variations. The density of morphological features on the surface of InGaAs(P)/InP heterostructures also was found to decrease exponentially with increased PL intensity, where a simple linear relationship between leakage current and feature density was then determined. The features are likely a manifestation of substrate defects which propagate from the surface of poor quality substrates.
Atomic Diffusion With Strain and Injection
Authors: Vechten J. A. Van
Published: March 2011

The inherent complexity of defect processes in III-V's and the consequent difficulties with ab initio and semi-empirical methods are recalled. A potential solution using massive Monte Carlo simulation on microcomputers is suggested. Evidence for the validity of the Ballistic Model, BM, of atomic diffusion in III-V's is noted. According to the BM the effect of strain (in the absence of any electrostatic, population, or recombination effect) is to increase the rate at which a given mobile atom hops where the sample is compressed. For the case of misfit strain at a (100) junction, we note that the anisotropy of the elastic constants implies that some planes running into the bulk will be compressed whichever the sign of the misfit. This implies that misfit strain of either sign should increase the observed rate of interdiffusion, in the absence of other effects. We also recall the importance (demonstrated at low T) of recombination enhancement of atomic diffusion, RED. Devices are processed at temperatures where the thermal rate of recombination is very high and often operated at high levels of injection. The interaction of strain with RED is clearly important and complicated. III-V crystals have the further complication of being piezoelectric. The active piezoelectric axes are <111>, so a pure <100> strain does not produce a field. However, the accommodation a device makes to misfit at (100) junctions can generate a strong field, which may fluctuate with bias voltage.
Consequences of Strain and Growth Kinetics on Growth Modes and Dislocation Formation in Strained Layer Epitaxy
Authors: Singh Jasprit
Published: March 2011

We examine the growth modes of compound semiconductors grown by molecular beam epitaxy in lattice matched and strained layers. While in lattice matched layers it is possible to grow in the layer by layer mode by choosing proper growth conditions, in strained layers we find that for large strain, it is not possible to do so. This is due to the competition between surface strain energy which favors 3D growth and surface chemical energy which favors a layer by layer growth mode. The growth mode is shown to have significant effects on the nature of the dislocations generated beyond critical thickness.
Reliable Metallization for Inp-Based Devices and Oeic's
Authors: Wada O. , Ueda O.
Published: March 2011

We describe techniques of reliable metallization in InP-based systems for application to discrete and opto-electronic integrated circuits (OEIC's). Strong metallurgical interaction between Au and InP-based compounds can cause serious contact degradation in light emitting diodes (LED's). By analyzing this interaction in detail, an improved thin Au/Zn/Au p-contact technique has been developed. The results are compared with Pt/Ti contacts, and it has shown that both provide sufficient reliability under temperature and current stresses in LED's. We then describe a metallization technique for flip-chip bonding of opto-electronic devices on other semiconductor chips for OEIC applications. An acceptable reaction barrier effect of Pt in AuSn/Pt/Ti metallization structure has been demonstrated and this structure has been used for a high-reliability, flip-chip integrated GaInAs/InP PIN photodiode/GaAs amplifier receiver circuit. We also discuss requirements for metallization for future monolithic OEIC's by taking up an example of metal-semiconductor-metal photodiodes in InP-based systems.
Thermal Behaviour of Au/Pd/Gaas Contacts
Authors: Pécz B. , Veresegyházy R. , Mojzes I. , Radnóczi G. , Sulyok A. , Malina V.
Published: March 2011

Au(85nm)/Pd(55nm)/GaAs(100) samples were heat treated in the 325–425°C temperature range. The annealed samples have been investigated using Rutherford Backscattering Spectrometry, Auger Electron Spectroscopy and Transmission Electron Microscopy. The gold layer remained largely unreacted up to 300°C. Significant Pd diffusion into GaAs consuming a 50–60 nm thick layer of GaAs is evident in the case of sample annealed at 325°C and a slight Au diffusion is also noticeable. In the sample annealed at 350°C the spreading of palladium was very quick. A strong reaction took place between the GaAs and the metallization in the case of sample heat treated at 375°C. At this temperature we have identified the PdGa phase using electron diffraction.
Thermoelectric Power in Quantum Confined Optoelectronic Materials under Classically Large Magnetic Field
Authors: Ghatak Kamakhya P. , De B. , Mondal M. , Biswas S. N.
Published: March 2011

