bluuebunny/crossref_metadata_2025 huggingface dataset:
Piezoelectric Poly(3-hydroxybutyrate)-Poly(lactic acid) Three Dimensional Scaffolds for Bone Tissue Engineering
Authors: Mendenhall Juana , Li Dapeng , Frey Margaret , Hinestroza Juan , Babalola Omotunde , Bonnasar Lawrence , Batt Carl A
Published: April 2011

Three dimensional scaffolds (3D) are promising for future nanoscale materials and tissue engineering applications being that they have architecture and mechanical properties similar to natural tissue. In this work, poly(lactic acid) fibers were prepared via electrospinnig with average diameters of 2580 nm. Using Enzymatic Surface-Initiated polymerization (ESIP), poly(3-hydroxybutyrate) were coated on poly(lactic acid) fibers. This provides an alternative method to enzymatic surface modification of fibers. ESIP of PHB produces a granular film providing surface topography and increases mechanical properties of PLA fibers alone. When using covalent approaches, PHB granules provide surface topography of 200-500 nm with a polydisperse coverage area. Compressive modulus measurements of PLA and PHB/PLA scaffolds were 25 kPa and 73 kPa, respectively. The percent crystallinity of PLA and PHB/PLA scaffolds was 17% and 30%, respectively. This rough topography, in addition to the crystallinity of the scaffold, facilitates Soas-2 osteoblast cell attachment. We have observed attachment of the osteoblast cells along the length of the oriented PLA and PHB/PLA composite scaffolds with different morphologies, rounded and stretched, throughout a depth of 90 µm.
Single Asperity Wear and Stress-Assisted Dissolution of Copper
Authors: Chua Bun H , Chandra Abhijit , Shrotriya Pranav
Published: April 2011

The focus of this paper is to investigate the synergistic influence of contact loads, surface stress state and chemical environment on material removal during mechanical stimulation of copper surface. A unique setup is used to generate well characterized stress states on a polished copper specimen. Stressed surface of copper specimen is stimulated using tip of the atomic force microscope (AFM) and material removed during stimulation is measured as a function of contact loads, surface stress state and chemical environment. Measured material removal rates display a complex dependence on contact pressures and in-plane stress state which changes as the pH of chemical environment changes from acidic to basic. A surface material removal mechanism based on a single asperity wear and stress-assisted dissolution is proposed to explain the experimental observations
Negative or Zero Thermal Expansion in Silicon Dicarbodiimide, Si(NCN)2
Authors: Kroll Peter , Yan Xuehua , Riedel Ralf , Ehrenberg Helmut
Published: April 2011

Using ab-initio molecular dynamics simulation we investigate the thermal expansion of β-Si(NCN)2 for temperatures up to 700 K. We find that the structure behaves isotropic, although its optimized ground state is tetragonal. Studying the zero-pressure volume as a function of temperature we find a negative expansion of the structure and a linear expansion coefficient αL of -2·10−5 K-1. We attribute this effect to a strong bending of the Si-N=C angle within the structure which increases on increasing the temperature. The stretching of Si-N and C=N bonds on the other side is regular.

Experiments motivated by the computational study were carried out on nano-crystalline Si(NCN)2 powders. The XRD Mo Kα data shows a negative thermal expansion for β-Si(NCN)2 up to 600 K. Synchrotron data indicates zero expansion of β-Si(NCN)2 between 460K and 800 K.
Growth and Characterization of High-Performance GaN and AlxGa1−xN Ultraviolet Avalanche Photodiodes Grown on GaN Substrates
Authors: Dupuis Russell D. , Yoo Dongwon , Ryou Jae-Hyun , Zhang Yun , Shen Shyh-Chinag , Limb Jae , Yoder Paul D. , Hanser A. Drew , Preble Edward , Evans Keith
Published: April 2011

Wide-bandgap III-nitride-based avalanche photodiodes (APDs) are important for photodetectors operating in UV spectral region. For the growth of GaN-based heteroepitaxial layers on lattice-mismatched substrates such as sapphire and SiC, a high density of defects is introduced, thereby causing device failure by premature microplasma breakdown before the electric field reaches the level of the bulk avalanche breakdown field, which has hampered the development of III-nitride based APDs. In this study, we investigate the growth and characterization of GaN and AlGaN-based APDs on free-standing bulk GaN substrates. Epitaxial layers of GaN and AlxGa1−xN p-i-n ultraviolet avalanche photodiodes were grown by metalorganic chemical vapor deposition (MOCVD). Improved crystalline and structural quality of epitaxial layers was achieved by employing optimum growth parameters on low-dislocation-density bulk substrates in order to minimize the defect density in epitaxially grown materials. GaN and AlGaN APDs were fabricated into 30μm- and 50μm-diameter circular mesas and the electrical and optoelectronic characteristics were measured. APD epitaxial structure and device design, material growth optimization, material characterizations, device fabrication, and device performance characteristics are reported.
Superluminescence in Green Emission GaInN/GaN Quantum Well Structures under Pulsed Laser Excitation
Authors: Senawiratne Jayantha , Tomasulo Stephanie , Detchprohm Theeradetch , Zhu Mingwei , Li Yufeng , Zhao Wei , Xia Yong , Zhang Zihui , Persans Peter , Wetzel Christian
Published: April 2011

