bluuebunny/crossref_metadata_2025 huggingface dataset:
CdTe detectors responses to pulsed X-rays : comparison of different materials
Authors: Verger L. , Cuzin M. , Glasser F. , Lajzerowicz J. , Mathy F. , Rustique J.
Published: March 2011

The goal of this work is to compare and analyze the transient responses to X-ray pulses of different cadmium telluride detectors:

- CdTe: Cl grown by the vertical Bridgman method (B.).

- CdTe: Cl grown by the Travelling Heater Method (T.H.M.).

- Cd0,8 Zn0,2 Te grown by the High Pressure Bridgman method (H.P.B.).

Photoconductive detectors were subjected to very short (20 ns) 100 keV X-ray pulses and short (4 µs) 2 MeV pulses. The transient response of the photoconductors CdTe: Cl and CdZnTe under high X-ray energy beam were characterized in terms of sensitivity, linearity and dynamic range vs different parameters such as bias voltage and X-ray beam fluence. Bridgman and T.H.M. detectors show similar behaviors while H.P.B. detectors which are highly resistance show shorter transient behavior after the 20 ns pulses irradiations and larger afterglow after the 4 µs pulses irradiations.
New Perspectives in Low Noise Preamplifier Design for Room Temperature Detector Applications
Authors: Manfredi P.F.
Published: March 2011

After reviewing the noise limits in room temperature preamplifiers based on discrete elements, the paper discusses some results obtained with monolithic circuits and the perspectives opened-up by active devices directly integrated on the chip of a silicon detector.
HgCdTe MBE Technology : A Focus On Chemical Doping
Authors: Wu Owen K.
Published: March 2011

HgCdTe MBE technology is becoming a mature growth technology for infrared focal plane array applications. The ability to dope HgCdTe with In(n-type) and As(p-type) dopants in-situ provides greater flexibilities for fabricating heterojunction devices. In this paper, we will first discuss the current status of HgCdTe MBE growth and then focus on the key results in the control of In(n-type) doping, various approaches and breakthroughs in the growth of As(p-type) doped HgCdTe and issues related to doping such as memory effects and dopants activation. In addition, device results from double layer heterojunction structure(DLHJ) will be briefly discussed.
Crystallographic and Metallurgical Characterization of Radiation Detector Grade Cadmium Telluride Materials
Authors: Johnson C.J. , Eissler E.E. , Cameron S.E. , Kong Y. , Fan S. , Jovanovic S. , Lynn K.G.
Published: March 2011

Radiation detector grade CdTe crystals are characterized by several crystallographic and metallurgical techniques including infrared microscopy, dislocation etch pitting and X-ray diffraction. Results are presented for 50 detectors fabricated from an ingot produced by the high pressure Bridgman method. Data on the temperature dependence of leakage current and pulse height analysis are presented, along with measurements of room temperature charge transport properties. Attempts to relate crystal structure to detector performance will be discussed.
Performance Characteristics of Cdte Gamma-Ray Spectrometers
Authors: Squillante Michael R. , Cole Herbert , Waer Peter , Entine Gerald
Published: March 2011

The use of cadmium telluride (CdTe) semiconductor nuclear detectors is continuing to expand into new areas because of their unique properties which include room temperature operation and high detection efficiency. In addition, they remain the material of choice in many critical applications such as nuclear medicine and power plant monitoring because of their reputation for reliability and long term stability1. CdTe is by far the most developed of the compound semiconductors used in nuclear detector applications and it offers a number of significant benefits to researchers, clinicians and engineers who have special requirements relating to size, sensitivity and operating temperature.

Recently, there have been improvements in the growth of the crystalline material and in the fabrication procedures which have resulted in better performance and in the ability to produce arrays. This article describes the physical and electronic properties of CdTe nuclear detectors, discusses how the crystal growth and device fabrication procedures can affect these properties, and compares the performance to CdZnTe detectors.
Junction Field Effect Transistor X-RAY Detectors
Authors: Lund J.C. , Olschner F. , Rehn L.
Published: March 2011

We describe the theory of operation, design, and estimated performance of an n-channel JFET designed to be operated as a detector in an X-ray spectrometer system. We estimate that a room temperature (300 K) JFET detector can be built with performance comparable to a small area, cryogenically cooled Si(Li) detector.
A Low Noise Silicon Detector Preamplifier System for Room Temperature X-Ray Spectroscopy
Authors: Bertuccio G. , Pullia A.
Published: March 2011

The design and performances of a system for high resolution X-ray spectroscopy are presented. The detector is a low capacitance diode built on high resistivity silicon. The signal preamplification is made by means of an ultra-low noise charge amplifier of new conception. Presently the system exhibits an equivalent noise charge of 61 r.m.s. electrons at 297 K and 32 r.m.s. electrons at 223 K. It is shown how an improvement down to 30 r.m.s. electrons at room temperature is expected employing an integrated transistor on the detector chip.
Growth of Single Crystals of Mercuric Iodide on the Ground and in Space
Authors: van den Berg L.
Published: March 2011

A short review will be given of the methods by which mercuric iodide is prepared and purified to obtain material suitable for the growth of single crystals. The method used in our laboratory to grow single crystals up to 1,000 grams in weight from the vapor will be discussed. The effects of gravity on the growth process will be described.

