bluuebunny/crossref_metadata_2025 huggingface dataset:
First-principles Studies of Phase Stability and the Neutral Atomic Vacancies in LiNbO3, NaNbO3 and KNbO3
Authors: Shigemi Akio , Wada Takahiro
Published: April 2011

We overall evaluated the enthalpies of formation and the formation energies of neutral vacancies in ANbO3 (A = Li, Na, K) using a plane-wave pseudopotential method within a density functional formalism. The LiNbO3 phase with the LiNbO3-type structure was confirmed to have lower enthalpy of formation than that with perovskite- or ilmenite-type structure. The NaNbO3 (R3c) and KNbO3 (Bmm2 and R3m) phases with the lowest symmetry were found to have the lowest enthalpy of formation. The formation energy of a A vacancy was found to be the lowest under an oxidizing atmosphere and that of an O vacancy was found to be the lowest under a reducing atmosphere. The formation energy of a Nb vacancy was the highest under both oxygen-rich and -poor conditions. These results are in agreement with the empirical rule that B site defects in perovskite-type oxide do not exist.
Out-of-phase Boundary (OPB) Nucleation in Layered Oxides
Authors: Zurbuchen Mark , Lettieri James , Jia Yunfa , Carim Altaf H. , Streiffer Stephen K. , Schlom Darrell G.
Published: April 2011

Out-of-phase boundaries (OPBs), planar faults between regions of a crystal that are misaligned by a fraction of a unit cell dimension, occur frequently in materials of high structural anisotropy. Rarely observed in the bulk, OPBs frequently exist in epitaxial films of layered complex oxides, such as YBCO-type, Aurivillius, and Ruddlesden-Popper phases, and frequently propagate through the entire thickness of a film, due to their large offset and the improbability of opposite-sign OPB annihilation. OPBs have previously been demonstrated to have a significant impact upon properties, so it is important to understand their generation. These faults arise through the same few mechanisms in the various layered complex oxides.

An effort is made to unify the discussion of nucleation of these defects, common to layered oxide materials. OPBs can nucleate at the film-substrate interface (primary) via steric, chemical, or misfit mechanisms, or post-growth (secondary) through crystallographic shear during decomposition of volatile components. Examples of the mechanisms observed during high-resolution transmission electron microscopy (HRTEM) study of Aurivillius and Ruddlesden-Popper phases are presented. A method for estimating the relative OPB density in a film from correlation of x-ray diffraction (XRD) θ-2θ data with TEM information on OPBs is presented.
Non-Destructive Electro- and Photo-Luminescence Imaging of Dislocations in SiC Epitaxy
Authors: Liu Kendrick , Stahlbush Robert E , Caldwell Joshua D , Hobart Karl D , Kub Francis J , Sumakeris Joseph J
Published: April 2011

Electroluminescence (EL) and photoluminescence (PL) imaging and stressing techniques are presented that are useful characterization tools for SiC epitaxial layers grown for power devices. Both EL and PL techniques are non-destructive, and the PL imaging is non-contact. These features are important for qualifying epitaxial layers before subjecting the layers to the time-consuming and costly process of device fabrication. By imaging at various emission spectral bands, the spectral information are correlated to the geometric features in the images. This correlation enables the differentiation of dissimilar defects having similar geometric shapes. Row average plots of images at various emission spectral bands revealed that threading dislocations (TDs) have strong emission above 900 nm and that basal plane dislocations (BPDs) have a broad spectral emission that are most easily distinguished in the range between 738 nm and 870 nm. The correlation between spectral information and the image features clearly distinguished TDs and BPDs from other defects, such as, organic substance and other surface blemishes. In addition to identifying the defects, understanding their origin can be useful in developing low-defect growth techniques. The defect origination depth is one of the important information for understanding defect origin. Two schemes for determining the defect origination depth are presented. Varying the focus depth by adjusting the objective lens height is a crude but quick scheme. Stressing the epilayer to grow the BPDs till they reach the surface or the epilayer/substrate interface is more time-consuming but more accurate. The scheme of varying the focus was demonstrated using PL imaging on a 50-mm thick n- epilayer with no p+ anode layer. Adjusting the focus on a partial dislocation in the n- epilayer revealed segments of the partial coming more in focus near the epilayer/substrate interface, suggesting the defect origination depth was at or near the interface. The stress and growth scheme was demonstrated on a straight string of half loop defects in a 100-mm thick n- epilayer. During electrical stressing, BPDs emanated from the half loops and eventually propagated to the surface at a lateral distance of 250 mm. With the basal plane at an 8° offcut from the surface, the origin of the BPDs was calculated to be 35 mm below the surface, suggesting the defects to be introduced during the growth process. Either EL or PL technique can be used with any of these two schemes to determine the defect origination depth. However, the PL technique has the benefit that the p+ anode layer and the procedure for forming a metal grid are not required.
Perchlorosilanes and Perchlorocarbosilanes as Precursors to Silicon Carbide
Authors: Sevastyanov Vladimir , Ezhov Yurij , Pavelko Roman , Kuznetsov Nikolaj
Published: April 2011

