bluuebunny/crossref_metadata_2025 huggingface dataset:
A new approach to the fabrication of “smart” near-surface nanostructure composites
Authors: Gea Laurence , Honda S. , Boatner L. A. , Haynes T. E. , Sales B. C. , Modine F. A. , Meldrum A. , Budai J. D. , Beckers L
Published: April 2011

A new method for the formation of “smart” near-surface nanoscale composites has been developed. In this approach, small precipitates of active phases are embedded in the near-surface region of the material that is to be modified by a combination of ion implantation and thermal processing. The dispersion, concentration, and microstructure of the nanocrystals formed in the substrate material can be tailored through a careful choice of processing parameters – making this approach well suited to high-value-added, high-technology applications. The applicability of this approach to forming “smart” surfaces on otherwise inactive materials was established in the case of VO2 precipitates which were embedded in A12O3 single crystals to create a medium suitable for optical applications – including optical data storage. Most recently, this concept has been extended to the fabrication of magnetic-field-sensitive nanostructured surfaces by forming magnetostrictive precipitates of materials such as Ni or RFe2 (with R = Tm, Tb, Sm) that are embedded in various single-crystal-oxide hosts. These nanostructured, active surface composites have been characterized using XRD, RBS, TEM, and magneto-optical techniques.
Nanoparticulate coating of functional ceramics by the vapor, solid and liquid phase reactions
Authors: Awano M. , Kameyama T. , Sando M. , Kuwahara Y.
Published: April 2011

Microstructure control of ceramics is expected to produce novel functions or to improve properties. Nanocomposite powders of functional ceramics were fabricated by vapor, solid and liquid phase reactions, respectively. Superconducting bulk materials were fabricated by thermal plasma method and mist pyrolysis method. Microstructure control of powders for sintering contributed to improve the microstructure at grain boundaries and to introduce magnetic flux pinning centers, both resulted in the improvement of superconducting transport current property. On the other hand, a magnetic nanocomposite for the remote sensing of stress in structural ceramics was fabricated by sol-gel method and solid state reaction. Successfully introduced nano-dispersoids of ferromagnetic materials by the sintering of nanocomposite powders resulted in the harmonization of added functionality and proper mechanical properties. Magnetic response to applied stress in structural ceramic matrix was detected as the result of amplified magnetostriction caused by the nano-size effect on ferromagnetic dispersoids.
Synthesis of high temperature superconductive and colossal magnetoresistive surfaces on insulating particles
Authors: Kumar D. , Fitz-Gerald J. , Singh R. K.
Published: April 2011

The surfaces of insulating alumina particles have been coated with high temperature superconducting, Yba2Cu3O7-x, and colossal magnetoresistive, Pr0.65Ba0.05 Ca0.3 Mn03-x, films. These coatings on particulate surfaces have been realized using a new technique which is based on laser assisted generation of homogeneous flux of ablated materials in front of a fluidized bed of host particles. The coated particulates have been characterized using scanning electron microscopy (SEM), energy dispersive x-ray (EDX) analysis, Auger electron spectroscopy (AES), and superconducting quantum interference device (SQUID) magnetometer.
Microstructure of Ultra High Dose Self Implanted Silicon
Authors: Zhu X. F. , Williams J. S. , Llewellyn D. J. , McCallum J. C.
Published: April 2011

This study has investigated the microstructure of ultra high dose (∼ 1018 cm−2) self implantation into Si. Implants have been carried out into both (100) Si and pre-amorphised Si as a function of implant temperature between liquid nitrogen temperature and 350°C. Results show that high dose implantation into completely amorphous Si (a-Si) produces layers which regrow quite well during subsequent solid phase epitaxy. In contrast, implantation into crystalline Si (c-Si) or part amorphous/part crystalline Si can lead to rich and varied microstructures at elevated temperatures, even extending to porous-like structures in some cases. Strong dynamic annealing and agglomeration of points defects in c-Si is thought to be responsible for such behaviour.
A Depth Selective Mössbauer Study of ion Implanted Stainless Steel
Authors: Walter G. , Stahl B. , Nagel R. , Gellert R. , Rück D. M. , Müller M. , Klingelhöfer G. , Kankeleit E. , Soltani-Farshi M. , Baumann H.
Published: April 2011

High austenitic stainless steel of composition Fe62Ni2OCrl8 was implanted with Eu ions and analyzed with Depth Selective Conversion Electron Mössbauer Spectroscopy (DCEMS). DCEMS gives information about the depth profile of phases, in this case about implantation induced changes in phase composition as function of depth. The samples were complementary analyzed with Rutherford Backscattering Spectrometry (RBS) to get the element profile of the implanted ions. The main experimental result is a martensitic transformed depth region that coincides with the Eu depth distribution. The potential of DCEMS for application in the field of materials modification by implantation techniques is demonstrated.
Crack Nucleation in ion Beam Irradiated Magnesium Oxide and Sapphire Crystals
Authors: Gurarie V. N. , Jamieson D. N. , Szymanski R. , Orlov A. V. , Williams J. S.
Published: April 2011