A crystal growth system suitable for operation in the reduced gravity environment of space was designed, and crystal growth experiments were performed during the flights of Spacelab 3 (April 1985) and the International Microgravity Laboratory (IML-1) (January 1992). The structural quality and electronic properties of the ground-based and spacegrown crystals were compared, and the results will be presented.
Mercuric Iodide X- and Gamma-Ray Deteciors for Space Applications
Authors: Iwanczyk Jan S.
Published: March 2011

Recently, substantial progress has been made in the development of HgI2 detectors and associated electronics for space instrumentation. The many technical challenges in the instrument development involving spectroscopy performance, power consumption, weight, size, operation over wide ranges of temperature and ambient gas pressure, and others have been overcome. Descriptions of instrumentation under development such as: x-ray and alpha backscattering spectrometer, scanning electron microscope and particle analyzer, Mössbauer spectrometer, and gamma-ray spectrometer are given.
Correlation Between Defect Density and Process Variables In Step-Graded, Relaxed Si0.7Ge0.3 Grown on Si by Rtcvd
Authors: Watson G. Patrick , Fitzgerald Eugene A. , Jalali Bahram , Xie Ya-Hong , Weir Bonnie , Feldman Leonard C.
Published: March 2011

The effect of the average grading rate and of the number of incremental Ge alloy steps on the threading dislocation density has been studied in 30% Ge relaxed films formed by rapid thermal chemical vapor deposition (RTCVD) on Si substrates. Electron beam induced current (EBIC) images and transmission electron microscopy (TEM) show that threading defects fall in two categories: individual threading dislocations (dark spot defects), and organized clusters of these threads (pile-ups, or dark line defects). The overall surface defect density must include both categories to properly characterize the material. The lowest defect density, 4 × 105cm−2, was found in specimens grown at an average grading rate of 10% Ge per pm thickness.
Evaluation of a vertical tube concept for RTP
Authors: Cho Byung-Jin , Vandenabeele Peter , Maex Karen
Published: March 2011

A new RTP system concept is proposed and demonstrated. The system uses a vertical cylindrical quartz tube, while the wafer is placed horizontally. Linear halogen lamps are arranged in an hexagonal shape. Optimal power control results in a temperature difference within ±1.5 °C over a 6 inch wafer in steady state. Oxidation under optimal conditions results in a 1.37% standard deviation for an average oxide thickness of 110.4 Å. The temperature nonuniformity during the transient has been greatly improved by using dynamic control. The main advantages of this new system concept are its excellent temperature uniformity and the good accessibility of the wafer for technological treatments and in situ measurements.
Investigation of Dynamical Temperature Behaviour in Rtp
Authors: Leitz Gunnar , Pezoldt JÖrg , Patzschke Ingo , ZÖllner Jens-Peter , Eichhorn G.
Published: March 2011

For Rapid Thermal Processing one of the essential problems is the dynamical temperature controlling to reduce temperature nonhomogeneities during heating up and cooling down, which are responsible for layer nonhomogeneities and slip generation. A pyrometer row consisting of five sensors is used for temperature distribution measurement in radial direction, which allows to investigate the dynamical behaviour during the heating cycles. Together with a developed software tool, which is suitable for calculation of the dynamical temperature distribution across the wafer under process conditions where the convective heat losses can be neglected, the influence of heating-up velocities is investigated. The obtained results show that in a scalar controlled system process conditions optimized for steady state lead to maximum temperature nonhomogeneity during the heating-up period, due to the changing heat balance in the system.
Rapid Thermal Processor Modeling, Control, and Design for Temperature Uniformity
Authors: Riley Terrence J. , Gyurcsik Ronald S.
Published: March 2011

With the ability to perform heat cycles on a wafer quickly and within low thermal budgets, Rapid Thermal Processor (RTP) systems offer potential advantages over conventional furnaces. However, RTP' have an inherent problem with wafer temperature uniformity which can cause process nonuniformity and wafer stress.

In this work, a thermodynamic model of a wafer is used to form an understanding of the wafer heating problem. This model shows that an idealized heating flux density profile can maintain thermal uniformity at steady-state temperatures. This profile uniformly heats the wafer while counteracting the additional cooling at the wafer edge. However, this profile induces temperature nonuniformities during wafer temperature transients, such as overheating of the edge during temperature rises. Therefore, a dynamic flux-density profile is needed during temperature transients to ensure continuous temperature uniformity. The model is used to predict the steady-state and dynamic profiles required to process a wafer with complete temperature uniformity. The predicted profiles can be used to adapt an RTP chamber and control system to approach production of uniform wafers and also for the design of new systems. This paper will explain the theory of wafer heating, describe the dynamic profiles required for continuous uniformity, review the wafer model, show the result of an idealized profile for steady state and transients processing, and present a new control methodology to achieve uniform temperatures.
Gate Oxide Integrity as Affected by Hf Last Wafer Treatments and Passivating Techniques
Authors: Hawthorne R.C. , Thakur R.P.S. , Morinville K. , Kauffman R.
Published: March 2011

As device performance requirements increase, device features become smaller and films become thinner. The resultant sensitivity to defect density is such that controlling the condition of wafer surfaces prior to primary process steps becomes more and more critical. Wafer cleaning technologies of the past may not be optimum in providing needed device characteristics and reliability of tomorrow's semiconductors. In this paper, we compare the currently used RCA wafer clean chemistries to newer HF last, vapor dry technologies which use direct displacement of liquids to minimize contaminants. Subsequent passivation of these hydrophobic wafer surfaces is accomplished by various methods of oxidation including chemical treatments and RTP processing. Data collected from I-V, SIMS and DEFECT DENSITY testing will be included in the presentation.
Titanium Disilicide Formation on Cmos Structures with Phosphorous Doped Gates
Authors: Chtttipeddi S. , Nanda A. K. , Kannan V. C. , Cochran W. T.
Published: March 2011

