bluuebunny/crossref_metadata_2025 huggingface dataset:
Microstructure Studies on Hexagonal Layered Ni-S Nanocrystals
Authors: Sun Xiang-Cheng , Reyes-Gasga J. , Toledo J. A.
Published: June 2019

Layered nickel-sulfides (Ni-S) nanocrystals had been successfully prepared by lowtemperature hydrothermal approach. Rietveld X-ray diffraction (XRD) analysis revealed that these layered Ni-S materials have two different hexagonal structure phases, NiS1.03 and NiS, both phases are NiAs-type with space group of P63/mmc. X-ray energy dispersive spectra (XEDS) analysis and TEM observations also confirmed these two nanocrystals of NiS1.03 and NiS. High-resolution transmission electron microscopy (HREM) lattice images indicated moiré fringes with rotational or translational patterns were observed in these layered Ni-S nanophases materials. In particular, it was found that all the simulated HREM images were in good agreement with the observed HREM lattice images. Especially, the simulated SAED patterns obtained from the hexagonal Ni-S crystallographic model showed that the experimental SAED patterns taken along [11.0], [00.1] and [10.0] zone axes presented reflections produced by double diffraction effect.
Manipulations of Nanoparticle Chain Aggregates in Transmission Electron Microscopy
Authors: Suh Yong J. , Prikhodko Sergey V. , Friedlander Sheldon K.
Published: June 2019

We have developed a nanostructure manipulation device (NSMD) to apply tension to a single nanoparticle chain aggregate (NCA) mounted in a transmission electron microscope. The system was used for studying stretching and contraction of carbon chain aggregates. Carbon NCAs generated by laser ablation of a graphite target were stretched and bent using the NSMD. The NCA was stretched up to 310% of its initial length before becoming taut and then breaking. The broken NCA contracted rapidly showing its elastic behavior. The NCA was plastically deformed during stretching through unraveling of kinks along the NCA. However, the unraveling was irreversible so that the chain formed a loop with a big curvature as its two ends were brought closer together.
Morphology and Atomic Structure of Grain Boundaries in GaN Grown by MOVPE
Authors: Takuma Eriko , Ichinose Hideki , Sanorpim Sakuntam , Onabe Kentaro
Published: June 2019

The morphology and the atomic structure of a hexagonal gallium nitride (h-GaN) grain boundary was investigated employing a conventional TEM and an atomic resolution high voltage transmission electron microscope (ARHVTEM).

GaN was grown on a patterned GaAs (001) substrate by the metalorganic vaporphase epitaxy (MOVPE) method using selective area growth (SAG) and epitaxial lateral overgrowth (ELO) process. The pattern mask was aligned along [110] direction of the GaAs (001) substrate. Cubic GaN (c-GaN) grew in the window of the patterned substrate. h-GaN was nucleated on the {111} plane of the c-GaN and grew in the lateral direction to fabricate a grain boundary in the halfway between two masks. The resulting symmetric tilt grain boundary was a Σ 9 CSL boundary. The boundary plane was in most cases parallel to the {3308} plane. Structural analysis revealed that the boundaries consist of ordinary 6-memebered rings and some 5-membered and 7-membered rings. Additionally, the expected atomic bonding angle deviates from the experimental findings. The different bonding angle was attributed to contributions of ionic bonding in GaN.
Rolled-up In(Ga)As/GaAs Nanotubes Diameter as a Function of Structural Properties
Authors: Deneke Ch. , Müller C. , Schmidt O.G.
Published: June 2019

Inherently strained bilayers of In(Ga)As/GaAs, Epitaxially grown on top of an AlAs sacrificial buffer layer roll-up into free-standing nanotubes if they are released from their substrate by selective underetching, Here, we preseant a systematic study of the tube diameter as a function of total bilayer thickness and the ratio between the two layer thinknesses. We show that the diameters of the tubes are well described by a continous mechanical model.
Stamp Deformation During Microcontact Printing
Authors: Jagota Anand , Sharp Kenneth G. , Kristunas David F.
Published: June 2019

Stamp deformation often produces undesirable effects that limit the practice and precision of micro-contact printing. We have experimentally studied one of the most pervasive consequences of undesired deformation: roof collapse of low-aspect-ratio recesses. Stamp behavior under increasing loads can readily be assessed by mounting stamps on flat glass and viewing stamps from below through an inverted microscope. Dynamic as well as limiting equilibrium behavior can be determined. Features with aspect ratios varying by a factor of ten were examined. We find that roof collapse initiates with the formation of a contact between the roof of the stamp and the substrate. This is followed by rapid growth of the contact region, driven by attractive interfacial forces. Contact growth usually terminates leaving a noncontacting “moat” region. Experimental measurements of the critical stress for roof collapse are in very good agreement with theory.
Nanostructured Carbon Capsules with Hollow Core/Mesoporous Shell Structure
Authors: Yu Jong-Sung , Yoon Suk Bon , Sohn Kwonnam , Kim Jeong Yeon , Hyeon Taeghwan
Published: June 2019

Carbon capsules with hollow macroporous core/mesoporous shell were synthesized using sacrificial submicrometer-size solid core/mesoporous shell (SCMS) silica spheres as templates. Size of the hollow macroporous core and thickness of the mesoporous shell can be easily controlled by the choice of silica spheres and the amount of TEOS/C18-TMS mixture, respectively.
Textured Zinc Oxide by Expanding Thermal Plasma CVD: the Effect of Aluminum Doping
Authors: Groenen R. , Kieft E.R. , Linden J.L. , Sanden M.C.M. van de
Published: June 2019