We report nonlinear optical investigation of green emission GaInN/GaN multi-quantum structures grown along c- and m-axes on sapphire and bulk GaN substrates, respectively. Under intense pulsed photo excitation, we observed strong superluminescence near the lasing condition in c-plane grown quantum well structures with full width at half maximum of 6 nm. The superluminescence couples out of the edge of the sample in a mode pattern consistent with gain in a high mode of the waveguide. The wavelength of the superluminescence is 474 nm. The threshold intensity of superluminescence was found to be 156 kW/cm2. Increasing pump intensity leads to a strong photoluminescence blueshift as large as 380 meV in samples grown along the c-axis on sapphire substrate, while under the same excitation conditions, the blue shift for the m-axis grown structure on bulk GaN substrate is less than 10 meV. The large emission blueshift is hereby attributed to the internal piezoelectric field in the c-axis grown structure. We observe a gain value of 20 cm-1 together with internal absorption losses of 2.3 – 6.0 cm-1 for the superluminescent samples.
Contact Characterizations of ZrN Thin Films Obtained by Reactive Sputtering
Authors: Pelleg Joshua , Bibi Asaf , Sinder Michael
Published: April 2011

The contact properties of ZrN on p-type Si obtained by magnetron reactive sputtering were investigated. Schottky diodes characteristics were evaluated by current-voltage (I-V) and capacitance voltage (C-V) measurements. The barrier heights obtained by I-V and C-V are in the range of 0.55-0.63V and 0.88-0.91V, respectively.
Magnetocaloric Effects of Binary Rare Earth Nitrides
Authors: Hirayama Yusuke , Nakagawa Takashi , Kusunose Takafumi , Yamamoto Takao A.
Published: April 2011

We synthesized HoxEr1−xN (x =0.1, 0.3, 0.5, 0.7, 0.9) by the carbothermic reduction method. The magnetic entropy change, ΔS, which is an indicator of performance of magnetocaloric effect, MCE, was obtained from data sets of magnetization M (H, T) measured at various temperature, T, and magnetic field, H, through the Maxwell equations. The Thus obtained ΔS vs. T curves have peaks at temperatures depending on x in a range of 8–18 K. ΔS values of HoxEr1−xN expressed in terms of J K−1 m−3 were higher than those of intermetallic compounds of rare earth and transition metals previously reported. These ΔS peak plots are along a convex curve, which may indicate an interaction between the two components.
NITRIDE BASED SCHOTTKY-BARRIER PHOTOVOLTAIC DEVICES
Authors: Jampana Balakrishnam R , Jani Omkar K , Yu Hongbo , Ferguson Ian T , McCandless Brian E , Hegedus Steven S , Opila Robert L , Honsberg Christiana B
Published: April 2011

Schottky-barrier photovoltaic devices are fabricated by selective metal deposition on p-GaN. A 1.25 V open-circuit voltage is observed for the best device. Devices were optimized by annealing in forming gas at temperatures ranging from 550°C to 700°C. Annealing time and forming gas flow rate are used to control the metal-semiconductor Schottky barrier formation. Optimum fabrication parameters are achieved based on photovoltaic response from the devices under UV illumination. Barrier heights (0.47 eV - 0.49 eV) were used as basis to compare the device response. The Schottky-barrier height is very sensitive to processing conditions, for example a 2.5% increase in barrier height is observed when Schottky contact annealing temperature is changed from 600 °C to 650 °C. Under UV illumination, the open-circuit voltage and short-circuit current increase with increasing annealing temperature while the series resistance decreases under such conditions.
GaN Photonic Crystal-Based, Enhanced Fluorescence Biomolecule Detection System
Authors: Dawson J. M. , Nightingale J. R. , Tompkins R. P. , Cao X. , Myers T. H. , Hornak L. A. , Korakakis D.
Published: April 2011

The need for small form factor, portable biosensing platforms is prevalent across a wide range of medical, environmental, and defense applications. This paper presents the design of a novel, integrated optofluidic photonic crystal biosensor architecture that shows potential for meeting the single molecule detection requirements of these application areas. GaN is being targeted as the photonic crystal slab material due to its transparency in the visible spectral range and also the potential for creating high aspect ratio photonic crystal lattices via polarity inverted MBE growth. Results of optical modeling efforts indicating 10-15x resonant enhancement of fluorescent emission and polarity inversion GaN growth techniques will be discussed.
TRANSMISSION ELECTRON MICROSCOPY STUDY OF INTERFACE REGION OF ALN / 6H-SIC
Authors: Chaudhuri Jharna , Nyakiti Luke Owuor , Lu Peng , Edgar James H , Li Peng
Published: April 2011

Transmission electron microscopy (TEM) study was performed to investigate the interface region of AlN/6H-SiC. Thick AlN layers were grown on a 3.5° off-axis 6H-SiC substrate at a temperature of 1790 °C for 100 hours by sublimation-recondensation method. The energy dispersive x-ray spectroscopy (EDXS) analysis indicated considerable amount of aluminum and nitrogen present in the substrate and Si and C present in AlN. Lattice images of cross-sectional TEM samples show a faceted interface with step growth.
Controlling Swelling of Portland Brownstone
Authors: Wangler Timothy , Scherer George W.
Published: April 2011

Many clay-bearing sedimentary stones such as Portland Brownstone will swell when exposed to water, and this can generate damaging stresses as differential strains evolve during a wetting cycle. Current swelling inhibitors, consisting of α,ω-diaminoalkanes, can reduce swelling in Portland Brownstone up to 50%. In this study, through X-ray diffraction and swelling strain experiments, we demonstrate that the α,ω-diaminoalkanes inhibit swelling by substituting for interlayer cations and partially hydrophobicizing the interlayer, then rehydrating on subsequent wetting cycles. We also introduce the copper (II) ethylenediamine complex as a potential treatment for swelling inhibition.
The Grolier Codex: A Non Destructive Study of a Possible Maya Document using Imaging and Ion Beam Techniques
Authors: Ruvalcaba Jose Luis , Zetina Sandra , Calvo del Castillo Helena , Arroyo Elsa , Hernández Eumelia , Van der Meeren Marie , Sotelo Laura
Published: April 2011

The Grolier Codex has been a controversial document ever since its late discovery in 1965. Because of its rare iconographical content and its unknown origin, specialists are not keen to assure its authenticity that would set it amongst the other tree known Maya codes in the world (Dresden, Paris Codex and Madrid Codex).

