bluuebunny/crossref_metadata_2025 huggingface dataset:
Electrochemical Characterization of Galena under Simulated Carbonate Rich Weathering Conditions
Authors: Cruz Roel , Lara-Castro Rene , Monroy Marcos
Published: November 2006

An electrochemical and mineralogical study of galena oxidation was carried out under similar conditions to those found on semiarid carbonate rich soils, which are characteristic of important Mexican mining sites. Investigation of galena behavior in calcareous and alkaline conditions is important to establish strategies for remediation, prevention or control of pollution associated with weathering of this mineral. Voltammetric analyses of galena oxidation lead to the proposition that Pb(OH)2 and Pb1-xS1-y layers are formed initially. Subsequently, oxidation of these species produces a PbO2 layer and SO42-. Electrochemical and mineralogical results indicate a low mobility of Pb, due to Pb(OH)2 and PbCO3 formation during a slow oxidation process.
Electrochemical Aspects of the Nitric Acid Leaching of Lead Sulfide Concentrates: on the Way to a Highly Effective Method for Pb Recovery
Authors: Mikhlin Yuri L. , Kholmogorov Alexander , Pashkov Gennady , Mikhlina Elena
Published: November 2006

Examination of the kinetics of hot nitric acid based leaching of a lead sulfide concentrate together with changes of potential of immersed Pt or PbS electrodes has revealed three stages of the leaching. The acidic decomposition of minerals that produces aqueous sulfide that is then oxidized by nitrate plays a major role in the first, slow leach stage. In the second stage, PbS oxidation is effectively accelerated by accumulated Fe3+/Fe2+ ions, yielding largely elemental sulfur and making the process electrochemical in nature. The formation of predominant sulfate and the process impeding in the third stage seem to be due to oxidative action of nitrogenous species. It is proposed that leaching in practice is performed using cold ferric nitrate solution as this was found to be a surprisingly effective and selective oxidant for PbS. A process flowsheet for the treatment of the Gorevsky flotation lead concentrate was developed.
Model Predictions of Metal Leaching from Waste Electrical and Electronic Equipment in Chlorine-Containing Acidic Aqueous Chloride
Authors: Kelsall Geoff , Cheng Chun-Yee , Robson Anna
Published: November 2006

Models were developed for a packed bed leach reactor for dissolving metals (Ag, Au, Cu, Pb, Pd, Sn) from waste electrical and electronic equipment (WEEE) by dissolved chlorine in acidic aqueous chloride solutions, the dissolution kinetics of non-precious metals being controlled by the mass transport of chlorine. Three particles shapes of shredded WEEE (sphere, cylinder, triclinic prism) were considered and the time evolution of metal surface area was computed using finite element software. The effects were calculated of particle shape, liquid flow rate, operational mode (single-pass and part batch recycle) and reaction rate coefficients for precious metals, on metal conversion and efflux chlorine concentration. For Re = 2.4, overall metal conversions of > 0.9 were predicted to be achieved in 8 hours with single-pass mode, 'breakthrough' occurring for metal conversions > 0.6, and in 10 hours with part batch recycle mode.
The Influence of Galena Galvanic Interaction on the Reactivity of Chalcopyrite Flotation Concentrate
Authors: Nava Dora , González Ignacio
Published: November 2006

A comparative study has been performed of the anodic dissolution reactivity of a high purity chalcopyrite (99.46%) and chalcopyrite concentrate (71.7% Chalcopyrite (CuFeS2), 16.6% Galena (PbS), 0.8% Arsenopyrite (AsS), 5.0% Sphalerite (ZnS), 3.1% Pyrite (FeS2), and 0.4% Tetrahedrite (Cu3(Sb,As) S3). A sequence of anodic potential pulses was applied to the carbon paste-chalcopyrite (CPE-CP) and concentrate chalcopyrite (CPE-CC) electrodes to characterize their electrochemical behavior in 1.7 M H2SO4. Copper and lead ions, dissolved by the potential pulses, were determined using anodic stripping voltammetry (ASV) with mercury film electrode (MFE) on a vitreous carbon disk. In addition, the modified surface of CPE- CP and CPE-CC were characterized, before and after the potential pulses, by cyclic voltammetry (CV). The characterization of the final surface state of each electrochemically modified electrode and the solution composition showed that the dissolution of chalcopyrite in a concentrate is favored by the presence of galena.
The Effect of Additives on the Electroless Deposition of Gold from a Thiosulfate-Ascorbic Acid Bath
Authors: Jeffrey Matthew I. , Angstetra Arnold
Published: November 2006

Conventional electroless gold plating utilises gold(I) cyanide as the gold source. However several factors, including safety and environmental issues, have driven efforts to develop alternative electroless baths. The performance of alternative thiosulfate baths, however, is still inferior to that of conventional gold electroless plating from cyanide. Possible methods of improving the performance have been investigated, including the addition of thallium and thiourea. It will be shown that although bath decomposition is a major problem when using ascorbic acid as the reducing agent, this can be largely overcome with the addition of thiosulfate. This has lead to the development of baths containing either thiourea or thallium which offer better plating rates and longer bath lifetime.
EQCM Study of the Influence of Copper Ions on the Adsorption of Polyethylene Glycol and Bis(sodium sulfopropyl) Disulfide at a Copper Cathode
Authors: Doyle F. , Ding Ran , Zhang Xueyuan , Evans James
Published: November 2006

