bluuebunny/crossref_metadata_2025 huggingface dataset:
Electrochemical Synthesis of Lamellar Structured Inorganic Films Using Interfacial Surfactant Templating
Authors: Choi Kyoung-Shin , Steinmiller Ellen M. P. , Yarger Matthew S.
Published: April 2011

Zinc oxide and cobalt hydroxide films with ordered lamellar structures were electrochemically produced via interfacial surfactant templating. This method utilizes interfacial amphiphile assemblies on a working electrode as a template to electrodeposit inorganic nanostructures. Surfactants with anionic head groups (e.g. sodium dodecyl sulfate, 1-hexadecanesulfonate sodium salt, dodecylbenzenesulfonate sodium salt, and dioctyl sulfosuccinate sodium salt) formed bilayer assemblies with Zn2+ and Co2+ ions on the working electrode and guided the lamellar growth of ZnO and Co(OH)2 films. In order to gain the ability to precisely tailor inorganic lamellar structures, the effect of co-solvent and type of working electrode on the repeat distances, homogeneity and orientation of the interfacial amphiphilic bilayers were investigated. The results described here will provide a useful foundation to design and optimize synthetic conditions for electrochemical construction of inorganic lamellar structures.
Role of Rare-Earth Element Doping in the Cycleability of LiMn2O4 Cathodes for Li-ion Rechargeable Batteries
Authors: Singhal Rahul , Tomar Maharaj S , Oviedo Osbert , Das Suprem R , Katiyar Ram S
Published: April 2011

We have synthesized spinel LiMn1.99Nd0.01O4 and LiMn1.99Ce0.01O4 powder by chemical synthesis method. The synthesized powders were used to prepare cathodes for Li ion coin cells. The structural and electrochemical properties were investigated using X-ray diffraction (XRD), scanning electron microscopy (SEM), cyclic voltammetry and charge-discharge studies, respectively. The cyclic voltammetry of the cathodes revealed the reversible nature of Li-ion intercalation in the cell. The charge-discharge characteristics for LiMn1.99Ce0.01O4 were obtained in 3.5 V – 4.8 V voltage range, while for LiMn1.99Nd0.01O4 the charge-discharge were carried out in 3.4 V – 4.4 V range. The initial discharge capacities of LiMn1.99Ce0.01O4 and LiMn1.99Nd0.01O4 were obtained as 134mAh/g and 149 mAh/g, respectively. The coin cells were tested for up to 25 charge-discharge cycles and after 25 cycles the discharge capacities were determined to 79.5 mAh/g and 132 mAh/g for LiMn1.99Ce0.01O4 and LiMn1.99Nd0.01O4 cathodes respectively. However, by doping with a small concentration of rare earth materials, like Ce and Nd reduces the capacity fading in pure LiMn2O4 cathodes making it suitable for Li-ion battery applications.
Preparation and Characterization of Li4/3Ti5/3O4 Thin Films by Sol-gel Method
Authors: Hu C. , Zhang W. , Hao H. , Cao M. H. , Lai S. J. , Zhu X. J. , Liu H. X.
Published: April 2011

In the study Li4/3Ti5/3O4 thin films were deposited on Pt substrates by sol-gel method using a spin coator. The coated films are dried at 310-360 °C, and then annealed at 500-800 °C for 30min. The prepared films were characterized by X-ray diffraction, atomic force microscope and scanning electron microscope. The results indicated that the prepared film belonged to a spinel structure and had a uniform morphology. Electrochemical properties of the prepared electrode films were evaluated by using a discharge and charge test. From these results, it can be showed that the thin film electrode annealed at 700 °C exhibited good crystallinity, smooth surface morphology, high capacity, and good rechargeability. Therefore, This film was therefore suitable for use as an anode for thin-film microbatteries.
Enabling Aspects of Metal Halide Nanocomposites for Reversible Energy Storage
Authors: Badway Fadwa , Mansour Azzam , Plitz Irene , Pereira Nathalie , Weinstein Larry , Yourey William , Amatucci Glenn G
Published: April 2011

The concept of reversible and non reversible conversion in high bandgap metal fluorides is expanded through the introduction of mixed conducting matrices to form dense nanocomposite structures capable of good transport to nanodomains of metal fluorides. Specific examples for BiF3 and especially CuF2 using matrices of nominal composition of MoO3 are discussed. The reversible conversion mechanism of the metal halides is expanded to enable a new concept of electrochemically self assembled microbatteries (ESAMs) based on alkali halides. Such technology enables the fabrication of a solid state microbattery between two current collectors of various configurations on the microscale. First examples demonstrated based on LiI have demonstrated cell formation, appreciable energy density, and preliminary reversibility.
Materials and Design Study for Micromachined Solid Oxide Fuel Cells Membranes
Authors: Rey-Mermet Samuel , Muralt Paul
Published: April 2011

Miniature solid oxide fuel cells (μSOFC) are very promising energy sources for portable devices. In this work we report on fabrication and on first experimental results of μSOFCs processed by means of silicon and thin film technology. All the layers involved in the PEN (Positive electrode-Electrolyte-Negative electrode) structure were sputter deposited on silicon wafer. The PEN membrane was liberated using deep silicon dry etching. The cathode is a combination of a very fine platinum grid covered by a thin LSC layer. The electrolyte is a bilayer of YSZ and CGO ionic conductors. Scanning electrons microscope and X-ray analysis show that the deposited films are polycrystalline with a columnar microstructure. The conductivities of these films are sufficiently high for cell operation at 550°C. The anode is composed of a NiO-Ni-CGO composite. A supporting structure consisting of an electroplated nickel grid is deposited on top of the anode and is part of it. The final PEN is a free standing 1 micron thick membrane, with a diameter of 5 mm. First measurements showed that this structure is mechanically stable up to 550°C and that the cell works with an OCV of 200 mV.
Low Temperature Synthesis and Electrochemical Properties of M0.8Sr0.2Co1-xFexO3(M = Ba, La, Pr) Nanoparticles: Effect of Grain Size on Lattice Symmetry
Authors: Magnone Enrico , Miyayama Masaru , Traversa Enrico
Published: April 2011