Self aligned refractory metal silicides such as titanium disilicide have been used extensively in VLSI and ULSI structures. Unlike earlier work which has relied on undoped substrates and a single implant species, in the present study TiSi2 formation on phosphorous doped poly-Si in the presence of multiple dopants has been investigated. TEM micrographs are discussed which show the difference in silicide formation for the case of the BF2 and arsenic implanted samples. We have found that the presence of fluorine in the BF2 implant retards the silicide formation for phosphorous doped poly-Si substrates. Additionally, the effect of substrate grain size on TiSi2 formation has been investigated using undoped α-Si and poly-Si substrates.
Influence of Rapid Thermal Processing Conditions on the Characteristics of Sputter Deposited Titanium Nitride Thin Films
Authors: Ramaswami Sesh , Iacoponi John , Cheung Robin
Published: March 2011

Sputter deposited TiN films are commonly used as diffusion barriers for an aluminum based metallization and as glue layers for tungsten films in ULSI device processing. TiN is also used in conjunction with Ti and/or a-Si for local interconnect and salicide processing. For the above applications, TiN films are also subjected to rapid thermal processing.

This paper discusses these applications focusing on sub-half micron technologies where high aspect ratio contacts causes poor step coverage at the base of the contacts and compact design rule requirements pose an additional burden to Ti-silicide processes. Preferred grain orientation, microroughness, film stress, sheet resistance, diffusion barrier qualities and analytical spectroscopy techniques have been used to characterize the material modifications by RTP of Ti and Ti/TiN thin films.
Diffusion of Cations Along the Polymer/Metal Interface Under an Applied Electrical Potential
Authors: Nguyen T. , Pommersheim J. M.
Published: March 2011

Diffusion of cations along the polymer/metal interface controls the rate of blistering of polymer coatings on metals exposed to electrolytes. Cations are driven by both concentration and electrical potential gradients. A theoretical and experimental study was carried out on the diffusion of sodium ion along the polymer coating/steel interface under an applied potential. Mathematical models, consisting of initial and propagation stages, are derived based on a moving boundary diffusion problem. Model variables include ion diffusivity, potential gradient and distance between defects and delamination sites. Models are solved to predict ion fluxes and concentration in the blistering areas. Experimental data are analyzed to extract model parameters. Model predictions agreed well with experimental data and practical observations
Grafting of Polymers to Solid Surfaces by using Immobilized Azoinitiators
Authors: Prucker O. , Rühe J.
Published: March 2011

The covalent attachment of polymers such as polystyrene, polymethylmethacrylate and polyacrylonitrile to microparticulate silica and to silicon wafers through immobilized radical chain initiators (especially azocompounds) is described. The initiator is bonded to the surface using α,ω-substituted silanes, which have only one functional group at the silane head group.

Up to 10 g of polymer per g of silica could be covalently bonded to the surface. The attached monolayers were characterized using diffuse reflectance FTIR spectroscopy, XPS and elemental analysis. After the cleaving off of the attached layers molecular weights up to 300.000 g/mol were measured. Transmission electron micrographs generated with an element specific imaging technique (ESI) clearly show a continuous, about 10 nm thick, polymer layer around the silica particles.
Oxygen Bombardment Induced Activation of Glassy Carbon
Authors: Jenkins G. M. , Ila D. , Williams E. K.
Published: March 2011

We have studied the effect of oxygen ion bombardment of glassy carbon at room temperature, using a composite bi-energy beam of 3.2 and 3.1 MeV ions. Carbon specimens were prepared in-house by pyrolysis of phenolic resin at 1000° C. Raman microprobe spectra of the surface and implanted volume before and after irradiation showed that the implanted oxygen ions had disrupted translational symmetry at the surface and caused maximum damage in the carbon 3.5 μm below the surface. By analogy to the “activation” of charcoals1 we conclude that pores are opened up by preferential attack of strained carbon sites.
Role of Coating/Oxide/Steel Interfaces on Cathodic Disbonding of Pipeline Coatings
Authors: Payer J. H. , Trautman B. , Gervasio D. , Song I.
Published: March 2011

Fusion bonded epoxies (FBE) in combination with cathodic protection (CP) are widely used to protect the soil side of buried pipelines from corrosion. Cathodic disbonding of the epoxy coating is a degradation process involving accelerated loss of adhesion of FBE because of chemical and electrochemical processes due to CP. Results are presented from our study to determine the mechanism of cathodic disbonding.
Cleavable Thermosetting Epoxies: a Tool for Monitoring Cure Chemistry Perturbation at an Interface
Authors: Gilbert Michael D.
Published: March 2011

A diepoxide containing a disulfide linkage, capable of being reductively cleaved was synthesized. This compound was cured with standard amine curing agents to form intractable network polymers, which were then decomposed into soluble fragments, allowing the effects of network formation on cure chemistry to be evaluated. This system was then used to investigate the effects of an alumina interface on epoxy network formation.
Ceramic-Polyimide Systems for Electronic Packaging
Authors: Marsh Wayne E. , Kanakarajan K. , Osborn Garry D.
Published: March 2011