An electrochemical quartz crystal microbalance (EQCM) has been used to examine the role of polyethylene glycol (PEG) and bis (sodiumsulfopropyl) disulfide (SPS) in the deposition of copper from acidified aqueous sulfate solutions containing chloride ions. Neither PEG nor SPS was observed to adsorb on copper at cathodic potentials in the absence of copper ions in solution. When a small amount of copper (principally Cu (II)) was introduced into solution by a double potential step, the adsorption of PEG was observed, as was the inhibition of that adsorption by SPS.
Electrocrystallization Behavior of Copper Electrodeposited from Aqueous Sulfuric Acid with Thiourea and Chloride Additives
Authors: Huang Chin An , Chang Jo Hsuan , Hsu Fu Yong
Published: November 2006

Copper was electroplated from cupric sulfate-sulfuric acid solutions with various concentrations of thiourea and chloride ions. The microstructures of deposits were analyzed by optical microscopy, X-ray diffraction (XRD) and transmission electron microscopy (TEM). XRD results indicated that the most preferred orientation of the copper deposits was (220) when thiourea concentrations were greater than 5 ppm. However, the preferred orientation changed obviously when chloride ions were added together with thiourea;, moreover, the grain type of the deposit changed from columnar to equiaxed. TEM images showed considerable twinning in copper plated from solutions containing less than 1 ppm thiourea. Grain sizes of copper deposits decreased when higher concentrations of thiourea were added to the plating bath, together with chloride ions.
Evaluation of the Effects of Additives, Pulsing, and Temperature on Morphologies of Copper Electrodeposited from Halide Media
Authors: Free Michael , Rodchanarowan Aphichart , Phadke Nikit , Bhide Ravindra
Published: November 2006

Most of world's copper reserves are in the form of the mineral chalcopyrite (CuFeS2). Traditional copper recovery from chalcopyrite is made by size reduction, flotation, smelting, and electrochemical purification. Alternative metal extraction technology using halide media allows for elimination of the smelting process. The use of halides has the additional advantage of reducing cell voltage and current requirements relative to sulfate based systems that are used in connection with copper extraction from oxide, silicate, hydroxide, and some sulfide minerals. The elimination of smelting and the reduction in energy utilization make this an attractive alternative for copper recovery. However, the halide based systems are more likely to produce irregular electrodeposits that cannot be removed by traditional methods. Halide solutions also present additional challenges related to the corrosive nature of the solutions. This study identifies the effects of additives, pulsing, and temperature on copper electrodeposit topography as characterized by root- mean-squared roughness for deposits made from halide media.
Cathode Guides for Conventional Copper Electrorefining Reactors Employing Starter Sheet Cathodes
Authors: Guerra Eduard , Shepherd Jeffrey
Published: November 2006

Though employed in a large fraction of copper electrorefining reactors, the use of copper starter sheet as cathodes has inherent problems of poor alignment and wrap-around currents at cathode edges. As an alternative to the use of reusable mother blanks, the design of electrically insulating cathode guides, similar to those developed for retrofitting of a nickel electrowinning plant, is examined. A procedure is outlined for designing cathode guides involving specific geometric considerations for facilitating installation and removal of electrodes. The design process is complimented by modeling the performance of the guides in terms of their ability to limit cathode misalignment and warping by solving for the corresponding primary current distributions for 2-D cross sections of the copper electrorefining cells. The potential use of cathode guides to decrease the energy consumption and improve the space-time-yield of conventional copper electrorefining is also discussed.
Development and Scale-up of the FFC Cambridge Process
Authors: Hodgson David , Fray Derek , Slevin Louise , Jackson David , Fones Andrew , Mellor Ian , Brewer Steven , Male Stewart
Published: November 2006

The FFC Cambridge Process was discovered at the University of Cambridge. The process is very elegant and environmentally friendly in that an oxide is made the cathode in a bath of a molten chloride of a very electropositive element. Under these conditions, the favoured cathodic reaction is the ionisation of the oxygen in the oxide to from oxygen ions that dissolve in the salt. The final product can be a sponge or a finely divided metal powder. Metalysis Ltd has an exclusive license to exploit the technology. This paper describes the progress made by Metalysis to develop and scale-up the process using a range of examples.
Development of Inert Anode Materials for Electrowinning in Calcium Chloride Melts
Authors: McGregor Katherine , Frazer Eric , Urban Andrew , Pownceby Mark , Deutscher Rex
Published: November 2006

The electroreduction of solid titanium dioxide in a calcium chloride melt is an attractive method for the production of titanium metal. Several groups have proposed versions of this route, but no commercial process yet exists. In laboratory studies, consumable carbon anodes are used, and these can give rise to a number of cell design and operational issues. The replacement of the carbon anode with an inert anode offers numerous benefits that include: elimination of carbon dioxide emissions; more efficient cell operation and reduced electrode costs. We have evaluated a wide range of candidate inert anode materials, including metals, alloys and conductive ceramics. The studies examined the chemical stability of these materials in a calcium chloride-based melt, and also performance in laboratory-scale electrolysis tests. All metals and alloys tested were either dissolved in the melt and/or formed a thick, highly resistive crust. A conductive ceramic, chromium titanate, was the best-performed candidate and gave an acceptable cell voltage during a 24 h electrolysis test. This work was undertaken as part of the CSIRO Light Metals Flagship.
Characterization of Cr-Ni Multilayers from Chromium(III)-Nickel(II) Baths Using Pulse-Current Plating
Authors: Chen Chao Yu , Hsu Chun Ching , Liu Ui Waio , Huang Chin An
Published: November 2006

