bluuebunny/crossref_metadata_2025 huggingface dataset:
Crystallization of Amorphous Thin BST/MgO(001) Films Grown by R.F. Magnetron Sputtering
Authors: Noh D. Y. , Lee H. H. , Je J. H. , Kim H. K.
Published: April 2011

The crystallization of amorphous BST thin films was studied in a synchrotron x-ray scattering experiment. At around 600°C, an intermediate phase, which was suspected to be a metastable pyrochlore phase, was formed. The x-ray reflectivity curves showed that the film-substrate interface became rough as the pyrochlore-like phase was formed. This suggests that the pyrochlore phase was nucleated near the interface area. Upon further annealing to higher temperatures, the film transformed to the crystalline perovskite phase. The crystallization was sensitive to the film thickness. In the thin 550Å thick film, the crystallization occurred at 750 °C with the <001> preferred orientation. On the other hand, the 5500Å thick film became crystalline even at 500°C with random crystalline orientation. The observed thickness dependence of the crystallization suggests that the crystalline perovskite phase was nucleated in the bulk of the film, rather than the near interface area.
Measurement of Effective Longitudinal Piezoelectric Coefficient of thin Films by Direct Piezoelectric Effect
Authors: Xu F. , Chu F. , Shepard J. F. , Trolier-McKinstry S.
Published: April 2011

This paper presents a new method for the measurement of the longitudinal piezoelectric coefficient of piezoelectric thin films using the direct piezoelectric effect. A uniform uniaxial stress was applied to the piezoelectric thin film by high-pressure gas and the induced charge was collected and measured by a charge integrator. The effective longitudinal piezoelectric coefficient of lead zirconate titanate (PZT) 52/48 thin films made by sol-gel processing was measured by this method. Undoped films typically have d33 values of ∼ 5 pC/N, while poled films have values up to 220 pC/N.
PZT/PVDF Composite for Actuator/Sensor Application
Authors: Kowbel W. , Xia X. , Withers J. C. , Crocker M. J. , Wada B. K.
Published: April 2011

Currently, smart structures utilize both polymeric sensor and PZT-based actuators. The benefit of self-sensing calls for the development of integrated actuator/sensor composites. This paper addresses the development of this new class of smart materials. Porous PZT ceramics were fabricated by several techniques. PVDF was subsequently infiltrated within the controlled porosity PZT. In addition, PVDF or its blends and PZT powders were in-situ processed to generate controlled piezo and mechanical property composites. Both actuating and sensing of this new class of composite materials were studied. The paper presents the processes-structure-property relationship of this new class of piezocomposites.
Strontium Bismuth Tantalate Based Ferroelectric Gate Field Effect Transistor with Yttrium Oxide as the Buffer Layer
Authors: Lim Myoung-Ho , Kalkur T. S. , Kim Yong-Tae
Published: April 2011

We report the first demonstration of an enhancement mode n-channel metal -ferroelectric-semiconductor field effect transistor (MFISFET) realized directly on silicon with yttrium oxide as the buffer layer. The capacitance-voltage (C-V) characteristics of Metal Ferroelectric Insulator Silicon (MFIS) structures show hysteresis and the direction of hysteresis corresponds to ferroelectric polarization. The memory window in the C-V characteristics was 2V for an applied voltage of ± 10V. The memory window did not show significant change due to decrease in rate of change of sweep voltage and temperature. The transmission electron microscopy (TEM) analysis confirms the formation of an amorphous oxide layer between silicon and yttrium oxide buffer layer.
A Multi-Technique Analysis of MOCVD- Grown Lead Lanthanum Titanate (Pb1−xLax)TiO3Thin Films on Quartz Substrates
Authors: Chen H. Y. , Lin J. , Tan K. L. , Feng Z. C. , Kwak B. S. , Erbil A.
Published: April 2011

A series of Lead lanthanum titanate (Pb1−xLax)TiO3thin films with different compositions of x = 0 − 0.33 have been grown on fused quartz substrates by metalorganic chemical vapor deposition (MOCVD) and analyzed by a variety of techniques including X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), Raman scattering spectroscopy (RSS) and diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) techniques. XPS results confirmed the film composition of (Pb1−xLax)TiO3and lanthanum enrichment in top surface layers. XRD indicates a preferred (100) orientation for the films with x values of 0.05–0.17, while the films with x values above 0.32 have randomly distributed orientations. A gradual change in the crystal structure from tetragonal to cubic arrangement with increasing La composition is noted. XPS data also show the variation of Ti-O, Pb-0 and La-0 bonding with the change in the La composition. The stretching vibrations corresponding to these oxygen related bonding are observed by DRIFT at 667, 826, 936 and 529 cm−1respectively. This combined investigation on epitaxial PLT films may enhance our understanding of the ferroelectric PLT materials.
The Impact of Domains on the Dielectric and Electromechanical Properties of Ferroelectric Thin Films
Authors: Trolier-McKinstry S. , Aungkavattana P. , Chu F. , Lacey J. , Maria J-P. , Shepard J. F. , Su T. , Xu F.
Published: April 2011

