bluuebunny/crossref_metadata_2025 huggingface dataset:
Low Energy Ion Assisted Vapor Deposition
Authors: Zhou X. W. , Wadley H. N. G.
Published: April 2011

The performance of multilayered thin film materials often depends sensitively upon the (physical) roughness and degree of (chemical) mixing at interfaces. Irradiation of a growth surface with an assisting ion beam is often used to modify surface roughness. Molecular dynamics has been used to explore the use of low energy (less than 20 eV) Xe+ and Ar+ assisted deposition of model Ni/Cu/Ni multilayers to control both physical roughness and chemical mixing. The study indicated that under normal ion incidence condition, ion energies as low as 3 eV could effectively flatten the relatively weakly bonded copper surface (and therefore the nickel on copper interface). Higher ion energies (at least 10 eV) were required to flatten the more strongly bonded nickel surface. Chemical intermixing by an exchange mechanism between a surface atom and an underlying atom in an already deposited layer depended upon the binding energy of the already deposited layer. As a result, significant chemical mixing occurred as 9 eV (and above) ions impacted with nickel atoms on an already deposited copper surface. At a given ion incident energy, (the heavier) Xe+ ions resulted in less roughness but more mixing. A modulated ion assistance strategy in which no assisting ion beam was used while depositing the first few monolayers of each new metal layer was found to successfully reduce both interfacial roughness and interlayer mixing.
Controlling the Diamond Film Morphology by Low-Energy Electron Bombardment
Authors: González J. A. , Figuero O. L. , Weiner B. R. , Morell G.
Published: April 2011

We studied the effects of low-energy electron bombardment during diamond growth over the film crystalline quality and morphology. The film growth was monitored via the effective extinction coefficient (k) at 1.96 eV with in situ ellipsometry, in order to determine the developmental stage of the film in real time. Taking advantage of this in situ monitoring, we triggered the electron bombardment over the growing surface at different growth stages and studied the corresponding induced changes in film morphology and crystalline quality. Ex situ Raman spectroscopy and scanning electron microscopy (SEM) were also employed to evaluate the crystalline quality and the morphology of the grown films, respectively. We found that electron bombardment can be used to control the surface morphology of the films (triangular, pyramidal, square, amorphous). The results also indicate that applying the electron bombardment over the diamond film during the whole time of growth is detrimental to its crystalline quality and favors the formation of non-sp3 carbon. However, when the electron bombardment is triggered just after high quality scattered diamond crystallites have formed, the resulting film is of similar quality as those grown without bombardment. Therefore, properly chosen and triggered electron bombardment during diamond growth by chemical vapor deposition (CVD) can be used to control the film morphology while maintaining the film crystalline quality.
Inclined Substrate Deposition by Evaporation of Magnesium Oxide for Coated Conductors
Authors: Bauer Markus , Metzger Ralf , Semerad Robert , Berberich Paul , Kinder Helmut
Published: April 2011

Biaxially textured MgO buffer layers were deposited on metal substrates using “inclined substrate deposition” (ISD). The influence of the substrate inclination angle, deposition rate, and film thickness on the texture is shown. Scanning electron microscopy reveals columnar growth. We developed a growth model to explain the texturing. To test this model we have carried out 3D Monte-Carlo simulations. We find that the preferred orientation arises from mutual shadowing of the columns and directional surface diffusion due to their initial momentum.

YBa2Cu3O7 (YBCO) films deposited on the ISD buffer layers are highly textured. The ab-planes of the YBCO are tilted with respect to the surface by typically 25° towards the direction of MgO vapor incidence. Therefore, the critical current density jc is anisotropic with up to 8 × 105 MA/cm2 in one direction and 4 × 105 MA/cm2 in the other. For tape coating the MgO deposition direction can be chosen so that the high jc is along the tape.
Flux Mapping and Magnetic Behavior of Grain Boundaries in Nd-Fe-B Magnets
Authors: Volkov V.V. , Zhu Yimei
Published: April 2011

Advanced Fresnel- & Foucault-Lorentz microscopy were applied to analyze magnetic behavior of the grain boundaries in Nd-Fe-B hard magnets. In-situ TEM magnetizing experiments combined with these imaging methods revealed the process of magnetization reversal in polycrystalline sintered and die-upset Nd-Fe-B under various magnetic fields. Fine details of magnetic flux distribution, derived from the magnetic interferograms created by phase-coherent Foucault imaging, provide a quantitative description of the local variation of magnetic flux. Our study suggests that the grain boundaries play an important multi-functional role in the reversal of magnetization, by acting as (a) pinning centers of domain walls, (b) centers of nucleation of reversal domains, and (c) sinks or sources for migrating magnetostatic charges and/or dipoles. They also ensure a smooth transition for irreversible remagnetization in polycrystalline samples.
Investigation of Copper Segregation to the Σ5(310)/[001] Symmetric Tilt Grain Boundary in Aluminum
Authors: Plitzko Jürgen M. , Campbell Geoffrey H. , King Wayne E. , Foiles Stephen M.
Published: April 2011

The Σ5 (31O)/[001] symmetric tilt grain boundary (STGB) in the face centered cubic (FCC) metal aluminum with 1at% copper has been studied. The model grain boundary has been fabricated by ultra-high vacuum diffusion bonding of alloy single crystals. The segregation of the copper has been encouraged by annealing the sample after bonding at 200 °C. TEM samples of this FCCmaterial were prepared with a new low voltage ion mill under very low angles.