The effects of plating conditions were investigated on the composition of Cr-Ni alloys electrodeposited on brass substrates from a chromium(III)-nickel(II) bath at 30oC. At 10 A/dm2, Ni-rich deposits were obtained, whereas and at 40 A/dm2, Cr-rich deposits were formed. Hence, pulsed-current electroplating was used to develop Cr- and Ni-rich multi- layers with a thickness modulation of tens of nanometers. Microstructures of Cr-Ni multilayers were investigated by transmission electron microscopy (TEM) and electron diffraction.
Atomic Layer Deposition of Ru by Using a New Ru-Precursor
Authors: Lee Jinhyung , Song Yong Won , Lee Kwangdong , Lee Youngmin , Jang Hyeok Kyu
Published: November 2006

An ALD (Atomic Layer Deposition) system is constructed. It has multi-channel shower head to deliver sequentially separated source pulses, and it also has a load-lock chamber to develop high vacuum in main chamber efficiently. In this system, Ru (Ruthenium) layers are deposited on 8-inch silicon wafer. A new Ru-precusor, Ru(CO)3(C4H6), is used as a Ru source. NH3 is used as a reactant, and Ar, a conventional purge gas, is used as a carrier gas. For each one cycle period, one second pulses of the source and the reactant with Ar are injected to the system separately, and Ar purge gas is injected for three second between the source and the reactant pulse. The mechanism and the process of Ru deposition by the new Ru- precursor are completely understood, and Ru is deposited successfully on the silicon wafer in our system. The physical properties and phase of the deposited Ru film are investigated by changing the physical variables including Ru flow rate. Our AES result of Ru thin film by using our new Ru precursor is shown in this paper. The oxygen impurity is barely detected. The proper control of the impurity is discussed. From our results, our ALD system with the new Ru-precursor is expected to be one of the future candidates for fabricating Ru electrode for capacitors below 50nm technology.
Study of a 4 Micron Oxide Etching Using C5F8/O2/Ar Plasma
Authors: Judong Fabienne , Depoyan Linda , Hotellier Nicolas , Baudrier Martial , Bouillon Pierre
Published: November 2006

While most of the SiO2 etch processes for microelectronics focus on very small dimensions, some specific embedded applications require thick oxide etching. For the purpose of a thick damascene copper layer, the morphological properties of a C5F8 (octafluorocyclopentene)/O2/Ar chemistry is investigated on a MERIE reactor by means of a Design of Experiment (DOE). Some experiments present 2 distinct etch states, inducing sloping profile on top of the trench and straighter profile on bottom of the trench. Polymer deposition on the photoresist sides and on the oxide walls is faster than polymer consumption by bombardment. A very simple model is issued for RIE-lag adjustment between small and large areas through the mean of residence time, thus allowing a fine depth tuning for both trenches and pads patterning.
Surface Activation Using Remote Plasma for a New Wafer Bonding Route to Strained-Si
Authors: Sood Sumant , Belford Rona
Published: November 2006

A pre-bonding remote plasma treatment is being used here to enable differential thermal (dT) bonding and heterogeneous wafer bonding of Si to Si and quartz at room temperature and at elevated temperature. The results presented here are part of an ongoing research, which if successful will yield Ge free strained-Si substrates. Various pre-bonding plasma treatments of wafers prior to room temperature and elevated temperature silicon on quartz (SOQ) and silicon on insulator (SOI) bonding are presented. Comparison of standard RCA surface activation versus remote plasma surface activation has been reported. Attention is focused on the results obtained by varying different plasma parameters - time, gas species, flow rate etc and their effect on the surface energy of the bonded pair. Defects introduced during bonding and annealing were detected using an in-situ IR camera and capture system and surface micro roughness measurements were made using AFM.
Materials Issues for the Heterogeneous Integration of III-V Compounds
Authors: Goorsky Mark , Hayashi Sumiko L. , Noori Atif , Bruno David
Published: November 2006

Materials integration can advance the performance of III-V semiconductor devices through the incorporation of wafer bonded template substrates. One example would be those with bulk high resistivity and with an appropriate lattice constant for large lattice parameter materials, and with compatible thermal expansion coefficients. The objective was to develop III-V based wafer bond templates for subsequent epitaxial growth of device structures using non-compliant layers. Issues of thermal-mismatch induced strain and stability during epitaxial growth were addressed. A key component of this research is to quantify the formation of defects in wafer-bonded structures under different processing conditions. In this study, InP and InAs layers are transferred to other III-V substrates using hydrogen ion exfoliation and wafer bonding.
High-Resolution Spectroscopic Measurements of InGaAs/GaAs Self-Assembled Quantum Dots
Authors: Silverman Kevin L. , Berry Joseph , Stevens Martin , Mirin Richard
Published: November 2006

We report development of two absorption-based spectroscopic methods that have been adapted from atomic physics techniques to elucidate the basic physical properties of InGaAs/GaAs self-assembled quantum dots(SAQDs). Absorptive spectroscopic measurements allow the examination of the SAQDs optical transitions free from carrier relaxation effects. In addition, we employ these techniques to study SAQDs' optical transition with a level of spectral resolution not available using ultra-fast techniques. The first of the two approaches we discuss is cavity ring-down spectroscopy (CRDS), which permits an absolute measurement of absorption. We report on initial application of CRDS to SAQDs and present an assessment based on these measurements for single SAQD spectroscopy using this technique. The second method, spectral hole burning, is applied to SAQDs in a semiconductor ridge waveguide and permits the homogeneous linewidth of the SAQDs to be separated from the broad inhomogeneous spectrum.
Role of Dislocations in Hydrogen-Induced Exfoliation of Narrow Bandgap Semiconductors
Authors: Noori Atif , Hayashi Sumiko L. , Goorsky Mark , Sandhu Rajinder , Cavus Abdullah , Gambin V. , Gutierrez-Aitken Augusto
Published: November 2006

