bluuebunny/crossref_metadata_2025 huggingface dataset:
Dislocation Core Structure Evolution During Dislocation Glide in FCC Lattices
Authors: Soare M.A. , Picu R.C.
Published: June 2019

A dislocation core model is developed in terms of a singular decomposition of the elastic field surrounding the defect in a power series of 1/rn. The decomposition is a Laurent expansion beginning with the term corresponding to the Volterra dislocation and continuing with a series of dipoles and multipoles. The analysis is performed for an edge dislocation in an fcc lattice. The field surrounding the dislocation is derived by means of atomistic simulations. The coefficients of the series expansion are determined from the elastic field using path independent integrals. When loaded by a shear stress smaller than the Peierls stress, the core distorts. The distortion up to the instability (Peierls stress) is monitored based on the variation of these coefficients. The stacking fault separating the two partials is characterized, by using a similar procedure, as a source of elastic field.
Dislocation and Grain Derived Theory for Kinematic Metrics of Finite Deformation to Replace Existing Elastic-Plastic Phenomenological Metrics
Authors: Stout Ray B.
Published: June 2019

Most existing continuum kinematic metrics used for correlating experimental data sets from finite deformation tests are traceable to a two reference state configuration analysis proposed primarily by Lee[1]; namely, a deformed elastic-plastic back to an idealized zero stress plastic state. These analyses admit that material discontinuities would exist in arriving at a virtual state of zero residual stress, however, the elastic-plastic deformation process is considered a mathematically continuous spatial function process. Hence, atomic length scale metrics are not analytically introduced because of the continuity requirements of the embedded deformation function space. This is not a valid physical description given that the microscopic dislocation mechanism for the non-recoverable kinematics of crystal material deformations creates discontinuities between atomic planes of grains in a material sample. In addition, the mathematical structure of current continuum kinematic metrics is deterministic. This is also not physically realistic in describing materials' responses that are dependent on intrinsic metallic grain characteristics. This follows since an ensemble of material specimens have a randomness for the physical numbers per unit material volume per unit species volume for both dislocation density and grain lattice structure density function characteristics. These random functions are best described as classical probability density functions in a spatial, time, and species variable domain. A stochastic description for dislocation density in solids has been developed, and explicitly introduced in a finite deformational functional[2]. This finite deformational functional will be extended to include an explicit dependence on a stochastic grain lattice structure density function. Finally, analyses of this dislocation-grain deformational functional provide stochastic kinematic metrics for void or microcrack-type opening deformations at grain boundaries that contain length scale measures based on the physical attributes of both dislocations and grains.
X-ray Microbeam Investigation of Deformation Microstructure in Microindented Cu
Authors: Yang Wenge , Larson B. C. , Pharr G. M. , Ice G. E. , Tischler J. Z. , Budai J. D. , Liu Wenjun
Published: June 2019

The deformation microstructure under spherical microindents in single crystal Cu has been investigated with submicron spatial resolution using x-ray structural microscopy. A polychromatic, submicron diameter (∼ 0.5 μm) microbeam was used in combination with micronresolution depth profiling to make direct, nondestructive measurements of plastic deformation induced lattice rotations under an indent made with a 69 μm radius spherical indenter and 200 mN maximum load. Lattice orientations relative to the undeformed crystal were determined as a function of position under the indent using differential-aperture x-ray structural microscopy (DAXM). Rotation-axes and misorientation-angles were determined for micron steps along selected microbeam penetration directions.
Mesostructure of Textured Metal Materials: Experimental Study and New-Discovered Regularities
Authors: Perlovich Yuriy , Isaenkova Margarita , Fesenko Vladimir
Published: June 2019

The substructure inhomogeneity of real textured metal materials was studied by use of recently developed methods of X-ray diffractometry and data treatment. Main regularities of substructure inhomogeneity were revealed for the first time by the analysis of generalized pole figures. The structure of deformed metal includes an extremely wide spectrum of substructure conditions. The crystallographic orientation of grains is the most effective criterion for systematization of substructure inhomogeneities in textured materials. The dispersity of grains and the distortion of their crystalline lattice are minimal in texture maxima and increase up to highest values by passing to texture minima. The distribution of lattice elastic deformation in rolled metals most often shows a cross-wise pattern, consisting in alternation of quadrants with predominance of elastic extension or elastic compression.
Using Fluctuations To Locate The Surface Roughening Transition
Authors: Bentz Daniel N. , Jackson Kenneth A.
Published: June 2019

An analysis of the fluctuations of a {100} FCC interface has been used to locate the surface roughening transition in kinetic Monte Carlo simulations. These simulations were conducted using a spin 1/2 Ising model treatment of the solid-liquid interface. A temperature gradient was imposed on the simulation cell providing a restoring force to the interface. Fluctuations in the number of solid atoms in the system were measured using time correlations. The fluctuation dissipation theorem was employed to relate the characteristic times retrieved from the time correlation to the kinetic coefficients of the system. A dramatic change was found in these characteristic times, which locates the surface roughening transition.
Structural Studies of Copper Sulfide Film Growth: Influence of Humidity
Authors: Campin M. J. , Zhu J. G. , Sullivan J. P. , Barbour J. C. , Braithwaite J. W. , Provencio P. P.
Published: June 2019