Monocrystals of magnesium oxide and sapphire have been subjected to ion implantation with 86 keV Si− ions to a dose of 5×1016 cm−2 and with 3 MeV H+ ions with a dose of 4.8×1017 cm−2 prior to thermal stress testing in a pulsed plasma. Fracture and deformation characteristics of the surface layer were measured in ion implanted and unimplanted samples using optical and scanning electron microscopy. Ion implantation is shown to modify the near-surface structure of samples by introducing damage, which makes crack nucleation easier under the applied stress. The effect of ion dose on the thermal stress resistance is investigated and the critical doses which produce a noticeable change in the stress resistance is determined for sapphire crystals implanted with 86 keV Si−. In comparison with 86 keV Si− ions the high energy implantation of sapphire and magnesium oxide crystals with 3 MeV H+ ions results in the formation of large-scale defects, which produce a low density crack system and cause a considerable reduction in the resistance to damage. Fracture mechanics principles are applied to evaluate the size of the implantation-induced microcracks which are shown to be comparable with the ion range and the damage range in the crystals tested. Possible mechanisms of crack nucleation for a low and high energy ion implantation are discussed.
Ternary Group-III-Nitrides Grown in Movpe Production Reactors
Authors: Schoen O. , Protzmann H. , Schwambera M. , Schineller B. , Heuken M. , Schmitz D. , Strauch G. , Juergensen H.
Published: April 2011

Using production scale AIXTRON MOCVD systems various heterointerfaces in the GaInN/GaN system have been studied in depth. GaInN single hetero layers were investigated to optimise photoluminescence properties. Several approaches of capping GaInN/GaN with another GaN layer to develop high quality double-hetero (DH) structures were presented. Using an optimised interfacing technique we obtain device quality DH structures with state of the art composition uniformity across a 2 inch wafer
The Effect of Doping On Nitrogen Activation Energy Level In 4H-SiC
Authors: Evwaraye A. O. , Smith S. R. , Mitchel W. C.
Published: April 2011

Thermal admittance spectroscopy has been used to study the thermal activation energy of nitrogen at the hexagonal and cubic sites in 4H-SiC as function of net doping concentration. The net doping concentration- of te samples, which was determined from 1/C2 vs. V plots, ranges from 1.5 × 1014 cm−3 to 4 × 1018 cm−3. The thermal activation energy of nitrogen was determined to be Ee O.054 eV and Ee O.101 eV for nitrogen at hexagonal and cubic sites respectively for ND - NA ≤ 1016 cm−3. As the free carrier concentration increases from 1016 cm−3 to 1.0 × 1018 cm3, the thermal activation energy of nitrogen at the hexagonal site decreases from 54 meV to 24 meV. At ND - NA ≥1.0 × 10 cm−3 hopping conduction is the only conduction mechanism and has an activation energy of 3-9 meV.
Influence of Metal Contamination on Minority Carrier Diffusion Length and Oxide Charge
Authors: Sakuma J. , Okui Y. , Miyazawa H. , Inoue F. , Miyajima M.
Published: April 2011

Many kinds of ULSI Circuit (DRAM, LOGIC, FRAM [1] etc.) are produced at the same production line to reduce the costs. So we have to control many kinds of metal contamination. We investigated the influence of metal contamination on minority carrier diffusion length and oxide charge. The metal impurities we studied are Fe, Cu, Ni, Cr, Al, Na, Ca, FRAM electrode metals (Pt, Ru), metals included in PZT ferro-electric capacitors (Pb, Zr, Ti) [2], metals added to PZT (La, Nb) [3], and metals used for SBT Ferro-electric capacitors (Sr, Bi, Ta) [4].
Deuterium Sintering of CMOS Technology for Improved Hot Carrier Reliability
Authors: Lee J. , Chen Z. , Hess K. , Lyding J.W.
Published: April 2011

It has been found that deuterium (D) instead of hydrogen (H) can be used to greatly strengthen the resistance of metal oxide semiconductor (MOS) transistors against hot carrier induced degradation. We have applied the new deuterium sintering process to CMOS technology and have obtained significantly improved hot carrier reliability resulting from the isotope effect. We will present a summary of these lifetime improvements from five different transistor structures of five different manufacturers, as well as the physical and electrical characterizations of the deuterium sintering process.
Defect Formation During Sublimation Bulk Crystal Growth of Silicon Carbide
Authors: Ohtani Noboru , Takahashi Jun , Katsuno Masakazu , Yashiro Hirokatsu , Kanaya Masatoshi
Published: April 2011

The defect formation during sublimation bulk crystal growth of silicon carbide (SiC) is discussed. SiC bulk crystals are produced by seeded sublimation growth (modified-Lely method), where SiC source powder sublimes and is recrystallized on a slightly cooled seed crystal at uncommonly high temperatures (≥2000°C). The crystals contain structural defects such as micropipes (hollow core dislocations), subgrain boundaries, stacking faults and glide dislocations in the basal plane. The type and density of the defects largely depend on the crystal growth direction, and many aspects are different between the growth parallel and perpendicular to the <0001> c-axis. Micropipes are characteristic defects to the c-axis growth, while a large number of stacking faults are introduced during growth perpendicular to the c-axis. We discuss the cause and mechanism of the defect formation
Noble Gas Induced Defects in Silicon
Authors: Weber J. , Estreicher S.K.
Published: April 2011

Low energy bombardment of silicon with noble gas ions generates a family of defects with characteristic low-temperature photoluminescence spectra. The defect distribution up to one gtm below the sample surface indicates an unusually enhanced migration mechanism during the bombardment of the specimen. Annealing the samples above 500 °C leads to the disappearance of the photoluminescence spectra and the formation of new, more extended defects, which are excellent gettering sites for transition metals, in particular copper. Systematic calculations of noble-gas vacancy interactions imply a model for the photoluminescing defect where the noble gas atom is trapped by a divacancy.
Highly Efficient Nitrogen Doping Into GaAs Using Low-Energy Nitrogen Molecular Ions
Authors: Shima Takayuki , Makita Yunosuke , Kimura Shinji , Sanpei Hirokazu , Fukuzawa Yasuhiro
Published: April 2011