In ferroelectric thin films for capacitive and piezoelectric applications, it is important to understand which mechanisms contribute to the observed dielectric constant and piezoelectricity. In soft PZT (PbZr1−xTixO3) ceramics, over half the room temperature response is associated with domain wall contributions to the properties. However, recent studies on bulk ceramics have demonstrated that the number of domain variants within grains, and the mobility of the twin walls depend on the grain size. This leads to a degradation in the dielectric and piezoelectric properties for grain sizes below a micron. This has significant consequences for thin films since a lateral grain size of 1 μm is often the upper limit on the observed grain size. In addition, since the pertinent domain walls are ferroelastic, the stress imposed on the film by the substrate could also clamp the piezoelectric response. To investigate these factors, controlled stress levels were imposed on PZT films of different thickness while the dielectric and electromechanical properties were measured. It was found that for undoped sol-gel PZT 40/60, 52/48, and 60/40 thin films under a micron in thickness, the extrinsic contributions to the dielectric and electromechanical properties make very modest contributions to the film response. No significant enhancement in the properties was observed even when the film was brought through the zero global stress condition. Comparable results were obtained from laser ablated films grown from hard and soft PZT targets. Finally, little twin wall mobility was observed in AFM experiments. The consequences of this in terms of the achievable properties in PZT films will be presented. Work on circumventing these limitations via utilization of antiferroelectric phase switching films and relaxor ferroelectric single crystal films will also be discussed.
An Important Failure Mechanism in MOCVD (Ba,Sr)TiO3 thin Films: Resistance Degradation
Authors: Basceri C. , Lash S. E. , Parker C. B. , Streiffer S. K. , Kingon A. I. , Grossmann M. , Hoffmann S. , Schumacher M. , Waser R. , Bilodeau S. , Carlt R. , Van Buskirk P. C. , Summerfelt S. R.
Published: April 2011

We have investigated the intrinsic resistance degradation behavior of fiber-textured MOCVD (Ba,Sr)TiO3 thin films appropriate for use in advanced DRAMs and integrated decoupling capacitors, as a function of applied voltage polarity, thickness, temperature, and dc bias/field. The results suggest that there is a significant stoichiometry effect on the measured resistance degradation lifetimes. The measured degradation lifetime increases as the Ti content is increased from 51.0 to 52.0 at%Ti, and then decreases with higher at%Ti. Predicted resistance degradation lifetimes obtained from both temperature and voltage extrapolations to DRAM operating conditions of 85°C and 1.6 V exceed the current benchmark of 10 years for all of the films studied.
New Magnesium Precursors for Doping Semiconductor Films
Authors: Winter Charles H. , Sebestl Jennifer L. , Heeg Mary Jane
Published: April 2011

Magnesium-doped semiconductors have existing and anticipated applications in the fabrication of blue and green light-emitting diodes, blue and green laser diodes, and in microelectronics devices. At present, the area is limited by the precursor characteristics of bis(cyclopentadienyl)magnesium and substituted derivatives. We will describe our efforts to identify new magnesium source compounds that are potentially superior to magnesocenes and can be used in chemical vapor deposition processes. Monomeric three- and four-coordinate amides have been synthesized and totally characterized. These complexes are low-melting solids and are significantly more volatile than magnesocene derivatives. We will also describe the synthesis and characterization of several other classes of volatile magnesium compounds that might be useful in chemical vapor deposition processes.
Low Pressure CVD Growth of AlxTi1-xN Films with Tetrakis- (Dimethylamido)Titanium (Tdmat) and Dimethyl Aluminum Hydride (DMAH) Precursors
Authors: Sun Y.-M. , Endle J. , Ekerdt J. G. , Russell N. M. , Healy M. D. , White J. M.
Published: April 2011

AlxTi1-xN film growth has been studied by a organometallic chemical vapor deposition andin-situX-ray photoelectron spectroscopy. Terakis(dimethylamido)titanium (TDMAT) and dimethyl aluminum hydride (DMAH) were used as the Ti, N and Al precursors. AlTiN film growth was observed on SiO2/Si(100) with substrate temperatures between 200 and 400 °C. The Al content in the film is controlled by the ratio of partial pressures of the two precursors in the gas phase. The metal to C to N ratio is approximately constant at 1:1:1 for most conditions studied. The chemical states of Ti, C, and N in AlxTi1-xN and titanium-carbo-nitride (TiCN) films are identical, while the Al chemical state is nitride at low, but increasingly carbidic at high Al concentration. The initial growth rate on SiO2was significantly suppressed by the presence of DMAH. At lower growth temperatures, the DMAH effect is more severe. Good step coverage was observed for AlxTi1-xN on 0.3 μm vias with a 3:1 aspect ratio.
Deposition of Ti(C,N) Thick Films by ILPCVD Starting from TDMAT
Authors: Gilles S. , Bourhila N. , Senateur J. P. , Madar R. , Levy R. A. , Blanquet E.
Published: April 2011

Ti(C,N) films have been deposited from tetrakis(dimethylamido)titanium (TDMAT) and ammonia by CVD at low pressure using pulsed Injection technique (ILPCVD). This procedure allows us to easily deposit Ti(C,N) films with a good reproducibility. It is an efficient technique to control growth rates and composition of coatings. The liquid TDMAT undergoes no degradation during deposition since it is kept at room temperature. Ti(C,N) films, with fee structure and fine grains were deposited at substrate temperature varying from 200 to 500 °C. Composition of films is controlled by substrate temperature and ammonia flow rate. Growth rates as high as 2 μm/min are reached for deposition of Ti(C,N) films at low temperature (350 °C).
Nanoporous Silica for Low κ Dielectrics
Authors: Ramos Teresa , Wallace Steve , Smith Douglas M.
Published: April 2011

As integrated circuit sizes decrease below 0.25 microns, device performance will no longer improve at the same rate as for past generations because of RC interconnect delay which becomes significant as compared to the intrinsic gate delay. The parallel approaches to partially address this fundamental problem are to use a lower resistance metal (i.e., copper instead of aluminum) and to use a dielectric material with a dielectric constant significantly below that of dense silica (∼4). Recently, considerable progress has been made in development of thin films of nanoporous silica (also known as aerogels or low density xerogels) for these ILD and IMD applications. Advantages of these materials include high thermal stability, small pore size, and similarity to conventional spin-on deposition processes, spin-on glass precursors and final material (silica). The dielectric constant of nanoporous silica can be tailored between ∼1 and 3 which allows its’ implementation at multiple technology nodes in integrated circuit manufacture starting with the 0.18 micron node.

