bluuebunny/crossref_metadata_2025 huggingface dataset:
Interaction of Alkalis (CS+) With Calcium Silicates Hydrates
Authors: Faucon P. , Charpentier T. , Henocq P. , Petit J.C. , Virlet J. , Adenot F.
Published: April 2011

C-S-H of different Ca/Si ratios were synthesized in suspension. Cesium chloride (0.5 M) was put in contact with these C-S-H in reactors for 30 days at 25 °C with solution/solid ratios of 50. The quantities of cesium fixed by the C-S-H was determined by microanalyses and the mechanisms of retention in relation with the C-S-H structure was investigated by 133Cs Nuclear Magnetic Resonance (NMR). The influence of the humidity yield in which the C-S-H were stored was also studied.

At 100% of humidity, some cesium ions are trapped in the pore network of the C-S-H. However, most cesium ions are incorporated in the hydrated interlayers of the C-S-H between the silica chains of the structure. They are mobile in this interlayer space. At high Ca/Si ratio, the charge of incorporated Cs+ ions in the structure should be compensated by the associated Cl- incorporation. At low Ca/Si, the presence of silanol groups in the C-S-H structure, which becomes closer to that of tobermorite (Ca/Si about 0.8), makes possible the exchange or substitution H'<->Cs'. The resulting retention of cesium in the C-S-H then becomes higher.
XRD Examination of Slags Produced by Incineration of Solid Wastes With Metal Fuel
Authors: Karlina O.K. , Ojovan M.I. , Stefanovsky S.V. , Varlakova G.A.
Published: April 2011

A mixture of powdered magnesium-aluminum alloy (with composition close to Mg4A13), calcium silicide, and potassium nitrate as oxidizer was applied as metal fuel to incinerate various solid radioactive wastes (biomaterials, ion-exchange resin, etc.) and to produce glass-like materials. Materials obtained were examined with X-ray diffraction to identify mineral phases formed during incineration and vitrification processes. It has been established that solid waste incineration resulted in a formation of a slag product composed of stable mineral phases: oxyapatite, nagelschmidtite, spinels, karnegiite, which can be considered as host phases for radionuclide immobilization. Waste vitrification with metal fuel yields an amorphous phase which is predominant in final products, and a small amount of crystalline phases. Preliminary leaching tests were carried out. Leach rate of 137Cs in deionized water at 20 °C was found to be by order of magnitude 10−5 g-cm−2 day−1. Leach rates of 90Sr and 238Pu were approximately one order of magnitude lower.
Interaction of Eu(III) and Th(IV) With Sulfate-Resisting Portland Cement
Authors: Wieland E. , Tits J. , Spieler P. , Dobler J.P.
Published: April 2011

The uptake of Eu(III) and Th(IV) by a sulphate-resisting Portland cement has been investigated in batch type sorption experiments using 152 Eu and 234Th as tracers. Prior to performing sorption studies, the experimental methodology was assessed. The kinetics of Eu(III) and Th(IV) interactions with cement were measured for times up to about 130 days. The effect of isosaccharinic acid added to artificial cement pore water on Eu(III) and Th(IV) uptake was examined to elucidate the effect of cellulose degradation products.
Perspectives on the Review of AECL's Proposal for Disposing of Canada's Nuclear Fuel Waste
Authors: Dormuth K.W. , Gillespie P.A. , Whitaker S.H.
Published: April 2011

A federal Environmental Assessment Panel has completed public hearings on the proposed concept for geological disposal of Canada's nuclear fuel waste. The Panel will make recommendations to assist the governments of Canada and Ontario in reaching decisions on the acceptability of the proposed concept and on the steps that must be taken to ensure the safe long-term management of nuclear fuel waste in Canada. It is instructive to review the background to the public hearings, to consider the issues that have been important in the public review, and to reflect on the opposing points of view presented at the hearings.
Modeling the Radionuclide Migration Experiments at Grimsel. What Have We Learned?
Authors: Heer W. , Smith P.A.
Published: April 2011

For several years, tracer migration experiments at Nagra's Grimsel Test Site have been performed with an exceptionally high degree of precision. A summary of the main findings obtained by modelling these experiments is presented, addressing, in particular the influence of sorption. A consistent description of tracer behaviour is achieved, giving confidence when applying broadly similar methodologies and models in geosphere performance assessment.
Removal and Containment of High-Level Radioactive Polonium From Liquid Lead-Bismuth Coolant
Authors: Yefimov E.I. , Pankratov D.V. , Ignatiev S.V.
Published: April 2011

The channels of polonium nuclide formation in lead-bismuth target irradiated by high energy protons and secondary neutrons are considered. Under off blanket condition the activity of 200po -210Po, as well as the fission and spallation product activity are calculated for 15 MW target after 1 year operation. Polonium separation methods, including removal using alkaline extraction, vacuum sublimation, and so-called carrier method are analyzed. The engineering design for experimental apparatus to test polonium removal and containment using alkaline extraction using tellurium as a chemical analog of polonium is developed. The necessary degree of polonium removal to keep concentration below levels appropriate to meet the US and Russia safety standards is estimated. Comparative analysis of alkaline extraction and vacuum sublimation techniques from the viewpoint to achieve the necessary removal depth is carried out.
Oxidation Phenomena and Processes in Opalinus Clay: Evidence From the Excavation-Disturbed Zones in Hauenstein and Mt. Terri Tunnels and Siblingen Open Clay Pit
Authors: Mäder Urs K. , Mazurek Martin
Published: April 2011

Constraints on oxidation phenomena and processes in Opalinus Clay are derived from studies at three localities: the 140-year old Hauenstein tunnel, the six-year old Mt. Terri tunnel, and an open clay pit at Siblingen that documents processes active over thousands of years. The excavationdisturbed zone (EDZ) in both tunnels is characterized by an extensive fracture network that extends to at least 1.6 m. The network consists of saturated fractures as well as some air-filled fractures with apertures up to several mm that contain effervescent gypsum. At Hauenstein, the fracture network displays regularly developed brownish oxidation zones extending 3-15 mm into matrix rock. Such oxidation zones are absent at Mt. Terri. Siblingen displays a remarkable decrease of both fracturing and oxidation phenomena with depth below surface.