We shall study the thermoelectric power under classically large magnetic field (TPM) in optoelectronic materials of quantum wells (QWs), quantum well wires (QWW's), quantum dots (QDs) and compare the same with the bulk specimens of optoelectronic materials by formulating the respective electron dispersion law. The TPM increases with decreasing electron concentration in an oscillatory manner in all the cases, taking n-Hg1−xCdxTe as an example. The TPM in QD is greatest and the least for quantum wells respectively. The thecoretical results are in agreement with the experimental observations as reported elsewhere.
Origin and Behavior of Main Electron Traps in Si-Implanted GaAs
Authors: Fang Z-Q. , Yamamoto H. , Look D. C.
Published: March 2011

The electron traps in Si-implanted active layers(n∼1017 cm−3) have been studied by capacitance and conductance DLTS techniques in conjunction with different anneal conditions, which include rapid thermal anneals at different temperatures and furnace anneals with a Si3N4 cap or capless in an AsH3 atmosphere. As compared to the electron traps in as-grown bulk n-GaAs (n∼4×1016 cm−3), nearly the same electron traps, i.e. EL2, EL3, ELM, EL5, EL6 and EL9 can be observed in the Si-implanted layers. Through a comparison with the annealing behavior of the main elect ron traps in bulk n-GaAs, the processing associated origins of some of the traps(EL2, EL3, EL4, EL5 and EL9) observed in Si-implanted GaAs layers have been determined. For some Si-implanted GaAs capped with Si3N4 and furnace annealed, traps EL3 and EMA dominate the trap EL2. In such layers it is found that emission due to EL3 is reduced while emission from EL12 is augmented by increasing the filling pulse width from 10 μs to 5×103 μs. This phenomenon can be explained in terms of a defect reaction enhanced by electron capture, showing a metastability or bistability.
Order-Disorder Phenomena in Complex Alloys: The Case of A15-Based Substitutional Alloys
Authors: Turchi P.E.A. , Finel A.
Published: March 2011

We first discuss the applicability of the Generalized Perturbation Method to the study of ordering phenomena in complex alloys for which stability properties are electronically driven. In particular, according to previous work, it is recalled that a 3D-generalized Ising model is appropriate to address the problem of configurational order in A 15-based substitutional alloys. A ground state analysis of this model, including 1st, 2nd and weak 3rd and 7th pair interactions, generates two new ordered states at the composition A5B3 and A7B, apart from the well known A3B configuration. The stability of these predicted configurations is examined as a function of temperature and concentration by means of standard statistical techniques. The results are discussed in relation with the experimental situation.
Recent Advances in Non Self-Consistent Total Energy Calculations in Alloys
Authors: Schilfgaarde M. van , Paxton A.T. , Pasturel A. , Methfessel M.
Published: March 2011

In recent years, total energy calculations based on the local density approximation (LDA) have begun to find applications in materials science [1]. In the context of the present symposium, the most relevant application is to the calculation of total and relative energies of ordered alloy phases and their mixing enthalpies. The first-principles LDA approach is now taking over from tight-binding or simple empirical schemes in providing input to phase diagram calculations, for example, using Connolly-Williams inversion [2]. We wish to make two points in our contribution to the symposium.
Phase Equilibria and Solidification of Al-Rich Ai-Ui-Cu Alloys
Authors: Chen Sinn-Wen , Chang Y. Austin
Published: March 2011

A liquidus projection of the Al-rich Al-Li-Cu system is proposed. The proposed liquidus projection was based on DTA, X-ray diffraction, metallography, EPMA, SEM, and chemical analysis of 50 ternary alloys. Using these data and those reported in the literature, and thermodynamic models of Al-Li, AI-Cu and Cu-Li, a thermodynamic description of the Al-rich AI-Li-Cu system was developed. The calculated isothermal sections at several temperatures and the liquidus projection are in agreement with the experimental determinations. Combining the thermodynamic models and a Scheil-type equation, quantitative solidification paths were described. The calculated amount of primary solidification phase was compared to the experimental determination.