The document that has been kept in the Museo Nacional de Antropología in Mexico City, after its exposure in 1971 at the Grolier Club of New York, has been analyzed by a set of non-destructive techniques in order to characterize its materials including paper fibers, preparation layer and colors composition. The methodology included UV imaging, IR reflectography and optic microscopy examinations as well as Particle Induced X-ray Emission (PIXE) and Rutherford Backscattering Spectrometry (RBS) using an external beam setup for elemental analysis. All the measurements were carried out at 3MV Pelletron Accelerator of the Instituto de Física, UNAM. The aim of this work is to verify if the materials in the Grolier Codex match those found for other pre-Hispanic documents.

From the elemental composition we concluded that the preparation layer shows the presence of gypsum (CaSO4), color red is due to red hematite (Fe2O3) and black is a carbon-based ink. These results agree with previous analyses carried out by Scanning Electron Microscopy (SEM-EDX) on few samples. However, the presence of Maya Blue in the blue pigment cannot be assured. The examination using UV and IR lights shows homogeneity in the inks and red color but dark areas that contain higher amounts of K in the preparation layer. This paper discusses the results obtained for the UV-IR examinations and the elemental analysis. A comparison with other studies on pre-Hispanic and early colonial codex is presented.
Replication of Glazed Quartzite from Kerma, Capital of Ancient Kush (Sudan)
Authors: Ellis Lisa , Newman Richard , Barsanti Michael
Published: April 2011

Glazes found on ancient Nubian quartzite sculpture were characterized in a previous study by scanning electron microscopy/energy-dispersive X-ray spectrometry (SEM/EDS). Now in the collection of the Museum of Fine Arts, Boston, these objects were excavated in the early 20th century by the joint Harvard University-Boston Museum of Fine Arts Expedition, in ancient Kerma, the capital of ancient Kush. The project presented here attempts to recreate the ancient technology used to glaze quartzite with compositions determined in the previous study. Raw and fritted experimental glazes were prepared, as well as an alkali paste mixed with a copper colorant. All of the samples were fired in modern kilns. After firing, samples of the glazes and their quartzite substrates were examined with SEM/EDS.
Formation of III-V Semiconductor Engineered Substrates Using Smart CutTM Layer Transfer Technology
Authors: Letertre Fabrice Jerome
Published: April 2011

Engineered substrates are expected to play a dominant role in the field of modern nano-electronic and optoelectronic technologies. For example, engineered substrates like SOI (Silicon On Insulator) make possible efficient optimization of transistors' current drive while minimizing the leakage and reducing parasitic elements, thus enhancing the overall IC performance in terms of speed or power consumption. Other generations of engineered substrates like strained SOI (sSOI) provide solutions to traditional scaling for 32 nm node and beyond [1] technologies.

The Smart Cutä technology, introduced in the mid 1990's by M. Bruel [2] is a revolutionnary and powerful thin film technology for bringing to industrial maturity engineered substrate solutions. It is a combination of wafer bonding and layer transfer via the use of ion implantation. It allows multiple high quality transfers of thin layers, from a single crystal donor wafer onto another substrate of a different nature, allowing the integration of dissimilar materials. As a consequence, it opens the path to the formation of III-V based engineered substrates by integrating, for example, materials like GaAs [3], InP [4], SiC [5], GaN [6], Germanium [7] ,and Si [8 ]on a silicon, poly SiC, sapphire, ceramic, or metal substrates?

In this paper, we will review the current wafer bonding and layer transfer technologies with a special emphasis on the Smart Cut technology applied to compound semiconductors. Beyond SOI, the innovation provided by substrate engineering will be illustrated by the case of Silicon and SiC engineered substrate serving as a platform for GaN and related alloys processing [9,10,11,12] as well as the case of Germanium/Si platform for the growth of GaAs/InP materials, opening the path to Si CMOS and III-V microelectronics/ optoelectronics functions hybrid integration [13, 14]. Recent results obtained in these two focused areas will be presented to emphasize the added functionalities offered by engineered substrates.

[1] B. Ghyselen et al., ICSI3 proc., 173 5 (2003)

[2] M. Bruel et al., Electron. Lett., vol 31, p. 1201 (1995)

[3] E. Jalaguier et al., Electron. Lett., 34(4), 408 (1998)

[4] E. Jalaguier et al. Proc. llth Intern. Conf. on InP and Related Materials, Davos, Switzerland, (1999)

[5] L. Di Cioccio et al., Mat. Sci. and Eng. B Vol. 46, p. 349 (1997)

[6] A. Tauzin and al., Semiconductor Wafer Bonding VIII, ECS Proc Vol. 2005-02, pp. 119-127

[7] F. Letertre, et al. MRS Symp. Proc., 809, B4.4 (2004).

[8] B. Faure et al., Semiconductor Wafer Bonding VIII, ECS Proc Vol. 2005-02, pp. 106-118

[9] H. Larèche et al., Mat. Sci. For., Vols. 457–460 pp.. 1621 – 1624 (2004)

[10] G. Meneghesso et al , IEDM 2007, to be published

[11] Y. Dikme et al., Journal of Crystal Growth, v.272 (1-4), pp. 500-505 (2004)

[12] J. Dorsaz and al., Proceedings, ICNS6 (2005)

[13] S.G. Thomas et al., IEEE EDL Vol. 26, July 2005.