This study was performed to investigate the effect of grain size on crystallographic structure and electrochemistry properties for nanocrystalline La0.8Sr0.2Co1-xFexO3(x = 0.1 and 0.9) powders, as a suitable model for SOFC cathodes. Different sets of perovskite-type mixed oxides were successfully prepared by the amorphous citrate method. A particle size dependent modification in the lattice parameters of La0.8Sr0.2Co1-xFexO3 nanocrystalline powders was observed. Clear correlations between crystal size, oxygen content, crystallographic structure, and electrochemical performance were observed
Electrochemical Features of Li-Ni-Mn-Co Oxides
Authors: Adbel-Ghany Ashraf , Zaghib Karim , Mauger Alain , Gendron François , Eid A.E. , Abbas H. , Hashem Ahmed M , Ramana Chintalapalle V , Julien Christian M
Published: April 2011

We report the electrochemical behavior of various layered oxides in Li cells. A series of LiNiyMnyCozO2 materials (with z=1-2y) was synthesized by “chimie douce” and investigated as positive electrodes in rechargeable lithium batteries. Electrochemical performances of LiNiyMnyCozO2 oxides are tested cell using non-aqueous 1M LiPF6 dissolved in EC-DEC. Charge discharge profiles are investigated as a function of the rate capability, the voltage window and the synthesis parameters of the cathode. A relation is found between the gravimetric capacity and the cation disorder of materials as indicated by magnetometry analysis.
Long-Term Stability of Primary Film Battery for Radio Frequency Identification(RFID) Tag and Ubiquitous Sensor Node
Authors: Lee Young-Gi , Yeo Junho , Pyo Cheol Sig , Kyhm Kwangseuk , Cho Kuk Young , Ryu Kwang Sun
Published: April 2011

We have prepared a primary film battery which shows improved shelf life and long-term stabiltiy. We tried to optimize a multi-layered packaging film by considering gas permeability, chemical affinity, and film thickness. We also optimized conducting layer thickness, cathode/anode thickness and their compositions taking N/P rato into account. We introduced a variety of hydrogel polymers, newly developed electrolyte solutions, and novel separators to enhance the ionic conductivity value of gel-type polymer electrolyte/separator system for peak power and high power property.
Synthesis, Structure, and Electrochemical Properties of Li4Ti5O12
Authors: Ramana Chintalapalle V , Utsunomiya Satoshi , Ewing Rodney C , Becker Udo , Zaghib Karim , Julien Christian M
Published: April 2011

Lithium titanium oxide (Li4Ti5O12) spinels are promising negative electrode materials for application in energy technology. In this work, we have synthesized Li4Ti5O12 and investigated its structure, electronic properties, and electrochemical features using several analytical spectroscopy and microscopy techniques. The equally spaced lattice fringes obtained using by the high-resolution transmission electron microscopy (HRTEM) along with electron diffraction reveal that the grown Li4Ti5O12 is well crystallized in the spinel structure without any indication of crystallographic defects such as dislocations or misfits. The electronic structure determination using high-resolution X-ray photoelectron spectroscopy (XPS) coupled with compositional studies using energy dispersive X-ray spectrometry (EDS) indicate excellent chemical quality of the Li4Ti5O12. Under the optimal synthetic condition, the sample delivers a discharge capacity of 161 mAh/g at C/12. The good cyclability of Li4Ti5O12 is attributed to the small expansion (δV≈1%) of the elementary unit-cell.
Improvement of Photovoltaic Response Using Triplet Excitons
Authors: Xu Zhihua , Hu Bin
Published: April 2011

We report an enhancement of photovoltaic response by dispersing phosphorescent dye fac tris (2-phenylpyridine) iridium (Ir(ppy)3) in organic solar cells of poly[2-methoxy-5-(2¡¦-ethylhexyloxy)-1,4-phenylenevinylene] (MEH-PPV) doped with surface-functionalized fullerene 1-(3-methyloxycarbonyl)propy(1-phenyl [6,6] C61 (PCBM). It is known that photoexcitation generates both singlet and triplet states through intersystem crossing caused by hyperfine or spin-orbital coupling. Due to long diffusion length the triplet excitons can migrate from their generation sites to the interfaces of donor-acceptor interaction and directly dissociate into charge carriers. We found, based on the studies of magnetic field-dependent photocurrent, that the dispersed Ir(ppy)3 molecules increase the spin-orbital coupling strength and triplet density in the MEH-PPV matrix due to the penetration of MEH-PPV π electrons into the large field of orbital dipoles of the Ir(ppy)3. Especially, the triplet excitons facilitate the direct dissociation into charge carriers at the donor-acceptor interacting interfaces in the composite of MEH-PPV and PCBM, and consequently improve the photovoltaic response in organic solar cells.
Novel Nanoscale Organic Materials for Optimal Photovoltaic Functions
Authors: Chen Lin X , Polshakov Dmitrii , Xiao Shengqiang , Liang Yongye , Yu Luping
Published: April 2011