Low-energy N2+ molecular-ions were irradiated during the epitaxial growth of GaAs. Ion acceleration energy and ion beam current density were varied in the range of 30-200 eV and 3-37 nA/cm2, respectively. GaAs growth rate was kept constant at 1µm/ h and the thickness of N-doped GaAs layer was about 1 µm. N concentration was obtained by using secondary ion mass spectroscopy. Strong N-related emissions were observed in the low-temperature photoluminescence spectra, which indicates that N atom is efficiently substituted at As site and is optically active as an isoelectronic impurity
Crack Propagation Experiments on Flip Chip Solder Joints
Authors: Wiese S. , Feustel F. , Rzepka S. , Meusel E.
Published: April 2011

The paper presents crack propagation experiments on real flip chip specimens applied to reversible shear loading. Two specially designed micro testers will be introduced. The first tester provides very precise measurements of the force displacement hysteresis. The achieved resolutions have been I mN for force and 20 nm for displacement. The second micro tester works similar to the first one, but is designed for in-situ experiments inside the SEM. Since it needs to be very small in size it reaches only resolutions of 10 mN and 100nm, which is sufficient to achieve equivalence to the first tester. A cyclic triangular strain wave is used as load profile for the crack propagation experiment. The experiment was done with both machines applying equivalent specimens and load. The force displacement curve was recorded using the first micro mechanical tester. From those hysteresis, the force amplitude has been determined for every cycle. All force amplitudes are plotted versus the number of cycles in order to quantify the crack length. With the second tester, images were taken at every 10th … 100th cycle in order to locate the crack propagation. Finally both results have been linked together for a combined quatitive and spatial description of the crack propagation in flip chip solder joints.
Quantitative Measurements of Segregation In Co-Cr-X Magnetic Recording Media by Energy-Filtered Transmission Electron Microscopy
Authors: Bentley J. , Wittig J.E. , Nolan T.P.
Published: April 2011

Reliable core-loss spectroscopic methods have been developed for mapping elemental segregation in Co-Cr-X magnetic recording media by energy-filtered transmission electron microscopy. Extraction of quantitative compositions at a spatial resolution approaching 1 nm involves sophisticated treatments for diffraction contrast, variations in specimen thickness, and closely-spaced oxygen K and chromium L23 ionization edges. These methods reveal that intergranular chromium levels are ∼25 at.% for random-angle boundaries and ∼15 at.% for 90° boundaries in films of Co84Cr12Ta4 d.c. magnetron sputtered at 250°C.
Macroscopic Probing of the Joint Between Metals in Mr Heads
Authors: Geng Jibin , Yan X. , Zhang X.X. , Zhang Xiaofeng , Wang N. , Fung K.K.
Published: April 2011

During the wafer manufacturing process of magnetoresistive (MR) heads which are widely used in Hard Disk Drives, the metal leads are deposited on both sides of the MR sensing element through the photoresist masks. Due to the shadowing effect of the photoresist, there may be some contamination at joint interfacial region even after ion etching. This introduces additional contact resistance and causes some region of the sensing element to be unpinned. As the geometry of the sensor element decreases, and the contamination, located in regions of few thousands of angstroms, is becoming more severe for MR head than ever. In this paper, we developed a systematic method to evaluate the contact resistance between the two metal layers. A comparison was made between the magnetic read width and the physical width. Finally TEM analysis successfully revealed the interfacial junction contamination.
Interparticle Interaction Effects in Nonmiscible CoAg Thin Films With High Co Concentration
Authors: Butera A. , Barnard J. A.
Published: April 2011

A series of Co-rich CoAg heterogeneous thin films, with Co concentrations greater than 65 % volume fraction and film thickness in the range 5 nm - 50 nm, was prepared by dc magnetron sputtering. Annealing in high vacuum (P < 3x10-7 Torr) above 400°C was necessary to promote phase separation between the two elements. Maximum room temperature coercivities, Hc ∼ 900 Oe, were obtained at a thickness of 20 nm for CoAg 70:30 vol % films. These coercivities are almost two orders of magnitude larger than the values observed in as-deposited films. The concentration of maximum coercivity, that is usually associated to the threshold for magnetic percolation, is much higher than the 40-50 vol % commonly observed in bulk granular materials. The shift in the magnetic percolation limit was related to the reduced dimensionality of the very thin films. Coercivity was found to vary both with film composition and with thickness. Delta M curves and time decay (magnetic viscosity) measurements were done to determine the interparticle interactions and the activation volumes. A maximum in the remanent coercivity (coincident with the maximum in Hc) was found for a film thickness φ ∼ 15-20 nm in all the alloys. At this same thickness a negative minimum in the interparticle interaction parameter α (indicating that the particle interactions favor the demagnetized state) was observed. The absolute value of a increases for larger Co concentrations. The irreversible susceptibility is an increasing function of film thickness and the magnetic viscosity has a minimum for φ ∼ 15-20 nm. The activation volume also increases with thickness, changing from (15 nm)3 to (40 nm)3 for the more diluted alloys, values similar to the average particle size determined by transmission electron microscopy.
Faraday Effect Devices, Optical Isolators
Authors: Wilson Donald K.
Published: April 2011

Although discovered over 150 years ago, it was not until the 1970's that materials were developed that enabled magneto-optic (Faraday) effect devices of practical sizes. These developments are: magneto-optic materials with high Verdet constants, and the rare-earth magnet materials, capable of extremely high magnetic fields.