Research and development efforts at Nanoglass over the last several years have focused on; 1) simpler and more reproducible deposition processes, 2) a more complete understanding of processing-property relationships for this material, 3) scale-up of manufacturing to yield a range of precursor products with stability for at least six months and very high purity, and 4) working with customers to integrate this material into both aluminum/gapfill and copper/damascene process flows. Nanoglass has now developed a new process which considerably reduces the number of process steps and allows independent control of both film thickness and porosity. The current status of process and precursor development and device integration efforts for nanoporous silica is discussed.
One and Two color Photorefractive Processes in Sputtered WO3 Films
Authors: Bussjager Rebecca , Osman Joseph M. , Chaiken J.
Published: April 2011

As-deposited and derivatized WO3-X films of various stoichiometry were examined in a “nonlinear interface” configuration. The optical properties of the films at 632 nm were modulated using 850 nm and 488 nm CW lasers either separately or simultaneously, Some films were modified by electrochemical reduction. Purely photoinduced changes were interpreted in the context of photoinduced chemistry involving water and/or oxygen exchange with the ambient atmosphere. Both reversible and irreversible changes were observed. Applications as either all-optical switches or logic devices are discussed.
New Liquid Precursors for Chemical Vapor Deposition
Authors: Gordon Roy G. , Chen Feng , Diceglie Nicholas J. , Kenigsberg Amos , Liu Xinye , Teff Daniel J. , Thornton John
Published: April 2011

New precursors have been found for chemical vapor deposition (CVD) of many metal oxides. Each precursor is a mixture formed by randomly attaching a selected set of organic groups, such as the isomers of the butyl group, to a metal 2,4-pentanedionate (also known as acetylacetonate) in place of the methyl groups of the 2,4-pentanedionate ligand. Most of these new mixed metal beta-diketonates are liquids at room temperature, whereas the corresponding metal 2,4-pentanedionates are solids. In the cases where they were solids or viscous liquids, small amounts of organic solvents were added to reduce the viscosity. We have so far prepared mixed beta-diketonate precursors for barium, strontium, calcium, magnesium, aluminum, indium, tin, lead, bismuth, titanium, zirconium, vanadium, niobium, tantalum, chromium, molybdenum, manganese, iron, ruthenium, cobalt, nickel, copper, zinc, yttrium, lanthanum and cerium.

Liquid sources are much more convenient for CVD than solid sources. These liquid mixtures or solutions were vaporized by ultrasonically nebulizing the liquid into a flow of hot nitrogen carrier gas preheated to 150–250 °C. These vapor mixtures were mixed with air or oxygen and flowed over substrates heated typically to 350–450 °C. Films of the corresponding metal oxide (or carbonate, in the case of barium, strontium and calcium) were deposited on substrates of silicon or glass. Gas pressures from 20–760 Torr were used.

Because a common set of ligands is used for each of these metal precursors, they can be mixed as liquids or vapors without any precipitation due to ligand exchange reactions. To demonstrate their use in forming mixed metal oxides, we have prepared films of ferroelectric barium titanate. This method should be applicable to other mixed metal oxides of current interest, such as high dielectric constant strontium titanate, ferroelectric bismuth strontium tantalate, superconducting yttrium barium copper oxide, refractory yttrium zirconium oxide, second-harmonic generating barium borate, metallic lanthanum strontium cobalt oxide and magnetoresistive lanthanum strontium manganate.
Single Source CVD of LiAlO2
Authors: Koh Wonyong , Ku Su-Jin , Kim Yunsoo
Published: April 2011

We successfully deposited LiAlO2 films on Si substrates at 400–600 °C by single source chemical vapor deposition using a heterometallic compound, Li(O'Pr)2Al(CH3)2, which contains Li, Al, and O at the same 1:1:2 ratio as LiAlO2. Li(O'Pr)2Al(CH3)2 is sufficiently volatile to be vapor-transported at 50 °C. Elastic recoil detection and Rutherford backscattering spectroscopy analyses of a deposited film indicate that the film is stoichiometric (Li:Al:O = 1.0:1.0:2.0) and contains a few atomic percent hydrogen (5 %) and carbon (2 %). Depth profile analysis of X-ray photoelectron spectroscopy also confirms the 1:1 ratio of metal contents in the films. As-deposited films were amorphous, however, crystallized to β- or γ-LiA1O2 after annealing at 950 °C.
On Extended X-Rays Absorption Fine Structure Characterisation of Iron Platinum Clusters
Authors: D'Agostino G. , Filipponi A. , Verrazzani A. , Vitulli G.
Published: April 2011

Present paper reports on Extended X-rays Absorption Fine Structure (EXAFS) Spectroscopy characterisation of Fe/Pt clusters. Samples of different nominal iron contents (FePt4 and FePt2) have been prepared and characterised by direct measurements of absorption coefficient at Pt L3 and Fe K edges. Catalysts were prepared by precipitation from suitable mixing (in the appropriate stoichiometry) of mesitylene suspentions containing small clusters of either platinum or iron. Single species suspention, in turn, were prepared by vapor metal deposition.