Covalently linked electron donor (D) and electron acceptor (A) with conjugated organic building blocks are novel materials for potential solar cell applications, because these molecular p-n junctions can minimize the exciton diffusion and transform the charge separation from interdomain to intramolecular processes. Hence, the bottleneck of the exciton diffusion in many bulk heterojuction materials can be eliminated. Meanwhile, these planar conjugated assemblies, such as supermolecules, multiblock oligomers and polymers, have strong tendency to π-π stacking to form continuous channels for charge carriers to hop/diffuse to respective electrodes. A quartet D-A assembly has been synthesized with bis-oligothiophene (BOTH) and bis-perylenediimide (BPDI) derivatives attached to a benzo template. The electronic structures and dynamics of photoinduced charge separation and recombination of this quartet molecule and reference compounds in solutions and films were studied at isolated the molecular level in solutions as well as at the molecular assembly level in films with stacked structures. Two different dynamics of charge separation and recombination associated with two types of donor/acceptor pair conformations in solution were observed. This molecular system exhibits a more efficient charge separation than charge recombination processes in both polar and non-polar organic solvents, as well as films. More efficient charge separation and slower charge recombination due to the covalent linkage indicating that the material is a potential candidate for photovoltaic studies in solid-state.
High-Efficiency Dye-Sensitized Solar Cell Based on ZnO Nanorod Arrays Electrode
Authors: Charoensirithavorn Patcharee , Yoshikawa Susumu
Published: April 2011

We have fabricated transparent ZnO nanorod arrays on the fluorine-doped SnO2 transparent conducting oxide (FTO) glass substrates and used them as the wide band gap semiconductor in dye-sensitized solar cells. Our objectives are to introduce and demonstrate new possibilities in designing the semiconductor morphology. The best performance with this cell structure produced an open circuit voltage (Voc) of 0.64 mV, a short circuit current density (Jsc) of 5.37 mA/cm2, a fill factor (FF) of 0.49, and a conversion efficiency (η) of 1.69 %, primarily limited by the surface area of the nanorod array.
Influence of Nitrogen Doping on Tungsten Oxide Thin Films for Photoelectrochemical Water Splitting
Authors: Cole Brian , Marsen Bjorn , Miller Eric
Published: April 2011

Thin films of tungsten oxide were investigated for use as a top junction in a hybrid photoelectrode. To increase the solar to hydrogen efficiency, the tungsten oxide requires a bandgap reduction to the range of 2.2 to 2.4 eV. Nitrogen doping of WO3 films was employed to reduce the bandgap via valence band modification. For low levels of doping, the bandgap was observed to increase, an effect attributed to decreased size of the polycrystals in the film. The photoelectrochemical efficiency was found to decrease from 80% for pure WO3 to 56% for films deposited at a nitrogen partial pressure of 1.5 mTorr. For even higher doping levels (to 5 mTorr N2), the bandgap was shown to decrease to a value of ∼1.9 eV, but the structural data indicates that significant disorder had been introduced. This disorder is consistent with recurrent dislocations, an effect that is common for the tungsten oxide material.
High Deposition Rate of Microcrystalline Silicon for n-i-p Solar Cell by Using VHF PECVD Method
Authors: Liu Jun-Chin , Huang Chin-jeng , Wong Techi , Wu Jian-Shu , Luo Yih-Rong , Chen Chi-Lin
Published: April 2011

P doped, intrinsic, and n doped microcrystalline silicon (μc-Si) thin films were successfully synthesized on 10×10 cm2 transparent conductive oxide (TCO) /glass substrate by using a Very High Frequency Plasma Enhanced Chemical Vapor Deposition (VHF-PECVD, 80MHz) single chamber system. The crystal fraction of p and n type μc-Si:H with a thickness of 100nm was over 70% and 80%, respectively. Intrinsic μc-Si:H was deposited at a substrate temperature of 250°C with a high deposition rate over 1 nm/s. Photo-current/dark-current ratio of intrinsic μc-Si:H was higher than 102. The optimum cell initial efficiency of μc-Si:H single junction solar cell had been achieved 7.03 % so far.
Microstructure Evolution in Deformed Copper and Nickel
Authors: Landau Peri , Shneck Roni Z. , Makov Guy , Venkert Arie
Published: April 2011

The combined effect of strain and temperature on the microstructure and detailed internal structure of dislocation boundaries was systematically studied in compressed pure polycrystalline copper and nickel and compared to the microstructure of compressed polycrystalline aluminum. Below 0.5Tm the microstructure of Cu and Ni consists of dislocation cells, however, only in Cu second generation microbands are formed. In Cu and Ni, the dislocations inside the boundaries rearrange themselves from tangles to ordered arrays of parallel dislocations following interplay between strain (requirement for cross slip) and temperature (dislocation mobility and ease of cross slip). The ordered detailed structure is similar to that observed in Al deformed at room temperature and lower strain levels. The amount of strain and temperature applied to Cu and Ni in order to achieve the same detailed structure formed in Al depends on the stacking fault energy (SFE) of the metal- higher strain and temperature as the SFE is lower.
High Quality a-Ge:H Films and Devices Through Enhanced Plasma Chemistry
Authors: Johnson Erik V. , Roca i Cabarrocas Pere
Published: April 2011

We present a material study on RF PECVD-grown a-Ge:H showing that thin films of such material can be produced without using the conventional techniques of high power density or powered-electrode substrate placement. We demonstrate the production of material with PDS signatures superior to material produced at ten times higher power density. This is achieved through the use of Ar and H2 dilution and by growing the films at high pressures under conditions where nanocrystals formed in the gas phase contribute significantly to the growth as confirmed by HRTEM. The conditions described result in material which demonstrates activated conduction down to room temperature. Additionally, the quality of the material has been demonstrated through its application in n-i-p diodes. A spectral response at 0.9um of 0.38 and an AM1.5 efficiency of 2.1% have been demonstrated utilizing an absorber layer thickness of only 60nm.
Low Temperature High Quality Growth of Silicon-Dioxide Using Oxygenation of Hydrogenation-Assisted Nano-Structured Silicon Thin Films
Authors: Rouhi Nima , Esfandyarpour Behzad , Mohajerzadeh Shams , Hashemi Pouya , Hekmat-Shoar Bahman , Robertson Michael D.
Published: April 2011