Homologues with the general stoichiometry a(SiCl4) : bSi : cC : d(SiC) are shown to be potential precursors for the low-temperature gas-phase synthesis of silicon carbide. Thermal decomposition of these precursors yields the chemically stable gaseous species SiCl4 and condensed Si, C, SiC, SiC+Si, or SiC+C. Thermodynamic modeling of the thermal decomposition of octachlorotrisilane, Si3Cl8, is used to analyze the key features of the thermolysis of perchlorosilanes with the general stoichiometry a(SiCl4) : bSi. The equilibrium compositions of reaction products in the Si3Cl8+CO system are determined. This reaction system enables low-temperature (400 – 1200 K) synthesis of silicon carbide.
Multiplication of Basal Plane Dislocations via Interaction with c-Axis Threading Dislocations in 4H-SiC
Authors: Chen Yi , Dhanaraj Govindhan , Dudley Michael , Zhang Hui , Ma Ronghui , Shishkin Yevgeniy , Saddow Stephen E
Published: April 2011

Silicon carbide (SiC) substrates with chemical vapor deposition (CVD) grown epilayers have been characterized by synchrotron white beam X-ray topography (SWBXT). Large numbers of circular basal plane dislocation loops (BPDs) were observed in the substrate which were anchored by threading screw dislocations (SDs). Threading edge dislocations (TEDs) are not observed to play an important role in the multiplication of BPDs. A SD-assisted “conservative climb” model is proposed to explain the multiplication of BPDs during growth and/or post-growth processes. BPDs are shown to multiply on adjacent parallel basal planes via single SD-assisted as well as opposite sign SD-pair-assisted “conservative climb”.
Demonstration of Hybrid Silicon-on-Silicon Carbide Wafers and Electrical Test Structures with Improved Thermal Performance
Authors: Whipple Steven G. , Torvik John T. , Treece Randolph E. , Bernacki Jeffrey T.
Published: April 2011

Multiple 50 mm hybrid Si-on-SiC substrates consisting of thin film [100] Si (1 μm) on bulk semi-insulating [0001] 6H-SiC wafers were fabricated using low-temperature (150°C) wafer bonding and slicing techniques. A set of samples were prepared comparing various thicknesses of SiO2 (60, 120, 190, 240 and 520 nm) as an intermediate bonding layer between the two materials. A variety of test structures such as Van der Pauw structures, linear transfer-length measurement arrays and resistors were fabricated in the Si layers using standard Si processing (such as lithography, B-diffusion, etching and oxidation) in order to characterize the robustness as well as the electrical and thermal properties of the hybrid substrates. Bulk Si and Si-on-insulator (SOI) substrates were used for comparison. We report the Si layers on the hybrid Si-on-SiC substrates to be device-grade in terms of mobility and crystal structure, and that their device-to-device electrical isolation properties are superior to those of bulk Si and comparable to those of SOI. Furthermore, electrical test structures on hybrid Si-on-SiC substrates exhibit vastly superior heat dissipation compared to equivalent devices on bulk Si or SOI. Specifically, the temperature rise can be as much as 102°C lower in resistor devices made on Si-on-SiC (Tj= 191°C) compared to on bulk Si (Tj= 293C) under high-power density operation (67 kW/cm2). We also describe the effects of intermediate oxide thickness on thermal resistance.
Simultaneous Formation of Ohmic Contacts for Both N- and P-Type 4H-Sic Using Nial-Based Contact Materials
Authors: Tsukimoto Susumu , Onishi Toshitake , Ito Kazuhiro , Murakami Masanori
Published: April 2011

In order to simplify a fabrication process of silicon carbide power MOSFETs (metal oxide semiconductor field effect transistors), development of a simultaneous formation process of ohmic contacts to both the p-well and n-source regions of the SiC devices using same contact materials and one step annealing was challenged. We succeeded to develop NiAl-based contact materials which provided ohmic behaviors for both n- and p-type 4H-SiC after one step annealing. The Ni/Al and Ni/Ti/Al ohmic contacts were prepared by depositing sequentially Ni, (Ti) and Al layers with various layer thicknesses onto the n- and p-type SiC substrates which were doped with N at 1 × 1019 cm-3 and with Al at 8 × 1018 cm-3, respectively. The Ni(50 nm)/Al(5 ~ 6 nm) contacts showed ohmic behaviors for both the n- and p-type SiC substrates after annealing at 1000 °C. The Ni(20 nm)/Ti(50 nm)/Al(50 ~ 70 nm) contacts showed ohmic behaviors for both the n- and p-type SiC substrates after annealing at a lower temperature of 800 °C. The specific contact resistances of these contacts were measured to be in the order of 10-3 Ω-cm2 for both p- and n-type SiC, and were found to have strong dependence of the Al layer thicknesses of materials. The interfacial microstructures of the NiAl-based contacts were also observed by transmission electron microscopy (TEM) to understand the current transport mechanism through the metal/SiC interfaces.
Development of A 4H-SiC CMOS Inverter
Authors: Hull Brett Adam , Ryu Sei-Hyung , Fatima Husna , Richmond Jim , Palmour John W. , Scofield James
Published: April 2011

In this paper we report the first 4H-SiC CMOS inverter, which was designed to be integrated in the process flow of a 4H-SiC power DMOSFET. The channels of both of the n channel and p-channel MOSFETs of the inverter were 50 um wide by 3 um long. NMOSFET threshold voltage (VTH) ranged from 4.4 V at 25°C to 2.2 V at 250°C and PMOSFET VTH ranged from -4.75 V at 25°C to just under -4 V at 300°C. The transfer threshold voltage (Vm) of the 4H-SiC CMOS inverter was in a very tight range of 2.8 V to 2.9 V over the entire temperature range of 25°C to 300°C when using a drive voltage (VDD) of 10 V.
Biocompatible Polymeric Nanoparticles and Films Containing Hydrophobic Quantum Dots
Authors: Lee Jisook , Kwon Ick Chan , Woo Kyoungja , Chung Hesson
Published: April 2011