[14] K. Chilukuri, Semi. Sci. Technol. 22 (2007) 29-34
Effect of Si and Er Co-doping on Green Electroluminescence from GaN:Er ELDs
Authors: Wang Rui , Steckl Andrew J
Published: April 2011

(Er, Si) co-doped GaN thin films were grown on Si substrates by molecular beam epitaxy (MBE) technique. Electroluminescent devices (ELDs) were fabricated and the effect of Si co-doping on the performance of GaN devices was studied. Previous results with GaN:Er ELDs reported that electroluminescence (EL) was much stronger in reverse bias than in forward bias condition, indicating that the dominant factor in EL intensity was the electric field. The results reported here show the first time GaN:Er ELDs where forward bias EL is very much larger, indicating that the dominant factor is forward bias current. The electrical properties of (Si, Er) co-doped GaN thin films are believed to be responsible for the current control mechanism.
Fabrication and Electrical Studies of P(VDF/TrFE)(72/28) Copolymer based Non-Volatile Memory Devices as a Function of Varying Device Structures
Authors: Kim Kap Jin , Choi Chang Woo , Prabu Arun Anand , Yoon Sun
Published: April 2011

Ferroelectric characteristics of poly(vinylidiene fluoride/trifluoroethylene) (P(VDF/TrFE) (72/28 mol%)) copolymer ultrathin films used as an insulator in varying memory device architectures such as metal-ferroelectric polymer-metal (MFM), MF-insulator-semiconductor (MFIS), MIS and organic field-effect transistor (OFET) were studied using different electrical measurements. A maximum data writing speed of 1.69 MHz was calculated from the switching time measured using MFM architecture. Capacitance-voltage measured using MFIS was found to be more suitable for distinguishing the ‘0’ and ‘1’ state compared to MFM device structure. In OFET, the decreasing channel length increased the measured drain current (Id) values as well as its memory window enabling easier identification of the ‘0’ and ‘1’ state comparable to MFIS case. The data obtained from this study will be useful in the fabrication of non-volatile random access memory (NVRAM) devices with faster data R/W/E speed and memory retention capacity.
Reproducible Electro-resistance Memory Effect in Ag/La0.67Sr0.33MnO3 Thin Films
Authors: Huang Lina , Qu Bingjun , Liu Litian
Published: April 2011

The hysteretic and reproducible electro-resistance memory effect has been investigated in epitaxial La0.67Sr0.33MnO3 (LSMO) films under DC-bias stress and voltage pulses. The bias-sensitive current-voltage characteristic of the Ag/LSMO system is distinctly nonlinear, asymmetric and hysteretic, which indicates the appearance of the resistive switching. The diffusive resistance transition, which occurred during the field increase/decrease processes, is likely ascribed to a large intrasystem charge transfer for the electronic inhomogeneous heterostructure. The pulsed voltage amplitude and duration dependence of the nonvolatile resistive switch were also provided. Clear resistance switching cycles were observed at room temperature under voltage pulses of ±5V and ∼150ns. Reproducible switching properties, involving voltage-induced stepwise resistance change, resistance state saturation, and pulse duration dependent multilevel switchable capability, demonstrate well controllability with respect to future nonvolatile random access memory applications.
Optical and Morphological Characterization of PTCDI-C13
Authors: Stella Marco , Villar Fernando , Rojas Fredy Enrique , Della Pirriera Mónica , Voz Cristobal , Puigdollers Joaquim , Asensi José Miguel , Andreu Jordi , Bertomeu Joan
Published: April 2011

The organic photovoltaic technology has developed much in the last few years thanks to the optimization of the solar cell geometry and, specially, to the research for new performing materials. Nevertheless, much work has still to be done in order to better know the real mechanisms regulating the function of such novel class of semiconductors. The study of thin-film micro-structure, and the influence of the deposition parameters on it, is an important issue in order to obtain best optical and electrical properties. Thermal evaporation in high-vacuum chambers is the more suitable deposition technique to obtain organic thin-films with well organize molecular structure. Deposition parameters such as the substrate temperature and deposition rate may have some important effect on the molecules ordering. In this paper the effects of substrate temperature on structural and optical properties have been studied forN,N′-ditridecyl perylene diimide (PTCDI-C13) thin-films. Four samples have been deposited at 30, 60, 90 and 120°C substrate temperature and their absorption has been investigated by photothermal deflection spectroscopy (PDS) and transmittance spectroscopy. Moreover, simulations of the transmittance spectra have been calculated in order to obtain the optical constantsnandk. Finally atomic force microscopy (AFM) has been employed to analyze the superficial morphology of the thin-films.
Fabrication and Optical Properties of Electrospun Organic Semiconductor Nanofibers from Blended Polymer Solution
Authors: Chuangchote Surawut , Sagawa Takashi , Yoshikawa Susumu
Published: April 2011