Copper is a critical material in electrical components and is subject to atmospheric sulfidation. This study characterized the product formed when Cu is exposed to a dilute (50-200ppb) H2S atmosphere at low (0.5%) to high (80%) relative humidity (RH). An important observation was that the Cu2S growth rate for long times is significantly higher for sulfides formed at low RH compared to high RH. In addition, it was found that for both low and high RH sulfidation, copper reacts to form the low chalcocite phase (Cu2S) as identified by x-ray and electron diffraction. Cross-section and plan-view TEM revealed that the Cu2S grains formed at high RH are 20-50 nm in size with a large amount of porosity, whereas the grains formed at low RH are 75-150+ nm and appear to undergo grain growth with little porosity as the film thickens.
Correlation between the Susceptibility to Breakdown and Surface Properties of Thin Films on Titanium Alloys in Physiological Fluids
Authors: Lopez Agustin Santana , Mirza-Rosca Julia , Popa Mihai V. , Demetrescu Ioana , Vasilescu Ecaterina , Drob Paula , Vasilescu Cora , Ionita Daniela
Published: June 2019

Correlation between the susceptibility to breakdown and surface properties of thin films on implant titanium alloys Ti-5Al-4V and Ti-6Al-4Fe in Ringer 1 and Ringer 2 solutions of different pH values (6.98, 4.35, 2.5) which simulate the conditions that can appear at the longterm (13,000 hours) contact between implant and tissues were studied in this paper. The passive films are very stable up to +1.8 V; Ti-6Al-4Fe alloy presents pitting attack at a pitting initiation potential of +3.5 V in Ringer 1 solution and at +3.9 V in Ringer 2 solution. The pitting protection potential is about +1.75 V in both solutions; this is a very noble potential. Impedance spectra were modeled with one time constant equivalent electrical circuit, typically for a compact oxide film, for all materials, in all tested solutions. The fitting parameters indicate a long-term stability.
Spatial separation mechanism in Si quantum dots deposited by chemical vapour deposition on SiO2
Authors: Puglisi Rosaria A. , Nicotra Giuseppe , Lombardo Salvatore , Spinella Corrado , Gerardi Cosimo
Published: June 2019

A systematic study on the Si inter-dot distance after nucleation on silicon oxide substrates is presented. The process has been followed from the very early stages of the dot formation up to 25% of coverages. Structural characterization has been performed by means of energy filtered transmission electron microscopy, which allowed us to observe dot sizes down to 0.5 nm in radius. Silicon nanodots are shown to be surrounded by a depleted zone, where no new Si dots are observed to nucleate. The average size of such a zone ranges between 4 and 9 nm, depending on the deposition conditions. The dot radius is shown to be proportional to the depleted region size, thus indicating the scaling behaviour of the process.
Semiconducting Aluminum Transition-Metal Quasicrystals
Authors: Krajčí Marian , Hafner Jürgen
Published: June 2019

We report on a class of icosahedral aluminum-transition-metal (Al-TM) alloys with a true semiconducting behavior. The existence of a semiconducting gap is found to depend critically on a particular kind of Al-TM ordering defined by a simple rule in a 6-dimensional superspace. Any deviation from this 6D order leads to the formation of strongly localized defect states in the gap. The structure of the semiconducting quasicrystals belongs to the face-center-icosahedral structural class, the same to which also icosahedral AlPdRe belongs. The description of the structure is based on a modified Katz-Gratias-Boudard model. We have calculated the electronic structure for series of quasicrystalline approximants. In the density of states of the 1/1 approximant with 128 atoms/unit cell relaxed with Hellmann-Feynman forces we have found a real gap at or close to the Fermi level. To get a semiconductor the critical band-filling is 648 electrons per cell. It can be achieved for several different stoichiometries. We investigated semiconducting 1/1 approximants with various combinations of 3d, 4d and 5d transition-metals. The gap widens as a 3d or 4d metal is replaced by a 5d metal. Calculations for the 2/1 approximant with 544 atoms/cell show the persistence of the gap. The chemical composition for which semiconducting behavior is achieved varies in the sequence of the approximants, but the existence of the gap in the electronic spectrum persists in higher order approximants, provided the Al-TM ordering is respected. Icosahedral AlPdRe represents the quasiperiodic limit in this hierarchyof approximants. As substitutional defects which obviously exist in real samples of any quasicrystal lead to formation of localized states, a real sample of icosahedral AlPdRe seems to be a semiconductor with a band-gap filled by localized states.
The Effect of Strain Rate on the Yield Behavior of Iron-Based Lro Alloys at Elevated Temperatures
Authors: Lin H. T. , Wilcox R. C. , Chin B. A.
Published: June 2019

The sensitivity of iron-based LRO alloys to strain rate at elevated temperatures was investigated. The tensile results indicate that the iron-based LRO alloys exhibit a positive temperature dependence of yield behavior, but are insensitive to variations in strain rate between 10-5and 100sec-1. These observations, along with SEM and TEM results, suggest that previous proposed diffusion-controlled mechanisms are not responsible for the increase in yield strength with increasing temperature.
‘Seed Layers’ for the Preparation of Hydrogenated Microcrystalline Silicon with Defined Structural Properties on Glass
Authors: Ross Christoph , Mai Yaohua , Carius Reinhard , Finger Friedhelm
Published: June 2019