We report a low temperature high quality oxide growth of nano-structured silicon thin films on silicon substrates obtained through a hydrogenation-assisted PECVD technique followed by a plasma enhanced oxidation process. The deposited layers were investigated and compared with respect to their electrical, optical and stoichiometrical properties by means of Ellipsometry, Rutherford backscattering (RBS), Raman spectroscopy, Fourier transform infrared (FTIR) spectroscopy, and by current voltage and capacitance voltage measurements on metal-oxide-semiconductor (MOS) structures.
Channel Reliability in MOSFETs with Gate Oxide Grown using ECR Plasma of O2/He
Authors: Jaju Vishwas , Dalal Vikram
Published: April 2011

In this paper we present the channel degradation properties of MOSFET with gate oxide grown using electron cyclotron resonance (ECR) plasma. Si was oxidized using ECR plasma of 10% O2/He at 450°C for 60 min. MOS and MOSFETs devices were fabricated, using ECR grown oxide as a gate oxide, to evaluate the electrical properties. We found that the n-MOSFET with ECR as-grown oxide shows poorer channel degradation properties, by approximately two orders of magnitude, compared to channel with thermally grown (at 950°C) dry oxide. When as-grown oxide was annealed at much higher temperature (~800oC), channel resistance for the hot carriers improved and became comparable to that of the thermally grown oxide. We have shown that because of the lower processing temperatures used during oxidation strain is present in the bulk oxide and also at Si-SiO2 interface. Annealing at higher temperature can relieve strain and this assumption was found be self consistent with the infrared absorption study.
Effects of Power Density and Thickness On Aluminum-Induced Crystallization of PECVD Amorphous Silicon
Authors: Hsu Kendrick S , Ou-Yang Jeremy , Ren Li P. , Pan Grant Z.
Published: April 2011

The effect of power density and thickness on aluminum-induced crystallization (AIC) of amorphous silicon (a-Si) formed with plasma enhanced chemical vapor deposition (PECVD) was studied by using N2-protected conventional furnace reaction and optical microscopy. With the deposition power density ranging from 0.05 to 1.00 W/cm2 and the thickness from 500 to 5000Å, it was found that a low power density as well as a large a-Si thickness could result in a decrease of activation energy and therefore a significant reduction of the AIC reaction temperature. Scanning and transmission electron microscopy and X-ray diffraction were used to check the crystallinity and quality of the AIC thin films. High quality polysilicon thin films were achieved at an AIC reaction temperature as low as 120°C.
Performance of Thin Film Silicon MEMS on Flexible Plastic Substrates
Authors: Patil Samadhan , Chu Virginia , Conde Joao Pedro
Published: April 2011

Microresonators based on thin film hydrogenated amorphous silicon microbridges were fabricated by surface micromachining on flexible polyethylene terephthalate (PET) substrates with a maximum processing temperature of 110°C. An aluminum sacrificial layer is used which is patterned by either wet etching or lift-off. Resonance in the MHz range was observed using electrostatic actuation. Processing of the microbridges on PET with sacrificial layer patterned by lift-off has higher yield than by etching. Bending measurements show that the thin film silicon microbridges on PET can withstand a higher compressive strain (-2.5%) than tensile strain (1.25%).
Effect of a Channel Length and Drain Bias on the Threshold Voltage of Field Enhanced Solid Phase Crystallization Polycrystalline Thin Film Transistor on the Glass Substrate
Authors: Lee Won-Kyu , Han Sang-Myeon , Park Sang-Geun , Chang Young-Jin , Park Kee-Chan , Kim Chi-Woo , Han Min-Koo
Published: April 2011

We have fabricated a new magnetic field enhanced solid phase crystallization (FESPC) polycrystalline silicon (poly-Si) thin film transistors (TFTs), which shows the excellent electrical characteristics and superior stability compared with hydrogenated amorphous silicon (a-Si:H) TFTs. The mobility (μ) and threshold voltage (VTH) of p-type TFTs of which the channel width and length are 5 μm and 7 μm, respectively are 31.98 cm2/Vs and -6.14 V, at VDS=-0.1 V. In the FESPC TFTs, the characteristics caused by grain boundary are remarkable due to large number of grain boundaries in the channel compared with poly-Si TFTs. The VTH of the TFT which have 5 μm channel length is smaller than that of 18 μm channel length by 1.36 V, which is considerably large value. It is due to the large number of grain boundaries in the channel and the high lateral electric field. The grain boundary potential barrier height is decreased, when the large lateral electric field is applied (which is called DIGBL effect). As a result of increased mobility, the drain current is increased, and VTH can be decreased. The activation energy (Ea) is strongly depended on the drain bias and the number of grain boundaries. is decreased, caused by the large drain bias and/or smaller number of grain boundaries. This decreased Ea can be reduced VTH due to increased the drain current. VTH of p-type poly-Si TFT employing FESPC on the glass substrate is affected by channel length and VDS due to energy barrier lowering effect at the grain boundary by increased lateral electrical field.
Improved Efficiency of Single Junction Microcrystalline Silicon n-i-p Solar Cells with an i-Layer Made by Hot-Wire CVD
Authors: Li Hongbo , Franken Ronald H.J. , Stolk Robert L. , van der Werf C. H.M. , Schuttauf Jan-Willem A. , Rath Jatin K. , Schropp Ruud E.I.
Published: April 2011