Micro- or nano-particles encapsulating hydrophobic quantum dots were prepared by the emulsion technique. Films containing quantum dots were also prepared by film casting methods. Quantum dots without hydrophilic coating were directly mixed with polymer solution to prepared extremely stable films or particles that do not phase-separate with time. The surface of the particles or films could be modified to have different hydrophilicity and/or functional groups. Particles with 1.5 ± 0.16 μm and 320 ± 26 nm in diameters and films of 300 μm in thickness were prepared. NIH 3T3 and EMT-6 were culture on the films containing quantum dots for 8 – 20 h. Compared to the control, quantum dot were delivered directly and efficiently into the cells without toxicity. When implanted near tumor cells in Balb/C mice, quantum dots migrated from the films into the tumor cells for at least 3 days. Considering that the quantum dot dispersion in aqueous media is relatively unstable and difficult to handle, our stable particles or films containing hydrophobic quantum dots can become versatile probes for biological applications.
Advances in SiGeSn/Ge Technology
Authors: Soref Richard , Kouvetakis John , Menendez Jose
Published: April 2011

We recently reported the CVD growth of binary Ge1−ySny and ternary Ge1−ySixSny alloys directly on Si wafers using SnD4, Ge2H6 (di-germane), SiH3GeH3, and (GeH3)2SiH2 sources. Ge1−ySny is an intriguing infrared material that undergoes an indirect-to-direct bandgap transition for y ≥ 0.09. In addition, we have found that Ge1−ySny layers have ideal properties as templates for the subsequent deposition of other semiconductors: (a) they are strain-relaxed and have low threading-defect densities (105 cm−2) even for films thinner than 1 μm; (b) their low growth temperatures between 250°C and 350°C are compatible with selective growth, and the films possess the necessary thermal stability for conventional semiconductor processing (up to 750°C depending on composition); (c) they exhibit tunable lattice constants between 5.65 Å and at least 5.8 Å, matching InGaAs and related III-V systems; (d) their surfaces are extremely flat; (e) they grow selectively on Si and not on SiO2; and (f) the film surface can be prepared by simple chemical cleaning for subsequent ex-situ epitaxy. The incorporation of Sn lowers the absorption edges of Ge. Therefore, Ge1−ySny is attractive for detector and photovoltaic applications that require band gaps lower than that of Ge. Spectroscopic ellipsometry and photoreflectance experiments show that the direct band gap is halved for as little as y = 0.15. Studies of a Ge0.98Sn0.02 sample yield an absorption coefficient of 3500 cm−1 at 1675 nm (0.74 eV). Thus infrared detectors based on Ge0.98Sn0.02 could easily cover the U-(1565 nm-1625 nm), L-(1565 nm-1625 nm), and C-(1530 nm-1565 nm) telecomm bands. Photoluminescence studies show bandgap emission on thin GeSn layers sandwiched between higher bandgap SiGeSn barriers. We have made advances in p and n doping of GeSn and present results on electrical characterizations. GeSn also has application in band-to-band laser heterodiodes. The ternary system Ge1−x−ySixSny grows on Ge1−ySny-buffered Si. It represents the first practical group-IV ternary alloy, since C can only be incorporated in minute amounts to the Ge-Si network. The most significant feature of Ge1−x−ySixSny is the possibility of independent adjustment of lattice constant and band gap. For the same value of the lattice constant one can obtain band gaps differing by more than 0.2 eV, even if the Sn-concentration is limited to the range y < 0.2. This property can be used to develop a variety of novel devices, from multicolor detectors to multiple junction photovoltaic cells. A linear interpolation of band gaps lattice constants between Si, Ge and α-Sn shows that it is possible to obtain SiGeSn with a band gap and a lattice constant larger than that of Ge. We shall use this feature to make a tensile-strained Ge-on-SiGeSn telecomm detector with improved performance. The tensile-strain-induced direct gap of Ge can be used also for laser diodes and electroptical modulators.
Fabrication and Characteristics of Low Doped Gallium-Zinc Oxide Thin Film Transistor
Authors: Verma Ved Prakash , Kim Dohyun , Jeon Minhyon , Choi Wonbong
Published: April 2011

Thin film transistor (TFT) with low (1%wt) Ga-doped ZnO (GZO) as an active channel on SiO2/Si substrate has been fabricated at room temperature by rf-magnetron sputtering. The devices show a mobility of 5.7 cm2/V.s at low operation voltage (<5V), a low turn-on voltage of 0.5 V and sub-threshold swing of 85 mV/decade. The TFT device performance is significantly affected by vacuum-level and annealing temperature, which can be attributed to the removal of chemisorped oxygen in the active channel surface. Low doped GZO is a new class of high performance TFT channel material that is easy to process.
Strain-Based Electrical Properties of Systems of Carbon Nanotubes Embedded in Parylene
Authors: Brame Jon , Getty Stephanie , Goodsell Johnathan , Allred David Dean
Published: April 2011

We have fabricated flexible electronic devices to test the strain-based change in resistance of a network of single-walled carbon nanotubes (SWCNTs) for use in microscale, high resolution magnetometry. To do this, we first develop a simple, reliable method to obtain catalyst nanoparticles for carbon nanotube growth through indirect, thin-film evaporation. Next we fabricate a two-terminal SWCNT device on a rigid substrate. We then transfer the device, intact, to a flexible substrate for strain testing. Herein, we report progress in growth and measurement techniques.
Electrochemical Sensing Properties of Ultra Long Aligned Multi-Walled Carbon Nanotube Microelectrodes
Authors: Punbusayakul Niramol , Ci Lijie , Talapatra Saikat , Surareungchai Werasak , Ajayan Pulickel M.
Published: April 2011