Microcrystalline silicon with properties relevant to highly efficient solar cells can be suc-cessfully prepared on glass for material characterization if a thin intrinsic ‘seed layer’ coating of the substrate is used. This is demonstrated by a detailed structure analysis on the base of Raman spectroscopy and photothermal deflection spectroscopy. The coating turns out to be crucial (1) for achieving a crystalline content as high as that of solar cell absorber material, (2) for creating a homogeneous structure in growth direction, and (3) for extending the range of deposition pa-rameters which lead to films with high crystallinity towards the regime of amorphous growth. Regarding electrical transport, ‘seed layer’ assisted growth results in a structure dependence of the dark conductivity which is very similar to that of material grown on bare glass. Regarding optical absorption spectra, residual interference fringes, which indicate structure non-uniformities, are clearly suppressed by means of ‘seed layers’. It is concluded that appropriate ‘seed layers’ play an important role for a comprehensive characterization and development of microcrystalline silicon layers for thin film devices.
The Nature of Native and Light Induced Defect States in i-layers of High Quality a-Si:H Solar Cells Derived from Dark Forward-Bias Current-Voltage Characteristics
Authors: Deng J. , Albert M. L. , Pearce J. M. , Collins R. W. , Wronski C. R.
Published: June 2019

Results are presented on the defect state distributions in intrinsic a-Si:H layers with and without hydrogen dilution in p-i-n solar cells obtained directly from the analysis of dark forwardbias current-voltage (JD-V) characteristics. It is shown that there are distinct differences in the distributions of both native and light induced defect states between the two types of i-layers. Computer simulations using these distributions are presented which show excellent agreement with the experimental results not only for the JD-V but more importantly for the bias dependent differential diode quality factor n(V) characteristics. Results are also presented on the nature of the gap states and their evolution with light induced degradation as well as their effects on the performance and stability of high quality a-Si:H solar cells.
Radiation hard amorphous silicon particle sensors
Authors: Wyrsch N. , Miazza C. , Dunand S. , Ballif C. , Shah A. , Despeisse M. , Moraes D. , Jarron P.
Published: June 2019

Radiation tests of 32 μm thick hydrogenated amorphous silicon n-i-p diodes have been performed using a high energy 24 GeV proton beam up to fluences in excess of 1016 protons/cm2. The results are compared to irradiation of similar 1 μm and 32 μm thick n-i-p diodes using a proton beam of 280 keV at a fluence of 3x1013 protons/cm2. Even though both types of irradiation cause a significant drop in photoconductivity of thin or thick diodes, all samples survived the experiment and recover almost fully after a subsequent thermal annealing.
High Electron Mobility (˜150 cm2/Vs) PECVD Nanocrystalline Silicon Top-Gate TFTs at 260 °C
Authors: Lee Czang-Ho , Sazonov Andrei , Nathan Arokia
Published: June 2019

Undoped nanocrystalline silicon (nc-Si:H) films were prepared by conventional 13.56 MHz plasma enhanced chemical vapor deposition (PECVD) at 260 °C, using highly H2-diluted SiH4 plasma. The nc-Si:H films were evaluated using electrical, structural, and chemical measurements. The optimized nc-Si:H film showed an oxygen concentration (CO) of ˜1.5 X 1017 at./cm3 and a dark conductivity (σD) of ˜10-6 S/cm, while the Raman crystalline volume fraction (XC) was ˜85 %. Top-gate staggered TFTs with a ˜100 nm nc-Si:H channel layer and an amorphous silicon oxide (a-SiOx) as the gate dielectric were fabricated. The TFTs showed a field effect mobility (μFE) of ˜150 cm2/Vs, a threshold voltage (VT) of ˜2 V, a subthreshold slope (S) of ˜0.25 V/dec, and an ON/OFF current ratio more than 106. To the best of our knowledge, the TFT mobility reported here is the highest achieved to date using state-of-the-art nc-Si:H films prepared by direct PECVD.
Stark Splitting in Photoluminescence Spectra of Er in a-Si:H
Authors: Kumeda Minoru , Takahashi Mitsuo , Morimoto Akiharu , Shimizu Tatsuo
Published: June 2019

The photoluminescence spectra due to Er ions doped in a-Si:H were decomposed into several lines. The 19-K spectrum was reproduced by adding four Gaussian lines whose linewidths were increased with decreasing the photon energy. Since only the lowest energy level of 4I13/2 contributes to the radiative transition at this low temperature, the energy levels in 4I15/2 split by the Stark effect can be determined. These splittings are not largely different from those for Er in aluminosilicate glass. This implies that the all nearest neighbors of Er are oxygens which have been introduced unintentionally in the sample during preparation. The change in the photoluminescence intensity by annealing is discussed in relation with the spectral change and the results of ESR measurements.
Characterization of Amorphous Silicon by Secondary Ion Mass Spectrometry
Authors: Li Yupu , Wang Shaw , Lin Xue-Feng , Wei Luncun
Published: June 2019

Based on various implanted standards, we have used SIMS (Secondary Ion Mass Spectrometry) to characterize amorphous Si thin films with high hydrogen content. SIMS and HFS (Hydrogen Forward Scattering) showed good agreement on the measured total H doses for H-implanted Si samples and the a-Si thin films. For the H-implanted Si samples, in the dose range of 2e15 atoms/cm2 to 2e17 atoms/cm2 (corresponding to peak H concentration from 0.32 at.% to 32 at.%), SIMS results showed that the calibration curve is a straight line. In other words, no correction for SIMS quantification is needed when moving from low to high hydrogen content samples. Analysis of P (Phosphorus) in a-Si thin films requires the use of high mass resolution magnetic sector SIMS to separate P and a mass interference from (30Si+H). Using a magnetic sector SIMS instrument, P-doped a-Si thin layers (˜ 50nm thick) were analyzed using 3keV O2 beam with oxygen leak for better depth resolution and improved detection limits. For the analysis of C, N, O in a-Si thin films (again approximately 50nm thick) the profiling energy typically needs to be lowered down to 3keV and the material needs to be sputtered at a high rate in order to reach real background levels. In this work, a-Si thin films were also analyzed using a 3keV Cs+ primary ion beam with (Cs2M)+ (M= C, N, O) detection for good depth resolution and detection limits.
High Density Plasma Processing of Microcrystalline Si Thin Films
Authors: Joshi P. C. , Voutsas A. T. , Hartzell J. W.
Published: June 2019