To investigate the role of dislocations in the exfoliation process, metamorphic buffer layers were implanted with a dose of 1.5E16 H2+/cm2 at an energy of 150 KeV. Two profiles were examined: a compositionally graded InxAl1-xAs buffer layer grown by molecular beam epitaxy on InP with an InAs cap layer (TD density = 5E6 cm-2) and an InAs layer grown directly on InP (TD density = 4E8 cm-2). Subsequent annealing of these implanted structures at 150{degree sign}C for 10 minutes caused interstitial hydrogen to diffuse away from the implanted region and settle at low energy sites - strained regions around dislocations. 5 hours annealing at 75{degree sign}C produced uniform surface blistering for both samples at the implantation depth. This effect is explained by the increased diffusivity of hydrogen at higher temperatures.
Silica Enhanced Growth of Gallium Nitride Nanowires on Si(111)
Authors: Chou L. , Hsieh Chin-Hua , Chueh Yu-Lun , Chang Mu-Tung
Published: November 2006

GaN nanowires were synthesized by reaction of metal gallium vapor with ammonia and hydrogen gases at the temperature of 700 °C on the amorphous SiO2 substrate. The morphologies of GaN nanowires are wirelike with a length up to 5 μm and the average diameter of GaN nanowires measured by transmission electron microscopy (TEM) is about 25 nm. The x-ray diffraction analysis of as-synthesized products indicates that the nanowires have the hexagonal wurtzite structure of GaN crystal. The corresponding electron diffraction pattern also indicates that the as-synthesized GaN nanowires exhibited a single-crystal feature with uniform oxygen doping characterized by electron energy loss spectroscopy.
Visualization of Electric and Magnetic Fields of Nanomaterials by Electron Holography
Authors: Shindo Daisuke , Kim Joong Jung , Murakami Yasukazu , Chueh Yu-Lun , Chou L.
Published: November 2006

Electron holography was carried out extensively to analyze the electric field around a single TaSi2 nanowire with applying the voltage and to visualize the lines of magnetic flux of Fe3O4 nanowires. In the electric field analysis, the electric potential distribution between the TaSi2 nanowire and anode was clearly visualized with an increase in the applied voltage. During the field electron emission condition, the equi-electric potential lines were blurred, which has been considered to result from the fluctuation of the electric potential between the nanowire and anode due to the field electron emission. In the magnetic field analysis, the lines of magnetic flux were basically parallel to the longitudinal direction of Fe3O4 nanowires, indicating that the shape anisotropy was significant in the magnetization distribution in these nanowires. In addition, the observation revealed the presence of a magnetic interaction between the neighboring nanowires.
Effect of Kinetics on the Morphology of Hydrogen Exfoliated Layers
Authors: Hayashi Sumiko L. , Sandhu Rajinder , Goorsky Mark
Published: November 2006

The effect of different heat treatments during the exfoliation of a thin InP layer onto a GaAs substrate is investigated. Hydrogen implantation was carried out by implanting the InP with 5 x 1016 H2+/cm2 at 150 keV. Exfoliation occurred at either 150 {degree sign}C or 300 {degree sign}C. The extended annealing at lower temperature produced smoother surfaces, 2.8 nm, compared to the sample exfoliated at 300 {degree sign}C, 8.5 nm. This change in surface morphology exhibits a much larger impact than the effect of implantation energy (i.e. straggle) on the surface morphology. The difference is attributed to the ability to trap hydrogen and form extended defects parallel to the surface at the lower temperature. Additionally, the exfoliation depth of the lower temperature specimen is slightly deeper than the specimen exfoliated at 300 {degree sign}C, indicating that the hydrogen diffuses towards the peak damage region at the higher temperatures.
Thermally Stable Boride Ohmic Contacts on n-ZnO
Authors: Wright Jonathan , Khanna Rohit , Norton David , Pearton Stephen , Ren Fan , Kravchenko I.
Published: November 2006

The annealing temperature dependence of contact characteristics on bulk single-crystal n- ZnO using a TiB2/Pt/Au metallization scheme deposited by sputtering are reported. The contacts are rectifying for anneal temperatures < 700C but transition to Ohmic behavior at higher temperatures and exhibit a minimum specific contact resistivity of 5x10-4 Ω. cm after 800C anneals. Higher temperatures lead to severe contact metallurgy intermixing and a sharp increase in specific contact resistivity associated with an increase in sheet resistance of the ZnO under the contact. Pt, Ti, Zn and B outdiffuse through the Au layer at 800C while at higher temperatures the contact morphology is destroyed. These boride- based contacts show much higher thermal stability than previous metal schemes used as Ohmic contacts on ZnO and are promising for high temperature device applications.
ZnO Light-Emitting Diodes Simulation
Authors: Jang Soohwan , Chen Jau-Jiun , Ren Fan , Han Sang-Youn , Norton David , Pearton Stephen
Published: November 2006

We have used ISE-TCAD simulator to examine the effect of active, n- and p-layer doping and thickness on the optical output intensity and current-voltage characteristics of both vertical and lateral geometry ZnO LEDs. The latter geometry is attractive for ultra-low structures with the ZnO deposited on glass substrates. The current density distribution is more uniform in the vertical structures but there is little difference in optical output power as a function of doping or layer thickness between the two geometries.
Fabrication of Carbon Modified Visible Light Active n-TiO2 Thin Films by Wet Process for Photoelectrochemical Water Splitting
Authors: Khan Shahed U. , Xu Chenkun , Killmeyer Richard , Gray Mcmahan
Published: November 2006