Microscopic observations, mass balance constraints, and estimated diffusion coefficients of oxygen indicate a minor extent of pyrite oxidation at Hauenstein possibly controlled by diffusionlimited oxygen transport into water saturated rock. Oxidation of siderite is quantitatively dominating over pyrite oxidation at Siblingen. There is evidence at Hauenstein and Siblingen that rock alteration penetrated deeper than the visible alteration zone.

During the operational phase (20-100 years) of a deep repository at least the major EDZ fractures are expected to become unsaturated, and gypsum to be precipitated. Fracture apertures reach locally several millimeters within a few years, which enhances hydraulic and gas conductivities. Oxidation rims bordering fractures in the EDZ develop over timescales of 10-100 years, but mass transfers are quantitatively minor.
Charge Compensation and the Incorporation of Cerium in Zirconolite and Perovskite
Authors: Begg B.D. , Vance E.R. , Lumpkin G.R.
Published: April 2011

The incorporation of cerium, as a simulant for plutonium, has been investigated in both zirconolite and perovskite under oxidising and reducing conditions. The Ce valence in zirconolite was very sensitive to the processing atmosphere, whilst in perovskite the valence of the Ce was determined essentially by the chemical design of the perovskite. Charge compensation in zirconolite and perovskite samples displaying an apparent excess of positive charge was inferred to occur by the formation of cation vacancies, in samples prepared under oxidising conditions, and by trivalent Ti being produced in samples subject to a reducing atmosphere. Oxygen vacancies are inferred to be present in samples exhibiting an apparent excess of negative charge.
On EBS Modeling for Performance Assessment: Using Shadow Models to Identify Robust System Responses
Authors: Takase H. , Grindrod P. , Einchcomb S.J. , Lee A.J. , Makino H. , Umeki H.
Published: April 2011

A new approach to identifying and characterising system responses of the EBS based on analysis of ensemble runs of a generic and flexible source term model is developed and applied. A discussion of issues relating to the use of this methodology as a complementary approach to existing scenario development/safety case definition is also included.
Excavation Disturbed Zone: Assessment of Its Hydraulic Properties Based on Surface Investigations
Authors: Vomvoris S. , Blomling P. , Lanyon G. W. , Watson C. R.
Published: April 2011

The approach followed by Nagra for the assessment of the hydraulic properties of the excavation disturbed zone (EDZ) around a potential future underground repository site for low-level and medium-level short-lived radioactive wastes is presented. In the approach particular emphasis was placed on assessing, under realistic-conservative assumptions1, an appropriate way to represent the EDZ within the context of performance assessment (PA). Calculated stress changes due to the openings were mapped onto changes of the mechanical aperture of the rock fractures. The resulting changes of hydraulic properties of the EDZ were then computed, with analytical (simple, continuum-type approximation) and numerical (fracture network representation) methods. The results of both computations were used as the basis to: i) provide hydraulic properties for the EDZ used in PA models; ii) assess whether these properties are conservative, i.e., higher values than expected, or not.
Preliminary Evaluation of Thermodynamic Mixing Properties and Miscibility Limits for Cubic Dioxide (Zr, M)O2 and Zircon (Zr, M)SiO4 Solid Solutions (M = An4+, Ln4+)
Authors: Kurepin V.A.
Published: April 2011

Cubic zirconia ZrO2 and zircon ZrSiO4 are considered as perspective crystalline form for immobilization of U, Pu and other radionuclides [1, 2]. The present study was undertaken to determine temperature dependence of solid solution limits in these compounds using thermodynamic theory of solid solutions and available equilibrium data. Thermodynamic mixing properties has been evaluated by means of the relationship between Margules parameter W and interatomic distances R in end-members AX and BX of a solid solution (A1−xBx)X

W = α(ΔR/R)2

where ΔR = R(BX) - R(AX), R = (1−x) R(AX) + x R(BX), α is a constant for isotypic isostructural compounds. According to the Urusov's energetic theory of enthalpy of mixing [3] such relationships exist between parameters W, AR and R of solid solutions with similar bonds between isomorphous atoms and their neighbors
Radionuclide Release From Spent MOX Fuel
Authors: Loida A. , Grambow B. , Karsten G. , Dressler P.
Published: April 2011

In Germany certain quantities of spent MOX fuel will be disposed in a rock salt repository. In order to assess the safety of the repository the corrosion behavior of spent MOX fuel in salt solution must be understood. Since material properties of spent MOX fuel are different compared to these of spent LWR UO2 fuel, it is not possible to deduce from corrosion behavior of the latter to that one of spent MOX fuel. It is expected that the most significant differences will occur in the dissolution kinetics, whereas similar solid alteration products are expected from the similar overall composition of the fuels. Various experiments were performed focused on the effect of fuel type on the dissolution kinetics. The results of this work are summarized and evaluated
Modeling of Radionuclides Sorption on Bentonite by Using Single Oxides Surface Complexation Models
Authors: Marmier N , Delisée A. , Fromage F , Giffaut E.
Published: April 2011