In the present work, we report on the fabrication of high quality microcrystalline Si thin films by high-density PECVD technique. The typical deposition rate of the HD-PECVD μ-Si thin films was greater than 350 Å/min in the H2/SiH4 ratio range of 20-100. For a 150-nm-thick film deposited at a H2/SiH4 ratio of 20, the typical microcrystalline volume fraction and the average crystallite size corresponding to <111> orientation were 75% and 160 Å, respectively. The observed growth and properties of the μ-Si thin films show the potential of the high-density PECVD technique for the low temperature processing of high quality films with superior control of bulk and interfacial characteristics.
Suppression of nucleation during the aluminum-induced layer exchange process
Authors: Schneider Jens , Klein Juliane , Sarikov Andrey , Muske Martin , Gall Stefan , Fuhs Walther
Published: June 2019

Formation of polycrystalline silicon (poly-Si) thin films on inexpensive glass substrates is of great interest for large area electronic devices. Large grain sizes are desirable to reduce grain boundary effects. In the aluminum-induced layer exchange process Al/a-Si bi-layers exchange their positions with a concurrent crystallization of the amorphous Si (a-Si) in a simple annealing step. The process is characterized by the self regulated suppression of nucleation by existing grains resulting in large grain sizes above 10 μm. This paper elucidates the process within the Al Si phase diagram. The change in Si concentration within the Al is shown to cause the nucleation suppression.
Application of Field-Enhanced Rapid Thermal Annealing to Activation of Doped Polycrystalline Si Thin Films
Authors: So B.S. , You Y.H. , Kim H.J. , Kim Y.H. , Hwang J.H. , Shin D.H. , Ryu S.R. , Choi K. , Kim Y.C.
Published: June 2019

Activation of polycrystalline silicon (poly-Si) thin films doped as n-type using selective ion implantation of phosphorous was performed employing field-enhanced rapid thermal annealing where rapid thermal annealing of halogen lamps is combined with alternating magnetic fields. The ion activation was evaluated using Hall effect measurements incorporating the resistivity, the charge carrier concentration, and the mobility. Statistical design of experiments is attempted in order to clarify the effects and interactions of processes variables on field-enhanced rapid thermal annealing towards ion activation: the three processing variables are furnace temperature, power of halogen lamp, and the alternating magnetic field. Hall effect measurements indicate that the furnace temperature and RTA power are found to be dominant in activating the doped polycrystalline Si in dose. The activation process results from the competition between charge carrier concentration and mobility: the increase in mobility is larger than the decrease in charge carrier concentration.
Use of Transparent Conductive Oxide Materials with Low Indices of Refraction in Amorphous Silicon-Based Solar Cell Technology
Authors: Jones Scott J. , Doehler Joachim , Liu Tongyu , Tsu David , Steele Jeff , Capangpangan Rey , Izu Masat
Published: June 2019

New types of transparent conductive oxides with low indices of refraction have been developed for use in optical stacks for the amorphous silicon (a-Si) solar cell and other thin film applications. The alloys are ZnO based with Si and MgF added to reduce the index of the materials through the creation of SiO2 or MgF2, with n=1.3-1.4, or the addition of voids in the materials. Alloys with 12-14% Si or Mg have indices of refraction at λ=800nm between 1.6 and 1.7. These materials are presently being used in optical stacks to enhance light scattering by Al/multi-layer/ZnO back reflectors in a-Si based solar cells to increase light absorption in the semiconductor layers and increase open circuit currents and boost device efficiencies. In contrast to Ag/ZnO back reflectors which have long term stability issues due to electromigration of Ag, these Al based back reflectors should be stable and usable in manufactured PV products. In this manuscript, structural properties for the materials will be reported as well as the performance of solar cell devices made using these new types of materials.
Influence of Hydrogen plasma on electrical and optical properties of transparent conductive oxides.
Authors: Raniero L. , Gonçalves A. , Pimentel A. , Ferreira I. , Zhang S. , Pereira L. , Águas H. , Fortunato E. , Martins R.
Published: June 2019

In this work we study the optical and electrical behavior of ZnO:Ga, ITO and IZO films deposited on glass after sustaining different hydrogen plasma conditions and exposure times. This work was complemented by analyzing the surface morphology of the set of films, which allow us to determine the role of hydrogen plasma on the film's properties such as Hall mobility, free carrier concentration, sheet resistance, optical transmittance, figure of merit and state of the surface. Apart from that, the performances of solar cells using an intrinsic layer constituted by nanocrystalline silicon will be also presented. The data show that the electrical properties of solar cells were improved by using ZnO:Ga as front contact, allowing a high current density collection and single pin solar cells with efficiencies exceeding 11%.
Growth Chemistry of Nanocrystalline Si:H Films
Authors: Dalal Vikram L. , Muthukrishnan Kamal , Stieler Daniel , Noack Max
Published: June 2019