The atomic structure of the Σ5(310)/[001] STGB for this system was modeled with electronic structure calculations. These theoretical calculations of the interface structure indicate that the Cu atoms segregate to distinct sites at the interface. High resolution electron microscopy (HRTEM) and analytical electron microscopy including electron energy spectroscopic imaging and X-ray energy dispersive spectrometry have been used to explore the segregation to the grain boundary. The HRTEM images and the analytical measurements were performed using different kinds of microscopes, including a Philips CM300 FEG equipped with an imaging energy filter. The amount of the segregated species at the interface was quantified in a preliminary way. To determine the atomic positions of the segregated atoms at the interface, HRTEM coupled with image simulation and a first attempt of a holographic reconstruction from a through-focal series have been used.
Fabrication and Field Emission Properties of Carbon Nanotube Cathodes
Authors: Bower C. , Zhou O. , Zhu W. , Ramirez A. G. , Kochanski G. P. , Jin S.
Published: April 2011

A variety of carbon nanotube films have been fabricated and tested as cold cathodes. A spray deposition technique was developed for processing as-grown bulk nanotubes, both single-walled and multi-walled, into films of randomly oriented nanotubes. Films of randomly oriented multi-walled nanotubes were grown using thermal chemical vapor deposition, and arrays of well-aligned multi-walled nanotubes have been fabricated using a microwave plasma enhanced chemical vapor deposition technique. The emission current-voltage (I-V) characteristics of these nanotube cathodes have been measured. Both multi-walled (random and aligned) and single-walled carbon nanotubes exhibit low turn-on fields (∼ 2 V/μm to generate 1 nA) and threshold fields (< 5 V/μm to generate 10 mA/cm2). Significantly, these cathodes were capable of operation at very large current densities (> 1A/cm2), making them candidates for application in a variety of vacuum microelectronic devices.
Aligned Carbon Nanotubes Via Microwave Plasma Enhanced Chemical Vapor Deposition
Authors: Cui H. , Palmer D. , Zhou O. , Stoner B. R.
Published: April 2011

Aligned multi-wall carbon nanotubes have been grown on silicon substrates by microwave plasma enhanced chemical vapor deposition using methane/ammonia mixtures. The concentration ratio of methane/ammonia in addition to substrate temperature was varied. The morphology, structure and alignment of carbon nanotubes were studied by scanning electron microscopy and transmission electron microscopy. Both concentric hollow and bamboo-type multi-wall carbon nanotubes were observed. Growth rate, size distribution, alignment, morphology, and structure of carbon nanotubes changed with methane/ammonia ratio and growth temperature. Preliminary results on field emission properties are also presented.
Effects of O2 Gas Addition on Diamond-Like Carbon Film Deposition
Authors: Nakamura N. , Itani T. , Chiba H. , Watanabe K. , Kurihara K.
Published: April 2011

The role of 02 gas addition on the deposition of Diamond-like Carbon (DLC) film was studied for hard disk drive (HDD) media application. The influence of 02 gas mixing ratio on DLC film quality was investigated using the dc magnetron sputtering method with a solid graphite target and Ar, CH4 and 02 mixing gases. The 02 mixing ratio was varied between 0% and 50%. Film quality was evaluated using Raman spectroscopy and XPS. When 02 gas mixing ratio increased the peak in Raman spectra shifted gradually to higher wavenumbers and its bandwidth became narrower. This indicates graphite component increased in the DLC film. In addition, the lubricant coverage on oxygen-containing DLC was improved. Because adding oxygen increases the terminations of carbonyl group on DLC surface, this result suggests that the polar surface causes higher affinity for the lubricant
High Reverse Breakdown a-C:H/Si Diodes Manufactured by rf-PECVD
Authors: Paul Shashi , Clough F.J
Published: April 2011

Thin films of hydrogenated amorphous carbon ( a-C:H ) deposited by radio frequency plasma-enhanced chemical vapour deposition (rf-PECVD) have been studied for various applications. An interesting property of these films is their high breakdown strength ( 107 Vcm−1 ). This property of a-C:H can be exploited in high breakdown heterostructure diodes or as passivation layers and insulator layers in MIS devices. Reports on the applications of a-C:H/Si diodes exist in the literature. Diodes in which the a-C:H films have been deposited by rf-PECVD, have been reported only once. In this article the diodes produced reportedly failed to exhibit reproducible I-V characteristics under high voltage stress. We have investigated the process dependence of structural and electrical properties of rf-PECVD a-C:H films deposited at room temperature from a CH4/Ar gas mixture (at a pressure of 100 mTorr) using a capacitively coupled rf-PECVD. We observe a clear correlation between the dc-self bias and the rectification ratio of a-C:H/Si heterojunction diodes. Optimised diodes show rectification ratios upto 104 and a stable reverse breakdown voltage, typically around 850 V. I-V and C-V measurements show no evidence of hystersis. Scanning Electron Microscopy was carried out to determine the quality of the films deposited. Micro-Raman analysis was used to estimate the ID/IG ratio in the films deposited under different dc-self bias.
UV Raman Studies of Microcrystalline Diamond
Authors: Okada Katsuyuk , Kanda Hisao , Komatsu Shojiro , Matsumoto Seiichiro
Published: April 2011