The influence of the surface roughness of Ag/ZnO coated substrates on the AM1.5 J-V characteristics of microcrystalline silicon (μc-Si:H) solar cells with an i-layer made by the hot-wire chemical vapour deposition (HWCVD) technique is discussed. Cells deposited on substrates with an intermediate rms roughness show the highest efficiency. When using reverse hydrogen profiling during i-layer deposition, an efficiency of 8.5 % was reached for single junction μc-Si:H n-i-p cells, which is the highest for μc-Si:H n-i-p cells with a hot-wire i-layer.
Hydrogen Passivation of Thin-film Polysilicon Solar Cells
Authors: Carnel Lode , Gordon Ivan , Van Gestel Dries , Beaucarne Guy , Poortmans Jef
Published: April 2011

Thin-film polysilicon solar cells are a promising low-cost alternative for bulk silicon solar cells. Due to their reduced material thickness, these solar cells are less dependent on the silicon feedstock price. Until now these devices showed a worse performance compared to bulk Si solar cells due to the small grain size and the high recombination velocity at the grain boundaries. A better understanding of hydrogen passivation is therefore of crucial importance to improve the efficiency of polysilicon solar cells. In this work we characterized fine-grained polysilicon layers with a grain size of only 0.2 μm before and after passivation. Plasma hydrogenation led to a higher hydrogen concentration in the first micron of the layer than nitride passivation. The highest efficiency of 5.0 % was reached when nitride passivation was followed by plasma passivation.
Preliminary Results on Large Area X-ray a-SiC:H Multilayer Detectors with Optically Addressed Readout
Authors: Vieira Manuela , Vygranenko Yuri , Fernandes Miguel , Louro Paula , Sanguino Pedro , Fantoni Alessandro , Schwarz Reinhard
Published: April 2011

This paper investigates a feasibility of using a large area image sensor with an optically addressed readout for medical X-ray diagnostic imaging. A device prototype comprises a multilayer glass/ZnO:Al/p (a-SiC:H)/i (a-Si:H)/ n (a-SiC:H)/ i(a-Si:H)/p (a-SiC:H)/ a SiNx/ITO structure coupled to a scintillator layer. Here, the p-i-n-i-p structure works in both sensing and switching modes depending on the biasing conditions. A numerical simulation is used to optimize the semiconductor layer thicknesses in order to achieve a photocurrent matching between back-to-back diodes in switching mode. The charge carrier transport within the p-i-n-i-p structure is also analyzed under different electric and optical biasing conditions. A physical model supports the results.
Hot-Wire Deposited Nanocrystalline Silicon TFTs on Plastic Substrates
Authors: Taghibakhsh Farhad , Adachi Michael M. , Karim Karim S.
Published: April 2011

Hot-wire chemical vapor deposition (HWCVD) technique was used to deposit nanocrystalline silicon (nc-Si) thin film transistors (TFT) on thin polyimide sheets. Two straight tantalum filaments at 1850°C with a substrate to filament distance of 4 cm was used to deposit HWCVD nc-Si with no thermal damage to plastic sheet. Top-gate staggered TFTs were fabricated at 150°C and 250°C using a HWCVD nc-Si channel, PECVD silicon nitride gate dielectric, and microcrystalline n+ drain/source contacts. Leakage current of 3.3×10-12 A, switching current ratio of 3×106, and sub threshold swing of 0.51 V/decade were obtained for TFTs with aspect ratio of 1400 µm / 100 µm fabricated at 150°C. The highest electron field effect mobility was found to be 0.3 cm2/V.s observed for TFTs deposited at lower substrate temperature. Measurements showed superior threshold voltage stability of HW nc-Si TFTs over their amorphous silicon (a-Si) counterparts.
Tailored Deposition by LPCVD of Non-stoichiometric Si Oxides and their Application in the Formation of Si Nanocrystals Embedded in SiO2 by Thermal Annealing
Authors: Morana Bruno , de Sande Juan Carlos G. , Rodríguez Andrés , Sangrador Jesús , Rodríguez Tomás , Avella Manuel , Prieto Ángel Carmelo , Jiménez Juan
Published: April 2011

Silicon oxide films with excess of Si were deposited by Low Pressure Chemical Vapor Deposition. The growth rate of the films and the excess of silicon in them have been modeled using a Face-centered Central Composite Design experiment. Samples annealed at 1100°C show luminescence (665 nm) at 80K and at room temperature associated to Si nanocrystals.
Interdigitated Back Contact Silicon Heterojunction (IBC-SHJ) Solar Cell
Authors: Lu Meijun , Bowden Stuart , Das Ujjwal , Burrows Michael , Birkmire Robert
Published: April 2011

Interdigitated back contact silicon heterojunction (IBC-SHJ) solar cells have been developed. This structure has interdigitated p/n amorphous silicon (a-Si:H) films deposited by plasma enhanced chemical vapor deposition (PECVD) on the backside of crystalline silicon (c-Si) wafers, with light irradiating the front surface. IBC-SHJ cells possess advantages over front junction a-Si:H/c-Si heterojunction cells due to minimized current losses in the illuminating side, and over traditional diffused back-junction cells due to low temperature processing combined with the potential of high voltages for the heterojunction. Current-voltage curves, spectral response and laser beam induced current maps have been used to characterize the IBC-SHJ cells. It was found that the IBC-SHJ cell has non-linear illumination level dependence that correlates with effective minority-carrier lifetime. As the performance of these cells is very sensitive to the quality of passivation on front surface, they are ideally suited as a diagnostic tool for detail characterization of surface passivation. Initial cell structures have achieved independently confirmed cell efficiencies of 11.8% under AM1.5 illumination. Device simulation shows an efficiency of higher than 20% can be expected after optimizing the IBC-SHJ cells.
Investigation of Diamond Grit Size and Conditioning Force Effect on CMP Pads Topography
Authors: Sun Ting , Borucki Leonard , Zhuang Yun , Philipossian Ara
Published: April 2011