Aluminum doped ZnO films are deposited on glass substrates at a temperature of 200°C by expanding thermal plasma CVD. Surface texture, morphology and crystal structure have been studied by AFM, SEM and XRD. A rough surface texture, which is essential for application as front electrode in thin film solar cells, is obtained during deposition. The addition of aluminum as a dopant results in distinct differences in film morphology, a transition from large, rounded crystallites to a more pyramid-like structure is observed. The structure of films is hexagonal with a preferred crystal orientation in the faces (002) and (004), indicating that films are oriented with their c-axes perpendicular to the substrate plane. In addition, spectroscopic ellipsometry is used to evaluate optical and electronic film properties. The presence of aluminum donors in doped films is confirmed by a shift in the ZnO band gap energy from 3.32 to 3.65 eV. In combination with reflection and transmission measurements in the visible and NIR ranges, film resistivities have been obtained from the free-carrier absorption. These results are consistent with direct measurements. Resistivities as low as 6.0 10-4 Ωcm have been obtained.
Chemically deposited antimony selenide thin films
Authors: Rodríguez-Lazcano Y. , Peña Y. , Nair M.T. S. , Nair P. K.
Published: June 2019

Chemical bath deposition of thin films of antimony selenide from aqueous solutions containing complexes of antimony with citrate, tartrate and thiosulfate as ligands and sodium selenosulfate as source of selenide is reported. The films obtained appear amorphous in the as-prepared form and become crystalline upon annealing at 300°C. The X-ray Diffraction (XRD) patterns of the annealed films show peaks attributable to Sb2Se3 and Sb2O3. Electron microprobe analyses have shown that the atomic ratio of Se/Sb is less than 1.5 in these films. The films are photoconductive and exhibit a high resistivity in the dark. Both direct (1.4 eV) and indirect (1.3-1.5 eV) band gaps are observed for the films.
Pattern density effects in fixed abrasive polishing
Authors: Venigalla Rajasekhar , Economikos Laertis , Babu S.V.
Published: June 2019

We investigated pattern density effects during chemical mechanical planarization (CMP) for shallow trench isolation (STI) applications using fixed abrasive pads to better control the fixed abrasive polishing process. We observed that the polishing characteristics of higher pattern density features are strongly dependent on the presence of lower pattern density features on the same die in the wafer. This has been attributed to the aggressive action of lower pattern density features on the fixed abrasive pad which results in a more effective activation of the pad by them. Thus even the 100% pattern density features are initially polished at a very high rate when lower density features are present.
Evolution of Charged Gap Statesin a- Si:H Under Light Exposure
Authors: Zeman M. , Nádaždy V. , Swaaij R.A.C.M.M. van , Durný R. , Metselaar J.W.
Published: June 2019

The charge deep-level transient spectroscopy (Q-DLTS) experiments on undoped hydrogenated amorphous silicon (a-Si:H) demonstrate that during light soaking the states in the upper part of the gap disappear, while additional states around and below midgap are created. Since no direct correlation is observed in light-induced changes of the three groups of states that we identify from the Q-DLTS signal, we believe that we deal with three different types of defects. Positively charged states above midgap are related to a complex formed by a hydrogen molecule and a dangling bond. Negatively charged states below midgap are attributed to floating bonds. Various trends in the evolution of dark conductivity due to light soaking indicate that the kinetics of light-induced changes of the three gap-state components depend on their initial energy distributions and on the spectrum and intensity of light during exposure.
Present Status Of Hot Wire Chemical Vapor Deposition Technology
Authors: Schropp R.E.I.
Published: June 2019

In the last few years, tremendous progress has been made in the field of Hot Wire Chemical Vapor Deposition (HWCVD): (1) It has been shown that there are no fundamental limitations in HWCVD with respect to substrate area. Using a periodic configuration of multiple short wires, good uniformity (± 7.5 %) has been demonstrated by Anelva over an area of 96 cm × 40 cm. (2) High quality microcrystalline Si can be produced. Solar cells in the n-i-p configuration are currently better than those made by PECVD. At Jülich, the efficiency of such cells is 9.4 %, and Utrecht has recently made the first HWCVD multibandgap triple junction solar cells, (3) HWCVD offers the potential of ultra high deposition rates. At NREL, a-Si:H has been deposited at rates in excess of 12 nm/s, and at Utrecht University μc-Si:H rates are in excess of 1 nm/s. (4) Thin film transistors (TFTs) with mobilities in excess of 1 cm2/Vs with an a-Si:H channel have been shown to be stable and μc-Si:H TFTs have been made with mobilities in excess of 40 cm2/Vs. (5) The efficient production of atomic H in HWCVD is beneficial in passivation processes, but it can also be applied in efficient etching processes. (6) Alloys of Si with various functions can be made, such as SiNx for antireflection and passivation coatings. Remarkably, all of the above results have been achieved without detailed knowledge about the primary reactions at the filament, the gas phase reactions, and the reactions with the growing film. The choice of filament material and its operation temperature have a large influence on the production of various reaction species and thus, on the structure of the resulting film. HWCVD is basically an ion-free deposition technique, which is an advantage for many kinds of thin films. HWCVD has also proven its feasibility in polymer deposition and nanotube formation.
Physicochemical Characterization of Porous Silicon Surfaces Etched in Salt Solutions of Varying Compositions and pH
Authors: Rosario-Canales Mariem , Guadalupe Ana R. , Fonseca Luis F. , Resto Oscar
Published: June 2019