Microcrystalline diamond films have been prepared in a 13.56 MHz low pressure inductively coupled plasma, in which the pressure of CH4/H2and CH4/CO/H2 plasmas was varied from 45 to 50 mTorr. The bonded structures of the obtained deposits were studied by Raman spectroscopy with 514, 325, and 244 nm excitation wavelength. 514 nm excited Raman spectra exhibit two peaks at ∼1355 cm−1 and ∼1580 cm−1 corresponding to sp2 bonding without CO additive (CH4/H2, plasma). New peaks at ∼1150 cm−1 assigned to sp3-bonded carbon network and at ∼1480 cm−1 appear with CO additive (CH4/CO/H2, plasma). 325 nm excited Raman spectra show a shoulder at ∼1150 cm−1, a clear 1332 cm−1 diamond peak, and the peak at ∼1580 cm−1 is remarkably enhanced. In 244 nm excited Raman scattering, the 1332 cm−1 diamond peak is only enhanced whereas the peak at ∼1580 cm−1 is correspondingly diminished. These features of the Raman spectra imply that the vibrational modes of sp2 sites are resonantly enhanced with 514 nm excitation because the 514 nm (2.4 eV) corresponds to the π-π* transition in sp2-bonded carbon, while the 325 nm (3.8 eV) and 244 nm (5.1 eV) excitations are possibly sufficient to excite the σ state of both sp2- and sp3-bonded carbon
Tensile Properties of Amorphous Diamond Films
Authors: LaVan D.A. , Hohlfelder R.J. , Sullivan J.P. , Friedmann T.A. , Mitchell M. , Ashby C.I.H.
Published: April 2011

Amorphous diamond is a new material for surface micromachined microelectromechanical systems (MEMS) and sensors. Its strength and modulus was tested in uniaxial tension by pulling laterally on a specially designed sample with a flat tipped diamond in a nanoindenter. Several sample designs were attempted. Of those, only the single layer specimen with a 1 by 2 μm gage cross section and a fixed end rigidly attached to the substrate was successful. Tensile load was calculated by resolving the measured lateral and normal forces into the applied tensile force and frictional losses. Displacement was corrected for machine compliance using the differential stiffness method. Post-mortem examination of the samples was performed to document the failure mode. The load-displacement data from those samples that failed in the gage section was converted to stress-strain curves using carefully measured gage cross section dimensions. Mean fracture strength was found to be 8.5 ± 1.4 GPa and the modulus was 831 ± 94 GPa. Tensile results are compared to hardness and modulus measurements made using a nanoindenter
Coalescence of C60 Molecules in Fullerite by Intense Femtosecond Laser Pulses: An Ab–Initio Simulation
Authors: Gambirasio A. , Bernasconi M. , Benedek G. , Silvestrelli P. L.
Published: April 2011

We present an ab–initio molecular dynamics study of the modifications induced on fullerite by the irradiation with ultrashort very intense laser pulses. We identified the threshold for the non–thermal cage–opening of the C60 molecules which is the analogue of the laserinduced non–thermal melting observed in semiconductors and graphite. The new phase formed by the non–thermal coalescence of the C60 molecules is fluid–like and mainly formed by small chains of 2–fold coordinated carbon atoms.
Dehydration Time Dependence on Piezoelectric and Mechanical Properties of Bovine Cornea
Authors: Jayasuriya A. C. , Scheinbeim J. I. , Lubkin V. , Bennett G. , Kramer P.
Published: April 2011

The Young's Modulus (E) and piezoelectric coefficient (d31) have been investigated as a function of dehydration time for bovine cornea at room temperature. The piezoelectric and mechanical responses observed were anisotropic for bovine cornea and d31 decreased, while E increased with dehydration. In addition, water molecules appear to increase the crystallinity (of collagen) in the cornea. With dehydration of the cornea, reduction of crystallinity and changes in hydrogen bonding were observed by Fourier Transform Infra Red (FTIR) and Wide Angle X-ray Diffracion (WAXD) measurements.
Novel Polymer Electrets
Authors: Sessler G. M. , Hillenbrand J.
Published: April 2011

Permanently charged films with a cellular or porous structure represent a new family of polymer electrets. These materials show piezoelectric properties with high transducer constants. The electromechanical response equations of such films are derived for their operation as sensors and as actuators. Experimental results are also presented for cellular polypropylene. In particular, measurements of the direct and inverse transducer constants, the thermal stability of the charge, and Young's modulus are discussed. Assuming reasonable charge distributions and charge densities, the calculated transducer constants are in good agreement with the measured values. Both the theoretical model and the measurements show the reciprocity of the transducer constants.
Polarization Stability of Amorphous Piezoelectric Polyimides
Authors: Park C. , Ounaies Z. , Su J. , Smith J. G. , Harrison J. S.
Published: April 2011

Amorphous polyimides containing polar functional groups have been synthesized and investigated for potential use as high temperature piezoelectric sensors. The thermal stability of the piezoelectric effect of one polyimide was evaluated as a function of various curing and poling conditions under dynamic and static thermal stimuli. First, the polymer samples were thermally cycled under strain by systematically increasing the maximum temperature from 50°C to 200°C while the piezoelectric strain coefficient was being measured. Second, the samples were isothermally aged at an elevated temperature in air, and the isothermal decay of the remanent polarization was measured at room temperature as a function of time. Both conventional and corona poling methods were evaluated. This material exhibited good thermal stability of the piezoelectric properties up to 100°C.
EQCM and Quartz Crystal Impedance Measurements for the Characterization of Thiophene-Based Conducting Polymers
Authors: Arbizzani C. , Soavi F. , Mastragostino M.
Published: April 2011

EQCM was extensively used to investigate ion-transport phenomena during dopingundoping processes of electronically conducting polymers. Several early studies assumed that the polymer films were rigidly coupled to the quartz crystal so as to relate the mass change to the quartz crystal resonant frequency change via the Sauerbrey equation. However, the rigidity of electronically conducting polymer films is doubtful and it has to be demonstrated. Quartz crystal impedance analysis near the resonance is of paramount importance to get insight into the viscoelastic properties of the film [1] and to avoid misleading in the interpretation of EQCM data.