We report on the growth of nanocrystalline Si:H films using both plasma CVD and remote hot wire deposition under systematically varied growth conditions. The films were grown from mixtures of silane and hydrogen. It was found that when the films were grown under low pressure VHF plasma growth conditions, the orientation of the film changed as the pressure increased. At the lowest pressures, the films were mainly <111> oriented, but changed to <220> orientation as the pressure increased. The grain size increased as the growth temperature increased. When the films were grown using remote hot wire deposition, the orientation depended upon both hydrogen dilution and growth temperature. As the hydrogen dilution increased, the <220> grain size became smaller. Grain size as large as 36 nm was obtained by controlling the growth conditions in hot wire deposition. As the growth temperature increased, the size of <220> grains increased. Growth rates also increased with increasing temperature. The data can be explained by invoking a growth model which recognizes that the natural growth direction for Si is <220>, since the surface energy is highest for (220) plane. Random nucleation leads to <220> grains. Bonded H is believed to inhibit the growth of <220> grains.
Metal Induced Growth of Poly-Si Solar Cells and Silicide Nanowires by use of Multiple Catalyst Layers
Authors: Kim Joondong , Ji Chunhai , Anderson Wayne A.
Published: June 2019

Polycrystalline Si thin films and single NiSi crystalline nanowires were made by the metal induced growth method. The different growth mechanisms for poly-Si and nanowires lie in the metal silicide formation. Poly-Si growth is based on metal disilicide formation and the growth of nanowires depends on metal monosilicide formation. The metal silicide formation depends on catalyst species and sputtering power. Following catalyst coating, Si was deposited in a DC magnetron sputtering system to grow poly-Si or nanowires. Several metals (Ni, Co, Co/Ni and Pd) were used as catalysts to confirm the nanowire growth mechanism as well as to fabricate solar cells. Poly-Si thin films were about 5 μm thick with up to 1 μm crystallite size. Nanowires were up to 10 μm long with about 50 nm diameter.
Annealing characteristics of Al-doped hydrogenated microcrystalline cubic silicon carbide films
Authors: Miyajima S. , Yamada A. , Konagai M.
Published: June 2019

Aluminum-doped hydrogenated microcrystalline cubic silicon carbide (μc-3C-SiC:H) films deposited by the hot wire chemical vapor deposition technique at a low substrate temperature of about 300 °C were annealed at various temperatures in vacuum atmosphere. The increase in conductivity was observed on annealing the films over 400°C. The onset of hydrogen desorption occurred in the undoped films at about 650°C, while the onset was shifted towards lower temperatures in the case of Al-doped films. These results indicate that hydrogen plays an important role on the conductivity of the Al-doped μc-3C-SiC:H films.
High-Yield Synthesis of Luminescent Silicon Quantum Dots in a Continuous Flow Nonthermal Plasma Reactor
Authors: Mangolini L. , Thimsen E. , Kortshagen U.
Published: June 2019

Light-emission from silicon based on quantum confinement in nanoscale structures has sparked intense research into this field ever since its discovery about 15 years ago. The lack of a simple high-yield synthesis approach for luminescent silicon nanocrystals has so far hampered their widespread application in such diverse areas as opto-electronics, solid-state lighting for general illumination, and fluorescent agents for biological applications. In this paper we discuss a nonthermal plasma process for the synthesis of luminescent silicon nanocrystals. The particle size is mainly controlled by the residence time in the plasma region. The system is capable of producing several tens of milligrams of luminescent powder per hour.
TCAD Modeling of Metal Induced Lateral Crystallization of Amorphous Silicon
Authors: Agapov Aleksey M. , Kalinin Valeri V. , Myasnikov Alexandre M. , Poon Vincent M.C. , Vermeire Bert
Published: June 2019

In our previous publications [1, 2] nickel diffusion and spreading resistance probe (SRP) measurements for quality control of metal induced lateral crystallization (MILC) of amorphous silicon (a-Si) were studied. Now we present TCAD modeling and an explanation of experimental results. By using ISE TCAD the Ni concentration distributions were calculated and compared with results obtained by experiments using SIMS analysis.
Morphology Change, Size Distribution, and Nano-sized Channels in Cu6Sn5 Intermetallic Compound Formation at the SnPb Solder and Copper Interface
Authors: Suh J. O. , Tu K. N. , Gusak A. M.
Published: June 2019

The growth and size distribution of scallop-type Cu6Sn5 intermetallic compound (IMC) at the interface between molten SnPb solder and Cu was investigated, along with a systematic study of morphology change of Cu6Sn5 morphology change as a function of SnPb solder composition. When SnPb solder composition was changed from eutectic (63Sn37Pb) to about 40Sn60Pb, Cu6Sn5 with round scallop-type morphology was found. In other compositions, the Cu6Sn5 scallops showed faceted scallop-type morphology. This morphological change is due to variation of interfacial energy between Cu6Sn5 and solder with a change of solder composition. The growth rate of Cu6Sn5 layer was proportional to cube root of time, and size distribution was in good agreement with the Flux-Driven-Ripening (FDR) theory. The pre-exponent factor k obtained by the measurement was 2.10×10-14 cm3/sec. Based on the k value, the calculated channel width with was about 2 nm, which was in good agreement with experimental observation by transmission electron microscopy.
Ultra low κ PECVD Porogen Approach: Matrix Precursors Comparison and Porogen Removal Treatment Study
Authors: Favennec L. , Jousseaume V. , Rouessac V. , Durand J. , Passemard G.
Published: June 2019