In this study, incremental loading and interferometry analysis were performed on Rohm and Haas IC1000 plain pad surfaces to investigate the effects of diamond size and conditioning force on pad topography. The Rohm and Haas IC1000 plain pad was conditioned by Mitsubishi Materials Corporation 100-grit and 325-grit diamond discs under 3.6 and 8.0 lb. Two pad samples were taken for each disc and each conditioning force test. For each pad sample, a custom-made incremental loading device (ILD) was used to measure pad surface mechanical response under different loads. When loads were applied to the pad sample surface, the pad surface displacement was measured. A decay length was extracted from the log plot of the pressure ratio vs. the change in pad surface displacement. The decay length generally increased with the diamond size and conditioning force. Both dry and wet pad samples were analyzed by the incremental loading device. Results showed that wet pad samples had higher decay lengths than dry pad samples. Separately, optical interferometry was used to probe dry pad sample surfaces without contact and produce surface height probability density functions (PDFs). For all pad samples, the pad surface height PDFs exhibited an exponential tail and a decay length was extracted, which represented the distance over which the pad surface height probability dropped by a factor of 1/e. The decay lengths extracted from the optical interferometry analysis were consistent with those extracted from the incremental loading experiments, indicating that the optically measurable pad surface characteristic had a practical interpretation in terms of the pad surface mechanical response.
Low Defect Ceria for ILD CMP
Authors: Kasthurirangan Jai , Parker John , Bettis Tiffany , Dowell Charles
Published: April 2011

The reduction of wafer scratching is a key goal driving the commercial development of CMP slurries. To better understand the underlying abrasive particle properties critical to the scratch performance of ILD CMP slurries, the scratching behavior of ceria slurries prepared with a range of particle size characteristics are characterized. Scratch results are presented and two effects are proposed to account for the findings. The Removal Rate Effect relies solely on the observed inverse proportionality between scratching and removal rate. This interpretation is consistent with a simple surface balance of scratches but suggests that removal rate differences dominate scratch performance. The Managed Tail Effect considers the effect of particle characteristics on both the creation and the removal of scratches. For a given particle population, the larger particles are assumed to dominate scratch creation. However, larger particles are also seen to drive removal rate which affects the removal of scratches during polishing. This interpretation implies that optimal scratch performance for a ceria ILD CMP slurry will be obtained when the width of the ceria particle's size distribution is optimized relative to its mean.
Micromachined Shear Stress Sensors for Characterization of Surface Forces During Chemical Mechanical Polishing
Authors: Mueller Andrew , White Robert , Manno Vincent , Rogers Chris , Anjur Sriram , Moinpour Mansour
Published: April 2011

This paper describes the fabrication and calibration of micromachined shear stress sensors intended for characterization of the local pad-wafer contact forces present during chemical-mechanical polishing. Sensors consist of arrays of microfabricated poly-dimethyl-siloxane (PDMS) posts and are able to measure forces ranging from 2 to 200 μN. The posts are 100 μm high and have diameters of 40-100 μm. Calibrated post deflection sensitivities are linear and lie between 0.2 μm/μN and 1.3μm/μN. Sensor design, fabrication, and calibration are detailed. Feasibility is established for sensor integration into a CMP scale model test setup, including an optical viewing method for observing post deflection during polishing. Initial micrographs of post deflection during polishing do not yet have sufficient resolution to determine the microscale forces during polishing.
Composite polymer core – ceria shell abrasive particles during silicon oxide CMP
Authors: Armini Silvia , De Messemaeker Joke , Burtovyy Ruslan , Luzinov Igor , Whelan Caroline M. , Moinpour Mansour , Maex Karen
Published: April 2011

Although dielectric polishing is primarily mechanical in nature, surface chemical effects can be tailored to enhance material removal, selectivity and planarity. The use of ceria abrasives in oxide polishing is particularly attractive because of favorable polishing characteristics that are generally not obtainable using conventional fumed or colloidal silica abrasives. Unfortunately, a characteristic of ceria abrasive is an enhanced tendency toward defectivity in comparison with conventional silica. Entirely novel composite structures comprising 300 nm polymer particles coated by ceria (specific surface area of the powder 61 m2/g), are achieved by either adding silane coupling agents (Composite A) or tuning the pH in order to form electrostatic attractive interactions between the core and the shell (Composite B). The polymer core shows mechanical properties that are highly tunable by variation of its synthesis parameters, while the major advantage of the ceria coating is an enhanced chemical action of the abrasive particles, commonly referred to as the chemical tooth model. In this study we report the evolution of RR, haze, and defects such as particles and scratches in CMP experiments on high-density plasma (HDP) silicon oxide using four abrasive types (14 nm primary size ceria particles, 300 nm polymer particles, composites A and B) at pH 3 and 10. Interestingly, the two types of composite exhibit different RR. This is attributed to differences in morphology and surface composition. Composite B presents more similarities with the ceria, as confirmed by particle / silica surface adhesion forces in different pH solutions, measured by a colloidal AFM technique.
Development and Optimization of Slurry for Ru CMP
Authors: Kim In-Kwon , Kwon Tae-Young , Park Jin-Goo , Park Hyung-Soon
Published: April 2011