This contribution presents and discusses quartz crystal impedance measurements, performed with a Frequency Response Analyzer in the 9MHz region, and EQCM data collected for a dithienothiophene based polymer.
Polythiophene Grafted on Polyethylene Film
Authors: Chanunpanich N. , Ulman A. , Strzhemechny Y. M. , Schwarz S. A. , Domicik J. , Rafailovich M. , Sokolov J. , Janke A. , Braun H. G. , Kratzmüller T.
Published: April 2011

We have successfully grafted polythiophene on polyethylene (PE) film with a three reactions step: gas phase bromination on PE, yielding PE-Br; substitution reaction of PE-Br with 2-thiophene thiolate anion, following by chemical oxidative polymerization. The polymerization was carried out in a suspension solution of anhydrous FeCl3 in CHCl3, yielding a reddish PE-PT film after dedoping with ethanol. ATR-FTIR shows that the polythiophene (PT) was grafted on PE in the 2,5-position; on the other hand, PT homopolymer shows a small amount of 2,4 coupling. XPS reveals higher intensity of the S2p, including neutral and positive sulfur. SEM image reveals the island of PT on the PE film. AFM analysis found the thickness of the island is in the range of 120–145 nm. The conductivity of these thin films is in the range of 10−6 S/cm.
Polymer Electrolyte Actuator Driven by Low Voltage
Authors: Oguro K. , Asaka K. , Fujiwara N. , Onishi K. , Sewa S.
Published: April 2011

Composites of perfluorinated polymer electrolyte membrane and gold electrodes bend in response to low-voltage electric stimuli and work as soft actuators like muscles. The composites were prepared by chemical plating. Charge on the electrode induces electric double layer and electro-osmotic drag of water by cation from anode to cathode through narrow channels in the perfluorinated ion-exchange resin. The electro-osmotic flow of water swells the polymer near the cathode rather than anode, and the membrane bends to the anode. The actuator comprises polymer electrolyte, electrodes, counter ion, solvent, lead wires, etc. Each component affects the performance of the actuator. Surface area of electrode and species of counter ion have drastic effect on voltage-displacement response. The response may depend on water channel structure of the polymer electrolyte. Modification of these factors improved the performance and resulted in the deflection over 360 degrees at a film actuator of 10 mm length. A tubular actuator was demonstrated as a multidirectional actuator. These actuators are applicable to artificial muscle, micro robots, or micro medical equipment inside body.
Compliant Actuators Based on Electroactive Polymers
Authors: Wax S G. , Sands R. R. , Buckley L. J.
Published: April 2011

The field of Electroactive Polymers has experienced a considerable amount of expansion over the last decade. Much of this work has been concentrated on developing polymeric materials that mimic biological systems or that exhibit electronic and optical properties similar to inorganic materials. This paper briefly reviews some of the nearer term applications that electroactive polymers might impact: image processing and sonar. In addition, a review of compliant actuators based on the unique properties inherent in electroactive polymers is provided. Emphasis will be placed on the mechanisms responsible for actuation and on the limited mechanical, electrical and chemical data current available. A comparison between mammalian muscle properties and electroactive polymer actuator properties is provided.
Assessing Failure Mechanisms During Transformation Superplasticity of Ti-6Al-4V
Authors: Schuh C. , Dunand D. C.
Published: April 2011

During thermal cycling through the α/β phase transformation under the action of a small external biasing stress, Ti alloys exhibit an average deformation stress exponent of unity and achieve superplastic strains. We report tensile experiments on Ti-6Al-4V with an applied stress of 4.5 MPa, aimed at understanding the failure processes during transformation superplasticity. The development of cavities is assessed as a function of superplastic elongation, and macroscopic neck formation is quantified at several levels of elongation by digital imaging techniques. The effects of thermal inhomogeneity on neck initiation and propagation are also elucidated experimentally.
Influence of Deformation Speed on Fatigue and Tensile Properties of a Ti-Ni-Cu Shape Memory Alloy
Authors: Kishi Y , Yajima Z. , Shimizu K , Asai M.
Published: April 2011

The mechanical fatigue life and tensile property of a Ti-41at.%Ni-8.5at.%Cu alloy, which was solution-treated after some thermo-mechanical treatments, were investigated at 370±1 K as a function of deformation speed. The tensile properties were also investigated at 295±1 K as a function of deformation speed. The B2→B19 martensitic transformation start temperature, Ms, of the alloy was determined to be 338 K by a differential scanning calorimetry, while that of the as-rolled alloy could not be determined. Two types of fatigue tests were carried out by using plate-shaped specimens of 3.5 mm width and 1.5 mm thickness with sinusoidal waveform stresses of 20 Hz and 0.5 Hz frequencies being applied respectively. The fatigue life obtained from the 20 Hz tests was superior to that from the 0.5 Hz tests, the former being about 2 times longer than the latter at the same stress level. Tensile tests were performed at three tensilem speeds of 8.3 × 106, 8.3 × 10−5 and 8.3 × 10−3 m/s. In all the stress - strain curves obtained, an apparent yielding was observed after the liner elastic deformation. The apparent yielding is due to the occurrence of martensitic transformation. The critical stress for inducing martensite and tensile fracture stress increased with increasing tensile speed. Therefore, it is clear that fatigue and tensile properties of Ti-Ni-Cu shape memory alloys are strongly affected by not only test temperature but also deformation speed.
Properties and Applications of Magnetorheological Fluids
Authors: Jolly M.R.
Published: April 2011