Catalitic activity of prepared samples was tested on cinnammic aldehyde. As a general result, platinum clusters exhibit activity in the hydrogenation of both carbon double bond and aldehyde group with a preference for the latter. Iron addition to the pure platinum catalyst reverts the selectivity while leaving the catalitic activity almost unchanged.

The present paper represents a temptative to achieve structural information on Fe and Pt short range environments, thus providing insights on the dynamics of the catalytic process.
Humidity Effects on the Electrical Properties of Epitaxial Rutile Thin Films
Authors: Burgess D. R. , Morris Hotsenpiller P. A. , Kryliouk O. , Anderson T. J.
Published: April 2011

Thin films of (001) and (100) oriented rutile phase TiO2, undoped or doped with Ga or Nb, have been grown using the MOCVD technique on sapphire substrates for use in studies of the effects of humidity on the electrical properties of rutile, lbe crystallographic and microstructural quality of the films decreases with increasing Ga and Nb concentrations. Heteroepitaxy is, however, maintained with Ga or Nb concentrations up to 4.5 at% for the (001) orientation and to 0.5 at% Ga for the (100) orientation. The electrical properties of the (001) oriented rutile films have been characterized from room temperature to 225 °C in dry and humid, N2 and air atmospheres. At constant temperature in dry atmospheres, the conductance of the Nb-doped rutile films is greater than that of the undoped, which is greater than the conductance of the Ga-doped films. The activation energies for conduction in die Nb-doped and undoped rutile films in dry atmospheres are similar (∼0.1 eV), whereas the activation energy in Ga-doped films is much greater (∼0.8 eV). The effects of humidity in reducing the resistance of rutile is greatest in the Ga-doped and very min (∼150 Å) undoped films. Humidity is observed to have similar effects on both the (001) and (100) oriented 0.5 at% Ga-doped films.
Textural and Acidic Properties of Mixed Alumina-Silica Oxides Prepared with Commercially Available Sols
Authors: Monaco Steven J. , Ko Edmond I.
Published: April 2011

In this study we have used commercially available preformed sols as building blocks to systematically explore the effects of composition, particle size, and packing on the textural and acidic properties of alumina-silica. We have prepared single oxides and alumina-silica mixed oxides with varying Al:Si atomic ratios using commercial sols from Vista Chemical Co. (alumina) and Eka Chemicals, Inc. (silica). Simple particle packing models based on the structure and experimentally determined particle size distributions of the sols explain the textural and acidic properties of both the single and mixed oxides. Comparisons with aerogels prepared from alkoxides show that materials with different atomic-scale homogeneity can be obtained. This continuum of precursor sizes from monomer through colloid allows a measure of control over textural and acidic properties in the mixed oxides, even at a fixed composition. These results show that systematic studies using preformed sols add insight into the effect of preparation upon catalytic materials.
Redox Behavior Below 1000K of Pt-Impregnated CeO2-ZrO2Solid Solutions: An In-Situ Neutron Diffraction Study
Authors: Loong C.-K. , Short S. M. , Ozawa M. , Suzuki S.
Published: April 2011

The Ce3+↔ Ce4+redox process in automotive three-way catalysts such as Ce-ZrO2/Pt provides an essential mechanism to oxygen storage/release under dynamic air-to-fuel ratio cycling. Such a function requires a metal-support interaction which is not completely understood. We have carried out anin-situneutron powder diffraction study to monitor the crystal structures (a mixture of a major tetragonal and a minor monoclinic phase) of 10mol% Ce-doped ZrO2with and without Pt (1wt%) impregnation under oxidizing and reducing conditions over the temperature range of 25°-700°C. The samples were heated first in flowing 2%O2/Ar from room temperature to 400°C and then in 1%CO/Ar to about 700°C. A discontinued increase of the tetragonal unit-cell volume, a decrease of tetragonality (c/a), and a change of color from light yellow to gray when changing from oxidizing to reducing atmosphere were observed only in the sample containing Pt. This result supports the model which assumes the formation of oxygen vacancies initially near the Pt atoms. As more Ce ions are reduced from 4+ to 3+ oxidation states at high temperatures, oxygen vacancies migrate to the bulk of the oxide particles.
Optical Properties of Carbon thin films Containing Nanoparticles
Authors: Chhowalla M. , Munindradasa A. I. , Lim K. G. , Amaratunga G. A. J. , Kiely C. J.
Published: April 2011

The incorporation of carbon nanoparticles in the forms of nanotubes and bucky onions have shown to improve the mechanical properties of amorphous carbon (a-C) thin films. In this paper we report on the change in the optical properties of a-C films containg nanoparticles. The optical band gap, index of refraction and extinction coefficient are studied. The optical band gap in highly tetrahedral amorphous carbon (ta-C) is found to be around 2 eV. It decreases almost linearly with the sp2 fraction. It is theorized that the clustering of the sp2 sites leads to a reduction in the band gap. In this paper, we study the influence of large sp2 clusters in forms of graphitic nanoparticles on the optical of ta-C. We find that the optical gap remains around 1.8 eV even with the large inclusions of clustered nanoparticles. Furthermore, the gap remains close to 1.8 eV even when the sp2 fraction in the amorphous matrix is increased. The index of refraction however is found to decrease with the sp2 fraction indicating a reduction in density.
Nonvolatile Memory Effects in Doped Tetrahedral Amorphous Carbon Thin Films
Authors: Gerstner E. G. , Mckenzie D. R.
Published: April 2011