We prepared porous silicon (PSi) structures by standard electrochemical processes using aqueous sodium fluoride (NaF) solutions. We report the dependence of the porous structure on the variation of pH and salt concentration of the etching solution, and the applied current density. The PSi structures were characterized by Scanning Electron Microscopy (SEM) and Secondary Ion Mass Spectroscopy (SIMS) to determine the pore size and distribution and the surface chemical composition. Results obtained from SEM show that the PSi grown has two different structures depending on the current density. Low current densities produce a uniform, high-density arrangement of pores while high current densities yield a sponge-like structural network. SIMS results indicate that the porous framework is covered with a silicon oxide layer.
Microcrystalline Silicon Thin Film Growth by Electron Cyclotron Resonance Chemical Vapour Deposition at 80°C for Plastic Application Ian
Authors: Bu Ian Y.Y. , Flewitt A.J. , Robertson J , Milne W.I.
Published: June 2019

Microcrystalline silicon deposited at low temperatures (<150°C) is a candidate material for use as the channel layer in thin film transistors deposited on plastic substrates. This would enable driver electronics to be integrated onto cheap flexible AMLCD panel.

In this study microcrystalline silicon was deposited by Electron Cyclotron Resonance Plasma Enhanced chemical Vapour Deposition (ECR-PECVD) at a temperature of 80°C, compatible with most plastic such as PET and PEN. A source gas mixture of SiH4 and H2 was employed. The structural and optical properties of samples deposited under a range of deposition conditions were measured.
Characterization of Nanocrystalline Silicon Film grown by LEPECVD for Photovoltaic Applications
Authors: Bollani M. , Binetti S. , Acciarri M. , Fumagalli L. , Arcari A. , Pizzini S. , Känel H. Von
Published: June 2019

This work deals with the structural properties of nanocrystalline (nc) silicon films for solar cell applications, grown using a new PECVD process based on an arc discharge plasma characterized by low ion energies, called LEPECVD (Low energy PECVD). This process permits to increase the intensity of the plasma discharge in the growth region and thus to achieve higher growth rates while avoiding ion-induced surface damage of films. The structural properties of the LEPECVD grown films were studied as a function of the deposition parameters (substrate temperature, growth rate, hydrogen dilution) by Raman Spectroscopy, SEM, and HRTEM analysis. The results of this work allowed us to identify the process requirements suitable for the growth of nc-grains in an amorphous matrix.
Influence of Substrate Temperature and Hydrogen Dilution Ratio on the Properties of Nanocrystalline Silicon Thin Films Grown by Hot-Wire Chemical Vapor Deposition
Authors: Moutinho H.R. , Jiang C.-S. , Nelson B. , Xu Y. , Perkins J. , To B. , Jones K.M. , Romero M.J. , Al-Jassim M.M.
Published: June 2019

We have studied the influence of substrate temperature and hydrogen dilution ratio on the properties of silicon thin films deposited on single-crystal silicon and glass substrates. We varied the initial substrate temperature from 200° to 400°C and the dilution ratio from 10 to 100. We also studied the effectiveness of the use of a seed layer to increase the crystallinity of the films. The films were analyzed by atomic force microscopy, X-ray diffraction, Raman spectroscopy, and transmission and scanning electron microscopy. We found that as the dilution ratio is increased, the films go from amorphous, to a mixture of amorphous and crystalline, to nanocrystalline. The effect of substrate temperature is to increase the amount of crystallinity in the film for a given dilution ratio. We found that the use of a seed layer has limited effects and is important only for low values of dilution ratio and substrate temperature, when the films have large amounts of the amorphous phase.
Correlation of Material Properties and Open-Circuit Voltage of Amorphous Silicon Based Solar Cells
Authors: Yan Baojie , Yang Jeffrey , Yue Guozhen , Guha Subhendu
Published: June 2019

Correlation of hydrogenated amorphous silicon (a-Si:H) alloy material properties and solar cell characteristics have been studied experimentally and by computer simulation. Simulation results show that all three solar cell parameters, short-circuit current density (Jsc), open-circuit voltage (Voc), and fill factor (FF), decrease with increased defect density. For a given intrinsic layer thickness, a larger band gap (Eg) results in a higher Voc but a lower Jsc. However, FF does not depend on band gap. This allows us to distinguish the effect of change in band gap from that in defect density on the variation in Voc. For solar cells with good interface characteristics, a linear relation FF = βVoc + γ is obtained by light soaking experiments and simulation with different defect densities. The slope β is in the range from 2 to 3 V-1 depending on cell properties and light soaking condition, and the intersect γ depends mainly on the band gap. Comparing cells made with high H2 dilution to no H2 dilution, we find that a 58 mV enhancement in Voc with H2 dilution is due to both widening of band gap and reduced defect density. Simulation results also show that a narrower valence band tail leads to a higher Voc. We did not include this effect in the analysis due to lack of available data for correlation between H2 dilution and band tail narrowing.
Deposition of Device Quality μc-Si Films and Solar Cells at High Rates by HWCVD in a W Filament Regime where W/Si Formation is Minimal
Authors: Iwaniczko E. , Mahan A.H. , Yan B. , Gedvilas L.N. , Williamson D.L. , Nelson P.
Published: June 2019

μc-Si has traditionally been deposited by Hot Wire CVD at a low filament temperature. At these temperatures, silicides rapidly form on the filament surface, leading in the case of a tungsten filament to both film reproducibility and filament lifetime issues. By depositing films consecutively using identical deposition parameters, these issues are chronicled for a filament temperature of ∼ 1750°C. Upon increasing the filament temperature to ∼1825-1850°C, these reproducibility and lifetime issues disappear and, by lowering both the substrate temperature and chamber pressure, device quality μc-Si is deposited at high deposition rates in a filament regime where tungsten silicide formation is minimal. Both single junction and tandem solar cells are fabricated using this material, confirming the validity of this approach.
4H-SIC Dmosfets for High Frequency Power Switching Applications
Authors: Ryu Sei-Hyung , Agarwal Anant K. , Richmond James , Palmour John W.
Published: June 2019