Magnetorheological (MR) fluids are materials that respond to an applied magnetic field with a change in rheological behavior. Typically, this change is manifested by the development of a yield stress that monotonically increases with applied field. Interest in MR fluids derives from their ability to provide simple, quiet and rapid response interfaces between electronic controls and mechanical systems. In this paper, the basic composition and properties of example MR fluids are reviewed. Some contemporary applications of MR fluids are then discussed.
Computer Microvision for MEMS
Authors: Freeman Dennis M.
Published: April 2011

We have developed a versatile instrument for in situ measurement of motions of MEMS. Images of MEMS are magnified with an optical microscope and projected onto a CCD camera. Stroboscopic illumination is used to obtain stop-action images of the moving structures. Stopaction images from multiple focal planes provide information about 3D structure and 3D motion. Image analysis algorithms determine motions of all visible structures with nanometer accuracy.

Hardware for the system includes the microscope, CCD camera and associated frame grabber, piezoelectric focusing element, and a modular stimulator that generates arbitrary periodic waveforms and synchronized stroboscopic illumination. These elements are controlled from a Pentium-based computer using a graphical user interface that guides the user through both data collection and data analysis. The system can measure motions at frequencies as high as 5 MHz with nanometer resolution, i.e., well below the wavelength of light.
Effect of As-Processed and Annealed Microstructures on the Mechanical Properties of Liga Ni MEMS
Authors: Xie Z. L. , Pan D. , Last H. , Hemker K. J.
Published: April 2011

Microstructure – mechanical property relations of 200 μm thick LIGA deposited Ni films have been investigated with a combination of optical cross-sectional microscopy and microsample tensile testing. Measurements of the grain size and morphology of nine different asdeposited films evidenced a predominantly columnar microstructure with significant variations in grain size. These as-deposited microstructural variations resulted in a range of Young's modulus, yield strength, and ultimate tensile strength values that are consistent with previously reported measurements, but these values did not appear to scale with the as-deposited microstructures. By contrast, significant changes in both the microstructure and mechanical properties were observed when these films were annealed at 800'C for 1 hour. Recrystallization and grain growth transformed the grain morphology from columnar to equiaxed, which resulted in a dramatic decrease in the tensile strength and corresponding increase in the ductility of the annealed films.
Static and Dynamic Characterization of Buckled Composite SiO2-Au Microbridges
Authors: Nicu L. , Bergaud C. , Martinez A. , Temple-Boyer P.
Published: April 2011

Theoretical and experimental investigations have been made to study the nonlinear static and dynamic behavior of composite Si02-Au microbridges. Measurements of maximal deflection amplitude were carried out on arrays of clamped-clamped SiO2-Au beams buckling under the effect of thin film effective residual stress. The static analysis adresses the issue of microfabricated beam buckling from an energy point of view. SiO2-Au and Au effective residual stresses are evaluated by considering the measured buckling maximal deflection and by through an adequate approximation of the shape of the microbeam deflection curve. The dynamic approach is based on a direct analytical model yielding an exact solution to the linear problem associated with the nonlinear vibrations of initially buckled clamped-clamped structures. Several experimental multi-mode dynamic responses of composite buckled beams are also given to illustrate the validity and accuracy of this analytical model.
Synthesis of High-K Titanium Oxide Thin Films Formed by Metalorganic Decomposition
Authors: Fukuda Hisashi , Ishikawa Yoshihiro , Namioka Seiogo , Nomura Shigeru
Published: April 2011

Titanium oxide (TiO2) thin ftlms were formed on a Si substrate by metalorganic decomposition(MOD) at temperatures ranging from 600 to 1100°C. As-deposited films were in the amorphous state and were completely transformed after annealing at 600°C to a crystalline structure with anatase as its main component. During crystallization, a reaction between TiO2 and Si occurred at the interface, which resulted in the formation of a thin interfacial SiO2 layer. Capacitance-voltage measurement showed good dielectric properties with a maximum dielectric constant of 76 for films annealed at 700°C. For the crystallized TiO2 films, the interface trap density was 1 × 1011 cm−2 eV−1, and the leakage current was 1 × 10−8 A/cm2 at 0.2 MV/cm. The modified structure of TiO2/SiO2/Si is expected to be suitable for the dielectric layer in an integrated circuit in place of conventional SiO2 films.
Selection and Design of Precursors for the MOCVD of Lead Scandium Tantalate
Authors: Jones A.C , Davies H.O. , Leedham T.J. , Crosbie M.J. , Wright P.J. , Brien P.O'. , Fleeting K.A.
Published: April 2011

Metalorganic chemical vapour deposition (MOCVD) is a promising technique for the deposition of the pyroelectric oxide lead scandium tantalate, Pb(Sc0.5Ta0.5)O3. In order to exploit the full potential of the method, it is important to identify the optimum combination of precursors so that process parameters and film properties are optimised. In this paper, the molecular design of new, more compatible Ta and Sc oxide precursors is described and it is shown how the use of carefully matched precursors allows the growth of Pb(Sc0.5Ta0.5)O3 in the required perovskite phase at low substrate temperatures.
Deposition of SiO2:F:C Films With Low Dielectric Constant and With High Resistance to Annealing
Authors: Lubguban J. , Kurata Y. , Inokuma T. , Hasegawa S.
Published: April 2011