Ultrafine organic semiconductor fibers with the average diameters ranging in sub-micro-down to nanometers (43 nm - 1.7 µm) were fabricated by electrospinning of a mixture of poly(2-methoxy-5-(2′-ethylhexyloxy)-1,4-phenylene-vinylene) (MEH-PPV) and polyvinylpyrrolidone (PVP) in various mixed solvents. The average diameter of the as-spun fibers decreased into nanometer scale with decreasing the concentration of PVP. Addition of a volatile organic salt (pyridinium formate, PF) or utilization of three-mixed solvent system was also effective to reduce the size of the diameter of as-spun fibers. After the removal of PVP from as-spun fibers by Soxhlet extraction, pure MEH-PPV fibers were obtained as a ribbon-like structure aligned with wrinkled surface in fiber direction. As-spun fibers showed relatively higher crystallinity, higher conjugation length, and a remarkable blue shift of photoluminescence (PL) peak was observed, in comparison with the cast film. The increase in composition of MEH-PPV and the removal of PVP from as-spun MEH-PPV/PVP fibers resulted in a significant blue-shift in UV-Vis absorption peak and red-shift in PL peak.
Fabrication of polycrystalline thin films of liquid crystalline materials by solution process and its application to OFETs
Authors: Iino Hiroaki , Hanna Jun-ichi
Published: April 2011

We have fabricated polycrystalline OFETs of two different liquid crystalline materials i.e., ω,ω'-dihexylquaterthipohene (6-QTP-6) and N, N'-ditridecylperylenediimide (13-Per-13) by solution process. Liquid crystalline materials help fabricating uniform thin films on the substrate when spin-coated at their temperature range of liquid crystalline phase. The FETs fabricated with 6-QTP-6 exhibited p-channel performance and its mobility was determined to be 0.04 cm2/Vs, which was comparable to that determined by time-of-flight experiments. The FETs fabricated with 13-Per-13 exhibited n-channel performance and its FET mobility was 0.008 cm2/Vs, while the mobility was increased up to 0.11 cm2/Vs after thermal annealing of the film at a liquid crystalline temperature of 220°C for an hour. Judging from these facts, the grain boundaries are controlled not so as to across the conduction channels formed by self-aligned π-conjugated aromatic cores in liquid crystalline molecules. We conclude that liquid crystalline material is a good candidate for quality polycrystalline thin films for OFETs.
Microstructural Characterization of Multi-Component Systems Produced by Mechanical Alloying
Authors: Pérez-Bustamante R. , Gómez-Esparza C.D. , Pérez-Bustamante F. , Estrada-Guel I. , Cabañas-Moreno J.G. , Herrera-Ramírez J.M. , Martínez-Sánchez R.
Published: April 2011

A series of binary to hexanary alloys (Ni, Co, Mo, Al, Fe, Cu) are produced by mechanical alloying. Formation of an FCC solid solution is observed in the binary system. For ternary to quinary systems the presence of an amorphous phase and a BCC solid solution is identified, and for the hexanary system a combination of BCC and FCC solid solutions is detected. There is a very small change in the lattice parameter of Mo, reflecting the limited solid solubility of other element in this structure. However, Mo induces the fast amorphization of other elements and the reduction of crystallite size.
Effect of Annealing on the Magnetic Properties of a Cold Rolled Non-Oriented Grain Electrical Steels
Authors: López G. N.M. , Salinas R. A.
Published: April 2011

The effect of plastic deformation and subsequent annealing on the microstructure and magnetic properties (hysteresis core losses) of non-oriented grain semi-processed Si-Al electrical steel sheet are investigated. Plastic deformation of strip samples is performed by cold-rolling (5–20% reduction in thickness) along the original rolling direction. Annealing is carried out in air during 1 or 60 minutes at temperatures between 650 and 850°C. Measurements of B-H hysteresis curves are performed using a Vibrating Sample Magnetometer and characterization of annealed microstructures is carried out using optical metallography. The results show that hysteresis losses increase by a factor between 1.2 and 2.0 as the magnitude of the applied plastic deformation increases from 5 to 20% reduction in thickness. The rate of recovery of energy losses as a result of annealing depends on annealing time. Short annealing times produce full recovery of the effect of cold work and values of energy losses lower than in undeformed material. The magnitude of the additional recovery increases with strain but does not depend on annealing temperature. Long annealing times, which induce complete recrystallization, and either normal or abnormal grain growth, enhance recovery of hysteresis losses. The rate of recovery increases as both the strain and annealing temperature increase. Recovery of the deformation microstructure and internal stress relief produce only limited recovery of the magnetic properties. However, recrystallization and grain growth brings about a significant decrease in hysteresis losses.
In-Situ Observation of Oxide Monolayer Formation on Copper Solid-Liquid Interfaces
Authors: Lagraff John R. , Cruickshank Brandon J. , Gewirth Andrew A.
Published: April 2011

It is extremely important to characterize the various bare copper surfaces in situ before any subsequent corrosion or deposition chemistry can be understood. In this paper, in situ Atomic Force Microscopy (AFM) was used to image the low-index faces of Cu single crystals in H2SO4 and HClO4 acidic solutions. Cu(100) surfaces exhibited potential-dependent c(2x2) adlayers in pH=1 solutions which were attributed to oxide (or hydroxide) overlayers. Images of Cu(1 10) obtained in pH 2.5-2.7 solutions revealed the growth of primarily [001] oriented (nxl) adlayer chain structures, where n is an integer. Preliminary measurements on Cu(111) did not reveal any adlayer structures between pH's of 1-3. The oxide monolayers on Cu(100) and Cu(110) crystals were observed in the thermodynamically forbidden region of the pH-potential phase diagram, which indicates that stable oxide adlayers develop prior to bulk oxide formation.
Electronic Structure and Bonding at Interfaces Between cvd Diamond and Silicon
Authors: Muller David A. , Tzou Yujiun , Raj Rishi , Silcox John
Published: April 2011