A family of new high performance thermoplastic polyimide adhesives have been developed that can be directly laminated to ceramic substrates, polyimide films, metals, and/or sputter metallized for eventual circuit fabrication. We have also developed new heat-sealable composite polyimide films that have improved CTE, that have good dimensional stability and that can also be directly bonded to ceramic and glass-ceramic substrates. With these new material sets various constructions of ceramic-polyimide rigid-flex systems can be conceived to meet the more demanding needs of the electronics industry. We have laminated these films to metals and various ceramic substrates such as alumina, aluminum nitride, glass, etc. and investigated the bond stabilities under thermal and humidity aging conditions.
In-Situ Synchrotron X-Ray Scattering Studies of Polybenzoxazole Fiber Spinning
Authors: Nolan S. J. , Broomall C. F. , Bubeck R. A. , Landes B. G. , Rudolf P. R. , Mills M. J. , Radler M. J.
Published: March 2011

Initial results are presented of in-situ wide angle x-ray scattering (WAXS) studies of structure and orientation development in the draw zone during fiber spinning of poly(p-phenylene benzobisoxazole) (PBO) in polyphosphoric acid (PPA). The diffraction patterns show strong [100] and [002] reflections. The coherence lengths found from the [100] and [002] reflections are consistent with those found by electron diffraction and suggest important elements of the microfibrillar morphology may already be present in the texture of the extrudate before coagulation. Increasing extrusion rate is found to produce little improvement in molecular orientation. Molecular orientation initially increases with increasing draw ratio from 1 to 10 but, remains constant for higher draw ratios. These results are compared to an affine deformation model during elongational flow.
“Recoil” Compressive Strength Test and the Evolution of Compressive Behavior in PAN-Based Carbon Fibers
Authors: Jiang Hao , Damodaran S. , Abhiraman A. S. , Desai P. , Kumar S.
Published: March 2011

The compressive properties of PAN-based carbon fibers were measured with the tensile recoil method. The recoil fracture morphology was also examined. In addition to the axial compression, flexure during recoil affects the test results. Compressive failure may be caused by shear failure and/or bending buckling of the microfibrils/fibrils. Study of the evolution of compressive and other mechanical properties discloses that, in general, the compressive strength bears a similar tendency to the tensile strength and torsion modulus up to the carbonization temperature of 1500 °C. However, the relative rate of evolution is different. To some extent, the bending buckling mechanism may relate to the structural units which govern the tensile strength.
The Influence of Sputter Deposited Coatings on Strain Transfer in Embedded Fiber Optic Sensors
Authors: Madsen J. S. , Jardine A. P. , Meilunas R. J. , Pak Y. E. , Tobin A.
Published: March 2011

Understanding elastic interactions that occur between an embedded optical fiber and its host matrix is important for implementation of optical strain sensors into aerospace structures. A previously developed analytical model predicted the effects of fiber coating thickness and elastic modulus on the strain transfer from an isotropic matrix to an embedded coated fiber optic.To verify this, a series of tungsten coatings were magnetron sputtered onto bare intrinsic Fabry-Perot sensors that were embedded into a neat epoxy resin block. The block was then compression loaded and the optical strain response measured. Comparisons between the responses of both coated and uncoated sensors indicated that the experimental measurements of strain transfer in embedded fiber-optic devices yielded good agreement with the analytical model.
Thermoplastic in-situ Molecular Composites
Authors: Wiff D. R. , Lenke G. M.
Published: March 2011

The basic concepts of in-situ molecular composite formation are presented with a polyazomethine/nylon 6 system as an example. All the encouraging attributes of molecular reinforcement - increased Tg, solvent resistance and mechanical properties were observed. This provides a commodity resin, such as nylon 6, with properties normally associated with higher priced engineering/specialty resins.
The Phase Behavior of a Hydrogen Bonding Molecular Composite
Authors: Dadmun M. D. , Han C. C.
Published: March 2011

The phase behavior of a blend containing poly(hydroxypropyl L-glutamine) (PHOPG), a rod-like polypeptide, and a coil-like random copolymer with 1.5% hydrogen bonding monomer is studied using light scattering, DSC, and optical microscopy. The results show that this system has an LCST. The phase behavior of this binary system is complicated by a glass transition and an ordering transition. Evidence is also observed of a possible change in phase demixing process, from nucleation and growth to spinodal decomposition, for a 50/50 blend with a change in temperature.
The Effects of Physical Ageing and of Prior Immersion on the Esc Behaviour of Polycarbonate in Ethanol
Authors: Arnold J. C. , Eccott A. R.
Published: March 2011

The effects of physical ageing and prior immersion time on the ESC behaviour of polycarbonate in ethanol were studied. Constant strain rate tensile tests were performed at a range of strain rates for samples with ageing times varying from 100 hours to 3000 hours and for prior immersion times of between 1 hour and 500 hours. Comparison of tests performed in ethanol and in air gave a good indication of the point of craze initiation. The results showed that there was a reduction in strain to crazing as the strain rate decreased, apart from with the lowest strain rate used. A longer prior immersion time also promoted craze formation. Both of these results are attributable to diffusion effects. Physical ageing had little effect on the ESC behaviour, due to the large amounts of deformation encountered in this system.
An Investigation of Stable Free Radicals in Polyimides Using EPR Spectroscopy
Authors: Ahn Myong K. , Stringfellow Thomas C. , Lei Jianming , Bowles Kenneth J. , Meador Michael
Published: March 2011