Much interest has been shown in the use of tetrahedral amorphous carbon (ta-C) deposited by filtered cathodic arc as an inexpensive, easily produced, wide band-gap semiconductor in the fabrication of electronic devices. There has, however, been limited success in producing devices with properties that might make its use in electronic applications commercially viable, which in part may be due to the high density of electronic trap states as reflected in ta-C's rather high ESR signal of ∼ 1020 spin/g. Recent results at the University of Sydney suggest, however, that a new range of possibilities exist in the utilisation of these traps as a means of producing nonvolatile digital information storage. Devices with write times of 100 μs, read times of 100 ns, and effective memory retention times approaching 1 year, have been fabricated.
Field Emission Properties of Disordered and Partially Ordered Nano Clustered Carbon Films
Authors: Coll B. F. , Jaskie J. E. , Markham J. L. , Menu E. P. , Talin A. A. , Von Allmen P.
Published: April 2011

The fabrication of an efficient cold cathode emitter from carbon is based on a combination of material properties, which must be carefully tailored during deposition. We present the electron emission characteristics of several carbon films deposited by cathodic arc evaporation, and their correlation with the chemical composition, microtexture and microstructure of the films. The emission threshold field voltage, emission site density, uniformity and stability of both tetrahedral amorphous carbon, nitrogen doped carbon and nanoclustered carbon films will be reviewed. We will also address issues related to the deposition method, such as substrate temperature, defect density and scalability, in connection with requirements for the fabrication of field emission displays.
High Pressure Studies of Quantum Well Emission and Deep Emission in GaInP(ordered)-GaAs Heterostructures
Authors: Kwok S. H. , Yu P. Y. , Uchida K. , Arai T.
Published: April 2011

We report on a high pressure study of emission from a series of GaInP(ordered)/GaAs heterostructures. A so-called “deep emission” band at 1.46 eV is observed in all our samples. At high excitation power, quantum well emission emerges in only one structure where thin GaP layers are inserted on both sides of the GaAs well. From the pressure dependent emission in this sample we have determined its band alignments. The role of the GaP layers in suppressing the deep emission is elucidated.
High Pressure Elasticity of MgSiO3 Perovskite, MgO and SiO2
Authors: Karki Bijaya B.
Published: April 2011

Full elastic constant tensors (cij) of three minerals namely, MgSiO3 perovskite, MgO and SiO2, are obtained as a function of pressure up to 140 GPa using first-principles computer simulations based on the local density and pseudopotential approximations. The zero pressure values and initial pressure dependence of athermal elastic constants derived from stress-strain relations are in excellent agreement with available experimental data. We find that elastic moduli, wave velocities and anisotropy of the minerals are strongly pressure dependent, particularly, in the vicinity of the structural transformations. In the view of the present experimental limitations at realistic conditions of the inner Earth, our results for high pressure elasticity are expected to be of substantial geophysical significance. Comparisons based on compressional and shear wave velocities support the prevailing hypothesis of Mg-rich silicate perovskite dominated composition for the lower mantle.
Laser Heating of Boron Nitride and Graphite in a Diamond Anvil Cell
Authors: Eremets M. I. , Takemura K. , Yusa H. , Golberg D. , Bando Y. , Sato Y. , Watanabe K. , Amaya K. , Stephan O. , Blank V. D.
Published: April 2011

Cubic, hexagonal BN, and graphite were heated with the aid of cw CO2 or pulsed YAG laser in a diamond anvil cell at pressures up to 35 GPa. The recovered samples were analyzed by high resolution and scanning electron microscopy, micro-Raman, and X-ray diffraction using synchrotron radiation. Melting of hBN and cBN was achieved. Microcrystals of hBN or cBN were grown from the fluid of BN in nitrogen or argon. Analysis of the hBN-cBN transitions in dependence on pressure showed that the hBN-cBN-liquid triple point is located at 9 GPa. In the transient region between the two phases in the same sample amorphous BN was found revealing the microscopic mechanism of diffusion-like first-order transitions. BN nanotubes growing from an amorphous state at the surface of the crystals were discovered. Under nanosecond pulse laser heating graphite transforms to a diamond-like structure. Spherical droplets and nanocrystals were condensed from the ablated carbon. A compound of nitrogen with carbon was found.
Thermodynamics and Growth of GaN Single Crystals Under Pressure
Authors: Porowski S. , Grzegory I. , Krukowski S.
Published: April 2011

GaN is recently considered as the most important material for blue and ultraviolet optoelectronics. The device structures are usually grown on foreign substrates which results in high density of dislocations above 108cm−2. The application of high N2 pressure gives a unique possibility of growing of GaN single crystalline substrates which allows to lower dislocation density in epitaxial layers by 3–4 orders of magnitude.

In this paper, the results of high nitrogen pressure study of properties of Al-N, Ga-N and In-N systems are presented. The results include the phase diagrams in large range of pressures and temperatures (up to 2 GPa and 2000K) and also growth of GaN single crystals from atomic nitrogen solution in liquid gallium. The kinetic limitations of dissolution of N2 in liquid Al, Ga and In will be discussed. It follows, that the best conditions for crystal growth at available pressures and temperatures can be achieved for GaN.

The high nitrogen pressure experimental system equipped with multi-zone internal furnace was used for growth of high quality GaN crystals. At present both n-type and semi-insulating substrate quality GaN crystals with surface area up to 1cm2, with dislocation density below 105 cm-2 are routinely obtained and successfully used for homoepitaxy.