Bentonite could be one of the materials used in Engineered Barrier Systems. The aim of this work is to assess its sorbing properties using surface complexation modelling of Cs+, Ni2+ and Yb3+ sorption on single oxides
CORALUS: An Integrated In Situ Corrosion Test on α-Active Glass
Authors: Iseghem Pierre Van , Valcke Elie , Godon Nicole , Jockwer Norbert
Published: April 2011

As part of the evaluation of the safety of the geologic disposal of HLW glass, a new in situ test on α-active glass will be started up in the underground research facility HADES (SCK•CEN, Mol, Belgium), situated in the Boom Clay formation, at a depth of 223 m. Besides a demonstration of the safe disposal of HLW glass containers in Boom Clay formation, the overall objective of this CORALUS test (CORrosion of Active gLass in Underground Storage conditions) is to study the performance of active HLW glass specimens in direct contact with different types of backfill materials, under conditions as representative as possible for those expected to prevail in a geologic repository in the Boom Clay formation. In order to meet this objective, the CORALUS test will integrate not only the experience of previous in situ tests performed at SCK•CEN and other research institutes, but also the expertise of the cooperating institutes. The paper presents the motivation for this new in situ test, its objectives, and the current status of its design
Use of Selective Sorbents for Liquid Wastes Treatment
Authors: El-Naggar I.M. , Belacy N. , Abou-Mesalam M.M. , Aly H.F.
Published: April 2011

Acidic salts of polyvalent metal antimonates(M-antimonates(M-Sb); M=Cerium, Tin, Titanium and Silicon) have been synthesized under different conditions( 1,2). The products were characterized by powdered X-ray diffraction patterns, Differential Thermal Analysis(DTA) and infrared spectrometry. Chemical stability of the product materials were studied by mixing 50 mg of the prepared materials with 50 ml of the desired medium(H20, HNO3 and HCI) with determination for the concentration of the metalions dissolved(Sb, Ce, Sn, Ti and Si) which showed high chemical stabilities in water and acid media up to I OM HNO 3 and 6M HCI.The data of the distribution coefficients showed that the selectivity decrease in the order; Eu3+> Co2+> Sr2+> Cs+ for cerium(IV) antimonate(CeSb), tin(IV) antimonate(SnSb) and silicon(IV) antimonate(SiSb), while the selectivity decrease in the order UO22+>Th4+ for titanium(IV) antimonate(TiSb). Besides, the effect of EDTA, citric acid, ferric nitrate and sodium nitrate as interfering ions in solution on the distribution coefficient of the studied cations for CeSb and SnSb were studied under certain conditions. The results showed that, the Kj values of CS+, Co2+ and Eu3+ are decreases with increasing the concentrations of ferric and sodium nitrates in the feed solutions for both materials and also Kd values are effected to some extent in case of EDTA and citric acid. Based on the obtained results, practical separation experiments on column were performed(3).

The following figures represents the break-through curves for CeSb and SnSb columns for some radionuclides 60Co (10-3M ) as example. From the above studies we conclude that, CeSb and SnSb have been successfully used for the quantitative separation of cesium which suggests its use in the treatment of radioactive liquid waste.
Microcrystalline Single-Junction and Micromorph Tandem Thin Film Silicon Solar Cells
Authors: Meier J. , Keppner H. , Dubail S. , Kroll U. , Torres P. , Pernet P. , Ziegler Y. , Selvan J.A. Anna , Cuperus J. , Fischer D. , Shah A.
Published: April 2011

Higher open circuit voltages of the microcrystalline silicon bottom cell have a direct impact on the efficiency of the micromorph (μc-Si:H/a-Si:H) tandem cell. In this paper it is shown that open circuit voltages over 500 mV can be achieved leading to gc-Si:H cell efficiencies of 8.5 %. The behaviour of such cells is characterised both by the illuminated and the dark I-V characteristics in function of cell temperature. Microcrystalline cells with Voc-values higher than 500 mV and micromorph tandems possess in general a lower value of the temperature coefficient of the fill factor and thus of the efficiency, when compared to c-Si. Temperature-dependent dark I-V measurements suggest that the dominant recombination mechanism in lgc-Si:H cells is different from that prevailing in a-Si:H solar cells.
Excess Charge Carrier Kinetics in Amorphous Silicon/Crystalline Silicon Heterojunctions
Authors: Aichberger S. v. , Hahneiser O. , Löffler J. , Feist H. , Kunst M.
Published: April 2011

By contactless transient photoconductivity measurements it is shown that i a-Si:H films, both of standard quality films and annealed low temperature films, passivate the c-Si surface for electron-hole pairs generated in the c-Si substrate. Films deposited at low temperature without annealing do not lead to passivation of the c-Si surface. The injection of excess electrons from a standard a-Si:H film into c-Si with a time constant of a few microseconds and a rather high efficiency was observed. For an annealed 120°C a-Si:H film a slower and less efficient injection was measured, whereas an annealed 50°C a-Si:H shows no appreciable injection.
Electric Field Profile in Jic-Si:H P-I-N Devices
Authors: Wyrsch N. , Beck N. , Meier J. , Torres P. , Shah A.
Published: April 2011