Very high critical field, reasonable bulk electron mobility, and high thermal conductivity make 4H-Silicon carbide very attractive for high voltage power devices. These advantages make high performance unipolar switching devices with blocking voltages greater than 1 kV possible in 4H-SiC. Several exploratory devices, such as vertical MOSFETs and JFETs, have been reported in SiC. However, most of the previous works were focused on high voltage aspects of the devices, and the high speed switching aspects of the SiC unipolar devices were largely neglected. In this paper, we report on the static and dynamic characteristics of our 4H-SiC DMOSFETs. A simple model of the on-state characteristics of 4H-SiC DMOSFETs is also presented.
Effect of Mn Doping in ZnO Thin Films Deposited by Pulsed Laser Deposition
Authors: Bhattacharya P. , Das Rasmi R. , Nieves J. , Yuzyuk Yu. I. , Katiyar Ram S.
Published: June 2019

Mn doped ZnO thin films were grown using pulsed laser deposition technique on (001) Al2O3 substrates. The x-ray diffraction data confirmed highly c-axis oriented and hexagonal structure of ZnO and Mn doped ZnO thin films. However, an unidentified secondary peak was observed at very close to ZnO (002) peak. Micro Raman spectra of ceramics as well as thin films showed disorder induced Raman bands besides standard wurtzite ZnO modes. The intensity of several LO modes of ZnO was increased with the increase of Mn concentration. Optical absorption data showed an additional absorption band towards lower than bandgap energy (3 eV) with the increase in Mn content. The incorporation of Mn in ZnO thin films reduced the value of resistivities and mobilities with an increase in carrier concentrations.
Quantitative Characterization of Dislocation Structure coupled with Electromigration in a Passivated Al (0.5wt%Cu) Interconnects
Authors: Barabash R.I. , Tamura N. , Valek B.C. , Spolenak R. , Bravman J.C. , Ice G.E. , Pate J.R.
Published: June 2019

New synchrotron x-ray microbeam methodology is used to analyze and test the reliability of interconnects. The early stage of plastic deformation induced by electromigration before any damages become visible has been recently revealed by white beam scanning X-ray microdiffraction during an accelerated test on Al interconnect lines. In the present paper, we provide a quantitative analysis of the dislocation structure generated in several micron-sized Al grains in both the middle region and ends of the interconnect line during anin-situelectromigration experiment. We demonstrate that the evolution of the dislocation structure during electromigration is highly inhomogeneous and results in the formation of randomly distributed geometrically necessary dislocations as well as geometrically necessary boundaries. The orientation of the activated slip systems and rotation axis depends on the position of the grain in the interconnect line. The origin of the observed plastic deformation is considered in view of constraints for dislocation arrangements under applied electric field during electromigration. The coupling between plastic deformation and precipitation in the Al (0.5% wt. Cu) is observed for the grains close to the anode/cathode end of the line.
Assessment of Reliability of cap layers used in Cu-Black DiamondTM Interconnects
Authors: Krishnamoorthy Ahila , Huang N.Y. , Chong Shu-Yunn
Published: June 2019

Black DiamondTM. (BD) is one of the primary candidates for use in copper-low k integration. Although BD is SiO2 based, it is vastly different from oxide in terms of dielectric strength and reliability. One of the main reliability concerns is the drift of copper ions under electric field to the surrounding dielectric layer and this is evaluated by voltage ramp (V-ramp) and time dependent dielectric breakdown (TDDB). Metal 1 and Metal 2 intralevel comb structures with different metal widths and spaces were chosen for dielectric breakdown studies. Breakdown field of individual test structures were obtained from V-ramp tests in the temperature range of 30 to 150°C. TDDB was performed in the field range 0.5 – 2 MV/cm. From the leakage between combs at the same level (either metal 1 or metal 2) Cu drift through SiC/BD or SiN/BD interface was characterized. It was found that Cu/barrier and barrier/low k interfaces functioned as easy paths for copper drift thereby shorting the lines. Cu/SiC was found to provide a better interface than Cu/SiN.
Plasma Enhanced Chemical Vapor Deposition of Porous Organosilicate Glass ILD Films With k ≤ 2.4.
Authors: Vrtis Raymond N. , O'Neill Mark L. , Vincent Jean L. , Lukas Aaron S. , Peterson Brian K. , Bitner Mark D. , Karwacki Eugene J.
Published: June 2019

We report on our work to develop a process for depositing nanoporous organosilicate (OSG) films via plasma enhanced chemical vapor deposition (PECVD). This approach entails codepositing an OSG material with a plasma polymerizable hydrocarbon, followed by thermal annealing of the material to remove the porogen, leaving an OSG matrix with nano-sized voids. The dielectric constant of the final film is controlled by varying the ratio of porogen precursor to OSG precursor in the delivery gas. Because of the need to maintain the mechanical strength of the final material, diethoxymethylsilane (DEMS) is utilized as the OSG precursor. Utilizing this route we are able to deposit films with a dielectric constant of 2.55 to 2.20 and hardness of 0.7 to 0.3 GPa, respectively.
Optimized Materials Properties for Organosilicate Glasses Produced by Plasma-Enhanced Chemical Vapor Deposition
Authors: O'Neill M.L. , Vrtis R.N. , Vincent J.L. , Lukas A.S. , Karwacki E.J. , Peterson B.K. , Bitner M.D.
Published: June 2019