Carbon modified (CM)-n-TiO2 exhibited reduced bandgap energy and improved photoresponse. In this study, the CM-n-TiO2 films of different carbon contents were made by spray pyrolysis from glucose containing TiCl4 solution and subsequent calcination. It was found that the CM-n-TiO2 films exhibit significant dependence of photocurrent on their carbon contents, and carbon doping reduced the bandgap energy of TiO2 from 3.2 eV to 2.78 eV and created a new energy band having bandgap of 1.45 eV within its intrinsic bandgap. Furthermore, the photocurrent responses both in UV and visible regions were found to be enhanced by increasing the amount of doped carbon in these films. It was proposed that the increased carbon doping density in the TiO2 thin films increases the density of states of the midgap band, thereby enhancing the photocurrent responses in the UV and visible region.
Comparison of ZnO Dry Etching in High Density Inductively Coupled CH4/H2 and C2H6/H2-Based Chemistries
Authors: Lim Wantae , Pearton Stephen , Voss Lars F. , Khanna Rohit , Wright Jonathan , Gila Brent , Norton David , Ren Fan
Published: November 2006

CH4/H2 and C2H6/H2-based discharges are attractive for dry etching of single crystal ZnO because of their non-corrosive nature. We show that substitution of C2H6 for CH4 increases the ZnO etch rate by approximately a factor of 2 both with and without any inert gas additive. The C2H6/H2/Ar mixture provides a strong enhancement over pure Ar sputtering, in sharp contrast to the case of CH4/H2/Ar.The threshold ion energy for initiating etching is 42.4 eV for C2H6/H2/Ar and 59.8eV for CH4/H2/Ar. The etched surface morphologies were smooth, independent of the chemistry and the Zn/O ratio in the near-surface region was unchanged within experimental error after etching with both chemistries. The plasma etching improved the band-edge photoluminescence intensity and suppressed the deep level emission from the bulk ZnO under our conditions, due possibly to removal of surface contamination layer.
Investigation of InP/InGaAs pnp Heterostructure-Emitter Bipolar Transistor
Authors: Tsai Jung-Hui , Kang Yu-Chi , Hsu I-Hsuan , Weng Tzu-Yen
Published: November 2006

The performance of an InP/InGaAs pnp heterostructure-emitter bipolar transistor is first demonstrated. Though the valence band discontinuity at InP/InGaAs heterojunction is relatively large, the addition of a heavy-doped as well as thin p+-InGaAs emitter layer between p-InP confinement and n+-InGaAs base layers effectively eliminates the potential spike at emitter- base junction, lowers the emitter-collector offset voltage, and increases the barrier for electrons, simultaneously. Experimentally, a high current gain of 88 and a low offset voltage of 54 mV are achieved.
Optical Gain Tuning Performance of Three-Terminal Dual-Emitter Phototransistors
Authors: Lour Wen-Shiung , Chen Wei-Tien , Chen Hon-Rung , Hsu Meng-Kai , Chiu Shao-Yen , Chang Ying-Chieh
Published: November 2006

We report on the InGaP/GaAs dual-emitter heterojunction phototransistors (DEPTs) with an emitter biased using a voltage for comparison to heterojunction phototransistors (HPTs) with a floating base operated in the p-i-n and transistor modes and to the HPTs with a base biased using a voltage. The optical gain of the DEPT is presented to be tunable with both of the voltage applied to the emitter and the incident optical power. On the contrary, a conventional HPT's configuration does not simultaneously exhibit both. The power-tunable optical gain is available when the base of the HPT is floated. Otherwise, the voltage-tunable optical is expected for the HPT with a voltage biased base. Experimental results show that (1) the HPT with a voltage biased base exhibits a gain-tuning efficiency of 4.4 V- 1 and (2) the DEPT with an emitter biased using a voltage exhibits a gain-tuning efficiency of 43.4 V-1.
High-K Materials for Nonvolatile Memories
Authors: Specht Michael , Staedele Martin , Hofmann Franz , Reisinger Hans , Grieb Michael , Risch Lothar
Published: November 2006

Nonvolatile memories based on charge storage currently dominate the high density data flash market. Multi-level floating gate in NAND array architecture as well as NROM dual bit feature lowest cost per bit and simplicity of processing and thus are likely to have largest market share. For sub 50nm flash scaling introduction of high K dielectrics will be probable. High-K materials allow for improved coupling of the word line to the floating gate still providing sufficiently large physical thickness for reliable retention properties. In this article we review the opportunities and improvements high-K materials can offer for floating gate type devices as well as for charge trapping devices such as SONOS and NROM.
Bulk and Interface Material and Electrical Properties of Hafnium-Doped Tantalum Oxide High-K Films
Authors: Kuo Yue , Lu Jiang
Published: November 2006

Physical and electrical properties of hafnium-doped tantalum oxide thin films were studied. The doping process affects not only the material properties of the bulk film but also the interface layer's structure and composition. Lightly hafnium- doped tantalum oxide high-k films, i.e., with an equivalent oxide thickness as low as 1.3 nm, have been prepared and studied. The doped film has a bulk layer dielectric constant greater than 28 and an interface layer dielectric constant greater than 8. The film with an EOT of 1.3 nm has a much lower leakage current than that of the SiO2 film with the same thickness. The post-deposition annealing atmosphere showed major impacts on material and electrical properties. The new high-k material is a viable gate dielectric film for future metal-oxide semiconductor transistors.
Crystallization and Wet Etching Characteristics of Atomic Layer Deposited HfO2 Films Using Hf([N(CH3)(C2H5)]3[OC(CH3)3]) Precursor and O3 Oxidant
Authors: Seo Minha , Kim Seong Keun , Kim Kyung-Min , Park Taejoo , Kim Jeong Hwan , Hwang C.S. , Cho Ho Jin
Published: November 2006