Solar cells based on microcrystalline silicon (ptc-Si:H) have demonstrated remarkable efficiencies and have been successfully incorporated in tandem structures; however, little work has so far been devoted to the understanding of these devices. The objective of this paper is to obtain more insight into their physical functioning by extensive characterisation of μc-Si:H devices. Charge-collection experiments shows that high electric field E(x) is present throughout the entire i-layer of thick p-i-n device. Furthermore, from capacitance studies, one concludes that the electric field profile is partly concentrated at grain boundaries. In contrast with these two observations, spectral response under forward bias voltage show that thick [tc-Si:H p-i-n devices are (unlike a-Si:H p-i-n devices) not fully field-controlled.
Internal Electric Field Profile of A-Si:H And A-Sige:H Solar Cells
Authors: Geng Xinhua , Wu Lei , Price Kent , Deng Xunming , Wang Qi , Han Daxing
Published: April 2011

By using the transient-null-current method, we have measured the internal electric field profiles Ei(x) near the p/i interface for two groups of solar cells: (a) a-Si:H p-i-n solar cells with varied i-layer thicknesses, and (b) a-SiGe:H cells with varied Ge content. When using an exponential function of Ei(x) to fit the experimental results, we obtained the field strength at the p/i interface E0, the screening length Lo, and the density of defect states Nd in the i-layer. The thinner the i-layer, the stronger the field strength obtained. For i-layer thickness increasing from 0.1 to 0.5 μm, the field strength E0 decreases from 1.15×105 to 2.0×104 V/cm; Lo decreases from 0.89 to 0.14 μm; and Nd is 3-4×1016 (cm3eV)−1. For the a-SiGe:H cells, as the Ge content increases from 40 to 55 %, E0 increases from 9.3×104 to 1.2×105 V/cm. The correlation of the internal electric field parameters with the cell‘s performance is discussed.
Amorphous Silicon/Crystalline Silicon Heterojunctions in Nuclear Radiation Detector Fabrication
Authors: Walton J.T. , Amman M. , Conti G. , Hong W.S. , Luke P.N. , Ziemba F.P
Published: April 2011

Application of amorphous silicon/crystalline silicon heterojunctions formed by RF sputter deposition and plasma enhanced chemical vapor deposition to the fabrication of nuclear radiation detectors is described. The performance of these heterojunctions as blocking contacts on highresisitivity p-type and n-type single crystal silicon and on lithium-ion compensated silicon (Si(Li)), which are commonly used in silicon detector fabrication, is presented. It is shown that an aluminum/amorphous-silicon contact on Si(Li) x-ray detectors results in about a factor of two reduction in the background counts when compared to a normal gold barrier contact.
Compact Spice Modeling and Design Optimization of Low Leakage a-Si:H TFTs for Large-Area Imaging Systems
Authors: Murthy R.V.R. , Pereira D. , Park B. , Nathan A. , Chamberlain S.G.
Published: April 2011

We present a SPICE model that takes into account the different mechanisms contributing to leakage current in hydrogenated amorphous silicon (a-Si:H) thin film transistors (TFTs). The main sources of leakage current in these devices have been identified to be the parasitic reverse-biased p-i-n diode at the vicinity of the drain as well as diffusion of phosphorous atoms from micro-crystalline (n+ μc-Si:H) contact layer into the intrinsic a-Si:H region. The latter gives rise to ohmic conduction which dominates at very low drain voltages (< I V) and very low gate voltages (< 5 V). At higher gate voltages (5V ≤ VG ≤ 20 V), the reverse current of the parasitic p-i-n diode can be attributed to thermal generation of electrons from the valence to conduction bands through the mid-gap states in the a-Si:H. At even higher gate voltages (> 20 V), the reverse current is due to trap-assisted tunneling, whereby the electrons tunnel to the conduction band via the mid-gap states. A systematic characterization of TFTs with different a-Si:H layer thicknesses shows that the optimal thickness for low leakage current is around 50 nm. The bias dependent leakage current behavior has been modeled and implemented in SPICE using simple circuit elements based on voltage controlled current sources (VCCS). Simulated and measured reverse leakage current characteristics are in reasonable agreement.
Kinetics of Light-Induced Deffect Formation and Annealing in Hydrogenated Amorphous Silicon Alloyed with Sulfur
Authors: Yan Baojie , Chen Shenlin , Taylor P. C.
Published: April 2011

The creation and annealing kinetics of light-induced defects in a-SiSx:H are studied by ESR and LESR measurements. The dispersion of defect creation after prolonged illumination with white light is greater for a-SiSx:H than that for undoped a-Si:H. In addition, the saturated value of the dark spin density is slightly lower for a-SiSx:H than that for a-Si:H. The annealing behavior can be fitted with a Gaussian distribution of annealing activation energies as is the case for undoped a-Si:H. The incorporation of sulfur decreases the peak energy and increases the width of the distribution of activation energies. Light-soaking does not change the low temperature LESR spectrum and LESR spin density.
Hydrogenated Amorphous Silicon Alloyed with Selenium
Authors: Chen Shenlin , Taylor P. C. , Viner J. M.
Published: April 2011

Hydrogenated amorphous silicon alloyed with selenium has been made by plasma enhanced chemical vapor deposition (PECVD). The activation energy for electrical conduction is essentially unchanged for selenium concentrations < 1 at.%. The photo conductivity changes for selenium concentrations > 0.5 at. %. Photothermal deflection spectroscopy (PDS) and electron spin resonance (ESR), respectively, show that the width of the valence band tail states and the density of neutral silicon dangling bonds also change for selenium concentrations > 0.5 at. %.
Deposition of Nanostructured Silicon Thin Films by Means of the Selective Contribution of Particles in Pecvd
Authors: Costa J. , Roura P. , Cabarrocas Procai , Viera G. , Bertran E.
Published: April 2011