In this paper we examine the relationship between precursor structure and material properties for films produced from several leading organosilicon precursors on a common processing platform. Results from our study indicate that for the precursors tested the nature of the precursor has little effect upon film composition but significant impact on film structure and properties.
Electrical, Mechanical, and Structural Properties of Fluoro-Containing Poly(silsesquioxanes) Based Porous Low k Thin Films
Authors: Hyeon-Lee Jingyu , Rhee Jihoon , Kim Jungbae , Yim Jin-Heong , Chang Seok
Published: June 2019

Low dielectric fluoro-containing poly(silsesquioxanes) (PSSQs) have been synthesized using trifluoropropyl trimethoxysilane (TFPTMS), methyl trimethoxysilane (MTMS), and 2, 4, 6, 8-tetramethyl-2, 4, 6, 8-tetra(trimethoxysilylethyl) cyclotetrasiloxane. The properties of fluorocontaining PSSQs based thin films were studied by electrical, mechanical, and structural characterization. Film was spun on a silicon substrate, baked at 150°C and 250°C for 1 minute, respectively, and cured in the furnace at 420°C for 1 hour under vacuum condition. Thermally decomposable trifluoropropyl groups of the fluoro-containing PSSQ were served as a pore generator and partially contributed to lower a dielectric constant. â-cyclodextrin (CD) was also employed as a pore generator. The concentration of the pore generator in the film was varied from 0 to 30 %. The dielectric constants of the porous PSSQ films were found to be in the range of 2.7 – 1.9 (at 100 kHz). Hardness and Young's modulus of the films were measured by nano-indentation. The elastic modulus and hardness of the porous films were well correlated with the concentration of the pore generators. Positronium Annihilation Lifetime Spectroscopy (PALS) was employed to characterize a pore size of the porous fluoro-containing PSSQ film. The pore size of the film was less than 2.2 nm. The nanoporous films showed quite promising properties for commercial application.
Determination of Pore Size Distributions in Nano-Porous Thin Films from Small Angle Scattering
Authors: Bauer Barry J. , Hedden Ronald C. , Lee Hae-Jeong , Soles Christopher L. , Liu Da-Wei
Published: June 2019

Small angle neutron and x-ray scattering (SANS, SAXS) are powerful tools in determination of the pore size and content of nano-porous materials with low dielectric constants (low-k) that are being developed as interlevel dielectrics. Several models have been previously applied to fit the scattering data in order to extract information on the average pore and/or matrix size. A new method has been developed to provide information on the size distributions of the pore and matrix phases based on the “chord length distribution” introduced by Tchoubar and Mering. Examples are given of scattering from samples that have size distributions that are narrower and broader than the random distribution typical of scattering described by Debye, Anderson, and Brumberger. An example of fitting SANS data to a phase size distribution is given.
Using multi-dimensional contact mechanics experiments to measure Poisson's ratio of porous low-k films
Authors: Lucas B. N. , Hay J. C. , Oliver W. C.
Published: June 2019

Using a new multi-dimensional contact mechanics system, it was recently shown that the experimentally measured tangential to normal stiffness ratio of a contact can be described as a function of the bulk Poisson's ratio of the material as predicted by Mindlin [1-3]. This system has been utilized to measure the normal and tangential elastic contact stiffness of a series of porous low-k films, with increasing starting porogen content. These results indicate a transition from a material-controlled elastic behavior to a structure-controlled elastic behavior as the porosity of the film is increased. These structural effects and their potential influence on the mechanical response to forces imposed on integrated circuits are discussed. The experimental details and apparatus are introduced and described.
Synthesis and Mechanical Properties of TiN-AIN Thin Film Heterostructures
Authors: Waters C. , Kumar D. , Yarmolenko S. , Xu Z. , Sankar J.
Published: June 2019

TiN and AlN are promising thin film materials. There is continuing interest in their mechanical, electronic and optoelectronic properties. Our studies have shown that mechanical properties can be changed by forming thin film heterostructures of the two materials. We report on our pulsed laser deposition assisted synthesis, microstructural characterizations and mechanical properties of TiN/AlN multi-layer structures. The TiN/AlN superlattice structures are fabricated on (100) silicon substrates at different temperatures (400-800oC) and different nitrogen ambient pressures. The nano-mechanical hardness properties of the multi-layered structures were examined as a function of thickness of individual layers keeping the overall thickness of heterostructures constant. Thickness variations of the films are measured with a optical phase-shift interferometer. The mechanical properties of the TiN-AlN heterostructures have been found to be associated with interfacial interaction between layers. The interfacial interaction, in turn, depends on processing parameters the most important among which is substrate temperature.
Determination of Ag/Co Interfacial Free Energies by Biaxial Zero Creep Experiments
Authors: An Bing , Zhang Tong-jun , Yuan Chao , Cui Kun , Zhang Wei
Published: June 2019

To measure the Ag/Co interfacial free energies, biaxial zero creep experiments were performed on Ag/Co multilayer films deposited on the Si (111) wafers. As the samples were heated from room temperature to 450°C, the residual stress in films, which was in situ monitored by substrate curvature technique, decayed gradually to zero due to the increasing plastic deformation in films. After held for several hours at 450°C, they reached a zero creep state while the equilibrium stresses were measured. The annealed element layers were immiscible, and exhibited the column grain distribution and (111) preferred orientations. Based on the Josell model, the free energy of Ag/Co (111) interfaces at 450°C was found to be 1.02 ± 0.17 J/m2.
Mechanical Behavior Of Elastomeric Stamps During Microcontact Printing Patterns: Direct Observation Of Stamps And Inks
Authors: Blackman Gregory S. , Jagota Anand , Sharp Kenneth G.
Published: June 2019