HfO2 films were deposited by atomic layer deposition (ALD) with a new Hf precursor-Hf([N(CH3)(C2H5)]3[OC(CH3)3]) and O3 as oxidant. The crystallization characteristics of the films were studied using XRD, TEM, AFM, and wet etching test. The results were compared with results from films deposited with Hf [N(CH3)2]4 precursor. The HfO2 films deposited with Hf([N(CH3) (C2H5)]3[OC(CH3)3]) had an amorphous structure after annealing with a temperature below 800 °C under an N2 atmosphere. This caused a difference in the interfacial layer properties and in the electrical performance.
Annealing Effect and Suppression of Hydration of La2O3 Thin Films
Authors: Eom Dail , No Sang Young , Hwang C.S. , Kim Hyeong Joon
Published: November 2006

Lanthanum oxide thin films were deposited using alternate injections of La(iPrCp)3 and H2O. The deposited films were hydrated easily when exposed to air, and Si diffusion during PDA in the La2O3 film was remarkable. An AlN capping layer on the La2O3 films was effective to prevent hydration. Annealing in NH3 gas increased thermal stability and the dielectric constant due to nitrogen incorporation. The film annealed in NH3 gas at 800oC showed an EOT of 2.2nm and a leakage current of 1.7 x 10-8 A/cm2 at -1 V. The amount of Si atoms diffused into the La2O3 films decreased in the sequence; O2-annealed, NH3-annealed and pre-nitrided samples. A pre-nitridation to form a SiN reaction barrier was effective to increase thermal stability.
Al/La2O3 Analysis of Post Metallization Annealed MISFET by XPS
Authors: Kuroki Yusuke , Ng Jin Aun , Kakushima Kuniyuki , Sugii Nobuyuki , Tsutsui Kazuo , Iwai H.
Published: November 2006

La2O3 gated MISFETs with various heat treatments were fabricated and measured. High effective mobility was obtained using a Post Metallization Anneal (PMA) with Al gate electrodes. XPS analysis showed the formation of a thin Al2O3 interface layer between the Al and La2O3 during the annealing. The formation of the Al2O3 layer increased the EOT and shifted the flatband shift in the positive direction. The improvement of the effective mobility can be explained by less formation of oxygen vacancies.
Probing Point Defects in Stacks of Ultrathin High-k Metal Oxides on Semiconductors by Electron Spin Resonance: The Si/HfO2 vs the Ge/HfO2 System
Authors: Stesmans Andre , Afanas'ev Valery , Clemer K.
Published: November 2006

Combined electron spin resonance and electrical analysis of (100)Si/HfO2 and (100)Ge/HfO2 interfaces reveals dramatic differences in their interface defect properties. No interfacial Ge dangling bond type defects could be revealed. The observed paramagnetic defects do not correlate with the slow acceptor states dominating the Ge/insulator trap spectrum, and are resistant to passivation. The dangling bond type defects observed, upon hydrogen detachment, at the (100)Si/HfO2 interfaces are the trivalent Si defects common for Si/SiO2 interfaces, Pb0 and Pb1 centers. The density of the Pb0 is higher than in the (100)Si/SiO2 structures and is sensitive to the deposition process. However, the density can be significantly reduced by annealing of the Si/HfO2 structures in O-containing ambient, likely through re-establishing the Si/SiO2 interface. The density of fast interface states closely follows the variations in the Pb0 center density, suggesting it as the dominant contribution to the fast interface states.
Improvement in Thermal Stability of MOCVD HfO2 Films Using an ALD SiNx Interfacial Layer
Authors: Jang Hyuck J. , Hong Sug H. , Park Taejoo , Heo J.H. , Yang Sang Ryol , Kim M.Y , Hwang C.S.
Published: November 2006

HfO2 thin films were deposited with and without SiNx interfacial layer (IL), which was deposited by atomic layer deposition (ALD). The role of SiNx IL was studied as a barrier of silicon and oxygen. The HfO2 films were investigated by high-resolution transmission electron microscopy (HRTEM) and X- ray photoelectron spectroscopy (XPS). Capacitance Equivalent Thickness (CET) of HfO2 without SiNx IL increased after PDA, while CET of HfO2 with SiNx IL decreased and the leakage current (Jg) also decreased. XPS analysis showed that the intensity of the Si4+ peak corresponding to SiO2 with SiNx IL was lower than the Si4+ peak intensity of the sample without SiNx IL. The interface trap density (Dit) of HfO2 with SiNx IL was 5.6 x 1010/cm2eV after PDA. The results indicated that the SiNx IL suppress the formation of SiO2 after PDA and improved electrical properties and a interface quality.
Determination of the Channel Doping Density in MOS Devices with High-K Gate Dielectrics
Authors: Kar S. , Reddy Dharmendar
Published: November 2006

A new technique is outlined here for the extraction of the channel doping density of MOS nano-transistors with high permittivity ultrathin (equivalent oxide thickness (EOT) = 0.5 to 2.0 nm) gate dielectrics, using either the accumulation or the strong inversion MOS capacitance or both. This technique also obtains the doping density at the edge of the space charge layer at the onset of strong inversion, if the device is a MOSFET. Comparision of results from the new technique is made with the interface doping density and the doping profile obtained from the Ziegler technique.
A Radar for Ultra-thin High-k Dielectric Film: Zero-Bias Thermally Stimulated Current Spectroscopy
Authors: Lau Wai Shing , Han Taejoon , Zhang G. L. , Qian P. W. , Leong L. L. , Che S. T. , Wong Parry
Published: November 2006