Polyimide resins are used as matrix materials in fiber reinforced composites. Such composites are lightweight, have relatively high strength, and can be used at temperatures above 300°C. Postcured PMR-15 produces room temperature electron paramagnetic resonance (epr) spectra from stable free radical species formed during the postcuring stages. The variable temperature EPR spectral intensities indicate the presence of at least two free radical species. The thermo-oxidative degradation involves free radicals generated during the postcuring process in the presence of oxygen gas. These and other recent results including ENDOR and HYSCORE work are discussed.
Synthesis and Characterization of Soluble, High Temperature 3-Phenylethynyl Aniline Functionalized Polyimides via the Ester-Acid Route
Authors: Meyer G. W. , Jayaraman S. , Lee Y. J. , Lyle G. D. , Glass T. E. , McGrath J. E.
Published: March 2011

The synthesis of soluble imide oligomers of controlled molecular weight endcapped with the 3-phenylethynyl aniline endcapping agent is described. The 3-phenylethynyl aniline was employed to afford a higher curing temperature (380 - 420°C) which widens the processing window compared to commercially available acetylene endcapped polyimides. The polyimides were synthesized via solution imidization techniques, using the ester-acid of various dianhydrides and various aromatic diamines. The “one pot” procedure utilizes NMP as the solvent and o-dichlorobenzene as the azeotroping agent, and reproducibly exhibit fully imidized soluble polyimides with Mw/Mn values of ∼2.0 determined by gel permeation chromatography. Thermally cured samples display good solvent resistance and exhibit glass transition temperatures comparable to their high molecular weight linear analogs. These polyimides show excellent thermal stability at 700°F aged in air up to 100 hours. Mechanical testing has been performed on a pyromellitic dianhydride (PMDA) and a phosphine oxide-based system. The flow properties have been studied by parallel plate rheology and the cure cycle has been monitored using 13CNMR.
Water Soluble Benzobisazole Rigid-Rod Copolymers
Authors: Dang Thuy D. , Arnold Fred E.
Published: March 2011

Although benzobisazole rigid-rod polymers are well recognized for their outstanding tensile and modulus properties as well as their excellent thermal and thermal-oxidative stabilities, they can only be fabricated from acidic solvents. Benzobisirnidazole polymers containing pendent benthiazole or sulfonic acid groups exhibit partial solubility in DMSO. Reaction of these systems with sodium methylsulfinylmethide in DMSO abstracts the acidic proton from the benzobisimidazo unit and forms the polyanion. Subsequent reaction of the polyanion with 1,3-propanesultone provides water soluble systems. Random copolymers containing benzobisimidazo and benzobisthiazole repeat units were prepared in polyphosphoric acid and subjected to the derivatization reaction. Benzobisimidazo content in the copolymers varied from 10–0 mole percent. Minimum ionic charge along the rigid-rod backbone to obtain water solubility was determined to be approximately 10 mole percent as reflected in the benzobisimidazole repeat units.
Polyphosphazene Composites: a Report on Initial Properties
Authors: Stone Mark L.
Published: March 2011

Polymers based upon inorganic elements are becoming more important in the field of high performance materials because of their outstanding mechanical, thermal, and chemical stabilities. Polyphosphazenes, which are based upon a nitrogen-phosphorus backbone, show promise as new engineering materials. The large number of different chemical structures possible allows the synthesis of phosphazene polymers for specific applications. Initial tests on one phosphazene-based set of materials show that they are very hard, stiff, and have excellent resistance to organic chemicals.
The Interphase in Fibre Reinforced Polymers; New Ideas on How This Controls the Composite Strength
Authors: Piggott Michael R.
Published: March 2011

Much work has recently been done on the interphases between fibres and polymers and it is now clear that they are usually brittle. This requires a re-examination of our basic ideas on how composites achieve their strength. The Kelly-Tyson approach, which is based on ductile metal behaviour, has never received unequivocal support. In addition, work during the last ten years in the author's laboratories indicates that it is incorrect in one of its major predictions: that the stress-strain plots of short aligned fibre composites should be curves. In this paper we present the evidence and introduce a new failure model which eliminates these difficulties.
Photoemission Measurements Of Photocathode Materials In The 115–400 Å Range
Authors: Grantham S. , Richardson M.C. , Watts R. , Lucatorto T. , Tarrio C. , Pollack F.
Published: March 2011

With the intent of finding a sensitive photocathode material in the 130 Å (100eV) X-ray range for use in a high resolution soft X-ray Conversion Microscope, photoelectron yields of several materials (mostly alkali halides), were measured at the National Institute of Standards and Technology's (NIST) Synchrotron Ultraviolet Radiation Facility II (SURF II). These measurements were made as a function of wavelength in the spectral range 115 Å-400 Å. The measured values are comparable to previous measurements of the photoelectron yields of these and similar materials, and to an existing model of photoemission [1–3]. We also determined the effects of prolonged exposure to X-ray light on performance. Moreover, because of the hygroscopic nature of Alkali Iodides, measurements of the photoelectron yield versus wavelength were repeated for samples of CsI that were kept in storage for periods of time to determine the effects of storage time and water absorption on the photoelectron yield.
Characterization Of SiC Films Deposited By Laser Ablation Technique For X-Ray Membranes
Authors: El Khakani M.A. , Chaker M. , Boily S. , Papadopoullos A. , Huai Y. , Jean A.
Published: March 2011