Microcontact printing is a straightforward and effective method for generating surface patterns of micron or submicron lateral dimensions. The fidelity of the ultimate pattern is a complex interplay of mechanical behavior of the elastomeric stamp, fluid transfer between surfaces and the ability of the ink to self-assemble on the new surface. We present here experimental observations and modeling of stamp deformation during precise external loads and visualization of inked surfaces by high contrast analytical methods. Stamp behavior was observed visually in an inverted microscope and load-displacement relationships used to determine onset of failure modes such as roof collapse and buckling of slender relief features as a function of stamp geometry. The load was applied with a glass sphere so as to obviate problems with alignment and to precisely determine contact areas.

A “robotic stamper” fabricated from an AFM instrument can deliver ink under conditions of precise load. Surfaces inked with varying densities or combinations of SAMs can be imaged with excellent contrast by scanning surface potential microscopy (SSPM). The same area of the sample can then be examined using time-of-flight SIMS or other surface analytical technique with no additional etching or sample preparation. In this way the fidelity and density of the patterned monolayers can be evaluated. The effect of load on ink pattern quality can also be established.
Dislocation Intersections and Reactions in FCC and BCC Crystals
Authors: Kubin Ladislas P. , Madec Ronan , Devincre Benoit
Published: June 2019

The various types of configurations formed in face-centered cubic (fcc) and body-centered cubic (bcc) structures by two interacting, non-coplanar, dislocation segments of various orientations are examined and discussed. The focus is on junction formation and on a particular interaction, the collinear interaction, which deserves much more attention than paid up to now.
In-Situ TEM Studies of Sessile Dislocation Arrangements and N Vacancy Ordering in ZrN
Authors: Li P. , Howe J.M.
Published: June 2019

Dissociation of perfect 1/2<110> single dislocations into two 1/6<112> Shockley partial dislocations in ZrN was observed by transmission electron microscopy (TEM). The 1/2<110> single dislocations have a super-jog character and are not coplanar with the dissociated Shockley partials. This sessile arrangement of dislocations may be responsible for the brittleness of ZrN. The wide separation of the partial dislocations bounding stacking faults indicates that the stacking-faults energy (SFE) is low in ZrN. The low SFE can be explained on the basis of a high vacancy concentration, which was confirmed by the appearance of diffuse intensity maxima in electron diffraction patterns due to short-range ordering (SRO) of N vacancies. In-situ heating experiments in the TEM revealed that the diffuse intensity maxima disappear during heating and reappear on cooling. This indicates that N (or N vacancy) diffusion scrambles the SRO arrangement of N vacancies during heating. The width of the stacking faults in ZrN increases with temperature, indicating that the SFE decreases as the vacancy concentration increases.
A Continuum Model for Single Crystal Cyclic Plasticity
Authors: Xu Biqiang , Jiang Yanyao
Published: June 2019

A constitutive model was developed to bridge the cyclic plasticity behavior of single crystals and the corresponding characteristic dislocation structures. Yield and flow were built on the individual slip systems. The Armstrong-Frederick kinematic hardening rule was invoked to capture the Bauschinger effect. A material memory parameter was introduced to consider the amplitude dependence of cyclic hardening. Latent hardening considering the interactions among the slip systems was used to describe the anisotropic cyclic behavior. The experimental results of copper single crystals were used to validate the model developed. It was found that the model was able to adequately describe the well-known three distinctive regions in the cyclic stress-strain curve of the FCC single crystal oriented for single slip and the associated dislocation substructures. The model was capable of capturing the enhanced hardening observed in copper single crystals in multi-slip orientations. For a given loading history, the model can predict not only the saturated stress-strain response but also the detailed evolution of the transient cyclic behavior. The characteristic dislocation structures can be featured with the slip evolution.
A Study of Localized Corrosion in Al Resulting From The Controlled Introduction of Cl
Authors: Johnson C. M. , Wall F. D. , Barbour J. C. , Martinez M. A.
Published: June 2019

High purity Al samples were implanted with 35 keV Cl+ then polarized in Cl--free electrolyte in order to ascertain corrosion behavior as a function of Cl content. Electrochemical data indicated implant fluences between 5x1015 and 2x1016 Cl+cm-2 resulted in little or no localized attack. Implant fluences of 3x1016 and 5x1016 Cl+cm-2 resulted in significant attack with the severity scaling as a function of implant fluence. The low variability in the behavior of localized corrosion for the 5x1016 Cl+cm-2 sample suggests that this implant dosage may result in a critical Cl- in the sample for pit nucleation. Optical and Electron microscopy images indicated some reactivity associated with lower fluences (1x1016Cl+cm-2), possibly indicating enhanced general dissolution. At high magnification the corrosion was observed to occur outside the implanted boundary through mechanisms of tunneling or altered local chemistry at those sites. The SEM images reveal a form of localized corrosion with a crystalline character.
Passive Layer Breakdown on Titanium in Doped and Undoped Artificial Saliva
Authors: Demetrescu Ioana , Popa Mihai V. , Vasilescu Ecaterina , Drob Paula , Popescu Belarisa , Ionita Daniela , Vasilescu Cora
Published: June 2019