We report on the electrochemical properties of ultra long aligned multiwalled carbon nanotube (MWNT) bundles synthesized using water-assisted chemical vapor deposition process. Cyclic voltammogram with diffusion-controlled-reversible reaction obtained at MWNT electrodes in 10 mM K3(Fe(CN)6) /0.1 M KCl solution with varying scan rates indicates that radial diffusion mass transport is dominant at these electrodes. We further show that these electrodes can detect very low concentrations of ascorbic acid (AA) and dopamine (DA) (0.7 μM for AA and 1.87 μM for DA ). The excellent electrochemical properties along with nice performance for single species detection suggest that these MWNTs are promising electrode materials for developing high sensitive chemical and/or biological sensors.
Electrochemical Depositon of End-Capped Triarylamine and CBP Dendrimers: Alternate Technique for the Fabrication of Organic Light-Emitting Devices
Authors: Son Ho-Jin , Han Won-Sik , Chun Ji-Yun , Wee Kyung Ryang , Kim Dae Hyun , Lee Kuk-Wha , Jung Ha Jin , Lee Chongmok , Ko Jaejung , Kang Sang Ook
Published: April 2011

Carbosilane dendrimers adorned with either triarylamine or carbazole units in their periphery exhibit novel electrochemical behavior in which the electrochemical deposition is controlled by dendrite generation. In addition, the deposited layers remained intact in the depositing solvent, methylene chloride, allowing a second layer to be deposited on top of the first layer. We have sought to establish the suitability of this electrochemical deposition technique for use in the construction of multi-layer OLEDs, which cannot be fabricated via conventional spin-coating with a polymeric precursor. Thus, the electrochemical deposition-based process could potentially offer an ideal combination of deposition control on the one hand and multi-layer fabrication on the other. We report herein the novel electrochemical deposition behavior of arylamine or carbazole end-capped carbosilane dendrimers of the type GnNPB or GnCBP (n = 1-4) and their use for the formation of multi-layer devices for OLEDs.
Rubrene Single-crystal Organic Field Effect Transistor with Laser Ablated BaTiO3 Epitaxial Growth Thin-film as High-k Insulator
Authors: Hiroshiba Nobuya , Kumashiro Ryotaro , Takenobu Taishi , Komatsu Naoya , Suto Yusuke , Iwasa Yoshihiro , Kotani Kenta , Kawayama Iwao , Tonouchi Masayoshi , Tanigaki Katsumi
Published: April 2011

High quality BaTiO3 thin film epitaxially grown on a Nb-doped SrTiO3 (BTO/Nb-STO) substrate by a laser ablation technique is employed as a high-k gate insulator for a field-effect transistor of a rubrene single crystal in order to search for the possibility of high carrier accumulation. The high dielectric constant of 280 esu for the prepared BaTiO3 thin film accumulates 0.1 holes/rubrene-molecule, which is 2.5 times as high as the maximum carrier number of 0.04 holes/rubrene-molecule attained in the case of SiO2 gate insulator. Important parameters of rubrene single crystal FETs on BTO/Nb- STO are also described in comparison with those on SiO2/doped-Si.
Nano-scale Conductive Films for High Performance Fine Pitch Interconnect
Authors: Li Yi , Yim Myung Jin , Moon Kyung Sik , Wong ChingPing
Published: April 2011

In this paper, a novel nano-scale conductive film which combines the advantages of both traditional anisotropic conductive adhesives/films (ACAs/ACFs) and nonconductive adhesives/films (NCAs/NCFs) is introduced and developed for next generation high performance ultra-fine pitch packaging applications. This novel interconnect film possesses the properties of electrical conduction along the z-direction with relatively low bonding pressure (ACF-like) and the ultra-fine pitch (< 100 nm) capability (NCF-like). Unlike typical ACF which requires 1–5 vol% of conductive fillers, the novel nano-scale conductive film only needs less than 0.1 vol% conductive fillers to achieve good electrical conductance in the z direction. The nano-scale conductive film also allows a lower bonding pressure than NCF to achieve a much lower joint resistance (over two orders of magnitude lower than typical ACF joints) and higher current carrying capability. With low temperature sintering of nano-silver fillers, the joint resistance of the nano-scale conductive film could be as low as 10−5 Ohm, even lower than the NCF and lead-free solder joints. The reliability of the nano-scale conductive film after high temperature and humidity test (85°C/85%RH) was also improved compared to the NCF joints. As such, a high performance, fine pitch conductive film was developed.
NanoCT: Visualizing of internal 3D-Structures with Submicrometer Resolution
Authors: Brunke Oliver , Neuber Dirk , Lehmann David K.
Published: April 2011

High-resolution Computed Tomography (CT) widely expands the spectrum of detectable internal micro-structures. The new nanotom CT system allows the analysis of samples with the exceptional voxel-resolution of less than 0.5 microns per volume pixel (voxel). Thus internal detail related to a variation in material, density or porosity can be visualised and precisely measured. This opens a new dimension of 3D-microanalysis and will partially substitute traditional destructive methods in industrial quality control and research.

The nanotom® is the first 180 kV nanoCT system world-wide which is tailored specifically to the highest-resolution applications in material science, micro electronics, geology and biology. Therefore it is particularly suitable for nanoCT-examinations of material samples of any type like synthetic materials, ceramics, composite materials, mineral and organic samples.