The magneto-optic effect has enabled development of equipment used in diverse laser applications, from industrial use to fiber-optic telecommunications.

The principle of operation of optical isolators and circulators is described herein, as well as descriptions of critical components in such equipment, such as the polarizers and the magnets.
Steel and Titanium Hollow Sphere Foams
Authors: Hurysz K. M. , Clark J. L. , Nagel A. R. , Hardwicke C. U. , Lee K. J. , Cochran J. K. , Sanders T. H.
Published: April 2011

Metal hollow sphere foams are fabricated by bonding millimeter sized metal alloy hollow spheres at points of contact. The spheres are formed as powder shells from slurries. For stainless steel spheres, the starting powder is a mixture of iron and chromium oxide. Thermal treatment in hydrogen reduces the oxides to Fe/Cr alloys with less than 2% porosity in sphere walls. The nominal composition is close to that of 405 stainless. Carburization in CO/CO2 atmosphere followed by heat treatment produces foams of either 410 or 420 type stainless steels depending on carbon content. Compressive stress-strain behavior was measured on point contact bonded stainless foams both before and after carburization. Hardness measurements on steel sphere walls were used to estimate the yield strength. Relative strengths of the foams were positioned between open and closed cell models. This was encouraging because bonding in the foams was less than optimum and the hollow sphere walls contained defects. As processing improves, strengths should increase. To produce titanium alloy spheres, the starting powder is titanium alloy hydride. Thermal treatment in an inert atmosphere decomposes the hydride and sinters the titanium powder in the sphere walls to greater than 96% relative density. Both titanium and Ti-6V-4V spheres and foams have been produced. Oxygen contents are a concern for titanium compositions and processing is being altered to reduce oxygen levels to increase ductility
Meeting RTP Temperature Accuracy Requirements: Measurement and Calibrations at Nist
Authors: Lovas F. J. , Tsai B. K. , Gibson C. E.
Published: April 2011

Although radiometric temperature measurement in rapid thermal processing (RTP) tools has substantially improved in terms of repeatability and uniformity, it still remains a technical challenge. The 1999 requirements of 180 nm line width technology in the 1997 National Technology Roadmap for Semiconductors (NTRS) imply an uncertainty of ± 2 °C in temperature measurement, which will continue the challenge in temperature measurement. In this paper we will discuss the NIST absolute radiometric temperature calibration, measurements, and uncertainty analysis.
Alternative Gate Dielectrics with BST/TIO2/(Barrier Oxide) Stacked Structure
Authors: Jeon Yongjoo , Lee Byoung Hun , Zawadzki Keith , Qi Wen-Jie , Lee Jack C.
Published: April 2011

BST/TiO2/(Barrier Layer) stacked dielectric structure has been proposed for ultra thin (<20Å) gate dielectric application to overcome the direct tunneling current problem of Si02. To characterize the alternative dielectrics, MIM and MIS capacitors were fabricated. TiO2 is believed to prevent BST and Si from reaction and interdiffusion while TiC2 itself is stable due to the strong binding energy. For better interfacial quality of TiO2/Si interface, proper barrier layer is needed between TiO2 and Si. Optimization of this barrier layer was performed by RTP grown N20 oxide and self-grown interfacial oxide layer with various annealing conditions. To monitor these barrier layers, TEM and electrical analysis were performed. From TEM observation, it was found that interfacial layer was formed in every sample whether it was intentionally grown or not. It was observed that the leakage current of Pt/TiO2/Si dramatically increased after 700'C or higher temperature annealing. This might be related to the transition of crystal structure of TiO2 from anatese to rutile at about 700°C[1]. It was also found that both Pt/BST/TiO2/Si and Pt/TiO2/Si showed lower leakage current compare to the conventional NO oxide at comparable equivalent SiO2 thickness. These results imply that these materials hold some promise as alternatives of pure SiO2 in very thin range.
Chemical Stability of Advanced Metal Gate and Ultra-thin Gate Dielectric Interface During Rapid Thermal Annealing
Authors: Claflin B. , Binger M. , Lucovsky G.
Published: April 2011

The chemical stability of the compound metals TiNx and WNx on SiO2 and SiO2/Si3N4 (ON) dielectric stacks is studied by on-line Auger electron spectroscopy (AES) following sequential rapid thermal annealing treatments of 15 - 180 s up to 850 °C. The TiNx/SiO2 interface reacts at 850 °C and the reaction is kinetics driven. The TiNx/Si3N4 interface is more stable than TiNx/SiO2 even after a 180 s anneal at 850 °C. WNx is stable below 650 °C both on SiO2 and Si3N4, but above this temperature the film changes, possibly due to crystallization or interdiffusion. The changes in the WNx film are not controlled by kinetics. The compound metals are chemically more stable at elevated temperatures than pure Ti or W on SiO2.
Simulation of Rapid Thermal Annealed Boron Ultra-Shallow Junctions in Inert and Oxidizing Ambient
Authors: Lerch W. , Glück M. , Stolwijk N. A. , Walk H. , Schäfer M. , Marcus S. D. , Downey D. F. , Chow J. W. , Marquardt H.
Published: April 2011