Some results concerning homoepitaxial growth by the MOCVD and MBE methods are shortly reviewed. In particular, it is shown that perfectly matched (strain free) GaN layers can be deposited on the highly resistive GaN:Mg substrates.
Binary self-assembled monolayers for surface control of liquid-crystal orientation: an x-ray study
Authors: Geer R. E. , Yang J. Y. , Frank C. W.
Published: April 2011

Chemisorbed monolayers of decyltrichlorosilane, [11-(2-Naphthyl)undecyl]trichlorosilane, and a coadsorbed binary mixture of the two were prepared and subsequently investigated using lowangle x-ray reflectivity. Electron density profiles calculated from this data combined reveal well-defined naphthyl and alkyl regions in the [11-(2-Naphthyl)undecyl]trichlorosilane monolayer indicating a high degree of registry along the film normal. These conclusions are consistent with previous spectroscopic measurements of the same system.
Poly(styrene-b-butadiene-b-styrene) self-organized Ultrathin films
Authors: Wang D. Y. , Liu F. Q. , Cao Y. A. , Liu Z. Q. , Shen D. F. , Qian X. M. , Song J. Q. , Liu Z. F. , Bai Y. B. , Li T. J. , Tang X. Y.
Published: April 2011

Direct images of the surface morphology of a series of the poly(styrene-b-butadiene-b-styrene) (SBS) ultrathin films have been obtained by atomic force microscopy (AFM). These films were formed under kinetic control. The resulting films consist of 25 nm-diameter spherical structures and/or cylindrical ones. These structures are surprisingly different fi-om alternative-lamellar structures which should be formed under annealed conditions because of the nearly equal length of two blocks of SBS. In nonselective solvents, the surface of the cast solution layer induces the copolymers to self-organize into micelle consisting of a polystyrene (PS) core and a polybutadiene (PB) shell in order to decrease film surface energy. The final structures depend on the property of the solvent used and filn-forming condition.
Microparticles of Functionalized Polylactide Copolymers
Authors: Gonsalves K. E. , Jin S. , Baraton M-I
Published: April 2011

Microparticles of poly(lactide) (PLac) and its copolymers with the amino acids, serine (P(Lac- Ser)), and aspartic acid (P(Lac-Asp)), respectively, were synthesized using the solvent evaporation microemulsion technique. Poly(vinyl alcohol) (PVA) was added as a non-ionic surfactant to stabilize the particles. The particle sizes are in the range of 200 nm. The surface of the particles was characterized by FTIR transmission spectroscopy under evacuation at room temperature and at 200°C. Hydroxy groups originating from PVA exist on the surfaces of the particles and they were observed at 3506 cm−1. Free hydroxy groups originating from the serine residue pendant to the copolymer P(Lac-Ser) backbone were observed at 3396 cm−1. Also, free carboxylic acid groups pendant to the copolymer P(Lac-Asp) backbone, originating from the aspartic acid residue, were observed at 3387 cm−1. The appearance of the free hydroxy or carboxylic acid groups in the IR spectra also showed that these hydrophilic functional groups moved to the surface of the particles in the process of microemulsion.
Influence of Ion Irradiation on the Microstructure of Fe/Ti Multilayers
Authors: Kopcewicz M. , Grabias A. , Jagielski J. , Stobiecki T.
Published: April 2011

The amorphization of the Fe/Ti multilayers due to ion-beam mixing induced by Ar and Kr ions is studied by conversion electron Mossbauer spectroscopy. Formation of the bcc-FeTi solid solution and the amorphous FeTi phase is studied as a function of ion dose for samples with the Fe to Ti thickness ratio of 1 and the modulation wavelengths of 20 and 60 nm. After reaching maximum abundance the amorphous fraction decreases at high ion doses.
Electron Paramagnetic Resonance Study of Ion-Implanted Photorefractive Crystals
Authors: Darwish A. , Ila D. , Willams E. K. , Poker D. B. , Hensley D. K.
Published: April 2011

The effect of the ion implantation (Fe) on LiNbO3, MgO, and A12O3 crystals is studied using electron paramagnetic resonance (EPR). EPR measurements on these crystals were performed as a function of fluence at room temperature. The fluence was 1 × 1014 and 1 × 1016 ions/cm2. The unpaired carrier concentration increases with increasing fluence. The photosensitivity of these crystals was determined by observing in situ the effect of the laser illumination on the EPR signal and measuring the decay and the growth of the EPR signal. The EPR signal of Fe3+ was found to decrease in both MgO, and Al2O3; and was found to increase in LiNbO3. This indicated that in case of MgO, and A12O3 Fe3+ will transfer into Fe2+/Fe4+, but in case of LiNbO3 Fe2+/ Fe4+ will transfer into Fe3+; increasing the EPR signal. This was found primary due to some Fe2+ and Fe4+ ions, which is not intentionally doped on the LiNbO3 crystal but exist as a defect on the crystal.
Formation of Nanocluster Colloids of Tin, Gold and Copper in Magnesium Oxide by MeV Ion Implantation
Authors: Zimmerman R. L. , Ila D. , Williams E. K. , Sarkisov S. , Poker D. B. , Hensley D. K.
Published: April 2011