SiO2:F:C films were deposited using a plasma-enhanced chemical vapor deposition (PECVD) technique from SiH4/O2/CF4/CH4 mixtures. Increasing amount of carbon were introduced to the SiO2:F films by changing the CH4 flow rate, [CH4], while keeping constant other conditions such as rf power and deposition temperature, TD. It was found that the addition of CH4 decreases the dielectric constant, k; from 3.36 for [CH4] = 0 sccm to 2.95 for [CH4] = 8 sccm. For the [CH4] condition where the film has a lowest k, the deposition temperature and rf power were optimized by depositing films using different values of TD and rf power The k for films in the new series as well as the stress and water absorption was investigated. Results show that the dielectric constant further decrease up to 2.85. Some films were then annealed from 400 - 800 °C and it was found that the k for films deposited with higher [CH4] has a better stability with respect to annealing up to a temperature of 600 °C.
Time-Resolved Photoluminescence Studies of InxGa1−xAs1−yNy
Authors: Smith M. , Mair R. A. , Lin J.Y. , Jiang H. X. , Jones E. D. , Allerman A. A. , Kurtz S. R.
Published: April 2011

Time-resolved photoluminescence spectroscopy has been used to investigate carrier decay dynamics in InxGa1−xAs1−yNy (x ∼ 0.03, y ∼ 0.01) epilayers grown on GaAs by metalorganic chemical vapor deposition. Time-resolved PL measurements, performed for various excitation intensities and sample temperatures, indicate that the broad PL emission at low temperature is dominated by localized exciton recombination. Lifetimes in the range of 0.07–0.34 ns are measured; these photoluminescence lifetimes are significantly shorter than corresponding values obtained for GaAs. In particular, we observe an emission energy dependence of the decay lifetime at 10 K, whereby the lifetime decreases with increasing emission energy across the PL spectrum. This behavior is characteristic of a distribution of localized states, which arises from alloy fluctuations. We have also studied the effects of post-growth rapid thermal annealing (RTA) on the integrated photoluminescence emission intensity, which indicate that the optimal annealing conditions is 690 °C when annealed for 120 seconds in a nitrogen ambient.
Germanium Photodetectors for Silicon Microphotonics by Direct Epitaxy on Silicon
Authors: Luan Hsin-Chiao , Lim Desmond R. , Colace Lorenzo , Masini Gianlorezo , Assanto Gaetano , Wada Kazumi , Kimerling Lionel C.
Published: April 2011

We have grown high-quality Ge epilayers on Si using two-step ultrahigh vacuum/chemical-vapor-deposition followed by post-growth cyclic thermal annealing. Cyclic annealing was effective in reducing threading dislocation densities. The annealing process was improved by optimizing the dislocation velocity. We fabricated and tested metal-semiconductor-metal planar photodetectors using Ge epilayers grown on Si. Our measurement showed an improvement in the photodetector performance as a result of the improved materials quality. The process described in this paper for making high-quality Ge on Si is uncomplicated and can be easily integrated with Si CMOS processes.
PbEuTe/PbTe Multi-Quantum Wells: Structural and Optical Properties
Authors: Abramof E. , Rappl P.H.O. , Ueta A.Y. , Motisuke P. , Ferreira S.O.
Published: April 2011

A series of Pb1−xEuxTe/PbTe multi-quantum well (MQW) samples were grown on (111) cleaved BaF2substrates by molecular beam epitaxy. The Eu content was maintained at x∼0.06 and the PbTe well width was varied from 50 to 200 Å. The co/2Θ scans of the (222) Bragg reflection showed very well resolved satellite peaks for all samples indicating that sharp interfaces were obtained. The strain inside the MQW structure was obtained as a function of the PbTe well width by fitting the ω/2Θ scans to the ones calculated by dynamical theory of x-ray diffraction. The transition energies between the confined states in the conduction and valence bands of the PbTe well were determined through the infrared transmission measurement analysis.
Development of Large High-Quality Chalcopyrite Single Crystals for Nonlinear Optical Applications
Authors: Ruderman W. , Zwieback I.
Published: April 2011

Striking progress has been made in the development of thigh optical quality, large size and low absorbing single crystals of ZnGeP2, AgGaS2 and CdGeAs2. This will now enable continuously tunable infrared laser sources to be built covering the spectral region from 3.9 to 11 µm.
Electronic Structure and Derived Linear and Nonlinear Optical Properties of Chalcopyrites
Authors: Lambrecht Walter R. L. , Rashkeev Sergey N. , Limpijumnong Sukit , Segall Benjamin
Published: April 2011

The electronic band structures were calculated for a number of chalcopyrites in both the II-IV-V2 and I-III-VI2 families using the linear muffin-tin orbital method. From these band structures, the second harmonic generation coefficients were calculated using a recently developed methodology in which a separation is made of inter- and intraband contributions. We found that the high value of d36 in CdGeAs2 is in large part due to the fact, that in this material, unlike in the other chalcopyrites, almost no compensation occurs between inter- and intraband contributions, the former one being unusually small. For the case of ZnGeP2, a detailed investigation of the band structure, reveals that it has an indirect band gap rather than a pseudodirect one. The implications of this for the interpretation of the optical spectra are discussed. Finally, for the I-III-VI2 materials, we find that the Te based materials have far higher d36 than the selenides. Combined with their potential for non-critical phase matching, this makes AgGaTe2 an interesting compound.
I-V CHARACTERISTICS OF a-Si:H p-i-n Diodes with Uniform and Non-Uniform Defect Distributions
Authors: Kroon M.A. , van Swaaij R.A.C.M.M. , Metselaar J.W.
Published: April 2011