Rapid Thermal Annealing (RTA) is indispensable for the formation of ultra-shallow source/drain junctions. To improve the annealing conditions, a fundamental understanding of the influences on the diffusion/activation process is necessary. Ion implantations of 1 keV boron at a dose of Φ≈1 I.1015 cm-2 are annealed in a SHS2800E RTP-system under controlled concentrations of oxygen in nitrogen ambient (0-1 ppm up to 1%). Concentration-depth profiles, measured by Secondary Ion Mass Spectroscopy (SIMS), are simulated within the framework of the kickout model involving diffusion enhancement via supersaturation of silicon self-interstitials. The validity of this interpretation is supported by the simulated results which are in good agreement with expenimental data. After RTA for 10 s at 1050°C the junctions are varying within a range of 800Å to 1400Ådepending on the annealing ambient. The results of the simulation yield finite values of self-interstitial supersaturation as a function of the oxygen concentration.
Novel Applications of Rapid Photothermal Chemical Vapor Deposition
Authors: Singh R. , Parihar V. , Chen Y. , Poole K. F. , DeBoer S. , Thakur R. P. S. , Sharangpani R. , Vasudev P. K.
Published: April 2011

In recent years, we have developed rapid photothermal chemical vapor deposition (RPCVD) technique. In RPCVD, photons with wavelength between 100–400 nm irradiate the side of the substrate where chemical reactions take place. RPCVD provides materials with minimum microscopic defects and minimum thermal and residual stress. Due to these features and low processing time and low processing temperature capabilities, RPCVD is ideal for process integration and manufacturibility. In this paper we have presented the results of high K and low K dielectrics. Detailed electrical, structural, characterization, and stress measurements combined with reliability of data indicate that RPCVD has the potential of meeting advanced manufacturing needs of semiconductor and other related industries.
Iron-Silicate Glassy Films by Sol-Gel Conversion Induced by Rapid Thermal Processing
Authors: Van De Leest René E. , Roozeboom Fred
Published: April 2011

The sol-gel system iron triethoxide - tetraethylorthosilicate (TEOS) with the Fe/Si atomic ratio ranging from 0 to 1 has been investigated. Our study leads to the conclusion that the annealing method of the hydrolyzed precursor film determines the type of solid film formed. Annealing by Rapid Thermal Processing (RTP) with its high heating and cooling rates yields amorphous, glassy iron silicate films. These films result from polycondensation reactions between Si-OH and Fe-OH groups of the hydrolyzed precursors forming Fe-O-Si and Si-O-Si bonds. These bonds show a characteristic vibration band in FTIR spectra, which is most intense for Fe/Si = 1, and shifts for increasing Fe/Si ratio from 1073 down to 965 cm-1.

The iron silicate film with Fe/Si =1 obtained by RTP displays an optical absorption band around 320 nm, which indicates that Fe3+-ions have a tetrahedral coordination similar to the Si4+-ions in Si02 and glass with tetrahedrally coordinated silicon and iron ions linked by bridging oxygen atoms. The films, typically 0.1 μm thick, annealed by RTP have a smooth, mechanically hard surface. This glassy structure can be formally presented as FeSiOx. Conventional furnace heating with low heating/cooling rates yields nanocrystalline films with predominantly Si-O-Si bonding in grains with sizes below 40 nm. More structural and chemical investigation is needed to elucidate the details of the structure and the formation mechanism of the amorphous compound, but we can conclude that the cooling rate has a direct effect on the degree of non-crystallinity of the compound. The high cooling rate of RTP will retain the Fe-O-Si bonds formed in a state of inequilibrium, and “quench” them in an amorphous, metastable glass compound, whereas slow cooling gives rise to nanocomposite film formation.
Three Dimensional Simulation of the Morphological Evolution of a Strained Film on a Thick Substrate
Authors: Chiu Cheng-hsin
Published: April 2011

This paper presents a three-dimensional simulation for the surface evolution of a strained film on a thick substrate. The simulation shows that an initially random morphology will first transform into a profile dominated by two-dimensional ridges, and then into a three-dimensional island surface. The simulation also demonstrates that the ridge-island transition is a kinetic process which can be delayed by changing the initial morphology.
The Origin of Mis-Oriented Diamond Grains Nucleated Directly on (001) Silicon Surface
Authors: Zhang R.Q. , Zhang W.J. , Sun C. , Jiang X. , Lee S.-T.
Published: April 2011

The origin of mis-oriented diamond grains frequently observed in heteroepitaxial diamond films on (001) silicon surfaces was studied. By statistically analyzing the in-plane rotation angles of diamond grains in scanning electron microscopy observations, it was found that the distribution of the grain orientation is not random and two satellite distribution peaks at about 20° and 30° accompany the main distribution peak at zero degree referenced to the <110> direction of substrate. The interface structure corresponding to the main distribution peak at zero degree of oriented diamond growth has been proposed in our previous studies. In this study, our molecular orbital PM3 simulation of a step-by-step diamond nucleation further reveals two other metastable diamond/silicon interfacial structures. The orientations of the corresponding diamond grains are parallel to the (001) silicon surface but with in-plane rotations of 20° and 30° respectively with respect to the <110> direction. We relate these two mis-oriented growths to the two satellite peaks of grain orientation distribution. Based on this study, the possibility in experiment to reduce the formation of mis-oriented configurations and to obtain a perfectly oriented diamond growth is discussed.
Simulating Phase Transformations with the Cahn-Hilliard Equation – Potential and Limitations –
Authors: Löchte Lothar , Gottstein Günter
Published: April 2011

An extension of the classical Cahn-Hilliard equation, including elastic interactions is presented. This generalized diffusion equation allows real time simulation of phase-transformations, such as GP-zone formation in a near-commercial ΔICu alloy. No a priori assumptions about kinetics, diffusion fields, as well as precipitate shape are necessary. Shape of precipitates and kinetic of simulated GP-zone formation are in qualitatively good agreement with experiments of Sato and Takahashi, and the concurrenltly derived interfacial energies are reasonable.