The interfacial structure of CVD diamond grown on silicon was studied using spatially resolved electron energy loss spectroscopy (EELS) in a UHV STEM with a subnanometer probe size. Both the plasmon and core excitations in the bulk appear to be localized on this scale. Spatial maps of the different bonding configurations of carbon were obtained by forming images from transmitted electrons that had undergone energy losses characteristic of threefold and fourfold coordinated carbon. Films grown on both prescratched silicon and intermediate amorphous carbon layers were examined. In the latter case, diamond nucleation on a narrow sp2 a-C occurred. For diamond grown directly on silicon, at some regions of the interface, threefold coordinated defect states smaller than 1 nm are observed on the diamond side of the interface while at other regions along the interface the presence of an intermediate 2nm thick SiC layer preserves the fourfold coordination of the carbon.
Porous Silicon Luminescence Study by Imaging Methods: Relationship to Pore Dimensions
Authors: Kontkiewicz Anna , Kontkiewicz Andrzej M. , Sen Sidhartha , Wesolowski Marek , Lagowski Jacek , Edelman Piotr , Kowalewski Tomasz
Published: April 2011

In a photoluminescence and surface photovoltage study of porous silicon films with crystallite dimensions assessed with the Atomic Force Microscope, we have found cases when the blue shifts of the luminescence spectrum and the optical absorption edge take place upon increasing crystallite dimensions, which is contrary to quantum size effects. Fourier transform infrared spectroscopy analysis of these samples shows significant differences in hydrogen and oxygen bonding, which imply that the origin of the luminescence is of chemical nature. Our results show that porous silicon luminescence is not a consequence of one mechanism, but rather results from several mechanisms with contributions depending on the chemistry and structure of porous silicon.
Composition and Strain Analysis of Semiconductor Heterostructures Using Thickness Fringes on Tem Images
Authors: Kakibayashi H. , Tsuneta R. , Nagata F.
Published: April 2011

Composition and strain depth profiles in heterostructures such as AlGaAs/GaAs, InGaAs/InP and SiGe/Si have been analyzed with a high resolution of 0.5 nm by using the thickness fringes in a transmission electron microscope image. This diagnostic method is found to successfully evaluate the compositional disordering caused by annealing multiple quantum well structures with abrupt interfaces, and determine the difference in strain distribution in the strained-layers with various lattice mismatches. Both the composition and strain depth-profiles are analyzed quantitatively by the image simulation based on the dynamical theory of electron diffraction. This method is also useful for sensitively detecting ion-implantation-induced defects.
Structural Investigation of NaNO3 Nanophase Confined in Porous Silica
Authors: Mu R. , Henderson D. O. , Jin F.
Published: April 2011

We have demonstrated that thermal and vibrational investigations of sodium nitrate (NaNO3) physically confined in the porous silica hosts is an effective approach to mimic the solute clustering effects in aqueous solution. The results show that the structure of the NaNO3 confined in nanopores can be divided into three regions, i.e., the regular solid phase region, solution-like molecular aggregates region, and a new solid-like phase region. Depending upon the pore size of the porous host, the physical range of the three regions varies accordingly. For pore size d <2.5 nm, only the solution-like molecular aggregates phase remains.
Nmr Studies of Electronic and Local Structure in Cu-Au Alloys
Authors: Chepin James , Ross Joseph H.
Published: April 2011

We have studied ordered and disordered Cu-Au alloys via 63Cu NMR, probing local electronic structure in the bulk and near anti-phase boundaries in CuAuII. A line-shape model has provided good agreement for disordered and partially ordered alloys, and we thus have obtained a measure of local site symmetries, and Knight shifts and local densities of states within the alloys. We have combined Knight shift and relaxation measurements to obtain detailed local information. We report effects of the ordering process in Cu3Au, CuAu, and CuAu3 intermetallics. We find enhanced susceptibility at the CuAuII anti-phase boundary which is heavily anti-site populated. We compare these results to other measurements of these properties.
The Field Emission Gun Scanning Electron Microscopehigh Resolution at Low Beam Energies
Authors: Joy David C
Published: April 2011

The scanning electron microscope (SEM) is the most widely used, as well as the most versatile, of electron-optical instruments. In all of the imaging modes of the instrument it is now possible to achieve a spatial resolution on the nanometer scale from a bulk specimen, provided that the electron-optical performance of the instrument is of the necessary quality. In practice this means that a field emission gun (FEG) as well as a highly excited probe forming lens must be used. With state-of-the-art instrumentation, image resolutions as good as 4 - 5 nm at lkeV, and lnm at 20keV, are now achievable. This paper outlines the design criteria for a high resolution FEG SEM and discusses the type of image information available. The performance achieved is compared to that of other types of microscope that offer similar capabilities.
Atom Probe Microscopy and its Future
Authors: Kelly T. F. , Camus P. P. , Larson D. J. , Holzman L. M.
Published: April 2011

Much of the current activity and excitement in materials science involves processing and understanding materials at the atomic scale. Accordingly, it is necessary for materials scientists to control and characterize materials at the atomic level. There are only a few microscopies that are capable of providing information about the structure of materials at the atomic level: the atom probe field ion microscope, the high resolution transmission electron microscope, and the scanning tunneling microscope. The three-dimensional atom probe (3DAP) determines the 3D location and elemental identity of each atom in a sample. It is the only technique that provides 3D information at the atomic scale.