The introduction of new dielectrics into silicon chip interconnection technology is necessary to increase electrical performance. Sub-65nm technologies need κ values below 2.5 and the main way to reduce the dielectric constant is to introduce porosity. This work reports results concerning a two steps PECVD porogen approach to perform Ultra Low κ (κ <2.5). The first step is an hybrid material deposition: i.e. an a-SiOC:H matrix containing organic sacrificial inclusions (porogen phase). In the second step, the porogen is removed by a suitable curing to generate porosity. Two siloxane precursors (decamethylcyclopentasiloxane and diethoxymethylsilane) were evaluated as matrix precursors. Their influences, as well as O2 addition in plasma gas feed, in terms of cross-linking and incorporation were evaluated by FTIR analysis. Thermal anneal and UV treatment (thermally assisted) were evaluated as a curing second step. It allows to better understand this critical step which combines porogen removal and material cross-linking. By optimizing deposition and curing parameters, κ value lower than 2.4 were obtained.
Constraint Effects on Cohesive Failures in Low-k Dielectric Thin Films
Authors: Tsui Ting Y. , McKerrow Andrew J. , Vlassak Joost J.
Published: June 2019

One of the most common forms of cohesive failure observed in brittle thin films subjected to a tensile residual stress is channel cracking, a fracture mode in which through-film cracks propagate in the film. The crack growth rate depends on intrinsic film properties, residual stress, the presence of reactive species in the environment, and the precise film stack. In this paper, we investigate the effect of various buffer layers sandwiched between a brittle carbon-doped-silicate (CDS) film and a silicon substrate on channel cracking of the CDS film. The results show that channel cracking is enhanced if the buffer layer is more compliant than the silicon substrate. Crack velocity increases with increasing buffer layer thickness and decreasing buffer layer stiffness. This is caused by a reduction of the constraint imposed by the substrate on the film and a commensurate increase in energy release rate. The degree of constraint is characterized experimentally as a function of buffer layer thickness and stiffness, and compared to the results of a simple shear lag model that was proposed previously.
Plasma-assisted Atomic Layer Deposition of TiN Films at low Deposition Temperature for High-aspect Ratio Applications
Authors: Heil S.B.S. , Langereis E. , Roozeboom F. , Kemmeren A. , Pham N.P. , Sarro P.M. , van de Sanden M.C.M. , Kessels W.M.M.
Published: June 2019

A plasma-assisted atomic layer deposition (PA-ALD) process of titanium nitride (TiN) using TiCl4 precursor dosing and H2/N2 plasma exposure is presented. In situ spectroscopic ellipsometry revealed a growth rate at 400 °C of ∼0.7 A/cycle independent of precursor dosing. Varying the plasma exposure time changed the stoichiometry [N]/[Ti] of the films within the range ∼0.93-1.15. At 100 °C a relatively low chlorine impurity level (∼2 at. %) and low resistivity (∼200 νΔcm) were obtained for a ∼45 nm thick film. The growth rate was found to be considerably lower (∼0.3 Å/cycle) at this temperature. Using TEM imaging we found that PAALD TiN films can be deposited conformally in 20:1 aspect-ratio features (1.5 Êm width) but that the step coverage still needs to be improved, probably by a prolonged plasma exposure step.
CVD Boron Carbo-Nitride as Pore Sealant for Ultra Low-K Interlayer Dielectrics
Authors: Fitzpatrick P. Ryan , Satyanarayana Sri , Sun Yangming , White John M. , Ekerdt John G.
Published: June 2019

Blanket porous methyl silsesquioxane (pMSQ) films on a Si substrate were studied with the intent to seal the pores and prevent penetration of a metallic precursor during barrier deposition. The blanket pMSQ films studied were approximately 220 nm thick and had been etched and ashed. When tantalum pentafluoride (TaF5) is exposed to an unsealed pMSQ sample, X-ray photoelectron spectroscopy (XPS) depth profiling and secondary ion mass spectroscopy (SIMS) depth profiling reveal penetration of Ta into the pores all the way to the pMSQ / Si interface. Boron carbo-nitride films were grown by thermal chemical vapor deposition (CVD) using dimethylamine borane (DMAB) precursor with Ar carrier gas and C2H4 coreactant. These films had a stoichiometry of BC0.9N0.07 and have been shown in a previous study to have a k value as low as 3.8. BC0.9N0.07 films ranging from 1.8 to 40.6 nm were deposited on pMSQ and then exposed to TaF5 gas to determine the extent of Ta penetration into the pMSQ. Ta penetration was determined by XPS depth profiling and sometimes SIMS depth profiling. XPS depth profiling of a TaF5 / 6.3 nm BC0.9N0.07 / pMSQ / Si film stack indicates the attenuation of the Ta signal to < 2 at. % throughout the pMSQ. Backside SIMS of this sample suggests that trace amounts of Ta (< 2 at. %) are due to knock-in by Ar ions used for sputtering. An identical film stack containing 3.9 nm BC0.9N0.07 was also successful at inhibiting Ta penetration even with a 370°C post-TaF5 exposure anneal, suggesting the stability of BC0.9N0.07 to thermal diffusion of Ta. All BC0.9N0.07 films thicker than and including 3.9 nm prevented Ta from penetrating into the pMSQ.
Analysis of the Interfacial Reaction Between Sn-3.5Ag and Electroplating Interlayers
Authors: Yang S.M. , Chang Y.Y. , Wu Weite
Published: June 2019