We have implanted ions of Sn, Au and Cu at energies between 160 keV and 2.0 MeV into single crystals of MgO (100) at room temperature. The formation of nanoclusters was confirmed using photospectrometry, in combination with Mie's theory, which was indirect but nondestructive. Using Doyle's theory, as well as Rutherford Backscattering Spectrometry (RBS), we correlated the full width half maximum of the absorption bands to the estimated size of the metallic nanoclusters between 1–10 nm. These clusters were formed both by over implantation and by a combination of threshold fluence of the implanted species and post thermal annealing. The changes in the estimated size of the nanoclusters, after annealing at temperatures ranging from 500°C to 1000°C, were observed using photospectrometry.
Enhancement of Adhesion Between Cu Thin Film and Polyimide Modified by Ion Assisted Reaction
Authors: Choi S. C. , Kim K. H. , Jung H-J. , Whang C. N. , Koha S. K.
Published: April 2011

Polyimide films are modified by ion assisted reaction method using various ion beams in various gases environments. Amount of ion and blown gases rate were changed from 5 × 1014 to 1 × 1017 and from 0 to 8 sccm, respectively. Wetting angles between water and polyimide films modified by Ar+ ion without oxygen blowing decrease from 67° to 400° and surface free energies increase from 46 to 64 dyne/cm2. Wetting angle of polyimide films modified by Ar+ ion in an oxygen environment decreases to 12° and surface free energy increases to 72 dyne/cm2. The lowest wetting angle was obtained by oxygen ion irradiation in the oxygen gas environment and its value was 7°. In the case of polyimide film modified by Ar+ ions in an oxygen environment, the wetting angle increases up to 65° when it kept in air and that increases up to 46° when it kept in water after 5 day. In the case of polyimide film modified by O2+ ion in oxygen environment, however, the wetting angle of polyimide film dose not increase. X-ray photoelectron analysis shows that the chemical bonds between polyimide components are severed by ion irradiation and hydrophilic groups such as CO and C=O are formed by the reaction between newly formed radicals and blown oxygen. It was found that adhesion between Cu and polyimide modified by ion assisted reaction was improved. The main reason of the enhanced adhesion is due to the reaction between Cu and C-O or C=O groups formed by ion assisted reaction on the polyimide surface.
Argon-surface interactions in ibad-deposited molybdenum films
Authors: van der Kuur Jan , Korevaar Bas , Pols Martin , van der Linden Jacqueline , Thijsse Barend
Published: April 2011

Argon incorporation and defect creation were studied experimentally. Direct desorption measurements have been used to establish the argon implantation profile. A projected range and range straggle of 0.8 and 3.5 Å were found. Argon is incorporated at substitutional positions. The creation rate of defects by argon was studied by helium desorption spectrometry. A net creation rate of (0.7 ± 0.4) × 10−3 vacancy/argon atom was found. Ion assisted deposition at elevated substrate temperatures shows that all incorporated argon acts as helium trap. Argon fluence variations show an effective cross-section for self sputtering of 31 Å2, a trapping probability of 6.5%, and a maximum achievable argon concentration of 4 × 10−3
Ion Yield, Sputter Rate, and Sims Matrix Effects in Quantitative Analysis of (AlxGa1−x)0.5N0.5
Authors: Lefforge D.L. , Chang Y.L. , Ludowise M. , Allen E.L.
Published: April 2011

Aluminum gallium nitride (AlGaN) material is used in GaN-based electronic and optoelectonic devices. The Al and Ga ratio can be adjusted to produce material with different compositions and electronic properties. In this set of experiments epitaxial films of (AlxGa1−x)0.5N0.5 with x ranging from 0 to 1 were investigated. Primary composition was determined with Rutherford backscattering spectrometry (RBS). From secondary ion mass spectrometry (SIMS) profiles a correlation of secondary ion counts was made to RBS determinations of primary composition. The SIMS data was also used to determine sputter rate and the relative sensitivity factor (RSF) of O, Mg and Si in (AlxGa1−x)0.5N0.5 material. The correlation of SIMS data with RBS and knowledge of the sputter rate and RSF dependence on composition are essential for the characterization of (AlxGa1−x)0.5N0.5 films
Intrinsic Gettering of Nickel and Copper for Advanced Low Temperature Device Processes
Authors: Ogushi S. , Reilly N. , Sadamitsu S. , Koike Y. , Sano M.
Published: April 2011

The formation and dissolution of Ni and Cu silicides were investigated to determine effective intrinsic gettering (IG) for low temperature processes. Ni formed silicides easily at low contamination levels and these silicides formed the nuclei for OSF during subsequent annealing at temperatures above 1000°C. Ni silicides were dissolved and gettered during low temperature deposition of a poly-back seal (PBS) at 620°C, whereas Cu silicides, once formed, easily induced secondary defects on further annealing even at low temperatures and could not be dissolved or gettered by PBS. The sizes and densities of oxygen precipitates necessary to intrinsically getter Ni and Cu contamination levels of 1012atoms/cm2 were also investigated with respect to generation lifetime. Cu contamination at this level did not degrade generation lifetime or gate oxide integrity (GOI) yield. For Ni contaminated samples, a strong dependence of generation lifetime on both oxygen precipitate density and size was observed. Effective IG for Ni during a low temperature process was demonstrated using a 2-step low temperature process simulation.
Near Surface Defect Distribution in Silicon Under Etching
Authors: Yarykin Nikolai A.
Published: April 2011