In this study, Ruthenium (Ru) chemical mechanical planarization (CMP) slurry was studied and developed to apply it for the formation of Ru bottom electrode in DRAM capacitor. An acidic chemical was chosen as both oxidant and etchant. The effects of the chemical on polishing and etching behavior were investigated as functions of chemical concentration and pHs. The static etch rate of Ru increased with increase of chosen chemical concentration. Also, thin Ru oxide was generated in chemical solution. The highest etching and removal rate were obtained in slurry of pH 6. Ru over etching was generated due to the high etch rate of Ru, and then good planarity was not obtained. However, because Ru over etching was prevented due to low etch rate of Ru, the plarnarity and isolation of each capacitor in slurry of pH 9 was acquired successfully.
Are the Materials Properties of Indiumnitride Dominated by Defects?
Authors: Specht Petra , Hong William , Weber Eicke R.
Published: April 2011

Indium nitride (InN) is a promising yet technologically challenging material with a high defect density and unusual material properties. Its high electron mobility may be utilized in high power electronic devices, and its high absorbance and low energy optical response make it a promising candidate for multi-junction, high-efficient solar cell technology. Studies of absorption and photoluminescence optical response of epitaxial InN resulted in a large correction of the fundamental bandgap from the originally proposed 1.9 eV to now below 0.7 eV. Yet, it is still debated if the commonly measured optical transitions below the original high bandgap values are actually caused by a large concentration of defects, on the order of 1020/cm3, rather than reflecting a low fundamental bandgap. Many applications of this material, e.g. in high-efficient solar cell technology, are primarily dependent on the successful production of a contacted p-n junction, which has not yet been achieved. This contribution addresses the controversy in the bandgap discussion of InN. Valence electron energy loss spectroscopy (VEELS) of InN allows spatially resolved analysis of the density of states in the transmission electron microscope (TEM). Standard optical characterization is compared with results from TEM characterization.
Defect Contribution to the Photoluminescence from Embedded Germanium Nanocrystals Prepared by Ion Implantation and Sputter Deposition Methods
Authors: Giri Pravat Kr , Das Kaustuv , Roy Samit K
Published: April 2011

In this work, we present a comparative study of vibrational and luminescent properties of Ge nanocrystals (NCs) prepared by ion implantation (Process I) and radio frequency (RF) sputter deposition techniques (Process II). Optical Raman studies reveal presence of strain in the Ge NCs embedded in SiO2 in both cases. Polarization dependent Raman scattering studies show that process I yields NCs with surface symmetrical Raman modes only, whereas process II yields additional surface quadrupolar Raman modes. Photoluminescence studies using 488 nm excitation show broad PL emissions peaked at ∼2.3 in all the samples with varying intensities. PL studies on Ar implanted and similarly annealed SiO2 layers confirm that 2.3 eV emission is originated from oxygen deficient defects in the SiO2 matrix. PL studies with 325 nm excitation show additional strong peaks at higher energies, which are believed to be due to Ge/O interface defects. It is concluded that room temperature visible light emission from embedded Ge NCs is primarily dominated by the oxygen deficient defects in SiOx matrix and non-bridging oxygen surrounding the Ge NCs, while light emission due to quantum confined carriers in the NCs are quenched perhaps due to inherent strain in the embedded NCs.
Thermally Induced Relaxation in GaInNAsSb Quantum Well Structures
Authors: Pickett Evan , Bank Seth , Yuen Homan , Bae Hopil , Sarmiento Tomás , Marshall Ann , Harris James
Published: April 2011

GaInNAsSb quantum wells with GaNAs barriers, grown via molecular beam epitaxy (MBE) on 100–oriented GaAs substrates at varying temperatures, were analyzed using photoluminescence (PL), high-resolution x-ray diffraction (XRD), transmission electron microscopy (TEM), and energy-dispersive spectrometry (EDS). Samples grown at 420 °C, 440 °C, and 470 °C were analyzed, as were two pieces of the 440 °C growth temperature sample that had been annealed at 740 °C and 820 °C. These measurements showed that the decrease in PL with higher growth temperatures was due to the onset of 3D growth and the nucleation of dislocations. The degradation associated with overannealing was likely due to dislocation nucleation. The poor PL associated with low growth temperatures was due to another mechanism, most likely arsenic anti-site defects. EDS measurements showed greater composition uniformity with lower growth temperatures, as expected, and also showed that there was no ordered indium-rich or indium-poor phase separation at any temperature. Phase separation upon annealing was not observed.
Anomalous Evolution of Bubbles in Krypton-Implanted SiO2
Authors: Assaf Hannan , Ntsoenzok Esidor , Barthe Marie-France , Leoni Elisa , Ruault Marie-Odile , Ashok S.
Published: April 2011

Thermally grown SiO2 was implanted at room temperature with 220 keV Kr in order to generate bubbles/cavities in the sample. The formation and thermal stability of these bubbles/cavities is studied in this work. Transmission Electron Microscopy (TEM), Rutherford Backscattering Spectrometry (RBS) and Positron Annihilation Spectroscopy (PAS) were used to provide a comprehensive characterisation of defects (bubbles, vacancy, Kr and other types of defects) created by Kr implantation in SiO2 layer. These measurements suggest that the bubbles observed with TEM were a consequence of the interaction between Kr and vacancies (V), with VnXem complexes created in the whole of implanted zone. After annealing, bubbles/cavities disappear from SiO2 due to the strongly desorption of Kr and the decrease in vacancy concentration.
Characteristics of Strained GaAsSb(N)/InP Quantum Wells Grown by Metalorganic Chemical Vapor Deposition on InP Substrates
Authors: Xu Dapeng , Huang Juno Yu-Ting , Park Joo Hyung , Mawst Luke J , Kuech Thomas F , SONG XUEYAN , Babcock Susan E
Published: April 2011