Laser Ablation Deposition (LAD) technique was used to produce hydrogen-free SiC films on (100) Si substrate. Deposition temperatures of 300°C and 450°C were investigated. The Si2p and C1s. core levels and the Si-C absorption band of the a-SiC LAD films were characterized by using X-ray Photoelectron Spectroscopy (XPS) and Fourier-Transform Infra Red (FTIR) absorption spectroscopy, respectively. The high compressive stress of the as-deposited SiC films was released and controlled by means of rapid thermal annealing. A correlation between the stress evolution and the Si-C bond density of the annealed films is pointed out. Optical transmission and mechanical properties (stress, Young's modulus) measurements were carried out on the free-standing membranes fabricated from SiC LAD films. The effect of the deposition temperature on the SiC membrane properties is discussed.
X-Ray Lithography Induced Radiation Effects In Deep Submicron Cmos Devices
Authors: Wang L.K. , Acovic A. , Chang W.H.
Published: March 2011

X-ray lithography introduces device radiation damage from the high energy photons during the lithography process. We have studied this effect on deep submicron n- and p-channel MOSFETs with gate dielectric thickness at 7 to 13 nm. After the x-ray irradiation the device characteristics are strongly affected by the generation of oxide charges, interface states and electron traps. These introduced damages cause the reduction of device transconductance, shift of the threshold voltages and increased leakage current. However, this degradation of device and circuit is lessened from technology scaling by thinning the gate oxide and lowering the supply voltage. The x-ray radiation damage, induces interface states and oxide charges which can be annealed out with a low temperature (400°C) forming gas (FG, 90% N2, 10% H2) annealing process. The device properties are essential unchanged after the annealing process. However, the residue damage is shown to enhance hot-carrier instability of p-channel devices if the remaining neutral traps act as electron or hole traps in the SiO2. In this paper, we investigate the radiation effects on the n- and p-channel MOSFETS fabricated with deep submicron device processes with thinner gate oxides and compare the hot carrier reliability of these devices after the synchrotron x-ray irradiation and also after the post metal forming gas annealing. The results indicate the device hot carrier instability has no effect on the devices with thin gate oxide with thickness approaching the electron tunneling range.
Modelling Photoelectron Effects In X-Ray Lithography
Authors: Ocola L. E. , Cerrina F.
Published: March 2011

The study of photoelectron effects in X-ray Lithography motivates the need for modeling codes to simulate these effects to have an estimate of the influence of x-ray generated photoelectrons in the exposure of resists. We have performed a series of Monte Carlo simulations to study the spatial distribution of photoelectrons in a resist, PMMA, and parametrized this distribution with a set of energy-dependent gaussians for monochromatic X-rays within an energy range of 0.5 KeV to 2.5 KeV. We discuss the effects of the the redistribution of the photoelectron kinetic energy as a function of the electrons generated by the x-ray absorption in various atomic species.
Materials And Fabrication Processes For Highly Accurate X-Ray Masks
Authors: Oda Masatoshi , Yoshihara Hideo
Published: March 2011

This paper discusses the properties of materials for x-ray masks used in synchrotron radiation lithography system. Through computer simulations and experimental analysis, we evaluate three kinds of membranes (Si, SiN, SiC) in terms of mechanical distortions, surface smoothness and optical transmittance. SiC exhibits the smallest distortion, but SiN has the best characteristics in the surface smoothness and the optical transmittance. By virtue of their high x-ray absorption coefficient and dry etching capabilities, Ta, W and Re are selected as potential absorber materials. We study their stress control characteristics, etching characteristics and the relation between their Young's modulus and distortions. We find that Ta is an excellent absorber because of its good stress controllability and good etching characteristics, such as a high etch rate and etch selectivity. By adopting a Ta/SiN structure, highly accurate masks can be fabricated by a process in which patterning the absorber is carried out before removing the bulk Si.
Magnetic Circular Dichroism in X-Ray Fluorescence
Authors: Duda L.-C. , Hague C. F. , Mancini D. C. , Mariot J.-M. , Marliere C. , Nordgren J. , Skytt P. , Wassdahl N.
Published: March 2011

X-ray fluorescence spectra from magnetized iron excited by circularly polarized synchrotron radiation are reported. The Fe L2.3 emission band gives rise to a distinct dichroic signal in confirmation of a recent theoretical prediction. These preliminary experiments carried out with “white” and only partially circularly-polarized synchrotron radiation nevertheless reveal an asymmetry which reflects the spin polarization of the Fe 3d valence electrons. The usefulness of developing specialized high flux circularly-polarized sources is clearly established.
A Soft X-Ray Photoemission Study of the Chemisorption and Reaction of Diethylsilane on SI(100)
Authors: Lapiano-Smith D. A. , Himpsel F. J. , Terminello L. J.
Published: March 2011