PECVD processes are the most common way of growing amorphous and microcrystalline silicon thin films. These low pressure plasmas are known to generate large amounts of particles in the gas phase which may be a source of contamination in the production of silicon based devices. In this report, however, we show that these particles can be incorporated profitably into a growing film, provided that their size is controlled. The Modulation of the RF power is a direct method of controlling particle size. Plasma characteristics determine the dynamics of particle formation, whereas the duration of the plasma-on period controls the particle's size and atomic structure. The size and atomic structure of particles from two different periods of the same discharge were investigated. Their main characteristics, monodisperse size distribution and ordered atomic structure, are discussed in the context of the latest findings on particle nucleation and coagulation.

A semi-phenomenological model was used to show that, during the first milliseconds of the discharge, particles of 1–2 nm that are electrically neutral may leave the plasma and contribute to the growth of the film. Although these particles could not be observed on the TEM grid, their contribution to film growth might be relevant.
Performance of μ-Si:H Solar Cells with Amorphous P-Layer
Authors: Siebke Frank , Yata Shigeo , Hishikawa Yoshihiro , Tanaka Makoto
Published: April 2011

We investigated p-i-n solar cells with microcrystalline absorber but amorphous contact layers. Fill factor and open circuit voltage depend sensitively on the p/i interface. Using an optimized design of the p/i interface, cells with fill factors up to 65% and open circuit voltages of 0.45 V were deposited on amorphous p-layers. They are comparable to cells on micro- crystalline p-layers. A further increase of the open circuit voltage was achieved by variation of the p/i interface treatment but up to now it was accompanied by a decrease of the fill factor. We attribute this effect to a thin undoped amorphous layer at the p/i interface. Under non-optimized deposition conditions an amorphous instead of a microcrystalline silicon layer is grown at the p/i interface which can be detected by Raman measurements on cell structures. While the proper design of the p/i interface is crucial for the cell performance we did not observe significant differences between cells with amorphous and microcrystalline n-layers. The results reveal that the open circuit voltage is limited by the bulk properties of the undoped microcrystalline silicon.
Grazing Incidence Measurements of Polarized Electroabsorption and Light Soaking Effect on Amorphous Silicon Based Solar Cells
Authors: Jiang Lin , Schiff Eric A. , Wang Qi , Guha S. , Yang J.
Published: April 2011

Grazing-incidence measurements of polarized electroabsorption (EA) in p-i-n solar cells based on hydrogenated amorphous silicon (a-Si:H) are presented. We confirm polarized electroabsorption effect of a-Si:H with the present “sandwich” electrodes, in fact, we find a significantly stronger polarization dependence compared with earlier work based on electroabsorption detected using coplanar electrodes on a-Si:H thin films. We did not reproduce the significant dependence of the polarized electroabsorption upon light soaking, which was found in previous work with coplanar electrodes. We speculate the difference between two electrode geometries is due to the space charge and two dimensional fields.
Identification of Vacancy-Like Defects in High-Rate Grown a-Si Before and After Light Soaking by Vepas
Authors: Zou X. , Chan Y. C. , Webb D. P. , Lam Y. W. , Lin S. H. , Chan F. Y. M. , Hu Y. F. , Weng X. , Beling C. D. , Fung S.
Published: April 2011

We show how positron annihilation can distinguish vacancies in undoped hydrogenated amorphous silicon by performing Variable Energy Positron Annihilation Spectroscopy experiments before and after light soaking. We find that vacancy clusters, di-vacancies and a new type of single vacancies are created in undoped as-grown a-Si:H thin film by light illumination. The fact that the vacancy clusters are eliminated by the thermal annealing suggests that the Staebler-Wronski effect is closely related to vacancy clusters in a-Si:H material. The creation of vacancy clusters and redistribution of di-vacancies and even single vacancies probably result in photo-induced structural changes in this material.
Atomic-Scale Analysis of Plasma-Enhanced Chemical Vapor Deposition from SiH4/2 Plasmas on Si Substrates
Authors: Ramalingam Shyam , Maroudas Dimitrios , Aydil Eray S.
Published: April 2011

We present a systematic atomic-scale analysis of the interactions of SiH3radicals originating in silane containing discharges with Si(001)-(2×1) and H-terminated Si(001)-(2×1) surfaces. Through simulations, we show that the hydrogen coverage of the surface is the key factor that controls both the surface reaction mechanism and the reaction probability. The SiH3radical reacts readily with the pristine Si(001)-(2×1) surface during the initial stages of growth while its reactivity with the corresponding H-terminated surface is considerably lower. Deposition of a-Si:H from SiH3 radicals has also been simulated by repeatedly impinging SiH3 radicals onto Si(001)-(2×1) surfaces maintained at 500 °C. During deposition under these conditions, the dominant mechanism of hydrogen removal from the surface is through abstraction by SiH3 radicals, which subsequently return to the gas phase as silane. The important reaction processes that take place during film growth have been identified and their energetics has been analyzed.
Localized or Delocalized Electrons in Microcrystalline Silicon?
Authors: Müller J. , Finger F. , Carius R. , Wagner H.
Published: April 2011