The origin and underlying concepts behind the 3DAP are described. Several examples of actual images from existing 3DAPs are shown with emphasis on nanometer-scale analysis. Current limitations of the technique and expected future developments in this form of microscopy are described. It is our opinion that 3D atomic-scale imaging will be an indispensable tool in materials science in the coming decades.
Determination of the Mechanical Behaviour of Thin Films on Substrate Systems from Micromechanical Experiments
Authors: Ignat M. , Scafidi P. , Duloisy E. , Dijon J.
Published: April 2011

Micromechanical tensile experiments in a Scanning Electron Microscope (SEM) allowed us to identify and follow the activation of a variety of different deformation mechanisms, on several sorts of films on substrate systems. The investigated systems consisted of SiO2 and YF3 films deposited on copper and aluminium substrates, with or without an interlayer. The experimental results show that the mechanical response of the films differs, in particular, with respect to the interface response: the cracking activity will depend on the film adhesion. An attempt is made to relate the microstructural parameters of the assembled materials with the observed mechanisms, through models which are based on the shear lag formalism. Critical parameters of the systems under stress are determined and compared to theoretical calculations: critical stresses and strains for cracking, stress transfer lengths, interfacial fracture energies. The approach gives some insights on the mechanical response of films on substrate systems submitted to a tensile state of stress.
The Effect of Ultra-Low Temperature Treatments on the Stress in Aluminum Metallization on Silicon Wafers
Authors: Baldwin Frank , Holloway Paul H. , Bordelon Mark , Watkins Thomas R.
Published: April 2011

The stresses in Al-0.75w%Si-0.5w%Cu unpatterned metallization on silicon wafers have been measured using substrate curvature and x-ray diffraction techniques after quenching in liquid nitrogen. Stresses were measured with and without phospho-silicate glass overlayers and SiO2 underlayers, and thermal cycling followed by relaxation at room temperature. It was found that cooling the substrates to 77 K and warming to room temperature caused the metallization stress to go from tensile to compressive. Subsequent heating of the substrates to above ∼70°C followed by cooling to room temperature caused the stress to become tensile. Both compressive and tensile stresses were found to relax at room temperature with a time constant of 2.3 ± 0.2 hours. The magnitude of stress relaxation was a function of temperature, being about 20 MPa after heating to 240°C. The metallization exhibited both compressive and tensile flow stresses of ∼100 MPa near room temperature.
Transgranular Slits in Aluminum Interconnects Caused by Thermal Stress and Electric Current
Authors: Wang W. , Suo Z. , Hao T.-H.
Published: April 2011

An aluminum interconnect can fail by a transgranular slit. We show how a rounded void collapses to such a slit, as atoms diffuse on the void surface, driven by electric current, thermal stress, and surface energy. We use a variational principle to simulate the shape evolution, and identify the critical conditions to trigger the shape instability.
Cracking Mechanisms of Fine Lines by Microwedge Scratch Testing
Authors: Boer M. P. dE , Huang H. , Nelson J. C. , Lilleodden E. T. , Gerberich W. W.
Published: April 2011

Three types of cracks associated with interfacial failure of a tungsten fine line on silicon oxide (SiO2) have been observed in microwedge scratch testing (MWST) of fine lines. They were identified by carefully controlling scratch conditions in a continuous microindenter system1, in conjunction with SEM micrographs. The first type is a hinge crack, which is responsible for nucleating an interfacial crack. The driving force for the hinge crack is the difference in stress conditions in the middle on theline (plane strain) and the outside of the line (plane stress). The second type is the interfacial crack, which is driven by the movement of the microwedge. This crack is modelled by the finite element method (FEM) to obtain an interfacial work of adhesion value. The third type of crack is a spallation crack, and is driven by tensile strains associated with buckling of the thin film once the interfacial crack becomes sufficiently long. Tensile strains in the film at the maximum crack length are calculated by FEM in order to arrive at a value of thin film fracture strength. A brittle failure mechanism has beenconfirmed by a micrograph of a spalled piece exhibiting no perceptible plastic deformation.
Atomic Force Microscopy Structural Characterization of Polyaniline Thin Film Sensors
Authors: Josefowicz Jack Y. , Yamagishi Frederick G. , Ast Camille I. van
Published: April 2011

Using Tapping Mode Atomic Force Microscopy (TMAFM), the surface structure was determinedfor polymer sensors which incorporated polyaniline (PAn) films that were deposited electrochemically across narrow insulating gaps between interdigitated gold electrodes. The sensitivity and response time for such sensors, which can be used for the detection of low levels of gases and low concentrations of impurities in liquid media critically dependon the quality and structure of the polymer film in the gap region between the gold electrodes. TMAFM images of the PAn films ranging in thickness between ≈1.5μtmand ≈5μm reveal that films approaching 5μm (typically used in such sensors) develop deep cracks at the edges and along the length of the Au electrodes. Thecracks, which appear to be a consequence of stress build-up in thick films, can lead to reliability problems and inferior sensor performance. Simple modeling analysis of cracked films indicates that they can lower sensitivity and increase response time. TMAFM images of sensors with thinner ≈2.5μm PAn films show no cracks as well as continuous PAn bridges across the gap between Au electrodes. Analyses of TMAFM images are presented and compared for thin and thick film PAn sensors.
Embedded Circuitry in Polymeric Films by Linear Energy Transfer (Let) of MeV Ions
Authors: Ila D. , Evelyn A. L. , Qian Y.
Published: April 2011

We have developed a technique to fabricate embedded variable conductivity paths in phenolformaldehyde, PF-resin, with resistivity as high as 109 Ω-cm. The resin used for this work consists of a monomer called Phenyl Methanol (Resol) which upon setting at 150ºC will form short chains of polymers with high resistivity. The conductive paths are produced at depths of 4 to 35 micrometers by changing the energy of thebombarding ions. The resistivity of each path is controlled between 109 Ω-cm to 10 Ω-cm by adjusting the ion dose. The ions used in this work are nitrogen, alphas and protons with energies between 0.5 and 6.5 MeV to form conductive paths as narrow as 0.5 mm and as wide as 4 mm.
Atomic Scale Structure and Chemistry of Interfaces by Z-Contrast Imaging and Electron Energy Loss Spectroscopy in the Stem
Authors: McGibbon M. M. , Browning N. D. , Chisholm M. F. , McGibbon A. J. , Pennycook S. J. , Ravikumar V. , Dravid V. P.
Published: April 2011