This paper compares a-Si:H p-i-n diodes having a spatially uniform distribution of defect states with diodes in which the defect distribution is non-uniform, i.e. equilibrated according to the Defect-Pool model. Diodes with a uniform defect distribution exhibit a clear dependence of the current-voltage characteristics on the width of the intrinsic region, whereas in equilibrated diodes, this dependence is absent. This difference is explained by comparing the space-charge distribution and the recombination profile of the intrinsic region in both types of diodes.
Er environment in a-Si:HEr> prepared by PECVD
Authors: Piamonteze Cínthia , Tessler Leandro R. , Tolentino Hélio , Alves Maria do Carmo Martins , Weiser Gerhard , Terukov Eugeny
Published: April 2011

The Er local environment of a-Si:H prepared by PECVD using a metalorganic precursor was determined by EXAFS. We found that in as-deposited samples Er is coordinated to 6 oxygen atoms at 2.28±0.01Å, very similar to Er2O3. Annealing at 420°C hardly affects the Er neighborhood, but higher annealing temperatures (starting at 600°C up to 1033°C) decrease the Er-O separation as much as 0.05Å, maintaining the Er average coordination around 6. This is interpreted as due to the formation of a carbon second neighbor shell. Our results show that the Er local environment is not related with the luminescence enhancement for annealing at moderate temperatures.
Large Area Flexible Amorphous Silicon Position Sensitive Detectors
Authors: Fortunato Elvira M.C. , Brida Donatello , Ferreira Isabel M.M. , Åguas H. M.B. , Nunes Patrícia , Cabrita Ana , Giuliani Franco , Nunes Yuri , Maneira Manuel J.P.
Published: April 2011

Large area thin film position sensitive detectors based on amorphous silicon technology have been prepared on polyimide substrates using the conventional plasma enhanced chemical vapour deposition technique. The sensors have been characterised by spectral response, illuminated I-V characteristics and position detectability measurements. The obtained one dimensional position sensors with 5 mm wide and 60 mm long present a maximum spectral response at 600 nm, an open circuit voltage of 0.6 V and a position detectability with a correlation of 0.9989 associated to a standard deviation of 1×10−2, comparable to those ones produced on glass substrates. The surface of the sensors at each stage of fabrication was investigated by Atomic Force Microscopy.
Hot-electron Phototransistors in Hydrogenated Amorphous Silicon
Authors: Shannon J. M. , Gerstner E. G.
Published: April 2011

It has been shown that useful current gains can be obtained in hot-electron device structures containing very thin chromium disilicide layers of nanometer dimensions in hydrogenated amorphous silicon [1]. The a-Si:H/a-CrSi2/a-Si:H device structure made using PECVD and sputtering techniques naturally forms a hot-electron transistor device where the electrons are emitted across a high potential barrier on one side of the silicide and are collected over a low barrier on the other. Recent results [2] have shown that current gains can be in excess of 40 in structures having a-CrSi2 bases ∼1 nm thick.

Here we outline the relatively simple technology used to make these devices and examine their performance as phototransistors in which the photo-current is amplified by hot-electron transistor action. The speed of response can be maximised by operating the phototransistor with high electric field across the collector since it is the transit time of the photo-induced carriers that determines the response time. We show that these devices provide a useful new active element for large area amorphous silicon electronics.
Increase of Hydrogen-Radical Density and Improvement of The Crystalline Volume Fraction of Microcrystalline Silicon Films Prepared by Hot-Wire Assisted Pecvd Method
Authors: Yoshida Norimitsu , Itoh Takashi , Inouchi Hiroki , Harada Hidekuni , Inagaki Katsuhiko , Yamana Noriyuki , Yamamoto Kanta , Nonomura Shuichi , Nitta Shoji
Published: April 2011

Higher crystalline Si volume fractions in hydrogenated microcrystalline silicon ( µc-Si:H) films have been achieved by the hot-wire assisted plasma enhanced chemical vapor deposition (HWA-PECVD) method compared with those in films by conventional PECVD. µc-Si:H films can also be prepared by HWA-PECVD under typical conditions used for preparing hydrogenated amorphous silicon (a-Si:H) films by PECVD, in which the hydrogen-dilution ratio (H2 / SiH4) is ∼ 10. The hot wire seems to produce hydrogen radicals. As a result, the HWA- PECVD method can control hydrogen-radical densities in the RF plasma, and this method can also control the ratio of hydrogen coverage at the surface of the film.
Real Time Optics of p-Type Microcrystalline Silicon Deposition On Specular and Textured ZnO-Coated Glass
Authors: Rovira Pablo I. , Ferlauto Andre S. , Koval Randy J. , Wronski Christopher R. , Collins Robert W. , Ganguly Gautam
Published: April 2011