Soft x-ray synchrotron radiation has been utilized as the excitation source in a high-resolution photoemission experiment designed to investigate the chemisorption and subsequent reaction of diethylsilane on the technologically important Si(100) surface. We have found that diethylsilane chemisorbs dissociatively to form Si-CH2CH3 surface species on Si(100) following a room temperature exposure. These species are identified by two very sharp peaks observed in the valence band spectra positioned at 17.9 and 14.3 eV binding energy. In addition, C Is core level spectra, measured following exposures of Si(100) substrates as a function of surface temperature, show that carbon, in some form, exists on the Si surface following exposures at every temperature from room temperature to about 600°C. While only -CH2CH3 ethyl groups are observed on the surface at room temperature, these species appear to partially dehydrogenate at 300°C, producing a mixture of -CH2CH3 groups and other intermediate carbonaceous species. At a growth temperature of about 400°C the intermixing of elemental carbon with Si begins. At higher temperatures, we observe the continued degradation of diethylsilane to produce a Si + C alloy on the surface at 600°C. Our results indicate that diethylsilane has potential as a molecular precursor for SiC formation by chemical vapor deposition techniques.
Soft X-Ray Photoelectron Spectroscopy Of Bi-Metallic Interfacial Bonding
Authors: Shinn N. D. , Kim B. , Andrews A. B. , Erskine J. L. , Kim K. J , Kang T.-H.
Published: March 2011

We report the first application of Soft X-ray Photoelectron Spectroscopy (SXPS) to probe the bonding at epitaxial, bi-metallic interfaces with atomic-layer spatial selectivity. Specifically, we have measured the W(4f)7/2 levels of interfacial tungsten atoms for (1×1)Fe/W(110), (1×1)Ni/W(110), and (1×1)PtW(110). For clean W(110), the surface atoms exhibit a W(4f)7/2 peak at -320 meV binding energy with respect to the bulk W(4f)7/2 peak. Upon formation of the metallic overlayers, the interfacial tungsten atoms contribute W(4f)7/2 peaks at -225 meV (Fe/W), -140 meV (Ni/W), and +70 meV (Pt/W) with respect to the bulk W(4f)7/2 peak. The systematic reduction in the binding energy difference between interfacial and bulk tungsten atoms for Fe, Ni, and Pt correlates with increasing heats of adsorption on W(110), as determined by Temperature Programmed Desorption. This suggests that SXPS, in combination with first principles calculations and Born-Haber thermochemical cycle analyses, can be used as a non-destructive probe of bi-metallic interfacial bonding energies.
High Energy Resolution Arpes Measurements of the Normal and Superconducting States of Bi2Sr2CaCu2O8+δ
Authors: Dessau D. S. , Shen Z.-X. , King D. M. , Wells B. O. , Marshall D. S. , Lombardo L. W. , Dickinson P. H. , Dicarlo J. , Park C.-H. , Loeser A. G. , Kapitulnik A. , Spicer W. E. , Arko A. J.
Published: March 2011

The near-EF electronic structure and Fermi surface of Bi2212 has been mapped out with ARPES. A key feature of our measured bandstructure is the existence of an extended region of flat CuO2-derived bands at EF. Comparative analysis of this data with that from NdCeCuO and YBCO7 suggests that many of the anomalous (normal) physical properties of Bi2212 and YBCO7 (NdCeCuO) may be related to the existence (absence) of such bands at EF. Superconducting gap anisotropy at least an order of magnitude larger than that of the conventional superconductors has been observed in the a-b plane of Bi2212 in ARPES. For samples with Tc of 88K, the gap size reaches a maximum of approximately 20 meV along the Cu-O bond direction, and a minimum of much smaller or vanishing magnitude 45° away. The experimental data is discussed within the context of various theoretical models. In particular, a detailed comparison with what is expected from a superconductor with a dx2-y2 order parameter is carried out, yielding a consistent picture.
Narrow-Band Synchrotron Radiation Excitation of Soft X-Ray Emission Spectra
Authors: Miyano K. E. , O'Brien W. L. , Ederer D. L. , Callcott T. A. , Jia J. J. , Dong Q.-Y. , Zhou L. , Woicik J. C. , Mueller D D. R.
Published: March 2011

Monochromatized synchrotron radiation has been employed as the excitation source for soft x-ray emission spectroscopy. In the present paper changes in the emission spectra that occur as the excitation energy is varied near the core-absorption threshold are discussed. In the case of crystalline silicon, strong variations are seen in the L2,3 emission for excitation energies up to 30 eV above threshold. These variations are shown to be dependent on the crystalline order of the material and can be interpreted in terms of restrictions on the crystal momentum that arise in an inelastic scattering description of the combined absorption and emission. On the other hand this description is less relevant to the excitation-energy dependence of ionic insulators, in which strong phonon coupling removes these restrictions on crystal momentum. In the insulators B2O3 and BN strong variations in the emission are observed at threshold, upon creation of a core exciton: the exciton affects the emission through its influence on the phonon coupling as well as on the initial and final-state screening.
The Changing Environments of Dopants in Amorphous Silicon at Various Stages of Annealing
Authors: Dent Andrew J. , Dobson B. R. , Greaves G. N. , Kalbitzer S. , Derst G. , Müller G.
Published: March 2011

X-ray Absorption Fine Structure (XAFS) spectroscopy measured at glancing angles of incidence has been used to record the varying environments of Ga and As ion-implanted in amorphous silicon at dose levels of 4 1014 atoms cm-2. Both glow discharge deposited films and silicon wafers previously amorphised by ion beam damage were used and apart from small differences relating to the presence of hydrogen in the former the environments of the same impurity in the two forms of amorphous Si were almost indistinguishable for the same beat treatment. The fact that only glow discharge deposited material is electronically active points to differences in the intrinsic defects in these two forms of a-Si. The local atomic structure of impurities in as-implanted specimens, however, was found to alter significantly with annealing. By 400°C, for instance the coordination numbers of both Ga and As approach 3 Si's indicating very few tetrahedral sites are present in the amorphous state. By 700°C, however, the coordination numbers of either impurity Ga and As have increased and the crystallisation local to the impurities can be detected in the XAFS by the appearance of outer shells of atoms. The fraction of crystalline substitutional sites, however, is only around 33% even though the thermal epitaxial regrowth of the remaining Si matrix is practically complete. Recrystallisation of Si is clearly inhibited in the vicinity of dopants by the persistence of 3-fold sites.
Synchrotron White Radiation X-Ray Topographic Investigation of Dislocation Configurations Developed in Indium Antimonide Single Crystals by Plastic Bending
Authors: Wu Jun , Dudley M.
Published: March 2011