The macroscopic properties of many materials are controlled by the structure and chemistry at grain boundaries. A basic understanding of the structure-property relationship requires a technique which probes both composition and chemical bonding on an atomic scale. High-resolution Z-contrast imaging in the scanning transmission electron microscope (STEM) forms an incoherent image in which changes in atomic structure and composition across an interface can be interpreted directly without the need for preconceived atomic structure models (1). Since the Z-contrast image is formed by electrons scattered through high angles, parallel detection electron energy loss spectroscopy (PEELS) can be used simultaneously to provide complementary chemical information on an atomic scale (2). The fine structure in the PEEL spectra can be used to investigate the local electronic structure and the nature of the bonding across the interface (3). In this paper we use the complimentary techniques of high resolution Zcontrast imaging and PEELS to investigate the atomic structure and chemistry of a 25° symmetric tilt boundary in a bicrystal of the electroceramic SrTiO3.
Crystallization of Epitaxial Lanthanum Aluminate and Spinel Thin Films Derived from Nitrate Precursors
Authors: Ng Man Fai , Cima Michael J.
Published: April 2011

Both lanthanum aluminate (LaAIO 3) and spinel (MgAl2O 4) epitaxial thin films have been deposited on either planar and stepped (100) SrTiO3 single crystal substrates by pyrolysis of mixed nitrate precursors. The precursors pyrolyze initially into amorphous films. Nucleation of lanthanum aluminate and spinel occurs at the filnVsubstrate interface at higher temperature. Crystallization of LaAlO3 on SrTiO3 substrates occurs at approximately 650°C, whereas nucleation occurs at approximately 800'C without lattice-matched substrates. Similarly, latticematched substrates reduce the crystallization temperature of spinel to below 700°C. The epitaxial film grows at the expense of the amorphous film after the initial nucleation at the interface. The rapid growth and volume change due to the crystallization leave behind an epitaxial film with nanoporosity of 15 to 30 nm. Nevertheless, the surfaces of these films have roughness of only 6–9 Å. Ba2Ycu3O7-x films derived from metalorganic deposition of metal trifluoroacetate precursors was deposited on these epitaxial LaAlO3 films on both planar and stepped SrTiO3 substrates. The resultant YBCO films on LaAlO3 film on planar SrTiO3 substrate have critical current densities of > 2 × 106 A/cm2 at 77K and zero field.
Epitaxial Dielectric Planarization for Multilayer HTSC Structures
Authors: Chang Bertha P. , Mcintyre Paul C. , Sonnenberg Neville , Cima Michael J.
Published: April 2011

Yttria-stabilized ZrO2 (YSZ) and CeO2 thin films were deposited on patterned (001) YSZ and (001) LaAIO3 substrates, respectively, using ion beam assisted deposition (IBAD) at normal incidence and an ion beam energy of 500eV. All deposition took place at 600°C. An initial 1000Å thick layer was evaporated at 0.2Å/s before beginning IBAD at rates of 0.3Å/s for YSZ and between 0.8Å/s and 1.2Å/s for CeO2. X-ray diffraction shows the YSZ films to grow epitaxially. The planarization mechanism for IBAD YSZ is similar to that previously observed for if-bias sputtering. CeO2 grows epitaxially on LaA103 but a second polycrystalline phase grows preferentially over the surface steps and inhibits the planarization process. The emergence of this phase appears to be related to highly incoherent growth of CeO2 over the stepped edges, which in turn is a function of the large lattice mismatch between CeO2 and LaA1O3 in the [001] direction.
Properties of Iron Oxide Films Grown by Pulsed Laser Deposition
Authors: Choi H. S. , Ahn J. S. , Jo William , Noh T. W. , Chun S. H. , Khim Z. G.
Published: April 2011

Epitaxial magnetite (Fe3O4) thin films have been grown on MgO(001) substrates by pulsed laser deposition. The films have characteristics of the “Verwey transition”: the electric conductivity decreases by about one order of magnitude and the magnetization curve shows anomaly at the transition temperature, i.e. about 125 K. Effects of annealing the Fe3O4 thin films at various oxygen partial pressures have also been investigated. Phase identification was made using XRD techniques and infrared reflectivity measurements. The surface morphologies were studied by SEM and AFM. Under an oxidizing atmosphere, the Fe3O4 phase is transformed mainly into α-Fe2O3, and this transformation is accompanied by development of needle-like structures along <110> directions of MgO substrate. It is also found that electrical and magnetic properties of the iron oxide films are changed significantly by the annealing process.
Deposition of Monolayer-Scale Germanium/Silicon Heterostructures by Rapid Thermal Chemical Vapor Deposition
Authors: Amour A. St. , Sturm J.C.
Published: April 2011

Deposition of monolayer scale Ge/Si heterostructures by Rapid Thermal Chemical Vapor Deposition has been achieved for the first time. All previous work in this area was by Molecular Beam Epitaxy. We have observed the change in Ge growth rate at 500°C as the Si substrate was covered by the first monolayer of Ge. Auger Electron Spectroscopy and Raman scattering experiments determined that the CVD growth mode for Ge on Si (100) at 550°C is Stranski-Krastanov, with the transition to islanding occurring after three monolayers.