In this study, we optimize the plasma-enhanced chemical vapor deposition (PECVD) process to achieve high-density nucleation of single-phase microcrystalline silicon (µc-Si:H) p-type layers on zinc oxide (ZnO) surfaces at 200 °C for applications in amorphous silicon (a-Si:H) based p-i-n solar cells. The phase evolution of the Si:H p-layers on specular ZnO-coated glass substrates is characterized using real time spectroscopic ellipsometry (RTSE). The resulting evolutionary phase diagram depicts the accumulated film thickness at which the amorphous-to- microcrystalline (→µc) transition occurs versus the H2-dilution ratio, with all other parameters fixed. Guided by this diagram, we find that high-density microcrystallite nucleation and fully- coalesced µc-Si:H p-layers ∼100 Å thick can be obtained on specular ZnO at 200 Å using a B(CH3)3 doping gas flow ratio of D=[B(CH3)3]/[SiH4]=0.02 and an optimized H2-dilution ratio of R=[H2]/SiH4]=200. Lower H2-dilution levels (R<160) generate purely amorphous or mixed (a+µc) phases, and higher dilution levels (R>200) generate longer induction periods, low-density nucleation, and incomplete coalescence of microcrystallites even after ∼100 Å. The time evolution of the microstructure and the resulting dielectric functions as determined by RTSE are similar for optimized µc-Si:H p-layers ∼200 Å thick prepared on specular and textured ZnO surfaces, indicating that the substrate texturing does not necessitate process reoptimization.
Nanocrystalline Undoped Silicon Films Produce by Hot Wire Plasma Assisted Technique
Authors: Ferreira Isabel M.M. , Martins Rodrigo F. P. , Cabrita Ana M. F. , Fortunato Elvira M. C. , Vilarinho Paula
Published: April 2011

In this work, we show results concerning electro-optical properties, composition and morphology of nanocrystalline hydrogenated undoped silicon (nc-Si:H) films produced by hot wire plasma assisted chemical vapour deposition process (HWPA-CVD) and exhibiting a compact granular structure, as revealed by SEM micrographs. This was also inferred by infrared spectra, which does not present the SiO vibration band located at 1050-1200 cm-1, even when samples have long atmospheric exposition. The photoconductivity measured at room temperature also does not change when samples have a long time exposition to the air or to the light irradiation. The influence of hydrogen dilution on the properties of the films was also investigated.
Roughness of TFT Gate Metallization and its Impact on Leakage, Threshold Voltage Shift and Mobility
Authors: Nathan A. , Park B. , Sazonov A. , Murthy R.V.R.
Published: April 2011

A comparison of the performance of aluminium (Al)-gated thin film transistors (TFTs) is presented in which we varied its sputter deposition conditions, such as deposition temperature, process pressure, and power. Gate films deposited at 30°C/5mTorr/300W yield TFT characteristics with low leakage current (~ 10 fA at low VDS), an ON/OFF ratio better than 108, and a mobility of 1.1 cm2/Vs. In contrast, films deposited at 150°C/10mTorr/400W, yield a significant degradation in leakage current (~ 1 pA) and mobility (0.77 cm2/Vs). The degradation stems from the high surface roughness of the a-SiNx:H gate insulator, and hence the TFT channel, caused by hillock formation on the Al gate. In addition, the high roughness leads to a correspondingly large shift in threshold voltage. After one-hour bias stress of +25 V applied to the gate, the shift in threshold voltage is ΔVT ~ 5 V, as compared to the small shift of ΔVT ~ 2.3 V associated with the smoother gate. Also included in our comparison is a TFT whose Al gate is now capped with 20 nm of molybdenum (Mo) to minimize propagation of the gate surface roughness to the active channel. Its cross sectional topography shows the interface smoothness to be as good or better, to yield improved leakage and stability characteristics.
Effect Of Nickel In Large Grain Poly-Si Film Formed By Nickel Induced Lateral Crystallization and New Grain Enhancement Method
Authors: Chan W.Y. , Myasnikov A.M. , Poon M.C. , Yuen C.Y. , Han P. G. , Chan M. , Ko P.K.
Published: April 2011

Large grain poly-silicon film (poly-Si) with high material quality and uniformity can have numerous novel applications such as providing a low cost alternative to form silicon-on-insulator (SOI) substrates and a breakthrough technology to ultra-dense 3-dimensional multi-layer SOI like devices and circuits. Nickel Induced Lateral Crystallization (NILC) of amorphous Si (a-Si) has been studied intensively, yet the grains are still small (∼ 1 μm). Recently, we have reported a novel method by combining NILC and a new annealing (at above 900 °C) to form poly-Si film with very large grains ranging from 10 μm to 100 μm. The film has good quality and the TFTs formed are highly comparable to SOI TFTs. This work further reports the effect of Ni to the new large-grain poly-Si film.
Effect of Deposition Conditions on the Structural and Mechanical Properties of Poly SiGe
Authors: Sedky Sherif , Witvrouw Ann , Caymax Matty , Saerens Annelies , Van Houtte Paul
Published: April 2011

MicroElectroMechanical Systems (MEMS) are used in a wide variety of applications such as accelerometers [1], gyroscopes [2], infrared detectors [3],…etc. For high volume applications, fabrication costs can be possibly reduced by monolithic integration of MEMS with the driving electronics. The easiest approach for monolithic integration is post processing MEMS on top of the driving electronics, as this does not introduce any change into standard fabrication processes used for realizing the driving electronics. On the other hand, post processing imposes an upper limit on the fabrication temperature of MEMS in order to avoid any damage or degradation in the performance of the driving electronics. Polycrystalline silicon (Poly Si) has been widely used for MEMS applications [4], but the main disadvantage of this material is that it requires a high processing temperature (higher than 800°C [5]) to achieve the desired physical properties. In particular, a low tensile stress is needed for MEMS. Polycrystalline silicon germanium (Poly SiGe) seems to be an attractive alternative to poly Si as it has similar properties, while the presence of germanium reduces its melting point. Hence, the desired physical properties are expected to be realized at lower temperature. Depending on the germanium concentration and the deposition pressure, the transition temperature from amorphous to polycrystalline can be reduced to 450°C [6], or even lower, compared to 580°C for LPCVD poly Si. Also, the residual mechanical stress in poly SiGe is lower than that in poly Si [7].