Several results of high-resolution nanoCT demonstrate the capability to analyse the 3D-microstructure of materials with only minimal sample preparation. For instance, it is possible to image different metal phases in solder joints, the texture of fibres in composites or the volume and distribution of voids in castings.

The volume data set is visualised by slices or compiled in a three-dimensional view which can be displayed in various ways. By means of volume visualisation software, the three-dimensional structure of the reconstructed volume can be easily analysed for pores, cracks, and materials density and distribution with the highest magnification and image quality available.

By granting the user the ability to navigate the internal structure of an object slice-by-slice with highest resolution in a non-destructive manner, the nanotom creates new possibilities for analysis which have so far been unreachable.
Charging and Aging Effects in Porous ULK Dielectrics
Authors: Guedj Cyril , Martinez Eugenie , Imbert Gregory
Published: April 2011

The down-scaling of CMOS interconnects increases dielectric reliability challenges. Porous ULK materials used in advanced interconnects may suffer from charge trapping and detrimental aging during bias-thermal stress experiments. We demonstrate that a threshold between charging and aging domains may occur for an injected electrical energy of 0.1 MJ/cm3. Electron injection in the dielectric induces hydrogen radical formation first. For more damaging current stressing, in-situ Auger experiments demonstrate that the degradation is mostly due to the modification around carbon bonds.
Fatigue of Damascene Copper Lines under AC Loading
Authors: Moreau Stéphane , Maitrejean Sylvain , Passemard Gérard
Published: April 2011

Fatigue in damascene copper line has been investigated by using alternating currents to generate cyclic temperatures and stresses/strains. Interconnects using beyond 65 nm node design rules and materials have been studied. We demonstrate that cyclic thermal strains lead to Cu or Cu/Co-based cap surface modification and open circuits in Cu lines during the application of an alternating electrical current. We underline that the narrower the copper lines are, the more reliable they are and the major role of the cap layer to improve the Cu lines reliability. Moreover, a statistical approach is presented in this paper in order to discuss about the thermal fatigue associated distribution model (exponential, lognormal and Weibull distributions). At present, the lognormal distribution seems to be the most appropriate one.
Low Temperature CVD of Ru from C6H8Ru(CO)3
Authors: Lazarz Teresa S , Yang Yu , Kumar Navneet , Kim Do Young , Noh Wontae , Girolami Gregory S , Abelson John R
Published: April 2011

Thin ruthenium films were deposited using chemical vapor deposition from the single-source precursor tricarbonyl(1,3-cyclohexadiene)Ru(0) onto silicon, silicon dioxide and c-plane sapphire substrates in the absence of a carrier gas by thermolysis. Growth rate, resistivity, purity, crystallinity and microstructure were determined. Tricarbonyl(1,3-cyclohexadiene)Ru(0) gave metallic ruthenium films with near bulk resistivities (11-21μΩ-cm), high growth rates (up to 20 nm/min), and nearly featureless microstructures. Nucleation was rapid on all substrates tested. These results suggest that tricarbonyl(1,3-cyclohexadiene)Ru(0) is an excellent, practical precursor to use for practical applications that require depositing thin ruthenium films.
Materials Challenges in Automotive Embedded Non-Volatile Memories
Authors: Prinz Erwin Josef
Published: April 2011

Silicon-based nonvolatile memory modules are widely used in microcontrollers, where they are embedded into a monolithic system on a chip (SoC) which also includes high speed logic transistors, cache SRAM, and peripheral circuits for communicating with the external world. The physical principle most widely exploited for nonvolatile code and data storage is charge storage in floating gates. Recently, charge storage in nitride traps and nanocrystals also has been explored.

The most demanding use profiles with respect to temperatures, data retention times, and low failure rates are encountered in automotive engine control applications, where junction temperatures up to 150°C are common, for 1000's of hours. Starting with the 130nm technology node, embedded Flash technology has been integrated with copper interconnects, and at the 90nm node, low dielectric constant interlevel dielectrics are also employed to increase circuit performance. To achieve automotive reliability, the materials surrounding the silicon floating gate, nanocrystal, or nitride charge storage area must be evaluated for parasitic charge storage, write/erase stress-induced leakage current, and other parameters important for reliability. Any movement of parasitic charge, potentially over a long period of time, can reduce the sensing window of the Flash EEPROM bitcell.
Resistance Switching In Ferroelectric Materials
Authors: Li Tingkai , Hsu Sheng Teng
Published: April 2011

A ferroelectric crystal with perovskite structure such as PbZr1−xTixO3 (PZT), SrBi2Ta2O9 (SBT), Bi3La1−xTixO12 (BLT) and non-perovskite structure such as Pb3Ge5O11 (PGO) have two polarization states, which can generate two resistance states: high resistance and low resistance states. These properties can be used for resistance random access memory applications (RRAM). When a ferroelectric capacitor is polarized an internal electric field opposite polarity to the external applied field is generated. As a result there is a large resistance change at a given bias voltage between the two polarization states of the capacitor. It is the purpose of this paper to show that the ferroelectric capacitor may be used as a current memory cell of non-destructive readout (NDRO) non-volatile Random Access Memory array. It will also be shown that each current sensing ferroelectric memory cell stores two bits of memory information and exhibits long memory retention and excellent endurance properties.
The Formation of CuIn(S,Se)2 Thin Film Solar Cell Absorbers from Electroplated Precursors
Authors: Jost Stefan , Hergert Frank , Hock Rainer , Voß Torsten , Schulze Jörg , Kirbs Andreas , Purwins Michael , Probst Volker , Palm Jörg
Published: April 2011