GaAsSb (N) superattices (SLs) grown on InP substrates using metalorganic vapor phase epitaxy are investigated by high resolution X-ray diffraction (XRD), low temperature photoluminescence (PL), and high resolution transmission electron microscopy (TEM). XRD shows very sharp satellite peaks and pendellosung fringes, which indicates excellent crystalline quality and abrupt interfaces in the GaAsSb (N)/InP SL, with Sb varies with 0.2 to 0.7. Low temperature PL shows clearly different features between the 25% Sb and 44% Sb samples. A band alignment difference is proposed to explain these behaviors. Experimental data establishes that the transition from a type-I to a type-II heterostructure occurs for a Sb-content of approximately 40%, which agrees well with the prediction by Model Solid Theory. While N incorporation degrades the PL intensity, it also provides the greater electron confinement needed to achieve mid-IR emission from GaAsSbN/GaAsSb type-II QWs
Nanocavity Buffer Induced by Gas Ion Implantation in Silicon Substrate for Strain Relaxation of Heteroepitaxial Si1-xGex/Si Thin Layers
Authors: Raïssi Mahfoudh , Regula Gabrielle , Belgacem Chokri Hadj , Coudreau Cyril , Nitsche Serge , Lancin Maryse , Holländer Bernhard , Robert Florent , Fnaiech Mustapha , Ntsoenzok Esidor , Lazzari Jean-Louis
Published: April 2011

To weight the importance of a nanocavity buffer in a SiGe deposition substrate, some P type (001) FZ Si wafers are implanted (A samples) or not (B samples) at room temperature with 5×1016 He+ cm–2 at 10keV. They are annealed at 700°C for one hour to form a nanocavity layer close to the Si surface. Then, the wafers are carefully chemically cleaned in a clean room to remove both organic and metallic impurities from the surface. They are coated either by 210 nm (A) or 430 nm (B) Si1−xGex (x=0.20±0.02) alloy grown at 575°C for 0.42 hour by low pressure chemical vapor deposition (LP-CVD) with a growth rate of 8 to 17 nm.mn−1. Both kinds of samples are studied by cross section transmission electron microscopy, X-rays diffraction, Rutherford backscattering, atomic force microscopy and etch pit counts. The association of these techniques demonstrates that the thin SiGe layer which is deposited on sample A is fully relaxed and that the threading dislocation density (estimated to hardly reach 4×103cm−2) is at least one order of magnitude lower than what is obtained so far using ion implantation assistance in SiGe layer growth on Silicon. The roughness of the SiGe surface is low enough to stand a further Si epitaxy. Nevertheless, the mechanism involved responsible for the threading dislocation annihilation and/or confinement is still unclear.
An Evaluation of an Automated Detection Algorithm to Count Defects Present in X-Ray Topographical Images of SiC Wafers
Authors: Brazil Ian , McNally Patrick J. , O'Reilly Lisa , Danilewsky Andreas , Tuomi Turkka O. , Lankinen Aapo , Säynätjoki Antti , Simon Rolf , Soloviev Stanislav , Rowland Larry B. , Sandvik Peter M.
Published: April 2011

An evaluation of an algorithm used to extract Threading Screw Dislocation defect data from Synchrotron White Beam X-Ray Topographical images of SiC wafers is reported. This extraction involves a two-fold process; firstly the algorithm highlights the appropriate defect and secondly updates the counter to provide a final result of defect count. The result of the automated algorithm is compared to hand counts in all cases, this allowing a critical analysis of the technique. Improvements to this algorithm have been made since last reported by the same authors, which are discussed. The analysis herein was also performed on a much larger sample of SiC wafer images than previously used by the same authors [1] allowing a better judgment of performance and critical evaluation. The algorithm is also compared with a previous algorithm that was used. Advantages and deficiencies in the algorithm are outlined and other potential avenues for extraction of the data are also discussed.
Gate-All-Around (GAA) Fully Depleted (FD) Cantilever Channel MOSFET with High-k Dielectric and Metal Gate
Authors: Dey Sagnik , Lee Se-Hoon , Joshi Sachin V. , Majhi Prashant , Banerjee Sanjay K.
Published: April 2011

A MOSFET formed by a Si cantilever channel suspended between source/drain “anchors” wrapped all-around by high-κ dielectric and metal gate is demonstrated. The device shows excellent subthreshold characteristics and low leakage currents due to the fully depleted body and the gate-all-around architecture implemented with a high-κ dielectric and metal gate. At the same time this also allows a high drive current due to mobility enhancements arising from volume inversion of the cantilever channel such that a large ION/IOFF is achieved.
Sub-30 nm FinFETs with Schottky-Barrier Source/Drain Featuring Complementary Metal Silicides and Fully-Silicided Gate for P-FinFETs
Authors: Lee Rinus Tek Po , Tan Kian-Ming , Liow Tsung-Yang , Lim Andy Eu-Jin , Lo Guo-Qiang , Samudra Ganesh S. , Chi Dong-Zhi , Yeo Yee-Chia
Published: April 2011

We investigated the material and electrical characteristics of platinum and ytterbium silicides for potential applications as metallic Schottky-barrier source/drain (S/D) and fully-silicided (FUSI) gate electrodes in fin field-effect transistors (FinFETs). Due to the low electro-negativity parameter of ytterbium, a low temperature silicidation process was developed to avoid the reaction of ytterbium with the isolation regions (i.e. SiO2 and SiN) to integrate ytterbium silicide successfully in mesa-isolated n-FinFETs. The integration of FUSI metal gate into p-FinFETs was also explored in this work and a novel two-step silicidation process that integrates simultaneously two different phases of platinum silicide with the appropriate work function values for gate electrode and source/drain application was demonstrated.