Two algorithms for a numerical solution of the Cahn-Hilliard equation are presented. While the simple finite difference scheme does not converge, a slightly more complicated Fourier spectral method behaves reasonable as tested for a synthetic chemical potential.
Dense-WDM Components and Systems: A Reliability Overview
Authors: Etemad Shahab
Published: April 2011

In this paper we review field data from failures related to materials and devices that are the building blocks of optically amplified dense-wavelength division multiplexed (DWDM) transmission systems. A DWDM transmission system consists of at least three distinct components: an optical multiplexer, one or more optical fiber amplifiers (OFAs), and an optical demultiplexer. A tandem arrangement of these components performs the function currently up to 40 independent high speed optical communications channels (about 2 million phone calls) over a single fiber link. Of these components, OFAs are considered the workhorse of this new technology, and, as with any new technology, their reliability is the focus of considerable attention. Commercially available OFAs are erbium-doped silica or fluoride fibers that operate in the 1550 nm optical communication window. Such OFAs consist of an active Er-doped fiber and pump laser(s) that collectively are referred to as the gain module, passive optical components used for routing, and electronic components for monitoring and operational support. We present the result of the failure analysis for each part as well as their role in the failure of the OFA. Using the data from systems deployed in the field, we summarize the history of failures of OFAs and other components and discuss their impact on the reliability of the DWDM system as a whole. From a material, packaging and system integration point of view, we address the reliability merits of different designs that, by and large, perform the same overall function. Finally, we shall outline how network providers that deploy such DWDM systems would benefit from a manufacturing strategy that incorporates reliability in its initial steps starting with the materials and packaging needs.
Fracture and Abrasion Resistance Tests for Optical Fiber Coatings
Authors: Wissuchek D. J. , Walter D. J. , Clark D. A. , Glaesemann G. S.
Published: April 2011

The properties of the optical fiber buffer coating play a critical role in the strength and handleability of optical fibers. Tests have been developed to measure a coating's resistance to mechanical damage. Two such tests are described here. The indentation rupture test involves indenting coated fiber with diamond pyramids and measuring the load at which the pyramid punctures the coating. Finite element analysis is used to determine the strain energy absorbed by plastic deformation of the coating. The toughness of the outer coating layer and the toughness of the inner coating/glass interface can be determined from the crack dimensions produced during rupture of the coating. Strength after mechanical abrasion is a procedure wherein a hollow tube of coating is removed from an optical fiber and subsequently bombarded with an abrasive grit. The effects of the abrasion event are measured by a tensile test of the tube. Results for both tests are obtained for two coating systems. The validity of the tests for measuring coating properties is discussed.
Impact Damage and Strength Degradation of Fused Silica
Authors: Ritter J. E. , Jakus K. , Panat R. P.
Published: April 2011

Fused silica in service can suffer from strength degradation due to a localized contact load or particle impact that can cause cracking about the indentation or impact site. This cracking generally consists of radial, lateral, and cone cracks and is independent of whether the indenter or particle is sharp or blunt or whether the impact is subsonic or hypervelocity. The impact site is generally characterized by a shallow pit surrounded by an array of microcracks. The pit is formed by the fragmentation of the glass due to the intersecting radial, lateral, and cone cracks. With either static indentation or particle impact, it is the radial crack that controls strength degradation. The applicability of indentation fracture mechanics in predicting this strength degradation is discussed.
Photoluminescence and Photoluminescence Excitation Spectroscopy of In Situ Er-Doped and Er-Implanted GaN Films Grown by Hydride Vapor Phase Epitaxy
Authors: Kim S. , Li X. , Coleman J. J. , Zhang R. , Hansen D. M. , Kuech T. F. , Bishop S. G.
Published: April 2011

Photoluminescence (PL) and photoluminescence excitation (PLE) spectroscopy have been carried out at 6K on the 1540 nm 4I13/2 ← 4I15/2 emission of Er3+ in in situ Er-doped and Er-implanted GaN grown by hydride vapor phase epitaxy (HVPE). The PL and PLE of these two different Er-doped HVPE-grown GaN films are compared with Er-implanted GaN grown by metal organic chemical vapor deposition (MOCVD).

In the in situ Er-doped HVPE-grown GaN, the lineshape of the broad PLE absorption bands and the broad PL bands is similar to that in Er-doped glass. The PL spectra of this in situ Er-doped sample are independent of excitation wavelength, unlike the PL of the Er-implanted GaN. These PL spectra are quite different from the site-selective PL spectra observed in the Er-implanted GaN, indicating that the seven different Er sites existing in the Er-implanted MOCVD-grown GaN are not observed in the in situ Er-doped HVPE-grown GaN. Four of the seven different Er3+ sites observed in the Er-implanted MOCVD-grown GaN annealed at 900°C under a flow of N2 are present in the Er-implanted HVPE-grown GaN annealed at 800°C in an NH 3/H2 atmosphere.
GaN Growth by Remote Plasma MOCVD: Chemistry and Kinetics by Real Time Ellipsometry
Authors: Losurdo M. , Capezzuto P. , Bruno G.
Published: April 2011