Synchrotron white beam x-ray topography has been used to study dislocation configurations induced in InSb single crystals by three point bending at temperatures above the brittle to ductile transition point. Semi-hexagonal dislocation loops with one long screw segment and two outcropping 60° segments, single 60° B(g) dislocation kinks on screw dislocations, and screw dislocation dipoles were observed. The relationship between these observed defect structures and the mobilities of A(g), B(g), and screw dislocations in InSb, which appear to control the plastic behavior of crystals with the sphalerite structure, is discussed. Dislocation interactions and their role in the plastic deformation process are also addressed.
Synchrotron X-Ray Topographic Study of Defects in High Quality, Flux Grown Ktiopo4 Single Crystals
Authors: Wang S. , Dudley M. , Cheng L. K. , Bierlein J. D.
Published: March 2011

Defect structures in large, high quality flux-grown KTP single crystals have been studied by using synchrotron white beam X-ray topography. Growth dislocations, inclusions, growth sector boundaries, growth bands and surface micro-scratches were imaged. A number of planar defects in the dislocation-free region are imaged and determined to be inversion twin lamellae (lamellar ferroelectric domains) which have never been previously reported in KTP crystals. These inversion twin lamellae were also studied by section topography. Detailed analysis of observed contrast revealed that the domain walls bounding the lamellae are faulted with a fault vector of ½[0±1±1]. This fault vector seems to be consistent with the atomic structure of KTP. A detailed analysis is presented and discussed.
Diffraction and Holography of Photoelectrons and Fluorescent X-Rays
Authors: Fadley Charles S.
Published: March 2011

Photoelectron diffraction is by now a powerful technique for studying surface structures, with special capabilities for resolving chemical and magnetic states of atoms and deriving direct structural information from both forward scattering and backscattering. Fitting experiment to theory can lead to structural accuracies in the 0.03 Å range. Holographic inversions of such diffraction data also show considerable promise for deriving local three-dimensional structures around a given emitter with accuracies of 0.2-0.3 Å. Resolving the photoelectron spin in some way and using circularly polarized radiation for excitation provide added dimensions for the study of magnetic systems and chiral experimental geometries. Synchrotron radiation with the highest brightness and energy resolution, as well as variable polarization, is crucial to the full exploitation of these techniques. X-ray fluorescence holography also has promise for structural studies, but will require intense excitation sources and multichannel detection to be feasible.
Reconstruction of the 3-D Atomic Structure of CoSi2 (111) by Photoelectron Holography
Authors: Zhoul Y. , Chen X. , Campuzano J. C. , Jennings G. , Gofron K. , Ding H. , Saldin D. K.
Published: March 2011

We report the use of photoelectron holography for the study of the atomic geometry of the (111) surface of single crystal CoSi2. We employ as a reference wave the Co 3p core electron emitted with a kinetic energy of 695 eV by absorption of synchrotron radiation. Remarkably sharp images of the nearest Si neighbors of the Co emitter were found using a computer reconstruction algorithm which compensates for the anisotropies of both reference and object waves. Comparison with other reconstruction schemes such as the Helmholtz-Kirchoff (HK) algorithm and the scattered-wave included Fourier transform (SWIFT), demonstrates the necessity of compensating for the reference-wave anisotropy.
Pre-Transitional Behavior in Cubic Potassium Niobate
Authors: Holma M. , Hong H. , Nelson M. , Chen Haydn
Published: March 2011

Pre-transitional behavior prior to the onset of the cubic-to-tetragonal phase transformation in KnbO3 has been studied with synchrotron x-ray scattering at NSLS, Brookhaven National Lab. Measurements of the Thermal Diffuse Scattering (TDS), Grazing Incidence X-ray Scattering (GIXS), and precursor Bragg scattering have been performed at a series of temperatures on a single crystal sample in the cubic phase (Tc = 405 °C). The TDS was measured in the (001), (011) and (111) cubic planes. The GIXS was measured above, at and below the critical scattering angle of the sample. Based on localized soft mode theory, dynamic tetragonal fluctuations may be expected prior to the onset of the phase transition initiated by defects or surfaces. The GIXS data indicate that the tetragonal phase is apparent prior to the phase transition of the bulk - - consistent with the notion that nucleation originates from potent defect sites during a martensitic-like displacive transformation. The TDS intensity distribution is disk-shaped; arising from a localized, low energy transverse optic mode in the [100] directions extending out to the Brillouin zone boundary (reduced wave vector, q =0.5). Scans made in the (011) planes show TDS intensity extending out to a reduced wave vector of q ˜ 0.2. Preliminary analysis indicates that a low energy transverse optic mode extends in the [011] direction as well. The TDS intensity decreases as the transition temperature is approached from above. Comparison of the TDS results with inelastic neutron scattering data will be made.