In this article structural properties as well as morphological aspects of CuIn(S,Se)2 thin film solar cell absorbers, produced by annealing of electroplated precursors, are discussed. Real-time X-ray diffraction (XRD) experiments while precursor annealing have shown, that a reduced amount of electrodeposited selenium is the key parameter to realize a chalcopyrite formation mechanism similar to the one known for sputtered stacked elemental layer (SEL) precursors. Absorber layers processed from precursors produced by simultaneous electrodeposition of copper, indium and selenium show a preferable absorber morphology with an average grain size on the micrometer scale when the electrochemically deposited amount of selenium is reduced to [Se] / [In] = 0.1. The amount of selenium, missing for the formation of a stoichiometric chalcopyrite, was deposited in a second process step prior to precursor annealing. Solar cells produced from these absorbers show light conversion efficiencies up to 10%.
Impact of Nonuniformities on Thin Cu(In,Ga)Se2 Solar Cell Performance
Authors: Kanevce Ana , Sites James R.
Published: April 2011

Solar-cell performance degradation due to physical nonuniformities becomes more significant as the thickness of polycrystalline absorbers is reduced. “Voltage” nonuniformities such as those due to band-gap fluctuations, variations in the back-contact proximity, and areas where the absorber is completely depleted can have very significant impact on cell performance. Similarly local shunts can seriously degrade the efficiency. “Current” nonuniformities such as optical defects have generally much less impact. The analysis presented is based on Cu(In,Ga)Se2 cells, but the qualitative results should be applicable to thin-absorber devices in general. For lateral nonuniformity studies, the solar cell is simulated by a two dimensional network of parallel diodes separated by resistors. The nonuniformities are approximated by small regions of reduced photovoltage, often referred to as “weak diodes”, and by isolated shunt resistors. The weak-diode approach allows investigation of device performance as a function of the weak-diode voltage deficit, the ratio of weak-to strong-diode area, and the weak diodes' spatial distribution. Increased TCO resistance can isolate weak diodes, thus limiting the voltage loss due to nonuniformities, but increasing fill-factor losses.
Can Grain Boundaries Improve the Performance of Cu(In,Ga)Se2 Solar Cells?
Authors: Rau Uwe , Rau Uwe
Published: April 2011

Two-dimensional numerical device simulations investigate the influence of grain boundaries on the performance of Cu(In,Ga)Se2 solar cells focussing on the question whether or not grain boundaries can improve the efficiency of those devices. The results unveil the following statements: (i) The mere introduction of a grain boundary by adding localized defects into a device that has a high performance from the beginning is not beneficial. (ii) Polycrystalline solar cells can outperform monocrystalline ones, if the total number of defects is equal in both devices. I.e. a given number of recombination centers is better dealt with if these defects are concentrated at the grain boundary rather than homogeneously distributed in the bulk. (iii) A significant improvement of carrier collection via the grain boundaries is found if the bulk of the devices is assumed as relatively poor. In this situation, addition of defects that are not much recombination ac-tive but provide a large charge density at the grain boundaries can improve the device performance. (iv) Passivation of grain boundaries by an internal band offset in the valence band is effective only if the internal barrier amounts at least to 300 meV.
Preserving Intangible Aspects of Cultural Materials: Bonpo Ritual Crafts of Amdo, Eastern Tibet
Authors: Reedy Chandra L.
Published: April 2011

Ancient and historic products of past technologies exist in the form of material culture and archaeological finds, available for materials analysis. Technical studies and analytical work, coupled with the study of historical texts and archival documents, can help in reconstructing past technologies. But the act of making an object is, by its very nature, also an intangible part of human heritage. Production of material culture may be accompanied by specific rituals, social behaviors and relationships, music, knowledge gained from oral histories, meanings, intents, beliefs, and reasoning processes. For ancient objects, gaining access to these intangible aspects of cultural heritage may be extremely difficult, if not impossible. However, there are many societies where traditional crafts are produced within a context where the intangible aspects can still be recorded. Yet, these opportunities are disappearing at an alarming rate as development and globalization rapidly overtake more and more traditional communities. Documenting intangible data about craft processes can promote fuller understanding of the objects themselves, and aid long-term preservation of both the objects and the processes used to make them. Examples here are drawn from fieldwork conducted in 2007 at a Bonpo monastery (Serling) and nearby villages in the Amdo region of the eastern Tibetan culture area (in Sichuan Province, China). Bonpo practices, which pre-date the introduction of Buddhism into Tibet, incorporate a variety of ritual crafts that are strongly rooted in a complex web of intangible relationships, behaviors, meanings, purposes, and beliefs. This paper focuses on votive clay objects (tsha-tshas) and barley-dough offering sculptures (tormas). Processes encompassing intangible aspects that are explored include the decision to make an object, when to make it and in what form, selection of raw materials, methods for processing the raw materials, fabrication procedures, selection of who will be involved in fabrication steps, where to place the finished object, and whether it will be preserved for the long term or considered to be only a temporary object. Results are placed in the context of larger theoretical issues regarding documentation and preservation of intangible elements of cultural heritage as part of a study of materials and technological processes.
Replications of Critical Technological Processes and the Use of Replicates as Characterization Standards: An Experiment in Undergraduate Education
Authors: Vandiver Pamela B. , Raftery Heather , Ratcliffe Stephanie , Moskalik Brian T. , Andaloro Michelle , Sandler Katelyn , Retamoza Alicia
Published: April 2011