The temperature dependence (4.2 - 300 K) of the electron spin resonance (ESR) signal at g = 1.998 and the electronic conductivity in microcrystalline silicon are measured and related with each other for a series of n-type samples. In addition the hyperfine interaction with the phosphorus donor states is investigated. The conductivity at low temperatures can be interpreted as hopping in impurity states with activation energies of a few meV very similar to n-doped crystalline silicon. The ESR intensity follows a 1/T-Curie law dependence. The carrier densities determined from the dopant concentration, electrical transport and ESR, respectively, agree surprisingly well. Little hyperfine intensity is found which is explained by exchange interaction of electrons with more than one dopant nucleus or occupation of tail states at low doping levels. It is concluded that the excess carriers introduced through doping do for their major part contribute to both transport and ESR. The results are in accordance with a position of the electrons with g=1.998 in impurity or tail states of the crystalline grains at low temperatures. With increasing temperature carriers get excited into the conduction band - a transition which is also monitored in the conductivity - where the ESR line is subject to considerable line broadening.
The Origin of the Enhanced Optical Absorption in Hot Wire Microcrystalline Silicon
Authors: Diehl F. , Schröder B. , Oechsner H.
Published: April 2011

The phenomenon of enhanced optical absorption in hot wire microcrystalline silicon (hw-μ-Si:H) has been investigated with respect to the structural properties of the as deposited as well as annealed films. The influence of the structural properties on the absorption behavior is explained within the framework of a model. In this model the μc-Si:H is assumed to consist of crystalline grains surrounded by grain boundaries embedded into an amorphous matrix. Because of the relaxation of the k-selection rule the absorption is supposed to be higher for the disordered grain boundaries than for the crystalline grains. The absorption coefficient α is derived from the superposition of the absorption coefficients for the amorphous, crystalline and grain boundary regions weighted by their appropriate volume fractions. According to experimental results it is furthermore assumed that the absorption of the grain boundary regions correlates with the hydrogen content of the films. The model is proven and confirmed by crucial experiments especially concerning the influence of the hydrogen content on the absorption coefficient. Other possible reasons that might influence the enhanced optical absorption such as strain induced changes of α and light scattering effects are also discussed and explicitely excluded by appropriate experiments to be the essential enhancement reasons.
Role of Hydrogen for Microcrystalline Silicon Formation
Authors: Saitoh K. , Kondo M. , Fukawa M. , Nishimiya T. , Futako W. , Shimizu I. , Matsuda A.
Published: April 2011

The role of hydrogen atoms in the formation process of hydrogenated microcrystalline silicon (μc-Si:H) by plasma enhanced chemical vapor deposition method has been investigated. Under the present conditions, the etching and the permeation of hydrogen atoms in the subsurface region do not cause the crystallization. The kinetics study of surface morphology and structure in the initial growth of μc-Si:H on an atomically flat substrate indicates that the onset thickness of island coalescence reduced under μc-Si:H formation condition. The results support the ‘surface diffusion model’ in which the surface diffusion of film precursors is enhanced by the sufficient hydrogen coverage of surface and by hydrogen atom recombination energy on the growing surface of the film.
A Fully Self-Aligned Amorphous Silicon Tft Technology for Large Area Image Sensors and Active-Matrix Displays
Authors: Powell M J , Glasse C , Curran J E , Hughes J R , French I D , Martin B F
Published: April 2011

We have developed a fully self-aligned amorphous silicon TFT technology, which is suitable for large area image sensors and active matrix displays. Self-alignment is achieved by defining the top nitride by back exposure and then forming source and drain contacts by ionimplantation and silicidation. We incorporate a low resistance gate metallisation process, by using Al metal, capped by Cr. We have compared the process of forming the silicide after the ion-implantation step, with a new process of forming the silicide first and then implanting through the formed silicide. We find a significant advantage to the latter method, where we can achieve a higher doping level and reduced contact resistance. We have therefore optimised our process based on this method. Transistor characteristics as a function of channel length for both methods show the improved contact resistance, obtained with the latter method. We obtain field effect mobilities of 0.7cm2V−1s−1, measured in the saturated region, for a channel length of 8μm.
Electronic Properties of Hot-Wire Deposited Nanocrystalline Silicon
Authors: Brüggemann R. , Hierzenberger A. , Wanka H.N. , Schubert M.B.
Published: April 2011

We compare the electronic properties of nanocrystalline silicon from hot-wire chemical vapor deposition in a high-vacuum and an ultra-high-vacuum deposition system, employing W and Ta as filament material. From the constant photocurrent method we identify a band gap around 1.15 eV while, in contrast, a Tauc plot from optical transmission data guides to a wide band gap above 1.9 eV. The sudden change-over from nanocrystalline to amorphous structure in a hydrogen dilution series is also find in the dark and photoconductivity measurements. The samples show a metastability effect in the dark conductivity upon annealing in vacuum with an increase in the dark conductivity, with the large dark conductivity decreasing slowly after the annealing cycle when the cryostat is flushed with air. We identify larger values for the mobility-lifetime products, which corresponds to the smaller defect density shoulder in constant photocur- rent spectra, for the ultra-high-vacuum deposited material compared to the high-vacuun counterpart.
Structural Properties of Polycrystalline Silicon Films Formed by Pulsed Rapid Thermal Processing
Authors: Wang Yongqian , Liao Xianbo , Diao Hongwei , He Jie , Ma Zhixun , Yue Guozhen , Sheng Shuran , Kong Guanglin , Zhao Yuwen , Li Zhongming , Yun Feng
Published: April 2011

A novel pulsed rapid thermal processing (PRTP) method has been used for realizing the solid-phase crystallization of amorphous silicon films prepared by PECVD. The microstructure and surface morphology of the crystallized films are investigated by X-ray diffraction (XRD) and atomic force microscopy (AFM). The results indicate that this PRTP is a suitable postcrystallization technique for fabricating large-area polycrystalline silicon films with good structural qualities such as large grain size, small lattice microstain and smooth surface morphology on low-cost substrate.
Polycrystalline Silicon Single Electron Island by Excimer Laser Irradiation on a-Si Film
Authors: Park C-M , Jeon J-H , Lim M-S , Yoo J-S , Han M-K
Published: April 2011

We propose a novel fabrication method for a room temperature operating single-electron memory using the size and location controlled poly-Si island by lithographic technique and excimer laser annealing.