Cubic and hexagonal GaN layers have been grown on GaAs (001) and α-Al2O3 (0001) substrates, respectively, by remote plasma metalorganic chemical vapor deposition (RPMOCVD). In situ spectroscopic ellipsometry is used to monitor in real time the chemistry and kinetics of the GaN growth. The subtrate/GaN interface formation is highlighted and the effect of the substrate plasma nitridation on the initial growth stage is discussed.
Characterization of Be-Implanted GaN Annealed at High Temperatures
Authors: Ronning C. , Linthicum K.J. , Carlson E.P. , Hartlieb P.J. , Thomson D.B. , Gehrke T. , Davis R.F.
Published: April 2011

Single crystalline (0001) gallium nitride layers were implanted with beryllium and subsequently annealed within the range of 300-1100°C for 10-60 minutes under a flux of atomic nitrogen obtained using a rf plasma source. The nitrogen flux protected the GaN surface from decomposition in vacuum at high temperatures. SIMS measurements revealed that no long range diffusion of the implanted Be occurred at 900 or 1100°C. XRD spectra showed defect-related peaks in the as-implanted samples; these peaks disappeared upon annealing at 900°C and higher for 10 minutes. Photoluminescence (PL) measurements showed one new line at 3.35 eV which provided strong evidence for the presence of optically active Be acceptors.
Thermal Residual Stress Modeling in Ain and GaN Multi Layer Samples
Authors: Wang Kai , Reeber Robert R.
Published: April 2011

Thermal residual stresses can detrimentally affect the electronic and optical properties of epitaxial films thereby shortening device lifetime. Based on our earlier work on thermal expansion of nitrides, we provide a finite element modeling analysis of the residual stress distribution of multilayered GaN and AlN on 6H-SiC. The effects of thickness and growth temperatures are considered in the analysis.
Gallium Nitride Growth Using Diethylgallium Chloride as an Alternative Gallium Source
Authors: Zhang Ling , Zhang Rong , Boleslawski Marek P. , Kuech T.F.
Published: April 2011

Metal organic vapor phase epitaxy (MOVPE) of GaN has been carried out using diethyl gallium chloride (DEGaCI) and ammonia. The growth rate and efficiency of the DEGaCl-based growth decreases with increasing temperature when compared to trimethyl gallium (TMG)-based growth under similar conditions. Both low temperature buffer and the high temperature GaN layers were grown using the DEGaCI-NH3 precursor combination on the basal plane of sapphire and compared to similar structures grown using TMG and NH3. DEGaCl-based growth reveals an improved growth behavior under identical growth conditions to the conventional TMGa and ammonia growth. X-ray, Hall, and atomic force microscopy (AFM) measurements have been carried out on these samples providing a direct comparison of materials properties associated with these growth precursors. For the DEGaCl-based growth, the x-ray rocking curve line width, using the (0002) reflection, is as low as 300 arcsec on a 2.5-micron thick film. A RMS surface roughness of ∼0.5nm measured over a 10x10 micron area.
Behavior of W and WSix Contact Metallization on n- and p- Type GaN
Authors: Cao X. A. , Ren F. , Lothian J. R. , Pearton S. J. , Abernathy C. R. , Zolper J. C. , Cole M. W. , Zeitouny A. , Eizenberg M. , Shul R. J.
Published: April 2011

Sputter-deposited W-based contacts on p-GaN (NA∼1018cm-3) display non-ohmic behavior independent of annealing temperature when measured at 25°C. The transition to ohmic behavior occurs above ∼250°C as more of the acceptors become ionized. The optimum annealing temperature is ∼700°C under these conditions. These contacts are much more thermally stable than the conventional Ni/Au metallization, which shows a severely degraded morphology even at 700°C. W-based contacts may be ohmic as-deposited on very heavily doped n-GaN, and the specific contact resistance improves with annealing up to ∼900°C.
Characterization of Flicker Noise in GaN Based Modfets at Low Drain Bias
Authors: Hol W.Y. , Fong W.K. , Suryal C. , Tong K.Y. , Kim W. , Botcharev A. , Morkoc H.
Published: April 2011

We report systematic characterizations of flicker noise in GaN based MODFETs. Flicker noise was measured across the channel of the devices from room temperature to 130 K. The voltage noise power spectra, Sv(f) were found to be proportional to l/f, where γ depends on the device temperature as well as the gate bias. Study of Sv(f) as a function of the biasing condition was conducted in detail and was found to vary as VD2/(VG-VT)β where β changes with temperature from about 2.1 at room temperature to about 0.9 at 130K. Analyses of the data showed that the noise originated from thermal activation of carriers to localized states in the channel area. The data suggested that the trapping and detrapping of carriers did not lead to fluctuations in the carrier concentration as postulated in the McWhorter's model. However, more work is needed to determine if surface mobility fluctuations played key role in the l/f noise.
Symmetry of Electrons and Holes in Lightly Photo-Excited InGaN LEDs
Authors: Kennedy T.A. , Glaser E.R. , Carlos W.E. , Ruden P.P. , Nakamura Shuji
Published: April 2011

The symmetry of the recombining electrons and holes in lightly photo-excited InGaN LEDs revealed through ODMR is related to the physical structure, band structure and defects present. Calculations of the electron-g within the k•p formalism give the average shift from the free-electron value for GaN but are not fully reconciled with the anisotropy. This theory is also extended to InGaN alloys for both pseudomorphic and relaxed layers. The average shift is close to the experimental values for the green LED. The strongly reduced hole anisotropies seen experimentally are explained by a recently published theory for acceptors in GaN.
Fabrication of Smooth GaN-Based Laser Facets
Authors: Stocker D. A. , Schubert E. F. , Boutros K. S. , Redwing J. M.
Published: April 2011