The technology of artifacts is analyzed and reconstructed by comparison with known craft practices, the physical and chemical constraints imposed by the raw materials, and the sequence and steps for processing those materials to achieve certain optical and mechanical properties. Understanding of craft knowledge is best pursued by practice, coupled with technical analysis. Six case studies of hands-on, undergraduate student laboratory projects are presented. The studies include testing parameters for the making of stenciled hand images similar to those at caves such as Gargas from the Upper Paleolithic period in France, the variation in processing required to produce Egyptian blue pigments and objects, controlling composition to form either green or turquoise-blue colors in Islamic lead-containing glazes, optimizing the ratio of various pigments to gum Arabic medium in tomb paintings to evaluate the application and durability, molding East Asian gokok beads in imitation of jade, and making and radiographing a mock-up of a damaged statue on the facade at the San Xavier Mission as a standard for comparison with the original. In each case, various parameters are varied to model the appearance, structure and composition of an object, and the students benefited from the experience of developing research questions and from their involvement in original research projects.
Copper Alloys Used in Barye's Hunt Scenes in the Surtout de Table of the Duc d'Orleans
Authors: Giaccai Jennifer , Lauffenburger Julie , Boulton Ann
Published: April 2011

The copper alloys of the statues by Antoine-Louis Barye were examined with energy-dispersive x-ray fluorescence. Barye experimented with casting techniques in his own workshop and regularly worked with the foundry of Honoré Gonon, who re-introduced lost wax casting to 19th century Paris. Two of the technically complex Barye sculptures in the surtout de table of the Duc d'Orleans were difficult to cast using the more common sand casting technique. Problems with the sand casts sent to other foundries resulted in Gonon completing the casting for problematic statues in the surtout, after Gonon had completed lost wax casting of the three hunt scenes initially sent to his foundry. Examination of the copper alloy compositions differentiates the casts from the various foundries and determines which parts of the surtout were ultimately cast by Gonon.
Self-assembled Multi-walled Carbon Nanotube Coatings
Authors: Behler Kristopher , Havel Mickael , Mattia Davide , Gogotsi Yury
Published: April 2011

Multi-walled carbon nanotube (MWCNT) grafting onto electrospun poly(acrylonitrile) (PAN) nanofibers yields a layer by layer deposition of self assembled (LBL-SA) nanotube filaments or nanowires. PAN fibers were first functionalized with carboxylic groups through a sodium hydroxide treatment. Then, poly(diallyldimethylammonium chloride) (PDDAC), a positively charged polyelectrolyte was adsorbed onto the fibers via electrostatic interaction. When placed in contact with the modified fibers, acid treated MWCNT (ac-MWCNT) self-assemble, producing a dense and continuous layer onto the polymer nanofibers, while the inherent structure and morphology of the polymer nanofibers are retained. This method is being investigated as a universal approach applicable to a variety of materials. By producing layers of nanotubes, the electrical conductivity of polymers may be improved due to formation of a continuous MWCNT monolayer on the surface as opposed to traditional incorporation of large amounts of nanotubes into the bulk of the polymer. This method can further be implemented on polymer systems that promote a positively charged surface for COOH functionalized MWCNT to attach. Polyamides offer a perfect scenario in which they do not need to be modified to allow hydrogen bonding between the polymer and the ac-MWCNTs. Electrospun polyamide 11 (PA 11) provides a network of 100 nm and greater, fibers for deposition of ac-MWCNTs. These MWCNT coated nanofibers possess high electrical conductivity, about 0.1 S/cm, resulting from a dense coverage of MWCNTs on the polymer surface.
Growth of AlGaN/GaN HEMTs on 3C-SiC/Si(111) Substrates
Authors: Cordier Yvon , Portail Marc , Chenot Sébastien , Tottereau Olivier , Zielinski Marcin , Chassagne Thierry
Published: April 2011

In this work, we study cubic SiC/Si (111) templates as an alternative for growing GaN on silicon. We first developed the epitaxial growth of 3C-SiC films on 50mm Si(111) substrates using chemical vapor deposition. Then, AlGaN/GaN high electron mobility transistors were grown by molecular beam epitaxy on these templates. Both the structural quality and the behavior of transistors realized on these structures show the feasibility of this approach.
Roll-to-Roll Fabrication of Bulk Heterojunction Plastic Solar Cells using the Reverse Gravure Coating Technique
Authors: Tobjork Daniel , Aarnio Harri , Mäkelä Tapio , Österbacka Ronald
Published: April 2011

The roll-to-roll reverse gravure (RG) coating technique was used to produce thin homogeneous films (∼100 nm) for organic bulk heterojunction solar cells. The conducting polymer poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) and the active layer regioregular poly(3-hexylthiophene-2,5-diyl):[6,6]-phenyl-C61-butyric acid methyl ester (P3HT:PCBM) were successfully subsequently RG coated on an ITO covered plastic substrate in ambient air. Working solar cells were achieved after annealing and thermal evaporation of the top contact. The AM1.5 power conversion efficiency (PCE) of the RG coated organic solar cells was determined to 0.74% (at 100 mW/cm2). This was very similar to the results of a reference device that was spin coated on a glass substrate in a nitrogen glove box.
Microwave-assisted Synthesis of Perylene-3,4-dicarboximides: Highly Photostable Fluorescent Dyes
Authors: Guthrie Brian , Wang Zixing , Li Jian
Published: April 2011