The aim of this work is to investigate the long term (3000 exposure hours) tendency of passive layers on titanium to breakdown in Tani-Zucchi and Carter-Brugirard artificial saliva undoped and doped with chloride and fluoride ions. The non-uniformity of the saliva pH (from 7.88 to 5.73 and extreme case 2.15) was simulated. The following techniques were used: potentiostatic, potentiodynamic and linear polarization, the monitoring of the open circuit potentials vs. exposure time and atomic force microscopy. The breakdown (pitting) potential at about +2.9 V and the re-passivation potential at +2.4 V in Tani-Zucchi artificial saliva were determined. So, the pitting protection potential is very noble and can not be reached in human body.
Pb Electrodeposition in the Presence of Chlorine Ions on Cu(100): An in Situ Optical Reflectivity Difference Study
Authors: Gray J. , Schwarzacher W. , Zhu X.D.
Published: June 2019

We studied the initial stages of the electrodeposition of Pb in the presence of chlorine ions on Cu(100), using an oblique-incidence optical reflectivity difference (OIRD) technique. The OI-RD results reveal that immediately following the underpotential deposition (UPD) of the first Pb monolayer, two different types of bulk-phase films grow depending upon the magnitude of overpotential and cyclic voltammetry (CV) scan rate. At low overpotentials and/or slow scan rates, we propose that a bulk-phase Pb film grows on top of the UPD monolayer. At high overpotentials and/or fast scan rates, either a PbO, PbCl2, or a rough Pb bulk-phase layer grows on top of the UPD layer such that the reflectivity difference signal from such a film has an opposite sign.
Doe Progress in Assessing the Long Term Performance of Waste Package Materials
Authors: Berusch A. , Gause E.
Published: June 2019

Each of the projects has made significant progress toward the eventual operation of a repository for the disposal of high-level radioactive wastes in the United States. Although much has been accomplished, much remains to be done. For example, the Site Characterization Plans for BWIP and NNWSI are nearing completion to be followed by initiation of site characterization activities. The Site Characterization Plan for the selected salt site is scheduled for completion later in 1987. Waste package advanced conceptual design studies are currently scheduled to begin at each project before the end of FY 1987. These efforts will lead to selections of concepts to be detailed in the license application design phase. Compliance with the NRC criteria that require long-term waste package performance will be demonstrated by DOE by performing all of the aforementioned activities. In doing so, the DOE will also be assured that its plan for the safe disposal of high-level waste will be satisfactorily implemented.
The Geochemistry of Natural Technetium and Plutonium
Authors: Curtis David B. , Cappis John H. , Perrin Richard E. , Rokop Donald J.
Published: June 2019

Technetium and plutonium in unprocessed nuclear reactor wastes are major concerns with regard to their containment in the geologic environment. Both nuclides have long half-lives; therefore, they will exist long after engineered barriers can be considered reliable. Consequently, strategies for the containment of these two elements depend on their retention in the geologic barrier until they have decayed to innocuous levels. Because these are the rarest elements in nature, there have been few direct observations of their geochemical behavior; predictions con- cerning their fate in the repository are based on properties that can be observed in the laboratory. We are attempting to complement the laboratory work by studying the geochemistry of natural plutonium and technetium.
Laboratory and Modelling Studies of Sodium Benionite Grounmater Interaction
Authors: Sneujman M. , Uotiia H. , Rantanen J.
Published: June 2019

According to the present Finnish concept sodium bentonite will be used as a buffer material in the repository for high-level waste. Experimental and theoretical studies treating the effect of bentonite upon the chemical conditions in a repository have been initiated with the object of specifying the chemistry of the near field.

Sodium bentonite was let react with water under anaerobic conditions at 25°C for 540 days, during which time six fluid samples were extracted for the chemical analysis of 15 chemical species. The generated fluid phase was alkaline (PH = 9…10) and contained a high amount of bicarbonate. Also a low redox-potential was measured. The fluid phase chemistry was investigated using the geochemical code PHREEM. Calcite saturation was observed in all fluid samples.

A modelling of sodium bentonite interaction with water based on the main mineral components of bentonite was also performed with PHREEQE. A fairly good agreement between experimental results and model calculations was observed.
Effects of N2O Fluence on the PECVD-grown Si-rich SiOx with Buried Si Nanocrystals
Authors: Lin Chun-Jung , Kuo Hao-Chung , Chen Chia-Yang , Chueh Yu-Lun , Chou Li-Jen , Chang Chih-Wei , Diau Eric Wei-Guang , Lin Gong-Ru
Published: June 2019

The optimized N2O fluence is demonstrated for plasma enhanced chemical vapor deposition (PECVD) of Si-rich substoichiometric silicon oxide (SiOx) films with buried Si nanocrystals. Strong room-temperature photoluminescence (PL) at 550-870 nm has been observed in SiOx films grown by PECVD under a constant SiH4 fluence of 20 sccm with an N2O fluence varying from 105 sccm to 130 sccm. A 22-nm-redshift in the central PL wavelength has been detected after annealing from 15 min to 180 min. The maximum PL irradiance is observed from the SiOx film grown at the optimal N2O fluence of 120 sccm after annealing for 30 minutes. Larger N2O fluence or longer annealing time leads to a PL band that is blue-shifted by 65 nm and 20 nm, respectively. Such a blue shift is attributed to shrinkage in the size of the Si nanocrystals with the participation of oxygen atoms from N2O incorporated within the SiOx matrix. The (220)-oriented Si nanocrystals exhibit radii ranging from 4.4 nm to 5.0 nm as determined by transmission electron microscopy (TEM). The luminescent lifetime lengthens to 52 μs as the nc-Si size increase to > 4 nm. Optimal annealing times for SiOx films prepared at different N2O fluences are also reported. A longer annealing process results in a stronger oxidation effect in SiOx films prepared at higher N2O fluences, yielding a lower PL irradiance at shorter wavelengths. In contrast, larger Si nanocrystals can be precipitated when the N2O fluence becomes lower; however, such a SiOx film usually exhibits weaker PL at longer wavelength due to a lower nc-Si density. These results indicate that a N2O/SiH4 fluence ratio of 6:1 is the optimized PECVD growth condition for the Si-rich SiO2 wherein dense Si nanocrystals are obtained after annealing.
Bifacial Silicon Heterojunction Solar Cell with Deposited Back Surface Field
Authors: Goldbach H. D. , Bink A. , Schropp R. E. I
Published: June 2019