At present, Pb-free process is imperative in the electronic packaging industry. Many reports focus on Pb-free solder to improve the solderability, it seems not obtain wettability as good as SnPb solder. In this study, an alloy interlayer with different content was deposited on Cu to balance wettability and diffusion barrier in the interface of joint by electroplating process. There are three types of interlayers including Cu, Ni, and SnNi alloy. The interlayer may react with Sn-3.5Ag solder during reflow process. Sn-Ni alloy plating layer is selected to improve wettability and provide diffusion barrier at the same time in soldering process. For interfacial microstructure examination, morphology characterization can be obtained by using scanning electron microscope (SEM) and energy-dispersive x-ray analysis (EDX). The structure of IMC is identified by x-ray diffraction (XRD).
Mesoporous Low Dielectric Poly(silsesquioxane) Thin Films Templated by Various Surfactants
Authors: Hyeon-Lee Jingyu , Seon Jong-Baek , Jung Myungsup , Kim Jongmin
Published: June 2019

Mesoporous low dielectric poly(silsesquioxane) thin films have been fabricated by templating various surfactants such as cetyltrimethyl ammonium bromide (CTAB) or 4-octylphenol polyethoxylate (OPE) in the silsesquioxane polymer matrix and their properties of the thin films characterized by electrical, mechanical and structural characterization. Depending on the types of the surfactants, mesoporous poly(silsesquioxane) thin films with different porosities have been formed. The dielectric constant (k) of the films depended on the content or porosity of the surfactants. The dielectric constants of ca. 2.2–2.4 were obtained for the films with relative porosities of about 15–30 vol. % to the polymer matrix itself. The elastic modulus of the films showed a dependency on the type, content of the surfactants and was ca. 2.9 GPa with the k value of ca. 2.38.
Fundamentals of Cu/Barrier-Layer Adhesion in Microelectronic Processing
Authors: Simka Harsono , Shankar Sadasivan , Duran Carolyn , Haverty Michael
Published: June 2019

Copper is most widely used interconnect material in present silicon microelectronic technologies. As such, multiple interfaces formed by a thin Cu layer and other materials must be engineered to achieve the desired chemical, mechanical, and electrical properties. Adhesion between Cu and the barrier layer, as well as between Cu and the dielectric, is of particular interest, due to its role in controlling interfacial stability and Cu electromigration behavior [1]. This work focuses on understanding how the interface chemistry affects adhesion. Firstprinciples density functional theory (DFT) calculations were used to determine chemical adhesion energies of interfaces formed by Cu and various metals considered as a diffusion barrier, including Ta, TiN, and W. Calculations predicted increasing adhesion strength in the order of TiN < Si-doped TiN < TaN < Ta, consistent with wetting experiments done using 100Å thick Cu layer samples. The effects of doping at the interface using light elements (C, N, O) were also determined. Calculations were also done for interfaces of Cu with two different classes of amorphous dielectric materials, i.e. silicon nitride and silicon carbide, for which detailed material characterizations are often difficult and time consuming. Calculations predicted Cu/Si-nitride and Cu/Si-carbide adhesion strengths consistent with 4-pt-bend experiments, including the improvement in adhesion energies when silicon was used to dope the interface. In addition, weaker interfaces provide low-resistance diffusion paths for Cu atoms during electromigration. The first-principles based modeling, validated by select adhesion measurements, provides a predictive approach to effectively determine adhesion strengths and predict electromigration reliability in interconnects.
Optimization of the metal/silicon ratio on nickel assisted crystallization of amorphous silicon
Authors: Pereira L. , Beckers M. , Martins R.M.S. , Fortunato E. , Martins R.
Published: June 2019

The aim of this work is to optimize the metal/silicon ratio on nickel metal induced crystallization of silicon. For this purpose amorphous silicon layers with 80, 125 and 220 nm thick were used on the top of which 0.5 nm of Ni was deposited and annealed during the required time to full crystallize the a-Si. The data show that the 80 nm a-Si layer reaches a crystalline fraction of 95.7% (as detected by spectroscopic ellipsometry) after annealed for only 2 hours. No significant structural improvement is detected by ellipsometry neither by XRD when annealing the films for longer times. However, on 125 nm thick samples, after annealing for 2 hours the crystalline fraction is only 59.7%, reaching a similar value to the one with 80 nm only after 5 hours, with a crystalline fraction of 92.2%. Here again no significant improvements were achieved by using longer annealing times. Finally, the 220 nm thick a-Si sample is completely crystallized only after 10 hours annealing. These data clear suggest that the crystallization of thicker a-Si layers requires thicker Ni films to be effective for short annealing times. A direct dependence of the crystallization time on the metal/silicon ratio was observed and estimated.
Co-firing of Low- and Middle Permittivity Dielectric Tapes in Low-Temperature Co-fired Ceramics
Authors: Park Jae-Hwan , Choi Young-Jin , Park Jae-Gwan
Published: June 2019

Compatibility in cofiring low-κ and middle-κ based on a same glass composition for the hybrid LTCC material systems was investigated. Designing of appropriate lithium borosilicate glass frit systems allowed us to develop an optimized glass frit system used for low-κ and middle-κ dielectric fillers, commonly. The effects of glass addition on the densification and electrical properties in low-κ and middle-κ dielectric materials were also examined. Controlling glass compositions and contents we tried to match low-κ and middle-κ tapes physically and chemically.
Macroporous Silicon Sensor Arrays for Chemical and Biological Detection
Authors: Clarkson Jeffrey , Rajalingam Vimalan , Hirschman Karl D. , Ouyang Huimin , Sun Wei , Fauchet Philippe M.
Published: June 2019