A new method for synthesis of perylene-3,4-dicarboximides (PDCIs) is reported. Modified from a literature reported synthetic method, microwave assisted heating was used to perform the reaction, which not only shortened the original reaction time, from 18 hours to 30 min, but also increased the corresponding reaction yield. A variety of PDCI derivatives were synthesized in order to correlate the influence of substituents on the reaction outcome. Moreover, the photophysical and electrochemical properties of PDCIs are characterized and reported.
The Synthesis and Magnetoelectric Properties of Tubular Polyaniline
Authors: Liu Yingli , Li Yuanxun , Zhang Huaiwu
Published: April 2011

The polyaniline was synthesized by in situ polymerization in the presence of ¦Â-naphthalenesulfonic acid which acts as template. The structure, morphology and magnetoeletric properties of samples were characterized by powder X-ray diffraction (XRD), Fourier transform infrared (FTIR), scanning electron microscopy (SEM), the standard Van Der Pauw DC four-probe method and vibrating sample magnetometer (VSM) techniques. The results indicated that polyaniline exhibited the hysteresis loops of the ferromagnetic nature and the conductance is high at 53.35 S/cm which possess both magnetic properties and electrical properties.
On the Solidification and Feeding of a Ductile Iron Casting
Authors: Ramos Gómez Eudoxio A. , Ramírez-Argáez Marco A. , González-Rivera Carlos
Published: April 2011

Solidification of a simple casting made of ductile iron is mathematically modeled in this work. The model is able to numerically simulate the cooling rate and solidification of the whole casting system composed by a cubic piece, a blind riser connected through a rectangular neck, and immersed in a green sand mold. The center of the neck acts as a valve that allows the flow of liquid metal between the casting and the riser based on the feeding technique known as Pressure Control Risering (PCR). The developed model couples the energy conservation equation and the solidification kinetics of ductile iron, through the statement of proper nucleation and growth laws. This model is satisfactorily validated by comparing the thermal histories predictions with experimental cooling curves obtained in the foundry laboratory for the same casting. According to a process analysis developed in this work, the pouring temperature is the variable that affects the most the solidification and the feeding behavior, since it increases significantly the solidification times in all regions of the casting system.
Thermochemical Method for Coating AISI 316L Stainless Steel with Ti
Authors: López-Cuevas Jorge , Camacho-Martínez José L. , Rendón-Angeles Juan C. , Pech-Canul Martín I. , Méndez-Nonell Juan
Published: April 2011

This paper presents a thermochemical method, based on a mixture of molten alkaline halides to produce a Ti coating on AISI 316L stainless steel. The thickness of the coatings is a function of temperature and time. It is observed that the physical form of the Ti source employed affects both coating thickness and morphology. The formation of several inter-diffusion layers is detected, each having a characteristic chemical composition, morphology and location at the substrate/coating interface. It is proposed that some of the produced Ti coatings can be employed to improve osseointegration of stainless steel for potential prosthetic devices.
Titanium Coatings on AISI 316L Stainless Steel Formed by Thermal Decomposition of TiH2 in Vacuum
Authors: López-Cuevas Jorge , Rodríguez-Galicia José L. , Rendón-Angeles Juan C. , Pech-Canul Martín I. , Méndez-Nonell Juan
Published: April 2011

Ti-coated AISI 316L stainless steel, for potential biomedical applications, is obtained by thermal decomposition of TiH2 under vacuum. The presence of hydrogen in the coating material facilitates the sintering process of Ti particles, with simultaneous formation of several inter-diffusion layers at the substrate/coating interface, whose thickness and chemical composition depend mainly on the treatment temperature. Coatings prepared at 1100°C exhibit formation of a wide zone at the substrate/coating interface, which is associated with the appearance of cracks, and which consists of a mixture of λ + χ + α-Fe phases. Formation of abundant microporosity is also observed in this region, which is attributed to the Kinkerdall effect.
A Cbed Procedure for Determining Local Residual Stresses from Nanoscale Areas in Cermets
Authors: Kim Gyeung Ho , Sarikaya Mehmet
Published: April 2011

A convergent beam electron diffraction method was used in a transmission electron microscope to determine residual thermal stresses from nanometer-scale areas in a ceramic-metal (cermet) composite material. It is demonstrated that the method is simple, but requires a standard sample for each of the phases in the composite. The principle of the technique is that the stresses are determined by comparing higher order Laue zone line shifts, due to lattice strain, in high-symmetry zone-axis electron diffraction patterns recorded under the same experimental conditions from the unknown phases and the standards. The application of the method to composite systems containing dissimilar phases, such as ceramic-metal composite systems, demonstrates the universality of the technique in obtaining local structural information of anisotropic strain unambiguously with a high accuracy. The procedure involved is described in detail with application to B4C-AI, a three-dimensional intertwined ceramic-metal composite.
Electron Holography of Flux Lattices in Niobium
Authors: Bonevich J.E. , Harada K. , Matsuda T. , Kasai H. , Yoshida T. , Pozzi G. , Tonomura A.
Published: April 2011

Magnetic lines of force penetrating a superconducting thin foil have been investigated by means of electron holography. A field-emission TEM with a specially constructed cold stage was used to cool a Nb thin foil down to 4.5 K and apply magnetic fields up to 100 G. The specimen is tilted by 45° to both the electron beam and the magnetic field (applied horizontally) allowing the 2-D lattice of penetrating flux-lines to be discerned. The phase distribution of electrons transmitted through the specimen were quantitatively measured. Interference micrographs revealed tiny regions where the phase distribution rapidly changed. These regions coincided spatially with the spot-like contrast observed by Lorentz microscopy and were found to be quantized vortices containing a flux of h/2e. The experimental results were in good agreement with those predicted by theoretical simulations. Experiments exploring the vortex inner core structure at high resolution are presented.