We have patterned tip shaped excimer laser windows and irradiated laser energy through windows for crystallizing amorphous silicon. As a result of laser energy, the poly-Si grains are growing from patterned window side so that the fine grain and isolated large poly-Si quantum dot are inherently formed by well-known ACSLG regime. The oxidation was then performed by RTP at 950 °C for 30 seconds in order to isolate quantum island and fine poly-Si grains for quantum dot. The peaks of the poly-oxide along the poly-Si grain boundaries were lowered during that oxidation and isolated the poly-Si grains and made oxide barriers.
Silicon Nanowire: a New Shape of Crystalline Silicon
Authors: Zhang Y.F. , Tang Y.H. , Wang N. , Lee C. S. , Yu D.P. , Bello I. , Lee S.T.
Published: April 2011

Silicon nanowires have been synthesized by using a high-temperature laser ablation method. Transmission electron microscopic investigation shows that the nanowires are crystalline Si, and have diameters ranging from 3 to 43 nm and lengths up to a few hundreds μm. Raman scattering spectrum shows an asymmetric peak at the same position as that of bulk crystalline silicon. The x-ray diffraction revealed an important contribution from surface oxide. This is due to the high surface-to-volume ratio. Visible photoluminescence (PL) was observed in nanowires with sub-5 nm diameter.
Low-Temperature PECVD Polysilicon Crystallization by Rapid Thermal Processing
Authors: Stewart Mark , Hovagimian Howard , Arakkal Jecko , Saha Sambit , Hatalis Miltiadis K.
Published: April 2011

This work investigates the solid phase crystallization of PECVD amorphous silicon films by rapid thermal processing (RTP) as an alternative to laser crystallization. It is shown that PECVD films can be crystallized by RTP at temperatures compatible with glass substrates. A statistical design approach was used to investigate the effect of the various deposition and annealing conditions on the crystallization temperature, material properties and TFT device performance. The investigated variables include deposition temperature, rf power, pressure, surface treatments, dehydrogenation treatment, source gas, dilutant gas, and RTP scan speed. Important deposition and crystallization parameters will be discussed regarding polysilicon film optimization.
A Dehydrogenation and Annealing Method of a-Si by Microwave
Authors: Park C-M , Jeon J-H , Kim C-H , Han M-K
Published: April 2011

We propose a new method for selective crystallization of amorphous silicon and source/drain ion impurities activation by microwave annealing. We have measured FTIR to investigate hydrogen content variation in PECVD a-Si film and examined the poly-Si grain structure by SEM. We have also observed the Raman spectroscopy in order to investigate the grain growth mechanism during microwave annealing.

In our experiment, a-Si layer between microwave absorbing layers was fully crystallized in 60 seconds and hydrogen content of a-Si under microwave reflective layer was not varied after 20 minutes microwave annealing. These results indicate that proposed method may be implemented for fabricating a-Si and poly-Si TFTs on the same glass substrate. We have fabricated the poly-Si and a-Si TFTs employing microwave annealing for active layer crystallization and source/drain activation by our method.
Controlling the Amount of Si-OH Bonds for the Formation of High-Quality Low-Temperature Gate Oxides for Poly-Si TFTs
Authors: Yuda Katsuhisa , Tanabe Hiroshi , Sera Kenji , Okumura Fujio
Published: April 2011

Lowering process temperatures for polysilicon thin-film-transistors (TFTs) has given rise to new worries about the quality of TFT gate oxides. Specifically, presence of large amounts of SiOH bonds in gate oxides has become a matter of concern. We discuss methods for suppressing the formation of Si-OH bonds during chemical vapor deposition (CVD) of low-temperature processed (LTP) gate oxides. The use of remote-plasma CVD and control of the reaction between the silicon source gas and the oxygen source gas are both shown to be effective. We also show that decreased amounts of Si-OH bonds in LTP-CVD gate oxides result in desirable decreases in fixed oxide charge densities.
Mechanism of Field Emission in Diamond and Diamond-Like Carbon
Authors: Robertson J
Published: April 2011

It is shown that the facile electron field emission from diamond and diamond-like carbon occurs because surface groups such as C-H can produce large changes in electron affinity, so that electric fields from the anode can be focused towards unhydrogenated surface areas of high affinity, the fields ending on negative charges in an underlying depletion layer. The resulting downwards band bending creates very large fields which cause Fowler-Nordheim emission, while not exceeding the breakdown field, which is the highest for any solid.
A Bistable Membrane Approach to Micromachined Displays
Authors: Fleming J.G.
Published: April 2011