A new class of silicon-based chemical and biological sensors that offer an electrical response to a variety of substances is described. The devices utilize silicon flow-through sensing membranes with deep trench structures formed to depths up to 100μm, fabricated by electrochemical etching which transforms the silicon into macro-porous silicon (MPS). The sensors have demonstrated the ability to detect the presence of certain chemical and biological materials. Although the principle of operation of the devices is fairly complex, the transduction mechanisms can be compared to chemiresistors and chemically sensitive field-effect transistors (chemFETs). The electrical responses that have shown the most sensitivity are AC conductance and capacitance. Previous work has demonstrated that upon exposure to organic solvents (i.e. ethanol, acetone, benzene) the devices exhibit a characteristic impedance signature. The devices have also shown the ability to detect the hybridization of complementary DNA. The incorporation of other materials that have demonstrated sensitivity to low ambient levels of contaminants is also under investigation. The sensors have been designed and fabricated in linear array configurations; a microfluidic transport chip/package co-design is currently in progress.
A Novel Technology to Create Monolithic Instruments for Micro Total Analysis Systems
Authors: Seibel Konstantin , Schöler Lars , Walder Marcus , Schäfer Heiko , Schäfer André , Pletzer Tobias , Püschl René , Waidelich Michael , Ihmels Heiko , Ehrhardt Dietmar , Böhm Markus
Published: June 2019

The feasibility of micro total analysis systems (μTAS) on microchips based on the concept of a monolithic instrument is demonstrated. In such a device a microfluidic layer system is deposited in a backend process on a conventional CMOS integrated circuit with the aim to achieve cost and performance enhancements through integration and miniaturization. Experimental results on elementary functional components of a μTAS are presented including a narrow channel electroosmotic micropump, a micro mass flow meter using the thermal anemometric principle, a micro cytometer with integrated optical detection, and elementary structures for on-chip micro-capillary electrophoresis.
Biosilica Nanofabrication in Diatoms: The Structures and Properties of Regulatory Silaffins
Authors: Kröger Nils , Poulsen Nicole
Published: June 2019

Diatoms are a large group of unicellular microalgae encased by silica cell walls that exhibit species-specific, mostly porous micro-and nanopatterns. Previously, from the diatomCylindrotheca fusiformisunique phosphoproteins (termed silaffins) and unusually long polyamine chains (termed LCPA) have been identified and implicated in silica formation. However, analysis of the general role of silaffins in species-specific silica morphogenesis has been hampered by lack of data about silaffins from other diatom species. Recently, we have isolated the five major silaffins from the diatomThalassiosira pseudonanaand aided by the genome data available from this organisms we were able structurally und functionally characterize these molecules. These data clearly support the hypothesis that silaffins play an important role in the nanofabrication of diatom biosilica. The basic insights into the mechanism of biomineral morphogenesis by silaffins and LCPA suggest future pathways for the fabrication of nanostructured minerals by synthetically available polymers.
A High-Throughput Crystallization Device to Study Biomineralization in Vitro
Authors: Becker Alexander , Epple Matthias
Published: June 2019

A new crystallization device, based on a constant-composition double-diffusion setup, was constructed to study biomineralization in vitro. The device was tested with poly(aspartic acid) as a model additive in the precipitation of calcium carbonate, showing a complete crystal growth inhibition.
Room-temperature Ferromagnetism in Nanostructured Co-doped ZnO
Authors: Wei M. , Khare N. , Yates K. A. , Zhi D. , MacManus-Driscoll J. L.
Published: June 2019

Nanosized Co-doped ZnO samples were synthesized using an ultrasonic spray assisted chemical vapour deposition method. Microstructural and magnetic properties of these samples were studied. The room-temperature ferromagnetism was observed in the Co-doped ZnO. Also, x-ray analysis revealed a wurtzite ZnO structure with a small change of the lattice constants due to the doping of Co in ZnO. Raman spectroscopy of the Co-doped ZnO films indicated direct substitution of Co. Scanning electron microscopy showed nanostructured Co-doped ZnO with a ring or cup shape. Transmission electron microscopy analysis revealed nano grains within the rings of an average diameter of around 10 nm. Both energy dispersive spectroscopy and energy-filtered transmission electron microscopy indicated a uniform distribution of Co.
Particle Size and Oxidation in CoNi Nanoparticles
Authors: Patel Jalpa , Farrell Dorothy , Parkin Ivan P. , Pankhurst Quentin A.
Published: June 2019

Cobalt nickel nanoparticles with an oxide shell were prepared by polyol reduction syntheses with varying heating rates, reflux times, surfactants, and reagent concentrations. Differences in particle formation temperature, as evidenced by the reaction medium changing color from violet to black, the UV-Vis absorption spectra of aliquots of reaction media extracted throughout the synthesis reaction, and the colloidal stability of the particle dispersions were observed when the surfactant was changed between otherwise identical reactions. These changes in the reaction kinetics, and therefore the particle sizes of the different samples, also resulted in varying magnetic properties and air stabilities of the samples. Particles with diameters of 15 nm, synthesized using oleic acid, displayed exchange biasing and enhanced coercivity below 50 K, with Hex = 650 Oe and an increase in Hc from 570 Oe to 910 Oe after cooling in field to 2 K. These particles were stable in air over a period of at least five months, showing no change in magnetic moment. Smaller (6 nm) particles synthesized with the same surfactant did not exhibit exchange biasing after field cooling and experienced degradation of their magnetic properties upon exposure to air for one month. Particles synthesized with trioctylphosphine and mixtures of trioctylphosphine and oleic acid were 5 nm and formed the most stable dispersions, but oxidized upon drying in air to non-ferromagnetic phases.