Ultra-thin high-k dielectric films have attracted world-wide interest for DRAM capacitor or gate dielectric applications. Defect states in high-k dielectric are responsible for leakage current or mobility degradation due to remote Coulomb scattering. Hence there is a need to develop a technology to detect those defect states. We have successfully developed a novel zero-bias thermally stimulated current (ZBTSC) spectroscopy technique which is applicable to capacitors with sub-10 nm high-k dielectric. Tantalum oxide was used as an example to demonstrate the value of this technique. The ZBTSC technique can be further improved by migration to zero- temperature-gradient ZBTSC (ZTGZBTSC).
CMOS Integration Issues with High-K/Metal Gate Stack
Authors: Kwong Dim-Lee
Published: November 2006

This paper reviews some of the integration challenges that high-K/metal gate stack technology is facing. This includes thermal stability of high-K against crystallization, phase separation, and interfacial reaction with underlying Si, charges/traps in high-K as well as at interfaces, channel carrier mobility degradation, EOT control and scaling, work function control for dual-gate CMOS integration, and gate stack reliability. The engineering of the high-K/Si as well as metal/high-K interfaces is identified as the most important factor for achieving EOT<<1nm with good performance and reliability.
Implementation of Atomic Layer Deposition in Advanced Semiconductor Processes
Authors: Schaekers Marc , Van Ammel Annemie , Travaly Youssef , Delabie Annelies , Martin Hoyas Ana , Zhao Chao
Published: November 2006

The integration of ALD films in MOS devices can reveal interactions between the substrate and the ALD process, or the impact of subsequent process steps on the ALD film. This is studied on three different films: for front-end applications hafnium oxide for as a high-K gate insulator and tantalum nitride for as a metal gate, for back-end application tungsten nitride carbide for as a Cu diffusion barrier. The surface sensitivity of the WNC barrier process leads to island formation on SiC and SiO2. Substrate interaction occurs when fluorine containing reaction byproducts interact with silicon oxide during WNC deposition. In porous low-K dielectrics, diffusion of precursors in the material is observed, depending on the precursor used. In front-end applications, a HfO2 high-k gate dielectric contains residual chlorine, which influences the dielectric leakage current. The composition and properties of thermal ALD TaN compromise its application as a metal gate.
ALD Precursor Development: Challenges, Opportunities and Managing Uncertainty
Authors: Hoover Cynthia A.
Published: November 2006

The challenges associated with producing next generation sub- nanometer films to meet conformality requirements on complex topographies and to improve semiconductor device performance characteristics have resulted in the consideration of a myriad of new materials, methods of deposition, and integration strategies. For many applications it has become apparent that atomic layer deposition (ALD) will become the method of choice for depositing films. Adoption of this technology is well underway for applications with aggressive architectures such as DRAM capacitors and electrodes, and it appears imminent for copper interconnect cladding applications. The time will soon come when every semiconductor device has at least one film that is generated by ALD. During the talk, an example of how Praxair has approached precursor development for interconnect barrier and seed applications will be illustrated, and how we have used a diverse series of learnings during development to benefit the ALD community at large.
Fabrication of Rare Earth-Transition Metal Alloy Nanowires and Nanotubes
Authors: Podlaha Elizabeth J. , Mishra Rohit
Published: November 2006

Rare earth-transition metal alloy nanowire and nanotube fabrication has been demonstrated from an aqueous electrolyte using template based deposition. Anodized aluminum oxide and polycarbonate templates were used. The similarity in electrochemical behavior between various rare earth elements (Gd, Sm, Tb) was investigated. The effect of pulsed potential deposition and pore depth on the composition of the deposit was investigated. The pore depth significantly affected the deposit composition whereas no significant influence of duty cycle was seen on the composition of the deposits. Multilayered nanowires were deposited by pulsed potential, depositing alternate layers of CoGd and Co.
Investigation of Flame-Retardant Additives for Safety Usage of Lithium-Ion Batteries
Authors: Otsuki Masashi , Ogino Takao , Amine Khalil
Published: November 2006

Phosphorous nitrogen compounds, so-called phosphazene, act as a novel flame-retardant additive for the electrolytes of lithium ion (Li-ion) batteries without hampering electrochemical performances. In particular partially fluorinated phosphazene compounds show excellent ability for safety usage of the Li-ion battery.
Modification of the Electrochemical Behavior of Carbon Nanofibers for Lithium-Ion Batteries by Impregnation, and Thermal and Hydrothermal Treatments
Authors: Tirado Jose L. , Lavela Pedro , Alcantara Ricardo , Ortiz Gregorio
Published: November 2006

The electrochemical behavior of Vapor Grown Carbon Nanofibers (VGCnF) has been evaluated in lithium test cells. Several treatments have been carried out in order to improve the performance. After activation with refluxing nitric acid, the ac impedance spectra and 7Li MAS NMR spectra show significant changes and the specific capacity increases. The hydrothermal and acid treatments treatments improve the surface properties of VGCnF, as evidences by ac impedance spectroscopy. Reversible capacities around 700 mAhg-1 are achieved for tin dioxide- carbon nanofibers composite electrodes. 119Sn Mössbauer results show the participation of tin in the redox processes and the formation of lithium-tin intermetallic compounds.
In Situ XRD of Highly Charged and Discharged LixNi0.8Co0.2O2 (x close to 0)
Authors: Nikolowski Kristian M. , Bramnik Natalia , Baehtz Carsten , Ehrenberg Helmut , Fuess Hartmut
Published: November 2006