A method is presented for fabricating fully wet-etched InGaN/GaN laser cavities using photoenhanced electrochemical wet etching followed by crystallographic wet etching. Crystallographic wet chemical etching of n- and p-type GaN grown on c-plane sapphire is achieved using H3PO4 and various hydroxides, with etch rates as high as 3.2 μm/min. The crystallographic GaN etch planes are {0001}, {1010}, {1011}, {1012}, and {1013}. The vertical {1010} planes appear perfectly smooth when viewed with a field-effect scanning electron microscope (FESEM), indicating a surface roughness less than 5 nm, suitable for laser facets. The etch rate and crystallographic nature for the various etching solutions are independent of conductivity, as shown by seamless etching of a p-GaN/undoped, high-resistivity GaN homojunction.
Group-III Nitride Etch Selectivity in BCl3/Cl2 ICP Plasmas
Authors: Shul R. J. , Zhang L. , Willison C. G. , Han J. , Pearton S. J. , Hong J. , Abernathy C. R. , Lester L. F.
Published: April 2011

Patterning the group-III nitrides has been challenging due to their strong bond energies and relatively inert chemical nature as compared to other compound semiconductors. Plasma etch processes have been used almost exclusively to pattern these films. The use of high-density plasma etch systems, including inductively coupled plasmas (ICP), has resulted in relatively high etch rates (often greater than 1.0 μm/min) with anisotropic profiles and smooth etch morphologies. However, the etch mechanism is often dominated by high ion bombardment energies which can minimize etch selectivity. The use of an ICP-generated BCl3/Cl2 plasma has yielded a highly versatile GaN etch process with rates ranging from 100 to 8000 Å/min making this plasma chemistry a prime candidate for optimization of etch selectivity. In this study, we will report ICP etch rates and selectivities for GaN, AIN, and InN as a function of BCl3/C12 flow ratios, cathode rf-power, and ICP-source power. GaN:InN and GaN:AIN etch selectivities were typically less than 7:1 and showed the strongest dependence on flow ratio. This trend may be attributed to faster GaN etch rates observed at higher concentrations of atomic Cl which was monitored using optical emission spectroscopy (OES).
Cross-Sectional and Plan-View Observation of Cracks Introduced in Si at the Ductile-Brittle Transition Temperature
Authors: Suprijadi  , Saka H.
Published: April 2011

Mode I cracks introduced in Si at the ductile-brittle transition temperature (DBTT) have been examined extensively using transmission electron microscopy. Cross-sectional as well as plane-view specimens suitable for the observation were prepared using a focused ion beam technique. Many small dislocation loops nucleate at the fracture surface of a mode I crack during the propagation at DBTT.
Unstable Stacking Fault Free Energies in Silicon through Empirical Modeling
Authors: De Koning M. , Antonelli A. , Bazant Martin Z. , Kaxiras Efthimios , Justo J.F.
Published: April 2011

The temperature dependence of unstable stacking fault free energies on glide and shuffle {111} planes in silicon is investigated using a finite temperature molecular dynamics approach which includes a full treatment of anharmonic vibrational effects. The results are compared to earlier zero temperature ab initio calculations in which finite temperature effects were estimated using a harmonic approximation to transition state theory (TST). The unstable stacking free energies are interpreted within the framework of Rice‘s dislocation nucleation criterium to characterize a possible change from shuffle to glide plane dominance in the context of dislocation nucleation processes at a sharp crack tip. Such a change may be related to the abrupt brittle-ductile transition observed in silicon.
Simulation of Void Growth at High Strain-Rate
Authors: Belak J. , Minich R.
Published: April 2011

The dynamic fracture (spallation) of ductile metals is known to initiate through the nucleation and growth of microscopic voids. Here, we apply atomistic molecular dynamics modeling to the early growth of nanoscale (2nm radius) voids in face centered cubic metals using embedded atom potential models. The voids grow through anisotropic dislocation nucleation and emission into a cuboidal shape in agreement with experiment. The mechanism of this nucleation process is presented. The resulting viscous growth exponent at late times is about three times larger than expected from experiment for microscale voids, suggesting either a length scale dependence or a inadequacy of the molecular dynamics model such as the perfect crystal surrounding the void.
Mechanisms of Intergranular Fracture
Authors: Farkas Diana
Published: April 2011

We present a study of the atomistic mechanisms of crack propagation along grain boundaries in metals and alloys. The failure behavior showing cleavage crack growth and/or crack-tip dislocation emission is demonstrated using atomistic simulations for an embedded-atom model. The simulations follow the quasi-equilibrium growth of a crack as the stress intensity applied increases. Dislocations emitted from crack tips normally blunt the crack and inhibit cleavage, inducing ductile behavior. When the emitted dislocations stay near the crack tip (sessile dislocations), they do blunt the crack but brittle cleavage can occur after the emission of a sufficient number of dislocations. The fracture process occurs as a combination of dislocation emission/micro-cleavage portions that are controlled by the local atomistic structure of the grain boundary. The grain boundary is shown to be a region where dislocation emission is easier, a mechanism that competes with the lower cohesive strength of the boundary region.
Mobility of Non-Planar Screw Dislocations ahead of a Mode III Crack Tip
Authors: Ngan A.H.W. , Zhang H.F.
Published: April 2011

The generalised Peierls-Nabarro model is used to study the transformation of screw dislocation cores from the three-fold, non-planar state to the planar, glissile state ahead of a mode mll crack tip.