The fabrication of bistable membrane structures with potential application to projection displays has been demonstrated. The use of a thin film in heavy compression combined with a central pivot point enables the fabrication of devices with two mechanically stable orientations. The demonstration structure consisted of a silicon dioxide membrane, a thin silicon nitride fillet pivot and thin aluminum electrodes. Polysilicon was used as the sacrificial material.
Correlation of Performance and Hot Carrier Stress Reliability of Polycrystalline Silicon Thin-Film Transistors With Substrates and Substrate Coating
Authors: Wang Y. Z. , Awadelkarim O. O.
Published: April 2011

We report on the performance and hot carrier stress (HCS) reliability of n-channel poly-Si TFTs fabricated on bare or SiO2-coated low-alkali glass, or fused silica substrates. Low-pressure chemical vapor deposited (LPCVD) SiO2 films with different thicknesses are used as impurity diffusion barrier layers. We have found that the performance and HCS reliability of n-TFTs on the SiO2-coated glass are superior to those of n-TFTs on bare glass, and comparable to those of TFTs on fused silica. We also explore the impact of the SiO2 coating thickness on the performance and HCS reliability of the TFTs. The HCS reliability of the TFTs on SiO2-coated glass substrates is observed to depend on the SiO2 coating thickness. This is explained in terms of a phenomenological model which involves impurity and grain boundary traps.
Characterization of Secondary Electron Emission from Materials with Low or Negative Electron Affinity
Authors: Yater J.E. , Shih A.
Published: April 2011

Secondary electron emission spectroscopy is used to examine the emission characteristics of diamond films as a function of the bulk and surface properties. We find significant variation in the secondary electron yields measured from diamond surfaces even when energy distribution measurements indicate that a low or negative electron affinity is present. In particular, we observe that the material properties, such as bulk and surface uniformity, surface composition, and impurity and defect concentrations, have a strong affect on the secondary electron yield measurements. Furthermore, the energy distribution of the emitted electrons is found to vary with adsorbate species. In certain cases, the energy distribution changes with adsorbate coverage even though the measured electron intensity remains unchanged. From an analysis of the data, we identify bulk and surface properties needed to optimize the emission characteristics.
Voltage Dependent Field Emission Energy Distribution Analysis of Wide Bandgap Materials
Authors: Mccarson B.L. , Schlesser R. , Sitar Z.
Published: April 2011

Field emission from wide bandgap materials was investigated through voltage dependent field emission energy distribution (V-FEED) analysis. As compared to classical I-V characterization, V-FEED analysis can provide additional, detailed information about the origin of and the mechanism responsible for the field emission of electrons. The V-FEED technique consists of measuring the energy distribution of field emitted electrons collected at various extraction voltages. By measuring changes in the energy of the field emission peak at different voltages, data can be extrapolated to flat-band condition to determine the energy of the band from which the electron emission originated. In this study, field emission from cubic boron nitride (c-BN) coated and diamond coated tip-shaped Mo emitters was examined. For the nominally intrinsic wide bandgap coating materials studied, a linear voltage drop across the wide bandgap material, usually on the order of 1% of extraction voltage was observed and explained by field induced band-bending. For the intrinsic c-BN and diamond samples studied, the electron emission originated from the conduction band minimum at the wide bandgap material/vacuum interface.
Effect of SP3/(SP2+SP3) Carbon Fraction on the Photoelectric Threshold and Electron Affinity of Diamond Films
Authors: Akwani I.A. , Sosa E.D. , Lim S.C. , Stallcup R.E. , Castillega J.N. , Bernhard J. , Golden D.E. , Perez J.M.
Published: April 2011

We report a significant decrease in the photoelectric threshold of chemical vapor deposition grown diamond films as the fraction of sp3 carbon to sp2 plus sp3 carbon in the films decreases. Raman spectroscopy and x-ray photoelectron spectroscopy are used to characterize the different forms of carbon in the films and the sp3/(sp2 + sp3) carbon fraction at the surface. We observe a decrease in the photoelectric threshold from 4.5 eV to 3.9 eV as the sp3/(sp2 + sp3) carbon fraction at the surface decreases from 71% to 55%. Ultraviolet photoelectron spectroscopy of the films shows that they have a negative electron affinity surface. Therefore, the work function of the films decreases from 4.5 eV to 3.9 eV. We propose that the decrease in photoelectric threshold is due to a decrease in the band gap of sp2-sp3 carbon networks at the grain boundaries. The observed decrease in photoelectric threshold can be used to tailor the electronic properties of diamond films for specific applications.
Morphology of Low Temperature Carbon Films Prepared by VHF CVD: Correlation with Field Emission
Authors: Titkov A.N. , Kosarev A.I. , Vinogradov A.J. , Waqar Z. , Makarenko I.V. , Felter T.
Published: April 2011

The effect of deposition parameters and substrate on the morphology of carbon films prepared in VHF plasma at low temperature has been studied by Atomic Force Microscopy. Carbon films demonstrating superior emission characteristics were the smoothest, but not all of the smoothest films demonstrated good emission. Significant influence of pre-growth treatment of the substrate surface on the emission characteristics of the films was found.
Development of Field Emission Flat Panel Displays at Motorola
Authors: Talin A. A. , Chalamala B. , Coll B. F. , Jaskie J. E. , Petersen R. , Dworsky L.
Published: April 2011

Over the past few years, Motorola, as well as several other companies around the world, have been developing a new type of flat panel display, called the field emission display (FED). The FED combines many of the advantages of its cousin, the cathode ray tube (CRT), including high brightness and contrast, wide angle viewability, and speed in a flat package that is only a few millimeters thick. A 14 cm diagonal FED prototype built at Motorola Flat Panel Display Division is shown below, in Figure 1.