Lithium has been electrochemically extracted and inserted from LixNi0.8Co0.2O2 (0{less than or equal to}xLi{less than or equal to}1) using a dedicated electrochemical cell. The behavior of this cathode material for lithium batteries was studied by in situ-X-ray diffraction using synchrotron radiation and analyzed by Rietveld refinement. Besides the accurate determination of the lattice parameters during cycling, an anisotropic broadening of specific reflections, most pronounced around xLi=0.1, is observed and attributed to reversible microstructural changes at this high degree of lithium extraction.
Determining the Phase Diagram of LixFePO4
Authors: Dodd Joanna L. , Fultz Brent , Yazami Rachid
Published: November 2006

The phase diagram for LixFePO4 has been determined for different lithium concentrations and temperatures. X-ray diffraction analysis was used to determine phase fractions at temperatures between room temperature and 400 oC for LixFePO4 at different states of lithiation. The two low- temperature phases, heterosite and triphylite, have previously been shown to transform to a disordered solid solution at elevated temperatures. This disordered phase allows for a continuous transition between the heterosite and triphylite phases and is stable at relatively low temperatures. At intermediate temperatures the proposed phase diagram resembles a eutectoid system, with eutectoid point at around x=0.6 and 200oC. Kinetics of mixing and unmixing transformations are reported, including the hysteresis between heating and cooling. The enthalpy of this transition is at least 700 J/mol.
A Comparative Study of AC Impedance Spectroscopic Analysis on LiMVO4 (M: Ni, Co)
Authors: Bhuvaneswari Modachur S. , Subramanian S.Selvasekarapandian
Published: November 2006

Inverse spinel LixNiVO4 and LixCoVO4 have been prepared by solid state reaction method. XRD analysis indicated the formation of a new phase for the samples with high Li composition. The electrical studies show that Li1.0NiVO4 is found to have high conductivity compared to all other samples. The dielectric analysis indicates the non-Debye nature of the samples.
A Novel Method to Improve Cycling Performance of LiMn2O4 Cathodes
Authors: Xu Youlong , Li Xifei , Zhang Lei , Wang Jie , Du Xianfeng
Published: November 2006

Polypyrrole-film was coated directly onto LiMn2O4 electrode by electrochemical polymerization. Both of bare electrode and modified electrode were characterized by X-ray diffraction and electrochemical techniques. The XRD patterns demonstrated that polypyrrole was deposited onto the LiMn2O4 electrode. The charge-discharge tests revealed that modified electrode by polypyrrole-film has an excellent rechargeability, 98.2% of the initial discharge capacity and 90.1% of the maximal discharge capacity after 150 cycles, but for bare electrode, only 53.4% of the initial discharge capacity. The CV curves showed that the new method is very efficient for restraining capacity fade of LiMn2O4, in fair agreement with the charge-discharge test. The EIS measurements in a frequency range from 100kHz to 1mHz were conducted on the electrodes. It was exhibited that the existence of polypyrrole-film decreases the charge transfer resistance and facilitates the charge-transfer reaction in the LiMn2O4 material, which is favorable for improving performance of LiMn2O4 cathode.
Electronic Properties of LiFePO4 and Li Doped LiFePO4
Authors: Zhuang Vera V. , Allen J.L. , Ross P.N. , Guo J.-H. , Jow T.R.
Published: November 2006

LiFePO4 has several advantages in comparison to transition metal oxide cathode material in commercial rechargeable lithium batteries. It has a high theoretical capacity (170 mAh/g). It occurs as the mineral triphylite in nature and is inexpensive, thermally stable, non-toxic and non-hygroscopic. However, its low intrinsic electronic conductivity (~ 10-9 S/cm) is problematic. We report here a study of the electronic properties of undoped LiFePO4 and Li doped material in which Li+ are substituted for Fe2+ ions in an attempt to increase the intrinsic electronic conductivity.
Studies of Ionic Liquids in Lithium-Ion Battery Test Systems
Authors: Salminen Justin P. , Prausnitz John , Newman John
Published: November 2006

In this work, thermal and electrochemical properties of neat and mixed ionic liquid - lithium salt systems have been studied. The presence of a lithium salt causes both thermal and phase-behavior changes. Differential scanning calorimeter DSC and thermal gravimetric analysis TGA were used for thermal analysis for several imidazolium bis(trifluoromethylsulfonyl) imide, trifluoromethansulfonate, BF4, and PF6 systems. Conductivities and diffusion coefficient have been measured for some selected systems. Chemical reactions in electrode - ionic liquid electrolyte interfaces were studied by interfacial impedance measurements. Lithium-lithium and lithium-carbon cells were studied at open circuit and a charged system. The ionic liquids studied include various imidazolium systems that are already known to be electrochemically unstable in the presence of lithium metal. In this work the development of interfacial resistance is shown in a Li|BMIMBF4 + LiBF4|Li cell as well as results from some cycling experiments. As the ionic liquid reacts with the lithium electrode the interfacial resistance increases. The results show the magnitude of reactivity due to reduction of the ionic liquid electrolyte that eventually has a detrimental effect on battery performance.
Studies of Interfacial Chemistry in Lithium and Li-Ion Battery Systems Using Infrared Spectroscopy
Authors: Ross Philip
Published: November 2006

Spectroscopic studies of the chemistry at electrochemical interfaces still face significant challenges even after decades of intense effort. No single methodology has emerged as the clear choice. Each method has advantages and disadvantages such that different types of interfacial chemistry are best studied by the methods that is the most advantageous for that chemistry. In this talk I present a review of recent studies in my laboratory of the chemistry at electrochemical interfaces using infrared reflection spectroscopy, with emphasis on use of attenuated total reflection spectroscopy (ATR) in the study of surface processes in Li-ion batteries.