Silicon heterojunction cells (SHJ) using crystalline silicon wafers and deposited heterojunction thin film emitters are interesting from an economical, technological, and sc ientific point of view. Modules using such cells (so called HIT cells) are commercially produced by Sanyo Electric Co., using single crystal wafers. Recently reported alternatives still comprise a high-temperature diffused back surface field (BSF). In order to provide a low cost alternative, our goal is to develop SHJ using multicrystalline silicon wafers with both a deposited emitter and a deposited BSF. The present approach truly allows the development of a cheap, low temperature, all-deposited alternative for the HIT cell.

We made a bifacial silicon heterojunction solar cell, with an emitter consisting of a 7 nm intrinsic a-Si:H layer and a 15 nm n-type μc-Si:H layer. The back surface field is formed by a 30 nm p++ μc-Si:H layer. In order to achieve a functional deposited BSF the thin p++-layer has to have higher effective dopant concentration than the substrate. We used a 375 μm thick FZ wafer with a resistance of 1 cm with an activation energy of 0.2 eV. The μc-Si:H p++-layer has an activation energy of Ea = 0.082 eV. To detect the operation of the BSF the cell was made bifacial. The cell has an efficiency of 14.87 %, Voc = 571.4 mV and Jsc = 33.3 mA/cm2, Rs = 1.2 Ωcm2 and Rp = 1.8 kΩcm2. The cell, illuminated from the back, shows a Voc of 0.1 V and Jsc of 7 mA/cm2. Reference bifacial cells without BSF show no cell behavior illuminated from the rear side. External quantum efficiency (EQE) measurements with illumination at the rear side of the bifacial heterojunction cell with BSF show a quantum efficiency value of 0.17 in the range 500-800 nm, while the reference cell without BSF shows zero quantum efficiency in this range. These results show evidence for the feasibility of a truly functioning deposited BSF combined with a SHJ with deposited emitter.
High-Performance Amorphous Silicon Emitter for Crystalline Silicon Solar Cells
Authors: Wang T.H. , Iwaniczko E. , Page M.R. , Wang Q. , Levi D.H. , Yan Y. , Xu Y. , Branz H.M.
Published: June 2019

Thin hydrogenated amorphous silicon (a-Si:H) layers deposited by hot-wire chemical vapor deposition (HWCVD) are studied for use as the emitter in silicon heterojunction (SHJ) solar cells on p-type crystalline silicon wafers. Low interface recombination velocity and high open-circuit voltage are achieved by a low substrate temperature (<150°C) intrinsic a-Si:H deposition which ensures immediate amorphous silicon deposition. This is followed by deposition of n-type a-Si:H at a higher temperature (>200°C) which improves dopant activation and other properties. A prolonged atomic H pretreatment to clean the c-Si surface is actually detrimental because it creates additional defects in the c-Si lattice. However, a brief H pretreatment is beneficial and may render the intrinsic interlayer unnecessary. The n-type a-Si:H thickness must be limited to ~5 nm to minimize current loss, because the phosphorous doped a-Si:H layer has significant absorption in the usable solar spectrum. Using the optimized a-Si:H emitter, we obtain efficiency of nearly 17% on planar float-zone (FZ) silicon and 15% on planar Czochralski (CZ) silicon substrates with aluminum back-surface-field (Al-BSF) and contacts.
Electrodeposition of Fluorescent Si Nanomaterial From Acidic Sodium Silicate Solutions
Authors: Abuhassan Laila H. , Nayfeh Munir H.
Published: June 2019

We developed a procedure for the electrodeposition of fluorescent silicon nanomaterial from silicates on conducting substrates. The electrodeposion solution used is a solution of sodium metasilicon salts (Na2SiO3) in HF/H2O2. When a positively biased platinum substrate is immersed in the bath, a current is drawn and a thin fluorescent coating is formed on the substrate. We discuss the results in terms of current-induced nucleation of silicon nanostructures.
Depth-profiling Pore Morphology in Nanoporous Thin Films Using Positronium Lifetime Annihilation Spectroscopy
Authors: Vallery Richard S. , Peng Hua-Gen , Frieze William E. , Gidley David W. , Moore Darren L. , Carter Richard J.
Published: June 2019

Positronium annihilation lifetime spectroscopy (PALS) using a positron beam is a proven technique to characterize porosity in amorphous thin film materials. The capability to control the depth of the implanted positrons is unique to beams as compared to traditional bulk PALS techniques. By increasing the positron beam energy, positrons are implanted deeper into the film. Control of the positron implantation depth in beam-PALS allows analysis of sub- micron films, investigation of depth-dependent film inhomogeneities, determination of pore interconnection lengths, and access to buried films under barrier layers. Details on PALS depth profiling and an example of applying the technique to a plasma-enhanced-chemical-vapor- deposited (PECVD) porous film are presented.