The distribution of hydrogen penetrated into n-type silicon crystals during chemical etching is described mathematically. The depth profiles of the defects passivated by hydrogen and of defect-hydrogen complexes are also calculated. Comparison with the experimental data obtained on the silicon crystals with radiation defects and doped with transition metals reveals that the model adequately describes the processes in the crystal. By comparing the parameters of the depth profiles, the passivation and appearance of different defects are shown to be caused by the same diffusing species. The number of hydrogen atoms contained in the defect-hydrogen complexes and the distance of the hydrogen-defect interaction are determined from the characteristic length of the defect distribution. The diffusion length (1 to 3 νm) and diffusivity (> 5-10−9 cm2s−1) of hydrogen at room temperature are found indirectly based on the other defect distribution.
Ion Implantation-Induced Defects and the Influence of Titanium Silicidation
Authors: Chi D.Z. , Ashok S. , Theodore D.
Published: April 2011

Thermal evolution of ion implantation-induced defects and the influence of concurrent titanium silicidation in pre-amorphized p-type Si (implanted with 25 KeV, 1016 cm2Si+) under rapid thermal processing (RTP) have been investigated. Presence of implantation-induced electrically active defects has been confirmed by current-voltage (IV) and deep level transient spectroscopy (DLTS) measurements. DLTS characterization results show that the evolution of electrically active defects in the Si implanted samples under RTP depend critically on the RTP temperature: Hole traps HI (0.33 eV) and H4 (0.47 eV) appear after the highest temperature (950 °C) anneal, while a single trap H3 (0.26 eV) shows up at lower anneal temperatures (≤ 900 °C). The thermal signature of H4 defect is very similar to that of the iron interstitial while those of HI and H3 levels appear to originate from some interstitial-related defects, possibly complexes. A most interesting finding is that the above interstitial related defects can be eliminated completely with Ti silicidation, apparently a result of vacancy injection. However the silicidation process itself introduces a new H2 (0.30 eV) level, albeit at much lower concentration. This same H2 level is also seen in unimplanted samples under RTP. The paper will present details of defect evolution under various conditions of RTP for samples with and without the self-implantation and silicidation.
Structural and Photoluminescence Studies of Er Implanted Lt-GaAs:Be
Authors: Maltez R.L. , Liliental-Weber Z. , Washburn J. , Behar M. , Klein P.B. , Specht P. , Weber E.R.
Published: April 2011

Characteristic 1.54 μm Era3+ emission has been observed from Er-implanted and annealed, low-temperature grown GaAs:Be samples. Cross-sectional transmission electron microscopy (TEM) studies reveal very little structural damage for elevated temperature implants up to an Er total fluence of 1.36 × 1014 Er/cm2. No Er emission was observed from any of the as-implanted samples, while post-implantation annealing optimized the Er emission intensity near 650°C. The Er-emission appears on top of a broad background luminescence peaking near 1500 nm. Significant enhancement of the optically active Er incorporation was achieved when the implantation was carried out at 300TC. The Er emission intensity was found to scale linearly with the Er implantation fluence for samples with an Er concentration up to ∼1019 Er/cm3. The sample with the highest Er concentration (∼1020 Er/cm3) began to show a sublinear dependence. The beginning of Er precipitation was observed after 750°C annealing, but it could even be observed after a 650°C annealing for the highest Er concentration sample. These precipitates are likely ErAs.
Boron Clusters in a Complex Defect in Silicon
Authors: Okamoto M. , Takayanagi K. , Takeda S.
Published: April 2011

We have investigated stability of a new kind of boron clusters in silicon crystal using the first-principles local density functional approach. In the calculation, we used three types of hydrogenterminated silicon clusters; one of these types included the four interstitial cluster I4 as a complex defect. According to our calculation, we found that a new kind of boron clustering of n-borons substituted I4 (n < 3) became most stable when the ratio r = N(Bi) / (N(Sii) + N(Bi) in a confined area was less than or equal to 1/2, where N(B) is a number of interstitial boron atoms and N(Sii) is that of interstitial silicon atoms. On the other hand, when r was greater than 1/2, the l4 would be destroyed to create the [100] split boron pair, the [110] split silicon pair, and/or the substitutional boron and interstitial silicon pair.
Point Defect Characterization of Zn- and Cd-Based Semiconductors Using Positron Annihilation Techniques
Authors: Tessaro G. , Mascher P.
Published: April 2011

A study of point defects in II-VI compound semiconductors was undertaken and has revealed that open volume defects are present in a wide variety of these samples. Zn-based binary compounds contain primarily neutral divacancy defects in concentrations in the mid 1016 cm−3. CdTe samples contain neutral monovacancy sized defect complexes in the high 1016 cm−3 range. When a small fraction of Zn or Se is alloyed into CdTe the defect profile changes dramatically to one dominated by divacancy sized defects at roughly half the original concentration.
A Novel Detection System for Defects and Chemical Contamination in Semiconductors Based Upon the Scanning Kelvin Probe
Authors: Lägel Bert , Baikie Iain D. , Petermann Uwe
Published: April 2011

A novel wafer scale detection system for defects and chemical contamination in semiconductors based upon the Scanning Kelvin Probe (SKP) is presented. It incorporates traditional work function (wf) topography with high resolution (<0.1 meV), Surface Photovoltage (SPV) measurement and the acquisition of SPV transients with time constants down to I ts. This permits quasi-simultaneous determination of surface charge, surface barrier height and bulk minority carrier lifetime. Monitoring variations of these parameters after chemical treatments give an accurate indication of the location and amount of contamination.

The SKP system is introduced and the SPV and SPV transient measurement modes are discussed. Measurements on Fe-contaminated and Au-implanted Si wafers demonstrate the feasibility of the system for defect and impurity characterisation in semiconductors. The system is both non-contact and non-destructive, requires no wafer preparation and can be applied in both ambient and vacuum environments.